Regensburg 2007 – scientific programme
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DS: Fachverband Dünne Schichten
DS 16: Organic Light Emitting Diodes (SYOE 9)
DS 16.6: Talk
Wednesday, March 28, 2007, 15:45–16:00, H32
Metal organic-interfaces and their impact on inverted top-emitting organic light emitting diodes — •Qiang Huang1, Sebastian Scholz1, Karsten Walzer1, Karl Leo1, and Michael Hofmann2 — 1Institut für Angewandte Photophysik, TU Dresden, D-01062 Dresden — 2Novaled AG, Tatzberg, D-01307 Dresden
In order to compete with other flat panel display technologies, amorphous silicon TFT (α-Si TFT) backplanes,which operate by n-channel transistors,are desired in active-matrix organic light-emitting displays (AMOLEDs). Thus, inverted top-emitting OLEDs with a bottom cathode and top anode have to be implemented. However, inverted top-emitting OLEDs reported so far show worse performance, e.g. increased operating voltage, than their corresponding non-inverted counterparts. This is mainly due to a charge carrier injection problem at the metal/organic interface. We use single carrier devices to study the difference between the metal-organic and organic-metal interface, where asymmetric I-V characteristics demonstrate different interface effects. It is found that when thermal metal deposition is used, the topmost organic layer is destroyed or reacts with hot metal atoms forming a deteriorated organic interlayer which hinders hole injection. In contrast, this effect is beneficial for electron injection in the non-inverted case due to the formation of additional gap states. Based on the study, highly efficient inverted top-emitting OLEDs are presented with a current efficiency well above 80 cd/A at a brightness of 1000 cd/m2.