Showing papers on "Electrochromism published in 1997"

High-Contrast Electrochromic Polymers from Alkyl-Derivatized Poly(3,4-ethylenedioxythiophenes)

Abstract: The syntheses of two new derivatives of 3,4-ethylenedioxythiophene (EDOT), specifically 5-octyldioxeno[2,3-c]thiophene (EDOT-C8) (2) and 5-tetradecyldioxeno[2,3-c]thiophene (EDOT-C14) (3), and their polymers are reported in this paper. Cyclic voltammetry of 2 and 3 in 0.1 M TBAP/CH3CN show irreversible monomer oxidation peaks (Ep,m) at 0.89 and 0.93 V, respectively. Multiple scans yield electroactive and conducting polymer films on electrode surfaces. The PEDOT-C8 and PEDOT-C14 formed oxidize with relatively low peak potentials at −0.22 and −0.19 V, respectively, indicating the doped form of the polymer to be quite stable. Both PEDOT-C8 and PEDOT-C14 show two reduction processes with peaks at −0.18 and −0.16 V (Ec2,p) and −0.55 and −0.36 V (Ec1,p) respectively. Optoelectrochemical studies reveal an Eg of 1.75 eV for both polymers. The polymers are electrochromic, relatively transmissive and light gray in the oxidized form, while being opaque and deep purple in the reduced form exhibiting high electrochrom...

Mott-Schottky analysis of nanometer-scale thin-film anatase TiO2

Abstract: Recently, much attention has been focused on the use of nanostructured metal oxide semiconductors for various applications, such as electrochromic windows, photocatalytic devices, lithium-ion batteries, dielectrics in integrated circuits, and dye-sensitized TiO{sub 2} solar cells. Smooth nanometer-scale films of anatase TiO{sub 2} on indium-tin oxide substrates (ITO) are obtained by electron-beam evaporation of reduced TiO{sub 2} powder. Mott-Schottky analysis shows an abrupt change in slope when the depletion layer reaches the TiO{sub 2}/ITO interface. An electrostatic model is derived, which gives a quantitative description of the observed change in slope. From the potential at which the slope changes, the dielectric constant of anatase could be accurately determined. A value of 55 is found, which is significantly lower than those reported for anatase TiO{sub 2}.

Multiply Colored Electrochromic Carbazole-Based Polymers

Abstract: We report the synthesis and electrochemical polymerization of a series of bisheterocycle-N-substituted carbazoles. These monomers exhibit low peak oxidation potentials (Ep,m) which range from 0.15 to 0.46 V vs Ag/Ag+, indicating facile polymerization. Repeated scan electrochemical polymerization for these monomers proceeds rapidly, relative to carbazole, to form stable electroactive films. Cyclic voltammetry of the polymers indicates that the films are well adhered to the electrode surface and that each of the polymers possess two distinct redox waves. At applied potentials greater than 1.15 V, a third irreversible oxidative process is observed, presumedly due to cross-linking. Optoelectrochemical analysis indicates that these polymers have an electronic bandgap (measured as the onset of the π-to-π* transition) between 2.4 and 2.5 eV. Three distinct colors are achievable by varying the redox state of the polymers suggesting potential use for multiply colored electrochromic displays. For the series of bis(...

Mechanism of WO 3 Electrodeposition from Peroxy‐Tungstate Solution

Abstract: Electrodeposition of amorphous electrochromic tungsten trioxide was studied. Good quality films were deposited cathodically onto tin‐doped indium oxide (ITO) from a water/isopropanol solution containing dissolved tungsten(VI) species. Three reducible species are present in this solution: unbound , polytungstate ions, and peroxy‐tungstate ions. The effects of the content, which is related to the age of the deposition solution, and of mass transport on the deposition current and deposition efficiency were determined and used to elucidate the mechanism of electrodeposition. Reduction of unbound and polytungstate did not result in film growth. This part of the current was under mixed diffusion‐kinetic control. The remainder of the current was due to reduction of peroxy‐tungstate and was kinetically limited. This process led to deposition. The current efficiency, defined as the number of electrons consumed by reduction of peroxy‐tungstate per W atom deposited, was about 1.6, in good agreement with the proposed deposition reaction.

Information display area on electrochromic mirrors having a third surface metal reflector

Abstract: An improved electrochromic rearview mirror for motor vehicles, the mirror incorporating an information display area by removing a portion of a reflective and conductive layer on the inside (third) surface of the back glass element of a dimming portion of the rearview mirror and aligning a display device with this information display area. The portion removed is laser ablated to leave lines devoid of reflective material separated by lines of the reflective material. The remaining lines of reflective material are in electrical contact with the remaining reflective and conductive layer on the third surface. The reflective layer forms an integral electrode in contact with the electrochromic media, and may be a single layer of a highly reflective material or may comprise a series of coatings where the outer coating is a highly reflecting material. The other electrode on the inside (second) surface of the front glass is a transparent electrode which also contacts the electrochromic media inside the mirror element.

Electrochromic medium capable of producing a pre-selected color

Abstract: An improved electrochromic device, the device incorporating an electrochromic medium that comprises at least three electroactive materials having absorption spectra that add together such that the color of the electrochromic medium can be pre-selected by individually choosing the concentrations of the at least three electroactive materials. The electrochromic medium generally maintains the pre-selected perceived color throughout its normal range of voltages when used in an electrochromic device. The at least three electroactive materials include at least one electrochemically reducible material (cathodic material), at least one electrochemically oxidizable material (anodic material) and at least one additional electroactive material which may be either an anodic or cathodic material. Thus, there are always three electroactive materials present in the medium, with at least two either being anodic or cathodic materials. The pre-selected color may be chosen from a wide variety of colors and may be, for example, red, orange, yellow, green, blue, purple. For electrochromic mirrors for motor vehicles, a presently preferred color is gray.

Photoelectrochemical study of thin anatase TiO 2 films prepared by metallorganic chemical vapor deposition

Abstract: Thin films of TiO{sub 2} have found application as antireflection coatings, transparent conductors, dielectrics, electrochromic films, and photoelectrodes. Titanium dioxide is also used as a self-cleaning coating on windows and tiles. Thin films of TiO{sub 2} have been prepared by metallorganic chemical vapor deposition. The resulting anatase films are highly resistive. By electrochemical doping, the donor density can easily be raised by two orders of magnitude, resulting in a conducting film. From optical and photocurrent measurements, an indirect bandgap of 3.26 eV is derived for polycrystalline anatase films. Electrolyte electroreflection reveals a direct optical transition of anatase at 3.8 eV. The anatase electrodes can be sensitized by zinc carboxyphenyl porphyrin.

Improvement in electrochromic stability of electrodeposited nickel hydroxide thin film

Abstract: The electrochromic nickel hydroxide thin film was anodically deposited from an aqueous solution. The effect of solution temperature, postheat-treatment temperature, and addition of cadmium on the electrochromic behavior (color/bleach durability cycle, response time, and coloration efficiency of the nickel hydroxide films in NaOH) were investigated. A significant increase in the color/bleach durability cycle from 500 (for the as-deposited film) to more than 5000 cycles (for the heat-treated film) was observed. The addition of cadmium increased the utilization of the active materials. It was found that the coloration efficiency was 40 cm{sup 2}/C and coloration and bleaching response time were 20 to 30 s and 8 to 10 s, respectively. The change in the electrochromic properties with heat-treatment temperature is discussed based on the physical and electrochemical analysis.

Towards the smart window: progress in electrochromics

Abstract: Electrochromic devices have the ability to produce reversible and persistent changes of their optical properties. The phenomenon is associated with joint ion and electron transport into/out of an electrochromic thin film, in most cases being a transition metal oxide. This paper outlines the various applications of such devices in smart windows suitable for energy-conscious architecture, in variable-reflectance mirrors, and in display devices. Critical materials issues and design concepts are discussed. The paper also covers two specific research topics: computed electronic structure of crystalline WO3 incorporating ionic species, showing how reflectance modulation emerges from a first-principles calculation; and Li+ dynamics in heavily disordered Ti oxide, illustrating how diffusion constants derived from impedance spectroscopy can be reconciled with the Anderson—Stuart model.

Architectural electrochromic pane

Abstract: This invention relates to an electrically controllable solar building pane composed of two panels spaced apart by a layer of an intermediate gas, the panel facing towards the outside of the building being constituted of a variable transmission system of the electrochromic type comprising two transparent substrates composed, notably, of glass sheets, joined together by an ion-conducting organic polymer and coated on the jointing face with transparent electrically conducting films and films of anodic and cathodic electrochromic materials.

Electrochemical and Electrochromic Behavior of Reactively Sputtered Nickel Oxide

Abstract: Nickel oxide thin films were deposited by reactive sputtering in a 20% oxygen/argon atmosphere for use as oxygen evolution catalysts in the photoelectrochemical production of hydrogen. The optical properties of the films were also characterized to evaluate their application as window layers. The polycrystalline films deposited at residual gas pressures of 6 or 10 mTorr exhibited moderate activity for oxygen evolution in 1 N KOH and pronounced coloration and bleaching during alternating anodic/cathodic bias. Properties of these films were not sensitive to growth rate over the range studied, 0.5 to 4 {angstrom}/s. In contrast, films deposited at 2 mTorr exhibited poor activity for oxygen evolution and severely limited electrochromic behavior which the authors attribute to marked changes in the morphology and crystallinity in the low-pressure films. The films grown at 6 mTorr and higher tended to be more oriented, to have a higher degree of crystallinity, and higher oxygen content. Strong linkages between the electrochemical and optical behaviors observed in this work provide new insights into the processes involved in oxygen evolution reaction catalysis and electrochromism in reactively sputtered NiO{sub x} films. The results presented indicate that reactive sites located on or near grain boundaries are responsible for both behaviors.

Electrochromism and Electrocatalysis in Viologen Polyelectrolyte Multilayers

Abstract: Polyelectrolyte multilayers were constructed from a polyviologen and poly(styrene sulfonate) using an alternating polyion solution deposition technique. In situ absorption spectroscopy showed multilayers to be strongly electrochromic. Oxygen reduction at multilayer-coated conducting glass electrodes was also shown to be facilitated.

Electrochromic thin film state-of-charge detector for on-the-cell application

Abstract: A tester for use in determining the voltage and state-of-charge of a battery. The tester can be permanently mounted on the battery and employs an electrochromic cell which changes visual appearance, for example, color or intensity of color when electrically connected across the terminals of a battery. The electrochromic cell undergoes an oxidation/reduction reaction on direct application of the DC potential of the battery. The color of the electrochromic cell can be compared with a color comparison chart to determine the condition of the battery. The tester can be permanently electrically connected to the battery or, preferably, can be connected momentarily to determine the state of the battery.

Synthesis of a novel family of electrochemically-doped vinyl polymers containing pendant oligothiophenes and their electrical and electrochromic properties

Abstract: Novel electrochemically-doped vinyl polymers containing 2,2‘:5‘,2‘‘:5‘‘,2‘‘‘-quaterthiophene, 4‘,3‘‘‘-dioctyl-2,2‘:5‘,2‘‘:5‘‘,2‘‘‘:5‘‘‘,2‘‘‘‘-quinquethiophene, and 4‘,3‘‘‘‘-dioctyl-2,2‘:5‘,2‘‘:5‘‘,2‘‘‘:5‘‘‘,2‘‘‘‘:5‘‘‘‘,2‘‘‘‘‘-sexithiophene as pendant groups were prepared by anodic polymerizations of the corresponding new vinyl monomers in the presence of tetra-n-butylammonium perchlorate as a supporting electrolyte, and their electrical and electrochromic properties were investigated. The electrochemically-doped polymers, which were obtained as deeply-colored, lustrous films on the surface of the working electrode, were identified as radical-cation salts of pendant oligothiophenes with ClO4- as a dopant, having a partially-cross-linked structure due to the coupling reaction of the radical cation of the pendant oligothiophene moiety. The electrical conductivity of these electrochemically-doped polymers increased with increasing conjugation length of the pendant oligothiophenes; the polymer containing the p...

Optical Properties of Sol-Gel Derived Vanadium Oxide Films

Abstract: Vanadium oxide gels can be made from vanadate aqueous solutions or from vanadium alkoxides. The condensation of vanadic acid gives long ribbon-like oxide particles which macroscopically orient in the same direction in aqueous sols when their concentration is larger than 0.12 mol · l-1. These anisotropic sols and gels should be considered as lyotropic nematic liquid crystals. Thick films in which ribbons align along the same direction can be deposited. These oriented coatings exhibit improved electrochemical properties as reversible cathodes for lithium batteries. Amorphous oxo-polymers are formed via the controlled hydrolysis of vanadium alkoxides. They allow the deposition of optically transparent thin films that exhibit interesting electrochromic properties and turn reversibly from yellow to green upon electrochemical reduction. Moreover these alkoxide derived films can be easily reduced into vanadium dioxide. These VO2 thin films exhibit thermochromic properties and could be used as optical switches in the infrared. The transition temperature of these VO2 films can be modified by doping the vanadium oxide with other cations.

Electrochromic device manufacturing process

Abstract: The present invention is directed to a method for manufacturing electrochromic devices (10), using laser ablation techniques. More specically, the present invention uses laser ablation to provide a simple, noncontact method of patterning electrochromic devices (230) to a controlled depth, to form an electrochromically active area (350). Furthermore, laser patterning is conducive to the formation of multiple electrochromic devices on a single substrate (44).