Fully Organic and Flexible Biodegradable Emitter for Global Energy-Free Cooling Applications

Abstract

In recent years, many researchers believe that global energy consumption can be significantly reduced by passive daytime radiative cooling (PDRC) without any electricity input. Over a decade, PDRC has been developed to enhance solar reflectivity and emissivity in the long-wavelength infrared (LWIR) region; however, sustainable materials for radiative cooling have not been sufficiently investigated. In the present study, the preparation of an eco-friendly polymer structure for effective radiative cooling via thermally induced phase separation is described. The as-fabricated radiative cooler exhibits reasonable durability for application to buildings, and furthermore, biodegradable polylactic acid (PLA) is environmentally benign with respect to end-of-life disposal. Moreover, the hierarchically porous PLA exhibits a solar reflectivity of 0.91 and an LWIR emissivity of 0.92, thus realizing high-performance passive radiative cooling without a silver coating for solar reflection. In addition, a radiative cooling power of 117 W m(-2) is achieved under direct sunlight, and the porous PLA cooled as much as 9 degrees C below the ambient temperature. This cooling effect is the highest among all organic-based passive radiation cooling emitters reported so far. The present work provides an ideal passive radiative cooling strategy for creating environmentally friendly buildings with reduced energy consumption.