Atomically Precise Ruddlesden–Popper Faults Induced Enhanced Emission in Ligand Stabilised 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 HAADF-STEM. We employ 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. Additionally, dislocations caused by lattice mismatch at grain boundaries (GBs) are identified. Lattice strain in GBs and RPs was determined and quantified, revealing that neither of these planar defects introduce 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 (QDs) leads to the formation of CsPbBr3-xIx NCs, resulting in a significant red shift in electroluminescence (~496 nm to ~623 nm) with enhanced intensity (±79%), attributed to higher exciton lifetime, increased exciton binding energy, and improved carrier confinement in flexible light-emitting devices. DFT calculations confirmed that additional carriers localized at the interface enhance electron-hole recombination ensuring stable charge transportation for lighting devices.