Ultra-violet degradation behavior of polymeric backsheets for photovoltaic modules

This study is designed to understand the process of ultra-violet (UV) degradation of polymeric backsheets that are widely used in PV modules. Commercial photovoltaic backsheets from four suppliers were UV-aged for up to 3000 h. The aged samples were tested using optical microscopy, scanning electron microscopy (SEM), color measurements, UV-Vis-NIR, Fourier transform infrared spectroscopy (FTIR), and dielectrical tests to study their microstructural, color, chemical and electrical properties. The color changes of the samples, as quantified by Yellowness Index (YI) and Delta E, were found to be in strong correlation with chemical changes observed by FTIR. A linear model was established between YI and the UV irradiation dosage, providing useful information for service life prediction of PV backsheets. Cracks started to form on the surfaces of three of the four samples after different periods of UV irradiation. The density and orientation of the cracks were found to be affected by degree of UV degradation and polymer chain alignment of the backsheets. Electrical properties were not significantly affected by UV irradiation because only the surfaces of the samples underwent degradation. The results from this study suggest insufficient UV aging time and intensity designated in current PV module test standards. A longer aging time and higher intensity are recommended for quality assurance.