Leveraging solvent affinity for phase-selective doping to enhance doping efficiency in a DPP-based n-type conjugated polymer

Abstract

Phase-selective doping holds promise for optimizing the electronic properties of conjugated polymers. This approach has been observed on a selection of polymer hosts and dopants, but it is unclear how to translate such an effect to other materials. In our study, we show that in coprocessing techniques, the affinity of the solvent to the polymer host, determined by Hansen solubility parameters, influences whether a dopant is primarily located within the amorphous phase or distributed across both the crystalline and amorphous phases. We used tetrabutylammonium fluoride (TBAF) as the dopant, an n-type DPP-based polymer host (2PyDPP-2CNTVT), and five common solvents. Optical, electrical, and structural characterizations reveal that solvents with high polymer affinity lead to low solid-state order and high Seebeck coefficients S but exhibit low electrical conductivity σ. Alternatively, solvents with partial affinity for both polymer and dopant produce films with mixed phases, where the dopant concentrates in amorphous regions. These films retain a higher structural order at elevated doping levels, achieving electrical conductivity σ, an order of magnitude higher than high-affinity solvents at similar doping concentrations. Our findings propose a solvent-centric strategy for phase-selective doping, potentially fine-tuning the electronic properties for various applications.