Indium diffusion in model polymer light-emitting diodes

The diffusion of indium into poly-(phenylenevinylene) (PPV) in model polyme r light-emitting diodes (p-LEDs) was studied with Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (ICPS), low energy io n scattering spectroscopy (LEIS) and particle induced X-ray emission (PIXE) . The model p-LEDs consisted of a glass substrate, an indium-tin-oxide (ITO ) electrode, a PPV layer obtained by thermal conversion of sulfonium precur sor PPV, and a patterned aluminium electrode. From RES measurements it was concluded that about 0.01 at.% indium was present in the PPV, homogeneously distributed in depth. Annealing at 230 degrees C for 19 h caused the amoun t of In in the PPV layer to increase by roughly an order of magnitude. Unde r the patterned aluminium electrode, the annealing treatment resulted in ac cumulation of In at the PPV/Al interface, whereas the depth distribution of In remained homogeneous in the uncovered region of the model LEDs. XPS spe ctra on annealed model LEDs show that In was present in the near surface re gion of the PPV films, although LEIS analysis showed that In was not situat ed in the outermost atomic layer. LEIS measurements on as-prepared model LE Ds showed that the patterned Al electrode had caused surface contamination of the uncovered PPV film with Al, which can have impact on the diffusion o f In to the outermost surface during annealing treatments. (C) 2000 Elsevie r Science S.A. All rights reserved.