Impact of the Atomic Structure at the BiVO₄/TiO₂ Interface on the Electronic Properties and Performance of BiVO₄/TiO₂ Photoanodes

In photoelectrochemical cells, semiconductor electrodes are usually interfaced with protection layers to extend their stability. Ideally, the protection layer should not decrease photocurrent generation. Hence, the conduction band minimum (CBM) and valence band maximum (VBM) of the protection layer should appropriately align with those of the underlying semiconductor electrode to facilitate the desired interfacial charge transfer with minimal interfacial recombination. However, predicting interfacial band alignment can be challenging, as it may vary depending on the detailed interfacial atomic structure. Investigating the effect of the atomic structure at the semiconductor/protection layer junction on the band alignment is also challenging as it requires samples with varied interfaces without altering the semiconductor and protection layers. Here, we considered TiO₂, the most widely used material as a protection layer, interfaced with a BiVO₄ photoanode, and we fabricated two n-type BiVO₄(010)/TiO₂ photoanodes where a thin (∼4 nm) amorphous TiO₂ layer was deposited by atomic layer deposition (ALD). While the individual BiVO₄(010) and TiO₂ layers were identical in these two samples, we modified the interfacial atomic structure at the BiVO₄/TiO₂ junction by changing which precursor, Ti or O, was introduced first upon deposition of TiO₂. By experimentally and computationally investigating the differences in these two samples, we show that the band alignments between BiVO₄ and TiO₂ at the interface may not be straightforwardly predicted by the CBM and VBM of bulk BiVO₄ and TiO₂ and that interfacial atomic arrangements can have a marked impact on the electronic properties and photoelectrochemical performance of the BiVO₄(010)/TiO₂ photoanode.