Electrochemical doping is central to energy storage, neuromorphic computing, and biosensing, yet the mechanisms governing efficient n-type doping and ion-structure correlations remain poorly understood. Here, efficient n-type electrochemical doping is reported in the polymeric mixed conductor gDPP-tB0 through tailored organic cation interactions, investigated via cyclic voltammetry, in situ spectroelectrochemistry, grazing-incidence wide-angle X-ray scattering, and molecular dynamics simulations. Compared to the choline cation (Ch+) system, the 1-ethylpyridinium cation (EPy+) system exhibited superior doping kinetics, achieving a higher reduction current density (0.47 mA cm−2), faster ion diffusion coefficient (6.77 × 10−9 cm2 s−1), more pronounced polaron generation, and improved OECT performance (µC* up to 18.7 F cm−1 V−1 s−1). These improvements stem from EPy+’s preferential backbone localization, which minimizes polymer distortion, maintains high crystallinity, and optimizes ion-electron coupling, thus resulting in more efficient n-type electrochemical doping. Moreover, further gains in doping efficiency are realized by tuning the pyridyl cation concentration and alkyl chain length. The work reveals a new paradigm for efficient n-type electrochemical doping in polymeric mixed conductors via organic cation engineering, offering new insights into the rational design of ionic liquids for enhancing n-type electrochemical doping and accelerating the development of wearable bioelectronics.