Transient Exciton-Charge Interconversion in Single-Crystal Hybrid Perovskites

Ultrafast oscillatory transient absorption (TA) dynamics are observed in single crystals of hybrid organic-inorganic perovskite (CH₃NH₃)PbX₃ with X = I, Br, Cl. High-density photoinduced charges, low binding energy of the excitons, efficient generation and high mobility of charges, and long diffusion length of both excitons and charges led to transient interconversion between excitons and charges with high efficiency, which is responsible for the oscillatory TA dynamics at re-excitation by the probe pulses. The pump pulses initiated a quasi-equilibrium scheme of coexisting excitons and charges with high densities, the probe pulse triggered a perturbation through interconversion between these two kinds of excited "particles," which was overlapped on the intrinsic exciton relaxation dynamics, producing an oscillatory modulation with time delay. This not only reveals important photoelectronic processes with determined time scales, but also supplies physics for applications of this group of materials.