Prussian Blue-Cobalt Oxide Double Layer for Efficient All-Inorganic Multicolor Electrochromic Device

An “all-inorganic”, fast, and power-efficient solid-state electrochromic device has been realized by choosing Co 3 O 4 and PB films as complementing electrodes. The prussian blue and cobalt oxide films have been synthesized via a simple galvanostatic method to achieve better film quality to be used in a device. Prior to fabricating a prototype solid-state device, the electrodes have been tested using in situ electrochemical and spectroscopic studies. This is followed by fabricating a solid-state device that shows switching between multiple colors with an applied bias of less than a couple of volts. A moderate color contrast of ∼40% with 1.5 s switching time has been observed with showing stability for more than 900 s of continuous switching. A redox-driven electrochromic behavior of individual electrodes makes it possible for the solid-state device to show beautiful colors with a small applied bias. Electrochemical and spectroscopic measurements have been carried out to establish the possible mechanism of color switching shown by the device. Moreover, a coloration efficiency of ∼250 cm 2 /C makes it comparable to an “all-organic” or hybrid solid-state device, with its strong nature being an additional advantage.