Highly improved passivation of PECVD p-type TOPCon by suppressing plasma-oxidation ion-bombardment-induced damages

Tunnel oxide passivated contact (TOPCon) integrated with a plasma-enhanced chemical vapor deposition (PECVD) boron-doped polysilicon has the potential to achieve high-efficiency and low-cost solar cells. In this contribution, we explore the feasibility of using PECVD technology to prepare high-performance p-type TOPCon (p-TOPCon) by growing two-step oxidation (TSO), i.e., a nitric acid oxidation (NAOS) SiOx without ion -bombardment followed by a plasma-assist N2O oxidation (PANO) SiOx layer. The experimental results reveal that for p-TOPCon structures on polished wafers with the conventional plasma oxidation SiOx, raising plasma oxidation powers to increase the thickness and oxidation degree of SiOx cannot ensure high-quality passivation due to the appearance of high-density defects caused by plasma ion-bombardment. In the presence of an additional NAOS SiOx layer, ion-bombardment-induced defects can be effectively suppressed, leading to a remarkable improvement in passivation properties. In detail, the optimal p-TOPCon with TSO SiOx achieves a maximum implied open-circuit voltage (iV(oc)) of -712 mV and a minimum single-sided saturation current density (J(0,s)) of-10 fA/cm(2), manifesting an increment of iV(oc) by-10 mV, and a reduction of J(0,s )by-5 fA/cm(2). Finally, the numerical simulations reveal that n-type Si solar cells featuring p-TOPCon rear junction and Al electrode could receive an efficiency of 24.6% based on the state-of-the-art device fabrication technology. In general, this work provides a new way to boost the passivation quality of PECVD p-TOPCon devices.

Automated summary

This study explores the feasibility of using PECVD technology to prepare high-performance p-type TOPCon by growing two-step oxidation. Experimental results reveal that raising plasma oxidation powers to increase the thickness and oxidation degree of SiOx cannot ensure high-quality passivation, but adding an additional NAOS SiOx layer can effectively suppress ion-bombardment-induced defects and improve passivation properties. The optimal p-TOPCon with TSO SiOx achieves a higher implied open-circuit voltage and a lower single-sided saturation current density. Numerical simulations also show the potential efficiency of n-type Si solar cells featuring p-TOPCon rear junction and Al electrode.