Critical Roles of Octahedron Bilayer Surface/Interior Bromide Defects in Photodynamics of Multi-Quantum-Well-Structured Cesium Bismuth Bromide.

We investigate theoretically the roles of the intrinsic point defects in the photophysics of wide-bandgap multi-quantum-well-structured Cs 3 Bi 2 Br 9 based on the Shockley-Read-Hall statistics and multiphonon recombination theory. The GW plus Bethe-Salpeter equation calculation reveals that there is a prominent exciton peak below the interband absorption edge, and it clarifies the experimental debate. The most energetically favorable native defects possess deep thermodynamic transition levels. The bromide self-interstitials within the octahedron bilayers exhibit as efficient carrier trapping centers through the non-radiative multiphonon recombination, with a lifetime of 184 ns being on the same order of magnitude as the experimental value. The octahedron bilayer surface bromide self-interstitials account for the experimentally observed dominant blue luminescence in Cs 3 Bi 2 Br 9 . These results reveal that the intrinsic point defects at different sites of the multi-quantum-well-like octahedron bilayers play different roles in the photodynamics of such unique layer-structured semiconductors.