Abstract

Doped organic semiconductors typically exhibit a thermal activation of their electrical conductivity, whose physical origin is still under scientific debate. In this study, we disclose relationships between molecular parameters and the thermal activation energy (EA) of the conductivity, revealing that charge transport is controlled by the properties of host–dopant integer charge transfer complexes (ICTCs) in efficiently doped organic semiconductors. At low doping concentrations, charge transport is limited by the Coulomb binding energy of ICTCs, which can be minimized by systematic modification of the charge distribution on the individual ions. The investigation of a wide variety of material systems reveals that static energetic disorder induced by ICTC dipole moments sets a general lower limit for EA at large doping concentrations. The impact of disorder can be reduced by adjusting the ICTC density and the intramolecular relaxation energy of host ions, allowing an increase of conductivity by many orders of magnitude.

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Acknowledgements

We thank O. Kaveh and D. Schütze for performing conductivity measurements, D. Wöhrle for supplying F8ZnPc, and M. L. Tietze for insightful discussions. M.S. acknowledges financial support by the German Research Foundation (DFG) through the project MatWorldNet LE-747/44-1, the German Academic Exchange Service within the frame of the IPID4all Program and the Graduate Academy of TU Dresden. A.H. acknowledges financial support from the project UNVEiL of the German Federal Ministry of Education and Research (BMBF). S.K. thanks JSPS for financial support (KAKENHI 26248062). N.U. acknowledges support of the Global-COE Program of MEXT (G03) and 21st Century-COE Program of MEXT(G-4) for developing an ultrahigh-sensitivity UPS system. B.N. received funding from the European Union Seventh Framework Programme under grant agreement no. 607232 (THINFACE). F.O. would like to thank the DFG for financial support (project OR-349/1). Grants for computing time from the Zentrum für Informationsdienste und Hochleistungsrechnen Dresden (ZIH) are gratefully acknowledged.

Author information

Author notes

    • Koen Vandewal

    Present address: Institute for Materials Research (IMO), Hasselt University, Diepenbeek, Belgium

    • Johannes Widmer

    Present address: Heliatek GmbH, Dresden, Germany

Affiliations

  1. Dresden Integrated Center for Applied Physics and Photonic Materials, Technische Universität Dresden, Dresden, Germany

    • Martin Schwarze
    • , Reinhard Scholz
    • , Andreas Hofacker
    • , Bernhard Nell
    • , Donato Spoltore
    • , Koen Vandewal
    • , Johannes Widmer
    •  & Karl Leo
  2. Center for Advancing Electronics Dresden and Dresden Center for Computational Materials Science, Technische Universität Dresden, Dresden, Germany

    • Christopher Gaul
    • , Karl Sebastian Schellhammer
    •  & Frank Ortmann
  3. Institute for Molecular Science, Department of Photo-Molecular Science, Myodaiji, Okazaki, Aichi, Japan

    • Fabio Bussolotti
    •  & Satoshi Kera
  4. Department of Chemical Engineering, Stanford University, Stanford, CA, USA

    • Benjamin D. Naab
    •  & Zhenan Bao
  5. Graduate School of Advanced Integration Science, Chiba University, Chiba, Japan

    • Nobuo Ueno

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Contributions

M.S. designed the study and acquired the UPS data in Dresden. C.G., R.S., K.S.S. and F.O. performed DFT simulations. A.H. performed transport simulations. B.N. performed part of the conductivity measurements. F.B. acquired UPS and LEIPS data in Okazaki. B.D.N. and Z.B. provided the highly efficient dopant (2-Cyc-DMBI)2. K.L., F.O., S.K., N.U., J.W. and K.V. supervised different parts of the study. D.S. contributed valuably to the physical understanding of charge transport. M.S. and F.O. wrote the manuscript and all authors contributed to discussions and finalizing the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Martin Schwarze or Frank Ortmann or Karl Leo.

Supplementary information

  1. Supplementary Information

    Supplementary Materials and Methods, Supplementary Tables 1–3, Supplementary Figures 1–15, Supplementary References 1–22

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DOI

https://doi.org/10.1038/s41563-018-0277-0