Molecular engineering of novel D-A conjugated polymers for electrochromic energy storage devices toward enhanced performance

Abstract

Donor-acceptor (D-A) type conjugated polymers with unique redox activity have been received great attention due to their widespread applications in electrochemical devices. In this work, two D-A-D type monomers (TCQH and TCQF) with similar conjugated backbone consisting of bithiophene and camphor substituted quinoxaline units were prepared and further polymerized and directly deposited on ITO glass via electrochemical polymerization. The target conjugated polymers PTCQH and PTCQF showed both electrochromism and charge/discharge behaviors during the redox process. Among them, the polymer PTCQF with additional fluoride atoms on the conjugated backbone exhibited superior performance involving a high optical contrast of 72 % at 740 nm, short switching time (colored time of 1.0 s and bleached time of 0.9 s), good coloration efficiency over 223 cm2/C, an area specific capacitance of 7.2 mF/cm2 at the current density of 0.02 mA/cm2 and a mass specific capacitance of 190F/g at the current density of 0.5 A/g, which was probably benefit from its porous structure morphology. Moreover, electrochromic energy storage devices based on these polymers were fabricated and achieved obvious color change from burgundy to grayish blue during charge/discharge process, which guaranteed their potential application in smart energy storage devices with visualized energy level.