Assessment of the effect of accelerated ultraviolet aging on mini‐PV modules encapsulated with different poly(ethylene‐co‐vinyl acetate) formulations

Abstract

One of the hindering issues for the long‐term reliability of the photovoltaic (PV) modules is the degradation of poly(ethylene‐co‐vinyl acetate) (PEVA)—a popular encapsulant material. As a globally accepted practice, PEVA is required to have the vinyl acetate (VA) content between 28–33% by weight for encapsulation application in the PV modules. Recent studies have indicated stability improvements in the bare encapsulant layer when the VA content is reduced up to 18%. However, effect of UV aging on the PEVA films encapsulated using these VA contents have not been studied at the module level. Therefore, in this work, we have fabricated mini‐modules containing PEVA films that contain 18, 24 or 33% VA content and have subsequently been subjected to UV aging (1000 hours at 340 nm wavelength and 65C). The assessment of the durability at both the mini‐module and materials level has been made using various characterization techniques such as current–voltage characteristics, adhesion strength measurement, fluorescence imaging and spectra, FTIR, Raman spectra, volume resistivity and TGA. YI for the free‐standing films of PEVA18, PEVA24 and PEVA33 after 1000 hours of UV aging was slightly less than the YI values for the corresponding laminated films of PEVAs in mini‐PV modules after similar hours of aging. This work shows for the first time that increasing the VA content in PEVA increases the fluorescence intensity and contour size in the encapsulated polymer after UV aging. FTIR analysis indicates deacetylation of PEVA33 which resulted in discoloration (increased ΔYI) and has adversely affected the adhesion strength and power output after UV aging. Compared to PEVA33, the modules containing PEVA18 and PEVA24 are resilient against UV aging for all the properties. Hence, this study recommends using PEVA with 24% VA content as an encapsulant as it presents best combination of the adhesion strength and the environmental stability.