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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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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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.
The authors declare no competing interests.
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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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