| Organic Light Emitting Diodes (OLEDs) are widely viewed as next generation platform for flat panel displays and solid state lighting. Currently, OLED efficiency is not high due to high driving voltage. Molybdenum trioxide (MoO 3) is ideal for p-type doping of the wide bandgap organic semiconductor 4,4'-bis-9-carbozyl biphenyl (CBP). With p-type doped CBP layer as Hole Transport Layer (HTL), driving voltage can be significantly reduced. Effective design for doped OLED structure consists of a HTL with doped layer from 20nm to 40nm and MoO3 concentration above 5%, the optimized OLED with doped CBP HTL present an 18% improvement over a standard device with CBP HTL at 100mA/cm2.;Injection is found to be the principle cause of the reduction of driving voltage and shows close relations to doped layer thickness. Also charge balance is an important factor for high current efficiency, doped layer can be used as tools to promote charge balance. |
