Stabilizing the CsSnCl3 Perovskite Lattice by B‑Site Substitution for Enhanced Light Emission

All-inorganic metal halide perovskites are noted for their excellent optoelectronic properties and good chemical stability but also a propensity to transform into nonperovskite phases. A case in point is lead-free CsSnCl3, whose perovskite Phase I is metastable at room temperature and could not be stabilized by partial substitution of Cs+ or Cl–. Judging from the radii of the constituent ions of CsSnCl3, we paid attention to octahedral cations smaller than Sn2+ and selected Mn2+ and In3+ for substitution at the B-site. A quantitative structural indicator, volume per formula unit (V/Z), guided the syntheses of CsSn0.9Mn0.1Cl3 (CTMC) and CsSn0.9In0.067Cl3 (CTIC), which are shown by single-crystal X-ray diffraction and differential scanning calorimetry to be homogeneous, stable perovskite phases at room temperature. CTMC turns into a disordered perovskite structure at 193 K, lower than the corresponding transition temperature of CsSnCl3 by nearly 100 K. Vacancies in CTIC result in a more flexible crystal structure than CTMC and CsSnCl3. CTMC and CTIC appear bright yellow with a steep absorption edge at ∼450 nm, and their photoluminescence peaks are located at 645 and 484 nm, respectively, with intensities significantly enhanced from CsSnCl3. Energy transfer processes are proposed to account for the Stokes shifts in the photoluminescence of CTMC and CTIC. Thin films of CTMC glow red under ultraviolet excitation and hold promise for electroluminescence devices. This study gives insights into the structural and electronic effects of ionic substitution in CsSnCl3 and can be extended to other metastable perovskite phases.