Polymer foil additives trigger the formation of snail trails in photovoltaic modules

After several months of operation, many photovoltaic (PV) modules develop a discoloration defect called "snail trails" or "snail traces", which appears as irregular dark traces across the cells. These traces have been identified as discolored silver grid fingers along the cell edges or at cell cracks. Previously we were able to show that silver nanoparticles accumulating within the encapsulation foil directly above the grid finger cause the brownish discoloration. In this work we present results showing that certain properties of the encapsulation and back-sheet foils trigger the formation of these nanoparticles. We developed a special test method to test polymer foils for their snail trail susceptibility in advance to module assembly.