A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films

•A water-dispersed Prussian blue (wPB) thin film was used as the working electrode.•A poly(butyl viologen) (PBV) thin film was used as the counter electrode.•Succinonitrile (SN) with a K+ salt and SiO2 was used as the solid electrolyte.•The electrochromic device (ECD) showed a transmittance change of 62.5% at 545 nm.•The ECD shows a long-term stability of >1000 cycles at RT with +1.7/−1.0 V.

Prussian blue (PB) powder, which could be dispersed uniformly in water, was prepared through a simple process, and is designated as water dispersible Prussian blue (wPB). A PB thin film was spray-coated on an ITO substrate using the ink of this powder. Another PB thin film was prepared by the electrochemical deposition method (EDPB) for comparison. The properties of these two thin films were compared by using cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). A solid-state complementary electrochromic device (ECD) was fabricated based on a wPB thin film as the anodically coloring electrode and a poly(butyl viologen) (PBV) thin film as the cathodically coloring electrode. Succinonitrile (SN) with 0.1 M potassium bis(trifluoromethanesulfonyl)imide (KTFSI) and silicon dioxide (SiO2) nanoparticles was used as the solid electrolyte. The device could be switched reversibly between blue–violet and transparent upon application of 1.7 V and −1.0 V, and showed an initial transmittance change of 62.5% with a coloration efficiency of 157 cm2/C at 545 nm. The switching time required for both darkening and bleaching was about 10 s for a sample of 2.0×2.0 cm2. As for the electrochemical stability of the ECD, the transmittance change reached 58.4% at 545 nm after 1000 cycles, and the darkened state transmittance remained relatively constant after the same period.

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