Enhanced Surface Passivation of InP/ZnSe Quantum Dots by Zinc Acetate Exposure

Indium phosphide (InP) quantum dots (QDs) represent the main alternative to restricted Cd-based QDs in lighting and display applications. Typically, the photoluminescence (PL) of InP QDs is increased by overgrowth of a zinc chalcogenide shell, consisting of ZnSe and/or ZnS. Here, we show that the outer surface of InP/ZnSe QDs synthesized using aminophosphine-based chemistry is passivated by oleylamine and zinc chloride, while zinc oleate, used as a precursor for shell growth, is absent from the surface. The resulting low surface concentration of zinc salts leads to an incomplete passivation of undercoordinated surface chalcogenides, a known source of trap states. We demonstrate that a subsequent exposure of the QDs to zinc acetate, a mild Lewis acid, drastically enhances the PL quantum yield (PLQY) from approximately 40% before to 90% after exposure. This outcome is highly reproducible and can be realized either through an in situ exposure by adding zinc acetate to the reaction mixture or an ex situ exposure on purified InP-based QDs. Given that zinc chalcogenides are frequently used as an outer shell for QDs, this method of passivating undercoordinated chalcogenides holds significant promise for enhancing the PLQY across a wide array of core/shell QD systems.