Flexible solar cell

Abstract

The objective of the present invention is to provide a solar cell that is easy to manufacture, has sheet glass that does not break readily even when made over a large area, and has excellent durability in high-temperature and high-humidity conditions. The present invention is a flexible solar cell having an electricity-generating part (1), an encapsulating layer (2), and a sheet glass layer (3) located on the upper-face side of the electricity-generating part (1) and covering over the upper face of the electricity-generating part (1), wherein the lower and lateral faces of the sheet glass layer (3) are encapsulated by the encapsulating layer (2) while the upper face of the sheet glass layer (3) is encapsulated by the encapsulating layer (2) or an adhesive layer (5).

Description

flexible solar cells

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

[0002] Conventionally, solar cells have been actively developed based on stacked bodies 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 primarily used as the N-type and P-type semiconductors. However, such inorganic solar cells have been problematic in that they are costly to manufacture and difficult to enlarge, limiting their range of application. Therefore, in recent years, attention has been focused on perovskite solar cells, which use organic-inorganic perovskite compounds having a perovskite structure with 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 a printing method, thereby significantly reducing manufacturing costs.

[0003] Meanwhile, 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 resistance to impact. For example, they are manufactured by laminating, in a thin film form, multiple layers, such as a photoelectric conversion layer that generates current when irradiated with light, on a flexible substrate. Furthermore, if necessary, the upper and lower surfaces of the flexible solar cell are sealed by laminating solar cell encapsulant sheets. For example, Patent Document 2 describes a substrate for a semiconductor device including a sheet-like aluminum substrate, and an organic thin-film solar cell including this substrate for a semiconductor device.

[0004] JP 2014-72327 A JP 2013-253317 A

[0005] M. M. Lee, et al., Science, 2012, 338, 643

[0006] Such flexible solar cells require high water vapor barrier performance to ensure long-term stability. Conventional flexible solar cells use thin glass as the base material for the power generation section to achieve both water vapor barrier properties and flexibility, and each layer of the power generation section is sequentially laminated on the thin glass to protect the power generation section from atmospheric moisture. However, because the thin glass is made as thin as possible to ensure flexibility, it has problems such as being easily broken during manufacturing, installation, and use, and its durability under high temperatures and high humidity is easily reduced. In particular, flexible solar cells have been increasing in area in recent years. As the area increases, it becomes difficult to uniformly support and compress the entire thin glass during transportation during the thin film glass manufacturing process and during the lamination process with a backsheet, etc., resulting in a very high probability of the thin glass breaking. Therefore, there is a demand for flexible solar cells that are easy to manufacture and that use thin glass that is less likely to break, even when the thin glass is large in area.

[0007] An object of the present invention is to provide a solar cell that is easy to manufacture, has thin glass that is resistant to cracking even when made large, and has excellent durability against high temperatures and high humidity.

[0008] The present invention includes the following Disclosures 1 to 7. The present invention is described in detail below. [Disclosure 1] A flexible solar cell comprising a power generation section, a sealing layer, and a thin glass layer disposed on the upper surface of the power generation section and covering the upper surface of the power generation section, wherein the bottom and side surfaces of the thin glass layer are sealed by the sealing layer, and the top surface is sealed by the sealing layer or adhesive layer. [Disclosure 2] The flexible solar cell according to Disclosure 1, which has a front sheet on the sealing layer or adhesive layer, and the front sheet is laminated on the top surface of the thin glass layer via the sealing layer or adhesive layer. [Disclosure 3] The flexible solar cell according to Disclosure 1 or 2, wherein the adhesive resin constituting the adhesive layer is the same as the sealing resin constituting the sealing layer. [Disclosure 4] The flexible solar cell according to any of Disclosures 1 to 3, wherein the minimum distance between the bottom surface of the thin glass layer and the power generation section is 1 μm or more. [Disclosure 5] The flexible solar cell according to any of Disclosures 1 to 4, wherein the power generation section contains an organic-inorganic perovskite compound. [Disclosure 6] The flexible solar cell according to any one of Disclosures 1 to 4, wherein the flexible solar cell includes an adhesive layer, the power generation section includes an organic-inorganic perovskite compound, and the adhesive resin constituting the adhesive layer has an SP value of 6 or more and 10 or less. [Disclosure 7] The flexible solar cell according to any one of Disclosures 1 to 4, wherein the flexible solar cell includes an adhesive layer, the power generation section includes an organic-inorganic perovskite compound, and the adhesive resin constituting the adhesive layer is polyisobutylene.

[0009] The flexible solar cell of the present invention has a power generation section. The power generation section is a section that converts sunlight into electricity and is composed of a substrate, 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 counter electrode, and a photoelectric conversion layer. In this specification, "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 measurement of a cross section of a solar cell to confirm the element distribution of a specific element. In addition, in this specification, "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.

[0010] The substrate is not particularly limited as long as it has flexibility, and examples thereof include resin films made of heat-resistant polymers such as polyimide and polyester, metal foils, thin glass sheets, etc. Among these, PET resin films are preferred from the viewpoints of cost and heat resistance.

[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, and Al / Al ２ O ３ Examples of the material include a mixture of Al and LiF, an Al / LiF mixture, etc. Examples also include gold, silver, titanium, molybdenum, tantalum, tungsten, carbon, nickel, chromium, etc. These materials may be used alone or in combination of two or more.

[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 preferably contains an organic-inorganic perovskite compound 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). Such a solar cell in which the power generation section contains an 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 further improved.

[0014] 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 (CH ３ NH ３ ) and phenethylammonium. Among 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 presence of this structure makes it easy to change the orientation of the octahedrons in the crystal lattice, 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. By crystalline semiconductor, we mean 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. The degree of crystallinity can be determined by separating the scattering peaks derived from crystalline materials and the halo derived from amorphous portions detected by X-ray scattering intensity distribution measurement by fitting, determining the respective intensity integrals, and calculating the ratio of the crystalline portion to the total. The preferred lower limit of the degree of 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. The more preferred lower limit of the degree of crystallinity is 50%, and even more preferred is 70%. Methods for increasing the degree of crystallinity of the organic-inorganic perovskite compound include, for example, thermal annealing, irradiation with high-intensity light such as a 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, polyvinyl carbazole skeleton, polyaniline skeleton, polyacetylene skeleton, etc. Other 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 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, and Cu. ２ O, CuI, MoO ３ , V ２ O ５ , W.O. ３ , MoS ２ , MoSe ２ , Cu ２ Examples include S.

[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 thin-film organic-inorganic perovskite compound portion is preferably 5 nm at the lower limit and 5000 nm at the upper limit. 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. The thickness is more preferably 10 nm at the lower limit and 1000 nm at the upper limit, and even more preferably 20 nm at the lower limit and 500 nm at the upper limit.

[0024] When the photoelectric conversion layer is a composite film in which an organic semiconductor or inorganic semiconductor portion and an organic-inorganic perovskite compound portion are combined, 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 possible, resulting in high photoelectric conversion efficiency. If the thickness is 3000 nm or less, charges can easily reach the electrode, resulting in high photoelectric conversion efficiency. A more preferred lower limit of the thickness is 40 nm, a more preferred upper limit is 2000 nm, an even more preferred lower limit is 50 nm, and an even more preferred upper limit is 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 a printing method makes it possible to easily form a large-area solar cell 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 generation unit may have an electron transport layer between the cathode or counter electrode and the photoelectric conversion layer. The material of 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, etc. 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.

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

[0029] The power generation section may have a hole transport layer between the electrode serving as the anode / cathode 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, or the like; molybdenum sulfide, tungsten sulfide, copper sulfide, tin sulfide, or the like; 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 an encapsulating layer. By wrapping the periphery of the power generation unit with the encapsulating layer, deterioration of the power generation unit due to components in the atmosphere can be suppressed. Examples of the encapsulating resin constituting the encapsulating layer include thermosetting resins and thermoplastic resins. Examples of the thermosetting resin or thermoplastic resin include epoxy resin, acrylic resin, silicone resin, phenolic resin, melamine resin, and urea resin. 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 because, when the photoelectric conversion efficiency is improved by including an organic-inorganic perovskite compound, the organic components of the organic-inorganic perovskite compound are less likely to dissolve.

[0031] The content of the sealing resin in the sealing layer is not particularly limited as long as it can exhibit its performance as a sealing layer, and for example, it is preferably 50% by weight or more, more preferably 80% by weight or more, and may be 100% by weight, based on 100% by weight of the sealing layer.

[0032] The flexible solar cell of the present invention has a thin glass layer disposed on the upper surface of the power generation section and covering the upper surface of the power generation section. By having a thin glass layer on the upper surface of the power generation section, the resulting flexible solar cell can be endowed with high water vapor barrier performance. Furthermore, the thin glass layer is thin, ensuring flexibility. In this specification, the term "top surface" refers to the surface in the direction in which light is incident when the flexible solar cell is installed, and the term "bottom surface" refers to the direction opposite to the "top surface," i.e., the surface on the installation side when the flexible solar cell is installed. Furthermore, the term "side surface" refers to the surface parallel to the thickness direction of the flexible solar cell.

[0033] Examples of glass constituting the thin glass layer include soda glass, lead glass, borosilicate glass, alkali-free glass, etc. Among these, alkali-free glass is preferred because it allows for a thinner thin glass layer to be formed.

[0034] The thickness of the thin glass layer is not particularly limited as long as it can ensure the flexibility of the resulting flexible solar cell, but from the viewpoint of the balance between flexibility and strength, it is preferably 10 μm or more, more preferably 30 μm or more, and is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 100 μm or less.

[0035] The thin glass layer has a water vapor permeability of 1×10 －３ g / m ２ When the water vapor transmission rate of the thin glass layer is in the above range, the water vapor barrier performance can be further improved. The water vapor transmission rate of the thin glass layer is preferably 1×10 －４ g / m ２ / day or less, more preferably 1 x 10 －５ g / m ２The lower limit of the water vapor transmission rate of the thin glass layer is not particularly limited, and the lower the better. －６ g / m ２ The water vapor transmission rate can be measured by a differential pressure method in accordance with the gas chromatography method of JIS K7129, under conditions of a temperature of 85°C, a humidity of 85%, and a sample thickness of 100 μm to 200 μm, with the surface actually located outside the module being used as the water vapor inlet surface.

[0036] The thin glass layer preferably has a modulus of longitudinal elasticity of 10,000 MPa or more and 100,000 MPa or less. When the modulus of longitudinal elasticity of the thin glass layer is within the above range, the flexibility of the flexible solar cell can be further increased. The modulus of longitudinal elasticity of the thin glass layer is more preferably 30,000 MPa or more, even more preferably 50,000 MPa or more, more preferably 90,000 MPa or less, and even more preferably 80,000 MPa or less. The modulus of longitudinal elasticity can be measured by a tensile test or a compression test.

[0037] The thin glass layer preferably has a Vickers hardness of 400 HV or more and 1000 HV or less. Having a Vickers hardness within the above range of the thin glass layer allows it to have impact resistance. The Vickers hardness of the thin glass layer is more preferably 500 HV or more, even more preferably 600 HV or more, more preferably 800 HV or less, and even more preferably 700 HV or less. The Vickers hardness can be determined, for example, by pressing an indenter into the thin glass layer using a nanoindenter (such as G200, manufactured by Keysight Technologies) and calculating from the resulting load-displacement curve.

[0038] The thin glass layer has an areal density of 60 g / m ２ More than 1000g / m ２ When the surface density of the thin glass layer is in the above range, the flexibility of the flexible solar cell can be further improved. The surface density of the thin glass layer is preferably 100 g / m or less. ２More preferably, it is 200 g / m or more. ２ More preferably, it is 800 g / m or more. ２ More preferably, it is 600 g / m or less. ２ It is more preferable that the surface density is not more than 100%. The surface density can be calculated from the density and film thickness of the thin glass layer.

[0039] The thin glass layer preferably covers 80% or more of the power generation section when the flexible solar cell is viewed in plan from the top side. Covering this range of the power generation section with the thin glass layer can better prevent moisture from entering the power generation section, thereby further improving water vapor barrier performance. The thin glass layer more preferably covers 100% or more of the power generation section when viewed in plan from the light-receiving surface side, and even more preferably covers 120% or more. There is no particular upper limit to the area covered by the thin glass layer, but it is preferably 130% or less of the power generation section from the viewpoints of cost and preventing the thin glass layer from being cut in the cutting process after lamination, which will be described later.

[0040] The thin glass layer is sealed at its bottom and side surfaces by the sealing layer, and at its top surface by the sealing layer or adhesive layer. Conventional flexible solar cells using thin glass have a structure in which the thin glass layer and the power generation section are laminated on top of the thin glass as a substrate, resulting in direct contact between the thin glass layer and the power generation section. Flexible solar cells with this structure are prone to cracking during manufacturing because the thin glass also undergoes the same harsh conditions and complex processes as those used to form the power generation section. Furthermore, in the case of large-area flexible solar cells in particular, the thin glass becomes more prone to cracking due to the increased area, making the thin glass more prone to cracking during installation and use.

[0041] On the other hand, in the flexible solar cell of the present invention, the entire thin glass layer is sealed by a sealing layer alone or by a sealing layer and an adhesive layer, and the thin glass layer and the power generation unit are separated by the sealing layer. Therefore, a flexible solar cell can be manufactured by bonding the power generation unit to the thin glass layer sealed by the sealing layer. The process of bonding thin glass sheets is much simpler than the process of forming a power generation unit on thin glass sheets, facilitating manufacturing. Furthermore, the number of steps involving the portion having thin glass sheets is reduced, making the thin glass sheet less likely to break during manufacturing. Furthermore, in the flexible solar cell of the present invention, the entire surface of the thin glass sheet is covered by a sealing layer alone or by a sealing layer and an adhesive layer, imparting a certain degree of elasticity to both sides of the thin glass sheet. As a result, the thin glass layer is less likely to break than conventional flexible solar cells in which the power generation unit is formed on thin glass sheets, thereby reducing breakage of the thin glass sheet during installation and use and improving durability. Furthermore, even if small cracks such as pinholes exist in the thin glass layer, the sealant or adhesive layer fills the cracks when the thin glass sheets are bonded, so that even if the cracks are small, a decrease in high-temperature, high-humidity durability can be suppressed. Even when the thin glass layer and the power generating unit are in direct contact with each other, it is possible to reduce the number of steps involving the thin glass layer by separately preparing the power generating unit and laminating it on the thin glass layer. However, if there is no sealing layer between the power generating unit and the thin glass, air bubbles will form between the power generating unit and the thin glass layer when the power generating unit is laminated, making it difficult for light to transmit, resulting in a significant decrease in photoelectric conversion efficiency.

[0042] Furthermore, since the thin glass layer is made of glass, it has a small coefficient of linear expansion, while the sealing layer and adhesive layer are often made of organic materials and have a high coefficient of linear expansion. Therefore, the adhesion between the thin glass layer and the sealing layer or adhesive layer is likely to decrease at the interface, and if the interface is exposed, moisture is likely to penetrate through it. In the flexible solar cell of the present invention, the side surfaces of the thin glass layer are covered with the sealing layer alone or with the sealing layer and the adhesive layer, so that the interface between the thin glass layer and the sealing layer or adhesive layer is not exposed, thereby further improving high-temperature and high-humidity durability.

[0043] Furthermore, since flexible solar cells are fixed in a flat state by pulling the edges, a process is performed to cut the edges after stacking each layer and remove any sealing layer or other layers that protrude from the sides, from the perspective of ease of handling during installation. In this process, cutting the portion where the thin glass layer is located can result in the thin glass layer cracking. Cracks in the thin glass caused by cutting tend to spread throughout the entire thin glass sheet. Furthermore, since there is no process of applying strong pressure to the thin glass sheet after cutting, the sealing layer is less likely to fill the cracks in the thin glass sheet, resulting in a significant decrease in high-temperature, high-humidity durability. In the flexible solar cell of the present invention, the sides of the thin glass sheet are sealed by a sealing layer alone or a sealing layer and an adhesive layer. In other words, the thin glass layer is not cut during the cutting process, which further reduces the risk of cracking the thin glass sheet.

[0044] The distance from the side surface of the thin glass layer to the side surface of the flexible solar cell is preferably 1 mm or more. When the distance from the side surface of the thin glass layer to the side surface of the flexible solar cell is within the above range, the sealing of the side surface of the thin glass sheet is more robust, and high-temperature, high-humidity durability can be further improved. The distance from the side surface of the thin glass layer to the side surface of the flexible solar cell is more preferably 2.5 mm or more, and even more preferably 5 mm or more. There is no particular upper limit to the distance from the side surface of the thin glass layer to the side surface of the flexible solar cell, but from the perspective of increasing the power generation area, 50 mm or less is preferred.

[0045] From the viewpoint of a balance between the protection performance of the power generation section and flexibility, the thickness of the sealing layer is preferably 10 μm or more, more preferably 50 μm or more, and is preferably 1000 μm or less, and more preferably 700 μm or less. Here, the thickness of the sealing layer refers to the maximum thickness in the portion consisting of only the sealing layer.

[0046] The sealing layer preferably has a modulus of longitudinal elasticity of 1000 MPa or less. Having the modulus of longitudinal elasticity of the sealing layer in the above range can impart flexibility to the sealing layer, allowing it to fill cracks and pinholes in the thin glass layer and further mitigate impacts on the thin glass layer. The modulus of longitudinal elasticity of the sealing layer is more preferably 500 MPa or less, and even more preferably 100 MPa or less. There is no particular restriction on the lower limit of the modulus of longitudinal elasticity of the sealing layer, but from the viewpoint of ease of production, it is preferably 1 MPa or more. The method for measuring the modulus of longitudinal elasticity of the sealing layer is the same as the method for measuring the modulus of longitudinal elasticity of the thin glass layer.

[0047] The sealing layer has a viscosity of 1000 Pa·s or less at 20°C. Having the viscosity of the sealing layer in this range can further improve the ability to fill cracks and pinholes in the thin glass layer and to mitigate impacts. The viscosity of the sealing layer at 20°C is more preferably 800 Pa·s or less, and even more preferably 600 Pa·s or less. There is no particular restriction on the lower limit of the viscosity of the sealing layer, but from the viewpoint of ease of production, it is preferably 200 Pa·s or more. The viscosity at 20°C can be measured using a BM-type rotational viscometer (BMII, manufactured by Toki Sangyo Co., Ltd. or an equivalent) at a rotation speed of 60 rpm.

[0048] The sealing layer has a water vapor permeability of 1 g / m ２ When the water vapor transmission rate of the sealing layer is in the above range, the water vapor barrier performance can be further improved. The water vapor transmission rate of the sealing layer is preferably 0.5 g / m or less. ２ / day or less, more preferably 0.1 g / m ２ The lower limit of the water vapor transmission rate of the sealing layer is not particularly limited, and the lower the better. ２ The water vapor transmission rate of the sealing layer is measured by the same method as that of the thin glass layer.

[0049] The flexible solar cell of the present invention may have a front sheet on the sealing layer or adhesive layer. The front sheet is disposed on the outermost surface of the upper surface of the flexible solar cell, and by forming a pattern such as unevenness or arcs on the surface, it serves to suppress light reflection and improve the drainage performance of the flexible solar cell surface. For example, providing a front sheet with a convex arc with an apex at the center of the flexible solar cell can provide a drainage gradient from the center to the edge of the flexible solar cell, while providing a front sheet with a concave arc with a bottom at the center of the flexible solar cell can provide a water collection area from the edge to the center of the flexible solar cell. By providing such a drainage gradient or water collection area, the accumulation of dirt and the like can be concentrated in a specific location. Furthermore, randomly forming unevenness on the front sheet can also improve design.

[0050] 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.

[0051] 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.

[0052] The front sheet is laminated on the upper surface of the thin glass layer via the sealing layer or the adhesive layer. When the thin glass layer of the flexible solar cell of the present invention is sealed with only the sealing layer, the front sheet is placed on the sealing layer covering the upper surface of the thin glass layer. On the other hand, if the sealing layer has poor adhesiveness, it is difficult to hold the front sheet in place, so the upper surface of the thin glass layer is sealed with an adhesive layer, and the front sheet is placed on the thin glass layer via the adhesive layer.

[0053] The adhesive resin constituting the adhesive layer is not particularly limited as long as it can bond the front sheet and the thin glass layer together, and examples thereof include epoxy resin, acrylic resin, silicone resin, vinyl acetate resin, and vinyl chloride resin.

[0054] The content of the adhesive resin in the adhesive layer is not particularly limited as long as it can bond the thin glass layer, but for example, it is preferably 50% by weight or more, more preferably 80% by weight or more, and preferably 100% by weight or less, more preferably 90% by weight or less, based on 100% by weight of the adhesive layer.

[0055] The adhesive layer may be formed on at least the entire upper surface of the thin glass layer, but may also be formed on the entire lower surface of the front sheet.

[0056] When the flexible solar cell of the present invention has an adhesive layer and the power generation section contains an organic-inorganic perovskite compound, the adhesive resin constituting the adhesive layer preferably has an SP value of 6 or more and 10 or less. The adhesive layer and the power generation section are separated by a sealing layer and a thin glass layer and are not in direct contact, but the adhesive resin constituting the adhesive layer may migrate and diffuse into the sealing layer. If the diffused adhesive resin reaches the power generation section, organic components in the organic-inorganic perovskite compound may dissolve into the adhesive resin at high temperatures, causing deterioration of the power generation section. When the SP value of the adhesive resin constituting the adhesive layer is within the above range, even if the adhesive resin diffuses to the power generation section, the organic components in the organic-inorganic perovskite compound are less likely to dissolve into the adhesive resin, thereby suppressing deterioration of the power generation section. The SP value of the adhesive resin constituting the adhesive layer is more preferably 6.5 or more, even more preferably 7 or more, particularly preferably 7.5 or more, more preferably 9.5 or less, and even more preferably 9 or less. The SP value is called the solubility parameter and is an index that can represent the ease of solubility. The SP value can be calculated using the method proposed by Fedors (R.F. Fedors, Polym. Eng. Sci., 14(2), 147-154 (1974)).

[0057] Examples of adhesive resins having the above SP values ​​include silicone resins (SP value of about 7.5), polyolefin resins (SP value of about 8), butyl rubber (SP value of about 8), Teflon (registered trademark) resins (SP value of about 7.5), polyisobutylene (SP value of about 7.5), acrylic resins (SP value of about 9.5), etc. Among these, polyisobutylene is preferred because it is more difficult for the organic components in the organic-inorganic perovskite compound to dissolve out.

[0058] It is preferable that the adhesive resin constituting the adhesive layer and the encapsulating resin constituting the encapsulating layer are the same. By using an encapsulating resin with high adhesiveness, in which the main component of the adhesive layer is the same as the main component (the component contained in the largest amount) of the encapsulating layer, the adhesive layer exhibits the same performance as the encapsulating layer, thereby further improving the durability of the flexible solar cell. Examples of such adhesive resins include polyisobutylene, ethylene-vinyl acetate copolymer, silicone resin, polyolefin resin, and butyl rubber.

[0059] The adhesive layer may contain additives such as a tackifier, a weathering agent, and a flame retardant, if necessary.

[0060] The flexible solar cell of the present invention may have a backsheet on the outermost surface on the lower surface side. The backsheet serves to prevent the penetration of substances that cannot be prevented by the sealing layer alone, thereby improving the weather resistance of the flexible solar cell. Examples of materials for the backsheet include polyethylene terephthalate.

[0061] The thickness of the back sheet is not particularly limited, but is preferably 50 μm or more, more preferably 100 μm or more, from the viewpoint of the balance between flexibility and functionality of the back sheet, and is preferably 1000 μm or less, more preferably 500 μm or less.

[0062] In the flexible solar cell of the present invention, the minimum distance between the lower surface of the thin glass layer and the power generation unit is preferably 1 μm or more. As described above, the adhesive resin constituting the adhesive layer may migrate and diffuse into the sealing layer, which may lead to deterioration of the power generation unit if it reaches the power generation unit. By ensuring that the minimum distance between the lower surface of the thin glass layer and the power generation unit is within the above range, i.e., by ensuring that the distance between the adhesive layer and the power generation unit is at least a certain level, even if the adhesive resin diffuses, it is difficult for it to reach the power generation unit, thereby suppressing deterioration of the power generation unit. Furthermore, even if the thin glass layer is sealed only with a sealant, ensuring that the minimum distance between the lower surface of the thin glass layer and the power generation unit is within the above range can impart appropriate elasticity to the thin glass layer and further suppress cracking of the thin glass layer. The minimum distance between the lower surface of the thin glass layer and the power generation unit is more preferably 70 μm or more, even more preferably 100 μm or more, and even more preferably 200 μm or more. There is no particular upper limit on the minimum distance between the lower surface of the thin glass layer and the power generation section, and the greater the distance the better from the viewpoint of suppressing deterioration of the power generation section. However, from the viewpoint of ensuring flexibility, it is preferably 5000 μm or less.

[0063] In the flexible solar cell of the present invention, the thickness of the sealing layer or adhesive layer sealing the upper surface of the thin glass layer is preferably 1 μm or more. When the thickness of the sealing layer or adhesive layer on the upper surface of the thin glass layer is within the above range, the thin glass layer can be imparted with appropriate elasticity, and cracking of the thin glass layer can be further suppressed. In addition, the protection performance from atmospheric components can be further improved. The thickness of the sealing layer or adhesive layer sealing the upper surface of the thin glass layer is more preferably 50 μm or more, even more preferably 100 μm or more, and preferably 5000 μm or less.

[0064] Schematic diagrams showing an example of the structure of a flexible solar cell of the present invention are shown in Figures 1 to 3. The flexible solar cell of Figure 1 has a structure in which a power generation section 1, all surfaces of which are sealed with a sealing layer 2, and a thin glass layer 3 are laminated on a back sheet 6, and a front sheet 4 is laminated on the sealing layer 2. By using such a structure in which the thin glass layer 3 and the power generation section 1 are not in direct contact, a flexible solar cell can be manufactured by bonding the thin glass layer 3, which is sealed with the sealing layer 2, to the power generation section 1. In conventional methods, the power generation section 1 is formed directly on the thin glass layer 3, which makes the thin glass layer 3 prone to cracking during the complex process of forming the power generation section 1. In particular, when forming a large-area power generation layer, such as one with a maximum side length exceeding 1 m, it is difficult to provide uniform support and compression across the entire width during transportation in the thin glass manufacturing process and during the process of pressing the thin glass with a back sheet or the like (lamination process), resulting in a very high probability of cracking. In the flexible solar cell of the present invention, since the flexible solar cell can be manufactured using the above method, the process performed on the portion having the thin glass layer 3 can be reduced to three steps: bonding to the sealing layer 2, sealing the thin glass layer 3, and bonding to the power generation section 1. As a result, the process performed on the portion having the thin glass layer 3 is significantly simpler and fewer than conventional processes, facilitating manufacturing and reducing cracking of the thin glass layer 3. Furthermore, since the entire surface of the thin glass layer 3 is sealed with the sealing layer 2, a certain degree of elasticity is imparted to both sides of the thin glass layer 3, thereby reducing cracking of the thin glass layer 3 during installation and use. The flexible solar cell of FIG. 2 differs from that of FIG. 1 in that a front sheet is laminated on the thin glass layer 3 via an adhesive layer 5. Because the adhesive layer 5 has a certain degree of elasticity, even in the embodiment of FIG. 2 in which not all surfaces of the thin glass layer 3 are sealed with the sealing layer 2, cracking of the thin glass layer 3 can be reduced to the same extent as in the embodiment of FIG. 1. Note that, although the adhesive layer 5 is present only on the thin glass layer 3 in FIG. 2, it may be laminated on the entire substrate-side surface of the front sheet 4. The flexible solar cell of FIG. 3 is similar to the embodiment of FIG. 2, but differs in that the power generating portion is formed directly on the backsheet.In the embodiment of Figure 3, a flexible solar cell can be manufactured by bonding together a back sheet on which a power generating section is formed and a front sheet on which a sealed thin glass layer 3 is laminated, thereby further simplifying the manufacturing process.

[0065] Although the method for manufacturing the flexible solar cell of the present invention is not particularly limited, a method in which a power generating unit is sandwiched between a portion having a thin glass layer sealed by a sealing layer or a sealing layer and an adhesive layer (sheet A) and a portion having a sealing layer (sheet B), and the edges are laminated and then cut, is preferred, because this method is easy to manufacture and can prevent cracking of the thin glass layer even when the flexible solar cell is large. By using such a manufacturing method, the number of steps performed on the portion having the thin glass layer can be minimized and the steps themselves can be simplified, making manufacturing easier and preventing cracking of the thin glass layer.

[0066] The sheet A can be obtained by sealing the periphery of the thin glass layer with a sealing layer and an adhesive layer, or with only a sealing layer. Specifically, when the flexible solar cell of the present invention has a front sheet and an adhesive layer, the sheet A can be obtained by performing the steps of laminating an adhesive layer on the front sheet, laminating a thin glass layer on the laminated adhesive layer, and laminating a sealing layer so as to cover the entire side and bottom surfaces of the thin glass layer. When the flexible solar cell of the present invention does not have a front sheet and an adhesive layer, the sheet A can be obtained by first laminating a layer consisting of a sealing layer, laminating a thin glass layer on top of that, and then laminating a sealing layer so as to cover the entire bottom and side surfaces of the thin glass layer.

[0067] The power generating section can be obtained by sequentially stacking layers such as an electrode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and a counter electrode on a substrate. Alternatively, the power generating section can be obtained by stacking each layer on an electrode instead of a substrate. Conventional methods can be used to stack each layer without any particular limitations.

[0068] When the flexible solar cell of the present invention does not have a back sheet, the sheet B can be obtained by forming a layer consisting of only the sealing layer by coating, etc. When the flexible solar cell of the present invention has a back sheet, the sheet B can be obtained by laminating the sealing layer on the back sheet.

[0069] A roll-to-roll method can be used as a method for laminating the sheet A, the power generation layer, and the sheet B. By using the roll-to-roll method, large-area flexible solar cells can be continuously produced.

[0070] The method for cutting the end portion is not particularly limited, and examples thereof include a method of cutting with a roller cutter, etc. The width of the cut is not particularly limited as long as the thin glass layer is not cut and the thin glass layer is not exposed on the cut surface.

[0071] When the flexible solar cell of the present invention has a structure as shown in Figure 3, the flexible solar cell of the present invention can be manufactured by bonding together a portion consisting of a thin glass layer sealed by a sealing layer or a sealing layer and an adhesive layer, and a portion in which a power generation layer is laminated on a back sheet, and then cutting the end portion.

[0072] A schematic diagram illustrating an example of a manufacturing method for a flexible solar cell of the present invention is shown in Figure 4. Figure 4 illustrates, as an example, the manufacturing process of the flexible solar cell of Figure 2. The flexible solar cell of the present invention does not have a conventional structure in which a power generating unit is directly laminated on a thin glass layer, but rather has a structure in which the periphery of the thin glass layer is covered with a sealing layer, or a sealing layer and an adhesive layer. Therefore, the flexible solar cell of the present invention can be manufactured by separately preparing a sheet A in which a front sheet 4, an adhesive layer 5, a thin glass layer 3, and a sealing layer 2 are laminated, and the periphery of the thin glass layer 3 is covered with the sealing layer 2 and the adhesive layer 5; a sheet B in which the sealing layer 2 is laminated on a back sheet 6; and the power generating unit 1; sandwiching the power generating unit between sheets A and B and laminating them; and finally cutting the edges (not shown). As a result, the manufacturing process for the power generating unit 1, which requires harsh conditions such as coating, heating, scribing, and sputtering and requires precise control of the film thickness, is not performed on the thin glass layer 3, making the thin glass less likely to break during manufacturing and facilitating manufacturing. Furthermore, because the sealing layer 2 and the adhesive layer 5 are in close contact with the thin glass layer 3 during lamination, even if the thin glass layer 3 has small cracks such as pinholes, the sealing layer 2 and the adhesive layer 5 can fill the cracks and prevent a decrease in high-temperature, high-humidity durability due to the cracks. Furthermore, by not cutting the thin glass layer 3 when cutting the edges, the risk of cracking of the thin glass layer 3 can be reduced, and because the sealing layer 2 seals even the side surfaces of the thin glass layer, high-temperature, high-humidity durability can be further improved.

[0073] According to the present invention, it is possible to provide a solar cell which is easy to manufacture, in which the thin glass is resistant to cracking even when it is made large in area, and which has excellent durability under high temperature and high humidity.

[0074] Fig. 1 is a cross-sectional view showing an example of the structure of a flexible solar cell of the present invention. Fig. 2 is a cross-sectional view showing an example of the structure of a flexible solar cell of the present invention. Fig. 3 is a cross-sectional view showing an example of the structure of a flexible solar cell of the present invention. Fig. 4 is a schematic diagram showing an example of a method for manufacturing a flexible solar cell of the present invention. Fig. 5 is a photograph of a flexible solar cell of Example 1. Fig. 6 is a photograph of a flexible solar cell of Comparative Example 2.

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0076] Example 1 A 95 cm x 95 cm x 100 μm PET film was prepared as a substrate. A 200 nm thick ITO film was formed on the substrate by sputtering as a counter electrode. A 20 nm thick thin-film electron transport layer was 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 onto the lead iodide by spin coating, and annealed at 150° C. for 10 minutes to form a 700 nm thick film of an organic-inorganic perovskite compound, CH ３ NH ３ PbI ３ A photoelectric conversion layer containing the above was formed. Next, a chlorobenzene solution containing 2 wt% Spiro-OMETAD (manufactured by Merck) was applied to the photoelectric conversion layer by spin coating and then dried to form a hole transport layer with a thickness of 80 nm. After that, a 100 nm thick Al film was formed as an electrode on the photoelectric conversion layer by sputtering, yielding a 95 cm x 95 cm power generation unit consisting of the substrate, counter electrode, electron transport layer, photoelectric conversion layer, hole transport layer, and electrode.

[0077] Next, UBF512 (manufactured by 3M, size: 110 cm x 110 cm x 200 μm, designated as commercial product A in the table) was prepared as a front sheet. Polyisobutylene was applied to the front sheet to a thickness of 70 μm as an adhesive layer, and four 45 cm x 45 cm x 0.05 mm thin glass sheets (area ratio to the power generation section: 90%) were laminated on top of the front sheet in a square shape at the center of the front sheet, without overlapping each other. Polyisobutylene (SP value: 7.5) was then applied as a sealing layer to the entire laminate surface of the front sheet to a height of 70 μm from the top surface of the thin glass sheets (the surface opposite the front sheet) (a height of 190 μm from the laminate surface of the front sheet), thereby obtaining Sheet A. Next, an aluminum-containing back sheet (manufactured by Toyo Aluminum Co., Ltd., FAPL) measuring 110 cm x 110 cm x 360 μm was prepared as a back sheet, and polyisobutylene was applied to the back sheet as a sealing layer to a thickness of 70 μm to obtain Sheet B.

[0078] The power generation unit was then sandwiched between the center of sheets A and B, with the sealing layer of sheet A facing the base material of the power generation unit and the sealing layer of sheet B facing the electrode of the power generation unit, and thermal vacuum lamination was performed at 100°C. The power generation unit was laminated so that the center of the power generation unit overlapped the center of the thin glass sheet. The four sides of the resulting laminate were then cut by 5 cm and the polyisobutylene that protruded from the sides was removed, yielding a 100 cm x 100 cm flexible solar cell having the structure shown in Figure 2. The distance from the side of the thin glass sheet layer to the side of the flexible solar cell was 5 cm. A photograph of the resulting flexible solar cell is shown in Figure 5.

[0079] (Examples 2 and 3, Comparative Example 1) A flexible solar cell was obtained in the same manner as in Example 1, except that the configurations of the front sheet, adhesive layer, sealing layer, and thin glass layer were as shown in Tables 1 and 2. Note that Cosmoshine (manufactured by Toyobo Co., Ltd., thickness: 188 μm) was used for the PET in Tables 1 and 2, and tesa 69404 (manufactured by TESA) was used for the OCA (optically transparent adhesive).

[0080] (Examples 4 and 5) Flexible solar cells were obtained in the same manner as in Example 1, except that the front sheet, adhesive layer, and sealing layer were configured as shown in Table 1, and thin glass that had been impacted to cause small cracks in some parts was used as the thin glass layer.

[0081] (Comparative Example 2) A flexible solar cell was obtained in the same manner as in Example 1, except that the configuration was as shown in Table 2, no sealing layer was laminated on the underside of the thin glass sheet in the production of Sheet A, and lamination of Sheet A, Sheet B, and the power generation section was performed so that the thin glass layer and the power generation layer were in direct contact with each other. A photograph of the flexible solar cell obtained here is shown in Figure 6. In Figure 6, bubbles have formed between the power generation section and the thin glass layer, making the cell opaque, and therefore the position of the cell is indicated by a dashed line.

[0082] (Comparative Example 3) The thin glass sheet of Example 1 was used instead of the PET film substrate, and a power generation section was formed on the thin glass sheet in the same manner as in Example 1. A flexible solar cell was produced in the same manner as in Example 1, except that Sheet A was produced using the thin glass layer on which the obtained power generation section was laminated, and that Sheet A and Sheet B were laminated together. However, because cracks and the like occurred throughout the thin glass sheet during the formation of the power generation section, during lamination, and upon slight movement, the initial conversion efficiency and moist heat durability, which will be described later, were not evaluated.

[0083] (Comparative Examples 4 and 5) Flexible solar cells were obtained in the same manner as in Comparative Example 2, except that the front sheet, adhesive layer, and sealing layer were configured as shown in Table 2, and thin glass that had been impacted to cause small cracks in some parts was used as the thin glass layer.

[0084] Comparative Example 6 A flexible solar cell was obtained in the same manner as in Example 1, except that the four sides of the laminate were cut so as to pass through the thin glass layer, thereby exposing the thin glass layer on the side surfaces of the four sides. The obtained flexible solar cell had cracks occurring over the entire surface of the thin glass layer.

[0085] <Evaluation> The solar cells obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 1 and 2.

[0086] (1) Evaluation of ease of manufacture In the manufacture of flexible solar cells, the ease of manufacture was evaluated by assigning "x" to cases where both the lamination work for laminating the power generating section on the thin glass layer and the lamination work for sealing had to be performed, and by assigning "o" to cases where only the lamination work for sealing was required. (2) Evaluation of initial conversion efficiency A power source (236 model, manufactured by Keithley) was connected between the electrodes of the obtained flexible solar cells, and an intensity of 100 mW / cm was applied. ２ The photoelectric conversion efficiency was measured using a solar simulator (manufactured by Yamashita Denso Co., Ltd.) The initial conversion efficiency was evaluated based on the photoelectric conversion efficiency of Comparative Example 2, with a photoelectric conversion efficiency of 1.05 or more being marked "good" and a photoelectric conversion efficiency of less than 1.05 being marked "poor."

[0087] (3) Evaluation of moist heat durability The obtained flexible solar cell was subjected to a moist heat resistance test under conditions of 85% RH and 85°C for 500 hours. After the moist heat resistance test, the photoelectric conversion efficiency was measured in the same manner as in the evaluation of the initial conversion efficiency, and the retention rate (%) relative to the initial conversion efficiency was calculated. The above measurement was performed on five samples, and the average value was used as the retention rate. The moist heat durability was evaluated for the obtained retention rates according to the following criteria: ○: Retention rate of 90% or more ×: Retention rate of less than 90%

[0088]

[0089]

[0090] According to the present invention, it is possible to provide a solar cell which is easy to manufacture, in which the thin glass is resistant to cracking even when it is made large in area, and which has excellent durability under high temperature and high humidity.

[0091] REFERENCE SIGNS LIST 1 power generation section 2 sealing layer 3 thin glass layer 4 front sheet 5 adhesive layer 6 back sheet

Claims

1. A flexible solar cell comprising a power generation unit, a sealing layer, and a thin glass layer disposed on the upper surface of the power generation unit and covering the upper surface of the power generation unit, wherein the bottom and side surfaces of the thin glass layer are sealed by the sealing layer, and the top surface is sealed by the sealing layer or an adhesive layer.

2. The flexible solar cell according to claim 1, which has a front sheet on the sealing layer or adhesive layer, and said front sheet is laminated on the top surface of the thin glass layer via said sealing layer or said adhesive layer.

3. The flexible solar cell according to claim 1 or 2, wherein the adhesive resin constituting the adhesive layer and the sealing resin constituting the sealing layer are the same.

4. A flexible solar cell according to any one of claims 1 to 3, wherein the minimum distance between the lower surface of the thin glass layer and the power generating section is 1 μm or more.

5. A flexible solar cell according to any one of claims 1 to 4, wherein the power generating section contains an organic-inorganic perovskite compound.

6. A flexible solar cell according to any one of claims 1 to 5, wherein the flexible solar cell includes an adhesive layer, the power generation section includes an organic-inorganic perovskite compound, and the SP value of the adhesive resin constituting the adhesive layer is 6 or more and 10 or less.

7. A flexible solar cell according to any one of claims 1 to 6, wherein the flexible solar cell includes an adhesive layer, the power generation section includes an organic-inorganic perovskite compound, and the adhesive resin constituting the adhesive layer is polyisobutylene.

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