Heterodimensional Epitaxy of CsSnI 3 Microcrystalline Cubes for Bright and Efficient Near‐Infrared Light‐Emitting Diode

Abstract Tin‐halide perovskites have attracted considerable attention as near‐infrared emitters due to their environmentally benign composition, optimal bandgap, and ultrafast radiative recombination kinetics. However, achieving bright and efficient emission from tin perovskite films remains challenging due to facile Sn 2+ oxidation and uncontrolled crystallization, which often results in small grains (<100 nm) and high defect density. Here, a surface‐templated strategy for the growth of heterodimensional epitaxial CsSnI 3 microcrystalline cubes is reported. These single‐crystalline three‐dimensional domains, together with a buried‐interface two‐dimensional epitaxial passivation layer, effectively suppress tin oxidation and minimize defect density. As a result, the fabricated infrared Light‐Emitting Diode achieves a radiance of 152 W sr −1 m −2 and an external quantum efficiency of 8.11%, establishing a new benchmark for bright and efficient lead‐free near‐infrared light emitters.