Adduct-Forming and Macromolecular Dopants for Semiconducting Polymers

The traditional vision of the dopant-semiconductor interaction, including organic and polymeric semiconductors, is direct electron transfer between the two, leaving a charge carrier on the semiconductor in the form of a mobile radical ion and an oppositely charged counterion. In this presentation, we explore a two-step alternative doping mechanism, by which the dopant forms a covalent adduct with a conjugated polymer segment, and that adduct subsequently participates in the electron transfer that leads to the charge carrier generation. We investigated both p-type and n-type versions of this process, using tris(pentafluorophenyl)borane (TPFB) and fluoride anion (F-), respectively, as the adduct-forming species. Many structures of conjugated segments were used as models for the polymer segments that might form adducts with TPFB or F-. Evidence that adducts could serve as dopants was obtained from conductivity and Seebeck coefficient measurements, electron paramagnetic resonance (EPR) spectroscopy, optical absorbance spectroscopy, and Density Functional Theory calculations. Furthermore, we paired the F- dopant with a pyridinium polymer to create an n-type analog of PEDOT-PSS, where the charge transporter and dopant counterion in the conducting composition are both macromolecular, and the electronic conductivity was especially high compared to that obtained from single-molecule dopants.