ABSTRACTPPV based light emitting thin film devices were fabricated using a layer-by-layer deposition technique involving the alternate spontaneous adsorption of a PPV precursor polymer and either poly(styrene-4-sulfonate) (SPS) or poly(methacrylic acid) (PMA). It was demonstrated that the polyanion used to self-assemble the PPV precursor strongly influences the characteristics and performance of the resulting LEDs. Devices fabricated with PPV created in the presence of SPS exhibited symmetric I–V curves, low luminance levels and very high current densities while PPV/PMA devices exhibited luminance levels in the range of 10–60 cd/m2 and classical rectifying behavior. These dramatic differences are primarily due to a low level of p-type doping activated during the thermal conversion of PPV and/or during device operation that confers excellent hole carrier transport capabilities to the PPV/SPS combination. Fabrication of a multi-slab type heterostructure device comprised of a PPV/SPS block (hole transporting block) and a PPV/PMA block (emitting block) resulted in improved performance with luminance levels significantly higher than previously obtained for a single slab PPV/PMA device (typically > 100 cd/m2). It was also demonstrated that the presence of very thin (about 20–30 Å thick) insulating layers at the Al/polymer interface improves device efficiency by a factor of 2–4.