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

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: (i) QD gels, where individual QDs are
covalently connected via di- or polysulfide bonds, and (ii) QD nanocrystals,
where individual QDs are bound via van der Waals interactions. Our
work illustrates how the electronic 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 di- or polysulfide
covalent bonds in the localization of the excitons, which highlights
the difference between QD gels and QD nanocrystals.