WO2024019707A1

WO2024019707A1 - Photovoltaic cells

Info

Publication number: WO2024019707A1
Application number: PCT/US2022/037595
Authority: WO
Inventors: Israel Patla; Faina KOGAN; Anna RAZGON; Itay EYAL; Mark Sandler; Yaron Grinwald
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2022-07-19
Filing date: 2022-07-19
Publication date: 2024-01-25

Abstract

Described herein is a hole transport liquid electrophotographic (LEP) ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier. Also described herein is an ink set comprising the hole transport LEP ink composition and an LEP photovoltaic ink composition, as well as a method of producing photovoltaic cells using the hole transport LEP ink composition and photovoltaic cells produced therefrom.

Description

Photovoltaic Cells

Background

A photovoltaic cell (solar cell) converts light energy into electrical energy. A photovoltaic cell may comprise one or more photovoltaic layers positioned between an anode and a cathode. When light falls on the photovoltaic layer, the light is absorbed and generates particles with a positive or negative charge (holes and electrons). When an external load is connected between electrodes, electricity flows through the cell.

Brief Description of the Figures

Figure 1 is a schematic representation of two different photovoltaic cells.

Figure 2 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Examples 2 and 3 (PANI emeraldine salt doped with sulfuric acid at a DMA (Density mass area) of 0.1 and 0.3, respectively).

Figure 3 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Examples 4 and 5 (PANI emeraldine salt composite with carbon black at a DMA of 0.1 and 0.3, respectively).

Figure 4 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Examples 6 and 7 (CuO at a DMA of 0.1 and 0.3, respectively).

Figure 5 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Examples 8 and 9 (NiO at a DMA of 0.1 and 0.3, respectively).

Figure 6 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Examples 10 and 11 (PPy at a DMA of 0.1 and 0.3, respectively).

Figure 7 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Example 12 (SWCNTs at a DMA of Figure 8 is an l-V graph showing the photovoltaic behavior of a photovoltaic cell according to Example 1 (Reference, no HTL) and Example 13 (carbon black at a DMA of 0.2).

Figure 9 is SEM-FIB images of deposited photovoltaic cells with carbon black (CB; a-c) and polypyrrole (PPy; d-f) as the material capable of transporting holes. Both the deposited CB and PPy layers have a smooth top surface (images a (scale bar 50 pm) and d (scale bar 50 pm)) and approximately 500 nm thick continuous HTL layers (images b (scale bar 5 pm), c (scale bar 1 pm), e (scale bar 5 pm) and f (scale bar 1 pm).

Detailed Description

Before the present disclosure is disclosed and described, it is to be understood that this disclosure is not limited to the particular process steps and materials disclosed herein because such process steps and materials may vary somewhat. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments. The terms are not intended to be limiting because the scope is intended to be limited by the appended claims and equivalents thereof.

It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

As used herein, “carrier fluid”, “carrier liquid,” “carrier,” or “carrier vehicle” refers to the fluid in which pigment particles, resin, charge directors and other additives can be dispersed to form a liquid electrostatic ink composition or liquid electrophotographic ink composition. The carrier liquids may include a mixture of a variety of different agents, such as surfactants, co-solvents, viscosity modifiers, and/or other possible ingredients.

As used herein, “liquid electrostatic ink composition” or “liquid electrophotographic composition” generally refers to an ink composition that is typically suitable for use in an electrostatic printing process, sometimes termed an electrophotographic printing process. It may comprise pigment particles having a thermoplastic resin thereon. The electrostatic ink composition may be a liquid electrostatic ink composition, in which the pigment particles having resin thereon are suspended in a carrier liquid. The pigment particles having resin thereon will typically be charged or capable of developing charge in an electric field, such that they display electrophoretic behaviour. A charge director may be present to impart a charge to the pigment particles having resin thereon.

As used herein, “co-polymer” refers to a polymer that is polymerized from at least two monomers.

As used herein, “melt flow rate” generally refers to the extrusion rate of a resin through an orifice of defined dimensions at a specified temperature and load, usually reported as temperature/load, e.g. 190°C/2.16 kg. Flow rates can be used to differentiate grades or provide a measure of degradation of a material as a result of molding. In the present disclosure, unless otherwise stated, “melt flow rate” is measured per ASTM D1238 Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer, as known in the art. If a melt flow rate of a particular polymer is specified, unless otherwise stated, it is the melt flow rate for that polymer alone, in the absence of any of the other components of the liquid electrostatic ink composition.

As used herein, “acidity,” “acid number,” or “acid value” refers to the mass of potassium hydroxide (KOH) in milligrams that neutralizes one gram of a substance. The acidity of a polymer can be measured according to standard techniques, for example as described in ASTM D1386. If the acidity of a particular polymer is specified, unless otherwise stated, it is the acidity for that polymer alone, in the absence of any of the other components of the liquid toner composition.

As used herein, “melt viscosity” generally refers to the ratio of shear stress to shear rate at a given shear stress or shear rate. Testing is generally performed using a capillary rheometer. A plastic charge is heated in the rheometer barrel and is forced through a die with a plunger. The plunger is pushed either by a constant force or at constant rate depending on the equipment. Measurements are taken once the system has reached steady-state operation. One method used is measuring Brookfield viscosity @ 140°C, units are mPa s or ePoise, as known in the art. Alternatively, the melt viscosity can be measured using a rheometer, e.g. a commercially available AR- 2000 Rheometer from Thermal Analysis Instruments, using the geometry of: 25mm steel plate-standard steel parallel plate, and finding the plate over plate rheometry isotherm at 120°C, 0.01 Hz shear rate. If the melt viscosity of a particular polymer is specified, unless otherwise stated, it is the melt viscosity for that polymer alone, in the absence of any of the other components of the electrostatic composition. A certain monomer may be described herein as constituting a certain weight percentage of a polymer. This indicates that the repeating units formed from the said monomer in the polymer constitute said weight percentage of the polymer.

If a standard test is mentioned herein, unless otherwise stated, the version of the test to be referred to is the most recent at the time of filing this patent application.

As used herein, “electrostatic printing” or “electrophotographic printing” generally refers to the process that provides an image that is transferred from a photo imaging substrate either directly or indirectly via an intermediate transfer member to a print substrate, such as a paper or a plastic substrate. As such, the image is not substantially absorbed into the photo imaging substrate on which it is applied. Additionally, “electrophotographic printers” or “electrostatic printers” generally refer to those printers capable of performing electrophotographic printing or electrostatic printing, as described above. “Liquid electrostatic printing” is a specific type of electrostatic printing in which a liquid composition is employed in the electrophotographic process rather than a powder toner. An electrostatic printing process may involve subjecting the electrostatic composition to an electric field, for example, an electric field having a field gradient of 50-400 V/pm, or more, in some examples, 600-900V/pm, or more.

As used herein, “NVS” is an abbreviation of the term “non-volatile solids”.

As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be a little above or a little below the endpoint to allow for variation in test methods or apparatus. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not just the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 wt% to about 5 wt%” should be interpreted to include not just the explicitly recited values of about 1 wt% to about 5 wt%, but also to include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3.5, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting a single numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.

As used herein, unless otherwise stated, wt.% values are to be taken as referring to a weight-for-weight (w/w) percentage of solids in the ink composition, and not including the weight of any carrier fluid present.

Unless otherwise stated, any feature described herein can be combined with any aspect or any other feature described herein.

In an aspect, there is provided a hole transport liquid electrophotographic ink composition. The hole transport liquid electrophotographic ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin; and a liquid carrier. The thermoplastic resin may comprise a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In another aspect, there is provided an ink set for producing a photovoltaic cell. The ink set may comprise a hole transport liquid electrophotographic ink composition and a liquid electrophotographic photovoltaic ink composition. The liquid electrophotographic photovoltaic ink composition may comprise a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion.

In a further aspect, there is provided a photovoltaic cell. The photovoltaic cell may be referred to herein as a printed photovoltaic cell. The photovoltaic cell may comprise an anode; a photovoltaic layer; a liquid electrophotographically printed hole transport layer; and a cathode; wherein the photovoltaic layer is disposed between the anode and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the photovoltaic layer and the cathode. The liquid electrophotographically printed hole transport layer may comprise a material capable of transporting electron holes; and a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide. The photovoltaic layer may comprise a material with a perovskite structure; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion.

In another aspect, there is provided a method of producing a photovoltaic cell comprising: printing a hole transport liquid electrophotographic ink composition onto a photovoltaic layer to form a liquid electrophotographically printed hole transport layer; wherein the photovoltaic layer is disposed on a substrate comprising an anode; and applying a composition to form a cathode; wherein the hole transport layer is disposed between the photovoltaic layer and the cathode. The hole transport liquid electrophotographic ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier. The photovoltaic layer may comprise a material with a perovskite structure; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion.

Significant research into perovskite based solar cells (PSCs) is currently ongoing as this type of solar cell may provide comparable performance to silicon based solar cells, at a much lower cost. However, current perovskite based solar cells have high sensitivity to humidity and oxygen, and are produced by processes that involve harmful solvents such as DMF and DMSO. Moreover, perovskite crystals produced by deposition from these solvents result in defects in the crystal structure.

Many solar cells contain a hole transporting layer to selectively transport holes to the cathode, improving cell performance and stability. Typically, hole transport layers (HTLs) are deposited by means of spin coating or spray coating and contain either an organic or an inorganic hole transport material (HTM). Many organic hole transport materials have been found to be unstable and require multi-step synthetic methods that are complex, time consuming and expensive. Although many inorganic hole transport materials are less costly, they are also generally less effective at hole transportation.

Examples of the photovoltaic cells, methods and compositions described herein have been found to avoid or at least mitigate at least one of these difficulties. It has been found that the photovoltaic cells produced with the compositions described herein show improved efficiencies and are stable, without requiring the use of harmful solvents and complex deposition processes. Additionally, the presence of this HTL prevents oxidation of the cathode (for example, of a copper cathode to copper iodide).

Indeed, these HTL layers improve the stability of the perovskite based solar cells by mechanically protecting the perovskite containing active layer from degradation (via decomposition by exposure to moisture and oxygen) and the cathode from oxidation (e.g., by halides).

Inks and Ink Sets

In an aspect, there is provided a hole transport liquid electrophotographic ink composition. There is also provided an ink set for producing a photovoltaic cell. The ink set for producing a photovoltaic cell may comprise a hole transport liquid electrophotographic ink composition and a liquid electrophotographic photovoltaic ink composition. In some examples, the ink set may further comprise an electrically conductive liquid electrophotographic ink composition. In some examples, the ink set may further comprise an electron transport composition.

In some examples, the hole transport liquid electrophotographic (LEP) ink composition comprises a material capable of transporting electron holes; a thermoplastic resin (e.g., a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide), and a liquid carrier. In some examples, the hole transport liquid electrophotographic ink composition comprises a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, and a liquid carrier.

In some examples, the ink set for producing a photovoltaic cell may comprise a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion. In some examples, the ink set for producing a photovoltaic cell may comprise a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion, wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and a monomer having acidic side groups; and/or a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof.

In some examples, the ink set for producing a photovoltaic cell further comprises an electrically conductive liquid electrophotographic ink composition. In some examples, the ink set for producing a photovoltaic cell comprises: a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally conductive particles, in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion; and an electrically conductive liquid electrophotographic ink composition comprising a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.

In some examples, the ink set for producing a photovoltaic cell further comprises an electrically conductive liquid electrophotographic ink composition. In some examples, the ink set for producing a photovoltaic cell comprises: a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally conductive particles, in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion; wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and a monomer having acidic side groups, and/or a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof; and an electrically conductive liquid electrophotographic ink composition comprising a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.

In some examples, the ink set for producing a photovoltaic cell further comprises an electrically conductive liquid electrophotographic ink composition. In some examples, the ink set for producing a photovoltaic cell comprises: a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally conductive particles, in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion; wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the ink set for producing a photovoltaic cell further comprises an electrically conductive liquid electrophotographic ink composition. In some examples, the ink set for producing a photovoltaic cell comprises: a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally conductive particles, in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion; wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and an electrically conductive liquid electrophotographic ink composition comprising a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.

In some examples, the electrically conductive liquid electrophotographic ink composition comprises a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.

Hole transport liquid electrophotoqraphic ink composition

In an aspect, there is provided a hole transport liquid electrophotographic (LEP) ink composition. The hole transport LEP ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin and a liquid carrier.

The hole transport liquid electrophotographic ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier.

In some examples, the hole transport LEP ink composition may further comprise a charge adjuvant. In some examples, the hole transport LEP ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin (e.g., a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide), a carrier liquid and a charge adjuvant.

In some examples, the hole transport LEP ink composition may further comprise a charge director. In some examples, the hole transport LEP ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin (e.g., a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide), a carrier liquid and a charge director. In some examples, the hole transport LEP ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin (e.g., a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide), a carrier liquid, a charge director, and a charge adjuvant.

In some examples, the hole transport LEP ink composition may further comprise additives. In some examples the hole transport LEP ink composition may comprise a material capable of transporting electron holes; a thermoplastic resin (e.g., a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide), a carrier liquid, a charge director, a charge adjuvant and other additives.

Material capable of transporting electron holes

The hole transport LEP ink composition may comprise a material capable of transporting electron holes. In some examples, the material capable of transporting electron holes may comprise a material capable of transporting electron holes and electrons. In some examples, the material capable of transporting electron holes may comprise a material capable of transporting only electron holes, i.e., a material that is selective for transporting electron holes. In some examples, the material capable of transporting electron holes is a material capable of transporting electron holes and electrons or a material selective for transporting electron holes.

In some examples, if the material capable of transporting electron holes is a material that is capable of transporting electron holes and electrons, it will be used in a photovoltaic cell that comprises an electron transport layer.

In some examples, the material capable of transporting electron holes may be any material capable of transporting electron holes. In some examples, the material capable of transporting electron holes may be a hole transport material. In some examples, the material capable of transporting electron holes may be an organic material capable of transporting electron holes or an inorganic material capable of transporting electron holes.

In some examples, the material capable of transporting electron holes may be selected from the group consisting of 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'- spirobifluorene (Spiro-OMeTAD), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), [poly(3-hexylthiophene-2,5-diyl) (P3HT), Cu₂O, CuO, Cui, CuSCN, NiOx (for example, NiO), MOS₂, polyaniline emeraldine salt (for example, polyaniline emeraldine salt doped with sulfuric acid or polyaniline emeraldine salt on carbon black), polypyrrole, carbon nanotubes (for example, single-walled carbon nanotubes), carbon black, tris(4- methoxyphenyl)amine (TPAA), (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz), [4- (3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), N4,N4,N4",N4"- tetra([1 , 1 '-bi p he ny l]-4-y I)- [ 1 , 1 ' : 4' , 1 "-terphenyl]-4,4"-diamine (T aT m), [2-(3,6-dibromo- 9H-carbazol-9-yl)ethyl]phosphonic acid (Br-2PACz), Tris(2-(1 H-pyrazol-1- yl)pyridine)cobalt(lll) tri(hexafluorophosphate) (FK102), Tris(2-(1 H-pyrazol-1-yl)-4-tert- butylpyridine)-cobalt(lll) Tris(bis(trifluoromethylsulfonyl)imide) (FK209), 2,2'-

(perfluorocyclohexa-2,5-diene-1 ,4-diylidene)dimalononitrile (F4TCNQ), Zinc(ll) bis(trifluoromethanesulfonyl)imide (Zn(TFSI)₂, 2,2'-(perfluoronaphthalene-2,6- diylidene)dimalononitrile (F6-TCNNQ), or combinations thereof. In some examples, the material capable of transporting electron holes may be selected from the group consisting of2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT: PSS), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), [poly(3-hexylthiophene- 2,5-diyl) (P3HT), Cu₂O, CuO, Cui, CuSCN, NiOx (for example, NiO), MoS₂, polyaniline emeraldine salt (for example, polyaniline emeraldine salt doped with sulfuric acid or polyaniline emeraldine salt on carbon black), polypyrrole, carbon nanotubes (for example, single-walled carbon nanotubes), carbon black or combinations thereof.

In some examples, the material capable of transporting electron holes may be selected from the group consisting of polyaniline emeraldine salts (for example, polyaniline emeraldine salt doped with sulfuric acid or polyaniline emeraldine salt on carbon black), CuO, NiO, polypyrrole, carbon nanotubes (for example, single-walled carbon nanotubes), carbon black or combinations thereof. In some examples, the material capable of transporting electron holes may be selected from the group consisting of polyaniline emeraldine salt on carbon black, polypyrrole, carbon black or combinations thereof. In some examples, the material capable of transporting electron holes may be selected from the group consisting of polypyrrole or carbon black.

In some examples, the material capable of transporting electron holes (for example, polypyrrole or carbon black) is present in the hole transport LEP ink composition in an amount of at least about 5 wt.% of the solids of the hole transport LEP ink composition, for example, at least about 10 wt.%, at least about 15 wt.%, at least about 20 wt.%, at least about 25 wt.%, at least about 30 wt.%, at least about 35 wt.%, at least about 40 wt.%, at least about 45 wt.%, at least about 50 wt.%, at least about 55 wt.%, at least about 60 wt.%, at least about 65 wt.%, at least about 70 wt.%, at least about 75 wt.%, at least about 80 wt.%, at least about 90 wt.%, at least about 95 wt.% of the solids of the hole transport LEP ink composition. In some examples, the material capable of transporting electron holes (for example, polypyrrole or carbon black) is present in an amount of up to about 95 wt.% of the solids of the hole transport LEP ink composition, for example, up to about 90 wt.%, up to about 85 wt.%, up to about 80 wt.% up to about 75 wt.%, up to about 70 wt.%, up to about 65 wt.%, up to about 60 wt.%, up to about 55 wt.%, up to about 50 wt.%, up to about 45 wt.%, up to about 40 wt.%, up to about 35 wt.%, up to about 30 wt.%, up to about 25 wt.%, up to about 20 wt.%, up to about 15 wt.%, up to about 10 wt.%, or up to about 5 wt.% of the solids of the hole transport LEP ink composition. In some examples, the material capable of transporting electron holes is present in an amount of from about 5 wt.% to about 95 wt.% of the solids of the hole transport liquid electrophotographic ink composition, for example, from about 10 wt.% to about 90 wt.%, about 15 wt.% to about 85 wt.%, about 20 wt.% to about 80 wt.%, about 25 wt.% to about 75 wt.%, about 30 wt.% to about 70 wt.%, about 35 wt.% to about 65 wt.%, about 40 wt.% to about 60 wt.%, about 45 wt.% to about 55 wt.%, or about 50 wt.% to about 95 wt.% of the solids of the hole transport LEP ink composition. In some examples, the material capable of transporting electron holes is present in an amount of about 30 wt.% to about 60 wt.% of the solids of the hole transport LEP ink composition.

Thermoplastic resin of the hole transport LEP ink composition (HT thermoplastic resin)

The hole transport liquid electrophotographic ink composition may comprise a thermoplastic resin. The thermoplastic resin may comprise any thermoplastic resin suitable for use in an LEP ink composition. In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

The thermoplastic resin of the hole transport LEP ink composition may be referred to herein as the HT thermoplastic resin to distinguish it from the thermoplastic resin of the LEP photovoltaic ink composition and the thermoplastic resin of the electrically conductive LEP ink composition.

Once printed, the epoxide may have been subjected to a ring-opening reaction and/or a cross-linking reaction. The inclusion of the polymer containing epoxide groups in the hole transport LEP ink composition may extend the lifetime of the perovskite containing photovoltaic layer.

In some examples, the thermoplastic resin may comprise multiple polymers, wherein one of the polymers is a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide. In some examples, the thermoplastic resin may consist of a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide and a copolymer of an alkylene monomer and a monomer having acidic side groups.

In some examples, the alkylene monomer may be selected from the group consisting of ethylene and propylene. In some examples, the alkylene monomer may ethylene. In some examples, the thermoplastic resin comprises a copolymer of ethylene or propylene and an ethylenically unsaturated monomer comprising an epoxide. In some examples, the thermoplastic resin comprises a copolymer of ethylene and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the ethylenically unsaturated monomer comprising an epoxide is any monomer comprising a carbon-carbon double bond and an epoxide. As used herein, the term “ethylenically unsaturated monomer” is used to indicate the presence of one carbon-carbon double bond in the monomer, which reacts during the polymerisation reaction to form the copolymer, thus forming a carbon-carbon single bond in the copolymer.

In some examples, the ethylenically unsaturated monomer comprising an epoxide is an ethylenically unsaturated ketone comprising an epoxide, an ethylenically unsaturated amide comprising an epoxide, an ethylenically unsaturated thioester comprising an epoxide, an ethylenically unsaturated ester comprising an epoxide, or a combination thereof. In some examples, the ethylenically unsaturated monomer comprising an epoxide is an ethylenically unsaturated ester comprising an epoxide. In some examples, the ethylenically unsaturated amide comprising an epoxide may be an amide of an ethylenically unsaturated carboxylic acid and an epoxide-containing amine, for example, an epoxide-containing primary amine or an epoxide-containing secondary amine. In some examples, the ethylenically unsaturated thioester comprising an epoxide may be a thioester of an ethylenically unsaturated carboxylic acid and an epoxide-containing thiol. In some examples, the ethylenically unsaturated ester comprising an epoxide may be an ester of an ethylenically unsaturated carboxylic acid and an epoxide-containing alcohol.

In some examples, the ethylenically unsaturated carboxylic acid may be any compound containing a carboxylic acid and a single carbon-carbon double bond. In some examples, the ethylenically unsaturated carboxylic acid comprises an a,|3-unsaturated carboxylic acid or an a, |3- unsaturated, a-alkyl carboxylic acid. In some examples, the a,p-unsaturated, a-alkyl carboxylic acid may be further substituted.

In some examples, the a,|3-unsaturated carboxylic acid comprises a C1 to C10 a,|3- unsaturated carboxylic acid, for example, a C1 to C6 a,|3-unsaturated carboxylic acid. In some examples, the a,|3-unsaturated carboxylic acid is selected from the group consisting of pent-2-enoic acid, butan-2-enoic acid and prop-2-enoic acid. In some examples, the a,|3-unsaturated carboxylic acid is prop-2-enoic acid.

In some examples, the a,|3-unsaturated, a-alkyl carboxylic acid comprises an a-alkyl substituted C1 to C10 a,|3-unsaturated carboxylic acid, for example, an a-alkyl substituted C1 to C6 a,|3-unsaturated carboxylic acid. In some examples, the a,|3- unsaturated, a-alkyl carboxylic acid is selected from the group consisting of a 2- alkylpent-2-enoic acid, 2-alkylbutan-2-enoic acid and a 2-alkylprop-2-enoic acid. In some examples, the a,|3-unsaturated, a-alkyl carboxylic acid is a 2-alkylprop-2-enoic acid.

In some examples, the a-alkyl group of the a,|3-unsaturated, a-alkyl carboxylic acid is a substituted or unsubstituted alkyl group. In some examples, the a-alkyl substituent of the a,p-unsaturated, a-alkyl carboxylic acid (for example, the 2-alkyl substituent of 2- alkylprop-2-enoic acid) is a C1 to C10 alkyl group, for example, a C1 to C6 alkyl, such as methyl, ethyl, propyl (e.g., n-propyl or isopropyl), or butyl (e.g., n-butyl, sec-butyl, isobutyl or tert-butyl). In some examples, the a-alkyl substituent of the a,|3-unsaturated, a-alkyl carboxylic acid (for example, the 2-alkyl substituent of 2-alkylprop-2-enoic acid) is selected from the group consisting of methyl, ethyl and propyl. In some examples, the a-alkyl substituent of the a,|3-unsaturated, a-alkyl carboxylic acid is methyl.

In some examples, the ethylenically unsaturated carboxylic acid is selected from the group consisting of 2-propylprop-2-enoic acid, 2-ethylprop-2-enoic acid and 2- methylprop-2-enoic acid. In some examples, the ethylenically unsaturated carboxylic acid is 2-methylprop-2-enoic acid, which is also known as methacrylic acid. In some examples, the epoxide-containing alcohol may be any compound containing an epoxide group and an alcohol group. In some examples, the epoxide-containing alcohol may be any alkane containing an epoxide group and an alcohol.

In some examples, the epoxide-containing alcohol comprises a primary alcohol, a secondary alcohol or a tertiary alcohol. In some examples, the epoxide-containing alcohol comprises a primary alcohol.

In some examples, the epoxide-containing alcohol may comprise a mono-substituted epoxide (also referred to herein as a terminal epoxide), a di-substituted epoxide, a trisubstituted epoxide or a tetra-substituted epoxide. In some examples, the epoxide- containing alcohol may comprise a mono-substituted or a di-substituted epoxide. In some examples, the epoxide-containing alcohol may comprise a terminal epoxide. In some examples, the di-substituted epoxide may have the formula -CR(O)CH₂. A terminal epoxide is an epoxide having the formula -CH(O)CH₂.

In some examples, the epoxide-containing alcohol may comprise a primary alcohol and a terminal epoxide.

In some examples, the epoxide-containing alcohol may be any epoxide-containing alcohol. In some examples, the epoxide-containing alcohol may comprise 2 to 30 carbon atoms, for example, 3 to 25 carbon atoms, 3 to 20 carbon atoms, 3 to 15 carbon atoms, 3 to 10 carbon atoms, 3 to 5 carbon atoms, 3 to 4 carbon atoms. In some examples, the epoxide-containing alcohol may be selected from the group consisting of glycidol (i.e., 2,3-epoxy-1 -propanol), epoxybutanol (e.g., 3,4-epoxy-1- butanol), and epoxypentanol (e.g., 4,5-epoxy-1 -pentanol). In some examples, the epoxide-containing alcohol may be glycidol.

In some examples, the ethylenically unsaturated ester comprising an epoxide may be selected from the group consisting of glycidyl methacrylate, glycidyl 2-ethylprop-2- enoate, glycidyl 2-propylprop-2-enoate, epoxybutanyl methacrylate, epoxybutanyl 2- ethylprop-2-enoate, epoxybutanyl 2-propylprop-2-enoate, epoxypentanyl methacrylate, epoxypentanyl 2-ethylprop-2-enoate, epoxypentanyl 2-propylprop-2-enoate. In some examples, the ethylenically unsaturated ester comprising an epoxide is glycidyl methacrylate. In some examples, the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide may be a copolymer of ethylene and an ethylenically unsaturated ester comprising an epoxide, such as glycidyl methacrylate.

In some examples, the ethylenically unsaturated monomer comprising an epoxide constitutes at least 1 wt.% of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, for example, at least

1.5 wt.%, at least 2 wt.%, at least 2.5 wt.%, at least 3 wt.%, at least 3.5 wt.%, at least 4 wt.%, at least 4.5 wt.%, at least 5 wt.%, at least 5.5 wt.%, at least 6 wt.%, at least

6.5 wt.% of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the ethylenically unsaturated monomer comprising an epoxide constitutes 50 wt.% or less of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, for example, 25 wt.% or less, 20 wt.% or less, 15 wt.% or less, 14 wt.% or less, 13 wt.% or less, 12 wt.% or less, 11 wt.% or less, 10.5 wt.% or less, 10 wt.% or less, 9.5 wt.% or less, 9 wt.% or less of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the ethylenically unsaturated monomer comprising an epoxide constitutes from about 1 wt.% to about 50 wt.% of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, for example, from about 1.5 wt.% to about 25 wt.%, from about 2 wt.% to about 20 wt.%, from about 2.5 wt.% to about 15 wt.%, from about 3 wt.% to about 14 wt.%, from about

3.5 wt.% to about 13 wt.%, from about 4 wt.% to about 12 wt.%, from about 4.5 wt.% to about 11 wt.%, from about 5 wt.% to about 10.5 wt.%, from about 5.5 wt.% to about 10 wt.%, from about 6 wt.% to about 9.5 wt.%, from about 6.5 wt.% to about 9 wt.% of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide. In some examples, the alkylene monomer may constitute the remaining weight percent of the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the thermoplastic resin of the hole transport LEP ink composition may be selected from the group consisting of poly(ethylene-co-glycidyl methacrylate) (sold by Merck), poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) (sold by Merck), Lotader AX8840, Lotader AX8820, Lotader™ AX8900, Lotader AX8930, Lotader™ AX8750, Lotader AX8670T, Igetabond™ CG5001 , Igetabond™ BF-2C, Igetabond™ BR-E, Igetabond™ BF-2B, Igetabond™ BF-7B, Igetabond™ BR-7L and Igetabond™ BF-7M.

In some examples, the thermoplastic resin of the hole transport liquid electrophotographic ink composition is present in an amount of from at least about 5 wt.% of the solids of the hole transport liquid electrophotographic ink composition for example, at least about 10 wt.%, at least about 20 wt.%, at least about 30 wt.%, at least about 40 wt.%, at least about 50 wt.%, at least about 55 wt.%, at least about 60 wt.%, at least about 65 wt.%, at least about 70 wt.%, at least about 75 wt.%, at least about 80 wt.%, at least about 85 wt.%, at least about 90 wt.%, or at least about 95 wt.% of the solids of the hole transport liquid electrophotographic ink composition. In some examples, the thermoplastic resin of the hole transport liquid electrophotographic ink composition is present in an amount of up to about 95 wt.% of the solids of the hole transport LEP ink composition, for example, up to about 90 wt.%, up to about 85 wt.%, up to about 80 wt.%, up to about 75 wt.%, up to about 70 wt.%, up to about 65 wt.%, up to about 60 wt.%, up to about 55 wt.%, up to about 50 wt.%, up to about 40 wt.%, up to about 30 wt.%, up to about 20 wt.%, up to about 10 wt.% or up to about 5 wt.% of the solids of the hole transport LEP ink composition. In some examples, the thermoplastic resin of the hole transport LEP ink composition is present in an amount of from about 5 wt.% to about 95 wt.% of the solids of the hole transport LEP ink composition, for example, about 10 wt.% to about 90 wt.%, about 20 wt.% to about 85 wt.%, about 30 wt.% to about 80 wt.%, about 40 wt.% to about 75 wt.%, about 50 wt.% to about 70 wt.%, about 55 wt.% to about 65 wt.%, about 60 wt.% to about 95 wt.% of the solids of the hole transport LEP ink composition.

Liquid carrier

During printing, the hole transport LEP ink composition may comprise a liquid carrier. Generally, the liquid carrier can act as a dispersing medium for the other components in the hole transport LEP ink composition. For example, the liquid carrier can comprise or be a hydrocarbon, silicone oil, vegetable oil, and so forth.

The carrier liquid/liquid carrier can include, but is not limited to, an insulating, non-polar, non-aqueous liquid that can be used as a medium for toner particles. The carrier liquid can include compounds that have a resistivity in excess of about 10⁹ ohm cm. The carrier liquid may have a dielectric constant below about 5, in some examples below about 3. The carrier liquid can include, but is not limited to, hydrocarbons. The hydrocarbon can include, but is not limited to, an aliphatic hydrocarbon, an isomerized aliphatic hydrocarbon, branched chain aliphatic hydrocarbons, aromatic hydrocarbons, and combinations thereof. Examples of the carrier liquids include, but are not limited to, aliphatic hydrocarbons, isoparaffinic compounds, paraffinic compounds, dearomatized hydrocarbon compounds, and the like.

In some examples, the carrier liquid may be a hydrocarbon. In some examples, the carrier liquid may be a branched chain hydrocarbon. In some examples, the branched chain hydrocarbon may comprise 5 to 15 carbon atoms, for example, 10 to 15 carbon atoms, or 11 to 12 carbon atoms. In some examples, the carrier liquid may be selected from liquids comprising a mixture of branched chain hydrocarbons having 5 to 15 carbon atoms, for example, 10 to 15 carbon atoms or 11 to 12 carbon atoms.

In particular, the liquid carriers can include, but are not limited to, Isopar-G™, Isopar- H™, Isopar-L™, Isopar-M™, Isopar-K™, Isopar-V™, Norpar 12™, Norpar 13™, Norpar 15™, Exxol D40™, Exxol D80™, Exxol D100™, Exxol D130™, and Exxol 0140™ (each sold by EXXON CORPORATION); Teclen N-16™, Teclen N-20™, Teclen N-22™, Nisseki Naphthesol L™, Nisseki Naphthesol M™, Nisseki Naphthesol H™, #0 Solvent L™, #0 Solvent M™, #0 Solvent H™, Nisseki Isosol 300™, Nisseki Isosol 400™, AF-4™, AF-5™, AF-6™ and AF-7™ (each sold by NIPPON OIL CORPORATION); IP Solvent 1620™ and IP Solvent 2028™ (each sold by IDEMITSU PETROCHEMICAL CO., LTD.); Amsco OMS™ and Amsco 460™ (each sold by AMERICAN MINERAL SPIRITS CORP.); and Electron, Positron, New II, Purogen HF (100% synthetic terpenes) (sold by ECOLINK™).

Before liquid electrophotographic printing, the carrier liquid can constitute about 20% to 99.5% by weight of the hole transport LEP ink composition, in some examples 50% to 99.5% by weight of the hole transport liquid electrostatic ink composition. Before printing, the carrier liquid may constitute about 40% to 90% by weight of the hole transport liquid electrostatic ink composition. Before printing, the carrier liquid may constitute about 60% to 80% by weight of the hole transport liquid electrostatic ink composition. Before printing, the liquid carrier may constitute about 90% to 99.5% by weight of the hole transport liquid electrostatic ink composition, in some examples 95% to 99% by weight of the hole transport liquid electrostatic ink composition. The hole transport liquid electrostatic ink composition, once electrostatically printed on the substrate, may be substantially free from liquid carrier. In an electrostatic printing process and/or afterwards, the liquid carrier may be removed, for example, by an electrophoresis processes during printing and/or evaporation, such that substantially just solids are transferred to the substrate. Substantially free from liquid carrier may indicate that the hole transport liquid electrostatically printed ink (i.e., the liquid electrophotographically printed hole transport layer) contains less than 5 wt.% liquid carrier, in some examples, less than 2 wt.% liquid carrier, in some examples less than 1 wt.% liquid carrier, in some examples less than 0.5 wt.% liquid carrier. In some examples, hole transport liquid electrostatically printed ink is free from liquid carrier.

Charge director

In some examples, the hole transport LEP ink composition further includes a charge director. The charge director may be added in order to impart and/or maintain sufficient electrostatic charge on the ink particles, which may be particles comprising the thermoplastic resin (of the hole transport LEP ink composition) and the hole transport material. In some examples, the charge director may comprise ionic compounds, particularly metal salts of fatty acids, metal salts of sulfo-succinates, metal salts of oxyphosphates, metal salts of alkyl-benzenesulfonic acid, metal salts of aromatic carboxylic acids or sulfonic acids, as well as zwitterionic and non-ionic compounds, such as polyoxyethylated alkylamines, lecithin, polyvinylpyrrolidone, organic acid esters of polyvalent alcohols, etc. The charge director can be selected from, but is not limited to, oil-soluble petroleum sulfonates (e.g. neutral Calcium Petronate™, neutral Barium Petronate™, and basic Barium Petronate™), polybutylene succinimides (e.g. OLOA™ 1200 and Amoco 575), and glyceride salts (e.g. sodium salts of phosphated mono- and diglycerides with unsaturated and saturated acid substituents), sulfonic acid salts including, but not limited to, barium, sodium, calcium, and aluminum salts of sulfonic acid. The sulfonic acids may include, but are not limited to, alkyl sulfonic acids, aryl sulfonic acids, and sulfonic acids of alkyl succinates. The charge director can impart a negative charge or a positive charge on the resin-containing particles of a LEP ink composition.

In some examples, the liquid electrostatic ink composition comprises a charge director comprising a simple salt. The ions constructing the simple salts are all hydrophilic. The simple salt may include a cation selected from the group consisting of Mg, Ca, Ba, NH₄, tert-butyl ammonium, Li⁺, and Al³⁺, or from any sub-group thereof. The simple salt may include an anion selected from the group consisting of SO₄ ²', PO₃', NO₃', HPO₄ ²', CO₃ ²', acetate, trifluoroacetate (TFA), Cl', BF₄', F’, CIO₄', and TiO₃ ⁴' or from any sub-group thereof. The simple salt may be selected from the group consisting of CaCO₃, Ba₂TiO₃, AI₂(SO₄), AI(NO₃)₃, Ca₃(PO₄)₂, BaSO₄, BaHPO₄, Ba₂(PO₄)₃, CaSO₄, (NH₄)₂CO₃, (NH₄)₂SO₄, NH₄OAC, tert-butyl ammonium bromide, NH₄NO₃, LiTFA, AI₂(SO₄)₃, l_iCIO₄ and LiBF₄, or any sub-group thereof.

In some examples, the liquid electrostatic ink composition comprises a charge director comprising a sulfosuccinate salt of the general formula MA_n, wherein M is a metal, n is the valence of M, and A is an ion of the general formula (I): [R¹-O-C(O)CH₂CH(SO₃-)- C(O)-O-R²], wherein each of R¹ and R² is an alkyl group. In some examples each of R¹ and R² is an aliphatic alkyl group. In some examples, each of R¹ and R² independently is a C6-25 alkyl. In some examples, said aliphatic alkyl group is linear. In some examples, said aliphatic alkyl group is branched. In some examples, said aliphatic alkyl group includes a linear chain of more than 6 carbon atoms. In some examples, R¹ and R² are the same. In some examples, at least one of R¹ and R² is C₁₃H₂₇. In some examples, M is Na, K, Cs, Ca, or Ba.

In some examples, the charge director comprises at least one micelle forming salt and nanoparticles of a simple salt as described above. The simple salts are salts that do not form micelles by themselves, although they may form a core for micelles with a micelle forming salt. The sulfosuccinate salt of the general formula MA_n is an example of a micelle forming salt. The charge director may be substantially free of an acid of the general formula HA, where A is as described above. The charge director may include micelles of said sulfosuccinate salt enclosing at least some of the nanoparticles of the simple salt. The charge director may include at least some nanoparticles of the simple salt having a size of 200 nm or less, and/or in some examples 2 nm or more.

The charge director may include one of, some of or all of (i) soya lecithin, (ii) a barium sulfonate salt, such as basic barium petronate (BBP), and (iii) an isopropyl amine sulfonate salt. Basic barium petronate is a barium sulfonate salt of a 21-26 carbon atom hydrocarbon alkyl, and can be obtained, for example, from Chemtura. An example isopropyl amine sulphonate salt is dodecyl benzene sulfonic acid isopropyl amine, which is available from Croda.

In some examples, the charge director constitutes about 0.001 % to 20% by weight, in some examples 0.01 % to 20% by weight, in some examples 0.01 % to 10% by weight, in some examples 0.01% to 5% by weight of the total solids of a liquid electrostatic ink composition. In some examples, the charge director constitutes about 1% to 4% by weight of the total solids of the liquid electrostatic ink composition, in some examples 2% to 4% by weight of the total solids of the electrostatic ink composition.

In some examples, the charge director is present in an amount sufficient to achieve a particle conductivity of 500 pmho/cm or less, in some examples, 450 pmho/cm or less, in some examples, 400 pmho/cm or less, in some examples, 350 pmho/cm or less, in some examples, 300 pmho/cm or less, in some examples, 250 pmho/cm or less, in some examples, 200 pmho/cm or less, in some examples, 190 pmho/cm or less, in some examples, 180 pmho/cm or less, in some examples, 170 pmho/cm or less, in some examples, 160 pmho/cm or less, in some examples, 150 pmho/cm or less, in some examples, 140 pmho/cm or less, in some examples, 130 pmho/cm or less, in some examples, 120 pmho/cm or less, in some examples, 110 pmho/cm or less, in some examples, about 100 pmho/cm. In some examples, the charge director is present in an amount sufficient to achieve a particle conductivity of 50 pmho/cm or more, in some examples, 60 pmho/cm or more, in some examples, 70 pmho/cm or more, in some examples, 80 pmho/cm or more, in some examples, 90 pmho/cm or more, in some examples, about 100 pmho/cm, in some examples, 150 pmho/cm or more, in some examples, 200 pmho/cm or more, in some examples, 250 pmho/cm or more, in some examples, 300 pmho/cm or more, in some examples, 350 pmho/cm or more, in some examples, 400 pmho/cm or more, in some examples, 450 pmho/cm or more, in some examples, 500 pmho/cm or more. In some examples, the charge director is present in an amount sufficient to achieve a particle conductivity of 50 pmho/cm to 500 pmho/cm, in some examples, 60 pmho/cm to 450 pmho/cm, in some examples, 70 pmho/cm to 400 pmho/cm, in some examples, 80 pmho/cm to 350 pmho/cm, in some examples, 90 pmho/cm to 300 pmho/cm, in some examples, 100 pmho/cm to 250 pmho/cm, in some examples, 110 pmho/cm to 200 pmho/cm, in some examples, 120 pmho/cm to 500 pmho/cm, in some examples, 130 pmho/cm to 450 pmho/cm, in some examples, 140 pmho/cm to 400 pmho/cm, in some examples, 150 pmho/cm to 350 pmho/cm, in some examples, 160 pmho/cm to 300 pmho/cm.

In some examples, the charge director is present in an amount of from 3 mg/g to 50 mg/g, in some examples from 3 mg/g to 45 mg/g, in some examples from 10 mg/g to 40 mg/g, in some examples from 5 mg/g to 35 mg/g, in some examples, 20 mg/g to 35 mg/g, in some examples, 22 mg/g to 34 mg/g (where mg/g indicates mg per gram of solids of the liquid electrostatic ink composition). Charge adjuvant

In some examples, the hole transport LEP ink composition further includes a charge adjuvant. A charge adjuvant may promote charging of the particles when a charge director is present. The method as described herein may involve adding a charge adjuvant at any stage. The charge adjuvant can include, for example, barium petronate, calcium petronate, Co salts of naphthenic acid, Ca salts of naphthenic acid, Cu salts of naphthenic acid, Mn salts of naphthenic acid, Ni salts of naphthenic acid, Zn salts of naphthenic acid, Fe salts of naphthenic acid, Ba salts of stearic acid, Co salts of stearic acid, Pb salts of stearic acid, Zn salts of stearic acid, Al salts of stearic acid, Zn salts of stearic acid, Cu salts of stearic acid, Pb salts of stearic acid, Fe salts of stearic acid, metal carboxylates (e.g., Al tristearate, Al octanoate, Li heptanoate, Fe stearate, Fe distearate, Ba stearate, Cr stearate, Mg octanoate, Ca stearate, Fe naphthenate, Zn naphthenate, Mn heptanoate, Zn heptanoate, Ba octanoate, Al octanoate, Co octanoate, Mn octanoate, and Zn octanoate), Co lineolates, Mn lineolates, Pb lineolates, Zn lineolates, Ca oleates, Co oleates, Zn palmirate, Ca resinates, Co resinates, Mn resinates, Pb resinates, Zn resinates, AB diblock copolymers of 2-ethylhexyl methacrylate-co-methacrylic acid calcium and ammonium salts, copolymers of an alkyl acrylamidoglycolate alkyl ether (e.g., methyl acrylamideglycolate methyl ether-co-vinyl acetate), or hydroxy bis(3,5-di-tert-butyl salicylic) aluminate monohydrate. In an example, the charge adjuvant is or includes aluminum di- or tristearate. In some examples, the charge adjuvant is VCA (aluminium stearate and aluminium palmitate, available from Sigma Aldrich).

The charge adjuvant may be present in an amount of about 0.001% to 5% by weight, in some examples about 0.1% to 1% by weight, in some examples about 0.3% to 0.8% by weight of the total solids of the liquid electrostatic ink composition, in some examples, about 1 wt.% to 5 wt.% of the total solids of the liquid electrostatic ink, in some examples about 1 wt.% to 3 wt.% of the total solids of the liquid electrostatic ink composition, in some examples about 1.5 wt.% to 2.5 wt.% of the total solids of the liquid electrostatic ink composition.

The charge adjuvant may be present in an amount of less than 5% by weight of total solids of the liquid electrostatic ink composition, in some examples in an amount of less than 4.5% by weight, in some examples in an amount of less than 4% by weight, in some examples in an amount of less than 3.5% by weight, in some examples in an amount of less than 3% by weight, in some examples in an amount of less than 2.5% by weight, in some examples, in an amount of less than 2% by weight of the total solids of the liquid electrostatic ink composition.

In some examples, the liquid electrostatic ink composition further includes, e.g. as a charge adjuvant, a salt of multivalent cation and a fatty acid anion. The salt of multivalent cation and a fatty acid anion can act as a charge adjuvant. The multivalent cation may, in some examples, be a divalent or a trivalent cation. In some examples, the multivalent cation is selected from the group consisting of Group 2, transition metals and Group 3 and Group 4 in the Periodic Table. In some examples, the multivalent cation includes a metal selected from the group consisting of Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al and Pb. In some examples, the multivalent cation is Al³⁺. The fatty acid anion may be selected from the group consisting of a saturated or unsaturated fatty acid anion. The fatty acid anion may be selected from the group consisting of a C8 to C26 fatty acid anion, in some examples a C14 to C22 fatty acid anion, in some examples a C16 to C20 fatty acid anion, in some examples a C17, C18 or C19 fatty acid anion. In some examples, the fatty acid anion is selected from the group consisting of a caprylic acid anion, capric acid anion, lauric acid anion, myristic acid anion, palmitic acid anion, stearic acid anion, arachidic acid anion, behenic acid anion and cerotic acid anion.

In some examples, the charge adjuvant comprises, consists essentially of or consists of an aluminium stearate (e.g., aluminium tristearate), aluminium palmitate and combinations thereof. In some examples, the charge adjuvant comprises, consists essentially of or consists of aluminium tristearate and aluminium palmitate.

The charge adjuvant, which may, for example, be or include a salt of a multivalent cation and a fatty acid anion, may be present in an amount of 0.1 wt.% to 5 wt.% of the total solids of the liquid electrostatic ink composition, in some examples in an amount of 0.1 wt.% to 3 wt.% of the total solids of the liquid electrostatic ink composition, in some examples about 1 wt.% to 3 wt.% of the total solids of the liquid electrostatic ink composition, in some examples about 1.5 wt.% to 2.5 wt.% of the total solids of the liquid electrostatic ink composition.

Other additives

The hole transport LEP ink composition may further include another additive or a plurality of other additives. The other additive or plurality of other additives may be added at any stage of the method. The other additive or plurality of other additives may be selected from the group consisting of a wax, a surfactant, viscosity modifiers, and compatibility additives. The wax may be an incompatible wax. As used herein, "incompatible wax" may refer to a wax that is incompatible with the resin. Specifically, the wax phase separates from the resin phase upon the cooling of the resin fused mixture on a substrate during and after the transfer of the ink film to the print substrate, e.g. from an intermediate transfer member, which may be a heated blanket. In some examples, the LEP ink composition comprises silica, which may be added, for example, to improve the durability of images produced using the LEP ink. The other additives may constitute 10 wt.% or less of the total solids of the electrostatic ink composition, in some examples, 5 wt.% or less of the total solids of the electrostatic ink composition, in some examples, 3 wt.% or less of the total solids of the electrostatic ink composition.

The liquid electrophotographic photovoltaic ink composition may comprise a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion. In some examples, the LEP photovoltaic ink composition further comprises conductive particles, the LEP photovoltaic ink composition may comprise a dispersion of a material with a perovskite structure; a thermoplastic resin; and conductive particles in a carrier liquid. In some examples, the LEP photovoltaic ink composition comprises a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally, conductive particles, in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and a monomer having acidic side groups; and/or a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the liquid electrophotographic photovoltaic ink composition comprises a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally, conductive particles, in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally, conductive particles, in a carrier liquid may comprise a carrier liquid and chargeable particles comprising a material with a perovskite structure and a thermoplastic resin, and optionally, conductive particles.

In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid may be producible by combining a liquid electrophotographic ink composition comprising a dispersion of a salt AX and a thermoplastic resin in a carrier liquid with a liquid electrophotographic ink composition comprising a dispersion of a salt BX₂ or a salt BX₄ and a thermoplastic resin in a carrier liquid. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may be producible by combining a liquid electrophotographic ink composition comprising a dispersion of a salt AX and a thermoplastic resin in a carrier liquid with conductive particles and with a liquid electrophotographic ink composition comprising a dispersion of a salt BX₂ or a salt BX₄ and a thermoplastic resin in a carrier liquid. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may be producible by combining a liquid electrophotographic ink composition comprising a dispersion of a salt AX, a thermoplastic resin and conductive particles in a carrier liquid with a liquid electrophotographic ink composition comprising a dispersion of a salt BX₂ or a salt BX₄ and a thermoplastic resin in a carrier liquid. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may be producible by combining a liquid electrophotographic ink composition comprising a dispersion of a salt AX and a thermoplastic resin in a carrier liquid with a liquid electrophotographic ink composition comprising a dispersion of a salt BX₂ or a salt BX₄, a thermoplastic resin and conductive particles in a carrier liquid. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and optionally conductive particles in a carrier liquid may be producible by combining a salt AX, a salt selected from the group consisting of BX₂ and BX₄, a thermoplastic resin, a carrier liquid, and, if present, conductive particles. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and optionally conductive particles in a carrier liquid, wherein the material with a perovskite structure has the chemical formula ABX₃, may be producible by combining a salt AX, a salt BX₂, a thermoplastic resin, a carrier liquid, and, if present, conductive particles. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and optionally conductive particles in a carrier liquid, wherein the material with a perovskite structure has the chemical formula A₂BX₆, may be producible by combining a salt AX, a salt BX₄, a thermoplastic resin, a carrier liquid, and, if present, conductive particles.

In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid may further comprise a charge adjuvant. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may further comprise a charge adjuvant.

In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid may further comprise a charge director. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid may further comprise a charge adjuvant and a charge director. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may further comprise a charge director. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may further comprise a charge adjuvant and a charge director. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid may further comprise additives. In some examples, the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure, a thermoplastic resin and conductive particles in a carrier liquid may further comprise additives.

The thermoplastic resin of the LEP photovoltaic ink composition may be referred to herein as the PV thermoplastic resin. The conductive particles of the LEP photovoltaic ink composition may be referred to herein as PV conductive particles to distinguish them from the electrically conductive metal particles of the electrically conductive LEP ink composition.

In some examples, the PV thermoplastic resin may constitute 5 wt.% or more of the total non-volatile solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, for example, 10 wt.% or more, 15 wt.% or more, 20 wt.% or more, 25 wt.% or more, 30 wt.% or more, 35 wt.% or more, 40 wt.% or more, 45 wt.% or more, 50 wt.% or more, 55 wt.% or more, or 60 wt.% or more of the total non-volatile solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid. In some examples, the PV thermoplastic resin may constitute 60 wt.% or less of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, for example, 55 wt.% or less, 40 wt.% or less, 45 wt.% or less, 40 wt.% or less, 35 wt.% or less, 30 wt.% or less, 25 wt.% or less, 20 wt.% or less, 15 wt.% or less, 10 wt.% or less, or 5 wt.% or less of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid. In some examples, the PV thermoplastic resin may constitute 5 wt.% to 60 wt.% of the total non-volatile solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, for example, 10 wt.% to 55 wt.%, 15 wt.% to 50 wt.%, 20 wt.% to 45 wt.%, 25 wt.% to 45 wt.%, 30 wt.% to 60 wt.%, 35 wt.% to 55 wt.%, or 40 wt.% to 45 wt.% of the total non-volatile solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid. In some examples, the material with a perovskite structure may constitute 20 wt.% or more of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, for example, 20 wt.% or more, 25 wt.% or more, 30 wt.% or more, 35 wt.% or more, 40 wt.% or more, 45 wt.% or more, 50 wt.% or more, 55 wt.% or more, 60 wt.% or more, 65 wt.% or more, 70 wt.% or more, 75 wt.% or more, 80 wt.% or more, 85 wt.% or more, 90 wt.% or more, or 95 wt.% or more of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid. In some examples, the material with a perovskite structure may constitute 95 wt.% or less of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, for example, 90 wt.% or less, 85 wt.% or less, 80 wt.% or less, 75 wt.% or less, 70 wt.% or less, 65 wt.% or less, 60 wt.% or less, 55 wt.% or less, 50 wt.% or less, 45 wt.% or less, or 40 wt.% or less of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid. In some examples, the material with a perovskite structure may constitute 40 wt.% to 95 wt.% of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid, for example, 45 wt.% to 90 wt.%, 50 wt.% to 85 wt.%, 45 wt.% to 80 wt.%, 50 wt.% to 75 wt.%, 45 wt.% to 70 wt.%, 50 wt.% to 65 wt.%, or 40 wt.% to 60 wt.% of the total solids of the liquid electrophotographic photovoltaic ink composition comprising a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid.

In some examples, the conductive particles (the PV conductive particles) may be present in the solids of the LEP photovoltaic ink composition in an amount below the percolation threshold. In these examples, the printed photovoltaic layer (produced by printing the LEP photovoltaic ink composition) comprises the conductive particles (the PV conductive particles) in an amount below the percolation threshold.

As used herein, the term “percolation threshold” may refer to the threshold amount (e.g., volume percentage) of conductive particles above which long-range connectivity between the conductive particles occurs in the printed photovoltaic layer and/or in the solids of the LEP photovoltaic ink composition. In some examples, the PV conductive particles may be present in an amount of up to about 50 vol.% of the solids of the LEP photovoltaic ink composition, for example, up to about 40 vol.%, up to about 30 vol.%, up to about 20 vol.%, up to about 15 vol.%, up to about 10 vol.%, up to about 9 vol.%, up to about 8 vol.%, up to about 7 vol.%, up to about 6 vol.%, up to about 5 vol.%, up to about 4 vol.%, up to about 3 vol.%, up to about 2 vol.%, up to about 1 vol.%, up to about 0.9 vol.%, up to about 0.8 vol.%, up to about 0.7 vol.%, up to about 0.6 vol.%, up to about 0.5 vol.%, up to about 0.4 vol.%, up to about 0.3 vol.%, up to about 0.2 vol.%, or up to about 0.1 vol.% of the solids of the LEP photovoltaic ink composition. In some examples, the PV conductive particles may be present in an amount of at least about 0.01 vol.% of the solids of the LEP photovoltaic ink composition, for example, at least about 0.1 vol.%, at least about 0.2 vol.%, at least about 0.3 vol.%, at least about 0.4 vol.%, at least about 0.5 vol.%, at least about 0.6 vol.%, at least about 0.7 vol.%, at least about 0.8 vol.%, at least about 0.9 vol.%, at least about 1 vol.%, at least about 2 vol.%, at least about 3 vol.%, at least about 4 vol.%, at least about 5 vol.%, at least about 6 vol.%, at least about 7 vol.%, at least about 8 vol.%, at least about 9 vol.%, at least about 10 vol.%, at least about 15 vol.%, at least about 20 vol.%, at least about 30 vol.%, at least about 40 vol.%, or at least about 50 vol.% of the solids of the LEP photovoltaic ink composition. In some examples, the PV conductive particles may be present in an amount of from about 0.01 vol.% to about 50 vol.% of the solids of the LEP photovoltaic ink composition, for example, about 0.1 vol.% to about 40 vol.%, about 0.2 vol.% to about 30 vol.%, about 0.3 vol.% to about 20 vol.%, about 0.4 vol.% to about 15 vol.%, about 0.5 vol.% to about 10 vol.%, about 0.6 vol.% to about 9 vol.%, about 0.7 vol.% to about 8 vol.%, about 0.8 vol.% to about 7 vol.%, about 0.9 vol.% to about 6 vol.%, about 1 vol.% to about 5 vol.%, about 2 vol.% to about 4 vol.%, or about 0.01 vol.% to 3 vol.% of the solids of the LEP photovoltaic ink composition.

In some examples, the PV conductive particles may be present in an amount of up to about 50 wt.% of the solids of the LEP photovoltaic ink composition, for example, up to about 40 wt.%, up to about 30 wt.%, up to about 20 wt.%, up to about 15 wt.%, up to about 10 wt.%, up to about 9 wt.%, up to about 8 wt.%, up to about 7 wt.%, up to about 6 wt.%, up to about 5 wt.%, up to about 4 wt.%, up to about 3 wt.%, up to about 2 wt.%, up to about 1 wt.%, up to about 0.9 wt.%, up to about 0.8 wt.%, up to about 0.7 wt.%, up to about 0.6 wt.%, up to about 0.5 wt.%, up to about 0.4 wt.%, up to about 0.3 wt.%, up to about 0.2 wt.%, or up to about 0.1 wt.% of the solids of the LEP photovoltaic ink composition. In some examples, the PV conductive particles may be present in an amount of at least about 0.01 wt.% of the solids of the LEP photovoltaic ink composition, for example, at least about 0.1 wt.%, at least about 0.2 wt.%, at least about 0.3 wt.%, at least about 0.4 wt.%, at least about 0.5 wt.%, at least about 0.6 wt.%, at least about 0.7 wt.%, at least about 0.8 wt.%, at least about 0.9 wt.%, at least about 1 wt.%, at least about 2 wt.%, at least about 3 wt.%, at least about 4 wt.%, at least about 5 wt.%, at least about 6 wt.%, at least about 7 wt.%, at least about 8 wt.%, at least about 9 wt.%, at least about 10 wt.%, at least about 15 wt.%, at least about 20 wt.%, at least about 30 wt.%, at least about 40 wt.%, or at least about 50 wt.% of the solids of the LEP photovoltaic ink composition. In some examples, the PV conductive particles may be present in an amount of from about 0.01 wt.% to about 50 wt.% of the solids of the LEP photovoltaic ink composition, for example, about 0.1 wt.% to about 40 wt.%, about 0.2 wt.% to about 30 wt.%, about 0.3 wt.% to about 20 wt.%, about 0.4 wt.% to about 15 wt.%, about 0.5 wt.% to about 10 wt.%, about 0.6 wt.% to about 9 wt.%, about 0.7 wt.% to about 8 wt.%, about 0.8 wt.% to about 7 wt.%, about 0.9 wt.% to about 6 wt.%, about 1 wt.% to about 5 wt.%, about 2 wt.% to about 4 wt.%, or about 0.01 wt.% to 3 wt.% of the solids of the LEP photovoltaic ink composition. In some examples, the weight percentage of conductive particles present in the LEP photovoltaic ink composition may be comparable to the volume percentage. However, if the conductive particles comprise, for example, metal particles, the high density of the conductive particles may result in a significant difference between these measurements and the volume percentage may be more suitable for determining the amount to use.

In some examples, the conductive particles may be or comprise elongate particles (e.g., elongate carbon particles, such as carbon nanotubes) and the elongate particles may be present in any amount mentioned herein, with a maximum amount of up to about 1 vol.%. In some examples, the conductive particles may be or comprise elongate particles (e.g., elongate carbon particles, such as carbon nanotubes) and the elongate particles may be present in any amount mentioned herein, with a maximum amount of up to about 1 wt.%. In some examples, the conductive particles may be or comprise spherical particles and the spherical particles may be present in any amount mentioned herein, with a maximum amount of up to about 50 vol.%. In some examples, the conductive particles may be or comprise spherical particles and the spherical particles may be present in any amount mentioned herein, with a maximum amount of up to about 50 wt.%. Salt AX

In some examples, the salt AX may be a salt of a cation and an anion. In some examples, the salt AX may be a salt of a monovalent cation and a monovalent anion. In some examples, the salt AX may be a salt of a divalent cation and a divalent anion. In some examples, the salt AX may be a mixture of salts comprising monovalent cations and monovalent anions. In some examples, A is a monovalent cation or a mixture of monovalent cations. In some examples, X is a monovalent anion or a mixture of monovalent anions.

In some examples, A is selected from the group consisting of a metal cation, an organic cation or a mixture thereof. In some examples, A is selected from the group consisting of a monovalent metal cation, a monovalent organic cation, or a mixture thereof. In some examples, A is a monovalent metal cation or a mixture thereof. In some examples, A is a monovalent organic cation or a mixture thereof. In some examples, A is a mixture of a monovalent metal cation and a monovalent organic cation.

In some examples, A is an organic cation selected from the group consisting of primary aliphatic ammonium cations and primary aromatic ammonium cations. In some examples, A is a primary aliphatic ammonium cation. In some examples, A is selected from the group consisting of methylammonium (MA), formamidinium (FA), rubidium (Rb), caesium (Cs), and mixtures thereof. In some examples, A is caesium (Cs). In some examples, A is methylammonium (MA).

In some examples, X is a monovalent anion or a mixture of monovalent anions. In some examples, X is a halide ion. In some examples, X is selected from the group consisting of iodide, bromide, chloride and mixtures thereof. In some examples, X is selected from the group consisting of iodide, bromide and chloride. In some examples, X is bromide. In some examples, X is iodide.

In some examples, AX may be selected from the group consisting of methylammonium iodide (MAI), methylammonium bromide (MABr), methylammonium chloride (MACI), formamidinium iodide (FAI), formamidinium bromide (FABr), formamidinium chloride (FABr), caesium iodide (Csl), caesium bromide (CsBr), caesium chloride (CsCI) rubidium iodide (Rbl), rubidium bromide (RbBr), rubidium chloride (RbCI) or mixtures thereof. In some examples, AX may be selected from the group consisting of methylammonium iodide (MAI), methylammonium bromide (MABr), formamidinium iodide (FAI), formamidinium bromide (FABr), caesium iodide (Csl), caesium bromide (CsBr), or mixtures thereof. In some examples, AX may be selected from the group consisting of methylammonium iodide (MAI), methylammonium bromide (MABr), formamidinium iodide (FAI), formamidinium bromide (FABr), caesium iodide (Csl) and caesium bromide (CsBr). In some examples, AX may be selected from the group consisting of Csl and CsBr. In some examples, AX may be CsBr. In some examples, AX is selected from the group consisting of methylammonium iodide, methylammonium bromide and methylammonium chloride. In some examples, AX is methylammonium iodide.

Salt BX₂

In some examples, the salt BX₂ may be a salt of a cation and an anion. In some examples, the salt BX₂ may be a salt of a divalent cation and a monovalent anion. In some examples, the salt BX₂ may be a salt of a tetravalent cation and a divalent anion. In some examples, the salt BX₂ may be a mixture of salts comprising divalent cations and monovalent anions. In some examples, B is a divalent cation or a mixture of divalent cations. In some examples, X is a monovalent anion or a mixture of monovalent anions. In some examples, X in BX₂ may be different from X in AX. In some examples, X in BX₂ may be the same as X in AX.

In some examples, B is a divalent metal cation or a mixture of divalent metal cations. In some examples, B is a divalent metal cation.

In some examples, B is selected from the group consisting of lead (Pb), germanium (Ge), tin (Sn), antimony (Sb), bismuth (Bi), copper (Cu), manganese (Mn²⁺), cobalt (Co²⁺) and mixtures thereof. In some examples, B is selected from the group consisting of lead (Pb), germanium (Ge), tin (Sn), antimony (Sb), bismuth (Bi), Copper (Cu) and mixtures thereof. In some examples, B is lead.

In some examples, X is as described above for AX.

In some examples, BX₂ may be selected from the group consisting of Snl₂, SnBr₂, SnCI₂, Pbl₂, PbBr₂, PbCI₂ and combinations thereof. In some examples, BX₂ may be selected from the group consisting of Snl₂, SnBr₂, Pbl₂, PbBr₂ and combinations thereof. In some examples, BX₂ may be selected from the group consisting of Snl₂, SnBr₂, Pbl₂ and PbBr₂. In some examples, BX₂ may be selected from the group consisting of Snl₂ and SnBr₂. In some examples, BX₂ may be SnBr₂. In some examples, BX₂ is Pbl₂.

Salt BX₄

In some examples, the salt BX₄ may be a salt of a cation and an anion. In some examples, the salt BX₄ may be a salt of a tetravalent cation and a monovalent anion. In some examples, the salt BX₄ may be a mixture of salts comprising tetravalent cations and monovalent anions. In some examples, B is a tetravalent cation or a mixture of tetravalent cations. In some examples, X is a monovalent anion or a mixture of monovalent anions. In some examples, X in BX₄ may be the same as X in AX.

In some examples, B is a tetravalent metal cation or a mixture of tetravalent metal cations. In some examples, B is a tetravalent metal cation. In some examples, B is Sn⁴⁺.

In some examples, BX₄ is selected from the group consisting of Snl₄, SnBr₄, SnCI₄ and combinations thereof.

Material with a perovskite structure

In some examples, the material with a perovskite structure may be a perovskite wherein A is a cation or a mixture of cations, B is a cation or a mixture of cations and X is an anion or a mixture of anions. In some examples, the material with a perovskite structure may have the chemical formula ABX₃ wherein A is a monovalent cation or a mixture of monovalent cations, B is a divalent cation or a mixture of divalent cations and X is a monovalent anion or a mixture of monovalent anions. In some examples, the material with a perovskite structure may have the chemical formula ABX₃ wherein A is a divalent cation or a mixture of divalent cations, B is a tetravalent cation or a mixture of tetravalent cations and X is a divalent anion or a mixture of divalent anions. In some examples, the material with a perovskite structure may have the chemical formula A₂BX₆ wherein A is a monovalent cation or a mixture of monovalent cations, B is a tetravalent cation or mixture of tetravalent cations and X is a monovalent anion or a mixture of monovalent anions. In some examples, the material with a perovskite structure may have the chemical formula ABX₃ wherein A is a monovalent cation, B is a divalent cation and X is a monovalent anion or a mixture of monovalent anions. In some examples, the material with a perovskite structure may have the chemical formula ABX₃ wherein A is a monovalent cation, B is a divalent cation and X is a monovalent anion.

In some examples, A is as described above for AX. In some examples, B is as described above for BX₂ or as described above for BX₄. In some examples, X is as described above for AX or BX₂ or BX₄.

As used herein, the term perovskite does not specifically refer to the perovskite mineral, CaTiO₃ but instead refers to any material that has the same type of crystal structure as calcium titanium oxide. As used herein, the term perovskite structure indicates that the material has the perovskite type crystal structure.

In some examples, the material with a perovskite structure may be selected from the group consisting of MAPbl₃, CsSnBr₃, Cs₂SnBr₆, Rb_z[Cs_y(MA_xFA_1.x)₁.y]_1.zPb₁M₁.| (1_1.n.mBr_mCln)₃ (wherein 0<x< 1, 0<y< 1, 0<z< 1, 0<l< 1, 0<m< 1, 0<n< 1; M=Sn or In), and Rb_z[Cs_y(MA_xFA_1.x)_1.y]_1.zB(l_1.n.mBr_mCln)₃ (wherein 0<x< 1,0<y< 1,0 <z<1,0<m<1,0<n<1; B=Ge, Sn, Sb, Bi or Cu). In some examples, the material with a perovskite structure may be CsSnBr₃. In some examples, the material with a perovskite structure may be MAPbl₃.

The material with a perovskite structure may have a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion. In some examples, the material with a perovskite structure has the chemical formula ABX₃. In some examples, the material with a perovskite structure has the chemical formula A₂BX₆.

In some examples, A is selected from the group consisting of a monovalent metal cation, a monovalent organic cation, or a mixture thereof; and/or B is a divalent metal cation or a tetravalent metal cation; and/or X is a halide ion. In some examples, X is a halide ion, for example, selected from the group consisting of iodide, bromide, chloride and mixtures thereof; and/or A is selected from the group consisting of methylammonium (MA), formamidinium (FA), rubidium (Rb), caesium (Cs), and mixtures thereof; and/or B is selected from the group consisting of lead (Pb), germanium (Ge), tin (Sn), antimony (Sb), bismuth (Bi), copper (Cu), manganese (Mn), cobalt (Co) and mixtures thereof; and/or the liquid carrier is a hydrocarbon. Conductive particles

The LEP photovoltaic ink composition may comprise conductive particles. The conductive particles may be present in an amount below the percolation threshold of the printed photovoltaic layer.

In some examples, the conductive particles may have any shape. In some examples, the shape of the conductive particles may be defined by the relative dimensions of the long, intermediate and short axes of the particles (where the three axes may be perpendicular to each other). In some examples, all three of the relative dimensions may be the same or different or any two of the relative dimensions may be the same and the third dimension may be different. In some examples, the conductive particles may comprise or consist of oblate particles, prolate particles, bladed particles, equant particles, or combinations thereof. In some examples, the conductive particles may comprise or consist of spherical particles, approximately spherical particles, elliptical particles, elongate particles, flat particles, flakes, prismatic particles, scalenohedral particles, dendrimers, amorphous particles, or combinations thereof.

In some examples, the conductive particles comprise or consist of elongate particles, spherical particles, approximately spherical particles (i.e., particles with a geometry that is close to spherical), or combinations thereof. In some examples, the conductive particles comprise or consist of elongate particles. The elongate particles may be elongate conductive carbon particles (e.g., carbon nanotubes).

Elongate particles may be particles having a first dimension that is longer than each of a second dimension and a third dimension, wherein the first, second and third dimensions are perpendicular to one another. In some examples, the second dimension and the third dimension may be the same or different. In some examples, the elongate particles are rod-shaped. In some examples, the elongate particles (e.g., carbon nanotubes) may have an aspect ratio between 2 and 10,000. As described herein, the aspect ratio may be defined as the ratio of the length of the longest dimension of an elongate conductive species (e.g., the first dimension described above) to the length of the next-to-longest dimension (e.g., the second or third dimension described above), wherein the dimensions are perpendicular to one another. The elongate particles (e.g., carbon nanotubes) may have an aspect ratio of at least about 2, for example, at least about 3, at least about 4, at least about 5, at least about 6, at least about 7, at least about 8, at least about 9, at least about 10, at least about 11 , at least about 12, at least about 13, at least about 14, at least about 15, at least about 16, at least about 17, at least about 18, at least about 19, at least about 20, at least about 25, at least about 30, at least about 40, at least about 50, at least about 60, at least about 70, at least about 80, at least about 90, at least about 100, at least about 150, at least about 200, at least about 300, at least about 400, at least about 500, at least about 1000, at least about 1500, at least about 2000, at least about 2500, at least about 3000, at least about 3500, at least about 4000, at least about 4500, at least about 5000, at least about 5500, at least about 6000, at least about 6500, at least about 7000, at least about 7500, at least about 8000, at least about 8500, at least about 9000, at least about 9500, at least about 10,000.

In some examples, the elongate particles (e.g., carbon nanotubes) may have an aspect ratio of up to about 50,000, for example, up to about 40000, up to about 35000, up to about 30000, up to about 25000, up to about 20000, up to about 10000, up to about 9500, up to about 9000, up to about 8500, up to about 8000, up to about 7500, up to about 7000, up to about 6500, up to about 6000, up to about 5500, up to about 5000, up to about 4500, up to about 4000, up to about 3500, up to about 3000, up to about

2500, up to about 2000, up to about 1500, up to about 1000, up to about 500, up to about 100, up to about 50, up to about 10.

In some examples, the elongate particles (e.g., carbon nanotubes) may have an aspect ratio of from about 2 to about 50,000, for example, 50 to 35000, 100 to 30000, 500 to 25000, 1000 to 20000, 2500 to 24000, 5000 to 20000, or 7000 to 10000.

In some examples, the conductive particles comprise or consist of metal particles, inorganic conductive particles, inorganic semiconductive particles, conductive carbon particles, conductive polymers or combinations thereof.

In some examples, the metal particles comprise or consist of elemental metal particles, metal alloy particles, metallic dendrimers, or a mixture thereof. In some examples, the metal particles may comprise or consist of a metal selected from the group consisting of copper, aluminium, silver, gold or a combination thereof. In some examples, the inorganic semiconductive particles may comprise or consist of nickel oxide (NiO), copper oxide (CuO) or a combination thereof. In some examples, the conductive carbon particles may comprise or consist of carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes or a mixture thereof), carbon black, or a combination thereof. In some examples, the conductive carbon particles comprise or consist of carbon nanotubes, for example, single-walled carbon nanotubes. In some examples, the conductive polymer may comprise or consist of polypyrrole, conductive polyaniline, polyfluorene, a polyphenylene (e.g., polyphenylene or a substituted polyphenylene), a polypyrene (e.g., polypyrene or a substituted polypyrene), a polyazulene (e.g., polyazulene or a substituted polyazulene), a polynaphthalene (e.g., polynaphthalene or a substituted polynaphthalene), a poly(acetylene) (PAC) (e.g., poly(acetylene) or a substituted polyacetylene), poly(p-phenylene vinylene) (PPV), a polycarbazole (e.g., polycarbazole or a substituted polycarbazole), a polyindole (e.g., polyindole or a substituted polyindole), a polyazepine (e.g., polyazepine or a substituted polyazepine), a poly(thiophene) (PT) (e.g., polythiophene or a substituted polythiophene), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene sulfide) (PPS), or a combination thereof. In some examples, the conductive polyaniline may be sulfuric acid doped polyaniline, polyaniline emeraldine base or a combination thereof.

In some examples, the conductive particles may be or comprise carbon nanotubes. The carbon nanotubes may be straight walled or bent nanotubes. In some examples, the carbon nanotubes may be selected from the group consisting of straight or bent multi-walled carbon nanotubes (MWCNTs), straight or bent double-walled carbon nanotubes (DWCNTs), straight or bent single-walled carbon nanotubes (SWCNTs), or combinations of these carbon nanotube forms and may comprise common by-products contained in carbon nanotube preparations.

In some examples, the elongate particles, for example, the carbon nanotubes (e.g., single-walled carbon nanotubes) may have an outer diameter of up to 4 nm, for example, up to 3.5 nm, up to 3.25 nm, up to 3 nm. In some examples, the elongate particles, for example, the carbon nanotubes (e.g., single-walled carbon nanotubes) may have an outer diameter of 0.5 nm to 2.5 nm, for example, 0.5 nm to 2 nm, 0.5 nm to 1 .5 nm, or 0.5 nm to 1 nm.

In some examples, such as in multi-walled carbon nanotubes, the carbon nanotubes have an outer diameter of at least 2 nm, for example, at least 3 nm, at least 5 nm, at least 10 nm, or at least 15 nm. In some examples, such as in multi-walled nanotubes, the carbon nanotubes have an outer diameter of 2 nm to 50 nm.

In some examples, the carbon nanotubes comprise single walled carbon-based SWNT- containing material. SWNTs can be formed by a number of techniques, such as laser ablation of a carbon target, decomposing a hydrocarbon, and setting up an arc between two graphite electrodes.

Thermoplastic resin of the LEP photovoltaic ink composition (PV thermoplastic resin)

The LEP photovoltaic ink composition may comprise a thermoplastic resin. The thermoplastic resin of the LEP photovoltaic ink composition may be referred to herein as the PV thermoplastic resin to distinguish it from the thermoplastic resin of the hole transport LEP ink composition (HT thermoplastic resin) and the thermoplastic resin of the electrically conductive LEP ink composition.

The thermoplastic resin of the LEP photovoltaic ink composition may comprise a copolymer of an alkylene monomer and a monomer having acidic side groups; and/or a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. The thermoplastic resin of the LEP photovoltaic ink composition may comprise a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide. Once printed, the epoxide may have been subjected to a ring-opening reaction and/or a cross-linking reaction.

The thermoplastic resin of the LEP photovoltaic ink composition (i.e., the PV thermoplastic resin) may comprise a thermoplastic polymer. The PV thermoplastic resin may be referred to herein as a resin. In some examples, the PV thermoplastic resin may comprise a copolymer of an alkylene monomer and a monomer having acidic side groups; and/or a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the PV thermoplastic resin may comprise a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer and a monomer having acidic side groups. In some examples, the copolymer of an alkylene monomer and a monomer having acidic side groups may be any copolymer described herein comprising an alkylene monomer and a monomer having acidic side groups, for example, as described for use in the electrically conductive LEP ink composition (e.g., as an EC thermoplastic resin).

In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide. In some examples, the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide may be any copolymer described herein comprising an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, for example, as described for use in the hole transport LEP ink composition (e.g., as an HT thermoplastic resin).

In some examples, the copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide may be a copolymer of ethylene and an ethylenically unsaturated ester comprising an epoxide, such as glycidyl methacrylate.

In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer having acidic side groups. In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer having ester side groups. In some examples, the thermoplastic resin may comprise a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, a monomer having acidic side groups and a monomer having ester side groups. In some examples, the alkylene monomer may be any alkylene monomer described herein. In some examples, the ethylenically unsaturated monomer comprising an epoxide may be any ethylenically unsaturated monomer comprising an epoxide described herein. In some examples, the monomer having acidic side groups may be any monomer having acidic side groups described herein.

In some examples, the monomer having ester side groups may be any monomer having ester side groups. In some examples, the monomer having ester side groups may be an ethylenically unsaturated ester, for example, an ester of an ethylenically unsaturated carboxylic acid and an alcohol or an ester of a carboxylic acid and an ethylenically unsaturated alcohol.

In some examples, the monomer having ester side groups may be an ester of an ethylenically unsaturated carboxylic acid and an alcohol. In some examples, the ethylenically unsaturated carboxylic acid may be an a,|3-unsaturated carboxylic acid. In some examples, the a,|3-unsaturated carboxylic acid may be an a,|3-unsaturated, a- alkyl carboxylic acid. In some examples, the a,|3-unsaturated carboxylic acid may be selected from the group consisting of propen-2-oic acid or an a,|3-unsaturated, a-alkyl carboxylic acid described herein. In some examples, the a,|3-unsaturated carboxylic acid may be propen-2-oic acid (also known as acrylic acid) or 2-methylprop-2-enoic acid (also known as methacrylic acid). In some examples, the alcohol may be a C1 to C10 alcohol, for example, methanol, ethanol, propanol, butanol, pentanol, or hexanol.

In some examples, the monomer having ester side groups may be an ester of a carboxylic acid and an ethylenically unsaturated alcohol. In some examples, the carboxylic acid may be methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid or hexanoic acid. In some examples, the ethylenically unsaturated alcohol may be vinyl alcohol, hydroxypropene, hydroxybutene, hydroxypentene, or hydroxyhexene. In some examples, the ethylenically unsaturated alcohol may be vinyl alcohol.

In some example, the monomer having ester side groups may be methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, pentyl acrylate, pentyl methacrylate, or vinyl acetate.

In some examples, the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide and a monomer having ester side groups may be a copolymer of ethylene, a monomer selected from the group consisting of glycidyl acrylate and glycidyl methacrylate, and a monomer selected from the group consisting of methyl acrylate, butyl acrylate and vinyl acetate. In some examples, the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide and a monomer having ester side groups may be a copolymer of ethylene, glycidyl methacrylate, and a monomer selected from the group consisting of methyl acrylate, butyl acrylate and vinyl acetate. In some examples, the monomer comprising an epoxide may constitute about 1 wt.% to about 20 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof, for example, about 2 wt.% to about 15 wt.%, about 3 wt.% to about 12 wt.%, about 4 wt.% to about 11 wt.%, about 5 wt.% to about 10 wt.%, about 6 wt.% to about 9 wt.%, about 7 wt.% to about 8 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the monomer comprising an epoxide may constitute at least about 1 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof, for example, at least about 2 wt.%, at least about 3 wt.%, at least about 4 wt.%, at least about 5 wt.%, at least about 6 wt.%, at least about 7 wt.%, at least about 8 wt.%, at least about 9 wt.%, at least about 10 wt.%, at least about 11 wt.%, at least about 12 wt.%, at least about 13 wt.%, at least about 14 wt.%, at least about 15 wt.%. In some examples, the monomer comprising an epoxide may constitute up to about 20 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof, for example, up to about 15 wt.%, up to about 14 wt.%, up to about 13 wt.%, up to about 12 wt.%, up to about 11 wt.%, up to about 10 wt.%, up to about 9 wt.%, up to about 8 wt.%, up to about 7 wt.%, up to about 6 wt.%, up to about 5 wt.%, up to about 4 wt.%, up to about 3 wt.%, up to about 2 wt.%, up to about 1 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the remaining weight percentage may constitute the alkylene monomer and the monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof.

In some examples, the monomer selected from the group consisting of a monomer having acidic side groups monomer, a monomer having ester side groups and mixture thereof may constitute about 1 wt.% to about 35 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof, for example, about 5 wt.% to about 30 wt.%, about 10 wt.% to about 28 wt.%, about 15 wt.% to about 27 wt.%, about 20 wt.% to 25 wt.%, about 23 wt.% to about 24 wt.% of the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the remaining weight percentage may constitute the alkylene monomer and the ethylenically unsaturated monomer comprising an epoxide.

In some examples, the copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof may comprise about 1 wt.% to about 20 wt.% of the ethylenically unsaturated monomer comprising an epoxide (for example, about 2 wt.% to about 15 wt.%, about 3 wt.% to about 12 wt.%, about 4 wt.% to about 11 wt.%, about 5 wt.% to about 10 wt.%, about 6 wt.% to about 9 wt.%, about 7 wt.% to about 8 wt.%); about 1 wt.% to about 35 wt.% of the monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof (for example, about 5 wt.% to about 30 wt.%, about 10 wt.% to about 28 wt.%, about 15 wt.% to about 27 wt.%, about 20 wt.% to 25 wt.%, about 23 wt.% to about 24 wt.%); and the remaining weight percentage may be alkylene monomer.

The polymer or polymers of the PV thermoplastic resin may be selected from the group consisting of poly(ethylene-co-glycidyl methacrylate) (sold by Merck), poly(ethylene-co- methyl acrylate-co-glycidyl methacrylate) (sold by Merck), Lotader AX8840, Lotader AX8820, Lotader™ AX8900, Lotader AX8930, Lotader™ AX8750, Lotader AX8670T, Igetabond™ CG5001 , Igetabond™ BF-2C, Igetabond™ BR-E, Igetabond™ BF-2B, Igetabond™ BF-7B, Igetabond™ BR-7L and Igetabond™ BF-7M.

Liquid carrier

The LEP photovoltaic ink composition may comprise a liquid carrier, which may also be termed a carrier liquid. The LEP photovoltaic ink composition may comprise the same or a different liquid carrier as the hole transport LEP ink composition. The LEP photovoltaic ink composition may comprise the same liquid carrier as the hole transport LEP ink composition.

In some examples, the liquid carrier of the LEP photovoltaic ink composition is as described above for the liquid carrier of the hole transport LEP ink composition. In some examples, the liquid carrier of the LEP photovoltaic ink composition may comprise a different liquid carrier than the hole transport LEP ink composition and the liquid carrier may be as described above for the liquid carrier of the hole transport LEP ink composition.

Charge director

The LEP photovoltaic ink composition may further comprise a charge director. The LEP photovoltaic ink composition may comprise the same or a different charge director as the hole transport LEP ink composition.

In some examples, the charge director of the LEP photovoltaic ink composition is as described above for the charge director of the hole transport LEP ink composition. In some examples, the charge director of the LEP photovoltaic ink composition may comprise a different charge director than the hole transport LEP ink composition and the charge director may be as described above for the charge director of the hole transport LEP ink composition.

Charge adjuvant

The LEP photovoltaic ink composition may further comprise a charge adjuvant. The LEP photovoltaic ink composition may comprise the same or a different charge adjuvant as the hole transport LEP ink composition.

In some examples, the charge adjuvant of the LEP photovoltaic ink composition is as described for the charge adjuvant of the hole transport LEP ink composition. In some examples, the charge adjuvant of the LEP photovoltaic ink composition may comprise a different charge adjuvant than the hole transport LEP ink composition and the charge adjuvant may be as described above for the charge adjuvant of the hole transport LEP ink composition. Other additives

The LEP photovoltaic ink composition may further comprise an additive or a plurality of additives. The LEP photovoltaic ink composition may comprise the same or different additive(s) as the hole transport LEP ink composition.

In some examples, the additive(s) of the LEP photovoltaic ink composition is as described for the additive(s) of the hole transport LEP ink composition. In some examples, the additive(s) of the LEP photovoltaic ink composition may comprise a different additive or additives than the hole transport LEP ink composition and the additive(s) may be as described above for the additive(s) of the hole transport LEP ink composition.

The electrically conductive liquid electrophotographic ink composition may comprise a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles. In some examples, the electrically conductive LEP ink composition comprises a liquid carrier; a thermoplastic resin and electrically conductive metal particles.

In some examples, the electrically conductive LEP ink composition further comprises a charge adjuvant. In some examples, the electrically conductive LEP ink composition comprises a liquid carrier; a charge adjuvant; and particles comprising a thermoplastic resin and electrically conductive metal particles.

In some examples, the electrically conductive LEP ink composition further comprises a charge director. In some examples, the electrically conductive LEP ink composition comprises a liquid carrier; a charge director; and particles comprising a thermoplastic resin and electrically conductive metal particles. In some examples, the electrically conductive LEP ink composition comprises a liquid carrier; a charge adjuvant; a charge director; and particles comprising a thermoplastic resin and electrically conductive metal particles.

As used herein, the phrase “electrically conductive liquid electrophotographic ink composition” may refer to a liquid electrophotographic ink composition that, once printed, produces an electrically conductive printed layer, for example, a printed layer that may function as a cathode. In some examples, the electrically conductive liquid electrophotographic ink composition itself may not be electrically conductive. Particles comprising a thermoplastic resin and electrically conductive metal particles

The electrically conductive LEP ink composition may comprise particles comprising a thermoplastic resin and electrically conductive metal particles. The electrically conducive LEP ink composition may comprise a thermoplastic resin and electrically conductive metal particles. In some examples, the thermoplastic resin of the electrically conductive LEP ink composition may be referred to herein as the EC thermoplastic resin.

In some examples, the electrically conductive metal particles may constitute at least about 75 wt.% of the solids of the electrically conductive LEP ink composition, for example, at least about 80 wt.%, at least about 81 wt.%, at least about 82 wt.%, at least about 83 wt.%, at least about 84 wt.%, at least about 85 wt.%, at least about 86 wt.%, at least about 87 wt.%, at least about 88 wt.%, at least about 89 wt.%, at least about 90 wt.%, at least about 91 wt.%, at least about 92 wt.%, at least about 93 wt.%, at least about 94 wt.%, at least about 95 wt.%, at least about 96 wt.%, or at least about 97 wt.% of the solids of the electrically conductive LEP ink composition. In some examples, the electrically conductive metal particles may constitute up to about 97 wt.% of the solids of the electrically conductive LEP ink composition, for example, up to about 96 wt.%, up to about 95 wt.%, up to about 94 wt.%, up to about 93 wt.%, up to about 92 wt.%, up to about 91 wt.%, or up to about 90 wt.% up to about 96 wt.%, up to about 95 wt.%, up to about 94 wt.%, up to about 93 wt.%, up to about 92 wt.%, up to about 91 wt.%, or up to about 90 wt.% up to about 89 wt.%, up to about

88 wt.%, up to about 87 wt.%, up to about 86 wt.%, up to about 85 wt.%, up to about

84 wt.%, up to about 83 wt.%, up to about 82 wt.%, up to about 81 wt.%, up to about

80 wt.%, or up to about 75 wt.% of the solids of the electrically conductive LEP ink composition. In some examples, the electrically conductive metal particles may constitute from about 75 wt.% to about 97 wt.% of the solids of the electrically conductive LEP ink composition, for example, from about 80 wt.% to about 96 wt.%, from about 81 wt.% to about 95 wt.%, from about 82 wt.% to about 94 wt.%, from about 83 wt.% to about 93 wt.%, from about 84 wt.% to about 92 wt.%, from about 85 wt.% to about 91 wt.%, from about 86 wt.% to about 90 wt.%, from about 87 wt.% to about

89 wt.%, or from about 87 wt.% to about 88 wt.% of the solids of the electrically conductive LEP ink composition.

In some examples, the EC thermoplastic resin constitutes up to about 25 wt.% of the electrically conductive LEP ink composition, for example, up to about 20 wt.%, up to about 21 wt.%, up to about 20 wt.%, up to about 19 wt.%, up to about 18 wt.%, up to about 17 wt.%, up to about 16 wt.%, up to about 15 wt.%, up to about 14 wt.%, up to about 13 wt.%, up to about 12 wt.%, up to about 11 wt.%, up to about 10 wt.%, up to about 9 wt.%, up to about 8 wt.%, up to about 7 wt.%, up to about 6 wt.%, up to about

5 wt.%, up to about 4 wt.%, or up to about 3 wt.% of the solids of the electrically conductive LEP ink composition. In some examples, the EC thermoplastic resin constitutes at least about 3 wt.% of the solids of the electrically conductive LEP ink composition, for example, at least about 4 wt.%, at least about 5 wt.%, at least about

6 wt.%, at least about 7 wt.%, at least about 8 wt.%, at least about 9 wt.%, at least about 10 wt.%, at least about 11 wt.%, at least about 12 wt.%, at least about 13 wt.%, at least about 14 wt.%, at least about 15 wt.%, at least about 16 wt.%, at least about 17 wt.%, at least about 18 wt.%, at least about 19 wt.%, at least about 20 wt.%, or at least about 25 wt.%. In some examples, the EC thermoplastic resin constitutes from about 3 wt.% to about 25 wt.% of the solids of the electrically conductive LEP ink composition, for example, from about 4 wt.% to about 20 wt.%, from about 5 wt.% to about 19 wt.%, from about 6 wt.% to about 18 wt.%, from about 7 wt.% to about 17 wt.%, from about 8 wt.% to about 16 wt.%, from about 9 wt.% to about 15 wt.%, from about 10 wt.% to about 14 wt.%, from about 11 wt.% to about 13 wt.%, or from about 11 wt.% to about 12 wt.% of the solids of the electrically conductive LEP ink composition. In an example, the EC thermoplastic resin constitutes about 5 to 90%, in some examples about 5 to 80% by weight of the total solids of the electrostatic ink composition. In another example, the resin constitutes about 10 to 60% by weight of the total solids of the electrostatic ink composition. In another example, the resin constitutes about 15 to 40% by weight of the total solids of the electrostatic ink composition. In another example, the resin constitutes about 60 to 95% by weight, in some examples, from 65 to 90% by weight, from 65 to 80% by weight of the total solids of the electrostatic ink composition.

In some examples, the electrically conductive metal particles may comprise any metal. In some examples, the electrically conductive metal particles may comprise a metal selected from the group consisting of copper, titanium, chromium, iron, manganese, nickel, silver, gold, platinum, rhodium, iridium, and combinations thereof.

In some examples, the electrically conductive metal particles comprise a first metal and a second metal, wherein the first metal is different from the second metal. In some examples, the electrically conductive metal particles comprise a core comprising a first metal and a shell comprising a second metal; wherein the shell at least partially encloses the core and wherein the first metal is different from the second metal.

In some examples, the shell may substantially completely enclose the core. In some examples, the shell may completely encloses the core. In some examples, the shell can enclose at least about 90% of the core surface area, for example, at about least 91% of the core surface area, at least about 92% of the core surface area, at least about 93% of the core surface area, at least about 94% of the core surface area, at least about 95% of the core surface area, at least about 96% of the core surface area, at least about 97% of the core surface area, at least about 98% of the core surface area, at least about 99% of the core surface area, about 100% of the core surface area. In some examples, the proportion of the core surface area enclosed by the shell may be measured using standard procedures known in the art, such as energy dispersive spectroscopy, for example, by using the procedure described in ASTM E1508 - 12a(2019).

In some examples, the shell thickness can be from about 0.01 pm to about 10 pm, for example, from about 0.1 pm to about 3 pm, from about 0.2 pm to about 2 pm, from about 0.3 pm to about 1 pm, from about 0.4 pm to about 0.9 pm, from about 0.5 pm to about 0.8 pm, from about 0.6 pm to about 0.7 pm, or the shell thickness can be from about 0.01 pm to about 0.1 pm. In some examples, the shell thickness can be less than about 2 pm, for example, less than about 1 pm, less than about 0.1 pm. The shell thickness may be measured by SEM imaging. In some examples, the shell thickness may be measured by scanning electron microscopy, for example, by using the procedure described in ASTM E2142 - 08(2015)

In some examples, the metal particles can have a diameter of from about 1 pm to about 20 pm, for example, from about 1 pm to about 10 pm, from about 1 pm to about 9 pm, from about 1 pm to about 8 pm, from about 1 pm to about 7 pm, about 1 pm to about 6 pm, about 1 pm to about 5 pm. In some examples, the metal particles can have a diameter of less than about 20 pm, for example, less than about 15 pm, less than about 12 pm, less than about 10 pm, less than about 9 pm, less than about 8 pm, less than about 7 pm, less than about 6 pm, or less than about 5 pm. In some examples, the diameter of the metal particles may be determined by scanning electron microscopy, for example, by using the procedure described in ASTM E2142 - 08(2015). In some examples, the metal particles have a particle size distribution such that the D50 is 4 pm or less, for example, 3.9 pm or less, 3.8 pm or less, 3.7 pm or less, 3.6 pm or less, 3.5 pm or less, 3.4 pm or less, 3.3 pm or less, 3.2 pm or less, 3.1 pm or less, 3 pm or less, 2.9 pm or less, 2.8 pm or less, 2.7 pm or less, 2.6 pm or less, 2.5 pm or less, 2.4 pm or less, 2.3 pm or less, 2.2 pm or less, 2.1 pm or less, 2 pm or less, 1.9 pm or less, 1.8 pm or less, 1.7 pm or less, 1.6 pm or less, 1.5 pm or less, 1.4 pm or less, 1 .3 pm or less, 1 .2 pm or less, 1.1 pm or less, or 1 pm or less. In some examples, the metal particles have a particle size distribution such that the D50 is 1 pm or more, for example, 1.1 pm or more, 1 .2 pm or more, 1 .3 pm or more, 1 .4 pm or more, 1 .5 pm or more, 1.6 pm or more, 1.7 pm or more, 1.8 pm or more, 1.9 pm or more, 2 pm or more, 2.1 pm or more, 2.2 pm or more, 2.3 pm or more, 2.4 pm or more, 2.5 pm or more, 2.6 pm or more, 2.7 pm or more, 2.8 pm or more, 2.9 pm or more, 3 pm or more, 3.1 pm or more, 3.2 pm or more, 3.3 pm or more, 3.4 pm or more, 3.5 pm or more, 3.6 pm or more, 3.7 pm or more, 3.8 pm or more, 3.9 pm or more, or 4 pm or more. In some examples, the metal particles have a particle size distribution such that the D50 is from 1 pm to 4 pm, for example, 1.1 pm to 4 pm, 1.2 pm to 3.9 pm, 1.3 pm to 3.8 pm, 1 .4 pm to 3.7 pm, 1 .5 pm to 3.6 pm, 1 .6 pm to 3.5 pm, 1 .7 pm to 3.4 pm, 1 .8 pm to

3.3 pm, 1 .9 pm to 3.2 pm, 2 pm to 3.1 pm, 2.1 pm to 3 pm, 2.2 pm to 2.9 pm, 2.3 pm to

2.8 pm, 2.4 pm to 2.7 pm, or 2.5 pm to 2.6 pm.

In some examples, the metal particles have a particle size distribution such that the D90 is 7 pm or less, for example, 6.9 pm or less, 6.8 pm or less, 6.7 pm or less, 6.6 pm or less, 6.5 pm or less, 6.4 pm or less, 6.3 pm or less, 6.2 pm or less, 6.1 pm or less, 6 pm or less, 5.9 pm or less, 5.8 pm or less, 5.7 pm or less, 5.6 pm or less, 5.5 pm or less, 5.4 pm or less, 5.3 pm or less, 5.2 pm or less, 5.1 pm or less, 5 pm or less, 4.9 pm or less, 4.8 pm or less, 4.7 pm or less, or 4.6 pm or less, or 4.5 pm or less. In some examples, the metal particles have a particle size distribution such that the D90 is 4.5 pm or more, for example, 4.6 pm or more, 4.7 pm or more, 4.8 pm or more, 4.9 pm or more, 5 pm or more, 5.1 pm or more, 5.2 pm or more, 5.3 pm or more, 5.4 pm or more, 5.5 pm or more, 5.6 pm or more, 5.7 pm or more, 5.8 pm or more, 5.9 pm or more, 6 pm or more, 6.1 pm or more, 6.2 pm or more, 6.3 pm or more, 6.4 pm or more, 6.5 pm or more, 6.6 pm or more, 6.7 pm or more, 6.8 pm or more, or 6.9 pm or more, or 7 pm or more. In some examples, the metal particles have a particle size distribution such that the D90 is 4.5 pm to 7 pm, for example, 4.6 pm to 7 pm, 4.7 pm to 6.9 pm, 4.8 pm to 6.8 pm, 4.9 pm to 6.7 pm, 5 pm to 6.6 pm, 5.1 pm to 6.5 pm, 5.2 pm to 6.4 pm, 5.3 pm to 6.3 pm, 5.4 pm to 6.2 pm, 5.5 pm to 6.1 pm, 5.6 pm to 6 pm, 5.7 pm to 5.9 pm, or 5.8 pm to 5.9 pm.

In some examples, the metal particles have a particle size distribution such that the D10 is 2.5 pm or less, for example, 2.4 pm or less, 2.3 pm or less, 2.2 pm or less, 2.1 pm or less, 2 pm or less, 1 .9 pm or less, 1 .8 pm or less, 1 .7 pm or less, 1 .6 pm or less, 1.5 pm or less, 1.4 pm or less, 1.3 pm or less, 1.2 pm or less, 1.1 pm or less, 1 pm or less, 0.9 pm or less, 0.8 pm or less, 0.7 pm or less, or 0.6 pm or less, or 0.5 pm or less. In some examples, the metal particles have a particle size distribution such that the D10 is 0.5 pm or more, 0.6 pm or more, 0.7 pm or more, 0.8 pm or more, 0.9 pm or more, 1 pm or more, 1.1 pm or more, 1 .2 pm or more, 1 .3 pm or more, 1 .4 pm or more, 1.5 pm or more, 1.6 pm or more, 1.7 pm or more, 1.8 pm or more, 1.9 pm or more, 2 pm or more, 2.1 pm or more, 2.2 pm or more, 2.3 pm or more, or 2.4 pm or more. In some examples, the metal particles have a particle size distribution such that the D10 is from 0.5 pm to 2.5 pm, for example, 0.6 pm to 2.5 pm, 0.7 pm to 2.4 pm, 0.8 pm to 2.3 pm, 0.9 pm to 2.2 pm, 1 pm to 2.1 pm, 1.1 pm to 2 pm, 1 .2 pm to 1 .9 pm, 1 .3 pm to 1.8 pm, 1.4 pm to 1.7 pm, or 1.5 pm to 1.6 pm.

In some examples, the particle size distribution is measured by laser diffraction, for example, by using a Honeywell X100 particle size analyser. In some examples, the particle size distribution is a volume based average particle size distribution.

In some examples, the first metal comprises a metal that oxidises in air (which may reduce the electrical conductivity of the first metal) and the second metal comprises a metal that does not oxidise in air. In some examples, the second metal comprises a metal that oxidises more slowly in air than the first metal.

In some examples, the first metal is selected from the group consisting of copper, titanium, chromium, iron, manganese, nickel, and combinations thereof. In some examples, the second metal is selected from the group consisting of silver, gold, platinum, rhodium, iridium, and combinations thereof. In some examples, the first metal is selected from the group consisting of copper, titanium, chromium, iron, manganese, nickel, and combinations thereof; and/or the second metal is selected from the group consisting of silver, gold, platinum, rhodium, iridium, and combinations thereof. In some examples, the first metal is copper and the second metal is silver or platinum. In some examples, the first metal is copper and the second metal is silver. In some examples, the metal particles are silver coated copper particles. In some examples, the second metal constitutes at least about 10 wt.% of the total weight of the metal particles, for example, at least about 15 wt.%, at least about 20 wt.%, at least about 30 wt.%, at least about 35 wt.%, at least about 40 wt.% of the total weight of the metal particles; and optionally, the first metal constitutes the remaining weight of the metal particles. In some examples, the second metal constitutes up to about 50 wt.% of the total weight of the metal particles, for example, up to about 40 wt.% up to about 35 wt.%, up to about 30 wt.%, up to about 25 wt.%, up to about 20 wt.%, up to about 15 wt.%, up to about 10 wt.% of the total weight of the metal particles, and optionally, the first metal constitutes the remaining weight of the metal particles. In some examples, t second metal constitutes from about 10 wt.% to about 40 wt.% of the total weight of the metal particles, for example, 15 wt.% to about 35 wt.%, about 20 wt.% to about 30 wt.%, or about 15 wt.% to about 25 wt.% of the total weight of the metal particles; and optionally, the first metal constitutes the remaining weight of the metal particles.

In some examples, the metal particles may be commercially available, for example, AZS-315 or AGCu0204-12, available from Ames Goldsmith Corp.

EC thermoplastic resin

In some examples, the thermoplastic resin of the electrically conductive LEP ink composition may comprise a thermoplastic polymer. The thermoplastic resin of the electrically conductive LEP ink composition may be referred to herein as the EC thermoplastic resin to distinguish it from the thermoplastic resin of the hole transport LEP ink composition (HT thermoplastic resin) and the thermoplastic resin of the LEP photovoltaic ink composition (PV thermoplastic resin).

The EC thermoplastic resin may be referred to herein as a resin. In some examples, the EC thermoplastic resin may comprise a polymer selected from the group consisting of ethylene acrylic acid copolymers; ethylene methacrylic acid copolymers; ethylene vinyl acetate copolymers; copolymers of ethylene (e.g. 80 wt.% to 99.9 wt.%), and alkyl (e.g. C1 to C5) ester of methacrylic or acrylic acid (e.g. 0.1 wt.% to 20 wt.%); copolymers of ethylene (e.g. 80 wt.% to 99.9 wt.%), acrylic or methacrylic acid (e.g. 0.1 wt.% to 20 wt.%) and alkyl (e.g. C1 to C5) ester of methacrylic or acrylic acid (e.g. 0.1 wt.% to 20 wt.%); polyethylene; polystyrene; isotactic polypropylene (crystalline); ethylene ethyl acrylate; polyesters; polyvinyl toluene; polyamides; styrene/butadiene copolymers; epoxy resins; acrylic resins (e.g. copolymer of acrylic or methacrylic acid and at least one alkyl ester of acrylic or methacrylic acid wherein alkyl is, in some examples, from 1 to about 20 carbon atoms, such as methyl methacrylate (e.g. 50 wt.% to 90 wt.%)/methacrylic acid (e.g. 0 wt.% to 20 wt.%)/ethylhexylacrylate (e.g. 10 wt.% to 50 wt.%)); ethylene-acrylate terpolymers: ethylene-acrylic esters-maleic anhydride (MAH) or glycidyl methacrylate (GMA) terpolymers; ethylene-acrylic acid ionomers and combinations thereof.

The EC thermoplastic resin may comprise a polymer having acidic side groups. The polymer having acidic side groups may have an acidity of 50 mg KOH/g or more, in some examples an acidity of 60 mg KOH/g or more, in some examples an acidity of 70 mg KOH/g or more, in some examples an acidity of 80 mg KOH/g or more, in some examples an acidity of 90 mg KOH/g or more, in some examples an acidity of 100 mg KOH/g or more, in some examples an acidity of 105 mg KOH/g or more, in some examples 110 mg KOH/g or more, in some examples 115 mg KOH/g or more. The polymer having acidic side groups may have an acidity of 200 mg KOH/g or less, in some examples 190 mg or less, in some examples 180 mg or less, in some examples 130 mg KOH/g or less, in some examples 120 mg KOH/g or less. Acidity of a polymer, as measured in mg KOH/g, can be measured using standard procedures known in the art, for example, using the procedure described in ASTM D1386.

The EC thermoplastic resin may comprise a polymer having acidic side groups that has a melt flow rate of less than about 60 g/10 minutes, in some examples about 50 g/10 minutes or less, in some examples about 40 g/10 minutes or less, in some examples 30 g/10 minutes or less, in some examples 20 g/10 minutes or less, in some examples 10 g/10 minutes or less. In some examples, all polymers having acidic side groups and/or ester groups in the particles each individually have a melt flow rate of less than 90 g/10 minutes, 80 g/10 minutes or less, in some examples 70 g/10 minutes or less, in some examples 60 g/10 minutes or less.

The polymer having acidic side groups can have a melt flow rate of about 10 g/10 minutes to about 120 g/10 minutes, in some examples about 10 g/10 minutes to about 70 g/10 minutes, in some examples about 10 g/10 minutes to 40 g/10 minutes, in some examples 20 g/10 minutes to 30 g/10 minutes. The polymer having acidic side groups can have a melt flow rate of in some examples about 50 g/10 minutes to about 120 g/10 minutes, in some examples 60 g/10 minutes to about 100 g/10 minutes. The melt flow rate can be measured using standard procedures known in the art, for example, as described in ASTM D1238. The EC thermoplastic resin may comprise a copolymer of an alkylene monomer and a monomer having acidic side groups. In some examples, the alkylene monomer may be selected from the group consisting of ethylene and propylene. In some examples, the monomer having acidic side groups may be selected from the group consisting of methacrylic acid and acrylic acid. In some examples, the EC thermoplastic resin may comprise a copolymer of an alkylene monomer and a monomer selected from the group consisting of methacrylic acid and acrylic acid. In some examples, the EC thermoplastic resin may comprise a copolymer of ethylene and a monomer selected from the group consisting of methacrylic acid and acrylic acid.

In some examples, the polymer having acidic side groups is a copolymer of an alkylene monomer and a monomer selected from the group consisting of acrylic acid and methacrylic acid. In some examples, the EC thermoplastic resin may comprise a copolymer of an alkylene monomer and a monomer selected from the group consisting of acrylic acid and methacrylic acid.

The acidic side groups may be in free acid form or may be in the form of an anion and associated with one or more counterions, typically metal counterions, e.g. a metal selected from the group consisting of the alkali metals, such as lithium, sodium and potassium, alkali earth metals, such as magnesium or calcium, and transition metals, such as zinc. The polymer having acidic side groups can be selected from the group consisting of resins such as copolymers of ethylene and an ethylenically unsaturated acid of either acrylic acid or methacrylic acid; and ionomers thereof, such as methacrylic acid and ethylene-acrylic or methacrylic acid copolymers which are at least partially neutralized with metal ions (e.g. Zn, Na, Li) such as SURLYN® ionomers. The polymer comprising acidic side groups can be a copolymer of ethylene and an ethylenically unsaturated acid of either acrylic or methacrylic acid, where the ethylenically unsaturated acid of either acrylic or methacrylic acid constitute from 5 wt.% to about 25 wt.% of the copolymer, in some examples from 10 wt.% to about 20 wt.% of the copolymer.

The EC thermoplastic resin may comprise two different polymers having acidic side groups. The two polymers having acidic side groups may have different acidities, which may fall within the ranges mentioned above. The EC thermoplastic resin may comprise a first polymer having acidic side groups that has an acidity of from 50 mg KOH/g to 110 mg KOH/g and a second polymer having acidic side groups that has an acidity of 110 mg KOH/g to 130 mg KOH/g. The resin may comprise two different polymers having acidic side groups: a first polymer having acidic side groups that has a melt flow rate of about 10 g/10 minutes to about 50 g/10 minutes and an acidity of from 50 mg KOH/g to 110 mg KOH/g, and a second polymer having acidic side groups that has a melt flow rate of about 50 g/10 minutes to about 120 g/10 minutes and an acidity of 110 mg KOH/g to 130 mg KOH/g. The first and second polymers may be absent of ester groups.

The resin may comprise a copolymer of ethylene and acrylic acid and a copolymer of ethylene and methacrylic acid.

The resin may comprise two different polymers having acidic side groups: a first polymer that is a copolymer of ethylene (e.g. 92 to 85 wt.%, in some examples about 89 wt.%) and acrylic or methacrylic acid (e.g. 8 to 15 wt.%, in some examples about 11 wt.%) having a melt flow rate of 80 to 110 g/10 minutes and a second polymer that is a copolymer of ethylene (e.g. about 80 to 92 wt.%, in some examples about 85 wt.%) and acrylic acid (e.g. about 18 to 12 wt.%, in some examples about 15 wt.%), having a melt viscosity lower than that of the first polymer, the second polymer for example having a melt viscosity of 15000 poise or less, in some examples a melt viscosity of 10000 poise or less, in some examples 1000 poise or less, in some examples 100 poise or less, in some examples 50 poise or less, in some examples 10 poise or less. Melt viscosity can be measured using standard techniques. The melt viscosity can be measured using a rheometer, e.g. a commercially available AR-2000 Rheometer from Thermal Analysis Instruments, using the geometry of: 25mm steel plate-standard steel parallel plate, and finding the plate over plate rheometry isotherm at 120°C, 0.01 Hz shear rate.

In any of the resins mentioned above, the ratio of the first polymer having acidic side groups to the second polymer having acidic side groups can be from about 10:1 to about 2:1. In another example, the ratio can be from about 6:1 to about 3:1 , in some examples about 4:1.

The resin may comprise a polymer having a melt viscosity of 15000 poise or less, in some examples a melt viscosity of 10000 poise or less, in some examples 1000 poise or less, in some examples 100 poise or less, in some examples 50 poise or less, in some examples 10 poise or less; said polymer may be a polymer having acidic side groups as described herein. The resin may comprise a first polymer having a melt viscosity of 15000 poise or more, in some examples 20000 poise or more, in some examples 50000 poise or more, in some examples 70000 poise or more; and in some examples, the resin may comprise a second polymer having a melt viscosity less than the first polymer, in some examples a melt viscosity of 15000 poise or less, in some examples a melt viscosity of 10000 poise or less, in some examples 1000 poise or less, in some examples 100 poise or less, in some examples 50 poise or less, in some examples 10 poise or less. The resin may comprise a first polymer having a melt viscosity of more than 60000 poise, in some examples from 60000 poise to 100000 poise, in some examples from 65000 poise to 85000 poise; a second polymer having a melt viscosity of from 15000 poise to 40000 poise, in some examples 20000 poise to 30000 poise, and a third polymer having a melt viscosity of 15000 poise or less, in some examples a melt viscosity of 10000 poise or less, in some examples 1000 poise or less, in some examples 100 poise or less, in some examples 50 poise or less, in some examples 10 poise or less; an example of the first polymer is Nucrel 960 (from DuPont), an example of the second polymer is Nucrel 699 (from DuPont), and an example of the third polymer is AC-5120 (from Honeywell). In some examples, the resin may comprise a first polymer having a melt viscosity of from 15000 poise to 40000 poise, in some examples 20000 poise to 30000 poise, and a second polymer having a melt viscosity of 15000 poise or less, in some examples a melt viscosity of 10000 poise or less, in some examples 1000 poise or less, in some examples 100 poise or less, in some examples 50 poise or less, in some examples 10 poise or less; an example of the first polymer is Nucrel 699 (from DuPont), and an example of the second polymer is AC-5120 (from Honeywell). The first, second and third polymers may be polymers having acidic side groups as described herein. The melt viscosity can be measured using a rheometer, e.g. a commercially available AR-2000 Rheometer from Thermal Analysis Instruments, using the geometry of: 25mm steel plate-standard steel parallel plate, and finding the plate over plate rheometry isotherm at 120°C, 0.01 Hz shear rate.

If the resin comprises a single type of resin polymer, the resin polymer (excluding any other components of the electrostatic ink composition) may have a melt viscosity of 6000 poise or more, in some examples a melt viscosity of 8000 poise or more, in some examples a melt viscosity of 10000 poise or more, in some examples a melt viscosity of 12000 poise or more. If the resin comprises a plurality of polymers all the polymers of the resin may together form a mixture (excluding any other components of the electrostatic ink composition) that has a melt viscosity of 6000 poise or more, in some examples a melt viscosity of 8000 poise or more, in some examples a melt viscosity of 10000 poise or more, in some examples a melt viscosity of 12000 poise or more. Melt viscosity can be measured using standard techniques. The melt viscosity can be measured using a rheometer, e.g. a commercially available AR-2000 Rheometer from Thermal Analysis Instruments, using the geometry of: 25mm steel plate-standard steel parallel plate, and finding the plate over plate rheometry isotherm at 120°C, 0.01 Hz shear rate.

The resin may comprise two different polymers having acidic side groups that are selected from the group consisting of copolymers of ethylene and an ethylenically unsaturated acid of either methacrylic acid or acrylic acid; and ionomers thereof, such as methacrylic acid and ethylene-acrylic or methacrylic acid copolymers which are at least partially neutralized with metal ions (e.g. Zn, Na, Li) such as SURLYN ® ionomers.

The resin may comprise (i) a first polymer that is a copolymer of ethylene and an ethylenically unsaturated acid of either acrylic acid and methacrylic acid, wherein the ethylenically unsaturated acid of either acrylic or methacrylic acid constitutes from 8 wt.% to about 16 wt.% of the copolymer, in some examples 10 wt.% to 16 wt.% of the copolymer; and (ii) a second polymer that is a copolymer of ethylene and an ethylenically unsaturated acid of either acrylic acid and methacrylic acid, wherein the ethylenically unsaturated acid of either acrylic or methacrylic acid constitutes from 12 wt.% to about 30 wt.% of the copolymer, in some examples from 14 wt.% to about 20 wt.% of the copolymer, in some examples from 16 wt.% to about 20 wt.% of the copolymer in some examples from 17 wt.% to 19 wt.% of the copolymer.

The resin may comprise a polymer having acidic side groups, as described above (which may be free of ester side groups), and a polymer having ester side groups. The polymer having ester side groups is, in some examples, a thermoplastic polymer. The polymer having ester side groups may further comprise acidic side groups. The polymer having ester side groups may be a copolymer of a monomer having ester side groups and a monomer having acidic side groups. The polymer may be a copolymer of a monomer having ester side groups, a monomer having acidic side groups, and a monomer absent of any acidic and ester side groups. The monomer having ester side groups may be a monomer selected from the group consisting of esterified acrylic acid or esterified methacrylic acid. The monomer having acidic side groups may be a monomer selected from the group consisting of acrylic or methacrylic acid. The monomer absent of any acidic and ester side groups may be an alkylene monomer, including, but not limited to, ethylene or propylene. The esterified acrylic acid or esterified methacrylic acid may, respectively, be an alkyl ester of acrylic acid or an alkyl ester of methacrylic acid. The alkyl group in the alkyl ester of acrylic or methacrylic acid may be an alkyl group having 1 to 30 carbons, in some examples 1 to 20 carbons, in some examples 1 to 10 carbons; in some examples selected from the group consisting of methyl, ethyl, iso-propyl, n-propyl, t-butyl, iso-butyl, n-butyl and pentyl.

The polymer having ester side groups may be a copolymer of a first monomer having ester side groups, a second monomer having acidic side groups and a third monomer which is an alkylene monomer absent of any acidic and ester side groups. The polymer having ester side groups may be a copolymer of (i) a first monomer having ester side groups selected from the group consisting of esterified acrylic acid or esterified methacrylic acid, in some examples an alkyl ester of acrylic or methacrylic acid, (ii) a second monomer having acidic side groups selected from the group consisting of acrylic or methacrylic acid and (iii) a third monomer which is an alkylene monomer selected from the group consisting of ethylene and propylene. The first monomer may constitute 1 to 50% by weight of the copolymer, in some examples 5 to 40% by weight, in some examples 5 to 20% by weight of the copolymer, in some examples 5 to 15% by weight of the copolymer. The second monomer may constitute 1 to 50% by weight of the copolymer, in some examples 5 to 40% by weight of the copolymer, in some examples 5 to 20% by weight of the copolymer, in some examples 5 to 15% by weight of the copolymer. In an example, the first monomer constitutes 5 to 40% by weight of the copolymer, the second monomer constitutes 5 to 40% by weight of the copolymer, and with the third monomer constituting the remaining weight of the copolymer. In an example, the first monomer constitutes 5 to 15% by weight of the copolymer, the second monomer constitutes 5 to 15% by weight of the copolymer, with the third monomer constituting the remaining weight of the copolymer. In an example, the first monomer constitutes 8 to 12% by weight of the copolymer, the second monomer constitutes 8 to 12% by weight of the copolymer, with the third monomer constituting the remaining weight of the copolymer. In an example, the first monomer constitutes about 10% by weight of the copolymer, the second monomer constitutes about 10% by weight of the copolymer, and with the third monomer constituting the remaining weight of the copolymer. The polymer having ester side groups may be selected from the group consisting of the Bynel ® class of monomer, including Bynel 2022 and Bynel 2002, which are available from DuPont ®. The polymer having ester side groups may constitute 1% or more by weight of the total amount of the resin polymers in the resin, e.g. the total amount of the polymer or polymers having acidic side groups and polymer having ester side groups. The polymer having ester side groups may constitute 5% or more by weight of the total amount of the resin polymers in the resin, in some examples 8% or more by weight of the total amount of the resin polymers in the resin, in some examples 10% or more by weight of the total amount of the resin polymers in the resin, in some examples 15% or more by weight of the total amount of the resin polymers in the resin, in some examples 20% or more by weight of the total amount of the resin polymers in the resin, in some examples 25% or more by weight of the total amount of the resin polymers in the resin, in some examples 30% or more by weight of the total amount of the resin polymers in the resin, in some examples 35% or more by weight of the total amount of the resin polymers in the resin. The polymer having ester side groups may constitute from 5% to 50% by weight of the total amount of the resin polymers in the resin, in some examples 10% to 40% by weight of the total amount of the resin polymers in the resin, in some examples 15% to 30% by weight of the total amount of the polymers in the resin.

The polymer having ester side groups may have an acidity of 50 mg KOH/g or more, in some examples an acidity of 60 mg KOH/g or more, in some examples an acidity of 70 mg KOH/g or more, in some examples an acidity of 80 mg KOH/g or more. The polymer having ester side groups may have an acidity of 100 mg KOH/g or less, in some examples 90 mg KOH/g or less. The polymer having ester side groups may have an acidity of 60 mg KOH/g to 90 mg KOH/g, in some examples 70 mg KOH/g to 80 mg KOH/g.

The polymer having ester side groups may have a melt flow rate of about 10 g/10 minutes to about 120 g/10 minutes, in some examples about 10 g/10 minutes to about 50 g/10 minutes, in some examples about 20 g/10 minutes to about 40 g/10 minutes, in some examples about 25 g/10 minutes to about 35 g/10 minutes.

In an example, the polymer or polymers of the resin can be selected from the group consisting of the Nucrel family of toners (e.g. Nucrel 403™, Nucrel 407™, Nucrel 609HS™, Nucrel 908HS™, Nucrel 1202HC™, Nucrel 30707™, Nucrel 1214™, Nucrel 903™, Nucrel 3990™, Nucrel 910™, Nucrel 925™, Nucrel 699™, Nucrel 599™, Nucrel 960™, Nucrel RX 76™, Nucrel 2806™, Bynell 2002, Bynell 2014, and Bynell 2020 (sold by E. I. du PONT)), the Aclyn family of toners (e.g. Aclyn 201 , Aclyn 246, Aclyn 285, and Aclyn 295), AC-5120 and AC 580 (sold by Honeywell), and the Lotader family of toners (e.g. Lotader 2210, Lotader, 3430, and Lotader 8200 (sold by Arkema)).

Liquid carrier

The electrically conductive LEP ink composition may comprise a liquid carrier, which may also be termed a carrier liquid. The electrically conductive LEP ink composition may comprise the same or a different liquid carrier as the hole transport LEP ink composition and/or the LEP photovoltaic ink composition. The electrically conductive LEP ink composition may comprise the same liquid carrier as the hole transport LEP ink composition and/or the LEP photovoltaic ink composition. In some examples, the electrically conductive LEP ink composition comprises the same liquid carrier as the hole transport LEP ink composition and the LEP photovoltaic ink composition.

In some examples, the liquid carrier of the electrically conductive LEP ink composition is as described above for the liquid carrier of the hole transport LEP ink composition. In some examples, the liquid carrier of the electrically conductive LEP ink composition may comprise a different liquid carrier than the hole transport LEP ink composition and the liquid carrier may be as described above for the liquid carrier of the hole transport LEP ink composition.

Charge director

The electrically conductive LEP ink composition may further comprise a charge director. The electrically conductive LEP ink composition may comprise the same or a different charge director as the hole transport LEP ink composition and/or the LEP photovoltaic ink composition. The electrically conductive LEP ink composition may comprise the same or a different charge director as the hole transport LEP ink composition and the LEP photovoltaic ink composition.

In some examples, the charge director of the electrically conductive LEP ink composition is as described above for the charge director of the hole transport LEP ink composition. In some examples, the charge director of the electrically conductive LEP ink composition may comprise a different charge director than the hole transport LEP ink composition and the charge director may be as described above for the charge director of the hole transport LEP ink composition. Charge adjuvant

The electrically conductive LEP ink composition may further comprise a charge adjuvant. The electrically conductive LEP ink composition may comprise the same or a different charge adjuvant as the hole transport LEP ink composition and/or the LEP photovoltaic ink composition. The electrically conductive LEP ink composition may comprise the same or a different charge adjuvant as the hole transport LEP ink composition and the LEP photovoltaic ink composition

In some examples, the charge adjuvant of the electrically conductive LEP ink composition is as described for the charge adjuvant of the hole transport LEP ink composition. In some examples, the charge adjuvant of the electrically conductive LEP ink composition may comprise a different charge adjuvant than the hole transport LEP ink composition and the charge adjuvant may be as described above for the charge adjuvant of the hole transport LEP ink composition.

Other additives

The electrically conductive LEP ink composition may further comprise an additive or a plurality of additives. The electrically conductive LEP ink composition may comprise the same or different additive(s) as the hole transport LEP ink composition and/or the LEP photovoltaic ink composition. The electrically conductive LEP ink composition may comprise the same or different additive(s) as the hole transport LEP ink composition and the LEP photovoltaic ink composition.

In some examples, the additive(s) of the electrically conductive LEP ink composition is as described for the additive(s) of the hole transport LEP ink composition. In some examples, the additive(s) of the electrically conductive LEP ink composition may comprise a different additive or additives than the hole transport LEP ink composition and the additive(s) may be as described above for the additive(s) of the hole transport LEP ink composition.

Photovoltaic cell

In another aspect, there is provided a photovoltaic cell. The photovoltaic cell may comprise an anode; a photovoltaic layer; a liquid electrophotographically printed hole transport layer; and a cathode; wherein the photovoltaic layer is disposed between the anode and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the photovoltaic layer and the cathode. In some examples, the photovoltaic cell may comprise an anode; a photovoltaic layer; a liquid electrophotographically printed hole transport layer; and a cathode; wherein the photovoltaic layer is disposed between the anode and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the photovoltaic layer and the cathode; wherein the photovoltaic layer comprises a material with a perovskite structure; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the liquid electrophotographically printed hole transport layer comprises a material capable of transporting electron holes; and a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, the photovoltaic layer comprises a liquid electrophotographically printed photovoltaic layer. In some examples, the liquid electrophotographically printed photovoltaic layer comprises a material with a perovskite structure, a thermoplastic resin and optionally conductive particles. In some examples, the material with a perovskite structure may be any material with a perovskite structure described herein. In some examples, the thermoplastic resin of the liquid electrophotographically printed photovoltaic layer may be any PV thermoplastic resin described herein. In some examples, the conductive particles may be any conductive particles described herein.

In some examples, the cathode comprises a liquid electrophotographically printed cathode. In some examples, the liquid electrophotographcially printed cathode comprises a thermoplastic resin; and electrically conductive metal particles. In some examples, the thermoplastic resin of the liquid electrophotographically printed cathode comprises any EC thermoplastic resin described herein. In some examples, the electrically conductive metal particles may comprise any electrically conductive metal particles described herein.

The photovoltaic cell may comprise an anode; a liquid electrophotographically printed photovoltaic layer; a liquid electrophotographically printed hole transport layer; and a liquid electrophotographically printed cathode; wherein the liquid electrophotographically printed photovoltaic layer is disposed between the anode and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the liquid electrophotographically printed photovoltaic layer and the liquid electrophotographically printed cathode. In some examples, the photovoltaic cell may comprise an anode; a liquid electrophotographically printed photovoltaic layer; a liquid electrophotographically printed hole transport layer; and a liquid electrophotographically printed cathode; wherein the liquid electrophotographically printed photovoltaic layer is disposed between the anode and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the liquid electrophotographically printed photovoltaic layer and the liquid electrophotographically printed cathode; wherein the liquid electrophotographically printed photovoltaic layer comprises a material with a perovskite structure, a PV thermoplastic resin, and optionally, conductive particles; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the liquid electrophotographically printed hole transport layer comprises a material capable of transporting electron holes; and an HT thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and wherein the liquid electrophotographically printed cathode comprises a EC thermoplastic resin; and electrically conductive metal particles.

In some examples, the photovoltaic cell further comprises an electron transport layer disposed between the anode and the photovoltaic layer. In some examples, the photovoltaic cell may comprise an anode; an electron transport layer; a photovoltaic layer (e.g., a liquid electrophotographically printed photovoltaic layer); a liquid electrophotographically printed hole transport layer; and a cathode (e.g., a liquid electrophotographically printed cathode); wherein the electron transport layer is disposed between the anode and the photovoltaic layer (e.g., the liquid electrophotographically printed photovoltaic layer); wherein the photovoltaic layer is disposed between the electron transport layer and the liquid electrophotographically printed hole transport layer; wherein the liquid electrophotographically printed hole transport layer is disposed between the photovoltaic layer (e.g., the liquid electrophotographically printed photovoltaic layer) and the cathode (e.g., the liquid electrophotographically printed cathode). In some examples, the electron transport layer may comprise a metal oxide.

In some examples, the photovoltaic cell may further comprise a supporting material on which the anode is disposed. Figure 1 shows schematic illustrations of example photovoltaic cells. Figure 1a shows, schematically, a photovoltaic cell comprising an anode (1), a photovoltaic layer (2), a liquid electrophotographically printed hole transport layer (3) and a cathode (4); wherein the photovoltaic layer (2) is disposed between the anode (1) and the liquid electrophotographically printed hole transport layer (3) and the liquid electrophotographically printed hole transport layer (3) is disposed between the photovoltaic layer (2) and the cathode (4). In some examples, the anode (1) may be disposed on a supporting material (not shown).

Figure 1 b shows, schematically, a photovoltaic cell further comprising an electron transport layer (5) disposed between the anode (1) and the photovoltaic layer (2). Thus, Figure 1 b shows, schematically, an anode (1), an electron transport layer (5) disposed on the anode (1), a photovoltaic layer (2) disposed on the electron transport layer (5), a hole transport layer (3) disposed on the photovoltaic layer (2), and a cathode (4) disposed on the hole transport layer (3). In some examples, the anode (1) may be disposed on a supporting material (not shown).

Anode

The photovoltaic cell may comprise an anode. In some examples, the anode may be disposed on a supporting material. In some examples, the photovoltaic cell may comprise a substrate comprising an anode. In some examples, the photovoltaic cell may comprise a substrate comprising or consisting of an anode. In some examples, the substrate comprising an anode may comprise a supporting material and an anode, wherein the anode may be disposed on the supporting material.

In some examples, the photovoltaic cell may comprise any suitable anode, for example, any suitable transparent anode.

In some examples, the anode may be transparent. In some examples, the substrate comprising the anode may be transparent. In some examples, the anode may be the layer through which light passes before contacting the LEP printed photovoltaic layer. In some examples, substantially all or all light of a suitable wavelength to interact with the LEP printed photovoltaic layer passes through the anode or the substrate comprising an anode. In some examples, substantially all light of the suitable wavelength may mean at least 95%, for examples, at least 99% of the light of the suitable wavelength. In some examples, the suitable wavelength may be the wavelength or wavelength range that interacts with the material with a perovskite structure.

In some examples, the anode may be flexible. In some examples, the substrate comprising an anode may be flexible. In some examples, the substrate may be flexible.

In some examples, the anode may comprise or consist of indium tin oxide (ITO), fluorine doped tin oxide (FTO), silver nanowires, poly(3,4-ethylenedioxythiophene) (PEDOT), metal mesh, graphene or carbon nanotubes. In some examples, the anode may comprise or consist of indium tin oxide (ITO). In some examples, the substrate comprising an anode may comprise a supporting material and an anode comprising or consisting of indium tin oxide or fluorine doped tin oxide, silver nanowires, poly(3,4- ethylenedioxythiophene) (PEDOT), metal mesh, graphene or carbon nanotubes. In some examples, the substrate comprising an anode may comprise a supporting material and an anode comprising or consisting of indium tin oxide.

In some examples, the supporting material may be glass or plastic. In some examples, the plastic may be polyethylene terephthalate.

In some examples, the photovoltaic cell may comprise indium tin oxide coated polyethylene terephthalate (PET-ITO), wherein the anode comprises or consists of the indium tin oxide.

In some examples, the anode has a thickness of at least about 50 nm, for example, at least about 55 nm, at least about 60 nm, at least about 65 nm, at least about 70 nm, at least about 75 nm, at least about 80 nm, at least about 85 nm, at least about 90 nm, at least about 95 nm, or at least about 100 nm. In some examples, the anode has a thickness of up to about 100 nm, for example, up to about 95 nm, up to about 90 nm, up to about 85 nm, up to about 80 nm, up to about 75 nm, up to about 70 nm, up to about 65 nm, up to about 60 nm, up to about 55 nm, or up to about 50 nm. In some examples, the anode has a thickness of from about 50 nm to about 100 nm, for example, about 55 nm to about 100 nm, about 60 nm to about 95 nm, about 65 nm to about 90 nm, about 70 nm to about 85 nm, or about 75 nm to about 80 nm.

In some examples, the supporting material, on which the anode may be disposed, may have a thickness of at least about 12 pm, for example, at least about 15 pm, at least about 20 pm, at least about 30 pm, at least about 40 pm, at least about 50 pm, at least about 60 pm, at least about 70 pm, at least about 80 pm, at least about 90 pm, at least about 100 pm, at least about 110 pm, at least about 120 pm, at least about 130 pm, at least about 140 pm, at least about 150 pm, at least about 160 pm, at least about 170 pm, at least about 180 pm, at least about 190 pm, or at least about 200 pm. In some examples, the supporting material, on which the anode may be disposed, may have a thickness of up to about 200 pm, for example, up to about 190 pm, up to about 180 pm, up to about 170 pm, up to about 160 pm, up to about 150 pm, up to about 140 pm, up to about 130 pm, up to about 120 pm, up to about 110 pm, up to about 100 pm, up to about 90 pm, up to about 80 pm, up to about 70 pm, up to about 60 pm, up to about 50 pm, up to about 40 pm, up to about 30 pm, up to about 20 pm, up to about 15 pm, or up to about 12 pm. In some examples, the supporting material, on which the anode may be disposed, may have a thickness of from about 12 pm to about 200 pm, for example, about 15 pm to about 195 pm, about 20 pm to about 200 pm, about 30 pm to about 190 pm, about 40 pm to about 180 pm, about 50 pm to about 170 pm, about 60 pm to about 160 pm, about 70 pm to about 150 pm, about 80 pm to about 140 pm, about 90 pm to about 130 pm, about 100 pm to about 120 pm, or about 110 pm to about 120 pm.

Photovoltaic layer

In some examples, the photovoltaic layer comprises a material with a perovskite structure. In some examples, the photovoltaic layer comprises any material with a perovskite structure described herein.

In some examples, the photovoltaic layer comprises a material with a perovskite structure and a thermoplastic resin. In some examples, the photovoltaic layer comprises a material with a perovskite structure, a thermoplastic resin and conductive particles.

In some examples, the photovoltaic layer comprises or consists of a liquid electrophotographically printed photovoltaic layer. In some examples, the photovoltaic layer comprises a material with a perovskite structure, a PV thermoplastic resin and optionally conductive particles. In some examples, the photovoltaic layer comprises any material with a perovskite structure described herein, any PV thermoplastic resin described herein; and optionally any conductive particles described herein. The liquid electrophotographically printed photovoltaic layer may be referred to herein as the printed photovoltaic layer. In some examples, the photovoltaic layer comprises a material with a perovskite structure, a PV thermoplastic resin and optionally conductive particles, wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation; B is a cation and X is an anion; and wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide

The photovoltaic layer may be formed or may have been formed by liquid electrophotographically printing a liquid electrophotographic photovoltaic ink composition. The liquid electrophotographically printed photovoltaic layer may be formed or may have been formed by liquid electrophotographically printing any liquid electrophotographic photovoltaic ink composition described herein. In some examples, during printing, the liquid carrier of the LEP photovoltaic ink composition may have been removed, for example, by an electrophoresis process during printing and/or by evaporation, such that the liquid electrophotographically printed photovoltaic layer comprises just (or substantially just) the solids of the LEP photovoltaic ink composition. The printed photovoltaic layer may be substantially free from, or free from, liquid carrier.

In some examples, the printed photovoltaic cell comprises a liquid electrophotographically printed photovoltaic layer, wherein the liquid electrophotographically printed photovoltaic layer comprises a thermoplastic resin, a material with a perovskite structure, and, in some examples, conductive particles. In some examples, the printed photovoltaic cell comprises a liquid electrophotographically printed photovoltaic layer, wherein the liquid electrophotographically printed photovoltaic layer comprises a thermoplastic resin, a material with a perovskite structure, and optionally conductive particles, wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and a monomer having acidic side groups; and/or a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof. In some examples, the printed photovoltaic cell comprises a liquid electrophotographically printed photovoltaic layer, wherein the liquid electrophotographically printed photovoltaic layer comprises a thermoplastic resin, a material with a perovskite structure, and optionally conductive particles, wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

In some examples, A is selected from the group consisting of a monovalent metal cation, a monovalent organic cation, or a mixture thereof; and/or B is a divalent metal cation or a tetravalent metal cation; and/or X is a halide ion. In some examples, X is a halide ion, for example, selected from the group consisting of iodide, bromide, chloride and mixtures thereof; and/or A is selected from the group consisting of methylammonium (MA), formamidinium (FA), rubidium (Rb), caesium (Cs), and mixtures thereof; and/or B is selected from the group consisting of lead (Pb), germanium (Ge), tin (Sn), antimony (Sb), bismuth (Bi), copper (Cu), manganese (Mn), cobalt (Co) and mixtures thereof.

In some examples, during or after printing, the thermoplastic resin of the photovoltaic layer is cured. Thus, the liquid electrophotographically printed photovoltaic layer (i.e., the photovoltaic layer) may comprise a cured thermoplastic resin. In some examples, the thermoplastic resin comprises a copolymer of an alkylene monomer and a monomer comprising an epoxide and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof; and the thermoplastic resin is cured during or after printing.

In some examples, during curing, the epoxide reacts. In some examples, the epoxide reacts by a ring-opening reaction or a cross-linking reaction. In some examples, the photovoltaic layer may comprise a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof, wherein the thermoplastic resin has been cured. In some examples, the photovoltaic layer may comprise a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; wherein the thermoplastic resin has been cured, for example, by a ring- opening reaction of the epoxide and/or a cross-linking reaction of the epoxide and/or a copolymer of an alkylene monomer, an ethylenically unsaturated monomer comprising an epoxide, and a monomer selected from the group consisting of a monomer having acidic side groups, a monomer having ester side groups and a mixture thereof; wherein the thermoplastic resin has been cured, for example, by a ring-opening reaction of the epoxide and/or a cross-linking reaction of the epoxide. In some examples, the photovoltaic layer may comprise a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, wherein the thermoplastic resin has been cured, for example, by a ring-opening reaction of the epoxide and/or a cross-linking reaction of the epoxide.

In some examples, the cross-linking reaction of the epoxide may be a reaction between the epoxide of the thermoplastic resin of the LEP photovoltaic ink composition and/or the photovoltaic layer and an acid, for example, a carboxylic acid, of the thermoplastic resin of the electrically conductive LEP ink composition and/or the liquid electrophotographically printed cathode.

In some examples, the printed photovoltaic layer may have a thickness of at least about 0.5 pm, for example, at least about 0.6 pm, at least about 0.7 pm, at least about 0.8 pm, at least about 0.9 pm, at least about 1 pm, at least about 1.1 pm, at least about 1.2 pm, at least about 1.3 pm, at least about 1.4 pm, at least about 1.5 pm, at least about 1.6 pm, at least about 1.7 pm, at least about 1.8 pm, at least about 1.9 pm, or at least about 2 pm. In some examples, the printed photovoltaic layer may have a thickness of up to about 2 pm, for example, up to about 1 .9 pm, up to about 1 .8 pm, up to about 1.7 pm, up to about 1.6 pm, up to about 1.5 pm, up to about 1.4 pm, up to about 1.3 pm, up to about 1.2 pm, up to about 1.1 pm, up to about 1 pm, up to about 0.9 pm, up to about 0.8 pm, up to about 0.7 pm, or up to about 0.6 pm, or up to about 0.5 pm. In some examples, the printed photovoltaic layer may have a thickness of from about 0.5 pm to about 2 pm, for example, about 0.6 pm to about 1.9 pm, about 0.7 pm to about 1.8 pm, about 0.8 pm to about 1.7 pm, about 0.9 pm to about 1.6 pm, about 1 pm to about 1.6 pm, about 1.1 pm to about 1.5 pm, about 1.2 pm to about 1.4 pm, about 1 .3 pm to about 2 pm. Liquid electrophotographically printed hole transport layer

The photovoltaic cell may comprise a liquid electrophotographically printed hole transport layer. The liquid electrophotographically printed hole transport layer may be referred to herein as the hole transport layer or the printed hole transport layer.

The hole transport layer is capable of functioning as a hole filter and may be capable of allowing the transfer of electron holes but not electrons from the photovoltaic layer.

The liquid electrophotographically printed hole transport layer may be formed or may have been formed by liquid electrophotographically printing a hole transport liquid electrophotographic ink composition. The liquid electrophotographically printed hole transport layer may be formed or may have been formed by liquid electrophotographically printing any hole transport liquid electrophotographic ink composition described herein. In some examples, during printing, the liquid carrier of the hole transport liquid electrophotographic ink composition may have been removed, for example, by an electrophoresis process during printing and/or by evaporation, such that the liquid electrophotographically printed hole transport layer comprises just (or substantially just) the solids of the hole transport liquid electrophotographic ink composition. The liquid electrophotographically printed hole transport layer may be substantially free from, or free from, liquid carrier.

In some examples, the liquid electrophotographically printed hole transport layer comprises a material capable of transporting electron holes and a thermoplastic resin (e.g., a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide).

In some examples, the material capable of transporting electron holes may be a material capable of transporting electron holes and electrons or a material that selectively transports electron holes. In some examples, the material capable of transporting electron holes may comprise polypyrrole, carbon black, or a combination thereof.

In some examples, the thermoplastic resin may comprise a copolymer of ethylene and an ethylenically unsaturated monomer comprising an epoxide. In some examples, the thermoplastic resin may comprise a copolymer of ethylene and an ethylenically unsaturated ester comprising an epoxide. In some examples, the thermoplastic resin may comprise a copolymer of ethylene and glycidyl methacrylate. In some examples, during or after printing, the thermoplastic resin of the hole transport layer (i.e., the liquid electrophotographically printed hole transport layer) is cured. Thus, the hole transport layer may comprise a cured thermoplastic resin. In some examples, the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide and the thermoplastic resin is cured during or after printing.

In some examples, during curing, the epoxide reacts. In some examples, the epoxide reacts by a ring-opening reaction or a cross-linking reaction. In some examples, the hole transport layer comprises thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide, wherein the thermoplastic resin has been cured, for example, by a ring opening reaction of the epoxide and/or a cross-linking reaction of the epoxide.

In some examples, the cross-linking reaction of the epoxide may be a reaction between the epoxide of the thermoplastic resin of the hole transport layer and an acid, for example, a carboxylic acid of the photovoltaic layer and/or of the cathode.

In some examples, the liquid electrophotographically printed hole transport layer has a thickness of at least about 0.1 pm, for example, at least about 0.15 pm, at least about 0.2 pm, at least about 0.25 pm, at least about 0.3 pm, at least about 0.35 pm, at least about 0.4 pm, at least about 0.45 pm, at least about 0.5 pm, at least about 0.55 pm, at least about 0.6 pm, at least about 0.65 pm, at least about 0.7 pm, at least about 0.75 pm, at least about 0.8 pm, at least about 0.85 pm, at least about 0.9 pm, at least about

0.95 pm, or at least about 1 pm. In some examples, the liquid electrophotographically printed hole transport layer has a thickness of up to about 1 pm, for example, up to about 0.95 pm, up to about 0.9 pm, up to about 0.85 pm, up to about 0.8 pm, up to about 0.75 pm, up to about 0.7 pm, up to about 0.65 pm, up to about 0.6 pm, up to about 0.55 pm, up to about 0.5 pm, up to about 0.45 pm, up to about 0.4 pm, up to about 0.35 pm, up to about 0.3 pm, up to about 0.25 pm, up to about 0.2 pm, or up to about 0.15 pm, or up to about 0.1 pm. In some examples, the liquid electrophotographically printed hole transport layer has a thickness of from about 0.1 pm to about 1 pm, for example, from about 0.15 pm to about 0.95 pm, about 0.2 pm to about 0.9, about 0.25 pm to about 0.85 pm, about 0.3 pm to about 0.8 pm, about 0.35 pm to about 0.75 pm, about 0.4 pm to about 0.7 pm, about 0.45 pm to about 0.65 pm, about 0.5 pm to about 0.6 pm, or about 0.1 pm to about 0.55 pm. In some examples, the liquid electrophotographically printed hole transport layer has a DMA (density mass area) of 0.05 mg/cm² to 0.5 mg/cm². The DMA is calculated by multiplying the weight of liquid electrophotographic ink composition by the solids content of the LEP ink composition, the density of the liquid carrier and the dilution factor (where the dilution factor is weight of the LEP ink composition divided by the sum of the weight of the LEP ink composition and the weight of liquid carrier added).

Cathode

The photovoltaic cell may comprise a cathode. The cathode may comprise any conductive layer in contact with the liquid electrophotographically hole transport layer. In some examples, the cathode may comprise any conductive layer deposited onto the liquid electrophotographically printed hole transport layer. In some examples, the cathode may comprise or consist of a printed cathode, for example, a liquid electrophotographically printed cathode.

cathode

The photovoltaic cell may comprise a liquid electrophotographically printed cathode. The liquid electrophotographically printed cathode may be referred to herein as the cathode or the printed cathode.

The liquid electrophotographically printed cathode may be formed or may have been formed by liquid electrophotographically printing an electrically conductive liquid electrophotographic ink composition. The liquid electrophotographically printed cathode may be formed or may have been formed by liquid electrophotographically printing any electrically conductive liquid electrophotographic ink composition described herein. In some examples, during printing, the liquid carrier of the electrically conductive LEP ink composition may have been removed, for example, by an electrophoresis process during printing and/or by evaporation, such that the liquid electrophotographically printed cathode comprises just (or substantially just) the solids of the electrically conductive LEP ink composition. The printed cathode may be substantially free from or free from liquid carrier.

In some examples, the photovoltaic cell comprises a liquid electrophotographically printed cathode, wherein the liquid electrophotographically printed cathode comprises a thermoplastic resin; and electrically conductive metal particles. In some examples, the printed photovoltaic cell comprises a liquid electrophotographically printed cathode, wherein the liquid electrophotographically printed cathode comprises a thermoplastic resin; and electrically conductive metal particles, wherein the electrically conductive metal particles comprise a core comprising a first metal and a shell comprising a second metal; wherein the shell at least partially encloses the core and wherein the first metal is different from the second metal. In some examples, the first metal is selected from the group consisting of copper, titanium, chromium, iron, manganese, nickel, and combinations thereof; and/or wherein the second metal is selected from the group consisting of silver, gold, platinum, rhodium, iridium, and combinations thereof. The shell may completely encloses the core; and/or the second metal may comprise from about 10 wt.% to about 40 wt.% of the total weight of the metal particles.

In some examples, the printed cathode may have a thickness of at least about 1 pm, for example, at least about 2 pm, at least about 3 pm, at least about 4 pm, at least about 5 pm, at least about 6 pm, at least about 7 pm, at least about 8 pm, at least about 9 pm, at least about 10 pm, at least about 11 pm, at least about 12 pm, at least about 13 pm, at least about 14 pm, at least about 15 pm, at least about 16 pm, at least about 17 pm, at least about 18 pm, at least about 19 pm, or at least about 20 pm. In some examples, the printed cathode may have a thickness of up to about 20 pm, for example, up to about 19 pm, up to about 18 pm, up to about 17 pm, up to about 16 pm, up to about 15 pm, up to about 14 pm, up to about 13 pm, up to about 12 pm, up to about 11 pm, up to about 10 pm, up to about 9 pm, up to about 8 pm, up to about 7 pm, up to about 6 pm, up to about 5 pm, up to about 4 pm, up to about 3 pm, up to about 2 pm, or up to about 1 pm. In some examples, the printed cathode may have a thickness of from about 1 pm to about 20 pm, for example, about 2 pm to about 20 pm, about 3 pm to about 19 pm, about 4 pm to about 18 pm, about 5 pm to about 17 pm, about 6 pm to about 16 pm, about 7 pm to about 15 pm, about 8 pm to about 14 pm, about 9 pm to about 13 pm, about 10 pm to about 12 pm, or about 11 pm to about 12 pm.

Electron transport layer

The printed photovoltaic cell may further comprise an electron transport layer. In some examples, the electron transport layer may be disposed between the anode and the photovoltaic layer (e.g., the liquid electrophotographically printed photovoltaic layer). The electron transport layer may be any layer capable of functioning as an electrical filter. The electron transport layer may be any layer capable of allowing the transfer of electrons but not holes from the printed photovoltaic layer to the anode. The printed photovoltaic layer creates both electrons and holes when the perovskite crystals are illuminated.

The electron transport layer may comprise or consist of a metal oxide. In some examples, the metal oxide may be selected from the group consisting of alumina (AI₂O₃), zinc oxide (ZnO), tin oxide (SnO₂), titanium dioxide (i.e., titanium (IV) oxide; TiO₂), WO₃, (CH₃)₂Sn(COOH)₂, SiO₂, or Zr0₂. In some examples, the electron transport layer may comprise or consist of zinc oxide.

In some examples, the electron transport layer may be formed or may have been formed by a chemical deposition method or a physical deposition method. The chemical deposition method may be selected from the group consisting of chemical vapour deposition (CVD), atomic layer deposition (ALD), and sol-gel processes. The physical deposition method may be selected from the group consisting of sputtering, pulsed laser deposition, and spray pyrolysis.

In some examples, the electron transport layer may be formed or may have been formed by the process described herein, for example, by deposition of a metal oxide from an organic solvent.

In some examples, the electron transport layer, for example, the electron transport layer comprising a metal oxide, has a thickness of at least about 50 nm, for example, at least about 60 nm, at least about 70 nm, at least about 80 nm, at least about 90 nm, or at least about 100 nm. In some examples, the electron transport layer, for example, the electron transport layer comprising a metal oxide, has a thickness of up to about 100 nm, for example, up to about 90 nm, up to about 80 nm, up to about 70 nm, up to about 60 nm, or up to about 50 nm. In some examples, the electron transport layer, for example, the electron transport layer comprising a metal oxide, may have a thickness of from about 50 nm to about 100 nm, for example, from about 60 nm to about 90 nm, or from about 70 nm to about 80 nm. In some examples, the thickness of the electron transport layer may be measured using standard procedures known in the art, for example, scanning electron microscopy with energy dispersive spectroscopy (SEM- EDS). Method of producing a photovoltaic cell

In another aspect, there is provided a method of producing a photovoltaic cell. The method of producing a photovoltaic cell may comprise printing a hole transport liquid electrophotographic ink composition onto a photovoltaic layer to form a liquid electrophotographically printed hole transport layer; wherein the photovoltaic layer is disposed on a substrate comprising an anode; and applying a composition to form a cathode; wherein the hole transport layer is disposed between the photovoltaic layer and the cathode. In some examples, the hole transport liquid electrophotographic ink composition may comprise any hole transport liquid electrophotographic ink composition described herein. In some examples, the photovoltaic layer may comprise any photovoltaic layer described herein (for example, any liquid electrophotographically printed photovoltaic layer described herein).

The method of producing a photovoltaic cell may comprise printing a hole transport liquid electrophotographic ink composition onto a photovoltaic layer to form a liquid electrophotographically printed hole transport layer; wherein the photovoltaic layer is disposed on a substrate comprising an anode; and applying a composition to form a cathode; wherein the hole transport layer is disposed between the photovoltaic layer and the cathode; wherein the photovoltaic layer comprises a material with a perovskite structure; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the hole transport liquid electrophotographic ink composition comprises a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier. The photovoltaic layer may additionally comprise a thermoplastic resin (i.e., a PV thermoplastic resin).

In some examples, the substrate further comprises an electron transport layer disposed on the anode. In some examples, the substrate comprises an anode disposed on a supporting material. In some examples, the substrate comprises an electron transport layer disposed on an anode, the anode disposed on a supporting material.

The method of producing a photovoltaic cell may comprise printing a hole transport liquid electrophotographic ink composition onto a printed photovoltaic layer (e.g., a liquid electrophotographically printed photovoltaic layer), wherein the printed photovoltaic layer is disposed on a substrate comprising an anode; and applying a composition to form a cathode (e.g., printing an electrically conductive liquid electrophotographic ink composition to form a cathode).

The method of producing a photovoltaic cell may comprise printing a liquid electrophotographic photovoltaic ink composition onto the substrate to form a photovoltaic layer disposed on a substrate comprising an anode; printing a hole transport liquid electrophotographic ink composition onto a photovoltaic layer to form a liquid electrophotographically printed hole transport layer; and applying a composition to form a cathode; wherein the hole transport layer is disposed between the photovoltaic layer and the cathode.

The method of producing a photovoltaic cell may comprise printing a liquid electrophotographic photovoltaic ink composition onto the substrate to form a photovoltaic layer disposed on a substrate comprising an anode; printing a hole transport liquid electrophotographic ink composition onto a photovoltaic layer to form a liquid electrophotographically printed hole transport layer; and applying a composition to form a cathode; wherein the hole transport layer is disposed between the photovoltaic layer and the cathode; wherein the liquid electrophotographic photovoltaic ink composition comprises a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally conductive particles, in a carrier liquid; and wherein the hole transport liquid electrophotographic ink composition comprises a material capable of transporting electron holes; a thermoplastic resin (e.g., a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide); and a liquid carrier.

In some examples, applying a composition to form a cathode comprises printing an electrically conductive liquid electrophotographic ink composition to form a cathode. In some examples, applying a composition to form a cathode comprises printing an electrically conductive liquid electrophotographic ink composition comprising a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.

The method of producing a photovoltaic cell may comprise printing any LEP photovoltaic ink composition described herein onto a substrate comprising an anode (and optionally comprising an electron transport layer disposed on the anode) to form a liquid electrophotographically printed photovoltaic layer; printing any hole transport LEP ink composition described herein onto the photovoltaic layer to form a liquid electrophotographically printed hole transport layer disposed on the printed photovoltaic layer; and printing any electrically conductive LEP ink composition described herein onto the printed hole transport layer to form a liquid electrophotographically printed cathode.

The method of producing a photovoltaic cell may comprise printing any LEP photovoltaic ink composition described herein onto a substrate comprising an anode (and optionally comprising an electron transport layer disposed on the anode) to form a liquid electrophotographically printed photovoltaic layer; printing a hole transport LEP ink composition (comprising a material capable of transporting electron holes (e.g., polypyrolle, carbon black or a combination thereof); a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenenically unsaturated monomer comprising an epoxide (e.g., a copolymer of ethylene and an ethylenically unsaturated ester comprising an epoxide such as poly(ethylene-co-glycidyl methacrylate)); and a liquid carrier) to form a liquid electrophotographically printed hole transport layer; and printing any electrically conductive LEP ink composition described herein onto the printed hole transport layer to form a liquid electrophotographically printed cathode.

In some examples, the method of producing a photovoltaic cell further comprises depositing an electrically conductive material on a supporting material to form the substrate comprising an anode disposed on a supporting material. In some examples, the method of producing a photovoltaic cell further comprises producing an electron transport layer disposed on the anode. In some example, the method of producing a photovoltaic cell further comprises depositing an electron transport composition on the anode to form substrate comprising an anode and an electron transport layer disposed on the anode.

In some examples, the electron transport composition may be deposited on the anode by a chemical deposition method or a physical deposition method. In some examples, the chemical deposition method may be selected from the group consisting of chemical vapour deposition (CVD), atomic layer deposition (ALD), and sol-gel processes. In some examples, the physical deposition method may be selected from the group consisting of sputtering, pulsed layer deposition, and spray pyrolysis.

In some examples, the electron transport composition may be deposited on the anode by deposition of a metal oxide from an organic solvent, for example, by an analogue printing technique. In some examples, the organic solvent may be a diol. In some examples, the diol may be selected from the group consisting of ethylene glycol, propylene glycol, butanediol, pentanediol and hexanediol. In some examples, the electron transport composition may be deposited on the anode by any suitable method of producing an electron transport layer, for example, by sputtering.

In some examples, the method of producing a photovoltaic cell comprises depositing an electron transport composition on an anode to form a substrate comprising an anode and an electron transport layer disposed on the anode; printing a an LEP photovoltaic ink composition onto the substrate to form a liquid electrophotographically printed photovoltaic layer, which may be disposed on the electron transport layer of the substrate; printing a hole transport LEP ink composition onto the photovoltaic layer to form a liquid electrophotographically printed hole transport layer; and applying a composition to form a cathode (for example, printing an electrically conductive LEP ink composition to form a liquid electrophotographically printed cathode); wherein the printed photovoltaic layer is disposed between the substrate and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the printed and the cathode (for example, the printed cathode).

In some examples, printing a hole transport LEP ink composition onto a photovoltaic layer to form a liquid electrophotographcially printed hole transport layer comprises contacting a hole transport LEP ink composition with a latent electrostatic image on a surface to create a developed image and transferring the developed image to the substrate, in some examples, via an intermediate transfer member.

In some examples, printing an LEP photovoltaic ink composition onto the substrate to form the photovoltaic layer comprises contacting the LEP photovoltaic ink composition with a latent electrostatic image on a surface to create a developed image and transferring the developed image to the substrate, in some examples, via an intermediate transfer member.

In some examples, printing an electrically conductive LEP ink composition to form the printed cathode comprises contacting the electrically conductive LEP ink composition with a latent electrostatic image on a surface to create a developed image and transferring the developed image to a substrate, in some examples, via an intermediate transfer member. In some examples, the surface on which the (latent) electrostatic image(s) is(are) formed or developed may be a rotating member, for example, in the form of a cylinder. The surface on which the (latent) electrostatic image(s) is(are) formed or developed may form a part of a photo imaging plate (PIP). The method may involve passing the ink composition (e.g., hole transport LEP ink composition; the LEP photovoltaic ink composition; or the electrically conductive LEP ink composition) between a stationary electrode and a rotating member, which may be a member having the surface having the (latent) electrostatic image thereon or a member in contact with the surface having the (latent) electrostatic image thereon. A voltage is applied between the stationary electrode and the rotating member, such that particles adhere to the surface of the rotating member. The intermediate transfer member, if present, may be a rotating flexible member, which may be heated, for example, to a temperature of from 80 to 160°C.

In some examples, printing (i.e., liquid electrophotographically printing) a composition onto the substrate comprises contacting the composition with a latent electrostatic image on a surface to create a developed image and transferring the developed image to the substrate, in some examples, via an intermediate transfer member and then curing the developed image on the substrate. In some examples, curing the developed image may comprise heating the developed image. In some examples, curing of the liquid electrophotographically printed hole transport layer may be performed after the liquid electrophotographic photovoltaic ink composition has been printed. In some examples, curing of the liquid electrophotographically printed hole transport layer may be performed after the liquid electrophotographic photovoltaic ink composition and the electrically conductive LEP ink composition have been printed. In some examples, curing of the photovoltaic layer may be performed after the electrically conductive LEP ink composition has been printed. In some examples, the method of producing a photovoltaic cell further comprises curing the thermoplastic resin of the liquid electrophotographically printed hole transport layer, for example, by heating at least the printed hole transport layer. In some examples, the method of producing a photovoltaic cell further comprises curing the thermoplastic resin of the liquid electrophotographically printed hole transport layer and the thermoplastic resin of the printed photovoltaic layer, for example, by heating at least the printed photovoltaic layer.

In some examples, the hole transport layer and/or the printed photovoltaic layer may be cured by heating at a temperature of at least about 110°C, for example, at least about 115°C, at least about 120°C, at least about 125°C, at least about 130°C, at least about 135°C, at least about 140°C, at least about 145°C, or at least about 150°C. In some examples, the hole transport layer and/or the printed photovoltaic layer may be cured by heating at a temperature of up to about 150°C, for example, up to about 145°C, up to about 140°C, up to about 135°C, up to about 130°C, up to about 125°C, up to about 120°C, up to about 115°C, up to about 110°C, up to about 105°C, or up to about 100°C. In some examples, the hole transport layer and/or the printed photovoltaic layer may be cured by heating at a temperature of from about 100°C to about 150°C, for example, about 115°C to about 150°C, about 120°C to about 145°C, about 125°C to about 140°C, or about 130°C to about 135°C.

In some examples, the method of producing a photovoltaic cell comprises printing (i.e., liquid electrophotographically printing) an LEP photovoltaic ink composition onto a substrate comprising an anode to form a liquid electrophotographically printed photovoltaic layer; printing (i.e., liquid electrophotographically printing) a hole transport liquid electrophotographic ink composition onto the liquid electrophotographically photovoltaic layer to form a liquid electrophotographically printed hole transport layer; and printing (i.e., liquid electrophotographically printing) an electrically conductive LEP ink composition onto the printed hole transport layer to form a liquid electrophotographically printed cathode disposed on the printed hole transport layer.

In some examples, the method of producing a printed photovoltaic cell comprises: (1) optionally, depositing an anode onto a supporting material to form a substrate comprising an anode; (2) optionally, depositing an electron transport composition on the anode to form a substrate comprising an anode and an electron transport layer disposed on the anode; (3) printing an LEP photovoltaic ink composition onto a substrate comprising an anode (and optionally comprising an electron transport layer disposed on the anode) to form a liquid electrophotographically printed photovoltaic layer disposed on the substrate; (4) printing a hole transport LEP ink composition onto the printed photovoltaic layer to form a hole transport layer disposed on the printed photovoltaic layer; and (5) applying a composition onto the printed hole transport layer to form a cathode. In some examples, the method of producing a photovoltaic cell comprises: (1) optionally, depositing an anode onto a supporting material to form a substrate comprising an anode; (2) optionally, depositing an electron transport composition on the anode to form a substrate comprising an anode and an electron transport layer disposed on the anode; (3) printing an LEP photovoltaic ink composition onto a substrate comprising an anode (and optionally comprising an electron transport layer disposed on the anode) to form a liquid electrophotographically printed photovoltaic layer disposed on the substrate; (4) printing a hole transport LEP ink composition onto the printed photovoltaic layer to form a printed hole transport layer; and (5) printing an electrically conductive LEP ink composition onto the printed hole transport layer.

In some examples, the method of producing a photovoltaic cell further comprises curing the thermoplastic resin of the liquid electrophotographically printed hole transport layer (which may be referred to as the HT resin or HT thermoplastic resin). In some examples, the HT resin is cured by heat treatment. In some examples, curing of the HT resin comprises causing the epoxide to react, for example, by initiating a ringopening reaction and/or a cross-linking reaction of the epoxide.

In some examples, the method of producing a photovoltaic cell further comprises curing the thermoplastic resin of the printed photovoltaic layer (which may be referred to as the PV resin). In some examples, the PV thermoplastic resin is cured by heat treatment. In some examples, curing of the PV thermoplastic resin comprises causing the epoxide to react, for example, by initiating a ring-opening reaction and/or a crosslinking reaction of the epoxide.

In some examples, the method of producing a photovoltaic cell further comprises curing the PV resin and HT resin. In some examples, the PV thermoplastic resin and the HT thermoplastic resin are cured by heat treatment. In some examples, curing of the PV thermoplastic resin and the HT thermoplastic resin comprises causing the epoxides to react, for example, by initiating a ring-opening reaction and/or a crosslinking reaction of the epoxide. In some examples, curing of the PV resin and curing of the HT resin is performed simultaneously, that is, after both the printed photovoltaic layer and the printed hole transport layer have been produced.

In some examples, curing the PV thermoplastic resin and/or curing the HT thermoplastic resin by heat treatment comprises raising the temperature to a temperature of at least about 100°C, for example, at least about 110°C, at least about 120°C, at least about 130°C, at least about 140°C, or at least about 150°C. In some examples, curing the PV thermoplastic resin and/or the HT thermoplastic resin by heat treatment comprises raising the temperature to a temperature of up to about 150°C, for example, up to about 140°C, up to about 130°C, up to about 120°C, up to about 110°C, or up to about 100°C. In some examples, curing the PV thermoplastic resin and/or the HT thermoplastic resin by heat treatment comprises raising the temperature to a temperature of from about 100°C to about 150°C, for example, from about 100°C to about 140°C, from about 110°C to about 130°C, or from about 120°C to about 150°C. In some examples, curing the PV thermoplastic resin by heat treatment may reduce the thickness of the photovoltaic layer. In some examples, curing the HT thermoplastic resin by heat treatment may reduce the thickness of the hole transport layer layer. In some examples, the thickness of the LEP printed photovoltaic layer comprising a cured thermoplastic resin (e.g., comprising a cured epoxide) may be about % the thickness of an LEP printed photovoltaic layer comprising a thermoplastic resin comprising a copolymer of an alkylene monomer and a monomer having acidic side groups.

In some examples, before printing the LEP photovoltaic ink composition onto a substrate comprising an anode, an electron transport composition may be deposited on the anode by, for example, a chemical deposition method or a physical deposition method. The chemical deposition method may be selected from the group consisting of chemical vapour deposition (CVD), atomic layer deposition (ALD), and sol-gel processes. The physical deposition method may be selected from the group consisting of sputtering, pulsed laser deposition, and spray pyrolysis.

In some examples, before printing the hole transport LEP ink composition, the method further comprises producing the hole transport LEP ink composition.

In some examples, before printing the LEP photovoltaic ink composition, the method further comprises producing the LEP photovoltaic ink composition. In some examples, the LEP photovoltaic ink composition was formed by dispersing a salt AX, a salt selected from the group consisting of BX₂ and BX4, and a thermoplastic resin in a carrier liquid. In some examples, LEP photovoltaic ink composition was formed by dispersing a salt AX, a salt selected from the group consisting of BX₂ and BX₄, a thermoplastic resin and conductive particles in a carrier liquid.

In some examples, before printing the electrically conductive LEP ink composition, the method further comprises producing the electrically conductive LEP ink composition.

Method of producina a hole transport LEP ink composition

Also provided herein is a method of producing a hole transport LEP ink composition. In some examples, the method of producing a hole transport LEP ink composition may comprise combining a material capable of transporting electron holes; a thermoplastic resin; and a liquid carrier.

In some examples, the method of producing a hole transport LEP ink composition may comprise suspending a thermoplastic resin in a carrier liquid. In some examples, the method of producing a hole transport LEP ink composition may comprise suspending in a carrier liquid chargeable particles comprising a thermoplastic resin.

In some examples, the method of producing a hole transport LEP ink composition may comprise combining a thermoplastic resin and a carrier liquid to form a transparent paste and then adding a material capable of transporting electron holes to the transparent paste.

In some examples, the thermoplastic resin and the carrier liquid are combined and heated to an elevated temperature. In some examples, the thermoplastic resin and the carrier liquid are combined and heated to a temperature above the melting point of the thermoplastic resin. The melting point of the thermoplastic resin may be determined by differential scanning calorimetry, for example, using ASTM D3418. In some examples, the thermoplastic resin and the carrier liquid are combined and heated to a temperature of temperature of at least 70°C, for example, at least 80°C, for example, at least 90°C, for example, at least 100°C, for example, at least 110°C, for example, at least 120°C, for example, 130°C, for example, to melt the resin. In some examples, the thermoplastic resin and carrier liquid are heated until the resin has melted and/or dissolved in the carrier liquid. Melting and/or dissolving of the resin in the carrier liquid may result in the carrier fluid appearing clear and homogeneous. In some examples, the resin and carrier liquid are heated before, during or after mixing. In some examples, the resin and the carrier liquid are mixed at a mixing rate of 500 rpm or less, for example, 400 rpm or less, for example, 300 rpm or less, for example, 200 rpm or less, for example, 100 rpm or less, for example, 75 rpm or less, for example, 50 rpm. In some examples, mixing may continue until melting and/or dissolution of the resin in the carrier liquid is complete.

In some examples, the thermoplastic resin and the carrier liquid are combined, causing the thermoplastic resin to swell with the carrier liquid. In some examples, the thermoplastic resin and the carrier liquid are combined and heated, causing the resin to swell with the carrier liquid. In some examples, the thermoplastic resin and the carrier liquid are combined and heated, causing swelling and solvation of the resin with the carrier liquid.

In some examples, after heating the combined thermoplastic resin and carrier liquid, the thermoplastic resin in the carrier liquid is cooled to a temperature below the melting point of the thermoplastic resin, for example, to room temperature.

In some examples, the method of producing a hole transport LEP ink composition comprises adding the material capable of transporting electron holes to the thermoplastic resin and the carrier liquid. In some examples, the method of producing a hole transport LEP ink composition comprises adding the material capable of transporting electron holes to the thermoplastic resin and the carrier liquid to form chargeable particles comprising the material capable of transporting electron holes and the thermoplastic resin.

In some examples, the method comprises grinding the material capable of transporting electron holes and the thermoplastic resin in the presence of the carrier liquid to form a paste. In some examples, the method comprising combining a material capable of transporting electron holes with the transparent paste and grinding to form a concentrated hole transport LEP ink composition.

In some examples, the method comprises adding a charge adjuvant to the thermoplastic resin and the carrier liquid and optionally grinding. In some examples, the method comprises adding a charge adjuvant and the material capable of transporting electron holes to the thermoplastic resin and carrier liquid and optionally grinding. In some examples, the method comprises adding a charge adjuvant to the material capable of transporting electron holes, thermoplastic resin and carrier liquid and optionally grinding.

In some examples, the method comprises grinding at a grinding speed of at least 50 rpm. In some examples, the method comprises grinding at a grinding speed of up to about 600 rpm. In some examples, the method comprises grinding for at least 1 h, in some examples, for at least 2 h. In some examples, the method comprises grinding for up to about 12 h. In some examples, the method comprises grinding at a temperature of at least about 35°C. In some examples, the method comprises grinding at a temperature of at least about 50°C for a first time period, in some examples, for at least 1 h, in some examples, for at least 1.5 h and then reducing the temperature to a temperature of at least 30°C, in some examples, at least 35°C and continuing grinding for at least 5 h, in some examples, at least 9 h, in some examples, at least 10 h.

Method of producina an LEP photovoltaic ink composition

In some examples, the LEP photovoltaic ink composition may be produced by the method described above for producing the hole transport LEP ink composition except that a combination of a salt AX and a salt selected from the group consisting of BX₂ and BX₄ is used instead of the material capable of transporting electron holes. In some examples, the LEP photovoltaic ink composition (wherein the material with a perovskite structure has the chemical formula ABX₃) may be produced by the method described above for producing the hole transport LEP ink composition except that a combination of a salt AX and a salt BX₂ (in a 1 :1 ratio, by number of moles of each salt) is used instead of the material capable of transporting electron holes. In some examples, the LEP photovoltaic ink composition (wherein the material with a perovskite structure has the chemical formula A₂BX₆) may be produced by the method described above for producing the hole transport LEP ink composition except that a combination of a salt AX and a salt BX₄ (in a 2:1 ratio, by number of moles of each salt) is used instead of the material capable of transporting electron holes.

In some examples, the LEP photovoltaic ink composition may be produced by the method described above for producing the hole transport LEP ink composition except that a combination of a salt AX, a salt selected from the group consisting of BX₂ and BX₄ and conductive particles was used instead of the material capable of transporting electron holes. In some examples, the LEP photovoltaic ink composition (wherein the material with a perovskite structure has the chemical formula ABX₃) may be produced by the method described above for producing the hole transport LEP ink composition except that a combination of a salt AX, a salt BX₂ (in a 1 :1 ratio, by number of moles of each salt) and conductive particles is used instead of the material capable of transporting electron holes. In some examples, the LEP photovoltaic ink composition (wherein the material with a perovskite structure has the chemical formula A₂BX₆) may be produced by the method described above for producing the hole transport LEP ink composition except that a combination of a salt AX, a salt BX₄ (in a 2:1 ratio, by number of moles of each salt) and conductive particles is used instead of the material capable of transporting electron holes. Method of

conductive LEP ink

In some examples, the electrically conductive LEP ink composition may be produced by the method described above for producing the hole transport LEP ink composition except that electrically conductive particles are used instead of the material capable of transporting electron holes. In some examples, the electrically conductive LEP ink composition comprising particles comprising a thermoplastic resin and electrically conductive metal particles in a carrier liquid may be produced by the method described above for producing the hole transport LEP ink composition except that electrically conductive particles are used instead of the material capable of transporting electron holes.

EXAMPLES

The following illustrates examples of the methods and other aspects described herein. Thus, these Examples should not be considered as limitations of the present disclosure, but are merely in place to teach how to make examples of the present disclosure.

Materials

Resins

Poly(ethylene-co-glycidyl methacrylate) (EPI-1 resin): a copolymer of ethylene and glycidyl methacrylate containing 6.5 to 9.0 wt.% glycidyl methacrylate with a melt index of 4.0 to 6.0 g/10 min (190°C/2.16 kg); available as pellets from Sigma-Aldrich™ under product number 430862.

Nucrel 599 (resin D): a copolymer of ethylene and methacrylic acid, made with nominally 10 wt.% methacrylic acid (available from DuPont).

Perovskite components

Methylammonium Iodide (MAI): >99.0 wt.% (available from TCI).

Lead iodide (Pbl₂) : >98.0 wt.% (available from Sigma-Aldrich or TCI). Electrically conductive metal particles of the electrically conductive LEP ink composition

AgCu0204-12: a silver coated copper powder pigment with a particle size distribution of 95% less than 7.43 pm, 90% less than 5.99 pm, 50% less than 3.24 pm and 10% less than 1.9 pm, as measured by using a Honeywell X100 Particle Size Analyzer (available from Ames Goldsmith) with about 12 wt.% silver that has a thickness of tens to hundreds of a nm (as shown by SEM imaging).

Conductive particles of the LEP photovoltaic ink composition

Single-walled carbon nanotubes (SWCNTs): 75 wt.% carbon nanotubes (available from OCSiAl).

Carrier Liquid

Isopar L™: an isoparaffinic oil comprising a mixture of C11-C13 isoalkanes (produced by Exxon Mobil™; CAS number 64742-48-9.

Charge Adjuvant

VCA (viscosity control agent): an aluminium stearate (available from Fishcher Scientific).

Charge Director

SCD: a barium bis(sulfosuccinate) salt, namely a barium phosphate and a sulfosuccinate moiety of the general formula [R¹-O-C(O)CH₂CH(SO₃')C(O)-O-R²], wherein each of R¹ and R² independently is a C₆.2s alkyl, generally mainly C13 alkyl.

Substrate with electron transport layer disposed thereon

A4 PET-ITO substrate coated with approximately 100 nm of ZnO by sputtering were purchased from GEOMATEC.

Hole transport material

Polyaniline (PANI) emeraldine base dopped with sulfuric acid (available from Sigma- Aldrich) This material was prepared by dissolving PANI emeraldine base in a water containing sulfuric acid in a stochiometric concentration (1 acid molecule per repeating aniline unit (equivalent to ~50% w/w). PANI emeraldine salt: 20% w/w on carbon black composite (available from Aldrich)

CuO: >99.0 wt.% (available from Sigma-Aldrich, ACS reagent)

NiO: 99.99 wt.% (available from Sigma-Aldrich)

Polypyrrole (PPy): polypyrrole composite with carbon black and doped with an organic sulfonic acid; 20 wt.% loading (available from Sigma-Aldrich under product number 530573).

Single walled carbon nanotubes (SWCNTs): 75 wt.% carbon nanotubes (available from OCSiAl)

Carbon black (CB): MONARCH® 800 by Cabot Corporation

Methods

Epoxy based LEP paste preparation

A transparent paste was prepared by mixing (60 rpm) 1000 g of poly(ethylene-co- glycidyl methacrylate) with 2000 g of Isopar L in a ROSS mixer (Model DPM-4 (33.4 wt.% non-volatile solids (NVS)). The mixing temperature and duration was varied as described in the table below:

LEP photovoltaic ink composition 1

A 5 wt.% NVS photovoltaic LEP ink formulation was prepared by placing 0.32 g of MAI, 0.92 g of Pbl₂, 0.93 g of epoxy based LEP paste (33.4%, descried above) and 28.8 g of Isopar L in a 300 ml glass vessel. To this mixture was added 0.0025 g of SWCNT and 80 g of Zirmil 0.9 mm ceramic beads. The vessel was tightly closed and placed in a fast&fluid SK550 1.1 shaker for 8 hours of grinding at 500 rpm. Hole transport liquid electrophotographic ink composition 1

A 5 wt.% NVS hole transport LEP ink formulation was prepared by placing 0.3 g of polyaniline emeraldine base with sulfuric acid, 3.6 g of epoxy based LEP paste (33.4%, descried above) and 28.5g of Isopar L in a 300 ml glass vessel. To this mixture was added 80 g of Zirmil 0.9 mm ceramic beads and the vessel was tightly closed and placed in a fast&fluid SK550 1.1 shaker for 8 hours of grinding at 500 rpm.

Hole transport LEP ink composition 2

A 5 wt.% NVS hole transport LEP ink composition was prepared by the method described for hole transport LEP ink composition 1 except that PANI emeraldine salt on carbon black composite (20% w/w) was used instead of the PANI emeraldine salt with sulfuric acid.

Hole transport LEP ink composition 3

A 5 wt.% NVS hole transport LEP ink composition was prepared by the method described for hole transport LEP ink composition 1 except that CuO was used instead of the PANI emeraldine salt with sulfuric acid.

Hole transport LEP ink composition 4

A 5 wt.% NVS hole transport LEP ink composition was prepared by the method described for hole transport LEP ink composition 1 except that NiO was used instead of the PANI emeraldine salt with sulfuric acid.

Hole transport LEP ink composition 5

A 5 wt.% NVS hole transport LEP ink composition was prepared by the method described for hole transport LEP ink composition 1 except that PPy was used instead of the PANI emeraldine salt with sulfuric acid.

Hole transport LEP ink composition 6

A 5 wt.% NVS hole transport LEP ink composition was prepared by the method described for hole transport LEP ink composition 1 except that SWCNTs were used instead of the PANI emeraldine salt with sulfuric acid. Hole transport LEP ink composition 7

A 5 wt.% NVS hole transport LEP ink composition was prepared by the method described for hole transport LEP ink composition 1 except that carbon black was used instead of the PANI emeraldine salt with sulfuric acid.

Electrically conductive LEP ink composition 1

A 40 wt.% conductive copper LEP ink was prepared by using the precipitation procedure as described below:

A 2 L glass reactor was filled with 198 g of resin D and 510 g of Isopar L and heated to 120°C. Following resin melting, the reactor was cooled to 90°C at a rate of 10°C/hour. At this temperature, 1300 g of metallic AgCu0204-12 powder pigment was added to obtain an 87% pigment to total NVS ratio (w/w) Pigment addition was performed at a controlled rate over 40 min using a 5000 rpm high shear mixer to break agglomerates.

After an additional 30 min of high shear mixing and cooling to 85°C at a rate of 10°C/hour, high shear mixing was stopped, and the reactor was cooled to 75°C at rate of 3°C/hour. An additional cooling step was performed to 70°C at a rate of 10°C/hour and Isopar L was added to dilute the obtained formulation to 63 wt.%.

A final cooling step to 40°C at 20°C/hour was followed by diluting to 40 wt.% NVS with addition of 0.1% w/w VCA.

A final gentle grinding step was performed on an S1 attritor for 1 hour at 80 Rpm.

Example 1 (Reference)

An A4 PET-ITO substrate coated with approximately 100 nm of ZnO by sputtering was purchased.

A 0.7 wt.% MAPbl₃ LEP photovoltaic ink formulation was prepared by diluting 1 .4 g of LEP photovoltaic ink composition 1 with 8.6 g of Isopar L. This ink composition was charged by using one drop of 0.5 wt.% SCD in Isopar L and deposited on top of the ZnO-coated PET-ITO substrate by electroplating (using a Q/M instrument operated at 1500 V). The obtained layer was dried at 60°C for 15 minutes to form a liquid electrophotographically printed photovoltaic layer disposed on the ZnO layer (an electron transport layer). A layer thickness (DMA) of 0.5 was achieved. Electrically conductive LEP ink composition 1 was deposited by drop-casting on top of the dried photovoltaic layer to form a printed cathode. Typically, 4-8 round spots (with an area of about 0.25 cm²) were formed on the 3 cm in diameter circles of printed photovoltaic layer. This photovoltaic cell structure was then annealed at 120°C for 5 minutes. The annealing enables the epoxide in the printed layers to cross-link, providing a hydrophobic network surrounding the perovskite crystals.

Although drop casting was used to deposit electrically conductive LEP ink composition 1 , this composition has also been LEP printed.

Example 2 (PANI emeraldine base doped with sulfuric acid, DMA=0.1)

A4 PET-ITO substrate coated with approximately 100 nm of ZnO by sputtering was purchased.

A 0.7 wt.% MAPbl₃ LEP photovoltaic ink formulation was prepared by diluting 1 .4 g of LEP photovoltaic ink composition 1 with 8.6 g of Isopar L. This ink composition was charged by using one drop of 0.5 wt.% SCD in Isopar L and deposited on top of the ZnO-coated PET-ITO substrate by electroplating (using a Q/M instrument operated at 1500 V). The obtained layer was dried at 60°C for 15 minutes to form a liquid electrophotographically printed photovoltaic layer disposed on the ZnO layer (an electron transport layer). A layer thickness (DMA) of 0.5 was achieved.

A 0.7 wt.% hole transport LEP ink formulation was prepared by diluting 1.4 g of the hole transport LEP ink 1 with 8.6 g of Isopar L. This ink composition was charged by using one drop of 0.5 wt.% SCD in Isopar L and deposited on top of the dried photovoltaic layer by electroplating (using a Q/M instrument operated at 1500 V). The obtained layer was dried at 60°C for 15 minutes to form a liquid electrophotographically printed hole transport layer disposed on the liquid electrophotographically printed photovoltaic layer. A layer thickness (DMA) of 0.1 was achieved.

Electrically conductive LEP ink composition 1 was deposited by drop-casting on top of the dried hole transport layer to form a printed cathode. Typically, 4-8 round spots (with an area of about 0.25 cm²) were formed on the 3 cm in diameter circles of electrodeposited photovoltaic layer and electro-deposited hole transport layer. This photovoltaic cell structure was then annealed at 120°C for 5 minutes. The annealing enables the epoxide in the printed layers to cross-link, providing a hydrophobic network surrounding the perovskite crystals. Although drop casting was used to deposit electrically conductive LEP ink composition 1 , this composition has also been LEP printed.

Example 3 (PANI emeraldine salt doped with sulfuric acid, DMA=0.3)

A photovoltaic cell was prepared by the method described in Example 2 except that the hole transport layer had a thickness (DMA) of 0.3.

Example 4 (PANI emeraldine base on carbon black composite, DMA=0.1)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 2 was used instead of hole transport LEP ink 1 .

Example 5 (PANI emeraldine base on carbon black composite, DMA=0.3)

A photovoltaic cell was prepared by the method described in Example 2 except that the hole transport LEP ink 2 was used instead of hole transport LEP ink 1 and the hole transport layer had a thickness (DMA) of 0.3.

Example 6 (CuO, DMA=0.1)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 3 was used instead of hole transport LEP ink 1 .

Example 7 (CuO, DMA=0.3)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 3 was used instead of hole transport LEP ink 1 and the hole transport layer had a thickness (DMA) of 0.3.

Example 8 (NiO, DMA=0.1)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 4 was used instead of hole transport LEP ink 1 .

Example 9 (NiO, DMA=0.3)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 4 was used instead of hole transport LEP ink 1 and the hole transport layer had a thickness (DMA) of 0.3. Example 10 (PPy, DMA=0.1)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 5 was used instead of hole transport LEP ink 1 .

Example 11 (PPy, DMA=0.3) A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 5 was used instead of hole transport LEP ink 1 and the hole transport layer had a thickness (DMA) of 0.3.

Example 12 (SWCNTs, DMA=0.3)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 6 was used instead of hole transport LEP ink 1 and the hole transport layer had a thickness (DMA) of 0.3.

Example 13 (carbon black, DMA=0.2)

A photovoltaic cell was prepared by the method described in Example 2 except that hole transport LEP ink 7 was used instead of hole transport LEP ink 1 and the hole transport layer had a thickness (DMA) of 0.2.

Summary of Photovoltaic cell structures

Test results

The obtained solar cell structure was analyzed by using a solar simulator with 1 sun illumination. HCI 3% solution (w/w, diluted) was used to clean the ZnO layer and reveal the PET-ITO anode contact. Four probes were placed on the tested cell, 2 on the PET- ITO anode and 2 on the copper cathode layer. The l-V curves obtained with and without illumination were recorded at different applied voltages.

Figures 2 to 8 show the l-V curves for each photovoltaic cell prepared and described in the table above in comparison with the l-V curve for a photovoltaic cell that does not contain a hole transport layer (Sample 1 , Reference). The photovoltaic cell efficiency calculated (by solar simulator software) is mentioned in each figure.

As can be seen from the figures, the addition of a hole transport layer typically resulted in decreased collected current and increased open circuit voltage (V_Oc)- In contrast, the hole transport layer containing carbon black (Example 13) shows increased V_Oc and short circuit current (l_Sc)-

The thickness of the hole transport layer is related to the DMA (density mass area). Thus, a higher DMA results in a thicker hole transport layer. The DMA is calculated by the following equation: m_ink x NVS_ink x p_LC x Df

Where: m_ink = the total weight of the LEP ink composition;

NVS_ink = the non-volatile solids content (in wt.%) of the LEP ink composition; p_LC = density of the liquid carrier in the LEP ink composition; and

Df = the (weight based) dilution factor (i.e., m_ink/(mjn_k+mLc)) m_Lc = the weight of liquid carrier used to dilute the LEP ink composition for printing.

As an example, for 1.32 g of an LEP ink composition with a non-volatile solids content of 5% w/w that is diluted 1/10 using Isopar L (i.e., for every 1 g of LEP ink composition, 9 g of Isopar L is added; density of Isopar L is 0.76), the DMA is 0.5. 0.5

Thus, a higher DMA indicates that the composition that was LEP printed had a higher solids content, resulting in a thicker printed layer.

The thickness of the hole transport layer did not affect the cell performance consistently. A significant increase in photovoltaic cell efficiency was seen for photovoltaic cells containing a hole transport layer with carbon black (Example 13), PANI emeraldine salt on carbon black composite (Examples 4 and 5) and polypyrrole (Examples 10 and 11) as the material capable of transporting holes. Under continuous illumination, the photovoltaic cell efficiency was found to decrease over time for photovoltaic cells containing PANI emeraldine salt on carbon black composite (Examples 4 and 5). The most effective hole transport layer was found to be the hole transport layer containing carbon black, which increased the cell efficiency by three times at a thickness (DMA) of 0.2.

Without wishing to be bound by theory, it is believed that the results for Sample 5 (shown in Figure 3) and Sample 8 (see Figure 5) are a result of an issue with the PET- ITO-ZnO substrate, which was not completely uniform. In deformed regions of the PET- ITO-ZnO substrate, ohmic behavior rather than photovoltaic behavior was observed.

Without wishing to be bound by theory, it is believed that carbon black, which is capable of transporting both holes and electrons, acts selectively as a hole transport layer in the photovoltaic cells. It is believed that the presence of a selective electron transport layer (ZnO) may improve the selectivity of the carbon black containing hole transport layer. Additionally, it is believed that the hole transport layer containing carbon black creates a gradient of work functions between the perovskite containing photovoltaic layer and the cathode layer, improving the withdrawal of holes.

To understand the morphology of the hole transport layers, SEM-FIB (scanning electron microscopy-focused ion beam) analysis was performed on some of the photovoltaic cells. Figure 9 shows the SEM-FIB analysis of photovoltaic cells in which the hole transport layer contains carbon black (a-c) and polypyrrole (d-f). SEM-FIB images are shown for the top view (a and d), a large scale view (b and e) and a zoomed in view (c and f).

As can be seen from Figure 9c, a hole transport layer produced from a hole transport LEP ink composition containing polypyrrole as the material capable of transporting electron holes provides a smooth and uniform hole transport layer with a thickness of approximately 500 nm. A hole transport layer produced from a hole transport LEP ink composition containing carbon black as the material capable of transporting electron holes provides a hole transport layer with a more granular morphology (Figure 9f), providing a layer thickness of from 300 nm to 1000 nm.

Electroplating and LEP printing

Electroplating exploits the same phenomenon as liquid electrophotographic printing and has therefore been used to demonstrate that the ink composition is capable of being liquid electrophotographically printed. In electroplating, two electrodes are placed in the liquid electrophotographic ink composition and a strong electric field is applied between the two electrodes. The substrate is attached to the positively charged electrode. The chargeable particles of the LEP ink composition are attracted to the positively charged electrode, forming a layer of the LEP ink composition on the substrate attached to the positively charged electrode. In LEP printing, a positively charged latent image is formed on the photoimaging plate (PIP) and the chargeable particles are attracted to the positively charged portions of the PIP. Thus, the formation of a layer of LEP ink composition on the substate during electroplating demonstrates that the composition is capable of being used as an LEP ink composition.

While the invention has been described with reference to certain examples, those skilled in the art will appreciate that various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the disclosure. It is intended, therefore, that the invention be limited by the scope of the following claims and their equivalents. Unless otherwise stated, the features of any dependent claim can be combined with the features of any of the other dependent claims and any of the independent claims.

Claims

1 . An ink set for producing a photovoltaic cell comprising: a hole transport liquid electrophotographic ink composition comprising: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier; and a liquid electrophotographic photovoltaic ink composition comprising: a dispersion of a material with a perovskite structure and a thermoplastic resin in a carrier liquid; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation; and X is an anion.

2. The ink set of claim 1 , wherein the material capable of transporting electron holes is also capable of transporting electrons or wherein the material capable of transporting electron holes is selective for transporting electron holes.

3. The ink set of claim 1 , wherein the material capable of transporting electron holes is selected from the group consisting of polypyrrole and carbon black.

4. The ink set of claim 1 , wherein the material capable of transporting electron holes is present in an amount of from 5 wt.% to 95 wt.% of the solids of the hole transport liquid electrophotographic ink composition.

5. The ink set of claim 1 , wherein the thermoplastic resin of the hole transport liquid electrophotographic ink composition is present in an amount of from at least 5 wt.% of the solids of the hole transport liquid electrophotographic ink composition.

6. The ink set of claim 1 , further comprising an electrically conductive liquid electrophotographic ink composition comprising a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.

7. A photovoltaic cell comprising: an anode; a photovoltaic layer; a liquid electrophotographically printed hole transport layer; and a cathode; wherein the photovoltaic layer is disposed between the anode and the liquid electrophotographically printed hole transport layer; and wherein the liquid electrophotographically printed hole transport layer is disposed between the photovoltaic layer and the cathode; wherein the photovoltaic layer comprises a material with a perovskite structure; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the liquid electrophotographically printed hole transport layer comprises: a material capable of transporting electron holes; and a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

8. The photovoltaic cell of claim 7, further comprising an electron transport layer disposed between the anode and the photovoltaic layer.

9. The photovoltaic cell of claim 7, wherein the photovoltaic layer is a liquid electrophotographically printed photovoltaic layer comprising a thermoplastic resin, a material with a perovskite structure and optionally conductive particles; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation; B is a cation and X is an anion; and wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide.

10. The photovoltaic cell of claim 7, wherein the cathode is a liquid electrophotographically printed cathode comprising: a thermoplastic resin; and electrically conductive metal particles. The photovoltaic cell of claim 7, wherein the liquid electrophotographically printed hole transport layer has a DMA (density mass area) of 0.05 mg/cm² to 0.5 mg/cm². A method of producing a photovoltaic cell comprising: printing a hole transport liquid electrophotographic ink composition onto a photovoltaic layer to form a liquid electrophotographically printed hole transport layer; wherein the photovoltaic layer is disposed on a substrate comprising an anode; and applying a composition to form a cathode; wherein the hole transport layer is disposed between the photovoltaic layer and the cathode; wherein the photovoltaic layer comprises a material with a perovskite structure; wherein the material with a perovskite structure has a chemical formula selected from the group consisting of ABX₃ and A₂BX₆; wherein A is a cation, B is a cation and X is an anion; and wherein the hole transport liquid electrophotographic ink composition comprises: a material capable of transporting electron holes; a thermoplastic resin comprising a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide; and a liquid carrier. The method of producing a photovoltaic cell of claim 12, wherein the substrate further comprises an electron transport layer disposed on the anode. The method of producing a photovoltaic cell of claim 12, further comprising, prior to printing the liquid electrophotographic hole transport ink composition onto the photovoltaic layer, printing a liquid electrophotographic photovoltaic ink composition onto the substrate to form the photovoltaic layer, wherein the liquid electrophotographic photovoltaic ink composition comprises a dispersion of a material with a perovskite structure, a thermoplastic resin, and optionally conductive particles, in a carrier liquid; wherein the thermoplastic resin comprises a copolymer of an alkylene monomer and an ethylenically unsaturated monomer comprising an epoxide. The method of producing a photovoltaic cell of claim 12, wherein applying a composition to form a cathode comprises printing an electrically conductive liquid electrophotographic ink composition comprising a liquid carrier; and particles comprising a thermoplastic resin and electrically conductive metal particles.