Investigation of the crack propensity of co-extruded polypropylene backsheet films for photovoltaic modules

Abstract

Co-extruded backsheets based on polypropylene (PP) are an interesting alternative to laminated backsheets based on polyester films (PET). Backsheet cracking has become a frequent aging induced failure mode in the last years, causing not only safety issues but also reducing the lifetime of PV modules on the long term. In this work the crack susceptibility of four different backsheet types was investigated using solder bump coupon specimens: two co-extruded backsheets based on polyamide (PA) and PP, two laminated backsheet containing a PET core layer and polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF) outer layers. The solder bump coupons were exposed to an accelerated stress test sequence of repeated exposure to UV light followed by thermal cycles (TC). Overall, the PP as well as the PVF-PET backsheet showed excellent stability and no susceptibility to material embrittlement or cracking. By comparison, the PA based backsheets showed next to significant discoloration also strong cracking after a few UV-TC test cycles. The PET-PVDF backsheet exhibited cracking after the same number of test cycles as the PA-based backsheets. Overall, the study confirms that co-extruded PP backsheets show great potential to be a valid replacement of standard PET based backsheets in PV modules.