Berlin 2008 – scientific programme

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 5: Poster Session SYSA

SYSA 5.24: Poster

Tuesday, February 26, 2008, 14:30–20:00, Poster A

Improving electron injection in organic light emitting diodes using a thin Li3PO4 layer — •Andrea Gassmann, Christian Melzer, and Heinz von Seggern — Technische Universität Darmstadt, Institute for Materials Science, Electronic Materials Division, Petersenstr. 23, 64287 Darmstadt

In this contribution a novel cathode material is introduced allowing for device performances comparable to the benchmark cathode LiF / Al. A thin layer of the metal salt lithium phosphate Li3PO4 is deposited between the organic semiconductor and an Al cathode. In normal OLED structures it will be disclosed that both the current density and the luminance increase similarly to the characteristics of reference devices fabricated with LiF / Al cathodes. This increase can be ascribed to an enhanced electron injection.

Regarding the origin of the observed device characteristic improvement through Li3PO4 / Al, a field enhanced injection due to piled - up holes at the cathode side can be excluded since the improvement of device characteristics holds also true in electron-only devices. Moreover, it was observed that Li3PO4 is most beneficial to the device performance at a thickness of 7 Å. Concerning the doping ability of Li3PO4, devices with co-evaporated organic semiconductor were prepared revealing a deterioration of device characteristics. Furthermore, in capacitance/ voltage measurements no evidence of doping was found. Therefore, the focal point of Li3PO4 / Al research is attributed to interface properties what is the subject of current and future investigations.