Fabrication of Tungsten Oxide/Graphene Quantum Dot (WO3@GQD) Thin Films on Indium Tin Oxide-Based Glass and Flexible Substrates for the Construction of Electrochromic Devices for Smart Window Applications

In the present study, we have prepared tungsten trioxide (WO3)/graphene quantum dot (GQD) thin films (WO3@GQD) on indium tin oxide (ITO)-based glass and flexible (polyethylene terephthalate, PET) substrates for smart window applications. Furthermore, electrochromic devices (ECDs) were fabricated using WO3 and WO3@GQD thin films as electrochromic layers on ITO-based glass and flexible PET substrates. The WO3-based ECDs on ITO glass substrates exhibited a coloration efficiency (C.E.) of 56 cm2/C, while an improved C.E. of 78 cm2/C was obtained for WO3@GQD (5 min)-based ECDs on ITO glass substrates. The improvement in C.E. may be attributed to the presence of the conductive GQD. The WO3@GQD (5 min)-based ECDs also showed good stability for up to 10000 cycles. After checking the effect of GQD in WO3@GQD (5 min)/ITO glass through comparison with WO3/ITO glass with a liquid electrolyte, WO3@GQD (5 min) was applied for flexible ECDs. The developed flexible ECDs exhibited that WO3@GQD (5 min) can be used as a potential electrochromic layer in developing flexible smart windows.