Solution-processed semiconducting transition metal dichalcogenides are at the centre of an ever-increasing research effort in printed (opto)electronics. However, device performance is limited by structural defects resulting from the exfoliation process and poor inter-flake electronic connectivity. Here, we report a new molecular strategy to boost the electrical performance of transition metal dichalcogenide-based devices via the use of dithiolated conjugated molecules, to simultaneously heal sulfur vacancies in solution-processed transition metal disulfides and covalently bridge adjacent flakes, thereby promoting percolation pathways for the charge transport. We achieve a reproducible increase by one order of magnitude in field-effect mobility (µFE), current ratio (ION/IOFF) and switching time (τS) for liquid-gated transistors, reaching 10−2 cm2 V−1 s−1, 104 and 18 ms, respectively. Our functionalization strategy is a universal route to simultaneously enhance the electronic connectivity in transition metal disulfide networks and tailor on demand their physicochemical properties according to the envisioned applications.
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We acknowledge funding from the European Commission through the Graphene Flagship, the ERC Grants SUPRA2DMAT (GA-833707), FUTURE-PRINT (GA-694101), Hetero2D and GSYNCOR, the EU Grant Neurofibres, the Agence Nationale de la Recherche through the Labex projects CSC (ANR-10-LABX-0026 CSC) and NIE (ANR-11-LABX-0058 NIE) within the Investissement d’Avenir programme (ANR-10-120 IDEX-0002-02), the International Center for Frontier Research in Chemistry (icFRC), EPSRC Grants EP/K01711X/1, EP/K017144/1, EP/N010345/1 and EP/L016057/1, and the Faraday Institution. The HAADF-STEM characterization was carried out at the Advanced Microscopy Laboratory (Dublin), a Science Foundation Ireland (SFI) supported centre.
The authors declare no competing interests.
Peer review information Nature Nanotechnology thanks Damien Voiry and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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a, UV-Vis spectra (solution). b, Raman spectra (film). c, Statistical AFM analysis performed on 300 individual MS2 flakes and comparison with values estimated via UV-Vis spectroscopy. d, Typical SEM image of drop-cast MoS2 flakes.
HAADF-STEM images and related histograms of Mo-Mo distance for the a, basal plane of LPE-MoS2, b, edge of LPE-MoS2, c, basal plane of MC-MoS2 and d, basal plane of CVD-MoS2. The histograms show a similar average Mo-Mo distance for the basal plane of all samples, with a significant decrease ~30 pm for the edge of LPE-MoS2, pointing to a higher defect density.
a, Sulfur/Metal XPS ratio before and after exposure to BDT molecules for MoS2, WS2 and ReS2. b, Summary of the XPS constraints (spin-orbit splitting and intensity ratio) implemented for the fitting of Mo3d, Re4f, W4f and S2p regions, before and after exposure to BDT molecules.
a, Schematic illustration for the ex-situ functionalization of MS2 inks with BDT. b, Outcome of stability test for pristine and BDT-functionalized MoS2 ink, along with the related zeta potential values. c, Optical image of a IDE device covered with BDT-functionalized MoS2 ink via ex-situ approach.
a, Tested reactions between MoS2 and thiolated molecules under exam (TP and BDT). Related NMR spectra at different time intervals for b, control experiment (BDT without MoS2), c, MoS2 + BDT and d, MoS2 + TP.
a, Experimental setup. b, Sketch of the samples subjected to bending deformation. c, Variation of the relative channel resistance ΔR/R0 of bare IDEs, MoS2 films, and MoS2 networks upon 5k and 10k bending cycles, along with related d, optical images of MoS2 films and networks before (left) and after (right) mechanical deformation.
Transfer curves for MoS2 LG-TFTs a, before and after treatment with BDT linkers and b, before and after treatment with PDT linkers. All curves are recorded at Vds = -100 mV, using EMI-TFSI as electrolyte and a Pt wire as gate electrode. The molecular structures of BDT and PDT are also indicated.
Ln I vs. 1000/T for VGback = + 80 V in a, MoS2 films b, TP-functionalized samples and c, MoS2 networks. EA is calculated from the curve slope with errors associated to different applied bias on the IDEs (from 1-2.5 V, that is, E = 4 x 105 – 1 x 106 V/m).
Source data for the XPS (Fig. 2a) and Raman (Fig. 2b) of MoS2 films and networks.
Source data for the electrical characterization of MoS2 films and networks reported in Fig. 3b and Fig. 3c.
Source data for the temperature-dependent electrical characteristics of MoS2 films and networks reported in Fig. 4.
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Ippolito, S., Kelly, A.G., Furlan de Oliveira, R. et al. Covalently interconnected transition metal dichalcogenide networks via defect engineering for high-performance electronic devices. Nat. Nanotechnol. 16, 592–598 (2021). https://doi.org/10.1038/s41565-021-00857-9
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