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Electrical Conductivity of Materials

Insulators

s ~ 10-7 S cm-1

Semiconductors s ~ 10-7 to 102 S cm-1

Metals

s > 10

2

S cm

-1

Units are expressed as resistivity ( cm or 

) or conductivity ( -1 cm-1 or S cm-1 or )

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Introduction

Conductive polymers or, more precisely,

Intrinsically conducting polymers (ICPs) are

organic polymers that conduct electricity.

Generally the polymers or organic compounds

are considered to be insulators and therefore

used in electrical equipments as such.

Conducting polymers have changed thescenario by getting from semi conducting to

almost conducting like metals.

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Discovery and synthesis.

In 1958, Natta et al synthesized polyacetylene

as black powder.

This was found to be a semi-conductor with a

conductivity between 7 x 10-11 to 7 x 10-3 S m-1.

Since then about a dozen different polymers and

polymer derivatives have been synthesized

which have been subjected to various types of doping to achieve metal like conductivities.

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Continued..

The conductivity of the polymers can beaccounted for the presence of pie bond orbitalinstead of sigma bonds which are more motile

as compared to latter. So, the more conjugated bonds are present in

the molecule, more conducting the polymer becomes.

Considering doping, the difference is that insemiconductors we use p-type or n-type dopingwhereas in CP we use oxidative or reductivedoping.

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Polymers with Unsaturated

(Conjugated) backbone structure A conjugated main chain with alternating

single and double bond

First example of conjugate polymer:Polyacetylene

Pure polyacetylene:  W ~ 10 -9 (cis) and 10 -5 (trans) S cm-1

High electrical conductivity was observed when the polymer was

³doped´ with oxidizing or reducing agents

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T he Conduction Process in Conjugate Polymers

Soliton: a defect in which the change in bond alternation is

extended over 5 to 9 repeating units

T he charge and spin of the defect will depend on the occupancy of the state

Chemical doping will create such defects in the polymer chain (e.g.

by iodine I 2 , which abstract an electron from the polymer and forms

I 3

- counter anion)

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N eutral soliton S 0 Positively charged 

Soliton S +N egatively charged 

Soliton S -

Conduction band 

Valence band 

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Isolated solitons are not stable in polymers, charge exchange will lead 

to the formation of S 0 -S + (or S 0 -S - ) pairs, which will be strongly localized 

to form a polaron

T he polaron is mobile along the

 polymer chain

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T wo polarons may collapse to form a bipolaron, which has zero spinbut with charges

T he two positive charges of bipolaron are not independent, but move as

a pair.

T he spins of the bipolarons sum to S = 0.

Q = +2e

S = 0 

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Dopants for conducting polymers

Oxidative dopants: include Iodine, Arsenic

pentachloride, Iron(III) chloride and

Nitrosium hexafluorophosphate NOPF6 (p-

type doping)

Reductive Dopants: Sodium naphthalide

K, lithium naphthalides (n-type doping)

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 Applications

Electrostatic materials

Molecular electronics

Electrical displaysThermal, biochemical and chemical

sensors

Rechargeable batteries and solidelectrolytes

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Organic Light Emitting Polymer 

First reported in 1990 ( N ature 1990, 347, 539)

Based on poly(p-phenylenevinylene) (PPV), with a

bandgap of 2.2 eV 

I TO: Indium-tin-oxide

-A transparent electrical 

conductor 

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 A commercial OLED device by SONY®

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Electrostatic materials and Molecular 

Electronics

A polymer Lithium

Sheet Battery

A Molecular Switch to be used

in Molecular Electronics

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Recent developments and Applications

Polymer film based transistors (Whole IC

in a single polymer sheet having thickness

of 200nm)

Use of self-assembled monolayer organic

field-effect transistors

Possibility of using ³single molecule´ for 

electronic devices(Nature 2001, 413, 713)

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