The electroluminescent investigation of double layer Eu-complex organic electronic luminescence diodes

Double layer organic electronic luminescence diodes (OLEDs) based on europium(dibenzoylmethanato)3monophenanthroline [Eu(DBM)3bath], ITO/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)/Eu(DBM)3bath/LiF/Al have been fabricated. With increasing the thickness of hole transporting layer, the maximum EL efficiency was increased, and the EL efficiency of 10 cd/A was achieved when the thickness of TPD layer was 80 nm; however, at high current density, the EL efficiency of all devices was decreased drastically. Besides, the evolution of EL emission spectra with increasing operating voltage was found, the mechanisms of the symmetry around the ion improved and the annihilation of excited state of Eu(DBM)3bath were discussed in explaining this phenomenon.