We report the fabrication and characterization of solution-processed organic bilayer field effect transistors with a middle-contact configuration. P3HT and PCBM were chosen for a hole and electron transporting material, respectively. The
P3HT:PCBM bilayer FET with a middle contact structure showed only p-type behavior with a hole mobility (μ<sub>h</sub>) of ~ 10<sup>-3</sup> cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup>, which is a different result compared to the conventional top-contact ambipolar device. Electron injection
was enabled by using a thin CPE layer beneath the PCBM layer. The thickness of the CPE layer is critical for achieving
balanced hole and electron mobilities and provides an important variable for consideration in future optimization studies.
More detailed mechanisms on the role of CPE layer and the middle-contact structure are currently under investigation.