JP4918329B2 - Solar cell sorting method - Google Patents

Description

  The present invention relates to a solar cell using a sealing film containing an ethylene / vinyl acetate copolymer as a main component, a sealing film useful for a solar cell, and a method for selecting a solar cell.

  In recent years, solar cells that directly convert sunlight into electrical energy have been widely used and further developed in terms of effective use of resources and prevention of environmental pollution.

  As shown in FIG. 1, a solar cell generally includes an EVA (ethylene / vinyl acetate copolymer) film between a front surface side transparent protective member 1 made of a glass substrate or the like and a back surface side protective member (back cover) 2. A plurality of silicon power generation element solar cell cells 4 are sealed through the front surface side sealing film 3A and the back surface side sealing film 3B.

  Such a solar cell is obtained by laminating the surface-side transparent protective member 1, the surface-side sealing film 3A, the solar cell 4, the back-side sealing film 3B, and the back-side protecting member 2 in this order, and applying heat and pressure. , EVA is produced by cross-linking and curing and integrating the EVA.

  In such a solar battery, it is strongly desired to collect light incident on the solar battery on the solar battery cell as efficiently as possible in terms of improving the power generation efficiency. That is, in a general solar cell, the function of condensing incident light is not given to itself, and among the light incident from the light receiving surface of the solar cell, between adjacent solar cell cells. The light passing through the solar cell and the light transmitted through the solar cell made of a thin film cell pass through the back cover as it is and pass almost without contributing to power generation. For this reason, the light which contributes to electric power generation is limited to the light which injects into the solar cell directly and was absorbed among the light which injected into the solar cell.

  For the purpose of improving the power generation efficiency, Patent Document 1 (Japanese Patent Laid-Open No. 11-307791) discloses a method of effectively using incident light by including a light-transmitting light scattering member on the light incident side, or Patent Document 2 (Japanese Patent Laid-Open No. 2002-43598) proposes a method of effectively utilizing incident light by imparting foamability to a sealing film and scattering light on an uneven surface formed by foaming.

  Further, it has been proposed to use a colored EVA film formed by forming an EVA resin composition containing a colorant as the backside sealing film EVA film 3B (for example, Patent Document 3 (Japanese Patent Laid-Open No. Hei 6-177712). Gazette) and Patent Document 4 (Japanese Patent Laid-Open No. 2003-177712). That is, by using the above-mentioned colored EVA film as the EVA film for the back side sealing film, light reflection at the interface between the colored EVA film and the transparent EVA film for the front side sealing film or irregular reflection by the colorant, Light incident between solar cells and light that has passed through cells can be diffusely reflected and re-entered into the cell, increasing the use efficiency of light incident on the solar cell and improving power generation efficiency To do.

Japanese Patent Application Laid-Open No. 11-307791 JP 2002-43598 A Japanese Patent Laid-Open No. 6-177412 Japanese Patent Laid-Open No. 2003-177412

An object of the present invention is to provide a method for selecting a solar cell that exhibits a good appearance and has improved power generation efficiency.

The present invention is a solar cell in which a solar cell is sealed between a front surface side transparent protective member and a back surface side protective member via a sealing film containing an ethylene / vinyl acetate copolymer. ,
The surface-side sealing film disposed between the surface-side transparent protective member and the solar battery cell is a transparent film obtained by curing a composition for a surface-side sealing film containing an ethylene / vinyl acetate copolymer, and The back side sealing film disposed between the back side protective member and the solar cell is a white film obtained by curing the back side sealing film composition containing an ethylene / vinyl acetate copolymer and a white inorganic pigment. A method for selecting a solar cell by whiteness, wherein the whiteness of the solar cell is measured in accordance with a method B of JIS-P-8148, and the whiteness is 87.0-93. Ru screening method near, characterized in that selecting a solar cell in the 2.0% range.

By measuring in conformity on xylo chromaticity B method JIS-P-8148, it is possible to easily sort useful backside sealing film for a solar cell.

  The structure of the solar cell of the present invention generally has the same structure as a conventionally known solar cell. However, a solar cell having any configuration is included in the present invention as long as it has the characteristic requirements of the present invention.

  In the solar cell of the present invention, for example, as shown in FIG. 1 described above, a plurality of solar cell cells 4 arranged between the front surface side transparent protective member 1 and the rear surface side transparent protective member 2 are sealed on the front surface side. Generally, a structure sealed by the film 3A and the back surface side sealing film 3B is employed. In the present invention, the light receiving surface side with respect to the solar cell is referred to as “front surface side”, and the surface opposite to the light receiving surface of the solar cell is referred to as “back surface side”.

  In the solar cell of the present invention, the surface-side sealing film 3A disposed between the surface-side transparent protective member 1 and the solar cell 4 includes a composition for the surface-side sealing film containing an ethylene / vinyl acetate copolymer. The back surface side sealing film 3B disposed between the back surface side protective member 2 and the solar cell 4 is a back surface containing an ethylene / vinyl acetate copolymer and a white inorganic pigment. It is a film in which the composition for side sealing film is cured, and the whiteness in accordance with JIS-P-8148 B method is in the range of 87.0 to 93.0% (preferably 88.0 to 93.0%. (White range). By using a white film having such a specific whiteness as the back surface side sealing film 3B, the resulting solar cell exhibits an excellent appearance with no appearance defects such as visible cells from the outside. Since many irregular reflections occur at the interface, the power generation efficiency is improved. That is, the white film having such specific whiteness has sufficient whiteness as necessary so that the appearance defect does not occur and irregular reflection effective for improving the power generation efficiency at the interface occurs.

  The degree of whiteness conforming to the JIS-P-8148 B method is the degree of whiteness (ISO whiteness) corresponding to the characteristic B of the whiteness test method by the diffuse illumination method defined in JIS-P-8148 (conforming to ISO2470). ). The outline of the measuring method is that a test piece (solar cell or sealing film) is irradiated with diffuse illumination using a diffuse reflectance meter having an integrating sphere (diameter 150 mm), and the reflected light is received at an angle of 0 degrees. The light source is a halogen lamp or a xenon lamp, and the standard white plate is a barium sulfate plate.

  In the present invention, the sealing film used on the surface side is obtained by curing (crosslinking) a surface-side sealing film composition containing an ethylene / vinyl acetate copolymer (surface-side pre-curing sealing film). ). In addition to the ethylene / vinyl acetate copolymer, the composition for the surface side sealing film may be used in combination with polyvinyl acetal resins such as polyvinyl formal, polyvinyl butyral (PVB resin), and modified PVB, and vinyl chloride resin. However, it is preferable to use only an ethylene / vinyl acetate copolymer.

  As the ethylene / vinyl acetate copolymer, the content of vinyl acetate in the ethylene / vinyl acetate copolymer is 10 to 40 parts by mass, particularly 20 to 30 parts by mass with respect to 100 parts by mass of the ethylene / vinyl acetate copolymer. Part. If the vinyl acetate content is less than the lower limit, the transparency of the resin film obtained when crosslinking and curing at a high temperature may not be sufficient, and if it exceeds the upper limit, processability may be reduced.

  The back side sealing film of the present invention is obtained by curing a back side sealing film composition containing an ethylene / vinyl acetate copolymer and a white inorganic pigment (sealing film before back side curing). Is obtained. As the resin such as an ethylene / vinyl acetate copolymer, the same resin as the above-mentioned composition for the front-side sealing film can be used. Reflection of light at the interface between the back side sealing film and the front side sealing film or irregular reflection due to the uniformly dispersed white inorganic pigment. It becomes possible to diffusely reflect the light and make it incident on the cell again, increasing the utilization efficiency of the light incident on the solar cell and improving the power generation efficiency.

  Examples of white inorganic pigments include titanium oxide (particularly titanium dioxide), calcium carbonate, and aluminum oxide. Titanium oxide is preferred. These can be used alone or in combination of two or more. Colorants other than white inorganic pigments, for example, blue colorants such as ultramarine, black colorants such as carbon black, and milky white colorants such as glass beads and light diffusing agents may be used in combination. Preferably, a white colorant based on titanium white can be used. The average particle size of the white inorganic pigment is preferably 0.01 to 0.5 μm, particularly preferably 0.01 to 0.3 μm.

  The white inorganic pigment is generally 1.0 to 7.0 parts by weight, preferably 2.0 to 5.8 parts by weight with respect to 100 parts by weight of the ethylene / vinyl acetate copolymer contained in the back side sealing film. Particularly preferably, it is contained in an amount of 3.0 to 5.6 parts by mass.

  The thickness of the front side and back side sealing films is generally in the range of 100 μm to 2 mm.

  The sealing film before curing on the front side or the back side is obtained by forming a film according to a known method using a composition for a front side or back side sealing film containing an ethylene / vinyl acetate copolymer or the like. It is done. In addition to the ethylene / vinyl acetate copolymer or the ethylene / vinyl acetate copolymer and the white inorganic pigment, the composition for the front-side or back-side sealing film comprises a cross-linking agent, a cross-linking aid, and others as necessary. Contains various additives.

  As a crosslinking agent used for the composition for front side or back side sealing film, an organic peroxide or a photopolymerization initiator is preferably used. Among these, it is preferable to use an organic peroxide because an intermediate 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 resin processing temperature and storage stability, benzoyl peroxide curing agent, tert-hexyl peroxypivalate, tert-butyl peroxypivalate, 3,5,5-trimethyl. Hexanoyl peroxide, di-n-octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, succinic acid peroxide, 2 , 5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate Ate, 4-methylbenzoyl peroxide, t rt-butylperoxy-2-ethylhexanoate, m-toluoyl + benzoyl peroxide, benzoyl peroxide, 1,1-bis (tert-butylperoxy) -2-methylcyclohexanate, 1,1-bis (Tert-hexylperoxy) -3,3,5-trimethylcyclohexanate, 1,1-bis (tert-hexylperoxy) cyclohexanate, 1,1-bis (tert-butylperoxy) -3 , 3,5-trimethylcyclohexanate, 1,1-bis (tert-butylperoxy) cyclohexanate, 2,2-bis (4,4-di-tert-butylperoxycyclohexyl) propane, 1,1 -Bis (tert-butylperoxy) cyclododecane, tert-hexylperoxyisop Pyrmonocarbonate, tert-butylperoxymaleic acid, tert-butylperoxy-3,3,5-trimethylhexanoate, tert-butylperoxylaurate, 2,5-dimethyl-2,5-di ( Methylbenzoylperoxy) hexane, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxy-2-ethylhexyl monocarbonate, tert-hexylperoxybenzoate, 2,5-di-methyl-2,5-di (benzoyl) Peroxy) hexane, and the like.

  As the benzoyl peroxide-based curing agent, any one can be used as long as it decomposes at a temperature of 70 ° C. or higher to generate radicals. The temperature can be appropriately selected in consideration of the preparation conditions, the film formation temperature, the curing (bonding) temperature, the heat resistance of the adherend, and the 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.

  In the composition, the content of the organic peroxide is generally 0.1 to 5 parts by weight, preferably 0.1 to 2 parts by weight, particularly preferably 0.1 parts by weight with respect to 100 parts by weight of the ethylene vinyl acetate resin. 2 to 1.5 parts by mass. If the content of the organic peroxide is small, the transparency of the resulting intermediate 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.

  In the composition, the content of the photopolymerization initiator is preferably 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the ethylene vinyl acetate resin.

  The composition for the front-side or back-side sealing film is an improvement or adjustment of various physical properties of the film (optical properties such as mechanical strength, adhesion, transparency, heat resistance, light resistance, crosslinking speed, etc.) In particular, various additives such as a crosslinking aid such as a plasticizer, an adhesion improver, an acryloxy group-containing compound, a methacryloxy group-containing compound and / or an epoxy group-containing compound are further included as necessary for improving mechanical strength. Also good.

  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 EVA.

  As the adhesion improver, a silane coupling agent can be used. Examples of the silane coupling agent include γ-chloropropylmethoxysilane, vinylethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltri Methoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- Mention may be made of β- (aminoethyl) -γ-aminopropyltrimethoxysilane. These silane coupling agents may be used alone or in combination of two or more. Moreover, it is preferable that content of an adhesive improvement agent is 5 mass parts or less with respect to 100 mass parts of EVA.

  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 amides include diacetone acrylamide.

  Each of the acryloxy group-containing compound, the methacryloxy group-containing compound, or the amide compound is generally contained in an amount of 0.5 to 5.0 parts by mass, particularly 1.0 to 4.0 parts by mass with respect to 100 parts by mass of EVA. preferable.

  Examples of polyfunctional compounds (crosslinking aids) include esters obtained by esterifying a plurality of acrylic acid or methacrylic acid with glycerin, trimethylolpropane, pentaerythritol, and the like, and the aforementioned triallyl cyanurate and triallyl isocyanurate. it can. The crosslinking aid is generally contained in an amount of 0.5 to 5.0 parts by mass, particularly 0.5 to 3.0 parts by mass, with respect to 100 parts by mass of EVA.

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.

  It is preferable that the epoxy group-containing compound is generally contained in an amount of 0.5 to 5.0 parts by mass, particularly 1.0 to 4.0 parts by mass with respect to 100 parts by mass of EVA.

  Further, the composition may contain an ultraviolet absorber, a light stabilizer and an anti-aging agent.

  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 vinyl acetate resin.

  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 Asahi Denka) (Inc.), Tinuvin 744, Tinuvin 770, Tinuvin 765, Tinuvin 144, Tinuvin 622LD, CHIMASSORB 944LD (all manufactured by Ciba Geigy), UV-3034 (manufactured by BF Goodrich), and the like. . In addition, the said light stabilizer may be used independently or may be used in combination of 2 or more types, and the compounding quantity shall be 0.01-5 mass parts with respect to 100 mass parts of ethylene vinyl acetate resin. Is preferred.

  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.

  The front-side or back-side sealing film composition is produced, for example, by heat rolling using calendar molding or the like, and the solar cell pre-curing sealing film of the present invention is produced according to a conventional method. Can do. Heating is generally in the range of 50-90 ° C. The solar cell sealing film of the present invention is obtained, for example, by curing (crosslinking) in the production of a solar cell as described below. Since the composition for back side sealing film contains the inorganic pigment, it is preferable to shape | mold as mentioned above, after kneading | mixing beforehand, for example with an extruder or a charge roll etc. here.

The solar cell of this invention is obtained by sealing the cell for solar cells between the surface side transparent protection member and the back surface side protection member through the surface side and back surface side sealing film before hardening. In the solar cell, in order to sufficiently seal the solar cell, as shown in FIG. 1, the surface-side transparent protective member 1, the surface-side sealing film 3A before curing, the solar cell 4 and the uncured cell The back surface side sealing film 3B and the back surface side protection member 2 are laminated, and the obtained laminate is subjected to a vacuum laminator at a temperature of 135 to 180 ° C., further 140 to 180 ° C., particularly 155 to 180 ° C. What is necessary is just to heat-press in the time 0.1-5 minutes, press pressure 0.1-1.5 kg / cm < ² >, and press time 5-15 minutes. By curing (crosslinking) the ethylene / vinyl acetate copolymer contained in the front side sealing film 3A and the back side sealing film 3B before curing at the time of heating and pressing, the front side sealing film 3A and the back side The solar cell 4 can be sealed by integrating the front surface side transparent protective member 1, the back surface side transparent member 2, and the solar cell 4 through the sealing film 3 </ b> B.

  Further, in the present invention, in order to improve the durability of the solar cell, the acid-accepting agent is disposed on the surface side sealing film disposed between the surface side transparent protective member and the solar cell, and / or the back surface side. It can contain in the back surface side sealing film arrange | positioned between a protection member and the cell for solar cells.

  In the present invention, the composition of the acid acceptor contained in the front or back side sealing film composition is not particularly limited as long as it has a function of absorbing and / or neutralizing an acid such as acetic acid.

  As the acid acceptor, a metal oxide, a metal hydroxide, a metal carbonate or a composite metal hydroxide is used, and can be appropriately selected according to the amount of acetic acid generated and the application. Specific examples of the acid acceptor include magnesium oxide, calcium oxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, magnesium carbonate, barium carbonate, calcium carbonate, calcium borate, zinc stearate, calcium phthalate, phosphorous acid Periodic table group 2 metal oxides such as calcium, zinc oxide, calcium silicate, magnesium silicate, magnesium borate, magnesium metaborate, calcium metaborate, barium metaborate, hydroxide, carbonate, carboxylic acid Salt, silicate, borate, phosphite, metaborate, etc .; tin oxide, basic tin carbonate, tin stearate, basic tin phosphite, basic tin sulfite, trilead tetraoxide, silicon oxide, stearic acid Group 14 metal oxides such as silicon, basic carbonate, basic carboxylate, basic sub Salts, such as basic sulfites; zinc oxide, aluminum oxide, aluminum hydroxide, iron hydroxide; composite metal hydroxide such as hydrotalcite; aluminum hydroxide gel compound; and the like. These may be used individually by 1 type, and may mix and use 2 or more types.

  The content of the acid acceptor in the composition for the front or back side sealing film is preferably 0.01 to 0.15 parts by mass, more preferably 0 with respect to 100 parts by mass of the ethylene / vinyl acetate copolymer. 0.01 to 0.12 parts by mass, particularly preferably 0.01 to 0.1 parts by mass. If the content of the acid acceptor exceeds 0.1 parts by mass, the transparency of the surface-side sealing film obtained may be reduced, and if it is less than 0.01 parts by mass, sufficient acid accepting performance by the acid acceptor May not be obtained.

  The surface side transparent protective member used for 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 side protective member used in the present invention is a plastic film such as PET, but a fluorinated polyethylene film is preferable in consideration of heat resistance.

The present invention, Ru method near to select the brightness of the solar cell. That is, as described above, a solar battery obtained by sealing a solar battery cell between the front-side transparent protective member and the back-side protective member via the front-side and back-side sealing films before curing. The whiteness is measured according to JIS-P-8148, and when the whiteness is in the range of 87.0 to 93.0%, the appearance is easily good and the power generation efficiency is high. Solar cells can be sorted or obtained.

  Hereinafter, the present invention will be described with reference to examples. The present invention is not limited by the following examples.

1. Preparation of surface side sealing film before curing A surface side sealing film before curing was prepared according to the following procedure using the following materials.

The material shown to the following mixing | blending was supplied to the roll mill, and it knead | mixed at 70 degreeC, and prepared the composition for surface side sealing films. The obtained composition was calendered at 80 ° C., allowed to cool, and then a sealing film (thickness 0.6 mm) was obtained.

(Formulation of surface side sealing film before curing)
EVA (vinyl acetate content 25% by mass) 100
Cross-linking agent (2,5-dimethyl-2,5-bis (t-butylperoxy) hexane) 1.0
Crosslinking aid (triallyl isocyanurate) 2.0
Silane coupling agent (3-methacryloxypropyltrimethoxysilane) 0.15

2. Production of Back Side Sealing Film Before Curing Using the following materials and the pigment content shown in Table 1, a back side sealing film before curing was produced according to the following procedure.

The material shown to the following mixing | blending was supplied to the roll mill, and it knead | mixed at 70 degreeC, and prepared the composition for back side sealing films. The obtained composition was calendered at 80 ° C., allowed to cool, and then a sealing film (thickness 0.6 mm or 0.4 mm) was obtained.

(Formulation of surface side sealing film before curing)
EVA (vinyl acetate content 25% by mass) 100
Cross-linking agent (2,5-dimethyl-2,5-bis (t-butylperoxy) hexane) 1.0
Crosslinking aid (triallyl isocyanurate) 2.0
Silane coupling agent (3-methacryloxypropyltrimethoxysilane) 0.15
White masterbatch (containing 60% by mass of titanium dioxide (average particle size 0.1 μm)) Notation In addition, in Table 1, the amount of white masterbatch is displayed as the content (% by mass) of titanium dioxide.

[Examples 1 to 22 and Comparative Examples 1 to 4]
Using the surface-side sealing film (1) before curing prepared above as the surface-side sealing film 3A (FIG. 1), the back-side sealing film (2) before curing prepared above is used as the back-side sealing film. As shown in FIG. 1, the surface side transparent protective member 1 made of a glass plate (thickness 0.3 mm) and the back side protective member 2 made of a fluorinated polyethylene film (thickness 50 μm) are used as 3B (FIG. 1). A solar battery cell 4 made of a silicon power generation element was sealed between the solar battery and a solar battery. The sealing was performed by cross-linking EVA with a vacuum laminator by thermocompression bonding under vacuum at a temperature of 150 ° C.

[Evaluation]
1. Whiteness The whiteness of the obtained solar cell was measured according to a whiteness test method (characteristic B) by a diffuse illumination method defined in JIS-P-8148 (based on ISO 2470). Light irradiation was performed from the surface side transparent protective member side.
2. Appearance The appearance of the obtained solar cell was visually observed from the back side and evaluated as follows.

○: Almost no electronic cell is observed. ×: The electronic cell is clearly observed.

  From the above results, it can be seen that the solar cell having whiteness of the present invention has a good appearance.

In addition to the above results, the solar cells obtained in Examples 1 to 13 were improved in power generation efficiency by at least 5% as compared with the solar cell obtained in Comparative Example 1. In addition, the solar cells obtained in Examples 14 to 19 improved the power generation efficiency by at least 5% as compared with the solar cell obtained in Comparative Example 3. Furthermore, the solar cells obtained in Examples 20 to 22 improved the power generation efficiency by at least 5% as compared with the solar cells obtained in Comparative Example 4.

A sectional view of a general solar cell is shown.

Explanation of symbols

1 surface side transparent protective member,
2 Back side protection member,
3A surface side sealing film,
3B Back side sealing film,
4 Solar cell.

Claims (1)

Between the front surface side transparent protective member and the back surface side protective member, a solar cell formed by sealing a solar cell through a sealing film containing an ethylene / vinyl acetate copolymer,
The surface-side sealing film disposed between the surface-side transparent protective member and the solar battery cell is a transparent film obtained by curing a composition for a surface-side sealing film containing an ethylene / vinyl acetate copolymer, and The back side sealing film disposed between the back side protective member and the solar cell is a white film obtained by curing the back side sealing film composition containing an ethylene / vinyl acetate copolymer and a white inorganic pigment. A method for selecting a solar cell by whiteness, wherein the whiteness of the solar cell is measured in accordance with a method B of JIS-P-8148, and the whiteness is 87.0-93. A screening method characterized by screening solar cells in the range of 0.0%.

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