Dry Passivation Process for Silicon Heterojunction Solar Cells Using Hydrogen Plasma Treatment Followed by In Situ a-Si:H Deposition

A fully dry and hydrofluoric-free low-temperature process has been developed to passivate n-type crystalline silicon (c-Si) surfaces. Particularly, the use of a hydrogen (H
₂
) plasma treatment followed by in situ intrinsic hydrogenated amorphous silicon (a-Si:H) deposition has been investigated. The impact of H
₂
gas flow rate and H2 plasma processing time on the a-Si:H/c-Si interface passivation quality is studied. Optimal H
₂
plasma processing conditions result in the best effective minority carrier lifetime of up to 2.5 ms at an injection level of 1 × 10
¹⁵
cm
^-3
, equivalent to the best effective surface recombination velocity of 4 cm/s. The reasons that enable such superior passivation quality are discussed in this paper based on the characterization of the a-Si:H/c-Si interface and c-Si substrate using transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, and deep-level transient spectroscopy.