Impact of surface treatments on the passivation effect for n-type crystalline silicon in heterojunction solar cells

In a-Si:H/c-Si heterojunction solar cells, we developed two methods to improve the passivation effect at the a-Si:H/c-Si interface. (i) Chemical polish, etched c-Si wafer with HF and HNO₃ mixtures to smooth the peaks and valleys of pyramids after the texturization with alkali; (ii) SiO_x interlayer, formed ultrathin SiO_x layers with a thickness of about 2 nm on c-Si surface after the chemical polish and standard RCA cleaning. This thin layer was formed by chemical oxidization in various hot solutions. The results demonstrated that these two methods improved the quality of a-Si:H/c-Si interface and the effective carrier lifetime. When they were applied to heterojunction solar cells, gains in V_oc and J_sc were successfully achieved. The simplicity of these methods suggested the possible applications to the industry production.