Homogeneous Crystallization of Micro-DispensedTIPS-Pentacene Using a Two-Solvent System toEnable Printed Inverters on Foil Substrates

Abstract

Abstract: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 ACCESSElectronics 2015, 4 566

Polymers and biopolymers at interfaces

“…That TIPS-pentacene segregated to the (silicon oxide) substrate in a blend with isotactic polystyrene was determined by XPS measurements of the substrate-segregated side of the film, after it had been lifted from the substrate [221]. Other experiments show indirect evidence of TIPS-pentacene segregating to a photoresist interface [219].…”

“…The addition of polymers to smallmolecule semiconductors is important because polymeric additives can allow greater control of the solution viscosity and the creation of good quality films from a variety of different coating methods, such as dip-coating, and particularly processing routes appropriate for real-world applications, such as ink-jet printing [211]. The first demonstration concerned the addition of different polymers to an important small-molecule semiconductor, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) with different polymeric additives [212], which was followed by further work using the same semiconductor [213][214][215][216][217][218][219]. In all of these, some effort was made to understand the location of the different comp onents, with XPS used to locate the polymer and small molecule near the surface [212]; time-of-flight SIMS [214] (in three dimensions, figure 20); neutron reflectometry [213]; optical absorption and x-ray diffraction coupled with solvent etching [216]; Raman spectroscopy [217]; electron microscopy [218]; and profilometry [219].…”

“…The first demonstration concerned the addition of different polymers to an important small-molecule semiconductor, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) with different polymeric additives [212], which was followed by further work using the same semiconductor [213][214][215][216][217][218][219]. In all of these, some effort was made to understand the location of the different comp onents, with XPS used to locate the polymer and small molecule near the surface [212]; time-of-flight SIMS [214] (in three dimensions, figure 20); neutron reflectometry [213]; optical absorption and x-ray diffraction coupled with solvent etching [216]; Raman spectroscopy [217]; electron microscopy [218]; and profilometry [219]. As an aside, it is worth noting that similar effects have been observed with a range of small molecules blended with TIPS-pentacene rather than polymers [220], but it is clear that polymeric additives have better film-forming properties.…”