First-Principles Analysis of Radiative Recombination in Lead-Halide Perovskites

Slow radiative recombination due to a slightly indirect band gap has been proposed to explain the high efficiency of lead-halide perovskite solar cells. In this work, we calculate the radiative recombination rate from first principles for the prototypical lead-halide perovskite, MAPbI₃ (MA=CH₃NH₃). Since the structure is dynamic, with the MA molecule rotating even at room temperature, we determine the momentum mismatch between the band edges as a function of the orientation of the MA molecule. Our results demonstrate that the indirect nature of the band gap suppresses the radiative recombination rate by less than a factor of two, and that the radiative recombination coefficient is as high as in traditional direct-gap semiconductors. Our study provides a rigorous assessment of the radiative recombination mechanisms and their relation to the high efficiency of lead-halide perovskite solar cells, and will provide a sound basis for accurate modeling.