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Nanoscale transport of charge-transfer states in organic donor–acceptor blends

Nature Materials volume 14, pages 1130–1134 (2015)Cite this article

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Abstract

Charge-transfer (CT) states, bound combinations of an electron and a hole on separate molecules, play a crucial role in organic optoelectronic devices. We report direct nanoscale imaging of the transport of long-lived CT states in molecular organic donor–acceptor blends, which demonstrates that the bound electron–hole pairs that form the CT states move geminately over distances of 5–10 nm, driven by energetic disorder and diffusion to lower energy sites. Magnetic field dependence reveals a fluctuating exchange splitting, indicative of a variation in electron–hole spacing during diffusion. The results suggest that the electron–hole pair of the CT state undergoes a stretching transport mechanism analogous to an ‘inchworm’ motion, in contrast to conventional transport of Frenkel excitons. Given the short exciton lifetimes characteristic of bulk heterojunction organic solar cells, this work confirms the potential importance of CT state transport, suggesting that CT states are likely to diffuse farther than Frenkel excitons in many donor–acceptor blends.

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Figure 1: m-MTDATA/3TPYMB charge-transfer blend.
Figure 2: Diffusion imaging.
Figure 3: Excitation-power-dependent and electric-field-dependent transient analysis.
Figure 4: Magnetic field effect.

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Acknowledgements

This work was supported by the US Department of Energy, Office of Basic Energy Sciences (Award No. DE-FG02-07ER46474).

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Author notes

  1. P. B. Deotare, W. Chang, E. Hontz, D. N. Congreve and L. Shi: These authors contributed equally to this work.

Authors and Affiliations

  1. Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

    P. B. Deotare, W. Chang, E. Hontz, D. N. Congreve, L. Shi, P. D. Reusswig, B. Modtland, M. E. Bahlke, C. K. Lee, A. P. Willard, V. Bulović, T. Van Voorhis & M. A. Baldo

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  1. P. B. Deotare
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Contributions

P.B.D., W.C. and P.D.R. made optical diffusion imaging measurements and analysis. W.C., D.N.C. and B.M. fabricated samples and made magnetic field effect measurements, including temperature and doping dependence. M.E.B. made transient electric field measurements. E.H., L.S. and C.K.L. provided valuable theoretical insights and performed Monte Carlo simulations. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to M. A. Baldo.

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The authors declare no competing financial interests.

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Deotare, P., Chang, W., Hontz, E. et al. Nanoscale transport of charge-transfer states in organic donor–acceptor blends. Nature Mater 14, 1130–1134 (2015). https://doi.org/10.1038/nmat4424

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