Fluorine‐Doped CdS Enables Oriented Growth and Defect Suppression in Sb ₂ Se ₃ Solar Cells with High Conversion Efficiency

Abstract Antimony selenide (Sb ₂ Se ₃ ) as a quasi‐1D absorber holds promising potential in photovoltaics, but its practical efficiency remains far below the theoretical limit due to challenges such as deep‐level defects and difficulties in crystal orientation control. High‐efficiency devices typically use cadmium sulfide (CdS) buffer layers made by chemical bath deposition (CBD), but achieving low‐defect, stable CdS films is challenging. In the superstrate configuration, the interfacial quality of CdS is recognized as a critical factor influencing the oriented growth of Sb ₂ Se ₃ and overall device efficiency. This study pioneers the use of fluorine (F)‐doping to modulate the microstructure and surface energy states of CBD‐CdS, aiming to passivate sulfur vacancies and expose non‐polar surface planes (100), thereby inducing preferential orientation of Sb ₂ Se ₃ along its high‐mobility growth direction. Furthermore, effective passivation of sulfur vacancies by F ions substantially improves Sb ₂ Se ₃ growth kinetics. The optimized films exhibit a reduced Se/Sb ratio (from 1.98 to 1.63), a three‐order‐of‐magnitude decrease in defect capture cross‐section (from 10 ⁻¹⁷ to 10 ⁻²⁰ ), and achieve an efficiency of 9.30%, representing an 18% improvement over the control device. The work proposes a low‐temperature, scalable interfacial engineering strategy with broad applicability, offering new insights into defect suppression and crystal orientation optimization for enhanced photovoltaic performance.