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

• Published in: ACS applied materials & interfaces Vol. 14; no. 35; pp. 40361 - 40370
• Main Authors: Brixi, Samantha, Radford, Chase L., Tousignant, Mathieu N., Peltekoff, Alexander J., Manion, Joseph G., Kelly, Timothy L., Lessard, Benoît H.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07.09.2022
• Subjects: Surfaces, Interfaces, and Applications; poly(ionic liquid); organic thin-film transistor (OTFT); grazing-incidence small-angle X-ray scattering (GISAXS); block copolymer self-assembly; electrolyte-gated transistor (EGT)
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.2c07912

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.