Multifunctional synergy of polydentate ligands enables high-performance all-bromine sky-blue perovskite light-emitting diodes

All‑bromine low-dimensional perovskites represent a compelling pathway to stable sky-blue luminescence. Nevertheless, the quasi-two-dimensional (quasi-2D) phases inevitably release numerous surface defects, which severely compromise the quality and performance of perovskite films. Herein, we report the rational design and synthesis of a novel polydentate passivator, (Z)-N′-hydroxybenzimidamide (HBMA), and systematically characterized its synergistic multifunctional role in highly efficient sky-blue perovskite light-emitting diodes (PeLEDs). HBMA incorporates both oxime and amine groups, featuring three conjugated Lewis base sites. These sites facilitated multiple interactions predominantly through hydrogen bonds (N···H-N and O···H-N) and coordination bonds (N···Pb²⁺ and O···Pb²⁺) with the perovskite lattice. The incorporation of these interactions effectively passivated a multitude of surface vacancies and mitigated ion migration, leading to a marked improvement in both film quality and device stability. Furthermore, density functional theory (DFT) simulations elucidated that HBMA facilitated the stabilization of the organic spacer phenethylammonium bromide (PEABr) through hydrogen bonding, reinforcing interfacial integrity. Consequently, HBMA-based PeLED demonstrated a peak external quantum efficiency (EQE) of 15.05% at 490 nm, representing more than a twofold increase compared to the pristine device. Additionally, during the ligand design period, the pivotal significance of dipole moment and steric hindrance in polydentate ligands were also discussed. This work will offer valuable insights into the judicious design of polydentate ligands and the underlying multifunctional synergistic mechanisms in the field of perovskite optoelectronics.