JP2011249701A - Solar cell sealing film and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing film used on a rear side of a solar cell, improving a reflectance and preventing deterioration in electric insulation.SOLUTION: A sealing film used on a rear side of a solar cell is arranged between a solar cell element of the solar cell and a rear side protective member and used for sealing the solar cell element. The solar cell sealing film contains an ethylene-polar monomer copolymer, a crosslinking agent and mica fine particles.

Description

  TECHNICAL FIELD The present invention relates to a solar cell sealing film containing an ethylene-polar monomer copolymer as a main component, and more particularly to a back side solar cell sealing film in which the electrical insulation is not lowered and the reflectance is improved.

  In recent years, solar cells that directly convert sunlight into electrical energy have been widely used from the standpoints of effective use of resources and prevention of environmental pollution, and development has been promoted from the viewpoint of productivity and durability.

  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. And the EVA film for sealing films has improved the crosslinking density using crosslinking agents, such as an organic peroxide, other than EVA, in order to improve film | membrane intensity | strength and durability (patent document 1).

  In solar cells, it is desired to further improve power generation efficiency. Therefore, by adding a colorant such as titanium dioxide to the solar cell sealing film used on the back surface side of the solar cell, the sunlight that has entered the solar cell module is reflected from the back surface sealing film and reflected solar. A solar cell sealing film in which the power generation efficiency of a solar cell is increased by making light incident on the solar cell is known (Patent Document 2).

JP 2009-239277 A Japanese Patent Laid-Open No. 6-177412

  However, when a coloring agent such as titanium dioxide is added to the sealing film for solar cells, there is a problem that the electric insulation is lowered and the power generation efficiency is lowered due to the occurrence of leakage current.

  Accordingly, an object of the present invention is to provide a sealing film for solar cells that is used on the back side of a solar cell and has improved electrical reflectivity and improved reflectivity. Another object of the present invention is to provide a solar cell with improved power generation efficiency by using this solar cell sealing film.

  This object is a sealing film for a back side solar cell for sealing a solar cell element, which is disposed between a solar cell element of a solar cell and a back side protection member, and is an ethylene-polar monomer copolymer This is achieved by a sealing film for a solar cell comprising a coalescence, a crosslinking agent and mica fine particles. By adding mica having characteristics of high electrical insulation and high light reflectivity to the solar cell sealing film, the reflectance can be improved without degrading the electrical insulation of the sealing film.

Preferred embodiments of the present invention are as follows.
(1) The aspect ratio of the mica fine particles is 20 or more.
(2) The aspect ratio of the mica fine particles is 20-80.
(3) The mica fine particles are synthetic mica fine particles.
(4) The mica fine particles contain 5 to 20 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer.
(5) The average particle diameter of the mica fine particles is 1 to 50 μm.
(6) The ethylene-polar monomer copolymer is an ethylene-vinyl acetate copolymer.

  This object can also be achieved by a solar cell using the above-described sealing film for back side solar cell.

  ADVANTAGE OF THE INVENTION According to this invention, an electrical insulating property does not fall and the sealing film for back surface side solar cells which the reflectance improved can be provided. Therefore, if the solar cell sealing film of the present invention is used in a solar battery, the sunlight incident from the light receiving surface side of the solar battery reaches the back surface side sealing film of the present invention from the gaps of the solar cells. In such a case, the solar light can be effectively used by reflecting the sunlight and entering the solar battery cell, and a solar cell with improved power generation efficiency can be provided because no leak current is generated.

It is a schematic sectional drawing of a common solar cell.

  As described above, the sealing film for backside solar cells of the present invention is characterized by containing an ethylene-polar monomer copolymer, a crosslinking agent, and mica fine particles. Hereinafter, the solar cell sealing film of the present invention will be described in more detail.

[Mica fine particles]
In the present invention, any mica fine particles may be used. It is preferable to use mica having a high aspect ratio because the reflectance can be improved more reliably. The aspect ratio is 20 or more, preferably 20 to 200, more preferably 20 to 80, particularly preferably 40 to 80, and still more preferably 60 to 80.

  If the aspect ratio is too high, workability and moldability may be deteriorated, and if the aspect ratio is low, insulating and reflective effects may not be obtained. The reason why the reflectance is improved as the aspect ratio is increased is that the area in which the flake-like mica overlaps in layers is increased.

  The mica used in the present invention may be synthetic mica or natural mica. However, since natural mica contains a pure product, it is preferable to use synthetic mica with few impurities and high uniformity in particle diameter.

Examples of the synthetic mica include synthetic phlogopite: KMg ₃ (AlSi ₃ O ₁₀ ) (OH) ₂ , synthetic fluorine phlogopite: KMg ₃ (AlSi ₃ O ₁₀ ) F ₂ , potassium tetrasilicon mica: KMg _2.5 ( Si ₄ O ₁₀ ) F ₂ , sodium tetrasilicon mica: NaMg _2.5 (Si ₄ O ₁₀ ) F ₂ , sodium teniolite: NaMg ₂ Li (Si ₄ O ₁₀ ) F ₂ , lithium teniolite: LiMg ₂ Li ( Si ₄ O ₁₀ ) F ₂ , sodium hectorite: Na _1/3 Mg _8/3 Li _1/3 (Si ₄ O ₁₀ ) F ₂ , lithium hectorite: Li _1/3 Mg _8/3 Li _1/3 ( Si ₄ O ₁₀ ) F ₂ or the like can be used. Among these, it is preferable to use a synthetic phlogopite that, when blended, makes the appearance of the solar cell sealing film black. Thereby, it can match | combine with the color tone of the photovoltaic cell normally black, and the design property of a solar cell can be improved.

  Synthetic mica can be produced by a known method. For example, a melt synthesis method, a hydrothermal synthesis method, a solid phase reaction method, or the like. The melt synthesis method is preferable from the viewpoint of obtaining good crystallinity. Examples of natural mica include muscovite, phlogopite, biotite, soda mica and sericite.

  These mica may be used individually by 1 type, and may be used in combination of 2 or more type. The compounding amount of mica is 5 to 20 parts by mass, preferably 10 to 20 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. If the amount is less than this range, the effect of the reflectance and electrical insulation may not be obtained. Moreover, the average particle diameter of the mica used by this invention is 1-50 micrometers normally from the point of the workability of the sealing film for solar cells, Preferably, you may be 10-40 micrometers.

  In addition, in this invention, an average particle diameter means the 50% median diameter measured with the laser diffraction type particle size distribution measuring apparatus (For example, the Seishin company make, LMS-30). The aspect ratio is an index indicating the shape of a plate-like particle or object, and refers to the ratio of the average major axis to the average thickness (average major axis / average thickness) of the mica fine particles. The average major axis and the average thickness are measured by observing about 100 fine particles using a scanning electron microscope, and can be calculated as a simple average thereof.

[Ethylene-polar monomer copolymer]
In the present invention, examples of the polar monomer of the ethylene-polar monomer copolymer include an unsaturated carboxylic acid, a salt thereof, an ester thereof, an amide thereof, a vinyl ester, and carbon monoxide. More specifically, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, fumaric acid, itaconic acid, monomethyl maleate, monoethyl maleate, maleic anhydride, itaconic anhydride, lithium of these unsaturated carboxylic acids, sodium, Salts of monovalent metals such as potassium, salts of polyvalent metals such as magnesium, calcium and zinc, methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutyl acrylate, n-butyl acrylate, isooctyl acrylate, methacrylic acid Examples include unsaturated carboxylic acid esters such as methyl, ethyl methacrylate, isobutyl methacrylate, and dimethyl maleate, vinyl esters such as vinyl acetate and vinyl propionate, carbon monoxide, sulfur dioxide, etc. be able to.

  More specifically, as the ethylene-polar monomer copolymer, ethylene-acrylic acid copolymer, ethylene-unsaturated carboxylic acid copolymer such as ethylene-methacrylic acid copolymer, the ethylene-unsaturated carboxylic acid Ionomer in which some or all of carboxyl groups of copolymer are neutralized with the above metal, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate 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-n-butyl acrylate -Ethylene-unsaturated carboxylic acid ester-unsaturated carboxylic acid such as methacrylic acid copolymer Some or all of the copolymer and its carboxyl group ionomer neutralized with the metal, ethylene - can be exemplified vinyl ester copolymer as a typical example - ethylene such as vinyl acetate copolymer.

  As the ethylene-polar monomer copolymer, it is preferable to use a copolymer having a melt flow rate defined by JIS K7210 of 35 g / 10 min or less, particularly 3 to 6 g / 10 min. According to the sealing film for solar cells using the ethylene-polar monomer copolymer having such a melt flow rate, the sealing film is melted or positioned at the time of heating and pressing in the sealing process at the time of manufacturing the solar battery. It is possible to suppress the occurrence of deviation and the protrusion from the end of the substrate.

  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.

  As the ethylene-polar monomer copolymer, an ethylene-vinyl acetate copolymer (also referred to as EVA) is particularly preferable. Thereby, it is cheap and can form the sealing film for solar cells excellent in a softness | flexibility.

  The content of vinyl acetate in the ethylene-vinyl acetate copolymer is 20 to 35 parts by mass, more preferably 22 to 30 parts by mass, especially 24 to 28 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. Is preferred. If the vinyl acetate content is less than 20 parts by mass, the sealing film obtained when crosslinked and cured at a high temperature may not be sufficiently transparent. If the content exceeds 35 parts by mass, carboxylic acid, alcohol, amine May occur, and foaming may easily occur at the interface between the sealing film and the protective member.

  In addition to the ethylene-polar monomer copolymer, the solar cell encapsulating film of the present invention further comprises a polyvinyl acetal resin (for example, polyvinyl formal, polyvinyl butyral (PVB resin), modified PVB), and a vinyl chloride resin. May be used. In that case, PVB is particularly preferable.

[Crosslinking agent]
In the present invention, the crosslinking agent is capable of forming a crosslinked structure of an ethylene-polar monomer copolymer. As the crosslinking agent, an organic peroxide or a photopolymerization initiator is preferably used. Among these, it is preferable to use an organic peroxide because a sealing film with improved temperature dependency of adhesive strength, 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, for example, benzoyl peroxide curing agent, tert-hexyl peroxypivalate, tert-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-di (tert-butylperoxy) hexane, 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethyl Peroxy-2-ethylhexanoate, tert-hexyl par Xyl-2-ethylhexanoate, 4-methylbenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, m-toluoyl + benzoyl peroxide, benzoyl peroxide, 1,1-bis (tert-butyl Peroxy) -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-trimethylcyclohexane, 1,1-bis (tert-butylperoxy) cyclohexane, 2,2-bis (4,4-di-tert) -Butylperoxycyclohexyl) propane, 1,1-bis (tert-butyl) -Oxy) cyclododecane, tert-hexylperoxyisopropyl monocarbonate, tert-butylperoxymaleic acid, tert-butylperoxy-3,3,5-trimethylhexane, 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 (benzoylperoxy) hexane, and the like.

  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-polar monomer copolymer. preferable. If the content of the organic peroxide is small, the insulating properties 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 cross-linking aid can improve the gel fraction of the ethylene-polar monomer copolymer and improve the adhesion and durability of the 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 preferably 0.3 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 cells of the present invention is a plasticizer, if necessary, for improving or adjusting various physical properties of the film (optical properties such as mechanical strength, heat resistance, light resistance, crosslinking speed, etc.). And various other additives 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 a structure of the solar cell of the present invention, if the solar cell sealing film of the present invention is used as a back surface side sealing film (a sealing film between the solar cell and the back surface side protective member), There is no particular limitation. For example, the structure etc. which sealed the cell 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 are mentioned. 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."

  In the solar cell of the present invention, to sufficiently seal the solar cell, 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 (sealing film for solar cell of the present invention) 13B 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 (light-receiving surface side sealing film), the solar cell sealing film of the present invention in which mica is blended is not suitable, and therefore a known solar cell seal in which mica is not blended. Use stop film. For example, a solar cell sealing film described in Patent Document 1 having high transparency can be used.

  The solar cell of the present invention using the solar cell sealing film of the present invention as the back surface side sealing film can effectively use reflected light, and further, the electric insulation is not lowered. It is.

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-polar monomer copolymer contained in the front side sealing film 13A and the back side sealing film 13B during this 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.

  The solar cell sealing film of the present invention is not limited to a solar cell using a single crystal or polycrystalline silicon crystal solar cell as shown in FIG. It can also be used for sealing films of thin film solar cells such as solar cells and copper indium selenide (CIS) solar cells. In this case, for example, the solar cell of the present invention is formed on a thin film solar cell element layer formed by a chemical vapor deposition method or the like on the surface of a surface side transparent protective member such as a glass substrate, a polyimide substrate, or a fluororesin transparent substrate. A battery sealing film, a structure in which a back side protective member is 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 side sealing film of the present invention, and a back side The structure etc. which laminated | stacked the side protection member in this order, and carried out adhesion integration are mentioned.

  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 a plastic film such as polyethylene terephthalate (PET), but in consideration of heat resistance and heat and moisture resistance, it is a fluorinated polyethylene film, particularly a fluorinated polyethylene film / Al / fluorinated. A film in which polyethylene films are laminated in this order is 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 surface side sealing film, such as the front surface side transparent protective member, the back surface side protective member, the front surface side sealing film, and the solar battery cell, have the same configuration as a conventionally known solar cell. There is no particular limitation.

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

[Examples 1 to 6, Comparative Example 1]
The materials shown in the table were kneaded with a roll at 70 ° C., calendered at 70 ° C., allowed to cool, and a solar cell sealing film (thickness 0.6 mm) was produced.

The physical properties of the mica used in the present invention are as follows.
Mica 1: synthetic phlogopite, aspect ratio 20, average particle diameter 10 μm,
Mica 2: synthetic phlogopite, aspect ratio 40, average particle size 10 μm,
Mica 3: synthetic phlogopite, aspect ratio 60, average particle size 10 μm,
Mica 4: synthetic phlogopite, aspect ratio 80, average particle diameter 40 μm.

[Evaluation methods]
(1) Reflectance For the solar cell sealing film, a sample having a size of 50 mm × 50 mm was prepared, a black vinyl tape (manufactured by YAMATO) was attached to one surface of the sample, and a vacuum laminator was used at 90 ° C. Was pre-pressed for 5 minutes and then heated in an oven at 155 ° C. for 20 minutes to crosslink to a gel fraction of 90% or more.

  About this laminated body, the total reflectance of the sealing film for solar cells of this invention was measured in the state which suppressed reflection of the surface by which the black vinyl tape was stuck. The total reflectance is measured by using a spectrophotometer (U-4100) manufactured by Hitachi, Ltd., with the total reflectance in the wavelength region 300 to 1200 nm being 100% of the total reflectance of the standard white plate (barium sulfate). Was measured as a relative value.

(2) Volume Specific Resistance A sample having a size of 100 mm × 100 mm was prepared for the solar cell sealing film, and using two release PET (manufactured by Toray), release PET / solar cell sealing film / Laminated so as to be in the order of release PET. The obtained laminate was temporarily pressed with a vacuum laminator at 90 ° C. for 5 minutes, and then heated in an oven at 155 ° C. for 20 minutes to crosslink to a gel fraction of 90% or more.

  Using the high resistivity (Hiresta UP (Mitsubishi Chemical Corporation)) and the probe (UR-100 (Mitsubishi Chemical Corporation)), the volume resistivity (LogΩ · cm) was measured in a 60 ° C environment. (Applied voltage, 1000 V × 1 minute). A score of 13.0 or higher was accepted.

[Evaluation results]
As shown in Table 1, in Examples 1 to 4, the solar cell sealing film containing 10 parts by mass of mica had improved reflectance without decreasing the volume resistivity. In particular, it has been clarified that the reflectance improves as the aspect ratio increases. Further, in Examples 5 and 6, the sealing film produced by changing the amount of mica also had a reduced volume specific resistance and an improved reflectance.

  From the above examples, it was shown that the solar cell sealing film containing mica fine particles has improved reflectivity and does not deteriorate electrical insulation.

  According to the present invention, it is possible to provide a solar cell with improved power generation efficiency by effectively using reflected light without lowering electrical insulation.

Claims (8)

A solar cell sealing film for sealing a solar cell element, disposed between the solar cell element of the solar cell and the back surface protective member,
A sealing film for solar cells, comprising an ethylene-polar monomer copolymer, a crosslinking agent and mica fine particles.   The solar cell sealing film according to claim 1, wherein an aspect ratio of the mica fine particles is 20 or more.   The solar cell sealing film according to claim 1 or 2, wherein the mica fine particles have an aspect ratio of 20 to 80.   The solar cell sealing film according to claim 1, wherein the mica fine particles are synthetic mica fine particles.   5. The solar cell sealing film according to claim 1, wherein the mica fine particles include 5 to 20 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. .   6. The solar cell sealing film according to claim 1, wherein the mica fine particles have an average particle diameter of 1 to 50 μm.   The solar cell sealing film according to any one of claims 1 to 6, wherein the ethylene-polar monomer copolymer is an ethylene-vinyl acetate copolymer.   A solar cell using the solar cell sealing film according to claim 1.

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