Investigation of Potential-Induced Degradation in n-PERT Bifacial Silicon Photovoltaic Modules with a Glass/Glass Structure

Potential-induced degradation (PID) in n-type passivated emitter, rear totally diffused (n-PERT) bifacial crystalline silicon photovoltaic modules with a glass/glass structure is investigated. From front-side measurements, a significant loss in the short-circuit current (Isc) and a relatively smaller loss in the open-circuit voltage (Voc) and fill factor (FF) are observed due to PID. A similar degradation behavior is observed from the rear side, except that there is negligible change in Isc. External quantum efficiency and photoluminescence measurements reveal that the losses in Iscand Vocare most likely due to an increase in the front surface recombination. FF loss analysis and two-diode model fitting demonstrate that the FF loss is mainly attributed to an increased recombination in the space charge regions. Moreover, n-PERT bifacial silicon modules also suffer from PID when they are stressed from the rear side. Furthermore, some ethylene-vinyl acetate and polyolefin, which show high PID-resistance to conventional p-type technologies, are found to be not as effective in preventing PID in n-PERT technologies. However, a PID-free n-PERT bifacial module design is possible with the application of the sodium-free glass. Finally, the progression of PID is heavily dependent on the bias voltage and stress temperature.