Optical Properties and Phase Transition in VO2 and Ti:ZnO/VO2 Thin Films

Energy saving methods/materials are becoming increasingly important for meeting society's energy demands. Smart windows made of thermochromic materials show great promise in reducing the energy consumption of buildings. Thermochromic vanadium dioxide (VO2) is a potential candidate for smart window applications; however, its commercial usage is limited by its low visible light transmittance. To address this issue, we integrated a VO2 layer with an antireflecting Ti-doped ZnO (TZO) layer. Single-layer VO2 and bilayer TZO/ VO2 thin films were fabricated on c-Al2O3 substrates using radio frequency sputtering, and their structural, morphological, and optical properties were investigated. The single-phase growth of the VO2 and TZO layers in single and bilayer samples was confirmed through room-temperature X-ray diffraction (XRD) measurements. Temperature-dependent grazing incidence XRD measurements during the heating and cooling cycle were performed in a synchrotron to explore the structural changes in the VO2 and TZO/VO2 thin-film samples. The structural phase transition curves were modified in the TZO/VO2 thin-film sample. The increase in visible light transmittance was examined using ultraviolet-visible spectroscopy in the transmittance mode at room temperature. The enhanced visible light transmittance of the TZO/VO2 bilayer shows promise for realizing more effective smart windows.