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Semiconducting polymer blends that exhibit stable charge transport at high temperatures

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Science  07 Dec 2018:
Vol. 362, Issue 6419, pp. 1131-1134
DOI: 10.1126/science.aau0759
  • Fig. 1 Morphology stabilization: Interdigitation and thermal stability can be tuned with blending ratio control.

    (A) Chemical structures of the semiconducting polymer (P1) and the insulating matrix polymer (PVK). (B) AFM phase images of the spin-cast thin films of the polymer blends with various amounts of PVK. An optimal amount of the semiconductor was required to establish interpenetrated morphology. Beyond this threshold, lateral phase separation occurs, and the interconnectivity was lost. (C) Temperature (temp.)–dependent charge carrier mobility in FET devices based on P1 blends containing various ratios of PVK. The data points represent the average hole mobility measured from 10 different devices for each blending ratio, and the error bars represent the standard deviation from the average. The pure P1 data are also plotted. (D) Normalized UV-Vis absorption spectra (Norm. abs.) of P1-PVK blends with varying amounts of the matrix polymer. The confinement of the semiconductor within rigid domains of the host led to increased ordering of the conjugated polymer chains. a.u., arbitrary units.

  • Fig. 2 Thermally stable packing behavior in PVK blends.

    (A and B) Temperature-dependent UV-Vis absorption spectra of pristine P1 films and the corresponding PVK blend. (C and D) Evolution of π-π d-spacing and lamellar stacking in thin films treated at different temperatures. The presence of PVK in the films not only induced closer packing of the conjugated polymer chains, but it also reduced their freedom to thermally expand and rearrange. π-π stacking distance as close as 3.72 Å can be retained at 200°C in the case of the PVK blend film. The peak position was extracted from Gaussian fits to the one-dimensional I(q) versus q plots. (E) Simulated dihedral distributions at different temperatures when π-π separations are confined to 3 Å and 5 Å. With the π-π restraint of 5 Å, the distribution broadens, indicative of chains twisting at all temperatures. (F and G) Packing behavior of DPP-T chains when confined to 3 Å and 5 Å, respectively.

  • Fig. 3 Effect of thermal stress on FET devices and thermal stability of PVK blends.

    (A) Measured hole mobilities under constant thermal stress for 6 hours. A sudden decline in mobility was observed for pure P1 when the FET device is heated. The blend can retain its original mobility after 6 hours. (B) Characteristic transfer curves of FET devices based on P1 with and without PVK after 1 hour of heating. SQRT, square root. (C) Impact of heating on the ION/IOFF. After 1 hour of heating, the ratio fell to nearly 10 for the devices based on P1 while remaining > 104 for the blend devices. (D) Threshold voltages (Vth) for FET devices based on the 60% PVK blends (below 3 V) and pure P1 (exceeding 20 V) upon prolonged heating. The data points represent the average values measured from 10 different devices, and the error bars represent the standard deviation from the average.

  • Fig. 4 Attaining universal thermal stability in semiconducting polymer blends.

    (A) Molecular structures and glass-transition temperatures of the representative matrix polymers tested for high-temperature charge transport. Matrimid 5218; PEI, polyetherimide. (B) Hole mobilities of FET devices based on the optimized blends of P1 in four different matrices measured in open air. (C) Molecular structures of additional semiconducting polymers studied for thermally stable blends. (D) Measured FET mobilities from the blend films of P2 and P3 with PVK and PAC used as the host matrices. The blend combinations that had stable close packing exhibited hole mobilities stable up to 220°C. The data points represent the average mobility values measured from 10 different devices, and the error bars represent the standard deviation from the average.

Supplementary Materials

  • Semiconducting polymer blends that exhibit stable charge transport at high temperatures

    Aristide Gumyusenge, Dung T. Tran, Xuyi Luo, Gregory M. Pitch, Yan Zhao, Kaelon A. Jenkins, Tim J. Dunn, Alexander L. Ayzner, Brett M. Savoie, Jianguo Mei

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods 
    • Tables S1 to S3
    • Figs. S1 to S20
    • References 

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