Potential-induced degradation (PID) is known as a severe degradation phenomenon. PID was first noticed in large photovoltaic (PV) plants where a significant amount of PV modules was connected in series, hence resulting in a significant voltage between the solar cells at one end of the string and the grounded frame. According to Naumann et al., the induced electrical field causes a leakage current and sodium ion (Na+) diffusion into stacking faults through the PN-junction of the solar cell, resulting in a substantial lowering of the shunt resistance.