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

Abstract

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.

Mechanically Robust Poly(ionic liquid) Block Copolymers as Self-Assembling Gating Materials for Single-Walled Carbon-Nanotube-Based Thin-Film Transistors

“…Furthermore, enhancements in PIL conductivity promise increased switching speeds . Finally, we have recently demonstrated additional performance benefits of ionic block copolymer self-assembly as applied to the formation of gating material layers in TFTs …”

“…28 Finally, we have recently demonstrated additional performance benefits of ionic block copolymer self-assembly as applied to the formation of gating material layers in TFTs. 29 In this work, we designed and synthesized three novel ionically conductive and mechanically robust block copolymers with AB−C type architecture (Figure 1). The AB blocks, responsible for ion conduction, were prepared by RAFT random copolymerization of highly conductive anionic (ILMA) or cationic (ILMC) monomers with PEGM.…”

“… 28 Finally, we have recently demonstrated additional performance benefits of ionic block copolymer self-assembly as applied to the formation of gating material layers in TFTs. 29 …”

Chitosan based dielectrics for use in single walled carbon nanotube-based thin film transistors

“…Gating media with higher dielectric constants (high- k dielectrics) generate larger currents which makes ultralow-voltage (<2 V) operation possible. 21–24…”

“…Gating media with higher dielectric constants (high-k dielectrics) generate larger currents which makes ultralow-voltage (o2 V) operation possible. [21][22][23][24] Chitosan is an abundant and inexpensive bio-sourced polysaccharide obtained by the deacetylation of chitin, extracted from crustacean shells. 25 It is a proton conducting polycation consisting of glucosamine units as the backbone with hydroxyl and protonated amine groups at pH o 6 (Fig.…”