Electrochromic Electrode Research Articles

Improved transparency and charge matching of electrochromic devices with Ce-doped NiO counter electrode

The quest for cost-effective and efficient electrochromic electrodes, featuring high color contrast and rapid response times, has sparked increasing interest in research of metal oxides for electrochromic applications. In this study, nickel oxide thin films with various cerium dopant concentrations are synthesized, with the optimized doping concentration identified as 1 at%. X-ray diffraction analysis confirmed that the dopant successfully reduces crystal size and alters the preferred orientation to (111). The 1 % Ce:NiO thin film exhibits enhanced electrochromic performance, with a transmittance modulation increase of 27.4 % at 633 nm, a 27.1 % rise in coloration efficiency and faster response time (tb=9.64 s and tc=6.76 s) compare to the undoped NiO. Importantly, the charge density of 1 % Ce:NiO thin film increases from 4.86 to 8.14 mC cm−2, representing a 67.5 % improvement, which becomes a better charge matching with WO3 in electrochromic devices. The incorporation of Ce into the NiO thin films not only leads to increased transmittance in the bleached state and optical modulation in the electrochromic devices but also contributes to a rise in the optical band gap of the NiO thin films and improved charge balance matching. These results underscore the positive impact of cerium doping on microstructure and electrochromic performance, indicating a promising future for electrochromic devices.

Dynamic multicolor electrochromic skin in high-brightness flexible WO3/Au asymmetric Fabry–Perot nanocavity fabricated on Nylon 66 porous substrate

Recently, the Fabry–Perot (F–P) cavity electrochromic devices, which are constructed by combining nano-size inorganic electrochromic material WO3 and reflective metal layers, have attracted considerable attention due to their potentials in the fields of dynamic multicolor displays and active camouflage. However, in the few studies that have been reported, the peak reflectance of flexible F–P cavity multicolor electrochromic devices in the visible wavelength band is generally lower than 30 %, which limits their reflective display and camouflage effects in high-brightness environments. Thus, we have combined multicolor reflective electrochromic electrodes in WO3/Au asymmetric F–P nanocavity constructed by magnetron sputtering on a Nylon 66 porous substrate with a highly transparent UV-cured gel electrolyte and a PET plastic sealing procedure. As a result, a flexible and dynamic multicolor electrochromic skin with high reflectance (Rmax＞50 %) and excellent flexibility (bending radius of 4 mm) has been fabricated. The WO3 electrochromic layer at the top works as the dynamic dielectric layer in the broadband absorption Fabry–Perot cavity, and the inert metal Au layer at the bottom works as the reflective layer. The WO3/Au asymmetric F–P cavity can acutely capture the variation in optical constants of WO3 due to the thickness change and electric-driven effects. This cavity facilitates the selective reflection and absorption of the energy distribution of the spectrum after the induced interferometric resonance. As a result, the cavity exhibits a rich array of structural colors, including ocher, taupe, yellow, orange, green, and violet. The electrochromic skin exhibits a fast switching time and maintains 99.43 % of the optical modulation amplitude (ΔR) after 110 coloring/bleaching cycles. It provides a potential option in the field of flexible high-brightness reflective displays and dynamic camouflage in the future.

Comparative Study of Electrochromic Supercapacitor Electrodes Based on PEDOT:PSS/ITO Fabricated via Spray and Electrospray Methods.

PSS stands out as a leading commercial conducting polymer due to its excellent water dispersibility, controllable miscibility, adjustable conductivity, and ability to form films through various techniques. This study investigates the electrochemical and electrochromic performance of electrodes prepared by depositing PEDOT:PSS onto ITO surfaces by using two distinct methods: conventional spray coating and electrospray deposition. Detailed characterization of the prepared electrodes was performed by using atomic force microscopy, scanning electron microscopy, Fourier-transform infrared, and Raman spectroscopy techniques. Our findings reveal that electrodes fabricated via electrospray deposition (PEDOT:PSS/ITO electrode_2) significantly outperform those made by spray coating (PEDOT:PSS/ITO electrode_1). Specifically, electrode_2 exhibits a capacitance of 1678.60 μF cm-2, compared to 826.14 μF cm-2 for electrode_1, at a current density of 10 μA cm-2. PSS electrodes exhibit areal energy densities of 0.41 and 0.84 mW h cm-2, along with power densities of 4.96 and 4.97 μW cm-2, respectively. Moreover, electrode_2 demonstrates a high coloration efficiency of 84.32 cm2 C-1 and fast response times of 1.36 s for coloration and 0.98 s for bleaching. This study highlights the advantages of electrospray deposition over traditional methods, showcasing the potential of electrospray-prepared PEDOT:PSS electrodes for use in multifunctional energy storage devices.

On the enhanced electrochromic performance of nano-structured V2O5 thin films developed by substrate temperature induced orientated Growth

Electrochromic society is keen to develop devices with multicolor displays with high stability, using eco-friendly inorganic materials. In the present research, Influence of substrate temperature on the electrochromic V2O5 active electrodes deposited using automated nebulizer spray pyrolysis was examined to demonstrate V2O5 nanostructured films with good cyclic stability, high color contrast, and a robust memory effect. The structural characterization of the V2O5 thin films was conducted through R-ray diffraction and thermogravimetric analysis to assess material stability. Nanostructure morphology under different conditions was analysed using SEM and TEM. The electrochromic studies revealed that the higher optical modulation (ΔT) was achieved (with 70.8 % at 550 nm) in a very short switching time. Feature studies on V2O5 under different potentials were conducted to understand the capacitive and diffusion effects. The electrochromic response V2O5 thin films to various potentials was analysed using ex-situ XRD, elucidates phase changes from V2O5 to LiVO5 and V4O9, and a 2000-cycle CV measurement comprehended the material stability. The significantly improved electrochromic performance is primarily attributed to the nanosheet structure of the V2O5 thin films, since the structures enhance the material stability during lithium-ion intercalation/deintercalation processes.

All-in-one flexible paper-based self-powered energy and display system employing complementary properties of printed PEDOT:PSS/PANI:PSS dual-electrode with a dual-sided triboelectric nanogenerator

A Self-powered energy and display system (SPEDS) has been developed by integrating functionalities of energy harvesting, storage, and multicolor display, heralding innovative solutions for integrated electronic devices. An all-in-one multi-information SPEDS is proposed through incorporating a multicolor electrochromic supercapacitor device (ESCD) with a dual-sided triboelectric nanogenerator (TENG), all screen-printed on a paper substrate. The synergistic enhancement in the conductive, capacitive, and electrochromic performance is realized by exploiting the complementary properties of PEDOT:PSS/PANI:PSS to form a simplified structure of ESCD, in which the electrode and electrochromic layers are integrated into one shared layer, resulting in a wide color gamut and an enhanced capacitive performance of 3.4 mF/cm². Electrochromic electrodes having identical composition exhibit independent color changes at the anode and cathode, thereby featuring a combined color display indicating multi energy-related information. Moreover, the conductive layer fabricated through patterned printing on the paper substrate, serves as both the electrode layer for TENG and the interconnect circuitry with the prepared ESCD. Furthermore, a double-sided TENG was realized by exploiting the triboelectric properties of the paper substrate and then a self-powered energy display wristband was constructed, exemplifying a novelty application utilizing the multi-information indicator properties for energy display derived from the dual-sided friction power generation.

Recent advances in multifunctional electrochromic devices

AbstractElectrochromic (EC) technology has been regarded as a promising energy‐saving technology in various applications, including smart windows, displays, thermal management, rear views, etc. Benefiting from the progress in electrochromic material synthesis, electrochromic electrode fabrication, and electrochromic device configuration design, the focus in electrochromic community has gradually shifted to multifunctional electrochromic devices (ECDs) in the era of Internet of Things. Multifunctional ECDs, such as electrochromic energy storage devices, multi‐color displays, deformable ECDs, smart windows, etc. have been showcased the ability to expand potential applications. In this review, the available device configurations, performance indexes and advanced characterization techniques for multifunctional ECDs are introduced and classified accordingly. The applications of multifunctional ECDs for energy storage, multicolor displays, deformable devices, self‐chargeable devices, smart windows, actuators, etc., are exemplified. The future development trends and perspectives of multifunctional ECDs are also overlooked. The aim of this review is to guide and inspire further efforts in the exploration of novel and advanced multifunctional ECDs.

Durability enhancement of all-solid-state electrochromic devices by adjusting the charge density ratio between electrochromic and counter electrode layers

Owing to an increase in global warming, smart-window devices based on charge-balanced electrochromic devices (ECDs), which exhibit high potential to increase the thermal efficiency of buildings, have gained prominence. However, studies on the fabrication and cycling stability of charge-balanced ECDs are scarce. In this study, WO3 and NiOx films were deposited on indium–tin–oxide (ITO)-coated glass substrates by reactive direct-current magnetron sputtering, and the deposition time was varied to control the thickness and charge density of the thin films. Subsequently, the NiOx/ITO/glass and WO3/ITO/glass substrates were laminated with a Li-based polymeric electrolyte to fabricate all-solid-state ECDs comprising electrochromic (EC) and counter-electrode (CE) layers in charge-density ratios of 12.6, 6.4, 2.3, and 1.1. Changes in the electrochromic properties, device-layer microstructure, crystal structure, and elemental composition of the as-constructed ECDs before and after degradation were investigated to understand the influence of the charge-density ratio of the EC and CE layers on the long-term durability of ECDs. Increasing the charge-density ratio decreased the cycling stability of the device owing to changes in the microstructure and crystal structure of the NiOx layer in the microstructural deep-trap sites. Among all the ECDs, those comprising EC and CE layers with similar charge densities showed the most stable optical modulation and highest long-term durability. Finally, based on the aforementioned results, a degradation mechanism for charge-imbalanced all-solid-state ECDs was proposed. This study is expected to open new frontiers in designing optimal-performance electrochemical devices with a wide variety of potential applications.

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.

Empowering Zero‐Energy Buildings with Cutting‐Edge Self‐Powered Electrochromic Smart Window Technology

The development of energy‐efficient window technology is crucial for zero‐energy building approaches, as windows play a pivotal role in minimizing heat loss, optimizing natural light utilization, and contributing to overall energy conservation. In this study, a self‐powered electrochromic smart window is presented together and its application as a self‐charging battery is showcased. The self‐powered system is composed of a WOx electrochromic working electrode, an Al counter electrode, and an AlCl3 liquid electrolyte similar to a voltaic cell. This device generates an open circuit voltage of around 0.95 V. When two electrodes are connected, this voltage is applied as an external voltage and changes the color of the transparent WOx electrode into a blue state with approximately 62% transmittance modulation. However, if the two electrodes are connected via an light‐emitting diode (LED), the LED lights up for up to 4 h.

Electrochromic Electrode Based on Polyaniline and Silver Nanowires Based Localized Surface Plasmon Resonance

Electrochromic Electrode Based on Polyaniline and Silver Nanowires Based Localized Surface Plasmon Resonance

Dynamically transflective multicolor modulation via single metal-dielectric inorganic electrochromic electrode

Transflective electrochromic (EC) materials with the ability to dynamically adjust color in both reflection and transmission mode are extremely attractive for tunable filter, smart windows, and ultralow-power displays due to their wide applicability in dark and bright environment and unique tunability of optical properties. However, simultaneously brilliant multicolor modulation of both reflection and transmission in one EC film is challenging. Here, integrated and metal/dielectric structured EC electrode composed of three-layered Cr/Ag/WO3 (CAW) films are demonstrated. Benefiting from the synergistic effect of the good conductivity, strong optical interference, and excellent substrate-film adhesion, these well-designed CAW films successfully demonstrate dynamic variegated modulation of both reflective and transmissive colors. This modulation encompasses a broad spectrum of hues, boasts high saturation, rapid response times, and exhibits impressive cycling stability. The flexible CAW film with superior bending stability is also achieved for the successful construction of the patterned flexible EC device.

Solid-State Supercapacitor Constructed with Organic Electrochromic Electrodes Based on Dithienothiophene and 3,4-Ethylenedioxythiophene

Solid-State Supercapacitor Constructed with Organic Electrochromic Electrodes Based on Dithienothiophene and 3,4-Ethylenedioxythiophene

Enhancing electrochromic supercapacitor electrode performance through different donor compartments in D-A-D type conjugated polymers

Conjugated polymers (CPs), particularly donor-acceptor-donor (D-AD) type polymers, have emerged as promising materials as supercapacitor electrode. In this study, 3-hexylthiophene and ethylenedioxythiophene (EDOT) as donor compartments in D-A-D type CPs, with an indenoquinoxalinone-based acceptor, were investigated for supercapacitor electrode performance. Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and UV–Vis spectroscopy were employed to analyze the chemical structures and optical properties of the monomers, respectively. For surface characterization of the polymers, scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) analysis were used. Electrochromic behaviors were investigated via spectroelectrochemistry and kinetic studies. The electrochemical performance of the polymers was evaluated through cyclic voltammetry, galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The specific capacitance, energy density, and power density of the polymers were compared. Results showed that they were promising electrochromic material for supercapacitor application due to their high specific capacitance. Since EDOT containing polymer exhibited enhanced electrochemical properties, it was used to construct supercapacitor. Besides cyclic voltammetry and GCD characterization of device, the electrochemical cycling performance of it was assessed to evaluate the long-term reliability of the polymer as supercapacitor electrode material. This study provides valuable insights into the role of donor compartments, specifically 3-hexylthiophene and EDOT in D-A-D type CPs. The findings also highlight the potential of the indenoquinoxalinone-based acceptors in electrochromic supercapacitors. The results contribute to the design and development of enhanced supercapacitor materials with improved energy storage capabilities, offering new possibilities for utilizing D-A-D type polymers with indenoquinoxalinone-based acceptors.

Convenient-assembled, open-ended solid-state electrochromic devices enabled by electrolyte glue

Electrochromic (EC) technology has a tremendous development over the past few decades and attracts wide attention due to its promising applications in smart windows, smart displays and wearable electronics. However, strict sealed requirements of EC devices increase the difficulty of manufacturing processing and production cost, limiting their practical application in common life. Moreover, the disassembly and replacement of EC devices are still enormous challenges in practical application. Here, open-ended solid-state EC devices were prepared by directly sticking the EC electrode and counter electrode with photocurable electrolyte glue which did not require additional encapsulation and could be conveniently assembled and replaced by ourselves in common life. The poly(butyl acrylate-co-methoxypolyethylene glycol acrylate) (P(BA-co-mPEGDA))-based solid-state electrolyte formed after UV curing of electrolyte glue exhibited excellent adhesion to electrodes through the construction of intimate contact interface, which improved the ion transport efficiency at the interface and interface stability of EC devices. The Open-ended solid-state EC devices exhibited excellent electrochemical, environmental and mechanical stability, and show promising applications in exchangeable smart windows and designable wearable displays.

Brookite TiO2 Nanorods as Promising Electrochromic and Energy Storage Materials for Smart Windows.

Electrochromic smart windows (ESWs) offer an attractive option for regulating indoor lighting conditions. Electrochromic materials based on ion insertion/desertion mechanisms also present the possibility for energy storage, thereby increasing overall energy efficiency and adding value to the system. However, current electrochromic electrodes suffer from performance degradation, long response time, and low coloration efficiency. This work aims to produce defect-engineered brookite titanium dioxide (TiO2 ) nanorods (NRs) with different lengths and investigate their electrochromic performance as potential energy storage materials. The controllable synthesis of TiO2 NRs with inherent defects, along with smaller impedance and higher carrier concentrations, significantly enhances their electrochromic performance, including improved resistance to degradation, shorter response times, and enhanced coloration efficiency. The electrochromic performance of TiO2 NRs, particularly longer ones, is characterized by fast switching speeds (20 s for coloration and 12 s for bleaching), high coloration efficiency (84.96 cm2 C-1 at a 600 nm wavelength), and good stability, highlighting their potential for advanced electrochromic smart window applications based on Li+ ion intercalation.

Design of Symmetric TiO2/LiI/TiO2 Electrochromic Devices for Gradient Shaded Smart Windows with Enhanced Switching and Cycling Properties

AbstractLi+ insertion and extraction inherently impact the switching dynamics and cycling stability of inorganic electrochromic (EC) electrodes. Herein, the extraction of Li+ out of the TiO2 lattice to release the electron is replaced by the charge recombination of the electron with I3− at the TiO2‐electrolyte interface, which avoids the mechanical breakdown of the electrodes and renders self‐bleaching with no applied voltages. A device design of the same two TiO2 nanocrystal (NC) electrodes combined with the redox lithium salt (LiI) electrolyte confers symmetric electrochromism. By applying a forward or reverse bias, the two TiO2 electrodes alternately serve as the electrochromic electrode and exhibit voltage‐controlled gradient coloration, a maximum optical modulation of 90% at 700 nm, and a doubled cycling performance. The microstructure of the TiO2 NC film is characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and Brunauer–Emmett–Teller methods. The electrochemical and electrochromic properties of the device are investigated using cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy, and Mott–Schottky method.

An efficient multi-color electrochromic electrode based on nanocomposite of aniline and o-toluidine copolymer with nickel oxide

As an electrochromic material, NiO has a distinct color conversion, but its single color variation limits its application. In this study, NiO-based multi-color electrochromic films were prepared by using simple hydrothermal and electrodeposition methods. The composite electrochromic film can achieve a variety of color changes in yellow, green, blue and dark brown. NiO provides the substrate for organic copolymers, bringing large contact areas and ion channels, while the copolymerization and recombination of aniline-o-toluidine copolymers achieve a series of rich color changes. The results show that five color changes from colorless to dark brown can be achieved between −1 and 1.5 V. By controlling the applied voltage and the transition between the redox states of the film, the composite film is yellow at 0.2 V, green at 0.5 V, blue at 0.8 V, and dark brown at 1.5 V. The composite film has unprecedented stability. The improvement of cyclic stability is attributed to the uniform and dense coating of nickel oxide on the surface after being combined with copolymer. This encapsulation form will affect the ions entering the deep layer of NiO, reduce the erosion of NiO, and improve the cycling stability of NiO to a certain extent. This is fully demonstrated by the cyclic stability test. After 1000 cycles, the composite film can still show excellent optical modulation range. This study provides reference for the development of NiO multi-color electrochromic materials.

Long-term stability electrochromic electrodes based on porous tungsten trioxide and nickel oxide films via a facile triple pulse electrodeposition

Herein, a facile triple pulse electrodeposition was used to fabricate porous films such as tungsten trioxide (WO3) and nickel oxide (NiO) on indium tin oxide (ITO) substrates. These porous films outperformed corresponding compact films formed by continuous electrodeposition in terms of long-term stability. The maximum transmittance modulation of P-WO3 and P–NiO films were 57.0% and 52.1%, respectively, and changed insignificantly after 10,000 cycles, whereas C-WO3 and C–NiO films were degraded after 2500 and 1000 cycles, respectively. Not only does the porous morphology increases the electrochemical active surface area, but it also provides an efficient pathway for ion diffusion and charge transfer, resulting in fast kinetics, low resistance, high electro-activity, and excellent ion reversibility. This work will hopefully inspire more researchers to improve electrodeposition film fabrication and promote electrochromic device industrialization.

Power‐Free Contact Lens for Glucose Sensing

AbstractRecent advances in wearable devices have enabled noninvasive monitoring for healthcare applications. Smart contact lenses have gained substantial attention for medical diagnosis through the analysis of vital signs in tear fluids. However, previous studies have mostly focused on designs embedded with electronic devices or antennas for wireless transmission, which are power‐intensive and require external receivers around the ocular system. Here, the study reports a power‐free smart contact lens for noninvasive glucose sensing according to the color changes of multiple electrochromic electrodes to achieve direct data transmission without the external wireless system. The device detects various glucose concentrations, from the ordinary range (0.16–0.5 mm) to abnormally high concentrations (0.9 mm). The multi‐electrode design exhibits acceptable accuracy, with a correlation coefficient r = 0.99543 to the controlled sample and allowed low‐glucose detections with concentrations down to 0.05 mm. The device shows good reproducibility, with standard deviations of determined glucose levels of 0.0462 and 0.025 for four continuous cycles and for an interval of several days, respectively. It is believed that the reported smart contact lens has the potential for daily health monitoring by ordinary users without a power supply and external devices. Its simple electronics‐free structure will allow for immediate application to the market with cost‐effective manufacturing.

Proton and Redox Couple Synergized Strategy for Aqueous Low Voltage-Driven WO3 Electrochromic Devices.

Aqueous electrolytes possess non-combustible and eco-friendly features compared to organic electrolytes, leading them to be more suitable for application in smart windows for daily use. However, limited by the narrow electrochemical window of water (1.23 V), its use in conventional electrochromic devices (ECDs) would result in irreversible performance loss, which arises from decomposition caused by high voltage. Here, we propose a synergistic scheme combining a redox couple-catalytic counter electrode (RC-CCE) strategy with protons as guest ions. With the help of the intelligent matching of the reaction potentials of the RC and amorphous WO3 electrochromic electrodes and the highly active and fast kinetic features of protons, it successfully reduces the working voltage range of the device to 1.1 V. The assembled HClO4-ECD can possess an overall modulation rate (350-1200 nm) of 0.43 and 0.94 at -0.1 and -0.7 V, respectively, and a modulation of 66.8% at 600 nm at -0.7 V. Moreover, compared with other guest ions, the proton-based ECD exhibits higher coloration efficiency, a broader color modulation capability, and better stability. In addition, the house model equipped with the proton-based ECD effectively blocks solar radiation, which provides a potential solution for the design of aqueous smart windows.