Stable Energy-Level Regulation of NiO_x for Efficient Deep-Blue Perovskite LEDs.

Abstract

NiO_x offers tunable energy-level via interfacial molecular modification, making it a promising hole injection layer for perovskite light-emitting diodes (PeLEDs). However, conventional modifiers often detach during perovskite deposition, reverting energy-level to the intrinsic state. While simply enhancing electron-withdrawing strength can improve anchoring, it causes excessive energy-level shifts. Here, we employ a multidentate anchoring strategy to enhance modifier adsorption stability on NiO_x, preventing the regulated energy-level from shifting back. These interactions correspondingly provide multiple charge-transfer pathways, which effectively disperse the charge density and thereby mitigate the localized strong electron transfer that causes excessive energy-level modulation. Specifically, tridentate anchor 4-bromophenylphosphonic acid (BPA) engages in multiple Ni-O coordination bonds, achieving a high adsorption strength of -6.47 eV and retaining over 95% surface-coverage after polar solvent rinsing. Concurrently, multiple charge-transfer pathways effectively distribute the electron-withdrawing effect of ─PO₃H₂ group, yielding favorable energy-level alignment with a small barrier of less than 0.69 eV. We integrate this strengthened NiO_x with pure-halide quasi-2D perovskites to fabricate deep-blue PeLEDs. The obtained PeLEDs exhibit a champion external quantum efficiency (EQE) of 15.8% at 463 nm and a record-low turn-on voltage of 2.4 V. This approach also enables large-area (3 × 3 cm²) PeLEDs fabrication, with an EQE of 11.2%.