Enhanced electrochromic performance by uniform surface morphology of tungsten oxide films

Tungsten oxide(WO₃) films with uniform surface morphology are fabricated using a spin-coating method for applications of electrochromic(EC) devices. To improve the EC performances of the WO₃ films, we control the heating rate of the annealing process to 10, 5, and 1 °C/min. Compared to the other samples, the WO₃ films fabricated at a heating rate of 5 °C/min shows superior EC performances for transmittance modulation(49.5%), response speeds(8.3 s in a colored state and 11.2 s in a bleached state), and coloration efficiency(37.3 cm²/C). This performance improvement is mainly related to formation of a uniform surface morphology with increased particle size without any cracks by an optimized annealing heating rate, which improves the electrical conductivity and electrochemical activity of the WO₃ films. Thus, the WO₃ films with a uniform surface morphology prepared by the optimized annealing heating rate can be used as a potential candidate for performance improvement of the EC devices.