Multilayer light-emitting diodes using poly(p-phenylene vinylene) copolymer

Multilayer diodes using poly((2,5-(dimethoxy)-p-phenylene vinylene)-p-phenylene vinylene) copolymer as an emitting layer have been investigated by electrical and electroluminescent characterizations. It has been demonstrated that three-layer devices composed of the copolymer sandwiched between poly(p-phenylene vinylene) (PPV) and polyphenylquinoxaline (PPQ) films have stronger emission than that of single- or bi-layer structures. The choice of the hole (PPV) and electron (PPQ) transport layers appeared well adapted to the energy band diagram of the copolymer, leading to the confinement of the excitons in the emitting layer and an enhancement of the light emission. The current density-electrical field characteristic of three-layer diodes showed that the transport property of the devices has been improved by lowering the turn-on threshold field.