Spectral Regulation Of Multilayered Interference Solar Absorbers

The solar thermal conversion is mainly achieved by solar collectors,and the core component of the collectors is the solar selective absorber.Therefore,the performance of solar selective absorbers will directly affect the solar thermal conversion efficiency.At the same time,the application of solar collectors to the buildings also needs to take into full account the aesthetic appearance of this important factor.At present,the colored solar selective absorbers studied at home and abroad cannot simultaneously consider the absorptivity of the absorbers,the emissivity of the absorbers,the color diversity and the difficulty of the preparation process,so new research and exploration are needed.In this thesis,a multilayered interference stack was used to design and prepare three solar selective absorbers with different colors,high absorptivity and low thermal emissivity,and the preparation process is relatively simple.The main work is as follows:(1)Based on maxwell's equations,the boundary conditions of electromagnetic field and Fresnel's formula,the reflectance and absorptance formulas of single-layer and multilayered dielectric thin films were presented.The graphic method of solar absorbers admittance was introduced and the calculation formulas of important parameters such as absorptance,thermal emittance and color chromaticity coordinates of the film were given.(2)Based on the multilayer interference stacks and by changing the thickness of each layer,three colored Cu/Al2O3/W/Al2O3/W/Al2O3 multilayered interference structures with blue,purple and yellow colors were designed.The three structures have high absorptivity in the region of 0.3~2.5 ?m and low emissivity in the region of 2.5~25 ?m at 80 ?,showing excellent spectral selective absorption.The performance of the three structures under oblique incident conditions were studied and absorptivity decreases with the increase of the incident angle.When the incident angle reaches up to 60? the structures have high absorptivity,showing that the designed structures are insensitive to the incident angle.The absorptivity spectra of each layer were calculated,and the contribution of each layer to the overall absorptivity were quantitatively analyzed.The results showed that the uppermost absorption layer contributes the most to the overall absorption and is the main absorption layer of the structure.(3)Three kinds of Cu/Al2O3/W/Al2O3/W/Al2O3 film samples were fabricated on a silicon substrate by magnetron sputtering.The thickness of each sub-layer of the sample were measured by a field emission scanning electron microscope,which were substantially consistent with the design thickness.The EDS spectrum of the sample showed that the main elements of the sample were O,Al,Cu and W,which matched with the component elements of the sample materials.The colors of the samples were blue,purple and yellow respectively,and the coordinates of each color were calculated.The reflectance spectra of the samples in the region of 0.3~25 ?m were measured.According to the law of conservation of energy,the absorption spectrum can be calculated.The results show that the three samples have high absorptivity in the region of 0.3~2.5 ?m and low thermal emissivity in the region of 2.5~25 ?m,all have spectral selective absorption characteristics.The experimental results show that the designed solar selective absorers have been successfully prepared.