Mixed excitonic nature in water-oxidized BiVO$_4$ surfaces with defects

TL;DR

This study investigates how oxygen vacancies on BiVO4 surfaces influence electronic and optical properties, revealing that defect-induced surface oxidation enhances charge transfer and reduces electron-hole trapping through hybridized excitations.

Contribution

The paper provides a detailed atomistic analysis of defect effects on BiVO4 surfaces, showing that optical excitations remain robust despite structural changes, which is novel.

Findings

Defects create localized states near the quasiparticle gap.

Optical excitations are largely unaffected by defects due to hybridization.

Surface oxidation with defects improves electron transport.

Abstract

BiVO$_4$ is a promising photocatalyst for efficient water oxidation, with surface reactivity determined by the structure of active catalytic sites. Surface oxidation in the presence of oxygen vacancies induces electron localization, suggesting an atomistic route to improve the charge transfer efficiency within the catalytic cycle. In this work, we study the effect of oxygen vacancies on the electronic and optical properties at BiVO$_4$ surfaces upon water oxidation. We use density functional theory and many-body perturbation theory to explore the change in the electronic and quasiparticle energy levels and to evaluate the electron-hole coupling as a function of the underlying structure. We show that while the presence of defects alters the atomic structure and largely modifies the wavefunction nature, leading to defect-localized states at the quasipatricle gap region, the optical excitations remain largely unchanged due to substantial hybridization of defect and non-defect electron-hole transitions. Our findings suggest that defect-induced surface oxidation supports improved electron transport, both through bound and tunable electronic states and via a mixed nature of the optical transitions, expected to reduce electron-hole defect trapping.