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Centimetre-scale electron diffusion in photoactive organic heterostructures

Nature volume 554, pages 7780 (01 February 2018) | Download Citation

Abstract

The unique properties of organic semiconductors, such as flexibility and lightness, are increasingly important for information displays, lighting and energy generation. But organics suffer from both static and dynamic disorder, and this can lead to variable-range carrier hopping1,2, which results in notoriously poor electrical properties, with low electron and hole mobilities and correspondingly short charge-diffusion lengths of less than a micrometre3,4. Here we demonstrate a photoactive (light-responsive) organic heterostructure comprising a thin fullerene channel sandwiched between an electron-blocking layer and a blended donor:C70 fullerene heterojunction that generates charges by dissociating excitons. Centimetre-scale diffusion of electrons is observed in the fullerene channel, and this can be fitted with a simple electron diffusion model. Our experiments enable the direct measurement of charge diffusivity in organic semiconductors, which is as high as 0.83 ± 0.07 square centimetres per second in a C60 channel at room temperature. The high diffusivity of the fullerene combined with the extraordinarily long charge-recombination time yields diffusion lengths of more than 3.5 centimetres, orders of magnitude larger than expected for an organic system.

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Acknowledgements

This work was supported by the United States Department of Energy SunShot Program under awards DE-EE0006708 and DE-EE0005310, and the Air Force Office of Scientific Research under award FA9550-14-1-0245. We thank M. Ware for discussions regarding numerical simulations.

Author information

Author notes

    • Quinn Burlingame
    •  & Caleb Coburn

    These authors contributed equally to this work.

Affiliations

  1. Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA

    • Quinn Burlingame
    • , Yue Qu
    •  & Stephen R. Forrest
  2. Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA

    • Caleb Coburn
    •  & Stephen R. Forrest
  3. Applied Physics Program, University of Michigan, Ann Arbor, Michigan 48109, USA

    • Xiaozhou Che
    •  & Stephen R. Forrest
  4. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA

    • Anurag Panda
    •  & Stephen R. Forrest

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Contributions

Q.B. fabricated all samples, performed all measurements, and assisted with data fitting and analysis. C.C. assisted with current measurements, formulated theory, and performed simulations and data analysis. X.C. analysed mismatch in organic photovoltaic devices between over- and under-filled device illumination measurements. A.P. assisted with ultraviolet photoelectron spectral measurement of film energy levels. Y.Q. calculated lateral electric field strength in the channel. S.R.F. supervised the project and analysed data. Q.B., C.C. and S.R.F. wrote the manuscript together.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Stephen R. Forrest.

Reviewer Information Nature thanks N. Banerji and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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DOI

https://doi.org/10.1038/nature25148

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