Transmittance correlated real-time resistivity modulation and insulator-metal transition of electrochromic WO3 thin films

Abstract

A quantitative relationship between optical and electrical properties of crystalline WO3 films during Li + insertion has been established in this work. Detailly, the exponential relationship between transmittance and resistivity of crystalline WO3 thin films in visible and near-infrared wavebands is determined, and the real-time characterization of the resistivity of WO3 thin films during electrochromic process is realized. The experimental results show the resistivity of WO3 film can be regulated in the range of 0.078–0.98 Ω m with rapid response (∼6 s) when applied ±1 V voltage for 30 s. By analyzing the fitted resistivity-transmittance curve of WO3 thin film, a high-efficiency optical modulation of WO3 film in near-infrared 1000 nm can be achieved. Combining the IMT phenomenon during Li+ insertion, when x of LixWO3 changes from 0.08 to 0.13, the WO3 film is in a transition state from the insulating state to the metallic state with the tetragonal crystalline phase. The symmetry structural evolution of crystalline WO3 thin films during the Li + insertion is further demonstrated by transmission electron microscopy (TEM). These results contribute to the development of WO3 based optoelectronic bifunctional electrochromic devices.