Initial Stability of PERC vs. Al-BSF Cells

Abstract

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 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.