Neutral-state black electrochromic polymer with enhanced supercapacitor electrode performance

Abstract

Neutral-state black electrochromic materials are attracting attention, especially in the applications of displays, car-rear views, sensors, and electronic papers. This study aimed to obtain a black electrochromic polymer via electrochemical techniques. For this aim, the monomer of a green-electrochromic polymer, 4-(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)-7-(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-8-yl)-2-cyclohexyl-2H-benzo-[d]imidazole (PBP), was copolymerized with 3,4-ethylenedioxythiophene (EDOT) with 2:1 and 2:2 (PBP: EDOT) monomer feed ratios. The resulting copolymer films were investigated in terms of their electrochromic properties. Equal feeded copolymerization resulted in a neutral-state black electrochromic polymer (L:11.5, a:1.5, b:-2.55) with satisfying responses in the electrochromic device application (100 % electroactivity maintenance after 300 switches with 1.4 s response time). Furthermore, increasing the quantity of EDOT in the copolymer chain improved the capacitive characteristics, showing that the equal-fed copolymer is a good candidate for a supercapacitor electrode (4.07 mF/cm²). The supercapacitor device application showed that the equal feeded copolymer has superior specific capacitance retention of 97 % after 500 charge/discharge cycle, with 100 % coulombic efficiency in each cycle. Moreover, the supercapacitor is capable of lighting a 1.5 V LED for >30 s.