Experimental and first-principles studies of BiVO4/BiV1-xMnxO4-y n-n+ homojunction for efficient charge carrier separation in sunlight induced water splitting

Abstract Though bismuth vanadate (BiVO 4 ) is extensively used as a photoactive material, its performance in harnessing solar energy is limited by ineffective separation of photo-excited charge carriers. We demonstrate here a concept of n-n + homojunction of BiVO 4 /BiV 1-x Mn x O 4-y , which improves its charge separation efficiency. Using first-principles theoretical calculations, we determine the effect of Mn substitution on oxygen vacancy formation energies and associated changes in the electronic structure of BiVO 4 . Showing that Mn substitution pushes the Fermi level of BiVO 4 towards its conduction band, we predict that the associated enhanced bending of bands at the homojunction (BiVO 4 /BiV 1-x Mn x O 4-y ) facilitates efficient separation of charge carriers. With Mott-Schottky experiments, we verify the increased band bending at the n-n + homojunction, and show that the maximum photocurrent density measured in a sample with n-n + homojunction is ten times higher than that obtained of the pristine sample. Secondly, Mn substitution in BiVO 4 also reduces the oxygen vacancy formation energy, promoting higher concentration of O-vacancies, further enhancing the photoelectrochemical response.