High quality thermochromic VO2 films prepared by magnetron sputtering using V2O5 target with in situ annealing

Vanadium dioxide (VO2), a well-known Mott insulator and a prominent thermochromic material, exhibits an intelligent optical response from the infrared-transparent state to the infrared-blocking state below and above its transition temperature, respectively. Despite there have been numerous studies on its synthesis, a few could readily obtain high quality VO2 thin films except on single crystal epitaxial substrates. Its lack of versatility to form onto various substrates while retaining the specific function also needs to be addressed. Here, we present a sputtering method using V2O5 target with in situ annealing to prepare high-quality VO2 thin films on Si and quartz substrates. The results show that pure monoclinic VO2 could be obtained in a narrow range of oxygen flow ratio (from 0 to 0.74%) in Ar/O-2 working gas during sputter deposition. The structural evolution was verified by Raman spectroscopy. At the transition temperature, the remarkably large optical transmittance contrasts of similar to 74% and similar to 77% were obtained at the incident wavelength of 2.5 and 3 pm, respectively. The luminous transmittance values at room temperature and high temperature were 36.63 and 38.87%, respectively. The measured solar transmittance modulation efficiency (Delta T-sol) was 5.87%, which is comparable to or even better than the reported values of VO2 films prepared using sputtering. We also demonstrated the spontaneous response of electrical performance with applying potential and varying temperature. Our results revealed the facile preparation of large area and high-performance thermochromic VO2 thin film on non-epitaxial substrates of Si and quartz which greatly augment its applications in solar-heat managements and optoelectronics.