Münster 1999 – scientific programme

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CP: Chemische Physik

CP 29: Poster: Opto-elektrische und optische Eigenschaften organischer Materialien

CP 29.15: Poster

Monday, March 22, 1999, 18:00–20:00, R52/R72

Kelvin probe investigations of metal work functions and correlation to device performance of organic light-emitting devices — •T. Beierlein¹, W. Br"utting², H. Riel¹, E. Haskal¹, P. M"uller¹, and W. Rie"s¹ — ¹IBM Research Division, Zurich Research Laboratory, CH-8803 R"uschlikon, Switzerland — ²Experimentalphysik II, Universit"at Bayreuth, D-95440 Bayreuth, Germany

Using the vibrating capacitor Kelvin probe technique the contact potential difference (CPD) to a reference electrode has been determined for various metals acting as injecting contacts in organic light emitting devices (OLEDs). The work function of anode materials for OLEDs like Pt, Ir, Au, and ITO (indium tin oxide) strongly depends on the surface treatment and can be enhanced by more than 1 eV via oxygen plasma and/or UV-ozone. The device performance of multilayer OLEDs consisting of these anodes and copper-phthalocyanine (CuPc), N,N’-di(naphthalene-1-yl)-N,N’-diphenyl-benzidine (NPB), tris-(8-hydroxyquinolinato) aluminium (Alq₃), and a low work function metal cathode is correlated with the results of the CPD measurements. It is found that the injection current at a given voltage scales with CPD values for different metals having the same pre-treatment. However, different treatments of the same metal indicate that apart from the measured work function other factors have an influence on the injection properties. The surfaces of these materials are analyzed with respect to roughness and binding conditions of the oxygen to the metal surface.