Application of dual-layer polysilicon deposited by PECVD in n-type TOPCon solar cells

Plasma-enhanced chemical vapor deposition (PECVD) has attracted much attention in the current mass-production of n-type tunnel oxide passivated contact (TOPCon) crystalline silicon (c-Si) solar cells because of the advantages of fast film forming rate and compatibility with in-situ doping. However, the PECVD technology is limited by the effect of ion bombardment on the ultra-thin SiO2 layer during gas ionization, together with the inevitable front wrap-around poly-Si. Here, the dual-layer poly-Si stack made up of the intrinsic poly-Si(i) and in-situ P-doped poly-Si(n+) has been achieved by adjusting the deposition power, pulse voltage duty cycle, and flow rate of the PH3, which effectively protects the tunneling SiO2 layer through the weakened ion bombardment to improve the interface passivation and contact resistivity. We have demonstrated that the pinhole density is an important reason for the thinner SiO2 layer optimized less than 1.0 nm. More importantly, the conversion efficiency of n-type TOPCon c-Si solar cells can be improved by more than 0.10% and 0.15%, respectively, by the combination of the dual-layer poly-Si stack and wrap-around poly-Si removal compared with the single-layer poly-Si counterpart with the same thickness.