The novel preparation method of thermochromic VO2 films with a low phase transition temperature by thermal oxidation of V–Mo cosputtered alloy films

Vanadium dioxide (VO2) has been studied extensively for its unique insulator-metal transition characteristics and potential applications in thermochromic smart windows, switching devices, and infrared detectors. However, how to balance the metal-insulator transition temperature, luminous transmittance (Tlum) and solar modulation ability (ΔTsol) of VO2 thin films remains a challenge. In this work, high-quality thermochromic VO2 thin films were prepared by a two-step method of magnetron sputtering and thermal oxidation annealing. Metallic and alloyed V–Mo layers were first deposited by direct-current reactive magnetron sputtering, and then a thermal oxidation annealing process was used to obtain pure and Mo-doped VO2 thin films. The Mo content in the films was regulated by changing the sputtering power of the vanadium target, and the effect of Mo doping on the crystallinity, microstructure, phase transition temperature and optical properties of VO2 thin films was studied. The shift of the VO2(011) peak to a lower 2θ angle in the XRD patterns showed that Mo was successfully diffused into vanadium dioxide films. The phase transition temperatures were decreased continuously from 57.4 to 32.7 °C by decreasing the sputtering power of vanadium. The thinner Mo-doped VO2 thin films showed higher luminous transmittance and lower transition temperature. Our results were shown to be an innovative preparation method to fabricate thermochromic VO2 films with a low phase transition temperature, balanced luminous transmittance and solar modulation ability by thermal oxidation of V–Mo cosputtered alloy films.