Electron Thermionic Field Emission and Flow Model of Rapid-Switching Energy-Saving Electrochromic WO3/ZnO Core-Shell Nanorod Channels

Abstract

This paper investigates electron transfer mechanism and charge flow model of rapid-switching energy-saving electrochromic WO3/ZnO core-shell nanorod channels. A 2–3 nm thick WO3 EC layer was coated uniformly onto high-aspect ratio ZnO nanorods. The stored charges were quickly de-intercalated, and the bleaching current decayed exponentially with a time constant of 0.75 s. The response time at bleaching was shorter than that at coloration, indicating that the effective potential barrier under bleaching was lower than that under coloring. Meanwhile, the holes trapped in the ZnO/WO3 interface enhanced electron transfer by the mechanism of thermionic field emission. A charge flow model with energy-band diagrams for the EC device at thermal equilibrium and during coloring and bleaching was presented. The WO3/ZnO nanorod channels had a high reversibility of 74% and a coloration efficiency of 70.6 cm2-C−1 at a wavelength of 450 nm, together with fast switching speed, demonstrating the high potential for intelligent green optical windows and energy-saving device applications.