NOVELTY - The backsheet (100) comprises a nanocomposite layer (110) comprising a polymeric matrix including a polymer consisting of polyethylene terephthalate and silicate nanoparticles dispersed in the polymeric matrix, a first polymeric layer (120) disposed above the nanocomposite layer, a second polymeric layer (130) disposed below the nanocomposite layer, a first adhesive layer disposed between the first polymeric layer and the nanocomposite layer, and a second adhesive layer disposed between the second polymeric layer and the nanocomposite layer.    USE - The backsheet is useful for a photovoltaic module.    ADVANTAGE - The backsheet protects the photovoltaic module against environmental degradation.    DETAILED DESCRIPTION - The backsheet (100) comprises a nanocomposite layer (110) comprising a polymeric matrix including a polymer consisting of polyethylene terephthalate and silicate nanoparticles dispersed in the polymeric matrix, a first polymeric layer (120) disposed above the nanocomposite layer, a second polymeric layer (130) disposed below the nanocomposite layer, a first adhesive layer disposed between the first polymeric layer and the nanocomposite layer, and a second adhesive layer disposed between the second polymeric layer and the nanocomposite layer. Each of the silicate nanoparticles has a multi-layered structure that is intercalated with the polymer of the polymeric matrix, or the layers of the multi-layered structure are exfoliated. The silicate nanoparticles are made from a silicate clay consisting of montmorillonite, sepiolite, fluoromica and vermiculite. The silicate clay exists in a concentration of 0.5-20 wt.% of the nanocomposite layer. The silicate nanoparticles exists in a concentration of 1-10 wt.% of the nanocomposite layer. Each layer of the multi-layered structure has a length of 0.5-2 nm. The nanocomposite layer has a thickness of 10-100 mu m. The first polymeric layer is made of a polymer that is the same as the polymeric matrix, and has a thickness of 0.01-2 mm. The second polymeric layer is made of a fluorinated polymer, and has a thickness of 0.01-2 mm. The first and second adhesive layers have a thickness of 0.01-0.5 mm. The nanocomposite layer, the first polymeric layer and the second polymeric layer are transparent layers. An INDEPENDENT CLAIM is included for a photovoltaic module.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a backsheet.    Backsheet (100)    Nanocomposite layer (110)    First polymeric layer (120)    Second polymeric layer. (130)