Alkyl chain length dependence of the field-effect carrier mobility in regioregular poly(3-alkylthiophene)s

The field-effect mobility of holes in regioregular poly(3-alkylthiophene)s was determined for a series of 5 alkyl chain lengths from C-4 (n-butyl) to C-12 (n-dodecyl). Contrary to a previous report, a non-monotonic dependence of field-effect mobility on alkyl chain length was found. The average hole mobility varied from 1.2 x 10(-3) cm(2)/Vs in poly(3-butylthiophene) and 1 x 10(-2) cm(2)/Vs in poly(3-hexylthiophene) to 2.4 x 10(-5) cm(2)/Vs for poly(3-dodecylthiophene). We believe that the hexyl side chain is optimum for charge transport because of better self-organization in poly(3-hexylthiophene) compared to other polymers in the series. The present results provide an important structure-carrier mobility relationship for the regioregular poly(3-alkylthiophene)s which are of wide interest for thin film transistors and photovoltaic cells. (C) 2004 Elsevier B.V. All rights reserved.