@article{PaulkeStranksKniepertetal.2016,
  author    = {Paulke, Andreas and Stranks, Samuel D. and Kniepert, Juliane and Kurpiers, Jona and Wolff, Christian Michael and Sch{\"o}n, Natalie and Snaith, Henry J. and Brenner, Thomas J. K. and Neher, Dieter},
  title     = {Charge carrier recombination dynamics in perovskite and polymer solar cells},
  series = {Applied physics letters},
  volume    = {108},
  journal   = {Applied physics letters},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/1.4944044},
  pages     = {252 -- 262},
  year      = {2016},
  abstract  = {Time-delayed collection field experiments are applied to planar organometal halide perovskite (CH3NH3PbI3) based solar cells to investigate charge carrier recombination in a fully working solar cell at the nanosecond to microsecond time scale. Recombination of mobile (extractable) charges is shown to follow second-order recombination dynamics for all fluences and time scales tested. Most importantly, the bimolecular recombination coefficient is found to be time-dependent, with an initial value of ca. 10(-9) cm(3)/s and a progressive reduction within the first tens of nanoseconds. Comparison to the prototypical organic bulk heterojunction device PTB7:PC71BM yields important differences with regard to the mechanism and time scale of free carrier recombination. (C) 2016 AIP Publishing LLC.},
  language  = {en}
}
@article{LigorioNardiSteyrleuthneretal.2016,
  author    = {Ligorio, G. and Nardi, M. V. and Steyrleuthner, Robert and Ihiawakrim, D. and Crespo-Monteiro, N. and Brinkmann, Martin and Neher, Dieter and Koch, N.},
  title     = {Metal nanoparticle mediated space charge and its optical control in an organic hole-only device},
  series = {Applied physics letters},
  volume    = {108},
  journal   = {Applied physics letters},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/1.4945710},
  pages     = {5},
  year      = {2016},
  abstract  = {We reveal the role of localized space charges in hole-only devices based on an organic semiconductor with embedded metal nanoparticles (MNPs). MNPs act as deep traps for holes and reduce the current density compared to a device without MNPs by a factor of 10(4) due to the build-up of localized space charge. Dynamic MNPs charged neutrality can be realized during operation by electron transfer from excitons created in the organic matrix, enabling light sensing independent of device bias. In contrast to the previous speculations, electrical bistability in such devices was not observed. (C) 2016 AIP Publishing LLC.},
  language  = {en}
}
@article{NeherKniepertElimelechetal.2016,
  author    = {Neher, Dieter and Kniepert, Juliane and Elimelech, Arik and Koster, L. Jan Anton},
  title     = {A New Figure of Merit for Organic Solar Cells with Transport-limited Photocurrents},
  series = {Scientific reports},
  volume    = {6},
  journal   = {Scientific reports},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2045-2322},
  doi       = {10.1038/srep24861},
  pages     = {E2348 -- E2349},
  year      = {2016},
  abstract  = {Compared to their inorganic counterparts, organic semiconductors suffer from relatively low charge carrier mobilities. Therefore, expressions derived for inorganic solar cells to correlate characteristic performance parameters to material properties are prone to fail when applied to organic devices. This is especially true for the classical Shockley-equation commonly used to describe current-voltage (JV)-curves, as it assumes a high electrical conductivity of the charge transporting material. Here, an analytical expression for the JV-curves of organic solar cells is derived based on a previously published analytical model. This expression, bearing a similar functional dependence as the Shockley-equation, delivers a new figure of merit a to express the balance between free charge recombination and extraction in low mobility photoactive materials. This figure of merit is shown to determine critical device parameters such as the apparent series resistance and the fill factor.},
  language  = {en}
}
@article{KurpiersNeher2016,
  author    = {Kurpiers, Jona and Neher, Dieter},
  title     = {Dispersive Non-Geminate Recombination in an Amorphous Polymer: Fullerene Blend},
  series = {Scientific reports},
  volume    = {6},
  journal   = {Scientific reports},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2045-2322},
  doi       = {10.1038/srep26832},
  pages     = {10},
  year      = {2016},
  abstract  = {Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer: fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions.},
  language  = {en}
}
@article{MuellerNanovaGlaseretal.2016,
  author    = {Mueller, Lars and Nanova, Diana and Glaser, Tobias and Beck, Sebastian and Pucci, Annemarie and Kast, Anne K. and Schroeder, Rasmus R. and Mankel, Eric and Pingel, Patrick and Neher, Dieter and Kowalsky, Wolfgang and Lovrincic, Robert},
  title     = {Charge-Transfer-Solvent Interaction Predefines Doping Efficiency in p-Doped P3HT Films},
  series = {Chemistry of materials : a publication of the American Chemical Society},
  volume    = {28},
  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.6b01629},
  pages     = {4432 -- 4439},
  year      = {2016},
  abstract  = {Efficient electrical doping of organic semiconductors is a necessary prerequisite for the fabrication of high performance organic electronic devices. In this work, we study p-type doping of poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) spin-cast from two different solvents. Using electron diffraction, we find strong dopant-induced pi-pi-stacking for films from the solvent chloroform, but not from chlorobenzene. This image is confirmed and expanded by the analysis of vibrational features of P3HT and polaron absorptions using optical spectroscopy. Here, a red-shifted polaron absorption is found in doped films from chloroform, caused by a higher conjugation length of the polymer backbone. These differences result in a higher conductivity of films from chloroform. We use optical spectroscopy on the corresponding blend solutions to shed light on the origin of this effect and propose a model to explain why solutions of doped P3HT reveal more aggregation of charged molecules in chlorobenzene, whereas more order is finally observed in dried films from chloroform. Our study emphasizes the importance of solvent parameters exceeding the bare solubility of pure dopant and host material for the preparation of highly conductive doped films.},
  language  = {en}
}
@article{ZersonNeumannSteyrleuthneretal.2016,
  author    = {Zerson, Mario and Neumann, Martin and Steyrleuthner, Robert and Neher, Dieter and Magerle, Robert},
  title     = {Surface Structure of Semicrystalline Naphthalene Diimide-Bithiophene Copolymer Films Studied with Atomic Force Microscopy},
  series = {Macromolecules : a publication of the American Chemical Society},
  volume    = {49},
  journal   = {Macromolecules : a publication of the American Chemical Society},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0024-9297},
  doi       = {10.1021/acs.macromol.6b00988},
  pages     = {6549 -- 6557},
  year      = {2016},
  language  = {en}
}
@article{PingelArvindKoellnetal.2016,
  author    = {Pingel, Patrick and Arvind, Malavika and K{\"o}lln, Lisa and Steyrleuthner, Robert and Kraffert, Felix and Behrends, Jan and Janietz, Silvia and Neher, Dieter},
  title     = {p-Type Doping of Poly(3-hexylthiophene) with the Strong Lewis Acid Tris(pentafluorophenyl)borane},
  series = {Advanced electronic materials},
  volume    = {2},
  journal   = {Advanced electronic materials},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {2199-160X},
  doi       = {10.1002/aelm.201600204},
  pages     = {7},
  year      = {2016},
  abstract  = {State-of-the-art p-type doping of organic semiconductors is usually achieved by employing strong -electron acceptors, a prominent example being tetrafluorotetracyanoquinodimethane (F(4)TCNQ). Here, doping of the semiconducting model polymer poly(3-hexylthiophene), P3HT, using the strong Lewis acid tris(pentafluorophenyl)borane (BCF) as a dopant, is investigated by admittance, conductivity, and electron paramagnetic resonance measurements. The electrical characteristics of BCF- and F(4)TCNQ-doped P3HT layers are shown to be very similar in terms of the mobile hole density and the doping efficiency. Roughly 18\% of the employed dopants create mobile holes in either F-4 TCNQ- or BCF-doped P3HT, while the majority of doping-induced holes remain strongly Coulomb-bound to the dopant anions. Despite similar hole densities, conductivity and hole mobility are higher in BCF-doped P3HT layers than in F(4)TCNQ-doped samples. This and the good solubility in many organic solvents render BCF very useful for p-type doping of organic semiconductors.},
  language  = {en}
}
@article{LuDiPietroKoellnetal.2016,
  author    = {Lu, Guanghao and Di Pietro, Riccardo and K{\"o}lln, Lisa Sophie and Nasrallah, Iyad and Zhou, Ling and Mollinger, Sonya and Himmelberger, Scott and Koch, Norbert and Salleo, Alberto and Neher, Dieter},
  title     = {Dual-Characteristic Transistors Based on Semiconducting Polymer Blends},
  series = {Advanced electronic materials},
  volume    = {2},
  journal   = {Advanced electronic materials},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {2199-160X},
  doi       = {10.1002/aelm.201600267},
  pages     = {2344 -- 2351},
  year      = {2016},
  abstract  = {A dual-characteristic polymer field-effect transistor has markedly different characteristics in low and high voltage operations. In the low-voltage range (<5 V) it shows sharp subthreshold slopes (0.3-0.4 V dec\&\#8722;1), using which a low-voltage inverter with gain 8 is realized, while high-voltage (>5 V) induces symmetric current with regard to drain and gate voltages, leading to discrete differential (trans) conductances.},
  language  = {en}
}
@article{HahnTscheuschnerSalleretal.2016,
  author    = {Hahn, Tobias and Tscheuschner, Steffen and Saller, Christina and Strohriegl, Peter and Boregowda, Puttaraju and Mukhopadhyay, Tushita and Patil, Satish and Neher, Dieter and B{\"a}ssler, Heinz and K{\"o}hler, Anna},
  title     = {Role of Intrinsic Photogeneration in Single Layer and Bilayer Solar Cells with C-60 and PCBM},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {120},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.6b08471},
  pages     = {25083 -- 25091},
  year      = {2016},
  language  = {en}
}
@article{StolterfohtArminPhilippaetal.2016,
  author    = {Stolterfoht, Martin and Armin, Ardalan and Philippa, Bronson and Neher, Dieter},
  title     = {The Role of Space Charge Effects on the Competition between Recombination and Extraction in Solar Cells with Low-Mobility Photoactive Layers},
  series = {The journal of physical chemistry letters},
  volume    = {7},
  journal   = {The journal of physical chemistry letters},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1948-7185},
  doi       = {10.1021/acs.jpclett.6b02106},
  pages     = {4716 -- 4721},
  year      = {2016},
  abstract  = {The competition between charge extraction and nongeminate recombination critically determines the current-voltage characteristics of organic solar cells (OSCs) and their fill factor. As a measure of this competition, several figures of merit (FOMs) have been put forward; however, the impact of space charge effects has been either neglected, or not specifically addressed. Here we revisit recently reported FOMs and discuss the role of space charge effects on the interplay between recombination and extraction. We find that space charge effects are the primary cause for the onset of recombination in so-called non-Langevin systems, which also depends on the slower carrier mobility and recombination coefficient. The conclusions are supported with numerical calculations and experimental results of 25 different donor/acceptor OSCs with different charge transport parameters, active layer thicknesses or composition ratios. The findings represent a conclusive understanding of bimolecular recombination for drift dominated photocurrents and allow one to minimize these losses for given device parameters.},
  language  = {en}
}