Proceedings of nanoGe Spring Meeting 2022 (NSM22)
DOI: https://doi.org/10.29363/nanoge.nsm.2022.293
Publication date: 7th February 2022
Understanding exciton transport in quantum dot (QD) solids is crucial to their broad applications in emerging devices. Here we reveal the early-time (femtosecond) dynamics of exciton in QD solids by transient absorption microscopy [1]. We find unusually high exciton diffusivities (~102 cm2 s-1 ) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation, followed by a transition to a slower transport regime (10-1~1 cm2 s-1). Counterintuitively, the initial diffusivity is higher in QD solids with larger interdot distances, and the transport phase also lasts longer. This initial fast transport only occurs in materials with exciton Bohr radii much larger than the QD sizes, suggesting this regime is based on delocalized excitons, and the transition to slower transport is related to the process of exciton localization. Both higher QD packing density and heterogeneity accelerate the transition. These results suggest new principals to control the optoelectronic properties of QD solids.Understanding exciton transport in quantum dot (QD) solids is crucial to their broad applications in emerging devices. Here we reveal the early-time (femtosecond) dynamics of exciton in QD solids by transient absorption microscopy. We find unusually high exciton diffusivities (~102 cm2 s-1 ) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation, followed by a transition to a slower transport regime (10-1~1 cm2 s-1). Counterintuitively, the initial diffusivity is higher in QD solids with larger interdot distances, and the transport phase also lasts longer. This initial fast transport only occurs in materials with exciton Bohr radii much larger than the QD sizes, suggesting this regime is based on delocalized excitons, and the transition to slower transport is related to the process of exciton localization. Both higher QD packing density and heterogeneity accelerate the transition. These results suggest new principals to control the optoelectronic properties of QD solids.
[1] Zhang et al., Nature Materials, 2022, In Press
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