Showing papers on "Electrochromism published in 2007"

TiO2 nanotubes: Self-organized electrochemical formation, properties and applications

Abstract: The present paper gives an overview and review on self-organized TiO2 nanotube layers and other transition metal oxide tubular structures grown by controlled anodic oxidation of a metal substrate We describe mechanistic aspects of the tube growth and discuss the electrochemical conditions that need to be fulfilled in order to synthesize these layers Key properties of these highly ordered, high aspect ratio tubular layers are discussed In the past few years, a wide range of functional applications of the layers have been explored ranging from photocatalysis, solar energy conversion, electrochromic effects over using the material as a template or catalyst support to applications in the biomedical field A comprehensive view on state of the art is provided

Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

Abstract: 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 Ni2O3. 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.

Electrochromism and Electrochromic Devices

Abstract: Electrochromic materials, both organic and inorganic, have widespread applications in light-attenuation, displays and analysis. Written in an accessible manner, this book provides a comprehensive treatment of all types of electrochromic systems and their many applications. Coverage develops from electrochromic scope and history to new searching presentations of optical quantification and theoretical mechanistic models. Non-electrode electrochromism and photo-electrochromism are summarised, with updated comprehensive reviews of electrochromic oxides (tungsten-trioxide particularly), metal co-ordination complexes and metal-cyanometallates, viologens and other organics; and more recent exotics such as fullerenes, hydrides, and conjugated electroactive polymers are also covered. The book concludes by examining device construction and durability. With an extensive bibliography, recent advances in the field, modern applications and a step-by-step development from simple examples to sophisticated theories, this book is ideal for researchers in materials science, polymer science, electrical engineering, physics, chemistry, bioscience and (applied) optoelectronics.

Printable All-Organic Electrochromic Active-Matrix Displays

Abstract: All-organic active matrix addressed displays based on electrochemical smart pixels made on flexible substrates are reported. Each individual smart pixel device combines an electrochemical transisto ...

Highly stable anodic green electrochromic aromatic polyamides: synthesis and electrochromic properties

Abstract: A 4-methoxy-substituted triphenylamine containing the aromatic diamine, 4,4′-diamino-4″-methoxytriphenylamine (2), was synthesized by the caesium fluoride-mediated condensation of p-anisidine with 4-fluoronitrobenzene, followed by palladium-catalyzed hydrazine reduction of the dinitro intermediate. A series of new polyamides with pendent 4-methoxy-substituted triphenylamine (TPA) units having inherent viscosities of 0.27–1.39 dL g−1 were prepared via the direct phosphorylation polycondensation of various dicarboxylic acids and the diamine (2). All the polymers were readily soluble in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into tough and flexible polymer films. These aromatic polyamides had useful levels of thermal stability associated with their relatively high softening temperature (242–282 °C), 10% weight-loss temperatures in excess of 470 °C, and char yields at 800 °C in nitrogen higher than 60%. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited reversible oxidation at 0.73–0.79 V versus Ag/AgCl in acetonitrile solution, and revealed excellent stability of electrochromic characteristics with a color change from colorless to green at applied potentials ranging from 0.00 to 1.05 V. These anodically polymeric electrochromic materials not only showed excellent reversible electrochromic stability with good green coloration efficiency (CE = 374 cm2 C−1) but also exhibited high contrast of optical transmittance change (ΔT %) up to 85% at 787 nm and 30% at 391 nm. After over 1000 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics.

Electro-optical element including IMI coatings

Abstract: An electrochromic element comprises a first substrate having a first surface and a second surface opposite the first surface, a second substrate in spaced-apart relationship to the first substrate and having a third surface facing the second surface and a fourth surface opposite the third surface, and an electrochromic medium located between the first and second substrates, wherein the electrochromic medium has a light transmittance that is variable upon application of an electric field thereto. The electrochromic element further comprises a transparent electrode layer covering at least a portion of at least a select one of the first surface, the second surface, the third surface, and the fourth surface, wherein the transparent electrode layer comprises an insulator/metal/insulator stack. The materials utilized to construct the insulator/metal/insulator stack are selected to optimize optical and physical properties of the electrochromic element such as reflectivity, color, electrical switch stability, and environmental durability.

A novel electrochromic polymer synthesized through electropolymerization of a new donor-acceptor bipolar system

Abstract: We have synthesized a novel 9,9‘-spirobifluorene-cored donor−acceptor (D−A) bichromophore system in which the electron-donating (D) moieties are triphenylamine (TPA) and carbazole (CBZ) groups and the electron-withdrawing (A) moieties are 1,3,4-oxadiazole (OXD) groups. The electron-deficient OXD groups efficiently blocked the radical cations delocalization between the two terminal TPA groups, rendering the electropolymerization of the TPA groups feasible. The resulting polymer could be cross-linked further at higher oxidation potentials through electrodimerization occurring at the C3 and C6 positions of the CBZ group. The polymer film obtained exhibited reversible electrochemical oxidation, accompanied by strong color changes with high coloration efficiency and contrast ratio, which could be switched through potential modulation.

Fabrication of nanostructured functional materials using exfoliated nanosheets as a building block

Abstract: A variety of layered transition metal oxides and layered double hydroxides have been exfoliated into unilamellar nanosheets such as Ti 0.91 O 2 , Ca 2 Nb 3 O 10 , MnO 2 , and M 1-x II Al x (OH) 2 (M II =Mg, Co, Zn, Ni). The exfoliation was promoted via the high degree of swelling driven by intercalation of quaternary ammonium ions for the layered oxides and solvation with formamide for the hydroxides. Various characterizations revealed very high two-dimensional anisotropy for the nanosheets thus obtained; a thickness of around 1 nm vs. a lateral size of submicrometers or larger. These nanosheets can be assembled or organized through various solution-phase processings to produce a range of nanostructured materials. Addition of electrolytes into a colloidal suspension of nanosheets promotes their restacking, yielding a flocculate. The combination of nanosheets and some counterions through this route led to a range of nanocomposites which exhibited fluorescent, photocatalytic, and electrochemical properties. On the other hand, the nanosheets can be deposited layer-by-layer with suitable polyelectrolytes to produce multilayer ultrathin films, in which the nanoarchitecture can be precisely controlled. The multilayer films of Ti 0.19 O 2 and MnO 2 nanosheets showed photoinduced superhydrophilicity and electrochromic properties, respectively. Furthermore, the films of ferromagnetic titania nanosheets such as Ti 0.8 Co 0.2 O 2 and Ti 0.6 Fe 0.4 O 2 were found to show very high magneto-optical properties at room temperature.

A Poly(3,4‐alkylenedioxythiophene) Electrochromic Variable Optical Attenuator with Near‐Infrared Reflectivity Tuned Independently of the Visible Region

Abstract: Disubstituted poly(3,4-propylenedioxythiophene)s (PProDOTs) exhibit large electrochromic contrasts in the near infrared (NIR) while showing essentially no color change in the visible region when incorporated into a reflective device platform. The source of this is attributed to a conductive front that propagates through the insulating polymer film, extending from the polymer/electrode interface to the top of the polymer film. A utility of the large contrasts seen in the NIR region is demonstrated with application of the device as an electrochromic variable optical attenuator modulating fiber-optic signals for optical telecommunications. With bis(ethylhexyloxy)-substituted PProDOT as the active electrochromic polymer in the device, an optical attenuation of 11 dB at the telecommunications wavelengths of 1.31 and 1.55 μm is achieved with only a 0.1–0.2 dB optical loss in the bleached state. Other favorable properties include optical memory in the absorbing state, switching speeds of under 1 s, a low operating voltage of ±1.2 V, and an improved processability that allows spray-casting from organic solvents.

New, Highly Stable Electrochromic Polymers from 3,4-Ethylenedioxythiophene−Bis-Substituted Quinoxalines toward Green Polymeric Materials

Abstract: Two new highly stable electrochromic polymers, poly(5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-di(thiophen-2-yl)quinoxaline) (PDETQ) and poly(5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)quinoxaline) (PDEQ) were synthesized, and their potential use as neutral state green polymeric materials was investigated. Spectroelectrochemistry showed that both polymers reveal two distinct absorption bands as expected for this type of donor–acceptor polymer, at 410 and 660 nm for PDEQ and 405 and 780 nm for PDETQ. The colorimetry analysis revealed that while PDEQ has a green-blue color, PDETQ showed a saturated green color in the neutral state which is a unique property of conjugated polymers for the completion of the RGB color system. Both polymers have excellent switching properties with satisfactory optical contrasts and very fast switching times. In addition, via both electrochemical and spectral analyses PDETQ was proven to be an n-type dopable polymer. Outstanding optical contrasts in the NIR regi...

Novel Organosoluble Poly(pyridine−imide) with Pendent Pyrene Group: Synthesis, Thermal, Optical, Electrochemical, Electrochromic, and Protonation Characterization

Abstract: A new diamine containing a pyridine heterocyclic group and a pyrene substituent, 4-(1-pyrene)-2,6-bis(4-aminophenyl)pyridine (PBAPP), was synthesized and used in a preparation of poly(pyridine−imide) by direct polycondensation with 4,4‘-hexafluoroisopropylidenediphathalic anhydride (6FDA) in N-methyl-2-pyrrolidinone (NMP). The poly(pyridine−imide) derived from diamine (PBAPP) was highly soluble in several solvents such as THF, NMP, DMAc, DMF, pyridine, DMSO, and cyclohexanone at room temperature or upon heating at 70 °C and exhibited good thermal stability both in nitrogen and air (Td10>520 °C) and a high dielectric constant of 4.32 at 1 kHz. The poly(pyridine−imide) could be cast into a flexible and tough film from DMAc solution. The poly(pyridine−imide) film had a tensile strength of 118 MPa and a tensile modulus of 2.2 GPa. The optical properties exhibited the UV−vis absorption bands at the region of 200−400 nm and possessed strong orange fluorescent (560 nm) after protonated with protic acid.

Fast switchable electrochromic properties of tungsten oxide nanowire bundles

Abstract: The authors prepared uniformly shaped WO2.72 nanowire bundles using the solvothermal synthesis method. They investigated the potential of the WO2.72 nanowire bundles to be used as a cathode electrode for electrochromic devices and the effect of the Li+ insertion (or extraction) kinetics and diffusion of Li+. An electrode consisting of arrays of WO2.72 nanowire bundles was formed and used in an experiment using the Langmuir-Blodgett technique. The one-dimensional nanostructure of WO2.72 has a high Li-ion diffusion coefficient (∼5.2×10−11cm2∕s) and low charge transfer resistance (∼28.6Ω), which result in its having a fast electrochromic response time (coloring time 55cm2∕C).

Electrochromic Stability of WO3 Thin Films with Nanometer-Scale Periodicity and Varying Degrees of Crystallinity

Abstract: Electrochromic tungsten oxide (WO3) thin films with nanometer-scale porosity have been synthesized via a sol−gel procedure making use of evaporation-induced self-assembly. According to wide-angle X-ray scattering data combined with electrochemical analyses, the degree of crystallinity ranging from fully amorphous to 100% crystalline can be adjusted by straightforward annealing. The three-dimensional cubic pore structure is thereby almost not affected. Aside from the material characterization, in this work we specifically focus on the overall electrochemical and electrochromic behavior (coloration efficiency, charge capacity, etc.) upon changes in the operating temperature. As a main result, only the mesoporous highly crystalline WO3 films display long-term cycling stability under realistic environmental conditions. We further demonstrate that sufficient crystallinity is needed to ensure stability of the inherent electrochemical properties at high operating temperatures (up to 70 °C). Thus, only the WO3 fi...

A Solution‐Processable High‐Coloration‐Efficiency Low‐Switching‐Voltage Electrochromic Polymer Based on Polycyclopentadithiophene

Abstract: A solution processable electrochromic (EC) polymer, poly(4,4-dioclyl-cyclopenta [2,1 -b:3,4-b']-dithiophene) (PDOCPDT) is prepared by means of chemical oxidative polymerization of the corresponding monomer. The HV vis spectrum of the spin-coated PDOCPDT film displays an absorption maximum of 580 nm. Although the polymer is deep blue in its neutral state, it turns to transparent bluish after being oxidized. PDOCPDT film (thickness 120 nm) exhibits high coloration efficiency (CE)-as high as 932 C cm -2 at 580 nm low response time (0.75 s), high optical density optical density (0,75 at 580 nm), and high-level stability for long term switch (it switches repetitively 1000 times with less than 8% contrast loss). The electrochemical stability and redox pontentials of PDOCPDT films are independant of film thickness (50-180 nm) and active area (up in 2 cm x 2 cm). Nevertheless, optical contrast increases as the film thickness increases, although the CE and response time changes irregularly with the film thickness. The good EC properties combined with the easy film fabrication proces make PDOCPDT a notable candidate for application in EC devices (ECDs) A simple transmissive-type ECD with good CE using PDOCFDT film as an active layer is also demonstrated.

From spinel Mn3O4 to layered nanoarchitectures using electrochemical cycling and the distinctive pseudocapacitive behavior

Abstract: In this letter the authors show the structure transformation from distorted spinel Mn3O4 to layered structure birnessite by cyclic voltammetry (CV) cycling in aqueous Na2SO4 using the high temperature (900°C) treated manganese oxide film as the electrode. The process is a dynamic-potential activated procedure, which causes the formation of sheet-shaped nanoarchitectures. During the cycling process, the specific capacitance of manganese oxide increases by more than 20 times, and the resulting film after 1000 CV cycles shows good power capability.

Defunctionalization of Ester-Substituted Electrochromic Dioxythiophene Polymers

Abstract: This work demonstrates a simple process to form insoluble poly(3,4-propylenedioxythiophene) (Poly[ProDOT]) films by defunctionalization of a soluble form, which is useful in the fabrication of multilayer polymer devices. Three new ester disubstituted Poly[ProDOTs], soluble in common organic solvents, including chloroform, methylene chloride, toluene, tetrahydrofuran, and ethyl acetate, have been synthesized by oxidative polymerization using iron(III) chloride. These Poly[ProDOT-diesters] have the expected repeat unit stuctures along with GPC determined number-average molecular weights ranging from 9000 to 12 000 g mol-1. Dilute polymer solutions in toluene exhibited red fluorescence with quantum efficiencies from 0.24 to 0.32. Homogeneous thin films were formed by spray casting polymer solutions onto ITO coated glass slides and compared to films prepared by electropolymerization. These Poly[ProDOT-diesters] are electroactive, switching from a dark blue-purple to a transmissive sky blue when potentials are...

Electro-optical element including metallic films and methods for applying the same

Abstract: A method for manufacturing an electrochromic element comprises providing a first substrate having first and second surfaces and a first edge surface, providing a second substrate having third and fourth surfaces and a second edge surface, the third surfaces facing the second surface, providing an electrochromic medium located between the first and second substrates, the medium having a light transmittance that is variable upon application of electric field thereto, applying a conductive layer on a portion of at least one of the surfaces, wherein applying the layer is accomplished at substantially atmospheric pressure, and applying at least one of metallic particles, an organometallic, a metallo-organic, and combinations thereof, wherein the conductive layer has a bulk resistivity of greater than or equal to 150 microohm•cm. The conductive layer may be applied via ink jetting, ultrasonic spraying, auger or jet pumping.

Synthesis and Characterization of Copper Hexacyanoferrate Nanoparticles for Building Up Long-Term Stability Electrochromic Electrodes

Abstract: Nanoparticles of a Prussian blue (PB) analogue, copper hexacyanoferrate, were synthesized by using ultrasonic radiation and characterized by spectroscopic and electrochemical techniques. The nanoparticles (ca. 10 nm diameter) were immobilized onto transparent indium tin oxide electrodes by electrostatic layer-by-layer deposition. These modified electrodes showed interesting electrochromic properties, changing the coloration during the redox process from brown to orange when oxidized. The nanostructured electrode presented high stability, in contrast to that observed for PB nanoparticles; this fact must be related to the maintenance of the electrostatic assembly because the oxidized compound, CuII/FeIII(CN)6, still possesses a negative excess of charge due to the high number of cyanide groups that link the nanoparticles with the polycation, assuring the integrity of the whole electrostatic assembled film.

Optical absorption in lithiated tungsten oxide thin films: Experiment and theory

Abstract: Amorphous tungsten oxide exhibits electrochromism when intercalated with protons, lithium, sodium, and other ions. Thin films of the material were prepared by dc magnetron sputtering and then electrochemically intercalated with lithium. The optical absorption in the wavelength range of 300–2500nm was measured for a number of lithium concentrations. The optical absorption shows a maximum for lithium/tungsten ratios of 0.3–0.5. The optical spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration is consistent with an extended site-saturation theory.

Inkjet deposition and characterization of transparent conducting electroactive polyaniline composite films with a high carbon nanotube loading fraction

Abstract: We report the synthesis and inkjet processing of water dispersable polyaniline composite materials with a high carbon nanotube loading fraction. Printed films displayed good optical transparency, sheet resistance and electrochromic behaviour, allowing switching between yellow, green and blue.