Temperature-Gradient Solution Deposition Amends Unfavorable Band Structure of Sb 2 (S,Se) 3 Film for Highly Efficient Solar Cells.

Band structure of a semiconducting film critically determines the charge separation and transport efficiency. In antimony selenosulfide (Sb 2 (S,Se) 3 ) solar cells, the hydrothermal method has achieved control of band gap width of Sb 2 (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 Sb 2 (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 Sb 2 (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.