Efficient non-doped blue phosphorescent organic light-emitting devices by incorporating Ag-island nanostructures

In this work, vacuum-evaporated Ag-island nanostructures were incorporated into the electron transporting layer (ETL) and their effects on the performance of non-doped blue phosphorescent organic light-emitting devices (PhOLEDs) using an ultrathin phosphorescent dye as the emitting layer (EML) were investigated systematically. By changing the thickness and deposition rate of Ag layer, the surface morphologies and resonance absorption spectra of the Ag-island nanostructures can be fine modulated. The device performance is significantly dependent on the structure and position of Ag layer. The experimental results indicate that 0.5 nm Ag layer deposited at a rate of 0.06 Å/s presents excellent spectral overlap between the resonance absorption spectra of Ag-island layer and the emission spectra of EML that impacts the electrical properties. Compared to the reference device without Ag-island layer, the current efficiency of the optimized device was enhanced by 54% from 15.1 cd/A to 23.2 cd/A when 0.5 nm Ag-island layer was incorporated into ETL with 20 nm away from EML. The performance enhancement is attributed to the synergistic effects for the improved electron transport properties induced by the Ag-island layer and the effective couplings between excitons and localized surface plasmons (LSPs).