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 blocking layer that is in contact with the entire surface of at least one side of the power section, and a sealing material that seals the entire laminate composed of the power section and the blocking layer, wherein the power section has an electrode, a photoelectric conversion layer, and a counter electrode, the photoelectric conversion layer contains an organic-inorganic perovskite compound, and the sealing material has a flame retardant site containing a flame retardant material and a non-flame retardant site not containing the flame retardant material, the flame retardant site is disposed on a side of a surface of the block layer not in contact with the power generation part, and the power generation part is in contact with the non-flame retardant site and not in contact with the flame retardant site.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 4. The present invention will be described in detail below. [Disclosure 1] A flexible solar cell having a power generation section, a blocking layer in contact with at least one entire surface of the power generation section, and a sealing material that seals the entire stack consisting of the power generation section and the blocking layer, 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 sealing material has a flame-retardant portion containing a flame-retardant material and a non-flame-retardant portion not containing the flame-retardant material, the flame-retardant portion is disposed on a surface of the block layer that is not in contact with the power generation section, The power generating unit is in contact with the non-flame retardant portion and is not in contact with the flame retardant portion. A flexible solar cell characterized by: [Disclosure 2] The flexible solar cell according to Disclosure 1, wherein the flame-retardant material contains chlorine atoms. [Disclosure 3] The flexible solar cell according to Disclosure 1 or 2, wherein the material constituting the blocking layer contains polyethylene terephthalate, polyethylene, polypropylene, polyethylene naphthalate, polymethyl methacrylate, polystyrene, or polycarbonate. [Disclosure 4] The flexible solar cell according to any one of Disclosures 1 to 3, wherein the interface of the laminate is in contact only with the non-flame retardant portion.

[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 flexible solar cell of the present invention has a blocking layer that contacts the entire surface of at least one of the power generating sections. The present inventors investigated the reasons for the deterioration of power generation performance in flexible solar cells in which a flame-retardant material is added to the encapsulant and found that the cause is contact of the flame-retardant material with the power generation section in flexible solar cells that use an organic-inorganic perovskite compound in the photoelectric conversion layer. Flame-retardant materials often have highly reactive molecular structures containing halogen-based atoms, etc., and the flame-retardant material reacts with the electrodes and photoelectric conversion layer of the power generation section, causing the power generation section to deteriorate. In the present invention, a blocking layer is provided that contacts the entire surface of at least one side of the power generation section to cover the power generation section, and an encapsulant containing the flame-retardant material described below is further laminated on the blocking layer, thereby improving flame retardancy while suppressing the deterioration of power generation performance caused by the flame-retardant material.

[0031] The blocking layer is not particularly limited as long as it can physically prevent contact between the power generation unit and the sealing material containing the flame-retardant material described below. The base material for forming the power generation unit may be used as the blocking layer, or a separate blocking layer may be provided. The blocking layer may be arranged so as to contact the top surface of the power generation unit, the bottom surface, or both the top and bottom surfaces. Furthermore, the blocking layer may cover the side surfaces of the power generation unit in addition to the top or bottom surface. In this specification, the base material for forming the power generation unit is included in the blocking layer, but not in the power generation unit.

[0032] The material constituting the blocking layer is not particularly limited as long as it is flexible and, when placed on the upper surface of the power generation section, is also 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.

[0033] 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 sealing material containing a flame-retardant material (described later) 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 sealing material containing a flame-retardant material 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.

[0034] The flexible solar cell of the present invention has a sealing material that seals the entire laminate made up of the power generation section and the blocking layer. By encasing and sealing the laminate consisting of the power generation section and the block layer with a sealing material, deterioration of the power generation section due to components in the atmosphere can be suppressed. Examples of sealing materials that are the main components of 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.

[0035] The sealing material has a flame-retardant portion containing a flame-retardant material and a non-flame-retardant portion not containing the flame-retardant material, the flame-retardant portion is arranged on the side of the block layer that is not in contact with the power generation unit, and the power generation unit is in contact with the non-flame-retardant portion but not with the flame-retardant portion. In flexible solar cells using an organic-inorganic perovskite compound 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, the encapsulant is divided into two sections: a flame-retardant section containing the flame-retardant material and a non-flame-retardant section not containing the flame-retardant material. The power generation section is in contact only with the non-flame-retardant section, and the flame-retardant section is laminated on the block layer side. This prevents contact between the flame-retardant material and the power generation section, thereby preventing a decrease in power generation performance. Meanwhile, the flame-retardant section is laminated on the block layer side, thereby improving flame retardancy, particularly in the planar direction. It is sufficient for the encapsulant to have the power generation section in contact only with the non-flame-retardant section, and for the flame-retardant section to be located on the side of the block layer that is not in contact with the power generation section. However, to further prevent a decrease in power generation performance, it is preferable for the interface of the laminate (the laminate of the power generation section and the block layer) to be in contact only with the non-flame-retardant section, i.e., for the block layer to also not be in contact with the flame-retardant section. In this specification, flame retardancy in the planar direction means the property of making it difficult for fire to spread in the planar direction when the flexible solar cell is brought into contact with a flame and then released.

[0036] The flame-retardant material is not particularly limited as long as it has flame retardancy and, when a block layer is laminated on the upper surface of the power generation section, also has transparency. Specific examples of the flame-retardant material include halogen-based flame retardants. Examples of halogen-based flame retardants include chlorinated paraffin and chlorinated fatty acid ester. In particular, from the viewpoints of flame retardancy and transparency, it is preferable that the flame-retardant material contains chlorine atoms.

[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 in the halogen-based flame retardant is within the above range, sufficient flame retardancy can be imparted even when added to an encapsulant. The halogen atom content in 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 flame-retardant portion preferably has a transmittance of 85% or more and 100% or less for light having a wavelength of 500 nm to 1000 nm. When the light transmittance of the flame-retardant portion 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 more preferably has a light transmittance of 90% or more at wavelengths of 500 nm to 1000 nm, and even more preferably has a light transmittance of 95% or more.

[0039] The content of the flame-retardant material in the flame-retardant portion 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 flame retardancy and further suppress a decrease in transparency. The content of the flame-retardant material in the sealing material is more preferably 5% by weight or more, even more preferably 10% by weight or more, more preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0040] The thickness of the flame-retardant portion of the sealing material is preferably 20 μm or more and 180 μm or less. By setting the thickness of the flame-retardant portion 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 increase flexibility. The thickness of the flame-retardant portion in the sealing material 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 there are multiple flame-retardant portions, the thickness of the flame-retardant portion refers to the thickness of each individual flame-retardant portion.

[0041] It is preferable that the ratio of the thickness of the non-flame-retardant portion in contact with the power generation portion to the thickness of the power generation portion (thickness of the non-flame-retardant portion:thickness of the power generation portion) is 1:2 or more and 6:1 or less (hereinafter also referred to as the power generation portion-non-flame-retardant portion thickness ratio). When the thickness of the non-flame-retardant portion in contact with the power generation section is in the above-mentioned ratio to the thickness of the power generation section, the flame-retardant material in the flame-retardant portion is less likely to reach the power generation section, and deterioration of power generation performance can be further suppressed. The thickness ratio between the power generation section and the non-flame-retardant portion is more preferably 1:1 or more, and more preferably 4:1 or less.

[0042] In the flexible solar cell of the present invention, the average distance from the power generating section to the interface between the flame-retardant portion and the non-flame-retardant portion is preferably 10 μm or more and 100 μm or less (hereinafter also referred to as interface distance). When the average distance from the power generation section to the interface between the flame-retardant section and the non-flame-retardant section is within the above range, the flame-retardant material in the flame-retardant section is less likely to reach the power generation section, further suppressing deterioration in power generation performance. The above interfacial distance is more preferably 30 μm or more, even more preferably 50 μm or more, more preferably 80 μm or less, and even more preferably 60 μm or less. Note that the above interfacial distance refers to the average distance from the electrode closest to the interface of the power generation section to the interface. Furthermore, the above interfacial distance is the interfacial distance when the power generation section and the flame-retardant section are not in contact; when the power generation section and the flame-retardant section are in contact (when the interface is on the side of the power generation section), there is no interfacial distance.

[0043] From the viewpoint of a balance between the protection performance of the power generation section and flexibility, the thickness of the entire sealing material is preferably 100 μm or more, 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 in the region where the power generation section and the blocking layer are arranged refers to the sum of the thicknesses of the power generation section and the blocking layer.

[0044] 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 a peak at the center of the flexible solar cell can provide a drainage gradient from the center to the edge of the solar cell, while providing a front sheet with a concave arc with a bottom 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 improve the design.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Schematic diagrams showing an example of the structure of a flexible solar cell of the present invention are shown in Figures 1 to 4. As shown in Figure 1, the flexible solar cell of the present invention has a structure in which a laminate consisting of a power generation unit 1 having an electrode 13, a photoelectric conversion layer 12, and a counter electrode 11, and a block layer 2 in contact with at least one entire surface of the power generation unit 1, is entirely sealed with an encapsulant 3, and a front sheet 4 and a back sheet 5 are disposed above and below the encapsulant. The encapsulant 3 is composed of a flame-retardant portion 31 containing a flame-retardant material and a non-flame-retardant portion 32 not containing a flame-retardant material, and the power generation unit 1 is in contact only with the non-flame-retardant portion 32, not with the flame-retardant portion 31. Furthermore, the flame-retardant portion 31 is laminated on the block layer 2 side of the laminate, and the block layer 2 prevents the flame-retardant portion 31 from coming into direct contact with the power generation unit 1. Disposing the encapsulant 3 in this manner reduces the likelihood of contact between the flame-retardant material and the power generation unit 1, thereby enhancing flame retardancy in the planar direction while suppressing deterioration of the power generation unit 1.

[0050] In the flexible solar cell shown in FIG. 2, the blocking layer 2 is disposed on the surface of the power generating unit 1 facing the electrode 13. Furthermore, because the blocking layer 2 is disposed below the power generating unit 1, the flame-retardant portion 31 is also disposed below. In the flexible solar cell shown in FIG. 3, the blocking layer 2 is disposed on both sides of the power generating unit 1. This arrangement can further reduce deterioration of the power generating unit 1. In the flexible solar cell shown in FIG. 4, the blocking layer 2 covers the surface of the power generating unit 1 facing the electrode 13 and the side surfaces of the power generating unit 1. By covering the side surfaces of the power generating unit 1 with the blocking layer 2, it becomes more difficult for the flame-retardant portion 31 that has wrapped around to the side surfaces of the blocking layer 2 to reach the power generating unit 1, thereby reducing deterioration of the power generating unit 1.

[0051] Although there are no particular limitations on the method for manufacturing the flexible solar cell of the present invention, a method in which a laminate of a power generating section 1 and a blocking layer 2 is sandwiched between a sheet (sheet A) having a flame-retardant section 31 and, if necessary, a front sheet 4, and a sheet (sheet B) having a non-flame-retardant section 32 and, if necessary, a back sheet 5, and the laminate is laminated as shown in Figure 5, because this method facilitates manufacturing over a large area.

[0052] When the flexible solar cell has a structure as shown in Figure 1, the sheet A can be obtained by laminating an encapsulant (flame-retardant portion) on the front sheet. 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 portion, and if the blocking layer is also not in contact with the flame-retardant portion, the non-flame-retardant portion is laminated after laminating the flame-retardant portion.

[0053] The laminate can be obtained by sequentially laminating layers such as an electrode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and a counter electrode on a block layer. Alternatively, the laminate can be obtained by laminating each layer on an electrode instead of a substrate. In this case, a step of adhering the resulting power generating section to the block layer is performed. Conventional methods can be used to laminate each layer without any particular limitations.

[0054] When the flexible solar cell has a structure as shown in Figure 1, the above-mentioned sheet B can be obtained by laminating a non-flame-retardant portion on a back sheet. When a back sheet is not provided, the sheet B can be obtained by forming a layer consisting of only an encapsulant (non-flame-retardant portion) by coating or the like. Furthermore, when the flexible solar cell has a structure as shown in Figure 3, the sheet B can be obtained by laminating a flame-retardant portion on a back sheet and then laminating a non-flame-retardant portion on the flame-retardant portion.

[0055] 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]

[0056] 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]

[0057] [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 the production of a flexible solar cell of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0059] Example 1 <Manufacturing flexible solar cells> A 100 μm-thick polyethylene terephthalate (PET) film was prepared as a blocking layer. A 200 nm-thick ITO film was formed on the blocking layer 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, which 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 CHNHPbI. 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 sputtered onto the photoelectric conversion layer as an electrode, yielding a laminate with a power generation section formed on the blocking layer, consisting of a counter electrode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an electrode.

[0060] Next, a 50 μm-thick PET sheet was prepared as the front sheet. Next, a flame-retardant encapsulant for the flame-retardant portion was prepared by adding 10 wt% of the flame-retardant material, Enpara 40 (chlorinated paraffin, chlorine content 40-42%, manufactured by Ajinomoto Fine-Techno Co., Inc.), to the main component, polyisobutylene. This encapsulant was then applied to the front sheet to a thickness of 100 μm, yielding Sheet A. Meanwhile, a 360 μm-thick aluminum back sheet (manufactured by Toyo Aluminum Co., Ltd., FAPL) was prepared as the back sheet, and a 70 μm-thick encapsulant for the non-flame-retardant portion, consisting solely of polyisobutylene, was applied to the front sheet to obtain Sheet B. The laminate was then sandwiched between Sheet A and Sheet B, with the encapsulant (flame-retardant portion) facing the block layer and the encapsulant (non-flame-retardant portion) facing the power generation portion, resulting in a flexible solar cell with a flame-retardant portion laminated only on the block layer side. The cross section of the obtained flexible solar cell was observed using an electron microscope, and the distance (interface distance) between the interface between the power generation portion and the blocking layer and the interfaces between the flame-retardant portion and the non-flame-retardant portion was measured.

[0061] Examples 2 to 5 A flexible solar cell was obtained in the same manner as in Example 1, except that the following flame-retardant material was used. Enpara K-50: Chlorinated paraffin, chlorine content 50-52%, manufactured by Ajinomoto Fine-Techno Co., Ltd. Empara A-1: ​​Chlorinated fatty acid ester, chlorine content 35-36.5%, manufactured by Ajinomoto Fine-Techno Co., Ltd. Empara A-3: Chlorinated fatty acid ester, chlorine content 31-33%, 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.

[0062] (Comparative Examples 1 to 5) A flexible solar cell in which the laminate was sealed only with the flame-retardant portion was produced in the same manner as in Example 1, except that the flame-retardant materials used were as shown in Table 1 and the sealing material applied to the backsheet was the same as the sealing material for the flame-retardant portion.

[0063] (Comparative Example 6) A flexible solar cell in which the laminate was sealed only with non-flame retardant portions was obtained in the same manner as in Example 1, except that the sealing material applied to the front sheet was a sealing material for non-flame retardant portions (polyisobutylene).

[0064] <Evaluation> The flexible solar cells obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0065] (1) Flame retardancy evaluation A sealant for flame-retardant portions similar to those in each Example and Comparative Example was prepared, and the sealant for flame-retardant portions was applied to a 0.3 mm thick aluminum sheet to a thickness of 100 μm to obtain an evaluation sample. The obtained evaluation sample was fixed vertically, and a flame was applied to the bottom edge for 10 seconds, and then the combustion of the sealant for flame-retardant portions 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 as "Poor" if the fire spread distance exceeded 15 cm.

[0066] (2) Evaluation of initial conversion efficiency 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 2 The photoelectric conversion efficiency was measured using a solar simulator (manufactured by Yamashita Denso Co., Ltd.) The initial conversion efficiency was evaluated by assigning a photoelectric conversion efficiency of 0.80 or more to the photoelectric conversion efficiency of Comparative Example 6 as the standard (1), and assigning an "O" to the photoelectric conversion efficiency of less than 0.80 to the standard (X).

[0067] (3) Durability evaluation The obtained flexible solar cells were subjected to a durability test by conducting a 500-hour moist heat resistance test at a temperature of 85°C and a humidity of 85%. After the durability test, the photoelectric conversion efficiency of the flexible solar cells was measured in the same manner as in the evaluation of the initial conversion efficiency, and the retention rate from the initial conversion efficiency was calculated. Durability was evaluated by assigning a "good" if the retention rate was 85% or more and an "unsatisfactory" if the retention rate was less than 85%.

[0068] [Table 1] [Industrial Applicability]

[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. [Explanation of symbols]

[0070] 1 Power Generation Department 11 Counter electrode 12 Photoelectric conversion layer 13 electrodes 2 Block Layer 3. Encapsulating material 31 Flame-retardant parts 32 Non-flame retardant parts 4 Front seats 5 Back Seat

Claims

1. A flexible solar cell having a power generation section, a blocking layer in contact with at least one entire surface of the power generation section, and a sealing material that seals the entire stack consisting of the power generation section and the blocking layer, 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 sealing material has a flame-retardant portion containing a flame-retardant material and a non-flame-retardant portion not containing the flame-retardant material, the flame-retardant portion is disposed on a surface of the block layer that is not in contact with the power generation section, The power generating unit is in contact with the non-flame retardant portion and is not in contact with the flame retardant portion. A flexible solar cell characterized by:

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

3. 3. The flexible solar cell according to claim 1, wherein the material constituting the blocking layer contains polyethylene terephthalate, polyethylene, polypropylene, polyethylene naphthalate, polymethyl methacrylate, polystyrene, or polycarbonate.

4. 3. The flexible solar cell according to claim 1, wherein the interface of the laminate is in contact only with the non-flame retardant portion.

Images