Towards the origin of photochemical EVA discoloration

The root cause of the photochemical ethylene vinyl acetate (EVA) discoloration in photovoltaic (PV) modules was investigated. Laminates containing EVA foils with a systematic variation of the additive formulation, i.e. the crosslinking agents, ultraviolet (UV) absorber, hindered amine light stabilizers and antioxidants, were subjected to UV aging. The influence of the additive combination on the photochemical aging of EVA was investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and UV/visible spectroscopy. The amount of EVA discoloration was found to be strongly depending on the additive formation. An important impact of the antioxidant in terms of chromophore formation inhibition could be found. Surprisingly, the highly stabilized EVA foils showed higher discoloration rates as well as a more intense fluorescence background in the Raman spectra.