Durability of acrylic: Stress and response characterization of materials for photovoltaics

In the development of materials for enhanced photovoltaic (PV) performance, it is critical to have quantitative knowledge of the initial performance, as well as the performance of these materials over the required 25-year lifetime of the PV system. Lifetime and degradation science (L&DS) allows for the development of new metrology and metrics, coupled to degradation mechanisms and rates. All PV systems are exposed to multifactor and cyclic environmental stressors including solar irradiance, temperature and humidity which can cause degradation over time. A stress and response framework is being used to link the intensity and accumulation of damaging environmental stressors to changes in materials properties. This allows for determination of appropriate techniques for accelerating environmental stressors, and also allows determination of the effects of stressors at multiple service conditions. Induced absorbance to dose (IAD), a new metric being developed for solar radiation durability studies of solar and environmentally exposed materials, is defined as the rate of photodarkening or photobleaching of a material as a function of total absorbed solar radiation dose. Yellowing rates, the change in ASTM E313 Yellowness Index as a function of absorbed dose, of two grades of acrylic poly(methyl-methacrylate) (PMMA) have been reported. IAD spectra for two formulations of acrylic PMMA are reported.