Effect of the A-Site Cation on the Biexciton Dynamics in Lead Bromide Perovskite Nanocrystals

A systematic and comprehensive understanding of different aspects of the carrier dynamics of lead halide perovskite nanocrystals (LHP NCs) is the key to improving the performance of this highly anticipated material. Recent research suggests that the A-site cation of LHP materials has a significant effect on their photophysical processes, but there is still a lack of a systematic study on how the A-site cation affects their biexciton dynamics. Herein, we fabricated CsPbBr3, MAPbBr3, and FAPbBr3 NCs with similar sizes and morphologies and conducted femtosecond transient absorption (FTA) experiments on them. By a global analysis, we found that all the FTA spectra of CsPbBr3, MAPbBr3, and FAPbBr3 NCs include three decay-associated spectra (DAS) components under high pump fluence, which, respectively, are attributed to hot carrier cooling, biexciton Auger recombination (AR), and exciton recombination. By analyzing the DAS component of biexciton of CsPbBr3, MAPbBr3, and FAPbBr3 NCs, we extract their biexciton AR lifetime and biexciton binding energy. It is found that the biexciton AR lifetime of APbBr3 NCs becomes shorter as the A-site cation changes from Cs+ to MA+ and to FA+ (∼77 ps for CsPbBr3, ∼56 ps for MAPbBr3, and ∼42 ps for FAPbBr3), while the biexciton binding energy of APbBr3 NCs becomes greater as the A-site cation changes from Cs+ to MA+ and to FA+ (∼32 meV for CsPbBr3, ∼39 meV for MAPbBr3, and ∼45 meV for FAPbBr3). We also investigated how the A-site cation of APbBr3 NCs affects their hot carriers cooling time and found a consistent result as the literature's report (J. Am. Chem. Soc. 2019, 141, 3532–3540).