Colloidal Synthesis of Air-Stable CH₃NH₃PbI₃ Quantum Dots by Gaining Chemical Insight into the Solvent Effects

Because of the superior optical properties and potential applications in display technology, colloidal synthesis of halide perovskite quantum dots has been intensively studied. Although great successes have been made in the fabrication of green emissive CH₃NH₃PbBr₃ quantum dots, the fabrication of stable iodide-based CH₃NH₃PbI₃ quantum dots remains a great challenge because of their sensitivity to moisture in the open air. Even in a glovebox, the colloidal CH₃NH₃PbI₃ quantum dots obtained from N,N-dimethylformamide suffer from instability caused by fast degradation within days to weeks. In this work, we investigated the interactions between perovskite precursors and various polar solvents as well as their influence on the crystallization of CH₃NH₃PbI₃ in reprecipitation synthesis. By gaining chemical insight into the coordination effects, we can explain the degradation of CH₃NH₃PbI₃ to the defective crystals with coordinated solvents on the surface and/or intrinsic inner iodine vacancies. On the basis of this understanding, we fabricated air-stable CH₃NH₃PbI₃ quantum dots with a tunable size from 6.6 to 13.3 nm by selecting noncoordinated acetonitrile as a good solvent through ligand-assisted precipitation synthesis. The fabrication can be processed under ambient conditions, and the resulting CH₃NH₃PbI₃ quantum dots exhibit tunable emission with high photoluminescence quantum yields (maximum of ∼46%) as well as good stability. Moreover, the quantum confinement effects in CH₃NH₃PbI₃ quantum dots were discussed by correlating the size-dependent photoluminescence properties with theoretical calculations, which can be described by the infinite quantum well approximation model.