Influence of deposition temperature on electrochromic properties of sputtered W03 thin films

The influence of deposition temperature on the electrochromic properties of reactively sputtered WO₃ films has been investigated. A set of W0₃ films produced in the temperature range of 47–400°C is electrochemically cycled with a constant current supply, which provides an easy control of the charge injected into the films. Optical absorption after coloration, and, hence, the coloration efficiency of the films, significantly increases with increasing deposition temperature (up to 400°C) in the wavelength range of ∼ 1000–2500 nm. Both optical absorption and coloration efficiency decrease at the highest temperatures studied (350–400°C) over most of the visible spectrum (∼ 500–800 nm). Optical modulation across the solar spectrum remains fairly constant for charge injection of 10 mC/cm², and the modulation is quite satisfactory for all films for electrochromic device applications. The films produced at higher substrate temperatures show smaller modulation of the visible spectrum, compared with the films sputtered at lower substrate temperatures. This could be more suitable for some applications of the solar control systems. The resistance of the films during the electrochemical process is found to increase with increasing substrate temperature. This causes difficulty in charge injection, requiring significantly larger voltages in techniques such as a cyclic voltammetry for the films deposited at higher temperatures. As a result the good electrochromic performance of the films deposited at higher temperatures can be masked by experimental conditions.     

Functional metallomacrocycle derivatives and their polymers. 31. Preparation and electrochromic properties of novel cobaltophathalocyanine thin films on electrodes

A novel cobaltphthalocyaninanine compound was deposited as a thin film on an indium/tin oxide-coated (ITO) glass electrode by electrodeposition from a solution of 2,9,16,23-tetracarboxyphthalocyaninatocobalto(II) [Co(II)-taPc] and CaCl₂ in DMF. Electrochromic properties of the thin film were investigated. Formation of a calcium chelate complex between Co(II)-taPc and Ca²⁺ and deposition as a thin film on the electrode was confirmed by IR and XMA measurements. Cyclic voltammogram and electron absorption spectra were carried out. Electrochemical reduction and oxidation of CoPc thin films showed a rapid, virtually quantitative reversible process in electrochromism (blue-green-brown). No change in voltammogram was observed after >10,000 cycles.     

Fabrication of TiO2/Au nanorod arrays employing a positive sacrificial ZnO template and their electrochromic property

A novel method to fabricate large scale TiO₂/Au nanorod array using a positive sacrificial ZnO template has been developed. This method includes a two-step process, (1) preparation of ZnO/Au nanorod array by a simple low-temperature hydrothermal process, and (2) preparation of TiO₂/Au nanorod array by electrochemically induced sol-gel process. The TiO₂/Au nanorod array has showed a reversible electrochromism in lithium-ion-containing organic electrolyte. The coloration and bleaching throughout a visible range can be switched on and off within a few seconds.     

Dynamically tuning the correlated color temperature of white light-emitting electrochemical cells with electrochromic filters

Recently, white solid-state light-emitting electrochemical cells (LECs) have drawn great attention since they exhibit advantages such as low-voltage operation, compatibility with solution processes and employing inert cathode metals. Since different correlated color temperatures (CCTs) of background illumination are necessary for various lighting applications, a real-time tunable CCT of white LECs would be highly desired in modern smart lighting systems. In this work, a widely and dynamically tuning CCT (>10000 K) of white LEC is demonstrated by employing an electrochromic device (ECD) as a real-time controllable color filter. By increasing the applied bias on the ECD to attenuate more the red parts of white EL from the white LEC, the LEC-based white light source becomes more bluish and, in consequence, shows higher CCT. This proposed LEC-based white light source with the characteristics of wide CCT range and real-time tunability is suitable for most lighting applications and modern smart lighting systems.     

Electrochemistry and electrochromism of a poly(cyclopentadithiophene) derivative with a viologen pendant

N-Methyl-N′-(6-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-4-ylhexyl)-4,4′-bipyridinium dihexafluorophosphate (CPDT-V²⁺-Me) was synthesized. The monomer was electropolymerized on a glassy carbon or an ITO electrode in a potentiodynamic mode to form the corresponding polymer P(CPDT-V²⁺-Me) on the electrodes. During the electropolymerization, two redox peaks of the viologen (V) moiety increased up to several cycles and then decreased while the redox peak of P(CPDT) moiety still increased. Especially, a new oxidative peak a in the range of ca. −0.4 and 0 V versus Ag/Ag⁺ appeared and increased up to several cycles. Peak a almost disappeared after the redox peaks of the viologen moiety almost disappeared. As a result of cyclic voltammetric study, it was shown that peak a originated from the oxidation of reduced viologen moiety via P(CPDT)-mediated electron transfer mechanism. We also found that the electroactivity of viologen moiety in P(CPDT-V²⁺-Me) decreased significantly when the potential was scanned to the second viologen redox (V⁰/V√⁺). In practical applications, the polymer can be used in the potential range from the first viologen redox to P(CPDT) redox. The polymer turned into highly transparent P(CPDT⁺-V²⁺-Me), blue P(CPDT-V²⁺-Me), dark violet P(CPDT-V√⁺-Me), and violet P(CPDT-V⁰-Me) approximately at 0.8, −0.4, −0.8, and −1.7 V versus Ag/Ag⁺, respectively.     

Phthalate-derivative/TiO2-modified electrode for electrochromic application

We studied electrochromic properties (EC) of phthalate derivatives (TP), which showed reversible color change from colorless clear to three primary colors by electrochemical reaction, from a viewpoint of color electronic paper. To improve the ability of keeping coloring state under an open circuit, we successfully prepared terephthalate-derivative/TiO₂-modified electrode and evaluated its EC properties. TP film also showed reversible color change from clear to magenta and enabled not only keeping the coloring state longer under open-circuit condition but also good bleaching response under short-circuit condition.     

A new low-voltage-driven polymeric electrochromic

Design, synthesis, and properties of a novel donor-acceptor-donor type low-voltage-driven green polymeric electrochrome, P1, which is based on 8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-11-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)acenaphtho[1,2-b]quinoxaline (1) are highlighted. It is noted that P1 has an ambipolar (n- and p-doping processes) character in 0.1 M tetrabutylammonium hexafluorophosphate/dichloromethane solution and switches to a transmissive blue state upon oxidation. Furthermore, this new polymeric electrochromic candidate exhibits high redox stability, high coloration efficiency and/or contrast ratio, high percent transmittance (%T) and low response time (1.0 s) with a band gap of 1.10 eV-1.25 eV.     

Electrochromic features of hybrid films composed of polyaniline and metal hexacyanoferrate

Hybrid organic/inorganic films, composed of polyaniline (PANI) matrix and Prussian blue-like nickel hexacyanoferrate redox centers, showed reversible electrochromic behavior in acidic potassium salt electrolytes. The system's coloration properties were assessed from various spectroelectrochemical measurements including voltabsorptometry that involved monitoring of the time-derivative signal of absorbance at 700 and 410 nm as a function of linearly scanned potential. Gold-covered foil was used as a conductive, optically transparent, substrate onto which the composite film was electrodeposited by potential cycling in the mixture for modification consisting of aniline monomer, Ni²⁺, Fe(CN)₆³⁻ and electrolyte containing K⁺ and H⁺ ions. An important feature of hybrid (composite) material was that its electrochromic properties were dominated by color changes occurring in the PANI component. Coloration originating from nickel hexacyanoferrate barely affected the system's electrochromic characteristics. But the cyanometallate redox centers distributed in the PANI matrix behaved reversibly as expected for a system capable of fast charge transport.