Carrier mobility enhancement in semiconducting poly(3-methylthiophene) by electrochemical inclusion of cooper

Films of poly(3-methylthiophene) (PMeT) are electrochemically grown onto platinum layers sputtered on glass slides. The PMeT is then electrochemically undoped, and gold contacts are vacuum evaporated on the polymer. The current-voltage characteristics of the PMeT-Au contacts show a clear transition between an Ohmic regime and a space-charge-limited current. This allows the mobility and carrier density of undoped PMeT to be determined independently. An enhancement of the mobility by a factor of 100 is observed after electrochemical inclusion of copper, whereas the carrier density is not changed. Such behaviour is not obtained when copper is replaced by nickel. A tentative explanation of this phenomenon is the formation of bonds between copper and the polymer chains, which would increase the interchain charge transfer.