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Flexible Thermoelectric Polymers and Systems. Группа авторовЧитать онлайн книгу.

Flexible Thermoelectric Polymers and Systems - Группа авторов


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n and p are the densities of the electrons in the conduction band and holes in the valence band, respectively, and μ e and μ p are the electron and hole mobilities, respectively.

Schematic illustration of band structures of (a) intrinsic, (b) n-type, and (c) p-type semiconductors.

      The conductivity of intrinsically conducting polymers can be dramatically increased by doping as well. But the nature of the doping for conducting polymers is fundamentally different from that of inorganic semiconductors. The doping of the former involves the oxidation or reduction of the conjugated backbone, while that of the latter arises from the ionization of the doping elements. Doping does not produce any new band in inorganic semiconductors. But new energy levels or bands are generated in conducting polymers after doping because the charge carriers including electrons and holes in doped inorganic semiconductors can be considered as free electrons while the charge carriers of conducting polymers strongly couple with the lattice vibration.

Schematic illustration of polyacetylene (PA) with (a) a positive soliton and (b) a negative soliton. Schematic illustration of structures of polyactylene in (a) neutral state, (b) low doping degree and, (c) high doping degree. Schematic illustration of polythiophene with (a) a polaron and (b) a bipolaron. Schematic illustration of band structures of conducting polymers with less symmetry in (a) neutral state, (b) low doping degree, (c) medium doping degree, and (d) high doping degree. There is one electron on the lower polaron level in (b), while no electron on the bipolaron levels and bipolaron bands in (c) and (d).

      1.1.5.2 Charge Carrier Mobility

      The conduction electrons in metals are the valence electrons of metal atoms. The conduction electrons can be scattered by the lattice consisted of metal cations, and the lattice scattering lowers the electron mobility. Because of the much higher ion concentration in metals than in inorganic semiconductors, metals usually have a much lower charge carrier mobility than inorganic semiconductors. The charge carrier mobility of inorganic semiconductors is mainly affected by impurities, defects, and lattice vibration. A doping atom can be considered as an impurity, and it forms a scattering center for the charge carriers. As a result, doping lowers the charge carrier mobility. Therefore, the charge carrier mobility of inorganic semiconductor and conducting polymers usually decreases with the increasing doping level.

Schematic illustration of (a) Intrachain, (b) interchain, and (c) inter-domain charge transports in conducting polymers.
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