Encapsulating material for solar cell
An encapsulating material for solar cell containing a laminated adhesive and heat resistant layer (A) and a buffering layer (B), wherein a difference in flexural modulus between the heat resistant layer (A) and the buffering layer (B) is at least 30 MPa or more, is provided. The adhesive and heat resistant layer (A) is preferably an olefin polymer (a) having a melting point (according to JIS K7121) of 75° C. or higher and having a storage elastic modulus at 150° C. of 10 3 Pa or more and the buffering layer (B) is preferably an olefin polymer (d) having a stiffness of 100 MPa or less. The encapsulating material for solar cell can provide superior transparency, flexibility, heat resistance and adhesiveness and can remarkably improve production efficiency of a solar cell module even when no organic peroxide is used. The encapsulating material can also exhibit a performance capable of corresponding to the thickness reduction of the solar cell element even when an organic peroxide is used. A solar cell module containing the encapsulating material is also provided.
1. An encapsulating material for solar cell comprising an adhesive and heat resistant layer (A) and a buffering layer (B), wherein the adhesive and heat resistant layer (A) and the buffering layer (B) are laminated to form a two-layered laminate and a difference in stiffness between the adhesive and heat resistant layer (A) and the buffering layer (B) is at least 30 MPa or more,
wherein the adhesive and heat resistant layer (A) comprises an olefin polymer (a) having a melting point of 75° C. or higher and a storage elastic modulus at 150° C. of 10 3 Pa or more,
wherein the buffering layer (B) comprises an olefin polymer (d) having a stiffness of 100 MPa or less, which is selected from the group consisting of: (i) a resin composition (g) comprising 50 to 100 parts by weight of an amorphous α-olefin polymer (e) satisfying the following requirements (1) to (3):
(1) a content of polymerization unit based on α-olefin having 3 to 20 carbon atoms is 20 mole % or more;
(2) melting peak of melting based on differential scanning calorimeter is not substantially observed;
(3) Mw/Mn is 5 or less;
and 50 to 0 part by weight of a crystalline α-olefin polymer (f), wherein a total of both polymers (e) and (f) is 100 parts by weight,
and (ii) an ethylene-unsaturated carboxylate ester copolymer containing 10 to 30% by weight of unsaturated carboxylate ester unit having a melting point (T° C.) and a content (X mole %) of unsaturated carboxylate ester unit which satisfy the following formula:
−3.0 X+ 125≧ T≧− 3.0 X+ 109,
wherein the adhesive and heat resistant layer (A) is for contacting with a protective material, and the buffering layer (B) is for contacting with a solar cell element.
2. The encapsulating material for solar cell according to claim 1 , wherein a silane coupling agent is compounded in the olefin polymer (a).
3. The encapsulating material for solar cell according to claim 1 , wherein said olefin polymer (a) is an ethylene-polar monomer copolymer (b).
4. The encapsulating material for solar cell according to claim 3 , wherein the ethylene-polar monomer copolymer (b) is an ethylene-unsaturated carboxylic acid copolymer in which content of unsaturated carboxylic acid unit is 4% by weight or more or an ionomer thereof.
5. The encapsulating material for solar cell according to claim 1 , wherein the olefin polymer (a) is a crystalline α-olefin polymer (c).
6. The encapsulating material for solar cell according to claim 5 , wherein said α-olefin polymer (c) is a homopolymer or a copolymer of an α-olefin having 2 to 10 carbon atoms and a degree of crystallinity as measured by X-ray is 5% or more.
7. The encapsulating material for solar cell according to claim 5 , wherein said α-olefin polymer (c) is a random copolymer of propylene and other α-olefin.
8. The encapsulating material for solar cell according to claim 1 , wherein said olefin copolymer (d) is an olefin copolymer (d) containing a cross-linking agent.
9. The encapsulating material for solar cell according to claim 1 , wherein said olefin copolymer (d) is an olefin copolymer (d) containing a silane coupling agent.
10. The encapsulating material for solar cell according to claim 1 , wherein said material is a sheet.
11. A solar cell module obtainable by encapsulating a solar cell element with the encapsulating material for solar cell according to claim 1 in such manner that the adhesive and heat resistant layer (A) side is in contact with the protective material and the buffering layer (B) side is in contact with the solar cell element.
12. The solar cell module according to claim 11 , wherein an adhesive strength between the adhesive and heat resistant layer (A) and the protective material is 3 N/10 mm or more.
13. The encapsulating material for solar cell according to claim 1 , wherein the olefin polymer (a) is a low crystalline α-olefin copolymer comprising at least two α-olefin having 2 to 10 carbon atoms and a degree of crystallinity of 40% or less.