Electrochromic Stability Research Articles

Effects of oxidation potential and retention time on electrochromic stability of poly (3-hexyl thiophene) films

Herein, we report the effects of applied voltage on the electrochromic (EC) stability of poly(3-hexylthiophene) (P3HT) films during EC reactions. The transmittance difference and cycling stability of these films were monitored to optimize the oxidation voltage, and their chemical compositions were analyzed by X-ray photoelectron spectroscopy after long-term electrochemical cycling. High oxidation voltages increased the color contrast of P3HT films but decreased their cycling stability due to facilitating chemical degradation. Furthermore, at an optimized oxidation voltage, the retention time during potential pulsing was adjusted utilizing the optical memory of P3HT, revealing that the decreased voltage application time reduced power consumption by 9.6% and enhanced EC stability without loss of color contrast.

Stable Electrochromic Polyschiff Bases Containing Triarylamine Units: Synthesis, Electrochemical, and Acidochromic Properties

ABSTRACTFour polySchiff bases containing different triphenylamine moieties were synthesized based on the polycondensation reaction of 4-methyl-4′,4″-diformyltriphenylamine with various aromatic diamines which contain triphenylamine groups. Especially, 4-methyl-4′,4″-diformyltriphenylamine was obtained by the reduction of compound with nitril groups with diisiobutylaluminum hydride. The structures of 4-methyl-4′,4″-diformyltriphenylamine and polySchiff bases were confirmed by Fourier transform infrared and the nuclear magnetic resonance techniques. The polySchiff bases displayed good thermal stability, with 5% weight loss above 450°C under nitrogen atmosphere. All the polymer films exhibited good electrochemical and electrochromic stability under repeatedly switching electrode voltages. Take the polySchiff base-d, for example, the color changed from the pale yellow neutral state to green and crimson oxidized state at applied potentials ranging from 0.0 to 1.6 V. The polySchiff bases showed obvious acidochromic properties. The polySchiff bases exhibited a typical photovoltaic response and good stability. Consequently, the polySchiff bases would be promising electrochromic and acidochromic materials.

Synthesis of highly branched conducting polymer architecture for electrochromic applications

Electrochromic materials have attracted enormous attention due to their potential applications, such as low-power displays, smart windows for energy efficient buildings, electrochromic e-skins, self-dimming rear mirrors for automobiles and so on. Synthetic strategies of new materials for electrochromic are believed to be the key factors that will help to significantly improve the electrochromic performance and extend their application areas. In this account, we designed and synthesized a novel star shape dithienylpyrrole derivative, namely N1,N3,N5-tris(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzene-1,3,5-tricarboxamide (TCA), to obtain high optical and electrical performance as functional electrochromic material. After electrochemical polymerization of the TCA, the polymer shows superior optical and electrical properties due to its more conjugated unique three-dimensional shape and highly-branched structure in comparison with its linear counterparts. It has been determined that optical properties and long term electrochromic stability of pTCA are the best among the PSNS derivatives in the literature after evaluating its electrochemical, spectroelectrochemical and EQCM experiment results.

Synthesis and Performance of Highly Stable Star-Shaped Polyaniline Electrochromic Materials with Triphenylamine Core

The molecular architecture of conducting polymers has a significant impact on their conjugated structure and electrochemical properties. We have investigated the influence of star-shaped structure on the electrochemical and electrochromic properties of polyaniline (PANI). Star-shaped PANI (SPANI) was prepared by copolymerization of aniline with triphenylamine (TPA) using an emulsion polymerization method. With addition of less than 4.0 mol.% TPA, the resulting SPANI exhibited good solubility in xylene with dodecylbenzenesulfonic acid (DBSA) as doping acid. The structure and thermal stability of the SPANI were characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis, and the electrochemical behavior was analyzed by cyclic voltammetry (CV). The electrochromic properties of SPANI were tested using an electrochemical workstation combined with an ultraviolet–visible (UV–Vis) spectrometer. The results show that, with increasing TPA loading, the thermal stability of SPANI increased. With addition of 4.0 mol.% TPA, the weight loss of SPANI was 36.9% at 700°C, much lower than the value of 71.2% for PANI at the same temperature. The low oxidation potential and large enclosed area of the CV curves indicate that SPANI possesses higher electrochemical activity than PANI. Enhanced electrochromic properties including higher optical contrast and better electrochromic stability of SPANI were also obtained. SPANI with 1.6 mol.% TPA loading exhibited the highest optical contrast of 0.71, higher than the values of 0.58 for PANI, 0.66 for SPANI-0.4%, or 0.63 for SPANI-4.0%. Overdosing of TPA resulted in slow switching speed due to slow ion transport in short branched chains of star-shaped PANI electrochromic material. Long-term stability testing confirmed that all the SPANI-based devices exhibited better stability than the PANI-based device.

Enhancing the electrochromic performances of polyaniline film through incorporating polyaniline nanofibers synthesized by interfacial polymerization approach

In this paper, we demonstrate a simple approach to improve the electrochromic performances of polyaniline (PANI) by incorporating PANI nanofibers (PANI-NFs) synthesized by interfacial polymerization into water-soluble PANI:poly(styrene sulfonate) (PANI:PSS). The one-dimensional PANI-NFs endow spin-coated PANI film high electrochemical activities and electrochromic properties. The structures and morphologies of PANI-NFs were characterized by FTIR spectroscopy and SEM observation. The electrochemical behaviors of PANI/PANI-NFs composites were analyzed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochromic properties of composites were tested using electrochemical working station combining a UV-Vis spectrometer. The results show that the PANI-NFs with even diameter of ~ 30 nm can be synthesized easily using interfacial polymerization method. With the increasing of feeding amount of PANI-NFs, the oxidation peaks of CV curves shift to low potential direction, indicating enhanced electrochemical activities. The electrochromic test confirms that the PANI/PANI-NFs composites films have higher electrochromic contrast of 0.67 as comparison to 0.49 of PANI:PSS film. The PANI/PANI-NFs also exhibit excellent electrochromic stability. After 2000 cycles switching, only less than 4% contrast decay is observed. The enhanced electrochromic properties can be attributed to the small charge-transfer resistance and facile ion diffusion process brought by PANI-NFs. The EIS tests exhibit that with incorporating of highly conductive PANI-NFs, the PANI/PANI-NFs composites possess relatively lower charge-transfer resistance of 76 Ω as comparison to 94 Ω of neat PANI:PSS.

Synthesis and Electrochromism of Highly Organosoluble Polyamides and Polyimides with Bulky Trityl-Substituted Triphenylamine Units.

Two series of polyamides and polyimides containing bulky trityl-substituted triphenylamine units were synthesized from condensation reactions of 4,4′-diamino-4′′-trityltriphenylamine with various dicarboxylic acids and tetracarboxylic dianhydrides, respectively. The polymers showed good solubility and film-forming ability. Flexible or robust films could be readily obtained via solution-casting. The use of aliphatic diacid or dianhydride reduces interchain charge transfer complexing and leads to colorless polyamide and polyimide films. These polymers showed glass-transition temperatures in the range of 206–336 °C. Cyclic voltammograms of the polyamide and polyimide films displayed reversible electrochemical oxidation processes in the range of 0–1.0 or 0–1.3 V. Upon oxidation, the color of polymer films changes from colorless to blue-green or blue. As compared to the polyimide counterparts, the polyamides showed lower oxidation potentials and thus a higher electrochromic stability and coloration efficiency. Simple electrochromic devices were also fabricated as a preliminary investigation for electrochromic applications of the prepared polymers.

The trade-off between electrochromic stability and contrast of a thiophene—Quinoxaline copolymer

The stability of organic electrochromic devices is a crucial issue for their applications. However, until now the degradation mechanism of electrochromic materials are still not fully understood especially for electrochromic conjugated polymers (ECPs). To improve device stability, intensive investigation on the degradation mechanism of ECPs is urgently needed. Here we report our study on the electrochromic degradation in a thiophene–quinoxaline copolymer: poly [2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1). The results of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectra (UPS) and UV–vis transmission spectra reveal that there are three main factors during the electrochromic degradation of TQ1. The first one is anion (ClO4−) irreversibly deep trapped, while the second is peroxidation of the thiophene group in TQ1. Both factors reduce the conductivity and electrochromism of TQ1. The third is structural relaxation resulting lager conjugated system of TQ1 molecules in film, which is gradually developed during 400 cycling of CV at a narrow potential range (0–1V). When a potential range 0–0.7V is applied, all three factors are prohibited, no electrochromism degradation is observed anymore, although the contrast becomes smaller. Our investigation systematically discloses the degradation mechanism during the electrochemistry processing of a ECP (TQ1), demonstrating the significance of trade-off between the electrochromic stability and contrast of the ECP.

Graphene-poly(nickel complex) as novel electrochromic nanocomposite for the fabrication of a robust solid-state device

An electrochromic nanocomposite based on a nickel-salen polymeric film – poly[Ni(3-Mesalen)], Mesalen=N,N’-bis(3-methylsalicylideneiminate) – and graphene nanoplatelets (GFNPs) with enhanced electrochromic stability was successfully prepared by anodic electropolymerization.Although the electrochemical processes typical of the polymer film were not changed by the presence of graphene, higher electroactive surface coverages could be obtained for nanocomposite films, which suggest the incorporation of GFNPs into the polymeric network. The nanocomposite showed multi-electrochromic behavior, with color changes between yellow (reduced state) and green (oxidized state). The inclusion of GFNPs into the poly[Ni(3-Mesalen)] structure accelerates the switching process, with the response time for green coloration decreasing by 50.7% and for yellow coloration by 60.0%, for films prepared with 30 electropolymerization cycles. In terms of electrochemical stability, after 10,000 electrochemical cycles the loss of charge was 7% for the graphene nanocomposite. The nanocomposite film was used as electrochromic material to assemble a flexible solid-state electrochromic device (ECD), which exhibited an outstanding electrochemical stability - only 3% of charge loss after 15days of continuous activity.

Synthesis and Properties of Redox-Active Polyimides with 3,5-Bis(trifluoromethyl)- or 3,5-Dimethyl-Substituted Triphenylamine Groups

ABSTRACTTwo series of novel redox-active polyimides 8a–8f and 9a–9f were prepared through a conventional two-step procedure from six commercially available tetracarboxylic dianhydrides with 3,5-bis(trifluoromethyl)-4′,4″-diaminotriphenylamine and 3,5-dimethyl-4′,4″-diaminotriphenylamine, respectively. All the polyimides were amorphous and most of them could afford flexible and tough films with good thermal and mechanical properties. Cyclic voltammograms of the polyimides 9a–9f showed reversible redox waves with half-wave potentials (E1/2) in the range 1.12−1.25 V versus Ag/AgCl in acetonitrile solution. The polymer films revealed good electrochemical and electrochromic stability, with a color change from neutral pale yellowish to blue doped form at applied potentials ranging from 0 to 1.70 V.

Electrochemical synthesis of polyaniline/inorganic salt binary nanofiber thin films for electrochromic applications

Polyaniline conductive polymer thin films without or with LiClO4 inorganic salt were coated by electrochemical deposition method on ITO surface. Electrochromic stability test, electrochemical behavior, coloring performance, optical properties and surface formations of the produced films were studied in detail. The deposited films were found to have a good stability. Electrochemical analysis showed that the conductivity of LiClO4 doped PANI film was higher than that of the PANI. Oxidation and reduction peaks, and potentials differed significantly depending on the content of the electrolytes. SEM studies demonstrated that the surface of each film consisted of completely nanofibers. Addition of LiClO4 to the deposition electrolyte decreased substantially the diameter of these nanofibers. PANI film with LiClO4 exhibited four colors, while pure PANI film had three different colors. The EDX results obtained from the surface of LiClO4 doped PANI material indicated that PANI and LiClO4 could be successfully linked to form PANI/LiClO4 binary thin film.

Fluorescent and electrochromic polymers from 2,8-di(carbazol-9-yl)dibenzothiophene and its S,S-dioxide derivative

We report the synthesis and characterization of two carbazole-endcapped monomers, namely 2,8-di(carbazol-9-yl)dibenzothiophene (SCz) and 2,8-di(carbazol-9-yl)dibenzothiophene S,S-dioxide (SO2Cz), and their derived polymers PSCz and PSO2Cz prepared by both FeCl3 oxidative coupling and electropolymerization processes. The dilute solutions of PSCz and PSO2Cz prepared by chemical oxidative coupling exhibited fluorescent and solvatochromic behavior. Thin polymeric films could be robustly electrodeposited onto the surface of the ITO-glass substrate by repetitive cyclic voltammetry scanning of monomers SCz and SO2Cz in an electrolyte solution between 0 and 1.8 V. The electrochemically generated polymer films exhibited two reversible oxidation redox couples due to successive oxidations of the biscarbazole unit. These polymer films also revealed good electrochemical and electrochromic stability, with coloration change from a colorless neutral state to yellow, green and blue oxidized states. Switching ability of the polymers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that the polymers exhibit moderate electrochromic performance.

Synthesis and characterisation of azobenzene-bridged cationic–cationic and neutral–cationic electrochromic materials

Azobenzene-bridged cationic–neutral and cationic–cationic were synthesized, characterized and compared with azobenzene-bridged neutral–neutral materials. Azobenzene-bridged cationic–cationic and neutral–neutral materials exhibited well-defined and reversible redox couples during redox processes, good electrochromic behavior, and appropriate contrast ratios in the visible regions. However, azobenzene-bridged cationic–neutral materials exhibited a quasi-reversible electrochemical process. The electrochromic stability of these compounds is in the order: azobenzene-bridged neutral–neutral materials>azobenzene-bridged cationic–cationic materials>azobenzene-bridged cationic–neutral materials. Electrochromic devices based on azobenzene-bridged neutral–neutral materials achieved maximum optical contrast, fast response time, and high coloration efficiency. The substituents of azobenzene-bridged cationic–cationic materials and the anions of azobenzene-bridged cationic–neutral materials did not significantly influence their electrochemical properties and response time, but slightly affected the maximum optical contrast, change in optical density, and coloration efficiency.

Electrochromism of interpolyelectrolyte poly(pyridinium) – Poly(styrene sulfonate) complexes

This paper represents a synthesis method of both soluble and insoluble interpolyelectrolyte complexes due to interaction of poly(4,4-(1,4-phenylene)bis(2,6-diphenylpyridinium) triflate) (PV) and sodium polystyrene sulfonate (PSS). Systematic evaluation of electrochromic properties of the both type complexes is given compared to the pristine electrochromic PV. The complexes composition and properties were studied as a function of polyanion and polycation concentrations and their ratios. It was demonstrated that non-stoichiometric insoluble complexes PV/PSS with an excess of PSS are formed in the initial mutual solvent DMF/H2O 5/1. Films prepared from that mixtures exhibit slower response times and deteriorated electrochromic stability. Non-stoichiometric interpolymer complexes PV/PSS with an excess of PV remain soluble in the initial solvent. Corresponding films have a superior electrochromic contrast than films obtained from the solution of pristine PV under identical conditions. Thus, optimum mixture ratios were found to obtain soluble interpolymer complexes with the advanced properties that may open up new possibilities for making novel electrochromic devices.

Influence of disordered morphology on electrochromic stability of WO3/PPy

Tungsten oxide (WO3) films are critical for smart windows because of their capacity of varying the throughput of visible light and solar energy. This study highlights the evolution of structural and morphological changes of electrodeposited WO3 thin films coated with polypyrrole (PPy) by using chemical bath deposition. The structural and surface properties of WO3 thin films were studied using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrochemical stability was inspected using repetitive cyclic voltammetry (CV) cycles for each sample in LiClO4-PC electrolyte for prolonged periods. The results showed an improvement in the electrochemical stability after the CV study.

Electrochemical synthesis and electrochromic properties of new conjugated polycarbazoles from di(carbazol-9-yl)-substituted triphenylamine and N-phenylcarbazole derivatives

Abstract Two carbazole end-capped monomers containing triphenylamine or N -phenylcarbazole as an interior core, namely 4,4′-di(carbazol-9-yl)-4″-methoxytriphenylamine (TPA-2Cz) and 3,6-di(carbazol-9-yl)- N -(4-methoxyphenyl)carbazole (PhCz-2Cz), were prepared by a well-known chemistry from readily available reagents. The electrochemistry and electropolymerization of these two monomers were investigated and compared with those of structurally similar analogs with tert -butyl groups attaching on the active sites of the end-capped carbazole units. The polymeric films were built onto ITO/glass surface by repetitive cyclic voltammetry (CV) scanning of the monomer solutions containing an electrolyte. The electro-generated polycarbazole films exhibited high redox-activity and strong color changes upon electro-oxidation, which can be switched by potential modulation. The remarkable electrochromic behavior of the film was clearly interpreted on the basis of spectroelectrochemical studies, and the electrochromic stability was evaluated by the electrochromic switching studies.

Electrosynthesis of ambipolar electrochromic polymer films from anthraquinone–triarylamine hybrids

ABSTRACTTwo ester derivatives featuring anthraquinone as an interior core and terminal electroactive triphenylamine or carbazole groups were prepared by the condensation of 2,6‐dihydroxyanthraquinone with 4‐(diphenylamino)benzoyl chloride and 4‐(9H‐carbazol‐9‐yl)benzoyl chloride, respectively. The electrochemistry and electropolymerization of these monomers were investigated. The polymeric films were built onto ITO/glass surface by repetitive cyclic voltammetry scanning of the monomer solutions containing an electrolyte. The electrogenerated polymer films exhibited reversible electrochemical processes and strong color changes upon electro‐oxidation or electro‐reduction, which can be switched by potential modulation. The remarkable electrochromic behavior of the film was clearly interpreted on the basis of spectroelectrochemical studies, and the electrochromic stability was evaluated by the electrochromic switching studies. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 644–655

Controllable synthesis of W18O49 nanowire arrays and their application in electrochromic devices

Tungsten oxide nanowire arrays as effective electrochromic working electrodes were fabricated on seed-free FTO glass through a facile solvothermal process. Polyethylene glycol was used as the structure-directing agent to control the crystal growth because of selective absorption on the facet of tungsten oxide crystals. Phase identification and growth mechanism of monoclinic W18O49 nanowire arrays are also extensively discussed. Uniform transparent W18O49 nanowire arrays film exhibits remarkable performance of electrochromic properties, which include high contrast (49.64 % at 632.8 nm), high electrochromic stability (>3000 CV cycles), and fast coloration/bleaching response (tc ~ 7.9 s, tb ~ 1.4 s). These properties of the W18O49 nanowire arrays film endow its promising practical applications in large-area smart windows.

Effect of precursors on the microstructural, optical, electrical and electrochromic properties of WO3 nanocrystalline thin films

Spray-deposited tungsten oxide (WO3) nanocrystalline thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electron mi- croscopy and atomic force microscopy in order to study the precursor induced changes in their structural and morpho- logical properties. The crystallite size and the root mean square surface roughness have been found to be minimum for the WO3 thin films prepared using ammonium tung- state. The optical and spectral studies of the films were carried out using UV-visible spectroscopy and photolu- minescence spectroscopy. Electrical transport properties of the films were studied by measuring the film resistivity as a function of temperature. Electrochromic studies of the WO3 films were carried out from cyclic voltammetry, chronocoulometry and chronoamperometry measurements. The films grown using ammonium tungstate exhibit high electrochromic reversibility (*91 %) and large charge storage capacity. The cyclic voltammograms of the films do not change even after 50 scan cycles, confirming the electrochromic stability in the WO3 films. Overall, the film prepared using ammonium tungstate may be a suitable candidate for electrochromic devices.

Synthesis of electroactive and electrochromic poly(amide-imide)s containing diphenylpyrenylamine moieties

A novel dicarboxylic acid monomer bearing two built-in imide rings, namely N,N-bis(4-trimellitimidophenyl)-1-aminopyrene, was synthesized from the condensation of N,N-di(4-aminophenyl)-1-aminopyrene and two equivalent amount of trimellitic anhydride. New poly(amide-imide)s (PAIs) with diphenylpyrenylamine segments were prepared by the direct phosphorylation polyamidation reactions from the newly synthesized diimide-diacid monomer with two different aromatic diamines or from N,N-di(4-aminophenyl)-1-aminopyrene with four different imide ring-preformed dicarboxylic acids. All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films. These PAIs showed glass-transition temperatures (T gs) in the range of 211–352 °C, and they did not show significant weight-loss before 500 °C. Cyclic voltammograms of the PAI films cast onto the indium-tin oxide (ITO)-coated glass substrate revealed reversible electrochemical oxidation processes accompanied with strong color changes from the pale yellow neutral state to the purplish blue oxidized state and the orange reduced state, respectively. Incorporating the diphenylpyrenylamine unit on the amide side of PAIs led to lower oxidation potentials and higher redox reversibility and, thus, better electrochromic performance such as high coloration efficiency, fast switching speed, and high electrochromic stability.

High coloration efficiency and fast switching speed of poly(amic acid-imide)s containing triphenylamine in acidic electrolyte

The PAA-IM-1 film showed excellent reversible electrochromic stability and short switching time in acidic electrolyte (MBSA).