Good Electrochromic Properties Research Articles

Improved electrochromic device based on mesoporous TiO2 and NiO films

Fabrication of electrochromic films with micro/nanostructures is one of the most feasible ways to improve their properties for high-performance electrochromic devices (ECDs). In this work, mesoporous TiO2 and NiO electrochromic films are prepared by sol-gel technique with an auxiliary solvent of F108 (PEO[Formula: see text]PPO[Formula: see text]PEO[Formula: see text]). By adjusting the content of F108 and heat treatment temperature, the transparent and uniform mesoporous films are successfully prepared. The TiO2 and NiO films are composed of inter-connected nanoparticles with a size of about 20 nm. The thicknesses of the films are about 300 nm and the mesoporous sizes are about 13 nm. The films have a short response time during the electrochromic process. When supplied with positive/negative voltages for 50 s, the coloring/bleaching times of TiO2 and NiO mesoporous films are 15/13 and 17/12 s, respectively. The ECD fabricated with TiO2 and NiO mesoporous films shows good electrochromic properties: short response time (14/19 s, for bleaching/coloring time), wide transmittance modulation range ([Formula: see text]37.21% at 540 nm), high coloration efficiency (CE) (100.6 cm2/C at 540 nm) and outstanding cycle stability (800 cycles). These are attributed to the mesoporous channels of films, which can increase reaction activity site, shorten ions transport path, and thus improve electrochromic reaction.

Adjustable optoelectronic properties of triphenylamine-ethylenedioxythiophene based hybrid electrochromic polymer with different electron-donating substituents

Due to the good optoelectronic properties of triphenylamine (TPA) and its derivatives-based organic conjugated polymers, they have been widely used in various organic electronic devices. They are easy to lose electrons to form stable cationic free radicals with color change under electrochemical oxidation conditions. Therefore, TPA derivatives-based electrochromism materials have attracted the widely attentions of researchers. In this work, a series of TPA derivatives were successfully obtained by Stille coupling reactions, and their basic optical and electrical properties were investigated in detail. Their corresponding polymer films (P(TPA-EDOT), P(PhTPA-EDOT), and P(OCH3TPA-EDOT)) were also prepared on transparent ITO glass by electrodeposition method and their electrochromic properties were further studied. Due to the relatively strong electron donating ability of OCH3– group on the TPA unit, the intramolecular charge transfer peak of OCH3TPA-EDOT is obvious red-shifted and its initial oxidation potential is relatively low, which is beneficial for it to get high-quality electrochromic polymers. Electrochemical analysis shows that all these three polymer films show reversible redox reaction with excellent redox stability. Spectroelectrochemistry shows that all of them have good electrochromic properties and show multi-electrochromic behavior with strong color change. The dynamic study show that all these three polymers have relatively fast switching time (as low as 0.8 s), high coloration efficiency (up to 206.2 C−1 cm2) and obvious optical contrast change. Especially in the near infrared region, the optical contrast is relatively high (P(TPA-EDOT) is 45.3 % at 1100 nm, P(PPhTPA-EDOT) is 53.1 % at 1100 nm, and P(OCH3TPA-EDOT) is 57.2 % at 1100 nm). All these results show that the different substituents on the TPA unit have a certain influence on the resultant monomers’ optoelectronic performances, and they also can adjust the optical band gap of the corresponding polymers with different electrochromic properties.

Polyacrylamide/sodium alginate double network hydrogel electrochromic devices based on 1,3,4-oxadiazole-extended viologen derivatives for energy-saving fields

In this paper, a novel electrochromic material of 1,3,4-oxadiazole-extended viologen derivative with good coplanarity and electron acceptor-electron donor-electron acceptor structure, BPYO-C6H13, was synthesized, and a polyacrylamide-sodium alginate dual network hydrogel (PAM-SA) with advantages of low cost, environmental protection, good biocompatibility, high optical transmittance (>85 %), good mechanical properties and good ionic conductivity (16.61 mS cm−1) was developed as the electrochromic hydrogel matrix for gel-state electrochromic devices based on BPYO-C6H13 (PAM-SA-ECD). BPYO-C6H13 showed good electrochromic properties in both solution-state electrochromic devices and gel-state electrochromic devices, and PAM-SA-ECD had a lower operating voltage (−1.4 V versus −1.7 V), a higher optical contrast (48.4 % versus 33.1 % and 22.1 %) as well as a higher coloration efficiency (348.7 cm2/C versus 234.8 and 120.7 cm2/C). Compared to PAM-SA gel-state electrochromic devices based on 1,1′-dihexyl-[4,4′-bipyridine]-1,1′-diium, BPYO-C6H13 with 1,3,4-oxadiazole π-extender showed a different colored state (green versus pink) and a higher coloration efficiency (348.7 cm2/C versus 275.9 cm2/C) due to different conjugated structure. PAM-SA-ECD was applied in smart windows and solar cell-powered displays, suggesting BPYO-C6H13 is promising in energy-saving fields.

Design and synthesis of donor-acceptor electrochromic polymers with remarkable near-infrared modulation

Developing electrochromic polymers (ECPs) for application in smart windows is highly desirable in the electrochromic field. However, most ECPs present weak solar irradiance regulation due to the inverse visible and NIR modulation. Herein, three donor-acceptor polymers containing 4,7-bis(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (HT-TZ) units are synthesized via direct arylation polymerization (DArP) method, and two copolymers with similar structure are prepared by electrochemical copolymerization for comparison. The copolymers synthesized by the DArP method present weak visible and high NIR modulation with an average visible (380 nm–780 nm) contrast below 15 % and NIR (750 nm–1400 nm) contrast above 60 %, inducing a high solar heat gain coefficient (SHGC) difference above 0.2 between the neutral and oxidized states, which is much higher than the reported high-performance ECPs. Additionally, these synthesized copolymers also present good electrochromic properties such as good stability and normal coloration efficiency, confirming their broad application potential in smart windows.

Stoichiometrically Optimized Electrochromic Complex [V2O2+ξ(OH)3-ξ] Based Electrode: Prototype Supercapacitor with Multicolor Indicator.

The systematic structure modification of metal oxides is becoming more attractive, and effective strategies for structural tunning are highly desirable for improving their practical color-modulating energy storage performances. Here, the ability of a stoichiometrically tuned oxide-hydroxide complex of porous vanadium oxide, namely [V2O2+ξ(OH)3-ξ]ξ = 0:3 for multifunctional electrochromic supercapacitor application is demonstrated. Theoretically, the pre-optimized oxide complex is synthesized using a simple wet chemical etching technique in its optimized stoichiometry [V2O2+ξ(OH)3-ξ] with ξ=0, providing more electroactive surface sites. The multifunctional electrode shows a high charge storage property of 610Fg-1 at 1Ag-1, as well as good electrochromic properties with high color contrast of 70% and 50% at 428 and 640nm wavelengths, faster switching, and high coloration efficiency. When assembled in a solid-state symmetric electrochromic supercapacitor device, it exhibits an ultrahigh power density of 1066mWcm-2, high energy density of 246mWhcm-2, and high specific capacitance of 290mFcm-2 at 0.2mAcm-2. A prepared prototype device displays red when fully charged, green when half charged, and blue when fully discharged. A clear evidence of optimizing the multifunctional performance of electrochromic supercapacitor by stoichiometrical tuning is presented along with demonstrating a device prototype of a 25cm2 large device for real-life applications.

Flexible Composite Electrochromic Device with Long-Term Bistability Based on a Viologen Derivative and Prussian Blue.

Viologen and Prussian blue (PB) exhibit good electrochromic properties, but certain limitations still exist. To improve the electrochromic properties of viologen, a viologen derivative 1,1'-bis(4-(bromomethyl)benzyl)-[4,4'-bipyridine]-1,1'-diium hexafluorophosphate (BBDV) was synthesized, and its electrochromic properties were investigated. Additionally, a flexible composite electrochromic device (FC-ECD) was prepared by using BBDV and PB as active materials. The structure of the FC-ECD was PET-ITO/gel electrolyte-BBDV/PB/PET-ITO. The applied voltage required for the FC-ECD was found to be lower than that of the ECD based on BBDV(FBBDV-ECD). Compared to FBBDV-ECD, FC-ECD exhibited a higher optical contrast (71.42%) and cyclic stability (89.51%). The FC-ECD exhibited multicolor changes under different applied voltages (ranging from -2.0 to +1.6 V). Especially, the color of the FC-ECD remained stable for 14 h after the removal of the applied voltage.

A double network AG/P(AAm-AAc)/P2W18 hydrogel with high stretchability for flexible electrochromic device

In this study, a novel electrochromic hydrogel AG/P(AAm-AAc)/P2W18 was prepared by loading polyoxometalate K6P2W18·10H2O (P2W18) into a double-network hydrogel formed with agar (AG) and copolymer of polyacrylamide (PAAm) and polyacrylic acid (PAAc). The mechanical properties of hydrogels can be tuned by adjusting the proportion of PAAc in the copolymer P(AAm-AAc). Electrochromic hydrogel shows the best mechanical properties when the proportion of PAAc is 10 % (AG/P(AAm-AAc)-10/P2W18), and the maximum elongation at break and the fracture stress are about 2.0 and 2.5 times higher than that of pure PAAm. P2W18 gives good electrochromic properties to the hydrogels without the addition of electrolytes. Under the external voltage, the electrochromic hydrogel changes from colorless to blue with the optical contrast up to 65.54 % at 700 nm. The electrochromic device based on this hydrogel is simple in structure, easy to manufacture and highly stretchable, which has good application potential in the field of wearable electronics.

High performance polythiophene derivative with good electrochromic and energy storage properties electrochemical synthesized in boron trifluoride diethyl etherate

In this study, novel poly(3,4-dibromothiophene) (PDBrTh) is firstly prepared through electrochemical polymerization method using boron trifluoride diethyl etherate (BF3·Et2O) as polymeric solvent. In BF3·Et2O, the electrochemical oxidation potential of 3,4-dibromothiophene is significantly reduced compared with in Acetonitrile/Tetrabutylammonium tetrafluoroborate (ACN/TBATFB) system, which provides conditions for high quality polymer preparation. The prepared PDBrTh in BF3·Et2O shows good electrochemical activity and thermal stability. The electrochromic and supercapacitive performance of the prepared PDBrTh are also studied. The color of the prepared PDBrTh can be reversibly changed between red and blue with fast response time and high optical contrast. Galvanostatic charge-discharge test shows that the prepared PDBrTh also has good electrochemical energy storage performance. The specific capacitance value of the PDBrTh can reach to 229.6 F g−1 under the current density of 1 A g−1, showing good energy storage capacity. An all-polythiophenes electrochromic supercapacitor device (ESD) is constructed by prepared PDBrTh and poly(3,4-ethylenedioxythiophene), the color of the device can change between red and dark blue. The ESD also shows good energy storage property and robust charge-discharge stability. Moreover, the ESD shows obvious color changes and corresponding light transmittance changes during the charging and discharging process, realizing intelligent visual monitoring of the energy storage state. This study shows that the prepared PDBrTh has good practical application potential in the field of intelligent wearable energy storage.

High Electrochromic Performance of Perylene Bisimide/ZnO Hybrid Films: An Efficient, Energy-Saving, and Green Route.

The composite or hybrid of organic and inorganic materials is one of the common ways to improve the properties of photoelectric functional materials. Perylene bisimide (PBI) derivatives, as large π-conjugated organic small molecules, are a class of photoelectric functional materials with excellent performance. However, there were few reports on PBIs in the electrochromic field due to the difficulty of film-forming caused by their generally poor solubility. Here, water-soluble PBI derivatives (PDI-COOH and PCl-COOH) were synthesized. The hybrid films (ZnO@PDI-COOH/PCl-COOH) formed by the coordination bond and π-π stacking were prepared via a simple solution immersion method. Fourier transform infrared spectrometry and X-ray diffraction as well as scanning electron microscopy, and energy-dispersive spectrometry results further confirmed the formation of hybrid films. At the same time, electrochemical and spectroelectrochemical analyses revealed that the films have reversible redox activity and cathodic electrochromic properties, which can change from orange-red to purple. The ZnO@PDI-COOH hybrid film formed by coordination bonds exhibits fast switching times (1.7 s colored time and 2.6 s bleached time), good stability (retain 92.41% contrast after 2400 cycles), a low driving voltage (-0.6-0 V), and a high coloration efficiency (276.14 cm2/C). The corresponding electrochromic devices also have good electrochromic properties. On this basis, a large-area (100 mm × 100 mm) electrochromic display device with fine patterning was fabricated by using the hybrid film, and the device shows excellent reversible electrochromic performance. This idea of constructing organic-inorganic hybrid materials with coordination bonds provides an effective, energy-saving, and green method, which is expected to promote the large-scale and fine production of electrochromic materials.

Morphology-Dependent Near-Infrared Electrochromic Properties of Tungsten Oxide

Vertically aligned WO3 nano-architectures on the transparent conducting substrate are produced via a hydrothermal method. The results revealed that different WO3 nano-architectures, including “nanoblocks”, “nanosheet” and “nanobelt” structures, can be obtained by adjusting the composition of the precursor solution, that shows that solvent composition plays an important role in the adjustment of the prepared material morphology. The nanostructured array films with thicknesses of about 600 nm show remarkable enhancement of the electrochromic properties in the infrared region. The obtained WO3 films have good electrochromic properties in the near-infrared range. In particular, significant optical modulation of the WO3 nanosheets (72% at 1200 nm), fast switching speed (6.5 s for colored and 8.7 s for bleached), and excellent cycling stability (maintained 90.2% of the initial optical modulation after 1000 cycles). The improved electrochromic performance is mainly due to the vertically arranged structure, which makes it easier for ions to diffuse in the nanoarray, and also provides a larger surface area for charge transfer reaction. The research results provide a certain reference value for the research of electrochromic near-infrared performance.

Solvent-soluble thiophene-benzene based electrochromic polymers as electrode materials for supercapacitor

The bis(alkoxy) group para-substituted para-phenylene (p-phenylene) based conjugated polymers exhibit good electronic property due to the existence of intra-molecular non-covalent interaction between oxygen and heteroatom. However, the strong inter-molecular aggregation inhibits the ionic transport of polymer. Here, the strategy of changing side chain substitution position is employed to improve the properties of conjugated polymer. Three organic solvent-soluble conjugated polymers based on the bis(hexyloxy) group ortho-substituted p-phenylene were synthesized. The three polymers display small dihedral angles between thiophene and benzene. As the conjugated chain length of repeat units increasing, the redox potentials of polymers decrease gradually. From P1 to P2 to P3, their optical absorption regions red shift gradually, leading to neutral polymers display yellow for P1, orange for P2, magenta for P3, respectively. And the three polymers display good electrochromic properties (coloration efficiency: 641 cm2 C−1; response time: 0.2 s; optical contrast: 54%). Also, P2 possess the specific capacitance value of 170 F g−1, which is higher than that of most reported soluble conjugated polymers. Combining energy storage and electrochromic performance of the three polymers, their visualization monitor of energy storage were investigated.

Electrochemical polymerization, characterization and spectroelectrochemical studies of a N-substituted-2,5-dithienil-pyrrole bearing an aniline moiety for cross-linking (TPTBA)

N-substituted-2,5-dithienil-pyrroles have demonstrated to be an interesting alternative for the preparation of π-conjugated polymers with good electrochromic properties. Herein the 4-(4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzyl)aniline (TPTBA) was chemically synthetized and its electrochemical behavior and polymerization was studied. The obtained film was characterized by electrochemical and spectroelectrochemical methods. Poly-TPTBA presents a quasi-symmetrical reversible redox system characteristic to well-ordered systems. This explained by the presence of the aniline moiety which can favor a cross-linking of the polymer backbone. Spectroelectrochemical studies reveal a moderate rapid electrochromic transition between both redox states, requiring 2 seconds to alternate between each color: 430 nm (discharged state) and 800 nm (charged state).

Covering visible light region of fused rings-based D-A type electrochromic polymer with high-coloration efficiency

The colorful electrochromic polymers have been prepared, however, the neutral black or gray polymers are reported rarely due to the optical absorption region couldn’t cover the whole visible light region. Here, three donor-acceptor (D-A) type conjugated polymers PCDT-X (X = 1, 2, 3) based on two fused ring (FR) conjugated units cyclopentadithiophene (CPDT) and trithiophene-phenylhexyl (3TT) as donors and diketopyrrolopyrrole (DPP) as acceptor were synthesized. The difference of the three D-A type polymers focuses on donor/acceptor (D/A) molar ratio. Due to the introduction of FR units as donors, the optical absorption of PCDT-X (X = 1, 2, 3) cover the whole visible region, making them display gray color. Electrochromic studies demonstrate that the optical contrasts of PCDT-X (X = 1, 2, 3) in high- and low-energy absorption bands could be optimized specifically through adjusting D/A molar ratio. And, the prepared PCDT-X (X = 1, 2, 3) display good electrochromic properties, such as high optical contrast (57.25%), fast response time (0.59 s), and superior coloration efficiency (1342 cm2 C−1). These results demonstrate that the introduction of FR units as donors is an efficient strategy to construct gray or black D-A type electrochromic polymers.

Synthesis of tungsten oxide films at low processing temperature and their electrochromic properties

Tungsten oxide films with electrochromic properties were prepared by spin coating WCl6 ethanol solution on indium tin oxide (ITO) glass and polyethylene terephthalate (PET) substrate, and followed heat treatment at 60–400 °C in air for 1 h. The films were characterized by X-ray powder diffraction, scanning electron microscopy, energy spectrum analysis, electrochemistry and ultraviolet–visible–near-infrared (UV–Vis–NIR) spectrophotometer. Tungsten oxide films with different components can be obtained at different heat treatment temperatures. With the increase of heat treatment temperature, the products gradually lose the crystal water from WO3·2H2O to WO3·H2O and finally to WO3. The as-prepared film has many tiny cracks, which is beneficial for effective electrolyte penetration. The tungsten oxide PET films also show good electrochromic properties, and the coloring and bleaching processes are consistent with that of tungsten oxide device. The treatment at low temperature is no damage to the substrate and maintains the flexibility of the films. The method provides a simple, low-cost and large-scale practical scheme for the flexible electrochromic films.

Electrochromic materials containing pyridinium salt and benzoate moieties with dual-colored and long-life performance

This study aimed to develop dual-colored electrochromic materials by combining two electrochromic active moieties (pyridinium quaternary salt and benzoate) in one molecule. Four star-shaped 4,4'-([4,4′-bipyridine]-2,6-diyl) dibenzoates with various alkyl, alkenyl, and aryl N-substituents were designed and their electrochemical/electrochromic performance studied. Electrochromic devices based on 4,4'-([4,4′-bipyridine]-2,6-diyl) dibenzoates exhibited dual-colored electrochromic behavior, good switching stability, and low power consumption. Compared to the compounds with alkenyl and aryl substituents, those with alkyl substituents showed longer lifetimes and better switching stabilities. Good electrochromic properties and low power consumption make this type of material a candidate for application in the fields of electronic paper, smart windows, and displays.

Analysis of structural morphological changes from 3DOM V2O5 film to V2O5 nanorods film and its application in electrochromic device

Nanoscale V 2 O 5 films possess excellent electrochemical properties and have great potential for application in electrochromic devices. Herein, we report a novel strategy for the transformation of three-dimensionally ordered macroporous(3DOM) V 2 O 5 films into V 2 O 5 nanorods film using a simple low-temperature annealing treatment, in which the heterogeneous nucleation sites provided by PS colloidal sphere surface, the anisotropic bonding of V 2 O 5 , atomic rearrangement, and Ostwald ripening are all important factors affecting the morphological transformation. According to this study, during the preparation of 3DOM V 2 O 5 films, a small number of oxygen vacancies were introduced into the V 2 O 5 lattice, and the annealing treatment (250–400 °C, 4–8 h) controlled the concentration of oxygen vacancies. Compared with the ion storage capacity of V 2 O 5 films prepared by conventional sol-gel dip-coating method (17.79 mC cm −2 for unannealed V 2 O 5 films and 13.90 mC cm −2 for V 2 O 5 films after 6 h of annealing at 350 °C), the 350°C-6h films with nanorod structure had the highest ion-storage performance, the initial value raised to 98.77 mC cm −2 . Further, the cycling stability was excellent, with only a 6.1% decrease after 5000 cycles. This was because of the special nanorod structure and the presence of a certain number of gradient oxygen vacancies in the 350°C-6h film. The 350°C-6h film also had good electrochromic properties, a wide range of transmittance modulation (73.6%), and a fast response time (3.2 s for coloring and 3.9 s for bleaching). In addition, electrochromic devices (ECDs) with 350°C-6h films as both ion-storage layers and electrochromic layers have been successfully assembled, which exhibit high performance. • 3DOM V 2 O 5 film was prepared on ITO substrate by Template assistance sol-gel method. • Annealing induced morphology change from 3DOM to nanorods in V 2 O 5 films. • The annealing affects oxygen vacancy concentration, and in turn affects on ion storage capacity. • V 2 O 5 nanorodsfilms presents excellent capacity and cycle performance for lithium storage. • The electrochromic device assembled with V 2 O 5 film showed fascinating performance.

Ester-functionalized pyrene derivatives: Effects of ester substituents on photophysical, electrochemical, electrochromic, and electrofluorochromic properties

Multifunctional electrochromic materials are widely used in optoelectronic devices. Pyrene is a π-electron-rich group with fluorescence properties. Ester-functionalized pyrene derivatives potentially have interesting multifunctional properties such as electrochromic and electrofluorochromic characteristics. In this work, mono-, di-, tri-, and tetra-ester-substituted pyrene derivatives were synthesized, and the effects of the number of ester substituents on their photophysical, electrochemical, electrochromic, and electrofluorochromic properties were investigated. The number of ester substituents significantly affected these properties. An increase in the number of ester substituents on the pyrene caused red shifts in the absorption and emission spectra, a decrease in the driving voltage, and changes in the electrochromic colored states and electrofluorochromic performance. Mono-, di-, and tri-ester-functionalized pyrene derivatives showed good electrochromic properties, namely good switching stabilities, high optical contrasts, rapid responses, and high coloration efficiencies. Mono- and tri-ester-functionalized pyrenes gave good electrofluorochromic performances with reversible fluorescence quenching–fluorescence restoring between colored and bleached states during the electrochromic process. Ester-functionalized pyrene derivatives were successfully used in two functional digital displays with vivid colors. These results show that ester-functionalized pyrene derivatives with good electrochromic and electrofluorochromic properties are promising candidates for use in various applications, e.g., digital displays, organic electroluminescence displays, electronic shelf labels, energy-saving windows, and electronic paper.

High-Performance Electrochromic Covalent Hybrid Framework Membranes via a Facile One-Pot Synthesis

Porous framework materials have sparked enormous interest in the electrochromic field, as they possess intrinsic high porosity and a large surface area that are beneficial for electron and ion transport. However, the fabrication of these porous framework materials often requires multiple processing steps or harsh reaction conditions, which significantly limit large-scale fabrication of such materials. In this work, we report a one-pot in situ polycondensation method to construct electrochromic covalent hybrid framework membranes via nucleophilic substitutions between hexachlorocyclotriphosphazene (HCCP) and triphenylamine (TPA) in an ambient environment. With the high transparency of polyphosphazene in a wide optical range, the constructed phosphazene-triphenylamine (PPTA) covalent hybrid framework membranes can be reversibly switched between light gray and dark blue, with a high transmittance change of up to 79.8%@668 nm and fast switching time (<4 s). Owing to the easy one-pot fabrication and good electrochromic properties, the PPTA covalent hybrid framework membrane has great potential in various fields such as displays and dynamic optical windows.

Unraveling the Effect of Cation Types on Electrochromic Properties of Titanium Dioxide Nanocrystals

Electrochromic (EC) devices have been regarded as promising candidates for energy-saving smart windows, next-generation displays, and wearable electronics. Monovalent ions such as H + - and Li + -based electrolytes are the benchmark insertion ions for EC devices but have serious limitations such as high cost, instability, and difficulty to handle. Seeking multivalent electrolytes is an effective alternative way to prepare high-performance EC devices; unfortunately, the related reports are currently limited to tungsten oxide EC materials. Herein, for the first time, we investigate the EC properties driven by different valence cationic (i.e., Li + , Zn 2+ , and Al 3+ ) electrolytes in the titanium dioxide system. It is found that the initial optical modulation ranges of TiO 2 nanocrystal (NC) films in Li + , Zn 2+ , and Al 3+ electrolytes are 76.8%, 77.4%, and 77.3%, respectively. After 250 cycles, the optical contrast of these films in Zn 2+ electrolyte decreased by only 2.3%, much lower than that in benchmark Li + electrolyte of 10.1% and Al 3+ electrolyte of 59.1%. Density functional theory calculation indicates that the potential barriers of Li + , Zn 2+ , and Al 3+ in TiO 2 are 0.59, 0.55, and 0.74 eV, respectively, which makes TiO 2 NCs show good EC properties in Zn 2+ electrolytes. This work unravels the effect of different valence cations on the electrochromic properties of titanium dioxide NCs, which may provide some new directions for the development of excellent EC devices with long-term stability and durability.

Preparation of porous polyamide films with enhanced electrochromic performance by electrostatic spray deposition

Porous polyamide films were prepared by a simple electrostatic spray deposition method for the first time. The polymer solution quickly was dispersed into micron-sized droplets and deposited on the substrate under the electrostatic field forces. With the continue depositing of the droplets and evaporating of the solvent, many voids formed between the droplets to form a porous structure. Thanks to existence of these porous channels, the ion transmission could be effectively increased. Therefore, compared with the film prepared by traditional blade coating, the porous film exhibited a smaller redox potential interval and shorter response time. Introducing of silver nanowires (AgNWs) into the polymer solution wouldn't impede the formation of porous structure, and electrochromic response time for the obtained polyamide/AgNWs film can be effectively improved. The bleaching/coloring time could reach 0.8 s/1.2 s, which is the best record for the polyamide based electrochromic film. These results showed that, electrostatic spraying technology is a promising and efficiently method to prepare polymer film with good electrochromic property. • The organic electrochromic polymer films with rough surface and stacked structure were prepared by electrostatic spraying. • Porous structure films were prepared by electrostatic spraying after introducing AgNWs into the solution. • Films exhibited small redox potential interval, short response time and high coloration efficiency.