Defects Passivation via Potassium Iodide Post‐Treatment for Antimony Selenosulfide Solar Cells with Improved Performance

Abstract Antimony selenosulfide (Sb₂(S,Se)₃) has been emerging as a promising light absorber in the past few years owing to tunable bandgap (1.1–1.7 eV), high absorption coefficient (>10⁵ cm⁻¹) and excellent phase and environmental stability. However, the efficiency of Sb₂(S,Se)₃ solar cells lags far behind the Shockley–Queisser limit. One of the critical obstacles originates from various extrinsic and intrinsic defects. They mostly locate in the deep energy levels and are prone to form recombination centers, inhibiting the improvement of device performance. Herein, surface post‐treatment via potassium iodide is introduced to fabricate high‐quality Sb₂(S,Se)₃ films and solar cells. The surface post‐treatment not only manipulates the crystal growth process to form compact films with larger grain size but also forms better band alignment and inhibits the formation of deep‐level defects antimony antisite (Sb_Se), thus improving the quality of heterojunction. Consequently, the resultant Sb₂(S,Se)₃ solar cells achieve a champion power conversion efficiency of 9.22%. This study provides a new strategy of passivating deep‐level intrinsic defects via surface post‐treatment for high‐efficiency Sb₂(S,Se)₃ solar cells.