WO2010063609A2

WO2010063609A2 - Hole injection material

Info

Publication number: WO2010063609A2
Application number: PCT/EP2009/065687
Authority: WO
Inventors: Beat Schmidhalter; Peter Nesvadba; Thomas Schäfer
Original assignee: Basf Se
Priority date: 2008-12-03
Filing date: 2009-11-24
Publication date: 2010-06-10
Also published as: WO2010063609A3

Abstract

The present invention relates to an electronic device, which comprises a compound of the formula (I), wherein R¹ and R² independently of one another are C₁-C₁₂alkyl, C₁-C₁₂alkyl, which is interrupted by one, or more oxygen atoms, C₃-C₈cycloalkyl which is unsubstituted or substituted by C₁-C₄alkyl, unsubstituted C₆-C₁₂aryl, or C₃-C₇heteroaryl, or benzyl, or C₆-C₁₂aryl, or C₃-C₇heteroaryl, or benzyl which is substituted by F, Cl, Br, C₁-C₆alkyl, C₁-C₆alkoxy or di(C₁-C₆alkylamino). The compound of the formula (I) is a n-type organic material, which is an intrinsically good semiconducting material, resulting in a high device stability and reliability.

Description

Hole Injection Material

The present invention relates to an electronic device, which comprises a compound of the formula I. The compound of the formula I is a n-type organic material, which is an intrinsically good semiconducting material, resulting in a high device stability and reliability.

US5,281 ,730 discloses compounds of the formula

, in which R^1' and R^2' independently of one another are Ci-C₆alkyl, C₃-C₈cycloalkyl which is unsubstituted or substituted by CrC₄alkyl, unsubstituted phenyl or benzyl, or phenyl or benzyl which is substituted by F, Cl, Br, C_rC₆alkyl, C_rC₆alkoxy or di(C_rC₆alkylamino).

US5464697 relates to a carrier material, which contains a layer of at least one compound of

the formula

on at least one surface.

The compounds of US5464697 form firmly adhering layers on the carrier materials. Owing to its electrical conductivities, the coated carrier material is outstandingly suitable for shielding from electrical and/or magnetic fields. US5464697 furthermore relates to the use of the coated material as an antistatic packaging material.

In recent years, an organic light emitting device comprising an anode (1 ), a hole injecting layer (2), a hole transporting layer (3), a light emitting layer (4), an electron transporting layer (5), an electron injecting layer (6) and a cathode, or other organic light emitting devices having a more complex structure comprising additional layers are used.

Studies on doping various materials for improving the conductivity of the organic material for a hole transporting layer have been conducted. The following documents provide background: For doping of electron donating matrix materials generally used as hole transporting layers 2,3,5,6-tetrafluorcyano-1 ,4-benzochinodimethane (F₄TCNQ) is well reported and described (see, for example, M. Pfeiffer et al. Appl. Phys. Lett. 73 (22), 3202- 3204 (1998) or J. Blochwitz et al. Appl.Phys.Lett., 73(6), 729-731 (1998)). The conductivities of those molecular materials are typically in the range of 1 • 10^"5 S/cm at a doping ratio of 4 wt%. Such compounds are too volatile and as matter of these production tolerances can not be met for manufacturing of OLED devices.

DE10357044 and EP1713136 describe mesomeric compounds of chinone based derivatives, which are less volatile than F₄TCNQ.

US7365360 discloses an electronic device, wherein the device is no longer using a molecular dopant, which includes a first electrode including a conductive layer and an n-type organic compound layer disposed on the conductive layer, a second electrode to inject or extract electron, a p-type organic compound layer disposed between the n-type organic compound layer and the second electrode. The p-type organic compound layer forms an np junction between the n-type organic compound layer and the p-type organic compound layer. The n-type organic compound layer can be formed by 2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane. The principle underlying US7365360 is capable of lowering the energy barriers for hole injection or hole extraction and the electronic devices can use various materials as electrodes, therefore simplifying a process and improving efficiency.

In the present invention it will now be proposed to use as an n-type organic material, a compound of formula I, which is an intrinsically good semiconducting material, which overcomes the drawbacks of the F₄TCNQ, resulting in a significantly higher device stability and reliability. Two key effects can be achieved, similar to the basic principle of molecular doping:

The ohmic resistance of the transport layers is reduced, so that the transport layers are nearly field-free under operation. This allows also to vary the thickness of the transport layers, which is advantageous both for rough substrates and for optical optimization being decoupled from the electrical properties.

The doped layers lead to very narrow space charge regions at the contacts thin enough to allow the carriers to tunnel through. Thus, allowing a nearly arbitrary choice of contact materials.

Overall, this can lead to a very cost-effective manufacturing process, since no longer a doping or co-evaporation step is required.

Further, the material, which is capable of fine tuning the hole injection, so that a proper charge balance can be established, should afford a significantly higher device stability. Accordingly, the present invention relates to an electronic device, which comprises a

compound of the formula

(I), wherein

R¹ and R² independently of one another are d-C^alkyl, d-C^alkyl, which is interrupted by one, or more oxygen atoms, C₃-C₈cycloalkyl which is unsubstituted or substituted by d-

C₄alkyl, unsubstituted C₆-Ci₂aryl, or C₃-C₇heteroaryl, or benzyl, or C₆-Ci₂aryl, or C₃-

C₇heteroaryl, or benzyl which is substituted by F, Cl, Br, d-C₆alkyl, d-C₆alkoxy or di(d-

C₆alkylamino).

The electronic device is in particular an electroluminescent device, a solar cell, or an organic transistor. It should be noted that the electronic device of the present invention is not limited to an electroluminescent device, a solar cell, or an organic transistor, but may be any electronic devices that use the compounds of formula I, preferably in a n-type organic compound layer, or as a electron accepting dopant of the p-type doped hole injection layer.

R¹ and R² independently of one another are CrC^alkyl, Ci-Ci₂alkyl, which is interrupted by one, or more oxygen atoms, C₃-C₈cycloalkyl which is unsubstituted or substituted by d- dalkyl, unsubstituted phenyl or benzyl, or phenyl or benzyl which is substituted by F, Cl, Br, Ci-C₆alkyl, d-C₆alkoxy or di(d-C₆alkylamino). R¹ and R² can be the same, or different, but are preferably the same. R¹ and R² are preferably a Ci-d₂alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. -butyl, isobutyl, tert. -butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2- dimethylpropyl, 1 ,1 ,3,3-tetramethylpentyl, n-hexyl, 1-methylhexyl, 1 ,1 ,3,3,5,5- hexamethylhexyl, n-heptyl, isoheptyl, 1 ,1 ,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl, 1 ,1 ,3,3-tetramethylbutyl and 2-ethylhexyl, n-nonyl, decyl, undecyl, and dodecyl. More preferred R¹ and R² are a d-C₆alkyl group. Examples of compounds of formula I are shown below:

In an exemplary embodiment of the present invention the electronic device, especially the organic electroluminescent device has a hole injection layer. The hole injection layer comprises compounds having the structure shown in formula I.

A first electrode such as an anode electrode is formed on the substrate, and can be a transparent electrode, metal electrode, or combinations thereof, comprising indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), Li, Mg, Ca, Al, Ag, In, Au, Ni, Pt, or alloys thereof, formed by a method such as sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition. An electroluminescent layer is formed on the anode electrode, wherein the electroluminescent layer at least comprises a p-doped hole injection layer and a light emitting layer, and can further comprise a hole transport layer, an electron transport layer, and an electron injection layer. The electroluminescent layer is an organic semiconductor material such as a small molecule material, polymer, or organometallic complex, and can be formed by thermal vacuum evaporation, spin coating, dip coating, roll-coating, injection-fill, embossing, stamping, physical vapor deposition, or chemical vapor deposition. The light emitting layer can comprise a light-emitting material and an electroluminescent dopant doped into the light- emitting material and can perform energy transfer or carrier trapping under electron-hole recombination in the emitting layer. The light-emitting material can be fluorescent or phosphorescent. Particularly, the p-doped hole injection layer includes a hole injection material, such as an aromatic amine serving as a host, that is doped with an electron accepting dopant. The hole injection layer contains at least one hole-transporting material, such as an aromatic tertiary amine, where the aromatic teriary amine is understood to be a compound containing at least one trivalent nitrogen atom that is bonded only to carbon atoms, at least one of which is a member of an aromatic ring. In one form the aromatic tertiary amine can be an arylamine, such as a monoarylamine, a diarylamine, a triarylamine , or a polymeric arylamine. A preferred class of aromatic tertiary amines is described in US20060251922. The dopants can include compounds having the structure of formula I. The doped concentration is preferably in the range of 0.01-20 vol.%. The compound having a formula I serves as a electron accepting dopant of the p-type doped hole injection layer. A second electrode serving as a cathode is formed on the electroluminescent layers (such as the electron injection layer). The second electrode (cathode) is capable of injecting electrons into the electroluminescent layers (via the electron injection layer), for example, a low work function material such as Ca, Ag, Mg, Al, Li, or alloys thereof, formed by sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition. Commonly used cathodes include a Mg:Ag alloy as decribed in US4,88,5221 , or a LiF/AI bilayer as described in US5,677,572.

In another exemplary embodiment of the present invention the electronic device, especially the organic electroluminescent device comprises an anode, (electroluminescent) layers formed on the anode, and a cathode formed on the (electroluminescent) layers. The (electroluminescent) layers comprise - a hole injection layer formed by an electron acceptor (n-type material) having the structure of formula I directly on the anode. The hole-injecting layer (HIL) is forming a np junction with the succeeding hole transporting material as illustrated in US7365360. The thickness of the HIL can be in the range from 1 nm, especially 5 nm to 200 nm, preferably in the range of from 10 nm to 150 nm.

Organic Luminescence Device

Organic luminescence devices include an anode, a cathode, and a p-type organic compound layer disposed between the anode and the cathode. The p-type organic compound layer includes a hole injection layer, a hole transporting layer, or an emitting layer. Organic luminescence devices further include at least one organic compound layer disposed between the p-type organic compound layer and the cathode. When the organic luminescence device includes a plurality of the organic compound layers, the organic compound layers may be formed of the same material or different materials.

An organic luminescence device includes a substrate, an anode disposed on the substrate, a p-type hole injection layer (HIL) disposed on the anode and to receive holes from the anode, a hole transporting layer (HTL) disposed on the hole injection layer and to transport the holes to an emitting layer (EML), the emitting layer disposed on the hole transporting layer and to emit light by using the electrons and holes, and an electron transporting layer (ETL) disposed on the emitting layer and to transport the electrons from a cathode to the emitting layer, and the cathode disposed on the electron transporting layer. The hole transporting layer, the emitting layer, or the electron transporting layer may be formed of the same organic compound or different organic compounds.

According to another exemplary embodiment of the present invention, an organic luminescence device may include a substrate, an anode disposed on the substrate, a p-type hole transporting layer disposed on the anode, an emitting layer disposed on the hole transporting layer, an electron transporting layer disposed on the emitting layer, and a cathode disposed on the electron transporting layer. The emitting layer or the electron transporting layer may be formed of the same organic compound or different organic compounds.

According to further exemplary embodiment of the present invention, an organic luminescence device may include a substrate, an anode disposed on the substrate, a p-type emitting layer disposed on the anode, an electron transporting layer disposed on the emitting layer, and a cathode disposed on the electron transporting layer. The electron transporting layer may be formed of organic compound.

The anode may include a conductive layer and an n-type organic compound layer. The conductive layer is formed of metal, metal oxide, or a conductive polymer. The conductive polymer may further include an electrically conductive polymer. An np junction is formed between the n-type organic compound layer of the anode and the p-type hole injection layer.

An organic luminescence device according to another exemplary embodiment of the present invention includes an anode having a conductive layer and an n-type organic compound layer, a p-type hole injection layer (HIL), a hole transporting layer (HTL), an emitting layer (EML), an electron transporting layer (ETL), and a cathode.

Because the n-type organic compound layer of the anode lowers the energy barrier for injecting holes from the anode to the p-type hole injection layer, the p-type hole transporting layer or the p-type emitting layer, the conductive layer of the anode can be formed of various conductive materials. The conductive layer, for example, can be formed of the same materials to the cathode. When the anode is formed of the same material to the cathode, such as, the conductive material having low work function, a stacked organic luminescence device can be manufactured.

Hereinafter, each layer of the organic luminescence device according to an exemplary embodiment of the present invention is illustrated. Each layer can be formed of a single compound or a combination of two or more compounds.

Anode

The anode includes a conducive layer and an n-type organic compound layer. The conductive layer includes metal, metal oxide or a conductive polymer. The conductive polymer may include an electrically conductive polymer.

Because the n-type organic compound layer lowers the energy barrier for injecting holes to the p-type organic compound layer, the conductive layer can be formed of various conductive materials. As exemplary conductive material, there are carbon, aluminum, vanadium, chromium, copper, zinc, silver, gold, or alloy of the forgoing materials; zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide, and similar metal oxide; or a combination of oxide and metal, such as ZnO:AI or SnO₂:Sb. A top emission type organic luminescence device may use both a transparent material and a non-transparent material having high light reflectance as the conductive layer. A bottom emission type organic luminescence device uses a transparent material or a non-transparent material having a thin thickness as the conductive layer.

The n-type organic compound layer is disposed between the conductive layer and the p-type organic compound layer, and injects holes into the p-type organic compound layer under a low electric field.

The n-type organic compound layer, for example, has the LUMO energy of about 4 to 7 eV and the electron mobility of about 10^"8 cm²Λ/s to 1 cm²Λ/s, specifically about 10^"6 cm²Λ/s to 10^"2 cm²Λ/s. When the electron mobility is less than about 10^"8 cm²Λ/s, it is not easy to inject holes from the n-type organic compound layer into the p-type organic compound layer.

The n-type organic compound layer is formed by a vacuum deposition or solution process. The n-type organic compound layer includes a compound of formula I. Besides a compound of formula I the n-type organic compound layer may comprise 2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane (F4TCNQ), fluoro-substituted 3,4,9, 10-perylenetetracarboxylic dianhydride (PTCDA), cyano-substituted PTCDA, naphthalene-tetracaboxylic-dianhydride (NTCDA), fluoro-substituted NTCDA, cyano-substituted NTCDA, or hexanitrile hexaazatriphenylene (HAT).

Hole Injection Layer (HIL) or Hole Transporting Layer (HTL) Either the hole injection layer or the hole transporting layer can be formed of a p-type organic compound layer disposed between the anode and the cathode. Because the p-type hole injection layer or the p-type hole transporting layer and the n-type organic compound layer of the anode form an np junction, the holes formed at the np junction are transported to the emitting layer through the p-type hole injection layer or the p-type hole transporting layer.

Emitting Layer (EML)

Because a hole transporting and an electron transporting are occurred at the same time in the emitting layer, the emitting layer has both p-type semiconductor property and n-type semiconductor property. The emitting layer has an n-type emitting layer in which the electron transporting is faster than the hole transporting, or a p-type emitting layer in which the hole transporting is faster than the electron transporting.

Because the electrons transporting is faster than the holes transporting in the n-type emitting layer, the light is emitted at the interface between the hole transporting layer and the emitting layer. The n-type emitting layer includes, but not limited to, aluminum tris(δ-hydroxyquinoline) (Alqβ); 8-hydroxy-quinoline berillyum (BAIq); benzoxazole compound, benzothiazole compound, or benzimidazol compound; polyfluorene compound; or silacyclopentadiene (silole).

In the p-type emitting layer, the holes transport faster than electrons do, so that the light is emitted at the interface between the electron transporting layer and the emitting layer.

Therefore, it would be better that HOMO energy of the electron transporting layer is lower than the HOMO energy of the emitting layer in order to have high luminescence efficiency.

The organic luminescence device having the p-type emitting layer may have the np junction between the n-type organic compound layer and the p-type emitting layer without forming the hole injection layer and the hole transporting layer. The p-type emitting layer includes, but is not limited to, a carbazole compound, an anthracene compound, a poly(phenylene vinylenes) (PPV), a spiro compound, or bis-, or tris-cyclometalated iridium complexes.

Electron Transporting Layer (ETL)

The electron transporting layer has a high electron mobility to easily receive and transport electrons from/to the cathode and the emitting layer. The electron transporting layer includes, but not limited to, aluminum tris(δ-hydroxyquinoline) (AIq₃), organic compound having AIq₃ structure, flavone hydroxide-metal complex, or silacyclopentadiene (silole). The electron transporting layer may comprise a compound of the formula

(Vl), wherein

R³ is C₆-Ci₈aryl; C₆-Ci₈aryl which is substituted by CrCi₈alkyl, Ci-Ci8perfluoroalkyl, -N(C₆- Ci₈aryl)₂, or d-Ci₈alkoxy; Ci-Ci₈alkyl; or Ci-Ci₈alkyl which is interrupted by -O-; X is N, CH, or CR⁷,

R⁴, R⁵, R⁶ and R⁷ independently of one another are hydrogen, cyano, CrC₂₅alkyl, d- C₂5alkoxy, triphenylsilyl, C₆-C₂₄aryl, which may optionally be substituted, or C₂-C₂6heteroaryl, which may optionally be substituted, and

Ar is benzene, naphthalene, biphenyl, anthracene, or a group derived from an aromatic heterocycle or an aromatic ring; or anthracene based electron transporting materials, which

are described, for example, in US20040018383 (

), or WO03060956 (

). Among the compounds of formula Vl compounds of formula

(Via) are more preferred, wherein R³ is C₆-Ci₈aryl; C₆-Ci₈aryl which is substituted by Ci-Ci₈alkyl, Ci-Ci8perfluoroalkyl, -N(C₆- Ci₈aryl)₂, or d-Ci₈alkoxy; Ci-Ci₈alkyl; or Ci-Ci₈alkyl which is interrupted by -O-; R⁴ and R⁵ independently of one another are hydrogen, cyano, CrC₂₅alkyl, CrC₂₅alkoxy, triphenylsilyl, C₆-C₂₄aryl, which may optionally be substituted, or C₂-C₂6heteroaryl, which may optionally be substituted. An example of a compound of formula Vl is

. The compounds of formula Vl are new and form a further aspect of the present invention. The compounds of formula Vl are preferably used as electron transport material.

Ci-C₂5alkyl (Ci-Ci₈alkyl) is typically linear or branched, where possible. Examples are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. -butyl, isobutyl, tert. -butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, 1 ,1 ,3,3-tetramethylpentyl, n-hexyl, 1-methylhexyl, 1 ,1 ,3,3,5,5- hexamethylhexyl, n-heptyl, isoheptyl, 1 ,1 ,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl, 1 ,1 ,3,3-tetramethylbutyl and 2-ethylhexyl, n-nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, eicosyl, heneicosyl, docosyl, tetracosyl or pentacosyl. Ci-C₈alkyl is typically methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. -butyl, isobutyl, tert. -butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethyl-propyl, n-hexyl, n- heptyl, n-octyl, 1 ,1 ,3,3-tetramethylbutyl and 2-ethylhexyl. Ci-C₄alkyl is typically methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. -butyl, isobutyl, tert. -butyl.

Ci-Ci₂alkyl interrupted by one or more oxygen atoms is, for example, (CH₂CH₂O)i_-6-R^x, where R^x is H. Ci-C₂5alkoxy (Ci-Ci₈alkoxy) groups are straight-chain or branched alkoxy groups, e.g. methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, amyloxy, isoamyloxy or tert-amyloxy, heptyloxy, octyloxy, isooctyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, tetradecyloxy, pentadecyloxy, hexadecyloxy, heptadecyloxy and octadecyloxy. Examples of Ci-C₈alkoxy are methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, isobutoxy, tert.-butoxy, n-pentyloxy, 2-pentyloxy, 3-pentyloxy, 2,2-dimethylpropoxy, n- hexyloxy, n-heptyloxy, n-octyloxy, 1 ,1 ,3,3-tetramethylbutoxy and 2-ethylhexyloxy, preferably Ci-C₄alkoxy such as typically methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, isobutoxy, tert.-butoxy. The term "alkylthio group" means the same groups as the alkoxy groups, except that the oxygen atom of the ether linkage is replaced by a sulfur atom. d-Ciβperfluoroalkyl, especially Ci-C₄perfluoroalkyl, is a branched or unbranched radical such as for example -CF₃, -CF₂CF₃, -CF₂CF₂CF₃, -CF(CF₃)₂, -(CF₂)₃CF₃, and -C(CF₃)₃. The terms "haloalkyl, haloalkenyl and haloalkynyl" mean groups given by partially or wholly substituting the above-mentioned alkyl group, alkenyl group and alkynyl group with halogen, such as trifluoromethyl etc.

Aryl is usually C₆-C₃₀aryl, preferably C₆-C₂₄aryl, or C₆-Ci₈aryl, which optionally can be substituted, such as, for example, phenyl, 4-methylphenyl, 4-methoxyphenyl, naphthyl, especially 1 -naphthyl, or 2-naphthyl, biphenylyl, terphenylyl, pyrenyl, 2- or 9-fluorenyl, phenanthryl, anthryl, tetracyl, pentacyl, hexacyl, or quaderphenylyl, which may be unsubstituted or substituted.

Heteroaryl is typically C_2-C₂₆heteroaryl, i.e. a ring with five to seven ring atoms or a condensed ring system, wherein nitrogen, oxygen or sulfur are the possible hetero atoms, and is typically an unsaturated heterocyclic group with five to 30 atoms having at least six conjugated π-electrons such as thienyl, benzo[b]thienyl, dibenzo[b,d]thienyl, thianthrenyl, furyl, furfuryl, 2H-pyranyl, benzofuranyl, isobenzofuranyl, dibenzofuranyl, phenoxythienyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, bipyridyl, triazinyl, pyrimidinyl, pyrazinyl, pyridazinyl, indolizinyl, isoindolyl, indolyl, indazolyl, purinyl, quinolizinyl, chinolyl, isochinolyl, phthalazinyl, naphthyridinyl, chinoxalinyl, chinazolinyl, cinnolinyl, pteridinyl, carbazolyl, carbolinyl, benzotriazolyl, benzoxazolyl, phenanthridinyl, acridinyl, pyrimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl, phenothiazinyl, isoxazolyl, furazanyl or phenoxazinyl, which can be unsubstituted or substituted.

Possible substituents of the above-mentioned groups are Ci-C₈alkyl, d-C₈alkoxy, d- C₈alkylthio, halo-Ci-C₈alkyl, a cyano group, or a silyl group.

Cathode The cathode has low work function in order to easily inject electrons into the p-type organic compound layer such as the hole transporting layer. The cathode includes, but is not limited to, metal, such as, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, and lead or alloy thereof or multiple structured materials such as LiF/AI or UO₂/AI. The cathode can be formed of the same material to the conductive layer of the anode. Alternatively, either the cathode or the conductive layer of the anode includes a transparent material.

In a preferred embodiment of the present invention, the organic luminescence device includes a substrate(glass), 2,5-bis-methylthio-7,7',8,8'-tetracyanoquinodimethane (2,5- DMeS-TCNQ) as hole injection layer, 4,4'-bis[N-1-naphthyl)-N-phenylamino]-biphenyl (α- NPD) as hole transport layer, TBADN 30 nm as blue emitter, 45 nm of tris(8- quinolate)aluminium (AIq₃) as electron transport layer, 1 nm LiF capped with 100 nm of

aluminium as top electrode. Instead Of AIq₃

can be used as electron transport material.

Organic Solar Cell

Organic solar cell includes an anode, a cathode, and an organic thin film disposed between the anode and the cathode. The organic thin film includes a plurality of layers in order to improve the effectiveness and stability of the organic solar cell.

An organic solar cell includes a substrate, an anode having a conductive layer and a n-type organic compound layer disposed on the substrate, an electron donor layer disposed on the n-type organic compound layer, an electron acceptor layer disposed on the electron donor layer, and a cathode disposed on the electron acceptor layer. In response to a photon from an external light, electrons and holes are generated between the electron donor layer and the electron acceptor layer. The generated holes are transported to the anode through the electron donor layer. The electron donor layer is formed of a p-type organic compound. The organic compound can be a combination of two or more compounds. The organic solar cell according to another exemplary embodiment of the present invention may further include additional organic thin films or omit any organic thin film to simplify the processing steps. The organic solar cell may further employ an organic compound having multiple functions to reduce the number of the organic thin films.

The organic solar cell according to an exemplary embodiment of the present invention, however, includes the anode, having both the conductive layer and the n-type organic compound layer, to extract holes. An np junction is formed between the n-type organic compound layer and the electron donor layer, so that holes are easily extracted. Therefore, the conductive layer can be formed of the materials having various Fermi energies, and the cathode and the anode can be formed of the same materials.

The conductive layer and cathode of the organic solar cell can be formed of the same materials for the conductive layer and cathode of the organic luminescence device. The same materials for the n-type organic compound layer of the organic luminescence device can form the n-type organic compound layer of the organic solar cell. The electron acceptor layer can be formed of the materials for the electron transporting layer or n-type emitting layer of the organic luminescence device or a fullerene compound. The electron donor layer can be formed of the materials for the p-type hole transporting layer or p-type emitting layer of the organic luminescence device, or a thiophene compound.

In a preferred embodiment of the present invention, the organic solar cell comprises: an anode to extract holes including a conductive layer and an n-type organic compound layer in contact with the conductive layer; a cathode to extract electrons; and an electron donor layer disposed between the n-type organic compound layer of the anode and the cathode, the electron donor layer including a p-type organic compound layer and forming an np junction between the n-type organic compound layer of the anode and the p-type organic compound layer, wherein the n-type organic compound layer comprises the compound of formula I.

Organic Transistor

An organic transistor according to an exemplary embodiment of the present invention includes a substrate, a source electrode, a drain electrode, a gate, an insulating layer disposed on the gate and the substrate, a p-type organic compound layer disposed on the insulating layer and forming holes, and an n-type organic compound layer disposed between the source electrode and/or drain electrode and the p-type organic compound layer. Because the np junction is formed between the n-type organic compound layer and the p-type organic compound layer, the holes are easily transported between the source electrode and the drain electrode. The n-type organic compound layer can form a portion of the source electrode or the drain electrode, according to another exemplary embodiment of the present invention. In this case, the materials having various Fermi energies can form the source electrode or the drain electrode.

The n-type organic compound layer can be formed of the same materials for the n-type organic compound layer of the organic luminescence device, according to an exemplary embodiment of the present invention. The gate can be formed of the same materials for the anode or cathode of the organic luminescence device. The source electrode or the drain electrode can be formed of the same materials for the anode of the organic luminescence device. The p-type organic compound layer includes, but not limited to, a pentacene compound, an anthradithiophene compound, a benzodithiophene compound, thiophene oligomers, polythiophenes, mixed-subunit thiophene oligomers, oxy-functionalized thiophene oligomers, diketopyrroloypyrrole-thiophene oligomers, or polymers. The insulating layer can be formed of silicon oxide, or silicon nitride; or a polymer, such as, polyimide, poly(2- vinylpyridine), poly(4-vinylphenol), polystyrene, fluoropolymer (such as, for example, Cytop™ fluoropolymers which are available from Asahi Glass), or poly(methylmethacrylate).

In a preferred embodiment of the present invention the organic transistor, comprises a substrate, a source electrode, a drain electrode, a gate, an insulating layer disposed on the gate and the substrate, a p-type organic compound layer disposed on the insulating layer and forming holes, and an n-type organic compound layer disposed between the source electrode and/or drain electrode and the p-type organic compound layer, wherein the n-type organic compound layer comprises the compound of formula I.

In the compounds of the formula I used according to the present invention R¹ and R² independently of one another are d-C^alkyl, d-C^alkyl, which is interrupted by one, or more oxygen atoms, C₃-C₈cycloalkyl which is unsubstituted or substituted by Ci-C₄alkyl, unsubstituted phenyl or benzyl, or phenyl or benzyl which is substituted by F, Cl, Br, d-

C₆alkyl, d-C₆alkoxy or di(d-C₆alkylamino).

R¹ and R² can be the same, or different, but are preferably identical radicals. R¹ and R² can be linear, or branched d-C₆alkyl, such as methyl, ethyl, n- and isopropyl, n-, iso- and tert- butyl, pentyl and hexyl, and preferably contain 1 to 4 carbon atoms. Preferred alkyl radicals are methyl and ethyl.

Examples of are phenyl, naphthyl, biphenyl, anthryl, or phenanthryl, which may optionally be substituted by F, Cl, Br, d-C₆alkyl, d-C₆alkoxy or di(Ci-C₆alkylamino). Examples of C3-C₇heteroaryl are thiazolyl, pyridyl, or benzothiazolyl, which may optionally be substituted by F, Cl, Br, d-C₆alkyl, d-C₆alkoxy or di(d-C₆alkylamino).

Examples of cycloalkyl are cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

Preferred cycloalkyl radicals are cyclopentyl and cyclohexyl. Examples of substituted cycloalkyl radicals are methylcyclopentyl and methylcyclohexyl. Examples of alkyl substituents, which preferably contain 1-4 carbon atoms, are methyl, ethyl, n- and isopropyl and n-, iso- and tert. -butyl.

Examples of alkoxy substituents, which preferably contain 1-4 carbon atoms, are methoxy, ethoxy, n-propoxy and t-butoxy.

Examples of dialkylamino substituents, in which the alkyl groups preferably contain 1-4 carbon atoms, are dimethylamino, diethylamino and di-n-propylamino.

Some examples of substituted phenyl and benzyl are 2,6-dimethylphen-4-yl, 2,6-diethylphen-

4-yl, toluyl, p-methoxyphenyl and 2,6-dimethoxyphen-4-yl.

Preferred examples of R¹ and R² are unsubstituted d-dalkyl, such as methyl, ethyl, and n- propyl, cyclopentyl, cyclohexyl, phenyl and benzyl. R¹ and R² particularly preferably are identical and represent methyl. The compound is then

2,5-bis(thiomethyl)-1 ,4-tetracyanoquinodimethane, abbreviated to 2,5-DMeS-TCNQ below.

The process for the preparation of the compounds of formula I is described in EP567429A1 and comprises

i) reacting a compound of the formula ^s (II), in which R¹ and R² are as defined above, with paraformaldehyde in the presence of concentrated HCI and CH₃COOH

to give a compound of the formula

ii) convening this compound of the formula III into a compound of the formula

^N (IV) by reaction with NaCN, i) subsequently convening this compound of the formula IV into a compound of the formula

(V) by reaction with CH₃ONa, (CH₃O)₂CO and CICN, and iv) dissolving this compound of the formula V in an aqueous base under an inert atmosphere and converting it into the compound of the formula I by the action of Br₂ and concentrated HCI.

Various aspects and features of the present invention will be further discussed in terms of the examples. The following examples are intended to illustrate various aspects and features of the present invention, but not to limit the scope of the present invention.

Examples

Example 1

a) 14.2 ml (2.7 M in heptane) of a n-butyllithium solution in heptane is added at -78 ⁰C under nitrogen to a solution of 7.68 g (37.1 mmol) 2-bromo-naphthalene in 60 ml THF. After 30 min this suspension is added to a suspension of 3.00 g (12.4 mmol) 2-chloro-anthraquinone in THF at -70 ⁰C under nitrogen. The reaction mixture is stirred for 30 min at -70 ⁰C and is then warmed-up to 25 ⁰C.

Water is added and the water phase is extracted with dichloromethane. The organic phase is dried with magnesium sulphate and the solvent is distilled off. Column chromatography on silica gel with toluene / ethyl acetate 95/5 results in the product (yield: 61 %).

b) 3.62 g (7.30 mmol) of the product of example 1 a) is dissolved in 190 ml THF. 4.13 g (21.8 mmol) tin(ll)chloride in 10 ml 36 % hydrochloric acid are added at 25 ⁰C. The reaction mixture is refluxed for 6 h. The solvent is distilled off and the residue is extracted with methanol. The organic solvent is distilled off. Column chromatography on silica gel with cyclohexane/ethyl acetate 1/1 results in the product (yield: 93 %).

c) 10.0 g (48.0 mmol) phenanthrene-9,10-dione, 10.7 g (57.6 mmol) 4-bromo-benzaldehyde, 12.4 g (96.1 mmol) aniline and 9.25 g (121 mmol) ammonium acetate in 200 ml acetic acid are heated for 18 h under nitrogen. The reaction mixture is cooled to 25 ⁰C, the product is filtered off, washed with ethanol, with a diluted solution of ammonia in water and with methanol (yield: 17.3 g (80 %)).

d) 2.45 ml (2.7 M in heptane) of a n-butyllithium solution in heptane are added at -78 ⁰C under nitrogen to 2.50 g (5.56 mmol) of the product of example 1c) in 65 ml water free THF. The reaction mixture is stirred for 30 min at -70 ⁰C and is then warmed-up to 25 ⁰C. Water is added and the water phase is extracted with dichloromethane. The organic phase is dried with magnesium sulphate and the solvent is distilled off. The residue is stirred with cyclo- hexane and the precipitate is filtered off (yield: 2.19 g (40 %)).

e) 1.00 g (2.15 mmol) of the product of example 1 b), 1.17 (2.37 mmol) of the product of example 1 d), 110 mg (0.26 mmol) 2-dicyclohexylphosphino-2',6'-di-methoxybiphenyl, and 95 mg (0.043 mmol) palladium acetate are degassed with argon. 5 ml degassed dioxane and 20 ml degassed toluene are added. A degassed solution of potassium phosphate tribasic in 4 ml water is added. The reaction mixture is stirred for 18 h at 90 ⁰C under argon and cooled to 25 ⁰C. The product is filtered off, washed with toluene, dissolved in hot chlorobenzene, methanol is added and the product is filtered off (yield: 1.00 g (59 %)). Melting point: 368 ⁰C. ¹H NMR (300 MHz, CDCI₃, δ): 8.84 (dd, J= 7.9 Hz, J= 1.2 Hz, 1 H), 8.74 (d, J= 8.3 Hz, 1 H), 8.68 (d, J= 8.2 Hz, 1 H), 8.12-7.10 (m, 35 H).

Device fabrication

Prior to device fabrication, indium tin oxide (ITO) on glass is patterned as 2mm wide stripes (sheet resistance 20 Ω/square). The substrates are cleaned by sonication in acetone, isopropanol and water for 15 minutes in each solvent. After that, the substrates are dried with a nitrogen steam and treated by O₂ vacuum plasma for 5 minutes. Organic layers of the OLEDS are sequentially deposited by thermal evaporation from resistively heated ceramic crucibles at a base pressure of 2x10^"7 Torr, at 2A/s. The evaporation rate of each single component source is controlled by a thickness monitor (Inficon) close to the substrate, or to the source. All the devices are measured in a nitrogen glove box, immediately after fabrication. Current-voltage and optical measurements are carried out with a Botest equipment. Electroluminescent spectra are measured with an Ocean Optic spectrometer. The structure of TBADN is as follows:

Structures of the other compounds are given in the text. Application Example 1

An organic light emitting device (OLED) is prepared having the following structure from the anode to the cathode: using 20 nm of 2,5-bis-methylthio-7,7',8,8'-tetracyanoquinodimethane (2,5-DMeS-TCNQ) as hole injection layer, 40 nm of 4,4'-bis[N-1-naphthyl)-N-phenylamino]- biphenyl (α-NPD), TBADN 30 nm as blue emitter, 45 nm of tris(8-quinolate)aluminium (AIq₃) as electron transport layer, 1 nm LiF capped with 100 nm of aluminium as top electrode. On driving using a current of density of 25 mA/cm² the device produced blue emission of 450 cd/m² and a colour purity corresponding to (0.15, 0.14) coordinates on the CIE chart. The driving voltage needed to operate the device at this conditions is 8.7 volts. After 50 hours of continuous operation at this current density in a nitrogen atmosphere the decay in emission intensity is less than 5% of the initial intensity. 2,5-DMeS-TCNQ is prepared according to Example A1 of EP567429A1.

Application Example 2

The same device structure is used as in application example 1 , except that the electron

transporting material, AIq₃, is replaced by

. The driving voltage decreases at these conditions to 4.5 V.

Comparative Application Example 1 The same device structure is used as in application example 1 , except that the hole injection layer is replaced by a 10 nm thick tetrafluorotetracyanoquinodimethane (F₄TCNQ₄) doped 4,4'-bis[N-1-naphthyl)-N-phenylamino]-biphenyl layer (α-NPD, ratio (3:7)). The operational half-life of this device decreases by a factor of 20 over the control device.

Application Example 3

An organic light emitting device is prepared having the following structure form the anode to the cathode: 60 nm 4,4',4"-tris [N-(2-naphtyl)-N-phenyl-amino]-triphenylamine (2-TNATA) as hole injection layer, 30 nm NPD, 20 nm of aluminium(lll) bis (2-methyl-8-quinolato) 4-phenyl- phenolate (BAIq) doped with 10 wt % of a orange-red emitter,

using 30 nm of

, 3nm caesium carbonate capped with 100 nm of aluminium as top electrode. The current efficiency (S) 1000 cd/m ² is 13.1 cd/A at a driving voltage of 8V. Replacing the electron transporting material by AIq₃ the current efficiency decreases to 8.8 cd/A at 1000 nits, whereas the driving voltage increases to 9.1 V. The corresponding colour coordinates are (0.62, 0.36) on the CIE chart.

Claims

1. An electronic device, which comprises a compound of the formula

(I), wherein

R¹ and R² independently of one another are CrC^alkyl, Ci-Ci₂alkyl, which is interrupted by one, or more oxygen atoms, C₃-C₈cycloalkyl which is unsubstituted or substituted by Ci-C₄alkyl, unsubstituted C₆-Ci₂aryl, or C₃-C₇heteroaryl, or benzyl, or C₆- Ci₂aryl, or C₃-C₇heteroaryl, or benzyl which is substituted by F, Cl, Br, d-C₆alkyl, d- C₆alkoxy, or di(Ci-C₆alkylamino).

The electronic device according to claim 1 , wherein R¹ and R² independently of one another are Ci-C₆alkyl.

3. The electronic device according to claim 1 , wherein the compound of formula I is a compound of formula

4. The electronic device according to any of claims claim 1 to 3, which is an organic electroluminescent device having a hole injection layer, wherein the hole injection layer comprises the compound of formula I.

5. The electronic device according to claim 4, wherein the compound of formula I serves as a electron accepting dopant of the p-type doped hole injection layer.

6. The electronic device according to any of claims claim 1 to 5, further comprising an anode, wherein the hole injection layer contacts the anode.

The electronic device according to any of claim 1 to 3, comprising: a first electrode to inject or extract holes, the first electrode including a conductive layer and an n-type organic compound layer in contact with conductive layer; a second electrode to inject or extract electrons; and a p-type organic compound layer disposed between the n-type organic compound layer of the first electrode and the second electrode, the p-type organic compound layer forming an np junction between the n-type organic compound layer of the first electrode and the p-type organic compound layer, wherein the n-type organic compound layer comprises the compound of formula I.

8. The electronic device of claim 7, wherein the p-type organic compound layer comprises a hole injection layer, a hole transporting layer, or an emitting layer.

9. The electronic device of claim 7, further comprising at least one organic compound layer disposed between the p-type organic compound layer and the second electrode, wherein the at least one organic compound layer includes a hole transporting layer, an emitting layer, or an electron transporting layer.

10. The electronic device of claim 7, which is an organic electroluminescent device.

1 1. The electronic device according to claim 7, which is an organic solar cell comprising: an anode to extract holes including a conductive layer and an n-type organic compound layer in contact with the conductive layer; a cathode to extract electrons; and an electron donor layer disposed between the n-type organic compound layer of the anode and the cathode, the electron donor layer including a p-type organic compound layer and forming an np junction between the n-type organic compound layer of the anode and the p-type organic compound layer, wherein the n-type organic compound layer comprises the compound of formula I.

12. The electronic device according to claim 7, which is an organic transistor, comprising a substrate, a source electrode, a drain electrode, a gate, an insulating layer disposed on the gate and the substrate, a p-type organic compound layer disposed on the insulating layer and forming holes, and an n-type organic compound layer disposed between the source electrode and/or drain electrode and the p-type organic compound layer, wherein the n-type organic compound layer comprises the compound of formula I.

13. The electronic device of claim 1 , or 7, which comprises an electron transporting layer, which comprises a compound of the formula

(Vl), wherein

R³ is C₆-Ci₈aryl; C₆-Ci₈aryl which is substituted by CrCi₈alkyl, Ci-Ci₈perfluoroalkyl, - N(C₆-Ci8aryl)₂, or d-Ci₈alkoxy; Ci-Ci₈alkyl; or d-Ci₈alkyl which is interrupted by -O-; X is N, CH, or CR⁷,

R⁴, R⁵, R⁶ and R⁷ independently of one another are hydrogen, cyano, CrC₂₅alkyl, d- C₂5alkoxy, triphenylsilyl, C₆-C₂₄aryl, which may optionally be substituted, or C₂- C₂6heteroaryl, which may optionally be substituted, and

Ar is benzene, naphthalene, biphenyl, anthracene, or a group derived from an aromatic heterocycle or an aromatic ring.

14. Use of a compound of the formula

(I), wherein

R¹ and R² independently of one another are CrC^alkyl, Ci-Ci₂alkyl, which is interrupted by one, or more oxygen atoms, C3-C₈cycloalkyl which is unsubstituted or substituted by Ci-C₄alkyl, unsubstituted C₆-Ci₂aryl, or C₃-C₇heteroaryl, or benzyl, or C₆- Ci₂aryl, or C₃-C₇heteroaryl, or benzyl which is substituted by F, Cl, Br, d-C₆alkyl, d- C₆alkoxy or di(Ci-C₆alkylamino) in an electronic device.

15. Use according to claim 14, wherein the electronic device is an electroluminescent device, a solar cell, or an organic transistor.

16. A compound of the formula

(Vl), wherein

R⁴, R⁵, R⁶ and R⁷ independently of one another are hydrogen, cyano, d-C₂₅alkyl, d- C₂5alkoxy, triphenylsilyl, C₆-C₂₄aryl, which may optionally be substituted, or C₂- C₂₆heteroaryl, which may optionally be substituted, and