It is well known that the earth’s atmosphere has a transparency window for electromagnetic waves between 8 and 13 µm. This transparency window coincides with thermal radiation wavelengths at typical ambient temperatures. Using this phenomenon, a body can be cooled just because its heat is radiated into cold outer space. It is the so-called passive radiative cooling. This mechanism is very interesting in the current context where we look for improve energy efficiency. This passive radiative cooling can, for example, be used in air-conditioning or to chill photovoltaic cells. The goal of this project is to design and optimize passive daytime radiative cooling systems based on nano/microstructured materials with specifics radiative properties. This project will be divided in three parts. A first part will concern the design and optimization of radiative coolers. Based on the expertise of the coordinator in the field of nano/micro structured systems thermal emission control and on the optimization numerical tools that he has developed, highly reflective systems for solar radiation and emitting only between 8 and 13 µm will be designed. The coordinator has already developed first numerical models based on systems coupling multilayer structures and surface gratings to obtain the desired radiative properties.
The second part of this project will deal with the fabrication of the system. Based on the results obtained in the first part, samples will be fabricated. Firstly, the coordinator will rely on the technology available in his laboratory. P' Institute has indeed a research bench composed of a dual-beam FIB (focused ion beam) that can etch the surface grating. The coordinator plan also to use the DRIE technique (Deep Reactive Ion Etching) available at ESIEE Paris. He will also collaborate with the team PPNa "Physics and Properties of Nanostructures" of the P' Institute. This team has extensive experience in the development of nanostructured materials. Two techniques will be used: the thin films deposits will be first done by sputtering and then by evaporation
The third part will concern the measurements of the radiative properties of the samples and the refractive index of each material composing the whole structure. To characterize the samples, the team TNR has an optical measurements bench using FTIR (Fourier Transform Infrared Spectroscopy). This experimental bench has already helped characterizing the selective thermal emitters that the coordinator has developed for thermophotovoltaics applications. The samples reflectivity spectra will be measured and compared with those obtained numerically. Spectral measurements can also be made at the LTEN (Nantes Thermal and Energy Laboratory). This team has recently acquired advanced equipment. This is an FTIR coupled to an IR microscope. To calculate the radiative properties of the system, each material is defined by its refractive index and at a first step, the coordinator will use the values available in the literature. However, the risk of having differences between these literature data and the actual properties of the synthesized thin layers is not negligible. Therefore, in order to carry out numerical simulations with input parameters closest to reality, measurements of refractive indexes over the entire range of wavelength under consideration will be systematically carried out. A great opportunity is the recent acquisition by the P' Institute of an IR spectroscopic ellipsometer. This experimental bench will be coupled with a visible ellipsometer. It is important to say that only two French laboratories have such an experimental bench.
Through these three scientific work packages, the final objective is the realization of one or more prototype of passive radiative coolers with high efficiency.
Monsieur Jérémie DREVILLON (Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
Help of the ANR 236,520 euros
Beginning and duration of the scientific project: December 2017 - 36 Months