Balancing Hole and Electron Conduction in Ambipolar Split-Gate Thin-Film Transistors

Complementary organic electronics is a key enabling technology for the development of new applications including smart ubiquitous sensors, wearable electronics, and healthcare devices. High-performance, high-functionality and reliable complementary circuits require n- and p-type thin-film transistors with balanced characteristics. Recent advancements in ambipolar organic transistors in terms of semiconductor and device engineering demonstrate the great potential of this route but, unfortunately, the actual development of ambipolar organic complementary electronics is currently hampered by the uneven electron (n-type) and hole (p-type) conduction in ambipolar organic transistors. Here we show ambipolar organic thin-film transistors with balanced n-type and p-type operation. By manipulating air exposure and vacuum annealing conditions, we show that well-balanced electron and hole transport properties can be easily obtained. The method is used to control hole and electron conductions in split-gate transistors based on a solution-processed donor-acceptor semiconducting polymer. Complementary logic inverters with balanced charging and discharging characteristics are demonstrated. These findings may open up new opportunities for the rational design of complementary electronics based on ambipolar organic transistors. ? 2017 The Author(s).114Ysciescopu

Molybdenum Disulphide (MoS₂)-Poly(3-hexylthiophene) (P3HT) Hybrid Ink for Printed Thin-Film Transistor Applications

Organic Thin-Film Transistors (OTFTs) based on Poly(3-hexylthiophene) (P3HT)-Molybdenum Disulphide (MoS₂) composite films as an active layer were prepared via inkjet printing. There have been many attempts to incorporate inorganic materials into organic semiconductors, however, the inkjet-printed MoS₂-P3HT hybrid ink for Thin-Film Transistor (TFT) applications is shown here for the first time. The P3HT-MoS₂ hybrid TFTs exhibited higher carrier mobility than the baseline TFT with pure P3HT. We assume this is attributed to the molecular ordering of P3HT improved with the existence of MoS₂ nanoparticles in the film and also the high hole carrier mobility of MoS₂ could act as a conducting bridge. In this research, the first step was to improve overall TFT performance by optimizing the OTFT process conditions. Various factors were examined including surface treatment, solution preparation, and post-processing to change the crystallization of polymer film through different process conditions. It was shown that the Self-Assembled Monolayer (SAM) treatment could give preferred molecular orientation to the film; the selection of organic solvents is important because their boiling point affects film formation; the film thickness and post-processing conditions also affect the mobility as well as the off-current. Meanwhile, the MoS₂-P3HT hybrid ink was formulated with simple steps. This ink was prepared for inkjet printing. The jetting and printing parameters are precisely controlled to enable the printing of a hybrid channel array on top of pre-patterned electrodes. Especially, the ink should be compatible with selected nozzles, otherwise, the nozzle can be blocked or the misprint may cause device failure. The TFTs with a MoS₂-P3HT hybrid channel were successfully fabricated via inkjet printing. With the incorporation of MoS₂ nanoparticles, the hybrid TFTs exhibit mobility as high as 2.35×10⁻² cm²/V-s which is more than two times higher than the P3HT-only TFTs while maintaining the on/off ratios and threshold voltages