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

Abstract

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 6s2 electron pair, which will provide valuable inspiration for the ligand passivation strategies in the future.

The Importance of Synthesis Conditions: Structure–Processing–Property Relationships

“…The presence of a ligand is essential for synthesizing nanoparticles. Ligands maintain the distance between nanoparticles and prevent them from either growing into larger particles or dissolving back into the solvent. , …”

Defect-Induced Circularly Polarized Luminescence of Chiral Perovskite Films

“…The Tauc plot is obtained from the UV–vis absorption curve, and the band gaps of the GECP- S -film and the NECP- S -film are estimated to be 3.69 and 3.60 eV, respectively, which indicate that the band gap of the GECP- S -film is larger than that of the GECP- S -film, as shown in Figure S18. The variations in electronic band-edge properties are induced by the strain of variations of Pb–Br bond length and Pb–Br–Pb bond angle within the PbBr 6 4– octahedral network of the perovskite lattice along with a jump of the band gap excitonic level to a higher energy. , …”

“…The variations in electronic band-edge properties are induced by the strain of variations of Pb−Br bond length and Pb−Br−Pb bond angle within the PbBr 6 4− octahedral network of the perovskite lattice along with a jump of the band gap excitonic level to a higher energy. 34,35 3.4. EPR Measurement and CPL Mechanism.…”

In Situ Tetraalkylammonium Ligand Engineering of Organic–Inorganic Hybrid Perovskite Nanoparticles for Enhancing Long-Term Stability and Optical Tunability

“…Moreover, they passivate the surface defects of the OIHP NPs, thereby reducing inefficient emission caused by trap-assisted nonradiative recombination. , Therefore, amphiphilic molecules such as oleylamine, oleic acid, and their mixtures, which contain terminal amine and carboxyl groups, have been typically used as surface ligands. They are sufficiently hydrophobic and strongly bound to the surface of OIHP NPs by electrostatic or coordinative interactions. − Although ligand engineering is efficient and convenient, careful consideration is required because ligands may degrade the optical or electrical properties of OIHP NPs. This failure primarily occurs because of the insulating nature of organic compounds; lengthy alkyl ligands hinder electronic carrier transport, whereas short ligands provide unsatisfactory stability. , Moreover, ligand binding is a highly dynamic process wherein ligands can be easily detached from the NP surfaces.…”