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

ABSTRACT 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.