From Benign to Fatal: Native Surface Chemistry Controls Acid-Triggered Trap Landscapes in CsPbBr3 Nanocrystals

Colloidal CsPbBr3 nanocrystals can be highly emissive, yet their chemical robustness is dictated by their native surface chemistry. Here, we show that aliphatic acids interact fundamentally differently with distinct CsPbBr3 surface terminations: they are largely benign toward conventional bromine-rich ammonium-passivated surfaces but strongly destabilizing toward carboxylate-capped, Pb-rich, Br-deficient surfaces synthesized in lauric acid-menthol deep eutectic solvent (DES). In the latter case, acid exposure quenches photoluminescence and sharply shortens the lifetime, indicating efficient activation of nonradiative decay pathways. X-ray photoelectron spectroscopy and 1H NMR reveal a PbBr2-terminated surface in which laurate is the dominant X-type ligand, while the DES stabilizes oleylammonium in the bulk through hydrogen-bonding interactions and thereby biases the nanocrystal surface toward carboxylate passivation. Density functional theory further shows that laurate is the thermodynamically viable bound ligand, whereas protonation to neutral lauric acid renders adsorption unfavorable once the entropic cost of binding is considered. Protonation-driven ligand desorption, therefore, exposes undercoordinated Pb and Br-vacancy motifs that act as electron traps. Further transient absorption spectroscopy links this surface transformation to ultrafast hot electron loss and rapid exciton trapping. These results reveal how the same class of aliphatic acids can be benign or fatal, depending on the initial surface termination and active ligand shell.