Ultra‐Low Resistivity Copper Mesh as Embedded Current Collector Layer for Inkjet‐Printed Flexible Electrochromic Device Realizing Fast Response and Uniform Coloration

Abstract Flexible electrochromic devices (FECDs) hold great promise for energy‐saving static displays. As the most widely used flexible transparent electrode (FTE) material for FECDs, the indium tin oxide (ITO) coated on polyethylene terephthalate (PET‐ITO) suffers from relatively high sheet resistance which can cause nonuniform coloration during the device operation, hindering the development of large‐area FECDs. Herein, a hybrid FTE is developed in which an additional copper (Cu) mesh as an embedded current collector layer underneath the ITO film to achieve ultra‐low sheet resistance (<0.2 Ω □⁻¹) compared to that of PET‐ITO (≈35 Ω □⁻¹). The figure of merit (FoM) of the fabricated Cu mesh‐ITO is calculated to be 9500, nearly 200 times better than that of PET‐ITO. A binary‐solvent ink of electrochromic polymer (ECP‐magenta) is also developed to realize the patterning of FECDs via the inkjet‐printing method. Consequently, the inkjet‐printed FECD exhibits a fast response (≤1.2/1.9 s for coloration/bleaching) and excellent stability (less than 15% degradation after 50 000 switching cycles). In addition, uniform coloration is realized within 1 s on a 10 × 10 cm² large size FECD, indicating great promise for Cu mesh‐ITO as a new FTE material to replace PET‐ITO for large‐area FECDs.