Tailoring of the electrical and optical properties of poly (p-phenylene vinylene)

The external quantum efficiency of monolayer light-emitting diodes (LEDs) prepared by poly(p-phenylene vinylene) (PPV) is usually in the range of 0.0005 and 0.002% for Al electrodes. These low efficiencies can be improved either by top electrodes having low work functions (e.g. Ca, Mg) or by the fabrication of multilayer structures. A third approach is to enhance the photoluminescence (PL) quantum efficiency of the emitting material. We reveal that large differences exist in the PL efficiency, strongly depending on the conversion conditions of the tetrahydrothiophene precursor polymer to the final polymer PPV. Following detailed investigations of this elimination reaction by different spectroscopic methods, like UV-Vis, PL, FT-IR, we were able to optimize the conversion conditions and thus obtain fully converted PPV films with high PL quantum efficiencies. In addition, a new elimination procedure, which was carried out in argon atmosphere and not as usually in vacuum, allowed us to reduce the required temperature for the elimination down to 160 °C (2 h). As a result, we have prepared flexible LEDs on poly(ethylene terephthalate) for the first time.