Choice of Layering and Band Alignment in 2D Heterostructures

Heterostructures are ubiquitous in many optoelectronic devices and as photocatalysts. One of the key features of a heterojunction is proper band alignment between the two materials. Estimation of the correct relative band positions with density functional theory (DFT)-based electronic structure calculations is often constrained by the accuracy and cost associated with the various DFT functionals. In this study, we introduce a novel computational approach that achieves band alignments closely matching experimental results with the widely used PBE functional. We specifically examine the well-documented MoO₃/MoS₂ system, a type-II heterojunction. In our setup, the MoS₂ layers are kept as they are, but for MoO₃, the individual layers are chosen differently. These alternative layers have higher surface energy, and hence, the band edges are higher than those of the conventional layers. This shift in band edges of the alternative MoO₃ layers changes the band alignment in the MoO₃/MoS₂ heterojunction from type-III to the experimentally observed type-II character. We also extend this computational strategy to additional systems, demonstrating its versatility and effectiveness.