Smart Window Technology Research Articles

Electrophoretic deposition of reduced graphene oxide thin films for reduction of cross-sectional heat diffusion in glass windows

Abstract Effective management of heat transfer, such as conduction and radiation, through glass windows is one of the most challenging issues in smart window technology. In this work, reduced Graphene Oxide (rGO) thin films of varying thicknesses are fabricated onto Fluorine-doped Tin Oxide (FTO) glass via electrophoretic deposition technique. The sample thicknesses increase with increasing number of deposition cycles (5, 10, 20 cycles). It is hypothesized that such rGO thin films, which are well-known for their high thermal conductivities, can conduct heat away laterally towards heat sinks and reduce near-infrared (NIR) transmittance through them, thus effectively slowing down the temperature increment indoors. The performance of rGO/FTO in reducing indoor temperatures is investigated with a solar simulator and a UV-Vis-NIR spectrophotometer. The 20-cycles rGO thin films showed 30% more NIR blocked at 1000 nm as compared to clean FTO, as well as the least temperature increment of 0.57 °C following 30 min of solar irradiation. Furthermore, the visible transmittance of the as-fabricated rGO films remain on par with commercial solar films, enabling up to 60% of visible light transmittance for optimal balance of transparency and heat reduction. These results suggest that the rGO thin films have great potential in blocking heat transfer and are highly recommended for smart window applications.

Efficient Near Infrared Modulation with High Visible Transparency Using SnO2–WO3 Nanostructure for Advanced Smart Windows

AbstractRenewable energy technology and effective energy management are the most crucial factors to consider in the progress toward worldwide energy sustainability. Smart window technology has a huge potential in energy management as it assists in reducing energy consumption of indoor lighting and air‐conditioning in buildings. Electrochromic (EC) materials, which can electrically modulate the transmittance of solar radiation, are one of the most studied smart window materials. In this work, highly transparent SnO2 inverse opal (IO) is used as the framework to electrochemically deposit amorphous WO3 layer to fabricate hybrid SnO2–WO3 core–shell IO structure. The hybrid structure is capable of effective near infrared (NIR) modulation while maintaining high visible light transparency in the colored and bleached states. By varying the initial diameter of the polystyrene (PS) opal template and the WO3 electrodeposition time, optimal results can be obtained with the smallest PS diameter of 392 nm and 180 s WO3 electrodeposition. In its colored state, the 392‐SnO2–WO3‐180 core–shell IO structure shows ≈70% visible light transparency, 62% NIR blockage at 1200 nm, and ≈15% drop in NIR blocking stability after 300 cycles. The SnO2–WO3 core–shell IO structure in this study is a promising EC material for advanced smart window technology.

Electrodeposition of amorphous WO3 on SnO2-TiO2 inverse opal nano-framework for highly transparent, effective and stable electrochromic smart window.

In recent years, there has been significant advancement in smart window technologies due to their effectiveness in reducing energy consumption of indoor lighting and air-conditioning in buildings. Electrochromic (EC) materials, in particular, have been widely studied as they provide a simple method for tuning or modulating visible light and infrared (IR) transmittance. In this work, a novel hybrid, multi-layered SnO2–TiO2–WO3 inverse opal (IO) nanostructure has been fabricated via dip-coating and electrodeposition process. This hybrid nanostructure allows an electrochromic smart window for effective near infrared (NIR) modulation, with high visible transparency and durable EC cycling stability. The visible transparency of as-fabricated hybrid multi-layered SnO2–TiO2–WO3 IO was measured to be in the range of 67.2–88.0% in the bleached state and 67.0–74.4% in the colored state, respectively. Furthermore, the hybrid nanostructure is also able to modulate up to 63.6% NIR radiation at the wavelength of 1200 nm and maintain approximately 82.6% of its NIR blockage capability after 750 reversible cycles. The hybrid multi-layered SnO2–TiO2–WO3 IO nanostructure in this study can potentially be an effective and stable EC material for advanced smart window technology.

Development of Tungsten Trioxide Using Pulse and Continuous Electrodeposition and Its Properties in Electrochromic Devices

To develop an economical, efficient, and highly stable electrode having high transmittance modulation, thin films of tungsten trioxide (WO3) were deposited on an Indium-doped tin oxide (ITO) glass substrate by using simple one-step pulse voltage electrodeposition (PVE) and continuous voltage electrodeposition (CVE) routes. Electrochemical and optical analyses demonstrated that the WO3 electrode prepared by PVE possessed high switching speed, high coloration efficiency, and excellent cyclic stability. Moreover, its stable performance in the colored state extended for a long duration even after the voltage was cutoff. The coloration efficiency values were determined to be 69.00 and 43.00 cm2/C for W-PVE-600s and W-CVE-200s, respectively. The excellent electrochemical and electrochromic properties were mainly attributed to large surface area of W-PVE-600s, which facilitated charge transfer and promoted insertion/exertion of H+ ions in electrolytes better than the WO3 electrode prepared by conventional methods. The significant electrocatalytic activity and stable performance have proved that the proposed W-PVE-600s film can be an alternative to conventional electrodes used in smart window technology applications.

Emerging Thermal‐Responsive Materials and Integrated Techniques Targeting the Energy‐Efficient Smart Window Application

AbstractArchitectural windows that smartly regulate indoor solar radiation by changing their optical transmittance in response to thermostimuli are developed as a promising solution toward reducing the energy consumption of buildings. Recently, energy‐efficient smart window technology has attracted increasing scientific interest, with the exploration of energy‐efficient novel materials as well as integration with practical techniques to generate various desired multifunctionalities. This review systematically summarizes emerging thermoresponsive materials for smart window applications, including hydrogels, ionic liquids, perovskites, metamaterials, and liquid crystals. These are compared with vanadium dioxide (VO2), a conventional and extensively studied material for thermochromic smart window applications. In addition, recent progress on cutting‐edge integrated techniques for smart windows is covered, including electrothermal techniques, self‐cleaning, wettability, and also integration with solar cells for bifunctional energy conservation and generation. Finally, opportunities and challenges relating to thermochromic smart windows and prospects for future development are discussed.

Electro-Optical Device with Tunable Transparency Using Colloidal Core/Shell Nanoparticles

Suspended particle devices (SPDs) adapted for controlling the transmission of electromagnetic radiation have become an area of considerable focus for smart window technology due to their desirable properties, such as instant and precise light control and cost-effectiveness. Here, we demonstrate a SPD with tunable transparency in the visible regime using colloidal assemblies of nanoparticles. The observed transparency using ZnS/SiO2 core/shell colloidal nanoparticles is dynamically tunable in response to an external electric field with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby modifies the photonic band structures, as confirmed by the finite-difference time-domain simulations of Maxwell’s equations. The transparency of the device can also be manipulated by changing the particle size and the device thickness. In addition to transparency, structural colorations and their dynamic tunabilit...

Dual-Band Modulation of Visible and Near-Infrared Light Transmittance in an All-Solution-Processed Hybrid Micro-Nano Composite Film.

Smart windows with controllable visible and near-infrared light transmittance can significantly improve the building's energy efficiency and inhabitant comfort. However, most of the current smart window technology cannot achieve the target of ideal solar control. Herein, we present a novel all-solution-processed hybrid micronano composite smart material that have four optical states to separately modulate the visible and NIR light transmittance through voltage and temperature, respectively. This dual-band optical modulation was achieved by constructing a phase-separated polymer framework, which contains the microsized liquid crystals domains with a negative dielectric constant and tungsten-doped vanadium dioxide (W-VO2) nanocrystals (NCs). The film with 2.5 wt % W-VO2 NCs exhibits transparency at normal condition, and the passage of visible light can be reversibly and actively regulated between 60.8% and 1.3% by external applied voltage. Also, the transmittance of NIR light can be reversibly and passively modulated between 59.4% and 41.2% by temperature. Besides, the film also features easy all-solution processability, fast electro-optical (E-O) response time, high mechanical strength, and long-term stability. The as-prepared film provides new opportunities for next-generation smart window technology, and the proposed strategy is conductive to engineering novel hybrid inorganic-organic functional matters.

Time-Dependent Density Functional Computations of the Spectrochemical Properties of Dithiolodithiole and Thiophene Electrochromic Systems.

The importance of organic electrochromic materials has grown considerably in recent decades due to their application in smart window, automotive, and aircraft technologies. Theoretical prediction of the optical properties should contribute to their better characterization and help the explanation of the experimental data. By using various exchange–correlation functionals, we show how density functional theory (DFT) and the related time-dependent formulation (TDDFT) are able to correctly reproduce the spectrochemical properties of dithiolodithiole and thiophene organic electrochromic systems.

(Invited) Durability of Electrochromic Films: Aging Kinetics and Rejuvenation

A major challenge for energy-efficient smart window technology is to ensure the durability of electrochromic (EC) devices over a service life of more than 20 years. In this paper, we report recent results from a fundamental study of the aging kinetics of EC tungsten oxide and nickel oxide thin films and describe electrochemical rejuvenation mechanisms that are able to restore the films to their initial state. The aging kinetics displays an approximate power-law decrease of the charge capacity as a function of cycle number. This decay of charge capacity can be understood in terms of models built on so-called dispersive chemical kinetics. Tungsten oxide and nickel oxide EC films can be rejuvenated by applying a high electrochemical potential or a small constant current. Trapped ions in the bulk or at the surface of the films can be released by these procedures.

Pairing of near-ultraviolet solar cells with electrochromic windows for smart management of the solar spectrum

Current smart window technologies offer dynamic control of the optical transmission of the visible and near-infrared portions of the solar spectrum to reduce lighting, heating and cooling needs in buildings and to improve occupant comfort. Solar cells harvesting near-ultraviolet photons could satisfy the unmet need of powering such smart windows over the same spatial footprint without competing for visible or infrared photons, and without the same aesthetic and design constraints. Here, we report organic single-junction solar cells that selectively harvest near-ultraviolet photons, produce open-circuit voltages eclipsing 1.6 V and exhibit scalability in power generation, with active layers (10 cm2) substantially larger than those typical of demonstration organic solar cells (0.04–0.2 cm2). Integration of these solar cells with a low-cost, polymer-based electrochromic window enables intelligent management of the solar spectrum, with near-ultraviolet photons powering the regulation of visible and near-infrared photons for natural lighting and heating purposes. Smart windows are used to regulate the amount of visible and near-infrared light entering buildings or cars. Here, Davy et al. develop near-UV harvesting organic solar cells, scalable up to 10 cm2, for powering electrochromic windows without competing for photons in the visible or near-infrared.

(Invited) Durability of Electrochromic Films: Ageing Kinetics and Rejuvenation

A major challenge for energy-efficient smart window technology is to ensure the durability of electrochromic (EC) devices over a service life of more than 20 years. Hence, their degradation under operating conditions must be better understood and preferably avoided. In this paper we review our recent results from a fundamental study of the ageing kinetics of EC tungsten oxide and nickel oxide thin films, as well as electrochemical rejuvenation mechanisms that are able to restore the films to their initial state. The ageing of tungsten oxide films upon cycling in the range 2-4 V vs. Li/Li+ displays a power-law decrease of the charge capacity as a function of cycle number. In the case of severe ageing at potentials below 2.0 V there is evidence for a superposition of two processes. In the case of nickel oxide the ageing process seems to be more complex and it can be described by either a power-law or a stretched exponential function. The ageing of nickel oxide was also observed to decrease and even stop after a few thousand cycles just prior to final breakdown of the film. The decay of charge capacity can be understood in terms of models built on so-called dispersive chemical kinetics. The term “rejuvenation” describes electrochemical processes that may restore aged films to full EC functionality. During severe ageing of tungsten oxide coatings, Li ions are trapped in the film, and subsequently these ions can be released by application of a high electrochemical potential for a few hours. The trapping/detrapping of Li has been verified by Elastic Recoil Detection Analysis (ERDA) measurements. Very recently we have found that a similar process can be applied to EC nickel oxide films, although using a lower potential than for the case of tungsten oxide. For nickel oxide, the rejuvenation mechanism is not yet clear, but ERDA measurements are in progress and are expected to give detailed information. An increased understanding of ageing and rejuvenation will facilitate large-scale practical application of electrochromic materials. Our phenomenological models of ageing may make it possible to predict the service life of EC devices using empirical relationships. An understanding of rejuvenation processes will be of major importance in order to prevent or minimize performance decrease under extended cycling. The next step will be to investigate whether rejuvenation treatments can be applied successfully to full EC devices.

Resonant Coupling between Molecular Vibrations and Localized Surface Plasmon Resonance of Faceted Metal Oxide Nanocrystals

Doped metal oxides are plasmonic materials that boast both synthetic and postsynthetic spectral tunability. They have already enabled promising smart window and optoelectronic technologies and have been proposed for use in surface enhanced infrared absorption spectroscopy (SEIRA) and sensing applications. Herein, we report the first step toward realization of the former utilizing cubic F and Sn codoped In2O3 nanocrystals (NCs) to couple to the C-H vibration of surface-bound oleate ligands. Electron energy loss spectroscopy is used to map the strong near-field enhancement around these NCs that enables localized surface plasmon resonance (LSPR) coupling between adjacent nanocrystals and LSPR-molecular vibration coupling. Fourier transform infrared spectroscopy measurements and finite element simulations are applied to observe and explain the nature of the coupling phenomena, specifically addressing coupling in mesoscale assembled films. The Fano line shape signatures of LSPR-coupled molecular vibrations are rationalized with two-port temporal coupled mode theory. With this combined theoretical and experimental approach, we describe the influence of coupling strength and relative detuning between the molecular vibration and LSPR on the enhancement factor and further explain the basis of the observed Fano line shape by deconvoluting the combined response of the LSPR and molecular vibration in transmission, absorption and reflection. This study therefore illustrates various factors involved in determining the LSPR-LSPR and LSPR-molecular vibration coupling for metal oxide materials and provides a fundamental basis for the design of sensing or SEIRA substrates.

Switchable Materials for Smart Windows.

This article reviews the basic principles of and recent developments in electrochromic, photochromic, and thermochromic materials for applications in smart windows. Compared with current static windows, smart windows can dynamically modulate the transmittance of solar irradiation based on weather conditions and personal preferences, thus simultaneously improving building energy efficiency and indoor human comfort. Although some smart windows are commercially available, their widespread implementation has not yet been realized. Recent advances in nanostructured materials provide new opportunities for next-generation smart window technology owing to their unique structure-property relations. Nanomaterials can provide enhanced coloration efficiency, faster switching kinetics, and longer lifetime. In addition, their compatibility with solution processing enables low-cost and high-throughput fabrication. This review also discusses the importance of dual-band modulation of visible and near-infrared (NIR) light, as nearly 50% of solar energy lies in the NIR region. Some latest results show that solution-processable nanostructured systems can selectively modulate the NIR light without affecting the visible transmittance, thus reducing energy consumption by air conditioning, heating, and artificial lighting.

PV 일체형 차세대 스마트 윈도우 기술개발 동향

Among several types of energy saving smart window technologies, the leader, the dynamic EC (electrochromic) window one needs integrated PV (photovoltaics), to minimize expensive electrical wiring as well as to obviate the need for external energy. Self-powered smart windows were reviewed according to PV types used. DSSCs (dye sensitized solar cells) were found to be compatible with EC cells, to have several categories of next generation smart windows such as PECCs (photoelectrochromic cells), PVCCs (photovoltachromic cells), EC polymer PECCs. In addition silicon solar cells and third generation solar cells were investigated. They are summarized in a table showing their advantages and disadvantages respectively for a fast comparison. The strategy to expedite the commercialization of these next generation smart windows includes developing retrofit smart window coverings for use on flexible polymer substrates adhered to the inside surface of a window and easily replaced after use for upto 10 years.

ChemInform Abstract: Flexible Solid-State Photoelectrochromic Windows.

Photoelectrochromic smart window technology is extended to include the use of flexible substrates and solid-state electrolytes. This should facilitate their application as retrofit modifications of office windows, where, by blocking incoming solar irradiation, they could substantially lower air-conditioning costs. These devices are based on a dye-sensitized TiO{sub 2} electrode coupled with a 500 nm thick WO{sub 3} electrochromic counter electrode, separated by a cross-linked polymer electrolyte containing LiI. A novel method for preparing conducting nanoporous TiO{sub 2} films is described that allows for the construction of these devices on flexible organic substrates. Colloidal solutions of TiO{sub 2} free of surfactants were spin-coated onto indium-tin oxide coated polyester substrates, resulting in highly transparent films ranging from 100 nm to 1 {micro}m in thickness. Upon annealing at 100 C, these films were strongly adherent and displayed excellent photoconductivity as shown by their current-voltage characteristics. The devices typically transmit 75% of visible light in the bleached state. After a few minutes of exposure to white light (75 mW/cm{sup 2}), the windows turn dark blue, transmitting only 30% of visible light. They spontaneously bleach back to their initial noncolored state upon removal of the light source.

2004 Survey of United States architects on the subject of switchable glazings

The 21st century has ushered in an era marked by the growing integration of technology and other scientific advances into commercial buildings and residential homes. Of particular interest to many architects, developers and builders are “switchable” glazing, a new category of technologically advanced glass and plastic building materials that can be used to control light, glare and heat entering an office or a home. Interest in switchable glazing technology is influenced by a variety of factors, including a growing movement to offer sustainable, energy-efficient building solutions, and the emerging desire by users to maintain greater control over their working and living environments. This paper examines the movement toward sustainable development and the end-user needs that are driving it. Further, it presents the results of a proprietary survey research study of United States architects on the subject of switchable glazing. This study includes an examination of the attributes most desired by architects regarding smart window technology, and provides additional insight into the potential application of this smart material to the building community.

Processing of Transparent Conducting Coatings Made With Redispersible Crystalline Nanoparticles

The present paper describes recent developments in the employment of ITO (In2O3:Sn) nanoparticles for the preparation of transparent conducting coatings and discusses capabilities and limits of this approach, especially for applications in display and smart window technology. Meanwhile, redispersible nanoparticles of ITO, which shows the best electrical properties among the transparent coating oxides (TCOs), can be produced reproducibly on an industrial scale and various products are on the market.

An electrochromic window based on poly( N-methyl-10,10-dimethylphenazasiline) and ITO electrodes

The performance of an electrochromic window with a poly ( N-methyl-10,10-dimethylphenazasiline) electrochromic electrode and indium-tin oxide optically passive counter-electrode has been tested both in liquid and solid-state configurations. Preliminary results, based on transmission spectra and electrical and optical responses to repeated potential switches between transparent and dark states, suggest the viability of this device in smart window technology.

Towards large-area photovoltaic nanocells: experiences learned from smart window technology

This investigation covers two technologies which have different applications but have many similar characteristics. One is the nanocell photoelectrochemical solar cell, the other is the electrochromic window