Conductive Polymers versus Metals and Insulators
This chapter is an introduction into the origin of the conductivity in intrinsically conducting polymers. The properties of metals, semiconductors, and insulators are rst described in general. The description of undoped and doped conjugated polymers then leads to a description of the charge transport in those materials. However, there is no model fully describing the conductive properties of all intrinsically conductive polymers. Nonetheless, signicant progress in understanding conductive polymers has been made over the last 20 years and many features can now be described. For more detailed descriptions the reader is referred to the literature.1,2
The properties of metals, semiconductors, and insulators can be most easily described using simple, nonpolymeric solids as an example. The changes in orbitals and energy levels starting from individual atoms to small molecules and then to three-dimensional solids are well understood.3 In small molecules with a well-dened number of atoms the atomic orbitals merge to form molecular orbitals with discrete and well-dened energy levels. The low lying orbitals are lled with electrons and typically have a bonding character, whereas high lying orbitals are often unlled and have an antibonding character.