Bistable Silver Electrodeposition‐Based Electrochromic Device with Reversible Three‐State Optical Transformation By Using WO3 Nanoislands Modified ITO Electrode

Abstract A bistable electrochromic (EC) device which can reversibly transform between transparent, mirror, and black states based on reversible metal Ag electrodeposition is achieved by introducing 1) a (3‐mercaptopropyl) trimethoxysilane (MPTMS)‐treated indium‐tin‐oxide (ITO) glass electrode modified with WO 3 nanoislands (WNs) as the rough surface and 2) ionic liquids (IL) into electrolyte to form an anion‐blocking layer, toward achieving long‐term memory performance. Typically, the EC cell is packaged by sandwiching gel electrolyte between the flat and WNs‐modified ITO electrodes. Under opposite voltages, this smart device can transfer from transparent to black (+2.5 V/9.4 s) or mirror (−2.5 V/8.3 s) state by depositing Ag on the WNs‐modified or flat ITO electrode surface, respectively. The assembled device exhibits over 80% mirror reflectance and below 10% transmittance of black state. After power off, both the black and mirror states remain bistability for a long time (>30 min) when IL are introduced into electrolyte for the EC device. The electrical double layer in the highly viscous electrolyte with IL contributes to form a barrier to bromide ions, which protects the Ag layer from dissolution at open circuit. This multifunctional energy‐efficient EC device has shown great potential and competitiveness for numerous applications compared to conventional EC devices.