Investigation of electrochromic properties of asymmetric alkylated viologen for all-in-one gel-based device for smart window application

Here in this work, we report the synthesis and electrochromic features of an asymmetric alkylated viologen i.e. 1-benzyl-1′-pentyl-[4,4′-bipyridine]-1,1′-diium bromide (AS-BNZ-P Vio) for smart window applications. This material has been synthesized from its basic unit i.e. 4,4’- bipyridine by attaching pentyl and benzyl units to it. To ensure the successful synthesis, the compound has been characterized by nuclear magnetic resonance(NMR) and Fourier transform infrared (FTIR) spectroscopy. AS-BNZ-P Vio has been disseminated in a polyvinyl alcohol (PVA) gel matrix along with a ferro-ferricyanide redox mediator sandwiched between two FTO-coated glasses for the fabrication of an electrochromic device to investigate the real-time application. Using cyclic voltammetry, chronoamperometry and in situ UV–vis spectroscopy, the electrochemical behavior and electrochromic features of the fabricated device were explored. The fabricated all-in-one gel-based device is found to be working efficiently in numerous wavelength regions with an optical contrast of 67 % (359 nm), 70.5 % (466 nm), and 70.6 % (650 nm), 82.3 % at 750 nm and a coloration efficiency of 126.6 cm²/C. The device exhibits a retention of 52 % and 61 % of its initial amount in terms of optical contrast and current density, respectively. The device has a quick time response of 3.0/0.3 s for its coloration/bleaching process. Such an all-in-one gel-based Electrochromic (EC) device with superior coloration efficiency and rapid response time has significant potential for the future of device applications.