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A solution-processed n-type conducting polymer with ultrahigh conductivity

Nature volume 611, pages 271–277 (2022)Cite this article

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Abstract

Conducting polymers (CPs) with high conductivity and solution processability have made great advances since the pioneering work on doped polyacetylene1,2,3, thus creating the new field of ‘organic synthetic metals,4. Various high-performance CPs have been realized, which enable the applications of several organic electronic devices5,6. Nevertheless, most CPs exhibit hole-dominant (p-type) transport behaviour7,8, whereas the development of n-type analogues lags far behind and only a few exhibit metallic state, typically limited by low doping efficiency and ambient instability. Here we present a facilely synthesized highly conductive n-type polymer poly(benzodifurandione) (PBFDO). The reaction combines oxidative polymerization and in situ reductive n-doping, greatly increasing the doping efficiency, and a doping level of almost 0.9 charges per repeating unit can be achieved. The resultant polymer exhibits a breakthrough conductivity of more than 2,000 S cm−1 with excellent stability and an unexpected solution processability without extra side chains or surfactants. Furthermore, detailed investigations on PBFDO show coherent charge-transport properties and existence of metallic state. The benchmark performances in electrochemical transistors and thermoelectric generators are further demonstrated, thus paving the way for application of the n-type CPs in organic electronics.

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Fig. 1: The chemical structure of PBFDO and its charge-balanced form under solution and film state.
Fig. 2: The temperature-dependent conductivity and Hall measurement of PBFDO.
Fig. 3: Investigation of charge transport of PBFDO.
Fig. 4: Demonstration of device applications of PBFDO in organic electronics.

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The main data supporting the findings of this study are available within the paper and its Supplementary Information file, and related source data are available from the corresponding author on reasonable request.

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Acknowledgements

This work was financially supported by the National Key Research and Development Program of China (no. 2019YFA0705900) funded by MOST, the Basic and Applied Basic Research Major Program of Guangdong Province (no. 2019B030302007) and the National Natural Science Foundation of China (no. U21A6002).

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Authors and Affiliations

  1. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology (SCUT), Guangzhou, China

    Haoran Tang, Yuanying Liang, Chunchen Liu, Zhicheng Hu, Ao Song, Haiyang Zhao, Duokai Zhao, Yuguang Ma, Yong Cao & Fei Huang

  2. Department of Chemistry, Southern University of Science and Technology (SUSTech), Shenzhen, China

    Yifei Deng & Yuanzhu Zhang

  3. Department of Materials Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen, China

    Han Guo & Xugang Guo

  4. Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center of Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing, China

    Zidi Yu & Jian Pei

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Contributions

H.T. conceived the project and conducted materials synthesis and characterizations under the supervision of Y.C. and F.H. H.T., C.L. and Z.H. discussed and analysed data. Y.L. fabricated and measured the OECTs. Y.D. and Y.Z. conducted the SQUID and M–H measurements. A.S. and H.Z. assisted the synthesis and characterization of oligomers. D.Z. and Y.M. performed parts of the Seebeck coefficient measurements. H.T., F.H., H.G., X.G. and J.P. discussed the mechanism in PBFDO synthesis and its charge-transport mechanism. J.P. and Z.Y. helped verify the conductivity and Hall effect. H.T., C.L. and F.H. wrote the draft of the paper and all authors read and approved the paper.

Corresponding author

Correspondence to Fei Huang.

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H.T. and F.H. have filed a PCT patent application (no. PCT/CN2021/124545). The other authors declare no competing interests.

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Nature thanks Simone Fabiano, Jianguo Mei and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Investigations of reaction mechanisms.

a, In situ monitoring of change in absorption for reactions in DMSO (with TMQ and protected by argon). (Note: the concentration of H-BFDO at the beginning was 5 mg ml−1 and the reaction mixture was left to stand without stirring to prevent influence on absorption collection.) b, The chemical structure of oligomers in different solvents obtained in the model reaction. c, The UV–vis absorption of different oligomers. Addition of 2,3,5,6-tetramethylbenzene-1,4-diol (TMQH, 10 mg ml−1 in DMF) in the undoped oligomers part (oligomers (THF), heating at 80 °C for 30 min after addition) would cause the increase of absorption around 900 nm (blue line), verifying the electron-transfer n-doping process from TMQH to the polymer. d, The corresponding electrochemical cyclic voltammetry curves of oligomers. The oxidation of oligomers (DMF) was not shown, owing to the very opaque signal, which is consistent with the oxidation of PBFDO (Fig. S42) and was attributed to the doping and conductive states of the material. e, Calculated distribution of LUMO profiles and energy levels of oligomers with different repeating units. Benefitting from the rigid conjugated backbones (dihedral angles between adjacent units are less than 6°), the LUMO could delocalize over more than six repeating units, which promoted electron transport and delocalization of negative (bi)polarons. Moreover, with increasing repeating units, the LUMO levels of oligomers decreased sharply, which was in accordance with the experimental results and would promote the electron-transfer doping from hydroquinone derivatives to the polymers.

Extended Data Fig. 2 The possible mechanisms of combined oxidative polymerization and reductive n-doping for the synthesis of PBFDO.

The reaction begins from TMQ-promoted lactone dimerization through a radical pathway, which is followed by oxidative dehydrogenation. Along with the oxidative polymerization proceeding, the formed polymer can be doped with the generated TMQH simultaneously. Doping also makes the doped polymer soluble in DMSO.

Extended Data Fig. 3 The microstructure analysis of PBFDO films.

a,b, Height image and current image of PBFDO films. c,d, GIWAXS characterization of PBFDO films deposited on Si substrates. e, Corresponding (100) lamellar packing analysis of PBFDO films. f, (010) π–π packing analysis of PBFDO films.

Extended Data Fig. 4 Investigations of transport mechanisms in PBFDO.

a,b, ESR spectroscopy of PBFDO at different temperatures. The ESR intensities of the PBFDO solid slightly increased with elevating temperature from 140 to 260 K (a), which was considered as a signature of open-shell diradical resonance54. Another phenomenon of line broadening of the ESR signal was observed above 298 K, implying the existence of conduction electrons, which is a typical signature in CPs25,42 (b). These conduction electrons are increasingly scattered by phonons with increasing temperature, resulting in a shortening of the spin-lattice relaxation time and, hence, a decrease in conductivity and broadening of the ESR signals above 298 K (ref. 55). c, The total electromagnetic-wave shielding percentage versus frequency. d, Electromagnetic-interference shielding efficiency (EMI SE) of PBFDO. SEr represents shielding efficiency from reflection and SEa represents that from absorption. The outstanding SE of PBFDO can be considered as another characteristic of metallic state. e,f, Temperature dependence of phase coherence time, τφ (e), and coherence length, Lφ (f), extracted from MC. Inelastic scattering would interfere with the coherence of delocalized charge wave, especially when the Lφ is comparable with the magnetic length, LB = (ħ/eB)1/2 ≈ 25.66 B−1/2 nm (ref. 56). g,h, The conductivity of PBFDO film under the applied magnetic field B = 5 T (g) (the values were corrected using the conductivity under B = −5 T to eliminate the deviation caused by the Hall effect; the error bar represents the standard deviation caused by the uncertainty of film thickness) and corresponding log–log plot of W versus temperature (h). The zero-field conductivity was also measured for the same sample, exhibiting the characteristic of critical region, thus eliminating the deviations between different samples.

Extended Data Fig. 5 The stability characterizations of PBFDO.

a, Stability of a PBFDO film under ambient environment (25 °C, 60% relative humidity). b, Stability of PBFDO films washed by common organic solvents through spin-coating (THF, chloroform (CF), chlorobenzene (CB), acetonitrile (MeCN) and water), showing changes in conductivity. Error bars indicate the standard deviations of six experimental replicates. c, Stability of PBFDO films dealt with acid or ammonia (thickness is around 3 μm). The film was immersed in the corresponding solution for 1 min and washed with water. Error bars indicate the standard deviations of six experimental replicates. The large error bar of PBFDO immersed in conc. H2SO4 may be caused by destroyed film morphology.

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Tang, H., Liang, Y., Liu, C. et al. A solution-processed n-type conducting polymer with ultrahigh conductivity. Nature 611, 271–277 (2022). https://doi.org/10.1038/s41586-022-05295-8

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