Interplay between the enhanced electrical conductivity and optical properties of metal chloride-intercalated graphene bilayers: A DFT study

Despite numerous attempts to incorporate various intercalants into graphene for transparent conductor applications, the fundamental interplay between doping mechanisms and optical transparency remains insufficiently understood. In this study, a detailed comparative study on the effects of different metal chloride intercalation on the conductivity and optical properties of graphene bilayers was carried out through density functional theory (DFT) calculations. MoCl₅, FeCl₃, CuCl₂, and NiCl₂ from previous experimental literatures were modeled as dimers intercalated between the 5 × 5 supercells of graphene bilayers with three different stacking configurations. For each model, conductivity was estimated from the band structure by the Landauer-Datta-Lundstrom approach, while optical properties were determined from the complex dielectric constants. The DFT results displayed an enhanced electrical conductivity and p-type characteristics, while the linear dispersion of graphene was mostly preserved. The MoCl₅ models were with the highest conductivity of 3.7 × 10⁶–4.3 × 10⁶ S/m and the highest number of flat bands near the Fermi level. As the results, MoCl₅ also possessed high refractive index and reflectivity, which might hinder their uses in solar cell applications. However, the NiCl₂ models with a lower flat band density near the fermi level possessed the second highest conductivity around 2.2 × 10⁶–2.9 × 10⁶ S/m and still retained the reflectivity of 0.34 % or lower. This complex interplay between electrical and optical properties due to the introduction of localized electronic states or flat bands near the fermi level would require further study towards the development of ideal transparent electrodes for applications on solar cells and tunable photonic devices.