XPS analysis of ethylene-based encapsulants and damp heat aged fractured glass laminate surfaces
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For long lifetimes of photovoltaic modules, the interaction of the various laminate plies is cru-cial. An essential component is the polymeric encapsulant. In this study X-ray photoelec-tron spectroscopy (XPS) was used to character-ize ethylene-vinyl acetate copolymer (EVA) with varying VA content. It was proven that XPS is a highly reliable method to quantify the VA content. The results were corroborated by Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC).
Further focus was given to the XPS analysis of damp heat aged glass laminates with three dif-ferent encapsulants. Experiments were per-formed on EVA, polyolefin elastomer (POE) and thermoplastic polyolefin (TPO) double glass laminates. After delamination by com-pressive shear testing, the fractured surfaces were investigated by XPS and FTIR at the pol-ymer side of the laminates. It was shown that EVA is more prone to degradation as the prom-ising alternatives POE and TPO1,3. The differ-ences were already discernible after 1000h and were even more pronounced with longer expo-sure times up to 10000h. Based on the obtained results, a possible degradation pathway was established for the encapsulant/glass interface and for the bulk of EVA, POE and TPO. Diffu-sion of Na ions from the glass substrate into the polymer matrix and the formation of Na-based salts at the interface were identified as primary mechanisms and degradation products.