Cs + ‐Induced Se/S Ratio Variation to Regulate Energy Band Structure for Efficient Sb 2 (S,Se) 3 Bulk Heterojunction Solar Cells

Abstract As an emerging photovoltaic material, antimony selenosulfide (Sb 2 (S,Se) 3 ) has attracted considerable attention and research enthusiasm. However, the current solution‐processed Sb 2 (S,Se) 3 layers suffer from severe unfavorable energy band structure problems attributed to the vertical gradient‐variable Se/S atomic ratio, making it a challenging and prospective subject. Herein, a novel and convenient alkali metal Cs + ‐induced Se/S atomic ratio variation strategy has been developed for the first time to regulate Sb 2 (S,Se) 3 energy band structure through hydrothermal‐processed CdS nanorod‐arrays (NAs)/Sb 2 (S,Se) 3 bulk heterojunction (BHJ) films. The Cs + ‐induced regulation strategy narrows Se‐elemental concentration gradient distribution adjusting effectively Se/S atomic ratio in longitudinal CdS‐NAs/Sb 2 (S,Se) 3 BHJ films. This generates a favorable energy band structure, contributing to rapid charge separation and extraction of photogenerated carriers of CdS‐NAs/Sb 2 (S,Se) 3 BHJ. Meanwhile, the Cs + ‐induced Se/S ratio variation not only passivates the defect‐state concentration and enhances crystal size of CdS‐NAs/Sb 2 (S,Se) 3 film, bust also extend the carrier lifetime for Sb 2 (S,Se) 3 BHJ photovoltaic devices. The resulting Cs‐Sb 2 (S,Se) 3 BHJ photovoltaic devices exhibit an impressing power conversion efficiency ( η ) of 8.23%, the highest one currently available for Sb 2 (S,Se) 3 BHJ solar cells. This study will undoubtedly facilitate the development of efficient Sb 2 (S,Se) 3 BHJ devices, and other similar inorganic semiconductor photovoltaic devices.