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Capacitance vs. DC bias of (a) undoped and (b) 1:40 000-doped MEH-PPV MIS samples. The inset depicts the MIS sample structure. (c) shows the corresponding loss spectra and the equivalent circuit in accumulation (at −5 V DC bias).
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(a) Hole density of undoped and doped P3HT layers. The line models a linear increase of hole density, starting from a background of m−3. (b) Low-field bulk conductivity and (c) hole mobility. The solid lines are calculated according to the model of Arkhipov et al. 15 using the parameters given in the inset. Physical symbols are the same as in Ref. 15.
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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.
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