Simultaneous solar rejection and infrared emission switching using an integrated dielectrics-on-VO2 metasurface

Passive infrared emittance switching can be achieved with a metal-to-insulating phase transition material vanadium dioxide (VO2), but its non-transitioning bandgap results in high absorptance in the visible wavelength range. To achieve a half-order reduction of absorptance in the visible to near-infrared region, we design integrated dielectric photonic metasurface structures on monolithic VO2 coatings. This combination of nano/micro-patterned dielectric diffractive and resonant gratings with a multilayer VO2 structure preserves the terrestrial thermal wavelength emission switching capabilities. We demonstrate a periodic microscale diffractive prism array, comparing the reflectance provided by either infrared-transparent germanium (Ge) or silicon (Si). Despite the advantage of total internal reflection in the broad near-infrared region, some bandgap absorption limits the performance in the visible wavelengths. A better theoretical means to reflect broadband light via waveguide-like Fabry–Pérot resonance are near-wavelength 1D and 2D High Contrast Grating (HCG) high-index metasurface structures surrounded by a low-index host medium. This HCG metasurface allows broadband high-quality reflection within the dual-mode (or tri-mode) region from 1.0 to 2.2 µm wavelengths for HCG with a refractive index of 4.0, which corresponds to Ge. This study investigates the advantages and disadvantages along with the thermal performance of these metasurface augments aimed to enable thermally switchable passive radiative cooling—thermal emission exceeding solar absorption—of solar cells, terrestrial buildings, and energy storage devices.