Triarylamine-based polyimides enable smart electrochromic displays with energy storage

Abstract

Color-to-color switching electrochromic polymers with a high contrast ratio and the additional ability to store energy are attractive for applications in smart display devices and energy recycling and reuse. However, developing materials that combine both optimized electrochromic and energy storage performances remains a significant challenge. To address the integration of polymer color switching and energy storage, the synthesis of a donor-acceptor-donor (D-A-D) triarylamine (TAA)-based diamine monomer with the benzothiadiazole unit as the acceptor unit and using heteroatom as ion adsorption sites is here detailed. The electroactive polyimide enabling energy storage with a visual display of the state of charge (SoC) is subsequently prepared by polycondensation of the diamine monomer with 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride. The final polyimide film electrode exhibits 90% optical contrast, provides a capacitance of 304.5 F g⁻¹ at a current density of 1 A g⁻¹, and enables SoC monitoring through multiple color changes. Besides, we further demonstrate here that symmetric quasi-solid-state electrochromic supercapacitors constructed with a polyimide film as functional layers also exhibit excellent optical contrasts above 60% and high capacitance for energy recovery and reuse in practical applications. Additionally, the ion adsorption energy and the density of states of polyimide are calculated using density functional theory to gain insight into the energy storage mechanism. Overall, we demonstrate and rationalize here the effectiveness in color switching, energy storage, and integrated SoC displaying of triarylamine-based monomers that use electron-withdrawing conjugated heterocycles as bridges along with the corresponding polyimides.