The effect of insulating spacer layers on the electrical properties of polymeric Langmuir-Blodgett film light emitting devices

We report on the use of insulating Langmuir-Blodgett (LB) films to improve the quantum efficiency of light emitting devices based on polymeric LB films. The insertion of arachidic acid layers between a poly-(2-methoxy,5-(2'ethylhexyloxy)-p-phenylenevinylene) (MEH-PPV) film and an aluminium cathode was found to decrease the turn-on voltage for electroluminescence and to double the quantum efficiency. In contrast, depositing the fatty acid layer between the polymer and the indium tin oxide anode produced little change in the device efficiency. Dual-layer structures using MEH-PPV as the light emissive layer and poly-(p-(3-hexyl pyridylene)) as an electron transport layer were also tested. Again, an increase in device efficiency could be obtained by placing arachidic acid LB layers immediately beneath the metallic cathode.