Smart glass electrochromic device fabrication of uniform tungsten oxide films from its powder synthesized by solution combustion method (original) (raw)
Related papers
Journal of Materials Chemistry, 2007
Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide (colouring under charge insertion) and nickel oxide (colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition (by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni 2 O 3 . It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural ''smart'' windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.
Electrodeposition of nano-granular tungsten oxide thin films for smart window application
Materials Letters, 2014
Tungsten oxide (WO 3 ) thin films have been electrodeposited in a solution containing tungsten and ethanol-water. The structural, morphological and electrochromic properties of electrodeposited WO 3 thin film were studied. The results indicate that electrodeposited WO 3 thin film exhibited amorphous nature, closed packed nano-granular morphology, good coloration efficiency of 140.79 cm 2 /C and visible high transmittance of 94.63%.
Electrochromism in tungsten oxide thin films prepared by chemical bath deposition
Journal of Electrochemical Science and Engineering, 2017
Tungsten oxide (WO3) thin films were prepared by a simple, economical, chemical bath deposition method onto fluorine doped tin oxide (FTO) coated glass substrates. The electrochemical properties of the films were characterized by cyclic voltammetry. The obtained films exhibited electrochromism, changing color from initially colorless to deep blue, and back to colorless. Visible transmittance spectra of (WO3) films were recorded insitu in their both, bleached and colored states. From those spectra, absorption coefficient () and the optical energy gaps were evaluated. The dependence of the optical density on the charge density was examined and the coloration efficiency () was calculated to be 22.11cm 2 C-1. The response times of the coloring and bleaching to an abrupt potential change from-2.5 V to +2.5 V and reverse, were found to be 9.3 and 1.2 s respectively. The maximum light intensity modulation ability of the films, when the AM1.5 spectrum is taken as an input, was calculated to be about 50 %.
Synthesis and Characterization of Macroporous Tungsten Oxide Films for Electrochromic Application
Journal of Sol-gel Science and Technology, 2003
Macroporous tungsten oxide films have been prepared by combining a nonhydrolytic sol-gel method with a molecular assembly templating strategy. The material has been prepared by hydrolysis of an ethanolic solution of tungsten ethoxide in the presence of polyethylene glycol (PEG), followed by calcination of the dip-coated films. AFM images indicated that an important morphological diversity can be obtained by simply varying the amount of PEG in the coating solution and the conditions of the heat-treatment. The formation of nanostructures of controlled shapes and patterns (fibrils or striped phases) with relatively uniform channel spacings is accounted for by strong hydrogen bonding interactions between the PEG and the partially hydrolyzed tungsten oxide oligomers. XRD and FTIR data showed that PEG delays the crystallization of WO3. When compared to sol-gel prepared tungsten oxide fims prepared without PEG, the coloration efficiency of the macroporous films appears to be significantly improved especially in the near-infrared region.
A simple method for chemical bath deposition of electrochromic tungsten oxide films
Materials Chemistry and Physics, 2007
A simple, economical, chemical bath method for depositing tungsten oxide films has been developed. The films have been prepared from aqueous solution containing Na2WO4·2H2O and diethyl sulfate in slightly acidic media at 90–95 °C on fluoride doped tin oxide substrates (FTO). The X-ray analysis clearly showed that the films do not correspond to any known tungsten oxide with its experimental d-values and in the text the composition is denoted as WOx. The thin films durability was tested in aqueous solution of LiClO4 (0.1 mol dm−3) for about 7000 cycles followed by cyclic voltammetry which confirmed that the coated material is highly stable. The optical transmittance spectra of colored and bleached states showed significant change in the transmittance, which make these films favorable for electrochromic devices.
Iranian Journal of Physics Research, 2019
Tungsten oxide (WO3) thin layers were prepared on Fluorine Tin Oxide glass using the electrodeposition method. WO3 layers were evaluated as a function of the deposition time (480 s, 600 s, 660 s and 720 s). SEM results showed that by increasing the deposition time, a gradual decrement in cracks on their surface occurred. The electrochromic properties of the WO3 thin layers were investigated in a nonaqueous LiClO4-PC electrolyte by means of optical transmittance, cyclic voltammogram (CV) measurements. The WO3 thin layer with the deposition of time 600 s exhibited a noticeable electrochromic performance with the variation of transmittance being up to 58.26% at 633nm. The CV measurements also revealed that the WO3 thin layer with the deposition time of 600 s had a high electrochemical reaction activity and reversibility due to its highly porous structure.
Model of electrochromic and related phenomena in tungsten oxide thin films
Journal of Solid State Electrochemistry, 2003
We have developed a model of electrochromic and related phenomena in tungsten oxide thin films based on the assumption that the constitution of such films is heterogeneous and built up of nanosized particles, pores and adsorbed substances (mainly water). It is discussed why a high-efficiency reversible blue colour is observed in amorphous tungsten oxide films (α-WO3 films) as well as why such porous thin films with polycrystalline or amorphous constitution and with a variety of particle properties can be easily obtained by a physical vapour deposition process in a low-pressure atmosphere in the presence of water. A substrate temperature in the range 450–550 K corresponds to some plateau on the water desorption curves which divided physically adsorbed water from chemically adsorbed water. Two types of structural units based on tetrahedrally and octahedrally coordinated tungsten ions have the main role in the formation of the film constitution. The tetrahedral structural units have a glass-forming function, but the octahedral ones have a modification function. From the electrochemistry point of view, the internal multiphase interfaces in such films are distributed multiphase electrodes. The adsorbed water together with defects of the oxide particles provide reagents for reversible coloration reactions in the film. The colour centres can be induced thermally (oxygen nonstoichiometry) or electrically (injected ions) or by radiation (photoinjected hydrogen). The electrochromism and related phenomenon of α-WO3 films can be directly related to ion insertion/extraction processes controlled by external forces.
Studies on electrochromic smart windows based on titanium doped WO3 thin films
Thin Solid Films, 2007
Titanium doped tungsten oxide thin films have been deposited by co-sputtering metallic titanium and tungsten in the presence of argon and oxygen. The oxygen chamber pressure was varied in the range 1 × 10 − 3-4 × 10 − 3 mbar keeping the sputtering power of titanium and tungsten constant at 2 W/cm 2 and 3 W/cm 2 respectively. The effect of oxygen chamber pressure on the electrochromic (EC) properties of titanium doped WO 3 has been investigated in three steps. First, the material properties of EC film were investigated by XRD, SEM, and UV-Vis spectrophotometer; the thickness and the optical constants were estimated from the reflectance measurements. Second, the electrochromic behavior of the EC films was characterized by cyclic voltammetry (CV) using 1.0 M HCl as electrolyte. The optical modulation (ΔT) and coloration efficiency (CE) of the titanium doped tungsten oxide thin film deposited at an O 2 pressure of 4 × 10 − 3 mbar was found to be better with typical values of ΔT = 70% and CE = 66 cm 2 /C (at λ = 550 nm). Finally, EC devices consisting of five layers (Glass/ITO/Ti:WO 3 /Ta 2 O 5 /NiO/ITO) have been fabricated and tested.
Surface and Coatings Technology, 2005
A change of water vapour partial pressure from 0 to 4 Pa was carried out in order to prepare sputtered tungsten oxide compounds with various oxygen and hydrogen concentrations. Oxygen, tungsten and hydrogen concentrations were determined by Rutherford Backscattering Spectroscopy (RBS) and by Elastic Recoil Detection (ERD) analysis. Structure of tungsten oxide films was analyzed by X-ray diffraction. At low water vapour partial pressure, the films are crystallized and WO 2 and W 3 O phases were observed. The electrochromic performances of such film/SnO 2 /glass substrate system were measured and discussed taking into account the influence of the water vapour partial pressure injected into the deposition process on the structure, chemical composition and optical properties of the films. D