Excellent Electrochromic Research Articles

Enhanced electrochromic performance of carbon-coated V2O5 derived from a metal–organic framework

In this study we synthesized a vanadium (V)-containing metal–organic framework (MOF) and used it as a template to prepare V2O5 NPs. We used MIL-47, a V-containing MOF having uniform C and V distributions, as a precursor for the preparation of carbon-coated V2O5 (C@V2O5) samples through annealing. The C@V2O5 structures were readily dispersed in poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) to form stable solutions, allowing the deposition of C@V2O5 on various substrates through simple low-temperature solution-based processes. The uniform coating of carbon on V2O5 was useful for two reasons: (i) the outer layer enhanced the electronic conductivity of a V2O5 electrode and its corresponding electrochemical properties and (ii) based on the electrochemical quartz crystal microbalance (EQCM) analysis, the carbon coating served as a buffer layer that allowed Li+ ion transport, but blocked migration of solvent into the V2O5 electrode, thereby improving the dimensional and electrochemical stability. Compared with the bare V2O5, C@V2O5 exhibited excellent electrochromic (EC) performance, with an EC contrast of 45.8%, a mean response time of 3.4 s, and a coloration efficiency of 89.3 cm2/C. C@V2O5 also displayed higher cycling stability (80.6% retention after 5000 cycles) and highly reversible ionic transport during redox reactions, compared with those of the bare V2O5.

Electrochromic properties of sputter-deposited rhodium oxide thin films of varying thickness

Amorphous rhodium (Rh) oxide thin films ranging in thickness from 50 to 400 nm were prepared by reactive sputtering at −20 °C in either an oxygen (O2) or water (H2O) vapor atmosphere. Their electrochemical and electrochromic (EC) properties were investigated in an aqueous KOH electrolyte solution. The transferred charge density increased linearly with increasing film thickness, and a 400 nm-thick H2O-deposited film displayed the highest transferred charge density of 60 mC/cm2. Electrochemically active Rh atoms comprised approximately 20% and 50% of the Rh atoms in the O2- and H2O-deposited films, respectively. Transmittance by the bleached and colored films decreased with increasing film thickness in accordance with Lambert's law. The 400 nm-thick H2O-deposited film exhibited the largest change in transmittance (57%) at 700 nm. In contrast, the maximum change in transmittance by an O2-deposited film (16%) was observed at a thickness of 200 nm. The molar absorption coefficients of the bleached H2O-deposited films were much smaller than those of the O2-deposited films. However, the molar absorption coefficients of the colored H2O- and O2-deposited films were very similar. The Rh oxide thin films prepared by sputtering in a H2O vapor atmosphere exhibited low molar absorption coefficients in the bleached state and exhibited excellent EC properties and stable transmittance through 25,000 cyclic voltammetry cycles.

Dual-Branched Dense Hexagonal Fe(II)-Based Coordination Nanosheets with Red-to-Colorless Electrochromism and Durable Device Fabrication.

Highly dense hexagonal Fe(II)-based coordination nanosheets (CONASHs) were designed by dual-branching, at the metal-coordination moieties and the tritopic ligands, which successfully obtained a liquid/liquid interface by the complexation of Fe(II) ions and the tritopic bidentate ligands. The 1:1 complexation was confirmed by titration. The obtained Fe(II)-based nanosheets were fully characterized by small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). A monolayer of the sheets was obtained, employing the Langmuir-Blodgett (LB) method, and the determined thickness was ∼2.5 nm. The polymer nanosheets exhibited red-to-colorless electrochromism because the electrochemical redox transformation between Fe(II) and Fe (III) ions controlled the appearance/disappearance of the metal (ion)-to-ligand charge-transfer (MLCT) absorption. The poor π-conjugation in the tritopic ligands contributed to the highly colorless electrochromic state. A solid-state device, with the robust polymer film, exhibited excellent electrochromic (EC) properties, with high optical contrast (ΔT > 65%) and high durability after repeated color changes for >15 000 cycles, upon applying low-operating voltages (+1.5/0 V).

High-performance and ultraflexible PEDOT/silver nanowires/graphene films for electrochromic applications.

We fabricate a kind of flexible electrochromic (EC) film by spraying the mixed dispersion of silver nanowires (AgNWs) and poly (3, 4-ethylenedioxythiophene) (PEDOT) on the graphene (GR) electrode. AgNWs are embedded in the PEDOT nanoparticles, forming an interlaced conductive network and double electron transport channels; therefore, the disadvantages of poor conductive GR electrodes have been remedied effectively. The subsequent GR-based PEDOT/AgNWs composite films have revealed remarkable optical contrast (63%), high coloration efficiency (${182.8}\;{{\rm cm}^{2}}\;{{\rm C}^{ - 1}}$182.8cm2C-1), and good cycle stability (keeping the optical contrast about 60% after switching cycles of 16,000 s). In addition, the GR-based composite films can keep good EC performance after 2000 cycles of bending tests, while those of the ITO/PET-based composite films decrease dramatically. The ultraflexible GR-based PEDOT/AgNWs composite films with excellent EC properties present an opportunity for fabricating large-area flexible EC devices.

Diphenyl sulfone based multicolored cathodically coloring electrochromic materials with high contrast

A series of multicolored cathodically coloring electrochromic (EC) materials based on diphenyl sulfone (DPS) moiety were synthesized and characterized. Herein two electron donors, N 1 ,N 1 ,N 3 ,N 3 -tetraphenylbenzene-1,3-diamine (TPA) and 1,3-di (9H-carbazol-9-yl)benzene (MCP), were employed to construct donor-acceptor (D-A) or donor-acceptor-donor (D-A-D) small molecules with DPS as the acceptor. These small molecules can achieve excellent EC properties, including multicolored electrochromism, high optical contrast over 90%, high coloration efficiency and good cyclic stability. Remarkably, the color of MCP-DPS could be switched from colorless to three primary colors gradually, containing green, magenta and yellow driven by the 3-step reversible reduction, meeting the requirements of full-color EC display. • Diphenyl sulfone was first employed as the acceptor moiety to construct D-A or D-A-D electrochromic small molecules. • The diphenyl sulfone derivatives exhibit multicolored electrochromism with optical contrast over 90%. • Through slight modification of chemical structure, the electrochromic properties can be changed to a large extent. • Coloration efficiency can be improved by enhancing the intramolecular charge transfer interactions.

A new green‐to‐transmissive polymer with electroactive poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) as an interface layer for achieving high‐performance electrochromic device

AbstractA new neutral green electrochromic (EC) polymer, namely poly(5,8‐bis(2,3‐dihydro[3,4‐B][1,4]dioxin‐5‐yl)‐2,3‐dual(4‐(hexadecyloxy) phenyl) quinoxaline) (PBOPEQ) was designed and synthesized. PBOPEQ‐poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film was further prepared by electrochemical polymerization on the PEDOT:PSS modified indium tin oxide (ITO) electrode. Scanning electron microscopy images and ultrasonic experiment indicate that PBOPEQ‐PEDOT:PSS film shows better film‐forming ability and stronger interface adhesive with ITO electrode compared to that of PBOPEQ film. It is worth mentioning that PBOPEQ‐PEDOT:PSS film presents more reversible redox characteristic, better optical contrast (~40%) and coloration efficiency (~230 cm2 C−1) at 678 nm, excellent EC stability and memory property (36 hr), which should be ascribed to that the electroactive PEDOT:PSS layer facilitates the charge transfer process and enhances the ion doping/dedoping properties. EC device based on PBOPEQ‐PEDOT:PSS film exhibits superior integrated performance such as reversible color change from green to transmissive, optical contrast of 41.0% and switching time less than 1 s. Accordingly, PBOPEQ‐PEDOT:PSS is an excellent EC material when combined with electroactive PEDOT:PSS interface layer for achieving high performance device, which shows potential applications in displays, electronic papers, and tags.

A Long‐Life Battery‐Type Electrochromic Window with Remarkable Energy Storage Ability

Electrochromic (EC) windows with controllable transmittances according to ambient temperature and solar irradiation strength are highly desired for energy‐efficient buildings. However, traditional EC windows operate via consuming electrical energy to trigger the chromogenic reactions, with negligible energy storage ability. Herein, a facile battery‐type Prussian blue (PB, Fe4III[FeII(CN)6]3)/Zn EC window with excellent EC properties (transmittance modulation = 84.9% at 633 nm), remarkable energy storage ability (average output voltage = 1.24 V and areal capacity = 78.9 mAh m−2), fast switching time (tbleaching = 4.1 s and tcoloring = 4.6 s), as well as an ultralong cycling lifetime (7000 cycles with 60.7% capacity retention and 92.7% transmittance modulation retention) is reported, thanks to the rational electrode and electrolyte design. As an EC window, this device can effectively promote energy efficiency and occupational comfort of buildings by regulating visible light transmittance. As a battery, this device can work as backup power or a component of smart grids, making the buildings more sustainable and functional. The design concept of this bifunctional device is helpful to further the development of next‐generation EC windows.

WO3 quantum-dots electrochromism

In the past decades, as an alternative to traditional sputtering deposition process, atmospheric pressure solution-based deposition (APSD), considered as a cost-effective method for the construction of nanostructured electrochromic (EC) films with improved EC performance, is widely studied. However, the inadequate EC performance of the films, especially the poor cycle stability, impedes the development of solution-processed EC films. This paper reports excellent EC performance results for WO3 quantum-dots films prepared by a common APSD process with either Li+ or Al3+ electrolyte: a large optical contrast (97.8% and 94.1% at 633 nm), a fast switching speed (4.5 s and 13.5 s for coloring, 4 s and 10 s for bleaching) and an ultralong cycle life (10000 cycles with 10% optical contrast loss and 20000 cycles without degeneration at 633 nm). The excellent EC performance can be attributed to the ultrasmall size in all three-dimensions and no organic overlayer of WO3 quantum dots, which would greatly shorten the diffusion paths of intercalation ions, decrease interface barrier, provide fast charge-transport and electron-transfer kinetics and high reaction rates. Trivalent Al3+, as an alternative to common monovalent insertion ions (H+, Li+, Na+), was proven to be as an effective insertion ion for WO3 quantum dots. Compared with Li+ electrolyte, the films possess longer cycle life in Al3+ electrolyte, which can be attributed to the smaller ionic radius and the ability to support multi-electron redox reactions of Al3+. This research is an important first step for the fabrication of inexpensive EC smart windows, and should shape the future research on solution-based processes.

Metallopolymers and non-stoichiometric nickel oxide: Towards neutral tint large-area electrochromic devices

Wet-chemical approaches were utilized to fabricate electrochromic (EC) thin films of different chemical nature, but compatible to each other in terms of coloration and electrochemical properties. A metallo-supramolecular polyelectrolyte (Fe-MEPE) thin film is shown to exhibit a large visible light transmittance change (Δτv) of 54% when switched from deep blue-violet (Fe2+) to colorless (Fe3+). On the other hand, a soft sol-gel peroxo-based approach was pursued to fabricate non-stoichiometric nickel oxide (Ni1-xO) thin films on transparent conductive glass at low process temperature. Ni1-xO, due to the Ni2+/Ni3+ redox couple, shows an EC response with a Δτv of 44% when switched from a colorless state (Ni2+) to a grey-brown mixed-valence state (Ni2+/Ni3+). Proof-of-concept is provided for a glass-based EC device combining Fe-MEPE and Ni1-xO electrodes. The excellent EC performance is manifested in a Δτv of 28% for the full cell and a low haze of <2%. The EC films presented can be deposited on transparent conductive substrates via spin-coating, dip-coating, or slot-die deposition. The viability of this approach for later industrial production is demonstrated by the example of roll-to-roll (R2R) processing on transparent conductive films (TCF).

Fast-switching quasi-solid state electrochromic full device based on mesoporous WO3 and NiO thin films

Mesoporous tungsten trioxide (WO3) and nickel oxide (NiO) electrochromic (EC) thin films have been fabricated by sol-gel method with assistant of tri-block copolymer [PEO132PEO50PEO132] (F108). By controlling weight ratio of F108 and calcination temperatures, uniform and transparent mesoporous films are fabricated. Both WO3 and NiO films are comprised by nanoparticles with diameters of ca.10 nm, mesopores with pore size of approximately 6 nm are distributed in the films. The thickness of the films are ca. 400 nm. The as-prepared films have ultra-fast switching time during EC redox reactions. Applied with positive and negative voltages of 40 s respectively, the coloration/bleaching time of WO3 and NiO films are 5.7 s/2.3 s and 0.9 s/3.8 s, which is faster than that of comparative EC films fabricated by sol-gel method without F108 (coloration/bleaching time of WO3 and NiO films are 17.5 s/14.5 s and 13.6 s/4.9 s) and EC films fabricated by magnetron sputtering method (coloration/bleaching time of WO3 and NiO films are 29.4 s/21.3 s and 9.6 s/7.5 s). Quasi-solid state electrochromic device assembled with mesoporous WO3 and NiO thin films has excellent EC performance, such as fast switching speed (3.2/1.1 s for coloration/bleaching time), large optical modulation of about 45% (at 600 nm), high coloration efficiency (130.8 cm2/C at the wavelength of 600 nm) and good cycle stability. These excellent properties are derived from mesoporous channels in the films. For the mesoporous channels can shorten the diffusion paths and make it easier for ions to transport in films.

Terpyridine-Based Monolayer Electrochromic Materials

Novel electrochromic (EC) materials were developed and formed by a two-step chemical deposition process. First, a self-assembled monolayer (SAM) of 2,2':6',2″-terpyridin-4'-ylphosphonic acid, L, was deposited on the surface of a nanostructured conductive indium-tin oxide (ITO)screen-printed support by simple submerging of the support into an aqueous solution of L. Further reaction of the SAM with Fe or Ru ions results in the formation of a monolayer of the redox-active metal complex covalently bound to the ITO support (Fe-L/ITO and Ru-L/ITO, respectively). These novel light-reflective EC materials demonstrate a high color difference, significant durability, and fast switching speed. The Fe-based material shows an excellent change of optical density and coloration efficiency. The results of thermogravimetric analysis suggest high thermal stability of the materials. Indeed, the EC characteristics do not change significantly after heating of Fe-L/ITO at 100 °C for 1 week, confirming the excellent stability and high EC reversibility. The proposed fabrication approach that utilizes interparticle porosity of the support and requires as low as a monolayer of EC active molecule benefits from the significant molecular economy when compared with traditional polymer-based EC devices and is significantly less time-consuming than layer-by-layer growth of coordination-based molecular assemblies.

Electrochromic and non-volatile bistable resistive switching behaviour of acid-doped poly(triphenylamine ether)s

PurposeThis paper aims to investigate the electrochromic (EC) properties of poly(triphenylamine alkyl ether) and poly(triphenylamine aryl ether) in two different electrolyte solution to study the resistive switching behaviour of acid-doped poly(triphenylamine alkyl ether).Design/methodology_appachBy Buchwald–Hartwig coupling reaction, two novel poly[N-p-phenoxy-N-[4-[2-(2-methoxyethoxy)ethoxy]ethoxy]triphenylamineandpoly[N,N-bis(4-phenoxy)]triphenylamine were synthesized from 4-phenoxyaniline and two dibromo aromatic compounds, 1,2-bis[β,β′-(p-bromophenoxy)ethoxy]ethane and bis(4-bromophenyl) ether.FindingsPoly(triphenylamine alkyl ether) displayed excellent EC characteristics, with a coloration change from a colourless neutral state to light blue and red oxidized states, while poly(triphenylamine aryl ether) showed coloration a change from a colourless neutral state to light blue oxidized state in tetrabutylammonium perchlorate electrolyte solution. Moreover, p-toluenesulfonic acid-doped poly(triphenylamine alkyl ether) exhibited a non-volatile bistable resistive switching behaviour with a high high-conductivity/low-conductivity ratio of up to 104, long retention time exceeding 2.5 × 103 s and the switching threshold voltage was also lower than −2V.Research limitations/implicationsIn this paper, the non-volatile bistable resistive switching behaviour of acid-dopedpoly(triphenylamine alkyl ether) was in accordance with the molar ratio of 1:1. The effects of different molar ratios remained to be studied.Practical implicationsPoly(triphenylamine ether)s may find optoelectronic applications as new EC and resistive switching materials.Originality/valueThe effects of alkyl and aryl ether structures in the main chain on the EC and resistive switching behaviour of triphenylamine unit have not yet been reported.

Hydrothermal Formation of Tungsten Trioxide Nanowire Networks on Seed-Free Substrates and Their Properties in Electrochromic Device

Facile and cost-efficient hydrothermally grown 3-D tungsten trioxide $({\rm WO}_{3})$ nanowires (NWs) network film on seed-free fluorine-doped tin oxide (FTO) substrates without using additive or capping agent is reported. The NW networks are hexagonal phase and the morphologies are changed by adjusting the pH of precursor solutions. Growth mechanism of ${\rm WO}_{3}$ NWs is also extensively discussed. The designed porous film exhibits remarkable enhancement of the electrochromic (EC) properties. In particular, a significant optical modulation (57% at 632 nm), fast color switching speed (bleaching: 7 s and coloration: 21 s), high coloration efficiency ( $120.3~{\rm cm}^{2}~{\rm C}^{-1}$ at 632 nm), high ${\rm Li}^{+}$ diffusion coefficient $(2.14\times{10}^{-9}{\rm cm}^{2}~{\rm s}^{-1})$ , and excellent cycling stability (87% after 1000 cycles) are achieved for the 3-D NWs film. The improved EC properties are mainly attributed to the highly porous film, which makes the ${\rm Li}^{+}$ diffusion becomes easier and provides larger specific surface area for charge-transfer reactions. Furthermore, we also reported an EC device (50 mm $\times\,$ 50 mm) with a simple two-electrode configuration showing high optical contrast. The 3-D ${\rm WO}_{3}$ NWs network film acts as an excellent EC material.

Synthesis and Characterization of Polyaniline Film

The electrochromic PANI film was prepared by emulsion polymerization with dodecyl benzene sulphonic acid (DBSA) as dopant and ammonium persulfate (APS) as initiator. Ultrasonic dispersion was adopted in the polymerization. The electrochemical properties, the surface morphology and structure of the prepared PANI film was characterized by means of Fourier Transform infrared spectroscopy (FT-IR), cyclic voltammograms (CV) and field emission scanning electron microscope (FE-SEM), respectively. The relationship between the morphology and properties of PANI film was detailedly discussed. The PANI film exhibited an excellent electrochromism with reversible color changes form yellow to purple. The PANI film also had quite good reaction kinetics with fast switching speed, and the response time for oxidation and reduction were 65 ms and 66 ms, respectively.

Facile fabrication of NiOxHy films and their unique electrochromic properties

The electrochromic (EC) NiOxHy films were fabricated through a facile sol–gel method. The formation of high quality NiOxHy films came from adding the xerogel back into the sol and prolonging the annealing time at gradually increasing temperature up to 250 °C. Scanning electron microscopy and atomic force microscopy characterizations indicated films were compact, homogenous, and smooth. Glance angle X-ray diffraction investigation testified NiOxHy films were of poor crystallization. The Fourier transform infrared, and thermogravimetry and differential thermal analysis showed that films contained the mixture of NiO, Ni(OH)2, NiOOH, water, and organic substance. With the increasing of the xerogel ratio, the optical absorbance and reflectance of films had larger differences between the colored and bleached state, respectively. The film with the xerogel ratio of 1:5 showed excellent EC properties with a transmittance contrast as high as 60.88% at λ = 560 nm, which was higher than other sol–gel nickel oxide films reported.

Dendritic Mixed-Valence Dinuclear Ruthenium Complexes for Optical Attenuation at Telecommunication Wavelengths

Novel dendritic mixed-valence dinuclear ruthenium complexes were prepared and chemically cross-linked to form thin films on ITO electrodes. The cross-linked films exhibited an excellent electrochromism in the near-infrared (NIR) region and optical attenuation of 5.4 dB/μm in thickness at 1550 nm with a switching time of 2 s. A variable optical attenuator based on these NIR electrochromic ruthenium complex materials could be envisioned.

Influence of Organic Additive on the Morphological, Electrical and Electrochromic Properties of Sol-Gel Derived WO3 Coatings

The WO3 electrode is ubiquitous in an electrochromic device (ECD) and is a common choice as the electrochromic (EC) layer. EC films were deposited on different substrates by spin coating using peroxotungstic acid based precursor solutions followed by appropriate thermal treatment. Many properties of the films, including some of the EC properties dependant on microstructure of the films, were found to be modified by the addition of small amounts of organic acid to the precursor solution. A study of structural, electrical and electrochromic properties of films cast by using precursor solution comprising 0 to 10 wt% of oxalic acid dihydrate (OAD) was carried out in terms of surface morphology, electrical resistance, structure and EC response. The important findings are that the addition of oxalic acid to the precursor solution results in films with excellent EC properties, devoid of cracks and decreases their dc electrical resistance.

All-solid-state electrochromic device of electrodeposited WO3 and prussian blue film with PVC gel electrolyte

An all-solid-state electrochromic device (SED) employing electrodeposited WO3 and prussian blue film with poly(vinyl chloride) (PVC) gel electrolyte that has high conductivity (10−3 S/cm) at room temperature has been fabricated. The SED has been found to have excellent electrochromism and memory characteristics. A reversible color change between blue and colorless was observed when an appropriate potential was applied repeatedly to the electrochromic display device. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1955–1958, 1998

All-solid-state electrochromic window of prussian blue and electrodeposited WO 3 film with poly(ethylene oxide) gel electrolyte

An all-solid-state electrochromic window (SEW) employing prussian blue and electrodeposited WO 3 film with poly(ethylene oxide) (PEO) gel electrolyte with high conductivity (2 mS/cm) has been fabricated. The SEW has been found to have excellent electrochromism and memory characteristics. The W 4f core level of WO 3 film at different levels of coloration has been investigated using X-ray photoelectron spectroscopy (XPS). W 4f peaks become broader after coloration. Composite structures of W 4f peaks have been attributed to the existence of different final states, screened by different numbers of W 5d electrons.

All solid-state electrochromic window of Prussian Blue and electrodeposited WO3 film with PMMA gel electrolyte

An all solid-state electrochromic window employing Prussian Blue and electrodeposited WO3 film with PMMA gel electrolyte has been fabricated. The electrochromic window shows excellent electrochromism and memory characteristics. The W 4f core level of the WO3 film at different levels of coloration has been investigated using XPS. W 4f peaks become broader after coloration.