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.