The Solar Selective Absorbing Coatings Prepared By Modulated Pulse Power Reactive Magnetron Sputtering

In order to relieve the strain on the energy problem,human beings are constantly developing new energy while using the existing energy in a reasonable and efficient way.Solar radiation has been recognized as the future world's most competitive energy because of its advantages of abundant reserves,non-pollution and so on.At present,researchers have developed a variety of ways to use solar energy,among which,solar thermal conversion technology with a very long history is the most simple and direct method.Meanwhile,solar water heaters are the most widely used technology among all the solar energy utilization technologies.Nowadays,solar water heater has been widely used in daily life of most families,and it is one of renewable energy industry with higher commercialization level.Solar energy is a kind of energy with low-quality and low energy density,so solar collectors must be used to collect solar energy in order to obtain a higher solar-thermal conversion efficiency.And solar selective absorbing coatings are the key to solar collectors,whose optical properties and quality determine the thermal trapping performance of the device.In order to improve the energy conversion efficiency,the solar selective absorbing coatings should have a higher absorption rate in the solar spectral region and a lower emissivity in the infrared wavelength region,and also the coatings should be with the good weather resistance,which determines durability and stability of the solar water heater.Therefore,we need to optimize the existing process,and develop better technology to prepare solar selective absorbing coatings with excellent optical properties and weather resistance.Based on the background,Cu/TiN/TiSiN/SiN solar selective absorbing coatings(SSACs)were deposited on stainless steel(SS)substrates via a home-made modulated pulse power reactive magnetron sputtering(MPPMS)system.In this tandem absorber system,Cu,TiN,TiSiN and SiN act as the infrared reflectance layer,the main absorbing layer,the semi-absorbing layer and the antireflection layer,respectively.An average absorptance(?)of 0.944 and emittance(?)of 0.057 were achieved in coatings prepared under optimized conditions.On the other hand,the SS/TiN/TiSiN/SiN SSACs without Cu under-layer showed a similar absorptance(?0.95)but a poorer emittance and solar selectivity.X-ray diffraction analysis showed that the Cu layer is polycrystalline,while TiN,TiSiN and SiN are amorphous.The solar selective absorbing performance of the SS/Cu/TiN/TiSiN/SiN SSAC did not show significant changes after they were heat-treated in vacuum up to 500? and in air up to 250? which demonstates the coatings have excellent heat resistance performance.Absorptance and emittance data,atomic force microscopy(AFM)images and XRD spectra were collected for coatings exposed to different levels of thermal stresses(2 h in air at 200?,250?,300?,350? and 2h in vacuum at 500?,600 ?,700 ?)to illustrate the microstructural and morphological stabilities of this SSACs.