Microstructure evolution and passivation quality of hydrogenated amorphous silicon oxide (a-SiO_x:H) on <100>- and <111>-orientated c-Si wafers

Hydrogenated amorphous silicon oxide (a-SiO_x:H) is an attractive passivation material to suppress epitaxial growth and reduce the parasitic absorption loss in silicon heterojunction (SHJ) solar cells. In this paper, a-SiO_x:H layers on different orientated c-Si substrates are fabricated. An optimal effective lifetime (τ_eff) of 4743 μs and corresponding implied open-circuit voltage (iV_oc) of 724 mV are obtained on <100>-orientated c-Si wafers. While τ_eff of 2429 μs and iV_oc of 699 mV are achieved on <111>-orientated substrate. The FTIR and XPS results indicate that the a-SiO_x:H network consists of SiO_x (Si-rich), Si-OH, Si-O-SiH_x, SiO₂≡Si-Si, and O₃≡Si-Si. A passivation evolution mechanism is proposed to explain the different passivation results on different c-Si wafers. By modulating the a-SiO_x:H layer, the planar silicon heterojunction solar cell can achieve an efficiency of 18.15%.