The importance of low-temperature deposition of organic emitting layer on electroluminescent device performance

In this paper, we have studied the electrical and light-emitting behaviour of an electroluminescent (EL) cell which consists of naphthoylimide (NPL) as the emitting layer and poly(3-octylthiophene) (P3OT) doped with poly(N-vinylcarbazole) (PVK) as the hole transport layer sandwiched between indium-tin oxide (ITO) and an aluminium electrode. The mixed polymer (P3OT:PVK) layer and the emitting layer was deposited by spin coating and by vacuum deposition. When the ITO substrate was cooled to near liquid N₂ temperature during the deposition of the NPL emitting layer, the brightness of the cells increased. Characterized by atomic force microscopy, the emitting layer became more amorphous when the deposition temperature decreased. The results collected in this paper show that low-temperature deposition of organic thin films would be a powerful technique for the enhancement of the contact between the organic layers and the polymer layer of EL devices.