Preparation and characterization of HfO2/VO2/HfO2 sandwich structures with low phase transition temperature, excellent thermochromic properties, and superior durability

In the last few decades, smart windows made from VO2-based thermochromic films have attracted extensive attention, but their actual commercial applications are limited by low luminous transmittance (T-lum), low solar modulation ability (Delta T-sol), high phase transition temperature (T-c), and poor durability. In this study, glass/HfO2/VO2/HfO2 tri-layer films were designed and deposited on glass substrates by pulse laser deposition. Crystal structures, surface morphology, surface roughness, electrical properties, and optical properties of as-prepared sandwich structure films were analyzed. Results showed that both HfO2 buffer layer and antireflection layer (ARL) were monoclinic phase and grew along the (020) and (-111) crystal planes, respectively. HfO2 buffer layer not only reduced T-c of VO2 film by about 20 degrees C, but also played an important role in regulating crystal quality and surface morphology of VO2 films. More importantly, by covering films with HfO2 ARL, T-lum and Delta T-sol of VO2 film were greatly improved. In particular, when the thicknesses of HfO2 buffer layer and ARL were 80 nm and 120 nm, the obtained HfO2/VO2/HfO2 tri-layer film reached a balance between high T-lum (-47.2%), high Delta T-sol (-9.1%) and low T-c (-49.1 degrees C). In addition, after 216 h of boiling water treatment, Tlum and Delta T-sol of HfO2/VO2/HfO2 film covered with 120 nm thick ARL still remained at 49.3% and 7.0%, showing excellent durability. This research provides a new strategy for designing VO2-based smart windows with high performance and good durability.