LiNbO3 thin films for all-solid-state electrochromic devices

Lithium niobate (LiNbO3) thin films were non-reactively deposited onto glass and ITO coated glass substrates by RF magnetron sputtering using a LiNbO3 target in an argon (Ar) atmosphere at room temperature. The deposition power was 75 W during the deposition process. The optical and electrochromic properties of the LiNbO3 films with various thicknesses were investigated. Coloration efficiencies and optical modulations of the LiNbO3 films were investigated for the visible and near infrared region. The amount of inserted/extracted charges into/from the films during the bleaching/coloring process were obtained. The ion conducting and ion storing capabilities of the films were also investigated in detail. The LiNbO3 film deposited at 20 mTorr with a thickness of 110 nm had both highest optical modulation (20.3%) and coloration efficiency (19.3 cm2/C) at 550 nm. The LiNbO3 film was used in a unique design all-solid-state electrochromic device. Dry lithiation of the WO3 film was performed by exposing the film in vacuum to Li vapor atoms, which are given off by RF magnetron sputtering of LiNbO3. An all-solid-state electrochromic device with a configuration of ITO / NiO / Ta2O5 / dry lithiated WO3 / ITO / glass was fabricated and studied for its electrochromic behavior using a dry-lithiated WO3 film as an EC layer and an ion source. The optical modulation of the device was 31.4% at 550 nm for the applied potentials of ±2 V.