UV resilient thermoplastic polyolefin encapsulant for photovoltaic module encapsulation

Abstract

A new UV-365 acceleration test is used to study the reliability of the newly developed thermoplastic polyolefin (TPO) encapsulant and the most commonly used ethylene vinyl acetate (EVA). Two orders of magnitude higher rate of decrease in transmittance and the rate of increment in yellowness have been found for EVA as compared to TPO. Fluorescence images show the fluorophores generation in EVA laminate as the UV dose increases. Fluorescence image and spectra clearly showed the development of brown-yellow color fluorophores emission in the visible region for the EVA laminate. No significant fluorescence is observed in the TPO laminate. The Raman spectra of TPO laminate showed a lower fluorescence background at the center than the edge, whereas the EVA laminate shows the opposite trend. A 35% and 12% increment in the crystallinity has been observed for EVA and TPO encapsulants, respectively. One order of magnitude lower increment rate in the carbonyl index and ether index has been found in TPO compared to EVA. Eighteen days of the UV-365 test is sufficient to identify the EVA early discoloration/fluorophores generation. This method can be very beneficial for the PV industry and encapsulant manufacturers for quickly assessing the reliability of any encapsulant.