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 - TY - JOUR A1 - Karageorgiev, Peter A1 - Neher, Dieter A1 - Schulz, Burkhard A1 - Stiller, Burkhard A1 - Pietsch, Ullrich A1 - Giersig, Michael A1 - Brehmer, Ludwig T1 - From anisotropic photo-fluidity towards nanomanipulation in the optical near-field N2 - An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it shows considerable fluidity only in the direction parallel to the light field vector under linear polarized light. The fluidization phenomenon is related to photoinduced motion of azobenzene-functionalized molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also describe here how the photofluidization allows nanoscopic elements of matter to be precisely manipulated Y1 - 2005 SN - 1476-1122 ER - TY - JOUR A1 - Galbrecht, Frank A1 - Yang, X. H. A1 - Nehls, B. S. A1 - Neher, Dieter A1 - Farrell, Tony A1 - Scherf, Ullrich T1 - Semiconducting polyfluorenes with electrophosphorescent on-chain platinum-salen chromophores N2 - The synthesis of statistical fluorene-type copolymers with on-chain Pt-salen phosphorescent units and their use in electrophosphorescent OLEDs is reported Y1 - 2005 SN - 1359-7345 ER - TY - JOUR A1 - Egbe, D. A. M. A1 - Ulbricht, C. A1 - Orgis, Thomas A1 - Carbonnier, B. A1 - Kietzke, Thomas A1 - Peip, M. A1 - Metzner, M. A1 - Gericke, M. A1 - Birckner, Eckhard A1 - Pakula, T. A1 - Neher, Dieter A1 - Grumm, U. W. T1 - Odd-even effects and the influence of length and specific positioning of alkoxy side chains on the optical properties of PPE-PPV polymers N2 - This contribution reports the combined influences of odd-even effects and the specific positioning of alkoxy side chains OR1 = (OCn+H-10(2(n+10)+1)) and OR2 = (OCnH2n+1) (with n = 6, 7, 8, 9) on the phenylene-ethynylene and phenylene- vinylene segments, respectively, on the optical properties of hybrid polymers P(n+10)/n of general repeating unit: -Ph-C equivalent to C-Ph-C equivalent to C-Ph-CH=CH-Ph-CH=CH-. For the polymeric materials, visual color impression varies alternatively between orange red (P16/6 and P18/8) and yellow (P17/7 and P19/9) according to the odd and even features of the alkoxy side chains, where odd or even relates to the total number of sp(3)-hybridized atoms within the side chains. This side chain related effect is ascribed to both absorptive and emissive behaviors of the polymers on the basis of photophysical investigations in the bulk. Almost identical thin film absorption spectra were obtained for all four materials; however, the photoluminescence of the odd polymers, P16/6 (lambda(f) = 556 nm) and P18/ 8 (lambda(f) = 614 nm), was red-shifted relative to that of their even counterparts (lambda(f) = 535 nm). Further, the P18/8 maximum at 614 nm can be readily assigned to excimer emission, as evidenced by the largest Stokes shift (5600 cm(- 1)), largest fwhmf-value (3700 cm(-1))(,) and the lowest Phi(f)-value of 24%. The strong pi-pi interchain interaction in P18/8, due to loose alkoxy side chains packing, does not only favor fluorescence quenching but also enable an effective inter- as well as intra-molecular recombination of the generated positive and negative polarons in electrolurninescence, which explains the good EL properties of this polymer irrespective of the solvent used. A voltage-dependent blue shift of the EL spectra of up to 100 nm was observed for P18/8 devices prepared from aromatic solvents. This red to green EL shift as observed with increasing voltage is assigned to conformational changes of the polymer chains with increasing temperature Y1 - 2005 SN - 0897-4756 ER - TY - JOUR A1 - Egbe, D. A. M. A1 - Carbonnier, B. A1 - Paul, E. L. A1 - Muhlbacher, D. A1 - Kietzke, Thomas A1 - Birckner, Eckhard A1 - Neher, Dieter A1 - Grummt, U. W. A1 - Pakula, T. T1 - Diyne-containing PPVs : Solid-state properties and comparison of their photophysical and electrochemical properties with those of their Yne-containing counterparts N2 - Diyne-containing poly(p-phenylene-vinylene)s, 4a-d, of general chemical structure-(Ph-C&3bond; C-C&3bond; C-Ph- CH&3bond; CH-Ph-CH&3bond; CH-)(n), obtained through polycondensation reactions of 1,4-bis(4-formyl-2,5-dioctyloxyphenyl)- buta-1,3-diyne (2) with various 2,5-dialkoxy-p-xylylenebis(diethylphosphonates), 3a-d, are the subject of this report. The polymers exhibit great disparity in their degree of polymerization, n, which might be ascribed to side-chain-related differences in reactivity of the reactive species during the polycondensation process and which led to n-dependent absorption (solution and solid state) and emission (solution) behaviors of the polymers. Polarizing optical microscopy and differential scanning calorimetry are employed to probe their thermal behavior. The structure is investigated by means of wide-angle X-ray diffraction for both isotropic and macroscopically oriented samples. Comparison of photophysical (experimental and theoretical) and electrochemical properties of the polymers with those of their yne- containing counterparts 6a-d [-(Ph-C&3bond; C-Ph-CH&3bond; CH-Ph-CH&3bond; CH-)(n)] has been carried out. Similar photophysical behavior was observed for both types of polymers despite the difference in backbone conjugation pattern. The introduction of a second yne unit in 4 lowers the HOMO and LUMO levels, thereby enhancing the electron affinity of polymers 4 compared to polymers 6. The "wider opening" introduced by the second yne unit facilitates moreover the movement of charges during the electrochemical processes leading to minimal discrepancy, Delta E-g between the optical and electrochemical band gap energies. Polymers 6, in contrast, show significant side-chain-dependent Delta E-g values. Low turn-on voltages between 2 and 3 V and maximal luminous efficiencies between 0.32 and 1.25 cd/A were obtained from LED devices of configuration ITO/PEDOT:PSS/polymer 4/Ca/Al Y1 - 2005 SN - 0024-9297 ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Bassler, H. A1 - Neher, Dieter T1 - Exciton dynamics in ladder-type methyl-poly(para-phenylene) doped with phosphorescent dyes N2 - The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with platinum-porphyrin dye PtOEP covering the concentration 10(-3)-5% by weight has been measured employing cw and transient techniques. Upon excitation into the range of absorption of the host, strong phosphorescence of the dopant is observed. Possible ways of populating the dopant triplet state are considered. (c) 2004 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0022-2313 ER - TY - JOUR A1 - Kietzke, Thomas A1 - Horhold, H. H. A1 - Neher, Dieter T1 - Efficient polymer solar cells based on M3EH-PPV N2 - We report on polymer blend solar cells with an external quantum efficiency of more than 30% and a hi-h overall energy conversion efficiency (ECE) under white light illumination (100 mW/cm(2)) Of Lip to 1.7% using a blend of M3EH- PPV (poly [2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5(2-ethylhexyloxy)-(1,4-pheiiylene-1,2-ethenylene)]) and CN-ether-PPV (poly[oxa-1,4-phenylene-1,2(1-cyano)ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)ethellyiene-1,4- phenylene]). We attribute these high efficiencies to the formation of a vertically composition graded structure during spin coating Photoluminescence measurements performed on the blend layers indicated the formation of exciplexes between both types of polymers, which we propose to be one factor preventing even higher efficiencies Y1 - 2005 ER - TY - JOUR A1 - Zen, Achmad A1 - Bilge, Askin A1 - Galbrecht, Frank A1 - Alle, Ronald A1 - Meerholz, Klaus A1 - Grenzer, Jörg A1 - Neher, Dieter A1 - Scherf, Ullrich A1 - Farrell, Tony T1 - Solution processable organic field-effect transistors utilizing an alpha,alpha '-dihexylpentathiophene- based swivel cruciform Y1 - 2006 UR - http://pubs.acs.org/doi/full/10.1021/ja0573357 U6 - https://doi.org/10.1021/Ja0573357 ER - TY - JOUR A1 - Yang, Xiaohui A1 - Müller, David C. A1 - Neher, Dieter A1 - Meerholz, Klaus T1 - Highly efficient polymeric electrophosphorescent diodes N2 - Polymeric electrophosphorescent LEDs with internal quantum efficiencies approaching unity have been fabricated. Such performance levels are previously unknown for OLEDs. The key to this success is redox chemically doped oxetane- crosslinkable hole-transporting layers with multilayer capability (see figure). They improve hole injection and act as electron-blocking layers, without the need to include exciton-or hole-blocking layers Y1 - 2006 UR - 1960 = DOI: 10.1002/adma.200501867 ER - TY - JOUR A1 - Kietzke, Thomas A1 - Egbe, Daniel A. M. A1 - Hörhold, Hans-Heinrich A1 - Neher, Dieter T1 - Comparative study of M3EH-PPV-based bilayer photovoltaic devices N2 - We have recently shown that efficient polymer solar cells can be fabricated by using a weakly soluble derivative of poly-p-vinylene (M3EH-PPV) as the electron donor. Here we present studies on bilayer devices using organic electron acceptors with varying LUMO levels and M3EH-PPV. It is found that the open-circuit voltage scales linearly with the LUMO level of the acceptor, reaching values as high as 1.5 V when cyano-substituted poly(p-phenyleneethynylene)-alt- poly(p-phenylenevinylene) copolymers are used. Further, we discovered that for an increasing number of triple bonds in the repeat unit of the acceptor polymer the device performance decreases with increasing thickness of the acceptor layer. Also, the quantum efficiency was smaller when using polymers with higher LUMO levels. Thus, further effort is needed to design optimum acceptor polymers for devices exhibiting large open-circuit voltage and high quantum efficiency Y1 - 2006 UR - http://pubs.acs.org/journal/mamobx U6 - https://doi.org/10.1021/Ma0601991 SN - 4018-4022 ER -