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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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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).

Data availability

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.

References

  1. 1.

    Walzer, K., Maennig, B., Pfeiffer, M. & Leo, K. Highly efficient organic devices based on electrically doped transport layers. Chem. Rev. 107, 1233–1271 (2007).

    CAS  Article  Google Scholar 

  2. 2.

    Lu, L. et al. Recent advances in bulk heterojunction polymer solar cells. Chem. Rev. 115, 12666–12731 (2015).

    CAS  Article  Google Scholar 

  3. 3.

    Salzmann, I. & Heimel, G. Toward a comprehensive understanding of molecular doping organic semiconductors (review). J. Electron Spectrosc. Relat. Phenom. 204, 208–222 (2015).

    CAS  Article  Google Scholar 

  4. 4.

    Lüssem, B. et al. Doped organic transistors. Chem. Rev. 116, 13714–13751 (2016).

    Article  Google Scholar 

  5. 5.

    Lu, G. et al. Moderate doping leads to high performance of semiconductor/insulator polymer blend transistors. Nat. Commun. 4, 1588 (2013).

    Article  Google Scholar 

  6. 6.

    Russ, B., Glaudell, A., Urban, J. J., Chabinyc, M. L. & Segalman, R. A. Organic thermoelectric materials for energy harvesting and temperature control. Nat. Rev. Mater. 1, 16050 (2016).

    CAS  Article  Google Scholar 

  7. 7.

    Jacobs, I. E. & Moule, A. J. Controlling molecular doping in organic semiconductors. Adv. Mater. 29, 1703063 (2017).

    Article  Google Scholar 

  8. 8.

    Kroon, R. et al. Thermoelectric plastics: from design to synthesis, processing and structure–property relationships. Chem. Soc. Rev. 45, 6147–6164 (2016).

    CAS  Article  Google Scholar 

  9. 9.

    Tietze, M. L. et al. Elementary steps in electrical doping of organic semiconductors. Nat. Commun. 9, 1182 (2018).

    Article  Google Scholar 

  10. 10.

    Jacobs, I. E. et al. Polymorphism controls the degree of charge transfer in a molecularly doped semiconducting polymer. Mater. Horiz. 5, 655–660 (2018).

    CAS  Article  Google Scholar 

  11. 11.

    Pingel, P. & Neher, D. Comprehensive picture of p-type doping of P3HT with the molecular acceptor F4TCNQ. Phys. Rev. B 87, 115209 (2013).

    Article  Google Scholar 

  12. 12.

    Kiefer, D. et al. Enhanced n-doping efficiency of a naphthalenediimide-based copolymer through polar side chains for organic thermoelectrics. ACS Energy Lett. 3, 278–285 (2018).

    CAS  Article  Google Scholar 

  13. 13.

    Jacobs, I. E. et al. Comparison of solution-mixed and sequentially processed P3HT:F4TCNQ films: effect of doping-induced aggregation on film morphology. J. Mater. Chem. C 4, 3454–3466 (2016).

    CAS  Article  Google Scholar 

  14. 14.

    Euvrard, J. et al. The formation of polymer–dopant aggregates as a possible origin of limited doping efficiency at high dopant concentration. Org. Electron. 53, 135–140 (2018).

    CAS  Article  Google Scholar 

  15. 15.

    Duong, D. T., Wang, C. C., Antono, E., Toney, M. F. & Salleo, A. The chemical and structural origin of efficient p-type doping in P3HT. Org. Electron. 14, 1330–1336 (2013).

    CAS  Article  Google Scholar 

  16. 16.

    Schlitz, R. A. et al. Solubility-limited extrinsic n-type doping of a high electron mobility polymer for thermoelectric applications. Adv. Mater. 26, 2825–2830 (2014).

    CAS  Article  Google Scholar 

  17. 17.

    Naab, B. D. et al. Effective solution- and vacuum-processed n-doping by dimers of benzimidazoline radicals. Adv. Mater. 26, 4268–4272 (2014).

    CAS  Article  Google Scholar 

  18. 18.

    Perry, E. E. et al. High conductivity in a nonplanar n-doped ambipolar semiconducting polymer. Chem. Mater. 29, 9742–9750 (2017).

    CAS  Article  Google Scholar 

  19. 19.

    Lin, X. et al. Beating the thermodynamic limit with photo-activation of n-doping in organic semiconductors. Nat. Mater. 16, 1209–1215 (2017).

    CAS  Article  Google Scholar 

  20. 20.

    Dixon, D. A., Calabrese, J. C. & Miller, J. S. Crystal and molecular structure of the 2:1 charge-transfer salt of decamethylferrocene and perfluoro-7,7,8,8-tetracyano-p-quinodimethane: {[Fe(C5Me5)2]•−}2[TCNQF4]2−. The electronic structure of [TCNQF4]n (n = 0, 1−, 2−). J. Phys. Chem. 93, 2284–2291 (1989).

    CAS  Article  Google Scholar 

  21. 21.

    Sutton, A. L. et al. Structural and optical investigations of charge transfer complexes involving the F4TCNQ dianion. CrystEngComm 16, 5234–5243 (2014).

    CAS  Article  Google Scholar 

  22. 22.

    Lu, J. et al. Synthetic precursors for TCNQF4 2− compounds: synthesis, characterization, and electrochemical studies of (Pr4N)2TCNQF4 and Li2TCNQF4. J. Org. Chem. 77, 10568–10574 (2012).

    CAS  Article  Google Scholar 

  23. 23.

    Panja, S. et al. Dianions of 7,7,8,8-tetracyano-p-quinodimethane and perfluorinated tetracyanoquinodimethane: information on excited states from lifetime measurements in an electrostatic storage ring and optical absorption spectroscopy. J. Chem. Phys. 127, 124301 (2007).

    Article  Google Scholar 

  24. 24.

    Ma, L. et al. Single photon triggered dianion formation in TCNQ and F4TCNQ crystals. Sci. Rep. 6, 28510 (2016).

    CAS  Article  Google Scholar 

  25. 25.

    Cochran, J. E. et al. Molecular interactions and ordering in electrically doped polymers: blends of PBTTT and F4TCNQ. Macromolecules 47, 6836–6846 (2014).

    CAS  Article  Google Scholar 

  26. 26.

    Mendez, H. et al. Charge-transfer crystallites as molecular electrical dopants. Nat. Commun. 6, 8560 (2015).

    CAS  Article  Google Scholar 

  27. 27.

    Yim, K. H. et al. Controlling electrical properties of conjugated polymers via a solution-based p-type doping. Adv. Mater. 20, 3319–3324 (2008).

    CAS  Article  Google Scholar 

  28. 28.

    Karpov, Y. et al. High conductivity in molecularly p-doped diketopyrrolopyrrole-based polymer: the impact of a high dopant strength and good structural order. Adv. Mater. 28, 6003–6010 (2016).

    CAS  Article  Google Scholar 

  29. 29.

    Kroon, R. et al. Polar side chains enhance processability, electrical conductivity, and thermal stability of a molecularly p-doped polythiophene. Adv. Mater. 29, 1700930 (2017).

    Article  Google Scholar 

  30. 30.

    Liu, J. et al. Enhancing molecular n-type doping of donor–acceptor copolymers by tailoring side chains. Adv. Mater. 30, 1704630 (2018).

    Article  Google Scholar 

  31. 31.

    Li, J. et al. The effect of thermal annealing on dopant site choice in conjugated polymers. Org. Electron. 33, 23–31 (2016).

    Article  Google Scholar 

  32. 32.

    Song, C. K., Eckstein, B. J., Tam, T. L., Trahey, L. & Marks, T. J. Conjugated polymer energy level shifts in lithium-ion battery electrolytes. ACS Appl. Mater. Interfaces 6, 19347–19354 (2014).

    CAS  Article  Google Scholar 

  33. 33.

    Moia, D. et al. A salt water battery with high stability and charging rates made from solution processed conjugated polymers with polar side chains. Preprint at http://arxiv.org/abs/1711.10457 (2017).

  34. 34.

    Brebels, J., Manca, J. V., Lutsen, L., Vanderzande, D. & Maes, W. High dielectric constant conjugated materials for organic photovoltaics. J. Mater. Chem. A 5, 24037–24050 (2017).

    CAS  Article  Google Scholar 

  35. 35.

    Giovannitti, A. et al. N-type organic electrochemical transistors with stability in water. Nat. Commun. 7, 13066 (2016).

    CAS  Article  Google Scholar 

  36. 36.

    Giovannitti, A. et al. Controlling the mode of operation of organic transistors through side-chain engineering. Proc. Natl Acad. Sci. USA 113, 12017–12022 (2016).

    CAS  Article  Google Scholar 

  37. 37.

    Nielsen, C. B. et al. Molecular design of semiconducting polymers for high-performance organic electrochemical transistors. J. Am. Chem. Soc. 138, 10252–10259 (2016).

    CAS  Article  Google Scholar 

  38. 38.

    Glaudell, A. M., Cochran, J. E., Patel, S. N. & Chabinyc, M. L. Impact of the doping method on conductivity and thermopower in semiconducting polythiophenes. Adv. Energy Mater. 5, 1401072 (2015).

    Article  Google Scholar 

  39. 39.

    Haworth, N. L. et al. Diagnosis of the redox levels of TCNQF4 compounds using vibrational spectroscopy. ChemPlusChem 79, 962–972 (2014).

    CAS  Article  Google Scholar 

  40. 40.

    Mityashin, A. et al. Unraveling the mechanism of molecular doping in organic semiconductors. Adv. Mater. 24, 1535–1539 (2012).

    CAS  Article  Google Scholar 

  41. 41.

    Patel, S. N. et al. Morphology controls the thermoelectric power factor of a doped semiconducting polymer. Sci. Adv. 3, e1700434 (2017).

    Article  Google Scholar 

  42. 42.

    Li, J. et al. Introducing solubility control for improved organic p-type dopants. Chem. Mater. 27, 5765–5774 (2015).

    CAS  Article  Google Scholar 

  43. 43.

    Bubnova, O. et al. Semi-metallic polymers. Nat. Mater. 13, 190–194 (2014).

    CAS  Article  Google Scholar 

  44. 44.

    Zuo, G., Abdalla, H. & Kemerink, M. Impact of doping on the density of states and the mobility in organic semiconductors. Phys. Rev. B 93, 235203 (2016).

    Article  Google Scholar 

  45. 45.

    Koech, P. K. et al. Synthesis and application of 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP): a conductivity dopant for organic light-emitting devices. Chem. Mater. 22, 3926–3932 (2010).

    CAS  Article  Google Scholar 

Download references

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).

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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.

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Correspondence to David Kiefer or Christian Müller.

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Supplementary Information

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

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Kiefer, D., Kroon, R., Hofmann, A.I. et al. Double doping of conjugated polymers with monomer molecular dopants. Nature Mater 18, 149–155 (2019). https://doi.org/10.1038/s41563-018-0263-6

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