Yttrium Cation Doping and Phenylphosphonic Acid Passivation for Pure-Red Perovskite Light-Emitting Diodes

Surface defects and instability in CsPbBrxI3–x nanocrystals (NCs) present significant obstacles to their potential application in high-performance pure-red perovskite light-emitting diodes (PeLEDs). Here, we report a synergistic approach involving Yttrium cation (Y3+) doping and phenylphosphonic acid (PPA) passivation to address the aforementioned issues. The introduction of Y3+ ion doping not only reduces the formation energy of NCs but also increases the iodide vacancy defect formation energy. PPAs can coordinate with uncoordinated Pb2+ ions through their phosphine oxide groups, effectively passivating the surface defects. Additionally, the hydroxyl groups of PPAs can form hydrogen bonds with adjacent halide ions, thereby suppressing their migration and further strengthening the passivation effect. Consequently, the Y/PPA comodified NCs exhibit significantly enhanced stability and near-unity photoluminescence quantum yields. PeLEDs based on these NCs possess outstanding spectral stability with a peak external quantum efficiency of 24.5%, representing one of the top-performing pure-red PeLEDs based on the CsPbBrxI3–x NCs reported so far.