Comment on "Uncovering the Complex Behavior of Hydrogen in Cu2O"

TL;DR

This paper challenges prior first principles results on hydrogen behavior in Cu2O, showing that H prefers to bind with oxygen and that H-VCu complexes do not introduce defect levels, aligning better with observed behaviors in oxides.

Contribution

It provides a corrected interpretation of hydrogen interactions in Cu2O, emphasizing oxygen binding and the absence of defect levels from H-VCu complexes.

Findings

H prefers to bind with oxygen rather than Cu in Cu2O

H-VCu complexes do not create defect levels in the band gap

Hydrogen behavior aligns with typical oxide defect passivation patterns

Abstract

In a recent Letter Scanlon and Watson reported their first principles results on hydrogen in Cu2O. Their main conclusions are: (1) an interstitial H in Cu2O prefers to occupy the tetrahedral site, which is coordinated with four Cu cations, in all three charge states (+1, neutral, and -1); (2) H will bind with a Cu vacancy and form an electrically active H-VCu defect complex, which is amphoteric with (+/0) and (0/-)transition levels at Ev + 0.1 and Ev + 1.1 eV, respectively. However, these two conclusions contradict two generally observed behaviors of H in oxides: (i) cationic H usually binds with an O atom, forming a single O-H bond, while the anionic H usually binds with cations with multi-coordination; (ii) H usually passivates cation vacancies in oxides. In this Comment, we explicitly show that with charge state +1, H prefers to bind with a single O anion rather than with four Cu cations and that H-VCu does not induce any defect levels inside the band gap.