The Photocatalytic Properties of Tandem Thin Films Based on Titania and Perovskite Oxide

In this study, we mainly discuss photocatalyst materials: (1) titanium dioxide with two primary phases: anatase and rutile, (2) perovskite oxide: AgNbO3 and SrTiO3. Synthesizing with sol-gel process and spin-coating method, we try to make tandem thin film with anatase, rutile and perovskite oxide. Later, we measure photocurrent response of our thin film which represents the hydrogen production capability of photocatalyst. Initially, we control annealing temperature in the anatase to rutile phase transitition window. This action implies the different mix ratios of anatase/rutile homogeneous thin films successfully. The resuls shows we can make pure anatase thin film at 550 oC and nearly pure rutile thin film at 700 oC. Combining UV-Vis spectrum and UPS, we can get the band structure of anatase and rutile after they join together. The band structure implies photogenerated electrons transfer from anatase to rutile, and photogenerated holes transfer from rutile to anatase. Same characterizations are conducted on AgNbO3 and SrTiO3. We stack four materials to make them tandem films. Such design enhances the photocurrent response due to the built-in potential when we have the correct and preferred alignment. Besides, stacking sequence from large to small band gap also improves photocurrent by increase the usage of incident light. In order to verify the stability of our samples, we also conduct fatigue experiments by long-term light illumination. We surprisely find out the photogenerated holes induce photocorrosion of titanium dioxide anatase phase which will decay photocurrent density. Finally, we also create different amounts of pores in SrTiO3 thin films by varing addition amounts of PVP. With this idea, we verify the correlation between surfaces states and the decay phenomenon.