Development of novel conjugated polymer materials and structures for organic electronics and energy applications

Abstract

While much research in the field of conducting polymers and organic electronics focuses on development of novel polymers and other related materials, or enhancing the properties of existing materials and understanding the mechanisms behind them, in many cases, clear and reliable future directions or applications of the research are unclear. Developing an understanding of the roles of different physical and chemical mechanisms and establishing simple, cheap and reliable manufacturing and processing technologies for conducting polymers will be crucial to guide future research to uncover modern materials for advanced practical applications. In the present work, several novel manufacturing and processing routes have been established to firstly create organic materials with desired properties and, later, to apply them in functional devices. Several adjustments have been made to the synthesis of conducting polymers, and novel ways for patterning of thin organic films developed, so that high-quality materials can be made cheaply and relatively quickly and then used to create functional devices with improved properties. Conducting polymers such as polyacetylene, polythiophene, polyaniline or poly(3,4-ethylenedioxythiophene) have been studied for several decades now; however, their properties have not been sufficient for widespread commercial application. Only recently have developments in the field and improvements in the properties of these materials, as well as better understanding of mechanisms underlying their functionality, allowed their use in prototype devices. The conductivity of organic materials is still relatively low compared to that of their inorganic counterparts, although some applications do not require such high electrical properties. A critical step was to better understand conductivity mechanisms and improve them using several different methods. Examples of methods to improve properties include blending two or more conducting or non-conducting polymers, co-polymerizing different monomers together or designing polymers and their surfaces on the nano-level. This work presents a study of two conducting polymers: poly(3,4-ethylenedioxythiophene) and poly(thiophene) and some attempts to increase their current properties or develop new properties to meet requirements for specific applications. Most of the effort focuses on the development of properties that are important for application in fields like energy production and storage, photonics and electronics. These critical properties include high electrical performance and high conductivity, good electrochemical properties, high surface area, broad light absorption spectra, biocompatibility, good mechanical properties and long lifetime. Chapter 3 discusses vapor phase co-polymerization of bithiophene and terthiophene as a route to widen absorption spectra of polythiophene materials. Chapter 4 describes processes responsible for formation of polythiophene nano-structures during vapor phase polymerization. It also explains conditions and polymerization parameters responsible for formation of different nano-structures so that those materials can be tuned for desired applications. Chapter 5 shows development of a laser ablation technique as a way to pattern conducting polymers to get the shape and architecture required for a specific device or application. The laser ablation technique is applied to manufacture organic electrochemical transistors and gas sensors. Lastly, Chapter 6 builds on knowledge from previous chapters to develop organic light sensors and opto-logic gates that can be used in an optical-to-electronic interface. This work significantly advances the state of knowledge of conducting polymers within the organic electronics field, and gives insights into how those materials interact with each other and how to tailor their properties. The findings here can serve as a basis for developing new conducting polymers, as well as direct investigations for new applications using the materials presented here.