Radiative Recombination in Hybrid Perovskites

Great progress has been made in hybrid-perovskite-based solar cells. However, the origin of the long carrier lifetimes that account for the high photovoltaic efficiency is still unclear. Various groups have proposed that the indirect band gap of hybrid perovskites, caused by spin mismatch or momentum mismatch at the band extrema, significantly suppresses radiative recombination and thus extends the carrier lifetime. In this work, we employ first-principles approaches to explicitly compute the spin texture and momentum mismatch for the prototypical hybrid perovskite, CH₃NH₃PbI₃, and assess their impact on the radiative recombination rate. We demonstrate that 1) the band extrema have similar spin orientation and 2) their slight momentum mismatch has only a minor impact on the radiative recombination rate. Our calculated radiative recombination coefficients are large, in agreement with experiments showing that radiative recombination coefficients in hybrid perovskites are of similar order of magnitude as in typical direct-gap semiconductors. These insights will guide future studies on hybrid perovskites.