Oxide semiconductor paste for solar cells, porous semiconductor electrode substrate, method for manufacturing porous semiconductor electrode substrate, solar cell, and solar cell module

Abstract

To provide an oxide semiconductor paste for a solar cell capable of suppressing the reduction of surface smoothness and the generation of pinholes on a porous semiconductor layer and allowing the solar cell to exert high photoelectric conversion efficiency.SOLUTION: The oxide semiconductor paste for a solar cell includes oxide semiconductor particles, water, a water-soluble solvent, and a leveling agent. The content ratio of the oxide semiconductor particles is 44 mass% or more and 57 mass% or less. The content ratio of water is 36 mass% or more and 48 mass% or less. The content ratio of the leveling agent is 0.01 mass% or more and 0.25 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, a method for producing a porous semiconductor electrode substrate, a solar cell, and a solar cell module. [Background technology]

[0002] In recent years, solar cells have attracted attention as photoelectric conversion elements that convert light energy into electricity. Solar cells consist of a layer that contributes to the movement of electrons and holes sandwiched between two electrodes. For example, a dye-sensitized solar cell, which is one type of solar cell, typically has a structure in which a photoelectrode including a semiconductor layer with a sensitizing dye adsorbed thereon, an electrolyte layer, and a counter electrode including a catalyst layer are arranged in this order. The semiconductor layer of the photoelectrode is typically formed on one side of a conductive substrate.

[0003] The semiconductor layer of the photoelectrode is formed, for example, by applying an oxide semiconductor paste for forming the semiconductor layer onto a conductive substrate to form a coating film, and then heating and drying the coating film. For example, Patent Document 1 describes a method of forming a coating film by applying a titania sol solution or the like as an oxide semiconductor paste onto a substrate, followed by heating and pressurizing the coating film to obtain a titanium oxide thin film as a semiconductor layer.

[0004] Patent Document 2 also describes a method for obtaining a semiconductor porous film by applying a viscous dispersion (paste) of semiconductor nanoparticles dispersed in a dispersion medium consisting of water and a hydrophilic organic solvent containing a predetermined alcohol as the main component onto an electrode substrate, followed by drying and heat treatment.

[0005] Patent Document 3 also describes a method for obtaining a semiconductor porous film by applying a viscous dispersion (paste) having a predetermined viscosity and solid content concentration, which is prepared by dispersing predetermined titanium dioxide nanoparticles in water, onto an electrode substrate, followed by drying and heat treatment.

[0006] Patent Document 4 also describes a method for obtaining a porous semiconductor film by applying a titanium dioxide paste containing titanium dioxide nanoparticles and water at a predetermined pH onto an electrode substrate, followed by drying and heat treatment. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-282160 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-76855 [Patent Document 3] International Publication No. 2016 / 006227 [Patent Document 4] International Publication No. 2020 / 158676 Summary of the Invention [Problem to be solved by the invention]

[0008] Here, solar cells are required to have high photoelectric conversion efficiency. However, conventional oxide semiconductor pastes for solar cells have poor fluidity and leveling properties during application, which causes problems such as a decrease in surface smoothness (i.e., an increase in surface roughness) of the porous semiconductor film (hereinafter also referred to as "porous semiconductor layer") obtained using the oxide semiconductor paste, or the occurrence of pinholes in the porous semiconductor layer. Furthermore, solar cells using such porous semiconductor layers have the problem of being unable to obtain high photoelectric conversion efficiency.

[0009] To address these problems, the present inventors came up with the idea of ​​adding a leveling agent to the oxide semiconductor paste for solar cells. However, it was found that simply adding a leveling agent to the oxide semiconductor paste for solar cells may not necessarily prevent the reduction in surface smoothness or the occurrence of pinholes in the resulting porous semiconductor layer, and may also reduce the photoelectric conversion efficiency of the solar cell.

[0010] Therefore, an object of the present invention is to provide an oxide semiconductor paste for solar cells that can suppress a decrease in surface smoothness and the occurrence of pinholes in a porous semiconductor layer and enable the solar cell to exhibit high photoelectric conversion efficiency.Another object of the present invention is to provide a porous semiconductor electrode substrate that can enable the solar cell to exhibit high photoelectric conversion efficiency, a method for producing the same, a solar cell including the porous semiconductor electrode substrate, and a solar cell module. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that by adding a leveling agent to an oxide semiconductor paste containing oxide semiconductor particles, water, and a water-soluble solvent, and by controlling the contents of the oxide semiconductor particles, water, and leveling agent in the oxide semiconductor paste to be within predetermined ranges, it is possible to improve the photoelectric conversion efficiency of a solar cell while suppressing a decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer, and have completed the present invention.

[0012] The present invention aims to advantageously solve the above-mentioned problems, and provides an oxide semiconductor paste for solar cells comprising oxide semiconductor particles, water, a water-soluble solvent, and a leveling agent, wherein the oxide semiconductor particle content is 44% by mass to 57% by mass, the water content is 36% by mass to 48% by mass, and the leveling agent content is 0.01% by mass to 0.25% by mass. Thus, by using an oxide semiconductor paste for solar cells that contains a leveling agent and in which the oxide semiconductor particle content, water content, and leveling agent content are each within a predetermined range, it is possible to improve the photoelectric conversion efficiency of the solar cell while suppressing a decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer.

[0013] In the oxide semiconductor paste for solar cells of the present invention, the oxide semiconductor particles preferably comprise at least one type of oxide semiconductor particles selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles. In this way, if the oxide semiconductor particles comprise at least one type of oxide semiconductor particles selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles, the photoelectric conversion efficiency of the solar cell can be further improved.

[0014] In the oxide semiconductor paste for solar cells of the present invention, the leveling agent preferably contains at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants. In this way, if the leveling agent contains at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants, it is possible to further improve the photoelectric conversion efficiency of the solar cell while further suppressing the decrease in surface smoothness and the occurrence of pinholes in the obtained porous semiconductor layer.

[0015] The present invention also aims to advantageously solve the above-mentioned problems, and provides a porous semiconductor electrode substrate comprising a conductive substrate and a porous semiconductor layer formed on the conductive substrate using any of the above-mentioned oxide semiconductor pastes for solar cells. In this way, a porous semiconductor electrode substrate comprising a porous semiconductor layer formed using any of the above-mentioned oxide semiconductor pastes for solar cells can enable a solar cell to exhibit high photoelectric conversion efficiency.

[0016] In addition, in the porous semiconductor electrode substrate of the present invention, it is preferable that the content of the leveling agent in the porous semiconductor layer is 0.01 parts by mass or more and 0.3 parts by mass or less relative to 100 parts by mass of the oxide semiconductor particles. Thus, if the content of the leveling agent in the porous semiconductor layer is within the above-mentioned predetermined range, it is possible to further improve the photoelectric conversion efficiency of the solar cell while further suppressing the decrease in surface smoothness and the occurrence of pinholes.

[0017] In the porous semiconductor electrode substrate of the present invention, the porous semiconductor layer preferably has an average surface roughness of 0.9 μm or less. If the average surface roughness of the porous semiconductor layer is 0.9 μm or less, the photoelectric conversion efficiency of a solar cell including the porous semiconductor electrode substrate can be further improved. In the present invention, the average surface roughness of the porous semiconductor layer can be measured by the method described in the Examples.

[0018] The present invention also aims to advantageously solve the above-mentioned problems, and is characterized in that the method for producing a porous semiconductor electrode substrate of the present invention comprises the steps of applying any of the oxide semiconductor pastes for solar cells described above onto a conductive substrate to obtain a coating film, and heating and drying the coating film at a temperature of 50° C. to 250° C. In this way, if the heating and drying temperature for the coating film is within the above range, thermal deterioration of the conductive substrate can be suppressed.

[0019] The present invention also aims to advantageously solve the above-mentioned problems, and provides a solar cell comprising any one of the porous semiconductor electrode substrates described above. As such, the solar cell of the present invention has high photoelectric conversion efficiency due to the inclusion of the porous semiconductor electrode substrate of the present invention.

[0020] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the solar cell module of the present invention is characterized in that the solar cells described above are connected in series and / or parallel. As such, the solar cell module of the present invention has high photoelectric conversion efficiency because it includes the solar cells of the present invention. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an oxide semiconductor paste for solar cells that can suppress the reduction in surface smoothness and the occurrence of pinholes in a porous semiconductor layer and can enable solar cells to exhibit high photoelectric conversion efficiency. Furthermore, according to the present invention, it is possible to provide a porous semiconductor electrode substrate that can enable a solar cell to exhibit high photoelectric conversion efficiency, a method for manufacturing the same, a solar cell including the porous semiconductor electrode substrate, and a solar cell module. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail. The oxide semiconductor paste for solar cells of the present invention can be used, for example, when producing the porous semiconductor electrode substrate of the present invention. The porous semiconductor electrode substrate of the present invention comprises a porous semiconductor layer formed using the oxide semiconductor paste for solar cells of the present invention. The porous semiconductor electrode substrate of the present invention can be produced, for example, by the method for producing a porous semiconductor electrode substrate of the present invention. The porous semiconductor electrode substrate of the present invention can be used, for example, when producing the solar cell of the present invention. The solar cell of the present invention comprises the porous semiconductor electrode substrate of the present invention. The solar cell module of the present invention comprises the solar cell of the present invention.

[0023] (Oxide semiconductor paste for solar cells) The oxide semiconductor paste for solar cells of the present invention is an oxide semiconductor paste for solar cells containing oxide semiconductor particles, water, a water-soluble solvent, and a leveling agent, and is characterized in that the content ratio of the oxide semiconductor particles, the content ratio of the water, and the content ratio of the leveling agent are each within a predetermined range. This makes it possible to suppress a decrease in surface smoothness and the occurrence of pinholes in a porous semiconductor layer obtained using this oxide semiconductor paste for solar cells, while enabling the solar cell to exhibit high photoelectric conversion efficiency. In the present invention, the term "paste" refers to a dispersion system in which solid particles are dispersed in a liquid such as water as a dispersion medium, and which has fluidity and viscosity. In the oxide semiconductor paste for solar cells of the present invention, oxide semiconductor particles as solid particles are dispersed as solids in water or the like as a dispersion medium. Furthermore, the oxide semiconductor paste for solar cells of the present invention may optionally contain other components in addition to the oxide semiconductor particles, water, water-soluble solvent, and leveling agent described above.

[0024] <Oxide semiconductor particles> The oxide semiconductor particles contained in the oxide semiconductor paste for solar cells of the present invention function as a semiconductor in which electrons are injected into the conduction band of the porous semiconductor layer of the porous semiconductor electrode substrate provided in the solar cell. In the present invention, the content of oxide semiconductor particles in the oxide semiconductor paste for solar cells must be 44% by mass or more and 57% by mass or less, when the weight of the oxide semiconductor paste for solar cells is taken as 100% by mass. If the content of oxide semiconductor particles is less than 44% by mass, the volume effective for power generation in the resulting porous semiconductor layer cannot be sufficiently secured, resulting in a decrease in photoelectric conversion efficiency. If the content of oxide semiconductor particles exceeds 57% by mass, the viscosity of the oxide semiconductor paste for solar cells increases excessively, resulting in a decrease in coatability. Therefore, even when a leveling agent is used, it is not possible to suppress a decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer, resulting in a decrease in photoelectric conversion efficiency. From the viewpoint of further improving the photoelectric conversion efficiency of the solar cell while further suppressing the decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer, the content of oxide semiconductor particles is preferably 45% by mass or more, more preferably 50% by mass or more, and is preferably 55% by mass or less, more preferably 53% by mass or less.

[0025] The oxide semiconductor particles contained in the oxide semiconductor paste for solar cells of the present invention are not particularly limited, but include metal oxide particles. Metal elements of the metal oxides include titanium, tin, zinc, iron, tungsten, zirconium, strontium, indium, cerium, vanadium, niobium, tantalum, cadmium, lead, antimony, and bismuth. These metal oxides can be used alone or in combination of two or more. Among these, from the viewpoint of enabling solar cells to exhibit a higher photoelectric conversion rate, titanium dioxide (TiO2), zinc oxide (ZnO), niobium oxide (Nb2O3), and tin oxide (SnO2) are more preferable as materials for oxide semiconductor particles, and titanium dioxide (TiO2) is particularly preferable.

[0026] Therefore, the oxide semiconductor particles preferably contain at least one selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles, more preferably contain at least one selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles as a main component, further preferably consist of at least one selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles, and particularly preferably consist of titanium dioxide particles.

[0027] Here, "main component" refers to a content ratio of 50% by mass or more. Therefore, when the oxide semiconductor particles contain at least one selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles as a main component, the content ratio is 50% by mass or more when the total mass of the oxide semiconductor particles is taken as 100% by mass. In such cases, the content ratio of the at least one selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles is preferably 80% by mass or more, and more preferably 90% by mass or more, when the total mass of the oxide semiconductor particles is taken as 100% by mass.

[0028] <<Other properties, etc.>> The average particle size of the primary particles of the oxide semiconductor blended in the oxide semiconductor paste for solar cells of the present invention is preferably 1 nm or more and 500 nm or less, more preferably 5 nm or more and 400 nm or less. The particle size of the particles in the paste may be one type alone or a combination of two or more types. In this specification, unless otherwise specified, the term "average particle size" refers to the particle size (D50) at which the cumulative mass calculated from the smallest diameter side in the mass-based particle size distribution measured by ultrasonic attenuation spectroscopy is 50%.

[0029] The particle shape of the oxide semiconductor particles is not particularly limited, and may be, for example, amorphous, spherical, flat, polyhedral, with a core-shell structure, hollow, rod-like (fiber-like, nanotube-like) or the like.

[0030] Furthermore, the state of the oxide semiconductor particles used in the production of the oxide semiconductor paste for solar cells of the present invention is not particularly limited. For example, oxide semiconductor particles in a powder state may be used, or oxide semiconductor particles in a sol (dispersion liquid) state in which the oxide semiconductor particles are dispersed in a dispersion medium such as water may be used.

[0031] The average particle size, particle shape, state, and the like of the oxide semiconductor particles may vary depending on the method for producing the oxide semiconductor particles.

[0032] <<Method of manufacturing oxide semiconductor particles>> The oxide semiconductor particles contained in the oxide semiconductor paste for solar cells of the present invention are not particularly limited and can be produced using known methods. Examples of methods for producing oxide semiconductor particles include the sol-gel method described in "The Science of Sol-Gel Method" (Agne Shofusha, 1998), a method in which metal chlorides are hydrolyzed in mineral salts at high temperatures to produce oxide fine particles, and a spray pyrolysis method in which metal compounds are thermally decomposed at high temperatures in a gas phase to produce ultrafine particles. Ultrafine and nanoparticles of semiconductors such as titanium dioxide produced by these methods are explained in "Fine Particle Engineering Series, Vol. II, Applied Technology," edited by Hiroaki Yanagida, Fuji Techno System (2002).

[0033] <Water> The water contained in the oxide semiconductor paste for solar cells of the present invention functions as a dispersion medium for dispersing components such as oxide semiconductor particles. The water content of the oxide semiconductor paste for solar cells of the present invention must be 36% by mass or more and 48% by mass or less, when the weight of the oxide semiconductor paste for solar cells is taken as 100% by mass. If the water content is less than 36% by mass, the viscosity of the oxide semiconductor paste for solar cells increases excessively, resulting in poor coatability. This makes it impossible to suppress a decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer, resulting in a decrease in photoelectric conversion efficiency. On the other hand, if the water content exceeds 48% by mass, the oxide semiconductor particle content is too low, making it impossible to ensure a sufficient volume effective for power generation in the resulting porous semiconductor layer. This reduces photoelectric conversion efficiency and also reduces productivity due to the long drying time. From the viewpoint of further improving the photoelectric conversion efficiency of the solar cell while further suppressing the decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer, the water content is preferably 37% by mass or more, more preferably 40% by mass or more, and is preferably 47% by mass or less, more preferably 46% by mass or less.

[0034] When an aqueous sol in which oxide semiconductor particles are dispersed in water is used in the production of an oxide semiconductor paste for solar cells, the water contained in the aqueous sol may be used as is as the water contained in the oxide semiconductor paste for solar cells.

[0035] <Water-soluble solvent> The water-soluble solvent contained in the oxide semiconductor paste for solar cells of the present invention is contained for the purpose of imparting fluidity to the paste and improving its coatability.

[0036] The content of the water-soluble solvent in the oxide semiconductor paste for solar cells of the present invention is not particularly limited, but from the viewpoint of improving the coatability of the paste, when the weight of the oxide semiconductor paste for solar cells is taken as 100 mass%, it is preferably 5.5 mass% or more, more preferably 6.5 mass% or more, and is preferably 8.5 mass% or less, more preferably 7.5 mass% or less.

[0037] The water-soluble solvent is not particularly limited, and alcohol-based solvents, ether-based solvents, etc. can be used. These water-soluble solvents can be used alone or in combination of two or more. Among them, it is preferable to use a mixed solvent of an alcohol-based solvent and an ether-based solvent as the water-soluble solvent.

[0038] Examples of alcohol-based solvents include keto alcohols such as diacetone alcohol, and linear or branched alcohols having 2 to 10 carbon atoms such as ethanol, 1-propanol, 2-propanol, 1-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-2-butanol, 2-ethyl-1-butanol, 2,3-dimethyl-2-butanol, 2-methyl-2-pentanol, 4-methyl-2-pentanol, tert-pentyl alcohol, cyclohexanol, 4-tert-butylhexanol, and α-terpineol. Of these, it is preferable to use diacetone alcohol as the alcohol-based solvent.

[0039] Examples of the ether solvent include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol mono-tert-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol mono-tert-butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethyl ether, etc. Among these, it is preferable to use ethylene glycol mono-tert-butyl ether as the ether solvent.

[0040] <Leveling agent> The leveling agent contained in the oxide semiconductor paste for solar cells of the present invention is contained for the purpose of improving the leveling properties of the coating film when the paste is applied. Here, the leveling agent used in the present invention has a molecular weight of 10,000 or less.

[0041] The content of the leveling agent in the oxide semiconductor paste for solar cells of the present invention must be 0.01% by mass or more and 0.25% by mass or less, when the weight of the oxide semiconductor paste for solar cells is taken as 100% by mass. If the content of the leveling agent is less than 0.01% by mass, the increase in surface roughness and the occurrence of pinholes in the resulting porous semiconductor layer cannot be suppressed. Furthermore, if the content of the leveling agent exceeds 0.25% by mass, the conductivity of the resulting porous semiconductor layer deteriorates, and the photoelectric conversion efficiency of the solar cell decreases. From the viewpoint of further suppressing the decrease in surface smoothness and the occurrence of pinholes in the porous semiconductor layer while achieving even higher photoelectric conversion efficiency in the solar cell, the content of the leveling agent is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and preferably 0.22% by mass or less, more preferably 0.20% by mass or less.

[0042] The leveling agent is not particularly limited, and various surfactants can be used, such as fluorine-based surfactants, silicone-based surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants, etc. These surfactants may be used alone or in combination of two or more. From the viewpoint of further suppressing the decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer while enabling the solar cell to exhibit even higher photoelectric conversion efficiency, the leveling agent preferably contains at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants, more preferably contains at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants as the main component, and particularly preferably consists of a fluorine-based surfactant and / or a silicone-based surfactant.

[0043] Here, "main component" refers to a content ratio of 50% by mass or more. Therefore, when the leveling agent contains at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants as the main component, the content ratio is 50% by mass or more when the weight of the leveling agent is taken as 100% by mass. In such a case, the content ratio of the at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants is preferably 80% by mass or more, and more preferably 90% by mass or more, when the weight of the leveling agent is taken as 100% by mass.

[0044] <<Fluorosurfactants>> The fluorosurfactant is not particularly limited, and examples thereof include compounds having a fluoroalkyl group and / or a fluoroalkylene group at least at any one of the terminal, main chain, and side chain. As the fluorosurfactant, a compound having a perfluoroalkyl group in the main chain is preferred. Specific examples of fluorosurfactants include anionic fluorosurfactants such as perfluoroalkyl group-containing carboxylates, perfluoroalkyl group-containing sulfonates, perfluoroalkyl group-containing sulfates, and perfluoroalkyl group-containing phosphates; cationic fluorosurfactants such as perfluoroalkyl group-containing amine salts and perfluoroalkyl group-containing quaternary ammonium salts; nonionic fluorosurfactants such as perfluoroalkyl group-containing oligomers, perfluoroalkyl group-containing polymers, and perfluoroalkyl group-containing sulfonamide polyethylene glycol adducts; and amphoteric fluorosurfactants such as perfluoroalkyl group-containing carboxyl betaines and perfluoroalkyl group-containing amino carboxylates. The perfluoroalkyl group preferably has 6 to 20 carbon atoms, and some of the fluorine atoms in the perfluoroalkyl group may be substituted with hydrogen atoms. These fluorosurfactants can be used alone or in combination of two or more. Among them, anionic fluorosurfactants are preferred from the viewpoint of further suppressing the decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer, while enabling the solar cell to exhibit higher photoelectric conversion efficiency. The fluorine-based surfactants exemplified above are not included in the anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants described below.

[0045] <<Silicone surfactants>> The silicone surfactant is not particularly limited, and examples thereof include surfactants having a siloxane bond in the molecule. Specific examples of silicone surfactants include polysiloxane compounds such as unmodified polyorganosiloxane, polyether-modified polyorganosiloxane, and polyester-modified polyorganosiloxane. These silicone surfactants can be used alone or in combination of two or more. Among them, polyether-modified polyorganosiloxane is preferred from the viewpoint of further suppressing the decrease in surface smoothness and the occurrence of pinholes in the resulting porous semiconductor layer while achieving higher photoelectric conversion efficiency in the solar cell.

[0046] <<Anionic surfactants>> The anionic surfactant is not particularly limited, and carboxylate, sulfate, sulfonate, and phosphate anionic surfactants can be used.

[0047] <<Cationic surfactants>> The cationic surfactant is not particularly limited, and cationic surfactants of quaternary ammonium salt type, amine salt type, and pyridinium salt type can be used.

[0048] <<Nonionic surfactants>> The nonionic surfactant is not particularly limited, and ether-type, ester-type, ester ether-type, alkanolamide-type, and alcohol-type nonionic surfactants can be used.

[0049] <<Amphoteric surfactants>> The amphoteric surfactant is not particularly limited, and examples thereof include alkyl betaine type, fatty acid amidopropyl betaine type, alkyl imidazole type, amino acid type, and amine oxide type amphoteric surfactants.

[0050] <Other ingredients> Other components optionally contained in the oxide semiconductor paste for solar cells of the present invention include an acid for adjusting the pH of the oxide semiconductor paste for solar cells, and binder materials such as latex and resins that are usually added for the purpose of increasing the viscosity of the paste or for the purpose of improving adhesion to the conductive substrate during film formation. Specific examples of the acid are not particularly limited as long as the desired effects of the present invention can be obtained, and include, for example, hydrochloric acid. The content of the acid in the oxide semiconductor paste for solar cells may be adjusted appropriately so that the pH of the oxide semiconductor paste for solar cells falls within a desired range, preferably 6 or less, more preferably 3 or more and 5 or less.

[0051] As the binder material, a cellulose compound, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyethylene glycol, polystyrene, acrylic resin, polylactic acid, or the like can be used. In addition, cellulose compounds such as ethyl cellulose, nitrocellulose, carboxy cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose are preferably used because they can form a porous semiconductor layer with high porosity and allow the thickness of the porous semiconductor layer to be controlled in a preferable manner. However, it is preferable that the oxide semiconductor paste for solar cells of the present invention is substantially free of binder material. If it is substantially free of binder material, even when a porous semiconductor layer is formed using the oxide semiconductor paste for solar cells at a low temperature (for example, 200°C or lower), substantially no binder material remains in the formed porous semiconductor layer, and therefore the conductivity of the porous semiconductor layer can be ensured to be sufficiently high. In the present invention, "substantially free of binder material" means that the content of binder material is 1% by mass or less in terms of solid content. The content of the binder material is preferably 0.5% by mass or less, and more preferably 0% by mass, calculated as solid content.

[0052] <Method of manufacturing oxide semiconductor paste for solar cells> The oxide semiconductor paste for solar cells of the present invention can be prepared by dispersing the above-mentioned components in a dispersion medium containing water using a known dispersion device such as a three-roll mill, a paint conditioner, a homogenizer, an ultrasonic dispersion device, a planetary mixer, a high-speed disperser, a rotation-revolution type mixing conditioner, etc. The order of addition of each component is not particularly limited.

[0053] (Porous semiconductor electrode substrate) The porous semiconductor electrode substrate of the present invention comprises 1) a conductive substrate, and 2) a porous semiconductor layer formed on the conductive substrate and made using the oxide semiconductor paste for solar cells of the present invention. In the porous semiconductor electrode substrate of the present invention, the porous semiconductor layer is formed using the oxide semiconductor paste for solar cells of the present invention. Because the porous semiconductor layer is formed using the oxide semiconductor paste for solar cells of the present invention, a decrease in surface smoothness and the occurrence of pinholes in the porous semiconductor layer are suppressed, and the solar cell can exhibit high photoelectric conversion efficiency.

[0054] <Conductive substrate> Examples of the conductive substrate that can be used include substrates that are conductive in themselves, such as metal substrates made of metal materials such as titanium and stainless steel, and substrates in which a conductive layer is formed on a base material (support) made of materials such as inorganic materials (e.g., glass) and organic materials (e.g., plastic).The material of the conductive substrate can be appropriately selected depending on the application of the porous semiconductor electrode substrate. For example, when optical transparency is required for the porous semiconductor electrode substrate, a transparent material can be used.

[0055] From the viewpoint of producing a solar cell with excellent flexibility, it is preferable to use a conductive substrate having a support made of flexible plastic as the conductive substrate, and it is particularly preferable to use a conductive substrate having a transparent plastic film as the support (transparent conductive plastic film).

[0056] A transparent conductive plastic film is composed of a transparent plastic film as a support and a conductive layer formed on the transparent plastic film. The transparent plastic film as a support is preferably made of a low-cost material that is colorless, has excellent transparency, heat resistance, chemical resistance, and gas barrier properties. From these perspectives, preferred materials for the transparent plastic film as a support include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PAr), polysulfone (PSF), polyester sulfone (PES), polyetherimide (PEI), and transparent polyimide (PI). Among these, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are preferred from the standpoints of chemical resistance, cost, and the like.

[0057] The conductive layer of the transparent conductive plastic film can be made of conductive materials such as metals such as platinum, gold, silver, copper, aluminum, and indium; carbon-based materials such as carbon nanotubes; and conductive metal oxides such as indium-tin composite oxide and tin oxide. Among these, conductive metal oxides are preferred from the viewpoint of optical transparency, and indium-tin composite oxide (ITO) and zinc oxide are particularly preferred. The transmittance of indium-tin composite oxide (ITO) preferably peaks at 500 to 600 nm from the viewpoints of photoelectric conversion efficiency and visibility of displays, etc.

[0058] The surface resistance value of the conductive layer is not particularly limited, but is usually 150 Ω / □ or less, preferably 50 Ω / □ or less, more preferably 20 Ω / □ or less, and even more preferably 10 Ω / □ or less.

[0059] An auxiliary lead wire for current collection can be disposed on this conductive layer by patterning or the like. Such an auxiliary lead wire is usually formed from a low-resistance metal material such as copper, silver, aluminum, platinum, gold, titanium, or nickel. In a conductive layer patterned with such an auxiliary lead wire, the surface resistance is measured as the resistance of the surface including the auxiliary lead wire, and this value is preferably 30 Ω / □ or less, more preferably 20 Ω / □ or less.

[0060] <Porous semiconductor layer> The porous semiconductor layer formed on the conductive substrate is formed using the oxide semiconductor paste for solar cells of the present invention described above. Specifically, the porous semiconductor layer is obtained by heating and drying the oxide semiconductor paste for solar cells of the present invention applied to the conductive substrate to remove liquid components such as water and water-soluble solvents. Therefore, the porous semiconductor layer contains at least the oxide semiconductor particles and leveling agent described above, and optionally contains other components. As described above, the porous semiconductor layer is prevented from reducing surface smoothness and generating pinholes.

[0061] Here, from the viewpoint of further improving the photoelectric conversion efficiency of the solar cell, the average surface roughness of the porous semiconductor layer is preferably 0.9 μm or less, more preferably 0.7 μm or less, and even more preferably 0.6 μm or less.

[0062] The thickness of the porous semiconductor layer is usually 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 30 μm or less, and more preferably 5 μm or more and 10 μm or less. If the thickness of the porous semiconductor layer is equal to or more than the above-mentioned lower limit, the amount of power generated by the solar cell can be ensured to be sufficiently high. On the other hand, if the thickness of the porous semiconductor layer is equal to or less than the above-mentioned upper limit, the diffusibility of electrons in the porous semiconductor layer can be ensured to be sufficiently high. In the present invention, the thickness of the porous semiconductor layer can be measured by the method described in the Examples.

[0063] Furthermore, from the viewpoint of further suppressing the decrease in surface smoothness and the occurrence of pinholes while enabling the solar cell to exhibit even higher photoelectric conversion efficiency, the content of the leveling agent in the porous semiconductor layer is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and is preferably 0.3 parts by mass or less, more preferably 0.2 parts by mass or less, relative to 100 parts by mass of the oxide semiconductor particles.

[0064] The porous semiconductor electrode substrate of the present invention can be used as a dye-sensitized electrode (photoelectrode) for a dye-sensitized solar cell, for example, by adsorbing a dye onto the porous semiconductor layer. The porous semiconductor electrode substrate of the present invention can also be used as a photoelectrode by adsorbing a light-absorbing material such as a perovskite compound onto the porous semiconductor layer instead of a dye. Examples of such dyes or light-absorbing materials include those described in International Publication No. 2016 / 006227. Furthermore, the porous semiconductor electrode substrate of the present invention can also be used as a perovskite solar cell by sequentially providing a component such as a perovskite compound layer on the porous semiconductor layer. The component such as the perovskite compound layer is not particularly limited, and examples of such components include those described in JP-A-2016-143708.

[0065] (Method of manufacturing a porous semiconductor electrode substrate) The method for producing a porous semiconductor electrode substrate of the present invention includes 1) a step of applying the oxide semiconductor paste for solar cells of the present invention onto a conductive substrate to obtain a coating film (coating step), and 2) a step of heating and drying the obtained coating film at a temperature of 50° C. or higher and 250° C. or lower (heat drying step). Each step will be described below.

[0066] <Coating process> In the coating step, the oxide semiconductor paste for solar cells of the present invention is coated onto a conductive substrate to obtain a coating film. Here, the method for coating the oxide semiconductor paste for solar cells onto a conductive substrate can be, for example, screen printing, gravure printing, metal mask printing, gravure offset printing, or inkjet printing. Among these, screen printing is preferred. As the conductive substrate, those described above in the section "Porous semiconductor electrode substrate" can be used. When a substrate (for example, a transparent conductive plastic film such as an ITO / PET film or an ITO / PEN film) having a conductive layer formed on a base material (support) made of a material such as plastic is used as the conductive substrate, the oxide semiconductor paste for solar cells is applied to the surface of the conductive substrate on the conductive layer side.

[0067] <Heat drying process> In the heat drying step, the coating film of the oxide semiconductor paste for solar cells formed on the conductive substrate is heated at a temperature of 50° C. or higher and 250° C. or lower to dry the coating film. When a conductive substrate having a support made of plastic such as the above-mentioned transparent conductive plastic film is used, from the viewpoint of efficiently drying while suppressing deterioration of the plastic support due to heat, the heating temperature in the heat drying is preferably 140° C. or higher, more preferably 150° C. or higher, and preferably 170° C. or lower, more preferably 160° C. or lower. The heating temperature may be multi-staged using multiple temperature ranges. The coating film can be dried by heating using, for example, an oven, a hot plate, an infrared (IR) drying furnace, or the like. The heat drying time is not particularly limited, and the heat drying may be carried out for a time sufficient to obtain a dried porous semiconductor film (layer) depending on the heat drying temperature. The heat drying time is usually 1 minute to 120 minutes, preferably 5 minutes to 60 minutes. The atmosphere during drying is not particularly limited, and may be an inert atmosphere such as air, nitrogen, or argon, and may be selected as appropriate.

[0068] Through the above steps, the porous semiconductor electrode substrate of the present invention is obtained.

[0069] (solar cells) The solar cell of the present invention includes the porous semiconductor electrode substrate of the present invention described above. Therefore, the solar cell of the present invention exhibits high photoelectric conversion efficiency. The solar cell of the present invention is not limited to, but is, for example, a dye-sensitized solar cell or a perovskite solar cell, and is preferably a dye-sensitized solar cell. The solar cell of the present invention will be described below by taking a dye-sensitized solar cell as an example.

[0070] A dye-sensitized solar cell, which is an example of the solar cell of the present invention, comprises, for example, a dye-sensitized electrode (photoelectrode) formed by adsorbing a dye to the porous semiconductor layer of the porous semiconductor electrode substrate of the present invention described above; a counter electrode; and an electrolyte layer interposed between the dye-sensitized electrode and the counter electrode.

[0071] The dye to be adsorbed onto the porous semiconductor layer of the porous semiconductor electrode substrate and the adsorption method are not particularly limited, and for example, those described in WO 2016 / 006227 can be used.

[0072] The counter electrode can be a substrate formed by forming a conductive layer and a catalyst layer on a substrate (support) made of, for example, glass, metal foil (e.g., titanium foil), or organic material (e.g., plastic). Examples of conductive materials for the conductive layer of the counter electrode include metals such as platinum, gold, silver, copper, titanium, aluminum, magnesium, and indium; carbon-based materials such as carbon black, acetylene black, graphene, and carbon nanotubes; and conductive metal oxides such as indium-tin composite oxide (ITO) and fluorine-doped tin oxide (FTO). Among these, platinum, titanium, ITO, and carbon-based materials are preferred from the viewpoint of corrosion resistance. Examples of catalyst layers include precious metal particles such as gold, rhodium, ruthenium, and platinum; coatings of these elements, including single elements and particles with a core-shell structure; conductive polymers such as polythiophene and polypyrrole; activated carbon; carbon fiber; carbon black; acetylene black; graphene; and carbon nanotubes. These may be used alone or in combination. The conductivity of the conductive layer is usually 30 Ω / □ or less, preferably 20 Ω / □ or less. The method for forming the catalyst layer is not particularly limited, and may be appropriately selected from known methods such as coating, sputtering, and spraying. The thickness of the catalyst layer may be designed to be 0.001 μm to 100 μm, for example, so that the desired catalyst, mechanical strength, and other performance properties can be obtained.

[0073] Furthermore, the electrolyte layer to be interposed between the dye-sensitized electrode and the counter electrode is not particularly limited, and examples thereof include electrolytes such as aqueous electrolytes, organic solvent electrolytes, and ionic liquid electrolytes (molten salt electrolytes) described in International Publication No. 2016 / 006227; P-type semiconductors; and the like. In addition, known materials may be used for the sealing material, collecting electrode, extraction electrode, protective layer, barrier layer such as a barrier film, antireflection layer, etc. For example, those described in WO 2007 / 046499, WO 2016 / 006227, etc. may be used.

[0074] <Solar cell manufacturing method> A dye-sensitized solar cell, which is an example of the solar cell of the present invention, is not particularly limited as long as it uses the porous semiconductor electrode substrate of the present invention described above, and can be produced by a known method. For example, as described in International Publication No. 2007 / 046499, the dye-sensitized solar cell can be produced using the dye-sensitized electrode (photoelectrode) described above. More specifically, the photoelectrode and the counter electrode are stacked via a spacer in a state where the surface of the photoelectrode on the porous semiconductor layer side on which the dye is adsorbed faces the surface of the counter electrode on the conductive layer side, and an electrolyte solution as an electrolyte layer is further injected between the photoelectrode and the counter electrode, thereby producing a dye-sensitized solar cell.

[0075] (solar cell module) The solar cell module of the present invention is formed by connecting the solar cells of the present invention described above in series and / or parallel, and the module structure may be any of known structures such as Z-type, W-type, parallel type, current collector wiring type, and monolithic type. The solar cell module of the present invention includes the solar cell of the present invention, and therefore exhibits high photoelectric conversion efficiency.

[0076] <Solar cell module manufacturing method> The solar cell module of the present invention can be obtained, for example, by arranging the solar cells of the present invention on a flat or curved surface, providing non-conductive partition walls between each cell, and electrically connecting the electrodes of each cell (e.g., photoelectrodes and counter electrodes of a dye-sensitized solar cell) using a conductive member. The number of solar cells used to manufacture the solar cell module is not particularly limited, and can be determined appropriately depending on the target voltage. [Example]

[0077] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. Various measurements and evaluations in the examples and comparative examples were carried out according to the following methods.

[0078] <Measurement of thickness and average surface roughness of porous semiconductor layer> The thickness and average surface roughness (Ra) of the porous semiconductor layer thus prepared were measured using a stylus profilometer (Dektak XT manufactured by Bruker, probe tip diameter: 12.5 μm). The average surface roughness (Ra) is a value calculated according to the standard in accordance with JIS B0601.

[0079] <Observation of pinholes in porous semiconductor layers> In each example and comparative example, the prepared porous semiconductor layer was observed for pinholes using a laser microscope (Keyence VHX-2000). Specifically, the prepared porous semiconductor electrode substrate (a porous semiconductor layer formed on a conductive substrate) was set on a transparent glass stage for measurement, and transmitted light was irradiated from the bottom side using a 50x objective lens to confirm the presence or absence of pinholes within the observation field.

[0080] <Measurement of light transmittance of porous semiconductor layer at a wavelength of 530 nm> In each example and comparative example, the conductive substrate used to prepare the porous semiconductor electrode substrate was set in an ultraviolet-visible spectrophotometer (Shimadzu Corporation, "UV1800"), and a baseline measurement was performed in the range of 200 to 1100 nm. Next, the prepared porous semiconductor electrode substrate (comprising a porous semiconductor layer formed on a conductive substrate) was set in the ultraviolet-visible spectrophotometer, and spectrophotometric measurement was performed to obtain the light transmittance value of the porous semiconductor layer at a wavelength of 530 nm. The lower the light transmittance, the more efficiently light can be utilized.

[0081] <Solar cell performance> The light source used was a simulated solar irradiation device (PEC-L11, manufactured by Peccel Technologies) equipped with a 150 W xenon lamp light source and an AM1.5G filter. The light intensity was 1 sun (AM1.5G, 100 mW / cm). 2 The dye-sensitized solar cell was adjusted to Class A of JIS C8912. The fabricated dye-sensitized solar cell was connected to a source meter (2400 type source meter, manufactured by Keithley) and the following current-voltage characteristics were measured. Under 1 sun of light irradiation, the output current was measured while changing the bias voltage from 0 V to 0.8 V in 0.01 V increments. The output current was measured by integrating the value from 0.05 seconds to 0.15 seconds after changing the voltage at each voltage step. Measurements were also performed while changing the bias voltage in the reverse direction from 0.8 V to 0 V, and the average value of the measurements in the forward and reverse directions was taken as the photocurrent. From the measurement results of the current-voltage characteristics described above, the short-circuit current (Isc [mA]) and current density (Jsc [mA cm]) of the fabricated dye-sensitized solar cell were -2 ]), open circuit voltage (Voc[V]), fill factor (FF), conversion efficiency (η[%]), maximum power (Pmax[mW]), maximum output operating current (Imax[mA]), maximum output operating voltage (Vmax[V]), and series resistance (Rs[Ω]) were measured to evaluate the battery performance.

[0082] Example 1 <Preparation of oxide semiconductor paste for solar cells> First, 45.0 parts by mass of titanium dioxide particle powder and 47.7 parts by mass of water were mixed. Then, 5.2 parts by mass of ethylene glycol mono-tert-butyl ether (EGTBE) and 2.0 parts by mass of diacetone alcohol (DAA) were added as water-soluble solvents and mixed. Finally, 0.1 parts by mass of a fluorine-based surfactant (AGC Sei Chemical's "Surflon S-211") was added as a leveling agent to obtain a mixture. This mixture was dispersed for 1 hour using a two-axis mixer consisting of a planetary mixer and a disperser to prepare a titanium dioxide paste as an oxide semiconductor paste for solar cells.

[0083] <Preparation of porous semiconductor electrode substrate> A transparent conductive plastic film (thickness: 125 μm, surface resistance value on the conductive layer side: 16 Ω / □) was prepared, which had a conductive layer made of ITO formed on a PEN substrate. A transparent conductive plastic film was cut into 2 cm x 10 cm pieces to obtain a conductive substrate. A pattern of six 7 mm diameter circles arranged at 1.5 cm intervals was printed on the conductive layer side of the substrate using the above titanium dioxide paste and a 200-mesh screen by screen printing. The resulting substrate was then dried by heating (155°C x 60 minutes) to form a porous semiconductor layer with a thickness of 6.0 μm. This resulted in a porous semiconductor electrode substrate in which a porous semiconductor layer was formed on the conductive layer side of the conductive substrate. The porous semiconductor layer formed on the porous semiconductor electrode substrate was used to measure or evaluate the thickness, average surface roughness (Ra), presence or absence of pinholes, and light transmittance. The results are shown in Table 1.

[0084] <Fabrication of dye-sensitized solar cells> The tetrabutylammonium salt of bisisocyanate bisbipyridyl Ru complex (N719) as a Ru bipyridyl complex dye was dissolved in a mixed solvent of acetonitrile:tert-butanol (1:1 (volume ratio)) at a concentration of 3 × 10 -4 The porous semiconductor electrode substrate was immersed in a sensitizing dye solution obtained by dissolving the dye to a concentration of 1 mole / L, and left to stand for 60 minutes at 40°C under stirring. This allowed the dye to be adsorbed onto the porous semiconductor layer of the porous semiconductor electrode substrate, producing a dye-sensitized electrode (photoelectrode). <Preparation of electrolyte> An electrolyte solution was obtained by dissolving 0.05 mol / L of iodine, 0.1 mol / L of lithium iodide, 0.5 mol / L of t-butylpyridine, and 0.6 mol / L of 1,2-dimethyl-3-propylimidazolium iodide in acetonitrile as a solvent.

[0085] A transparent conductive plastic film (thickness: 200 μm, surface resistance on the ITO film side: 15 Ω / □) consisting of an ITO film formed on a PEN substrate was coated with a 100 nm thick platinum film on the ITO film side using a sputtering method to create a conductive film (surface resistance: 0.8 Ω / □) with a conductive layer consisting of two layers of ITO film and platinum film as a counter electrode.

[0086] The photoelectrode was cut to a 2 cm x 1.5 cm size with the 7 mm diameter circular porous semiconductor layer at the center. The counter electrode was also cut to a 2 cm x 1.5 cm size, and an electrolyte injection port (1 mm diameter) was drilled. The dye-adsorbed porous semiconductor layer side of the photoelectrode and the conductive layer side of the counter electrode were then aligned with each other, with a 25 μm thick ionomer resin film (Himilan 1652, manufactured by Mitsui DuPont Polychemicals) interposed between them as a spacer. The photoelectrode and counter electrode were then superimposed and cured at 110°C for 5 minutes. The electrolyte was then injected through the injection port by capillary effect. Finally, a cover glass coated with UV-curable resin was placed over the injection port, and the injection port was sealed by spot irradiation with UV light. By sealing the holes in this manner, a dye-sensitized solar cell was fabricated. The cell performance of the fabricated dye-sensitized solar cell was evaluated. The results are shown in Table 1.

[0087] Example 2 An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 1, except that in preparing the oxide semiconductor paste for solar cells of Example 1, the amount of titanium dioxide particle powder added was 50.0 parts by mass and the amount of water added was 42.7 parts by mass, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0088] Example 3 An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 1, except that in preparing the oxide semiconductor paste for solar cells of Example 1, the amount of titanium dioxide particle powder added was 55.0 parts by mass and the amount of water added was 37.7 parts by mass, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0089] Example 4 In preparing the oxide semiconductor paste for solar cells of Example 1, except that the amount of water added was 47.6 parts by mass and the amount of leveling agent added was 0.2 parts by mass, an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0090] Example 5 In preparing the oxide semiconductor paste for solar cells of Example 2, except that the amount of water added was 42.6 parts by mass and the amount of leveling agent added was 0.2 parts by mass, an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 2, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0091] Example 6 In preparing the oxide semiconductor paste for solar cells of Example 3, except that the amount of water added was 37.6 parts by mass and the amount of leveling agent added was 0.2 parts by mass, an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 3, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0092] Example 7 In preparing the oxide semiconductor paste for solar cells of Example 2, 0.1 parts by mass of a silicone surfactant (Disparlon "LS-480" manufactured by Kusumoto Chemicals Co., Ltd., main component 100%) was added as the leveling agent instead of 0.1 parts by mass of the fluorine-based surfactant. An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 2, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0093] Example 8 In preparing the oxide semiconductor paste for solar cells of Example 1, except that the amount of water added was 47.78 parts by mass and the amount of leveling agent added was 0.02 parts by mass, an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0094] Example 9 In preparing the oxide semiconductor paste for solar cells of Example 1, except that the amount of water added was 47.55 parts by mass and the amount of leveling agent added was 0.25 parts by mass, an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0095] Example 10 In preparing the oxide semiconductor paste for solar cells of Example 1, except that 52.8 parts by mass of zinc oxide powder was added instead of 45.0 parts by mass of titanium dioxide particle powder, and the amount of water added was 41.0 parts by mass, the amount of ethylene glycol mono-tert-butyl ether (EGTBE) added was 4.7 parts by mass, and the amount of diacetone alcohol (DAA) added was 1.4 parts by mass, an oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0096] (Comparative Example 1) An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 2, except that in the preparation of the oxide semiconductor paste for solar cells of Example 2, the amount of water added was 42.8 parts by mass and no leveling agent was added, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0097] (Comparative Example 2) An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 2, except that the amount of water added was 42.3 parts by mass and the amount of leveling agent added was 0.52 parts by mass in preparing the oxide semiconductor paste for solar cells of Example 2, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0098] (Comparative Example 3) An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 4, except that in preparing the oxide semiconductor paste for solar cells of Example 4, the amount of titanium dioxide particle powder added was 58.0 parts by mass and the amount of water added was 34.6 parts by mass, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0099] Comparative Example 4 An oxide semiconductor paste for solar cells, a porous semiconductor electrode substrate, and a dye-sensitized solar cell were prepared or fabricated in the same manner as in Example 4, except that in preparing the oxide semiconductor paste for solar cells of Example 4, the amount of titanium dioxide particle powder added was 43.0 parts by mass and the amount of water added was 49.6 parts by mass, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0100] [Table 1]

[0101] The results in Table 1 show that in Examples 1 to 10, which used an oxide semiconductor paste for solar cells containing oxide semiconductor particles, water, a water-soluble solvent, and a leveling agent, in which the content ratio of the oxide semiconductor particles, the content ratio of the water, and the content ratio of the leveling agent were each controlled within a predetermined range, it was possible to suppress an increase in the surface roughness of the resulting porous semiconductor layer and the occurrence of pinholes, while enabling the dye-sensitized solar cell to exhibit high photoelectric conversion efficiency. In contrast, in Comparative Example 1, which used an oxide semiconductor paste for solar cells that did not contain a leveling agent, an increase in surface roughness of the porous semiconductor layer and the occurrence of pinholes were observed, and the photoelectric conversion efficiency of the dye-sensitized solar cell was found to be deteriorated. Furthermore, in Comparative Example 2, which used an oxide semiconductor paste for solar cells with a leveling agent content of more than 0.25 mass%, no increase in surface roughness of the porous semiconductor layer and the occurrence of pinholes were observed, but the photoelectric conversion efficiency of the dye-sensitized solar cell was found to be deteriorated. Furthermore, in Comparative Examples 3 and 4, which used oxide semiconductor pastes for solar cells with oxide semiconductor particle content and water content outside the specified ranges, pinholes were found to be generated in the porous semiconductor layer, and the photoelectric conversion efficiency of the dye-sensitized solar cell was found to be deteriorated. [Industrial Applicability]

[0102] According to the present invention, it is possible to provide an oxide semiconductor paste for solar cells that can suppress the reduction in surface smoothness and the occurrence of pinholes in a porous semiconductor layer and can enable solar cells to exhibit high photoelectric conversion efficiency. Furthermore, according to the present invention, it is possible to provide a porous semiconductor electrode substrate that can enable a solar cell to exhibit high photoelectric conversion efficiency, a method for manufacturing the same, a solar cell including the porous semiconductor electrode substrate, and a solar cell module.

Claims

1. An oxide semiconductor paste for a solar cell, comprising oxide semiconductor particles, water, a water-soluble solvent, and a leveling agent, a content ratio of the oxide semiconductor particles is 44% by mass or more and 57% by mass or less, a content ratio of the water is 36% by mass or more and 48% by mass or less, and a content ratio of the leveling agent is 0.01% by mass or more and 0.25% by mass or less, An oxide semiconductor paste for solar cells used to form a porous semiconductor layer of a porous semiconductor electrode substrate.

2. 2. The oxide semiconductor paste for solar cells according to claim 1, wherein the oxide semiconductor particles comprise at least one type of oxide semiconductor particles selected from the group consisting of titanium dioxide particles, zinc oxide particles, niobium oxide particles, and tin oxide particles.

3. 3. The oxide semiconductor paste for solar cells according to claim 1, wherein the leveling agent comprises at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants.

4. a conductive substrate; A porous semiconductor electrode substrate comprising: a porous semiconductor layer formed on the conductive substrate and formed using the oxide semiconductor paste for solar cells according to any one of claims 1 to 3.

5. 5. The porous semiconductor electrode substrate according to claim 4, wherein the content of the leveling agent in the porous semiconductor layer is 0.01 parts by mass or more and 0.3 parts by mass or less with respect to 100 parts by mass of the oxide semiconductor particles.

6. 6. The porous semiconductor electrode substrate according to claim 4, wherein the average surface roughness of the porous semiconductor layer is 0.9 μm or less.

7. A step of applying the oxide semiconductor paste according to any one of claims 1 to 3 onto a conductive substrate to obtain a coating film; and drying the coating film by heating at a temperature of 50°C or higher and 250°C or lower.

8. A solar cell comprising the porous semiconductor electrode substrate according to any one of claims 4 to 6.

9. A solar cell module comprising the solar cells according to claim 8 connected in series and / or in parallel.

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