JP2017228549A - Sealing film for solar cell and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing film for a solar cell which does not cause filling failure and is excellent in durability even when the thickness is thin.SOLUTION: A sealing film for a solar cell including a sealing resin further includes thermally expandable particles. The content of the thermally expandable particles is 0.1 to 50 parts by mass with respect to 100 parts by mass of the sealing resin.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solar cell sealing film used for a solar cell and a solar cell manufactured using the same.

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

  As shown in FIG. 1, a solar cell generally includes a surface side transparent protective member 11 made of a glass substrate or the like, a surface side sealing film 13A, a power generation element 14 such as a silicon crystal cell, a back surface side sealing film 13B, and The back side protection member (back cover) 12 is laminated in this order, deaerated under reduced pressure, and then heated and pressurized to cross-link and cure the front side sealing film 13A and the back side sealing film 13B to integrate and integrate. It is manufactured by.

  As sealing resin used as the base of the surface side sealing film and the back side sealing film, ethylene-polar monomers such as ethylene-vinyl acetate copolymer (EVA) and ethylene-methyl methacrylate copolymer (EMMA) An ethylene / α-olefin copolymer polymerized using a copolymer or a metallocene catalyst is generally used because of its excellent insulation and sealing properties.

  In order to manufacture a solar cell using a solar cell sealing film, each member is laminated in a vacuum laminator such as a double vacuum chamber method, degassed, and then heated and pressurized. Is. After the solar cell sealing film is melted by heating, the power generation element is firmly sealed by further crosslinking the sealing resin contained in the solar cell sealing film.

JP 2011-192694 A

  When manufacturing a solar cell, it is necessary to seal with a solar cell sealing film without causing insufficient filling between the power generation elements. To prevent insufficient charging, solar cell sealing is required. The film must be formed to have a predetermined thickness, and the melt of the solar cell sealing film melted by heating must be sufficiently distributed between the power generation elements.

  However, since sealing resins such as EVA are generally expensive, there is a problem that manufacturing cost is required to produce a solar cell sealing film having a predetermined thickness. Therefore, it is desired to develop a sealing film for a solar cell that can be sealed without insufficient filling and has a small thickness. If the solar cell sealing film can be made thin, it is possible to pack and transport a large number of solar cell sealing films in a packing material during transportation. There is a demand for a thinner film.

  In addition, since solar cells are usually installed outdoors, the solar cell sealing film may be deteriorated by repeating the daytime high temperature environment and the nighttime low temperature environment every day. Therefore, improvement of the durability of the sealing film for solar cells under the condition of repeating the high temperature environment and the low temperature environment is also demanded.

  Accordingly, an object of the present invention is to provide a solar cell sealing film that is excellent in durability without causing defective filling even when the thickness is thin. Moreover, the objective of this invention is providing the manufacturing method of the solar cell which uses this sealing film for solar cells.

  The above object is a solar cell sealing film containing a sealing resin, further including thermally expandable particles, and the content of the thermally expandable particles is 0 with respect to 100 parts by mass of the sealing resin. 0.1 to 50 parts by mass, which is achieved by a solar cell sealing film.

  According to this configuration, when the thermally expandable particles expand, the volume of the entire solar cell sealing film increases, and the expanded solar cell sealing film spreads between the power generating elements without gaps. It is possible to seal without generating. In addition, since the thermally expandable particles expand and the volume of the solar cell sealing film increases, it is possible to reduce the thickness of the solar cell sealing film before the thermal expandable particles expand. Furthermore, the solar cell sealing film is excellent in durability under repeated conditions of high temperature and low temperature.

Preferred embodiments of the present invention are as follows.
(1) The thermally expandable particles are particles containing a substance that is vaporized by heat in a thermoplastic resin.
(2) The sealing resin is an ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymer (EVA) generates acid over time and causes corrosion of solar cell electrodes. However, the present invention reduces the amount of EVA used compared to the prior art by making the sealing film thinner. Therefore, corrosion of the electrode can be suppressed.
(3) Further contains a crosslinking agent. By crosslinking the sealing resin, it is possible to firmly hold the bubbles formed by the expansion of the thermally expandable particles.

In addition, the above object is to obtain a laminate by laminating a surface side transparent protective member, a surface side sealing film, a power generating element, a back side sealing film, and a back side protective member in this order, and pressurize the laminate. And a solar cell manufacturing method including a heating step,
The solar cell sealing film is used as a back surface side sealing film, and the thermally expandable particles are expanded by the heating. Heating is preferably performed at a temperature of 100 to 250 ° C.

  The sealing film for solar cells of the present invention does not cause poor filling even when the thickness is small, and is excellent in durability. Since the amount of the sealing resin used can be reduced by the thin thickness, the manufacturing cost can be reduced, and more solar cell sealing films can be packed and transported at the time of packing. It is possible. Moreover, the solar cell produced using the solar cell sealing film of this invention is excellent also in durability.

It is a schematic sectional drawing which shows a common solar cell. It is a schematic sectional drawing which shows an example of a vacuum laminator.

[Thermal expandable particles]
Hereinafter, the present invention will be described in detail. As described above, the solar cell sealing film of the present invention includes a sealing resin and thermally expandable particles. As the heat-expandable particles, particles containing a substance that is vaporized by heat in a thermoplastic resin can be used. Preferably, thermally expandable particles having an outer shell portion made of a thermoplastic resin and a substance that is vaporized by heat contained in the outer shell portion are used. Such a heat-expandable particle vaporizes a substance that is vaporized by heat, and the thermoplastic resin softened by heating expands to form voids. In addition, it is necessary to mix thermally expansible particle | grains directly in the sealing film for solar cells. In the case of a thermosetting type in which the solar cell sealing film is cured by heating, the voids are stable without being crushed. Further, if the thermally expandable particles are not mixed in the portion in contact with the power generating element, the effect of improving cushioning and filling properties due to the mixing of the thermally expandable particles cannot be exhibited.

  Examples of the thermoplastic resin include polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, polyethylene terephthalate, and polybutylene terephthalate. These thermoplastic resins may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the substance that is vaporized by heat include hydrocarbons that are liquid at room temperature, preferably hydrocarbons having 2 to 10 carbon atoms, specifically, n-butane, isobutane, n-pentane, isopentane, neopentane, and n-hexane. And low molecular hydrocarbons such as heptane. These thermal expansion compounds may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the substance that is vaporized by heat in the thermally expandable particles is not particularly limited, but is 2 to 60% by mass, preferably 5 to 50% by mass based on the mass of the thermally expandable particles.

The average particle diameter of the thermally expandable particles after expansion is preferably 2 to 200 μm, particularly preferably 20 to 150 μm. The average particle diameter of the thermally expandable particles before expansion is, for example, 1 to 100 μm, preferably 10 to 70 μm, more preferably 10 to 45 μm, and particularly 26 to 34 μm. The average particle diameter in the present invention, using a laser diffraction type particle size distribution measuring device corresponds to a volume mean diameter D ₅₀ values obtained by measuring the thermal expansive particle by a wet measuring method.

  The content of the thermally expandable particles in the solar cell sealing film is 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, more preferably 0.5 to 100 parts by weight of the sealing resin. To 15 parts by mass, more preferably 0.8 to 10 parts by mass, particularly 1 to 5 parts by mass. If the amount is larger than this range, the contact area with the glass is reduced by the amount of bubbles formed by expansion, and the adhesive force may be reduced. On the other hand, if it is less than this range, it may not be possible to achieve both the prevention of filling defects between the power generating elements and the reduction in the thickness of the solar cell sealing film.

  The expansion start temperature of the thermally expandable particles is, for example, 100 to 180 ° C., preferably 120 to 150 ° C., particularly 130 to 140 ° C. The thermal expansion start temperature is appropriately set and selected according to the softening temperature of the thermoplastic resin constituting the thermally expandable particles, the heating temperature at the time of manufacturing the solar cell, the melting point of the sealing resin used, the reaction temperature of the crosslinking agent, and the like. Can do. The maximum expansion temperature of the thermally expandable particles is 150 to 180 ° C, preferably 160 to 175 ° C.

[Resin for sealing]
In the present invention, the sealing resin may be any resin as long as it is a resin used for sealing the power generation element. Preferably, the sealing resin is a thermoplastic polymer such as an olefin (co) polymer or a polyvinyl acetal resin (for example, polyvinyl formal, polyvinyl butyral (PVB resin), modified PVB).

  Here, the olefin (co) polymer means an ethylene / α-olefin copolymer (for example, an ethylene / α-olefin copolymer (m-LLDPE) polymerized using a metallocene catalyst), polyethylene (for example, Olefin polymers such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene, polybutene, and the like, and copolymers of olefins and polar monomers such as ethylene-polar monomer copolymers. It means a copolymer and has adhesiveness and transparency required for a sealing film for solar cells. As the olefin (co) polymer, one of these may be used, or two or more may be mixed and used. In the present invention, as the olefin (co) polymer, an ethylene / α-olefin copolymer (m-LLDPE) polymerized using a metallocene catalyst, a low density polyethylene (LDPE), a linear low density polyethylene (LLDPE). ), At least one polymer selected from the group consisting of polypropylene, polybutene and ethylene-polar monomer copolymers. In particular, the olefin (co) polymer is an ethylene-polar monomer copolymer because it is excellent in processability, can form a crosslinked structure with a crosslinking agent, and can form a solar cell sealing film with high adhesion. An ethylene / α-olefin copolymer (m-LLDPE) polymerized using a polymer and / or a metallocene catalyst is preferred.

  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. By using an ethylene-polar monomer copolymer having such a melt flow rate, a solar cell sealing film having excellent processability can be obtained. 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.

  Examples of the ethylene-polar monomer copolymer include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl methacrylate copolymer, and ethylene-methyl acrylate copolymer. An ethylene-ethyl acrylate copolymer is preferable, and EVA is particularly preferable.

  When EVA is used as the resin material, the content of vinyl acetate in EVA is preferably 20 to 35% by mass, more preferably 22 to 32% by mass, and particularly preferably 24 to 30% by mass. If the vinyl acetate content is less than 20% by mass, the adhesiveness of the sealing film may not be sufficient. If it exceeds 35% by mass, acid is likely to be generated, which causes corrosion of the electrodes of the solar cell. There is.

  m-LLDPE is composed mainly of a structural unit derived from ethylene and further has an α-olefin having 3 to 12 carbon atoms, such as propylene, 1-butene, 1-hexene, 1-octene, 4-methylpentene-1, An ethylene / α-olefin copolymer (including a terpolymer and the like) having one or more structural units derived from 4-methyl-hexene-1, 4,4-dimethyl-pentene-1, and the like. Specific examples of the ethylene / α-olefin copolymer include an ethylene / 1-butene copolymer, an ethylene / 1-octene copolymer, an ethylene-4-methyl-pentene-1 copolymer, an ethylene / butene / hexene copolymer. Center polymers, ethylene / propylene / octene terpolymers, ethylene / butene / octene terpolymers, and the like. The content of the α-olefin in the ethylene / α-olefin copolymer is preferably 5 to 40% by mass, more preferably 10 to 35% by mass, and still more preferably 15 to 30% by mass. When the content of α-olefin is small, the flexibility and impact resistance of the solar cell sealing film may not be sufficient, and when it is too large, the heat resistance may be low.

  A known metallocene catalyst may be used as the metallocene catalyst for polymerizing m-LLPDE, and is not particularly limited. The metallocene catalyst is generally a compound having a structure in which a transition metal such as titanium, zirconium or hafnium is sandwiched between unsaturated cyclic compounds containing a π-electron cyclopentadienyl group or a substituted cyclopentadienyl group. And a promoter such as an aluminum compound such as alkylaluminoxane, alkylaluminum, aluminum halide, and alkylaluminum halide. Metallocene catalysts are characterized by a uniform active site (single site catalyst), and usually a polymer having a narrow molecular weight distribution and an approximately equal comonomer content of each molecule is obtained.

In the present invention, the density of m-LLDPE (according to JIS K 7112; the same applies hereinafter) is not particularly limited, but is preferably 0.860 to 0.930 g / cm ³ . The melt flow rate (MFR) of m-LLDPE (according to JIS-K7210) is not particularly limited, but is preferably 1.0 g / 10 min or more, more preferably 1.0 to 50.0 g / 10 min. 3.0 to 30.0 g / 10 min is more preferable. In addition, MFR is measured on condition of 190 degreeC and load 21.18N.

  In the present invention, commercially available m-LLDPE may be used. For example, Harmolex series, Kernel series manufactured by Nippon Polyethylene Co., Ltd., Evolution series manufactured by Prime Polymer Co., Ltd., Excellen GMH series, Excellen FX series manufactured by Sumitomo Chemical Co., Ltd. and the like can be mentioned.

  The encapsulating resins listed above may be used alone or in combination of two or more.

[Crosslinking agent]
The sealing film for solar cell of the present invention preferably contains a crosslinking agent to form a crosslinked structure of the sealing resin. By forming a crosslinked structure, it is possible to maintain the cell structure after expansion of the expandable particles for a long period of time. 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 can be used as long as it decomposes at a temperature of 100 ° C. or higher to generate 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, 1,1-bis (tert-hexylperoxy)- 3,3,5-trimethylcyclohexane, 2,2-bis (4,4-di tert-butylperoxycyclohexyl) propane, 1,1-bis (tert-butylperoxy) cyclododecane, tert-hexylperoxyisopropyl monocarbonate, tert-butylperoxymaleic acid, tert-butylperoxy-3, 3,5-trimethylhexane, tert-butylperoxylaurate, 2,5-dimethyl-2,5-di (methylbenzoylperoxy) hexane, tert-butylperoxyisopropylmonocarbonate, tert-butylperoxy-2 -Ethylhexyl monocarbonate, tert-hexyl peroxybenzoate, 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-2,5-di (tert-butylperoxy) hexane or tert-butylperoxy-2-ethylhexyl monocarbonate is particularly preferable. Thereby, the sealing film for solar cells which is bridge | crosslinked favorably and has the outstanding transparency is obtained.

  The content of the organic peroxide used for the solar cell sealing film is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the sealing resin. Preferably there is. If the content of the organic peroxide is small, the crosslinking speed may be lowered during the crosslinking and curing, and if the content is large, 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.

  Content of the said photoinitiator is 0.1-5 mass parts with respect to 100 mass parts of sealing resin, Preferably it is 0.2-3 mass parts.

[Crosslinking aid]
It is preferable that the sealing film for solar cells of the present invention further contains a crosslinking aid. The crosslinking aid can improve the gel fraction of the sealing resin and improve the adhesion and weather resistance of the solar cell sealing film.

  The content of the crosslinking aid is usually 0.1 to 5 parts by weight, preferably 0.1 to 3 parts by weight, particularly preferably 0.3 to 2.0 parts by weight with respect to 100 parts by weight of the sealing resin. Used in. Thereby, the sealing film which the hardness after bridge | crosslinking improved further 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 solar cell sealing film of the present invention may further contain an adhesion improver. As the adhesion improver, a silane coupling agent can be used. Thereby, it can be set as the sealing film for solar cells which has the further outstanding adhesive force. Examples of the silane coupling agent include γ-chloropropyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, and γ-glycidoxypropyl. Trimethoxysilane, 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. Of these, γ-methacryloxypropyltrimethoxysilane is particularly preferred.

  The content of the silane coupling agent in the solar cell sealing film of the present invention is 5 parts by mass or less, preferably 0.1 to 2 parts by mass with respect to 100 parts by mass of the sealing resin.

[Others]
The sealing film for solar cells of the present invention improves or adjusts various physical properties of the film (optical properties such as mechanical strength and transparency, heat resistance, light resistance, crosslinking speed, etc.), especially improvement of mechanical strength. Therefore, if necessary, various additives such as a plasticizer, an acryloxy group-containing compound, a methacryloxy group-containing compound and / or an epoxy group-containing compound may further be included.

  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. 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. In extrusion molding, since the heat-expandable particles may expand unintentionally due to a temperature rise in the vicinity of the die, it is preferable to carry out by calendar molding.

  As described above, the thickness of the solar cell sealing film of the present invention can be made thinner than before. For example, it is 0.1 to 2 mm, preferably 0.25 to 1 mm, more preferably 0.25 to 0.6 mm, and most preferably 0.25 to 0.4 mm.

  The structure of the solar cell of the present invention is not particularly limited as long as it includes a structure in which the solar cell element is sealed with the solar cell sealing film of the present invention. For example, the structure etc. which sealed the cell for solar cells by interposing the sealing film for solar cells of this invention between the surface side transparent protection member and the back surface side protection member, and making it bridge-integrate are mentioned. .

  In addition, in this invention, the side (light-receiving surface side) where the light of the solar cell is irradiated 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, in order to sufficiently seal the solar cell, for example, as shown in FIG. 1, power generation of the surface side transparent protective member 11, the surface side sealing film 13A, a single crystal or polycrystalline silicon cell, etc. What is necessary is just to laminate | stack the element 14, the back surface side sealing film 13B, and the back surface side protection member 12, and bridge-harden a sealing film according to a conventional method, such as heating and pressurization.

  The surface side transparent protective member 11 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 protection member 12 is preferably a plastic film such as polyethylene terephthalate (PET) or polyamide. Further, 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 the case of a solar cell having a double glass structure, a glass plate may be used.

  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 a sealing film of a thin film solar cell such as a solar cell and a copper indium selenide (CIS) solar cell. 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. On the solar cell element formed on the surface of the back surface side protective member, the structure for laminating the battery sealing film and the back surface side protective member and adhering and integrating them, the front surface side Laminated transparent protective member, bonded and integrated structure, or front side transparent protective member, front side sealing film, thin film solar cell element, back side sealing film, and back side protective member are laminated in this order, For example, a structure that is bonded and integrated. In addition, in this invention, the cell for solar cells and a thin film solar cell element are named generically, and it is called an electric power generation element.

  Next, the manufacturing method of the solar cell of this invention is demonstrated. As shown in FIG. 1, the method for manufacturing a solar cell of the present invention includes a front side transparent protective member 11, a front side sealing film 13 </ b> A, a power generation element 14, a back side colored sealing film 13 </ b> B, and a back side protective member 12. It has the process of obtaining the laminated body 10 by laminating in order, and pressurizing and heating this laminated body 10. FIG. The step of pressurizing and heating the laminate 10 is preferably performed using, for example, a vacuum laminator having an inflatable diaphragm, particularly a vacuum laminator of the double vacuum chamber system shown in FIG.

  A vacuum laminator 100 shown in FIG. 2 includes an upper chamber 102 having a diaphragm 103 and a lower chamber 101 having a mounting table 105 for mounting the stacked body 10. In the vacuum laminator 100, the laminated body 10 is pressurized by the diaphragm 103 after evacuating the upper chamber 102 and the lower chamber 101. The evacuation in the upper chamber 102 and the lower chamber 101 is performed by dividing the lower chamber vacuum pump 107 connected to the lower chamber exhaust port 106 and the upper chamber vacuum pump 109 connected to the upper chamber exhaust port 108. Is done.

  In order to pressurize the laminate 10 using such a vacuum laminator, first, the surface-side transparent protective member 11, the surface-side sealing film 13A, the power generation element are placed on the mounting table 105 provided in the lower chamber 101. 14, The laminated body 10 which laminated | stacked the back surface side colored sealing film 13B and the back surface side protection member 12 in this order is mounted. Next, after the upper chamber 102 and the lower chamber 101 are evacuated by the upper chamber vacuum pump 109 and the lower chamber vacuum pump 107, respectively, the inside of the upper chamber 102 is preferably set to a pressure equal to or higher than the atmospheric pressure. . Thereby, the uppermost surface of the laminated body 10 is pressed by the diaphragm 103, and the laminated body 10 is pressurized.

  In order to make each of the upper chamber 102 and the lower chamber 101 vacuum, it is preferable that the upper chamber 102 and the lower chamber 101 are first depressurized to 50 to 150 Pa, particularly 50 to 100 Pa, respectively. The vacuum time is, for example, 0.1 to 5 minutes. Then, the laminated body is uniformly pressed by the diaphragm 103 by setting the inside of the upper chamber to 40 to 110 kPa, particularly 60 to 105 kPa.

It is preferable to adjust the degree of expansion of the diaphragm so that the laminate is pressurized at a pressure of 1.0 × 10 ³ Pa to 5.0 × 10 ⁷ Pa, particularly 60 to 105 kPa. The pressing time is, for example, 5 to 15 minutes.

  In the method of the present invention, heating is performed together with pressurization. As a heating method, the entire vacuum laminator 100 shown in FIG. 2 is heated in a high-temperature environment such as an oven, and a heating medium such as a heating plate is introduced into the lower chamber 101 of the vacuum laminator 100 shown in FIG. The method of heating the body 10 etc. are mentioned. In the latter method, for example, a heating plate is used as the mounting table 105, a heating plate is arranged on the upper side and / or lower side of the mounting table 105, or a heating plate is arranged on the upper side and / or lower side of the stacked body. It is done by doing. The laminate 10 is preferably heated to a temperature of 100 to 250 ° C, preferably 120 to 170 ° C. The heating temperature is preferably set as appropriate according to the expansion start temperature and the maximum expansion temperature of the thermally expandable particles to be used.

  Heating may be performed in two stages using a vacuum laminator and an oven. That is, first, in a vacuum laminator, after heating and pre-pressing at a temperature at which the crosslinking agent does not react and the thermally expandable particles do not expand, for example, at a temperature of 80 to 110 ° C., put in an oven at a temperature of 120 to 170 ° C. The sealing resin may be crosslinked while being heated to expand the thermally expandable particles.

  In the present invention, since the expandable particles contained in the solar cell sealing film expand, the gap between the power generation elements is filled by the expanded portion, and thus a solar cell can be manufactured without causing poor filling. . In addition, since the expandable particles expand and the volume of the entire solar cell sealing film increases, the thickness of the solar cell sealing film before expansion can be reduced, and the manufacturing cost can be reduced and transportation and transportation can be reduced. Efficiency is improved. Furthermore, the solar cell manufactured using the solar cell sealing film of the present invention is excellent in durability under conditions of repeated high temperature environment and low temperature environment. The solar cell sealing film of the present invention is preferably used as a back-side sealing film because the expandability of the expandable particles decreases the transparency.

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

(1-1) Preparation of solar cell sealing film (back surface side sealing film) (Examples 1 to 9, Comparative Examples 2 to 7)
Each material was supplied to a roll mill with the formulation shown in the following table, and kneaded at 70 ° C. to prepare a solar cell sealing film composition. This solar cell sealing film composition was calendered at 70 ° C., allowed to cool, and then a solar cell sealing film (thickness 0.3 mm) was produced.

(1-2) Production of solar cell Surface side protection member (white plate glass 100 × 160 cm, thickness 3.0 mm) / surface side sealing film / solar cell (155 × 155 mm, thickness 0.2 mm, length 6) , 10 on the side) / back side sealing film / back side protection member (PET film 100 × 160 cm, thickness 3.0 mm) is placed on the mounting table 105 in the lower chamber 101 of the vacuum laminator 100 of the type shown in FIG. Each member was laminated | stacked on the (heating board) in the order shown, and the laminated body 10 was obtained.

  Next, the inside of the lower chamber 101 was evacuated, and the inside of the lower chamber was maintained at 0.1 Pa for 5 minutes. After the evacuation was completed, pressurization by the diaphragm 103 was started. The pressurization was performed at a pressure of 0.1 Pa to 101 kPa over 1 minute 20 seconds, and this pressure was maintained for 10 minutes. Heating was started simultaneously with evacuation, and the temperature of the mounting table (heating plate) 105 was raised to 165 ° C. and maintained at this temperature until the pressurization was completed. After allowing to cool, a solar cell was obtained.

  The back side sealing film is the solar cell sealing film prepared in (1-1), and the front side sealing film is EVA (VA content: 26% by mass, MFR: 4 g / 10 min) 100 parts by mass. , T-butylperoxy-2-ethylhexyl monocarbonate 1 part by mass, triallyl isocyanurate 1 part by mass, and γ-methacryloxypropyltrimethoxysilane 0.5 part by mass, as in (1-1), calender It was obtained by molding and has a thickness of 0.3 mm.

(2-1) Production of solar cell sealing film not containing thermally expandable particles (Comparative Example 1)
A solar cell sealing film (0.6 mm, used in Comparative Example 1) was prepared in the same manner as (1) except that the thermally expandable particles were not blended.

(2-2) Production of Solar Cell (Comparative Example) The solar cell was produced in the same manner as (1-2) except that the solar cell encapsulation film produced in (2-1) was used as the back-side encapsulation membrane. A battery was produced.

<Evaluation method>
(1) Poor filling About the produced solar cell, it was confirmed whether the filling defect had generate | occur | produced visually. ◎ indicates that no filling failure was observed, ○ indicates that there were 3 or less filling failures with a diameter of 1 mm or less, and △ indicates 3 filling failures with a diameter of 2 mm or less. The number is less than or equal to the number of places, and x is something other than these.
(2) Heat shock test (durability)
About the produced solar cell, it heated and cooled by making 2 hours into 1 cycle in the range of -40 degreeC-120 degreeC, and after performing 100 cycles, the presence or absence of peeling of the sealing film for solar cells was confirmed visually. ◎ indicates that no peeling was observed, ○ indicates that the diameter of the peeling was less than 10 mm, Δ indicates that the diameter of the peeling was 10 mm or more and less than 30 mm, Indicates that the diameter of the peeling is 30 mm or more.
The results are shown in the table below.

The details of the materials shown in the following table are as follows.
EVA: vinyl acetate content 26 mass%, MFR 4.3 g / 10 min (manufactured by Tosoh, Ultrasen 634)
Cross-linking agent: t-butyl peroxy-2-ethylhexyl monocarbonate (manufactured by NOF Corporation, perbutyl E)
Crosslinking aid: triallyl isocyanurate (Nippon Kasei, TAIC)
Silane coupling agent: γ-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicone, KBM503)
Thermally expandable particles (1): Advancel EHM303 (manufactured by Sekisui Chemical Co., Ltd., average particle size: 26 to 34 μm, expansion start temperature: 130 to 140 ° C., maximum expansion temperature: 160 to 170 ° C.)
Thermally expandable particles (2): Advancel EML101 (manufactured by Sekisui Chemical Co., Ltd., average particle size: 14-20 μm, thermal expansion start temperature: 120-130 ° C., maximum expansion temperature: 160-170 ° C.)
Thermally expandable particles (3): Advancel EMH204 (manufactured by Sekisui Chemical Co., Ltd., average particle size 38 to 44 μm, thermal expansion start temperature 120 to 130 ° C., maximum expansion temperature 165 to 175 ° C.)

<Evaluation results>
When the thermally expandable particles are 0.1 to 50 parts by mass, even if the thickness of the solar cell sealing film (back surface side sealing film) is as thin as 0.3 mm, filling failure does not occur, Further, good results were obtained in the heat shock test, and it was recognized that the durability was excellent. In Comparative Example 1, when a solar cell sealing film (back surface side sealing film) having a thickness of 0.6 mm was used, large peeling was observed in the heat shock test. When the content of the thermally expandable particles was 0.08 parts by mass, good results were not obtained in the heat shock test. When the content of the heat-expandable particles was 60 parts by mass, poor filling was observed. In addition, when the bubble structure of the sealing film for solar cells after the expansion | swelling of Examples 1-6 was confirmed, it was confirmed that it is a closed-cell structure.

DESCRIPTION OF SYMBOLS 10 Laminated body 11 Front surface side transparent protective member 12 Back surface side protective member 13A Front surface side sealing film 13B Back surface side sealing film 14 Power generation element 15 Connection tab 100 Vacuum laminator 101 Lower chamber 102 Upper chamber 103 Diaphragm 105 Mounting stand 106 Lower side Exhaust port for chamber 107 Vacuum pump for lower chamber 108 Exhaust port for upper chamber 109 Vacuum pump for upper chamber

Claims (6)

A sealing film for solar cells containing a sealing resin,
The solar cell sealing film further comprising thermally expandable particles, wherein the content of the thermally expandable particles is 0.1 to 50 parts by mass with respect to 100 parts by mass of the sealing resin.   2. The solar cell sealing film according to claim 1, wherein the thermally expandable particles are particles containing a substance that is vaporized by heat in a thermoplastic resin.   The solar cell sealing film according to claim 1, wherein the sealing resin is an ethylene-vinyl acetate copolymer.   Furthermore, a crosslinking agent is included, The solar cell sealing film of any one of Claims 1-3 characterized by the above-mentioned. A step of laminating a surface side transparent protective member, a surface side sealing film, a power generation element, a back surface side sealing film, and a back surface side protecting member in this order includes a step of pressing and heating the layered body. In the method for manufacturing a solar cell,
As the back surface side sealing film, using the solar cell sealing film according to any one of claims 1 to 4,
A production method comprising expanding the thermally expandable particles by the heating.   The manufacturing method according to claim 5, wherein the heating is performed at a temperature of 100 to 250 ° C.

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