Chapter 2 Conducting Polymers

In general, conducting polymers include electronically conducting polymers and ionically conducting polymers. Ionically conducting polymers are usually called polymer electrolytes. Electronically conducting polymers can also include conjugated conducting polymers and the insulating polymers blending with conducting materials. In this chapter, the conducting polymers are limited to conjugated conducting polymers, unless otherwise stated. Traditionally, polymers are thought of as insulators. However, in 1977 a discovery by Alan G. MacDiarmid, Hideki Shirakawa, and Alan J. Heeger et al. changed the traditional concept. They found that conductivity of polyacetylene— after doping with electron-withdrawing AsF5—increased ninefold, reaching the order of 10 S/cm [1, 2]. Soon after this discovery, a series of stable conducting polymers, including polypyrrole (PPy), polyaniline (PAn), and polythiophene (PTh), were reported from the end of the 1970s to the beginning of the 1980s, which greatly promoted the research on conducting polymers. Actually, the conductivity of almost all conjugated polymers can reach the order of 10–10 S/cm after doping. Now we can expand the class of conducting polymers to include all the doped conjugated polymers. In 1990, Friends et al. found the electroluminescent properties of poly(p-phenylene vinylene) (PPV) [3] and opened up a new field of polymer light-emitting diodes (PLEDs) with semiconducting intrinsic conjugated polymers as the active light-emitting layer. In 1995, Heeger et al. reported bulk-heterojunction polymer solar cells (PSCs) with a conjugated polymer MEH-PPV as donor and a fullerene derivative PCBM as acceptor [4], which further extended the research on conjugated polymers to the field of organic photovoltaics. Since then, conjugated polymer