Electronic, Optical and Transport Properties of PbS Nanocrystal Superlattices

Optoelectronic devices made from colloidal quantum dots (CQDs) often take advantage of the combination of tunable quantum confined optical and electronic properties and carrier mobilities of strongly coupled systems. For lattices of connected CQDs, of interest is the interplay between confinement effects and band-like behavior. In this work, first-principles calculations are applied to investigate the electronic, optical and transport properties of PbS CQD superlattices. Our results show that even in the regime of strong necking between CQDs, quantum confinement can be preserved. In the bandlike regime, computed carrier mobilities for simple cubic and 2D square lattices fused along the {100} facets are 2-4 orders of magnitude larger than those of superlattices fused along {110} and {111} facets. The relative magnitude of the electron and hole mobilities strongly depends on the crystal and electronic structures. We also find that the carrier mobilities of CQD solids increases as the size of the quantum dot increases due to the stronger coupling between neighboring CQDs. Our results illustrate the importance of understanding the effects of crystal structure and connectivity of CQD films.