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

The proliferation of high-performance thin-film electronics depends on the development of highly conductive solid-state polymeric materials. We report on the synthesis and properties investigation of well-defined cationic and anionic poly(ionic liquid) AB-C type block copolymers, where the AB block was formed by random copolymerization of highly conductive anionic or cationic monomers with poly(ethylene glycol) methyl ether methacrylate, while the C block was obtained by post-polymerization of 2-phenylethyl methacrylate. The resulting ionic block copolymers were found to self-assemble into a lamellar morphology, exhibiting high ionic conductivity (up to 3.6 × 10-6 S cm-1 at 25 °C) and sufficient electrochemical stability (up to 3.4 V vs Ag+/Ag at 25 °C) as well as enhanced viscoelastic (mechanical) performance (storage modulus up to 3.8 × 105 Pa). The polymers were then tested as separators in two all-solid-state electrochemical devices: parallel plate metal-insulator-metal (MIM) capacitors and thin-film transistors (TFTs). The laboratory-scale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼103 Hz and high areal capacitance (up to 17.2 µF cm-2). For solid-state TFTs, low hysteresis was observed at 10 Hz due to the completion of EDL formation and the devices were found to have low threshold voltages of -0.3 and 1.1 V for p-type and n-type operations, respectively.

Not Just Surface Energy: The Role of Bis(pentafluorophenoxy) Silicon Phthalocyanine Axial Functionalization and Molecular Orientation on Organic Thin-Film Transistor Performance.

Understanding the effect of surface chemistry on the dielectric-semiconductor interface, thin-film morphology, and molecular alignment enables the optimization of organic thin-film transistors (OTFTs). We explored the properties of thin films of bis(pentafluorophenoxy) silicon phthalocyanine (F10-SiPc) evaporated onto silicon dioxide (SiO2) surfaces modified by self-assembled monolayers (SAMs) of varying surface energies and by weak epitaxy growth (WEG). The total surface energy (γtot), dispersive component of the total surface energy (γd), and polar component of the total surface energy (γp) were calculated using the Owens-Wendt method and related to electron field-effect mobility of devices (µe), and it was determined that minimizing γp and matching γtot yielded films with the largest relative domain sizes and highest resulting µe. Subsequent analyses were completed using atomic force microscopy (AFM) and grazing-incidence wide-angle X-ray scattering (GIWAXS) to relate surface chemistry to thin-film morphology and molecular order at the surface and semiconductor-dielectric interface, respectively. Films evaporated on n-octyltrichlorosilane (OTS) yielded devices with the highest average µe of 7.2 × 10-2 cm2·V-1·s-1 that we attributed to it having both the largest domain length, which were extracted from power spectral density function (PSDF) analysis, and a subset of molecules with a pseudo edge-on orientation relative to the substrate. Films of F10-SiPc with the mean molecular orientation of the π-stacking direction being more edge-on relative to the substrate also generally resulted in OTFTs with a lower average VT. Unlike conventional MPcs, F10-SiPc films fabricated by WEG experienced no macrocycle in an edge-on configuration. These results demonstrate the critical role of the F10-SiPc axial groups on WEG, molecular orientation, and film morphology as a function of surface chemistry and the choice of SAMs.