White organic light-emitting diodes using double electron transporting layers

The authors have demonstrated white organic light-emitting diodes (WOLEDs) with doublue electron transporting layers (D-ETL) using 9-dimethyl-4,7-diphenyl-1,10-phenanhroline / 4,7-diphenyl-1,10-phenanthroline (BPhen) and bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminium / BPhen. Ste pwise D-ETL can transport electron easily to emitting layer and reduce leakage of electrons. Therefore, WOLEDs with D-ETL exhibited higher external quantum efficiency (EQE) than control WOLED with single ETL device. The optimized WOLEDs showed an EQE of 11.4%, a current efficiency of 24.1 cd/A, and a Commission Internationale de I´Eclairage coordinates of (0.40, 0.39) at 1 mA/cm².