Inverse Temperature Dependence of Charge Carrier Hopping in Quantum Dot Solids
Gilmore, R.H.; Winslow, S.W.; Lee, E.M.Y.; Ashner, M.N.; Yager, K.G.; Willard, A.P. Tisdale, W.A.
"Inverse Temperature Dependence of Charge Carrier Hopping in Quantum Dot Solids" ACS Nano 2018
We study the lattice spacing of a nanoparticle superlattice, and find that the lattice rearranges upon cooling to cryogenic temperatures.
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 (GISAXS), 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.