Inkjet-printed PEDOT Research Articles

The role of substrates and electrodes in inkjet-printed PEDOT:PSS thermoelectric generators

.Conductivity and Seebeck coefficient of inkjet-printed PEDOT:PSS thin films were found to depend on the substrate (polyimide, silicon oxide, glass) and electrode (e-beam evaporated vs. inkjet-printed). The printing direction was also found to strongly impact the thermoelectric power factor.

Semiconductor‐to‐Metal‐like Transition Behavior under Temperature Variation for Inkjet Printed PEDOT:PSS Tracks Embedded in Polymer

Herein, it is intended to show the effect of embedding an inkjet printed poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) track in an insulator polymer, impacting its electronic transition behavior, as a consequence of temperature variation. A transition from semiconductor‐to‐metal‐like behavior is observed, when the temperature is seen to exceed a certain value, which is of a nonchemical origin. Both the presented experimental and simulation results show how this transition really occurs. The proposed physical mechanism for explaining such a behavior is verified with good repeatability. The main conclusion indicates consideration of special precautions, while enclosing inkjet‐printed PEDOT:PSS‐based tracks or sensors operating under ambient conditions, along with fluctuations. This conclusion can potentially be applied to any other inkjet printed conductive organic polymer film embedded in an insulator that fulfills the conditions encountered in the experiments. The impact of this effect may be reduced and mitigated by using inkjet printing, in combination with other additive manufacturing technique. The results presented here are considered very important, as they lay the foundation for the correct compensation of the thermal drift of organic electronics‐based circuits.

Highly Conductive Inkjet-Printed PEDOT:PSS Film under Cyclic Stretching.

Inkjet-printed conductive polymer PEDOT:PSS films have provided a new developing direction for realizing the stretchable transparent electrodes in optoelectronic devices. However, their conductivity and stretchability are limited as the presence of insulating PSS chains, rigid PEDOT conjugated backbone, and stronger inter-chain interactions in the pristine polymer, respectively. Here, we report a PEDOT:PSS film with preferable electrical and mechanical performances by inkjet-printing the formulated printable ink containing PEDOT:PSS, formamide (FA), d-sorbitol (SOR), sodium dodecyl benzene sulfonate (DBSS), and ethylene glycol (EG). The inkjet-printed uniform PEDOT:PSS film exhibits a high conductivity of 1050 S/cm and sheet resistance of less than 145 Ω/sq on both rigid and flexible substrates. Moreover, the resistance can remain stable after 200 cycles of stretching at 55% strain. The film also presents good stability during repetitive stretching-releasing cycles. The significantly enhanced conductivity of the film lies on the conformational transition of the backbone by secondary doping and post-treatment with FA as well as removing the excess PSS components after phase separation between PEDOT and PSS. Meanwhile, SOR serves as a plasticizer to break the original hydrogen bonds between PSSH chains and provides larger free volume for polymer chain extension, which gives the PEDOT:PSS film the ability to tolerant cyclic tension. This is one of the optimal performances currently reported for inkjet-printed stretchable PEDOT:PSS films. The inkjet-printed PEDOT:PSS film with high conductivity, stretching properties, as well as good biocompatibility exhibits promising prospects as anodes on optoelectronic devices.

Printed soft skin electrodes for seamless bio-impedance measurements

Bio-impedance measurements are widely used to assess various physiological parameters. Contemporary skin electrodes for bio-impedance measurements are cumbersome and novel electrode designs are needed to allow fast and easy placement, long-term stability and user comfort. This investigation introduces dry, printed, bio-compatible electrode arrays, made of screen-printed carbon and inkjet-printed PEDOT:PSS that measure bio-impedance non-invasively and stably. Two contact impedance measurements yield the lowest normalized values of soft electrodes reported to date. Four contact bio-impedance measurements from the radial, ulnar, common carotid and superficial temporal arteries were performed, demonstrating the ability to capture blood pulsation in different areas with small form factor. Owing to the unique properties of the printed electrodes reported here, we were able to demonstrate for the first time blood pulsation in the face, continuous blood pulsation measurement during simultaneous muscle activation and signal stability over many hours.

Tailoring inkjet-printed PEDOT:PSS composition toward green, wearable device fabrication.

Inkjet printing remains one of the most cost-efficient techniques for device prototyping and manufacturing, offering considerable freedom of digital design, non-contact, and additive fabrication. When developing novel wearable devices, a balanced approach is required between functional, user-safe materials and scalable manufacturing processes. Here, we propose a tailor-made ink formulation, based on non-hazardous materials, to develop green electronic devices aimed at interfacing with humans. We demonstrate that developed ink exhibits high-resolution inkjet printability, in line with theoretical prediction, on multiple wearable substrates. The ink's chemical composition ensures the pattern's enhanced electrical properties, mechanical flexibility, and stability in water. The cytocompatibility evaluations show no noxious effects from printed films in contact with human mesenchymal stem cells. Finally, we fabricated a printed wearable touch sensor on a non-woven fabric substrate, capable of tracking human steps. This is a step toward the development of green wearable electronics manufacturing, demonstrating a viable combination of materials and processes for biocompatible devices.

Effect of surface tension and drying time on inkjet-printed PEDOT:PSS for ITO-free OLED devices

Highly conductive PEDOT:PSS is one of the most promising materials for indium tin oxide (ITO) substitution in printed electronics. Here, we report the development and optimisation of two PEDOT:PSS ink formulations for the fabrication of inkjet-printed transparent conductive layers. Starting from aqueous commercial solutions, co-solvents and a non-ionic surfactant were employed to modify the surface tension, improve the wetting capability of the ink, and obtain uniform and homogeneous thin films. In particular, the quantities of ethanol and surfactant were systematically adjusted to determine the optimal conditions for inkjet printing. The results demonstrate that a surface tension value between 28 and 40 mN/m and approximately 40 vol.% of a low-boiling-point co-solvent are fundamental to ensure the proper wetting of the glass substrate and a quick-drying process that confers uniformity to the printed thin film. The printed PEDOT:PSS thin films show good morphological, optical, and electrical properties that are similar to those observed for the corresponding spin-coated layers. The organic light-emitting diodes (OLEDs) fabricated with the inkjet-printed PEDOT:PSS electrodes showed a maximum quantum efficiency of 5.5% and a maximum current efficiency of 15 cd/A, which is comparable to spin-coated reference devices. Our study demonstrates the great potential of polymeric electrodes for the fabrication of high-efficiency printed OLED devices that are compatible with flexible and stretchable substrates.

A paper-based inkjet-printed PEDOT:PSS/ZnO sol-gel hydrazine sensor

Hydrazine is widely used in industries as a precursor for blowing agents, pharmaceuticals, and pesticides. It is a highly toxic compound; therefore, it is of paramount interest to develop new analytical methods for the detection and control of hydrazine exposure. In this work, we describe the fabrication of an all inkjet-printed paper sensor composed of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) electrode functionalized with zinc oxide (ZnO) and encapsulated in a Nafion matrix for the amperometric determination of low concentrations of hydrazine. The electrochemical properties of the fully inkjet-printed PEDOT:PSS/Nafion and PEDOT:PSS/ZnO/Nafion sensors are compared in the presence and absence of different concentrations of hydrazine. The stability and sensitivity of these electrodes are significantly enhanced after modification with ZnO particles. The layer-by-layer deposition of the materials on the electrode surface is characterized by SEM, XRD, and AFM. The printed sensor exhibits a linear response in the 10–500 μM hydrazine concentration range and a ∼5 μM detection limit (at S/N = 3). The electrochemical sensitivity is 0.14 μA μM−1 cm−2, and the best working voltage is 0.5 V. The developed sensor was applied successfully for the determination of hydrazine content in tap, sea, and mineral water samples validating the accuracy of this sensor.

Overcoming Electrochemical Instabilities of Printed Silver Electrodes in All-Printed Ion Gel Gated Carbon Nanotube Thin-Film Transistors.

Silver ink is the most widely used conductive material for printing electrodes in the fabrication of all-printed ion gel gated transistors because of their high conductivity and low cost. However, electrochemical instability of printed silver electrodes is generally one of the biggest issues, whether it is in air where silver gets oxidized or in a moisture environment where electrochemical migration occurs. Notwithstanding, the electrochemical stability of printed silver electrodes in ion gel medium has not been studied so far. In this work, we studied the electrochemical instabilities of printed silver electrodes in fully printed ion gel gated single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) and developed some strategies to overcome these issues. All-printed ion gel-based p-type SWCNT TFTs were employed to investigate the impact of electrochemical instabilities on the electrical behavior of printed SWCNT TFTs. The results have demonstrated that printed silver was unstable at anodic and cathodic polarization because of the corrosion by the ionic liquid. Besides, anodic corrosion of silver source/drain electrodes was shown to be responsible for the electrical failure of printed SWCNT TFTs in both the linear and saturated regime. These issues were completely resolved when preventing printed silver electrodes from coming into direct contact with ion gels. For example, ion gels were partially printed in device channels to avoid contacting the printed silver source and drain electrodes. At the same time, silver side-gate electrodes were replaced by inkjet-printed PEDOT:PSS electrodes to avoid gate electrode-related instabilities. Consequently, all-printed electrochemically stable SWCNT TFTs fabricated were obtained with enhanced performance of higher ION/IOFF ratios (105 to 106), smaller subthreshold slopes (∼70 mV/dec), and smaller hysteresis (ΔV = 0.025 V) at gate voltages from 1.2 to -0.5 V. Additionally, the polarity of all-printed SWCNT TFTs was converted from the p-channel to ambipolar while achieving lower leakage currents.

Robust Photodetectable Paper from Chemically Exfoliated MoS2-MoO3 Multilayers.

Photodetectors, which are capable of detecting light with varied wavelength, have nowadays been widely applied onto emerging fields such as security, entertainment, healthcare, environment, and so on. As the one with a two-dimensional layered structure, molybdenum disulfide (MoS2) possesses striking optical and electrical properties that can be used in photodetecting, yet the challenges remain in terms of material processing, device fabrication simplicity, and enhancement of overall photodetection performance. In this work, a photodetectable paper based on a mixture of double-phased MoS2 (1T and 2H) and MoO3 was successfully fabricated through a straightforward route, that is, chemical exfoliation and deposition of MoS2 powder on a flexible cellulose ester membrane, followed by inkjet-printed PEDOT:PSS as electrodes. The obtained device shows varied sensitivity to the light with different wavelengths. Compared with that under green and red lights, the prepared photodetector has the highest internal quantum efficiency (0.063%) and responsivity (0.134 mA W-1), while having longest response/recovery time (17.5/15.3 s) when illuminated with purple light (405 nm). The achieved responsivity is much higher than other reported liquid exfoliation- and solution-derived MoS2 photodetectors. This is ascribed to (1) the enhanced photoelectron generation caused by both MoS2 and MoO3 and (2) the good electric conductivity and efficient charge transport caused by the metallic 1T MoS2. This work demonstrates the feasibility of fabricating the MoS2-based photodetector with excellent performance through a simple exfoliation/filtration and inject printing route, and the detailed study on the response to light with different wavelengths unveils the interaction between the device and the incident light, further broadening the potential applications of such design.

Quantitative assessment by local probe methods of the mechanical and electrical properties of inkjet-printed PEDOT:PSS thin films over Indium Tin Oxide substrates

Thin films of Poly(3,4-ethylenedioxythiophene) complexed with Poly(styrenesulfonate) (PEDOT:PSS) on Indium Tin Oxide (ITO) have been prepared by inkjet printing technology. The process allows obtaining thin films over large areas. A relatively broad range of thicknesses can be obtained by the addition of subsequent polymer layers resembling an additive manufacturing process. The resulting inkjet PEDOT:PSS films are homogeneous as regard both electrical and mechanical properties. In spite of the characteristic parallel line topography of these inkjet printed films, both the Quantitative Nanomechanical Mapping (QNM) and the Conductive-Atomic Force Microscope (C-AFM) characterization reveal homogeneous values throughout the polymer surface regardless of the welding zones. The results discussed in this work provide the basis for the application of inkjet printing as deposition method for electrically conducting PEDOT:PSS into a large area with mechanical stability. • Thin films of PEDOT:PSS on Indium Tin Oxide (ITO) have been prepared by inkjet printing technology over large areas. • Inkjet PEDOT:PSS films are homogeneous as regard both electrical and mechanical properties even through the welding zones.

Improved Sensitivity of Inkjet-Printed PEDOT:PSS Ammonia Sensor With “Nonideal” Morphology

Piezoelectric inkjet printing is used for fabricating poly (3,4-ethylene-dioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) ammonia (NH3) sensors; it has the advantages of drop-on-demand maskless manufacturing, great material saving, and compatibility with large area flexible substrates. Different from previous research efforts on forming line structures of smooth surface and even edge, this article shows that the inkjet-printed PEDOT:PSS line structures with nonideal morphology of scalloped edges can bring benefits of improved sensitivity. By simply controlling the drop spacing, narrower and thinner local regions are formed between adjacent ink drops in the fabricated line structures. Adsorption of NH3 gas molecules onto any of these regions, causing hole depletion, can significantly affect the carrier transport, thus improving sensitivity. Inkjet-printed PEDOT:PSS sensors present obviously improved response compared to the spin-coated ones. Compared to that of devices with smooth and straight lines, the responsivity of the devices at a drop spacing of 40m is improved by nearly threefold.

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.

Fully Solution Processed Organic Light-emitting Electrochemical Cells (OLEC) with ZnO Interlayer for Lab-on-Chip Applications

Microfluidic lab-on-a-chip devices can be used for chemical and biological analyses such as DNA tests or environmental monitoring. In order to make a monolithic and cost-efficient/disposable sensing device, direct integration of excitation light source for fluorescent sensing is often required. A manufacturing process for fully solution-processed blue organic light-emitting electrochemical cells (OLECs) is presented, which consist of pre-patterned ITO, spin-coated ZnO buffer layer and blue light-emitting polymer plus dopants and an inkjet-printed PEDOT:PSS transparent top anode. Furthermore, the fully transparent blue OLEC is able to emit > 2000 cd/m2 light under pulsed driving mode, which fulfils requirements for simple fluorescent on-chip sensing applications. Furthermore, ITO electrodes can be replace by PEDOT:PSS transparent electrodes when a ZnO interlayer is solution processed on top, which enable the mask-free and fully solution processing integration on chips.

Inkjet Printed Organic Light-emitting Electrochemical Cells for Disposable Lab-on-chip Applications Manufactured at Ambient Atmosphere

Microfluidic lab-on-a-chip devices can be used for chemical and biological analyses such as DNA tests or environmental monitoring. Such devices integrate most of the basic functionalities needed for the analysis on a microfluidic chip. When using such devices, cost and space intensive lab equipment is thus not necessary. However, in order to make a monolithic and cost-efficient/disposable sensing device, direct integration of excitation light source for fluorescent sensing is often required. Organic light emitting diodes (OLEDs) have the advantages of self-emitting property, high luminous efficiency, full-color capability, wide viewing angle, high contrast, low power consumption, low weight and flexibility. All these capacitate OLEDs to be a suitable optical source for microfluidic devices. However, low work function cathode and/or electron injection layer like Ba, LiF are indispensable for high bright OLEDs, which require vacuum deposition and inert fabrication atmosphere. Hereby we introduce a fully solution processable deviation of OLEDs, organic light-emitting electrochemical cells (OLECs) as a low-cost excitation light source for a microfluidic sensing platform. By mixing metal ions and a solid electrolyte with light-emitting polymers as active materials, an in-situ doping and in-situ PN-junction can be generated within a three layer sandwich device. Because of this doping effect, work function adaption is not necessary and air-stable cathodes like silver can be used. A manufacturing process for fully solution-processed OLECs is presented, which consist of an inkjet-printed silver cathode, spin-coated blue light-emitting polymer plus dopants and an inkjet-printed PEDOT:PSS transparent top anode. Furthermore, by replacing silver with ITO, a fully transparent blue OLEC is able to emit>2500cd/m2 light under pulsed driving mode, which fulfils requirements for simple fluorescent on-chip sensing applications.

Inkjet-printing of hybrid transparent conducting electrodes for organic solar cells

We developed metal-grid hybrid transparent conducting electrodes (TCEs) by combining a metal grid with a conducting polymer. Metal-grid hybrid TCEs were prepared by inkjet-printing with both PEDOT:PSS and Ag nanoparticle inks and applied to the fabrication of organic solar cells (OSCs) instead of indium tin oxide (ITO). The electrical and optical properties of the metal-grid hybrid TCEs were optimized by modulating the Ag grid's line-to-line spacing (pitch). With a Ag-grid pitch of 1 mm, the metal-grid hybrid TCEs exhibited a sheet resistance of 10.3 Ω sq−1 and an optical transmittance of 73% which represented ≤10% reduction when compared to the optical transmittance of inkjet-printed PEDOT:PSS films without Ag grids. Ag covering factor (ACF) was defined using the geometry of the Ag-grid and incorporated in a theoretical model to calculate the electrical and optical properties of the inkjet-printed metal-grid hybrid TCEs. It was found that the experimental values of the TCEs' electrical and optical properties were in good agreement with the calculation results based on the ACF-incorporated theoretical model. OSCs fabricated with the metal-grid hybrid TCEs showed a power-conversion cell efficiency comparable to those of conventional OCSs using ITO. This indicates that the inkjet-printed metal-grid hybrid TCE is a promising replacement for ITO to realize cost-effective OSCs.

Characterization of drop-on-demand microdroplet printing

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been used extensively in the fabrication of polymer light-emitting diode displays by drop-on-demand inkjet printing technique. In order to make a good thin film with high uniformity, it is crucial to control the drying behavior of inkjet-printed PEDOT:PSS droplets. In this work, the morphology of printed drops of ∼10 pL after drying was examined and explained in a qualitative manner, which would extend the comparison with previous work described in published literature. Results show that drying behavior is sensitive to substrate temperature due to the high surface-to-volume ratio of a microfluid. There exists an appropriate range of temperatures to obtain a good drop with sharp edge and flat surface. On the other hand, when the temperature exceeds a limit, a ring-like structure was observed. Results from this experiment would be considered as a reference to achieve uniform film after drying and has potential to be applied in the modeling of drop impact.

Polymer solar cells based on inkjet-printed PEDOT:PSS layer

In this article, we have demonstrated solar cell performance of the inkjet-printed PEDOT:PSS layer and the roles of additives in device efficiency. The newly proposed PEDOT:PSS inks with additives of glycerol and surfactant show the improved surface morphology and high conductivity resulting in the enhanced photovoltaic performance. Using the optimized ink formulation of PEDOT:PSS, we have demonstrated a 3.16% efficient solar cell with an inkjet printing.

Solvent effect of inkjet printed source/drain electrodes on electrical properties of polymer thin-film transistors

We show that the electrical properties of polymer thin-film transistors (PTFTs) can be enhanced by controlling the solvent properties of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT/PSS) solution used as the inkjet-printed source and drain electrodes. Specifically, addition of dimethyl sulfoxide (DMSO) into the PEDOT/PSS solution increased the conductivity of the inkjet-printed PEDOT electrodes and remarkably reduced the contact resistance of the electrodes. The lower contact resistance of the DMSO-treated PEDOT electrode compared to the corresponding electrode without DMSO treatment may be due to enhanced interfacial stability at the contact between the printed PEDOT electrodes and the semiconductor layers.