Improving Conductivity and Stability in Molecularly Doped Conjugated Polymers

Molecular doping is an effective strategy for enhancing the electrical conductivity of conjugated polymers, but high doping levels often lead to strong carrier–counterion interactions, structural disorder, and limited long-term stability. Here, we introduce TAB–2TFSI, a dicationic ion-pair dopant designed to simultaneously improve charge transport and operational stability in p-type conjugated polymers. TAB–2TFSI combines a strongly oxidizing TAB²⁺ core with two weakly coordinating TFSI⁻ counterions, enabling efficient polymer oxidation while establishing a spatially uniform ionic environment.
Using poly(3-hexylthiophene) (P3HT) as a model system, TAB–2TFSI doping produced high electrical conductivity without substantially disrupting the semicrystalline polymer structure. Grazing-incidence wide-angle X-ray scattering revealed reduced π–π paracrystalline disorder compared with conventional FeCl₃/Li-TFSI doping, while AFM-IR mapping indicated a more homogeneous distribution of TFSI-containing species. Optical analysis of the polaron absorption showed that TAB–2TFSI-doped P3HT possesses a carrier density comparable to other highly conductive doping systems but exhibits the highest estimated carrier mobility, demonstrating that its conductivity advantage primarily originates from preserved charge transport rather than excessive carrier generation.
The optimized P3HT films achieved a power factor of 40 ± 6 μW m⁻¹ K⁻² and retained 23 ± 2 μW m⁻¹ K⁻² after 720 h under nitrogen and ambient light. The applicability of the dopant was further demonstrated in PDPP-3T, which exhibited a power factor of 65 ± 9 μW m⁻¹ K⁻² and maintained 41 ± 9 μW m⁻¹ K⁻² after 25 days. These results establish dicationic ion-pair doping as a versatile approach for balancing doping efficiency, microstructural integrity, charge transport, and long-term stability in organic thermoelectric materials