Sandwich-like composite membrane for advanced radiative cooling applications

Abstract

Passive daytime radiative cooling (PDRC) offers an energy-efficient method of cooling by reflecting sunlight and emitting heat to the cold outer space through the atmospheric transparent window (ATW). For optimal performance, radiative coolers require high reflectance in the solar spectrum to minimize solar heat absorption and near-unity emissivity in the ATW to maximize heat dissipation. Here, we present a scalable composite radiative cooling membrane (cRCM) composed of a hierarchically porous polysulfone (PSF) layer, sandwiched between two flexible polydimethyl-siloxane (PDMS) layers. The PSF layer, fabricated using a simple non-solvent induced phase separation (NIPS) method, exhibits a high solar reflectance of 98.2 ​% across wavelengths of 0.3–2.5 ​μm owing to its high refractive index of 1.64. The PDMS layers, attached on both sides of the PSF membrane via roll-to-roll lamination, offer excellent mid-infrared (MIR) emissivity of 94.2 ​% across wavelengths of 2.5–20 ​μm. Under midday conditions, the membrane achieves an average temperature reduction of 5.0 ​°C below ambient air temperature, with a theoretical cooling power of 114 ​W/m². Year-round simulations indicate significant cooling energy saving in warm and tropical regions. The new membrane represents a significant advance in PDRC technology, offering promising applications in energy-efficient cooling systems.