Complementary Electrochromic Device Research Articles

Enhanced Performance of Complementary Electrochromic Device with Hierarchical‐Porous NiO x Decorated ITO Glasses as the Transparent Conductive Electrodes

To pursuit advancing electrochromic technology, the preparation of a novel hierarchical‐porous NiOx‐decorated ITO transparent conductive electrode was developed through the vapor‐assisted conversion and subsequent calcination processes. The modified transparent electrode exhibited advantages in the electrodeposition of conductive polymer films, which significantly enhanced electrochromic cycling stability. Moreover, the complementary electrochromic device based on NiOx‐decorated ITO transparent electrode was fabricated, demonstrating rapid response time (1.75 s for coloration and 0.87 s for bleaching), high optical contrast (53.4%), and remarkable cycling stability (90% optical contrast retention over 2000 cycles). This finding holds prominent potential for applications in related fields.

Constructing an Al3+/Zn2+-Based Solid Electrolyte Interphase to Enable Extraordinarily Stable Al3+-Based Electrochromic Devices.

The interface between the electrochromic (EC) electrode and ionic conductor is crucial for high-performance and extraordinarily stable EC devices (ECDs). Herein, the effect of the ALD-AZO interfacial layer on the performance of the WO3 thin film was examined, revealing that an introduction of the ALD-AZO interfacial layer to the Al3+-based complementary ECDs can lead to improved EC performance and stability, such as an extraordinary cyclability of more than 20,000 cycles, an outstanding coloration efficiency of 109.69 cm2 C-1, and a maximum transmittance modulation of 63.44%@633 nm. The probable explanation is that the introduced ALD-AZO interfacial layer can effectively regulate the band gap of WO3, promote the electron transport process, and induce the formation of a robust solid electrolyte interphase to protect the electrode during cycling. These findings offer valuable insights for enhancing the EC performance of the EC thin films and new space for the construction of advanced multivalent Al3+-based ECDs.

Homogeneous and Nanogranular Prussian Blue to Enable Long-Term-Stable Electrochromic Devices.

The increasing demand for the state-of-the-art electrochromic devices has received great interest in synthesizing Prussian blue (PB) nanoparticles with a uniform diameter that exhibit excellent electrochromism, electrochemistry, and cyclability. Herein, we report the controllable synthesis of sub-100 nm PB nanoparticles via the coprecipitation method. The diameter of PB nanoparticles can be modulated by adjusting the reactant concentration, the selection of a chelator, and their purification. The self-assembled nanogranular thin films, homogeneously fabricated by using optimized PB nanoparticles with an average diameter of 50 nm as building blocks via the blade coating technique enable excellent performance with a large optical modulation of 80% and a high coloration efficiency of 417.79 cm2 C-1. It is also demonstrated by in situ and ex situ observations that the nanogranular PB thin films possess outstanding structural and electrochemical reversibility. Furthermore, such nanogranular PB thin films can enjoy the enhanced long-term cycling stability of the PB-WO3 complementary electrochromic devices having a 91.4% optical contrast retention after 16,000 consecutive cycles. This work provides a newly and industrially compatible approach to producing a complementary electrochromic device with extraordinary durability for various practical applications.

Long-lived electrochromic device with protonated viologen and Poly(ethylenedioxythiophene-carbazole)/Prussian blue composite for smart windows

A complementary electrochromic device (ECD) configuration featuring a protonated viologen (VNH2+) as the cathodically coloring electrochrome and a composite of poly(ethylenedioxythiophene-carbazole) (i.e. poly(EDOT-Cz)) and Prussian blue (PB) as the anodically coloring electrochrome marks the first implementation of this innovative high contrast device. A comparative analysis of VNH2+//poly(EDOT-Cz) and VNH2+//poly(EDOT-Cz)/PB ECDs demonstrates a superior integrated visible light transmission modulation (ΔT) of 50.4%, versus 76.7%, higher diffusion coefficient of 4.4 × 10−11versus 3.9 × 10−10 cm2 s−1, higher coloration efficiency (CE) of 424 versus 562 cm2 C−1 (at 550 nm), faster color-bleach switching times of (7.0 and 4.0 s) versus (1.2 and 1.0 s) and a CIE chromaticity coordinate corresponding an intense deep blue state (y: 0.058 versus 0.218) achieved with the composite relative to the pure polymer. The VNH2+//PB ECD also shows lower CE (69 cm2 C−1) and slower coloration-bleaching kinetics (20 and 2 s) compared to the composite based ECD. In addition, long-term cycling stability attained for the VNH2+//poly(EDOT-Cz)/PB ECD, whereby it endures 5000+ color-bleach cycles without showing any major deterioration in optical modulation or switching kinetics underscores the suitability of the composite based ECD for practical smart window applications.

Porous NiMoO4 Nanosheet Films and a Device with Ultralarge Optical Modulation for Electrochromic Energy-Storage Applications.

Reducing building energy consumption, improving aesthetics, and improving occupant privacy as well as comfort by dynamically adjusting solar radiation are important application areas for electrochromic (EC) smart windows. However, the current transition metal oxides still cannot meet the requirements of neutral coloration and large optical modulation. We report NiMoO4 nanosheet films directly grown on fluorine-doped tin oxide glasses. The as-grown NiMoO4 film not only achieves neutral coloration from transparent to dark brown but also shows an ultralarge optical modulation (86.8% at 480 nm) and excellent cycling stability (99.4% retention of maximum optical modulation after 1500 cycles). Meanwhile, an EC device demonstrating good EC performance was constructed. These results will greatly promote the research and development of binary transition metal oxides for both EC and energy-storage applications, and NiMoO4 films may be an excellent candidate to replace NiO films as ion-storage layers in complementary EC devices with WO3 films as EC layers.

Ionic Storage Materials for Anodic Discoloration in Electrochromic Devices

The ion storage layer in electrochromic devices (ECDs) stores protons or lithium ions to provide electrochemical stability and extend cycle durability. This paper reports on the performance and stability of ECDs paired with various ion storage layers (NiO, V2O5, and IrO2 films). The complementary ECD using a V2O5 ion storage layer presented the fastest response time, but the lowest optical contrast. In addition, the ECD using an IrO2 ion storage layer proved the most effective as an ion storage layer, due to its high optical modulation ability capability and long-term stability. Chronoamperometry analysis revealed that IrO2-based ECD (glass/IZTO/WO3/liquid electrolyte/IrO2/IZTO/glass) can be highly effective in modulating optical transmittance, as indicated by T = 61.5% (from Tbleaching (69.6%) to Tcoloring (8.1%)) and switching times of 5.3 s for coloring and 7.3 s for bleaching at 633 nm.

Long-life Inorganic Electrochromic Device Based on WO3 and PB Films with Fast Switching Respond

Complementary electrochromic devices were fabricated by using tungsten trioxide (WO3) film as working electrode, Prussian blue (PB) film as counter electrode and 0.1 M lithium perchlorate in propylene carbonate as electrolyte. The XRD result presents that WO3 and PB films are amorphous, which is favourable for a fast ion intercalation-deintercalation process. The device was tested under potentiostatic control using ±1.3 V steps, and changed its color between blue and colorless. It has a fast-switching respond (about 1.5 s for colouring and 2 s for bleaching) and could withstand 100,000 cycles with little change in its optical contrast.

Long-Term Stable Complementary Electrochromic Device Based on WO3 Working Electrode and NiO-Pt Counter Electrode.

Complementary electrochromic devices (ECDs) composed of WO3 and NiO electrodes have wide applications in smart windows. However, they have poor cycling stability due to ion-trapping and charge mismatch between electrodes, which limits their practical application. In this work, we introduce a partially covered counter electrode (CE) composed of NiO and Pt to achieve good stability and overcome the charge mismatch based on our structure of electrochromic electrode/Redox/catalytic counter electrode (ECM/Redox/CCE). The device is assembled using a NiO-Pt counter electrode with WO3 as the working electrode, and PC/LiClO4 containing a tetramethylthiourea/tetramethylformaminium disulfide (TMTU/TMFDS2+) redox couple as the electrolyte. The partially covered NiO-Pt CE-based ECD exhibits excellent EC performance, including a large optical modulation of 68.2% at 603 nm, rapid switching times of 5.3 s (coloring) and 12.8 s (bleaching), and a high coloration efficiency of 89.6 cm2·C-1. In addition, the ECD achieves a good stability of 10,000 cycles, which is promising for practical application. These findings suggest that the structure of ECC/Redox/CCE could overcome the charge mismatch problem. Moreover, Pt could enhance the Redox couple's electrochemical activity for achieving high stability. This research provides a promising approach for the design of long-term stable complementary electrochromic devices.

Facile synthesis of hybrid WO3/MoOx electrochromic films for application in complementary electrochromic devices

In this study, WO3 nanoparticles and MoO3 nanoribbons were prepared using a microwave-assisted hydrothermal method. Following a grinding treatment, a stable WO3/MoO3 suspension having a nanoheterojunction structure was obtained. Moreover, oxygen vacancies were introduced in the MoO3 nanoribbons (MoOx) during the grinding process. Consequently, the ground WO3/MoOx composite film exhibited an enhanced electrochromic (EC) performance compared to the ground WO3 and MoO3 films not only due to its favorable morphology for ion transport but also the enhanced intervalence electron transfer. To further evaluate the potential of ground WO3/MoOx electrodes for practical applications, a complementary electrochromic device (ECD) was constructed using ground WO3/MoOx and polyaniline:poly(4-styrenesulfonate) (PANI:PSS) as cathodic and anodic coloring materials, respectively. This complementary ECD yielded a transmittance modulation of 55.4% at 650 nm with rapid switching times of 7.4 s (bleaching) and 3.6 s (coloring). The ECD also exhibited a high coloration efficiency of 154 cm2/C and a high cycling stability with an 80.6% transmittance retention after 2000 cycles. These results demonstrate that ground WO3/MoOx composites are attractive materials for fabricating high-performance ECDs.

One-dimensional physical model for complementary electrochromic device

Eletrochromic devices are electrochemical systems that can undergo the optical modulation in response to an applied electrical stimulus. In order to investigate the electrochromic (EC) process mechanism and predict the electrochromic behavior, this paper proposes a physical model that employs tungsten trioxide (WO3), nickel oxide (NiO) and LiClO4-propylene carbonate (PC) solution. Within electrochromic films, electrolytes can transport lithium ions and anions through porous layers of electrochromic films. At the interfaces between solution and porous layers, lithium-ion intercalation and deintercalation take place. Considering both ion diffusion and electromigration, ion transport kinetics is described by Nernst-Plank equation. The partial differential equations (PDEs) for potential consist of Poisson equations for electrolytes and Ohm’s law for WO3 and NiO films. Moreover, the ion injection behavior at the interface is governed by Frumkin-Butler-Volmer (FBV) equation and potential conditions of the stern layer. Finally, a modified Beer–Lambert law incorporating porosity is proposed to explain the mechanism of transmittance. Under constant step potential conditions, the state variables of multiphysics field can be tracked, and the dynamic process of the transmittance and electrode current can be accurately predicted. This physical model can be applied for parameter design and precise control of ECDs, based on the optimization of device characteristics.

A complementary electrochromic device based on Prussian Blue and Tungsten Trioxide: The influence of switching time operation on high performance and long-term stability

The sustainability of electrochromic devices has been heavily focused on both novel materials and electrolytes. Nonetheless, profound research into the operation of electrochromic devices have typically gone unnoticed. Accordingly, there is still a scarcity of research related to a systematic approach to driving principles of electrochromic devices such as the balanced electrochemical process between the anodic and the cathodic electrodes. Based on fundamental electrochemistry, there are three possible causes of poor performance and cycle stability in an electrochromic device: (1) charge is not equally shuttled between Prussian blue (PB) and tungsten trioxide (WO3), (2) irreversible ions are trapped within PB and/or WO3, and (3) PB and/or WO3 deterioration. Herein, this study discovered the impact of switching time operation on a complementary electrochromic device based on PB and WO3, providing a potentially novel direction for enhancing and controlling the electrochromic performance in smart windows or display applications.

A polyacrylic acid/polyacrylamide-based hydrogel electrolyte containing gelatin for efficient electrochromic device with outstanding cycling stability and flexible compatibility

Hydrogel electrolytes have been attracted intense research interest due to their widespread applications in advanced electronic devices. In this work, we developed a new hydrogel electrolyte to overcome two critical issues in electrochromic devices, involving long-term cycling stability and flexible compatibility. Briefly, gelatin was introduced into a hydrogel polymer matrix based on polyacrylic acid/polyacrylamide, resulting in high transparency, high electronic conductivity, durable electrochemical stability, inherent adhesiveness. Complementary electrochromic devices employing the present hydrogel electrolyte exhibited efficient performance with high optical contrast over 85 %, short response time, high coloration efficiency of 205.7 cm2/C. Remarkably, an excellent operation stability was achieved with less than 3 % loss of the initial optical contrast after 15,000 cycles switching, which was the best case among those based on the same electrochromic materials reported so far. Moreover, the efficient adhesiveness of the present hydrogel electrolyte enabled the compatibility with flexible device and improved the device bending stability. These findings might shed light on the development of durable and flexible electrochromic devices toward practical application.

A Dual‐Mode Electrochromic Platform Integrating Zinc Anode‐Based and Rocking‐Chair Electrochromic Devices

AbstractThe complementary electrochromic device, where the optical transmittance changes upon the flow of cations back and forth between anodic and cathodic electrodes, operates in a rocking‐chair fashion if it can inherently self‐discharge. Herein, the first demonstration of a dual‐mode electrochromic platform having self‐coloring and self‐bleaching characteristics is reported, which is realized by sandwiching zinc metal within a newly‐designed Prussian blue (PB)‐WO3 rocking‐chair type electrochromic device. It is demonstrated that the redox potential differences between the zinc metal and the WO3/PB electrodes endow the self‐color‐switching of these electrodes. By employing a hybrid electrolyte of Zn2+/K+, it is further shown that the colored PB‐WO3 rocking‐chair device is capable of spontaneously bleaching when the anodic and cathodic electrodes are coupled. This dual‐mode light‐control strategy enables the electrochromic devices to exhibit four distinct optical states with the highest optical contrast of 72.6% and fast switching times (<5 s for the bleaching/coloration processes). Furthermore, the built‐in voltage of the dual‐mode electrochromic devices not only promotes energy efficiency, but also augments the bistability of the devices. It is envisioned that the broad implication of the present platform is in the development of self‐powered smart windows, colorful displays, optoelectronic switches, and optical sensors.

Black-to-Transmissive dual polymer complementary electrochromics with high coloration efficiency

In a complementary electrochromic device (ECD), both the anode and the cathode can synergistically change color in response to an electrical bias, allowing for a high coloration efficiency. Complementary ECD that can switch from black to transmissive state is rare, due to the difficulty of pairing two electrochromic electrodes. In this study, we report the construction of high coloration efficiency complementary ECDs by pairing polyazoisoindigo (PAI), an n-type electrochromic polymer that undergoes green-to-transmissive switching, with p-type magenta (ECP-M) and red (ECP-R) electrochromic polymers to obtain black-to-transmissive ECD. Physical modeling tool, COMSOL, is introduced for complementary color matching. Through balancing the charge densities of two electrochromic electrodes, black-to-transmissive ECDs with record-high coloration efficiencies of 688 cm2/C and 437 cm2/C have been achieved for PAI|ECP-M and PAI|ECP-R, respectively. This study provides a general protocol for the design and fabrication of complementary ECDs.

High-performance complementary electrochromic energy storage device based on tungsten trioxide and manganese dioxide films

In this work, we have selected a representative pseudocapacitive material of manganese dioxide (MnO2) film as the complementing electrode of tungsten trioxide (WO3) film to construct a smart electrochromic energy storage device (EESD), with the aim to simultaneously provide the optical modulation and energy storage performance. WO3 and MnO2 films have been respectively synthesized via simple hydrothermal and electrodeposition methods to achieve desirable matched performance. For the constructed EESD, an obvious optical contrast (38.63% at 633 nm), fast switching times (tb/tc = 9.37/5.19 s), high coloration efficiency (85.36 cm2·C−1), satisfactory specific capacitance (10.69 mF·cm−2 at the discharge current density of 0.1 mA·cm−2) as well as excellent cycle stability (initial capacitance retention rate of 95.90% after 1000 charge/discharge cycles) have been derived. After charging, the obtained EESD could light up an LED bulb or an LCD screen, showing high promising application prospect in energy storage.

Improved diffusion and storage of lithium ions via recrystallization induced conducting pathways in a Li:Ta2O5-based electrolyte for all-solid-state electrochromic devices with enhanced performance

In this study, we have investigated the improvements in the performance of an all-solid-state complementary electrochromic device (ECD) by using the proposed high pressure treatment (HPT). The Li:Ta2O5 electrolyte layer was recrystallized by the HPT utilizing pressurized CO2 gas (∼200 atm) and at low temperature (<60 °C), which enhanced the coloration performance of the WO3/Li:Ta2O5/NiO complementary ECD by ∼20%. The reliability and durability of the ECD were confirmed by long term transmittance retention measurements, which indicated an improvement in the coloration performance by ∼14% upon the release of the bias voltages. The ability of the devices that were fabricated with and without the HPT process to withstand high temperature environments was also verified. In addition, photoluminescence (PL) and transmittance measurements were carried out to examine the effects of the bonding between WO3 and NiO. To determine the differences in lithium-ion (Li+) injection, electrical measurements were performed by utilizing varying pulse rising speeds to confirm device characteristics. The materials were characterized in terms of their composition and structure using high-resolution transmission electron microscopy along with energy-dispersive x-ray spectroscopy. Finally, a mechanistic model has been proposed to explain the improved EC characteristics based on the amorphous to crystalline transition accompanying the HPT process.

Preparation of complementary electrochromic devices with WO3/PANI and NiO/PB double-hybrid electrodes

Preparation of complementary electrochromic devices with WO3/PANI and NiO/PB double-hybrid electrodes

Enhanced Electrochromic Performance of All-Solid-State Electrochromic Device Based on W-Doped NiO Films

Electrochromic materials have attracted much attention due to their promising applications in smart windows and thermal control. However, NiO is a weak point for a complementary ECD and needs to be improved due to its low optical modulation and charge density. In this work, the W-doped NiO films are designed and prepared by RF magnetron co-sputtering to improve the performance of the NiO. The results shows that the optical modulation of the W-NiO (52.7%) is significantly improved compared with pure NiO (33.8%), which can be assigned to the increase in lattice boundaries due to the W doping. The response time of W-NiO is 8.8 s for coloring and 7.2 s for bleaching, which is similar to that of NiO film. The all-solid-state electrochromic devices (ECDs) that employed W-NiO as a complementary layer are prepared and exhibit a high-transmittance modulation of 48.5% in wavelengths of 450–850 nm and an emittance modulation of 0.28 in 2.5–25 μm, showing great application potential in the field of smart windows and spacecraft thermal control devices. The strategy of preparing NiO doped by W indicates an innovative direction to obtain ECDs with high performance.

NiO films prepared by e-beam evaporation for Mg2+ based electrochromic devices

Electrochromic devices (ECDs) with reversible change of optical properties applying an external voltage, are the promising candidate for smart windows technology. In order to solve the unsafety of Li+ based electrolytes and the corrosiveness of acids, the Mg2+ has been used as the efficient insertion ion used in ECDs. However, all previous studies are present in cathode EC materials, in order to improve the optical modulation of complementary ECDs, it is relevant to study in anodic EC materials. In this work, the NiO films were deposited by e-beam evaporation and the annealing effect on the structure, morphology and optical properties were studied. For NiO films annealed at RT, the good cyclic stability and lager ΔT were obtained simultaneously. Meanwhile, the ECDs with the unique structure of ITO/WO3/MgCl2 aqueous solution/NiO/ITO were assembled. The devices showed the large optical transmittance modulations (50% at 630 nm) and the fast response (5.3 s for bleaching and 6.4 s for coloring). These findings not only demonstrate NiO films prepared by e-beam evaporation method are suitable to be applied as complementary EC layer, but also provide the broad prospect for the application of Mg2+ based ECDs.

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.