Study of the density of states and optical absorption profile for PbS quantum dots with Cl and Fa ligands

Experimental studies of chalcogenides show that the higher mobility of Cl- and FA-liganded PbS quantum dots may be useful for efficient solar cell applications. However, a theoretical understanding of this mechanism is still lacking. This paper presents the results of modeling the electronic and optical structure as well as the carrier mobility of an array of Cl- and FA-liganded PbS quantum dots at different temperatures using the density functional theory in combination with the nonequilibrium Green’s function method and the Landauer molecular dynamics approach. No signs of the formation of intermediate bands were found for the band structure of the quantum dot array with FA ligands. Instead, a continuum of bands with a lower band boundary was formed at an energy of about 0.6 eV. To better understand this phenomenon, the density of states and the optical absorption profile of PbS quantum dots with Cl and FA ligands were studied. It is found that FA-liganded quantum dots have higher mobility and improved optical absorption compared to Cl-liganded quantum dots. The differences can be explained by the features in the intermediate electronic structure.