Effect of plasma-assisted N2O/Ar oxidation on TOPCon solar cells

Abstract

N2O/Ar gas mixture are used to deposit ultra-thin silicon oxide (SiOx) layer by plasma enhanced chemical vapor deposition (PECVD), which is used as the tunneling oxide layer in the TOPCon (tunnel oxide passivated contacts) structure. It is found that the N2O/Ar flow ratios strongly affect the properties of SiOx layer, such as deposition rate, the resistance of high temperature, passivation quality, etc., thus significantly affect the properties of polysilicon passivated contact structures and the efficiency of TOPCon solar cells. The deposition rate of SiOx layer and contact resistivity of SiOx/poly-Si(n+)/SiNx:H structure decrease with the increases of Ar flow. However, there is an optimal N2O/Ar flow ratio to obtain the best passivation quality and the champion efficiency. The optimal flow ratio of N2O/Ar= 5:2 is found, and obtain the optimum thickness of SiOx and uniform polysilicon passivated contact. The highest minority carrier lifetime (τ) of 5751 μs, highest implied open circuit voltage (iVoc) of 741.3 mV, lowest single side recombination saturation current density(J0) of 4.79 fA/cm2, contact resistivity(ρcontact) of 2.23 mΩ/cm2 and champion efficiency of 25.06% are obtained at the flow ratio of N2O/Ar= 5:2.