High mobility n-channel organic field-effect transistors based on soluble C-60 and C-70 fullerene derivatives

We report on n-channel organic field-effect transistors (OFETs) based on the solution processable methanofullerenes [6,6]-phenyl-C-61-butyric acid ester ([60]PCBM) and [6,6]-phenyl-C-71-butyric acid methyl ester (170]PCBM). Despite the fact that both derivatives form glassy films when processed from their electron mobilities are high and on the order of 0.21 cm(2/)V s and 0.1 cm(2)/V s, for [60]PCBM solution, and [70]PCBM, respectively. Although the derived mobility of [60]PCBM is comparable to the best values reported in the literature, the electron mobility of [70]PCBM is the highest value reported to date for any C-70 based molecule. We note that this is the only report in which C-60 and Cd-70 methanofullerenes exhibit comparable electron mobilities. The present findings could have significant implications in the area of large-area organic electronics and organic photovoltaics where C-60 derivatives have so far been the most widely used electron acceptor materials. (C) 2008 Elsevier B.V. All rights reserved