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 behav iour of an electroluminescent (EL) cell which consists of naphthoylimi de (NPL) as the emitting layer and poly(3-octylthiophene) (P3OT) doped with poly(N-vinylcarbazole) (PVK) as the hole transport layer sandwic hed between indium-tin oxide (ITO) and an aluminium electrode. The mix ed polymer (P30T:PVK) layer and the emitting layer was deposited by sp in coating and by vacuum deposition. When the ITO substrate was cooled to near liquid Nz temperature during the deposition of the NPL emitti ng layer, the brightness of the cells increased. Characterized by atom ic 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 org anic layers and the polymer layer of EL devices. (C) 1997 Elsevier Sci ence Ltd. All rights reserved.