JP2010182950A - Rear-face protection sheet for solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rear-face protection sheet for a solar cell module that has a superior gas barrier property using neither a metal foil nor an inorganic thin film and is also superior in adhesion to a solar cell module to thereby contribute to improvement in weatherability and long-period reliability of the solar cell module. <P>SOLUTION: The rear-face protection sheet for the solar cell module includes a low-anisotropic liquid crystal polymer film. The rear-face protection sheet for the solar cell module preferably further includes a surface protection layer. The surface protection layer suppresses deterioration in the liquid crystal polymer film which is caused by ultraviolet light, water, etc., to achieve the higher long-period reliability of the solar cell module. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a back surface protection sheet for a solar cell module.

  In recent years, as the problem of global warming grows, solar cells have been attracting attention as an energy source that does not emit carbon dioxide, and the market distribution volume has shown a remarkable increase worldwide.

  However, the ratio of the electric power derived from the solar cell to the total electric power consumption is still small, and reduction of power generation cost is one of the major issues for further spread of the solar cell. Specifically, it is necessary to improve long-term reliability in addition to reducing manufacturing costs including improving yield and improving energy conversion efficiency.

  Conventionally, in order to improve the long-term reliability of a solar cell, a back surface protection sheet has been provided on the solar cell module. This back surface protective sheet contributes to improvement of the weather resistance, water resistance, gas barrier property, chemical resistance, etc. of the solar cell module, and can also impart design properties to the solar cell module. Such a back surface protection sheet is mainly composed of a weather resistant resin film and a gas barrier material. A metal foil such as an aluminum foil is often used as the gas barrier material, and many back surface protection sheets have a structure in which both surfaces of the metal foil are sandwiched between weather resistant resin films. When a metal foil was not used, a sheet in which an inorganic thin film such as an inorganic oxide film or an inorganic nitride film and a weather resistant resin film were combined as a gas barrier material layer was used.

  However, there are some problems with the back surface protection sheet using metal foil or inorganic thin film. For example, when using a metal foil, a weather-resistant resin film is laminated on both sides as described above, but if the strength of the film is insufficient, the electrode of the solar cell element penetrates when adhering to the solar cell module. Then, the metal foil was reached and a short circuit could be caused. In addition, when an inorganic thin film is used, peeling or cracking may occur due to a change in temperature or humidity, bending, or the like in addition to an increase in cost. More specifically, in the case of the backside protective sheet having an inorganic thin film, even if there is no initial problem, peeling may occur due to an accelerated test, so the performance may deteriorate due to use under severe conditions or long-term use. However, its long-term reliability is not sufficient.

  Therefore, in order to increase the gas barrier property of the resin film without using these metal foils and inorganic thin films, it is conceivable to increase the thickness and the number of laminated layers of the resin film. However, such a back surface protection sheet increases material costs and manufacturing costs. Furthermore, since it is difficult to uniformly apply pressure to the thick back surface protective sheet, a stacking failure occurs when laminating the solar cell module via the sealing resin, and the yield decreases. In addition, since it can be deformed along the circuit shape of the solar cell element if it is a thin film, it is easy to laminate without a gap. However, since a thick back surface protection sheet is difficult to deform according to the circuit shape, A gap is formed between the resin and the circuit, and moisture or the like enters from the gap to reduce the long-term reliability of the solar cell.

  As described above, in the solar cell module, a back surface protection sheet is generally used in order to improve long-term reliability.

  In this back surface protection sheet, since a gas barrier property cannot be sufficiently ensured only by a resin film, a metal foil or an inorganic thin film is usually used in combination. However, when these metal foils and the like are used in combination, problems such as an increase in material cost, a decrease in insulation characteristics, and peeling due to impact or bending occur. On the other hand, if the thickness is increased in order to increase the gas barrier property of the resin film without using a metal or an inorganic thin film, a problem arises in adhesion and the like.

  Accordingly, an object of the present invention is to provide a solar cell that can contribute to improving the weather resistance and long-term reliability of a solar cell module because it has excellent gas barrier properties and excellent adhesion to the solar cell module without using a metal foil or an inorganic thin film. It is providing the back surface protection sheet for battery modules.

  The present inventor has intensively studied to solve the above problems. As a result, the inventors have found that the above-mentioned problems can be solved by using a liquid crystal polymer film as a core layer for ensuring gas barrier properties, thereby completing the present invention.

  The back surface protection sheet for solar cell modules which concerns on this invention is characterized by including a low anisotropic liquid crystal polymer film.

  As the back surface protective sheet for a solar cell module according to the present invention, a sheet further provided with a surface protective layer is suitable. The surface protective layer can suppress deterioration of the liquid crystal polymer film caused by ultraviolet rays, moisture, etc., and can further enhance the long-term reliability of the solar cell module.

  The surface protective layer is preferably made of a weather resistant resin. The back surface protective sheet having a surface protective layer made of a weather resistant resin can surely improve the long-term reliability of the solar cell module.

  As the surface protective layer, an ultraviolet absorbing layer is also suitable. In order to increase the UV resistance of liquid crystal polymers, liquid crystal polymers caused by UV rays are provided by providing UV-absorbing surface protective layers such as those containing UV absorbers and those made of resins having UV-absorbing functional groups. Deterioration of film characteristics can be more reliably suppressed.

  As the surface protective layer, those containing a pigment are also preferable. The pigment can improve the ultraviolet blocking property, the light reflectivity, the design property, etc. of the surface protective layer, and consequently the back surface protective sheet, according to the characteristics.

  As the back surface protective sheet for a solar cell module according to the present invention, a sheet further having an adhesive layer is suitable. If the adhesive layer is provided, adhesion between the respective layers in the back surface protective sheet is facilitated, and if the adhesive layer is provided on the outermost layer, the back surface protective sheet is easily adhered to the solar cell module.

  Since the back surface protective sheet according to the present invention includes a liquid crystal polymer film as an essential component, it has sufficient gas barrier properties without using a metal foil or an inorganic thin film in combination or increasing the film thickness. Therefore, since it has excellent insulation resistance, weather resistance, and adhesion to the solar cell module, the performance of the solar cell can be maintained over the long term, and it can be greatly contributed to the practical use of the solar cell. is there.

FIG. 1 is a schematic diagram showing a configuration of a general crystalline solar cell module including a solar cell element using single crystal silicon or polycrystalline silicon. FIG. 2 shows a general thin film solar cell module including amorphous silicon solar cells, microcrystalline silicon solar cells, multi-junction solar cells thereof, compound semiconductor solar cells, organic solar cells, and dye-sensitized solar cells. It is a schematic diagram which shows the structure of these. FIG. 3 is a schematic view of the back protective sheet according to the present invention, which is composed only of a low anisotropic liquid crystal polymer film. FIG. 4 is a schematic view of a back surface protective sheet according to the present invention, which is composed of a low anisotropic liquid crystal polymer film having a surface protective layer on one side. FIG. 5 is a schematic view of a back surface protective sheet according to the present invention, which is made of a low anisotropic liquid crystal polymer film having an adhesive layer. FIG. 6 is a schematic view of a back surface protective sheet according to the present invention, which is composed of a low anisotropic liquid crystal polymer film having a surface protective layer on one side and an adhesive layer on the opposite side. FIG. 7 is a schematic view of a back surface protective sheet according to the present invention, which has an adhesive layer on both surfaces of a low anisotropic liquid crystal polymer film, and further has a surface protective layer on one outer side of the adhesive layer. . FIG. 8 is a schematic view of the back protective sheet according to the present invention, which is composed of a low anisotropic liquid crystal polymer film having a surface protective layer on both sides. FIG. 9 is a schematic view of a back surface protective sheet according to the present invention, which has an adhesive layer on both surfaces of a low anisotropic liquid crystal polymer film, and further has a surface protective layer on both outer sides of the adhesive layer. . FIG. 10 is a schematic view of a back surface protective sheet according to the present invention, which has a surface protective layer on both surfaces of a low anisotropic liquid crystal polymer film, and further has an adhesive layer on one outer side of the surface protective layer. is there.

  The back protective sheet for a solar cell module according to the present invention includes a low anisotropic liquid crystal polymer film as an essential component in order to ensure gas barrier properties and the like. First, the liquid crystal polymer film used in the present invention will be described.

  As the liquid crystal polymer, polyester known as a thermotropic liquid crystal polymer is preferable. For example, it is an aromatic polyester synthesized mainly with aromatic dicarboxylic acid and monomers such as aromatic diol and aromatic hydroxycarboxylic acid, and exhibits liquid crystallinity when melted.

  Typical examples of thermotropic liquid crystal polymers include a first type synthesized from parahydroxybenzoic acid (PHB), terephthalic acid, and biphenol [the following formula (1)], PHB and 2,6- The second type synthesized from hydroxynaphthoic acid [the following formula (2)], and the third type synthesized from PHB, terephthalic acid and ethylene glycol [the following formula (3)]. . In the back surface protective sheet of the present invention, any of the first to third polyesters can be used. However, from the viewpoint of heat resistance, dimensional stability, and water vapor barrier properties, fully aromatic polyesters (first and second types). ) Is preferred, and the second type of polyester is particularly preferred.

  The liquid crystal polymer film that is an essential component of the back surface protective sheet according to the present invention has low anisotropy. Usually, when a thermotropic liquid crystal polymer is formed into a film by melt extrusion, most of the polymer molecules are oriented in the extrusion direction (MD direction), and the film physical properties are anisotropic due to the molecular orientation. When a liquid crystal polymer film having a large anisotropy is used for a back protective sheet for a solar cell module, various drawbacks occur. For example, a difference between the liquid crystal polymer film and other layers is caused by thermal fluctuation accompanying environmental changes, and the back surface protection sheet is likely to be wrinkled or warped. In an extreme case, the liquid crystal polymer film peels off from other layers, which adversely affects the long-term reliability of the solar cell module. Therefore, in the present invention, a low anisotropic liquid crystal polymer film is used.

  In the present invention, a low-anisotropy liquid crystal polymer film is a film in which the anisotropy of planar physical properties is reduced or eliminated by reducing or eliminating the molecular orientation described above. Is included. Here, the plane physical properties include linear expansion coefficient, thermal expansion coefficient, thermal contraction ratio, tensile strength, tensile elongation, tensile elastic modulus, and the like. More specifically, “low anisotropy” in the present invention means that the ratio of the linear expansion coefficient in an arbitrary plane direction X of the liquid crystal polymer film to the linear expansion coefficient in the plane direction Y orthogonal to the X direction is 1. / 3 or more and 3 or less.

  A low-anisotropy liquid crystal polymer film can be produced by randomly orienting molecules oriented in the plane direction by film molding or the like. For example, an anisotropic liquid crystal polymer film is once manufactured by melt extrusion, and then uniaxially stretched in the direction perpendicular to the MD direction (TD direction, width direction) or simultaneously stretched in the MD and TD directions. can get. The anisotropy of planar physical properties such as the linear expansion coefficient can be reduced or eliminated by adjusting the conditions during the stretching, whereby a low anisotropy liquid crystal polymer film is obtained.

  The thickness of the liquid crystal polymer film used in the present invention is preferably about 10 μm to 200 μm. If the thickness is less than 10 μm, gas barrier properties may not be sufficiently secured. On the other hand, when the thickness exceeds 200 μm, it may not be possible to apply pressure uniformly when pressure-bonding to the solar cell module, and there is a possibility that sufficient adhesion with the solar cell module cannot be ensured. The thickness is more preferably 25 μm or more and 100 μm or less.

  The liquid crystal polymer film may be subjected to a surface treatment in accordance with the compatibility with the sealing resin and the like in order to improve the adhesion to the sealing resin, adhesive, and other layers. Such a surface treatment method is not particularly limited, and examples thereof include corona treatment, plasma treatment, ultraviolet treatment, flame treatment, chemical treatment, and primer treatment.

  Although the back surface protection sheet which concerns on this invention has a liquid crystal polymer film as a core layer for gas-barrier property ensuring, you may provide a surface protection layer further. The liquid crystal polymer film is affected by light and moisture entering the sheet from the outside, light transmitted through the solar cell module, and the like, and there is a possibility that the appearance is deteriorated due to yellowing or the mechanical strength is lowered. Therefore, by providing a surface protective layer, the liquid crystal polymer film can be protected and its ultraviolet resistance and hydrolysis resistance can be improved.

  The surface protective layer may be provided only on one side of the liquid crystal polymer film, or may be provided on both sides as necessary. For example, as a silicon-based solar cell module, a crystalline solar cell module composed of a bulky body such as a silicon wafer, and a thin-film system in which solar cell elements are formed on the entire surface of a glass substrate by a plasma CVD method or the like There is a solar cell module. In the thin-film solar cell module, since the solar cell elements are entirely formed as shown in FIG. 2, the incident light basically does not reach the back surface protection sheet. Therefore, in order to reduce adverse effects such as light from the back surface side, a mode in which a surface protective layer is provided only on the surface opposite to the solar cell module may be taken. On the other hand, in the crystalline solar cell module, there is a gap between the solar cell elements as shown in FIG. In this power generation loss portion, incident light reaches the back surface protection sheet without being used in the semiconductor wafer, so there is a concern about discoloration due to long-term outdoor installation due to the influence of ultraviolet rays contained in the incident light. Therefore, in the back surface protection sheet of the crystalline solar cell module, it is preferable to provide a surface protection layer on both sides of the liquid crystal polymer film. In the above description, a silicon solar cell has been described as an example. However, the back surface protection sheet of the present invention can be used for other solar cells such as a compound semiconductor solar cell, an organic solar cell, and a dye-sensitized solar cell. It is preferable to provide a surface protective layer as appropriate according to circumstances.

  When surface protective layers are provided on both sides of the liquid crystal polymer film, the materials and thicknesses of the plurality of surface protective layers may be the same, but the materials and thicknesses may be different depending on the purpose.

  The thickness of the surface protective layer is recommended to be 5 μm or more, more preferably 10 μm or more, and 100 μm or less, more preferably 50 μm or less.

  The material for the surface protective layer may be appropriately selected according to necessity or purpose, but a resin having excellent weather resistance is preferable. The type of weather-resistant resin is not particularly limited, but fluorine resin, acrylic resin, polyethylene resin, polyolefin resin, cyclic polyolefin resin, polystyrene resin, acrylonitrile-styrene copolymer (AS resin), acrylonitrile- Butadiene-styrene copolymer (ABS resin), polyvinyl chloride resin, polycarbonate resin, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyamide resins such as various nylons, polyimide resins, polyamideimide resins, Examples include polyaryl phthalate resins, silicone resins, polysulfone resins, polyphenylene sulfide resins, polyether sulfone resins, polyurethane resins, acetal resins, and cellulose resins. Can. Further, in order to impart desired properties to these resins, an ultraviolet absorbing functional group or the like may be introduced. These resins can be used alone, or two or more suitable ones can be selected and mixed for use.

  It is preferable to add an ultraviolet absorber to the surface protective layer in order to protect the liquid crystal polymer film from the influence of ultraviolet rays. Although it does not specifically limit as a ultraviolet absorber, For example, a benzophenone series, a benzotriazole series, a benzoate series, a salicylate series etc. are mentioned. Moreover, as an inorganic type ultraviolet absorber, fine particles such as zinc oxide, titanium oxide, zirconium oxide, and cerium oxide can be typically used.

  The addition amount of the ultraviolet absorber is not particularly limited, but is usually preferably in the range of 0.1% by mass or more and 10% by mass or less in the resin, and particularly in the range of 0.3% by mass or more and 10% by mass or less. preferable.

  It is preferable to add a pigment to the surface protective layer in order to improve performance such as ultraviolet blocking properties, light reflectivity, and design properties. Examples of the inorganic pigment include titanium oxide, zinc oxide, silicon oxide, aluminum oxide, calcium carbonate, magnesium oxide, and barium sulfate. Examples of organic pigments include polycyclic pigments such as azo pigments and phthalocyanine pigments. These pigments may be added to a melted weather resistant resin or varnish-like resin and mixed for use. In addition, the blending ratio of the pigment may be appropriately adjusted according to the purpose of adding each pigment, but in order to fully exhibit the characteristics, it is necessary to blend 5% by mass or more with respect to the entire surface protective layer. preferable. On the other hand, since the intensity | strength of a surface protective layer, etc. may fall when it mix | blends excessively, it is preferable to make the said ratio into 80 mass% or less.

  Furthermore, you may mix | blend a crosslinking agent, an antistatic agent, a flame retardant, etc. with a surface protective layer.

  The surface protective layer can be formed by melt-extruding a molten mixture of the weather resistant resin and the ultraviolet absorber onto the liquid crystal polymer film, or coating the liquid crystal polymer film with a varnish-like resin. Alternatively, the surface protective layer on the film and the liquid crystal polymer film may be thermocompression bonded, or both may be laminated via an adhesive layer. Since the surface protective layer does not need to be processed into a film once, it is preferably formed on the liquid crystal polymer film by a coating method.

  You may provide an adhesive layer further in the back surface protection sheet of this invention. Such an adhesive layer can be appropriately provided for adhesion between layers that need to improve adhesion, and facilitates lamination of a liquid crystal polymer film, which is a core layer for ensuring gas barrier properties, and a surface protective layer. It may be provided for this purpose, or may be provided on the outermost surface of the back surface protection sheet to improve the adhesion between the sealing resin of the solar cell module and the back surface protection sheet.

  As the resin constituting the adhesive layer, a resin excellent in water resistance and chemical resistance is preferable. Examples of such resins include acrylic resins, epoxy resins, styrene resins, urethane resins, polyester resins, olefin resins, vinyl acetate resins, cyanoacrylate resins, polyimide resins, polyamide resins, amino resins, and the like. Based resins and the like. These resins can be used alone, or two or more suitable ones can be selected and mixed for use. Moreover, a pigment, an ultraviolet absorber, a crosslinking agent, etc. can also be suitably added to these adhesive layers as needed.

  The back surface protective sheet according to the present invention has a liquid crystal polymer film as an essential component, and includes a surface protective layer and an adhesive layer as necessary, but when further improvement in gas barrier properties is desired depending on the use environment of the solar cell module. Further, a metal foil or an inorganic thin film can be appropriately provided on any layer in the back surface protective sheet. In addition, when it is necessary to increase the surface height, a hard coat layer may be appropriately provided on the outermost part. This hard coat layer may be antistatic.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1 Back Protective Sheet Consisting of Low Anisotropy Liquid Crystal Polymer Film FIG. 3 is a back protective sheet consisting of only a low anisotropic liquid crystal polymer film. Since the liquid crystal polymer film is a thermoplastic resin, the back surface protection sheet can be bonded to the sealing resin layer of the solar cell module by thermocompression bonding.

Example 2 Back Protective Sheet Having a Surface Protective Layer on One Side FIG. 4 is a back protective sheet provided with a surface protective layer on one side of a low anisotropic liquid crystal polymer film. This back surface protection sheet prevents the deterioration of the liquid crystal polymer film from light entering from the back surface side by adhering the surface opposite to the surface provided with the surface protection layer to the sealing resin layer of the solar cell module. The long-term reliability of the battery module can be further improved.

Example 3 Back Protective Sheet Having Adhesive Layer FIG. 5 is a back protective sheet in which an adhesive layer is provided on one side of a low anisotropic liquid crystal polymer film. Such a back surface protection sheet can be easily adhered to the sealing resin layer of the solar cell module via the adhesive layer.

Example 4 Back Protective Sheet Having Adhesive Layer and Surface Protective Layer FIG. 6 shows a back surface in which a surface protective layer is provided on one side of a low anisotropic liquid crystal polymer film and an adhesive layer is provided on the opposite side. It is a protective sheet. Such a back surface protective sheet can further enhance the long-term reliability of the solar cell module and can be easily adhered to the sealing resin layer of the solar cell module.

Example 5 Back Protective Sheet Having Adhesive Layer and Surface Protective Layer FIG. 7 shows the back protective sheet of Example 4 above, in which an adhesive layer is further provided between the low anisotropic liquid crystal polymer film and the surface protective layer. It is a protective sheet. Such a back surface protective sheet is efficiently manufactured because the low anisotropic liquid crystal polymer film as a raw material and the surface protective layer can be easily bonded via the adhesive layer in addition to the characteristics of the sheet according to Example 4 above. It is possible.

Example 6 Back Protective Sheet Having a Surface Protective Layer FIG. 8 is a back protective sheet in which a surface protective layer is provided on both sides of a low anisotropic liquid crystal polymer film. Such a back surface protection sheet is mainly used in a crystalline solar cell module, and the liquid crystal polymer film is protected not only from light entering from the back surface side, but also from light transmitted through gaps between semiconductor wafers. Therefore, the deterioration of the liquid crystal polymer film is further suppressed.

Example 7 Back Protective Sheet Having Surface Protective Layer and Adhesive Layer FIG. 9 shows the back protective sheet of Example 6 above, in which an adhesive layer is provided between the low anisotropic liquid crystal polymer film and the two surface protective layers. It is the back surface protection sheet. Such a back surface protective sheet is efficiently manufactured because the low anisotropic liquid crystal polymer film as a raw material and the surface protective layer can be easily bonded via the adhesive layer in addition to the characteristics of the sheet according to Example 6 above. It is possible.

Example 8 Back Protective Sheet Having Surface Protective Layer and Adhesive Layer FIG. 10 shows one side of one surface protective layer in the back protective sheet of Example 6 above, and an adhesive layer is provided on the outermost surface of the sheet. It is a back surface protection sheet. In addition to the characteristics of the sheet according to Example 6, the back surface protection sheet can be easily bonded to the sealing resin layer of the solar cell module via the adhesive layer.

  1: Back surface protective sheet, 10: Liquid crystal polymer film, 11: Surface protective layer, 12: Adhesive layer, 2a: Transparent substrate such as protective glass, 2b: Transparent substrate such as glass substrate with transparent electrode, 3: Solar cell element, 4: sealing resin layer, 5a: crystalline solar cell module, 5b: thin film solar cell module

Claims (6)

  A back surface protective sheet for a solar cell module, comprising a low anisotropic liquid crystal polymer film.   Furthermore, the back surface protection sheet for solar cell modules of Claim 1 containing a surface protection layer.   The back surface protection sheet for solar cell modules according to claim 2, wherein the surface protection layer is made of a weather resistant resin.   The back surface protective sheet for a solar cell module according to claim 2 or 3, wherein the surface protective layer is an ultraviolet absorbing material.   The back protective sheet for a solar cell module according to any one of claims 2 to 4, wherein the surface protective layer contains a pigment.   Furthermore, the back surface protection sheet for solar cell modules in any one of Claims 1-5 containing an contact bonding layer.