Highly enhanced thermoelectric performance of WS2 nanosheets upon embedding PEDOT:PSS

Two‐dimensional (2D) WS₂ nanosheets (NSs) as a promising thermoelectric (TE) material have gained great concern recently. The low electrical conductivity significantly limits its further development. Herein, we reported an effective method to enhance the TE performance of WS₂ NSs by combining poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS). The restacked WS₂ NSs thin film with 1T phase structure obtained by a common chemical lithium intercalation show a high Seebeck coefficient of 98 μV K^?1 and a poor electrical conductivity of 12.5 S cm^?1. The introduction of PEDOT:PSS with different contents obviously improve the electrical conductivity of WS₂ NSs thin films. Although a declining Seebeck coefficient was observed, an optimized TE power factor of 45.2 μW m^?1 k^?1 was achieved for WS₂/PEDOT:PSS composite thin film. Moreover, the as‐prepared WS₂/PEDOT:PSS thin film can be easily peeled off and transferred to other substrate leading to a more promising application. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 997–1004     

Effects of additives and post‐treatment on the thermoelectric performance of vapor‐phase polymerized PEDOT films

Vapor‐phase polymerization (VPP) is an important method for the fabrication of high‐quality conducting polymers, especially poly(3,4‐ethylenedioxythiophene) (PEDOT). In this work, the effects of additives and post‐treatment solvents on the thermoelectric (TE) performance of VPP‐PEDOT films were systematically investigated. The use of 1‐butyl‐3‐menthylinidazolium tetrafluoroborate ([BMIm][BF₄], an ionic liquid) was shown to significantly enhance the electrical conductivity of VPP‐PEDOT films compared with other additives. The VPP‐PEDOT film post‐treated with mixed ethylene glycol (EG)/[BMIm][BF₄] solvent displayed the high power factor of 45.3 μW m^?1 K^?2 which is 122% higher than that prepared without any additive or post‐treatment solvent, along with enhanced electrical conductivity and Seebeck coefficient. This work highlighted the superior effect of the [BMIm][BF₄] additive and the EG/[BMIm][BF₄] solvent post‐treatment on the TE performance of the VPP‐PEDOT film. These results should help with developing the VPP method to fabricate high‐performance PEDOT films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1738–1744     

A platform to synthesize a soluble poly(3,4‐ethylenedioxythiophene) analogue

Alkyl‐substituted polyhedral oligomeric silsesquioxane (POSS) cage is combined with 3,4‐ethylenedioxythiophene under the same roof. The corresponding monomer called EDOT‐POSS is used to get soluble poly(3,4‐ethylenedioxythiophene) (PEDOT‐POSS) analogue. Both chemically and electrochemically obtained polymers are soluble in common organic solvents like dichloromethane, chloroform, tetrahydrofuran, and so forth. The PEDOT‐POSS has somewhat higher band gap (1.71 eV at 618 nm) than its parent PEDOT (1.60 eV at 627 nm) and as expected the PEDOT‐POSS exhibits higher optical contrast (74% at 618 nm) and coloration efficiency (582 cm²/C for 100% switching), lower switching time (0.9 s), higher electrochemical stability (93% of its electroactivity retains after 5000 cycles under ambient conditions) when compared to the PEDOT. A number of advantages of the PEDOT‐POSS over the PEDOT can make it a promising material in the areas of electro‐optical applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3935–3941     

Paper: An effective substrate for the enhancement of thermoelectric properties in PEDOT:PSS

A novel strategy via paper as an effective substrate has been introduced as a thermoelectric material in this work. Free‐standing poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/paper composite films are conveniently prepared by a one‐step method of directly writing PEDOT:PSS solution on paper, making the process simple, rapid, and facile. The free‐standing composite films display excellent flexibility, light weight, soaking stability in water, and great potential in large‐scale production. Improved thermoelectric properties are obtained in PEDOT:PSS/paper composite films, owing to the simultaneously enhanced Seebeck coefficient (30.6 μV K^?1) and electrical conductivity, and a low thermal conductivity (0.16 W m^?1 K^?1) compared with pristine PEDOT:PSS films. The results indicate that paper as an effective substrate is suitable for the preparation of high‐performance and flexible thermoelectric materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 737–742     

Growth of poly(3,4‐ethylenedioxythiophene) films prepared by base‐inhibited vapor phase polymerization

Transparent [90% transmittance at 550 nm at a sheet resistance (R_s) of 279 Ω sq^?1] poly(3,4‐ethylenedioxythiophene) (PEDOT) films with electrical conductivities up to 1354 S cm^?1 are prepared using base‐inhibited vapor phase polymerization at atmospheric pressure. The influence of reaction conditions, such as temperature and growth time, on the film formation is investigated. A simple and convenient two‐electrode method is used for the in situ measurement of resistance, enabling to investigate the growth mechanism of polymer films and the influence of different parameters (relative humidity and the amount of oxidant) on the film growth. Low humidity exerts a detrimental effect on film growth and conductivity. In situ R_s measurements suggest that a large structural change occurs upon washing the PEDOT‐oxidant film. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2014 , 52, 561–571     

A Free‐standing electrochromic material of poly(5,7‐bis(2‐(3,4‐ethylenedioxy)thienyl)‐indole) and its application in electrochromic device

Free‐standing poly(5,7‐bis(2‐(3,4‐ethylenedioxy)thienyl)‐indole) (PETI) was electrochemically obtained from 5,7‐bis(2‐(3,4‐ethylenedioxy)thienyl)‐indole (ETI) prepared by Stille coupling reaction of 5,7‐dibromoindole and 3,4‐ethylenedioxythiophene. For comparison, poly(5,7‐bis(2‐thiophene)‐indole) was also electrosynthesized from 5,7‐bis(2‐thiophene)‐indole (BTI) which was prepared from the 5,7‐dibromoindole and thiophene. Characterizations of ETI and BTI were performed by cyclic voltammetry, scanning electron microscopy, ¹H NMR, and ¹³C NMR spectroscopy. Spectroelectrochemical studies showed PETI had better electrochromic properties and showed two different colors (brown and blue‐violet) under various potentials with better maximum contrast (ΔT%) and coloration efficiency (CE). An electrochromic device (ECD) based on PETI and poly(3,4‐ethylenedioxythiophene) (PEDOT) was also constructed and characterized. This ECD had fast response time, high CE, better optical memory, and long‐term stability. These results indicated that PETI had potential applications for ECD. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2356–2364     

Thermoelectric behavior of organic thin film nanocomposites

Organic thin film nanocomposites, prepared by liquid‐phase exfoliation, were investigated for their superior electrical properties and thermoelectric behavior. Single‐walled carbon nanotubes (SWNT) were stabilized by intrinsically conductive poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in an aqueous solution. The electrical conductivity (σ) was found to increase linearly as 20 to 95 wt % SWNT. At 95 wt % SWNT, these thin films exhibit metallic electrical conductivity (～4.0 × 10⁵ S m^?1) that is among the highest values ever reported for a free‐standing, fully organic material. The thermopower (S) remains relatively unaltered as the electrical conductivity increases, leading to a maximum power factor (S²σ) of 140 μW m^?1 K^?2. This power factor is within an order of magnitude of bismuth telluride, so it is believed that these flexible films could be used for some unique thermoelectric applications requiring mechanical flexibility and printability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Effect of (3‐glycidyloxypropyl)trimethoxysilane (GOPS) on the electrical properties of PEDOT:PSS films

Poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) has been reported as a successful functional material in a broad variety of applications. One of the most important advantages of PEDOT:PSS is its water‐solubility, which enables simple and environmental friendly manufacturing processes. Unfortunately, this also implies that pristine PEDOT:PSS films are unsuitable for applications in aqueous environments. To reach stability in polar solvents, (3‐glycidyloxypropyl)trimethoxysilane (GOPS) is typically used to cross‐link PEDOT:PSS. Although this strategy is widely used, its mechanism and effect on PEDOT:PSS performance have not been articulated yet. Here, we present a broad study that provides a better understanding of the effect of GOPS on the electrical and electronic properties of PEDOT:PSS. We show that the GOPS reacts with the sulfonic acid group of the excess PSS, causing a change in the PEDOT:PSS film morphology, while the oxidation level of PEDOT remains unaffected. This is at the origin of the observed conductivity changes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 814–820     

Properties of In situ polymerized poly(3,4‐ethylenedioxythiophene)/alumina composites for energy storage applications

Composites formed by poly(3,4‐ethylenedioxythiophene) and alumina (PEDOT/Al₂O₃) have been prepared by in situ anodic polymerization. For this purpose, the stability of 1:1 and 4:1 monomer:alumina aqueous solutions has been examined as a function of the pH (2.3, 4.0, 7.0, 8.8, or 10.8). Results indicate that the monomer behaves as a dispersant that remains stable at the studied basic pHs despite they are close to the isoelectric point of alumina. Although the thermal stability of the composites is considerably affected by the pH of the reaction medium, its influence on the surface morphology is very small. Independently, of the synthetic conditions, the electrochemical properties were better for PEDOT/Al₂O₃ than for pure PEDOT, reflecting that alumina particles promote the charge mobility. The highest specific capacitance (SC; 141 F/g), which was 55% higher than that obtained for pure PEDOT, was achieved for the composite prepared at pH = 8.8 using a 4:1 monomer:alumina ratio. These conditions favor the participation of OH^– groups as secondary doping agents without degrading the polymer matrix and enhance the specific surface of the films, facilitating the ionic mobility. On the other hand, application of a multi‐step polymerization strategy has shown that interfaces originated by consecutive steps enhance the SC. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1131–1141     

Fabrication of poly(vinyl alcohol)‐graphene quantum dots coated with poly(3,4‐ethylenedioxythiophene) for supercapacitor

Conducting nanofiber composed of poly(vinyl alcohol) (PVA), graphene quantum dots (GQDs) and poly(3,4‐ethylenedioxythiophene) (PEDOT) was prepared for symmetrical supercapacitor through electrospinning and electropolymerization techniques. The formation of PVA nanofibers with the addition of GQDs was excellently prepared with the average diameter of 55.66 ± 27 nm. Field emission scanning electron microscopy images revealed that cauliflower‐like structure of PEDOT was successfully coated on PVA‐GQD electrospun nanofibers. PVA‐GQD/PEDOT nanocomposite exhibited the highest specific capacitance of 291.86 F/g compared with PVA/PEDOT (220.73 F/g) and PEDOT (161.48 F/g). PVA‐GQD/PEDOT also demonstrated a high specific energy and specific power of 16.95 and 984.48 W/kg, respectively, at 2.0 A/g current density. PVA‐GQD/PEDOT exhibited the lowest resistance of charge transfer (R_ct) and equivalent series resistance compared with PEDOT and PVA/PEDOT, indicating that the fast ion diffusion between the electrode and electrolyte interface. PVA‐GQD/PEDOT nanocomposite also showed an excellent stability with retention of 98% after 1000 cycles. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 50–58     

Influence of imidazole‐based acidity control of PEDOT:PSS on its electrical properties and environmental stability

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been studied for a wide range of applications due to its potential as a transparent electrode. Herein, the use of imidazole and its derivatives as a neutralizing additive for PEDOT:PSS dispersion and in‐depth studies of their effects in terms of electrical properties and stability is reported. Although the neutralization in general reduces the electrical conductivity of PEDOT:PSS, the conductivity after imidazole treatment (685.2 S cm^?1) is higher than that after treatment of other derivatives. Spectroscopic and thermoelectric studies show that the de‐doping effect resulted in the conductivity reduction. As a trade‐off of the conductivity reduction, greatly enhanced long‐term stability and noncorrosive characteristics are obtained after neutralization. The change in sheet resistance of imidazole‐treated PEDOT:PSS after 500 h under harsh conditions (85 °C and 85% humidity) is half that of the untreated samples, demonstrating the great enhancement of the stability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1530–1536     

Understanding volumetric capacitance in conducting polymers

Recent measurements in poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films show that capacitance scales with film volume. We discuss the ramifications of this finding and propose a simple model that describes capacitance in terms of sites in which ions injected from the electrolyte replace holes that are extracted from the film by a metal contact. We propose that volumetric capacitance is inversely proportional to the average distance between these sites. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1433–1436     

Secondary doping in poly(3,4‐ethylenedioxythiophene):Poly(4‐styrenesulfonate) thin films

The electrical and structural properties of poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion using different concentrations of selected secondary dopants are studied in detail. An improvement of the electrical conductivity by three orders of magnitude is achieved for dimethyl sulfoxide, sorbitol, ethylene glycol, and N,N‐dimethylformamide, and the secondary dopant concentration dependence of the conductivity exhibits almost identical behavior for all investigated secondary dopants. Detailed analysis of the surface morphology and Raman spectra reveals no presence of the secondary dopant in fabricated films, and thus the dopants are truly causing the secondary doping effect. Although the ratio of benzenoid and quinoid vibrations in Raman spectra is unaffected by doping, the phase transition in PEDOT:PSS films owing to doping is confirmed. Further analysis of temperature‐dependent conductivity reveals 1D variable range hopping (VRH) charge transport for undoped PEDOT:PSS, whereas highly conductive doped PEDOT:PSS films exhibit 3D VRH charge transport. We demonstrate that the charge ‐ hopping dimensionality change should be a fundamental reason for the conductivity enhancement. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1139–1146     

Electrochromic enhancement of poly(3,4‐ethylenedioxythiophene) films functionalized with hydroxymethyl and ethylene oxide

2‐((2,3‐Dihydrothieno[3,4‐b]dioxin‐2‐yl)methoxy)methyl oxirane (EDOT‐MO) was successfully synthesized by the reaction of epichlorohydrin with hydroxymethylated‐3,4‐ethylenedioxylthiophene (EDOT‐MeOH), which was synthesized via a simple four‐step sequence. Poly(hydroxymethylated‐3,4‐ethylenedioxylthiophene) (PEDOT‐MeOH) and poly(2‐((2,3‐dihydrothieno[3,4‐b]dioxin‐2‐yl)methoxy)methyl oxirane) (PEDOT‐MO) were electrosynthesized through electropolymerization of EDOT‐MeOH and EDOT‐MO, respectively. Structural, electrochemical, optical, and thermal properties of as‐formed polymers were investigated by FTIR, cyclic voltammetry, UV–vis, and thermogravimetry. Spectroelectrochemistry studies demonstrated that PEDOT‐MeOH and PEDOT‐MO could be reversibly oxidized and reduced accompany with obvious color changes. Further kinetic studies demonstrated that the introduction of hydroxymethyl or ethylene oxide group significantly improved electrochromic properties of 3,4‐ethylenedioxythiophene (PEDOT) and resulted in high contrast ratios (57.3% at 585 nm) and coloration efficiencies (338.5 cm² C^?1), low switching voltages, and fast response time. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1989–1999     

Tuning of PEDOT:PSS Properties Through Covalent Surface Modification

Conductive polymer (poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) is an attractive platform for the design of flexible electronic, optoelectronic, and (bio)sensor devices. Practical application of PEDOT:PSS often requires an incorporation of specific molecules or moieties for tailoring of its physical–chemical properties. In this article, a method for covalent modification of PEDOT:PSS using arenediazonium tosylates was proposed. The procedure includes two steps: chemisorption of diazo‐cations on the PEDOT:PSS surface followed by thermal decomposition of the diazonium salt and the covalent bond formation. Structural and surface properties of the samples were evaluated by XPS, SEM‐EDX, AFM, goniometry, and a range of electric and optical measurements. The developed modification procedure enables tuning of the PEDOT:PSS surface properties such as conductivity and optical absorption. The possibility to introduce various organic functional groups (from hydrophilic to hydrophobic) and to create new groups for further functionalization makes the developed procedure multipurpose. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 378–387     

Charge transport and structure in semimetallic polymers

Owing to changes in their chemistry and structure, polymers can be fabricated to demonstrate vastly different electrical conductivities over many orders of magnitude. At the high end of conductivity is the class of conducting polymers, which are ideal candidates for many applications in low‐cost electronics. Here, we report the influence of the nature of the doping anion at high doping levels within the semi‐metallic conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) on its electronic transport properties. Hall effect measurements on a variety of PEDOT samples show that the choice of doping anion can lead to an order of magnitude enhancement in the charge carrier mobility > 3 cm²/Vs at conductivities approaching 3000 S/cm under ambient conditions. Grazing Incidence Wide Angle X‐ray Scattering, Density Functional Theory calculations, and Molecular Dynamics simulations indicate that the chosen doping anion modifies the way PEDOT chains stack together. This link between structure and specific anion doping at high doping levels has ramifications for the fabrication of conducting polymer‐based devices. © 2017 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 97–104     

Electro‐conductive double‐network hydrogels

Novel electro‐conductive and mechanically‐tough double network polymer hydrogels (E‐DN gels) were synthesized by polymerization of 3, 4‐ethylenedioxythiophene in the presence of a double network hydrogel (DN gel) matrix. The E‐DN gels showed not only excellent mechanical performance, having a fracture stress of 1.4–2.1 MPa, but also electrical conductivity as high as 10^?3 S cm^?1, both under dry and water‐swollen states. The fracture stress and fracture energy of the E‐DN gel was increased by 1.7 and 3.4 times, respectively, as compared with the DN gel. From scanning electron microscope and AFM observations, it was found that electro‐conductive poly(3,4‐ethylenedioxythiophene) (PEDOT) was incorporated into DN gel matrix, apparently due to the formation of a poly‐ion complex with sulfonic acid group of the DN gel network. Thus, PEDOT incorporated into the DN gel matrix greatly improves not only electronic conductivity, but also mechanical properties, reinforcing the double network gel matrix. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis of Poly(3,4‐ethylenedioxythiophene) latexes using poly(N‐vinylpyrrolidone)‐based copolymers as reactive stabilizers

The synthesis by oxidative polymerization of well‐defined poly(3,4‐ethylenedioxythiophene) (PEDOT) nano‐objects in the presence of modified and unmodified poly(N‐vinylpyrrolidone)‐based copolymers used as stabilizers in aqueous media is reported. Ammonium persulfate or a mixture of ammonium persulfate with CuCl₂ or CuBr₂ was used as oxidants. The effects of several parameters such as the molar mass and the concentration of the stabilizer as well as the nature of the oxidants on the size, morphology, and the conductivity of the PEDOT particles have been investigated. The distribution of the reactive moieties along the copolymer stabilizer backbone was shown to be crucial to get well‐defined PEDOT nano‐objects. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3841–3855, 2010     

Synthesis of highly conductive EDOT copolymer films via oxidative chemical in situ polymerization

Poly(3,4‐ethylenedioxythiophene)s (PEDOT) represent a class of conjugated polymers that can be potentially used as an electrode material for flexible organic electronics due to their superior conductivity and transparency. In this study, we demonstrate that the conductivity of a PEDOT containing copolymer film can be further enhanced by the oxidative chemical in situ copolymerization of a liquid film spun coated from monomer mixture (3,4‐ethylenedioxythiophene (EDOT) and 3‐thienyl ethoxybutanesulfonate (TEBS)), oxidant (iron(III) p‐toluenesulfonate (Fe(OTs)₃)), weak base (imidazole), and solvent (methanol). We investigated that the effect of the processing parameters such as the molar ratios TEBS/EDOT, IM/EDOT, and Fe(OTs)₃/EDOT on the surface morphology, optical property, and the conductivity of the resulting copolymer films. These parameters have been optimized to achieve conductivities for the copolymer films as high as 170 S/cm compared with a conductivity of 30 S/cm for the pure PEDOT film synthesized using the same fabrication method. This conductivity enhancement for the copolymer films was found to be resulted from the fact that the addition of TEBS monomer reduces the copolymerization rate, leading to the formation of much more uniform film surface without defects and copolymers of higher molecular weight which increase the conductivity of the resulting copolymer film. The composition of two monomers in the copolymer film is not related to the variation of conductivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1662–1673, 2008     

Improvement in carrier mobility of poly(3,4‐ethylenedioxythiophene) nanowires synthesized in porous alumina templates

Polymeric nanowires of poly(3,4‐ethylenedioxythiophene) (PEDOT) are electrochemically synthesized using porous anodic alumina oxide (AAO) membranes as templates. Four‐point resistivity measurements on more than 100 PEDOT nanowires with different diameters (50–250 nm) reveal a statistically significant size‐dependent phenomenon in which the nanowires with a smaller diameter exhibit higher conductivity. Structural characterization with Raman spectroscopy and doping level estimation with energy‐dispersive X‐ray spectrometry and X‐ray photoelectron spectroscopy indicate that the observed conductivity enhancement can be attributed to improved carrier mobility in PEDOT nanowires having an elongated conjugation structure because of the effect of the AAO template. From the estimated doping levels (～5%) and conductivity data (～100 S/cm), it is found that the carrier mobility reach 2.0 cm²/V s for the nanowire with the smallest diameter, as compared with 4.0 × 10^?4 cm²/V s for a bulk PEDOT film. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011