JP6542782B2 - Sealing material for solar cell and solar cell module - Google Patents

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 by the solar cell sealing material.

In recent years, the system voltage of the solar cell module has been increased to a high system voltage, and in Japan, the detached house is moving to a high system voltage of 600V for voltage and 1000V for industrial and mega solar for power generation applications. . Furthermore, there is also a prospect that the voltage can be raised to 1500 V in the future.
Among them, due to the insulation failure of the solar cell module, the problem of failure due to leakage current, in particular, the output reduction phenomenon due to the deterioration of the solar cell element called PID (Potential Induced Degradation) is becoming apparent.
The PID is caused by the occurrence of a leakage current due to the occurrence of a potential difference between the aluminum frame of the solar cell module and the solar cell element, and the reduction of the insulation between the aluminum frame and the solar cell element. Due to the occurrence of the leakage current, sodium (Na) ions contained in the glass of the protective member and the like move to the surface of the solar cell element and accumulate in the antireflective film of the solar cell element, and electrochemical corrosion progresses It is said that the solar cell element is degraded by losing the semiconductor property of the solar cell element.

  Heretofore, as a sealing material for a solar cell, one having an ethylene / vinyl acetate copolymer (EVA) as a main component has often been used. For example, in JP 2009-298046 A, as a multilayer sheet having improved breaking 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 consisting of a layer consisting mainly of the ionomer and an outer layer consisting of a layer consisting mainly of an ethylene-vinyl acetate copolymer formed on both sides thereof. It is done.

Moreover, in Unexamined-Japanese-Patent No. 2014-27034, it consists of a crosslinking cured film of the composition containing an ethylene-polar monomer copolymer and a crosslinking agent as a solar cell sealing material film | membrane which can suppress generation | occurrence | production of PID, A sealing film for a solar cell having a volume resistivity of 5.0 × 10 ¹³ or more at 25 ° C. is disclosed.

  However, in all of the three-layer sheet described in JP2009-298046A and the sealing material for a solar cell described in JP2014-27034A, the main component of the layer forming the outermost layer is EVA, Since the volume resistivity is low, the occurrence of PID may not be sufficiently suppressed.

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

Specific means for achieving the above object include the following aspects.
<1> Volume resistivity disposed between the outermost layer of two layers having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less and the outermost layer of the two layers The sealing material for solar cells in which the middle layer which is 1.0 * 10 < ¹¹ > ohm * cm or more and less than 1.0 * 10 < ¹⁵ > ohm * cm, and at least 3 layers were laminated | stacked.

<2> The solar cell sealing material according to <1>, wherein the outermost layer contains an ethylene / (meth) acrylic acid based copolymer, and the intermediate layer contains an ethylene / vinyl acetate copolymer.
The sealing material for solar cells as described in <1> or <2> on which three layers, the outermost layer of <3> said 2 layers, and the said intermediate layer were laminated | stacked.
The volume resistivity of the whole <4> sealing material is described in any one of <1> to <3> which is 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less Sealant for solar cells.
The sealing for solar cells as described in any one of <1>-<4> whose ratio of the thickness of one side of the outermost layer of the said 2 layers with respect to the <5> said intermediate layer is 1/2-1/8. Material.

The solar cell module provided with the sealing material for solar cells as described in any one of <6> <1>-<5>.

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

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

<Sealing material for solar cells>
The sealing material for a solar cell according to an embodiment of the present invention has two volume outermost layers having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less. At least three layers including a middle 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 outermost layers of two layers are stacked and formed. Be done.
In the sealing material for a solar cell according to an embodiment of the present invention, 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 preferable.

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

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

If the volume resistivity of the outermost layer is less than 1.0 × 10 ¹⁵ Ω · cm, the insulating property of the sealing material is inferior, and the leakage current at the time of high voltage operation can not be suppressed. Further, when the volume resistivity of the outermost layer is 1.0 × 10 ¹⁸ Ω · cm or less, it becomes easy to obtain the material for forming the outermost layer.
From the above viewpoint, 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.
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 materials having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less. 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 of another range as a material for forming the outermost layer You may use the material which has these.
The materials of the outermost layers of the two layers present in the encapsulant for a solar cell 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" as used herein 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. Further, from the above viewpoint, the outermost layer preferably contains 80% by mass or more, preferably 90% by mass or more, of the ethylene / (meth) acrylic acid based copolymer with respect to the total mass of the outermost layer. Is more preferable.
It is preferable that an ethylene / (meth) acrylic acid type copolymer is contained in the outermost layer within the above range, since good transparency and good PID resistance can be obtained.

(Ethylene / (meth) acrylic acid copolymer)
It is preferable that content of the structural unit derived from ethylene is 75 mass%-95 mass% with respect to the total mass of a copolymer, and ethylene-(meth) acrylic acid type copolymer is 75 mass%- It is more preferable that it is 92 mass%.
The heat resistance of a copolymer, mechanical strength, etc. improve more because content of the structural unit derived from ethylene is 75 mass% or more. On the other hand, when the content of structural units derived from ethylene is 95% by mass or less, the transparency, the flexibility, and the adhesiveness of the copolymer are further improved.

In the ethylene (meth) acrylic acid-based copolymer, the content of the constituent unit derived from (meth) acrylic acid is preferably 5% by mass to 25% by mass with respect to the total mass of the copolymer, and 8 It is more preferable that it is mass%-25 mass%.
The structural unit derived from (meth) acrylic acid in the above-mentioned copolymer plays an important role in adhesion to a substrate such as glass, etc. When the content is 5% by mass or more, it is transparent or flexible. When the content is 25% by mass or less, the stickiness is suppressed and the processability is good.
When the silane coupling agent to be 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 the copolymer from the viewpoint of processability. 8 mass% or more and 18 mass% or less is preferable with respect to the total mass. The content of the structural unit derived from (meth) acrylic acid is most preferably 13% by mass to 18% by mass with respect to the total mass of the copolymer from the viewpoint of processability and optical properties.

  The ethylene / (meth) acrylic acid-based copolymer includes a constituent unit derived from another copolymerizable monomer in addition to a constituent unit derived from ethylene and a constituent unit derived from (meth) acrylic acid. It may be The content of the constituent unit derived from the other copolymerizable monomer is more than 0% by mass with respect to the total 100% by mass of the constituent unit derived from ethylene and the constituent unit derived from (meth) acrylic acid. % Or less is preferable, and more than 0% by mass and 25% by mass or less are more preferable.

  Other copolymerizable monomers include, for example, 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. When an unsaturated ester is contained in the said range as another copolymerizable monomer, since the softness | flexibility of an ethylene (meth) acrylic acid type copolymer improves, it is preferable.

  The ethylene / (meth) acrylic acid type copolymer can be obtained by radical copolymerization of the respective polymerization components under high temperature and high pressure.

  The melt flow rate (MFR) (JIS K 7210: 1999) of an ethylene / (meth) acrylic acid copolymer at 190 ° C. under a load of 2160 g is 0.1 g / 10 min to from the viewpoint of processability and mechanical strength. 150 g / 10 min is preferable, and in particular, 30 g / 10 min to 100 g / 10 min is more preferable.

  In the outermost layer, various additives can be contained as long as the object of the present invention is not impaired. Such additives include, for example, crosslinking agents, crosslinking aids, silane coupling agents, UV absorbers, light stabilizers and antioxidants.

The crosslinking agent is preferably an organic peroxide having a decomposition temperature of usually 90 ° C. to 180 ° C., and more preferably 100 ° C. to 150 ° C. As such an organic peroxide, for example, t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl carbonate, t-butylperoxyacetate, t-butylperoxybenzoate, 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 assistant 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 (meth) ene such as ethylene glycol diacrylate, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate Acryloxy compounds; divinylbenzene and the like.

  5 mass parts or less are preferable with respect to 100 mass parts of ethylene (meth) acrylic acid type copolymers, and, as for content of the crosslinking adjuvant in outermost layer, 0.1 mass part-3 mass parts are more preferable.

The silane coupling agent includes a silane coupling agent having a vinyl group, an amino group or an epoxy group, and a hydrolyzable 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 Diethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane and the like can be mentioned.

  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, based on 100 parts by mass of the total mass of the outermost layer. When the silane coupling agent is contained in the outermost layer in the above range, the adhesion between the solar cell sealing material and the transparent protective material or the solar cell element or the like is improved.

  Examples of UV absorbers include 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2-carboxybenzophenone and 2-hydroxy-4-n- Benzophenone-based UV absorbers such as octoxybenzophenone; 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) benzotriazole, 2- (2'-hydroxy-5-methylphenyl) benzotriazole and Benzotriazole-based ultraviolet absorbers such as 2- (2′-hydroxy-5-t-octylphenyl) benzotriazole; salicylic acid ester-based ultraviolet absorbers such as phenyl salicylate and p-octylphenyl salicylate.

Examples of light stabilizers 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-n-octyl-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-tricarboxylate 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; Tetrakis (2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate and the like can be mentioned.

Examples of the antioxidant include various hindered phenol-based antioxidants and phosphite-based antioxidants.
Specific examples of hindered phenolic antioxidants include 2,6-di-t-butyl-p-cresol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2 , 6-di-tert-butyl-4-ethylphenol, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 4,4'-Methylenebis (2,6-di-t-butylphenol), 2,2'-methylenebis [6- (1-methylcyclohexyl) -p-cresol], bis [3,3-bis (4-hydroxy) -3-tert-Butylphenyl) butyric acid] glycol ester, 4,4′-butylidene bis (6-t-butyl-m-cresol), 2,2′-ethylidene bis (4-sec -Butyl-6-t-butylphenol), 2,2'-ethylidenebis (4,6-di-t-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-t-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-t-butyl-m-cresol), tocopherol, 3,9-bis [1,1-dimethyl-2- [β- (3-t-butyl-4-hydroxy-5) -Methylphenyl) propionyloxy] ethyl] 2,4,8,10-tetraoxaspiro [5,5] undecane, 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzylthio) And the like.
Specific examples of phosphite antioxidants include 3,5-di-t-butyl-4-hydroxybenzyl phosphonate dimethyl ester, bis (3,5-di-t-butyl-4-hydroxybenzyl phosphonic acid) Ethyl, tris (2,4-di-t-butylphenyl) phosphate and the like can be mentioned.

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

When using the said sealing material on the opposite side to the light-receiving surface side, in addition to the additive mentioned above as needed, it is made to contain additives, such as a coloring agent, a light diffusing agent, a flame retardant, and a metal deactivator. Can.
As a coloring agent, a pigment (inorganic pigment, organic pigment), dye, etc. are mentioned. These colorants can be appropriately selected from various known ones.

  As the inorganic pigment, for example, white inorganic pigments such as titanium oxide, zinc white, lead white, lithopone, barite, precipitated barium sulfate, calcium carbonate, gypsum, precipitated silica, carbon black, lamp black, titanium black, synthesis Black inorganic pigments such as iron black, gray inorganic pigments such as zinc powder, lead oxide, slate powder, cadmium red, cadmium mercury red, silver glaze, red iron oxide, red inorganic pigments such as molybutene red, red lead, amber, iron oxide tea Brown inorganic pigments such as cadmium yellow, zinc yellow, oca, siena, synthetic inorganic pigments such as yellow inorganic pigments such as yellow lead, titanium yellow, green inorganic pigments such as chromium oxide green, cobalt green, chromium green etc, ultramarine blue, bitumen, iron Blue inorganic pigments such as blue and cobalt blue, and metal powder inorganic pigments can be mentioned.

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 yellow.・ Carmine 6 B, Brilliant Scarlet G, Brilliant Bordeaux 10 B, Bordeaux 5 B, Permanent Red F 5 R, Permanent Carmin FB, Resol Red R, Resol Red B, Lake Red C, Lake 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, and naphthol yellow S etc. Pigment, basic dye based lake such as Rhodamine B lake, Rhodamine 6G lake, Mordant dye based lake such as Alizarin lake, Constructed dye based pigment such as Indanthrene Blue, Phthalocyanine blue, Phthalocyanine green, Fast Examples thereof include phthalocyanine pigments such as sky blue, and dioxazine-based pigments such as dioxazine violet.
Examples of the pigment include organic fluorescent pigments and pearl pigments in addition to the above-mentioned inorganic pigments and organic pigments.

  In the case of using a sealing material for a solar cell containing these additives as a sealing material on the light receiving side of the solar cell element, the transparency may be impaired, but the sealing on the opposite side to the light receiving side of the solar cell element When used as a material, it is suitably used.

  As a light diffusing agent, glass beads, silica beads, silicon alkoxide beads, hollow glass beads, etc. may be mentioned as inorganic spherical substances. Examples of organic spherical substances include plastic beads such as acrylic beads and vinylbenzene beads.

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

  As a metal deactivator, what is known as a compound which suppresses the metal damage of a thermoplastic resin is mentioned. Two or more metal deactivators may be used in combination. Preferred examples of metal deactivators include hydrazide derivatives or triazole derivatives. Specifically, as the hydrazide derivative, for example, decamethylenedicarboxyl-disalicyloylhydrazide, 2 ', 3-bis [3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionyl] propy Onohydrazide and bis (2-phenoxypropionyl-hydrazide) isophthalic acid can be mentioned. Examples of the triazole derivative include 3- (N-salicyloyl) amino-1,2,4-triazole. As metal deactivators, in addition to hydrazide derivatives and triazole derivatives, 2,2′-dihydroxy-3,3′-di- (α-methylcyclohexyl) -5,5′-dimethyl diphenylmethane, tris- (2 And -methyl-4-hydroxy-5-tert-butylphenyl) butane, a mixture of 2-mercaptobenzimidazole and a phenol condensate, and the like.

[Intermediate]
The encapsulant for a solar cell 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 outermost layers of the two layers, the encapsulant for a solar cell may include 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 materials having a volume resistivity of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm, and the volume resistivity is 1.0 It is also possible to use a general-purpose low-PID-resistant material of 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 of another range as a material for forming the intermediate layer You may use the material which has these.
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" as used herein 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. Further, from the above viewpoint, the intermediate layer preferably contains 80% by mass or more, more preferably 90% by mass or more of the ethylene / vinyl acetate copolymer.
Within the above range, when the interlayer contains an ethylene-vinyl acetate copolymer, good transparency, flexibility, impact resistance and puncture resistance can be obtained.

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

It is preferable that content of the structural unit derived from ethylene is 60 mass%-85 mass% with respect to the total mass of a copolymer, and ethylene ethylene-vinyl acetate copolymer is 65 mass%-82 mass%. It is more preferable that
When the content of the structural unit derived from ethylene is 60% by mass or more, the impact resistance and the 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 constituent unit derived from vinyl acetate is preferably 15% by mass to 40% by mass, and preferably 18% by mass to 35% by mass, with respect to the total mass of the copolymer It is more preferable that
When the constituent unit derived from vinyl acetate is 15% by mass or more, the transparency and the flexibility of the intermediate layer are further improved. On the other hand, tackiness is suppressed as the structural unit derived from vinyl acetate is 40 mass% or less, and processability is good.

  The ethylene-vinyl acetate copolymer may further include a structural unit derived from another monomer in addition to the structural unit derived from vinyl acetate and the structural unit derived from ethylene, but in one embodiment of the present invention It is preferable that the ethylene-vinyl acetate copolymer is formed by the structural unit derived from vinyl acetate and the structural unit derived from ethylene without containing 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 ethylene / vinyl acetate copolymer is preferably 0.1 g / 10 min to 150 g / 10 min from the viewpoint of processability and mechanical strength, 0.1 g / 10 minutes to 50 g / 10 minutes are more preferable.

  The intermediate layer may contain various additives as long as the object of the present invention is not impaired. As such an additive, the same as those described above as the additive which can be contained in the outermost layer can be mentioned. Moreover, the preferable range of the content of the additive in the intermediate layer is the same as the preferable range of the content of the additive in the outermost layer.

[Form of sealing material for solar cell]
The encapsulant for solar cells 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 outermost layers of the two layers.
The sealing material for a solar cell preferably has a three-layer structure in which the outermost layer contains an ethylene / (meth) acrylic acid copolymer and the intermediate layer contains an ethylene / vinyl acetate copolymer. That is, as a structure of a solar cell sealing material, the structure of an ethylene (meth) acrylic acid type copolymer / ethylene vinyl acetate copolymer / ethylene (meth) acrylic acid type copolymer is preferable.
When the sealing material for solar cells has the above-described three-layer structure, in addition to excellent PID resistance, it is excellent in shrinkage resistance and storage stability when exposed to a high temperature environment, and extrusion molding is possible Excellent in moldability.

The ratio of the thickness of the outermost layer to the thickness of the intermediate layer (outer layer / intermediate layer) of the solar cell sealing material 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 (the outermost layer / intermediate layer) is in the above range, the volume resistivity of the entire solar cell sealing material can be maintained, and the solar cell sealing material imparts high PID resistance. Can.

1 micrometer-500 micrometers are preferable, as for the thickness of outermost layer, 10 micrometers-500 micrometers are more preferable, and 20 micrometers-300 micrometers are still more preferable.
The thickness of the outermost layer referred to herein means the thickness of each of the two outermost layers (the layer on the protective material side and the layer on the solar cell element side). 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, the PID resistance and the adhesiveness are further improved. In addition, when the thickness of the outermost layer is 500 μm or less, it is excellent due to the transparency and the unevenness followability to the transparent protective material.

50 micrometers or more and 1000 micrometers or less are preferable, and, as for the thickness of an intermediate | middle layer, 50 micrometers or more and 700 micrometers or less are more preferable.
The thickness of the intermediate layer referred to herein means the total thickness of the intermediate layer having a specific volume resistivity, and when the intermediate layer is formed of two layers, it indicates the total thickness of the two layers.
When the thickness of the intermediate layer is 100 μm or more, the processability can be further improved. Moreover, it is excellent by transparency in the thickness of an intermediate | middle layer being 1000 micrometers or less.
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 solar cell sealing material 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 preferably in the range of 100 μm to 1500 μm (0.1 mm to 1.5 mm).
When the total thickness is in the range of 5 μm to 2000 μm, the economy is excellent (that is, while the cost is appropriate as a product), and excellent in PID resistance, adhesion and transparency.

It is preferable that the volume resistivity of the whole sealing material is 1.0 * 10 < ¹⁵ > ohm * cm or more and 1.0 * 10 < ¹⁸ > ohm * cm or less, and the sealing material for solar cells is 1.0 * 10 < ¹⁶ >. More preferably, Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less.
It is advantageous at the point of insulation that the volume resistivity of the whole sealing material is the said range.
The volume resistivity of the whole sealing material here means the value which measured the volume resistivity of the whole laminated body laminated | stacked on at least 3 layers.
The volume resistivity can be measured by the above method.

The sealing material for solar cells is bonded by a double vacuum tank bonding machine in a state in which the sealing material for solar cells is sandwiched between two 3.2 mm thick white sheet glass (condition: 150 ° C., The total light transmittance can be 83% or more in accordance with JIS K 7361-1: 1997 when it is allowed to cool (that is, slow cooling) in the atmosphere at 23 ° C. for 13 minutes) and thereafter.
That is, in general, transparency tends to deteriorate when it is cooled after being bonded, so it is customary to rapidly cool after bonding, which is evaluated by the total light transmittance after the rapid cooling. In one embodiment of the invention, the total light transmittance after cooling is extremely good, 83% or more. 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.). In addition, leaving-to-stand (cooling) means cooling at a temperature-fall rate of 15 ° C./min or less (calculated from the temperature 5 minutes after the start of the cooling).

[Molding of encapsulant for solar cells]
The molding of the sealing material for solar cells can be performed 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, molding of a sealing material for a solar cell having a three-layer structure in which two outermost layers and an intermediate layer are laminated is, for example, ethylene / (meth) acrylic acid based copolymer for forming the outermost layer. A mixture dry-blended with additives such as a crosslinking agent, a crosslinking assistant, an adhesion promoter, an antioxidant, a light stabilizer, and a UV absorber as required, and an ethylene / vinyl acetate co-polymer for forming an intermediate layer A mixture obtained by adding an additive such as a crosslinking agent, a crosslinking aid, an adhesion-imparting agent, an antioxidant, a light stabilizer, and an ultraviolet light absorber to a polymer, as required, and dry-blended; It can be carried out by feeding to a main extruder and a secondary extruder of an extruder and performing multilayer extrusion on a sheet.

In addition, the molding of the three-layer sealing material for a solar cell may be carried out, for example, using a melt obtained by melting an ethylene / (meth) acrylic acid copolymer for forming the outermost layer, as needed, a crosslinking agent, or crosslinking aid A mixture obtained by melt-blending a mixture of an additive or various additives with a melt obtained by melting an ethylene / vinyl acetate copolymer for forming an intermediate layer, as required, with a crosslinking agent, a cross-linking aid, or various additives And may be supplied from the hopper to the extruder, and multilayer extrusion may be performed in the form of a sheet.
Furthermore, as another means, if necessary, additives such as a crosslinking agent, an antioxidant, a light stabilizer, an ultraviolet light absorber and the like are used as a master batch in advance, and an ethylene (meth) acrylic acid based heavy weight for forming the outermost layer is formed. It is also possible to add to the melt of the coalescence or the melt of the ethylene-vinyl acetate copolymer for the interlayer.
It is preferable that the processing temperature in shaping | molding of the sealing material for solar cells is the range of 80 degreeC-230 degreeC, and processing temperature can be selected according to the processability of the component to be 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 manufactured by fixing a solar cell element by upper and lower protective materials using the sealing material for solar cells which is one embodiment of the present invention. As such a solar cell module, various types can be exemplified.
For example, it is formed on the surface of a substrate such as an upper transparent protective material / sealing material / solar cell element / sealing material / lower protective material, which is sandwiched by the sealing material from both sides of the solar cell element Of the upper transparent protective material, such as an upper transparent protective material / encapsulant / solar cell element / encapsulant / lower protective material, in which the solar battery element is sandwiched by the encapsulant from both sides, A solar cell element formed on the peripheral surface, for example, one having an amorphous solar cell element prepared by sputtering or the like on a fluorocarbon resin-based sheet, is formed to have a sealing material and a lower protective material formed thereon.
Since the solar cell module includes the sealing material for a solar cell according to an embodiment of the present invention, which is excellent in PID resistance, the sealing material can maintain high insulation even when operated at high voltage. And the occurrence of leakage current is suppressed and the PID resistance is excellent.

  As a solar cell element, silicon-based materials such as single crystal silicon, polycrystalline silicon and amorphous silicon, gallium-arsenic, copper-indium-selenium, copper-indium-gallium-selenium and cadmium-tellurium group III-V or II Various solar cell elements such as a group VI compound semiconductor can be used. The sealing material for solar cells which is one embodiment of the present invention is particularly useful for sealing single crystal and polycrystalline solar cell elements.

  As an upper transparent protective material which comprises a solar cell module, glass, an acrylic resin, a polycarbonate, polyester, a fluorine-containing resin etc. can be illustrated. Moreover, as a lower protective material, single sheets or multilayer sheets, such as metal and various thermoplastic resin films, can be illustrated. Specific examples of the lower protective material include tin, aluminum, metals such as stainless steel, inorganic materials such as glass, polyester, inorganic vapor deposited polyester, fluorine-containing resin, and single layer or multilayer sheets such as polyolefin. The sealing material for solar cells which is one embodiment of the present invention shows good adhesiveness to these upper protection material or lower protection material.

  When laminating and bonding the solar cell element, the upper protective material, and the lower protective material as described above using the sealing material for a solar cell according to an embodiment of the present invention, the conventional ethylene / vinyl acetate copolymer Even if it is not subjected to the crosslinking step by long-term pressure heating which has been carried out in the above-mentioned systems, it is possible to impart practically acceptable adhesive strength and long-term stability of the adhesive strength. However, from the viewpoint of imparting stronger adhesive strength and adhesive strength stability, it is recommended to perform a pressure heating process for a short time.

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

(1) The 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 min Volume resistivity = 2.00 × 10 ¹⁷ Ω · cm
・ Ethylene-vinyl acetate copolymer (EVA1)
Structural unit content derived from vinyl acetate = 28% by mass
MFR (190 ° C., 2160 g load) = 15 g / 10 min Volume resistivity = 6.29 × 10 ¹⁴ Ω · cm
The volume resistivity was measured according to JIS C 2139: 2008.
・ Ethylene-vinyl acetate copolymer (EVA2)
Structural 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) Preparation of the sealing material for solar cells was performed using the molding machine shown below.
Multi-layer T-die molding machine: Tanabe Plastics Co., Ltd. Feed block type: manufactured by EDI Co., Ltd. Extruder is 40 mm in diameter Single screw extruder Die width 500 mm
・ Single-layer T-die molding machine: Tanabe Plastics Co., Ltd. product extruder is 40 mm diameter single screw extruder die width 500 mm

Example 1
The outer layer 1 and the outer layer are a resin composition obtained by adding 0.2 parts by mass of a silane coupling agent (trade name: KBM 602, manufactured by Shin-Etsu Chemical Co., Ltd.) to 100 parts by mass of the ethylene / methacrylic acid copolymer Used in 2. In addition, 1.5 parts by mass of a crosslinking agent (trade name: Lupasol 101, manufactured by Atofina Yoshitomi Co., Ltd.) and 0.1 parts by mass of a light stabilizer (trade name: tinuvin 770DF, BASF) relative to 100 parts by mass of the EVA1. Ltd., 0.3 parts by mass of a UV absorber (trade name: Chimasorb 81 FL, manufactured by BASF Corp.), 0.03 parts by mass of an antioxidant (trade name: Irganox 1010, BASF Corp.) Product) and a resin composition containing 0.5 parts by mass of a silane coupling agent (trade name: KBM 503, Shin-Etsu Chemical Co., Ltd.) as an intermediate layer to form a multilayer sheet (sealing material for solar cells) Made.
In the preparation of the multilayer sheet, the layer ratio (thickness of outer layer 1 / thickness of intermediate layer / thickness of outer layer 2) = 1 at a resin temperature of 100 ° C. using a multilayer T-die molding machine for the outer layer 1 and the outer layer 2 and the intermediate layer It carried out by shape | molding to become / 4/1 and 450 micrometers in total thickness.

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

Comparative Example 1
A single layer sheet (sealing material for solar cells) having a total thickness of 400 μm was produced using a single layer T-die molding machine at a resin temperature of 100 ° C. using only EVA1.

<Evaluation of encapsulant for solar cells>
The volume resistivity, the optical properties, the glass adhesion, and the shrinkage resistance shown below were evaluated for the sheets of the produced examples and comparative examples. The evaluation results are shown in Table 1.

(1. Volume resistivity)
A sample for volume resistivity measurement was produced in which the total thickness of the sealing material was 3 mm so as to have the same layer ratio 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 characteristics)
The sample for optical property evaluation is a vacuum heating pasting device (NPC corporation make, LM-50x50S) of a 3.2 mm thick white board embossed glass (75 mm x 120 mm) and each sheet of an example or a comparative example. The samples were bonded in this order under the conditions of 75 kPa, 150 ° C., 13 minutes, and a sample having a configuration of 3.2 mm thick white plate embossed glass / sheet of Example or Comparative Example / 3.2 mm thick white plate embossed glass was prepared. The total light transmittance and the haze of the sample were measured with a haze meter (manufactured by Suga Test Instruments Co., Ltd.) according to JIS K 7136: 2000, and used as an index for evaluating the optical characteristics of the sealing material for solar cells.

(3. Glass adhesion)
A degree of vacuum of 75 kPa, 150 ° C., using a vacuum heating bonding device (manufactured by NPC, LM-50 × 50 S), with a 3.2 mm thick blue sheet tempered glass (75 mm × 120 mm) and each sheet of Example or Comparative Example. It bonded together in this order on the conditions for 13 minutes, and produced the sample for adhesive evaluation of the structure which consists of a sheet | seat of blue sheet tempered glass / an Example, or a comparative example.
Using the obtained sample for evaluation of adhesion, the evaluation of glass adhesion was carried out under the conditions 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 into a size of 200 mm × 200 mm is placed on the entire surface of blue plate tempered glass of size 250 mm × 250 mm × 3.2 mm thickness, and vacuum heat bonding device (NPC) A vacuum degree of 75 kPa and heating at 75 ° C. for 10 minutes were carried out using LM-50 × 50S. Next, the sheets of the example and the comparative example were cooled at 23 ° C. in the atmosphere.
The appearance of the sheet of the example and the comparative example after the heating and cooling was observed to evaluate the shrinkage resistance.
In addition, the sheet | seat which did not have the change of an external appearance in the sheet | seat after heating-cooling, and wrinkles etc. did not generate | occur | produce shrinkage resistance good.

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

FIG. 1 is a photograph of the state of the sheet after the evaluation of shrinkage resistance was performed on the multilayer sheet (the sealing material for a solar cell) of Example 2, and a single layer sheet of the comparative example 1 (a sealing material for a solar cell) A photograph of the state of the sheet after the evaluation of shrinkage resistance was carried out is shown in FIG.
In Example 2, as shown in FIG. 1, it turns out that there are few changes of an external appearance and the shrinkage resistance of the sealing material for solar cells is favorable.
In Comparative Example 1, as shown in FIG. 2, it can be seen that wrinkles occur in the sheet and the shrinkage resistance is poor.

[Examples 3 to 5 and Comparative Examples 2 to 3]
A resin composition was used in which 0.2 parts by mass of a silane coupling agent (trade name: KBM 602, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to 100 parts by mass of the ethylene / methacrylic acid copolymer. In addition, 1.5 parts by mass of a crosslinking agent (trade name: Lupasol 101, manufactured by Atofina Yoshitomi Co., Ltd.) and 0.1 parts by mass of a light stabilizer (trade name: tinuvin 770DF, BASF) relative to 100 parts by mass of the above EVA 2 Ltd., 0.3 parts by mass of a UV absorber (trade name: Chimasorb 81 FL, manufactured by BASF Corp.), 0.03 parts by mass of an antioxidant (trade name: Irganox 1010, BASF Corp.) The multilayer sheet or single layer sheet described in Table 2 was produced using a resin composition containing a mixture of 0.5 parts by mass and 0.5 parts by mass of silane coupling agent (trade name: KBM 503, Shin-Etsu Chemical Co., Ltd.). . The multi-layered sheets were produced by overlapping each sheet and heating and pressing. The sample for a PID tolerance test was produced with the following method using the obtained sealing material sheet.
The sealing material sheet, the solar cell element (p-type or n-type), the back side sealing material (EVA sheet), and the back sheet were laminated in this order on a 3.2 mm thick glass surface. Next, in the vacuum heating bonding apparatus (made by NPC), it bonded together in 45 minutes (75 kPa) of heating pressure bonding time for 3 minutes for vacuum heating time. 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 described below. The evaluation results are shown in Table 2 below.
(1) The output before the test of each test sample was measured.
(2) A metal frame was arranged 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 with the lower protective material at the bottom, and water was applied to the glass surface.
When the constant temperature and humidity layer becomes a condition of temperature 60 ° C and humidity 85%, test the test voltage of 1000Vdc with the metal frame as the anode and the wire connecting the plus terminal and the minus terminal 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 outputs before and after the test, the output retention ratio was calculated using the following formula, and the PID resistance of the sealing material sheet produced in each example and comparative example was evaluated.
Output maintenance ratio [%] = Output after test / Output before test x 100
In the evaluation of the PID resistance, the output maintenance rate is 95% or more as A, and less than 95% as B.

[Example 6]
The outer layer 1 and the outer layer are a resin composition obtained by adding 0.2 parts by mass of a silane coupling agent (trade name: KBM 602, manufactured by Shin-Etsu Chemical Co., Ltd.) to 100 parts by mass of the ethylene / methacrylic acid copolymer Used in 2. In addition, 1.5 parts by mass of a crosslinking agent (trade name: Lupasol 101, manufactured by Atofina Yoshitomi Co., Ltd.) and 0.1 parts by mass of a light stabilizer (trade name: tinuvin 770DF, BASF) relative to 100 parts by mass of the EVA1. Ltd., 0.3 parts by mass of a UV absorber (trade name: Chimasorb 81 FL, manufactured by BASF Corp.), 0.03 parts by mass of an antioxidant (trade name: Irganox 1010, BASF Corp.) Product) and a resin composition containing 0.5 parts by mass of a silane coupling agent (trade name: KBM 503, Shin-Etsu Chemical Co., Ltd.) as an intermediate layer to form a multilayer sheet (sealing material for solar cells) Made.
The multi-layered sheets were produced by overlapping each sheet and heating and pressing. 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
1.5 parts by mass of a crosslinking agent (trade name: Lupazol 101, manufactured by Atofina Yoshitomi Co., Ltd.) and 0.1 parts by mass of a light stabilizer (trade name: Tinuvin 770DF, BASF (based on 100 parts by mass of EVA1) Ltd.), 0.3 parts by mass of a UV absorber (trade name: Chimasorb 81 FL, made by BASF Corp.), 0.03 parts by mass of an antioxidant (trade name: Irganox 1010, made by BASF Corp.) ) And 0.5 parts by mass of a silane coupling agent (trade name: KBM 503, 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 shelf life)
The sheets of Example 6 and Comparative Example 4 were exposed to light from 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 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 solution was filtered through a wire mesh to collect an insoluble matter (gel fraction), and after drying, the gel fraction to the sheet weight (gel fraction [mass%]) was determined by weighing. The larger 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 light irradiation.
Gel fraction retention rate = Gel fraction after 3 months / initial gel fraction x 100

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

  It can be seen from Table 3 that the storage stability is more excellent if the E-MAA layer is the outermost layer compared to the EVA 1-layer single layer. It is presumed that this is because the outermost layer can suppress volatilization, deterioration, etc. of the crosslinking agent contained in the EVA1 layer.

The disclosure of Japanese Patent Application 2014-190239 filed on September 18, 2014 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards described herein are as specific and distinct as when individual documents, patent applications, and technical standards are incorporated by reference. Hereby incorporated by reference.

Claims (6)

Two outermost layers having a volume resistivity of 1.0 × 10 ¹⁵ Ω · cm or more and 1.0 × 10 ¹⁸ Ω · cm or less,
An intermediate layer disposed between the outermost layers of the two layers and having a volume resistivity of 1.0 × 10 ¹¹ Ω · cm or more and less than 1.0 × 10 ¹⁵ Ω · cm;
At least three layers are stacked including,
The outermost layer mainly comprises an ethylene / (meth) acrylic acid copolymer in which the content of the structural unit derived from (meth) acrylic acid is 8% by mass to 25% by mass with respect to the total mass of the copolymer The sealing material for solar cells which contains as a component . Before Symbol intermediate layer, the sealing material for a solar cell according to claim 1 comprising a vinyl ethylene acetate copolymer.   The solar cell sealing material according to claim 1, wherein three layers of the outermost layer of the two layers and the intermediate layer are stacked. The volume resistivity of the whole sealing material is 1.0 * 10 < ¹⁵ > ohm * cm or more and 1.0 * 10 < ¹⁸ > ohm * cm or less, The solar cell of any one of Claims 1-3. Sealant.   The ratio of the thickness of the said outermost layer with respect to the said intermediate | middle layer is 1 / 2-1 / 8, The sealing material for solar cells of any one of Claims 1-4.   The solar cell module provided with the sealing material for solar cells of any one of Claims 1-5.