WO2026004389A1 - Flexible solar cell - Google Patents

Abstract

The purpose of the present invention is to provide a flexible solar cell that has excellent flame retardancy in the planar direction while also suppressing a reduction in power generation performance. The present invention is a flexible solar cell comprising a power generation part (1), a flame retardant layer (3), a blocking layer (2) that is disposed between the power generation part (1) and the flame retardant layer (3), and a sealing material (4) that seals the power generation part (1), wherein: the power generation part (1) has an electrode (13), a photoelectric conversion layer (12), and a counter electrode (11); the photoelectric conversion layer (12) contains an organic inorganic perovskite compound; the flame retardant layer (3) contains a resin material and a flame retardant material; and the blocking layer (2) contains a resin which has a higher crystallinity and/or glass transition temperature than the resin material.

Description

flexible solar cells

The present invention relates to flexible solar cells.

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, and inorganic semiconductors such as silicon are mainly used as the N-type and P-type semiconductors. However, such inorganic solar cells have problems in that they are costly to manufacture and difficult to enlarge, 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 their photoelectric conversion layers (see, for example, Patent Document 1 and Non-Patent Document 1). Perovskite solar cells are expected to have high photoelectric conversion efficiency, and can be manufactured by printing, which significantly reduces manufacturing costs.

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.

JP 2014-72327 A Japanese Patent Application Laid-Open No. 2013-253317

M. M. Lee, et al., Science, 2012, 338, 643

Such flexible solar cells often use organic materials to give them 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 of the solar cell, flame retardancy in the planar direction (the surface direction perpendicular to the thickness direction) has not been sufficiently studied. In particular, in recent years, advances in manufacturing technology have resulted in larger areas per flexible solar cell unit, and as poor flame retardancy in the planar direction not only could result in the burning of a large number of solar cells, but also increases the risk of the fire spreading to other areas, flame retardancy in the planar direction is becoming even more important.

In response to this issue, one proposed method for improving the flame retardancy of flexible solar cells is to add 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.

The objective of the present invention is to provide a flexible solar cell that has excellent flame retardancy in the planar direction while minimizing degradation of power generation performance.

The present invention includes the following Disclosures 1 to 7. The present invention will be described in detail below.
[Disclosure 1]
A flexible solar cell having a power generation unit, a flame-retardant layer, a blocking layer disposed between the power generation unit and the flame-retardant layer, and a sealing material that seals the power generation unit,
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 resin material and a flame-retardant material,
The flexible solar cell is characterized in that 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.
[Disclosure 2]
The flexible solar cell according to Disclosure 1, wherein the interface between the power generating section and the blocking layer is in contact with only the encapsulant.
[Disclosure 3]
The flexible solar cell according to Disclosure 1, wherein the blocking layer is in contact with the flame-retardant layer.
[Disclosure 4]
The flexible solar cell according to any one of Disclosures 1 to 3, wherein the average distance from the power generation section to the interface between the flame-retardant layer and the sealing material is 10 μm or more and 100 μm or less.
[Disclosure 5]
The flexible solar cell according to any one of Disclosures 1 to 4, wherein the flame-retardant layer is disposed on the upper surface side of the power generating section.
[Disclosure 6]
The flexible solar cell according to any one of Disclosures 1 to 5, wherein the flame-retardant material contains chlorine atoms.
[Disclosure 7]
The flexible solar cell described in any one of Disclosures 1 to 6, wherein 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.

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 having a clear boundary, but also to a layer having 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.

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/Al ₂ O ₃ 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 two or more may be used in combination.

The thickness of the electrode and 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 still functioning as an electrode. If the thickness is 1000 nm or less, the light transmittance can be further improved. A more preferred lower limit for the thickness of the electrode and counter electrode is 50 nm and a more preferred upper limit is 500 nm.

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.

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 ( _CH3NH3 )), 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.

The above-mentioned M is a metal atom and is a lead or tin atom. These metal atoms may be used alone or in combination of two or more types.

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

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.

The organic-inorganic perovskite compound is preferably a crystalline semiconductor. A crystalline semiconductor refers to a semiconductor in which a scattering peak can be detected by measuring the 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.

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 by fitting, determining the respective intensity integrals, and calculating the ratio of the crystalline parts 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 mobility of electrons 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.

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, or the like. Further examples include compounds having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, or a benzoporphyrin skeleton, or a spirobifluorene skeleton, as well as carbon-containing materials such as carbon nanotubes, graphene, and fullerene, which may be surface-modified.

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 .

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 it may be 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.

The preferred lower limit of the thickness of the photoelectric conversion layer is 5 nm, and the preferred upper limit is 5,000 nm. If the thickness is 5 nm or more, sufficient light absorption is possible, resulting in high photoelectric conversion efficiency. If the thickness is 5,000 nm or less, the occurrence of regions where charge separation is not possible 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 1,000 nm, an even more preferred lower limit is 20 nm, and an even more preferred upper limit is 500 nm.

When the photoelectric conversion layer is a composite film formed by combining an organic semiconductor or inorganic semiconductor portion 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.

The method for forming the photoelectric conversion layer is not particularly limited, and examples 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 achieve high photoelectric conversion efficiency. Examples of printing methods include spin coating and casting, and examples of methods using printing include roll-to-roll methods.

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, naphthalene tetracarboxylic 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.

The electron transport layer may consist solely of 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 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, as this results in a more complex composite film (a more intricate and intricate structure) and higher photoelectric conversion efficiency.

The preferred lower limit of the thickness of the electron transport layer is 1 nm, and the preferred upper limit is 2000 nm. If the thickness is 1 nm or more, holes can be sufficiently blocked. If the thickness is 2000 nm or less, resistance during electron transport is unlikely to occur, resulting in high photoelectric conversion efficiency. A more preferred lower limit of the thickness of the electron transport layer is 3 nm, and a more preferred upper limit is 1000 nm, and an even more preferred lower limit is 5 nm, and an even more preferred upper limit is 500 nm.

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 low-molecular-weight organic semiconductors, p-type metal oxides, p-type metal sulfides, surfactants, etc. 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, 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. Molybdenum sulfide, tungsten sulfide, copper sulfide, tin sulfide, etc. Fluoro-containing phosphonic acid, carbonyl-containing phosphonic acid, and copper compounds such as CuSCN and CuI.

The power generation 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. From the standpoint of flexibility and transparency, it is preferable that the substrate contain polyethylene terephthalate, polyethylene, polypropylene, polyethylene naphthalate, polymethyl methacrylate, polystyrene, or polycarbonate. Note that, in this specification, the substrate is not included in the power generation unit.

The substrate preferably has a thickness of 30 μm or more and 200 μm or less.
When the thickness of the substrate is within the above range, even when the substrate is in contact with the flame-retardant layer described below, the flame-retardant layer is less likely to come into contact with the power generation section by wrapping around the side surface of the substrate, 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 substrate 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 substrate is more preferably 150 μm or less, and even more preferably 100 μm or less.

The flexible solar cell of the present invention has a sealing material that seals the power generation section.
By encasing and sealing the power generation section in a sealing material, deterioration of the power generation section due to components in the atmosphere can be suppressed.

Examples of sealing materials that make up the sealing material include thermosetting resins, thermoplastic resins, and inorganic materials. Examples of 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.

The flexible solar cell of the present invention has a flame-retardant layer. By having the flame-retardant layer in the flexible solar cell, the flame retardancy, particularly the flame retardancy in the planar direction, can also be improved.
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.

The flame-retardant layer contains a resin material.
The resin material is the main component (the component with the highest content) of the flame-retardant layer, and 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.

The content of the resin material in the flame-retardant layer is not particularly limited, but is preferably 50% by weight or more, more preferably 60% by weight or more, and is preferably 99% by weight or less, more preferably 90% by weight or less.

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

The flame-retardant layer contains a flame-retardant material.
The flame-retardant layer contains a flame-retardant material, which provides 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 when added to the resin material.

The flame-retardant material is preferably liquid at 23°C.
When the flame-retardant material is liquid at room temperature, it is more compatible with the resin material, and therefore the flame retardancy can be improved while further suppressing a decrease in the transparency of the flame-retardant layer. Examples of the flame-retardant material that is liquid at 23°C include the halogen-based flame retardants described above.

When the flame-retardant material is a halogen-based flame retardant, the halogen-based flame retardant preferably has a halogen atom content (composition ratio) of 30% or more and 60% or less.
When 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 the resin material. 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.

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.
When the content of the flame-retardant material is within the above range, the flame retardancy can be further improved and the decrease in the transparency of the flame-retardant layer can be further suppressed. 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.

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.

When the flame-retardant layer is disposed on the upper surface of the power generation section, the flame-retardant layer preferably has a transmittance of 85% or more and 100% or less for light in the wavelength range of 500 nm to 1000 nm.
By ensuring that the light transmittance of the flame-retardant layer is within the above range, the degradation of power generation performance due to the presence of the flame-retardant material can be further suppressed. 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 achieving the light transmittance of the flame-retardant layer 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 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.

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.

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 thickness ratio of the power generation unit to sealing material).
The thickness of each of the sealing materials laminated on the upper and/or lower sides of the power generation unit is within the above-mentioned range relative to the thickness of the power generation unit, i.e., the sealing material seals the periphery of the power generation unit to a certain thickness or more, making it more difficult for the flame-retardant material in the flame-retardant layer to reach the power generation unit, thereby further suppressing deterioration in power generation performance. The thickness ratio of the power generation unit to the sealing material is more preferably 1:1 or more, and more preferably 4:1 or less.

The thickness ratio of the flame-retardant layer to the sealing material (flame-retardant layer:sealant) is preferably 10:90 or more and 50:50 or less (hereinafter also referred to as the flame-retardant layer-sealant thickness ratio).
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.

From the viewpoint of balancing the protection performance of the power generation unit with 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, and even more preferably 200 μm or more, and is preferably 1000 μm or less, and more preferably 700 μm or less. Note that the total thickness of the sealing material and the flame-retardant layer refers to the sum of the thicknesses of the power generation unit and the blocking layer, as will be described later, in the region where the power generation unit and the blocking layer are disposed.

The flexible solar cell of the present invention has a blocking layer disposed between the power generation section and the flame-retardant layer.
In conventional flexible solar cells that use 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, by disposing a blocking layer between the flame-retardant layer containing the flame-retardant material and the power generation section, contact between the flame-retardant material and the power generation section can be prevented, thereby preventing a decrease in power generation performance.

The blocking layer contains a resin having at least one of a crystallinity and a glass transition temperature higher than those of the resin material.
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.

The resin of the block layer is not particularly limited as long as it has at least one of a higher crystallinity or a higher glass transition temperature than the resin material, is flexible, and, when placed 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 foil, and thin glass sheets. From the standpoints of flexibility and transparency, it is preferable that the block layer contain polyethylene terephthalate, polyethylene, polypropylene, polyethylene naphthalate, polymethyl methacrylate, polystyrene, or polycarbonate.

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

The blocking layer may be the base material, 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. The blocking layer may also cover the side surfaces of the power generation unit in addition to the top or bottom surface. Furthermore, the blocking layer and the power generation unit do not necessarily need to be in direct contact; the sealing material may be arranged between the blocking layer and the power generation unit.

The resin constituting the blocking 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.

The resin constituting the block layer preferably has a glass transition temperature difference of 20° C. or more than 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.

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.

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

In the flexible solar cell of the present invention, the average distance from the power generation section to the interface between the flame-retardant layer and the sealing material 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 layer and the sealing material is within the above range, the flame-retardant material in the flame-retardant layer is less likely to reach the power generation section, thereby 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 layer are not in contact; when the power generation section and the flame-retardant layer are in contact (when the interface is on the side of the power generation section), there is no interfacial distance.

In the flexible solar cell of the present invention, the shortest distance from the power generation section to the flame-retardant layer is preferably 100 μm or more.
By ensuring that the shortest interfacial distance to the flame-retardant layer is 100 μm or more, even if the flame-retardant material in the flame-retardant layer diffuses into the encapsulant, it is difficult for the flame-retardant material to reach the power generation section, thereby preventing a decrease in power generation performance. Furthermore, although the overall thickness of the flexible solar cell increases, as long as the shortest distance to the flame-retardant layer is met, contact between the flame-retardant material and the power generation section is unlikely to occur, even without providing a blocking layer between the flame-retardant layer and the power generation section, thereby preventing a decrease in power generation performance.
That is, the effects of the present invention can be achieved even with a flexible solar cell having a power generation unit, a sealing material that seals the entire power generation unit, and a flame-retardant layer that is in contact with the sealing material, wherein 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, and the flame-retardant layer contains a flame-retardant material, and the shortest distance from the power generation unit to the flame-retardant layer is 100 μm or more.

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; the longer the distance, the more likely it is to prevent a decrease in power generation performance due to the flame-retardant material. However, from the perspective of making flexible solar cells thinner, it is preferably 1000 μm or less.

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.

The material for the front sheet is not particularly limited as long as it is transparent, and examples 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 due to their excellent weather resistance.

The thickness of the front sheet is not particularly limited, but from the viewpoint of the balance between light transmittance and the 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.

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.

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

Here, Figures 1 to 4 show schematic diagrams illustrating an example of the structure of a flexible solar cell of the present invention, and Figures 5 and 6 show schematic diagrams illustrating an example of the structure of a flexible solar cell having a minimum interfacial distance to the flame-retardant layer. The flexible solar cell shown in Figure 1 has a power generation unit 1 including an electrode 13, a photoelectric conversion layer 12, and a counter electrode 11; a flame-retardant layer 3; a blocking layer 2 disposed between the power generation unit 1 and the flame-retardant layer 3; and a sealing material 4 that seals the power generation unit 1. A front sheet 5 and a back sheet 6 are disposed at the top and bottom. The power generation unit 1 is in contact only with the sealing material 4, not with the flame-retardant layer 3. The blocking layer 2 prevents the flame-retardant layer 3 from coming into direct contact with the power generation unit 1. By arranging the layers in this way and by ensuring that at least one of the crystallinity or glass transition temperature of the resin constituting the blocking layer 2 is higher than that of the resin material constituting the flame-retardant layer 3, the flame-retardant material is less likely to come into contact with the power generation unit 1, thereby enhancing flame retardancy in the planar direction while suppressing deterioration of the power generation unit 1.

In the flexible solar cell shown in Figure 2, the blocking layer 2 is arranged on the electrode 13 side of the power generation unit 1. Furthermore, because the blocking layer 2 is arranged below the power generation unit 1, the flame-retardant layer 3 is also arranged below. In the flexible solar cell shown in Figure 3, the blocking layer 2 is arranged on both sides of the power generation unit 1. This arrangement can further prevent deterioration of the power generation unit 1. In the flexible solar cell shown in Figure 4, the blocking layer 2 covers the electrode 13 side of the power generation unit 1 and the side surfaces of the power generation unit 1. By covering the side surfaces of the power generation unit 1 with the blocking layer 2, it becomes more difficult for the flame-retardant layer 3 that has wrapped around to the side surfaces of the blocking layer 2 to reach the power generation unit 1, thereby preventing deterioration of the power generation unit 1.

The flexible solar cell shown in Figure 5 is a flexible solar cell with a minimum interfacial distance to the flame-retardant layer of at least a certain level, and has a structure in which flame-retardant layers 3 are laminated above and below the encapsulant 4. Furthermore, the minimum distance from the electrode 13 and counter electrode 11 to the flame-retardant layer 3 is at least 100 μm. This structure further enhances flame retardancy in the planar direction and makes it difficult for the flame-retardant material in the flame-retardant layer 3 to reach the power generation unit 1 even if it diffuses into the encapsulant 4, thereby suppressing a decrease in power generation performance. The flexible solar cell shown in Figure 6 does not have a blocking layer disposed between the flame-retardant layer 3 and the power generation unit 1, and instead has a structure in which the flame-retardant layer 3 and the power generation unit 1 are separated by the encapsulant 4. Like the flexible solar cell of Figure 5, the flexible solar cell of Figure 6 has a minimum interfacial distance to the flame-retardant layer of at least 100 μm, thereby suppressing a decrease in power generation performance while exhibiting high flame retardancy in the planar direction. Note that in the flexible solar cell of Figure 6, the blocking layer 2 is not laminated on the flame-retardant layer 3 side, and therefore does not contribute to the effects of the present invention.

The method for manufacturing the flexible solar cell of the present invention is not particularly limited, but a method in which the power generating unit 1 is sandwiched between a sheet (sheet A) having a flame-retardant layer 3 and, if necessary, a sealant 4 and a front sheet 5, and a sheet (sheet B) having a sealant 4 and, if necessary, a flame-retardant layer 3 and a back sheet 6, and then laminated, as shown in Figure 7, is preferred because it allows for easy manufacturing over a large area.

When the flexible solar cell has a structure as shown in Figure 1, the above-mentioned sheet A can be obtained by laminating a flame-retardant layer on the front sheet. Also, when the flexible solar cell has a structure as shown in Figure 5, the sheet A can be obtained by laminating a flame-retardant layer on the front sheet and then laminating an encapsulant 4 on it. Furthermore, when the flexible solar cell has an adhesive layer that bonds the encapsulant and front sheet, the adhesive layer is laminated on the front sheet before laminating the flame-retardant layer.

The power generation unit can be obtained by sequentially stacking layers such as an electrode, electron transport layer, photoelectric conversion layer, hole transport layer, and counter electrode on a substrate (blocking layer). It can also be obtained by stacking each layer on an electrode instead of a substrate. Conventional methods can be used to stack each layer, with no particular restrictions.

When the flexible solar cell has the structure shown in Figure 1, the above-mentioned sheet B can be obtained by laminating an encapsulant onto a backsheet. Furthermore, when there is no backsheet, it can be obtained by laminating an encapsulant by coating or the like.

One example of a method for laminating sheet A, the power generation unit, and sheet B is the roll-to-roll method. Using the roll-to-roll method, large-area flexible solar cells can be continuously manufactured.

The present invention makes it possible to provide a flexible solar cell that exhibits excellent flame retardancy in the planar direction while minimizing degradation of power generation performance.

1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. 1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. 1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. 1 is a schematic diagram showing an example of the structure of a flexible solar cell of the present invention. 1 is a schematic diagram showing an example of the structure of a flexible solar cell in which the shortest interfacial distance to the flame-retardant layer is equal to or greater than a certain distance. 1 is a schematic diagram showing an example of the structure of a flexible solar cell in which the shortest interfacial distance to the flame-retardant layer is equal to or greater than a certain distance. 1A to 1C are schematic diagrams illustrating an example of the production of a flexible solar cell of the present invention.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

Example 1
<Manufacturing flexible solar cells>
A 100 μm-thick polyethylene terephthalate (PET) film (crystallinity: 60%, glass transition temperature: 70°C) 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 formed on the formed counter electrode by sputtering. Furthermore, a titanium oxide paste containing titanium oxide was applied to the thin-film electron transport layer by spin coating and then dried to form a 100 nm-thick porous electron transport layer. Next, lead iodide, as 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, as an amine compound, was dissolved in 2-propanol to prepare an 8 wt % solution. This solution was applied to the lead iodide substrate by spin coating, followed by annealing 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 (manufactured by Merck) was applied to the photoelectric conversion layer by spin coating, followed by drying to form an 80 nm thick hole transport layer. A 100 nm thick Al film was then formed as an electrode on the photoelectric conversion layer by sputtering, yielding a laminate in which a power generation unit consisting of a counter electrode, electron transport layer, photoelectric conversion layer, hole transport layer, and electrode was formed on the blocking layer.

Next, a 50 μm-thick PET sheet was prepared as the front sheet. Next, 10 wt% of the flame-retardant material, Enpara 40 (chlorinated paraffin, chlorine content 40-42%, manufactured by Ajinomoto Fine-Techno Co., Inc.), was added to the main component, polyisobutylene (crystallinity: 40%, glass transition temperature: -70°C), to prepare a flame-retardant-containing resin. This resin was then applied to the front sheet to a thickness of 100 μm, yielding Sheet A with a 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 obtain Sheet B. The laminate was then sandwiched between Sheets A and B and laminated so that the flame-retardant layer of Sheet A faced the block layer, and the encapsulant of Sheet B faced the power generation section. This resulted in a flexible solar cell with the structure shown in Figure 1, in which the flame-retardant layer was laminated on the block layer side. The cross section of the resulting flexible solar cell was observed using an electron microscope, and the shortest distance to the flame-retardant layer was measured.

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.
Empara 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.

(Reference example 1)
A laminate was obtained in the same manner as in Example 1. Next, a 360 μm thick aluminum-containing back sheet (manufactured by Toyo Aluminum Co., Ltd., FAPL) was prepared as the back sheet. A flame-retardant material-containing resin was prepared on the back sheet by adding 10 wt% of the flame-retardant material, Enpara A-1, to the main component, polyisobutylene (crystallinity: 40%, glass transition temperature: -70°C). This resin was then applied to the front sheet to a thickness of 100 μm to form a flame-retardant layer. Sheet A, which had a flame-retardant layer, was then applied to the formed flame-retardant layer with an encapsulant consisting solely of polyisobutylene to a thickness of 100 μm. Meanwhile, a 50 μm thick PET sheet was prepared as the front sheet, and a 70 μm encapsulant was applied to obtain Sheet B. The laminate was then sandwiched between Sheet A and Sheet B and laminated so that the flame-retardant layer of Sheet A faced the power generation section, and the encapsulant of Sheet B faced the block layer. This produced a flexible solar cell having the structure shown in FIG. 6. In addition, since the blocking layer of the obtained flexible solar cell was on the sheet B side, it was not necessary to consider changes in thickness due to the sealing material wrapping around the side of the blocking layer, and therefore the thickness of the sealing material of sheet A was used as the shortest interface distance.

(Reference Examples 2 to 6, Comparative Examples 7 and 8)
A flexible solar cell was obtained in the same manner as in Reference Example 1, except that the thickness of the encapsulant applied during the production of Sheet A was adjusted to set the shortest distance to the flame-retardant layer as shown in Table 1, and the flame-retardant material used was as shown in Table 1.

(Comparative Examples 1 to 5)
A flexible solar cell in which the laminate was sealed only with a flame-retardant layer 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 a resin containing a flame-retardant material.

(Comparative Example 6)
A flexible solar cell in which the laminate was sealed only with the sealing material was obtained in the same manner as in Example 1, except that only the sealing material (polyisobutylene) was applied to the front sheet.

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

(1) Evaluation of Flame Retardancy: 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 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 as "Poor" if the fire spread distance exceeded 15 cm. Comparative Example 6 did not have a flame-retardant layer, so it was evaluated using an encapsulant.

(2) Evaluation of Light Transmittance One of the sheets A and B, which included a flame-retardant layer, was prepared using the method described above 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 above the power generation section was evaluated by marking it as "○" if the transmittance in the 400-1000 nm range of the obtained absorption spectrum was 85% or higher, and "×" if it was less than 85%. Note that evaluation was performed using Sheet A for Comparative Example 6.

(3) Evaluation of Durability Immediately after manufacturing the flexible solar cell, a power supply (KEITHLEY, Model 236) was connected between the electrodes of the flexible solar cell, and the photoelectric conversion efficiency was measured using a solar simulator (Yamashita Denso Co., Ltd.) with an intensity of 100 mW/cm ^2. The obtained photoelectric conversion efficiency was calculated relative to Comparative Example 6, which was set to 1, and this was defined 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 performed by conducting 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 maintenance rate from the initial conversion efficiency was calculated. Durability was evaluated as follows: a maintenance rate of 90% or more was evaluated as "◎", a maintenance rate of 80% or more but less than 90% was evaluated as "○", a maintenance rate of 70% or more but less than 80% was evaluated as "△", and a maintenance rate of less than 70% was evaluated as "×".

The present invention makes it possible to provide a flexible solar cell that exhibits excellent flame retardancy in the planar direction while minimizing degradation of power generation performance.

REFERENCE SIGNS LIST 1 power generation section 11 counter electrode 12 photoelectric conversion layer 13 electrode 2 substrate 3 flame retardant layer 4 sealing material 5 front sheet 6 back sheet

Claims (7)

A flexible solar cell having a power generation unit, a flame-retardant layer, a blocking layer disposed between the power generation unit and the flame-retardant layer, and a sealing material that seals the power generation unit,
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 resin material and a flame-retardant material,
The flexible solar cell is characterized in that the blocking layer contains a resin having at least one of a crystallinity and a glass transition temperature higher than those of the resin material. The flexible solar cell described in claim 1, characterized in that the interface between the power generation section and the blocking layer is in contact only with the sealing material. The flexible solar cell of claim 1, wherein the blocking layer is in contact with the flame-retardant layer. A flexible solar cell according to any one of claims 1 to 3, characterized in that the average distance from the power generation section to the interface between the flame-retardant layer and the sealing material is 10 μm or more and 100 μm or less. A flexible solar cell as described in any one of claims 1 to 4, characterized in that the flame-retardant layer is arranged on the upper surface side of the power generation section. A flexible solar cell according to any one of claims 1 to 5, characterized in that the flame-retardant material contains chlorine atoms. A flexible solar cell as described in any one of claims 1 to 6, characterized in 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.