Ultrathin flexible electrochromic devices enabled by highly transparent ion-conducting films

Flexible electrochromic devices (ECDs) have generated widespread interest due to their attractive application prospects in emerging wearable and portable electronics, electronic papers/billboards, and other advanced display applications. However, the lack of rational design for flexible electrochromic devices with both high flexibility and ultrathin nature remains a challenge, limiting its development toward practical applications. Herein, a flexible and ultrathin ion-conducting film (ICF) is proposed by combining poly(vinylidene fluoride) polymer matrix with electrolyte to assemble into multicolor electrochromic devices. As a result, the as-obtained ICF exhibits extremely high visible-range transmittance of over 90%, ionic conductivity of 0.11 mS cm(-1) at room temperature, large electrochemical window (3.55 V), and excellent mechanical flexibility, making it an excellent candidate for the electrochromic applications. By taking advantage of the ion-conducting film, the fabricated ICF-based electrochromic device based on polyaniline (PANI) electrode exhibits reversible color transformations from chartreuse to green and dark blue, as well as ultrathin characteristics, excellent flexibility, and strong mechanical stability, superior to the behavior of the ECDs fabricated with traditional gel electrolytes. The electrochromic behavior in the PANI during the electrochemical process is comprehensively studied by density functional theory (DFT) calculations. In addition, the device also shows an effective electrochromism with multicolor properties at a wide temperature range (-10 to 60 degrees C). This work provides a feasible way for assembling high-performance flexible ECDs for potential applications in multicolor displays and wearable electronics.