Fabrication of Transparent Al:LiF Composite/MoO3 Interconnecting Layers for Tandem White Organic Light Emitting Devices

We report transparent Al:LiF composite/molybdenum oxides (MoO3) as interconnecting layers for tandem white organic light emitting diodes (WOLEDs) consisting of blue and red phosphorescent unit devices. The Al:LiF (3 nm)/MoO3 (10 nm) interconnecting layers show a high transmittance, good carrier generation and injection capability for tandem WOLEDs. The performance of tandem WOLEDs is sensitive to the LiF doping concentration, which is mainly attributed to the difference in efficiency of carrier injection into the adjoining electroluminescent units. For 10~20% LiF concentration, the external quantum efficiency of tandem device is almost equal to the sum of the efficiencies of blue and red OLEDs at high current density; furthermore, a small variation of Commission Internationale de l'Eclairage (CIE) coordinates with the current density is obtained.