PEDOT Thin Films Research Articles

Mechanistic Insights into the Potentiodynamic Electrosynthesis of PEDOT Thin Films at a Polarizable Liquid|Liquid Interface.

Conducting polymer (CP) thin films find widespread use, for example in bioelectronic, energy harvesting and storage, and drug delivery technology. Electrosynthesis at a polarizable liquid|liquid interface using an aqueous oxidant and organic soluble monomer provides a route to free-standing and scalable CP thin films, such as poly(3,4-ethylenedioxythiophene) (PEDOT), in a single step at ambient conditions. Here, using the potentiodynamic technique of cyclic voltammetry, interfacial electrosynthesis involving ion exchange, electron transfer, and proton adsorption charge transfer processes is shown to be mechanistically distinct from CP electropolymerization at a solid electrode|electrolyte interface. During interfacial electrosynthesis, the applied interfacial Galvani potential difference controls the interfacial concentration of the oxidant, but not the CP redox state. Nevertheless, typical CP electropolymerization electrochemical behaviors, such as steady charge accumulation with each successive cycle and the appearance of a nucleation loop, were observed. By combining (spectro)electrochemical measurements and theoretical models, this work identifies the underlying mechanistic origin of each feature on the cyclic voltammograms (CVs) due to charge accumulated from Faradaic and capacitive processes as the PEDOT thin film grows. To prevent overoxidation during interfacial electrosynthesis with a powerful cerium aqueous oxidant, scan rates in excess 25 mV·s-1 were optimal. The experimental methodology and theoretical models outlined in this article provide a broadly generic framework to understand evolving CVs during interfacial electrosynthesis using any suitable oxidant/monomer combination.

Vapor phase polymerization of PEDOT on ITO/glass surfaces for nonenzymatic detection of dopamine

This study demonstrates the deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) as an electrically conductive polymer on the ITO-coated glass surfaces for the production of a non-enzymatic electrochemical sensor to detect dopamine. For this purpose, thin films of PEDOT were synthesized using vapor phase polymerization (VPP) from the corresponding monomer 3,4-ethylenedioxythiophene, in which iron(III)chloride was used as the oxidant. Films were deposited at different substrate temperatures, where the temperature dependence of doping and conjugation levels were studied using FTIR and XPS analyses. The highest doping and conjugation levels, as well as the highest film thickness (380 nm) was observed for the film deposited at 40 °C, which represented the highest conductivity of 111 S/cm. Significant differences were observed between the electrochemical responses of ITO/glass and PEDOT/ITO electrodes. Amperometric measurements indicated a limit of detection value of 2.02 µM for dopamine using as-synthesized PEDOT/ITO electrode.

Investigations on Impact of YSZ Nanoparticles on Morphology & Electrical conductivity of PEDOT: PSS

Conductive polymer nanocomposites, which combine the flexibility and conductivity of polymers with the unique properties of nanofillers, have generated interest in various fields such as energy storage, sensors, coatings, and corrosion protection. This study discusses the effect of Yttria-stabilized zirconium nanoparticles (YSZ NPs) on the morphology and electrical conductivity of poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT: PSS). Thin films of PEDOT: PSS and PEDOT: PSS: YSZ were fabricated using spin coating technique. FTIR and XRD characterizations confirmed the interaction between YSZ nanoparticles and the PEDOT: PSS matrix, leading to changes in chemical morphology and film crystallinity. The investigation of the current-voltage (I-V) relationship showed improved electrical conductivity in PEDOT: PSS films with the addition of YSZ nanoparticles, with respective conductivities of 0.028×10−6 S cm−1 and 0.0885×10−4 S cm−1 for pristine and YSZ-containing films. Additionally, the sensing properties of the PEDOT: PSS: YSZ film in detecting organic vapours were studied. These findings suggest that these conducting polymer nanocomposite thin films could potentially be used as electrolyte components in battery cells, supercapacitors, and fuel cells, as well as serve as sensors for certain organic vapours.

Printing PEDOT:PSS optimized using Response surface method (RSM) and genetic algorithm (ga) via modified 3D printer for perovskite solar cell applications

Despite significant improvements in solar cell fabrication processes, there are still significant challenges in the fabrication technology owing to poor production efficiency, large equipment and preparatory costs, substrate dependencies, material limitation, etc. This research proposes the use of a modified extrusion-based three-dimensional (3D) printing technology to print thin films of PEDOT:PSS (Poly 3,4-ethylenedioxythiophene:poly styrene sulfonate) for perovskite solar cell (PSC) applications and beyond. The main objective of the research is to induce the benefits of 3D printing technology into thin film printing for PSC applications. The central composite design (CCD) of the response surface method (RSM) in design expert software (Design Expert V13) and a genetic algorithm (GA) in MATLAB software are used to design and optimize the experiment, respectively. Accordingly, a uniformly thin PEDOT:PSS film with a 115 nm thickness is printed with the modified 3D printer at a print speed of 82 mm/s, a bed temperature of 80 °C, and an extrusion start position of 160 mm with a 0.1 mm inner diameter blunt needle and a 0.25 mm x-distance offset. To validate the printed PEDOT:PSS film for PSC application, other PSC layers, except for aluminum electrodes, are spin-coated on top of the 3D-printed PEDOT:PSS film, and the PSC is tested for its performance using a solar simulator. From the test, a competitive open-circuit voltage of 860 mV was produced. In general, printing PSC layers by modifying a cheap and easily available 3D printer has the benefits of excellent material utilization, substrate independence, rapid design, manufacture, and testing of solar cells in the electronic industry.

Structural and optical study of conducting polymer PEDOT:PSS and its composite with GO

Conducting polymers such as PEDOT:PSS have received tremendous attention as possible substitute for ITO as transparent and conductive material in flexible electronic devices. Due to its extraordinary electrical, physical, and chemical properties Graphene has sparked huge interest in many advanced technologies. To enhance the aggregate properties, conducting polymers have been reinforced with graphene, graphene oxide (GO), reduced graphene oxide (rGO) etc. In this study, thin films of PEDOT:PSS and GO composites were deposited on glass substrates by spin-coating technique. Dimethyl sulfoxide (DMSO) was added to PEDOT:PSS to enhance the conductivity. The films were characterized by four probe, XRD, Scanning electron microscopy (SEM) and Ellipsometry. Conductivity measurement by four probe technique shows highest conductivity of 1170 S/cm for 5% DMSO doped PEDOT:PSS films. XRD shows shift in peak position of PEDOT:PSS films due to addition of DMSO and GO. Spectroscopic ellipsometry study indicates an increase in refractive index due to addition of GO in PEDOT:PSS.

Cerium-based metal–organic framework-conducting polymer nanocomposites for supercapacitors

Nanocomposites consisting of a cerium-based metal–organic framework (Ce-MOF-808) and a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), are synthesized by performing the pulse electrodeposition of PEDOT within the Ce-MOF-808 thin films. Ratios between MOF and PEDOT in the composites are tunable by simply adjusting the charge density used for electropolymerization, and the crystallinity, morphology, and elemental distributions of the resulting nanocomposites are characterized. Electrochemical behaviors and capacitive performances of the pristine MOF, pristine PEDOT thin films, and composite thin films are investigated with the use of the neutral sodium sulfate aqueous electrolytes. The reversible electrochemical reactivity of the highly porous Ce-MOF-808 provides a pseudocapacitance, and the electronically conducting PEDOT can not only offer a remarkable double-layer capacitance but also facilitate the electronic conduction between the redox-active cerium sites present in the MOF. As a result, the composite can outperform both the pristine MOF and pristine electrodeposited PEDOT as the active materials for supercapacitors. Findings here suggest that the highly porous and redox-active cerium-based MOF thin films are capable to enhance the capacitive performances of the electrodeposited PEDOT thin films.

A nuanced understanding of the doping of poly(3,4-ethylenedioxythiophene) with tosylate

The conducting polymer poly(3,4-ethylenedioxythiophene) (known as PEDOT) is routinely fabricated into doped thin films for investigation of its inherent properties as well as for a range of applications. Fabrication of PEDOT is often achieved via oxidative polymerisation, where the conducting polymer is polymerised and doped (oxidised) to yield a conductive polymer thin film. The oxidiser and the polymerisation temperature are two parameters that may influence the properties and performance of the resultant PEDOT thin film. In this study, the role of temperature for the chemical polymerisation of PEDOT using the oxidiser iron tosylate is investigated from a computational and experimental viewpoint. While computations of the doping energetics suggest increasing doping with increasing temperature, x-ray photoelectron spectroscopy of fabricated PEDOT thin films indicate doping is much more complicated. With the aid of computations of the spatial distribution functions for tosylate in PEDOT, experiments indicate that two different populations of tosylate anions exist in the PEDOT matrix. Their relative populations change as a function of the polymerisation temperature. Therefore, polymerisation temperature plays a critical role in tailoring the properties of PEDOT in pursuit of being fit-for-purpose for the desired application.

Retraction Note to: Highly conductive organic thin films of PEDOT–PSS: silver nanocomposite treated with PEG as a promising thermo-electric material

Retraction Note to: Highly conductive organic thin films of PEDOT–PSS: silver nanocomposite treated with PEG as a promising thermo-electric material

A Moisture-Enabled Nanogenerator Activated by a Thin Film of Pedot:Pss with Graded Thickness

A Moisture-Enabled Nanogenerator Activated by a Thin Film of Pedot:Pss with Graded Thickness

Counter Anion Effects on PEDOT Properties and Implications on Photosystem I Incorporation

As energy consumption increases in tandem with the global warming crisis, the need for cleaner, renewable energy is at an all-time high. Inspired by nature’s billion-year-old process for energy production, biohybrid solar approaches have been shown to hold much promise in many aspects that are required in renewable energy. By leveraging Photosystem I (PSI), a key protein of the electron transport chain in photosynthesis, it is possible to hijack the electrons to perform an array of light-driven processes. In many areas of PSI research, conductive polymers are employed to wire the protein so that electrons can be directed to and from the reaction centers along favorable paths. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is commonly used in these applications as it is water soluble and thus compatible with PSI. Electro-polymerization allows for direct contact of the PEDOT with an electrode surface; however, electropolymerized PEDOT:PSS is mechanically unstable. Limited research has been conducted to demonstrate the effects of other counter anions on PEDOT properties and their implications on the incorporation of PSI into a hybrid device. In this work, we describe the methodologies employed to synthesize and characterize PEDOT thin films with varying counter anions. Our findings indicate that the counter anion during the electropolymerization process affects morphology, charge transfer kinetics, and optical properties of the resulting film. Coupling these observations to the photoactivity of PEDOT-PSI hybrid films, we provide explanations for the varied performance based upon fundamental understandings of chemical and electrochemical phenomena.

Modifying the conductive properties of poly(3,4-ethylenedioxythiophene) thin films in green solvents.

With the rapid development of flexible electronic devices, flexible transparent conductive materials acted as the charge transport layer or electrical interconnect in the devices are of great need. As one of the representative conductive materials, poly(3,4-ethylenedioxythiophene) (PEDOT) has received more and more attention due to its high transparency in the visible region, good flexibility, especially the tunable conductivity. In order to achieve high conductivities, various of effective approaches have been adopted to modify the PEDOT thin films. However, some strategies need to be carried out in hazardous solvents, which may pollute the environment and even hinder the application of PEDOT thin films in emerging bioelectronics. Therefore, in this mini review, we focus on the discussion about the modification methods for PEDOT thin films in green solvents. According to the source of PEDOT, the modification methods of PEDOT thin films are mainly described from two aspects: 1) modification of in-situ PEDOT, 2) modification of PEDOT complex with poly(styrenesulfonic acid) (PEDOT:PSS). Finally, we conclude with the remaining challenges for future development on the PEDOT thin films prepared by green methods.

Micropatterned Poly(3,4-ethylenedioxythiophene) Thin Films with Improved Color-Switching Rates and Coloration Efficiency.

Electrochromic materials carry out redox reactions and change their colors upon external bias. These materials are the primary component in constructing smart windows for energy saving in buildings or vehicles. Enhancing the electrochromic performances of the materials is crucial for their practical applications. Micropatterned poly(3,4-ethylenedioxythiophene) (mPEDOT) thin films are electrodeposited on indium tin oxide conducting glass in this study. Their electrochromic properties, including transmittance modulation ability, color-switching rates, and coloration efficiency, are investigated and compared with nonpatterned PEDOT thin films. The mPEDOT thin films exhibited faster coloring and bleaching speeds and higher coloration efficiency than the PEDOT thin films while keeping similar transmittance modulation ability. The results suggest that micropatterning an electrochromic material thin film might enhance its electrochromic performances. This research demonstrates the possibility of promoting the color-switching rate of a PEDOT thin film by micropatterning it.

Oxidative Molecular Layer Deposition of Amine-Containing Conjugated Polymer Thin Films

Conjugated polymers such as polyethylenedioxythiophene (pEDOT), polypyrrole (pPy), and polyaniline (pAni) exhibit high electrochemical capacities, making them appealing as electrode materials for energy storage, electrochemical desalination, and chemical sensing. Recent work has established the growth of thin films of pEDOT using alternating gas-phase exposures of the EDOT monomer and a metal chloride (e.g., MoCl5) oxidant in a process termed oxidative molecular layer deposition (oMLD). Here, we describe the first demonstration of oMLD of amine-containing conjugated polymers. We find that pyrrole (Py) and MoCl5 undergo self-limiting surface reactions during oMLD exposures to form conformal pPy thin films, but oMLD using aniline (Ani) and p-phenylenediamine (PDA) monomers yields unexpected azo functionality. The formation of azo groups is attributed to an MoCl5-amine surface adduct that spatially constrains polymerization reactions near the amine group and produces azo groups when coupling two primary amines. pPy grown by oMLD exhibits a record-breaking 282 mAh/g capacity in an aqueous electrolyte, and PDA/MoCl5 oMLD yields azo polymers of interest as anode materials for alkali-ion batteries. Alternating between Py and PDA monomers during oMLD produces molecularly assembled copolymers with qualitatively different electrochemical responses from the isolated monomer structures. This work lays the foundation for the growth of conformal thin films of conjugated amine polymers with molecular-level control of composition and thickness.

Electrosynthesis of Biocompatible Free-Standing PEDOT Thin Films at a Polarized Liquid|Liquid Interface.

Conducting polymers (CPs) find applications in energy conversion and storage, sensors, and biomedical technologies once processed into thin films. Hydrophobic CPs, like poly(3,4-ethylenedioxythiophene) (PEDOT), typically require surfactant additives, such as poly(styrenesulfonate) (PSS), to aid their aqueous processability as thin films. However, excess PSS diminishes CP electrochemical performance, biocompatibility, and device stability. Here, we report the electrosynthesis of PEDOT thin films at a polarized liquid|liquid interface, a method nonreliant on conductive solid substrates that produces free-standing, additive-free, biocompatible, easily transferrable, and scalable 2D PEDOT thin films of any shape or size in a single step at ambient conditions. Electrochemical control of thin film nucleation and growth at the polarized liquid|liquid interface allows control over the morphology, transitioning from 2D (flat on both sides with a thickness of <50 nm) to “Janus” 3D (with flat and rough sides, each showing distinct physical properties, and a thickness of >850 nm) films. The PEDOT thin films were p-doped (approaching the theoretical limit), showed high π–π conjugation, were processed directly as thin films without insulating PSS and were thus highly conductive without post-processing. This work demonstrates that interfacial electrosynthesis directly produces PEDOT thin films with distinctive molecular architectures inaccessible in bulk solution or at solid electrode–electrolyte interfaces and emergent properties that facilitate technological advances. In this regard, we demonstrate the PEDOT thin film’s superior biocompatibility as scaffolds for cellular growth, opening immediate applications in organic electrochemical transistor (OECT) devices for monitoring cell behavior over extended time periods, bioscaffolds, and medical devices, without needing physiologically unstable and poorly biocompatible PSS.

Thickness dependent thermal performance of a poly(3,4-ethylenedioxythiophene) thin film synthesized via an electrochemical approach.

Polymer-based thermal interface materials (TIMs) have attracted wide attention in the field of thermal management because of their outstanding properties including light weight, low cost, corrosion resistance and easy processing. However, the low thermal conductivity (∼0.2 W m−1 K−1) of the intrinsic polymer matrix largely degrades the overall thermal performance of polymer-based TIMs even those containing highly thermal conductive fillers. Hence, enhancing the intrinsic thermal conductivity of the polymer matrix is one of the most critical problems needed to be solved. This paper studies the thermal conductivity of poly(3,4-ethylenedioxythiophene) (PEDOT) films fabricated via cyclic voltammetry. By controlling the number of cycles in the electrochemical synthesis, different thickness of PEDOT films could be obtained. A time-domain thermoreflectance (TDTR) system was employed to evaluate the thermal performance of such as-prepared PEDOT films. We have demonstrated that a PEDOT film with thickness of 40 nm achieves the highest out-of-plane thermal conductivity of ∼0.60 W m−1 K−1, which is almost three folds the thermal conductivity of commercially available pristine PEDOT:PSS film with similar thickness. The X-ray diffraction spectrum reveals that the PEDOT thin film with high crystallinity at the initial stage of electrochemical synthesis leads to enhanced thermal transportation. The findings in this work not only offer an opportunity to fabricate polymer materials exhibiting enhanced thermal conductivity, but also allow one to adjust the thermal performance of conducting polymers in practical applications.

Structural and electrical behaviours of PEDOT:PSS thin films in presence of negatively charged gold and silver nanoparticles: A green synthesis approach

Negatively charged gold and silver nanoparticles are prepared using the dry leaf of Annona reticulata and are used to prepare thin films of PEDOT:PSS nanocomposites. Significant changes in structure, morphology and electrical behaviours of nanocomposite thin films are observed depending upon the type and concentration of nanoparticles. The composite nature of the films are evidenced from the X-ray diffraction, Fourier transform infrared and Raman spectroscopy, while the surface morphology and film thickness are obtained from the analysis of atomic force microscopy. The in-plane DC conductivity of the composite films is enhanced by a moderate value with increase in nanoparticle concentration. Electrical responses obtained from the impedance spectroscopy over a broad frequency range show that both the real and imaginary parts of the impedance vary as a function of nanoparticles concentration and applied frequency. Structural changes after composite formation and the corresponding modifications in electrical behaviors are explained.

Concurrent Enhancement of Conductivity and Stability in Water of Poly(3,4‐Ethylenedioxythiophene):Poly(Styrenesulfonate) Films Using an Oxetane Additive

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most used conducting polymer in organic electronics and bioelectronics owing to its high conductivity combined with high optical transparency and availability as a stable colloidal aqueous dispersion, that can be processed as a conducting ink to produce thin and flexible films and electrodes. In this work, water‐resistant films of PEDOT:PSS showing enhanced conductivity are prepared by solely adding one reagent, 3‐methyl‐3‐oxetanemethanol, to PEDOT:PSS aqueous dispersions. The stability of the resultant thin films in water is attributed to the covalent cross‐linking of benzene rings anchored in PSS chains to polyether chains originated from the polymerization of oxetane groups, as indicated by NMR studies. A phase‐segregation within the PEDOT:cross‐linked PSS film is suggested to facilitate charge transport within the PEDOT network and to be at the origin of the improved conductivity. When immersed in water, the films exhibit increased water‐resistance towards resuspension and delamination and exhibit an increase of conductivity, by two to three orders of magnitude, depending on the used raw PEDOT:PSS formulation. The method described in this work is advantageous in originating water‐stable and highly conducting thin films of PEDOT:PSS as it does not involve high temperatures nor strong acids.

(Invited) Performance of Poly(3,4-ethylenedioxythiophene) Thin Films on Fabrics for Wearable Device Applications Using Oxidative Chemical Vapor Deposition

Wearable electronics is a growing field of electronic devices integrated into wearable applications such as clothing. These electronic devices can be fabricated onto any flexible materials including fabrics and other clothing materials. The potential for the creation of new wearable device applications can range from the most important medical applications to ones for novel enjoyment. While this type of technology is emerging, limits from traditional inorganic conductive materials have not lent themselves to the development of these technologies. These traditional materials lack the overall flexibility and fabric performance to apply themselves to the development of wearable devices. Polymeric materials have been found to have superior mechanical flexibility when integrated into fabrics, and are advantageous to the development of wearable electronic components. Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of a number of promising conjugated polymers due to its high electrical conductivity, visible regime transparency, and tunable work function. It is also extremely stable and has shown promise in organic electronic and optoelectronic devices such as solar cells, thin film transistors and chemical sensors. This stability and PEDOT’s mechanical flexibility make it a promising material for use in various wearable electronic applications.As an emerging technique, oxidative chemical vapor deposition (oCVD) is a deposition process that utilizes mild temperatures and vacuum to generate a chemical reaction between a vaporized source monomer (in this case EDOT) and an oxidizer (in this case FeCl3). Through the use of a temperature controlled vacuum chamber the synthesized resulting material (PEDOT) can be deposited onto specific substrates of almost any kind, in a controllable thin film form. Thin film thickness can be accurately controlled depending on target substrate temperature, deposition time, and monomer introduction rate. In comparison to conventional solution-based deposition processes, oCVD has specific advantages which grants itself to the creation of wearable electronic devices. Films deposited from the use of oCVD better conform to the target substrate. This conformality gives PEDOT the ability to maintain a fabrics breathability by maintaining areas in the fabric where air can pass through. This PEDOT’s excellent stability allows flexible properties to be maintained when depositing on fabric substrates. This allows oCVD to be extremely versatile and promising for wearable electronic devices.What will be presented is the performance of PEDOT thin films on fabric substrates compared to reference samples grown on glass and Si substrates. Performance of electrical, mechanical, surface, and chemical properties will be analyzed through the use of various testing equipment. To mimic the daily use in clothing and confirm the stability and mechanical flexibility of PEDOT thin films, films deposited on fabric will be compared before and after undergoing mechanical bending cycles, where sheet resistance and conductivity will be measured after each cycle to monitor potential film degradation. After undergoing 100 mechanical bending cycles, PEDOT films deposited on glass shown that they can maintain nominal conductivity measurements with an average variation from nominal of 10% depending on substrate temperature. Note that due to the nature of fabric having a rough and curvy surface, precise contact with the film is difficult to obtain measurements. Therefore, the term nominal is used for the values of conductivity. Due to the measured conductivity not degrading after 100 bending cycles, it shows PEDOT’s ability to maintain its performance and its mechanical flexibility. Atomic force microscopy (AFM) will be utilized to obtain topographical microstructure images and to analyze root mean square (RMS) roughness. Scanning electron microscopy (SEM) will be used to determine visual conformality of PEDOT thin films on fabric substrates. Fourier-transform infrared spectroscopy (FTIR) is utilized to confirm specific chemical bonding typical to PEDOT films, and UV-Vis spectroscopy to investigate optical properties such as onset of absorption to accurately determine band gap, which has been found to be between 1.8 and 2.0 eV depending on film thickness. All of these properties will be compared across different target substrate temperatures ranging from 30 °C to 90 °C. These findings on vapor-processed conjugated polymers on fabrics with high conductivity and mechanical flexibility are expected to significantly contribute to the realization of high performance and sustainable wearable electronic devices, in which development requires enhanced uniformity, flexibility, and breathability.The authors gratefully acknowledge the financial supports of the U.S. NSF Award No. ECCS-1931088; the Purdue Research Foundation (Grant No. 60000029); and the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. Figure 1

Switching of the ion exchange behaviour of PEDOT thin films during a potential cycling: An electrochemical atomic force microscopy study

Thickness variations of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films placed under potential conditioning were measured with the help of electrochemical atomic force microscopy (EC-AFM). In this purpose, in-situ AFM operating in the contact mode was coupled with either cyclic voltammetry (CV) or advanced cyclic voltammetry (AdCV). A PEDOT functionnalized platinum electrode was used simultaneously as a sample for in-situ AFM measurements and a working electrode in a usual three electrode electrochemical setup. PEDOT films were electrodeposited with the help of the CV technique from lithium perchlorate aqueous solutions. From these EC-AFM investigations, brand new PEDOT films were found to be anion exchangers, in good agreement with conclusions of investigations reported in literature. Unexpectedly, PEDOT films having undergone a comprehensive electrochemical cycling (i.e. an electrochemical aging) in a potential range encompassing narrowly their redox process by using tens of CV or AdCV potential cycles behave as cation exchangers. Such observation strongly suggests that the electrochemo-mechanical and ion exchange behaviours of PEDOT can be both switched by simply using a potential cycling. Interestingly, the initial steps of this switching process were observed on a brand new PEDOT film during 26 consecutive CV scans. In the course of this process still ongoing at the end of the 26th cycle, a second swelling peak appears and grows progressively beside the initial swelling peak attributed to an anion exchange behaviour. This leads to a dual ion exchange behaviour for the resulting PEDOT film within the explored potential range. Indeed, this new swelling peak can be attributed to a cation exchange behaviour from the comparison of the potential dependant chronothicknograms and corresponding voltathicknograms with those obtained previously in this work.

An Inkjet-Printed PEDOT:PSS-Based Stretchable Conductor for Wearable Health Monitoring Device Applications.

A stretchable conductor is one of the key components in soft electronics that allows the seamless integration of electronic devices and sensors on elastic substrates. Its unique advantages of mechanical flexibility and stretchability have enabled a variety of wearable bioelectronic devices that can conformably adapt to curved skin surfaces for long-term health monitoring applications. Here, we report a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-based stretchable polymer blend that can be patterned using an inkjet printing process while exhibiting low sheet resistance and accommodating large mechanical deformations. We have systematically studied the effect of various types of polar solvent additives that can help induce phase separation of PEDOT and PSS grains and change the conformation of a PEDOT chain, thereby improving the electrical property of the film by facilitating charge hopping along the percolating PEDOT network. The optimal ink formulation is achieved by adding 5 wt % ethylene glycol into a pristine PEDOT:PSS aqueous solution, which results in a sheet resistance of as low as 58 Ω/□. Elasticity can also be achieved by blending the above solution with the soft polymer poly(ethylene oxide) (PEO). Thin films of PEDOT:PSS/PEO polymer blends patterned by inkjet printing exhibits a low sheet resistance of 84 Ω/□ and can resist up to 50% tensile strain with minimal changes in electrical performance. With its good conductivity and elasticity, we have further demonstrated the use of the polymer blend as stretchable interconnects and stretchable dry electrodes on a thin polydimethylsiloxane (PDMS) substrate for photoplethysmography (PPG) and electrocardiography (ECG) recording applications. This work shows the potential of using a printed stretchable conducting polymer in low-cost wearable sensor patches for smart health applications.