Synergistic Passivation of Bulk and Heterojunction Defects via Dual‐Functioned Interlayer Treatment for High‐Efficiency Sb2(S,Se)3 Solar Cells

Abstract The performance of Sb 2 (S,Se) 3 ‐based photovoltaics is largely limited by intrinsic defects in the absorber layer and suboptimal electronic characteristics at the heterojunction. Extensive efforts have been devoted to improving the quality of the absorber layer and distinctly modifying the electron transport layer (ETL) through targeted doping and surface treatments. Herein, a unified approach is presented that simultaneously addresses both of these challenges and establishes a paradigm shift from conventional sequential optimization strategies. A thin layer of KI is spin‐coated between the CdS and Sb 2 (S,Se) 3 , whereupon annealing, iodide ions diffuse into the Sb 2 (S,Se) 3 film, promoting grain growth, enhancing crystallization, and elevating the work function. Simultaneously, the KI treatment enhances the conductivity of the CdS, adjusts its energy band positions, and creates a favorable spike‐like alignment at the heterojunction, effectively suppressing interfacial carrier recombination. Furthermore, the KI treatment also mitigates detrimental vacancy defects (V S/Se ) and reduces antisite defects (Sb S/Se ) within Sb 2 (S,Se) 3 film. Consequently, the champion device exhibits a remarkable power conversion efficiency (PCE) of 10.06%, a significant improvement over the control device's PCE of 8.14%. This work presents a holistic approach to optimizing both absorber quality and ETL characteristics, offering a promising pathway to enhance the performance of Sb 2 (S,Se) 3 ‐based solar cells.