Contact Resistance Increase in Ga-Doped Silicon Solar Cells at Current Injection and Elevated Temperature Treatments

PERC solar cells based on Gallium p-type doping were treated at elevated temperatures in the range of 80…160°C and current injection. Current injection is conducted in a current-induced degradation (CID) setup in the dark, measuring voltage while applying a current at 0.06, 0.53 and 1.0 times the short-circuit current – ranging from maximum power point to open-circuit injection conditions. The results of the CID treatment show no significant light and elevated temperature induced degradation (LeTID) behaviour for these Ga-doped PERC cells. PERC cells treated at temperatures above 110°C show an increase in relative voltage during CID starting the earliest at a measurement time of 50 hours. It was found that the voltage increase could be related to increased contact resistance between the front silver metallization and the phosphourus emitter as indicated by comparing electroluminescence imaging before and after CID treatment and confirmed by transfer length method measurements. These measurements on a cut-out stripe showed an increase in contact resistivity and a lateral intensity variation as visible in the post electroluminescence image.