Time-Resolved Investigation of Transient Field Effect Passivation States during Potential-Induced Degradation and Recovery of Bifacial Silicon Solar Cells

Various types of potential-induced degradation (PID) with fundamentally different physical root causes have been observed recently ranging from shunting (PID-s), corrosion (PID-c) to degradation of surface passivation (PID-p). Herein, PID-p is investigated for the first time at the rear side of bifacial silicon solar cells with enhanced time-resolution during degradation and recovery under simultaneous illumination. The tests reveal fast transient changes of rear-side short-circuit current within minutes and thus allow to understand the degradation process related to PID-p. The short-circuit current with rear-side illumination first decreases significantly by more than 80% resulting in an intermediate degraded state. Subsequently, it increases to a regenerated state. Under reversed bias, a total recovery of the cell parameters is observed and confirmed by I-V measurements under standard testing conditions (STCs). The underlying transient PID-p degradation and recovery mechanism is well described by a PC-1D simulation of the field-induced band bending at the rear surface. Finally, a qualitative model involving the migration of mobile charged species and their impact on the charge equilibrium in the field effect passivation layer is presented. Thus, time-resolved analysis of transient PID effects can serve as a clear characteristic for PID of polarization type.