Organic thin film used for a photoelectric conversion element, and the photoelectric conversion element

Abstract

The main purpose of the present invention is to provide: an organic thin film which utilizes a compound that has excellent heat resistance and charge transport properties, and which is applicable to various photoelectric conversion elements; a photoelectric conversion element which uses this organic thin film; and an imaging element.　The present invention provides: an organic thin film which contains a compound that has an indenophenanthrene ring structure represented by general formula (1); and a photoelectric conversion element which uses this organic thin film. (In the formula, A represents a single bond, a divalent substituted or unsubstituted aromatic hydrocarbon group, or the like; each of Ar1 and Ar2 represents a substituted or unsubstituted aromatic hydrocarbon group or the like; each of R1 to R11 represents a hydrogen atom, an optionally substituted linear or branched alkyl group having from 1 to 6 carbon atoms, or the like; and each of R12 and R13 represents an optionally substituted linear or branched alkyl group having from 1 to 6 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group, or the like.)

Description

Technical Field

[0001] The present invention relates to an organic thin film used for a photoelectric conversion element and the photoelectric conversion element, and more particularly to an organic thin film containing a compound having an indenophenanthrene ring structure, various photoelectric conversion elements using the organic thin film, and particularly an imaging element.

Background Art

[0002] Photoelectric conversion elements are widely used in, for example, solar cells and optical sensors. Among them, image sensors, which are imaging elements, are starting to be used not only in television cameras and cameras mounted on smartphones but also in applications such as driving assistance systems, and both the applications and the market are expanding.

[0003] In the materials of conventional imaging elements, inorganic materials such as Si films and Se films have been used, and as the imaging methods, there are two main types: a three-plate type that separates colors using a prism and a single-plate type that uses a color filter. However, although the three-plate type has a high light utilization rate, it is difficult to miniaturize because a prism is used. The single-plate type is relatively easy to miniaturize because it does not use a prism, but instead uses a color filter, so the resolution and light utilization rate are poor (Non-Patent Document 1).

[0004] Since organic substances absorb light of a specific wavelength better than inorganic substances, it is possible to construct an imaging element that can efficiently utilize light for each of the three primary colors without using a prism by combining materials suitable for each wavelength. Therefore, the light utilization efficiency is high, and it is possible to manufacture a small imaging element. In addition, there is a possibility of adding values such as flexibility and large-area formation by coating in the manufacturing process, which cannot be achieved with inorganic substances (Non-Patent Document 2).

[0005] For these reasons, organic photoelectric conversion elements are expected to be developed for next-generation imaging devices, and reports have been made by several groups. For example, there are examples of using quinacridone derivatives or quinazoline derivatives in photoelectric conversion elements (Patent Document 1), examples of using benzothieno[3,2-b]benzothiophene derivatives in photoelectric conversion elements (Patent Document 2), examples of using indolocarbazole in photoelectric conversion elements (Patent Document 3), and so on.

[0006] Generally, organic imaging devices are considered to improve their performance by aiming to reduce dark current for the purpose of high contrast and power saving. To reduce dark current, a method of inserting a hole-blocking layer or an electron-blocking layer between the photoelectric conversion part and the electrode part may be used.

[0007] The hole-blocking layer and the electron-blocking layer are generally used methods in the field of organic electronics. They are respectively arranged at the interface between the electrode or the conductive film and the other films in the constituent films of the device, and have the function of quickly moving the necessary charges while controlling the reverse movement of holes or electrons.

[0008] In addition, thermal stability is cited as a characteristic required for electron-blocking materials. Especially in imaging devices, considering application to manufacturing processes with heating steps such as installing a color filter, installing a protective film, soldering the element, etc., and improving storage stability, higher thermal stability is required than other organic electronics devices. Patent Document 4 reports that the thermal stability of the device is improved by using an electron-blocking material with a glass transition temperature (Tg) of 140°C or higher. However, the compounds proposed here had a problem of a decrease in hole transport ability due to steric hindrance.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

[0010] [Non-Patent Document 1] Journal of the Image Information and Television Engineers Society, 60, 3, 291 (2006) [Non-Patent Document 2] Adv. Mater., 28, 4766 (2016) [Summary of the Invention]

[0011] The present invention has been made in view of such circumstances, and an object thereof is to provide an organic thin film for use in a photoelectric conversion element using a compound having excellent heat resistance and charge transport properties, and various photoelectric conversion elements using the organic thin film, particularly an imaging element, and an optical sensor using the same.

[0012] In order to achieve the above object, the present inventors focused on the fact that a compound having an indenophenanthrene ring structure has high charge transport properties and further excellent heat resistance, and conducted intensive development aiming at further improvement of heat resistance. As a result, it was found that an organic thin film containing a specific compound represented by the following general formula (1) solves the above problems, and the present invention has been completed.

[0013] That is, the present invention relates to the following items. 1) An organic thin film for use in a photoelectric conversion element, wherein the organic thin film is an organic thin film containing a compound having an indenophenanthrene ring structure represented by the following general formula (1).

[0014] [Chemical Formula] (wherein A represents a single bond, a divalent substituted or unsubstituted aromatic hydrocarbon group, a divalent substituted or unsubstituted aromatic heterocyclic group, or a divalent substituted or unsubstituted condensed polycyclic aromatic group, Ar1 and Ar2 may be the same as or different from each other, and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted condensed polycyclic aromatic group, A, Ar1 and Ar2 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, R1 to R 11 may be the same as or different from each other, and represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 10 carbon atoms which may have a substituent, a linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent, a linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent, 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, R1 to R 11 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 12 and R 13 may be the same as or different from each other, and represent a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 10 carbon atoms which may have a substituent, a linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent, a linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent, 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, R 12 and R 13 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.)

[0015] 2) The organic thin film according to 1), wherein the compound having an indenophenanthrene ring structure represented by the general formula (1) is a compound having an indenophenanthrene ring structure represented by the following general formula (2).

[0016]

Chemical formula

[0017] 3) The organic thin film according to 1), wherein the compound having an indenophenanthrene ring structure represented by the general formula (1) is a compound having an indenophenanthrene ring structure represented by the following general formula (3).

[0018]

Chemical formula

[0019] 4) A photoelectric conversion element in which at least an anode, a buffer layer, a photoelectric conversion layer, and a cathode are laminated in this order, and having a layer made of the organic thin film according to any one of 1) to 3).

[0020] 5) The photoelectric conversion element according to 4), wherein the layer made of the organic thin film is a buffer layer.

[0021] 6) The photoelectric conversion element according to 4), wherein the layer made of the organic thin film is a photoelectric conversion layer.

[0022] 7) An imaging device having the photoelectric conversion element according to any one of 4) to 6).

[0023] The organic thin film containing the compound having the indenophenanthrene ring structure represented by the general formula (1) 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. Thereby, a photoelectric conversion element having good dark current characteristics and conversion efficiency, particularly an imaging device, and an optical sensor using the same can be provided.

Brief Description of the Drawings

[0024]

Figure 1

Embodiments for Carrying Out the Invention

[0025] The present invention is a photoelectric conversion element characterized by using an organic thin film containing a compound having the indenophenanthrene ring structure represented by the general formula (1) for a photoelectric conversion element and using the organic thin film.

[0026] Examples of the “divalent substituted or unsubstituted aromatic hydrocarbon group”, “divalent substituted or unsubstituted aromatic heterocyclic group”, or “divalent substituted or unsubstituted condensed polycyclic aromatic group” in the general formula (1) include a phenylene group, a biphenylene group, a terphenylene group, a naphthylene group, an anthracenylene group, a thienylene group, a furanylene group, and a phenanthrenylene group. Further, 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.

[0027] In the “substituted or unsubstituted aromatic hydrocarbon group”, “substituted or unsubstituted aromatic heterocyclic group”, or “substituted or unsubstituted condensed polycyclic aromatic group” in the general formula (1) above, examples of the “aromatic hydrocarbon group”, “aromatic heterocyclic group” or “condensed polycyclic aromatic group” include phenyl group, biphenylyl group, terphenylyl group, naphthyl group, anthracenyl group, phenanthrenyl group, fluorenyl group, spirobifluorenyl group, indenyl group, pyrenyl group, perylenyl group, fluoranthenyl 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 and carbolinyl group, etc. Further, it can also be selected from an aryl group having 6 to 30 carbon atoms and a heteroaryl group having 2 to 30 carbon atoms.

[0028] In the “linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent”, “cycloalkyl group having 5 to 10 carbon atoms which may have a substituent” or “linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent” in the general formula (1) above, examples of the “linear or branched alkyl group having 1 to 6 carbon atoms”, “cycloalkyl group having 5 to 10 carbon atoms”, or “linear or branched alkenyl group having 2 to 6 carbon atoms” include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, cyclopentyl group, cyclohexyl group, 1-adamantyl group, 2-adamantyl group, vinyl group, allyl group, isopropenyl group and 2-butenyl group, etc.

[0029] The "linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent" or "cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent" in the general formula (1) above, the "linear or branched alkyloxy group having 1 to 6 carbon atoms" or "cycloalkyloxy group having 5 to 10 carbon atoms" may 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, a 2-adamantyloxy group, and the like.

[0030] The "aryloxy group" in the "substituted or unsubstituted aryloxy group" in the general formula (1) above may include aryloxy groups having 6 to 30 carbon atoms such as a phenyloxy group, a biphenylyloxy group, a terphenylyloxy group, a naphthyloxyl group, an anthracenyloxy group, and a phenanthrenyloxy group.

[0031] In the “substituted aromatic hydrocarbon group”, “substituted aromatic heterocyclic group”, “substituted condensed polycyclic aromatic group”, “substituted methylene group”, “linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent”, “cycloalkyl group having 5 to 10 carbon atoms which may have a substituent”, “linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent”, “linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent”, or “cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent” in the general formula (1) above, examples of the “substituent” include a deuterium atom, a cyano group, a nitro group; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, an iodine atom; a silyl group such as a trimethylsilyl group, a triphenylsilyl group; a linear or branched alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group; a linear or branched alkyloxy group having 1 to 6 carbon atoms such as a methyloxy group, an ethyloxy group, a propyloxy group; an alkenyl group such as a vinyl group, an allyl group; an aryloxy group such as a phenyloxy group, a tolyloxy group; an arylalkyloxy group such as a benzyloxy group, a phenethyloxy group; an aromatic hydrocarbon group or a condensed polycyclic aromatic group such as 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 fluoranthenyl group, a triphenylenyl group; an aromatic heterocyclic group 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, a carbolinyl group, and these substituents may be further substituted with the substituents exemplified above.

[0032] In the present invention, since the synthesis is easy, it is preferable that R1 to R in the general formula (1) above 11 are hydrogen atoms.

[0033] Also, from the viewpoints of heat resistance and charge mobility, Ar1 and Ar2 are preferably substituted or unsubstituted aromatic hydrocarbon groups, and R 12 and R 13 are preferably a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, or a substituted or unsubstituted aromatic hydrocarbon group. Incidentally, R 12 and R 13 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.

[0034] From the viewpoints of heat resistance and charge mobility, as one of the preferred embodiments in the present invention, Ar1 and Ar2 in the above general formula (1) are substituted or unsubstituted aromatic hydrocarbon groups, and a compound in which they are 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 can be mentioned. In particular, a compound in which Ar1 and Ar2 are unsubstituted aromatic hydrocarbon groups and are bonded to each other via a single bond to form a ring is preferable.

[0035] As the compound in which Ar1 and Ar2 in the above general formula (1) are substituted or unsubstituted aromatic hydrocarbon groups and Ar1 and Ar2 are bonded to each other via a single bond to form a ring, a compound represented by the above general formula (2) can be mentioned. In particular, a compound in which A in the above general formula (2) is a single bond is preferable, and specifically, Exemplified Compounds 1-16, 1-20, 1-39, 1-61, 1-62, 1-63, 1-64, 1-65 and 1-66 can be mentioned.

[0036] A and R1 to R 13 in the above general formula (2) are the same as the definitions of R1 to R 13 in the above general formula (1), and R 14 to R 21 are the same as the definitions of R1 to R 11 in the above general formula (1). That is, as all the substituents related to the above general formula (2), the groups exemplified in the description of the above general formula (1) can be mentioned.

[0037] In the present invention, from the viewpoints of heat resistance and mobility, R in the general formula (2) 12 and R 13 are preferably a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, or a substituted or unsubstituted aromatic hydrocarbon group, more preferably a linear or branched alkyl group having 1 to 6 carbon atoms or an unsubstituted aromatic hydrocarbon group, and particularly preferably an unsubstituted aromatic hydrocarbon group. Note that R 12 and R 13 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.

[0038] Also, from the viewpoint of easy synthesis, R1 to R 11 and R 14 to R 21 in the general formula (2) are preferably hydrogen atoms.

[0039] From the viewpoints of heat resistance and charge mobility, as one of the preferred embodiments in the present invention, A in the general formula (1) is a substituted or unsubstituted aromatic hydrocarbon group, and compounds in which A and Ar1, or A and Ar2 are bonded to each other via a single bond to form a ring are exemplified. Such compounds include the compounds represented by the general formula (3). More specifically, exemplified compounds 1-2, 1-6, 1-7, 1-12, 1-23, 1-25, 1-26, 1-31, 1-44, 1-47 and 1-48 are included.

[0040] Ar in the general formula (3) has the same definition as Ar1 and Ar2 in the general formula (1), R1 to R 13 has the same definition as R1 to R 13 in the general formula (1), and R 14 to R 20 has the same definition as R1 to R 11 in the general formula (1). That is, as all the substituents related to the general formula (3), the groups exemplified in the description of the general formula (1) are included.

[0041] In the present invention, from the viewpoints of heat resistance and charge mobility, Ar in the general formula (3) is preferably a substituted or unsubstituted aromatic hydrocarbon group, more preferably an aryl group having 6 to 30 carbon atoms, and particularly preferably an aryl group having 6 to 18 carbon atoms.

[0042] From the same viewpoints, R in the general formula (3) 12 and R 13 are preferably a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent or a substituted or unsubstituted aromatic hydrocarbon group, and more preferably a linear or branched alkyl group having 1 to 6 carbon atoms or an unsubstituted aromatic hydrocarbon group. Note that R 12 and R 13 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.

[0043] Further, since the synthesis is easy, R1 to R 11 and R 14 to R 20 in the general formula (3) are preferably hydrogen atoms.

[0044] Among the compounds having an indenophenanthrene ring structure represented by the general formula (1), specific examples of preferred compounds are shown below, but the present invention is not limited to these compounds.

[0045]

Chemical formula

[0046]

Chemical formula

[0047]

Chemical formula

[0048]

Chemical formula

[0049]

Chem.

[0050]

Chem.

[0051] The compounds having the above-mentioned indeno[1,2-b]phenanthrene ring structure can be synthesized according to methods known per se (for example, Patent Document 5).

[0052] These compounds can be purified by purification by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization with a solvent, crystallization method, etc. The identification of the compounds can be carried out by NMR analysis. As physical property values, it is preferable to measure the glass transition point (Tg) and the work function. The glass transition point (Tg) is an index of the stability in the thin film state, and the work function is an index of the hole transport property.

[0053] The glass transition point (Tg) can be determined using a powder by a high-sensitivity differential scanning calorimeter (manufactured by Bruker AXS, DSC3100SA).

[0054] The work function can be determined by forming a 100-nm thin film on an ITO substrate and using an ionization potential measuring device (manufactured by Sumitomo Heavy Industries, Ltd., PYS-202).

[0055] The compound having an indenophenanthrene ring structure represented by the above general formula (1) can form an organic thin film by known methods such as vapor deposition method, spin coating method, and inkjet method. Further, the compound having an indenophenanthrene ring structure represented by the above general formula (1) may form a film alone, but can also form a film by mixing a plurality of types. Furthermore, within a range not impairing the effects of the present invention, it can also form a film by mixing with other compounds.

[0056] The organic thin film containing the compound having an indenophenanthrene ring structure represented by the above general formula (1) is suitable for use in a photoelectric conversion element, particularly an imaging element. As a configuration of the photoelectric conversion element, for example, it has a first electrode (anode), a first buffer layer, a photoelectric conversion layer, and a second electrode (cathode) in this order, and a configuration in which the first buffer layer is an organic thin film containing the compound having an indenophenanthrene ring structure represented by the above general formula (1) can be mentioned. In such a multilayer structure, it is possible to add layers. For example, it can also be configured to have a first electrode, a first buffer layer, a photoelectric conversion layer, a second buffer layer, and a second electrode in this order. Further, the organic thin film containing the compound having an indenophenanthrene ring structure represented by the above general formula (1) can also be used for the photoelectric conversion layer.

[0057] The photoelectric conversion layer in the photoelectric conversion element of the present invention may be made of an organic material or an inorganic material, as long as it can generate signal charges corresponding to the amount of received light. When the photoelectric conversion layer is made of an organic material, the organic semiconductor film may be a single layer or a plurality of 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 (bulk heterostructure) is used. In the case of a plurality of layers, it is a structure in which any 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 are laminated, and it is also possible to insert a buffer layer between the layers.

[0058] By using a compound having an indenophenanthrene ring structure represented by the general formula (1) in the organic thin film serving as the first buffer layer contained in the element, the photoelectric conversion element of the present invention can obtain stability against the heat load.

[0059] The p-type organic semiconductor used in the photoelectric conversion layer is a donor-type organic semiconductor and is a compound having a property of easily donating electrons, mainly represented by hole-transporting organic compounds. Examples of the p-type organic semiconductor include 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 heterocyclic compounds as ligands, benzothiophene derivatives, dinaphthothienothiophene derivatives, dianthracenothienothiophene derivatives, benzobisbenzothiophene derivatives, thienobisbenzothiophene, dibenzothienobisbenzothiophene derivatives, dithienobenzodithiophene derivatives, dibenzothienodithiophene derivatives, benzodithiophene derivatives, naphthodithiophene derivatives, anthracenodithiophene derivatives; tetracenodithiophene derivatives, pentacenodithiophene derivatives, and other thienoacene-based materials represented by them; amine-based derivatives such as triarylamine compounds and carbazole compounds; indenocarbazole derivatives, and the like.

[0060] The n-type organic semiconductor used in the photoelectric conversion layer is an acceptor-type organic semiconductor, which is mainly an organic compound having a property of easily accepting electrons typified by an electron-transporting organic compound. More specifically, it is an organic compound with a larger electron affinity when two organic compounds are brought into contact. Therefore, any organic compound can be used as the n-type organic semiconductor as long as it is an organic compound with electron-accepting properties. For example, condensed aromatic carbocyclic compounds (naphthalene, anthracene, fullerene, phenanthrene, tetracene, pyrene, perylene, fluoranthene, or derivatives thereof); 5- to 7-membered heterocyclic compounds containing nitrogen atoms, oxygen atoms, or sulfur atoms (e.g., pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole, imidazole, thiazole, oxazole, indazole, benzimidazole, benzotriazole, benzoxazole, benzothiazole, carbazole, purine, triazolopyridazine, triazolopyrimidine, tetrazaindene, oxadiazole, imidazopyridine, pyralidine, pyrrolopyridine, thiadiazolopyridine, dibenzazepine, tribenzazepine, etc.); polyarylene compounds; fluorene compounds; cyclopentadiene compounds; silyl compounds; metal complexes having a nitrogen-containing heterocyclic compound as a ligand, and the like. Note that it is not limited thereto, and as described above, any organic compound with a larger electron affinity than the organic compound used as the donor-type organic compound can be used as the acceptor-type organic semiconductor.

[0061] As the anode and cathode, any material can be used as long as it is a conductive material generally 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; titanium oxynitride (TiN x O xand metal nitrides such as titanium nitride (TiN); metals such as gold (Au), platinum (Pt), silver (Ag), chromium (Cr), nickel (Ni), and aluminum (Al), and mixtures or laminates of these metals and conductive metal oxides; organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, and laminates of these and ITO, etc.

[0062] The second buffer layer may be inserted between the second electrode (cathode) and the photoelectric conversion layer, and as the material used for this, a material having a work function value larger than the material used for the first buffer layer is preferable. For example, organic molecules and organometallic complexes containing a nitrogen-containing heterocyclic ring such as pyridine, quinoline, acridine, indole, imidazole benzimidazole, and phenanthroline, and materials having less absorption in the visible light region are preferable. Also, when forming a thin film of about 5 nm to 20 nm, fullerenes and their derivatives having absorption in the visible light region can also be used.

Example

[0063] Hereinafter, embodiments of the present invention will be specifically described by examples, but the present invention is not limited to the following examples.

[0064] [Example 1] <Synthesis of 11-(3,6-Diphenylcarbazol-9-yl)-13,13-diphenylindenol[1,2-I]phenanthrene (Compound 1-35)> Into a reaction vessel purged with nitrogen, 50.0 g of methyl 3-bromoanthranilate, 124.0 g of p-toluenesulfonic acid hydrate, and 500 ml of acetonitrile were added, and the mixture was cooled to 0 °C. 22.5 g of sodium nitrite was added, and the mixture was stirred for 1 hour. After adding 72.2 g of potassium iodide, the mixture was stirred at room temperature. The reaction solution was concentrated, ethyl acetate was added, and liquid separation was performed. The organic layer was washed with an aqueous sodium thiosulfate solution and saturated brine, dehydrated with anhydrous sodium sulfate, and then concentrated under reduced pressure to obtain a crude product. The crude product was purified by column chromatography (carrier: silica gel, eluent: chloroform / n-hexane) to obtain 71.2 g (yield 96.1%) of a light purple powder of methyl 5-bromo-2-iodobenzoate.

[0065] Into a reaction vessel purged with nitrogen, 50.0 g of 9-bromophenanthrene, 54.3 g of bis(pinacolato)diboron, 28.6 g of potassium acetate, and 500 ml of 1,4-dioxane were added. After nitrogen bubbling, 1.59 g of 1,1'-bis(diphenylphosphino)ferrocene dichloropalladium(II) dichloromethane adduct was added, and the mixture was stirred at 90 °C for 6.5 hours. The reaction solution was concentrated, toluene and water were added, and the mixture was stirred at 80 °C. After hot filtration using a filter aid, the filtrate was subjected to liquid separation. The organic layer was washed with saturated brine, dehydrated with anhydrous sodium sulfate, filtered, and silica gel was added to the filtrate for adsorption purification. After filtration, the filtrate was concentrated, and then n-hexane was added for recrystallization to obtain 39.4 g (yield 66.6%) of a white solid of 9-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)phenanthrene.

[0066] 52.4 g of the obtained methyl 5-bromo-2-iodobenzoate, 39.0 g of 9-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)phenanthrene, 26.6 g of potassium carbonate, 312 ml of toluene, 117 ml of water, and 156 ml of ethanol were added to a reaction vessel. After nitrogen bubbling, 0.26 g of tetrakis(triphenylphosphine)palladium was added and heated, and stirred at 73 °C for 20 hours. After liquid separation of the reaction solution, the organic layer was washed with saturated brine and dehydrated with anhydrous magnesium sulfate. After filtration, the filtrate was concentrated and purified by column chromatography (carrier: silica gel, eluent: chloroform / n-hexane) to obtain 33.6 g (yield 67.0%) of white powder of methyl 5-bromo-2-(9-phenanthrenyl)benzoate.

[0067] 14.4 g of bromobenzene was dissolved in 150 ml of tetrahydrofuran. After dropping n-butyllithium (1.6 M) at -70 °C, 13.8 g of methyl 5-bromo-2-(9-phenanthrenyl)benzoate was added, and stirred at room temperature for 18 hours. After adding water, toluene was added for liquid separation. Anhydrous sodium sulfate was added to the organic layer for dehydration, followed by filtration. The filtrate was concentrated, n-hexane was added to precipitate a solid, and the solid was filtered. The obtained solid was recrystallized using ethyl acetate / n-hexane to obtain 11.1 g (yield 61.2%) of white powder of [5-bromo-2-(9-phenanthrenyl)phenyl]diphenylmethanol.

[0068] 13.3 g of the obtained [5-bromo-2-(9-phenanthrenyl)phenyl]diphenylmethanol, 130 ml of acetic acid, and 4 ml of 35% hydrochloric acid were added to a reaction vessel and stirred at 110 °C for 3 hours. After allowing to cool to room temperature, filtration was carried out while washing with methanol and water. The obtained solid was subjected to reflux dispersion washing with methanol and water and then filtered to obtain 12.4 g (yield 96.5%) of white powder of 11-bromo-13,13-diphenylinden[1,2-I]phenanthrene.

[0069] 5.50 g of the obtained 11-bromo-13,13-diphenylindeno[1,2-i]phenanthrene, 3.53 g of 3,6-diphenylcarbazole, 2.29 g of potassium carbonate, 0.035 g of copper powder, 0.14 g of 3,5-di-t-butylsalicylic acid, and 30 ml of dodecylbenzene were added to a reaction vessel purged with nitrogen, and the mixture was stirred at 210°C for 27 hours. The reaction solution was diluted with toluene, and insoluble matters were removed by filtration. The filtrate was concentrated, n-hexane was added, and the precipitated solid was collected by filtration. Recrystallization was carried out once with toluene and once with toluene / methanol, respectively, to obtain 2.68 g (yield 32.9%) of white powder of 11-(3,6-diphenylcarbazol-9-yl)-13,13-diphenylindeno[1,2-i]phenanthrene (Compound 1-35).

[0070] The structure of the obtained white powder was identified using NMR. 1 Thirty-seven hydrogen signals were detected by 1H-NMR (CDCl3) as follows. δ (ppm) 9.08 - 9.06 (1H), 8.91 - 8.89 (1H), 8.79 - 8.77 (1H), 8.69 - 8.66 (1H), 8.37 (2H), 7.89 - 7.77 (4H), 7.73 - 7.70 (5H), 7.63 - 7.55 (3H), 7.50 - 7.33 (13H), 7.26 - 7.19 (6H).

[0071] [Chemical formula]

[0072] [Example 2] [Synthesis of 11-(carbazol-9-yl)-13,13-diphenylindeno[1,2-i]phenanthrene (Compound 1-66)] 4.48 g of 11-bromo-13,13-diphenylindeno[1,2-i]phenanthrene, 1.50 g of carbazole, 1.87 g of potassium carbonate, 0.057 g of copper powder, 0.22 g of 3,5-di-t-butylsalicylic acid, 0.19 g of sodium bisulfite, and 10 ml of dodecylbenzene were added to a reaction vessel purged with nitrogen and stirred at 220°C for 7 hours. The reaction solution was diluted with toluene, and insoluble substances were removed by filtration. The filtrate was concentrated, acetone was added, and the precipitated solid was collected by filtration. Recrystallization was carried out with toluene / methanol to obtain 2.1 g (yield 40.0%) of white powder of 11-(carbazol-9-yl)-13,13-diphenylindeno[1,2-i]phenanthrene (Compound 1-66).

[0073] The structure of the obtained white powder was identified using NMR. 1 The following 29 hydrogen signals were detected by 1H-NMR (CDCl3). δ (ppm) 9.04 - 9.03 (1H), 8.86 - 8.84 (1H), 8.74 - 8.73 (1H), 8.63 - 8.61 (1H), 8.11 - 8.10 (2H), 7.88 - 7.86 (1H), 7.83 - 7.80 (1H), 7.77 - 7.73 (2H), 7.66 - 7.64 (1H), 7.54 - 7.51 (1H), 7.43 - 7.42 (4H), 7.35 - 7.32 (5H), 7.26 - 7.16 (8H).

[0074]

Chemical formula

[0075] <Measurement of glass transition temperature> The glass transition temperatures of the compound of Example 1 (1-35) and the compound of Example 2 (1-66) were measured using a high-sensitivity differential scanning calorimeter (manufactured by Bruker AXS, DSC3100SA). Also, EBL-1 with the following structure, which is a compound with a high glass transition temperature (see Patent Document 1), was measured in the same manner. The results of the measured glass transition temperatures are summarized in Table 1.

[0076] [Chemical formula]

[0077] [Table 1]

[0078] The glass transition temperature of Compound (1-35) is 190 °C, and the glass transition temperature of Compound (1-66) is as high as 155 °C, indicating that the thin film state is stable. Also, the glass transition temperature of Compound (1-35) is higher than that of EBL-1. By using Compound (1-35) instead of EBL-1, an element with better thermal stability can be fabricated.

[0079] [Measurement of work function] Using Compound (1-35) of Example 1 and EBL-1, a vapor-deposited film with a thickness of 100 nm was fabricated on an ITO substrate, and the measurement results of the work function were summarized in Table 2 by an ionization potential measuring device (Sumitomo Heavy Industries, Ltd., PYS-202).

[0080] [Table 2]

[0081] Compared with the work function of 5.3 - 6.0 eV of hole transport materials such as carbazole compounds, which are regarded as suitable materials, Compound (1-35) of Example 1 shows a suitable energy level, indicating that it has good hole transport ability.

[0082] [Evaluation of hole transport characteristics] On a glass substrate on which an ITO electrode was previously formed as a transparent anode, molybdenum oxide was deposited by vacuum evaporation to a thickness of 50 nm as a hole injection layer. On this hole injection layer, Compound (1-35) of Example 1 was deposited by vacuum evaporation to a thickness of 100 nm. Subsequently, Al was evaporated to a thickness of 100 nm as the cathode to fabricate a hole-only device (HOD).

[0083] These were heated on a hot plate at 180°C for 3 hours and unheated elements were fabricated inside a glove box under a nitrogen atmosphere. A voltage was applied to each element, and the equation of SCLC (space charge limited current) was fitted to the current-voltage curve in which current flowed under forward bias to measure the mobility. Also, for comparison, element fabrication and measurement were performed on the said EBL-1 under the same conditions. Table 3 summarizes the mobility and the leakage current when -3V was applied.

[0084]

Table 3

[0085] For the compound (1-35) of Example 1, the decrease in mobility due to heating is suppressed as compared with EBL-1. Also, in terms of the current density when -3V is applied, the leakage current of the compound (1-35) is significantly suppressed as compared with EBL-1. This is due to the fact that the compound having an indenophenanthrene ring structure has good hole transport ability and a higher glass transition temperature.

[0086] Thus, the organic thin film containing the compound having an indenophenanthrene ring structure represented by the general formula (1) of the present invention is an organic thin film having excellent heat resistance and charge transportability and can be applied to various photoelectric conversion elements.

[0087] [Example 3] [Fabrication of Photoelectric Conversion Element] As shown in FIG. 1, the photoelectric conversion element was fabricated by 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 was previously formed as a transparent anode.

[0088] Specifically, a glass substrate 1 coated with ITO, which is a transparent anode 2, was ultrasonically cleaned in isopropyl alcohol for 20 minutes, and then dried on a hot plate heated to 200°C for 10 minutes. Subsequently, after performing UV ozone treatment for 15 minutes, this glass substrate with ITO was placed in a vacuum evaporator and the pressure was reduced to 0.0001 Pa or less. Subsequently, as the first buffer layer 3 covering the transparent anode 2, the compound (1-35) of Example 1 was vapor-deposited so that the film thickness was 5 nm. On this first buffer layer 3, a p-type semiconductor (SubPC) of the following structural formula and an n-type semiconductor (C60) of the following structural formula were co-evaporated at an evaporation rate ratio of SubPC:C60 = 50:50 so that the film thickness was 100 nm. Finally, on this photoelectric conversion layer 4, gold was formed as the metal cathode 5 so that the film thickness was 100 nm.

[0089]

Chemical formula

[0090] <Evaluation of the photoelectric conversion element> Regarding the spectral sensitivity and photocurrent of the fabricated organic photoelectric conversion element, measurements were carried out under the following measurement conditions using a spectral sensitivity measuring device. The irradiation intensity at a specific wavelength during measurement was calibrated using a Si photodiode (S1337-1010BQ, manufactured by Hamamatsu Photonics). Regarding the dark current, the spectral radiation intensity to the photoelectric conversion element was set to zero, and the current value was measured under the same bias conditions. The measurement results are summarized in Table 4. (Measurement conditions) Device: Spectral sensitivity measuring device SM-250A (manufactured by Spectro Instruments) Light source: Xenon 150W Spectral irradiance: 2.0 mW / cm 2 (550 nm) Effective irradiation area: 10×10 mm Receiving area: 0.04 cm 2 In-plane non-uniformity: within ±5% Source meter: Keithley 2635B (manufactured by KEITHLEY) Applied bias: -1 to -3 V

[0091] [Comparative Example 1] As a comparison, in Example 3, a photoelectric conversion element was fabricated in the same manner and its electrical characteristics were evaluated, except that the EBL-1 was used instead of the compound (1-35) as the material of the first buffer layer 2. The measurement results are summarized in Table 4.

[0092]

Table 4

[0093] As shown in Table 4, the dark current at the time of applying a bias of -3V in the element of Example 3 is significantly lower, being 1 / 40 that of the element of Comparative Example 1. Also, in terms of the conversion efficiency EQE at the time of applying a bias of -3V, Example 3 is 64%, showing a 6% improvement compared to 58% of Comparative Example 1. Even when a bias of -1V and -2V is applied to the element, the element of Example 3 shows a lower dark current and a higher conversion efficiency EQE compared to the element of Comparative Example 1. This indicates that the high electron blocking property and good hole transport property of the compound having an indenophenanthrene ring structure can significantly improve the dark current characteristics and conversion efficiency of the photoelectric conversion element.

Industrial Applicability

[0094] The organic thin film of the present invention, which has high heat resistance and good charge mobility, can be applied to various photoelectric conversion elements, and thus can provide a photoelectric conversion element having good dark current characteristics and conversion efficiency, particularly an imaging element, and an optical sensor using the same.

Claims

1. An organic thin film used in a photoelectric conversion element, wherein the organic thin film is an organic thin film containing a compound having an indenophenanthrene ring structure represented by the following general formula (2). 【Chemical 1】 (In the formula, A represents a single bond, a divalent substituted or unsubstituted aromatic hydrocarbon group, a divalent substituted or unsubstituted aromatic heterocyclic group, or a divalent substituted or unsubstituted condensed polycyclic aromatic group, R1 to R11 and R14 to R21 may be the same as or different from each other, and are a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 10 carbon atoms which may have a substituent, a linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent, a linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent, 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, R1 to R11 and R14 to R21 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, R12 and R13 may be the same as or different from each other, and are a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyl group having 5 to 10 carbon atoms which may have a substituent, a linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent, a linear or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent, a cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent, 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, R12 and R13 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 photoelectric conversion element in which at least an anode, a buffer layer, a photoelectric conversion layer, and a cathode are laminated in this order, and having a layer made of the organic thin film according to Claim 1.

3. The photoelectric conversion element according to claim 2, wherein the layer made of the organic thin film is a buffer layer.

4. The photoelectric conversion element according to claim 2, wherein the layer made of the organic thin film is a photoelectric conversion layer.

5. An imaging device having the photoelectric conversion element according to any one of claims 2 to 4.

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