Engineering Interface Polarity via Halide-Functionalized Self-Assembled Monolayers for NiO-Based QLEDs with High External Quantum Efficiency.

Quantum dot light-emitting diodes (QLEDs) hold immense potential for next-generation display technologies, yet their progress has been hampered by the lack of efficient inorganic hole-injection layers (HILs), which typically suffer from poor energy-level alignment and interfacial traps. Herein, a powerful interfacial engineering strategy is reported that transforms the performance of inorganic HILs by integrating Cu-doped NiO (Cu:NiO) with halide-functionalized self-assembled monolayers (SAMs) of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz). Halide-SAMs induce strong dipoles that shift the Cu:NiO valence band to deeper levels, enhance hole density, suppress surface defects, and lower the hole-injection barrier into the hole-transport layer. Furthermore, density functional theory (DFT) calculations identify that the high polarizability of the halide substituents plays a decisive role. This high polarizability enhances van der Waals (vdW) dispersion forces, promoting robust molecular anchoring and the formation of a dense, stable passivation layer that effectively suppresses surface defects. Consequently, QLEDs incorporating I-2PACz-modified Cu:NiO achieve a record-high external quantum efficiency (EQE) of 26.95% (Mean 19.53%), a 3.5-fold improvement over unmodified devices. This represents the highest efficiency reported for green QLEDs employing inorganic HILs. This work demonstrates that simultaneously tuning interface polarity and molecular polarizability offers a viable pathway to trap-suppressed, charge-balanced, and high-performance QLED architectures.