Operation mechanism investigation of electrochromic display devices using tungsten oxides based on solid-state metal–oxide–metal capacitor structures

• Electrochromic mechanism correlated with oxygen vacancy concentration was proposed.
• The degraded switching distributions are originated randomly distributed conduction paths.
• The occurrence of irreversible redox process could deteriorate the coloration efficiency.
• Large operating current and overdrive voltage lead to poor electrochromic efficiency.

In this work, we investigate the electrochromic effect of WO3 electrochromic display device and operation mechanism based on a solid-state TaN/WO3/ITO metal–oxide–metal capacitor. The electrochromic switching mechanism correlated with the oxygen vacancy concentration was proposed and well-predicted. The experimental results reveal that electrochromic device using electrodeposited WO3 without post annealing exhibits the much better coloration and bleach process than those of annealed sample. The cycling test of WO3 metal–oxide–metal capacitor also demonstrates that the degradations of current/voltage distributions are mainly originated from randomly distributed connected paths consisting of oxygen vacancies. Thus, oxygen vacancies formed during WO3 electrodeposition process or post film annealing need to be well controlled.