Importance of surface oxygen vacancies for ultrafast hot carrier relaxation and transport in Cu2 O

Abstract

Cu2O has appealing properties as an electrode for photoelectrochemical water splitting, yet its practical performance is severely limited by inefficient charge extraction at the interface. Using hybrid DFT calculations, we investigate carrier capture processes by oxygen vacancies (VO) in the experimentally observed (3×3)R30∘ reconstruction of the dominant (111) surface. Our results show that these VO are doubly ionized and that associated defects states strongly suppress electron transport. In particular, the excited electronic state of a singly charged VO plays a crucial role in the nonradiative electron capture process with a capture coefficient of about 10-9cm3/s and a lifetime of 0.04 ps, explaining the experimentally observed ultrafast carrier relaxation. These results highlight that engineering the surface VO chemistry will be a crucial step in optimizing Cu2O for photoelectrode applications.