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  - 
TY  - JOUR
A1  - Yang, X. H.
A1  - Neher, Dieter
A1  - Hertel, D.
A1  - Daubler, T. K.
T1  - Highly efficient single-layer polymer electrophosphorescent devices
N2  - A commercially available Ir complex has been employed for the preparation of highly efficient (see Figure) single-layer phosphorescent polymer light,emitting diodes by use of appropriate thermal treatment and proper adjustment of the layer composition. These devices exhibit essentially no dependence of the driving field on the concentration of the Ir complex, suggesting that the build-up of space-charge in the layer is insignificant
Y1  - 2004
SN  - 0935-9648
ER  - 
TY  - JOUR
A1  - Qu, J. Q.
A1  - Zhang, J. Y.
A1  - Grimsdale, A. C.
A1  - Mullen, K.
A1  - Jaiser, Frank
A1  - Yang, X. H.
A1  - Neher, Dieter
T1  - Dendronized perylene diimide emitters : Synthesis, luminescence, and electron and energy transfer studies
N2  - Aggregation of chromophores in the solid state commonly causes undesirable red shifts in the emission spectra and/or emission quenching. To overcome this problem, we have prepared soluble perylenetetracarboxidiimide dyes in which the chromophores are effectively shielded by polyphenylene dendrimers attached in the bay positions. Models show that attachment of the shielding units in the bay position should provide more efficient shielding than attaching them via the imide moieties. The dendrimers possess excellent film-forming properties due to alkyl substituents on their peripheries. The lack of a red shift in emission upon going from solution to the solid state indicates the dendrons suppress interaction of the emissive cores, leading to pure red-orange emission. Single-layer LEDs produce red-orange emission with relatively low efficiency especially for the higher generation dendrons, which is attributed to poor charge conduction. LEDs using blends of the dendrimers and the undendronized dye as a model compound in PVK have been investigated, and a model to extract relative charge injection rates through the dendritic scaffold from the spectral contributions in the EL spectra is developed
Y1  - 2004
SN  - 0024-9297
ER  - 
TY  - JOUR
A1  - Egbe, D. A. M.
A1  - Kietzke, Thomas
A1  - Carbonnier, B.
A1  - Muhlbacher, D.
A1  - Horhold, H. H.
A1  - Neher, Dieter
A1  - Pakula, T.
T1  - Synthesis, characterization, and photophysical, electrochemical, electroluminescent, and photovoltaic properties of yne-containing CN-PPVs
N2  - Alkoxy-substituted CN-containing phenylene-vinylene-alt-phenylene-ethynylene hybrid polymers (CN-PPV-PPE), 3a, 3b, and 7a, were obtained from luminophoric dialdehydes 1 by step growth polymerization via Knoevenagel reaction as high molecular-weight materials. Corresponding CN-free polymers 3c and 7b and an ethynylene-free polymer 5 with similar side chains were synthesized for the purpose of comparison. The chemical structures of the polymers were confirmed by IR, H-1 and C-13 NMR, and elemental analysis. Thermal characterization was conducted by means of thermogravimetric analysis and differential scanning calorimetry. Morphology was investigated by means of optical microscopy and small-angle light scattering. The final morphologies are determined by the molecular characteristics (side chains volume fraction, backbone stiffness) of the studied polymers. All the CN-containing polymers 3b, 5, and 7a exhibit higher fluorescence quantum yield in solid state (50 to 60%), but lower quantum yields (12-40%) in dilute chloroform solution, in total contrast to CN-free polymers 3c, 3d, and 7b. Identical optical, E-g(opt), and electrochemical band gap energies, E- g(ec), were obtained for 3b, 3c and 3d with intrinsic self-assembly ability, whereas a discrepancy, DeltaE(g), was observed in the cases of the fully substituted polymers 5, 7a, and 7b, whose values are dependent on the level of backbone stiffness and length of the side groups combined with the presence or absence of CN units. The incorporation of CN units in 3b and 7a lowers their respective LUMO level by 220 and 350 meV compared to their corresponding CN-free counterparts 3c and 7b, suggesting an improvement of the electron-accepting strength. Polymers 3b and 7a are efficient electron acceptors suitable for photovoltaic application. The experiments indicate that 3b is a better electron acceptor when used together with M3EH-PPV, but transport properties seem to be better for 7a. With 3b, high external quantum efficiencies of up to 23%, an open circuit voltage of up to 1.52 V, and a white light energy efficiency of 0.65% could be realized in bilayer solar cell devices. LED-devices of configuration ITO/PEDOT:PSS/polymer/Ca/Al from 3b, 3c, 7a, and 7b showed low turn-on voltages between 2 and 2.5 V. The CN-free polymers 3c and 7b exhibit far better EL parameters than their corresponding CN containing counterparts 3b and 7a
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Kulikovsky, Lazar
A1  - Neher, Dieter
A1  - Mecher, E.
A1  - Meerholz, Klaus
A1  - Horhold, H. H.
A1  - Ostroverkhova, O.
T1  - Photocurrent dynamics in a poly(phenylene vinylene)-based photorefractive composite
N2  - All parameters describing the charge carrier dynamics in a poly(phenylene vinylene)-based photorefractive (PR) composite relevant to PR grating dynamics were determined using photoconductivity studies under various illumination conditions. In particular, the values of the coefficients for trap filling and recombination of charges with ionized sensitizer molecules could be extracted independently. It is concluded that the PR growth time without preillumination is mostly determined by the competition between deep trap filling and recombination with ionized sensitizer molecules. Further, the pronounced increase in PR speed upon homogeneous preillumination (gating) as reported recently is quantitatively explained by deep trap filling
Y1  - 2004
SN  - 1098-0121
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  - 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  -