Investigation of the crack propensity of co-extruded polypropylene based backsheets

Co-extruded backsheets based on polypropylene (PP) are an interesting alternative to laminated backsheets containing polyester films (PET). Backsheet cracking has become a frequent failure mode in the last years, causing not only safety issues but on the long term also reducing the lifetime of PV modules. In this work the crack susceptibility of three different backsheets was investigated using solder bump coupon specimens: two co-extruded backsheets based on polyamide (P A) and PP, together with one laminated backsheet containing a PET core layer and polyvinyl fluoride (PVF) outer layers. The solder bump coupons were exposed to test sequence of exposure to UV light followed by thermal cycles. Overall, the PP as well as the PVF-PE T 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 test cycles. 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.