Self-assembled monolayer field-effect transistors (SAMFETs) of BTBT functionalized phosphonic acids are fabricated. The molecular design enables device operation with charge carrier mobilities up to 10(-2) cm(2) V(-1) s(-1) and for the first time SAMFETs which operate on rough, flexible PEN substrates even under mechanical substrate bending.

We report a quantitative study that describes and correlates the threshold voltage of low-voltage organic field-effect transistors with the molecular structure of self-assembled monolayer dielectrics. We have observed that the component of the dipole moment of such self-assembled molecules perpendicular to the surface correlates linearly with the threshold voltage shift in devices. The model was validated using three different organic semiconductors (pentacene, α,α'-dihexylsexithiophene, and fullerene-C(60)) on six different self-assembled monolayers. The correlation found can help optimize future devices, by tuning the dipole moments of the molecules that constitute the self-assembled monolayer.

We report on bulk structures of a family of quaterthiophene (4T) derivatives with linear and branched end groups such as alpha,alpha'-dihexylquaterthiophene (Hex-4T-Hex), alpha,alpha'-didecyl-quaterthiophene (Dec-4T-Dec) and alpha,alpha'-bis(2-ethylhexyl)quaterthiophene (EH-4T-EH), tetramethyldisiloxane-based dimers D2-Und-4T-EH and D2-Und-4T-Hex, and carbosilane-siloxane-based tetramers D4-Und-4T-EH and D4-Und-4T-Hex. The dimers and tetramers contain undecylenic (Und) spacers between the disiloxane and 4T- units of the molecule. The impact of the molecular architecture on the bulk structure at different temperatures is addressed with X-ray diffraction and differential scanning calorimetry. For all of the studied quaterthiophene-containing organosilicon multipods the formation of 4T-crystal sublattice is observed. The alkyl periphery plays an important role in the molecular packing and thermal stability of the ordered phase. They can stabilize or destabilize the crystal phase, depending on their length and architecture. The quaterthiophenes with 2-ethylhexyl end groups adopt a zig-zag conformation in the crystalline state at room temperature. This change of conformation leads to a significant decrease of the polymorphic transition and isotropization temperatures. The efficiency of 4T packing in the sublattice is estimated from the molecular cross-section (S) in the plane normal to the molecular axis. Correlations between S and field-effect charge carrier mobility are established.

An asymmetric n-alkyl substitution pattern was realized in 2-tridecyl[1]benzothieno[3,2-b][1]benzothiophene (C(13)-BTBT) in order to improve the charge transport properties in organic thin-film transistors. We obtained large hole mobilities up to 17.2 cm(2)/(V·s) in low-voltage operating devices. The large mobility is related to densely packed layers of the BTBT π-systems at the channel interface dedicated to the substitution motif and confirmed by X-ray reflectivity measurements. The devices exhibit promising stability in continuous operation for several hours in ambient air.

The concept of self-asssembling monolayer formation of organic semiconductors using highly reactive chlorosilane linker groups has been extended to the phosphonic acid linker which can be handled in air. A first proof of concept using an oxidized Al-gate electrode to form a hybrid thin dielectric resulted in a low voltage field effect transistor with hole mobilities of 10-5 cm2/Vs. PEDOT based hole-transport and conductive materials have been improved for use in organic photovoltaics and wide area devices that require Ag busbars. A novel etchant can provide an invisible pattern for conductive transparent electrodes comprised of CleviosTM PEDOT:PSS.

We investigated two different (2,7-dialkyl-[1]benzothieno[3,2-b][1]benzothiophenes; C(n)-BTBT-C(n), where n = 12 or 13) semiconductors in low-voltage operating thin-film transistors. By choosing functional molecules in nanoscaled hybrid dielectric layers, we were able to tune the surface energy and improve device characteristics, such as leakage current and hysteresis. The dipolar nature of the self-assembled molecules led to a shift in the threshold voltage. All devices exhibited high charge carrier mobilities of 0.6-7.0 cm(2) V(-1) s(-1). The thin-film morphology of BTBT was studied by means of atomic force microscopy (AFM), presented a dependency upon the surface energy of the self-assembled monolayer (SAM) hybrid dielectrics but not upon the device performance. The use of C(13)-BTBT-C(13) on hybrid dielectrics of AlO(x) and a F(15)C(18)-phosphonic acid monolayer led to devices with a hole mobility of 1.9 cm(2) V(-1) s(-1) at 3 V, on/off ratio of 10(5), small device-device variation of mobility, and a threshold voltage of only -0.9 V, thus providing excellent characteristics for further integration.

We report on p- and n-type organic self-assembled monolayer field effect transistors. On the base of quaterthiophene and fullerene units, multifunctional molecules were synthesized, which have the ability to self-assemble and provide multifunctional monolayers. The self-assembly approach, based on phosphonic acids, is very robust and allows the fabrication of functional devices even on larger areas. The p- and n-type transistor devices with only one molecular active layer were demonstrated for transistor channel lengths up to 10 μm. The monolayer composition is proven by electrical experiments and by high-resolution transmission electron microscopy, electron energy loss spectroscopy, XPS, and AFM experiments. Because of the molecular design and the contribution of isolating alkyl chains to the hybrid dielectric, our devices operate at low supply voltages (-4 V to +4 V), which is a key requirement for practical use and simplifies the integration in standard applications. The monolayer devices operate in ambient air and show hole and electron mobilities of 10(-5) cm(2)/(V s) and 10(-4) cm(2)/(V s) respectively. In particular the n-type operation of self-assembled monolayer transistors has not been reported before. Hereby, structure-property relations of the SAMs have been studied. Furthermore an approach to protect the sensitive C(60) from immediate degradation within the molecular design is provided.

PEDOT based polyelectrolyte complexes are widely used as hole injection layers in OLEDs. They are available with high and low work functions. A new polystyrenesulfonic acid free water based complex has been developed that offers easy processing. Due to its high stability it gives rise to efficient and long living devices.Small molecule semiconductors can exhibit high charge carrier mobilities due to their high crystallinity. Oligomeric semiconductor materials with mobilities >3 cm(2)/Vs have been synthesized using the benzothienobenzothiophene (BTBT) core.

Unsymmetrical dimethylchlorosilyl-substituted alpha,alpha'-dialkylquater-, quinque-, and sexithiophenes were designed and successfully synthesized by a combination of Kumada and Suzuki cross-coupling reactions followed by hydrosilylation. Optimization possibilities of the hydrosilylation of low-soluble linear oligothiophenes by dimethylchlorosilane as well as the nonreactive byproducts formed are described. The molecular structures of the obtained dimethylchlorosilyl-functionalized oligothiophenes were proven by NMR and DCI MS techniques. These compounds were found to be stable and reactive enough, even in the presence of the nonreactive byproducts, to form semiconducting monolayers on dielectric hydroxylated SiO2 surfaces by self-assembly from solution. The semiconducting properties of these oligothiophene SAMs were as good as those of bulk oligothiophenes. This allowed the production of stable, even under ambient conditions, SAMFETs with a mobility of up to 0.04 cm(2)/(V s) and an on/off ratio up to 1 x 10(8).

The preparation and characterization of novel electron donor compounds with two (D1) and four (D2) quaterthiophene-containing arms attached to the flexible carbosilane–siloxane core are described. These materials were investigated in organic field effect transistors and photovoltaic cells. A power conversion efficiency of ∼0.9% obtained for D1:[70]PCBM blends is one of the highest values achieved up to now for solution-processible small molecular bulk heterojunction solar cells with large band-gap oligothiophene-based donor materials comprising no other chromophore units.

A series of five alpha,omega-substituted septithiophenes. which differ in the geometry of the peripheral branched alkyl substitutents, is presented. The position of the branching point has a substantial effect on the solubility and melting points of the oligomers. In contrast, organic field-effect transistors (OFETs) that have been prepared from those materials via vapor deposition show all mobilities in the same range (0.18-0.018 cm(2) V-1 s(-1)). The relative unsusceptibility of the mobilities on the molecular structure is attributed to the fact that all septithiophenes form smectic-like structures at room temperature under solid-state conditions, as revealed by temperatrue-dependent X-ray diffraction. Furthermore, four of the five oligomers exhibit thermotropic liquid crystalline smectic C phases. Strong interactions between the thiophene cores assumed as driving forces for those structural features. Thus, tailoring the peripheral substituents makes it possible to fine-tune thhe thermal and solubility properties and, to a certain extent, the ordering under solid-state conditions. The ordering and the electrical properties are mainly domin ated by the length of the core of the oligothiophenes.

The synthesis of new soluble tetrasubstituted quater- and quinquethiophenesilanes and their application as donor materials in bulk heterojunction solar cells and photodetectors has been described. The solubility of these compounds is governed by their 3D molecular structure, solubilizing linear n-hexyl (for quaterthiophenesilane), and branched 2-ethylhexyl groups (for quinquethiophenesilane). It was demonstrated that oligothiophenesilanes blended with fullerene derivatives can be used as promising active layer materials in organic bulk heterojunction solar cells. The maximum power conversion efficiency of the devices increased proportionally with the conjugation length of the oligothiophene units and reached 1.0% and 1.4% for quater- and quinquethiophenesilane respectively. Photodetectors based on the oligothiophenesilane/fullerene composites showed unusually high speeds of operation, which suggests another direction for the practical implementation of the three-dimensional organic semiconductor family designed herein.