This study concerns the photodegradation and stabilization of a solar cell encapsulating material made from ethylene/vinyl acetate copolymer (EVA). EVA was compounded with various additives in a twin-screw extruder. After that, the extruded film was cured in a hydraulic compression mold before being exposed to ultraviolet (UV) radiation at an ambient temperature for 800 h. The thermal stability of the material was also studied through the aging of the sample at 90 degrees C for 2000 h. The tensile strength of the unstabilized EVA decreased only slightly after the thermal aging. On the other hand, the strength of the material decreased noticeably after the UV irradiation. Fourier transform infrared spectra of various EVA films revealed that there was no deacetylation occurring after the UV irradiation. However, results from the swelling test and swollen-state NMR suggested that the polymer degraded via a chain-scission mechanism. After compounding with some antioxidants, most of the EVA films scarcely degraded after the UV irradiation, with the exception of the EVA compounded with a combination of the aromatic phosphate compound (0.1 phr) and hindered amine light stabilizer (0.1 phr). The results are discussed in light of an antagonism effect that occurred because of the aforementioned combination. (C) 2007 Wiley Periodicals, Inc.