Eco‐Friendly Transparent Silk Fibroin Radiative Cooling Film for Thermal Management of Optoelectronics

Abstract Although transparent radiative cooling is a passive cooling strategy with practical applications and aesthetic appeal, complex manufacturing processes and the use of environmentally unfriendly thermal emitters remain latent problems. Herein, eco‐friendly transparent silk radiative cooling (TSRC) films are developed, regenerated from natural silkworm cocoons, for zero‐energy‐consumption thermal management of optoelectronic devices. These TSRC films can dissipate heat radiatively through molecular vibrations of the protein backbone and side chains, while retaining the function and appearance of the associated devices, due to their high visible transparency. Theoretical and experimental investigations revealed that the thermal emission increases rapidly upon increasing the film thickness, but slowly thereafter achieves saturation; nevertheless, the intrinsic solar absorption of silk in the ultraviolet and near‐infrared regions also grows linearly, unavoidably weakening the cooling effect. After spectroscopic optimization, the maximum cooling power during the daytime and nighttime is improved to 77.6 and 101.7 W m −2 , respectively. Gratifyingly, the films have a remarkable effect on the cooling performance of electronic devices under sunlight. For example, the TSRC film provides a temperature drop of 5.1 °C for a smartphone during multitasking and charging, and 14 °C for a silicon solar panel with an improvement in the photoelectronic conversion efficiency (≈7%).