Organic light-emitting diodes (OLEDs) is strongly influenced by both the injection barrier height and the number of carriers in the metal/organic contact formed between the Fermi levels (EF) of the electrodes and the relevant levels for conduction in the OLED.

In this study, this study elucidates the enhancement of the optoelectronic properties of OLEDs by n-doping effect of rubidium carbonate (Rb₂CO₃)-doped tris(8-quinolinolato)aluminum (III) (Alq₃). The device performance strongly depends on both doping concentrations of the Rb₂CO₃-doped Alq₃ layer and the thickness. As the doping concentration is increased from 2.5% to 50%, the electron ohmic properties of the electron-only device with the glass/ITO/ Rb₂CO₃-doped Alq₃ (10 nm)/Al structure were improved at doping concentration of 10%, due to the increase in the n-type doping effect. However, the Alq₃ molecules were decomposed above the doping concentration of 10%. Also, the photoemission spectra revealed that the n-type doping effect cause the lowering of the electron-injecting barrier height, as well as the improvement of the electron conductivity. The OLED with the glass/ITO/MOOX-doped NPB (25%, 5 nm)/NPB (63 nm)/Alq₃ (32 nm)/ Rb₂CO₃-doped Alq₃ (10%, 10 nm)/Al (100 nm) structure showed both a high maximum luminance of 114,400 cd/m2 at 9.8 V and a high power efficiency of 2.7 lm/W at about a luminance of 1000 cd/m2.