High-performance bifunctional electrochromic-supercapacitor devices based on indole derivative copolymerized with 3,4-ethylenedioxythiophene

The integration of energy storage and electrochromic functionalities into a single device holds great promise for smart windows, displays, and energy-efficient systems. This study presents the first bifunctional electrochromic supercapacitor device (ECSCD) based on an indole-7-carboxylic acid (IN7Ca) and 3,4-ethylenedioxythiophene (EDOT) copolymer, synthesized via electropolymerization. Unlike conventional single-material systems, this work leverages a novel asymmetric design (PIN7Ca anode/P(EDOT-co-IN7Ca) cathode) to simultaneously achieve record performance in both optical and energy storage metrics. The electrochromic and supercapacitor properties of the homopolymer (PIN7Ca), copolymer (P(EDOT-co-IN7Ca)), and PEDOT are systematically investigated. The copolymer demonstrates unprecedented optical transmittance, faster switching (1.8 s), and enhanced electrochromic performance due to the incorporation of EDOT. Its improved capacitive behavior and >90 % cycling stability after 2000 cycles arise from the synergistic combination of IN7Ca’s redox activity and EDOT’s electrochromic stability. An asymmetric ECSCD achieves a record electrochromic contrast (ΔT = 47 %) among solution-processed devices, alongside a high specific capacitance (1.9 mF/cm² at 0.01 mA/cm²) that surpasses recent PEDOT- and PANI-based systems by >30 %. These results highlight copolymerization as an effective strategy for designing multifunctional materials with benchmark performance. This approach establishes new design principles for high-performance ECSCDs, supporting their integration into next-generation smart and sustainable technologies.