PEDOT Thin Films Research Articles

Quality dependence of vapor phase-polymerized poly(3,4-ethylenedioxythiophene) nanofilm on substrate pre-treatment methods.

The quality of a vapor phase-polymerized PEDOT thin film is highly dependent upon a uniform coating of an oxidant such as Fe(III)Cl3 on a SiO2 surface. The phase states of a coated oxidant solution are deeply affected by the surface character of base substrates, which can be altered via various pre-treatment methods. Therefore, in this study, in order to identify the optimum surface pre-treatment method, four different pre-treatment techniques (Ar plasma, O2 plasma, H2O/Ar plasma, and a SC-1 treatment methods), were carried out on a thermally oxidized Si-wafer surface using a uniform oxidant solution coating. And then, PEDOT films were grown on the oxidant coated surfaces using a vapor phase polymerization method. Those films were further analyzed using several thin film analyzing tools such as a contact angle analyzer, FE-SEM, an optical microscope, FT-IR, and a four point probe. From this analysis, it was discovered that the quality of a PEDOT thin film can be deeply affected by the surface pre-treatment method. In particular, a H2O/Ar plasma-treated SiO2 surface was the most uniformly coated with the oxidant solution, and the PEDOT thin films grown on the SiO2 surface showed a quite low sheet resistance value (543.84 Ω/sq). Such a high quality ultrathin film could be a potential candidate for a transparent flexible electrode for the next-generation of display and/or photovoltaic devices.

동시-기상중합법을 이용한 Poly(3,4-ethylenedioxythiophene)(PEDOT)-TiO2하이브리드 박막 제조

PEDOT-TiO2 hybrid conductive thin film including semiconductive metal oxide was successfully prepared via simultaneous vapor phase polymerization (VPP). The mechanical properties such as pencil hardness and antiscratch property as well as optoelectrical properties of PEDOT-TiO2 hybrid thin film could be improved as compared with pristine PEDOT thin film. Physicochemically stable crosslinked TiO2 layer derived from a sol-gel process by FTS was generated in the PEDOT thin film layer by simultaneous VPP, resulting in improving mechanical properties of the hybrid thin films without any deterioration of their original optoelectrical properties. PEDOT-TiO2 hybrid thin film showed better electrical conductivity as compared with PEDOT film. It might be due to the fact that the surface morphology of hybrid thin film prepared by simultaneous VPP showed smoother than that of pristine PEDOT thin film.

The reversibility of ionic transport in PEDOT with application to a complementary electrochromic device

Abstract The electrochemistry and ion transport properties of PEDOT in different solvents have been investigated. Conductivity enhancement has been observed in dimethyl sulfoxide (DMSO) and ethylene glycol (EG). This is attributed to the transformation of polymer chains from compact to linear structure induced by such high dipole moment solvent treatment (DMSO or EG). The results of electrochemical quartz crystal microbalance (EQCM) indicate that the solvent plays an important role in redox process. The poly(3,4-ethylenedioxythiophene) (PEDOT) reveals a better reversibility of ionic transfer in DMSO compared with that measured in acetonitrile (ACN). A solution and thin film system electrochromic device (ECD) based on 4-phenothiazin-10-yl-anisole (APS) solution and a PEDOT thin film was assembled and studied. The device demonstrates the color change from colorless (0 V) to deep blue violet (1.6 V). A maximum transmittance window 65% was obtained at 520 nm with the operating potentials between 0 and 1.6 V in DMSO electrolytes. Coloration efficiency of the ECD has been found to be 410 cm 2 /C. No pre-darkening or pre-bleaching of the electrodes is required for assembly of such ECD.

Electrochemical behaviour of graphene–poly (3,4-ethylenedioxythiophene) (PEDOT) composite electrodes for supercapacitor applications

In this paper, we report on the electrochemical characteristics of graphene–PEDOT composite electrodes. The electrodes were made of indium tin oxide (ITO) substrates by simple processes of electrophoretic deposition of graphene followed by electropolymerization of EDOT monomer. The composite electrode was obtained by electrochemical measurements, a median specific capacitance of 1410 F/g and a median area capacitance of 199 mF cm −2 at a scan rate of 40 mVs −1. The composite showed good stability characteristics after repeated scans in cyclic voltammmetry and fared much better than a thin film of PEDOT. The thermal stability of the composite is also much superior when compared to the polymer with a weight loss temperature of 350 °C for the composite and 250 °C for the polymer, respectively. The above electrochemical and thermal behaviours of the composite are correlated to the unique morphology of electrodeposited graphene that provides a conductive and high surface area template for electropolymerization.

Metal-free oxygen reduction electrodes based on thin PEDOT films with high electrocatalytic activity

Oxygen reduction reaction (ORR) electrodes play an important role in the development of new battery and fuel cell technologies. However most of the presented electrode materials cannot provide the efficiency required for these applications, and/or they are based on economically unfavourable noble metals. In this article, multi-layer electrodes of high conductivity PEDOT prepared by vacuum vapour phase polymerization in the presence of a PEG–PPG–PEG triblock copolymer are used to fabricate a metal-free oxygen reduction electrode. After optimizing the main production parameters, measuring ORR performance of the metal-free PEDOT based electrodes confirms that they have the ability to deliver a stable electrocatalytic activity. A chemical treatment is also used for further enhancing the electrocatalytic activity of these electrodes. Depending on pH, the electrocatalytic activity of these treated electrodes reaches a higher or the same level as platinum based electrodes.

Effect of HF and Plasma Treated Glass Surface on Vapor Phase-Polymerized Poly(3,4-ethylenedioxythiophene) Thin Film : Part I

In this study, in order to investigate how consecutive treatments of glass surface with HF acid and water vapor/Ar plasma affect the quality of 3-aminopropyltriethoxysilane self-assembled monolayer (APS-SAM), poly(3,4-ethylenedioxythiophene) (PEDOT) thin films were vapor phase-polymerized immediately after spin coating of FeCl3 and poly-urethane diol-mixed oxidant solution on the monolayer surfaces prepared at various treatment conditions. For the film characterization, various poweful tools were used, e.g., FE-SEM, an optical microscope, four point probe, and a contact angle analyzer. The characterization revealed that HF treatment is not desirable for the synthesis of a high quality PEDOT thin film via vapor phase polymerization method. Rather, sole treatment with plasma noticeably improved the quality of APS-SAM on glass surface. As a result, a highly dense and smooth PEDOT thin film was grown on uniform oxidant film-coated APS monolayer surface.

Temperature sensing behavior of poly(3,4-ethylenedioxythiophene) thin film

Temperature sensing behavior of poly(3,4-ethylenedioxythiophene) (PEDOT) thin film was investigated at the temperature range of −20°C to 60°C. PEDOT thin films were fabricated by in situ polymerization, where 3,4-ethylenedioxythiophene (EDOT) and ferric p-toluene sulfonate (FTS) were used as a monomer and an oxidant, respectively. The monomer and the oxidant solutions in 1-butanol were prepared separately and mixed just before in situ polymerization. The mixed solution was cast on a substrate and polymerization was carried out at 70°C for 30min, followed by washing with methanol and drying under vacuum.Resistance change of PEDOT film with temperature was monitored using two probe method. It was observed that resistance of PEDOT film monotonically decreased with increasing temperature, confirming a typical temperature dependence of the electrical resistance of semiconductors with negative temperature coefficient (NTC). However, resistance of PEDOT thin film was not stable with repeated heating and cooling. Resistance at the same temperature increased with repeated heating and cooling cycles. We found that stability of PEDOT thin film could be significantly improved by heat treatment of PEDOT film at 150°C for 1h and sealing the PEDOT thin film. Temperature-dependent resistance of the stabilized PEDOT thin film could be fitted to the Steinhart–Hart equation from −20°C to 60°C range even after repeated cycles, suggesting its potential application as a flexible thin film thermistor.

Uniform bipolar organic memory using vapor phase polymerized poly (3,4-ethylenedioxythiophene)

Organic memory device has emerged as an excellent candidate for the next generation storage devices due to its high performance and low production cost. In this paper, we report the fabrication and electrical characterization of an organic memory device made of vapor-phase polymerized PEDOT thin films that are highly uniform and free of PSS and free of unreacted reactants. The PEDOT memory device exhibited a typical bipolar resistive switching with a high ON/OFF current ratio of at least 103, which was maintained for more than 103dc sweeping cycles. The device performance was stable for more than 105s. Moreover, the device containing 64 cells has very high cell to cell uniformity as demonstrated by (1) at least 93% of the cells displaying the ON/OFF current ratio of at least 103 and (2) the deviation of the set and reset voltages from the average values being less than 0.5V and 0.4V, respectively. The maximum current before switching in the reset process was found to increase linearly with increase in the compliance current applied during the set process.

Is the Enhanced Adhesion of PEDOT Thin Films on Electrodes Due to Sulfur - Gold Interaction? - An XPS Study

Electrode materials obtained through electropolymerization of 3,4-ethylenedioxythiophene (EDOT) have sparked interest toward applications in neuroscience and neuroprosthetics due to their favorable electrochemical properties and their biocompatibility. However, insufficient mechanical stability had been an unresolved issue and hindered practical applications, until recent research by our group demonstrated proper adhesion of poly(3,4- ethylenedioxythiophene) (PEDOT) to a gold surface. In the present study, X-ray photoelectron spectroscopy (XPS) was employed and in particular the chemical shift of the S2p band, which is indicative of binding between sulfur and gold, was used to assess the degree of interaction between 3,4-ethylenedioxythiophene (EDOT), thiophene, and 3- thiophenecarboxylic acid (thiophene-COOH), with the gold surface. The results of the XPS investigations indicate a covalent bond between EDOT and gold, which should indeed contribute to improved adhesion.

The Curious Out‐of‐Plane Conductivity of PEDOT:PSS

AbstractFor its application as transparent conductor in light‐emitting diodes and photovoltaic cells, both the in‐plane and out‐of‐plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out‐of‐plane conductivity and those that do, report widely varying results. Here a systematic study of the out‐of‐plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out‐of‐plane conductivity with only a 3‐4‐fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model.

Electrocatalysis of the hydroquinone/benzoquinone redox couple at platinum electrodes covered by a thin film of poly(3,4-ethylenedioxythiophene)

The hydroquinone/benzoquinone (HQ/BQ) redox reaction is studied on platinum electrodes coated by poly(3,4-ethylenedioxythiophene) (PEDOT) thin films using cyclic voltammetry and chronocoulometry. It was found that HQ is weakly adsorbed on PEDOT and that the HQ/BQ redox reaction is well described by a reversible diffusion-governed charge transfer on platinum electrodes coated by a thin film of PEDOT and in the presence of very low HQ concentration, indicating that the modification of PEDOT on Pt can greatly accelerate the electron transfer rate and that PEDOT seems to be the best electrocatalyst for this reaction reported until know. The reaction kinetics is very sensitive to the local environment around the active sites of the electrocatalyst, which is affected by the amount of adsorbed HQ and the PEDOT film thickness. Finally, the porous nature of PEDOT films, which have a high internal surface area, allows the HQ adsorption, deep inside the PEDOT film. In this sense, we suggest that the first step of hydroquinone oxidation is the formation of an acid–base complex between HQ and PEDOT.

Noninvasive Photodetachment of Stem Cells on Tunable Conductive Polymer Nano Thin Films: Selective Harvesting and Preserved Differentiation Capacity

Viable mesenchymal stem cells (MSCs) were efficiently and selectively harvested by near-infrared (NIR) light using the photothermal effect of a conductive polymer nano thin film. The poly(3,4-ethylenedioxy thiophene) (PEDOT)-coated cell culture surfaces were prepared via a simple and fast solution-casting polymerization (SCP) technique. The absorption of PEDOT thin films in the NIR region was effectively triggered cell harvesting upon exposure to an NIR source. By controlling the NIR absorption of the PEDOT film through electrochemical doping or growing PEDOT with different thin film thickness from 70 to 300 nm, the proliferation and harvesting of MSCs on the PEDOT surface were controlled quantitatively. This light-induced cell detachment method based on PEDOT films provides the temporal and spatial control of cell harvesting, as well as cell patterning. The harvested stem cells were found to be alive and well proliferated despite the use of temperature increase by NIR. More importantly, the harvested MSCs by this method preserved their intrinsic characteristics as well as multilineage differentiation capacities. This PEDOT surfaces could be used for repetitive culture and detachment of MSCs or for efficient selection or depletion of a specific subset from heterogeneous population during culture of various tissue-derived cells because there were no photodegradation and photobreakage in the PEDOT films by NIR exposure.

Synthesis and Physical Vapor Deposition of Low-Molecular-Weight Poly(3,4-ethylenedioxythiophene)

Thin films of poly(3,4-ethylenedioxythiophene) (PEDOT) were obtained by physical vapor deposition. To this end, low-molecular-weight PEDOT was synthesized by oxidative polymerization using oxygen as the oxidizing reagent with palladium acetate and copper acetate as the catalysts. The degree of polymerization was controlled by adjusting reaction time. The material can be vapor-deposited by thermal evaporation when the degree of polymerization was about 10. Formation of PEDOT thin films was confirmed by infrared spectroscopy. The optical absorption edge of the deposited film showed a redshift with increasing degree of polymerization. The electrical conductivity of the deposited film was in the range from 10-4 to 10-3 S/cm. The deposited films are expected to be in the nondoped state since the oxidizing reagent (oxygen) is unlikely to remain in the films.

Structural, morphology and optical properties of ITO/PEDOT:PSS and ITO/Ag nanoparticles/PEDOT:PSS thin films

In order to investigate the effects and optical properties in the mid-infrared region, thin films of PEDOT:PSS were spin-coated on ITO glasses and ITO/Ag nanoparticles substrates. Scanning Electron Microscopy, SEM, has been applied to investigate the surface morphology and measure the size of nanoparticles. Dielectric and optical coefficients such as refractive index, n, and extinction coefficient, k, were calculated by applying Kramers-Kronig dispersion relations to the experimentally recorded near normal reflection FTIR spectra. Different analyses confirm that Ag nanoparticles are present in the structure of the synthesized thin films. The recorded Raman spectra have shown that the intensity enhancement of Raman peaks of PEDOT:PSS increases due to the plasmon resonance of Ag colloidal silver nanoparticles layer and optical properties investigation has confirmed the electrical conductivity increase in the mid-infrared region.

Fast switching and high contrast electrochromic device based on PEDOT nanotube grown on ZnO nanowires

The present work reports preparation of an electrochromic device based on poly(3,4-ethylenedioxythiophene) (PEDOT) modified ZnO nanowires. The vertically aligned ZnO nanowires, being 70nm in diameter, were prepared as a template by hydrothermal process on 65nm ZnO seed layer sputtered on transparent conductive fluorine doped tine oxide substrate. PEDOT was synthesized by electropolymerization using two approaches. The first was prepared at 1.6V constant potential (CP) and the second by 0–2V cyclic voltammetry (CV). The PEDOT nanotubes were successfully grown on ZnO nanowires array by CV electrochemical polymerization but CP method led to formation of PEDOT thin film. The average wall thickness of nanotubes was 20nm. The CV and CP electrodes and devices were characterized by scanning electron microscope, cyclic voltammetry analysis and UV–visible spectrophotometery to study the effect of preparation method on electrode morphology and device stability, response time (tR) and contrast. The CV approach gave rise to tR and contrast of 66ms and 46.1%, respectively; CP method resulted in tR and contrast of 300ms and 37.84%, respectively. While the conventional thin films had response time in order of second.

Bioelectronics meets nanomedicine for cardiovascular implants: PEDOT-based nanocoatings for tissue regeneration

BackgroundAn exciting direction in nanomedicine would be to analyze how living cells respond to conducting polymers. Their application for tissue regeneration may advance the performance of drug eluting stents by addressing the delayed stent re-endothelialization and late stent thrombosis. MethodsThe suitability of poly (3, 4-ethylenedioxythiophene) (PEDOT) thin films for stents to promote cell adhesion and proliferation is tested in correlation with doping and physicochemical properties. PEDOT doped either with poly (styrenesulfonate) (PSS) or tosylate anion (TOS) was used for films' fabrication by spin coating and vapor phase polymerization respectively. PEGylation of PEDOT: TOS for reduced immunogenicity and biofunctionalization of PEDOT: PSS with RGD peptides for induced cell proliferation was further applied. Atomic Force Microscopy and Spectroscopic Ellipsometry were implemented for nanotopographical, structural, optical and conductivity measurements in parallel with wettability and protein adsorption studies. Direct and extract testing of cell viability and proliferation of L929 fibroblasts on PEDOT samples by MTT assay in line with SEM studies follow. ResultsAll PEDOT thin films are cytocompatible and promote human serum albumin adsorption. PEDOT:TOS films were found superior regarding cell adhesion as compared to controls. Their nanotopography and hydrophilicity are significant factors that influence cytocompatibility. PEGylation of PEDOT:TOS increases their conductivity and hydrophilicity with similar results on cell viability with bare PEDOT:TOS. The biofunctionalized PEDOT:PSS thin films show enhanced cell proliferation. ConclusionsThe application of PEDOT polymers has evolved as a new perspective to advance stents. General significanceIn this work, nanomedicine involving nanotools and novel nanomaterials merges with bioelectronics to stimulate tissue regeneration for cardiovascular implants. This article is part of a Special Issue entitled Organic Bioelectronics — Novel Applications in Biomedicine.

Glucose Sensing by Glucose Oxidase/PEDOT Thin Film Electrode

Glucose oxidase (GOX)/poly(3,4-ethylenedioxythiophene) (PEDOT) electrode was prepared for glucose sensing. PEDOT thin film was first electrochemically or chemically polymerized on Pt substrate, followed by dipping it into GOX solution to immobilize GOX on PEDOT surface. It was observed that GOX was adsorbed much more efficiently on the chemically polymerized PEDOT than on the electrochemically polymerized PEDOT. The cyclic voltammetry of the thin film electrode showed a clear anodic peak at −0.43 V. It was also observed that the anodic current monotonically decreased with the increase of glucose concentration dissolved in the electrolyte solution, implying that the electrode can be applied as a simple glucose sensor.

OCVD poly(3,4-ethylenedioxythiophene) conductivity and lifetime enhancement via acid rinse dopant exchange

Reduced sheet resistance and longer film stability of oCVD (oxidative chemical vapour deposition) PEDOT films were achieved by including a post-process acid rinse step in the production of the thin films. PEDOT films were rinsed in multiple concentrations of hydrobromic acid, sulfuric acid, and hydrochloric acid to test the effect of acid rinsing on sheet resistance, doping concentration, chemical composition, optical transmittance, and film morphology. XPS, FTIR, Raman spectroscopy, and XRD measurements were taken to determine the morphology and composition of the rinsed films. On average, rinsing films in HCl, HBr, and H2SO4 produced conductivity increases of 37%, 135%, and 117%. The dc to optical conductivity ratio, σdc/σop, was increased to 6, 12, and 10, for HCl, HBr, and H2SO4 rinsed films respectively as compared to σdc/σop = 4 for MeOH rinsed films. This study found evidence of dopant exchange within the films facilitated by the acid rinsing step, as well as complete removal of residual iron chloride oxidant. The acid rinse step also resulted in improved film conductivity stability at elevated temperatures. The XRD measurements in particular show signs of semi crystallinity in the PEDOT film after acid rinsing in comparison to an amorphous structure observed before this step. In this study, acid rinsing applied as a post-process step alters thin PEDOT films in ways that enhance their ability to function as electrode materials in photovoltaic devices.

Improvement of Electrical Conductivity of Poly(3,4-ethylenedioxythiophene) (PEDOT) Thin Film

In order to improve the electrical conductivity of in-situ polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) thin film, we investigated the effect of doping level and co-dopant on the electrical conductivity. Doping level of PEDOT thin film was determined by X-ray photoelectron spectroscopy (XPS) and it was found that the higher doping level led to higher electrical conductivity. We also used several kinds of co-dopants such as methanesulfunic acid, naphthalenesulfonic acid and p-toluenesulfonic acid to increase the conductivity of PEDOT. When methanesulfonic acid was used as co-dopant, electrical conductivity of PEDOT thin film increased up to 1,500 S/cm. It is considered that the enhanced conductivity resulted from higher interchain conduction or more expanded chain structure due to small dopant size of methanesulfunic acid.

Conductivity enhancement of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) films post-spincasting

Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) thin films on indium tin oxide and glass substrates have been fabricated and subjected to a non-adiabatic annealing process. The films showed subtle changes in their structure and optical properties as well as an increase in conductivity due to the effects of rapid thermal annealing. Through a combination of Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy studies in conjunction with electrical characterization, and four-point probe measurements, material enrichment of conductive PEDOT domains at the polymer-metal interface have been demonstrated, which well explains the surface conductivity improvement of a thin film of PEDOT:PSS after annealing.