Initial Stability of PERC vs. Al-BSF Cells

PERC cells are projected to comprise 35% of the p-type silicon cells produced in 2018, due to their 10% relative improvement in power conversion efficiency over AlBSF with only a marginal increase in manufacturing costs. Known risks of PERC cells, including light-induced degradation and passivation layer stability, are of key concern in this fastgrowing market. Here we measure performance and mechanistic parameters of bare PERC and Al-BSF cells stepwise through UV + heat exposure by ${Suns} - V_{OC}$, external quantum efficiency, and microwave photoconductive decay to obtain timeseries of mechanistic and performance variables to evaluate in our < Stress|Stress|Mechanism|Response> analytic framework. With the creation of statistical models relating these variables, individual degradation modes are determined and ranked for PERC and Al-BSF cells. By comparing PERC and Al-BSF cells, we can identify PERC-specific degradation modes and inform future mitigation strategies. In this study, PERC cells showed two significant pathways related to power loss: one via degradation of the minority carrier lifetime and diffusion/rear side recombination, and another via bulk/emitter recombination and voltage losses.