FABRICATION AND PROPERTIES OF LIGHT-EMITTING-DIODES BASED ON SELF-ASSEMBLED MULTILAYERS OF POLY(PHENYLENE VINYLENE)

Light-emitting diodes have been fabricated from self-assembled multila yers of poly(p-phenylene vinylene) (PPV) and two different polyanions; polystyrene sulfonic acid (SPS) and polymethacrylic acid (PMA). The t ype of polyanion used to assemble the multilayer thin films was found to dramatically influence the behavior and performance of devices fabr icated with indium tin oxide and aluminum electrodes. Light-emitting d evices fabricated from PMA/PPV multilayers were found to exhibit lumin ance levels in the range of 20-60 cd/m(2), a thickness dependent turn- on voltage and classical rectifying behavior with rectification ratios greater than 10(5). In sharp contrast, the devices based on SPS/PPV e xhibited near symmetric current-voltage curves, thickness independent turn-on voltages and much lower luminance levels. The significant diff erence in device behavior observed between these two systems is primar ily due to a doping effect induced either chemically or electrochemica lly by the sulfonic acid groups of SPS. It was also found that the per formance of these devices depends on the type of layer that is in cont act with the Al top electrode thereby making it possible to manipulate device efficiency at the molecular level. (C) 1996 American Institute of Physics.