The durability of contemporary PV encapsulants relative to UV induced cell degradation

Modern c-Si photovoltaic (PV) cells provide high performance but are vulnerable to ultraviolet light induced degradation (UV-ID). Encapsulants, if chosen correctly, can mitigate UV-ID of the PV cell. Here, we explore performance and durability of 15 commercial encapsulant varieties with the goal of deconvoluting simultaneous-but-distinct degradation pathways under UV illumination. Materials include contemporary products with EVA-, POE-, and EPE-based polymers. Encapsulant formulations include UV-blocking, UV-transmitting, opaque (white), and UV-downconverting additives. Coupons were constructed to compare the rate of degradation from UV weathering under xenon, UVA-340 fluorescent (UV-A light), and UV deficient (visible only) light sources. Characteristics examined include specimen temperature, spectral transmittance, color, spectral fluorescence, volume resistivity, polymer structure (from FTIR), thermal decomposition, glass transition-, melt-, and freeze-temperature, degree of crystallinity, vinyl acetate content, composition quality ratio, x-ray diffraction, and the solarization of glass. Initial differences in chemical and optical properties between encapsulants of the same material class, e.g. POEs, are identified both as-manufactured and after lamination. Degradation modes in the first 2000 hours of UV aging include discoloration, changes to UV cutoff wavelength, and changes to solar-weighted transmittance. We further discuss correlations between the initial characteristics and the long-term durability.