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

• Published in: 2023 IEEE 50th Photovoltaic Specialists Conference (PVSC) pp. 1 - 3
• Main Authors: Gu, Xiaohong, Aiello, Ashlee R., Mitterhofer, Stefan, Smith, Soshana, Moffitt, Stephanie L., Perry, LaKesha N., Jhang, Song-Syun, Watson, Stephanie S., Sung, Li-Piin
• Format: Conference Proceeding
• Language: English
• Published: IEEE 11-06-2023
• Subjects: bifacial modules; Degradation; depth profiling; Elastomers; Fluorescence; Glass; glass/transparent backsheet; Microscopy; Optical microscopy; Photovoltaic systems; polyolefin elastomer; yellowing
• DOI: 10.1109/PVSC48320.2023.10359624

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 °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.