Surface Pattern over a Thick Silica Film to Realize Passive Radiative Cooling.

Yuhong Liu,Jing Li,Chang Liu

doi:10.3390/ma14102637

Abstract

Passive radiative cooling, which cools an item without any electrical input, has drawn much attention in recent years. In many radiative coolers, silica is widely used due to its high emissivity in the mid-infrared region. However, the performance of a bare silica film is poor due to the occurrence of an emitting dip (about 30% emissivity) in the atmospheric transparent window (8–13 μm). In this work, we demonstrate that the emissivity of silica film can be improved by sculpturing structures on its surface. According to our simulation, over 90% emissivity can be achieved at 8–13 μm when periodical silica deep grating is applied on a plane silica film. With the high emissivity at the atmospheric transparent window and the extremely low absorption in the solar spectrum, the structure has excellent cooling performance (about 100 W/m2). The enhancement is because of the coupling between the incident light with the surface modes. Compared with most present radiative coolers, the proposed cooler is much easier to be fabricated. However, 1-D gratings are sensitive to incident polarization, which leads to a degradation in cooling performance. To solve this problem, we further propose another radiative cooler based on a silica cylinder array. The new cooler’s insensitivity to polarization angle and its average emissivity in the atmospheric transparent window is about 98%. Near-unit emissivity and their simple structures enable the two coolers to be applied in real cooling systems.

Highlights

Radiative cooling is necessary in many semiconductor devices where undesired heating takes place
We propose and theoretically demonstrate that simple micro-structures, such as 1-D silica grating, can improve emissivity in the atmospheric transparent window such as 1-D silica grating, can improve emissivity in the atmospheric transparent window and realize radiative cooling
The absorption the solar spectrum can be Periodical as: boundary conditions were applied on both sides of a simulated cell

Summary

Introduction

Radiative cooling is necessary in many semiconductor devices where undesired heating takes place. Previous works on daytime radiative cooling have shown remarkable achievements For example, Raman, Li, and Ali proposed high-index and low-index alternating layers [22,23,24,25,26,27,28,29]. Zhu proved that tapered photonics tals can realize near-ideal emittance in the transparent window and achieved a high crystals can realize near-ideal emittance in the transparent window and achieved a radiative cooling efficiency in their work [26]. The micro- or nano-silica structures present in these types of radiative coolers might be too complicated to fabricate on a large scale. We propose and theoretically demonstrate that simple micro-structures, such as 1-D silica grating, can improve emissivity in the atmospheric transparent window such as 1-D silica grating, can improve emissivity in the atmospheric transparent window and realize radiative cooling.

Physical

Results

For100 both of the coolers coolinghave efficiency of around

4.4.Conclusions