The Role of Surface Oxygen Vacancies in BiVO4
2020
Bismuth vanadate
(BiVO4) is a widely studied oxide in
solar water splitting, known for its ease of synthesis, high charge
extraction yields, and advantageous band alignment with water. We
present a combined first-principles and experimental study of the
electronic structure of the (010) surface of BiVO4 aimed
at disentangling the impact of the surface and bulk oxygen vacancies
on the electronic structure and transport properties. We found that
oxygen vacancies are deep donors at the surface as they are in the
bulk; our calculations on defect and polaron formation energies suggest
that, while polarons formed from oxygen vacancies in the bulk can
contribute to conductivity, those at the surface likely do not. Our
results also show that out-of-plane structural relaxations at the
surface contribute to the relatively immobile nature of electron polarons
derived from surface oxygen vacancies. The structural model derived
from first-principles calculation was validated by comparing computed
results with experimental measurements of single-crystal and epitaxially
grown single-crystalline BiVO4 samples. We also found a
reasonably good agreement between our calculated and measured work
functions for BiVO4 samples with and without oxygen vacancies.
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