Transfer of the sputter technique for deposition of strongly thermochromic VO2-based coatings on ultrathin flexible glass to large-scale roll-to-roll device

Abstract

The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. We report on transfer of the sputter technique for deposition of strongly thermochromic ZrO2/W-doped VO2/ZrO2 coatings on ultrathin (0.1 mm) flexible glass from a laboratory-scale device with three (V, W and Zr) planar magnetron targets to a large-scale roll-to-roll device with two (W-doped V and ZrO2) rotatable magnetron targets. The depositions were performed at a relatively low substrate surface temperature (330–350 °C) and without any substrate bias voltage. The W-doped VO2 layers were deposited using a reactive high-power impulse magnetron sputtering with a pulsed O2 flow control. We compare the process parameters used in both deposition devices and explain the basic principle of this sputter technique using the discharge characteristics measured during a large-scale roll-to-roll deposition. We characterize the design, structure (X-ray diffraction) and optical properties (spectrophotometry and spectroscopic ellipsometry) of the three-layer coatings. The coatings prepared on ultrathin flexible glass using the large-scale roll-to-roll device at a temperature close to 350 °C exhibit a low transition temperature of 22 °C, an integral luminous transmittance over 45% and a modulation of the solar energy transmittance approaching 10%. This is a promising first step to a cost-effective and high-rate preparation of large-area thermochromic VO2-based coatings for future smart-window applications.