JP2018174202A - Sealing material for solar cell and solar cell module including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing material for solar cells, which, even under a high-temperature and high-humidity environment and under an environment exposed to ultraviolet rays for a long period of time, can maintain an acid capture function over a long period of time, is suppressed in yellowing, has high transparency, and is excellent in crosslinking efficiency.SOLUTION: A sealing material for solar cells contains an ethylene/polar monomer copolymer, a crosslinking agent, an ultraviolet absorber, and a carbodiimide compound. The crosslinking agent has a specific structure, the ultraviolet absorber is a benzotriazole-based ultraviolet absorber, and the carbodiimide compound is a cyclic carbodiimide compound having a specific structure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a novel solar cell encapsulant and a solar cell module using the same.

  In recent years, solar cell modules 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 are being developed further in terms of durability and power generation efficiency. .

  As the structure of the solar cell module, for example, as shown in FIG. 1, a surface side transparent protective member 11 made of a glass substrate or the like, a surface side sealing material 13A, a solar cell element 14 such as a silicon crystal cell, a back side sealing There is known a structure in which a stopper 13B and a back surface side protection member (back cover) 12 are laminated in this order and bonded and integrated.

  In the solar cell module, a plurality of solar cell elements 14 are connected by connection tabs 15 in order to obtain a high electric output. Therefore, in order to ensure the insulation of the solar cell element 14, the solar cell element 14 is sealed using the insulating sealing materials 13A and 13B.

  As such a sealing material, an ethylene-polar monomer copolymer such as an ethylene-vinyl acetate copolymer (EVA) excellent in adhesiveness and transparency is a main component, and a crosslinking agent such as an organic peroxide is added thereto. The film which mix | blended is generally used. However, in a film made of an ethylene-polar monomer copolymer, an acid such as carboxylic acid may be generated due to the influence of moisture or the like entering the solar cell, which corrodes the conductor or electrode of the solar cell module. There is a problem.

  Therefore, an acid acceptor such as magnesium hydroxide for neutralizing the acid and a carbodiimide compound for capturing the acid are added to the sealing material for solar cells (for example, Patent Document 1). In particular, when a carbodiimide compound is added, it is preferably used because the transparency of the solar cell encapsulant is less likely to be lower than an acid acceptor such as magnesium hydroxide.

Japanese Patent No. 4863812

  The solar cell module is used in a harsh outdoor environment. However, when the carbodiimide compound described in Patent Document 1 is used, it may continue to exhibit an acid scavenging function for a long time in a high temperature and high humidity environment. It was sometimes difficult. Furthermore, the solar cell encapsulant described in Patent Document 1 may have a reduced crosslinking efficiency during the production of the solar cell module, or yellowing may occur over time when the solar cell module is used.

  Therefore, the object of the present invention is to maintain the acid scavenging function over a long period of time in a high-temperature and high-humidity environment and in an environment exposed to ultraviolet rays for a long period of time, yellowing is suppressed, and transparency is high. It is providing the sealing material for solar cells which is excellent in crosslinking efficiency.

  Moreover, the objective of this invention is providing the solar cell module which the solar cell element was sealed with this solar cell sealing material which consists of this solar cell sealing material, and this solar cell sealing material.

（式中、Ｒ^１及びＲ^２は各々独立に、炭素数１〜１０のアルキル基である。）
で表され、
前記紫外線吸収剤が、ベンゾトリアゾール系紫外線吸収剤であり、
前記カルボジイミド化合物が、下記式（ＩＩ）

（式中、
Ｘは、下記式（ＩＩ−１）〜（ＩＩ−３）で表される２価の基または下記式（ＩＩ−４）で表される４価の基であり、
Ｘが２価のときｑは０で、Ｘが４価のときｑは１であり、
Ａｒ^１〜Ａｒ^４は、各々独立に芳香族基であり、これらは炭素数１〜６のアルキル基またはフェニル基で置換されていてもよい。）

（式中、ｎは１〜６の整数である。）

（式中、ｙ及びｚは各々独立に０〜３の整数である。）

（式中、Ｒ^３及びＲ^４は各々独立に、炭素数１〜６のアルキル基、フェニル基を表す。）

で表される環状カルボジイミド化合物であることを特徴とする太陽電池用封止材により達成される。 The above object is a solar cell encapsulant containing an ethylene-polar monomer copolymer, a crosslinking agent, an ultraviolet absorber, and a carbodiimide compound,
The crosslinking agent is represented by the following formula (I)

(In the formula, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms.)
Represented by
The ultraviolet absorber is a benzotriazole ultraviolet absorber,
The carbodiimide compound is represented by the following formula (II)

(Where
X is a divalent group represented by the following formulas (II-1) to (II-3) or a tetravalent group represented by the following formula (II-4);
Q is 0 when X is divalent, q is 1 when X is tetravalent,
Ar ^{1 to} Ar ⁴ are each independently an aromatic group, and these may be substituted with an alkyl group having 1 to 6 carbon atoms or a phenyl group. )

(In the formula, n is an integer of 1 to 6.)

(In the formula, y and z are each independently an integer of 0 to 3.)

(In the formula, R ³ and R ⁴ each independently represents an alkyl group having 1 to 6 carbon atoms or a phenyl group.)

It achieves by the sealing material for solar cells characterized by being the cyclic carbodiimide compound represented by these.

  The linear carbodiimide compound described in Patent Document 1 is easily decomposed due to its low decomposition temperature, so that the acid scavenging function is lowered with time, and the low molecular weight compound generated by the decomposition causes crosslinking inhibition. It was. The carbodiimide compound used in the present invention has a cyclic structure and is not easily decomposed and stable. In addition to being able to continue to exhibit the acid-trapping function of the cyclic carbodiimide compound over a long period of time, the carbodiimide compound is also sealed for solar cells. It does not cause cross-linking inhibition of the stop material. In addition, the present inventors have found that a solar cell encapsulant that is excellent in prevention of yellowing and transparency can be obtained by using this cyclic carbodiimide compound in combination with the above specific crosslinking agent and ultraviolet absorber. .

  Preferred embodiments of the present invention are as follows.

（式中、Ｒ^５及びＲ^６は各々独立に、フェニル基で置換されていてもよい炭素数１〜１５のアルキル基である。）
で表される。 (1) The ultraviolet absorber is represented by the following formula (III)

(In the formula, R ⁵ and R ⁶ are each independently an alkyl group having 1 to 15 carbon atoms which may be substituted with a phenyl group.)
It is represented by

(2) In the formula (II), Ar ^{1 to} Ar ⁴ are each independently an orthophenylene group or 1,2-naphthalene-diyl optionally substituted with an alkyl group having 1 to 6 carbon atoms or a phenyl group. It is a group.

  (3) The cross-linking agent is t-butylperoxy-2-ethylhexyl monocarbonate.

  (4) The carbodiimide compound has an average particle size of 1 to 100 μm.

  (5) Content of the said crosslinking agent is 0.1-0.5 mass part with respect to 100 mass parts of said ethylene-polar monomer copolymers.

  (6) The said ultraviolet absorber is 0.1-0.5 mass part with respect to 100 mass parts of said ethylene-polar monomer copolymers.

  (7) The said carbodiimide compound is 0.01-1 mass part with respect to 100 mass parts of said ethylene-polar monomer copolymers.

  Further, the object is to have a solar cell encapsulant made of the solar cell encapsulant, a front surface side protective member, a solar cell element and a back surface side protective member, and the solar cell element is sealed for this solar cell. This is achieved by a solar cell module sealed with a stopper.

  The solar cell encapsulant according to the present invention is capable of maintaining the acid scavenging function for a long period of time even under a high temperature and high humidity environment and in an environment exposed to ultraviolet rays for a long period of time. And excellent cross-linking efficiency. Therefore, a solar cell that can sufficiently maintain power generation efficiency over a long period can also produce joules.

It is a schematic sectional drawing of a common solar cell module.

  As described above, the solar cell encapsulant of the present invention includes an ethylene-polar monomer copolymer, a specific crosslinking agent, an ultraviolet absorber, and a carbodiimide compound. Each will be described in detail below.

[Ethylene-polar monomer copolymer]
Examples of the polar monomer of the ethylene-polar monomer copolymer include an unsaturated carboxylic acid, a salt thereof, an ester thereof, an amide thereof, a vinyl ester, and carbon monoxide. More specifically, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, fumaric acid, itaconic acid, monomethyl maleate, monoethyl maleate, maleic anhydride, itaconic anhydride, lithium of these unsaturated carboxylic acids, sodium, Salts of monovalent metals such as potassium, salts of polyvalent metals such as magnesium, calcium and zinc, methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutyl acrylate, n-butyl acrylate, isooctyl acrylate, methacrylic acid Examples include unsaturated carboxylic acid esters such as methyl, ethyl methacrylate, isobutyl methacrylate, and dimethyl maleate, vinyl esters such as vinyl acetate and vinyl propionate, carbon monoxide, sulfur dioxide, etc. be able to.

  More specifically, as the ethylene-polar monomer copolymer, ethylene-acrylic acid copolymer, ethylene-unsaturated carboxylic acid copolymer such as ethylene-methacrylic acid copolymer, the ethylene-unsaturated carboxylic acid Ionomer in which some or all of carboxyl groups of copolymer are neutralized with the above metal, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene- Isobutyl acrylate copolymer, ethylene-unsaturated carboxylic acid ester copolymer such as ethylene-n-butyl acrylate copolymer, ethylene-isobutyl acrylate-methacrylic acid copolymer, ethylene-n-butyl acrylate -Ethylene-unsaturated carboxylic acid ester-unsaturated carboxylic acid such as methacrylic acid copolymer Some or all of the copolymer and its carboxyl group ionomer neutralized with the metal, ethylene - can be exemplified vinyl ester copolymer as a typical example - ethylene such as vinyl acetate copolymer.

  As the ethylene-polar monomer copolymer, it is preferable to use a copolymer having a melt flow rate defined by JIS K7210 of 35 g / 10 min or less, particularly 3 to 6 g / 10 min. By using an ethylene-polar monomer copolymer having such a melt flow rate, a solar cell encapsulant having excellent processability can be obtained. In the present invention, the value of the melt flow rate (MFR) is measured based on conditions of 190 ° C. and a load of 21.18 N according to JIS K7210.

  As the ethylene-polar monomer copolymer, it is preferable to use an ethylene-vinyl acetate copolymer (EVA) excellent in adhesiveness and transparency. The content of vinyl acetate in EVA is preferably 20 to 35% by mass, more preferably 22 to 32% by mass, and particularly preferably 24 to 30% by mass. If the vinyl acetate content is less than 20% by mass, the sealing material may not be sufficiently transparent, and if it exceeds 35% by mass, carboxylic acid or alcohol may be easily generated and cause yellowing. .

  In the present invention, in addition to the ethylene-polar monomer copolymer, polyolefin such as polyethylene, ethylene-α-olefin copolymer, polyvinyl acetal resin (for example, polyvinyl formal, polyvinyl butyral (PVB resin), modified PVB) ) And the like may be contained.

[Carbodiimide compound]
The carbodiimide compound used in the present invention is a compound represented by the following formula (II).

In formula (II), Ar ^{1 to} Ar ⁴ are each independently an aromatic group, and these may be substituted with an alkyl group having 1 to 6 carbon atoms or a phenyl group. Ar ^{1 to} Ar ⁴ are each independently preferably an orthophenylene group or a 1,2-naphthalene-diyl group which may be substituted with an alkyl group having 1 to 6 carbon atoms or a phenyl group.

  As an alkyl group having 1 to 6 carbon atoms, methyl group, ethyl group, n-propyl group, sec-propyl group, iso-propyl group, n-butyl group, tert-butyl group, sec-butyl group, iso-butyl group N-pentyl group, sec-pentyl group, iso-pentyl group, n-hexyl group, sec-hexyl group, iso-hexyl group and the like. The presence of such an alkyl group having 1 to 6 carbon atoms or a phenyl group can be expected to increase the compatibility with the polymer and enhance the action of the cyclic carbodiimide compound. Moreover, the effect which suppresses the volatility of a cyclic carbodiimide compound can be anticipated.

  In the formula (II), X is a divalent or tetravalent group. Q is 0 when X is divalent and q is 1 when X is tetravalent.

  When q is 0, X is preferably a divalent group of the following formula (II-1).

  In formula (II-1), n is an integer of 1-6. As the group (II-1), a methylene group, an ethylene group, a 1,3-propylene group, a 1,4-butylene group, a 1,5-pentane group, and a 1,6-hexane group are preferable. In the 1,3-propylene group, 1,4-butylene group, 1,5-pentane group, and 1,6-hexane group, carbons not directly bonded to oxygen are an alkyl group having 1 to 6 carbon atoms and a phenyl group, respectively. It may be substituted with at least one selected from the group of As an alkyl group having 1 to 6 carbon atoms, methyl group, ethyl group, n-propyl group, sec-propyl group, iso-propyl group, n-butyl group, tert-butyl group, sec-butyl group, isobutyl group , N-pentyl group, sec-pentyl group, iso-pentyl group, n-hexyl group, sec-hexyl group, iso-hexyl group and the like.

  When q is 0, X is preferably a group of the following formula (II-2).

  In formula (II-2), y and z are each independently an integer of 0 to 3. A methylene group of m = 0 represents a single bond. When X has a 1,3-phenylene group, there is an advantage that the stability of the cyclic carbodiimide compound is further increased.

  When q is 0, X is preferably a group of the following formula (II-3).

In formula (II-3), R ³ and R ⁴ are each independently an alkyl group having 1 to 6 carbon atoms or a phenyl group. As an alkyl group having 1 to 6 carbon atoms, methyl group, ethyl group, n-propyl group, sec-propyl group, iso-propyl group, n-butyl group, tert-butyl group, sec-butyl group, iso-butyl group , N-pentyl group, sec-pentyl group, iso-pentyl group, n-hexyl group, sec-hexyl group, iso-hexyl group and the like.

  When q is 1, X is preferably a tetravalent group of the following formula (II-4).

  The number of atoms in the cyclic structure of the cyclic carbodiimide compound is preferably 8 to 50, more preferably 10 to 30, further preferably 10 to 20, and particularly preferably 10 to 115. Here, the number of atoms in the ring structure means the number of atoms that directly constitute the ring structure, and is, for example, 8 for an 8-membered ring and 50 for a 50-membered ring. This is because if the number of atoms in the cyclic structure is smaller than 8, the stability of the cyclic carbodiimide compound is lowered, and it may be difficult to store and use. From the viewpoint of reactivity, there is no particular restriction on the upper limit of the number of ring members, but cyclic carbodiimide compounds having more than 50 atoms are difficult to synthesize, and the cost may increase significantly. From this viewpoint, the number of atoms in the cyclic structure is preferably 10-30, more preferably 10-20, and particularly preferably 10-15.

  The molecular weight of the cyclic carbodiimide compound is preferably 100 to 1,000. If it is lower than 100, the structural stability and volatility of the cyclic carbodiimide compound may be problematic. On the other hand, if it is higher than 1,000, synthesis in a diluting system is required for the production of cyclic carbodiimide, and the yield is lowered, which may cause a problem in cost. From this viewpoint, it is more preferably 100 to 750, and further preferably 250 to 750.

  The cyclic carbodiimide compound of the present invention has one carbodiimide group in one ring. When two or more carbodiimide groups are contained in one ring, an isocyanate compound is generated, which may cause a bad odor.

  The following compounds are illustrated as a cyclic carbodiimide compound of this invention.

  The content of the cyclic carbodiimide compound is generally 0.01 to 1 part by mass, preferably 0.05 to 0.75 part by mass, more preferably 0.1 to 100 parts by mass of the ethylene-polar monomer copolymer. It is -0.3 mass part. If it is this range, it can be set as the sealing material for solar cells which not only can ensure a sufficient acid capture | acquisition function but is excellent in crosslinking property and transparency.

  The average particle diameter of the cyclic carbodiimide compound is generally 1 to 200 μm, preferably 1 to 100 μm, and more preferably 20 to 100 μm. By setting it as this range, it can be set as the sealing material for solar cells which is further excellent in transparency. The average particle diameter means a median diameter determined by a laser diffraction / scattering particle size distribution measuring method.

  The said cyclic carbodiimide compound can be manufactured by a conventionally well-known method. For example, a method of producing from an amine body via an isocyanate body, a method of producing from an amine body via an isothiocyanate body, a method of producing from a carboxylic acid body via an isocyanate body, and the like can be mentioned. Moreover, it can manufacture also by the method as described in international publication 2010/072111.

[Crosslinking agent]
The crosslinking agent used in the present invention is an organic peroxide represented by the following formula (I).

（式中、Ｒ^１及びＲ^２は各々独立に、炭素数１〜１０のアルキル基である。）

(In the formula, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms.)

The alkyl group for R ¹ and R ² may be linear or branched. R ¹ is preferably an alkyl group having 1 to 6 carbon atoms, preferably a methyl group, an ethyl group, a propyl group, a propyl group, a butyl group, a pentyl group or a hexyl group, particularly preferably a t-butyl group.

R ² is preferably an alkyl group having 5 to 10 carbon atoms, particularly 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1-ethylpentyl group, 2-ethylpentyl group, 3-methylpentyl group. 1-methylhexyl group, 2-methylhexyl group, 3-methylhexyl group, 1-ethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group are preferable, and 2-ethylhexyl group is more preferable.

  The cross-linking agent represented by formula (I) is particularly preferably t-butylperoxy-2-ethylhexyl monocarbonate.

  By using the said crosslinking agent, it can be set as the sealing material for solar cells which is hard to produce yellowing compared with another crosslinking agent. The content of the crosslinking agent in the solar cell encapsulant is generally 0.1 to 2.0 parts by mass, preferably 0.2 to 1.5 parts by mass, with respect to 100 parts by mass of the ethylene-polar monomer copolymer. Part. If the amount is less than this range, the crosslinking efficiency may be lowered. If the amount is more than this range, there may be an increase in by-products that cause yellowing.

[Ultraviolet absorber]
As described above, the ultraviolet absorber used in the present invention is a benzotriazole ultraviolet absorber. A benzotriazole-based ultraviolet absorber refers to an ultraviolet absorber having a benzotriazole group. Preferably, a benzotriazole-based ultraviolet absorber represented by the following formula (III) can be used.

In formula (III), R ⁵ and R ⁶ are each independently an alkyl group having 1 to 15 carbon atoms which may be substituted with a phenyl group.

  Examples of the alkyl group having 1 to 15 carbon atoms which may be substituted with a phenyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, Examples thereof include an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, and a group in which part of hydrogen atoms of these groups is substituted with a phenyl group.

In the formula (III), a compound in which R ¹ and R ² are both 2-phenylpropyl groups, or a compound in which R ¹ is an n-dodecyl group and R ² is a methyl group is particularly preferable.

  By using a benzotriazole type ultraviolet absorber, it can be set as the sealing material for solar cells which is hard to produce yellowing compared with another ultraviolet absorber. The content of the ultraviolet absorber is generally 0.1 to 0.5 parts by mass, preferably 0.1 to 0.3 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer.

  About content of the carbodiimide compound mentioned above, a crosslinking agent, and an ultraviolet absorber, it is preferable that mass ratio of a crosslinking agent / carbodiimide compound is generally 7-0.4, especially 1-3.5. Moreover, it is preferable that mass ratio of an ultraviolet absorber / carbodiimide compound is generally 0.2 to 4, particularly 0.5 to 2. If it is in the range of these mass ratios, it is possible to obtain further excellent effects in terms of durability, yellowing prevention, and crosslinkability.

  In the present invention, since the carbodiimide compound has a cyclic structure, the carbodiimide compound is not easily decomposed and stable, and not only can continue to exhibit an acid scavenging function for a long time, but also inhibits crosslinking of a solar cell sealing material. It does not cause. Moreover, the sealing material for solar cells which is excellent in prevention of yellowing and transparency can be obtained by using this cyclic carbodiimide compound in combination with the specific crosslinking agent and ultraviolet absorber.

  The sealing material for solar cells of this invention may contain the following other components other than the crosslinking agent mentioned above, a ultraviolet absorber, and a carbodiimide compound.

[Crosslinking aid]
It is preferable that the sealing material for solar cells of this invention contains the crosslinking adjuvant further. The crosslinking aid can improve the gel fraction of the ethylene-polar monomer copolymer and improve the adhesion and weather resistance of the solar cell encapsulant.

  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). And monofunctional or bifunctional crosslinking aids. Of these, triallyl cyanurate and triallyl isocyanurate are preferable, and triallyl isocyanurate is particularly preferable.

  The content of the crosslinking aid is usually 0.1 to 5 parts by mass, preferably 0.1 to 3 parts by mass, and particularly preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. Used at 5 parts by weight. Thereby, the sealing material which the hardness after bridge | crosslinking improved further is obtained.

[Adhesion improver]
The solar cell encapsulant of the present invention may further contain an adhesion improver. As the adhesion improver, a silane coupling agent can be used. Thereby, it can be set as the sealing material for solar cells which has the further outstanding adhesive force. Silane coupling agents include γ-chloropropyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltri Methoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- Mention may be made of β- (aminoethyl) -γ-aminopropyltrimethoxysilane. These silane coupling agents may be used alone or in combination of two or more. Of these, γ-methacryloxypropyltrimethoxysilane is particularly preferred.

  The content of the silane coupling agent in the solar cell encapsulant of the present invention is 5 parts by mass or less, preferably 0.1 to 2 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. preferable.

[Others]
The sealing material 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.

[Manufacture of sealing materials for solar cells]
What is necessary is just to perform according to a well-known method in order to form the sealing material for solar cells. For example, the solar cell encapsulant of the present invention containing 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. The thickness of the solar cell encapsulant of the present invention is not particularly limited, but is 0.05 to 2 mm, preferably 0.3 to 0.8 mm, and more preferably 0.4 to 0.7 mm. The solar cell encapsulant may have a multilayer structure or a single layer structure.

[Solar cell module]
The structure of the solar cell module of the present invention is not particularly limited as long as it includes a structure in which solar cell elements are sealed using the solar cell sealing material of the present invention. For example, a solar cell element (single crystal or polycrystalline silicon cell or the like) is formed by crosslinking and integrating the solar cell sealing material of the present invention between the front surface side transparent protective member and the back surface side protective member. Examples include a sealed structure.

  In the present invention, the side of the solar cell element irradiated with light (front side) is referred to as “front side”, and the side opposite to the light receiving surface of the solar cell element is referred to as “back side”.

  In the solar cell module, in order to sufficiently seal the solar cell element, for example, as shown in FIG. 1, the front surface side transparent protective member 11, the front surface side sealing material 13A, the solar cell element 14, the back surface side sealing material 13B. And the back surface side protection member 12 is laminated | stacked, and a sealing material should just be bridge | crosslinked and hardened | cured according to conventional methods, such as heating and pressurization.

In order to heat and pressurize, the laminated body which laminated | stacked each member is 135-180 degreeC with a vacuum laminator, Furthermore, 140-180 degreeC, Deaeration time 0.1-5 minutes, Press pressure 0.1-1. What is necessary is just to heat-press in 5 kg / cm < ² > and press time for 5 to 15 minutes.

  By crosslinking the ethylene-polar monomer copolymer contained in the front surface side sealing material 13A and the back surface side sealing material 13B during this heating and pressurization, the front surface side sealing material 13A and the back surface side sealing material 13B are interposed. Thus, the solar cell element 14 can be sealed by integrating the front surface side transparent protective member 11, the back surface side transparent member 12, and the solar cell element 14. The solar cell elements 14 are electrically connected to each other by connection tabs 15.

  The solar cell encapsulant of the present invention is not limited to a solar cell module using a single crystal or polycrystalline silicon crystal solar cell as shown in FIG. It can also be used as a sealing material for thin film solar cell modules 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, a structure in which the battery sealing material and the back surface side protective member are laminated and bonded and integrated, on the surface side Laminated transparent protective member, bonded and integrated structure, or front side transparent protective member, front side sealing material, thin film solar cell element, back side sealing material, and back side protective member are laminated in this order, For example, a structure that is bonded and integrated. In addition, in this invention, a photovoltaic cell and a thin film solar cell element are named generically, and are called a solar cell element.

  The surface side transparent protective member 11 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.

  For the back side protection member 12, a plastic sheet such as polyethylene terephthalate (PET) or polyamide is preferably used. Further, a film obtained by laminating a fluorinated polyethylene sheet, in particular, a fluorinated polyethylene sheet / Al / fluorinated polyethylene sheet in this order in consideration of heat resistance and wet heat resistance. Further, a glass plate may be used.

  The cyclic carbodiimide used in the present invention also has a function of preventing hydrolysis of polyester such as PET. Therefore, when a polyester film such as PET is used as the back surface side protective member and the solar cell sealing material of the present invention is used as the back surface side sealing agent, the cyclic carbodiimide contained in the back surface side sealing material is on the back surface side. Since it comes into contact with the sealing material, it is possible to prevent deterioration of the polyester film as the back surface side protective member.

  In the present invention, after the solar cell encapsulant is crosslinked, a pressure cooker (PCT) test is conducted for 240 hours under an environmental condition of a temperature of 121 ° C., a relative humidity of 100% RH, and 2 atmospheres, and then the solar cell encapsulant is sealed. After taking out the stop material and weighing 0.5 g of a test piece and immersing it in 2 ml of acetone for 48 hours, the amount of free acetic acid contained in the acetone extract is generally 250 ppm or less, particularly 150 ppm or less. However, the acid scavenging function can be fully exhibited.

  In addition, the sealing material for solar cells of this invention has the characteristics in the sealing material used for the surface side and / or back surface side of a solar cell module (a thin film solar cell module is included). Therefore, members other than the sealing material such as the front surface side transparent protective member, the back surface side protective member, and the solar cell element may have the same configuration as that of a conventionally known solar cell module, and are not particularly limited.

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

[1] Production of solar cell encapsulant The materials shown in the following table were supplied to a roll mill and kneaded at 75 ° C. to obtain the solar cell encapsulant of the present invention. This composition was calendered at 70 ° C., allowed to cool, and then a sheet-shaped solar cell sealing material (thickness: 0.5 mm) was produced.

[2] Preparation of laminate for evaluation White plate glass (thickness: 3.2 mm), the above solar cell sealing material, white plate glass (thickness: 3.2 mm) are laminated in this order, and the resulting laminate is vacuum vacuum laminator. The laminate for evaluation was produced by using and crimping | bonding at 90 degreeC for vacuum time 2 minutes, press time 9 minutes, and heating for 30 minutes in 155 degreeC oven for 30 minutes.

[3] Fabrication of solar cell module A laminated body was obtained by laminating white glass (thickness: 3.2 mm), the solar cell encapsulant, the solar cell, the solar cell encapsulant, and the back sheet in this order. Thereafter, this laminate was pressure-bonded at 90 ° C. with a vacuum laminator at a vacuum time of 2 minutes and a press time of 8 minutes, and then crosslinked and heated in an oven at 155 ° C. for 30 minutes to obtain a solar cell module. .

[4] Light transmittance For the evaluation laminate, a spectrophotometer (manufactured by Hitachi, Ltd., U-4100) is used to perform spectrum measurement at 400 to 1000 nm at a plurality of locations within the plane, and the average value is measured for light transmission. Rate (%).

[5] Haze The haze value (%) of the laminate for evaluation was measured using a haze meter (NDH 2000 model, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K 7105 (2000).

[6] Amount of acetic acid generated The laminated body for evaluation was subjected to a pressure cooker (PCT) test for 240 hours under an environmental condition of a temperature of 121 ° C., a relative humidity of 100% RH, and 2 atmospheres, and the amount of acetic acid generated after the test was measured. The amount of acetic acid generated is measured by taking out the solar cell encapsulant from the laminate after the test, weighing 0.5 g of a test piece, immersing it in 2 ml of acetone for 48 hours, and then adding it to the acetone extract. The amount of acetic acid (ppm) was measured using a gas chromatograph.

[7] Yellowness (YI)
Using the s-UV irradiation tester (eye super UV tester (manufactured by Iwasaki Electric Co., Ltd.) and a metal halide lamp as a light source, the evaluation laminate was irradiated with ultraviolet rays at an irradiation intensity of 1000 W / m ² for 200 hours. Yellowness (YI) after irradiation was measured according to JIS-K-7105 (1981) using a color difference meter (color computer SM-5-IS-2B, manufactured by Suga Test Instruments Co., Ltd.).

[8] Cure torque 5 g of the solar cell encapsulant produced in [1] is weighed and heated at a temperature of 150 ° C., and the torque value after 15 minutes is read with a curast meter (manufactured by Nippon Synthetic Rubber). Was measured.

[9] Power generation efficiency maintenance rate The solar cell module was subjected to a pressure cooker (PCT) test for 160 hours under an environmental condition of a temperature of 121 ° C., a relative humidity of 100% RH, and 2 atmospheres. Before and after the test, the maximum output (P _max ) of the solar cell module was measured, and the power generation efficiency maintenance ratio ((post test P _max / pre test P _max ) × 100 (%)) was calculated.

  The results are shown in the table below. The details of each material used are as follows.

-Polymer: EVA (vinyl acetate content 26 mass%)
Crosslinking agent 1: t-butylperoxy-2-ethylhexyl monocarbonate Crosslinking agent 2: 2,5-dimethyl-2,5-di (t-butylperoxy) hexane Crosslinking aid: triallyl isocyanurate Silane coupling agent: γ-methacryloxypropyltrimethoxysilane / ultraviolet absorber 1: Compound in which R ¹ is an n-dodecyl group and R ² is a methyl group in the above formula (III) (TINUV 571 manufactured by BASF)
UV absorber 2: A compound in which R ¹ and R ² are both 2-phenylpropyl groups in the above formula (III) (TINUVIN 234 manufactured by BASF)
UV absorber 3: 2-hydroxy-4-n-octoxybenzophenone UV absorber 4: ubinal 3049
Carbodiimide compound 1-1: “Cyclic carbodiimide (TCC)” manufactured by Teijin Limited (average particle size 50 μm)
Carbodiimide compound 1-2: “Cyclic carbodiimide (TCC)” manufactured by Teijin Limited (average particle size 100 μm)
Carbodiimide compound 1-3: “Cyclic carbodiimide (TCC)” manufactured by Teijin Limited (average particle size 180 μm)
Carbodiimide compound 1-4: “Cyclic carbodiimide (TCC)” manufactured by Teijin Limited (average particle size 20 μm)
Carbodiimide compounds 1-1 to 1-4 are compounds of the above formula (II).
-Carbodiimide compound 2: Linear carbodiimide-Acid acceptor: Magnesium hydroxide

11 Front-side transparent protective member 12 Back-side protective member 13A Front-side sealing material 13B Back-side sealing material 14 Solar cell element 15 Connection tab

Claims (9)

A solar cell encapsulant comprising an ethylene-polar monomer copolymer, a crosslinking agent, an ultraviolet absorber, and a carbodiimide compound,
The crosslinking agent is represented by the following formula (I)

(In the formula, R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms.)
Represented by
The ultraviolet absorber is a benzotriazole ultraviolet absorber,
The carbodiimide compound is represented by the following formula (II)

(Where
X is a divalent group represented by the following formulas (II-1) to (II-3) or a tetravalent group represented by the following formula (II-4);
Q is 0 when X is divalent, q is 1 when X is tetravalent,
Ar ^{1 to} Ar ⁴ are each independently an aromatic group, and these may be substituted with an alkyl group having 1 to 6 carbon atoms or a phenyl group. )

(In the formula, n is an integer of 1 to 6.)

(In the formula, y and z are each independently an integer of 0 to 3.)

(In the formula, R ³ and R ⁴ each independently represents an alkyl group having 1 to 6 carbon atoms or a phenyl group.)

It is a cyclic carbodiimide compound represented by these, The sealing material for solar cells characterized by the above-mentioned. The ultraviolet absorber is represented by the following formula (III)

(In the formula, R ⁵ and R ⁶ are each independently an alkyl group having 1 to 15 carbon atoms which may be substituted with a phenyl group.)
The sealing material for solar cells of Claim 1 represented by these. In the formula (II), Ar ^{1 to} Ar ⁴ are each independently an orthophenylene group or a 1,2-naphthalene-diyl group which may be substituted with an alkyl group having 1 to 6 carbon atoms or a phenyl group. The sealing material for solar cells of Claim 1 or 2.   The solar cell sealing material according to any one of claims 1 to 3, wherein the crosslinking agent is t-butylperoxy-2-ethylhexyl monocarbonate.   The sealing material for solar cells of any one of Claims 1-4 whose average particle diameter of the said carbodiimide compound is 1-100 micrometers.   The solar cell according to any one of claims 1 to 5, wherein a content of the crosslinking agent is 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. Sealing material.   The solar cell seal according to any one of claims 1 to 6, wherein the ultraviolet absorbent is 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. Stop material.   The solar cell sealing material according to any one of claims 1 to 7, wherein the carbodiimide compound is 0.01 to 1 part by mass with respect to 100 parts by mass of the ethylene-polar monomer copolymer. A solar cell module having a front surface side transparent protective member, a solar cell element and a back surface side protective member,
The said solar cell element is sealed with the sealing material for solar cells of any one of Claims 1-8, The solar cell module characterized by the above-mentioned.

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