Graphene-based van der Waals heterostructures have emerged as promising platforms for next-generation electronic and optoelectronic devices due to their tunable electronic properties and atomic-scale thickness. This study uses density functional theory (DFT) to thoroughly investigate the electronic and structural properties of graphene–post-transition metal chalcogenide (PTMC) heterostructures. This work is emphasizing how the number of layers and the presence of defects affect these properties. Van der Waals heterostructures are created by stacking monolayer and bilayer PTMCs, such as In₂Se₃ and InTe, with graphene. A systematic analysis is then performed to study their structural stability, band alignment, and the effects of interlayer coupling. This abstract indicates that the thickness of PTMC layers is a critical factor in influencing the electronic structure of the heterostructures. This causes significant changes to how energy bands behave, the size of the band gap, and how charges move at the graphene–PTMC interface. Bilayer PTMC systems show stronger interactions between their layers compared to single-layer systems. This difference leads to changes in the electronic states near the Fermi level. Moreover, the introduction of intrinsic point defects in the PTMC layers creates localised states. These states then strongly influence the electronic and structural properties of the heterostructures. These defect states facilitate charge redistribution and modify the local density of states, thereby impacting the overall electronic response of the system. Our findings demonstrate that defect engineering and layer thickness control offer effective routes for tailoring the electronic properties of graphene–PTMC heterostructures. The results provide useful information for designing and improving graphene-based electronic and tunnelling devices that use post-transition metal chalcogenides as their main components.

Keywords: Graphene Heterostructures; Post-Transition Metal Chalcogenides; Density Functional Theory; Van Der Waals Interactions; Defect Engineering;