The influence of the additive composition on degradation induced changes in poly(ethylene-co-vinyl acetate) during photochemical aging

Comprehensive knowledge about the influence of the additive composition on the degradation behavior of the most important photovoltaic (PV) module encapsulant, ethylene vinyl actetate (EVA), is crucial for enhancing its durability. To analyze this influence, EVA foils with different additive compositions were exposed to UV irradiation (135 W/m2) at 60 °C with a UV-A lamp, and characterized by spectroscopic methods (UV-vis, Raman spectroscopy) and DSC measurements. The reference foil with minimal additives showed significant changes in consistency during UV exposure. Those changes were explained by chain scissions, changes in conformation and crystallinity. In particular, degradation induced changes in the intensity of the symmetric compared to the asymmetric CH2 stretching vibrations, detected by Raman spectroscopy, indicate modifications in the conformational and crystalline setup. Therefore, their intensity ratio offers a nondestructive method to follow EVA degradation in PV modules. A major influence of additives on the development of fluorescent and chromophoric species was found. A quenching effect of oxygen on the development of fluorescent species was observed.