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

ABSTRACT 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 (2.0 Pa) resulted in a WO3 film with the lowest mass density (5.72 g/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.