Charge Transfer and Percolation in C60/Pentacene Field-Effect Transistors

Charge transfer at organic-organic heterojunctions is fundamental to several organic electronics devices, including light-emitting diodes, photovoltaic cells, light-emitting transistors, and ambipolar fi eld-effect transistors. Here, probe charge transfer (CT) processes during the formation of an organic-organic heterojunction are probed by performing in situ real-time electrical characterization during the growth of pentacene/C 60 ambipolar transistors. N-type C 60 channel formation follows two different percolation pathways, one being associated to linear C 60 structures growing along pentacene grain boundaries and the other to C 60 island percolation. Upon n-channel formation a shift of pentacene p-type transfer characteristics is observed, which is attributed to CT across the heterojunction interface as a result of Fermi level alignment. The fi ndings allow estimation of the energy of thermally accessible CT-states and their mobility along the interface. Finally, a model is proposed that relates the amount of transferred charge to details in the bilayer morphology and layer thicknesses. The model relies on the capacitive coupling between C 60 and pentacene in the accumulation layer, which is consistent with a single hole transport channel.