JP2000183385A - Solar cell sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell sealing material with high volume-specific resistance, whose main component is ethylene-vinyl acetate copolymer. SOLUTION: Using a solar cell sealing material, which is an ethylene-vinyl acetate copolymer with the content of vinyl acetate being 10-30 mass % or less, while the volume-specific resistance is 5.0×1014 Ω or above, even a thin- layer improves the insulation characteristics of a solar cell module. Thus, a current leakage from a solar cell is effectively suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing ethylene-
The present invention relates to a solar cell encapsulant made of a vinyl acetate copolymer.

[0002]

2. Description of the Related Art In recent years, the depletion of fossil fuels such as petroleum and coal has been threatened, and there is an urgent need for development to secure alternative energy to the energy obtained from these fossil fuels. For this reason, nuclear power, hydropower,
Various methods such as wind power generation and photovoltaic power generation have been studied, and have been extended to practical use. However, waste nuclear power has always been associated with waste problems and concerns about adverse effects on the environment, and hydropower and wind power are inferior in terms of energy conversion efficiency. On the other hand, the photovoltaic power generation system has remarkably improved the price / performance ratio when actually used, and the expectations as a clean energy source are also very high.

In photovoltaic power generation, solar energy is directly converted into electric energy by using a semiconductor such as silicon. However, the function of the semiconductor used here is reduced when it comes into direct contact with the outside air, so that a solar cell module is used. It is necessary to provide a protective film or a sealing material on the surface. Furthermore, in order to stabilize the function of the solar cell, it is necessary to improve the insulation performance in addition to the withstand voltage performance of the sealing material, and to prevent leakage of current in the semiconductor as much as possible. That is, an increase in the volume resistivity of the sealing material is an important point for improving the performance of the photovoltaic power generation system.

At present, crosslinked ethylene-vinyl acetate (EVA) is generally considered promising as a sealing material that comes into direct contact with the power generating element from the viewpoint of cost reduction and the like, and its practical use is progressing. EVA as a conventional solar cell encapsulant has a vinyl acetate content exceeding 30% by mass in consideration of transparency and flexibility.

[0005]

As described above, in photovoltaic power generation, research and development for cost reduction from various parts and improvement of performance are being carried out. There is a need to improve energy conversion efficiency and reduce and reduce material costs. In other words, besides the power generating element itself, improving the members and methods used when modularizing the power generating element is considered to improve the performance, reduce the price, reduce the size, and improve the entire system. Can be

[0006] While promoting such a rationalization,
The low volume resistivity of EVA as a sealing material is cited as a problem. For example, the above-mentioned EVA having a vinyl acetate content of more than 30% by mass improves transparency and flexibility as compared with the case where no vinyl acetate is added, but remarkably reduces the volume resistivity. That is, when EVA is used, the thickness is increased to satisfy the withstand voltage performance of the module. However, such a use method not only increases the cost of materials but also increases the volume of the entire module. This is considered to be a factor inhibiting the spread of solar cells and solar power generation.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solar cell encapsulant containing ethylene-vinyl acetate copolymer as a main component and having a sufficient volume resistivity. is there.

[0008]

In order to achieve the above object, the vinyl acetate content of the present invention is 10 to 30% by mass, preferably 10 to 26% by mass, more preferably 10 to 20% by mass.
% By weight of an ethylene-vinyl acetate copolymer.
When a solar cell encapsulant having a volume resistivity A of 5.0 × 10 ¹⁴ Ω or more is used, it is possible to seal the photovoltaic element with a small amount of encapsulant used. This makes it possible to keep the energy conversion efficiency high.

In the production, the vinyl acetate content is 10 to 30.
If necessary, a silane coupling agent, an organic peroxide, a crosslinking aid, a stabilizer, a colorant, an ultraviolet absorber, an antioxidant, a discoloration inhibitor, and the like can be added to the EVA of mass%. . These components are mixed using a mixer to obtain a solar cell encapsulant comprising the ethylene-vinyl acetate copolymer of the present invention.

In order to further improve the performance of the EVA as a sealing material and the adhesive force mainly to the lower substrate of the solar cell or the power generating element, a known silane coupling agent such as γ
-Chloropropyltrimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyl-tris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, β- (3,4-ethoxycyclohexyl) ethyl-trimethoxy Silane, γ-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, N-
β- (aminoethyl) -γ-aminopropyltrimethoxysilane and the like can be mentioned. The compounding amount of these silane coupling agents is 5 parts by mass or less, preferably 0.02 parts by mass or less based on 100 parts by mass of EVA. E
When the addition ratio of the silane coupling agent is 0.0001 to 0.02 parts by mass with respect to 100 parts by mass of VA, stable adhesive strength and high volume resistivity can be obtained, which is particularly preferable.

In order to further improve the volume resistivity of the solar cell encapsulant of the present invention, a silane coupling agent having a functional group having 4 or less carbon atoms, which is directly bonded to a silicon atom, is particularly preferable. Vinyl trimethoxysilane to E
It is also effective to add it to VA.

In the present invention, even if a silane coupling agent having a functional group having 5 or more carbon atoms directly bonded to a silicon atom, such as γ-metachlorooxypropyltrimethoxysilane, an EVA 100 mass If the amount added to the parts is 0.02 parts by mass or less, the volume resistivity of the EVA can be improved.

The EVA used in the present invention preferably has a crosslinked structure. For this reason, for example, an organic peroxide is added in advance, and this is thermally decomposed, so that the EVA can have a crosslinked structure. As the organic peroxide used in the present invention, any organic peroxide that generates radicals at 100 ° C. or higher can be used. However, taking into consideration the stability during compounding, a half-life of 10 hours and a decomposition temperature 70 ° C. or higher, for example, 2,5-dimethylhexane-
2,5-dihydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane-3,
Di-t-butyl peroxide, t-dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, dicumyl peroxide, α,
α'-bis (t-butylperoxyisopropyl) benzene, n-butyl-4,4-bis (t-butylperoxy) butane, 2,2-bis (t-butylperoxy) butane, 1,1- Bis (t-butylperoxy) cyclohexane, 1,1-bis (t-busilperoxy) 3,
3,5-trimethylcyclohexane, t-butylperoxybenzate, benzoyl peroxide and the like can be used. The compounding amount of these organic peroxides is EV
5 parts by mass or less based on 100 parts by mass of A is sufficient.

In particular, when 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane is added to give a crosslinked structure to EVA by thermal decomposition, the decrease in the volume resistivity of EVA is small and effective. It is.

In the present invention, it is also possible to add a photosensitizer to EVA in advance, decompose the photosensitizer by light irradiation, and give EVA a crosslinked structure. The photosensitizer used in the present invention may be any photosensitizer that generates a radical upon irradiation with light, such as benzoin, benzomethyl ether, benzoin isoethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, dibenzoyl, and Nitriacenaphthene, hexachlorocyclopentadiene, paranitrodiphenyl, paranitroaniline, 2,4,6-trinitroaniline, 1,2-
And benzanthraquinone. These photosensitizers are E
It is generally used in an amount of 10 parts by mass or less based on 100 parts by mass of VA.

Further, since the EVA sealing material is used for a long time and is expected to be exposed to wind and rain, durability is also important. In order to improve the durability, it is also possible to add a crosslinking agent to EVA to improve the gel fraction. Examples of the cross-linking auxiliary used for this purpose include monofunctional cross-linking auxiliary in addition to trifunctional cross-linking auxiliary such as triallyl isocyanurate or triallyl isocyanate. These crosslinking assistants are used at a ratio of 10 parts by mass or less based on 100 parts by mass of EVA.

Further, in the present invention, for the purpose of improving stability, hydroquinone, hydroquinone monomethyl ether,
EVA1 with P-benzoquinone, methylhydroquinone, etc.
5 parts by mass or less can be added to 00 parts by mass.

Further, in addition to the above, a coloring agent, an ultraviolet absorber,
Additives such as anti-aging agents and anti-tarnish agents can be used.

Examples of the coloring agent include inorganic pigments such as metal oxides and metal powders, and organic pigments such as azo-based, phthalocyanine-based, achi-based, acidic or basic dye-based lakes.

The ultraviolet absorbers include 2-hydroxy-4-
Benzophenones such as octoxybenzophenone and 2-hydroxy-4-methoxy-5-sulfobenzophenone, benzotriazoles such as 2- (2'-hydroxy-5-methylphenyl) benzotriazole, phenylsalicylate, pt Hindered amines such as -butylphenyl salicylate.

Antioxidants include amines, phenols, bisphenyls and hindered amines.
For example, di-t-butyl-p-cresol, bis (2,
2,6.6-tetramethyl-4-piperazyl) sebacate.

It is possible to form a three-layered solar cell encapsulant by processing the obtained EVA as a solar cell encapsulant into a plate shape and using two sheets, sandwiching a film other than EVA therebetween. By obtaining such a structure, the volume resistivity can be further improved. Examples of the film other than EVA used here include a polyester film, a polyethylene film, a polypropylene film, a polycarbonate film, and a fluorinated polyethylene.

Among them, the polyester film is particularly excellent in insulating properties and inexpensive, and is practical.

[0024]

EXAMPLES Examples 1 to 3 and Comparative Example 1 The components shown in Table 1 were mixed in a roll mill heated to 80 ° C. to prepare EVA resin compositions. The EVA resin composition thus obtained was formed into a cross-linked sheet having a thickness of 1 mm using a press at 150 ° C. Each sheet was sandwiched between electrodes from both sides, a voltage was applied, and the volume resistivity was measured.

[0025]

[Table 1] The mixing ratio of each component in the above table is expressed in units of parts by mass.

It can be seen that the sheets comprising the compositions obtained in Examples 1 to 3 have a clearly higher volume resistivity than the sheet of Comparative Example 1.

Examples 4 to 6 and Comparative Example 2 Production of sealing material as laminate and measurement of leakage current
EVA composition according to Comparative Example 1 and EVA obtained in Comparative Example 1.
The compositions were each weighed 0.25 m using a 90 ° C. press.
It was processed into a sheet having a thickness of m. Two EVA sheets were used, and a 100 μm-thick polyethylene terephthalate (PET) film was sandwiched between the two sheets, and integrated with a laminator. Thereafter, EVA was heated and cross-linked in an oven at 150 ° C. to obtain each laminate of the present invention and a comparative laminate (Examples 4 to 6 and Comparative Example 2 respectively).

Each of the above-mentioned laminates was punched out to 50φ, a voltage of 1000 V was applied, the current was measured, and the leakage current value was obtained. The results are shown in Table 2 below.

[0029]

[Table 2] As is clear from Table 2, the leak current obtained for the laminate of the present invention is extremely small as compared with the leak current of the comparative laminate.

[0030]

As described above, the solar cell encapsulant made of the ethylene-vinyl acetate copolymer of the present invention has a high volume resistivity, and the encapsulant as a cross-linked sheet is capable of transmitting current from the solar cell. Leaks can be efficiently prevented. As a result, the solar cell encapsulant of the present invention improves the insulation properties of the solar cell module even when used in a thin layer, thereby achieving a reduction in the size of the solar cell module itself and a reduction in material costs.

Claims (6)

[Claims] 1. An ethylene-vinyl acetate copolymer having a vinyl acetate content of 10 to 30% by mass, and a volume resistivity of 5.0 × 10 ^{14 of the} ethylene-vinyl acetate copolymer.
A solar cell encapsulating material having a resistance of Ω or more. 2. The solar cell encapsulant according to claim 1, wherein the vinyl acetate content is 10 to 26% by mass. 3. The solar cell encapsulant according to claim 1, wherein said vinyl acetate content is 10 to 20% by mass. 4. The ethylene-vinyl acetate copolymer 10
The silane coupling agent is added at a ratio of 5 parts by mass or less with respect to 0 parts by mass.
The solar cell sealing material according to any one of the above. 5. The ethylene-vinyl acetate copolymer 10
The solar cell sealing material according to any one of claims 1 to 4, wherein a silane coupling agent is added in a ratio of 0.0001 to 0.02 parts by mass with respect to 0 parts by mass. 6. The solar cell encapsulant according to claim 1, wherein the ethylene-vinyl acetate copolymer has a crosslinked structure.