Nanometer optical coatings with absorbing materials allow the tuning of structured absorption spectra, thus developing ultrathin color devices. However, these coatings are limited by the narrow bandwidth and tunability of wavelength that restrict the chroma and hue characteristics of colors, respectively, apart from imposing adverse thermal problems under sunlight exposure. Here, we demonstrate that inversely designed TiN/ZnS/Ag coatings attain a wide color gamut in the trilayer configuration and efficiently dissipate heat through thermal radiation when transfer-printed on high-emissivity polymers. Daytime experiments reveal that fabricated optical films yield an almost color-independent heat dissipation rate against solar heating. Moreover, they outperform commercial paints of the same color when applied to three-dimensional miniature houses. All magenta, green, cyan, and yellow optical films lower the roof temperature by 10, 6, 8, and 2 °C below one sun irradiance, respectively, compared to their paint counterparts; the temperature gradient increases directly with the level of sunlight.
Keywords: colored optical film; mid-infrared photonics; multiscale design; nanometer optical coating; radiative cooling.