Günther Götz

Highly Efficient p-Type Dye-sensitized Solar Cells based on Tris(1,2-diaminoethane)Cobalt(II)/(III) Electrolytes

Co-produced: using [Co(en)(3)](2+/3+) based-electrolytes in p-type dye-sensitized solar cells (p-DSCs) gives record energy conversion efficiencies of 1.3 % and open-circuit voltages up to 709 mV under simulated sun light. The increase in photovoltage is due to the more negative redox potential of [Co(en)(3)](2+/3+) compared to established mediators.

Photoactivated Preparation and Patterning of Self-Assembled Monolayers with 1-Alkenes and Aldehydes on Silicon Hydride Surfaces

Direct lateral patterning in the formation of self-assembled monolayers (SAMs) on silicon was achieved by the photoinduced reaction of aldehydes with Si(111)-H surfaces by using the usual masking techniques (see the schematic illustration; on the right-hand side is a microscopy image of a patterned SAM formed from octadecanal).

Dithienopyrrole-based oligothiophenes for solution-processed organic solar cells

Isomeric dicyanovinylene-terminated oligothiophenes 1 and 2 comprising a central dithienopyrrole (DTP) unit have been developed for solution-processed small molecule organic solar cells (SMOSCs) giving the highest power conversion efficiency of 4.8% for DTP-based oligomeric materials.

Molecular and electronic structure of cyclo[10]thiophene in various oxidation states: polaron pair vs. bipolaron

The molecular structure of a cyclic oligothiophene, C10T, has been determined by single-crystal X-ray structure analysis. The exclusive syn-conformation of all thiophene units as confirmed in the solid state and the ring strain in this macrocycle result in its unusual and optoelectronic properties. This does not only apply to neutral C10T but also to its oxidized states, as demonstrated by absorption and ESR spectroscopy, supporting the formation of a polaron-pair structure upon oxidation of C10T to C10T2(·+) as has been discussed for linear oligothiophenes. To the best of our knowledge, C10T2(·+) represents an unambiguous example comprising a two-polaron structure (polaron-pair) of a thiophene-based conjugated macrocycle.

Thermal Behavior of α-Alkylated Oligothiophenes

Abstract The thermal behavior of several α-alkylated quaterthiophenes is investigated. Polarizing microscopy and differential scanning calorimetry reveal that 5,5‴-dipropylquaterthiophene exhibits a nematic liquid crystalline phase while oligothiophenes bearing longer alkyl chains have more ordered high temperature phases.

Self-Assembly of Alkylsubstituted Oligothiophenes

Several α-alkylated quaterthiophenes adsorb from solution to a surface of molybdenum disulfide and form ordered monolayers. Scanning tunneling microscopy was used to investigate the molecular arrangement of the various oligomers in the monolayer.

Design, synthesis and assembly of new thiophene-based molecular functional units with controlled properties

Abstract Individual aspects in the field of ‘molecular electronics’ are addressed using new materials which are based on conjugated thiophenes as key building blocks. Among then, functionalized polythiophenes represent prototype compounds in which the three-dimensional network of ‘molecular wires’ can interact with the specific functional groups. Corresponding structurally defined oligothiophenes serve as model compounds and allow the correlation of various properties with structure. In addition, novel properties and superior processibility of these oligomers lead to interesting applications. Light emitting diodes and metal/organic/metal nanostructures are constructed by evaporation of thin oligomer films. A clear dependence of electroluminescence and electrical transport properties on chain length is found. Finally, the supramolecular assembly of functionalized (oligo)thiophenes is achieved by oriented adsorption on single crystal surfaces and self-organization in highly ordered LB films.

Optical properties of fully conjugated cyclo[n]thiophenes - An experimental and theoretical approach.

Summary Optical properties of two series of fully conjugated cyclo[n]thiophenes were analyzed experimentally and theoretically. The absorption spectra reveal a shift to higher wavelengths with increasing size of the cycles, which can be successfully described by an excitonic approach based on a Frenkel exciton Hamiltonian. Furthermore, intriguing new bands in the absorption and fluorescence spectra of the smaller macrocycles disclose the dominance of their ring strain.

Tuning the contact resistance in nanoscale oligothiophene field effect transistors

Nanoscale organic transistors for high frequency applications are often limited by contact resistances. We report on tuning of those resistances by shifting the transport level for dihexyl-n-thiophene (DHnT) semiconductors by variation of the number of thiophenes n from 4 to 7. The intrinsic mobility as well as contact resistance were determined from individual transfer curves of bottom-contact transistors with channel lengths down to 50nm. Best values were found for DH7T with μ=0.12cm2∕Vs and Rc=1kΩcm. While the contact resistance remains fairly constant for a given n as expected, the intrinsic mobility still decreases with decreasing channel length.Nanoscale organic transistors for high frequency applications are often limited by contact resistances. We report on tuning of those resistances by shifting the transport level for dihexyl-n-thiophene (DHnT) semiconductors by variation of the number of thiophenes n from 4 to 7. The intrinsic mobility as well as contact resistance were determined from individual transfer curves of bottom-contact transistors with channel lengths down to 50nm. Best values were found for DH7T with μ=0.12cm2∕Vs and Rc=1kΩcm. While the contact resistance remains fairly constant for a given n as expected, the intrinsic mobility still decreases with decreasing channel length.

From functionalized polythiophenes to oligomers with a defined structure

Abstract The importance and merit of oligomers in the field of conducting polymers is demonstrated for some special substituted oligothiophenes. These oligomers can serve on one hand as model compounds for the corresponding polythiophenes. Due to their well-defined chemical structure, i.e. defined chain and conjugation length; on the other hand, novel properties of these compounds can be exploited. Synthesis and polymerization of new annelated heterocycles as model compounds for low band gap-polymers is described.