Enhancement of Electroluminescence by Low-Temperature Deposition of Organic Thin Solid Films

The electrical and light-emitting behaviors of electroluminescent cells, which consist of naphthoylimide (NPL) as emitting layer and poly(3-octylthiophene)(P3OT) doped with poly(N-vinylcarbazoe) (PVK) as hole transport layer sandwiched between indium-tin-oxide(ITO) and aluminum electrode, have been studied. The mixed polymer (P3OT:PVK) layer and the emitting layer were deposited by spin coating and by vacuum deposition respectively. It was found that the visible blue emission could be observed from the cells at low bias voltage. And when the ITO substrate was cooled to near the liquid N₂ temperature during the deposition of NPL emitting layer, the brightness of the cell increased. It was confirmed that holes could be easily injected into NPL layer with deposition temperature decreased.