Organic light-emitting diode with 20 lm/W efficiency using a triphenyldiamine side-group polymer as the hole transport layer

We have used triphenyldiamine side-group polymers as hole transport layers in multilayer organic light-emitting diodes using 8-hydroxyquinoline alumin um (Alq(3)) as an emission layer. The device efficiency systematically incr eases as the ionization potential of the hole transport layer is shifted fu rther from the work function of the indium-tin-oxide anode. We attribute th is trend to better balance of hole and electron charges in the device. An o ptimized device consisting of a fluorinated version of the polymer as the h ole transport layer, quinacridone doped Al as the emission layer, and a LiF /Al cathode results in a peak external luminous efficiency of 20 lm/W. (C) 1999 American Institute of Physics. [S0003-6951(99)02421-3].