Understanding the doping dependence of the conductivity of conjugated polymers: Dominant role of the increasing density of states and growing delocalization

In variable-range-hopping theories for the dc conductivity, the extension of sites where the charges are located and the energy dependence of the density of states (DOS) are usually neglected. We show that these dependences are the dominant factors for understanding the strong doping dependence, and present an analytical theory for arbitrary DOS. We verify the theory with systematic data over a broad range of temperature and doping for FeCl₃-doped poly (p-phenylene vinylene). By combining theory and data, we reconstruct the energy-dependent DOS and the extension of sites.