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Ground-state electron transfer in all-polymer donor–acceptor heterojunctions

Abstract

Doping of organic semiconductors is crucial for the operation of organic (opto)electronic and electrochemical devices. Typically, this is achieved by adding heterogeneous dopant molecules to the polymer bulk, often resulting in poor stability and performance due to dopant sublimation or aggregation. In small-molecule donor–acceptor systems, charge transfer can yield high and stable electrical conductivities, an approach not yet explored in all-conjugated polymer systems. Here, we report ground-state electron transfer in all-polymer donor–acceptor heterojunctions. Combining low-ionization-energy polymers with high-electron-affinity counterparts yields conducting interfaces with resistivity values five to six orders of magnitude lower than the separate single-layer polymers. The large decrease in resistivity originates from two parallel quasi-two-dimensional electron and hole distributions reaching a concentration of 1013 cm–2. Furthermore, we transfer the concept to three-dimensional bulk heterojunctions, displaying exceptional thermal stability due to the absence of molecular dopants. Our findings hold promise for electro-active composites of potential use in, for example, thermoelectrics and wearable electronics.

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Fig. 1: Energetics of the all-polymer D–A heterojunctions.
Fig. 2: Electrical characterization of the all-polymer D–A heterojunctions.
Fig. 3: Kinetic Monte Carlo simulation of GSET heterojunctions.
Fig. 4: GSET confirmed by EPR and UV–vis–NIR spectroscopies.
Fig. 5: Electrical characterization of BBL:P(g42T-T) blend films.

Data availability

The authors declare that the main data supporting the findings of this study are available within the paper and its Supplementary Information files. Source data for Figs. 25 are provided with the paper.

References

  1. 1.

    Reineke, S., Thomschke, M., Lussem, B. & Leo, K. White organic light-emitting diodes: status and perspective. Rev. Mod. Phys. 85, 1245–1293 (2013).

    CAS  Google Scholar 

  2. 2.

    Peumans, P., Yakimov, A. & Forrest, S. R. Small molecular weight organic thin-film photodetectors and solar cells. J. Appl. Phys. 93, 3693–3723 (2003).

    CAS  Google Scholar 

  3. 3.

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

    CAS  Google Scholar 

  4. 4.

    Bubnova, O. & Crispin, X. Towards polymer-based organic thermoelectric generators. Energy Environ. Sci. 5, 9345–9362 (2012).

    CAS  Google Scholar 

  5. 5.

    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  Google Scholar 

  6. 6.

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

    CAS  Google Scholar 

  7. 7.

    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  Google Scholar 

  8. 8.

    Salzmann, I., Heimel, G., Oehzelt, M., Winkler, S. & Koch, N. Molecular electrical doping of organic semiconductors: fundamental mechanisms and emerging dopant design rules. Acc. Chem. Res. 49, 370–378 (2016).

    CAS  Google Scholar 

  9. 9.

    Rivnay, J. et al. Organic electrochemical transistors. Nat. Rev. Mater. 3, 17086 (2018).

    CAS  Google Scholar 

  10. 10.

    Sun, H. et al. Complementary logic circuits based on high-performance n-type organic electrochemical transistors. Adv. Mater. 30, 1704916 (2018).

    Google Scholar 

  11. 11.

    Nardes, A. M. et al. Microscopic understanding of the anisotropic conductivity of PEDOT: PSS thin films. Adv. Mater. 19, 1196–1200 (2007).

    CAS  Google Scholar 

  12. 12.

    Qiu, L. et al. Enhancing doping efficiency by improving host-dopant miscibility for fullerene-based n-type thermoelectrics. J. Mater. Chem. A. 5, 21234–21241 (2017).

    CAS  Google Scholar 

  13. 13.

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

    Google Scholar 

  14. 14.

    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).

    Google Scholar 

  15. 15.

    Li, J. et al. Quantitative measurements of the temperature-dependent microscopic and macroscopic dynamics of a molecular dopant in a conjugated polymer. Macromolecules 50, 5476–5489 (2017).

    CAS  Google Scholar 

  16. 16.

    Li, J. et al. Measurement of small molecular dopant F4TCNQ and C60F36 diffusion in organic bilayer architectures. ACS Appl. Mater. Interfaces 7, 28420–28428 (2015).

    CAS  Google Scholar 

  17. 17.

    Hynynen, J. et al. Enhanced electrical conductivity of molecularly p-doped poly(3-hexylthiophene) through understanding the correlation with solid-state order. Macromolecules 50, 8140–8148 (2017).

    CAS  Google Scholar 

  18. 18.

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

    Google Scholar 

  19. 19.

    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).

    Google Scholar 

  20. 20.

    Reiser, P. et al. Dopant diffusion in sequentially doped poly(3-hexylthiophene) studied by infrared and photoelectron spectroscopy. J. Phys. Chem. C. 122, 14518–14527 (2018).

    CAS  Google Scholar 

  21. 21.

    Fahlman, M. et al. Interfaces in organic electronics. Nat. Rev. Mater. 4, 627–650 (2019).

    CAS  Google Scholar 

  22. 22.

    Alves, H., Molinari, A. S., Xie, H. X. & Morpurgo, A. F. Metallic conduction at organic charge-transfer interfaces. Nat. Mater. 7, 574–580 (2008).

    CAS  Google Scholar 

  23. 23.

    Odom, S. A. et al. Restoration of conductivity with TTF-TCNQ charge-transfer salts. Adv. Funct. Mater. 20, 1721–1727 (2010).

    CAS  Google Scholar 

  24. 24.

    Hiraoka, M. et al. On-Substrate synthesis of molecular conductor films and circuits. Adv. Mater. 19, 3248–3251 (2007).

    CAS  Google Scholar 

  25. 25.

    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  Google Scholar 

  26. 26.

    Jérome, D. Organic conductors: from charge density wave TTF−TCNQ to superconducting (TMTSF)2PF6. Chem. Rev. 104, 5565–5592 (2004).

    Google Scholar 

  27. 27.

    Chen, X. L. & Jenekhe, S. A. Bipolar conducting polymers: blends of p-type polypyrrole and an n-type ladder polymer. Macromolecules 30, 1728–1733 (1997).

    CAS  Google Scholar 

  28. 28.

    Grancini, G. et al. Hot exciton dissociation in polymer solar cells. Nat. Mater. 12, 29–33 (2013).

    CAS  Google Scholar 

  29. 29.

    Kawamura, Y., Yanagida, S. & Forrest, S. R. Energy transfer in polymer electrophosphorescent light emitting devices with single and multiple doped luminescent layers. J. Appl. Phys. 92, 87–93 (2002).

    CAS  Google Scholar 

  30. 30.

    Yoshida, H. Principle and application of low energy inverse photoemission spectroscopy: a new method for measuring unoccupied states of organic semiconductors. J. Electron Spectrosc. Relat. Phenom. 204, 116–124 (2015).

    CAS  Google Scholar 

  31. 31.

    Yoshida, H. Near-ultraviolet inverse photoemission spectroscopy using ultra-low energy electrons. Chem. Phys. Lett. 539-540, 180–185 (2012).

    CAS  Google Scholar 

  32. 32.

    Oehzelt, M., Koch, N. & Heimel, G. Organic semiconductor density of states controls the energy level alignment at electrode interfaces. Nat. Commun. 5, 4174–4174 (2014).

    CAS  Google Scholar 

  33. 33.

    Greiner, M. T. et al. Universal energy-level alignment of molecules on metal oxides. Nat. Mater. 11, 76–81 (2012).

    CAS  Google Scholar 

  34. 34.

    Bokdam, M., Çakır, D. & Brocks, G. Fermi level pinning by integer charge transfer at electrode-organic semiconductor interfaces. Appl. Phys. Lett. 98, 113303–113303 (2011).

    Google Scholar 

  35. 35.

    Braun, S., Salaneck, W. R. & Fahlman, M. Energy-level alignment at organic/metal and organic/organic interfaces. Adv. Mater. 21, 1450–1472 (2009).

    CAS  Google Scholar 

  36. 36.

    Bao, Q., Braun, S., Wang, C., Liu, X. & Fahlman, M. Interfaces of (ultra)thin polymer films in organic electronics. Adv. Mater. Interfaces 6, 1800897 (2018).

    Google Scholar 

  37. 37.

    Kiefer, D. et al. Double doping of conjugated polymers with monomer molecular dopants. Nat. Mater. 18, 149–155 (2019).

    CAS  Google Scholar 

  38. 38.

    Pasveer, W. F. et al. Unified description of charge-carrier mobilities in disordered semiconducting polymers. Phys. Rev. Lett. 94, 206601 (2005).

    CAS  Google Scholar 

  39. 39.

    Bässler, H. Charge transport in disordered organic photoconductors a Monte Carlo simulation study. Phys. Status Solidi B. 175, 15–56 (1993).

    Google Scholar 

  40. 40.

    Zuo, G., Abdalla, H. & Kemerink, M. Conjugated polymer blends for organic thermoelectrics. Adv. Electron. Mater. 5, 1800821 (2019).

    CAS  Google Scholar 

  41. 41.

    Zuo, G., Li, Z., Wang, E. & Kemerink, M. High seebeck coefficient and power factor in n-type organic thermoelectrics. Adv. Electron. Mater. 4, 1700501 (2018).

    Google Scholar 

  42. 42.

    Melianas, A. et al. Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells. Nat. Commun. 6, 8778 (2015).

    CAS  Google Scholar 

  43. 43.

    Wang, S. et al. Thermoelectric properties of solution-processed n-doped ladder-type conducting polymers. Adv. Mater. 28, 10764–10771 (2016).

    CAS  Google Scholar 

  44. 44.

    Fazzi, D., Fabiano, S., Ruoko, T.-P., Meerholz, K. & Negri, F. Polarons in π-conjugated ladder-type polymers: a broken symmetry density functional description. J. Mater. Chem. C. 7, 12876–12885 (2019).

    CAS  Google Scholar 

  45. 45.

    Yao, C. J., Zhang, H. L. & Zhang, Q. Recent progress in thermoelectric materials based on conjugated polymers. Polymers 11, 107 (2019).

    Google Scholar 

  46. 46.

    Arnold, F. E. & Van Deusen, R. L. Preparation and properties of high molecular weight, soluble oxobenz[de]imidazobenzimidazoisoquinoline ladder polymer. Macromolecules 2, 497–502 (1969).

    CAS  Google Scholar 

  47. 47.

    Yoshida, H. Note: low energy inverse photoemission spectroscopy apparatus. Rev. Sci. Instrum. 85, 016101 (2014).

    Google Scholar 

  48. 48.

    Jiang, Z. et al. The dedicated high-resolution grazing-incidence X-ray scattering beamline 8-ID-E at the advanced photon source. J. Synchrotron Radiat. 19, 627–636 (2012).

    CAS  Google Scholar 

  49. 49.

    Jiang, Z. GIXSGUI: a MATLAB toolbox for grazing-incidence X-ray scattering data visualization and reduction, and indexing of buried three-dimensional periodic nanostructured films. J. Appl. Crystallogr. 48, 917–926 (2015).

    CAS  Google Scholar 

  50. 50.

    Pettersson, H., Nik, S., Weidow, J. & Olsson, E. A method for producing site-specific TEM specimens from low contrast materials with nanometer precision. Microsc. Microanal. 19, 73–78 (2013).

    CAS  Google Scholar 

  51. 51.

    Frisch, M. J. et al. Gaussian 16, Revision B.01 (Gaussian, Inc., 2016).

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Acknowledgements

We thank C. Musumeci (Linköping University) for assistance with atomic force microscopy and S. Gustafsson (Chalmers) for assistance with TEM specimen preparation. This work was supported by the Knut and Alice Wallenberg foundation, VINNOVA (grant no. 2015-04859), the Swedish Research Council (grant agreement nos. 2016-03979, 2016-06146, 2016-05498, 2016-05990, 2018-03824), the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO Mat LiU no. 2009 00971), ÅForsk (18-313) and the European Research Council (ERC) under grant agreement no. 637624. We also thank the Chalmers Material Analysis Laboratory for their support of microscopes. T.P.R acknowledges funding from the Finnish Cultural Foundation and the Finnish Foundation for Technology Promotion. N.S. thanks the National Natural Science Foundation of China (grant no. 61805211). H.Y. acknowledges JST ALCA (JPMJAL1404) and the Futaba Foundation. Work at the University of Washington was supported by the National Science Foundation (DMR-1708450). D.F. acknowledges the Deutsche Forschungsgemeinschaft (DFG) for the grant ‘Molecular Understanding of Thermo-Electric Properties in Organic Polymers (FA 1502/1-1)’, and the Regional Computing Centre (RRZK) of Universität zu Köln, for providing computing time and resources on the HPC CHEOPS.

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S.F. conceived, designed and supervised the project. H.S. initiated the study. K.X. and H.S. prepared the samples, performed the electrical measurements and analysed the data. T.P.R. recorded and analysed the UV–vis–NIR data. G.W. performed the grazing-incidence wide-angle X-ray scattering and atomic force microscopy measurements. R.K. synthesized P(g42T-T) and P(g42T-TT). N.B.K. synthesized BBL, under S.A.J.’s supervision. Y.P. and W.M.C. performed and analysed the EPR data. X.L. and M.F. recorded and analysed the UPS spectra. D.F. performed the DFT calculations. K.S. and H.Y. performed and analysed the LEIPS data. C.Y.Y fabricated and tested the paper circuits. N.S. fabricated and tested the OLEDs. G.P., A.B.Y. and E.O. performed and analysed TEM. M.K. performed the kMC simulations. K.X., H.S., M.K., C.M. and S.F. wrote the manuscript. All authors contributed to discussion and manuscript preparation.

Corresponding authors

Correspondence to Hengda Sun or Magnus Berggren or Simone Fabiano.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–26, Table 1 and first principles calculations data.

Source data

Source Data Fig. 2

Source Data for electrical characterization of bilayers.

Source Data Fig. 3

Statistical Source Data for kinetic Monte Carlo simulation.

Source Data Fig. 4

Source Data for EPR and UV–vis–NIR spectroscopies.

Source Data Fig. 5

Source Data for electrical characterization of blend films.

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Xu, K., Sun, H., Ruoko, TP. et al. Ground-state electron transfer in all-polymer donor–acceptor heterojunctions. Nat. Mater. 19, 738–744 (2020). https://doi.org/10.1038/s41563-020-0618-7

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