The Role of Surface Oxygen Vacancies in BiVO₄

Abstract

Bismuth vanadate\n(BiVO₄) is a widely studied oxide in\nsolar water splitting, known for its ease of synthesis, high charge\nextraction yields, and advantageous band alignment with water. We\npresent a combined first-principles and experimental study of the\nelectronic structure of the (010) surface of BiVO₄ aimed\nat disentangling the impact of the surface and bulk oxygen vacancies\non the electronic structure and transport properties. We found that\noxygen vacancies are deep donors at the surface as they are in the\nbulk; our calculations on defect and polaron formation energies suggest\nthat, while polarons formed from oxygen vacancies in the bulk can\ncontribute to conductivity, those at the surface likely do not. Our\nresults also show that out-of-plane structural relaxations at the\nsurface contribute to the relatively immobile nature of electron polarons\nderived from surface oxygen vacancies. The structural model derived\nfrom first-principles calculation was validated by comparing computed\nresults with experimental measurements of single-crystal and epitaxially\ngrown single-crystalline BiVO₄ samples. We also found a\nreasonably good agreement between our calculated and measured work\nfunctions for BiVO₄ samples with and without oxygen vacancies.