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 angstrom and c = 5.697 angstrom, with an equilibrium volume of 57.24 angstrom(3). 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 (similar to 610,000 cm(-1) at 14.8 eV), followed by monolayer (similar to 13 eV) and bulk (similar to 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.