WO₃ electrochromic devices (ECDs) are representative inorganic devices, despite their slow bleaching speed. During coloration, Li⁺ ions are inserted into the WO₃ film, while some remain trapped after bleaching. These trapped ions slow the bleaching process. In this study, we fabricate a complementary ECD with aligned grid patterns to overcome problems with bleaching speed. A complementary ECD uses a cathodic coloring layer and an anodic coloring layer together. Tungsten oxide (WO₃) acts as the cathodic coloring layer, while prussian blue (PB) acts as the anodic coloring layer. In the complementary device, WO₃ and PB contribute together to the transmittance change. As a result, less Li⁺ insertion into WO₃ is required to reach the same ΔT. This reduces Li⁺ trapping in WO₃ and lowers the required operating voltage.
The WO₃ layer and the counter electrode are both deposited as grids. The grid structure exposes the large surface area of the patterned lines to the electrolyte, compared to the film structure. Since both the top and side surfaces are exposed, the reaction area between the electrochromic material and the electrolyte increases. The grid pattern also maintains open areas between the lines, which helps maintain transmittance even when two coloring layers are used.
The grid patterns are fabricated using the AFN (Aerodynamically focused nanoparticle system) deposition process ^[1]. AFN forms micro-sized patterns in a single step at room temperature by aerodynamically focusing dry nanoparticles onto the substrate. Therefore, AFN can directly form grid patterns without a separate wet-patterning process. This makes AFN suitable for fabricating aligned WO₃ and counter electrode grid patterns. The counter electrode consists of PB and antimony doped tin oxide (ATO) powders mixed at a 20:80 wt% ratio ^[2]. PB acts as an anodic coloring material, while ATO stores ions. The two grids are aligned and assembled with a gel electrolyte.
Two grid-patterned devices are prepared with different counter electrodes for comparison: an ATO grid and a PB/ATO grid. ATO stores ions but does not provide anodic coloration. Therefore, the ATO grid device does not have the complementary coloring effect of the PB/ATO grid device. Their ΔT, coloration and bleaching times, coloration efficiency, and Q_ex/Q_in are compared. The PB/ATO grid device is expected to show faster bleaching due to its complementary structure with the WO₃ layer. This study presents new insights to improve the bleaching speed of WO₃ ECDs by fabricating complementary grid patterns.

Electrochromism,Tungsten oxide,Prussian blue,Complementary electrochromic device,Patterning,Dry deposition