Highly Transparent and Fast‐Switching Solid‐State Electrochromic Devices With Nanostructured Solid Polymer Electrolytes

ABSTRACT While electrochromic devices employing solid polymer electrolytes offer advantages in safety and mechanical durability compared with conventional devices using liquid electrolytes, their performance is often limited by slow switching speeds and low coloration efficiency mainly due to slow ion transport within the solid medium. To address these challenges, we introduced a nanostructured solid polymer electrolyte (NSPE) featuring high‐density nanoscale ion‐transport channels embedded within a mechanically robust polymer matrix. These nanochannels provide efficient ion‐conduction pathways while minimizing light scattering. Using a complementary WO 3 /NiO electrochromic configuration, we evaluated the effect of the NSPE architecture on device performance. The resulting device exhibited a high bleached‐state transmittance of 74.5% and a large optical modulation of 63.7% in the visible region. Notably, the device exhibited rapid switching kinetics, with coloration and bleaching times of 11.8 and 2.1 s, respectively, together with a high coloration efficiency of 146.7 cm 2 C − 1 . Furthermore, the electrolyte enabled the successful fabrication of both large‐area (80 mm × 80 mm) and flexible electrochromic devices while retaining electrochromic functionality, highlighting its scalability and mechanical adaptability. These results demonstrate that nanochannel‐engineered solid electrolytes provide an effective strategy for achieving high‐performance, transparent, and mechanically versatile electrochromic devices for next‐generation smart window applications.