Dual-Mode Integrated Janus Films with Highly Efficient NaH PO -Enhanced Infrared Radiative Cooling and Solar Heating for Year-Round Thermal Management.

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 NaH PO 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 NaH PO and 3D porous structure leads to efficient radiant cooling with high solar reflectance (R̅ ≈ 92.6%) and high IR emittance (ε̅ ≈ 97.2%), especially the ε̅ value is much greater than that of the reported best porous polymer films. In outdoor environments under 750 mW cm 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.