Research ArticleSEMICONDUCTORS

Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive

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Science Advances  13 May 2016:
Vol. 2, no. 5, e1600076
DOI: 10.1126/sciadv.1600076
  • Fig. 1 Chemical structures of DPPTTT and NMe4I.
  • Fig. 2 OFET characteristics for DPPTTT and DPPTTT-NMe4I.

    Transfer (VDS = −60 V) and output characteristics of neat DPPTTT and DPPTTT-NMe4I at a molar ratio of 30:1; the transistor channel width (W) and channel length (L) were 8800 and 80 μm, respectively.

  • Fig. 3 Transfer characteristics and mobility distribution for DPPTTT-NMe4I.

    (A) Hole mobilities were extracted in two ways: (i) fitting the linear part of the plot of IDS1/2 versus VGS (purple line) and (ii) taking the two points at VTh and VGS = −30 V of the plot of IDS1/2 versus VGS (blue line) to provide a very conservative estimate of hole mobility. (B) Hole mobility (obtained by fitting the linear part of the plot of IDS1/2 versus VGS) distribution for the DPPTTT-NMe4I thin films at a molar ratio of 30:1. (C) Hole mobility (obtained by conservative estimate) distribution for the DPPTTT-NMe4I thin films at a molar ratio of 30:1.

  • Fig. 4 Operational stability of OFETs with DPPTTT-NMe4I thin films.

    (A) Cyclic stability of a representative device with the DPPTTT-NMe4I thin film at a molar ratio of 30:1 showing maintenance of ON and OFF currents during 300 continuous on/off cycles. (B) Variation of hole mobility and Ion/Ioff for DPPTTT-NMe4I FET at a molar ratio of 30:1 after the device was left in air for different periods.

  • Fig. 5 PDS spectra of DPPTTT and DPPTTT-NMe4I thin films.

    PDS spectra of thin films of DPPTTT and DPPTTT-NMe4I at a molar ratio of 30:1. The inset shows the respective Urbach energies.

  • Fig. 6 AFM images of DPPTTT and DPPTTT-NMe4I.

    (A to D) AFM height and phase images of the neat DPPTTT thin film (A and B) and the DPPTTT-NMe4I thin film at a molar ratio of 30:1 (C and D). The circles in (C) highlight the formation of more connected and larger fiber aggregates within the DPPTTT-NMe4I thin film in comparison with those marked by circles in (A) for the neat DPPTTT thin film.

  • Fig. 7 GIWAXS patterns of DPPTTT and DPPTTT-NMe4I thin films.

    (A and B) 2D GIWAXS images of DPPTTT (A) and DPPTTT-NMe4I (B) at a molar ratio of 30:1. (C) Out-of-plane linecuts of 2D GIWAXS of DPPTTT and DPPTTT-NMe4I at a molar ratio of 30:1. (D) In-plane linecuts of 2D GIWAXS of DPPTTT-NMe4I at a molar ratio of 30:1.

  • Fig. 8 Theoretical calculation of the torsion of the side alkyl chains.

    (A) The ESP map of DPPTTT (in unit of Hartree); the unit is elementary charge. (B) Illustration of the positions (including the interatomic distances) of I and NMe4+ on DPPTTT and the rotation angle of the side alkyl chain that is highlighted in cyan. (C) The variation of the calculated torsion potential versus the dihedral angle between the side chain and conjugated backbone for neat DPPTTT and those after incorporation of either I or NMe4+. (D) Schematic diagram of the torsion of the alkyl chain and indication of the dihedral angle.

  • Fig. 9 Chemical structures of PDPP4T, PBDTTT-C-T, P3HT, and P3EHT.
  • Table 1 The mobilities (μ), threshold voltages (VTh), on/off ratios (Ion/Ioff), Ioff, and subthreshold slop (S) for as-prepared BGBC FET devices.
    DPPTTT*DPPTTT/NMe4I *
    7.5153045
    μ (cm2 V−1 s−1)0.8 (2.1)8.1 (12.9)15.4 (20.1)19.5 (26.2)13.6 (17.3)
    μ§ (cm2 V−1 s−1)0.6 (0.8)1.6 (2.2)2.8 (3.8)3.6 (4.4)2.4 (3.5)
    VTh (V)−4 to 2−1 to 2−3 to 1−3 to 1−3 to 2
    Ion/Ioff (log10)6–73–45–66–76–7
    Ioff (A) (average)5.5 × 10−108.5 × 10−75.4 × 10−86.1 × 10−92.5 × 10−9
    S (V decade−1)3–3.20.9–1.11.0–1.41.0–1.21.0–1.3

    *All data were obtained in air based on more than 50 FET devices with W = 8800 μm and L = 80 μm at VDS = −60 V.

    †Molar ratio of the repeat moiety of DPPTTT versus NMe4I.

    ‡Hole mobility, extracted by fitting the linear part of the plot of IDS1/2 versus VGS, in the form of average (high).

    §Hole mobility, on the basis of two points of the plot of IDS1/2 versus VGS at VTh and VGS = −30 V using the equation IDS = Ciμ(VGSVTh)2W/2L (see text), in the form of average (high).

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/5/e1600076/DC1

      fig. S1. Transfer and output characteristics of FETs with DPPTTT and the DPPTTT-NMe4I thin film at a molar ratio of 30:1 by using CYTOP-modified dielectric layers.

      fig. S2. Extraction of hole mobilities from the transfer characteristics of DPPTTT and DPPTTT-NMe4I thin film at a molar ratio of 30:1.

      fig. S3. Variation of hole mobility for FETs with DPPTTT-NMe4I thin film at a molar ratio of 30:1 before and after thermal annealing at 80°, 100°, and 120°C.

      fig. S4. Transfer characteristics of FETs with DPPTTT-NMe4I thin films at different molar ratios.

      fig. S5. Transfer and output characteristics of FETs with DPPTTT-NMe4Br thin films at a molar ratio of 30:1.

      fig. S6. Transfer characteristics of FETs with DPPTTT thin films without NMe4I after addition of DMSO to the polymer solutions.

      fig. S7. The initial output/transfer curves for DPPTTT and DPPTTT-NMe4I (30:1) thin film and those after the third, fifth, seventh, and tenth forward voltage sweeps (1st, black; 3rd, blue; 5th, red; 7th, yellow; 10th, cyan).

      fig. S8. The transfer and output curves of FETs with DPPTTT-NMe4I thin films at a molar ratio of 30:1 measured with forward (black) and reverse (blue) voltage sweeps (VGS from 5 to −40 and to 5 V; VDS from 0 to −60 and to 0 V).

      fig. S9. ESR spectra of DPPTTT and DPPTTT-NMe4I.

      fig. S10. Absorption, IR, and Raman spectra of thin films of DPPTTT and DPPTTT-NMe4I at molar ratios of 15:1 and 30:1.

      fig. S11. The SKPM potential profiles of DPPTTT and DPPTTT-NMe4I thin films at a molar ratio of 30:1 under different gate voltages.

      fig. S12. The dependence of the ratio of corrected mobility to uncorrected mobility of DPPTTT thin film on the gate voltage.

      fig. S13. Transfer characteristics of FETs with other conjugated D-A polymers after incorporation of NMe4I.

      fig. S14. X-ray photoelectron spectra of thin films of DPPTTT and DPPTTT-NMe4I at a molar ratio of 15:1.

      fig. S15. The plot of the capacitances at different frequencies (1 to 2000 Hz) for the dielectric layers measured with the configuration Au/NMe4I/OTS-modified SiO2/Si.

      fig. S16. Hysteresis in transfer characteristics of FETs with DPPTTT using the NMe4I-OTS-SiO2 as the dielectric layer.

      table S1. The hole mobilities (μ) extracted by the two-point method with VTh and different values of VGS for as-prepared BGBC FETs with DPPTTT neat film and DPPTTT-NMe4I at a molar ratio of 30:1.

      table S2. Relaxation times of carbon atoms of the side alkyl chains of DPPTTT in the absence and presence of NMe4I on the basis of solid state of 13C NMR.

      table S3. The mobilities (μ), threshold voltages (VTh), on/off ratios (Ion/Ioff), Ioff, and subthreshold slop (S) for as-prepared BGBC FETs with neat thin films of PDPP4T, PBDTTT-C-T, P3HT, and P3EHT and the respective thin films after incorporation of NMe4I at a molar ratio of 30:1.

    • Supplementary Materials

      This PDF file includes:

      • fig. S1. Transfer and output characteristics of FETs with DPPTTT and the DPPTTT-NMe4I thin film at a molar ratio of 30:1 by using CYTOP-modified dielectric layers.
      • fig. S2. Extraction of hole mobilities from the transfer characteristics of DPPTTT and DPPTTT-NMe4I thin film at a molar ratio of 30:1.
      • fig. S3. Variation of hole mobility for FETs with DPPTTT-NMe4I thin film at a molar ratio of 30:1 before and after thermal annealing at 80°, 100°, and 120°C.
      • fig. S4. Transfer characteristics of FETs with DPPTTT-NMe4I thin films at different molar ratios.
      • fig. S5. Transfer and output characteristics of FETs with DPPTTT-NMe4Br thin films at a molar ratio of 30:1.
      • fig. S6. Transfer characteristics of FETs with DPPTTT thin films without NMe4I after addition of DMSO to the polymer solutions.
      • fig. S7. The initial output/transfer curves for DPPTTT and DPPTTT-NMe4I (30:1) thin film and those after the third, fifth, seventh, and tenth forward voltage sweeps (1st, black; 3rd, blue; 5th, red; 7th, yellow; 10th, cyan).
      • fig. S8. The transfer and output curves of FETs with DPPTTT-NMe4I thin films at a molar ratio of 30:1 measured with forward (black) and reverse (blue) voltage sweeps (VGS from 5 to −40 and to 5 V; VDS from 0 to −60 and to 0 V).
      • fig. S9. ESR spectra of DPPTTT and DPPTTT-NMe4I.
      • fig. S10. Absorption, IR, and Raman spectra of thin films of DPPTTT and DPPTTT-NMe4I at molar ratios of 15:1 and 30:1.
      • fig. S11. The SKPM potential profiles of DPPTTT and DPPTTT-NMe4I thin films at a molar ratio of 30:1 under different gate voltages.
      • fig. S12. The dependence of the ratio of corrected mobility to uncorrected mobility of DPPTTT thin film on the gate voltage.
      • fig. S13. Transfer characteristics of FETs with other conjugated D-A polymers after incorporation of NMe4I.
      • fig. S14. X-ray photoelectron spectra of thin films of DPPTTT and DPPTTT-NMe4I at a molar ratio of 15:1.
      • fig. S15. The plot of the capacitances at different frequencies (1 to 2000 Hz) for the dielectric layers measured with the configuration Au/NMe4I/OTS-modified SiO2/Si.
      • fig. S16. Hysteresis in transfer characteristics of FETs with DPPTTT using the NMe4I-OTS-SiO2 as the dielectric layer.
      • table S1. The hole mobilities (μ) extracted by the two-point method with VTh and different values of VGS for as-prepared BGBC FETs with DPPTTT neat film and DPPTTT-NMe4I at a molar ratio of 30:1.
      • table S2. Relaxation times of carbon atoms of the side alkyl chains of DPPTTT in the absence and presence of NMe4I on the basis of solid state of 13C NMR.
      • table S3. The mobilities (μ), threshold voltages (VTh), on/off ratios (Ion/Ioff), Ioff, and subthreshold slop (S) for as-prepared BGBC FETs with neat thin films of PDPP4T, PBDTTT-C-T, P3HT, and P3EHT and the respective thin films after incorporation of NMe4I at a molar ratio of 30:1.

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