Since the first discovery of polymer-based light emitting diodes (PLED) in 1990
the interest in the charge transport phenomena in such devices increased rapidly.
The efficiency of the injection of electrons and holes plays an important role
for the electroluminescence of LED's. The typical structure of an
electroluminescence device can be described as metal-polymer/polymer-semiconductor
interface. For the hole injection sputtered indium-tin-oxides (ITO) electrodes on
glass substrates are used. The sputtering parameters have an influence on the
work function of the ITO-electrode. We investigated the current-voltage (I-U)
characteristics for testing the diode character and capacitance-voltage (C-V)
behaviour of different single and multilayer structures to describe the function of
such devices. From the C-V measurements we decided the recombination depth and the
carrier concentration in several polymer layers. It was found that the
electroluminescence increases with an additional electron transport layer.
