Switchable daytime radiative cooling and nighttime radiative warming by VO2

Abstract

With the increasing prominence of energy issues, the radiative thermal management techniques hold great potential in sustainable energy research, which attracted much attention. In this study, a temperature-adaptive selective emission structure is proposed to control the phase transition state of doped vanadium dioxide (VO₂) by the difference of daytime and nighttime temperatures to achieve all-day radiative thermal management. During the day, the ambient temperature increases. When the VO₂ temperature exceeds the phase transition temperature, the structure has high reflectivity in the solar spectral band and high emissivity in the atmospheric transparent band (8–14 μm), resulting in radiative cooling. At night, the ambient temperature decreases. When the temperature of VO₂ is lower than the phase transition temperature, the structure has low emissivity in the atmospheric transparent band (8–14 μm) and high absorptivity in the atmospheric radiative bands (5–8 and 14–16 μm), thus realizing the warming effect. Additionally, the impact of variation in material thickness and angle of incidence on the spectral characteristics of the designed structures are also investigated, and the results indicated that the impact on the spectral characteristics of the structures are not significant. This study provides an innovative approach to regulating energy efficiency in buildings, vehicles and utilities, which can help to promote diversity in energy utilization.