Kinetics of degradation-induced photoluminescence in ethylene-vinyl-acetate as used in photovoltaic modules

The degradation-induced polymer photoluminescence and absorbance spectra of two differently stabilized commercial EVA grades are investigated under conditions of exposure to dry heat at 85 degrees C, 115 degrees C and 135 degrees C and moisture of 85% relative humidity at 85 degrees C. In addition to the photoluminescence signal as described before, new features are identified for both, absorbance and photoluminescence spectra. Most prominently, the formerly suggested initial luminescence signal of the model of degradation-induced polymer photoluminescence is identified at an emission wavelength of about 310 nm. It is shown to exhibit a sequential reaction kinetics and to be related to the absorbance of carbonyl sates at 285 nm. The kinetic parameters of these signals are quantitatively evaluated and discussed in the scope chemical degradation and physical relaxation processes. We demonstrate that additive formulations can be distinguished by means of degradation-induced polymer photoluminescence, enabling its application for the characterization and optimization of polymeric materials.