Role of Ammonium Derivative Ligands on Optical Properties of CH₃NH₃PbBr₃ Perovskite Nanocrystals

Amines, ammonium salts, and their combination with organic acids are commonly employed ligands during the synthesis of colloidal perovskite nanocrystals (PNCs). However, the role of surface coordination, derived from different ammonium derivative ligands, on the optical properties of PNCs remains poorly understood. In this study, octylamine (OA), octylammonium bromide (OABr), and oleic acid (OAc) were applied, standing for amine, ammonium salt, and organic acid, respectively. The effects of four different types of ligands, including OA, OABr, OA-OAc, and OABr-OAc, on the surface coordination and subsequently optical properties of CH3NH3PbBr3 PNCs were comparatively investigated. Compared to amine ligand, the ammonium salt could coordinate to both surface cations and anions of PNCs to passivate their surface defects more effectively, leading to enhanced optical properties including higher photoluminescence (PL) spectral intensities and PL quantum yield. Moreover, the combination of OAc with amine rather than ammonium salt ligand could trigger the protonation–deprotonation reaction to further improve their coordination effect on a PNC’s surface, thus leading to significantly enhanced optical properties of PNCs. This study clarified the surface coordination of different ammonium derivative ligands and their role on the optical properties of PNCs, which could guide the design of ligands during the synthesis of PNCs.