The effect of sputtering Ar gas pressure on optical and electrical properties of flexible ECD device with WO3 electrode deposited by RF magnetron sputtering on ITO/PET substrate

Abstract

In this study, the electro-optical properties of a flexible electrochromic device (ECD) with WO3 film were investigated according to the pressure of Ar gas during RF magnetron sputtering process. The ECD was fabricated using WO3 film as the cathode electrode and NiO as the anode electrode. Both electrodes were deposited using RF magnetron sputtering over indium tin oxide coated on polyethylene terephthalate film (PET/ITO). The electrolyte for the ECD used the lithium percolate mixed with poly methyl methacrylate and propylene carbonate to form the gel type electrolyte. The sputtering time was controlled while measuring with a thickness/rate monitor (Sycon STM-100) to have the identical WO3 film thickness at different Ar pressures. Also, argon working gas pressure in sputtering chamber was varied at 5 mTorr, 10 mTorr, and 15mTorr, respectively. The deposition rate of WO3 film was 14 nm/min for Ar gas pressure 5 mTorr then after the pressure was increased until 15 mTorr the deposition rate was 8.6 nm/min. The sputtering process was operated until the thickness of the WO3 film reach 250 nm. In order to investigate electro-optical properties of the ECD, such as coloration efficiency (CE), transmittance of bleached state (Tb), transmittance of coloured state (Tc), optical modulation, bleaching time, and coloration time were analyzed. The ECD with Ar pressure at 5 m Torr for WO3 film shows the coloration efficiency was 57.58 cm2C-1, Tb was 17%, Tc was 5%. Also, the bleaching time was 15 s, and coloration time was 30 s. When the sputtering pressure was increased to 15 mTorr, the ECD showed the better optical properties but the bleaching time and coloration time was rise to 50 s, and 58 s, respectively. The ECD at 15mTorr show the higher optical modulation of 55%.