Ultrafast exciton transport at early times in quantum dot solids

Quantum dot (QD) solids are an emerging platform for developing a range of optoelectronic devices. Thus, understanding exciton dynamics is essential towards developing and optimizing QD devices. Here, using transient absorption microscopy, we reveal the initial exciton dynamics in QDs with femtosecond timescales. We observe high exciton diffusivity (similar to 10(2)cm(2)s(-1)) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (similar to 10(-1)-1 cm(2)s(-1)). QD solids with larger interdot distances exhibit higher initial diffusivity and a delayed transition to the slower regime, while higher QD packing density and heterogeneity accelerate this transition. The fast transport regime occurs only in materials with exciton Bohr radii much larger than the QD sizes, suggesting the transport of delocalized excitons in this regime and a transition to slower transport governed by exciton localization. These findings suggest routes to control the optoelectronic properties of QD solids.

Automated summary

This study reveals the exciton dynamics in quantum dot solids using transient absorption microscopy and observes the changes and transitions in initial exciton diffusion. The spacing between quantum dots, packing density, and heterogeneity all have an impact on exciton dynamics. These findings contribute to the control of optoelectronic properties in quantum dot solids.