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 (F 10 -SiPc) evaporated onto silicon dioxide (SiO 2 ) surfaces modified by self-assembled monolayers (SAMs) of varying surface energies and by weak epitaxy growth (WEG). The total surface energy (γ tot ), dispersive component of the total surface energy (γ d ), and polar component of the total surface energy (γ p ) were calculated using the Owens−Wendt method and related to electron field-effect mobility of devices (μ e ), and it was determined that minimizing γ p and matching γ tot yielded films with the largest relative domain sizes and highest resulting μ e . 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 μ e of 7.2 × 10 −2 cm 2 •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 F 10 -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 V T . Unlike conventional MPcs, F 10 -SiPc films fabricated by WEG experienced no macrocycle in an edge-on configuration. These results demonstrate the critical role of the F 10 -SiPc axial groups on WEG, molecular orientation, and film morphology as a function of surface chemistry and the choice of SAMs.
Silicon phthalocyanines (R 2 -SiPcs) are a family of promising tunable materials for organic electronic applications. We report the chemistry of the synthesis of axially substituted fluorinated SiPcs (tb-Ph) 2 -F x SiPc (where X = 0, 4, 8, or 16) and explore how the degree of fluorination effects optical and electronic properties. A new treatment with boron trichloride was included to obtain Cl 2 -F X SiPcs from F 2 -F X SiPcs, activating the axial position for further functionalization. We observed that as the degree of fluorination increased, so did the electron affinity of the compounds, leading to a drop in frontier orbital levels, as measured by electrochemistry and ultraviolet photoelectron spectroscopy (UPS). The deeper energy levels enabled successful (tb-Ph) 2 -F 4 SiPc and poly [[6,7-difluoro[(2-hexyldecyl)oxy]-[5,8quinoxalinediyl]-2,5-thiophenediyl]] (PTQ10) blends for organic photovoltaics and photodetectors. All four compounds were incorporated in organic thin-film transistors (OTFTs), where the degree of fluorination influenced device operation, changing it from p-type conduction for (tb-Ph) 2 -F 0 SiPc, to ambipolar for (tb-Ph) 2 -F 4 SiPc, and n-type for (tb-Ph) 2 -F 8 SiPc and (tb-Ph) 2 -F 16 SiPc. The OTFT devices made with (tb-Ph) 2 -F 16 SiPc achieved a low average threshold voltage of 7.0 V in N 2 and retained its n-type mobility when exposed to air.
Chitosan, a sustainable biopolymer, is a naturally-occurring solution processable polyelectrolyte that can form electrical double layers at high frequencies (<1 kHz) and be integrated as the dielectric in metal-insulator-metal (MIM)...
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 postpolymerization 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 × 10 5 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 laboratoryscale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼10 3 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.
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