Self‐Organization of Inkjet‐Printed Organic Semiconductor Films Prepared in Inkjet‐Etched Microwells

Abstract

The high‐precision deposition of highly crystalline organic semiconductors by inkjet printing is important for the production of printed organic transistors. Herein, a facile nonconventional lithographic patterning technique is developed for fabricating banks with microwell structures by inkjet printing solvent droplets onto a polymer layer, thereby locally dissolving the polymer to form microwells. The semiconductor ink is then inkjet‐printed into the microwells. In addition to confining the inkjet‐printed organic semiconductor droplets, the microwells provide a platform onto which organic semiconductor molecules crystallize during solvent evaporation. When printed onto the hydrophilic microwells, the inkjet‐printed 6,13‐bis(triisopropylsilylethynyl) pentacene (TIPS_PEN) molecules undergo self‐organization to form highly ordered crystalline structures as a result of contact line pinning at the top corner of the bank and the outward hydrodynamic flow within the drying droplet. By contrast, small crystallites form with relatively poor molecular ordering in the hydrophobic microwells as a result of depinning of the contact line along the walls of the microwells. Because pinning in the hydrophilic microwells occurred at the top corner of the bank, treating the surfaces of the dielectric layer with a hydrophobic organic layer does not disturb the formation of the highly ordered TIPS_PEN crystals. Transistors fabricated on the hydrophilic microwells and the hydrophobic dielectric layer exhibit the best electrical properties, which is explained by the solvent evaporation and crystallization characteristics of the organic semiconductor droplets in the microwell. These results indicate that this technique is suitable for patterning organic semiconductor deposits on large‐area flexible substrates for the direct‐write fabrication of high‐performance organic transistors.

Large-area formation of self-aligned crystalline domains of organic semiconductors on transistor channels using CONNECT

“…S7). In comparison, other patterning methods used to create patterned OSCs for isolated OTFTs have shown relative variances ranging from 20% to 84% (9,15,17,22,31,32,35,42,(48)(49)(50)(51)(52)(53)(54). For example, Li et al (15) have shown that using a PMMA:C8BTBT blend on a solution wetting pattern can deposit crystal plates that have a mobility relative variance of >40%.…”

“…To address the above challenges, various groups have developed methods to pattern OSCs (3,9,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), such as templating OSCs (14,(19)(20)(21), inkjet printing (9,18), gravure printing, and other roll-to-roll coating methods (25)(26)(27). In addition, the use of solvent wetting/dewetting surface treatments has been widely used in conjunction with the patterning methods described above (10, 11, 13, 15-17, 22, 28, 29).…”

A pneumatically driven inkjet printing system for highly viscous microdroplet formation

“…Thus, inkjet technology has been regarded as an effective fabrication tool for the use of liquid functional materials and has been implemented into research areas such as fabrication of organic thin-film transistors [2], organic solar cells [3], 3D structures [4], and cellular structures [5]. The properties (i.e., viscosity, surface tension, and density) of the printing liquids govern the operation of an inkjet printing system.…”

Inkjet printed thin and uniform dielectrics for capacitors and organic thin film transistors enabled by the coffee ring effect

“…It has been shown that this effect can be suppressed by careful solvent selection or optimised printing parameters [16]. Although the coffee ring effect is usually seen as undesirable, useful applications have been demonstrated such as microwells [22], microelectromechanical relays [23] and narrow features [24]. It has been shown that the coffee ring effect can lead to thin and uniform films in the centre of a feature [18,20].…”