Quantum dots (QDs) are colloidal semiconductor nanocrystals (NCs) that exhibit unique optical and electronic properties. In particular, due to quantum confinement, their band gap can be tuned by changing their size. Their discovery and synthesis were awarded with the Nobel Prize of Chemistry in 2023. QDs can be used in many very diverse applications such as bio-imaging, energy conversion, or displays. Today, PbS QDs have been identified as an appealing candidate for applications requiring near-infrared/shortwave infrared (NIR/SWIR) absorption and/or emission. They exhibit an exciton Bohr radius of 18 nm, a bulk band gap of 0.41 eV and decent transport properties in thin films. This work focuses on different strategies to synthesize and functionalize luminescent PbS-based QDs to serve as emitting materials for efficient NIR/SWIR quantum dot light emitting diodes (QLEDs). For the synthesis of PbS core QDs we selected lead oleate as the Pb and substituted thioureas as the S precursor, which enables the tuning of the QDs size as a function of the molecular structure of the latter. A library of around 25 different thioureas was prepared with the excitonic peak of the obtained PbS QDs covering a range from 890 to 1680 nm. The reactivity of the used thioureas was correlated with their molecular structure by means of DFT calculations. To increase the photoluminescence quantum yield (PLQY), the PbS core NCs were passivated with different shells. The first strategy was to synthesize PbS/CdS core/shell QDs using the well-established cation exchange (CE) method. Optimization of the final excitonic peak position was performed with small additions of the cadmium precursor (cadmium oleate), resulting in a PLQY close to unity at 940 nm, 70% at 1150 nm, and 50% at 1360 nm. These wavelengths are of particular interest for practical applications due to the absence of solar stray light. Quasi-identical optical properties were obtained when the PbS/CdS QDs synthesis was transferred from classical batch conditions to an automated continuous flow system. However, this transfer implied several changes in the used solvent mixtures to assure the solubility of all precursors at room temperature. Different ligand exchange reactions were performed on PbS and PbS/CdS QDs with the goal to replace the pristine insulating ligands with shorter ones for subsequent QLED integration. Quantitative 1H-NMR and diffusion-ordered spectroscopy (DOSY) were used to study the surface ligand density as well as the hydrodynamic radius after ligand exchange. Attempts to mix PbS/CdS NCs with perovskite NCs aimed at improving the carrier mobility in thin solid films within a complete QLED stack. Further studies concerning the shell growth on PbS core QDs aimed to avoid the hypsochromic shift of the absorption and emission peaks encountered in CE as well as to grow thicker shells. First, a PbS/CdS(thin)/CdS(thick) heterostructure was grown using the monomolecular precursor cadmium ethyl xanthate for the outer shell, which resulted in a bathochromic shift of the absorption peak albeit with decreasing PLQY. The use of a wide band gap ZnS buffer layer shell to confine the carriers inside the PbS QDs core and obtain larger particles was also explored. Single-layer self-limited reactions were successfully used to add a controlled number of monolayers of ZnS and of CdS, and the optical and structural properties of the resulting QDs were studied. X-ray diffraction and Raman spectroscopy were performed on assess the influence of strain on the optical properties in these novel PbS/ZnS/CdS QDs​.​​
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