Mr. Tanmoy Sarkar, PhD. Candidate
The race to miniaturize complementary circuits incited intense research in ambipolar transistors, i.e. transistors that can transport holes and electrons, separately or concurrently, within the semiconducting channel. The accumulation and transport of both charge carriers in a transistor requires that the semiconducting material is capable of efficiently transporting both charge carriers, and the careful alignment of the energy levels between the semiconductor and the metal electrodes for efficient ambipolar charge injection. Organic semiconductors (OSCs) often show ambipolar transport character and moderate charge injection barriers from several metals, but rarely show truly balanced ambipolar performance because hole and electron mobilities and injection depend differently on film morphology and interfacial energy alignment.
Here I will show how electron and hole motilities can be tuned by directing the type and extent of polymer aggregation through processing parameters, characterized by UV-Vis absorption and Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS). After mobilities are balanced, we turn to enhance carrier injection (electron and hole) by introducing self-generated interlayer (SGI) at the OSC/contact interfaces. These interlayers modify the effective work function by imposing a dipole at the interface that reduces the potential barrier of charge transfer. The reduction of contact resistance was confirmed by the Transfer line method (TLM). Finally, by optimizing bulk morphology and charge injection we were able to fabricate truly balanced ambipolar OFETs.