WO2025211155A1 - Charge-transporting composition - Google Patents

Abstract

Provided is a charge-transporting composition for forming a charge-transporting thin film for an organic photoelectric conversion element, the charge-transporting composition being ideal for the formation of a charge-transporting thin film for a photoelectric conversion element. In particular, when used as the hole transport layer of an inverted perovskite solar cell, this composition enables large improvement in hole transport layer formability and film stability when the film is left to stand in atmosphere, while maintaining the photoelectric conversion efficiency (PCE) of the resulting element at a high level. The charge-transporting composition comprises a nickel oxide precursor, a polymer compound, and a solvent.

Description

Charge transporting composition

The present invention relates to a charge transport composition, and more specifically to a charge transport composition for forming a charge transport thin film used in an organic photoelectric conversion element.

BACKGROUND ART Electronic elements, particularly organic photoelectric conversion elements, are devices that convert light energy into electrical energy using organic semiconductors, and examples thereof include organic solar cells.
Organic solar cells are solar cell elements that use organic materials in the active layer or charge transport material, and well-known examples include the dye-sensitized solar cell developed by M. Graetzel and the organic thin-film solar cell developed by C. W. Tang (Non-Patent Documents 1 and 2).
Both solar cells have features that set them apart from the currently mainstream inorganic solar cells, such as being lightweight, thin, flexible, and capable of roll-to-roll production, and so are expected to create new markets.

On the other hand, in recent years, research results have been reported showing that solar cells using metal halides as compounds with a perovskite crystal structure (hereinafter referred to as "perovskite semiconductor compounds") can achieve relatively high photoelectric conversion efficiencies, and these have attracted attention. For example, Patent Document 1 describes a photoelectric conversion element and solar cell with an active layer containing a perovskite semiconductor compound.

Furthermore, in photoelectric conversion elements that use perovskite semiconductor compounds in the active layer, further investigation is being conducted into the conditions of not only the active layer but also the other layers that are combined with it, in order to further improve the element characteristics.

JP 2016-178193 A

Nature, vol.353, 737-740(1991) Appl. Phys. Lett., Vol.48, 183-185 (1986)

The present invention was made in consideration of the above circumstances, and aims to provide a charge-transporting composition that is suitable for forming charge-transporting thin films in photoelectric conversion elements, and in particular, when used as a hole-collection layer in inverted-stack perovskite solar cells, can improve the film-forming process during mass-production of elements while maintaining high photoelectric conversion efficiency (PCE) in the resulting elements.

As a result of extensive research to achieve the above-mentioned objective, the inventors have discovered that a charge transporting composition containing a nickel oxide precursor, a polymer compound, and a solvent is suitable for forming a charge transporting thin film in an organic photoelectric conversion element. In particular, when this charge transporting thin film is used as a hole collection layer in an inverted stack-type perovskite solar cell, the PCE of the resulting element is maintained at a high level, while the film formability of the hole collection layer and the stability of the film when left standing in air are greatly improved, resulting in superior mass production process capabilities, and this led to the completion of the present invention.

That is, the present invention provides the following charge transport composition.
1. A charge transporting composition for forming a charge transporting thin film in an organic photoelectric conversion element, comprising:
A charge transporting composition comprising a nickel oxide precursor, a polymer compound, and a solvent.
2. The charge transporting composition according to claim 1, wherein the solvent is an organic solvent.
3. The charge transport composition of 1, wherein the nickel oxide precursor is at least one selected from the group consisting of inorganic acid nickel salts and organic acid nickel salts.
4. The charge transporting composition of 3, wherein the inorganic acid nickel salt is at least one selected from the group consisting of nickel nitrate, nickel sulfate, nickel phosphate, nickel carbonate, nickel hydrogen carbonate, nickel borate, nickel chloride, and nickel hydrofluoride.
5. The charge transport composition of 3, wherein the organic acid nickel salt is at least one selected from the group consisting of nickel acetate, nickel formate, nickel oxalate, and nickel (II) acetylacetonate.
6. The charge transport composition of any one of 1 to 5, wherein the polymer compound comprises at least one polyimide polymer selected from the group consisting of a polyimide precursor obtained from a diamine component and a tetracarboxylic acid component, an ester of the polyimide precursor, and an imidized product of the polyimide precursor.
7. Any of the charge-transporting compositions according to 6, wherein the polymer compound comprises at least one polyimide polymer selected from the group consisting of a polyimide precursor obtained from a diamine component having a structure represented by any one of the following formulas (1) to (3) and a tetracarboxylic acid component, an ester of the polyimide precursor, and an imidized product of the polyimide precursor:
(In the formula, ^R1 represents a hydrogen atom or a monovalent organic group. * represents a bonding site to another group. Any hydrogen atom forming the benzene ring may be substituted with a monovalent organic group.)
8. The charge transport composition of 1, wherein the polymer compound contains polyethyleneimine.
9. The charge transport composition of any one of 1 to 8, wherein the content of the polymer compound is 5 to 20 parts by mass per 100 parts by mass of the nickel oxide precursor.
10. The charge transport composition according to any one of 1 to 9, which is used for a hole collection layer of a perovskite photoelectric conversion element.
11. A charge transporting thin film obtained from the charge transporting composition of any one of 1 to 9.
12. The charge transport thin film of 11, wherein the charge transport thin film is a hole collection layer of a perovskite photoelectric conversion element.
13. A perovskite photoelectric conversion element comprising the charge transport thin film of 12.
14. Perovskite photoelectric conversion element 13, which is an inverted stacking type.
15. A solar cell comprising the perovskite photoelectric conversion element of 14.
16. A method for producing a charge transport thin film for a hole collection layer of a perovskite photoelectric conversion element, comprising the steps of:
A method for producing a charge transport thin film for use as a hole collection layer in a perovskite photoelectric conversion element, comprising applying a charge transport composition containing a nickel oxide precursor, a polymer compound, and a solvent, and baking the applied composition at 260°C or higher.

The charge-transporting composition of the present invention is suitable for forming a charge-transporting thin film for a photoelectric conversion element. In particular, when this charge-transporting thin film is used as a hole-collecting layer in an inverted-layer-type perovskite photoelectric conversion element, the PCE of the resulting element is maintained at a high level, while the film-forming properties of the hole-collecting layer and the stability of the film when left standing in the air are greatly improved, resulting in a perovskite photoelectric conversion element with excellent mass-production process capabilities.

The present invention will be described in more detail below.
The charge transport composition of the present invention is a charge transport composition for forming a charge transport thin film in an organic photoelectric conversion element, and is characterized by containing a nickel oxide precursor, a polymer compound, and a solvent.

[Nickel oxide precursor]
In the charge-transporting composition of the present invention, the nickel oxide precursor refers to a substance that exists in a state other than nickel oxide in the composition and generates nickel oxide upon firing during film formation. Nickel oxide generally has poor solubility in organic solvents, making it difficult to obtain an organic solvent-based charge-transporting composition. However, by using a nickel oxide precursor that has excellent solubility in organic solvents, a stable charge-transporting composition can be obtained. Furthermore, since the nickel oxide precursor can be easily mixed with a polymer compound, film formation defects such as whitening and pinholes that tend to occur during the formation of a charge-transporting thin film can be suppressed.

Examples of the nickel oxide precursor include inorganic acid nickel salts and organic acid nickel salts.

Specific examples of the inorganic nickel salts include nickel nitrate, nickel sulfate, nickel phosphate, nickel carbonate, nickel bicarbonate, nickel borate, nickel hydrochloride, and nickel hydrofluoride.

Specific examples of the above-mentioned organic acid nickel salts include nickel acetate, nickel formate, nickel oxalate, and nickel(II) acetylacetonate.

The above nickel oxide precursors may be used alone or in combination of two or more.

[Polymer compound]
In the charge-transporting composition of the present invention, the polymer compound is not particularly limited and can be appropriately selected from charge-transporting polymers used in the field of organic photoelectric conversion elements, etc. Examples of the charge-transporting polymer include polythiophene derivatives, polyaniline derivatives, polypyrrole derivatives, polyimide polymers, etc. In the present invention, polyimide polymers are preferred from the viewpoint of heat resistance and light resistance, and at least one polyimide polymer selected from the group consisting of polyimide precursors obtained from a diamine component and a tetracarboxylic acid component, esters of the polyimide precursors, and imidized products of the polyimide precursors is particularly preferred. Examples of the diamine component include diamine components having a structure represented by any of the following formulas (1) to (3) and diamine components represented by the following formula (E1), with diamine components having a structure represented by any of the following formulas (1) to (3) being preferred.

(In the formula, ^R1 represents a hydrogen atom or a monovalent organic group. * represents a bonding site to another group. Any hydrogen atom forming the benzene ring may be substituted with a monovalent organic group.)

(In the formula, ^A1 and ^A2 each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms, and ^Y1 represents a divalent organic group.)

Hereinafter, diamines having the structures of formulas (1) to (3) may be referred to as "specific diamines." Furthermore, polymers containing the specific diamines of the present invention may be referred to as "specific polymers."

<Specific diamine>
The specific diamine has any of the structures represented by the following formulas (1) to (3).

In the above formulas (1) to (3), ^R1 represents a hydrogen atom or a monovalent organic group. * represents a site for bonding to another group. Any hydrogen atom forming the benzene ring may be substituted with a monovalent organic group. Examples of the monovalent organic group include an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a fluoroalkenyl group having 2 to 10 carbon atoms, a fluoroalkoxy group having 1 to 10 carbon atoms, and a tert-butoxycarbonyl group.

Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl groups.

Examples of alkenyl groups having 2 to 10 carbon atoms include ethenyl, n-1-propenyl, n-2-propenyl, 1-methylethenyl, n-1-butenyl, n-2-butenyl, n-3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylethenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, n-1-pentenyl, and n-1-decenyl.

Alkoxy groups having 1 to 10 carbon atoms include methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, n-pentoxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, and n-decyloxy.

The fluoroalkyl group having 1 to 10 carbon atoms is not particularly limited as long as it is an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom on the carbon atom has been substituted with a fluorine atom, but specific examples include a fluoromethyl group, a difluoromethyl group, a perfluoromethyl group, a 1-fluoroethyl group, a 2-fluoroethyl group, a 1,2-difluoroethyl group, a 1,1-difluoroethyl group, a 2,2-difluoroethyl group, a 1,1,2-trifluoroethyl group, a 1,2,2-trifluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, a 1,2,2,2-tetrafluoroethyl group, a perfluoroethyl group, a 1-fluoropropyl group, a 2-fluoropropyl group, a 3-fluoropropyl group, a 1,1-difluoropropyl group, a 1,2-difluoropropyl group, a 1,3-difluoropropyl group, a 2,2-difluoropropyl group, a 2,3-difluoropropyl group, a 3,3-difluoropropyl group, and a 1,1,2-trifluoropropyl group. group, 1,1,3-trifluoropropyl group, 1,2,3-trifluoropropyl group, 1,3,3-trifluoropropyl group, 2,2,3-trifluoropropyl group, 2,3,3-trifluoropropyl group, 3,3,3-trifluoropropyl group, 1,1,2,2-tetrafluoropropyl group, 1,1,2,3-tetrafluoropropyl group, 1,2,2,3-tetrafluoropropyl group, 1,3,3,3-tetrafluoropropyl group, 2,2,3,3-tetrafluoropropyl group , 2,3,3,3-tetrafluoropropyl group, 1,1,2,2,3-pentafluoropropyl group, 1,2,2,3,3-pentafluoropropyl group, 1,1,3,3,3-pentafluoropropyl group, 1,2,3,3,3-pentafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, perfluoroheptyl group, perfluorooctyl group, etc.

The fluoroalkenyl group having 2 to 10 carbon atoms is not particularly limited as long as it is a fluoroalkenyl group having 2 to 10 carbon atoms in which at least one hydrogen atom on the carbon atom has been substituted with a fluorine atom, but specific examples include a 2-fluoroethenyl group, a 2,2-difluoroethenyl group, a 2-fluoro-2-propenyl group, a 3,3-difluoro-2-propenyl group, a 2,3-difluoro-2-propenyl group, a 3,3-difluoro-2-methyl-2-propenyl group, a 3-fluoro-2-butenyl group, a perfluorovinyl group, a perfluoropropenyl group, and a perfluorobutenyl group.

The fluoroalkoxy group having 1 to 10 carbon atoms is not particularly limited as long as it is an alkoxy group having 1 to 10 carbon atoms in which at least one hydrogen atom on the carbon atom is substituted with a fluorine atom, but specific examples include a fluoromethoxy group, a difluoromethoxy group, a perfluoromethoxy group, a 1-fluoroethoxy group, a 2-fluoroethoxy group, a 1,2-difluoroethoxy group, a 1,1-difluoroethoxy group, a 2,2-difluoroethoxy group, and a 1,1,2-trifluoroethoxy group. groups, 1,2,2-trifluoroethoxy groups, 2,2,2-trifluoroethoxy groups, 1,1,2,2-tetrafluoroethoxy groups, 1,2,2,2-tetrafluoroethoxy groups, perfluoroethoxy groups, 1-fluoropropoxy groups, 2-fluoropropoxy groups, 3-fluoropropoxy groups, 1,1-difluoropropoxy groups, 1,2-difluoropropoxy groups, 1,3-difluoropropoxy groups, 2,2-difluoropropoxy groups, 2,3-difluoropropoxy groups, 3,3-difluoropropoxy group, 1,1,2-trifluoropropoxy group, 1,1,3-trifluoropropoxy group, 1,2,3-trifluoropropoxy group, 1,3,3-trifluoropropoxy group, 2,2,3-trifluoropropoxy group, 2,3,3-trifluoropropoxy group, 3,3,3-trifluoropropoxy group, 1,1,2,2-tetrafluoropropoxy group, 1,1,2,3-tetrafluoropropoxy group, 1,2,2,3-tetrafluoropropoxy group Examples include a 1,3,3,3-tetrafluoropropoxy group, a 2,2,3,3-tetrafluoropropoxy group, a 2,3,3,3-tetrafluoropropoxy group, a 1,1,2,2,3-pentafluoropropoxy group, a 1,2,2,3,3-pentafluoropropoxy group, a 1,1,3,3,3-pentafluoropropoxy group, a 1,2,3,3,3-pentafluoropropoxy group, a 2,2,3,3,3-pentafluoropropoxy group, and a perfluoropropoxy group.

R ¹ is preferably a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkenyl group having 2 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a fluoroalkenyl group having 2 to 3 carbon atoms, a fluoroalkoxy group having 1 to 3 carbon atoms, or a tert-butoxycarbonyl group, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom or a methyl group.

In the structure of formula (1) above, from the standpoint of charge transport properties, the bonding position of the benzene ring to the pyrrole ring is preferably the carbon atom next to the nitrogen atom on the pyrrole ring, as shown in formula (1-1) below.

A preferred example of a diamine having the structure of formula (1) above is a diamine represented by formula (1-2) below.

In the above formula (1-2), ^R1 is the same as in formula (1). Two ^R2s each independently represent a single bond or a structure of the following formula (1-3). As in formula (1), any hydrogen atom forming the benzene ring may be substituted with a monovalent organic group.

In formula (1-3), ^R3 represents a divalent organic group selected from the group consisting of a single bond, -O-, -COO-, -OCO-, -( _CH2 ) _i- , -O( _CH2 ) _jO- , -CONH-, -NHCO-, -CON( _CH3 )-, -N( _CH3 )CO-, and -NR1-. Here, i represents an integer of 1 to ¹⁴ , and j represents an integer of 1 to 14. ^R1 is the same as in formula (1). Among these, from the viewpoint of charge transport properties, ^R3 is preferably a single bond, -O-, -COO-, -OCO-, -CONH-, -NHCO-, or -N(CH3)-. Furthermore, * ₁ represents the site of bonding to the benzene ring in formula ( ₂ ). * ₂ represents the site of bonding to the amino group in formula (1-2). In formula (1-2), k1 is an integer of 1 to 3, preferably 1 or 2.

Specific examples of the above formula (1-2) include, but are not limited to, those represented by the following formulas (1-2-1) to (1-2-17). Among these, from the viewpoint of charge transportability, formula (1-2-1), formula (1-2-2), formula (1-2-3), formula (1-2-5), formula (1-2-8), formula (1-2-9), formula (1-2-10), formula (1-2-11), formula (1-2-12), formula (1-2-13), formula (1-2-14), formula (1-2-15), formula (1-2-16) and formula (1-2-17) are preferred, and formula (1-2-1), formula (1-2-2), formula (1-2-3), formula (1-2-11), formula (1-2-12), formula (1-2-13), formula (1-2-14), formula (1-2-15), formula (1-2-16) and formula (1-2-17) are more preferred. In the following formulas (1-2-6) and (1-2-7), x1 is an integer from 1 to 14. Also, Boc represents a tert-butoxycarbonyl group.

In the structure of formula (2) above, the bonding position of other groups to the carbazole ring is preferably as shown in formula (2-1) in terms of steric hindrance.

In the above formula (2-1), R ¹ is as defined above.

The specific diamines mentioned above include diamines represented by the following formulas (2-2) to (2-7). In particular, from the viewpoint of charge transport properties, diamines represented by formulas (2-3) to (2-7) are preferred, and diamines represented by formulas (2-4) to (2-7) are more preferred.

In the above formula, ^R1 is defined as in the above formula (1), ^R4 is each independently a hydrogen atom or a monovalent organic group, and ^R5 is each independently a single bond or a divalent organic group. k2 is each independently 2 or 3. Any hydrogen atom on the benzene ring may be substituted with a monovalent organic group.

Examples of the monovalent organic group in R ⁴ include the same as those exemplified in the description of R ^1. R ⁴ is preferably a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkenyl group having 2 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a fluoroalkenyl group having 2 to 3 carbon atoms, a fluoroalkoxy group having 1 to 3 carbon atoms, or a tert-butoxycarbonyl group, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom or a methyl group.

The divalent organic group for ^R5 includes groups having the structure of the following formula (2-8).

In the above formula, ^R6 represents a divalent organic group selected from the group consisting of a single bond, -O-, -COO-, -OCO-, -( _CH2 ) _r- , -O( _CH2 ) _sO- , ^-NR61- , ^-CONR61- , and ^-NR61CO- , and k3 represents an integer of 1 to 5. ^R61 represents hydrogen or a monovalent organic group, r represents an integer of 1 to 5, and s represents an integer of 1 to 5. As the monovalent organic group, an alkyl group having 1 to 3 carbon atoms is preferred, and a methyl group is more preferred. * ₃ represents the site of bonding to the benzene ring in formulas (2-5) to (2-7), and * ₄ represents the site of bonding to the amino group in formulas (2-5) to (2-7).

Specific examples of the specific diamine include, but are not limited to, diamines represented by the following formulas (2-1-1) to (2-1-19). Among these, from the viewpoint of charge transport properties, formulas (2-1-1) to (2-1-7) and (2-1-10) to (2-1-17) are preferred, and formulas (2-1-1) to (2-1-7) and (2-1-15) to (2-1-17) are more preferred. In the following formulas, x2 is an integer from 1 to 14.

In the structure of formula (3) above, the bonding position of other groups relative to the benzene ring is preferably as shown in formula (3-1) in terms of steric hindrance.

In the above formula (3-1), R ¹ is as defined above.

The specific diamines include those represented by the following formulas (3-2) to (3-7). From the standpoint of charge transport properties, the diamines represented by formulas (3-3) to (3-7) are preferred, and the diamines represented by formulas (3-4) to (3-7) are more preferred.

In the above formula, ^R1 is defined as in the above formula (1), ^R7 is each independently a hydrogen atom or a monovalent organic group, and ^R8 is each independently a single bond or a divalent organic group. k4 is each independently 2 or 3. Any hydrogen atom on the benzene ring may be substituted with a monovalent organic group.

Examples of the monovalent organic group in R ⁷ include the same as those exemplified in the description of R ^1. R ⁷ is preferably a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkenyl group having 2 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a fluoroalkenyl group having 2 to 3 carbon atoms, a fluoroalkoxy group having 1 to 3 carbon atoms, or a tert-butoxycarbonyl group, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom or a methyl group.

The divalent organic group for R ⁸ includes groups having the structure of the following formula (3-8).

In the above formula, ^R9 represents a divalent organic group selected from the group consisting of a single bond, -O-, -COO-, -OCO-, -( _CH2 ) _r- , -O( _CH2 ) _sO- , ^-NR91- , ^-CONR91- , and ^-NR91CO- , and k5 represents an integer of 1 to 5. ^R91 represents hydrogen or a monovalent organic group, r represents an integer of 1 to 5, and s represents an integer of 1 to 5. As the monovalent organic group, an alkyl group having 1 to 3 carbon atoms is preferred, and a methyl group is more preferred. * ₅ represents the site of bonding to the benzene ring in formulas (3-5) to (3-7), and * ₆ represents the site of bonding to the amino group in formulas (3-5) to (3-7).

Specific examples of the specific diamine include, but are not limited to, diamines represented by the following formulas (3-1-1) to (3-1-19). Among these, from the viewpoint of charge transport properties, formulas (3-1-1) to (3-1-7) and (3-1-10) to (3-1-17) are preferred, and formulas (3-1-1) to (3-1-7) and (3-1-15) to (3-1-17) are more preferred. In the following formulas, x3 is an integer from 1 to 14.

<Method for synthesizing specific diamine>
The specific diamine can be synthesized by any known method, and is not particularly limited. For example, the specific diamine can be synthesized by the methods described in WO 2018/062197, WO 2018/110354, etc.

<Diamine component represented by formula (E1)>
In the present invention, in addition to the specific diamine component described above, a diamine component represented by the following formula (E1) may be used as a diamine component for obtaining a polyimide-based polymer. Furthermore, this diamine component may be contained in the diamine component for obtaining the specific polymer.

In the above formula (E1), ^A1 and ^A2 each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms, and ^Y1 represents a divalent organic group.

Examples of alkyl groups having 1 to 5 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, i-butyl, s-butyl, t-butyl, and n-pentyl groups.

Examples of alkenyl groups having 2 to 5 carbon atoms include ethenyl, n-1-propenyl, n-2-propenyl, 1-methylethenyl, n-1-butenyl, n-2-butenyl, n-3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylethenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, and n-1-pentenyl.

Examples of alkynyl groups having 2 to 5 carbon atoms include ethynyl, n-1-propynyl, n-2-propynyl, n-1-butynyl, n-2-butynyl, n-3-butynyl, 1-methyl-2-propynyl, n-1-pentynyl, n-2-pentynyl, n-3-pentynyl, n-4-pentynyl, 1-methyl-n-butynyl, 2-methyl-n-butynyl, 3-methyl-n-butynyl, and 1,1-dimethyl-n-propynyl.

Among these, from the viewpoint of the reactivity of the monomer, A ¹ and A ² are preferably a hydrogen atom or a methyl group.

Examples of ^Y1 include groups represented by the following formulas (Y-1) to (Y-171). In the following formulas, x4 is an integer of 1 to 14, and where there is a preferred range, that range is also noted. In addition, where there is no description of the range of x4, an integer of 1 to 6 is preferred. In addition, in the following formulas, Me represents a methyl group, and Boc represents a tert-butoxycarbonyl group.

The diamines represented by formula (E1) described above may be used alone or in combination of two or more.

Furthermore, the diamine represented by formula (E1) above may be contained in the diamine component used to obtain the specific polymer. When the diamine component used to obtain the specific polymer contains the diamine represented by formula (E1), the content of the specific diamine in the diamine component can be preferably 10 to 100 mol%, more preferably 30 to 100 mol%, and even more preferably 50 to 100 mol%.

<Tetracarboxylic acid component>
Examples of tetracarboxylic acid components for obtaining polyimide-based polymers such as specific polymers include tetracarboxylic acids, tetracarboxylic acid dianhydrides, tetracarboxylic acid dihalides, tetracarboxylic acid dialkyl esters, and tetracarboxylic acid dialkyl ester dihalides. In the present invention, these are also collectively referred to as tetracarboxylic acid components.

The tetracarboxylic acid component may also be a tetracarboxylic acid dianhydride or its derivatives, such as a tetracarboxylic acid, a tetracarboxylic acid dihalide, a tetracarboxylic acid dialkyl ester, and a tetracarboxylic acid dialkyl ester dihalide (collectively referred to as the first tetracarboxylic acid component).

Examples of tetracarboxylic acid dianhydrides include aliphatic tetracarboxylic acid dianhydrides, alicyclic tetracarboxylic acid dianhydrides, and aromatic tetracarboxylic acid dianhydrides. Specific examples of these include those in the following groups [1] to [5].

[1] Examples of aliphatic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride.

[2] Examples of alicyclic tetracarboxylic acid dianhydrides include acid dianhydrides such as those represented by the following formulae (X1-1) to (X1-13).

In the above formulas (X1-1) to (X1-4), R ^1a to R ^21a each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms and containing a fluorine atom, or a phenyl group. R ^M represents a hydrogen atom or a methyl group. Furthermore, in the above formula (X1-13), X ^a represents a tetravalent organic group represented by the following formulas (Xa-1) to (Xa-7):

[3] Examples include 3-oxabicyclo[3.2.1]octane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',5'-dione), 3,5,6-tricarboxy-2-carboxymethylnorbornane-2:3,5:6-dianhydride, and 4,9-dioxatricyclo[5.3.1.02,6]undecane-3,5,8,10-tetraone.

[4] Examples of aromatic tetracarboxylic acid dianhydrides include pyromellitic anhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, and acid dianhydrides represented by the following formulas (X2-1) to (X2-10).

[5] Examples include acid dianhydrides represented by the following formulas (X3-1) to (X3-9), and tetracarboxylic acid dianhydrides described in JP 2010-97188 A.

The tetracarboxylic acid components described above may be used alone or in combination of two or more. Depending on the properties required for the charge transport layer of the organic photoelectric conversion element, either one type may be used alone or two or more types may be used in combination, and if two or more types are used in combination, the ratios, etc., can be adjusted as appropriate.

<Method of producing polyimide polymer>
As described above, polyimide polymers such as specific polymers can be obtained by reacting a diamine component with a tetracarboxylic acid component. For example, one method involves reacting a diamine component consisting of one or more diamines with at least one tetracarboxylic acid component selected from the group consisting of tetracarboxylic dianhydrides and derivatives of such tetracarboxylic acids to obtain a polyamic acid. Specifically, a method is used in which a primary or secondary diamine is polycondensed with a tetracarboxylic dianhydride to obtain a polyamic acid.

Polyamic acid alkyl esters can be obtained by polycondensing a tetracarboxylic acid in which the carboxylic acid group has been dialkyl esterified with a primary or secondary diamine, by polycondensing a tetracarboxylic acid dihalide in which the carboxylic acid group has been halogenated with a primary or secondary diamine, or by converting the carboxy group of a polyamic acid into an ester. Polyimides can be obtained by ring-closing the above polyamic acid or polyamic acid alkyl ester to form a polyimide.

The reaction between the diamine component and the tetracarboxylic acid component is typically carried out in a solvent. The solvent used is not particularly limited, as long as it dissolves the resulting polyimide precursor. Examples of solvents include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, 3-methoxy-N,N-dimethylpropanamide, dimethyl sulfoxide, and 1,3-dimethyl-imidazolidinone. Furthermore, if the polyimide precursor has high solvent solubility, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, or solvents represented by the following formulas [s1] to [s3] can also be used.

In formula [s1], D ^s1 represents an alkyl group having 1 to 3 carbon atoms. In formula [s2], D ^s2 represents an alkyl group having 1 to 3 carbon atoms. In formula [s3], D ^s3 represents an alkyl group having 1 to 4 carbon atoms.

Examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, i-butyl, s-butyl, and t-butyl groups. Examples of alkyl groups having 1 to 3 carbon atoms include the above alkyl groups having 1 to 4 carbon atoms, but with 1 to 3 carbon atoms.

These solvents may be used alone or in combination of two or more. Even if the solvent does not dissolve the polyimide precursor, it may be mixed with the above solvent as long as the resulting polyimide precursor does not precipitate. Furthermore, moisture in the solvent inhibits the polymerization reaction and can even cause the resulting polyimide precursor to hydrolyze, so it is preferable to use a dehydrated and dried solvent.

When reacting a diamine component and a tetracarboxylic acid component in a solvent, any of the following methods may be used: a solution in which the diamine component is dispersed or dissolved in a solvent is stirred, and the tetracarboxylic acid component is added as is or dispersed or dissolved in the solvent; conversely, the diamine component is added to a solution in which the tetracarboxylic acid component is dispersed or dissolved in a solvent; or the diamine component and the tetracarboxylic acid component are added alternately. Furthermore, when reacting multiple types of diamine components or multiple types of tetracarboxylic acid components, they may be reacted in a pre-mixed state, or they may be reacted individually in sequence. Furthermore, low molecular weight components that have been reacted individually may be mixed and reacted to form a polymer.

The temperature at which the diamine component and tetracarboxylic acid component are polycondensed can be selected from the range of -20 to 150°C, but is preferably in the range of -5 to 100°C. The reaction can be carried out at any concentration, but if the concentration is too low, it becomes difficult to obtain a high-molecular-weight polymer, and if the concentration is too high, the reaction solution becomes too viscous, making uniform stirring difficult. Therefore, the concentration is preferably 1 to 50% by mass, and more preferably 5 to 30% by mass. The reaction can also be carried out at a high concentration initially, with additional solvent added later.

In the polymerization reaction of the polyimide precursor, the ratio of the total number of moles of the diamine component to the total number of moles of the tetracarboxylic acid component is preferably 0.8 to 1.2. As with a typical polycondensation reaction, the closer this molar ratio is to 1.0, the higher the molecular weight of the resulting polyimide precursor.

Polyimides are obtained by ring-closing the polyimide precursors described above. In these polyimides, the ring-closure rate of the amic acid groups (also called the imidization rate) does not necessarily have to be 100% and can be adjusted as desired depending on the application and purpose. Methods for imidizing polyimide precursors include thermal imidization, in which a solution of the polyimide precursor is heated as is, and catalytic imidization, in which a catalyst is added to a solution of the polyimide precursor.

When thermally imidizing a polyimide precursor in a solution, the temperature is 100 to 400°C, preferably 120 to 250°C, and it is preferable to carry out the process while removing the water produced by the imidization reaction from the system. Catalytic imidization of a polyimide precursor can be carried out by adding a basic catalyst and an acid anhydride to a solution of the polyimide precursor and stirring the mixture at -20 to 250°C, preferably 0 to 180°C.

The amount of basic catalyst is 0.5 to 30 times the molar amount of amide acid groups, preferably 2 to 20 times the molar amount, and the amount of acid anhydride is 1 to 50 times the molar amount of amide acid groups, preferably 3 to 30 times the molar amount. Examples of basic catalysts include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Pyridine is preferred because it has the appropriate basicity to promote the reaction. Examples of acid anhydrides include acetic anhydride, trimellitic anhydride, and pyromellitic anhydride. Acetic anhydride is particularly preferred because it facilitates purification after the reaction. The imidization rate by catalytic imidization can be controlled by adjusting the amount of catalyst, reaction temperature, and reaction time.

When recovering the resulting polyimide precursor or polyimide from a reaction solution of polyimide precursor or polyimide, the reaction solution can be precipitated by pouring it into a solvent. Examples of solvents that can be used for precipitation include methanol, ethanol, isopropyl alcohol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, toluene, benzene, and water. The polymer precipitated by pouring it into a solvent can be recovered by filtration and then dried at normal or reduced pressure, or at room temperature or by heating. Furthermore, the precipitated polymer can be redissolved in a solvent and reprecipitated and recovered 2 to 10 times, reducing the amount of impurities in the polymer. Examples of solvents that can be used in this process include alcohols, ketones, and hydrocarbons. Using three or more solvents selected from these is preferable, as this further increases the efficiency of purification.

More specific examples of methods for producing the polyamic acid alkyl ester of the present invention are shown below in (1) to (3).

(1) Production method by esterification reaction of polyamic acid: This method involves producing polyamic acid from, for example, a diamine component and a tetracarboxylic acid component, and then chemically reacting its carboxyl group (COOH group), i.e., esterifying it, to produce a polyamic acid alkyl ester. The esterification reaction involves reacting polyamic acid with an esterifying agent in the presence of a solvent at −20 to 150° C. (preferably 0 to 50° C.) for 30 minutes to 24 hours (preferably 1 to 4 hours).

The esterifying agent is preferably one that can be easily removed after the esterification reaction, and examples include N,N-dimethylformamide dimethyl acetal, N,N-dimethylformamide diethyl acetal, N,N-dimethylformamide dipropyl acetal, N,N-dimethylformamide dineopentyl butyl acetal, N,N-dimethylformamide di-t-butyl acetal, 1-methyl-3-p-tolyltriazene, 1-ethyl-3-p-tolyltriazene, 1-propyl-3-p-tolyltriazene, and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride. The amount of esterifying agent used is preferably 2 to 6 molar equivalents per mole of polyamic acid repeating units. Of these, 2 to 4 molar equivalents is preferred.

The solvent used in the esterification reaction may be the same as the solvent used in the reaction between the diamine component and the tetracarboxylic acid component, in terms of the solubility of the polyamic acid in the solvent. Of these, N,N-dimethylformamide, N,N-diethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, 3-methoxy-N,N-dimethylpropanamide, or γ-butyrolactone is preferred. These solvents may be used alone or in combination of two or more. The concentration of polyamic acid in the solvent used in the esterification reaction is preferably 1 to 30% by mass, in order to prevent precipitation of the polyamic acid. Of these, 5 to 20% by mass is preferred.

(2) Production method by reacting a diamine component with a tetracarboxylic acid diester dichloride. This method involves reacting a diamine component with a tetracarboxylic acid diester dichloride in the presence of a base and a solvent at −20 to 150° C. (preferably 0 to 50° C.) for 30 minutes to 24 hours (preferably 1 to 4 hours). Examples of the base that can be used include pyridine, triethylamine, and 4-dimethylaminopyridine. Of these, pyridine is preferred because the reaction proceeds mildly. The amount of base used is preferably an amount that can be easily removed after the reaction, and is preferably 2 to 4 times the molar amount of the tetracarboxylic acid diester dichloride, and more preferably 2 to 3 times the molar amount.

The solvent may be one used in the reaction between the diamine component and the tetracarboxylic acid component, taking into account the solubility of the resulting polymer, i.e., polyamic acid alkyl ester, in the solvent. Among these, N,N-dimethylformamide, N,N-diethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, 3-methoxy-N,N-dimethylpropanamide, or γ-butyrolactone is preferred. These solvents may be used alone or in combination of two or more.

The concentration of the polyamic acid alkyl ester in the solvent used in the reaction is preferably 1 to 30% by mass, as this reduces the likelihood of precipitation of the polyamic acid alkyl ester. Of these, 5 to 20% by mass is preferred. Furthermore, to prevent hydrolysis of the tetracarboxylic acid diester dichloride, it is preferable that the solvent used to prepare the polyamic acid alkyl ester be as dehydrated as possible. Furthermore, it is preferable to carry out the reaction in a nitrogen atmosphere to prevent the inclusion of outside air.

(3) Method of producing by reaction of a diamine component with a tetracarboxylic acid diester. This method is, for example, a method of polycondensation reaction of a diamine component with a tetracarboxylic acid diester in the presence of a condensing agent, a base, and a solvent at 0 to 150°C (preferably 0 to 100°C) for 30 minutes to 24 hours (preferably 3 to 15 hours).

Condensing agents that can be used include triphenyl phosphite, dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-carbonyldiimidazole, dimethoxy-1,3,5-triazinylmethylmorpholinium, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, and (2,3-dihydro-2-thioxo-3-benzoxazolyl)diphenyl phosphonate. The amount of condensing agent used is preferably 2 to 3 times the molar amount of the tetracarboxylic acid diester, and more preferably 2 to 2.5 times the molar amount.

The base can be a tertiary amine such as pyridine or triethylamine. The amount of base used is preferably an amount that can be easily removed after the polycondensation reaction, and is preferably 2 to 4 times the molar amount of the diamine component, and more preferably 2 to 3 times the molar amount. The solvent used in the polycondensation reaction can be the same as the solvent used in the reaction between the diamine component and the tetracarboxylic acid component, in terms of the solubility of the resulting polymer, i.e., the polyamic acid alkyl ester, in the solvent. Of these, N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone is preferred. These solvents can be used alone or in combination of two or more.

Furthermore, in the polycondensation reaction, adding a Lewis acid as an additive allows the reaction to proceed efficiently. A preferred Lewis acid is a lithium halide such as lithium chloride or lithium bromide. The amount of Lewis acid used is preferably 0.1 to 10 times the molar amount of the diamine component. Of these, 2.0 to 3.0 times the molar amount is preferred.

To recover a polyamic acid alkyl ester from a solution of polyamic acid alkyl ester obtained by methods (1) to (3) above, the reaction solution may be precipitated by pouring the reaction solution into a solvent. Examples of solvents used for precipitation include water, methanol, ethanol, 2-propanol, hexane, butyl cellosolve (ethylene glycol monobutyl ether), acetone, and toluene. The polymer precipitated by pouring into the solvent is preferably washed multiple times with the solvent to remove the additives and catalysts used above. After washing and filtration, the polymer can be dried under atmospheric pressure or reduced pressure, at room temperature, or by heating. Furthermore, the precipitated polymer can be redissolved in a solvent and reprecipitated and recovered 2 to 10 times to reduce the amount of impurities in the polymer. The polyamic acid alkyl ester is preferably produced by the method (2) or (3) above.

In the charge transport composition of the present invention, polyethyleneimine can also be used as the polymer compound. In the present invention, polyethyleneimine is not particularly limited as long as it is a polymer obtained by polymerizing ethyleneimine, and it can be a linear polyethyleneimine or a branched polyethyleneimine containing a tertiary amine. It can also be a modified polyethyleneimine in which the active hydrogen of the amino group in polyethyleneimine has been modified, or a branched polyethyleneimine-graft-polyethylene glycol. In the present invention, the above-mentioned polyethyleneimine is preferably a branched polyethyleneimine containing a tertiary amine.

Commercially available polyethyleneimine can be used as the polyethyleneimine. Examples of such commercially available products include polyethyleneimine 10000 manufactured by Junsei Chemical Co., Ltd., and the Epomin (registered trademark) series, SP-012, SP-018, SP-200, HM-2000, and P-1000 manufactured by Nippon Shokubai Co., Ltd.

Taking into consideration the solvent resistance of the resulting thin film, the content of the above polymer compound is preferably 5 to 100 parts by mass, more preferably 5 to 50 parts by mass, and even more preferably 20 to 50 parts by mass, per 100 parts by mass of the nickel oxide precursor. The above polymer compounds may be used alone or in combination of two or more types.

[solvent]
The charge transporting composition is generally in the form of a coating liquid so that it can form a uniform thin film. The charge transporting composition of the present invention is also preferably in the form of a coating liquid containing the above polymer component and a solvent capable of dissolving the polymer component.

The solvent contained in the charge transport composition is not particularly limited, as long as it uniformly dissolves the nickel oxide precursor and polymer components. Specific examples include water, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethyl sulfoxide, N,N-diethylformamide, N,N-diethylformamide, 3-methoxy-N,N-dimethylpropanamide, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, etc. Among these, water, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, or γ-butyrolactone is preferred.

In addition to the above solvents, the solvent contained in the charge-transporting composition of the present invention can also be a solvent that improves the coatability of the charge-transporting composition when applied and the surface smoothness of the coating film. Specific examples of such solvents are listed below, but are not limited to these.

For example, ethanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pentyl alcohol, 3-methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol ethanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 2,6-dimethyl-4-heptanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, diisopropyl ether, dipropyl ether, dibutyl ether, dihexyl ether, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, 1,2-butoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, 4-hydroxy-4-methyl-2-pentanone, diethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, 2,6-dimethyl-4-heptanone, 4,6-dimethyl-2-heptanone, 3-ethoxybutyl acetate, 1-methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, Propylene carbonate, ethylene carbonate, 2-(methoxymethoxy)ethanol, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, furfuryl alcohol, diethylene glycol, propylene glycol, propylene glycol monobutyl ether, 1-(butoxyethoxy)propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol Examples of suitable lactic acid lactates include ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol acetate, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, methyl ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, and isoamyl lactate.

Among these, it is preferable to use 1-hexanol, cyclohexanol, 1,2-ethanediol, 1,2-propanediol, propylene glycol monobutyl ether, diethylene glycol diethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monobutyl ether, or dipropylene glycol dimethyl ether as the solvent.

These solvents can be used alone or in combination of two or more. The type and content of such solvents are selected appropriately depending on the coating device, coating conditions, coating environment, etc. of the charge transport composition.

[Surfactant]
In order to improve the film-forming properties of the charge transporting composition, a surfactant may be added to the solvent. As the surfactant, a fluorine-based surfactant is preferred, and a nonionic fluorine-based surfactant is more preferred.
Specific examples thereof include the Ftergent series manufactured by Neos Corporation, such as 212M, 215M, 250, 222F, FTX-218, and DFX-18, but are not limited to these.
When a surfactant is used, the amount of the surfactant to be added is not particularly limited, but is preferably 0.001 to 0.5% by mass, more preferably 0.005 to 0.1% by mass, based on the solvent.

[Electron-accepting dopant material]
The charge transport ink composition of the present invention may contain an electron-accepting dopant substance (hereinafter, sometimes simply referred to as a "dopant substance") for the purpose of improving the charge transport ability of the thin film to be obtained, depending on the application of the thin film to be obtained.
The dopant substance is not particularly limited as long as it dissolves in at least one solvent used in the ink composition, and both inorganic and organic dopant substances can be used. The inorganic and organic dopant substances may be used alone or in combination of two or more.

Inorganic dopant substances include inorganic acids such as hydrogen chloride, sulfuric acid, nitric acid, and phosphoric acid; metal halides such as aluminum chloride (III) (AlCl ₃ ), titanium tetrachloride (IV) (TiCl ₄ ), boron tribromide (BBr ₃ ), boron trifluoride ether complex (BF ₃ .OEt ₂ ), iron chloride (III) (FeCl ₃ ), copper chloride (II) (CuCl ₂ ), antimony pentachloride (V) (SbCl ₅ ), antimony pentafluoride (V) (SbF ₅ ), arsenic pentafluoride (V) (AsF ₅ ), phosphorus pentafluoride (PF ₅ ), and tris(4-bromophenyl)aluminum hexachloroantimonate (TBPAH); and metal halides such as Cl ₂ , Br ₂ , I ₂ , ICl, ICl ₃ , IBr, and IF. ₄ and the like; heteropolyacids such as phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid, silicotungstic acid, and phosphotungstomolybdic acid.

Also, organic dopant substances include tetracyanoquinodimethanes such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane; halotetracyanoquinodimethanes (haloTCNQ) such as tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), tetrachloro-7,7,8,8-tetracyanoquinodimethane, 2-fluoro-7,7,8,8-tetracyanoquinodimethane, 2-chloro-7,7,8,8-tetracyanoquinodimethane, 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane, and 2,5-dichloro-7,7,8,8-tetracyanoquinodimethane. ) compounds; benzoquinone derivatives such as tetrachloro-1,4-benzoquinone (chloranil) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); benzenesulfonic acid, tosylic acid, p-styrenesulfonic acid, 2-naphthalenesulfonic acid, 4-hydroxybenzenesulfonic acid, 5-sulfosalicylic acid, p-dodecylbenzenesulfonic acid, dihexylbenzenesulfonic acid, 2,5-dihexylbenzenesulfonic acid, dibutylnaphthalenesulfonic acid, 6,7-dibutyl-2-naphthalenesulfonic acid, dodecylnaphthalenesulfonic acid, 3-dodecyl-2-naphthalenesulfonic acid, hexylnaphthalenesulfonic acid, and 4-hexyl-1-naphthalenesulfonic acid arylsulfonic acid compounds such as octylnaphthalenesulfonic acid, 2-octyl-1-naphthalenesulfonic acid, hexylnaphthalenesulfonic acid, 7-hexyl-1-naphthalenesulfonic acid, 6-hexyl-2-naphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, 2,7-dinonyl-4-naphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, 2,7-dinonyl-4,5-naphthalenedisulfonic acid, 1,4-benzodioxanedisulfonic acid derivatives described in WO 2005/000832, arylsulfonic acid derivatives described in WO 2006/025342, and dinonylnaphthalenesulfonic acid derivatives described in JP 2005-108828 A; Examples of suitable aryl sulfonic acid compounds include aromatic sulfone compounds such as the aryl sulfonic acid compounds described in International Publication No. 2022/181587, polystyrene sulfonic acid, and the fluorinated aryl sulfonic acid polymer compounds described in International Publication No. 2023/008176; aryl sulfonic acid ester compounds such as the aryl sulfonic acid ester compounds described in International Publication No. 2017/217455, the aryl sulfonic acid ester compounds described in International Publication No. 2017/217457, the aryl sulfonic acid ester compounds described in International Publication No. 2019/124412, and the aryl sulfonic acid ester compounds described in International Publication No. 2022/209892; and non-aromatic sulfone compounds such as 10-camphorsulfonic acid.

If a dopant substance is included, its content cannot be generally determined as it is determined appropriately taking into account the type of dopant and the desired level of charge transport properties, but it is usually in the range of 0.0001 to 100.0 parts by mass per 1 part of nickel oxide precursor.

[Organosilane Compound]
The charge transporting composition of the present invention may contain an organosilane compound in order to improve the stability of the resulting photoelectric conversion element.

As the organic silane compound, alkoxysilanes are preferred, with trialkoxysilanes and tetraalkoxysilanes being more preferred. Examples of the alkoxysilanes include tetraethoxysilane (TEOS), tetramethoxysilane, tetraisopropoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, dimethyldiethoxysilane, and dimethyldimethoxysilane. Among these, TEOS, tetramethoxysilane, and tetraisopropoxysilane are preferred for use in the present invention. These organic silane compounds can be used alone or in combination of two or more.

The content of the organosilane compound is preferably 0.1 to 10 times, more preferably 0.5 to 7 times, and even more preferably 1.0 to 5 times, the amount of the nickel oxide precursor, or, if an electron-accepting dopant substance is included, the total amount of the nickel oxide precursor and the electron-accepting dopant substance, in parts by mass. By keeping the amount of the organosilane compound within the above range, the stability of the resulting photoelectric conversion element can be improved.

The composition of the present invention may contain other additives as long as the object of the present invention can be achieved.
The type of additive can be appropriately selected from known additives depending on the desired effect.

The solids concentration of the charge transport composition of the present invention is set appropriately taking into consideration the viscosity and surface tension of the composition, the thickness of the thin film to be produced, and other factors, but is generally preferably approximately 0.1 to 20.0% by mass, more preferably 0.5 to 10.0% by mass, and even more preferably 1.0 to 5.0% by mass. Note that the solids in the solids concentration referred to here refer to the components other than the solvent contained in the charge transport composition of the present invention.

The viscosity of the charge-transporting composition of the present invention is adjusted appropriately depending on the coating method, taking into account the thickness of the thin film to be produced and the solids concentration, but is typically approximately 0.1 to 50 mPa·s at 25°C.

The charge transport composition of the present invention can be prepared by mixing a nickel oxide precursor, a polymeric compound, a solvent, and, if necessary, an electron-accepting dopant substance, an organosilane compound, and other additives in any order, as long as the solids are uniformly dissolved or dispersed in the solvent. That is, for example, a method of separately preparing a solution of a nickel oxide precursor and a solution of a polymeric compound such as a polyimide-based polymer (e.g., a specific polymer) and then mixing the two solutions; a method of dissolving a nickel oxide precursor in a solvent and then dissolving the polymeric compound in the solution; or a method of mixing a nickel oxide precursor and a polymeric compound and then adding the mixture to a solvent and dissolving it can all be used, as long as the solids are uniformly dissolved or dispersed in the solvent. When using an electron-accepting dopant substance, an organosilane compound, and other additives, mixing can be performed at any time, as long as the solids are uniformly dissolved or dispersed in the solvent.

In addition, the preparation of the charge-transporting composition is usually carried out in an inert gas atmosphere at room temperature and atmospheric pressure, but it may also be carried out in an air atmosphere (in the presence of oxygen) or while heating, as long as the compounds in the composition are not decomposed or the composition does not change significantly.

[Charge transporting thin film]
The charge transport composition described above can be suitably used to form a charge transport thin film in an organic photoelectric conversion element. It is particularly preferred when the organic photoelectric conversion element is a perovskite photoelectric conversion element, and the composition is particularly effective when used as a hole collection layer in the perovskite photoelectric conversion element. Perovskite solar cells equipped with a perovskite photoelectric conversion element are either normal stacking type or reverse stacking type. The hole collection layer of the present invention can be formed by applying the charge transport composition of the present invention to the anode in the case of a reverse stacking type perovskite solar cell, or to the active layer in the case of a normal stacking type perovskite solar cell, followed by baking. From the viewpoint of the solvent resistance of the resulting charge transport thin film, the reverse stacking type is a preferred embodiment of the present invention.
For application, an optimum method may be selected from various wet process methods such as drop casting, spin coating, blade coating, dip coating, roll coating, bar coating, die coating, inkjet printing, printing methods (relief printing, intaglio printing, lithography, screen printing, etc.), taking into consideration the viscosity and surface tension of the composition, the desired thickness of the thin film, and the like.
Generally, the coating is carried out under an inert gas atmosphere at room temperature and atmospheric pressure. However, the coating may be carried out under an air atmosphere (in the presence of oxygen) or while heating, as long as the compounds in the composition are not decomposed or the composition is not significantly changed.

When the charge transport composition described above is applied to the anode in the case of an inverted stacking perovskite solar cell, or to the active layer in the case of a normal stacking perovskite solar cell, and then fired, the firing temperature is preferably 260°C or higher, more preferably 280°C or higher, and even more preferably 300°C or higher, from the viewpoint of producing nickel oxide from the nickel oxide precursor by firing. There is no particular upper limit to the firing temperature, but considering the heat resistance of the resulting thin film, 350°C or lower is preferred. The firing time cannot be generally determined as it varies depending on the temperature, but is typically 1 minute to 2 hours. Furthermore, multi-stage firing at two or more different temperatures may be performed, if necessary.

There are no particular limitations on the film thickness, but in either case, a thickness of approximately 0.1 to 500 nm is preferred, with approximately 1 to 100 nm being even more preferred. Methods for changing the film thickness include changing the solids concentration in the composition or changing the amount of solution used during application.

[Perovskite solar cells]
Hereinafter, a method for producing a perovskite solar cell using the charge transport composition of the present invention as a composition for forming a hole collection layer will be described, but the method is not limited thereto.
(1) Inverted stacked perovskite solar cell [anode layer formation]: A process of forming a layer of anode material on the surface of a transparent substrate to produce a transparent electrode. Examples of anode materials that can be used include inorganic oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO), metals such as gold, silver, and aluminum, and highly charge-transporting organic compounds such as polythiophene derivatives and polyaniline derivatives. Among these, ITO is the most preferred. The transparent substrate can be made of glass or a transparent resin.
The method for forming the anode material layer (anode layer) is appropriately selected depending on the properties of the anode material. Typically, in the case of a poorly soluble or poorly dispersible sublimable material, a dry process such as a vacuum deposition method or a sputtering method is selected. In the case of a solution material or a dispersion material, an optimal method is selected from the above-mentioned various wet processes taking into consideration the viscosity and surface tension of the composition, the desired thickness of the thin film, and the like.

Alternatively, a commercially available transparent anode substrate can be used, and in this case, it is preferable to use a substrate that has been subjected to a smoothing treatment from the viewpoint of improving the yield of the device. When a commercially available transparent anode substrate is used, the method for producing a perovskite solar cell of the present invention does not include the step of forming an anode layer.
When forming a transparent anode substrate using an inorganic oxide such as ITO as the anode material, it is preferable to wash the substrate with detergent, alcohol, pure water, etc. before laminating an upper layer. Furthermore, it is preferable to perform a surface treatment such as UV ozone treatment or oxygen-plasma treatment immediately before use. When the anode material is mainly composed of an organic substance, surface treatment may not be necessary.

[Formation of hole-collecting layer]: Step of forming a hole-collecting layer on the formed layer of anode material According to the method described above, a hole-collecting layer is formed on the layer of anode material using the charge-transporting composition of the present invention.

[Formation of Active Layer]: Step of forming an active layer on the formed hole-collecting layer In the present invention, an active layer containing a perovskite semiconductor compound is used as the active layer.
A perovskite semiconductor compound refers to a semiconductor compound having a perovskite structure. Known compounds can be used as perovskite semiconductor compounds, and although there are no particular limitations, examples include those represented by the general formula A ⁺ M ²⁺ X ⁻ ₃ and those represented by the general formula A ⁺ ₂ M ²⁺ X ⁻ _4. Here, A ⁺ represents a monovalent cation, M ²⁺ represents a divalent cation, and X ⁻ represents a monovalent anion.

Examples of the monovalent cation A ⁺ include cations containing elements of Groups 1 and 13 to 16 of the periodic table. Among these, a cesium ion, a rubidium ion, an ammonium ion which may have a substituent, or a phosphonium ion which may have a substituent is preferred.

Examples of ammonium ions that may have a substituent include primary ammonium ions and secondary ammonium ions. There are no particular restrictions on the substituents, but alkylammonium ions or arylammonium ions are preferred. In particular, monoalkylammonium ions, which form a three-dimensional crystal structure to avoid steric hindrance, are more preferred. The alkyl group contained in the alkylammonium ion preferably has 1 to 30 carbon atoms, more preferably 1 to 20, and even more preferably 1 to 10. The aryl group contained in the arylammonium ion preferably has 6 to 30 carbon atoms, more preferably 6 to 20, and even more preferably 6 to 12.

Specific examples of the monovalent cation A ⁺ include methylammonium ion, ethylammonium ion, isopropylammonium ion, n-propylammonium ion, isobutylammonium ion, n-butylammonium ion, t-butylammonium ion, dimethylammonium ion, diethylammonium ion, phenylammonium ion, benzylammonium ion, phenethylammonium ion, guanidium ion, formamidinium ion, acetamidinium ion, and imidazolium ion. The above cation A ⁺ can be used alone or in combination of two or more.

The divalent cation M2 ⁺ is preferably a divalent metal cation or semimetal cation, and more preferably a cation of a Group 14 element of the periodic table. Specific examples of the divalent cation M include lead cation (Pb2 ⁺ ), tin cation (Sn2 ⁺ ), germanium cation (Ge2 ⁺ ), etc. In the present invention, it is preferable to contain a lead cation from the viewpoint of obtaining a photoelectric conversion element with excellent stability. The above cation M2 ⁺ can be used alone or in combination of two or more.

Examples of the monovalent anion ^X include a halide ion, acetate ion, nitrate ion, acetylacetonate ion, thiocyanate ion, and 2,4-pentanedionate ion, and the halide ion is preferred. The above anions ^X can be used alone or in combination of two or more.

Halide ions include chloride ions, bromide ions, and iodide ions. In the present invention, it is preferable to include iodide ions in order to prevent the band gap of the semiconductor from becoming too wide.

As the perovskite semiconductor compound, for example, an organic-inorganic perovskite semiconductor compound is preferred, and a halide-based organic-inorganic perovskite semiconductor compound is more preferred. Specific examples of perovskite semiconductor compounds include MAPbI3, _MAPbBr3 , _MAPbCl3 , _MASnI3 , _MASnBr3 , _MASnCl3 , MAPbI _{( 3-x) Clx ,} MAPbI(3-x)Brx, MAPbBr _{(3-x) Clx} , MAPb _{(1-y) SnyI3} , MAPb _{(1-y) SnyBr3 ,} MAPb _{(1-y) SnyCl3} , MAPb _{( 1-y) SnyI} ( _{3 -x) Clx} , MAPb _{(1-y) SnyI (3-x) Brx ,} MAPb _{(1-y) SnyBr (3-x) Clx} , and FAPbI3 _. , FAPbBr ₃ , FAPbI _(3-x) Br _x , FA _(1-V) MA _V PbI _(3-x) Br _x , Cs _(1-WV) FA _w MA _V PbI _(3-x) Br _x . MA represents methylammonium (CH ₃ NH ₃ ⁺ ), and FA represents formamidinium (NH=CHNH ₂ ⁺ ). Furthermore, x represents any number from 0 to 3, and y represents any number from 0 to 1.

From the perspective of improving photoelectric conversion efficiency, it is preferable to use a perovskite semiconductor compound with an energy band gap of 1.0 to 3.5 eV.

The active layer may contain two or more types of perovskite semiconductor compounds. For example, the active layer may contain two or more types of perovskite semiconductor compounds that are different in at least one of A ⁺ , M ²⁺ , and X ⁻ .

From the viewpoint of obtaining good photoelectric conversion characteristics, the content of the perovskite semiconductor compound in the active layer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. There is no particular upper limit, but it is usually 100% by mass or less.

As with the above, the method for forming the active layer is determined by taking into consideration the viscosity and surface tension of the composition, the desired thickness of the thin film, etc., and selecting the most suitable method from the various wet process methods mentioned above.

[Formation of Electron Collecting Layer]: Step of Forming an Electron Collecting Layer on the Formed Active Layer If necessary, an electron collecting layer may be formed between the active layer and the cathode layer for the purpose of improving the efficiency of charge transfer, etc.
Materials for forming the electron collection layer include fullerenes, lithium oxide (Li ₂ O), magnesium oxide (MgO), alumina (Al ₂ O ₃ ), lithium fluoride (LiF), sodium fluoride (NaF), magnesium fluoride (MgF ₂ ), strontium fluoride (SrF ₂ ), cesium carbonate (Cs ₂ CO ₃ ), 8-quinolinol lithium salt (Liq), 8-quinolinol sodium salt (Naq), bathocuproine (BCP), 4,7-diphenyl-1,10-phenanthroline (BPhen), polyethyleneimine (PEI), ethoxylated polyethyleneimine (PEIE), etc.

Fullerenes and their derivatives are preferred as fullerenes, but are not limited thereto. Specific examples include fullerenes and their derivatives with a basic skeleton of C60, C70, C76, C78, C84, etc. In fullerene derivatives, the carbon atoms in the fullerene skeleton may be modified with any functional group, and these functional groups may be bonded to each other to form a ring. Fullerene derivatives include fullerene-bonded polymers. Fullerene derivatives that have functional groups with high affinity for solvents and are highly soluble in solvents are preferred.

Functional groups in fullerene derivatives include, for example, hydrogen atoms, hydroxy groups, halogen atoms such as fluorine atoms and chlorine atoms, alkyl groups such as methyl groups and ethyl groups, alkenyl groups such as vinyl groups, alkoxy groups such as cyano groups, methoxy groups and ethoxy groups, aromatic hydrocarbon groups such as phenyl groups and naphthyl groups, and aromatic heterocyclic groups such as thienyl groups and pyridyl groups. Specific examples include hydrogenated fullerenes such as C60H36 and C70H36, oxide fullerenes such as C60 and C70, and fullerene metal complexes. It is more preferable to use [6,6]-phenyl C61 butyric acid methyl ester ([60]PCBM) or [6,6]-phenyl C71 butyric acid methyl ester ([70]PCBM) as the fullerene derivative.

As with the above, when the electron collection material is a sparingly soluble sublimable material, the various dry processes mentioned above are selected as the method for forming the electron collection layer. When the electron collection material is a solution or dispersion material, the viscosity and surface tension of the composition, the desired thin film thickness, etc. are taken into consideration, and the most appropriate method is selected from the various wet processes mentioned above.

[Formation of cathode layer]: A step of forming a cathode layer on the formed electron collection layer. Examples of cathode materials include metals such as aluminum, magnesium-silver alloy, aluminum-lithium alloy, lithium, sodium, potassium, cesium, calcium, barium, silver, and gold; inorganic oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO); and organic compounds with high charge transport properties such as polythiophene derivatives and polyaniline derivatives. A plurality of cathode materials can be stacked or mixed for use.
Similarly to the above, when the cathode layer material is a poorly soluble or poorly dispersible sublimable material, the above-mentioned various dry processes are selected as the method for forming the cathode layer. When the cathode layer material is a solution material or a dispersion material, an optimum one is adopted from the above-mentioned various wet processes in consideration of the viscosity and surface tension of the composition, the desired thickness of the thin film, and the like.

[Formation of Carrier Block Layer]
If necessary, a carrier blocking layer may be provided between any layers for the purpose of controlling the rectification of photocurrent, etc. When a carrier blocking layer is provided, an electron blocking layer is usually inserted between the active layer and the hole collecting layer or the anode, and a hole blocking layer is often inserted between the active layer and the electron collecting layer or the cathode, but this is not limited thereto.
Examples of materials for forming the hole blocking layer include titanium oxide, zinc oxide, tin oxide, bathocuproine (BCP), and 4,7-diphenyl-1,10-phenanthroline (BPhen).
Examples of materials for forming the electron blocking layer include triarylamine-based materials such as N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) and poly(triarylamine) (PTAA).

As with the above, when the carrier block layer material is a poorly soluble or poorly dispersible sublimable material, the various dry processes mentioned above are selected as the method for forming the carrier block layer. When the carrier block layer material is a solution or dispersion material, the viscosity and surface tension of the composition, the desired thin film thickness, etc. are taken into consideration, and the most suitable method is selected from the various wet processes mentioned above.

(2) Forward stacking type perovskite solar cell [Formation of cathode layer]: A step of forming a layer of a cathode material on the surface of a transparent substrate to produce a transparent cathode substrate. In addition to the above-mentioned examples of the reverse stacking type anode material, examples of the cathode material include fluorine-doped tin oxide (FTO). Examples of the transparent substrate include the above-mentioned examples of the reverse stacking type anode material.
As a method for forming a layer of a cathode material (cathode layer), the above-mentioned dry process is selected in the case of a poorly soluble or poorly dispersible sublimable material, and in the case of a solution material or a dispersion material, an optimum method is adopted from among the above-mentioned various wet processes in consideration of the viscosity and surface tension of the composition, the desired thickness of the thin film, and the like.
In this case, a commercially available transparent cathode substrate can also be suitably used, and from the viewpoint of improving the yield of the device, it is preferable to use a substrate that has been subjected to a smoothing treatment. When a commercially available transparent cathode substrate is used, the method for producing a perovskite solar cell of the present invention does not include the step of forming a cathode layer.
When an inorganic oxide is used as the cathode material to form a transparent cathode substrate, the substrate may be subjected to the same cleaning treatment and surface treatment as in the case of the reverse stack type anode material.

[Formation of Electron Collecting Layer]: Step of forming an electron collecting layer on the formed cathode. If necessary, an electron collecting layer may be formed between the active layer and the cathode layer for the purpose of improving the efficiency of charge transfer, etc.
Examples of materials for forming the electron collection layer include zinc oxide (ZnO), titanium oxide (TiO), tin oxide (SnO), and the like, in addition to the materials exemplified above for the inverse stacking type.
Regarding the method for forming the electron collection layer, the above-mentioned dry process is selected in the case of a poorly soluble or poorly dispersible sublimable material, and in the case of a solution material or dispersion material, the optimum method is selected from the above-mentioned various wet processes taking into consideration the viscosity and surface tension of the composition, the desired thickness of the thin film, etc. Alternatively, a method can be used in which a precursor layer of an inorganic oxide is formed on the cathode using a wet process (particularly a spin coating method or a slit coating method), and then baked to form an inorganic oxide layer.

[Formation of Active Layer]: Step of forming an active layer on the formed electron-collecting layer An active layer containing the above-described perovskite semiconductor compound is formed as the active layer.
The method for forming the active layer is the same as that described for the inverted stacked type active layer.

[Formation of hole-collecting layer]: Step of forming a hole-collecting layer on the layer of active layer material formed According to the method described above, a hole-collecting layer is formed on the layer of active layer material using the composition of the present invention.

[Formation of anode layer]: A step of forming an anode layer on the formed hole collection layer. Examples of the anode material include the same anode materials as those of the above-mentioned reverse stack type, and the method of forming the anode layer is also the same as that of the reverse stack type cathode layer.

[Formation of Carrier Block Layer]
As with the inverted stack type element, a carrier blocking layer may be provided between any of the layers as needed for the purpose of controlling the rectification of the photocurrent.
The materials for forming the hole blocking layer and the electron blocking layer are the same as those described above, and the method for forming the carrier blocking layer is also the same as described above.

To prevent element degradation due to atmospheric air, the perovskite solar cell element produced by the method exemplified above is placed back into the glove box and sealed in an inert gas atmosphere such as nitrogen. In this sealed state, the element can be allowed to function as a solar cell or its solar cell characteristics can be measured.
Examples of sealing methods include a method in which a concave glass substrate with a UV-curable resin attached to the edge is attached to the film-forming surface of the perovskite solar cell element in an inert gas atmosphere and the resin is cured by UV irradiation, and a method in which film-sealing type sealing is performed by a technique such as sputtering in a vacuum.

The present invention will be described in further detail below based on examples, but the present invention is not limited to these examples in any way.

[1] Preparation of Nickel Oxide Precursor Liquid The compounds used in the preparation of the nickel oxide precursor are as follows:
Ni(NO ₃ ) ₂ ·6H ₂ O: Nickel(II) nitrate hexahydrate Ni(CH ₃ COO) ₂ ·4H ₂ O: Nickel(II) acetate tetrahydrate Ni(acac) ₂ : Nickel(II) acetylacetonate acac: Acetylacetone NEP: N-ethyl-2-pyrrolidone NMP: N-methyl-2-pyrrolidone BCS: Butyl cellosolve (ethylene glycol monobutyl ether)

[Preparation Example 1-1]
_1.00 g of Ni( _NO3 ) _2.6H2O was weighed into a 50 mL vial, 8.80 g of water was added, and the mixture was stirred on a hot plate at 50°C for 1 hour to completely dissolve the Ni( _NO3 ) _2.6H2O . Then, 0.20 g _of Futergent 212M (1.0 wt% aqueous solution) was added as a surfactant. The mixture was filtered through a syringe filter with a pore size of 0.45 μm to obtain a 10 wt% nickel oxide precursor liquid (N1).

[Preparation Example 1-2]
_2.91 g of Ni( _NO3 ) _2.6H2O was weighed into a 50 mL vial, 18.40 g of NEP was added, and the mixture was stirred on a hot plate at 50°C for 1 hour to completely dissolve the Ni( _NO3 ) _2.6H2O . _2.00 g of acac and 5.80 g of BCS were added to this solution, and the mixture was stirred at 25°C for 1 hour. The mixture was then filtered through a syringe filter with a pore size of 0.45 µm to obtain a 10 mass% nickel oxide precursor liquid (N2).

[Preparation Example 1-3]
_2.91 g of Ni( _NO3 ) _2.6H2O was weighed into a 50 mL vial, and 20.40 g of NEP was added. The mixture was stirred on a hot plate at 50°C for 1 hour to completely dissolve the Ni( _NO3 ) _2.6H2O . _5.80 g of BCS was added to this solution, and the mixture was stirred at 25°C for 1 hour. The solution was then filtered through a syringe filter with a pore size of 0.45 µm to obtain a 10 mass% nickel oxide precursor liquid (N3).

[Preparation Example 1-4]
_2.91 g of Ni( _NO3 ) _2.6H2O was weighed into a 50 mL vial, 20.40 g of NMP was added, and the mixture was stirred on a hot plate at 50°C for 1 hour to completely dissolve the Ni( _NO3 ) _2.6H2O . _5.80 g of BCS was added to this solution, and the mixture was stirred at 25°C for 1 hour. The mixture was then filtered through a syringe filter with a pore size of 0.45 µm to obtain a 10 mass% nickel oxide precursor liquid (N4).

[Preparation Example 1-5]
_1.00 g of Ni( _CH3COO ) _2.4H2O was weighed into a 50 mL vial, and 8.80 g of water was added. The mixture was stirred on a hot plate at 50°C for 1 hour to completely dissolve the Ni( _CH3COO ) _2.4H2O . _0.20 g of Futergent 212M (1.0 wt% aqueous solution) was then added as a surfactant. The mixture was filtered through a syringe filter with a pore size of 0.45 μm to obtain a 10 wt% nickel oxide precursor liquid (N5).

[Preparation Example 1-6]
2.91 g of Ni(acac) ₂ was weighed into a 50 mL vial, and 20.40 g of NMP was added. The mixture was stirred on a hot plate at 50 °C for 1 hour to completely dissolve the Ni(acac) ₂ . 5.80 g of BCS was added to this solution, and the mixture was stirred at 25 °C for 1 hour. The solution was then filtered through a syringe filter with a pore size of 0.45 μm to obtain a 10 wt% nickel oxide precursor solution (N6).

[2] Analysis of Calcined Nickel Oxide Precursor Film In an embodiment of the present invention, after forming a nickel oxide precursor film, the nickel oxide precursor is thermally decomposed by calcination to form nickel (II) oxide (NiO), which becomes a hole-collecting layer having a charge transport function.
Here, the firing temperature and time were changed to study the firing conditions under which nickel (II) oxide was produced from the nickel oxide precursor. To confirm that NiO was produced from the nickel oxide precursor in the fired coating film, the coating film was identified by work function measurement and X-ray photoelectron spectroscopy (XPS) measurement.
The work function of the coating film was measured and calculated using an atmospheric photoelectron yield spectrometer (AC-3 manufactured by Riken Keiki Co., Ltd.).
XPS measurement was performed using a PHI 5000 VersaProbe II (manufactured by ULVAC-PHI, Inc.), and it was confirmed that the main component was NiO by comparing the spectrum with that of a coating film of NiO fine particle dispersion (P-21 manufactured by Avantama).
The results are shown in Table 1.

The results in Table 1 above show that the nickel oxide precursor decomposes to NiO at firing temperatures of 250°C or higher. Furthermore, work function measurements revealed that the work function of NiO is 5.4 eV.

[3] Fabrication and Evaluation of Perovskite Solar Cells Using Nickel Oxide Precursor Liquid [3-1] Preparation of Perovskite Precursor Liquid In a nitrogen-filled glove box, 504 mg of formamidinium iodide, 65 mg of methylammonium bromide, 1,487 mg of lead(II) iodide, and 214 mg of lead(II) bromide were weighed into a 5 mL vial. Next, 2,346 μL of dimethyl sulfoxide (DMSO) and 586 μL of N,N-dimethylformamide were added to the vial, and the mixture was heated and stirred at 70°C for 15 minutes to completely dissolve the weighed materials. To this solution, 134 μL of a cesium iodide solution dissolved in DMSO was added to make the concentration 1.5 mol/L, thereby preparing a perovskite precursor solution (PVSK) containing a perovskite semiconductor compound (Cs _0.05 (FA _0.83 MA _0.17 ) _0.95 Pb(I _0.83 Br _0.17 ) ₃ ).

[3-2] Preparation of composition for electron collection layer [Preparation Example 2-1]
150 mg of [6,6]-phenyl-C ₆₁ -methyl acetate (manufactured by Frontier Carbon Co., Ltd.) and 5,000 μL of chlorobenzene were added to a 3 mL vial and stirred for 15 minutes to prepare a composition for an electron collection layer ETL1.

[Preparation Example 2-2]
2.5 mg of bathocuproine (Tokyo Chemical Industry Co., Ltd.) and 5,000 μL of 2-propanol (Kanto Chemical Co., Ltd.) were added to a 3 mL vial and stirred for 1 hour to prepare a composition for electron collection layer ETL2.

[3-3] Fabrication of inverted stacked perovskite solar cell [Fabrication Example 1-1]
A 25 mm x 25 mm glass substrate on which an ITO transparent conductive layer serving as an anode was patterned into 10 mm x 25 mm stripes was subjected to UV/ozone treatment for 15 minutes. The nickel oxide precursor liquid (N2) prepared in Preparation Example 1-2 was applied to this substrate by spin coating and dried on a hot plate at 100°C for 2 minutes. The substrate was then baked on a hot plate at 300°C for 60 minutes to form a hole-collecting layer. The thickness of the hole-collecting layer was approximately 20 nm.

The substrate with the hole-collecting layer was moved into a glove box, and the perovskite precursor liquid Pvsk was applied to the formed hole-collecting layer using the spin coating method. Furthermore, chlorobenzene was dripped onto the substrate during spin coating. The resulting substrate was heated on a hot plate at 105°C for 30 minutes to form an active layer made of a perovskite semiconductor compound. The film thickness of the active layer was approximately 400 nm.

The electron collection layer composition ETL1 prepared in Preparation Example 2-1 was applied by spin coating onto the formed active layer, and then heated on a hot plate at 100°C for 10 minutes. The electron collection layer composition ETL2 prepared in Preparation Example 2-2 was then applied to this substrate by spin coating and dried at room temperature, forming an electron collection layer. The layer obtained from electron collection layer composition ETL1 had a thickness of approximately 30 nm, and the layer obtained from electron collection layer composition ETL2 had a thickness of approximately 8 nm.

Finally, the substrate with each layer laminated thereon was placed in a vacuum deposition apparatus, and the apparatus was evacuated until the degree of vacuum inside the apparatus was 1×10 ⁻³ Pa or less. A silver layer to serve as the cathode was deposited to a thickness of 100 nm using a resistance heating method, thereby producing an inverted structure perovskite solar cell (C-N1) in which the area of the intersection of the striped ITO layer and silver layer was 8 mm × 3 mm.

The resulting perovskite solar cell element was moved into a glove box, and a 0.7 mm thick sealing glass was placed over the element electrodes, and the solar cell was sealed by UV curing with a UV-curable resin.

[Production Examples 1-2 to 1-8]
Inverted stacking type perovskite solar cells (C-N2 to C-N8) were fabricated under the same conditions as in Production Example 1-1, except that the firing conditions for the nickel oxide precursor liquid coating film were changed.

The power generation performance of the inverted stacked perovskite solar cell fabricated above was evaluated using a solar simulator adjusted to a light intensity of 100 mW/ ^cm2 . The results are shown in Table 2.
The conversion efficiency PCE (%) was calculated using the following formula.
PCE [%] = Jsc [mA/cm ² ] × Voc [V] × FF ÷ Incident light intensity (100 [mW/cm ² ]) × 100
(Short-circuit current density: Jsc [mA/cm ² ], open circuit voltage: Voc [V], fill factor: FF)

The results in Table 2 confirm that the coating film obtained from the nickel oxide precursor solution turns into NiO through thermal decomposition, resulting in good perovskite solar cell elements.

[4] Synthesis of Polyimide Precursor The compounds used in the preparation of the polyimide precursor are as follows:
(Tetracarboxylic acid dianhydride)
BODA: bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride (diamine)
Diamine compounds represented by the following formulae DA-1 to DA-3

The conditions for measuring the molecular weight of polyimide are as follows:
Apparatus: Room temperature gel permeation chromatography (GPC) apparatus (SSC-7200) manufactured by Senshu Scientific Co., Ltd.
Column: Shodex column (KD-803, KD-805)
Column temperature: 50°C
Eluent: N,N'-dimethylformamide (additives: lithium bromide monohydrate (LiBr·H ₂ O) 30 mmol/L, phosphoric acid anhydrous crystal (o-phosphoric acid) 30 mmol/L, tetrahydrofuran (THF) 10 ml/L)
Flow rate: 1.0 ml/min. Standard samples for creating calibration curves: TSK standard polyethylene oxide (molecular weight: approximately 900,000, 150,000, 100,000, 30,000) manufactured by Tosoh Corporation, and polyethylene glycol (molecular weight: approximately 12,000, 4,000, 1,000) manufactured by Polymer Laboratory Co., Ltd.

The conditions for measuring the viscosity of polyimide are as follows:
Measurement was performed using an E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) with a sample volume of 1.1 mL, a cone rotor TE-1 (1°34', R24), and a temperature of 25°C.

[Synthesis Example 1-1]
BODA (3.53 g, 14.1 mmol) and DA-1 (6.32 g, 10 mmol) were dissolved in NEP (88.66 g) and reacted at 40° C. for 20 hours to obtain a 10% by mass polyamic acid solution.
The viscosity of the resulting polyamic acid solution was 101 mPa·s, and the number average molecular weight of this polyamic acid was 12,400 and the weight average molecular weight was 53,300.
2.0 g of this polyamic acid solution was taken and diluted with NEP (6.0 g) and BCS (2.0 g) to obtain a 2 mass % polyamic acid solution (P1).

[Synthesis Example 1-2]
CBDA (0.95 g, 4.9 mmol) and DA-2 (1.19 g, 5.0 mmol) were dissolved in NMP (19.24 g) and reacted at 40° C. for 20 hours to obtain a 10% by mass polyamic acid solution.
The viscosity of the resulting polyamic acid solution was 140 mPa·s, and the number average molecular weight of this polyamic acid was 12,800 and the weight average molecular weight was 44,500.
2.0 g of this polyamic acid solution was taken and diluted with NEP (6.0 g) and BCS (2.0 g) to obtain a 2 mass % polyamic acid solution (P2).

[Synthesis Example 1-3]
CBDA (0.95 g, 4.9 mmol) and DA-3 (1.21 g, 14 mmol) were dissolved in NMP (19.46 g) and reacted at 40° C. for 20 hours to obtain a 10% by mass polyamic acid solution (P3).
The viscosity of the resulting polyamic acid solution was 31 mPa·s, and the number average molecular weight of this polyamic acid was 4,200 and the weight average molecular weight was 8,200.
2.0 g of this polyamic acid solution was taken and diluted with NEP (6.0 g) and BCS (2.0 g) to obtain a 2 mass % polyamic acid solution (P3).

[Synthesis Example 1-4]
BODA (3.68 g, 14.7 mmol) and DA-1 (6.53 g, 15.5 mmol) were dissolved in NMP (91.97 g) and reacted at room temperature for 25 hours to obtain a 10% by mass polyamic acid solution.
The viscosity of the resulting polyamic acid solution was 133 mPa·s, and the number average molecular weight of this polyamic acid was 43,159 and the weight average molecular weight was 85,474.
2.0 g of this polyamic acid solution was taken and diluted with NMP (6.0 g) and BCS (2.0 g) to obtain a 2 mass % polyamic acid solution (P4).

[5] Preparation of Charge-Transporting Composition The compounds used in the preparation of the following charge-transporting composition are as follows: PEI: polyethyleneimine [Example 1-1]
A predetermined amount of the nickel oxide precursor solution (N1) obtained in Preparation Example 1-1, a PEI aqueous solution (Polyethyleneimine 10000, manufactured by Junsei Chemical Co., Ltd.) prepared to have a solid content of 10% by mass and a Ftergent 212M content of 2,000 ppm, and water were added to a sample bottle, and the mixture was stirred at 25°C for 1 hour to prepare a charge-transporting composition (HTL1).
The solid content of Ni(NO ₃ ) ₂ .6H ₂ O in the resulting charge transporting composition was 8% by mass, and the mixing ratio (weight ratio) of Ni(NO ₃ ) ₂ .6H ₂ O to PEI was 100:5.

[Examples 1-2 to 1-3]
Charge transporting compositions (HTL2-3) were prepared in the same manner as in Example 1-1, except that the mixing ratio (weight ratio) of Ni(NO ₃ ) _{2.6H 2} O to PEI in the charge transporting composition was 100:10 and 100:20.

[Examples 1-4]
A charge-transporting composition (HTL4) was prepared by adding predetermined amounts of the nickel oxide precursor solution (N2) obtained in Preparation Example 1-2, the polyamic acid solution (P1) obtained in Synthesis Example 1-1, and a mixed solution adjusted so that the weight ratio of NEP to BCS was 8:2 to a sample bottle and stirring for 1 hour at 25° C. The solid content of Ni(NO ₃ ) _{2.6H 2} O in the obtained charge-transporting composition was 8 mass %, and the mixing ratio (weight ratio) of Ni(NO ₃ ) _{2.6H 2} O to P1 was 100:5.

[Examples 1-5 to 1-21]
Charge-transporting compositions (HTL5 to 21) were prepared by performing the same operations as in Example 1-1 or Example 1-4, and mixing the nickel oxide precursor solution, polyamic acid solution, and solvent types, as well as the mixing ratios of both components, as shown in Table 3.

[Example 1-22]
A charge-transporting composition (HTL22) was prepared by adding predetermined amounts of the nickel oxide precursor solution (N6) obtained in Preparation Example 1-6, the polyamic acid solution (P4) obtained in Synthesis Example 1-4, and a mixed solution prepared so that the weight ratio of NMP to BCS was 8:2 to a sample bottle and stirring at 25°C for 1 hour. The solid content of Ni(acac) ₂ in the resulting charge-transporting composition was 5 mass% and the mixing ratio (weight ratio) of Ni(acac) ₂ to P4 was 100:20.

[Comparative Example 1-1]
A charge-transporting composition (HTL23) was prepared by adding predetermined amounts of the nickel oxide precursor solution (N1) obtained in Preparation Example 1-1 and water to a sample bottle and stirring for 1 hour at 25° C. The solid content of Ni(NO ₃ ) _{2.6H 2} O in the obtained charge-transporting composition was 8 mass %.

[Comparative Examples 1-2 to 1-6]
The same procedure as in Comparative Example 1-1 was carried out, and the nickel oxide precursor solution, polymer solution, and solvent type were mixed as shown in Table 3 to prepare charge transporting compositions (HTL24 to 28).

<Evaluation of film-forming properties>
The charge transport composition HTL1 prepared in Example 1-1 was dropped onto a 3 cm x 4 cm glass substrate with an ITO transparent conductive film, and a film was formed by spin coating. The spin coating conditions were changed as shown in Table 4. After drying at 100°C for 2 minutes, the coating was cooled to room temperature, and after 1 hour, the coating was judged as good if no pinholes, cissing, whitening, or other phenomena occurred on the surface, and judged as poor if any occurred.
The same evaluation was carried out for Examples 1-2 to 1-22 and Comparative Examples 1-1 to 1-6.
The evaluation results of the film-forming properties are summarized in Table 4.

The results in Table 4 show that coatings made only from nickel oxide precursor liquid are prone to whitening, pinholes, and poor film formation, posing challenges in the process for mass production of solar cell elements. On the other hand, the charge transport composition blended with polymer components, which is an embodiment of the present invention, exhibits good film-forming properties and high film stability when left standing in the air, demonstrating its superiority in terms of mass production processes. This is thought to be because the inclusion of an organic polymer component with excellent film-forming properties changes the physical properties of the charge transport composition as a whole, improving film formation characteristics.

[6] Evaluation of inverted stacked perovskite solar cells [Examples 2-1 to 2-16, Comparative Examples 2-1 to 2-2]
Using the same procedure as for fabricating an inverted stacking type perovskite solar cell using a nickel oxide precursor liquid, inverted stacking type perovskite solar cells C1 to C18 were fabricated using the charge transport composition prepared above, and their power generation performance was evaluated. The work function of the coated film was also measured. The nickel oxide precursor liquid coated film was baked at 300°C for 60 minutes.

[Comparative Example 2-3]
A perovskite solar cell C19 was produced in the same manner as in Example 2-16, except that the firing conditions for the nickel oxide precursor liquid were set to 230°C and 60 minutes, and the power generation performance was evaluated.
Table 5 below summarizes the power generation performance and work function of each of the inverted stacking type perovskite solar cells C1 to C17.

The results in Table 5 confirm that good power generation performance can be obtained even when the charge transport composition of the present invention is used. Even when the charge transport composition of the present invention is used, the thermal decomposition of the nickel precursor is not suppressed, and NiO is produced, which is thought to be why charge transport performance is not affected.

<Durability test of inverted stacked perovskite solar cells>
The inverted stacking type perovskite solar cells fabricated in Examples 2-2 and 2-4 and Comparative Example 2-1 were placed in a thermostatic chamber at 85° C. for a predetermined period of time to conduct a heat resistance test.
Table 6 shows the power generation performance after the passage of time, assuming that the power generation performance at the start of the heat resistance test is 100%.

The results in Table 6 show that the heat resistance of the embodiment of the present invention is equal to or better than that of the comparative example.

These results demonstrate that the use of the charge transport composition of the present invention provides a highly productive method for manufacturing inverted stacked perovskite solar cells that have the same power generation performance and heat resistance as conventional solar cells, while also improving the film formation process during mass production.

Claims (16)

A charge transport composition for forming a charge transport thin film in an organic photoelectric conversion element, comprising:
A charge transporting composition comprising a nickel oxide precursor, a polymer compound, and a solvent. The charge transport composition according to claim 1, wherein the solvent is an organic solvent. The charge transport composition according to claim 1, wherein the nickel oxide precursor is at least one selected from the group consisting of inorganic acid nickel salts and organic acid nickel salts. The charge transport composition according to claim 3, wherein the inorganic acid nickel salt is at least one selected from the group consisting of nickel nitrate, nickel sulfate, nickel phosphate, nickel carbonate, nickel bicarbonate, nickel borate, nickel chloride, and nickel hydrofluoride. The charge transport composition according to claim 3, wherein the organic acid nickel salt is at least one selected from the group consisting of nickel acetate, nickel formate, nickel oxalate, and nickel(II) acetylacetonate. The charge transport composition according to claim 1, wherein the polymer compound comprises at least one polyimide polymer selected from the group consisting of a polyimide precursor obtained from a diamine component and a tetracarboxylic acid component, an ester of the polyimide precursor, and an imidized product of the polyimide precursor. 7. The charge transport composition according to claim 6, wherein the polymer compound comprises at least one polyimide polymer selected from the group consisting of a polyimide precursor obtained from a diamine component having a structure represented by any one of the following formulas (1) to (3) and a tetracarboxylic acid component, an ester of the polyimide precursor, and an imidized product of the polyimide precursor:
(In the formula, ^R1 represents a hydrogen atom or a monovalent organic group. * represents a bonding site to another group. Any hydrogen atom forming the benzene ring may be substituted with a monovalent organic group.) The charge transport composition according to claim 1, wherein the polymer compound contains polyethyleneimine. The charge transport composition according to claim 1, wherein the content of the polymer compound is 5 to 20 parts by mass per 100 parts by mass of the nickel oxide precursor. The charge transport composition according to any one of claims 1 to 9, which is used for a hole collection layer of a perovskite photoelectric conversion element. A charge-transporting thin film obtained from the charge-transporting composition according to any one of claims 1 to 9. The charge transport thin film according to claim 11, wherein the charge transport thin film is a hole collection layer of a perovskite photoelectric conversion element. A perovskite photoelectric conversion element comprising the charge transport thin film according to claim 12. The perovskite photoelectric conversion element according to claim 13, which is of an inverted stacking type. A solar cell comprising the perovskite photoelectric conversion element according to claim 14. A method for producing a charge transporting thin film for a hole collection layer of a perovskite photoelectric conversion element, comprising:
A method for producing a charge transport thin film for use as a hole collection layer in a perovskite photoelectric conversion element, comprising: applying a charge transport composition containing a nickel oxide precursor, a polymer compound, and a solvent; and baking the applied composition at 260°C or higher.