Janus Interface Engineering Boosting Visibly Transparent Radiative Cooling for Energy Saving

Visibly transparent radiative cooling (VTRC) shows great potential in energy-saving buildings or car glasses for lighting and cooling. How to balance the lighting and cooling performance is of significance to VTRC. In addition, the thermal radiative performance on the inner side should also be determined for cooling. Here, we designed a Janus VTRC coating consisting of a thermal emitter, PDMS, and a transparent near-infrared reflector, TiO2/Ag/TiO2. On the outer side, the visible transmittance T̅vis = 0.70, while the solar reflectance R̅solar = 0.40, and the thermal emittance in the atmospheric window ε̅LWIR = 0.94 can be achieved experimentally. On the inner side, the thermal emittance ε̅IR can be 0.90 or 0.01 depending on the substrate (glass or near-infrared reflector), which acts as the radiative conductor or barrier for energy saving in hot or cold internal situations. Compared with glass, the designed PDMS/NIR/glass achieves an average temperature drop of 14.6 °C experimentally. The energy-saving calculation based on seven cities in China shows that the VTRC coating can save 34-44% of the annual cooling energy consumption. This Janus visibly transparent radiative cooling technology with internal and external regulation provides a potential strategy for energy saving under the requirement of simultaneous lighting and cooling.