A composite electrodynamic mechanism to reconcile spatiotemporally resolved exciton transport in quantum dot superlattices

TL;DR

This paper introduces a new composite electrodynamic model combining near-field FRET and far-field effects to better understand exciton transport in quantum dot superlattices, advancing optoelectronic device design.

Contribution

It presents a novel spatiotemporal measurement technique and a kinetic Monte Carlo simulation revealing a combined transport mechanism in QD solids.

Findings

Identified the significant role of far-field emission/reabsorption in exciton transport.

Provided a unified framework for understanding energy transfer in QD superlattices.

Enhanced the accuracy of exciton hopping rate predictions.

Abstract

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.