JPH1154768A - Solar cell sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solar cell sealing material which is mainly formed of ethylene-vinyl acetate high in volume resistivity, and used as a laminate. SOLUTION: Organic peroxide whose half-value period is 30 minutes or less at 140 deg.C is previously added to ethylene-vinyl acetate copolymer, and these elements are interlinked into solar cell sealing material by heating. When a solar cell module is sealed up with the solar cell sealing material, it is improved in insulating even if a thin layer of the above sealing material is used. Furthermore, two sheets of the solar cell sealing material are prepared, and a film formed of material other than ethylene-vinyl acetate copolymer is sandwiched in between the solar cell sealing material sheets for the formation of a three- layered laminate more enhanced in volume resistivity.

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 and a solar cell encapsulant having a laminated structure using the same.

[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 solar electrons, 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. For example, a sealing material obtained by adding an organic peroxide such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexane to EVA as a crosslinking agent is used.

[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, it is considered that improving the members and methods used when modularizing the power generating element other than the power generating element itself leads to improvement in performance, cost reduction, and compactness, and also improves 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. That is, when the conventional 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 an ethylene-vinyl acetate copolymer having a sufficient volume resistivity.

[0008]

In order to achieve the above object, an organic peroxide having a half-life at 140 ° C. of 30 minutes or less according to the present invention is added to an ethylene-vinyl acetate copolymer in advance, and heat crosslinking is carried out. When the solar cell encapsulant obtained by the above is used, the photovoltaic power generation element can be encapsulated with a small amount of the encapsulant and the energy conversion efficiency can be kept high.

Further, the solar cell encapsulant of the present invention is EVA
If the volume specific resistance of the photovoltaic element is 5.0 × 10 ¹⁴ Ω or more, the solar power generation element can be sealed more favorably.

At the time of production, an organic peroxide having a half-life at 140 ° C. of 30 minutes or less is added to the EVA. If necessary, a silane coupling agent, a crosslinking assistant, a stabilizer, a colorant, an ultraviolet ray It is also possible to add an absorbent, an antioxidant, a discoloration inhibitor and the like. These components are mixed using a mixer to obtain the solar cell encapsulation of the present invention.

As the organic peroxide used in the present invention, any organic peroxide having a half-life at 140 ° C. or more of 30 minutes or less can be used. Examples of this are 2,5-
Dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-dicumyl peroxide, 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-butylsiloxy) 3,3,5
-Trimethylcyclohexane, t-butylperoxybenzate, benzoyl peroxide and the like can be used. It is sufficient that the amount of these organic peroxides is not more than 5 parts by weight based on 100 parts by weight of EVA.

When 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane is particularly added to the above organic peroxide and EVA has a crosslinked structure by thermal decomposition, The reduction of the volume resistivity of the EVA is small and effective.

As the EVA used in the present invention, those having a vinyl acetate content of 50% by weight or less can be used. In particular, considering the volume resistivity of the EVA itself, the vinyl acetate content is 30% by weight or less. Are preferred.

Further, in order to further improve the performance of the EVA as a sealing material and mainly the adhesion to the solar cell lower substrate or the power generating element, a silane coupling agent such as γ-chloropropyltrimethoxysilane, vinyl Trichlorosilane, vinyltriethoxysilane, vinyl-tris (β
-Methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, β- (3,4-ethoxycyclohexyl) ethyl-trimethoxysilane, γ-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-mercaptopropyl Trimethoxysilane, γ-aminopropyltrimethoxysilane, N-β-
And (aminoethyl) -γ-aminopropyltrimethoxysilane. The amount of these silane coupling agents is 5 parts by weight or less, preferably 0.02 parts by weight or less, based on 100 parts by weight of EVA.

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 directly bonded to a silicon atom, particularly preferably. Vinyl trimethoxysilane to E
It is also effective to add it to VA.

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

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 as long as it 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 weight or less based on 100 parts by weight of VA.

Further, since the EVA sealing material is used for a long period of 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 aids are used in a proportion of 10 parts by weight or less based on 100 parts by weight 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 weight or less can be added to 00 parts by weight.

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

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

The obtained EVA as a solar cell encapsulant is processed into a plate shape and two sheets thereof are used, and a film other than EVA is sandwiched between the plates to form a three-layer solar cell encapsulant. 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.

[0026]

EXAMPLES Examples 1 and 2 and Comparative Examples 1 and 2 Each component shown in Table 1 was mixed with a roll mill heated to 80 ° C. to prepare an EVA resin composition. 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.

[0027]

[Table 1] The mixing ratio of each component in the above table is based on parts by weight.

The sheets composed of the compositions obtained in Examples 1 and 2 were compared with the sheets of Comparative Examples 1 and 2 conventionally used.
It can be seen that it has a clearly large volume resistivity.

Examples 3 and 4 and Comparative Examples 3 and 4 Production of sealing materials as laminates and measurement of leakage current EVA compositions according to Examples 1 and 2, and Comparative Examples 1 and 2
Each of the EVA compositions obtained in the above was processed into a 0.25 mm thick sheet using a press at 90 ° C. 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. After this, E was placed in an oven at 150 ° C.
VA was crosslinked by heating to obtain each of the laminates of the present invention and comparative laminates (Examples 3, 4 and Comparative Examples 3 and 4, respectively).
4).

Each of the above laminates was punched into 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.

[0031]

[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.

[0032]

As described above, the solar cell encapsulant made of the ethylene-vinyl acetate copolymer of the present invention has a high volume resistivity, and is used as a laminate of the encapsulant and other materials. The sealing material can efficiently prevent current leakage from the solar cell. 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 (9)

[Claims] 1. A solar cell encapsulant obtained by adding an organic peroxide having a half-life at 140 ° C. of 30 minutes or less to an ethylene-vinyl acetate copolymer in advance and crosslinking by heating. 2. The solar cell encapsulant according to claim 1, wherein the volume resistivity is 5.0 × 10 ¹⁴ Ω or more. 3. An organic peroxide comprising 1,1-bis (t
-Butyl peroxy) -3,3,5-trimethylcyclohexane is added.
3. The solar cell encapsulant according to 2. 4. The solar cell encapsulant according to claim 1, wherein the ethylene-vinyl acetate copolymer has a vinyl acetate content of 30% by weight or less. 5. A silane coupling agent having a functional group having 4 or less carbon atoms directly bonded to a silicon atom in a proportion of 5 parts by weight or less based on 100 parts by weight of the ethylene-vinyl acetate copolymer. The solar cell encapsulant according to any one of claims 1 to 4, wherein the solar cell encapsulant is added. 6. The solar cell sealing material according to claim 5, wherein vinyltrimethoxysilane is used as the silane coupling agent. 7. The ethylene-vinyl acetate copolymer 10
The solar cell encapsulant according to claim 5 or 6, wherein the amount of the silane coupling agent added to 0 parts by weight is 0.02 parts by weight or less. 8. A plate other than the ethylene-vinyl acetate copolymer sandwiched between two plates made of the solar cell encapsulant according to claim 1, and a film sandwiched between the plates. When,
A solar cell sealing material comprising: 9. The solar cell encapsulant according to claim 8, wherein the film other than the ethylene-vinyl acetate copolymer is a polyester film.