Surface Ligand Tuning of Coordination Geometry and Pb 6s2 Electronic Pair Stereochemical Activity in MAPbBr3 Perovskite Nanoparticles: A Joint Experimental and Theoretical Insight

Surface ligand passivation strategies have been extensively used to produce metal halide perovskite nanoparticles (NPs) with excellent optoelectronic properties, and a better understanding of the ligand-NP interactions is essential to unleash the full potential of perovskite NPs. Here, the well-passivated methyl ammonium lead bromide NPs were obtained when (3-aminopropyl) triethoxysilane (APTES) and oleic acid (OA) were involved as efficient dual surface ligands. We systematically explored ligand-NP interactions by using spectroscopic analysis and theory calculations. Our results demonstrated that -[-OOC-R](-) from OA would preferably occupy the Br vacancies on the surface under-coordinated Pb sites in the corner-sharing octahedral framework to form [PbBr5](3-)-[-OOC-R](-) complexes, whereas -NH3+ of APTES can connect with Br- on the NP surface via hydrogen bonds. These surface binding interactions can trigger the lattice contraction of NPs, which can lead to an increased Pb2+ off-centering by promoting the lone pair stereochemical activity. Furthermore, the electronic band structure can be modulated by orbital interactions within the inorganic Pb-Br frame through the surface ligand effect. This work not only increases our understanding of ligand-NP interactions in terms of coordination geometry but also reveals their influence on the stereochemical activity of the Pb 6s(2) electron pair, which will provide valuable inspiration for the ligand passivation strategies in the future.