Resonant-Cavity-Enhanced Electrochromic Materials and Devices

Diatom Cribellum-Inspired Hierarchical Metamaterials: Unifying Perfect Absorption Toward Subwavelength Color Printing

Diatom exoskeletons, known as frustules, exhibit a unique multilayer structure that has attracted considerable attention across interdisciplinary research fields as a source of biomorphic inspiration. These frustules possess a hierarchical porous structure, ranging from millimeter-scale foramen pores to nanometer-scale cribellum pores. In this study, this natural template for nanopattern design is leveraged to showcase metamaterials that integrates perfect absorption and subwavelength color printing. The cribellum-inspired hierarchical nanopatterns, organized in a hexagonal unit cell with a periodicity of 300 nm, are realized through a single-step electron beam lithography process. By employing numerical models, it is uncovered that an additional induced collective dipole mode is the key mechanism responsible for achieving outstanding performance in absorption, reaching up to 99%. Analysis of the hierarchical organization reveals that variations in nanoparticle diameter and inter-unit-cell distance lead to shifts and broadening of the resonance peaks. It is also demonstrated that the hierarchical nanopatterns are capable of color reproduction with high uniformity and fidelity, serving as hexagonal pixels for high-resolution color printing. These cribellum-inspired metamaterials offer a novel approach to multifunctional metamaterial design, presenting aesthetic potential applications in the development of robotics and wearable electronic devices, such as smart skin or surface coatings integrated with energy harvesting functionalities.

Bistable Electrochromic Ionogels via Supramolecular Interactions for Energy-Efficient Displays

Bistable electrochromic (EC) materials and systems offer significant potential for building decarbonization through their optical modulation and energy efficiency. However, challenges such as limited design strategies and bottlenecks in cost, fabrication, and color have hindered the full commercialization of energy-saving EC windows and displays, with few materials achieving true bistability. Herein, a novel strategy for designing bistable electrochromic materials is proposed by leveraging supramolecular interactions. These interactions facilitate reversible color transitions, stabilize the colored structure, and enable spatial confinement to inhibit diffusion, thereby achieving bistable electrochromism. The mechanisms and materials underlying these unconventional electrochromic systems are substantiated through detailed characterization. This strategy enables the preparation of low-cost and sustainable transparent electrochromic displays with high performance. Notably, the display information remains clearly visible for more than 2 h without consuming energy. Involving biomass materials and removable device structures also enhances the sustainability and scalability of EC technology applications and development. These results demonstrate the crucial role of supramolecular chemistry in the development of cutting-edge materials for applications such as energy-saving smart windows.

Chemically and geometrically programmable photoreactive polymers for transformational humidity-sensitive full-color devices

Humidity-sensitive structural color has emerged as a promising technology due to its numerous advantages that include fast response, intuitiveness, stand-alone capability, non-toxicity, as well as resistance to thermal and chemical stresses. Despite immense technological advancements, these structural colors lack the ability to present independent multiple images through transformation. Herein, we present an approach to address this constraint by introducing a chemically and geometrically programmable photoreactive polymer which allows preparation of transformational humidity-sensitive full-color devices. Utilizing azido-grafted carboxymethyl cellulose (CMC-N3) allows adjustments in swelling properties based on the grafting ratio (Γ) of azido groups upon UV-induced crosslinking. Also, the distinctive photo-curability of the polymer enables precise geometric control to achieve vivid colors in combination with disordered plasmonic cavities. Our work culminates in the development of an advanced anti-counterfeiting multiplexer capable of displaying different full-color images with variation in humidity levels. The showcased color displays signify pivotal breakthroughs in tunable optical technologies, illustrating how chemical modifications in hydrogels provides additional degrees of freedom in the design of advanced optical devices.

Designed Growth of Covalently Bonded WO3/PEDOT Hybrid Nanorods Array with Enhanced Electrochromic Performance

A covalently bonded WO3/PEDOT hybrid nanorods array has been prepared through solvothermal, oil bath, and electrochemical deposition methods using KH57 as a coupling agent. The obtained WO3/PEDOT shows substantially increased electrochromic performance with an increased response speed (3.4 s for coloring and 1.2 s for bleaching), excellent optical modulation (86.7% at 633 nm), high coloration efficiency (122.0 cm2/C at 633 nm), and distinguished cyclic stability. It was found that the covalent bond interaction between WO3 and PEDOT plays an essential role in property enhancement. The covalently bonded inorganic/organic hybrid nanorods array may promise great potential in developing smart-display and energy-efficient materials and devices featuring low energy consumption, cost effectiveness, and environmental protection.

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.

Electrically Responsive Photonic Crystals with Enhanced Suspension Stability and Color Saturation for Electrophoretic Displays and Smart Windows

Electrophoretic displays (EPDs) based on photonic crystals show great potential due to their reduced eye fatigue and low power consumption. However, the current image quality and service life of this system still face great challenges. In this work, we fabricated a new kind of electrically responsive photonic crystal (ERPC) device based on PSMA@SiO2 liquid colloidal crystals (LCCs) for EPDs. By introduction of the PSMA core with lower density and higher refractive index, the suspension stability and color saturation of PSMA@SiO2 LCCs were greatly enhanced compared with those of bare SiO2 LCCs. The PSMA@SiO2 LCCs showed brilliant colors, wide color tuning range (∼200 nm), and good reversibility under low voltages (<4 V). Interestingly, the transparency of PSMA@SiO2 LCCs could also be obviously regulated by an electric field, which was different from the traditional ways that change the thickness of PCs or contrast of refractive index (Δn) between the nanospheres and matrix. This transparency modulation offered a novel idea for the transmittance control of smart windows. As a proof of concept, we fabricated a new type of patterned ERPC device to demonstrate their potential in electrophoretic displays and smart windows with controllable transmittance under an electric field.

Glass Disorder Modulated Luminescence in Zero-Dimensional Antimony-Chloride Coplanar Dimers for Optical Anti-counterfeiting

Zero-dimensional metal halides have received wide attention due to their structural diversity, strong quantum confinement, and associated excellent photoluminescence properties. A reversible and tunable luminescence would be desirable for applications such as anti-counterfeiting, information encryption, and artificial intelligence. Yet, these materials are underexplored, with little known about their luminescence tuning mechanisms. Here we report a pyramidal coplanar dimer, (TBA)Sb2Cl7 (TBA = tetrabutylammonium), showing broadband emission wavelength tuning (585-650 nm) by simple thermal treatment. We attribute the broad color change to structural disorder induced by varying the heat treatment temperatures. Increasing the heating temperature transitions the material from long-range ordered crystalline phase to highly disordered glassy phase. The latter exhibits stronger electron-phonon coupling, enhancing the self-trapped exciton emission efficiency. The work provides a new material platform for manifold optical anti-counterfeiting applications and sheds light on the emission color tuning mechanisms for further design of stimuli-responsive materials.

Sustainable, low-cost, high-contrast electrochromic displays via host-guest interactions

Electrochromic (EC) displays with electronically regulating the transmittance of solar radiation offer the opportunity to increase the energy efficiency of the building and electronic products and improve the comfort and lifestyle of people. Despite the unique merit and vast application potential of EC technologies, long-awaited EC windows and related visual content displays have not been fully commercialized due to unsatisfactory production cost, durability, color, and complex fabrication processes. Here we develop a unique EC strategy and system based on the natural host and guest interactions to address the above issues. A completely reusable and sustainable EC device has been fabricated with potential advantages of extremely low cost, ideal user-/environment friendly property, and excellent optical modulation, which is benefited from the extracted biomass EC materials and reusable transparent electrodes involved in the system. The as-prepared EC window and nonemissive transparent display also show comprehensively excellent properties: high transmittance change (>85%), broad spectra modulation covering Ultraviolet (UV), Visible (Vis) to Infrared (IR) ranges, high durability (no attenuation under UV radiation for more than 1.5 mo), low open voltage (0.9 V), excellent reusability (>1,200 cycles) of the device's key components and reversibility (>4,000 cycles) with a large transmittance change, and pleasant multicolor. It is anticipated that unconventional exploration and design principles of dynamic host-guest interactions can provide unique insight into different energy-saving and sustainable optoelectronic applications.

Quadruple Control Electrochromic Devices Utilizing Ce4W9O33 Electrodes for Visible and Near-Infrared Transmission Intelligent Modulation

Electrochromic smart windows are promising for building energy savings due to their dynamic regulation of the solar spectrum. Restricted by materials or traditional complementary device configuration, precisely and independently controlling of visible (VIS) and near-infrared (NIR) light is still on the drawing board. Herein, a novel Zn2+ electrochemically active Ce4W9O33 electrode is reported, which demonstrates three distinct states, including VIS and NIR transparent "bright and warm" state, VIS and NIR opaque "dark and cool" state, VIS transparent and NIR opaque "bright and cool" state. A dual-operation mode electrochromic platform is also presented by integrating Ce4W9O33/NiO complementary device and Zn anode-based electrochromic device (Ce4W9O33/Zn/NiO device). Such a platform enables an added VIS opaque and NIR transparent "dark and warm" state, thus realizing four color states through individually controlling Ce4W9O33 and NiO electrodes, respectively. These results present an effective approach for facilitating electrochromic windows more intelligent to weather/season conditions and personal preferences.

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.

Soluble polymer facilely self-grown in situ on conducting substrates at room temperature towards electrochromic applications

Electrochromic polymer film preparation methods such as spin coating, spray coating, and electrochemical polymerization, are commonly used. At present, developing new film preparation technology is an important aspect in the field of electrochromics. Herein, a continuous in situ self-growing method based on the chemical reaction occurring on the surface of an ITO glass between a metal oxide and organic acid groups was successfully applied to prepare electrochromic polymer films at a mild room temperature. SEM, FT-IR spectroscopy, XPS, and XRD characterization methods were combined to reveal the process and mechanism of film formation. The following notable electrochromic properties were observed: switching time within 6 s, contrast reached 35%, and minimal decrease of stability after 600 cycles. Finally, the patterned films were obtained through the directional growth of polymers in solution. This study provides an effective strategy for designing and preparing electrochromic films by self-growing methods in future applications.

Recent advances in dynamic dual mode systems for daytime radiative cooling and solar heating

Thermal management, including heating and cooling, plays an important role in human productive activities and daily life. Nevertheless, in the actual environment, almost all the ambient scenarios come with the challenge that the objects are located in a quite dynamic and variable environment, which includes fluctuations in aspects such as space, time, sunlight, season, and temperature. It is imperative to develop low-energy or even zero-energy thermal-management technologies with renewable and clean energy. In this review, we summarised the latest technological advances and the prospects in this burgeoning field. First, we present the fundamental principles of the daytime passive radiative cooling (PDRC) thermal management device. Next, In the domain of dual-mode systems, they are classified into various types based on the diverse mechanisms of transitioning between cooling and heating states, including electrical responsive, mechanical responsive, temperature responsive, and solution responsive. Furthermore, we conducted an in-depth analysis of the principles and design methodologies associated with these categories, followed by a comparative assessment of their performance in radiative cooling and solar heating applications. Finally, this review presents the challenges and opportunities of dynamic dual mode thermal management, while also identifying future directions.