@article{ShalomInalNeheretal.2014, author = {Shalom, Menny and Inal, Sahika and Neher, Dieter and Antonietti, Markus}, title = {SiO2/carbon nitride composite materials: The role of surfaces for enhanced photocatalysis}, series = {Catalysis today : a serial publication dealing with topical themes in catalysis and related subjects}, volume = {225}, journal = {Catalysis today : a serial publication dealing with topical themes in catalysis and related subjects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0920-5861}, doi = {10.1016/j.cattod.2013.12.013}, pages = {185 -- 190}, year = {2014}, abstract = {The effect of SiO2 nanoparticles on carbon nitride (C3N4) photoactivity performance is described. The composite SiO2-C3N4 materials exhibit a higher activity in the photo degradation of RhB dye. A detailed analysis of the chemical and optical properties of the composite C3N4 materials shows that the photo activity increases with higher SiO2 concentration. We found out that the presence of SiO2 nanoparticles strongly affects the fluorescence intensity of the matrix and life time by the creation of new energy states for charge transfer within the C3N4. Furthermore, the use of SiO2 in the synthesis of C3N4 leads to new morphology with higher surface area which results in another, secondary improvement of C3N4 photoactivity. The effect of different surfaces within C3N4 on its chemical and electronic properties is discussed and a tentative mechanism is proposed. The utilization of SiO2 nanoparticles improves both photophysical and chemical properties of C3N4 and opens new possibilities for further enhancement of C3N4 catalytic properties by the formation of composites with many other materials.}, language = {en} } @article{AlbrechtGrootoonkNeubertetal.2014, author = {Albrecht, Steve and Grootoonk, Bjorn and Neubert, Sebastian and Roland, Steffen and Wordenweber, Jan and Meier, Matthias and Schlatmann, Rutger and Gordijn, Aad and Neher, Dieter}, title = {Efficient hybrid inorganic/organic tandem solar cells with tailored recombination contacts}, series = {Solar energy materials \& solar cells : an international journal devoted to photovoltaic, photothermal, and photochemical solar energy conversion}, volume = {127}, journal = {Solar energy materials \& solar cells : an international journal devoted to photovoltaic, photothermal, and photochemical solar energy conversion}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-0248}, doi = {10.1016/j.solmat.2014.04.020}, pages = {157 -- 162}, year = {2014}, abstract = {In this work, the authors present a 7.5\% efficient hybrid tandem solar cell with the bottom cell made of amorphous silicon and a Si-PCPDTBT:PC70BM bulk heterojunction top cell. Loss-free recombination contacts were realized by combing Al-doped ZnO with either the conducting polymer composite PEDOT:PSS or with a bilayer of ultrathin Al and MoO3. Optimization of these contacts results in tandem cells with high fill factors of 70\% and an open circuit voltage close to the sum of those of the sub-cells. This is the best efficiency reported for this type of hybrid tandem cell so far. Optical and electrical device modeling suggests that the efficiency can be increased to similar to 12\% on combining a donor polymer with suitable absorption onset with PCBM. We also describe proof-of-principle studies employing light trapping in hybrid tandem solar cells, suggesting that this device architecture has the potential to achieve efficiencies well above 12\%. (C) 2014 Elsevier B.V. All rights reserved.}, language = {en} } @article{TremelFischerKayunkidetal.2014, author = {Tremel, Kim and Fischer, Florian S. U. and Kayunkid, Navaphun and Di Pietro, Riccardo and Tkachov, Roman and Kiriy, Anton and Neher, Dieter and Ludwigs, Sabine and Brinkmann, Martin}, title = {Charge transport anisotropy in highly oriented thin films of the acceptor polymer P(NDI2OD-T2)}, series = {dvanced energy materials}, volume = {4}, journal = {dvanced energy materials}, number = {10}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201301659}, pages = {13}, year = {2014}, abstract = {The nanomorphology of the high mobility polymer poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} P(NDI2OD-T2) in thin films is explored as a function of different annealing conditions and correlated to optical and electrical properties. While nanofibrils with face-on orientation in form I are obtained directly after spin-coating and annealing below the melt transition temperature, clear evidence of lamellar structures is found after melt-annealing followed by slow cooling to room temperature. Interestingly these structural changes are accompanied by distinct changes in the absorption patterns. Electron diffraction measurements further show clear transitions towards predominant edge-on oriented chains in form II upon melt-annealing. Large-scale alignment with dichroic ratios up to 10 and improved order is achieved by high temperature rubbing and subsequent post-rubbing annealing. These highly oriented morphologies allow anisotropic in-plane charge transport to be probed with top-gate transistors parallel and perpendicular to the polymer chain direction. Mobilities up to 0.1 cm(2) V-1 s(-1) are observed parallel to the polymer chain, which is up to 10 times higher than those perpendicular to the polymer chain.}, language = {en} } @article{AlbrechtVandewalTumblestonetal.2014, author = {Albrecht, Steve and Vandewal, Koen and Tumbleston, John R. and Fischer, Florian S. U. and Douglas, Jessica D. and Frechet, Jean M. J. and Ludwigs, Sabine and Ade, Harald W. and Salleo, Alberto and Neher, Dieter}, title = {On the efficiency of charge transfer state splitting in polymer: Fullerene solar cells}, series = {Advanced materials}, volume = {26}, journal = {Advanced materials}, number = {16}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201305283}, pages = {2533 -- 2539}, year = {2014}, language = {en} } @article{SchubertCollinsMangoldetal.2014, author = {Schubert, Marcel and Collins, Brian A. and Mangold, Hannah and Howard, Ian A. and Schindler, Wolfram and Vandewal, Koen and Roland, Steffen and Behrends, Jan and Kraffert, Felix and Steyrleuthner, Robert and Chen, Zhihua and Fostiropoulos, Konstantinos and Bittl, Robert and Salleo, Alberto and Facchetti, Antonio and Laquai, Frederic and Ade, Harald W. and Neher, Dieter}, title = {Correlated donor/acceptor crystal orientation controls photocurrent generation in all-polymer solar cells}, series = {Advanced functional materials}, volume = {24}, journal = {Advanced functional materials}, number = {26}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201304216}, pages = {4068 -- 4081}, year = {2014}, abstract = {New polymers with high electron mobilities have spurred research in organic solar cells using polymeric rather than fullerene acceptors due to their potential of increased diversity, stability, and scalability. However, all-polymer solar cells have struggled to keep up with the steadily increasing power conversion efficiency of polymer: fullerene cells. The lack of knowledge about the dominant recombination process as well as the missing concluding picture on the role of the semi-crystalline microstructure of conjugated polymers in the free charge carrier generation process impede a systematic optimization of all-polymer solar cells. These issues are examined by combining structural and photo-physical characterization on a series of poly(3-hexylthiophene) (donor) and P(NDI2OD-T2) (acceptor) blend devices. These experiments reveal that geminate recombination is the major loss channel for photo-excited charge carriers. Advanced X-ray and electron-based studies reveal the effect of chloronaphthalene co-solvent in reducing domain size, altering domain purity, and reorienting the acceptor polymer crystals to be coincident with those of the donor. This reorientation correlates well with the increased photocurrent from these devices. Thus, effi cient split-up of geminate pairs at polymer/polymer interfaces may necessitate correlated donor/acceptor crystal orientation, which represents an additional requirement compared to the isotropic fullerene acceptors.}, language = {en} } @misc{MouleNeherTurner2014, author = {Moule, Adam J. and Neher, Dieter and Turner, Sarah T.}, title = {P3HT-Based solar cells: structural properties and photovoltaic performance}, series = {Advances in Polymer Science}, volume = {265}, journal = {Advances in Polymer Science}, editor = {Ludwigs, S}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-662-45145-8; 978-3-662-45144-1}, issn = {0065-3195}, doi = {10.1007/12_2014_289}, pages = {181 -- 232}, year = {2014}, abstract = {Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic photovoltaic devices are easy to sketch, but the materials, processing steps, and ways of measuring the properties of the materials are very complicated. It is not trivial to make a systematic measurement that will change the way other research groups think or practice. In approaching this chapter, we thought about what a new researcher would need to know about organic photovoltaic devices and materials in order to have a good start in the subject. Then, we simplified that to focus on what a new researcher would need to know about poly-3-hexylthiophene: phenyl-C61-butyric acid methyl ester blends (P3HT: PCBM) to make research progress with these materials. This chapter is by no means authoritative or a compendium of all things on P3HT: PCBM. We have selected to explain how the sample fabrication techniques lead to control of morphology and structural features and how these morphological features have specific optical and electronic consequences for organic photovoltaic device applications.}, 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{DiPietroVenkateshvaranKlugetal.2014, author = {Di Pietro, Riccardo and Venkateshvaran, Deepak and Klug, Andreas and List-Kratochvil, Emil J. W. and Facchetti, Antonio and Sirringhaus, Henning and Neher, Dieter}, title = {Simultaneous extraction of charge density dependent mobility and variable contact resistance from thin film transistors}, series = {Applied physics letters}, volume = {104}, journal = {Applied physics letters}, number = {19}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.4876057}, pages = {5}, year = {2014}, abstract = {A model for the extraction of the charge density dependent mobility and variable contact resistance in thin film transistors is proposed by performing a full derivation of the current-voltage characteristics both in the linear and saturation regime of operation. The calculated values are validated against the ones obtained from direct experimental methods. This approach allows unambiguous determination of gate voltage dependent contact and channel resistance from the analysis of a single device. It solves the inconsistencies in the commonly accepted mobility extraction methods and provides additional possibilities for the analysis of the injection and transport processes in semiconducting materials. (C) 2014 AIP Publishing LLC.}, language = {en} } @article{SteyrleuthnerDiPietroCollinsetal.2014, author = {Steyrleuthner, Robert and Di Pietro, Riccardo and Collins, Brian A. and Polzer, Frank and Himmelberger, Scott and Schubert, Marcel and Chen, Zhihua and Zhang, Shiming and Salleo, Alberto and Ade, Harald W. and Facchetti, Antonio and Neher, Dieter}, title = {The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer}, series = {Journal of the American Chemical Society}, volume = {136}, journal = {Journal of the American Chemical Society}, number = {11}, publisher = {American Chemical Society}, address = {Washington}, issn = {0002-7863}, doi = {10.1021/ja4118736}, pages = {4245 -- 4256}, year = {2014}, language = {en} } @article{PradhanAlbrechtStilleretal.2014, author = {Pradhan, Basudev and Albrecht, Steve and Stiller, Burkhard and Neher, Dieter}, title = {Inverted organic solar cells comprising low-temperature-processed ZnO films}, series = {Applied physics : A, Materials science \& processing}, volume = {115}, journal = {Applied physics : A, Materials science \& processing}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-014-8373-8}, pages = {365 -- 369}, year = {2014}, abstract = {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.}, language = {en} }