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 effective conjugation lengths poly(p-phenylene vinylene)s (PPVs) formed by heat-treatment of PPV precursors in self-assembled films based on the layer-by-layer deposition between PPV and poly(sodium 4-styrenesulfonate) (PSS). It was demonstrated that the increased adsorbed amount of negatively charged PSS layer by adding NaCl salt to the PSS solution caused a blue spectral shift in electroluminescence and at the same time yielded a high turn-on voltage. The changes of electrical properties of PPV in the self-assembled films were mainly attributed to the restricted growth of conjugation bond length of PPVs induced by the increase of binding sites with the adsorbing PSS and the subsequent formation of sulfonic ester group during the thermal elimination reaction. Consequently, it is shown that the electrical properties of PPV can be simply tuned by the variation of physical parameters for the fabrication of self-assembled films without a change of PPV chemistry.