Mechanism of electrochromism for amorphous WO3 thin films

Abstract

The mechanism of electrochromism for an amorphous WO3 film has been studied. The film was prepared by using vacuum evaporation. X-ray phototelectron spectroscopy analysis has revealed that a state appears below the Fermi level after coloration in a LiClO4-propylene carbonate electrolyte and that the Fermi level increases in proportion to the amount of injected lithium. In addition, a decrease in the density of state of the conduction band has been observed in a colored film by using electron energy loss spectroscopy analysis in transmission electron microscopy. It has been concluded that the electrons injected occupy the conduction band after coloration and that electrochromism of amorphous WO3 film is due to an intraband transition between an electron injected in the conduction band and an empty state.