Dipole-tunable interfacial engineering strategy for high-performance all-inorganic red quantum-dot light-emitting diodes

All-inorganic quantum dot (QD) light-emitting diodes (AI-QLEDs) with excellent stability received enormous interest in the past few years. Nevertheless, the vast energy offset and the high trap density at the NiO_X/QDs interface limit hole injection leading to fluorescence quenching and hampering the performance. Here, we present self-assembled monolayers (SAMs) with phosphonic acid (PA) anchoring groups modifying NiO_X hole transport layer (HTL) to tune energy level and passivate trap states. This strategy facilitates hole injection owning to the well-aligned energy level by interface dipole, downshifting the vacuum level, reducing the hole injection barrier from 0.94 eV to 0.28 eV. Meanwhile, it mitigates the interfacial recombination by passivating surface hydroxyl group (-OH) and oxygen vacancy (V_O) traps in NiO_X. The electron leakage from QDs toward NiO_X HTL is significantly suppressed. The all-inorganic R-QLEDs exhibit one of the highest maximum luminance, external quantum efficiency and operational lifetime of 88980 cd m⁻², 10.3 % and 335045 h (T₅₀ @100 cd m⁻²), respectively. The as-proposed interface engineering provides an effective design principle for high-performance AI-QLEDs for future outdoor and optical projection-type display applications.