Research ArticleMATERIALS SCIENCE

Molecular engineered conjugated polymer with high thermal conductivity

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Science Advances  30 Mar 2018:
Vol. 4, no. 3, eaar3031
DOI: 10.1126/sciadv.aar3031
  • Fig. 1 oCVD synthesis process, molecular structure, and film morphology.

    (A) P3HT/FeCl3 thin film. Left: Initialization of the film growth with adsorbed monomer (3-hexylthiophene) and oxidant (FeCl3) from their vapor phase and the continuous growth of the nanorod-like structures. Middle: Schematic of the microstructure of the doped P3HT film; ordered chain grains (red and blue shades) are π-π stacking assemblies, whereas disordered chain grains have rigid backbones with suppressed distortions. Right: Extended chains in quinoid form grown on FeCl3. The (bi)polarons are present in the doped P3HT backbone. (B) P3HT thin film. Methanol rinsing removes excess oxidant and de-dopes (reducing) the P3HT backbone. Middle: Schematic of the microstructure of the de-doped P3HT film showing ordered chain assemblies via π-π stacking (red shades) and extended chains with suppressed distortions, which originate from the quinoid structures in (A). Unlike coiled and entangled chains in typical polymers (fig. S2A), the extended chains of the de-doped P3HT are obtained (fig. S2B). (C to F) Film morphology characterized by tapping-mode AFM. (C) P3HT/FeCl3 grown at 45°C (40-min polymerization). (D) P3HT/FeCl3 grown at 85°C (40-min polymerization). The surface roughness (Ra) for both 45°C- and 85°C-grown P3HT/FeCl3 is more than 80 nm. (E) For the 45°C-grown P3HT, the roughness is ~13.8 nm. (F) For the 85°C-grown P3HT, the roughness is ~14.5 nm.

  • Fig. 2 Measured thermal conductivity using TDTR.

    Temperature-dependent thermal conductivity of P3HT films grown on glass substrates. The green spheres were measured from a 45°C-grown P3HT film and show a thermal conductivity as high as 2.2 W/m·K. The averages of 20 transient thermoreflectance measurements at 9-, 6-, and 3-MHz modulation frequencies are plotted. The error bars mark 2 SDs (95% confidence interval). All the samples measured were intrinsic P3HT (de-doped), rather than P3HT/FeCl3 (doped).

  • Fig. 3 Absorption and emission spectra.

    (A) UV-vis-NIR spectra of the 45°C- and 85°C-grown P3HT/FeCl3 films on glass substrates. Typical absorption bands of the (bi)polarons are observed at 700 to 900 nm and 1800 nm, suggesting that quinoid structures are formed during polymerization (Fig. 1A). The (bi)polaron peaks in the 85°C-grown sample are blue-shifted. a.u., arbitrary units. (B) Absorption and emission spectra of intrinsic P3HT films on glass substrates. In the absorption spectra, the absorbance peak occurs at a longer wavelength for the 45°C-grown P3HT sample, suggesting a longer conjugation length than in the 85°C-grown P3HT. In the photoluminescence spectra, a smaller Stokes shift in the 45°C-grown P3HT film suggests less conformational strain in the ground state than in the 85°C-grown P3HT. All spectral intensities have been normalized with respect to their peaks corresponding to the π-π* transition.

  • Fig. 4 Atomic-level characterization by x-ray scattering.

    (A) GIWAXS pattern of the 45°C-grown P3HT on glass substrate and characteristic Bragg scatterings by the {0k0} and {h00} plane groups are observed. The ring-shaped scattering pattern suggests that, in addition to an amorphous phase, there are crystalline regions with no preferred orientation. (B) GIWAXS pattern of the 85°C-grown P3HT on glass substrate suggests that the amorphous phase is dominant.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaar3031/DC1

    section S1. Materials and Methods

    section S2. Characterizations

    table S1. Molecular weight and molecular weight distribution.

    fig. S1. Synthesis mechanism and molecular structure.

    fig. S2. Cartoon for P3HT backbone conformation.

    fig. S3. Morphology, thickness, elemental analysis, and x-ray scattering characterization.

    fig. S4. NMR spectroscopy.

    fig. S5. Specific heat analysis and Raman spectroscopy.

    fig. S6. Schematic of the TDTR method for thermal conductivity measurement.

    fig. S7. Measured thermal conductivity for multiple samples at 300 K.

    fig. S8. Temperature-dependent TDTR data.

    fig. S9. TDTR sensitivity analysis.

    fig. S10. TDTR uncertainty analysis.

    References (3640)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Materials and Methods
    • section S2. Characterizations
    • table S1. Molecular weight and molecular weight distribution.
    • fig. S1. Synthesis mechanism and molecular structure.
    • fig. S2. Cartoon for P3HT backbone conformation.
    • fig. S3. Morphology, thickness, elemental analysis, and x-ray scattering characterization.
    • fig. S4. NMR spectroscopy.
    • fig. S5. Specific heat analysis and Raman spectroscopy.
    • fig. S6. Schematic of the TDTR method for thermal conductivity measurement.
    • fig. S7. Measured thermal conductivity for multiple samples at 300 K.
    • fig. S8. Temperature-dependent TDTR data.
    • fig. S9. TDTR sensitivity analysis.
    • fig. S10. TDTR uncertainty analysis.
    • References (36–40)

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