Hysteresis and pyroelectric behaviour at isomorphic transition in green CsSnI₃

Lead-free perovskite halide CsSnI₃has emerged as a promising material for optoelectronic applications due to its direct bandgap (1.3-1.4 eV), high charge carrier mobility, and strong visible-spectrum absorption. Among its polymorphs, the green phase, with a favorable bandgap of ∼1.24 eV, demonstrates enhanced structural stability and resistance to phase degradation under ambient conditions. In this study, we investigate the green polymorph of CsSnI₃and observe pyroelectric behavior, indicative of ferroelectric-like properties despite its globally centrosymmetric (Pa3-) cubic structure. Utilizing Piezo-force microscopy, dielectric measurements, impedance spectroscopy, and Raman spectroscopy, we identified local non-centrosymmetry influencing hysteresis and conduction properties. Impedance spectroscopy further reveals the interaction of grains and grain boundaries under a low AC electric field, both before and after light exposure and poling. A reduction in relaxation time with increasing temperature in poled samples is observed, while the combined effects of light exposure and poling result in an increased relaxation time. Our results indicate that local non-centrosymmetry plays a critical role in influencing hysteresis and conduction behavior. These findings highlight the importance of phase transitions and vibrational mode dynamics in optimizing the performance of CsSnI₃-based devices, paving the way for their broader application in advanced optoelectronic technologies.