Single‐Particle Insights Into the Electronic Structure and Enhanced Stability of CsPbBr ₃ /FAPbBr ₃ Core/Crown Nanoplatelets at the Nanometer Scale

ABSTRACT Colloidal perovskite nanoplatelets (NPLs), despite their exceptional optoelectronic properties, face significant challenges due to their intrinsic instability and trap‐assisted non‐radiative recombination. Although many studies employing surface engineering, such as selecting ligands or coating to passivate defects, have demonstrated improved optoelectronic properties, these enhancements are typically inferred from bulk‐ensemble measurements; the effects at the single‐particle level remain elusive. Here, we conduct single‐particle‐level studies using scanning tunneling spectroscopy (STS) on a unique core–crown system, CsPbBr ₃ @FAPbBr ₃ NPLs, where the lateral surfaces of the CsPbBr ₃ core are coated with an FAPbBr ₃ crown. Experimental density‐of‐states (DOS) analysis reveals a 47% reduction in deep‐trap states in core‐crown NPLs compared to core‐only NPLs, consistent with nearly two‐fold enhancements in photoluminescence quantum yields. Progressive I – V sweep measurements demonstrate superior electrical stability in core‐crown NPLs, preserving band structure with minimal degradation, while core‐only NPLs exhibit rapid bandgap shrinkage and trap formation. Density functional theory (DFT) calculations indicate that FA incorporation distorts Pb octahedral lattice, widening the bandgap. This study elucidates how surface engineering modulates charge localization, passivates defects, and enhances stability at the single‐particle level. Moreover, by uncovering bias‐induced trap states in single unpassivated NPLs, this study establishes a precise, robust approach for characterizing emerging perovskite nanocrystals.