Defect-induced modifications in electronic and thermoelectric properties of pentagonal PdX2 (X = Se, S) monolayers

The point defects induced in crystalline solids during the growth process unintentionally or doped intentionally after the growth process significantly modify their properties. The intentionally controlled doping of point defects in crystalline solids has been widely used to tune their properties. In this paper, we investigate the effect of vacancy and substitutional point defects on the electronic and thermoelectric properties of pentagonal PdX2 (X = Se, S) monolayers using the density functional theory (DFT) and semi-classical Boltzmann transport theory. We find that the point defects in pentagonal PdX2 (X = Se, S) monolayers modify their electronic structures. The contributions of d orbitals of Pd atoms and p orbitals of Se/S atoms are significantly affected due to the presence of point defects in the lattice. The defect states are appeared within the band gap region which effectively reduces the band gap of the monolayer. These defect states could be helpful in tuning the electrical and optical properties of the monolayer. The defect states appear within the band gaps of defective monolayer structures which effectively modifies the electronic properties of these monolayer structures. The transport calculations show that the presence of the point defects in the lattice reduces the thermoelectric performance of these PdX2 monolayers. Both the Seebeck coefficient and electrical conductivity show deteriorated behaviour under the influence of point defects in the lattice. Thus, the influence of these defects must be carefully taken into account while fabricating these materials for practical applications.