A highly visible-transparent thermochromic smart window with broadband infrared modulation for all-season energy savings.

Thermochromic smart windows effectively reduce the energy consumption for buildings through passive light modulation including the transmission of visible (T) and near-infrared (T) light, and the emissivity of mid-infrared (ε) light in response to ambient temperature change. However, thermochromic windows that maintain high T while modulating T and ε simultaneously are highly desirable but still challenging. Here, we develop a thermochromic smart window based on a two-way shape memory polymer to enable reversible transformation and achieve T modulation of 44.0% and ε modulation of 76.5% while maintaining high T (>50%). Compared to traditional windows based on silica glass, this device shows 4°C lower temperature in summer daytime, 2°C higher in winter daytime, and 1°C higher in spring nighttime. It is expected that our device can achieve greater annual energy savings in comparison with commercial glass anywhere in the world and promote the progress of thermochromic windows for energy-efficient buildings.