Observation of Ultrafast Exciton–Exciton Annihilation in CsPbBr3 Quantum Dots

Excited-state dynamics of CsPbBr3 quantum dots (QDs) are studied through femtosecond transient absorption spectroscopy measurements. The band-edge recombination is dominated by a single exciton process at low excitation density (<0.1 exciton QD−1). While a density-dependent quadratic decay is found in early probe decay at high excitation density (>0.25 exciton QD−1), which is attributed to exciton–exciton annihilation. Moreover, ultrafast biexcitons and slow trap-state excitons are also found with resonant energy slightly below the band edge.