Multi-Functional Silver Nanoparticles Interlayer Modified ZnO as Electron Injection Layer for Efficient Inverted Organic Light-Emitting Diodes.

The insufficient electron injection constitutes the major obstacle to achieving high performance inverted organic light-emitting diodes (OLEDs). Here, a facile electron-injection architecture featuring silver nanoparticles (AgNPs) interlayer modified sol-gel-derived transparent zinc oxide (ZnO) ultrathin film is proposed and demonstrated. The optimized external quantum efficiencies of the developed inverted fluorescent and phosphorescent OLEDs capitalized on our proposed electron-injection structure reached 4.0% and 21.2% at current density of 20 mA cm-2, and increased by a factor of 1.90 and 2.86 relative to a reference device without AgNPs interlayer, while simultaneously reducing the operational voltage and substantially ameliorating the device efficiency. Detailed analyses reveal that the local surface plasmon resonance (LSPR) emanated from AgNPs plays three meaningful roles simultaneously: suppressing the surface plasmon polariton (SPP) mode loss, aiding in energy level alignments, and inducing and reinforcing the local exciton-plasmon coupling electric field. Among these interesting and multi-functional roles, the enhanced local exciton-plasmon coupling electric field dominates the electron injection enhancement and substantial increase in device efficiency. Additionally, the light scattering effect also helps for recovering the trapped light energy flux and thus benefits for improving device efficiency. The proposed approach and findings provide an alternative path to fabricating high performance inverted OLEDs and other related organic electronic or optoelectronic devices.