DFT-based numerical study of Cs ₃ QR ₆ (Q = In, Tl, Ga; R = I, Cl, Br) compounds for opto-solar applications

Abstract Due to their prospective applications in high-efficiency optoelectronic and photovoltaic devices, lead-free halide materials increasingly attract much attention. Despite this interest, basic electrical and optical characteristics of the Cs 3 QR 6 (Q = In, Tl, Ga; R = I, Br, Cl) family remain poorly described. By performing a first-principles study of their electronic structure and optical response, this paper attempts to fill this knowledge gap. Using Density Functional Theory, we investigate the electronic band structures, total and partial density of states, and the optical properties for nine Cs 3 QR 6 compounds. The bandgap values of the materials studied here range within 0.74–1.60 eV when computed with the GGA-PBE functional and within 0.54–2.79 eV with the hybrid HSE06 functional. This is suggested to depend on the electronegativity of the corresponding halide and metal–halide orbital hybridization. The calculation of the total and partial density of states show that p-orbitals dominate near the Fermi level. Optical calculations reveal significant absorption in both the visible and ultraviolet parts of the spectrum. These results stress the possibility of employing Cs 3 QR 6 compounds for further photovoltaic and optoelectronic applications.