Sodium distribution at the surface of silicon nitride film after potential-induced degradation test and recovery test of photovoltaic modules

Abstract

Migration routes of Na ions towards the surface and into SiNx films of Si cells during the potential-induced degradation (PID) test were analyzed by microscale measurements such as X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and conductive atomic force microscopy. These measurements showed the appearance of high Na concentrations near the finger electrodes and at the top of texture structures of the SiNx film surface. However, a high current conductivity of SiNx films was observed at halfway between two finger electrodes and at the top of texture structures. These results suggest that focusing of electric fields originating from finger electrodes and the shape of texture structures affected the Na distributions and migration into the SiNx films. The influence of the PID recovery test on the Na ion migration and SiNx films is also discussed in the paper.