Importance of surface oxygen vacancies for ultrafast hot carrier relaxation and transport in Cu_{2}O

Abstract

Cu_{2}O 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 (V_{O}) in the experimentally observed (sqrt[3]×sqrt[3])R30^{∘} reconstruction of the dominant (111) surface. Our results show that these V_{O} are doubly ionized and that associated defects states strongly suppress electron transport. In particular, the excited electronic state of a singly charged V_{O} plays a crucial role in the nonradiative electron capture process with a capture coefficient of about 10^{−9}cm^{3}/s and a lifetime of 0.04 ps, explaining the experimentally observed ultrafast carrier relaxation. These results highlight that engineering the surface V_{O} chemistry will be a crucial step in optimizing Cu_{2}O for photoelectrode applications.