Correlation of dopant solution on doping mechanism and performance of F4TCNQ-doped P3HT

Understanding the doping mechanism between the dopants and the conjugated polymers (CPs) is crucial for efficiently utilizing the doping process in a controllable manner. In this work, we doped the poly(3-hexylthiophene) (P3HT) films with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) from a chlorobenzene/acetonitrile (CB/AN) solvent blend and pure AN solvent by using the common sequential doping method. We found that the dissolution ability of the dopant solvent to P3HT and the concentration of the dopant solution were two critical factors to determine the doping process (solution doping or sequential doping) and the doping region (the amorphous or the crystalline phase). When the concentration of the dopant solution was low, solution doping was dominant in the P3HT film doped with F4TCNQ CB/AN solution, and the amorphous regions were doped in the P3HT film doped with F4TCNQ AN solution. With the increase of the dopant solution concentration, the ratio of ordered integer charge transfer (ICT) species, which formed from sequentially doped crystalline domains in the P3HT precast film, increased. Based on the above doping mechanism, a P3HT film with good electrical and tensile performance could be constructed by doping from F4TCNQ CB/AN solution with a relatively low concentration. Our work indicates that the dissolution or swelling ability of the dopant solvent to CP is an important factor in determining not only the doping mechanism but also the electrical and mechanical performances of doped CP films.