The thermoelectric effect is a physical phenomenon which intricately relates the thermal energy of charge carriers to their charge transport. Understanding the mechanism of this interaction in different systems lies at the heart of inventing novel materials which can revolutionize thermoelectric power gener- ation technology. Despite a recent surge of interest in organic thermoelectric materials, the community has had difficulties in formulating the charge trans- port mechanism in the presence of a significant degree of disorder. Here, we analyze the thermoelectric properties of various conducting polymers doped by a solid-state diffusion of dopant molecules based on a transport model with a power-law energy-dependence of transport function. A fine control of the degree of doping via post-doping annealing provides an accurate empirical evidence of a strong energy dependence of the carrier mobility in the conducting polymers. A superior thermoelectric power factor of conducting polymers doped by solid-state diffusion to that of other doping methods can be attributed to a resulting higher intrinsic mobility and higher free carrier concentration.