Publication date: 15th December 2025
Lead chalcogenides colloidal quantum dots (CQDs) represent a class of materials with rich optoelectronic properties targeted for short wavelength infrared (SWIR) applications. Particularly, by self-assembling this family of CQDs into highly ordered superlattices, significant enhancement of transport properties was experimentally observed, reaching mobility values close to the bulk counterparts while maintaining quantum confinement [1,2]. To achieve electronic coupling, chemical treatments capable of stripping bulky surface organic ligands have been used. In specific conditions, the CQDs in the solid have been shown to undergo epitaxial necking and form connected arrays. Nonetheless, for systems self-assembled at a liquid-liquid interface, the suitable classes of ligands are still rather limited, and poor control over the surface chemistry remains as a major bottleneck. As of now, the most widely used ligand in studies correlating superlattice structure to transport properties, remains ethylenediamine (EDA) despite the structural defects and surface traps formed post ligand treatment [3].
To achieve highly coupled, epitaxially-connected superlattices, both the thermodynamics and kinetics of the ligand exchange reaction need to be considered. In this work, we demonstrate the use of methylammonium lead iodide (MAPbI3) as a chemical trigger for ligand exchange in 3D superlattices of PbS CQDs. The resulting superlattices showcase high degree of CQD alignment and limited macroscopic defects and cracking due to the slower reaction kinetics compared to the prototypical EDA, as demonstrated by correlating electron microscopy and grazing-incidence x-ray scattering. Through XPS and FTIR, we find that the native oleic acid is completely removed and that the surface is passivated with iodide species although no methylammonium remains on the surface after the thin film preparation. Finally, we characterize the intrinsic charge transport properties of the superlattices with ion liquid gating in a 4-probe geometry. By comparing our results with EDA-based samples, we show that we can achieve improved transport properties because of reduced structural disorder owing to the slower reaction kinetics with the MAPbI3 ligand.
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