Electrostatic Control of Carrier–Dopant Interactions for Efficient Free Carrier Generation in Doped Conjugated Polymers

In molecularly doped conjugated polymers (CPs), weak dielectric screening leads to a high Coulomb binding energy of charge carriers within integer charge transfer complexes (ICTCs), resulting in a significantly low doping efficiency. Therefore, the Coulomb interaction between carriers and dopants, which determines the separation barrier for ICTC dissociation, is crucial for optimizing the electrical properties of CPs. In this study, the impact of carrier-dopant interactions on free carrier generation in doped CPs has been systematically demonstrated by decoupling the contributions of free carrier ratio and carrier mobility to electrical conductivity in doped poly(3-hexylthiophene-2,5-diyl) (P3HT) films. Our results demonstrate that carrier-dopant interactions and dopant size have opposing effects on charge dissociation depending on the doping level. In the low-doping regime, large dopants weaken the carrier-dopant interactions, thereby enhancing free carrier generation and conductivity. In the high-doping regime, Coulomb potential overlap effectively reduces the activation energy for ICTC dissociation, allowing small dopants with low steric hindrance to achieve a high saturation carrier density and conductivity. These findings offer fundamental insights into free carrier release in doped CPs and suggest a dopant selection strategy tailored to the target electrical conductivity of various organic electronic devices.