Ligand Exchange-Induced Shape Transformation of CsPbBr3 Nanocrystals Boosts the Efficiency of Perovskite Light-Emitting Diodes

The ligand exchange of perovskite nanocrystals is crucial for achieving highly efficient and stable light-emitting diodes (PeLEDs). Here, we report the shape transformation of CsPbBr3 nanocrystals from dodecahedron to cube during the ligand exchange using dimethylammonium bromide (DDAB). The shape transformation is thoroughly investigated by experimental characterization and density functional theory calculations, revealing the surface selective etching effect of DDAB. Among the {002}, {220}, and {112} facets in dodecahedron CsPbBr3 nanocrystals, DDAB has the highest binding energy with the (220) facet, which accounts for surface selectivity and shape transformation. PeLEDs based on DDAB-capped CsPbBr3 nanocrystals exhibit average and maximum external quantum efficiencies (EQE) of 14.6 and 18.5%, respectively. Therefore, the ligand exchange using DDAB is an effective strategy for the production of high-quality perovskite nanocrystals for optoelectronic applications.