Flexible Electrochromic Devices Research Articles

Freely Deformable Electrochromic Fabric Devices Exhibiting Durable Chromatic Switching and All-Around Stability

Electrochromic devices (ECDs) show reversible color changes on applying external voltages by electrochemical redox reactions. Most ECDs are fabricated using ITO-coated electrodes on glass substrates. With a growing interest in wearable devices, many attempts have been made concerning flexible ECDs. Compared to the conventional devices, the ECDs fabricated on the textile substrate feature highly conformal and curvilinear properties similar to inherent textile aspects. In line with the demand, this study presents the freely deformable and highly durable electrochromic fabric devices (ECFDs) prepared by the spray-coating process. The ECFDs are constructed using a layer-by-layer structure on polyester fabric, consisting of electrodes, electrochromic, electrolyte, and protective layers. Conducting electrodes are designed with the mixture of silver nanowire and PEDOT:PSS, and, on top of it, viologen functionalized polyhedral oligomeric silsesquioxane is subsequently stacked. The additional electrolyte layer is placed for surface hardening and ion transporting purposes. The protection is formed in the outer layer, providing remarkable waterproofness and laundry fastness. The prepared ECFDs reveal reversible and repeated electrochromic performances, along with bending and twisting stability, waterproofness, and washing fastness. The current approach demonstrates the feasibility of color-changing textiles for real-life applications.

Preparation of Highly Adhesive Urethane-Acrylate-Based Gel-Polymer Electrolytes and Their Optimization in Flexible Electrochromic Devices

Preparation of Highly Adhesive Urethane-Acrylate-Based Gel-Polymer Electrolytes and Their Optimization in Flexible Electrochromic Devices

Flexible electrochromic devices having remarkable color change from golden to green and their application in smart windows and electronic labels

The ECDs based on viologen derivatives exhibit high optical contrast, fast-response, and rich color changes.

A Light-Weight, Thin-Thickness, Flexible Multifunctional Electrochromic Device Integrated with Variable Optical, Thermal Management and Energy Storage

A Light-Weight, Thin-Thickness, Flexible Multifunctional Electrochromic Device Integrated with Variable Optical, Thermal Management and Energy Storage

Fabrication of flexible electrochromic devices based on silver nanowires transparent electrode

Fabrication of flexible electrochromic devices based on silver nanowires transparent electrode

Optimization of oxide materials in oxide-metal-oxide(OMO) electrodes for flexible electrochromic devices

Optimization of oxide materials in oxide-metal-oxide(OMO) electrodes for flexible electrochromic devices

Preparation and electrochromic properties of flexible transparent WO3/AgNW-decorated nanofiber composite film

It is well-known that tungsten oxide (WO3) is extensively used for electrochromic (EC) devices due to its special properties, such as high coloration/bleaching response time, good coloration efficiency, etc. The preparation of flexible EC devices is highly desirable for various applications. However, the fabrication of flexible EC devices with improved performance is still a major task due to their limited experimental protocols. In this study, we have prepared highly flexible transparent films consisting of WO3 and silver nanowires coated on nanofiber-reinforced composite films (WO3/AgNW-NCF). A novel flexible transparent WO3/AgNW-NCF is used for EC applications. The as-fabricated EC device based on WO3/AgNW-NCF demonstrated good coloration efficiency (161.3 cm2 C−1), excellent stability (81.5%) and rapid response time for coloration (2.9 s) and bleaching (3.2 s). The fabricated transparent flexible EC device may potentially be useful for designing an outstanding EC device for smart window applications.

New practical device structure for graphen-based electrochromic devices

In this study, we fabricate a simple, low-cost, high-efficiency, and easy-to-design electrochromic device. Multilayer graphene (MLG) samples were obtained by chemical vapor deposition method (CVD) at four different growth temperatures of 900 , 950 , 1000 , and 1050 ∘ C . Electrical and optical characterizations of MLG samples were carried out by transferring them to the polyvinyl chloride (PVC) surface by thermal lamination method. After the characterization of the samples the so called coplanar surface is produced in order to obtain an efficient electrochromic device consisting of a flexible graphene surface without an extra electrode Optical measurements show that threshold voltage for the change in the optical modulation is 2.5 V in the near-infrared region and that there exists an increase of 60 % just over 3 V value. Also, in the electrical characterization studies, a decrease of up to approximately 50 % of the layer resistance was seen. • Multilayer graphene thin films were obtained by CVD method. • The device structure consisting of the graphene surface, which we call the coplanar structure, was developed. • A low-cost, easy-to-build, high-efficiency, flexible electrochromic device has been designed”. • Experimental results show that there was an increase of 60% in optical modulation value after the 3 V value and a decrease of up to approximately 50% of the layer resistance.

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.

The effect of sputtering Ar gas pressure on optical and electrical properties of flexible ECD device with WO3 electrode deposited by RF magnetron sputtering on ITO/PET substrate

In this study, the electro-optical properties of a flexible electrochromic device (ECD) with WO3 film were investigated according to the pressure of Ar gas during RF magnetron sputtering process. The ECD was fabricated using WO3 film as the cathode electrode and NiO as the anode electrode. Both electrodes were deposited using RF magnetron sputtering over indium tin oxide coated on polyethylene terephthalate film (PET/ITO). The electrolyte for the ECD used the lithium percolate mixed with poly methyl methacrylate and propylene carbonate to form the gel type electrolyte. The sputtering time was controlled while measuring with a thickness/rate monitor (Sycon STM-100) to have the identical WO3 film thickness at different Ar pressures. Also, argon working gas pressure in sputtering chamber was varied at 5 mTorr, 10 mTorr, and 15mTorr, respectively. The deposition rate of WO3 film was 14 nm/min for Ar gas pressure 5 mTorr then after the pressure was increased until 15 mTorr the deposition rate was 8.6 nm/min. The sputtering process was operated until the thickness of the WO3 film reach 250 nm. In order to investigate electro-optical properties of the ECD, such as coloration efficiency (CE), transmittance of bleached state (Tb), transmittance of coloured state (Tc), optical modulation, bleaching time, and coloration time were analyzed. The ECD with Ar pressure at 5 m Torr for WO3 film shows the coloration efficiency was 57.58 cm2C-1, Tb was 17%, Tc was 5%. Also, the bleaching time was 15 s, and coloration time was 30 s. When the sputtering pressure was increased to 15 mTorr, the ECD showed the better optical properties but the bleaching time and coloration time was rise to 50 s, and 58 s, respectively. The ECD at 15mTorr show the higher optical modulation of 55%.

Self-Powered Flexible Electrochromic Smart Window.

Electrochromic devices have attracted considerable interest for smart windows. However, current development suffers from the requirement of the external power sources and rigid ITO substrate, which not only causes additional energy consumption but also limits their applications in flexible devices. Inspired by galvanic cell, we demonstrate a self-powered flexible electrochromic device by integrating Ag/W18O49 nanowire film with the Al sheet. The Ag nanowire film first acted as the electrode to replace the ITO substrate, then coupled with the Al sheet to induce an open-circuit voltage of ∼0.83 V, which is high enough to drive the coloration of W18O49 nanowires. Remarkably, the flexible self-powered electrochromic device only expends ∼6.8 mg/cm2 of the Al sheet after 450 electrochromic switching cycles and the size can be easily expanded with an area of 20 × 20 cm2, offering significant potential applications for the next generation of flexible electrochromic smart window.

Micropatterned PEDOT with Enhanced Electrochromism and Electrochemical Tunable Diffraction

Micro-nanofabrication of conductive polymers (CPs) with functional structures is in great demand in organic electronic devices, micro-optics, and flex sensors. Here, we report the fabrication of micropatterned poly(3,4-ethylenedioxythiophene) (PEDOT) and its applications on flexible electrochromic devices and tunable diffractive optics. The localized electropolymerization of 3,4-ethylenedioxythiophene at the electrode/agarose gel stamping interface through an electrochemical wet stamping (E-WETS) technique is used to fabricate PEDOT with functional microstructures. PEDOT microdots, micro-rectangles, and interdigitated array microelectrodes are fabricated with submicron tolerance and ∼2 μm smallest feature size. Furthermore, the flexible PEDOT electrochromic devices consisting of the logo of Xiamen University are fabricated with a reversible switch of absorptivity. The improved optical and coloration-amperometric responses of electrochromism are demonstrated because of the enhanced charge transport rate of the micropatterned PEDOT. The electrochromism of the 2D PEDOT micropatterns is further used as a binary diffractive optical element to modulate the intensity and efficiency of diffracted 2D structural light because of the switchable absorptivity during doping and dedoping processes. When the potential is switched from 1 to -1 V to tune the absorptivity at ∼600 nm from low to high, the intensity of zero-order diffraction light spot decreases with the intensity of other order diffraction light spots increasing dramatically. The results demonstrate that E-WETS provides an alternative method for the fabrication of CPs with functional micro-nanostructures. The electrochemical tunable diffraction with high reversibility and fast response is of potential applications in micro-optics and flex sensors.

Dynamically Cross-Linked Hydrogel Electrolyte with Remarkable Stretchability and Self-Healing Capability for Flexible Electrochromic Devices.

It is desired to develop self-healing gel electrolytes for flexible electrochromic devices (ECDs) due to the demand of healing damages caused during operations. We here report a hydrogel electrolyte with remarkable self-healing capability, excellent stretchability, and ionic conductivity. The hydrogel electrolyte was synthesized via one-step copolymerization of glycerol monomethacrylate (GMA) and acrylamide (AAm) in the presence of borate. Within the hydrogel electrolyte, dynamic cross-linking is expected to be formed due to the borate-didiol complexation and hydrogen-bonding interactions. As a result, the hydrogel electrolyte demonstrates an excellent self-healing efficiency of up to 97%, a fracture strain of 1155%, a fracture toughness of 136.6 kJ m-3, and a fracture stress of 13.0 kPa. Additionally, a flexible ECD based on the hydrogel electrolyte and an electrochromic layer of poly(3,4-(2,2-dimethyl-propylenedioxy)thiophene) (PProDOT-Me2) was assembled and evaluated. The device is found to be stable in both mechanical and optical properties over 1000 operation cycles. This study may provide a promising way for self-healing electrolyte gels to be utilized in a variety of flexible electrochemical devices, including ECDs, supercapacitors, and batteries.

Development of Pore-filled Polymer Electrolyte Membranes for Flexible Electrochromic Devices

Development of Pore-filled Polymer Electrolyte Membranes for Flexible Electrochromic Devices

Use of Different Metal Oxide Coatings in Stainless Steel Based ECDs for Smart Textiles

Electrochromism is the ability of a material to selectively change its coloration under the influence of an external electric current/potential and maintain it even after the power source has been disconnected. Devices that use such a mechanism are known as electrochromic devices (ECDs). Over the years, significant effort has been invested into the development of flexible ECDs. Such electrochromic tapes or fibers can be used as smart textiles. Recently, we utilized a novel geometrical approach in assembling electrochromic tapes which does not require the use of optically transparent electrodes. The so-called inverted sandwich ECD configuration can employ various color-changing mechanisms, e.g., intercalation, redox reactions of electrolytes or reactions on electrode surfaces. One of the most frequently used electrochromic metal oxides is WO3. However, other metal oxides with different coloration responses also exist. In this paper, we explore the use of V2O5 and TiO2 in metal-tape-based ECDs in the inverted sandwich configuration and compare their performance with WO3-based devices. Morphological features of metal oxide thin layers were investigated with scanning electron microscopy (SEM), and the performance of the tapes was investigated electrochemically and spectroscopically. We demonstrate that well-established preparation techniques (e.g., sol–gel synthesis) along with coating approaches (e.g., dipping) are adequate to prepare optically nontransparent fiber electrodes. Depending on the metal oxide, flexible electrochromic fiber devices exhibiting different coloration patterns can be assembled. Devices with TiO2 showed little coloration response, while much better performance was achieved in the case of V2O5 and WO3 ECDs.

Enhanced adhesion of Ag nanowire based transparent conducting electrodes for application in flexible electrochromic devices

Silver nanowires (Ag NWs) are currently the most likely to replace indium tin oxide (ITO) as flexible transparent conducting electrodes (FTCEs), but conventional preparation methods such as solution deposition will lead to weak conductivity and low adhesion to the substrate. In this work, polymethyl methacrylate (PMMA) as a superior mediate for the pressure embedding of Ag NW networks as transparent electrodes with 120 °C is demonstrated. The sheet resistance of the PMMA/Ag NWs FTCEs decreases from 32 Ω/sq. to 8.1 Ω/sq. at an optical transmittance of ~77.5 %. The calculated value of figures of merit ( FoM )is as high as 9.77 × 10 −3 Ω −1 . At the same time, after 10 min of ultrasonication and 30 times of wiping cycle, the sheet resistance is almost unchanged, indicating that the Ag NW networks have good adhesion to the flexible substrate. Meanwhile, the PMMA/Ag NWs FTCEs exhibit good mechanical flexibility with a bending radius up to 0.75 mm. Finally, the successful implementation of the PMMA/Ag NWs FTCEs into a flexible electrochromic device is demonstrated, verifying the applicability of PMMA/Ag NWs FTCEs. • High-reliable PMMA/AgNW FTCEs are obtained by hot lamination process. • PMMA/AgNW FTCEs show simultaneously improved conductivity and adhesion. • Resistance does not show significant change after ultrasonication and wiping test. • Flexible electrochromic device based on FTCEs is prepared and demonstrated.

Mass-producible slit coating for large-area electrochromic devices

The recent trend of some countries opting to ban the sale of new gasoline and diesel vehicles has led to an increase in the use of electric vehicles and automated driving. In an automobile, windows are the largest source of heat energy between the interior and exterior of the vehicle. By modulating the window material, we can precisely control the amount of heat from sunlight that is allowed to enter the car, reduce the load on heating and cooling. Thus, suppress the energy loss associated with air conditioning by introducing technology to control heat energy in windows, which can also help reduce electricity costs. To this end, our research group has been developing complementary electrochromic devices (ECDs) using Prussian blue and tungsten oxide, which consist of nanoparticles dispersed in aqueous solvents to make inks. Spin coating is used for film deposition at the laboratory level; however, it has a major limitation in terms of uniformity. Therefore, in this study, we fabricated functional thin films by using these inks with slit coating, which is a commercial process. The results obtained confirm that slit coating can be used to deposit approximately 1-μm-thick films as fast as within 20 s and even on large G2 size substrates; further, the uniformity of the films measured based on chromaticity and haze is high. In addition, this effect improves the response time of the ECD. As a future direction, this can be applied to flexible ECD, etc.

Novel dithienoazaborine viologen derivatives with two different π-conjugated extensions for electrochromic application

Two kinds of dithienoazaborine viologen derivatives (3a and 3b) with different π-conjugated extensions were synthesized via late-stage functionalization of dithienoazaborine precursor (BNDT). In sharp contrast to 3a (conjugation I), 3b (conjugation II) showed red-shifted absorption (∼468 nm), narrower optical bandgap (2.65 eV), and aggregation-induced emission (AIE) property. Meanwhile, 3b-based electrochromic device (ECD) showed longer switching times (21.6 s for coloration and 34.9 s for bleaching), higher color contrast ratios (21.3%), higher coloration efficiency (13.29 cm2/C), as well as better stability compared with 3a-based ECD. In addition, an electronic information (E-information) tag and a flexible ECD were assembled using 3b, further manifesting its potential applications in display areas. The research not only expands the structural types of viologen derivatives but also compares the effects of different conjugation on the properties of viologen derivatives for the first time, which may provide a feasible way to design new electrochromic materials.

Multifunctional polyimides containing triarylamine for electrochromic flexible device, photodetector and resistance memory device

Integrating different functions in one material will decrease the volume, responding time, and price of device. Polyimides (PIs) are the optimal candidates because of excellent flexible mechanics, thermal stability, and transparent properties. In this work, a series of multifunctional flexible PIs were designed and synthesized from a novel functional triarylamine for electrochromic (EC) device. The PIs show promising application in EC with the efficiency of 205 cm2 C−1, memory devices with the ON/OFF ratio of 3.7 × 104, and photodetectors with a limit being of 0.07 V. Furthermore, the flexible EC device of PI-3 (short for PI 3 made of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride) keeps excellent stability, and the optical contrast does not decrease even after 2000 cycles.

Low-Temperature Deposition of Transparent Conducting Films Applied to Flexible Electrochromic Devices.

Here, we compare two different transparent conducting oxides (TCOs), namely indium tin oxide (ITO) and indium zinc tin oxide (IZTO), fabricated as transparent conducting films using processes that require different temperatures. ITO and IZTO films were prepared at 230 °C and at room temperature, respectively, on glass and polyethylene terephthalate (PET) substrates using reactive magnetron sputtering. Electrochromic WO3 films deposited on ITO-based and IZTO-based ECDs using vacuum cathodic arc plasma (CAP) were investigated. IZTO-based ECDs have higher optical transmittance modulation, ΔT = 63% [from Tbleaching (90.01%) to Tcoloration (28.51%)], than ITO-based ECDs, ΔT = 59%. ECDs consisted of a working electrochromic electrode (WO3/IZTO/PET) and a counter-electrode (Pt mesh) in a 0.2 M LiClO4/perchlorate (LiClO4/PC) liquid electrolyte solution with an active area of 3 cm × 4 cm a calculated bleaching time tc of 21.01 s and a coloration time tb of 4.7 s with varying potential from −1.3 V (coloration potential, Vc) to 0.3 V (bleaching potential, Vb).