  Transport properties of doped conjugated polymers (CPs) have been widely
analyzed with the Gaussian Disorder Model (GDM) in conjunction with hopping
transport between localized states. These models reveal that even in highly
doped CPs, a majority of carriers are still localized because dielectric
permittivity of CPs is well below that of inorganic materials, making Coulomb
interactions between carriers and dopant counter-ions much more pronounced.
However, previous studies within the GDM did not consider the role of screening
the dielectric interactions by carriers. Here we implement carrier screening in
the Debye-H\"uckel formalism in our calculations of dopant-induced energetic
disorder, which modifies the Gaussian density of states (DOS). Then we solve
the Pauli Master Equation using Miller-Abrahams hopping rates with states from
the resulting screened DOS to obtain conductivity and Seebeck coefficient
across a broad range of carrier concentrations and compare them to
measurements. Our results show that screening has significant impact on the
shape of the DOS and consequently on carrier transport, particularly at high
doping. We prove that the slope of Seebeck coefficient vs electric
conductivity, which was previously thought to be universal, is impacted by
screening and decreases for systems with small dopant-carrier separation,
explaining our measurements. We also show that thermoelectric power factor is
underestimated by a factor of $\sim10$ at higher doping concentrations if
screening is neglected. We conclude that carrier screening plays a crucial role
in curtailing dopant-induced energetic disorder, particularly at high carrier
concentrations.
