ABSTRACT 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 Sn 4+ ‐based Cs 2 SnCl 6 system through gradient HCl‐mediated approach to address Sn 2+ 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 Cs 2 SnCl 6 , with a carrier concentration (1.35 × 10 14 cm −3 ) and resistivity (0.55 × 10 5 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 SnCl 6 2− octahedra, which affects both morphology and defect states, contributing better material performance. These observation suggests that Cs 2 SnCl 6 is a promising candidate for lead‐free optoelectronic applications.
Karthikeyan et al. (Mon,) studied this question.