Ionic Liquid‐Assisted Crystallization Strategy Enables Simultaneous Regulation of Microstructure and Trap States for High‐Efficiency Sb 2 (S,Se) 3 Solar Cells

ABSTRACT Developing a feasible and effective crystallization approach to simultaneously amend microstructure and trap states in antimony sulfoselenide (Sb 2 (S,Se) 3 ) absorber is extremely crucial and challenging for high‐efficient solar cells. Herein, a regulation strategy is proposed to control crystallization process of Sb 2 (S,Se) 3 using ionic liquids (ILs) consisted of halide (X) anions (Cl − , Br − , and I − ) and [BMIM] + cations. In particular, the [BMIM]Br creates a liquid microenviroment on Sb 2 (S,Se) 3 surface before decomposition, accelerating the mass transfer, which induces micron‐size grains. Moreover, the [BMIM]Br can promote the [211]‐oriented growth via stronger adsorption on (211) facets of Sb 2 (S,Se) 3 . Additionally, the inhibited S and Se loss results in a near stoichiometric composition of Sb 2 (S,Se) 3 film, which greatly raises the hole concentration and optimizes the band alignment. Very important transformation from severe antisite defect Sb S to slight vacancy defect V Se2 remarkably suppresses the non‐radiative recombination. As a result, with more effective carrier transport and collection, the [BMIM]Br‐modulated device achieves a 10.89% efficiency and a 72.74% fill factor, which are separately one of the highest values for Sb 2 (S,Se) 3 solar cells so far. This work shines a new light on breaking the bottleneck in the development of Sb 2 (S,Se) 3 solar cells.