Degradation of Silicone Encapsulants in CPV Optics

Concentrator photovoltaic (CPV) modules operate in extreme conditions, which poses a unique materials challenge for guaranteeing operational lifetimes of at least 25 years. The encapsulants used in the optical elements are critically susceptible to environmental degradation during operation. We studied the effects of weatherings on adhesion using an outdoor concentrator operating in excess of 1100 times the AM1.5 direct irradiance and in environmental chambers with broadband ultraviolet (UV) irradiation combined with controlled temperature and humidity. We observed a sharp initial increase in adhesion energy followed by a gradual decrease in adhesion as a result of both outdoor concentrator exposure and indoor UV weathering. We characterized changes in mechanical properties and chemical structures using XPS, FTIR, and DMA to understand the fundamental connection between mechanical strength and the degradation of the silicone encapsulant.