Depth Profiling of Glass/POE/Transparent Backsheet Degradation for Bifacial Photovoltaics

Decarbonatization drives rapid growth of the global bifacial solar market. However, the long-term durability of bifacial technology has not yet been clearly demonstrated. Here, the durability of three types of glass/polyolefin elastomer (POE)/transparent backsheet (G/CB) coupons was investigated under UV/65 degrees C/50 % RH, followed by thermal cycling. Spatially resolved depth-dependent techniques were used to characterize the degradation of transparent backsheets, POEs, and their interfaces in G/CB coupons. Non-destructive depth profiling of optical and chemical degradation of G/CB was developed by confocal-based Raman microscopy and fluorescence microscopy. Cross-sectional mechanical analyses of transparent backsheets and encapsulants were performed by nanoindentation. The results indicate that aged G/CB coupons show a higher yellowness index than the glass/glass construction, and their values depend on the type of backsheet. Depth-dependent confocal Raman spectra and fluorescence mapping show that the highest emission comes from the POE region closest to the glass, and the yellowness of the glass side-exposed G/CB comes from both encapsulant and backsheet yellowing, which could be related to the migration and interaction of additives in these components. Furthermore, the results from nanoindentation clearly reveal the depth-dependent mechanical changes of individual layers of G/CB coupons after aging.