High-contrast energy-efficient flexible electrochromic devices based on viologen derivatives and their application in smart windows and electrochromic displayers

Abstract

Electrochromic materials and corresponding devices display reversible optical changes under applied voltage. While inorganic and organic electrochromic materials are extensively studied, enhancing their performance is crucial. This study presents a high-contrast energy-efficient flexible electrochromic device based on viologen derivatives and driven by film solar cell. The aims are to foster applications in smart windows, displays, and energy-efficient technologies. Two symmetric viologen derivatives of 1,1′-bis(4-(dimethylamino) phenyl)- [4,4′-bipyridine]dihexafluorophosphate (DNPV) and 1,1′-bis(4-acetamidophenyl)-[4,4′-bipyridine]dihexafluorophosphate (DAcPV) and two asymmetric viologen derivatives of 1-benzyl-1'-(4-(dimethylamino)phenyl)-[4,4′-bipyridine]dihexafluoro-phosphate (Bn-NPV) and 1-(4-acetamidophenyl)-1′-benzyl-[4,4′-bipyridine]dihexa-fluorophosphate (Bn-AcPV) were synthesized. These viologen derivatives as active materials were used to assemble both flexible and rigid electrochromic devices (ECDs). After applying voltage of 1.0 V, both of flexible and rigid ECDs based on DNPV and Bn-NPV exhibited reversible color change from purple to deep purple and red to deep viologen respectively, while ECDs based on DAcPV and Bn-AcPV exhibited a color change from yellow to black and pale yellow to green under applied voltage of 1.2 V, respectively. After 1000 cycles, flexible and rigid ECDs showed good stability. Especially, the flexible ECDs maintained good performance after 1000 bending cycles. In additional, the ECDs based on these viologen derivatives were prepared to displayer, which showed clear display function. And ECDs driven by solar cells demonstrated good stability after 100 cycles. Furthermore, it showed that the rigid ECD based on DAcPV with high solar irradiation modulation of 70.3 %, holds great potential in smart window applications.