DEVICE PERFORMANCE OF LIGHT-EMITTING DIODE WITH POLY(PHENYLENESULFIDEPHENYLENEAMINE) AS A PROMOTOR OF HOLE INJECTION

Charge carrier injection into and electroluminescence from single-laye r, bilayer, and trilayer light-emitting diodes have been studied under cw and pulsed operation. The active materials were poly(phenylenesulf idephenyleneamine) (PPSA), poly(p-phenylphenylenevinylene) (PPPV), and a blend of oxadiazole and polystyrene. Owing to its low oxidation pot ential PPSA promotes hole injection from ITO into the emitting PPPV la yer. The energy level structure of the trilayer assembly leads to an e nhancement of electron injection owing to the accumulation of positive space charge and prevents sweep out of holes and electrons from the e mitting PPPV layer. An external quantum efficiency of 1% has been meas ured with an aluminium cathode. Time-resolved electroluminescence stud ies yield information on the kinetics of charge carrier recombination.