  Quantum dot (QD) solids are promising optoelectronic materials; further
advancing their device functionality depends on understanding their energy
transport mechanisms. The commonly invoked near-field F\"orster resonance
energy transfer (FRET) theory often underestimates the exciton hopping rate in
QD solids, yet no consensus exists on the underlying cause. In response, we use
time-resolved ultrafast stimulated emission depletion (TRUSTED) microscopy, an
ultrafast transformation of stimulated emission depletion (STED) microscopy to
spatiotemporally resolve exciton diffusion in tellurium-doped
CdSe-core/CdS-shell QD superlattices. We measure the concomitant time-resolved
exciton energy decay due to excitons sampling a heterogeneous energetic
landscape within the superlattice. The heterogeneity is quantified by
single-particle emission spectroscopy. This powerful multimodal set of
observables provides sufficient constraints on a kinetic Monte Carlo simulation
of exciton transport to elucidate a composite transport mechanism that includes
both near-field FRET and previously-neglected far-field emission/reabsorption
contributions. Uncovering this mechanism offers a much-needed unified framework
in which to characterize transport in QD solids and additional principles for
device design.
