Mesophase Transitions, Surface Functionalization, and Growth Mechanism of Semiconducting 6PTTP6 Films from Solution

Organic field-effect transistors based on highly ordered single polymer fibers

Ultrahigh-mobility organic field-effect transistors (OFETs) based on a CDT-BTZ donor-acceptor copolymer are realized by reaching high molecular order and pronounced alignment in single fibers within a short OFET channel via solution processing. The macromolecules directionally self-assemble in a quasi crystal-like order in the fibers providing in this way an unhindered charge carrier pathway with mobilities as high as 5.5 cm(2) V(-1) s(-1).

Synthesis, monolayer formation, characterization, and nanometer-scale photolithographic patterning of conjugated oligomers bearing terminal thioacetates

The synthesis of alpha-thioacetate terminated quaterthiophene and phenylene-thiophene materials, possessing thioacetate, oxetane, and alkyl groups at their omega-termini, is described. After deprotection these molecules were adsorbed onto Au films and the resulting self-assembled monolayers were characterized by X-ray photoelectron spectroscopy (XPS) and friction force microscopy (FFM). FFM indicated that monolayers formed by the dithioacetates had the highest coefficients of friction, followed by the oxetane-terminated adsorbates, with the alkyl-functionalized materials showing the lowest friction coefficients. These data may be understood in terms of differences in molecular packing. The quaterthiophene adsorbates also yielded higher friction coefficients than their phenylene-thiophene counterparts. Micrometer-scale patterns were fabricated by mask-based exposure to 244 nm light, and characterized by FFM. Nanometer-scale patterns were fabricated using near-field exposure and characterized by FFM. The images obtained demonstrated that features of conjugated oligomers with high spatial resolution (59 nm, ca. lambda/4) were achievable.

Water-stable organic transistors and their application in chemical and biological sensors

The development of low-cost, reliable sensors will rely on devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors because of their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated low-operating voltage OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over >10(4) electrical cycles using the p-channel semiconductor 5,5'-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2'-bithiophene (DDFTTF). OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine, and glucose. This work demonstrates of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.

Solution-processed organic field-effect transistors and unipolar inverters using self-assembled interface dipoles on gate dielectrics

Self-assembled monolayers (SAMs) of polarized and nonpolarized organosilane molecules on gate insulators induced tunable threshold voltage shifting and current modulation in organic field-effect transistors (OFETs) made from solution-deposited 5,5'-bis(4-hexylphenyl)-2,2'-bithiophene (6PTTP6), defining depletion-mode and enhancement-mode operation. p-Channel inverters were made from pairs of OFETs with an enhancement-mode driver and a depletion-mode load to implement full-swing and high-gain organic logic circuits. The experimental results indicate that the shift of the transfer characteristics is governed by the built-in electric field of the SAM. The effect of surface functional groups affixed to the dielectric substrate on the grain appearance and film mobility is also determined.

Effect of morphology on organic thin film transistor sensors

This review provides a general introduction to organic field-effect transistors and their application as chemical sensors. Thin film transistor device performance is greatly affected by the molecular structure and morphology of the organic semiconductor layer. Various methods for organic semiconductor deposition are surveyed. Recent progress in the fabrication of organic thin film transistor sensors as well as the correlation between morphology and analyte response is discussed.

Organic thin-film electronics from vitreous solution-processed rubrene hypereutectics

Electronic devices based on single crystals of organic semiconductors provide powerful means for studying intrinsic charge-transport phenomena and their fundamental electronic limits. However, for technological exploitation, it is imperative not to be confined to the tedious growth and cumbersome manipulation of molecular crystals-which generally show notoriously poor mechanical properties-but to be able to process such materials into robust architectures by simple and efficient means. Here, we advance a general route for facile fabrication of thin-film devices from solution. The key beneficial feature of our process-and the principal difference from existing vapour deposition and solution-processing schemes-is the incorporation of a glass-inducing diluent that enables controlled crystallization from an initial vitreous state of the organic semiconductor, formed in a selected area of the phase diagram of the two constituents. We find that the vitrifying diluent does not adversely affect device performance. Indeed, our environmentally stable, discrete rubrene-based transistors rival amorphous silicon devices, reaching saturated mobilities of up to 0.7 cm2 V-1 s-1, ON-OFF ratios of >or=10(6) and subthreshold slopes as steep as 0.5 V per decade. A nearly temperature-independent device mobility, indicative of a high crystalline quality of our solution-processed, rubrene-based films, corroborates these findings. Inverter and ring-oscillator structures are also demonstrated.