JP5604335B2 - Solar cell sealing film and solar cell using the same - Google Patents

Description

  The present invention relates to a sealing film for solar cells containing an ethylene-polar monomer copolymer and a crosslinking agent, and particularly relates to a sealing film for solar cells in which a decrease in electrical insulation is suppressed.

  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, the 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 battery cell 14 such as a silicon power generation element, a back-side sealing film 13B, And the back side protection member (back cover) 12 are laminated in this order, degassed under reduced pressure, and heated and pressurized to crosslink and cure the front side sealing film 13A and the back side sealing film 13B, thereby bonding and integrating. It is manufactured by doing. In a conventional solar battery, a plurality of solar battery cells 14 are connected and used in order to obtain a high electric 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.

  A transparent substrate such as a glass substrate is used for a surface-side transparent protective member used in a conventional solar cell in order to make sunlight enter the battery as efficiently as possible and concentrate it on the solar cell. On the other hand, in order to prevent moisture intrusion into the inside of the battery, the back side protective member uses a plastic film such as polyethylene terephthalate (PET) or a film on which the vapor deposition film made of silver is formed. It has been.

  In addition, the sealing film used on the front side and the back side can prevent foreign matter and moisture from entering the battery and ensure insulation between the solar cells and electrodes inside the battery. There is a demand for a film made of an ethylene-polar monomer copolymer such as an ethylene-vinyl acetate copolymer (EVA) or an ethylene-ethyl acrylate copolymer (EEA).

  In solar cells, it is necessary to reliably extract electricity generated from incident sunlight to the outside of the cell. Therefore, it is necessary for the sealing film for solar cells to ensure insulation between the solar cells and electrodes inside the battery and prevent the occurrence of leakage current.

  And solar cells are used in harsh environments exposed to high temperatures, high humidity, and wind and rain, such as outdoors, for a long period of time, which is said to be several decades or longer. In particular, when used in a high-temperature environment such as a hot summer sun, a conventional solar cell may have poor insulation, resulting in reduced power generation performance. Therefore, a sealing film made of an ethylene-polar monomer copolymer is required to have excellent insulating properties even under a high temperature environment.

  Moreover, in order to improve the power generation efficiency of a solar cell, it is desired to make light enter the solar cell as efficiently as possible and collect it on the solar cell. For this reason, by using a sealing film colored white or the like as the back surface side sealing film, sunlight incident from gaps or the like of a plurality of solar cells is reflected to improve the power generation efficiency of the solar cell ( Patent Document 1).

JP 2002-170971 A

  However, when a colorant is added to the sealing film, the insulating property of the sealing film may be lowered. Thereby, there is a problem that current leakage occurs and the power generation efficiency of the solar cell is lowered.

  Accordingly, an object of the present invention is a solar cell sealing film used as a sealing film on the back surface side of a solar cell, in which a decrease in electrical insulation, particularly a decrease in electrical insulation in a high temperature environment, is suppressed. An object of the present invention is to provide a solar cell sealing film having high sunlight reflectance. Moreover, it is providing the solar cell using this sealing film.

The object is a sealing film for solar cells containing an ethylene-polar monomer copolymer and a crosslinking agent, and further, white fluororesin fine particles are added to 3 parts by mass of 100 parts by mass of the ethylene-polar monomer copolymer. It is achieved by a solar cell sealing film characterized by containing ˜40 parts by mass. By blending the fluororesin fine particles, it is possible to suppress a decrease in electrical insulation under a high temperature environment and to obtain a high light reflectance.

Preferred embodiments of the solar cell sealing film according to the present invention are as follows.
(1) The average particle diameter of the fluororesin fine particles is 1 to 50 μm.
(2) The fluororesin is polytetrafluoroethylene.
(3) The ethylene-polar monomer copolymer is an ethylene-vinyl acetate copolymer.
(4) Furthermore, it is a solar cell sealing film containing a crosslinking aid.
(5) The crosslinking aid is triallyl isocyanurate.

  In addition, in the solar battery in which the solar battery cell is sealed by interposing a sealing film between the front surface side transparent protective member and the back surface side protective member, the solar cell and the back surface side protection are provided. It is also achieved by a solar cell in which the sealing film between the members is the solar cell sealing film.

  According to the present invention, it is possible to provide a solar cell sealing film that suppresses a decrease in electrical insulation under a high-temperature environment and has a high sunlight reflectance. Therefore, a solar cell with high power generation efficiency can be provided by using this as a back surface side sealing film of a solar cell.

It is a schematic sectional drawing of a common solar cell. It is the schematic for demonstrating the 180 degreeC peel test method which is evaluation of adhesive force.

  As described above, the solar cell sealing film of the present invention contains fluororesin fine particles in addition to the ethylene-polar monomer copolymer and the crosslinking agent. Content of a fluororesin fine particle is 3-40 mass parts with respect to 100 mass parts of ethylene-polar monomer copolymers. When the fluororesin fine particles are blended in the sealing film, the electrical insulation of the fluororesin can suppress a decrease in insulation even under a high temperature environment. Moreover, the sealing film which has a high light reflectivity is obtained by mix | blending the white fluororesin microparticles | fine-particles. Moreover, according to this compounding quantity, the adhesive force of a sealing film does not fall.

  Hereinafter, the solar cell sealing film of the present invention will be described in more detail.

[Fluorine resin fine particles]
In the present invention, the fluororesin may be Re white der I resin der containing fluorine atoms. Examples of fluororesins include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) ) And the like. PTFE is particularly preferable. These may be used alone or in combination of two or more.

  The average particle size of the fluororesin fine particles is preferably 1 to 50 μm (maximum particle size 10 to 250 μm), particularly preferably 2 to 20 μm (maximum particle size 10 to 120 μm). If the average particle size is smaller than the above range, the fluororesin fine particles are likely to aggregate and may be difficult to disperse. If the average particle size is larger than the above range, sufficient adhesion may not be obtained.

  In the present invention, the average particle diameter is a diameter equivalent to the projected area of at least 100 fluororesin fine particles when the solar cell sealing film is observed with an electron microscope (preferably a transmission electron microscope) at a magnification of about 1,000,000 times. Is the number average value obtained.

  Further, the content of the fluororesin fine particles is preferably 3 to 40 parts by mass, particularly preferably 5 to 30 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. If the content of the fluororesin fine particles is less than this range, the effect of suppressing the decrease in electrical insulation may not be sufficiently exhibited. On the other hand, if the amount is more than the above range, the adhesive force may be reduced.

[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 preferably 20 to 35% by mass, more preferably 22 to 30% by mass, and particularly preferably 24 to 28% by mass with respect to the ethylene-vinyl acetate copolymer. . When the content of vinyl acetate is less than 20% by mass, the fluidity of the composition for sealing film is lowered, and the workability of the sealing film for solar cell may be lowered, and when it exceeds 35% by mass. Carboxylic acid, alcohol, amine and the like may be generated, 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 for In that case, PVB is particularly preferable.

[Crosslinking agent]
The crosslinking agent used for the sealing film of the present invention 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, the one having a decomposition temperature of 70 ° C. or more with a half-life of 10 hours is preferable.

  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. 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 organic peroxides, in particular, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, 1,1-bis (tert-hexylperoxy) -3,3,5-trimethylcyclohexane 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 3 parts by mass, more preferably 0.2 to 2 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. 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]
Furthermore, it is preferable that the sealing film for solar cells before crosslinking curing contains a crosslinking aid. The crosslinking aid can improve the crosslinking density of the ethylene-polar monomer copolymer and form a solar cell sealing film having a low degree of swelling after crosslinking and curing.

  The crosslinking aid is preferably used in an amount of 0.1 to 3.0 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. With such a content of the crosslinking aid, there is no generation of gas due to the addition of the crosslinking aid, and the crosslinking density of the ethylene-polar monomer copolymer can be improved.

  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). Etc.) of monofunctional or bifunctional crosslinking aids. Of these, triallyl cyanurate and / or triallyl isocyanurate are preferable, and triallyl isocyanurate is particularly preferable.

[Adhesion improver]
The sealing film of the present invention may further contain a silane coupling agent for the purpose of improving the adhesive strength. As silane coupling agents, γ-chloropropylmethoxysilane, vinylethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane , Γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β- (Aminoethyl) -γ-aminopropyltrimethoxysilane and the like can be mentioned. These silane coupling agents may be used alone or in combination of two or more.

  Moreover, it is preferable that content of a silane coupling agent is 0.01-5 mass parts with respect to 100 mass parts of ethylene-polar monomer copolymers, and 0.1-2 mass parts is especially preferable.

[Others]
The sealing film of the present invention is used for improvement or adjustment of various physical properties (mechanical strength, optical characteristics, heat resistance, light resistance, crosslinking speed, etc.) of the film, especially for improvement of mechanical strength as necessary. 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.

  The plasticizer is not particularly limited, but polybasic acid esters and polyhydric alcohol esters are generally used. Examples thereof include dioctyl phthalate, dihexyl adipate, triethylene glycol-di-2-ethylbutyrate, butyl sebacate, tetraethylene glycol diptanoate, and triethylene glycol dipelargonate. One plasticizer may be used, or two or more plasticizers 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 methyl, ethyl, dodecyl, stearyl, lauryl and other linear alkyl groups, cyclohexyl group, tetrahydrofurfuryl group, aminoethyl group, 2-hydroxyethyl group, 3-hydroxypropyl group, A 3-chloro-2-hydroxypropyl group can be mentioned. 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 the epoxy-containing compound 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, 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 a light stabilizer and / or an anti-aging agent.

  By containing the light stabilizer, it is possible to suppress deterioration of the ethylene-polar monomer copolymer due to the influence of the irradiated light and the like, and the yellowing of the solar cell sealing film. 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 of which are ADEKA) , Tinuvin 744, Tinuvin 770, Tinuvin 765, Tinuvin 144, Tinuvin 622LD, CHIMASSORB 944LD (all manufactured by Ciba Specialty Chemicals), UV-3034 (manufactured by BF Goodrich), and the like. . 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 anti-aging agent include lactone heat stabilizers, vitamin E heat stabilizers, sulfur heat stabilizers and the like in addition to the above antioxidants.

  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, the composition containing each of the above-described components can be produced by a method of obtaining a sheet-like material by molding by ordinary extrusion molding, calendar molding (calendering) or the like. 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. When a film is formed by heating and rolling using extrusion molding or the like, heating is generally in the range of 50 to 100 ° C. The thickness of the solar cell sealing film is not particularly limited, but may be in the range of 50 μm to 2 mm.

  The structure of the solar cell of the present invention is not particularly limited as long as at least the solar cell sealing film of the present invention is used as the back surface side sealing film. For example, the structure etc. which sealed the photovoltaic cell (it is also called a solar cell element) by interposing the sealing film between the surface side transparent protection member and the back surface side protection member, etc. 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, in order to sufficiently seal the solar cell, as shown in FIG. 1, the surface side transparent protective member 11, the surface side sealing film 13A, the solar cell 14 and the back side sealing of the present invention. The sealing film 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 13A, a normal transparent solar cell sealing film is used.

  The solar cell of the present invention is a solar cell with high power generation efficiency because it effectively uses reflected light and suppresses a decrease in insulation.

In order to perform the heating and pressurization, for example, the laminate is heated with a vacuum laminator at a temperature of 135 to 180 ° C., further 140 to 180 ° C., particularly 150 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. The structure which laminated | stacked the battery sealing film and the back surface side protective member, and united and integrated is 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 preferably a plastic film such as polyethylene terephthalate (PET). 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 wet heat resistance may be used.

  In addition, the solar cell (including a thin film solar cell) of the present invention is characterized by the sealing film used on the back surface side as described above. Therefore, the members other than the sealing film such as the front-side transparent protective member, the back-side protective member, and the solar cell need only have the same configuration as the conventionally known solar cell, and are not particularly limited. .

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

[Examples 1-8, Comparative Examples 1-7]
Each material was supplied to a roll mill with each formulation shown in Tables 1 and 2 and kneaded at 60 to 100 ° C. to prepare a solar cell sealing film composition. The solar cell sealing film composition was calendered at 60 to 100 ° C., allowed to cool, and then a solar cell sealing film (thickness 0.4 mm) was produced.

(Evaluation method)
(1) Volume resistivity value The produced sealing film for solar cell is in the order of release PET / solar cell sealing film / release PET using two release PETs (0.75 mm thickness). Thus, a laminated body was obtained. This laminated body was temporarily pressure-bonded at 100 ° C. for 10 minutes under vacuum with a vacuum laminator, and then heated and crosslinked in an oven at 150 ° C. for 30 minutes to obtain a sample (sample shape: 100 mm ×
100 mm).

  About each produced sample, the volume specific resistance (log (ohm * m)) in a 60 degreeC environment was measured using the high rest tap (made by Mitsui Chemicals) (applied voltage, 1000V x 1 minute). With reference to the volume specific resistance (less than 14.2) of the conventional product, those that were 14.2 or more were accepted.

(2) Reflectance For the solar cell sealing film prepared above, a laminate was prepared in the same manner as in (1) and crosslinked to obtain a sample (sample shape: 50 mm × 50 mm).

  About each produced sample, the reflectance of 400-1000 nm was measured in the total reflection mode using the spectrophotometer U4100 (made by Hitachi High-Tech Fielding). The reflectance for aluminum oxide, which is a reference white plate, is used as a value. With reference to the integrated value of reflectance (10% or less) of the conventional product, an integrated value of reflectance of 15% or more was accepted.

(3) Glass adhesive force About the sealing film for solar cells produced above, it laminated | stacked so that it might become the order of glass plate / sealing film for solar cells / release PET (0.75 mm thickness). The obtained laminate was crosslinked in the same manner as described above. About the produced sample, the adhesive force was evaluated by the 180 degreeC peel test (JIS K6584, 1994). FIG. 2 shows the test method.

  As shown in the figure, a part between the glass substrate 21 and the solar cell sealing film 23 is peeled off, and the solar cell sealing film 23 is folded back at 180 ° C. to produce a tensile tester (manufactured by Shimadzu Corporation, Autograph). Was used to measure the peeling force at a tensile speed of 100 mm / min as the glass adhesive strength [N / cm]. 15 N / cm or more was determined to be acceptable.

  The results of the above evaluations are shown in Tables 1 and 2.

(Evaluation results)
In Examples 1-8, the sealing film for solar cells produced by mix | blending PTFE microparticles | fine-particles (average particle diameter: 5 micrometers) in the range of 3-40 mass parts with respect to 100 mass parts of EVA was evaluated. As a result, all the items of volume resistivity, reflectance and glass adhesion were acceptable.

  In Comparative Examples 1 and 2, the sealing film for a solar cell produced by changing the amount of the PTFE fine particles (2 parts by mass and 45 parts by mass with respect to 100 parts by mass of EVA) was evaluated. As a result, the sealing film containing 2 parts by mass of PTFE fine particles had a reduced volume resistivity. Further, the sealing film containing 45 parts by mass had a reduced glass adhesive force.

  In Comparative Examples 3 to 6, another resin fine particle (polyethylene fine particle (average particle size: 20 to 30 μm), polypropylene fine particle (average particle size: 4 μm)) was blended in the amounts shown in Table 2, and the produced sealing film evaluated. As a result, the reflectance did not satisfy the reference value in any case.

  As described above, if the sealing film is blended with 3 to 40 parts by mass of fluororesin fine particles with respect to 100 parts by mass of the ethylene-polar monomer copolymer, the volume resistivity and the reflectance in a high temperature environment are high, It was shown that the glass adhesion does not decrease.

  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.

  A solar cell with high power generation efficiency can be obtained by using a solar cell sealing film having high electrical insulation and high light reflectance even in a high temperature environment.

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 21 Glass substrate 23 Sealing film for solar cells

Claims (7)

An encapsulating film for solar cells containing an ethylene-polar monomer copolymer and a crosslinking agent,
Furthermore, 3-40 mass parts of white fluororesin microparticles | fine-particles are contained with respect to 100 mass parts of said ethylene-polar monomer copolymers, The sealing film for solar cells characterized by the above-mentioned.   2. The solar cell sealing film according to claim 1, wherein the fluororesin fine particles have an average particle diameter of 1 to 50 μm.   The sealing film for solar cells according to claim 1 or 2, wherein the fluororesin of the fluororesin fine particles is polytetrafluoroethylene.   The solar cell sealing film according to any one of claims 1 to 3, wherein the ethylene-polar monomer copolymer is an ethylene-vinyl acetate copolymer.   Furthermore, the sealing film for solar cells of any one of Claims 1-4 containing a crosslinking adjuvant.   The solar cell sealing film according to claim 5, wherein the crosslinking aid is triallyl isocyanurate. In the solar cell formed by interposing a sealing film between the front surface side transparent protective member and the back surface side protective member, and sealing the solar cell,
The solar cell which is the sealing film for solar cells of any one of Claims 1-6 in which the sealing film between the said cell for solar cells and the said back surface side protection member.

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