Ultra-thin Al₂O₃ capped with SiN_x enabling implied open-circuit voltage reaching 720 mV on industrial p-type Cz c-Si wafers for passivated emitter and rear solar cells

In this study, we report on the passivation quality of atomic layer deposition grown ultra-thin Al₂O₃ and Al₂O₃ capped with plasma-enhanced chemical vapor deposition deposited SiN_x on Cz p-type wafers for the rear side of a passivated emitter and rear cell (PERC). Different activation recipes using N₂, forming gas (FG), and two-step annealing for different durations are investigated before SiN_x deposition. The effect of different Al₂O₃ thicknesses and corresponding activation processes on the Al₂O₃/SiN_x passivation performance, after a high temperature firing step, is studied to reach a new optimization toward higher efficiency and lower cost. A record high iV_oc of 720 mV is obtained after firing step from Al₂O₃/SiN_x stacks with Al₂O₃ thickness as thin as ∼2 nm with FG annealing. Our results demonstrate that, under well-optimized process conditions, ultra-thin Al₂O₃ thicknesses provide superior passivation quality as compared to the larger thicknesses which are commonly applied in the PERC industrial line and the potential for further improvement of industrial PERC solar cells in terms of cost reduction and efficiency.