Dopant Induced Interchain Interactions Enhance Polythiophene Electrical Conductivity at Low Dopant Concentrations

Enhancing the electrical conductivity of organic semiconductors at low dopant concentrations while preserving morphology remains a critical challenge for solution-processed optoelectronic devices. We show that tetracyanoquinodimethane (TCNQ)-based dopants increase the conductivity of poly(3-hexylthiophene) (P3HT) films to >0.01 S/cm at concentrations as low as 3 wt %, over 2 orders of magnitude higher than barely conducting neat films. The comparable performance of TCNQ relative to the higher electron-affinity dopant F4TCNQ demonstrates that transport is not dictated solely by dopant electron affinity but also influenced by the subtle interplay between dopant-induced structural disorder and ionized polymer-dopant Coulomb interactions. Two-dimensional electronic and pump-probe spectroscopies reveal uniform film morphology with no preferential doping in the crystalline domains, absence of strongly bound ion-pairs, and rapid polaron pair formation with exciton quenching. The results suggest that polaron-induced backbone planarization extends intrachain hole delocalization, thereby enhancing π-π overlap and interchain electronic coupling within crystalline domains.