Bridging Grains with Cs ₂ ZnBr ₄ Enables Record 25.2% EQE Large-Area Perovskite LEDs

Large-area perovskite light-emitting diodes (LEDs) remain limited by severe performance losses arising from grain boundary defects and nonuniform film formation. Here we introduce a ZnBr2-mediated crystallization strategy that selectively passivates grain boundary defects while inducing the in situ formation of the wide-bandgap Cs2ZnBr4 interphase. This intergranular phase bridges adjacent CsPbBr3 grains, suppressing trap-assisted recombination, directing preferential crystal orientation, and enhancing environmental stability. Leveraging this approach, we realize large-area quasi-2D perovskite LEDs (active area: 225 mm2) exhibiting record-high external quantum efficiencies (EQEs) of 25.2% for green emission at 516 nm and 23.7% for red emission at 640 nm, which are the highest reported to date for devices of this scale. These results establish intergranular phase engineering as an effective and generalizable route to overcome intrinsic scaling challenges in quasi-2D perovskites, paving the way for efficient, stable, and manufacturable perovskite light-emitting technologies.