JP2012004146A - Sealing film for solar cell and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing film on the rear surface side of solar cell containing an ethylene-vinyl acetate copolymer and a coloring agent and capable of enhancing power generation efficiency of a solar cell, and to provide a solar cell using this sealing film.SOLUTION: A sealing film 13B on the rear surface side of solar cell is arranged between a solar cell element 14 and a protective member 12 on the rear surface side in order to seal the solar cell element 14. The sealing film 13B for solar cell is a hardened film of a composition for sealing film containing an ethylene-vinyl acetate copolymer and a white inorganic pigment, where the content of the white inorganic pigment is 10-30 mass% based on the composition for sealing film. A solar cell using the sealing film 13B is also provided.

Description

  TECHNICAL FIELD The present invention relates to a solar cell sealing film containing an ethylene-vinyl acetate copolymer as a main component, and in particular for a solar cell in which a coloring agent such as titanium white (titanium dioxide) is used on the back side of the solar cell. The present invention relates to a sealing film.

  In recent years, solar cells that directly convert sunlight into electrical energy have been widely used in terms of effective use of resources and prevention of environmental pollution, and further development has been promoted in terms of power generation efficiency and weather resistance. .

  As shown in FIG. 1, a solar cell generally has a surface side transparent protective member 11 made of a glass substrate or the like, a surface side sealing film 13A, a solar cell 14 such as a silicon crystal power generation element, a back side sealing film. 13B and the back surface side protection member (back cover) 12 are laminated in this order, and after deaeration under reduced pressure, the surface side sealing film 13A and the back surface side sealing film 13B are cross-linked and cured by heating and pressurizing, and integrated by bonding. Is manufactured.

  In such a solar battery, a plurality of solar battery cells 14 are connected and used in order to obtain a high electrical output. Therefore, in order to ensure the insulation of the solar cell 14, the solar cell is sealed using the insulating sealing films 13 </ b> A and 13 </ b> B.

  In addition, thin-film solar cells such as thin-film silicon-based, thin-film amorphous silicon-based solar cells, and copper indium selenide (CIS) -based solar cells are being developed. In this case, the surface of a transparent substrate such as glass or polyimide substrate In addition, a power generation element layer such as a semiconductor layer is formed by chemical vapor deposition or the like, and a sealing film or the like is laminated thereon and bonded and integrated.

  Conventionally, as a sealing film used in these solar cells, an ethylene-polar monomer copolymer such as an ethylene vinyl acetate copolymer (hereinafter also referred to as EVA) or an ethylene ethyl acrylate copolymer (EEA) is used. A film is used. In particular, EVA films are preferably used because they are inexpensive and have high transparency.

  Furthermore, in order to improve the power generation efficiency of the solar cell, the light incident on the solar cell is converted as efficiently as possible into a cell for a solar cell or a power generation element for a thin film solar cell (in the present invention, these are also collectively referred to as a solar cell element). ) To be condensed. Therefore, as a back surface side sealing film (a sealing film used on the side opposite to the light receiving surface), a sealing film colored with white or the like by mixing a colorant such as titanium white (titanium dioxide) has been developed (for example, Patent Document 1 and Patent Document 2). That is, by using a colored back surface side sealing film, the light reflection at the interface between the back surface side sealing film and the front surface side sealing film or the irregular reflection of light by the colorant causes a gap between the plurality of solar cell elements. The light incident on the solar cell and the light transmitted through the solar cell element are reflected to increase the light use efficiency and improve the power generation efficiency of the solar cell. In patent document 2, the whiteness degree based on JIS-P-8148 B system of a back surface side sealing film is made into the range of 87.0-93.0%, an external appearance defect is improved, and the electric power generation of a solar cell Improves efficiency.

Japanese Patent Laid-Open No. 6-177412 JP 2008-103471 A

  However, further improvement in power generation efficiency is desired, and it has been found by the inventor that the light incident on the solar cell cannot be sufficiently effectively utilized even by the back surface side sealing film of Patent Document 2. .

  Accordingly, an object of the present invention is a backside solar cell sealing film containing an ethylene-vinyl acetate copolymer and a colorant, which can further improve the power generation efficiency of the solar cell. It is to provide a membrane.

  Moreover, the objective of this invention is providing the solar cell using this sealing film.

  In Patent Document 2, importance is attached to the effect of improving the appearance defect of the back side sealing film, and whiteness is used as an index. When whiteness was used as an index, the content of the white inorganic pigment was not significantly changed at about 7 parts by mass with respect to 100 parts by mass of ethylene-vinyl acetate, and it was determined that such a blending amount was sufficient. . However, in terms of improving power generation efficiency, solar cell elements can also use light outside the visible light region for power generation. Therefore, it is not possible to use only whiteness as an index only for light having a wavelength in the visible light region. It was considered sufficient. Then, this inventor examined the composition for back surface side sealing films by using the reflectance for light including the wavelength of an ultraviolet region or an infrared region as an index, and reached the present invention.

  That is, the object is a back-side solar cell sealing film disposed between a solar cell element of a solar cell and a back-side protective member, for sealing the solar cell element, and comprising ethylene-acetic acid It is a cured film of the composition for sealing films containing a vinyl copolymer and a white inorganic pigment, and content of a white inorganic pigment is 10-30 mass% based on the composition for sealing films It is achieved by a solar cell sealing film characterized by the following. By making content of the white inorganic pigment of the composition for sealing films into said range, it can be set as the back surface side sealing film in which the reflectance was fully improved.

  Preferred embodiments of the solar cell sealing film according to the present invention are as follows.

(1) Content of the said white inorganic pigment is 10-20 mass% based on the said composition for sealing films. When the content of the white inorganic pigment is excessively increased, the fluidity of the sealing film composition may be reduced, and the processability during film formation may be reduced. By making content of a white inorganic pigment into said range, it can be set as the sealing film provided with sufficient workability as a sealing film.
(2) The white inorganic pigment is titanium dioxide. Titanium dioxide is suitable as a white inorganic pigment because of its high colorability.
(3) Vinyl acetate content in the said ethylene vinyl acetate copolymer is 20-35 mass parts with respect to 100 mass parts of ethylene-vinyl acetate copolymers. Thereby, the fluidity | liquidity of a sealing film composition can further be optimized, and it can be set as the sealing film provided with sufficient workability as a sealing film.

  Moreover, the said objective is achieved by the solar cell characterized by using the solar cell sealing film of this invention between the element for solar cells, and the back surface side protection member.

  By using the solar cell sealing film of the present invention, the utilization efficiency of light incident on the solar cell can be further improved, so that the solar cell can be further improved in power generation efficiency.

  In addition, in this invention, the side (light-receiving surface side) by which the light of a photovoltaic cell is irradiated is called "front surface side", and the surface opposite to the light-receiving surface of a photovoltaic cell is called "back surface side."

  According to the present invention, a solar cell sealing film with higher reflectivity can be obtained, so that the utilization efficiency of light incident on the solar cell can be improved by using the solar cell sealing film as the back surface side sealing film.

  Therefore, the solar cell with improved power generation efficiency can be provided by using the solar cell sealing film of the present invention as the back side sealing film of the solar cell.

It is a schematic sectional drawing of a common solar cell. It is a figure which shows the reflectance evaluation result of the sealing film for demonstrating the effect of this invention.

  Below, the sealing film for solar cells of this invention is demonstrated in detail.

  The solar cell sealing film of the present invention is a cured film of a sealing film composition containing at least an ethylene-vinyl acetate copolymer and a white inorganic pigment. About content of a white inorganic pigment, the optimal range was found by measuring the reflectance of a sealing film. In the present invention, the reflectance is an average value of the reflectance of 300 to 1200 nm using a spectrophotometer U-4100 (manufactured by Hitachi High-Technologies Corporation) with powdered barium sulfate as a reference.

  As in Examples described later, the reflectance increased until the content of the white inorganic pigment in the sealing film was 10% by mass, and a high reflectance was maintained up to 30% by mass. However, when the content of the white inorganic pigment in the sealing film is further increased, the reflectance is decreased. This was thought to be because the reflection effect was lowered due to aggregation of the white inorganic pigment in the sealing film composition. Therefore, in the solar cell sealing film of this invention, content of a white inorganic pigment is 10-30 mass% based on a sealing film composition.

  In addition, the solar cell sealing film of the present invention naturally requires a function as a sealing film. In some cases, the fluidity of the composition for a sealing film in which the content of the white inorganic pigment is blended at a high concentration is lowered. When the fluidity of the composition for sealing film decreases, it becomes difficult to wrap around between the solar cell elements when encapsulating the solar cell element as the solar cell sealing film, and air is bitten, etc. There is a risk of causing problems. From the viewpoint of preventing such deterioration of workability, the content of the white inorganic pigment is preferably 10 to 20% by mass based on the composition for sealing film.

  In the present invention, examples of white inorganic pigments include titanium white (titanium dioxide), calcium carbonate, and aluminum oxide. These can be used alone or in combination of two or more. The white inorganic pigment is preferably titanium dioxide because of its high colorability. The average particle size of the white inorganic pigment is preferably in the range of 0.01 to 0.5 μm, and more preferably in the range of 0.01 to 0.3 μm.

  In the present invention, a colorant other than the white inorganic pigment may be contained in the sealing film composition as a secondary component. Examples of other colorants include blue such as ultramarine, black such as carbon black, and milky white such as glass beads and a light diffusing agent.

[Ethylene-vinyl acetate copolymer]
Any ethylene-vinyl acetate copolymer (EVA) may be included in the solar cell sealing film of the present invention. The content of EVA vinyl acetate is preferably 20 to 35 parts by mass, more preferably 22 to 30 parts by mass, and particularly preferably 24 to 28 parts by mass. There exists a tendency for the sealing film obtained to become hard, so that content of the vinyl acetate unit of EVA is low. In particular, in the present invention, since the white inorganic pigment is blended at a higher concentration than before, when the content of vinyl acetate is less than 20 parts by mass, the fluidity of the composition for sealing film is lowered, and sealing for solar cells The processability of the film may be reduced. In addition, if the amount exceeds 35 parts by mass, the sealing film composition may have insufficient hardness, and when sealing a solar cell element as a solar cell sealing film, the sealing film is melted or misaligned. May cause problems such as

  In the present invention, it is preferable to use EVA having a melt flow rate (MFR) defined by JIS K7210 of 2 to 40 g / 10 minutes, particularly 3 to 30 g / 10 minutes. According to such a solar cell sealing film using EVA having MFR, the fluidity is appropriate even if the white inorganic pigment is blended at a relatively high concentration, and there is a problem in workability as a solar cell sealing film. It can be set as the composition for sealing films which does not exist. In the present invention, the value of the melt flow rate (MFR) is measured based on conditions of 190 ° C. and a load of 21.18 N according to JIS K7210.

  In the solar cell sealing film of the present invention, if EVA is included as a main component, in addition thereto, an ethylene-unsaturated carboxylic acid copolymer such as an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, Ionomer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid in which a part or all of the carboxyl groups of the ethylene-unsaturated carboxylic acid copolymer are neutralized with the above metal Methyl copolymer, ethylene-isobutyl acrylate copolymer, ethylene-unsaturated carboxylic acid ester copolymer such as ethylene-n-butyl acrylate copolymer, ethylene-isobutyl acrylate-methacrylic acid copolymer, Ethylene-unsaturated carboxylic acid ester such as ethylene-n-butyl acrylate-methacrylic acid copolymer Ethylene-polar such as a ru-unsaturated carboxylic acid copolymer and an ionomer in which a part or all of the carboxyl group is neutralized with the above metal, an ethylene-vinyl ester copolymer such as an ethylene-vinyl acetate copolymer A monomer copolymer, polyvinyl acetal resin (for example, polyvinyl formal, polyvinyl butyral (PVB resin), modified PVB), and vinyl chloride resin may be used as secondary agents.

  Hereinafter, other materials used for the solar cell sealing film of the present invention will be described.

[Crosslinking agent]
It is preferable that the sealing film for solar cells of this invention contains a crosslinking agent further. By forming a crosslinked structure of the ethylene-vinyl acetate copolymer with the crosslinking agent, the film strength and durability of the solar cell sealing film can be improved. As the crosslinking agent, an organic peroxide or a photopolymerization initiator is preferably used. Among them, it is preferable to use an organic peroxide because a sealing film having improved temperature dependency of adhesive strength, transparency, moisture resistance, and penetration resistance can be obtained.

  Any organic peroxide may be used as long as it decomposes at a temperature of 100 ° C. or higher and generates radicals. The organic peroxide is generally selected in consideration of the film formation temperature, the adjustment conditions of the composition, the curing temperature, the heat resistance of the adherend, and the storage stability. In particular, those having a decomposition temperature of 70 hours or more with a half-life of 10 hours are preferred.

  Examples of the organic peroxide include, from the viewpoint of processing temperature and storage stability of the resin, for example, benzoyl peroxide-based curing agent, t-hexyl peroxypivalate, t-butyl peroxypivalate, 3, 5, 5- Trimethylhexanoyl peroxide, di-n-octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, succinic acid peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethyl Peroxy-2-ethylhexanoate, t-hexyl peroxy-2-ethylhex Noate, 4-methylbenzoyl peroxide, t-butylperoxy-2-ethylhexanoate, m-toluoyl + benzoyl peroxide, benzoyl peroxide, 1,1-bis (t-butylperoxy) -2-methyl Cyclohexanate, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexanate, 1,1-bis (t-hexylperoxy) cyclohexanate, 1,1-bis ( t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane 1,1-bis (t-butylperoxy) cyclododecane, t-hexylperoxyisopropyl monocar Nate, t-butylperoxymaleic acid, t-butylperoxy-3,3,5-trimethylhexane, t-butylperoxylaurate, 2,5-dimethyl-2,5-di (methylbenzoylperoxy) ) Hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-di-methyl-2,5-di (benzoylperoxy) hexane , Etc.

  As the benzoyl peroxide-based curing agent, any can be used as long as it decomposes at a temperature of 70 ° C. or higher to generate radicals, and those having a decomposition temperature of 50 hours or higher with a half-life of 10 hours are preferable, It can be appropriately selected in consideration of preparation conditions, film formation temperature, curing (bonding) temperature, heat resistance of the adherend, and storage stability. Usable benzoyl peroxide curing agents include, for example, benzoyl peroxide, 2,5-dimethylhexyl-2,5-bisperoxybenzoate, p-chlorobenzoyl peroxide, m-toluoyl peroxide, 2, Examples include 4-dichlorobenzoyl peroxide and t-butyl peroxybenzoate. The benzoyl peroxide curing agent may be used alone or in combination of two or more.

  As the organic peroxide, 2,5-dimethyl-2,5di (tert-butylperoxy) hexane and 1,1-bis (tert-hexylperoxy) -3,3,5-trimethylcyclohexane are particularly preferable. . Thereby, the sealing film for solar cells which has the outstanding insulating property is obtained.

The content of the organic peroxide is preferably 0.1 to 2 parts by mass, more preferably 0.2 to 1.5 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. preferable. If the content of the organic peroxide is small, the insulating property of the resulting sealing film may be lowered, and if it is increased, the compatibility with the copolymer may be deteriorated.
As the photopolymerization initiator, any known photopolymerization initiator can be used, but a photopolymerization initiator having good storage stability after blending is desirable. Examples of such a photopolymerization initiator include 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1- (4- (methylthio) phenyl). Acetophenones such as 2-morpholinopropane-1, benzoins such as benzyldimethylketal, benzophenones such as benzophenone, 4-phenylbenzophenone and hydroxybenzophenone, thioxanthones such as isopropylthioxanthone and 2-4-diethylthioxanthone, As other special ones, methylphenylglyoxylate can be used. Particularly preferably, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- (4- (methylthio) phenyl) -2-morpholinopropane-1, Examples include benzophenone. These photopolymerization initiators may contain one or two or more kinds of known and commonly used photopolymerization accelerators such as benzoic acid-based or tertiary amine-based compounds such as 4-dimethylaminobenzoic acid as required. Can be mixed and used. Moreover, it can be used individually by 1 type of only a photoinitiator, or 2 or more types of mixture.

  It is preferable that content of the said photoinitiator is 0.5-5.0 mass parts with respect to 100 mass parts of ethylene-polar monomer copolymers.

[Crosslinking aid]
The solar cell sealing film of the present invention may further contain a crosslinking aid, if necessary. The said crosslinking adjuvant can improve the gel fraction of an ethylene-vinyl acetate copolymer, and can improve the adhesiveness and durability of a sealing film.

  The content of the crosslinking aid is generally 10 parts by mass or less, preferably 0.1 to 5 parts by mass, more preferably 0.1 to 2.5 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. Used in the department. Thereby, the sealing film excellent in adhesiveness is obtained.

  Examples of the crosslinking aid (compound having a radical polymerizable group as a functional group) include trifunctional crosslinking aids such as triallyl cyanurate and triallyl isocyanurate, and (meth) acrylic esters (eg, NK ester) ) Monofunctional or bifunctional crosslinking aids. Of these, triallyl cyanurate and triallyl isocyanurate are preferable, and triallyl isocyanurate is particularly preferable.

[Adhesion improver]
The sealing film for solar cell of the present invention preferably has excellent adhesive strength in consideration of the sealing performance inside the solar cell. Therefore, an adhesion improver may be further included. As the adhesion improver, a silane coupling agent can be used. Thereby, it becomes possible to form the sealing film for solar cells which has the outstanding adhesive force. Examples of the silane coupling agent include γ-chloropropylmethoxysilane, vinylethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, and γ-glycidoxypropyltrimethoxy. Silane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β Mention may be made of-(aminoethyl) -γ-aminopropyltrimethoxysilane. These silane coupling agents may be used alone or in combination of two or more. Of these, γ-methacryloxypropyltrimethoxysilane is particularly preferred.

  The content of the silane coupling agent is preferably 0.1 to 0.7 parts by mass, particularly 0.15 to 0.65 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer.

[Others]
The sealing film for solar cell of the present invention is used as necessary for improving or adjusting various physical properties of the film (optical properties such as mechanical strength and transparency, heat resistance, light resistance, crosslinking speed, etc.). In addition, various additives such as a plasticizer, an acryloxy group-containing compound, a methacryloxy group-containing compound and / or an epoxy group-containing compound may be further included.

  Although it does not specifically limit as a plasticizer, Generally the ester of a polybasic acid and the ester of a polyhydric alcohol are used. Examples thereof include dioctyl phthalate, dihexyl adipate, triethylene glycol-di-2-ethylbutyrate, butyl sebacate, tetraethylene glycol diheptanoate, and triethylene glycol dipelargonate. One type of plasticizer may be used, or two or more types may be used in combination. The content of the plasticizer is preferably in the range of 5 parts by mass or less with respect to 100 parts by mass of the ethylene-polar monomer copolymer.

  The acryloxy group-containing compound and the methacryloxy group-containing compound are generally acrylic acid or methacrylic acid derivatives, and examples thereof include acrylic acid or methacrylic acid esters and amides. Examples of ester residues include linear alkyl groups such as methyl, ethyl, dodecyl, stearyl, lauryl, cyclohexyl group, tetrahydrofurfuryl group, aminoethyl group, 2-hydroxyethyl group, 3-hydroxypropyl group. Group, 3-chloro-2-hydroxypropyl group. Examples of amides include diacetone acrylamide. In addition, polyhydric alcohols such as ethylene glycol, triethylene glycol, polypropylene glycol, polyethylene glycol, trimethylolpropane, and pentaerythritol, and esters of acrylic acid or methacrylic acid can also be used.

Examples of epoxy-containing compounds include triglycidyl tris (2-hydroxyethyl) isocyanurate, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and phenol. (Ethyleneoxy) ₅ glycidyl ether, pt-butylphenyl glycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, glycidyl methacrylate, butyl glycidyl ether can be mentioned.

  The acryloxy group-containing compound, the methacryloxy group-containing compound, or the epoxy group-containing compound is generally 0.5 to 5.0 parts by weight, particularly 1.0, respectively, with respect to 100 parts by weight of the ethylene-polar monomer copolymer. It is preferable that -4.0 mass part is contained.

  Furthermore, the solar cell sealing film of the present invention may contain an ultraviolet absorber, a light stabilizer and an anti-aging agent. By including the ultraviolet absorber, it is possible to suppress deterioration of the ethylene-polar monomer copolymer due to the influence of irradiated light and the like, and yellowing of the solar cell sealing film. The ultraviolet absorber is not particularly limited, but 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxy. Preferred examples include benzophenone-based ultraviolet absorbers such as benzophenone and 2-hydroxy-4-n-octoxybenzophenone. In addition, it is preferable that the compounding quantity of the said benzophenone series ultraviolet absorber is 0.01-5 mass parts with respect to 100 mass parts of ethylene-polar monomer copolymers.

  Moreover, it can suppress that an ethylene-polar monomer copolymer deteriorates and the solar cell sealing film yellows by influence of the irradiated light etc. also by including a light stabilizer. As the light stabilizer, a light stabilizer called a hindered amine type is preferably used. For example, LA-52, LA-57, LA-62, LA-63LA-63p, LA-67, LA-68 (all ADEKA), Tinuvin 744, Tinuvin 770, Tinuvin 765, Tinuvin 144, Tinuvin 622LD, CHIMASSORB 944LD (all manufactured by Ciba Specialty Chemicals Co., Ltd.), UV-3034 (BF Goodrich) Can be mentioned. In addition, the said light stabilizer may be used individually or may be used in combination of 2 or more types, and the compounding quantity is 0.01-5 mass parts with respect to 100 mass parts of ethylene-polar monomer copolymers. It is preferable that

  Examples of the antioxidant include hindered phenolic antioxidants such as N, N′-hexane-1,6-diylbis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamide], Examples thereof include phosphorus heat stabilizers, lactone heat stabilizers, vitamin E heat stabilizers, and sulfur heat stabilizers.

  What is necessary is just to perform according to a well-known method in order to form the sealing film for solar cells of this invention mentioned above. For example, a composition in which each of the above materials is mixed by a known method using a super mixer (high-speed fluid mixer), a roll mill, etc., is molded by ordinary extrusion molding, calendar molding (calendering) or the like, and then a sheet-like material It can manufacture by the method of obtaining. Alternatively, a sheet-like material can be obtained by dissolving the composition in a solvent and coating the solution on a suitable support with a suitable coating machine (coater) and drying to form a coating film. The heating temperature during film formation is preferably a temperature at which the crosslinking agent does not react or hardly reacts. For example, it is preferably 50 to 90 ° C, particularly 40 to 80 ° C. Although the thickness in particular of the sealing film for solar cells is not restrict | limited, What is necessary is just the range of 50 micrometers-2 mm.

[Solar cell]
As the structure of the solar cell of the present invention, at least the solar cell sealing film of the present invention includes a solar cell element (including a single crystal or polycrystalline silicon crystal solar cell or a thin film solar cell power generation element). If it uses as a back surface side sealing film between a back surface side protection member, it will not restrict | limit in particular. For example, the structure etc. which sealed the element for solar cells by carrying out bridge | crosslinking integration by interposing the sealing film for solar cells between the surface side transparent protection member and the back surface side protection member, etc. are mentioned.

  In the solar cell, in order to sufficiently seal the solar cell element, for example, as shown in FIG. 1, the front surface side transparent protective member 11, the front surface side sealing film 13A, the solar cell cell 14, the back surface side sealing. The film 13B (the solar cell sealing film of the present invention) and the back surface side protective member 12 may be laminated, and the sealing film may be cross-linked and cured according to a conventional method such as heating and pressing. As the surface-side sealing film, since the solar cell sealing film of the present invention containing a white inorganic pigment is not suitable, a known solar battery sealing film that does not contain a colorant such as a white inorganic pigment is used. be able to.

In order to heat and pressurize, for example, the laminate is heated with a vacuum laminator at a temperature of 135 to 180 ° C., further 140 to 180 ° C., particularly 155 to 180 ° C., a degassing time of 0.1 to 5 minutes, and a press pressure of 0.1. What is necessary is just to heat-press in about 1.5 kg / cm < ² > and press time 5-15 minutes. By crosslinking the ethylene-vinyl acetate copolymer contained in the front side sealing film 13A and the back side sealing film 13B during the heating and pressurization, the front side sealing film 13A and the back side sealing film 13B are interposed. And the surface side transparent protection member 11, the back surface side transparent member 12, and the cell 14 for solar cells can be integrated, and the cell 14 for solar cells can be sealed.

  Moreover, the sealing film for solar cells of this invention can also be used for the sealing film of thin film solar cells, such as a thin film silicon type, a thin film amorphous silicon type solar cell, and a copper indium selenide (CIS) type solar cell. . In this case, for example, the back side sealing is performed on the thin film solar cell element layer formed by chemical vapor deposition on the surface of the front side transparent protective member such as a glass substrate, a polyimide substrate, or a fluororesin transparent substrate. A structure in which a film (a solar cell sealing film of the present invention) and a back surface side protective member are laminated and bonded and integrated, or a surface side transparent protective member, a surface side sealing film, a thin film solar cell element, a back surface side sealing The structure etc. which laminated | stacked the film | membrane (seal film | membrane for solar cells of this invention) and the back surface side protection member in this order, and were made to adhere and integrate are mentioned.

  Since the solar cell of the present invention using the solar cell sealing film of the present invention as the back side sealing film has higher utilization efficiency of light incident on the solar cell than the conventional sealing film, This is a solar cell with improved power generation efficiency.

  The surface side transparent protective member 11 used in the solar cell of the present invention is usually a glass substrate such as silicate glass. As for the thickness of a glass substrate, 0.1-10 mm is common, and 0.3-5 mm is preferable. The glass substrate may generally be chemically or thermally strengthened.

  The back surface side protective member 12 used in the present invention is preferably a plastic film such as polyethylene terephthalate (PET). Also, a film obtained by laminating a fluorinated polyethylene film, particularly a fluorinated polyethylene film / Al / fluorinated polyethylene film in this order, in consideration of heat resistance and heat-and-moisture resistance, is also preferable.

  In addition, the solar cell of this invention has the characteristics in a back surface side sealing film as above-mentioned. Therefore, members other than the back-side sealing film, such as the front-side transparent protective member, the back-side protective member, the front-side sealing film, and the solar cell element, have the same configuration as that of conventionally known solar cells. There is no particular limitation.

  Hereinafter, the present invention will be described with reference to examples.

(Examples 1-4, Comparative Examples 1-3)
The materials shown in Table 1 were supplied to a roll mill and kneaded at 70 ° C. to prepare a solar cell sealing film composition. The solar cell sealing film composition was calendered at 70 ° C., allowed to cool, and then a solar cell sealing film (thickness: 0.6 mm) was produced.

  Next, a sample having a size of 100 mm × 100 mm was prepared, and after temporarily press-bonding at 90 ° C. with a vacuum laminator, the sample was heated in an oven at 155 ° C. for 30 minutes to crosslink to a gelation fraction of 90% or more.

(Evaluation methods)
(1) Reflectance For each of the prepared samples, an average reflectance of 300 to 1200 nm was measured using a spectrophotometer U-4100 (manufactured by Hitachi High-Technologies Corporation) with barium sulfate powder as a reference.
(2) Workability When calendering the solar cell encapsulating film composition, the case where it was able to be molded without problems such as kneading failure, and the case where there was no problem in kneading, but it was somewhat difficult to form, Δ When it was difficult to knead, x was marked.

(Evaluation results)
The evaluation results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 2, the content of the white inorganic pigment (titanium dioxide) in the sealing film composition is 3.75%, 5% by mass (Comparative Examples 1 and 2), and 10% by mass ( When increasing with Example 1), the average reflectance increased up to 10% by weight. Moreover, when the content of the white inorganic pigment was increased to 15, 20, and 30% by mass (Examples 2 to 4), a high average reflectance was maintained. On the other hand, when the content of the white inorganic pigment was 60% by mass (Comparative Example 3), the average reflectance was lower than that of the sealing film having the white inorganic pigment of 10% by mass. This was thought to be because the reflection effect was lowered due to aggregation of the white inorganic pigment in the sealing film composition. Therefore, it was shown that the content of the white inorganic pigment is 10 to 30% by mass based on the composition for sealing film.

  In addition, the processability is slightly reduced in Example 4 where the content of the white inorganic pigment is 30% by mass. From the viewpoint of preventing the processability from being deteriorated, the content of the white inorganic pigment is the sealing. It was shown that 10-20 mass% is preferable based on the composition for membranes.

  In addition, this invention is not limited to the structure and Example of said embodiment, A various deformation | transformation is possible within the range of the summary of invention.

  According to the present invention, a solar cell with higher power generation efficiency can be provided.

DESCRIPTION OF SYMBOLS 11 Surface side transparent protective member 12 Back surface side protective member 13A Surface side sealing film 13B Back surface side sealing film 14 Cell for solar cells

Claims (5)

A solar cell sealing film for sealing a solar cell element disposed between a solar cell element and a back surface protection member of a solar cell,
It is a cured film of the composition for sealing films containing an ethylene-vinyl acetate copolymer and a white inorganic pigment, and content of a white inorganic pigment is 10-30 mass% based on the said composition for sealing films The sealing film for solar cells characterized by being.   2. The solar cell sealing film according to claim 1, wherein the content of the white inorganic pigment is 10 to 20% by mass based on the sealing film composition.   The solar cell sealing film according to claim 1, wherein the white inorganic pigment is titanium dioxide.   The solar cell according to any one of claims 1 to 3, wherein the vinyl acetate content in the ethylene vinyl acetate copolymer is 20 to 35 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. Sealing film.   The solar cell which used the sealing film for solar cells of Claims 1-4 between the element for solar cells and the back surface side protection member.

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