Doping, density of states, and conductivity in polypyrrole and poly(p-phenylene vinylene) -: art. no. 054208

The evolution of the density of states (DOS) and conductivity as a function of well-controlled doping levels in OC1C10-poly(p-phenylene vinylene) [OC1C10-PPV] doped by FeCl3 and PF6, and PF6-doped polypyrrole (PPy-PF6), 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 PPy-PF6, when compared to doped OC1C10-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 sigma proportional to T-1/4 as in variable range hopping, for highly doped PPy-PF6 the usual interpretation of the hopping parameters leads to seemingly too high values for the density of states.