Multiband k.p Model for Tetragonal Crystals: Application to Hybrid Halide Perovskite Nanocrystals.

We investigate the theoretical band structure of organic-inorganic perovskites APbX3, with tetragonal crystal structure. Using D4h point group symmetry properties, we derive a general 16-band Hamiltonian describing the electronic band diagram in the vicinity of the wave-vector point corresponding to the direct band-gap. For bulk crystals, a very good agreement between our predictions and experimental physical parameters, as band-gap energies and effective carrier masses, is obtained. Extending this description to three-dimensional confined hybrid halide perovskite, we calculate the size dependence of the excitonic radiative lifetime and fine structure. We describe the exciton fine structure of cube-shaped nanocrystals by an interplay of crystal-field and electron-hole exchange interaction (short- and long-range part) enhanced by confinement. Using very recent experimental results on FAPbBr3 nanocrystals, we extract the bulk short-range exchange interaction in this material and predict its value in other hybrid compounds. Finally, we also predict the bright-bright and bright-dark splittings as a function of nanocrystals size.