JP7589454B2 - 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.

In recent years, however, it has been reported that semiconductor particles (quantum dots) such as PbS are used as photoelectric conversion materials for photoelectric conversion elements and solar cells. For example, Non-Patent Document 1 discloses that by replacing the oleic acid around PbSe semiconductor particles with ethanedithiol, the semiconductor particles are brought closer to each other and electrical conductivity is improved. Patent Document 1 also describes ultrafine particles in which multiple ultrafine particles such as CdS are bonded with molecular chains such as benzenedithiol, and discloses that they can be used for various applications such as optical materials and electronic materials. Furthermore, Patent Document 2 discloses that by replacing the oleic acid around PbSe semiconductor particles with 2-aminoethane-1-thiol, the semiconductor particles are brought closer to each other and a high photocurrent value can be obtained.

Japanese Patent Application Publication No. 7-60109 International Publication No. 2014/103536

J. M. Luther et al., “Structural, Optical, and Electrical Properties of Self-Assembled Films of PbSe Nanocrystals Treated with 1,2-Ethanedithiol” (ACS Nano 2008, 2, 2, 271-280)

However, while conventional techniques can produce photoelectric conversion elements that exhibit high photocurrent values, there is a problem in that the elements have low durability over time. Therefore, the problem that the present invention aims to solve is to provide a photoelectric conversion element with excellent durability and a photoelectric conversion layer-forming composition for obtaining the same.

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 represented by the following general formula (1) and semiconductor particles:
General formula (1): QR ¹ -Z
[In general formula (1), Q represents a sulfanyl group, an alkylsulfanyl group, or a monovalent heterocycle containing a sulfur atom, ^R represents a direct bond or a divalent linking group, and Z represents a monovalent heterocyclic group.]

The present invention also relates to the photoelectric conversion element in which the semiconductor particles contain a compound semiconductor.

The present invention also relates to the photoelectric conversion element in which the semiconductor particles are capable of absorbing electromagnetic waves with wavelengths of 700 to 2500 nm.

The present invention also relates to the above photoelectric conversion element, in which Z is a monovalent group obtained by removing one hydrogen atom from at least one heterocyclic compound selected from the group consisting of lactone, tetrahydropyran, morpholine, pyridine, and pyrimidine.

［一般式（２）中、
Ｑは、スルファニル基、アルキルスルファニル基、又は硫黄原子を含有する一価の複素環基であり、
Ｒ¹は、直接結合又は二価の連結基であり、
Ａは、脂肪族複素環又は芳香族複素環であり
Ｒ²は、メチン基、一価の有機残基を一つ有する炭素原子又は窒素原子であり、
Ｘは、酸素原子、窒素原子、エステル結合、－Ｃ(＝Ｏ)－ＮＲ⁵－、－ＮＲ⁶－、硫黄原子又はスルホニル基であり、Ｒ⁵及びＲ⁶は、水素原子又はアルキル基を表す。］ The present invention also relates to the above photoelectric conversion element, wherein the surface treatment agent is a surface treatment agent represented by the following general formula (2):
General formula (2)

[In the general formula (2),
Q is a sulfanyl group, an alkylsulfanyl group, or a monovalent heterocyclic group containing a sulfur atom;
R ¹ is a direct bond or a divalent linking group;
A is an aliphatic heterocycle or an aromatic heterocycle; ^R2 is a methine group or a carbon atom or a nitrogen atom having one monovalent organic residue;
X represents an oxygen atom, a nitrogen atom, an ester bond, -C(=O) ^-NR5- , ^-NR6- , a sulfur atom or a sulfonyl group, and ^R5 and ^R6 each represent a hydrogen atom or an alkyl group.]

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 represented by the above general formula (1) and semiconductor particles.

The present invention also relates to a composition for forming a photoelectric conversion layer, in which the compound represented by general formula (1) is a compound represented by the above general formula (2).

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 a 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 contains a surface treatment agent represented by general formula (1) and semiconductor particles.

<Semiconductor particles>
The photoelectric conversion layer contains semiconductor particles. The semiconductor particles refer to particles made of a semiconductor and having an average particle size of 0.5 nm to 100 nm, and are preferably particles 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 represented by general formula (1)>
Next, the surface treatment agent represented by the general formula (1) will be described. Examples of the monovalent heterocyclic group having a sulfur atom in Q include a thienyl group, a tetrahydrothienyl group, a thianyl group, a thiazolyl group, and a thiadinyl group. These may be substituted with an alkyl group. A thienyl group or a thianyl group is more preferred.

In terms of performance as an adsorption group and performance as a surface treatment agent, Q is preferably a sulfanyl group, an alkylsulfanyl group, a thienyl group, or a thianyl group, and more preferably a sulfanyl group.

Specific examples of the alkyl group in the alkylsulfanyl group in Q include methyl, ethyl, butyl, hexyl, octyl, cyclohexyl, and 9-octadecanoyl groups, but from the perspective of performance as an adsorption group, alkyl groups having 1 to 6 carbon atoms are preferred, alkyl groups having 1 to 3 carbon atoms are more preferred, and methyl groups are particularly preferred.

The monovalent heterocyclic group in Z of general formula (1) is not particularly limited as long as it is a monovalent substituent in which one hydrogen atom is formally removed from a heterocyclic compound. Examples of heterocyclic compounds include lactones, lactams, tetrahydropyran, tetrahydrothiopyran, oxathiane, piperazine, tetrahydrothiophene, oxazolane, dithiolane, oxathiolane, dioxane, tetrahydrofuran, morpholine, piperidine, pyrrolidine, sulfolane, pyran, pyridine, pyrimidine, pyridazine, triazine, pyrrole, imidazole, furan, thiophene, thiazole, and quinoline. In terms of performance as a surface treatment agent, lactones, tetrahydropyran, morpholine, pyridine, and pyrimidine are more preferable as heterocyclic compounds. The above heterocyclic compounds may be substituted with alkyl groups, etc.

The divalent linking group in R ¹ of general formula (1) is not particularly limited, and examples thereof include an alkylene group, an arylene group, a heteroarylene group, an ether bond, an ester bond, a sulfide bond, a carbonyl group, an imino group, or a divalent linking group formed by linking these groups. These divalent linking groups may have an unsaturated bond. The divalent linking group is preferably an alkylene group, an ester bond, an amide bond, a carbonyl group, an imino group, or a divalent linking group formed by linking these groups, and more preferably an alkylene group having 1 to 4 carbon atoms, an ester bond, or an amide bond.

The surface treatment agent is preferably a compound represented by the general formula (2).
Specific examples of the alkyl group in ^R5 and ^R6 include a methyl group, an ethyl group, a butyl group, a hexyl group, an octyl group, a cyclohexyl group, and a 9-octadecanoyl group. An alkyl group having 1 to 6 carbon atoms is preferable, an alkyl group having 1 to 3 carbon atoms is more preferable, and a methyl group is particularly preferable.

In particular, it is preferable that in A of the general formula (2), R ² and X are not directly bonded to each other.
Furthermore, it is preferred that R ² and X are bonded together via one or two carbon atoms to form a ring.

From the viewpoint of increasing the content ratio of the quantum dots and ensuring compatibility, the molecular weight of the surface treatment agent is preferably 80-400, and more preferably 100-250.
Specific examples of the surface treatment agent represented by the general formula (1) are shown in Tables 1 to 4 below.

Furthermore, the semiconductor particles may contain organic ligands and halogen elements. Examples of organic ligands include carboxy group-containing compounds, amino group-containing compounds, sulfanyl group-containing compounds, and phosphino group-containing compounds.

<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 known methods 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 electrodes are generally flat in shape, but may be wavy, pyramidal, comb-shaped, etc., to improve energy conversion efficiency. These electrodes can be formed using general electrode formation methods, such as vacuum deposition, sputtering, ion plating, and other PVD methods, CVD, chemical reaction methods (sol-gel method, etc.), casting, spray coating, inkjet, and spin coating.

The photoelectric conversion element may have layers 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 excellent hole injection effect for the photoelectric conversion layer and has excellent adhesion to the anode interface and thin film formability. In addition, 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 are sometimes called hole injection material and hole transport material. These hole injection materials and hole transport materials need to have high hole mobility and small ionization energy, usually 5.5 eV or less. As 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 at least 10 ^-6 cm ² /V·sec when an electric field of, for example, 10 ⁴ to 10 ⁶ V/cm is applied is preferable. The hole injection material and the hole transport material are not particularly limited 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 an organic EL element.

Examples of such hole injection materials and hole transport materials include triazole derivatives, oxadiazole derivatives, imidazole derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, silazane derivatives, thiophene oligomers, porphyrin compounds, aromatic tertiary amine compounds, styrylamines, phthalocyanine derivatives, and inorganic oxides.

Among the above, aromatic tertiary amine compounds are preferred, and specific examples thereof include, for example, 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-f Examples of the compounds include phenyl-cyclohexane, 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, and N,N'-bis(4'-phenyl(1-naphthyl)amino-4-phenyl)-N,N'-di(1-naphthyl)benzidine, which can be used as both a hole injection material and a hole transport material. Particularly preferred examples of hole injection materials are shown in Tables 5 and 6.

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 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, silole derivatives, calcium acetylacetonate, sodium acetate, inorganic oxides, 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, nitrogen-containing five-membered ring derivatives are preferred, and examples thereof include oxazole derivatives, thiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, and triazole derivatives. More specifically, 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. Particularly preferred specific examples of oxadiazole derivatives, triazole derivatives, and silole derivatives are shown in Tables 7 to 9. In addition, Ph in the tables represents a phenyl group.

The photoelectric conversion element may also include other components. For example, it may include an optical film (filter) that blocks ultraviolet light. Ultraviolet light has high energy and is one of the causes of deterioration of organic materials. Blocking this ultraviolet light can extend the life of the element.

A protective film may be provided to protect 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, or polyethylene-polyvinyl alcohol copolymer; an inorganic oxide film or nitride film such as silicon oxide, silicon nitride, or aluminum oxide; a metal plate or foil such as aluminum; or a laminate film of these. 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.

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". All measurements were performed at 25°C unless otherwise specified. The structures of the surface treatment agents used in the comparative examples are shown in Table 10.

<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 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 a 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 22 and Comparative Examples 1 to 8>
PbS-2 to 24, 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 11. Of these, PbS-2 to 18, 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-19 to 24, 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 1
(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 these 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 2 to 22>
Photoelectric conversion elements were fabricated and evaluated in the same manner as in Example 1, except that PbS-2 to 18, PbSe-1 to 2, and Ag ₂ S-1 to 2 were used instead of PbS-1 used in Example 1. The results are shown in Table 10.

<Comparative Examples 1 to 8>
Photoelectric conversion elements were fabricated and evaluated in the same manner as in Example 1, except that PbS-19 to 24, PbSe-3, and Ag ₂ S-3 were used instead of PbS-1 used in Example 1. The results are shown in Table 12.

It was clear that the photoelectric conversion element of the present invention (Examples 1 to 22) had better durability over time than the elements of the comparative examples. Surface treatment agents 1 to 18 used in Examples 1 to 22 were capable of binding or adsorbing to the semiconductor particle surface by heterocyclic groups, and it is speculated that as a result, deterioration due to oxygen, water, etc. was suppressed and the durability of the element was improved. Particularly high durability was observed in Examples 1 to 13. It is speculated that this is because the thiol groups and heterocyclic groups in the surface treatment agent adsorb to the semiconductor particle surface at multiple points, and the semiconductor particles are arranged at an appropriate distance from each other, which further suppresses the approach of water. As is clear from Comparative Examples 1 and 2, when the thiols of Compounds 19 and 20 were used, the desired durability was not obtained. In addition, when the compounds having multiple sulfanyl groups used in Comparative Examples 3 and 4 were used, it is thought that the aggregation of the semiconductor particles became stronger and they were no longer arranged at an appropriate distance.

Claims (7)

A photoelectric conversion element having a photoelectric conversion layer between a pair of electrodes, the photoelectric conversion layer comprising a surface treatment agent represented by the following general formula ( 2 ) and semiconductor particles:
General formula (2)

[In the general formula (2),
Q is a sulfanyl group, an alkylsulfanyl group, or a monovalent heterocyclic group having a sulfur atom;
R ¹ is an alkylene group having 1 to 4 carbon atoms, an arylene group, a heteroarylene group, an ether bond, an ester bond, a sulfide bond, a carbonyl group, an imino group, or a divalent linking group formed by linking these groups;
A is an aliphatic heterocycle or an aromatic heterocycle;
R2 is a methine group or a carbon atom or a nitrogen atom having one monovalent organic residue ^;
X represents an oxygen atom, a nitrogen atom, an ester bond, -C(=O)-NR5- ^, -NR6- ^, a sulfur atom or a sulfonyl group, and ^R5 and R6 ^each represent a hydrogen atom or an alkyl group.] The photoelectric conversion element according to claim 1, wherein the semiconductor particles comprise a compound semiconductor. The photoelectric conversion element according to claim 1 or 2, wherein the semiconductor particles are capable of absorbing electromagnetic waves having a wavelength of 700 to 2500 nm. 4. The photoelectric conversion element according to claim 1, wherein the semiconductor particles have an average particle size of 0.5 nm to 100 nm . 5. The photoelectric conversion element according to claim 1, wherein the molecular weight of the surface treatment agent is 80 to 400 . 6. 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. A composition for forming a photoelectric conversion layer, comprising a surface treatment agent represented by the following general formula ( 2 ) and semiconductor particles:
General formula (2)

[In the general formula (2),
Q is a sulfanyl group, an alkylsulfanyl group, or a monovalent heterocyclic group having a sulfur atom;
R ¹ is an alkylene group having 1 to 4 carbon atoms, an arylene group, a heteroarylene group, an ether bond, an ester bond, a sulfide bond, a carbonyl group, an imino group, or a divalent linking group formed by linking these groups;
A is an aliphatic heterocycle or an aromatic heterocycle;
R2 is a methine group or a carbon atom or a nitrogen atom having one monovalent organic residue ^;
X represents an oxygen atom, a nitrogen atom, an ester bond, -C(=O)-NR5- ^, -NR6- ^, a sulfur atom or a sulfonyl group, and ^R5 and R6 ^each represent a hydrogen atom or an alkyl group.]