Exploring the structural and optical properties in Cs3Fe2Cl9 perovskite through ruthenium doping

Lead-free inorganic perovskites, such as Cs3Fe2Cl9, have emerged as promising alternatives to address the challenges of toxicity and instability issues. However, the wide bandgap of Cs3Fe2Cl9 limits its applicability in some applications. In this study, we systematically investigate the influence of ruthenium (Ru) doping on the structural and optical properties of Cs3Fe2Cl9 perovskite with the various doping concentrations (0%, 5%, 20%, 50%, 70% and 100%). Comprehensive characterization was performed through X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and scanning electron microscopy (SEM). Structural analysis revealed a phase transition from Cs3Fe2Cl9 (hexagonal structure) at 0% Ru doping to Cs2RuCl6 (cubic structure) at 100% Ru doping. Notably, ruthenium was successfully replaced into the pristine Cs3Fe2Cl9 perovskite due to the similar ionic radii of Fe and Ru. Optical measurements confirmed a significant bandgap reduction from 2.29 eV for pristine Cs3Fe2Cl9 to 1.79 eV at 100% Ru doping, correlating with the formation of single crystals. This tunable bandgap highlights the potential of Ru-doped Cs3Fe2Cl9 for next-generation optoelectronic applications, such as photovoltaics and photodetectors.