https://www.fkit.unizg.hr/_download/repository/Smart_Windows-_Review.pdf

Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of-the-art review

Hydrogen storage in Mg: A most promising material

Electrochromics for smart windows: Oxide-based thin films and devices

Research on the luminescent solar concentrator (LSC) over the past thirty-odd years is reviewed. The LSC is a simple device at its heart, employing a polymeric or glass waveguide and luminescent molecules to generate electricity from sunlight when attached to a photovoltaic cell. The LSC has the potential to find extended use in an area traditionally difficult for effective use of regular photovoltaic panels: the built environment. The LSC is a device very flexible in its design, with a variety of possible shapes and colors. The primary challenge faced by the devices is increasing their photon-to-electron conversion efficiencies. A number of laboratories are working to improve the efficiency and lifetime of the LSC device, with the ultimate goal of commercializing the devices within a few years. The topics covered here relate to the efforts for reducing losses in these devices. These include studies of novel luminophores, including organic fluorescent dyes, inorganic phosphors, and quantum dots. Ways to limit the surface and internal losses are also discussed, including using organic and inorganic-based selective mirrors which allow sunlight in but reflect luminophore-emitted light, plasmonic structures to enhance emissions, novel photovoltaics, alignment of the luminophores to manipulate the path of the emitted light, and patterning of the dye layer to improve emission efficiency. Finally, some possible ‘glimpses of the future’ are offered, with additional research paths that could result in a device that makes solar energy a ubiquitous part of the urban setting, finding use as sound barriers, bus-stop roofs, awnings, windows, paving, or siding tiles.

Thirty Years of Luminescent Solar Concentrator Research: Solar Energy for the Built Environment

Composite Titanium Dioxide Nanomaterials

A novel multifunctional window was demonstrated using VO2-based thermochromic films with a TiO2 antireflection coating. A strong enhancement in luminous transmittance of VO2 was calculated using either a single layer or a double layer of TiO2 for antireflection, with the double layer giving the better performance. A TiO2 (25 nm)/VO2 (50 nm)/TiO2 (25 nm) structure, of which the film thickness has been optimized to a maximum integrated luminous transmittance (Tlum) by calculation, was formed on SiO2 glass by sputtering in turn a V target in Ar+O2 for VO2 and a TiO2 target in Ar for TiO2. Optical properties were measured with a spectrophotometer, and the integrated solar and luminous properties were calculated based on the measured spectra. A maximum increase in Tlum by 86% (from 30.9% to 57.6%) was obtained for VO2 after double-layer TiO2 antireflection coating. The deposited VO2 film on SiO2 exhibits good thermochromism with a sharp optical transition at 58.5 °C, which decreased slightly to 57.5 °C after TiO2 coating. The proposed window is the most advanced among those similarly reported in being multifunctional with automatic solar/heat control, ultraviolet stopping and possibly a wide range of photocatalytic functions in addition to a high value of the luminous transmittance.

Design, formation and characterization of a novel multifunctional window with VO2 and TiO2 coatings

Mg–Ni alloy thin films were prepared by dc magnetron sputtering using Mg and Ni targets, and their optical switching property for hydrogen exposure has been investigated. Pd-capped MgNix (0.1<x<0.3) films show a good switchable mirror property. Optical transmittance of these Mg-rich Mg–Ni thin films in the hydride state is much improved compared with that of Mg2Ni thin film. We speculate that the variation of the ratio of Mg2NiH4 to MgH2 formed in the hydride state may cause this difference. Such a wide modulation range of optical switching is important for the application of this material to energy efficient smart windows.

Optical switching of Mg-rich Mg–Ni alloy thin films

In an investigation of smart-window applications of switchable mirror thin films, Pd-capped magnesium-titanium thin films were prepared by dc magnetron sputtering. Their optical properties, switching durability and crystalline structures have been investigated. We show that Pd/Mg-Ti thin films with specific thicknesses are completely color-neutral in the transparent state and their optical switching properties are suitable for building and automobile window glass applications. The ternary hydrides of Mg(1-x)Tix thin films with Pd overlayers are identified by in situ X-ray diffraction measurements during a hydrogen gas loading of 4%. Pd/Mg(1-x)Tix thin film switchable mirrors show fast hydriding and dehydriding kinetics as compared to a Pd-capped pure Mg thin film due to the catalytic role of doped metallic Ti.

Color-neutral switchable mirrors based on magnesium-titanium thin films

Magnesium–titanium alloy thin-film switchable mirrors

Switchable mirrors based on magnesium-calcium alloy thin films were prepared using a direct-current magnetron sputtering method and their gasochromic properties have been investigated. Pd-capped Mg1−zCaz (0.04<z<0.20) films showed excellent switchable mirror properties. The visible transmittance in the transparent state increased with Ca composition, z, and after reaching a maximum of ∼46% at z∼0.06, the transmittance decreased gradually with increasing Ca composition. In the transparent state with z<0.08, the optical transmittance spectra of these switchable mirrors were fairly flat in the visible range and their color looked completely neutral. The achromatic properties with high visible transmittance may be because the hydrogenated switchable mirrors are composed of MgH2 and MgCaH3.72 with grayish neutral color appearance.

K. Yoshimura

Papers

Design, formation and characterization of a novel multifunctional window with VO2 and TiO2 coatings

Optical switching of Mg-rich Mg–Ni alloy thin films

Color-neutral switchable mirrors based on magnesium-titanium thin films

Magnesium–titanium alloy thin-film switchable mirrors

Optical properties of switchable mirrors based on magnesium-calcium alloy thin films