The influence of exposed surface on trap state of PbS quantum dots

Abstract In this work, the PbS quantum dots (PbS QDs) are successfully prepared by the hot-injection method. The experimental results show that the surfaces of PbS QDs mainly exposed are (200), (110), and (111) with some minor exposed surfaces (311), (420), (422), and (511). The first-principle method is carried out to study the relationship between the trap state levels of PbS QDs and the exposed surfaces. Projected density of states (PDOS) discussions imply that it is impossible for stoichiometric PbS QDs to introduce trap state levels, while the QDs with {110} and {111} surfaces exposed will introduce the trap energy levels in the bandgap. Charge analysis shows that the Pb atoms on the {111} and {110} surfaces are the main sources of trap states. In comparison with the {110} surface, the Pb atoms on the {111} surface are easier to introduce the trap energy levels. The population distribution results indicate that the broadened charge densities of Pb atoms are mainly concentrated on the {110} surface for QDs containing {110} surface, while for QDs with {111} surface, the broadened charge densities of Pb atoms are mainly located on the {111} surface.