Multicolor Electrochromic Device Research Articles

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.

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.

Performance Optimization for Multicolor Electrochromic Devices: Morphology and Composition Regulation of Inorganic Electrochromic Materials and Selectivity of Ions

AbstractIn recent years, multicolor electrochromic devices (ECDs) have attracted much attention due to their application potential for rich color similar to RGB mode. Although organic electrochromic (EC) materials are widely used in multicolor electrochromism because of their multicolor properties, remarkable weatherability remains challenging. Inorganic EC materials especially transition metal oxide are particularly attractive for excellent weatherability in ECD fabrication. Moreover, by selection of electrolytes, better ionic transfer efficiency can be rendered in the EC process. Although the morphology regulation of the EC film and the selection of electrolytes in the ion transmission layer play important roles in optimizing EC performance and have been extensively studied, a systematic and comprehensive review is lacking. In this review, the morphology regulation of the EC film and selection rules of electrolytes in the multicolor ECDs is focused, and the advantages and disadvantages of existing ways are discussed. The current application of multicolor ECDs is also outlined and it is hoped that this review can contribute some inspiration to designing and improving multicolor ECDs.

Recent progress in transmissive and reflective electrochromic devices for multi-color modulation

Multi-color electrochromic devices (M-ECDs), which dynamically and reversibly regulate the visible optical properties of the objects, have received significant interest in various fields such as displays, flexible intelligent electronics, smart windows and military camouflage. This review provides comprehensive summaries of the latest advances in inorganic electrochromic materials and M-ECDs. We discuss the basic principles for achieving M-ECDs, from the intrinsic multicolor characteristics of materials to a combination with optical structures. The progress on the construction of multicolor electrochromic thin-films and associated devices are unfolded in detail based on their transmissive or reflective working scenarios. Moreover, the limitations and challenges are also outlined for consideration for the future development of M-ECDs.

Multi-pattern polyaniline electrochromic device by controllable three-dimensional movement of ions

Multi-mode and multi-color electrochromic devices (ECDs) have enormous potential for a wide range of applications. However, achieving diverse electrochromic modulation often requires the compounding of different electrochromic materials and the design of complex device structures, which poses a significant challenge. Herein, we propose a novel pre-nucleation electrodeposition method to fabricate polyaniline (PANI) films with high homogeneity and adhesion, and demonstrate a multi-pattern polyaniline electrochromic device by controllable three-dimensional movement of ions for the first time. The resulting PANI films exhibit good cycling stability, retaining approximately 89 % of the active charge after 100 cycles. By combining voltage and current drive modes, the ECDs are able to achieve different optical states in different regions. This dual-mode control strategy results in the highest optical contrast of 44.3 % between different regions of the ECDs, fast switching times (bleaching time and coloring time are 11.06 s and 12.42 s, respectively), and excellent cycle stability (93 % of the maximum transmittance modulation is maintained after 150 cycles). Our discovery provides a new approach to achieve multi-pattern electrochromism using a single electrochromic layer. It has potential applications in multifunctional smart windows and multi-mode color displays.

Facile, low-cost and scalable preparation of V2O5/PEDOT:PSS inks for solution-processed multicolor electrochromic films

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) is extensively used as a commercial ink for electrochromic coatings. However, PEDOT:PSS film has the defect of a single color change, which limits the wide range of applications. The development of hybrid electrochromic inks containing PEDOT:PSS has attracted considerable attention attributed to their high electrical conductivity, large optical modulation, excellent cycling stability and multicolor variation. In this work, the color range of electrochromic PEDOT:PSS ink was adjusted by a simple and low-cost solution blending process method. The solution-processable multicolor vanadium pentoxide (V2O5) nanoribbons synthesized by a facile solution treatment process were used as additives to enlarge the color range of PEDOT:PSS ink. The electrochromic performance of V2O5-PEDOT:PSS hybrid films with V2O5 nanoribbon inclusions ranging from 0 wt% to 100 wt% was systematically studied. Our results demonstrate that the V2O5/PEDOT:PSS hybrid film can combine the color range of mixing inorganic and organic electrochromic materials. The spray-coated hybrid film with 40 % V2O5 nanoribbon (40VPE) shows a reversible multicolor change ranging from navy blue, yellow-green, orange, grey to blue. Moreover, the 40VPE hybrid film also exhibits high optical contrast (50.2 % at 660 nm), rapid response speed (2.7/3.8 s) and excellent cycling stability (sustaining 97 % of initial contrast after 100 cycles). The solution-processable and large-scale V2O5-PEDOT:PSS hybrid inks exhibit promising applications in multicolor electrochromic devices.

Employing polyaniline/viologen complementarity to enhance coloration and charge dissipation in multicolor electrochromic display with wide modulation range

Multicolor electrochromic devices have gained attention widely. To support the development of multicolor electrochromic devices, we studied complementary combinations of a multicolor switchable polyaniline (PANI) electrode and 1-methyl-4,4′-bipyridyl iodide (MBI). In particular, MBI acting as an electrolyte and cathodic electrochromic layer can not only simplify the architecture of a device, but also support the color richness of the device simultaneously. Wide band optical modulation in visible light (58.1% at 550 nm) and near-infrared light (35% at 800 nm) confirms the advantageous optical properties of the combination, possessing a wide color gamut range over a range of working voltages adjustable for red, yellow, green, blue, and purple, each having a high color contrast of up to 73.8. This is accompanied by the excellent electrochemical performances of the mentioned combination, such as a fast response time of 1 s/1.9 s (modulating 77%-colored/bleached) with good cycle stability, and high coloration efficiency of 140.63 cm2/C. In addition, utilizing a screen-printed polyvinyl alcohol (PVA) as a masking barrier layer, it is possible to display patterned anti-counterfeit information within the application. Given these electrochromic performance properties, it is considered a readily feasible strategy to utilize PANI and MBI combination to develop novel electrochromic devices, which can be used widely in the areas of smart packaging, smart labels, and flexible smart windows associated with specific application scenarios.

Resonant-Cavity-Enhanced Electrochromic Materials and Devices.

With rapid advances in optoelectronics, electrochromic materials and devices have received tremendous attentions from both industry and academia for their strong potentials in wearable and portable electronics, displays/billboards, adaptive camouflage, tunable optics, and intelligent devices, etc. However, conventional electrochromic materials and devices typically present some serious limitations such as undesirable dull colors, and long switching time, hindering their deeper development. Optical resonators have been proven to be the most powerful platform for providing strong optical confinement and controllable lightmatter interactions. They generate locally enhanced electromagnetic near-fields that can convert small refractive index changes in electrochromic materials into high-contrast color variations, enabling multicolor or even panchromatic tuning of electrochromic materials. Here, resonant-cavity-enhanced electrochromic materials and devices, an advanced and emerging trend in electrochromics, are reviewed. In this review, w e will focus on the progress in multicolor electrochromic materials and devices based on different types of optical resonators and their advanced and emerging applications, including multichromatic displays, adaptive visible camouflage, visualized energy storage, and applications of multispectral tunability. Among these topics, principles of optical resonators, related materials/devices and multicolor electrochromic properties are comprehensively discussed and summarized. Finally, the challenges and prospects for resonant-cavity-enhanced electrochromic materials and devices are presented.

Fabry-Perot cavity tunable multicolor flexible electrochromic device based on porous filter membrane

In recent years, Fabry-Perot (F-P) cavity-type electrochromic devices composed of more stable inorganic materials have been extensively investigated for achieving colorful reflective displays and military camouflage functions. However, the majority of reported substrates for colorful F-P cavity electrochromic devices are rigid conductive glasses, which hinders their practical application in flexible reflective displays and camouflage. Herein, we construct a WO3/W/Au bilayer F-P cavity multicolor tunable electrochromic device based on a flexible porous filter membrane, in which WO3, an inorganic electrochromic material, is used as the electrochromic layer, metallic W as the partial reflective layer, and metallic Au as the total reflective and conductive layer. Highly flexible bilayer F-P cavity multicolor electrochromic devices have been prepared by combining UV-curable electrolytes and thermoplastic sealing procedures. By adjusting the thickness of the WO3 layer, a wide spectrum of colors including yellow, purplish red, violet, blue, green, olivine, peach, etc. can be obtained. In addition, by adjusting the driving voltage of the electrochromic device, more precise color adjustment can be achieved. The electrochromic device has a fast coloring (2.06 s) and bleaching (2.70 s) response time, providing a new solution for future flexible colorful reflective display devices.

Complementary multicolor electrochromic devices with excellent stability based on porous tin oxide nanosheet scaffold

Complementary multicolor electrochromic devices with excellent stability based on porous tin oxide nanosheet scaffold

Triarylamine-based polyamide containing adamantane group as Fe3+ probe and electrochromic smart devices

A new triarylamine-based polyamide was synthesized from 1,4-cyclohexanedicarboxylic acid and diamine monomer containing adamantane group (PA-CA), which exhibits high fluorescence quantum up to 46.1% and excellent electrochromic behaviors. The photoluminescence of PA-CA was quenched by coordination and internal filtration effect to realize Fe3+ response. Neutral colorless PA-CA film was converted to the oxidized blue in the electrochemical oxidation process and the maximum transmittance reached 80%, and the transmittance still exceeded 55% after 10,000 s. A Sandwich structure electrochromic device with PA-CA as the active layer was constructed with a simple strategy and different contents were displayed through patterned customization. Electrofluorochromic performance was regulated and decoding information was customized by applying voltage changes of the light and dark for PA-CA film. The applications of multifunctional integrated PA-CA responding to stimulus have broad prospects in the field of Fe3+ fluorescence sensors, photodetectors and multicolor electrochromic display devices.

A stretchable patch of multi-color electrochromic devices for driving integrated sensors and displaying bio-signals

We report a stretchable patch of multi-color electrochromic devices (ECDs) for powering integrated bio-sensors and visually displaying bio-signals. The fabricated ECD consists of a polyaniline cathode and an In-coated Zn anode, on transparent electrodes of Ti/Au grid, sandwiching poly(vinyl alcohol)/zinc chloride gel electrolyte in between. The ECD exhibits five colors, gray, light green, green, teal blue, and blue, depending on the applied bias voltage and shows a capacity of 64.1 mAh/m2 with a driving voltage window of 1.3 V at a current density of 0.01 mA/cm2.The ECDs, a temperature sensor, and a strain sensor are integrated on a stretchable elastomer film of Ecoflex/PDMS using patterned liquid metal galinstan interconnections, to form a skin-attachable patch device. Within this patch, the strain sensor is powered by the ECDs to detect the bending of wrist and the measured strains are displayed as different colors with the aid of an Arduino micro-controller. Simultaneously, the change in skin temperature and the extent of wrist bending are displayed as the changes in color of the corresponding ECD.This study clearly demonstrates that our flexible ECD can be used as both an integrated energy storage device and a display device, applicable to a wide range of wearable electronic systems.

Flexible Inorganic All-Solid-State Electrochromic Devices toward Visual Energy Storage and Two-Dimensional Color Tunability

Multicolor display has gradually become a sought-after trend for electrochromic devices due to its broadened application scope. Meanwhile, the advantages of inorganic electrochromic devices such as stable electrochemical performance and good energy storage ability also have great attraction in practical production applications. However, there are still huge challenges for inorganic electrochromic materials to achieve multicolor transformation due to their single-color hue change. Herein, we design an inorganic and multicolor electrochromic energy storage device (MEESD) exhibiting flexibility and all-solid-state merits. Prussian blue (PB) and MnO2, as the asymmetrical electrodes of this MEESD, show good pseudocapacitance property, matching charge capacity, and obvious color change. As a typical electrochromic device, the MEESD shows a fast response of 0.5 s and good coloration efficiency of 144.2 cm2/C. As an energy storage device, the MEESD presents excellent rate capability and volumetric energy/power density (84.2 mWh cm-3/23.3 W cm-3). Its energy level can be visually monitored by color contrast and optical modulation. In the charging/discharging process, its color can obviously change to various degrees of yellow, green, and blue along with 40% wide optical modulation at 710 nm. Meanwhile, the stability of the MEESD in a common and humidity environment was analyzed in detail from electrochemical, optical, and energy storage aspects. This work provides feasible thoughts to design multifunctional electrochromic devices integrated with inorganic, flexible, all-solid-state, multicolor, and energy storage properties.

Colloidal synthesis tantalum oxide nanowires as the minimally color-changing counter electrode for multicolor electrochromic devices

Colloidal synthesis tantalum oxide nanowires as the minimally color-changing counter electrode for multicolor electrochromic devices

Advances in multicolor electrochromic devices based on inorganic materials

This review article focuses on the latest research progress in the construction of multicolor EC devices based on the intrinsic chemical and structural colors of inorganic materials.

Self-Powered Flexible Multicolor Electrochromic Devices for Information Displays.

The development of self-powered flexible multicolor electrochromic (EC) systems that could switch different color without an external power supply has remained extremely challenging. Here, a new trilayer film structure for achieving self-powered flexible multicolor EC displays based on self-charging/discharging mechanism is proposed, which is simply assembled by sandwiching an ionic gel film between 2 cathodic nickel hexacyanoferrate (NiHCF) and Prussian blue (PB) nanoparticle films on indium tin oxide substrates. The display exhibits independent self-powered color switching of NiHCF and PB films with fast responsive time and high reversibility by selectively connecting the Al wire as anodes with the 2 EC films. Multicolor switching is thus achieved through a color overlay effect by superimposing the 2 EC films, including green, blue, yellow, and colorless. The bleaching/coloration process of the displays is driven by the discharging/self-charging mechanism for NiHCF and PB films, respectively, ensuring the self-powered color switching of the displays reversibly without an external power supply. It is further demonstrated that patterns can be easily created in the self-powered EC displays by the spray-coating method, allowing multicolor changing to convey specific information. Moreover, a self-powered ionic writing board is demonstrated based on the self-powered EC displays that can be repeatedly written freehand without the need of an external power source. We believe that the design concept may provide new insights into the development of self-powered flexible multicolor EC displays with self-recovered energy for widespread applications.

Color Palette Tactic for Multicolor Electrochromics Enabled by Electrolyte Thermochromic Engineering

AbstractElectrochromism is a reversible color change triggered by the external electrical field, which can be utilized in smart windows, displays, etc. The ability to display multiple colors in a single electrochromic device is highly beneficial for the versatile applications of the electrochromic technique. Yet, achieving the ability to adopt multiple colors in one electrochromic device has proven to be a challenging task by merely using the conventional chemical structure engineering of the electrochromic materials. In this study, a thermochromic electrolyte is introduced. A multicolor electrochromic prototype device is produced by integrating the thermochromic engineered electrolyte together with electrochromic material in which both can independently contribute to the coloring of the device. This “color palette” strategy gives an additional degree of freedom and extensive flexibility to the design of multicolor electrochromic devices. It introduces a new pathway for producing multicolor electrochromic devices and removes a bottleneck imposed by conventional strategies merely depending on the electrochromic material structure engineering. Moreover, it inspires further development of electrolytes, that share the responsibility of tuning the optical properties of electrochromic devices together with the electrochromic materials, thereby accelerating and diversifying the applications of electrochromics in industry.

Multicolor electrochromic device based on reversible metal electrodeposition of Bi-Cu with controlled morphology and composition ratio

Reversible metal electrodeposition (RME) devices with optical tunability in multiple optical states are exciting alternatives to conventional electrochromic (EC) smart windows. In this work, we studied Bi-Cu electrodeposition carefully by applying the step-potential method and constant-potential method. Five optical states—transparent, purple transparent, purple mirror, yellow transparent and yellow mirror—are achieved, which is firstly reported in Bi-Cu RME devices. The acquisition of polychromatic states could be attributed mainly to the localized surface plasmon resonance (LSPR) effect, which is related to morphologies and composition ratios of the electrodeposited bimetal films. Our device exhibits excellent cycling stability switched between purple transparent state and transparent state, maintaining 80% transmittance window after 2500 cycles. The yellow mirror state generated by the step-potential method shows superior color retention stability and heat blocking ability than the purple mirror state generated by the constant-potential method, meaning that the more uniform and denser metal film deposited by the step-potential method is more suitable to the EC applications. In brief, Our RME device exhibits multiple optical states, competitive switching speeds, superior cycling stability, color retention stability and heat blocking ability, making it promising for use in light modulating devices, such as smart windows and information displays.

Interfacial Charge Transfer and Zinc Ion Intercalation and Deintercalation Dynamics in Flexible Multicolor Electrochromic Energy Storage Devices

Bifunctional electrochromic devices integrating electrochromism and energy storage have attracted extensive attention in recent years. Here, zinc-ion-intercalation-based multicolor electrochromic energy storage devices (EESDs) based on a free-standing Zn2+-based polymeric electrolyte membrane (ZPEM) and a nanocrystal-in-glass V2O5 thin film were constructed. Evolution of the interlayer spacing, V–O-related bonds, and chemical compositions of the V2O5 thin films with zinc ion intercalation and deintercalation is elaborated in a liquid Zn(CF3SO3)2-propylene carbonate (PC) electrolyte. Impressively, highly reversible multi-electrochromism among greenish-blue, yellowish-green, greenish-yellow, faint-yellow, yellowish-orange, and reddish-orange colors is observed in both flexible V2O5 thin films and flexible ZPEM/V2O5/indium tin oxide (ITO) EESDs, which enjoy the benefits from the free channel originating from the large interlayer spacing, the buffering effect of the amorphous phase in the host nanocrystal-in-glass V2O5 matrix, the robust electrostatic interactions between the host V2O5 and guest Zn2+, and Faradaic redox reactions at the Zn2+/V2O5 active interface. The flexible multicolor EESD based on zinc ion intercalation and deintercalation exhibits remarkable electrochromic and energy storage performance with a high transmittance modulation of 57.88%, an excellent coloration efficiency of 36.91 cm2 C–1, a superior specific capacitance of 51 μF cm–2, an enhanced rate capacity, and a pseudocapacitive feature, making it a promising candidate for cost-efficient, environmentally friendly, and bifunctional electrochromic devices.

Manipulating Nanowire Assemblies toward Multicolor Transparent Electrochromic Device.

Assembling various nanowires together, enabling the assemblies with tailored optical, electrical, and multifunctional properties, represents a promising technology for next generation multifunctional electronics. Here we demonstrate a novel multicolor electrochromic device by coassembling W18O49 and V2O5 nanowires using solution-based Langmuir-Blodgett technique. The transparent W18O49 nanowire film became orange with the increasing addition of V2O5 nanowires and the film underwent a dynamic color change (orange, green, and gray) on application of different electrochemical biases of 2, 0, and -0.5 V (vs Ag/AgCl). Both the transmittance and color of the device can be easily controlled by manipulating the layers of coassembled nanowires and the ratios between the two nanowires. On the basis of this approach, different patterns can be easily fabricated with the addition of corresponding masks, and the solid electrochromic device is assembled, suggesting its significant potentials in smart windows and multicolor electrochromic displays.