Potential-induced degradation in photovoltaic modules composed of interdigitated back contact solar cells in photovoltaic systems under actual operating conditions

Polarization-type potential-induced degradation (PID-p) of photovoltaic (PV) modules composed of n-type interdigitated back contact (IBC) solar cells can decrease the performance of the PV modules under positive potential conditions. The purpose of this study is to observe and describe the reduction and stabilization of the electrical performance of every PV module installed in an operating PV system with the progress of the PID-p over a time duration of 6 years. The direct current circuit of the investigated PV system is not grounded. Therefore, all the PV strings are under floating potential conditions. The results show that the performance of the n-type IBC PV modules exhibits a two-step degradation. In the first step of degradation, the PV performance at positive potential decreases with increasing the PV module potential, whereas the PV modules at negative potential show little performance degradation. The PV performance reduction due to PID-p is mainly caused by the decreases in both open-circuit voltage (V-OC) and short circuit current (I-SC). A PV performance reduction, which principally arises from the decrease inI(SC), is observed at every PV module in the PV strings regardless of the PV module potential in the second step of degradation. Therefore, solar cell manufacturers who produce n-type IBC, as well as those producing passivated emitters and rear totally diffused solar cells, are advised that processes to prevent the PID-p are required.