Showing papers on "Electrochromism published in 2010"

Spectral engineering in π-conjugated polymers with intramolecular donor-acceptor interactions.

Abstract: With the development of light-harvesting organic materials for solar cell applications and molecular systems with fine-tuned colors for nonemissive electrochromic devices (e.g., smart windows, e-papers), a number of technical challenges remain to be overcome. Over the years, the concept of “spectral engineering” (tailoring the complex interplay between molecular physics and the various optical phenomena occurring across the electromagnetic spectrum) has become increasingly relevant in the field of π-conjugated organic polymers. Within the spectral engineering toolbox, the “donor−acceptor” approach uses alternating electron-rich and electron-deficient moieties along a π-conjugated backbone. This approach has proved especially valuable in the synthesis of dual-band and broadly absorbing chromophores with useful photovoltaic and electrochromic properties. In this Account, we highlight and provide insight into a present controversy surrounding the origin of the dual band of absorption sometimes encountered in...

Metal-oxide films for electrochromic applications: present technology and future directions

Abstract: Many transition metal-oxide films exhibit an electrochromic (EC) effect as they change their optical transmittance upon charge insertion or extraction. These materials may be integrated into multilayer devices, and the optical modulation is then produced by application of a small electrical voltage. Electrochromic films are therefore being developed for application in dynamic or “smart” windows that are at the forefront of emerging energy-saving advances in building technologies. Here we will describe the state-of-the-art technology that is being implemented in commercial applications. It predominantly relies on the use of tungsten oxide-based films (coloring with ion insertion) and nickel oxide-based films (coloring with ion extraction). We also suggest future research directions that are motivated by the need to reduce the production costs of large-area EC windows. Specifically, we describe the possibility of alternative less expensive manufacturing processes, as well as the development of flexible EC devices that allow for an inexpensive “retrofit” installation to existing structures.

Major Effect of Electropolymerization Solvent on Morphology and Electrochromic Properties of PEDOT Films

Abstract: Although significant efforts were devoted to improving the properties of conductive polymers, the effects of solvent and supporting electrolytes on the morphology and electrochromic features of electropolymerized materials have been scantly investigated. In this work, the effects of the polymerization conditions, such as the solvents and supporting electrolytes, on the morphological structure and electrochromic properties of PEDOT films were systematically studied. Surprisingly, we find a very significant solvent effect and a small supporting electrolyte effect. We show that morphological properties also strongly correlate with electrochromic properties. Films prepared in propylene carbonate have a smoother structure than those prepared in acetonitrile and this leads to superior electrochromic properties, such as an exceptionally high contrast ratio (71%), transparency in the doped state (80%), and coloration efficiency (193 cm2/C) for the films prepared in propylene carbonate. Significant differences bet...

Electrode materials with high surface conductivity

Abstract: The present invention concerns electrode materials capable of redox reactions by electron and alkali-ion exchange with an electrolyte. The applications are in the field of primary (batteries) or secondary electrochemical generators, supercapacitors and light modulating systems of the electrochromic type.

Conductivity Trends of PEDOT-PSS Impregnated Fabric and the Effect of Conductivity on Electrochromic Textile

Abstract: A stretchable e-textile was fabricated by simply soaking Spandex fabric in a conductive polymer aqueous dispersion, PEDOT-PSS. The resulting conductive fabric had an average conductivity of 0.1 S/cm. Subjecting the fabric to more than one soaking step increased the conductivity of the fabric up to ca. 2.0 S/cm resulting in a 33% faster switching speed. This simple methodology is not limited to Spandex (50% nylon/50% polyurethane). Several other fabric compositions were investigated for their conductivity via this process, including 100% cotton, 60% cotton/40% polyester, 95% cotton/5% Lycra, 60%polyester/40% rayon, 100% polyester, and 80% nylon/20% Spandex, listed in order of decreasing hydrophilicity. Those fabrics with higher water uptake resulted in higher conductivities upon soaking in PEDOT-PSS. Electrochromic polymers coated on the fabric could be switched between their different colored states, even upon stretching of the Spandex. SEM revealed that the electrochromic polymer coated on the substrate ...

Broadly absorbing black to transmissive switching electrochromic polymers.

Abstract: Non-emissive electrochromic devices (ECDs), which can be operated under a wide range of viewing and lighting conditions, are especially attractive in applications that include smart windows, displays, electronic paper and mirrors. [ 1–4 ] Consequently, the processability, fl exibility, high optical contrast, rapid redox switching and long-term stability of easily oxidized conjugated polymers has made them desired materials for various refl ective/transmissive ECDs. [ 5–7 ] Although many polymeric electrochromes which are colored (red and orange, [ 8 ] green, [ 9–11 ]

Processable Multipurpose Conjugated Polymer for Electrochromic and Photovoltaic Applications

Abstract: A benzotriazole and 3-hexylthiophene (3HT) bearing a donor−acceptor−donor (D-A-D) type conjugated polymer (PHTBT) was synthesized. The polymer is both p and n-dopable, fluorescent, soluble in common organic solvents, and processable. Electrochemical and spectroelectrochemical characterization of PHTBT and its photovoltaic performance in organic bulk heterojunction (BHJ) solar cells (SC) have been measured. Using PHTBT as donor material in BHJ solar cells resulted in increased open circuit voltage (Voc) up to 0.85 V.

Donor-Acceptor Polymer Electrochromes with Tunable Colors and Performance

Abstract: To demonstrate the effect of donor (D) and acceptor (A) units on the structure−property relationships of electrochromic polymers, design, synthesis, characterization and polymerization of a series of D−A type systems, 1−5, based on thiophene, 3,4-ethylenedioxythiophene, and 3,3-didecyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine as D units and 2,1,3-benzoselenadiazole, 2,1,3-benzothiadiazole and 2-decyl-2H-benzo[d][1,2,3]triazole as A units are highlighted. It is found that these units play key roles on the redox behavior, band gap, neutral state color, and the electrochromic performance (stability, optical contrast, coloration efficiency, and switching time) of the system. It is noted that electropolymerization of these D−A systems provides processable low band gap electrochromes, P1-P5, exhibiting high redox stability, coloration efficiency, transmittance and/or contrast ratio and low response time. Furthermore, P1-P5 reflect various hues of blue and green pallets of the RGB color-space in the neutral st...

Orange and Red to Transmissive Electrochromic Polymers Based on Electron-Rich Dioxythiophenes

Abstract: As the color palette of available solution processable electrochromic polymers expands, there has remained the need for red, orange, and yellow to transmissive switching materials. Here we report on the synthesis and characterization of two such polymers, the orange to transmissive switching (poly{3,4-di(2-ethylhexyloxy)thiophene}) electrochromic polymer-orange (ECP-orange) and the red to transmissive switching processable polymer (poly{3,4-di(2-ethylhexyloxy)thiophene-co-3,4-di(methoxy)thiophene}) electrochromic polymer-red (ECP-red). The ECP-orange has a bandgap of 2.04 eV, an absorption λmax centered at 483 nm, and an E1/2 of 0.37 V versus Ag/Ag+. The electrochromic contrast is 48% T at 483 nm with a time to reach 95% of the full optical contrast of 5.3 s for a film that has an absorbance of 0.98 au at λmax. Because of steric relaxations from the random copolymerization of a branched dialkoxy-substituted thiophene with a dimethoxy-substituted thiophene, the red to transmissive switching ECP-red has a b...

Nanostructured Liquid Crystals Combining Ionic and Electronic Functions

Abstract: New molecular materials combining ionic and electronic functions have been prepared by using liquid crystals consisting of terthiophene-based mesogens and terminal imidazolium groups. These liquid crystals show thermotropic smectic A phases. Nanosegregation of the pi-conjugated mesogens and the ionic imidazolium moieties leads to the formation of layered liquid-crystalline (LC) structures consisting of 2D alternating pathways for electronic charges and ionic species. These nanostructured materials act as efficient electrochromic redox systems that exhibit coupled electrochemical reduction and oxidation in the ordered bulk states. For example, compound 1 having the terthienylphenylcyanoethylene mesogen and the imidazolium triflate moiety forms the smectic LC nanostructure. Distinct reversible electrochromic responses are observed for compound 1 without additional electrolyte solution on the application of double-potential steps between 0 and 2.5 V in the smectic A phase at 160 degrees C. In contrast, compound 2 having a tetrafluorophenylterthiophene moiety and compound 3 having a phenylterthiophene moiety exhibit irreversible cathodic reduction and reversible anodic oxidation in the smectic A phases. The use of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-PSS) as an electron-accepting layer on the cathode leads to the distinct electrochromic responses for 2 and 3. These results show that new self-organized molecular redox systems can be built by nanosegregated pi-conjugated liquid crystals containing imidazolium moieties with and without electroactive thin layers on the electrodes.

Variable transmittance optical filter and uses thereof

Abstract: Variable transmittance optical filters capable of transitioning from a light state to a dark state on exposure to UV radiation and from a dark state to a light state with application of an electric voltage are provided. The optical filters comprise a switching material that comprises one or more chromophores that have electrochromic and photochromic properties.

Cobalt Oxide Ordered Bowl-Like Array Films Prepared by Electrodeposition through Monolayer Polystyrene Sphere Template and Electrochromic Properties

Abstract: In this paper, we report a facile method to produce large-area periodical bowl-like cobalt oxide (Co3O4) array films based on a self-assembled monolayer polystyrene sphere template and electrodeposition. After the template is removed, the resulting Co3O4 films consist of periodic, interconnected networks of monodisperse submicrometer pores with a diameter of 1 μm. Moreover, the individual bowl contains a large number of pores with a diameter of 50 ± 20 nm and the interstices between bowls are filled with Co3O4 nanoflakes. As a preliminary test, the electrochromic properties of the Co3O4 macrobowl arrays have been investigated and it is found that the film annealed at lower temperature exhibits better electrochromic performance. The Co3O4 array film annealed at 200 °C exhibits good electrochromism with color changes from dark gray to pale yellow and fast response times. The coloration efficiency is calculated to be 29 cm2 C−1 at 633 nm, with a variation of transmittance up to 33%.

A high-speed passive-matrix electrochromic display using a mesoporous TiO2 electrode with vertical porosity.

Abstract: Chemical Equation Presentation On display: A high-speed and high-quality passive-matrix electrochromic display (ECD) is constructed from a leuco dye and a TiO nanoporous electrode (see picture). The vertical pores prevent the drifting of the colored dye molecules, leading to a clear image at high driving speeds. With full-color features, this kind of ECD promises to be a competitive candidate for a reflective electric display.

All-Organic Electrochromic Spandex

Abstract: Herein we describe the preparation and characterization of reflective-type electrochromic devices using stretchable, conductive fabric electrodes. Two fabrics were used in this study: woven stainless steel mesh and Lycra spandex impregnated with a conducting polymer (poly[3,4-ethylenedioxythiophene]-poly[styrene sulfonate], PEDOT-PSS). Electrochromic polymers were prepared on the surface of these fabric electrodes and devices were assembled. The time taken for the electrochromic polymer to switch between colored states in devices prepared with stainless steel electrodes (conductivity ca. 9,800 S/cm) was ca. 0.3 s, whereas that using PEDOT-PSS loaded Lycra (conductivity ca. 0.1 S/cm) was a few seconds. The iris effect was evaluated for each of the device architectures, showing no effect for steel mesh/steel mesh devices and a propagating front for spandex-based devices. The electrochromic spandex functioned in solution while being stretched. In addition, stenciled devices were built. Such fabric electrochr...

Covalently Bonded Polyaniline−TiO2 Hybrids: A Facile Approach to Highly Stable Anodic Electrochromic Materials with Low Oxidation Potentials

Abstract: In this article, we report the synthesis, structures, morphologies, and electrochromic properties of covalently bonded polyaniline (PANI)−TiO2 hybrids. The hybrids were synthesized via a sol−gel process, followed by oxidative polymerization, using a bifunctional compound to bridge the two phases. In comparison with PANI, the hybrids show significant enhancement in optical contrast and coloration efficiency. Furthermore, when covalently bonded to PANI, the TiO2 nanodomains can act as electron acceptors, reducing the oxidation potential and band gap of PANI, and improving the long-term electrochromic stability.

Hydrothermally grown nanostructured WO3 films and their electrochromic characteristics

Abstract: We report the synthesis of nanostructured tungsten trioxide (WO3) films and their electrochromic characteristics. Plate-like monoclinic WO3 nanostructures were grown directly on fluorine-doped tin oxide glass substrates by a simple and low-cost crystal-seed-assisted hydrothermal method. The growth mechanism of the film is investigated. HRTEM analysis reveals the single crystalline quality of the WO3 nanostructure. The film exhibits tunable transmittance modulation under different voltages and repetitive cycling between the clear and blue states has no deleterious effect on its electrochromic performance after 3000 cycles. The electrochromic device composed of the WO3 film has high electrochromic stability, colour contrast and reasonable switching response with a colouration efficiency of 38.2 cm2 C−1 at 632.8 nm.

Enhanced Electrical Switching and Electrochromic Properties of Poly(p-phenylenebenzobisthiazole) Thin Films Embedded with Nano-WO3

Abstract: The electrical switching and electrochromic phenomena of a novel nanocomposite comprising poly(p-phenylenebenzobisthiazole) (PBZT) and tungsten oxide (WO 3 ) nanoparticles are investigated as a function of the nanoparticle loading. Both dissolving PBZT and doping PBZT backbone structure with acid are achieved by one simple step. Chlorosulfonic acid (CSA) is used as a solvent and spontaneously transformed to sulfuric acid upon exposure to moisture. The formed sulfuric acid serves as doping agent to improve the electrical conductivity of PBZT. The most significant enhancement of electrical switching is observed in the nanocomposites with low weight fraction (5%). The electrical conductivity of 5% WO 3 /PBZT nanocomposite thin film is increased by about 200 times and 2 times, respectively, as compared to those of the as-received PBZT and PBZT/CSA thin films. As the nanoparticle loading increases to 20% and 30%, the nanocomposites follow an ohmic conduction mechanism. Stable electrical conductivity switching is observed before and after applying a bias on the pristine PBZT and WO 3 /PBZT nanocomposite thin films. Electrochromic phenomena of both PBZT and WO 3 / PBZT nanocomposite thin films with high contrast ratio are observed after applying a bias (3 V). The mechanisms of the nanoparticles in enhancing the electrical switching and electrochromic properties are proposed.

Structure, optical and electrochromic properties of NiO thin films

Abstract: Nickel oxide thin films were prepared by sol–gel dip coating process. Nickel acetate tetrahydrate [Ni(CH3COO)2·4H2O] has been used as the starting material with absolute ethyl alcohol to prepare NiO thin films on both glass and indium tin oxide glass (ITO) substrates with heat treatment at different annealing temperatures from 673 to 733 K. Thermogravimetric analysis (TGA) was studied for the xerogel sample. Polycrystalline structures of the prepared films were detected by X-ray diffraction analysis (XRD), and the particle size was determined by Scherrer formula. The morphology and the structure of the prepared thin films were investigated by the transmission electron microscope (TEM). The optical properties of NiO thin films were examined. The optical constants such as the absorption coefficient (α), extinction coefficient (k), the energy gap (Eg) and the refractive index (n) of the prepared films were determined. The effect of annealing temperature on the electrochromic behavior was observed providing that good electrochromic performance was T

Rapid microwave synthesis of mesoporous TiO2 for electrochromic displays

Abstract: The fabrication of paper quality electrochromic displays based on the viologen modified TiO2 electrodes (Vio2+/TiO2) requires a cost-effective, energy efficient and rapid synthesis of mesoporous TiO2 with high yield in short reaction time. A straightforward and industrially viable process for the preparation of mesoporous nanocrystalline titania (meso-nc-TiO2) for NanoChromics™ display device applications by the use of microwave synthesis is presented here. Spherical aggregates of meso-nc-TiO2 were rapidly achieved using titanium butoxide, deionised water and common alcohols (isopropanol, ethanol and butanol) at comparatively low microwave power intensity (300 W) for 2 min irradiation. The material has been characterised by a range of different techniques such as XRD, Raman spectroscopy, SEM and BET surface area analysis. These materials possess surface areas up to 240 m2 g−1, which is significantly higher than similar traditional sol–gel or commercial samples. This meso-nc-TiO2 prepared was used as the working electrode for an electrochromic display device with Sb doped SnO2 as the counter electrode material on an ITO coated conducting glass. A working prototype of a NanoChromics™ display was successfully fabricated using this approach.

Fabrication of low defectivity electrochromic devices

Abstract: Prior electrochromic devices frequently suffer from high levels of defectivity. The defects may be manifest as pin holes or spots where the electrochromic transition is impaired. This is unacceptable for many applications such as electrochromic architectural glass. Improved electrochromic devices with low defectivity can be fabricated by depositing certain layered components of the electrochromic device in a single integrated deposition system. While these layers are being deposited and/or treated on a substrate, for example a glass window, the substrate never leaves a controlled ambient environment, for example a low pressure controlled atmosphere having very low levels of particles. These layers may be deposited using physical vapor deposition.

Application of Nanostructures in Electrochromic Materials and Devices: Recent Progress.

Abstract: The recent progress in application of nanostructures in electrochromic materials and devices is reviewed. ZnO nanowire array modified by viologen and WO₃, crystalline WO₃ nanoparticles and nanorods, mesoporous WO₃ and TiO₂, poly(3,4-ethylenedioxythiophene) nanotubes, Prussian blue nanoinks and nanostructures in switchable mirrors are reviewed. The electrochromic properties were significantly enhanced by applying nanostructures, resulting in faster switching responses, higher stability and higher optical contrast. A perspective on the development trends in electrochromic materials and devices is also proposed.

Electrochemical surface plasmon resonance and waveguide-enhanced glucose biosensing with N-alkylaminated polypyrrole/glucose oxidase multilayers.

Abstract: In this work, we report an electrochemical surface plasmon resonance/waveguide (EC-SPR/waveguide) glucose biosensor that could detect enzymatic reactions in a conducting polymer/glucose oxidase (GOx) multilayer thin film. In order to achieve a controlled enzyme electrode and waveguide mode, GOx (negatively charged) was immobilized with a water-soluble, conducting N-alkylaminated polypyrrole (positively charged) using the layer-by-layer (LbL) electrostatic self-assembly technique. The electrochemical and optical signals were simultaneously obtained from the composite LbL enzyme electrode upon the addition of glucose as mediated by the electroactivity and electrochromic property of the polypyrrole layers. Signal enhancement in EC-SPR detection is obtained by monitoring the doping−dedoping events on the polypyrrole. The real-time optical signal could be distinguished between the change in the dielectric constant of the enzyme layer and other nonenzymatic reaction events such as adsorption of glucose and the ...

Design, Synthesis, and Study of Main Chain Poly(N-Heterocyclic Carbene) Complexes: Applications in Electrochromic Devices

Abstract: A series of poly(N-heterocyclic carbene) complexes in which the carbene functionalities are orthogonally connected to the main chains of the respective polymers have been synthesized via oxidative electropolymerization of various bis(bithiophene)-substituted monomers with appended transition metal or main group entities (M = Ir, Au, Ag, or S). The polymers were characterized using a range of electrochemical, X-ray photoelectron spectroscopy, UV−vis spectroscopy, profilometry, and four-point probe conductivity measurements. Most of the polymers exhibited an intense absorbance wave at 700 nm under oxidative conditions which was attributable to the formation of polarons along the main chains. The iridium-containing thin film poly(8) was found to possess a significant NIR absorbance at 1100 nm in which the metal moiety effectively functioned as an electron sink. Electrochemical analyses of the polymer thin films revealed that they exhibited highly reversible electrochromic phenomena.

Electrochromic properties of MoO3 thin films derived by a sol–gel process

Abstract: Molybdenum trioxide (MoO3) films were deposited on ITO/Glass substrates by the sol–gel method using a spin-coating technique and heat treated at various temperatures under different ambient atmosphere. Effects of the process parameters on the electrochromic properties of MoO3 films were studied using cyclic voltammetry (CV) in a propylene carbonate (PC) non-aqueous solution containing 1 M lithium perchlorate (LiClO4). Electrochromic MoO3 film on lithium intercalation was investigated by in-situ transmittance measurement during the CV process. The MoO3 films showed reversible recharge ability on Li+/e− intercalation/deintercalation. Experimental results revealed that the heat-treatment temperature, the ambient atmosphere, and the thickness will have the string influence on the electrochromic properties of MoO3 thin films. X-ray diffraction (XRD) results show that the amorphous MoO3 films can be obtained with the heat-treatment temperature below 300 °C in O2 ambient atmosphere. The optimum electrochromic MoO3 film, with a thickness of 130 nm, exhibits a maximum transmittance variation (ΔT%) of 30.9%, an optical density change (ΔOD) of 0.213, an intercalation charge (Q) of 8.47 mC/cm2, an insertion coefficient x in Li x MoO3 was 0.21 and a coloration efficiency (η) of 25.1 cm2/C between the colored and bleached states at a wavelength (λ) of 550 nm.