Tungsten trioxide thin films are successfully synthesized by a sol-gel method using tungsten hexachlorideas precursors. The structural, chemical, and optical properties of the prepared films are characterized by scanning elec-tron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometry. The electrochem-ical and electrochromic properties of the films before and after heat treatment are also investigated by cyclicvoltammetry, chronoamperometry, and in situ transmittance measurement system. Compared to as-prepared films, heat-treated tungsten trioxide thin films exhibit a higher electrochemical reversibility of 0.81 and superior coloration effi-ciency of 65.7 cm2/C, which implies that heat treatment at an appropriate temperature is a crucial process in a sol-gelmethod for having a better electrochromic performance.

1. Introduction
 2. Experimental
 3. Results and Discussion
 4. Conclusions
 Acknowledgements
 References

• Tae-Ho Kim(Interdisciplinary Program in Creative Engineering, School of Energy, Materials, and Chemical Engineering, Korea University of Technology and Education, Cheonan 31253, Korea)
• Yoon-Chae Nah(Interdisciplinary Program in Creative Engineering, School of Energy, Materials, and Chemical Engineering, Korea University of Technology and Education, Cheonan 31253, Korea) Corresponding Author