Angle-Independent and Polarization-Insensitive Colored Daytime Radiative Cooler Design Based on Ultra-Broadband Metasurface Thermal Emitter

Abstract

We numerically demonstrate a broadband long-wave infrared (LWIR) absorber with near-zero visible–near-infrared (Vis–NIR) absorption, enabling daytime radiative cooling with colored display. The structure comprises two patterned black phosphorus (BP) resonator layers separated by a dielectric spacer and backed by an optically thick metallic reflector. Although BP inherently exhibits strong in-plane optical anisotropy, polarization- and angle-insensitive behavior is achieved through the fourfold rotational symmetry of the metasurface unit cell. Full-wave electromagnetic simulations show an average absorptance exceeding 98% across the LWIR (8–14 $\mu m$) for both transverse electric (TE) and transverse magnetic (TM) polarizations, with stable performance for incident angles up to ${70}^{\circ }$, while absorptance in the VIS–NIR range (0.4–2.5 $\mu m$) remains below 5.5%. Under realistic daytime conditions, the resulting spectral emissivity yields a maximum net cooling power of approximately 94 W $m^{-2}$ and a steady-state temperature reduction of about 7.8${}^{\circ }C$ below ambient. Colorimetric analysis based on the CIE 1931 standard illuminant D65 confirms a warm-yellow reflected appearance, demonstrating stable color display alongside efficient radiative cooling. The proposed BP-based dual-layer metasurface thus offers a compact, polarization- and angle-insensitive, spectrally selective platform for infrared thermal management, daytime radiative cooling, and multifunctional photonic applications.