Hole-transporting small molecules as a mixed host for efficient solution processed green phosphorescent organic light emitting diodes.

We have demonstrated highly efficient and reduced efficiency roll-off solution processed green phosphorescent organic light emitting diodes (OLEDs) utilizing two hole-transporting small molecular materials of 1,3-bis(carbazol-9-yl)benzene (mCP) and 4,4′,4″-tris( N -carbazolyl)-triphenylamine (TCTA) as a mixed host. Compared with the corresponding two single host devices, the mixed host one shows a superior overall performance. A low driving voltage of 5.5 V at 1000 cd/m 2 with a current efficiency of 39.5 cd/A is achieved in the mCP:TCTA (3:1) mixed host device. Even at the luminance of 10000 cd/m 2 , the efficiency still reaches 28.6 cd/A. The enhanced charge carrier balance and broadened exciton recombination zone due to the mixed host contribute to the improvement of efficiency and efficiency roll-off. [ABSTRACT FROM AUTHOR]