Impact of permeation properties and back-sheet-encapsulation interactions on the reliability of PV-modules

The reliability of photovoltaic modules is highly influenced by the material properties of the backsheet and encapsulation material. Currently, little attention is paid to the permeation properties of the back-sheet material or to its impact on encapsulation degradation and module reliability. We investigated the interaction of different types of solar encapsulation and back-sheet materials. Therefore, various laminates were made to examine the environmental impact on such materials during the aging processes. One focus of our study lay in oxygen and water vapor permeability of the back-sheet materials. The encapsulants used were an Ethylene vinyl acetate (EVA), a TPSE (thermoplastic silicone elastomer) and an Ionomer and a PVB (Polyvinyl Butyral). Back-sheet materials were a TPT (Tedlar-PET-Tedlar) foil, a polyamide sheet and a PET composite film. Raman spectroscopic and FT-IR/vis-reflectance measurements were carried out before and after different accelerated aging procedures. The water vapor and oxygen permeation properties were measured. A clear correlation between the permeation properties and the observed aging behavior was found. The degradation, especially of the encapsulant, resulted in increased fluorescence background in the Raman Spectra. It could be shown that the encapsulation-cell-back-sheet system should be optimized in order to minimize the stress on the PV-module components.