LIGHT-EMITTING-DIODES BASED ON POLY(2,3-DIPHENYL-1,4-PHENYLENE VINYLENE)

In this paper we report polymer light-emitting diodes based on (2,3-di phenyl-1,4-phenylene vinylene) (DP-PPV), a novel pi-conjugated polymer made by using the chlorine precursor route (CPR). Thin films of the p recursor polymer were formed by spin-casting on indium-tin oxide (ITO) coated glass substrates, followed by thermal conversion to give DP-PP V thin films. Single layer DP-PPV LEDs were completed by thermally eva porating magnesium (Mg) electrodes. The electroluminescent characteris tics of ITO/DP-PPV/Mg devices as well as variations between precursor polymer batches am presented. Bilayer LEDs were also made, for which t ris(8-hydroxyquinoline)aluminum (Alq(3)) was thermallysublimed on the fully converted DP-PPV films in vacuum, followed by Mg deposition. Bot h significant improvement in the quantum efficiency (up to 0.7% ph/el) and a reduction in the turn-an voltage of the device were found upon incorporation of the Alq(3) layer. These observations suggest that Alq (3) enhances the injection of electrons and also participates in the r ecombination process. (C) 1997 by John Wiley & Sons, Ltd.