The objective of this work is to determine the ionization potential of a series of ligated PbS quantum dots and to investigate the effect of surface coverage on the ionization potential. Surface ligation has a substantial impact on both the valence and conduction band properties of quantum dots. The ionization potential of quantum dots provides important information about the valence band states and can provide insight into electron-transfer and electron-detachment processes. Because of this, it is crucial to determine how ligation and surface coverage affects the properties of quantum dots. In this work, we present a first-principles computational investigation of the effect of surface coverage of PbS nanoparticles on ionization potential. This was achieved by combining Green's function theory with the recently developed stochastically-enumerated stratified sampling of molecular orbitals (SESSMO) method for solving the Dyson equation. The method was used to investigate ligation of Pb4S4, Pb28S28, Pb44S44, and Pb140S140 quantum dots with QD-OOC-(CH)n-R ligands and 0-100% surface coverage. The results from this work demonstrate that the addition of ligands increases the ionization potential of the QDs. Discussion on the role of electronic coupling and energy-level ordering between the QD and ligands will be presented. The results from this study demonstrate that ionization potential is a relevant property to study ligand-QD electronic coupling and the presence of dangling surface bonds in nanoparticles.

Impact of surface ligand coverage on ionization potential of semiconductor nanoparticles

ACS Spring 2022

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