TEMPERATURE DEPENDENCES OF ELECTROLUMINESCENT CHARACTERISTICS IN THE DEVICES FABRICATED WITH NOVEL TRIPHENYLAMINE DERIVATIVES

In this paper, we investigated the temperature dependences of the elec troluminescent (EL) characteristics of two-layer devices fabricated us ing four hole-transporting materials based on triphenylamine, and a ty pical emitting material, tris (8-quinolinolato) aluminum. The thermal stability of the organic EL devices is clearly seen to depend on the g lass transition temperature (T-g) of the hole-transporting material. T he EL device with a pentamer of triphenylamine exhibits uniform light emission in a continuous operation up to 155 degrees C without breakdo wn. A lowering of the ''turn-on voltage'' for light emission and an in crease of luminous efficiency with increasing temperature are found in the devices. Excellent durability of continuous operation is also ach ieved at high temperatures. Our results indicate that the linear linka ge of triphenylamine provides the high T-g material and the high devic e performance at high temperatures.