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Double doping of conjugated polymers with monomer molecular dopants

Abstract

Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.

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The authors declare that the main data supporting the findings of this study are available within the article and its Supplementary Information files. Additional data are available from the corresponding authors upon request.

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Acknowledgements

We gratefully acknowledge financial support from the Swedish Research Council through grant no. 2016-06146, the Knut and Alice Wallenberg Foundation through a Wallenberg Academy Fellowship and the European Research Council (ERC) under grant agreement no. 637624. The authors thank the Cornell High Energy Synchrotron Source (CHESS) (supported by the NSF & NIH/NIGMS through NSF award DMR-1332208) for providing experimental time for GIWAXS measurements. We thank the Freiburg Materials Research Center (FMF) and Anders Mårtensson (Chalmers) for help with SEC measurements. We would like to thank Professor Koen Vandewal for helpful discussions. S.R.M. and Y.Z. thank the US National Science Foundation for support of this work, under award no. DMR-1729737. S.F. and H.S. acknowledge financial support from VINNOVA (grant no. 2015-04859) and the Swedish Research Council (grant no. 2016-03979). DFT simulations by T.F.H., D.N. and A.J.M. were supported by the US Department of Energy, Office of Basic Energy Sciences under award DE-SC0010419. M.F. and X.L. acknowledge support by the Swedish Research Council (grant no. 2016-05498). A.G. and I.M. acknowledge funding from the Engineering and Physical Sciences Research Council (EP/G037515/1).

Author information

D.K., R.K. and C.M. conceived the project. R.K., A.G., D.S. and Y.Z. synthesized the materials. D.K., A.C. and J.H. prepared samples, performed electrical and spectroscopic measurements and analysed data. D.K. and L.Y. recorded and analysed the GIWAXS data. A.I.H., X.L. and M.F. recorded and analysed UPS spectra. H.S. conducted temperature-dependent conductivity and dielectric constant measurements. A.I.H. and A.G. performed the cyclic voltammetry measurements. T.F.H., D.N. and A.J.M. carried out DFT calculations and M.K. performed kinetic Monte Carlo modelling. D.K., A.I.H. and C.M. wrote the manuscript. S.R.M., I.M., M.F., S.F., M.S. and all the authors contributed to the data analysis, discussion and manuscript preparation.

Competing interests

The authors declare no competing interests.

Correspondence to David Kiefer or Christian Müller.

Supplementary information

Supplementary Information

Supplementary Sections 1–17, Supplementary Figures 1–32, Supplementary Table 1, Supplementary References 1–15

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Further reading

Fig. 1: UV–vis and FTIR spectra of F4TCNQ anions and dianions.
Fig. 2: Energy diagram summarizing the formation of dopant dianions.
Fig. 3: Amount of neutral, anionic and dianionic F4TCNQ in doped p(g42T-TT) films.
Fig. 4: Comparison of doping of p(g42T-TT) with F4TCNQ and Li+F4TCNQ•−.
Fig. 5: Work function and temperature-dependent conductivity of F4TCNQ doped p(g42T-TT).