Advanced chemical characterization of organic electronic materials and devices

Abstract

This thesis is directed towards the development of novel characterization protocols to probe the chemical composition at the nano scale of devices that are used in organic electronics. This enables the investigation of chemical processes like the degradation of molecules or dopant migration that occur during device operation as well as the detection of contaminants. This information is much needed to improve the lifetime and the efficiency of the device. Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS) are two commonly used techniques to study the chemistry of inorganic and organic materials. Combined with a sputter gun, depth profiling can be performed to gain 3 dimensional chemical reconstructions of the sample. However, modern organic electronic devices like OLEDs represent a real challenge for chemical depth profiling because of film thicknesses of only a few nanometers, molecules with very similar structure that can be damaged during analysis, and inorganic-organic interfaces that are problematic to sputter through because of substantial differences in sputter rates.
To overcome these obsacles, single layers and bilayers are studied as simplified systems to develop reliable and precise characterization protocols with minimal analysis induced damage to the organic materials. The combination of ToF-SIMS and XPS is key in this part.
Then,these protocols are adapted to study complete OLED devices. Electrically aged devices are compared to non-aged devices to study the degradation of the molecules.
Finally a new sample preparation technique with the creation of extremely shallow beveled craters is explored for an even gentler analysis. This technique is very promessing and could lead to an improvement of the characterization protocol in the future.

Date of Award	26 Mar 2019
Original language	English
Awarding Institution	University of Namur
Sponsors	CEA-LETI
Supervisor	Laurent Houssiau (Supervisor), J. P. Barnes (Jury), Olivier Renault (Jury), Jean-Jacques Pireaux (Jury), Robert Sporken (Jury) & Cécile Courrèges (Jury)