Mixed Ligand Passivation as the Origin of Near-Unity Emission Quantum Yields in CsPbBr₃ Nanocrystals

Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr₃ nanocrystals (NCs), include stable, reproducible, and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA⁺)-passivated CsPbBr₃ NCs where robust QYs stem from interactions between DDDMA⁺ and NC surfaces. Despite widespread adoption of this synthesis, specific ligand-NC surface interactions responsible for large DDDMA⁺-passivated NC QYs have not been fully established. Multidimensional nuclear magnetic resonance experiments now reveal a new DDDMA⁺-NC surface interaction, beyond established "tightly bound" DDDMA⁺ interactions, which strongly affects observed emission QYs. Depending upon the existence of this new DDDMA⁺ coordination, NC QYs vary broadly between 60 and 85%. More importantly, these measurements reveal surface passivation through unexpected didodecyl ammonium (DDA⁺) that works in concert with DDDMA⁺ to produce near-unity (i.e., >90%) QYs.