Advanced analysis of ethylene vinyl acetate copolymer materials for photovoltaic modules

Abstract

Ethylene vinyl acetate (EVA) copolymers are commonly used as encapsulation material and as adhesive layer for backsheet laminates of photovoltaic (PV) modules. While Fourier-Transform Infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) are well established to analyse EVA encapsulants in PV modules, X-ray Photoelectron Spectroscopy (XPS) is seldomly used. Hence, the objective of this paper was to evaluate the potential and limitations of XPS for advanced analysis and testing of EVA encapsulants. Consequently, EVA grades of different vinyl acetate (VA) comonomer content were characterized and evaluated systematically by XPS, FTIR and DSC. Independent on the analytic technique linear relationships between the obtained values and VA contents were confirmed. Slightly higher VA contents on the surface deduced by XPS were attributed to a surface layer rich of amorphous phase material. In addition, XPS analysis of peroxide modified encapsulants with a VA comonomer content of 30.2 wt% revealed a higher carbon content on the surface after crosslinking. Hence, it is proposed that peroxide crosslinking is associated with deacetylation and the subsequent release of low molar mass decomposition products. Overall, the exceptional surface sensitivity of XPS was clearly confirmed for analysis and testing of EVA grades, highlighting the potential of the method for further degradation and interaction studies of components of PV modules.