Electrochromic-photothermal Film May Solve Switchable Window Production Challenges

Newer forms of smart windows are going well beyond blocking light or providing privacy. For example, some smart windows can turn light into thermal energy that may be used to support the building’s heating system. Antimicrobial smart windows are also in development for sterile environments, such as laboratories and hospitals.

Challenges in Making Switchable Windows

The sun’s rays are composed of lightwave frequencies ranging from UV rays to visible light, through to infrared energy at the other end of the spectrum. When trying to use these varying parts of the light spectrum in different ways — such as blocking some frequencies of light waves while harnessing others to create heat — switchable window design gets very complicated.

Creating a window that addresses all components of sunlight requires specific materials to address each type of light wave. For example:

• Many smart windows block light by using tungsten trioxide (WO3). This material is electrochromic, meaning that electrochemical activity changes how much light it lets through. This provides an adjustable tint level in the window itself.
• Smart windows that absorb near-infrared solar radiation to create heat often use metal nanoparticles.
• Switchable windows designed with antimicrobial properties generally incorporate copper particles.

Combining all of these elements into a single smart window is difficult, so researchers are working to design materials that can do it all.

Light-blocking Smart Window Solutions

One research team from China seems to have found a solution with an elegantly designed electrochromic-photothermal film. This film consists of a honeycomb-shaped structure made of 3D WO3. Tiny gold nanoparticles and nanorods exist within the cells of the structure, providing a way for all of the wanted elements to fit into the same space. TheWO3 modifies the amount of light that gets through the window, while the gold nanostructures turn light into heat.

This film responds to light by making the windows change from transparent to black very quickly. Near-infrared radiation heats the windows by24° C within five minutes, making them an effective heat source. The gold nanostructures and theWO3 have very effective antimicrobial properties when combined, so the windows eliminate nearly all bacteria when in their dark state.

Standard switchable windows can be useful in many different applications, such as skylights and conservatory windows. However, anti-microbial windows are especially promising for facilities where bacterial protection is important, such as medical facilities. Windows that can also be used as a heat source also provide an intriguing source of carbon-free energy.

As Windows Get Smarter, New Applications Emerge

Given the quick rate of expansion for the technology, it is likely that we will see new and innovative capabilities from smart windows in the near future. Scientists are finding ways to incorporate diverse elements in one window, creating glass that has multiple benefits for different situations. Fromlight and heat blocking applicationsin people’s homes to advanced antimicrobial capabilities for use in hospitals, the potential of smart windows is expanding.