Surface Termination, Morphology, and Bright Photoluminescence of Cesium Lead Halide Perovskite Nanocrystals

Colloidal cesium lead halide perovskite nanocrystals (CsPbX3 PNCs, X = Cl, Br, I) exhibit important optoelectronic properties that make them amenable for a plethora of applications. However, the origin of these properties, even for as-synthesized and unpurified PNCs, is largely unknown. Electronic structure calculations are therefore essential to understand with atomistic detail the properties of these nanomaterials; however, finding a model for PNCs that resembles the experiments is a challenging task. Essentially, the main problem is how to correctly terminate a PNC surface that is comprised of a large fraction of the nanocrystal atoms and of ligands employed in the synthesis. Here, we construct nominally trap-free models for PNCs taking into account experimental conditions. With density functional theory we analyze the effect of size, shape, and halide composition on the electronic structure of PNCs. We confirm that the PNC crystalline core exhibits an orthorhombic structure, and we demonstrate that PNCs can be robust light emitters even when a large number of ligands are displaced from the surface.