Fabrication Of Electrochromic Devices Research Articles

The preparation of low-cost tungsten oxide films by solution-coating technique and NIR annealing for high-performance complementary electrochromic devices

Electrochromic devices can adjust their transparency by applying an electrical voltage and serve as intelligent window systems for managing incoming sunlight. In this study, we employed an environmentally friendly, large-area solution coating method to form tungsten oxide (WO3) thin films for the fabrication of electrochromic devices. We applied a WO3 precursor solution, with water as the primary solvent, onto ITO glass through blade coating and utilized near-infrared (NIR) light annealing for drying in order to rapidly optimize the film characteristics. The resulting WO3 film, combined with an ion storage layer – either sputtered NiO or blade-coated Prussian Blue (PB) - and injected with a UV-curable electrolyte, resulted in a complementary electrochromic device that exhibited good performance characteristics. For the device with NiO as the ion storage layer, the optical transmittance modulation (ΔT) can achieve 50 % at a wavelength of 680 nm, maintaining a ΔT of 45 % after 3000 coloration-bleaching cycles. For the device with PB as the ion storage layer, the ΔT achieved 64 % at 630 nm, maintaining a ΔT of 60 % after 3000 coloration-bleaching cycles. Therefore, we believe this WO3 solution coating technique combined with rapid NIR annealing technology holds promise as a low-cost and efficient method for the future production of electrochromic devices.

Significantly enhanced oxygen vacancies in W18O49 nanowires for electrochromic films by annealing in argon

Owing to the energy-efficient attributes of electrochromic technology, there has been a growing emphasis on the fabrication of electrochromic devices with high-contrast and stable performance. As an electron donor, the deliberate incorporation of oxygen vacancies into an electrochromic material is poised to significantly elevate the film's electrochromic characteristics. In this study, we successfully synthesized one-dimensional W18O49 nanowires thin films with enhanced oxygen vacancies using a straightforward combination of solvothermal reactions and annealing in Ar. In comparison to films annealed in air, those treated in argon (Ar) exhibited a higher concentration of oxygen vacancies, resulting in improved light absorption characteristics. The optimal annealing conditions were determined to be 400 °C for 40 min. Under these conditions, the thin film demonstrates enhanced electrochromic performance, exhibiting a notable 71.6% modulation in transmittance, a 27.2% increase compared to the air condition. It displays a rapid response time (Tb = 3.3 s, Tc = 3 s), high coloration efficiency (CE = 55.9 cm2 C−1), and excellent cycling stability (with a ΔT retention rate of 93.9% after 750 cycles).

Steaming‐Assisted Conversion: A New Strategy for the Synthesis of Anatase TiO2, Nb, and W‐doped Anatase TiO2 2D Inverse Opal Films

AbstractSteaming‐assisted conversion route, a new strategy, is first adapted for the synthesis of highly crystallized anatase TiO2 2D inverse opal (IO) monolayer films, and then to Nb‐doped TiO2 and W‐doped TiO2 2D IO monolayer films. Pure water, ammonia, or HCl solutions are used as a source of steaming vapor to convert dry films of amorphous TiO2 IO, NbCl5/TiO2, and WCl6/TiO2 composite IOs into anatase TiO2, Nb‐doped TiO2, and W‐doped TiO2 IO films. This new strategy renders possible the doping of metal ions within the framework of the anatase TiO2 IO films under low temperature and liquid‐free conditions. Further, the ordered array structure of the IO films is also effectively retained. The low steaming conversion temperature allows high dopant rates of homogeneously distributed heteroatoms, resulting in Nb doping as high as ≈34%. The thus prepared TiO2, Nb‐doped TiO2, and W‐doped TiO2 anatase IO films are successfully used as active electrodes in the fabrication of electrochromic devices.

The Multifaceted Opportunities Provided by the Pheomelanin-Inspired 1,4-Benzothiazine Chromophore: A Still-Undervalued Issue.

1,4-Benzothiazines are the main building blocks of the naturally occurring pheomelanin pigments, and their chromophoric properties have been strongly related to the well-known phototoxicity of these pigments, partly responsible for the high incidence of melanoma and other skin cancers in red-haired people. However, some peculiar features of the 1,4-benzothiazine chromophore could be functionally exploited in several sectors. Within this context, in this perspective, an overview of the very recently reported applications of the 1,4-benzothiazine chromophore in pH sensing, filter permeability control, smart packaging, electrochromic device fabrication, bioimaging, photocatalysis, and HPLC detection systems is provided, together with a brief presentation of recently developed synthetic approaches to the 1,4-benzothiazine scaffold, with the aim of emphasizing the still-undervalued multifunctional opportunities offered by this class of compounds.

Heteroacene-Based Polymer with Fast-Switching Visible-Near Infrared Electrochromic Behavior.

The electrochromic properties and application of electronically conducting polymers (ECPs) (PTRPZ-EDOT) consisting of a 3,4-ethylenedioxythiophene (EDOT) and the heteroacene-based molecular scaffold, 6H-pyrrolo[3,2-b:4,5-b'] bis [1,4] benzothiazine (TRPZ), are reported. Known for its high electron mobility and conducting properties, the novel TRPZ scaffold was synthesized to possess two EDOT molecules termini affording TRPZ-EDOT. Electropolymerization of TRPZ-EDOT resulted in remarkable spectroscopic and conductive properties suitable for electrochromic device fabrication. Using atomic force microscopy (AFM), the average surface roughness and surface topography of PTRPZ-EDOT polymer thin films were determined. Spectroelectrochemical data showed that the polymer achieved switching times of 4.07 (coloration) and 0.47 s (bleaching) at 539 nm. The PTRPZ-EDOT film exhibits an optical contrast of 36-44% at 539 nm between its neutral and colored states, respectively. The NIR region from 1000 to 1700 nm shows the appearance of charge carrier bands with a 0-1 V potential range. An electrochromic device was successfully fabricated from PTRPZ-EDOT, showcasing the potential and applicability of the polymer material for advanced technologies such as smart windows, flexible electrochromic screens, and energy storage devices.

Low-cost gel polymeric electrolytes for electrochromic applications

Solid-state ionic conductors embodying either protons or lithium ions are very attractive for large-area electrochromic (EC) devices. In this work, aiming at the preparation of a gel polymer electrolyte (GPE), two cheaper and non-toxic commercial resins are used: a urethane-based prepolymer (NOA65) and a vinyl acetate-based resin (MASTIFLEX). They are employed as host matrices to trap the liquid constituents, made of lithium perchlorate-propylene carbonate (LiClO 4 -PC). Thermogravimetric analyses indicate that both resins show excellent thermal performance. Several GPE formulations are investigated with respect to electrical and optical properties, varying the polymer-to-liquid ratio and LiClO 4 concentration. The EC devices made with the two GPEs are also characterized in terms of optical contrast, switching kinetics and repetitive switching cycles. These activities made it possible to find the best formulations finally employed for the fabrication of 100 cm 2 large area EC devices. The obtained results demonstrate that low-cost GPEs based on commercial polymers are electrochemically stable as ion-conducting media for EC devices. • Two low cost polymeric resins have been used as gel polymer electrolytes for the fabrication of electrochromic devices. • Optimization of electrolytes formulation in order to maximize the ionic conductivity. • Fabrication of a 100 cm 2 large area electrochromic device.

Fabrication of electrochromic devices by laser patterning of spin-sprayed transparent conductive Ga:ZnO films

Despite their significant economic benefits, wet processes are rarely adopted in optoelectronics industries because of their inherent difficulties in producing high-quality functional films compared with dry processes. Unlike other conventional wet processes, spin-spraying promotes surficial heteronucleation by continuously providing fresh source ions onto the substrate surface and removing excess ions left after nucleation from the surface. Surficial heteronucleation ensures the formation of high-quality films with dense microstructures that are comparable to those obtained by dry processes. This study describes a novel spin-spraying method for growing Ga-doped ZnO (Ga:ZnO) films on glass substrates. The optimum Ga doping concentration of the spin-sprayed Ga:ZnO (SSedGZO) films was determined from the electrical and optical properties of the films. Further, the feasibility of employing UV laser patterning to produce patterned SSedGZO films for application as transparent electrodes (TEs) in optoelectronic devices was evaluated, and the optimum laser power required for effective patterning was determined by analyzing the surface microstructures of the patterned films. Finally, to confirm the practical applicability of the SSedGZO films as TEs, electrochromic devices (ECDs) comprising the SSedGZO TEs were fabricated. The laser-patterned SSedGZO TEs functioned successfully in the fabricated ECDs, displaying reversible color changes through electrochromic switching.

A method to achieve full incorporation of PMMA-based gel electrolyte in fiber-structured PVB for solid-state electrochromic device fabrication

Based on the modified PMMA-PEG polymer loading with LiClO4/PC, a flexible, transparent free-standing quasi-solid polymer electrolyte (QSPE) was prepared. The ionic conductivity of QSPE membrane was carefully studied through electrochemical impedance spectroscopy. It was found that the QSPE membrane with 30 wt% 0.1 M LiClO4/PC displays a high conductivity (5.23 × 10−6 S/cm at room temperature), good transparency (over 70% in visible ranges) and a certain of mechanical strength. Furthermore, a novel fiber-network structured membrane of polyvinyl butyral (PVB) was designed and prepared via electro-spinning, which would allow the liquid QSPE fully complex with PVB polymer structurally. A great improvement for interfacial adhesion between the gel electrolyte and electrodes was achieved, the tensile strength increased to 0.31 MPa (QSPE-PVB) from 0.05 MPa (QSPE), while remaining a good transparency. Meanwhile, the ionic conductivity of the composite electrolyte reached a level of 10−5 S/cm.Using the gel composite electrolyte (QSPE-PVB membrane), all-solid-state electrochromic device (ECD) was assembled with a configuration of PProDot-Me2/QSPE-PVB/V2O5. This novel electrolyte could guarantee that PProDot-Me2 was able to switch its color from bleached state (Tb= 71.4% at 580 nm) to colored state (Tc= 23.7% at 580 nm) within 6 s under the applied potential of ±1.5 V. The as-fabricated QSPE-PVB ECD also exhibited an impressive stability of almost no transmittance attenuation. This new all-solid ECDs offered a certain operational advantage in real-world applications.

Facile sol–gel fabrication of MoS2 bulk, flake and quantum dot for electrochromic device and their enhanced performance with WO3

Low–temperature fabrication of electrochromic device (ECD) is an attractive characteristic, supporting their use in smart windows and flexible devices. In this study, different MoS2 morphologies (bulk, flake and quantum dots) are fabricated onto indium tin oxide using the sol–gel method. The ECD performance of the fabricated MoS2 devices is optimized, and then the MoS2 bulk, flake and quantum dots are used as electrochromic anodic layers, with WO3 as cathodic layer to prepare MoS2/WO3–based ECDs. The fabricated MoS2/WO3 ECDs are found to exhibit high optical contrasts (59–75%) at 1.5–0 V and 700 nm. In addition, the stability, switching time and coloration efficiency of the MoS2 devices are found to be improved by the WO3 layer. When MoS2 quantum dot film is used as an electrochromic layer, it shows better ECD performance with WO3 than films prepared with either bulk or flake MoS2. It could be expected that the MoS2 quantum dot morphology allows more Li+ ions to penetrate the crystal lattice, promoting a greater charge transfer, which is crucial for the enhanced electrochromic property. This work provides an encouraging support for the application of cost effective, solution–processed MoS2/WO3–based ECDs, working at low temperature and low voltage, to the processing of flexible and optical devices.

Effects of anodic layer thickness on overall performance of all-solid-state electrochromic device

In the present study, the effects of the anodic electrochromic layer employed in the all-solid-state ECD in the structure of ITO/NiO/Ta2O5/WO3/ITO/glass on the optical and electrochromic performances of the device are investigated. For this purposes, the nickel oxide films with various thicknesses were deposited onto glass and ITO-coated glass substrates by RF magnetron sputtering technique using a NiO target in pure Ar atmosphere at room temperature. The optical, structural and electrochromic properties of the NiO films with various thicknesses (140 nm, 230 nm, 310 nm and 480 nm) were investigated. The optical transmission of the films decreased as the thickness of the films increased. The X-ray diffraction patterns showed that the films were polycrystalline phase and the peak density increased with the film thickness. The optical band gap was found to decrease from 3.71 to 3.50 eV with increasing film thickness. The root-mean-square (rms) surface roughnesses of the films increased (from 1.43 nm to 2.94 nm) with increased film thickness. Coloration efficiencies and optical modulations of the NiO films were obtained for a wide spectral range. The amount of inserted/extracted charges into/from the films during bleaching/coloring were obtained as a function of the film thickness. The highest coloration efficiency (40.7 cm2/C) and optical modulation (27.8%) at a wavelength of 550 nm were obtained for the NiO film with a thickness of 480 nm. Finally, all-solid-state electrochromic devices were fabricated by using the thinnest and thickest NiO films with a configuration of ITO/NiO/Ta2O5/WO3/ITO/glass. The ECD-1 device with a thinner NiO layer showed a high optical modulation (36.4%). On the other hand, the ECD-2 with a thicker NiO layer showed a very low optical modulation (1.5%) at 550 nm. Our results indicated that the thicker NiO film exhibited better electrochromic properties in the half-cell configuration, while the thinner one showed higher optical modulation in electrochromic device fabrication with a complete-cell configuration. Therefore, the effect of the thickness of a NiO layer on the electrochromic performance of both the half-cell and complete cell configuration electrochromic coatings were investigated in detail.

Smart glass electrochromic device fabrication of uniform tungsten oxide films from its powder synthesized by solution combustion method

Recently, there has been renewed interest in tungsten oxide based electrochromic (EC) materials. A variety of studies related to these materials have been reported, however, no serious studies so far have been reported on the electrochromic effect of tungsten oxide that is synthesized by solution combustion method. The major advantage of this process is the ease and simplicity with preparing nanosize oxides. Herein, the principal objective of this project was to produce uniform and adhesive tungsten oxide thin films from as-synthesized powder by solution combustion route for EC device. Although extensive research has been carried out on EC properties of tungsten oxide, limited study exists in e-beam evaporated tungsten oxide thin film studies for smart window application. Therefore, tungsten oxide thin films were deposited from our own produced powder by e-beam evaporation. To present the effect of new powder on the properties of the thin films, their physical and morphological properties were compared with thin film deposited by commercial tungsten oxide powder. Finally, electrochemical and optical characteristics of an all-solid-state EC device with a structure of glass/ITO/SCS-WO3/Nafion/ITO/glass with high optical transmittance modulation (63% at 550 nm) was fabricated. This study has been one of the first attempts to thoroughly examine in detail of tungsten oxide powder synthesized by solution combustion method for EC active layer. These findings contribute in several ways to our understanding of solution combustion synthesized powder to be used for production of EC active layer of thin film and provide a basis for developing and designing energy-efficient EC active materials and devices.

Fabrication of Large Area Crack‐Free 2D and 3D WO3 Inverse Opal Films by “Dynamic Hard Template Infiltration Strategy”

AbstractLarge‐area crack‐free 2D and 3D WO3 inverse opal (IO) films, using a wide range of sizes of sacrificial PS spheres as colloidal crystal template, were fabricated by “dynamic hard template infiltration strategy”. First a dynamic PS opal film was formed floating on the surface of water followed by infiltration of a preformed WO3 sol underneath the PS opal film. The resultant PS/WO3 opal composite film was then deposited on various types of substrates (rigid and flexible) and 2D WO3 IO films were obtained following the removal of the PS template by chemical method. Based on this strategy, multiple layer WO3 IOs were fabricated through a layer by layer route. The WO3 IO films deposited on indium tin oxide coated conductive (ITO) substrates were used as active electrode in the fabrication of electrochromic devices, demonstrating their advanced properties for electrochromic application.

Improved performance and stability of solid state electrochromic devices with eco-friendly chitosan-based electrolytes

Development of chitosan (Ch)-based green solid polymer electrolyte was attained with addition of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) using solvent casting method for electrochromic device. In the electrochromic device configuration, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-methylthiophene) (PMeT) were used as counter polymer electrodes. The effect of chitosan/PEDOT:PSS-based electrolyte on PEDOT/PMeT-based electrochromic devices was evaluated. In order to deeply compare all electrochromic devices, electrochemical, transmittance, electrochemical impedance measurements were used. PEDOT:PSS can assist both electronic and ionic conduction leading to reduced charge transfer resistance and better electrochromic performance. Presented electrochromic device with use of PEDOT:PSS displayed higher optical modulation (20.6%/±1 V; 32.2%/±2 V at 650 nm, faster response times (coloration time (tc): 0.1 s/±1 V, 0.24 s/±2 V and bleaching time (tb): 0.11 s/±1 V, 0.52 s/±2 V)). These results signify that the addition of PEDOT:PSS to electrolyte is useful for improved electrochromic characteristics as the electrolyte for the fabrication of electrochromic device.

Preparation and characterization of nanocrystalline tungsten oxide thin films for electrochromic devices: Effect of deposition parameters

Abstract In the present work, we have reported on deposition of tungsten oxide thin films by DC magnetron sputtering for the fabrication of electrochromic device and the effect of deposition parameters like oxygen partial pressure and substrate temperature on optical, structural, morphological and electrochromic properties of the films. The films were deposited on to Silicon, Quartz and ITO coated glass plates to characterize the properties of the films. The thickness of the films was measured from stylus profilometry and it is 350 nm and the optical transmittance of the films was in the range of 53–75% in the visible region, measured from UV–Visible spectrometer. The films are nanocrystalline in nature and crystallinity improved by increasing the substrate temperature analyzed from X-Ray diffraction. The morphology and composition of the films was determined from SEM, AFM and EDS and the films are nanocrystalline in nature of the size 38 nm and stoichiometric. The phase composition and bonding in the films were investigated from FTIR and Micro-Raman studies. The diffusion coefficient and coloration efficiency of the films were measured from cyclicvoltammetry studies and the values are 3.61 × 10−18 cm2/s and 34.35 cm2/C at 550 nm.

RF sputtered electrochromic wool textile in different liquid media

A flexible e-textile has growing curiosity in the NEMS and MEMS of science and technology. This work has been done fabrication of electrochromic device based on wool textile substrates. Indium tin oxide (ITO) or platinum (Pt) and tungsten oxide WO3 film layers were used as conductive and the electrochromic material, respectively. All active layers were coated onto the wool textile surface by using Radio Frequency (RF) magnetron sputtering technique. The surface morphologies of all samples were investigated by using Scanning Electron Microscopy/Energy-dispersive X-ray spectroscopy (SEM/EDX) analysis. Characteristic properties of electrochromic electrodes were compared for two type electrolyte systems including Li+ cation source effect lithium perchlorate/Propylene Carbonate (LiClO4/PC) and lithium trifluoromethane sulfonate/Propylene Carbonate (LiTRIF/PC). Promising experimental results were obtained.

Direct fabrication of electrochromic devices with complex patterns on three-dimensional substrates using polymeric stencil films

This article describes a direct fabrication technique for electrodes and further electrochromic devices with complex shapes on three-dimensional substrates.

Multichromic Polymers Containing Alternating Bi(3-Methoxythiophene) and Triphenylamine Based Units with Para-Protective Substituents

Two novel triphenylamine-based thiophene derivative monomers, 4-cyano-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine and 4-methoxy-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine, were successfully synthesized. The corresponding polymers including poly (4-cyano-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine) and poly (4-methoxy-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine) were electrochemically synthesized and characterized by multiple test method. The electrochemical measurements and spectroelectrochemical analyses revealed that both of the two polymers had quasi-reversible redox behavior and multi-electrochromic properties. The two polymer films showed reversible electrochemical oxidation, excellent optical contrasts in NIR region (62% at 1070 nm for the first polymer, and 86% at 1255 nm for the second polymer), satisfactory coloration efficiencies and fast switching times. The research on the application of the as prepared polymer in the fabrication of electrochromic device was also conducted, employing PCMTPA or PMMTPA as the anodically coloring materials.

Cross-Linkable Fluorene-Diphenylamine Derivatives for Electrochromic Applications.

Multicolor electrochromic systems based on heat cross-linkable arylamine-substituted fluorene derivatives, FD and FDOMe, are reported. These derivatives with pendant vinyl groups have been synthesized by the Buchwald-Hartwig amination reaction and were well-characterized using various analytical and spectroscopic techniques such as NMR, ESI-MS, and single-crystal X-ray diffraction analysis. FD and FDOMe exhibited thermally activated cross-linking above their melting temperatures, which was confirmed through absorption, differential scanning calorimetry (DSC), FT-IR, and wide-angle X-ray diffraction (WAXD) techniques. Cross-linked FD films (FD-X) on ITO showed two reversible redox peaks at 0.74 and 0.91 V (versus Ag/AgCl) that correspond to the formation of radical cations and dications, respectively. The corresponding redox peaks were observed at 0.6 and 0.8 V for cross-linked FDOMe films (FDOMe-X). Spectroelectrochemical studies of the electrochromic films on ITO revealed multicolor electrochromism of FD-X (colorless-yellow-dark cyan) and FDOMe-X (colorless-brick red-blue) with a color contrast of ∼44% at 485 nm for FD-X and ∼63% at 500 nm for FDOMe-X and good switching stability between the neutral and oxidized states (>300 cycles) with low switching voltages (<0.9 V for the first oxidation and <1.3 V for the second oxidation). Furthermore, fabrication of electrochromic devices using FD-X and FDOMe-X on FTO substrate with PMMA-based solid electrolyte was demonstrated, where the devices exhibited reasonably low switching time between the redox states (<30 s) with good optical contrast.

Fabricating polypyrrole/tungsten oxide hybrid based electrochromic devices using different ionic liquids

A facile approach of polypyrrole (PPy)/tungsten oxide (WO3) composites electrosynthesized in ionic liquids for fabrication of electrochromic devices is discussed. The electrochromic properties of PPy/tungsten oxide nanocomposite films (PPy/WO3) prepared in the presence of four different ionic liquids, 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4), 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF6), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIMTFSI), and 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMPTFSI) were investigated in detail. Cyclic voltammetry results revealed that PPy/WO3 nanocomposite films have much more electrochemical activity than those of WO3 and PPy film. The electrochromic contrast, coloration efficiency, and switching speed of the composite films were determined for electrochromic characteristics. The maximum contrast and the maximum coloration efficiency values were measured as 33.25% and 227.89 cm2/C for the PPy/WO3/BMIMTFSI composite film. Copyright © 2015 John Wiley &amp; Sons, Ltd.

High Efficient Electrochromic WO3 Nanofibers

Hydrothermal synthesis facilitates the hierarchical growth of hexagonal WO3 nanofibers that consist of high interactive space and surface area. Prime processing parameters known as hydrothermal temperature, time and directional growth reagent sodium chloride concentration synchronizes both of the hexagonal crystal structure and nanostructured 1D fibrous morphology of WO3. Hexagonal nanofiber WO3 has specific surface area of 25.2m2/gm and their dip coated WO3/ITO glass substrate exhibits uniform thickness, interconnectivity and high degree of electrochromic properties. The optimized dip coated electrode depicts the current density of 8.9mA/cm2, excellent cyclic stability and the coloration efficiency in high acidic electrolyte solution. Crystal structure, morphology formation and their electrochromic responses are illustrated to support the fabrication of electrochromic device.