TY  - JOUR
A1  - Schulz, Burkhard
A1  - Stiller, Burkhard
A1  - Zetzsche, Thomas
A1  - Knochenhauer, Gerald
A1  - Brehmer, Ludwig
T1  - Characterization of crystals based on 1,3,4-oxadiazoles by atomic force microscopy
N2  - The surface structures of crystals based on aromatic oxadiazoles were investigated by AFM. The crystal structure for 2,5-di(p-tolyl)-1,3,4-oxadiazole (DTO) differs from that of 2,5-di (4-methoxycarbonyl-phenyl)-1,3,4- oxadiazole (DMPO). In DMPO all molecules show parallel orientation to the surface in such a way that the surface is formed as well as by the nitrogen atoms of the heterocyclic rings and the methyl groups of the ester substituents. By contrast, the oxadiazole molecules in DTO crystals are oriented perpendicular to the crystal surface. The experimental data are interpreted by molecular modelling. It is shown that there is a difference between molecular structure of the surface, as detected by AFM, and the bulk structure determined by X-ray diffraction.
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Bruma, Maria
A1  - Sava, Ion
A1  - Mercer, Frank W.
A1  - Reddy, Victor N.
A1  - Köpnick, Thomas
A1  - Stiller, Burkhard
A1  - Schulz, Burkhard
T1  - Silicon-containing poly(amide-ether)s
N2  - New aromatic poly(amide-ether)s (II) have been synthesized by solution polycondensation of various aromatic diamines having two ether bridges (I) with a diacid chloride containing silicon, namely bis(chlorocarbonylphenyl)- diphenyIsilane. These polymers are easy soluble in polar amidic solvents such as N-methylpyrrolidinone or dimethylformamide and can be cast into thin flexible films or coatings from such solutions. They show high thermal stability with initial decomposition temperature being above 400 °C. Their glass transition temperatures lie in the range of 220-250 °C, except for polymer He which did not show a clear Tg when heated in a differential scanning calorimetry experiment up to 300 °C. The large interval between the glass transition and decomposition temperatures of pnlymers Ia-Id could be advantageous for their processing via compression molding. The polymer coatings deposited by the spincoating, technique onto silicon wafers showed a very smooth, pinhole-free surface in atomic force microscopy investigations. The free-standing films of 20-30 mm thickness show low dielectric constant, in the range of 3.65-3.78, which is promising for future application as high performance dielectrics.
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Bruma, Maria
A1  - Schulz, Burkhard
A1  - Köpnick, Thomas
A1  - Dietel, Reinhard
A1  - Stiller, Burkhard
A1  - Mercer, Frank W.
T1  - Investigation of thin films made from silicon-containing poly(phenylquinoxaline-amide)s
N2  - Thin films in the range of 50 nm to 10 mm thickness have been prepared from NMP solutions of silicon-containing polyphenylquinoxaline-amides which had been synthesized by the polycondensation reaction of aromatic diaminophenylquinoxalines with bis(p-chlorocarbonylphenyl)diphenylsilane. A spin-coating technique onto glass plates or onto silicon wafers was used to make the film, followed by gradual heating to remove the solvent. The resulting films were very smooth and free of pinholes when studied by atomic force microscopy (AFM). They showed a strong adhesion to silicon wafers, were thermally stable in air to above 400 °C and their dielectric constant was in the range of 3.5-3.7. Thermal treatment of the films was performed in order to induce crosslinking. Such treated films became completely insoluble in organic solvents, maintained their smoothness and strong adhesion to the silicon substrate, and did not show any Tg, in DSC experiments. Their FTIR spectra in reflection mode did not show any changes compared with the untreated films, meaning on the one hand that the polymers maintain their structural integrity at high temperature and on the other hand that the number of crosslinks was very low and could not be detected by IR spectroscopy.
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Bruma, Maria
A1  - Schulz, Burkhard
A1  - Köpnick, Thomas
A1  - Stiller, Burkhard
A1  - Hamciuc, Elena
A1  - Mercer, Frank W.
A1  - Cassidy, Peter
T1  - Aromatic polyamides with hexafluoroisopropylidene groups and study of the thin
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Schulz, Burkhard
A1  - Stiller, Burkhard
A1  - Zetzsche, Thomas
A1  - Knochenhauer, Gerald
A1  - Dietel, Reinhard
A1  - Brehmer, Ludwig
T1  - Characterization of 2,5-di(p-tolyl-1,3,4- oxadiazole) crystals by IR-spectroscopy and atomic force microscopy
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Schulz, Burkhard
A1  - Stiller, Burkhard
A1  - Zetzsche, Thomas
A1  - Knochenhauer, Gerald
A1  - Dietel, Reinhard
A1  - Brehmer, Ludwig
T1  - Crystal structure of 2,5-Di(4- methoxycarbonyl-phenyl)-1,3,4-oxadiazole characterized by AFM and IR- spectroscopy
Y1  - 1994
ER  - 
TY  - JOUR
A1  - Karageorgiev, Peter
A1  - Stiller, Burkhard
A1  - Prescher, Dietrich
A1  - Dietzel, Birgit
A1  - Schulz, Burkhard
A1  - Brehmer, Ludwig
T1  - Modification of the surface potential of azobenzene-containing langmuir-blodgett films in the near field of a scanning kelvin microscope tip by irradiation
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Bruma, Maria
A1  - Schulz, Burkhard
A1  - Köpnick, Thomas
A1  - Stiller, Burkhard
A1  - Belomoina, Nataliya
A1  - Mercer, Frank W.
T1  - Synthesis and study of aromatic polyamides containing silicon and phenylquinoxaline rings in the main chain
N2  - New poly(phenylquinoxaline-amide)s with silicon in the main chain have been prepared by polycondensation reaction of a diacid chloride, namely bis(p-chlorocarbonyl-phenyl)-diphenylsilane, with aromatic diamines containing one or two phenylquinoxaline rings separated by a flexible bridge such as ether or methylene. These polymers were easily soluble in polar aprotic solvents such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF) and showed high thermal stability with decomposition temperature being above 450°C and glass transition temperature in the range of 260- 304°C. Polymer solutions in NMP were processed into thin flexible films which exhibited very smooth surfaces, free of pinholes when studied by atomic force microscopy. The free-standing films showed a dielectric constant in the range of 3.6-3.7.
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Bruma, Maria
A1  - Hamciuc, Elena
A1  - Schulz, Burkhard
A1  - Köpnick, Thomas
A1  - Stiller, Burkhard
A1  - Mercer, Frank W.
T1  - Synthesis of fluorinated poly(phenylquinoxaline-amide)s and study of thin films made therefrom
N2  - A series of five fluorinated poly(phenylquinoxaline-amide)s were synthesized by a polycondensation reaction of a diacid chloride containing the hexafluoroisopropylidene (6F) group, namely 2,2-bis(p-chlorocarbonylphenyl)- hexafluoropropane, with various aromatic diamines incorporating two phenyl-substituted quinoxaline rings. These polymers were easily soluble in polar aprotic solvents such as N-methylpyrrolione (NMP), dimethylformamide (DMF), and tetrahydrofurane (THF), and showed a high thermal stability with decomposition temperatures above 400 °C and glass transition temperatures in the range of 260-290 Tg. Polymer solutions in NMP were processed into free-standing films that showed low dielectric constant values, in the range of 3.4-3.9, and good mechanical properties, with tensile strength in the range of 40-80 MPa and elongation to break in the range of 22-55%. Very thin films, in the range of tens of nanometer, which were deposited onto silicon wafers exhibited very smooth surfaces, free of pinholes when studied by atomic force microscopy (AFM).
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Bruma, Maria
A1  - Schulz, Burkhard
A1  - Köpnick, Thomas
A1  - Stiller, Burkhard
A1  - Mercer, Frank W.
T1  - Study of thin films made from aromatic polyamides with silicon and phenylquinoxaline rings in the main chain
N2  - Aromatic polyamides containing silicon and phenylquinoxaline rings in the main chain have been prepared by polycondensation reaction of a silicon-containing diacid chloride, namely bis(p-chlorocarbonylphenyl) -diphenylsilane, with various aromatic diamines having preformed phenylquinoxaline units. These polymers were easily soluble in polar aprotic solvents, such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF), and in tetrahydrofurane. They showed high thermal stability with decomposition temperature being above 450°C and glass transition temperature in the range of 253-304°C. Polymer solutions in NMP were processed into thin films having the thickness of tens of nanometer to 10 mm, by spin-coating onto glass plates or silicon wafers. The films had strong adhesion to substrates and exhibited very smooth surfaces, free of pinholes, in atomic force microscopy (AFM) studies. The free-standing films had dielectric constant in the range of 3.48-3.69. Thermal treatment of the films up to 350°C rendered them completely insoluble in organic solvents, while maintaining their smoothness and strong adhesion to the silicon substrate, and with no Tg in DSC experiments. Their FTIR spectra did not show any changes compared to the untreated films, meaning that polymers maintain their structural integrity at high temperature. Ó 1999 Elsevier Science S.A. All rights reserved.
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Reiche, Jürgen
A1  - Freydank, Anke-Christine
A1  - Helms, Andreas
A1  - Geue, Thomas
A1  - Schulz, Burkhard
A1  - Brehmer, Ludwig
A1  - Stiller, Burkhard
A1  - Knochenhauer, Gerald
T1  - Vacuum deposition films of oxadiazole compounds : formation and structure investigation
N2  - The search for alternative routes of organic thin film formation is stimulated by the outstanding properties of these films in such fields as nonlinear optics, photonic data processing and molecular electronics. The formation of highly ordered multilayer structures by thermal vacuum deposition (VD) of organic compounds is an essential step toward the application of supramolecular organic architectures in technical systems. The VD of an amphiphilic substituted 2,5- diphenylene-1,3,4-oxadiazole 1 onto silicon substrates at defined temperature was used for the formation of ultrathin films. The structural data obtained for the VD-films of oxadiazole 1 by means of X-ray reflectivity, X-ray grazing incidence diffraction and atomic force microscopy (AFM) investigations indicate the formation of well ordered oxadiazole multilayers. The structure of the VD-multilayers is compared with that of Langmuir-Blodgett (LB) films and thermally treated LB-multilayers prepared from the same compound.
Y1  - 1999
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  - Hegewald, J.
A1  - Schmidt, T.
A1  - Gohs, U.
A1  - Gunther, M.
A1  - Reichelt, R.
A1  - Stiller, Burkhard
A1  - Arndt, K. F.
T1  - Electron beam irradiation of poly(vinyl methyl ether) films : 1. Synthesis and film topography
N2  - Temperature-sensitive hydrogel layers on silicon (Si) substrates were synthesized by electron beam irradiation of spin-coated poly(vinyl methyl ether) (PVME) films. The influences of the used solvent, the polymer concentration, and the spinning velocity on the homogeneity and the thickness of the PVME film were investigated. In the range of concentration c(p) = 1-15 wt% PVME in ethanol solution, homogeneous films with a thickness between d = 50 nm and 1.7 mu m were obtained. The films were cross-linked by electron beam irradiation under inert atmosphere and analyzed by sol-gel- analysis. The results were compared with bulkgels formed by electron beam irradiation of PVME in the dry state. The film topography was analyzed by high-resolution field emission scanning electron microscopy and atomic force microscopy. An islandlike structure in the dry, swollen, and shrunken state of the hydrogel films was observed
Y1  - 2005
SN  - 0743-7463
ER  - 
TY  - JOUR
A1  - Tejedor, R. M.
A1  - Oriol, L.
A1  - Pinol, M.
A1  - Serrano, J. L.
A1  - Strehmel, Veronika
A1  - Stiller, Burkhard
A1  - Stumpe, Joachim
T1  - Photoreactive main-chain liquid-crystalline polyesters : Synthesis, characterization, and photochemistry
N2  - Three series of semiflexible and rigid main-chain polyesters containing photoreactive mesogenic units derived from p-phenylenediacrylic acid (PDA) and cinnamic acid have been synthesized by high-temperature polycondensation. The thermal and mesomorphic properties of the polymers have been determined. The photochemical behavior of polymer P-[1]-T, which contains a PDA unit, has been studied both in solution and in films. In solution, [2+2] photocycloaddition, E/Z photoisomerization, and photo-Fries rearrangement can take place. In contrast, the dominant process in spin-coated films is the [2+2] photocycloaddition reaction, which causes crosslinking of the polymer. In films, the photochemistry and induction of anisotropy are strongly influenced by the aggregation of the PDA phenylester unit. A dichroism of about 0.2 has been induced in films by irradiation with linearly polarized UV light, and thus the capability of these films to induce optical anisotropy and align liquid crystals has been demonstrated. Liquid-crystalline cells have been made with polarized irradiated films of P[1]-T as aligning layers. A commercial liquid-crystalline mixture has been used for this study, and a similar liquid-crystalline order determined by polarized Fourier transform infrared to a commercial cell with rubbed polyimide as an aligning layer has been detected. Because of crosslinking of the irradiated P[1]-T photoaligning layer, the photoinduced anisotropy is stable at high temperatures, and the liquid-crystalline molecules are insoluble in the irradiated polymer. (c) 2005 Wiley Periodicals, Inc
Y1  - 2005
SN  - 0887-624X
ER  - 
TY  - BOOK
A1  - Muzikante, I.
A1  - Fonavs, E.
A1  - Brehmer, Ludwig
A1  - Stiller, Burkhard
T1  - Photoinuced phenomena in corona poled polar organic films
N2  - Organic materials have received considerable attention because of their large dipole moments and optical nonlinearities. The optically induced switching of material properties is important for studying the optoelectronic effects including second harmonic generation. Organic materials for photonic applications contain chromophore dipole which consist of acceptor and donor groups bridged by a delocalized pi-electron system. Both theoretical and experimental data show a reversible highly dipolar photoinduced intra molecular charge transfer in betaine type molecules accompanied by change of the sign and the value of the dipole moment. The arrangement of polar molecules in films is studied both by atom force microscopy and surface potential measurements. To understand the photo response of these materials, their spectroscopic and electrical properties are studied. The morphology and photoinduced surface potential switching of the self-assembled monolayers and polymer films are investigated. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Dimitriev, O. P.
A1  - Smertenko, P. S.
A1  - Stiller, Burkhard
A1  - Brehmer, Ludwig
T1  - Polyaniline-transition metal salt complexes: insight into formation mechanisms
N2  - Two basic morphologies of emeraldine base of polyaniline-transition metal salt complex films cast from N- methylpyrrolidinone solutions are described. The first morphology consists of grains and the other consists of loose aggregates, respectively. The correlation of the film morphology with formation of precipitate in the complex solution, kinetics of solvent evaporation from the cast film, amount of solvent entrapped in the film, film conductivity, and IR absorption spectra is shown. Two different mechanisms of the complex formation as a result of competition in the polymer- inorganic salt-solvent trio interactions are discussed; the first mechanism results in folding of macromolecules into compact coils being then a core of grains in the complex films, and the second mechanism leads to blending of the polymer chains with solvent giving rise to formation of loose aggregates. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0379-6779
ER  - 
TY  - JOUR
A1  - Muzikante, I.
A1  - Fonavs, E.
A1  - Tokmakov, A.
A1  - Cepite, D.
A1  - Stiller, Burkhard
A1  - Brehmer, Ludwig
A1  - Neilands, O.
T1  - Optical and electrical properties of oriented thin films of oligomer containing betaine-type moiety in side chain
N2  - Non-linear optical and electrical properties of polymer films obtained by dipole orientation of active units are reported. Novel polar oligomer with N-(indan-1,3-dion-2-yl)pyridinium betaine (IPB) as a side group is studied. Orientation of polar groups in oligomer thin films causes an increase of the photo-induced change of surface potential on irradiation in the region of photo-induced electron transfer (PIET) where the IPB group exhibits a reversible change of the value and sign of the dipole moment. At longer wavelengths, the value of the surface potential of the oligomer may be determined by transport of photo-generated charge carriers
Y1  - 2005
SN  - 0370-1972
ER  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Karageorgiev, Peter
A1  - Buchsteiner, Andrea
A1  - Geue, Thomas
A1  - Henneberg, Oliver
A1  - Brehmer, Ludwig
A1  - Natansohn, Almeria
A1  - Hollricher, Olga
T1  - Using light as a tool : optically Induced mass transport generated in Near-Fields
Y1  - 2003
SN  - 0038-7355 -
ER  - 
TY  - JOUR
A1  - Helms, Andreas
A1  - Reiche, Jürgen
A1  - Stiller, Burkhard
A1  - Kobloch, H.
A1  - Brehmer, Ludwig
T1  - Herstellung dünner organischer Schichten durch Vakuumdeposition
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Angelova, Angelina
A1  - Penacorada, Florencio
A1  - Stiller, Burkhard
A1  - Zetzsche, Thomas
A1  - Ionov, Radoslav
A1  - Kamusewitz, Helmut
A1  - Brehmer, Ludwig
T1  - Wettability, surface morphology and stability of long chain ester multilayers obtained by different Langmuir- Blodgett deposition type
Y1  - 1994
ER  - 
TY  - JOUR
A1  - Penacorada, Florencio
A1  - Reiche, Jürgen
A1  - Dietel, Reinhard
A1  - Zetzsche, Thomas
A1  - Stiller, Burkhard
A1  - Knobloch, Harald
A1  - Brehmer, Ludwig
T1  - Monolayers and multilayers of uranyl arachidate : 2. Influence of the subphase pH on the structure and stability of Langmuir-Blodgett films
N2  - In this second paper we describe the comprehensive structure investigations on multilayers of uranyl arachidate formed by Langmuir-Blodgett deposition from subphases of different pH on solid substrates by means of a combination of infrared spectroscopy, X-ray specular reflection, ellipsometry, and scanning force microscopy, The structure of these multilayers and their stability are obviously influenced by the subphase pH. The pH range of the acid to salt conversion determined for the Langmuir films is confirmed by the infrared spectroscopic data of the multilayers. While arachidic acid films, deposited from an uranyl acetate subphase of low pH, are found to have strongly distorted rough surface, the films of uranyl structure, The influence of the counterions on the alkyl chain conformation, chain packing, reorganization probability, and stability of the multilayer is discussed.
Y1  - 1996
ER  - 
TY  - JOUR
A1  - Stracke, A.
A1  - Wendhorff, Joachim Heinz
A1  - Goldmann, Daniela
A1  - Janietz, Dietmar
A1  - Stiller, Burkhard
T1  - Gain effects in optical storage : thermal induction of a surface relief grating in a smectic liquid crystal
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Karageorgiev, Peter
A1  - Perez, E.
A1  - Valez, M.
A1  - Reiche, Jürgen
A1  - Prescher, Dietrich
A1  - Dietzel, Birgit
A1  - Brehmer, Ludwig
T1  - Scanning kelvin microscopy as a tool for visualisation of optically induced molecular switching in azobenzene self assembling films
Y1  - 2000
SN  - 0142-2421
ER  - 
TY  - JOUR
A1  - Mahler, J.
A1  - Rafler, G.
A1  - Stiller, Burkhard
T1  - Modified melamines and melamine resins for E/Z-isomerization
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Köpnick, Thomas
A1  - Muzikante, I.
A1  - Neilands, O.
A1  - Utinans, M.
A1  - Dubrovich, O.
A1  - Karageorgiev, Peter
A1  - Brehmer, Ludwig
T1  - Optically induced switching effect of polymer containing indandione-1,3-pyridinium betaine side chains
Y1  - 1999
SN  - 0378-2271
ER  - 
TY  - JOUR
A1  - Gustina, D.
A1  - Markava, E.
A1  - Muzikante, I.
A1  - Stiller, Burkhard
A1  - Brehmer, Ludwig
T1  - Photoisomerisation process of self-assembled monolayers of some novel azobenzenes
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Geue, Thomas
A1  - Morawetz, Knut
A1  - Saphiannikova, Marina
T1  - Optical patterning in azobenzene polymer films
N2  - Thin azobenzene polymer films show a very unusual property, namely optically induced material transport. The underlying physics for this phenomenon has not yet been thoroughly explained. Nevertheless, this effect enables one to inscribe different patterns onto film surfaces, including one- and two-dimensional periodic structures. Typical sizes of such structures are of the order of micrometers, i.e. related to the interference pattern made by the laser used for optical excitation. In this study we have measured the mechanical properties of one- and two-dimensional gratings, with a high lateral resolution, using force-distance curves and pulse force mode of the atomic force microscope. We also report on the generation of considerably finer structures, with a typical size of 100 nm, which were inscribed onto the polymer surface by the tip of a scanning near-field optical microscope used as an optical pen. Such inscription not only opens new application possibilities but also gives deeper insight into the fundamentals physics underlying optically induced material transport
Y1  - 2005
SN  - 0022-2720
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  - Pradhan, Basudev
A1  - Albrecht, Steve
A1  - Stiller, Burkhard
A1  - Neher, Dieter
T1  - Inverted organic solar cells comprising low-temperature-processed ZnO films
JF  - Applied physics : A, Materials science & processing
N2  - Inverted organic solar cells are fabricated using low-temperature-annealed ZnO film as an electron transport layer. Uniform ZnO films were prepared by spin coating a diethylzinc (DEZ) precursor solution in air, followed by annealing at 100 A degrees C. Organic solar cells prepared on these ZnO films with a 1:1 P3HT:PCBM blend as the active layer show a high power conversion efficiency of 4.03 %, which is more than 10 % higher than the PCE of solar cells comprising ZnO prepared via a high-temperature sol-gel route.
Y1  - 2014
U6  - https://doi.org/10.1007/s00339-014-8373-8
SN  - 0947-8396
SN  - 1432-0630
VL  - 115
IS  - 2
SP  - 365
EP  - 369
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Schubert, Marcel
A1  - Dolfen, Daniel
A1  - Frisch, Johannes
A1  - Roland, Steffen
A1  - Steyrleuthner, Robert
A1  - Stiller, Burkhard
A1  - Chen, Zhihua
A1  - Scherf, Ullrich
A1  - Koch, Norbert
A1  - Facchetti, Antonio
A1  - Neher, Dieter
T1  - Influence of aggregation on the performance of All-Polymer Solar Cells containing Low-Bandgap Naphthalenediimide Copolymers
JF  - dvanced energy materials
N2  - The authors present efficient all-polymer solar cells comprising two different low-bandgap naphthalenediimide (NDI)-based copolymers as acceptors and regioregular P3HT as the donor. It is shown that these naphthalene copolymers have a strong tendency to preaggregate in specific organic solvents, and that preaggregation can be completely suppressed when using suitable solvents with large and highly polarizable aromatic cores. Organic solar cells prepared from such nonaggregated polymer solutions show dramatically increased power conversion efficiencies of up to 1.4%, which is mainly due to a large increase of the short circuit current. In addition, optimized solar cells show remarkable high fill factors of up to 70%. The analysis of the blend absorbance spectra reveals a surprising anticorrelation between the degree of polymer aggregation in the solid P3HT:NDI copolymer blends and their photovoltaic performance. Scanning near-field optical microscopy (SNOM) and atomic force microscopy (AFM) measurements reveal important information on the blend morphology. It is shown that films with high degree of aggregation and low photocurrents exhibit large-scale phase-separation into rather pure donor and acceptor domains. It is proposed that, by suppressing the aggregation of NDI copolymers at the early stage of film formation, the intermixing of the donor and acceptor component is improved, thereby allowing efficient harvesting of photogenerated excitons at the donoracceptor heterojunction.
KW  - aggregation
KW  - morphology
KW  - naphthalenediimide
KW  - organic semiconductors
KW  - organic photovoltaics
Y1  - 2012
U6  - https://doi.org/10.1002/aenm.201100601
SN  - 1614-6832
VL  - 2
IS  - 3
SP  - 369
EP  - 380
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Ye, Fangyuan
A1  - Zhang, Shuo
A1  - Warby, Jonathan
A1  - Wu, Jiawei
A1  - Gutierrez-Partida, Emilio
A1  - Lang, Felix
A1  - Shah, Sahil
A1  - Saglamkaya, Elifnaz
A1  - Sun, Bowen
A1  - Zu, Fengshuo
A1  - Shoai, Safa
A1  - Wang, Haifeng
A1  - Stiller, Burkhard
A1  - Neher, Dieter
A1  - Zhu, Wei-Hong
A1  - Stolterfoht, Martin
A1  - Wu, Yongzhen
T1  - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane
JF  - Nature Communications
N2  - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.
Y1  - 2022
U6  - https://doi.org/10.1038/s41467-022-34203-x
SN  - 2041-1723
VL  - 13
IS  - 1
PB  - Springer Nature
CY  - London
ER  - 
TY  - JOUR
A1  - Yin, Chunhong
A1  - Schubert, Marcel
A1  - Stiller, Burkhard
A1  - Castellani, Mauro
A1  - Neher, Dieter
A1  - Kumke, Michael Uwe
A1  - Hörhold, Hans-Heinrich
T1  - Tuning of the excited-state properties and photovoltaic performance in PPV-based polymer blends
Y1  - 2008
U6  - https://doi.org/10.1021/Jp803977k
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  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Karageorgiev, Peter
A1  - Geue, Thomas
A1  - Morawetz, Knut
A1  - Saphiannikova, Marina
A1  - Mechau, Norman
A1  - Neher, Dieter
T1  - Optically induced mass transport studied by scanning near-field optical- and atomic force microscopy
N2  - Some functionalised thin organic films show a very unusual property, namely the light induced material transport. This effect enables to generate three-dimensional structures on surfaces of azobenzene containing films only caused by special optical excitation. The physical mechanisms underlying this phenomenon have not yet been fully understood, and in addition, the dimensions of structures created in that way are macroscopic because of the optical techniques and the wavelength of the used light. In order to gain deeper insight into the physical fundamentals of this phenomenon and to open possibilities for applications it is necessary to create and study structures not only in a macroscopic but also in nanometer range. We first report about experiments to generate optically induced nano structures even down to 100 nm size. The optical stimulation was therefore made by a Scanning Near-field Optical Microscope (SNOM). Secondly, physical conditions inside optically generated surface relief gratings were studied by measuring mechanical properties with high lateral resolution via pulse force mode and force distance curves of an AFM
Y1  - 2004
SN  - 0204-3467
ER  - 
TY  - JOUR
A1  - Yang, Xiao Hui
A1  - Jaiser, Frank
A1  - Stiller, Burkhard
A1  - Neher, Dieter
A1  - Galbrecht, Frank
A1  - Scherf, Ullrich
T1  - Efficient polymer electrophosphoreseent devices with interfacial layers
JF  - Advanced functional materials
N2  - 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.
Y1  - 2006
U6  - https://doi.org/10.1002/adfm.200500834
SN  - 1616-301X
SN  - 1616-3028
VL  - 16
IS  - 16
SP  - 2156
EP  - 2162
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - GEN
A1  - Ye, Fangyuan
A1  - Zhang, Shuo
A1  - Warby, Jonathan
A1  - Wu, Jiawei
A1  - Gutierrez-Partida, Emilio
A1  - Lang, Felix
A1  - Shah, Sahil
A1  - Saglamkaya, Elifnaz
A1  - Sun, Bowen
A1  - Zu, Fengshuo
A1  - Shoaee, Safa
A1  - Wang, Haifeng
A1  - Stiller, Burkhard
A1  - Neher, Dieter
A1  - Zhu, Wei-Hong
A1  - Stolterfoht, Martin
A1  - Wu, Yongzhen
T1  - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1317 
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-587705
SN  - 1866-8372
IS  - 1317
ER  -