Atomic-level thick TiO2–CoTiO3 multilayer p-n junction with extended built-in electric field as efficient photoanode

Formation of p-n junction was an effective method to improve the photocatalytic performance due to its built-in electric field. However, the electric field was distributed only on the interface between two semiconductors, which was insufficient in comparison to the entire material. In this work, a multilayer TiO₂–CoTiO₃ p-n junction was designed and fabricated by atomic layer deposition. The charge transport and photoelectrochemical properties of multilayer TiO₂–CoTiO₃ films of various thicknesses are thoroughly investigated. The PL and electrochemical tests demonstrate that TiO₂–CoTiO₃ exhibits enhanced charge separation and transport. Additionally, the extra visible light response was achieved by introduction of CoTiO₃. Also, theoretical calculations indicate that the electrons prefer to immigrate from TiO₂ to CoTiO₃ in a multilayer TiO₂–CoTiO₃ structure. Benefited from the boosted light absorption and charge transfer, the multilayer TiO₂–CoTiO₃ composite film exhibits a significantly increased photocurrent, much higher than pure TiO₂ and a single TiO₂–CoO p-n junction. This multilayer p-n junction structure opens a rational and novel way for nanostructure construction in the energy conversion region.