WO2018029160A1

WO2018029160A1 - Method to achieve efficient charge injection for electron and/or hole transport in semiconducting layers

Info

Publication number: WO2018029160A1
Application number: PCT/EP2017/069991
Authority: WO
Inventors: David Sparrowe; Tomas Backlund
Original assignee: Merck Patent Gmbh
Priority date: 2016-08-11
Filing date: 2017-08-08
Publication date: 2018-02-15
Also published as: TW201818575A

Abstract

The present invention relates to a method for preparing an organic electronic device and to an organic electronic device prepared according to this method.

Description

Method to achieve efficient charge injection for electron and/or hole transport in semiconducting layers

Technical Field

Background

High performance organic electronic devices, in particular such devices with short channel length, for example organic thin film transistors, organic photovoltaic cells or organic light emitting devices, require either an ohmic contact, i.e. a non- rectifying electrical junction, or a negligible contact resistance compared to the channel resistance. In order to reduce contact resistance and finally the energy barrier for charge injection from the electrode to the semiconductor, the work function of the injection interface has to be matched to the HOMO/LUMO energy level of the p-type/n-type semiconductor. Several approaches to solve this problem are known from literature. In most cases, the semiconductor material and, thus, the HOMO/LUMO energy levels are fixed, leaving the electrode the only controllable variable to align the energy level. One approach following this strategy is to match the electrode work function to either the HOMO or LUMO energy level of the semiconductor. For example, metals having a low work function may be used for electron injection and metals having a high work function may be used for hole injection.

This approach, however, may cause problems relating to costs, processing and stability. For example, in case of p-type semiconductors having deep HOMO energy levels, platinum or palladium or alloys of such may be used as the electrode material, which are very expensive. In case of n-type semiconductors having shallow LUMO energy levels, calcium is the commonly used electrode material, which is however unstable to air.

A widely-used alternative approach consists in using an electrode modification layer or intermediate layer between the electrode and the semiconductor, which may act as an electron donor or acceptor and which may incorporate a dipole moment that alters the work function of the electrode. Specifically, it is known from literature that self-assembled monolayers (SAMs) formed between the electrode and the semiconductor may be used to effectively affect the work function of the electrode (J. Niederhausen et al., Phys. Rev B 84, 165302 (2011); H. Kim et al., Organic Electronics 14 (2013) 2108-2113; D.M. Alloway et al., J. Phys. Chem. C (2009), 113, 20328-20334).

According to state of the art methods, the electrode modification layer or self- assembled monolayer is directly deposited onto the electrode surface for this purpose.

For example, WO 2013/113389 discloses an organic semiconductor device, wherein an intermediate layer is interposed between the organic semiconducting material and the electrode. The intermediate layer is prepared on the electrode by spin-coating a solution containing the layer-forming material onto the electrode, or by dipping the electrode into such a solution. The sample processed this way is then coated with the organic semiconducting material.

US 2010/0176387 Al relates to an organic thin-film transistor having a thiol compound layer provided on the electrode surface. The thiol compound layer is formed by bringing a gas, liquid or solid containing the thiol compound into contact with the electrode surface. Finally, an organic semiconductor layer is formed to overlap the electrode. However, a major drawback of these methods is that the electrode modification layer or self-assembled monolayer is directly deposited onto the electrode, that is, prior to semiconductor deposition. The electrode modification layer on the one hand may improve charge injection, but on the other hand may also result in unintentional changes in the surface energy of the electrode. For example, the surface energy of an untreated electrode may be high, thereby making it easier to deposit the semiconducting material, whereas when the surface has been treated with, for example, a fluorinated compound, the electrode has a low surface energy. This change in surface energy may cause unwanted side effects, such as de-wetting, non-optimum semiconductor orientation and complications relating to crystal growth and detrimental grain boundary formation. For example, the contact angle ca n be too high when the modification layer is directly deposited onto the electrode, which may lead to poor morphology as described above or incomplete/non-existent film formation. These unwanted side effects are often unavoidable with substrates that possess a high contact angle. High contact angles greater than 85° often result in these problems. The contact angles for various thiol compounds have been demonstrated in the literature for example by Boudinet et al. (D. Boudinet et al., Organic Electronics (2010), 11, pp. 227-237).

Thus, there is a need in industry for a method for preparing organic electronic devices that overcomes the drawbacks of state of the art methods.

It is therefore an object of the present invention to provide a method for preparing organic electronic devices that diminishes or eliminates the drawbacks resulting from methods known from prior art. Specifically, it is an object of the present invention to provide an effective method for achieving good charge injection for electron and/or hole transport in semiconducting layers of organic electronic devices, thereby improving the device performance. Further, it is an object of the present invention to provide a method that facilitates the production of low cost commercial organic electronic devices. Summary

The present inventors have now surprisingly found that the above objects may be attained either individually or in any combination by the present method for producing organic electronic devices.

The present application therefore provides for a method for preparing an organic electronic device, the method comprising

(a) depositing a semiconductor material onto an electrode to form a semiconducting layer, and

(b) subsequently generating an intermediate layer between said electrode and the semiconducting layer of step (a) by applying a surface-modifying compound onto said semiconducting layer, wherein the surface-modifying compound comprises a compound of the formula HX-R, wherein X is Se, Te or S, and R is a hydrocarbyl group comprising 1 to 12 carbon atoms, wherein optionally one or more hydrogen is substituted by a functional group including at least one heteroatom.

Further preferred methods provided for by the present application are as indicated in the dependent claims.

The present application also provides for an organic electronic device prepared by the method according to the present application.

Brief description of the figures

Figure 1 shows the transfer characteristics and the charge carrier mobility of the top-gate bottom-contact thin film transistor of Example 1. Figure 2 shows the transfer characteristics and the charge carrier mobility of the top-gate bottom-contact thin film transistor of Example 2.

Figure 3 shows the transfer characteristics and the charge carrier mobility of the top-gate bottom-contact thin film transistor of Example 3.

Figure 4 shows the transfer characteristics and the charge carrier mobility of the top-gate top-contact thin film transistor of Example 4.

Figure 5 shows the transfer characteristics and the charge carrier mobility of the top-gate top-contact thin film transistor of Example 5.

Figure 6a shows a schematic exemplary representation of a top gate organic field effect transistor.

Figure 6b shows a schematic exemplary representation of a bottom gate organic field effect transistor.

Detailed description

As used herein, the term "organic field effect transistor" (OFET) will be understood to be inclusive of the subclass of such devices known as "organic thin film transistor" (OTFT).

Further, as used herein, the term "organic electronic device" will be understood to be inclusive of the term "organic semiconductor device" and the several specific implementations of such devices, such as the organic field effect transistors as defined above. ln the present application, the terms "intermediate layer", "electrode modification layer" and "surface-modification layer" are used interchangeably.

In a general aspect, the present application provides for a method for preparing an organic electronic device. The method comprises a step (a) of depositing a semiconductor material onto an electrode to form a semiconducting layer and a subsequent step (b) of generating an intermediate layer between said electrode and said semiconducting layer.

As used herein, the term "semiconductor material" refers to a compound that can act as either an electrical conductor or insulator depending upon the voltage applied to it. The term "semiconducting layer" refers to a continuous system of material that is semiconducting.

Further, as used herein, the term electrode is used for an element which is adapted to be electrically contacted and which is adapted to inject negative and/or positive charge carriers into a semiconducting layer and/or which is adapted to extract negative and/or positive charge carriers from a semiconducting layer.

For example, said electrode may be a source electrode and/or a drain electrode in an organic field effect transistor, wherein the source electrode and the drain electrode both contact the semiconducting layer such that a semiconducting channel connects the source and drain electrodes. Preferably, such electrodes are provided on a supporting layer or substrate. Examples of suitable supporting layers or substrates, as they may be referred to in the context of organic electronic devices, are given below.

The electrode material that may be used in the present invention for preparing organic electronic devices is not particularly limited. Suitable electrode materials include electrically conducting organic and inorganic materials, or blends thereof. Exemplary organic electrode materials or blends include polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene) (PEDOT) or doped conjugated polymers, further dispersions or pastes of graphite.

As electrode material inorganic materials are preferred, which are preferably selected from metals and metal oxides. The types of metal and metal oxide that may be used in the present invention also include alloys and any blend of metals, any blend of metal oxides as well as any blend of metals and metal oxides.

Exemplary metals, which are particularly suitable as electrodes in organic electronic devices may be selected from the group consisting of gold (Au), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti), calcium (Ca), molybdenum (Mo), scandium (Sc), and any blend thereof. Of these, gold, copper and silver are particularly preferred, since they bond very well to chalcogenol groups, i.e., to groups -OH (hydroxyl), -SH (thiol), - SeH (selenol) and -TeH (tellurol), preferably to -SH. Silver is most preferred, since it is more stable than copper and cheaper than gold. Exemplary alloys, which are particularly suitable as electrodes in organic electronic devices include stainless steel (e.g., 332 stainless steel, 316 stainless steel), alloys of gold, alloys of silver, alloys of copper, alloys of aluminum, alloys of nickel, alloys of palladium, alloys of platinum, alloys of titanium, alloys of calcium, alloys of molybdenum and alloys of scandium.

Exemplary electrically conducting metal oxides include indium tin oxide (ITO), fluorine-doped tin oxide, tin oxide, zinc oxide, aluminum-doped zinc oxide, and any blend thereof.

The electrode may be deposited or formed by liquid coating such as for example spray-coating, dip-coating, web-coating or spin-coating, or by vacuum deposition methods including for example physical vapor deposition, chemical vapor deposition, or thermal evaporation methods. Suitable electrode materials and methods for forming the electrodes are generally known to the skilled person and can easily be found in the literature. Organometallic precursors may also be used and deposited from a liquid phase.

In general, the organic electronic device may be or may comprise any type of organic electronic device.

For example, the organic electronic devices may be selected from the group consisting of organic field effect transistors (OFET), thin film transistors (TFT), integrated circuits (IC), logic circuits, capacitors, radio frequency identification (RFID) tags, devices or components, organic light emitting diodes (OLED), organic light emitting transistors (OLET), flat panel displays, backlights of displays, organic photovoltaic devices (OPV), organic solar cells (OSC), photodiodes, laser diodes, photoconductors, organic photodetectors (OPD), electrophotographic devices, (e.g. electrophotographic recording devices), organic memory devices, sensor devices, charge injection layers, charge transport layers or interlayers in polymer light emitting diodes (PLEDs), Schottky diodes, planarising layers, antistatic films, polymer electrolyte membranes (PEM), conducting substrates, conducting patterns, electrode materials in batteries, alignment layers, biosensors, biochips, security markings, security devices, and components or devices for detecting and discriminating DNA sequences.

The electrode may be applied to a substrate by any of the methods described above. Various substrates may be used for the preparation of organic electronic devices, for example silicon wafers, glass or polymeric materials. Preferred polymeric material include but are not limited to alkyd resins, allyl esters, benzocyclobutenes, butadiene-styrene, cellulose, cellulose acetate, epoxide, epoxy polymers, ethylene-chlorotrifluoro ethylene copolymers, ethylene-tetra- fluoroethylene copolymers, fiber glass enhanced polymers, fluorocarbon polymers, hexafluoropropylenevinylidene-fluoride copolymer, high density polyethylene, parylene, polyamide, polyimide, polyaramide, polydimethylsiloxane, polyethersulphone, polyethylene, polyethylenenaphthalate, polyethyleneterephthalate, polyketone, polymethylmethacrylate, polypropylene, polystyrene, polysulphone, polytetrafluoroethylene, polyurethanes, polyvinylchloride, polycycloolefin, silicone rubbers, and silicones. Of these polyethyleneterephthalate, polyimide, polycycloolefin and polyethylenenaphthalate substrate materials are more preferred. Additionally, for some embodiments of the present invention the substrate can be any suitable material, for example a polymeric material, metal or glass material coated with one or more of the above listed materials. It will be understood that in forming such a substrate, methods such as extruding, stretching, rubbing or photochemical techniques can be employed to provide a homogeneous surface for device fabrication as well as to provide pre-alignment of an organic semiconductor material in order to enhance carrier mobility therein. Alternatively, the substrate can be a polymeric material, metal or glass coated with one or more of the above polymeric materials.

The semiconductor materials and methods for applying the semiconductor layer can be selected from standard materials and methods known to the person skilled in the art, and are described in the literature.

The semiconductor material that can be used in the method according to the present invention may be either an oxide semiconductor material or an organic semiconductor (OSC) material. Organic semiconductor materials are preferred. Moreover, the semiconductor material can either be an n-type or p-type semiconductor material. Preferably, said semiconductor material has a field effect transistor mobility of at least 1 · 10^~5 cm² V ¹ s^"1. ln a preferred embodiment of the present invention, the semiconductor material is an organic semiconductor material. Organic semiconducting materials are for example used as the active channel material in an organic field effect transistor or a layer element of an organic rectifying diode. Organic semiconducting materials that may be deposited by liquid coating to allow ambient processing are preferred. Organic semiconducting materials are preferably spray-, dip-, web- or spin-coated or deposited by printing methods such as ink-jet printing, flexo printing or gravure printing. The organic semiconducting material may optionally be vacuum or vapor deposited.

The semiconducting channel may also be a composite of two or more of the same types of semiconductor materials. Furthermore, a p-type channel material may for example be mixed with n-type materials for the effect of doping the layer. Multilayer semiconductor layers may also be used. For example the semiconductor may be intrinsic near the insulator interface and a highly doped region can additionally be coated next to the intrinsic layer.

The organic semiconducting material may be a monomeric compound, also referred to as "small molecule", as compared to a polymer or macromolecule, or a polymeric compound, or a mixture, dispersion or blend containing one or more compounds selected from either or both of monomeric and polymeric compounds. Preferably the organic semiconducting material is selected from the group of polymeric compounds.

In case of monomeric materials, the OSC can be any conjugated molecule, for example an aromatic molecule containing preferably two or more, very preferably at least three aromatic rings. In some preferred embodiments of the present invention, the OSC contains aromatic rings selected from 5-, 6- or 7-membered aromatic rings, while in other preferred embodiments the OSC contains aromatic rings selected from 5- or 6-membered aromatic rings. The OSC material may be a monomer, oligomer or polymer, including mixtures, dispersions and blends of one or more of monomers, oligomers or polymers.

Each of the aromatic rings of the OSC optionally contains one or more heteroatoms selected from Se, Te, P, Si, B, As, N, 0 or S, preferably from Si, N, 0 or S. Further, the aromatic rings may be optionally substituted with alkyl, alkoxy, polyalkoxy, thioalkyl, acyl, aryl or substituted aryl groups, halogen, where fluorine, cyano, nitro or an optionally substituted secondary or tertiary alkylamine or arylamine represented by -N(R')(R")_/ where R' and R" are each independently H, an optionally substituted alkyl or an optionally substituted aryl, alkoxy or polyalkoxy groups are typically employed. Further, where R' and R" is alkyl or aryl these may be optionally fluorinated.

The aforementioned aromatic rings can be fused rings or linked to each other by a conjugated linking group such as -C(Ti)=C(T₂)-, -C≡C-, -N(R"')-, -N=N-, (R"')=N-, - N=C(R"')-, where Ti and T₂ each independently represent H, CI, F, -C≡N or lower alkyl groups such as Ci-₄ alkyl groups; R'" represents H, optionally substituted alkyl or optionally substituted aryl. Further, where R'" is alkyl or aryl, it may be optionally fluorinated.

Further preferred examples of organic semiconductor materials that can be used in this invention include compounds, oligomers and derivatives of compounds selected from the group consisting of conjugated hydrocarbon polymers such as polyacene, polyphenylene, poly(phenylene vinylene), polyfluorene including oligomers of those conjugated hydrocarbon polymers; condensed aromatic hydrocarbons, such as, tetracene, chrysene, pentacene, pyrene, perylene, coronene, or soluble, substituted derivatives of these; oligomeric para substituted phenylenes such as p-quaterphenyl (p-4P), p-quinquephenyl (p-5P), p-sexiphenyl (p-6P), or soluble substituted derivatives of these; conjugated heterocyclic polymers such as poly(3-substituted thiophene), poly(3,4-bisubstituted thiophene), optionally substituted polythieno[2,3-b]thiophene, optionally substituted polythieno[3,2-b]thiophene, poly(3-substituted selenophene), polybenzothiophene, polyisothianapthene, poly(/V-substituted pyrrole), poly(3- substituted pyrrole), poly(3,4-bisubstituted pyrrole), polyfuran, polypyridine, poly- 1,3,4-oxadiazoles, polyisothianaphthene, poly(/V-substituted aniline), poly(2- substituted aniline), poly(3-substituted aniline), poly(2,3-bisubstituted aniline), polyazulene, polypyrene; pyrazoline compounds; polyselenophene; polybenzofuran; polyindole; polypyridazine; benzidine compounds; stilbene compounds; triazines; substituted metallo- or metal-free porphines, phthalocyanines, fluorophthalocyanines, naphthalocyanines or fluoronaphthalocyanines; C6o and C70 fullerenes; Λ/,Λ/'-dialkyl, substituted dialkyl, diaryl or substituted diaryl-l,4,5,8-naphthalenetetracarboxylic diimide and fluoro derivatives; Λ/,Λ/'-dialkyl, substituted dialkyl, diaryl or substituted diaryl 3,4,9,10- perylenetetracarboxylicdiimide; bathophenanthroline; diphenoquinones; 1,3,4- oxadiazoles; ll,ll,12,12-tetracyanonaptho-2,6-quinodimethane; a,a'-bis(dithieno[3,2-b2',3'-d]thiophene); 2,8-dialkyl, substituted dialkyl, diaryl or substituted diaryl anthradithiophene; 2,2'-bisbenzo[l,2-b:4,5-b']dithiophene. Where a liquid deposition technique of the OSC is desired, compounds from the above list and derivatives thereof are limited to those that are soluble in an appropriate solvent or mixture of appropriate solvents.

Further, in some preferred embodiments in accordance with the present invention, the OSC materials are polymers or copolymers that encompass one or more repeating units selected from thiophene-2,5-diyl, 3-substituted thiophene- 2,5-diyl, optionally substituted thieno[2,3-b]thiophene-2,5-diyl, optionally substituted thieno[3,2-b]thiophene-2,5-diyl, selenophene-2,5-diyl, or 3- substituted selenophene-2,5-diyl.

Further preferred p-type OSCs are copolymers comprising electron acceptor and electron donor units. Preferred copolymers of this preferred embodiment are for example copolymers comprising one or more benzo[l,2-b:4,5-b']dithiophene-2,5- diyl units that are preferably 4,8-disubstituted by one or more groups R as defined above, and further comprising one or more aryl or heteroaryl units selected from Group A and Group B, preferably comprising at least one unit of Group A and at least one unit of Group B, wherein Group A consists of aryl or heteroaryl groups having electron donor properties and Group B consists of aryl or heteroaryl groups having electron acceptor properties, and preferably

Group A consists of selenophene-2,5-diyl, thiophene-2,5-diyl, thieno[3,2- b]thiophene-2,5-diyl, thieno[2,3-b]thiophene-2,5-diyl, selenopheno[3,2- b]selenophene-2,5-diyl, selenopheno[2,3-b]selenophene-2,5-diyl, selenopheno[3,2-b]thiophene-2,5-diyl, selenopheno[2,3-b]thiophene-2,5-diyl, benzo[l,2-b:4,5-b']dithiophene-2,6-diyl, 2,2-dithiophene, 2,2-diselenophene, dithieno[3,2-b:2',3'-c/]silole-5,5-diyl, 4H-cyclopenta[2,l-b:3,4-b']dithiophene-2,6- diyl, 2,7-di-thien-2-yl-carbazole, 2,7-di-thien-2-yl-fluorene, indaceno[l,2-b:5,6- b']dithiophene-2,7-diyl, benzo[l",2":4,5;4",5":4',5']bis(silolo[3,2-b:3',2'- b']thiophene)-2,7-diyl, 2,7-di-thien-2-yl-indaceno[l,2-b:5,6-b']dithiophene, 2,7-di- thien-2-yl-benzo[l",2":4,5;4",5":4',5']bis(silolo[3,2-b:3',2'-b']thiophene)-2,7-diyl, and 2,7-di-thien-2-yl-phenanthro[l,10,9,8-c, /,e,/,g]carbazole, all of which are optionally substituted by one or more, preferably one or two groups R as defined above, and

Group B consists of benzo[2,l,3]thiadiazole-4,7-diyl, 5,6-dialkyl- benzo[2,l,3]thiadiazole-4,7-diyl, 5,6-dialkoxybenzo[2,l,3]thiadiazole-4,7-diyl, benzo[2,l,3]selenadiazole-4,7-diyl, 5,6-dialkoxy-benzo[2,l,3]selenadiazole-4,7- diyl, benzo[l,2,5]thiadiazole-4,7,diyl, benzo[l,2,5]selenadiazole-4,7,diyl, benzo[2,l,3]oxadiazole-4,7-diyl, 5,6-dialkoxybenzo[2,l,3]oxadiazole-4,7-diyl, 2H- benzotriazole-4,7-diyl, 2,3-dicyano-l,4-phenylene, 2,5-dicyano,l,4-phenylene, 2,3- difluro-l,4-phenylene, 2,5-difluoro-l,4-phenylene, 2,3,5, 6-tetrafluoro-l,4- phenylene, 3,4-difluorothiophene-2,5-diyl, thieno[3,4-b]pyrazine-2,5-diyl, quinoxaline-5,8-diyl, thieno[3,4-b]thiophene-4,6-diyl, thieno[3,4-b]thiophene-6,4- diyl, and 3,6- pyrrolo[3,4-c]pyrrole-l,4-dione, all of which are optionally substituted by one or more, preferably one or two groups R as defined above.

In other preferred embodiments of the present invention, the OSC materials are substituted oligoacenes such as pentacene, tetracene or anthracene, or heterocyclic derivatives thereof. Bis(trialkylsilylethynyl) oligoacenes or bis(trialkylsilylethynyl) heteroacenes, as disclosed for example in US 6,690,029 or WO 2005/055248 Al or US 7,385,221, are also useful.

Further preferred organic semiconducting materials are selected from the group consisting of small molecules or monomers of the tetra-heteroaryl indacenodithiophene-based structural unit as disclosed in WO 2016/015804 Al, and polymers or copolymers comprising one or more repeating units thereof, such as, for example, one of the following polymers (P-1) to (P-3):

Where appropriate and needed to adjust the rheological properties as described for example in WO 2005/055248 Al, some embodiments of the present invention employ OSC compositions that include one or more organic binders.

The binder, which is typically a polymer, may comprise either an insulating binder or a semiconducting binder, or mixtures thereof may be referred to herein as the organic binder, the polymeric binder, or simply the binder.

Preferred binders according to the present invention are materials of low permittivity, that is, those having a permittivity ε of 3.3 or less. The organic binder preferably has a permittivity ε of 3.0 or less, more preferably 2.9 or less. Preferably the organic binder has a permittivity ε of 1.7 or more. It is especially preferred that the permittivity of the binder is in the range from 2.0 to 2.9. Whilst not wishing to be bound by any particular theory it is believed that the use of binders with a permittivity ε of greater than 3.3, may lead to a reduction in the OSC layer mobility in an electronic device, for example an OFET. In addition, high permittivity binders could also result in increased current hysteresis of the device, which is undesirable.

Examples of suitable organic binders include polystyrene, or polymers or copolymers of styrene and a-methyl styrene; or copolymers including styrene, a- methylstyrene and butadiene may suitably be used. Further examples of suitable binders are disclosed for example in US 2007/0102696 Al.

In one type of preferred embodiment, the organic binder is one in which at least 95%, more preferably at least 98% and especially all of the atoms consist of hydrogen, fluorine and carbon atoms.

The binder is preferably capable of forming a film, more preferably a flexible film.

The binder can also be selected from crosslinkable binders such as acrylates, epoxies, vinylethers, and thiolenes, preferably having a sufficiently low permittivity, very preferably of 3.3 or less. The binder can also be mesogenic or liquid crystalline.

In another preferred embodiment the binder is a semiconducting binder, which contains conjugated bonds, especially conjugated double bonds and/or aromatic rings. Suitable and preferred binders are for example polytriarylamines as disclosed for example in US 6,630,566.

The proportions of binder to OSC is typically 20:1 to 1:20 by weight, preferably 10:1 to 1:10 more preferably 5:1 to 1:5, still more preferably 3:1 to 1:3 further preferably 2:1 to 1:2 and especially 1:1. Dilution of the compound of formula I in the binder has been found to have little or no detrimental effect on the charge mobility, in contrast to what would have been expected from the prior art.

The method according to the invention further comprises a step (b) of generating an intermediate layer between the electrode and the semiconducting layer, which step is performed subsequent to step (a) of depositing the semiconducting layer onto the electrode. As used herein, the term "intermediate layer" refers to a layer which is situated between the electrode and the semiconducting layer. In other words, the electrode surface and the semiconducting layer are in contact with said intermediate layer. Preferably, said contact is a direct physical contact. Expressed differently, it is preferred that the intermediate layer is directly adjacent to the electrode surface and the semiconducting layer. As a consequence, the electrode surface is covered by the intermediate layer which comprises the surface- modifying compound. The term "covered" as used herein means that at least 10%, or 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 95%, or 97%, or 99% of the electrode surface is covered by said intermediate layer. In cases where the organic electronic device prepared by the method according to the present invention comprises more than one electrode, for example one or more source electrodes and one or more drain electrodes, the electrode(s) to be covered by the intermediate layer can be freely selected depending, for example, on the electrode material used. For example, the intermediate layer may be situated between the one (or more) source electrode(s) and the semiconducting layer and/or may be situated between the one (or more) drain electrode(s) and the semiconducting layer. Preferably, the intermediate layer is situated between all of these electrodes and the semiconducting layer.

The intermediate layer according to the present invention efficiently modifies the surface of the electrode so that charge injection for electron and/or hole transport from the electrode to the semiconducting layer is improved as described above.

According to the method of the present invention, the surface-modifying compound is applied to the semiconducting layer, which has already been deposited onto the electrode. As mentioned before, according to methods known from the prior art an intermediate or surface-modification layer is deposited onto the electrode prior to depositing the semiconductor material on top. In other words, the electrode is directly treated with the surface-modifying compound. In contrast, according to the method of the present invention the semiconducting layer and ultimately the electrode are treated with the surface-modifying compound after deposition of the semiconductor material. Following the application of the semiconducting layer, the surface-modifying compound effectively permeates the semiconducting layer and subsequently diffuses to the electrode through the semiconducting layer, thereby generating the intermediate layer between the electrode and the semiconducting layer. In other words, the application of the surface-modifying compound onto said electrode is indirectly made via diffusion to the electrode through the thin semiconductor layer.

This "retrospective", diffusion-based treatment of the semiconductor electrode enables good charge injection but avoids creation of a low surface energy electrode surface, which results from directly treating the electrode surface with a surface-modifying compound and which makes subsequent film coating more difficult, as described above. Consequently, changes to the semiconductor's microstructure, crystal growth rate and semiconductor orientation being detrimental to the device performance and being observed with known methods, are eliminated or at least reduced by the method according to the present invention. This results in improved device performance and facilitates the production of low cost commercial organic based electronic devices.

As already mentioned, the term semiconducting layer refers to a permeable, continuous system of material that is semiconducting.

Preferably the thickness of the semiconducting layer being deposited onto the electrode prior to generating the intermediate layer using the methods as described above is < 200 nm. More preferably, the thickness of the semiconducting layer is in the range between 2 nm and 200 nm, even more preferably between 2 nm and 100 nm, still even more preferably between 2 nm and 50 nm, and most preferably 20 nm.

Without wishing to be bound by any theory, it is believed that if the thickness of the semiconducting layer is greater than 200 nm, permeation of the surface- modifying compound through the semiconducting layer to the electrode may not be effective or it would take too long for generating the intermediate layer between the electrode and the semiconducting layer, thereby enabling good charge injection for electron and/or hole transport and at the same time diminishing or eliminating the unwanted side-effects mentioned above.

The surface-modifying compound may be applied onto the semiconducting layer by vacuum or vapor deposition methods or by liquid coating methods. Exemplary deposition methods include physical vapor deposition (PVD), chemical vapor deposition (CVD), sublimation or liquid coating methods. Liquid coating methods are preferred. Particularly preferred are solvent-based liquid coating methods.

In a preferred embodiment of the present invention, the surface-modifying compound is applied to the semiconductor layer by liquid-coating using a formulation comprising the surface-modifying compound and at least one organic solvent. Optionally, following deposition, the solvent may be at least partially evaporated.

Preferred solvent-based liquid coating methods include, without limitation, dip coating, spin coating, ink jet printing, letter-press printing, screen printing, doctor blade coating, roller printing, reverse-roller printing, offset lithography printing, flexographic printing, gravure printing, web printing, spray coating, brush coating and pad printing. Suitable solvents for use in step (b) of the above process may be selected from the group consisting of alcohols, ethers, ketones, aromatic hydrocarbons, and any mixture of any of these. Suitable alcohols may for example be selected from the group consisting of methanol, ethanol, iso-propanol and n-propanol. Suitable ethers may have a linear or a cyclic structure and may for example be selected from the group consisting of diethylether, tetrahydrofuran (THF), butyl phenyl ether, methyl ethyl ether and 4-methylanisole. Suitable ketones may for example be selected from the group consisting of acetone, 2-heptanone and cyclohexanone. Suitable aromatic hydrocarbons may for example be selected from the group consisting of toluene, mesitylene, cyclohexylbenzene and halogenated aromatic hydrocarbons. Examples of such halogenated aromatic hydrocarbons are chlorobenzene, dichlorobenzene and trichlorobenzene as well as any mixture of any of these.

Preferably the surface-modifying compound is present in the formulation or solution in from 0.01 wt% to 10 wt%, preferably from 0.01 wt% to 5 wt%, and most preferably from 0.05 wt% to 2 wt%, with wt% being relative to the total weight of the formulation or solution.

As used herein, the term "surface-modifying compound" denotes a compound that is capable of migrating to the electrode through the semiconducting layer and suitable of forming a layer between said electrode and said semiconducting layer, i.e. the intermediate or surface-modification layer, in order to cover the electrode surface. Thereby, the contact resistance between the electrode and the semiconducting layer is reduced by altering the work function of the electrode, as described above.

Preferably the surface-modifying compound forms a self-assembled monolayer (SAM) between the electrode and the semiconducting layer. That means, the intermediate layer generated between the electrode and the semiconducting layer is preferably a self-assembled monolayer. As used herein, the term self- assembling monolayer refers to an organized layer of amphiphilic molecules, in which one end of the molecule, which is often referred to as the head group, shows a special affinity to a substrate, for example an electrode and/or the semiconductor material (depending on the manufacturing techniques). SAMs may be created by chemisorption of hydrophilic head groups on a substrate followed by a relatively slow two-dimensional organization of a hydrophobic residue, which is often referred to as the tail. Typically, the thickness of the self-assembled monolayer is within the range of 0.1 to 10 nm.

The surface-modifying compound used in the method according to the present invention comprises a compound of the formula HX-R, wherein X is Se, Te or S, and R is a hydrocarbyl group comprising 1 to 12 carbon atoms.

As used herein, the term "hydrocarbyl" refers to a functional group which is related to a hydrocarbon, i.e. an organic compound that consists entirely of hydrogen and carbon, from which at least one hydrogen atom has been removed.

Preferably, the hydrocarbyl functional group R of the present invention is selected from saturated, unsaturated and aromatic hydrocarbyl groups comprising 1 to 12 carbon atoms.

As used herein, the term "saturated hydrocarbyl group" refers to hydrocarbyl groups which are composed entirely of carbon-carbon single bonds and which are saturated with hydrogen. This includes acyclic saturated hydrocarbyls, which may be linear or branched (i.e. alkyls), and saturated hydrocarbyls containing at least one ring (i.e. cycloalkyls).

The term "unsaturated hydrocarbyl group" as used herein refers to hydrocarbyl groups which have one or more carbon-carbon double bonds (i.e. alkenyls) and/or one or more carbon-carbon triple bonds (i.e. alkynyls) and which may be linear or branched. The one or more carbon-carbon double or triple bonds can be internal or terminal.

The term "aromatic hydrocarbyl group" as used herein refers to hydrocarbyl groups which have at least one aromatic ring (i.e. aryls) including alkyl- alkenyl- or alkynylaryls and polycyclic aromatic hydrocarbyls.

In a preferred embodiment of the present invention, the hydrocarbyl group R is selected from the group consisting of:

Alkyl, wherein the alkyl group is linear, cyclic or branched and may comprise 1 to 12 carbon atoms, preferably methyl, ethyl, propyl (e.g. n-propyl iso-propyl), butyl (e.g. n-butyl, iso-butyl, sec-butyl, tert-buttyl), pentyl (e.g. n-pentyl, iso-pentyl, neo-pentyl), hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and cyclohexyl; alkenyl, alkynyl, wherein the alkenyl or alkynyl group is linear or branched and may comprise 2 to 12 carbon atoms, preferably ethenyl, propenyl, propadienyl, butenyl, butadienyl, pentenyl, pentadienyl, hexenyl, hexadienyl,heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, ethynyl, propynyl, butynyl, pentynyl, hexynyl; phenyl, benzyl, napthyl; alkylphenyl, wherein the alkyl group of the phenyl may comprise 1 to 6 carbon atoms, is linear or branched and preferably located at the phenyl in 2- or 4- position with respect to the HX-group, such as 2-methylphenyl, 3- methylphenyl or 4-methylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2,6- dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl, 2,3,4-trimethylphenyl, 2,4,5- trimethylphenyl, 2,4,6-trimethylphenyl, 2,3,5,6-tetramethylphenyl, 2,3,4,6- tetramethylphenyl or 2,3,4,5-tetramethylphenyl, 2,3,4,5, 6-pentamethylphenyl, n- butylphenyl, preferably 2-n-butylphenyl, 4-n-butylphenyl, t- butylphenyl, pentylphenyl, hexylphenyl, cyclohexylphenyl, and more preferably 4-methyl phenyl or 4-n- butylphenyl; and arylphenyl, preferably 4-phenylphenyl.

In a further preferred embodiment, R is a heteroaryl group comprising 5 to 12 atoms.

The term "heteroaryl group" as used herein refers to cyclic aromatic hydrocarbyl groups which have at least one aromatic ring, wherein one or more of the atoms in the aromatic ring is of an element other than carbon. Preferably, the heteroatom of the heteroaryl group is selected from Si, N, 0 and S. Further preferably, the heteroaryl group is a five- or six-membered ring, such as pyrrolyl, furyl, thienyl, pyridyl, pyrimidyl, pyranyl, or thiopyranyl.

Optionally, one or more hydrogen of the hydrocarbyl group R is substituted by a functional group including at least one heteroatom. In other words, the hydrocarbyl group R may be unsubstituted or substituted by one or more functional groups that each includes at least one heteroatom.

The at least one heteroatom of the functional group is preferably selected from the group consisting of 0, N, S, Se, P, F, CI and Br.

In a more preferred embodiment, the functional group substituting one or more hydrogen from R is an electron-withdrawing group or an electron-donating group. Preferred electron-withdrawing functional groups are -F, -CI, -Br, -N0₂, -CN, -NC, - SO3H, -SO3R', -SO2R', -SO2N H R', -COOH, -COR', -COOR', -CONHR' and CON(R')₂, wherein R' may be selected from methyl, ethyl, methyl wherein one or more hydrogen is substituted by fluorine, and ethyl wherein one or more hydrogen is substituted by fluorine. Preferably, R' is methyl or ethyl wherein one or more hydrogen is substituted by fluorine. Preferred electron-donating functional groups are -OH, -OR", -SR", -NH₂, -NH R", -N(R")₂, wherein R" may be selected from methyl or ethyl.

The functional groups that may be used as substituent at the hydrocarbyl group R can be selected according to their electron-withdrawing or electron-donating properties and as a function of their desired effect on the effective work function of the electrode. For exam ple, a hydrocarbyl group having one or more hydrogen substituted by an electron-withdrawing group may be used in a surface-modifying compound to increase the work function of an electrode. Or a hydrocarbyl group having one or more hydrogen substituted by an electron-donating group may be used in a surface-modifying compound to decrease the work function of an electrode (Boudinet et al., Organic Electronics (2010), 11, pp. 227-237).

I n yet another preferred embodiment, the surface-modifying compound has a molecular weight of < 500 g/mol, more preferably < 300 g/mol. Without wishing to be bound by any theory, it is believed that the permeability of said surface- modifying compound through said semiconducting layer is such that migration is too slow for a llowing commercially viable production in case the surface- modifying compound used has a molecular weight of greater than 500 g/mol.

I n still another preferred embodiment of the present invention, in the surface- modifying compound of the formula HX-R, X = S. The inclusion of a thiol group on the surface-modifying compound facilitates its diffusion through the permeable semiconducting layer and also improves monolayer formation. This is especially true for the case that the electrode material is selected from Au, Ag or Cu. Most preferably, the surface-modifying compound is pentafluorobenzene thiol for operation using p-type semiconducting materials or methyl benzene thiol for operation using n-type semiconducting materials.

In a further preferred embodiment, the surface-modifying compound comprises a combination of two or more of the above cited compounds. For example, two different surface-modifying compounds can be selected from the above cited compounds to create a two-component intermediate layer.

A preferred method for the preparation of organic electronic devices in accordance with the present invention comprises the steps of

(a) depositing an electrically conducting material on a substrate to form an electrode;

(b) depositing a semiconductor material onto the electrode to form a semiconducting layer;

(c) subsequently generating an intermediate layer between said electrode and the semiconducting layer by applying a surface-modifying compound as defined above onto said semiconducting layer;

(d) depositing a gate insulator material onto said semiconducting layer, thereby forming a gate insulator layer;

(e) depositing a gate electrode onto said gate insulator layer; and

(f) optionally depositing a passivation layer onto said gate electrode.

Optionally, in the method according to the invention the deposition of the semiconductor material in step b) may be followed by at least partial removal of any solvents present and/or by annealing the semiconductor material.

Optionally, the application of the surface-modifying compound in step c) may be followed by an annealing step. Optionally, annealing of the semiconductor material may be performed before and after the surface modifying compound has been added.

It has been found that the method of the present invention, wherein an intermediate or surface-modification layer that improves charge injection is generated by applying a surface-modifying compound to a semiconducting layer which has already been deposited onto an electrode, allows for simplified material- and cost-efficient production of organic electronic devices having improved device performance, because the surface energy of the electrode surface will be high upon deposition of the semiconducting layer. In other words, the present invention allows for efficient production of such electronic devices by eliminating the need for depositing the semiconducting layer onto an electrode whose surface has already been treated by deposition of the surface-modification layer. An electrode surface, which has been treated like this, has a low surface energy making subsequent film coating more difficult.

The present inventors have found that the present invention permits the preparation of organic electronic devices having good charge injection via a "retrospective", diffusion-based treatment of the device electrode, that is, without directly treating the electrode with a surface-modifying compound, for example, a compound that forms a self-assembled monolayer. First experiments have very surprisingly shown that the present method allows the production of organic electronic devices that exhibit a mobility and current equal or higher with better processing than under the same conditions compared to organic electronic devices, where the electrode has been directly treated with a surface-modifying compound.

Thus, in a further aspect, the present application also relates to an organic electronic device which is prepared by the method according to any one or more of the embodiments disclosed above. The organic electronic device comprises an electrode, a semiconducting layer and an intermediate layer between said electrode and said semiconducting layer. The intermediate layer comprises a compound of the formula HX-R, wherein X is Se, Te or S, and R is a hydrocarbyl group comprising 1 to 12 carbon atoms as defined above. Optionally, one or more hydrogen of R is substituted by a functional group including at least one heteroatom as defined above.

In a preferred embodiment of the present invention, the intermediate layer is a self-assembled monolayer as defined above.

The organic electronic device prepared by the method according to the present application may be selected from a large number of devices, as mentioned above. Preferably, said organic electronic devices are selected from the group consisting of organic field effect transistors (OFET), organic thin film transistors (OTFT), organic light emitting diodes (OLED), organic light emitting transistors (OLET), organic photovoltaic devices (OPV), organic photodetectors (OPD), organic solar cells, laser diodes, Schottky diodes, photoconductors and photodetectors.

The above-mentioned electronic devices are well known to the skilled person and will in the following be illustrated using organic field effect transistors (OFETs). An organic thin film transistor may comprise a gate electrode, an insulating (or gate insulator) layer, a source electrode, a drain electrode and an organic semiconducting channel connecting the source and drain electrodes, wherein at least one of the source and drain electrodes or all may be in contact with the intermediate layer in accordance with the present invention. Other features of the OFET are well known to those skilled in the art. OFETs where an organic semiconducting material is arranged as a thin film between a gate dielectric and a drain and a source electrode, are generally known and are described for example in US 5,892,244, US 5,998,804 and US 6,723,394. The gate, source and drain electrodes and the insulating layer and the semiconducting layer in the OFET device may be arranged in any sequence, provided that the source electrode and the drain electrode are separated from the gate electrode by the insulating layer, the gate electrode and the semiconductor layer both contact the insulating layer, and the source electrode and the drain electrode both contact the semiconducting layer.

Therefore, an OFET device prepared by the method according to the present invention comprises:

- a source electrode,

- a drain electrode,

- a gate electrode,

- an intermediate layer in accordance with the present invention,

- a semiconducting layer,

- one or more gate insulator layers, and

- optionally a substrate,

wherein the intermediate layer is situated between the semiconducting layer and at least one of said source and drain electrodes.

The OFET device according to the present invention can be a top gate device or a bottom gate device. Suitable structures of an OFET device are known to the skilled person and are described in the literature, for example in US 2007/0102696 Al.

For the present invention it is also possible that the device is a top contact device. For technical reasons it is generally accepted that top contact devices do not use an intermediate layer. The present process would aid in overcoming such technical problems and allow treatment of a top contact device by means of the present method. Figure 6a shows a schematic representation of a typical top gate OFET prepared according to the present invention, including source (S) and drain (D) electrodes (2) provided on a substrate (1), an intermediate layer, preferably a self-assembled monolayer (3), of a surface-modifying compound of the present invention provided on the S/D electrodes, a layer of semiconductor material (4) provided on the S/D electrodes and the intermediate (3), a layer of dielectric material (5) as gate insulator layer provided on the semiconducting layer (4), a gate electrode (6) provided on the gate insulator layer (5), and an optional passivation or protection layer (7) provided on the gate electrode (6) to shield it from further layers or devices that may be provided later or to protect it from environmental influence. The area between the source and drain electrodes (2), indicated by the double arrow, is the channel area.

Figure 6b shows a schematic representation of a typical bottom gate-bottom contact OFET prepared according to the present invention, including a gate electrode (6) provided on a substrate (1), a layer of dielectric material (5) (gate insulator layer) provided on the gate electrode (4), source (S) and drain (D) electrodes (2) provided on the gate insulator layer (6), an intermediate layer, preferably a self-assembled monolayer (3), of a surface-modifying compound of the present invention provided on the S/D electrodes, a layer of an organic semiconductor material (4) provided on the S/D electrodes and the intermediate layer (3), and an optional protection or passivation layer (7) provided on the organic semiconducting layer (4) to shield it from further layers or devices that may be later provided or protect it from environmental influences.

In an OFET device according to the present invention, the dielectric material for the gate insulator layer is preferably an organic material that is preferably solution coated so that ambient processing is allowed, but it could also be deposited by vacuum deposition techniques. The transistor device prepared by the method according to the present invention may also be a complementary organic thin film transistor (CTFT) which comprises both a layer of a p-type semiconductor material and a layer of an n-type semiconductor material.

In addition to organic thin film transistors the present method may also be applied to organic photovoltaic (OPV) devices (any type known from the literature, see e.g. Waldauf et al., Appl. Phys. Lett. 89, 233517 (2006)) as well as to organic light emitting devices (OLEDs).

A preferred organic photovoltaic device (OPV) which can be prepared according to the method of the present invention comprises:

- a low work function electrode, for example a metal, such as aluminum or gold, and a high work function electrode, for example indium tin oxide, frequently referred to as "ITO", one of which is transparent,

- a layer (also referred to as "active layer") comprising a hole transporting material and an electron transporting material selected from organic semiconducting materials, which is situated between the low work function electrode and the high work function electrode; the active layer can exist for example as a bilayer or two distinct layers or blend or mixture of p-type and n-type semiconductor, forming a bulk heterojunction (BHJ) (see for example Coakley, K. M. and McGehee, M. D. Chem. Mater. 2004, 16, 4533),

- an intermediate layer in accordance with the present invention,

- an optional coating, for example of LiF on the side of the low work function electrode facing the active layer and/or of TiOx on the side of the high work function electrode facing the active layer, to provide an ohmic contact for electrons and holes, respectively,

wherein the intermediate layer is located between said active layer and at least one of the electrodes, preferably the high work function electrode, in accordance with the present invention. Common OLEDs are realized using multilayer structures. An emission layer is generally sandwiched between one or more electron-transport and/or hole- transport layers. By applying an electric voltage electrons and holes as charge carriers move towards the emission layer where their recombination leads to the excitation and hence luminescence of the lumophor units contained in the emission layer. The selection, characterization as well as the processing of suitable monomeric, oligomeric and polymeric compounds or materials for the use in OLEDs is generally known by a person skilled in the art, see, e.g., Miller et a I, Synth. Metals, 2000, 111-112, 31-34, Alcala, J. Appl. Phys., 2000, 88, 7124-7128 and the literature cited therein.

The present invention may also prove useful for making CMOS (Complementary Metal Oxide Semiconductor) circuit devices where a separate injection layer is needed for different parts of the circuit, e.g. an n-type or p-type self-assembled monolayer on the same circuit.

The present method may also prove useful in helping to mitigate the effects of cross-contamination from the particular electrode treatments relating to n-type or p-type injection.

Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components. It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the features of the invention are still applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

Examples

The invention will now be described in more detail by reference to the following examples, which is illustrative only and does not limit the scope of the invention.

For all examples, the electrical characterization of the transistor devices was carried out in ambient air atmosphere using a computer-controlled Agilent 4155C Semiconductor Parameter Analyser. Charge carrier mobility in the saturation regime ^_sat) was calculated for the compound. Field-effect mobility was calculated in the saturation regime (Vd > (Vg-V0)) using equation (eq. 1): dl_A

s^a' (V - V₀ ) (eq. 1) dV g, v L where W is the channel width, L the channel length, C, the capacitance of insulating layer, V_g the gate voltage, Vo the turn-on voltage, and μ_δ3ΐ is the charge carrier mobility in the saturation regime. Turn-on voltage (Vo) was determined as the onset of source-drain current.

Example 1 - Top-gate bottom-contact TFT without intermediate layer

Top-gate bottom-contact thin film transistors (TFTs) were fabricated on glass substrates. Au was evaporated through a shadow mask to make the source electrode and the drain electrodes. Subsequently, a 7 mg/cm³ solution of an organic polymeric semiconductor compound with polycyclic thiophene-based monomer units in dichlorobenzene was spin-coated on top to yield an approximately 40 nm thick semiconductor layer. In the following an approximately 1 μιη thick dielectric layer was deposited by spin coating, on top of which an Au gate electrode was deposited by evaporation.

The resulting devices were determined to have a mobility of 0.2 cm²/V-s at -40 V. The respective transfer characteristics and the charge carrier mobility of the resulting devices are shown in Figure 1.

Example 2 - Top-gate bottom-contact TFT with intermediate layer produced by conventional method

Top-gate bottom-contact thin film transistors (TFTs) were fabricated on glass substrates. Au was evaporated through a shadow mask to make the source electrode and the drain electrodes. A self-assembled monolayer was then prepared thereon by submersion in a solution of a benzene-thiol derivative and allowed to dry. Subsequently, a 7 mg/cm³ solution of an organic polymeric semiconductor compound with polycyclic thiophene-based monomer units in dichlorobenzene was spin-coated on top to yield an approximately 40 nm thick semiconductor layer. In the following an approximately 1 μιη thick dielectric layer was deposited by spin coating, on top of which an Au gate electrode was deposited by evaporation. The resulting devices were determined to have a mobility of 0.38 cm²/V-s at -40 V. The respective transfer characteristics and the charge carrier mobility of the resulting devices are shown in Figure 2.

Example 3 - Top-gate bottom-contact TFT with intermediate layer produced in accordance with the present invention

Top-gate bottom-contact thin film transistors (TFTs) were fabricated on glass substrates. Au was evaporated through a shadow mask to make the source electrode and the drain electrodes. A 7 mg/cm³ solution of an organic polymeric semiconductor compound with polycyclic thiophene-based monomer units in dichlorobenzene was spin-coated on top to yield an approximately 40 nm thick semiconductor layer. Subsequently, a solution of a benzene-thiol derivative was applied to the semiconductor layer. In the following an approximately 1 μιη thick dielectric layer was deposited by spin coating, on top of which an Au gate electrode was deposited by evaporation.

The resulting devices were determined to have a mobility of 0.45 cm²/V-s at -40 V. The respective transfer characteristics and the charge carrier mobility of the resulting devices are shown in Figure 3.

Example 4 - Top-gate top-contact TFT without intermediate layer

Top-gate top-contact thin film transistors (TFTs) were fabricated analogously to the ones of Example 1.

The respective transfer characteristics and the charge carrier mobility of the resulting devices are shown in Figure 4. No working devices could be obtained.

Example 5 - Top-gate top-contact TFT with intermediate layer produced in accordance with the present invention

Top-gate top-contact thin film transistors (TFTs) were fabricated analogously to the ones of Example 3. The resulting devices were determined to have a mobility of 0.1 cm²/V-s at -40 V. The respective transfer characteristics and the charge carrier mobility of the resulting devices are shown in Figure 5.

Generally stated, the present examples show that the method of the present application yields electronic devices that are characterized by excellent charge carrier mobility. In fact, the results obtained for a device prepared in accordance with the present method, i.e. wherein the self-assembled monolayer is produced by applying the present "retrospective" method, were found superior to those for a device prepared by using the conventional method, i.e. wherein the self- assembled monolayer is prepared by immersion of the substrate with the source and drain electrodes in a solution of a suitable compound, for example a thiol.

Claims

1. A method for preparing an organic electronic device, the method comprising

(b) subsequently generating an intermediate layer between said electrode and the semiconducting layer of step (a) by applying a surface- modifying compound onto said semiconducting layer, wherein the surface-modifying compound comprises a compound of the formula HX-R, wherein X is Se, Te or S, and R is a hydrocarbyl group comprising 1 to 12 carbon atoms, wherein optionally one or more hydrogen is substituted by a functional group including at least one heteroatom.

2. The method according to claim 1, wherein the thickness of the semiconducting layer deposited in step (a) is < 200 nm.

3. The method according to any one or more of the preceding claims, wherein R is selected from saturated, unsaturated and aromatic hydrocarbyl groups.

4. The method according to any one or more of the preceding claims, wherein the at least one heteroatom is selected from the group consisting of O, N, S, Se, P, F, CI and Br.

5. The method according to any one or more of the preceding claims, wherein the surface-modifying compound has a molecular weight of < 500 g/mol.

6. The method according to any one or more of the preceding claims, wherein in the surface-modifying compound X = S.

7. The method according to any one or more of the preceding claims, wherein the surface-modifying compound is pentafluorobenzene thiol or methyl benzene thiol.

8. The method according to any one or more of the preceding claims, wherein the surface-modifying compound applied in step (b) forms a self-assembled monolayer.

9. The method according to any one or more of the preceding claims, wherein the electrode comprises at least one material selected from the group consisting of Au, Ag, Cu, Al, Ni, Pd, Pt, Ti, Ca, Mo, Sc, and any blend thereof.

10. The method according to any one or more of the preceding claims, wherein the surface-modifying compound is applied to the semiconductor layer by liquid-coating using a formulation comprising said surface-modifying compound and at least one organic solvent.

11. The method according to claim 8, wherein the at least one organic solvent is selected from the group consisting of alcohols, ethers, ketones, aromatic hydrocarbons, and any mixture of any of these.

12. An organic electronic device prepared by the method according to any one or more of claims 1 to 10, the device comprising an electrode, a semiconducting layer and an intermediate layer between said electrode and said semiconducting layer,

wherein the intermediate layer comprises a compound of the formula HX-R, wherein X is Se, Te or S, and R is a hydrocarbyl group comprising 1 to 12 carbon atoms, wherein optionally one or more hydrogen is substituted by a functional group including at least one heteroatom.

13. The organic electronic device according claim 12, wherein the intermediate layer is a self-assembled monolayer.

14. The organic electronic device according to claim 12 or claim 13, wherein the organic electronic device is selected from the group consisting of organic field effect transistors (OFET), thin film transistors (TFT), integrated circuits (IC), logic circuits, capacitors, radio frequency identification (RFID) tags, devices or components, organic light emitting diodes (OLED), organic light emitting transistors (OLET), flat panel displays, backlights of displays, organic photovoltaic devices (OPV), organic solar cells (OSC), photodiodes, laser diodes, photoconductors, organic photodetectors (OPD), electrophotographic devices, electrophotographic recording devices, organic memory devices, sensor devices, charge injection layers, charge transport layers or interlayers in polymer light emitting diodes (PLEDs), Schottky diodes, planarising layers, antistatic films, polymer electrolyte membranes (PEM), conducting substrates, conducting patterns, electrode materials in batteries, alignment layers, biosensors, biochips, security markings, security devices, and components or devices for detecting and discriminating DNA sequences.

15. The organic electronic device according to any one or more of claims 12 to 14, wherein the device is a top gate Organic Field Effect Transistor or a bottom gate Organic Field Effect Transistor.