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Figure 4

In organic semiconducting polymer, this continuous string of orbitals creates degeneracy

in the highest occupied and unoccupied orbitals and leads to the filled and unfilled bands

that define a semiconductor. However, conductive polymers generally exhibit very low

conductivities. This is because conduction in such relatively disordered materials are due

to mobility gaps with phonon-assisted hopping, tunneling between localized states but not

band gaps as in crystalline semiconductors.8

As mentioned before, organic semiconductor can be doped either by removing an

electron from valence band or adding an electron to the conduction band to increase its

conductivity. Doping organic semiconductor creates more charge carriers which move in

an electric field. This movement of charge is responsible for electrical conductivity in

organic semiconductor. Doping a polymer is different from that of inorganic

semiconductor in which elements with excess and shortage of electrons are introduced. In

polymer, both doping process involves an oxidation and reduction process. The first

method involves exposing a polymer to an oxidant such as iodine or bromine or a

reductant such as alkali metals.2 The second is electrochemical doping in which a

polymer-coated electrode is suspended in an electrolyte solution. The polymer is

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