In situ seed layer bandgap engineering leading to the conduction band offset reversion and efficient Sb2Se3 solar cells with high open-circuit voltage

Sb₂Se₃ solar cells have achieved a power conversion efficiency (PCE) of over 10%. However, the serious open-circuit voltage deficit (V_OC-deficit), induced by the hard-to-control crystal orientation and heterojunction interface reaction, limits the PCE of vapor transport deposition (VTD) processed Sb₂Se₃ solar cells. To overcome the V_OC-deficit problem of VTD processed Sb₂Se₃ solar cells, herein, an in-situ bandgap regulation strategy is innovatively proposed to prepare a wide band gap Sb₂(S,Se)₃ seed layer (WBSL) at CdS/Sb₂Se₃ heterojunction interface to improve the PCE of Sb₂Se₃ solar cells. The analysis results show that the introduced Sb₂(S,Se)₃ seed layer can enhance the [001] orientation of Sb₂Se₃ thin films, broaden the band gap of heterojunction interface, and realize a “Spike-like” conduction band alignment with ΔE_c = 0.11 eV. In addition, thanks to the suppressed CdS/Sb₂Se₃ interface reaction after WBSL application, the depletion region width of Sb₂Se₃ solar cells is widened, and the quality of CdS/Sb₂Se₃ interface and the carrier transporting performance of Sb₂Se₃ solar cells are significantly improved as well. Moreover, the harmful Se vacancy defects near the front interface of Sb₂Se₃ solar cells can be greatly diminished by WBSL. Finally, the PCE of Sb₂Se₃ solar cells is improved from 7.0% to 7.6%; meanwhile the V_OC is increased to 466 mV which is the highest value for the VTD derived Sb₂Se₃ solar cells. This work will provide a valuable reference for the interface and orientation regulation of antimony-based chalcogenide solar cells.