Analysis of Potential-Induced Degradation in Soda-Lime Glass and Borosilicate-Glass Cu(In,Ga)Se2 Samples

Potential-induced degradation (PID) is investigated in small-size Cu(In,Ga)Se₂ (CIGS) submodules of individual cells. Samples with conventional soda-lime glass (SLG) and low-alkaline glass (borosilicate glass, BSG) were analyzed applying positive and negative 1000 V bias at 85 °C and low relative humidity after a heat-soaking phase. During the heat-soaking phase, BSG samples showed degradation, with variations in their dark current-voltage (I-V) curve parameters compared with the stability of SLG samples. During the PID stress phase, back-grounded SLG samples with -1000 V applied to the cell experienced fast degradation, with complete failure in 25 h, whereas, BSG samples only showed changes because of the dark heat environment. When grounded on their front face, SLG samples remained stable during more than 150 h of PID testing, beginning degradation after longer applications of stress. The analysis of the dark I-V curves of SLG samples through the single-diode model showed that an increase in saturation current J₀ occurs first, attributed to Na⁺ ions migrating into the CdS/ZnO layer; later, a decrease in shunt resistance occurs. The application of the model in BSG samples showed an increase in series resistance evaluated at 25 °C. When the bias is reversed, SLG samples gradually recover their performance.