Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 20: POSTER A

CPP 20.67: Poster

Montag, 24. März 2003, 19:00–21:00, ZEU/250

The effect of keto defects on light emitting diodes based on polyfluorene and its polarized optical characteristics — •Xiao Hui Yang¹, Frank Jaiser¹, Dieter Neher¹, E. Zojer², J.L. Brédas², Roland Güntner³ und Ullrich Scherf³ — ¹Universität Potsdam, Experimentalphysik, Am Neuen Palais 10, 14469 Potsdam, Germany — ²Department of Chemistry, The University of Arizona, Tucson, Arizona 85721-0041, USA — ³Bergische Universität Wuppertal, Makromolekulare Chemie, Gaußstr. 20, 42097 Wuppertal, Germany

We report on the influence of keto defects on the performance of light emitting diodes based on polyfluorene (PF). The undesired green emission can be related to keto defects, as suggested by the EL spectra of blends of intrinsic PF and Fluorene/fluorenone copolymer. But even though the keto defect was shown to act as an electron trap, doping with typical hole transporting molecules at a low concentration significantly reduces the green emission in EL. It is thus reasonable to assume that additional weakly emissive sites (e.g. hole-trapping aggregates) exist in the PF layer. In EL, these sites compete with the hole capture and recombination on undisturbed PF chains, leading to a reduction in the blue emission contribution in the EL spectra. Further, polarized optical characteristics of the keto defects are presented. The experimental studies show that the transition dipole of the keto CT exciton is oriented parallel to the chain direction, which is consistent with quantum mechanical calculations.