NOVELTY - The process comprises providing a first material constituted of discrete elements such as granules of polyester having an average molecular weight of 18000-40000 and an intrinsic viscosity of 0.6-1.2 dl/g, drying the first material, optionally mixing the raw materials to promote homogenization, extruding the first material through a die for forming a monolayer or a multilayer and the rapidly cooling, optionally coating a side of the film to impart specific properties to the film, biaxially stretching the film according to a draw ratio and a draw temperature to obtain a crystalline phase.    USE - The process is useful for fabricating a polyester film such as biaxially oriented polyethylene terephthalate film comprising crystallites, where the film is useful for manufacturing a panel or a photovoltaic cell (all claimed).    ADVANTAGE - The process enables efficient fabrication of the polyester film with improved hydrolysis resistance and performance and excellent thermal and dimensional stability and durability thus enhancing the operational efficiency of the photovoltaic cell.    DETAILED DESCRIPTION - The process comprises providing a first material constituted of discrete elements such as granules of polyester having an average molecular weight of 18000-40000 and an intrinsic viscosity of 0.6-1.2 dL/g, drying the first material, optionally mixing the raw materials to promote homogenization, extruding the first material through a die for forming a monolayer or a multilayer and the rapidly cooling, optionally coating a side of the film to impart specific properties to the film, biaxially stretching the film according to a draw ratio and a draw temperature to obtain a crystalline phase, thermosetting the film at a temperature of 180-250 degrees C, performing transverse relaxation of the film, winding the film and then performing cutting, coating, vacuum coating, annealing and/or UV, plasma or corona treatment, controlling the hydrolysis resistance and/or performance of the film, and increasing the thickness of crystallites to increase adhesion of film. The parameters of the steps are selected to control a thickness of the film or to increase a thickness of the film. The longitudinal stretching is performed at a draw ratio of 2-6, 2.5-5 or 2.8-4.5 and a draw temperature of 70-150 degrees C, 85-140 degrees C or 90-135 degrees C. The transverse stretching is performed at a draw ratio of 2-6, 3.5-5 and 3.5-4.5 and at a draw temperature of 95-150 degrees C, 105-145 degrees C and 110-140 degrees C. During the thermosetting process of the film, the rise in temperature is 4-14 degrees C/second. An INDEPENDENT CLAIM is included for a biaxially oriented polyester film.