![]() ![]() ![]() PVDF-based backsheets currently make up ~ 50% of the world market share 1. In this work, we will focus on the PVDF-based backsheet structure (i.e., backsheets containing at least one layer of PVDF polymer). Polyethylene terephthalate (PET) is a popular choice for the core layer, and fluoropolymers, such as polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF), are commonly used for the inner/outer backsheet layers. Thinner inner and outer layers are designed for good adhesion to the encapsulant and resistance to the outdoor environment. A thicker core layer provides insulating properties and mechanical strength. One typical backsheet type is comprised of an opaque multi-layer laminated polymeric sheet on the rear side of the module. We conclude that both MAST and C-AST are relevant tests for screening outdoor failure mechanisms in PVDF backsheets, as they were successful in producing material degradation that led to cracking.īacksheets constitute the rear side outermost layer of protection for the active components of standard photovoltaic (PV) modules. No excessive β-phase formation was observed after aging with any test condition however, the presence of β-phase was identified locally by Fourier transform infrared spectroscopy (FTIR). The MAST regimen used here was too extreme to produce realistic degradation, but the test was useful in discovering weaknesses of the particular PVDF-based outer layer structure studied. MAST and C-AST protocols were, to some extent, able to replicate the increase in crystallinity seen in PVDF after ~ 7 years in the field, but no single-stress test condition (UV, damp heat, thermal cycling) resulted in significant changes in the material properties. In field-aged samples from Arizona and India, where PVDF crystallizes in its predominant α-phase, the degree of crystallinity greatly increased. We observed depletion of PMMA upon aging with sequential (MAST) and combined (C-AST) accelerated stress testing. The PVDF-based backsheet outer layer can have a different structure and composition, and is often blended with a poly(methyl methacrylate) (PMMA) polymer. ![]() This work seeks to provide a better understanding of the changes in material properties that lead to crack formation and find appropriate accelerated tests to replicate them. Commercial backsheets based on polyvinylidene fluoride (PVDF) can experience premature field failures in the form of outer layer cracking. ![]()
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