Electrochromic Windows Research Articles

Organic Ligand‐Free Scalable Dual‐Band Electrochromic Smart Windows

AbstractDual‐band electrochromic (DBEC) smart windows are an emerging energy‐saving technology, especially those constructed from single‐component DBEC materials as they offer an easy way to independently regulate visible (VIS) and near‐infrared (NIR) light. However, the current complicated organic ligand approach used to synthesize single‐component DBEC materials necessitates a post‐annealing treatment, which may severely compromise the scalability of DBEC smart windows. Herein, one organic ligand‐free process is developed to produce well‐controlled Nb‐doped anatase TiO2 nanocrystals (NTO NCs) followed by spraying on arbitrary substrates, giving NTO rigid or flexible films with good DBEC properties and a high optical modulation over 92%. A prototype of a 20 cm × 20 cm DBEC smart window is built. The simplicity and scalability of the synthesis and fabrication process make it a scalable approach to constructing large‐area electrochromic smart windows and foils, with promising applications in fields such as buildings and automobiles.

Electrically Controlled Smart Window for Seasonally Adaptive Thermal Management in Buildings.

Smart windows offer a sustainable solution for energy-efficient buildings by adapting to various weather conditions. However, the challenge lies in achieving precise control over specific sunlight bands to effectively respond to complex weather changes and individual needs. Herein, a novel electrochromic smart window fabricated by integrating a self-assembled cellulose nanocrystals (CNCs) layer with an electrochromic poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) layer is reported, which exhibits high near-infrared transmittance, low solar reflectivity (26%), and infrared emissivity (20%) in winter, and low near-infrared transmittance, high solar reflectivity (91%), and infrared emissivity (≈94%) in summer. Interestingly, the material offers dynamic temperature control based on its photothermal properties, maintaining the internal temperature of buildings within a comfortable range of 20-25 °C from morning to night, particularly in winter with significant daily temperature fluctuations. Simulations show that the CNC-PED device demonstrates excellent energy-saving and CO2 emission reduction capacities across various global climate zones. This study presents a feasible pathway for constructing season-adaptive smart windows, making them suitable for energy-efficient buildings.

Dynamic optical and thermal modulation of electrochromic smart windows and sunglasses based on benzothiadiazole-extended viologen derivatives

Dynamic optical and thermal modulation of electrochromic smart windows and sunglasses based on benzothiadiazole-extended viologen derivatives

Simulation of Responsive Envelopes in Current and Future Climate Scenarios: A New Interactive Computational Platform for Energy Analyses

Despite the strong interest concerning the responsive façades, today there are still few built examples and few tools to assess their benefits due to the complex description of the phenomenon. Energy simulations should consider the interactions between a time-varying environment and an environment-dependent envelope, increasing the intricacy of the problem; moreover, these strong environment–envelope interlinkages increase the importance of the location and climate scenarios considered. The aim of this study is to provide a tool to easily model these phenomena in different geographical and climate contexts. For this purpose, an innovative interactive computational platform (ICP) was developed based on EnergyPlus as a simulation engine, Python as a simulation manager, and Grasshopper as a user interface. Thanks to a single user-friendly environment, the users can simply select the climate scenario, the location, the responsive technology, and its main properties to set and run the dynamic energy simulation. After an overview of the current state of the art, this study provides a description of the structure and workflow adopted for developing this platform and details regarding its functioning and input management. Finally, the platform was tested to run an evolutionary optimization of an electrochromic window control strategy in different climate scenarios.

Bridging to Commercialization: Record-Breaking of Ultra-Large and Superior Cyclic Stability Tungsten Oxide Electrochromic Smart Window.

Electrochromic smart windows (ESWs) can significantly reduce energy consumption in buildings, but their cost-effective, large-scale production remains a challenge. In this study, the instability of black phosphorus is leveraged to induce the growth of the tungsten oxide film through its decomposition process, inspired by the 2D material-assisted in situ growth (TAIG) method. This approach results in the preparation of large-scale, high-performance WO3-x·nH2O (n<2) films. Characterization techniques and DFT calculations confirm efficient regulation ofstructural water and oxygen vacancies during TAIG preparation. The WO3-x·nH2O films exhibit excellent electrochromic (EC) properties, including high transmittance modulation (74.2%@1100nm), fast switching time (tc=5.5s, tb=3.8s), high coloration efficiency (124.7cm2C-1), and superior cyclic stability (transmittance modulation retained 94.7% after 20000 cycles). Ultra-largeWO3-x·nH2O film are prepared via a simple immersion process, and fabricated into a large-area ESW under facile laboratory conditions, demonstrating the economic and practical feasibility of this approach in industrial-scale production. Operated by the intelligent control circuit, the ESWexhibits remarkable EC properties and cyclic stability This research represents a milestone in improving the performance and industrial-scale production of ESWs, bridging the gap to the commercialization of EC technology.

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.

Fast-switching electrochromic smart windows based on WO3 doped NiO thin films

Nickel oxide (NiO) is a very promising material for the counter electrode in electrochromic devices (ECDs). In the current research, WO3 incorporated NiO thin films were fabricated via RF sputtering to enhance the electrochromic performance of NiO thin films. An XRD analysis revealed that the addition of WO3 to the cubic NiO thin film disrupts its long-range crystalline structure, resulting in an amorphous state. FESEM revealed the formation of columnar structure which favours ECDs. XPS analysis revealed that the addition of WO3 into NiO enhanced the hole concentration by creating nickel vacancies (nickel defects). Compared to pristine NiO, WO3 mixed NiO thin films showed enhanced optical modulation (66 %) with rapid switching speed (0.6 s/1.0 s for bleaching/colouring). This is mainly because the defect- induced amorphous structure of the nickel tungsten oxide thin film can provide large number of diffusion channels which facilitates the rapid ion intercalation process, and can accommodate large number of ions, and hence enhances the electrochromic performance. This advancement might have a substantial impact on the development of nickel tungsten oxide as a potential counter electrode in high-performance energy saving smart windows.

Advanced Dual‐Band Smart Windows: Inorganic All‐Solid‐State Electrochromic Devices for Selective Visible and Near‐Infrared Modulation

AbstractDual‐band electrochromic smart windows (DESWs), capable of actively and selectively modulate visible (VIS) light and near‐infrared (NIR) heat, have emerged as a practical technology for enhancing user comfort and reducing building energy consumption. However, the design and development of DESWs remain a significant challenge due to the difficulty in obtaining suitable materials and high‐durability electrolytes. Here, the first all‐solid‐state DESW based on an orthorhombic oxygen‐deficient tungsten oxide (o‐WO3‐x) film is presented. Benefiting from the synergistic effects of the efficient oxygen‐vacancy‐enhanced charge transfer process and the secure transfer pathway enabled by the orthorhombic crystal structure, the o‐WO3‐x film showcases remarkable dual‐band electrochromic properties, including selective modulation of VIS light and NIR heat, large optical modulation (89.1%), rapid response time (tb/tc = 6.8/17.9 s), high coloration efficiency (155.92 cm2 C−1), and ultrastable cyclic performance (8000 cycles) even in acidic aqueous electrolyte. Furthermore, the all‐solid‐state DESWs incorporating o‐WO3‐x deliver a significant and stable dual‐band electrochromic response with excellent thermal regulation and energy‐saving capabilities. These findings underscore the considerable potential of o‐WO3‐x films and their all‐solid‐state smart windows in decreasing building energy consumption.

Controlled assembly and synthesis of oxygen-deficient W18O49 films based on solvent molecular strategy for electrochromic energy storage smart windows

18O49 is a promising electrochromic material with abundant oxygen vacancy and high carrier mobility. However, the electrochromism of W18O49 is not satisfactory, the regulation and synthesis of high-performance W18O49 have become the research hotspot. In this work, it is found that the main chain and side chain structure of solvent molecules can control the assembly and synthesis of W18O49 film, so as to achieve excellent electrochemical and electrochromic properties. The porous reticular W18O49 film synthesized in short-chain molecular solvent shows the excellent transmittance modulation (81.6 % at 633 nm, 77.0 % at 1050 nm), and exhibits the high energy storage of 41.7 mF cm−2 at 0.1 mA cm−2. Solvent molecular strategy provides a new way for the synthesis and regulation of W18O49 electrochromic films and promotes the further development of high-performance electrochromic materials.

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 2.6V 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 366MJ 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.

Optical and Structural Properties of V2O5 Electrochromic Thin Films

The increase in global temperature has led to a significant surge in energy consumption within the air conditioning industry, resulting in environmental deterioration. Electrochromic (EC) windows have emerged as a promising solution to address these challenges. Vanadium pentoxide (V2O5) stands out among all metal oxide materials due to its remarkable EC properties, including substantial Li+ ion insertion capacity and multicolor capabilities. Despite the potential of V2O5, there remains a lack of comprehensive research on the structural and optical properties of V2O5 films with varying thicknesses. Therefore, this study aims to investigate the structural and optical properties of V2O5 thin films with thicknesses ranging from 46 to 344 nm. By employing the sol-gel spin coating method, V2O5 thin films were fabricated and analyzed using X-ray diffraction (XRD) spectroscopy and ultraviolet-visible (UV-Vis) spectrophotometry. The fabricated V2O5 thin films with thicknesses of 46-274 nm demonstrated an average film transparency of 83 %. XRD analysis further revealed that the V2O5 thin films reached their peak crystallinity at a thickness of 344 nm. Moreover, CV analysis revealed that the V2O5 device, with a thickness of 274 nm, exhibited a cathodic peak current of -1.63 mA, indicating its excellent ability to facilitate Li+ ion diffusion. Additionally, CA measurements displayed a high optical modulation of 37.78 %. Ultimately, this research contributes to the development of energy-efficient solutions for sustainable environmental practices.

A review of complex window-glazing systems for building energy saving and daylight comfort: Glazing technologies and their building performance prediction

The increasing energy consumption and detrimental CO2 emissions contributing to global warming underscore the urgent necessity for energy conservation, especially within buildings. Among different building components, fenestration plays a pivotal role as it accounts for the majority of heat transfer across the building envelope. This emphasises the significance of window-glazing technologies in enhancing their thermal performance. Furthermore, window-glazing systems can lead to overheating issues, particularly in summer, and glare issues, especially in winter. These challenges have spurred the development of various advanced glazing systems. This paper provides a comprehensive review of these advanced glazing technologies based on their functionalities and working principles, with a focus on parameters such as U-value, solar heat gain coefficient and visible transmittance. Among these technologies, vacuum and aerogel glazing systems exhibit superior thermal insulation properties, with U-values below 1 W/m2 K, making them suitable for heating-dominated climates. Smart window systems, such as electrochromic windows, are ideal for cooling-dominated climates due to their low solar heat gain coefficient (0.09–0.47) and visible transmittance (0.02–0.62). Photovoltaic window systems not only provide effective thermal insulation and solar shading but also produce additional power for on-site use. Some of these glazing systems feature complex structures, which present challenges when integrating them into existing building simulation software to assess their impact on building performance. Therefore, this paper also examines techniques for conducting energy and daylight performance simulations for buildings that make use of complex window systems. Ultimately, the authors propose an approach to characterise the thermal, optical and electrical properties of a complex photovoltaic window system within existing building simulation software, such as EnergyPlus. This approach facilitates a thorough investigation into the effects of complex window systems on building energy efficiency and indoor comfort.

A TOC- and deposition-free electrochromic window driven by redox flow battery

Under “green architecture” principles, electrochromic smart windows are employed to adjust optical transmittance and indoor temperature, yet their high costs limit the wide application. Here, an electrochromic window is driven by a redox flow battery (RFB), where TOC and deposition layers are no longer needed. The transmittance of the electrochromic window is modulated by the state of oxidation (SOC) of aqueous posolyte Fe(phen)3Cl2, which is coupled with BTMAP-Vi negolyte in RFB. Under optimized conditions, average CE, VE, and EE reach 93.25 %, 92.61 %, and 86.35 % for RFB with a capacity fading rate of 1.57 % per cycle. 88.66 % optical modulation and 9.36 cm2/C coloration efficiency are achieved in the electrochromic process, and 72.34 % optical modulation is maintained after 12000 s. Essentially, the indoor temperature declines 3 °C for posolyte with 100 % SOC when compared with the control experiment using circulating water for a model house. This means minimum electricity of 0.0185 kWh is saved when using an air conditioner to cool a 100 m3 house, which corresponds to declined CO2 emission (COE) of 0.0185 kg. This work provides a novel and cost-efficient strategy for modulating indoor comfort via electrochromic windows driven by RFB.

Role of Dopant in Enabling Electrodeposition of Polymer Thin Films with High Solar Transmittance Modulation

Buildings consume approximately one-third of the energy used in developed countries, with much of this energy tied to building heating and cooling. Electrochromic “smart” windows have the potential to mitigate some of this energy use through on-demand modulation of solar energy transmission. Therefore, electrochromic window devices based on low cost and facile solution-based processing routes are sought. In this work, we describe the electropolymerization and deposition of electrochromic poly(arylamine) thin films with exceptional broadband solar transmittance modulation, reaching ΔT sol values of over 60% (Figure 1). Through high-resolution, near-field spectroscopic imaging we show that the structure of the acid dopant present in the electrodeposition solution plays a key templating role that determines the electrochromic performance of these films. Our findings indicate that polyanionic dopants are especially adept at directing polymer chain conformational order, which in turn improves charge delocalization and transport. These factors lead to films with high smoothness and optical clarity through the visible (T lum > 80%) and near-infrared ranges. Further details regarding the cycling stability of these films and their integration into full electrochromic devices will be discussed. In summary, this work demonstrates the value of polyanionic dopants for templating high quality electrochromic polymer thin films capable of energy-relevant solar transmittance modulation for smart window applications. Figure 1

Utilization of Poly(Ethylene Terephthalate) Waste Bottle into Disodium Terephthalate: A Sustainable Electrolyte for Visible to Near‐Infrared Broadband Electrochromic Modulation

AbstractThe growing challenge of poly(ethylene terephthalate) (PET) plastic bottle waste underscores the urgent need for innovative solutions. This study introduces a pioneering approach to repurpose PET waste into valuable electrolytic material for electrochromic (EC) smart windows, presenting a novel strategy to address environmental concerns while advancing technology. Through alkaline depolymerization, disodium terephthalate (DST) electrolyte is derived from PET waste, offering an eco‐friendly and cost‐effective alternative. Integrated with chromogens such as 1‐hexyl‐[4,4′‐bipyridin]‐1‐ium iodide [MV(I)], or 1,1′‐dihexyl‐[4,4′‐bipyridine]‐1,1′‐diium iodide [DVH(I)], or 1,1′‐dihexyl‐[4,4′‐bipyridine]‐1,1′‐diium dihexafluorophosphate [DVH(PF6)], alongside hydroquinone [HQ] and poly(ethyene glycol) diacrylate [PEGDA]: water, novel EC gel‐based devices are fabricated. Notably, ED‐3 exhibits dual‐band absorption across the visible to near‐infrared spectrum, enabling seamless color transitions and exceptional optical contrast. With (ΔT) values of 88.03% at 550 nm and 73.7% at 900 nm, along with a coloration efficiency of 277 cm2C⁻¹ and cyclic stability exceeding 2000 cycles, this innovative approach marks a significant advancement in PET waste upcycling for EC applications. Furthermore, this research contributes to addressing the global challenges of plastic waste pollution and energy consumption, underscoring the transformative potential of sustainable material development.

Electrochromic windows with fast response and wide dynamic range for visible-light modulation without traditional electrodes

Electrochromic (EC) devices represent an emerging energy-saving technology, exhibiting the capability to dynamically modulate light and heat transmittance. Despite their promising potential, the commercialization of EC devices faces substantial impediments such as high cost, intricate fabrication process, and low optical contrast inherent in conventional EC materials relying on the ion insertion/extraction mechanism. In this study, we introduce an innovative “electrode-free” electrochromic (EC) device, termed the EECD, which lacks an EC-layer on the electrodes during device assembling and in the bleached state. This device features a simplified fabrication process and delivers superior optical modulation. It achieves a high optical contrast ranging from 68-85% across the visible spectrum and boasts a rapid response time, reaching 90% coloring in just 17 seconds. In addition, EECD exhibits stable cycling for over 10,000 cycles without noticeable degradation and maintains functionality across a broad temperature range (0 °C to 50 °C). Furthermore, the fabricated large-area devices (40 cm × 40 cm) demonstrate excellent tinting uniformity, suggesting excellent scalability of this approach. Our study establishes a paradigmatic breakthrough for EC smart windows.

Self-powered electrochromic smart window helps net-zero energy buildings

Net-zero energy buildings are becoming an important energy-saving and low-carbon technology for global environmental protection and resource conservation. As the least energy-efficient building components, windows have promoted the development of electrochemically light/thermal management, where smart windows without external electrical supplies are highly desired for net-zero energy buildings. Here, we develop a self-powered electrochromic smart window system to regulate solar radiation transmittance, constructed by a triboelectric nanogenerator (TENG) and a high-performance electrochromic device. The visible–near-infrared (VIS-NIR) dual-band electrochromic device is well-designed based on an eco-friendly low-energy demand phenothiazine redox ionic liquid, demonstrating a fast switching response of ﹤1.9 s, a large transmittance modulation of >51.8 %, and outstanding electrochemical durability (5.5 % attenuation after 4000 cycles). Upon continuous pressing/releasing motions, the integrated TENG-powered electrochromic smart window (TECSW) displays a prompt light/thermal management behavior with desirable privacy preservation performance (transmittance modulation of 51 % in the visible region) and excellent thermal management property (12.3 °C reducti°n). The whole-building energy simulations show that TECSW can save 347.79 MJ/m2yr (amounting to 96.60 kWh/m2yr) of operational Heating Ventilation Air Conditioning (HVAC) warming/cooling energy consumption among 34 cities in China, accounting for 17.25 % of the total energy consumption. This research provides new insight into designing green and energy-efficient smart windows for net-zero energy buildings.

Continuous Solar Energy Conversion Windows Integrating Zinc Anode-Based Electrochromic Device and IoT System.

Integration of solar cells and electrochromic windows offers crucial contributions to green buildings. Solar-charging zinc anode-based electrochromic devices (ZECDs) present opportunities for addressing the solar intermittency issue. However, the limited energy storage capacity of ZECDs results in wasted harnessing of solar energy as well as overcharging. Herein, spectral-selective dual-band ZECDs that continuously transport solar energy to indoor appliances by remotely controlling the repeated bleached-tinted cycles during the daytime, are reported. Hexagonal phase cesium-doped tungsten bronze (h-Cs0.32WO3, CWO) nanocrystals are adopted for dual-band ZECDs due to their independent control ability of near-infrared (NIR) and visible (VIS) light transmittance (∆T=73.0%, 700nm; ∆T = 83.7%, 1200nm) and excellent cycling stability (0.8% optical contrast decay at 1200nm after 10000 cycles). The prototype device (i.e., CWO//Zn//CWO) delivers extraordinary thermal insulation capability, displaying a 10°C difference between "bright" and "dark" modes. Furthermore, an Internet of Things (IoT) controller to control the NIR and VIS lights of the CWO//Zn//CWO window wirelessly with a smartphone, empowering the continuous discharging of the solar-charged window during the daytime remotely, is developed. Such windows represent an intriguing potential technology whose future impact on green buildings may be substantial.

Ultra-fast switching of energy efficient electrochromic nickel oxide thin films for smart window applications

In today's modern world, energy consumption continues to escalate. In such cases, smart windows play a crucial role in reducing energy consumption and enhancing the quality of life. Electrochromic devices (ECDs) -based smart windows rely profoundly on nickel oxide (NiO) thin films, which act as a counter electrode in ECDs. This work aims to fabricate NiO thin films, with the intention of achieving ultrafast ECD. Through the sputtering technique, energy-efficient ECD is obtained with the highest optical modulation of 60 % at a rapid switching speed of 0.55s for bleaching and 0.95s for coloration. We have also investigated the structural, morphological, vibrational, and optical properties of NiO thin films. XRD analysis revealed the less crystalline or near amorphous nature of NiO thin film. XPS, PL, and Raman studies confirm the existence of defects in the film. The favourable, less crystalline nature, along with the presence of defects, facilitates ultra-fast ion intercalation and de-intercalation process. We believe that prepared NiO film can be used as a promising anodic colourant in electrochromic smart windows with applications in energy-efficient buildings.

Design and Implementation of Electrochromic Smart Windows with Self-Driven Thermoelectric Power Generation.

Electrochromic smart windows can achieve controllable modulation of color and transmittance under an external electric field with active light and thermal control capabilities, which helps reduce energy consumption caused by building cooling and heating. However, electrochromic smart windows often rely on external power circuits, which greatly affects the independence and portability of smart windows. Based on this, an electrochromic smart window driven by temperature-difference power generation was designed and implemented. This smart window provides automatic and manual control of the reversible cycle of electrochromic glass from light blue to dark blue according to user requirements and changes in the surrounding environment, achieving adaptive adjustment of visual comfort and reducing energy consumption. The infrared radiation rejection (from 780 to 2500 nm) of the electrochromic smart window is as high as 77.3%, and its transmittance (from 380 to 780 nm) fluctuates between 39.2% and 56.4% with changes in working state. Furthermore, the temperature in the indoor simulation device with electrochromic glass as the window was 15 °C lower than that with ordinary glass as the window after heating with a 250 W Philips infrared lamp for ten minutes. After 2000 cycles of testing, the performance of the smart window was basically maintained at its initial values, and it has broad application prospects in buildings, vehicles, and high-speed rail systems.