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Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals

Nature Materials volume 13, pages 1039–1043 (2014)Cite this article

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Abstract

Triplet excitons are ubiquitous in organic optoelectronics, but they are often an undesirable energy sink because they are spin-forbidden from emitting light and their high binding energy hinders the generation of free electron–hole pairs. Harvesting their energy is consequently an important technological challenge. Here, we demonstrate direct excitonic energy transfer from ‘dark’ triplets in the organic semiconductor tetracene to colloidal PbS nanocrystals, thereby successfully harnessing molecular triplet excitons in the near infrared. Steady-state excitation spectra, supported by transient photoluminescence studies, demonstrate that the transfer efficiency is at least (90 ± 13)%. The mechanism is a Dexter hopping process consisting of the simultaneous exchange of two electrons. Triplet exciton transfer to nanocrystals is expected to be broadly applicable in solar and near-infrared light-emitting applications, where effective molecular phosphors are lacking at present. In particular, this route to ‘brighten’ low-energy molecular triplet excitons may permit singlet exciton fission sensitization of conventional silicon solar cells.

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Figure 1: Schematic of triplet exciton transfer from tetracene to a PbS nanocrystal with decanoic acid ligands.
Figure 2: Steady-state observations of triplet transfer.
Figure 3: Energy transfer efficiency versus the number of carbon–carbon single bonds in the nanocrystal ligand.
Figure 4: Monitoring triplet transfer via singlet fission.
Figure 5: Monitoring triplet transfer in the time domain.

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Acknowledgements

This work was supported as part of the Center for Excitonics, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001088 (MIT). D.N.C. was partially supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1122374. J.M.S. was partially supported under FA9550-11-C-0028 awarded by the Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a, and by the US Army through the Institute for Soldier Nanotechnology (W911NF-13-D-0001). The authors thank O. Chen, C-H. Chuang, D. D. Grinolds, D. K. Harris and G. W. Hwang for stimulating discussions and their considerable help with nanocrystal synthesis, as well as R. Murphy for help in obtaining access to equipment.

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Author notes

  1. Nicholas J. Thompson, Mark W. B. Wilson and Daniel N. Congreve: These authors contributed equally to this work.

Authors and Affiliations

  1. Energy Frontier Research Center for Excitonics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    Nicholas J. Thompson, Mark W. B. Wilson, Daniel N. Congreve, Patrick R. Brown, Thomas S. Bischof, Mengfei Wu, Nadav Geva, Matthew Welborn, Troy Van Voorhis, Vladimir Bulović, Moungi G. Bawendi & Marc A. Baldo

  2. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    Mark W. B. Wilson, Jennifer M. Scherer, Thomas S. Bischof & Moungi G. Bawendi

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  1. Nicholas J. Thompson
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Contributions

N.J.T., D.N.C. and M.Wu fabricated the samples and made steady-state measurements. P.R.B. performed UPS and AFM measurements. M.W.B.W. and T.S.B. made transient measurements and M.W.B.W. prepared nanocrystal solutions for sample fabrication. J.M.S., M.W.B.W. and P.R.B. fabricated the nanocrystals. N.G. and M.Welborn simulated the nanocrystal structure. The project was conceived by N.J.T. and M.A.B. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Moungi G. Bawendi or Marc A. Baldo.

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Competing interests

MIT has filed a provisional application for patent based on this technology that names D.N.C., N.J.T., M.W.B.W., M.Wu, M.A.B., V.B. and M.G.B. as inventors.

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Thompson, N., Wilson, M., Congreve, D. et al. Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals. Nature Mater 13, 1039–1043 (2014). https://doi.org/10.1038/nmat4097

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