Improvement of Passivation Quality by Post-Crystallization Treatments with Different Methods for High Quality Tunnel Oxide Passivated Contact c-Si Solar Cells

Abstract

We report a systematic study of the post-crystallization treatment effects on the passivation quality of tunnel oxide passivated contact (TOPCon) on n-type CZ c-Si wafers with different methods, including thermal annealing in forming gas, and moisture carried by nitrogen, as well as capping with atomic layer deposition (ALD) Al 2 O 3 and plasma-enhanced chemical vapor deposition (PECVD) SiN x :H following a thermal annealing in nitrogen. We found that the annealing at a moderate temperature of ~450°C within a mixture of nitrogen and moisture is an effective way for improving the passivation quality, with which a high quality passivation with an implied open circuit voltage (iV oc ) of 729 mV is achieved. A hydrogen containing capping layer with ALD Al 2 O 3 on the poly-Si contact layer is found to be the most effective way for improving the passivation, with which an outstanding passivation quality with an iV oc of 747 mV, effective life time (τ eff ) of 4.07 ms (∆n= 5.0×1015 cm-3), and single-side saturated recombination current density (J 0 ) of 1.9 fA/cm2 is attainted. Using the optimized TOPCon passivation layer on solar grade CZ wafers, we achieved a solar cell efficiency of 22.2%.