Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter

We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs₂CO₃) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm² V^-1 s^-1 for the p-channel and 0.027 cm² V^-1 s^-1 for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs₂CO₃ onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area.