TY - JOUR A1 - Romanovskii, Y. V. A1 - Bassler, H. A1 - Scherf, Ullrich T1 - Relaxation processes in electronic states of conjugated polymers studied via spectral hole-burning at low temperature N2 - Persistent and transient hole-burning (HB) at 4.2 K have been applied to study the intrinsic properties of electronic excitations of a ladder type pi-conjugated poly(para-phenylene) in solutions. A narrow spectral hole less than I meV wide has been detected. The dependencies of the HB efficiency on the burn dose and wavelength, on doping the samples by electron scavenger are interpreted in terms of a photo reaction related to the two-level systems - specific low energy excitations in amorphous materials. In transient HB an additional hole broadening was observed which stems from the triplet energy transfer under conditions of lack of correlation of site energies of the singlet and triplet states of chromophores. (C) 2003 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0009-2614 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 - 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 - 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 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Neher, Dieter A1 - Lawson, PaDreyia V. A1 - Brédas, Jean-Luc A1 - Zojer, Egbert A1 - Güntner, Roland A1 - Scanduicci de Freitas, Patricia A1 - Forster, Michael A1 - Scherf, Ullrich T1 - Suppression of the keto-emission in polyfluorene light-emitting diodes : Experiments and models N2 - The spectral characteristics of polyfluorene (PF)-based light-emitting diodes (LEDs) containing a defined low concentration of either keto-defects or of the polymer poly(9.9-octylfuorene-co-benzothiadiazole) (F8BT) are preseneted. Both types of blend layers were tested in different device configurations with respect to the relative and absolute intensities of green blue emission components. It is shown that blending hole-transporting molecules into the emission layer at low concentration or incorporation of a suitable hole-transport layer reduces the green emission contribution in the electroluminescence (EL) spectrum of the PF:F8BT blend, which is similar to what is observed for the keto- containing PF layer. We conclude that the keto-defects in PF homopolymer layers mainly constitute weakly emissive electron traps, in agreement with the results of quantum-mechanical calculations Y1 - 2004 SN - 1616-301X ER - TY - JOUR A1 - Zen, Achmad A1 - Pflaum, J. A1 - Hirschmann, S. A1 - Zhuang, W. A1 - Jaiser, Frank A1 - Asawapirom, Udom A1 - Rabe, J. P. A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - Effect of molecular weight and annealing of poly (3-hexylthiophene)s on the performance of organic field-effect transistors N2 - The optical, structural, and electrical properties of thin layers made from poly(3-hexylthiophene) (P3HT) samples of different molecular weights are presented. As reported in a previous paper by Kline et al., Adv. Mater 2003, 15, 1519, the mobilities of these layers are a strong function of the molecular weight, with the largest mobility found for the largest molecular weight. Atomic force microscopy studies reveal a complex polycrystalline morphology which changes considerably upon annealing. X-ray studies show the occurrence of a layered phase for all P3HT fractions, especially after annealing at 1.50 degreesC . However, there is no clear correlation between the differences in the transport properties and the data from structural investigations. In order to reveal the processes limiting the mobility in these layers, the transistor properties were investigated as a function of temperature. The mobility decreases continuously with increasing temperatures; with the same trend pronounced thermochromic effects of the P3HT films occur. Apparently, the polymer chains adopt a more twisted, disordered conformation at higher temperatures, leading to interchain transport barriers. We conclude that the backbone conformation of the majority of the bulk material rather than the crystallinity of the layer is the most crucial parameter controlling the charge transport in these P3HT layers. This interpretation is supported by the significant blue-shift of the solid-state absorption spectra with decreasing molecular weight, which is indicative of a larger distortion of the P3HT backbone in the low-molecular weight P3HT layers Y1 - 2004 ER -