NOVELTY - A back membrane comprises fluorine-containing layer on its outer surface, and interlayer and ethylene-vinyl acetate copolymer layer on its inner surface. The fluorine-containing layer is a fluorine-containing layer compounded on polyester layer, or fluorine-containing paint applied to polyester layer. The fluorine-containing layer is formed using polytetrafluoroethylene, polyperfluoropropylene, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene-ethylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.    USE - Back membrane is used for solar-cell assembly (claimed).    ADVANTAGE - The back membrane has high insulation property, excellent separation property, packaging function, and reduced water-vapor transmissivity.    DETAILED DESCRIPTION - A back membrane comprises a fluorine-containing layer on outer surface, and an interlayer and an ethylene-vinyl acetate copolymer layer on inner surface. The interlayer is formed by co-extruding polyester layer, ethylene-vinyl alcohol copolymer layer, and adhesive layer. The fluorine-containing layer is a fluorine-containing layer compounded on the polyester layer, or fluorine-containing paint applied on the polyester layer. The fluorine-containing layer is formed using polytetrafluoroethylene, polyperfluoropropylene, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene-ethylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. The fluorine-containing paint is vinylidene fluoride paint, trifluorochloroethylene-alkyl vinyl ether copolymer, trifluorochloroethylene-alkyl vinyl ester copolymer, tetrafluoroethylene-alkyl vinyl ether copolymer, or tetrafluoroethylene-alkyl vinyl ester copolymer. The polyester material is polyethylene glycol terephthalate, polyethylene naphthalate, or polybutylene terephthalate. The ethylene content in the ethylene-vinyl alcohol copolymer is 30-50%. The adhesive layer material is polyhexamethylene sebacamide, polydodecanoyl hexamethylenediamine, polydiethyl succinate, or ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer layer is formed on the adhesive layer by curtain coating.