We investigate fundamental properties of thin organic layers under ultrahigh vacuum condi- tions. Our focus lies especially on doped layers, on interfaces and on self-assembled monolayers.
Heidelberg University (KIP)
Our research group is directed by Prof. Annemarie Pucci from the Kirchhoff Institute for Physics (KIP) at Heidelberg University. Together with the research groups of Prof. Wolfgang Kowalsky (TU Braunschweig) and Prof. Wolfram Jaegermann (TU Darmstadt), we form the competence center Analytics at the InnovationLab joint research and development platform.
We investigate the fundamental properties of thin organic layers under ultrahigh vacuum conditions. We focus especially on doped layers, on interfaces and self-assembled monolayers (SAMs).
For our experimental investigations at InnovationLab, we use primarily in situ Fourier-transform infrared spectroscopy. For further investigations, we also have an infrared ellipsometer that is located at the KIP. In the section methods, you can find more details about our experimental setups. Our homepage gives you further information about our ongoing research and our team at the InnovationLab. For further questions about our research just contact us personally.
Internal interfaces and phase boundaries play an important role in electronic devices. This holds especially for organic electronics due to a large number of organic and inorganic layers in such devices. Very often complicated layer structures with a wide variety of different materials are used to optimize device performances. The electronic and morphologic properties of these materials have to be matched up precisely demanding a detailed understanding of the underlying mechanisms at interfaces.
Furthermore, numerous types of mixed layers are applied in different functions in organic electronic devices, e.g. doped transport- and emission-layers in organic light-emitting diodes and bulk-hetero-junctions in organic photovoltaic. In these mixed systems, a fundamental understanding of the interactions that affect the morphology and electronic properties is of great importance.
Interfaces of organic semiconductors
We investigate interfaces of organic semiconductors using in-situ infrared spectroscopy in ultra-high vacuum (UHV). With that technique, we can measure IR spectra of interfaces during controlled layer deposition in UHV. By evaluation of the spectral changes for interface layers compared to the spectra of the pure layers, we identify the charge transfer between the different materials. Moreover, it is possible to quantify the number of transferred charges per dopant molecule even with thickness resolution.
By comparing experimental spectra to calculations, also a possible preferential orientation of the molecules can be determined for different interfaces. The relative molecular orientation at interfaces is crucial both for energy- and charge-transport across the interface. Furthermore, by performing temperature-dependent measurements, we can influence the morphology of the system under investigation and can learn about the involved mechanisms, e.g. diffusion.
The controlled specific modification of the electronic and morphological properties of interfaces using self-assembled monolayers and polyelectrolytes represents the overall goal of the interdisciplinary research network.
Doping of organic semiconductors
The diffusion of molecules is particularly important for the issue of doping of organic semiconductors. Common problems are the unwanted agglomeration and diffusion of doping molecules, both of which generally lead to a decrease in device efficiency.
In analogy to the studies at interfaces, the charge transfer efficiency in doped layers can be carried out by the careful quantitative analysis of vibrational modes. For this purpose, shifts in the excitation energies, as well as changes in the intensity of the vibrational bands, are evaluated to conclude the ratio between charged and neutral molecules.
Our research on the morphology and electronic properties of organic semiconductors at interfaces and in mixed phases is funded by the Federal Ministry of Education and Research (BMBF) within the InterPhase project (FKZ 13N13657).
We use a Fourier-transform infrared (FTIR) spectrometer (Vertex80v, Bruker) that is coupled to an ultrahigh vacuum (UHV) chamber. By making use of in-house developed mirror-optics, the IR beam is directed into the UHV chamber and focused onto the sample. This setup allows us to measure infrared spectra during the evaporation of thin layers of organic semiconductors under very well defined conditions. Using several different radiation sources, beamsplitters and detectors, we can cover the spectral range from 10 cm-1 to about 10 000 cm-1.
Infrared spectroscopy is a powerful analytic tool with high chemical sensitivity, that not only allows investigating molecular vibrations, but also electronic excitations.
We investigate thin organic layers with an infrared ellipsometer (IR-VASE, Woollam) that is located at the KIP. Using a DTGS detector, we can measure the mid-infrared range (350 - 6000 cm-1) with a resolution of up to 1 cm-1. The advantage of ellipsometry is, that the index of refraction as well as the extinction coefficient and by that the complete dielectric function, can be determined at the same time. This method allows it, to determine for example the orientation of molecules in thin organic layers or the conductivity of a well-conducting material.
Master & Bachelor
contact via email
Room: E 4.08
Phone (iL): +49 (0) 6221 54 19 124
Phone (KIP): +49 (0) 6221 54 9891
- Dr. Milan Alt
- Rainer Bäuerle
- Dr. Sebastian Beck
- Jakob Bernhardt
- Dr. David Gerbert
- Dr. Tobias Glaser
- Sebastian Hell
- Dr. Sabina Hillebrandt
- Robin Kaissner
- Peter Krebsbach
- Johannes Kröner
- Joshua Kress
- Dominik Lüke
- Heiko Mager
- Schko Sabir
- Patrick Schilling
- Dr. Michael Sendner
- Vipilan Sivanesan
- Sven Tengeler
- Dr. Jens Trollmann
- Johannes Zimmermann