Highly Efficient Hybrid White Tandem Organic Light-Emitting Diodes with MoO3 Layer

Electroluminescence （EL） characteristics have been studied for a hybrid tandem white organic light emitting diode （OLED） with a blue emitting fluorescent EL1 unit based on BCzVBi and a yellow emitting phosphorescent EL2 unit based on （fbi）2Ir（acac）, where a MoO3 layer is inserted between EL1 and EL2 units as charge generation layer （CGL）. Maximum current and power efficiencies of 68.1 cd/A and 29.2 lm/W were obtained, respectively, while the current and power efficiencies at luminance of 1000 cd/m2 were 68.0 cd/A and 24.6 lm/W. The yellow emission appears from about 4.5 V firstly, while the blue emission starts to appear from about 5.4 V. It was found that charge generation from CGL of MoO3/NPB bilayer occurred at high voltages of above 5.4 V but not at low voltages below 5.2 V.