A broadband selective high-emissivity thin-film emitter for efficient passive radiative cooling

Abstract Passive radiative cooling is a promising thermal management technology that requires no external energy to achieve cooling. By emitting thermal radiation through the atmospheric transparency window to the cold outer space, it can maintain a temperature below the ambient environment. In this work, a broadband selective-emissivity emitter for daytime radiative cooling is proposed. The presented emitter achieves strong solar reflectivity and enhanced thermal emissivity within the atmospheric window. Simulation findings demonstrate that the proposed thin-film structure possesses excellent reflective performance from 0.3 μ m to 2.5 μ m, achieving an average reflectivity of 0.98. Meanwhile, an average emissivity of 0.93 is obtained from 8 μ m to 13 μ m, enabling efficient thermal radiation to outer space. Owing to its broadband selective-emission characteristics, the emitter effectively enhances the spectral matching between thermal radiation and the atmospheric window. Based on thermal equilibrium equations, the net cooling heat flux of the emitter is determined to be 117.64 W m −2 under typical daytime conditions. Compared with conventional broadband emitters, the proposed structure concentrates thermal emission predominantly during the atmospheric window, exhibiting excellent broadband selective-emission characteristics. The proposed design also shows promising potential for energy-efficient buildings, electronic heat dissipation, and temperature regulation of photovoltaic systems.