Electrical Characterisation and Optimisation of Organic Semiconductor Materials towards Roll-to-Roll Transistor Devices

The objective of this work is to explore, understand and exploit the properties of solution processable organic semiconductors. The work contained within this thesis has lead to two first author peer-reviewed published papers, several co-author papers and seven thesis chapters: these, augmented with experimental data have evolved to provide a significant contribution to this area of science. Chapter 1 of my thesis gives the reader a detailed introduction to the area of field effect transistors based on solution processable organic semiconductor materials. Chapter 2 is a short overview of some of the experimental techniques used within this body of work. The aim of this chapter, is not only to document the detailed experimental conditions used, but also to provide the experimentalist with practical advice. Chapter 3 identifies a route to achieve a significant material cost reduction by employing a commodity polymer as a low cost diluent. Chapter 4 focuses on the influence of the semiconductor’s side chain substituents on the material’s performance and leads to the provision of material set pathway for improved compatibility of the organic semiconductor (OSC) with its dielectric counterpart. This work could effectively reduce limitations placed on the dielectric, facilitating large scale production. Chapter 5 discusses the benefits and science behind molecular alignment and anisotropy. Chapter 6 demonstrates the benefit of blending a high and low molecular weight semiconductor. Chapter 7 investigates charge injection from the electrodes into the semiconductor layer, thereby optimizing the material’s performance by way of not being limited by contact resistance, which is known to impair the transistor device performance of some OSCs. Each of the chapters is aimed at highlighting the progress that has been made within this thesis and to provoke further research in the field of organic electronics. The majority of this research was carried out at Merck Chemicals Ltd