Composition for forming carbon electrode, carbon electrode, photoelectric conversion element, perovskite solar cell, method for producing carbon electrode, and method for producing perovskite solar cell

Abstract

An object of the present invention is to provide a composition for forming a carbon electrode capable of producing a carbon electrode suitable for production of a perovskite solar cell having more excellent photoelectric conversion efficiency, a carbon electrode capable of producing a perovskite solar cell having more excellent photoelectric conversion efficiency and a method for producing the same, a photoelectric conversion element having more excellent photoelectric conversion efficiency, a perovskite solar cell, and a method for producing a perovskite solar cell.SOLUTION: The content of the tin oxide particles is 3 to 24 mass% with respect to the content of the carbonaceous material, and the average particle size of the tin oxide particles is 2 to 200nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composition for forming a carbon electrode, a carbon electrode, a photoelectric conversion element, a perovskite solar cell, a method for producing a carbon electrode, and a method for producing a perovskite solar cell. [Background technology]

[0002] Photovoltaic power generation is one of the clean energy sources that has attracted the most attention in modern times. Among these, perovskite solar cells using organic-inorganic perovskite crystals are expected to be promising in terms of performance and commercialization cost. Conventionally, perovskite solar cells have used a collector layer made of precious metals such as silver and gold as the anode. However, in perovskite solar cells using such a collector layer, the ionic perovskite crystals decompose when reacting with moisture in the atmosphere, resulting in a rapid deterioration of photoelectric conversion efficiency, posing challenges in durability and long-term stability. From these perspectives, there has been growing interest in the use of perovskite solar cells that use carbon electrodes containing carbon materials as the anodes. Carbon electrodes are cheaper than precious metals and, because they are water-repellent, they suppress the decomposition of perovskite crystals present inside the cells, resulting in superior durability and long-term stability.

[0003] For example, Patent Document 1 describes an invention relating to a solar cell including a conductive substrate, a hole-blocking layer, a mesoporous nanocrystal layer, a mesoporous spacer, and a mesoporous carbon electrode layer. Also, Non-Patent Document 1 describes a technology relating to a perovskite solar cell having a carbon electrode layer containing NiO nanoparticles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2020-504455 [Non-patent literature]

[0005] [Non-Patent Document 1] Liang Chu et al., Solar Energy Materials and Solar Cells, Volume 178 (2018) Pages 164-169. Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, the use of carbon electrodes containing carbon materials as anodes is expected to improve durability and long-term stability in perovskite solar cells. However, compared to electrodes containing metals, there is room for improvement in the cell characteristics of perovskite solar cells using carbon electrodes, particularly in terms of photoelectric conversion efficiency (PCE).

[0007] Therefore, an object of the present invention is to provide a composition for forming a carbon electrode that can produce a carbon electrode suitable for producing a perovskite solar cell having superior photoelectric conversion efficiency. Another object of the present invention is to provide a carbon electrode capable of producing a perovskite solar cell with superior photoelectric conversion efficiency and a method for producing the same, as well as a photoelectric conversion element, a perovskite solar cell, and a method for producing a perovskite solar cell with superior photoelectric conversion efficiency. [Means for solving the problem]

[0008] As a result of extensive investigations, the present inventors have found that the above problems can be solved by employing the following configuration, and have thus completed the present invention.

[0009] [1] A carbon electrode-forming composition comprising a carbon material and tin oxide particles, wherein the content of the tin oxide particles is 3 to 24 mass % relative to the content of the carbon material, and the average particle size of the tin oxide particles is 2 to 200 nm. [2] The carbon electrode-forming composition according to [1], wherein the tin oxide particles have an average particle size of 5 to 80 nm. [3] The carbon electrode-forming composition according to [1] or [2], wherein the content of the tin oxide particles is 12 to 24 mass % relative to the content of the carbon material. [4] The carbon electrode-forming composition according to any one of [1] to [3], which is a composition for forming a carbon electrode provided in a perovskite solar cell. [5] A carbon electrode formed using the carbon electrode-forming composition according to any one of [1] to [4]. [6] A photoelectric conversion element having, in this order, a light-transmitting support, a light-transmitting conductive layer, a porous layer, and the carbon electrode according to [5], wherein the porous layer and the carbon electrode contain a compound having a perovskite crystal structure. [7] The photoelectric conversion element according to [6], further comprising a dense electron transport layer between the light-transmitting conductive layer and the porous layer, and the porous layer comprising, in order from the light-transmitting conductive layer side, a porous electron transport layer and a porous spacer layer. [8] A perovskite solar cell comprising the photoelectric conversion element according to [7]. [9] A method for producing a carbon electrode, comprising a step of forming a carbon electrode using the carbon electrode-forming composition according to any one of [1] to [4].

[10] A method for producing a carbon electrode, comprising the steps of: pulverizing and stirring a mixture containing a carbon material and tin oxide particles to obtain a composition; and forming a carbon electrode using the composition, wherein the content of the tin oxide particles is 3 to 24 mass% relative to the content of the carbon material, and the average particle size of the tin oxide particles is 2 to 200 nm.

[11] The method for producing a carbon electrode according to

[10] , wherein the tin oxide particles have an average particle size of 5 to 80 nm.

[12] The method for producing a carbon electrode according to

[10] or

[11] , wherein the content of the tin oxide particles is 12 to 24 mass % relative to the content of the carbon material.

[13] The method for producing a carbon electrode according to any one of

[10] to

[12] , wherein the step of forming the carbon electrode comprises a step of forming a coating film using the composition, and a step of baking the coating film to form a carbon electrode.

[14] A method for producing a photoelectric conversion element having, in this order, a light-transmitting support, a light-transmitting conductive layer, a porous layer, and a carbon electrode, wherein the porous layer and the carbon electrode contain a compound having a perovskite crystal structure, the method comprising the steps of: forming a carbon electrode on a surface of a laminate having, in this order, a light-transmitting support, a light-transmitting conductive layer, and a porous layer, on the porous layer side, using the carbon electrode-forming composition according to any one of [1] to [4]; and permeating a solution containing a precursor of the compound having a perovskite crystal structure from the surface of the carbon electrode.

[15] A method for producing a photoelectric conversion element having, in this order, a light-transmitting support, a light-transmitting conductive layer, a porous layer, and a carbon electrode, wherein the porous layer and the carbon electrode contain a compound having a perovskite crystal structure, the method comprising the steps of: forming a carbon electrode on a surface of a laminate having, in this order, a light-transmitting support, a light-transmitting conductive layer, and a porous layer, on the porous layer side, by the carbon electrode production method according to any one of

[10] to

[13] ; and permeating a solution containing a precursor of the compound having a perovskite crystal structure from the surface of the carbon electrode.

[16] The method for manufacturing a photoelectric conversion element described in

[14] or

[15] , wherein the laminate further has a dense electron transport layer disposed between the light-transmitting conductive layer and the porous layer, and the porous layer has, in order from the light-transmitting conductive layer side, a porous electron transport layer and a porous spacer layer. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a carbon electrode-forming composition capable of producing a carbon electrode suitable for producing a perovskite solar cell having superior photoelectric conversion efficiency. Also, according to the present invention, it is possible to provide a carbon electrode capable of producing a perovskite solar cell having superior photoelectric conversion efficiency and a method for producing the same, as well as a photoelectric conversion element, a perovskite solar cell, and a method for producing a perovskite solar cell having superior photoelectric conversion efficiency. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of the configuration of a photoelectric conversion element. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are merely examples, and the present invention is not limited to the embodiments described below. In the drawings, the scale of the components may differ from the actual scale for easier viewing and explanation. In this specification, when a range is expressed using "to", the range is inclusive. For example, the range "A to B" includes A and B. In this specification, when two or more types of a certain component are present, the description of the content of that component refers to the total content of the two or more components.

[0013] [Carbon electrode-forming composition] A carbon electrode-forming composition according to one embodiment of the present invention (hereinafter also referred to as "the composition") contains a carbon material and tin oxide particles, the content of the tin oxide particles being 3 to 24 mass % relative to the content of the carbon material, and the average particle size of the tin oxide particles being 2 to 200 nm.

[0014] The present inventors speculate as follows about the reason why the present composition enables the production of a carbon electrode suitable for producing a perovskite solar cell with superior photoelectric conversion efficiency. A known method for manufacturing a perovskite solar cell having a carbon electrode as the anode involves applying a composition containing a carbon material to the surface of a laminate including a light-transmitting conductive layer and an intermediate layer, baking the laminate to form a carbon electrode, and then immersing the carbon electrode in a precursor solution of a compound having a perovskite crystal structure (hereinafter also referred to as "perovskite crystal") to precipitate the perovskite crystal on the carbon electrode and the intermediate layer. In a carbon electrode formed using the composition according to this embodiment, tin oxide particles penetrate into the carbon material, forming appropriate voids. However, the affinity between the carbon material and the tin oxide particles allows the tin oxide particles to be uniformly dispersed among the carbon material. Furthermore, the excellent affinity (wettability) between the tin oxide particles and the perovskite is presumably responsible for the improved penetration of a solution containing a precursor of a compound having a perovskite crystal structure (hereinafter also referred to as "perovskite precursor solution") into the carbon electrode. Furthermore, it is believed that the average particle size and content of tin oxide particles falling within the respective specified ranges made the size and density of the voids inside the carbon electrode suitable for the penetration of the perovskite precursor solution, resulting in uniform dispersion of perovskite crystals in the carbon electrode and the internal porous layer, which is thought to have contributed to the increase in photoelectric conversion efficiency. The composition will be described in more detail below.

[0015] <Carbon materials> The carbon material contained in the composition may be any known carbon material used for forming carbon electrodes, such as graphite, carbon black, graphene, and carbon nanotubes. The shape of the carbon material is not particularly limited, and may be, for example, spherical, flaky, fibrous, needle-like, tubular, columnar, or the like. In particular, the present composition preferably contains a scaly carbon material. In the carbon electrode, tin oxide particles enter between the scaly carbon material, forming voids of a size suitable for the penetration of a perovskite precursor solution and the generation and filling of perovskite crystals, making it easier to produce a photoelectric conversion element in which the perovskite crystals are sufficiently and uniformly dispersed and filled inside the carbon electrode and porous layer. The particle size of the carbon material is appropriately selected according to known carbon materials used in carbon electrodes.

[0016] <Tin oxide particles> The composition contains tin oxide (SnO2) particles having an average particle size of 2 to 200 nm. The average particle size of the tin oxide particles is preferably 5 to 80 nm, and more preferably 5 to 50 nm, from the viewpoints of better photoelectric conversion efficiency of a photoelectric conversion element having a carbon electrode formed using the present composition and easier production of the tin oxide particles. The shape of the tin oxide particles is not particularly limited, and may be, for example, spherical, scaly, fibrous, needle-like, tubular, columnar, or the like.

[0017] In this specification, the average particle size (D) of tin oxide particles refers to the 50% cumulative particle size in the volume-based particle size distribution measured by a laser light dynamic scattering method. The average particle size of tin oxide particles can be measured using an apparatus such as a ZETASIZER-NANO (manufactured by Malvern). When commercially available tin oxide particles are used, the average particle size of the tin oxide particles may be the catalog value listed in the catalog.

[0018] The tin oxide particles used in the present composition are not particularly limited as long as their average particle size is within the above range, and tin oxide particles produced by known methods can be used. Examples of methods for producing tin oxide particles include a liquid phase method, a hydrothermal method, and a sol-gel method. Commercially available tin oxide particles may also be used.

[0019] In this composition, the content of tin oxide particles is 3 to 24% by mass relative to the content of the carbon material. When the content of tin oxide particles is 3% by mass or more relative to the content of the carbon material, the addition of tin oxide particles can achieve a sufficient improvement in photoelectric conversion efficiency. Furthermore, when the content of tin oxide particles is 24% by mass or less relative to the content of the carbon material, an increase in the resistance of the carbon electrode due to the tin oxide particles is suppressed, and improved photoelectric conversion efficiency can be maintained. From the above viewpoints, the content of the tin oxide particles is preferably 12 to 24 mass %, more preferably 15 to 20 mass %, based on the content of the carbon material.

[0020] The composition may contain other ingredients in addition to the carbon material and tin oxide particles. The other components include, for example, a dispersion medium and a binder. Examples of the dispersion medium include organic solvents such as terpineol, ethylene glycol, and polyethylene glycol. As the binder, known binders and thickeners used in carbon electrode-forming compositions can be used.

[0021] <Method of manufacturing carbon electrode-forming composition> The composition can be prepared by mixing ingredients including the carbon material and tin oxide particles. The composition is preferably prepared by pulverizing and stirring a mixture containing a carbon material and tin oxide particles in a predetermined ratio. For example, a powdered carbon material can be used to prepare the composition, and the tin oxide particles can be in the form of a colloidal dispersion or in the form of a powder. The grinding and stirring is preferably carried out using a ball mill, an ultrasonic homogenizer, etc. As the ball mill, for example, a zirconia ball mill can be mentioned. The average particle size of the ball mill is, for example, 1 to 20 mm. The conditions for the grinding and stirring are not particularly limited as long as the composition obtained by grinding and stirring is uniformly mixed, but it is desirable to carry out the grinding and stirring under conditions such that the composition remains in a state where it has not separated into a solid phase and a liquid phase overnight (12 hours) after the grinding and stirring is completed.

[0022] The composition is used to form a carbon electrode. A carbon electrode formed using the present composition can be used as an electrode for a photoelectric conversion element, and is particularly useful as an anode for a perovskite solar cell. That is, the present composition is preferably used to form a carbon electrode included in a perovskite solar cell. A method for producing a carbon electrode using the present composition and specific embodiments of a carbon electrode formed using the present composition will be described later.

[0023] [Photoelectric conversion element] A photoelectric conversion element according to one embodiment of the present invention (hereinafter also referred to as "the present photoelectric conversion element") comprises, in this order, a light-transmitting support, a light-transmitting conductive layer, a porous layer, and the carbon electrode, and the porous layer and the carbon electrode contain a compound having a perovskite-type crystal structure (perovskite crystal).

[0024] FIG. 1 is a schematic diagram showing an example of the configuration of the present photoelectric conversion element. 1 includes, in this order, a light-transmitting support 1, a light-transmitting conductive layer 2, a dense electron transport layer 3, a porous layer 4, and a carbon electrode 5. The porous layer 4 includes a porous electron transport layer 41 and a porous spacer layer 42. The porous layer 4 and the carbon electrode 5 each contain perovskite crystals (not shown).

[0025] The configuration of the present photoelectric conversion element is not limited to the configuration shown in FIG. For example, the photoelectric conversion element 10 shown in FIG. 1 has a dense electron transport layer 3, but the dense electron transport layer may not be provided and the light-transmitting conductive layer and the porous layer may be in direct contact with each other. Furthermore, although the porous layer 4 is composed of a porous electron transport layer 41 and a porous spacer layer 42, the porous layer possessed by the photoelectric conversion element may be only one of the porous electron transport layer and the porous spacer layer. Furthermore, the present photoelectric conversion element may further have a porous hole transport layer between the porous spacer layer 42 and the carbon electrode 5 .

[0026] Each layer of the photoelectric conversion element will be described below. In the present photoelectric conversion element, unless otherwise specified, the thickness of each layer of the photoelectric conversion element is set appropriately.

[0027] <Light-transparent support> The light-transmitting support is a member that transmits visible light and has the function of supporting each layer of the photoelectric conversion element, and for example, known transparent substrates for photoelectric conversion elements such as glass substrates and resin films can be used.

[0028] <Light-transparent conductive layer> The light-transmitting conductive layer is a layer that contains a light-transmitting conductive compound and functions as an electrode. Examples of optically transparent conductive compounds include conductive metal oxides such as fluorine-doped tin oxide (FTO), indium tin oxide (ITO), niobium-doped titanium oxide, aluminum-doped zinc oxide, and gallium-doped zinc oxide, as well as metal nanowires and carbon nanotubes. The light-transmitting electrode layer may be a film made of a conductive metal oxide provided on the surface of a light-transmitting support.

[0029] <Dense electron transport layer> The dense electron transport layer is a layer containing an electron transport material and having a dense structure. By providing the dense electron transport layer, holes can be prevented from flowing into the light-transmitting conductive layer, thereby suppressing leakage current. The electron transport material contained in the dense electron transport layer is not particularly limited, and known photoconductive materials can be used, such as titanium oxide, tin oxide, niobium oxide, yttrium oxide, tungsten oxide, zinc oxide, tantalum oxide, and strontium titanate. The electron transport material may be used alone or in combination of two or more thereof. The electron transport material may be doped with a donor.

[0030] The thickness of the dense electron transport layer is preferably from 1 to 100 nm, more preferably from 10 to 80 nm, from the viewpoints of suppressing leakage current and improving photoelectric conversion efficiency.

[0031] <Porous layer> The porous layer is a layer having a porous structure that is disposed between the light-transmitting conductive layer and the carbon electrode, and examples thereof include a porous electron transport layer containing an electron transport material, a porous spacer layer containing an insulating material, and a porous hole transport layer containing a hole transport material. In the porous layer, the perovskite crystals are dispersed in the internal voids. The porous structure of the porous layer is preferably one in which particles of the material constituting the porous layer are aggregated to form a structure with nanoscale voids as a whole. The shape of the particles may be, for example, spherical, scale-like, fibrous, needle-like, tubular, columnar, or the like.

[0032] The perovskite crystal is composed of, for example, a perovskite compound represented by the composition formula ABX3 (wherein A is a monovalent cation, B is a divalent cation, and X is a halide ion). The monovalent cation represented by A in the perovskite compound (ABX3) is, for example, [R1R2R3NH] + and cations of Group 1 elements such as Rb and Cs. In the above ammonium cation, when R1 and R2 are H and R3 is CH3, A is a methylammonium cation ([CH3NH3] +) In the above formula, the functional groups R1, R2, and R3 each contain at least one element selected from carbon, hydrogen, nitrogen, and oxygen. When the functional groups R1, R2, and R3 each contain a carbon atom, the total number of carbon atoms in the functional groups R1, R2, and R3 is preferably 4 or less. The functional groups R1, R2, and R3 may each contain a Group 1 element such as Rb or Cs. As described above, B in ABX3 is a divalent cation. Examples of B include divalent cations of transition metals, Group 13 elements, Group 14 elements, and Group 15 elements. Preferred specific examples of B include Pb 2+ , Ge 2+ , Sn 2+ B is Pb 2+ and Sn 2+ It is more preferable that the material contains at least one selected from the group consisting of Pb 2+ or Sn 2+ A part of the elements may be substituted with other elements, such as Bi, Sb, In, Ge, and Ni. X in ABX3 is a halide ion, and is preferably at least one selected from Cl, Br and I. Each of the A, M, and X sites may be occupied by multiple types of ions.

[0033] Specific examples of perovskite compounds (ABX3) include CH3NH3PbI3, CH3CH2NH3PbI3, NH2CHNH2PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CsPbI3, CsPbBr3, CH(NH2)2PbI3, CsPbI3, CH3NH3SnI3, CH3NH3Sn x Pb (1-x) I3, CH(NH2)2SnI3, etc.

[0034] The porous structure of the porous layer and the carbon electrode can be confirmed, for example, by observing a cross section of the photoelectric conversion element in the thickness direction using a scanning electron microscope (SEM). Furthermore, whether the porous layer and the carbon electrode contain perovskite crystals can be confirmed, for example, by measuring the composition including elements (e.g., Pb, I, etc.) that make up the perovskite crystals along the thickness direction of the photoelectric conversion element using energy dispersive X-ray spectroscopy (EDX).

[0035] (Porous electron transport layer) The present photoelectric conversion element may have, and preferably has, a porous electron transport layer as the porous layer. By providing a porous electron transport layer, the electron collection ability and photoelectric conversion efficiency of the photoelectric conversion element can be improved. The porous structure of the porous electron transport layer and the perovskite crystals contained in the porous electron transport layer are as described above. The electron transport material contained in the porous electron transport layer can be the same as the electron transport material contained in the dense electron transport layer. The electron transport material contained in the porous electron transport layer and the electron transport material contained in the dense electron transport layer may be the same or different, and are preferably the same. The thickness of the porous electron transport layer is preferably 0.1 to 1 μm, more preferably 0.3 to 0.7 μm, from the viewpoint of electron collection ability and photoelectric conversion efficiency.

[0036] (Porous spacer layer) The photoelectric conversion element may have a porous spacer layer as the porous layer, and preferably has a porous spacer layer. The porous spacer layer is a layer having a porous structure made of an insulating material. The porous spacer layer is preferably disposed between one or both of the dense electron transport layer and the porous electron transport layer and the carbon electrode. By disposing the porous spacer layer between the electron transport layer and the carbon electrode, the electron transport layer and the carbon electrode are physically separated, thereby suppressing the recombination of generated electrons and holes. From the above viewpoint, when the porous layer has a porous electron transport layer and a porous spacer layer, it is preferable that the porous electron transport layer, the porous spacer layer and the carbon electrode are arranged in this order. The porous structure of the porous spacer layer and the perovskite crystal contained in the porous electron transport layer are as described above.

[0037] The insulating material constituting the porous spacer layer may be, for example, an insulating oxide. Among these, zirconium oxide (ZrO), aluminum oxide (AlO), or silicon oxide (SiO) is preferred from the viewpoint of the stability of the porous spacer layer against moisture and heat. The thickness of the porous spacer layer is preferably 0.1 to 5.0 μm, more preferably 1.0 to 3.0 μm, and even more preferably 1.0 to 1.5 μm, from the viewpoints of suppressing the recombination of electrons and holes and photoelectric conversion efficiency.

[0038] (Porous hole transport layer) The photoelectric conversion element may have a porous hole transport layer as the porous layer, and preferably has a porous hole transport layer. By providing a porous hole transport layer, it is possible to prevent electrons from flowing to the carbon electrode and suppress leakage current. From the above viewpoint, when the porous layer has a porous spacer layer and a porous hole transport layer, it is preferable that the porous spacer layer, the porous hole transport layer, and the carbon electrode are arranged in this order. The porous structure of the porous hole transport layer and the perovskite crystals contained in the porous hole transport layer are as described above. The hole transport material contained in the porous hole transport layer is not particularly limited, and known photoelectron conductive materials can be used, such as nickel oxide, niobium oxide, molybdenum oxide, vanadium oxide, CuOx, and CuSCN. The hole transport material may be used alone or in combination of two or more kinds. The hole transport material may be doped with an acceptor. The thickness of the porous hole transport layer is preferably 0.1 to 1 μm, more preferably 0.3 to 0.7 μm, from the viewpoint of hole collection ability and photoelectric conversion efficiency.

[0039] <Carbon electrode> The photoelectric conversion element has a carbon electrode containing a carbon material and tin oxide particles. The content of the tin oxide particles in the carbon electrode is 3 to 24 mass % relative to the content of the carbon material, and the average particle size of the tin oxide particles is 2 to 200 nm. The carbon electrode is formed using, for example, the composition.

[0040] In conventional carbon electrodes, the effect of perovskite crystals on improving battery characteristics was sometimes insufficient. This is thought to be due to the fact that, during the manufacture of a photoelectric conversion element, the perovskite precursor solution did not penetrate sufficiently into the carbon electrode, resulting in the formation of perovskite crystals within the carbon electrode and the formation of voids in the porous layer that were not filled with perovskite crystals. In contrast, in the present photoelectric conversion element, the carbon electrode contains a predetermined amount of tin oxide particles with an average particle size within a predetermined range, allowing the perovskite precursor solution to quickly pass through the carbon electrode and penetrate into the porous layer. This allows the perovskite crystals to be more uniformly dispersed throughout the carbon electrode and the porous layer, resulting in improved photoelectric conversion efficiency.

[0041] Furthermore, measurements of pore size distribution using nitrogen adsorption / desorption confirmed that carbon electrodes containing tin oxide particles have a relatively increased number of pores of approximately 350 to 700 nm compared to carbon electrodes without oxide particles. This also supports the assumption that tin oxide particles promote the penetration of the perovskite precursor solution into the carbon electrode.

[0042] The carbon electrode preferably has a porous structure with nanoscale voids as a whole, formed by the aggregation of carbon material particles, and the tin oxide particles and perovskite crystals contained in the carbon electrode are dispersed within the voids inside the carbon electrode. The types and properties of the carbon material, tin oxide particles, and perovskite crystals contained in the carbon electrode, including their preferred embodiments, have been described above.

[0043] From the viewpoint of efficient charge transport and the amount of perovskite precursor solution that penetrates into the porous layer, the thickness of the carbon electrode is preferably 1 to 30 μm, more preferably 3 to 20 μm, and even more preferably 5 to 15 μm.

[0044] The photoelectric conversion element can be preferably applied to a perovskite solar cell. The photoelectric conversion element can also be used in applications such as organic thin-film solar cells, dye-sensitized solar cells, photodiodes, and optical sensors.

[0045] [Perovskite solar cells] A perovskite solar cell according to one embodiment of the present invention includes the above-described photoelectric conversion element. A more specific example of the perovskite solar cell is one that includes the photoelectric conversion element or a module having a plurality of the photoelectric conversion elements, and a predetermined external circuit.

[0046] [Method of manufacturing photoelectric conversion element] The method for manufacturing a photoelectric conversion element according to one embodiment of the present invention is not particularly limited as long as it is a method for manufacturing a photoelectric conversion element having a light-transmitting support, a light-transmitting conductive layer, a porous layer, and a carbon electrode in this order, in which the porous layer and the carbon electrode contain perovskite crystals, and in which the carbon electrode is the carbon electrode described above. A preferred method for manufacturing a photoelectric conversion element according to this embodiment includes step A of forming a carbon electrode using a carbon electrode-forming composition on the surface of the porous layer side of a laminate (hereinafter also referred to as "laminate A") having a light-transmitting support, a light-transmitting conductive layer, and a porous layer in this order, and step B of infiltrating a solution containing a precursor of a compound having a perovskite crystal structure from the surface of the carbon electrode. Hereinafter, a method for producing a photoelectric conversion element including the above steps A and B will be described.

[0047] The laminate A has at least a light-transmitting support, a light-transmitting conductive layer, and a porous layer. The laminate A may have a dense electron transport layer between the light-transmitting conductive layer and the porous layer. Each layer of the laminate A has been described above. The method for producing the laminate A is not particularly limited as long as it is a method that allows each layer to be formed to the desired thickness. For example, by forming a light-transmitting conductive layer on one surface of a light-transmitting support, forming a dense electron transport layer on the surface of the light-transmitting conductive layer, forming a porous electron transport layer on the surface of the dense electron transport layer, and forming a porous spacer layer on the surface of the porous electron transport layer, each using a known method, the laminate A having a light-transmitting support, a light-transmitting conductive layer, a dense electron transport layer, a porous electron transport layer, and a porous spacer layer in this order is produced.

[0048] The light-transmitting conductive layer can be formed by forming a film of the above-mentioned conductive compound on one surface of the light-transmitting support by a known method such as vacuum deposition or sputtering.

[0049] As a method for forming a porous layer (e.g., a porous electron transport layer and a porous spacer layer, etc.), it is preferable to form the layer by screen printing, because film formation can be performed in the atmosphere, which makes it easy to increase the size of the device, and from the viewpoint of cost. More specifically, it is preferable to carry out a coating step in which a paste composition containing materials constituting each layer is applied by a screen printing method to the surface of a target laminate having at least a light-transmitting support and a light-transmitting conductive layer to form a coating film. The paste composition is a mixture obtained by dispersing particles of the material constituting each layer (for example, particles of an electron transport material such as titanium oxide in the case of a paste composition used to form a porous electron transport layer) in a dispersion medium made of an organic solvent such as terpineol. After forming the coating film, it is preferable to carry out a firing step in which the coating film is fired. The firing step is carried out, for example, using an electric furnace. The firing step temperature range is, for example, 200 to 500°C, and the firing time is, for example, several minutes to about 1 hour.

[0050] When the laminate A has a dense electron transport layer, the dense electron transport layer can be formed, for example, by a spray pyrolysis method. More specifically, a mixed solution containing a precursor compound of the electron transport material and a solvent such as ethanol is prepared, and while a light-transmitting support having a light-transmitting conductive layer is heated, the mixed solution is sprayed onto the surface of the light-transmitting conductive layer, and the solvent is removed, thereby forming a dense film of the electron transport material. The method for forming the dense electron transport layer is not limited to the spray pyrolysis method, and the dense electron transport layer can be formed by any known method.

[0051] The porous electron transport layer can be formed, for example, by applying a paste for a porous electron transport material layer to the surface of the dense electron transport layer by screen printing or the like, and then firing at 500°C.

[0052] <Process A> Step A is a carbon electrode forming step in which a carbon electrode is formed on the surface of the laminate A on the porous layer side using a carbon electrode forming composition. The carbon electrode-forming composition used in step A, including preferred embodiments thereof, has already been described.

[0053] The specific method for forming the carbon electrode is not particularly limited as long as it is a method that can form a carbon electrode containing tin oxide particles to a desired thickness. In step A, it is preferable to form the carbon electrode by a screen printing method, because it is possible to form a film in the atmosphere, which makes it easy to increase the size of the device, and from the viewpoint of cost. Specifically, it is preferable to form a coating film by applying the carbon-forming composition to the surface of the porous layer side of the laminate A by a screen printing method. Furthermore, it is more preferable to bake the coating film after forming it. The baking of the coating film is carried out, for example, using an electric furnace. The baking temperature range is, for example, 200 to 500°C, and the baking time is, for example, several minutes to about 1 hour.

[0054] <Process B> In step B, a solution containing a precursor of a compound having a perovskite crystal structure (perovskite precursor solution) is infiltrated from the surface of the carbon electrode. By performing step B on the carbon electrode-attached laminate A formed in step A, perovskite crystals are filled into the voids in the carbon electrode and porous layer.

[0055] The inventors have found that with conventional carbon electrodes that do not contain metal oxides, the perovskite precursor solution spreads on the surface of the carbon electrode, causing the perovskite crystals to aggregate at the periphery of the carbon electrode surface, resulting in non-uniform formation of the perovskite crystals. In the method for producing a photoelectric conversion element according to the present embodiment, by using a carbon electrode containing a predetermined amount of tin oxide particles having an average particle size within a predetermined range, the perovskite precursor solution in contact with the surface of the carbon electrode is prevented from spreading, and the perovskite precursor solution penetrates in the thickness direction (i.e., toward the porous layer). This allows the perovskite precursor solution to quickly penetrate the porous layer, resulting in more uniform filling of the porous layer with perovskite crystals.

[0056] The composition of the perovskite precursor solution used in step B is appropriately selected depending on the perovskite crystal used in the photoelectric conversion element. For example, when filling (CH3NH3)PbI3 doped with Sn ions as the perovskite crystal, a mixed solution in which PbI2 and SnI2 are mixed so that the molar ratio of Pb to Sn is the desired doping amount can be used as the perovskite precursor solution. Examples of the solvent contained in the perovskite precursor solution include polar solvents such as γ-butyrolactone, N-methyl-2-pyrrolidone, N,N-dimethylformamide, and isopropanol. The perovskite precursor solution can be prepared, for example, by mixing a precursor of the perovskite crystal and the above-mentioned solvent while heating and stirring.

[0057] A preferred method for infiltrating the perovskite precursor solution from the surface of the carbon electrode is to place the carbon electrode-attached laminate A with the carbon electrode facing upward and drip the perovskite precursor solution onto the surface of the carbon electrode. The concentration of the perovskite precursor solution and the amount of perovskite precursor used when immersing the carbon electrode in step B are adjusted appropriately depending on the constituent materials and thicknesses of the carbon electrode and porous layer, and the amount of perovskite crystals to be dispersed. The concentration of the perovskite precursor solution is preferably 0.8 to 1.4 mol / L, more preferably 1.1 to 1.3 mol / L.

[0058] After the perovskite precursor solution is permeated (preferably dropped) onto the surface of the carbon electrode, the laminate with the carbon electrode is preferably dried, which removes the solvent and produces perovskite crystals in the carbon electrode and porous layer. The drying is preferably carried out by heating the laminate with the carbon electrodes. The heating temperature and heating time are not particularly limited, but the heating temperature is preferably 50 to 100° C., and the heating time is preferably 10 to 120 minutes.

[0059] The method for producing the photoelectric conversion element and perovskite solar cell according to this embodiment is not limited to the above-described method, and any conventionally known method can be used as appropriate. [Example]

[0060] The present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples.

[0061] [Example 1] <Preparation of carbon electrode-forming composition> The tin oxide particles used were a tin oxide colloidal dispersion liquid manufactured by Alpha Ether Co., Ltd. The average particle size of the tin oxide particles contained in this dispersion liquid was 15 nm (catalog value). A mixture of 3.6 g of flake graphite, 0.4 g of carbon black, 0.48 g of ethyl cellulose, the tin oxide particles (5 mass % of the total mass of the carbon material, i.e., the combined content of flake graphite and carbon black), and 14.5 g of α-terpineol was prepared. The mixture was then milled and stirred at 700 rpm for 2 hours in a ball mill containing ZrO2 balls (a mixture of three diameters: 2 mm, 5 mm, and 10 mm), to obtain a carbon electrode-forming composition.

[0062] <Production of laminate> As a light-transmitting support, a glass substrate with an FTO (fluorine-doped tin oxide) film was prepared, in which an FTO film was laminated as a light-transmitting conductive layer on one surface of a glass substrate (20 mm x 20 mm, thickness 2.2 mm). Next, a dense titanium oxide layer was formed by spray pyrolysis. Specifically, a solution of titanium oxide and ethanol was sprayed onto the surface of the FTO film while the FTO film-coated glass substrate was heated using a hot plate controlled at 500°C, and then dried to form a dense titanium oxide layer (50 nm thick) as a dense electron transport layer. Furthermore, a titanium oxide paste was applied to the surface of the formed dense titanium oxide layer by screen printing to form a titanium oxide coating film, and the laminate including this coating film was fired in an electric furnace at 500°C for 1 hour to form a porous titanium oxide layer (thickness: approximately 5 μm) that served as a porous electron transport layer. A paste containing zirconium oxide was applied by screen printing to the surface of the porous titanium oxide layer obtained by firing to form a coating film containing porous zirconium. The laminate including this coating film was fired in an electric furnace at 200°C for 20 minutes to form a porous zirconium oxide layer (thickness: 1.0 μm) that served as a porous spacer layer. As a result, a laminate including a glass substrate, an FTO film, a dense titanium oxide layer, a porous titanium oxide layer, and a porous zirconium oxide layer was obtained.

[0063] <Formation of carbon electrodes> The composition 1 was applied by screen printing to the surface of the porous zirconium oxide layer of the prepared laminate to form a coating film containing a carbon material. The laminate including this coating film was fired in an electric furnace at 400°C for 50 minutes to form a carbon electrode (thickness: 10 μm). As a result, a laminate with a carbon electrode was obtained, which included a glass substrate, an FTO film, a dense titanium oxide layer, a porous titanium oxide layer, a porous zirconium oxide layer, and a carbon electrode.

[0064] <Preparation of perovskite precursor solution and fabrication of solar cells for evaluation> In a glove box purged with nitrogen gas, lead iodide (PbI), methylammonium iodide (MAI), 5-aminovaleric acid hydroiodide (5-AVAI), and γ-butyrolactone (GBL) were mixed to obtain a mixture. The mixture was heated on a hot plate at 70°C and stirred at 800 rpm for approximately 18 hours to obtain a perovskite precursor solution. The laminate with the carbon electrode was placed so that the carbon electrode faced vertically upward, and the perovskite precursor solution prepared above was dropped onto the upper surface of the carbon electrode. After protecting the upper surface of the carbon electrode, the laminate with the carbon electrode was placed on a hot plate and annealed at 25°C for 30 minutes, then at 50°C for 80 minutes, and then cooled to room temperature (23°C) to produce a perovskite solar cell for evaluation.

[0065] [Example 2] A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that when preparing the carbon electrode-forming composition, the amount of tin oxide colloidal dispersion added was adjusted so that the content of tin oxide particles was 10 mass % relative to the total mass of the carbon material.

[0066] [Example 3] A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that when preparing the carbon electrode-forming composition, the amount of tin oxide colloidal dispersion added was adjusted so that the content of tin oxide particles was 15 mass % relative to the total mass of the carbon material.

[0067] [Example 4] A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that when preparing the carbon electrode-forming composition, the amount of tin oxide colloidal dispersion added was adjusted so that the content of tin oxide particles was 20 mass % relative to the total mass of the carbon material.

[0068] [Example 5] A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that when preparing the carbon electrode-forming composition, a dispersion containing tin oxide particles with an average particle size of 50 nm was used instead of a tin oxide colloidal dispersion containing tin oxide particles with an average particle size of 15 nm, and the amount of dispersion added was adjusted so that the content of tin oxide particles was 20 mass % relative to the total mass of the carbon material. Tin oxide particles with an average particle size of 50 nm were prepared as follows: 0.7 mol / L of stannous chloride was dissolved in n-butyl alcohol, and 50 mL of 25 wt % aqueous ammonia was added dropwise at a rate of 5 mL / min while stirring at 50°C. The resulting reaction product was filtered. The filtered material was then dried at 60°C under atmospheric pressure and heat-treated at 550°C for 1 hour to obtain tin oxide particles (average particle size: 50 nm). The average particle size of the obtained tin oxide particles was the 50% cumulative particle size in the volume-based particle size distribution measured by the laser light dynamic scattering method, as described above.

[0069] [Example 6] A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that when preparing the carbon electrode-forming composition, a dispersion containing tin oxide particles with an average particle size of 100 nm was used instead of a tin oxide colloidal dispersion containing tin oxide particles with an average particle size of 15 nm, and the amount of dispersion added was adjusted so that the content of tin oxide particles was 20 mass % relative to the total mass of the carbon material. Tin oxide particles with an average particle size of 100 nm were prepared as follows: 1.0 mol / L of stannous chloride was dissolved in ethyl alcohol. While stirring at 40°C, 50 mL of a 12 mol / L aqueous solution of caustic soda was added dropwise at a rate of 50 mL / min, and the resulting reaction product was filtered. The resulting residue was then washed three times with a mixed solution containing ethyl alcohol and water in a volume ratio of 7:3, air-dried at room temperature, and further heat-treated at 550°C for 1 hour to obtain tin oxide particles (average particle size: 100 nm).

[0070] [Comparative Example 1] A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that a carbon electrode-forming composition was prepared without adding tin oxide and the obtained carbon electrode-forming composition was used.

[0071] Comparative Example 2 A carbon electrode-forming composition was prepared by adding tin oxide particles in an amount equivalent to 2.5% by mass relative to the total mass of the carbon material, and a carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that the obtained carbon electrode-forming composition was used.

[0072] Comparative Example 3 A carbon electrode-forming composition was prepared by adding tin oxide particles in an amount equivalent to 25 mass % of the total mass of the carbon material, and a carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that the obtained carbon electrode-forming composition was used.

[0073] Comparative Example 4 A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that when preparing the carbon electrode-forming composition, a dispersion containing tin oxide particles with an average particle size of 250 nm was used instead of a tin oxide colloidal dispersion containing tin oxide particles with an average particle size of 15 nm, and the amount of dispersion added was adjusted so that the content of tin oxide particles was 20 mass % relative to the total mass of the carbon material. Tin oxide particles with an average particle size of 250 nm were prepared by the following method. Stannous chloride (0.25 mol / L) was dissolved in a mixed solution containing ethyl alcohol and water in a volume ratio of 1:1. While stirring the mixture at 70°C, 1920 mL of 25% by mass ammonia water was added dropwise at a rate of 4 mL / min to induce a reaction. The resulting reaction product was filtered. The filtered material was then air-dried at room temperature and further heat-treated at 550°C for 1 hour to obtain tin oxide particles (average particle size: 250 nm).

[0074] Comparative Example 5 A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that a composition for forming a carbon electrode was prepared by adding titanium oxide (TiO2) particles instead of tin oxide particles, and the obtained composition for forming a carbon electrode was used. The titanium oxide particles used were "P-25" manufactured by Degussa, Inc. The average particle size of these titanium oxide particles was 21 nm.

[0075] Comparative Example 6 Nickel oxide (NiO) was used instead of tin oxide particles. x A carbon electrode was formed and a perovskite solar cell was fabricated in the same manner as in Invention Example 1, except that the carbon electrode-forming composition was used. The nickel oxide particles used were "NO-0026-HP" manufactured by IoLiTec, Inc. The average particle size of these nickel oxide particles was 20 nm.

[0076] [Evaluation of battery characteristics] Photocurrent density-voltage (JV) curves were obtained using a solar simulator (AM1.5G, 100 mW cm) equipped with a 500 W xenon lamp (YSS-100A, Yamashita Denso Co., Ltd., Japan). -2 The output of the AM1.5G solar simulator was measured using a DC voltage and current source (B2901A, Agilent, USA) under the following conditions: (1) The output of the AM1.5G solar simulator was calibrated using a reference silicon photodiode (Bunkokeiki Co., Ltd., Japan). The illuminated area was 0.3 cm × 0.3 cm (the active area of ​​the device was 0.8 cm). 2 , mask opening is 0.09cm 2 ) was. The measurement voltage was -0.05 to 1.05 V, and forward and reverse scans were performed with a step of 0.01 V, an integration time of 16.7 ms, and a scan delay time of 10 ms (the measurement scan rate was 250 mV s-1). Before measuring the cell characteristics, each solar cell was irradiated with AM1.5G light for 1 minute. Measurements were performed three times at 1-minute intervals, with each solar cell being continuously irradiated with light between measurements for photoactivation. AM1.5G light aging was performed under open-circuit conditions. The spectral response of each solar cell was evaluated by IPCE measurement (Pexel Technologies, Japan). Here, the IPCE spectrum is a plot of the ratio of the number of electrons (current) output to the number of irradiated photons (light intensity) at each wavelength in the photoelectric conversion element for the wavelength range of 300-800 nm.

[0077] For each solar cell, photocurrent density-voltage measurements were performed using the method described above, and the short-circuit current density (J SC ), open circuit voltage (V OC ) and fill factor (FF) were determined, and the photoelectric conversion efficiency (PCE) was calculated as the product of these.

[0078] Table 1 shows, for each example, the type, content (mass%) and average particle size (nm) of oxide particles contained in the carbon electrode-forming composition used to form the carbon electrode, as well as the evaluation results of the produced perovskite solar cells. In the table, the "Content (mass%)" column for "Oxide particles" indicates the content (unit: mass%) of oxide particles relative to the total mass of the carbon material contained in the carbon electrode-forming composition.

[0079] [Table 1]

[0080] As shown in Examples 1 to 6 of Table 1 above, it was confirmed that the photoelectric conversion element of the present invention, which has a carbon electrode formed using a carbon electrode-forming composition containing a carbon material and tin oxide particles, wherein the content of the tin oxide particles is 3 to 24 mass % relative to the content of the carbon material, and the average particle size of the tin oxide particles is 2 to 200 nm, has excellent photoelectric conversion efficiency (PCE). In particular, it was confirmed that Examples 3 to 5, in which the content of tin oxide particles was 12 to 24 mass % relative to the carbon material and the average particle size of the tin oxide particles was 5 to 80 nm, had better photoelectric conversion efficiency (PCE).

[0081] In contrast, it was confirmed that the photoelectric conversion efficiency was insufficient in Comparative Example 1, in which the carbon electrode did not contain oxide particles; Comparative Example 2, in which the tin oxide particle content was 2.5 mass% relative to the carbon material content; Comparative Example 3, in which the tin oxide particle content was 25 mass% relative to the carbon material content; Comparative Example 4, in which the tin oxide particles had an average particle size of 250 nm; Comparative Example 5, in which the carbon electrode did not contain tin oxide particles but contained titanium oxide particles; and Comparative Example 6, in which the carbon electrode did not contain tin oxide particles but contained nickel oxide particles.

[0082] Comparing Examples 1 to 4 and Comparative Examples 1 to 3, which contain different amounts of tin oxide particles in the carbon electrode, the photoelectric conversion efficiency was "△" when the tin oxide particles were mixed so that the content was 3 mass% or more relative to the carbon material content, but the photoelectric conversion efficiency improved to "◯" when the tin oxide particles were mixed so that the content was 15 to 20 mass% relative to the carbon material content. This is presumably because the addition of tin oxide particles formed pores in the carbon electrode, improving the permeability of the perovskite precursor solution from the carbon electrode to the porous layer and promoting the formation of perovskite crystals in the porous spacer layer. Furthermore, a comparison between Comparative Example 3 and Invention Example 1 shows that when tin oxide particles were mixed so that the content of tin oxide particles was 24 mass % or less relative to the content of the carbon material, the photoelectric conversion efficiency improved to "Fair." This is presumably because the content of tin oxide particles was reduced to an appropriate range, whereas an excessively high content of tin oxide particles increases the resistance of the carbon electrode.

[0083] Comparing Examples 3, 5, and 6 with Comparative Example 4, which have different average particle sizes of tin oxide particles contained in the carbon electrode, the photoelectric conversion efficiency was rated as "Good" when the average particle size of the tin oxide particles was 2 nm or more. This is presumably because tin oxide particles of an appropriate particle size penetrate into the carbon material contained in the carbon electrode, forming pores that promote the penetration of the perovskite precursor solution. Furthermore, when the average particle size of the tin oxide particles was 200 nm or less, the photoelectric conversion efficiency was rated as "△," and when the average particle size of the tin oxide particles was 80 nm or less, the photoelectric conversion efficiency was rated as "○." This is presumably because when the average particle size of the tin oxide particles is too large, the tin oxide particles have difficulty penetrating between the carbon materials, making it difficult to form pores, thereby reducing the permeability of the perovskite precursor solution from the carbon electrode to the porous spacer layer. In addition, it is presumed that the tin oxide particles that have penetrated between the carbon materials prevent contact between the carbon materials, increasing the resistance of the carbon electrode.

[0084] Comparing Inventive Example 3 and Comparative Examples 5 and 6, which use different types of oxide particles, the photoelectric conversion efficiency was improved to "good" only when tin oxide particles were used. [Explanation of symbols]

[0085] 10 Photoelectric conversion element 1 Light-transparent support 2 Light-transparent conductive layer 3 Dense electron transport layer 4 Porous layer 41 Porous electron transport layer 42 Porous spacer layer 5 Carbon electrodes

Claims

1. A carbon material and tin oxide particles are included, the content of the tin oxide particles is 3 to 24 mass% relative to the content of the carbon material, The carbon electrode-forming composition, wherein the tin oxide particles have an average particle size of 2 to 200 nm.

2. 2. The carbon electrode-forming composition according to claim 1, wherein the tin oxide particles have an average particle size of 5 to 80 nm.

3. 2. The carbon electrode-forming composition according to claim 1, wherein the content of the tin oxide particles is 12 to 24 mass % relative to the content of the carbon material.

4. The carbon electrode-forming composition according to claim 1 , which is a composition for forming a carbon electrode provided in a perovskite solar cell.

5. A carbon electrode formed using the carbon electrode-forming composition according to any one of claims 1 to 4.

6. A light-transmitting substrate, a light-transmitting conductive layer, a porous layer, and the carbon electrode according to claim 5, in this order; The photoelectric conversion element, wherein the porous layer and the carbon electrode contain a compound having a perovskite crystal structure.

7. a dense electron transport layer between the light-transmitting conductive layer and the porous layer; The photoelectric conversion element according to claim 6 , wherein the porous layer has, in order from the light-transmitting conductive layer side, a porous electron transport layer and a porous spacer layer.

8. A perovskite solar cell comprising the photoelectric conversion element according to claim 7.

9. A method for producing a carbon electrode, comprising the step of forming a carbon electrode using the carbon electrode-forming composition according to any one of claims 1 to 4.

10. A step of pulverizing and stirring a mixture containing a carbon material and tin oxide particles to obtain a composition; forming a carbon electrode using the composition; the content of the tin oxide particles is 3 to 24 mass% relative to the content of the carbon material, The method for producing a carbon electrode, wherein the tin oxide particles have an average particle size of 2 to 200 nm.

11. The method for producing a carbon electrode according to claim 10, wherein the tin oxide particles have an average particle size of 5 to 80 nm.

12. The method for producing a carbon electrode according to claim 10, wherein the content of the tin oxide particles is 12 to 24 mass % with respect to the content of the carbon material.

13. the step of forming the carbon electrode includes forming a coating film using the composition; The method for producing a carbon electrode according to claim 10, further comprising the step of firing the coating film to form a carbon electrode.

14. a light-transmitting support, a light-transmitting conductive layer, a porous layer, and a carbon electrode, in this order; A method for manufacturing a photoelectric conversion element, wherein the porous layer and the carbon electrode contain a compound having a perovskite crystal structure, forming a carbon electrode on a surface of a laminate having a light-transmitting support, a light-transmitting conductive layer, and a porous layer in this order, using the carbon electrode-forming composition according to any one of claims 1 to 4, on the porous layer side of the laminate; and permeating the surface of the carbon electrode with a solution containing a precursor of a compound having a perovskite crystal structure.

15. a light-transmitting support, a light-transmitting conductive layer, a porous layer, and a carbon electrode, in this order; A method for manufacturing a photoelectric conversion element, wherein the porous layer and the carbon electrode contain a compound having a perovskite crystal structure, forming a carbon electrode on a surface of a laminate having a light-transmitting support, a light-transmitting conductive layer, and a porous layer in this order, on the porous layer side, by the carbon electrode manufacturing method according to any one of claims 10 to 13; and permeating the surface of the carbon electrode with a solution containing a precursor of a compound having a perovskite crystal structure.

16. the laminate further comprises a dense electron transport layer disposed between the light-transmitting conductive layer and the porous layer; The method for producing a photoelectric conversion element according to claim 14 , wherein the porous layer has, in order from the light-transmitting conductive layer side, a porous electron transport layer and a porous spacer layer.

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