Research ArticleAPPLIED SCIENCES AND ENGINEERING

A highly stretchable, transparent, and conductive polymer

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Science Advances  10 Mar 2017:
Vol. 3, no. 3, e1602076
DOI: 10.1126/sciadv.1602076
  • Fig. 1 Chemical structures and schematic representation.

    (A and B) Chemical structures of PEDOT:PSS (A) and representative STEC enhancers (B) (see complete list in the Supplementary Materials). (C and D) Schematic diagram representing the morphology of a typical PEDOT:PSS film (C) versus that of a stretchable PEDOT film with STEC enhancers (D). (E) Photograph showing a freestanding PEDOT/STEC film being stretched. (F and G) Stress/strain (F) and strain cycling behavior (G) of freestanding PEDOT/STEC films.

  • Fig. 2 Electrical and optical properties of stretchable PEDOT under strain.

    (A) Conductivity under various strains for PEDOT with different STEC enhancers. Film thicknesses are around 600 to 800 nm. (B) Conductivities under various strain presented in this work compared to representative stretchable conductors reported in literature. PU, polyurethane. (C and D) Cycling stability of PEDOT/STEC1 under 50% strain (C) and 100% strain (D). G, conductance; σ, conductivity; a.u., arbitrary units. (E and F) AFM images of a PEDOT/STEC1 film under different magnifications under 0% strain after it was cycled for 1000 times to 100% strain. The vertical profile across the line on the image is shown below the corresponding image. The deep folds have an amplitude of ~100 nm and a periodicity of ~1.5 μm, whereas those for the wrinkles are ~20 nm and ~0.25 μm, respectively. (G) Dichroic ratio of the PEDOT/STEC1 films under different strains calculated at 785 and 1100 nm for the 1st and the 1000th cycle. There is no change in dichroic ratio from 0 to 100% strain after 1000 cycles, potentially because of the folds formed in the film and a steady concentration of STEC enhancers being reached.

  • Fig. 3 Chemical and crystallographic characterization of stretchable PEDOT.

    (A) Raman spectra illustrating the Cα=Cβ peak position shift for the different films. The dashed line indicates the peak position for the PEDOT control film without any STEC. (B) UV-vis-NIR spectra showing the doping effect of STEC on PEDOT, as evidenced by increased absorption intensity from bipolaron delocalization at >1000 nm. (C) Near out-of-plane intensity plot of PEDOT:PSS films with various amounts of STEC2 additives extracted from GIWAXS patterns of PEDOT:PSS films with no STEC (D) and 45.5 wt % of STEC1 (E), STEC2 (F), and STEC8 (G) (see also section S3). For the standard PEDOT film without any STEC additives, three peaks were observed along qz: qz = 0.57 Å−1 (d = 11.2 Å), 1.33 Å−1 (d = 4.9 Å), and 1.87 Å−1 (d = 3.4 Å), which can be indexed as PEDOT (200), PSS amorphous scattering, and PEDOT (010), respectively (40, 45). (H to K) AFM phase images of regular PEDOT:PSS (H) compared to PEDOT with high stretchability by incorporating STEC1 (I), STEC2 (J), and STEC3 (K).

  • Fig. 4 Electrical properties and patterning of the stretchable PEDOT/STEC (STEC content is 45.5 wt % for all).

    (A) Conductivity of the PEDOT films via spin coating followed by various STEC aqueous solution treatments. (B) XPS C60 ion gun sputtering depth profile of a stretchable PEDOT/STEC film. (C) Temperature dependence of the conductivity and (D) Arrhenius fitting for conventional PEDOT compared to those with STEC additives. (E) Sheet resistance of the PEDOT/STEC1 films in relation to their transparency. Transmittance values are extracted at 550 nm. (F) Patterned PEDOT/STEC film on SEBS (top) and the film being stretched (bottom). The line width is 1 mm. (G and H) Photograph (G) and optical microscope image (H) showing micrometer-scale patterns produced by inkjet-printing the PEDOT/STEC. (I) Illustration of the control of feature size, with a line width as small as 40 μm printed on a SEBS substrate.

  • Fig. 5 Stretchable PEDOT/STEC as interconnects for LED and FET devices.

    (A) Schematic representation of an LED device bridged by PEDOT wires to the power source. (B and C) Photographs illustrating the minimal change in LED brightness as the device is stretched under twisting and poked with a sharp object, respectively. (D) Finite element simulation showing the cross-sectional strain distribution of the rigid-island arrays under 0% (top) and 100% (bottom) strains. (E) Plot summarizing the relationship between array density and strain on PEDOT interconnects when stretching the array to 100% from the simulation results. (F) Schematic diagram of the rigid-island FET array with stretchable PEDOT interconnects. (G and H) Photographs showing the FET array being stretched in all directions on a flat surface and spherical object, respectively. (I) Normalized mobility of individual transistors when the array is stretched to different strains.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1602076/DC1

    section S1. Selection of STEC enhancers

    section S2. Mechanical characterization of bulk freestanding films

    section S3. Effect of STEC on PEDOT:PSS

    section S4. Morphology of PEDOT/STEC film interior

    section S5. Microscopy study of the effect of tensile strain on PEDOT/STEC films

    section S6. Electrical properties of PEDOT/STEC films

    section S7. Composition of PEDOT/STEC films

    section S8. Low-temperature measurements

    section S9. FoM for transparent conductors

    section S10. Testing geometry for PEDOT films under tensile strain

    section S11. Polarized UV-vis-NIR spectra for PEDOT films under tensile strain

    section S12. Cycling stability and morphological change of PEDOT with STEC additives

    section S13. Mixed ion-electron conductivity

    section S14. PEDOT/STEC as interconnects for FET arrays

    table S1. Summary of STEC structures and their effects on the electrical and mechanical properties of freestanding PEDOT:PSS films (thickness range, 150 to 200 μm) with 45.5 wt % of STEC.

    table S2. Summary of mobility and threshold voltage shift for the 3 × 3 transistor arrays under 0 and 125% strain.

    fig. S1. Plot summarizing the conductivity, maximum tensile strain, and Young’s modulus for freestanding PEDOT:PSS films (~150 μm in thickness) with all additives investigated in this paper.

    fig. S2. Mechanical characterization of bulk freestanding films.

    fig. S3. Mechanism behind STEC-induced morphology change for PEDOT:PSS films.

    fig. S4. AFM phase images of PEDOT with various additives.

    fig. S5. GIWAXS analyses of PEDOT films.

    fig. S6. Diffraction data for PSS and insoluble PEDOT control samples.

    fig. S7. Plasticizing effect of STEC on PEDOT and NaPSS individually.

    fig. S8. SEM characterization of the cross section of a stretchable PEDOT film.

    fig. S9. Optical microscope images of a PEDOT/STEC1 film supported on a SEBS substrate under various strains.

    fig. S10. Optical microscope images of a PEDOT/STEC1 film supported on a SEBS substrate after being stretched to various strains and returned to its original length.

    fig. S11. Surface profile analyses of PEDOT films after stretching.

    fig. S12. Optical microscope images of a PEDOT/STEC1 film upon unloading from 100% strain.

    fig. S13. Optical microscope images of a PEDOT/STEC2 film held under various tensile strains.

    fig. S14. Optical microscope images of a PEDOT/STEC2 film upon stretching to various tensile strains.

    fig. S15. Conductivity values of PEDOT/STEC films processed under different conditions.

    fig. S16. Conductivity of PEDOT/STEC films with various STEC weight % before and after further STEC solution treatment.

    fig. S17. Effect of further doping using STEC solution on spin-coated films.

    fig. S18. Chemical composition of PEDOT/STEC films.

    fig. S19. Temperature-dependent conductivity and first- and second-order temperature coefficients for PEDOT films.

    fig. S20. Arrhenius plots for temperature dependent conductivity.

    fig. S21. Schematic diagrams of tensile testing and conductivity measurement geometries.

    fig. S22. Tension-induced chain-alignment behavior of PEDOT/STEC films.

    fig. S23. XPS analysis of film surfaces under 0% versus 100% strain, after returning from 100% to 0% strain, and after 1000 stretching cycles to 100% strain.

    fig. S24. Cycling stability of PEDOT/STEC1 films.

    fig. S25. Cycling stability of PEDOT/STEC2 films.

    fig. S26. Mixed ion-electron conductivity measurements.

    fig. S27. Schematic showing the cross-sectional view of a linear rigid-island array connected with stretchable PEDOT.

    fig. S28. Schematic diagrams illustrating strain calculation for rigid-island devices.

    fig. S29. Schematic and transfer characteristics for a 3 × 1 FET array.

    fig. S30. Schematic and transfer characteristics for a 3 × 3 FET array.

    fig. S31. A 3 × 3 FET array being stretched on a spherical object.

    video S1. A stretchable LED device poked with a sharp object.

    video S2. Twisting and stretching of a stretchable LED device.

    video S3. A 3 × 3 FET array stretched on a spherical object.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Selection of STEC enhancers
    • section S2. Mechanical characterization of bulk freestanding films
    • section S3. Effect of STEC on PEDOT:PSS
    • section S4. Morphology of PEDOT/STEC film interior
    • section S5. Microscopy study of the effect of tensile strain on PEDOT/STEC films
    • section S6. Electrical properties of PEDOT/STEC films
    • section S7. Composition of PEDOT/STEC films
    • section S8. Low-temperature measurements
    • section S9. FoM for transparent conductors
    • section S10. Testing geometry for PEDOT films under tensile strain
    • section S11. Polarized UV-vis-NIR spectra for PEDOT films under tensile strain
    • section S12. Cycling stability and morphological change of PEDOT with STEC additives
    • section S13. Mixed ion-electron conductivity
    • section S14. PEDOT/STEC as interconnects for FET arrays
    • table S1. Summary of STEC structures and their effects on the electrical and mechanical properties of freestanding PEDOT:PSS films (thickness range, 150 to 200 μm) with 45.5 wt % of STEC.
    • table S2. Summary of mobility and threshold voltage shift for the 3 × 3 transistor arrays under 0 and 125% strain.
    • fig. S1. Plot summarizing the conductivity, maximum tensile strain, and Young’s modulus for freestanding PEDOT:PSS films (~150 μm in thickness) with all additives investigated in this paper.
    • fig. S2. Mechanical characterization of bulk freestanding films.
    • fig. S3. Mechanism behind STEC-induced morphology change for PEDOT:PSS films.
    • fig. S4. AFM phase images of PEDOT with various additives.
    • fig. S5. GIWAXS analyses of PEDOT films.
    • fig. S6. Diffraction data for PSS and insoluble PEDOT control samples.
    • fig. S7. Plasticizing effect of STEC on PEDOT and NaPSS individually.
    • fig. S8. SEM characterization of the cross section of a stretchable PEDOT film.
    • fig. S9. Optical microscope images of a PEDOT/STEC1 film supported on a SEBS substrate under various strains.
    • fig. S10. Optical microscope images of a PEDOT/STEC1 film supported on a SEBS substrate after being stretched to various strains and returned to its original length.
    • fig. S11. Surface profile analyses of PEDOT films after stretching.
    • fig. S12. Optical microscope images of a PEDOT/STEC1 film upon unloading from 100% strain.
    • fig. S13. Optical microscope images of a PEDOT/STEC2 film held under various tensile strains.
    • fig. S14. Optical microscope images of a PEDOT/STEC2 film upon stretching to various tensile strains.
    • fig. S15. Conductivity values of PEDOT/STEC films processed under different conditions.
    • fig. S16. Conductivity of PEDOT/STEC films with various STEC weight % before and after further STEC solution treatment.
    • fig. S17. Effect of further doping using STEC solution on spin-coated films.
    • fig. S18. Chemical composition of PEDOT/STEC films.
    • fig. S19. Temperature-dependent conductivity and first- and second-order temperature coefficients for PEDOT films.
    • fig. S20. Arrhenius plots for temperature dependent conductivity.
    • fig. S21. Schematic diagrams of tensile testing and conductivity measurement geometries.
    • fig. S22. Tension-induced chain-alignment behavior of PEDOT/STEC films.
    • fig. S23. XPS analysis of film surfaces under 0% versus 100% strain, after returning from 100% to 0% strain, and after 1000 stretching cycles to 100% strain.
    • fig. S24. Cycling stability of PEDOT/STEC1 films.
    • fig. S25. Cycling stability of PEDOT/STEC2 films.
    • fig. S26. Mixed ion-electron conductivity measurements.
    • fig. S27. Schematic showing the cross-sectional view of a linear rigid-island array connected with stretchable PEDOT.
    • fig. S28. Schematic diagrams illustrating strain calculation for rigid-island devices.
    • fig. S29. Schematic and transfer characteristics for a 3 × 1 FET array.
    • fig. S30. Schematic and transfer characteristics for a 3 × 3 FET array.
    • fig. S31. A 3 × 3 FET array being stretched on a spherical object.

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    Other Supplementary Material for this manuscript includes the following:

    • video S1 (.mov format). A stretchable LED device poked with a sharp object.
    • video S2 (.mov format). Twisting and stretching of a stretchable LED device.
    • video S3 (.mov format). A 3 × 3 FET array stretched on a spherical object.

    Files in this Data Supplement:

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