Exciton, Biexciton, and Hot Exciton Dynamics in CsPbBr₃ Colloidal Nanoplatelets

Lead halide perovskites have emerged as promising materials for light-emitting devices. Here, we report the preparation of colloidal CsPbBr₃ nanoplatelets (3 × 4 × 23 nm³) experiencing a strong quasi-one-dimensional quantum confinement. Ultrafast transient absorption and broadband fluorescence up-conversion spectroscopies were employed to scrutinize the carrier and quasiparticle dynamics and to obtain a full description of the spectroscopic properties of the material. An exciton binding energy of 350 meV, an absorption cross section at 3.2 eV of 5.0 ± 0.3 × 10^-15 cm^-2, an efficient biexciton Auger recombination lifetime of 9 ± 1 ps, and a biexciton binding energy of 74 ± 4 meV were determined. Moreover, a short-lived emission from hot excitons was observed, which is related to the formation of band-edge excitons. The time constant of both processes is 300 ± 50 fs. These results show that CsPbBr₃ nanoplatelets are indeed quite promising for light-emitting technological applications.