All-Polymer-Based Flexible Supercapacitor with Smart Yellow to Green Visualization of the Energy Level Afforded by a Nonconjugated Polyamide

Flexible electrochromic energy-storage systems represent an emerging class of multifunctional optoelectronic devices that can simultaneously modulate light transmission and store electrical energy. In this work, a nonconjugated polyamide incorporating two redox-active centers, propylenedioxythiophene (ProDOT) and triphenylamine (TPA), was introduced as a multifunctional electrode material for flexible electrochromic supercapacitors based on ITO-PET substrates. The polymer exhibited good wettability and a granular morphology on flexible electrodes, enabling efficient electrochemical performance. In a three-electrode configuration, the polyamide-modified ITO-PET electrode delivered an areal capacitance of up to 3.95 mF·cm –2 at 5 mV·s –1 and 4.73 mF·cm –2 at 0.1 mA. Flexible electrochromic supercapacitor prototypes were further assembled and evaluated in both planar and bent configurations. The planar device achieved a maximum areal capacitance of 0.564 mF·cm –2 and an energy density of 0.490 μWh·cm –2, while the bent configuration retained comparable values of 0.527 mF·cm –2 and 0.457 μWh·cm –2, demonstrating mechanical robustness. Notably, the bent device exhibited improved cycling stability, maintaining Coulombic efficiencies above 96% over 500 cycles. The polymer also displayed pronounced electrochromic performance, with a reversible yellow-to-green transition, optical contrast up to 67.12% at 880 nm, and fast switching times (3.3/2.3 s). Enhanced coloration efficiency after prolonged cycling further confirmed operational stability. These findings highlight the potential of redox-active nonconjugated polyamides as promising candidates for flexible capacitive electrochromic windows and next-generation wearable energy devices.