Poly(3-alkylthiophenes) form the basis Veliparib PARP for organic solar cells and transistors. The molecular basis of conductive properties lies in the conjugation of their bonds. Conductive polymers have continuous backbones of sp2 hybridised electrons, compared to the sp3 hybridised covalent bonds of nonconducting polymers. The valence electron of each sp2 hybridised carbon center combines a molecule wide delocalized orbital. These intrinsic organic semiconductors are typically doped oxidatively to form p-type organic semiconductors through dopants. Analogous to doping of inorganic intrinsic semiconductors, a small amount of doping (of around 0.1wt%) causes the conductivity of the polymer to surge by 7�C9 orders of magnitude. For example, undoped conjugated polymers such as polyacetylene may increase from 10?10 to 10?8S/cm to around 0.

1S/cm upon doping. The frontrunner in the conductivity performance of conducting polymers is poly(3,4-ethylenedioxythiophene) (PEDOT), which, when doped with polystyrene sulfonate (PSS) or tosylate (Tos), may achieve conductivities of up to 3000S/cm [46]. Figure 1Various polymer structures of (a) polyaniline, (b) poly(2,7-carbazolenevinylene) [47], (c) polyacetylene and (d) poly(p-phenylene vinylene).Table 1Thermoelectric property of various polymers.2.2.2. Polymer Concentration Hiroshige et al. [40] showed that the electrical conductivity of poly (2,5-dimethoxy phenylenevinylene) (PMeOPV) increases with increasing monomer content of (methoxy phenylene vinylene) MeOPV whilst the Seebeck coefficient remains the same regardless of the monomer concentration.

In their research, a relatively high Seebeck coefficient PMeOPV was observed at 39.1��V/K. To date, the thermal conductivity data and ZT of this material are not available. As the (methoxy phenylene vinylene) MeOPV content in the monomer feed is increased from 0 to 100mol%, the conductivity increases from about 10?3 to 101S/cm. Figure 2 shows the relationship of conductivity and monomer content. In the case of PEDOT:PSS blend [48], the trend is the same as the one described earlier. At high PSS content, PSS is the dominating factor and it is responsible for limiting the carrier transport within itself. But as the PSS content reduces, the distance between PEDOT:PSS cores effectively reduces as well and this affects the charge carrier mobility instead of affecting the charge carrier density.

This is confirmed by the constant Seebeck coefficient even after reducing the PSS content. Similar observation has also been observed elsewhere [49]. Figure 2Conductivity dependence of monomer concentration [40].2.2.3. Polymer Molecular Weight and Chain Length It is found that the molecular weights of the polymers have a substantial effect on the electron mobility and consequently Entinostat affect the electrical conductivity. Kline et al.