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Chapter 3. Organic Conductor
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Conductivity Of Organic Materials
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Conductivity = en n: number of carriers; m: mobility of the carriers
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Electronic structures of Organic Molecules (1) Core electrons. (2) electrons, localized between two atoms. (3) n electrons, located at a particular heteroatom, usually have high orbital energy and could be promoted easily. (4) electrons, delocalized over an array of atoms, usually have high MO energy and could be promoted easily.
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Discovery of Conducting Organic Crystals
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Conductivity is controlled by the phthalocyanine ring. The metal core does not interfere the conductivity. Phthalocyanine channel I-I-
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Chain length: Si:120 30 Ge: 74 40 Sn:100 40
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Conjugated Polymers
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Polyacetylene
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(1) Could a charge through delocalize through the array? (2) Is there any one dimensional conductor in principle? (3) How a charge hop from one array to another adjacent array?
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Electrical conductivity of polyacetylene Cis-PA = 1.7 x 10 -9 S/cm Trans-PA = 4.4 x 10 -5 S/cm I 2 doped = 5.5 x 10 2 S/cm AsF 5 doped = 1.2 x 10 3 S/cm Electrochemical Oxidation = 1 x 10 3 S/cm Li doped = 2 x 10 2 S/cm Na doped = 10 1 -10 -2 S/cm
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Polyparaphenylene (PPP)
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Drawbacks: low solubility. Alkyl side chain for enhancing solubility
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When no of phenylene units is larger than 12, the material becomes metallic after doped
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Synthesis of Polythiophenes PEDOT.PSS
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Polyaniline (PANI) Conductor Insulator
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Preparation
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Doping and Undoping PANI doped with H 3 PO 4 was found to be most stable.
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Conductivity could go up to 200-400 S/cm after doping
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Poly-4-phenylene-(E)-vinylene (PPV) Highly insoluble Precursor for thin film formation
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Knoevenagel Condensation Wittig Horner reaction Hsieh, B. R. (Xerox)
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Lithium Battery
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Rechargeable Battery With PA electrode Oxidation (CH) x +xy(ClO 4 - ) [(CH) +y (ClO 4 - ) y]x + xye - Reduction (CH) x +xy(Li + ) + xye - [(CH) -y (Li + ) y]x
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Battery Structures based on PA (a)P type (CH) x anode/Li cathode (b)P type (CH) x anode/n type (CH) x cathode (c)n type (CH) x anode /Li cathode When the battery is doped at 6%, the Voltages are 3.7, 2.5, 1.2V respectively
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Rechargeable Battery with poly-4-phenylene electrode
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Organic Photoconductors
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Scher-Montrol Theory on dispersive photocurrent
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Organic Photoconductors (1) Conjugated polymers (2) Polymers containing aromatic side-chains (3) Small molecules
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Organic Solar Cell
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Example
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Self-Organized Discotic Liquid Crystals for High-Efficiency Organic Photovoltaics
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