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

Abstract 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.