A green-yellow reflective electrochromic device

All solid state green-yellow electrochromic devices (ECD) performing in reflexion and built with Prussian Blue (PB) as electrochromic (EC) layer, CeO2–TiO2 as counter-electrode and PVB-based membrane as electrolyte have been assembled and characterized. The PB films were deposited by galvanostatic method and stabilized by cyclic voltammetry evidencing two cathodic and two anodic peaks and confirming their blue, green and transparent states. The analysis of PVB-based polymer electrolyte revealed an Arrhenius type ionic conductivity with values increasing from 7.7 × 10−4 S cm−1 at 27 °C to 3.6 × 10−3 S cm−1 at 70 °C. The Raman spectra of the membrane evidenced two peaks, centered at 113 and 145 nm, attributed to I3− and I5−, respectively, and related to the yellow color of the sample. The ECD changed its reflectance from 46% (at −2.0 V) to 23% (at +2.0 V) at 550 nm. The digital system for color management of pictures confirmed the change of color and the CIE LAB 1976 color scale evaluation revealed the total color difference between green (+2.0 V) and yellow (−2.0 V) of ΔE = 40.34. After 400 green-yellow color chronoamperometric cycles between −1.5 V and +1.5 V one observed a decrease of the charge density from −5.5 mC cm−2 to −4.9 mC cm−2; moreover a memory test realized with the device in open circuit conditions revealed an increase of the reflectance from 27.5% to 30% for the deep green state and a decrease from 36.5% to 33% for the yellow state of, during 120 min. All the obtained results suggest that the investigated green-yellow reflective ECD performed well and can be a promising solution for display applications.

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