Source:APS March Meeting Abstracts, adsabs.harvard.edu (2015)
Transport of nanoscale energy in the form excitons is at the core of the operation of a wide range of nanostructured optoelectronic devices such as
solar cells, light emitting diodes and excitonic transistors. Particularly
important is the relationship between exciton transport and nanoscale
disorder, the defining characteristic of molecular and nanostructured
materials. Here we report a spatial, temporal, and spectral visualization
of exciton transport in molecular crystals and quantum dot solids. Using
tetracene as an archetype molecular crystal, the imaging reveals that
exciton transport occurs by random walk diffusion, with a transition to
subdiffusion as excitons become trapped. By controlling the morphology of
tetracene, we show that the transition to subdiffusive transport occurs at
earlier times as disorder is increased. In colloidal quantum dot films, we
show that diffusion does not occur by a random-walk process; instead,
energetic disorder causes the exciton diffusivity to decrease over time.
Our findings demonstrate that the mechanism of exciton transport depends
strongly on the nanoscale morphology and disorder.