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

Abstract The quality of P‐N heterojunction is crucial for the performance of antimony selenide (Sb 2 Se 3 ) 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 Sb 2 Se 3 layer, forming Cd Sb defects, which enhances the P‐type conductivity of Sb 2 Se 3 and reduces the density of deep‐level centers. With further chemical etching treatment on the CdS surface, the quality of the CdS/Sb 2 Se 3 P‐N heterojunction is distinctly improved, making the energy band alignment of CdS/Sb 2 Se 3 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 Sb 2 Se 3 solar cells. This work provides a strategy to simultaneously optimize the CdS and Sb 2 Se 3 functional layers and enhance the quality of P‐N heterojunction for efficient Sb 2 Se 3 solar cells.