All-ionic liquid electrochromic devices based on viologen-type and ferrocene-type room-temperature ionic liquids with temperature adaptability and environmental friendliness

Ionic liquids have been recognized as promising electrolytes in electrochromic devices (ECDs). However, the limited solubility of commercial electrochromic materials (ECMs) in ionic liquid effects the electrochromic performance of ECDs. This work synthesized viologen-type (Vio-IL) and ferrocene-type (Fc-IL) room-temperature ionic liquids (RTILs), which have melting points of −22.5 °C and −43.6 °C, respectively. ECDs prepared using these two RTILs exhibit superior optical modulation ability (ΔT = 79.4 %) and good cyclic stability (1000cycles 96.2 %). These two RTILs exhibit advantages because they can be miscible with commonly ionic liquids solvent. Further, ultra-thin (10 μm) ECDs prepared using these RTILs with 20 wt% ionic liquid diluent not only have good electrochromic performance (ΔT = 73.1 %, 1000cycles 95.6 %, 3.7 s for coloring and 13.3 s for bleaching) but also have a wide temperature working window (−30°C–70 °C). These ultra-thin and low-solvent ECDs have the potential to enable temperature adaptability and lightweight and eco-friendly smart windows.