Direct-Written Silver Electrodes for All-Solution-Processed Low-Voltage Organic Thin Film Transistors Towards Flexible Electronics Applications

Abstract

Recent progress in printed electronics has offered the possibility of fabricating various organic-based electronic devices, such as organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs). As one of the important deposition methods in printed electronics, an inkjet printing technique offers the deposition of solution-processable materials onto a variety of substrates using simpler fabrication steps at lower processing temperatures, which is suitable for flexible electronic applications. Despite being the leading choice in OTFT fabrication, the clogging issues that frequently occurred at the printhead nozzle have not only limited the material selection but also restrained the efforts to bring organic electronic devices to the market. Apart from that, although remarkable progress has been made to enhance the performance of the OTFT, the high operating voltage resulting from the low gate capacitance density of the inorganic oxide-based dielectric layer remains a critical limitation that hinders the practical application of the OTFT. Hence, in this paper, we propose a simple solution-based method to develop a low-voltage OTFT. This work utilized a direct-write printing technique to print silver source/drain and gate electrodes incorporated into a bottom gate bottom contact OTFT structure, a spin-coating deposition method to deposit both small molecule TIPS-pentacene organic semiconducting layer and high-k PVA dielectric layer. Notably, the proposed OTFT achieved a micrometre channel length with a saturation mobility of 4.49 × 10^-1 cm²/Vs, a threshold voltage of -1.5 V, an on/off current ratio of 10⁸, and a subthreshold swing of 66.8 mV/dec while the overall fabrication temperature and operating voltage are kept below 150 °C and -15 V, respectively. The direct ink writing technology incorporated into the high-k dielectric layer provides a new strategy to fabricate organic-related components, particularly the OFTFs at lower manufacturing cost and temperature towards flexible and low-operating voltage electronic devices.