In situ sol–gel synthesis of tungsten trioxide networks in polymer electrolyte: Dual-functional solid state chromogenic smart film

The novel electro-photochromic solid electrolyte films were successfully synthesized by in situ sol–gel synthesis of tungsten trioxide (WO₃) working electrode within gelatin/lithium cosolvent system. The transparent free-standing single-layer film with adhesiveness and flexibility, darken significantly under the UV radiation with photo-response time of 30 s and gradually reversed once the source of UV was blocked. Moreover, casted film on the indium tin oxide (ITO) glass showed electrochromic (EC) behavior as well in presence of ion storage counter electrode. X-ray diffraction analysis indicates the amorphous nature of an in situ synthesized gelatin-based film. The prepared film containing 30 wt% LiClO₄ and 10 wt% WO₃ (sample designated as GLi30W10) shows ionic conductivity value of 1.1 × 10⁻⁴ S/cm. The EC performances of the device with the following configuration; ITO/GLi30W10/NiO/ITO, was investigated by means of UV and cyclic voltammograms. Good performances and fast electro-response times (2 s/1 s) of the device were demonstrated with coloration efficiency of 51.54 cm²/C.     

Solid-state electrochromic devices using pTMC/PEO blends as polymer electrolytes

Flexible, transparent and self-supporting electrolyte films based on poly(trimethylene carbonate)/poly(ethylene oxide) (p(TMC)/PEO) interpenetrating networks doped with LiClO₄ were prepared by the solvent casting technique. These novel solid polymer electrolyte (SPE) systems were characterized by measurements of conductivity, cyclic voltammetry, differential scanning calorimetry and thermogravimetry.The incorporation of solid electrolytes as components of electrochromic devices can offer certain operational advantages in real-world applications. In this study, all-solid-state electrochromic cells were characterized, using Prussian blue (PB) and poly-(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT) as complementary electrochromic compounds on poly(ethyleneterphthalate) (PET) coated with indium tin oxide (ITO) as flexible electrodes. Assembled devices with PET/ITO/PB/SPE/PEDOT/ITO/PET “sandwich-like” structure were assembled and successfully cycled between light and dark blue, corresponding to the additive optical transitions for PB and PEDOT electrochromic layers. The cells required long cycle times (>600 s) to reach full color switch and have modest stability towards prolonged cycling tests. The use of short duration cycling permitted the observation of changes in the coloration-bleaching performance in cells with different electrolyte compositions.     

Gel electrolyte-based flexible electrochromic devices showing subtractive primary colors

We studied flexible electrochromic devices containing phthalate derivative which showed reversible color change between water transparent and subtractive primary color by electrochemical reaction. Poly(vinyl butyral) (PVB)-based gel electrolyte was prepared to apply the flexible electrochromic device. The ionic conductivity of the gel electrolyte depended on the polymer content, and was higher than 10⁻⁴ S/cm at 25 °C at the PVB content of 33 wt%. Redox reaction of phthalate derivatives was successfully achieved in the gel electrolyte. It is revealed that PVB-based gel electrolyte works well as the material for flexible electrochromic devices showing subtractive primary colors.     

A tungsten-trioxide/prussian blue complementary electrochromic cell with a polymer electrolyte

Optically variable windows (smart windows), which control the transmission of light into buildings and vehicles, are of interest both for the control of solar heat load and for privacy applications. Such windows are likely to utilize electrochromic technology to achieve optical control. An electrochromic device consisting of a cathodically colouring tungsten trioxide (WO₃) film, an anodically colouring Prussian blue (PB) film, and a polymer electrolyte was made. The polymer electrolyte was prepared from polyvinyl alcohol doped with H₃PO₄ and KH₂PO₄ to accommodate the conduction of both H⁺ and K⁺ ions. The electrochromic WO₃ and PB films functioned in a complementary way such that the device was coloured or bleached by the application of –0.5 V or +0.5 V (WO₃ films vs PB film), respectively. The spectral characteristics of the coloured device confirmed the complementary colouration of WO₃ and PB in the device.     

Influence of Ag incorporation on the structural,optical and electrical properties of ITO/Ag/ITO multilayers for inorganic all-solid-state electrochromic devices

Indium tin oxide/silver/indium tin oxide (ITO/Ag/ITO, IAI) multilayer structures were prepared by DC magnetron sputtering as a conductive transparent electrode for inorganic all-solid-state electrochromic devices. A thin layer of silver (Ag) with various thicknesses was inserted between two layers of ITO films. The XRD and SEM results revealed that the microscopic morphology of Ag film was closely related to the thickness. Besides, the electrical and optical properties of the IAI multilayers were significantly influenced by the Ag layer thickness. The optimized IAI multilayers demonstrated the best combination of electrical and optical properties with a figure of merit of 54.05 (sheet resistance of 6.14 Ω/cm²and optical transmittance of 90.83%) when the Ag film was 10 nm thick. In order to evaluate the IAI multilayers as a transparent electrode for electrochromic applications, two ECDs with the structures of ITO/NiO_x/LiPON/WO₃/ITO and ITO/NiO_x/LiPON/WO₃/IAI were prepared, and their electro-optical properties were characterized by cyclic voltammetry (CV), chronoamperometry (CA) and spectroscopic measurements. Compared with ECD the pure ITO top electrode (ITO/NiO_x/LiPON/WO₃/ITO), the ECD with the IAI top electrode (ITO/NiO_x/LiPON/WO₃/IAI) presented a slightly smaller optical modulation amplitude, but a faster switching speed. All our findings indicate that the IAI multilayer structure is a promising alternative to the ITO thin film for inorganic all-solid state electrochromic applications.     

Synthesis of high-performance electrochromic thin films by a low-cost method

Metal-doping is an effective method to adjust the physical and chemical properties of semiconductor metal oxides. This work adopts a simple solvothermal method to synthesize Mo-doped tungsten oxide nanoparticles. The high-performance electrochromic films can be homogenously formed on ITO glass without post-annealing. Compared with pure WO₃ films, the optimized Mo-doped WO₃ films show improved electrochromic properties with significant optical contrast (68.3% at 633 nm), the short response time (6.3 s and 3.9 s for coloring and bleaching, respectively), and excellent coloration efficiency (107.2 cm² C^?1). The improved electrochromic behavior is mainly due to the increasing diffusion rate of Li⁺ in Mo-doped WO₃ films (increased 20% than that of pure WO₃ films). The porous surface of Mo-doped WO₃ film shortens the diffusion path of Li⁺. Besides, Mo doping reduces the resistance and improves conductivity. Furthermore, 2at% Mo-doped WO₃ films indicate satisfactory energy-storage properties (the specific capacitance is 73.8 F g^?1), resulting from the enhanced electrochemical activity and fast electrical conductivity. This work presents a practical and economical way of developing high-performance active materials for bifunctional electrochromic devices.     

Characteristics of Li–P–W–O–N electrolyte for all solid state electrochromic devices

A LiPON–WO₃ composite thin film (LPWON) was evaluated for use as a solid electrolyte in solid state electrochromic (EC) devices. LiPO₄ and a WO₃ (2 wt%) composite sputtering target was synthesized by a ball milling process. The LPWON thin films were deposited by RF magnetron sputtering in Ar + N₂ and N₂ atmospheres. The structural, electrochemical, and optical properties of the LPWON electrolytes were characterized by X-ray diffraction (XRD), UV–visible spectroscopy, and an impedance analyzer. EC mirrors with WO₃ (coloring layer), LPWON (solid electrolyte), and stainless steel (mirror electrode) on ITO (transparent electrode) glass were fabricated to analyze the improved EC properties due to the LPWON electrolyte. The LPWON may lead to electrolytes with more stable potential cycle properties.     

Synthesis and electrochromic performance of a novel polymer based on an oxidative polymer derived from carbazole and thiophene

A polymer derived from poly-9-bis[4-(thiophen-3,4-yloxy)biphenyl)]-9H-carbazole containing a carbazole and thiophene group, abbreviated as B2, was synthesized via the oxidation method by using FeCl₃ as an oxidant. Additionally, the electrochemical polymer of B2 was synthesized and coated onto an ITO–glass surface via electrochemical oxidative polymerization. The electrochemical synthesis of the polymer was performed in 0.05 M AN/LiClO₄ solvent/electrolyte solution containing 0.1 M concentration of B2 between +0.3 and +1.4 V potentials. The compounds were characterized by FT-IR, NMR, and elemental analysis techniques. The spectroelectrochemical and electrochromic properties of this polymer were also investigated in 0.05 M AN/LiClO₄ solvent/electrolyte solution for 200 s and at a constant potential of +1.4 V. Switching ability of this polymer was measured as the percent transmittance (?T%) at its changing point of maximum contrast. Additionally, the scan rate study was performed at different scan rates: 400, 300, 200, 100, 50, 20 mV/s. According to the electrochromic measurements, the synthesized polymer had a light blue color when it was oxidized, and when it was reduced, it had a transparent color. As a result, the synthesized polymer P(B2) can be used to produce new polymeric electrochromic devices, and it can be considered a good candidate for applications of electrochromic devices (ECDs) because of its short response time of 3.5 s.     

Effect of Ar/O2 ratio on double-sided electrochromic glass performance

This paper reports the qualities of WO₃ film and NiO film added to a counter electrode and their use in a double-sided electrochromic glass device. A mixture of argon and oxygen gasses with ratios of Ar/O₂ of 1.5, 2, 3, and 5 were used for the deposition of the working electrode of WO₃ film for EC glass. The structure of double-side EC glass consists of glass/ITO/NiO/electrolyte/WO₃/ITO/glass/ITO/WO₃/electrolyte/NiO/ITO/glass layers. The working electrode of WO₃ film controls the color presented, the applied voltage controls the color depth, and the counter electrode controls the transparency in the bleached state. The double-sided EC glass with double WO₃ films and double NiO films have faster coloration/bleaching rates than do single-sided EC glass. A mixture of Ar/O₂ ratio of 3.0 has the best coloration/bleaching property of the ratios tested. Compared to the single-sided EC glass, the double-sided EC glass has lower transmittance of about 72% and 6% than the 78% and 12% during coloration and bleaching states in the visible light region with +1.5 V and ?3.5 V applied.     

Electrochromic properties of porous NiO thin film as a counter electrode for NiO/WO3 complementary electrochromic window

Highly porous nickel oxide (NiO) thin films were prepared on ITO glass by chemical bath deposition (CBD) method. SEM results show that the as-deposited NiO film is constructed by many interconnected nanoflakes with a thickness of about 20 nm. The electrochromic properties of the NiO film were investigated in a nonaqueous LiClO₄–PC electrolyte by means of optical transmittance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The NiO film exhibits a noticeable electrochromic performance with a variation of transmittance up to 38.6% at 550 nm. The CV and EIS measurements reveal that the NiO film has high electrochemical reaction activity and reversibility due to its highly porous structure. The electrochromic (EC) window based on complementary WO₃/NiO structure shows an optical modulation of 83.7% at 550 nm, much higher than that of single WO₃ film (65.5% at 550 nm). The response time of the EC widow is found to be about 1.76 s for coloration and 1.54 s for bleaching, respectively. These advantages such as large optical modulation, fast switch speed and excellent cycle durability make it attractive for a practical application.     

Fast electrochromic response and high coloration efficiency of Al-doped WO3 thin films for smart window applications

Herein, vertically aligned Al:WO₃ nanoplate arrays were directly grown on ITO glass by a facile electrodeposition method and annealed in an argon atmosphere at 450 °C for 2h. Besides, this study reports the influence of Al doping on the electrochromic properties of WO₃ film in detail. Electrochromic properties such as cyclic voltammetry, chronoamperometry and optical transmittance were analyzed by protonic insertion/extraction in the 1 M LiClO₄/propylene carbonate as an electrolyte. The noticeable reversible color changing from transparent to the blue can be realized under the potential bias of ±1.0 V. XRD studies show that the produces films have highly crystalline structure. The EDS results clearly confirm the incorporation of Al element into the WO₃ network. From the optical absorption measurement, direct band gap energies are calculated as 3.62 and 3.34 eV for the WO₃ and the Al:WO₃, respectively. Compared to the as-prepared WO₃, the Al:WO₃ film exhibits outstanding electrochromic performance, including wide optical modulation (55.9%), high coloration efficiency (148.1 cm²C^-1), quick reaction kinetics (1.23 s and 1.01 s for colored and bleaching times, respectively), good rate capability and cycle durability at a wavelength of 632.8 nm. EIS measurements based on a charge-transfer resistance reveal that the dramatic improvement in the electrochemically active surface is achieved in the Al:WO₃ film. The increase of active surface facilitates transport kinetics for electron and ion intercalation/deintercalation within the porous metal oxide to enhance coloration efficiency. Comparatively energy levels of the WO₃ and the Al:WO₃ electrochromic films are also represented. From the Mott-Schottky studies, it is estimated that the donor concentration of the films is of the order of 10²⁰ cm⁻³. Taken together, these results not only provide important insight into a promising electrode for electrochromic displays applications, but also offer an economic and effective strategy for manufacturing of other doped metal oxide films.     

Logotype-selective electrochromic glass display

This paper describes a fabrication method of a logotype-selective electrochromic (EC) glass. The EC glass performance based on the sample size, WO₃ film thickness, and internal impedances under various applied voltages are also discussed. The logotype-selective electrochromic glass was fabricated by the sputter deposition process. Both working and counter electrode were coated with ITO/WO₃ films. The specific logotypes of “NCUT” and “NUU” can be displayed with positive and negative voltages applied to the EC glass. EC glasses of various sizes (1 cm², 4 cm², 9 cm², 25 cm², and 100 cm²) were also fabricated by sputter deposition process. When voltage (?3.5 V) was applied to the device, the active layer of the assembled device changed from almost transparent to a translucent blue color (colored). The average transmittance in the visible region of the spectrum for a 100 cm² EC device was 73% in the bleached state. The best device, with a 140 nm WO₃ active layer, had average transmittances in the colored and bleached states of 11.9% and 54.8%, respectively. Cyclic voltammogram tests showed that reproducibility of the colored/bleached cycles was good. Nyquist plots showed that increasing the device size decreased the current density, and the electrolyte impedance increased because of a low conductive electrolyte in the device.     

Vacancy-engineered V2O5-x films for ultrastable electrochromic applications

In the present study, we prepared vacancy-engineered V₂O_5-x films for electrochromic (EC) applications. To investigate the vacancy effect of V₂O_5-x films with high EC performance capabilities, precursor concentrations of V-based sol solutions were varied at 1 wt%, 5 wt%, and 10 wt%. Among them, V₂O_5-x films with a precursor concentration of 5 wt% (V₂O₅-5wt%) showed superior EC performance outcomes due to the (001)-plane-oriented crystal structure, which provides high electrical conductivity with the oxygen vacancy (V_o). In addition, the gravel-like uniform surface morphology with the optimized film thickness provides a stable electrochemical reaction during the EC measurement. As a result, V₂O₅-5wt% exhibited fast switching speeds (2.1 s for coloration and 3.6 s for bleaching), high transmittance modulation (ΔT) (51.32%), high coloration efficiency (CE) (52.3 cm²/C), and excellent cycle stability (85.85% ΔT retention after 500 cycles). In addition, V₂O₅-5wt% showed energy storage capability of 443.7 F/g at a current density of 2 A/g, thus proving its potential for use in multi-functional applications. Therefore, these results provide valuable insight related to the engineering of vacancies in EC films to achieve high-performance EC devices and additional multi-functional applications.     

Ionic liquids in electrochromic devices

The ionic liquid (PYR₁₄TFSI) has proved to be the key material to make a Li-ion conducting element of a complete electrochromic device, when interposed between transparent film electrodes like WO₃ and Li-charged V₂O₅. The key features of this ionic liquid and its mixtures with LiTFSI are the excellent transparency in the visible and NIR optical regions, the good ionic conductivity and the electrochemical compatibility with inorganic Li-intercalation oxide thin film electrodes used in electrochromic devices. The higher optical contrast found during WO₃ colouration with PYR₁₄TFSI-LiTFSI, compared to that in a conventional non-aqueous electrolyte like PC-LiTFSI, was attributed to the larger inertness of the former one (no decomposition reaction at the lowest electrode potential). This highly conductive ionic liquid has been incorporated into a polymer matrix (P(EO)₁₀LiTFSI), in order to obtain a transparent solid electrolyte with high Li ion conductivity and good mechanical stability. Finally this solid PYR₁₄TFSI-P(EO)₁₀LiTFSI transparent ion conductor was interposed between the same electrodes as above in order to yield a fully solid-state, Li-ion electrochromic device. This new solid electrolyte was able to transfer reversibly a Li ionic charge between 5 mC cm⁻² and 10 mC cm⁻² from the lithium storage electrode Li_xV₂O₅ to the WO₃ electrochromic electrode in less than 100 s at room T, darkening the device from an initial 80% to a final 30% transmittance (at 650 nm). Such a device has been tested first under various constant current conditions, and later under potentiostatic control using ±2 V steps. The latter method allows not only for a faster response of the electrochromic system, but provides also an easier life stability test of the device, which withstood 2000 cycles with little changes in its optical contrast.     

Spectroelectrochemical behaviour of poly (3-octylthiophene): application to electrochromic windows with polyaniline and iridium oxide

The spectroelectrochemical behaviour of cast poly(3-octylthiophene) (POT) films (0.2 and 0.5 m) on indium-tin-oxide (ITO) glass electrodes has been investigated in organic media. These thin films exhibit interesting electrochromic properties and their application in electrochromic devices has been examined in liquid (CH₃CN + LiClO₄ 0.3 M) and viscous electrolyte (PEO + CH₃CH + LiClO₄). Polyaniline (PANI) film appears to be a convenient complementary counter electrode since its transmission maximum corresponds to its oxidized state and that of POT film to its reduced state. Thin films of iridium oxide (IrO₂) are also possible counter electrodes, even in acetonitrile, the electrochemical behaviour being mostly capacitive with a low transmission change. However, the best contrast is obtained with the POT/PANI system.     

Effect of the thicknesses of the Al2SiO5 ion conductor on the opto-electrical properties for all-solid electrochromic devices

In this study, an all-solid-state electrochromic device (ECD) with the structure of ITO/WO₃/Al₂SiO₅/NiO_x/ITO was prepared, and the effect of the Al₂SiO₅ solid electrolyte thicknesses on the opto-electrical performance was investigated. The microstructure and surface morphology were characterized using XRD, SEM and AFM, and the surface morphology and degree of surface looseness demonstrate a significant influence on the opto-electrical properties of ECDs. The charge transfer dynamics at the solid-solid interface were characterized using EIS to obtain an ionic conductivity of 4.637 × 10^-8 S/cm. CV, CA and UV–Visible spectra were employed to record the in situ electrochemical and optical properties. The results revealed that the highest optical modulation was 44.58%, the coloring and bleaching times were 14.8 s and 3.7 s, and the highest coloring efficiency was 98.17 cm²/C, which indicates that excellent opto-electrical properties were obtained. When the thickness increases, the degree of surface dense morphology transforms, and the loose morphology is more favorable for ion conductivity, which improves the opto-electrical properties. The results in this study provide insights into the understanding of Al³⁺-based all-solid-state ECDs, which promote the exploration of new types of Al³⁺ ionic conductors for all-solid-state ECDs.     

Preparation and Characterization of Bioblends from Gelatin and Linear Low Density Polyethylene (LLDPE) by Extrusion Method

Abstract

Bioblends are composites of at least one biodegradable polymer with a non-biodegradable polymer. Successful development of bioblends requires that the biodegradable polymers be compatible with other component biodegradable/synthetic (non-biodegradable) polymers. Bioblends from LLDPE and gelatin were prepared by extrusion and hydraulic heat press technique. The gelatin content in the bioblends was varied from 5 to 20 wt%. Various physico-mechanical properties such as tensile, bending, impact strength (IS), thermal ageing and soil degradation properties of the LLDPE/gelatin bioblends with different gelatin contents were evaluated. The effect of thermal ageing on mechanical properties was studied. The mechanical properties such as tensile modulus (TM), bending strength (BS), bending modulus (BM) were found to increase with increasing gelatin content up to 20 wt%, however tensile strength (TS) and elongation at break (%E _b) were decreased with increasing gelatin content. Impact strength value increased with increasing gelatin content up to 10 wt% and then decreased slightly with increasing gelatin content. The blend containing 20 wt% gelatin showed relatively better mechanical properties than other blends. The values of TS, TM,%E _b, BS, BM and IS for the bioblend with 20 wt% gelatin content are 5.9MPa, 206.3MPa, 242.6%, 12.1MPa, 8 MPa and 13.7 J/cm², respectively. Water uptake increases with increasing soaking time in water and weight loss due to soil burial also increases with increasing gelatin content in the blends but both are significantly lower than that of pure gelatin sheet. Weight loss values after thermal ageing increase with time, temperature and increasing gelatin content in the blend but are much lower than pure gelatin. Mechanical properties such as TS, TM are increased and %E _b is decreased after thermal ageing at 60°C for 30 min. Consequently, among all of the bioblends prepared in this work the blend having 20% gelatin content yields properties such that it can be used as a semi-biodegradable material.     

Conducting copolymers of polytetrahydrofuran and their electrochromic properties

Living polytetrahydrofuran (PTHF) was terminated with sodium thiophene methonate to yield a polymer with a thiophene group at one end. Copolymerizations of PTHF with pyrrole and thiophene were achieved in water‐p‐toluene sulfonic acid and acetonitrile‐tetrabutylammonium tetrafluoroborate (TBAFB) solvent‐electrolyte couples via constant potential electrolyses. Characterizations of the samples were performed by NMR, cyclic voltammetry, FT‐IR, thermal analyses, and scanning electron microscopy. Electrical conductivities were measured by the four‐probe technique. PTHF/PTh film that was deposited on ITO‐glass in a dichloromethane‐TBAFB solvent‐electrolyte couple was found to exhibit electrochromic behavior and it electrochemically switches between blue oxidized and red reduced states. Optical analyses were carried out to investigate the electronic structure of PTHF/PTh electrochromic copolymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1014–1023, 2005     

Study and optimization of a flexible electrochromic device based on polyaniline

The synthesis of polyaniline (PANI) thin films was made onto commercially available  cm polyethylene terephthalate (PET)/indium tin oxide (ITO) substrates. By depositing a gold frame previously to the electrochemical PANI synthesis, homogeneous electrochromic PANI layers were obtained. Complete flexible cells could then be built by using a transparent gel electrolyte and a simple PET/ITO counter-electrode. Branched poly(ethyleneimine) (BPEI)-H₃PO₄ and polymethylemethacrylate (PMMA)-PC-LiClO₄ were both tested as electrolytes, but only the latter led to a non-degrading system when the device undergoes several switching potential steps. This flexible, middle-scale and inexpensive device enabled to get a 18% transmission contrast at 780 nm within 3 min.