An encapsulant film having a ratio (S a /S m) of 0.6 or more, of a peak area (S a) of silanol groups and amine groups in a wavenumber range of 3,100 cm -1 to 3,600 cm -1 to a peak area (S m) of methylene groups in a wavenumber range of 705 cm -1 to 735 cm -1, as measured by FT-IR using an attenuated total reflection method, wherein the encapsulant film comprises a copolymer comprising: a main chain comprising a polymerization unit of an olefin-based monomer; and a branched chain bound to the main chain and represented by the following Formula 1; and a branched chain bound to the main chain and represented by the following Formula 2; wherein an unsaturated silane and an aminosilane compound engrafted to the main chain, and the aminosilane compound is included in an amount of 1 to 40 parts by weight with respect to 100 parts by weight of the silane compound in the copolymer: [Formula 1] -SiR 1 1 R 2 R 3 wherein R 1 and R 2 each independently represent a halogen, an amine group, -R 4 R 5, or -R 5 bound to a silicon atom; R 4 represents oxygen, or a sulfur atom; R 5 represents hydrogen, an alkyl group, an aryl group, an aralkyl group, or an acyl group; 1 is an integer of 1 or 2; R 3 represents -OSiR 6 m R 7 (2-m) R 8 bound to a silicon atom; R 6 and R 7 each independently represent a halogen, an amine group, -R 9 R 10, or -R 10 bound to a silicon atom; R 9 represents oxygen, or a sulfur atom; R 10 represents hydrogen, an alkyl group, an aryl group, an aralkyl group, or an acyl group; R 8 represents -(CH 2) n NR 11 R 12 bound to a silicon atom; R 11 and R 12 each independently represent a halogen or R 13 NH 2 bound to a silicon atom; R 13 represents alkylene group; m is an integer of 1 or 2; and n is an integer greater than or equal to 0; [Formula 2] -SiR 14 o R 15 (3-o) wherein R 14 and R 15 each independently represent a halogen, an amine group, - R 16 R 17, or -R 17 bound to a silicon atom; R 16 represents oxygen, or a sulfur atom; R 17 represents hydrogen, an alkyl group, an aryl group, an aralkyl group, or an acyl group; and o is an integer ranging from 1 to 3. a main chain comprising a polymerization unit of an olefin-based monomer; and a branched chain bound to the main chain and represented by the following Formula 1; and a branched chain bound to the main chain and represented by the following Formula 2; wherein R 1 and R 2 each independently represent a halogen, an amine group, -R 4 R 5, or -R 5 bound to a silicon atom; R 4 represents oxygen, or a sulfur atom; R 5 represents hydrogen, an alkyl group, an aryl group, an aralkyl group, or an acyl group; 1 is an integer of 1 or 2; R 3 represents -OSiR 6 m R 7 (2-m) R 8 bound to a silicon atom; R 6 and R 7 each independently represent a halogen, an amine group, -R 9 R 10, or -R 10 bound to a silicon atom; R 9 represents oxygen, or a sulfur atom; R 10 represents hydrogen, an alkyl group, an aryl group, an aralkyl group, or an acyl group; R 8 represents -(CH 2) n NR 11 R 12 bound to a silicon atom; R 11 and R 12 each independently represent a halogen or R 13 NH 2 bound to a silicon atom; R 13 represents alkylene group; m is an integer of 1 or 2; and wherein R 14 and R 15 each independently represent a halogen, an amine group, - R 16 R 17, or -R 17 bound to a silicon atom; R 16 represents oxygen, or a sulfur atom; R 17 represents hydrogen, an alkyl group, an aryl group, an aralkyl group, or an acyl group; and