In-situ switchable nanofiber films based on photoselective asymmetric assembly towards year-round energy saving

Abstract

Buildings thermal management consumes 51% of the world’s energy use. Optimization of the energy use can be potentially achieved via daylight harvesting and radiative cooling approaches, yet their simultaneous utilization under static conditions is challenging due to opposite operation principles. Here, an in-situ switchable photoselective polymer (PSP) material was prepared by sequential electrospinning of light-reflecting and light-absorbing layers made of contrasting polymer nanofibers. As-prepared PSP material exhibited high solar light reflectance of 97.7% and high broadband emissivity of 94.9% resulting in radiative cooling power 111.1 W·m-2. Such “cooling” state of the PSP film can be easily switched to a “heating” one via impregnation of the index matching liquid that suppresses scattering at the film-air interface and reduces solar band reflectivity of the film. Thanks to the highly porous structure of the designed PSP film, its switching takes less than 5 min and allows to achieve an integrated solar absorbance of ~95.6% resulting in the estimated heating power of 781.6 W·m-2. Performed numerical calculations further supported high potential of the developed PSP film for thermal management of the buildings located at high latitudes with the energy savings up to 89.74 GJ m-2·y-1 and reduced CO2 emissions down to 21.69 t.