Highly Efficient and Stable CsPbI ₃ Perovskite Quantum Dots Light‐Emitting Diodes Through Synergistic Effect of Halide‐Rich Modulation and Lattice Repair

Abstract Currently, CsPbI ₃ quantum dots (QDs) based light‐emitting diodes (LEDs) are not well suited for achieving high efficiency and operational stability due to the binary‐precursor method and purification process, which often results in the nonstoichiometric ratio of Cs/Pb/I. This imbalance leads to amounts of iodine vacancies, inducing severe non‐radiative recombination processes and phase transitions of QDs. Herein, red‐emitting CsPbI ₃ QDs are reported with excellent optoelectronic properties and stability based on the synergistic effects of halide‐rich modulation passivation and lattice repair. First, a ternary‐precursor method is employed to better control the feed ratio of Cs/Pb/I and create a halide‐rich environment. Second a solvent‐free solid–liquid reaction employing a multifunctional guanidinium iodide (GAI) additive is used after purification to repair iodine vacancies and partially replace surface Cs atoms, thereby effectively modifying its tolerance factor. Additionally, this short‐chain GA ⁺ can be used as the surface ligand to improve the conductivity of the QDs and suppress trap‐assisted non‐radiative Auger recombination. Consequently, PeLEDs based on GAI‐QDs exhibit a great maximum external quantum efficiency (EQE) of 27.1% and an operational half‐lifetime (T ₅₀ ) of 1001.1 min at an initial luminance of 100 cd m ⁻² .