High contrast blue organic light-emitting diodes using inorganic multilayers of Al and ZnSe

High contrast blue organic light-emitting diodes were fabricated using an inorganic multilayer of NPB (700 Å)/MADN (200 Å)/Alq3 (300 Å)/LiF (10 Å)/Al (70 Å)/ZnSe (300 Å)/Al (1000 Å). The optical and electrical characteristics were measured and compared to conventional organic light-emitting devices (OLEDs) and OLEDs with polarizers. OLEDs with the metal multilayer cathodes had an improved contrast ratio of 135∶1 compared to 104∶1 for OLEDs with polarizers. In addition, the multilayer OLEDs had a low turn-on voltage of 3.5 V due to energy band fitting of ZnSe with Al and the electron transport layer.