Change in electrical characteristics of poly(p-phenylene vinylene)-based self-assembled devices by addition of ionic salt to poly(sodium 4-styrenesulfonate)

A systematic study was performed on the effect of added salt on the effecti ve conjugation lengths polyp-phenylene vinylene)s (PPVs) formed by heat-tre atment of PPV precursors in self-assembled films based on the layer-by-laye r deposition between PPV and poly(sodium 4-styrenesulfonate) (PSS). It was demonstrated that the increased adsorbed amount of negatively charged PSS l ayer by adding NaCl salt to the PSS solution caused a blue spectral shift i n electroluminescence and at the same time yielded a high turn-on voltage. The changes of electrical properties of PPV in the self-assembled films wer e mainly attributed to the restricted growth of conjugation bond length of PPVs induced by the increase of binding sites with the adsorbing PSS and th e subsequent formation of sulfonic ester group during the thermal eliminati on reaction. Consequently, it is shown that the electrical properties of PP V can be simply tuned by the variation of physical parameters for the fabri cation of self-assembled films without a change of PPV chemistry. (C) 2001 Elsevier Science B.V All rights reserved.