Organic thin film for use in photoelectric conversion element

Abstract

To provide an organic thin film excellent in charge transport, heat resistance, dark current characteristics and conversion efficiency and applicable to various photoelectric conversion elements.SOLUTION: An organic thin film for photoelectric conversion elements comprises a compound having an indolocarbazole ring structure represented by the general formula in the figure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an organic thin film used in a photoelectric conversion element, and more particularly to an organic thin film containing a compound having an indolocarbazole ring structure. The organic thin film of the present invention is applicable to various photoelectric conversion elements. [Background technology]

[0002] Photoelectric conversion elements are widely used in solar cells, optical sensors, etc., and among them, image sensors, which are imaging elements, are expanding in both applications and the market, not only being used in television cameras and cameras installed in smartphones, but also in driver assistance systems.

[0003] Because organic materials have higher absorbance than inorganic materials, they have the potential to efficiently convert light into electricity with thinner film thicknesses than inorganic materials. They also offer high wavelength selectivity, and by combining materials corresponding to each wavelength, it is possible to efficiently utilize each of the three primary colors. Therefore, optical sensors using organic thin films are promising as new optical sensors. Furthermore, depending on the selection of materials, they may be able to sense not only visible light but also near-infrared or infrared light. Furthermore, they may offer added value, such as flexibility and the ability to increase the area by coating during the fabrication process, which are not possible with inorganic materials (see, for example, Non-Patent Document 1).

[0004] For these reasons, photoelectric conversion elements using organic materials are expected to be developed into next-generation optical sensors, and several groups have reported on this. For example, there are examples in which quinacridone or quinazoline derivatives are used in photoelectric conversion elements (see, for example, Patent Document 1), and examples in which benzothienobenzothiophene derivatives are used in photoelectric conversion elements (see, for example, Patent Document 2). In order to improve the sensitivity of optical sensors, it is necessary to reduce the current that flows when light is incident (dark current). One method for reducing this dark current is to insert a hole-blocking layer or an electron-blocking layer between the photoelectric conversion unit and the electrode unit.

[0005] The hole-blocking layer and electron-blocking layer are commonly used in the field of organic electronics. These blocking layers are placed at the interface between an electrode or conductive film and another film in the device's constituent films, and their function is to rapidly transfer the necessary charges while controlling the reverse movement of holes or electrons.

[0006] In addition, the properties required for materials used in blocking layers include control of charge reverse migration and rapid charge transfer, as well as higher thermal stability than organic electroluminescence (EL) and other organic electronic devices, in order to consider application to manufacturing processes involving heating, such as color filter installation, protective film installation, and element soldering, and to improve shelf life when fabricating optical sensor devices. Patent Document 3 reports that the thermal stability of elements can be improved by using an electron blocking material with a glass transition temperature (Tg) of 140°C or higher. Furthermore, in examples where indolocarbazole is used in photoelectric conversion elements (see, for example, Patent Document 4), the indolocarbazole skeleton exhibits an even higher glass transition temperature (Tg). However, the reports in these documents were insufficient in terms of the properties of photoelectric conversion elements. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4945146 [Patent Document 2] Japanese Patent Application Publication No. 2018-170487 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-187937 [Patent Document 4] Japanese Patent Application Publication No. 2018-085427 [Patent Document 5] International Publication No. 2012 / 114928 [Non-patent literature]

[0008] [Non-Patent Document 1] Adv. Mater.28,4766(2016) Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide an organic thin film that has excellent charge transport properties, heat resistance, dark current characteristics, and conversion efficiency and is applicable to various photoelectric conversion elements. [Means for solving the problem]

[0010] In order to achieve the above object, the present inventors have focused on the fact that an indolocarbazole ring structure has excellent heat resistance, and have conducted extensive research into the structure of a compound that improves charge transport properties and dark current characteristics. As a result, they have found that an organic thin film containing a compound represented by the following general formula (1) can solve the above problems, and have thus completed the present invention.

[0011] That is, the present invention relates to the following items. 1) An organic thin film used in a photoelectric conversion element, which contains a compound having an indolocarbazole ring structure represented by the following general formula (1):

[0012] [ka] (1)

[0013] In general formula (1), X and Y may be the same or different and represent a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted aromatic heterocycle, or a divalent group of a substituted or unsubstituted condensed polycyclic aromatic ring. R1 to R9 may be the same or different and represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, an optionally substituted linear or branched alkyl group of 1 to 6 carbon atoms, an optionally substituted cycloalkyl group of 5 to 10 carbon atoms, an optionally substituted linear or branched alkenyl group of 2 to 6 carbon atoms, an optionally substituted linear or branched alkyloxy group of 1 to 6 carbon atoms, an optionally substituted cycloalkyloxy group of 5 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted fused polycyclic aromatic group, or a substituted or unsubstituted aryloxy group, and adjacent R1 to R9 may be bonded to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom, or a sulfur atom to form a ring. Ar1 to Ar4 may be the same or different and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted fused polycyclic aromatic group, and Ar3 and Y, Ar4 and Y, or Ar3 and Ar4 may be bonded to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom, or a sulfur atom to form a ring.

[0014] 2) An organic thin film used in the photoelectric conversion element according to 1) above, characterized in that R1 to R9 in the general formula (1) above are a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted fused polycyclic aromatic group.

[0015] 3) An organic thin film used in a photoelectric conversion element according to 1) or 2) above, characterized in that X and Y in the general formula (1) are divalent groups obtained by removing two hydrogen atoms from benzene, biphenyl, terphenyl, naphthalene, thiophene, furan, or thienothiophene.

[0016] 4) An organic thin film used in a photoelectric conversion element according to any one of 1) to 3) above, characterized in that the glass transition temperature of the organic thin film is 160° C. or higher.

[0017] 5) An organic thin film used in a photoelectric conversion element according to any one of 1) to 3) above, wherein the organic thin film has a work function of 5.5 eV or more.

[0018] 6) An organic thin film used in a photoelectric conversion element according to any one of 1) to 5) above, characterized in that the organic thin film is a blocking layer.

[0019] 7) The organic thin film used in the photoelectric conversion element according to any one of 1) to 5) above, wherein the organic thin film is a photoelectric conversion layer. [Effects of the Invention]

[0020] An organic thin film containing a compound having an indolocarbazole ring structure represented by general formula (1) has excellent heat resistance, allowing the fabrication of devices with even better thermal stability. Furthermore, the organic thin film has excellent charge transport properties and can be applied to various photoelectric conversion devices. This allows the provision of photoelectric conversion devices with good dark current characteristics and conversion efficiency. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows one example of the configuration of a photoelectric conversion element of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] In the following explanation, the term "to" is used to indicate a range. For example, "5 to 10" means "5 or more and 10 or less," and indicates a range that includes the numerical values ​​written before and after "to."

[0023] The "aromatic hydrocarbon", "aromatic heterocycle", or "fused polycyclic aromatic" in the "divalent aromatic hydrocarbon group", "divalent aromatic heterocycle", or "divalent fused polycyclic aromatic group" of the "substituted or unsubstituted aromatic hydrocarbon group", "divalent aromatic heterocycle", or "divalent fused polycyclic aromatic group" represented by X and Y in general formula (1) is not particularly limited, and examples thereof include benzene, biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, pyridine, furan, thiophene, benzofuran, benzothiophene, thienothiophene, bithiophene, and bifuran. The "divalent aromatic hydrocarbon group," "divalent aromatic heterocyclic group," or "divalent fused polycyclic aromatic group" of the "divalent substituted or unsubstituted aromatic hydrocarbon group," "divalent substituted or unsubstituted aromatic heterocyclic group," or "divalent fused polycyclic aromatic group" represented by X and Y in general formula (1) represent a divalent group obtained by removing two hydrogen atoms from the above-mentioned "aromatic hydrocarbon," "aromatic heterocyclic group," or "fused polycyclic aromatic group." In addition, the "divalent aromatic hydrocarbon group," "divalent aromatic heterocyclic group," or "divalent fused polycyclic aromatic group" of the "divalent substituted or unsubstituted aromatic hydrocarbon group," "divalent substituted or unsubstituted aromatic heterocyclic group," or "divalent fused polycyclic aromatic group" represented by X and Y in general formula (1) can also be selected from an arylene group having 6 to 30 carbon atoms or a heteroarylene group having 2 to 30 carbon atoms. When these groups have a "substituent," the "substituent" is not particularly limited, and examples thereof include deuterium atoms, cyano groups, and nitro groups; halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms; silyl groups such as trimethylsilyl and triphenylsilyl groups; linear or branched alkyl groups having 1 to 6 carbon atoms such as methyl groups, ethyl groups, and propyl groups; linear or branched alkyloxy groups having 1 to 6 carbon atoms such as methyloxy groups, ethyloxy groups, and propyloxy groups; alkenyl groups such as vinyl groups and allyl groups; aryloxy groups such as phenyloxy groups and tolyloxy groups; arylalkyloxy groups such as benzyloxy groups and phenethyloxy groups; phenyl groups, biphenylyl groups, tabenyl groups, and the like. Examples of the substituent include aromatic hydrocarbon groups or condensed polycyclic aromatic groups such as a phenylyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a fluorenyl group, a spirobifluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, and a triphenylenyl group; and aromatic heterocyclic groups such as a pyridyl group, a thienyl group, a furyl group, a pyrrolyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, and a carbolinyl group, and these substituents may be further substituted with the substituents exemplified above.

[0024] The "aromatic hydrocarbon group", "aromatic heterocyclic group", or "fused polycyclic aromatic group" in the "substituted or unsubstituted aromatic hydrocarbon group", "substituted or unsubstituted aromatic heterocyclic group", or "substituted or unsubstituted fused polycyclic aromatic group" represented by R1 to R9 and Ar1 to Ar4 in general formula (1) is not particularly limited, and examples thereof include a phenyl group, a biphenylyl group, a terphenylyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a fluorenyl group, a spirobifluorenyl group, an indenyl group, a pyrenyl group, Examples include a perylenyl group, a fluoranthenyl group, a triphenylenyl group, a pyridyl group, a pyrimidinyl group, a triazinyl group, a furyl group, a pyrrolyl group, a thienyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, a naphthyridinyl group, a phenanthrolinyl group, an acridinyl group, a carbolinyl group, etc. Furthermore, the alkyl group may be selected from an aryl group having 6 to 30 carbon atoms and a heteroaryl group having 2 to 30 carbon atoms.

[0025] The "C-C linear or branched alkyl group," "C-C cycloalkyl group," or "C-C linear or branched alkenyl group" in the "C-C linear or branched alkyl group which may have a substituent," "C-C cycloalkyl group which may have a substituent," or "C-C linear or branched alkenyl group which may have a substituent," represented by R1 to R9 in general formula (1), is not particularly limited, and examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, cyclopentyl, cyclohexyl, 1-adamantyl, 2-adamantyl, vinyl, allyl, isopropenyl, and 2-butenyl.

[0026] The "linear or branched alkyloxy group having 1 to 6 carbon atoms" or the "cycloalkyloxy group having 5 to 10 carbon atoms" in the "linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent" or the "cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent" represented by R1 to R9 in the general formula (1) is not particularly limited, and examples thereof include a methyloxy group, an ethyloxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, a tert-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, a cyclopentyloxy group, a cyclohexyloxy group, a cycloheptyloxy group, a cyclooctyloxy group, a 1-adamantyloxy group, and a 2-adamantyloxy group.

[0027] The "aryloxy group" in the "substituted or unsubstituted aryloxy group" represented by R1 to R9 in general formula (1) is not particularly limited, and examples thereof include aryloxy groups having 6 to 30 carbon atoms, such as a phenyloxy group, a biphenylyloxy group, a terphenylyloxy group, a naphthyloxy group, an anthracenyloxy group, and a phenanthrenyloxy group.

[0028] The "substituents" in the "substituted aromatic hydrocarbon group," "substituted aromatic heterocyclic group," "substituted fused polycyclic aromatic group," "substituted C linear or branched alkyl group," "substituted C cycloalkyl group," "substituted C linear or branched alkenyl group," "substituted C linear or branched alkyloxy group," or "substituted C cycloalkyloxy group," and the "substituted methylene group" which is the linking group when these are bonded to each other, represented by R1 to R9 and Ar1 to Ar4 in general formula (1), are not particularly limited, and examples thereof include deuterium atoms, cyano groups, nitro groups; halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms; silyl groups such as trimethylsilyl groups and triphenylsilyl groups; C linear or branched alkyl groups such as methyl groups, ethyl groups, and propyl groups; methyloxy groups, ethyloxy groups, propyl groups, linear or branched alkyloxy groups having 1 to 6 carbon atoms, such as oxy; alkenyl groups, such as vinyl and allyl; aryloxy groups, such as phenyloxy and tolyloxy; arylalkyloxy groups, such as benzyloxy and phenethyloxy; phenyl, biphenylyl, terphenylyl, naphthyl, anthracenyl, phenanthrenyl, fluorenyl, spirobifluorenyl, indenyl, pyrenyl, perylenyl, fluoranthenyl, and triphenylenyl. and aromatic heterocyclic groups such as a pyridyl group, a thienyl group, a furyl group, a pyrrolyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, and a carbolinyl group, and these substituents may be further substituted with the substituents exemplified above.

[0029] From the viewpoint of heat resistance and charge mobility, X and Y in general formula (1) are preferably each independently selected from a divalent group (phenylene group) obtained by removing two hydrogen atoms from benzene, a divalent group (biphenylene group) obtained by removing two hydrogen atoms from biphenyl, a divalent group (terphenylene group) obtained by removing two hydrogen atoms from terphenyl, a divalent group (naphthalenylene group) obtained by removing two hydrogen atoms from naphthalene, a divalent group (thienylene group) obtained by removing two hydrogen atoms from thiophene, a divalent group (furanylene group) obtained by removing two hydrogen atoms from furan, or a divalent group (thienothienylene group) obtained by removing two hydrogen atoms from thienothiophene.

[0030] Furthermore, from the viewpoint of synthesis, Ar1 and Ar2 in general formula (1) are preferably a phenyl group, a biphenyl group, a thienyl group, or a furyl group, R5 is preferably a hydrogen atom or a phenyl group, and R1 to R4 and R6 to R9 are preferably hydrogen atoms.

[0031] Among the compounds having an indolocarbazole ring structure represented by general formula (1), specific examples of preferred compounds are shown below, but the present invention is not limited to these compounds.

[0032] [ka]

[0033] [ka]

[0034] [ka]

[0035] The compound having an indolocarbazole ring structure represented by the general formula (1) and suitable for use in the organic thin film of the present invention can be synthesized according to a method known per se (see, for example, Patent Document 5).

[0036] The compound having an indolocarbazole ring structure represented by the general formula (1) and suitable for use in the organic thin film of the present invention can be purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, or the like, or recrystallization or crystallization using a solvent. The compound can be identified by NMR analysis. It is preferable to measure the glass transition temperature (Tg) and work function as physical property values. The glass transition temperature (Tg) is an index of the stability of the thin film state, and the work function is an index of the hole transport property.

[0037] The compound having an indolocarbazole ring structure represented by the general formula (1), which is suitable for use in the organic thin film of the present invention, can be formed into an organic thin film by known methods such as vapor deposition, spin coating, and inkjet printing. The compound having an indolocarbazole ring structure represented by the general formula (1) may be used to form a film alone, or multiple types of compounds may be mixed to form a film. Furthermore, the compound may be mixed with other compounds to form a film within a range that does not impair the effects of the present invention.

[0038] An organic thin film containing a compound having an indolocarbazole ring structure represented by the general formula (1) is suitable for use in photoelectric conversion elements, particularly imaging elements. The photoelectric conversion element may have, for example, a first electrode (transparent anode), a first blocking layer (electron-blocking layer), a photoelectric conversion layer, and a second electrode (cathode) in this order. In such a multilayer structure, additional layers can be added, for example, a configuration having, in this order, a first electrode, a first blocking layer, a photoelectric conversion layer, a second blocking layer, and a second electrode. The organic thin film containing a compound having an indolocarbazole ring structure represented by the general formula (1) can also be used in the first blocking layer and / or the photoelectric conversion layer.

[0039] The photoelectric conversion layer in a photoelectric conversion element may be made of either an organic or inorganic material, as long as it can generate signal charges according to the amount of light received. When the photoelectric conversion layer is made of an organic material, the organic thin film (organic semiconductor film) may be a single layer or multiple layers. If it is a single layer, it can be a p-type organic semiconductor film, an n-type organic semiconductor film, or a mixed film of p-type organic semiconductor and n-type organic semiconductor. If it is made of multiple layers, it can be a stacked structure of two or more of a p-type organic semiconductor film, an n-type organic semiconductor film, or a mixed film of p-type organic semiconductor and n-type organic semiconductor, or a bulk heterostructure, and it can also be formed by inserting a blocking layer between the layers.

[0040] The photoelectric conversion element using the organic thin film of the present invention can obtain stability against thermal load by using a compound having an indolocarbazole ring structure represented by the general formula (1) in the first blocking layer constituting the element. In addition, the high mobility also improves the image retention characteristics.

[0041] The p-type semiconductor used in the photoelectric conversion layer is a donor organic semiconductor, and a compound that has a tendency to easily donate electrons, such as a hole-transporting organic compound, is used. Examples of p-type semiconductors include, but are not limited to, metal complexes having a heterocyclic compound as a ligand, such as naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, pentacene derivatives, quinacridone derivatives, chrysene derivatives, fluoranthene derivatives, phthalocyanine derivatives, subphthalocyanine derivatives, and SubPC; thienoacene-based materials typified by benzothiophene derivatives, dinaphthothienothiophene derivatives, dianthracenothienothiophene derivatives, benzobisbenzothiophene derivatives, thienobisbenzothiophene, dibenzothienobisbenzothiophene derivatives, dithienobenzodithiophene derivatives, dibenzothienodithiophene derivatives, benzodithiophene derivatives, naphthodithiophene derivatives, anthracenodithiophene derivatives, tetracenodithiophene derivatives, and pentacenodithiophene derivatives; amine-based derivatives such as triarylamine compounds and carbazole compounds; and indenocarbazole derivatives.

[0042] The n-type organic semiconductor used in the photoelectric conversion layer is an acceptor organic semiconductor, and an organic compound that has a tendency to accept electrons, such as an electron-transporting organic compound, is used. More specifically, an organic compound that has a tendency to accept electrons refers to the organic compound that has a larger electron affinity when two organic compounds are used in contact. Therefore, any organic compound that has electron-accepting properties can be used as an acceptor organic semiconductor. For example, condensed polycyclic aromatic compounds (e.g., naphthalene, anthracene, fullerene, phenanthrene, tetracene, pyrene, perylene, perylene diimide, fluoranthene, or derivatives thereof), quinacridone, 5- to 7-membered heterocyclic compounds containing a nitrogen atom, an oxygen atom, or a sulfur atom (e.g., pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole ... Examples of the acceptor organic semiconductor include metal complexes having a ligand such as midazole, thiazole, oxazole, indazole, benzimidazole, benzotriazole, benzoxazole, benzothiazole, carbazole, purine, triazolopyridazine, triazolopyrimidine, tetrazaindene, oxadiazole, imidazopyridine, pyrazine, pyrrolopyridine, thiadiazolopyridine, dibenzazepine, tribenzazepine, etc.), polyarylene compounds, fluorene compounds, cyclopentadiene compounds, silyl compounds, and nitrogen-containing heterocyclic compounds. However, the acceptor organic semiconductor is not limited thereto, and any organic compound having a larger electron affinity than the organic compound used as the donor organic compound may be used as the acceptor organic semiconductor.

[0043] The transparent anode and cathode may be made of any conductive material commonly used as an electrode, including metals, metal oxides, metal nitrides, metal borides, organic conductive compounds, and mixtures thereof. Specific examples include conductive metal oxides such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), indium tungsten oxide (IWO), molybdenum oxide (MoO), and titanium oxide; metal nitrides such as titanium oxynitride (TiNxOx) and titanium nitride (TiN); metals such as gold (Au), platinum (Pt), silver (Ag), chromium (Cr), nickel (Ni), and aluminum (Al); mixtures or laminates of these metals and conductive metal oxides; organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and laminates of these compounds with ITO.

[0044] A second blocking layer may be inserted between the second electrode (cathode) and the photoelectric conversion layer, but the material used for this is preferably a material with a deeper work function than the material used for the first blocking layer. For example, organic compounds and / or organometallic complexes containing nitrogen-containing heterocycles such as pyridine, quinoline, acridine, indole, imidazole, benzimidazole, and phenanthroline are preferred, as are materials with low absorption in the visible light region. Furthermore, when forming a thin film of about 5 nm to 20 nm, fullerenes and their derivatives that absorb light in the visible light region can also be used.

[0045] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples. [Example]

[0046] Synthesis of 5-[4'-di(biphenyl-4-yl)aminobiphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (Compound 1-3) A reaction vessel was charged with 3.50 g of 5-bromo-11,12-diphenylindolo[2,3-a]carbazole, 5.17 g of [4'-(4,4,5,5-tetramethyl-[1,3,2]dioxaboran-2-yl)biphenyl-4-yl]-di(biphenyl-4-yl)amine, 3.96 g of potassium carbonate, 150 mL of toluene, 11 mL of water, and 26 mL of ethanol. After degassing, 0.50 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux and stirred for 35 hours. After cooling, 100 mL of methanol was added, and the precipitated solid was collected by filtration and dried. The resulting solid was completely dissolved in 1.2 L of chlorobenzene by heating under reflux, then purified by adsorption using silica gel. The filtrate was concentrated and then precipitated by adding acetone and methanol. Repeated recrystallization using orthodichlorobenzene gave 3.75 g (yield 59%) of a white powder.

[0047] The resulting white powder was identified by NMR as 5-[4'-di(biphenyl-4-yl)aminobiphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (compound 1-3).

[0048] 1 The following 45 hydrogen signals were detected by H-NMR (CDCl3). δ(ppm)=8.19-8.18(1H), 8.03(1H), 7.93-7.89(2H), 7.82-7.79(4H), 7.65-7.60(8H), 7.54-7 .52(1H), 7.42-7.38(4H), 7.32-7.22(12H), 7.19-7.14(7H), 6.99-6.94(1H), 6.83-6.79(4H).

[0049] [ka] Compound (1-3) [Example]

[0050] Synthesis of 5-[4'-[(4-naphthalen-2-yl-phenyl)-phenylamino]biphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (Compound 1-5) A reaction vessel was charged with 3.00 g of 5-bromo-11,12-diphenylindolo[2,3-a]carbazole, 3.88 g of [4'-(4,4,5,5-tetramethyl-[1,3,2]dioxaboran-2-yl)biphenyl-4-yl]-(4-naphthalen-2-yl-phenyl)-phenylamine, 1.70 g of potassium carbonate, 76 mL of toluene, 5.3 mL of water, and 13 mL of ethanol. After degassing, 0.14 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux and stirred for 35 hours. After cooling, 100 mL of methanol was added, and the precipitated solid was collected by filtration and dried. The resulting solid was completely dissolved in 1.2 L of chlorobenzene by heating under reflux, purified by adsorption using silica gel, and filtered. The filtrate was concentrated and purified by silica gel column chromatography to give 3.87 g of a white powder (74% yield).

[0051] The resulting white powder was identified by NMR as 5-[4'-[(4-naphthalen-2-yl-phenyl)-phenylamino]biphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (compound 1-5).

[0052] 1 H-NMR (CDCl3) showed the following 43 hydrogen signals: δ (ppm) = 8.17-8.14 (1H), 8.05 (1H), 8.00 (1H), 7.93-7.84 (8H), 7.78-7.75 (1H), 7.74-7.71 (2H), 7.68-7.65 (2H), 7.56-7.54 (1H), 7.53-7.45 (2H), 7.36-7.22 (12H), 7.15-7.08 (7H), 7.05-7.01 (1H), 6.82-6.79 (4H).

[0053] [ka] Compound (1-5) [Example]

[0054] Synthesis of 5-[4'-(9H-carbazol-9-yl)-biphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (Compound 1-10) A reaction vessel was charged with 3.40 g of 5-bromo-11,12-diphenylindolo[2,3-a]carbazole, 3.42 g of 9-[4'-(4,4,5,5-tetramethyl-[1,3,2]dioxaboran-2-yl)-biphenyl-4-yl]-9H-carbazole, 1.93 g of potassium carbonate, 100 mL of THF, and 13 mL of water. After degassing, 0.16 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux and stirred for 22 hours. After cooling, 100 mL of methanol was added, and the precipitated solid was collected by filtration and dried. The resulting solid was completely dissolved in 500 mL of toluene by heating under reflux, followed by adsorption purification using silica gel. The filtrate was concentrated and then repeatedly crystallized using toluene, acetone, and methanol to obtain 3.20 g of a white powder (62% yield).

[0055] The resulting white powder was identified by NMR as 5-[4'-(9H-carbazol-9-yl)-biphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (compound 1-10).

[0056] 1 H-NMR (CDCl3) detected the following 35 hydrogen signals: δ (ppm) = 8.19-8.16 (3H), 8.03 (1H), 7.97-7.85 (5H), 7.70-7.68 (2H), 7.53-7.51 (2H), 7.47-7.43 (2H), 7.36-7.23 (10H), 7.17-7.10 (6H), 6.83-6.80 (4H).

[0057] [ka] Compound (1-10) [Example]

[0058] Synthesis of 5-(4'''-diphenylamino-[1,1';4',1'';4'',1''']quaterphenyl-4-yl)-11,12-diphenylindolo[2,3-a]carbazole (Compound 1-28) A reaction vessel was charged with 5.00 g of 5-(4'-bromobiphenyl-4-yl)-11,12-diphenylindolo[2,3-a]carbazole, 3.53 g of 4'-[(4,4,5,5-tetramethyl-[1,3,2]dioxaboran-2-yl)biphenyl-4-yl]diphenylamine, 3.24 g of potassium carbonate, 130 mL of 1,4-dioxane, and 19 mL of water. After degassing, 0.27 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux for 8.5 hours. After cooling, 50 mL of chlorobenzene was added and heated under reflux for 1 hour, followed by hot filtration. The filtrate was concentrated to dryness and dissolved in 50 mL of chlorobenzene. 15.0 g of silica gel and 5.00 g of activated clay were added for adsorption purification. After filtration, the filtrate was concentrated to dryness, and the resulting solid was repeatedly recrystallized using toluene to obtain 3.80 g (yield 56%) of a white powder.

[0059] The resulting white powder was identified using NMR as 5-(4'''-diphenylamino-[1,1';4',1'';4'',1'']quaterphenyl-4-yl)-11,12-diphenylindolo[2,3-a]carbazole (compound 1-28).

[0060] 1 H-NMR (CDCl3) detected the following 45 hydrogen signals: δ (ppm) = 8.18-8.15 (1H), 8.01 (1H), 7.91-7.89 (6H), 7.83-7.76 (4H), 7.71-7.69 (2H), 7.59-7.54 (3H), 7.36-7.11 (22H), 7.07-7.03 (2H), 6.83-6.79 (4H).

[0061] [ka] Compound (1-28) [Example]

[0062] Synthesis of 5-[4''-(biphenyl-4-yl-phenylamino)-[1,1';4',1'']terphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (Compound 1-33) A reaction vessel was charged with 4.50 g of 5-(4'-bromobiphenyl-4-yl)-11,12-diphenylindolo[2,3-a]carbazole, 3.18 g of 4-(4,4,5,5-tetramethyl-[1,3,2]dioxaboran-2-yl)phenyl-(biphenyl-4-yl)phenylamine, 2.92 g of potassium carbonate, 120 mL of 1,4-dioxane, and 17 mL of water. After degassing, 0.24 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux for 7 hours. After cooling, 100 mL of chlorobenzene was added and heated under reflux for 1 hour, followed by hot filtration. The filtrate was concentrated to dryness and dissolved in 100 mL of chlorobenzene. 15.0 g of silica gel and 5.00 g of activated clay were added for adsorption purification. After filtration, the filtrate was concentrated to dryness, and the resulting solid was repeatedly recrystallized using chlorobenzene to obtain 2.10 g (yield 34%) of a white powder.

[0063] The resulting white powder was identified using NMR as 5-[4''-(biphenyl-4-yl-phenylamino)-[1,1';4',1'']terphenyl-4-yl]-11,12-diphenylindolo[2,3-a]carbazole (compound 1-33).

[0064] 1 The following 45 hydrogen signals were detected by H-NMR (CDCl3). δ(ppm)=8.17-8.15(1H), 8.01(1H), 7.89-7.85(6H), 7.76-7.74(2H), 7.62-7.51(7H) , 7.45-7.42(2H), 7.32-7.21(15H), 7.16-7.08(6H), 7.06-7.02(1H), 6.82-6.79(4H).

[0065] [ka] Compound (1-33) [Example]

[0066] <Measurement of glass transition temperature (Tg)> The glass transition temperature (Tg) of the compound having an indolocarbazole ring structure represented by general formula (1) was measured using a high-sensitivity differential scanning calorimeter (DSC3100SA, manufactured by Bruker AXS). The same measurement was also carried out for a comparative compound (EBL-1), a known compound of the following structural formula known to have a high glass transition temperature (see, for example, Patent Document 4). The results of the measured glass transition temperatures are summarized in Table 1.

[0067] [ka] (EBL-1)

[0068] [Table 1]

[0069] As described above, the glass transition temperatures (Tg) of the compounds having an indolocarbazole ring structure represented by general formula (1) are all high, at 170°C or higher, indicating that the thin film state is stable. Furthermore, the glass transition temperatures (Tg) of the compounds having an indolocarbazole ring structure represented by general formula (1) are all higher than that of the comparative compound (EBL-1), indicating that devices with better thermal stability can be fabricated by using a compound having an indolocarbazole ring structure represented by general formula (1) instead of EBL-1. [Example]

[0070] <Work function measurement> Using the compound having an indolocarbazole ring structure represented by general formula (1) and the comparative compound (EBL-1), a 100 nm thick film was prepared by vapor deposition on an ITO substrate, and the work function was measured using an ionization potential measurement device (Sumitomo Heavy Industries, Ltd., PYS-202). The measurement results are summarized in Table 2.

[0071] [Table 2]

[0072] It can be seen that all of the compounds having an indolocarbazole ring structure represented by general formula (1) exhibit a suitable energy level and have good hole transport ability. From these results, it can be seen that the compounds having an indolocarbazole ring structure represented by general formula (1), which are preferably used in the organic thin film of the present invention, exhibit a similarly suitable energy level and have good hole transport ability, even when compared with the work function (5.3 to 6.0 eV) of carbazole compounds and the like, which are considered to be suitable hole transport materials, and therefore the work function can be easily adjusted by widening the range of compounds selected. [Example]

[0073] <Hall mobility measurement> A compound having an indolocarbazole ring structure represented by general formula (1) and a comparative compound (EBL-1) were used to form thin films with a thickness of 3 to 4 μm on an ITO-coated glass substrate by vacuum deposition. Subsequently, an aluminum film with a thickness of approximately 100 nm was formed to prepare a device for measuring Hall mobility. This device was sealed in a nitrogen atmosphere with a glass cap to which a moisture getter sheet for organic electroluminescence (EL) had been attached to prevent deterioration due to adsorption of moisture and oxygen.

[0074] The hole mobility of the fabricated device was measured under the following conditions using a transient photocurrent measurement device. The measurement results are summarized in Table 3.

[0075] (Measurement conditions) Equipment: Time-of-flight measurement device TOF-401 (Optel) Excitation light source: Nitrogen laser (337.1 nm) Light pulse width: 1nsec or less Measurement area: 0.04cm 2 Sample temperature: 25℃ Load resistance: 50Ω Electric field strength: 0.25MV / cm

[0076] [Table 3]

[0077] The hole mobility of the comparative compound (EBL-1) is 8.3 × 10 -5 cm 2 / Vs, whereas the hole mobility of the compound having an indolocarbazole ring structure represented by general formula (1) is 1.1 × 10 -4 ~8.3×10 -4 cm 2 / Vs, which is a high value. It can be determined that the hole mobility is superior to that of the comparative compound (EBL-1), which is a known compound. [Example]

[0078] <Evaluation of photoelectric conversion elements> The dark current of a photoelectric conversion element can be evaluated using an element configured as shown in Figure 1. Specifically, the element can be fabricated by depositing an electron blocking layer 3, a photoelectric conversion layer 4, and a cathode (metallic cathode) 5 in this order on an ITO electrode previously formed as a transparent anode 2 on a glass substrate 1. The fabricated element can be used to evaluate the dark current of the photoelectric conversion element.

[0079] <Photoelectric conversion element-1> Specifically, an ITO film was formed on a glass substrate 1 as a transparent anode 2, followed by ultrasonic cleaning in isopropyl alcohol for 20 minutes and drying on a hot plate heated to 200°C for 10 minutes. This was followed by 15 minutes of UV ozone treatment, after which the ITO-coated glass substrate was placed in a vacuum deposition machine and the pressure was reduced to 0.0001 Pa or less. Subsequently, compound (1-3) from Example 1 was deposited to a thickness of 10 nm to form an electron blocking layer (first buffer layer) 3 covering the transparent anode 2. A photoelectric conversion layer 4 was formed on this electron blocking layer (first buffer layer) 3 by binary deposition of a p-type semiconductor (SubPC) having the following structural formula and an n-type semiconductor (C60) having the following structural formula at a deposition rate ratio of p-type semiconductor (SubPC):n-type semiconductor (C60) = 50:50, resulting in a thickness of 200 nm. On this photoelectric conversion layer 4, a cathode (metallic cathode) 5 made of gold was formed to a film thickness of 100 nm. The evaluation results of the fabricated photoelectric conversion element-1 are shown in Table 4.

[0080] [ka]

[0081] [ka] [Example]

[0082] <Photoelectric conversion element-2> Photoelectric conversion element-2 was fabricated under the same conditions as in Example 9, except that compound (1-5) of Example 2 was used as the material for the electron blocking layer (first buffer layer) 3 instead of compound (1-3) of Example 1, and the electrical characteristics were evaluated. The measurement results are summarized in Table 4. [Example]

[0083] <Photoelectric conversion element-3> Photoelectric conversion element-3 was fabricated under the same conditions as in Example 9, except that compound (1-10) of Example 3 was used as the material for electron blocking layer (first buffer layer) 3 instead of compound (1-3) of Example 1, and the electrical characteristics were evaluated. The measurement results are summarized in Table 4. [Example]

[0084] <Photoelectric conversion element-4> Photoelectric conversion element-4 was fabricated under the same conditions as in Example 9, except that compound (1-28) of Example 4 was used instead of compound (1-3) of Example 1 as the material for electron blocking layer (first buffer layer) 3, and the electrical characteristics were evaluated. The measurement results are summarized in Table 4. [Example]

[0085] <Photoelectric conversion element-5> Photoelectric conversion element-5 was fabricated under the same conditions as in Example 9, except that compound (1-33) of Example 5 was used as the material for electron blocking layer (first buffer layer) 3 instead of compound (1-3) of Example 1, and the electrical characteristics were evaluated. The measurement results are summarized in Table 4.

[0086] [Comparative Example 1] <Photoelectric conversion element-6> For comparison, a photoelectric conversion element-6 was fabricated under the same conditions as in Example 9, except that the comparative compound (EBL-1) was used instead of the compound (1-3) in Example 1 as the material for the electron blocking layer (first buffer layer) 3, and the electrical characteristics were evaluated. The measurement results are summarized in Table 4.

[0087] The spectral sensitivity and light current of the photoelectric conversion elements fabricated in Examples 9 to 13 and Comparative Example 1 were measured using a spectral sensitivity measurement device under the following measurement conditions. The irradiance at a specific wavelength during measurement was calibrated using a Si photodiode (S1337-1010BQ, manufactured by Hamamatsu Photonics Co., Ltd.). The dark current was measured under the same bias conditions with the spectral irradiance of the photoelectric conversion element set to zero. The measurement results are summarized in Table 4.

[0088] (Measurement conditions) Equipment: Spectral sensitivity measuring device SM-250A (Bunkokeiki Co., Ltd.) Light source: Xenon 150W Spectral irradiance: 2.0mW / cm 2 (550nm) Effective irradiation area: 10 x 10 mm Light receiving area: 0.04cm 2 In-plane non-uniformity: within ±5% Source meter: Keithley 2635B (Keithley) Applied bias: -1 to -3V

[0089] [Table 4]

[0090] As shown in Table 4, the dark current when −3 V was applied was −9.9E−9 A / cm2 for the device of Comparative Example 1, while it was −6.7E−9 to −4.6E−9 A / cm2 for the devices of Examples 9 to 13. 2 and low values. Furthermore, the conversion efficiency EQE when −3 V was applied was 61% for the device of Comparative Example 1, and was improved to 63 to 66% for Examples 9 to 13. Even when biases of −1 V and −2 V were applied, the devices of Examples 9 to 13 exhibited lower dark currents and higher conversion efficiencies EQE than the device of Comparative Example 1. This indicates that the compound having an indolocarbazole ring structure represented by general formula (1), which is preferably used in the organic thin film of the present invention, has high electron blocking properties and good hole transport properties, and can significantly improve the dark current characteristics and conversion efficiency of photoelectric conversion devices.

[0091] From the above results, it can be seen that a photoelectric conversion element using an organic thin film containing a compound having an indolocarbazole ring structure represented by general formula (1), which is preferably used in the organic thin film of the present invention, has a HOMO level required for an electron blocking layer and high heat resistance, and therefore it is possible to fabricate a photoelectric conversion element with low dark current. [Industrial Applicability]

[0092] The compound having an indolocarbazole ring structure represented by general formula (1), which is preferably used in the organic thin film of the present invention, has high heat resistance and good charge mobility, and therefore, when applied to various photoelectric conversion elements, it can provide photoelectric conversion elements having excellent dark current characteristics and conversion efficiency, such as image sensors, and photosensors using the same. Furthermore, because it has excellent charge transport properties, it can also provide organic devices such as organic solar cells, organic light-emitting diodes, and organic transistors, in addition to photosensors. [Explanation of symbols]

[0093] 1. Glass substrate 2 transparent anode 3. Electron Blocking Layer 4 Photoelectric conversion layer 5 cathode

Claims

1. An organic thin film for use in a photoelectric conversion element, comprising a compound having an indolocarbazole ring structure represented by the following general formula (1): 【Chemistry 1】 （１） In the formula, X and Y may be the same or different and represent a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted aromatic heterocycle, or a divalent group of a substituted or unsubstituted condensed polycyclic aromatic ring. １ ~R ９ may be the same or different and represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, an optionally substituted linear or branched alkyl group of 1 to 6 carbon atoms, an optionally substituted cycloalkyl group of 5 to 10 carbon atoms, an optionally substituted linear or branched alkenyl group of 2 to 6 carbon atoms, an optionally substituted linear or branched alkyloxy group of 1 to 6 carbon atoms, an optionally substituted cycloalkyloxy group of 5 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, or a substituted or unsubstituted aryloxy group, and adjacent R １ ~R ９ They may be bonded to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom, or a sulfur atom to form a ring. １ ~Ar ４ may be the same or different and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted fused polycyclic aromatic group; Ar ３ and Y, Ar ４ and Y, or Ar ３ and Ar ４ may be bonded to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom or a sulfur atom to form a ring.

2. R in the general formula (1) １ ~R ９ is a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted fused polycyclic aromatic group.

3. 3. The organic thin film used in the photoelectric conversion element according to claim 1 or 2, characterized in that X and Y in the general formula (1) are divalent groups obtained by removing two hydrogen atoms from benzene, biphenyl, terphenyl, naphthalene, thiophene, furan, or thienothiophene.

4. 3. The organic thin film used in the photoelectric conversion element according to claim 1, wherein the glass transition temperature of the organic thin film is 160° C. or higher.

5. 3. The organic thin film used in the photoelectric conversion element according to claim 1, wherein the organic thin film has a work function of 5.5 eV or more.

6. 3. The organic thin film used in a photoelectric conversion element according to claim 1, wherein the organic thin film is a blocking layer.

7. 3. The organic thin film used in a photoelectric conversion element according to claim 1, wherein the organic thin film is a photoelectric conversion layer.

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