Spectral and Dynamical Properties of Single Excitons,
Biexcitons, and Trions in Cesium–Lead-Halide Perovskite Quantum
Dots
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Abstract
Organic–inorganic lead-halide
perovskites have been the subject of recent intense interest due to
their unusually strong photovoltaic performance. A new addition to
the perovskite family is all-inorganic Cs–Pb-halide perovskite
nanocrystals, or quantum dots, fabricated via a moderate-temperature
colloidal synthesis. While being only recently introduced to the research
community, these nanomaterials have already shown promise for a range
of applications from color-converting phosphors and light-emitting
diodes to lasers, and even room-temperature single-photon sources.
Knowledge of the optical properties of perovskite quantum dots still
remains vastly incomplete. Here we apply various time-resolved spectroscopic
techniques to conduct a comprehensive study of spectral and dynamical
characteristics of single- and multiexciton states in CsPbX<sub>3</sub> nanocrystals with X being either Br, I, or their mixture. Specifically,
we measure exciton radiative lifetimes, absorption cross-sections,
and derive the degeneracies of the band-edge electron and hole states.
We also characterize the rates of intraband cooling and nonradiative
Auger recombination and evaluate the strength of exciton–exciton
coupling. The overall conclusion of this work is that spectroscopic
properties of Cs–Pb-halide quantum dots are largely similar
to those of quantum dots of more traditional semiconductors such as
CdSe and PbSe. At the same time, we observe some distinctions including,
for example, an appreciable effect of the halide identity on radiative
lifetimes, considerably shorter biexciton Auger lifetimes, and apparent
deviation of their size dependence from the “universal volume
scaling” previously observed for many traditional nanocrystal
systems. The high efficiency of Auger decay in perovskite quantum
dots is detrimental to their prospective applications in light-emitting
devices and lasers. This points toward the need for the development
of approaches for effective suppression of Auger recombination in
these nanomaterials, using perhaps insights gained from previous studies
of II–VI nanocrystals