Potential-Induced Degradation (PID): Introduction of a novel test approach and explanation of increased depletion region recombination

In recent years, a detrimental degradation mechanism of solar cells in large photovoltaic fields called potential-induced degradation (PID) has been intensively investigated and discussed. Here, the module efficiency is decreasing down to a fractional part of their original efficiency. In this study, we introduce a PID test at a solar-cell level and for individual module components applicable as a tool for process control in industries and root cause analyses in science departments. Using the proposed method, one example analysis of a solar cell that is degraded by the PID tester is presented. It is shown that PID of the shunting type influences both the parallel resistance (R-p) and the depletion region recombination behavior (J(02)) of the solar cell. Increased recombination in the depletion region is caused by Na decorated stacking faults crossing the depletion region. This strongly influences recombination behavior in the depletion region, leading to an increased J(02) and an ideality factor n(2) > 2. However, the defects leave the base of the solar cell primarily unaffected, and hence, J(01) recombination remains rather low. Based on these findings, a model for the shunting and the increased depletion region recombination behavior is discussed.