Thermo-Mechanical Coupling Driven Charge Trapping and Electrical Degradation in Polymeric PV Backsheets

Polymeric backsheets used in photovoltaic (PV) modules are subjected to coupled thermal and mechanical stresses during long-term outdoor service. However, current qualification standards primarily evaluate thermal aging and mechanical integrity separately, which may overlook synergistic degradation behavior under operating conditions. While thermal exposure accelerates thermo-oxidative degradation, superimposed mechanical damage can further destabilize the surface and interfacial structure of multilayer backsheets, thereby promoting electrical deterioration. Here, the thermo-mechanical coupling effect is investigated, revealing a synergistic degradation mechanism of PV backsheets under coupled aging conditions. The results indicate that pre-existing mechanical damage of PV backsheets introduces surface defects that become preferential regions for accelerated degradation during subsequent thermal exposure. Critically, under electrical stress, these degraded regions act as charge-trapping sites, intensifying partial discharge (PD) activity and ultimately reducing breakdown strength. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) link these macroscopic electrical failures to molecular-level chain scission and microstructural changes associated with embrittlement. These findings clarify the coupling relationship between microstructural degradation and electrical failure in polymeric insulating materials under multi-stress conditions.