Unveiling the optoelectronic properties of bulk, monolayer, and bilayer TiS₂: A DFT approach

Over the years, there has been significant research aimed at improving the performance of titanium disulfides (TiS₂) in a wide range of applications, including lubricants, batteries, thermoelectric and electronic devices, catalysts, superconductors, photovoltaic devices, and more. This work investigates the optoelectronic properties of TiS₂ using Density Functional Theory (DFT) calculations. The slab models were constructed for bulk, bilayer, and monolayer TiS₂ (001) planes based on the 1T-TiS₂ hexagonal phase. The GGA-PBE functional yielded the most accurate bandgaps: 0.178 eV (bulk), 0.047 eV (bilayer), and 0.112 eV (monolayer). The calculated lattice constants for bulk TiS₂ with GGA-PBE were a = b = 3.407 Å and c = 5.697 Å, with an equilibrium volume of 57.24 ų. Electronic density of states (DOS) analysis revealed semiconducting behavior for both bulk and monolayer TiS₂, with dominant peaks at the valence band. Bilayer TiS₂ exhibited a higher DOS in the conduction band, indicating a more conductor-like character. Light absorption calculations showed the strongest peak for bilayer TiS₂ (∼610,000 cm⁻¹ at 14.8 eV), followed by monolayer (∼13 eV) and bulk (∼12 eV). These results suggest that bulk TiS₂ is preferable for applications requiring superior electrical properties, while bilayer TiS₂ is more advantageous for applications focusing on light capture.