Abstract
Nanoresolved doping of polymeric semiconductors can overcome scaling limitations to create highly integrated flexible electronics, but remains a fundamental challenge due to isotropic diffusion of the dopants. Here we report a general methodology for achieving nanoscale ion-implantation-like electrochemical doping of polymeric semiconductors. This approach involves confining counterion electromigration within a glassy electrolyte composed of room-temperature ionic liquids and high-glass-transition-temperature insulating polymers. By precisely adjusting the electrolyte glass transition temperature (Tg) and the operating temperature (T), we create a highly localized electric field distribution and achieve anisotropic ion migration that is nearly vertical to the nanotip electrodes. The confined doping produces an excellent resolution of 56 nm with a lateral-extended doping length down to as little as 9.3 nm. We reveal a universal exponential dependence of the doping resolution on the temperature difference (Tg − T) that can be used to depict the doping resolution for almost infinite polymeric semiconductors. Moreover, we demonstrate its implications in a range of polymer electronic devices, including a 200% performance-enhanced organic transistor and a lateral p–n diode with seamless junction widths of <100 nm. Combined with a further demonstration in the scalability of the nanoscale doping, this concept may open up new opportunities for polymer-based nanoelectronics.
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Data availability
The relevant raw data for this study are available for research purposes from the corresponding authors upon reasonable request. Source data are provided with this paper.
Code availability
The code that supports the theoretical plots within this paper is available from the corresponding authors upon reasonable request.
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Acknowledgements
The authors acknowledge financial support from the National Natural Science Foundation (22125504, 22021002, 22305253, U22A6002), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB0520000), the Beijing Municipal Natural Science Foundation (Z220025), the K. C. Wong Education Foundation (GJTD-2020-02), the China Postdoctoral Science Foundation (119103S395), Fundamental Research Funds for the Central Universities (E1E40301X2, E2E40305X2), CAS (ZDBS-LYSLH034). We thank W. Zhang and I. Mcculloch (Imperial College London) for providing the PBTTT polymers. We appreciate J. Jiang (Institute of Chemistry, Chinese Academy of Sciences) for the valuable discussion on the mechanism part. The work in Mons has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 964677 (MITICS) and computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (FRS-FNRS) under grant number 2.5020.11 and by the Walloon Region. D.B. is FNRS Research Director.
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C.D. and F.Z. conceived and led the research. D.Z. supervised the project. C.D., L.X., F.Z. and Z.H. proposed the concept and designed the experiments. L.X. did the device fabrication, measurements, analysed the data and performed the simulations. C.D. and L.X. wrote the main manuscript with comments from all authors. C.Y. measured the Tg of semiconductors and performed the grazing-incidence wide-angle X-ray scattering experiments. Y. Zhao performed the time-of-flight secondary ion mass spectrometry measurements. Z.L. performed the infrared temperature measurements. Y.M. commented on the organization of the manuscript. Z.J. helped with the lithography process for the electrode pattern. V.L. and D.B. performed the infrared simulation of the charged polymer. Q.M. and L.J. helped with electrochemical doping. L.L. helped with scanning electron microscopy/energy-dispersive spectroscopy measurements. X.D. performed X-ray and ultraviolet photoelectron spectroscopy measurements and DFT calculations. Y. Zou helped with the X-ray and ultraviolet photoelectron spectroscopy analysis. D.Z. guided the synthesis of PNDI2TEG-2Tz polymer and commented on the manuscript. All authors contributed to the preparation of the final draft.
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Nature Nanotechnology thanks Ying Diao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 Determination of the electrolyte Tg.
a-c, Differential scanning calorimeter thermal analysis curves of (a), PMMA/EMIM-TFSI, (b), PVDF-HFP/EMIM-TFSI and (c), PEO/EMIM-TFSI electrolytes with different weight ratio of EMIM-TFSI ionic liquid. The determination of electrolyte Tg was shown in the figure by extracting the midpoint between rubber and glass baselines. d, Comparison of the glass transition temperature these three electrolytes with varying weight ratio of EMIM-TFSI. Data are presented as mean ± standard error from 3 uncertain values in fitting of the DSC curve.
Extended Data Fig. 2 Doping depth analysis of the films with different electrolyte Tg values.
a, TOF-SIMS profiles of the TFSI− and SiO2 signals as a function of sputtering time. The thickness of the films was 100 nm and were doped under different electrolyte Tg values. b, 3D tomography images of TFSI− anion in the PBTTT film that constructed from the depth profiles of graph (a). The blue and green points represent the distribution of TFSI− anion and SiO2 substrate, respectively. It can be observed that the TFSI− dopant existed within the whole thickness of 100 nm for all electrolyte Tg, although the injected ion dose decreased at the high electrolyte Tg.
Extended Data Fig. 3 Determination of the contact size (Lc) between AFM tip and electrolyte.
a, Schematic illustration of the contact between the AFM tip and electrolyte. Given the soft nature of the electrolyte, regular hollows on the electrolyte would be induced by the AFM tip that could be used to estimate the contact area between the tip and electrolyte. b, AFM height image of the PMMA/EMIM-TFSI (10%) electrolyte surface after NEII doping. c, Height profiles of the hollow array, which are derived from 9 sites as depicted in graph (b). d, Statistical distribution histograms of Lc (left) and Dc (right). The Dc means the depth of the hollow. All data are presented as mean ± standard error from 9 values that extracted from the hollows.
Supplementary information
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Supplementary Note 1, Table 1, Figs. 1–36 and references.
Source data
Source Data Fig. 1
Source data for Fig. 1 are in sheet 1. Source Data Fig. 2 Source data for Fig. 2 are in sheet 2. Source Data Fig. 3 Source data for Fig. 3 are in sheet 3. Source Data Fig. 4 Source data for Fig. 4 are in sheet 4. Source Data Fig. 5 Source data for Fig. 5 are in sheet 5.
Source Data Extended Data Fig./Table 1
Source data for extended data Fig. 1 are in sheet 1. Source Data Extended Data Fig./Table 2 Source data for extended data Fig. 1 are in sheet 2. Source Data Extended Data Fig./Table 3 Source data for extended data Fig. 1 are in sheet 3.
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Xiang, L., He, Z., Yan, C. et al. Nanoscale doping of polymeric semiconductors with confined electrochemical ion implantation. Nat. Nanotechnol. (2024). https://doi.org/10.1038/s41565-024-01653-x
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DOI: https://doi.org/10.1038/s41565-024-01653-x
