THE ROLE OF INTERFACES IN POLYMERIC LIGHT-EMITTING-DIODES

Langmuir-Blodgett films of poly(3-hexylthiophene) and poly(methyl meth acrylate) have been used to prepare organic de and ac light-emitting d iodes (LEDs). The transient as well as steady state properties of the LEDs have been studied. In order to explain electroluminescence (EL), charge transport mechanisms, and the role of interfaces in organic LED s, transient EL, luminance-voltage and luminance-current measurements have been performed both for single layer and multilayer devices. The transient measurements were performed by applying a single square-wave voltage pulse or a square-wave ac voltage. We have shown that the tim e delay observed in transient EL measurements of single layer LEDs is mainly due to accumulation of charge carriers and not due to carrier t ransit times. The interfaces were found to have a major role on the op eration of organic LEDs. (C) 1998 American Institute of Physics.