Study Of Magnetron Sputtering Of Cr-CrO Solar Selective Absorbing Films

Solar selective absorbing films, which are the key technology for solar energy thermal utilization, have some lasting defects, such as poor stability, low repeatability and low conversion efficiency. How better does the use solar selective absorbing films technology became the particularly important question. The Ti-O films, CrO films and Cr-CrO films which have the concentration gradient of metal atom were deposited by RF reactive magnetron sputtering technology in this paper. The microstructure and optical properties of the films have been studied. The films'structure and performance effect of oxygen content, RF power, target-substrate separation and time have been analyzed. The preparation method and mechanism of solar selective absorbing films with high stability, high performance, low cost have been discussed.Firstly, the influence of RF reactive magnetron sputtering technology process parameters on the structure and absorption UV and visible spectrum of Ti-O films were discussed. The result shows that oxygen flow rate was the key factors on the structure and absorption spectrum red-shifted of the Ti-O films.The influences of RF reactive magnetron sputtering technology process parameters on optical properties of CrO films were discussed. The results showed that the process parameters, such as oxygen flow rate, target-substrate separation, time and target power on optical properties of CrO films were affected. The Cr atomic in films was decreased and absorbance was increasing with increasing oxygen partial pressure. The band gap of CrO films was decreased with increasing RF power. With further increase the RF power, the bombarding effect for the film surface will became too large, and smoothness of film surface will be damage, the roughness of film surface was became worse. The deposition time was proportional to film thickness. The crystallization degree of films was improved and beneficial to absorption with increasing deposition time. The transmittance of films will decreases gradually with decreasing target-substrate separation. The sputter erosion was formed on films surface and damage the morphology and structure and goes against the absorption when further decrease the target-substrate separation.Performances of the graded Cr-CrO solar selective absorbing films were studied. The results showed that the UV and visible spectrum reflectance of Cr-CrO films was obviously reduced with decreasing the Cr composition gradual slope of Cr-CrO films from substrate to top; The UV and visible spectrum reflectance of Cr-CrO films was reduced with increasing the layer number of Cr-CrO absorbing layer, and it could be further decreased after depositing SnO2 antireflection layer. The UV and visible spectrum average reflectance of graded Cr-CrO solar selective absorbing films was less than 10% by optimizing process parameters, and the spectrum selective absorbing is obviously.Through the research of the relevance between RF reactive magnetron sputtering process and optical properties of the Ti-O, CrO, Cr-CrO materials, and obtain the ideal solar selective absorbing films, the low cost and high efficiency of solar selective absorbing films will be developed in possible. It will promote the development of the solar heat utilization in some degree.