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Doping of molecular semiconductors through proton-coupled electron transfer

Nature volume 622, pages 285–291 (2023)Cite this article

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Abstract

The chemical doping of molecular semiconductors is based on electron-transfer reactions between the semiconductor and dopant molecules; here, the redox potential of the dopant is key to control the Fermi level of the semiconductor1,2. The tunability and reproducibility of chemical doping are limited by the availability of dopant materials and the effects of impurities such as water. Here we focused on proton-coupled electron-transfer (PCET) reactions, which are widely used in biochemical processes3,4; their redox potentials depend on an easily handled parameter, that is, proton activity. We immersed p-type organic semiconductor thin films in aqueous solutions with PCET-based redox pairs and hydrophobic molecular ions. Synergistic reactions of PCET and ion intercalation resulted in efficient chemical doping of crystalline organic semiconductor thin films under ambient conditions. In accordance with the Nernst equation, the Fermi levels of the semiconductors were controlled reproducibly with a high degree of precision—a thermal energy of about 25 millielectronvolts at room temperature and over a few hundred millielectronvolts around the band edge. A reference-electrode-free, resistive pH sensor based on this method is also proposed. A connection between semiconductor doping and proton activity, a widely used parameter in chemical and biochemical processes, may help create a platform for ambient semiconductor processes and biomolecular electronics.

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Fig. 1: Confirmation of chemical doping in aqueous solutions.
Fig. 2: pH dependence of doping levels in PBTTT thin films.
Fig. 3: Elemental analysis of thin films doped at various pH values.
Fig. 4: Repeatable control of doping levels through PCET.
Fig. 5: High doping levels achieved in aqueous doping solutions.

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Data availability

The data supporting the plots within this study are available from Zenodo at https://doi.org/10.5281/zenodo.8166159.

References

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

    Article  Google Scholar 

  2. Scaccabarozzi, A. D. et al. Doping approaches for organic semiconductors. Chem. Rev. 122, 4420–4492 (2021).

    Article  PubMed  Google Scholar 

  3. Efremov, R. G., Baradaran, R. & Sazanov, L. A. The architecture of respiratory complex I. Nature 465, 441–445 (2010).

    Article  ADS  CAS  PubMed  Google Scholar 

  4. Reece, S. Y. & Nocera, D. G. Proton-coupled electron transfer in biology: results from synergistic studies in natural and model systems. Annu. Rev. Biochem. 78, 673–699 (2009).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  5. Sze, S. M. Semiconductor Devices: Physics and Technology (John Wiley & Sons, 2008).

  6. Wang, T. et al. Transporting holes stably under iodide invasion in efficient perovskite solar cells. Science 377, 1227–1232 (2022).

    Article  ADS  CAS  PubMed  Google Scholar 

  7. Karki, A. et al. Doped semiconducting polymer nanoantennas for tunable organic plasmonics. Commun. Mater. 3, 48 (2022).

    Article  CAS  Google Scholar 

  8. Zhao, W., Ding, J., Zou, Y., Di, C.-A. & Zhu, D. Chemical doping of organic semiconductors for thermoelectric applications. Chem. Soc. Rev. 49, 7210–7228 (2020).

    Article  CAS  PubMed  Google Scholar 

  9. Lüssem, B., Riede, M. & Leo, K. Doping of organic semiconductors. Phys. Status Solidi A 210, 9–43 (2013).

    Article  ADS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  11. Kang, K. et al. 2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion. Nat. Mater. 15, 896–902 (2016).

    Article  ADS  CAS  PubMed  Google Scholar 

  12. Untilova, V., Biskup, T., Biniek, L., Vijayakumar, V. & Brinkmann, M. Control of chain alignment and crystallization helps enhance charge conductivities and thermoelectric power factors in sequentially doped P3HT:F4TCNQ films. Macromolecules 53, 2441–2453 (2020).

    Article  ADS  CAS  Google Scholar 

  13. 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).

    Article  CAS  PubMed  Google Scholar 

  14. De Leeuw, D., Simenon, M., Brown, A. & Einerhand, R. Stability of n-type doped conducting polymers and consequences for polymeric microelectronic devices. Synth. Met. 87, 53–59 (1997).

    Article  Google Scholar 

  15. Guo, S. et al. n-doping of organic electronic materials using air-stable organometallics. Adv. Mater. 24, 699–703 (2012).

    Article  CAS  PubMed  Google Scholar 

  16. Zhang, Y. et al. Electron transport and nanomorphology in solution-processed polymeric semiconductor n-doped with an air-stable organometallic dimer. Adv. Electron. Mater. 3, 1600546 (2017).

    Article  Google Scholar 

  17. Yamashita, Y. et al. Highly air-stable, n-doped conjugated polymers achieved by dimeric organometallic dopants. J. Mater. Chem. C 9, 4105–4111 (2021).

    Article  CAS  Google Scholar 

  18. Yamashita, Y. et al. Efficient molecular doping of polymeric semiconductors driven by anion exchange. Nature 572, 634–638 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  19. Thomas, E. M. et al. Effects of counter-ion size on delocalization of carriers and stability of doped semiconducting polymers. Adv. Electron. Mater. 6, 2000595 (2020).

    Article  CAS  Google Scholar 

  20. Jacobs, I. E. et al. High-efficiency ion-exchange doping of conducting polymers. Adv. Mater. 34, 2102988 (2022).

  21. Tang, C. G. et al. Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts. Nature 539, 536–540 (2016).

    Article  CAS  PubMed  Google Scholar 

  22. Yurash, B. et al. Towards understanding the doping mechanism of organic semiconductors by Lewis acids. Nat. Mater. 18, 1327–1334 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  23. Dixon, A. L., Vezin, H., Nguyen, T.-Q. & Reddy, G. M. Structural insights into Lewis acid- and F4TCNQ-doped conjugated polymers by solid-state magnetic resonance spectroscopy. Mater. Horiz. 9, 981–990 (2022).

    Article  CAS  PubMed  Google Scholar 

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

    Article  ADS  CAS  PubMed  Google Scholar 

  25. Yang, C.-Y. et al. A thermally activated and highly miscible dopant for n-type organic thermoelectrics. Nat. Commun. 11, 3292 (2020).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  26. Guo, H. et al. Transition metal-catalysed molecular n-doping of organic semiconductors. Nature 599, 67–73 (2021).

    Article  ADS  CAS  PubMed  Google Scholar 

  27. Huynh, M. T., Anson, C. W., Cavell, A. C., Stahl, S. S. & Hammes-Schiffer, S. Quinone 1e− and 2e−/2H+ reduction potentials: identification and analysis of deviations from systematic scaling relationships. J. Am. Chem. Soc. 138, 15903–15910 (2016).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  28. Ding, Y., Li, Y. & Yu, G. Exploring bio-inspired quinone-based organic redox flow batteries: a combined experimental and computational study. Chem 1, 790–801 (2016).

    Article  CAS  Google Scholar 

  29. Bratsch, S. G. Standard electrode potentials and temperature coefficients in water at 298.15 K. J. Phys. Chem. Ref. Data 18, 1–21 (1989).

    Article  ADS  CAS  Google Scholar 

  30. Trasatti, S. The absolute electrode potential: an explanatory note (recommendations 1986). Pure Appl. Chem. 58, 955–966 (1986).

    Article  CAS  Google Scholar 

  31. Hayes, J. C. & Lietzke, M. The standard electrode potential of the quinhydrone electrode from 25 to 55°. J. Phys. Chem. 64, 374–376 (1960).

    Article  CAS  Google Scholar 

  32. McCulloch, I. et al. Liquid-crystalline semiconducting polymers with high charge-carrier mobility. Nat. Mater. 5, 328–333 (2006).

    Article  ADS  CAS  PubMed  Google Scholar 

  33. Yamashita, Y. et al. Supramolecular cocrystals built through redox-triggered ion intercalation in π-conjugated polymers. Commun. Mater. 2, 45 (2021).

    Article  CAS  Google Scholar 

  34. Vijayakumar, V. et al. Effect of alkyl side chain length on doping kinetics, thermopower, and charge transport properties in highly oriented F4TCNQ-doped PBTTT films. ACS Appl. Mater. Interfaces 11, 4942–4953 (2019).

    Article  CAS  PubMed  Google Scholar 

  35. Bischak, C. G., Flagg, L. Q. & Ginger, D. S. Ion exchange gels allow organic electrochemical transistor operation with hydrophobic polymers in aqueous solution. Adv. Mater. 32, 2002610 (2020).

    Article  CAS  Google Scholar 

  36. Koh, Q.-M. et al. Overcoming the water oxidative limit for ultra-high-workfunction hole-doped polymers. Nat. Commun. 12, 3345 (2021).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  37. Hofmann, A. I., Kroon, R., Yu, L. & Müller, C. Highly stable doping of a polar polythiophene through co-processing with sulfonic acids and bistriflimide. J. Mater. Chem. C 6, 6905–6910 (2018).

    Article  CAS  Google Scholar 

  38. Cendra, C. et al. Role of the anion on the transport and structure of organic mixed conductors. Adv. Funct. Mater. 29, 1807034 (2019).

    Article  Google Scholar 

  39. Flagg, L. Q., Giridharagopal, R., Guo, J. & Ginger, D. S. Anion-dependent doping and charge transport in organic electrochemical transistors. Chem. Mater. 30, 5380–5389 (2018).

    Article  CAS  Google Scholar 

  40. Cho, E. et al. Three-dimensional packing structure and electronic properties of biaxially oriented poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) films. J. Am. Chem. Soc. 134, 6177–6190 (2012).

    Article  CAS  PubMed  Google Scholar 

  41. Guardado, J. O. & Salleo, A. Structural effects of gating poly(3-hexylthiophene) through an ionic liquid. Adv. Funct. Mater. 27, 1701791 (2017).

    Article  Google Scholar 

  42. Reyes Cruz, E. A. et al. Molecular-modified photocathodes for applications in artificial photosynthesis and solar-to-fuel technologies. Chem. Rev. 122, 16051–16109 (2022).

    Article  CAS  PubMed  Google Scholar 

  43. Boettcher, S. W. et al. Potentially confusing: potentials in electrochemistry. ACS Energy Lett. 6, 261–266 (2020).

    Article  Google Scholar 

Download references

Acknowledgements

M.I. was supported by JST, the establishment of university fellowships towards the creation of science technology innovation (grant number JPMJFS2144). This work was supported in part by JSPS KAKENHI grants (numbers JP20K15358, JP20H00392, JP22H02160 and JP22H04959). This work was supported in part by JST, CREST grant number JPMJCR21O3, Japan.

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Authors and Affiliations

  1. Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba, Japan

    Masaki Ishii, Yu Yamashita, Katsuhiko Ariga & Jun Takeya

  2. Graduate School of Science and Technology, Tokyo University of Science, Noda, Japan

    Masaki Ishii & Katsuhiko Ariga

  3. Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan

    Yu Yamashita, Shun Watanabe, Katsuhiko Ariga & Jun Takeya

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Contributions

M.I. and Y.Y. conceived, designed and performed the experiments, and analysed the data. M.I. and Y.Y. wrote the paper. S.W., K.A. and J.T. supervised the work. All authors discussed the results and reviewed the paper.

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Correspondence to Yu Yamashita.

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Extended data figures and tables

Extended Data Fig. 1 Effects of dissolved oxygen on the p-type doping of PBTTT thin films.

a, Conductivities of PBTTT thin films immersed in aqueous solutions with LiTFSI at pH 1-4. Solution pH was adjusted by H2SO4 and KOH. The error bars indicate uncertainties in the conductivity mainly stemming from uncertainties in the thickness of the PBTTT thin films and represent 1 s.d. among four individual samples. The markers indicate average values. b, UV-vis-NIR spectra of PBTTT thin films immersed in aqueous solutions with LiTFSI at pH 1. The red and blue lines refer to samples immersed without and with Ar bubbling, respectively. The plots suggest that dissolved oxygen promotes p-type doping at lower pH by the uncontrolled way in contrast to BQ/HQ.

Extended Data Fig. 2 Measurements of electrode potentials during doping processes.

a, A setup for electrode potential measurements. Ag/AgCl and PBTTT electrodes were immersed in aqueous solutions with BQ/HQ and LiTFSI. The PBTTT electrode was fabricated by forming a PBTTT thin film on a Au-coated glass substrate. b, Doping measurement setup based on the in situ monitoring of the Fermi level of PBTTT. The doping level of the OSCs (not necessarily PBTTT), which varies depending on the redox potential of PCET-type agents, can be monitored using potential measurements and precisely controlled by the addition of an acid or base.

Extended Data Fig. 3 Maintained crystalline structures of PBTTT thin films in repeated oxidation and reduction processes.

a, b, Grazing-incidence wide-angle X-ray scattering images of a PBTTT thin film repeatedly immersed in aqueous solutions at pH 2 (a) and 4 (b), resulting in the oxidation and reduction, respectively, of the PBTTT film. The numbers above the images correspond to the cycle number shown in Fig. 4a in the main text. The similar diffraction patterns of (a) and (b) show no significant change in crystalline structure by successive immersion processes. c, d, XRD spectra of a PBTTT thin film repeatedly immersed in aqueous solutions at pH 2 and 4, whose conditions are same as (a) and (b), in the out-of-plane (c) and in-plane (d) directions.

Extended Data Fig. 4 Effective p-type doping over a wide range of pH values.

a-d, UV-vis-NIR spectra and the chemical structure of poly(3-hexylthiophene-2,5-diyl) (P3HT) (a–c) and conductivities of P3HT thin films immersed in aqueous solutions with BQ/HQ and LiNFSI at pH 1-7 (see Supplementary Information for details on the solution preparation). The error bars represent uncertainties in the conductivity due to uncertainties in the thickness of the P3HT thin films and represent one standard deviation. e, f, Summary of the d-spacing values calculated from the XRD results in the direction of out-of-plane (c) and in-plane (d). The error bars indicate uncertainties in the d-spacings due to compound errors resulting from the propagation of uncertainties in the fitting of the diffraction peaks and represent one standard deviation. All results show a trend similar to that of PBTTT (Fig. 2 in the main text), thus suggesting that our doping method is versatile and allows for the selection of materials to meet the desired purpose.

Extended Data Fig. 5 Evaluation of doping levels based on elemental analysis.

F/C atomic ratio of samples doped under various conditions (same conditions as that of Fig. 5 in the main text). The error bars represent uncertainties in the atomic ratio due to uncertainties in the fitting and represent one standard deviation. The horizontal dotted line corresponds to the doped state with one hole and one anion for the each monomer unit of polymer, which is calculated based on the atomic composition of PBTTT and dopant anions.

Supplementary information

Supplementary Information

Supplementary Methods and Discussion, including Supplementary Tables 1–4 and Figs 1–8.

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Ishii, M., Yamashita, Y., Watanabe, S. et al. Doping of molecular semiconductors through proton-coupled electron transfer. Nature 622, 285–291 (2023). https://doi.org/10.1038/s41586-023-06504-8

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