Electronic and gap properties of Sb and Bi based halide perovskites: An ab-initio study

Halide perovskites are currently under intense investigation due to their potential applications in optoelectronics and solar cells. Among them several crystallize in low symmetry lattice structures like trigonal, hexagonal, orthorhombic and monoclinic. Employing \textit{ab-initio} electronic structure calculations in conjunction with generalized gradient approximation and hybrid functionals we study a series of perovskites with the formula A$_3$B$_2$X$_9$ which have been grown experimentally. A stands for a monovalent cation like Cs, Rb, K or the organic methylammonium molecule (MA), B is Sb or Bi, and X is a halogen. Moreover we include in our study both the effect of spin-orbit coupling in the halide perovskites and the influence of the orientation disorder of the MA cation on the energy band gaps of these compounds. Most compounds under study exhibit absorption in or close to the optical regime and thus can find application in various optoelectronic devices. Our results pave the way for further investigation on the use of these materials in technology relevant applications.