Interface Etching Leads to the Inversion of the Conduction Band Offset between the CdS/Sb₂Se₃ Heterojunction and High-Efficient Sb₂Se₃ Solar Cells

Antimony selenide (Sb2Se3) has gained extensive attention owing to its excellent properties of stability and optoelectronic characteristics. However, the band-gap alignment of CdS/Sb2Se3 heterojunction is still a significant bottleneck in the improvement of the efficiency of Sb2Se3 thin-film solar cells. In this study, the quality of a vapor transport deposition (VTD)-processed Sb2Se3 thin film is improved by ammonia etching, wherein the surface potential of the CdS buffer layer is modified and the band-gap alignment of CdS/Sb2Se3 is changed from a “clifflike” to a “spikelike” structure. Moreover, the growth orientation of the Sb2Se3 absorber is tailored. Finally, the reduced carrier recombination, improved band-gap structure, and enhanced crystal orientation lead to the fabrication of a Sb2Se3 solar cell with the best efficiency of 7.48% in this work, which is comparable with the highest efficiency of VTD-processed Sb2Se3 thin-film solar cells. This is expected to provide a valuable reference for the future development of Sb2Se3 thin-film solar cells and other photoelectronic devices.