β-ketoenamine-linked covalent organic frameworks ultrathin film for transparent supercapacitors with enhanced charge storage capability

Abstract

With the development of electronic products toward optical transparency and intelligent portability, transparent supercapacitors (TSCs) have been considered as one of the ideal and efficient power sources. However, it is still a challenge to explore covalent organic frameworks (COFs) based transparent conductive electrodes (TCEs) with high photoelectric property and capacitive activity. Herein, β-ketoenamine DqTp (DAAQ-TFP, DAAQ = 2,6-diaminoanthraquinone, and TFP = 1,3,5-triformylphluroglucinol) COFs ultrathin films are synthesized for TCEs through the Schiff base reaction of DAAQ and TFP. The DqTp ultrathin films fully expose the redox-active anthraquinone moieties, shorten the ion/electron transport path, accelerate the transport and diffusion rate, and thus enhance charge storage capability. DqTp-1 TCEs possess the excellent optoelectronic property with optical transmittance (T550 nm) of 69.46%, sheet resistance (Rs) of 7.45 Ω sq−1, and remarkable areal capacitance (CA) of 355.67 μF cm−2. The corresponding asymmetric DqTp-1//PANI TSCs (T550 nm = 58.06%) yield a high CA of 64.55 μF cm−2 at 3 μA cm−2 and have a maximum areal energy density of 0.015 μWh cm−2 at 1.95 μW cm−2. After 5000 cycles, the capacitance retention is 96.9%. This work provides key insights into the design and synthesis of transparent redox-active COFs-based TSCs with excellent photoelectric property and enhanced charge storage capability.