Research ArticleCONDENSED MATTER PHYSICS

Charge transport physics of a unique class of rigid-rod conjugated polymers with fused-ring conjugated units linked by double carbon-carbon bonds

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Science Advances  28 Apr 2021:
Vol. 7, no. 18, eabe5280
DOI: 10.1126/sciadv.abe5280
  • Fig. 1 Chemical structures and thin-film UV-Vis-NIR absorption spectra.

    (A) Chemical structure of NN1, NN2, AN1, AN2, and P(NDI2OD-T2) polymers. (B) Thin-film UV-Vis-NIR absorption spectra of the polymers. The films were spun from hot 1,2,4-trichlorobenzene solution.

  • Fig. 2 SANS of NN1, NN2, AN2, and P(NDI2OD-T2) in hot, dichlorobenzene solution.

    The NN1, NN2, and AN2 fused polymers adopt a rigid-rod shape with a scaling of Iq−1 over a large region, while the semiflexible P(NDI2OD-T2) polymer shows a characteristic worm-like chain behavior. The curves have been shifted vertically for clarity. The incoherent scattering background was subtracted.

  • Fig. 3 Structural characterization of the representative rigid-rod polymer thin films.

    (A) 2D GIWAXS patterns of NN1, NN2, and AN2 thin-film samples. (B) In-plane and out-of-plane 1D linecuts of NN1, NN2, and AN2’s 2D GIWAXS patterns.

  • Fig. 4 PDS of rigid-rod polymer thin films.

    Absorbance of the NN1, NN2, AN1, and AN2 thin films measured by PDS. Dotted lines represent exponential tail fits for extraction of the Urbach energies Eu (inset).

  • Fig. 5 Temperature-dependent and molecular weight–dependent charge transport investigation of rigid-rod polymer FETs.

    (A) Transfer curves measured on top-gate, bottom-contact FETs (L = 20 μm, W = 1 mm) fabricated from the spin-coated AN2 film. (B) Linear and saturation mobility extracted from transfer curves measured on the same device. (C) Molecular weight–dependent saturation mobility for spin-coated NN1, NN2, AN1, and AN2 top-gate, bottom-contact FETs (L = 20 μm, W = 1 mm). (D) Temperature-dependent saturation electron mobility (at VG = 60 V, VD = 60 V) for spin-coated NN1, NN2, AN1, and AN2 top-gate, bottom-contact FETs (L = 20 μm, W = 1 mm).

  • Fig. 6 Environmental and stress stability investigation of rigid-rod polymer FETs.

    (A) Saturation electron mobility of NN1, NN2, AN1, AN2, and P(NDI2OD-T2) top-gate, bottom-contact OFETs (L = 20 μm, W = 1 mm) measured under various air exposure time, highlighting the air stability of electron transport of fused polymer OFETs in comparison to the P(NDI2OD-T2) OFET. (B) Saturation transfer curves (with p- and n-channel accumulation) for a representative AN2 OFET measured in the air after 450-hour continuous air exposure to demonstrate the operational stability of the sufficiently air-exposed device.

  • Fig. 7 FI-ESR characterization of rigid-rod polymers.

    FI-ESR spectra of the top-gate, bottom-contact sample (L = 100 μm, W = 243 mm) fabricated from spin-coated (A) NN1 and (D) AN2 film at 5 and 170 K. Spin lifetimes T1 and T2 for electron polarons in (B) NN1 and (E) AN2 FI-ESR sample at VG = 60 V. Motion frequency of charges determined from T2 (left axis) and saturation mobilities from FET measurements at VG = 60 V (right axis) of (C) NN1 and (F) AN2 FI-ESR samples. Labels show the calculated hopping distances in the motional narrowing regime by relating the motion frequency and saturation electron mobility with the Einstein relation for charge transport.

  • Table 1 Polymer ionization energies, electron affinities, and optical properties.

    PolymersEopt.gap (eV)*IE (eV)EA (eV)
    NN11.01−5.20−4.19
    NN21.04−5.16−4.12
    AN1-−5.39-
    AN21.03−5.13−4.10

    *Estimated optical gap was calculated using onset of the thin-film (spin-coated on glass substrates) absorption spectra (Eopt = 1240/λonset).

    †Measured by the Photoelectron Spectroscopy in Air (PESA) system.

    ‡EA is calculated from EA = IE − Eopt.

    • Table 2 Chain parameters extracted from the fitting of the SANS curves.

      PolymerModelLength (nm)SD of L (nm)Radius (nm)Kuhn length (b) (nm)
      P(NDI2OD-T2)Worm-like46.837.41.4010.2
      NN1Cylinder17.314.81.48>L
      NN2Cylinder30.926.91.65>L
      AN2Cylinder39.232.11.65>L
    • Table 3 GIWAXS spacing parameters for the NN1, NN2, and AN2 samples.

      N/A denotes not available.

      Crystallographic parametersNN1NN2AN2
      Lamella stacking (out-of-plane)q−1)0.2400.2170.232
      d spacing (Å)26.429.027.4
      ΔFWHM−1)0.0470.0550.061
      Coherence length (Å)135115105
      Lamella stacking (in-plane)q−1)0.2400.2200.230
      d spacing (Å)26.628.627.3
      ΔFWHM−1)0.0210.0270.043
      Coherence length (Å)300235145
      π-π stacking (out-of-plane)q−1)1.691.701.70
      d spacing (Å)3.723.693.69
      ΔFWHM−1)0.2180.2040.194
      Coherence length (Å)28.830.832.4
      π-π stacking (in-plane)q−1)N/A1.701.70
      d spacing (Å)N/A3.693.69
      ΔFWHM−1)N/A0.1410.20
      Coherence length (Å)N/A44.531.4
      Backbone repeat (004)
      (in-plane)
      q−1)1.421.391.25
      d spacing (Å)17.718.120.1
      ΔFWHM−1)0.0640.054N/A
      Coherence length (Å)100115N/A
    • Table 4 Motion frequency comparison between different polymers.

      MaterialsMotion frequency (MHz)
      PBTTT-C14 (150 K)100 (p-channel)
      P(NDI2OD-T2) (150 K)100 (n-channel)
      IDTBT-C16 (150 K)1000 (p-channel)
      NN1 (170 K)28 (n-channel)
      AN2 (170 K)65 (n-channel)

    Supplementary Materials

    • Supplementary Materials

      Charge transport physics of a unique class of rigid-rod conjugated polymers with fused-ring conjugated units linked by double carbon-carbon bonds

      Mingfei Xiao, Remington L. Carey, Hu Chen, Xuechen Jiao, Vincent Lemaur, Sam Schott, Mark Nikolka, Cameron Jellett, Aditya Sadhanala, Sarah Rogers, Satyaprasad P. Senanayak, Ada Onwubiko, Sanyang Han, Zhilong Zhang, Mojtaba Abdi-Jalebi, Youcheng Zhang, Tudor H. Thomas, Najet Mahmoudi, Lianglun Lai, Ekaterina Selezneva, Xinglong Ren, Malgorzata Nguyen, Qijing Wang, Ian Jacobs, Wan Yue, Christopher R. McNeill, Guoming Liu, David Beljonne, Iain McCulloch, Henning Sirringhaus

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