Vibrational Spectroscopic, Optical Properties and Electrical Conduction Mechanism of Lead-Free Perovskite Cs2ZnCl4

In recent years, the metallic halide perovskite materials without lead have drawn a lot of interest as incredibly fascinating materials for photovoltaic applications. These materials offer exceptional stability, lower toxicity, and convenient process ability making them attractive alternatives to traditional lead-based perovskites. Recent studies have demonstrated its successful utilization in indoor energy applications, thereby suggesting its potential for integration into building-integrated devices. Using the slow evaporation solution growth technique, we have successfully synthesized a non-toxic Cs2ZnCl4 metal halide compound. The X-ray diffraction measurement at room temperature that the Cs2ZnCl4 crystallizes in the orthorhombic phase of the Pnma space group. The morphological characteristics and the ratios of the constituents of Cs2ZnCl4 were determined by the SEM–EDX study. The assignment of the Raman spectrum was based on DFT calculations. The optimized geometries, vibrational frequencies, and Raman intensities were calculated using the CAM-B3LYB technique with the 6-31G(d,p) basis set. Furthermore, the direct band gap of Cs2ZnCl4 was determined to be 4.04 eV based on UV–Visible spectroscopy measurement and DFT calculations. In order to model the electrical response of the grain and the grain boundary, we have chosen an equivalent circuit composed by a series combination of two cells which are composed by a parallel combination of resistance (R) and constant phase element (CPE). The conductivity frequency dependence is interpreted using the non-overlapping small polar tunneling model (NSPT).