Prediction of Potential-Induced Degradation Rate of Thin-Film Modules in the Field Based on Coulombs Transferred

We validated the use of coulombs transferred between the active cell circuit and ground as an index for quantitatively predicting degradation rate in the field for two thin-film module types undergoing potential-induced degradation (PID). The dependence was determined by comparing the degradation rate and leakage current in the field (Cocoa, Florida) to accelerated tests (85°C, 85% relative humidity), both with the application of -1,000 V bias to the cell circuit. The two module types, which degraded about 4% and 11% in power after application of 96 h of bias in chamber, degraded 5% in the field by PID within 200 days and 6 days, respectively. The signatures of PID in the thin-film modules by electroluminescence, photoluminescence, and thermography are shown so that PID in fielded thin-film modules can be identified.