Doping, density of states, and conductivity in polypyrrole and poly(p-phenylene vinylene)

The evolution of the density of states (DOS) and conductivity as a a function of well-controlled doping levels in $OC_{1}C_{10}-poly(p-phenylene vinylene)$ $[OC_{1}C_{10}-PPV]$ doped by $FeCl_{3}$ and $PF_{6}$, and $PF_{6}$-doped polypyrrole $(PP_{y}-PF_{6})$, has been investigated. At a doping level as high as 0.2 holes per monomer, the former one remains nonmetallic while the latter crosses the metal-insulator transition. In both systems, a similar almost linear increase in DOS as a function of charges per unit volume (c*) has been observed from the electrochemical gated transistor data. In $PP_{y}-PF_{6}$, when compared to doped $OC_{1}C_{10}-PPV$, the energy states filled at low doping are closer to the vacuum level; by the higher c* at high doping, more energy states are available, which apparently enables the conduction to change to metallic. Although both systems on the insulating side show log TA�¢A��A��1/4 as in variable range hopping, for highly doped $PP_{y}-PF_{6}$ the usual interpretation of the hopping parameters leads to seemingly too high values for the density of states.