Atomically Precise Ruddlesden-Popper Faults Induced Enhanced Emission in Ligand Stabilized Mixed Halide Perovskites

Atomic-resolution imaging of Ruddlesden-Popper (RP) interfaces is challenging due to their concealment within perovskite nanocrystals (NCs) and the inherent limitations of conventional characterization techniques. In this study, distinctly oriented RP faults have been detected using double-Cs-corrected high-angle annular dark-field scanning transmission electron microscopy (STEM). A simple yet reliable STEM approach to achieve atomically precise identification of Pb, Cs, Br, and I atoms and analyze their spatial atomic arrangements in a single NC is employed. In addition, dislocations caused by lattice mismatch at grain boundaries (GBs) are identified. Lattice strain in GBs and RPs is determined and quantified, revealing that neither of these planar defects introduces the deep trap levels. Therefore, in absence of Pb dangling bonds or Pb─Pb bonds in GBs and RPs plays a crucial role in stabilizing NCs and preventing ion migration. Incorporating n-octylammonium iodide in pristine CsPbBr₃ quantum dots leads to the formation of CsPbBr_{3- x}I_x NCs, resulting in a significant redshift in electroluminescence (≈496-623 nm) with enhanced intensity (≈79%), attributed to higher exciton lifetime, increased exciton binding energy, and improved carrier confinement in flexible light-emitting devices. Density functional theory calculations confirm that additional carriers localized at the interface enhance electron-hole recombination, ensuring stable charge transportation for lighting devices.