Temperature‐Mediated Dielectric Relaxation and Charge Transfer Mechanism in Cs₃Bi₂I₉ Single Crystals

Lead‐free metal halide perovskite materials have received significant attention for optoelectronic devices due to their excellent properties and ecofriendly composition. Utilizing the inverse temperature crystallization technique, the Cs 3 Bi 2 I 9 bismuth‐based ternary halide perovskite single crystals measuring ≈5 mm are successfully grown. This study investigates dielectric relaxation and conduction mechanism using temperature‐dependent impedance spectroscopy correlated with modulus spectroscopy across a frequency range (10 2 –10 6 Hz) at temperatures ranging from 288 to 408 K. Negative temperature coefficient of resistance‐type characteristics and temperature‐dependent relaxation behavior in Cs 3 Bi 2 I 9 lead‐free single crystals with an estimated activation energy of 30 ± 1 meV is observed. Furthermore, significant temperature‐dependent changes in dielectric properties, loss factor, electric modulus, and conductivity are observed and discussed. Notably, a pivotal transition of relaxation from non‐Debye type to Debye type with increasing temperature is observed.