Flexible Substrate-Compatible and Efficiency-Improved Quantum-Dot Light-Emitting Diodes with Reduced Annealing Temperature of NiO x Hole-Injecting Layer.

The growing demand for wearable and attachable displays has sparked significant interest in flexible quantum-dot light-emitting diodes (QLEDs). However, the challenges of fabricating and operating QLEDs on flexible substrates persist due to the lack of stable and low-temperature processable charge-injection/-transporting layers with aligned energy levels. In this study, we utilized NiO x nanoparticles that are compatible with flexible substrates as a hole-injection layer (HIL). To enhance the work function of the NiO x HIL, we introduced a self-assembled dipole modifier called 4-(trifluoromethyl)benzoic acid (4-CF 3 -BA) onto the surface of the NiO x nanoparticles. The incorporation of the dipole molecules through adsorption treatment has significantly changed the wettability and electronic characteristics of NiO x nanoparticles, resulting in the formation of NiO(OH) at the interface and a shift in vacuum level. The alteration of surface electronic states of the NiO x nanoparticles not only improves the carrier balance by reducing the hole injection barrier but also prevents exciton quenching by passivating defects in the film. Consequently, the NiO x -based red QLEDs with interfacial modification demonstrate a maximum current efficiency of 16.1 cd/A and a peak external quantum efficiency of 10.3%. This represents a nearly twofold efficiency enhancement compared to control devices. The mild fabrication requirements and low annealing temperatures suggest potential applications of dipole molecule-modified NiO x nanoparticles in flexible optoelectronic devices.