Excitations Partition into Two Distinct Populations in Bulk Perovskites

摘要

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 CH_3NH_3PbBr_3 and CH_3NH_3PbI_3 crystals, but that they are more pronounced in CH_3NH_3PbBr_3. Single-crystal CH_3NH_3PbBr_3 could represent the key to understanding the impact of polarons on the transport properties of perovskite optoelectronic devices.