Screening Ligands for Passivating Surface Defects in CsPbCl ₃ Nanocrystals for Enhanced Blue Light Emission: <i>In-Silico</i> Approach

Surface engineering has produced remarkable advances in green- and red-light-emitting CsPbX3 (X = Br, I) nanocrystals. However, realizing efficient and stable blue-light emission from the higher-bandgap CsPbCl3 remains challenging due to its intrinsically defect-prone nature. This work computationally screens diverse X-type ligands to establish rational design principles for effectively passivating the trap-forming halide vacancies in CsPbCl3 nanocrystals. The multidentate anionic oxygen donors from phosphonic, sulfonic, and carboxylic acids passivate undercoordinated Pb sites with strong, stable binding. Out of these, electronic structure analyses identify 16 ligands that eliminate midgap defect states and restore a clean bandgap in CsPbCl3 nanocrystals. Such surface passivation not only removes trap states but also restores delocalized band edges, leading to the desired shortened radiative lifetimes. The fast radiative process suggests enhanced blue light emission from these passivated CsPbCl3 nanocrystals. Crucially, the effective passivation does not depend solely on the headgroup but is equally dictated by the molecular backbone and substituents. While the aliphatic chains in the ligand backbone promote a clean bandgap, π-conjugated aromatic moieties often introduce in-gap molecular states. Moreover, bulky ligand tails introduce steric hindrance, weakening adsorption energies despite an optimal binding headgroup. Overall, our findings outline a roadmap to achieve high-efficiency blue light emission from CsPbCl3 nanocrystals through strategic ligand engineering.