  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.
