Flexible solar cells

Abstract

This invention provides a flexible solar cell with high condensation resistance, which is less prone to cracking and pinholes even when the condensation-preventing layer is made thin. [Solution] A power generation unit having a first electrode, a photoelectric conversion layer and a second electrode, and a water vapor transmittance of 1 × 10⁻¹⁰⁻¹ -3 g / m 2 A flexible solar cell having a first dew-proof section with a lifespan of less than / day, wherein the first dew-proof section is made of an inorganic material, and the first dew-proof section and the power generation section are not in contact.

Description

[Technical Field]

[0001] This invention relates to a flexible solar cell. [Background technology]

[0002] Conventionally, solar cells have been extensively developed as laminates in which an N-type semiconductor layer and a P-type semiconductor layer are arranged 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 such as high manufacturing costs and difficulty in scaling up, which limits their range of applications. Therefore, in recent years, perovskite solar cells have attracted attention, which use organic-inorganic perovskite compounds having a perovskite structure with lead, tin, etc. as the central metal as the photoelectric conversion layer (for example, Patent Document 1, Non-Patent Document 1). Perovskite solar cells can be expected to have high photoelectric conversion efficiency, and since they can be manufactured by printing, manufacturing costs can be significantly reduced.

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

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

[0005] [Non-Patent Document 1] MMLee,et al,Science,2012,338,643 [Overview of the project] [Problems that the invention aims to solve]

[0006] Such flexible solar cells require high condensation resistance to ensure long-term stability. Conventional flexible solar cells used inorganic materials such as thin glass sheets as both a condensation-resistant layer and substrate, on which the power generation layer was formed. However, inorganic materials are hard and brittle, making them prone to cracks and pinholes. In particular, recent flexible solar cells have become larger in area and lighter in weight, and the condensation-resistant layer also needs to be made thinner, making them more susceptible to cracks and pinholes, thus posing an even greater problem.

[0007] The present invention aims to provide a flexible solar cell that is less prone to cracking and pinholes even when the condensation-preventing portion is made into a thin film, and that offers high condensation resistance. [Means for solving the problem]

[0008] A power generation unit having a first electrode, a photoelectric conversion layer, and a second electrode, and a water vapor transmittance of 1 × 10⁻¹⁰⁻¹ -3 g / m 2 The present invention is a flexible solar cell having a first dew-preventing section with a lifespan of less than / day, wherein the first dew-preventing section is made of an inorganic material, and the first dew-preventing section and the power generation section do not come into contact. The present invention will be described in detail below.

[0009] The flexible solar cell of the present invention has a power generation section having a first electrode, a photoelectric conversion layer, and a second electrode. The above-mentioned power generation unit is the part that converts sunlight into electricity, and is composed of a base material, the first electrode, the second electrode, the photoelectric conversion layer, the electron transport layer, the hole transport layer, and the like. In this specification, "layer" refers not only to layers with clear boundaries, but also to layers with a concentration gradient in which the contained elements gradually change. Elemental analysis of a layer can be performed, for example, by FE-TEM / EDS line analysis of a cross-section of a solar cell to confirm the elemental distribution of specific elements. Furthermore, in this specification, "layer" refers not only to flat, thin-film layers, but also to layers that can combine with other layers to form a complex, interwoven structure.

[0010] The above-mentioned substrate is not particularly limited as long as it is flexible, and examples include resin films made of polyimide or polyester-based heat-resistant polymers, metal foils, thin glass sheets, etc. Among these, PET resin films are preferred from the viewpoint of cost and heat resistance.

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

[0012] The thickness of the first and second electrodes 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 electrodes can function while suppressing resistance. 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 first and second electrodes is 50 nm and a more preferred upper limit is 500 nm.

[0013] The above photoelectric conversion layer preferably contains an organic-inorganic perovskite compound represented by the general formula AMX (where A is an organic base compound and / or an alkali metal, M is a lead or tin atom, and X is a halogen atom). A solar cell in which such a power generation unit contains an organic-inorganic perovskite compound is also called an organic-inorganic hybrid solar cell. By using the above organic-inorganic perovskite compound in the above photoelectric conversion layer, the photoelectric conversion efficiency of the flexible solar cell can be further improved. In addition, since the above organic-inorganic perovskite compound has a property of being vulnerable to moisture, the effects of the present invention are greatly exerted.

[0014] The above A is an organic base compound and / or an alkali metal. Specific examples of the above organic base compound include, for example, 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 their ions (for example, methylammonium (CH3NH3), etc.), phenethylammonium, and the like. Among them, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, formamidine, acetamidine, and their ions and phenethylammonium are preferred, and methylamine, ethylamine, propylamine, formamidine, and their ions are more preferred. Examples of the above alkali metal include lithium, sodium, potassium, rubidium, cesium, and the like.

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

[0016] X above is a halogen atom. Examples of the halogen atom include chlorine, bromine, iodine, sulfur, selenium, etc. These halogen atoms may be used alone or two or more of them may be used in combination. By containing halogen in the structure, the above-mentioned organic-inorganic perovskite compound becomes soluble in an organic solvent, enabling its application to an inexpensive printing method or the like. Among them, since the energy band gap of the above-mentioned organic-inorganic perovskite compound becomes narrow, X is preferably iodine.

[0017] The above-mentioned organic-inorganic perovskite compound preferably has a cubic crystal structure in which a metal atom M is at the body center, an organic base compound or an alkali metal A is at each vertex, and a halogen atom X is at the face center. Although the details are not clear, by having the above structure, the orientation of the octahedra in the crystal lattice can be easily changed, so it is presumed that the mobility of electrons in the above-mentioned organic-inorganic perovskite compound increases and the photoelectric conversion efficiency of the solar cell improves.

[0018] The above-mentioned organic-inorganic perovskite compound is preferably a crystalline semiconductor. A crystalline semiconductor means a semiconductor in which an X-ray scattering intensity distribution is measured and scattering peaks can be detected. Since the above-mentioned organic-inorganic perovskite compound is a crystalline semiconductor, the mobility of electrons in the above-mentioned organic-inorganic perovskite compound increases and the photoelectric conversion efficiency of the flexible solar cell improves.

[0019] Also, the crystallinity can be evaluated as an index of crystallization. The crystallinity can be obtained by separating the scattering peak derived from the crystalline part and the halo derived from the amorphous part detected by measuring the X-ray scattering intensity distribution by fitting, obtaining the intensity integral of each, and calculating the ratio of the crystalline part in the whole. The preferred lower limit for the crystallinity of the above organic-inorganic perovskite compound is 30%. When the crystallinity is 30% or higher, the electron mobility in the organic-inorganic perovskite compound increases, improving the photoelectric conversion efficiency of the solar cell. A more preferred lower limit for the crystallinity is 50%, and an even more preferred lower limit is 70%. Furthermore, methods for increasing the crystallinity of the above-mentioned organic-inorganic perovskite compounds include, for example, thermal annealing, irradiation with high-intensity light such as lasers, and plasma irradiation.

[0020] The above-mentioned photoelectric conversion layer may further contain an organic semiconductor or an inorganic semiconductor in addition to the organic-inorganic perovskite compound, as long as it does not impair the effects of the present invention. The organic semiconductor or inorganic semiconductor referred to herein may function as a hole transport layer or an electron transport layer. Examples of the above-mentioned organic semiconductors include compounds having a thiophene skeleton such as poly(3-alkylthiophene). Other examples include conductive polymers having a poly(p-phenylenevinylene) skeleton, polyvinylcarbazole skeleton, polyaniline skeleton, polyacetylene skeleton, etc. Furthermore, examples include compounds having a porphyrin skeleton such as a phthalocyanine skeleton, naphthalocyanine skeleton, pentacene skeleton, benzoporphyrin skeleton, spirobifluorene skeleton, etc., as well as carbon-containing materials such as carbon nanotubes, graphene, and fullerene, which may be surface-modified.

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

[0022] When the photoelectric conversion layer includes the organic-inorganic perovskite compound and the organic semiconductor or inorganic semiconductor, it may be a laminate formed by stacking thin-film organic semiconductor or inorganic semiconductor portions and thin-film organic-inorganic perovskite compound portions, or it may be a composite film formed by combining the organic semiconductor or inorganic semiconductor portion and the organic-inorganic perovskite compound portion. A laminate is preferred in terms of ease of manufacture, while a composite film is preferred in terms of being able to improve the charge separation efficiency in the organic semiconductor or inorganic semiconductor.

[0023] The thickness of the thin film-like organic-inorganic perovskite compound portion described above has a preferred lower limit of 5 nm and a preferred upper limit of 5000 nm. If the thickness is 5 nm or more, sufficient light absorption becomes possible, and the photoelectric conversion efficiency increases. If the thickness is 5000 nm or less, the occurrence of regions where charge separation is not possible can be suppressed, leading to an improvement in photoelectric conversion efficiency. A more preferred lower limit for the thickness is 10 nm, a more preferred upper limit is 1000 nm, an even more preferred lower limit is 20 nm, and an even more preferred upper limit is 500 nm.

[0024] When the photoelectric conversion layer is a composite film 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 can be absorbed, and the photoelectric conversion efficiency will be high. If the thickness is 3000 nm or less, the charge can reach the electrodes more easily, and the photoelectric conversion efficiency will be high. 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 above-mentioned photoelectric conversion layer is not particularly limited and includes methods such as vacuum deposition, sputtering, vapor deposition (CVD), electrochemical deposition, and printing. In particular, by employing the printing method, solar cells that can exhibit high photoelectric conversion efficiency can be easily formed over a large area. Examples of printing methods include spin coating and casting, and methods using the printing method include roll-to-roll.

[0026] The above-mentioned power generation unit may have an electron transport layer between the first or second electrode, which acts as the cathode, and the photoelectric conversion layer. The material of the electron transport layer is not particularly limited, and examples 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. Specifically, examples include cyano group-containing polyphenylene vinylene, boron-containing polymers, vasocuproin, vasophenanthrene, hydroxyquinolinatoaluminum, oxadiazole compounds, benzimidazole compounds, naphthalenetetracarboxylic acid compounds, perylene derivatives, phosphine oxide compounds, phosphine sulfide compounds, fluoro group-containing phthalocyanines, titanium dioxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, zinc sulfide, etc.

[0027] The electron transport layer described above may consist only of a thin-film electron transport layer, but it is preferable to include a porous electron transport layer. In particular, 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, a more complex composite film (a more intricately interwoven structure) can be obtained, and the photoelectric conversion efficiency is higher, so it is preferable that the composite film is fabricated on a porous electron transport layer.

[0028] The preferred lower limit for 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, it will not be a resistance during electron transport, and the photoelectric conversion efficiency will be high. A more preferred lower limit for the thickness of the electron transport layer is 3 nm, a more preferred upper limit is 1000 nm, an even more preferred lower limit is 5 nm, and an even more preferred upper limit is 500 nm.

[0029] The above-mentioned power generation unit may have a hole transport layer between the first or second electrode, which acts as the anode or cathode, 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. Specifically, examples include compounds having a thiophene skeleton such as poly(3-alkylthiophene). Also, examples include conductive polymers having a triphenylamine skeleton, poly(p-phenylenevinylene) skeleton, polyvinylcarbazole skeleton, polyaniline skeleton, polyacetylene skeleton, etc. Furthermore, examples include compounds having a phthalocyanine skeleton, naphthalocyanine skeleton, pentacene skeleton, benzoporphyrin skeleton or other porphyrin skeletons, spirobifluorene skeleton, etc., molybdenum sulfide, tungsten sulfide, copper sulfide, tin sulfide, etc., fluoro group-containing phosphonic acid, carbonyl group-containing phosphonic acid, CuSCN, CuI, etc.

[0030] The flexible solar cell of the present invention has a water vapor transmission rate of 1 × 10⁻¹⁰ arranged on the light-receiving surface of the power generation unit (hereinafter, the direction toward the light-receiving surface is also referred to as "up"). -3 g / m 2 It has a first condensation prevention section of less than / day. By having a first dew-proof section with a water vapor transmission rate less than or equal to the above-mentioned water vapor transmission rate on the light-receiving surface side of the power generation section, high dew-proof performance can be provided. The water vapor transmission rate of the first dew-proof section is 1 × 10⁻⁶ -4 g / m 2 Preferably less than / day, 1 × 10 -5 g / m2 It is more preferable that it is 10 g / m2 / day or less. The lower limit of the water vapor transmission rate of the first dew prevention part is not particularly limited, and the lower it is, the better. However, due to manufacturing technology, it is about 0.5×10−3 g / m2 / day. -6 g / m 2 / day or so. The water vapor transmission rate can be measured by the differential pressure method in accordance with the gas chromatography method of JIS K7129, with the surface actually located outside the module as the water vapor introduction surface under the conditions of a temperature of 85°C, a humidity of 85%, and a sample thickness of 100 μm or more and 200 μm or less.

[0031] Since the organic-inorganic perovskite compound is very weak against moisture, the measurement is carried out at a temperature of 85°C and a humidity of 85%. The water vapor transmission rate can be obtained by the differential pressure method with the surface actually located outside the module as the water vapor introduction surface. The measurable thickness of the dew prevention part depends on the device, but it is preferably unified at 100 μm or more and 200 μm or less.

[0032] The first dew prevention part is made of an inorganic material. Since the first dew prevention part is made of an inorganic material, it is easy to satisfy the above water vapor transmission rate and can exhibit high dew prevention performance. Examples of the inorganic material include glass, aluminum oxide, titanium oxide, etc. Examples of the glass include soda glass, lead glass, borosilicate glass, alkali-free glass, etc. Among them, since it can be made thinner, the inorganic material is preferably alkali-free glass.

[0033] The first dew prevention part preferably has a longitudinal elastic modulus of 10000 MPa or more and 100000 MPa or less. When the longitudinal elastic modulus of the first dew prevention part is within the above range, the flexibility of the entire solar cell module can be further enhanced. The longitudinal elastic modulus of the first dew prevention part is more preferably 30000 MPa or more, further preferably 50000 MPa or more, more preferably 90000 MPa or less, and further preferably 80000 MPa or less. Particularly when the first dew prevention part is made of glass, the longitudinal elastic modulus is preferably 80000 MPa or less. The above-mentioned Young's modulus can be measured by tensile or compression tests.

[0034] The first condensation prevention section described above preferably has a Vickers hardness of 400 HV or more and 1000 HV or less. Impact resistance can be provided by having a Vickers hardness within the above range for the first condensation prevention section. The Vickers hardness of the first condensation prevention section is more preferably 500 HV or higher, even more preferably 600 HV or higher, even more preferably 800 HV or lower, and even more preferably 700 HV or lower. In particular, when the first condensation prevention section is made of glass, the Vickers hardness is preferably 700 HV or lower. The Vickers hardness can be determined, for example, by using a nanoindenter (G200, manufactured by Keysight Technologies, etc.) to press an indenter into the first dew-proof section and calculating the hardness from the resulting load-displacement curve.

[0035] The above-mentioned first condensation prevention section has a surface density of 60 g / m². 2 More than 1000g / m 2 The following is preferable: The surface density of the first dew-preventing section is within the above range, which ensures the flexibility of the entire solar cell module. The surface density of the first dew-preventing section is 100 g / m². 2 It is more preferable that the amount be greater than or equal to 200 g / m². 2 It is even more preferable that the amount be greater than or equal to 800 g / m². 2 It is more preferable that the following conditions apply: 600 g / m² 2 The following is even more preferable: The above surface density can be calculated from the density and film thickness of the first dew-proof section.

[0036] Preferably, the first condensation prevention section covers 80% or more of the power generation section when viewed from the light-receiving surface side. By having the first condensation prevention section cover the above-mentioned area of ​​the power generation section, moisture can be more effectively prevented from entering the power generation section, thereby further enhancing condensation prevention. It is more preferable that the first condensation prevention section covers 100% or more of the power generation section when viewed from the light-receiving surface side, and even more preferable that it covers 120% or more. There is no particular upper limit to the area covered by the first condensation prevention section, but from a cost perspective, it is preferable that it covers 130% or less of the power generation section.

[0037] The thickness of the first dew-preventing portion described above is not particularly limited as long as the flexibility of the resulting flexible solar cell can be ensured, but it is preferably 10 μm or more, more preferably 30 μm or more, preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 100 μm or less. The flexible solar cell of the present invention can improve dew prevention by making the hard and brittle first dew-preventing portion thin as described above, while also being less prone to cracking and pinholes.

[0038] In the flexible solar cell of the present invention, the first dew-preventing section and the power generation section do not come into contact with each other. Because the power generation section has a surface made of hard materials such as a substrate and electrodes, when it comes into contact with the first dew-proof section, which is made of a hard and brittle inorganic material, impacts can easily cause cracks and pinholes in the first dew-proof section. In this invention, by creating a distance between the power generation section and the first dew-proof section, it is possible to suppress the occurrence of cracks and pinholes even when the first dew-proof section is made of a thin film.

[0039] The shortest distance between the first condensation prevention section and the power generation section is preferably 1 μm or more. When the shortest distance between the first dew-preventing section and the power-generating section is within the above range, the force from the power-generating section is further reduced, thereby further suppressing the occurrence of cracks and pinholes in the first dew-preventing section. The shortest distance between the first dew-preventing section and the power-generating section is more preferably 100 μm or more, and even more preferably 200 μm or more. There is no particular upper limit to the shortest distance between the first dew-preventing section and the power-generating section, but from the viewpoint of making the flexible solar cell thinner, it is preferably 5000 μm or less.

[0040] The flexible solar cell of the present invention has a second dew-preventing portion between the first dew-preventing portion and the power-generating portion, and the second dew-preventing portion is in contact with the surface of the first dew-preventing portion on the power-generating portion side. The second condensation prevention section is flexible, and by filling the space between the first condensation prevention section and the power generation section with the second condensation prevention section, the impact on the first condensation prevention section is mitigated. Therefore, even if the first condensation prevention section is made into a thin film, the occurrence of cracks and pinholes can be further suppressed. Furthermore, even if cracks or pinholes occur in the first condensation prevention section, the second condensation prevention section can fill the cracks and pinholes, suppressing their expansion and further reducing the intrusion of moisture. From the viewpoint of preventing moisture that has passed through the first condensation prevention section from entering the power generation section, it is sufficient for the second condensation prevention section to be in contact with a part of the surface of the first condensation prevention section on the power generation section side. However, to further enhance the above effect, it is preferable for the second condensation prevention section to be in contact with the entire surface on the power generation section side, and more preferably, to cover the entire first condensation prevention section.

[0041] Preferably, the second condensation prevention section fills the entire space between the first condensation prevention section and the power generation section. Because the second condensation prevention section has condensation-preventing properties, filling the space between the first condensation prevention section and the power generation section with the second condensation prevention section makes it more difficult for moisture to reach the power generation section even if it passes through the first condensation prevention section.

[0042] It is more preferable that the second condensation prevention section covers the entire power generation section. By covering the entire power generation section with the second condensation prevention section, condensation prevention can be enhanced not only on the side of the first condensation prevention section but also around the entire perimeter of the power generation section.

[0043] The material constituting the second dew-proof section described above is not particularly limited as long as it satisfies the following Young's modulus and has dew-proof properties, but examples 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 layer contains an organic-inorganic perovskite compound, the organic components of the organic-inorganic perovskite compound are less likely to dissolve.

[0044] The second condensation prevention section described above preferably has a Young's modulus of 1000 MPa or less. The fact that the Young's modulus of the second dew-proof section is within the above range provides flexibility to the second dew-proof section, allowing it to fill cracks and pinholes in the first dew-proof section and further mitigate impacts to the first dew-proof section. The Young's modulus of the second dew-proof section is more preferably 500 MPa or less, and even more preferably 100 MPa or less. The lower limit of the Young's modulus of the second dew-proof section is not particularly limited, but it is preferably 1 MPa or more from the viewpoint of facilitating manufacturing. The method for measuring the Young's modulus of the second dew-proof section is the same as the method for measuring the Young's modulus of the first dew-proof section.

[0045] The above-mentioned second condensation prevention section has a viscosity of 1000 Pa·s or less at 20°C. By having a viscosity within the above range for the second dew-preventing portion, the ability to fill cracks and pinholes in the first dew-preventing portion and to mitigate impact can be further improved. The viscosity of the second dew-preventing portion at 20°C is more preferably 800 Pa·s or less, and even more preferably 600 Pa·s or less. The lower limit of the viscosity of the second dew-preventing portion is not particularly limited, but it is preferably 200 Pa·s or more from the viewpoint of facilitating manufacturing. The viscosity at 20°C can be measured using a BM-type rotational viscometer (BMII, manufactured by Toki Sangyo Co., Ltd., or equivalent) at a rotational speed of 60 rpm.

[0046] The above-mentioned second condensation prevention section has a water vapor transmission rate of 1 g / m³. 2 It is preferable that it be less than / day. The water vapor transmission rate of the second dew-preventing section is within the above range, which further enhances dew prevention. The water vapor transmission rate of the second dew-preventing section is 0.5 g / m³. 2 It is preferable that the amount be less than / day, and 0.1 g / m 2 It is more preferable that the rate is less than or equal to / day. The lower limit of the water vapor transmission rate of the second dew prevention section is not particularly limited, and a lower rate is better, but for manufacturing reasons it is 0.01 g / m³. 2 It's about per day. The method for measuring the water vapor transmission rate of the second dew prevention section is the same as the method for measuring the water vapor transmission rate of the first dew prevention section.

[0047] When the second dew-preventing portion covers the upper surface of the first dew-preventing portion, it is preferable that the thickness of the second dew-preventing portion covering the upper surface of the first dew-preventing portion is 1 μm or more in the flexible solar cell of the present invention. When the thickness of the second condensation-preventing portion on the upper surface of the first condensation-preventing portion is within the above range, the first condensation-preventing portion can be given appropriate elasticity, and the occurrence of cracks and pinholes in the first condensation-preventing portion can be further suppressed. Furthermore, even if cracks or pinholes occur on the upper surface of the first condensation-preventing portion, these can be sufficiently filled, thereby further improving condensation prevention. The thickness of the second condensation-preventing portion covering the upper surface of the first condensation-preventing portion is more preferably 50 μm or more, even more preferably 100 μm or more, and preferably 5000 μm or less.

[0048] The flexible solar cell of the present invention may have a front sheet on the outermost surface on the light-receiving side. The front sheet plays a role in suppressing light reflection and improving the drainage performance of the flexible solar cell surface by forming patterns such as bumps and arcs on its surface. For example, if a front sheet with a convex arc having its apex at the center of the flexible solar cell is provided, a drainage slope can be created from the center to the edges of the flexible solar cell. If a front sheet with a concave arc having its lowest point at the center of the flexible solar cell is provided, a water collection area can be created from the edges to the center of the flexible solar cell. By providing such drainage slopes and water collection areas, the accumulation of dirt and other debris can be concentrated in specific areas. Furthermore, the design can be improved by randomly forming bumps and arcs on the front sheet.

[0049] The material of the front sheet mentioned above is not particularly limited as long as it is transparent, and examples include fluorine-containing resins, vinyl chloride resins, polyethylene resins, and polycarbonate resins. Specifically, examples include polycarbonate, polyvinyl chloride, tetrafluoroethylene resin, polyvinylidene fluoride, and polychlorotrifluoroethylene. Among these, fluorine-containing resins are preferred because they have excellent weather resistance.

[0050] The thickness of the front sheet is not particularly limited, but from the viewpoint of balancing light transmittance and the functionality of the front sheet, it is preferably 25 μm or more, more preferably 50 μm or more, preferably 1000 μm or less, and more preferably 300 μm or less.

[0051] The above-mentioned front sheet is laminated via the above-mentioned second anti-condensation section. When the flexible solar cell of the present invention has a front sheet, the first dew-proof portion does not have adhesive properties, so the second dew-proof portion is laminated on the upper surface of the first dew-proof portion, and the front sheet is placed on the first dew-proof portion via the second dew-proof portion.

[0052] The flexible solar cell of the present invention may have a back sheet on the outermost surface facing the installation surface. The backsheet plays a role in improving the weather resistance of the flexible solar cell by preventing the intrusion of substances that cannot be completely prevented by the second condensation prevention section alone. Examples of materials for the backsheet include polyethylene terephthalate.

[0053] The thickness of the backsheet is not particularly limited, but from the viewpoint of balancing flexibility and the functionality of the backsheet, it is preferably 50 μm or more, more preferably 100 μm or more, preferably 1000 μm or less, and most preferably 500 μm or less.

[0054] Here, Figure 1 shows a schematic diagram illustrating an example of the structure of the flexible solar cell of the present invention. In the flexible solar cell of Figure 1, a power generation unit 1 and a first dew-proof unit 3, both sealed on all sides by a second dew-proof unit 2, are laminated on a backsheet 5, and a frontsheet 4 is laminated on the second dew-proof unit 2. By having a structure in which the first dew-proof unit 3 and the power generation unit 1 are not in contact, impacts from the hard power generation unit are not directly transmitted to the hard and brittle first dew-proof unit 3, so that cracks and pinholes can be suppressed even when the first dew-proof unit 3 is made into a thin film. Furthermore, by filling the space between the first dew-proof unit 3 and the power generation unit 1 with the flexible second dew-proof unit 2, impacts can be further mitigated, and even if cracks or pinholes occur in the first dew-proof unit 3, the second dew-proof unit 2 can fill them, thus suppressing the expansion of cracks and pinholes. In addition, the dew-proof properties of the second dew-proof unit 2 itself can further enhance dew-proof performance.

[0055] The method for manufacturing the flexible solar cell of the present invention is not particularly limited, but a preferred method is to laminate a power generation unit between a portion (sheet A) having a first dew-proof portion covered by a second dew-proof portion and a portion (sheet B) having a second dew-proof portion, as this method allows for easy manufacturing over a large area.

[0056] Sheet A is obtained by covering the periphery of the first dew-proof section with the second dew-proof section. Specifically, if the flexible solar cell of the present invention has a front sheet, Sheet A can be obtained by performing the steps of laminating the second dew-proof section on the front sheet, laminating the first dew-proof section on the laminated second dew-proof section, and further laminating the second dew-proof section so as to cover the entire side and bottom surface of the first dew-proof section. If the flexible solar cell of the present invention does not have a front sheet, Sheet A can be obtained by first laminating a layer consisting of the second dew-proof section, laminating the first dew-proof section on top of it, and then laminating the second dew-proof section so as to cover the entire bottom and side surface of the first dew-proof section.

[0057] The above-described power generation unit can be obtained by sequentially stacking various layers, such as electrodes, electron transport layers, photoelectric conversion layers, hole transport layers, and counter electrodes, on a substrate. Alternatively, it can be obtained by using electrodes instead of a substrate and stacking the various layers on top of the electrodes. Conventional methods for stacking each layer can be used without any particular limitations for flexible solar cells.

[0058] The above-mentioned sheet B can be obtained by forming a layer consisting only of the second dew-preventing portion by coating or the like if the flexible solar cell of the present invention does not have a backsheet. Alternatively, if the flexible solar cell of the present invention has a backsheet, the sheet B can be obtained by laminating the second dew-preventing portion on the backsheet.

[0059] One method for laminating sheet A, the power generation layer, and sheet B is the roll-to-roll method. By using the roll-to-roll method, large-area flexible solar cells can be manufactured continuously.

[0060] Here, Figure 2 shows a schematic diagram illustrating an example of a manufacturing method for the flexible solar cell of the present invention. Figure 2 shows the manufacturing process of the flexible solar cell of Figure 1. The flexible solar cell of the present invention can be manufactured by separately fabricating a sheet A in which a front sheet 4, a first anti-condensation section 3, and a second anti-condensation section 2 are laminated, with the periphery of the first anti-condensation section 3 covered by the second anti-condensation section 2, a sheet B in which the second anti-condensation section 2 is laminated on a back sheet 5, and a power generation section 1, and then laminating the power generation section between sheet A and sheet B. The above method allows for easy manufacturing of large areas, and because there are few processes involving the first anti-condensation section, it is possible to make it difficult for cracks or pinholes to occur in the first anti-condensation section during manufacturing. [Effects of the Invention]

[0061] According to the present invention, even when the condensation-preventing portion is made into a thin film, cracks and pinholes are less likely to occur, and a highly condensation-preventing flexible solar cell can be provided. [Brief explanation of the drawing]

[0062] [Figure 1] This is a cross-sectional view showing an example of the structure of the flexible solar cell of the present invention. [Figure 2] This is a schematic diagram illustrating an example of a method for manufacturing the flexible solar cell of the present invention. [Figure 3] This is a photograph of the flexible solar cell obtained in Comparative Example 2. [Modes for carrying out the invention]

[0063] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0064] (Example 1) A PET film measuring 25 mm × 25 mm × 100 μm was prepared as the substrate. A 200 nm thick ITO film was formed on the substrate by sputtering to serve as the counter electrode. A thin-film electron transport layer with a thickness of 20 nm was formed on the formed counter electrode by sputtering. Furthermore, a titanium dioxide paste containing titanium dioxide was applied to the thin-film electron transport layer by spin coating and then dried to form a porous electron transport layer with a thickness of 100 nm. Next, a 1 M solution of lead iodide was prepared by dissolving it in a mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) as the metal halide compound, and this solution was formed on the porous electron transport layer by spin coating. Furthermore, an 8 wt% solution of methylammonium iodide was prepared by dissolving it in 2-propanol as the amine compound. This solution was applied to the lead iodide by spin coating and annealed at 150°C for 10 minutes to form a photoelectric conversion layer containing the organic-inorganic perovskite compound CH3NH3PbI3 with a thickness of 700 nm. Next, a chlorobenzene solution containing 2% by weight of Spiro-OMETAD (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. Subsequently, a 100 nm thick Al film was formed on the photoelectric conversion layer as an electrode by sputtering, and a power generation unit consisting of a substrate, counter electrode, electron transport layer, photoelectric conversion layer, hole transport layer, and electrode was obtained.

[0065] Next, UBF512 (manufactured by 3M, size: 50mm x 50mm x 200μm, indicated as commercial product A in the table) was prepared as the front sheet. Polyisobutylene was applied to the front sheet to a thickness of 70μm as the second anti-condensation layer, and a thin glass sheet measuring 45mm x 45mm x 0.05mm was laminated on top of it as the first anti-condensation layer. Then, sheet A was obtained by applying polyisobutylene (SP value: 7.5) to the entire laminated surface of the front sheet from the top surface of the thin glass sheet (the side opposite the front sheet) to a height of 70μm (190μm from the laminated surface of the front sheet). Next, a 50mm x 50mm x 360μm aluminum-reinforced backsheet (FAPL, manufactured by Toyo Aluminum Co., Ltd.) was prepared as a backsheet, and sheet B was obtained by applying polyisobutylene to the backsheet as a second anti-condensation layer to a thickness of 70μm.

[0066] Subsequently, the power generation section was sandwiched between sheets A and B so that the base material of the second dew-proof section of sheet A and the base material of the power generation section faced each other, and the electrodes of the second dew-proof section of sheet B and the power generation section faced each other, and thermal vacuum lamination was performed at 100°C to obtain a flexible solar cell having the structure shown in Figure 1.

[0067] (Measurement of water vapor transmission rate in the first condensation prevention section) A 100 μm thick glass plate made of the same material as the thin glass used in Example 1 was prepared as a measurement sample. The water vapor transmission rate of the measurement sample was measured using the differential pressure method in accordance with the gas chromatography method of JIS K7129, under conditions of 85°C and 85% humidity, with the surface actually located outside the module designated as the water vapor introduction surface. The result was 0.5 × 10⁻⁶. -5 g / m 2 It was / day.

[0068] (Measurement of the longitudinal modulus of the second dew-proof section) The polyisobutylene used as the second condensation prevention layer in Example 1 underwent a tensile test in accordance with JIS K 7161, and its Young's modulus was measured to be 70,000 MPa.

[0069] (Measurement of viscosity at 20°C in the second dew prevention section) The polyisobutylene used as the second dew prevention component in Example 1 had a viscosity of 560 Pa·s at 20°C measured using a BM-type rotational viscometer (BMII, manufactured by Toki Sangyo Co., Ltd.) at a rotational speed of 60 rpm.

[0070] (Example 2, Comparative Example 1) A flexible solar cell was obtained in the same manner as in Example 1, except that the configuration of the front sheet, the second anti-condensation layer, and the first anti-condensation layer was as shown in Table 1. For the PET in Table 1, CosmoShine (manufactured by Toyobo Co., Ltd., thickness: 188 μm) was used.

[0071] (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 1, the second anti-condensation section was not laminated on the lower side of the first anti-condensation section during the manufacturing of sheet A, and the first anti-condensation section and the power generation layer were laminated so that they were in direct contact during the lamination of sheet A, sheet B and the power generation section. A photograph of the flexible solar cell obtained here is shown in Figure 3. In Figure 3, air bubbles have formed between the power generation section and the thin glass layer, making it opaque.

[0072] (Comparative Example 3) Instead of a PET film substrate, a thin glass sheet from Example 1 was used, and a power generation unit was formed on the thin glass sheet in the same manner as in Example 1. A flexible solar cell was fabricated in the same manner as in Example 1, except that sheet A was made using the thin glass layer on which the power generation units were laminated, and sheet A and sheet B were laminated together. However, because cracks occurred in the thin glass sheet during the formation of the power generation unit, during lamination, and during minor movement, the evaluation of the initial conversion efficiency and moist heat durability described later was not performed.

[0073] <Rating> The solar cells obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0074] (1) Evaluation of ease of manufacture In the manufacturing of flexible solar cells, the ease of manufacturing was evaluated by marking "×" if both the lamination of the power generation section and the lamination work for sealing had to be performed on the first dew prevention section, and "○" if either one of them was sufficient.

[0075] (2) Evaluation of whether or not there are cracks in the first condensation prevention section. The first condensation prevention section of the obtained flexible solar cell was visually inspected, and the presence or absence of cracks in the first condensation prevention section was evaluated.

[0076] (3) Evaluation of initial conversion efficiency A power supply (KEITHLEY, Model 236) was connected between the electrodes of the resulting flexible solar cell, and the intensity was set to 100 mW / cm². 2 The photoelectric conversion efficiency was measured using a solar simulation software (manufactured by Yamashita Densou Co., Ltd.). The initial conversion efficiency was evaluated using the photoelectric conversion efficiency of Comparative Example 2 as a baseline, with a value of "○" indicating a value of 1.05 or higher and "×" indicating a value of less than 1.05.

[0077] (4) Evaluation of resistance to moist heat The obtained flexible solar cells were subjected to a humidity and heat resistance test by being placed under conditions of 85% RH and 85°C for 500 hours. After the humidity and heat resistance test, the photoelectric conversion efficiency was measured in the same manner as the evaluation of the initial conversion efficiency described above, and the maintenance 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 maintenance rate. The humidity and heat durability of the obtained maintenance rates was evaluated according to the following criteria. ○: Maintenance rate of 90% or higher ×: Maintenance rate less than 90%

[0078] [Table 1] [Industrial applicability]

[0079] According to the present invention, even when the condensation-preventing portion is made into a thin film, cracks and pinholes are less likely to occur, and a highly condensation-preventing flexible solar cell can be provided. [Explanation of Symbols]

[0080] 1. Power Generation Section 2 2nd dew protection section 3 1st dew protection section 4 Front seats 5 Backseat

Claims

1. A power generation unit having a first electrode, a photoelectric conversion layer, and a second electrode, A water vapor permeability of 1 × 10 is arranged on the light-receiving surface of the power generation unit. －３ g / m ２ It has a first condensation prevention section of less than / days, The first condensation prevention section is made of an inorganic material. A flexible solar cell characterized in that the first dew-preventing section and the power generation section do not come into contact.

2. A second condensation prevention section is provided between the first condensation prevention section and the power generation section. The second dew-preventing part is in contact with the surface of the first dew-preventing part on the power generation part side. The flexible solar cell according to claim 1, characterized in that its Young's modulus is 1000 MPa or less.

3. The flexible solar cell according to claim 2, characterized in that the second dew prevention portion has a viscosity of 1000 Pa·s or less at 20°C.

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