Abstract
${\mathrm{Cu}}_{2}\mathrm{O}$ 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 (${V}_{\mathrm{O}}$) in the experimentally observed ($\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R{30}^{\ensuremath{\circ}}$ 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 nonradiative electron capture process with a capture coefficient of about ${10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}$/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 ${\mathrm{Cu}}_{2}\mathrm{O}$ for photoelectrode applications.
Highlights
Cuprous oxide (Cu2O) is a promising material for a variety of industrial applications due to its small direct band gap, its high absorbance, the abundance and nontoxicity of its constituent elements, and the large flexibility and low cost ofCu2O-based thin-film preparation methods [1]
Our hybrid density functional theory (DFT) results show that bulk defects in Cu2O cannot trap electrons and are highly inefficient hole
For the valence band, determined using 1PPE, we compare with the ground-state VOX DOS, whereas for the empty states, determined using 2PPE, we compare with the excited-state VO DOS
Summary
Cuprous oxide (Cu2O) is a promising material for a variety of industrial applications due to its small direct band gap, its high absorbance, the abundance and nontoxicity of its constituent elements, and the large flexibility and low cost ofCu2O-based thin-film preparation methods [1]. Cuprous oxide (Cu2O) is a promising material for a variety of industrial applications due to its small direct band gap, its high absorbance, the abundance and nontoxicity of its constituent elements, and the large flexibility and low cost of. Cuprous oxide has recently attracted much attention as an electrode material for photoelectrochemical water splitting with efficient light absorption, high positive onset voltage, and high photocurrent density [2,3]. The electrode performance is highly sensitive to the presence of defect states generally appearing within the semiconductor band gap [4,5]. Such defect states may trap excited charge carriers resulting in a reduction of the generated photovoltage and photocurrent. The first corresponds to the ideal O-terminated and stoichiometric surfa√ce is a reconstructed
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