Thermodynamically guided kilogram-scale precipitation of copper iodide clusters for efficient solution-processed light-emitting diodes

Copper halide clusters are emerging as attractive electroluminescent materials due to their strong emission and heavy metal–free nature, but their cost-effective practical application has been limited by the inherent trade-off between scalable synthesis and solution processability. This dilemma motivates us to design a universal thermodynamically motivated molecular design strategy. Alkyl-free aromatic ligand diphenyl-2-pyridylphosphine (Ph 2 PPy) reduces the entropy gain and increases the enthalpy change in dissolution, which maximizes the tunability of solubility and allows the coexistence of scalable single-step precipitation and solution processability. The kilogram-scale synthesis demonstrates near-unity yield, high reproducibility, operational robustness, and high product purity, while also being applicable to other alkyl-free precursors. We achieve uniform crystalline films with a photoluminescence quantum yield of 85.49% by kinetically controlled hot solution process. The electroluminescent devices achieve a record external quantum efficiency of 21.08% and a maximum luminance of 66,388 candela per square meter—the highest among doping-free, solution-processed copper halides, paving the way toward cost-effective light-emitting technologies.