JP2011238862A - Solar cell encapsulation film and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell encapsulation film in which yellow discoloration is suppressed and which has an excellent adhesive strength by finding an optimum combination and an optimum additive amount of a crosslinking agent and an ultraviolet absorber to be added.SOLUTION: A solar cell encapsulation film comprises an ethylene-vinyl acetate copolymer, a crosslinking agent, and an ultraviolet absorber, wherein the crosslinking agent is 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and is 0.1-1.2 pt.mass with respect to 100 pts.mass of the ethylene-vinyl acetate copolymer, and the ultraviolet absorber is 2-hydroxy-4-n-octoxybenzophenone and is 0.02-0.28 pt.mass with respect to 100 pts.mass of the ethylene-vinyl acetate copolymer.

Description

  The present invention relates to a solar cell sealing film containing an ethylene-vinyl acetate copolymer as a main component, and more particularly to a solar cell sealing film in which yellowing is prevented and adhesion is good. Moreover, it is related with the solar cell using this sealing film.

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

  For example, as shown in FIG. 1, the solar cell includes a surface side transparent protective member 11 made of a glass substrate or the like, a surface side sealing film 13 </ b> A, a solar cell 14 such as a silicon power generation element, a back side sealing film 13 </ b> B, And the back-side protection member 12 are laminated in this order, degassed under reduced pressure, and then heated and pressurized to crosslink and cure the surface-side sealing film 13A and the back-side sealing film 13B to be bonded and integrated. The In a conventional solar battery, a plurality of solar battery cells 14 are connected and used in order to obtain a high electric output. Therefore, in order to ensure insulation between the solar battery cells 14, the solar battery cells are sealed using the sealing films 13A and 13B having insulation properties.

  As the sealing films 13A and 13B, an ethylene-vinyl acetate copolymer (EVA) film or the like has been conventionally used because it is inexpensive and has high transparency and adhesiveness (for example, Patent Document 1). EVA film for sealing film has high adhesion and adhesive strength to ensure the mechanical durability of solar cells and prevent rusting of internal conductors and electrodes due to moisture or water permeation. A function for bonding and integrating the members is necessary.

  The EVA film is produced by depositing a composition containing an ethylene-vinyl acetate copolymer and a crosslinking agent. By cross-linking EVA using a cross-linking agent, the adhesion and durability of the EVA film can be improved.

  As the crosslinking agent, for example, in Patent Document 1, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane or n-butyl-4,4-bis (t-butylperoxy) palate is used. In Patent Document 2, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is used.

  Moreover, in a solar cell, it is desired from the point of the improvement of electric power generation efficiency that the light which injected into the solar cell can be taken in in the cell for solar cells as efficiently as possible. Therefore, it is desirable that the solar cell sealing film has as high a transparency as possible, does not absorb or reflect incident sunlight, and transmits most of sunlight.

  However, when a solar cell is used for a long period of time, a phenomenon in which the sealing film turns yellow due to the influence of sunlight, particularly ultraviolet rays, and the transmittance of sunlight decreases, and the appearance defect due to the yellowing is observed. Is a problem. Due to this problem, an ultraviolet absorber has been conventionally added to the sealing film.

  As the ultraviolet absorber, for example, in Patent Document 1, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone is used, and in Patent Document 2, 2,4-dihydroxybenzophenone is used.

JP 2002-170971 A JP2008-159856

  When a crosslinking agent undergoes a crosslinking reaction, reaction residues and unreacted residues remain, and such residues are unstable, so radicals are generated by light and heat, and once radicals are generated, new radicals are generated. And may cause yellowing of the sealing film due to oxidative degradation of the polymer and generation of conjugated double bonds. Also, the ultraviolet absorber may cause yellowing in the sealing film due to deterioration over time. Therefore, there is a problem that when the crosslinking agent and the ultraviolet absorber are used in combination, there is a high possibility that the sealing film is yellowed. Further, unless an appropriate amount of the crosslinking agent and the ultraviolet absorber is added, the adhesive force between the sealing film, the front surface side protective member and the back surface side protective member is reduced, leak current is generated, and power generation efficiency is reduced. There is a case.

  Accordingly, an object of the present invention is to find an optimal combination and an optimal addition amount of a crosslinking agent and an ultraviolet absorber to be added, and to provide a sealing film for a solar cell in which yellowing is suppressed and adhesion is good. is there. Moreover, it is providing the solar cell using this sealing film for solar cells.

  As a result of studying the combinations and addition amounts of a number of crosslinking agents and ultraviolet absorbers, the present inventor has conducted an experiment. As a result, the above object is for a solar cell including an ethylene-vinyl acetate copolymer, a crosslinking agent, and an ultraviolet absorber. A sealing film, wherein the crosslinking agent is 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (hereinafter also referred to as “crosslinking agent A”), and the ethylene-vinyl acetate. The ultraviolet absorber is 2-hydroxy-4-n-octoxybenzophenone (hereinafter also referred to as “ultraviolet absorber A”) in an amount of 0.1 to 1.2 parts by mass with respect to 100 parts by mass of the copolymer. The present invention has been found to be achieved by a solar cell sealing film characterized by containing 0.02 to 0.28 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer.

Preferred embodiments of the present invention are as follows.
(1) The content of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is 0.3 to 0.9 parts by mass.
(2) The content of 2-hydroxy-4-n-octoxybenzophenone is 0.02 to 0.2 parts by mass.
(3) The vinyl acetate content of the ethylene-vinyl acetate copolymer is 20 to 35 mass% based on the mass of the ethylene-vinyl acetate copolymer.

  Moreover, this object is achieved by a solar cell characterized by using the solar cell sealing film.

  In the sealing film for solar cells of the present invention, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and 2-hydroxy-4-n-octoxybenzophenone are used in combination. By optimizing the amount added, good adhesiveness can be obtained, and yellowing can be remarkably suppressed even when used for a long time. Therefore, according to the sealing film for solar cells, it is possible to provide a solar cell that can exhibit high power generation performance over a long period from the initial installation.

It is a schematic sectional drawing of a common solar cell. It is the schematic for demonstrating the 180 degree peel test method which is evaluation of adhesive force.

  As described above, the solar cell sealing film of the present invention has 0.1 to 1.2 parts by mass of the crosslinking agent A and 0.02 to 0.02 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. Contains 28 parts by weight of UV absorber A. According to this combination and addition amount, yellowing can be suppressed while ensuring good adhesion of the solar cell sealing film.

  Hereinafter, the solar cell sealing film of the present invention will be described in more detail.

[2,5-dimethyl-2,5-di (t-butylperoxy) hexane (crosslinking agent A)]
The crosslinking agent A used in the present invention has the following formula (I)

で表されるパーオキサイド系有機過酸化物である。加熱することによりラジカルを発生し、エチレン−酢酸ビニル共重合体を架橋させる。常温で液体であるためにエチレン−酢酸ビニルとの相溶性が良く、また外観は無色透明であるので、添加することによって封止膜の透明性を低下させることがない。

It is a peroxide type organic peroxide represented by these. By heating, radicals are generated to crosslink the ethylene-vinyl acetate copolymer. Since it is liquid at normal temperature, it has good compatibility with ethylene-vinyl acetate, and its appearance is colorless and transparent, so that the addition does not lower the transparency of the sealing film.

  The crosslinking agent A is blended in an amount of 0.1 to 1.2 parts by mass, preferably 0.3 to 0.9 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. If it is less than this range, sufficient adhesion may not be obtained, and if it exceeds this range, yellowing may occur.

[2-Hydroxy-4-n-octoxybenzophenone (UV absorber A)]
The ultraviolet absorber A used in the present invention is represented by the following formula (II)

で表されるベンゾフェノン系紫外線吸収剤である。

It is a benzophenone series ultraviolet absorber represented by these.

  The ultraviolet absorber A is blended in an amount of 0.02 to 0.28 parts by mass, preferably 0.02 to 0.2 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. If it is less than this range, the effect of absorbing ultraviolet rays may not be obtained, and if it exceeds this range, yellowing may occur.

[Ethylene-vinyl acetate copolymer]
By using an ethylene-vinyl acetate copolymer (also referred to as EVA) as a main component, a solar cell sealing film that is inexpensive and excellent in transparency and flexibility can be formed.

  The content of vinyl acetate in the ethylene-vinyl acetate copolymer is preferably 20 to 35% by mass, more preferably 22 to 30% by mass, and particularly preferably 24 to 28% by mass with respect to the ethylene-vinyl acetate copolymer. . When the content of vinyl acetate is less than 20% by mass, the transparency of the film obtained when crosslinked and cured at a high temperature may not be sufficient, and when it exceeds 35% by mass, carboxylic acid, alcohol, amine, etc. There is a possibility that foaming is likely to occur at the interface between the solar cell sealing film and the protective member.

  In addition to the ethylene-vinyl acetate copolymer, the solar cell sealing film of the present invention further comprises polyvinyl acetal resin (for example, polyvinyl formal, polyvinyl butyral (PVB resin), modified PVB), and vinyl chloride resin. May be used. In that case, PVB is particularly preferable.

[Crosslinking aid]
Furthermore, it is preferable that the sealing film for solar cells before crosslinking curing contains a crosslinking aid. The cross-linking aid can improve the cross-linking density of the ethylene-vinyl acetate copolymer and improve the adhesion and durability of the sealing film.

  The crosslinking aid is preferably used in an amount of 0.1 to 3.0 parts by mass, and more preferably 0.1 to 2.5 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. With such a content of the crosslinking aid, there is no generation of gas due to the addition of the crosslinking aid, and the crosslinking density of the ethylene-vinyl acetate copolymer can be improved.

  Examples of the crosslinking aid (compound having a radical polymerizable group as a functional group) include trifunctional crosslinking aids such as triallyl cyanurate and triallyl isocyanurate, and (meth) acrylic esters (eg, NK ester) ) Monofunctional or bifunctional crosslinking aids. Of these, triallyl cyanurate and triallyl isocyanurate are preferable, and triallyl isocyanurate is particularly preferable.

[Adhesion improver]
The solar cell sealing film of the present invention preferably contains a silane coupling agent for the purpose of further enhancing the adhesive force. As silane coupling agents, γ-methacryloxypropyltrimethoxysilane, γ-chloropropylmethoxysilane, vinylethoxysilane, vinyltris (β-methoxyethoxy) silane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane , Γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β- (Aminoethyl) -γ-aminopropyltrimethoxysilane and the like can be mentioned. In particular, γ-methacryloxypropyltrimethoxysilane is preferable. These silane coupling agents may be used alone or in combination of two or more. Moreover, it is preferable that it is 0.01-5 mass parts with respect to 100 mass parts of ethylene-vinyl acetate copolymers, and, as for content of a silane coupling agent, 0.1-2 mass parts is especially preferable.

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

  The plasticizer is not particularly limited, but polybasic acid esters and polyhydric alcohol esters are generally used. Examples thereof include dioctyl phthalate, dihexyl adipate, triethylene glycol-di-2-ethyl butyrate, butyl sebacate, tetraethylene glycol diptanoate, and triethylene glycol dipelargonate. One plasticizer may be used, or two or more plasticizers may be used in combination. The content of the plasticizer is preferably in the range of 5 parts by mass or less with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer.

  The acryloxy group-containing compound and the methacryloxy group-containing compound are generally acrylic acid or methacrylic acid derivatives, and examples thereof include acrylic acid or methacrylic acid esters and amides. Examples of ester residues include methyl, ethyl, dodecyl, stearyl, lauryl and other linear alkyl groups, cyclohexyl group, tetrahydrofurfuryl group, aminoethyl group, 2-hydroxyethyl group, 3-hydroxypropyl group, A 3-chloro-2-hydroxypropyl group can be mentioned. Examples of amides include diacetone acrylamide. In addition, polyhydric alcohols such as ethylene glycol, triethylene glycol, polypropylene glycol, polyethylene glycol, trimethylolpropane, and pentaerythritol, and esters of acrylic acid or methacrylic acid can also be used.

Examples of the epoxy-containing compound include triglycidyl tris (2-hydroxyethyl) isocyanurate, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, Phenol (ethyleneoxy) ₅ glycidyl ether, pt-butylphenyl glycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, glycidyl methacrylate, butyl glycidyl ether can be mentioned.

  The acryloxy group-containing compound, the methacryloxy group-containing compound, or the epoxy group-containing compound is generally 0.5 to 5.0 parts by mass, particularly 1.0 to 100 parts by mass of the ethylene-vinyl acetate copolymer. It is preferable that -4.0 mass part is contained.

  Furthermore, the solar cell sealing film of the present invention may contain an anti-aging agent. Examples of the antioxidant include hindered phenolic antioxidants such as N, N′-hexane-1,6-diylbis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamide], Examples thereof include phosphorus heat stabilizers, lactone heat stabilizers, vitamin E heat stabilizers, and sulfur heat stabilizers.

  What is necessary is just to perform according to a well-known method in order to form the sealing film for solar cells of this invention mentioned above. For example, the composition containing each of the above-described components can be produced by a method of obtaining a sheet-like material by molding by ordinary extrusion molding, calendar molding (calendering) or the like. Alternatively, a sheet-like material can be obtained by dissolving the composition in a solvent and coating the solution on a suitable support with a suitable coating machine (coater) and drying to form a coating film. The heating temperature during film formation is preferably a temperature at which the crosslinking agent does not react or hardly reacts. For example, it is preferably 50 to 90 ° C, particularly 40 to 80 ° C. Although the thickness in particular of the sealing film for solar cells of this invention is not restrict | limited, It is 0.05-2 mm.

  The structure of the solar cell of the present invention is not particularly limited as long as the solar cell sealing film of the present invention is used. For example, the structure etc. which sealed the cell for solar cells by interposing the sealing film for solar cells of this invention between the surface side transparent protection member and the back surface side protection member, and making it bridge-integrate are mentioned. . In addition, in this invention, the side (light-receiving surface side) by which the light of a photovoltaic cell is irradiated is called "front surface side", and the surface opposite to the light-receiving surface of a photovoltaic cell is called "back surface side."

  In the solar cell, in order to sufficiently seal the solar cell, for example, as shown in FIG. 1, the front surface side transparent protective member 11, the front surface side sealing film 13A, the solar cell cell 14, the back surface side sealing. The film 13B and the back surface side protection member 12 may be laminated, and the sealing film may be cross-linked and cured according to a conventional method such as heat and pressure.

In order to heat and pressurize, for example, the laminate is heated with a vacuum laminator at a temperature of 135 to 180 ° C., further 140 to 180 ° C., particularly 155 to 180 ° C., a degassing time of 0.1 to 5 minutes, and a press pressure of 0.1. What is necessary is just to heat-press in about 1.5 kg / cm < ² > and press time 5-15 minutes. By crosslinking the ethylene-vinyl acetate copolymer contained in the front side sealing film 13A and the back side sealing film 13B during the heating and pressurization, the front side sealing film 13A and the back side sealing film 13B are interposed. And the surface side transparent protection member 11, the back surface side transparent member 12, and the cell 14 for solar cells can be integrated, and the cell 14 for solar cells can be sealed.

  The solar cell sealing film of the present invention is not limited to a solar cell using a single crystal or polycrystalline silicon crystal solar cell as shown in FIG. It can also be used for sealing films of thin film solar cells such as solar cells and copper indium selenide (CIS) solar cells. In this case, for example, the solar cell of the present invention is formed on a thin film solar cell element layer formed by a chemical vapor deposition method or the like on the surface of a surface side transparent protective member such as a glass substrate, a polyimide substrate, or a fluororesin transparent substrate. On the solar cell element formed on the surface of the back surface side protective member, the structure for laminating the battery sealing film and the back surface side protective member and adhering and integrating them, the front surface side Laminated transparent protective member, bonded and integrated structure, or front side transparent protective member, front side sealing film, thin film solar cell element, back side sealing film, and back side protective member are laminated in this order, For example, a structure that is bonded and integrated.

  The surface side transparent protective member 11 used in the solar cell of the present invention is usually a glass substrate such as silicate glass. As for the thickness of a glass substrate, 0.1-10 mm is common, and 0.3-5 mm is preferable. The glass substrate may generally be chemically or thermally strengthened.

  The back surface side protective member 12 used in the present invention is preferably a plastic film such as polyethylene terephthalate (PET). Further, a film obtained by laminating a fluorinated polyethylene film, particularly a fluorinated polyethylene film / Al / fluorinated polyethylene film in this order in consideration of heat resistance and wet heat resistance may be used.

  In addition, the solar cell (including a thin film solar cell) of the present invention is characterized by a sealing film used on the front surface side and / or the back surface side as described above. Therefore, the members other than the sealing film such as the front-side transparent protective member, the back-side protective member, and the solar cell need only have the same configuration as the conventionally known solar cell, and are not particularly limited. .

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

(Examples 1-10, Comparative Examples 1-7)
Each material was supplied to a roll mill with the formulation shown in Tables 1 and 2, and kneaded at 70 ° C. to prepare a solar cell sealing film composition. The solar cell sealing film composition was calendered at 70 ° C., allowed to cool, and then a solar cell sealing film (thickness 0.6 mm) was produced.

(Evaluation methods)
(1) Yellowness White glass (thickness 3 mm) / the solar cell sealing film (thickness 0.6 mm) / white glass (thickness 3 mm) are laminated in this order, and the resulting laminate is used as a vacuum laminator. Then, after temporarily pressing at a temperature of 100 ° C. for 10 minutes, it was placed in an oven and crosslinked at a temperature of 155 ° C. for 45 minutes. About this laminated body, the yellow degree (YI) 200 hours after ultraviolet irradiation was measured based on JIS-K-7105 (1981) using the color meter (HZ-2, Suga Test Instruments Co., Ltd.). .

(2) Glass adhesive strength The adhesive strength was evaluated by a 180 ° peel test (JIS K 6854, 1994). Laminated in the order of float glass (3 mm thickness) / sealing film for solar cell (0.6 mm thickness) / released PET film (75 μm thickness), and the resulting laminate was heated to 100 ° C. with a vacuum laminator. And then temporarily crimped for 10 minutes, and then placed in an oven and crosslinked at a temperature of 155 ° C. for 45 minutes. As shown in FIG. 2, a part between the glass plate 21 and the solar cell sealing film 23 is peeled off, and the solar cell sealing film 23 is folded back 180 ° to obtain a tensile tester (Shimadzu Corporation). The peel strength at a tensile speed of 100 mm / min was measured as glass adhesive strength (N / cm) using an autograph produced by the company.

(Evaluation results)
In Examples 1 to 10, as shown in Table 1, the crosslinking agent A and the ultraviolet absorber A were mixed in various addition amounts, and both the yellowness and the glass adhesive force were good. In particular, Examples 3 to 5 and 7 and 8 containing 0.3 to 0.9 parts by mass of the crosslinking agent A and 0.02 to 0.2 parts by mass of the ultraviolet absorber A have low yellowness and adhesion. It was found to be good.

  In Comparative Examples 1-4, when the sealing film produced combining various crosslinking agents and ultraviolet absorbers was evaluated, it was recognized that yellowness is high. In Comparative Examples 5 to 7, the sealing films prepared by changing the blending amounts of the crosslinking agent A and the ultraviolet absorber A had high yellowness or reduced glass adhesion.

  As described above, the solar cell sealing film containing 0.1 to 1.2 parts by mass of the crosslinking agent A and 0.02 to 0.28 parts by mass of the ultraviolet absorber A has a low yellowness and good adhesion. It was shown that.

  By using a solar cell sealing film that is prevented from yellowing and has a good adhesive force for a solar cell, it is possible to provide a solar cell with high power generation efficiency over a long period from the initial installation.

DESCRIPTION OF SYMBOLS 11 Surface side transparent protective member 12 Back surface side protective member 13A Surface side sealing film 13B Back surface side sealing film 14 Cell for solar cells 21 Glass plate 23 Sealing film for solar cells

Claims (5)

A solar cell encapsulating film comprising an ethylene-vinyl acetate copolymer, a crosslinking agent and an ultraviolet absorber,
The crosslinking agent is 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, and is included in an amount of 0.1 to 1.2 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. ,
The ultraviolet absorber is 2-hydroxy-4-n-octoxybenzophenone, and 0.02 to 0.28 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer. Sealing film.   2. The solar cell sealing film according to claim 1, wherein the content of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is 0.3 to 0.9 parts by mass.   3. The solar cell sealing film according to claim 1, wherein the content of the 2-hydroxy-4-n-octoxybenzophenone is 0.02 to 0.2 parts by mass.   The sun according to any one of claims 1 to 3, wherein a vinyl acetate content of the ethylene-vinyl acetate copolymer is 20 to 35 mass% based on a mass of the ethylene-vinyl acetate copolymer. Battery sealing film.   A solar cell using the solar cell sealing film according to claim 1.

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