Phase-change-coupled thermochromic radiative cooling smart windows

Smart windows capable of adaptive solar regulation, thermal energy storage, and radiative heat management are promising for improving building thermal regulation efficiency under variable climatic conditions. Herein, a phase-change-coupled thermochromic radiative cooling (PTRC) smart window with a multilayer asymmetric structure is developed for all-day passive building thermal regulation. The device integrates a high-emissivity polyethylene terephthalate (PET) outer layer, a paraffin-based phase change material (PCM) layer, a PET supporting layer, a hydroxypropyl cellulose (HPC) thermochromic hydrogel layer, and a low-emissivity ITO inner layer. This architecture enables synergistic regulation of solar transmittance, latent heat storage, and directional long-wave infrared radiation, in which the outdoor-facing PET layer promotes radiative heat dissipation, while the indoor-facing ITO layer suppresses indoor radiative heat loss. The optimized P29TRC smart window exhibits temperature-selective optical modulation, with luminous transmittance values of 5.3%, 80.3%, and 13.1% at 10, 40, and 60 °C, respectively, enabling low-temperature privacy protection, intermediate-temperature daylighting, and high-temperature solar shielding. In model house tests, P29TRC reduced the room-center temperature to 29.2 °C and decreased the inner and outer surface temperatures by 22.7 and 11.4 °C, respectively, compared with ordinary single-pane glass. Outdoor tests further confirmed its ability to suppress daytime overheating, delay nighttime cooling, and reduce morning temperature rise, achieving a temperature reduction of up to 6.4 °C under outdoor solar irradiation. This work provides a feasible strategy for integrating thermochromic modulation, phase-change thermal buffering, and asymmetric radiative management toward energy-efficient smart windows for passive building thermal regulation.