Highly efficient and stable lead-free cesium copper halide perovskites for optoelectronic applications: A DFT based study

Abstract

Recently synthesized industrially significant perovskites Cs3Cu2X5 (X=Cl,Br,I) are subjected to a density functional theory (DFT) investigation utilizing the CASTEP code. This study explores various physical features, including structural, optical, thermodynamic, elastic, mechanical, and electronic properties. There is a strong correlation between the optimized structure parameters and the existing experimental data, which demonstrates the reliability of our DFT-based computations. The band structure and density of states (TDOS and PDOS) analysis revealed that all the studied perovskites are direct band gap semiconductors, and Cs3Cu2Br5 has the smallest band gap (2.092 eV). We also discussed the mechanical and cell stability using the Born stability criterion and formation energy, respectively. The mechanical and dynamic stability of each phase is confirmed by the analysis of the elastic constants. According to the computed values of Pugh's and Poisson's ratios as well as Cauchy's pressure, all of the studied compounds are ductile in nature. The study of density of states, total charge density, and Mulliken atomic populations reveal that all the compounds have complex bonding with both ionic and covalent properties. Finally, utilizing the elastic constant data, the Debye temperatures of Cs3Cu2Cl5, Cs3Cu2Br5, and Cs3Cu2I5 have been determined as 82.90 K, 100.00 K, and 80.70 K, respectively. The analysis of thermodynamics (relatively low values of both ΘD and Kmin) as well as optical properties indicate that all the investigated materials have the potential to serve as thermal barrier coating (TBC) materials.