Investigation of interface quality and passivation improvement with a-SiO:H deposited by ECRCVD at low temperature

•Hydrogenated amorphous silicon oxide is investigated for passivation.•A small amount of CO2 could suppress the partial epitaxy growth at interface.•Optical band gap could be effectively modulated by varying [CO2]/[SiH4] ratio.•Abrupt interface and hydrogen content are important for surface passivation.•Surface recombination velocity about 17.4 cm/s was obtained.

Hydrogenated amorphous silicon oxide (a-SiO:H) is an attractive passivation material to replace hydrogenated amorphous silicon (a-Si:H) in heterojunction solar cells due to its properties of high-transparency and a wide band gap. In this study, we investigated the structural properties, optical properties, and passivation quality of a-SiO:H films by varying the ratio of [CO2]/[SiH4]. Both the optical band gap and the absorption coefficient of a-SiO:H films could be conveniently modulated by varying the CO2 partial pressure. High quality passivation with a low surface recombination velocity of approximately 17.4 cm/s can be obtained when the ratio of [CO2]/[SiH4] = 0.32, due to the suppression of partial epitaxial growth at the interface, resulting in an abrupt interface, which was verified by transmission electron microscopy. Furthermore, the optical absorption coefficient of a-SiO:H ([CO2]/[SiH4] = 0.32) decreased by 25% compared with that of the a-Si:H (without CO2) at a wavelength of 300 nm. As a result, the high passivation quality was attributed to the properties of the abrupt interface and the sufficient hydrogen content between the a-SiO:H/c-Si interface.