PSS Formulation Research Articles

Electrical Conductivity, Thermo-Mechanical Properties, and Cytotoxicity of Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) (PEDOT:PSS)/Sulfonated Polyurethane Blends.

Electrically conductive polymeric materials have recently garnered significant interest from researchers due to their potential applications in the biomedical field, including medical implants, tissue engineering, flexible electronic devices, and biosensors. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is considered the most successful conducting polymer due to its higher electrical conductivity and chemical stability, but it suffers from limited solubility in common organic solvents, poor mechanical properties, and low biocompatibility. An area of tremendous interest is in combining PEDOT:PSS with another polymer to form a blend or composite material in order to access the beneficial properties of both materials. However, the hydrophilic nature of PEDOT:PSS makes it difficult to produce composites with non-polar polymers. In order to overcome these problems, we have specifically designed and synthesized two new sulfonated polyurethanes (PUS) with high sulfonic acid functionality. The two polyurethanes, one water-soluble (PUS1) and one water-insoluble (PUS2), were used to make blends with two commercially available PEDOT:PSS formulations (CleviosTM FET and PH1000). Solvent cast films on glass substrates were made from water-soluble PEDOT:PSS/PUS1 blends while free-standing films of PEDOT:PSS/PUS2 blends were fabricated by compression-moulding. Ethylene glycol was used as conductivity enhancer, which showed an increase in the conductivity by several orders of magnitude in most of the compositions investigated. The highest conductivity of 438 S cm-1 was achieved for the blend with 80 wt% of PEDOT:PSS (PH1000) in PUS1.

Tissue-like interfacing of planar electrochemical organic neuromorphic devices

Abstract Electrochemical organic neuromorphic devices (ENODes) are rapidly developing as platforms for computing, automation, and biointerfacing. Resembling short- and long-term synaptic plasticity is a key characteristic in creating functional neuromorphic interfaces that showcase spiking activity and learning capabilities. This potentially enables ENODes to couple with biological systems, such as living neuronal cells and ultimately the brain. Before coupling ENODes with the brain, it is worth investigating the neuromorphic behavior of ENODes when they interface with electrolytes that have a consistency similar to brain tissue in mechanical properties, as this can affect the modulation of ion and neurotransmitter diffusion. Here, we present ENODEs based on different PEDOT:PSS formulations with various geometries interfacing with gel-electrolytes loaded with a neurotransmitter to mimic brain-chip interfacing. Short-term plasticity and neurotransmitter-mediated long-term plasticity have been characterized in contact with diverse gel electrolytes. We found that both the composition of the electrolyte and the PEDOT:PSS formulation used as gate and channel material play a crucial role in the diffusion and trapping of cations that ultimately modulate the conductance of the transistor channels. It was shown that paired pulse facilitation can be achieved in both devices, while long-term plasticity can be achieved with a tissue-like soft electrolyte, such as agarose gel electrolyte, on spin-coated ENODes. Our work on ENODe-gel coupling could pave the way for effective brain interfacing for computing and neuroelectronic applications.

Functionalization of PEDOT:PSS for aptamer-based sensing of IL6 using organic electrochemical transistors

Here we propose a strategy to functionalize poly(ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) based organic electrochemical transistors (OECTs) for sensing the inflammatory cytokine interleukin 6 (IL6). For this aim we use diazonium chemistry to couple 4-aminobenzoic acid to sulfonate moieties on the PSS, which can act as anchors for aptamers or other recognition elements (e.g., fluorescent, or redox probes). We investigated this approach with a commercial screen-printable PEDOT:PSS formulation but also studied the effect of PEDOT to PSS ratio as well as the amount of crosslinker in other PEDOT:PSS formulations. For screen printed OECTs, it was possible to distinguish between IL6 and bovine serum albumin (BSA) in buffer solution and detect IL6 when added in bovine plasma in the nanomolar range. Furthermore, functionalization of PEDOT:PSS formulations with higher PSS content (compared to the “standard” solutions used for OECTs) combined with frequency dependent measurements showed the potential to detect IL6 concentrations below 100 pM.

Silver Nanoparticle-PEDOT:PSS Composites as Water-Processable Anodes: Correlation between the Synthetic Parameters and the Optical/Morphological Properties.

The morphological, spectroscopic and rheological properties of silver nanoparticles (AgNPs) synthesized in situ within commercial PEDOT:PSS formulations, labeled PP@NPs, were systematically investigated by varying different synthetic parameters (NaBH4/AgNO3 molar ratio, PEDOT:PSS formulation and silver and PEDOT:PSS concentration in the reaction medium), revealing that only the reagent ratio affected the properties of the resulting nanoparticles. Combining the results obtained from the field-emission scanning electron microscopy analysis and UV-Vis characterization, it could be assumed that PP@NPs' stabilization occurs by means of PSS chains, preferably outside of the PEDOT:PSS domains with low silver content. Conversely, with high silver content, the particles also formed in PEDOT-rich domains with the consequent perturbation of the polaron absorption features of the conjugated polymer. Atomic force microscopy was used to characterize the films deposited on glass from the particle-containing PEDOT:PSS suspensions. The film with an optimized morphology, obtained from the suspension sample characterized by the lowest silver and NaBH4 content, was used to fabricate a very initial prototype of a water-processable anode in a solar cell prepared with an active layer constituted by the benchmark blend poly(3-hexylthiophene) and [6,6]-Phenyl C61 butyric acid methyl ester (PC60BM) and a low-temperature, not-evaporated cathode (Field's metal).

A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes.

The concept of a metal-free and all-organic electroluminescent device is appealing from both sustainability and cost perspectives. Herein, we report the design and fabrication of such a light-emitting electrochemical cell (LEC), comprising a blend of an emissive semiconducting polymer and an ionic liquid as the active material sandwiched between two poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) conducting-polymer electrodes. In the off-state, this all-organic LEC is highly transparent, and in the on-state, it delivers uniform and fast to turn-on bright surface emission. It is notable that all three device layers were fabricated by material- and cost-efficient spray-coating under ambient air. For the electrodes, we systematically investigated and developed a large number of PEDOT:PSS formulations. We call particular attention to one such p-type doped PEDOT:PSS formulation that was demonstrated to function as the negative cathode, as well as future attempts towards all-organic LECs to carefully consider the effects of electrochemical doping of the electrode in order to achieve optimum device performance.

Two-in-one alcohol-processed PEDOT electrodes produced by solvent exchange for organic solar cells

A solvent-exchange method is introduced to obtain an alcohol-processed PEDOT:PSS formulation with good wettability, high conductivity and hole-transporting-layer property.

High Performance Fully Inkjet-Printed Organic Electrochemical Transistor (OECT) Biosensor

High throughput, high sensitivity, and scalability point-of-care biosensors have the potential to significantly improve diagnosis and disease monitoring. Organic electrochemical transistors (OECTs) are a powerful platform for point-of-care biosensing given their sensitivity and performance. Unfortunately, this is seldom achieved with novel and cost-effective fabrication methods. In this work, we built high-performance OECTs using state-of-the-art inkjet printing technology a, scalable, highly reproducible, and low-cost fabrication process. The design utilizes unique high conductivity PEDOT: PSS formulations driving higher ion-to-electron conversion, and volumetric capacitance reaching a value of 18.524 F cm−3. The design included a high ratio of channel cross-sectional area to length reaching a maximum corresponding transconductance (gm) value of 15.2 mS, an order of magnitude improvement on published work. The design was also tested with Bovine Serum Albumin (BSA) protein and showed a limit of detection on the order of 1 pM of BSA. This work shows the potential of inkjet printing for fabricating low-cost, high-performance OECT-based point-of-care biosensors.

How varying surface wettability of different PEDOT:PSS formulations and their mixtures affects perovskite crystallization and the efficiency of inverted perovskite solar cells.

The physico-chemical interaction, surface, and electrical properties of hole transport layers (HTLs) significantly affect the wettability and film crystallization of the deposited perovskite and the corresponding performance of inverted perovskite solar cells (PSCs). One of the most frequently used HTLs for inverted PSCs is poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). Various commercial PEDOT:PSS formulations have already been tested as HTLs. Until now mixtures of these remained rather unexplored. In this study, three commercially available PEDOT:PSS formulations (PH, PH1000, and AI4083), as well as three mixtures (PH:PH1000, PH:AI4083, and PH:PH1000:AI4083; in a 1 : 1 and 1 : 1 : 1 ratios) were used as HTLs to investigate the crystallization of perovskite films and the performance of associated PSCs. Of the three formulations, PEDOT:PSS PH showed better perovskite crystallization, resulting in better solar cell performance followed by both PH:AI4083 and PH:PH1000:AI4083 layers. The pioneering work on mixing PEDOT:PSS resulted in new combinations of PEDOT:PSS, with new properties (work function, surface wettability, and roughness) which are very important parameters for perovskite crystallization and corresponding device efficiencies and stabilities. All PSCs that use the mixed PEDOT:PSS as HTLs revealed higher fill factor and open-circuit voltage values above 900 mV, which is not the same except for PEDOT:PSS PH. As a result, we believe that such a mixing strategy could aid in the creation of various PEDOT:PSS combinations with tuneable properties for certain applications.

Green ink formulation for inkjet printed transparent electrodes in OLEDs on biodegradable substrates

In this manuscript we present a green ink formulation for inkjet-printed and blade coated highly conductive PEDOT:PSS thin film. By the addition of a biodegradable surfactant we reduced the surface tension of a water-based PEDOT:PSS formulation enabling the deposition of high quality layers. Finally, we demonstrate the use of inkjet printed PEDOT:PSS films on the basis of these formulation as bottom transparent electrode of organic light-emitting diodes deposited on a biodegradable cellulose acetate (CA) substrate. Our devices outperformed a reference fabricated with a commercially available low-ST PEDOT:PSS that includes unknown additives.

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.

Performance Comparison of Low-Voltage non-Ionic Gel Organic Field Effect Transistors with Gold and PEDOT:PSS Gate Electrodes

Low-voltage non-ionic gel organic-field effect transistors (NIGOFETs) with two kinds of gate electrode materials namely gold (Au) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) formulation were fabricated in top-gate bottom-contact geometry to investigate the effects of gate electrodes on the electrical performance of the OFETs. In addition, three kinds of gate dielectrics were used for both types of transistors to understand the effects more thoroughly. As a result, it can be deduced from the data that NIGOFETs with Au gate electrodes (Au-NIGOFETs) display better performance considering higher mobility and on-to-off current ratio (ION/IOFF) as well as lower Subthreshold Swing (SS) of them. Besides, the threshold voltage (VTH) effects-free drain currents (IDS) of the Au-NIGOFETs surpasses those of the PEDOT:PSS formulation gated NIGOFETs (Pedot-NIGOFETs). This is probably due to having greater WF gate electrode (in our case Au) provides less injection barrier eventually leads to relatively unimpeded charge transportation. Nevertheless, Au-NIGOFETs interestingly proves to have further negative VTH and lower off-current (IOFF), which may be attributed to lower electrical resistivity (ρ) of the Au leading to denser charge carrier traps formation along with intensified charge carrier induction at the semiconductor-dielectric interface when the gate-to-source voltage (VGS) is less than VTH. However, because of the same reason, when VGS exceeds the VTH for example, IDS of Au-NIFOFET1 starts to increase in such a quick manner that enabling it to have higher ION/IOFF and lower SS.

Tailoring the Seebeck Coefficient of Spray-Coated Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) Films with Nitrogen Doped Multiwalled Carbon Nanotubes.

The thermoelectric properties of flexible thin films fabricated from two commercial poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) formulations filled with multiwalled carbon nanotubes (MWCNT) and nitrogen-doped MWCNT (N-MWCNT) were investigated. A simple spray-coating method for the fabrication of such flexible films on a polyethylene terephthalate substrate was developed. While increasing the MWCNT concentration had little effect on the thermoelectric properties, increasing the N-MWCNT concentration resulted in the emergence of an overall n-type semiconducting behavior and, thereby, tailoring the Seebeck coefficient of the composite films from p-type to n-type was shown. The Seebeck coefficient of the two PEDOT:PSS formulation films was inverted from 4.1 to -13.3 μV/K and from 12.5 to -10.9 μV/K respectively, with increasing N-MWCNT concentration from 0 to 95 wt.%. The importance of these results for future work stems from the possibility of tailoring the behavior of a typical p-type polymer such as PEDOT:PSS and the effect that the polymer conductive grade has on the switching concentration.

All solution-processed ITO free flexible organic light-emitting diodes

A top-emitting organic light-emitting diode is fabricated by a solution-process exclusively, using a PEDOT:PSS formulation with a low contact angle.

Direct Observation of Conductive Polymer Induced Inversion Layer in n‐Si and Correlation to Solar Cell Performance

AbstractHeterojunctions formed by ultrathin conductive polymer [poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate)—PEDOT:PSS] films and n‐type crystalline silicon are investigated by photoelectron spectroscopy. Large shifts of Si 2p core levels upon PEDOT:PSS deposition provide evidence that a dopant‐free p–n junction, i.e., an inversion layer, is formed within Si. Among the investigated PEDOT:PSS formulations, the largest induced band bending within Si (0.71 eV) is found for PH1000 (high PEDOT content) combined with a wetting agent and the solvent additive dimethyl sulfoxide (DMSO). Without DMSO, the induced band bending is reduced, as is also the case with a PEDOT:PSS formulation with higher PSS content. The interfacial energy level alignment correlates well with the characteristics of PEDOT:PSS/n‐Si solar cells, where high polymer conductivity and sufficient Si‐passivation are also required to achieve high power conversion efficiency.

Ambulatory Evaluation of ECG Signals Obtained Using Washable Textile-Based Electrodes Made with Chemically Modified PEDOT:PSS.

A development of washable PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) polyamide textile-based electrodes is an interesting alternative to the traditional Ag/AgCl disposable electrodes, usually used in clinical practice, helping to improve medical assessment and treatment before apparition or progress of patients’ cardiovascular symptoms. This study was conducted in order to determine whether physical properties of PEDOT:PSS had a significant impact on the coated electrode’s electrocardiogram (ECG) signal quality, particularly after 50 washing cycles in a domestic laundry machine. Tests performed, included the comparison of two PEDOT:PSS solutions, in term of viscosity with emphasis on wetting tests, including surface tension and contact angle measurements. In addition, polyamide textile fabrics were used as substrate to make thirty electrodes and to characterize the amount of PEDOT:PSS absorbed as a function of time. The results showed that surface tension of PEDOT:PSS had a significant impact on the wetting of polyamide textile fabric and consequently on the absorbed amount. In fact, lower values of surface tension of the solution lead to low values contact angles between PEDOT:PSS and textile fabric (good wettability). Before washing, no significant difference has been observed among signal-to-noise ratios measured (SNR) for coated electrodes by the two PEDOT:PSS solutions. However, after 50 washing cycles, SNR decreased strongly for electrodes coated by the solution that had low viscosity, since it contained less solid contents. That was confirmed by scanning electron microscopy images (SEM) and also by analyzing the color change of electrodes based on the calculation of CIELAB color space coordinates. Moreover, spectral power density of recorded ECG signals has been computed and presented. All cardiac waves were still visible in the ECG signals after 50 washing cycles. Furthermore, an experienced cardiologist considered that all the ECG signals acquired were acceptable. Accordingly, our newly developed polyamide textile-based electrodes seem to be suitable for long-term monitoring. The study also provided new insights into the better choice of PEDOT:PSS formulation as a function of a specific process in order to manufacture cheaper electrodes faster.

Stable and highly conductive carbon nanotube enhanced PEDOT:PSS as transparent electrode for flexible electronics

Abstract Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a popular polymeric material for solution-processed transparent conductive electrodes (TCE), especially on flexible substrates. PEDOT:PSS electrical properties are often improved with a variety of additives. Here, we present an innovative way to furtherly improve the performances of this material by incorporating single walled carbon nanotubes (SWCNTs) into commercially available conductive PEDOT:PSS formulation (Heraeus Clevios™ FE-T). With a load of 0.01 wt% SWCNT, we observed the best trade-off between transparency (91.0% at 550 nm) and sheet resistance (89.1 Ω sq−1). Moreover, we developed a simple and effective lithographic structuring process for these TCEs and we investigated the process effects on its optoelectronic and morphological properties. The developed SWCNT/FE-T electrodes, processed on both glass and flexible PET substrates, were incorporated in organic photodiodes (OPDs), with P3HT:PCBM as active layer. These OPDs show dark current densities, on-off ratios and external quantum efficiencies (EQE) comparable to reference devices comprising indium-tin-oxide (ITO) as TCE. Additionally, this TCE shows superior mechanical and chemical stability, under bending and damp-heat test condition compared to ITO and PEDOT:PSS, respectively.

The role of donor polymer and PEDOT:PSS formulation on adhesion processes in inverted organic solar cells

Organic photovoltaic devices (OPVs) are one of the most promising applications of organic semiconductors due to their compatibility with flexible plastic substrates resulting in lightweight, inexpensive, ergonomic and aesthetic products. While the electrical failure mechanisms in OPVs have been thoroughly investigated, little is known about their mechanical stability, which is as important and critical to ensure long term reliability. The characteristic thin films stresses of each layer present in organic solar cells, in combination with other possible fabrication, handling and operational stresses, provide the mechanical driving force for delamination of weak interfaces or even their decohesion, leading to a loss of device integrity and performance. In this study, we developed a technique to probe weak layers or interfaces in inverted polymer:PC60BM solar cells, establishing a new set-up for the so-called probe tack making it similar to a pull-off test. With this in hand, the adhesion of a variety of active layers towards a standard water-based poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) formulation was compared against that of a new organic-solvent based PEDOT:PSS. The organic-solvent based PEDOT:PSS formulation showed improved adhesion compared to the standard water-based formulation. Chemical characterization of the exposed surfaces indicated a difference in their composition, suggesting a stronger interaction of the organic-solvent based PEDOT:PSS with the active layer and resulting in a different fracture path. Indeed, all OPVs with water-based PEDOT:PSS showed a delamination localized at the active layer/PEDOT:PSS interface, while those with the organic-solvent formulation were not fractured at this interface but rather, in the active layer.

Insights on the Optical Properties of Poly(3,4-Ethylenedioxythiophene):Poly(styrenesulfonate) Formulations by Optical Metrology.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is among the most widely used polymers that are used as printed transparent electrodes for flexible Organic Electronic (OE) devices, such as Organic Photovoltaics (OPVs). The understanding of their optical properties and the correlation of the optical properties with their electronic properties and metallic-like behavior can lead to the optimization of their functionality as transparent electrodes in multilayer OE device architectures. In this work, we study the optical properties of different PEDOT:PSS formulations by non-destructive Spectroscopic Ellipsometry (SE), from the infrared to the far ultraviolet spectral regions. The optical response of PEDOT:PSS includes an intense optical absorption originated from the conductive part (PEDOT) at lower photon energies, whereas the electronic transition energies of the non-conductive PSS part have been measured at higher photon energies. Based on the different PEDOT:PSS formulations, the optical investigation revealed significant information on the relative contribution of conductive PEDOT and insulating PSS parts of the PEDOT:PSS formulation in the overall optical response, which can strongly impact the final device functionality and its optical transparency.

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.

Photovoltaic analysis of the effects of PEDOT:PSS-additives hole selective contacts on the efficiency and lifetime performance of inverted organic solar cells

Solution processed inverted organic photovoltaics (OPVs) usually use (Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS derivatives as hole selective contact. In this study the effect of different PEDOT:PSS formulations, Al4083, PH and PH500 in inverted structured OPVs is investigated. Through detailed device physics analysis PEDOT:PSS PH is proposed as most suitable hole selective contact for inverted OPVs device function. Furthermore, PEDOT:PSS PH hole selective contact is treated with 3 different wetting agents, Zonyl FS-300 fluorosurfactant (Zonyl), 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate (Dynol) and Zonyl:Dynol mixture and the corresponding non-encapsulated inverted OPVs investigated under accelerated humidity lifetime conditions. The inverted OPVs incorporating PEDOT:PSS:Zonyl hole selective contact shown limitations on humidity lifetime performance due to the poorest adhesion properties of Zonyl-treated PEDOT:PSS PH compared with Dynol and Zonyl/Dynol mixture treaded PEDOT:PSS PH.