High Electrochromic Efficiency Research Articles

Enhanced Contrast of WO3-Based Smart Windows by Continuous Li-Ion Insertion and Metal Electroplating.

The electrochromic WO3 smart window based on an aqueous electrolyte shows an excellent liquid/solid interface and thus can achieve a fast electrochromic response, while the aqueous electrolyte has a limited electrochemical window, which probably induces the H+ reduction and degrades the practical application. Here, we propose a strategy to modify the traditional Li+ acidic aqueous electrolyte by adding some selective inert metal ions, which not only improve the electrochromic performance but also avoid the possible production of hydrogen bubbles due to the broadened electrochemical window. Furthermore, reversible electroplating of inert metal ions will occur, leading to an enhanced optical transmission change of up to 77.5% at 500 nm and 70.4% at 700 nm. This combination of Li-ion insertion and metal electroplating in the ESW device makes it superior to all of the previous reports. The device also demonstrates high stability and high electrochromic efficiency after 1000 cycles. The current study not only emphasizes the rational design for aqueous electrolytes but also demonstrates a practical way to realize an excellent electrochromic window for practical applications.

Optical constants and electrochromic characteristics of HxMoO3 and LixMoO3 bronzes.

Ellipsometric concentration dependent data of ZxMoO3 (Z=H+, Li+) bronze thin films are interpreted from different prospects to unravel a detailed account of electrochromic characteristics. From the linear parts of the electronic energy loss functions (-1/ϵ), and from the dips in the optical density data, it is very difficult to decide about crystallographic phase shifts in these bronzes, simply because of the difficulty of the structural determination of these microcrystalline materials. MoO3 bronze thin films are found to have high electrochromic efficiency, and therefore require higher charge density, and less substoichiometry, to obtain the same contrast ratio as observed in tungsten bronze thin films. The values of oscillator strengths, dipole strengths, and the degrees of delocalization of polaron wave functions have been calculated at different doping levels, and all are found to reveal the characteristics of localized in-bandgap states of electrons, and do not give any symptom of formation of Bloch states in these bronzes even at higher values of concentration, x.

Carbon nanotube thin films modified with a mixture of Prussian blue and ruthenium purple: combining materials and properties

Thin films of iron-filled carbon nanotubes prepared through the liquid/liquid interfacial method were modified with a mixture of hexacyanometallates (HCMs) Prussian blue and ruthenium purple. Two different approaches were used in order to obtain both materials in the composites, based on a direct reaction starting from a mixture of both precursors or a step-by-step deposition of each compound. The modified films were characterized by cyclic voltammetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and UV-Vis spectroscopy, confirming the formation of a mixture of HCMs in both methods of synthesis. Stability studies were evaluated in different supporting electrolytes, and composites presented good performances due to carbon nanotube stabilization. Electrochromic properties were also evaluated for selected composites, showing high electrochromic efficiency and stability.

Electrochromic modulation of near-infrared light by WO3 films deposited on silver nanowire substrates

Silver nanowire (Ag NW) transparent conductive electrodes with high conductivity and optical transmittance are fabricated. Then, WO3 films are deposited on Ag NW electrodes by an electrochemical deposition method. The WO3/Ag NW films act as obvious optical modulators in the visible region. More importantly, the WO3/Ag NW films have distinct advantage on NIR modulation over conventional WO3/ITO electrode. Meanwhile, the WO3/Ag NW films own high electrochromic efficiency of 86.9 cm2 C−1 at NIR region of 1100 nm. Furthermore, electrochromic devices (ECDs) based on Ag NW substrates are fabricated in this study, which exhibit excellent cycling stability and distinct modulation of near-infrared light compared with ITO-based ECDs. This work is the first study that reports the application of Ag NW-based electrochromic films and electrochromic devices in modulation of NIR light. It exhibits bright prospects that the electrochromic materials deposited on Ag NW electrodes may find potential application in thermal control and emission detectors for spacecraft.

Hydrothermal Growth of Hierarchical NiO Nanostructures and Their Application in a Complemetary Electrochromic Device

NiO is one of the most popular electrochromic (EC) materials due to its high EC efficiency, good cyclic reversibility and low material cost. As an anodic EC material, NiO can be used as a complementary electrode with WO3, where the optical modulation increases due to the simultaneous modulation of both electrodes. We have demonstrated that porous NiO nanostructures film can be grown directly on FTO-coated glass substrates using a template-free hydrothermal technique. A variety of NiO nanostructures, including nanoflake array, nanorod-based networks, hexagonal nanoplates and hierarchical microflakes, could be obtained by tuning the composition of the precursor solution. Among the obtained NiO nanostructures, hierarchical structure holds the advantages of both nanometre-sized building blocks and microsized assemblies. Thus, the complementary EC device based hierarchical NiO microflake and self-weaving WO3 nanoflake film shows a high optical modulation (73.2% at 550 nm), large coloration efficiency (146.9 cm2 C-1 at 550 nm) and fast switching responses with a coloring time of 1.8 s and a bleaching time of 3.2 s, making it attractive for practical applications.

Synthesis and near infrared electrochromic properties of metallodithiolene complexes

Four metallodithiolene complexes [4,8-bis(octyloxy)-1,3,5,7-tetrathia]·di[1,1′-bis(diphenylphosphino)ferrocene·palladium(II)] (3), [4,8-bis(octyloxy)-1,3,5,7-tetrathia]di[1,3-bis(diphenylphosphino)propane·nickel(II)] (4), [4,8-bis(octyloxy)-1,3,5,7-tetrathia] ·[1,1′-bis(diphenylphosphino)ferrocene·palladium(II)]·[1,3-bis(diphenylphosphino)propane·nickel(II)] (5) and di[4,8-bis (octyloxy)-1,3,5,7-tetrathia]·[1,1′-bis(diphenylphosphino)ferrocene·palladium(II)]·nickel(II) (6) were synthesized and the near-infrared (NIR) electrochromic properties were studied. The spectroelectrochemical spectra and the electrochromic parameters such as optical contrast, switching time, optical density change, electrochromic efficiency and optical attenuation of complexes 3–6 were investigated in detail. The symmetric binuclear complex 4 showed relatively high electrochromic efficiency of 63.0 and 75.4 cm2/C both in the two oxidation states. The complexes exhibited excellent electroactive/electrochromic stability characterized by chronoamperometry (>4000 cyclic switches).

Electrodeposited non-stoichiometric tungstic acid for electrochromic applications: film growth modes, crystal structure, redox behavior and stability

Bath composition for cathodic electrodeposition of non-stoichiometric hydrated tungstic acid with high electrochromic efficiency is optimized with account for selective electroreduction of certain isopolytungstates. XRD data for thin electrodeposited films and chemically synthesized bulk tungstic acid dihydrate are compared in the context of reversible oxidation and reduction in hydrogen atmosphere, in presence of Pt catalyst. XPS and ТЕМ techniques are attracted to understand the nature of reversible and less reversible transformations of films in the course of their storage and operation.

An Electropolymerized Crystalline Film Incorporating Axially-Bound Metalloporphycenes: Remarkable Reversibility, Reproducibility, and Coloration Efficiency of Ruthenium(II/III)-Based Electrochromism.

Oxidative electropolymeization of an axially bound, bithiophene-pyridine complex of ruthenium(III)-porphycene [Ru(TPrPc) (btp)2]PF6 (1) gives a submicrometer-thick, polymeric film on an ITO electrode with a crystalline morphology. The polymeric film, the first example of axially linked multimetalloporphycene coordination arrays, exhibits highly stable and reproducible electrochromic response with high electrochromic efficiency upon electrochemical control over the metal-centered electron transfer process (Ru(II)/Ru(III)).

Electrochromic Properties of a Metallo-supramolecular Polymer Derived from Tetra(2-pyridyl-1,4-pyrazine) Ligands Integrated in Thin Multilayer Films

The electrochromic behavior of iron complexes derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) and a hexacyanoferrate species in polyelectrolytic multilayer adsorbed films is described for the first time. This complex macromolecule was deposited onto indium-tin oxide (ITO) substrates via self-assembly, and the morphology of the modified electrodes was studied using atomic force microscopy (AFM), which indicated that the hybrid film containing the polyelectrolyte multilayer and the iron complex was highly homogeneous and was approximately 50 nm thick. The modified electrodes exhibited excellent electrochromic behavior with both intense and persistent coloration as well as a chromatic contrast of approximately 70%. In addition, this system achieved high electrochromic efficiency (over 70 cm(2) C(-1) at 630 nm) and a response time that could be measured in milliseconds. The electrode was cycled more than 10(3) times, indicating excellent stability.

Electrochemical and electrochromic response of poly(thiophene-3-acetic acid) films

Abstract Thiophene-3-acetic acid has been polymerized in chloroform by a chemical method using FeCl 3 as oxidant. The films were prepared casting the solubilized polymer on ITO electrodes and studied using cyclic voltammetry, chronoamperometry and spectroelectrochemistry. During the potential sweep, an electrochromic process is observed in which the film color changes from red to black. High electrochromic efficiency was observed for more than 600 cycles, although it decreases to 73% of the initial value. Until 264 cycles, the electrochromic efficiency at 750 nm is stable and the value is 242 cm 2 C −1 .

Tungsten Oxide Films of High Electrochromic Efficiencies Obtained by Deposition

Amorphous tungsten oxide films of high electrochromic efficiency were produced by a chemical vapor deposition technique in which the precursors of film formation are generated at the surface of a heated tungsten filament by reactions of tungsten with oxygen. The film deposition rate was determined as a function of the filament temperature and oxygen pressure. Molecular structure investigations using X-ray photoelectron spectroscopy revealed that the tungsten oxide was in the WO 3 stoichiometry. The electrochromic properties of the films were studied for Li + intercalation. Optical efficiencies as high as 78 and 125 cm 2 /C at 632.8 and 950 nm, respectively, and absorbance changes from 0.07 to 1.1 were measured between the bleached and the colored states at 632.8 nm.

Electrochromic properties of NiO xH y thin films

NiO x H y films were prepared by DC magnetron sputtering in H 2/O 2 atmosphere. NiO x H y coatings with transparency and high electrochromic efficiency were obtained by changing H 2 content. A 60 nm thick NiO x H y film with transmittance of 0.57 (as-deposited state), 0.78 (bleached state) and 0.24 (coloured state) at wavelength of 550 nm was deposited in an atmosphere of H 2(60%)+O 2(40%). Analysis of infrared spectra (6000∼2400 cm −1) showed that the absorption peaks for bleached and colored states are associated with free ‘OH’ and OH stretching vibrations, respectively. XPS Ni2p core level spectra of colored NiO x H y film exhibited a peak at 856.2±0.2 eV which is attributed to Ni 3+. Ni2p core level spectra of the bleached and as-deposited films exhibited two peaks at 856.4±0.2 and 854.6±0.2 eV which are attributed to Ni 3+ and Ni 2+.

Electrochromism in Sputtered WO 3 Thin Films

There are large variations in the properties of sputtered under different conditions and two samples sputtered from an oxide target and reactively sputtered from a metal target were compared in detail. The thin film sputtered from an oxide target was found to color and bleach rapidly in 1 M in propylene carbonate, while the thin film reactively sputtered from a metal target could be colored deeply, but bleached only slowly. By calculating the rate of change of optical density during cyclic voltammetry, it was possible to directly compare the coloration response with the current/voltage behavior of the electrodes. In both cases at least two lithium insertion reactions appear to occur. The distinction between the two reactions was especially clear in the sample sputtered from a metal target, in which an insertion of high electrochromic efficiency occurred up to and then an insertion of considerably lower electrochromic efficiency up to . Although a small amount of coloration and bleaching continued to occur after switching the reactively sputtered sample to open circuit during the coloration and bleaching cycles, transmission change was largely halted by disconnecting the external current supply. The slow end to the bleach of the reactively sputtered sample corresponded to a reaction of high electrochromic efficiency.

Conducting polymers as electrochromic materials

The data of a comparative study on electrochromic phenomena of poly-3methylthiophene, poly-2,2′bithiophene and poly-dithieno(3,2-b;2′,3′-d) thiophene in propylene carbonate with 1M LiClO 4 are reported. The best results were found with polymethylthiophene. This electrosynthesized conducting polymer is a very promising electrochromic material with high electrochromic efficiency, fast switching response, long life-time and good optical memory.