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