Strong Correlation Between A‐Site Cation Order and Self‐Trapped Exciton Emission in 0D Hybrid Perovskites

Metal halide perovskites and their derived materials have garnered significant attention as promising materials for solar cell and light-emitting applications. Among them, 0D perovskites, characterized by unique crystallographic/electronic structures with isolated metal halide octahedra, exhibit tremendous potential as light emitters with self-trapped exciton (STE). However, the modulation of STE emission characteristics in 0D perovskites primarily focuses on regulating B- or X-site elements. In this work, a lead-free compound, Sb³⁺-doped ((C₂H₅)₂NH₂)₃InCl₆ single crystal, which exhibits a high photoluminescence quantum yield, is synthesized, and with increasing temperature, the A-site organic cations undergo a transition from an ordered configuration to a disordered one, accompanied by a redshift in the STE emission. Furthermore, Hirshfeld surface calculations reveal that high temperatures enhance the thermal vibrations of SbCl₆ ^3- clusters and the octahedra distortion, which are responsible for the redshift. Since this thermally triggered transition of A-site order is reversible, it can be exploited for temperature-sensing applications. Overall, in this work, valuable insights are provided into the role of A-site cations in modulating STE emission and the design of efficient light emitters.