| AVS 60th International Symposium and Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS-ThP |
| Session: | Applied Surface Science Poster Session |
| Presenter: | M. Bruns, Karlsruhe Institute of Technology, Germany |
| Authors: | M. Bruns, Karlsruhe Institute of Technology, Germany K. Peters, Karlsruhe Institute of Technology, Germany P. Scharfer, Karlsruhe Institute of Technology, Germany W. Schabel, Karlsruhe Institute of Technology, Germany H. Hummel, Philips Technologie GmbH, Germany T.S. Nunney, ThermoFisher Scientific, UK E. Tallarek, Tascon GmbH, Germany S. Kayser, ION-TOF GmbH, Germany |
| Correspondent: | Click to Email |
Research on organic light-emitting diodes (OLEDs) has gained much attention due to the potential for cheap and ultrathin illumination sources with high color range. In multilayer OLEDs the carrier injection efficiency from the electrodes into the light emitting layer is improved by layers for hole or electron transport and blocking. Vacuum evaporation is the standard method to produce precisely defined interfaces, but it is an expensive process with high material usage. Alternatively, the wet chemical processing has advantages in production cost, deposition rate and area, but shows problems with the intermixing of the subsequently coated functional layers. The specific nature of small molecules used for OLEDs with their high mobility for diffusion in combination with low dry film thicknesses of only a few nanometers is challenging. For a better understanding of the physical limitations of liquid-phase processed multilayer OLED structures, the possibility to characterise the material mixing between two layers during coating and drying, and the comparison to evaporated layers is crucial.
The present study focusses on the surface analytical characterization of OLED multilayer films using X-ray photoelectron spectroscopy (XPS) and complementary time-of-flight secondary mass spectrometry (ToF-SIMS). In the case of (bio-) organic materials, both methods provide the chemical composition of the topmost layer, XPS mostly in a non-destructive manner. However, information on the in-depth distribution of the constituents in multilayer OLED systems, e.g. to prove chemistry and sharp interfaces, is unavailable via sputter depth profiling when using monoatomic Ar+ (XPS) and Cs+ (ToF-SIMS) ion sources for material erosion. Here the high fluence of even low energy monoatomic ions with a projected range in all cases greater than the XPS/ToF-SIMS sampling depth causes decomposition of the organic material. But since the recent introduction of high mass Ar cluster ion sources for both XPS and ToF-SIMS, enabling sputter depth profiling of organic materials while preserving the chemical/molecular information, this drawback can be overcome [1,2]. We present quantitative in-depth information on the desired OLED structures and, moreover, compare results achieved from monoatomic and cluster ion source depth profiling.
This work was carried out with the support of the KNMF, a Helmholtz Research Infrastructure at KIT.