Electrochromic device response controlled by an in situ polymerized ionic liquid based gel electrolyte

摘要

Polymer electrolytes were synthesized by two different approaches and applied to electrochromicuddevices based on electrodeposited tungsten oxide (WO3) or poly(3,4-ethylenedioxythiophene)ud(PEDOT) films as the cathode, and a Prussian blue (PB) film as the anode. The first method involvedudthe entrapping of an ionic liquid in a polymer host (poly(methylmethacrylate) or PMMA) and theudsecond approach relied on the in situ thermal polymerization of methylmethacrylate (MMA) in theudhydrophobic ionic liquid, yielding a solidified transparent gel. The effect of in situ solid polymerudelectrolyte formation on device performance characteristics was realized in terms of a largerudcoloration efficiency of 119 cm2 C21 (l = 550 nm) achieved for the WO3–PB (MMA) device, asudcompared to a value of 54 cm2 C21 obtained for the WO3–PB (PMMA) device. Similar enhancementsudin electrochromic coloring efficiency, reflectance contrast, and faster switching kinetics were obtainedudfor the PEDOT–PB (MMA) device. The strategy of introducing an electrolyte to the electrochromicuddevice in a liquid state and then subjecting the same to gradual polymerization allows greaterudaccessibility of the electrolyte ions to the active sites on the electrochromic electrodes and superiorudinterfacial contact. As a consequence, larger optical contrast and faster kinetics are achieved in theudMMA based devices. While PEDOT films were amorphous, PB films were semi-crystalline but only inudthe case of WO3; the hexagonal structure of WO3, equipped with three/four/six-coordinated voids wasudfound to affect bleaching kinetics favorably. The performance of PMMA based electrolyte is limitedudby high resistance at the electrode–electrolyte interface, and a smaller number of ions available forudoxidation and reduction. Large area (y10 cm 6 4 cm) devices were also fabricated using this simpleudwet chemistry method and their ability to color uniformly without any pinholes was demonstrated.