2 research outputs found
Inverse Temperature Dependence of Charge Carrier Hopping in Quantum Dot Solids
In
semiconductors, increasing mobility with decreasing temperature
is a signature of charge carrier transport through delocalized bands.
Here, we show that this behavior can also occur in nanocrystal solids
due to temperature-dependent structural transformations. Using a combination
of broadband infrared transient absorption spectroscopy and numerical
modeling, we investigate the temperature-dependent charge transport
properties of well-ordered PbS quantum dot (QD) solids. Contrary to
expectations, we observe that the QD-to-QD charge tunneling rate increases
with decreasing temperature, while simultaneously exhibiting thermally
activated nearest-neighbor hopping behavior. Using synchrotron grazing-incidence
small-angle X-ray scattering, we show that this trend is driven by
a temperature-dependent reduction in nearest-neighbor separation that
is quantitatively consistent with the measured tunneling rate
Subdiffusive Exciton Transport in Quantum Dot Solids
Colloidal
quantum dots (QDs) are promising materials for use in
solar cells, light-emitting diodes, lasers, and photodetectors, but
the mechanism and length of exciton transport in QD materials is not
well understood. We use time-resolved optical microscopy to spatially
visualize exciton transport in CdSe/ZnCdS core/shell QD assemblies.
We find that the exciton diffusion length, which exceeds 30 nm in
some cases, can be tuned by adjusting the inorganic shell thickness
and organic ligand length, offering a powerful strategy for controlling
exciton movement. Moreover, we show experimentally and through kinetic
Monte Carlo simulations that exciton diffusion in QD solids does not
occur by a random-walk process; instead, energetic disorder within
the inhomogeneously broadened ensemble causes the exciton diffusivity
to decrease over time. These findings reveal new insights into exciton
dynamics in disordered systems and demonstrate the flexibility of
QD materials for photonic and optoelectronic applications