Nanometer-optical-coating-based visibly tinted films with 24-hour sub-atmospheric passive cooling

Colored films absorb solar radiation at specific visible wavelengths, and they consequently heat up above atmospheric temperatures when exposed to sunlight. In this Letter, we report nanometer-thick TiN-based multilayers of light cyan, magenta, and yellow colors that can provide 24 h sub-atmospheric cooling when covered with high-emissivity polymers. Outdoor experiments have demonstrated that these visibly tinted films retain sub-atmospheric temperatures during daytime and nighttime. All fabricated films generated almost color-independent cooling powers and even surpassed commercial white paint at TiN thicknesses <5nm. Our work thus highlights the potential of multispectral selective absorbers as esthetic passive coolers.