3D printed multicolor Prussian blue-viologen hybrid electrochromic devices: Toward high contrast ratio and fast switching electrochromic devices

A new 3D printed multicolor Prussian blue-viologen inorganic-organic hybrid electrochromic device was successfully developed using digital light processing. Photocurable 1-(2 cyanophenyl)-1 '-(2-hydroxyethyl)-[4,4 ' bipyridine]-1,1 '-diium (CPHEV)-based ionogel was printed on ITO glass as an electrochromic layer. The thin film of Prussian blue (PB) was electrodeposited on another ITO glass as an ion storage layer. With PB thin film, the ECDs exhibited a bleaching time 330 times faster than that of ECDs without PB. The ECD showed excellent electrochromic performance with a high color contrast ratio of 93.4 % at -2.5 V with a pulse width of 5 s. Moreover, the ECDs also exhibited multi-coloration in L*a*b* color space with the highest different color points (Delta E*ab) value of 75.2 between the bleaching state and coloring state. A high coloration efficiency of the ECD was obtained at 296 cm2 C-1 corresponding to 60 % of a full optical switch at -2.5 V. The 3D printed ECD was successfully demonstrated using digital light processing (DLP) with high dimensional accuracy and resolution.