Question

briefly explain on a fundamental chemical basis what effect adding charges has on the polymer chain and how this relates to polarons and charge transport within the organic material. Then describe three different methods or devices through which charge carriers are added to an OSC, the main purpose or function of each

Answer 1

Metals, polymers and ceramics have contrasting physical and chemical properties. Polymers have low densities; do not reflect or absorb light (they are white or colorless); do not conduct electricity; and are flammable. polymer properties are completely different than chemical compositions of metals and ceramics.

Long, strong chains or nets made of thousands of carbon atoms form the backbone of a polymer. Many different nonmetal atoms could be covalently attached to a polymer backbone. Groups of atoms that contribute something besides C-C and C-H bonds are called functional groups. They affect the chemical and physical properties of a polymer. Positive and negative charges can be localized on a covalent molecule since they have no path for conduction of electrons. The carbon atoms in the backbone always follow the octet rule with four covalent bonds, so can't pass extra electrons along the chain. If polymer fibers are rubbed together they can build up a static electricity charge. conducting polymer to exhibit electrically conducting behaviour is the conjugation i.e. alternation of single and double bonds resulting into the overlap of pie-electrons. Bond conjugation in a typical degenerate system such as trans-potyacetylene can be disrupted giving rise to solitonic excitations which are not only believed to carry electricity but have been shown to be responsible for the spin-charge reversal observed in this well-studied material.n another series of conducting polymers such as polypyrrole, polythiophene, polyfuran and polyindole etc, whose ground states are energetically inequivalent, it is the polaronic excitations which transport electrical charge (Malhotra et al 1986a). With increased doping concentration in the non-degenerate (figure 2b) conducting polymers, the concentration of polarons may increase resulting in the formation of bipolarons which occupy distinct energy levels in the band-gap. Bipolarons are doubly charged compared to polarons but are spinless. Recently, there have been some controversies relating 1o the existence of bipolarons as fundamental charged species. In this paper some of the current hypotheses concerning bipolarons are discussed. It has been ascertained that conducting polymers are largely amorphous with a small degree of crystallinity or polycrystallinity. Like solid polymers, conducting polymeric materials contain different kinds of structural irregularities or defects such as branch-points, cross-links and conformational defects etc. Such defects can arise

Organic semiconductor devices consist of an organic active layer with semiconductor properties, sandwiched between two electrodes. This structure is going to be referred to in the following as ‘device’. To induce a current through the organic semiconductor, charge carriers must first be injected or photogenerated, and later transported through the semiconductor. Injection and photogeneration corresponds to the functioning principle of organic light emitting diodes and organic solar cells, respectively.