Additive‐Free Facet Engineering of Lead‐Free Double Perovskite Single‐Crystalline Microsheets for Defect‐Related Optoelectronic Properties

ABSTRACT Facet engineering of lead‐free halide double perovskites is pivotal for regulating their microscopic physicochemical properties but remains highly challenging. Here, we synthesize Cs 2 AgBiBr 6 single‐crystalline microsheets with exposed (100) and (111) facets via an additive‐free, intermediate state‐dependent spatially confined anti‐solvent crystallization method. The (111) facet of Cs 2 AgBiBr 6 is thermodynamically preferred, possessing the lowest intrinsic surface energy, while our synthetic strategy effectively stabilizes the energetically unfavorable (100) facet. We demonstrate remarkable optoelectronic differences in different exposed facets of Cs 2 AgBiBr 6 . Specifically, the (100)‑faceted Cs 2 AgBiBr 6 possesses a higher surface defect‑state density, which directly results in a dark current one order of magnitude lower than that of its (111)‑faceted counterpart, while the (111)‑faceted crystals yield a higher photocurrent. This work not only provides a synthetic strategy for the facet engineering of lead‐free halide perovskites, but it also offers key insights into the directed optimization of their optoelectronic properties.