Evidence and Effect of Photogenerated Charge Transfer for Enhanced Photocatalysis in WO 3 /TiO 2 Heterojunction Films: A Computational and Experimental Study

Semiconductor heterojunctions are used in a wide range of applications including catalysis, sensors, and solar‐to‐chemical energy conversion devices. These materials can spatially separate photogenerated charge across the heterojunction boundary, inhibiting recombination processes and synergistically enhancing their performance beyond the individual components. In this work, the WO 3 /TiO 2 heterojunction grown by chemical vapor deposition is investigated. This consists of a highly nanostructured WO 3 layer of vertically aligned nanorods that is then coated with a conformal layer of TiO 2 . This heterojunction shows an unusual electron transfer process, where photogenerated electrons move from the WO 3 layer into TiO 2 . State‐of‐the‐art hybrid density functional theory and hard X‐ray photoelectron spectroscopy are used to elucidate the electronic interaction at the WO 3 /TiO 2 interface. Transient absorption spectroscopy shows that recombination is substantially reduced, extending both the lifetime and population of photogenerated charges into timescales relevant to most photocatalytic processes. This increases the photocatalytic efficiency of the material, which is among the highest ever reported for a thin film. In allying computational and experimental methods, this is believed to be an ideal strategy for determining the band alignment in metal oxide heterojunction systems.