Grain‐Boundary Elimination via Liquid Medium Annealing toward High‐Efficiency Sb₂Se₃ Solar Cells

Suppression of charge recombination caused by unfavorable grain boundaries (GBs) in polycrystalline thin films is essential for improving the optoelectronic performance of semiconductor devices. For emerging antimony selenide (Sb₂Se₃) materials, the unique quasi-1D structure intensifies the dependence of GB properties on the grain size and orientation, which also increases the impact of defects related to grain structure on device performance. However, these characteristics pose significant challenges in the preparation of thin films. In this study, a novel annealing approach using ammonia-thiourea is developed mixed solution as the liquid medium (LM) to finely regulate the crystallization of Sb₂Se₃ films, resulting in micron-sized large grains with enhanced [hk1] orientation and fewer defects. Mechanistic studies indicate that the intermediate phase formed at the GBs promotes the growth of large grains. Moreover, LM creates a closed and uniform environment for thin-film annealing, suppressing the volatilization of Se and reducing the types of deep-level defects. Consequently, the film delivers a device efficiency of 9.28%, the highest efficiency achieved for Sb₂Se₃ solar cells fabricated via thermal evaporation. Hence, this study provides a facile and effective annealing method for controlling the crystallization of low-dimensional materials and offers valuable guidance for the development of chalcogenide materials.