Comparative study of optoelectronic properties of various Europium complexes used in organic electroluminescent structures

摘要

In order to obtain a red emission with organic electroluminescent device, we realized multilayer structures using various Europium complexes as emitting layer. The multilayer structures were obtained with the emitting layer deposited on a ITO substrate; a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) layer was used as hole blocking layer and a tris-(8-hydroxyquinoline) aluminium (Alq3) layer as electron transport layer. Cathode of the devices was realized with a calcium layer covered with an protective aluminium layer. Two different europium complexes have been tested: 1. Eu (TTA)_3 phen (TTA = thenoyltrifluoroacetone), 2. Eu (DTP)_3 (dipphen) (DTP = 1,3-di(2-thienyl)propane-1,3-dione, dipphen = 4,7-Diphenyl-1,10-phenanthroline) The Europium complexes were inserted in a poly-9-vinylcarbazole (PVK) matrix and the "spin-coating" process was used to obtain the emitting layers. The maximum emission of the OLEDs are centered arround 610 nm according to the ~5D_0 → ~7F_2 transition of the rare earth. Europium complexes absorption spectra in chloroform and electroluminescence spectra are presented. Current-voltage and luminance-voltage characteristics are also presented and we discuss about the results obtained with various molar concentration of Europium complexes in the PVK matrix.