  High-performance $n$-type organic field-effect transistors were developed
with ionic-liquid gates and N,N$^"$-bis(n-alkyl)-(1,7 and
1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s single-crystals. Transport
measurements show that these devices reproducibly operate in ambient atmosphere
with negligible gate threshold voltage and mobility values as high as 5.0
cm$^2$/Vs. These mobility values are essentially identical to those measured in
the same devices without the ionic liquid, using vacuum or air as the gate
dielectric. Our results indicate that the ionic-liquid and $n$-type organic
semiconductor interfaces are suitable to realize high-quality $n$-type organic
transistors operating at small gate voltage, without sacrificing electron
mobility.
