LAUSR

Lead‐free perovskites exhibit unique crystal structures and optical properties due to their low‐dimensional structure. However, the 0D structure of Cs2InCl5·H2O usually demonstrates poor optical properties at room temperature due to their extremely strong electron–phonon coupling interaction. In this study, a doping strategy is employed by introducing Pb2+ into Cs2InCl5·H2O, resulting in the achievement of an efficient broadband blue emission, with a photoluminescence quantum yield (PLQY) of 58%. The temperature‐dependent PL spectra reveal that the efficient emission is attributed to the weakening of the electron–phonon coupling strength in the lattice and the inhibition of the phonon‐assisted non‐radiative recombination process through Pb2+ doping. The validity of this deduction is further corroborated by the results of the Raman spectra. The results of the first‐principle calculation demonstrate that the broadband emission originates from multiple emission paths in In3+ and Pb2+ polyhedrons. In addition, Pb2+‐doped Cs2InCl5·H2O can realize the transformation from sky‐blue emission to deep‐blue emission by absorbing water in the air. Remarkably, this change is reversible during the heating–cooling cycles, demonstrating excellent optical stability with repeatable recyclability.