TY - JOUR A1 - Blakesley, James C. A1 - Schubert, Marcel A1 - Steyrleuthner, Robert A1 - Chen, Zhihua A1 - Facchetti, Antonio A1 - Neher, Dieter T1 - Time-of-flight measurements and vertical transport in a high electron-mobility polymer JF - Applied physics letters N2 - We investigate charge transport in a high-electron mobility polymer, poly(N, N-bis 2-octyldodecyl-naphthalene-1,4,5,8-bis dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) [P(NDI2OD-T2), Polyera ActivInk (TM) N2200]. Time-of-flight measurements reveal electron mobilities approaching those measured in field-effect transistors, the highest ever recorded in a conjugated polymer using this technique. The modest temperature dependence and weak dispersion of the transients indicate low energetic disorder in this material. Steady-state electron-only current measurements reveal a barrier to injection of about 300 meV. We propose that this barrier is located within the P(NDI2OD-T2) film and arises from molecular orientation effects. Y1 - 2011 U6 - https://doi.org/10.1063/1.3657827 SN - 0003-6951 VL - 99 IS - 18 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Steyrleuthner, Robert A1 - Di Pietro, Riccardo A1 - Collins, Brian A. A1 - Polzer, Frank A1 - Himmelberger, Scott A1 - Schubert, Marcel A1 - Chen, Zhihua A1 - Zhang, Shiming A1 - Salleo, Alberto A1 - Ade, Harald W. A1 - Facchetti, Antonio A1 - Neher, Dieter T1 - The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer JF - Journal of the American Chemical Society Y1 - 2014 U6 - https://doi.org/10.1021/ja4118736 SN - 0002-7863 VL - 136 IS - 11 SP - 4245 EP - 4256 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sini, Gjergji A1 - Schubert, Marcel A1 - Risko, Chad A1 - Roland, Steffen A1 - Lee, Olivia P. A1 - Chen, Zhihua A1 - Richter, Thomas V. A1 - Dolfen, Daniel A1 - Coropceanu, Veaceslav A1 - Ludwigs, Sabine A1 - Scherf, Ullrich A1 - Facchetti, Antonio A1 - Frechet, Jean M. J. A1 - Neher, Dieter T1 - On the Molecular Origin of Charge Separation at the Donor-Acceptor Interface JF - Advanced energy materials N2 - Fullerene-based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor-acceptor (D-A) interface. Model systems comprised of polythiophene-based donor and rylene diimide-based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct-contact intermolecular polarization play in establishing a driving force ( energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules. KW - donor-acceptor interfaces KW - energy gradients KW - geometrical deformations KW - nonfullerene acceptors KW - organic photovoltaics KW - photocurrent generation KW - polymer solar cells Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201702232 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 12 PB - Wiley-VCH CY - Weinheim 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 - Roland, Steffen A1 - Schubert, Marcel A1 - Collins, Brian A. A1 - Kurpiers, Jona A1 - Chen, Zhihua A1 - Facchetti, Antonio A1 - Ade, Harald W. A1 - Neher, Dieter T1 - Fullerene-free polymer solar cells with highly reduced bimolecular recombination and field-independent charge carrier generation JF - The journal of physical chemistry letters N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1021/jz501506z SN - 1948-7185 VL - 5 IS - 16 SP - 2815 EP - 2822 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Rivnay, Jonathan A1 - Steyrleuthner, Robert A1 - Jimison, Leslie H. A1 - Casadei, Alberto A1 - Chen, Zhihua A1 - Toney, Michael F. A1 - Facchetti, Antonio A1 - Neher, Dieter A1 - Salleo, Alberto T1 - Drastic control of texture in a high performance n-Type polymeric semiconductor and implications for charge transport JF - Macromolecules : a publication of the American Chemical Society N2 - Control of crystallographic texture from mostly face-on to edge-on is observed for the film morphology of the n-type semicrystalline polymer [N,N-9-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diy1]alt-5,59-(2,29-bithiophene)}, P(NDI2OD-T2), when annealing the film to the polymer melting point followed by slow cooling to ambient temperature. A variety of X-ray diffraction analyses, including pole figure construction and Fourier transform peak shape deconvolution, are employed to quantify the texture change, relative degree of crystallinity and lattice order. We find that annealing the polymer film to the melt leads to a shift from 77.5% face-on to 94.6% edge-on lamellar texture as well as to a 2-fold increase in crystallinity and a 40% decrease in intracrystallite cumulative disorder. The texture change results in a significant drop in the electron-only diode current density through the film thickness upon melt annealing while little change is observed in the in-plane transport of bottom gated thin film transistors. This suggests that the texture change is prevalent in the film interior and that either the (bottom) surface structure is different from the interior structure or the intracrystalline order and texture play a secondary role in transistor transport for this material. Y1 - 2011 U6 - https://doi.org/10.1021/ma200864s SN - 0024-9297 VL - 44 IS - 13 SP - 5246 EP - 5255 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schubert, Marcel A1 - Collins, Brian A. A1 - Mangold, Hannah A1 - Howard, Ian A. A1 - Schindler, Wolfram A1 - Vandewal, Koen A1 - Roland, Steffen A1 - Behrends, Jan A1 - Kraffert, Felix A1 - Steyrleuthner, Robert A1 - Chen, Zhihua A1 - Fostiropoulos, Konstantinos A1 - Bittl, Robert A1 - Salleo, Alberto A1 - Facchetti, Antonio A1 - Laquai, Frederic A1 - Ade, Harald W. A1 - Neher, Dieter T1 - Correlated donor/acceptor crystal orientation controls photocurrent generation in all-polymer solar cells JF - Advanced functional materials N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1002/adfm.201304216 SN - 1616-301X SN - 1616-3028 VL - 24 IS - 26 SP - 4068 EP - 4081 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Steyrleuthner, Robert A1 - Schubert, Marcel A1 - Jaiser, Frank A1 - Blakesley, James C. A1 - Chen, Zhihua A1 - Facchetti, Antonio A1 - Neher, Dieter T1 - Bulk electron transport and charge injection in a high mobility n-type semiconducting polymer N2 - Bulk electron transport in a high mobility n-type polymer is studied by time-of-flight photocurrent measurements and electron-only devices. Bulk electron mobilities of similar to 5 x 10(-3) cm(2)/Vs are obtained. The analysis of the electron currents suggests the presence of an injection barrier for all conventionally used low workfunction cathodes. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/10008336 U6 - https://doi.org/10.1002/adma.201000232 SN - 0935-9648 ER - TY - JOUR A1 - Steyrleuthner, Robert A1 - Schubert, Marcel A1 - Howard, Ian A1 - Klaumünzer, Bastian A1 - Schilling, Kristian A1 - Chen, Zhihua A1 - Saalfrank, Peter A1 - Laquai, Frederic A1 - Facchetti, Antonio A1 - Neher, Dieter T1 - Aggregation in a high-mobility n-type low-bandgap copolymer with implications on semicrystalline morphology JF - Journal of the American Chemical Society N2 - We explore the photophysics of P(NDI2OD-T2), a high-mobility and air-stable n-type donor/acceptor polymer. Detailed steady-state UV-vis and photoluminescence (PL) measurements on solutions of P(NDI2OD-T2) reveal distinct signatures of aggregation. By performing quantum chemical calculations, we can assign these spectral features to unaggregated and stacked polymer chains. NMR measurements independently confirm the aggregation phenomena of P(NDI2OD-T2) in solution. The detailed analysis of the optical spectra shows that aggregation is a two-step process with different types of aggregates, which we confirm by time-dependent PL measurements. Analytical ultracentrifugation measurements suggest that aggregation takes place within the single polymer chain upon coiling. By transferring these results to thin P(NDI2OD-T2) films, we can conclude that film formation is mainly governed by the chain collapse, leading in general to a high aggregate content of similar to 45%. This process also inhibits the formation of amorphous and disordered P(NDI2OD-T2) films. Y1 - 2012 U6 - https://doi.org/10.1021/ja306844f SN - 0002-7863 VL - 134 IS - 44 SP - 18303 EP - 18317 PB - American Chemical Society CY - Washington ER -