Effect of oxygen on the electrochromism of RF reactive magnetron sputter deposited tungsten oxide

High coloration efficient WO3, deposited by reactive sputtering, is influenced by the oxygen concentrations in a sputtering system. In this study, a survey on the effect of oxygen concentration in the rf sputtering atmosphere and the subsequent deposited film was studied to reveal the microstructural changes in relation to the electrochromic properties. The electrochromic properties determined include cyclic voltammetric behavior, coloring and bleaching response time, x(LixWO3), optical density changes and coloration efficiency. Experimental results show that the maximum current, as well as the x(LixWO3) value, occurred in the O2/Ar flow ratio at 0.3–0.4. This may be compromised by the low valence tungsten ions that play a role in expelling cations in the films deposited at a low O2/Ar flow ratio and hypothetically due to the limitation of electron conduction for high oxidation films deposited at high O2/Ar flow ratios. The response time, decreased with the increasing O2/Ar flow ratio, can be considered separately by the ion diffusion difficulty already established elsewhere. As a whole, the optimized O2/Ar flow ratio would be in the range of 0.3–0.4 for transmittance control applications.