Characterisation 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 reasearch is focussing on a development of new organic molecules as well as on the optimisation of the OLED layer sequence. It is therefore understood that a chemical characterisation of OLEDs is preferable for the clarification of the following analytical questions:
- structure elucidation in research and development
- patent issues (e.g. identification of molecules used in OLED stacks)
- effect of operating parameters (e.g. operating time, effect of temperature, humidity, oxygen, ...)
- failure analysis
So far ToF-SIMS depth profiling could provide mainly elemental information on layer sequences. 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 strucure 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 analyse organic layer systems in detail and to address analytical problems which could not be solved wth ToF-SIMS so far.