Self-assembled ionic multilayers on the surface of a nonionic, soluble, poly( p-phenylene vinylene) and its influence on the performance of light-emitting diodes

Abstract

In this paper, we report on the self-assembly of polyelectrolyte bilayers on the surface of the nonionic poly[2-methoxy-5-(2′-ethylhexyloxy)- p-phenylene vinylene] (MEH-PPV), and on its role on the performance of light-emitting diodes (LEDs), fabricated with the thus surface-modified polymer. In order to promote the alternate polyelectrolyte self-assembly, the surface of the nonionic MEH-PPV is first modified by adsorption of poly(stryrenesulfonic acid) (PSSH). Up to five bilayers of poly(allylamonium)/poly(4-styrenesulfonate) were then deposited. We find that the optoelectronic properties of LEDs fabricated with these structures are strongly dependent on the number of layers inserted between the MEH-PPV and the Al cathodes. In particular, we find that the electroluminescence efficiency improves upon insertion of PSSH, but decreases when polyelectrolyte bilayers are further inserted. We attribute this variation of device characteristics to the combination of the electrically insulating nature of the polyelectrolytes and of the surface doping of MEH-PPV by PSSH.