Enhancing crystallinity of C60 layer by thickness-control of underneath pentacene layer for high mobility C60/pentacene ambipolar transistors

We present systematic control of the crystallinity and electrical transport properties of C60 films that are deposited onto pentacene layers, based on simple tuning of the underneath pentacene layer thickness. With increasing the pentacene layer thickness from 0 to 2 monolayers, we observed improvement in crystallinity and grain size of the C60 layer, which led to dramatic enhancement in electron conduction. Also, hole transport in this bilayer structure could be generated when the thickness of the pentacene layer was above one monolayer. The resulting ambipolar transport thin-film transistors yielded electron and hole mobilities as high as 2.8 and 0.3 cm2 V−1 s−1, respectively, and complementary inverters with gain value above 20.