JP7567223B2 - Photoelectric conversion element and composition for forming photoelectric conversion layer - Google Patents

Description

The present invention relates to a photoelectric conversion element and a composition for forming a photoelectric conversion layer.

Photoelectric conversion elements that convert light energy into electrical energy are used in solar cells, optical sensors, copiers, etc. Among these, optical sensors that use near-infrared light as light energy are attracting attention for their potential applications in night vision, distance measurement, security, semiconductor wafer inspection, etc. Quantum dots are nano-sized semiconductor particles that exhibit broad absorption spectra and the wavelength of the absorption edge can be controlled by the particle size. In recent years, research has been conducted into their use as photoelectric conversion materials for photoelectric conversion elements and solar cells. In particular, investigations are being conducted into ligands that coordinate to the surface of quantum dots in order to improve the properties of photoelectric conversion elements.

For example, Patent Document 1 reports that by changing the ligand on the surface of quantum dots made of PbSe from oleic acid to 1,3-benzenedithiol, the quantum dots are brought into close proximity with each other, and the electrical conductivity of the photoactive layer is increased.
Furthermore, Patent Document 2 discloses that the energy level of quantum dots can be controlled by using benzenethiol, benzenedithiol, 3-mercaptopropionic acid, ethylenediamine, a halide salt of tetrabutylammonium, or the like as a ligand, thereby improving the characteristics of a photoelectric conversion element.
In addition, Non-Patent Document 1 discloses that the energy level of quantum dots can be controlled and the characteristics of photoelectric conversion elements can be improved by using cinnamic acid, 4-cyanocinnamic acid, 4-trifluoromethylcinnamic acid, 3,5-difluorocinnamic acid, 2,6-difluorocinnamic acid, 4-methoxycinnamic acid, or 4-dimethylaminocinnamic acid as a ligand.

Special table 2016-532301 publication Special table 2017-516320 publication

Daniel M. Kropa et al., “Tuning colloidal quantum dot band edge position through solution-phase surface chemistry modification” (NATURE COMMUNICATION S | DOI: 10.1038/noomms15257)

However, the above technology has the problem that the performance of elements created using quantum dots is poorly stable over time and has poor durability. Therefore, the problem that the present invention aims to solve is to provide a photoelectric conversion element and a composition for forming a photoelectric conversion layer that are excellent in durability.

The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.
That is, the present invention relates to a photoelectric conversion element having a photoelectric conversion layer between a pair of electrodes, the photoelectric conversion layer comprising a surface treatment agent and semiconductor particles, and the surface treatment agent has at least one partial structure selected from the group consisting of a diarylamine skeleton, a quinoline skeleton, and an indole skeleton, and at least one group selected from the group consisting of a carboxyl group and a sulfanyl group.

The present invention also relates to the above photoelectric conversion element, wherein the surface treatment agent has a structure represented by the following general formula (1), general formula (2) or general formula (3):
General formula (1)

[In general formula (1), X ¹ is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, or an acyl group which may have a substituent; R ¹ to R ⁸ are each independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an acyl group which may have a substituent, an amino group which may have a substituent, a (poly)organosiloxy group which may have a substituent, a carboxyl group, or a sulfanyl group; and at least one of X ¹ and R ¹ to R ⁸ is a carboxyl group, a sulfanyl group, a group having a carboxyl group, or a group having a sulfanyl group.]

General formula (2)

[In general formula (2), R ¹¹ to R ²⁵ each independently represent a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an acyl group which may have a substituent, a (poly)organosiloxy group which may have a substituent, a nitro group, an amino group which may have a substituent, a carboxyl group, or a sulfanyl group, and at least one of R ¹¹ to R ²⁵ is a carboxyl group, a sulfanyl group, a group having a carboxyl group, or a group having a sulfanyl group.]

General formula (3)

[In general formula (3), X ² is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent (excluding a phenyl group), or an acyl group which may have a substituent; R ²⁶ to R ³⁵ are each independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a (poly)organosiloxy group which may have a substituent, an amino group which may have a substituent, an acyl group which may have a substituent, a carboxyl group, or a sulfanyl group; and at least one of X ² and R ²⁶ to R ³⁵ is a carboxyl group, a sulfanyl group, a group having a carboxyl group, or a group having a sulfanyl group.]

The present invention also relates to a photoelectric conversion element according to claim 1 or 2, in which the semiconductor particles are capable of absorbing electromagnetic waves having a wavelength of 700 to 2500 nm.

The present invention also relates to the above photoelectric conversion element, wherein the semiconductor particles contain at least one member selected from the group consisting of PbS, PbSe and Ag ₂ S.

The present invention also relates to a composition for forming a photoelectric conversion layer, comprising a surface treatment agent having at least one partial structure selected from the group consisting of a diarylamine skeleton, a quinoline skeleton, and an indole skeleton, and at least one group selected from the group consisting of a carboxyl group and a sulfanyl group, and semiconductor particles.

According to the present invention, a photoelectric conversion element with excellent durability can be obtained.

Hereinafter, an embodiment of the present invention will be described.
<Photoelectric conversion layer>
The photoelectric conversion layer contributes to charge separation and has the function of transporting electrons and holes generated by absorption of electromagnetic waves (mainly light) toward electrodes in the opposite directions, respectively. The photoelectric conversion layer used in the present invention comprises semiconductor particles and a surface treatment agent having at least one partial structure selected from the group consisting of a diarylamine skeleton, a quinoline skeleton, and an indole skeleton, and at least one group selected from the group consisting of a carboxyl group and a sulfanyl group.

<Semiconductor particles>
The photoelectric conversion layer contains semiconductor particles. In this specification, the semiconductor particles refer to particles made of a semiconductor and having an average particle size of 0.5 nm to 100 nm. The average particle size of the semiconductor particles is preferably 1 nm or more, more preferably 1.5 nm or more, and even more preferably 2 nm or more, from the viewpoint of improving stability and photoelectric conversion efficiency, and is preferably 20 nm or less, more preferably 10 nm or less, from the viewpoint of improving film formability and photoelectric conversion efficiency. The particle size of the semiconductor particles in this specification is a value measured by observation with a transmission electron microscope. The semiconductor particles preferably contain a compound semiconductor. The compound semiconductor is preferably a semiconductor made of a compound containing at least two or more elements selected from the group consisting of Group 1 elements, Group 2 elements, Group 10 elements, Group 11 elements, Group 12 elements, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, and Group 17 elements of the periodic table. The semiconductor particles are preferably capable of absorbing electromagnetic waves with a wavelength of 700 to 2500 nm. Electromagnetic waves with wavelengths of 700 to 2500 nm are generally called near-infrared light (also called near-infrared rays), and in order for semiconductor particles to be able to absorb electromagnetic waves with wavelengths of 700 to 2500 nm, it is preferable that the semiconductor particles contain a compound semiconductor capable of absorbing electromagnetic waves with wavelengths of 700 to 2500 nm. Examples of compound semiconductors capable of absorbing electromagnetic waves with wavelengths of 700 to 2500 nm include compound semiconductors having a perovskite crystal structure and metal chalcogenides (e.g., oxides, sulfides, selenides, tellurides, etc.). Specific examples of compound semiconductors having _{a perovskite crystal} structure include _{CH3NH3PbF3 , CH3NH3PbCl3} , _CH3NH3PbBr3 , _CH3NH3PbI3 , _CsPbF3 , CsPbCl3 _{, CsPbBr3} , _CsPbI3 , _RbPbF3 , _RbPbCl3 , _{RbPbBr3 , RbPbI3 , KPbF3} , _KPbCl3 , _KPbBr3 , _{KPbI3 , etc.} Specific examples of metal chalcogenides include _PbS , PbSe, PbTe, CdS, CdSe, CdTe _{, Sb2S3} , _Bi2S3 , _Ag2S , _Ag2Se , _Ag2Te , Au2S, _Au2Se , _Au2Te , _Cu2S , Cu2Se, Cu2Te, _Fe2S , _Fe2Se , _Fe2Te , _In2S3 , SnS, SnSe, SnTe, _CuInS2 , _CuInSe2 , _CuInTe2 , EuS, _EuSe , _EuTe , etc. Among these, PbS, PbSe, and _Ag2S are preferred _.

<Surface treatment agent>
The surface treatment agent in the present invention has at least one partial structure selected from the group consisting of a diarylamine skeleton, a quinoline skeleton, and an indole skeleton, and at least one group selected from the group consisting of a carboxyl group and a sulfanyl group. Here, the carboxyl group and the sulfanyl group act as adsorption sites for the semiconductor particle surface. The surface treatment agent can be used alone or in combination of two or more types. The diarylamine skeleton further includes a triarylamine skeleton having an aryl group on the amine nitrogen atom, and a carbazole skeleton in which aryl groups are bonded to each other to form a ring.

From the viewpoint of durability over time of the photoelectric conversion element, it is preferable that the surface treatment agent has a diarylamine skeleton. More preferably, the surface treatment agent has a structure represented by general formula (1), general formula (2), or general formula (3). This is presumed to have an excellent shielding effect against oxygen and water that deteriorate semiconductor particles.

The substituents in the above general formulas (1) to (3) will be described below.
The alkyl group is a straight-chain or branched alkyl group, and since it is possible to increase the content of semiconductor fine particles in the composition, it is preferable that the molecular weight of the treating agent is small, and the number of carbon atoms of the alkyl group is preferably from 1 to 30. Examples of the alkyl group include straight-chain alkyl groups such as a methyl group, an ethyl group, a hexyl group, a dodecyl group, and an eicosyl group; and branched alkyl groups such as a 2-ethylhexyl group.

An aryl group is a residue in which one hydrogen atom has been formally removed from an aromatic hydrocarbon ring, and more preferably, a residue in which one hydrogen atom has been formally removed from an aromatic hydrocarbon ring having 6 to 30 carbon atoms. Examples of aromatic hydrocarbon rings include a benzene ring, a naphthalene ring, a pyrene ring, a biphenyl group, and a terphenyl group.

An alkoxy group is a group in which an alkyl group is bonded to an oxygen atom, and the alkyl group has the same meaning as the alkyl group described above. In order to increase the content of semiconductor particles in the composition, it is preferable that the molecular weight of the surface treatment agent is small, and the number of carbon atoms in the alkyl group is preferably 1 to 6.

An aryloxy group is a group in which an aryl group is bonded to an oxygen atom, and the aryl group has the same meaning as the aryl group described above. In order to increase the content of semiconductor particles in the composition, it is preferable that the molecular weight of the surface treatment agent is small, and the number of aryl groups is preferably 1 to 2.

The acyl group is a group in which an alkyl group or an aryl group is bonded via a carbonyl group, and the alkyl group and the aryl group have the same meaning as the alkyl group and the aryl group described above. In order to increase the content of semiconductor particles in the composition, it is preferable that the molecular weight of the surface treatment agent is small, and in the case of an alkyl group, the number of carbon atoms is preferably 1 to 6. In the case of an aryl group, the number of aryl groups is preferably 1 to 2.

Examples of the amino group which may have a substituent include an amino group and a substituted amino group. Examples of the substituent of the substituted amino group include an alkyl group, an aryl group, and an acyl group. The above alkyl group, aryl group, and acyl group are synonymous with the above alkyl group, aryl group, and acyl group. In order to increase the content of semiconductor particles in the composition, it is preferable that the molecular weight of the surface treatment agent is small, and the alkyl group and the alkyl group constituting the acyl group preferably have 1 to 4 carbon atoms. In addition, it is preferable that the aryl group and the aryl group constituting the acyl group have 1 to 2 aryl groups.

In addition, the alkyl group, aryl group, alkoxy group, amino group, aryloxy group and acyl group in the general formulae (1) to (3) may have a substituent. Examples of the substituent that may be had include a halogeno group, a cyano group, a hydroxyl group, a nitro group, an alkoxy group, an alkyl group, an aralkyl group, an aryl group, an aryloxy group, a siloxy group, an alconoyloxy group, an alkoxycarbonyloxy group, an aryloxyalconoyl group, an amino group, an anilino group, an alconoylamino group, a carbamoylamino group, an aryloxycarbonylamino group, a sulfamoylamino group, an alkylsulfonylamino group, a carbamoylarylamino group, a sulfanyl group, an alkylthio group, an arylthio group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, an imido group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a silyl group, a group containing a siloxane bond, a carboxyl group, and a sulfanyl group.
The substituent that may be possessed in the present invention may be a monovalent group in which the above-mentioned monovalent substituent is bonded to a divalent linking group such as an alkylene group, an arylene group, an ether group, an ester group, a sulfide group, a carbonyl group, or an imino group.

In addition, examples of groups having a carboxyl group or a sulfanyl group include monovalent groups such as alkyl groups, alkylene groups, aryl groups, alkoxy groups, and aryloxy groups, each of which has a carboxyl group or a sulfanyl group as a substituent.

Examples of the alkyl group having a carboxyl group or the aryl group having a carboxyl group include a 2-carboxyethyl group, a 2,2-dicarboxyethyl group, a 2-carboxylethenyl group, a 2-cyano-2-carboxylethenyl group, a 2-trifluoromethyl-2-carboxylethenyl group, and a 2-fluoro-2-carboxylethenyl group.
The carboxyl group is preferably directly bonded to the diarylamine skeleton, the quinoline skeleton, or the indole skeleton, or is preferably bonded to a position where the carboxyl group can be conjugated with the diarylamine skeleton, the quinoline skeleton, or the indole skeleton.

Examples of the alkyl group having a sulfanyl group, the aryl group having a sulfanyl group, or the acyl group having a sulfanyl group include the [(3-sulfanylpropanoyl)oxy]ethyl group, the [(2-sulfanylacetyl)oxy]ethyl group, the 4-(sulfanylmethyl)phenyl group, the [(3-sulfanylpropanoyl)oxy]propyl group, the 3-sulfanyl[(3-sulfanylpropanoyl)oxy]ethyl group, and the {[(2-sulfanylethoxy)propanoyl]oxy}ethyl group. In order to increase the content of semiconductor particles in the composition, it is preferable that the molecular weight of the surface treatment agent is small, and the molecular weight of the alkyl group having a sulfanyl group, the aryl group having a sulfanyl group, or the acyl group having a sulfanyl group is preferably 200 or less.

When cis- and trans-geometric isomers exist, the surface treatment agent may be either the cis- or trans-type, or may be a mixture of cis- and trans-type isomers. The same applies to syn-anti geometric isomerism.

<Photoelectric conversion element>
The photoelectric conversion element of the present invention has the photoelectric conversion layer between a pair of electrodes. The photoelectric conversion element of the present invention can be configured as a known photoelectric conversion element. The photoelectric conversion element of the present invention can be manufactured by a known method except for the photoelectric conversion layer.

Here, we will explain in detail the photoelectric conversion element that can be produced using the photoelectric conversion layer forming composition of the present invention. Generally, a photoelectric conversion element using semiconductor particles is composed of at least a pair of electrodes and a photoelectric conversion layer. With the aim of improving photoelectric conversion efficiency, various types of element structures have been proposed, such as by matching the energy between the electrodes and the semiconductor particles and by using a method for producing a photoelectric conversion layer made of semiconductor particles. For example, a photoelectric conversion element having the known configuration shown below can be produced using the photoelectric conversion layer forming composition of the present invention.

1. Schottky-type photoelectric conversion element This is a photoelectric conversion element that obtains photovoltaic power by utilizing a Schottky barrier formed at the interface between an electron-donating (p-type) or electron-accepting (n-type) semiconductor particle and an electrode. For example, when a p-type photoelectric conversion layer is used, a Schottky barrier is formed at the interface with the electrode having the smaller work function of the pair of electrodes, and charge separation occurs at the interface to perform photoelectric conversion.

2. Bilayer heterojunction photoelectric conversion element This is a photoelectric conversion element in which electron-donating (p-type) and electron-accepting (n-type) semiconductor particles or other semiconductor materials are individually formed between a pair of electrodes, and photoinduced charge separation occurs at the pn junction interface to obtain a photocurrent.

3. Bulk heterojunction photoelectric conversion element An organic semiconductor layer is formed by mixing electron-donating (p-type) and electron-accepting (n-type) semiconductor particles and other semiconductor materials in any ratio between a pair of electrodes. In this case, the p-type and n-type materials may be uniformly or non-uniformly dispersed. Since photocharge separation occurs at the interface formed by the individual p-type and n-type materials, a wider pn junction can be formed than in the bilayer heterojunction type.

<Electrodes>
At least one of the pair of electrodes constituting the photoelectric conversion element is preferably light-transmitting. Specific examples include conductive metal oxides such as tin oxide, zinc oxide, indium oxide, and indium tin oxide (ITO), metals such as gold, silver, platinum, chromium, nickel, lithium, indium, aluminum, calcium, and magnesium, and mixtures or laminates of these metals and conductive metal oxides.

The electrode generally has a flat shape, but may have a corrugated, pyramidal, comb-like shape, etc., in order to improve the energy conversion efficiency. As a method for forming these electrodes, a general electrode formation method can be used, and examples of the method include PVD methods such as vacuum deposition, sputtering, and ion plating, CVD, chemical reaction methods (such as the sol-gel method), casting, spray coating, inkjet, and spin coating.
The photoelectric conversion element may include a layer other than the photoelectric conversion layer between the pair of electrodes, and may have a hole injection layer, a hole transport layer, an electron transport layer, and/or an electron injection layer.

<Hole injection layer>
For the hole injection layer, a hole injection material is used that can form a hole injection layer that exhibits an excellent hole injection effect for the photoelectric conversion layer and has excellent adhesion to the anode interface and thin film formability. When such materials are laminated in multiple layers, and a material with a high hole injection effect and a material with a high hole transport effect are laminated in multiple layers, the materials used for each layer may be called a hole injection material and a hole transport material. These hole injection materials and hole transport materials must have a high hole mobility and a small ionization energy, usually 5.5 eV or less. For such a hole injection layer, a material that transports holes to the light emitting layer at a lower electric field strength is preferable, and further, a material that has a hole mobility of, for example, 10 ⁴ to 1
It is preferable that the electric field strength is at least ^{10-6 cm2} /Vsec when an electric field of ^0.6 V/cm is applied. There are no particular limitations on the hole injection material and hole transport material as long as they have the above-mentioned preferable properties, and any material may be selected and used from those conventionally used as charge transport materials for holes in photoconductive materials and known materials used in the hole injection layer of organic EL elements.

Examples of such hole injection materials and hole transport materials include triazole derivatives (see U.S. Patent No. 3,112,197, etc.), oxadiazole derivatives (see U.S. Patent No. 3,189,447, etc.), imidazole derivatives (see Japanese Patent Publication No. 37-16096, etc.), polyarylalkane derivatives (see U.S. Patent Nos. 3,615,402, 3,820,989, and 3,54 No. 2,544, JP-B-45-555, JP-B-51-10983, JP-A-51-93224, JP-A-55-17105, JP-A-56-4148, JP-A-55-108667, JP-A-55-156953, JP-A-56-36656, etc.), pyrazoline derivatives and pyrazolone derivatives (see U.S. Pat. Nos. 3,180,729 and 4,278,746, phenylenediamine derivatives (see U.S. Pat. No. 3,615,404, JP-B-5105, JP-B-51086, JP-B-55088064, JP-B-55088065, JP-B-49105537, JP-B-55051086, JP-B-560051081, JP-B-56088141081, JP-B-574545085, JP-B-54112637085, JP-B-55074546, etc.) arylamine derivatives (see U.S. Pat. Nos. 3,567,450, 3,180,703, 3,240,597, 3,658,520, 4,232,103, and 4,175,961); JP-B-4,012,376, JP-B-49-35702, JP-B-39-27577, JP-A-55-144250, JP-A-56-119132, JP-A-56-22437, West German Patent No. 1,110,518, etc.), amino-substituted chalcone derivatives (see U.S. Pat. No. 3,526,501, etc.), oxazole derivatives (see U.S. Pat. No. 3,257,203, etc. those disclosed in the specification, etc.), styrylanthracene derivatives (see JP-A-56-46234, etc.), fluorenone derivatives (see JP-A-54-110837, etc.), hydrazone derivatives (U.S. Pat. No. 3,717,462, JP-A-54-59143, JP-A-55-52063, JP-A-55-52064, JP-A-55-46760, JP-A-55-85495, JP-A-55-17126, JP-A-55-17127, JP-A-55-17128, JP-A-55-17129 ... 1350, 57-148749, JP 2-311591, etc.), stilbene derivatives (JP 61-210363, JP 61-228451, JP 61-14642, JP 61-72255, JP 62-47646, JP 62-47646, etc.) -36674 publication, 62-10652 publication, 62-30255 publication, 60-93455 publication, 60-60 Examples include silazane derivatives (see U.S. Patent No. 4,950,950), polysilanes (JP Patent Publication No. 2-204996), aniline copolymers (JP Patent Publication No. 2-282263), and conductive polymer oligomers (particularly thiophene oligomers) disclosed in JP Patent Publication No. 1-211399.

In addition, porphyrin compounds (JP Patent Publication No. 63-2956965), aromatic tertiary amine compounds and styrylamine compounds (see U.S. Patent No. 4,127,412, JP Patent Publication Nos. 53-27033, 54-58445, 54-149634, 54-64299, 55-79450, 55-144250, 56-119132, 61-295558, 61-98353, 63-295695, etc.) can also be used as hole injection materials and hole transport materials. For example, 4,4'-bis(N-(1-naphthyl)-N-phenylamino)biphenyl having two condensed aromatic rings in the molecule, as described in U.S. Pat. No. 5,061,569, and 4,4',4"-tris(N-(3-methylphenyl)-N-phenylamino)triphenylamine having three triphenylamine units linked in a starburst configuration, as described in Japanese Patent Laid-Open No. 4-308688, can be mentioned. In addition, phthalocyanine derivatives such as copper phthalocyanine and hydrogen phthalocyanine can also be used as hole injection materials. Furthermore, aromatic dimethylidene compounds, p-type Si, p-type SiC, and other inorganic compounds can also be used as hole injection materials or hole transport materials.

Additionally, materials that can be used for the hole injection layer include inorganic oxides such as molybdenum oxide ( _MnOx ), vanadium oxide ( _VOx ), ruthenium oxide ( _RuOx ), copper oxide ( _CuOx ), tungsten oxide ( _WOx ), iridium oxide ( _IrOx ), and doped versions thereof.

Specific examples of the aromatic tertiary amine compound include N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine, N,N,N',N'-(4-methylphenyl)-1,1'-phenyl-4,4'-diamine, N,N,N',N'-(4-methylphenyl)-1,1'-biphenyl-4,4'-diamine, N,N'-diphenyl-N,N'-dinaphthyl-1,1'-biphenyl-4,4'-diamine, N,N'-(methylphenyl)-N,N'-(4-n-butylphenyl)-phenanthrene-9,10-diamine, and N,N-bis(4-di-4-tolylaminophenyl)-4-phenyl-cyclohexane. n-hexane, N,N'-bis(4'-diphenylamino-4-biphenylyl)-N,N'-diphenylbenzidine, N,N'-bis(4'-diphenylamino-4-phenyl)-N,N'-diphenylbenzidine, N,N'-bis(4'-diphenylamino-4-phenyl)-N,N'-di(1-naphthyl)benzidine, N,N'-bis(4'-phenyl(1-naphthyl)amino-4-phenyl)-N,N'-diphenylbenzidine, N,N'-bis(4'-phenyl(1-naphthyl)amino-4-phenyl)-N,N'-di(1-naphthyl)benzidine, and the like. These can be used as either a hole injection material or a hole transport material.
Particularly preferred examples of the hole injection material are shown in Tables 1 and 2.

To form the hole injection layer, the above-mentioned compound is formed into a thin film by a known method such as vacuum deposition, spin coating, casting, or the Langmuir-Blodgett method (LB method). There are no particular limitations on the thickness of the hole injection layer, but it is usually 5 nm to 5 μm.

<Electron injection layer>
For the electron injection layer, an electron injection material is used that can form an electron injection layer that exhibits excellent electron injection effect for the photoelectric conversion layer and has excellent adhesion to the cathode interface and excellent thin film formability. Examples of such electron injection materials include metal complex compounds, nitrogen-containing five-membered ring derivatives, fluorenone derivatives, anthraquinodimethane derivatives, diphenoquinone derivatives, thiopyran dioxide derivatives, perylene tetracarboxylic acid derivatives, fluorenylidenemethane derivatives, anthrone derivatives, silole derivatives, triarylphosphine oxide derivatives, polyquinoline and its derivatives, polyquinoxaline and its derivatives, polyfluorene and its derivatives, calcium acetylacetonate, sodium acetate, etc. In addition, inorganic/organic composite materials in which a metal such as cesium is doped into bathophenanthroline (Proceedings of the Society of Polymer Science, Vol. 50, No. 4, p. 660, published in 2001) and Proceedings of the 50th Joint Conference on Applied Physics, No. No. 3, p. 1402, published in 2003, BCP, TPP, T5MPyTZ, and the like are given as examples of the electron injection material, but the material is not particularly limited to these, so long as it can form a thin film necessary for element production, can inject electrons from the cathode, and can transport electrons.

Among the above electron injection materials, preferred are metal complex compounds, nitrogen-containing five-membered ring derivatives, silole derivatives, and triarylphosphine oxide derivatives. Preferred metal complex compounds are metal complexes of 8-hydroxyquinoline or its derivatives. Specific examples of metal complexes of 8-hydroxyquinoline or derivatives thereof include tris(8-hydroxyquinolinato)aluminum, tris(2-methyl-8-hydroxyquinolinato)aluminum, tris(4-methyl-8-hydroxyquinolinato)aluminum, tris(5-methyl-8-hydroxyquinolinato)aluminum, tris(5-phenyl-8-hydroxyquinolinato)aluminum, bis(8-hydroxyquinolinato)(1-naphtholate)aluminum, bis(8-hydroxyquinolinato)(2-naphtholate)aluminum, bis(8-hydroxyquinolinato)(phenolate)aluminum, and bis(8-hydroxyquinolinato)(4-cyano-1-naphtholate)aluminum. aluminum complex compounds such as bis(4-methyl-8-hydroxyquinolinate)(1-naphtholate)aluminum, bis(5-methyl-8-hydroxyquinolinate)(2-naphtholate)aluminum, bis(5-phenyl-8-hydroxyquinolinate)(phenolate)aluminum, bis(5-cyano-8-hydroxyquinolinate)(4-cyano-1-naphtholate)aluminum, bis(8-hydroxyquinolinate)chloroaluminum, and bis(8-hydroxyquinolinate)(o-cresolate)aluminum; tris(8-hydroxyquinolinate)gallium, tris(2-methyl-8-hydroxyquinolinate)gallium, and tris(4-methyl-8-hydroxyquinolinate ) gallium, tris(5-methyl-8-hydroxyquinolinato)gallium, tris(2-methyl-5-phenyl-8-hydroxyquinolinato)gallium, bis(2-methyl-8-hydroxyquinolinato)(1-naphtholate)gallium, bis(2-methyl-8-hydroxyquinolinato)(2-naphtholate)gallium, bis(2-methyl-8-hydroxyquinolinato)(phenolate)gallium, bis(2-methyl-8-hydroxyquinolinato)(4-cyano-1-naphtholate)gallium, bis(2,4-dimethyl-8-hydroxyquinolinato)(1-naphtholate)gallium, bis(2,5-dimethyl-8-hydroxyquinolinato)(2-naphtholate)gallium, bis(2-methyl- In addition to gallium complex compounds such as 5-phenyl-8-hydroxyquinolinate) (phenolate), bis(2-methyl-5-cyano-8-hydroxyquinolinate) (4-cyano-1-naphtholate) gallium, bis(2-methyl-8-hydroxyquinolinate) chlorogallium, and bis(2-methyl-8-hydroxyquinolinate) (o-cresolate) gallium, metal complex compounds such as 8-hydroxyquinolinate lithium, bis(8-hydroxyquinolinate) copper, bis(8-hydroxyquinolinate) manganese, bis(10-hydroxybenzo[h]quinolinate) beryllium, bis(8-hydroxyquinolinate) zinc, and bis(10-hydroxybenzo[h]quinolinate) zinc are also included.

In addition, preferred nitrogen-containing five-membered ring derivatives include oxazole derivatives, thiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, and triazole derivatives. Specific examples of the nitrogen-containing five-membered ring derivatives include 2,5-bis(1-phenyl)-1,3,4-oxazole, 2,5-bis(1-phenyl)-1,3,4-thiazole, 2,5-bis(1-phenyl)-1,3,4-oxadiazole, 2-(4'-tert-butylphenyl)-5-(4"-biphenyl)1,3,4-oxadiazole, 2,5-bis(1-naphthyl)-1,3,4-oxadiazole, 1,4-bis[2-(5-phenyloxadiazolyl)]benzene, 1,4-bis[2-(5-phenyloxadiazolyl)-4-tert-butylbenzene], 2-(4'-tert- butylphenyl)-5-(4"-biphenyl)-1,3,4-thiadiazole, 2,5-bis(1-naphthyl)-1,3,4-thiadiazole, 1,4-bis[2-(5-phenylthiadiazolyl)]benzene, 2-(4'-tert-butylphenyl)-5-(4"-biphenyl)-1,3,4-triazole, 2,5-bis(1-naphthyl)-1,3,4-triazole, 1,4-bis[2-(5-phenyltriazolyl)]benzene, etc.

Additionally, materials that can be used for the electron injection layer include inorganic oxides such as zinc oxide (ZnO _x ), titanium oxide (TiO _x ), and doped versions thereof.

Specific examples of particularly preferred oxadiazole derivatives, triazole derivatives, and silole derivatives are shown below. In the table, Ph represents a phenyl group.

The photoelectric conversion element may be provided with an ultraviolet blocking layer in order to prevent photodegradation due to ultraviolet rays or the like.
The photoelectric conversion element may have a protective film for the purpose of protecting the photoelectric conversion layer against external impact. The protective film may be composed of, for example, a polymer film such as styrene resin, epoxy resin, acrylic resin, polyurethane, polyimide, polyvinyl alcohol, polyvinylidene fluoride, polyethylene polyvinyl alcohol copolymer, inorganic oxide film or nitride film such as silicon oxide, silicon nitride, aluminum oxide, metal plate or metal foil such as aluminum, or a laminate film thereof. Note that only one type of material for these protective films may be used, or two or more types may be used.

It is generally said that semiconductor particles are subject to deterioration due to moisture and oxygen in the air. To prevent this, a barrier film may be provided. For example, metal or inorganic oxides are preferred, such as Ti, Al, Mg, Zr, silicon oxide, aluminum oxide, silicon oxynitride, aluminum oxynitride, magnesium oxide, zinc oxide, indium oxide, tin oxide, yttrium oxide, boron oxide, and calcium oxide. There is no particular order in which these various functional films are stacked, and a functional film that combines these functions may be used.

<Photoelectric conversion layer forming composition>
The photoelectric conversion layer forming composition of the present invention contains the above-mentioned surface treatment agent and semiconductor particles, and may further contain a solvent. The solvent that may be contained in the photoelectric conversion layer forming composition is used to disperse the semiconductor particles and to facilitate coating the photoelectric conversion layer forming composition of the present invention on a substrate such as a glass substrate so that the dry film thickness becomes a desired film thickness.

(solvent)
The solvent is not particularly limited, and examples thereof include 1,2,3-trichloropropane, 1,3-butylene glycol, 1,3-butylene glycol diacetate, 1,4-dioxane, 2-heptanone, 2-methyl-1,3-propanediol, 3,5,5-trimethyl-2-cyclohexen-1-one, 3,3,5-trimethylcyclohexanone, 3-ethoxyethylpropionate, 3-methyl-1,3-butanediol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-3-methylbutyl acetate, 3-methoxybutanol, 3-methoxybutyl acetate, 4-heptanone, m-xylene, m-diethylbenzene, m-dichlorobenzene, N,N-dimethylacetamide, N,N-dimethylformamide, n-butyl alcohol, n-butylbenzene, n-propyl acetate, and N-methylpyrrolidone. , toluene, octane, nonane, hexane, o-xylene, o-chlorotoluene, o-diethylbenzene, o-dichlorobenzene, p-chlorotoluene, p-diethylbenzene, sec-butylbenzene, tert-butylbenzene, gamma-butyrolactone, water, methanol, ethanol, isopropyl alcohol, tert-tert-butanol, isobutyl alcohol, isophorone, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monotert-butyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monopropyl ether, ethylene glycol monohexyl ether, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, diisobutyl ketone, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether, cyclohexanol, cyclohexanol acetate, cyclohexanone, dipropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol Examples of the solvent include pyrene glycol monomethyl ether, diacetone alcohol, triacetin, tripropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, propylene glycol diacetate, propylene glycol phenyl ether, propylene glycol monoethyl ether, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether propionate, benzyl alcohol, methyl isobutyl ketone, methylcyclohexanol, n-amyl acetate, n-butyl acetate, isoamyl acetate, isobutyl acetate, propyl acetate, and dibasic acid esters. These solvents can be used alone or in a mixture of two or more in any ratio as necessary.

The present invention will now be described in detail with reference to examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". Unless otherwise specified, all measurements were performed at 25°C. The structures of the surface treatment agents used in the examples are shown in Tables 6 and 7, and the structures of the surface treatment agents used in the comparative examples are shown in Table 8.

<Preparation of semiconductor particles PbS-0>
First, 0.40 parts of elemental sulfur and 6.0 parts of oleylamine were heated to 120°C in a reaction vessel under a nitrogen atmosphere to obtain a homogeneous solution, and then cooled to 25°C. Next, 0.32 parts of lead chloride and 6.0 parts of oleylamine were heated to 120°C in a separate reaction vessel under a nitrogen atmosphere to obtain a lead source solution. After that, the lead source solution was prepared at 40°C, and 1.8 parts of the above sulfur source solution were added at once. After reacting for 30 seconds, the vessel was immersed in an ice bath to rapidly cool, and then diluted with 13 parts of hexane. After centrifuging (4000 rpm, 5 minutes) to remove unreacted raw materials, 12 parts of a mixture consisting of butanol:methanol = 2:1 (volume ratio) was added to precipitate the semiconductor particles, and centrifuging (4000 rpm, 5 minutes) was performed to recover the semiconductor particles. Then, 24 parts of a mixed solution consisting of hexane:oleic acid = 1:2 (volume ratio) was added, stirred for 30 minutes, centrifuged, and the supernatant was collected. Semiconductor particle sedimentation, redispersion, and impurity sedimentation were repeated two more times, and finally the semiconductor particles were sedimented and dried in vacuum, and then the solid content was adjusted to 5% using n-octane, to obtain semiconductor particles PbS-0 (average particle size 3.5 nm).

<Synthesis of semiconductor particles PbSe-0>
As a lead source solution, 0.22 parts of lead oxide, 0.73 parts of oleic acid, and 10 parts of 1-octadecene were heated to 150°C in a reaction vessel under a nitrogen atmosphere. Then, a mixture consisting of 2.5 parts of 1M-trioctylphosphine-selenium solution and 0.028 parts of diphenylphosphine was quickly added, and the reaction solution was heated to 180°C, and then kept at 160°C and reacted for 2 minutes, after which the reaction solution was quenched. The solution was diluted with 10 parts of hexane and precipitated with acetone. The precipitate was washed five times with acetone and dried in vacuum to obtain semiconductor particles PbSe-0 (average particle size 2.7 nm).

<Synthesis of semiconductor fine particles Ag ₂ S-0>
0.04 parts of silver oleate, 8 parts of octanethiol, and 4 parts of dodecylamine were heated in a reaction vessel under an Ar atmosphere at 200° C. for 0.5 hours. After the solution was allowed to cool to room temperature, 40 parts of absolute ethanol were added. The resulting mixture was centrifuged and vacuum dried to obtain semiconductor particles Ag ₂ S-0 (average particle size 2.5 nm).

<Preparation of Photoelectric Conversion Layer Forming Composition>
Example 1
Semiconductor particles PbS-0 were prepared in a toluene solution with a solid content concentration of 1%. One part of the prepared solution was mixed with one part of a toluene solution of 5% surface treatment agent 1, and then stirred for 12 hours. Purification was performed by a reprecipitation method using toluene and ethanol. The precipitate was vacuum dried and made into a 5 mass % solution in n-octane to prepare a photoelectric conversion forming composition PbS-1.

<Examples 2 to 25 and Comparative Examples 1 to 7>
PbS-2 to 26, PbSe-1 to 3, and Ag ₂ S-1 to 3 were prepared in the same manner as in Example 1, except that surface treatment agent 1 was changed to the surface treatment agent shown in Table 9. Of these, PbS-2 to 21, PbSe-1 and 2, and Ag ₂ S-1 and 2 are compositions for forming a photoelectric conversion layer of the present invention, and PbS-22 to 26, PbSe-3, and Ag ₂ S-3 are compositions that are not the composition for forming a photoelectric conversion layer of the present invention.

<Example 101>
(Fabrication of photoelectric conversion element)
The preparation and evaluation of the photoelectric conversion element will be described below. The deposition was performed in a vacuum of 10 ^-6 Torr under conditions where temperature control such as heating or cooling of the substrate was not performed. The element was evaluated using a photoelectric conversion element with an element area of 2 mm x 2 mm. First, PEDOT/PSS (poly(3,4-ethylenedioxy)-2,5-thiophene/polystyrene sulfonic acid, CLEVIOS (registered trademark) PVP CH8000 manufactured by Heraeus) was applied by spin coating on a cleaned glass plate with an ITO electrode, and dried at 110°C for 20 minutes to obtain a hole injection layer with a thickness of 35 nm. The photoelectric conversion layer forming composition PbS-1 was applied by spin coating on the hole injection layer to form a photoelectric conversion layer with a thickness of 150 nm. Next, a 50 nm-thick electron transport layer was formed on the photoelectric conversion layer by spin coating ZnO Dispersion N-10 manufactured by Avantama Corp. Next, an electrode was formed on the electron transport layer by vapor deposition of aluminum (hereinafter, Al) to a thickness of 200 nm, thereby obtaining a photoelectric conversion element.

(Evaluation of photoelectric conversion element)
The durability of the obtained element was evaluated by the method shown below. The IV curves of the element before and after storage were measured, and the durability was calculated by calculating the ratio of the measured values. The IV curve of the cell was measured using a xenon lamp white light source (PEC-L01, manufactured by Peccell Technologies, Inc.) with a light intensity (100 mW/cm ² ) equivalent to sunlight (AM1.5) under a mask with a light irradiation area of 0.0363 cm ² (2 mm square) using an IV characteristic measuring device (PECK2400-N, manufactured by Peccell Technologies, Inc.) under the conditions of a scanning speed of 0.1 V/sec (0.01 Vstep), a waiting time after voltage setting of 50 msec, a measurement integration time of 50 msec, a starting voltage of -0.1 V, and an end voltage of 1.1 V. The durability was calculated by measuring the I-V curves of the photoelectric conversion element before storage (immediately after the element was fabricated) and after storage for 4 days under conditions of light-shielded, 25°C, and 60% humidity, and calculating the ratio of the conversion efficiency after storage to the conversion efficiency before storage (immediately after the element was fabricated).
(Evaluation Criteria)
◎: Ratio is 95% or more: Good ○: Ratio is 90% or more but less than 95%: Usable for practical use △: Ratio is 80% or more but less than 90%: Unusable for practical use ×: Ratio is less than 80%: Poor

<Examples 102 to 125>
Photoelectric conversion elements were prepared and evaluated in the same manner as in Example 1, except that PbS-2 to 21, PbSe-1, 2, Ag ₂ S-1, 2 were used instead of PbS-1 used in Example 101. The results are shown in Table 10.

<Comparative Examples 101 to 107>
Photoelectric conversion elements were prepared and evaluated in the same manner as in Example 101, except that PbS-22 to 26, PbSe-3, and Ag ₂ S-3 were used instead of PbS-1 used in Example 101. The results are shown in Table 10.

It was clear that the photoelectric conversion element of the present invention (Examples 101 to 125) had better durability over time than the comparative example. Surface treatment agents 1 to 21 used in Examples 101 to 125 have carboxyl or sulfanyl groups that can be adsorbed to the semiconductor particle surface and have many aromatic rings in the molecule. As a result, it is presumed that the shielding effect of the aromatic rings suppresses deterioration caused by attacks on the semiconductor particle surface by oxygen, water, etc., and improves the durability of the element. In Examples 101 to 110, 112 to 114, and 116 to 125, particularly high durability was observed. This is presumed to be the result of the surface treatment agents 1 to 10, 12 to 14, and 16 to 21 having a diphenylamino skeleton, and the shielding effect is particularly effective.

Claims (5)

A photoelectric conversion element having a photoelectric conversion layer between a pair of electrodes, the photoelectric conversion layer containing a surface treatment agent and semiconductor particles, the surface treatment agent having a structure represented by the following general formula (1), general formula (2) or general formula (3), and the semiconductor particles being capable of absorbing electromagnetic waves having a wavelength of 700 to 2500 nm .

General formula (1)
[In general formula (1), X ¹ is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, or an acyl group which may have a substituent; R ¹ to R ⁸ are each independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an acyl group which may have a substituent, an amino group which may have a substituent, a (poly)organosiloxy group which may have a substituent, a carboxyl group, or a sulfanyl group; and at least one of X ¹ and R ¹ to R ⁸ is a carboxyl group, a sulfanyl group, or a group having a sulfanyl group.]

General formula (2)
[In general formula (2), R ¹¹ to R ²⁵ each independently represent a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an acyl group which may have a substituent, a (poly)organosiloxy group which may have a substituent, a nitro group, an amino group which may have a substituent, a carboxyl group, or a sulfanyl group, and at least one of R ¹¹ to R ²⁵ is a carboxyl group, a sulfanyl group, or a group having a sulfanyl group.]

General formula (3)
[In general formula (3), X ² is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent (excluding a phenyl group), or an acyl group which may have a substituent; R ²⁶ to R ³⁵ are each independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a (poly)organosiloxy group which may have a substituent, an amino group which may have a substituent, an acyl group which may have a substituent, a carboxyl group, or a sulfanyl group; and at least one of X ² and R ²⁶ to R ³⁵ is a carboxyl group, a sulfanyl group, a group having a carboxyl group, or a group having a sulfanyl group.] In the general formula (1), at least one of X ¹ and R ¹ to R ⁸ is a carboxyl group;
In the general formula (2), at least one of R ¹¹ to R ²⁵ is a carboxyl group.
2. The photoelectric conversion element according to claim 1, wherein , in formula (3), at least one of X ² and R ²⁶ to R ³⁵ is a carboxyl group . In the general formula (1), at least one of X ¹ and R ¹ to R ⁸ is an alkyl group having a sulfanyl group or an acyl group having a sulfanyl group;
In the general formula (2), at least one of R ¹¹ to R ²⁵ is an alkyl group having a sulfanyl group or an acyl group having a sulfanyl group;
3. The photoelectric conversion element according to claim 1 , wherein in formula (3), at least one of X ² and R ²⁶ to R ³⁵ is an alkyl group having a sulfanyl group or an acyl group having a sulfanyl group . 4. The photoelectric conversion element according to claim 1, wherein the semiconductor particles contain at least one member selected from the group consisting of PbS, PbSe and Ag ₂ S. The composition for forming a photoelectric conversion layer comprises a surface treatment agent and semiconductor particles , wherein the surface treatment agent has a structure represented by the following general formula (1), general formula (2) or general formula (3), and the semiconductor particles are capable of absorbing electromagnetic waves having a wavelength of 700 to 2500 nm .

General formula (1)
[In general formula (1), X ¹ is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, or an acyl group which may have a substituent; R ¹ to R ⁸ are each independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an acyl group which may have a substituent, an amino group which may have a substituent, a (poly)organosiloxy group which may have a substituent, a carboxyl group, or a sulfanyl group; and at least one of X ¹ and R ¹ to R ⁸ is a carboxyl group, a sulfanyl group, or a group having a sulfanyl group.]

General formula (2)
[In general formula (2), R ¹¹ to R ²⁵ each independently represent a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an acyl group which may have a substituent, a (poly)organosiloxy group which may have a substituent, a nitro group, an amino group which may have a substituent, a carboxyl group or a sulfanyl group, and at least one of R ¹¹ to R ²⁵ is a carboxyl group, a sulfanyl group or a group having a sulfanyl group.]

General formula (3)
[In general formula (3), X ² is a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent (excluding a phenyl group), or an acyl group which may have a substituent; R ²⁶ to R ³⁵ are each independently a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a (poly)organosiloxy group which may have a substituent, an amino group which may have a substituent, an acyl group which may have a substituent, a carboxyl group, or a sulfanyl group; and at least one of X ² and R ²⁶ to R ³⁵ is a carboxyl group, a sulfanyl group, a group having a carboxyl group, or a group having a sulfanyl group.]