Prof. William Salaneck, Linköping University

Spontaneous charge transfer between weakly interacting electronic systems: Hybrid interfaces in polymer electronics

Polymer films spin coated on metallic substrates are fundamental to polymer-based electronics, including transistors and light emitting devices. Control of charge injection at hybrid interfaces, both polymer-metal and "small molecule"-metal interfaces, is essential for understanding and eventual commercial device applications. There are two limiting cases of polymer-metal interactions of interest: strong coupling and weak coupling. Strong coupling applies mostly to organic molecules vapor deposited on clean metal surfaces in UHV, while weak coupling applies mostly to spin-coated films (of molecules or polymers) on metallic substrates, or electrodes. Aspects of charge transfer at hybrid interfaces in the weak coupling limit will be discussed. Over a narrow range of values of the work function of a metallic electrode, charge injection follows a simple Schottky-Mott model, as report in many systems previously [1]. Of special interest are charge-transfer states in organic thin films that come into play when the work function of the metallic electrode is very high or very low, which, in certain, cases may pin the Fermi level of the metallic electrode at the interface, leading to a complete breakdown of ideal Schottky-Mott behavior [2]. In addition, some new, as yet unpublished, results will be included.

[1] "Hybrid interfaces of conjugate polymers: Band edge alignment studied by ultraviolet photoelectron spectroscopy", W. R. Salaneck, M. Fahlman, Journal of Materials Research 19, 1917 (2004).
[2] "Fermi-level pinning at conjugated polymer interfaces", C. Tengstedt, W. Osikowicz, W. R. Salaneck, I. D. Parker, C.-H. Hsu, and M. Fahlman, Appl. Phys. Lett. 88 053502 (2006).

For more information contact Dr. Jean-Luc Brédas (404-385-4986).