Heterolayer light-emitting diodes based on new oxadiazole polymers

Monolayer light-emitting diodes (LEDs) from poly(1,4-phenylene vinylene) (PPV) usually exhibit relatively low quantum efficiencies. Thus, the external efficiency of an indium-tin oxide (ITO)/PPV/Al LED is typically 0.001%. In order to increase the quantum yield heterolayer devices with new oxadiazole polymers have been fabricated. These polymers with the electron-withdrawing oxadiazole units facilitate electron injection and transport in bilayer LEDs with PPV as hole transport and emitting layer. Thus, LEDs with external quantum efficiencies up to 0.2% have been achieved. Compared to conventional PPV LEDs no temperature dependence of the quantum efficiency is detectable, indicating improved balanced charge carrier injection at room temperature.