Holistic Synergistic Modulation for Efficient Blue Quasi-2D Perovskite Light-Emitting Diodes

The bromide-chloride mixed quasi-two-dimensional (quasi-2D) perovskites with high exciton binding energy have demonstrated remarkable potential for efficient blue perovskite light-emitting diodes (PeLEDs). However, challenges persist due to the poor energy transfer efficiency in quasi-2D perovskites and imbalanced charge injection at the interface, which results in notable exciton quenching. This study employs an effective approach termed "systematic synergistic engineering" by introducing 4-guanidinobenzoic acid methanesulfonate (GAMS) into the perovskites and 2-bromoethylphosphonic acid (BPA) molecules at the buried interface, respectively. Benefiting from the high absorption energy with charge defects of the guanidinobenzoic acid (GA) group as a spacer, contributing to a homogeneous phase distribution, the small-sized methanesulfonate (MS) group serves as a synergistic passivator to reduce trap states, which accelerates energy transfer efficiency. Moreover, the BPA buffer layer with strongly electronegative groups not only reduces buried interface defects but also deepens the valence band maximum (VBM) of poly(9-vinylcarbazole) (PVK), ultimately enhancing hole-injection efficiency. As a result, efficient and spectrally stable blue PeLEDs achieve a maximum external quantum efficiency (EQE) of 9.1% and a maximum luminance of 2460 cd m^-2 at 480 nm. This work delineates an effective method for the efficient blue quasi-2D PeLEDs.