  Long term stability is the most pressing issue that impedes commercialization
of Vanadium Dioxide (VO2) based functional films, which show a gradual loss of
relative phase transition performance, especially in humid conditions when
serving as smart windows. Here, we investigated the impact of different
interface on the deterioration process of VO2 films and proposed a novel
encapsulation structure for largely extended service life. Hydrophobic and
stable hafnium dioxide (HfO2) layers have been incorporated with VO2 films for
encapsulated surfaces and cross sections. With modified thickness and structure
of HfO2 layers, the degradation process of VO2 can be effectively suppressed.
The proposed films can retain stable phase transition performances under high
relative humidity (90%) and temperature (60 Celsius) over 100 days, which is
equal to about 16 years in the real environment. Improving the stability of VO2
materials is a necessary step towards commercializing production of high
performance films for long term use.
