Solution‐Shearing of Highly Smooth Ion‐Gel Thin Films: Facilitating the Deposition of Organic Semiconductors for Ion‐Gated Organic Field Effect Transistors

Abstract A straightforward method is developed to produce ion‐gels (IGs) with surface roughness at the nanometer level using a solution‐shearing process, enabling the first successful growth of crystalline, small‐molecule organic semiconductor (OSC) films directly on the IG layer. The effectiveness of this approach is demonstrated by fabricating top‐contact electrolyte‐gated organic field‐effect transistors (EGOFETs) using thermal vapor deposition and solution‐shearing. The gel matrix consists of polymethyl methacrylate (PMMA) or its blend with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF:HFP), and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) serves as ionic liquid. X‐ray photoemission spectroscopy (XPS) reveals that the shearing speed controls the polymer phase separation in the blended gels, producing capacitance values of up to 10.1 µF cm⁻². The exceptional smoothness of the gel films permits vacuum deposition polycrystalline films of 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophen (C8‐BTBT), dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophen (DNTT), and 2,9‐didecyldinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (C10‐DNTT), and solution‐shearing of C8‐BTBT and 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) on their surfaces. Grazing incidence wide‐angle X‐ray scattering (GIWAXS) can now be conducted directly on the OSC films without obstruction by the gel. EGOFETs with minimal hysteresis and mobilities up to 1.46 cm² V⁻¹ s⁻¹ are obtained for C10‐DNTT. This study underscores the possibility of producing transistor‐grade polycrystalline organic semiconductor films on top of IGs, making them attractive for surface characterization techniques and in situ measurements.