Deep eutectic solvent‐based gel electrolytes for flexible electrochromic devices with excellent high/low temperature durability

With the increasing interest in the application of electrochromism to flexible and wearable electronics in recent years, flexible electrochromic devices (ECDs) that can function at extreme temperatures are required. However, the functionalities of flexible ECDs are severely hampered by the inadequate choice of electrolytes, which might ultimately result in performance fading during low- and high-temperature operations. Here, we develop a deep eutectic solvent (DES)-based gel electrolyte that can maintain its optical, electrical, and mechanical properties over a wide range of temperatures (-40 to 150 degrees C), exhibiting an extremely high visible-range transmittance over 90%, ion conductivity of 0.63 mS cm(-1), and fracture strain exceeding 2000%. Owing to the excellent processability of the DES-based electrolytes, provided by dynamic interactions such as the lithium and hydrogen bonding between the DES and polymer matrix, a directly written patterning in ECDs is realized for the first time. The fabricated ECDs exhibit an excellent electrochromic behavior superior to the behavior of the ECDs fabricated with traditional gel electrolytes. The introduction of such DES-based electrolytes is expected to pave the way for a widespread application of electrochromic products.