| Summary: | Wavelength‐selective light trapping has been widely applied in fields such as energy utilization, optical sensing, optical imaging, and so forth. Though metasurfaces have exhibited to efficiently trap the light for diverse optical responses with specific configurations, the manufacturing costs and processing precision both limit the extensive applications. Here, a compact optical coating to trap light either at a single wavelength or across a broadband within a nanometer‐thick single‐layer metallic coating based on mirror|phase tuning layer|absorptive (MPA) and MPA|anti‐reflection coating stacks is proposed. The intermediate phase‐tuning dielectric provides a specific phase shift for the cavity to achieve destructive or constructive interference for ≈100% absorption or reflection correspondingly by switching from ultrahigh‐index dielectric behavior to epsilon‐near‐zero material behavior. And the additional dielectric is introduced to reduce the increasing reflection for the final broadband absorption with a thicker absorptive metal. Furthermore, the efficient color‐preserving solar–thermal conversion based on this compact coating (4‐layer) with the entire thickness of ≈300 nm is demosntrated experimentally. Various perceived colors are produced by simply changing the thickness of the top dielectric layer with the efficient solar–thermal conversion remained, verified by the temperature difference between the fabricated device and the dye‐based plastic exceeding 13 °C with the solar irradiance ≈850 W m−2.
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