Boosting coloration efficiency in an electrochromic device using an ITO/Ag/ITO multilayered electrode and porous WO₃ chromic layer

High-performance electrochromic devices (ECDs) were fabricated by introducing indium tin oxide/silver/indium tin oxide (IAI) multilayers as a transparent conducting oxide (TCO) electrode in conjunction with microstructural tailoring of tungsten trioxide (WO₃) as an electrochromic (EC) layer. A 15-nm-thick Ag film with a preferential orientation of (111) and smooth morphology resulted in a high optical transmittance of 90.9% and sheet resistance 16.7 Ω/sq, making it a suitable TCO. In addition, the open network WO₃ film used as an EC layer was deposited by carefully controlling the chamber pressure during the sputtering process. A high chamber pressure (2.0Pa) resulted in a WO₃ film with the lowest mass density (5.72g/cm³) and a rough morphology. Half-cell ECDs consisting of a TCO bottom electrode (BE)/WO₃ stack immersed in LiClO₄ electrolyte were fabricated to verify the impact of using the IAI multi-layer stack and tailored WO₃ film as a TCO and EC layer, respectively. Significant enhancement in terms of coloration efficiency was achieved for the ECDs by adopting the IAI TCO and open network WO₃ EC layer compared to counterpart devices with an ITO TCO or dense WO₃ EC film. This can be explained by the facile carrier extraction (injection) and transport of Li ions.