Inorganic all-solid-state electrochromic devices with reversible color change between yellow-green and emerald green

A Soluble ProDOT-Based Polymer and Its Electrochromic Device with Yellow-to-Green Color Switching Towards Camouflage Application

Yellow-to-green electrochromic color switching plays a key role in the intelligent adaptive camouflage under the visible light environment in future military camouflage applications. Here, we designed and synthesized a soluble electrochromic conjugated pDPTD polymer, mainly based on perylo[1,12-bcd]thiophene and the novel ProDOT groups. The pDPTD polymer displayed a yellow-to-green electrochromism with large optical contrast and fast switching times. Based on the pDPTD polymer film, a yellow-to-green electrochromic device was achieved, showing an orange-yellow color at -0.4 V with L*a*b* color coordinates of 88.5, 18.5, and 34.2 and a pale green color at 0.7 V with L*a*b* color coordinates of 85.6, -4.8, and 11.5, together with a large optical contrast of 43.5% and fast switching times of 2.4/3.2 s. These results indicated that the pDPTD polymer could serve as a potential electrochromic material for yellow/green system camouflage applications.

Optical-Cavity-Incorporated Colorful All-Solid-State Electrochromic Devices for Dual Anti-Counterfeiting

The fusion of electrochromic technology with optical resonant cavities presents an intriguing innovation in the electrochromic field. However, this fusion is mainly achieved in liquid electrolyte-based or sol-gel electrolyte-based electrochromic devices, but not in all-solid-state electrochromic devices, which have broader industrial applications. Here, a new all-solid-state electrochromic device is demonstrated with a metal-dielectric-metal (MDM) resonant cavity, which can achieve strong thin-film interference effects through resonance, enabling the device to achieve unique structural colors that have rarely appeared in reported all-solid-state electrochromic devices, such as yellow green, purple, and light red. The color gamut of the device can be further expanded due to the adjustable optical constants of the electrochromic layer. What is more, this device exhibits remarkable cycling stability (maintaining 84% modulation capability after 7200 cycles), rapid switching time (coloration in 2.6 s and bleaching in 2.8 s), and excellent optical memory effect (only increasing by 13.8% after almost 36 000 s). In addition, this exquisite structural design has dual-responsive anti-counterfeiting effects based on voltage and angle, further demonstrating the powerful color modulation capability of this device.

Amorphous bismuth and GO co-doped WO3 electrochromic film with fast-switching time and long-term stability

The sol-gel process for fabricating electrochromic thin films is straightforward, offering advantages such as low cost and ease of compositional control. Herein we prepared GO-Bi-WO3 films with improved electrochromic performance using a simple sol-gel spin-coating method. The sample shows a fast-switching time (1.8 s for coloring and 1.8 s for bleaching), large optical modulation (85% at 630 nm), excellent stability (86.4% retention after 10 200 cycles), and high coloration efficiency (65.9 cm2 C-1). This work indicates the electrochromic performance of WO3-based films can be enhanced by incorporating GO, which provides an effective strategy for the rapid, safe, and efficient fabrication of electrochromic thin films.

New electric field responsive photonic crystals with remarkable yellow-to-green switch for adaptive camouflage

Electric field responsive photonic crystals take on critical significance in developing adaptive camouflage technology, which are promising materials for adaptive camouflage devices with better fabrication processes and color saturation. However, electric field responsive photonic crystals are primarily susceptible to poor fusion with typical background colors and necessitate the continuous implementation of electric fields to attain specific colors, thus limiting their practical applications. Monodisperse polyvinylpyrrolidone modified cadmium sulfide (PVP/CdS) microspheres with large refractive index are well prepared in this study. Liquid photonic crystals, exhibiting earth-yellow and light green under specific electric field, are obtained with PVP/CdS particles dispersed in propylene carbonate in accordance with the subtractive color mixing principle of structural color and initial color. The resulting electric field responsive photonic crystals are characterized by a simple preparation process, fast electrical response, long-time holding of the earth-yellow state, and reversible color changes between earth-yellow and light green in -3.5 V and + 3.5 V electric field switching. This study can contribute to the development of color-changing devices designed for adaptive camouflage applications.

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.

Reflective Structural Color Tunability of Inorganic Electrochromic Devices by Interferometric Modulation

In the multicolor regulation of visible-light band, the inorganic electrochromic multicolor modulation has always been the bottleneck of expanding the application of inorganic electrochromic reflection display. An electrochromic device (ECD) based on an ultracompact unsymmetric Fabry–Perot resonator was designed. Electrochromic oxides such as tungsten oxide, offer the possibility to tune their refractive index and extinction coefficient upon ion insertion, allowing active control over resonance conditions for Fabry–Perot cavity-type devices. The spectrum colors of red, yellow, green and blue can be obtained by adjusting the thickness of tungsten oxide in the W/(WO[Formula: see text]H2O) electrode. The optical constants of tungsten oxide can be adjusted reversibly by using electrochemical ion insertion/stripping, and the reflection peak of W/(WO[Formula: see text]H2O) electrode in the visible-light band can be adjusted. The dynamic color control of the ECDs can be achieved finely.

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.

Nd-Nb Co-doped SnO2/α-WO3 Electrochromic Materials: Enhanced Stability and Switching Properties

The fabrication of Nd-Nb co-doped SnO2/α-WO3 electrochromic (EC) materials for smart window applications is presented in the present paper. Nb is a good dopant candidate for ECs owing to its ability to introduce active sites on the surface of α-WO3 without causing much lattice strain due to the similar ionic radius of Nb5+ and W6+. These active sites introduce more channels for charge insertion or removal during redox reactions, improving the overall EC performance. However, Nb suffers from prolonged utilization due to the Li+ ions trapped within the ECs. By coupling Nd with Nb, the co-dopants would transfer their excess electrons to SnO2, improving the electronic conductivity and easing the insertion and extraction of Li+ cations from the ECs. The enhanced Nd-Nb co-doped SnO2/α-WO3 exhibited excellent visible light transmission (90% transmittance), high near-infrared (NIR) contrast (60% NIR modulation), rapid switching time (∼1 s), and excellent stability (>65% of NIR modulation was retained after repeated electrochemical cycles). The mechanism of enhanced EC performance was also investigated. The novel combination of Nd-Nb co-doped SnO2/α-WO3 presented in this work demonstrates an excellent candidate material for smart window applications to be used in green buildings.

Liquid/Liquid Interfacial Suzuki Polymerization Prepared Novel Triphenylamine-Based Conjugated Polymer Films with Excellent Electrochromic Properties

Preparing conjugated polymer films via interfacial Suzuki polymerization is a promising method for obtaining desirable electrochromic materials with desired structures. Here, a series of aryl boronic esters and triphenylamine-based aryl bromides were applied as precursors, and several polymer films were finally obtained via the liquid/liquid interfacial Suzuki polymerization reaction under mild conditions. FT-IR, UV, and Raman as well as electrochemistry, SEM, and EDS results all provide strong evidence for the formation of the desired polymer structures. Among them, the TPA-Wu (containing triphenylamine and alkyl-fluorene) film exhibits the best film-forming quality. Besides, these polymer films were applied in electrochromic applications. The results show that electrochromic properties can be affected by the quality of film formation. It is worth mentioning that the TPA-Wu film could achieve excellent electrochromic properties with reversible multicolor changes from transparent yellow to orange-red to blue-green under varying potentials. Compared to other triphenylamine-based electrochromic materials, the TPA-Wu film possessed the most desirable coloring efficiency, higher optical contrast, and shorter switching time. This work provides an existing general approach of liquid/liquid interfacial Suzuki polymerization for constructing conjugated polymer films toward electrochromic applications.

The effect of electrolytes on the electrochromic performance of nickel-substituted tungstophosphate and TiO2 nanowire composite films

A film based on POM and TiO₂ nanowires in Li⁺-based media displays enhanced electrochromic performance compared to that in H⁺-based electrolyte.