Ordered Porous Polymer Films for Highly Efficient Passive Daytime Radiative Cooling

Constructing porous polymer films for passive radiative cooling has proved an efficient way to dissipate heat to cold outer space in the form of thermal radiation and concurrently reflect incident sunlight without additional energy input. Nevertheless, most researches focus on randomly distributed pores, which cannot precisely control the pore arrangement and size and may restrict the optical properties. Herein, an ordered porous poly­(methyl methacrylate) (PMMA) film comprising three-dimensional (3D) ordered micropores and highly interconnected nanopores is presented via a sacrificial template method. It exhibits prominent solar reflectance (0.94), long-wave infrared (LWIR) thermal emissivity (0.95), and low thermal conductivity (0.044 W m^–1 K^–1). The ordered porous PMMA film can achieve a sub-ambient temperature drop of up to 10.6 °C during midday under an average solar irradiance intensity of ∼829 W m^–2 and promisingly realize a maximum daytime cooling power of ∼75.6 W m^–2. This work will significantly influence the design of porous structural radiative cooler and is conducive to understanding the underlying relationship between pore arrangement, pore size, and optical/thermal performance, facilitating the development of high-performance passive daytime radiative cooling porous polymer films.