Plasma treatment for chemical SiOx enables excellent passivation of p-type polysilicon passivating contact featuring the lowest J of ∼6 fA/cm2

We study the preparation of high-quality p-type tunnel oxide passivated contact (p-TOPCon) using plasma-enhanced chemical vapor deposition (PECVD) technology in this work. We propose to use different plasmas to treat the ultrathin SiOx to improve the passivation quality of p-TOPCon. Experimentally, we use the nitric acid oxidation (NAOS) SiOx as the precursor and use pure N2, pure H2, and N2O/H2 plasmas to treat the SiOx precursor layer. Three observations are found. 1) Pure H2 plasma treatment can improve the SiOx quality by increasing the Si4+ content, but the passivation quality is not improved because of the etching effect of H2 plasma and the reduction of SiOx thickness. 2) The pure N2O plasma can improve the passivation quality but increases the contact resistivity (ρc) because of the increase of the SiOx thickness. 3) The N2O/H2 plasma treatment improves the passivation quality more effectively than pure N2O plasma, and meanwhile, it also keeps the contact resistivity at an acceptable value for high-efficiency solar cells. We assume that the atomic H provides the energy to etch the weak and dangling bonds and make SiOx thinner, while the atomic O that makes SiOx thickness unchanged balances the etching effect of atomic H. With the optimized N2O/H2 plasma treatment, the passivation quality of p-TOPCon is improved, featuring the best implied open-circuit voltage (iVoc) of ∼732 mV and the lowest single-sided saturation current density (J0,s) of ∼6 fA/cm2 on the lifetime sample with the n-type silicon substrate and the AlOx/SiNx capping layer. These results demonstrate that the plasma treatment is a promising way to boost the passivation quality of PECVD p-TOPCon structures. Finally, as an example, we use numerical simulation to predict the performances of the solar cells integrating the p-TOPCon structure on the rear side of n-c-Si and demonstrate a 24.8% efficiency with the p-TOPCon whose SiOx is improved by the optimized plasma treatment.