@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} } @article{DiPietroNasrallahCarpenteretal.2016, author = {Di Pietro, Riccardo and Nasrallah, Iyad and Carpenter, Joshua and Gann, Eliot and K{\"o}lln, Lisa Sophie and Thomsen, Lars and Venkateshvaran, Deepak and Sadhanala, Aditya and Chabinyc, Michael and McNeill, Christopher R. and Facchetti, Antonio and Ade, Harald W. and Sirringhaus, Henning and Neher, Dieter}, title = {Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors}, series = {Advanced functional materials}, volume = {26}, journal = {Advanced functional materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201602080}, pages = {8011 -- 8022}, year = {2016}, language = {en} } @article{RolandSchubertCollinsetal.2014, author = {Roland, Steffen and Schubert, Marcel and Collins, Brian A. and Kurpiers, Jona and Chen, Zhihua and Facchetti, Antonio and Ade, Harald W. and Neher, Dieter}, title = {Fullerene-free polymer solar cells with highly reduced bimolecular recombination and field-independent charge carrier generation}, series = {The journal of physical chemistry letters}, volume = {5}, journal = {The journal of physical chemistry letters}, number = {16}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz501506z}, pages = {2815 -- 2822}, year = {2014}, abstract = {Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67\%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors.}, language = {en} } @article{LiAbrechtYangetal.2014, author = {Li, Wentao and Abrecht, Steve and Yang, Liqiang and Roland, Steffen and Tumbleston, John R. and McAfee, Terry and Yan, Liang and Kelly, Mary Allison and Ade, Harald W. and Neher, Dieter and You, Wei}, title = {Mobility-controlled performance of thick solar cells based on fluorinated copolymers}, series = {Journal of the American Chemical Society}, volume = {136}, journal = {Journal of the American Chemical Society}, number = {44}, publisher = {American Chemical Society}, address = {Washington}, issn = {0002-7863}, doi = {10.1021/ja5067724}, pages = {15566 -- 15576}, year = {2014}, abstract = {Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structureproperty relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by mass production technologies.}, language = {en} } @article{GieblerSchulzReicheetal.1999, author = {Giebler, Rainer and Schulz, Burkhard and Reiche, J{\"u}rgen and Brehmer, Ludwig and W{\"u}hn, Mario and W{\"o}ll, Christoph and Smith, Andrew Phillip and Urquhart, Steven G. and Ade, Harald W. and Unger, Wolfgang E. S.}, title = {Near-edge x-ray absorption fine structure spectroscopy on ordered films of an amphiphilic derivate of 2,5- Diphenyl-1,3,4-oxadiazole}, year = {1999}, abstract = {The surfaces of ordered films formed from an amphiphilic derivative of 2,5-diphenyl-1,3,4-oxadiazole by the Langmuir-Blodgett (LB) technique and organic molecular beam deposition (OMBD) were investigated by the use of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. For the assignment of the spectral features of the C, N, and O K- edge absorption spectra, fingerprint spectra of poly(p-phenylene terephthalamide)(Kevlar), poly(ethylene terephthalate), poly(p-phenylene-1,3,4-oxadiazole), and 2,5-di- (pentadecyl)-1,3,4-oxadiazole, which contain related chemical moieties, were recorded. Ab initio molecular orbital calculations, performed with explicit treatment of the core hole, are used to support the spectral interpretations. Angle-resolved NEXAFS spectroscopy at the C, N, and O K-edges suggests a preferentially upright orientation of the oxadiazole derivative in the outermost layer of the films. X-ray specular reflectivity data and molecular modeling results suggest a similar interpretation.}, 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{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{DiPietroErdmannCarpenteretal.2017, author = {Di Pietro, Riccardo and Erdmann, Tim and Carpenter, Joshua H. and Wang, Naixiang and Shivhare, Rishi Ramdas and Formanek, Petr and Heintze, Cornelia and Voit, Brigitte and Neher, Dieter and Ade, Harald W. and Kiriy, Anton}, title = {Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility}, series = {Chemistry of materials : a publication of the American Chemical Society}, volume = {29}, journal = {Chemistry of materials : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.7b04423}, pages = {10220 -- 10232}, year = {2017}, 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} }