JPWO2016043235A1 - Solar cell encapsulant and solar cell module - Google Patents

Abstract

Two outermost layers having a volume resistivity of 1.0 × 10 15 Ω · cm to 1.0 × 10 18 Ω · cm, and a volume resistivity of 1.0 × 10 11 Ω · cm disposed between the two outermost layers. A solar cell encapsulant in which at least three layers including an intermediate layer that is not less than 1.0 cm and less than 1.0 × 10 15 Ω · cm are laminated.

Description

  One embodiment of the present invention relates to a solar cell sealing material for fixing a solar cell element in a solar cell module, and a solar cell module in which a solar cell element is sealed with the solar cell sealing material.

In recent years, the system voltage of solar cell modules has been increasing, and in Japan, the voltage is 600V for detached houses, and the system voltage is shifting to a high system voltage of 1000V for mega solar for industrial and power generation applications. . There is also a prospect that the voltage will be raised to 1500V in the future.
Among them, due to poor insulation of the solar cell module, a problem of failure due to leakage current, in particular, a phenomenon of output reduction due to deterioration of the solar cell element called PID (Potential Induced Degradation) is becoming obvious.
PID is generated when a potential difference is generated between the aluminum frame and the solar cell element of the solar cell module, and the insulation between the aluminum frame and the solar cell element is lowered to generate a leakage current. Due to the occurrence of this leakage current, sodium (Na) ions contained in the protective member glass move to the surface of the solar cell element, accumulate in the antireflection film of the solar cell element, and electrochemical corrosion proceeds. However, it is said that the solar cell element is deteriorated by losing the semiconductor property of the solar cell element.

  Conventionally, many solar cell encapsulants are mainly composed of an ethylene / vinyl acetate copolymer (EVA). For example, in JP 2009-298046 A, a multilayer sheet having improved fracture strength, impact resistance and puncture resistance while maintaining transparency and noise level, an ethylene / (meth) acrylic acid copolymer or Disclosed is a three-layer sheet comprising an intermediate layer composed of the (A) layer mainly composed of the ionomer, and an outer layer composed of the (B) layer composed mainly of the ethylene / vinyl acetate copolymer formed on both surfaces thereof. Has been.

Japanese Patent Application Laid-Open No. 2014-27034 includes a crosslinked cured film of a composition containing an ethylene-polar monomer copolymer and a crosslinking agent as a solar cell sealing material film capable of suppressing the generation of PID, A solar cell sealing film having a volume resistivity at 25 ° C. of 5.0 × 10 ¹³ or more is disclosed.

  However, the three-layer sheet described in JP-A-2009-298046 and the solar cell sealing material described in JP-A-2014-27034 are both EVA as a main component of the layer forming the outermost layer, Since the volume resistivity is low, the occurrence of PID may not be sufficiently suppressed.

  One embodiment of the present invention has been made in view of the above, and it is an object to achieve the following object. That is, one embodiment of the present invention aims to provide a solar cell sealing material excellent in PID resistance and a solar cell module using the solar cell sealing material.

Specific means for achieving the above object includes the following aspects.
<1> Volume resistivity disposed between two outermost layers having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm to 1.0 × 10 ¹⁸ Ω · cm, and the two outermost layers. And a solar cell encapsulant in which at least three layers including an intermediate layer of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm are laminated.

<2> The solar cell sealing material according to <1>, wherein the outermost layer includes an ethylene / (meth) acrylic acid copolymer, and the intermediate layer includes an ethylene / vinyl acetate copolymer.
<3> The solar cell encapsulant according to <1> or <2>, in which three layers of the outermost layer of the two layers and the intermediate layer are laminated.
<4> The volume resistivity of the whole sealing material is 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less, according to any one of <1> to <3>. Solar cell encapsulant.
<5> The solar cell encapsulation according to any one of <1> to <4>, wherein the ratio of the thickness of one of the two outermost layers to the intermediate layer is 1/2 to 1/8. Wood.

<6> A solar cell module comprising the solar cell sealing material according to any one of <1> to <5>.

  According to one embodiment of the present invention, a solar cell sealing material excellent in PID resistance and a solar cell module using the solar cell sealing material are provided.

It is a photograph which shows the state of the sheet | seat after implementing shrinkage resistance evaluation with respect to the multilayer sheet of Example 2. FIG. It is a photograph which shows the state of the sheet | seat after implementing shrinkage resistance evaluation with respect to the single layer sheet of the comparative example 1.

<Sealant for solar cell>
The solar cell encapsulant according to an embodiment of the present invention has two outermost layers having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm to 1.0 × 10 ¹⁸ Ω · cm, At least three layers including an intermediate layer having a volume resistivity of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm provided between the two outermost layers are laminated. Is done.
In the solar cell encapsulant that is one embodiment of the present invention, the volume resistivity of the entire encapsulant is 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less. preferable.

The reason why the effect of the embodiment of the present invention appears is not clear, but is estimated as follows.
That is, in one embodiment of the present invention, the solar cell encapsulant has at least a three-layer structure, and the volume resistivity of the outermost layer is 1.0 × 10 ¹⁵ Ω · cm or more, whereby the solar cell module is Even when operated at a high voltage, it is considered that the sealing material can maintain high insulation and the occurrence of leakage current is suppressed. Thereby, it is thought that the sealing material for solar cells will be excellent in PID tolerance.
Below, the sealing material for solar cells which is one Embodiment of this invention is demonstrated in detail.

[Outermost layer]
The sealing material for solar cells includes an outermost layer having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm to 1.0 × 10 ¹⁸ Ω · cm.
The outermost layer is a layer located on the outermost side of the solar cell encapsulant, and the solar cell encapsulant having at least a three-layer structure has two outermost layers.
The sealing material for solar cells has an intermediate layer described later between one outermost layer (for example, a layer on which sunlight is incident) and the other outermost layer (for example, a layer on the solar cell element side). .

When the volume resistivity of the outermost layer is less than 1.0 × 10 ¹⁵ Ω · cm, the insulating material of the sealing material is inferior and leakage current during high voltage operation cannot be suppressed. Moreover, when the volume resistivity of the outermost layer is 1.0 × 10 ¹⁸ Ω · cm or less, it becomes easy to obtain a material for forming the outermost layer.
The volume resistivity of the outermost layer is preferably 1.0 × 10 ¹⁶ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less from the above viewpoint.
The volume resistivity can be measured according to JIS C 2139: 2008.
The volume resistivity can be adjusted by the material forming the outermost layer.

The material forming the outermost layer can be selected from those having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm to 1.0 × 10 ¹⁸ Ω · cm. Moreover, if the volume resistivity of the outermost layer to be formed satisfies 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less, the volume resistivity in another range as a material for forming the outermost layer. You may use the material which has.
The materials of the two outermost layers present in the solar cell encapsulant may be the same or different.
The outermost layer preferably contains an ethylene / (meth) acrylic acid copolymer as a main component from the viewpoint of easily adjusting the volume resistivity to the above range.

The “main component” here means a component contained in the outermost layer in an amount of 70% by mass or more based on the total mass of the outermost layer. From the above viewpoint, the outermost layer preferably contains 80% by mass or more, and 90% by mass or more of the ethylene / (meth) acrylic acid copolymer with respect to the total mass of the outermost layer. More preferably.
Within the above range, it is preferable that the outermost layer contains an ethylene / (meth) acrylic acid copolymer because good transparency and good PID resistance can be obtained.

(Ethylene (meth) acrylic acid copolymer)
In the ethylene / (meth) acrylic acid copolymer, the content of structural units derived from ethylene is preferably 75% by mass to 95% by mass with respect to the total mass of the copolymer, and 75% by mass to More preferably, it is 92 mass%.
When the content of the structural unit derived from ethylene is 75% by mass or more, the heat resistance, mechanical strength, and the like of the copolymer are further improved. On the other hand, when the content of the structural unit derived from ethylene is 95% by mass or less, the transparency, flexibility, and adhesiveness of the copolymer are further improved.

In the ethylene (meth) acrylic acid copolymer, the content of structural units derived from (meth) acrylic acid is preferably 5% by mass to 25% by mass with respect to the total mass of the copolymer. It is more preferable that it is mass%-25 mass%.
The structural unit derived from (meth) acrylic acid in the copolymer plays an important role in adhesion to a substrate such as glass, and if the content is 5% by mass or more, it is transparent and flexible. When the content is 25% by mass or less, the stickiness is suppressed and the workability is good.
When the silane coupling agent described later is contained in the outermost layer, the content of the structural unit derived from (meth) acrylic acid in the ethylene / (meth) acrylic acid copolymer is determined from the viewpoint of workability. 8 mass% or more and 18 mass% or less are preferable with respect to the total mass. Further, the content of the structural unit derived from (meth) acrylic acid is most preferably 13% by mass or more and 18% by mass or less with respect to the total mass of the copolymer from the viewpoint of processability and optical properties.

  In addition to the structural unit derived from ethylene and the structural unit derived from (meth) acrylic acid, the ethylene / (meth) acrylic acid copolymer includes structural units derived from other copolymerizable monomers. It may be. The content of structural units derived from other copolymerizable monomers is more than 0% by mass and 30% by mass with respect to a total of 100% by mass of structural units derived from ethylene and structural units derived from (meth) acrylic acid. % Or less, more preferably 0% by mass to 25% by mass or less.

  Examples of other copolymerizable monomers include unsaturated esters. Examples of unsaturated esters include vinyl esters such as vinyl acetate and vinyl propionate; methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, and isobutyl methacrylate. And (meth) acrylic acid alkyl esters. It is preferable that an unsaturated ester is contained in the above range as another copolymerizable monomer because the flexibility of the ethylene / (meth) acrylic acid copolymer is improved.

  The ethylene / (meth) acrylic acid copolymer can be obtained by radical copolymerization of each polymerization component under high temperature and high pressure.

  The melt flow rate (MFR) at 190 ° C. and 2160 g load of the ethylene / (meth) acrylic acid copolymer is from 0.1 g / 10 min from the viewpoint of workability and mechanical strength. 150 g / 10 min is preferable, and 30 g / 10 min to 100 g / 10 min is particularly preferable.

  The outermost layer can contain various additives within the range not impairing the object of the present invention. Examples of such additives include a crosslinking agent, a crosslinking aid, a silane coupling agent, an ultraviolet absorber, a light stabilizer, and an antioxidant.

As the cross-linking agent, an organic peroxide having a decomposition temperature with a half-life of 1 hour is usually 90 ° C. to 180 ° C., more preferably 100 ° C. to 150 ° C. Examples of such organic peroxides include t-butyl peroxyisopropyl carbonate, t-butyl peroxy-2-ethylhexyl carbonate, t-butyl peroxyacetate, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, di-t-butylperoxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexyne-3, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, Methyl ethyl ketone peroxide, 2,5-dimethylhexyl-2,5-bisperoxybenzoate t-butyl hydroperoxide, p- menthane hydroperoxide, benzoyl peroxide, p- chlorobenzoyl peroxide, t- butyl peroxy isobutyrate, include hydroxy heptyl peroxide and di cyclohexanone peroxide.
The content of the crosslinking agent in the outermost layer is preferably 0.1 parts by mass to 5 parts by mass and more preferably 0.5 parts by mass to 3 parts by mass with respect to 100 parts by mass of the ethylene / (meth) acrylic acid copolymer. preferable.

  Examples of the crosslinking aid include polyunsaturated compounds such as polyallyl compounds and poly (meth) acryloxy compounds. Specifically, polyallyl compounds such as triallyl isocyanurate, triallyl cyanurate, diallyl phthalate, diallyl fumarate and diallyl maleate; poly (meta) such as ethylene glycol diacrylate, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate ) Acryloxy compounds; divinylbenzene and the like.

  The content of the crosslinking aid in the outermost layer is preferably 5 parts by mass or less, and more preferably 0.1 part by mass to 3 parts by mass with respect to 100 parts by mass of the ethylene / (meth) acrylic acid copolymer.

Examples of the silane coupling agent include a silane coupling agent having a vinyl group, an amino group or an epoxy group, and a hydrolyzing group such as an alkoxy group, and a titanate coupling agent.
Specific examples of the silane coupling agent include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-acryloxypropyltrimethoxysilane, and γ-glycidoxypropyltrimethoxy. Silane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropylmethyl Examples include diethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane.

  When the total mass of the outermost layer is 100 parts by mass, the content of the silane coupling agent in the outermost layer is preferably 5 parts by mass or less, and more preferably 0.02 parts by mass to 3 parts by mass. When the outermost layer contains the silane coupling agent in the above range, the adhesion between the solar cell sealing material and the transparent protective material or solar cell element is improved.

  Examples of the ultraviolet absorber include 2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2-carboxybenzophenone and 2-hydroxy-4-n-. Benzophenone ultraviolet absorbers such as octoxybenzophenone; 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2- (2′-hydroxy-5-methylphenyl) benzotriazole and Examples include benzotriazole ultraviolet absorbers such as 2- (2′-hydroxy-5-t-octylphenyl) benzotriazole; salicylic acid ester ultraviolet absorbers such as phenyl salicylate and p-octylphenyl salicylate.

Examples of the light stabilizer include hindered amine light stabilizers.
Specific examples of the hindered amine light stabilizer include 4-acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2. , 2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-cyclohexanoyloxy-2,2,6,6-tetramethylpiperidine, 4- ( o-chlorobenzoyloxy) -2,2,6,6-tetramethylpiperidine, 4- (phenoxyacetoxy) -2,2,6,6-tetramethylpiperidine, 1,3,8-triaza-7,7, 9,9-tetramethyl-2,4-dioxo-3-noctyl-spiro [4,5] decane, bis (2,2,6,6-tetramethyl-4-piperidyl Sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) terephthalate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, Tris (2,2,6,6 -Tetramethyl-4-piperidyl) benzene-1,3,5-tricarboxylate, tris (2,2,6,6-tetramethyl-4-piperidyl) -2-acetoxypropane-1,2,3-tri Carboxylate, tris (2,2,6,6-tetramethyl-4-piperidyl) -2-hydroxypropane-1,2,3-tricarboxylate, tris (2,2,6,6-tetramethyl-4 -Piperidyl) triazine-2,4,6-tricarboxylate, tris (2,2,6,6-tetramethyl-4-piperidine) phosphite, tris (2,2,6,6) Tetramethyl-4-piperidyl) butane-1,2,3-tricarboxylate, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) propane-1,1,2,3-tetracarboxylate, Examples include tetrakis (2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate.

Examples of the antioxidant include various hindered phenol-based antioxidants and phosphite-based antioxidants.
Specific examples of the hindered phenol antioxidant include 2,6-di-t-butyl-p-cresol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2 , 6-di-t-butyl-4-ethylphenol, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2,2'-methylenebis (4-ethyl-6-t-butylphenol), 4,4′-methylenebis (2,6-di-t-butylphenol), 2,2′-methylenebis [6- (1-methylcyclohexyl) -p-cresol], bis [3,3-bis (4-hydroxy) -3-t-butylphenyl) butyric acid] glycol ester, 4,4′-butylidenebis (6-t-butyl-m-cresol), 2,2′-ethylidenebis (4-sec) -Butyl-6-tert-butylphenol), 2,2'-ethylidenebis (4,6-di-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butyl) Phenyl) butane, 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -2,4,6-trimethylbenzene, 2,6-diphenyl-4-octadecyloxyphenol, Tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 4,4′-thiobis (6-tert-butyl-m-cresol), tocopherol, 3,9-bis [1,1-dimethyl-2- [β- (3-tert-butyl-4-hydroxy-5) -Methylphenyl) propionyloxy] ethyl] 2,4,8,10-tetraoxaspiro [5,5] undecane, 2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzylthio ) -1,3,5-triazine and the like.
Specific examples of phosphite antioxidants include 3,5-di-t-butyl-4-hydroxybenzyl phosphonate dimethyl ester and bis (3,5-di-t-butyl-4-hydroxybenzylphosphonic acid). Examples thereof include ethyl and tris (2,4-di-t-butylphenyl) phosphinate.

  The content of the ultraviolet absorber, light stabilizer and antioxidant in the outermost layer is preferably 5 parts by mass or less, and 0.1 to 3 parts by mass, respectively, when the total mass of the outermost layer is 100 parts by mass. Part is more preferred.

When using the sealing material on the side opposite to the light-receiving surface side, it may contain additives such as a colorant, a light diffusing agent, a flame retardant, and a metal deactivator in addition to the above-described additives as necessary. Can do.
Examples of the colorant include pigments (inorganic pigments, organic pigments), dyes, and the like. These colorants can be appropriately selected from various known ones.

  Examples of inorganic pigments include white inorganic pigments such as titanium oxide, zinc white, lead white, lithopone, barite, precipitated barium sulfate, calcium carbonate, gypsum, and precipitated silica, carbon black, lamp black, titanium black, synthetic Black inorganic pigments such as iron black, gray inorganic pigments such as zinc powder, lead suboxide, slate powder, red inorganic pigments such as cadmium red, cadmium mercury red, silver vermilion, red rose, molybten red, red lead, amber, iron oxide tea Brown inorganic pigments such as cadmium yellow, zinc yellow, ocher, sienna, synthetic ocher, yellow inorganic pigments such as yellow lead, titanium yellow, green inorganic pigments such as chromium oxide green, cobalt green, chromium green, ultramarine blue, bitumen, iron Examples include blue inorganic pigments such as blue and cobalt blue, and metal powder inorganic pigments.

Examples of organic pigments include Permanent Red 4R, Para Red, First Yellow G, First Yellow 10G, Disazo Yellow G, Disazo Yellow GR, Disazo Orange, Pyrazolone Orange, Brilliant Carmine 3B, Brilliant Carmine 6B, Brilliant Scarlet G, Brilliant Bordeaux 10B, Bordeaux 5B, Permanent Red F5R, Permanent Carmine FB, Risole Red R, Risole Red B, Rake Red C, Rake Red D, Brilliant Fast・ Azo pigments such as Scarlet, Pyrazolone Red, Bon Maroon Light, Bon Maroon Medium, Fire Red, Nitroso Pigments such as Naphthol Green B, Nito such as Naphthol Yellow S Pigments, basic dyes such as rhodamine B lake and rhodamine 6G lake, mordant dyes such as alizarin and lake, vat dyes such as indanthrene blue, phthalocyanine blue, phthalocyanine green, fast Examples thereof include phthalocyanine pigments such as sky blue and dioxazine pigments such as dioxazine violet.
Examples of the pigment include organic fluorescent pigments and pearl pigments in addition to the above-described inorganic pigments and organic pigments.

  When a solar cell sealing material containing these additives is used as a sealing material on the light receiving side of a solar cell element, transparency may be impaired, but sealing on the surface opposite to the light receiving side of the solar cell element may occur. When used as a material, it is preferably used.

  Examples of the light diffusing agent include inorganic beads such as glass beads, silica beads, silicon alkoxide beads, and hollow glass beads. Examples of the organic spherical material include plastic beads such as acrylic beads and vinylbenzene beads.

  Examples of the flame retardant include halogen-based flame retardants such as bromide, phosphorus-based flame retardants, silicone-based flame retardants, and metal hydrates such as magnesium hydroxide and aluminum hydroxide.

  As a metal deactivator, a well-known thing is mentioned as a compound which suppresses the metal damage of a thermoplastic resin. Two or more metal deactivators may be used in combination. Preferable examples of the metal deactivator include hydrazide derivatives or triazole derivatives. Specifically, examples of the hydrazide derivative include decamethylene dicarboxyl-disalicyloyl hydrazide, 2 ′, 3-bis [3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionyl] propionate. Onohydrazide, and bis (2-phenoxypropionyl-hydrazide) isophthalate. Examples of the triazole derivative include 3- (N-salicyloyl) amino-1,2,4-triazole. In addition to hydrazide derivatives and triazole derivatives, 2,2′-dihydroxy-3,3′-di- (α-methylcyclohexyl) -5,5′-dimethyl diphenylmethane, tris- (2 -Methyl-4-hydroxy-5-tert-butylphenyl) butane, a mixture of 2-mercaptobenzimidazole and a phenol condensate.

[Middle layer]
The sealing material for solar cells includes an intermediate layer having a volume resistivity of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm.
The intermediate layer is a layer disposed between the two outermost layers, and the solar cell encapsulant includes at least one intermediate layer, and the intermediate layer may be composed of two or more layers. .
The volume resistivity of the intermediate layer is preferably 1.0 × 10 ¹² Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm.
The volume resistivity can be measured by the method described above.
The volume resistivity can be adjusted by the material forming the intermediate layer.

The material forming the intermediate layer can be selected from those having a volume resistivity of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm. It is also possible to use a general-purpose material with low PID resistance, such as × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm. Moreover, if the volume resistivity of the intermediate layer to be formed satisfies 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm, the volume resistivity in another range as a material for forming the intermediate layer You may use the material which has.
The intermediate layer preferably contains an ethylene / vinyl acetate copolymer as a main component from the viewpoint of easily adjusting the volume resistivity to the above range.

The “main component” here means a component contained in the intermediate layer in an amount of 70% by mass or more based on the total mass of the intermediate layer. From the above viewpoint, the intermediate layer preferably contains 80% by mass or more of ethylene / vinyl acetate copolymer, and more preferably 90% by mass or more.
When the ethylene / vinyl acetate copolymer is contained in the intermediate layer within the above range, good transparency, flexibility, impact resistance and puncture resistance can be obtained.

(Ethylene / vinyl acetate copolymer)
The ethylene / vinyl acetate copolymer includes a structural unit derived from ethylene and a structural unit derived from vinyl acetate. The ethylene / vinyl acetate copolymer may be a random copolymer, a block copolymer, or an alternating copolymer.

In the ethylene / vinyl acetate copolymer, the content of structural units derived from ethylene is preferably 60% by mass to 85% by mass, and 65% by mass to 82% by mass with respect to the total mass of the copolymer. More preferably.
When the structural unit derived from ethylene is 60% by mass or more, the impact resistance and puncture resistance of the intermediate layer are further improved. On the other hand, when the structural unit derived from ethylene is 85% by mass or less, the transparency and flexibility of the intermediate layer are further improved.

In the ethylene / vinyl acetate copolymer, the content of the structural unit derived from vinyl acetate is preferably 15% by mass to 40% by mass with respect to the total mass of the copolymer, and 18% by mass to 35% by mass. More preferably.
When the structural unit derived from vinyl acetate is 15% by mass or more, the transparency and flexibility of the intermediate layer are further improved. On the other hand, when the structural unit derived from vinyl acetate is 40% by mass or less, stickiness is suppressed and workability is good.

  In addition to the structural unit derived from vinyl acetate and the structural unit derived from ethylene, the ethylene / vinyl acetate copolymer may further include a structural unit derived from another monomer, but in one embodiment of the present invention, It is preferable that an ethylene / vinyl acetate copolymer is formed by a structural unit derived from vinyl acetate and a structural unit derived from ethylene without including a structural unit derived from another monomer.

The ethylene / vinyl acetate copolymer may be produced by a conventionally known method, or a commercially available product may be used.
The melt flow rate (JIS K 7210: 1999) at 190 ° C. and 2160 g load of the ethylene / vinyl acetate copolymer is preferably 0.1 g / 10 min to 150 g / 10 min from the viewpoint of workability and mechanical strength. 0.1g / 10min-50g / 10min are more preferable.

  The intermediate layer can contain various additives within a range not impairing the object of the present invention. As this additive, the same thing as what was mentioned above as an additive which can be contained in an outermost layer is mentioned. The preferred range of the additive content in the intermediate layer is the same as the preferred range of the additive content in the outermost layer.

[Solar Cell Sealant Form]
The solar cell encapsulant has at least a three-layer structure including the outermost layer described above and the intermediate layer described above, and the intermediate layer is located between the two outermost layers.
The solar cell encapsulant preferably has a three-layer structure in which the outermost layer includes an ethylene / (meth) acrylic acid copolymer and the intermediate layer includes an ethylene / vinyl acetate copolymer. That is, the structure of the solar cell encapsulant is preferably an ethylene / (meth) acrylic acid copolymer / ethylene / vinyl acetate copolymer / ethylene / (meth) acrylic acid copolymer.
When the solar cell encapsulant has the above three-layer structure, it has excellent PID resistance, as well as excellent shrinkage resistance and storage stability when exposed to high-temperature environments, and can be extruded. Excellent moldability.

The ratio of the thickness of the outermost layer and the intermediate layer of the solar cell encapsulant (outermost layer / intermediate layer) is preferably 1/1 to 1/10, more preferably 1/2 to 1/8, Most preferably, it is 1/2 to 1/5.
When the thickness ratio (outermost layer / intermediate layer) is within the above range, the volume resistivity of the entire solar cell encapsulant can be maintained, and a higher PID resistance can be imparted to the solar cell encapsulant. Can do.

The thickness of the outermost layer is preferably 1 μm to 500 μm, more preferably 10 μm to 500 μm, and still more preferably 20 μm to 300 μm.
The thickness of the outermost layer here means the thickness of each of the two outermost layers (the protective material side layer and the solar cell element side layer). The thickness of the layer on the protective material side and the thickness of the layer on the solar cell element side may be the same or different.
When the thickness of the outermost layer is 1 μm or more, PID resistance and adhesiveness are further improved. Further, when the outermost layer thickness is 500 μm or less, it is excellent in transparency and uneven follow-up property with respect to the transparent protective material.

The thickness of the intermediate layer is preferably 50 μm or more and 1000 μm or less, and more preferably 50 μm or more and 700 μm or less.
The thickness of the intermediate layer here means the total thickness of the intermediate layer having a specific volume resistivity. When the intermediate layer is formed of two layers, the total thickness of the two layers is shown.
If the thickness of the intermediate layer is 100 μm or more, the workability can be further improved. Further, when the thickness of the intermediate layer is 1000 μm or less, the transparency is more excellent.
When the intermediate layer is composed of two or more layers, the thickness of each layer may be the same or different.

The total thickness of the encapsulant for solar cells is not particularly limited, but the total thickness is preferably in the range of 5 μm to 2000 μm (0.005 mm to 2 mm), and 100 μm to 2000 μm (0.1 mm to 2 mm). Is more preferable, and it is still more preferable that it is the range of 100 micrometers-1500 micrometers (0.1 mm-1.5 mm).
When the total thickness is in the range of 5 μm to 2000 μm, it is excellent in economic efficiency (that is, at an appropriate cost as a product), and is excellent in PID resistance, adhesiveness and transparency.

The encapsulant for solar cell preferably has a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less, and 1.0 × 10 ¹⁶ or less. More preferably, it is Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less.
When the volume resistivity of the entire sealing material is in the above range, it is advantageous in terms of insulation.
The volume resistivity of the whole sealing material here means a value obtained by measuring the volume resistivity of the whole laminate laminated in at least three layers.
The volume resistivity can be measured by the above method.

The solar cell encapsulant is bonded with a double vacuum chamber laminating machine in a state where the solar cell encapsulant is sandwiched between two 3.2 mm thick white glass (conditions: 150 ° C., 13 minutes), and then allowed to cool in the atmosphere at 23 ° C. (ie, cooling), the total light transmittance based on JIS K 7361-1: 1997 can be 83% or more.
In other words, since transparency tends to deteriorate when the film is cooled after bonding, it is usual to cool rapidly after bonding, and the total light transmittance after the rapid cooling is evaluated. In one embodiment of the invention, the total light transmittance after cooling is as high as 83% or more, showing very good transparency. The total light transmittance is more preferably 85% or more.
The total light transmittance is a value measured according to JIS K 7136: 2000 using a haze meter (manufactured by Suga Test Instruments Co., Ltd.). The term “cooling (removal)” refers to cooling at a rate of temperature decrease of 15 ° C./min or less (calculated from the temperature 5 minutes after the start of cooling).

[Formation of solar cell encapsulant]
The solar cell sealing material can be molded by a known method using a multilayer T-die molding machine, a calendar molding machine, a multilayer inflation molding machine, or the like.
For example, the molding of a solar cell encapsulant having a three-layer structure in which two outermost layers and an intermediate layer are laminated is performed, for example, on an ethylene / (meth) acrylic acid copolymer for outermost layer formation. If necessary, a dry-blended mixture with additives such as cross-linking agents, cross-linking aids, adhesion-imparting agents, antioxidants, light stabilizers and UV absorbers, and ethylene / vinyl acetate for intermediate layer formation. A multi-layer T-die from a hopper with a mixture obtained by adding a cross-linking agent, a cross-linking aid, an adhesion-imparting agent, an antioxidant, a light stabilizer, an ultraviolet absorber and the like as necessary to the polymer and dry blending. It can supply by supplying to the main extruder and a subextruder of an extruder, and can carry out by carrying out multilayer extrusion molding to a sheet form.

In addition, the molding of the solar cell encapsulant having a three-layer structure is performed by, for example, adding a cross-linking agent and a cross-linking aid to a melt obtained by melting an ethylene / (meth) acrylic acid copolymer for forming the outermost layer. Mixture obtained by melt blending an agent or various additives and a melt obtained by melting an ethylene / vinyl acetate copolymer for forming an intermediate layer and, if necessary, a mixture obtained by melt blending a crosslinking agent, a crosslinking aid or various additives. Can also be supplied to the extruder from the hopper and multilayer extrusion molding into a sheet shape.
As another means, if necessary, additives such as a crosslinking agent, an antioxidant, a light stabilizer, and an ultraviolet absorber are preliminarily used as a master batch to form an ethylene / (meth) acrylic acid heavy polymer for outermost layer formation. It is also possible to add to the melt of the coalescence or the melt of the ethylene / vinyl acetate copolymer for the intermediate layer.
The processing temperature in the molding of the solar cell encapsulant is preferably in the range of 80 ° C. to 230 ° C., and the processing temperature can be selected according to the processability of the components used.

<Solar cell module>
The solar cell module which is one Embodiment of this invention is equipped with the sealing material for solar cells which is one Embodiment of this invention.
For example, a solar cell module can be produced by using a solar cell sealing material according to an embodiment of the present invention and fixing solar cell elements with upper and lower protective materials. Examples of such solar cell modules include various types.
For example, it is formed on the surface of a substrate such as glass or the like having a structure sandwiched between both sides of the solar cell element, such as upper transparent protective material / encapsulant / solar cell element / encapsulant / lower protective material. In the upper transparent protective material, the solar cell element is sandwiched between both sides of the solar cell element, such as upper transparent protective material / encapsulant / solar cell element / encapsulant / lower protective material. Examples thereof include a solar cell element formed on the peripheral surface, for example, a structure in which an encapsulant and a lower protective material are formed on an amorphous solar cell element formed on a fluororesin-based sheet by sputtering or the like.
Since the solar cell module includes the solar cell encapsulant that is one embodiment of the present invention having excellent PID resistance, the encapsulant can maintain high insulation even when operated at a high voltage. The generation of leakage current is suppressed, and the PID resistance is excellent.

  Examples of solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, III-V groups such as gallium-arsenic, copper-indium-selenium, copper-indium-gallium-selenium, cadmium-tellurium, and II. Various solar cell elements such as -VI group compound semiconductor systems can be used. The solar cell encapsulant which is an embodiment of the present invention is particularly useful for encapsulating single crystal and polycrystalline solar cell elements.

  Examples of the upper transparent protective material constituting the solar cell module include glass, acrylic resin, polycarbonate, polyester, and fluorine-containing resin. Moreover, as a lower protective material, a single-piece | unit or multilayer sheet | seat, such as a metal and various thermoplastic resin films, can be illustrated. Specific examples of the lower protective material include metals such as tin, aluminum, and stainless steel, inorganic materials such as glass, polyester, inorganic material-deposited polyester, fluorine-containing resins, and single-layer or multilayer sheets such as polyolefin. The solar cell sealing material which is one embodiment of the present invention exhibits good adhesion to these upper protective material or lower protective material.

  A conventional ethylene / vinyl acetate copolymer is used when laminating and bonding together with the solar cell element, the upper protective material, and the lower protective material, using the solar cell encapsulant according to an embodiment of the present invention. Even if the cross-linking step by pressurization and heating for a long time, which has been performed in the above system, is not performed, it is possible to impart adhesive strength that can withstand practical use and long-term stability of adhesive strength. However, from the viewpoint of imparting stronger adhesive strength and adhesive strength stability, it is recommended to perform pressurizing and heating treatment for a short time.

  Hereinafter, an embodiment of the present invention will be described in more detail by way of examples, but the embodiment of the present invention is not limited thereto.

(1) Resin used for preparation of the sealing material for solar cells is shown below.
・ Ethylene / methacrylic acid copolymer (E-MAA)
Constituent unit content derived from methacrylic acid = 15% by mass
MFR (190 ° C., 2160 g load) = 60 g / 10 minutes Volume resistivity = 2.00 × 10 ¹⁷ Ω · cm
・ Ethylene / vinyl acetate copolymer (EVA1)
Constituent unit content derived from vinyl acetate = 28% by mass
MFR (190 ° C., 2160 g load) = 15 g / 10 minutes Volume resistivity = 6.29 × 10 ¹⁴ Ω · cm
The volume resistivity was measured according to JIS C 2139: 2008.
・ Ethylene / vinyl acetate copolymer (EVA2)
Constituent unit content derived from vinyl acetate = 28% by mass
Volume resistivity = 1.70 × 10 ¹⁴ Ω · cm
The volume resistivity was measured according to JIS C 2139: 2008.

(2) The solar cell encapsulant was produced using the molding machine shown below.
・ Multi-layer T-die molding machine: Tanabe Plastics Machine Co., Ltd. Feed block type: EDI Co., Ltd.
・ Single layer T-die molding machine: Tanabe Plastics Machine Co., Ltd. Extruder is 40mmφ single screw extruder Die width 500mm

[Example 1]
The outer layer 1 and the outer layer were prepared by adding 0.2 parts by mass of a silane coupling agent (trade name: KBM602, manufactured by Shin-Etsu Chemical Co., Ltd.) to 100 parts by mass of the ethylene / methacrylic acid copolymer. Used for 2. Further, with respect to 100 parts by mass of the above EVA1, 1.5 parts by mass of a crosslinking agent (trade name: Lupazole 101, manufactured by Atofina Yoshitomi Co., Ltd.), 0.1 parts by mass of a light-resistant stabilizer (trade names: Tinuvin 770DF, BASF) Manufactured by Co., Ltd.), 0.3 part by weight of an ultraviolet absorber (trade name: Kimasorb 81FL, manufactured by BASF), 0.03 part by weight of an antioxidant (trade name: Irganox 1010, BASF) Product) and 0.5 parts by mass of a silane coupling agent (trade name: KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.) as an intermediate layer, a multilayer sheet (sealant for solar cells) is used. Produced.
The multilayer sheet is produced by using a multilayer T-die molding machine to form the outer layer 1, the outer layer 2 and the intermediate layer at a resin temperature of 100 ° C. and the layer ratio (the thickness of the outer layer 1 / the thickness of the intermediate layer / the thickness of the outer layer 2) = 1. / 4/1, and the total thickness was 450 μm.

[Example 2]
A multilayer sheet (solar cell sealing material) was produced in the same manner as in Example 1 except that the layer ratio in Example 1 was set to 1/7/1.

[Comparative Example 1]
A single layer sheet (sealant for solar cells) having a total thickness of 400 μm was produced with a single layer T-die molding machine using only EVA 1 at a resin temperature of 100 ° C.

<Evaluation of sealing material for solar cell>
About the produced sheet | seat of the Example and the comparative example, the volume resistivity shown below, an optical characteristic, glass adhesiveness, and shrinkage resistance were evaluated. The evaluation results are shown in Table 1.

(1. Volume resistivity)
A sample for volume resistivity measurement in which the total thickness of the sealing material was 3 mm was prepared so that the layer ratio was the same as that of each sheet of the example and the comparative example.
The volume resistivity of the produced sample was measured according to JIS C 2139: 2008.

(2. Optical properties)
The sample for optical property evaluation is a 3.2 mm thick white plate embossed glass (75 mm × 120 mm) and each sheet of the example or the comparative example, and vacuumed by a vacuum heat bonding machine (manufactured by NPC, LM-50 × 50S). The samples were bonded in this order under the conditions of a degree of 75 kPa, 150 ° C., and 13 minutes, and a sample having a configuration of 3.2 mm thick white plate embossed glass / Example or Comparative Example sheet / 3.2 mm thick white plate embossed glass was prepared. The total light transmittance and haze of the sample were measured according to JIS K 7136: 2000 using a haze meter (manufactured by Suga Test Instruments Co., Ltd.), and used as an index for evaluating the optical characteristics of the solar cell sealing material.

(3. Glass adhesion)
3.2 mm thick blue plate tempered glass (75 mm × 120 mm) and each sheet of the examples or comparative examples were vacuum heated at 75 kPa, 150 ° C., using a vacuum heat bonding machine (manufactured by NPC, LM-50 × 50S). Bonding was performed in this order under a condition of 13 minutes, and a sample for evaluating adhesiveness having a structure comprising a sheet of blue sheet tempered glass / example or comparative example was produced.
Using the obtained sample for evaluating adhesiveness, glass adhesiveness was evaluated under the condition of a width of 15 mm and a tensile speed of 100 mm / min.

(4. Shrink resistance)
Each sheet of the example or comparative example cut to a size of 200 mm × 200 mm after applying nicky powder on the entire surface of the blue plate tempered glass having a size of 250 mm × 250 mm × 3.2 mm is placed on a vacuum heating pasting machine (NPC LM-50x50S), and heated at 75 kPa, 75 ° C. for 10 minutes. Subsequently, the sheet | seat of the Example and the comparative example was cooled in air | atmosphere at 23 degreeC.
The external appearance of the sheet | seat of the Example after this heating cooling and a comparative example was observed, and shrinkage resistance was evaluated.
In addition, the sheet having little change in appearance and having no wrinkles or the like after heating and cooling was regarded as having good shrinkage resistance.

  From Table 1, the multilayer sheet (solar cell sealing material) of the examples has the volume resistivity of the outermost layer and the intermediate layer within a predetermined range, and such a solar cell sealing material is used for the solar cell module. If applied to the production, it is expected that a solar cell module excellent in PID resistance will be obtained.

A photograph of the state of the sheet after the shrinkage resistance evaluation is performed on the multilayer sheet of Example 2 (sealant for solar cell) is shown in FIG. 1, and the single-layer sheet of comparative example 1 (sealant for solar cell) FIG. 2 shows photographs of the state of the sheet after the shrinkage resistance evaluation is performed on the sheet.
In Example 2, as shown in FIG. 1, it can be seen that the change in appearance is small and the shrinkage resistance of the solar cell encapsulant is good.
In Comparative Example 1, as shown in FIG. 2, it can be seen that the sheet is wrinkled and the shrinkage resistance is poor.

[Example 3 to Example 5, Comparative Example 2 to Comparative Example 3]
A resin composition in which 0.2 parts by mass of a silane coupling agent (trade name: KBM602, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to 100 parts by mass of the ethylene / methacrylic acid copolymer was used. Further, with respect to 100 parts by mass of the EVA2, 1.5 parts by mass of a crosslinking agent (trade name: Lupazole 101, manufactured by Atofina Yoshitomi Co., Ltd.), 0.1 parts by mass of a light-resistant stabilizer (trade names: Tinuvin 770DF, BASF) Manufactured by Co., Ltd.), 0.3 part by weight of an ultraviolet absorber (trade name: Kimasorb 81FL, manufactured by BASF), 0.03 part by weight of an antioxidant (trade name: Irganox 1010, BASF) Manufactured) and 0.5 parts by mass of a silane coupling agent (trade name: KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.) were used to produce a multilayer sheet or a single layer sheet described in Table 2. . The multilayer sheet was produced by stacking the sheets and heat-pressing them. A sample for PID resistance test was produced by the following method using the obtained sealing material sheet.
On the glass surface of 3.2 mm thickness, the produced sealing material sheet | seat, the solar cell element (p type or n type), the back side sealing material (EVA sheet), and the back sheet | seat were laminated | stacked in order. Next, in a vacuum heating pasting machine (manufactured by NPC), bonding was performed with a vacuum heating time of 3 minutes and a thermocompression bonding time of 45 minutes (75 kPa). Next, an aluminum frame was placed on each test body, and the positive terminal and the negative terminal of the solar cell element (p-type or n-type) in the test sample were connected. The PID resistance test of the obtained test sample was performed by the following method.

<Evaluation of PID resistance>
(Chemitox method)
The PID resistance of each test sample was evaluated by the method shown below. The evaluation results are shown in Table 2 below.
(1) The output of each test sample before the test was measured.
(2) A metal frame was disposed so as to cover the end of each test sample, and the positive terminal and the negative terminal of the solar cell element (p-type or n-type) in the test sample were connected. The test sample was placed in a constant temperature and humidity chamber so that the lower protective material was down, and water was applied to the glass surface.
When the temperature and humidity of the thermostatic layer reaches 60 ° C and humidity of 85%, test the test voltage of 1000Vdc using the metal frame as the anode and the lead wire connecting the positive and negative terminals of the solar cell element as the cathode. The sample was applied for 96 hours.
(3) After 96 hours, the test sample was taken out and the output of the test sample after the test was measured.
(4) From the output before and after the test, the output retention rate was calculated using the following formula, and the PID resistance of the sealing material sheets produced in each of the examples and comparative examples was evaluated.
Output maintenance ratio [%] = output after test / output before test × 100
In the evaluation of the PID resistance, an output maintenance ratio of 95% or more was set as A, and less than 95% was set as B.

[Example 6]
The outer layer 1 and the outer layer were prepared by adding 0.2 parts by mass of a silane coupling agent (trade name: KBM602, manufactured by Shin-Etsu Chemical Co., Ltd.) to 100 parts by mass of the ethylene / methacrylic acid copolymer. Used for 2. Further, with respect to 100 parts by mass of the above EVA1, 1.5 parts by mass of a crosslinking agent (trade name: Lupazole 101, manufactured by Atofina Yoshitomi Co., Ltd.), 0.1 parts by mass of a light-resistant stabilizer (trade names: Tinuvin 770DF, BASF) Manufactured by Co., Ltd.), 0.3 part by weight of an ultraviolet absorber (trade name: Kimasorb 81FL, manufactured by BASF), 0.03 part by weight of an antioxidant (trade name: Irganox 1010, BASF) Product) and 0.5 parts by mass of a silane coupling agent (trade name: KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.) as an intermediate layer, a multilayer sheet (sealant for solar cells) is used. Produced.
The multilayer sheet was produced by stacking the sheets and heat-pressing them. The following long-term storage stability was evaluated with respect to the produced multilayer sheet. The evaluation results are shown in Table 3.

[Comparative Example 4]
With respect to 100 parts by mass of the EVA1, 1.5 parts by mass of a crosslinking agent (trade name: Lupazole 101, manufactured by Atofina Yoshitomi Co., Ltd.), 0.1 parts by mass of a light-resistant stabilizer (trade names: Tinuvin 770DF, BASF ( Co., Ltd.), 0.3 part by weight of an ultraviolet absorber (trade name: Kimasorb 81FL, manufactured by BASF Corp.), 0.03 part by weight of an antioxidant (trade name: Irganox 1010, manufactured by BASF Corp.) ) And 0.5 parts by mass of a silane coupling agent (trade name: KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.) were used to prepare a sheet. The following long-term storage stability was evaluated with respect to the produced single layer sheet. The evaluation results are shown in Table 3.

(Long-term storage)
The sheets of Example 6 and Comparative Example 4 were exposed to a room fluorescent lamp for 3 months (light irradiation), and the rate of change in gel fraction was measured.

-Gel fraction measurement method-
The sheets of Example 6 and Comparative Example 4 before and after the light irradiation were each heated in an oven at 150 ° C. for 30 minutes to produce a crosslinked sheet. The crosslinked sheet was cut to a size of 1 g, and 1 g of the cut sheet was immersed in 100 ml of xylene and heated at 110 ° C. for 24 hours. Thereafter, the insoluble content (gel content) was collected by filtration through a wire mesh, and the ratio (gel fraction [mass%]) of the gel content to the sheet mass was determined by weighing after drying. The higher the gel fraction, the higher the degree of crosslinking. The long-term storage stability of the sheet was evaluated according to the following criteria from the gel fraction retention before and after the light irradiation.
Gel fraction retention = gel fraction after 3 months / initial gel fraction × 100

-Evaluation criteria-
A: The gel fraction retention is 90% by mass or more.
B: The gel fraction retention is 50% by mass or more and less than 90% by mass.
C: The gel fraction retention is less than 50% by mass.

  From Table 3, it can be seen that the storage stability is better when the outermost layer has the E-MAA layer as compared with the EVA single layer. This is presumed to be because the outermost layer can suppress the cross-linking agent contained in the EVA1 layer from volatilizing, degrading, and the like.

The disclosure of Japanese Patent Application No. 2014-190239 filed on September 18, 2014 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

Claims (6)

Two outermost layers having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm to 1.0 × 10 ¹⁸ Ω · cm,
An intermediate layer having a volume resistivity of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm disposed between the two outermost layers;
A solar cell encapsulant comprising at least three layers including   The solar cell encapsulant according to claim 1, wherein the outermost layer includes an ethylene / (meth) acrylic acid copolymer, and the intermediate layer includes an ethylene / vinyl acetate copolymer.   The sealing material for solar cells according to claim 1 or 2, wherein three layers of the two outermost layers and the intermediate layer are laminated. The volume resistivity of the whole encapsulant is 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less. 4. The solar cell according to claim 1. Sealing material.   The solar cell encapsulant according to any one of claims 1 to 4, wherein a ratio of the thickness of one of the outermost layers of the two layers to the intermediate layer is 1/2 to 1/8.   The solar cell module provided with the sealing material for solar cells of any one of Claims 1-5.