Crystal structure of the rhombohedral vacancy-ordered perovskite (CH3NH3)2[SnCl6] for deep-UV optoelectronic applications.

Lead-free zero-dimensional (0D) hybrid halide perovskites A2SnX6 are promising candidates for stable deep-UV optoelectronics; however, the chloride end-members of the series remain underexplored. This study presents a comprehensive structural, optical, and electrical characterization of the vacancy-ordered hybrid hexachlorostannate, (CH3NH3)2[SnCl6], synthesized via controlled slow evaporation. Single crystal X-ray diffraction, combined with Raman spectroscopy, shows that this hybrid halide has a trigonal structure (space group R3̄m) composed of isolated [SnCl6]2- octahedra dynamically coupled to methylammonium cations via a robust N-H⋯Cl hydrogen-bonding network. Optical absorption analysis reveals behaviour characteristic of wide-bandgap semiconductor, dominated by ligand-to-metal charge-transfer (LMCT) transitions. Tauc and Urbach analyses yield a direct optical bandgap of ∼3.54 eV and an Urbach energy of 0.17 eV, highlighting the role of dynamic cation disorder in broadening the absorption edge. Furthermore, temperature-dependent impedance spectroscopy (323-413 K) demonstrates thermally activated small-polaron hopping. The AC conductivity is rigorously described by the Correlated Barrier Hopping (CBH) model (W M = 0.201 eV, E a = 0.30 eV). The frequency exponent decreases monotonically with temperature, confirming that charge transport is governed by coulombically correlated hopping between localized Sn-centered states, heavily modulated by grain boundary resistance and organic sublattice dynamics. These findings establish (CH3NH3)2[SnCl6] as a structurally robust, lead-free reference material, offering a tunable platform for deep-UV photodetection and wavelength-selective optoelectronic applications.