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

Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr nanocrystals (NCs), include stable, reproducible, and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA)-passivated CsPbBr 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.