DFT study on the electronic and optical properties of graphene-Ti2CO2 bilayer heterostructure

Abstract

This work presents a density functional theory (DFT) investigation into the structural, electronic, and optical characteristics of a van der Waals bilayer formed by oxygen-terminated titanium carbide (O-terminated Ti2C or Ti2CO2) and graphene. Calculations were performed using the PBE functional with dispersion corrections, complemented by HSE06 hybrid functional evaluations to refine electronic structure predictions. The relaxed heterostructure shows a small lattice mismatch (< 2%) and a strong binding energy of -0.85 eV per unit cell. Bader charge analysis indicates a net electron transfer of roughly 0.3 e⁻ from graphene to Ti2CO2, which shifts the Dirac point, induces a finite band gap of 0.12 - 0.38 eV depending on the theory level, and maintains high carrier transport potential. The work function is modulated from 4.22 eV in pristine graphene to 4.65 eV in the bilayer. Optical simulations within the random phase approximation (RPA) reveal amplified light absorption across both visible and ultraviolet regions, with absorption coefficients surpassing 10 µ cm⁻¹ and an almost isotropic dielectric profile. These findings indicate that O-terminated Ti2CO2 interfaces can be tailored for use in transparent electrodes, energy storage devices, and optoelectronic systems, offering a theoretical foundation for engineering MXene-graphene heterostructures with tunable performance.