Effects of Encapsulant-Backsheet Combinations on Durability of Optical Properties

The compatibility and interactions between encapsulants and backsheets in photovoltaic (PV) modules have received limited attention in aging studies, despite their critical role in module reliability. This research addresses this gap by investigating the effects of encapsulant-backsheet combinations starting with optical durability, a key factor influencing PV module performance and longevity. To this end, the optical durability of two common encapsulant materials, Ethylene Vinyl Acetate copolymer (EVA) and Polyolefin Elastomer (POE), a transparent Polyethylene terephthalate backsheet (PET) and combinations thereof was investigated. The individual components as well as their combinations were subjected to accelerated weathering under Damp Heat, Damp Heat with UV exposure (DHUV), and the environmental conditions specified in IEC 62788-7-2 A3. The optical durability was subsequently characterized by means of the visual inspection and UV-Vis spectroscopy, whose results were correlated with the Fourier Transform Infrared Spectroscopy (FTIR) data to provide molecular insights. Results revealed distinct degradation patterns among material combinations. Remarkably, a EVA/PET combination exhibited superior resistance to optical degradation compared to POE/PET, particularly under DHUV conditions. Notably, materials behaved differently in combinations versus when weathered alone, observed by PET's reduced degradation when combined with the encapsulants under DHUV exposure. This study establishes a foundation for understanding encapsulant-backsheet compatibility in the context of optical durability. The findings highlight the importance of considering material interactions in PV module design and testing protocols. This approach paves the way for developing mechanistic degradation models, potentially enhancing material selection processes, and improving predictions of module lifetime and performance.