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Band structure of a semiconducting film critically determines the charge separation and transport efficiency. In antimony selenosulfide (Sb2(S,Se)3) solar cells, the hydrothermal method has achieved control of band gap width of Sb2(S,Se)3 thin film through tuning the atomic ratio of S/Se, resulting in an efficiency breakthrough towards 10 %. However, the obtained band structure exhibits an unfavorable gradient distribution in terms of carrier transport, which seriously impedes the device efficiency improvement. To solve this problem, here we develop a strategy by intentionally regulating hydrothermal temperature to control the chemical reaction kinetics between S and Se sources with Sb source. This approach enables the control over vertical distribution of S/Se atomic ratio in Sb2(S,Se)3 films, forming a favorable band structure which is conducive to carrier transport. Meanwhile, the adjusted element distribution not only ensures the uniformity of grain structure, but also increases the Se content of the films and suppress sulfur vacancy defects. Ultimately, the device delivers a high efficiency of 10.55 %, which is among the highest reported efficiency of Sb2(S,Se)3 solar cells. This study provides an effective strategy towards manipulating the element distribution in mixed‐anion compound films prepared by solution‐based method to optimize their optical and electrical properties. [ABSTRACT FROM AUTHOR]

The preparation of thin films with flat, compact morphology and fewer defects is the key to the efficiency of solar cells. For antimony selenosulfide (Sb2(S,Se)3), developing flexible preparation methods that can regulate the structure of the films is crucial for the defect control and performance of the devices. Herein, an effective strategy is developed of intervening in the intermediate deposition process of Sb2(S,Se)3 film to regulate its growth on the titanium dioxide (TiO2) electron transport layer (ETL). Thioacetamide (TA) is introduced as an additive and sulfur source during the chemical bath deposition. By reacting with (SbO)OH, it not only eliminates the Sb2O3 phase, but also in‐situ patches the pinholes in the Sb2(S,Se)3 film. In addition, it is found that the increase in sulfur content promotes the transformation of SbS defect to VS defect, while a lower S/Se atomic ratio can simultaneously reduce the formation of SbS and VS defects. As a result, a PCE of 8.52% is obtained, which is the champion efficiency for the solution‐processed TiO2/Sb2(S,Se)3 solar cells. This work provides a guidance for synthesizing high‐quality metal chalcogenide films on oxide substrates in terms of morphology and defect control. [ABSTRACT FROM AUTHOR]