TY - JOUR A1 - Asawapirom, Udom A1 - Bulut, F. A1 - Farrell, Tony A1 - Gadermaier, C. A1 - Gamerith, S. A1 - Güntner, Roland A1 - Kietzke, Thomas A1 - Patil, S. A1 - Piok, T. A1 - Montenegro, Rivelino V. D. A1 - Stiller, Burkhard A1 - Tiersch, Brigitte A1 - Landfester, Katharina A1 - List, E. J. W. A1 - Neher, Dieter A1 - Torres, C. S. A1 - Scherf, Ullrich T1 - Materials for polymer electronics applications semiconducting polymer thin films and nanoparticles N2 - The paper presents two different approaches to nanostructured semiconducting polymer materials: (i) the generation of aqueous semiconducting polymer dispersions (semiconducting polymer nanospheres SPNs) and their processing into dense films and layers, and (ii) the synthesis of novel semiconducting polyfluorene-block-polyaniline (PF-b-PANI) block copolymers composed of conjugated blocks of different redox potentials which form nanosized morphologies in the solid state Y1 - 2004 SN - 1022-1360 ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Bassler, H. A1 - Neher, Dieter T1 - Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene) N2 - The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP. The phosphorescence decay on the short time scale is close to an exponential law with a time decay of 15 ms. This indicates that benzil can efficiently sensitize the phosphorescence of the polymer. In addition, a broad and featureless emission is observed in the delayed luminescence spectra of benzil-doped MeLPPP, which is attributed to an exciplex formed between the polymer host and the dopant. We further observe that the delayed fluorescence is enhanced by the addition of benzil. It is concluded that the delayed fluorescence of benzil-doped MeLPPP is mainly due to the annihilation of triplet excitons on the polymer. Finally, efficient triplet-triplet energy transfer from the benzil-doped polymer to the red-emitting phosphorescent dye Pt(II)octaethylporphyrin is established. (C) 2004 American Institute of Physics Y1 - 2004 SN - 0021-9606 ER - TY - JOUR A1 - Kietzke, Thomas A1 - Neher, Dieter A1 - Kumke, Michael Uwe A1 - Montenegro, Rivelino V. D. A1 - Landfester, Katharina A1 - Scherf, Ullrich T1 - A nanoparticle approach to control the phase separation in polyfluorene photovoltaic devices N2 - Polymer solar cell devices with nanostructured blend layers have been fabricated using single- and dual- component polymer nanospheres. Starting from an electron-donating and an electron-accepting polyfluorene derivative, PFB and F8BT, dissolved in suitable organic solvents, dispersions of solid particles with mean diameters of ca. 50 nm, containing either the pure polymer components or a mixture of PFB and F8BT in each particle, were prepared with the miniemulsion process. Photovoltaic devices based on these particles have been studied with respect to the correlation between external quantum efficiency and layer composition. It is shown that the properties of devices containing a blend of single-component PFB and F8BT particles differ significantly from those of solar cells based on blend particles, even for the same layer composition. Various factors determining the quantum efficiency in both kinds of devices are identified and discussed, taking into account the spectroscopic properties of the particles. An external quantum efficiency of ca. 4% is measured for a device made from polymer blend nanoparticles containing PFB:F8BT at a weight ratio of 1:2 in each individual nanosphere. This is among the highest values reported so far for photovoltaic cells using this material combination Y1 - 2004 ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Im, C. A1 - Bassler, H. A1 - Neher, Dieter A1 - Scherf, Ullrich T1 - Energy transfer in a ladder-type methyl-poly(para-phenylene) doped by Pt(II)octaethylporphyrin N2 - The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped by platinum-porphyrin dye PtOEP covering the concentration 10(-3) to 5% by weight has been measured employing cw and transient techniques. Upon excitating into the range of absorption of the host strong phosphorescence of the dopant is observed. Possible ways of populating of the dopant triplet state are considered. It is shown that the main channel is singlet-singlet energy transfer among chromophor groups of the polymer followed by Forster-type transfer to the guest and subsequent intersystem crossing. (C) 2003 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0301-0104 ER - TY - JOUR A1 - Zentel, Rudolf A1 - Behl, Marc A1 - Neher, Dieter A1 - Zen, Achmad A1 - Lucht, Sylvia T1 - Nanostructured polytriarylamines : orientation layers for polyfluorene Y1 - 2004 SN - 0065-7727 ER - TY - JOUR A1 - Zen, Achmad A1 - Saphiannikova, Marina A1 - Neher, Dieter A1 - Asawapirom, Udom A1 - Scherf, Ullrich T1 - Comparative study of the field-effect mobility of a copolymer and a binary blend based on poly(3- alkylthiophene)s N2 - The performance of highly soluble regioregular poly[ (3-hexylthiophene)-co-(3-octylthiophetie)] (P3HTOT) as a semiconducting material in organic field-effect transistors (OFETs) is presented in comparison to that of the corresponding homopolymers. Transistors made from as-prepared layers of P3HTOT exhibit a mobility of ca. 7 x 10(-3) cm(2) V-1 s(-1), which is comparable to the performance of transistors made from as-prepared poly(3-hexylthiophene) (P3HT) and almost 6 times larger than the mobility of transistors prepared with poly(3-octylthiophene) (P3OT). On the other hand, the solubility parameter delta(p) of P3HTOT is close to that of the highly soluble P3OT. Moreover, compared to a physical blend of poly(3-hexylthiophene) and poly(3-octylthiophene), the mobility of P3HTOT devices is almost twice as large and the performance does not degrade upon annealing at elevated temperatures. Therefore, the copolymer approach outlined here may be one promising step toward an optimum balance between a Sufficient processability of the polymers from common organic solvents, a high solid state order, and applicable OFET performances Y1 - 2005 SN - 0897-4756 ER - TY - JOUR A1 - Zen, Achmad A1 - Neher, Dieter A1 - Silmy, Kamel A1 - Hollander, A. A1 - Asawapirom, Udom A1 - Scherf, Ullrich T1 - Improving the performance of organic field effect transistor by optimizing the gate insulator surface N2 - The effect of oxygen plasma treatment and/or silanization with hexamethyldisilazane (HMDS) on the surface chemistry and the morphology of the SiO2-gate insulator were studied with respect to the performance of organic field effect transistors. Using X-ray photoelectron spectroscopy (XPS), it is shown that silanization leads to the growth of a polysiloxane interfacial layer and that longer silanization times increase the thickness of this layer. Most important, silanization reduces the signal from surface contaminations such as oxidized hydrocarbon molecules. In fact, the lowest concentration of these contaminations was found after a combined oxygen plasma/silanization treatment. The results of these investigations were correlated with the characteristic device parameters of polymer field effect transistors with poly(3-hexylthiophene)s as the semiconducting layer. We found that the field effect mobility correlates with the concentration of contaminations as measured by XPS. We, finally, demonstrate that silanization significantly improves the operational stability of the device in air compared to the untreated devices Y1 - 2005 ER - TY - JOUR A1 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Thermodynamic theory of light-induced material transport in amorphous azobenzene polymer films N2 - It was discovered 10 years ago that the exposure of an initially flat layer of an azobenzene-containing polymer to an inhomogeneous light pattern leads to the formation of surface relief structures, accompanied by a mass transport over several micrometers. However, the driving force of this process is still unclear. We propose a new thermodynamic approach that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. Our basic assumption is that under homogeneous illumination, an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film. Orientational distributions of chromophores predicted by our model are compared with those deduced from Raman intensity measurements Y1 - 2005 SN - 1520-6106 ER - TY - JOUR A1 - Mechau, Norman A1 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Dielectric and mechanical properties of azobenzene polymer layers under visible and ultraviolet irradiation N2 - Photoinduced changes in the mechanical and dielectric properties of azobenzene polymer films were measured utilizing the method of electromechanical spectroscopy. The measurements revealed a strong correlation between the time- dependent behavior of the plate compliance and the dielectric constant under irradiation. Actinic light causes a light softening of the film that also manifests itself in the increase of the dielectric constant, whereas ultraviolet irradiation results in an initial plasticization of the film followed by its hardening. The latter is accompanied by decrease of the dielectric constant. A semiquantitative model based on the kinetics of the photoisomerization process in azobenzene polymers is proposed. We assume that both visible and ultraviolet irradiation increase the free volume in the layer due to photoisomerization. Additionally, ultraviolet light increases the modulus of the polymer matrix due to the presence of a high density of azobenzene moieties in the cis state. These assumptions allowed us to reproduce the time- dependent behavior of the bulk compliance as well as the dielectric constant at different irradiation intensities, for both visible and ultraviolet light, with only two adjustable parameters Y1 - 2005 SN - 0024-9297 ER - TY - JOUR A1 - Kietzke, Thomas A1 - Stiller, Burkhard A1 - Landfester, Katharina A1 - Montenegro, Rivelino V. D. A1 - Neher, Dieter T1 - Probing the local optical properties of layers prepared from polymer nanoparticles N2 - It is well known that the performance of solar cells based on a blend of hole-accepting and electron-accepting conjugated polymers as the active material depend crucially on the length scale of the resulting phase separated morphology. However, a direct control of this morphology is difficult if the layer is prepared from an organic solvent. To circumvent this difficulty, recently a universal method to fabricate defined nano-structured blend layer using nanoparticles dispersed in water was demonstrated. These nanoparticles were prepared with the miniemulsion method, which allows for the preparation of semiconducting polymer nanospheres (SPNs) with diameters in the range of 30 to 300 nanometres. Since the process starts from the active material dissolved in a common solvent, it can be applied to the fabrication of nanoparticles of blends of polymers with oligomers or even with inorganic materials. We present here for the first time scanning near field optical microscopy (SNOM) investigations on these novel nanostructured polymer layers. We show that by spin-coating a mixture of two different dispersions a nanoparticle monolayer with a statistically distribution of the nanoparticles can be obtained. Mixing conjugated polymer nanoparticles with some inert particles like polystyrene beads may allow for the preparation of nano-sized light emitters Y1 - 2005 SN - 0379-6779 ER -