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 (I_sc) and a relatively smaller loss in the open-circuit voltage (V_oc) 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 I_sc. External quantum efficiency and photoluminescence measurements reveal that the losses in I_sc and V_oc are 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.