Liquid composition, perovskite solar cell, and method for producing perovskite solar cell

Abstract

The present invention provides: a liquid composition that is suitably used for forming a photoelectric conversion layer in a perovskite solar cell and that imparts excellent durability to the perovskite solar cell; a perovskite solar cell that includes the photoelectric conversion layer formed using the liquid composition; and a method for producing the perovskite solar cell using the liquid composition.　The photoelectric conversion layer in the perovskite solar cell is formed using a liquid composition containing: a lead halide and / or a tin halide (A); a formamidine hydrohalide and / or a methylamine hydrohalide (B); and as a solvent (C), a high boiling point solvent (C1) having a boiling point under atmospheric pressure of more than 130°C, and a low boiling point solvent (C2) having a boiling point under atmospheric pressure of 0-130°C.

Description

Liquid composition, perovskite solar cell, and method for manufacturing a perovskite solar cell

[0001] The present invention relates to a liquid composition, a perovskite solar cell, and a method for manufacturing a perovskite solar cell.

[0002] The use of solar cells is expanding as an energy source with a low environmental impact. When installing solar cells in various devices, vehicles, buildings, etc., the available installation area is limited, so the photoelectric conversion efficiency of the solar cells can be important. Perovskite solar cells, which use organic materials, are being researched as solar cells with high photoelectric conversion efficiency. A basic perovskite solar cell consists of a substrate on which a first electrode (anode or cathode), a charge transport layer (hole transport layer or electron transport layer), a photoelectric conversion layer (perovskite layer), a charge transport layer (electron transport layer or hole transport layer), and a second electrode (cathode or anode) are stacked in this order.

[0003] Furthermore, Patent Document 1 describes a solar cell in which a monolayer is formed on the surface of a first electrode laminated on a substrate, a photoelectric conversion layer is directly laminated on the monolayer, and an electron transport layer and a transparent electrode are further laminated.

[0004] Japanese Patent Publication No. 2010-141165

[0005] However, in perovskite solar cells with the structure described above, various organic compounds are used in each layer that makes up the cell. Organic compounds are generally susceptible to modification, degradation, or decomposition due to the effects of light, oxygen, moisture, etc. Due to this instability of organic compounds, there is room for improvement in terms of durability in perovskite solar cells.

[0006] The present invention has been made in view of the above problems, and aims to provide a liquid composition that is suitably used for forming a photoelectric conversion layer in a perovskite solar cell and that provides a perovskite solar cell with excellent durability, a perovskite solar cell including a photoelectric conversion layer formed using the above-mentioned liquid composition, and a method for manufacturing a perovskite solar cell using the above-mentioned liquid composition.

[0007] A liquid composition for forming a photoelectric conversion layer in a perovskite solar cell according to a first aspect of the present invention comprises (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, and (C) a solvent, wherein (C) the solvent comprises a high-boiling point solvent (C1) having a boiling point greater than 130°C at atmospheric pressure and a low-boiling point solvent (C2) having a boiling point of 0°C or more and 130°C or less at atmospheric pressure.

[0008] In the liquid composition described above, the (C1) high-boiling point solvent may be a nitrogen-containing polar organic solvent and / or dimethyl sulfoxide.

[0009] In the above-described liquid composition, the nitrogen-containing polar organic solvent may be one or more selected from the group consisting of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone.

[0010] In the liquid composition described above, the ratio of the mass of the (C2) low-boiling point solvent to the mass of the liquid composition may be 0.1% by mass or more and 50% by mass or less.

[0011] In the liquid composition described above, the ratio of the mass of the (C2) low-boiling point solvent to the mass of the liquid composition may be 0.1% by mass or more and 30% by mass or less.

[0012] The above-mentioned liquid composition may contain one or more selected from the group consisting of (D) cesium halide, (E) passivation material, and (F) hole transport material.

[0013] A perovskite solar cell according to a second aspect of the present invention comprises a first electrode layer, a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a second electrode layer in this order, wherein the photoelectric conversion layer is a layer formed by removing volatile components from a coating film containing the liquid composition according to the first aspect.

[0014] In the perovskite solar cell described above, the first electrode layer is laminated on a substrate, the shape of the substrate is plate-like or sheet-like, and the substrate may be at least one of metal, resin, or glass.

[0015] In the perovskite solar cell described above, the first electrode layer is stacked on a substrate, and the perovskite solar cell may be a tandem solar cell comprising a silicon semiconductor substrate as the substrate.

[0016] A third aspect of the present invention relates to a method for manufacturing a perovskite solar cell comprising a first electrode layer, a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a second electrode layer in this order, wherein the photoelectric conversion layer is formed by removing volatile components from a coating film containing the liquid composition according to the first aspect.

[0017] According to the present invention, it is possible to provide a liquid composition that is suitably used for forming a photoelectric conversion layer in a perovskite solar cell and that provides a perovskite solar cell with excellent durability, a perovskite solar cell comprising a photoelectric conversion layer formed using the above-mentioned liquid composition, and a method for manufacturing a perovskite solar cell using the above-mentioned liquid composition.

[0018] This is a schematic cross-sectional view showing the configuration of an embodiment of the solar cell according to the present invention. This is a flowchart showing the procedure of an embodiment of the solar cell manufacturing method according to the present invention.

[0019] Embodiments of the present invention will be described below with reference to the drawings. Note that the dimensions of various components in the drawings have been adjusted for ease of viewing. Furthermore, in embodiments described later, components similar to those described earlier are denoted by the same reference numerals, and redundant explanations may be omitted.

[0020] [Embodiment] FIG. 1 is a schematic cross-sectional view showing a preferred configuration of a perovskite solar cell 1. In the perovskite solar cell 1, the photoelectric conversion layer 40 is formed using a liquid composition described below, which contains (A) lead halide and / or tin halide, (B) formamidinium hydrogen halide and / or methylamine hydrogen halide, and (C) a solvent. In the liquid composition described below, the (C) solvent includes a (C1) high-boiling solvent having a boiling point above 130°C under atmospheric pressure and a (C2) low-boiling solvent having a boiling point between 0°C and 130°C under atmospheric pressure.

[0021] The perovskite solar cell 1 includes a plate-shaped or sheet-shaped substrate 10, a first electrode layer 20 laminated on one main surface (the lower side in FIG. 1) of the substrate 10, a hole transport layer 30 laminated on one surface of the first electrode layer 20, a photoelectric conversion layer 40 laminated on one surface of the hole transport layer 30, an electron transport layer 50 laminated on one surface of the photoelectric conversion layer 40, and a second electrode layer 60 (cathode) laminated on one side of the electron transport layer 50.

[0022] A passivation material (not shown) may be present on the surface and / or inside of the photoelectric conversion layer 40.

[0023] Hereinafter, each component constituting the perovskite solar cell 1 will be described.

[0024] The substrate 10 is a structure that supports other layers and ensures the strength of the perovskite solar cell 1.

[0025] The shape of the substrate 10 is usually preferably a plate-shaped or sheet-shaped substrate. The substrate as the substrate 10 typically preferably contains metal and / or resin. Also, the substrate as the substrate 10 may be a silicon semiconductor substrate. In this case, the perovskite solar cell 1 may be a tandem-type solar cell.

[0026] When the perovskite solar cell 1 receives light from the side of the substrate 10, the substrate 10 is formed of a transparent material. Specifically, when emphasizing the strength of the solar cell 1, the substrate 10 preferably includes glass. When emphasizing the lightweight and flexibility of the solar cell 1, the substrate 10 is preferably made of resin. As the resin as the material of the substrate 10, polyimide, polyamide, and polyethylene terephthalate are preferable. From the viewpoint of dimensional stability, polyimide is particularly preferable. When emphasizing the cost as a product, polyethylene terephthalate is particularly preferable. Further, when the perovskite solar cell 1 receives light from the side of the second electrode layer 60, the substrate 10 may be formed of a composite material including a metal layer or the like.

[0027] The first electrode layer 20 collects the holes generated in the photoelectric conversion layer 40 through the hole transport layer 30 and outputs them to the outside. The first electrode layer 20 can be formed of a transparent conductive oxide (TCO: Transparent Conductive Oxide) having conductivity and light transmittance. As the transparent conductive oxide forming the first electrode layer 20, for example, indium oxide, tin oxide, zinc oxide, titanium oxide, and their composite oxides can be used. Among these, indium-based composite oxides mainly composed of indium oxide, indium zinc oxide, indium tungsten oxide, indium molybdenum oxide, etc., or fluorine-doped tin oxide are preferable. From the viewpoint of high conductivity and transparency, indium oxide is particularly preferable. The first electrode layer 20 is preferably subjected to a surface treatment such as ozone treatment in order to improve the formability of the hole transport layer 30, and may have a multilayer structure having a layer of a p-type oxide semiconductor mainly composed of, for example, nickel oxide, niobium oxide, etc. on the surface.

[0028] The hole transport layer 30 effectively transmits the holes generated in the photoelectric conversion layer 40 to the first electrode layer 20. Preferably, the hole transport layer 30 is a self-assembled monolayer film including a hole transport material having an attractive interaction with the first electrode layer or a bonding group capable of forming a bond with the first electrode layer.

[0029] The hole transport material is preferably a compound in which the difference between the HOMO (Highest Occupied Molecular Orbital) of the hole transport material and the VB edge (Valence Band) of the perovskite compound constituting the photoelectric conversion layer 40 is small.

[0030] The above difference is preferably 0.00 to 1.00 eV, more preferably 0.00 to 0.50 eV, and even more preferably 0.00 to 0.30 eV.

[0031] HOMO and LUMO (Lowest Unoccupied Molecular Orbital) can be determined by photoelectron spectroscopy or quantum chemical calculations based on density functional theory.

[0032] As the exchange-correlation functional, B3LYP can be suitably used. For basis functions, 6-311G(d) can be suitably used for optimizing the molecular structure, and 6-311++G(d,p) can be suitably used for calculating the energy.

[0033] As the hole transport material, any compound that has been conventionally used to form the hole transport layer in perovskite solar cells can be used without particular limitation. Preferably, the hole transport material is a compound having an atomic group involved in hole transport and the above-mentioned bonding group.

[0034] Examples of atomic groups involved in hole transport include aromatic compounds containing a triphenylamine skeleton such as Spiro-MeOTAD (CAS number: 207739-72-8), TOP-HTM-α1 (CAS number: 872466-50-7), and TOP-HTM-α2 (CAS number: 2411528-61-3); aromatic compounds containing a carbazole skeleton such as 2PACz (CAS number: 20999-38-6), 4PACz (CAS number: 20999-36-4), MeO-2PACz (CAS number: 2922526-56-3), and Me-2PACz (CAS number: 2747959-96-0); compounds containing a phenothiazine skeleton; compounds containing a thiophene skeleton; and compounds containing a diarylamine skeleton.

[0035] A suitable bonding group is the group represented by the following formula (A): -R １ -R ２ ... (A)

[0036] R １ R is a divalent organic group with 1 to 12 carbon atoms. ２ However, these are phosphonic acid groups, carboxyl groups, sulfonic acid groups, boric acid groups, hydroxyl groups, amino groups, silyl groups, or mercapto groups.

[0037] R １ A divalent organic group may contain heteroatoms in addition to carbon and hydrogen atoms. Examples of heteroatoms include O, N, S, halogen atoms, P, B, and Si.

[0038] R １ The divalent organic group is preferably a hydrocarbon group. The number of carbon atoms in the hydrocarbon group is not particularly limited, but is preferably 1 to 12, and more preferably 1 to 6.

[0039] R １ The hydrocarbon group can be an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination of an aliphatic hydrocarbon group and an aromatic hydrocarbon group.

[0040] If the hydrocarbon group is an aliphatic hydrocarbon group, the structure of the aliphatic hydrocarbon group may be linear, cyclic, or a combination of linear and cyclic.

[0041] R １ Preferred specific examples of aliphatic hydrocarbon groups include methylene group, ethane-1,2-diyl group (ethylene group), ethane-1,1-diyl group, propane-1,3-diyl group (propylene group), propane-1,2-diyl group (methylethylene group), propane-2,2-diyl group, butane-1,4-diyl group, butane-1,3-diyl group, butane-1,2-diyl group, pentane-1,5-diyl group, and hexane-1,6-diyl group.

[0042] Among these groups, a methylene group, an ethane-1,2-diyl group (ethylene group), a propane-1,3-diyl group (propylene group), a butane-1,4-diyl group, and a butane-1,3-diyl group (butylene group) are preferred, and an ethane-1,2-diyl group (ethylene group), a propane-1,3-diyl group (propylene group), and a butane-1,3-diyl group (butylene group) are more preferred.

[0043] R １ Preferable specific examples of the aromatic hydrocarbon group as R include a p-phenylene group, an m-phenylene group, a naphthalene-2,6-diyl group, a naphthalene-2,7-diyl group, a naphthalene-1,4-diyl group, a naphthalene-1,5-diyl group, a naphthalene-1,7-diyl group, a biphenyl-4,4'-diyl group, a biphenyl-3,4'-diyl group, and a biphenyl-3,3'-diyl group, etc.

[0044] R ２ is a phosphonic acid group, a carboxy group, a sulfonic acid group, a boric acid group, a hydroxy group, an amino group, a silyl group, or a mercapto group. The silyl group is usually a reactive silicon group capable of generating a silanol group by hydrolysis. Such a reactive silicon group has a hydrolyzable group bonded to a silicon atom.

[0045] Specific examples of the hydrolyzable group include a halogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amide group, an acid amide group, an aminooxy group, a mercapto group, and an alkenyloxy group, etc. Among these, an alkoxy group, an acyloxy group, a ketoximate group, and an alkenyloxy group are preferred, and an alkoxy group such as a methoxy group and an ethoxy group is more preferred because of its mild hydrolyzability and easy handling.

[0046] Specific examples of reactive silicon groups include dimethoxymethylsilyl group, diethoxymethylsilyl group, trimethoxysilyl group, triethoxysilyl group, dimethoxyphenylsilyl group, methoxymethyldimethoxysilyl group, methoxymethyldiethoxysilyl group, triisopropenyloxysilyl group, and triacetoxysilyl group. Among these, dimethoxymethylsilyl group, trimethoxysilyl group, and methoxymethyldimethoxysilyl group are preferred.

[0047] Since hole transport materials are easy to obtain and prepare, and the hole transport layer 30 is easily formed, in formula (A), R １ However, it is an alkylene group with 1 to 6 carbon atoms, R ２ It is preferable that the group is a phosphonic acid group.

[0048] Suitable specific examples of hole transport materials include N-(2-phosphonoethyl)carbazole (2PACz), N-(2-phosphonoethyl)-3,6-dimethoxycarbazole (MeO-2PACz), N-(2-phosphonoethyl)-3,6-dimethylcarbazole (Me-2PACz), N-(3-phosphonopropyl)carbazole (3PACz), N-(3-phosphonopropyl)-3,6-dimethoxycarbazole (MeO-3PACz), N-(3-phosphonopropyl)-3,6-dimethylcarbazole (Me-3PACz), N-(4-phosphonobutyl)carbazole (4PACz), N-(4-phosphonobutyl)-3,6-dimethoxycarbazole (MeO-4PACz), and N-(4-phosphonobutyl)-3,6-dimethylcarbazole (Me-4PACz).

[0049] Among these, 2PACz, MeO-2PACz, Me-2PACz, MeO-4PACz, and Me-4PACz are more preferred.

[0050] The hole transport layer 30 may contain, in addition to the hole transport material, phosphonic acid compounds such as n-butylphosphonic acid, n-pentylphosphonic acid, n-hexylphosphonic acid, n-octylphosphonic acid, n-decylphosphonic acid, n-octadecylphosphonic acid, 2-ethylhexylphosphonic acid, methoxymethylphosphonic acid, 3-acryloyloxypropylphosphonic acid, 11-hydroxyundecylphosphonic acid, and 1H,1H,2H,2H-perfluorophosphonic acid, as well as other compounds such as acetic acid, propionic acid, isobutyric acid, nonanoic acid, fluoroacetic acid, α-chloropropionic acid, and glyoxylic acid. These compounds do not constitute the hole transport material. They may be used individually or in combination of two or more.

[0051] The hole transport layer 30 is formed, for example, by coating a liquid composition containing a hole transport material onto the first electrode layer and drying the coated film.

[0052] The liquid composition used to form the hole transport layer 30 typically contains an organic solvent. Examples of organic solvents include alcohols such as methanol, ethanol, 2-methoxyethanol, isopropanol, and butanol; ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran, 4-methyltetrahydropyran, 2-methyltetrahydrofuran, and cyclopentyl methyl ether; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; amides such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); esters such as ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isoamyl acetate, and γ-butyrolactone (GBL); nitriles such as acetonitrile, propionitrile, and 3-methoxypropionitrile; aromatic compounds such as benzene, toluene, chlorobenzene, and nitrobenzene; chlorinated hydrocarbons such as dichloromethane, chloroform, and 1,2-dichloroethane; and fluorinated hydrocarbons such as chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons. These can be used individually or in combination of two or more.

[0053] The total concentration of the materials constituting the self-assembled monolayer contained in the liquid composition used to form the hole transport layer 30 is preferably 0.00001 mg / mL or more and 5.0 mg / mL or less, more preferably 0.00005 mg / mL or more and 4.0 mg / mL or less, and even more preferably 0.0001 mg / mL or more and 3.0 mg / mL or less.

[0054] Furthermore, it is preferable that a passivation material be present between the hole transport layer 30 and the photoelectric conversion layer 40. The passivation material between the hole transport layer 30 and the photoelectric conversion layer 40 is not shown in Figure 1.

[0055] The passivation material is an organic compound that suppresses defects in the photoelectric conversion layer 40 by interacting with anionic and cationic species on the surface and / or inside the photoelectric conversion layer 40. By passivating the defects in the photoelectric conversion layer 40, the recombination of charge and holes is suppressed, and the photoelectric conversion efficiency is improved.

[0056] The passivation material may exist as a layer of a certain thickness on the surface of the photoelectric conversion layer 40, or it may exist as a single molecule or a composite of multiple molecules inside the photoelectric conversion layer 40 (for example, inside the perovskite crystal bulk or at the grain boundaries).

[0057] The mode of presence of the passivation material in the photoelectric conversion layer 40 may be any of the above modes. In any of the above modes, the photoelectric conversion efficiency of the perovskite solar cell 1 is improved.

[0058] When the passivation material is present as a layer on the surface of the photoelectric conversion layer 40, the surface of the photoelectric conversion layer 40 is passivated by applying the passivation material to the interface between the hole transport layer 30 and the photoelectric conversion layer 40, and / or the interface between the electron transport layer 50 and the photoelectric conversion layer 40.

[0059] In this case, the layer made of passivation material may be present in at least a part of the main surface of the photoelectric conversion layer 40, or it may be present throughout the entire surface, and it is preferable that it is present throughout the entire main surface of the photoelectric conversion layer 40.

[0060] When the passivation material exists inside the photoelectric conversion layer 40 as a single molecule or a composite of multiple molecules, the interaction between the passivation material (as a single molecule or composite of multiple molecules) and the perovskite crystal causes the defects inside the photoelectric conversion layer 40 to be passivated. In this case, typically, the passivation material acts on the crystal lattice of the perovskite compound inside the photoelectric conversion layer 40, causing the grain boundaries and the like to be passivated.

[0061] The passivation material is not particularly limited as long as the desired effect is not impaired. The passivation material can be appropriately selected from various compounds that have been conventionally used as passivation materials in perovskite solar cells. Suitable examples of passivation materials include various amines or their hydrohalides. Examples of hydrohalides include hydrofluoric acid, hydrochloride, hydrobromide, and hydroiodide, with hydrobromide and hydroiodide being preferred, and hydroiodide being more preferred.

[0062] Suitable examples of passivation materials include n-butylamine hydrobromide, n-butylamine hydroiodide, n-hexylamine hydrobromide, n-hexylamine hydroiodide, n-decylamine hydrobromide, n-octadecylamine hydroiodide, pyridine hydrobromide, aniline hydroiodide, hydrazine dibromide, ethylenediamine hydroiodide, phenethylamine hydroiodide, 4-fluorinated phenethylamine hydroiodide, phenylenediamine dihydrochloride, diphenylamine hydrobromide, diphenylamine hydroiodide, benzylamine hydroiodide, and 4-diphenylaminophenethylamine hydroiodide.

[0063] Fluorine-containing amine compounds and their salts are also preferred as passivation materials. Preferred specific examples of fluorine-containing amine compounds include, for example, compounds having a fluorinated aromatic group and an amino acid group, such as pentafluorophenylethylalanine hydroiodide, and their salts; fluoroalkylamines such as 6,6,6,5,5,4,4,3,3,2,2-undekafluorohexylamine hydroiodide and 5,5,5,4,4,3,3,2,2-nonafluoropentylamine hydroiodide, and their salts; and compounds having a fluorinated aromatic group and an amino group, such as 4-fluorophenylethylamine hydroiodide, and their salts.

[0064] When a passivation material is present between the hole transport layer 30 and the photoelectric conversion layer 40, a thin film of the passivation material is formed by coating the hole transport layer 30 with a passivation material solution containing the passivation material and an organic solvent, and then drying it. The same solvent used for forming the hole transport layer 30 described above is preferably used as the organic solvent.

[0065] The coating method is not particularly limited. Coating can be performed using, for example, a spin coater, die coater, or bar coater.

[0066] The temperature during application is not particularly limited, but -20°C to 200°C is preferred, and 0°C to 150°C is more preferred.

[0067] The application time is not particularly limited, but 1 second to 24 hours is preferred, and 5 seconds to 1 hour is more preferred.

[0068] Furthermore, by including a passivation material in the liquid composition containing the materials constituting the self-assembled monolayer described above, a layer containing the passivation material can be formed on the surface of the hole transport layer 30.

[0069] The photoelectric conversion layer 40 contains a perovskite compound that performs photoelectric conversion and absorbs incident light to generate photocarriers. The photoelectric conversion layer 40 is formed using a liquid composition described later, which includes (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, and (C) a solvent. In the liquid composition described later, (C) the solvent includes a high-boiling point solvent (C1) having a boiling point greater than 130°C at atmospheric pressure, and a low-boiling point solvent (C2) having a boiling point of 0°C or more and 130°C or less at atmospheric pressure.

[0070] By forming a photoelectric conversion layer 40 using the above liquid composition, a perovskite solar cell 1 with excellent durability can be manufactured.

[0071] A preferred example of a perovskite compound contained in the photoelectric conversion layer 40 is a perovskite compound comprising: an organic atomic group A containing at least one of a monovalent organic ammonium ion and an amidinium-based ion; a metal atom B that generates a divalent metal ion; and a halogen atom X containing at least one of iodide ion I, bromide ion Br, chloride ion Cl, and fluoride ion F, such that ABX ３ Compounds represented by can be used. Organic group A is not particularly limited as long as the desired effect is not impaired, and can be appropriately selected from well-known organic compounds. Examples of organic group A include methylammonium MA (CH ３ NH ３ ), and formamidinium FA (CH(NH ２ ) ２ (CH ５ N ２ Examples include:

[0072] The metal atom B is not particularly limited as long as it is a metal atom that has been conventionally used in the formation of perovskite compounds. Preferred metal atoms B include lead (Pb) and tin (Sn). When the power generation efficiency of the perovskite solar cell 1 is important, it is preferable that the metal atom B is mainly lead. The lower limit of the lead content in metal atom B is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass, in order to achieve the desired performance. On the other hand, when the environmental impact of lead is important, it is preferable that the metal atom B is mainly tin (Sn). The lower limit of the tin content in metal atom B is preferably 50% by mass, more preferably 80% by mass, and especially preferably 90% by mass, in order to achieve the desired performance.

[0073] The halogen atom is not particularly limited. At least one of iodide I, bromide Br, and chloride Cl is preferred as the halogen atom X. Furthermore, substituting part or all of the organic atomic group A with alkali metal Am has also been considered, and such perovskite compounds can also be used. The alkali metal Am is not particularly limited. Preferred alkali metal Ams include potassium K, cesium Cs, and rubidium Rb. Among these, cesium Cs and rubidium Rb are preferred as alkali metal Ams when durability and water resistance of the perovskite solar cell 1 are important, and cesium Cs is particularly preferred from the viewpoint of cost and availability.

[0074] Specifically, preferred perovskite compounds include, for example, MAPbI ３ MAPbBr ３ MAPbCl ３ Methylammonium lead halide (MAPbX) ３ ), and FAPbi ３ FAPbBr ３ , and FAPbCl ３ Formamidine lead halide (FAPbX) ３ ) are examples. Note that halogen atoms X may contain multiple types, and FA may contain both methylammonium and formamidinium as organic atomic group A. ｙ MA １－ｙ PbX ３It may also be included. In addition, if it contains the alkali metal Am, Am ｙ FA ｚ MA １－ｙ－ｚ PbX ３ Am ｙ FA １－ｙ PbX ３ Examples include the following. Am may be a single type of Cs, Rb, or K, or it may contain multiple types (where y and z are mole fractions (continuous values) for 0 ≤ y and z ≤ 1).

[0075] A liquid composition, described later, comprising (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, and (C) solvent, may also contain (F) a hole transport material.

[0076] When using a liquid composition comprising (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, (C) solvent, and (F) hole transport material, the hole transport layer 30 and the photoelectric conversion layer 40 can be formed simultaneously by coating the liquid composition onto the first electrode layer 20, drying it, and crystallizing the perovskite precursor. In this case, during the process of forming the photoelectric conversion layer 40, compounds such as the hole transport material contained in the liquid composition form a self-assembled monolayer on the first electrode layer 20.

[0077] When a passivation material is present between the photoelectric conversion layer 40 and the electron transport layer 50, recombination of photocarriers at the interface between the photoelectric conversion layer 40 and the electron transport layer 50 is prevented, and the arrival of electrons to the electron transport layer 50 is promoted.

[0078] The passivation material placed between the photoelectric conversion layer 40 and the electron transport layer 50 can be the same material as the passivation material placed between the hole transport layer 30 and the photoelectric conversion layer 40.

[0079] As the passivation material to be placed between the photoelectric conversion layer 40 and the electron transport layer 50, the above-mentioned amine hydrohalides, amines having alkyl fluoride, or hydrohalides thereof are preferred.

[0080] As mentioned above, the passivation material can be an amine compound rather than a hydrohalide, but it will still produce the desired effect. In this case, the amine compound interacts with lead ions and other elements that form the perovskite crystal through the lone pair of electrons on the nitrogen atom, thereby preventing charge recombination.

[0081] When a passivation material is present between the photoelectric conversion layer 40 and the electron transport layer 50, it can be formed by coating the photoelectric conversion layer 40 with a passivation material solution containing the passivation material and an organic solvent, and then drying it, similar to the passivation material present between the hole transport layer 30 and the photoelectric conversion layer 40.

[0082] When a passivation material is included in the perovskite precursor solution used to form the photoelectric conversion layer 40, the passivation material can be present on the surface and / or inside the photoelectric conversion layer 40 by coating the perovskite precursor solution onto the hole transport layer 30, drying it, and crystallizing the perovskite precursor.

[0083] Furthermore, the aforementioned liquid composition containing the material constituting the self-assembled monolayer may also contain a perovskite precursor for forming the photoelectric conversion layer 40 and a passivation material. In this case, by coating and drying the liquid composition on the first electrode layer 20 and crystallizing the perovskite precursor, the hole transport layer 30 and the photoelectric conversion layer 40 can be formed simultaneously, while the passivation material can be present on the surface and / or inside the photoelectric conversion layer 40.

[0084] When the perovskite precursor solution contains a passivation material and a perovskite precursor, fluorine-containing amine compounds and their salts are preferred as passivation materials because they are easily precipitated at the interface and surface of the perovskite polycrystal by utilizing the hydrophobic interaction of fluorine atoms. The fluorine content in the fluorine-containing amine compound is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, as the mass of fluorine atoms relative to the molecular weight of each compound. When the fluorine-containing amine compound and its salt contain fluorine atoms in the above ratios, the fluorine-containing amine compound is easily precipitated on the perovskite crystal surface by sufficient hydrophobic interaction.

[0085] The electron transport layer 50 effectively transmits electrons to the second electrode layer 60. The material constituting the electron transport layer 50 is not particularly limited as long as the desired effect is not impaired. The material constituting the electron transport layer 50 can be appropriately selected from various compounds that have been conventionally used to form electron transport layers in perovskite solar cells. The electron transport layer 50 is preferably formed from an electron transport material mainly composed of, for example, fullerene or naphthalene diimide. Examples of fullerenes include C60, C70, their hydrides, oxides, metal complexes, alkyl groups, etc., derivatives to which such as PCBM ([6,6]-Phenyl-C61-Butyric Acid Methyl Ester) can be added. In addition, a hole block layer of bathocuproine (BCP), lithium fluoride (LiF), or magnesium fluoride (MgF) can be placed between the electron transport layer 50 and the second electrode layer 60. ２ ), tin oxide (SnO ２ ), aluminum-doped zinc oxide (ZnO), and / or titanium oxide (TiO ２ ) may contain. The inorganic oxide layer may be doped with another metallic material. The material of the hole block layer is not limited to these.

[0086] The second electrode layer 60 preferably includes a metal layer, such as copper, to reduce electrical resistance when the perovskite solar cell 1 receives light from the substrate 10 side. However, the metal constituting the metal layer is not limited to copper. Furthermore, when the perovskite solar cell 1 receives light from the second electrode layer 60 side, the second electrode layer 60 may be formed from a transparent conductive oxide.

[0087] <Liquid Composition> The liquid composition comprises (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, and (C) solvent. The solvent (C) includes a high-boiling point solvent (C1) having a boiling point greater than 130°C at atmospheric pressure, and a low-boiling point solvent (C2) having a boiling point of 0°C or higher and 130°C or lower at atmospheric pressure. Such a liquid composition can be suitably used as a liquid composition for forming a photoelectric conversion layer in a perovskite solar cell.

[0088] (A) Lead halides and / or tin halides, and (B) Formamidine hydrohalides and / or methylamine hydrohalides are so-called perovskite precursors.

[0089] (C1) As high-boiling point solvents, nitrogen-containing polar organic solvents and / or dimethyl sulfoxides are preferred. Specific examples of (C1) high-boiling point solvents include amide solvents such as N,N-dimethylformamide (DMF), N,N-diethylformamide, N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone; sulfoxides such as dimethyl sulfoxide (DMSO); and esters such as amyl acetate and γ-butyrolactone (GBL). Among these (C1) high-boiling point solvents, one or more selected from the group consisting of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone are preferred. The boiling point of the high-boiling solvent (C1) at atmospheric pressure is above 130°C, preferably between 130°C and 300°C, and more preferably between 150°C and 250°C.

[0090] (C2) Specific examples of low-boiling point solvents include ketones such as acetone and 2-butanone; nitriles such as acetonitrile and propionitrile; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and 2-methoxyethanol; ethers such as diethyl ether, cyclopentyl methyl ether, and tetrahydrofuran; esters such as methyl formate, ethyl acetate, butyl acetate, propyl acetate, and isopropyl acetate; and phosphite triesters such as trimethyl phosphite. (C2) The boiling point of low-boiling point solvents at atmospheric pressure is preferably 0°C to 130°C, more preferably 15°C to 120°C, and even more preferably 30°C to 110°C.

[0091] (C2) The vapor pressure of the low-boiling point solvent at 25°C is preferably 0.1 kPa or higher, more preferably 1 kPa or higher, and even more preferably 10 kPa or higher, from the viewpoint of facilitating the volatilization of the low-boiling point components, including the low-boiling point solvent (C2), during the solvent drying process.

[0092] (C2) The dielectric constant of the low boiling point solvent at 25°C is preferably 50 or less, more preferably 40 or less, and even more preferably 30 or less, from the viewpoint of ensuring solubility with other components in the liquid composition.

[0093] (C2) The donor number of the low-boiling point solvent is preferably 30 or less, more preferably 25 or less, and even more preferably 23 or less, from the viewpoint of ensuring solubility with other components in the liquid composition. For a definition of donor number, see V. Gutmann, Elecrochim. Acta, 21, 661, 1976.

[0094] When using a solvent (C) with such a boiling point, less of the solvent (C) remains in the perovskite crystal, making it easier to manufacture a perovskite solar cell 1 with the desired performance.

[0095] The ratio of the mass of the (C2) low-boiling point solvent to the mass of the liquid composition is preferably 0.1% by mass or more and 50% by mass or less, and more preferably 0.1% by mass or more and 30% by mass or less.

[0096] (C2) The mechanism by which the low-boiling point solvent contributes to the improved durability of the photoelectric conversion layer is not entirely clear. It is presumed that the improved durability is due to the fact that the low-boiling point solvent (C2) has a lower boiling point than the high-boiling point solvent (C1). Therefore, when solvent (C) is removed by drying, the low-boiling point solvent (C2) azeotropes with water, oxygen, and other low-boiling point components contained in the liquid composition, resulting in the formation of a high-purity perovskite polycrystalline layer in the photoelectric conversion layer.

[0097] The content of (A) lead halide and / or tin halide in the above liquid composition is preferably 1.0% by mass or more and 99.0% by mass or less, and more preferably 5.0% by mass or more and 90.0% by mass or less, based on the total mass of the liquid composition, in terms of solubility, growth rate of perovskite polycrystals, photoelectric conversion efficiency, and cost.

[0098] The content of (B) formamidine hydrohalide and / or methylamine hydrohalide in the above liquid composition is preferably 0.5 molar equivalents or more and 10 molar equivalents or less, and more preferably 0.8 molar equivalents or more and 5.0 molar equivalents or less, relative to the content (number of moles) of (A) lead halide and / or tin halide.

[0099] The above liquid composition may contain one or more selected from the group consisting of (D) cesium halide, (E) passivation material, and (F) hole transport material. The (E) passivation material and (F) hole transport material are as described above.

[0100] When the liquid composition contains (D) cesium halide, a perovskite solar cell 1 with excellent durability and water resistance can be easily obtained by forming a photoelectric conversion layer 40 using the liquid composition.

[0101] The advantages of the liquid composition including (E) a passivation material and / or (F) a hole transport material are as described above.

[0102] The content of (D) cesium halide in the above liquid composition is preferably 0 to 10 molar equivalents, and more preferably 0.01 to 5.0 molar equivalents, relative to the content (number of moles) of (A) lead halide and / or tin halide, in terms of the durability of the perovskite solar cell.

[0103] The content of (E) passivation material in the above liquid composition is preferably 0.001% by mass or more and 10% by mass or less, and more preferably 0.01% by mass or more and 5.0% by mass or less, relative to the total mass of (A) lead halide and / or tin halide and (B) formamidine hydrohalide and / or methylamine hydrohalide, in terms of photoelectric conversion efficiency, durability and cost.

[0104] The content of (F) hole transport material in the above liquid composition is preferably 0.001% by mass or more and 10% by mass or less, and more preferably 0.01% by mass or more and 5.0% by mass or less, relative to the total mass of the liquid composition, in terms of photoelectric conversion efficiency, durability, and cost.

[0105] By using the above liquid composition to form the photoelectric conversion layer 40 in the perovskite solar cell 1, a perovskite solar cell with excellent durability can be obtained.

[0106] ≪Method for Manufacturing Perovskite Solar Cells≫ A perovskite solar cell comprising a first electrode layer 20, a hole transport layer 30, a photoelectric conversion layer 40, an electron transport layer 50, and a second electrode layer 60 in this order can be manufactured by a method that includes forming the photoelectric conversion layer 40 by removing volatile components from a coating film containing a liquid composition containing the above-mentioned components (A) to (C).

[0107] A preferred method for manufacturing a perovskite solar cell 1 is a method comprising: coating a first electrode layer 20 formed on one main surface of a plate-shaped or sheet-shaped substrate 10 with the aforementioned liquid composition to form a hole transport layer 30; forming a photoelectric conversion layer 40 containing a perovskite compound on the hole transport layer 30 by removing volatile components from a coating film containing the liquid composition containing the above components (A) to (C); forming an electron transport layer 50 on the photoelectric conversion layer 40; and forming a second electrode layer 60 on the electron transport layer 50.

[0108] Specifically, the perovskite solar cell 1 can be manufactured by the embodiment of the solar cell manufacturing method shown in Figure 2. The solar cell manufacturing method of this embodiment comprises a first electrode layer formation step (step S11), a hole transport layer formation step (step S12), a precursor liquid coating step (step S13), a crystallization step (step S14), an electron transport layer formation step (step S15), and a second electrode layer formation step (step S16).

[0109] The embodiment of the solar cell manufacturing method shown in Figure 2 may include a first passivation material coating step (step S01, not shown in Figure 2) between the hole transport layer formation step (step S12) and the precursor liquid coating step (step S13).

[0110] Furthermore, if a precursor liquid that does not contain passivation material is used in the precursor liquid coating step (step S13), the embodiment of the solar cell manufacturing method shown in Figure 2 may include a second passivation material coating step (step S02, not shown in Figure 2).

[0111] In the first electrode layer formation step S11, a first electrode layer 20 is formed on the main surface of one side of the substrate 10. The first electrode layer 20 can be laminated using a vacuum deposition technique such as sputtering. In addition, in the first electrode layer formation step, it is preferable to modify the surface of the deposited first electrode layer 20 in order to promote the formation of the hole transport layer 30 in the next step. Specific methods for modifying the surface of the first electrode layer 20 include, for example, surface hydroxylation by ultraviolet-ozone treatment or ozonated water washing, deposition of oxides such as nickel oxide that facilitate the growth of self-assembled films using a vacuum deposition technique such as sputtering, deposition of oxide nanoparticles using a coating technique, and heat treatment to activate the surface and remove impurities so that self-assembled films can grow easily.

[0112] In step S12, the hole transport layer formation step, the hole transport layer 30 is laminated onto the first electrode layer 20. The hole transport layer 30 can be formed by coating a solution containing the material constituting the hole transport layer 30 and an organic solvent, and then drying. The drying temperature is preferably 50°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. The drying time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. When drying is performed under the above conditions, the organic solvent is sufficiently removed from the coated film, making it easier to obtain the desired crystals in the subsequent step of forming the perovskite polycrystal.

[0113] After forming the hole transport layer 30 in step S12, a first passivation material coating step (step S01) may be performed as needed to coat the hole transport layer 30 with passivation material. In the first passivation material coating step (step S01), a passivation material solution containing passivation material and an organic solvent is coated onto the hole transport layer 30, and then the coated film is dried. In this case, the passivation material can be present on the hole transport layer 30.

[0114] The passivation material solution can be applied using, for example, a spin coater, die coater, and bar coater.

[0115] Furthermore, in step S12, the passivation material can also be present on the hole transport layer 30 by coating it with a liquid composition containing the material constituting the hole transport layer 30 and the passivation material to form the hole transport layer 30.

[0116] In the precursor liquid coating step S13, a liquid composition containing the above components (A) to (C) is coated onto the laminate of the substrate 10, the first electrode layer 20, and the hole transport layer 30 as a perovskite precursor liquid.

[0117] When step S01 is performed, the liquid composition containing components (A) to (C) described above is coated onto the passivation material applied on the hole transport layer 30.

[0118] The liquid composition containing components (A) to (C) can be applied using, for example, a spin coater, die coater, and bar coater.

[0119] A liquid composition containing components (A) to (C) comprises solvent (C), and (A) lead halide and / or tin halide as perovskite precursors that form a perovskite compound that performs photoelectric conversion, and (B) formamidine hydrohalide and / or methylamine hydrohalide. A liquid composition containing components (A) to (C) may also contain perovskite precursors other than components (A) and (B) along with components (A) and (B). Furthermore, a liquid composition containing components (A) to (C) may further contain a hydrogen chloride salt that promotes the growth of crystals of the perovskite compound.

[0120] By using a liquid composition containing components (A) to (C), the photoelectric conversion layer 40 can be formed in steps S13 and S14.

[0121] The photoelectric conversion layer 40 may be formed using a liquid composition containing (F) a hole transport material and a perovskite precursor as materials constituting the hole transport layer 30. In this case, step S12 for forming the hole transport layer 30 can be omitted. This is because the hole transport layer 30 is formed during the process of forming the photoelectric conversion layer 40 in steps S13 and S14. By using a liquid composition containing (F) a hole transport material and a perovskite precursor, the photoelectric conversion layer 40 and the hole transport layer 30 can be formed simultaneously in steps S13 and S14.

[0122] A passivation material may be further added to the liquid composition containing (F) a hole transport material and a perovskite precursor as materials constituting the hole transport layer 30. When using a liquid composition containing the material constituting the hole transport layer 30, a perovskite precursor, and a passivation material, the photoelectric conversion layer 40 can be formed while forming the hole transport layer 30 by steps S13 and S14, and the passivation material can be present on the surface and / or inside the photoelectric conversion layer 40.

[0123] The concentration of the liquid composition containing components (A) to (C) is related to the conditions of the crystallization process. The solid content concentration of the liquid composition containing components (A) to (C) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0124] When the solid content concentration of the liquid composition containing components (A) to (C) is such that, the organic solvent can be volatilized with less energy when forming the photoelectric conversion layer 40, and the perovskite solar cell 1 can be manufactured at low cost while reducing the environmental impact.

[0125] Generally, a metal halide BX and a halogenated organic compound AX are used as the perovskite precursor in predetermined proportions, preferably a metal halide BX, a halogenated organic compound AX, and, if necessary, an alkali metal halide AmX are used in predetermined proportions. As the metal halide BX, lead halide and / or tin halide are preferably used. As the halogenated organic compound AX, formamidine hydrohalides and methylamine hydrohalides are preferably used. As the alkali metal halide AmX, cesium halides such as cesium iodide are preferably used. The molar concentration of metal atom B is preferably in excess of 0.5 mol% to 10 mol% relative to the sum of the molar concentration of the organic compound and the molar concentration of alkali metal Am. This makes it possible to expel other materials to the front and back interfaces of the perovskite precursor solution during the crystallization process, and to suppress the decrease in photoelectric conversion efficiency caused by the retention of other materials in the perovskite crystal. The amounts used in a liquid composition containing components (A) to (C), namely (A) lead halide and / or tin halide, and (B) formamidine hydrohalide and / or methylamine hydrohalide, are determined appropriately considering the above.

[0126] When the liquid composition containing components (A) to (C) also contains a passivation material, the recombination of photocarriers (holes and electrons) at the interface of the photoelectric conversion layer 40 is suppressed by the action of the passivation material present on and / or inside the photoelectric conversion layer 40.

[0127] Hydrochloride salts promote the crystallization of perovskite compounds and increase the grain size of the perovskite crystals. This reduces the area of ​​grain boundaries in the photoelectric conversion layer 40 and suppresses the decrease in photoelectric conversion efficiency due to impurities between the perovskite crystals. Examples of hydrochloride salts include methylamine hydrochloride (MACl), formamidine hydrochloride (FACl), and / or methylenediaminium hydrochloride (MDACl). ２) etc. are used. The portion other than the hydrogen chloride is preferably smaller than the crystal lattice of the perovskite crystal and has an amino group. The concentration of the hydrogen chloride in the liquid composition containing components (A) to (C) may be 1 mol% to 40 mol% with respect to the molar concentration of the metal atom B ion of the perovskite compound.

[0128] In the crystallization step S14, a film containing the liquid composition with components (A) to (C) is dried (the solvent is evaporated) to generate crystals of the perovskite compound. This forms a photoelectric conversion layer 40 mainly composed of the perovskite compound.

[0129] When the liquid composition containing components (A) to (C) contains a passivation material, a photoelectric conversion layer 40 is formed, and the passivation material can be present on the surface and / or inside the photoelectric conversion layer 40. As a method to promote the formation of crystals of the perovskite compound in the coating film containing the liquid composition containing components (A) to (C), it is preferable to employ, for example, poor solvent quenching, vacuum quenching, gas quenching, or laser treatment. In the crystallization step of step S14, the dried coating film containing the liquid composition containing components (A) to (C) may be further heated.

[0130] After forming the photoelectric conversion layer 40 in steps S13 and S14, a second passivation material coating step (step S02) may be performed as needed to provide the passivation material on the main surface of the photoelectric conversion layer 40 opposite to the hole transport layer 30. In the second passivation material coating step (step S02), a passivation material solution containing the passivation material and an organic solvent is coated onto the photoelectric conversion layer 40, and then the coating film is dried to provide the passivation material on the photoelectric conversion layer 40.

[0131] In step S15, the electron transport layer formation step, the electron transport layer 50 is formed by methods such as coating or vacuum deposition. A hole block layer may also be formed on the electron transport layer 50 by vacuum deposition or atomic layer deposition.

[0132] In the second electrode layer formation step S16, the second electrode layer 60 is formed by a method such as sputtering, vacuum deposition, plating, or coating, depending on the material being formed.

[0133] As described above, perovskite solar cells exhibit high photoelectric conversion efficiency.

[0134] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. The solar cell according to the present invention may have further functional layers, for example, in a perovskite solar cell, the electron transport layer may be omitted. Furthermore, the perovskite solar cell may be a tandem solar cell using a photoelectric converter such as a crystalline silicon solar cell as a substrate.

[0135] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples.

[0136] [Examples 1-25 and Comparative Examples 1-10] (Preparation of Liquid Compositions) A mixture consisting of lead iodide (2.00 g), formamidine hydroiodide (0.634 g), cesium iodide (0.0834 g), methylamine hydrochloride (0.0943 g), N-(4-phosphonobutyl)-3,6-dimethoxycarbazole (MeO-4PACz) (0.00179 g), 6,6,6,5,5,4,4,3,3,2,2-undecafluorohexylamine hydroiodide (0.00086 g), and (C1) a high-boiling point solvent consisting of N,N-dimethylformamide (2.90 g) and N-methyl-2-pyrrolidone (0.522 g) was prepared by adding a (C2) low-boiling point solvent of the type listed in Table 1 to obtain a liquid composition. The concentrations of the (C2) low-boiling point solvent in the liquid composition are as shown in Table 1. In Comparative Example 1, a mixture without the (C2) low-boiling point solvent was used as the liquid composition.

[0137] (Fabrication of Perovskite Solar Cells) A glass substrate with an ITO film measuring 3 cm x 3 cm was washed in the following order: with pure water, with acetone, and with 2-propanol. The washed glass substrate was dried at 180°C for 1 hour. The dried glass substrate was cooled to room temperature. Next, the above liquid composition was applied onto the ITO film on the glass substrate using a spin coater in an environment of 24-25°C, 60-70% relative humidity, and 20.9% ± 0.2% oxygen concentration. The solvent was removed from the coated film by placing it under vacuum at room temperature for 5 minutes. Next, a photoelectric conversion layer containing a perovskite compound was formed on the ITO film on the glass substrate by heating the glass substrate on a hot plate at 120°C for 30 minutes in an environment of 60-70% relative humidity and 20.9% ± 0.2% oxygen concentration. In Comparative Examples 3, 9, and 10, the photoelectric conversion layer could not be formed properly. Therefore, perovskite solar cells could not be manufactured in Comparative Examples 3, 9, and 10. Furthermore, the following durability evaluations were not performed for Comparative Examples 3, 9, and 10.

[0138] Furthermore, a fullerene is deposited on the photoelectric conversion layer to a thickness of 20 nm as an electron transport layer, followed by a 20 nm thick SnO layer as a buffer layer. ２ A perovskite solar cell was obtained by forming a thin film using atomic layer deposition, and then depositing copper to a thickness of 100 nm to create a second electrode layer on top of the electron transport layer.

[0139] (Durability Evaluation) The durability of perovskite solar cells formed using the liquid compositions of each example and each comparative example was evaluated using the following method. For durability evaluation, a laminate in which the electron transport layer and the second electrode layer were not formed and the photoelectric conversion layer was exposed was used.

[0140] Specifically, the durability of the perovskite solar cell was evaluated by observing the decomposition of the perovskite crystal in the photoelectric conversion layer while the above-mentioned laminate was placed in an environment of 23°C, 50% relative humidity, and 20.9% oxygen concentration.

[0141] A photoelectric conversion layer with the desired power generation capacity has a metallic luster, while a photoelectric conversion layer whose power generation capacity has decreased or has no power generation capacity due to the decomposition of the perovskite crystal does not have a metallic luster. The decomposition products of the perovskite crystal exhibit a pale yellow to translucent white color. For these reasons, the durability of a perovskite solar cell can be evaluated by observing the appearance of the photoelectric conversion layer in an environment of 23°C, 50% relative humidity, and 20.9% oxygen concentration.

[0142] T50 was defined as the time at which the ratio of the area with metallic luster to the area of ​​the photoelectric conversion layer fell below 50%. T50 was determined for each of the laminates formed using the liquid compositions of Examples 1 to 25, and Comparative Examples 2 and 4 to 8. T50 was also determined for the laminate formed using the liquid composition of Comparative Example 1. The durability index, as a dimensionless number, was calculated by dividing the T50 of the laminates formed using the liquid compositions of Examples 1 to 25, and Comparative Examples 1, 2, and 4 to 8 by the T50 of the laminate formed using the liquid composition of Comparative Example 1. Based on the calculated durability index, the durability of the perovskite solar cells of each example and comparative example was evaluated according to the following criteria. The evaluation results are shown in Table 1. Evaluation 1: Index was less than 1. Evaluation 2: Index was 1. Evaluation 3: Index was greater than 1 and less than 1.5. Evaluation 4: Index was 1.5 or greater and less than 2. Evaluation 5: Index was 2 or greater.

[0143]

[0144] Table 1 shows that the durability of the perovskite solar cell of the example, which has a photoelectric conversion layer formed using a liquid composition containing (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, (C1) a high-boiling-point solvent with a boiling point greater than 130°C at atmospheric pressure, and (C2) a low-boiling-point solvent with a boiling point between 0°C and 130°C at atmospheric pressure, is superior to that of the perovskite solar cell of the comparative example, which has a photoelectric conversion layer formed using a liquid composition that does not contain the (C2) low-boiling-point solvent. As mentioned above, the mechanism by which the (C2) low-boiling-point solvent contributes to the improvement of the durability of the photoelectric conversion layer is not entirely clear, but it is presumed that, as shown in Examples 1 to 25, in the crystallization process of the power generation layer, water, oxygen, and other low-boiling-point impurity components contained in the liquid composition are azeotropized, resulting in the formation of a high-purity perovskite polycrystalline layer in the photoelectric conversion layer. Conversely, as shown in Comparative Examples 2 to 10, high-boiling-point solvents remain in the power generation layer without evaporating during the crystallization process, hindering the crystallization of the power generation layer. This is presumed to prevent the acquisition of a high-purity perovskite polycrystalline layer, thus reducing durability.

[0145] 1 Perovskite solar cell 10 Substrate 20 First electrode layer 30 Hole transport layer 40 Photoelectric conversion layer 50 Electron transport layer 60 Second electrode layer

Claims

1. A liquid composition for forming a photoelectric conversion layer in a perovskite solar cell, comprising (A) lead halide and / or tin halide, (B) formamidine hydrohalide and / or methylamine hydrohalide, and (C) a solvent, wherein the (C) solvent comprises a high-boiling point solvent (C1) having a boiling point greater than 130°C at atmospheric pressure and a low-boiling point solvent (C2) having a boiling point of 0°C or more and 130°C or less at atmospheric pressure.

2. The liquid composition according to claim 1, wherein the (C1) high-boiling point solvent is a nitrogen-containing polar organic solvent and / or dimethyl sulfoxide.

3. The liquid composition according to claim 2, wherein the nitrogen-containing polar organic solvent is one or more selected from the group consisting of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone.

4. The liquid composition according to claim 1, wherein the ratio of the mass of the (C2) low-boiling point solvent to the mass of the liquid composition is 0.1% by mass or more and 50% by mass or less.

5. The liquid composition according to claim 4, wherein the ratio of the mass of the (C2) low-boiling point solvent to the mass of the liquid composition is 0.1% by mass or more and 30% by mass or less.

6. The liquid composition according to claim 1, comprising one or more selected from the group consisting of (D) cesium halide, (E) passivation material, and (F) hole transport material.

7. A perovskite solar cell comprising a first electrode layer, a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a second electrode layer in this order, wherein the photoelectric conversion layer is a layer formed by removing volatile components from a coating film containing the liquid composition described in any one of claims 1 to 6.

8. The perovskite solar cell according to claim 7, wherein the first electrode layer is laminated on a substrate, the shape of the substrate is plate-shaped or sheet-shaped, and the substrate comprises at least one of metal, resin, or glass.

9. The perovskite solar cell according to claim 7, wherein the first electrode layer is laminated on a substrate, and the substrate is a silicon semiconductor substrate, wherein the tandem solar cell is a perovskite solar cell.

10. A method for manufacturing a perovskite solar cell comprising a first electrode layer, a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a second electrode layer in this order, wherein the photoelectric conversion layer is formed by removing volatile components from a coating film containing the liquid composition described in any one of claims 1 to 6.

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