American Chemical Society
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Poly(ionic liquid) Gating Materials for High-Performance Organic Thin-Film Transistors: The Role of Block Copolymer Self-Assembly at the Semiconductor Interface

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journal contribution
posted on 2022-08-23, 18:17 authored by Samantha Brixi, Chase L. Radford, Mathieu N. Tousignant, Alexander J. Peltekoff, Joseph G. Manion, Timothy L. Kelly, Benoît H. Lessard
The widespread realization of wearable electronics requires printable active materials capable of operating at low voltages. Polymerized ionic liquid (PIL) block copolymers exhibit a thickness-independent double-layer capacitance that makes them a promising gating medium for the development of organic thin-film transistors (OTFTs) with low operating voltages and high switching speed. PIL block copolymer structure and self-assembly can influence ion conductivity and the resulting OTFT performance. In an OTFT, self-assembly of the PIL gate on the semiconducting polymer may differ from bulk self-assembly, which would directly influence electrical double-layer formation. To this end, we used poly­{[N,N′-bis­(2-octyldodecyl)-naphthalene-1,4,5,8-bis­(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P­(NDI2OD-T2)) as a model semiconductor for our OTFTs, on which our PILs exhibited self-assembly. In this study, we explore this critical interface by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) of P­(NDI2OD-T2) and a series of poly­(styrene)-b-poly­(1-(4-vinylbenzyl)-3-butylimidazolium-random-poly­(ethylene glycol) methyl ether methacrylate) (poly­(S)-b-poly­(VBBI+[X]-r-PEGMA)) block copolymers with varying PEGMA/VBBI+ ratios and three different mobile anions (where X = TFSI, PF6, or BF4). We investigate the thin-film self-assembly of block copolymers as a function of device performance. Overall, a mixed orientation at the interface leads to improved device performance, while predominantly hexagonal packing leads to nonfunctional devices, regardless of the anion present. These PIL gated OTFTs were characterized with a threshold voltage below 1 V, making understanding of their structure–property relationships crucial to enabling the further development of high-performance gating materials.