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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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.
The authors declare no competing financial interests.
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Schwarze, M., Gaul, C., Scholz, R. et al. Molecular parameters responsible for thermally activated transport in doped organic semiconductors. Nature Mater 18, 242–248 (2019). https://doi.org/10.1038/s41563-018-0277-0
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