Interface instabilities in polymer light emitting diodes due to annealing

✍ Scribed by F.J.J. Janssen; J.M. Sturm; A.W. Denier van der Gon; L.J. van IJzendoorn; M. Kemerink; H.F.M. Schoo; M.J.A. de Voigt; H.H. Brongersma

• Book ID: 104443254
• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 319 KB
• Volume: 4
• Category: Article
• ISSN: 1566-1199
• DOI: 10.1016/s1566-1199(03)00017-x

✦ Synopsis

In polymer light emitting diodes (PLEDS) with an (ITO/PPV/Ca) structure we observed a significant reduction of both the current and the light output at constant voltage after heat treatment for only 30 min at 65 °C. Electroluminescence spectroscopy experiments showed that the shape as well as the amplitude of the spectra were changed.

The reduction of current and light output was investigated by measuring I-V and E-V (current-voltage and brightness-voltage) characteristics of PLEDs, I-V characteristics of single carrier devices, and by performing low energy ion scattering and X-ray photoelectron spectroscopy experiments on the Ca/PPV interface.

It was concluded that the current and light output reduction could be ascribed to the degradation of the Ca/PPV and the ITO/PPV interfaces. The degradation of the ITO/PPV interface resulted in a reduction of the zero field hole mobility and a small increase of the field dependence of the mobility. The degradation of the Ca/PPV interface, probably by diffusion of calcium into the PPV, resulted in carrier traps and quenching sites, which influenced the field dependent electron mobility.