Signatures of Polaron Dynamics in Photoexcited MAPbBr₃ by Infrared Spectroscopy

Hybrid organic–inorganic perovskites (HOIPs) have attracted considerable attention in the past years as photoactive materials for low-cost, high-performance photovoltaics. Polaron formation through electron–phonon coupling has been recognized as the leading mechanism governing charge carrier transport and recombination in HOIPs. In this work, two types of MAPbBr₃ film samples deposited on different substrates (transparent insulating SrTiO₃ and a heterostructure mimicking a functioning photovoltaic cell) were photoexcited with above-bandgap radiation at 450 nm, and the effects of illumination on the sample were analyzed in the infrared region. The infrared absorbance detected at different powers of the photoexciting laser allowed us to obtain an estimate of the characteristic decay time of photoexcited polaron population of the order of 100–1000 ns. When focusing on the absorption features of the MA molecular cation in the region of the NH stretching modes, we observed the influence of hydrogen bonding and the effect of the polaron dynamics on the cation reorientation.