Vanadium oxide is a well-known solid state thermochromic material. It undergoes a phase transition which is accompanied by a sharp change in the electrical conductivity as well as in the reflectivity for infrared radiation. This makes the material interesting for intelligent windows. However, it is very challenging to deposit Vanadium oxide in the correct crystallographic structure on a large area with sufficient reliability.
The authors present results achieved in a roll-to-roll deposition process of vanadium oxide on flexible glass of 0.1 mm thickness. The deposition width was 300 mm. The thermochromic material was embedded in zirconium oxide top and bottom layers which served as an antireflection layer and a crystalline template, respectively. A reactive high power impulse magnetron sputtering (HIPIMS) process was implemented. It was applied to a metallic rotatable vanadium target of 650 mm length. A closed loop control stabilized the oxygen partial pressure during the sputtering process. The tungsten doping (1.2 at%) of the target resulted in reduction in the phase transition temperature of the deposited layers from 68°C for pure vanadium oxide to a temperature below 30 °C. This is well suited for intelligent glazing solutions. The exact control of the sputtering process is essential for achieving the correct crystalline structure of the layer.
The thin glass with the thermochromic layer system was laminated to thicker panes for the integration in roofs and windows. First performance data in mockups will be presented.