Electrochromic Windows Research Articles

Insights into the deposition of nanostructured nickel oxides by amino acid chelated Complexes: Benefits of mixed side chains in the formation of nanostructures for Energy-efficient Electrochromic windows

Electrochromic (EC) windows enhance the energy efficiency of climate control systems in the building sector. Here, we evaluate a strategy for electrodeposition of a high-performance EC nickel oxide by controlled release of Ni(II) ions from amino acid ligands. We compare the structural properties and EC characteristics of the samples deposited from Ni(II)-L-alanine or Ni(II)-phenylalanine complexes. During the deposition process, a film containing closely packed nanodeposits was formed by rapid release of Ni(II) ions from L-alanine ligands. This structure led to a high coloration efficiency of 76.4 cm2/C and nearly 100% retention of the initial optical modulation value even after 60 cycles of coloration. In contrast, the slow release of Ni(II) ions from phenylalanine ligands resulted in the formation of conglomerated island structures, which caused a low coloration efficiency and poor cycling stability. However, the bulky aromatic side chains on phenylalanine could passivate the sample surface, thereby lowering the transmittance loss to 1.38% under 24 h voltage-off. The aromatic side chains also contributed to the charge transfer between the solid–liquid interface of the sample. Furthermore, the sample deposited from the mixed L-alanine and phenylalanine complexes show greatly improved EC performance without compromising its superior optical memory and fast charge transfer characteristics.

Biomimetic adaptive electrochromic windows for enhancing building energy efficiency

The concept of bioinspiration, which is a new design paradigm inspired by solutions found in biological systems, has led to many innovative designs in different fields in recent years. This study presents the design of biomimetic adaptive façade (BAF) to enhance the energy efficiency of buildings, which approximately accounts for 40% of the global energy consumption. A comprehensive analysis was conducted to identify the similarities between the mechanism of electrochromic window and chameleon’s skin. From that, the design of the BAF system was proposed based on the bioinspired analogy. In addition, a building energy modeling software (EnergyPlus), a Python package (Eppy toolkit), and a decision-making assistance tool were integrated into a computational tool to support the design and evaluate the feasibility of BAF systems. A medium office building was used as a case study to validate the capability of the proposed approach for two weather conditions in Melbourne, Australia, and Texas, United State. The results show that the proposed BAF can reduce energy consumption by 9.3–23.5% and 14.6–19.6% for Melbourne and Texas, respectively, compared to the benchmarking facades. The effect of window-to-wall ratio and orientation of the BAF system on the energy-efficiency and cost-efficiency of buildings were also investigated. The results confirm the potential of BAF in improving building energy efficiency.

Electrochromic Properties of PANI/TiO2 Nanocomposite Films Prepared by Electropolymerization

PANI/nc-TiO2/ITO composite films were prepared by electrochemical method where the monomer aniline was polymerized onto nano-porous TiO2/ITO films (PANI/nc-TiO2/ITO). The PANI/nc-TiO2 heterojunctions were formed in the composite films due to the insertion of PANI in nano-porous TiO2 particles. PANI/ITO films exhibited a reversible electrochromic display (ECD) performance when cycled in 0.1M LiClO4 + propylene carbonate. The response times of the electrochromic coloration and bleaching of the PANI/nc-TiO2/ITO electrode were 15 s and 20 s, respectively. Electrochromic efficiency of the films reached a value as large as 12.25 cm2´C-1. Taking advantage of the large EC efficiency and electrochemical stability as well as the simplicity of the fabrication process, PANI/nc-TiO2 composite films can be used for preparation of electrochromic smart windows, in term of the large-area production in particular.

Adhesive electrochromic WO3 thin films fabricated using a WO3 nanoparticle-based ink

Nanotechnology has advanced rapidly in recent years, mainly due to the unique properties of basic elements, which can be tuned by altering their chemical composition and size. Owing to their unique properties, nanoparticles (NPs) are applied in many fields, such as catalysis, electronics, and coatings. In this study, we synthesized a coatable WO3 NP dispersed ink and aimed to highlight the importance of developing an appropriate design strategy for achieving optimal physicochemical properties of the inks. Polyvinyl alcohol (PVA) was added to the WO3 NP ink to improve its adhesion to indium tin oxide-coated glass substrates. The contact angle of the inks on the substrate decreased with the addition of PVA, indicating their good wettability. Furthermore, the WO3 NP films exhibited an excellent transmittance change of 77 % at 633 nm and a coloration efficiency of 35 cm2/C. Their optical transmittance in the visible and near-infrared regions varied with the applied voltage, indicating their potential for applications in electrochromic devices and smart windows.

High optical contrast and radiant heat blocking properties of hierarchically structured electrodes for electrochromic windows

To prepare the electrochromic electrode, a hierarchical structure of ZnO nanorods (2s-ZnR) was grown via the two-step hydrothermal process and used to mitigate electron scattering and improve the optical transmittance of the electrodes. Compared to the electrode with 1s-ZnR, a 36.6% increase in ΔT% (an increase from 24.3 to 33.2) along with fast coloring and bleaching processes (time reduced by 0.4 and 0.6 s, respectively) were achieved with the 2s-ZnR structured electrode. When an optimal sp-WO3 thickness was prepared, the Hier-electrode with a double-hierarchical structure of dip-WO3/sp-WO3/2s-ZnR exhibited a high ΔT% of 50.8, compared to 41.7 and 33.8 analyzed from the Sput- and Dip-electrodes, respectively. When the voltage was switched, the Hier-electrode responded quickly, with tc of 12.7 s and tb of 3.8 s. Moreover, when the heat-irradiation time was extended from 60 to 150 s, the temperature of Hier-electrode only slightly increased by 8.15%. Clearly, the Hier-electrodes exhibit a high contrast ratio, fast response, and high radiant heat blocking capability, which has high potential for smart window applications.

Stable and multicolored electrochromic device based on polyaniline-tungsten oxide hybrid thin film

In this study, tungsten oxide (WO3) film was used to enhance the stability as well as the performance of electrochromic window (ECW) based on famous conductive polymer-polyaniline (PANI). PANI and WO3 films were prepared and employed to fabricate hybrid ECW with an unprecedented stability (over 1000 cycles) and more colorful device with various color (green, blue, and violet of neat PANI, and deep blue of WO3). The multicolor nature of device maybe due to the simultaneous change of the band gaps of both PANI and WO3 in the reversible redox process. The present device based on the PANI-WO3 hybrid film shows superior electrochromic performance compare with that of neat PANI film. A short switching time (1.5 s each for colored and bleached processes), a high coloration efficiency (195 cm2 C−1), a prolonged lifetime (over 1000 cycles) and multicolor are the significant advantages of the PANI-WO3 hybrid film. The result indicates that ECW based on PANI-WO3 hybrid film is great candidate for next generation of electrochromic device such as electronic display and smart window.

Portable Photovoltaic-Self-Powered Flexible Electrochromic Windows for Adaptive Envelopes

Variable transmission applications for light control or energy saving based on electrochromic materials have been successfully applied in the past in the building, sports, or automotive fields, although lower costs and ease of fabrication, installation, and maintenance are still needed for deeper market integration. In this study, all-printed large area (900 cm2 active area) flexible electrochromic devices were fabricated, and an autoregulating self-power supply was implemented through the use of organic solar cells. A new perspective was applied for automotive light transmission function, where portability and mechanical flexibility added new features for successful market implementation. Special emphasis was placed in applying solution-based scalable deposition techniques and commercially available materials (PEDOT-PSS as an electrochromic material; vanadium oxide, V2O5, as a transparent ion-storage counter electrode; and organic solar modules as the power supply). A straightforward electronic control method was designed and successfully implemented allowing for easy user control. We describe a step-by-step route following the design, materials optimization, electronic control simulation, in-solution fabrication, and scaling-up of fully functional self-powered portable electrochromic devices.

Movable window insulation as an instantiation of the adaptive building envelope: An investigation of its cost-effectiveness in the U.S

Improving the performance of building envelope is essential to energy conservation and emission reduction. Adaptive building envelope (ABE) has the potential to effectively reduce building energy consumption at a lower cost. Movable window insulation is an instantiation of the ABE with great application potential in buildings, but it has not been systematically studied. Trying to fill this gap, this paper proposes an automatic control system and a manual control rule for movable window insulation. The energy consumption of double-glazed windows, triple-glazed windows, movable insulation with automatic/manual control, and electrochromic windows is compared in different scenarios using building energy simulation (BES). In some scenarios, the optimal solar heat gain coefficient (SHGC) for windows with movable insulation is higher than that required by the building code. Triple-glazed windows are only effective in reducing the heating energy, while electrochromic windows are only effective in reducing the cooling energy. Infiltration has a great impact on the performance of movable insulation. The net preset value (NPV) analysis shows that movable insulation has a great application potential in Minneapolis, Atlanta, and Phoenix, while triple-glazed windows are only viable in some cases in Minneapolis. Electrochromic windows are not a profitable investment at their current prices.

Effect of electrochromic windows on energy consumption of high-rise office buildings in different climate regions of Iran

Traditional windows cannot adapt to external and internal environmental conditions. Smart windows are the next generation of windows, which can change their thermal and optical properties to control indoor environmental conditions. Electrochromic (EC) windows can control solar energy and provide visual comfort. These windows can be used with other tools such as various glazing types, building integrated photovoltaic (BIPV) and building energy management system (BEMS). This paper aims to evaluate the effect of EC windows, various glazing types, BIPVs and BEMS on energy consumption of high-rise office buildings. A model was created and several inputs were entered into the model. Then, annual simulations evaluated the effect of EC windows and other parameters on energy consumption of the building in four climate conditions of Iran. First, the effect of EC windows and various glazing types on energy consumption of the building were identified separately. Afterward, 12 different scenarios were defined to evaluate the effect of using both EC windows and optimal glazing type on energy consumption of the building. Then, BIPVs were combined with EC windows and photovoltachromic (PVC) windows were modeled using inputs of EC windows and BIPVs. In the end, BEMS was combined with PVC windows and had a positive effect on energy consumption of the building in all climate conditions. Finally, simulation results indicated that energy consumption of the building reduced up to 35.57% using EC windows and other tools. The difference between simulation and actual results is predicted to be at least 1.60% and maximum 6.22%.

Optimal Window to Wall Ratio Ranges of Photovoltachromic Windows in High-Rise Office Buildings of Iran

Windows are one of the weakest building components concerning high thermal losses. Traditional windows cannot adapt to external and internal environmental conditions. On the other hand, smart windows such as electrochromic (EC) windows do not emit greenhouse gases and adapt to environmental conditions and increase indoor environmental quality. The combination of EC windows and building integrated photovoltaic system (BIPV) is called photovoltachromic (PVC) windows. This paper aims to find optimal window to wall ratio (WWR) ranges of PVC windows in a high-rise office building model in four different cities in Iran. This paper uses several simulations to find the optimal WWR ranges of PVC windows using Radiance and EnergyPlus. First, the minimum acceptable WWR value in each climate condition was identified using several simulations without any optimization tools. Afterward, traditional windows were replaced with EC windows and results indicated that energy consumption of the building reduced up to 15.94%. In the next stage, BIPV was combined with EC windows, and results indicated that BIPV reduced energy consumption of the building up to 7.55%. Finally, simulation results showed that PVC windows reduced energy consumption of the building up to 16.31% in Kermanshah, 19.69% in Tehran, 18.59% in Yazd and 17.36% in Bandar Abbas. Also, the optimal WWR range of PVC windows in Kermanshah was 80-90%, while it was 70-80% in Tehran, Yazd and Bandar Abbas. Simulation results indicated that cooling degree days (CDD) of the site, where buildings were located, effected on the optimal WWR range of PVC windows in high-rise office buildings. An analytical approach was used to validate simulation results, and it showed that simulation results had 1.60-6.22% error.

Integrating exceptional visible modulation, near-infrared shielding and energy storage in an all-solid-electrochromic bilayer device

A generic strategy of incorporating diverse functions in electrochromic dynamic windows is presented by sensibly choosing the individual layers of a bilayered active electrode. Here, all-solid electrochromic devices (ECD) with a remarkably high visible modulation (60–80%) and superior near-infrared (NIR) shielding performance (>90% full scale) were fabricated by simple solution-processing. The concept is demonstrated by selecting materials with identical chemical composition, i.e., porous amorphous-WO3 (a-WO3) coated on top of polycrystalline WO3·H2O nanosheets. These ECDs show four distinct voltage-selective modes in the ± 2.8 V range for enhanced privacy and energy saving. The IR modulation efficiency (IRME) of the devices stands at a record ~85%, with an outstanding solar modulation efficiency (SME) of ~63%. The initial energy storage estimations for the ECDs revealed superior volumetric stored charge density of ~400 Ccm−3@ 10 mVs−1, which is excellent for secondary energy sourcing. The fabricated EC glasses (with 50% usage) could directly save ~165 kWhm-2 yr-1 worth of energy by equating the energy-saving and generation. With reflected radiation reduction, the total saving may surpass the total energy generation from standard Si-Solar cells (~18% efficiency) of equal areal coverage.

Reflections on surface morphology

Electrochromic windows can reduce buildings’ energy demand and improve occupants’ comfort, yet they struggle to fully meet market needs. Now, researchers demonstrate that polymer additives improve light and solar heat modulation of reflective electrochromic windows, with potential for durable, large-scale and low-cost manufacturing.

Enhancing energy efficiency and comfort in buildings through model predictive control for dynamic façades with electrochromic glazing

Reducing building energy consumption while ensuring indoor comfort conditions is driving the building envelope transition from static to responsive . In this context, electrochromic windows represent a promising solution to manage optical and thermal requirements in response to changing boundary conditions or user requirements, and control strategies play a central role in the exploitation of this technology. The present paper proposes a Hybrid Model Predictive Control strategy for the online operation optimization of an electrochromic-based active façade . The controller was implemented and tested on a simulated case study. This was achieved by co-simulating the optimal controller which used reduced data-driven grey-box model, with a high accuracy white-box physical model. This setup enabled to close the control loop and to perform an accurate performance benchmarking. Results showed that the proposed Hybrid Model Predictive Control strategy outperformed two baseline Rule Based Controllers, reducing simultaneously energy consumption, peak power and percentage of discomfort hours by up to 82%, 71% and 51% respectively. In comparison with the two baseline controllers and considering all the scenarios, the overall energy consumption could be reduced by approximately 40%–60% on average. In addition the work demonstrates how tuning the Hybrid Model Predictive Control weights adds flexibility to the controller, significantly changing its behaviour to meet the requirements of the designer. • A test cell equipped with a switchable electrochromic window was modelled. • A grey-box model of the zone and window was developed and calibrated. • A Hybrid Model Predictive Control strategy was formulated for the window control. • A comprehensive controller performance benchmarking was performed.

Strong coloration of nanoporous tungsten oxides by in-vacuo lithiation for all-solid-state electrochromic devices

Electrochromic windows allow for an improved management of solar heat gains in buildings and enhanced visual comfort of building users. All-solid-state electrochromic devices can be especially durable. During their fabrication lithium has to be inserted, preferably in-vacuo. For such a dry lithiation process it is essential to determine to which extent sufficiently thick electrochromic layers can be colored and with which efficiency. In this study, we focus on the dry lithiation of sputtered nanoporous tungsten trioxide films and the induced optical response. The porosity of the WO3 films was in the order of 18 %, as determined from variable angle spectroscopic ellipsometry and effective medium approximation. Films with a thickness above 1 µm were dry-lithiated yielding a deep coloration, with a lithiation efficiency LE up to 1.5⋅106 cm2⋅mol−1. Hereby the light transmittance was reduced from 85.7% to 2.0%, with the spectral transmittance approaching 0% in the range from 600 nm to 1500 nm. These results suggest that lithium can diffuse over a large distance in nanoporous WO3. The columnar morphology and nanoporous structure of the thin films deposited at high working pressure is beneficial for the displacement of the lithium ions. All-solid-state devices were prepared using in-vacuo lithiation, tantalum pentoxide as a solid electrolyte and nickel oxide as a counter electrode. During cycling the solar transmittance varied between 8 % and 52 % and the light transmittance from 7.8% to 53.1%, the latter with a coloration efficiency CE up to 63 cm2⋅C−1. Accordingly, switching times of 17 s for coloration and 13 s for bleaching were determined. The gained insights are of high practical relevance for the fabrication of all-solid-state electrochromic devices.

Sol-Gel coated WO3 thin films based complementary electrochromic smart windows

The WO3 films were prepared via sol- gel dip coating method. The optical, structural, morphological, electrochemical and electrochromic properties of the prepared films were studied. The WO3 film coated on glass substrate exhibits 74% transmission at 550 nm. XRD studies indicate the WO3 films in the amorphous state. FTIR spectrum confirms the formation of WO3. The FESEM image confirms the formation of smooth surface. The cyclic voltammetric study reveals the anodic/cathodic diffusion coefficients of 2.31/4.79 × 10−12 cm2/s for WO3 films. The film thickness was about 260 nm. The same film shows a change in optical transmission of 55.37% at 550 nm. The sol–gel coated WO3 films were used to develop the complementary electrochromic smart windows in conjugation with NiO and Ni0.95Co0.05O as an anode. A five layered EC windows were developed and studied with Li+ and H+ conducting gel electrolytes.

Redox targeting of energy materials

The redox-mediated electrochemical–chemical process, when it involves the redox-targeting reaction with energy materials, has shown intriguing potential for various energy-related applications. This review starts with a brief discussion on the evolution of redox-targeting reactions for high-energy redox-flow batteries and the critical future studies for large-scale energy storage. Then, with spatially decoupled water electrolysis as an example, the merits of redox-targeting reaction by liberating the catalyst from electrode surface are highlighted, followed by an introduction of redox targeting–based thermal-to-electrical conversion. We have also featured various redox-targeting processes in other fields of study, such as electrochromic window, redox catalysis, and spent battery material recycling. Overall, this review attempts to demonstrate the incredible versatility and prospects of redox-targeting process for energy-related applications.

Transparent-to-black electrochromic smart windows based on N, N, N′, N′-Tetraphenylbenzidine derivatives and tungsten trioxide with high adjustment ability for visible and near-infrared light

N,N,N′,N′-tetraphenylbenzidine (TPB) and N,N,N′,N′-tetra(p-tolyl)benzidine (TPB-4Me), were synthesized. Their optoelectrochemical and electrochromic properties were discussed. Both TPB and TPB-4Me exhibited a reversible color change between colorless and dark-green under applied bias voltages. Furthermore, TPB or TPB-4Me and ethyl viologen (EV) or tungsten trioxide (WO3) were used as anode and cathode electrochromic materials, respectively; a series of color complementary ambipolar gel electrochromic devices (ECDs), ECD-3, ECD-4, ECD-5, and ECD-6, were fabricated and investigated. All of ambipolar ECDs displayed reversible color changes between transparent and black under different voltages. In addition, they exhibited high optical contrast in both visible and near-infrared regions; their corresponding optical contrasts were 74.6%, 87.9%, 78.2%, and 78.5% at 750 nm, respectively. In comparison, ECDs based on WO3 exhibited higher optical contrast (in near-infrared region) and shorter bleaching time than ECDs based on EV. The optical contrasts of ECD-5 and ECD-6 based on WO3 were greater than 57.6% and 54.0% in the wavelength range of 420–1000 nm, respectively. Their corresponding coloring/bleaching times were found to be 6.6 s/21.7 s and 6.0 s/24.6 s, respectively. The transparent-to-black attributes of these ambipolar ECDs are promising for electrochromic smart windows.

Local Substrate Heterogeneity Influences Electrochemical Activity of TEM Grid-Supported Battery Particles.

Understanding how particle size and morphology influence ion insertion dynamics is critical for a wide range of electrochemical applications including energy storage and electrochromic smart windows. One strategy to reveal such structure–property relationships is to perform ex situ transmission electron microscopy (TEM) of nanoparticles that have been cycled on TEM grid electrodes. One drawback of this approach is that images of some particles are correlated with the electrochemical response of the entire TEM grid electrode. The lack of one-to-one electrochemical-to-structural information complicates interpretation of genuine structure/property relationships. Developing high-throughput ex situ single particle-level analytical techniques that effectively link electrochemical behavior with structural properties could accelerate the discovery of critical structure-property relationships. Here, using Li-ion insertion in WO3 nanorods as a model system, we demonstrate a correlated optically-detected electrochemistry and TEM technique that measures electrochemical behavior of via many particles simultaneously without having to make electrical contacts to single particles on the TEM grid. This correlated optical-TEM approach can link particle structure with electrochemical behavior at the single particle-level. Our measurements revealed significant electrochemical activity heterogeneity among particles. Single particle activity correlated with distinct local mechanical or electrical properties of the amorphous carbon film of the TEM grid, leading to active and inactive particles. The results are significant for correlated electrochemical/TEM imaging studies that aim to reveal structure-property relationships using single particle-level imaging and ensemble-level electrochemistry.

The Effects of Chromophore Halogenation on the Stability of UV‐Absorbing Organic Solar Cells

AbstractTransparent photovoltaics that harvest ultraviolet photons are promising point‐of‐use power sources for lower power applications, such as electrochromic windows that regulate the flow of visible and infrared photons for lighting and temperature regulation. Organic photovoltaic cells employing contorted hexabenzocoronene (cHBC) and its derivatives as chromophores have shown promise for transparent solar cells due to their high open‐circuit voltages, large‐area scalability, and high photoactive layer transparency. Here, the operational stability of such devices is investigated and it is found that the solar cell active layers that include peripherally halogenated chromophores undergo rapid morphological degradation during operation, while control cells employing cHBC and other non‐halogenated derivatives as donors with archetype C70 as an acceptor are highly stable. This study suggests halogenation of chromophores can play an outsized role in determining the operational stability of devices comprising them, which should be considered during the molecular design process.

Flexible electrochromic and thermochromic hybrid smart window based on a highly durable ITO/graphene transparent electrode

Abstract A flexible smart window with electrochromic (EC) and thermochromic (TC) properties is fabricated on a highly durable transparent indium-tin oxide (ITO)/graphene/polyethylene terephthalate (PET) electrode. An amorphous WO3 film and crystalline VO2 film are used as the EC and TC material, respectively, in the device. The ITO film deposited via atomic layer deposition acts as a protective layer and suppresses the plasma-induced damage of graphene, which typically occurs during the sputtering process. In this device, the amorphous WO3 film undergoes cathodic electrochromic reactions with high coloration efficiency, while the crystalline VO2 film shows characteristic thermochromic behavior. Thus, the flexible EC–TC hybrid smart window shows the controlled transmission of optical and solar energies according to the surrounding temperature and the applied voltage, allowing selective modulation of the visible and near-infrared light. The flexible EC–TC hybrid device is also very stable under mechanical bending, owing to the robust adhesion of the ITO film on the graphene support and the reduced plasma-induced damage of graphene. The fabricated high-performance, durable ITO/graphene/PET transparent electrode can pave the way for next-generation flexible optoelectronic devices as well as multifunctional flexible smart windows.