Transparent Indium Tin Oxide Electrodes Research Articles

Spray-Coating As a Versatile Tool for Electrode Surface Modification – from Nanostructured Electrodes to Enzyme Based Sensors

Electrochemical biodevices (e.g. biosensors and biofuel cells) do not only rely on the general stability and activity of the utilized biocatalyst but also on the architecture of the entire electrode. In particular, the choice of suitable electrode surface structuring, enzyme immobilization tech­nique, as well as the co-immobilization of electron-transfer mediators is crucial for highly accu­rate sensing systems. Recently, we presented the fabrication of a membrane-free glucose/O2 powered enzymatic biosupercapacitor based on transparent nanostructured indium tin oxide (ITO) electrodes prepared by means of a spray-coating process.1,2 Compared to ITO nanoparticle (NP) based electrodes obtained by drop-casting, the performance and stability of the glucose/oxygen biosupercapacitor was significantly improved by utilizing spray-coated ITO-NP based electrodes. Optimization of the spray-parameters led to a high electrochemically active surface area with substantially increased porosity, thus enhancing the catalytic currents due to higher biocatalyst loading. In this work, we used a specifically designed spray-coating system as a tool for electrode surface modification. The automated process ensures the formation of homogeneous and reproducible electrode surfaces. Moreover, the system cannot only be used for the preparation of nano-struc­tured electrode surfaces, such as ITO-NP based electrodes, but also allows spraying of enzyme and polymer solutions. By layered spraying of glucose oxidizing enzymes, embedded in an Os complex modified polymer onto the porous surface, so prepared electrodes were utilized in a self-powered glucose biosensor operated by charge/discharge of a Nernstian biosupercapacitor. Addi­tional surface modification has been achieved by the development and optimization of meso- and macro-porous ITO-NP based electrodes. A mixture of ITO nanoparticles and spherical, monodis­perse polymer beads acting as template for pore formation was sprayed onto flat electrodes. The polymer beads were removed by calcination of the material which generates macro-pores of the size of the used polymer beads (see sketch). Based on the porous 3D surface structure, an effective wiring of a subsequently immobilized enzyme redox polymer hydrogel is achieved which minimizes limitations caused by a slow electron transfer within the polymer. Our results demonstrate the high versatility of the developed spray-coater not only for surface structuring, but also for whole modification of entire electrode designs with enzymes wired in hydrogels with applications in fuel cells, bio-supercapacitors and self-powered biosensors.

Analysis of impedance data from bubble flow in a glass/SU8 microfluidic device with on-channel sensors

This paper presents the design and original fabrication of a fully transparent microfluidic reactor with integrated electrical sensors over the microchannel. The transparent chip design allows for microscale photochemistry, and permits direct, real-time visual and electrical observation. The microchip uses optically transparent indium tin oxide (ITO) electrodes as sensing elements for in-channel phase tracking. High-speed videography was used to validate the electrical measurement data. The device permits visual observation of microchannel bubble flow while simultaneously acquiring electrical data. The aim of this work is to develop and optically verify electrical data acquisition and signal analysis methodologies, which in future applications may be used for inexpensive non-destructive monitoring of two-phase microchannel flows, in systems where detailed visual observation may be infeasible.

Light-extraction enhancement of GaN-based 395 nm flip-chip light-emitting diodes by an Al-doped ITO transparent conductive electrode.

The distinct ultraviolet (UV) light absorption of indium tin oxide (ITO) limits the performance of GaN-based near-UV light-emitting diodes (LEDs). Herein, we report an Al-doped ITO with enhanced UV transmittance and low sheet resistance as the transparent conductive electrode for GaN-based 395nm flip-chip near-UV LEDs. The thickness dependence of optical and electrical properties of Al-doped ITO films is investigated. The optimal Al-doped ITO film exhibited a transmittance of 93.2% at 395nm and an average sheet resistance of 30.1 Ω/sq. Meanwhile, at an injection current of 300mA, the forward voltage decreased from 3.14 to 3.11V, and the light output power increased by 13% for the 395nm near-UV flip-chip LEDs with the optimal Al-doped ITO over those with pure ITO. This Letter provides a simple and repeatable approach to further improve the light extraction efficiency of GaN-based near-UV LEDs.

Anodic Deposition of Enantiopure Hexahelicene Layers

AbstractHelicenes are polyaromatic compounds with chiral properties useful for many applications in optoelectronics, separation processes, chiral recognition and catalysis. Here we focused on the electrochemistry of carbo[n]helicenes (n=5,6,7). The cyclic voltammograms of racemic mixtures of target compounds in acetonitrile/0.1 M tetrabutylammonium perchlorate at a glassy carbon electrode reveal the diffusion‐controlled reactions in both anodic and cathodic potential regions. Electrochemical behaviors are different for individual helicenes, [7]helicene undergoes redox transformation easily in comparison to the other investigated compounds, which is in agreement with DFT (density functional theory) calculations. Generally, the multi‐component anodic process of helicenes is observable at potentials from +1.5 to +2.5 V, leading to the formation of deposited structures (layers) on the electrode surface. The helicenes were electrodeposited onto transparent indium tin oxide (ITO) electrodes and characterized by atomic force microscopy, UV/Vis, Raman spectroscopy and ellipsometry. Finally, the anodic deposition of P and M enantiomers of [6]helicene was performed using ITO substrates, resulting in the formation of enantiopure layers of nanometer thicknesses, as confirmed by circular dichroism spectroscopy. The discovered electrosynthetic procedure opens up a new possibility for the immobilization of chiral helicene layers onto solid supports.

Improve the surface of silver nanowire transparent electrode using a double-layer structure for the quantum-dot light-emitting diodes

We developed a double-layer structured transparent electrode for use in flexible quantum-dot light-emitting diodes (QLEDs). Silver nanowires (AgNWs) and highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were coated on a transparent substrate to obtain a highly conductive and flexible transparent electrode. The highly conductive PEDOT:PSS improved the surface roughness of the AgNWs transparent electrode film as well as the surface coverage area of the film. The double-layer structured transparent electrode showed superior mechanical properties than conventional indium–tin oxide (ITO) and AgNWs transparent electrodes. QLEDs with the double-layer structured transparent electrode also showed good reliability under cyclic bending conditions. These results indicate that the double-layer structured AgNWs/PEDOT:PSS transparent electrode described here is a feasible alternative to ITO transparent electrodes for flexible QLEDs.

Highly flexible transparent electrodes based on mesh-patterned rigid indium tin oxide

We developed highly bendable transparent indium tin oxide (ITO) electrodes with a mesh pattern for use in flexible electronic devices. The mesh patterns lowered tensile stress and hindered propagation of cracks. Simulations using the finite element method confirmed that the mesh patterns decreased tensile stress by over 10% because of the escaped strain to the flexible film when the electrodes were bent. The proposed patterned ITO electrodes were simply fabricated by photolithography and wet etching. The resistance increase ratio of a mesh-patterned ITO electrode after bending 1000 times was at least two orders of magnitude lower than that of a planar ITO electrode. In addition, crack propagation was stopped by the mesh pattern of the patterned ITO electrode. A mesh-patterned ITO electrode was used in a liquid-based organic light-emitting diode (OLED). The OLED displayed the same current density-voltage-luminance (J-V-L) curves before and after bending 100 times. These results indicate that the developed mesh-patterned ITO electrodes are attractive for use in flexible electronic devices.

Evaluating the Practical Use of Digital Video to Study the Effect of Sheet Resistance of Transparent Indium-Tin Oxide Electrodes Using the Galvanostatic Deposition of Poly(o-toluidine)

The galvanostatic deposition of poly(o-toluidine) (POT), a polyaniline derivative, on a long, narrow transparent indium-tin oxide (ITO) electrode was monitorized by digital video. This mixed electrochemical-optic technique allowed us to obtain sequential digital images of the deposition process synchronized with the electrochemical response. From each pixel of a digital image, red, green, and blue (RGB) color components were obtained and the color evolution against elapsed time during the electrodeposition and along the ITO surface was analyzed. Thus, we obtained spatiotemporal information about the effect of sheet resistance on the electrochemical reactions, the relative film coating, which can be an approximation of relative film thickness, the kinetics together with the spatial distribution of electrochemical reactions and the homogeneity of deposited film on ITO. Digital video monitorization provided very useful information about the quality of deposited POT, which could be extrapolated to control the coloration of any electrode surface used for electrochromic devices, smart windows, or dye-synthetized solar cells.

Highly Enhanced Light-Outcoupling Efficiency in ITO-Free Organic Light-Emitting Diodes Using Surface Nanostructure Embedded High-Refractive Index Polymers.

We develop the high-performance internal light-outcoupling (HRLOC) system based on the high-refractive index polyimide (PI) and metal oxide nanoparticles for organic light-emitting diodes (OLEDs) with silver nanowires (AgNWs). The spontaneously formed nanobump structures, high refractive index, and light-scattering properties of HRLOC significantly enhance the light-extraction efficiency of OLEDs. Not only do the outcoupling structures improve the light-extraction efficiency, but also remarkably enhance the electrical properties of OLEDs. HRLOC leads to the regular and smooth formation of AgNWs, resulting in the improvement of the electrical properties of devices by preventing electrical shorts and leakage currents. The power efficiency of the AgNW-based OLEDs with PI is improved by a factor of 1.31 compared to the reference device with indium tin oxide (ITO) transparent electrode at a luminance of 20 000 cd/m2. The efficiency is further improved by incorporating TiO2 nanoparticles into the PI matrix by a factor of 1.69. To our knowledge, the optically and electrically enhanced OLEDs show one of the highest enhancement factors reported for ITO-free OLEDs with internal outcoupling structures. In addition, the outcoupling structures are solution processable, thermally stable, and can be scaled up to 200 × 200 mm2 for large-area applications. We believe that the light-outcoupling structures developed here have great potential for efficient, low-cost, and flexible ITO-free OLEDs.

Electrodeposition of silver amalgam particles on ITO – Towards novel electrode material

Silver solid amalgam represents up to now the most suitable alternative electrode material to metallic mercury in electroanalytical chemistry. Controlled electrodeposition of variable (sub)micrometer-sized silver amalgam particles (AgAP) on the surface of transparent indium-tin oxide (ITO) electrode from an electrolyte containing Ag+ and Hg2+ ions is reported here, as a novel perspective method suitable for preparation of nano-structured silver amalgam electrode material. Elemental analysis of the composition and morphology of the AgAP decorating the ITO was studied by scanning electron microscopy including energy-disperse X-ray spectroscopy and by image processing software. Particle composition, size, and surface coverage are controllable by selection of the Ag+/Hg2+ ratio in the electrodeposition solution and by setting of individual parameters of applied double pulsed/potential chronoamperometry. Applicable potential window of thus prepared ITO-AgAP electrode was found to be within +0.2 to −1.0V in 0.2acetate buffer pH5.0. Utilized voltammetric and chronoamperometric methods revealed significant enhancement in electrochemical reducibility of selected model organic nitro-compound (shift of the peak potential about 300mV to more positive potentials). Its further employment in UV/Vis spectroelectrochemical cell provided information about number of consumed electrons and kinetic characteristics. Furthermore preferential adsorption of calf thymus DNA at AgAP than ITO was observed by fluorescence microscopy indicating its potential applicability in (bio-)spectroelectrochemical methods. Further advantages and potential applications are also proposed and discussed.

Highly Interconnected Macroporous and Transparent Indium Tin Oxide Electrode

AbstractA macroporous indium tin oxide (ITO) electrode has been obtained by electrospinning nanofibers from polyvinylpyrrolidone and ITO precursors on a fused silica substrate covered by polystyrene, followed by a heat treatment that induced a drastic modification in the material texture. The resulting electrode structure is consisting of highly interconnected nanofilaments of sizes between 70 and 170 nm. The electrode is robust, fixed to the substrate, transparent in the visible light region, and possesses excellent electrochemical properties in comparison to a planar ITO electrode, that is, improved reversibility with ferrocenedimethanol and greatly enhanced oxidation for ascorbic acid. SEM and XRD measurements confirm ITO formation. This porous ITO electrode can be modified electrochemically with mesostructured methylated silica and applied to a combined electrochemical and spectral detection of industrial dyes (methylene blue, Meldola's blue, and methylene green) from water. For methylene blue analysis, a linear range of detection between 20 nM and 2 μM and a limit of detection of 17 nM are observed. Finally, the spectroelectrochemical analysis of a solution with mixed dyes has been performed.

Dual light-activated microfluidic pumps based on an optopiezoelectric composite

In this paper, a new type of microfluidic pump that can be activated and controlled by a masked light source is presented. The actuation of this micropump is based on an optopiezoelectric composite. This composite is constructed by having one of the electrodes of a piezoelectric PVDF (polyvinylidene fluoride) polymer replaced by a layer of TiOPc (titanyl phthalocyanine) photoconductive coating and an ITO (indium-tin-oxide) transparent electrode. This layer of photoconductive electrode provides the capability to activate multiple locations of this optopiezoelectric composite independently using a masked light source and a single voltage source. To verify the feasibility of this concept, dual light-activated microfluidic pumps based on this optopiezoelectric composite are implemented and studied. Experimental results verify that two microfluidic pumps can be created by one optopiezoelectric composite and that each pump can be optically turned on and off independently or be turned on simultaneously. These results suggest that integrating an optopiezoelectric composite into a lab-on-a-chip system can reduce the size and the number of driving units significantly, since every operation can be done optically and only one driving source is needed. The equivalent circuit, design, and implementation of dual light-activated optopiezoelectric micropumps are discussed in this paper.

Real-Time Bioimpedance Sensing of Antifibrotic Drug Action in Primary Human Cells

Fibrotic diseases are among the most serious health issues with severe burdens due to their chronic nature and a large number of patients suffering from the debilitating effects and long-term sequelae. Collagenase treatment is a nonsurgical option but has limited results. To date, there is no potent noninvasive solution for fibrosis. Part of the reason for this is the lack of appropriate in vitro live cell screening tools to assess the efficacy of new therapeutical agents. Here, we demonstrate the utility of a cell-based electrochemical impedance biosensor platform to screen the efficacy of potential antifibrotic compounds. The platform employs a label-free and noninvasive strategy to detect the progression of fibrosis and the potency of the antifibrotic molecules in real-time. The fundamental principle that governs thisnovel system is that dynamic changes in cell shape and adhesion during fibrosis can be measured accurately by monitoring the changes in the impedance. This is achieved by growing the cells on a transparent interdigitated indium tin oxide (ITO) electrodes. It was demonstrated by monitoring the efficacy of a model antifibrotic compound, PXS64, on cells collected from patients with Dupuytren's contracture. We confirmed the validity of the developed biochemical impedance biosensor as an tool for in vitro screening of antifibrotic compounds and provided quantitative information on subcellular influences of the examined chemical molecules using correlative microscopy analyses that monitor the average cell area, cell morphology, and the amount and directionality of the deposited extracellular matrix protein collagen and measurement of cytosolic Ca2+ changes.

Dual role of TiO2 buffer layer in Pt catalyzed BiFeO3 photocathodes: Efficiency enhancement and surface protection

Polycrystalline ferroelectric BiFeO3 (BFO) films deposited on transparent indium tin oxide (ITO) electrodes have shown to be an interesting photocathode for photoelectrochemical (PEC) water splitting; however, its PEC performance and stability are far from perfection. Herein, we reported an amorphous TiO2 buffer layer, inserted between BFO and Pt catalyst, improves significantly both its PEC activity and stability. A photocathodic current density of −460 μA/cm2 at 0 V vs. reversible hydrogen electrode (RHE) and an onset potential of 1.25 V vs. RHE were obtained in ITO/BFO/TiO2/Pt photocathode under 100 mW/cm2 Xe-lamp illumination. TiO2 functions as a buffer layer to remove the upward barrier between BFO and Pt, and makes the photogenerated carriers separate efficiently. The photocathode also shows high stability in acid solution after a 10-h PEC continuous testing.

KARAKTERISTIK RANGKAIAN EKIVALEN DIODA BLEND ORGANIK P3OT : PCBM

Has conducted research diode characteristics equivalent circuit of the organic blend P3OT: PCBM. In this study, the blend of P3OT:PCBM was sandwiched between a transparent indium tin oxide (ITO) electrode and an Al backside contact. The current-voltage characteristic of the diode was measured under the dark and illumination. In order to determine the electrical parameters of the diode, we employed an equivalent circuit model developed originally for inorganic diode. As a result, the series resistance decreases while the reverse saturation current density increases by decreasing the thickness of P3OT:PCBM layer. This result may be useful for improving the performance of developing organic diode.

Synthetic Melanin Films As Potential Interfaces for Peroxynitrite Detection and Quantification

Peroxynitrite (PON) is a highly reactive oxygen-nitrogen species that facilitates both oxidation and nitration reactions. PON is the primary product of the reaction of superoxide anion-radical with nitric oxide radical. It has been well established that PON is a major noxious molecule, which is implicated in a host of pathophysiological conditions. Recently, PON has emerged as a new member of the nitroxidative array of reactive metabolites. Early clinical reports have emphasized the deleterious physiological reactivity of PON with many cellular targets including DNA, proteins, and lipids at cell/tissue levels. Melanin is a natural pigment that has many physiologic functions including the neutralization of highly reactive oxidative species. Tyrosine and its derivative 5,6-dihydroxyindole (DHI) are precursors of eumelanin, a brown or black forms of melanin that is also photo-stable. Recent studies have suggested that melanin can act as antioxidative therapy to scavenge reactive oxygen and nitrogen species including PON. In this project, we examine the chemical interaction between synthesized PON and polymerized films of DHI as a model of synthetic melanin. First, we studied the electrochemical characteristics of polymerized 5,6-dihydroxyindole on graphite electrodes, and then monitored the changes after adding aliquots of PON. This part of the work reports primarily on chemical changes within the electro-polymerized films of melanin on the electrode. We also studied the rates of chemical decay of PON in the presence of the transparent Indium Tin Oxide (ITO) electrodes coated with melanin films using absorbance spectroscopy. Ultraviolet-visible spectroscopy showed a significant difference between the decomposition rates of PON alone and in the presence of DHI films. The melanin films were characterized with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) to image and determine the surface chemical composition of the synthetic film. X-ray Photoelectron Spectroscopy (XPS) has been used to detect and analyze the change on the synthetic melanin films coated ITO slides before and after exposure to PON. Finally, we report on the possibility of using DHI films as a platform for the quantitative detection of PON in solutions using amperometry and impedance.

(Invited) Photoelectrochemical Hydrogen Evolution Based on Plasmon-Induced Charge Separation

Plasmon-induced charge separation (PICS) occurs at the interface between plasmonic nanostructures of gold, silver, or copper and a semiconductor such as titanium oxide.1-3 PICS involves energetically uphill transfer of electrons (or holes) from the plasmonic nanostructure to the semiconductor, so that the active carriers are retained in the semiconductor for a certain period of time and used for electrochemical reduction (or oxidation). We reported PICS for the first time more than 10 years ago1-3 and studied its mechanisms1-6 and applications2,3 including photocatalysis. We have reported oxidation of alcohols and aldehydes by PICS,1 and recently worked on photocatalytic reduction of water to hydrogen based on PICS at gold nanoparticle/titanium oxide systems. We coated an indium-tin oxide transparent electrode with a titanium oxide thin film. We deposited a hexagonal array of small plasmonic gold nanoparticles on the titanium oxide film, followed by deposition of cocatalysts such as platinum nanoparticles. This working electrode was connected with a counter electrode such as a platinum wire and those electrodes were immersed in an electrolyte solution containing an electron donor such as methanol. The working electrode was irradiated with visible light, and hydrogen was evolved at the counter electrode even without bias voltage application, although the hydrogen evolution rate was enhanced when a bias voltage was applied. We will report optimization of the cocatalyst systems. 1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). 2 . T. Tatsuma, Bull. Chem. Soc. Jpn., 86, 1 (2013) [account]. 3. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., in press (doi: 10.1039/C7SC00031F) [review]. 4. E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014). 5. H. Nishi and T. Tatsuma, Angew. Chem. Int. Ed., 55, 10771 (2016). 6. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).

Dynamic Windows with Neutral Color, High Contrast, and Excellent Durability Using Reversible Metal Electrodeposition

Summary Dynamic windows, which switch between transparent and opaque states upon application of a voltage, have applications in buildings, automobiles, and switchable sunglasses. Here, we describe dynamic windows based on the reversible electrodeposition of Cu and a second metal on transparent indium tin oxide electrodes modified by Pt nanoparticles. Three-electrode cyclic voltammetry experiments reveal that the system possesses high Coulombic efficiency (99.9%), indicating that the metal electrodeposition and stripping processes are reversible. Two-electrode 25-cm 2 windows without bus bars uniformly switch between a transparent state (∼80% transmission) and a color-neutral opaque state (

Mixed‐Mode Electro‐Optical Operation of Ge2Sb2Te5 Nanoscale Crossbar Devices

The use of phase‐change materials for a range of exciting new optoelectronic applications from artificial retinas to ultrahigh‐resolution displays requires a thorough understanding of how these materials perform under a combination of optical and electrical stimuli. This study reports for the first time the complex link between the electronic and optical properties in real‐world crossbar nanoscale devices constructed by confining a thin layer of Ge2Sb2Te5 between transparent indium tin oxide electrodes, forming an optical nanocavity. A novel proof‐of‐concept device that can be operated by a combination of optical and electrical stimuli is presented, leading the way for the development of further applications based on mixed‐mode electro‐optical operation.

CuPc/C60 heterojunction photodetector with near-infrared spectral response

Photodetector based on copper phthalocyanine/fullerene (CuPc/C60) heterojunction with transparent indium tin oxide (ITO) and aluminum (Al) electrodes was prepared by thermal evaporation method at room temperature. The spectral response of ITO/CuPc/C60/Al photodetector was broadened from ultraviolet–visible band to near-infrared band (800–1100nm) at zero bias. The near-infrared detectivity under 800nm illumination with light intensity of 0.016mW/cm2 was 4.5×1011cm·Hz1/2/W. And the near-infrared detectivities under 900 to 1100nm illumination were also exhibited bigger than 1010cm·Hz1/2/W. Thus CuPc/C60 heterojunction was one of the most promising materials for photodetectors with high detectivity and wide spectral rang. Those photodetectors can be used in a variety of possible sensor applications.

Low Voltage Charge/Discharge Behavior of Manganese Hexacyanoferrate

Recently, Prussian blue analogues (PBAs) have been reported to exhibit a low voltage charge/discharge behavior with high capacity (300–545 mAh/g) in lithium-ion secondary batteries (LIBs) [...]