Optimized thermochromic properties for smart window application of VO2 films by wet-etching process.

Vanadium dioxide (VO 2) is a potential candidate in smart window application field owing to its reversible and automatic first-order insulator-to-metal transition (IMT) at 341K which can induce dramatic changes of transmittance in near infrared band through MIT. However, the low T lum (visible light transmittance) below 40% and ΔT sol (solar modulation efficiency) below 10% of pure VO 2 films have severely constrained the practical application in smart windows. In this paper, by etching the VO 2 films fabricated by magnetron sputtering with sodium hydroxide solution, the VO 2 films with improved optical properties were obtained. Specifically, the T lum increased to 42.6% and the ΔT sol decreased to 15.5% for 150 nm VO 2 films after 9 min etching, the T lum increased to 56.4% and the ΔT sol decreased to 12.2% for 150 nm VO 2 films after 12 min etching, respectively, comparing with the unetched film of 150 nm (T lum :16.9%, ΔT sol :16.3%). Furthermore, we synthetically investigated the influences of etching on the IMT properties and molecular structure of the VO 2 films through characterizations such as Raman spectra, XRD, XPS and SEM. The proposed methods represented a facile and cost-effective approach for enhancing thermochromic properties that could promote the application of VO 2 thin films in smart windows. • Optimizing the etching process of vanadium oxide film. • The main mechanism of sodium hydroxide etching vanadium oxide film is figured out by characterization. • Optimized optical properties (T lum : 42.6%, ΔT sol : 15.5% and T lum : 56.4%, ΔT sol : 12.2%) are obtained. • This alkalinity etching method could be an alternative approach to improve the thermochromic properties of VO 2 thin films. [ABSTRACT FROM AUTHOR]