Wavelength Sensitivity in Photodegradation of Polymer PV Backsheets

Spectral wavelength of the terrestrial sunlight is an important factor in the degradation of photovoltaic (PV) modules and components. In this study, the effect of wavelength on the degradation of PPE backsheets based on poly (ethylene terephthalate) (PET) and ethylene vinyl acetate (EVA) has been investigated under four different wavelength ranges having center wavelengths (CW) of 306 nm, 326 nm, 354 nm, and 452 nm at 65°C, and 0 % relative humidity (RH). Chemical degradation, yellowing, and surface morphological changes were measured as a function of radiation doses from different wavelengths. Mathematical models were developed for depicting the relationship between degradation and spectral wavelength. Both physical and chemical degradation of the PPE backsheet exhibited a very strong sensitivity toward wavelength, with the CW306 nm caused the greatest damage while the CW354 nm and higher exhibited minimal or photobleaching effects. This wavelength sensitivity can be modeled satisfactorily by an exponential function. The study highlights that caution should be made when comparing results from different light sources.