Illuminating Morphological Evolution: Unveiling the Photoluminescence Secrets of Cs₂SnCl₆ Lead-Free Halide Perovskite

Controlling defect chemistry and crystal morphology in lead-free halide perovskites can provide a new pathways leads to high-performance optoelectronic devices. This work investigates a stable Sn⁴⁺-based Cs₂SnCl₆ system through gradient HCl-mediated approach to address Sn²⁺ instability. The influence of HCl concentration shows clear effects on crystal growth, defects, and optoelectronic properties. The optimized 0.048 mol/L HCl sample shows a well-defined truncated octahedral morphology, with better structural ordering and a sharper A_1g Raman mode. It has strong UV absorption of around 3.83 eV, and better photoluminescence with a PLQY of ~27.3%. The corresponding large Stokes shift (~0.6 eV) owing to controlled defect states that balance radiative and non-radiative recombination pathways. Significantly, this sample displays n-type conductivity with enhanced carrier transport, an unreported electrical behavior in Cs₂SnCl₆, with a carrier concentration (1.35 × 10¹⁴ cm^-3) and resistivity (0.55 × 10⁵ Ω cm). This material shows good structural stability over 200 days at ambient conditions and thermally stable up to 600°C. Variation in HCl concentration controls the growth of [SnCl₆]^2- octahedra, which affects both morphology and defect states, contributing better material performance. These observation suggests that Cs₂SnCl₆ is a promising candidate for lead-free optoelectronic applications.