Silver nanoparticles cause snail trails in photovoltaic modules

After some months of operation, a number of PV modules develop a discolouration defect called ""snail trails"", or ""snail traces"", which appear as irregular dark stripes across the cells. Whereas these traces were soon identified as discoloured silver contacts along the cell edges or at micro cracks, the chemical and mechanistic reasons for this phenomenon have not yet been resolved in detail. In this work we show that silver nanoparticles accumulating within the encapsulation foil cause the brownish discolouration, and that certain additives of encapsulation and back sheet foils trigger the formation of these nanoparticles.