Conducting Polymers: Concepts and Applications
Journal of Atomic Molecular Condensate and Nano Physics
The developments in the field of electrically conducting polymers have grown very rapidly since the discovery and there is a very sharp increase in conductivity when intrinsically insulating organic conjugated polymers are doped with oxidizing and reducing agents. An overview of technological developments involving conducting polymers clearly indicates that the field expands at unprecedented rates. The manuscript first introduces the conducting polymers (CPs), conducting mechanism, concepts of
... oping and briefly introduces main applications. Different types of CPs, their unique properties and synthesis is discussed. The present review will help the effective implementation of conducting polymers in different fields, which directly depends on the degree of understanding of their behaviour and properties. properties of the conjugated polymers can be varied to a very large extent by appropriate functionalization. Most extensively studied area of the application of undoped conjugated polymers is the fabrication of the polymeric light-emitting diodes, i.e. electronic devices which exploit the phenomenon of electroluminescence. Electroluminescence of conjugated polymers and more precisely poly(p-phenylene vinylene) was first reported by Burroughes et al.  in 1990. These undoped conjugated polymers can also be used in the fabrication of a large variety of other devices like organic field-effect transistors. Polymer LEDs show attractive characteristics, including efficient light generation, with great potential for commercialisation. Again the polymer interests in polymers is in their potential use for rapid, low-cost processing using film-forming polymer solutions. Like the conductive polymers, the semi-conductive polymers obtain their properties from their conduction-molecular orbitals and valence molecular orbitals, i.e., bonding π and antibonding π * orbitals, respectively. In electro-chemical light emitting cells, the semi-conductive polymer could be surrounded asymmetrically with a hole-injection electrode on one side, and a low work function, electron injecting metal contact like aluminum, magnesium, calcium etc. on the other side. The emission of light is then the result of radiative charge carrier recombination in the polymer as electrons from one side and holes from the other recombine. Conducting polymers are conjugated polymers, namely organic compounds that have an extended p-orbital system, through which electrons can move from one end of the polymer to the other. In conjugated polymers, the bonding leads to one unpaired electron (the π-electron) per carbon atom. Moreover, π-bonding, in which the carbon orbitals are in the sp 2 pz configuration and in which the orbitals of successive carbon atoms along the backbone overlap, leads to electron delocalization along the backbone of the polymer. This electronic delocalization provides the "highway" for charge mobility along the backbone of the polymer chain. Electronically conducting polymers are extensively conjugated molecules, and it is believed that they possess a spatially delocalized band-like electronic structure. These bands stem from the splitting of interacting molecular orbitals of the constituent monomer units in a manner reminiscent of the band structure of solid-state semiconductors. Doping The concept of doping is the unique, central, underlying, and unifying theme which distinguishes conducting polymers from all other types of polymers [12, 13] . During the doping process, an organic polymer, either an insulator or semiconductor having a small conductivity, typically in the range 10 −10 to 10 1 S/cm, is converted to a polymer which is in the 'metallic' conducting regime (−1 to 10 4 S/cm). The controlled addition of known, usually small (≤ 10 per cent) nonstoichiometric quantities of chemical species results in dramatic changes in the electronic, electrical, magnetic, optical, and structural properties of the polymer. Doping is reversible to produce the original polymer with little or no degradation of the polymer backbone.