Investigation of characteristics of tungsten oxide with different work pressures in photoelectrochromic cell

In this study, the tungsten trioxide (WO3) electrochromic layer of photoelectrochromic cell (PECC) was fabricated on an indium tin oxide/polyethylene terephthalare (ITO/PET) flexible substrate at room temperature by R.F. sputtering. The photoelectrode of PECC was prepared by screen printing technique. In order to fabricate transparent tungsten oxide thin films, a different work pressures was set from 10 mTorr to 50 mTorr in the process. The optical properties of these thin films were measured by Ultraviolet-visible (UV-vis) spectrophotometer. The transmittance of tungsten oxide thin films increases with increasing work pressure. The thin film which was deposited at 10 mTorr shows dark blue and has low transmittance, light blue film was deposited at 20 mTorr, and the transparent films were deposited above 30 mTorr. The optimum pressure was 30 mTorr because the resistivity of thin films was smaller than 40 mTorr and 50 mTorr. It is observed that the optical band gap energy of thin films increases with increasing work pressure. Thus, the WO3 thin film which was deposited at 30 mTorr was chosen and applied to PECC, and then the transmittance of PECC was decreased to 13.1 % for 30 seconds at near infrared range under illumination. In addition, the transmittance variation (ΔT%) and the optical density change (ΔOD) were 52.6 % and 0.70, respectively.