PSS Electrodes Research Articles

Brush-paintable and highly stretchable Ag nanowire and PEDOT:PSS hybrid electrodes

Highly transparent and stretchable Ag nanowire (NW)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid electrodes were prepared on stretchable polyurethane substrates by using simple and cost-effective brush painting technique. The optimized Ag NW/PEDOT:PSS hybrid electrode showed a sheet resistance of 19.7 Ohm/square and a high optical transmittance of 88.64% comparable to conventional ITO electrode. It was found that shear stress of the paintbrush led to an effective lateral alignment of the Ag NWs into the PEDOT:PSS matrix during brush painting process. In addition, we investigated mechanical properties of the brush painted Ag NW/PEDOT:PSS hybrid electrode using inner/outer bending test, stretching tests, twisting test and rolling test in detail. The optimized brush painted Ag NW/PEDOT:PSS electrode showed a higher strain (~30%) than brush painted Ag NW or sputtered ITO electrode. Furthermore, we demonstrated the outstanding stretchability of brush painted Ag NW/PEDOT:PSS hybrid electrode in two applications: stretchable interconnectors and stretchable electrodes for stretchable and wearable thin film heaters. These results provide clear evidence for its potential and widespread applications in next-generation, stretchable displays, solar cells, and electronic devices.

Laminated Free Standing PEDOT:PSS Electrode for Solution Processed Integrated Photocapacitors via Hydrogen‐Bond Interaction

AbstractIn this work, a novel lamination method employing hydrogen‐bond interaction to assemble a highly conductive free standing poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film as a common electrode is demonstrated in a solution processed metal‐free foldable integrated photocapacitor (IPC) composed of a monolithic organic solar cell (OSC) and a capacitor. The highlights of the work are: (1) micrometer free standing PEDOT:PSS electrode is successfully laminated onto a relatively large area (1 cm2) OSCs; (2) a free standing capacitor based on the PEDOT:PSS electrode is achieved; (3) the IPC demonstrates an overall efficiency of 2% and an energy storage efficiency of 58%, which is comparable with those of IPCs based on metallic common electrodes; (4) the novel lamination method for PEDOT:PSS electrode enables free standing PEDOT:PSS broad applications in solution processed flexible organic electronics, especially tandem or/and integrated organic electronic devices. Furthermore, the IPC is foldable with excellent cycling stability (no decay after 100 recycles at 1 mA cm−2). These results indicate that free standing PEDOT:PSS film is a promising candidate as common electrodes for IPCs to break the restrictions of metal electrodes. The demonstrated lamination method will greatly extend the applications of PEDOT:PSS electrodes to large area flexible organic electronic devices.

Screen-Printed PEDOT:PSS Electrodes on Commercial Finished Textiles for Electrocardiography.

Electrocardiography (ECG) is an essential technique for analyzing and monitoring cardiovascular physiological conditions such as arrhythmia. This article demonstrates the integration of screen-printed ECG circuitry from a commercially available conducting polymer, PEDOT:PSS, onto commercially available finished textiles. ECG signals were recorded in dry skin conditions due to the ability of PEDOT:PSS to function as both ionic and electronic conductors. The signal amplifies when the skin transpires water vapor or by applying a common lotion on the skin. Finally, PEDOT:PSS wires connected to PEDOT:PSS electrodes have been shown to record ECG signals comparable to Ag/AgCl connected to copper wires.

Environmentally Friendly Plasma-Treated PEDOT:PSS as Electrodes for ITO-Free Perovskite Solar Cells

Solution processed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) transparent electrodes (TEs) offer great potential as a low cost alternative to expensive indium tin oxide (ITO). However, strong acids are typically used for enhancing the conductivity of PEDOT:PSS TEs, which produce processing complexity and environmental issues. This work presents an environmentally friendly acid free approach to enhance the conductivity of PEDOT:PSS using a light oxygen plasma treatment, in addition to solvent blend additives and post treatments. The plasma treatment was found to significantly reduce the sheet resistance of PEDOT:PSS TEs from 85 to as low as 15 Ω sq-1, which translates to the highest reported conductivity of 5012 S/cm for PEDOT:PSS TEs. The plasma treated PEDOT:PSS TE resulted in an ITO-free perovskite solar cell efficiency of 10.5%, which is the highest reported efficiency for ITO-free perovskite solar cells with a PEDOT:PSS electrode that excludes the use of acid treatments. This research presents the first demonstration of this technology. Moreover, the PEDOT:PSS TEs enabled better charge extraction from the perovskite solar cells and reduced hysteresis in the current density-voltage (J-V) curves.

Scaling Effects on the Electrochemical Performance of poly(3,4‐ethylenedioxythiophene (PEDOT), Au, and Pt for Electrocorticography Recording

AbstractReduced contact size would permit higher resolution cortical recordings, but the effects of diameter on crucial recording and stimulation properties are poorly understood. Here, the first systematic study of scaling effects on the electrochemical properties of metallic Pt and Au and organic poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes is presented. PEDOT:PSS exhibits better faradaic charge transfer and capacitive charge coupling than metal electrodes, and these characteristics lead to improved electrochemical performance and reduced noise at smaller electrode diameters. PEDOT:PSS coating reduces the impedances of metallic electrodes by up to 18x for diameters <200 µm, but has no effect for millimeter scale contacts due to the dominance of series resistances. Therefore, the performance gains are especially significant at smaller diameters and lower frequencies essential for recording cognitive and pathological activities. Additionally, the overall reduced noise of the PEDOT:PSS electrodes enables a lower noise floor for recording action potentials. These results permit quantitative optimization of contact material and diameter for different electrocorticography applications.

All Organic Screen Printed Electrodes for Continuous Recording of Electrocardiogram

Electrocardiography (ECG) is an essential technique for analyzing the proper electrical functioning of heart. Traditionally Ag/AgCl electrodes have been used for monitoring ECG signal from the body. However, Ag/AgCl is known to cause skin irritation on prolonged usage and measurements cannot be done in wet conditions. Conjugated polymers, with their mixed ionic and electronic conduction, offer an alternative to Ag/AgCl. This work provides an easy to fabricate ECG sensor from commercially available PEDOT:PSS using screen printing technique onto a commercially sold T-shirt. ECG signals from screen printed PEDOT:PSS electrodes were recorded during motion at a heart rate of up to 180 bpm. Variation of ECG signal amplitude vs impedance of electrodes was studied. In addition, PEDOT:PSS was also demonstrated to work as an organic wire for copper lead replacement used in recording ECG signals. Reusability of the shirt was demonstrated by recording ECG signal under active exercise even after 3 wash cycles and subsequent drying. Figure 1

Mechanical stability of roll-to-roll printed solar cells under cyclic bending and torsion

The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules are used that differ slightly in thickness as well as on the basis of the electrode materials: silver nanowires or carbon-based inks. Each type of module is subjected to two different mechanical modes of deformation, bending and torsion, of several thousand cycles per module using a purpose-built robotic device. Analysis of the distribution of stress in the devices performed by finite-element modeling predicts the locations of failure. Failure upon bending originates at the laser-cut edges of the modules from shear at the clamp/module interface leading to crazing of the plastic barrier encapsulant foils. This crazing leads to eventual delamination due first to decohesion of the active layer at the edge of the modules and later to deadhesion between the PEDOT:PSS (electrode) and P3HT:PCBM (semiconductor) layers. The torsion mode imposes greater stresses than the bending mode and thus leads to failure at fewer strain cycles. Failure during torsion occurs through crack propagation initiated at stress concentrations on the edges of the module that were imposed by their rectangular geometry and ultimately leads to bifurcation of the entire module. Rather than the differences in electrode materials, the differences in survivability between the two types of modules are attributed mostly to the thickness of the substrate materials used, with the thinner substrate used in the carbon-based modules (~160µm) failing at fewer strain cycles than the substrate used in the silver-nanowire-based modules (~190µm). Taken together, the results suggest ways in which the lifetimes of devices can be extended by the layouts of modules and choices of materials.

Liquid‐Gated Organic Electronic Devices Based on High‐Performance Solution‐Processed Molecular Semiconductor

High‐mobility organic semiconductors such as [1]benzothieno[3,2‐b]benzothiophene (BTBT) derivatives are potential candidates for ultrasensitive biosensors. Here 2,7‐dioctyl BTBT (C8‐BTBT‐C8)‐based liquid‐gated organic electronic devices are demonstrated with two device architectures, viz. electrolyte‐gated organic field‐effect transistor (EGOFET) and electrolyte‐gated organic synapstor (EGOS), and different electrode materials, viz. gold and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). EGOFETs exhibit a mean transconductance of about 45 µS, on a par with literature, and a max value up to 256 µS at the state‐of‐the‐art in aqueous electrolyte, with a mean product of charge mobility and effective capacitance of about 0.112 and 0.044 µS V−1 for gold and PEDOT:PSS electrodes, respectively. EGOSs exhibit a dynamic response with 15 ms characteristic timescale with Au electrodes and about twice with PEDOT:PSS electrodes. These results demonstrate a promising route for sensing applications in physiological environment based on fully solution‐processed whole‐organic electronic devices featuring ultrahigh sensitivity and fast response.

Exploring the ultrasonic nozzle spray-coating technique for the fabrication of solution-processed organic electronics

The ultrasonic nozzle (US) spray method was investigated for its utility in fabricating organic electrodes composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a standard conductive polymer material used to produce large-area low-cost OFETs. The US spray technique involves generating a solution spray by first passing the solution through a head and nozzle subjected to ultrasonic vibrations that induce atomization. This method is advantageous in that the resulting spray comprises extremely small solution droplets a few micrometers in diameter, unlike the spray produced using conventional air spray methods. The PEDOT:PSS US solution spraying process was optimized by controlling the flow rate of the N2 carrier gas and the substrate temperature while monitoring the quality of the resulting PEDOT:PSS electrode films. The pentacene field-effect transistors prepared using the US spray method displayed a maximum field-effect mobility of 0.47 cm2V−1s−1 (with an average value of 0.31 cm2V−1s−1), 35% better than the mobilities achieved using the conventional air spray method. In addition, the device-to-device reproducibility was improved, as indicated by a decrease in the standard deviation of the mobility values from 30% for the air spray devices to 24% for the US spray devices. These results indicated that the US spray technique is efficient and superior to the conventional air spray method for the development of low-cost large-area organic electronics.

Spray-coated contacts from an organic charge transfer complex solution for organic field-effect transistors

We demonstrate the deposition of films of the conducting charge transfer complex TTF-TCNQ from solution by spray-coating. The benefit of spray-coating is the ability to process large volumes of solution, therefore allowing the utilisation of compounds with very low solubility. The sheet resistance in the TTF-TCNQ film is similar to that of the commonly used organic PEDOT:PSS electrodes, with the added benefit of room temperature deposition and no additional thermal treatments. Spray-coated TTF-TCNQ is used as source and drain electrodes for transistors based on the organic semiconductor C8-BTBT, achieving similar performances in terms of mobility and turn-on voltage than when conventional contacts of MoOx/Au are used, whilst exhibiting a slight improvement in the linearity of the output characteristics.

Influence of Electrical and Ionic Conductivities of Organic Electronic Ion Pump on Acetylcholine Exchange Performance.

By using an easy and effective method of depositing conjugated polymers (PEDOT:PSS) on flexible substrates, a new design for organic bioelectronic devices has been developed. The purpose was to build up a system that mimics the motion of neurotransmitters in the synaptic cleft by obtaining an electrical to chemical signal transport. Fourier transform infrared (FTIR) spectroscopy and Raman measurements have demonstrated that electrochemical overoxidation region which separates the pristine PEDOT:PSS electrodes and allows ionic conduction has been achieved successfully. The influence of both electrical and ionic conductivities on organic electronic ion pump (OEIP) performances has been studied. The ultimate goal was to achieve the highest equilibrium current density at the lowest applied voltage via enhancing the electrical conductivity of PEDOT:PSS and ionic conductivity of electrochemically overoxidized region. The highest equilibrium current density, which corresponds to 4.81 × 1017 number of ions of acetylcholine was about 41 μA cm−2 observed for the OEIP with the electrical conductivities of 54 S cm−1. This was a threshold electrical conductivity beyond which the OEIP performances were not changed much. Once Nafion™ has been applied for enhancing the ionic conductivity, the equilibrium current density increased about ten times and reached up to 408 μA cm−2. Therefore, it has been demonstrated that the OEIP performance mainly scales with the ionic conductivity. A straightforward method of producing organic bioelectronics is proposed here may provide a clue for their effortless mass production in the near future.

A paper-based electrode using a graphene dot/PEDOT:PSS composite for flexible solar cells

We have synthesized a metal-free composite ink that contains graphene dots (GDs) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) that can be used on paper to serve as the counter electrode in a flexible dye-sensitized solar cell (DSSC). This paper-based GD/PEDOT:PSS electrode is low-cost, light-weight, flexible, environmentally friendly, and easy to cut and process for device fabrication. We determined the GD/PEDOT:PSS composite effectively fills the dense micro-pores in the paper substrate, which leads to improved carrier transport in the electrode and a 3-fold enhanced cell efficiency as compared to the paper electrode made with sputtered Pt. Moreover, the DSSC with the paper electrode featuring the GD/PEDOT:PSS composite did not fail in photovoltaic tests even after bending the electrode 150 times, whereas the device made with the Pt-based paper electrode decreased in efficiency by 45% after such manipulation. These exceptional properties make the metal-free GD/PEDOT:PSS composite ink a promising electrode material for a wide variety of flexible electronic applications.

Conductive PEDOT:PSS Electrodes in Electrochromic Devices

We present new electrochemical device designs made entirely of electrically conducting polymer electrodes to reversibly switch a magenta colored poly(3,4-propylenedioxy-thiophene) (PProDOT) electrochromic polymer (ECP) film. Thin conductive PEDOT:PSS films have been incorporated as conductive transparent electrodes in solution processable absorptive/transmissive (window type) electrochromic devices making it available for high-throughput processing on a wide range of substrates. Different (in)organic acid and polar solvent post-treatments have been used to tune the conductivity of the blade coated PEDOT:PSS electrodes. We reached a conductivity up to 2000 S cm-1 on different substrates, enough to reversibly switch our ECP film between -1 V and 1 V. We will demonstrate how the structural design, construction, charge-balancing, electrode conductivity and the electrochemical properties of the PProDOT have an influence on the device performance quantified by its contrast, switching speed, bending capabilities and long-term switching stability. We combine our device design with a fundamental study of the electrochemical processes occurring at both electrodes. Using these new designs, we have developed an all-polymer solution processed electrochromic device approaching the characteristics of a device made using inorganic transparent conducting electrodes, e.g. indium tin oxide (ITO), with the added advantage of using flexible and rough substrates. Figure 1

Tuning the Work Function of Printed Polymer Electrodes by Introducing a Fluorinated Polymer To Enhance the Operational Stability in Bottom-Contact Organic Field-Effect Transistors.

Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is a promising electrode material for organic electronic devices due to its high conductivity, good mechanical flexibility, and feasibility of easy patterning with various printing methods. The work function of PEDOT:PSS needs to be increased for efficient hole injection, and the addition of a fluorine-containing material has been reported to increase the work function of PEDOT:PSS. However, it remains a challenge to print PEDOT:PSS electrodes while simultaneously tuning their work functions. Here, we report work function tunable PEDOT:PSS/Nafion source/drain electrodes formed by electrohydrodynamic printing technique with PEDOT:PSS/Nafion mixture solutions for highly stable bottom-contact organic field-effect transistors (OFETs). The surface properties and work function of the printed electrode can be controlled by varying the Nafion ratio, due to the vertical phase separation of the PEDOT:PSS/Nafion. The PEDOT:PSS/Nafion electrodes exhibit a low hole injection barrier, which leads to efficient charge carrier injection from the electrode to the semiconductor. As a result, pentacene-based OFETs with PEDOT:PSS/Nafion electrodes show increased charge carrier mobilities of 0.39 cm2/(V·s) compared to those of devices with neat PEDOT:PSS electrodes (0.021 cm2/(V·s)). Moreover, the gate-bias stress stability of the OFETs is remarkably improved by employing PEDOT:PSS/Nafion electrodes, as demonstrated by a reduction of the threshold voltage shift from -1.84 V to -0.28 V.

Enhanced electrical properties of PEDOT:PSS films using solvent treatment and its application to ITO-free organic light-emitting diodes

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films are prepared by introducing a new solvent 2-ethoxyethanol and are optimized by acid-free solvent post treatment. The behavior of samples are investigated with various coating conditions. The change of electrical performance for 2-ethoxyethanol added PEDOT:PSS films with various post treatment methods is studied. Upon post treatment, the sheet resistance greatly decreases attributed to a structural change with removal of insulating PSS in the film. Based on these conductive films, we demonstrate efficient ITO-free green phosphorescent organic light-emitting diodes (OLEDs). The efficiency of OLEDs with post-treated PEDOT:PSS electrodes is greater than that of OLEDs with untreated PEDOT:PSS electrodes. The results illustrate a promising future for flexible, low-cost, ITO-free OLEDs employing PEDOT:PSS electrodes optimized by 2-ethoxyethaol with acid-free solvent post treatment.

Inkjet-printed embedded Ag-PEDOT:PSS electrodes with improved light out coupling effects for highly efficient ITO-free blue polymer light emitting diodes

We report on solution processed polymer light emitting diodes (PLEDs) using inkjet-printed embedded and non-embedded metal grid anodes. Metal grids were inkjet-printed in a honeycomb layout. Honeycomb dimensions were varied from 3 mm to 8 mm to optimize device performance. Inkjet-printed grids were then coated with a highly conductive PEDOT:PSS formulation. First experiments on PEDOT:PSS coated, non-embedded metal grid anodes showed that grids with a 3 mm honeycomb diameter have a similar efficiency as optimized indium tin oxide (ITO) based reference devices. To further improve the efficiency of the devices, the honeycomb Ag-grids were embedded in an Ormocer®-based material. A detailed performance analysis of PLEDs fabricated on ITO, non-embedded and embedded grids was carried out. It is shown that reduced leakage current and enhanced light outcoupling by embedding result in a significant efficiency enhancement of 250% in inkjet-printed embedded Ag-PEDOT:PSS ITO-free PLEDs, compared to the ITO-based reference PLEDs.

One-Step Interface Engineering for All-Inkjet-Printed, All-Organic Components in Transparent, Flexible Transistors and Inverters: Polymer Binding.

We report a one-step interface engineering methodology which can be used on both polymer electrodes and gate dielectric for all-inkjet-printed, flexible, transparent organic thin-film transistors (OTFTs) and inverters. Dimethylchlorosilane-terminated polystyrene (PS) was introduced as a surface modifier to cured poly(4-vinylphenol) dielectric and poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) electrodes without any pretreatment. On the untreated and PS interlayer-treated dielectric and electrode surfaces, 6,13-bis(triisopropylsilylethynyl)pentacene was printed to fabricate OTFTs and inverters. With the benefit of the PS interlayer, the electrical properties of the OTFTs on a flexible plastic substrate were significantly improved, as shown by a field-effect mobility (μFET) of 0.27 cm2 V-1 s-1 and an on/off current ratio (Ion/Ioff) of greater than 106. In contrast, the untreated systems showed a low μFET of less than 0.02 cm2 V-1 s-1 and Ion/Ioff ∼ 104. Additionally, the all-inkjet-printed inverters based on the PS-modified surfaces exhibited a voltage gain of 7.17 V V-1. The all-organic-based TFTs and inverters, including deformable and transparent PEDOT:PSS electrodes with a sheet resistance of 160-250 Ω sq-1, exhibited a light transmittance of higher than 70% (at wavelength of 550 nm). Specifically, there was no significant degradation in the electrical performance of the interface engineering-assisted system after 1000 bending cycles at a radius of 5 mm.

A facile way to pattern PEDOT:PSS film as an electrode for organic devices

We report a facile and high resolution patterning method for conductive polymer films as transparent electrodes for organic devices on various substrates. The reliable pattern of PEDOT:PSS film is demonstrated by selective oxygen plasma etching via a defined copper (Cu) protection layer deposited by thermal evaporation. The overcoated Cu layer is removed by a wet etching process without damage to the underlying PEDOT:PSS layer. The minimum patterning feature size is determined by the resolution of the mask for Cu deposition and has shown to reach twenties of micro-meters. The patterned PEDOT:PSS film is successfully applied as source-drain electrodes for the organic field effect transistors (OFETs), and as a transparent anode in organic photodiodes (OPDs). Performance of flexible PEDOT:PSS-based OPDs exceeds a conventional flexible IZO-anode OPDs (6.6 mA/W vs. 1.4 mA/W, respectively). The contact resistance of PEDOT:PSS electrodes in OFETs is found to be 10 times lower (9.8 × 102 Ω cm), than that for Au counterparts. The hole mobility was 0.29 cm2/V s for both electrode materials and used DPPT-TT semiconductor polymer.

Inkjet-Printed PEDOT:PSS Electrodes on Paper for Electrocardiography.

Inkjet-printed PEDOT:PSS electrodes are shown to record cutaneous electrophysiological signals such as electrocardiograms via a simple finger-to-electrode contact. The recordings are of high quality and show no deterioration over a 3 month period, paving the way for the development of the next generation of low-cost, convenient-to-use healthcare monitoring devices.

Solution-processed hybrid light emitting and photovoltaic devices comprising zinc oxide nanorod arrays and tungsten trioxide layers

The goal of this research is to prepare inverted optoelectronic devices with improved performance by combining zinc oxide (ZnO) nanorod arrays and tungsten trioxide (WO3) layer. ZnO seed layers with thickness of 52 nm were established, followed by growth of ZnO nanorods with length of 300 nm vertical to the ITO substrates in the precursor bath. The ZnO nanorod arrays possess high transmittance up to 92% in the visible range. Inverted light-emitting devices with the configuration of ITO/ZnO nanorods/ionic PF/MEH-PPV/PEDOT:PSS/Au were constructed. The best device achieved a max brightness and current efficiency of 10,620 cd/m2 and 0.25 cd/A at 10 V, respectively, revealing much higher brightness compared with conventional devices using Ca/Al as cathode, or inverted devices based on ZnO thin film. By inserting a WO3 thin layer between PEDOT:PSS and Au electrode, the max brightness and current efficiency were further improved to 21,881 cd/m2 and 0.43 cd/A, respectively. Inverted polymer solar cells were also fabricated with the configuration of ITO/ZnO nanorods/ionic PF/P3HT:PC61BM/PEDOT/WO3/Au. The best device parameters, including the open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency, reached 0.54 V, 14.87 mA/cm2, 41%, and 3.31%, respectively