Conductive Polymer In The Carrier Dynamics Study

Since the discovery in 1977 that polyacetylene can be doped to very high electrical conductivity and becomes conductor, there has great interest in the studying of conductive conjugated polymers. On the one hand, many new concepts have been proposed during the study of conducting polymer, for example, soliton in conducting polymer, organic superconductor, fractional charge in polymer and so on. On the other hand, conducting polymer is a new promising materials with the processing and performance advantages for low-cost and large-area application. At present, numerous high-performance photoelectric devices fabricated from organic polymers have been made, including light-emitting diodes, field effect transistors, photovoltaic cells, etc.Design of these devices requires understanding such processes as photochemical reaction, dynamics of photo-excitation, and energy and charge transport, which in turn involve strongly coupled electron-lattice dynamics. In this paper, we mainly discuss the charge carriers' dynamics in conjugated polymers.In the first chapter, we will discuss the chemical structure of some basic conjugated polymers. Because of the chain-structure, conducting polymers can be considered as quisa-one dimensional systems. And these systems can exhibit new characters such as Peierls instability and dimerization. In the following, we introduce a model to describe such systems — Su-Schrieffer-Heeger model. In the second chapter, we will discuss the elementary excitation. As we know, due to strong electron-lattice coupling, the elementary excitations are those including both charge and lattice distortion, such as soliton, polaron and bipolaron. We will introduce their charge and spin properties, and energy band structures. The charge carriers in conducting polymers are believed to be these elementary excitations.In the third chapter, we will introduce the dynamical method. In addition, we discuss the electron-electron interaction within the mean field approximation. In the following chapters, we turn to the dynamical processes. We first study polaron interaction with impurity. Two processes will be discussed: one is polaron depinning from impurity by the electric field, the other is polaron scattering with impurity. Recently, how to utilize the charge carrier's spin degree of freedom has attracted much interest and so wealso study polaron dynamics under the local magnetic field induced by magnetic impurity. In chapter 5, we investigate bipolaron dynamics. First, we discuss the bipolaron generation in a metal/polymer/metal structure, which is found to depend on the external field closely. Then bipolaron dissociation is studied and the result is that bipolaron can sustain to much higher electric field than polaron. In the last chapter, we discuss a new excitation in polymer — intrinsic localized mode or breather, which can occur in discrete and nonlinear system and has attracted much interest presently.