Compound having an indolocarbazole ring, material for light-receiving element, organic thin film, light-receiving element, and image sensor

Abstract

To provide: a compound utilizing a compound excellent in heat resistance and charge transport; organic devices based on the same, particularly an organic thin film for use in a photodetector; various photodetectors to which the organic thin film is applied, particularly an imaging device; and a photosensor based on the same.SOLUTION: The invention provides a compound having an indolocarbazole ring represented by general formula (1) in the figure. (In the formula, L represents a single bond, or a divalent group of a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group or a substituted or unsubstituted condensed polycyclic aromatic group.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a compound having an indolocarbazole ring, a material for a light-receiving element, an organic thin film, a light-receiving element, and an imaging element. [Background technology]

[0002] Photodetectors 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 mounted on smartphones, but also in driver assistance systems.

[0003] Until now, imaging elements have been made of inorganic materials such as Si films and Se films, and the two main imaging methods were a three-plate type that uses a prism to separate colors, and a single-plate type that uses a color filter. However, while the three-plate type has a high light utilization rate, it is difficult to miniaturize it because it uses a prism, while the single-plate type does not use a prism and is relatively easy to miniaturize, but instead uses a color filter, resulting in poor resolution and light utilization (Non-Patent Document 1).

[0004] Compared to inorganic materials, organic materials absorb light of specific wavelengths better, so by combining materials corresponding to each wavelength, it is possible to construct an imaging element that can efficiently utilize light for each of the three primary colors without using a prism, making it possible to create a compact imaging element with high light utilization efficiency. Furthermore, depending on the material selection, it may be possible to sense not only visible light but also near-infrared and infrared light, and there is also the possibility of adding value such as flexibility and large area by coating during the manufacturing process, which cannot be achieved with inorganic materials (Non-Patent Document 2).

[0005] For these reasons, organic photodetectors are expected to be used in next-generation imaging devices, and several groups have reported on their applications. Examples include the use of quinacridone and quinazoline derivatives in photodetectors (Patent Document 1), benzothienobenzothiophene derivatives in photodetectors (Patent Document 2), and indolocarbazole in photodetectors (Patent Document 3). Image sensors have contrast and power as indicators of their performance, and to improve these characteristics, it is necessary to reduce the current that flows when no light is incident (dark current). One method for reducing this dark current is to insert a hole-blocking layer or electron-blocking layer between the photodetector and the electrode.

[0006] The insertion of hole-blocking or electron-blocking layers is a common technique 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, respectively, and function to rapidly transfer the necessary charges while controlling the reverse movement of holes or electrons.

[0007] Another characteristic required for materials used in blocking layers is thermal stability. Imaging devices, in particular, require higher thermal stability than organic electroluminescence (EL) and other organic electronic devices, due to considerations of application to manufacturing processes involving heating, such as color filter installation, protective film installation, and device soldering, as well as improved shelf life. Patent Document 4 reports that the thermal stability of devices can be improved by using an electron-blocking material with a glass transition temperature (Tg) of 140°C or higher. However, the characteristics were insufficient. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4945146 [Patent Document 2] Japanese Patent Application Publication No. 2018-170487 [Patent Document 3] Japanese Patent Application Publication No. 2018-085427 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-187937 [Patent Document 5] International Publication No. 2012 / 114928 [Non-patent literature]

[0009] [Non-Patent Document 1] Journal of the Institute of Image Information and Communications Technology, 60,3,291 (2006) [Non-patent document 2] Adv. Mater.28,4766(2016) Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a compound having excellent heat resistance and charge transport properties, and to provide an organic device using the compound, particularly an organic thin film used in a light-receiving element, various light-receiving elements, particularly an image sensor, to which the organic thin film is applied, and an optical sensor using the same. [Means for solving the problem]

[0011] To achieve the above object, the present inventors focused on the fact that an indolocarbazole ring has high charge transport properties and also excellent heat resistance. Furthermore, inspired by the fact that highly symmetric compounds tend to have high thermal stability, they conducted extensive research aimed at further improving heat resistance and found that an organic thin film containing a specific compound represented by the following general formula (1) can solve the above problems, thereby completing the present invention.

[0012] That is, the present invention relates to the following items. 1) A compound having an indolocarbazole ring, represented by the following general formula (1):

[0013] [ka] (In the formula, L represents a single bond, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a divalent group of a substituted or unsubstituted fused polycyclic aromatic group; R 1 ~R 9 , R 12 ~R 20 are the same or different and are 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, a optionally substituted cycloalkyl group of 5 to 10 carbon atoms, a optionally substituted linear or branched alkenyl group of 2 to 6 carbon atoms, a optionally substituted linear or branched alkyloxy group of 1 to 6 carbon atoms, a 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, which 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, R 10 , R 11 , R 21 , and R 22 are the same or different and are 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 R 10 and R 11 , R 21 and R22 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) A material for a light-receiving element comprising the compound according to 1). 3) An organic thin film comprising the material for a light-receiving element according to 2). 4) A light-receiving element comprising the organic thin film according to 3). 5) A light-receiving element comprising the organic thin film according to 3) as a blocking layer. 6) A light-receiving element comprising the organic thin film according to 3) as a photoelectric conversion layer. 7) An imaging device including the light receiving element according to any one of 4) to 6). 8) The compound according to 1), wherein L in the general formula (1) is a divalent group of a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted fused polycyclic aromatic group (excluding a pyrimidinylene group). [Effects of the Invention]

[0014] The organic thin film containing the compound having an indolocarbazole ring of the present invention is an organic thin film having excellent heat resistance and charge transport properties and can be applied to various light-receiving elements. As a result, it is possible to provide light-receiving elements, particularly image sensors and photosensors, having excellent dark current characteristics and conversion efficiency. The compound having an indolocarbazole ring of the present invention is suitable as a material for light-receiving elements. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows an example of the configuration of a light-receiving element of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a compound having an indolocarbazole ring represented by the following general formula (1), an organic thin film containing the compound, and a photoelectric conversion element, particularly a light-receiving element, using the organic thin film.

[0017] [ka] (In the formula, L represents a single bond, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a divalent group of a substituted or unsubstituted fused polycyclic aromatic group; R 1 ~R 9 , R 12 ~R 20 are the same or different and are 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, a optionally substituted cycloalkyl group of 5 to 10 carbon atoms, a optionally substituted linear or branched alkenyl group of 2 to 6 carbon atoms, a optionally substituted linear or branched alkyloxy group of 1 to 6 carbon atoms, a 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, which 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, R 10 , R 11 , R 21 , and R 22 are the same or different and are 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 R 10 and R 11 , R 21 and R 22may 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.

[0018] Furthermore, "to" is a term that expresses a range; for example, "5 to 10" means "5 or more and 10 or less," and expresses a range that includes the numerical values ​​written before and after "to."

[0019] The divalent group of 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" in the general formula (1) is not particularly limited, and examples thereof include a phenylene group, a biphenylene group, a terphenylene group, a naphthylene group, an anthracenylene group, a thienylene group, a furanylene group, a phenanthrenylene group, a pyridylene group, a benzofuranylene group, a benzothylene group, etc. Furthermore, it can also be selected from an arylene group having 6 to 30 carbon atoms and a heteroarylene group having 2 to 30 carbon atoms.

[0020] 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" in the 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, a perylenyl group, a fluoren ... Examples of the alkyl group include anthenyl group, triphenylenyl group, pyridyl group, pyrimidinyl group, triazinyl group, furyl group, pyrrolyl group, thienyl group, quinolyl group, isoquinolyl group, benzofuranyl group, benzothienyl group, indolyl group, carbazolyl group, benzoxazolyl group, benzothiazolyl group, quinoxalinyl group, benzimidazolyl group, pyrazolyl group, dibenzofuranyl group, dibenzothienyl group, naphthyridinyl group, phenanthrolinyl group, acridinyl group, carbolinyl group, etc. Furthermore, the alkyl group may be selected from aryl groups having 6 to 30 carbon atoms and heteroaryl groups having 2 to 30 carbon atoms.

[0021] In the "optionally substituted linear or branched alkyl group of 1 to 6 carbon atoms," "optionally substituted cycloalkyl group of 5 to 10 carbon atoms," or "optionally substituted linear or branched alkenyl group of 2 to 6 carbon atoms" in general formula (1), the "linear or branched alkyl group of 1 to 6 carbon atoms," "cycloalkyl group of 5 to 10 carbon atoms," or "linear or branched alkenyl group of 2 to 6 carbon atoms" 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.

[0022] In the "optionally substituted linear or branched alkyloxy group of 1 to 6 carbon atoms" or "optionally substituted cycloalkyloxy group of 5 to 10 carbon atoms" in the general formula (1), there is no particular limitation to the "linear or branched alkyloxy group of 1 to 6 carbon atoms" or the "optionally substituted cycloalkyloxy group of 5 to 10 carbon atoms", 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.

[0023] The "aryloxy group" in the "substituted or unsubstituted aryloxy group" 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 naphthioxyl group, an anthracenyloxy group, and a phenanthrenyloxy group.

[0024] The "substituents" in the "substituted aromatic hydrocarbon group," "substituted aromatic heterocyclic group," "substituted fused polycyclic aromatic group," "substituted methylene group," "optionally substituted linear or branched alkyl group of 1 to 6 carbon atoms," "optionally substituted cycloalkyl group of 5 to 10 carbon atoms," "optionally substituted linear or branched alkenyl group of 2 to 6 carbon atoms," "optionally substituted linear or branched alkyloxy group of 1 to 6 carbon atoms," or "optionally substituted cycloalkyloxy group of 5 to 10 carbon atoms" 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; linear or branched alkyl groups of 1 to 6 carbon atoms such as methyl groups, ethyl groups, and propyl groups; and carbon atoms such as methyloxy groups, ethyloxy groups, and propyloxy groups. linear or branched alkyloxy groups having 1 to 6 carbon atoms; alkenyl groups such as vinyl and allyl; aryloxy groups such as phenyloxy and tolyloxy; arylalkyloxy groups such as benzyloxy and phenethyloxy; aromatic groups such as phenyl, biphenylyl, terphenylyl, naphthyl, anthracenyl, phenanthrenyl, fluorenyl, spirobifluorenyl, indenyl, pyrenyl, perylenyl, fluoranthenyl, and triphenylenyl; aromatic hydrocarbon groups or condensed polycyclic aromatic groups; 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.

[0025] In the present invention, from the viewpoint of heat resistance and charge mobility, L in general formula (1) is preferably a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a divalent group of a substituted or unsubstituted fused polycyclic aromatic group (excluding a pyrimidinylene group), more preferably an unsubstituted aromatic hydrocarbon group, and particularly preferably a phenyl group.

[0026] In addition, from the viewpoint of heat resistance and charge mobility, R 1 From R 22 is preferably a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group, and R 1 ~R 4 , R 6 ~R 9 , R 12 ~R 15 , and R 17 ~R 20 is a hydrogen atom, and R 10 , R 11 , R 21 and R 22 is more preferably an unsubstituted aromatic hydrocarbon group. 1 From R 22 may be the same or different from each other.

[0027] In particular, the compound represented by general formula (1) is R 10 , R 11 , R 21 and R 22 is a phenyl group, a thienyl group, or a methyl group, and R 5 and R 16 is a hydrogen atom or a phenyl group, and R 1 ~R 4 , R 6 ~R 9 , R 12 ~R 15 , and R 17 ~R 20 is preferably a hydrogen atom, and L is preferably a single bond, a phenylene group, a biphenylene group, a naphthylene group, a thienylene group, a furanylene group, or a benzofuranylene group. 1 From R22 may be the same or different from each other.

[0028] Among the compounds having an indolocarbazole ring represented by general formula (1), specific examples of preferred compounds are shown below, but the present invention is not limited to these compounds.

[0029] [ka]

[0030] The above-mentioned compound having an indolocarbazole ring can be synthesized according to a method known per se (for example, Patent Document 5).

[0031] These compounds can be purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization using a solvent, crystallization, etc. The compounds can be identified by NMR analysis. As physical property values, it is preferable to measure the glass transition temperature (Tg) and work function. 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.

[0032] The compound having an indolocarbazole ring represented by the general formula (1) can be used to form an organic thin film by known methods such as vapor deposition, spin coating, and inkjet printing. The compound having an indolocarbazole ring may be used alone to form a film, 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, provided that the effects of the present invention are not impaired.

[0033] The organic thin film containing the compound having an indolocarbazole ring is suitable for use in a light-receiving element, particularly an image sensor. The light-receiving element may have, in order, a first electrode (anode), a first buffer layer, a photoelectric conversion layer, and a second electrode (cathode), with the first buffer layer being an organic thin film containing the compound having an indolocarbazole ring. Additional layers can be added to such a multilayer structure, and the structure may include, for example, a first electrode, a first buffer layer, a photoelectric conversion layer, a second buffer layer, and a second electrode, in order. The organic thin film containing the compound having an indolocarbazole ring can also be used in a photoelectric conversion layer.

[0034] The material constituting the photoelectric conversion layer in a light-receiving element may be either organic or inorganic, as long as it can generate signal charges corresponding to the amount of light received. When the photoelectric conversion layer is made of an organic material, the organic semiconductor film may be a single layer or multiple layers. In the case of a single layer, a p-type organic semiconductor film, an n-type organic semiconductor film, or a mixed film of a p-type organic semiconductor and an n-type organic semiconductor is used. In the case of a multiple layer, a structure in which two or more of a p-type organic semiconductor film, an n-type organic semiconductor film, or a mixed film of a p-type organic semiconductor and an n-type organic semiconductor is stacked, or a bulk heterostructure, and a buffer layer may be inserted between the layers.

[0035] The light-receiving element can obtain stability against thermal loads by using the compound having an indolocarbazole ring in the first buffer layer included in the element. In addition, the high hole mobility improves image retention.

[0036] The p-type semiconductor used in the photoelectric conversion layer is a donor organic semiconductor, which is a compound that has the property of readily donating electrons, and is mainly represented by a hole-transporting organic compound. The p-type semiconductor is not particularly limited, and examples thereof include thienoacene-based materials typified by naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, pentacene derivatives, quinacridone derivatives, chrysene derivatives, fluoranthene derivatives, phthalocyanine derivatives, subphthalocyanine derivatives, metal complexes having a heterocyclic compound as a ligand, 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.

[0037] The n-type organic semiconductor used in the photoelectric conversion layer is an acceptor organic semiconductor, which refers to an organic compound that has a tendency to accept electrons, mainly represented by an electron-transporting organic compound. More specifically, it refers to the organic compound that has a larger electron affinity when two organic compounds are contacted. Therefore, any organic compound that has electron-accepting properties can be used as the acceptor organic compound. For example, condensed aromatic carbocyclic compounds (naphthalene, anthracene, fullerene, phenanthrene, tetracene, pyrene, perylene, perylene diimide, fluoranthene, or derivatives thereof), quinacridone, 5- to 7-membered heterocyclic compounds containing nitrogen, oxygen, or sulfur atoms (e.g., pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole, imidazoline, etc.) are suitable. Examples of suitable acceptor organic semiconductors include metal complexes having as a ligand a compound selected from the group consisting of tetraazoindene, 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 to these, 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, as described above.

[0038] The anode and cathode may be made of any conductive material that is generally used as an electrode, without any particular limitation. Examples include 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; titanium oxynitride (TiN); xO x metal nitrides such as gold (Au), platinum (Pt), silver (Ag), chromium (Cr), nickel (Ni), and aluminum (Al); mixtures or laminates of these metals with conductive metal oxides; organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and laminates of these organic conductive compounds with ITO.

[0039] A second buffer layer may be inserted between the second electrode (cathode) and the photoelectric conversion layer, and the material used therefor preferably has a work function greater than that of the material used for the first buffer layer. Examples include organic compounds and organometallic complexes containing nitrogen-containing heterocycles such as pyridine, quinoline, acridine, indole, imidazole, benzimidazole, and phenanthroline, and materials with low absorption in the visible light region are preferred. Furthermore, when forming a thin film of approximately 5 to 20 nm, fullerenes and their derivatives that absorb light in the visible light region can also be used. [Example]

[0040] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0041] [Example 1] <Synthesis of 5,5'-bi(11,12-diphenylindolo[2,3-a]carbazole) (Compound 1-1)> A reaction vessel was charged with 3.71 g of 5-bromo-11,12-diphenylindolo[2,3-a]carbazole, 4.49 g of 11,12-diphenyl-5-(4,4,5,5-tetramethyl-[1,3,2]dioxaboran-2-yl)-indolo[2,3-a]carbazole, 1.60 g of potassium carbonate, 70 mL of toluene, 11 mL of water, and 18 mL of ethanol. After degassing, 0.189 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux and stirred for 6 hours. After cooling, 100 mL of brine was added and the organic layer was separated. Anhydrous magnesium sulfate, 7.0 g of silica, and 7.0 g of activated clay were added to the organic layer, stirred, and filtered to remove inorganic components. After concentration, the resulting crude was crystallized by adding 20 mL of tetrahydrofuran and 50 mL of diisopropyl ether. The solid obtained by filtration was repeatedly crystallized using tetrahydrofuran and diisopropyl ether to obtain 4.37 g (yield 64%) of white powder of 5,5'-bi(11,12-diphenylindolo[2,3-a]carbazole).

[0042] The structure of the obtained white powder was identified using NMR. 1 H-NMR (CDCl3) at 50°C detected the following 38 hydrogen signals. δ(ppm)=8.33(2H),8.15(2H),7.38-7.25(6H),7.25-7.11(14H),7.08(2H),6.95-6.90(8H),6.89(2H),6.72(2H).

[0043] [Example 2] <Synthesis of 1,4-bis(11,12-diphenylindolo[2,3-a]carbazol-5-yl)benzene (Compound 1-2)> A reaction vessel was charged with 11.0 g of 5-bromo-11,12-diphenylindolo[2,3-a]carbazole, 1.80 g of benzene-1,4-diboronic acid, 4.45 g of potassium carbonate, 150 mL of 1,4-dioxane, and 50 mL of water. After degassing, 0.625 g of tetrakis(triphenylphosphine)palladium was added and heated under reflux and stirred for 12.5 hours. After cooling, 150 mL of methanol was added, and the precipitated solid was collected by filtration. This solid was dissolved in 100 mL of 1,2-dichlorobenzene with heating, and 10 g of silica and 10 g of activated clay were added and stirred. After stirring for 30 minutes, the mixture was filtered while hot to remove inorganic components. 200 mL of methanol and a small amount of ethyl acetate were added to the filtrate, and the precipitated solid was collected. This solid was repeatedly crystallized using 1,2-dichlorobenzene and ethyl acetate to obtain 1.72 g (yield 18%) of a white powder of 1,4-bis(11,12-diphenylindolo[2,3-a]carbazol-5-yl)benzene.

[0044] The structure of the obtained white powder was identified using NMR. 1 H-NMR (CDCl3) at 60°C detected the following 42 hydrogen signals. δ(ppm)=8.23(2H),8.16(2H),8.01(4H),7.81(2H),7.36-7.26(10H),7.21-7.10(14H),6.88-6.81(8H).

[0045] [Example 3] <Synthesis of 1,3-bis(11,12-diphenylindolo[2,3-a]carbazol-5-yl)benzene (Compound 1-3)> The same procedure as in Example 2 was repeated, except that benzene-1,3-diboronic acid was used instead of benzene-1,4-diboronic acid, to obtain 1.96 g (yield 20%) of a white powder of 1,3-bis(11,12-diphenylindolo[2,3-a]carbazol-5-yl)benzene.

[0046] The structure of the obtained white powder was identified using NMR. 1H-NMR (CDCl3) at 50°C detected the following 42 hydrogen signals. δ(ppm)=8.23-8.09(5H),7.96(2H),7.85-7.78(3H),7.34-7.03(24H),6.84-6.74(8H).

[0047] [Example 4] <Measurement of glass transition temperature> The glass transition temperatures of compound (1-1) of Example 1, compound (1-2) of Example 2, and compound (1-3) of Example 3 were measured using a high-sensitivity differential scanning calorimeter (DSC3100SA, manufactured by Bruker AXS). The glass transition temperatures of compounds with high glass transition temperatures, EBL-1 (see Patent Document 1) and EBL-2 (see Patent Document 3), which have the following structures, were also measured in the same manner. The results of the measured glass transition temperatures are summarized in Table 1.

[0048] [ka]

[0049] [ka]

[0050] [Table 1]

[0051] The glass transition temperatures of compounds (1-1) to (1-3) are high, at 190°C or higher, indicating that they are stable in thin film form. The glass transition temperatures of compounds (1-1) to (1-3) are also higher than those of EBL-1 and EBL-2, indicating that devices with better thermal stability can be fabricated by using compounds (1-1) to (1-3) instead of EBL-1 and EBL-2.

[0052] [Example 5] <Work function measurement> Using compound (1-1) of Example 1, compound (1-2) of Example 2, compound (1-3) of Example 3, and comparative compounds (EBL-1) and (EBL-2), vapor-deposited films with a thickness of 100 nm were prepared on ITO substrates, and the work functions were measured using an ionization potential measurement device (Sumitomo Heavy Industries, Ltd., PYS-202). The measurement results are summarized in Table 2.

[0053] [Table 2]

[0054] The compounds (1-1) to (1-3) have a favorable energy level compared to the work function of 5.3 to 6.0 eV of hole transport materials such as carbazole compounds, which are considered to be suitable materials, and it is clear that they have good hole transport ability. It is also clear that the work function can be easily adjusted.

[0055] [Example 6] <Hall mobility measurement> Using compounds (1-1) to (1-3) and comparative compounds (EBL-1) and (EBL-2), the organic compounds to be measured were deposited on a glass substrate with an ITO coating by vacuum deposition to a thickness of 3 to 4 μm. Subsequently, an aluminum film was deposited to a thickness of approximately 100 nm to prepare a device for measuring Hall mobility. This device was sealed in a nitrogen atmosphere with a glass cap to which an organic EL moisture getter sheet had been attached to prevent deterioration due to adsorption of moisture and oxygen.

[0056] Using this device, hole mobility was measured under the following conditions using a transient photocurrent measurement device. The measurement results are summarized in Table 3.

[0057] (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

[0058] [Table 3]

[0059] The Hall mobility of compounds (1-1) to (1-3) is 2.9 × 10 -5 ~3.9×10 -4 cm 2 This is a value equivalent to that of EBL-2 used for a similar purpose in Patent Document 3, and it can be determined that the hole mobility is sufficient.

[0060] [Example 7] <Evaluation of hole-only devices (HODs)> A 50-nm thick molybdenum oxide film was formed on a glass substrate with an ITO electrode as a transparent anode by vacuum deposition, and 100-nm thick films of compounds (1-1) to (1-3) and comparative compound (EBL-1) were then formed on the hole injection layer by vacuum deposition. Subsequently, a 100-nm thick Al film was deposited on the cathode to prepare an HOD.

[0061] The leakage current of the fabricated HODs was measured using a source meter (Keithley 2635B, manufactured by Keithley) when a voltage of -3 V was applied. Furthermore, these HODs were heated on a hot plate at 190°C for 3 hours in a glove box under a nitrogen atmosphere, and then the leakage current was measured in the same manner. The measurement results are summarized in Table 4.

[0062] [Table 4]

[0063] Image sensors are exposed to heat of 180 to 190°C during device fabrication, and must be able to withstand this. Compounds (1-1) to (1-3) have lower leakage currents when a voltage of -3V is applied than comparative compounds (EBL-1) and (EBL-2). Furthermore, even after heating, the increase in leakage current is suppressed. This demonstrates that the compounds of the present invention have good hole transport capability and also have high heat resistance.

[0064] That is, an organic thin film containing the compound of the present invention is an organic thin film having excellent heat resistance and charge transport properties, and can be applied to various photoelectric conversion elements, particularly light-receiving elements.

[0065] [Example 8] <Evaluation of light receiving elements> As shown in Figure 1, the light-receiving element was fabricated by vapor-depositing a first buffer layer 3, a photoelectric conversion layer 4, and a metal cathode 5 in this order on a glass substrate 1 on which an ITO electrode had previously been formed as a transparent anode 2.

[0066] Specifically, a glass substrate 1 on which an ITO film serving as a transparent anode 2 had been formed was subjected to ultrasonic cleaning in isopropyl alcohol for 20 minutes, followed by drying for 10 minutes on a hot plate heated to 200°C. 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 (1-1) of Example 1 was vapor-deposited to a thickness of 5 nm to form a first buffer layer 3 covering the transparent anode 2. A photoelectric conversion layer 4 was formed on this first buffer layer 3 by binary vapor 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 vapor deposition rate ratio of SubPC:C60 = 50:50, resulting in a thickness of 100 nm. Gold was then formed on this photoelectric conversion layer 4 as a metal cathode 5 to a thickness of 100 nm. The evaluation results of the fabricated photodetectors are summarized in Table 5.

[0067] [ka]

[0068] [ka]

[0069] [Example 9] A light-receiving element was fabricated in the same manner as in Example 8, except that compound (1-2) was used instead of compound (1-1) as the material for the first buffer layer 3, and the electrical characteristics were evaluated. The measurement results are summarized in Table 5.

[0070] [Example 10] A light-receiving element was fabricated in the same manner as in Example 8, except that compound (1-3) was used instead of compound (1-1) as the material for the first buffer layer 3, and the electrical characteristics were evaluated. The measurement results are summarized in Table 5.

[0071] [Comparative Example 1] For comparison, a light-receiving element was fabricated in the same manner as in Example 8, except that EBL-1 was used instead of compound (1-1) as the material for the first buffer layer 3, and the electrical characteristics were evaluated. The measurement results are summarized in Table 5.

[0072] The spectral sensitivities and light currents of the organic light-receiving elements fabricated in Examples 8 to 10 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 to the light-receiving element set to zero.

[0073] (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

[0074] [Table 5]

[0075] As shown in Table 5, the dark current when −3 V was applied was −5.4×10 -7 A / cm 2 In contrast, the elements of Examples 8 to 10 were −6.5×10 -9 ~-1.2×10 -8 A / cm 2 , which is an order of magnitude lower. Furthermore, the conversion efficiency EQE when -3 V was applied was 58% for the device of Comparative Example 1, and was improved to 63-66% for Examples 8-10. Even when a bias voltage of -1 V and -2 V was applied to the device, the devices of Examples 8-10 exhibited lower dark currents and higher conversion efficiencies EQE than the device of Comparative Example 1. This indicates that the high electron-blocking properties and favorable hole-transporting properties of the compounds of the present invention can significantly improve the dark current characteristics and conversion efficiency of the light-receiving device.

[0076] As is clear from the above results, the compound of the present invention has a HOMO value, high heat resistance, and sufficiently high mobility required for the blocking layer of an organic photoelectric conversion element, and can be suitably used particularly as a material for a light-receiving element. [Industrial Applicability]

[0077] The organic thin film provided by the present invention, which has high heat resistance and good charge mobility, can be applied to various photoelectric conversion elements, and therefore can provide a light-receiving element, particularly an image sensor, having good dark current characteristics and conversion efficiency, and a photosensor using the same. Furthermore, because the organic thin film 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.

Claims

1. A compound having an indolocarbazole ring, represented by the following general formula (1): 【Chemistry 1】 (In the formula, L represents a divalent unsubstituted aromatic hydrocarbon group; R １ ~R ９ , R １２ ~R ２０ may be the same or different and represent a hydrogen atom or a deuterium atom, R １０ , R １１ , R ２１ , and R ２２ may be the same or different and represent an unsubstituted aromatic hydrocarbon group.

2. A material for a light-receiving element, comprising the compound according to claim 1.

3. An organic thin film comprising the material for a light-receiving element according to claim 2 .

4. A light-receiving element comprising the organic thin film according to claim 3 .

5. A light-receiving element comprising the organic thin film according to claim 3 as a blocking layer.

6. A light-receiving element comprising the organic thin film according to claim 3 as a photoelectric conversion layer.

7. An imaging device comprising the light receiving element according to any one of claims 4 to 6.

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