Pressure Cooker Test on PV Backsheets: Comparison of Degradation in Standalone and Module Aged Backsheets

ABSTRACT Photovoltaic (PV) backsheets, are a critical polymeric component for a module's reliability, providing electrical insulation and protection against the ingress of moisture and gasses. However, backsheets themselves have caused critical reliability issues due to delamination and cracking. The question addressed in this work on highly accelerated test methods for material qualification is whether the pressure cooker test (PCT) induced degradation in standalone backsheets differs from the degradation caused in backsheets that are exposed within a module compound. If the degradation is the same, backsheets can be aged standalone in these conditions for an indication about their quality. This saves time, resources and enables characterization such as tensile testing and dynamic scanning calorimetry (DSC) measurements. To evaluate this question, two backsheet types ‐ polypropylene and polyethylene terephthalate (PP and PET) ‐ were exposed standalone and within a laminate compound to the PCT (120°C, 12–96 h) and characterized by tensile tests, DSC and color measurements. For both backsheets no difference in degradation of the mechanical or optical properties could be detected between the exposure modes. However, significant differences between the degradation of the backsheet types were detected. It is concluded that the PCT‐induced degradation of optical and mechanical properties of the tested backsheet types is independent of the exposure mode.