Cs3(Sb0.5Bi0.5)2Br9 Cs3Bi2Br9 For the pure Sb and Bi species, the contribution of valence band is primarily given from bromine 4p orbitals with slight metal contribution, while the conduction band is mainly due to the metal cation (for Sb 5p orbitals and Bi 6p orbitals) and its interaction with bromine 4p orbitals, see Figure . Moving to the mixed Bi/Sb material, we observe substantial differences depending on the arrangement of the metal ions. The fully mixed system, with alternating SbBr6 and BiBr6 octahedra, interestingly shows a negligible difference in band gaps, with indirect and direct bandgap of 2.90 and 3.00 eV, compared to the pure Sb and Bi species, see Figure .