Improvement of Passivation Quality by Post-Crystallization Treatments with Different Methods for High Quality Tunnel Oxide Passivated Contact c-Si Solar Cells
Zhi Zhang1, Yuheng Zeng1, Yuqing Huang1, Xueqi Guo1, Zhixue Wang1, Qing Yang1, Chunhui Shou2, Baojie Yan1, Jichun Ye1
1Ningbo Materials Institute of Technology and Engineering, Ningbo, China
/2Zhejiang Energy Group R&D, Hangzhou, China

We report a systematic study of the post-crystallization treatment effects on the passivation quality of tunnel oxide passivated contact (TOPCon) on n-type c-Si wafers with different methods, including thermal annealing in forming gas, and moisture carried by nitrogen, as well as additional coatings with atomic layer deposition (ALD) Al2O3 and plasma chemical vapor deposition (PECVD) SiNx:H plus a thermal annealing in nitrogen. From the simplicity point of view, especially for manufacturing, a direct annealing in a given atmosphere without additional coating is preferred. For this approach, the annealing at an elevated 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 (iVoc) of 729 mV, minority carrier life time (t) of 1.97 ms, and single-side saturated recombination current density (J0) of 4.06 fA/cm2 is achieved. An additional ALD Al2O3 coating on the poly-Si contact layer is found to be the most effective way for improving the passivation quality, with which an outstanding passivation quality with iVoc of 747 mV, t of 4.07 ms, and J0 of 1.9 fA/cm2 is attainted. Using the optimized TOPCon passivation layer on solar grade CZ wafers, we achieved small area cell (2x2 cm2) solar cell efficiency of 22.2% and large area cell (15.6x15.6 cm2) efficiency of 21.5%.