https://phys.org/news/2018-07-smart-window-microorganisms.html

As the researchers explain, integrating multiple functions into a single smart window presents a challenge, since each function typically requires a different material composition. For example, one of the most widely used materials for smart windows that control visible light transmission is WO3 (tungsten trioxide). As an electrochromic material, WO3 can reversibly change its optical transmittance in response to electrochemical charging and discharging. On the other hand, smart windows that convert near-infrared solar radiation into heat typically involve metal nanoparticles. Also, a wide range of materials have antimicrobial properties, most notably copper. So far, however, combining all of these properties into one material has remained a challenge.

In the new study, the researchers designed an electrochromic-photothermal film composed of 3D WO3 in a honeycomb-like structure embedded with gold nanoparticles and nanorods. While the WO3 controls the amount of visible light that passes through the window, the gold nanostructures convert incoming sunlight into thermal energy for heating the building interior.