Dresden 2009 – wissenschaftliches Programm
DS 16.12: Poster
Dienstag, 24. März 2009, 09:30–12:30, P5
Charge carrier injection in organic light-emitting diodes studied by impedance spectroscopy and Kelvin probe measurements — •Stefan Nowy, Wei Ren, Julia Wagner, Josef A. Weber, and Wolfgang Brütting — Institute of Physics, University of Augsburg, Germany
Impedance spectroscopy (IS) is a powerful method for characterising the electrical properties of materials and their interfaces. In this study we use IS to investigate the charge carrier injection properties of different anodes and anode treatments in bottom-emitting organic light-emitting diodes (OLEDs). These are ITO-based (indium tin oxide) hetero-layer devices with TPD (N,N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4-diamine) as hole transporter and Alq3 (tris-(8-hydroxyquinoline) aluminum) as emission and electron transporting layer. The charge carrier injection is mainly determined by the work functions of the materials used as electrodes. Kelvin probe measurements allow the quantification of the work functions and the estimation of the energy level alignment inside the OLED. A more detailed analysis of the (not very well known) interfaces is provided by IS, yielding information about trapped and interfacial charges as well as the dynamics of injected charges. Furthermore we show that IS can be used to identify degradation processes in OLEDs.