@article{LandfesterMontenegroScherfetal.2002, author = {Landfester, Katharina and Montenegro, Rivelino V. D. and Scherf, Ullrich and G{\"u}nter, R. and Asawapirom, Udom and Patil, S. and Neher, Dieter and Kietzke, Thomas}, title = {Semiconducting polymer nanospheres in aqeous dispersion prepared by a miniemulsion process}, year = {2002}, language = {en} } @article{ZenNeherSilmyetal.2005, author = {Zen, Achmad and Neher, Dieter and Silmy, Kamel and Hollander, A. and Asawapirom, Udom and Scherf, Ullrich}, title = {Improving the performance of organic field effect transistor by optimizing the gate insulator surface}, year = {2005}, abstract = {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}, language = {en} } @article{DaeublerGlowackiScherfetal.1999, author = {D{\"a}ubler, Thomas Karl and Glowacki, Ireneusz and Scherf, Ullrich and Ulanski, J. and H{\"o}rhold, Hans-Heinrich and Neher, Dieter}, title = {Photogeneration and transport of charge carriers in hybrid materials of conjugated polymers and dye-sensitized TiO2}, year = {1999}, language = {en} } @article{GhaniOpitzPingeletal.2015, author = {Ghani, Fatemeh and Opitz, Andreas and Pingel, Patrick and Heimel, Georg and Salzmann, Ingo and Frisch, Johannes and Neher, Dieter and Tsami, Argiri and Scherf, Ullrich and Koch, Norbert}, title = {Charge Transfer in and Conductivity of Molecularly Doped Thiophene-Based Copolymers}, series = {Journal of polymer science : B, Polymer physics}, volume = {53}, journal = {Journal of polymer science : B, Polymer physics}, number = {1}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0887-6266}, doi = {10.1002/polb.23631}, pages = {58 -- 63}, year = {2015}, abstract = {The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design.}, language = {en} } @article{BagnichImBassleretal.2004, author = {Bagnich, Sergey A. and Im, C. and Bassler, H. and Neher, Dieter and Scherf, Ullrich}, title = {Energy transfer in a ladder-type methyl-poly(para-phenylene) doped by Pt(II)octaethylporphyrin}, issn = {0301-0104}, year = {2004}, abstract = {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}, language = {en} } @article{ZenBilgeGalbrechtetal.2006, author = {Zen, Achmad and Bilge, Askin and Galbrecht, Frank and Alle, Ronald and Meerholz, Klaus and Grenzer, J{\"o}rg and Neher, Dieter and Scherf, Ullrich and Farrell, Tony}, title = {Solution processable organic field-effect transistors utilizing an alpha,alpha '-dihexylpentathiophene- based swivel cruciform}, doi = {10.1021/Ja0573357}, year = {2006}, language = {en} } @article{AsawapiromBulutFarrelletal.2004, author = {Asawapirom, Udom and Bulut, F. and Farrell, Tony and Gadermaier, C. and Gamerith, S. and G{\"u}ntner, Roland and Kietzke, Thomas and Patil, S. and Piok, T. and Montenegro, Rivelino V. D. and Stiller, Burkhard and Tiersch, Brigitte and Landfester, Katharina and List, E. J. W. and Neher, Dieter and Torres, C. S. and Scherf, Ullrich}, title = {Materials for polymer electronics applications semiconducting polymer thin films and nanoparticles}, issn = {1022-1360}, year = {2004}, abstract = {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}, language = {en} } @article{AlbrechtTumblestonJanietzetal.2014, author = {Albrecht, Steve and Tumbleston, John R. and Janietz, Silvia and Dumsch, Ines and Allard, Sybille and Scherf, Ullrich and Ade, Harald W. and Neher, Dieter}, title = {Quantifying charge extraction in organic solar cells: The case of fluorinated PCPDTBT}, series = {The journal of physical chemistry letters}, volume = {5}, journal = {The journal of physical chemistry letters}, number = {7}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz500457b}, pages = {1131 -- 1138}, year = {2014}, abstract = {We introduce a new and simple method to quantify the effective extraction mobility in organic solar cells at low electric fields and charge carrier densities comparable to operation conditions under one sun illumination. By comparing steady-state carrier densities at constant illumination intensity and under open-circuit conditions, the gradient of the quasi-Fermi potential driving the current is estimated as a function of external bias and charge density. These properties are then related to the respective steady-state current to determine the effective extraction mobility. The new technique is applied to different derivatives of the well-known low-band-gap polymer PCPDTBT blended with PC70BM. We show that the slower average extraction due to lower mobility accounts for the moderate fill factor when solar cells are fabricated with mono- or difluorinated PCPDTBT. This lower extraction competes with improved generation and reduced nongeminate recombination, rendering the monofluorinated derivative the most efficient donor polymer.}, language = {en} } @article{YangJaiserStilleretal.2006, author = {Yang, Xiao Hui and Jaiser, Frank and Stiller, Burkhard and Neher, Dieter and Galbrecht, Frank and Scherf, Ullrich}, title = {Efficient polymer electrophosphoreseent devices with interfacial layers}, series = {Advanced functional materials}, volume = {16}, journal = {Advanced functional materials}, number = {16}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.200500834}, pages = {2156 -- 2162}, year = {2006}, abstract = {It is shown that several polymers can form insoluble interfacial layers on a poly (ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layer after annealing of the double-layer structure. The thickness of the interlayer is dependent on the characteristics of the underlying PEDOT.PSS and the molecular weight of the polymers. It is further shown that the electronic structures of the interlayer polymers have a significant effect on the properties of red-light-emitting polymer-based electrophosphorescent devices. Upon increasing the highest occupied molecular orbital and lowest unoccupied molecular orbital positions, a significant increase in current density and device efficiency is observed. This is attributed to efficient blocking of electrons in combination with direct injection of holes from the interlayer to the phosphorescent dye. Upon proper choice of the interlayer polymer, efficient red, polymer-based electrophosphorescent devices with a peak luminance efficiency of 5.5 cd A(-1) (external quantum efficiency = 6 \%) and a maximum power-conversion efficiency of 5 Im W-1 can be realized.}, language = {en} } @article{HoermannZeiskeParketal.2019, author = {H{\"o}rmann, Ulrich and Zeiske, Stefan and Park, Soohyung and Schultz, Thorsten and Kickhoefel, Sebastian and Scherf, Ullrich and Blumstengel, Sylke and Koch, Norbert and Neher, Dieter}, title = {Direct observation of state-filling at hybrid tin oxide/organic interfaces}, series = {Applied physics letters}, volume = {114}, journal = {Applied physics letters}, number = {18}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.5082704}, pages = {5}, year = {2019}, abstract = {Electroluminescence (EL) spectra of hybrid charge transfer states at metal oxide/organic type-II heterojunctions exhibit bias-induced spectral shifts. The reasons for this phenomenon have been discussed controversially and arguments for either electric field-induced effects or the filling of trap states at the oxide surface have been put forward. Here, we combine the results of EL and photovoltaic measurements to eliminate the unavoidable effect of the series resistance of inorganic and organic components on the total voltage drop across the hybrid device. For SnOx combined with the conjugated polymer [ladder type poly-(para-phenylene)], we find a one-to-one correspondence between the blue-shift of the EL peak and the increase of the quasi-Fermi level splitting at the hybrid heterojunction, which we unambiguously assign to state filling. Our data are resembled best by a model considering the combination of an exponential density of states with a doped semiconductor. Published under license by AIP Publishing.}, language = {en} }