Editing Conductive polymer (section)

==Molecular basis of electrical conductivity==
The conductivity of such polymers is the result of several processes. For example, in traditional polymers such as [[polyethylene]]s, the valence electrons are bound in sp<sup>3</sup> hybridized [[covalent bond]]s. Such "sigma-bonding electrons" have low mobility and do not contribute to the electrical conductivity of the material. However, in [[Conjugated system|conjugated]] materials, the situation is completely different. Conducting polymers have backbones of contiguous sp<sup>2</sup> [[Hybridized orbital|hybridized]] carbon centers. One valence electron on each center resides in a p<sub>z</sub> orbital, which is orthogonal to the other three sigma-bonds. All the p<sub>z</sub> orbitals combine with each other to a molecule wide delocalized set of orbitals. The electrons in these delocalized orbitals have high mobility when the material is "doped" by oxidation, which removes some of these delocalized electrons. Thus, the [[Conjugated system|conjugated p-orbitals]] form a one-dimensional [[electronic band structure|electronic band]], and the electrons within this band become mobile when it is partially emptied. The band structures of conductive polymers can easily be calculated with a [[Tight binding|tight binding model]]. In principle, these same materials can be doped by reduction, which adds electrons to an otherwise unfilled band. In practice, most organic conductors are doped oxidatively to give p-type materials. The redox doping of organic conductors is analogous to the doping of silicon semiconductors, whereby a small fraction of silicon atoms are replaced by electron-rich, ''e.g.'', [[phosphorus]], or electron-poor, ''e.g.'', [[boron]], atoms to create [[n-type semiconductor|n-type]] and [[p-type semiconductor]]s, respectively.

Although typically "doping" conductive polymers involves oxidizing or reducing the material, conductive organic polymers associated with a [[protic solvent]] may also be "self-doped."

Undoped conjugated polymers are semiconductors or insulators. In such compounds, the energy gap can be > 2 eV, which is too great for thermally activated conduction. Therefore, undoped conjugated polymers, such as polythiophenes, [[polyacetylene]]s only have a low electrical conductivity of around 10<sup>−10</sup> to 10<sup>−8</sup> [[Siemens (unit)|S]]/cm. Even at a very low level of doping (< 1%), electrical conductivity increases several orders of magnitude up to values of around 0.1 S/cm. Subsequent doping of the conducting polymers will result in a saturation of the conductivity at values around 0.1–10 kS/cm (10–1000 S/m) for different polymers. Highest values reported up to now are for the conductivity of stretch oriented polyacetylene with confirmed values of about 80 kS/cm (8 MS/m).<ref name="ReferenceA">{{cite journal |doi= 10.1038/347539a0 |title=Light-emitting diodes based on conjugated polymers|date=1990|last1=Burroughes|first1=J. H.|last2= Bradley|first2=D. D. C.|last3=Brown|first3=A. R.|last4=Marks|first4=R. N.|last5=MacKay|first5=K.|last6=Friend|first6=R. H. |last7=Burns|first7=P. L.|last8=Holmes|first8=A. B.|journal=Nature|volume=347|pages=539–541|issue=6293|bibcode=1990Natur.347..539B|s2cid=43158308}}</ref><ref>{{cite journal|doi=10.1103/RevModPhys.60.781|title=Solitons in conducting polymers|date=1988|last1=Heeger|first1=A. J.|last2=Schrieffer|first2=J. R.|last3=Su|first3=W. -P.|journal=Reviews of Modern Physics|volume=60|pages=781–850|last4= Su |first4= W.|bibcode=1988RvMP...60..781H|issue=3}}</ref><ref>{{cite book|last=Heeger|first= A. J.|chapter = Nature of the primary photo-excitations in poly(arylene-vinylenes): Bound neutral excitons or charged polaron pairs|title=  Primary photoexcitations in conjugated polymers: Molecular excitons versus semiconductor band model|editor-link=Niyazi Serdar Sarıçiftçi|editor-last =Sarıçiftçi|editor-first = N. S.|publisher = World Scientific|location= Singapore|date = 1998|isbn=9789814518215|chapter-url = https://books.google.com/books?id=U5jsCgAAQBAJ&pg=PA20}}</ref><ref>Handbook of Organic Conductive Molecules and Polymers; Vol. 1–4, edited by H.S. Nalwa (John Wiley & Sons Ltd., Chichester, 1997).</ref><ref name=h1>{{cite book|title=Handbook of Conducting Polymers|volume=1,2| editor1= Skotheim, T.A.|editor2=Elsenbaumer, R.L.|editor3=Reynolds, J.R. |publisher=Marcel Dekker|place=New York|year= 1998}}</ref><ref>{{cite journal|doi=10.1126/science.258.5087.1474|title=Photoinduced Electron Transfer from a Conducting Polymer to Buckminsterfullerene |date=1992|last1=Sariciftci|first1=N. S.|last2=Smilowitz|first2=L.|last3=Heeger|first3=A. J. |last4= Wudl|first4=F.|journal=Science|volume=258|pmid=17755110|issue=5087|pages=1474–6|bibcode = 1992Sci...258.1474S |s2cid=44646344 }}</ref><ref>{{cite journal|doi=10.1002/adma.200501152|title=Device Physics of Solution-Processed Organic Field-Effect Transistors|date=2005 |last1= Sirringhaus|first1=H.|journal=Advanced Materials|volume=17|pages=2411–2425|issue=20|bibcode=2005AdM....17.2411S | s2cid=10232884 }}</ref>{{Excessive citations inline|date=March 2023}} Although the pi-electrons in polyacetylene are delocalized along the chain, pristine polyacetylene is not a metal. Polyacetylene has alternating single and double bonds which have lengths of 1.44 and 1.36 Å, respectively.<ref>{{cite journal|doi=10.1103/PhysRevLett.51.1191|title=Molecular Geometry of cis- and trans-Polyacetylene by Nutation NMR Spectroscopy|date=1983|last1=Yannoni|first1=C. S.|last2=Clarke|first2=T. C.|journal=Physical Review Letters|volume=51|pages=1191–1193|bibcode=1983PhRvL..51.1191Y|issue=13}}</ref> Upon doping, the bond alteration is diminished in conductivity increases. Non-doping increases in conductivity can also be accomplished in a [[field effect transistor]] (organic FET or [[OFET]]) and by [[photoconductivity|irradiation]]. Some materials also exhibit [[negative differential resistance]] and voltage-controlled "switching" analogous to that seen in inorganic amorphous semiconductors.

Despite intensive research, the relationship between morphology, chain structure and conductivity is still poorly understood.<ref name=h1/> Generally, it is assumed that conductivity should be higher for the higher degree of crystallinity and better alignment of the chains, however this could not be confirmed for [[polyaniline]]<ref>{{Cite journal |last=Wessling |first=Bernhard |date=2010-12-17 |title=New Insight into Organic Metal Polyaniline Morphology and Structure |journal=Polymers |language=en |volume=2 |issue=4 |pages=786–798 |doi=10.3390/polym2040786 |doi-access=free |issn=2073-4360}}</ref> and was only recently confirmed for [[Poly(3,4-ethylenedioxythiophene)|PEDOT]],<ref>{{cite journal | title = ''In situ'' studies of strain dependent transport properties of conducting polymers on elastomeric substrates | last1 = Vijay | first1 = Venugopalan | last2 = Rao | first2 = Arun D. | last3 = Narayan | first3 = K. S. | date = 2011 | journal = J. Appl. Phys. | volume = 109 | issue = 8 | pages = 084525–084525–6 | doi = 10.1063/1.3580514 |bibcode = 2011JAP...109h4525V }}</ref><ref>{{cite journal | title = Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable Substrates | last1 = Darren | last2 = Vosgueritchian | first2 = Michael | last3 = Tee | first3 = C.-K. | last4 = Bolander | first4 = John A. | last5 = Bao | first5 = Zhenan | date = 2012 | journal = Chem. Mater. | volume = 24 | issue = 2| pages = 373–382 | doi = 10.1021/cm203216m }}</ref> which are largely amorphous.