Conductive polymers

Conductive polymers are organic polymer semiconductors.

Related Topics:
Organic - Polymer - Semiconductor

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Most commercially produced organic polymers are electrical insulators. Conductive polymers, which are almost always organic, have extended delocalized bonds (often comprised of aromatic units) that creates a band structure similar to silicon. When charge carriers (from the addition or removal of electrons) are introduced into the conduction or valence bands (see below) the electrical conductivity increases dramatically. Technically almost all known conductive polymers are semiconductors due to the band structure, however so-called zero band gap conductive polymers may behave like metals. The most notable difference between conductive polymers and inorganic semiconductors is the mobility which, until very recently, was dramatically lower in conductive polymers than their inorganic counterparts, though recent advancements in self assembly is closing that gap.

Related Topics:
Organic - Polymers - Electrical insulators - Delocalized bonds - Aromatic - Silicon - Electrons - Semiconductors - Semiconductors - Mobility - Inorganic - Self assembly

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Delocalization can be accomplished by forming a conjugated backbone of continuous overlapping orbitals, for example, alternating single and double carbon-carbon bonds, which leaves a continuous path of overlapping p orbitals. This continuous string of orbitals creates degeneracy in the frontier molecular orbitals (the highest occupied and unoccupied orbitals named HOMO and LUMO respectively) which leads to the filled (electron containing) and unfilled bands (valence and conduction bands respectively) that define a semiconductor. As synthesized, conductive polymers exhibit very low conductivities. In fact, conduction in such relatively disordered matererials is mostly a function of "mobility gaps" with phonon-assisted hopping between localized states and not band gaps as in crystalline semiconductors.

Related Topics:
Conjugated - Orbitals - Bonds - Degeneracy - HOMO and LUMO - Electron - Semiconductor

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It is not until an electron is removed from the valence band (p-doping) or added to the conduction band (n-doping, which is far less common) does a conducting polymer become highly conductive. Doping (p or n) generates charge carriers which move in an electric field. Positive charges (holes) and negative charges (electrons) move to opposite electrodes. This movement of charge is what is actually responsible for electrical conductivity.

Related Topics:
Electric field - Holes - Electrons

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McGinness, Corry, and Proctor reported a high conductivity state in a polyacetylene (melanin) and the first organic electronic device. This was a voltage-controlled switch (Science, vol 183, 853-855 (1974)). Their orginal "gadget" is now in the Smithsonian's collection of early electronic devices. The chemistry Nobel prize in 2000 was awarded for the discovery and study of conducting polymers.

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