Evidence of Polarization-Type Potential-Induced Degradation (PID-p) in the Field and Investigation of the Recovery Mechanism on Bifacial p-PERC Modules

This study investigates the polarization-type potential-induced degradation (PID-p) of bifacial glass/glass p-type passivated emitter rear contact (p-PERC) modules in the field and their recovery behavior. Modules were installed with three mounting configurations providing different albedo conditions. System voltage (-600, -1500, and +1500 V) was applied to the cell circuits, with respect to the grounded module frames. No degradation was observed for positively biased modules, but PID-p was identified on the rear side when cells are negatively biased, with maximum power dropping during the first days and stabilizing at values up to 8% loss. Electroluminescence images revealed a variation of the cells' PID-p susceptibility within a module. Three parameters were shown to impact the degradation rate: rear albedo light, voltage, and wetness conditions. Degraded modules were recovered either by (1) a positive bias (+1500 V), (2) outdoor illumination with the front side facing sun, (3) outdoor illumination with the rear side facing sun, or (4) dark storage. A recovery pattern was identified with I-V parameters decreasing to a local minimum before increasing to full recovery. The proposed mechanism is based on the band bending at the rear p-type Si/AlO x/SiNx interface, going from inversion to depletion and accumulation states. Full recovery was achieved in 2-7 h for the modules recovered with the rear side facing sun, four to eight nights for the modules positively biased at night, and 10-20 days for the modules with the front side facing sun. Dark storage showed slower recovery rates as I-V parameters were not improving even after 1 month. The recovery rates were correlated with the net Coulombs transferred during the preceding PID stress: When more Coulombs are transferred during the degradation, the extent of degradation is greater, leading to slower recovery rates.