Homogeneous Crystallization of Micro-Dispensed TIPS-Pentacene Using a Two-Solvent System to Enable Printed Inverters on Foil Substrates

We report on a micro-dispensing system for 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) to enable homogenous crystallization and uniform film morphology of the dispensed droplets using a two-solvent mixture along with the use of an insulating binder. This solution composition results in a controlled evaporation of the droplet in ambient air such that the Marangoni flow counteracts the outward convective flow to enable uniform radial crystal growth from the edge towards the center of the drops. The consequence of this process is the high degree of uniformity in the crystallization of the drops, which results in a reduction in the performance spread of the organic field effect transistors (OFET) created using this process. The addition of the insulating binder further improves the reduction in the spread of the results as a trade-off to the reduction in mobility of the transistors. The transfer curves of the OFETs show a tight grouping due to the controlled self-alignment of the TIPS-pentacene crystals; this repeatability was further highlighted by fabricating p-type inverters with driver to load ratios of 8:1, wherein the output inverter curves were also grouped tightly while exhibiting a gain of greater than 4 in the switching region. Therefore, the reliability and repeatability of this process justifies its use to enable large area solution-processed printed circuits at the cost of reduced mobility. OPEN ACCESS Electronics 2015, 4 566