KR20120039868A - Encapsulation composition for a solarcell module having an improved durability and the encapsulation sheet using the same - Google Patents

Abstract

PURPOSE: An encapsulation composition for a solar cell and an encapsulating material sheet molded by thereof are provided to improve safety after cross linking and prevent generation of acetic acid, thereby improving long term endurance and cohesiveness. CONSTITUTION: An encapsulation composition for a solar cell comprises an ethylene vinyl acetate copolymer resin as base material and 0.1-5 parts by weight of peroxide, and 0.01-2.5 parts by weight of radical scavenger as a kernel additive based on weight of the resin. The encapsulating material composition additionally includes less than 2 parts by weight of crosslinking aid and 0.01-3 parts by weight of silane compound. The peroxide produces radical intermediate having 85-95 kcal/mol of dissociation energy by being decomposed.

Description

Encapsulation composition for a solarcell module having an improved durability and the encapsulation sheet using the same}

The present invention relates to a solar cell encapsulation composition and a molded encapsulant sheet having a long-term durability, and more particularly, the cause of discoloration or corrosion through the control of the crosslinking reaction of the ethylene-vinylacetate copolymer used as the encapsulant With regard to the solar cell encapsulation composition and the molded encapsulant sheet formed therein which have long-term durability and excellent adhesion by keeping the solar cell module stable without any problem of discoloration or corrosion even during long-term use from the outside by preventing the occurrence of acetic acid. will be.

Recently, solar cells using the sun have been in the spotlight recently because they overcome energy shortages of limited energy resources and are environmentally friendly, energy-free, noiseless, and infinitely supplying energy. Module is a semiconductor device that converts light energy into electrical energy by using the photoelectric effect, which is a key material in the use of solar cells. Generally, modules of such solar cells are glass substrates, encapsulant sheets, solar cells, and encapsulation. The laminated sheet and the back sheet are laminated in order, and then heated and pressurized to manufacture the encapsulant sheet by crosslinking curing and constituting adhesive components. Various researches on encapsulants essential for solar cell modules are being conducted. For example, the optoelectronic device rod of Korean Patent Application No. 2005-0000829 Ash and a solar cell module employing the same are "optoelectronic device encapsulation material comprising a phosphor and a quantum dot, comprising a first wavelength conversion layer containing a phosphor and a second wavelength conversion layer containing a quantum dot, Optoelectronic device encapsulant, characterized in that the average particle diameter of the phosphor is 10 to 300nm ", and also the solar cell module encapsulant sheet of the Korean Patent Application No. 2008-0121324 and a solar cell module comprising the same, A solar cell module encapsulant sheet " is formed in which a plurality of hemispherical recesses having different sizes are formed on one surface or both surfaces of a transparent soft film.

On the other hand, the most widely used encapsulation material in the production of the solar cell module as described above is ethylene-vinylacetate copolymer and vinyl acetate is generally used in a weight ratio of 20-40%. As for the composition of the encapsulation material, in the ethylene-vinylacetate film of Korean Patent Application No. 2008-0138495 and the solar cell module including the same, "(a) Ethylene-vinyl acetate having a vinyl acetate content of 21-40% by weight (Ethylene- vinylacetate; a core layer composed mainly of EVA), and (b) a surface layer mainly composed of an ethylene-vinylacetate copolymer having a vinyl acetate content of 10-20% by weight. To ethylene-vinylacetate films. However, since the solar cell is used for a long time from the outside, the encapsulant used in the module is discolored through structural deformation due to factors such as UV, heat, and moisture over time. This efficiency is lowered. In order to prevent this, additives such as an ultraviolet absorber, an antioxidant, a heat stabilizer, etc. have been used together during the molding of the encapsulant, but the efficiency deterioration due to the deterioration of the encapsulant stability remains an important problem. Especially. As can be seen in the prior art document "Solar Energy Materials and Solar Cells, 91, pp 315-329, 2007", due to the structural properties of the polyethylene-vinylacetate copolymer, an acetyl group is present in the encapsulant. Acetic acid not only causes discoloration by facilitating decomposition of the encapsulant, but also causes serious problems by causing corrosion of metallic elements in the module.

As described above, the encapsulant of the conventional solar cell module has a number of excellent advantages, but is still presented as a problem that must be preceded by various problems to be solved, namely, the discoloration and corrosion problems caused by decomposition. At present, no suitable solution has been proposed.

Patent Document 1: Republic of Korea Patent Application No. 2005-0000829 Patent Document 2: Republic of Korea Patent Application No. 2008-0121324 Patent Document 3: Republic of Korea Patent Application No. 2008-0138495

Non-Patent Document 1: Solar Energy Materials and Solar Cells, 91, pp 315-329, 2007

Accordingly, the present invention has been made in view of the above technical problems in the prior art, and a main object of the present invention is to improve the stability after crosslinking of polyethylene-vinylacetate used as the conventional solar cell encapsulation material, It is to provide a solar cell encapsulant composition with improved functionality such as adhesion as well as long-term durability by suppressing the occurrence.

Another object of the present invention is to provide an encapsulant sheet using a solar cell encapsulant composition having the above excellent characteristics.

The present invention may also be directed to accomplishing other objects that can be easily derived by those skilled in the art from the overall description of the present specification, other than the above-described and obvious objects.

The object of the present invention described above is that the inventors of the polyethylene-vinylacetate sheet used as an encapsulant, as described above, the acetic acid remains after crosslinking and decomposing acetic acid due to UV, heat, moisture, etc. The amount of acetic acid is released in the amount of 3.31 × 10 ^-12 g / min per 1g of encapsulant under room temperature, and the acetic acid thus released promotes the hydrolysis reaction of the encapsulant sheet and ultimately discolors the encapsulant. It can be seen from the above Non-Patent Document 1 that the efficiency of the cell through the reduction, and also from the recognition of the fact that it causes corrosion of the metallic element used as a component of the solar cell to reduce the durability of the module, a) polyethylene The vinyl acetate encapsulant is crosslinked by radicals generated by the decomposition of peroxides added during module manufacture. B) the crosslinking reaction can occur at many positions of the encapsulant resin molecules, and in particular, the reaction through radical generation by decomposition of the carbon-hydrogen bond of the acetyl group is the most easy. And c) many carbon-hydrogen bonds in the encapsulant molecular structure participate in radical substitution reactions to cause crosslinking, and d) most acetyl groups are crosslinked through carbon-carbon bonds with other molecular chains. Residual acetyl groups, which become part of the molecular structure but do not finally participate in the crosslinking reaction, are found to be more prone to hydrolysis due to external factors and consequently to acetic acid molecules;

Therefore, the present inventors have taken into consideration the above-mentioned properties of the polyethylene-vinylacetate copolymer encapsulant from the above facts, and thus a method capable of proceeding the crosslinking reaction by a method of dramatically reducing the remaining acetyl group through the proper selection of the peroxide at the time of crosslinking. The remaining acetyl group was selected by selecting and applying the energy and stability of radicals, which are decomposition products of peroxides, which can identify and distinguish the characteristics of the bonds between atoms in the encapsulant molecule, in particular, the difference in the binding energy. The crosslinking reaction can be minimized, and ultimately, the result of suppressing the generation of acetic acid can be obtained. Thus, a method of obtaining a solar cell which does not cause discoloration and corrosion even in long-term use has been achieved.

Solar cell encapsulant composition having a long-term durability of the present invention for achieving the above object;

It is based on ethylene vinyl acetate copolymer resin, and it is characterized in that it is composed by adding 0.1 to 5 parts by weight of the peroxide and 0.01 to 2.5 parts by weight of the radical scavenger based on the weight of the resin.

According to another configuration of the present invention, the encapsulant composition is characterized in that the addition of a crosslinking aid not exceeding 2 parts by weight and 0.01 to 3 parts by weight of the silane compound is further added.

According to another configuration of the present invention, the peroxide is decomposed to generate a radical intermediate having a dissociation energy of 85 to 95 kcal / mol, characterized in that to cause a selective crosslinking reaction in the acetyl group.

According to another configuration of the present invention, the peroxide generates radicals having an energy of 85 to 95 kcal / mol also by a secondary decomposition reaction within a short time after the first decomposition to cause a selective crosslinking reaction in the acetyl group It is done.

According to another configuration of the present invention, the peroxide is characterized in that the peroxy ketal or peroxy carbonate-based.

According to another configuration of the present invention, the radical scavenger is hindered phenol (hindered phenol) form, flavonoid compounds, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alkylphenol (alkylphenol), alkoxyphenol (alkoxyphenol) It is selected from the group consisting of hydroxychalcone (hydroxychalcone) compound, alkyl (alkyl) or arylnitrone (arylnitrone) compound, characterized in that to replace the high-energy oxy radicals generated by the decomposition of the peroxide.

According to another configuration of the invention, the radical scavenger is characterized in that added to 50 parts by weight or less relative to the peroxide.

Solar cell encapsulant sheet having a long-term durability of the present invention for achieving the above another object;

It is based on ethylene vinyl acetate copolymer resin, and the sheet is formed and vacuumed by using the encapsulant composition formed by adding 0.1 to 5 parts by weight of peroxide and 0.01 to 2.5 parts by weight of a radical scavenger based on the weight of the resin. It is characterized in that the acetyl group remaining when crosslinked by melt compression using a compactor does not exceed 1%.

Since the encapsulant composition for a solar cell having a long-term durability of the present invention configured as described above is formed by adding a specific peroxide and radical scavenger, generation of acetic acid, which is one of the causes of efficiency reduction due to discoloration and corrosion by a selective crosslinking reaction. Solves the technical problem by providing a solar cell encapsulant composition and a molded sheet having excellent long-term stability by minimizing the structure and maintaining the structure and function of the solar cell encapsulant even in long-term use under severe conditions. It was.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in more detail by preferable embodiment.

The solar cell encapsulant composition having long-term durability with excellent stability by a selective crosslinking reaction according to a preferred embodiment of the present invention is a suitable peroxide and radical scavenger capable of proceeding a selective crosslinking reaction through an ethylene-vinylacetate resin and an acetyl group. And a crosslinking aid and a silane coupling agent.

According to a preferred embodiment of the present invention, the peroxide for the selective crosslinking reaction dissociates B1 in consideration of the difference in bond dissociation energy of the carbon-hydrogen bond (B1) of the acetyl group and the other carbon-hydrogen bond (B2) of the polymer backbone. Peroxides are selected and used to generate radicals with energy that can selectively cause radical crosslinking reactions. Crosslinking agents for this purpose are preferred to produce radicals having an energy of 95 kcal / mol or less. On the other hand, radicals having a high energy of 95 kcal / mol or more can minimize the influence on the crosslinking reaction by the use of a suitable radical scavenger.

In general, low-energy radicals are difficult to break the carbon-hydrogen bonds present in the polyethylene molecular structure, while carbon-hydrogen bonds in acetyl groups with low bond dissociation energy can be easily broken, thereby allowing crosslinking to proceed. . When the peroxide is selected and used in consideration of the energy of the radicals thus generated, a desired encapsulant crosslinked product can be obtained through a selective crosslinking reaction. Peroxides used herein include 1,1-di (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-di (t-butylperoxy) cyclohexane, 1,1-di (t Peroxyketal species such as amylperoxy) cyclohexane, ethyl-3,3-di (t-butylperoxy) butylate, ethyl-3,3-di (t-amylperoxy) butylate, dicumylper Oxide, di (t-butylperoxy) -m / p-diisopropylbenzene, 2,5-dimethyl-2,5- (t-butylperoxy) hexane, t-butylcumylperoxide, 2 Dialkyl peroxides such as, 5-methyl-2,5- (t-butylperoxy) hexyn-3 and the like, peroxycarbonates such as t-butyl peroxy 2-ethylhexyl monocarbonate, t-butyl peroxybenzoate Although it may be used, it is preferable to select and use a peroxide that generates a radical having an energy of 95 kcal / mol or less in consideration of the energy of the generated radicals.

According to the configuration of the present invention it is possible to lower the remaining acetyl group to 1% or less to obtain a more stable solar cell encapsulant composition.

As described above, the encapsulant composition for solar cells according to the present invention is subjected to a selective cross-linking reaction in the acetyl group through the selection of a suitable peroxide to minimize the generation of acetic acid by hydrolysis by UV, heat, moisture, etc. Excellent long-term stability of the ash composition and the sheet produced thereby.

Peroxides used in the present invention may be a peroxy ketal type, dialkyl peroxide, peroxy carbonate-based as described above, among these, dialkyl peroxide is highly reactive by generating a high energy oxy radical after decomposition. Since it is large, it does not give selectivity according to the bond type of the hydrogen atom deodorized in a radical reaction. Thus, it is possible to deodorize most of the hydrogen present in the main chain of the polyethylene-vinylacetate copolymer, which reduces the participation of the reaction of carbon-hydrogen bonds in the acetyl group, leaving more residue. These results can be confirmed through TGA or solid-state NMR analysis after crosslinking of the encapsulant using dialkylperoxide. On the other hand, peroxyketals and peroxycarbonates, together with the oxide radicals, form a low-energy alkyl radical after decomposition, which is a relatively stable radical, which survives for a long time, causing crosslinking reactions and relatively low dissociation energy in the acetyl group. Deodorization of hydrogen is possible and most of the generated radicals proceed the crosslinking reaction through this pathway. As a result, by activating the reaction participation of the acetyl group to minimize the remaining amount through it is possible to cross-link to a stable encapsulant. These results could be confirmed through TGA or NMR analysis as above.

Therefore, according to another preferred embodiment of the invention, it is preferable to use peroxyketal or peroxycarbonate as the peroxide.

Among the peroxyketal or peroxycarbonate-based peroxides, the energy range of the stable radicals generated after decomposition can be varied in a range of less than 100 kcal / mol, but considering the selective reactivity with acetyl groups, radicals having a value of 95 kcal / mol are generated. It is particularly preferable to select a peroxide that can. If the energy is 95kcal / mol or more, the reaction selectivity is not good, and thus the residual acetyl group of the desired level cannot be obtained. In addition, if the energy of the generated radical is less than 85kcal / mol there is a problem that the reaction with the acetyl group and the cross-linking reaction as a whole does not proceed due to low reactivity. At this time, due to the structural characteristics of the peroxide, high-oxygen oxy radicals are always generated after decomposition, and these highly reactive radicals do not show the selectivity for the bonding type of the hydrogen atom and proceed with the crosslinking reaction very quickly. Therefore, for selective crosslinking in the acetyl group, which is an object of the present invention, it is necessary to convert the generated oxy radical into a more stable form of radical in a short time. For this purpose, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and alkylphenol ( stable form of oxy radicals by the addition of small amounts of radical scavengers such as alkylphenols, hindered phenols such as alkoxyphenols, flavonoid compounds, hydroxychalcone compounds, alkyls or arylnitrones It is necessary to change. This facilitates the selected crosslinking reaction in the acetyl group and enables crosslinking reaction in the polymer backbone.

Therefore, in the present invention, it is preferable to use a peroxide capable of generating radicals having an energy of 85-95 kcal / mol by primary decomposition as a crosslinking agent that satisfies the above two conditions simultaneously at 0.1 to 5 parts by weight. If less than 0.1 part by weight can not be obtained a sufficient crosslinking rate, when more than 5 parts by weight it is not desirable to affect the product due to the control of the crosslinking time and the residual peroxide product. In addition, it is also preferred to use 0.1 to 5 parts by weight of a peroxide capable of producing radicals also having an energy of 85-95 kcal / mol by secondary decomposition reaction in a short time after primary decomposition. In order to replace the high-energy oxy radicals generated in the two cases, the radical scavenger is preferably used in an amount of 0.01 to 2.5 parts by weight relative to the resin, but preferably 50 parts by weight or less relative to the peroxide. If the radical scavenger is used in an amount of 0.01 parts by weight or less, sufficient oxy radical substitution effect cannot be seen. If the radical scavenger is used in an amount of 2.5 parts by weight or more, the product may affect the appearance of the radical scavenger.

In the use of the peroxide according to the present invention, the conditions of use may be different in consideration of the respective decomposition temperatures, but nevertheless, the result of the selective crosslinking by the selective use of the peroxide as described in the present invention always appears effective.

According to another preferred embodiment of the present invention, the solar cell encapsulant sheet of the present invention is 200 to 1000㎛ thickness by T-die extrusion or calendering process using the encapsulant composition according to the present invention as described above. By processing with an encapsulant sheet can be produced.

Hereinafter, although an Example and a comparative example demonstrate this invention more concretely, it is a matter of course that the scope of the present invention is not limited to these Examples.

Examples 1 and 2, Comparative Examples 1 and 4

Ethylene vinyl acetate (EVA) compound blended in the ratio of Table 1 was extruded at a temperature of less than 105 ℃ using a 105mm twin extruder to prepare a sheet having a thickness of 500㎛.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 EVA 100 100 100 100 100 100 Crosslinking aid 0.5 0.5 0.5 0.5 0.5 0.5 Silane compound 2 2 2 2 2 2 Peroxide 1 0.45 0.45 Peroxide 2 0.45 0.45 Peroxide 3 0.45 0.45 Radical scavengers 0.1 0.1 0.1

EVA: VA content 33%, MI 40

Crosslinking aid: Triallyl isocyanurate

Silane Compound: Methacryloxypropyltrimethoxysilane

Peroxide 1: Peroxy Ketal Compound

Peroxide 2: Peroxycarbonate Compound

Peroxide 3: Dialkyl Peroxide Compound

Radical scavengers: hindered phenol

Experimental Example 1

Using the encapsulant sheet prepared in each of the above Examples and Comparative Examples and put between the low iron tempered glass and the back sheet and melt compression bonding for 150 minutes, 20 minutes using a vacuum press to produce a simple module 85 ℃, 85% The change in the relative humidity conditions (EHS-411M, ESPEC Co., Ltd.) was measured by a yellowing meter (Spectro Color meter SE 2000, Nippon Denshoku), and the experimental results are shown in Table 2 below.

Time (h) Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 2000  0.2 0.2 0.4 0.5 3.1 4.2

Experimental Example 2

Using the encapsulant sheet prepared in each of the above examples, the low iron tempered glass was placed between the back sheet and the melt press for 20 minutes at 150 ° C. using a vacuum press to prepare a simple module, followed by 85 ° C. and 85% relative humidity conditions. (EHS-411M, ESPEC Co., Ltd.) and then peeled off by hand to confirm the change in adhesion strength. The results are shown in Table 3 below.

Time (h) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 0 ◎ ◎ ◎ ◎ ◎ ◎ 1000 ◎ ◎ ◎ ◎ ○ ○ 2000 ○ ○ ○ ○ × ×

◎: excellent adhesion, ○: reduced adhesion but good, ×: poor adhesion

As can be seen from the results of each experimental example, the use of a suitable peroxide for the selective crosslinking reaction according to the present invention can suppress the generation of acetic acid due to decomposition after crosslinking can be used as a stable sheet of encapsulant even when used continuously for a long time It can be seen that.

Claims (8)

Based on the ethylene vinyl acetate copolymer resin, 0.1 to 5 parts by weight of the peroxide, 0.01 to 2.5 parts by weight of the radical scavenger based on the weight of the resin is added to the core additives, characterized in that the composition for the solar cell having a long-term durability Ash composition.
The method of claim 1, wherein the encapsulant composition is a solar cell encapsulant composition having a long-term durability, characterized in that the addition of 0.01 to 3 parts by weight of the cross-linking aid and not more than 2 parts by weight is added.
The method of claim 1, wherein the peroxide decomposes to produce a radical intermediate having a dissociation energy of 85 to 95 kcal / mol to cause a selective crosslinking reaction in the acetyl group solar cell sealing material having a long-term durability, characterized in that Composition.
4. The selective crosslinking reaction according to any one of claims 1 to 3, wherein the peroxide generates radicals which also have an energy of 85 to 95 kcal / mol by secondary decomposition reaction in a short time after primary decomposition. Encapsulant composition for a solar cell having a long-term durability, characterized in that to occur.
The solar cell encapsulation composition of claim 1, wherein the peroxide is peroxyketal or peroxycarbonate-based.
2. The radical scavenger according to claim 1, wherein the radical scavenger is a hindered phenol type such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alkylphenol, alkoxyphenol, flavonoid compound, or hydroxychalcone. long-term durability solar cell, characterized in that it is selected from the group consisting of (hydroxychalcone) compound, alkyl (alkyl) or arylnitrone compound to replace the high-energy oxy radical produced by the decomposition of peroxide Encapsulant composition.
The encapsulant composition of claim 1, wherein the radical scavenger is added in an amount of 50 parts by weight or less relative to the peroxide.
Claims 1 to 7 using the encapsulant composition according to any one of the solar cell having a long-term durability, characterized in that the acetyl group remaining when forming a sheet and melt-crosslinked using a vacuum press does not exceed 1% Encapsulant sheet.