Visible to Near-IR Electrochromism and Photothermal Effect of Poly(3,4-propylenedioxyselenophene)s

A new selenophene derivative, 3,4-propylenedioxyselenophene (ProDOS), was electropolymerized to a polymeric thin film which demonstrated wide spectral tunability from the visible to near-infrared (NIR) region. The anodic and cathodic peaks of the polymeric ProDOS (PProDOS) were observed at +0.22 and −0.30 V, showing a narrow band gap. In the visible region, the PProDOS film showed color change from navy blue in its dedoped state (−0.12 V vs Ag/AgCl) to highly transparent pale gray green in its doped state (0.68 V vs Ag/AgCl) with a high coloration efficiency (CE) of 273 cm2 C–1 and large transmittance change (contrast ratio of 5.7). The color change of the PProDOS film by electrochromism in the visible region was simultaneously accompanied by NIR electrochromism. Upon exposure to a NIR source (0.7 W cm–2), the doped PProDOS film resulted in a temperature rise of 10.7 °C compared to that of the bare indium tin oxide (ITO) coated glass, while the navy blue colored PProDOS film experienced a temperature rise of 10.2 °C. This photothermal effect by NIR light exposure was switchable between the colored and bleached state by simply dedoping and doping the film electrochemically, respectively. Furthermore, bleached PProDOS particles dispersed in water (0.05 mg mL–1) also showed a high photothermal effect (2 W cm–2) with a temperature rise of 13.1 °C, as compared to pure water. Compared with poly(3,4-ethylenedioxythiophene) (PEDOT), it was found that the new selenophene polymer (PProDOS) provided efficient visible to NIR electrochromism in addition to the high photothermal effect, resulting in a large temperature rise and heat conversion upon exposure to a NIR source

Spatially Resolved Detection of a Nanometer-Scale Gap by Scanning Electrochemical Microscopy

Nanowires with nanometer-scale gaps are an emerging class of nanomaterials with potential applications in electronics and optics. Here, we demonstrate that the feedback mode of scanning electrochemical microscopy (SECM) allows for spatially resolved detection of a nanogap on the basis of its electrical conductivity. A gapped nanoband is used as a model system to describe a mechanism of a unique feedback effect from a nanogap. Interestingly, both experiments and numerical simulations confirm that a peak current response is obtained when an SECM tip is laterally scanned above an insulating nanogap formed in an unbiased nanoband. On the other hand, no peak current response is expected for a highly conductive nanogap, which must be extremely narrow or filled with highly conductive molecules for efficient electron transport

Flexible Conductive Polymer Patterns from Vapor Polymerizable and Photo-Cross-Linkable EDOT

We explored direct photopatterning of a vapor polymerizable and photo-cross-linkable 3,4-ethylenedioxythiopene (EDOT) to make it suitable for use in electronics applications. We prepared a conductive polymer, PEDOT-MA, using vapor phase polymerization (VPP) of the (2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methyl methacrylate (EDOT-MA) and photochemically induced a conductivity change of the PEDOT-MA film to ensure a flexible conductive pattern. The room-temperature conductivity (σRT) of the PEDOT-MA film on PET was 30−120 S/cm, depending on the oxidant layer thickness and was increased ∼30% when the PEDOT-MA film was doped with aqueous solution of p-toluenesulfonic acid. Photoreaction of PEDOT-MA decreased the σRT to 1.7 × 10−3 S/cm because of the photo-cross-linking of the side chain. The transparency of the conductive films was tuned using the vapor polymerization time to control the film thickness. The photo-cross-linking reaction of the side chain generated micropatterns having line widths of 50−0.9 μm, in which the light-exposed areas appeared as bleached and less conductive. A diffractive, flexible, conductive film with 41% of diffraction efficiency was obtained from the line-patterned film having a spacing of 0.9 μm

Solvatochromic Fluorescence of Piperazine-Modified Bipyridazines for an Organic Solvent-Sensitive Film

Bipyridazines were modified with heterocyclic amines such as piperazine to give symmetric quadrupolar (SPBP) and asymmetric dipolar (APBP) bipyridazine. The fluorescence of SPBP and APBP was highly sensitive to solvent polarity, giving a synthetic rainbow of emission in different organic solvents. The solvent-induced changes in the Stokes shift of the bipyridazines resulted in positive solvatochromism. The symmetric bipyridazine showed higher solvatochromic sensitivity than that of the asymmetric bipyridazine and diazines. The positive solvatochromic fluorescence properties were reproduced in a binary system of toluene/dimethyl sulfoxide (DMSO) mixture, which showed a synthetic rainbow of emission by varying the DMSO content in toluene. An organic sensitive poly(methyl methacrylate) film containing SPBP exhibited a visible sensitivity for the detection of solvents by their polarity upon exposure to organic solvent molecules

Electrochromic Diffraction from Nanopatterned Poly(3-hexylthiophene)

Poly(3-hexylthiophene) (P3HT) films were patterned by a soft lithography technique using a nanopatterned polydimethylsiloxane (PDMS) mold to generate one-dimensional (1D) grating and two-dimensional (2D) crossed line pillar patterns. The redox currents (ip) were significantly increased due to the facilitated diffusion of ClO4− counterions associated with redox processes at the P3HT electrode as analyzing cyclic voltammetry (CV) was performed at different scan rates (ν). It was found that the diffusion coefficient (Df, cm2 s−1) for ion diffusion in the patterned electrode was much larger than that of the pristine P3HT electrode. Furthermore, the value of Df in the 2D electrode was three times higher than that in a pristine film. As a result of such facilitated charge transport, the electrochromic (EC) properties of the patterned P3HT electrode were greatly enhanced and dependent on the dimension of the pattern. Thus, the electrochromic efficiency (Ee), including the coloration (Ec) and bleaching efficiencies (Eb), was higher as the dimension of the pattern was increased; Ee was maximized in the 2D patterned P3HT film. In a patterned cell, electrochromic diffraction was reversibly observed with a switching efficiency (RDE) of 2 and 2.5 for the 1D and 2D patterned cells, respectively

Preparation of Bismuth Telluride Films with High Thermoelectric Power Factor

Highly conductive n-type Bi2Te3 films on a flexible substrate were prepared via electrodeposition followed by a transfer process using an adhesive substrate. The growth of the Bi2Te3 crystals was precisely controlled by an electrochemical deposition potential (Vdep), which was critical to the preferred orientation of the crystal growth along the (110) direction and thus to the properties of a flexible thermoelectric generator (FTEG). A Bi2Te3 film prepared under Vdep of 0.02 V showed high electrical conductivity (691 S cm–1) with a maximum power factor of 1473 μW m–1 K–2, which is the highest among the Bi2Te3 films prepared by the electrodeposition methods. As-prepared FTEG was bendable, showing only a small resistance change after 300 repeated bending cycles. Combined with the n-type Bi2Te3 FTEG, a prototype p-n-type flexible thermoelectric (pn-FTEG) was prepared using p-type poly­(3,4-ethylene dioxythiophene)­s. The pn-FTEG (5-couples) generated an output voltage of 5 mV at ΔT = 12 K with high output power of 56 nW (or 105 nWg–1). These results indicate that the FTEG can reproducibly work well in a bent state and has high application potential for harvesting thermal energy from curved sources such as human body temperature

Electrical Chiral Assembly Switching of Soluble Conjugated Polymers from Propylenedioxythiophene-Phenylene Copolymers

A π-conjugated polymer of propylenedioxythiophene-phenylene (ProDOT-Ph) with a chiral alkyl substituent on the propylene bridge of ProDOT was prepared to explore reversible multiswitching chiral conjugated polymers (CCPs) capable of electrochromic, electrofluorochromic, and chirality switching. The chiral assembly of the yellow colored poly­(ProDOT-Ph)­s (YPCr) was optimized by annealing the YPCr films at 120 °C. From the thermally annealed YPCr films, we demonstrated the electrical switching of chirality, color, and fluorescence in a single device, for the first time, which was precisely controlled electrochemically to achieve highly efficient and reversible switching of chiral assembly at a low working potential. The YPCr films showed electrochromism with a high coloration efficiency of 690 cm² C^–1 by changing color between yellow and blue. The film also exhibited fluorescence switching with a quantum yield change from 3.8 to 0.21 during the reversible electrochemical switching. The chirality of the YPCr, which showed a negative bisignate Cotton effect, was switched reversibly with 97% change in the anisotropy factor (<i>g</i>_abs). The multiswitching properties were correlated to the electrochemical switching in chiral assembly of conjugated polymers according to the electrochemical doping/dedoping process. To the best of our knowledge, the change in Cotton effect during the switching is the highest reported value of a chirality tunable polymer without any chiral inducer. In addition, the YPCr showed a sustainable memory effect for both chirality and coloration

PEDOT as a Flexible Organic Electrode for a Thin Film Acoustic Energy Harvester

An efficient thin film acoustic energy harvester was explored using flexible poly­(3,4-ethylene dioxythiophene) (PEDOT) films as electrodes in an all-organic triboelectric generator (AO-TEG). A thin film AO-TEG structured as PEDOT/Kapton//PET/PEDOT was prepared by the solution casting polymerization­(SCP) on the dielectric polymer films. As-prepared AO-TEG showed high flexibility and durability due to the strong adhesion between the electrodes and the dielectric polymer. The short-circuit current density (<i>J</i>_sc), open-circuit voltage (<i>V</i>_oc), and maximum power density (Pw) reached 50 mA/m², 700 V, and 12.9 W/m² respectively. The output current density decreased with the increase in the electrode resistance (<i>R</i>_e), but the energy loss in the organic electrodes was negligible. The AO-TEG could light up 180 LEDs instantaneously upon touching of the AO-TEG with a palm (∼120 N). With the flexible structure, the AO-TEG was worn as clothes and generated electricity to light LEDs upon regular human movement. Furthermore, the AO-TEG was applicable as a thin film acoustic energy harvester, which used music to generate electricity enough for powering of 5 LEDs. An AO-TEG with a PEDOT electrode (<i>R</i>_e = 200 Ω) showed instantaneous peak-to-peak voltage generation of 11 V under a sound pressure level (SPL) of 90–100 dB. The harvested acoustic energy through the AO-TEG was 350 μJ from the 4 min playing of the same single song. This is the first demonstration of a flexible triboelectric generator (TEG) using an organic electrode for harvesting acoustic energy from ambient environment

PEDOT as a Flexible Organic Electrode for a Thin Film Acoustic Energy Harvester

An efficient thin film acoustic energy harvester was explored using flexible poly­(3,4-ethylene dioxythiophene) (PEDOT) films as electrodes in an all-organic triboelectric generator (AO-TEG). A thin film AO-TEG structured as PEDOT/Kapton//PET/PEDOT was prepared by the solution casting polymerization­(SCP) on the dielectric polymer films. As-prepared AO-TEG showed high flexibility and durability due to the strong adhesion between the electrodes and the dielectric polymer. The short-circuit current density (<i>J</i>_sc), open-circuit voltage (<i>V</i>_oc), and maximum power density (Pw) reached 50 mA/m², 700 V, and 12.9 W/m² respectively. The output current density decreased with the increase in the electrode resistance (<i>R</i>_e), but the energy loss in the organic electrodes was negligible. The AO-TEG could light up 180 LEDs instantaneously upon touching of the AO-TEG with a palm (∼120 N). With the flexible structure, the AO-TEG was worn as clothes and generated electricity to light LEDs upon regular human movement. Furthermore, the AO-TEG was applicable as a thin film acoustic energy harvester, which used music to generate electricity enough for powering of 5 LEDs. An AO-TEG with a PEDOT electrode (<i>R</i>_e = 200 Ω) showed instantaneous peak-to-peak voltage generation of 11 V under a sound pressure level (SPL) of 90–100 dB. The harvested acoustic energy through the AO-TEG was 350 μJ from the 4 min playing of the same single song. This is the first demonstration of a flexible triboelectric generator (TEG) using an organic electrode for harvesting acoustic energy from ambient environment

PEDOT as a Flexible Organic Electrode for a Thin Film Acoustic Energy Harvester

An efficient thin film acoustic energy harvester was explored using flexible poly­(3,4-ethylene dioxythiophene) (PEDOT) films as electrodes in an all-organic triboelectric generator (AO-TEG). A thin film AO-TEG structured as PEDOT/Kapton//PET/PEDOT was prepared by the solution casting polymerization­(SCP) on the dielectric polymer films. As-prepared AO-TEG showed high flexibility and durability due to the strong adhesion between the electrodes and the dielectric polymer. The short-circuit current density (<i>J</i>_sc), open-circuit voltage (<i>V</i>_oc), and maximum power density (Pw) reached 50 mA/m², 700 V, and 12.9 W/m² respectively. The output current density decreased with the increase in the electrode resistance (<i>R</i>_e), but the energy loss in the organic electrodes was negligible. The AO-TEG could light up 180 LEDs instantaneously upon touching of the AO-TEG with a palm (∼120 N). With the flexible structure, the AO-TEG was worn as clothes and generated electricity to light LEDs upon regular human movement. Furthermore, the AO-TEG was applicable as a thin film acoustic energy harvester, which used music to generate electricity enough for powering of 5 LEDs. An AO-TEG with a PEDOT electrode (<i>R</i>_e = 200 Ω) showed instantaneous peak-to-peak voltage generation of 11 V under a sound pressure level (SPL) of 90–100 dB. The harvested acoustic energy through the AO-TEG was 350 μJ from the 4 min playing of the same single song. This is the first demonstration of a flexible triboelectric generator (TEG) using an organic electrode for harvesting acoustic energy from ambient environment