High Solar Transmittance Research Articles

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

The potential of radiative cooling enhanced photovoltaic systems in China

Soaring solar cell temperature hindered photovoltaic (PV) efficiency, but a novel radiative cooling (RC) cover developed in this study offered a cost-effective solution. Using a randomly particle-doping structure, the radiative cooling cover achieved a high “sky window” emissivity of 95.3% while maintaining a high solar transmittance of 94.8%. The RC-PV system reached a peak power output of 147.6 W/m2. A field study to explore its potential in various provinces in China revealed significant efficiency improvements, with yearly electricity outputs surpassing those of ordinary PV systems by a relative improvement of 2.78%–3.72%. The largest increases were observed under clear skies and in dry, cool climates, highlighting the potential of RC-PV systems under real weather and environmental conditions. This work provided the theoretical foundation for designing scalable radiative cooling films for PV systems, unlocking the full potential of solar energy.

Performance Assessment of Novel Transparent Insulation Materials for Integrated Storage Collectors

Transparent insulation structures play a pivotal role in harnessing solar energy efficiently, akin to the greenhouse effect in the atmosphere. This study undertakes a systematic evaluation of a novel sorbitol- or bio-based polycarbonate (bio-PC) for thermal insulation (TI) structures and hot water collector systems. Employing optical and mechanical methods, the bio-PC was comprehensively characterized on the polymer film level. Subsequently, the technical and ecological performance of these structures in various hot water collectors and systems was rigorously modelled and simulated. Results indicated that the novel bio-PC exhibited superior properties compared to conventional materials like cellulose acetate or fossil-based PC, showcasing promising prospects for widespread adoption. Drawing parallels to the greenhouse effect of CO2, the functional principle of transparent insulation structures is rooted in high solar transmittance and infrared absorbance, primarily governed by carbon-oxygen bonds. While fossil-fuel based transparent insulation materials have been prevalent, they suffer from drawbacks such as average infrared absorbance and susceptibility to yellowing. In contrast, the newly introduced bottom-up biopolymer bio-PC, derived from sorbitol derivatives, offers a compelling alternative. The study sheds light on the potentials and limitations of bio-PC for transparent insulation structures in integrated storage or flat plate collectors, aiming to mitigate environmental impacts associated with traditional materials. Future research directions emphasize refining modelling tools and addressing input data deficiencies, particularly for life cycle analysis. Concurrently, efforts are directed towards enhancing simulation accuracy and reliability through concurrent measurements of collector systems equipped with bio-PC-based transparent insulation. This research underscores the critical role of innovative materials in advancing sustainable energy solutions, with bio-PC emerging as a promising candidate in the realm of transparent insulation technology.

Free‐Standing Bacterial Cellulose‐Templated Radiative Cooling Liquid Crystal Films with Self‐Adaptive Solar Transmittance Modulation

AbstractPassive radiative cooling materials can efficiently reflect solar radiation and spontaneously dissipate heat through the long‐wave infrared (LWIR) transmission window to the coldouter space. They are highly attractive for application in walls and roofs of sustainable energy‐efficient buildings, but it is a challenging task to develop switchable radiative coolers for transparent windows. Herein, free‐standing bacterial cellulose‐templated radiative cooling liquid crystal films with high LWIR emissivity and self‐adaptive solar transmittance are reported. Biosynthetic silanized bacterial cellulose with 3D interconnected porous nanostructure is harnessed as a robust template for confining novel liquid crystals with smectic A to chiral nematic phase transition, thereby endowing the film with high solar transmittance modulation ability. The resulting film is found to not only exhibit a remarkable LWIR emissivity, but also adaptively change its solar transmittance between a transparent state and an opaque state according to environmental temperature variation. Outdoor radiative cooling experiments are performed, and the energy‐saving performance is evaluated through a simulation of a 12‐story reference office building with the films applied as radiative cooling windows. This research can shine light on the development of advanced radiative cooling materials with switchable transmittance and their widespread applications in buildings, vehicles, and transparent photovoltaics.

All‐Solid‐State Transparent Variable Infrared Emissivity Devices for Multi‐Mode Smart Windows

AbstractSmart windows that incorporate photothermal modulators (PMs) can independently regulate solar transmittance and infrared (IR) emissivity to improve building comfort and reduce energy consumption. Herein, a novel all‐solid‐state variable IR emissivity device (VED) is first designed and fabricated with a high visible irradiation transmittance (T′vis = 0.79) and solar irradiation transmittance (T′sol = 0.75) using an ITO/SiO2/ITO Fabry–Perot cavity structure. The VED exhibits different IR emissivity (ɛ) values at positive (ɛP = 0.80) and negative (ɛN = 0.38) bias, allowing for dynamic regulation of radiation by controlling the electrical conductivity of the indium tin oxide (ITO) layer. Furthermore, an all‐solid‐state PM with a structure of ITO/SiO2/ITO/Glass/ITO/NiO/ZrO2/Li/WO3/ITO, which is capable of independently regulating solar transmittance (ΔT'sol = 0.31) and IR emissivity (Δɛ2.5–25 µm = 0.42), is fabricated. The multi‐mode smart window incorporating PMs can achieve “bright,” “dark,” “warm,” and “cool” modes, making them suitable for deployment in diverse climate zones. The innovative smart window holds a massive potential for use in reducing building energy consumption.

Energy-saving thermochromic smart shield based on double network hydrogel with intelligent light management and robust mechanical property

Smart-Windows, which automatically regulate the intensity of sunlight entering the building, have attracted tremendous interest in reducing energy consumption by controlling the solar transmittance. Herein, a microgel-based double-network hydrogel (A-DN hydrogel) was prepared as flexible self-adaptable Smart-Shield to regulate sunlight. A novel thermochromic material, P(NIPAm-co-AA) microgels, was synthesized and used to construct a tough double-network hydrogel with polyacrylamide (PAAm). A-DN hydrogel, with a high solar transmittance of 87.2% at 25 °C but gradually decreased to 0% with increasing temperature to 40 °C, can intelligently select the appropriate solar transmittance according to the ambient temperature. In addition, due to the special double network structure of A-DN hydrogel and small characteristic size of microgel, A-DN hydrogel has no volume change after phase transformation and has excellent mechanical properties and high response speed. Energy Plus simulation software was used to construct the application form of simulated Smart-Shield in buildings. Simulations suggested that A-DN shield can cut off 21.04% energy consumption compared with the normal glass, and its energy saving efficiency is higher than that of commercial low-E glass (10.89%). In general, this strategy will provide new avenues for the preparation of intelligent materials with excellent mechanical properties and temperature response.

Facile preparation of porous SiO2 antireflection film with high transmittance and hardness via self-templating method for perovskite solar cells

An antireflection (AR) film on the surface of the photovoltaic glass can significantly improve the photoelectric conversion efficiency of solar cells. However, AR films prepared by a facile and low-cost sol-gel method usually exhibit poor mechanical properties, which limits their applications. Herein, hexamethoxy methyl melamine resin (CYMEL 303LF) was employed as a pore-forming agent in the sol and sacrificial template to prepare porous SiO2 film on glass by a facile sol-gel method and subsequent heat treatment. The obtained SiO2 film showed a high solar transmittance increase of 3.24% in the wavelength range of 380–1100 nm and a good hardness of H when the dosage of CYMEL 303LF is 10 wt%, the short circuit current density and photoelectric conversion efficiency of the solar cell are increased respectively by 1.44 mA/cm2 and 1.08%, compared with the substrate, which is better than most SiO2 films in the previous works. With increasing the dosage of CYMEL 303LF from 0% to 12%, the solar transmittance gain was increased at first and then decreased, while the film hardness was decreased straightly. This was probably because that the introduction of CYMEL 303LF can facilitate the formation of more pores in the SiO2 film, leading to a decrease in the refractive index and film adhesion. Therefore, this work can provide a facile method to prepare high-performance SiO2 as AR film for solar cells.

A three-dimensional unsteady numerical model on a novel aerogel-based PV/T-PCM system with dynamic heat-transfer mechanism and solar energy harvesting analysis

The daily increasing energy demand combined with global environmental issues has promoted the development of a photovoltaic thermal (PV/T) system with onsite electrical and thermal energy supply in buildings. However, suffering from massive radiative and convective heat losses, the overall efficiency of PV/T systems is relatively low (normally lower than 70%). In this paper, silica aerogel, a spectral selective porous material with high solar transmittance, extra-low thermal conductivity and low mid-infrared emissivity, is integrated into the upper surface of PV/T systems to reduce heat losses. Meanwhile, composite phase change material (PCM) with active heat-transfer enhancement strategies is integrated at the backside for accumulated heat dissipation. Subsequently, a three-dimensional numerical model based on the finite volume method and enthalpy-porosity method is established in the commercial software Ansys Fluent to simulate the dynamic performance. Dynamic heat-transfer mechanism is studied with solar energy harvesting analysis subjected to the typical weather conditions in Guangzhou, China. A series of comparative and parametric studies are performed for optimal structural design and operation. Results indicate that, the incorporation of aerogel and composite PCM with high thermal conductivity are beneficial to improve electrical and thermal efficiencies, while the integration of nanofluid shows negligible effects. The optimal results show the improvement on overall energy and exergy efficiencies by 40.2% and 1.5% in summer and by 42.4% and 0.43% in winter, together with annual CO2 mitigation of 104.1 kg/m2 and return on investment (ROI) of 0.169. This study provides a novel structural design and optimal operation on a novel aerogel-based PV/T-PCM system, together with guidelines on techno-economic-environmental performance improvement, promoting the solar energy harvesting for decarbonization transformations in buildings.

Plasmon silica aerogel for improving high-temperature solar thermal conversion

The next generation concentrated solar thermal (CST) plants need to move toward higher operation temperatures to achieve higher thermodynamic efficiency. However, solar absorbers operating at high temperatures have a significant radiative thermal loss. In present study, a hybrid plasmon aerogel doped with ITO nanocylinders was proposed for improving the photothermal conversion in high-temperature CST plants. For the first time, the localized surface plasmon resonance was applied in high-temperature photothermal conversion to achieve the greenhouse effect of aerogel. The effects of nanoparticle morphology, size, and doping concentration on the infrared absorption performance of the hybrid aerogel were investigated by the combination of the T-matrix and Monte Carlo method. The operation temperature of the solar absorber was calculated to evaluate the insulation performance of the hybrid plasmon aerogels. The results show that, at the solar concentration ratio C = 20, the maximum increase of 113.9 °C in operation temperature can be achieved withaerogel thickness l = 5 mm and ITO nanocylinder doping concentration f v = 0.016%. This study sheds light on high-efficiency hybrid plasmon aerogel serving as a transparent thermal insulation barrier for high-temperature CST plants with high solar transmittance, low thermal conductivity, and low radiative thermal loss. • A kind of hybrid plasmon aerogel based on ITO nanocylinders and silica aerogel matrix is proposed and optimal designed for the CST plants. • The combination of T-matrix method and Monte Carlo method is applied to compute the radiative properties of the hybrid aerogel. • The operation temperature of solar absorber is calculated to assess the thermal insulating performance of the hybrid plasmon aerogel.

Aerosol-based deposition of broadband antireflective silica coating with closed mesoporous structure

Solar energy will be a crucial part of the sustainable, fossil free energy production of the future. A majority of this will be produced by solar collectors and photovoltaics. Important for the efficient utilization of the incident solar energy for both technologies are a cover glass with antireflective coatings giving it a high solar transmittance. In the current paper we describe the development of antireflective mesoporous silica coatings on low-iron float glass using the aerosol-based nFOG™ deposition technique. The coatings exhibit a hexagonal and closed pore structure, high smoothness, superhydrophilic properties (contact angle <5°) and consistent thicknesses of approximately 110 nm. This is in line with optimal thickness determined from simulations of the antireflective behavior. Low-iron float glass coated on both sides show a highly reproducible solar weighted transmittance of 95% in the wavelength range 300–2500 nm and an antireflective effect increasing with incident angle. The smoothness, closed pores and low contact angle indicate a high cleanability, which in combination with the high transmittance render a competitive broadband antireflective coating well adapted for solar glass applications. • Sol-gel synthesis of antireflective silica coatings based on evaporation induced self-assembly using the aerosol-based nFOG™ technique. • Mesoporous coatings exhibiting hexagonally ordered pores, aligned parallel to the substrate, but closed to the surface. • Smooth, consistent, 110 nm thick coatings were produced, which is close to the simulated optimal thickness of 120 nm. • Low-iron float glass with the antireflective coating exhibit a solar weighted transmittance of 95%.

Vapor–Liquid Transition‐Based Broadband Light Modulation for Self‐Adaptive Thermal Management

AbstractConsiderable research efforts have aimed to control indoor temperatures to improve daily life and industrial production. However, current strategies, which involve active regulation of energy input or passive regulation of sunlight transmission, cannot control indoor temperatures under all weather conditions. Herein, a self‐adaptive thermal management device (STMD) that uses solar energy (heating) and radiative cooling (cooling) by exploiting the temperature differences across the device is reported. The adaptive heating and cooling functions are achieved by modulating sunlight transmittance and reflectance using a porous SiO2 coating separated/merged with a refractive index‐matched liquid which serves as a shutter. As a result, the STMD in the opaque mode exhibits low transmittance and in the transparent mode exhibits sufficiently high solar transmittance. Taking advantage of this self‐regulated shuttering mechanism, the developed STMD enables i) an increase of ≈10 °C relative to the ambient temperature under a solar intensity of 400 W m−2 in cold weather and ii) a temperature reduction of ≈5 °C under a solar intensity exceeding 900 W m−2 in hot weather. The described design strategy offers an approach for constructing smart light‐controlling devices and thermal‐controlling building materials.

Incorporating phase change materials into glazing units for building applications: Current progress and challenges

• Both light and heat transfer characteristics of glazing systems should be considered. • Usage of phase change materials helps reducing energy loss through glazing systems. • Measurement and numerical models are inadequate to study photo-thermal transmission. • More research on effect of phase change materials on acoustic performance is needed. • Database lacks optical properties of solid and molten nano-phase change materials. Building envelopes consist of transparent and non-transparent components, and pose distinct opportunities and challenges in energy conservation. Glazing envelopes, which are transparent, are mainly responsible for the lighting and ventilation of buildings, but the acoustic performance may be weakened. Since glazing envelopes suffer from the defects of high solar transmittance, poor thermal insulation, and low thermal inertia, their energy-saving technologies are significantly different from those of non-transparent envelopes. Different energy-saving technologies have been studied to improve the optical and thermal performance of glazing envelopes. However, there is a lack of a review study involving the phase transition process and the improvement of photo-thermal transmission in glazing envelopes containing phase change materials. The present work provides a comprehensive overview of research advances in optical transmittance, thermal resistance, and thermal inertia along with photo-thermal transmittance in glazing envelopes, with a special focus on the integration of phase change materials. The study reveals that measurement and numerical models are inadequate to study photo-thermal transmission. Besides, it is identified that there is a research gap in the acoustic performance of glazing systems incorporating phase change materials, and there is a lack of database on the optical properties of phase change materials containing nanoparticles.

Cicada wing-inspired solar transmittance enhancement and hydrophobicity design for graphene-based solar steam generation: A novel gas phase deposition approach

The severe light reflection phenomenon has become a critical challenge for the sufficient utilization of solar energy. For preventing the predation risk, cicada’s wings are gradually evolved into transparent morphology to preferably blend into the natural environment. The high solar transmittance in cicada wings is due to the presence of surface micro/nanostructures which avoids the large change of refractive index between air and wings. Herein, inspired by the high solar transmittance of cicada’s wings, an extremely-simple gaseous phase deposition with low heating temperature is developed to cover graphene film with methyl-modified silicon dioxide (CH3-SiO2) nanospheres that decelerate the refractive index reduction. The destructive interference effect of CH3-SiO2 nanospheres effectively increases the solar transmittance to promote the absorption and conversion of solar energy into heat by graphene nanosheets. As a result, compared to pure graphene film, CH3-SiO2 nanospheres covered graphene (SiO2-graphene) film presents a temperature increase of ∼6.3 °C with solar illumination of 1.0 kW/m2. After being combined with zwitterion-modified cotton fabric, a novel solar steam generation system mainly composed of SiO2-graphene film is prepared. Due to the hydrophobicity of CH3-SiO2 nanosphere and the hydration effect of zwitterionic polymer, the salt precipitation and oil fouling problems regarded as major challenges in solar desalination are simultaneously solved, thus achieving water evaporation rate near 1.40 kg/m2h at oily seawater environment. Most importantly, the solar transmittance enhancement and anti-reflection design inspired by cicada wings provide a valuable reference to promote the solar absorption capacity of other photo-thermal conversion materials.

Selectively emissive fluoropolymer film for passive daytime radiative cooling

Passive daytime radiative cooling is an attractive method to reduce overheating and the heat island effect, thus addressing the global warming effect. This technology does not require any input energy, noise, vibrations, and polluting gas to produce sub-ambient temperatures. In this study, we propose a simple passive daytime radiative cooler, composed of a silver back layer and commercial ethylene tetrafluoroethylene film. With many molecular vibration peaks in the sky window and high solar transmittance of ethylene tetrafluoroethylene, the silver-deposited film exhibits only 3.5% solar absorption and 88.6% emissivity in the sky window, resulting in a substantial sub-ambient cooling effect of up to 9.7 °C in outdoor measurements. The theoretical prediction was confirmed to match well with experimental results, and the passive daytime radiative cooling ability of the film was examined using global-scale cooling energy density maps.

Thermal and Optical Properties of the Sunspace Casing as Factors Influencing Temperature Rise in Greenhouse Systems.

In sunspaces, there is an observable temperature rise above the external air temperature, caused by solar gains and the buffering effect of their enclosure. In addition, their external partitions form a barrier preventing the direct influence of the external environment and delaying the natural deterioration of elevation surface. In the paper, the temperature rise in a glazed balcony attached to a typical flat in a multifamily building, together with the energy demand in the living zone, were assessed with the use of dynamic computer simulations. Ten variants of the sunspace casing were analysed, with different thermal and solar energy transmittance of the glazing (which is a novel subject in the research area). This enabled us to evaluate average values of the temperature reduction factor during the year and to choose the most efficient variant of the sunspace external partitions. It turned out to be an insulated, double-glazed casing with a spectrally selective coating (type O 21), combining high insulative properties with high solar transmittance. These features allowed the temperature in the sunspace to rise by almost 10°C (compared with the external air) and lower total energy demand in the flat by 33% (compared with a flat with an open balcony).

A Theoretical Study for Designing Optical Multilayer Films Using NdF3/ ThF4

An idea of a colored glaze is presented in this study to hide and dispose all the obstacles of using solar systems as facades integrated with buildings. This aim is achieved by designing multilayer optical interference filters by using Mat lab program . Appropriate dielectric materials, namely NdF3 of high refractive index (nH =1.6) and ThF4 of low refractive index (nL =1.5143) were employed. Quarter wave thicknesses of high (H) and low (L) refractive index were deposited on a microscopic slide substrate with n=1.513 and 550 nm design wavelength (l°). Two optical models were designed, which are Air//HL//glass and Air//LH//glass, for even numbers of layers (2-32 layers). The challenge in this study is to find the most efficient design which has lower solar reflectance (Rsol.) and higher solar transmittance (Tsol.) to raise the efficiency of the solar systems and, in parallel, obtain the colored reflection to achieve the esthetic appearance of the buildings integrated with the solar system facades. The Tsol. value was high (94-95 %), whereas the Rsol. was very low (4-5 %). Hence, the efficiency of the solar system was increased. The two optical models exhibited green color reflectance in the visible region. The first design, i.e. Air/HL/glass, showed higher values of Rvis. and the merit factor (M) than the second model, resulting in a higher potential of coloration. The first design requires fewer materials and layers, thus, it is more cost-effective as compared to the second one.

Enhancement of solar thermoelectric power generation by optical and thermal management with highly transparent aerogel window

Solar thermoelectric generators (STEGs), which convert solar thermal energy into electricity, are studied as an environmentally friendly energy source. The unique properties of aerogels (i.e., high thermal insulation and solar light transmission) are essential factors in the solar-receiving components of STEGs. Herein, STEG power generation is enhanced through optical and thermal management using a highly transparent aerogel window. The aerogel window (thickness: 5 mm) exhibits an extremely low thermal conductivity and a high solar transmittance of 96.5%, higher than that of soda-lime glass (89.9% at 0.5 mm thickness) in the wavelength range of 300–2500 nm. Furthermore, we use a copper oxide (CuO) nanoflake structure as a cost-effective solar absorber for the STEG. Under 1-sun (1 k W m −2 ) illumination, power generation of the STEG with the aerogel window is 21% and 17% higher than that of glass-covered and uncovered STEGs, respectively. To demonstrate the performance of aerogel in an open environment, we measure the power generation of aerogel-covered, glass-covered, and uncovered STEGs under wind conditions. Under 1-sun illumination and a wind speed of 3 m s −1 , the power generation of the STEG with the aerogel window is 54% and 71% higher than that of glass-covered and uncovered STEGs, respectively. - Aerogel has the unique properties of high thermal insulation while transmitting light - Solar transmittance of the aerogel is higher than that of soda-lime glass - Aerogel exhibits ultra-low thermal conductivity of 0.01422 W m −1 K -1 - The power generation of the STEG is enhanced by transparent aerogel window

Plasmon-Enhanced Greenhouse Selectivity for High-Temperature Solar Thermal Energy Conversion.

The greenhouse effect arises when thermal radiation is forced to undergo absorption and re-emission many times before escaping, while sunlight transmits largely unimpeded. Although this effect is responsible for global warming, it is generally weak in solid-state materials because radiation can be easily overpowered by other modes of heat transfer. Here, we report on the use of infrared plasmonic nanoparticles to enhance the greenhouse effect in transparent mesoporous materials. Local surface plasmon resonances in transparent conducting oxide nanoparticles (TCO NPs) selectively shorten the mean free path of thermal photons while maintaining high solar transmittance. The addition of a small amount of TCO NPs (<0.1% by volume) nearly halves the heat losses at 700 °C. This leads to an experimentally demonstrated effective thermal emittance of ∼0.17 at 700 °C, which is the lowest reported value to date, among all selective surfaces and transparent insulating materials measured at 650 °C or above. Our results show that plasmon-enhanced greenhouse selectivity (PEGS) is a promising mechanism for spectral control of radiative heat transfer, and more specifically, for conversion of minimally concentrated sunlight into high-temperature heat.

Photo-thermochromic properties of oxygen-containing yttrium hydride and tungsten oxide composite films

Monolayer oxygen-containing yttrium hydride (YHx:O) and tungsten oxide (WO3) films show photochromic properties and have many potential energy-saving applications. YHx:O/WO3 composite films have better solar energy regulation properties than their monolayers because of the photochromic synergistic effects between the YHx:O and WO3 thin films. However, the reversion of these films to their initial transparent state is slow at room temperature, which limits their use in energy-saving windows. In this work, we developed a photo-thermochromic optical switching method that reversibly changes YHx:O/WO3 films between their transparent and infrared (IR) absorption states smoothly. The YHx:O/WO3 composite films were prepared by DC magnetron sputtering, and the reversible optical switching properties and photochromic mechanism were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and Fourier transform infrared (FTIR) spectroscopy. The composite films changed from their transparent state to their absorption state under illumination within 10 min, and returned to their transparent state when they were heated at 60–100 °C for 5 min. Compared with the single-layer YHx:O film, the YHx:O/WO3 composite films had a high color change rate and high solar transmittance (ΔTsol = 50.46%). We speculate that the mobile H in the YHx:O layer diffuses to the WO3 layer after illumination, converting WO3 to a tungsten bronze structure, increasing the IR absorption of the composite films. The diffusion of H in the YHx:O and WO3 layers was reversible and had good switching repeatability, and FTIR spectroscopy confirmed that H moved reversibly in films and played an important role in the photochromic process.

VO2-based thermally active low emissivity coatings

Vanadium dioxide is one of the likeliest candidates for future smart window applications due to its self-regulating nature and potentially simple implementation. However, the material is plagued with multiple drawbacks which need to be addressed before its commercialization. Amongst these, its low luminous transmittance has been the subject of many studies. In the present work, we propose to integrate a VO2 film into a traditional silver-containing low emissivity coating architecture. We first model and discuss the theoretical performance of such a coating in comparison with more standard configurations and demonstrate that the addition of silver offers many advantages for thin VO2 coatings; mainly an increase of luminous transmittance due to the presence of antireflective coatings while maintaining a high solar transmittance variation vs. temperature. The latter is shown to be the result of a displacement of the maximum transmission variation to lower wavelengths where the solar intensity is higher. We then fabricate prototype samples which confirm the predicted performance. Indeed, a silver-containing sample based on the following architecture Si3N4 [57 nm] | VO2 [27 nm] | Ag [11 nm] | Si3N4 [66 nm] is shown to possess the unique combination of a high luminous transmittance of 58.2% in its low temperature state, a solar transmittance variation of 7.1% with the added benefit of a low emissivity of 10%.