Potential-Induced Degradation (PID): Incomplete Recovery of Shunt Resistance and Quantum Efficiency Losses

Potential-induced degradation (PID), specifically PID leading to shunts (PID-s), has recently been identified as one of the major field durability issues of photovoltaic (PV) modules. The industry is attempting to address this issue at the module/cell production level by modifying the cell, glass, and/or encapsulant properties, as well as at the system level through the application of reverse potential at night. However, there is a lingering question on the full recovery of the cells through the reverse potential application technique. The results obtained in this study indicate that the near-full recovery of efficiency at high irradiance levels can be achieved, but the full recovery of efficiency at low irradiance levels, shunt resistance, and quantum efficiency (QE) at low wavelengths could not be achieved. The wavelength-dependent QE response after PID and recovery has been modeled based on experimental data. We address the challenge in measuring accurate QE of shunted cells and the input impedance of traditional QE test equipment. A new very low impedance method minimizes, but does not totally eliminate, the scaling error in the QE system data for solar cells that have very low shunt resistances. We also evaluate previously proposed models on the effects of sodium experimentally and through simulation.