Highly efficient red organic light-emitting diodes based on an oxadiazole-functionalized europium complex

Electroluminescence (EL) properties of an oxadiazole-unctionalized europium complex (OXD-PyBM)Eu (DBM)(3) (OXD = oxadiazole, PyBM = 2-(2-Pyridyl) benzimidazole, DBM = dibenzoylmethane) were studied. The electron mobility in (OXD-PyBM)Eu(DBM)3 was determined via transient EL from bilayer device with the structure of indium-tin-oxide (ITO)/ N, N'-diphenyl - N, N'-bis(3-methylphenyl)- 1,1'- biphenyl - 4,4'- diamine (TPD)/ (OXD-PyBM)Eu(DBM)3/LiF/Al. The electron mobility in (OXD-PyBM)Eu(DBM)3 is about 1.0x10(-6) cm/Vs, and shows field dependence. The (OXD-PyBM)Eu(DBM)(3) also exhibits better EL performance in the case of structure of ITO/TPD(30 nm)/TPD: (OXD-PyBM)Eu(DBM)3 (1:1) (20 nm)/ (OXD-PyBM)Eu(DBM)(3) (40 nm)/LiF (10 nm)/Al. The EL quantum efficiency of 3.0%, current efficiency of 3.3 cd/A, power efficiency of 1.0 lm/W at current density of 0.5 mA/cm(2) and maximum brightness of 380 cd/m(2) at 19.6 V bias were obtained, and the EL quantum efficiency reached 1.9% at current density of 4.4 mA/cm(2) with brightness of 100 cd/m(2). We attributed the improved EL performance to the improvement of the electron transport property due to the introduction of the oxadiazole units.