Growth of Highly Stable and Luminescent CsPbX₃ (X = Cl, Br, and I) Nanoplates via Ligand Mediated Anion Exchange of CsPbCl₃ Nanocubes with AlX₃

Two-dimensional metal halide perovskite nanocrystals are attractive for their blue-shifted absorption relative to their 3D counterparts, narrow emission line widths, high absorption cross sections, and high radiative recombination. Herein, we report a ligand mediated anion exchange reaction that transforms CsPbCl₃ nanocubes into anisotropic CsPbX₃ nanoplates (NPs) through adding a mixture of dodecanethiol (DDT) and AlX₃ (X = Cl, Br, I) to a solution of CsPbCl₃ nanocrystals. The anion-exchanged nanocrystals consist of mostly plate-shaped CsPbX₃ nanocrystals along {010} facets. Although DDT or AlX₃ treatment alone results in increased photoluminescence quantum yield, Φ_PL, the combination of both DDT and AlX₃ leads to the formation of plate-shaped nanocrystals, higher Φ_PL, and improved stability as compared to when only one of these is used. We suspect nanocrystal exfoliation driven by ligand penetration and self-assembly both play important roles in transforming the parent nanocubes into NPs. The NPs are highly emissive and stable due to the introduction of both an anion source and surface ligand. Nanoplates synthesized through DDT-AlX₃ ligand mediated anion exchange show photoluminescence quantum yields of 47 and 65% for violet and blue emitters (CsPbCl₃ and CsPbCl_3–xBr_x), respectively, near 100% for green emitters (CsPbBr₃), and 81% for red emitters (CsPbI₃), while maintaining good long-term stability.