LAUSR

Tin(IV)‐based metal halides are promising optoelectronic materials due to their robust structure and eco‐friendly nature, but these materials exhibit poor photoluminescence (PL) properties and the underlying mechanisms are still elusive. Here, a novel air‐stable hybrid Sn4+‐halide material (C8H22N2Cl)2SnCl6 that is resistant to moisture (>70% relative humidity) for >1 year is reported. The inferior PL property of (C8H22N2Cl)2SnCl6 is limited by the lattice defects and robust crystal structure, which however could be effectively improved by introducing Sb3+ ion with stereoactive 5s2 lone pair. As a result, Sb3+‐doped (C8H22N2Cl)2SnCl6 exhibits a superbly stable room‐temperature PL centered at 690 nm with an unprecedented quantum yield (QY) of 41.76% from self‐trapped excitons, which is the highest PLQY of hybrid tin(IV)‐based perovskite materials. The improved PL efficiency is attributed to the defect passivation and remarkable structure distortion induced by Sb3+ dopants. This dopant‐induced defect passivation and exciton self‐trapping approach offers an avenue to improve optoelectronic material performance.