  We have investigated the electron mobility on field-effect transistors based
on PDIF-CN$_{2}$ single crystals. The family of the small molecules
PDI8-CN$_{2}$ has been chosen for the promising results obtained for
vapour-deposited thin film FETs. We used as gate dielectric a layer of PMMA
(spinned on top of the SiO$_{2}$), to reduce the possibility of electron
trapping by hydroxyl groups present at surface of the oxide. For these devices
we obtained a room temperature mobility of 6 cm$^{2}$/Vs in vacuum and 3
cm$^{2}$/Vs in air. Our measurements demonstrate the possibility to obtain
n-type OFETs with performances comparable to those of p-type devices.
