• • The single-step self-stratification process eliminates multi-step fabrication, reducing production time and cost; the bilayer ethyl cellulose (BCEC) coating achieves a solar reflectance of 0.97 for the thickest film (BCEC-5), enabling near-ideal solar rejection for daytime radiative cooling.
• • The dense top layer thickness, tunable via precursor concentration, enables a palette of structural colors (blue, yellow, red, pink, green) without parasitic absorption, overcoming the aesthetic limitation of conventional white or silver coolers.
• • The porous bottom layer, formed via non-solvent-induced phase separation (NIPS), provides strong light scattering, achieving high solar reflectance while maintaining the cooling function; the intrinsic C–O bond absorption contributes to thermal emission in the atmospheric window.
• • The coating exhibits angle-dependent iridescence, a characteristic of thin-film interference, which may require optical design considerations for uniform color appearance in architectural applications.