Ultrafast Exciton\nDynamics of CH₃NH₃PbBr₃ Perovskite\nNanoclusters

Abstract

Exciton dynamics of perovskite nanoclusters has been\ninvestigated\nfor the first time using femtosecond transient absorption (TA) and\ntime-resolved photoluminescence (TRPL) spectroscopy. The TA results\nshow two photoinduced absorption signals at 420 and 461 nm and a\nphotoinduced bleach (PB) signal at 448 nm. The analysis of the PB\nrecovery kinetic decay and kinetic model uncovered multiple processes\ncontributing to electron–hole recombination. The fast component\n(∼8 ps) is attributed to vibrational relaxation within the\ninitial excited state, and the medium component (∼60 ps) is\nattributed to shallow carrier trapping. The slow component is attributed\nto deep carrier trapping from the initial conduction band edge (∼666\nps) and the shallow trap state (∼40 ps). The TRPL reveals longer\ntime dynamics, with modeled lifetimes of 6.6 and 93 ns attributed\nto recombination through the deep trap state and direct band edge\nrecombination, respectively. The significant role of exciton trapping\nprocesses in the dynamics indicates that these highly confined nanoclusters\nhave defect-rich surfaces.