Tuning of Coupling and Surface Quality of PbS Nanocrystals via a Combined Ammonium Sulfide and Iodine Treatment.

Surface states of colloidal nanocrystals are typically created when organic surfactants are removed. We report a chemical process that reduces surface traps and tunes the interparticle coupling in PbS nanocrystal thin films after the surfactant ligands have been stripped off. This process produces PbS/PbI2 core/shell nanocrystal thin films via a combined ammonium sulfide and iodine treatment. These all-inorganic nanocrystal thin films are air-stable and exhibit bright emission with optimum photoluminescence quantum yield close to that of pristine PbS nanocrystals passivated by oleate ligands. Interparticle coupling of post-treatment nanocrystal thin films is continuously tunable by varying the iodine treatment process. Optical studies reveal that this method can produce PbS nanocrystal thin films superior in both coupling and surface quality to nanocrystals linked by small molecules such as ethanedithiol or 3-mercaptopropionic acid.