FULL-COLOR ELECTROLUMINESCENCE USING DYE-DISPERSED POLYMER BLENDS

By blending suitable dyes into poly(N-vinylcarbazole) (PVK) we have fa bricated devices which emit light in the whole visible spectrum. Their current-voltage (I-V) characteristics can be described by space-charg e limited currents (SCLC) with effective trapping of the charge carrie rs by the dye molecules, while the light intensity shows a Fowler-Nord heim-like behaviour as a function of the mean electric field, We were able to model the electroluminescence characteristics by assuming tunn elling of the minority charge carriers through a triangular barrier. T he obtained barrier heights showed a strong dependence on the dye mole cules, suggesting that the injection of minority charge carriers takes place directly into the LUMO levels of the chromophors. The recombina tion along with the space charge leads to a steeper increase of the cu rrent and a Fowler-Nordheim-like I-V characteristic in the double inje ction regime though the majority carrier current is not injections lim ited. (C) 1997 Elsevier Science S.A.