Decoupled Black–White Thermochromic Dual Layers Achieving 36.7% Solar Reflectance Tunability for All-Season Thermal Regulation

Abstract Thermochromic coatings enable passive building energy management, but approaches lack broad tuning ranges, continuous tunability, practical transition temperatures, or scalability. This work introduces a dual-layer thermochromic coating (DLTC) that functionally decouples the black and white states between layers, achieving a transition temperature of 25 °C, solar reflectance tunability of 36.7% (51.4–88.1%), and visible reflectance tunability of 81.2% (6.0–87.2%). DLTC integrates a thin (∼68 μm) black-to-translucent topcoat on an opaque ultrawhite basecoat (>400 μm). Under cold conditions, the topcoat darkens, absorbing solar radiation; as the temperature rises, the topcoat becomes translucent, exposing the ultrawhite basecoat and producing a radiative cooling surface. Outdoor tests show up to 23 °C cooling relative to a black roof in hot weather and 12 °C warming relative to a white roof in cold weather. EnergyPlus simulations predict HVAC energy savings over traditional gray and white cool roofs across U.S. climate zones.