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Cooperative singlet and triplet exciton transport in tetracene crystals visualized by ultrafast microscopy

Nature Chemistry volume 7, pages 785–792 (2015)Cite this article

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Abstract

Singlet fission presents an attractive solution to overcome the Shockley–Queisser limit by generating two triplet excitons from one singlet exciton. However, although triplet excitons are long-lived, their transport occurs through a Dexter transfer, making them slower than singlet excitons, which travel by means of a Förster mechanism. A thorough understanding of the interplay between singlet fission and exciton transport is therefore necessary to assess the potential and challenges of singlet-fission utilization. Here, we report a direct visualization of exciton transport in single tetracene crystals using transient absorption microscopy with 200 fs time resolution and 50 nm spatial precision. These measurements reveal a new singlet-mediated transport mechanism for triplets, which leads to an enhancement in effective triplet exciton diffusion of more than one order of magnitude on picosecond to nanosecond timescales. These results establish that there are optimal energetics of singlet and triplet excitons that benefit both singlet fission and exciton diffusion.

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Figure 1: Excited-state absorption spectra of singlet and triplet excitons.
Figure 2: Triplet exciton propagation imaged with a probe wavelength of 810 nm.
Figure 3: Singlet exciton propagation imaged with a probe wavelength of 633 nm.
Figure 4: Modelling of singlet and triplet exciton transport.
Figure 5: Population equilibrium and exciton transport in tetracene crystals.

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Acknowledgements

L.H. acknowledges start-up funding from Purdue University. The authors acknowledge the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the US Department of Energy for funding work carried out at the Radiation Laboratory at the University of Notre Dame and at National Renewable Energy Laboratory under grant no. DE-FC02-04ER15533 and DE-AC36-08GO28308, respectively. The authors thank J. Parkhill for discussions and J. Mei for the TIPS pentacene sample.

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Authors and Affiliations

  1. Department of Chemistry, Purdue University, West Lafayette, 47907, Indiana, USA

    Yan Wan, Tong Zhu & Libai Huang

  2. Radiation Laboratory, University of Notre Dame, Notre Dame, 46556, Indiana, USA

    Zhi Guo & Suxia Yan

  3. National Renewable Energy Laboratory, 15013 Denver West Pkwy, Golden, 80401, Colorado, USA

    Justin Johnson

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Contributions

L.H. and Y.W. designed the experiments. Y.W., S.Y. and T.Z. carried out the measurements. J.J. contributed materials and provided inputs in editing the manuscript. Y.W., Z.G. and L.H. analysed and modelled the data. Y.W. and L.H. wrote the manuscript.

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Correspondence to Libai Huang.

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Wan, Y., Guo, Z., Zhu, T. et al. Cooperative singlet and triplet exciton transport in tetracene crystals visualized by ultrafast microscopy. Nature Chem 7, 785–792 (2015). https://doi.org/10.1038/nchem.2348

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