Exciton-Polaron Transform and Its Effect on the Ultrafast Carrier Dynamic in CsPbBr3 Single Crystals

The success of CsPbBr 3 in a host of optoelectrical fields is chiefly attributed to its remarkable carrier transport properties, which have been described as unique compared with other semiconductors. Therefore, the dynamics of carriers continue to captivate the interest of researchers. In this study, by utilizing the optical-pump terahertz-probe (OPTP) techniques under a 400 nm laser excitation with varying pump fluences, the existence of polaron was directly confirmed from the THz photoconductivity spectra. Meanwhile, a two-step exciton-polaron transform model was introduced to elucidate the dynamics of polaron formation in the CsPbBr 3 single crystal, with an exciton dissociation time of 3 ps. Moreover, the exciton-polaron transform was found to be reversible, which exerted a significant impact on the bimolecular recombination process, thereby prolonging the carrier lifetime. Eventually, based on the Drude–Lorentz model in conjunction with Feynman’s theory, the polaron mobility was calculated as 197 cm 2 ·V –1 ·s –1 for CsPbBr 3 . These findings not only clarify the role of excitons in polaron dynamics but also provide essential guidance for optimizing CsPbBr 3 -based optoelectrical devices.