Conjugated materials and their interfaces in organic electronics studied by photoelectron spectroscopies

Abstract: Conjugated materials have attracted a large amount of attention since the discovery of high conductivity in donor and acceptor doped polyacetylene over two decades ago. Over the years, however, interest has shifted to the pristine semi-conducting state of conjugated polymers. Ibis was largely due to their electronic properties suitable for electronics applications, such as field-effect transistors (FET), light emitting devices (LED) or photovoltaic cells. Enhancement of device performance required continued intensive research in materials development. Thus research in this area resulted in the interactive overlap of traditionally separated disciplines, such as synthesis of materials, molecular based electronics and advanced materials characterization. One of methods, which turned out to be a very suitable for the examination of physical and chemical properties of conjugated materials, is photoelectron spectroscopy. The complementary exploitation of the results of photoelectron spectroscopy and the quantum chemical calculations enabled the study of many particular aspects related to basic electronic properties of conjugated materials as well as application oriented problems.This thesis is based on work focused on experimental studies of the electronic properties of conjugated materials by means of different branches of photoelectron spectroscopy. The thesis includes also the results of quantum chemical calculations carried out for the sake of comparison with the experiments as an aid in proper interpretation of experimental results. Particular investigations concern the following topics: (i) The electronic structure of the recently synthesized phenyl capped 3,4-ethylenedioxythiophene oligomers, which are potential candidates for high performance FETs; (ii) The detailed analysis of the role of counter ion on the properties of widely applied polymeric blend: poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate), PEDOT/PSS; (iii) The electronic structure of novel derivative of polyfluorene, commonly applied polymer, design to improve its performance in organic FETs; (iv) Exploitation of redox reaction between a mono-layer of electron-donor molecules, tetrakis (dimethylamino) ethylene, and the indium tin oxide surface, as a new potential route for fabrication of inexpensive cathodes for organic/polymeric (opto) electronic devices; and finally (v) energy level alignment at hybrid interfaces of vapor-deposited gold on conjugated polymers.