Emerging materials and engineering strategies for performance advance of radiative sky cooling technology

Herein, we present a comprehensive review of the recent research efforts in addressing the challenge of low cooling power of radiative sky cooling (RSC) and offer promising avenues for further performance breakthroughs of this technology, mainly from reducing solar absorption, enhancing infrared emission, switchable emission and hybrid strategy. • The emerging materials and engineering strategies for performance advance of radiative sky cooling are summarized. • The efforts in reducing solar absorption and enhancing infrared emission are discussed in detail. • The great potential of thermochromic materials for switchable cooling/heating is highlighted. • The promising applications of hybrid strategies with evaporative cooling and electronics are discussed. • The remaining challenges and the insights are presented for the further performance breakthrough. With the growing global warming and climate change, the demand for clean cooling technologies has witnessed a sharp increase. Radiative sky cooling (RSC) can dissipate heat via the atmospheric window without pollution and energy consumption. Nevertheless, the low cooling power greatly blocks the large-scale application of this technology. Herein, a critical review of the recent efforts in addressing this challenge is presented to offer promising avenues for further performance breakthroughs of RSC technology. Firstly, working principles are presented to reveal the critical factors for efficient radiative cooling performance. Subsequently, systematic discussions on the efforts of reducing solar absorption are delivered and the promising structures for 99% solar reflectivity are highlighted. Particularly, the two promising strategies for enhancing infrared emission are discussed to evaluate their potential in commercial applications. Additionally, the promising designs for switchable solar reflectance and infrared emission are further outlined with a focus on switchable radiative cooling. More strikingly, hybrid strategies are highlighted for their great improvement in radiative cooling power and application scope. The last section outlines the remaining challenges and the corresponding insights for the further advance of RSC technology.