A Mixed Host Emitting Interlayer Based on CBP:TPBi in Green Phosphorescent Organic Light-Emitting Diodes

A series of green phosphorescent organic light-emitting diodes based on bipolar-transporting material 4,4'-bis-(carbazol-9-yl) biphenyl (CBP) are prepared. We insert a mixed host emitting interlayer (CBP_x: electron-transporting material 1,3,5-tris (N-phenylbenzimidazole-2yl) (TPBi)_1-x) in the middle of the emitting layer, and the best performance appears when x is 2/3. The position of this interlayer can also affect the performance of phosphorescent organic light-emitting diodes. When this interlayer is close to the side of the electron transporting layer, the maximum value of luminance, the current efficiency and the power efficiency are 34090 cd/m^2 at 12 V, 60.6 cd/A and 56.6 lm/W, respectively.