Lead-free double perovskite Cs2MBiCl6 (M = Ag, Cu): insights into the optical, dielectric, and charge transfer properties

Abstract

Recently, double perovskites have shown excellent potential considering the instability and toxicity problems of lead halide perovskites in optoelectronic devices. Here, the double perovskites Cs₂MBiCl₆ (M = Ag, Cu) were successfully synthesized via the slow evaporation solution growth technique. The cubic phase of these double perovskite materials was verified through the X-ray diffraction pattern. The investigation of Cs₂CuBiCl₆ and Cs₂AgBiCl₆ utilizing optical analysis showed that their respective indirect band-gap values were 1.31 and 2.92 eV, respectively. These materials, which are double perovskites, were examined using the impedance spectroscopy technique within the 10⁻¹ to 10⁶ Hz frequency and 300–400 K temperature ranges. Jonncher's power law was utilized to describe AC conductivity. The outcomes of the study on charge transportation in Cs₂MBiCl₆ (where M = Ag, Cu) suggest that the non-overlapping small polaron tunneling mechanism was present in Cs₂CuBiCl₆, whereas the overlapping large polaron tunneling mechanism was present in Cs₂AgBiCl₆.