Electrochromic Applications Research Articles

Structure engineering in hexagonal tungsten trioxide/oriented titanium dioxide nanorods arrays with high performances for multi-color electrochromic energy storage device applications

• A novel porous structure of WO 3 /TiO 2 was fabricated by a hydrothermal method. • Superior transmittance modulation and fast Li + ions insertion kinetics was obtained. • V 2 O 5 is chosen as counter electrode based on the strategy of color superposition. • EESD can supply six multi-color modulation modes and light up a LED. A novel porous structure of hexagonal WO 3 /oriented TiO 2 nanorods arrays ( h -WO 3 /TiO 2 NRAs) hybrid film was successfully prepared by a facile hydrothermal method. Benefiting from elaborately structure engineering, the hybrid film exhibited large transmittance modulation (ΔT 633nm = 73.45%), high coloration efficiency (69.2 cm 2 ·C -1 ), fast Li + ions insertion kinetics (6.6 s/2.0 s for t c / t b ), stable cyclic stability (maintains 92.9% of initial ΔT after 2000 cycles) as well as areal specific capacitance of 10.93 mF·cm −2 at the current density of 0.1 mA·cm −2 . An electrochromic energy storage device (EESD) with six multi-color modulation modes (light gray, dark olive green, yellow green, lime green, dark green and dark blue) was successfully assembled by h -WO 3 /TiO 2 NRAs hybrid film and electrodeposited-V 2 O 5 film. Based on the excellent electrochromic and pseudocapacitive properties, the EESD promised a smart visual monitoring of the energy storage level and can light up a LED after charging, indicating a good energy storage application prospect.

High-Performance Complementary Electrochromic Device Based on Iridium Oxide as a Counter Electrode.

In complementary electrochromic devices (ECDs), nickel oxide (NiO) is generally used as a counter electrode material for enhancing the coloration efficiency. However, an NiO film as a counter electrode in ECDs is susceptible to degradation upon prolonged electrochemical cycling, which leads to an insufficient device lifetime. In this study, a type of counter electrode iridium oxide (IrO2) layer was fabricated using vacuum cathodic arc plasma (CAP). We focused on the comparison of IrO2 and NiO deposited on a 5 × 5 cm2 indium tin oxide (ITO) glass substrate with various Ar/O2 gas-flow ratios (1/2, 1/2.5, and 1/3) in series. The optical performance of IrO2-ECD (glass/ITO/WO3/liquid electrolyte/IrO2/ITO/glass) was determined by optical transmittance modulation; ∆T = 50% (from Tbleaching (75%) to Tcoloring (25%)) at 633 nm was higher than that of NiO-ECD (ITO/NiO/liquid electrolyte/WO3/ITO) (∆T = 32%). Apart from this, the ECD device demonstrated a fast coloring time of 4.8 s, a bleaching time of 1.5 s, and good cycling durability, which remained at 50% transmittance modulation even after 1000 cycles. The fast time was associated with the IrO2 electrode and provided higher diffusion coefficients and a filamentary shape as an interface that facilitated the transfer of the Li ions into/out of the interface electrodes and the electrolyte. In our result of IrO2-ECD analyses, the higher optical transmittance modulation was useful for promoting electrochromic application to a cycle durability test as an alternative to NiO-ECD.

Low voltage colour modulation in hydrothermally grown Ni‐Co nanoneedles for electrochromic application

Low voltage colour modulation in hydrothermally grown Ni‐Co nanoneedles for electrochromic application

Unprecedented Electrochromic Stability of a-WO3-x Thin Films Achieved by Using a Hybrid-Cationic Electrolyte.

With large interstitial space volumes and fast ion diffusion pathways, amorphous metal oxides as cathodic intercalation materials for electrochromic devices have attracted attention. However, these incompact thin films normally suffer from two inevitable imperfections: self-deintercalation of guest ions and poor stability of the structure, which constitute a big obstacle toward the development of high-stable commercial applications. Here, we present a low-cost, eco-friendly hybrid cation 1,2-PG-AlCl3·6H2O electrolyte, in which the sputter-deposited a-WO3-x thin film can exhibit both the long-desired excellent open-circuit memory (>100 h, with zero optical loss) and super-long cycling lifetime (∼20,000 cycles, with 80% optical modulation), benefiting from the formation of unique Al-hydroxide-based solid electrolyte interphase during electrochromic operations. In addition, the optical absorption behaviors in a-WO3-x caused by host-guest interactions were elaborated. We demonstrated that the intervalence transfers are primarily via the "corner-sharing" related path (W5+ ↔ W6+) but not the "edge-sharing" related paths (W4+ ↔ W6+ and/or W4+ ↔ W5+), and the small polaron/electron transfers taking place at the W-O bond-breaking positions are not allowed. Our findings might provide in-depth insights into the nature of electrochromism and provide a significant step in the realization of more stable, more excellent electrochromic applications based on amorphous metal oxides.

Reversible Metal Electrodeposition Devices: An Emerging Approach to Effective Light Modulation and Thermal Management

AbstractThe reversible metal electrodeposition device (RMED) is a novel electrochromic application that utilizes the appearance and disappearance of a metal layer to achieve spectrum control. A thin metal film with a thickness of a few tens of nanometers would be highly reflective in the visible and infrared region, making it an ideal material to achieve light and heat modulation. Because of their outstanding spectrum control ability, RMEDs can be applied to displays, smart windows, and thermal camouflage. However, as is the case with many other electrochromic devices, difficulties in device enlargement pose significant challenges to the application of RMEDs. Herein, an overview of the milestone advances of RMEDs is provided, with a focus on their application as smart windows, which is the most extensively studied topic. Recent attempts to improve their open‐circuit stability and designs for device enlargement are highlighted. Finally, insight into the remaining challenges and future prospects in this field is provided.

The thin and flexible triple-layered electrochromic device based on the multifunctional hydrogel

Electrochromic devices (ECDs) are widely used in smart color changing windows, automotive antiglare rear-view mirrors and electronic wearable devices owing to their controllable for colouration, reduced energy consumption and modulated incident light. Traditional ECDs composed of complicated configurations, commonly five layers of structure, extremely increased the complexity of structure and fabrication process, especially cut down the performance of the device. In this paper, the introduction of hydrogel (The transmittance in the visible light spectrum reached up to 95%), both acted as the conductive layer and the dielectric layer, simplified the structure of the device to a triple-layered one. Flexible electronic products require good flexibility of conductive materials, so we introduced flexible Indium tin oxide (ITO) as the transparent conductive substrate, which have excellent bending properties, the sheet resistance increased only from 12.6 Ω/sq to 31.4 Ω/sq, after 2500 bending cycles. The assembled ECD has a slight transmittance attenuation (ΔTe/ΔT0=7%) after 1500 bending cycles. Importantly, the device showing excellent cycling performance, has just 2% attenuation of transmittance at wavelength of 640 nm, after 1000 cycles (ΔT changes from 32% to 30%), which also has a fast coloration and bleaching time, respectively 3 and 4.7 seconds. Compared with five layered structure, three layered ECDs show prominent advantages, accelerating the development of simple structure electrochromic applications in the future.

Temperature-Controlled Crystal Size of Wide Band Gap Nickel Oxide and Its Application in Electrochromism.

Nickel oxide (NiO) is a wide band gap semiconductor material that is used as an electrochromic layer or an ion storage layer in electrochromic devices. In this work, the effect of annealing temperature on sol-gel NiO films was investigated. Fourier transform infrared spectroscopy (FTIR) showed that the formation of NiO via decomposition of the precursor nickel acetate occurred at about 300 °C. Meanwhile, an increase in roughness was observed by Atomic force microscope (AFM), and precipitation of a large number of crystallites was observed at 500 °C. X-ray Diffraction (XRD) showed that the NiO film obtained at such a temperature showed a degree of crystallinity. The film crystallinity and crystallite size also increased with increasing annealing temperature. An ultraviolet spectrophotometer was used to investigate the optical band gap of the colored NiO films, and it was found that the band gap increased from 3.65 eV to 3.74 eV with the increase in annealing temperature. An electrochromic test further showed that optical modulation density and coloring efficiency decreased with the increase in crystallite size. The electrochromic reaction of the nickel oxide film is more likely to occur at the crystal interface and is closely related to the change of the optical band gap. An NiO film with smaller crystallite size is more conducive to ion implantation and the films treated at 300 °C exhibit optimum electrochromic behavior.

Heteroatom-Doped Nickel Oxide Hybrids Derived from Metal-Organic Frameworks Based on Novel Schiff Base Ligands toward High-Performance Electrochromism.

The tenets of coordination chemistry enable researchers to design and develop nanostructured materials based on metal-organic frameworks (MOFs). Herein, for the first time, we applied the Schiff base system to MOF derivatives as a strategy for the heteroatom introduction into carbon-based metal oxides toward electrochromic applications. The presented Ni-MOF thin films based on Schiff base ligands were prepared by a facile and economical reductive electrosynthesis approach, facilitating the scalable fabrication of large-size electrochromic films derived from MOFs. After the pyrolysis, the desired N-doped NiO@C (N-C@NiO) films can achieve a high cycling stability (500 cycles with 7% contrast attenuation) and coloration efficiency (80.18 cm2/C) via different pyrolysis procedures. In addition, the one-step fabricated N-C@NiO shows an excellent ability of contrast modulation (68%@580 nm) with merely 3.6% transmittance at the colored state. These improvements in electrochromic properties are attributed to hierarchical porous heterostructures and influenced by the N/C ratio and C-N bonding configuration, indicating that N-C@NiO systems derived from Schiff base MOFs are promising for low-transmittance displays.

A simple way to fabricate pure anatase 2D TiO2 IO monolayer: structure, color control and its application in electrochromism.

Pure anatase two dimensional (2D) TiO2 inverse opal (IO) films, consisting of a highly ordered hexagonal-patterned structure, are synthesized from various sized polystyrene spheres (PS) as colloidal template simply coupled with TiOSO4 aqueous solution as TiO2 precursor using a “dynamic-hard-template infiltration” strategy. Herein, the TiOSO4 solution is directly infiltrated into the interstices of the 2D self-assembled PS opal template at an air/water interface resulting in a TiOSO4/PS opal composite film floating on the surface of water which was further deposited onto ITO or silicon substrates. Calcination of the obtained opal composite films at temperatures ranging from 300 to 550 °C resulted in 2D TiO2 IO films with various pore sizes having an inverse moth's eye structure. Based on EDS measurements, sulfur ions S6+ were detected in the IO films calcined up to 550 °C. In order to eliminate these S6+ ions and obtain pure anatase 2D TiO2 IO, aqueous immersion was performed after calcination without disturbance of the IO ordered structure. Surface morphology, crystal phase and optical transmittance of the TiO2 IO films, were concurrently investigated by SEM, Raman and UV-vis-NIR. Owing to their precisely adjustable structure, the obtained TiO2 2D IO films exhibited structural colors varying from pale purple, to blue, to polychrome as the array period increases. The films obtained on ITO substrates were successfully used as active electrodes in the fabrication of electrochromic (EC) devices.

PANI/MoO3−x shell–core composites with enhanced rate and cycling performance for flexible solid-state supercapacitors and electrochromic applications

PANI/MoO3−x shell–core composites show enhanced electrochemical and electrochromic performance as a bi-functional electrode material for flexible solid-state supercapacitors, attributed to a synergistic effect from PANI nanorods and MoO3−x nanobelts.

Polyoxotungstate-based nanocomposite films with multi-color change and high volumetric capacitance toward electrochromic energy-storage applications

A facile fabrication strategy is proposed to construct a POMs-based nanocomposite film. It realizes multi-color transition during charging and discharging process, thereby links electrochromic behavior with energy storage performance.

Synthesis and applications of WO3 nanosheets: the importance of phase, stoichiometry, and aspect ratio.

Tungsten trioxide (WO3) is an abundant, versatile oxide that is widely explored for catalysis, sensing, electrochromic devices, and numerous other applications. The exploitation of WO3 in nanosheet form provides potential advantages in many of these fields because the 2D structures have high surface area and preferentially exposed facets. Relative to bulk WO3, nanosheets expose more active sites for surface-sensitive sensing/catalytic reactions, and improve reaction kinetics in cases where ionic diffusion is a limiting factor (e.g. electrochromic or charge storage). Synthesis of high aspect ratio WO3 nanosheets, however, is more challenging than other 2D materials because bulk WO3 is not an intrinsically layered material, making the widely-studied sonication-based exfoliation methods used for other 2D materials not well-suited to WO3. WO3 is also highly complex in terms of how the synthesis method affects the properties of the final material. Depending on the route used and subsequent post-synthesis treatments, a wide variety of different morphologies, phases, exposed facets, and defect structures are created, all of which must be carefully considered for the chosen application. In this review, the recent developments in WO3 nanosheet synthesis and their impact on performance in various applications are summarized and critically analyzed.

A coral-like polyaniline/barium titanate nanocomposite electrode with double electric polarization for electrochromic energy storage applications

A hybrid electrode based on a coral-like BT/PANI nanocomposite exhibits ultra-high capacitance (340 F g−1) and excellent electrochromic performance ( reaching 42.9).

Novel core-substituted naphthalene diimide-based conjugated polymers for electrochromic applications

The strategic implementation of using a core-substituted naphthalene diimide derivative to electropolymerize an ionized polymer for a better electrochromic performance is proposed.

Advanced developments in nonstoichiometric tungsten oxides for electrochromic applications

This review summarizes the recent progress of WO3−x for switchable smart devices, focusing on the synthesis, film fabrication, and strategies to improve EC properties, followed by challenges and future development in multifunctional devices.

Band structure and absorption spectra of NH4XI3 (X = Pb, Mg) based hybrid Perovskite for UV ray protector and electrochromic materials applications

Modeling Perovskite materials and tuning their properties by monovalent or divalent cations substitution produce several choice Perovskite compounds, studied extensively to improve the power conversion efficiency, reduce toxicity, and enhance stability. We modeled NH4PbI3 and NH4MgI3 from the parent compound CH3NH3PbI3, by replacing the monovalent CH3NH3+ with NH4+ and the divalent Pb atom with Mg. In this study, the electronic band structure, as well as the electronic bandgaps, were calculated using the Perdew-Burke-Enzenhoff (PBE) and Perdew-Burke-Enzenhoff for solid (PBEsol) exchange-correlation functionals of the Density-functional Theory (DFT) and GW quasiparticle method of the Many-Body Perturbation Theory (MBPT). Similarly, we used Time-Dependent Density Functional Perturbation Theory (TDDFPT) and the solution of the Bethe-Salpeter equation (BSE) of the Many-Body Perturbation Theory to determine the real and imaginary dielectric tensors with and without spin-orbit coupling (SOC). Direct bandgaps at R high symmetry point were reported for NH4PbI3, while NH4MgI3 showed indirect bandgaps at Γ→R high symmetry points with lower bandgaps compared to NH4PbI3. The projected density of state around the Fermi level reveals that the iodine (I) p orbital is most responsible for the valence band in both NH4PbI3 and NH4MgI3, while the Lead (Pb) p orbital and the Magnesium (Mg) s orbitals, show the most prominent contribution to the Conduction bands. Similar Optical spectra were achieved with BSE-SOC, TDDFPT, and TDDFPT-SOC for NH4PbI3 without the absorption onsets, while NH4PbI3 predicts higher values of absorbance and absorption coefficient compared to NH4MgI3 which predict lower reflectivity and higher transmittance. Both compounds show maximum absorption coefficient in the order of 105 in the ultraviolet region like CH3NH3PbI3 and silicon. Therefore, we suggest that NH4PbI3 will be useful as solar cell absorber and UV ray protector, while NH4MgI3 would have more applications in the production of electrochromic materials.

Annealing Effect on the Properties of Electrochromic V2O5 Thin Films Grown by Spray Deposition Technique

Nanostructured electrochromic V2O5 thin films were prepared using spray pyrolysis technique growth at a temperature of 250 °C using air-carrier spray deposition, starting from ammonium metavanadate precursor in water, followed by annealing at 400 °C in O2 atmosphere for 2 h. The V2O5 films were characterized by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy, and their electrochromic behavior was studied using optical spectroscopy and cyclic voltammetry in both the as-deposited and postannealing case. The studies showed that the simple, cost -effective, suitable for large area deposition method used can lead to an interesting surface structuring with large active surface properties suitable for electrochromic applications. Further studies for growth optimization and improvements of films properties and stability are to be performed.

Fast Proton Insertion in Layered H2W2O7 via Selective Etching of an Aurivillius Phase

AbstractH2W2O7, a metastable material synthesized via selective etching of the Aurivillius‐related Bi2W2O9, is demonstrated as an electrode for high power proton‐based energy storage. Comprehensive structural characterization is performed to obtain a high‐fidelity crystal structure of H2W2O7 using an iterative approach that combines X‐ray diffraction, neutron pair distribution function, scanning transmission electron microscopy, Raman spectroscopy, and density functional theory modeling. Electrochemical characterization shows a capacity retention of ≈80% at 1000 mV s–1 (1.5‐s charge/discharge time) as compared to 1 mV s–1 (≈16‐min charge/discharge time) with cyclability for over 100 000 cycles. Energetics from density functional theory calculations indicate that proton storage occurs at the terminal oxygen sites within the hydrated interlayer. Last, optical micrographs collected during in situ Raman spectroscopy show reversible, multicolor electrochromism, with color changes from pale yellow to blue, purple, and last, orange as a function of proton content. These results highlight the use of selective etching of layered perovskites for the synthesis of metastable transition metal oxide materials and the use of H2W2O7 as an anode material for proton‐based energy storage or electrochromic applications.

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/NiOx/LiPON/WO3/ITO and ITO/NiOx/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/NiOx/LiPON/WO3/ITO), the ECD with the IAI top electrode (ITO/NiOx/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.

Electrochemical preparation of donor-acceptor type conjugated polymer films: Effect of substitute units on electrochromic performance

Conjugated polymers exhibiting adjustable color changes under an electric field have been receiving great research interest due to their potential use in electrochromic applications. High-performance electrochromic materials are required to have well-defined donor-acceptor (D-A) units, a low optical bandgap, and fast response time. To fulfill these demands, herein, for the first time, two conducting macromolecules poly-3,8-diaminobenzo[ c ]cinnoline (P1) and poly-4,7-bis(phenyldiazenyl)benzo[ c ]cinnoline-3,8-diamine (P2) were successfully fabricated on the ITO substrate via electrochemical polymerization from their corresponding monomers in 0.1 M TBAP/acetonitrile solution. Consequently, two conjugated polymeric films show well-defined azo and amine functional groups, which are responsible for electron-withdrawing and electron-donating, respectively. The optical bandgaps (E g ) of P1 and P2 films were found 1.87 eV and 1.81 eV, respectively. The P1 exhibited a yellowish-brown color in neutral states and reduced states and a dark brown color in oxidized states while the P2 showed an orange color in neutral states, brownish orange color in oxidized states and a dark brown color in reduced states. It has been found that the P1 shows a higher conductivity, shorter switching time and better stability while P2 exhibits advanced the chromic and electron-withdrawing characteristics, which were attributed to the substituted phenyldiazenyl units contacted to the benzo[ c ]cinnoline (BCC) and lower oxidation potential of P2. This study opens a new avenue into the electrochromic application via the effective electropolymerization of corresponding monomers. The polymeric films also displayed distinct color changes in the oxidation process, and it was exciting that especially P1 displayed saturated green color in the neutral state. Furthermore, the P1 and P2 films coated on the ITO substrate depicted high optical contrast, excellent coloration, efficiency short response time, and satisfactory stabilities. • The as-prepared conductive films have strongly contacted to the substrate and show decent stability. • The P1 and P2 films have good electrical conductivity.