jz9b00764_si_001.pdf (3.1 MB)
Temperature-Dependent Transient Absorption Spectroscopy Elucidates Trapped-Hole Dynamics in CdS and CdSe Nanorods
journal contribution
posted on 2019-05-08, 00:00 authored by James
K. Utterback, Jesse L. Ruzicka, Hayden Hamby, Joel D. Eaves, Gordana DukovicCharge-carrier
traps play a central role in the excited-state dynamics
of semiconductor nanocrystals, but their influence is often difficult
to measure directly. In CdS and CdSe nanorods of nonuniform width,
spatially separated electrons and trapped holes display relaxation
dynamics that follow a power-law function in time that is consistent
with a recombination process limited by trapped-hole diffusion. However,
power-law relaxation can originate from mechanisms other than diffusion.
Here we report transient absorption spectroscopy measurements on CdS
and CdSe nanorods recorded at temperatures ranging from 160 to 294
K. We find that the exponent of the power law is temperature-independent,
which rules out several models based on stochastic activated processes
and provides insights into the mechanism of diffusion-limited recombination
in these structures. The data point to weak electronic coupling between
trap states and suggest that surface-localized trapped holes couple
strongly to phonons, leading to slow diffusion. Trap-to-trap hole
hopping behaves classically near room temperature, while quantum aspects
of phonon-assisted tunneling become observable at low temperatures.