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Microelectronic circuits/arrays produced via high-speed printing instead of traditional photolithographic processes offer an appealing approach to creating the long-sought after, low-cost, large-area flexible electronics. Foremost among critical enablers to propel this paradigm shift in manufacturing is a stable, solution-processable, high-performance semiconductor for printing functionally capable thin-film transistors — fundamental building blocks of microelectronics. We report herein the processing and optimisation of solution-processable polymer semiconductors for thin-film transistors, demonstrating very high field-effect mobility, high on/off ratio, and excellent shelf-life and operating stabilities under ambient conditions. Exceptionally high-gain inverters and functional ring oscillator devices on flexible substrates have been demonstrated. This optimised polymer semiconductor represents a significant progress in semiconductor development, dispelling prevalent skepticism surrounding practical usability of organic semiconductors for high-performance microelectronic devices, opening up application opportunities hitherto functionally or economically inaccessible with silicon technologies, and providing an excellent structural framework for fundamental studies of charge transport in organic systems.

Large disc-like ovalene diimides (ODI and ODI-CN) were prepared for the first time mainly via Diels-Alder cycloaddition reactions at the bay regions of bisanthene. The CN-substituted ovalene diimide (ODI-CN) exhibited typical n-type semiconducting behaviour in solution processing OFET devices, showing high electron mobility up to 1.0 cm 2 V À1 s À1 in nitrogen atmosphere and 0.51 cm 2 V À1 s À1 in air together with good device stability.

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The dielectric‐semiconductor interfacial interactions critically influence the morphology and molecular ordering of the organic semiconductor molecules, and hence have a profound influence on mobility, threshold voltage, and other vital device characteristics of organic field‐effect transistors. In this study, p‐channel small molecule/polymer (evaporated pentacene and spin‐coated poly(3,3‴;‐didodecylquarterthiophene) – PQT) and n‐channel fullerene derivative ({6}‐1‐(3‐(2‐thienylethoxycarbonyl)‐propyl)‐{5}‐1‐phenyl‐[5,6]‐C61 – TEPP‐C61) show a significant enhancement in device mobilities ranging from ∼6 to ∼45 times higher for all classes of semiconductors deposited on sol–gel silica gate‐dielectric than on pristine/octyltrichlorosilane (OTS)‐treated thermally grown silica. Atomic force microscopy, synchrotron X‐ray diffraction, photoluminescence/absorption, and Raman spectroscopy studies provide comprehensive evidences that sol–gel silica dielectrics‐induced enhancement in both p‐ and n‐channel organic semiconductors is attributable to better molecular ordering/packing, and hence reduced charge trapping centers due to lesser structural defects at the dielectric‐semiconductor interface.

N,N'-Disubstituted naphthalenediimides (NDIs), planar, electron-deficient building blocks, play an important role in materials and biological sciences. Naphthalene core substituents control the HOMO and LUMO energies, whereas the N-alkyl or aryl substituents affect the solubility, aggregation, and packing propensity in condensed phases. N,N'-Dihydroxynaphthalenediimide (DHNDI) allows expanding the chemical diversity by O-alkylation, acylation, or sulfonylation; these derivatives also allow fine-tuning of the HOMO/LUMO levels. The synthesis, UV-vis, electrochemical, solid state, and computational prediction of the properties of such derivatives are presented.

Thiophene (T) and thienothiophene (TT) containing 2,5-dihydro-pyrrolo [3,4-c]pyrrole-1,4-dione (DPP) compounds were prepared according to the succinic ester route from the corresponding heterocyclic nitrile precursors. As is typical of most DPP pigments, the new compounds showed high thermal stability and could be obtained in pure form as determined by elemental analysis. The bulk properties and molecular structure of the compounds were further characterized by thin lm, powder XRD and solid state CP-MAS 13 C NMR. Density functional theory (DFT) and time-dependent (TD) DFT were employed to study the geometric and electronic structures of these molecules in the ground state. The optical properties were investigated by UV-Vis absorption and°uorescence spectroscopies in dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMA), which revealed that the absorption maximum of the thiophene diketo-pyrrolopyrroles (TDPP) and thienothiophene diketo-pyrrolo-pyrroles (TTDPP) in solution were red shifted up to 25 nm and 60 nm, respectively, relative to Pigment Red 255 (PhDPP), while a new absorption band appeared at longer wavelengths in N-methyl pyrolidone (NMP) and N,N 0 -dimethylpropylene urea (DMPU) which is ascribed to solvent induced charge transfer (CT) complex. The molecular conformations and absorption spectra of TDPP and TTDPP were §, ¶ Corresponding authors. J. Mol. Eng. Mater. 2013.01. Downloaded from www.worldscientific.com by TUBITAK NATIONAL OBSERVATORY (TUG) on 01/02/15. For personal use only.characterized by quantum chemical methods in order to better understand the observed behavior.

Organic field-effect transistors (OFETs) exhibiting high mobilities and lowoperating voltages is key for their successful realization in plastic electronics applications. It has become increasingly evident that the dielectric and dielectric-semiconductor interface is of critical importance to OFETs' device performance, influencing mobility, low voltage operation and output currents. This thesis reports on the concept of introducing high k silica films prepared via a sol-gel (SG) methodology as potential gate dielectrics that enable high performance OFETs on plastic substrates. Compared to OFETs fabricated on thermal oxide (SiO 2) and SiNx, an improved device characteristic is distinctively and consistently observed in OFETs fabricated on sol-gel silica dielectric. In particular, through the innovative approach of tri-layer sol-gel silica gate dielectric architecture, both Pentacene and P3HT FETs with gate bias of ≤-5 V, demonstrated saturation mobilities of ~6.55cm 2 /Vs,~ 0.5cm 2 /Vs respectively with current on-off ratio of > 10 5 on plastic substrates. X-Ray diffraction, photoluminescence/absorption, Raman spectroscopy and near edge X-ray absorption fine studies display enhanced molecular ordering and packing through a more homogeneous and better in-phase intermolecular coupling in the pentacene organic semiconductor deposited on sol-gel silica. This phenomenon is induced by the excellent surface properties of sol-gel silica (Roughness of < 0.3nm and low surface energy) promoting lesser structural defects at the dielectric-semiconductor interface. These studies provide consistent proof that dielectric-semiconductor interface, film morphology and structural defects are the determining factors which impact charge carrier mobility, threshold voltage and other figures of merit of OFETs.