Morphology‐Controlled Silica Nanoparticle Coatings for Transparent Radiative Cooling

ABSTRACT In this study, transparent passive radiative cooling coatings are introduced by immobilizing solid and hollow silica (SiO 2 ) spheres on glass substrates. It is showcased that particle morphology within a sub‐monolayer coating strongly influences visible and atmospheric window reflectance of glass. Solid and hollow‐sphere particles of total diameter within the Mie regime reduce atmospheric window reflectance ( R AW ) at the expense of higher visible reflectance ( R VIS ). This trade‐off is dependent on particle and core diameter. Solid particles with particle diameter >1000 nm can reduce the R AW of glass by up to 65 %, though increase R VIS by 25 %. Meanwhile, the use of hollow‐sphere nanoparticles of similar diameters and thin shells (25–50 nm) can reduce the R AW of glass by up to 35 % with minimal changes to R VIS . These spectroscopic trends are validated numerically via both Mie theory and effective medium theory. The work demonstrates that hollow‐sphere morphology is a valuable lever to control passive radiative cooling for various solar applications requiring transparency, such as coatings for windows or photovoltaic devices.