Comparative Study of Covalent and van der Waals CdS Quantum Dot Assemblies from Many-Body Perturbation Theory

TL;DR

This study uses many-body perturbation theory to compare the electronic and optical properties of covalently bonded and van der Waals CdS quantum dot assemblies across different dimensionalities, revealing how bonding type influences exciton localization.

Contribution

It provides a systematic first-principles comparison of covalent and van der Waals CdS QD assemblies, highlighting the impact of bonding on their electronic and optical behaviors.

Findings

Covalent bonds localize excitons more strongly than van der Waals interactions.

Dimensionality affects the evolution of electronic and optical properties.

Bonding type significantly influences exciton localization and system behavior.

Abstract

Quantum dot (QD) assemblies are nanostructured networks made from aggregates of QDs and feature improved charge and energy transfer efficiencies compared to discrete QDs. Using first-principles many-body perturbation theory, we systematically compare the electronic and optical properties of two types of CdS QD assemblies that have been experimentally investigated: QD gels, where individual QDs are covalently connected via di- or poly-sulfide bonds, and QD nanocrystals, where individual QDs are bound via van der Waals interactions. Our work illustrates how the electronic, excitonic, and optical properties evolve when discrete QDs are assembled into 1D, 2D, and 3D gels and nanocrystals, as well as how the one-body and many-body interactions in these systems impact the trends as the dimensionality of the assembly increases. Furthermore, our work reveals the crucial role of the covalent di- or poly-sulfide bonds in the localization of the excitons, which highlights the difference between QD gels and QD nanocrystals.