Importance of surface oxygen vacancies for ultrafast hot carrier relaxation and transport in Cu$_2$O

TL;DR

This study reveals that surface oxygen vacancies in Cu₂O significantly influence ultrafast hot carrier relaxation and transport, impacting its efficiency as a photoelectrode in water splitting applications.

Contribution

The paper provides a detailed theoretical analysis of how oxygen vacancies affect charge dynamics in Cu₂O, highlighting the importance of defect engineering for improved performance.

Findings

Oxygen vacancies are doubly ionized and create defect states that suppress electron transport.

The excited state of a singly charged vacancy facilitates ultrafast non-radiative electron capture.

Carrier lifetime due to vacancy-related processes is approximately 0.04 ps.

Abstract

Cu$_2$O has appealing properties as an electrode for photo-electrochemical 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$_\mathrm{O}$) in the experimentally observed ($\sqrt{3} \times \sqrt{3}$)R30$^{\circ}$ reconstruction of the dominant (111) surface. Our results show that these V$_\mathrm{O}$ are doubly ionized and that associated defects states strongly suppress electron transport. In particular, the excited electronic state of a singly charged V$_\mathrm{O}$ plays a crucial role in the non-radiative 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$_\mathrm{O}$ chemistry will be a crucial step in optimizing Cu$_2$O for photoelectrode applications.