The mechanism and damage of snail trails

We found Sulfur in module's EVA film which has snail trails by Atomic Absorption spectrometer, Sulfur reacted with “Ag” in silver paste and become black Silver sulfide, this is the reason of snail trails. As the EVA film can't reach the requirements of photovoltaic yellowing test, there's no choice but to add high temperature anti-yellowing agent, such as mercaptan, sulfide, thioester. In fact, the appearance of a snail trail is just a superficial phenomenon. due to the reaction of these additives with silver paste, the surface resistivity of conductor increases and the conductivity decreases. It will greatly damage the efficiency of modules, reduce their reliability and life cycle, and even serious will lead to their burning.