Effect of random microstructure of the film surface on daytime radiative cooling performance

Abstract

Radiative cooling film has been widely concerned due to its green energy-saving, low-carbon, and environmentally friendly features. Its surface morphology greatly influences radiative cooling performance. However, traditional morphology designs are cumbersome and costly to prepare limiting the widespread application. In this study, the polydimethylsiloxane (PDMS) radiative cooling film with random microstructure surfaces was investigated experimentally and numerically. The simulation results show that the optical properties of the film surface are optimized when the random microstructure root mean square (RMS) roughness is 3 μm and the correlation length (CL) is 6 μm. Moreover, radiative cooling films with random microstructure surfaces were prepared by simple template reprinting with different roughness, and their effectiveness on silicon solar cell cooling was verified by indoor or outdoor experiments. Specifically, the film surface was selected for subsequent radiative cooling experiments by polishing the substrate and reprinting the random microstructure with 500 mesh sandpaper. The results demonstrated that the random microstructure of the film surface was capable of cooling the bare silicon solar cell by 6.6℃ and increasing the power generation efficiency by 44 % under the standard solar light in indoor experiments. For outdoor experiments, a cooling of 2.40 °C has been demonstrated. Moreover, the random microstructure of the film surface displays the potential for cooling another material, including copper, aluminum and glass. Under sunny weather, temperature reductions of 2.12, 2.28, and 0.18 °C were observed, respectively.