The electronic structure of Cs2AgBiBr6 at room temperature

Cs2AgBiBr6 is a stable halide double perovskite with a bandgap of about 2.2 eV. Therefore, it is intensively studied as a potential lead-free alternative to hybrid perovskite solar cell absorber materials such as methylammonium lead iodide. However, power conversion efficiencies of solar cells with this material have not yet exceeded 3%. A detailed understanding of the electronic structure of this material is difficult, due to the variance of reported data and experimental as well as theoretical difficulties that occur in going beyond a qualitative understanding of such an indirect semiconductor at device operation temperature. Herein, self-energy-corrected electronic structure theory including spin–orbit coupling and structural dynamics at room temperature are combined to model and understand this compound in a quantitative manner as compared with experimental findings. It is proposed that the observed low power conversion efficiencies are intrinsic and can be attributed to the density of states in the conduction band region.