The strong doping dependence of the dc conductivity in conjugated polymers below the metal–insulator transition (MIT), illustrated for PPV, is argued to be due to an increase in the density of states and the growth in size of the regions, in which the charge is delocalized. Obviously in the metallic states these regions have to overlap. Phase sensitive dielectric spectroscopy data show that when this overlap is achieved less than 1% of the donated charges (at least in polypyrrole) participates in metallic transport. The data up to the MIT allow a tentative picture of the density of states.
Brom, H. B., Martens, H. C. F., Romijn, I. G., Hulea, I. N., Hupkes, H. J., Pasveer, W. F., ... Menon, R. (2004). Charge carrier properties below and above the metal-insulator transition in conjugated polymers : recent results. Physica Status Solidi C: Conferences, 1(1), 144-147. https://doi.org/10.1002/pssc.200303609