Dual‐Mode Integrated Janus Films with Highly Efficient NaH2PO2‐Enhanced Infrared Radiative Cooling and Solar Heating for Year‐Round Thermal Management

Abstract The currently available materials cannot meet the requirements of human thermal comfort against the hot and cold seasonal temperature fluctuations. In this study, a dual‐mode Janus film with a bonded interface to gain dual‐mode functions of both highly efficient radiative cooling and solar heating for year‐round thermal management is designed and prepared. The cooling side is achieved by embedding NaH2PO2 particles with high infrared radiation (IR) emittance into a porous polymethyl methacrylate (PMMA) film during pore formation process, which is reported for the first time to the knowledge. A synergistic enhancement of NaH2PO2 and 3D porous structure leads to efficient radiant cooling with high solar reflectance (R̅solar ≈ 92.6%) and high IR emittance (ε̅IR ≈ 97.2%), especially the ε̅IR value is much greater than that of the reported best porous polymer films. In outdoor environments under 750 mW cm−2 solar radiation, the dual‐mode Janus film shows subambient cooling temperature of ≈8.8 °C and heating temperature reaching ≈39.3 °C, indicating excellent thermal management capacity. A wide temperature range is obtained only by flipping the dual‐mode Janus film for thermal management. This work provides an advanced zero‐energy‐consumption human thermal management technique based on the high‐performance dual‐mode integrated Janus film material.