Electrochromic Energy Storage Devices with Polyimide Electrode Containing a Dibenzofuran-/Dibenzothiophene-Based Triphenylamine Group

Abstract

Dibenzofuran (DBF) and dibenzothiophene (DBT), which contain oxygen and sulfur atoms, possess high triplet energy levels and strong electron transport properties. With the heteroatoms fused with two benzene rings, these molecules combine the stability of aromatic rings with the electronic modulating properties of heteroatoms, which make them prone to forming charge transfer with other conjugated units; with a planar structure, without steric hindrance, it facilitates intermolecular π–π stacking, thereby increasing carrier mobility between adjacent chains, which makes it a structural block in optoelectronic polymers. Due to its unique propeller-like 3D structure and delocalized electronic characteristics, which decreases intense interactions between chains and provides a channel of ion transfer, triphenylamine (TPA) is widely used in optoelectronic materials, such as electrochromic materials (ECMs) and electrochemical energy storage materials (EESMs). Grafting different electron-donating or electron-accepting groups onto TPA, or copolymerizing them with units of varying properties can improve optoelectronic performance. In this research, two DBT (DBF)-TPA-containing diamine monomers were designed and synthesized. Then, four polyimides (PIs, DBT-TPA-NTCDA, DBT-TPA-DSDA, DBF-TPA-NTCDA, and DBF-TPA-DSDA), which exhibit excellent EC and supercapacitive (SC) performances, were obtained through a reaction with two dianhydrides containing naphthalene and benzene rings, respectively. To investigate the influence of structure on capacitance, two PIs (DBT-TPA-NTCDA and DBT-TPA-DSDA) with the best specific capacitance performance among these PIs were fabricated into ECSCs. As a result, at a current density of 1 A g–1, the specific capacitances reached 56.6 F g–1 and 52.3 F g–1, respectively; after 2500 charge–discharge cycles, ECSCs retain 75% and 72% of initial specific capacitances, respectively. It indicates that these PIs can be used as promising photoelectric materials in dual function energy storage devices.