Study of electrochromic behavior of the supporting electrolyte free electrochromic devices based on the graphene quantum dots functionalized viologens for energy-saving smart window application

Here in this work, two electrochromic systems have been prepared by functionalizing di-pentyl viologen (DPV) and di-heptyl viologen (DHV) with graphene quantum dots (GQDs). Strong molecular forces like cation pi interactions, 7C-7C stacking interactions, electrostatic interactions, etc., ensure an adequate interaction between GQDs and viologens, hence, responsible for stabilizing the electrochromic system. All solid electrolyte-free electrochromic devices have been fabricated by dispersing DPV-GQD and DHV-GQD in poly(vinyl)alcohol (PVA) gel. Electrochemical behavior and electrochromic responses of the fabricated devices were investigated using chronoamperometry, cyclic voltammetry and in situ UV-vis spectroscopy. Both devices were found to work efficiently without the help of supporting electrolytes. Both DPV-GQD and DHV-GQD devices exhibit high optical contrast of 53.4% and 60%, with superior coloration efficiency of 143.9 cm2/C and 66 cm2/C, respectively. Swift electrochromic responses of 4.4 s/3.5 s and 6.2 s/2.5 s have been recorded for coloration/bleaching for DPVGQD and DHV-GQD devices, respectively. Fabricated DPV-GQD device was found to retain 73% of its initial optical contrast while DHV-GQD depicts retention of only 63% after 3000 cycles. The superior coloration efficiency and balanced response time of DPV-GQD make it a potential material for the device application.

Automated summary

In this work, two electrochromic systems were prepared by functionalizing di-pentyl viologen (DPV) and di-heptyl viologen (DHV) with graphene quantum dots (GQDs). The fabricated devices showed high optical contrast and superior coloration efficiency, with DPV-GQD exhibiting faster response time.