Photon Energy-Dependent Ultrafast Photoinduced Terahertz Response in a Microcrystalline Film of CH₃NH₃PbBr₃

Time-resolved terahertz (THz) spectroscopy is applied for a microcrystalline film of methylammonium lead bromide perovskite, CH₃NH₃PbBr₃, to observe the carrier dynamics around the band edge. The ultrafast response of the transmitted THz electric field amplitude after carrier generation is modeled with a biexponential curve with ∼5 and 180 ps time constants, which are ascribed to Auger and electron–hole recombination processes, respectively. From the pump photon energy dependence of the time evolution of the THz electric field amplitude, it is shown that the bound exciton states and free interband excited carrier states show a clearly different temporal response. These measurements support the idea that the bound excitons generated in CH₃NH₃PbBr₃ remain as stable excitons even at room temperature (RT). This is in clear contrast to the cases in CH₃NH₃PbI₃ in which the excitons and band-edge free carriers are interchangeable at RT.