All-Season Thermochromic Window With Customizable Optical Switching Temperature and Directional Thermal Radiation.

Abstract

Dynamic all-season window is a key energy-saving solution for maintaining indoor thermal comfort. However, current progress faces challenges in balancing weather adaptability, functional tunability, and fabrication costs. This study introduces an all-season, polyvinyl propional-liquid-based asymmetric window. It features a tunable switching temperature ranging from 10 to 70 °C, maintains transparency at temperatures as low as -15 °C for extended periods, and delivers optimal net cooling (≈246.5 W m^- ²) and heating (≈113.9 W m^- ²) power as derived from the modulation of the optical spectrum, and boasts a service life of over 8 years, with resistance to 1000 thermal shock cycles. The synthesis of the polyvinyl propional liquid involves a zero-emission process, and the transparent-to-cloudy phase transition provides a visually identifiable and theoretically predictable indicator for reaction termination. Additionally, the liquid contains an in situ doped dispersant that functions as a cryoprotectant. Encapsulated between an outward-facing transparent glass layer and an inward-facing low-emissivity glazing, the asymmetric window directional scattering of solar radiation and thermal re-emission, effectively delivers net cooling in summer and heat retention in winter. This window presents a complementary, affordable, and sustainable solution for enhancing energy efficiency and thermal comfort in diverse climatic conditions.