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     

Structural modulation induced by cobalt-based ionic liquids for enhanced thermoelectric transport in PEDOT:PSS

Poly(3,4ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has been intensively studied for its thermoelectric applications. Structural modulation to improve crystalline ordering, chain conformation and film morphology is a promising way to decouple the trade-off between conductivity and Seebeck coefficient and thus improve the thermoelectric power factor. Post treatment with ionic liquid ([CoCl₂ ⋅ 6H₂O]:[ChCl]) bearing cobalt-containing anions resulted in a remarkable enhancement of the power factor to 76.8 μW m⁻¹ K⁻². This IL combines the influence of a high-boiling polar organic solvent and diffusing ions. A high σ mainly resulted from the efficient removal of PSS chains, ordering of the structure and delocalization of bipoloran-dominant transport after conformational change. The increase in S was not due to dedoping of PEDOT chains, but rather the sharp feature of the density of states at the Fermi level induced by ion-exchange with unconventional anions.     

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     

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     

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     

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 different formulation PEDOT:PSS hole transport layers on photovoltaic performance of organic solar cells

In this study, the effects of the various types of PEDOT:PSS with different conductivities on the photovoltaic parameters of organic solar cells were investigated. The performances of five various commercially available PEDOT:PSS with formulations such as FET, PT2, PH1000, PH500 and PH were compared. It was observed that the device employing PH1000 as an interlayer between ITO and the active layer exhibited the highest photovoltaic performance as compared to other devices with FET, PT2, PH500 and PH. Copyright © 2015 John Wiley & Sons, Ltd.     

Enzymatic‐catalyzed polymerization of water‐soluble electrically conductive polymer PEDOT:PSS

Water‐soluble electrically conductive polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) was synthesized by the enzymatic‐catalyzed method using 3,4‐ethylenedioxythiophene (EDOT) as monomer, poly(styrenesulfonate) (PSS) as water‐soluble polyelectrolyte, horseradish peroxidase enzyme as catalyst, and hydrogen peroxide (H₂O₂) as oxidant. Fourier transform infrared spectra and UV–vis absorption spectra confirm the successful enzymatic‐catalyzed polymerization of PEDOT. Dynamic light scattering data confirm the formation of a stable PEDOT:PSS aqueous dispersion. The thermo gravimetric data show that the obtained PEDOT is stable over a fairly high range of temperatures. The atomic force microscopy height images show that the PEDOT:PSS aqueous dispersion can form excellent homogeneous and smooth films on various substrates by conventional solution processing techniques, which renders this PEDOT:PSS aqueous dispersion a very promising candidate for various application in electronic devices. This enzymatic polymerization is a new approach for the synthesis of optical and electrical active PEDOT polymer, which benefits simple setting, high yields, and environmental friendly route. Copyright © 2014 John Wiley & Sons, Ltd.     

Fast Visible-Light 3D Printing of Conductive PEDOT:PSS Hydrogels

Functional inks for light-based 3D printing are actively being searched for being able to exploit all the potentialities of additive manufacturing. Herein, a fast visible-light photopolymerization process is showed of conductive PEDOT:PSS hydrogels. For this purpose, a new Type II photoinitiator system (PIS) based on riboflavin (Rf), triethanolamine (TEA), and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated for the visible light photopolymerization of acrylic monomers. PEDOT:PSS has a dual role by accelerating the photoinitiation process and providing conductivity to the obtained hydrogels. Using this PIS, full monomer conversion is achieved in less than 2 min using visible light. First, the PIS mechanism is studied, proposing that electron transfer between the triplet excited state of the dye (³Rf*) and the amine (TEA) is catalyzed by PEDOT:PSS. Second, a series of poly(2-hydroxyethyl acrylate)/PEDOT:PSS hydrogels with different compositions are obtained by photopolymerization. The presence of PEDOT:PSS negatively influences the swelling properties of hydrogels, but significantly increases its mechanical modulus and electrical properties. The new PIS is also tested for 3D printing in a commercially available Digital Light Processing (DLP) 3D printer (405 nm wavelength), obtaining high resolution and 500 µm hole size conductive scaffolds.     

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     

Enhanced electrical properties of PEDOT:PSS via synergistic effect

As a representing conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been widely employed in organic electronics. However, the electrical conductivity for pristine PEDOT:PSS is only between 0.1 and 0.5 S/cm. In order to enhance the conductivity, the silver nanowires (Ag NWs) were synthesized to dope PEDOT:PSS. It was found the electrical conductivity of PEDOT:PSS was improved to about 200 S/cm with Ag NWs. When double-wall carbon nanotube (DWCNT) was employed together with Ag NWs, the electrical conductivity was further improved to over 2800 S/cm. We proposed the synergistic working model between Ag NWs and CNTs for such enhancement. In this work, UV-vis-NIR spectra and SEM images were also employed to investigate the mechanism of electrical conductivity enhancement.     

Highly Conductive PEDOT:PSS Films with 1,3‐Dimethyl‐2‐Imidazolidinone as Transparent Electrodes for Organic Light‐Emitting Diodes

Highly conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as transparent electrodes for organic light‐emitting diodes (OLEDs) are doped with a new solvent 1,3‐dimethyl‐2‐imidazolidinone (DMI) and are optimized using solvent post‐treatment. The DMI doped PEDOT:PSS films show significantly enhanced conductivities up to 812.1 S cm⁻¹. The sheet resistance of the PEDOT:PSS films doped with DMI is further reduced by various solvent post‐treatment. The effect of solvent post‐treatment on DMI doped PEDOT:PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PEDOT:PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PEDOT:PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PEDOT:PSS films with the new solvent of DMI can be a promising transparent electrode for low‐cost, efficient ITO‐free white OLEDs.

     

Photolithographic patterning of highly conductive PEDOT:PSS and its application in organic light‐emitting diodes

Photolithographically patterned highly conductive (～1400 S/cm) poly(3,4‐ethylenedioxythio‐phene):poly(styrenesulfonate) (PEDOT:PSS) films are demonstrated as electrodes for organic light emitting diodes (OLEDs). With the assistance of hydrofluoroether (HFE) solvents and fluorinated photoresists, high‐resolution passive‐matrix OLEDs with PEDOT:PSS electrodes are fabricated, in which the OLEDs show comparable performance to those devices prepared on the indium tin oxide (ITO) electrodes. This photolithographic patterning process for PEDTO:PSS has great potential for applications which require flexible electrodes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1221–1226     

Improving Efficiency of Organic Photovoltaic Cells Using PEDOT:PSS and MWCNT Nanocomposites as a Hole Conducting Layer

In this study, polymeric nanocomposites of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and functionalized multi-walled carbon nanotubes (MWCNTs) were spin coated on a pre-patterned ITO glass and used as a hole conducting layer in organic photovoltaic cells. The multi-layered ITO/MWCNT-PEDOT:PSS/CuPc/C60/Al devices were fabricated to investigate the current density-voltage characteristics and power conversion efficiency. The power conversion efficiency obtained from the device with a concentration of 1.0 wt% MWCNT in the PEDOT:PSS layer was increased twice as those adopted from device without MWCNT doping in the PEDOT:PSS layer and current density-voltage characteristics was also improved well with incorporation of MWCNTs.     

Thermoelectric properties of PEDOT films prepared by electrochemical polymerization

Thermoelectric (TE) properties of flexible and free‐standing poly(3,4‐ethylenedioxythiophene) (PEDOT) films synthesized via galvanostatic polymerization of 3,4‐ethylenedioxythiophene in propylene carbonate containing sulfated poly(β‐hydroxyethers) (S‐PHE) as polymer electrolyte were elaborately studied. Both electrical conductivities (σ ) and Seebeck coefficients (S ) of the PEDOT:S‐PHE films were increased by decreasing the temperature (T ) or by increasing the current density (J ) during electrosynthesis. Possible reasons for the lack of a trade‐off relation commonly observed between σ and S are discussed on the basis of SEM and oxidation‐level measurements. Preparation of the PEDOT:S‐PHE films was optimized with respect to T and J . In addition, the oxidation level of the PEDOT:S‐PHE films was controlled by potential and the change of their TE performances was discussed in conjunction with the change of chemical species involved. The power factor (PF = σS ²) of the PEDOT:S‐PHE films reached 7.9 μW m^?1 K^?2, leading to a dimensionless TE figure‐of‐merit (ZT ) of 0.013. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 524–531     

Synthesis and microwave absorbing properties of poly(3,4‐ethylenedioxythiophene) (PEDOT) microspheres

Poly(3,4‐ethylenedioxythiophene) (PEDOT) solid and hollow microspheres were successfully synthesized by simply adjusting the concentration of 3,4‐ethylenedioxythiophene (EDOT) and the molar ratio of EDOT to ammonium persulfate (APS) (represented by (EDOT)/(APS)), respectively. Microwave absorbing properties of PEDOT microspheres with tunable reflection loss (RL) and microwave frequency band were described in detail. The relationships between the conductivity and RL of PEDOT microspheres were also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Metal Free Acid‐Mediated Solid‐State Polymerization and Processability of Polymers Based on 3,4‐Alkylenedioxythiophenes

The present article reports metal free acid‐mediated polymerization of 3,4‐alkylenedioxythiophenes in a solvent free medium and processability of insoluble polymers. It also describes structural variants and functional aqueous dispersions based on 3,4‐alkylenedioxythiophenes. Polymers were processed by dispersing the insoluble polymer powders in aqueous media using polymeric aromatic surfactant (polystyrenesulfonate, PSS) and aliphatic surfactant (sodiumdodecylsulfonate, SDS), respectively. The effect of surfactant on particle size, stability, and conductivity of the dispersions was investigated in detail. Polymer particles in SDS‐based dispersions tend to agglomerate which resulted enhanced conductivity of the thin films. Electrochemical studies revealed that the polymers are electroactive in nature and are transparent in oxidized state. The electrochromic contrast between the oxidized and reduced states of the polymers was in the range of 40–46%. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 783–791     

Electrochemical synthesis of PEDOT derivatives bearing imidazolium‐ionic liquid moieties

Novel poly(3,4‐ethylenedioxythiophene) (PEDOT) polymers bearing imidazolium‐ionic liquid moieties were synthesized by electrochemical polymerizations. For this purpose, new functional monomers were synthesized having an 3,4‐ethylenedioxythiophene (EDOT) unit and an imidazolium‐ionic liquid with different anions such as tetrafluoroborate (BF), bis(trifluoromethane)sulfonimide ((CF₃SO₂)₂N^?), and hexafluorophosphate (PF). Next, polymer films were obtained by electrochemical synthesis in dicholoromethane solutions. Obtained polymers were characterized, revealing the characteristics of PEDOT in terms of electrochemical and spectroelectrochemical properties, FTIR, ¹H NMR, and AFM microscopy. Interestingly, the hydrophobic character of electropolymerized films could be modified depending on the anion type. The hydrophobicity followed the trend PF > (CF₃SO₂)₂N^? > BF > pure PEDOT as determined by water contact angle measurements. Furthermore, the polymers could be dissolved in a range of polar organic solvents such as dimethylformamide, propylene carbonate, and dimethyl sulfoxide making these polymers interesting candidates for wet processing methods. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3010–3021, 2009