Size-Dependent Ternary Halide Solid Solutions in Perovskite Nanocrystals.

Crystalline solid solutions incorporate guest atoms by substituting host lattice sites up to a solubility limit dictated by solute-host similarity. Solid solutions enable tuning of various material properties, such as the optoelectronic behavior of halide perovskites. In bulk, the incompatibility of Cl:I halide mixtures restricts exploration throughout the ternary halide Cl:Br:I compositional range. However, solubility is extended in nanocrystals, which better accommodate a wider range of ions within their lattice. For this reason, data-driven strategies struggle to accurately predict the solubility boundaries in nanocrystal systems. Through high-throughput synthesis and spectroscopic characterization of over 3000 samples, along with density functional theory and cluster expansion models, we determine the solubility boundaries of ternary halide perovskite nanocrystals and demonstrate their extended size-dependent miscibility. Smaller nanocrystals, with sufficient Br content, stabilize the Cl:Br:I ternary halide solid solutions, suppress the formation of planar stacking fault defects, and improve their optical light emission.