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

Abstract

Polymer electrolytes were synthesized by two different approaches and applied to electrochromic devices based on electrodeposited tungsten oxide (WO 3) or poly(3,4-ethylenedioxythiophene) (PEDOT) films as the cathode, and a Prussian blue (PB) film as the anode. The first method involved the entrapping of an ionic liquid in a polymer host (poly(methylmethacrylate) or PMMA) and the second approach relied on the in situ thermal polymerization of methylmethacrylate (MMA) in the hydrophobic ionic liquid, yielding a solidified transparent gel. The effect of in situ solid polymer electrolyte formation on device performance characteristics was realized in terms of a larger coloration efficiency of 119 cm 2 C 21 (l = 550 nm) achieved for the WO 3-PB (MMA) device, as compared to a value of 54 cm 2 C 21 obtained for the WO 3-PB (PMMA) device. Similar enhancements in electrochromic coloring efficiency, reflectance contrast, and faster switching kinetics were obtained for the PEDOT-PB (MMA) device. The strategy of introducing an electrolyte to the electrochromic device in a liquid state and then subjecting the same to gradual polymerization allows greater accessibility of the electrolyte ions to the active sites on the electrochromic electrodes and superior interfacial contact. As a consequence, larger optical contrast and faster kinetics are achieved in the MMA based devices. While PEDOT films were amorphous, PB films were semi-crystalline but only in the case of WO 3 ; the hexagonal structure of WO 3 , equipped with three/four/six-coordinated voids was found to affect bleaching kinetics favorably. The performance of PMMA based electrolyte is limited by high resistance at the electrode-electrolyte interface, and a smaller number of ions available for oxidation and reduction. Large area (y10 cm 6 4 cm) devices were also fabricated using this simple wet chemistry method and their ability to color uniformly without any pinholes was demonstrated.

A new organo-inorganic hybrid of poly(cyclotriphosphazene-4,4′-bipyridinium)chloride with a large electrochromic contrast

“…More details about device fabrication can be found in our previous report. 25 A transparent, pale blue colored device encompassing the electrolyte in the form of a gel was obtained and all the edges were sealed with epoxy. The device is hereaer referred to as the PPBP-PB device.…”

A WO3–poly(butyl viologen) layer-by-layer film/ruthenium purple film based electrochromic device switching by 1 volt application

“…In the past, amorphous WO 3 was widely studied owing to fast electrochromic switching response arising from its large specific surface areas [4]. Electrochromic WO 3 films can be prepared by several methods such as sputtering, evaporation, chemical vapor deposition (CVD), pulsed laser deposition (PLD), sol-gel, electrochemical deposition, hydrothermal reaction, and layer-by-layer (LbL) fabrication [9][10][11][12][13]. Layer-by-layer deposition of polymeric thin films was developed by Decher et al wherein a substrate is immersed in alternating solutions of polycations and polyanions, resulting in linear film growth with the ultimate thickness being controlled by the number of bilayers deposited [14,15].…”

Correlation between electrochromism and electronic structures of tungsten oxide films

“…Among various EC materials such as WO 3 , MoO 3 , NiO and Nb 2 O 5 , WO 3 is one of the most extensively studied because of its useful EC properties. [7][8][9][10][11] The evaluation of EC materials is typically based on their coloration efficiency (CE), reliability, response time and durability (which measures how long the EC properties of the material can be sustained when cations are intercalated/deintercalated under a cyclically applied electrical bias). 12,13 Previous studies have shown that the crystal structure (crystalline or amorphous) and microstructure of tungsten oxide greatly inuence its EC properties.…”