Thickness Of WO3 Research Articles

Thermomechanical and Structural Analysis of WO3 Array for Optimized Photoelectrochemical Chloride Oxidation Performance.

Understanding the crystal structure of WO3 is essential for optimizing its photoelectrochemical performance. This study comprehensively analyzes the structural characteristics of WO3 during synthesis and investigates their correlation with photoelectrochemical activity. Structural analysis, incorporating annealing procedure and WO3 thickness, identifies a blend of hexagonal, monoclinic, and orthorhombic phases within WO3 array. Specifically, detailed analysis reveals a predominance of monoclinic WO3 phase alongside the orthorhombic WO3 phase, both of which are commonly characterized by their monoclinic structure. Three-dimensional thermomechanical simulations using the finite element method reveal that thermal displacement in WO3 layers increases with thickness during the thermally induced synthesis process. These results highlight a direct correlation between WO3 thickness, thermal displacement, and phase transition, with thicker layers favoring the transformation from orthorhombic to monoclinic structures due to increased thermally induced deformation. The heightened monoclinic structure, which possesses lower symmetry than the orthorhombic structure, induces more defect sites, suggesting increased donor density. Notably, the monoclinic-dominated WO3 exhibits superior performance under UV-visible irradiation in 0.5 M NaCl. Furthermore, the WO3 array demonstrates over 85% Faradaic efficiency for chloride oxidation, indicating preferential selectivity over oxygen evolution reaction in 0.5 M NaCl. This study emphasizes the pivotal role of the crystal structure of WO3 in achieving efficient photoelectrochemical seawater splitting.

Influence of WO3-Based Antireflection Coatings on Current Density in Silicon Heterojunction Solar Cells.

Antireflection coatings (ARCs) with an indium thin oxide (ITO) layer on silicon heterojunction solar cells (SHJ) have garnered significant attention, which is due to their potential for increasing current density (Jsc) and enhancing reliability. We propose an additional tungsten trioxide (WO3) layer on the ITO/Si structure in this paper in order to raise the Jsc and demonstrate the influence on the SHJ solar cell. First, we simulate the Jsc characteristics for the proposed WO3/ITO/Si structure in order to analyze Jsc depending on the thickness of WO3 using an OPAL 2 simulator. As a result, the OPAL 2 simulation shows an increase in Jsc of 0.65 mA/cm2 after the 19 nm WO3 deposition on ITO with a doping concentration of 6.1 × 1020/cm2. We then fabricate the proposed samples and observe an improved efficiency of 0.5% with an increased Jsc of 0.75 mA/cm2 when using a 20 nm thick WO3 layer on the SHJ solar cell. The results indicate that the WO3 layer can be a candidate to improve the efficiency of SHJ solar cells with a low fabrication cost.

The erosion and retention properties of tungsten trioxide films exposed to low energy deuterium ions: Temperature dependence

The erosion behavior and retention properties of tungsten trioxide (WO3) and W films exposed to low energy (∼50 eV) deuterium (D) ions were studied at surface temperature from 403 K to 758 K. The initial thickness of WO3 and W films are approximately 7.0 × 1018 atoms cm−2 and 1.8 × 1018 atoms cm−2, respectively. The erosion rate of oxygen (O) by deuterium is thermally enhanced, and tungsten (W) atoms can be sputtered rapidly in the form of WxOy molecules and/or W atoms at higher temperatures due to the relatively weak binding energy between W and O, resulting on an increase in the W sputtering yield with temperature. Nano-sized pinholes appear on the surface at 403 K, however, pinholes with much smaller sizes and cracks appear on the surface at higher temperatures, and their density increases with increasing temperatures. The synergistic effects of ion irradiation and temperature cause the structure change of tungsten oxide films according to Raman spectra. X-ray photoelectron spectroscopy shows that after irradiation with D ions, metallic W appears on the surface, but the tungsten oxide is still present. Trapped D is almost uniformly distributed in WO3 and its concentration is much higher than that in W at lower irradiation temperature, which is mainly related to D atoms chemically bonded to O atoms with the formation of deuterium tungsten bronze. The thermal desorption peak temperatures of D2 (∼465 K or 500 K) and D2O (∼495 K, 730 K (or 790 K) and 825 K) are related to the heating rate (1 K s−1) and it implies that the deuterium tungsten bronze is decomposed under the low D ion irradiation temperatures.

Variation of Sputtered WO3 Film Thickness in Ag (NPs)/WO3/Au (NPs) System for Optimizing Sensing Behaviors to NH3

Introduction Ammonia (NH3) is one of the major air pollutants. It can cause serious damage to the eyes, skin, and respiratory system when its concentration exceeds 300 ppm [1]. Therefore, it is necessary to develop an efficient NH3 gas sensor to monitor its concentrations in the environment and varies industrial sectors. So far, several nanostructured materials have been investigated to detect NH3 gas, such as ZnO, SnO2, and WO3 [2]. However, these materials usually suffer from a lack of sensitivity, especially at low operating temperatures. Several strategies have been applied in the literature to improve the NH3 sensing performance, including surface treatment, doping with other materials, and forming a heterojunction. Furthermore, it is generally accepted that the decoration of the thin films will noble metals such as Au, Pt, or Pd will improve the sensor response owing to the increased depletion layer thickness of gas sensing materials and additional electrical resistance changes due to the built-in barrier high formed at noble metal nanoparticles and sensing material junctions. In our previous studies, we developed a method to decorate oxide thin-film surfaces with well-dispersed and uniform noble metal nanoparticles and tested their gas sensing performance toward different gases such as [3-4]. Additionally, the flow of charge carriers between the metal oxide and the attached nanoparticles was found to depend on the work function difference between them. For instance, silver (work function = 4.33 eV), or gold (work function = 5.1 eV) decorated metal oxide has a different impact on the gas sensing properties. The flow of electrons between metal oxides such as WO3 and the attached silver, or gold nanoparticles has two opposite directions: one from metal oxide to the Au and the second one from Ag to the metal oxide owing to the work function difference between Ag/ metal oxide, and Au/metal oxide. This work intends to fabricate double side noble metals activated sputtered WO3 thin film and investigate the effect of the WO3 thickness on the NH3 gas sensing properties. Method Ag (NPs)/WO3/Au (NPs) films were fabricated by DC sputtering followed by post annealing treatment in nitrogen atmosphere. The deposition of the Ag (NPs)/WO3/Au (NPs) films was carried out into three steps. First, Ag thin film was deposited for a period of 30 s by applying 20W. Afterward, WO3 films having a different thickness ranging from 5nm to 150 nm were deposited via DC reactive sputtering at 100 W in oxygen. In the third step, Au was sputtered using DC sputtering at 25 W for 30 s. Subsequently, the samples were heated at 600 ⁰C in a nitrogen atmosphere for 3 h to convert the Ag, and Au layer to nanoparticles. Different analytical techniques were used to study the physical and the chemical properties of the fabricated films. Results and Conclusions Figure 1(a) shows the FESEM image of the Ag (NPs)/WO3/Au (NPs) film. As can be observed, two different size distributions of nanoparticles can be seen which could be ascribed to the formation of Ag and Au nanoparticles. The formation of WO3 film, Ag and Au nanoparticles was also confirmed using FESEM-EDX mapping (not shown). Gas sensing results showed Ag (NPs)/WO3/Au (NPs) sensor with a thickness of 30 nm demonstrated the highest gas response to NH3. Fig. 1(b) shows the dynamic response-recovery curves of the Ag (NPs)/WO3/Au (NPs) sensor for different concentrations of NH3. It can be noticed that all the sensing responses increased with the increase of NH3 concentration. The repeatability of the fabricated sensor was implemented up to five cycles in 100 ppm. As can be observed, the developed sensor displayed high repeatability under the tested conditions. Figure 1(c) shows the five-cyclic response of the fabricated sensor towards 100 ppm NH3 at 250 ⁰C. As can be noticed, the sensor capable of complete recovery upon removal of NH3. The deviation in the sensing response was less than 2% thus ensuring excellent repeatability. The long-term stability of a sensor is of great importance for almost all practical applications. To investigate the long-term stability of the sensor, the gas sensitivity was recorded at 100 ppm NH3 for over 20 days and the obtained sensing results plotted in Figure 1 (d). The response of the fabricated sensor decreased by about 5% in comparison to its original characteristic, confirming its excellent stability.

Enhanced NH3 and H2 gas sensing with H2S gas interference using multilayer SnO2/Pt/WO3 nanofilms

The selective detection and classification of NH3 and H2S gases with H2S gas interference based on conventional SnO2 thin film sensors is still the main problem. In this work, three layers of SnO2/Pt/WO3 nanofilms with different WO3 thicknesses (50, 80, 140, and 260 nm) were fabricated using the sputtering technique. The WO3 top layer were used as a gas filter to further improve the selectivity of sensors. The effect of WO3 thickness on the (NH3, H2, and H2S) gas-sensing properties of the sensors was investigated. At the optimal WO3 thickness of 140 nm, the gas responses of SnO2/Pt/WO3 sensors toward NH3 and H2 gases were slightly lower than those of Pt/SnO2 sensor film, and the gas response of SnO2/Pt/WO3 sensor films to H2S gas was almost negligible. The calcification of NH3 and H2 gases was effectively conducted by machine learning algorithms. These evidences manifested that SnO2/Pt/WO3 sensor films are suitable for the actual NH3 detection of NH3 and H2S gases.

Fast Switching of Photoelectrochromic Device Using Ligand Attached TiO2 Layer

We fabricated a scalable and economical photoelectrochromic smart window that can be darkened under illumination and bleach in dark conditions. The materials used in this device can cut the cost by omitting transparent conducting oxide and ruthenium dye. The device is composed of a screen-printed WO3 layer on the soda-lime glass, a screen-printed TiO2 layer that is modified by attaching a ligand (5-methyl salicylic acid), a redox mediator and a soda-lime cover glass. The performance of the different types of salicylic acid ligands is investigated first in the dye-sensitized solar cells. The best performing ligand (5-methyl salicylic acid) was then used in the photoelectrochromic device. Using soda-lime glass and 5-methyl salicylic acid instead to conducting glass and ruthenium dye results in higher stability with additional benfit of low cost. The change in transmittance of the device also depends upon the thickness of WO3 and TiO2 layers and the optimized thickness was used in the device. The device showed fast coloring with a change in transmittance of 40% at 550nm within 3 minutes. However, the device showed slow bleaching and took 3 hours to bleach partially and 24 hours to bleach fully. To address the issue of slow bleaching, platinum particles were added in the WO3 and TiO2 layers to speed up the back reaction. The Pt particles used as a catalyst showed a dramatic improvement in the bleaching speed of photoelectrochromic device without affecting the coloring performance of the device. The device bleached fully within 30 minutes in the dark when Pt was incorporated in the WO3 layer.

Reliable, High-Performance Electrochromic Supercapacitors Based on Metal-Doped Nickel Oxide.

Herein, high-performance, reliable electrochromic supercapacitors (ECSs) are proposed based on tungsten trioxide (WO3) and nickel oxide (NiO) films. To maximize device performance and stability, the stoichiometric balance between anode and cathode materials is controlled by carefully adjusting the thickness of the anodic NiO film while fixing the thickness of WO3 to ∼660 nm. Then, a small amount (≤10 mol %) of metal (e.g., copper) is doped into the NiO film, improving the electrical conductivity and electrochemical activity. At a Cu doping level of 7 mol %, the resulting ECS exhibited the highest performance, including a high areal capacitance (∼14.9 mF/cm2), excellent coulombic efficiency (∼99%), wide operating temperature range (0-80 °C), reliable operation with high charging/discharging cyclic stability (>10,000 cycles), and good self-discharging durability. Simultaneously, the change in transmittance of the device is well synchronized with the galvanostatic charging/discharging curve by which the real-time energy storage status is visually indicated. Furthermore, the practical feasibility of the device is successfully demonstrated. These results imply that the ECS fabricated in this work is a promising potential energy storage platform and an attractive component for future electronics.

Enhanced Visible Light Active WO3 Thin Films Toward Air Purification: Effect of the Synthesis Conditions.

Taking our current environmental situation in the world into consideration, people should face growing problems of air and water pollution. Heterogeneous photocatalysis is a highly promising tool to improve both air and water quality through decomposition/mineralization of contaminants directly into harmless CO2 and H2O under ambient conditions. In this contribution, we focused on the synthesis of self-assembly WO3 thin films via an electrochemical approach in the aqueous electrolyte containing fluoride ions toward air purification. The effect of preparation conditions such as applied potential (10–50 V), anodization time (15–120 min), concentration of H2SO4 (0.5–1.5 M) and NaF (0.1–1.0 wt.%) on the morphology, photocurrent response, and photocatalytic activity addressed to removal of air pollutant in the presence of as-prepared WO3 samples were thoroughly examined and presented. The results revealed the growth of nanoplatelets and their gradual transformation into flower-like structures. The oxide layers and platelet thickness of the WO3 samples were found to be proportionally related with the synthesis conditions. The photocatalytic ability toward air purification was evaluated by degradation of toluene from air mixture using low-powered LEDs as an irradiation source (λmax = 415 nm). The highest photoactivity was achieved in presence of the sample which possessed a well-ordered, regular shape and repeatable distribution of flower buds (100% of degradation). The results have confirmed that the oxide layer thickness of the anodic WO3 significantly affected the photocatalytic activity, which increased with the increasing thickness of WO3 (to 1.05 μm) and then had a downward trend. The photocurrent response evidenced that the well-organized sample had the highest ability in photocurrent generation under UV-Vis and Vis irradiation. Finally, a possible growth mechanism of WO3 NFs was also discussed.

Scalable photoelectrochromic glass of high performance powered by ligand attached TiO2 photoactive layer

A scalable photoelectrochromic (PEC) glass which can be darkened on exposure to sunlight and return to its original clear state in the absence of sunlight without any expensive materials like ruthenium dye or transparent conductive oxide was fabricated. The PEC glass is composed of light absorbing layer of ligand attached titanium oxide, color changing layer of tungsten oxide and the electrolyte containing redox mediator. This work reports, for the first time, on an application of salicylic acid attached TiO2 photoactive layer for PEC devices. The applicability of various salicylic acid derivatives attached TiO2 films in PEC device is individually investigated in dye solar cells. Among various salicylic acid derivatives studied, 5-methylsalicylic acid showed the best performance in terms of charge generation for coloration of WO3. By using 5-methylsalicylic acid instead of ruthenium dye, lower cost, higher stability, and simpler electrolyte composition have been realized. The changes in transmittance for coloration (ΔTC) depend on the thickness of WO3 and TiO2 in this device. Thus, we changed the thickness of WO3 and TiO2 to get the highest variation of transmittance for coloration. The preliminary optimization of PEC device exhibits ΔTC of 40.8% at 550 nm, the wavelength most sensitive to the human eye, and of 64.3% at 700 nm.

NO2 Sensing Characteristics of Si MOSFET Gas Sensor Based on Thickness of WO3 Sensing Layer

This study investigates the nitrogen dioxide (NO2) sensing characteristics of an Si MOSFET gas sensor with a tungsten trioxide (WO3) sensing layer deposited using the sputtering method. The Si MOSFET gas sensor consists of a horizontal floating gate (FG) interdigitated with a control gate (CG). The WO3 sensing layer is deposited on the interdigitated CG-FG of a field effect transistor(FET)- type gas sensor platform. The sensing layer is deposited with different thicknesses of the film ranging from 100 nm to 1 μm by changing the deposition times during the sputtering process. The sensing characteristics of the fabricated gas sensor are measured at different NO2 concentrations and operating temperatures. The response of the gas sensor increases as the NO2 concentration and operating temperature increase. However, the gas sensor has an optimal performance at 180℃ considering both response and recovery speed. The response of the gas sensor increases significantly from 24% to 138% as the thickness of the sensing layer increases from 100 nm to 1 μm. The sputtered WO3 film consists of a dense part and a porous part. As reported in previous work, the area of the porous part of the film increases as the thickness of the film increases. This increased porous part promotes the reaction of the sensing layer with the NO2 gas. Consequently, the response of the gas sensor increases as the thickness of the sputtered WO3 film increases.

Effect of residual ions of hydrothermal precursors on the thickness and capacitive properties of WO3 nanoplates

The morphology and size of nanostructures have been considered to be directly related to capacitive performance. Additionally, hydrothermal synthesis is a common method to control nanostructures. In practice, researchers paid more attention to the direct effect of “useful ions” on morphology or size of nanostructures, e.g. the combination and decomposition processes of H+ and WO42− to form WO3. Unfortunately, the effects of other incidental residual ions on the nanostructures have been often neglected. Herein, we add an extra procedure (cleaning the precursor) in the as-optimized hydrothermal synthesis routine to remove residual ions in the solution around tungstic acid colloids. A comparative study shows such an extra procedure would result in a further considerable reduction of WO3 nanoplates in the thickness by 50% and in a prominent enhancement of the specific capacitance from 203.5 F g−1 to 334.0 F g−1 at a scan rate of 2 mV s−1. The thin WO3 nanoplates also show outstanding cycle stability for 5000 cycles. Interestingly, when we refilled the precursors solution with the Na+ and Cl− ions again, the thickness of WO3 nanoplates gradually thickens as the increase of NaCl content. In this way, the effect of residual ions on the thickness of nanoplates has been experimentally demonstrated. Otherwise, this facile method can be helpful to establish a bridge between the physical deposition method, which is suitable for the complete fabrications of single thin layer materials with less active sites and the common hydrothermal synthesis method, which tends to produce thicker fragmental nanoplates but more abundant reaction sites. Also, this simple and efficient method can be extended to the preparation of thin nanoplates of other transition metal oxides and better electrochemical performance can be expected.

Photoinduced electron transfer in WO3/BiVO4 heterojunction photoanodes: effects of the WO3 layer thickness

The PEC performance of WO3/BiVO4 heterojunction photoanodes with a fixed BiVO4 thick top layer and different WO3 layer thicknesses was investigated under backside irradiation, in comparison with the performance of the same electrodes without a top BiVO4 layer. While the performance of these latter increase with increasing WO3 thickness, the presence of a BiVO4 layer, besides leading to an effective sensitization up to 520 nm, leads to a decrease of incident photon to current efficiency in the short wavelength’s range. After having excluded major WO3 filter effects, this has been attributed to charge carrier recombination effects occurring when both oxides get excited and becoming more relevant with increasing WO3 thickness and decreasing excitation wavelength.

Electrochromic device with magnetron sputtered tungsten oxide (WO3) and nafion membrane: performance with varying tungsten oxide thickness- a report

Electrochromics is the emerging technology for energy conservation and indoor climatic control through smart windows. In this study we are reporting four layer electrochromic device: ITO (400 nm)/commercially procured Nafion (183 μm)/WO3 (44 nm to 200 nm)/ITO (400 nm). The active area (A) of the electrochromic devices are 3 cm2. The tungsten oxide (WO3) and ITO thin films have been deposited at room temperature (300 K) by reactive DC Magnetron sputtering. The sheet resistance of ITO is 20 Ω/◻. The ‘as deposited’ WO3 films are amorphous and have high optical transmission (75%–85%) in the visible spectrum. The optical band gap decreases with increasing thickness of WO3 thin films. The coloration efficiency (CE) of the electrochromic device increases with increasing thickness of the WO3 layer. The CE for the device with WO3 thickness 200 nm is 184 cm2 C−1: the highest reported so far for a hybrid electrochromic device. The increase in the CE with thickness has been explained (for the first time) by replacing the surface charge density (Q/A) with the volume charge density (Q/A*t) in the coloration efficiency formula derived from the Beer Lambert’s law.

Temperature Dependent Electrical Characteristics of Nanostructured WO3 Based Ambipolar Bottom Gate FET

A detailed experimental investigation on nanostructured tungsten trioxide (WO3) based bottom gate field effect transistor (FET) is presented. These were fabricated using scalable process and thoroughly characterized for morphology and device performance. It was also observed that thickness of WO3 and ambient during annealing played a key role in tuning the morphology. The transistors bearing nanostructured morphology of WO3 were tested for device performance such as input-output and transfer characteristics at low, room, and high temperatures. Of all the devices tested, best on-off ratio obtained was 105 and sub-threshold slope obtained was 150 mV/decade inferring an efficient performance of the FET. A tradeoff between the on-off ratio ( I ON/ I OFF) and sub-threshold slope was noticed at higher temperatures. This was attributed to the ambipolar nature of the WO3 films. At a given temperature and bias, either the holes or electrons were present for transport and conduction. Such ambipolar films find great potential in transistors that can be used in switching applications.

Strong microcavity effects in hybrid quantum dot/blue organic light-emitting diodes using Ag based electrode

We investigated the color conversion characteristics of a quantum dot/organic light-emitting diode (QD/OLED) by altering blue emission using the microcavity effect. Compared to the ITO-based OLED, the WO3/Ag/WO3 (WAW)-based OLED has a narrow shape of resonance and high cavity enhancement factor. As a result, the peak emission intensity wavelength remarkably shifts as the thickness of the WO3 layer increases and the WAW-based OLED with inner WO3 thickness of 120 nm shows an additional emission peak at 420 nm due to the second resonance. As the thickness of the WO3 layer increases, the color coordinates of the hybrid QD/OLED with the ITO anode are nearly unchanged. However, hybrid WAW-based devices exhibit distinct color coordinates, such as nearly blue light, nearly green light and nearly white light with color coordinates of (0.31, 0.37).

Influence of cycling temperature on the electrochromic properties of WO3//NiO devices built with various thicknesses

Electrochromic smart windows, which are able to vary their optical transmittance by the application of a voltage, improve the indoor comfort in buildings by controlling light and temperature. Among electrochromic devices, ECDs, WO3 and NiO are often associated leading to neutral color. This work focuses on the influence of the thickness of WO3 and NiO single layers on the ECD electrochemical and optical properties. Initial characterizations in lithium-based liquid electrolyte, show a non-linear evolution of the electrochemical capacity for each oxides vs. thickness while for similar thickness, WO3 thin films exhibit larger EC properties than NiO ones. The combinations of various WO3 and NiO thicknesses lead to ECDs of which capacity appears limited by the one of NiO, while the switch to a neutral color always remain. Besides, the influence of each oxide on the ECD cyclic voltammogram shape is discussed. Finally, the study of the cycling temperature, in the range −40°C to 80°C on the electrochromic properties of ITO/650nm-WO3/LiClO4-PC +PMMA/360nm-NiO/ITO shows an increase in performance with temperature nevertheless associated with signs of degradation above 60°C. At low temperature, the decrease in capacity is interestingly associated with a remaining significant optical contrast and the capacity recovery if the ECD is further cycled at RT.

Solid State Electrochemical WO3 Transistors with High Current Modulation

In this paper, the role of electrode architecture (conventional and interdigital), device structure (vertical or planar), and tungsten oxide (WO3) channel thickness on the electro‐optical performances of room temperature sputtered electrochromic transistors (EC‐Ts) is reported. A larger number of electro‐reducible tungsten sites in thicker WO3 films provide improved optical density and coloration efficiency. However, overall transistor performance is found to suffer in planar EC‐Ts with the conventional electrode architecture, where the step to planar interdigital electrodes leaves the devices to be almost insensitive to WO3 thickness. Vertical structures result in improved device properties and stability, given to the shorter distance between gate electrode and semiconductor and to the encapsulation effect provided by such structures. These devices show an On–Off ratio of 5 × 106 and a transconductance (g m) of 3.59 mS, for gate voltages (V G) between −2 and 2 V, which to the authors' knowledge are the best values ever reported for electrochemical transistors. The simple and low‐cost processing together with the electrical/optical performances well supported into a comprehensive analysis of device physics opens doors for a wide range of new applications in display technologies, biosensors, fuel cells, or electrochemical logic circuits.

Preparation of ultra-thin and high-quality WO3 compact layers and comparision of WO3 and TiO2 compact layer thickness in planar perovskite solar cells

In this paper, the ultra-thin and high-quality WO3 compact layers were successfully prepared by spin-coating-pyrolysis method using the tungsten isopropoxide solution in isopropanol. The influence of WO3 and TiO2 compact layer thickness on the photovoltaic performance of planar perovskite solar cells was systematically compared, and the interface charge transfer and recombination in planar perovskite solar cells with TiO2 compact layer was analyzed by electrochemical impedance spectroscopy. The results revealed that the optimum thickness of WO3 and TiO2 compact layer was 15nm and 60nm. The planar perovskite solar cell with 15nm WO3 compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60nm TiO2 compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency.

Effect of annealing temperature on anodized nanoporous WO3

Nanoporous tungsten oxide (WO3) was produced on W foil by anodization method. The nanoporous WO3 thickness obtained was 450 nm with pore diameter size of 50–80 nm and pore wall thickness of 15–20 nm. The effect of annealing temperature (200–700 °C) on the morphological, structural, and electrochromic properties of nanoporous WO3 were reported. Nanoporous WO3 transformed from amorphous to monoclinic phase after annealing at 300 °C. The nanoporous structure was retained after annealing; however, the pore wall thickness increased with increasing annealing temperature. A compact oxide layer underneath the nanoporous layer was formed after annealing at 500 °C. The as-anodized oxide showed faster electron and ion intercalation process (with the highest current density of −11.53 and +7.73 mA cm−2) than the annealed oxides. Moreover, the current density decreased with increasing annealing temperature because the annealing process increased the crystallinity and reduced the surface area of the oxide. The as-anodized oxide also exhibited shorter coloring and bleaching times of ~7.4 and ~3.9 s, respectively.

Flexible organic light-emitting diodes with ZnS/Ag/ZnO/Ag/WO3 multilayer electrode as a transparent anode

We investigated the highly flexible, transparent and very low resistance ZnS/1st Ag/ZnO/2nd Ag/WO3 (ZAZAW) multilayer electrodes on PET substrate as an anode in flexible organic light-emitting diodes (OLEDs). A theoretical calculation was first conducted to obtain the optimal thickness of the ZAZAW multilayer for high transparency. Its measured luminous transmittance was over 80% in the visible range with a very low sheet resistance of 2.17Ω/sq., and it had good mechanical flexibility due to the ductility of Ag. Ag’s effect on optical and electrical properties was also studied. Flexible OLEDs devices that were fabricated on ZAZAW multilayer anode showed good hole injection properties comparable to those of ITO-based OLEDs due to the use of WO3 as a hole injection layer. However, the electroluminescent properties of the ZAZAW-based OLEDs varied depending on WO3 thickness. Although the transmittance of the ZAZAW electrode was reduced by tuning the WO3 thickness to adjust the microcavity effect, the device efficiency could be enhanced above that of ITO-based OLEDs.