Transparent Electrochromic Polymers with High Optical Contrast and Contrast Ratio.

Colored-to-transmissive electrochromic polymers, known for their wide selection of colors and solution processability, have gained great attraction in thin film electrochromic devices that have entered the market. However, their adoption in the real world is limited due to their limited optical transparency and contrast. This study introduces a new molecular design strategy to overcome these issues. This strategy involves using meta-conjugated linkers (MCLs) and aromatic moieties along polymer backbones, which enable transparent-to-colored electrochromic switching. The MCL interrupts charge delocalization, increasing the band gap in the neutral state and ensuring transparency in the visible region. This innovative approach achieves nearly 100% transmittance in the neutral state and a high absorption in the oxidized state, overcoming residue absorption issues in conventional electrochromic polymers. Simultaneously, the MCL and aromatic moieties enable low oxidation potential, facilitating stable transparent-to-color switching. Polymers developed using this approach exhibit wide color tunability, optical contrast exceeding 93%, and cycling stability over 5000 cycles with less than 3% contrast decay. Our research represents a major advancement in overcoming existing challenges, enabling polymer-based electrochromic devices for visual comfort and energy conservation.