Anomalous Electron Doping in CdS to Promote the Efficiency Improvement in Sb2Se3 Thin Film Solar Cells

The quality of P-N heterojunction is crucial for the performance of antimony selenide (Sb₂Se₃) solar cells and thus attracting urgent attention. In this work, the monovalent cation Ag⁺ is doped in CdS, which enhances the N-type conductivity of CdS film anomalously and reduces its parasitic absorption simultaneously. Furthermore, Ag doping of CdS promotes the diffusion of Cd into the Sb₂Se₃ layer, forming Cd_Sb defects, which enhances the P-type conductivity of Sb₂Se₃ and reduces the density of deep-level centers. With further chemical etching treatment on the CdS surface, the quality of the CdS/Sb₂Se₃ P-N heterojunction is distinctly improved, making the energy band alignment of CdS/Sb₂Se₃ more favorable for carrier transportation. Finally, a remarkable efficiency of 8.14%, which is the highest efficiency among those with J_sc of 30.96 mA cm⁻², is achieved for vapor transport deposition processed Sb₂Se₃ solar cells. This work provides a strategy to simultaneously optimize the CdS and Sb₂Se₃ functional layers and enhance the quality of P-N heterojunction for efficient Sb₂Se₃ solar cells.