Photosensitive Dielectric and Conductivity Relaxation in Lead-Free Cs₃Bi₂Cl₉ Perovskite Single Crystals

Abstract

Photosensitive dielectric and conductivity relaxation was observed in all inorganic lead-free Cs3Bi2Cl9 perovskite single crystals. Using impedance and modulus spectroscopy in dark and with subsequent light-on and -off conditions, a reversible shift in modulus peak frequencies was observed. Relevant phenomenological methods based on modified Cole–Cole- and Debye-type relaxation models were applied to analyze the light-sensitive dielectric and conductivity behavior. The detailed analysis of this reversible change in modulus spectra confirms the light-induced trap-assisted reversible dipolar relaxation phenomena in Cs3Bi2Cl9 crystals. The conductivity follows Jonscher's power law, and the value of power "n" was found to be ∼1, which further validates the Debye-type relaxation process. Our study provides an in-depth understanding and new insights into the dielectric and conductivity relaxation mechanism in perovskite single crystals, which motivates the future design of the perovskite single crystal-based energy storage devices.