Characterization of OLED layers

Organic light emitting diodes (OLEDs) are considered to be one of the most promising technical approaches for the production of diffuse, large area light sources. OLEDs are built-on layer sequences of organic, semiconductive molecules. This diode type is already in use for production of small displays and a fast development of this optical technology is expected in the next years.
Right now OLED research is focusing on a development of new organic molecules as well as on the optimization of the OLED layer sequence.  The ability to chemically characterize OLEDs will help answer important analytical questions, such as:
  • Structure elucidation in research and development
  • Patent issues (e.g., identification of molecules used in OLED stacks)
  • Effect of operating parameters (e.g.; time, temperature, humidity, oxygen, etc.)
  • Failure Analysis

 

An exciting advancement in the last 5 – 10 years has been the development of cluster primary ion sources such as Aun+, Bin+, SF5+, C60+, and Arn+.1,2   Relative to atomic primary ion sources, cluster ion sources provide higher secondary ion yields. Furthermore, C60+, and Arn+ in particular have been found to impart significantly less chemical damage to the sample thus enabling molecular depth profiling; i.e., the ability to measure the concentration of molecular species as a function of depth. The invention of a new Ar cluster ion source for sample erosion offers now the possibility to gain detailed organic information from molecular layer sequences. As an example a depth profile of an OLED test structure is presented in the given plot. In this depth profile all listed substances were detected by means of their molecular ions (e.g. NPD: C44H33N2+). Thus, this new approach of organic depth profiling makes it possible to analyze organic layer systems in detail and to address analytical problems which could not be solved with ToF-SIMS so far.



(1) J. C. Vickerman, Molecular Surface Mass Spectrometry by SIMS, in Surface Analysis – The Principle Techniques, eds. J. C. Vickerman and I. S. Gilmore, John Wiley and Sons, Ltd., West Susses, Chapter 4, 2009.
(2) N. Toyoda, J. Matsuo, T. Aoki, I. Yamada, D. B. Fenner, Appl. Surf. Sci., 203 – 204, 214 – 218 (2003).