Showing papers on "Electrochromism published in 2009"

Layered vanadium and molybdenum oxides: batteries and electrochromics

Abstract: The layered oxides of vanadium and molybdenum have been studied for close to 40 years as possible cathode materials for lithium batteries or electrochromic systems. The highly distorted metal octahedra naturally lead to the formation of a wide range of layer structures, which can intercalate lithium levels exceeding 300 Ah/kg. They have found continuing success in medical devices, such as pacemakers, but many challenges remain in their application in long-lived rechargeable devices. Their high-energy storage capability remains an encouragement to researchers to resolve the stability concerns of vanadium dissolution and the tendency of lithium and vanadium to mix changing the crystal structure on cycling the lithium in and out. Nanomorphologies have enabled higher reactivities to be obtained for both vanadium and molybdenum oxides, and with the latter show promise for electrochromic displays.

Conjugated polyelectrolytes: synthesis, photophysics, and applications.

Abstract: Organic optoelectronic polymers have evolved to the point where fine structural control of the conjugated main chain, coupled with solubilizing and property-modifying pendant substituents, provides an entirely new class of materials. Conjugated polyelectrolytes (CPEs) provide a unique set of properties, including water solubility and processability, main-chain-controlled exciton and charge transport, variable band gap light absorption and fluorescence, ionic interactions, and aggregation phenomena. These characteristics allow these materials to be considered for use in applications ranging from light-emitting diodes and electrochromic color-changing displays, to photovoltaic devices and photodetectors, along with chemical and biological sensors. This Review describes the evolution of CPE structures from simple polymers to complex materials, describes numerous photophysical aspects, including amplified quenching in macromolecules and aggregates, and illustrates how the physical and electronic properties lead to useful applications in devices.

Novel Metastable Hexagonal MoO3 Nanobelts: Synthesis, Photochromic, and Electrochromic Properties

Abstract: In this work, we report the crystalline structure, morphology, and optical properties of novel metastable hexagonal phase MoO3 (h-MoO3) nanobelts prepared by a simple hydrothermal route from peroxomolybdate solution with the presence of sodium nitrate as a mineralizer. During the reaction process, NaNO3 has been proposed to influence the deoxidation, condensation, and further dehydration of the water-soluble peroxomolybdate precursor for connecting the [MoO6] octahedra with vertex sharing and edge sharing arrangements on determining the generation of metastable phase. The present work comparatively investigates the photochromic and electrochromic behaviors of the resultant hexagonal h-MoO3 nanobelts and the common thermodynamically stable orthorhombic α-MoO3 nanobelts. The performances concerning photochromism on two types of MoO3 nanobelt suspensions show that the photochemical efficiency of h-MoO3 is more excellent than that of α-MoO3 under UV light irradiation based on a remarkable coloration phenomeno...

Controlled synthesis of WO3 nanorods and their electrochromic properties in H2SO4 electrolyte

Abstract: Uniform crystalline WO3 nanorods were synthesized by a lithium- or sulfate-free hydrothermal process with NaCl as a capping agent. It is found that variations in the pH and amount of capping agent have critical influence on the morphologies of the resultant WO3 nanostructures. The electrochromic film comprised of the as-synthesized crystalline WO3 nanorods exhibits a fast coloration/bleaching switching, coloration efficiency comparable to that of conventional amorphous WO3 films, and a high H+ ion-insertion ability in 0.5 mol/L H2SO4 solution without degradation.

The incorporation of noble metal nanoparticles into host matrix thin films: synthesis, characterisation and applications

Abstract: This feature article focuses on the synthesis of noble metal nanoparticles and how these particles can be incorporated into thin films. The functional properties of the nanoparticles when embedded in a host matrix are covered. In particular the optical properties of noble metal nanoparticles, numerical theory, including Mie and Maxwell–Garnet equations are explained with particular attention on photoluminescence, photochromic and electrochromic properties. The dielectric effect of the host matrix and the influence on the surface plasmon resonance are explored. Future research applications and trends in the field are highlighted.

Multicolored Electrochromic Cells Based On Poly(2,7-Carbazole) Derivatives For Adaptive Camouflage

Abstract: We report the synthesis and characterization of three new poly(2,7-carbazole) derivatives, namely, poly[N-9-heptadecanyl-2,7-carbazole-alt-5,7-di(3-octylthien-2-yl)-2,3-di(thien-3-yl)-thieno[3,4-b]pyrazine (P1), poly[N-9-heptadecanyl-2,7-carbazole-alt-5,7-di(3-octylthien-2-yl)-2,3-di(phen-1-yl)-thieno[3,4-b]pyrazine (P2), and poly[N-9-heptadecanyl-2,7-carbazole-alt-5,7-di(3-octylthien-2-yl)-2,3-di(4-octylphen-1-yl)-thieno[3,4-b]pyrazine (P3), which reflect green light in their neutral state and show transmissive brown when oxidized. These two colors are compatible for adaptive camouflage for military assets. All solid-state electrochromic cells were prepared using spray-coated films of electrochromic conjugated polymer (P1−P3) as active layer. We report the development of multicolored electrochromic cells (MEC) based on the additive color mixing theory. MEC of various sizes were prepared from 2.5 × 2.5 cm, and up to 12.5 × 12.5 cm. Finally, we also describe the fabrication of a multicolored electrochromic...

Alkali metal crystalline polymer electrolytes

Abstract: The transport and mechanical properties of polymer electrolytes make them important materials for all-solid-state electrochemical devices such as batteries or electrochromic displays. Crystalline polymer electrolytes containing alkali metal salts are now found to exhibit ionic conductivity 1.5 orders of magnitude higher than the best conductor reported so far.

Organized Nanostructured Complexes of Polyoxometalates and Surfactants that Exhibit Photoluminescence and Electrochromism

Abstract: A variety of functional nanostructured organic/inorganic hybrid materials from the europium-exchanged derivative of a Preyssler-type polyoxometalate (POM), [EuP5W30O110]12−, and functional organic surfactants were prepared by the ionic self-assembly (ISA) route. The effect of organic surfactants on the structure, photoluminescent, electrochemical and electrochromic properties of the POM anions was investigated in detail. All obtained hybrid materials are amphotropic, i.e., exhibit both thermotropic and lyotropic liquid-crystalline phase behaviour. Investigations of their photophysical properties have shown that the interactions of the various surfactants with the polyanions influence the coordination environments and site symmetry of Eu3+ in different ways. The functional groups in the organic surfactants significantly influence the electrochromic properties and photoluminescence of POMs. Different from normal and pyridine-containing complexes, no photoluminescence and no electrochromism were observed from the ferrocene-containing complexes. This may be explained in view of charge transfer between the POM anion and the ferrocenyl group.

Improving the contrast of all-printed electrochromic polymer on paper displays

Abstract: PEDOT:PSS-based electrochromic displays have been explored for manufacture on flexible paper substrates in roll-to-roll printing presses at high volumes and low costs. Here, we report the improvement of the optical contrast of such devices by adding an extra layer of a dihexyl-substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx2) to complement the optical absorption spectrum of PEDOT:PSS. The oxidized state of PProDOT-Hx2 is highly transparent and is an intense magenta color while in the reduced state. By adding a layer of PProDOT-Hx2 directly on top of PEDOT:PSS, we were able to improve the optical contrast by nearly a factor of two. In this report, we present optical and electrochemical data of PProDOT-Hx2/PEDOT:PSS-based electrochromic paper displays and compare their performance with PEDOT:PSS-only equivalents.

Hexyl‐Derivatized Poly(3,4‐ethylenedioxyselenophene): Novel Highly Stable Organic Electrochromic Material with High Contrast Ratio, High Coloration Efficiency, and Low‐Switching Voltage

Abstract: Currently, there is significant interest in the design of new electrochromic (EC) materials exhibiting a high contrast ratio (a large change in percent transmittance between the colored and bleached states), high coloration efficiency (efficient color changes in response to applied charge) and long-term stability. EC materials could be employed in the fabrication of efficient displays and ECwindows if they could bemade to exhibit a large change in transmittance upon application of a small charge. While considerable research was performed on inorganic EC materials, better performance has been reported recently using conducting polymers, mostly based on poly(3,4ethylenedioxythiophene) (PEDOT) and its derivatives. Conducting polymers offer better processability and better color tunability than their inorganic andmolecular counterparts. PEDOT film can be quite rapidly switched between the absorptive (neutral) and transmissive (doped) states at low switching potentials. The neutral PEDOT film shows a band gap of around 1.6 eV and a light sky blue appearance as a doped film. The coloration efficiency (CE) of PEDOT is 137 cm C 1 at full switch, 183 cm C 1 at 95% of full switch, 206 cm C 1 at 85% of full switch, and the dibutyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT(Bu)2) [13] obtained by Reynolds’ group achieves a CE of 1365 cm C , which is currently the highest CE value reported for an electropolymerized EC film measured in liquid electrolyte. The stability of the electrochromic materials is another crucially important feature for practical application. Reynolds’ group studied PEDOT, PEDOT-C8, and PEDOT-C14 films and found that the films retained 65%, 50%, and 62% of their electroactivity after 6000, 9000, and 16000 switching cycles, respectively. However, the contrast ratios were less than 65%. Kumar’s group obtained a dibenzyl poly(3,4-propylenedioxythiophene) (PProDOT-Bz2) that has the highest known contrast ratio (89%), a CE of 575 cm C 1 and high stability after 5000 switching cycles. The poly(1,4-bis(2-(30,40-ethylenedioxy)thienyl)-2-methoxy-5-200ethylhexyloxybenzene) (P(BEDOT-MEHB)) reported by Wudl’s group has a CE of 680 cm C 1 and also exhibits high stability after 5000 switching cycles, though it has a contrast ratio of only 57%. Catellani et al. reported that poly(3-butylthiophene) can

Transparent TiO2 nanotube electrodes via thin layer anodization: fabrication and use in electrochromic devices.

Abstract: In the present work, we describe an anodization process that is able to fully transform a thin Ti metal layer on a conductive glass into a TiO2 nanotubular array. Under optimized conditions, nanotube electrodes can be obtained that are completely transparent and defect-free and allow electrochromic switching. These electrochromic electrodes show remarkable properties and can be directly integrated into devices.

Solution-Processable Novel Near-Infrared Electrochromic Aromatic Polyamides Based on Electroactive Tetraphenyl-p-Phenylenediamine Moieties

Abstract: A series of solution-processable near-infrared (NIR) electrochromic aromatic polyamides with N,N,N′,N′-tetraphenyl-p-phenylenediamine (TPPA) units in the backbone were prepared from the phosphorylation polyamidation reactions of a newly synthesized diamine monomer, N,N′-bis(4-aminophenyl)-N,N′-di(4-methoxylphenyl)-1,4-phenylenediamine, with various aromatic dicarboxylic acids. These polymers were readily soluble in many organic solvents and showed useful levels of thermal stability associated with high glass-transition temperatures (236−246 °C) and high char yields (higher than 58% at 800 °C in nitrogen). The polymer films showed reversible electrochemical oxidation with high contrast ratio both in the visible range and NIR region, which also exhibited high coloration efficiency (CE), low switching time, and the highest stability for long-term electrochromic operation to date. At the first oxidation stage, the polyamide Ib thin film revealed high coloration efficiency in visible (CE = 388 cm2/C) and NIR (...

Poly(3,4-ethylenedioxythiophene)-multiwalled carbon nanotube composite films: structure-directed amplified electrochromic response and improved redox activity.

Abstract: Composite thin films of poly(3,4-ethylenedioxythiophene) (PEDOT)-enwrapped functionalized multiwalled carbon nanotubes (MWCNTs) have been synthesized over multiple length scales by electropolymerization of the monomer without the use of any other supporting electrolyte. The functionalized MWCNTs are incorporated into the positively charged polymer deposit as counterions during oxidative electropolymerization. The morphology, electrochemistry, and electrochromism of the PEDOT−MWCNT films have been compared with those of control PEDOT films doped by triflate ions. Such a comparison enabled us to demonstrate the profound effect of MWCNTs as counterions, realized in terms of better electropolymerization rate, higher conductivity, faster color−bleach kinetics, higher charge storage capacity, and substantially amplified coloration efficiency (η = 414 cm2 C−1, λmax = 575 nm, E = −1.5 V) in comparison to the values of η reported to date for PEDOT. The strong interaction between the polymer and MWCNTs, the interco...

Tuning the Electrochromic Properties of Poly(alkyl-3,4-ethylenedioxyselenophenes) Having High Contrast Ratio and Coloration Efficiency

Abstract: A systematic study of the electrochemical, spectroelectrochemical and electrochromic (EC) properties of poly(alkyl-3,4-ethylenedioxyselenophene) (PEDOS-Cn) (n = 0, 2, 4, 6, 8 and 12) films is reported. The alkyl substituents lead PEDOS-Cn films to exhibit sharper redox peaks than the parent PEDOS film and raise an onset of their oxidation potentials by 0.20−0.62 V. As expected, the introduction of alkyl chains significantly improves the EC properties and the electrochemical stability of PEDOS-Cn films and results in high contrast ratios and coloration efficiencies, low switching voltages, and fast switching times. As the length of the alkyl chain increases, the broad absorption peak of PEDOS sharpens and splits into three distinct peaks for PEDOS-Cn films starting from n = 4. We have identified the correlations between EC properties (such as coloration efficiency) and other observed properties of PEDOS-Cn films (such as their peak width, the position of the maximum absorption peak, the ratio of the absorp...

Iron-Catalyzed Polymerization of Alkoxysulfonate-Functionalized 3,4-Ethylenedioxythiophene Gives Water-Soluble Poly(3,4-ethylenedioxythiophene) of High Conductivity

Abstract: Chemical polymerization of a 3,4-ethylenedioxythiophene derivative bearing a sulfonate group (EDOT-S) is reported. The polymer, PEDOT-S, is fully water-soluble and has been produced by polymerizing EDOT-S in water, using Na2S2O8 and a catalytic amount of FeCl3. Elemental analysis and XPS measurements indicate that PEDOT-S is a material with a substantial degree of self-doping, but also contains free sulfate ions as charge-balancing counterions of the oxidized polymer. Apart from self-doping PEDOT-S, the side chains enable full water solubility of the material; DLS studies show an average cluster size of only 2 nm. Importantly, the solvation properties of the PEDOT-S are reflected in spin-coated films, which show a surface roughness of 1.2 nm and good conductivity (12 S/cm) in ambient conditions. The electro-optical properties of this material are shown with cyclic voltammetry and spectroelectrochemical experiment reveals an electrochromic contrast (∼48% at λmax = 606 nm).

The role of water in the synthesis and performance of vapour phase polymerised PEDOT electrochromic devices

Abstract: Parameters affecting the quality of vapour phase polymerised (VPP) PEDOT and their influence on electrochromic device performance were investigated. Specifically, the role of water during synthesis was examined and a polymerisation mechanism proposed. Paradoxically, water vapour is essential for PEDOT polymerisation, however, too high a loading leads to crystallite formation in the oxidant layer, rendering the oxidant inactive. Changes in water vapour affect the doping level of the polymer, presumably due to poor conjugation along the polymer's backbone during synthesis. The addition of a surfactant, PPG-ran-PEG, was studied using XPS. The surfactant inhibited oxidant crystal growth and slowed the rate of PEDOT polymerisation, reducing film defects and improving PEDOT conductivity. Controlling and optimising the levels of water vapour and surfactant during synthesis resulted in reproducible, high conductivity, high optical switch, PEDOT films. Finally, complementary dual-polymer electrochromic devices utilising (pre- and post-process-enhanced) VPP PEDOT and PMAS (control) were fabricated and changes in switching transmission evaluated.

Electrochromic Organic-Metallic Hybrid Polymers: Fundamentals and Device Applications

Abstract: Organic—metallic hybrid polymers are formed by the complexation of metal ions with organic ligands or polymers bearing coordination sites. Hybrid polymers consisting of bis(terpyridine)s and metal ions such as Fe(II) or Ru(II) have specific colors based on metal-to-ligand charge transfer (MLCT) absorption. The cyclic voltammograms of the polymers revealed a reversible redox wave that depends on the redox reaction of the metal ions. Interestingly, polymer films cast on indium tin oxide (ITO) electrodes have excellent electrochromic properties; the color of the film disappears when a potential higher than the redox potential of the metal ions is applied to the polymer film. Various colors such as purple, blue, red, and orange can be observed by changing the metal species and/or by modifying the organic ligands used to synthesize the polymers. In addition, multicolor electrochromic changes in a polymer film occur upon the introduction of two types of metal ions into the polymer. Electrochromic solid-state devices have been successfully fabricated by using these polymers.

Unsaturated Linkages in Dioxythiophene−Benzothiadiazole Donor−Acceptor Electrochromic Polymers: The Key Role of Conformational Freedom

Abstract: The perspective of generating new colors commonly difficult to attain such as cyan blue and greens of various tones and saturations has motivated the design of conjugated polymer finely tuned in their molecular structure to reassemble the optical features desired in the context of non-emissive electrochromic device (ECD) applications Herein, we report on a series of soluble donor−acceptor (DA) conjugated polymers involving 3,4-dioxythiophenes (DOTs) and 2,1,3-benzothiadiazole (BTD) constructed in combination with unsaturated linkages, namely ethynylene and trans-ethylene, and compare these to their fully polyheterocyclic DA control analogues with careful emphasis on optical, electrochemical, and electrochromic (EC) properties As confirmed by spectroelectrochemical analysis, ethynylene linkers hindered the formation of a defined bipolaronic transition in the near-IR and were thus found disruptive with respect to the EC potential of their subsequent alternating copolymers On the other hand, the presence

Electrochromic behavior of a self-propagating molecular-based assembly.

Abstract: A metallo-supramolecular network undergoes reversible redox chemistry on indium−tin oxide (ITO) coated glass substrates with concurrent color change. The switching time, long-term stability, and coloration efficiency are competitive with polymeric materials such as the industrially important PEDOT.