Engineering Charge Transport and Polarity through Heavy Doping-Induced Structural Transformations in Conjugated Polymers

Heavy doping is a widely adopted strategy for enhancing the electrical performance of conjugated polymers by increasing charge-carrier density. However, growing evidence suggests that heavy doping induces substantial structural and chemical transformations beyond conventional charge-transfer processes, thereby fundamentally altering charge transport behavior. Despite its importance, the relationship between doping-induced structural evolution and electronic properties remains poorly understood.

Here, we investigate the structural and electronic consequences of heavy doping in conjugated polymers using AuCl₃ as a model dopant. In poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), acetonitrile-assisted sequential doping promotes efficient dopant incorporation and pronounced microstructural reorganization. Structural characterization reveals the evolution of polymer packing toward a highly interconnected crystalline network, accompanied by enhanced carrier mobility, electrical conductivity, and thermoelectric performance.

We further show that heavy AuCl₃ doping fundamentally alters carrier transport in indacenodithiophene-co-benzothiadiazole (IDTBT). With increasing dopant concentration, IDTBT undergoes an unusual polarity inversion from p-type to n-type transport. Spectroscopic and electronic analyses indicate that this transition is closely associated with doping-induced chemical and structural transformations under extreme doping conditions.

Collectively, these findings demonstrate that heavy doping functions not only as a carrier-generation process but also as an effective structural engineering strategy for modulating polymer packing, charge transport pathways, and carrier polarity. This work provides fundamental insights into structure–property relationships in heavily doped conjugated polymers and establishes design principles for next-generation organic electronic and thermoelectric materials.