Optical properties of Cs2NaTlBr6 double perovskite using GW correction and Bethe-Salpeter equation

Abstract

To avoid the toxicity of organic-inorganic perovskites, including Tl, environmentally-friendly double perovskites have drawn much attention recently due to their stability compared to normal perovskites. Despite its favorable gap, there is insufficient research on the double perovskite Cs2NaTlBr6, and its photoelectric properties are still unclear. This work investigated the electronic band structure and optical absorption spectrum of Cs2NaTlBr6 based on the excitonic effect using density functional theory, GW, and Bethe-Salpeter equation (BSE) correction. GW method, by considering the electron-hole interaction, combined with the BSE derived from two-particle Green’s function, is an accurate approach to studying the optical properties and excitonic effects. The results show that BSE correction significantly affects the optical absorption spectrum. It turns out that there is a high bounded dark exciton before the first bright one. The first bright excitons are strongly localized and have a strong binding energy. This high binding energy can cause high luminescence in light-emitting devices.