Barrier film and solar cell using the same

Abstract

To provide a barrier film which can obtain enough transparency to be used as a protective layer on a light-receiving side of a solar cell, has high moisture barrier performance, prevents increase in a bulk, and can be easily formed, and a solar cell using the same.SOLUTION: A barrier film 10 is used in a protective layer 21 on a light-receiving side of a solar cell 20, and is formed by sandwiching a high water absorbing layer 13 between and fixing it to synthetic resin film layers, wherein the high water absorbing layer 13 is formed so that nano-sized high water absorbing materials 15 are scattered in a fiber assembled material 14 composed of nano-sized synthetic resin fibers 14a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a barrier film used as a protective layer on the light-receiving side of a solar cell, and a solar cell using the same. [Background technology]

[0002] Conventionally, a solar cell has been proposed that includes a highly water-absorbent layer (moisture-absorbing layer) made by impregnating a highly water-absorbent material such as sodium polyacrylate into a nonwoven fabric as a protective layer to block moisture from the outside (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4194457 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the base material of the moisture absorbing layer is a nonwoven fabric, it cannot be said that it is appropriate to use it as a protective layer on the light receiving side of a solar cell, which requires transparency.

[0005] Another potential protective layer for solar cells is a film coated with inorganic materials by vapor deposition, but vapor deposition can result in a large volume, making it unsuitable for the protective layer of thin-film solar cells such as perovskite solar cells. Vapor deposition is also time-consuming and potentially costly.

[0006] The present invention has been proposed in consideration of the above circumstances, and an object of the present invention is to provide a barrier film that has sufficient transparency for use as a protective layer on the light-receiving side of a solar cell, has high moisture barrier performance, is not easily bulky, and can be easily formed, and a solar cell using the same. [Means for solving the problem]

[0007] In order to achieve the above object, the barrier film of the present invention is a transparent barrier film used as a protective layer on the light-receiving side of a solar cell, which is formed by sandwiching and fixing a high water-absorbent layer between synthetic resin film layers, and is characterized in that the high water-absorbent layer is formed by interspersing nano-sized high water-absorbent materials in a fiber assembly made of nano-sized synthetic resin fibers. [Effects of the Invention]

[0008] The barrier film of the present invention has the above-mentioned configuration, and therefore has sufficient transparency for use as a protective layer on the light-receiving side of a solar cell, has high moisture barrier properties, is less likely to become bulky, and can be easily formed. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are a schematic longitudinal sectional view and a partially enlarged view of a barrier film according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view of a solar cell using the barrier film. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the basic structure of the barrier film 10 according to the embodiment will be described.

[0011] The barrier film 10 is a transparent film used for the protective layer 21 on the light-receiving side of the solar cell 20, and is formed by sandwiching and fixing a high water-absorbent layer 13 between synthetic resin film layers (between the protective film 11 and the base film 12). The high water-absorbent layer 13 is formed by interspersing nano-sized high water-absorbent materials 15 in a fiber assembly 14 made of nano-sized synthetic resin fibers 14a.

[0012] Next, the detailed configuration of the barrier film 10 will be described below with reference to FIG.

[0013] The barrier film 10 is a film having at least three layers: a base film 12 made of a synthetic resin film layer, a highly water-absorbent layer 13 disposed on top of the base film 12, and a protective film 11 made of a synthetic resin film layer disposed on top of that.

[0014] When the high water absorbent layer 13 is formed by the electrospinning method described below, it is desirable that the base film 12 has a surface that has good adhesion to the high water absorbent layer 13. The base film 12 may be made up of multiple layers, in which case it is sufficient that the layer disposed on the upper surface has good adhesion to the high water absorbent layer 13.

[0015] The protective film 11 is a film for protecting the high water absorption layer 13, and is desirably resistant to oil, solvents, water, physical external forces, etc. The protective film 11 may also be made up of multiple layers.

[0016] Furthermore, the base film 12 and the protective film 11 may be made of a transparent material with low water vapor permeability, and it is desirable that the base film 12 and the protective film 11 be made of the same synthetic resin material that satisfies the above-mentioned conditions.

[0017] Examples of highly transparent synthetic resin materials include low-density polyethylene (LDPE), high-density polyethylene (HDPE), plain polypropylene (CPP), oriented polypropylene (OPP), polyethylene terephthalate (PET), and cycloolefin polymer (COP).

[0018] The fiber assembly 14 formed by assembling nano-sized synthetic resin fibers 14a is called a nanofiber assembly. Examples of materials for the synthetic resin fibers 14a include nylon, polyurethane, polyvinylidene fluoride, polyamide, and polyacrylonitrile.

[0019] As will be described later, the present barrier film 10 is used as a protective layer 21 on the light-receiving side of a perovskite solar cell (see FIG. 2). Perovskite solar cells are designed to be approximately 0.1 mm to 1.0 mm thick, and the barrier film 10 must be thin enough to accommodate this thickness. Naturally, the high-water-absorption layer 13 and fiber assembly 14, which are components of the barrier film 10 used in such a thin-film solar cell 20, are desirably even thinner.

[0020] Although the high water absorbent layer 13 is thus an ultra-thin film, the individual synthetic resin fibers 14a that make up the fiber assembly 14 are nano-sized, so that the multiple synthetic resin fibers 14a are irregularly arranged in the thickness direction as well, as shown in the enlarged view of Figure 1. In other words, the fiber assembly 14 is formed into a three-dimensional network of multiple synthetic resin fibers 14a.

[0021] The high water absorbent layer 13 is formed by three-dimensionally scattering nano-sized high water absorbency materials 15 in such a fiber assembly 14. As shown in the enlarged view of FIG. 1, the high water absorbency materials 15 are scattered at various depth positions in the thickness direction inside the fiber assembly 14. In this way, it is desirable for the high water absorbency materials 15 to be scattered randomly in the thickness direction as well in order to improve the water absorption performance of the high water absorbency layer 13. Note that the high water absorbency layer 13 may also be formed by attaching the high water absorbency materials 15 only to the surface of the fiber assembly 14.

[0022] Here, the fiber diameter of the nano-sized synthetic resin fibers 14a is preferably about 100 nm, but the upper limit of the fiber diameter is sufficient if it is 1 μm to ensure transparency. Also, it is preferable to use synthetic resin fibers 14a with long fiber length so that the highly water-absorbent material 15 can be efficiently scattered among the fibers of the fiber assembly 14 and easily entangled.

[0023] Examples of the highly water-absorbent material 15 include superabsorbent polymers (SAP) such as sodium polyacrylate, polyethylene oxide (PEO), polyvinyl alcohol (PVAL), and polyacrylamide. Alternatively, inorganic materials such as aluminum oxide (chemical formula: AlOx) and silicon oxide (chemical formula: SiOx) can also be used as the highly water-absorbent material 15.

[0024] Although the highly water-absorbent material 15 is in a fine powder state, it does not dissolve in water and has the ability to absorb and retain water inside (between molecular chains). Some highly water-absorbent materials 15 can absorb water several hundred times their own weight, and do not release water even when pressure is applied.

[0025] In this way, since the highly water-absorbent material 15 has water-retentive properties, its volume increases as it absorbs water. Because the highly water-absorbent material 15 is disposed in the space within the fiber assembly 14, it is desirable that the diameter of the highly water-absorbent material 15 be such that it can fit within the space even if it absorbs water and increases in volume.

[0026] Therefore, at the stage when the barrier film 10 is manufactured, it is desirable that the highly water-absorbent material 15 is in a fine powder state containing almost no moisture or solvent, that is, nano-sized (1 μm or less).

[0027] The high water-absorbent layer 13 is primarily made of transparent synthetic resin fibers 14a, ensuring sufficient transparency for use as the protective layer 21 (see FIG. 2) on the light-receiving side of the solar cell 20. Although the transparency of the synthetic resin fibers 14a is impaired by diffuse reflection of light, this is not a problem as long as there is sufficient space between the fibers.

[0028] Furthermore, there is no problem with the highly water-absorbent material 15 as long as it is a transparent material itself, and even if it is not transparent, there is no risk of the transparency being impaired depending on the content. Also, the light transmittance can be increased by making the highly water-absorbent material 15 nano-sized.

[0029] The thin, highly water-absorbent layer 13 described above can be formed by, for example, electrospinning, which is also called electrospinning, and is a manufacturing method in which a resin solution contained in a syringe is sprayed onto a substrate by applying high voltage, and then dried to produce nanofibers (fine fibers).

[0030] The substrate may be a synthetic resin sheet that forms the base film (synthetic resin film layer) 12. The resin solution is a solution in which a synthetic resin material that is the base of the fiber assembly 14 is dissolved in a solvent.

[0031] Alternatively, a solution of the highly water-absorbent material 15 in the same solvent as or another liquid used to generate the resin solution may be prepared in another syringe. Specifically, two syringes may be used to spray two types of solution onto the substrate from two nozzles by electrospinning. The solution on the substrate may then be dried to evaporate the solvent.

[0032] The superabsorbent material 15 is mixed with the solvent in the syringe, but by quickly ejecting the solution using the electrospinning method and drying it, it is possible to produce superabsorbent material 15 that contains almost no solvent within the fiber assembly 14. In particular, it is preferable to quickly evaporate the surrounding solvent by drying so that the superabsorbent material 15 can maintain a fine powder state. In this way, the fine powder state of the superabsorbent material 15 is scattered throughout the fiber assembly 14.

[0033] Alternatively, a solution in which a synthetic resin material that is the base of the fiber assembly 14 and the highly water-absorbent material 15 are mixed may be prepared in one syringe, and the solution may be sprayed from one nozzle.

[0034] In this way, the high water absorption layer 13 can be formed in close contact with the base film 12. Then, the protective film 11 is fixed onto the high water absorption layer 13 using an adhesive or the like, thereby producing the present barrier film 10.

[0035] Alternatively, after forming the fiber assembly 14 on the base film 12 by electrospinning, another method may be used to intersperse the high water absorbency material 15 on the surface or inside of the fiber assembly 14. By interspersing the high water absorbency material 15 in fine powder form on the dried fiber assembly 14, a high water absorbency layer 13 (barrier film 10) containing the high water absorbency material 15 that contains almost no moisture or solvent can be formed.

[0036] As described above, this barrier film 10 is suitable for use as a protective layer 21 (see FIG. 2) on the light-receiving side of a thin-film solar cell 20 such as a perovskite solar cell.

[0037] A perovskite solar cell is a solar cell 20 that has a perovskite layer made of an organic material with a unique crystal structure called a perovskite structure as a power generation layer (not shown). The perovskite layer itself is extremely thin, about 1 μm thick.

[0038] 2, the solar cell 20 has a laminate 20A in which a photovoltaic layer 23 is sandwiched between protective layers 21 and 22. In the laminate 20A, a light-receiving-side protective layer 21 and a base-side protective layer 22 are arranged so as to be in close contact with the upper and lower surfaces of the photovoltaic layer 23, respectively, and the protective layers 21 and 22 are fixed together with an adhesive.

[0039] Although a plan view of the solar cell 20 is omitted, the protective layers 21 and 22 have the same planar shape and dimensions and are not misaligned. The planar shapes of these protective layers 21 and 22 generally correspond to the planar shape of the laminate 20A, and may be, for example, a substantially rectangular shape.

[0040] The photovoltaic layer 23 has smaller planar dimensions than the protective layers 21 and 22, and is disposed in a central position between the protective layers 21 and 22 in plan view. At least one surface of the photovoltaic layer 23 serves as a light-receiving surface for receiving light, and the light-receiving-side protective layer 21 made of the barrier film 10 is disposed on that surface.

[0041] An adhesive layer 24 is formed on all sides of the photovoltaic layer 23 between the protective layers 21 and 22, up to the peripheral edges of the protective layers 21 and 22. This adhesive layer 24 is a filling layer formed by hardening an adhesive used to bond the protective layers 21 and 22 to each other, and is disposed without gaps in the lateral space around the entire periphery of the photovoltaic layer 23 disposed between the protective layers 21 and 22.

[0042] The barrier film 10 shown in FIG. 1 is used for the protective layer 21 on the light-receiving side of this solar cell 20, but as shown in the example, a similar barrier film 10 may also be used for the protective layer 22 on the base side.

[0043] In the barrier film 10 according to this embodiment, the base film 12 and the protective film 11 are made of the same material, and therefore the barrier film 10 can be turned upside down and used as the protective layers 21, 22. When the base film 12 and the protective film 11 are different, or when they are the same, one may be arranged on the outer surface side and the other on the inner surface side depending on the degree of uneven distribution of the highly water-absorbent material 15 in the thickness direction within the fiber assembly 14.

[0044] Furthermore, since the layered surface (cross section of multiple layers) including the organic adhesive layer 24 appears on the end surface 20Aa of the entire periphery of the laminate 20A, it is desirable to cover the end surface 20Aa with a coating that has a high moisture barrier property. For example, the coating may be made of silica glass obtained by converting polysilazane.

[0045] In this type of solar cell 20, the barrier film 10 used as the protective layers 21, 22 has a high water absorption layer 13, so that moisture entering from the outside can be contained within the high water absorption material 15 in the high water absorption layer 13. As a result, it is possible to improve the moisture barrier performance of the solar cell 20. Note that the high water absorption material 15 gradually expands as it absorbs moisture, but this poses little problem because there are many spaces between the synthetic resin fibers 14a in the fiber assembly 14 and the high water absorption material 15 is scattered throughout these spaces.

[0046] Furthermore, since the high water absorbent material 15 is nano-sized, it is possible to prevent the high water absorbent layer 13, the barrier film 10, and the solar cell 20 using them from becoming too bulky. Since the high water absorbent material 15 is nano-sized, the transparency of the protective layer 21 on the light-receiving side of the solar cell 20 is also ensured.

[0047] The solar cell 20 in which the barrier film 10 is used is not limited to a perovskite solar cell, but may also be, for example, an amorphous silicon solar cell, a dye-sensitized solar cell, an organic thin-film solar cell, etc. The photovoltaic layer 12 may be silicon-based, compound-based, organic-based, or the like, and is not particularly limited.

[0048] The configuration and shape of the barrier film 10 according to the embodiment described above are merely examples, and it goes without saying that the configuration and shape can be changed as appropriate to other than those shown in the drawings. [Explanation of symbols]

[0049] 10 Barrier Film 11 Protective film (synthetic resin film) 12 Base film (synthetic resin film) 13 High water absorption layer 14 Fiber composite materials 14a Synthetic resin fiber 15 High water absorbency material 20 Solar Cells 20A laminate 20Aa end face 21 Protective layer on the light receiving side 22 Base side protective layer 23 Photovoltaic layer 24 Adhesive layer 25 Edge coating

Claims

1. A transparent barrier film used as a protective layer on the light-receiving side of a solar cell, which comprises a synthetic resin film layer and a high water-absorption layer sandwiched and fixed between the film layers, The barrier film is characterized in that the high water absorbency layer is made of a fiber assembly made of nano-sized synthetic resin fibers with nano-sized high water absorbency materials scattered throughout.

2. In claim 1, A barrier film characterized in that the fiber assembly is in a three-dimensional network shape.

3. A solar cell having a laminate in which a photovoltaic layer is sandwiched between protective layers, 3. A solar cell, wherein at least one of the protective layers is made of the barrier film according to claim 1.

Images