Flexible solar cell

Abstract

To provide a flexible solar cell excellent in flame retardancy in a planar direction while suppressing deterioration of power generation performance.SOLUTION: A flexible solar cell comprising a power section, a sealing material that seals the entire power section, and a flame-retardant layer that is in contact with the sealing material, wherein the power section comprises an electrode, a photoelectric conversion layer, and a counter electrode, the photoelectric conversion layer contains an organic-inorganic perovskite compound, the flame-retardant layer contains a flame-retardant material, and the shortest distance from the power section to the flame-retardant layer is 100 μm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to flexible solar cells. [Background technology]

[0002] Conventionally, solar cells have been actively developed using laminates in which an N-type semiconductor layer and a P-type semiconductor layer are disposed between opposing electrodes, with inorganic semiconductors such as silicon being mainly used as the N-type and P-type semiconductors. However, such inorganic solar cells have problems such as high manufacturing costs and difficulty in increasing their size, limiting the range of their use. Therefore, in recent years, perovskite solar cells have been attracting attention, which use organic-inorganic perovskite compounds with a perovskite structure using lead, tin, or the like as the central metal in the photoelectric conversion layer (for example, Patent Document 1, Non-Patent Document 1). Perovskite solar cells are expected to have high photoelectric conversion efficiency, and can be manufactured by a printing method, which allows for significant reductions in manufacturing costs.

[0003] On the other hand, in recent years, flexible solar cells using heat-resistant polymer materials such as polyimide and polyester, or metal foil as a substrate have been attracting attention. Flexible solar cells have advantages such as ease of transportation and installation due to their thinness and light weight, and are impact resistant. For example, they are manufactured by laminating multiple layers, such as a photoelectric conversion layer that generates current when irradiated with light, in a thin film form on a flexible substrate. Furthermore, if necessary, an encapsulating sheet is laminated on the top and bottom surfaces of the flexible solar cell for encapsulation. For example, Patent Document 2 describes a substrate for a semiconductor device including a sheet-like aluminum base material, and an organic thin-film solar cell including this substrate for a semiconductor device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-72327 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-253317 [Non-patent literature]

[0005] [Non-Patent Document 1] MMLee,et al,Science,2012,338,643 Summary of the Invention [Problem to be solved by the invention]

[0006] Such flexible solar cells often use organic materials to provide transparency and flexibility. Because organic materials are more flammable than inorganic materials, flexible solar cells require more fire prevention measures than conventional solar cells. However, while conventional solar cells have been proposed that are flame-retardant in the thickness direction, flame-retardant properties in the planar direction (the surface direction perpendicular to the thickness direction) have not been fully studied. In particular, in recent years, advances in manufacturing technology have led to larger areas per flexible solar cell unit. Therefore, if flame-retardant properties in the planar direction are poor, not only will a large number of solar cells burn, but there is also an increased risk of the fire spreading to other cells. Therefore, flame-retardant properties in the planar direction are becoming even more important.

[0007] To address this issue, a method has been proposed for improving the flame retardancy of flexible solar cells by adding a flame-retardant material to the encapsulant that protects the power generation section of the flexible solar cell. Hydrocarbon-based resins are preferably used as encapsulants due to their low moisture permeability, but they are highly flammable. Therefore, adding a flame-retardant material to a highly flammable encapsulant can significantly improve flame retardancy, and can also improve flame retardancy in the planar direction. However, some flexible solar cells that have had a flame-retardant material added to the encapsulant have experienced a deterioration in power generation performance.

[0008] An object of the present invention is to provide a flexible solar cell that has excellent flame retardancy in the planar direction while suppressing a decrease in power generation performance. [Means for solving the problem]

[0009] The present invention includes the following Disclosures 1 to 3. The present invention will be described in detail below. [Disclosure 1] A flexible solar cell having a power generation section, a sealing material that seals the entire power generation section, and a flame-retardant layer that is in contact with the sealing material, the power generation unit has an electrode, a photoelectric conversion layer, and a counter electrode, the photoelectric conversion layer contains an organic-inorganic perovskite compound, the flame-retardant layer contains a flame-retardant material, A flexible solar cell, characterized in that the shortest distance from the power generation section to the flame-retardant layer is 100 μm or more. [Disclosure 2] The flexible solar cell according to Disclosure 1, wherein the flame-retardant layer is disposed on the upper surface side of the power generating section. [Disclosure 3] The flexible solar cell according to Disclosure 1, wherein the flame-retardant material contains chlorine atoms.

[0010] The flexible solar cell of the present invention has a power generation section, and the power generation section has an electrode, a photoelectric conversion layer, and a counter electrode. The power generating section is a section that converts sunlight into electricity, and is composed of an electrode, a counter electrode, a photoelectric conversion layer, an electron transport layer, a hole transport layer, etc., and has at least an electrode, a photoelectric conversion layer, and a counter electrode. In this specification, the term "layer" refers not only to a layer with a clear boundary but also to a layer with a concentration gradient in which the contained elements gradually change. Elemental analysis of a layer can be performed, for example, by performing FE-TEM / EDS line analysis of a cross section of a solar cell to confirm the element distribution of a specific element. Furthermore, in this specification, the term "layer" refers not only to a flat thin-film layer, but also to a layer that can form a complex, intricate structure together with other layers. Furthermore, in this specification, "upper" refers to the direction toward the light incident surface in the thickness direction of the flexible solar cell, and "lower" refers to the opposite direction of "upper," i.e., the direction toward the installation surface.

[0011] The materials for the electrodes and counter electrodes are not particularly limited, and examples thereof include FTO (fluorine-doped tin oxide), ITO (tin-doped indium oxide), AZO (aluminum zinc oxide), IZO (indium zinc oxide), GZO (gallium zinc oxide), sodium, sodium-potassium alloy, lithium, magnesium, aluminum, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, Al / Al2O3 mixture, and Al / LiF mixture. Other examples include gold, silver, titanium, molybdenum, tantalum, tungsten, carbon, nickel, and chromium. These materials may be used alone or in combination.

[0012] The thickness of the electrode and the counter electrode is not particularly limited, but a preferred lower limit is 10 nm and a preferred upper limit is 1000 nm. If the thickness is 10 nm or more, the resistance can be reduced while the electrode functions. If the thickness is 1000 nm or less, the light transmittance can be further improved. A more preferred lower limit of the thickness of the electrode and the counter electrode is 50 nm and a more preferred upper limit is 500 nm.

[0013] The photoelectric conversion layer contains an organic-inorganic perovskite compound. The organic-inorganic perovskite compound is represented by the general formula AMX (wherein A is an organic base compound and / or an alkali metal, M is a lead or tin atom, and X is a halogen atom), and a solar cell containing the organic-inorganic perovskite compound is also called an organic-inorganic hybrid solar cell. By using the organic-inorganic perovskite compound in the photoelectric conversion layer, the photoelectric conversion efficiency of the flexible solar cell can be improved.

[0014] The above A is an organic base compound and / or an alkali metal. Specific examples of the organic base compound include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, ethylbutylamine, formamidine, acetamidine, guanidine, imidazole, azole, pyrrole, aziridine, azirine, azetidine, azeto, azole, imidazoline, carbazole, and ions thereof (e.g., methylammonium (CHNH)), phenethylammonium, and the like. Of these, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, formamidine, acetamidine, ions thereof, and phenethylammonium are preferred, and methylamine, ethylamine, propylamine, formamidine, and ions thereof are more preferred. Examples of the alkali metal include lithium, sodium, potassium, rubidium, and cesium.

[0015] The metal atom M is a lead or tin atom. These metal atoms may be used alone or in combination of two or more.

[0016] The X is a halogen atom, and examples of the halogen atom include chlorine, bromine, iodine, sulfur, and selenium. These halogen atoms may be used alone or in combination of two or more. By including a halogen in the structure, the organic-inorganic perovskite compound becomes soluble in organic solvents, enabling application to inexpensive printing methods and the like. In particular, X is preferably iodine, since this narrows the energy band gap of the organic-inorganic perovskite compound.

[0017] The organic-inorganic perovskite compound preferably has a cubic structure in which a metal atom M is located at the body center, an organic base compound or alkali metal A is located at each vertex, and a halogen atom X is located at the face center. Although the details are not clear, it is presumed that the above structure allows the orientation of the octahedra within the crystal lattice to be easily changed, thereby increasing the mobility of electrons in the organic-inorganic perovskite compound and improving the photoelectric conversion efficiency of solar cells.

[0018] The organic-inorganic perovskite compound is preferably a crystalline semiconductor. A crystalline semiconductor refers to a semiconductor from which a scattering peak can be detected by measuring an X-ray scattering intensity distribution. When the organic-inorganic perovskite compound is a crystalline semiconductor, the mobility of electrons in the organic-inorganic perovskite compound increases, improving the photoelectric conversion efficiency of the flexible solar cell.

[0019] The degree of crystallinity can also be evaluated as an index of crystallization by separating the scattering peaks derived from crystalline materials and the halo derived from amorphous parts detected by X-ray scattering intensity distribution measurement through fitting, determining the intensity integrals of each, and calculating the ratio of the crystalline part to the whole. The preferred lower limit of the crystallinity of the organic-inorganic perovskite compound is 30%. A crystallinity of 30% or more increases the electron mobility in the organic-inorganic perovskite compound, improving the photoelectric conversion efficiency of the solar cell. A more preferred lower limit of the crystallinity is 50%, and an even more preferred lower limit is 70%. Methods for increasing the crystallinity of the organic-inorganic perovskite compound include, for example, thermal annealing, irradiation with high-intensity light such as laser, and plasma irradiation.

[0020] The photoelectric conversion layer may further contain an organic or inorganic semiconductor in addition to the organic-inorganic perovskite compound, as long as the effects of the present invention are not impaired. The organic or inorganic semiconductor may function as a hole transport layer or an electron transport layer. Examples of the organic semiconductor include compounds having a thiophene skeleton such as poly(3-alkylthiophene). Other examples include conductive polymers having a polyparaphenylene vinylene skeleton, a polyvinyl carbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton, etc. Further examples include compounds having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, or a benzoporphyrin skeleton, a spirobifluorene skeleton, etc. Also included are carbon-containing materials such as carbon nanotubes, graphene, and fullerenes, which may be surface-modified.

[0021] Examples of the inorganic semiconductor include titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, zinc sulfide, CuSCN, Cu2O, CuI, MoO3, V2O5, WO3, MoS2, MoSe2, and Cu2S.

[0022] When the photoelectric conversion layer contains the organic-inorganic perovskite compound and the organic semiconductor or inorganic semiconductor, it may be a laminate in which a thin-film organic semiconductor or inorganic semiconductor portion is laminated with a thin-film organic-inorganic perovskite compound portion, or a composite film in which an organic semiconductor or inorganic semiconductor portion is composited with an organic-inorganic perovskite compound portion. A laminate is preferred in that it can be produced easily, and a composite film is preferred in that it can improve the charge separation efficiency in the organic semiconductor or inorganic semiconductor.

[0023] The thickness of the photoelectric conversion layer preferably has a lower limit of 5 nm and an upper limit of 5000 nm. If the thickness is 5 nm or more, sufficient light absorption is possible, resulting in high photoelectric conversion efficiency. If the thickness is 5000 nm or less, the occurrence of regions incapable of charge separation can be suppressed, leading to improved photoelectric conversion efficiency. A more preferred lower limit of the thickness is 10 nm, a more preferred upper limit is 1000 nm, an even more preferred lower limit is 20 nm, and an even more preferred upper limit is 500 nm.

[0024] When the photoelectric conversion layer is a composite film in which an organic semiconductor or inorganic semiconductor portion is combined with an organic-inorganic perovskite compound portion, the preferred lower limit of the thickness of the composite film is 30 nm, and the preferred upper limit is 3000 nm. If the thickness is 30 nm or more, sufficient light absorption is achieved, resulting in high photoelectric conversion efficiency. If the thickness is 3000 nm or less, charges can more easily reach the electrode, resulting in high photoelectric conversion efficiency. A more preferred lower limit of the thickness is 40 nm, and a more preferred upper limit is 2000 nm, with an even more preferred lower limit being 50 nm and an even more preferred upper limit being 1000 nm.

[0025] The method for forming the photoelectric conversion layer is not particularly limited, and examples thereof include vacuum deposition, sputtering, chemical vapor deposition (CVD), electrochemical deposition, and printing. Among these, the use of printing allows for the easy formation of large-area solar cells that can exhibit high photoelectric conversion efficiency. Examples of printing methods include spin coating and casting, and examples of methods using printing include roll-to-roll methods.

[0026] The power generating section may have an electron transport layer between the cathode electrode or the counter electrode and the photoelectric conversion layer. The material for the electron transport layer is not particularly limited, and examples thereof include N-type conductive polymers, N-type low-molecular-weight organic semiconductors, N-type metal oxides, N-type metal sulfides, alkali metal halides, alkali metals, surfactants, and the like. Specific examples thereof include cyano group-containing polyphenylene vinylene, boron-containing polymers, bathocuproine, bathophenanthrene, hydroxyquinolinatoaluminum, oxadiazole compounds, benzimidazole compounds, naphthalenetetracarboxylic acid compounds, perylene derivatives, phosphine oxide compounds, phosphine sulfide compounds, fluoro group-containing phthalocyanines, titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, and zinc sulfide.

[0027] The electron transport layer may consist of only a thin-film electron transport layer, but preferably includes a porous electron transport layer. In particular, when the photoelectric conversion layer is a composite film obtained by combining an organic semiconductor or inorganic semiconductor portion with an organic-inorganic perovskite compound portion, it is preferable that the composite film be formed on a porous electron transport layer, since a more complex composite film (more intricately intricate structure) can be obtained and the photoelectric conversion efficiency can be increased.

[0028] The thickness of the electron transport layer is preferably 1 nm at the lower limit and 2000 nm at the upper limit. A thickness of 1 nm or more ensures sufficient hole blocking. A thickness of 2000 nm or less reduces resistance during electron transport, resulting in high photoelectric conversion efficiency. The electron transport layer more preferably has a lower limit of 3 nm and a higher limit of 1000 nm, an even more preferred lower limit of 5 nm, and an even more preferred upper limit of 500 nm.

[0029] The power generating section may have a hole transport layer between the electrode serving as the anode or the counter electrode and the photoelectric conversion layer. The material of the hole transport layer is not particularly limited, and the hole transport layer may be made of an organic material. Examples of materials for the hole transport layer include p-type conductive polymers, p-type small-molecular-weight organic semiconductors, p-type metal oxides, p-type metal sulfides, and surfactants. Specific examples include compounds having a thiophene skeleton, such as poly(3-alkylthiophene). Other examples include conductive polymers having a triphenylamine skeleton, polyparaphenylenevinylene skeleton, polyvinylcarbazole skeleton, polyaniline skeleton, and polyacetylene skeleton. Further examples include compounds having a porphyrin skeleton, such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, or a benzoporphyrin skeleton; a spirobifluorene skeleton; molybdenum sulfide, tungsten sulfide, copper sulfide, tin sulfide, fluoro-group-containing phosphonic acid, carbonyl-group-containing phosphonic acid; and copper compounds, such as CuSCN and CuI.

[0030] The power generating unit may be formed on a substrate. Examples of the substrate include a resin film made of a heat-resistant polymer such as polyimide or polyester, a metal foil, or thin glass. In particular, from the viewpoint of flexibility and transparency, the substrate preferably contains polyethylene terephthalate, polyethylene, polypropylene, polyethylene naphthalate, polymethyl methacrylate, polystyrene, or polycarbonate. In addition, the base material is not included in the power generation section in this specification because contact with the flame-retardant material described below does not affect power generation performance. Therefore, when the flexible solar cell of the present invention has a base material, that is, when the power generation section is formed on the base material, the base material may be in contact with the flame-retardant layer described below.

[0031] The substrate preferably has a thickness of 30 μm or more and 200 μm or less. By setting the thickness of the substrate within the above range, flexibility can be further improved. When the substrate is located on the flame-retardant layer side described below, the thickness of the substrate is more preferably 50 μm or more, and even more preferably 70 μm or more, from the viewpoint of making it more difficult for the flame-retardant material to reach the power generation section. From the viewpoint of further improving flexibility, the thickness of the substrate is more preferably 150 μm or less, and even more preferably 100 μm or less.

[0032] The flexible solar cell of the present invention has a sealing material that seals the entire power generation section. By encasing and sealing the power generation unit in a sealing material, deterioration of the power generation unit due to components in the atmosphere can be suppressed. Note that, when the power generation unit is formed on the substrate, the sealing material seals the entire laminate consisting of the power generation unit and the substrate.

[0033] Examples of sealing materials constituting the sealing material include thermosetting resins, thermoplastic resins, and inorganic materials. Examples of the thermosetting resins and thermoplastic resins include epoxy resins, acrylic resins, silicone resins, phenolic resins, melamine resins, and urea resins. Other examples include butyl rubber, polyester, polyurethane, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, ABS resin, polybutadiene, polyamide, polycarbonate, polyimide, and polyisobutylene. Among these, polyisobutylene is preferred due to its excellent sealing performance.

[0034] The flexible solar cell of the present invention has a flame-retardant layer in contact with the encapsulant. The flame retardancy, particularly the flame retardancy in the planar direction, can be improved by providing a flame retardant layer in contact with the upper and / or lower surfaces of the encapsulant in the flexible solar cell. In this specification, the flame retardancy in the planar direction means that the flexible solar cell is less likely to spread fire in the planar direction when it is brought into contact with a flame and then released.

[0035] The flame-retardant layer contains a flame-retardant material. The flame-retardant layer contains a flame-retardant material, thereby imparting flame retardancy. The flame-retardant material is not particularly limited as long as it has flame retardancy. Specific examples of the flame-retardant material include metal hydroxide-based flame retardants, nitrogen compound-based flame retardants, and halogen-based flame retardants. Among these, halogen-based flame retardants are preferred because they have high flame retardancy, high transparency, good compatibility with the sealing material, and are less likely to cause a decrease in power generation even when a flame-retardant layer is formed on the upper surface of the power generation section. Examples of halogen-based flame retardants include chlorinated paraffin, chlorinated fatty acid ester, and bromide-based flame retardants. Among these, it is preferable that the flame-retardant material contains chlorine atoms, as this provides higher transparency.

[0036] The flame retardant material is preferably liquid at 23°C. When the flame-retardant material is liquid at room temperature, it becomes more compatible with the resin material that is the main component of the flame-retardant layer, and therefore, it is possible to further suppress a decrease in the transparency of the flame-retardant layer while improving the flame retardancy. Examples of the flame-retardant material that is liquid at 23°C include the above-mentioned halogen-based flame retardants.

[0037] When the flame-retardant material is a halogen-based flame retardant, the halogen-based flame retardant preferably has a content (composition ratio) of halogen atoms of 30% or more and 60% or less. By ensuring that the halogen atom content of the halogen-based flame retardant is within the above range, sufficient flame retardancy can be imparted even when added to a resin material that is the main component of the flame-retardant layer. The halogen atom content of the halogen-based flame retardant is more preferably 40% or more, and more preferably 50% or less. The halogen atom content can be measured by elemental analysis.

[0038] The content of the flame-retardant material in the flame-retardant layer is preferably 1% by weight or more and 50% by weight or less. By setting the content of the flame-retardant material within the above range, it is possible to further improve the flame retardancy and further prevent the decrease in the transparency of the flame-retardant layer. The content of the flame-retardant material in the flame-retardant layer is more preferably 5% by weight or more, even more preferably 10% by weight or more, more preferably 30% by weight or less, even more preferably 20% by weight or less, and even more preferably 15% by weight or less.

[0039] The resin material that is the main component (the component with the highest content) of the flame-retardant layer is not particularly limited as long as it has flexibility, but is preferably a sealing material because it can also impart sealing performance. The sealing material can be the same as the sealing material of the sealing material.

[0040] The resin material that is the main component of the flame-retardant layer preferably has a crystallinity of 10% or more and 50% or less. When the resin material that is the main component of the flame-retardant layer has a crystallinity of 10% or more, flexibility can be increased while maintaining the layer structure, and when it is 50% or less, the balance between adhesion and water vapor permeability can be improved. From the viewpoint of increasing flexibility while maintaining the layer structure, the crystallinity of the resin material that is the main component of the flame-retardant layer is more preferably 20% or more, and from the viewpoint of improving the balance between adhesion and water vapor permeability, it is more preferably 40% or less, and even more preferably 30% or less.

[0041] The flame-retardant layer is preferably disposed on the upper surface of the power generation section. In this specification, the "upper surface" refers to the surface that will be the light-receiving surface when the flexible solar cell is installed, and the "lower surface" refers to the surface that will be the installation surface. Flexible solar cells do not require consideration of translucency below the power generation section, making it easy to use non-flammable materials such as metals. On the other hand, highly translucent materials must be used above the power generation section. However, because flexibility is also required for flexible solar cells, materials such as hard, easily broken glass cannot be used, and flammable organic materials must be used. Therefore, by placing the flame-retardant layer above the power generation section, flame retardancy can be further improved. Furthermore, many commonly available flame retardants are solid, and using a flame-retardant layer containing such a material on the top surface reduces translucency, leading to a decrease in the power generation efficiency of the solar cell. On the other hand, using a highly translucent flame retardant can make both the top and bottom surfaces of the flexible solar cell flame-retardant, achieving even higher flame retardancy. When placing the flame-retardant layer on the top surface of the power generation section, a highly transparent flame-retardant material must be selected to minimize its impact on power generation.

[0042] When the flame-retardant layer is disposed on the upper surface side of the power generation section, the flame-retardant layer preferably has a transmittance of 85% or more and 100% or less for light having a wavelength of 500 nm to 1000 nm. By ensuring that the light transmittance of the flame-retardant layer is within the above range, it is possible to further suppress a decrease in power generation performance due to the presence of the flame-retardant material. The flame-retardant material preferably has a light transmittance of 90% or more at wavelengths of 500 nm to 1000 nm, and more preferably 95% or more. One method for ensuring that the light transmittance of the flame-retardant layer falls within the above range is to use a flame retardant with high light transmittance. However, even if a flame retardant with high light transmittance is used, if its compatibility with the resin material that serves as the main component is low, the flame retardant will be omnipresent in some areas, resulting in a decrease in light transmittance. Therefore, it is necessary to select a flame retardant taking into consideration its compatibility with the resin material that serves as the main component.

[0043] The thickness of the flame-retardant layer is preferably 20 μm or more and 180 μm or less. By setting the thickness of the flame-retardant layer within the above range, it is possible to further improve the flame retardancy in the planar direction and the protection performance of the power generation section, as well as to further improve flexibility. The thickness of the flame-retardant layer is more preferably 50 μm or more, even more preferably 70 μm or more, more preferably 150 μm or less, and even more preferably 100 μm or less. Note that when multiple flame-retardant layers are present, the thickness of the flame-retardant layer refers to the thickness of each individual flame-retardant layer.

[0044] It is preferable that the ratio of the thickness of the sealing material laminated on the upper and / or lower surfaces of the power generation unit to the thickness of the power generation unit (thickness of sealing material:thickness of power generation unit) is 1:2 or more and 6:1 or less (hereinafter also referred to as the power generation unit-sealing material thickness ratio). When the thickness ratio of the sealing material laminated on the upper and lower surfaces of the power generation section to the thickness of the power generation section is within the above range, the flame-retardant material in the flame-retardant layer is less likely to reach the power generation section, and deterioration of power generation performance can be further suppressed. The power generation section-to-sealing material thickness ratio is more preferably 1:1 or more, and more preferably 4:1 or less.

[0045] The thickness ratio of the flame-retardant layer to the sealing material (flame-retardant layer:sealing material) is preferably 10:90 or more and 50:50 or less (hereinafter also referred to as the thickness ratio of the flame-retardant layer to the sealing material). By setting the thickness ratio of the flame-retardant layer to the sealing material within the above range, it is possible to further improve the flame retardancy in the planar direction while further suppressing the deterioration of power generation performance. The thickness ratio of the flame-retardant layer to the sealing material is more preferably 30:70 or more and more preferably 40:60 or less.

[0046] From the viewpoint of a balance between the protection performance of the power generation section and flexibility, the total thickness of the sealing material and the flame-retardant layer is preferably 10 μm or more, more preferably 50 μm or more, even more preferably 100 μm or more, even more preferably 200 μm or more, and is preferably 1000 μm or less, and more preferably 700 μm or less. Note that the thickness of the sealing material refers to the sum of the thicknesses of the power generation section and the substrate in the region where the power generation section and the substrate are arranged.

[0047] The flexible solar cell of the present invention may have a front sheet on top. The front sheet can suppress light reflection and improve the drainage performance of the flexible solar cell surface by forming a pattern of irregularities, arcs, etc. on its surface. For example, providing a front sheet with a convex arc with its apex at the center of the flexible solar cell can provide a drainage gradient from the center to the edge of the flexible solar cell, while providing a front sheet with a concave arc with its lowest point at the center of the flexible solar cell can provide a water collection area from the edge to the center of the solar cell. By providing such a drainage gradient or water collection area, the accumulation of dirt and other contaminants can be concentrated in specific areas. Furthermore, randomly forming irregularities on the front sheet can also improve the design.

[0048] The material of the front sheet is not particularly limited as long as it is transparent, and examples thereof include fluorine-containing resins, vinyl chloride resins, polyethylene resins, polycarbonate resins, etc. Specific examples include polycarbonate, polyvinyl chloride, tetrafluoroethylene resin, polyvinylidene fluoride, polychlorotrifluoroethylene, etc. Among these, fluorine-containing resins are preferred because of their excellent weather resistance.

[0049] The thickness of the front sheet is not particularly limited, but from the viewpoint of the balance between light transmittance and functionality of the front sheet, it is preferably 25 μm or more, more preferably 50 μm or more, and is preferably 1000 μm or less, more preferably 300 μm or less.

[0050] The flexible solar cell of the present invention may have a backsheet at the bottom. The back sheet has the role of preventing the penetration of substances such as moisture that cannot be prevented by the sealing layer alone, thereby improving the weather resistance of the flexible solar cell. Examples of materials for the back sheet include polyethylene terephthalate.

[0051] The thickness of the back sheet is not particularly limited, but from the viewpoint of the balance between flexibility and functionality of the back sheet, it is preferably 50 μm or more, more preferably 100 μm or more, and is preferably 1000 μm or less, more preferably 500 μm or less.

[0052] In the flexible solar cell of the present invention, the shortest distance from the power generation section to the flame-retardant layer is 100 μm or more. In conventional flexible solar cells that use organic-inorganic perovskite compounds in the photoelectric conversion layer, when a flame-retardant material is added to the encapsulant, contact between the flame-retardant material and the power generation section can result in a decrease in power generation performance. In the present invention, a flame-retardant layer containing a flame-retardant material is provided separately from the encapsulant, and the shortest distance from the power generation section to the flame-retardant layer is set to 100 μm or more, thereby preventing contact between the flame-retardant material and the power generation section and preventing a decrease in power generation performance.

[0053] The shortest distance to the flame-retardant layer is preferably 140 μm or more, more preferably 200 μm or more, and even more preferably 300 μm or more. There is no particular upper limit to the shortest distance to the flame-retardant layer, and the longer the distance, the more the reduction in power generation performance due to the flame-retardant material can be suppressed. However, from the viewpoint of making the flexible solar cell thinner, the shortest distance is preferably 1000 μm or less.

[0054] The flexible solar cell of the present invention may have a blocking layer disposed between the power generation section and the flame-retardant layer. By disposing a blocking layer between the flame-retardant layer and the power generation section, contact between the flame-retardant material and the power generation section is reduced, making it possible to further prevent a decrease in power generation performance.

[0055] The blocking layer contains a resin having at least one of a degree of crystallinity and a glass transition temperature higher than those of the resin material that is the main component of the flame-retardant layer. When the resin that is the main component of the block layer has at least one of a degree of crystallinity or a glass transition temperature higher than that of the resin material that is the main component of the flame-retardant layer, it becomes difficult for the flame-retardant material to pass through the block layer, thereby suppressing a decrease in power generation performance. The crystallinity and glass transition temperature can be measured in accordance with JIS K 7121-1987 using a differential scanning calorimeter (DSC-60, manufactured by Shimadzu Corporation or an equivalent product) at a temperature rise rate of 10°C / min.

[0056] The resin of the blocking layer is not particularly limited as long as it has at least one of a higher crystallinity and a higher glass transition temperature than the resin material of the flame-retardant layer, is flexible, and, when disposed on the upper surface of the power generation section, is transparent. Specific examples include resin films made of heat-resistant polymers such as polyimide and polyester, metal foils, and thin glass sheets. From the viewpoints of flexibility and transparency, it is preferable that the blocking layer contains polyethylene terephthalate, polyethylene, polypropylene, polyethylene naphthalate, polymethyl methacrylate, polystyrene, or polycarbonate.

[0057] The content of the resin in the block layer may be more than 50% by weight, preferably 70% by weight or more, and more preferably 80% by weight or more, and may be 100% by weight.

[0058] The blocking layer may be the base material, or a separate blocking layer may be provided. The blocking layer may be disposed so as to contact the top surface of the power generation unit, the bottom surface, or both the top and bottom surfaces. The blocking layer may cover the side surfaces of the power generation unit in addition to the top or bottom surface. The blocking layer and the power generation unit do not necessarily need to be in direct contact with each other; the sealing material may be disposed between the blocking layer and the power generation unit.

[0059] The resin constituting the block layer preferably has a crystallinity of 30% or more and 80% or less. When the crystallinity of the resin constituting the block layer is 30% or more, the mechanical strength of the block layer can be further increased, and when it is 80% or less, the adhesion to other layers can be further increased. From the viewpoint of further increasing the mechanical strength, the crystallinity of the resin constituting the block layer is more preferably 40% or more, and even more preferably 50% or more. Furthermore, from the viewpoint of further increasing the adhesion to other layers, the crystallinity of the resin constituting the block layer is more preferably 70% or less, and even more preferably 60% or less.

[0060] The resin constituting the block layer preferably has a glass transition temperature difference of 20 degrees or more from that of the resin material that is the main component of the flame-retardant layer (hereinafter referred to as the glass transition temperature difference between the block layer and the flame-retardant layer). When the difference in glass transition temperature between the main components of the blocking layer and the flame-retardant layer is equal to or greater than the lower limit, the gaps between the molecular chains of the blocking layer become narrower than the gaps between the molecular chains of the sealing material, making it more difficult for the flame-retardant material to pass through. The difference in glass transition temperature between the blocking layer and the flame-retardant layer is more preferably 30°C or more, and even more preferably 40°C or more.

[0061] The blocking layer preferably has a thickness of 30 μm or more and 200 μm or less. When the thickness of the blocking layer is within the above range, it becomes more difficult for the flame-retardant layer to reach the power generation section by wrapping around the side surface of the blocking layer, and flexibility can be further improved. From the viewpoint of making it more difficult for the flame-retardant layer to reach the power generation section, the thickness of the blocking layer is more preferably 50 μm or more, and even more preferably 70 μm or more. From the viewpoint of further improving flexibility, the thickness of the blocking layer is more preferably 150 μm or less, and even more preferably 100 μm or less.

[0062] From the viewpoint of further suppressing a decrease in power generation performance, it is preferable that the interface between the power generation unit and the blocking layer be in contact with only the sealing material, i.e., the power generation unit and the blocking layer are not in contact with the flame-retardant layer. On the other hand, from the viewpoint of making the flexible solar cell thinner, it is preferable that the blocking layer be in contact with the flame-retardant layer.

[0063] Schematic diagrams illustrating an example of the structure of a flexible solar cell of the present invention are shown in Figures 1 to 4. As shown in Figures 1 to 3, the flexible solar cell of the present invention includes a power generation unit 1 having an electrode 13, a photoelectric conversion layer 12, and a counter electrode 11; an optional substrate 2; an encapsulant 4 that encapsulates the entire power generation unit 1; and a flame-retardant layer 3 disposed on the encapsulant 4 so as to contact the encapsulant 4. A front sheet 5 and a back sheet 6 are disposed at the top and bottom of the flexible solar cell. Furthermore, in the flexible solar cell of the present invention, the shortest distance from the power generation unit 1 to the flame-retardant layer 3 is 100 μm or more. This arrangement reduces the likelihood of the flame-retardant material coming into contact with the power generation unit 1, thereby enhancing the flame retardancy in the planar direction while suppressing deterioration of the power generation unit 1. Furthermore, as shown in Figure 4, the substrate 2 may be disposed on the flame-retardant layer 3 side of the power generation unit 1. This structure allows the flame-retardant layer 3 to be disposed so as to contact the substrate 2, eliminating the need to wrap the entire power generation unit 1 in the encapsulant 4, further simplifying the manufacturing process.

[0064] Although there are no particular limitations on the method for manufacturing the flexible solar cell of the present invention, a method in which the power generating unit 1 is sandwiched between a sheet (sheet A) having a flame-retardant layer 3, a sealing material 4, and optionally a front sheet 5, and a sheet (sheet B) having a sealing material 4, and optionally a flame-retardant layer 3 and a back sheet 6, as shown in Figure 5, and laminated together is preferred because it allows for easy manufacturing over a large area.

[0065] When the flexible solar cell has a structure as shown in Figure 1, the above-mentioned sheet A can be obtained by performing the steps of laminating a flame-retardant layer on the front sheet and laminating an encapsulant on the flame-retardant layer. If the flexible solar cell has an adhesive layer that bonds the encapsulant to the front sheet, the adhesive layer is laminated on the front sheet before laminating the flame-retardant layer. Furthermore, when the flexible solar cell has a structure as shown in Figure 3, sheet A can be obtained by simply laminating a flame-retardant layer on the front sheet.

[0066] The power generating section can be obtained by sequentially stacking layers such as an electrode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and a counter electrode on a substrate. Alternatively, the power generating section can be obtained by stacking each layer on an electrode instead of a substrate. Conventional methods can be used to stack each layer without any particular limitations.

[0067] When the flexible solar cell has a structure as shown in Figure 1, the above-mentioned sheet B can be obtained by carrying out the steps of laminating a flame-retardant layer on a back sheet and laminating an encapsulant on the flame-retardant layer. Furthermore, when a back sheet is not provided, the sheet B can be obtained by laminating the flame-retardant layer and the encapsulant by coating or the like. Furthermore, when the flexible solar cell has a structure as shown in Figure 2, the sheet B can be obtained by only the step of laminating the encapsulant on the back sheet.

[0068] A roll-to-roll method can be used as a method for laminating the sheet A, the power generation section, and the sheet B. By using the roll-to-roll method, large-area flexible solar cells can be continuously produced. [Effects of the Invention]

[0069] According to the present invention, it is possible to provide a flexible solar cell that has excellent flame retardancy in the planar direction while suppressing a decrease in power generation performance. [Brief explanation of the drawings]

[0070] [Figure 1]1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. [Figure 2] 1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. [Figure 3] 1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. [Figure 4] 1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. [Figure 5] 1A to 1C are schematic diagrams illustrating an example of manufacturing a flexible solar cell of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0072] Example 1 <Manufacturing flexible solar cells> A 100 μm-thick polyethylene terephthalate (PET) film was prepared as the substrate. A 200 nm-thick ITO film was formed on the substrate by sputtering as a counter electrode. A 20 nm-thick thin-film electron transport layer was then formed on the formed counter electrode by sputtering. A titanium oxide paste containing titanium oxide was then applied to the thin-film electron transport layer by spin coating and dried to form a 100 nm-thick porous electron transport layer. Next, lead iodide, a metal halide compound, was dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) to prepare a 1 M solution, and this was then spin-coated onto the porous electron transport layer. Furthermore, methylammonium iodide, an amine compound, was dissolved in 2-propanol to prepare an 8 wt % solution. This solution was spin-coated onto the lead iodide substrate and annealed at 150°C for 10 minutes to form a 700-nm-thick photoelectric conversion layer containing the organic-inorganic perovskite compound CH3NH3PbI3. Next, a chlorobenzene solution containing 2 wt% Spiro-OMETAD (Merck) was spin-coated onto the photoelectric conversion layer and then dried to form an 80-nm-thick hole transport layer. A 100-nm-thick Al film was then formed on the photoelectric conversion layer as an electrode by sputtering, yielding a laminate with a power generation unit formed on the substrate, consisting of a counter electrode, electron transport layer, photoelectric conversion layer, hole transport layer, and electrode.

[0073] Next, a 50 μm-thick PET sheet was prepared as the front sheet. Next, a flame-retardant resin containing 10 wt% of the flame-retardant material, Enpara A-1 (chlorinated fatty acid ester, chlorine content 35–36.5%, manufactured by Ajinomoto Fine-Techno Co., Inc.), was added to the main component, polyisobutylene, to prepare a flame-retardant resin. This resin was then applied to the front sheet to a thickness of 100 μm to form a flame-retardant layer. Sheet A was then obtained by applying a 100 μm thick encapsulant consisting solely of polyisobutylene to the flame-retardant layer. Meanwhile, a 360 μm-thick aluminum-containing back sheet (manufactured by Toyo Aluminum Co., Ltd., FAPL) was prepared as the back sheet, and a 70 μm thick encapsulant consisting solely of polyisobutylene was applied to the back sheet to obtain Sheet B. The laminate was then sandwiched between Sheet A and Sheet B, with the encapsulant facing the power generation section of Sheet A and the encapsulant facing the substrate of Sheet B, to obtain a flexible solar cell with the structure shown in Figure 2.

[0074] (Examples 2 to 6, Comparative Examples 7 and 8) A flexible solar cell was obtained in the same manner as in Example 1, except that the following flame-retardant materials were used and the thickness of the encapsulant applied during the production of Sheet A was adjusted to make the shortest distance to the flame-retardant layer as shown in Table 1. Empara A-3: Chlorinated fatty acid ester, chlorine content 31-33%, manufactured by Ajinomoto Fine-Techno Co., Ltd. Enpara 40 (chlorinated paraffin, chlorine content 40-42%, manufactured by Ajinomoto Fine-Techno Co., Ltd.) Enpara K-50: Chlorinated paraffin, chlorine content 50-52%, manufactured by Ajinomoto Fine-Techno Co., Ltd. Empara M-3: Chlorinated fatty acid ester, chlorine content 32-34%, manufactured by Ajinomoto Fine-Techno Co., Ltd.

[0075] (Comparative Examples 1 to 5) The flame-retardant materials used were as shown in Table 1, and a resin containing a flame-retardant material was used instead of the sealing material in the preparation of sheets A and B. The laminate was sandwiched so that sheet A and the substrate faced each other, and other than this, a flexible solar cell in which the laminate was sealed only with a flame-retardant layer was prepared in the same manner as in Example 1.

[0076] (Comparative Example 6) A flexible solar cell in which the laminate was sealed only with a sealing material was obtained in the same manner as in Example 1, except that the flame-retardant material-containing resin applied to the front sheet was changed to a sealing material (polyisobutylene).

[0077] <Evaluation> The flexible solar cells obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0078] (1) Flame retardancy evaluation A flame-retardant resin similar to that used in each example and comparative example was prepared and applied to a 0.3 mm thick aluminum plate to a thickness of 100 μm to obtain an evaluation sample. The obtained evaluation sample was fixed vertically, and a flame was applied from the bottom edge for 10 seconds, and then the combustion of the flame-retardant resin was confirmed after removal. Flame retardancy was evaluated as "Good" if the fire was extinguished or the fire spread distance was 15 cm or less, and "Poor" if the fire spread distance exceeded 15 cm. Note that Comparative Example 6 did not have a flame-retardant layer, so it was evaluated using an encapsulant.

[0079] (2) Translucency evaluation Using the above method, one of the sheets A and B, which included a flame-retardant layer, was prepared and used as a measurement sample. The ultraviolet-visible absorption spectrum of the obtained measurement sample was measured in the range of 200 nm to 1000 nm using a spectrophotometer (U-4100, manufactured by Hitachi, Ltd.). The light transmittance of the layer laminated on the upper side of the power generation section was evaluated by marking it as "Good" if the transmittance in the 400 to 1000 nm range of the obtained absorption spectrum was 85% or higher, and "Poor" if it was less than 85%. Note that evaluation was performed using sheet A for Comparative Example 6.

[0080] (3) Durability evaluation Immediately after manufacturing the flexible solar cell, a power supply (KEITHLEY, 236 model) was connected between the electrodes of the flexible solar cell, and the intensity was 100 mW / cm 2The photoelectric conversion efficiency was measured using a solar simulator (manufactured by Yamashita Denso Co., Ltd.). The photoelectric conversion efficiency obtained was calculated as a relative value when Comparative Example 6 was set to 1, and this was designated as the initial conversion efficiency. An initial conversion efficiency of 0.8 or more was evaluated as "○", and an initial conversion efficiency of less than 0.8 was evaluated as "×". Next, a durability test was conducted by carrying out a 500-hour moist heat resistance test at a temperature of 85°C and a humidity of 85%. The photoelectric conversion efficiency of the flexible solar cell after the durability test was measured in the same manner as the initial conversion efficiency, and the retention rate from the initial conversion efficiency was calculated. Durability was evaluated by assigning a "◎" when the retention rate was 90% or more and less than 90% to "○", a "△" when the retention rate was 70% or more and less than 80%, and an "×" when the retention rate was less than 70%.

[0081] [Table 1] [Industrial Applicability]

[0082] According to the present invention, it is possible to provide a flexible solar cell that has excellent flame retardancy in the planar direction while suppressing a decrease in power generation performance. [Explanation of symbols]

[0083] 1 Power Generation Department 11 Counter electrode 12 Photoelectric conversion layer 13 electrodes 2 Base material 3. Flame-retardant layer 4. Encapsulating material 5 Front seats 6 Back Seat

Claims

1. A flexible solar cell having a power generation section, a sealing material that seals the entire power generation section, and a flame-retardant layer that is in contact with the sealing material, the power generation unit has an electrode, a photoelectric conversion layer, and a counter electrode, the photoelectric conversion layer contains an organic-inorganic perovskite compound, the flame-retardant layer contains a flame-retardant material, A flexible solar cell, characterized in that the shortest distance from the power generation section to the flame-retardant layer is 100 μm or more.

2. The flexible solar cell according to claim 1 , wherein the flame-retardant layer is disposed on the upper surface side of the power generating section.

3. 3. The flexible solar cell according to claim 1, wherein the flame-retardant material contains chlorine atoms.

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