Voltage- and Polarity-Tunable Multicolor Organic Electroluminescent Devices

Electroluminescent (EL) properties of organic EL devices with a three-layer structure of tris(8-hydroxyquinoline aluminum) (Alq)-doped poly(2,5-dinonyloxy- p-phenylenevinylene) (NOPPV)/an aromatic diamine derivative/ poly(9,9-dihexylfluorene) (PDHF) have been studied. Their electroluminescence was blue for negative voltage on the PDHF side electrode, and varied from orange dominated by the emission from NO-PPV to green dominated by the emission from Alq as the positive voltage on the PDHF side electrode was increased. The mechanism of the multicolor emission is discussed in terms of an energy band diagram of the devices.