Decoding the structure–property relationships of quasi-two-dimensional semiconductor nanoplatelets

Nanoplatelets (NPLs)—colloidal quantum wells—exhibit photophysical properties generally attributed to their precisely tunable thickness of a few atomic layers. However, recent experiments show that their structural and optical properties are affected by organic ligands passivating their facets. Here we report a theoretical study aimed at identifying the main factors determining the photophysical properties of NPLs. We focus on CdSe NPLs passivated by chloride ligands, and we use many body perturbation theory at the G₀W₀ level and solve the Bethe Salpeter equation to obtain electronic and excitonic properties. Our results are in good agreement with recent experimental reports. We then present a simple model that permits us to disentangle the effects of quantum confinement, ligand-induced strain, and dielectric contrast on the NPL electronic properties. We find that to accurately reproduce our first-principles results, it is critical to account for strain and to consider a finite (rather than infinite) potential barrier, as well as energy-dependent effective masses, when describing quantum confinement. The model presented here can be easily generalized to describe NPL heterostructures.