This work covers advances in large-area switchable glazing and flat panel displays. Large flat panels and glazing are being developed by a number of company and university groups. Certain novel flat panels display are made for electronic paper applications. Switchable glazing offers a new way of visualizing the function of a window. Switchable glazing can have a range of adjustable visible properties and shading coefficients. Technologies covered for glazing are electrochromism, suspended particles, encapsulated liquid crystals. Technologies being developed for electronic paper and certain flat display panels include electrophoretics, liquid crystals and bichromal balls. Beyond glazing applications, products based on this technology are flexible displays, electronic paper, switchable modulators, mirrors, and eyeglasses. This study covers developments from several companies including the one square meter electrochromic glazing made by Pilkington/Flabeg and Asahi/Nippon Mitsubishi Oil.

Thin films of Buckminsterfullerene exhibit a reversible electrochromic effect when electrochemically intercalated with alkali metal or alkali earth ions. The degree of reversibility depends on the ratio of intercalated ions to fullerene molecules, both in the bulk film thickness and in localized stoichiometric gradients. High ratios of ions to fullerenes product films with limited electrochromic reversibility. These films are also soluble in the polar organic electrolyte system, leading to cycling and durability issues. If the intercalating ion current is modulated, rather than continuously applied, improved durability and reversibility result. The relationship of stoichiometric gradients to intercalation ion current density and ion mobility in the fullerene film are considered, as are optimum pulse-widths. Film preparation and electrolyte preconditioning are detailed.

User-controlled photochromic devices are currently under investigation due to their unique ability to harness solar energy for coloration while retaining user control over the depth of coloration. Such devices utilize both a chromogenic electrode and a photosensitive layer. One highly active photosensitive layer of interest for this application is titania, and this paper focuses on a highly porous titania film with low scattering loss and good uniformity that is deposited from a stable colloidal suspension. The stability of the suspension along with the low temperature heat treatment and ease of coating by dip-coating provide an attractive method for the deposition of these films. The performance of a user-controlled photochromic device containing such films is described.

V_l-x-yW_xTi_yO₂ (0 < x < 0.02, y equals 0.03, 0.10) thin films were fabricated by spin-coating of polyoxometalate solution and successive thermal treatment in a reduction atmosphere. We investigated the films' thermochromic properties by measuring absorbance as a function of temperature. The film thus obtained had good thermochromic properties with large absorbance changes in the infrared region. Doping with Ti for VO₂ raised the transition temperature (T₁) and reduced the width of the hysteresis loop (W_h). In the case of doping with W and Ti for VO₂, both T_t and W_h were lowered. The rate (approximately 10 degree(s)C/at.%-W) of T_t-lowering by W-doping in a W-Ti-doped sample become smaller than that (18 degree(s)C/at.%-W) in a W-doped sample, which seems to be caused by the coexistence of W and Ti.

ITO films are widely used for optically switching systems. Many research papers have been published but most of them are focused on optical and electrical properties. In this paper, electrochemical properties of ITO films are analyzed from the view point of semiconductor electrode.

Nondegenerate four-wave mixing technique has been used to investigate the third-order nonlinear susceptibility for nanocomposite material with Au nanocrystals formed inside a SiO₂ glass matrix. High concentrations of encapsulated Au nanocrystals are formed by implantation of Au⁺ ions into fused silica glass substrates and thermal annealing. The size distribution and the depth profiles of the Au nanoparticles can be controlled by the implantation dose, energy and annealing temperatures. The high value of the third-order susceptibility approximately (0.26 - 1.3) X 10^-7 esu was found in the range of the frequency detunings (Delta) (1/(lambda) ) -1 near the surface plasmon resonance. Two characteristic relaxation times, 0.66 ps and 5.3 ps, have been extracted from the detuning curve of the third-order susceptibility as the probe-beam frequency changes and the pump-beam frequency fixed at the plasmon resonance. The first relaxation time was attributed to electron-phonon relaxation, and the second to thermal diffusion to the host medium. The efficient nondegenerate conversion is attractive for optical processing.

Adiabatic planning for building is a good idea for saving energy and favor of earth environment. Windows of housing are important for providing natural lighting and ventilation, however, they obstruct adiabatic planning. Light-controllable windows, which are called `smart windows' are of use and one solution for adiabatic planning. Smart windows can control the intensity of light as user pleases. Their driving mechanism uses some kind of chromism, thermochromism, photochromism and/or electrochromism. Electrochromic device (ECD) can control both light-holding and heat-radiation by electrochemical redox. Most ECDs using transitional metal oxide which have been studied have colored states such as blue or brown. We consider that white ECD is more suitable for living spaces. In our study, white ECD materials were developed for smart-windows by using a zinc compound. This window changes between a transparent- state and a white-state, like a Japanese-SHOJI', in response to electric conditions. This smart-window can also control light-intensity (transparency) by both applied pulse width and pulse voltage, and no power is consumed to maintain a state. A test trial device which was assembled by our project can change its states between transparency and white, in stable, during over 500 trials.

This paper summarizes efforts at the National Renewable Energy Laboratory to develop self-powered electrochromic window coatings that could be used for economical retrofit to existing building windows. The self-power is provided in either of two ways in separate approaches to the electrochromic (EC) design: by very thin, nearly transparent a-silicon PV cells or by dye-sensitized titania half-cells built into the multi-layer structure of the window coating. The goal of both designs is the ability to incorporate the self-powered EC coating into a laminated flexible polymer film. This film could then be retrofitted to a building window by bonding it to the interior surface and attaching it to local electronic controls that also derive their power from the windows that they control. Laboratory-scale prototype self-powered EC window coatings have been fabricated using both approaches. These are described and the remaining development challenges are discussed.

Electrochromic windows using Nb₂O₅, Nb₂O₅- Li₂O, Nb₂O₅-TiO₂ and Nb₂O₅-MoO₃ sol-gel layers as cathodic coloring electrodes and CeO₂- TiO₂ as anodic ion-storage electrode have been assembled and tested. In agreement with a theoretical estimation, the switching behavior of these devices is strongly dependent on the difference between the internal potential of the electrochromic and the ion-storage electrodes. Only the configuration using a Nb₂O₅-MoO₃ layer enters in consideration for long-time switching within the safe voltage range -2.5 V < V < +2.5 V. All other cells require larger negative potentials. The 8 X 4 cm² devices built with Nb₂O₅:Mo are transparent with a slightly yellow color in the bleached state (+2.5 V) and dark gray in the colored state (-2.5 V). For a fixed thickness of the EC electrode (180 nm) the photopic transmittance increases with the thickness of the ion storage layer d_IS in agreement with the model prediction. It reaches a maximum of ca. 0.3, corresponding to a Li⁺ intercalated charge density of 18 mC/cm². For d_IS is congruent to 950 nm, such devices are stable up to at least 12,000 cycles under potentiostatic cycling between +/- 2.5 V, 120 s.

A tungsten oxide film has been widely employed as an electrochromic material dye to its great electrochemical durability. Durability of carbon materials as electrodes have been more clearly verified in many practical use, a lithium ion battery and an electric double layer capacitor, for example. We then focused on a large electric double layer capacitance and the electrochemical durability in carbon materials. The chief purpose of this paper is to examine electro-optical performance and durability of the electrochromic windows (ECW) fabricated with the carbon- based electrode. The ECWs have been tested for durability under various weather conditions. Most of the tests were carried out on the ECWs with UV-cut filters installed. The filters allowed us to improve the ECW durability greatly. Main results are as follows: (1) we were successful in developing carbon-based electrodes for ECWs and in fabricating an ECW (a carbon-based electrode/a polymeric solid electrolyte/a tungsten oxide electrode), (2) the utilization of the carbon-based electrode increased the ECW durability against high temperature, UV radiation, heat cycle and so forth, and (3) their electrochromic performance were found out to be sufficiently high enough for architectural and automotive purposes.

Two-layer coatings of Nb₂O₅ and niobia doped with tin (up to 15 at%), zirconium (up to 15 at%), lithium (up to 15 at%), titanium (up to 30 at%) and molybdenum (up to 30 at%) have been prepared by the sol-gel process and deposited by dip-coating on conductive ITO coated glass (R_{(open square}) equals 10 (Omega) _{(open square})). They have been sintered in air between 450 degree(s)C and 600 degree(s)C. Their structure, morphology, electrochemical and optical properties (measured in a liquid electrolyte (1 M LiClO₄ in PC)) are reported. All systems exhibit electrochromic properties. Those are essentially determined by the structure and the morphology of the layers which can be changed in a controlled manner by the amount of doping and the sintering temperature. After Li⁺-insertion all amorphous coatings present a brown color, a blue one when the structure is hexagonal and a gray one when the structure is orthorhombic (pure, titanium or molybdenum doped niobia) or monoclinic (Li-doped niobia). Samples with two different structures color either blue or gray.

Ceria (CeO₂) films were prepared by a sol-gel technique onto fluorine doped tin oxide coated glass substrates. The coating solution was derived from cerium ammonium nitrate dissolved in ethanol with diethanolamine used as a complexing agent. Lithium intercalating properties of the films were investigated using cyclic voltammetry (CV) and UV-visible spectroscopy. The electrochemical examinations were performed in a 0.5 M LiClO₄ propylene carbonate electrolyte. The additional film characterizations were performed in X-ray diffractometry (XRD), x-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy. XRD of the films showed that they had an cerianite structure for heat treatment temperatures at or above 450 degree(s)C. The SEM examinations showed that the surface texture was uniform and homogeneous. CV examinations showed a reversible electrochemical insertion or extraction of Li⁺/e^- ions maintaining a high optical transmissivity. Spectroelectrochemistry showed that these films can be used as optically passive counter-electrode in transmissive electrochromic devices.

Amongst various sol-gel routes to deposit large area WO₃ films for electrochromic applications, the one using peroxotungstic acid based precursor solution gives superior electrochromic films. Further improvements in the properties are possible by chemical modification of the precursor material and by controlling the post deposition thermal treatment. Both these parameters affect physical, structural, electrical and as a result electrochromic properties of the films significantly. A detailed study of these properties of the films deposited with precursor solution modified with various organic additives and different thermal parameters was undertaken. X-ray diffraction, electron microscopy and resistance measurements were used to characterize and compare the films. These properties of the films correlated to their electrochromic behavior are reported in this paper.

Hybrid inorganic/organic complementary electrochromic device (ECD), comprising a tungsten oxide (WO₃) and polyaniline (PAni) thin film couple in combination with a proton- conducting polymer electrolyte, is studied. Spectroelectrochemical measurements were done to characterize both the electrochromic thin films and the devices. The safe operating voltage of the device can be determined from these data and ranging from +1.0 V to -0.3 V. The primary motivation of the present investigation is to examine the connection between the optical attenuation range and the charge capacity ratio of WO₃ relative to PAni. It was found, experimentally, that the performance of the complementary ECD is limited by the electrode with the least charge capacity. Furthermore, it has been verified experimentally that, for two complementary electrochromic layers each with an individual thickness, the charge capacities of the two electrochromic layers have to be matched in order to achieve the maximum optical attenuation range. That is, the principle in obtaining the maximum optical attenuation in a complementary ECD is to equalize the charge capacity on both electrochromic layers.

The hypothesis of resistance-limited device behavior and the efficacy of equivalent circuits in modeling the behavior of electrochromic devices are considered. Two types of electrochromic systems, both based on tungsten oxide, are investigated. One is an all-solid-state-stack device, and the other is an aqueous, three-electrode cell system. The general appropriateness of the resistance-limited hypothesis is well-demonstrated, implying that diffusive processes are not important kinetically. The results suggest that development of useful equivalent circuits for electrochromic devices, which would prove invaluable for systems integration, should be pursued aggressively.

A novel approach to tailor the electrochromic properties of polythiophenes utilizing a silyl bridge to form discrete electrochromes is described. The monomer bis[2-(5,2'- dithienyl)]dimethyl silane was chemically synthesized and electrochemically polymerized. Electrochromic properties of devices incorporating this polymer as active material were studied and analyzed following CIE L*a*b* formalism. This polymer exhibits a yellow to green electrochromism from neutral to oxidized state.

Electrochromic materials are of great interest, owing to their potential application in large area displays, active camouflage and energy saving smart windows. The effectiveness of devices fabricated for most applications depends in part on the ability to tailor the observed color in a predictable manner. Several color-tailoring strategies such as polymer blends, copolymers, and layered composites have been investigated recently. Another technique utilizing patterns of electrochromes is currently under development in our labs and affords a false way to modify a device's observed color. The pattern is composed of materials that have different observed colors; at least one of which is an electrochrome. When the pattern is viewed at a distance, the observer perceives a different color than those of the materials comprising the pattern. This `confusion' is due to diffraction. By knowing the color of the patterning materials the observed color can be predicted in a straight forward manner by color subtraction theory. The patterns are produced by screen-printing the electrochrome and other materials onto a Mylar/ITO substrate that is then used as the working electrode in a device. Following this strategy, geometrical patterns composed of thick stripes, fine stripes, small dots, and checkerboards were studied using different materials as the foreground and background colors. We will report on the fabrication of these patterned devices and their characterization by spectrocolorimetry.

After being successfully implemented as self-dimming minors in the automotive industry, electrochromic technologies are moving toward large-area applications. These applications often demand high levels of durability; warranties of ten to twenty years are commonly required in Europe for applications such as car sunroofs and insulated glass units for buildings. These active solar-control glazings need to be priced competitively. Very few EC technologies match all of these requirements. Mixed polymer/metal oxide-layer systems often fail in terms of durability and cost effectiveness, and inexpensive all-organic systems do not usually pass the severe high-temperature and UV tests.