Alkali-Stable Metal-Organic Frameworks with Enhanced Electroconductivity for Black-Brown Electrochromic Energy Storage Smart Window.

Metal-organic frameworks (MOFs) deliver potential applications in electrochromism and energy storage. However, the poor intrinsic conductivity of MOFs in electrolytes seriously hampers the development of the above-mentioned electrochemical applications, especially in one MOF electrode. Herein, a new Ni-based MOF (denoted Ni-DPNDI) is proposed with enhanced conductivity by π-delocalized DPNDI connectors. Predictably, the obtained Ni-DPNDI MOF achieves a conductivity of up to 4.63 S∙m-1 at 300 K. Profiting from its unique electronic structure, the Ni-DPNDI MOF delivers excellent electrochromic and energy storage performance with a great optical modulation (60.8%), a fast switching speed (tc = 7.9 s and tb = 6.4 s), a moderate specific capacitance (25.3 mAh·g-1) and good cycle stability over 2000 times. Meanwhile, energy storage capacity is visual by the coloration states of Ni-DPNDI film. As a proof of the potential application, a large-area (100 cm2) electrochromic energy storage smart window is further designed and displayed. The strategy provides an interesting alternative to porous multifunctional materials for the new generation of electronic devices with diverse applications.

Carboxyl-functionalized dual pH/temperature-responsive poly(N-vinylcaprolactam) microgels based on isogenous comonomers for smart window applications.

Stimuli-responsive poly(N-vinylcaprolactam) (PVCL)-based microgels, which could response to small external environmental changes, have attracted great interests in the fields of biomedicine and nanotechnology. However, the preparation of such microgels meets severe challenge due to their low incorporation efficiency and thermoresponsivity passivation. To address these issues, we select 3-(tert-butoxycarbonyl)-N-vinylcaprolactam (TBVCL), a carboxyl-functionalized VCL derivative, as a comonomer to develop pH/temperature dual-responsive microgels. TBVCL, with a structure similar to VCL, enhances incorporation efficiency and colloidal stability, while reducing thermoresponsivity passivation. The volume phase transition temperature (VPTT) of the microgels can be adjusted over a broad range (19.0-49.5 °C). Notably, the radial swelling ratios of the microgels can be modulated by pH, achieving a maximum swelling ratio of 3. The distinct changes in dissolution-precipitation behavior under different temperatures or pH conditions make these microgels suitable for applications such as smart windows and sensors. Furthermore, this novel approach for fabricating microgels with pH-tunable phase-transition temperatures demonstrates significant potential for the controlled release of nanoparticles (e.g., drugs, catalysts, and quantum dots) and the development of smart nanocrystal-polymer composite sensors.

Reusing the Wasted Energy of Electrochromic Smart Window for Near-Zero Energy Building.

Electrochromic smart windows (ESWs) are an effective energy-saving technology for near-zero energy buildings. They consume electric energy unidirectionally during a round-trip coloring-bleaching process, with the energy involved in the bleaching process being wasted. It is highly desirable to reuse this wasted electric energy directly and/or transfer it into other energy storage equipment, further enhancing the overall efficiency of electric energy usage. Herein, a zinc anode-based ESW (ESW-PZ) is reported that not only has fascinating visible-near-infrared (VIS-NIR) dual-band electrochromic performance (a high optical contrast of 63%) but also showcases good energy storage characteristics (a wide voltage window of 2.6 V and a high energy density of 127.5 µWh cm-2). The buildings utilizing ESW-PZ to modulate indoor environments demonstrated an average annual energy saving of 366 MJ m-2 based on energy simulations, which is about 16% of the total energy consumption. Impressively, a high utilization efficiency of 90% (855 mWh m-2) of the wasted electric energy is realized through an ingenious circuit-switching strategy, which can be reused to power small household appliances.

An ITO free All Tungsten-Based Electrochromic Energy Storage Device as Smart Window.

Excessive electricity usage in buildings, notably for heating and cooling, accounts for over 30% of energy consumption, creating a pressing need for energy-saving solutions. Electrochromic Smart Windows (ECSW) aims to reduce energy use while maintaining comfort but faces high costs due to materials like tin-doped indium oxide (ITO) and thick electrochromic films. Moreover, achieving full opacity in the colored state of ECSW is a bottleneck for the industry to overcome privacy concerns. Herein, efforts are directed toward finding cost-efficient alternatives, with all-tungsten-based mesh networks showing promise due to enhanced stability. This newly developed ITO-free, all-tungsten ECSW displays minimal transmittance (≈3%) in the colored state using only 260 nm thick sub-stoichiometric tungsten oxide (WO3-x) film within a lithium-ion-based electrolyte. The ECSW device of size (25 cm2) also demonstrates areal capacitance of ≈13 mF cm-2 to power a liquid crystal display (LCD) for ≈25 min, showcasing its energy storage capabilities. Additionally, to confirm scalability and cost-effectiveness, a larger 15 × 15 cm2 ECSW utilized a single hybrid electrode, highlighting the potential for reducing costs when scaling up production processes. This advancement represents a significant stride toward accessible and energy-efficient smart window technology, offering broader applicability within modern architectural practices.

Smart Window with Reversible and Instantaneous Photoluminescence based on Microsphere Structure.

A smart window that dynamically regulates light transmittance is crucial for modern life end-users and promising for on-demand optical devices. The advent of three-dimensional (3D) photonic crystal microspheres has enriched the functions of a smart window. However, the smart window formed by polymer microspheres encounters poor mechanical strength and microstructural defects. Herein, to solve this limitation, we report the microsphere-based smart window composed of tightly packed cross-linked polymer microspheres (as a precursor) containing organic photochromic dyes, followed by compression under a high elastic state. When excited under an ultraviolet supply, our smart window showed a rapid and reversible fluorescent photoluminescence without fatigue (50 cycles). Moreover, the bulk devices with a microsphere cross-linked network structure enable excellent mechanical strength (hardness reached 0.158 GPa) and visible-light transparency. Interestingly, a QR code can be recognized under visible light exposure but not under ultraviolet light exposure because of photoluminescence of the smart window. Our method generally provided a paradigm for various amorphous polymers, which can be regarded as a simple and effective approach to build a versatile strategy to introduce an ideal marketplace with economic and community benefits.

Ionic Gel Electrolytes for Electrochromic Devices.

Ionic gels are emerging as a promising solution for improving the functionality of electrochromic devices. They are increasingly drawing attention in the fields of electrochemistry and functional materials due to their potential to address issues associated with traditional liquid electrolytes, such as volatility, toxicity, and leakage. In extreme scenarios and/or the design of flexible devices, ionic gel electrolytes offer unique and invaluable advantages. This perspective delves into the application of ionic gels in electrochromic devices, exploring various methods to enhance their performance. After briefly introducing developments in ionic gels for electrochromic devices, the trends and key points of future development are discussed in detail.

Fabrication of smart sunlight window using silver vanadate nanorods (ß-AgVO3) and its effect on phytochemical properties of several agricultural species.

Silver vanadate nanorods were synthesized for the first time via co-precipitation, followed by ambient drying. X-ray diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscope (SEM) analyses were utilized to investigate the structure and morphology of the nanorods. The results of these analyses confirmed the fabrication of silver vanadate nanorods. Then, to check the ability of these nanostructures to be used in the smart window, their optical properties, including the visible-ultraviolet absorption spectrum and photoluminescence (PL), were studied. The results showed that this nanostructure has maximum absorption and emission at wavelengths of 530 and 670 nm, respectively. Next, the new smart window was made with a layer of silver vanadate nanorods, and wheat, barley, millet, and beet were placed under this smart window to perform phytochemical tests. It was observed that silver vanadate nanorods could shift the green wavelength to higher wavelengths and efficiently improve the phytochemical properties of the mentioned plants.

Energy-Efficient Smart Window Based on a Thermochromic Hydrogel with Adjustable Critical Response Temperature and High Solar Modulation Ability.

Thermochromic smart windows realize an intelligent response to changes in environmental temperature through reversible physical phase transitions. They complete a real-time adjustment of solar transmittance, create a livable indoor temperature for humans, and reduce the energy consumption of buildings. Nevertheless, conventional materials that are used to prepare thermochromic smart windows face challenges, including fixed transition temperatures, limited solar modulation capabilities, and inadequate mechanical properties. In this study, a novel thermochromic hydrogel was synthesized from 2-hydroxy-3-butoxypropyl hydroxyethyl celluloses (HBPEC) and poly(N-isopropylacrylamide) (PNIPAM) by using a simple one-step low-temperature polymerization method. The HBPEC/PNIPAM hydrogel demonstrates a wide response temperature (24.1-33.2 °C), high light transmittance (Tlum = 87.5%), excellent solar modulation (ΔTsol = 71.2%), and robust mechanical properties. HBPEC is a functional material that can be used to adjust the lower critical solution temperature (LCST) of the smart window over a wide range by changing the degree of substitution (DS) of the butoxy group in its structure. In addition, the use of HBPEC effectively improves the light transmittance and mechanical properties of the hydrogels. After 100 heating and cooling cycles, the hydrogel still has excellent stability. Furthermore, indoor simulation experiments show that HBPEC/PNIPAM hydrogel smart windows have better indoor temperature regulation capabilities than traditional windows, making these smart windows potential candidates for energy-saving building materials.

Ultralong Bistable, Electrolytic MnO2-Based, Electrochromic Battery Enabled by Porous, Low-Barrier, Hydroxylated TiO2 Interface.

Electrochromic (EC) battery technology shows great potential in future "zero-energy building" by controlling outdoor solar transmission to tune heat gain as well as storing the consumed energy to reuse across other building systems. However, challenges still exist in exploring an electrochemical system to satisfy requirements on both ultra-long optical memory (also called bistability) without continuous power supply and high energy density. Herein, an EC battery is proposed to demonstrate ultra-long bistability (>760 h) based on the reversible deposition and dissolution of manganese oxide (MnO2) without the addition of any mediators. A porous low-barrier hydroxylated titanium dioxide (TiO2) interface is incorporated to synergistically enrich Mn2+-affinity active sites for deposition and effectively reduce the electron transport barrier of MnO2 for dissolution, thereby significantly improving the reversibility, high optical modulation (60.2% at 400 nm), and energy density (352 mAh m-2). The modification strategy is also verified on the cathode-less button cells with a much higher average coulombic efficiency (99.9%) compared to the batteries without the porous hydroxylated TiO2 interface (74.6%). These achievements lay a foundation for advancements in both electrochromism and Zn-Mn aqueous batteries.

Bio-inspired Mechanically Responsive Smart Windows for Visible and Near-Infrared Multiwavelength Spectral Modulation.

Mechanochromic light control technology that can dynamically regulate solar irradiation is recognized as one of the leading candidates for energy-saving windows. However, the lack of spectrally selective modulation ability still hinders its application for different scenarios or individual needs. Here, inspired by the generation of structure color and color change of living organisms, a simple layer-by-layer assembly approach toward large-area fabricating mechanically responsive film for visible and near-infrared multiwavelength spectral modulation smart windows is reported here. The assembled SiO2 nanoparticles and W18O49 nanowires enable the film with an optical modulation rate of up to 42.4% at the wavelength of 550 nm and 18.4% for the near-infrared region, separately, and the typical composite film under 50% stretching shows ≈41.6% modulation rate at the wavelength of 550 nm with NIR modulation rate less than 2.7%. More importantly, the introduction of the multilayer assembly structure not only optimizes the film's optical modulation but also enables the film with high stability during 100 000 stretching cycles. A cooling effect of 21.3 and 6.9 °C for the blackbody and air inside a model house in the real environmental application is achieved. This approach provides theoretical and technical support for the new mechanochromic energy-saving windows.

Electrochromic and Energy Storage Performance Enhancement by Introducing Jahn-Teller Distortion: Experimental and Theoretical Study.

Aqueous electrochromic batteries (ECBs) have recently garnered significant attention within the realm of renewable rechargeable technology due to their potential applicability in diverse multifunctional devices featuring visible-level indicator batteries. However, there exists an imperative to comprehend the underlying structural factors that contribute to achieving an elevated electrochemical performance. In this context, we have synthesized and compared WO3·H2O (HWO) specifically for heightened ECB application as against the performance of a standard anhydrous WO3 (AWO). To unravel the underlying cause, a density functional theory (DFT) investigation is carried out, disclosing a structural deformation of HWO, unlike AWO, due to Jahn-Teller distortion induced by the presence of interlayer water. It results in a fully compatible HWO ion host to devise a zinc-ion aqueous electrolyte electrochromic battery, exhibiting superior redox reactivity, optical modulation (50%), capacity (200 mAh/m2), and cyclic stability. To glean insights into the dynamic structural alterations during the intercalation and deintercalation processes of Zn2+, ex situ X-ray diffraction and Raman spectroscopic studies are carried out. These investigations culminate in the determination that HWO films are better suited for the application than their AWO counterparts. This finding holds promise for advancing the applications of ECBs and represents a significant step forward in this field.

Redox Potential Based Self-Powered Electrochromic Devices for Smart Windows.

Energy-efficient glass windows are pivotal in modern infrastructure striving toward the "Zero energy" concept. Electrochromic (EC) energy storage devices emerge as a promising alternative to conventional glass, yet their widespread commercialization is impeded by high costs and dependence on external power sources. Addressing this, redox potential-based self-powered electrochromic (RP-SPEC) devices are introduced leveraging established EC materials like tungsten oxide (WO3) and vanadium-doped nickel oxide (V-NiO) along with aluminum (Al) as an anode. These devices produce open circuit voltages (OCV) exceeding ±0.3 V, enabling autonomous operation for multiple cycles. The WO3 film exhibits 1% transmission and 88% modulation in the colored state at 550 nm with a mere 260 nm thickness. The redox interactions facilitate coloring and bleaching cycles without external power, while photo-charging rejuvenates the system. Notably, the inherent voltages of the RP-SPEC device offer dual functionality, powering electronic devices for up to 81 h. Large-area (≈28 cm2) device feasibility is demonstrated, paving the way for industrial adoption. The RP-SPEC device promises to revolutionize smart window technology by offering both energy efficiency and autonomous operation, thus advancing sustainable infrastructure.

Development of gum Arabic/chitosan-infiltrated photoluminescent wooden smart window with multifunctional properties.

Photochromic wood materials are very important and appealing for smart windows. Herein, we describe the development of transparent photochromic wood that can change its color under ultraviolet and visible lights. Photoluminescent transparent wood was prepared by delignification of wood followed by infiltration with a combination of gum Arabic/chitosan/acrylic acid (ACA), lanthanide-activated aluminum strontium oxide (LASO) as a photoluminescent, and Genipin as a cross-linking agent. The produced mixture was then infused into the lignin-modified wood substrate. In order to develop a luminescent colorless wood, the LASO phosphor must be well-distributed in the ACA solution without aggregation. According to the colorimetric parameters and photoluminescence spectra, this optically active wooden window switched color from transparent in daylight to green when UV-irradiated. Transmission electron microscopy (TEM) was employed to examine the morphological features of phosphor nanoparticles. The morphological features of the developed smart wooden window were investigated by scanning electron microscopy (SEM), X-ray fluorescent spectroscopy (XRF), and energy-dispersive X-ray analyzer (EDX). The mechanical performance was explored by investigating both hardness and resistance to scratches. The luminescent woods displayed an emission band at 518 nm when excited at 365 nm. The superhydrophobic performance and ultraviolet shielding of woods were improved upon increasing the phosphor content.

Thermochromic Vanadium Dioxide Nanostructures for Smart Windows and Radiative Cooling.

The pursuit of energy-saving materials and technologies has garnered significant attention for their pivotal role in mitigating both energy consumption and carbon emissions. In particular, thermochromic windows in buildings offer energy-saving potential by adjusting the transmittance of solar irradiation in response to temperature changes. Radiative cooling (RC), radiating thermal heat from an object surface to the cold outer space, also offers a potential way for cooling without energy consumption. Accordingly, smart window and RC technologies based on thermochromic materials can play a crucial role in improving energy efficiency and reducing energy consumption in buildings in response to the surrounding temperature. Vanadium dioxide (VO2) is a promising thermochromic material for energy-saving smart windows and RC due to its reversible metal-to-insulator transition, accompanying large changes in its optical properties. This review provides a brief summary of synthesis methods of VO2 nanostructures based on nanoparticles and thin films. Moreover, this review emphasizes and summarizes modulation strategies focusing on doping, thermal processing, and structure manipulation to improve and regulate the thermochromic and emissivity performance of VO2 for smart window and RC applications. In last, the challenges and recent advances of VO2-based smart window and RC applications are briefly presented.

Dual-Band Electrochromic Devices Utilizing Niobium Oxide Nanocrystals.

In this study, we realize functioning electrochromic devices based on colloidal niobium oxide nanocrystals, which show dual-band electrochromic behavior, with spectral selectivity between near-infrared and visible wavelengths. Minimally coloring vanadium oxide counter electrodes allow for full electrochromic devices that embody the dual-band electrochromic behavior of the niobium oxide component. The devices are fabricated using solution processing on both glass and flexible substrates, demonstrating that our platform has potential for the development of low-cost dual-band electrochromic devices for dynamic solar control in a variety of form factors and applications.

Annual Energy-Saving Smart Windows with Actively Controllable Passive Radiative Cooling and Multimode Heating Regulation.

Smart windows with radiative heat management capability using the sun and outer space as zero-energy thermodynamic resources have gained prominence, demonstrating a minimum carbon footprint. However, realizing on-demand thermal management throughout all seasons while reducing fossil energy consumption remains a formidable challenge. Herein, an energy-efficient smart window that enables actively tunable passive radiative cooling (PRC) and multimode heating regulation is demonstrated by integrating the emission-enhanced polymer-dispersed liquid crystal (SiO2@PRC PDLC) film and a low-emission layer deposited with carbon nanotubes. Specifically, this device can achieve a temperature close to the chamber interior ambient under solar irradiance of 700 W m-2, as well as a temperature drop of 2.3 °C at sunlight of 500 W m-2, whose multistage PRC efficiency can be rapidly adjusted by a moderate voltage. Meanwhile, synchronous cooperation of passive radiative heating (PRH), solar heating (SH), and electric heating (EH) endows this smart window with the capability to handle complicated heating situations during cold weather. Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer SiO2@PRC PDLC, normal glass, and commercial low-E glass when applied in different climate zones. This work provides a feasible pathway for year-round thermal management, presenting a huge potential in energy-saving applications.

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.

Multivalent-Ion versus Proton Insertion into Nanostructured Electrochromic WO3 from Mild Aqueous Electrolytes.

Mild aqueous electrolytes containing multivalent metal salts are currently scrutinized for the development of ecosustainable energy-related devices. However, the role of soluble multivalent metal ions in the electrochemical reactivity of transition metal oxides is a matter of debate, especially when they are performed in protic aqueous electrolytes. Here, we have compared, by means of (spectro)electrochemistry, the reversible electrochromic reduction of transparent nanostructured γ-WO3 thin films in mild aqueous electrolytes of various chemical composition and pH. This study reveals that reversible proton insertion is the only charge storage mechanism over a large pH range and that it is effective for aqueous electrolytes prepared from either organic (such as acetic acid) or inorganic (such as solvated multivalent cations) Bro̷nsted acids. By refuting charge storage mechanisms relying on the reversible insertion of multivalent metal ions, notably in aqueous electrolytes based on Al3+ ions or a mixture of Al3+ and Zn2+ ions, these fundamental results pave the way for the rational development of electrolytes and active materials for a range of aqueous-based devices, such as the emerging concept of an energy-saving smart window, which we also address in this study.

Smart windows based on ultraviolet-B persistent luminescence phosphors for bacterial inhibition and food preservation.

Herein, ultraviolet B (UVB) persistent luminescence phosphors containing SrAl12O19: Ce3+, Sc3+ nanoparticles were reported. Thermoluminescence (TL) spectrum analysis reveals that the shallow trap induced by Sc3+ co-doping plays an important role in photoluminescence persistent luminescence (PersL) development, while the deep trap dominates the generation of optical stimulated luminescence (OSL). Owing the appearance of deep trap, the OSL is observed under light (700 nm - 900 nm) excitation. UVB luminescence exerts good bactericidal effects on pathogenic bacteria involved in the process of food spoilage. Thus, the smart window with SrAl12O19: Ce3+, Sc3+/PDMS produces UVB PersL to efficiently inactivate Escherichia coli and Staphylococcus aureus. In addition, the presence of the smart window delays the critical point of pork decay, and greatly reduces the time of pork spoilage. It maximizes the convenience of eradicating bacteria and preserving food, thus offering a fresh perspective on the use of UV light for food sterilization and preservation.

Refractive Index Modulation for Metal Electrodeposition-Based Active Smart Window Applications.

One of the remarkable choices for active smart window technology is adopting a metal active layer via reversible metal electrodeposition (RME). As the metal layer efficiently blocks the solar energy gain, even a hundred-nanometer-thick scale, RME-based smart window has great attention. Recent developments are mainly focused on the various cases of electrolyte components and composition meeting technological standards. As metal nanostructures formed through the RME process involve plasmonic phenomena, advanced analysis, including plasmonic optics, which is beyond Beer-Lambert's law, should be considered. However, as there is a lack of debates on the plasmonic optics applied to RME smart window technology, as research is mainly conducted through an exhaustive process. In this paper, in order to provide insight into the RME-based smart window development and alleviate the unclear part of plasmonic optics applied to the field, finite-difference time-domain electromagnetic simulations are conducted. In total, two extremely low-quality (Cr) and high-quality (Mg) plasmonic materials based on a nanoparticle array are considered as a metal medium. In addition, optical effects caused by the metal active layer, electrolyte, and nanoparticle embedment are investigated in detail. Overall simulations suggest that the effective refractive index is a decisive factor in the performance of RME-based smart windows.