Ultrafast exciton transport at early times in quantum dot solids

Zhilong Zhang; Jooyoung Sung; Daniel T.W. Toolan; Sanyang Han; Raj Pandya; Michael P. Weir; James Xiao; Simon Dowland; Mengxia Liu; Anthony J. Ryan; Richard A.L. Jones; Shujuan Huang; Akshay Rao

doi:10.1038/s41563-022-01204-6

Ultrafast exciton transport at early times in quantum dot solids

Zhilong Zhang, Jooyoung Sung, Daniel T.W. Toolan, Sanyang Han, Raj Pandya, Michael P. Weir, James Xiao, Simon Dowland, Mengxia Liu, Anthony J. Ryan, Richard A.L. Jones, Shujuan Huang, Akshay Rao

Department of Physics and Chemistry

Research output: Contribution to journal › Article › peer-review

63 Scopus citations

Abstract

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 (~10² cm² s^–1) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (~10^–1–1 cm² 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.

Original language	English
Pages (from-to)	533-539
Number of pages	7
Journal	Nature Materials
Volume	21
Issue number	5
DOIs	https://doi.org/10.1038/s41563-022-01204-6
State	Published - May 2022

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© 2022, The Author(s), under exclusive licence to Springer Nature Limited.

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abstract = "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 (~102 cm2 s–1) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (~10–1–1 cm2 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.",

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AU - Zhang, Zhilong

AU - Sung, Jooyoung

AU - Toolan, Daniel T.W.

AU - Han, Sanyang

AU - Pandya, Raj

AU - Weir, Michael P.

AU - Xiao, James

AU - Dowland, Simon

AU - Liu, Mengxia

AU - Ryan, Anthony J.

AU - Jones, Richard A.L.

AU - Huang, Shujuan

AU - Rao, Akshay

PY - 2022/5

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N2 - 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 (~102 cm2 s–1) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (~10–1–1 cm2 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.

AB - 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 (~102 cm2 s–1) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (~10–1–1 cm2 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.

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Ultrafast exciton transport at early times in quantum dot solids

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