Eco-Friendly Zn–Ag–In–Ga–S Quantum Dots: Amorphous Indium Sulfide Passivated Silver/Sulfur Vacancies Achieving Efficient Red Light-Emitting Diodes

I–III–VI quantum dots (QDs) and derivatives (I, III, and VI are Ag+/Cu+, Ga3+/In3+, and S2–/Se2–, respectively) are the ideal candidates to replace II–VI (e.g., CdSe) and perovskite QDs due to their nontoxicity, pure color, high photoluminescence quantum yield (PLQY), and full visible coverage. However, the chaotic cation alignment in multielement systems can easily lead to the formation of multiple surface vacancies, highlighted as VI and VVI, leading to nonradiative recombination and nonequilibrium carrier distribution, which severely limit the performance improvement of materials and devices. Here, based on Zn–Ag–In–Ga–S QDs, we construct an ultrathin indium sulfide shell that can passivate electron vacancies and convert donor/acceptor level concentrations. The optimized In-rich 2-layer indium sulfide structure not only enhances the radiative recombination rate by preventing further VS formation but also achieves the typical DAP emission enhancement, achieving a significant increase in PLQY to 86.2% at 628 nm. Moreover, the optimized structure can mitigate the lattice distortion and make the carrier distribution in the interior of the QDs more balanced. On this basis, red QD light-emitting diodes (QLEDs) with the highest external quantum efficiency (EQE; 5.32%) to date were obtained, providing a novel scheme for improving I–III–VI QD-based QLED efficiency.