Structure-Dependent Photophysical and Thermal Properties of Lead-Free Antimony Perovskites

Antimony halide perovskites have emerged as a potential alternative for lead halide perovskites in the fields of indoor photovoltaics, photodetectors, light-emitting diodes, and CO₂ photoreduction. Despite significant advances in device engineering, the fundamental properties and low-temperature dynamics of these materials remain unexplored. In this work, we have grown Cs₃Sb₂X₉ (X = Cl, Br, I) single crystals and investigated their low-temperature characteristics to gain insights into bonding interactions and lattice connectivity. Our findings show that changing the halide anion from X = Cl to Br and I can change their lattice connectivity and octahedral arrangement. Optical absorption spectroscopy, Raman spectroscopy, and other temperature-dependent measurements confirm lattice connectivity-driven photophysical properties in these lead-free perovskites. Additionally, low-temperature specific heat measurements reveal structurally dependent transitions within these crystals. The Debye–Einstein model was used to analyze the low-temperature heat capacity and observed low-frequency Einstein modes in all three crystals, generated from localized vibrations of Sb-X. These findings highlight the intricate relationship between lattice dimensionality and specific heat in antimony halide perovskites, providing insights into their fundamental properties and potential applications in a variety of fields.