Trioctylphosphine Oxide Acts as Alkahest for SnX₂/PbX₂: A General Synthetic Route to Perovskite ASn_xPb_1–xX₃ (A = Cs, FA, MA; X = Cl, Br, I) Quantum Dots

Bulk halide Sn–Pb alloyed perovskites show great promise as alternatives to lead counterparts with attractive properties such as extended spectral response and improved phase stability. However, until now there has been no efficient way of making such alloyed materials in quantum dots (QD) endowed with a full range of halide covering. Although a recently reported trioctylphosphine (TOP)-based technique demonstrates efficacy in synthesizing perovskite CsSn_xPb_1–xI₃ QDs, it is incapable of producing those pure Br/Cl-based Sn–Pb alloyed QDs due to the insufficient solubility of PbBr₂ and PbCl₂ in TOP. Here, by taking advantage of the strong solvent ability of trioctylphosphine oxide (TOPO) for both SnX₂ and PbX₂ halide salts, we present the first synthesis of pure halogen-based prototype ASn_xPb_1–xX₃ (A = Cs, FA, MA; X = Cl, Br, I) QDs, which exhibit distinctive structural and physicochemical features that can be facilely controlled by varying halide species and Sn/Pb ratios. TOPO plays a key role in delivering reactive precursors but NMR measurement suggests it is not present on the QD surface after a postwashing process. The successful making of halide-tunable Sn–Pb perovskite QDs has offered great material versatility for the perovskite QD family, which enables a more systematic investigation of their fundamental photoexcited charge carrier dynamics that have not been explored.