Effect of molecular p-doping on hole density and mobility in poly(3-hexylthiophene)

Employing impedance spectroscopy, we have studied the hole density, conductivity, and mobility of poly(3-hexylthiophene), P3HT, doped with the strong molecular acceptor tetrafluorotetracyanoquinodimethane, F4TCNQ. We find that the hole density increases linearly with the F4TCNQ concentration. Furthermore, the hole mobility is decreased upon doping at low-to-medium doping level, which is rationalized by an analytic model of carrier mobility in doped organic semiconductors [V. I. Arkhipov, E. V. Emelianova, P. Heremans, and H. Bässler, Phys. Rev. B 72, 235202 (2005)]. We infer that the presence of ionized F4TCNQ molecules in the P3HT layer increases energetic disorder, which diminishes the carrier mobility.