VO metasurface smart thermal emitter with high visual transparency for passive radiative cooling regulation in space and terrestrial applications.

Smart radiative cooling devices based on thermochromic materials such as vanadium dioxide (VO) are of practical interest for temperature regulation and artificial homeostasis, i.e., maintaining stable equilibrium conditions for survival, both in terrestrial and space applications. In traditional solar reflector configurations, solar absorption in the VO layer is a performance limiting factor due to the multiple reflections of sunlight in the stack. Here, we demonstrate a visually transparent, smart radiator panel with reduced solar absorption. An Al-doped ZnO transparent conducting oxide layer acts as a frequency selective infrared back-reflector with high transmission of solar radiation. In this study we make use of high-quality VO thin films deposited using atomic layer deposition and optimized annealing process. Patterning of the VO layer into a metasurface results in a further reduction of the solar absorption parameter to around 0.3, while exhibiting a thermal emissivity contrast Δ of 0.26 by exploiting plasmonic enhancement effects. The VO metasurface provides a visual spectrum transmission of up to 62%, which is of interest for a range of applications requiring visual transparency. The transparent smart metasurface thermal emitter offers a new approach for thermal management in both space and terrestrial radiative cooling scenarios.