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Smart radiative cooling devices based on thermochromic materials such as vanadium dioxide (VO2) 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 VO2 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 VO2 thin films deposited using atomic layer deposition and optimized annealing process. Patterning of the VO2 layer into a metasurface results in a further reduction of the solar absorption parameter α to around 0.3, while exhibiting a thermal emissivity contrast Δε of 0.26 by exploiting plasmonic enhancement effects. The VO2 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.

The unique structural transition of VO2 between dielectric and metallic phases has significant potential in optical and electrical applications ranging from volatile switches and neuromorphic computing to smart devices for thermochromic control and radiative cooling. Critical condition for their widespread implementation is scalable deposition method and reduction of the phase transition to near room temperature. Here, a W:VO2 process based on atomic layer deposition (ALD) is presented that enables precise control of W‐doping at the few percent level, resulting in a viable controllable process with sufficient W incorporation into VO2 to reduce the phase transition to room temperature. It is demonstrated that the incorporation of 1.63 at.% W through ALD growth leads to a state‐of‐the‐art phase transition at 32 °C with emissivity contrast between the low‐temperature and high‐temperature phase exceeding 40% in a metasurface‐based radiative cooling device configuration. The process is shown to be viable on 200 mm silicon substrates as well as flexible polyimide films. The full and self‐consistent temperature‐dependent characterization of the W‐doped VO2 using spectroscopic ellipsometry, electrical conductivity, mid‐wave infrared camera, and Fourier transform infrared emissivity, allows for a fully validated material model for the theoretical design of various smart and switchable device applications. [ABSTRACT FROM AUTHOR]

Smart radiative cooling devices based on thermochromic materials such as vanadium dioxide (VO2) 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 VO2 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 VO2 thin films deposited using atomic layer deposition and optimized annealing process. Patterning of the VO2 layer into a metasurface results in a further reduction of the solar absorption parameter α to around 0.3, while exhibiting a thermal emissivity contrast Δε of 0.26 by exploiting plasmonic enhancement effects. The VO2 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. [ABSTRACT FROM AUTHOR]

Metasurfaces with sub‐wavelength nanoscale features have emerged as a platform to achieve desirable electromagnetic responses. However, it remains technically challenging to fabricate metasurfaces in large size and at low cost for mass production. This work demonstrates a 200 mm wafer‐scale Al:ZnO metasurface coating based on deep‐UV lithography. The metasurfaces are targeted to achieve infrared (IR) reflectivity and emissivity characteristics at bandwidths across the two atmospheric windows in the IR spectrum. The wafers demonstrate a high uniformity of optical response with tailored reflectivity of around 50% at the 3–5 µm mid‐wave IR band and less than 10% at the 8–13 µm long‐wave IR band. This article furthermore shows that the design principle allows achieving a wide range of dual‐band reflectivity values using a single underlying materials stack, offering a versatile platform. The proposed approach is compatible with CMOS‐compatible mass‐production manufacturing and brings IR metasurface coatings closer to commercially relevant and scalable technology. [ABSTRACT FROM AUTHOR]