Bandgap Engineering through Fe Doping in Cs₂SnCl₆ Perovskite: Photoluminescence Characteristics and Electronic Structure Insights

The potential use of vacancy ordered double halide perovskites Cs₂SnX₆, where X = Cl, Br, and I, has increased because of recent progress in bandgap engineering and material science, giving them designable photovoltaic applications. Here, we disclose the straightforward solvothermal approach to synthesize Fe-doped Cs₂SnCl₆ perovskite. Both the pristine (Cs₂SnCl₆) and Fe:Cs₂SnCl₆ crystals show a cubic arrangement of crystals with Fm3̅m space symmetry. A subsequent crystalline phase on doping is confirmed by the examination of the (220) XRD peak and the strong correlation between Rietveld refinement and the cubic phase. Fe²⁺ ion doping allows for a steady room-temperature photoluminescence (PL) emission center at 440 nm by lowering the band gap to 3.1 eV. Notably, an optimal 5% Fe doping concentration manifests the highest PL intensity, reaching a remarkable photoluminescence quantum yield (PLQY) of up to 55%. However, beyond this threshold, concentration quenching diminishes the PL intensity, highlighting the delicate balance in doping effects. The Cs₂SnCl₆ crystal lattice exhibits band splitting confirmed from density functional theory simulations. The anisotropic development results in a huge micrometer-sized nearly 10–20 μm truncated octahedral morphology, which is confirmed by SEM. This work not only advances the empirical understanding of Fe:Cs₂SnCl₆ PL characteristics but also shows its potential for applications in various optoelectronic devices such as LEDs and solar cells. Moreover, the ability to tailor the bandgap in perovskite materials offers opportunities for improved efficiency and performance in these devices.