Mechanism-Guided Redox Protection Suppresses Iodide Oxidation for Air-Stable Red-Emitting Perovskite Quantum Dots

Mixed-halide perovskite quantum dots (CsPbBr_xI_3-x PQDs) have emerged as high-efficiency red-emitting materials due to their intense, spectrally tunable photoluminescence. However, their operational stability is fundamentally limited by photoinduced degradation and oxygen exposure. Herein, we identify that iodide desorption followed by its oxidative conversion to iodine serves as the primary degradation pathway, which has yet to be fully addressed via traditional postsynthesis treatment methods. Conversely, this cascade degradation process can be feasibly suppressed by modifying the surface chemistry of PQDs with a reductive sulfide salt that blocks iodide-to-iodine oxidation. By combining the redox protection strategy with established organic ligand engineering, we achieve CsPbBrI₂ PQDs exhibiting near-unity photoluminescence quantum yield and exceptional stability against continuous-wave irradiation and oxygen exposure. The redox protection strategy is further demonstrated to be universally effective for both colloidal dispersions and solid-state configurations, which establishes a critical design principle for versatile air-stable PQD optoelectronics.