Electrical Impedance Spectroscopy: A Complementary Approach Differentiating PID Mechanisms in Photovoltaics

Potential-induced degradation (PID) presents a critical reliability issue for solar photovoltaic (PV) modules, with three primary types identified in the literature, namely, PIDs (shunting type), PIDp (polarization type), and PIDc (corrosion type). Electrochemical/electrical impedance spectroscopy (EIS) is a highly effective but underutilized technique for differentiating between these PID mechanisms. When used alongside conventional I–V measurements (e.g., Isc, Voc, and FF), EIS offers direct insights into parameters such as Rs, Rp, and Cp, making it a valuable tool for PID type differentiation. In this study, two four-cell glass–glass modules were investigated using p-base PERC monofacial cells with EVA and POE encapsulants. Results indicate that Voc and FF remained nearly unchanged under +1000 V stress for both EVA and POE modules, suggesting a minimal impact of PID stress on these parameters. However, Isc was reduced by approximately 8.5% in the EVA module and 10% in the POE module. For the POE module, surface recombination (PIDp) is likely responsible for the Isc loss, as Rs, Rp, and Cp showed no significant variation. Conversely, in the EVA module, the combined effects of surface recombination and junction recombination (PIDjr) are the probable cause of the Isc loss, as evidenced by remarkable changes in Rp and Cp. The observed decrease in Rp for the EVA module is attributed to reduced dynamic diode resistance rather than ohmic shunt resistance. This reduction is linked to recombination currents induced by junction trap centers, formed by the positive voltage PID stress in the encapsulant, which contains trace amounts of oxidizable species such as CH3COOH and/or H2O. The objective of this study is to evaluate the impact of PID stress on the electrical characteristics of glass–glass PV modules with different encapsulants, utilizing a combined EIS and I–V approach to distinguish between PID mechanisms. The findings highlight the critical role of the encapsulant type in determining PID susceptibility, with the EVA module exhibiting significant degradation linked to junction recombination losses. These insights underscore the necessity of optimizing encapsulant materials to enhance PV module durability and reliability in real-world applications.