Optical Durability of Contemporary PV Encapsulants Through Artificial UV Weathering

ABSTRACT Modern c‐Si photovoltaic (PV) cells provide high performance but can be 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 14 commercial encapsulant materials before, during, and after irradiation with UV‐containing light. Materials include contemporary, polymer‐based encapsulants with a base polymer of poly (ethylene co‐vinyl acetate) (EVA), polyethylene‐α‐olefin (POE), or their composite (EPE). Polymers contain additives that induce UV‐blocking, UV‐transmitting, or UV‐downshifting properties. We use test coupons to study degradation in a chamber held at 65°C under a xenon light source for up to 4000 h of exposure, corresponding to a cumulative dose of 11.5 MJ/m 2 at 340 nm. We examine optical properties including spectral transmittance, yellowness index and spectral fluorescence, considering changes to both the encapsulant and glass as a function of weathering time. Degradation modes identified include discoloration, changes to UV cutoff wavelength, changes to solar‐weighted transmittance, and most notably a change to the UV‐managing properties of some additives. We propose the use of solar‐weighted transmittance in the 300‐ to 400‐nm range to better track performance changes in the UV region associated with the UV‐related additive. This is especially relevant for the emerging class of UV‐downshifting additives, as metrics like UV‐cutoff can understate the degree of degradation or change in these materials. While most encapsulants show very little change after weathering, some show significant changes that directly impact how much UV light would reach an underlying cell.