The Crucial Role of Solvation Forces in Inter-Nanoplatelet Interactions and Stack Formation

Semiconductor nanoplatelets can possess desirable optical properties. For example, CdSe nanoplatelets show a high fluorescence quantum yield, a large one- and two-photon absorption cross section, and the ability to emit polarized light. However, their usage in devices requires control over their self-assembly, particularly the formation of stacks. The interplay of the various forces leading to stack formation in experiments remains unclear. Here, we use coarse grained molecular dynamics simulations of nanoplatelets in octane solvent to investigate the role of solvation forces in nanoplatelet interactions. We demonstrate that solvation forces resulting from solvent layering are sufficiently strong to stabilize nanoplatelet stacks. We examine the dependence of solvation forces on the nanoplatelets' ligand shell, size, and other parameters. In particular, we demonstrate that for sufficiently large nanoplatelets, solvation forces are proportional to the interacting facet area, and their strength is intrinsically tied to the softness of the ligand shell. The solvation forces exhibit an oscillatory nature; increases in their strength leads to a stronger attraction between close nanoplatelet facets and in addition to an increase in the kinetic barriers.