Thermochromic Oxide-Based Thin Films and Nanoparticle Composites for Energy-Efficient Glazings

Abstract

Today's advances in materials science and technology can lead to better buildings with improved energy efficiency and indoor conditions. Particular attention should be directed towards windows and glass facades-jointly known as "glazings"-since current practices often lead to huge energy expenditures related to excessive inflow or outflow of energy which need to be balanced by energy-intensive cooling or heating. This review article outlines recent progress in thermochromics, i.e., it deals with materials whose optical properties are strongly dependent on temperature. In particular, we discuss oxide-based thin surface coatings (thin films) and nanoparticle composites which can be deposited onto glass and are able to regulate the throughput of solar energy while the luminous (visible) properties remain more or less unaltered. Another implementation embodies lamination materials incorporating thermochromic (TC) nanoparticles. The thin films and nanocomposites are based on vanadium dioxide (VO 2 ), which is able to change its properties within a narrow temperature range in the vicinity of room temperature and either reflects or absorbs infrared light at elevated temperatures, whereas the reflectance or absorptance is much smaller at lower temperatures. The review outlines the state of the art for these thin films and nanocomposites with particular attention to recent developments that have taken place in laboratories worldwide. Specifically, we first set the scene by discussing environmental challenges and their relationship with TC glazings. Then enters VO 2 and we present its key properties in thin-film form and as nanoparticles. The next part of the article gives perspectives on the manufacturing of these films and particles. We point out that the properties of pure VO 2 may not be fully adequate for buildings and we elaborate how additives, antireflection layers, nanostructuring and protective over-coatings can be employed to yield improved performance and durability that make TC glazings of considerable interest for building-related applications. Finally, we briefly describe recent developments towards TC light scattering and draw some final conclusions.

Selective IR response of highly textured phase change VO2 nanostructures obtained via oxidation of electron beam deposited metallic V films

“…With the ever increasing need for materials with new functionalities for integrated circuits and smart surface technologies, VO 2 has entered the agenda of groups focusing on applications and device design. Some interesting examples include thermochromic smart window coatings [6][7][8][9][10], tunable antennas [11][12][13], tunable metamaterials [14], and electronic switch components [15] in integrated circuits. VO 2 can be synthesized both in bulk powder form as well as in thin film form.…”

Biophotonics for improving algal photobioreactor performance: A review

“…Thermochromic materials are usually employed as glazing materials in architecture, allowing them to regulate the amount of light transmitted or reflected, depending on atmospheric temperature . They not only act as specific wavelength transmitters but are also effective in optimizing heat exchanges.…”

“…They not only act as specific wavelength transmitters but are also effective in optimizing heat exchanges. Thermochromic materials transmit more solar energy at low temperatures than at high temperatures . For temperatures below the transition, thermochromic materials transmit more heat associated with IR and near‐IR radiations.…”

Electrochromics on a roll: Web-coating and lamination for smart windows

“…An interesting possibility, which remains to be tested for glazing applications, is to use nanoparticles with properties that are thermochromic, i.e., different above and below a certain temperature in the neighborhood of room temperature. The most well-known thermochromic material is vanadium dioxide (VO 2 ) [34], which is semiconducting at low temperature and metallic-like at high temperature; the transition between the two regimes takes place around 68 ºC in bulk VO 2 but is typically somewhat lower in a thin coating or in nanoparticles. If needed, the transition temperature can be deceased by adding a minor amount of tungsten to the VO 2 [35].…”