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ABSTRACT
Tungsten oxide, has many interesting optical, electrical, structural, and chemicalproperties, are an ideal choice material for electrochromic smart windows devices. Inthis study, tungsten oxide thin films were prepared by the thermal oxidization onTungsten/ITO/glass substrates at different heat-treatment temperatures. The optimumheat-treatment temperature, corresponding to the maximum electrochromicperformance, was achieved by 550 oC. X-ray diffraction (XRD) analysis indicates thata tetragonal WO3 phase formed at temperatures below 550 oC and the phasetransformed to monoclinic W18O49 after the temperature was raised to 650 oC. Theelectrical properties analysis confirmed that the highest electrical conductivity showthe superior electrochromic performance, with the maximum coloration efficiencyvalue of 60.4 cm2/C. The tetragonal WO3 films, with heat-treatment temperature 550oC and 450 oC, exhibit good electrochromic properties such as a high diffusioncoefficient (1.7x10-11 cm2/s), fast electrochromic response time (coloration time 1.6 s,bleaching time 1.2 s), and high coloration efficiency (60.4 cm2/C).Furthermore, tungsten oxide nanowires were prepared on a tungsten film(W)/ITO-glass substrate at 500 oC for electrochromic devices using the heat-treatment technique. The electrical properties analysis confirmed that the highest electricalconductivity achieve the superior electrochromic performance with the maximumcoloration efficiency value. The tungsten oxide nanowires shows excellentelectrochromic properties such as a higher diffusion coefficient (2x10-9 cm2/s), fasterelectrochromic response time (coloration time 1.7 s, bleaching time 1.1 s), and highercoloration efficiency (67.41 cm2/C) than other tungsten oxide films withoutnanowires. Therefore, the tungsten oxides nanowire prepared by heat-treatmenttechnique, corresponding to the maximum electrochromic performance, would befurther adopted in the commercial application of smart windows.