PSS Electrodes Research Articles

Enhancing the conductivity of PEDOT:PSS films for biomedical applications via hydrothermal treatment

This paper reports a new biocompatible conductivity enhancement of poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) films for biomedical applications. Conductivity of PEDOT:PSS layer was reproducibly from 0.495 to 125.367 S cm−1 by hydrothermal (HT) treatment. The HT treatment employs water (relative humidity > 80%) and heat (temperature > 61 °C) instead of organic solvent doping and post-treatments, which can leave undesirable residue. The treatment can be performed using the sterilizing conditions of an autoclave. Additionally, it is possible to simultaneously reduce the electrical resistance, and sterilize the electrode for practical use. The key to conductivity enhancement was the structural rearrangement of PEDOT:PSS, which was determined using atomic force microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscopy. It was found that PEDOT inter-bridging occurred as a result of the structural rearrangement. Therefore, the conductivity increased on account of the continuous conductive pathways of the PEDOT chains. To test the biocompatible enhancement technique for biomedical applications, certain demonstrations, such as the monitoring of joint movements and skin temperature, and measuring electrocardiogram signals were conducted with the hydrothermal-treated PEDOT:PSS electrode. This simple, biocompatible treatment exhibited significant potential for use in other biomedical applications as well.

A Scalable and Low Stress Post-CMOS Processing Technique for Implantable Microsensors

Implantable active electronic microchips are being developed as multinode in-body sensors and actuators. There is a need to develop high throughput microfabrication techniques applicable to complementary metal–oxide–semiconductor (CMOS)-based silicon electronics in order to process bare dies from a foundry to physiologically compatible implant ensembles. Post-processing of a miniature CMOS chip by usual methods is challenging as the typically sub-mm size small dies are hard to handle and not readily compatible with the standard microfabrication, e.g., photolithography. Here, we present a soft material-based, low chemical and mechanical stress, scalable microchip post-CMOS processing method that enables photolithography and electron-beam deposition on hundreds of micrometers scale dies. The technique builds on the use of a polydimethylsiloxane (PDMS) carrier substrate, in which the CMOS chips were embedded and precisely aligned, thereby enabling batch post-processing without complication from additional micromachining or chip treatments. We have demonstrated our technique with 650 μm × 650 μm and 280 μm × 280 μm chips, designed for electrophysiological neural recording and microstimulation implants by monolithic integration of patterned gold and PEDOT:PSS electrodes on the chips and assessed their electrical properties. The functionality of the post-processed chips was verified in saline, and ex vivo experiments using wireless power and data link, to demonstrate the recording and stimulation performance of the microscale electrode interfaces.

Dielectric and electroacoustic assessment of screen-printed piezoelectric polymer layers as flexible transducers: Influence of the electrode material

Here, piezoelectric transducers consisting of a P(VDF-TrFE) layer with either silver or PEDOT:PSS screen-printed electrodes are studied. The influence of electrodes on the dielectric and electroacoustic properties are studied in dielectric-spectroscopy and ferroelectric-hysteresis measurements. Only when both the bottom and the top electrodes are made of silver, the typical dielectric relaxation of the P(VDF-TrFE) layer is clearly observed. When one or two of the electrodes are of PEDOT:PSS, a Debye-like relaxation is present. Compared with silver electrodes, PEDOT:PSS electrodes allow for moderate self-healing. Consequently, samples with bottom and top PEDOT:PSS electrodes can be poled to saturation, while samples with silver electrodes can hardly be poled to saturation due to destructive electric breakdown. Acoustic transducer measurements show that silver electrodes facilitate higher and broader frequency operation, while PEDOT:PSS electrodes bring slightly lower total harmonic distortion. Overall, the acoustic performance shows no significant deviations between differently electroded samples so that silver electrodes do not offer any advantages for the transducers studied here due to their much higher tendency for destructive electric breakdown.

In-Depth Investigation of the Correlation between Organic Semiconductor Orientation and Energy-Level Alignment Using In Situ Photoelectron Spectroscopy.

Organic semiconductors (OSCs) are of interest for replacing traditional Si-based semiconductors as their flexibility and transparency enable new applications. The properties of OSC materials greatly depend on their orientation and molecular arrangement, which are strongly dependent on the underlying substrate material. Hence, in this study, in situ ultraviolet photoelectron spectroscopy (UPS) is used to elucidate the effect of the substrate on OSC orientation. Two types of OSCs, namely those with shape anisotropy (pentacene, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene, and dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene) and those with shape isotropy (N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine, tris(4-carbazoyl-9-ylphenyl)amine, and [6,6]-phenyl C71 butyric acid methyl ester), are deposited on different electrode materials. The differences in the UPS spectra of these materials are observed directly. In general, the orientation of anisotropic OSC molecules significantly depends on the substrate properties, while that of the isotropic ones do not. All the anisotropic OSC molecules grown on poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) electrodes show a greater degree of molecular ordering than those grown on Au and multiwalled carbon nanotube/PEDOT:PSS electrodes. The molecular arrangements within the OSC/electrode structures are reflected in the energy-level shifts in the corresponding UPS spectra and hence in the electronic configurations. The results of this study should aid the design and synthesis of OSC materials with configurations suitable for organic electronic devices.

Low impedance and highly transparent microelectrode arrays (MEA) for in vitro neuron electrical activity probing

In this study, we present the microfabrication and characterization of a transparent microelectrode array (MEA) system based on PEDOT:PSS for electrophysiology. The influence of the PEDOT:PSS electrode dimensions on the impedance was investigated and the stability over time under physiological environment was demonstrated. A very good transparency value was obtained by our system displaying one of the best impedance and transmittance values when compared to other transparent MEA. After biocompatibility validation, we successfully recorded spontaneous neuronal activity of primary cortical neurons cultured over 4 weeks on the transparent PEDOT:PSS electrodes. This work shows that microelectrodes composed of PEDOT:PSS are very promising as a new tool for both electrophysiology and fluorescence microscopy studies on neuronal cell cultures.

Robust metal ion-chelated polymer interfacial layer for ultraflexible non-fullerene organic solar cells

Achieving high power conversion efficiency and good mechanical robustness is still challenging for the ultraflexible organic solar cells. Interlayers simultaneously having good mechanical robustness and good chemical compatibility with the active layer are highly desirable. In this work, we present an interlayer of Zn2+-chelated polyethylenimine (denoted as PEI-Zn), which can endure a maximum bending strain over twice as high as that of ZnO and is chemically compatible with the recently emerging efficient nonfullerene active layers. On 1.3 μm polyethylene naphthalate substrates, ultraflexible nonfullerene solar cells with the PEI-Zn interlayer display a power conversion efficiency of 12.3% on PEDOT:PSS electrodes and 15.0% on AgNWs electrodes. Furthermore, the ultraflexible cells show nearly unchanged power conversion efficiency during 100 continuous compression-flat deformation cycles with a compression ratio of 45%. At the end, the ultraflexible cell is demonstrated to be attached onto the finger joint and displays reversible current output during the finger bending-spreading.

Comparative Study of Machine Learning Algorithms to Classify Hand Gestures from Deployable and Breathable Kirigami-Based Electrical Impedance Bracelet

Wearable devices are gaining recognition for their use as a biosensor platform. Electrical impedance tomography (EIT) is one of the sensing techniques that utilizes wearable sensors as its primary data acquisition system. It measures the impedance or resistance at the peripheral (skin) level and calculates the conductivity distribution throughout the body. Even though the technology has existed for several decades, modern-day EIT devices are still costly and bulky. The paper proposes a novel low-cost kirigami-based wearable device that has soft PEDOT: PSS electrodes for sensing skin impedances. Simulation results show that the proposed kirigami structure for the bracelet has a large deformation during actuation while experiencing relatively lower stress. The paper also presents a comparative study on a few machine learning algorithms to classify hand gestures, based on the measured skin impedance. The best classification accuracy (91.49%) was observed from the quadratic support vector machine (SVM) algorithm with 48 principal components.

Ultra-low noise PEDOT:PSS electrodes on bacterial cellulose: A sensor to access bioelectrical signals in non-electrogenic cells

This study is focused on the particular advantages of organic-based devices to measure cells that do not generate action potentials, also known as non-electrogenic cells. While there is a vast literature about the application of organic conductors to measure neurons, cardiomyocytes and brain tissues, electrical measurements of non-electrogenic cells are rare. This is because non-electrogenic cells generate weak signals with frequencies below 1 Hz. Designing low noise devices in a millihertz frequency range is extremely challenging due to the intrinsic thermal and 1/f type noise generated by the sensing electrode. Here, we demonstrate that the coating of cellulose nanofibers with conducting PEDOT:PSS ink allows the fabrication of a nanostructured surface that establishes a low electrical double-layer resistance with liquid solutions. The low interfacial resistance combined with the large effective sensing area of PEDOT:PSS electrodes minimizes the thermal noise and lowers the amplitude detection limit of the sensor. The electrode noise decreases with frequency from 548 nV r.m.s at 0.1 Hz to a minimum of 6 nV r.m.s for frequencies higher than 100 Hz. This low noise makes it possible to measure low frequency bioelectrical communication signals, typical of non-electrogenic cells, that have until now been difficult to explore using metallic-based microelectrode arrays. The performance of the PEDOT:PSS-based electrodes is demonstrated by recording signals generated by populations of glioma cells with a signal-to-noise ratio as high as 140.

Neuromorphic Organic Devices: Neuromorphic Organic Devices that Specifically Discriminate Dopamine from Its Metabolites by Nonspecific Interactions (Adv. Funct. Mater. 28/2020)

In article number 2002141, Fabio Biscarini and co-workers demonstrate that the current response of a device made of two PEDOT:PSS electrodes is selective for dopamine even without specific recognition moieties. The dynamic measurement of the short-term plasticity transient current allows to discriminate dopamine from other chemical species that are produced from dopamine metabolic and catabolic pathways. This is explained by means of the density functional theory, the kinetic Eyring theory, and a simple equivalent RC circuit.

Stretchable screen-printed PEDOT:PSS electrodes for upper-arm surface electromyography.

In the past ten years, wearable electronics underwent tremendous growth. Undoubtedly, one of the fields that led this trend is represented by biomedical applications. In this field, wearable technologies can provide unique features such as the unobtrusive monitoring of biopotentials. Polymerbased electrodes developed for this purpose can take advantage of their seamless integration in the garments. However, the available solutions exhibit fragility in relation with the stretchability of the fabric, causing significant performance degradation.In this work, this problem is tackled by a novel deposition approach based on screen-printing technology. The electrodes are deposited onto the pre-stretched fabric to ensure the full functionality during common operating conditions. To this aim, a novel PEDOT:PSS conductive ink formulation and printing procedure were conceived. In order to prove the electrode performance for surface electromyography, we printed the electrodes directly onto a commercial stretchable polyester sleeve for sport applications. The electrodes allowed to reliably record the muscular activity of the forearm with performance comparable to that of commercial gelled Ag/AgCl electrodes. The obtained results suggest that the proposed approach can be valuably used in health and fitness applications.

Fully Inkjet‐Printed, Ultrathin and Conformable Organic Photovoltaics as Power Source Based on Cross‐Linked PEDOT:PSS Electrodes

AbstractUltra‐lightweight solar cells have attracted enormous attention due to their ultra‐conformability, flexibility, and compatibility with applications including electronic skin or miniaturized electronics for biological applications. With the latest advancements in printing technologies, printing ultrathin electronics is becoming now a reality. This work offers an easy path to fabricate indium tin oxide (ITO)‐free ultra‐lightweight organic solar cells through inkjet‐printing while preserving high efficiencies. A method consisting of the modification of a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink with a methoxysilane‐based cross‐linker (3‐glycidyloxypropyl)trimethoxysilane (GOPS)) is presented to chemically modify the structure of the electrode layer. Combined with plasma and solvent post‐treatments, this approach prevents shunts and ensures precise patterning of solar cells. By using poly(3‐hexylthiophene) along rhodanine‐benzothiadiazole‐coupled indacenodithiophene (P3HT:O‐IDTBR), the power conversion efficiency (PCE) of the fully printed solar cells is boosted up to 4.73% and fill factors approaching 65%. All inkjet‐printed ultrathin solar cells on a 1.7 µm thick biocompatible parylene substrate are fabricated with PCE reaching up to 3.6% and high power‐per‐weight values of 6.3 W g−1. After encapsulation, the cells retain their performance after being exposed for 6 h to aqueous environments such as water, seawater, or phosphate buffered saline, paving the way for their integration in more complex circuits for biological systems.

Flexible and transparent supercapacitors using electrospun PEDOT:PSS electrodes

Electrospun poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT: PSS) nanofibers were deposited onto flexible polyethylene terephthalate (PET) substrates to obtain electrodes for flexible and all solid-state supercapacitors (SCs). The solution used for electrospinning contained a conducting polymer (PEDOT:PSS), an insulating polymer (polyethylene oxide or PEO), a solvent (dimethylformamide) and a surfactant (Triton-X).The nanofibers improved considerably their conductivity when they were immersed in ethylene glycol (EG), producing a removal of the excedent of PEO around the nanofibers, which causes that the PEDOT:PSS nanofibers became more conductive, then improving their electrochemical performance. The removal of PEO was observed by scanning electronmicroscopy (SEM) and corroborated by energy-dispersive X-ray spectroscopy (EDS). The PEDOT:PSS electrodes were used in supercapacitors, with poly (vinyl alcohol)/phosphoric acid (PVA/H3PO4) gel polyelectrolyte, forming an all solid-state SC. The SCs reach an areal capacitance of 1.8 m F/cm2 and a gravimetric capacitance of 3.6 F/g at a discharging current of 5μA/cm2 by galvanostatic charge discharge technique (GCD). The capacitances of the SCs were also calculated by cyclic voltammetry showing very similar results than GCD. These results using PEDOT:PSS nanofibers as electrodes showed better performance in comparison with doped PEDOT:PSS films with the same gel polyelectrolyte. The devices showed very good stability since they were charged and discharged at 20 μA /cm2 by 1000 cycles maintaining ∼92 % of the initial capacitance. These results open the possibility of fabricating wearable and 3-D interconnected electrodes for energy-storage devices that could be implemented on clothes and on any non-flat surface.

Enhanced electroluminescence in fully printable powder electroluminescent device with flexible invisible silver‐grid transparent electrode

Powder electroluminescent devices (PELDs) have a high potential for commercial application because of flat light emission devices and simple printing process fabrication with low-cost production, without semiconductor processes using vacuum and plasma. In conventional PELDs, indium tin oxide (ITO) has been used as a transparent electrode. However, ITO is unfavourable in flexible electronic devices due to its intrinsic brittleness. The authors evaluated the current and luminance characteristics of PELDs prepared on gravure offset-printed invisible silver-grid (Ag-grid) electrodes that were laminated with and without poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS) transparent electrodes. The PELD on the Ag-grid laminated with PEDOT:PSS electrode shows the maximum luminance of ∼250 cd/m2 at 200 μm spacing, which is five-fold greater than the luminance of PELD without PEDOT:PSS electrode lamination.

Optical and Electronic Ion Channel Monitoring from Native Human Membranes.

Transmembrane proteins represent a major target for modulating cell activity, both in terms of therapeutics drugs and for pathogen interactions. Work on screening such therapeutics or identifying toxins has been severely limited by the lack of available methods that would give high content information on functionality (ideally multimodal) and that are suitable for high-throughput. Here, we have demonstrated a platform that is capable of multimodal (optical and electronic) screening of ligand gated ion-channel activity in human-derived membranes. The TREK-1 ion-channel was expressed within supported lipid bilayers, formed via vesicle fusion of blebs obtained from the HEK cell line overexpressing TREK-1. The resulting reconstituted native membranes were confirmed via fluorescence recovery after photobleaching to form mobile bilayers on top of films of the polymeric electroactive transducer poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS). PEDOT:PSS electrodes were then used for quantitative electrochemical impedance spectroscopy measurements of ligand-mediated TREK-1 interactions with two compounds, spadin and arachidonic acid, known to suppress and activate TREK-1 channels, respectively. PEDOT:PSS-based organic electrochemical transistors were then used for combined optical and electronic measurements of TREK-1 functionality. The technology demonstrated here is highly promising for future high-throughput screening of transmembrane protein modulators owing to the robust nature of the membrane integrated device and the highly quantitative electrical signals obtained. This is in contrast with live-cell-based electrophysiology assays (e.g., patch clamp) which compare poorly in terms of cost, usability, and compatibility with optical transduction.

Transparent and Stretchable Supercapacitors Based on PEDOT:PSS/Nano-Metal Oxide Composite Electrodes

Owing to advances in technology, people focus more on electronic devices that are both aesthetic and functional. Therefore, stretchable and transparent electronic devices have been widely used in wearable devices, transparent displays, and other fields. In the meanwhile, stretchable and transparent energy storage devices are developed to support those electronic devices. Therefore, this study aims to fabricate stretchable and transparent supercapacitors with high electrochemical performance.Conductive polymer poly(3,4-ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonate) (PSS) is a promising candidate for the transparent electrode of supercapacitors as it is highly transparent, stretchable and provides well electrochemical performance. However, the PEDOT:PSS electrode suffers from low capacitance. This study focus on combining PEDOT:PSS with nano-metal oxides as hybrid electrodes. All-solid-state asymmetric supercapacitors assembled with those hybrid electrodes and gel electrolyte are highly transparent, stretchable and possess superior electrochemical performance. This research demonstrates the great potential of highly stretchable and robust all-solid-state asymmetric supercapacitor based on PEDOT:PSS/nano-metal oxide composite electrodes.

Spin and doctor-blade coated PEDOT:PSS back electrodes in inverted organic solar cells

Spin and doctor-blade coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) back electrodes are evaluated in inverted organic solar cells (OSCs) geometry. The doctor-blade coating which has the potential to be used in roll-to-roll processing, is demonstrated by coating PEDOT:PSS manually over the active layer and hence, this sets-up an effort for the concept of much easier fabrication options for large-scale manufacturing like hand-painting, sketching etc. The spin and doctor-blade coated PEDOT:PSS films showed comparable sheet resistance values of 39.7 ± 2.3 and 40.2 ± 5.5 Ω/□ respectively for a thickness of ≈400 nm. The absorbance in the active layer (≈0.7 at 500 nm) had negligible effect due to these coating styles of PEDOT:PSS layer as well as its thickness. The OSC devices that have PEDOT:PSS electrodes formed by the two coating methods were fabricated, characterized, and comparatively evaluated. The results demonstrated an on-par performance for films as well as devices with a manually doctor-blade coated PEDOT:PSS layer when compared to devices that have a spin-coated PEDOT:PSS layer. The atomic force microscopy probe reveals similar surface morphological behaviour for two coating styles with surface roughness values of 16.5 ± 4.1 nm and 17.4 ± 4.9 nm for spin and manual-doctor-blade coating methods, respectively. From spectral response measurement, the evaluated variation in the charge collection efficiency, ηcc at the interface between active layer and PEDOT:PSS interface was within 6% of error for both kind of devices. It indicates similar interface behaviour for both coating styles of PEDOT:PSS, reinforcing the similar performance of manually-doctor-blade coated PEDOT:PSS electrode to that of spin coated one.

Abstract 112: Galvanotactic Smart Bandage For Wireless Wound Healing

Background: Approximately thirty million people in the United States suffer from diabetes. The prevalence of diabetic foot ulcers (DFUs) in this population is 13%. There is a pressing need to develop effective therapies to treat chronic wounds robustly. Current standard of care wound dressings are passive and cannot actively respond to variations in the wound environment. Smart bandages are well positioned to address these challenges with their ability to integrate (bio)sensors for real-time monitoring and active wound care treatment. Current smart bandage technologies have demonstrated significant promise in their ability to sense physiological conditions. This includes detecting pH of the wound, temperature, oxygen, moisture, mechanical and electrical changes. To our knowledge there have not been significant advancements in incorporating sensing technologies to deliver active wound care. We believe this can be achieved using a multidisciplinary approach combining electrical and chemical engineering with the fundamentals of cellular and biomolecular processes in wound healing directed towards high resolution, in situ tissue regeneration. Methods: A flexible printed wireless stimulator was designed and fabricated to deliver directional energy across a wound gradient. Subsequently a low impedance PEDOT:PSS electrode was designed to optimize the skin and stimulator interface, producing a robust gel with tunable adhesion properties. The smart bandage was evaluated in an excisional diabetic and C57BL6/J murine wound healing model. A parabiosis model was used to evaluate circulating cell migration into the wound bed. Single cell analyses were performed to evaluate changes in cell populations as a direct result of induced electrical stimulation. In vitro validation was performed to elucidate in vivo results. Results: Wireless electrical stimulation resulted in significantly accelerated wound closure, when compared to controls, in both a diabetic and C57BL6/J murine excisional wound healing model. Complete epidermal recovery was observed, with a thicker collagen network and increased dermal thickness. Greater neovascularization and appendage formation were observed in the treatment groups. Single cell analyses revealed higher proliferation and remodeling regulatory markers expressed across treated groups. In vitro co-culture validation experiments demonstrated accelerated proliferation, mitotic rate and tube formation when compared to controls. Conclusion: Our data demonstrates the functionality of a robust wireless interface for wound healing. This novel treatment modality will integrate AI processing components for the development of a closed-loop functional stimulator. By combining the domain expertise of nanofabrication, mechanotransduction, fibrosis and molecular/cellular analyses, we are developing a novel chronically stable and robust smart bandage that will pave the way for the next generation of palliative wound care.

Work Function Engineering of Electrohydrodynamic-Jet-Printed PEDOT:PSS Electrodes for High-Performance Printed Electronics.

Poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) has demonstrated outstanding performance as a charge transport layer or an electrode in various electronic devices, including organic solar cells, organic light-emitting diodes, and organic field-effect transistors (OFETs). The electrical properties of these devices are affected by the contact properties at the PEDOT:PSS-semiconductor junction. In this research, we performed work function (WF) engineering of electrohydrodynamic (EHD)-jet-printed PEDOT:PSS and successfully used it as an electrode to fabricate high-performance OFETs and complementary logic circuits. Two types of PEDOT:PSS materials-one with a high WF (HWF, 5.28 eV) and the other with a low WF (LWF, 4.53 eV)-were synthesized and EHD-jet-printed. The WF of PEDOT:PSS was deterministically modulated by approximately 0.75 eV through simple mixing of the two synthesized PEDOT:PSS materials in various ratios. OFETs fabricated with HWF and LWF PEDOT:PSS electrodes showed excellent electrical properties, including the ON/OFF switching ratio higher than 107 and the highest carrier mobility greater than 1 cm2·V-1·s-1. Furthermore, the HWF and LWF PEDOT:PSS electrodes were integrated to fabricate complementary metal-oxide-semiconductor (CMOS) NOT, NOR, and NAND circuits.

Over 14% Efficiency Folding-Flexible ITO-free Organic Solar Cells Enabled by Eco-friendly Acid-Processed Electrodes.

SummaryEnvironment-friendly manufacturing and mechanical robustness are imperative for commercialization of flexible OSCs as green-energy source, especially in portable and wearable self-powered flexible electronics. Although, the commonly adopted PEDOT:PSS electrodes that are treated with severely corrosive and harmful acid lack foldability. Herein, efficient folding-flexible OSCs with highly conductive and foldable PEDOT:PSS electrodes processed with eco-friendly cost-effective acid and polyhydroxy compound are demonstrated. The acid treatment endows PEDOT:PSS electrodes with high conductivity. Meanwhile, polyhydroxy compound doping contributes to excellent bending flexibility and foldability due to the better film adhesion between PEDOT:PSS and PET substrate. Accordingly, folding-flexible OSCs with high efficiency of 14.17% were achieved. After 1,000 bending or folding cycles, the device retained over 90% or 80% of its initial efficiency, respectively. These results represent one of the best performances for ITO-free flexible OSC reported so far and demonstrate a novel approach toward commercialized efficient and foldable green-processed OSCs.

Highly conductive PEDOT:PSS electrode obtained via post-treatment with alcoholic solvent for ITO-free organic solar cells

We demonstrated a simple and effective processing protocol to improve the electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films via post-treatment with an alcohol-based solvent, 2-chloroethanol (2-CE), and to enhance their performance as a transparent anode in organic photovoltaic cells (OPVs). Owing to its moderate boiling point, in contrast to previously reported chemicals, 2-CE is advantageous both for handling as a liquid-phase chemical and for drying from the films via evaporation. We compared the optical and electrical properties of the 2-CE-treated PEDOT:PSS with those of standard PEDOT:PSS-based electrodes with the addition of 5vol% dimethyl sulfoxide (DMSO). With a similar thickness and transmittance in the visible region, the 2-CE-treated polymer electrodes outperformed the DMSO-added films with regard to the electrical conductivity (762Scm−1 vs. 439Scm−1). The work functions were almost identical: ∼5eV. We fabricated and characterized organic photovoltaic devices using the anodes and polymer:fullerene blends and found that the 2-CE treatment resulted in higher device performance. Additionally, the 2-CE treatment was applicable to OPVs on a flexible plastic substrate, indicating the effectiveness of the proposed protocol.