Hybrid passive cooling: towards the next breakthrough of radiative sky cooling technology

Radiative sky cooling is a promising passive cooling technology that dose not consume energy or produce greenhouse gas. It has been extensively studied in the past decades. However, its relatively low cooling power (similar to 100 W m-2) presents a significant barrier to its commercial deployment. For broader applications, integrating phase change and evaporative cooling can significantly enhance the cooling performance and temperature control capabilities of radiative sky cooling. In this review, we summarize the recent advances in hybrid cooling achieved by incorporating radiative cooling with phase change cooling or evaporative cooling. The regulatory mechanism of hybrid cooling is first discussed to reveal the detailed working principle. Subsequently, the structure form and cooling performance of hybrid cooling are summarized to fully clarify the core points of material design and highlight their benefits. In addition, the application scenarios of hybrid cooling are further discussed to underline their promising application potential. Last but not least, the challenges and prospects are presented to advance the commercial application of hybrid cooling. A critical review of the regulatory mechanisms, structural design, cooling performance, and applications of hybrid cooling to advance its commercial use in passive cooling.