Abstract: This disclosure generally relates to films capable of use in photovoltaic modules, to films, to methods of use and manufacture of these films, and to photovoltaic cells and/or modules including these films. One exemplary embodiment of such a film is a barrier layer having a moisture vapor transmission rate of less than 3.0 g/m2-day, wherein the barrier layer includes a polyethylene terephthalate having an apparent crystal size of less than 65 angstroms. Another exemplary embodiment of such a film is a multilayer film for use as a backsheet in a photovoltaic module including: a first layer including a fluoropolymer; a second layer including a polyethylene terephthalate having an apparent crystal size of less than 65 angstroms; and a third layer including an olefinic polymer. The first layer and the third layer are bonded to opposing major surfaces of the second layer.