Excellent Electrochromic Performance Research Articles

Design and fabrication of MoSe2/WO3 thin films for the construction of electrochromic devices on indium tin oxide based glass and flexible substrates

Electrochromic devices (ECDs) have the ability to block the heat generated by sunlight, making them ideal for use in smart windows. Herein, we report the fabrication of ECDs using MoSe 2 /WO 3 (MSW) as the electrochromic material, for smart windows applications. A solvothermal method was used for the synthesis of MoSe 2 , while WO 3 was synthesized using a sol-gel approach. Subsequently, MoSe 2 /WO 3 (MSW) hybrids with different wt% of MoSe 2 (0.05 wt%, 0.2 wt%, 0.5 wt%) were synthesized using an ultra-sonication approach. The physicochemical features of these MSW hybrids herein termed as MSW 0.05, MSW 0.2 and MSW 0.5, were investigated using X-ray diffraction (XRD), X-ray photon electron spectroscopic (XPS), scanning electron microscope (SEM), and EDS techniques and compared with pristine MoSe 2 and WO 3 . The ECDs synthesized using MSW 0.05 showed increased coloration efficiency (62 cm 2 C-1 ) with an applied potential range of 0 to −1.5 V. Subsequently, the ECDs based on indium tin oxide (ITO) and MSW 0.05 demonstrated excellent electrochromic performance and stability for 10,000 cycles. The enhanced electrochromic performance of the MSW-based ECDs may be attributed to the conductive nature as well as the synergistic effects between MoSe 2 and WO 3 when compared to the WO 3 -based ECDs. The synthesized MSW also showed promise as an electrochromic material in flexible ECDs for smart windows applications.

Complementary electrochromic devices based on acrylic substrates for smart window applications in aircrafts

Electrochromic devices (ECDs) fabricated using resin substrates are attracting considerable interest owing to their advantages of shape deformability and low weight. Acrylic substrates are used to fabricate aircraft windows because they are lighter and more impact-resistant than glass substrates. In this study, the wettability of an indium tin oxide (ITO) surface was enhanced using ultraviolet (UV) treatment prior to the spin-coating and deposition of Prussian blue (PB) and WO3 thin films, which were prepared using functional nanoparticle-dispersed inks on an ITO/acrylic substrate. The fabricated ECD was structured as acrylic/ITO/PB/K+-base gel electrolyte/WO3/ITO/acrylic, and was observed to exhibit excellent electrochromic performance. A high optical modulation and coloration efficiency of 76% and 112.99 cm2/C at a wavelength of 633 nm, respectively, and satisfactory cyclic durability over 1800 cycles were observed. The fabricated ECD possesses immense potential for application in various fields, especially in the field of smart windows for aircrafts.

A high-performance electrochromic battery based on complementary Prussian white/Li4Ti5O12 thin film electrodes

Electrochromic energy storage devices (EESDs) have a wide range of applications from static displays to building windows. However, it is a great challenge to assemble EESDs with both high performance of energy storage and electrochromism. In this work, we design a multifunctional EESD composed of a Li4Ti5O12 and a Prussian white. Li4Ti5O12 (E = 1.55 V vs Li/Li+) film with excellent lithium-ion storage performance is used as the anode, and Prussian white film (E = 3.2 V vs Li/Li+) as the cathode. Thanks to the complementary electrochromic behavior, the suitable redox voltage gap, and the intrinsic electrochemical stability of Li4Ti5O12 film and Prussian white film, the as-assembled EESD exhibits excellent electrochromic performances including broad optical modulation (55.3% at 529 nm), high coloration efficiency (170.1 cm2 C−1), and long-term cycling stability (retention of 95.8% of initial optical modulation after 1000 cycles). And the EESD shows high energy density of 127.2 mWh cm−2 and exceptionally high power density of 24 mW cm−2. This EESD with an output voltage of 1.5 V and Coulombic efficiency of 98.8% is promising for applications of electrochromic smart windows and static displays to significantly reduce their energy consumption.

Robust Cu-Au alloy nanowires flexible transparent electrode for asymmetric electrochromic energy storage device

Flexible electrochromic energy storage (EES) systems have attracted tremendous attention because of their combined advantages of color-changing and energy-storing. Although copper nanowires (Cu NWs) flexible transparent electrodes (FTEs) have been considered as one of the most promising candidates for next-generation flexible electronics, its instinct electrochemical instability hindered its application in flexible electrochemical energy system, including EES device. Herein, we proposed a highly conductive electrochemically stable FTE based on Cu-Au alloy NWs network synthesized in a facile and simple electrochemical method. Compared with the pristine Cu NWs network that breaks into disconnected nanorods less than 10 s in 1 M H2SO4 solution during electrochemical anodic corrosion, the Cu-Au NWs network remained stable after 4000 s under the same condition. Furthermore, thanks to the forming of firm joints between the stacked NWs during inducting Au atoms, the optical-electrical performance (a sheet resistance of 23.2 Ohm/sq at a transmittance of 87%) and mechanical flexibility were highly improved. Based on these improvements, anodic PANI and cathodic WO3 layer were successfully deposited onto the Cu-Au NWs FTE by electrochemical method. An asymmetric-EES (AEES) device was assembled utilizing these complementary electrodes, which concurrently exhibited excellent electrochromic (coloration efficiency: 153.77 cm2/C at 633 nm) and energy storage performance (areal capacitance: 2.29 mF/cm2), demonstrating their potential for smart multifunctional flexible electronics.

Electropolymerization of V-shape D-A-D type monomers for efficient and tunable electrochromics

Five novel donor-acceptor-donor (D-A-D) type monomers (VQ1 ~ VQ5) with a common V-shape configuration have been developed and further electropolymerized for electrochromic applications. The monomers were designed by introducing two triphenylamine groups into the 2- and 3- position of the quinoxaline derivates, respectively. These redox-active monomers could be electrodeposited robustly on the ITO electrodes in an electrolyte solution via the oxidative coupling reactions between triphenylamine radical cations. The obtained thin polymer films (PVQ1 ~ PVQ5) exhibited reversible redox behaviours and obvious color changes upon voltage variation. All these polymers exhibited excellent electrochromic performances involving high optical contrast (over 70%), short response time (less than 2 s) and high coloration efficiency (over 200 cm2 C−1). Moreover, the optical properties of these polymers in both neutral state and oxidation state can be tuned by variation of the additional substituents on the quinoxaline parts, respectively.

Bio-inspired electrochromic skin based on tungsten oxide

Some animals, such as the chameleon, have great capability of camouflage by changing their skin color to avoid detection. This outstanding property have inspired researchers to develop the ability of the materials and devices to mimic chameleon for applications in intelligent wearable and camouflage devices. Tungsten oxide (WO3), switching between blue and transparent, is widely studied due to its large optical modulation but it is difficult to obtain multicolor and flexibility. Here, we design a bio-inspired chameleon skin electrochromic device (ECD) assembled by inorganic electrochromic materials WO3, which can achieve the reversible color changes from yellow, light green to dark green according to subtractive color mixture theory. The flexible ECD exhibits a high optical reflectance modulation of 38.9% at voltage of ± 1.5 V in the wavelength range of 250–2500 nm. Fast response speed of 0.32 s for both coloring and bleaching process is obtained which can be attributed to the porous structure of the WO3 electrochromic layer. The ECD keeps excellent electrochromic performance even under bending conditions, indicating the great flexibility. The inorganic bio-inspired chameleon skin ECD opens new avenues for the design of intelligent and wearable devices.

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).

A multi-responsive indium-viologen hybrid with ultrafast-response photochromism and electrochromism.

A novel 0D organic-inorganic metal halide hybrid (C13H16N2O2)2InCl6·Cl (1) has been obtained by integrating the mono-viologen derivative with InCl3. Compound 1 exhibits reversible and ultrafast UV/sunlight/X-ray induced photochromic properties, as well as excellent electrochromic performance, which is the first example of an indium-based organic-inorganic chromic hybrid.

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.

Preparation of Sn-NiO films and all-solid-state devices with enhanced electrochromic properties by magnetron sputtering method

In this paper, Sn-NiO films for a superior electrochromic performance were prepared by a simple one-step magnetron sputtering process. The amount of Sn in the Sn-NiO films was controlled by adjusting the sputtering power of the SnO2 target. The modification of the microstructure of the NiO film by Sn4+ ions refined the grain size, enlarged the electrochemically active surface and promoted the diffusion of lithium ions, thereby enhancing the electrochromic performances of a NiO film. Compared to pure NiO, the Sn-NiO film prepared at a 10 W sputtering power of SnO2 target obtained outstanding electrochromic performances, including large transmittance modulation (65.1%), high coloration efficiency (39.3 cm2·C−1), fast switching speed (1.3 s and 1.4 s) and good cycling durability at a wavelength of 550 nm. Besides, an optimized Sn-NiO film was used as an anodic electrochromic layer to prepare inorganic all-solid-state electrochromic device (ECD) and the ECD displayed excellent electrochromic performance. The strategy of preparing NiO modified by Sn4+ ions presents an innovative direction to obtain high-performance electrochromic materials for energy-saving smart windows.

Boosting Transport Kinetics of Ions and Electrons Simultaneously by Ti3C2Tx (MXene) Addition for Enhanced Electrochromic Performance

HighlightsMXene/WO3−x composite film with excellent electrochromic performances was fabricated for the first time.The addition of MXene is an effective strategy for simultaneously enhancing electron and ion transport behaviors in the electrochromic layer.The kinetics of ion diffusion in electrochromic devices are studied in depth based on both experiment and simulation.

Improved the response time of WO3 thin film by deposition of Ag nanolayers

The effects of different Ag layer thicknesses on the optical properties of WO3-Ag-WO3 composite films are studied by magnetron sputtering. The research of WO3-Ag-WO3 composite films reveals that the introduction of Ag layer is not conducive to improving the transmittance ability of the film, and the transmittance modulation amplitude decreases with the increase of Ag layer thickness. However, with the increase of the Ag layer thickness, the response time and the cycle stability of the films have been significantly improved. However, electrochromic performances will decline when Ag was sputtered too long. Taken together, in this experiment, when the sputtering time of Ag layer is about 6min, the electrochromic device assembled by composite thin film can obtain the most excellent electrochromic performances.

Boosting the Zn2+-based electrochromic properties of tungsten oxide through morphology control

Zn2+-based electrochromic is a newly born technology in recent years and has attracted the attention of most researchers due to its low cost and high safety. The design of high-performance Zn2+-based electrochromic devices, such as large light modulation and fast color change, is still a challenge. Here, we report the improvement of Zn2+-based electrochromic properties by morphology control, using common electrochromic material WO3 as the research model. The hexagonal WO3 films with shape of nanorods and nanoflakes were prepared by hydrothermal method, where the diameter of the nanorods and the thickness of the nanoflakes are almost the same. The electrochromic characterization of WO3 nanorods and nanoflakes at 550 nm showed that their modulation ranges were 72.4% and 61.0%, their coloration times were 3 and 9 s, their bleaching times were 2.2 and 7 s, and their coloration efficiencies were 67.6 and 53.8 cm2 C-1, respectively. Compared with WO3 nanoflakes, the excellent Zn2+-based electrochromic properties of WO3 nanorods show rapid electron transfer kinetics caused by large surface area. Furthermore, the prototype electrochromic devices with WO3 nanorods were fabricated, which showed good specific capacitance and excellent electrochromic performance. The fast and large optical modulation synchronous as well as good energy storage makes the electrochromic device become a potential intelligent power supply. This morphology dependent electrochromic work provides a new vision for the construction of high-performance Zn2+- based electrochromic devices.

One-Dimensional π-d Conjugated Coordination Polymer for Electrochromic Energy Storage Device with Exceptionally High Performance.

The rational design of previously unidentified materials that could realize excellent electrochemical‐controlled optical and charge storage properties simultaneously, are especially desirable and useful for fabricating smart multifunctional devices. Here, a facile synthesis of a 1D π–d conjugated coordination polymer (Ni‐BTA) is reported, consisting of metal (Ni)‐containing nodes and organic linkers (1,2,4,5‐benzenetetramine), which could be easily grown on various substrates via a scalable chemical bath deposition method. The resulting Ni‐BTA film exhibits superior performances for both electrochromic and energy storage functions, such as large optical modulation (61.3%), high coloration efficiency (223.6 cm2 C−1), and high gravimetric capacity (168.1 mAh g−1). In particular, the Ni‐BTA film can maintain its electrochemical recharge‐ability and electrochromic properties even after 10 000 electrochemical cycles demonstrating excellent durability. Moreover, a smart energy storage indicator is demonstrated in which the energy storage states can be visually recognized in real time. The excellent electrochromic and charge storage performances of Ni‐BTA films present a great promise for Ni‐BTA nanowires to be used as practical electrode materials in various applications such as electrochromic devices, energy storage cells, and multifunctional smart windows.

Solution-processable core/shell structured nanocellulose/poly(o-Methoxyaniline) nanocomposites for electrochromic applications

In this research, core/shell structured nanocellulose (NC)/poly(o-Methoxyaniline) (POANI) nanocomposites for electrochromic applications were synthesized by controllable in situ chemical oxidative polymerization. The NC/POANI nanocomposites with different contents of NC can be obtained simply by controlling the relative proportions of the monomers and NC in the polymerization system with hydrochloric acid as the dopant and ammonium persulfate as the oxidant. Films based on the NC/POANI nanocomposites were successfully fabricated by spray-coating technique. The nanocomposite films showed the combination of good film-forming properties and excellent electrochromic behavior. The film based on NC/POANI nanocomposites containing 40% NC exhibited higher optical contrast (81% at 665 nm) and better cycling stability (sustaining 84% of its initial optical contrast after 500 times cyclic test) compared with pure POANI film. Such NC/POANI nanocomposites with excellent electrochromic performance demonstrate great promise towards achieving the ideal electrochromic applications.

Pyrazine-EDOT D-A-D type Hybrid Polymer for Patterned Flexible Electrochromic Devices

Two donor-acceptor type pyrazine-EDOT hybrid polymers are developed as high performance electrochromic materials and employed to fabricate flexible electrochromic devices via electropolymerization patterning. By coupling EDOT with pyrazine at 2,5-positions, the resultant precursor 2,5-BEP can facilely electropolymerize to yield high quality pyrazine-EDOT hybrid polymer films with excellent electrochemical stability. Spectroelectrochemistry and kinetic studies demonstrate that as-formed pyrazine-EDOT hybrid polymer exhibits reversible color-changing nature from purple to gray with high coloration efficiency (134 cm2 C−1), fast response time (0.2 s) and high optical contrast (> 55%) over a wide wavelength range of 800–2200 nm in near-infrared (NIR) region. To harness its excellent electrochromic performance as well as the ease of electropolymerization patterning, we fabricate patterned flexible electrochromic devices (ECDs) via facile electropolymerization and such ECDs display reversible color changes with decent optical stability (25% reduction in optical contrast upon 1000 cycling) and excellent mechanical stability (9.6% reduction in optical contrast upon bending 5000 cycles). The excellent electrochromic performance and stability of pyrazine-EDOT hybrid polymers as well as their-based ECDs make them good candidates towards near infrared electrochromic applications.

Unveiling the electrochromic mechanism of Prussian Blue by electronic transition analysis

Abstract Prussian blue (PB) represents a class of metal-organic coordinated compounds with fascinating electrochromic properties. Although the electronic structure has been studied intensively, its electrochromic mechanism remains unresolved due to the lack of electronic-transition analysis. Herein, we investigate the electrochromism of Prussian blue (PB) and its derivatives by combining optical characterization and density functional theory (DFT) calculations. We unambiguously determine the optical gaps of PB-related derivatives and construct a smart window exhibiting excellent electrochromic performance and temperature control. DFT calculations demonstrate that the coloring of Prussian yellow (PY) is critically governed by two absorption bands centered at ca. 2.4 eV and 3.0 eV respectively. The former is weak and is generated by the charge-transfer transitions from the Fe(I)-t2g (Fe ions connected with C) band to the Fe(II)-t2g (Fe ions connected with N) band. The latter is strong and is induced by the electronic excitations from the Fe(I)-t2g band to the antibonding Fe(II)-eg band. The color change from yellow to blue is induced by the reduction of Fe(I) ions, which redshifts and enhances the former transitions but suppresses the latter transitions. In contrast, the color change from blue to transparency (Prussian white) is induced by the reduction of Fe(II) ions, which enlarges the bandgap and permits transmittance of visible light. The band-edge transition oscillator strengths are critically governed by the state weight of C-p, which provides opportunities for optical modulation via anionic doping. The insights obtained in this work are fundamental for understanding and controlling the opto-electronic properties of PB-related compounds for intelligent applications.

Fluorinated Oleophilic Electrochromic Copolymer Based on 3‐(N‐Trifluoroacetamido)thiophene and 3,4‐Ethylenedioxythiophene (EDOT)

AbstractA new fluorine‐containing monomer 3‐(N‐trifluoroacetamido)thiophene (F‐TH) was synthesized and characterized for the first time. Its molecular structure was determined through a single‐crystal X‐ray study. F‐TH functions as a building block in electropolymerization with 3,4‐ethylenedioxythiophene (EDOT) and subsequently gives a novel conjugated copolymer P(F‐TH : EDOT). Compared with the parent homopolymer poly(3,4‐ethylenedioxythiophene) (PEDOT) film, the sponge‐like nanoporous P(F‐TH : EDOT) film has a slightly larger band gap with a reduced hydrophilic and increased oleophilic surface. Spectroelectrochemical analysis results reveal that P(F‐TH : EDOT) exhibits excellent electrochromic performances with a higher optical contrast (55 %) and much shorter coloring time (0.70 s) than that of PEDOT (43 %, 1.54 s). The coloration efficiency value of P(F‐TH : EDOT) achieves up to 167.9 cm2/C, 55 % higher than that of PEDOT (108.1 cm2/C). These improved electrochromic properties of P(F‐TH : EDOT) are probably related with the enhanced wettability to electrolyte solution.

LixNa2-xW4O13 nanosheet for scalable electrochromic device.

The printed electronics technology can be used to efficiently construct smart devices and is dependent on functional inks containing well-dispersed active materials. Two-dimensional (2D) materials are promising functional ink candidates due to their superior properties. However, the majority 2D materials can disperse well only in organic solvents or in surfactant-assisted water solutions, which limits their applications. Herein, we report a lithium (Li)-ion exchange method to improve the dispersity of the Na2W4O13 nanosheets in pure water. The Li-ion-exchanged Na2W4O13 (LixNa2-xW4O13) nanosheets show highly stable dispersity in water with a zeta potential of -55 mV. Moreover, this aqueous ink can be sprayed on various substrates to obtain a uniform LixNa2-xW4O13 nanosheet film, exhibiting an excellent electrochromic performance. A complementary electrochromic device containing a LixNa2-xW4O13 nanosheet film as an electrochromic layer and Prussian white (PW) as an ion storage layer exhibits a large optical modulation of 75% at 700 nm, a fast switching response of less than 2 s, and outstanding cyclic stability. This Na2W4O13-based aqueous ink exhibits considerable potential for fabricating large-scale and flexible electrochromic devices, which would meet the practical application requirements.

Large-scale preparation of solution-processable one-dimensional V2O5 nanobelts with ultrahigh aspect ratio for bifunctional multicolor electrochromic and supercapacitor applications

Abstract Solution-processable V2O5 nanobelts are successfully synthesized by a very simple and large-scale solution treatment method using commercial bulk V2O5 powders as precursor. The prepared V2O5 nanobelts with lengths up to 20 μm, widths of 10–30 nm, and aspect ratio of over 1000 displays excellent electrochromic and electrochemical capacitance performance. A large optical modulation, rapid switching speed and remarkable cycling stability (sustaining 94% of its initial optical contrast after 1000 cycles) are achieved for V2O5 nanobelt film (V2O5-nb film). And the V2O5-nb film also shows large specific capacitance and excellent capacitance retention (capacitance decay of only 5% after 500 cycles). In addition, the level of stored energy for V2O5-nb film could be simultaneously monitored by a reversible and fast color change even at high current charge/discharge conditions (16 A/g). The spray-processable large-scale patterned electrochromic displays based on V2O5 nanobelts exhibited various color variation and large optical contrast. The solution-processable V2O5 nanobelt shows promising features for applications in energy efficient displays, lithium-ion batteries, supercapacitors and electrochromic devices.