Bilayer CdS Structure: A Promising Candidate for Photocatalytic and Optoelectronic Applications

Density functional theory methodology has been adopted to investigate the structural, electronic, and optical properties of the CdS bilayer system and compare it with the CdS monolayer. For the bilayer system, five different types of stacking modes have been considered. The binding energy calculation suggests that the AA2 stacking mode is the most energetically favorable. Both the CdS monolayer and AA2 stacked CdS bilayer possess hexagonal symmetry, but the lattice constant slightly increases in the case of the AA2 stacked CdS bilayer compared to the monolayer. The negative formation energy also concludes that the formation of both systems is thermodynamically favorable. Ab initio molecular dynamics simulation further confirms the thermodynamic stability of the AA2 stacked CdS bilayer system. The band gap increases in the bilayer system compared to the monolayer as well as the bulk form, and both systems show direct band gap semiconducting character. Similar to the monolayer, the CdS bilayer system is also a promising candidate for visible light-driven photocatalysis. The optical band gap calculation for CdS sheets shows its possible usage as a light harvester. Moreover, the optical band gap, as well as absorption spectra, shows a redshift for the AA2 stacked CdS bilayer as compared to the CdS monolayer. A redshift in the optical band gap, as well as the absorption spectra, is observed for the AA2 stacked CdS bilayer with respect to the monolayer. The CdS monolayer and bilayer systems exhibit outstanding optical responses that confirm their potential applications in optoelectronics.