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Download fileCarrier Transport in PbS and PbSe QD Films Measured by Photoluminescence Quenching
journal contribution
posted on 24.07.2014, 00:00 authored by Jing Zhang, Jason Tolentino, E. Ryan Smith, Jianbing Zhang, Matthew
C. Beard, Arthur J. Nozik, Matt Law, Justin C. JohnsonThe temperature-dependent quantum
yield of photoluminescence (PL)
has been measured in films of various sizes of PbS and PbSe quantum
dots (QDs) capped with alkanedithiol ligands with lengths varying
from 4 to 20 Å. We demonstrate that PL within QD films can provide
information about transport in a regime that is relevant to solar
photoconversion. The ligand-length dependent PL quenching reveals
behavior similar to that of ligand-length dependent carrier mobility
determined from field-effect transistor (FET) measurements in the
dark. The data are described by a model in which band tail luminescence
is quenched upon thermal activation by charge separation and hopping
followed by nonradiative recombination. We extract the tunneling parameter
β and find values of 1.1 ± 0.2 Å–1 except for a value of 0.7 for the smallest QD sample. Changes in
the transport mechanism may be due to unique surface faceting or QD-ligand
coupling that occurs in small QDs. Furthermore, we compare all-organic
capped PbS QD films with those infilled by Al2O3, discovering a surprisingly small value of β less than 0.3
for the latter, which may be related to a graded potential barrier
because of amorphous Al2O3 at the QD surface
or interfacial chemistry inherent in the atomic layer deposition process.