Long-lived electrochromic device with protonated viologen and Poly(ethylenedioxythiophene-carbazole)/Prussian blue composite for smart windows

A complementary electrochromic device (ECD) configuration featuring a protonated viologen (VNH2+) as the cathodically coloring electrochrome and a composite of poly(ethylenedioxythiophene-carbazole) (i.e. poly(EDOT-Cz)) and Prussian blue (PB) as the anodically coloring electrochrome marks the first implementation of this innovative high contrast device. A comparative analysis of VNH2+//poly(EDOT-Cz) and VNH2+//poly(EDOT-Cz)/PB ECDs demonstrates a superior integrated visible light transmission modulation (ΔT) of 50.4%, versus 76.7%, higher diffusion coefficient of 4.4 × 10−11 versus 3.9 × 10−10 cm2 s−1, higher coloration efficiency (CE) of 424 versus 562 cm2 C−1 (at 550 nm), faster color-bleach switching times of (7.0 and 4.0 s) versus (1.2 and 1.0 s) and a CIE chromaticity coordinate corresponding an intense deep blue state (y: 0.058 versus 0.218) achieved with the composite relative to the pure polymer. The VNH2+//PB ECD also shows lower CE (69 cm2 C−1) and slower coloration-bleaching kinetics (20 and 2 s) compared to the composite based ECD. In addition, long-term cycling stability attained for the VNH2+//poly(EDOT-Cz)/PB ECD, whereby it endures 5000+ color-bleach cycles without showing any major deterioration in optical modulation or switching kinetics underscores the suitability of the composite based ECD for practical smart window applications.