Structural, optical, and electrical dynamics of Cs3Fe2Cl9: a lead-free triple perovskite candidate for advanced optoelectronics

Abstract

Research on perovskites is increasingly concentrating on lead-free compounds due to their superior structural stability and lower biological toxicity compared to lead-based alternatives. Those compounds provide a safer and more sustainable path with improved durability, making them suitable for demanding technological uses. This work reports a detailed study of the structural, optical, and electrical properties of the lead-free triple perovskite Cs₃Fe₂Cl₉. The material crystallizes in the hexagonal system with the space group P6₃/mmc, as confirmed by X-ray diffraction. The refined lattice parameters indicate better crystallinity and structural strength. Optical absorption measurements show a strong response in the ultraviolet range, with an indirect band gap of about 2.8 eV and a low Urbach energy of 0.98 eV, suggesting a lower density of defect states. Infrared spectroscopy reveals vibrational features characteristic of bioctahedral groups, thereby confirming the structural architecture of our compound. Electrical testing through AC conductivity measurements reveals thermally stimulated charge carrier hopping with activation energy near 1.38 eV. Conductivity increases with temperature, showing a shift in the conduction mechanism from orientational localized polaron hopping (single polaron hopping) at lower temperatures to more effective translational movement at higher temperatures.