HETEROLAYER LIGHT-EMITTING-DIODES BASED ON NEW OXADIAZOLE POLYMERS

Monolayer light-emitting diodes (LEDs) from poly(1,4-phenylene vinylen e) (PPV) usually exhibit relatively low quantum efficiencies. Thus, th e external efficiency of an indium-tin oxide (ITO)/PPV/Al LED is typic ally 0.001%. In order to increase the quantum yield heterolayer device s with new oxadiazole polymers have been fabricated. These polymers wi th the electron-withdrawing oxadiazole units facilitate electron injec tion and transport in bilayer LEDs with PPV as hole transport and emit ting layer. Thus, LEDs with external quantum efficiencies up to 0.2% h ave been achieved. Compared to conventional PPV LEDs no temperature de pendence of the quantum efficiency is detectable, indicating improved balanced charge carrier injection at room temperature.