Influence of Multi-Round Annealing Process on the Optical and Electrical Properties of Sol-Gel Derived TiO2-δ Films

Abstract

Anatase TiO2- thin films on glass substrates were prepared by sol-gel dip-coating method. We designed a multi-round annealing process which was under the air pressure of 5 Pa and then 5×10-2 Pa for one hour each at 550 °C, and such process was repeated for three times. The special designed annealing process can obviously improve the conductivity of the udoped TiO2- thin films. The minimum resistivity of the undoped TiO2- thin films reached 0.8 Ω cm after being treated by the multi-round annealing process. It was demonstrated that such annealing process was an effective way to increase the defects in TiO2- thin films such as oxygen vacancies. The average transmittances of the films were approximately 60~80% in the visible range with the forbidden gaps of 3.25~3.35 eV. After the multi-round annealing process, the optical forbidden gaps of the films became narrowed slightly, which might be also related to the defects introduced during the multi-annealing process.