Reconfigurable Low-Emissivity Optical Coating Using Ultrathin Phase Change Materials

A method for controlling the optical properties of a solid-state film over a broad wavelength range is highly desirable and could have significant commercial impact. One such application is smart glazing technology where near-infrared solar radiation is harvested in the winter and reflected it in the summer.an impossibility for materials with fixed thermal and optical properties. Here, we experimentally demonstrate the first spectrally tunable, low-emissivity coating using a chalcogenidebased phase-change material (Ge20Te80), which can modulate the solar heat gain of a window while maintaining neutral-coloration and constant transmission of light at visible wavelengths. We additionally demonstrate the controlled transfer of absorbed nearinfrared energy to far-infrared radiation, which can be used to heat a building's interior and show fast, sub-millisecond switching using transparent electrical heaters integrated on glass substrates. These combined properties result in a smart window that is efficient and aesthetically pleasing. crucial for successful adoption of green technology.