Ultrafast Charge Carrier Dynamics of CsPbBr3/Cs4PbBr6 Nanocomposites

Deep insight into the ultrafast charge carrier dynamics is fundamentally significant for the development of high-performance optoelectronic devices. The CsPbBr3/Cs4PbBr6 nanocomposite, as an important member of the perovskite family, has attracted extensive research interest. However, the underlying ultrafast carrier dynamics is still elusive. Herein, an endeavor has been made to investigate the impact of Cs4PbBr6 encapsulation on the ultrafast carrier dynamics of CsPbBr3 nanoinclusions. The hot-carrier cooling time is about 190-302 fs, relying on the pump fluence, which is relatively shorter than that of pure CsPbBr3. Thus, the encapsulation of Cs4PbBr6 shortens the hot-carrier cooling time, which is attributed to the participation of longitudinal optical (LO) phonons from Cs4PbBr6 and dissipation of the energy via coupling to surface encapsulation. The biexciton binding energy is estimated to be 69 meV, with a biexciton lifetime of 40 ps. The biexciton binding energy is a relatively high value compared to those of CsPbBr3 nanostructures with similar biexciton lifetimes, which is mainly due to the smaller sizes of the CsPbBr3 inclusions in the composites.