Synergistic Dual-Interface Engineering via P═O-Functionalized Molecules for Efficient Sky-Blue All-Bromine Quasi-2D Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) are promising candidates for next-generation displays owing to their exceptional color purity, solution processability, and spectral tunability. However, blue PeLEDs still suffer from inferior efficiency and stability, primarily due to energy level misalignment, imbalanced charge injection, and severe nonradiative recombination. To tackle these challenges, we propose a dual-interface synergistic regulation strategy employing P═O-functionalized small molecules. At the bottom interface, the P═O-functionalized small molecule [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) is incorporated, enabling precise phase distribution management and reducing hole injection barriers via hydrogen bonding. Simultaneously, at the top interface, bis[2-(diphenylphosphino)phenyl]ether oxide, another P═O-containing molecule is introduced, which coordinates with uncoordinated Pb²⁺ ions to passivate surface defects. Encapsulating the all-bromine quasi-2D perovskite emissive layer with these high-triplet-energy molecules further suppresses exciton energy loss. This dual-interface engineering strategy optimizes the phase distribution. Consequently, the photoluminescence quantum yield rises dramatically from 31% to 68%, while the surface roughness decreases to 3.1 nm. The optimized blue PeLEDs achieve a peak external quantum efficiency of 15.12% at 490 nm and a maximum luminance of 2948 cd m^–2, alongside improved spectral stability and operational lifetime. This work provides a robust interface engineering strategy for high-performance blue PeLEDs.