Multi‐Ligand Synergy Enables Flash Synthesis of Bright AgInS ₂ Quantum Dots With Defect Control

The synthesis of luminescent ternary AgInS 2 quantum dots (QDs) is typically constrained by slow reaction kinetics and uncontrolled defect formation, which compromise optical efficiency. Herein, a multi‐ligand synergy strategy that enables ultrafast (30 s) cation exchange from Ag 2 S to AgInS 2 at room temperature is reported. Trioctylphosphine mediates rapid Ag + extraction and In 3+ coordination, while octylamine dynamically modulates the exchange kinetics. Crucially, 1‐dodecanethiol passivates deleterious sulfur vacancies and promotes the formation of beneficial emissive defect complexes. Optical and compositional analyses collectively indicate that the luminescence likely originates from radiative recombination via donor–acceptor pairs (e.g., a silver vacancy and an indium‐on‐silver antisite defect), stabilized by the ligand shell. This cooperative mechanism achieves a 10 4 ‐fold kinetic acceleration and low‐cost gram‐scale production (<$63/mmol). After ZnS shelling, the QDs attain a photoluminescence quantum yield of 86% and yield luminescent solar concentrators with a power conversion efficiency of 2.86% and an optical efficiency of 8.85%. This work establishes a non‐equilibrium synthesis paradigm that overcomes the traditional trade‐off between speed and defect control in ternary chalcogenides.