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Ultrafast exciton transport at early times in quantum dot solids

Nature Materials volume 21, pages 533–539 (2022)Cite this article

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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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Fig. 1: The fs-TAM measurement of QD thin films with different capping ligands.
Fig. 2: Quantitative fs-TAM measurement results of the series of QD thin films.
Fig. 3: Quality and structural information of the QDs and films with different ligands and correlation to the fs-TAM results.
Fig. 4: The fs-TAM measurement results of other QD materials and schematics of exciton delocalization in QD solids.

Data availability

The data underlying all figures in this article are publicly available from the University of Cambridge repository at https://doi.org/10.17863/CAM.80070.

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Acknowledgements

This work has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 758826). Z.Z. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Actions grant (no. 842271, TRITON project). J.S. acknowledges support from the DGIST Start-up Fund Program of the Ministry of Science and ICT (2022010005). We acknowledge support from the Engineering and Physical Sciences Research Council (UK) via grants EP/P027741/1, EP/P027814/1 and EP/M006360/1. We thank D. Paleček and C. Schnedermann (University of Cambridge) for the assistance with the TA spectroscopy measurements and for the useful discussion on transport dynamics. We also thank Y. Wu (A*STAR Singapore) for the support on figure preparations.

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Authors and Affiliations

  1. Cavendish Laboratory, University of Cambridge, Cambridge, UK

    Zhilong Zhang, Jooyoung Sung, Sanyang Han, Raj Pandya, James Xiao, Simon Dowland, Mengxia Liu & Akshay Rao

  2. Department of Emerging Materials Science, DGIST, Daegu, Republic of Korea

    Jooyoung Sung

  3. Department of Chemistry, The University of Sheffield, Sheffield, UK

    Daniel T. W. Toolan & Anthony J. Ryan

  4. Laboratoire Kastler Brossel, École Normale Superiéure-Université PSL, CNRS, Sorbonne Université, College de France, Paris, France

    Raj Pandya

  5. Department of Physics and Astronomy, The University of Sheffield, Sheffield, UK

    Michael P. Weir

  6. School of Physics and Astronomy, The University of Nottingham, University Park, Nottingham, UK

    Michael P. Weir

  7. Department of Materials Science, University of Manchester, Manchester, UK

    Richard A. L. Jones

  8. School of Engineering, Macquarie University, Sydney, New South Wales, Australia

    Shujuan Huang

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Contributions

Z.Z., J.S. and A.R. conceived the project. Z.Z. performed the sample synthesis and fabrication. Z.Z. and J.S. performed fs-TAM and other optical measurements. R.P. performed measurements on cadmium chalcogenide QD solids. D.T.W.T., M.P.W., A.J.R. and R.A.L.J. supported and performed the GISAXS measurements and analysis. S. Han and M.L. provided input into the sample preparation. J.X. conducted electron microscopy measurements. S.D. contributed to the PLQY measurements. S. Huang provided input into the design of the experiments and discussion of results. Z.Z., J.S. and A.R. wrote the paper with input from all authors.

Corresponding authors

Correspondence to Jooyoung Sung or Akshay Rao.

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Supplementary Figs. 1–37, Tables 1–4, Discussion and experimental details.

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Zhang, Z., Sung, J., Toolan, D.T.W. et al. Ultrafast exciton transport at early times in quantum dot solids. Nat. Mater. 21, 533–539 (2022). https://doi.org/10.1038/s41563-022-01204-6

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