Excitations Partition into Two Distinct Populations in Bulk Perovskites

Abstract Organolead halide perovskites convert optical excitations to charge carriers with remarkable efficiency in optoelectronic devices. Previous research predominantly documents dynamics in perovskite thin films; however, extensive disorder in this platform may obscure the observed carrier dynamics. Here, carrier dynamics in perovskite single‐domain single crystals is examined by performing transient absorption spectroscopy in a transmissive geometry. Two distinct sets of carrier populations that coexist at the same radiation fluence, but display different decay dynamics, are observed: one dominated by second‐order recombination and the other by third‐order recombination. Based on ab initio simulations, this observation is found to be most consistent with the hypothesis that free carriers and localized carriers coexist due to polaron formation. The calculations suggest that polarons will form in both CH₃NH₃PbBr₃ and CH₃NH₃PbI₃ crystals, but that they are more pronounced in CH₃NH₃PbBr₃. Single‐crystal CH₃NH₃PbBr₃ could represent the key to understanding the impact of polarons on the transport properties of perovskite optoelectronic devices.