Photo and Electrochemical Characteristics Dependent on the Phase Ratio of Nanocolumnar Structured TiO2 Films by RF Magnetron Sputtering Technique

Nanostructured titanium dioxide (TiO2) prepared by RF magnetron sputtering was grown at substrate ternperatures (T-sub) ranging from RT (25 degrees C) to 450 degrees C. At lower temperatures, the TiO2 film deposited at a high sputtering pressure (12 mTorr) was amorphous. This was due to adatoms being unable to migrate effectively on the Substrate. However, an increase in T-sub, provides additional thermal energy and promotes the formation of the rutile at high temperature. The postannealing process provides additional driving force for nucleating the amorphous phase to anatase or rutile, followed by the growth of the rutile grain size. A 2.2 mu m thick TiO2 film sputtered at 350 degrees C had a columnar structure and showed the best performance as a photoanode layer for a dye-sensitized solar cell (DSSC), with a V-oc of 0.65 J(sc) a Jsc of 7.93 mA/cm(2), a fill factor of 0.533, and efficiency of 2.74%. In addition, the durable electrochromic performance was also confirmed using 400 nm thick TiO2 films sputtered at 350 degrees C. The improved properties were attributed to the formation of a mixed crystalline phase with anatase and rutile, a porous structure, and the narrowing of the optical band gap because of the formation of rutile, trap sites, and surface states. Furthermore, the calculated porosity of the TiO2 film sputtered at 350 degrees C also showed a high value (similar to 60%). which contributes to the increase in surface area and is in close contact to the electrolyte.