Doping of polymeric semiconductors is often limited by the miscibility issue between polymers and dopants. Although significant efforts have been devoted to enhancing the miscibility via chemical modification, the electrical conductivities of n-doped polymeric semiconductors are usually below 10 S cm−1. Here, we report a different approach to overcome the miscibility issue by modulating the solution-state aggregates of conjugated polymers. We found that the solution-state aggregates of conjugated polymers not only change with solvent and temperature but also change with solution aging time. Modulating the solution-state polymer aggregates can directly influence their solid-state microstructures and miscibility with dopants. As a result, both high doping efficiency and high charge carrier mobility were simultaneously obtained. The n-doped electrical conductivity of P(PzDPP-CT2) can be tuned up to 32.1 S cm−1 after exploring the dynamics of the polymer aggregates. This method can also be used to improve the doping efficiency of other polymer systems (e.g. N2200) with different aggregation tendencies and behaviors. Our results highlight the importance of understanding the dynamics of the polymer aggregates and the influence on the solid-state microstructures and doping efficiency.