Insights into the Structure and Self‐Assembly of Organic‐Semiconductor/Quantum‐Dot Blends

Abstract

Controlling the dispersibility of crystalline inorganic quantum dots (QD) within organic-QD nanocomposite films is critical for a wide range of optoelectronic devices. A promising way to control nanoscale structure in these nanocomposites is via the use of appropriate organic ligands on the QD, which help to compatibilize them with the organic host, both electronically and structurally. Here, using combined small-angle X-ray and neutron scattering, the authors demonstrate and quantify the incorporation of such a compatibilizing, electronically active, organic semiconductor ligand species into the native oleic acid ligand envelope of lead sulphide, QDs, and how this ligand loading may be easily controlled. Further more, in situ grazing incidence wide/small angle X-ray scattering demonstrate how QD ligand surface chemistry has a pronounced effect on the self-assembly of the nanocomposite film in terms of both small-molecule crystallization and QD dispersion versus ordering/aggregation. The approach demonstrated here shows the important role which the degree of incorporation of an active ligand, closely related in chemical structure to the host small-molecule organic matrix, plays in both the self-assembly of the QD and small-molecule components and in determining the final optoelectronic properties of the system.

Effective Hard-Sphere Repulsions between Oleate-Capped Colloidal Metal Oxide Nanocrystals

“…The measured virial coefficients are remarkably consistent with this simple model with a fixed solvent-ligand shell thickness t shell = 2.03 ± 0.15 nm, i.e., NCs with an effective thermodynamic diameter of D thermo = D core + 4.06 nm. This shell thickness is approximately equal to the sum of the oleate ligand shell thickness, as measured using small-angle neutron scattering (1.5-1.6 nm), 36,37 and one intermolecular spacing in liquid toluene, consistent with its density and neutron scattering analysis (0.6 nm). 38 The observed size dependence contrasts with the non-monotonic trends in B 2 found in earlier studies that necessitated the consideration of more complex inter-NC potentials with competing attractive and repulsive interactions and multiple fit parameters.…”

“…Per our results, this effective shell thickness is approximately equal to the solvent-swollen oleate ligand shell thickness, as measured using small-angle neutron scattering (1.5−1.6 nm). 44,45 The observed size dependence contrasts with the nonmonotonic trends in B 2 found in earlier studies that necessitated the consideration of more complex inter-NC potentials with competing attractive and repulsive interactions and multiple fit parameters. 11,12 Likewise, attractive square-well and sticky-sphere potentials have been required to model SAXS and neutron scattering results to extract the B 2 and effective ligand shell thickness for materials whose interactions exhibit similar complexities.…”

“…The effective pairwise interactions do not appear to be significantly influenced by the core–core van der Waals interactions, but rather are mediated by the intervening solvent–ligand layer between them. Per our results, this effective shell thickness is approximately equal to the solvent-swollen oleate ligand shell thickness, as measured using small-angle neutron scattering (1.5–1.6 nm). , The observed size dependence contrasts with the nonmonotonic trends in B 2 found in earlier studies that necessitated the consideration of more complex inter-NC potentials with competing attractive and repulsive interactions and multiple fit parameters. , Likewise, attractive square-well and sticky-sphere potentials have been required to model SAXS and neutron scattering results to extract the B 2 and effective ligand shell thickness for materials whose interactions exhibit similar complexities. , However, none of these complexities appear to be inherent to oleate-capped NCs, as the simpler size-dependent B 2 data presented here illustrates.…”

Mixed Small-Molecule Matrices Improve Nanoparticle Dispersibility in Organic Semiconductor-Nanoparticle Films

“…A successful surface chemistry approach for achieving good QD dispersibility within a host material has been through ligand exchange approaches utilizing ligands that are chemically similar to the host material. This has been demonstrated in QD:polymer, QD:perovskite, and QD:organic semiconductor (OSC) materials. , …”

Linking microscale morphologies to localised performance in singlet fission quantum dot photon multiplier thin films

“…Thus the resultant PbS-TET-CA dots have a surface character intermediate between OA and TET-CA and this has proved to be an important factor in their self-assembly. 18 Grazing incidence small-angle X-ray scattering (GISAXS) has been extensively utilized to study QD superlattices, where QDs form highly ordered crystalline thin films, demonstrating the power of X-ray scattering for characterizing QD morphologies. [19][20][21][22] For photon multiplier thin films, requiring intimate contact between the OSC and QDs, the optimal structure is one of highly dispersed, separated (by distances on the order of the exciton diffusion length) QDs within a crystalline matrix of the OSC (as opposed to the highly ordered crystalline QD morphologies features reported in QD superlattices).…”