Innovative smart film can change between heating and cooling properties based on temperature

Buildings account for 30% to 40% of the world’s total energy consumption. Much of this comes from building heating, ventilation, and air conditioning systems, creating a need for more energy efficient alternatives to achieve conservation and emission reduction goals.

Xie and Liu presented an alternative — a film that can switch between cooling and heating modes.

While intelligent control of film radiation — which causes heat transfer — has developed quickly, previous research focused on individual parameters, such as solar absorbance, transmittance, or infrared emittance. Xie and Liu found a way to modulate all these parameters synergistically.

The smart film relies on In₃SbTe₂ (IST), a material whose optical and radiation properties change based on temperature.

“The IST undergoes a transition from an amorphous state to a crystalline state, accompanied by changes in its optical properties,” said author Bowei Xie. “These changes result in abrupt alterations in the film’s infrared emittance and solar absorptance, which in turn affects the temperature.”

Their film was able to provide a wide modulation of heat flux, from solar heating when exposed to temperatures below 0 F (250 K) to radiative cooling over 130 F (330 K).

Since IST’s crystallization changes its optical properties, the heating and cooling from the film can be precisely modulated based on external temperature. The temperature can be further, more precisely controlled through manual control of the IST crystallization percentage, allowing multilevel modulation. The film’s elegant, simple structure is fairly easy to replicate.

“In the future, our research will emphasize the further optimization of the modulation performance of the smart film, as well as preparation for experimenting with it in real situations,” Xie said.

Source: “In₃SbTe₂-based all-season smart film with synergistic modulation of solar and thermal radiation,” by Bowei Xie and Linhua Liu, Applied Physics Letters (2025). The article can be accessed at https://doi.org/10.1063/5.0253948 .