Preparation of a highly-reflective TiO2/SiO2/Ag thin film with self-cleaning properties by magnetron sputtering for solar front reflectors

A novel highly-reflective thin film with self-cleaning properties consisting of TiO2–SiO2–Ag was successfully prepared by magnetron sputtering for solar front reflectors. The reflectivity of the film was experimentally tested and for comparison with values predicted from Essential Macleod Program (EMP). The effect of annealing temperature on the thin film structure, morphology, hydrophilic and photocatalytic properties was detailedly studied. Thereafter, the sequent tests were performed to investigate the influence of annealing temperature and thickness on the thin film reflectivity and aging properties. The results show that the TiO2 layer can form an excellent rutile structure with particles sized around 42 nm when annealed at about 500 °C. When increasing annealing temperature, the reflectivity of the film peaks at 400 °C while the hydrophilcity is characterized with a continuous growth. Though reflectivity of prepared film indicates a declining trend, it still vibrates in an uncertain range when increasing the film thickness gradually. In comparison with predicted values, an optimal structure of thin film is: glass/Ag (130 nm)/SiO2 (400 nm)/TiO2 (300 nm), with a reflectivity about 0.9601 and excellent hydrophilcity when annealed at about 500 °C. Finally, this prepared film can maintain a stable and high reflectivity at 0.9578 after a 1200 h aging test, indicating potential application in solar front reflectors.