TY  - JOUR
A1  - Ran, Niva A.
A1  - Roland, Steffen
A1  - Love, John A.
A1  - Savikhin, Victoria
A1  - Takacs, Christopher J.
A1  - Fu, Yao-Tsung
A1  - Li, Hong
A1  - Coropceanu, Veaceslav
A1  - Liu, Xiaofeng
A1  - Bredas, Jean-Luc
A1  - Bazan, Guillermo C.
A1  - Toney, Michael F.
A1  - Neher, Dieter
A1  - Thuc-Quyen Nguyen, 
T1  - Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency
JF  - Nature Communications
N2  - A long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics-however, the results have important implications on the operation of all optoelectronic devices with donor/ acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting in larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.
Y1  - 2017
U6  - https://doi.org/10.1038/s41467-017-00107-4
SN  - 2041-1723
VL  - 8
PB  - Nature Publ. Group
CY  - London
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  - 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  - Ilnytskyi, Jaroslav M.
A1  - Neher, Dieter
A1  - Saphiannikova, Marina
T1  - Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture molecular dynamics study
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases.
KW  - amorphous state
KW  - light polarisation
KW  - liquid crystal polymers
KW  - molecular dynamics method
KW  - optical hole burning
KW  - photochemistry
Y1  - 2011
U6  - https://doi.org/10.1063/1.3614499
SN  - 0021-9606
VL  - 135
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Kniepert, Juliane
A1  - Schubert, Marcel
A1  - Blakesley, James C.
A1  - Neher, Dieter
T1  - Photogeneration and recombination in P3HT/PCBM solar cells probed by time-delayed collection field experiments
JF  - The journal of physical chemistry letters
N2  - Time-delayed collection field (TDCF) experiments are performed on bulk heterojunction solar cells comprised of a blend of poly(3-hexylthiophene) and [6,6]-phenyl C-71 butyric acid methyl ester. TDCF is analogous to a pump-probe experiment using optical excitation and an electrical probe with a resolution of < 100 ns. The number of free charge carriers extracted after a short delay is found to be independent of the electric field during illumination. Also, experiments performed with a variable delay between the optical excitation and the electrical probe do not reveal any evidence for the generation of charge via field-assisted dissociation of bound long-lived polaron pairs. Photocurrent transients are well fitted by computational drift diffusion simulations with only direct generation of free charge carriers. With increasing delay times between pump and probe, two loss mechanisms are identified; first, charge-carriers are swept out of the device by the internal electric field, and second, bimolecular recombination of the remaining carriers takes place with a reduced recombination coefficient.
Y1  - 2011
U6  - https://doi.org/10.1021/jz200155b
SN  - 1948-7185
VL  - 2
IS  - 7
SP  - 700
EP  - 705
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kuehn, Sergei
A1  - Pingel, Patrick
A1  - Breusing, Markus
A1  - Fischer, Thomas
A1  - Stumpe, Joachim
A1  - Neher, Dieter
A1  - Elsaesser, Thomas
T1  - High-Resolution Near-Field Optical Investigation of Crystalline Domains in Oligomeric PQT-12 Thin Films
JF  - Advanced functional materials
N2  - The structure and morphology on different length scales dictate both the electrical and optical properties of organic semiconductor thin films. Using a combination of spectroscopic methods, including scanning near-field optical microscopy, we study the domain structure and packing quality of highly crystalline thin films of oligomeric PQT-12 with 100 nanometer spatial resolution. The pronounced optical anisotropy of these layers measured by polarized light microscopy facilitates the identification of regions with uniform molecular orientation. We find that a hierarchical order on three different length scales exists in these layers, made up of distinct well-ordered dichroic areas at the ten-micrometer-scale, which are sub-divided into domains with different molecular in-plane orientation. These serve as a template for the formation of smaller needle-like crystallites at the layer surface. A high degree of crystalline order is believed to be the cause of the rather high field-effect mobility of these layers of 10(-3) cm 2 V(-1) s(-1), whereas it is limited by the presence of domain boundaries at macroscopic distances.
Y1  - 2011
U6  - https://doi.org/10.1002/adfm.201001978
SN  - 1616-301X
VL  - 21
IS  - 5
SP  - 860
EP  - 868
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Blakesley, James C.
A1  - Neher, Dieter
T1  - Relationship between energetic disorder and open-circuit voltage in bulk heterojunction organic solar cells
JF  - Physical review : B, Condensed matter and materials physics
N2  - We simulate organic bulk heterojunction solar cells. The effects of energetic disorder are incorporated through a Gaussian or exponential model of density of states. Analytical models of open-circuit voltage (V(OC)) are derived from the splitting of quasi-Fermi potentials. Their predictions are backed up by more complex numerical device simulations including effects such as carrier-density-dependent charge-carrier mobilities. It is predicted that the V(OC) depends on: (1) the donor-acceptor energy gap; (2) charge-carrier recombination rates; (3) illumination intensity; (4) the contact work functions (if not in the pinning regime); and (5) the amount of energetic disorder. A large degree of energetic disorder, or a high density of traps, is found to cause significant reductions in V(OC). This can explain why V(OC) is often less than expected in real devices. Energetic disorder also explains the nonideal temperature and intensity dependence of V(OC) and the superbimolecular recombination rates observed in many real bulk heterojunction solar cells.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevB.84.075210
SN  - 1098-0121
VL  - 84
IS  - 7
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Lange, Ilja
A1  - Blakesley, James C.
A1  - Frisch, Johannes
A1  - Vollmer, Antje
A1  - Koch, Norbert
A1  - Neher, Dieter
T1  - Band bending in conjugated polymer layers
JF  - Physical review letters
N2  - We use the Kelvin probe method to study the energy-level alignment of four conjugated polymers deposited on various electrodes. Band bending is observed in all polymers when the substrate work function exceeds critical values. Through modeling, we show that the band bending is explained by charge transfer from the electrodes into a small density of states that extends several hundred meV into the band gap. The energetic spread of these states is correlated with charge-carrier mobilities, suggesting that the same states also govern charge transport in the bulk of these polymers.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevLett.106.216402
SN  - 0031-9007
VL  - 106
IS  - 21
PB  - American Physical Society
CY  - College Park
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  - Moule, Adam J.
A1  - Neher, Dieter
A1  - Turner, Sarah T.
ED  - Ludwigs, S
T1  - P3HT-Based solar cells: structural properties and photovoltaic performance
JF  - Advances in Polymer Science
JF  - Advances in Polymer Science
N2  - 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.
KW  - Free carrier generation
KW  - Non-geminate recombination
KW  - Organic solar cells
Y1  - 2014
SN  - 978-3-662-45145-8; 978-3-662-45144-1
U6  - https://doi.org/10.1007/12_2014_289
SN  - 0065-3195
VL  - 265
SP  - 181
EP  - 232
PB  - Springer
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Albrecht, Steve
A1  - Tumbleston, John R.
A1  - Janietz, Silvia
A1  - Dumsch, Ines
A1  - Allard, Sybille
A1  - Scherf, Ullrich
A1  - Ade, Harald W.
A1  - Neher, Dieter
T1  - Quantifying charge extraction in organic solar cells: The case of fluorinated PCPDTBT
JF  - The journal of physical chemistry letters
N2  - 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.
Y1  - 2014
U6  - https://doi.org/10.1021/jz500457b
SN  - 1948-7185
VL  - 5
IS  - 7
SP  - 1131
EP  - 1138
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Di Pietro, Riccardo
A1  - Venkateshvaran, Deepak
A1  - Klug, Andreas
A1  - List-Kratochvil, Emil J. W.
A1  - Facchetti, Antonio
A1  - Sirringhaus, Henning
A1  - Neher, Dieter
T1  - Simultaneous extraction of charge density dependent mobility and variable contact resistance from thin film transistors
JF  - Applied physics letters
N2  - 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.
Y1  - 2014
U6  - https://doi.org/10.1063/1.4876057
SN  - 0003-6951
SN  - 1077-3118
VL  - 104
IS  - 19
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  - 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  - Foertig, Alexander
A1  - Kniepert, Juliane
A1  - Gluecker, Markus
A1  - Brenner, Thomas J. K.
A1  - Dyakonov, Vladimir
A1  - Neher, Dieter
A1  - Deibel, Carsten
T1  - Nongeminate and geminate recombination in PTB7: PCBM solar cells
JF  - Advanced functional materials
KW  - organic semiconductors
KW  - organic solar cells
KW  - conjugated polymers
KW  - charge carrier recombination
Y1  - 2014
U6  - https://doi.org/10.1002/adfm.201302134
SN  - 1616-301X
SN  - 1616-3028
VL  - 24
IS  - 9
SP  - 1306
EP  - 1311
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Piersimoni, Fortunato
A1  - Schlesinger, Raphael
A1  - Benduhn, Johannes
A1  - Spoltore, Donato
A1  - Reiter, Sina
A1  - Lange, Ilja
A1  - Koch, Norbert
A1  - Vandewal, Koen
A1  - Neher, Dieter
T1  - Charge Transfer Absorption and Emission at ZnO/Organic Interfaces
JF  - The journal of physical chemistry letters
N2  - We investigate hybrid charge transfer states (HCTS) at the planar interface between a-NPD and ZnO by spectrally resolved electroluminescence (EL) and external quantum efficiency (EQE) measurements. Radiative decay of HCTSs is proven by distinct emission peaks in the EL spectra of such bilayer devices in the NIR at energies well below the bulk a-NPD or ZnO emission. The EQE spectra display low energy contributions clearly red-shifted with respect to the a-NPD photocurrent and partially overlapping with the EL emission. Tuning of the energy gap between the ZnO conduction band and a-NPD HOMO level (E-int) was achieved by modifying the ZnO surface with self-assembled monolayers based on phosphonic acids. We find a linear dependence of the peak position of the NIR EL on E-int, which unambiguously attributes the origin of this emission to radiative recombination between an electron on the ZnO and a hole on a-NPD. In accordance with this interpretation, we find a strictly linear relation between the open-circuit voltage and the energy of the charge state for such hybrid organicinorganic interfaces.
Y1  - 2015
U6  - https://doi.org/10.1021/jz502657z
SN  - 1948-7185
VL  - 6
IS  - 3
SP  - 500
EP  - 504
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Lange, Ilja
A1  - Reiter, Sina
A1  - Kniepert, Juliane
A1  - Piersimoni, Fortunato
A1  - Paetzel, Michael
A1  - Hildebrandt, Jana
A1  - Brenner, Thomas J. K.
A1  - Hecht, Stefan
A1  - Neher, Dieter
T1  - Zinc oxide modified with benzylphosphonic acids as transparent electrodes in regular and inverted organic solar cell structures
JF  - Applied physics letters
N2  - An approach is presented to modify the work function of solution-processed sol-gel derived zinc oxide (ZnO) over an exceptionally wide range of more than 2.3 eV. This approach relies on the formation of dense and homogeneous self-assembled monolayers based on phosphonic acids with different dipole moments. This allows us to apply ZnO as charge selective bottom electrodes in either regular or inverted solar cell structures, using poly(3-hexylthiophene): phenyl-C71-butyric acid methyl ester as the active layer. These devices compete with or even surpass the performance of the reference on indium tin oxide/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Our findings highlight the potential of properly modified ZnO as electron or hole extracting electrodes in hybrid optoelectronic devices. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4916182
SN  - 0003-6951
SN  - 1077-3118
VL  - 106
IS  - 11
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Roland, Steffen
A1  - Neubert, Sebastian
A1  - Albrecht, Steve
A1  - Stannowski, Bernd
A1  - Seger, Mark
A1  - Facchetti, Antonio
A1  - Schlatmann, Rutger
A1  - Rech, Bernd
A1  - Neher, Dieter
T1  - Hybrid Organic/Inorganic Thin-Film Multijunction Solar Cells Exceeding 11% Power Conversion Efficiency
JF  - Advanced materials
N2  - Hybrid multijunction solar cells comprising hydrogenated amorphous silicon and an organic bulk heterojunction are presented, reaching 11.7% power conversion efficiency. The benefits of merging inorganic and organic subcells are pointed out, the optimization of the cells, including optical modeling predictions and tuning of the recombination contact are described, and an outlook of this technique is given.
Y1  - 2015
U6  - https://doi.org/10.1002/adma.201404698
SN  - 0935-9648
SN  - 1521-4095
VL  - 27
IS  - 7
SP  - 1262
EP  - 1267
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kegelmann, Lukas
A1  - Wolff, Christian Michael
A1  - Awino, Celline
A1  - Lang, Felix
A1  - Unger, Eva L.
A1  - Korte, Lars
A1  - Dittrich, Thomas
A1  - Neher, Dieter
A1  - Rech, Bernd
A1  - Albrecht, Steve
T1  - It Takes Two to Tango-Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis
JF  - ACS applied materials & interfaces
N2  - Solar cells made from inorganic organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 degrees C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C-60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop, the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The herein demonstrated improvements of multilayer selective contacts may serve as a general design guideline for perovskite solar cells.
KW  - perovskite solar cell
KW  - electron contact
KW  - double-layer
KW  - regular planar architecture
KW  - hysteresis
KW  - fullerene
KW  - metal oxide
Y1  - 2017
U6  - https://doi.org/10.1021/acsami.7b00900
SN  - 1944-8244
VL  - 9
SP  - 17246
EP  - 17256
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Qiong
A1  - Mosconi, Edoardo
A1  - Wolff, Christian Michael
A1  - Li, Junming
A1  - Neher, Dieter
A1  - De Angelis, Filippo
A1  - Suranna, Gian Paolo
A1  - Grisorio, Roberto
A1  - Abate, Antonio
T1  - Rationalizing the molecular design of hole-selective contacts to improve charge extraction in Perovskite solar cells
JF  - dvanced energy materials
N2  - Two new hole selective materials (HSMs) based on dangling methylsulfanyl groups connected to the C-9 position of the fluorene core are synthesized and applied in perovskite solar cells. Being structurally similar to a half of Spiro-OMeTAD molecule, these HSMs (referred as FS and DFS) share similar redox potentials but are endowed with slightly higher hole mobility, due to the planarity and large extension of their structure. Competitive power conversion efficiency (up to 18.6%) is achieved by using the new HSMs in suitable perovskite solar cells. Time-resolved photoluminescence decay measurements and electrochemical impedance spectroscopy show more efficient charge extraction at the HSM/perovskite interface with respect to Spiro-OMeTAD, which is reflected in higher photocurrents exhibited by DFS/FS-integrated perovskite solar cells. Density functional theory simulations reveal that the interactions of methylammonium with methylsulfanyl groups in DFS/FS strengthen their electrostatic attraction with the perovskite surface, providing an additional path for hole extraction compared to the sole presence of methoxy groups in Spiro-OMeTAD. Importantly, the low-cost synthesis of FS makes it significantly attractive for the future commercialization of perovskite solar cells.
KW  - hole extraction
KW  - hole selective materials
KW  - perovskite solar cells
KW  - sulfur
KW  - triple-cation perovskite
Y1  - 2019
U6  - https://doi.org/10.1002/aenm.201900990
SN  - 1614-6832
SN  - 1614-6840
VL  - 9
IS  - 28
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Deschler, Felix
A1  - Neher, Dieter
A1  - Schmidt-Mende, Lukas
T1  - Perovskite semiconductors for next generation optoelectronic applications
JF  - APL Materials
Y1  - 2019
U6  - https://doi.org/10.1063/1.5119744
SN  - 2166-532X
VL  - 7
IS  - 8
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Hörmann, Ulrich
A1  - Zeiske, Stefan
A1  - Park, Soohyung
A1  - Schultz, Thorsten
A1  - Kickhoefel, Sebastian
A1  - Scherf, Ullrich
A1  - Blumstengel, Sylke
A1  - Koch, Norbert
A1  - Neher, Dieter
T1  - Direct observation of state-filling at hybrid tin oxide/organic interfaces
JF  - Applied physics letters
N2  - Electroluminescence (EL) spectra of hybrid charge transfer states at metal oxide/organic type-II heterojunctions exhibit bias-induced spectral shifts. The reasons for this phenomenon have been discussed controversially and arguments for either electric field-induced effects or the filling of trap states at the oxide surface have been put forward. Here, we combine the results of EL and photovoltaic measurements to eliminate the unavoidable effect of the series resistance of inorganic and organic components on the total voltage drop across the hybrid device. For SnOx combined with the conjugated polymer [ladder type poly-(para-phenylene)], we find a one-to-one correspondence between the blue-shift of the EL peak and the increase of the quasi-Fermi level splitting at the hybrid heterojunction, which we unambiguously assign to state filling. Our data are resembled best by a model considering the combination of an exponential density of states with a doped semiconductor. Published under license by AIP Publishing.
Y1  - 2019
U6  - https://doi.org/10.1063/1.5082704
SN  - 0003-6951
SN  - 1077-3118
VL  - 114
IS  - 18
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - GEN
A1  - Phuong, Le Quang
A1  - Hosseini, Seyed Mehrdad
A1  - Sandberg, Oskar J.
A1  - Zou, Yingping
A1  - Woo, Han Young
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1384 
KW  - nonfullerene acceptors
KW  - organic solar cells
KW  - quasi-Fermi level
KW  - splitting
KW  - quasi-steady-state photoinduced absorptions
KW  - surface
KW  - recombinations
KW  - voltage losses
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-570018
SN  - 1866-8372
IS  - 1
ER  - 
TY  - JOUR
A1  - Jošt, Marko
A1  - Albrecht, Steve
A1  - Kegelmann, Lukas
A1  - Wolff, Christian Michael
A1  - Lang, Felix
A1  - Lipovšek, Benjamin
A1  - Krč, Janez
A1  - Korte, Lars
A1  - Neher, Dieter
A1  - Rech, Bernd
A1  - Topič, Marko
T1  - Efficient light management by textured nanoimprinted layers for perovskite solar cells
JF  - ACS photonics
N2  - Inorganic-organic perovskites like methylammonium-lead-iodide have proven to be an effective class of 17 materials for fabricating efficient solar cells. To improve their performance, light management techniques using textured surfaces, similar to those used in established solar cell technologies, should be considered. Here, we apply a light management foil created by UV nanoimprint lithography on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3% efficiency. The obtained 1 mA cm(-2) increase in the short-circuit current density translates to a relative improvement in cell performance of 5%, which results in a power conversion efficiency of 17.1%. Optical 3D simulations based on experimentally obtained parameters were used to support the experimental findings. A good match between the simulated and experimental data was obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current density of up to 10% is possible for large-area devices. Therefore, our results present the potential of light management foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in the field of perovskite solar cells.
KW  - perovskite solar cells
KW  - antireflection
KW  - light management
KW  - UV nanoimprint lithography
KW  - optical simulations
Y1  - 2017
U6  - https://doi.org/10.1021/acsphotonics.7b00138
SN  - 2330-4022
VL  - 4
SP  - 1232
EP  - 1239
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Vandewal, Koen
A1  - Benduhn, Johannes
A1  - Schellhammer, Karl Sebastian
A1  - Vangerven, Tim
A1  - Rückert, Janna E.
A1  - Piersimoni, Fortunato
A1  - Scholz, Reinhard
A1  - Zeika, Olaf
A1  - Fan, Yeli
A1  - Barlow, Stephen
A1  - Neher, Dieter
A1  - Marder, Seth R.
A1  - Manca, Jean
A1  - Spoltore, Donato
A1  - Cuniberti, Gianaurelio
A1  - Ortmann, Frank
T1  - Absorption Tails of Donor
BT  - C-60 Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation
JF  - Journal of the American Chemical Society
N2  - In disordered organic semiconductors, the transfer of a rather localized charge carrier from one site to another triggers a deformation of the molecular structure quantified by the intramolecular relaxation energy. A similar structural relaxation occurs upon population of intermolecular charge-transfer (CT) states formed at organic electron donor (D)-acceptor (A) interfaces. Weak CT absorption bands for D A complexes occur at photon energies below the optical gaps of both the donors and the C-60 acceptor as a result of optical transitions from the neutral ground state to the ionic CT state. In this work, we show that temperature-activated intramolecular vibrations of the ground state play a major role in determining the line shape of such CT absorption bands. This allows us to extract values for the relaxation energy related to the geometry change from neutral to ionic CT complexes. Experimental values for the relaxation energies of 20 D:C-60 CT complexes correlate with values calculated within density functional theory. These results provide an experimental method for determining the polaron relaxation energy in solid-state organic D-A blends and show the importance of a reduced relaxation energy, which we introduce to characterize thermally activated CT processes.
Y1  - 2017
U6  - https://doi.org/10.1021/jacs.6b12857
SN  - 0002-7863
VL  - 139
IS  - 4
SP  - 1699
EP  - 1704
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Tait, Claudia E.
A1  - Reckwitz, Anna
A1  - Arvind, Malavika
A1  - Neher, Dieter
A1  - Bittl, Robert
A1  - Behrends, Jan
T1  - Spin-spin interactions and spin delocalisation in a doped organic semiconductor probed by EPR spectroscopy
JF  - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies
N2  - The enhancement and control of the electrical conductivity of organic semiconductors is fundamental for their use in optoelectronic applications and can be achieved by molecular doping, which introduces additional charge carriers through electron transfer between a dopant molecule and the organic semiconductor. Here, we use Electron Paramagnetic Resonance (EPR) spectroscopy to characterise the unpaired spins associated with the charges generated by molecular doping of the prototypical organic semiconductor poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) and tris(pentafluorophenyl)borane (BCF). The EPR results reveal the P3HT radical cation as the only paramagnetic species in BCF-doped P3HT films and show evidence for increased mobility of the detected spins at high doping concentrations as well as formation of antiferromagnetically coupled spin pairs leading to decreased spin concentrations at low temperatures. The EPR signature for F(4)TCNQ-doped P3HT is found to be determined by spin exchange between P3HT radical cations and F(4)TCNQ radical anions. Results from continuous-wave and pulse EPR measurements suggest the presence of the unpaired spin on P3HT in a multitude of environments, ranging from free P3HT radical cations with similar properties to those observed in BCF-doped P3HT, to pairs of dipolar and exchange-coupled spins on P3HT and the dopant anion. Characterisation of the proton hyperfine interactions by ENDOR allowed quantification of the extent of spin delocalisation and revealed reduced delocalisation in the F(4)TCNQ-doped P3HT films.
Y1  - 2021
U6  - https://doi.org/10.1039/d1cp02133h
SN  - 1463-9076
SN  - 1463-9084
VL  - 23
IS  - 25
SP  - 13827
EP  - 13841
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Bange, Sebastian
A1  - Schubert, Marcel
A1  - Neher, Dieter
T1  - Charge mobility determination by current extraction under linear increasing voltages : case of nonequilibrium charges and field-dependent mobilities
N2  - The method of current extraction under linear increasing voltages (CELIV) allows for the simultaneous determination of charge mobilities and charge densities directly in thin-film geometries as used in organic photovoltaic (OPV) cells. It has been specifically applied to investigate the interrelation of microstructure and charge-transport properties in such systems. Numerical and analytical calculations presented in this work show that the evaluation of CELIV transients with the commonly used analysis scheme is error prone once charge recombination and, possibly, field- dependent charge mobilities are taken into account. The most important effects are an apparent time dependence of charge mobilities and errors in the determined field dependencies. Our results implicate that reports on time-dependent mobility relaxation in OPV materials obtained by the CELIV technique should be carefully revisited and confirmed by other measurement methods.
Y1  - 2010
UR  - http://prb.aps.org/
U6  - https://doi.org/10.1103/Physrevb.81.035209
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Pingel, Patrick
A1  - Zen, Achmad
A1  - Neher, Dieter
A1  - Lieberwirth, Ingo
A1  - Wegner, Gerhard
A1  - Allard, Sybille
A1  - Scherf, Ullrich
T1  - Unexpectedly high field-effect mobility of a soluble, low molecular weight oligoquaterthiophene fraction with low polydispersity
N2  - Layers made from soluble low molecular weight polythiophene PQT-12 with low polydispersity exhibit a highly ordered structure and charge-carrier mobilities of the order of 10(-3) cm(2)/(V s), which we attribute to its proximity to monodispersity. We propose that polydispersity is a decisive factor with regard to structure formation and transport properties of soluble low molecular weight polythiophenes.
Y1  - 2009
UR  - http://www.springerlink.com/content/100501
U6  - https://doi.org/10.1007/s00339-008-4994-0
SN  - 0947-8396
ER  - 
TY  - JOUR
A1  - Gattinger, P.
A1  - Gurka, M.
A1  - Craats, A. M. van de
A1  - Rengel, Heiko
A1  - Warman, J. M.
A1  - Buck, M.
A1  - Neher, Dieter
T1  - Mechanism of charge transport in anisotropic layers of a phthalocyanine polymer
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Däubler, Thomas Karl
A1  - Bittner, Reinhard
A1  - Meerholz, Klaus
A1  - Neher, Dieter
T1  - Charge carrier photogeneration, trapping and space-charge field formation in PVK-based photorefractive materials
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Däubler, Thomas Karl
A1  - Cimrova, V.
A1  - Pfeiffer, S.
A1  - Hörhold, Hans-Heinrich
A1  - Neher, Dieter
T1  - Field and wavelength dependence of charge carrier photogeneration in soluble PPV derivatives
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Rengel, Heiko
A1  - Gattinger, P.
A1  - Silverova, R.
A1  - Neher, Dieter
T1  - Conductivity measurements of electrochemically oxidized Langmuir-Blodgett films of phthalocyaninato- polysiloxanes
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Däubler, Thomas Karl
A1  - Neher, Dieter
A1  - Rost, H.
A1  - Hörhold, Hans-Heinrich
T1  - Efficient bulk photogeneration of charge carriers in arylamino-PPV polymer sandwich cells
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Däubler, Thomas Karl
A1  - Pfeiffer, S.
A1  - Hörhold, Hans-Heinrich
A1  - Neher, Dieter
T1  - Photogeneration of charge carriers in segmented arylamino-PPV derivatives
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Sainova, Dessislava
A1  - Fujikawa, H.
A1  - Scherf, Ullrich
A1  - Neher, Dieter
T1  - The effect of hole traps on the performance of single layer polymer light emitting diodes
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Fiesel, R.
A1  - Neher, Dieter
A1  - Scherf, Ullrich
T1  - On the solid state aggregation of chiral substituted poly(para-phenylene)s (PPPs)
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Cimrová, V.
A1  - Neher, Dieter
A1  - Kostromine, S.
A1  - Bieringer, Thomas
T1  - Optical anisotropy in films of photoaddressable polymers
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Roland, Steffen
A1  - Kniepert, Juliane
A1  - Love, John A.
A1  - Negi, Vikas
A1  - Liu, Feilong
A1  - Bobbert, Peter
A1  - Melianas, Armantas
A1  - Kemerink, Martijn
A1  - Hofacker, Andreas
A1  - Neher, Dieter
T1  - Equilibrated Charge Carrier Populations Govern Steady-State Nongeminate Recombination in Disordered Organic Solar Cells
JF  - The journal of physical chemistry letters
N2  - We employed bias-assisted charge extraction techniques to investigate the transient and steady-state recombination of photogenerated charge carriers in complete devices of a disordered polymer-fullerene blend. Charge recombination is shown to be dispersive, with a significant slowdown of the recombination rate over time, consistent with the results from kinetic Monte Carlo simulations. Surprisingly, our experiments reveal little to no contributions from early time recombination of nonequilibrated charge carriers to the steady-state recombination properties. We conclude that energetic relaxation of photogenerated carriers outpaces any significant nongeminate recombination under application-relevant illumination conditions. With equilibrated charges dominating the steady-state recombination, quasi-equilibrium concepts appear suited for describing the open-circuit voltage of organic solar cells despite pronounced energetic disorder.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpclett.9b00516
SN  - 1948-7185
VL  - 10
IS  - 6
SP  - 1374
EP  - 1381
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Inal, Sahika
A1  - Chiappisi, Leonardo
A1  - Kölsch, Jonas D.
A1  - Kraft, Mario
A1  - Appavou, Marie-Sousai
A1  - Scherf, Ullrich
A1  - Wagner, Manfred
A1  - Hansen, Michael Ryan
A1  - Gradzielski, Michael
A1  - Laschewsky, André
A1  - Neher, Dieter
T1  - Temperature-regulated fluorescence and association of an Oligo(ethyleneglycol)methacrylate-based copolymer with a conjugated Polyelectrolyte-the effect of solution ionic strength
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - Aqueous mixtures of a dye-labeled non-ionic thermoresponsive copolymer and a conjugated cationic polyelectrolyte are shown to exhibit characteristic changes in fluorescence properties in response to temperature and to the presence of salts, enabling a double-stimuli responsiveness. In such mixtures at room temperature, i.e., well below the lower critical solution temperature (LCST), the emission of the dye is strongly quenched due to energy transfer to the polycation, pointing to supramolecular interactions between the two macromolecules. Increasing the concentration of salts weakens the interpolymer interactions, the extent of which is simultaneously monitored from the change in the relative emission intensity of the components. When the mixture is heated above its LCST, the transfer efficiency is significantly reduced, signaling a structural reorganization process, however, surprisingly only if the mixture contains salt ions. To elucidate the reasons behind such thermo- and ion-sensitive fluorescence characteristics, we investigate the effect of salts of alkali chlorides, in particular of NaCl, on the association behavior of these macromolecules before and after the polymer phase transition by a combination of UV-vis, fluorescence, and H-1 NMR spectroscopy with light scattering and small-angle neutron scattering measurements.
Y1  - 2013
U6  - https://doi.org/10.1021/jp408864s
SN  - 1520-6106
VL  - 117
IS  - 46
SP  - 14576
EP  - 14587
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Lange, Ilja
A1  - Kniepert, Juliane
A1  - Pingel, Patrick
A1  - Dumsch, Ines
A1  - Allard, Sybille
A1  - Janietz, Silvia
A1  - Scherf, Ullrich
A1  - Neher, Dieter
T1  - Correlation between the open circuit voltage and the energetics of organic bulk heterojunction solar cells
JF  - The journal of physical chemistry letters
N2  - A detailed investigation of the open circuit voltage (V-OC) of organic bulk heterojunction solar cells comprising three different donor polymers and two different fullerene-based acceptors is presented. Bias amplified charge extraction (BACE) is combined with Kelvin Probe measurements to derive information on the relevant energetics in the blend. On the example of P3HT:PC70BM the influence of composition and preparation conditions on the relevant transport levels will be shown. Moderate upward shifts of the P3HT HOMO depending on crystallinity are observed, but contrarily to common believe, the dependence of V-OC on blend composition and thermal history is found to be largely determined by the change in the PCBM LUMO energy. Following this approach, we quantified the energetic contribution to the V-OC in blends with fluorinated polymers or higher adduct fullerenes.
Y1  - 2013
U6  - https://doi.org/10.1021/jz401971e
SN  - 1948-7185
VL  - 4
IS  - 22
SP  - 3865
EP  - 3871
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Gross, M.
A1  - Müller, David C.
A1  - Nothofer, Heinz-Georg
A1  - Scherf, Ullrich
A1  - Neher, Dieter
A1  - Bräuchler, C.
A1  - Meerholz, Klaus
T1  - Improving the performance of doped p-conjugated polymers for use in organic light-emitting diodes
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Joshi, Siddharth
A1  - Pingel, Patrick
A1  - Grigorian, Souren
A1  - Panzner, Tobias
A1  - Pietsch, Ullrich
A1  - Neher, Dieter
A1  - Forster, Michael
A1  - Scherf, Ullrich
T1  - Bimodal temperature behavior of structure and mobility in high molecular weight p3ht thin films
N2  - We report a temperature dependent crystalline structure of spin-coated thin films of high molecular weight regioregular poly(3-hexylthiophene) (P3HT) (M-n similar to 30000 g/mol) and its correlation with charge carrier mobility. These investigations show a reversible change of the crystalline structure, where the interlayer lattice spacing (100)along the alkyl side chains continuously increases up to a temperature of about 220 degrees C; in contrast, the in-plane pi-pi distance reduces with increasing temperature. These changes in structure are reversible and can be repeated several times. The temperature-induced structural properties differ for thick and thin films, pointing to a surface/interface role in stabilization of the layer morphology. In contrast to the structural changes, the carrier mobility is rather constant in the temperature range from room temperature up to 100-120 degrees C, followed by a continuous decrease. For thick layers this drop is significant and the transistor performance almost vanishes at high temperature, however, it completely recovers upon cooling back to roorn temperature. The drop of the charge carrier mobility at higher temperatures is in contrast with expectations front the structural studies, considering the increase of crystalline fraction of the polycrystalline layer. our electrical measurements Underscore that the reduction of the macroscopic mobility is mostly caused by it pronounced decrease of the intergrain transport. The thermally induced crystallization along(100) direction and the creation of numerous small crystallites at the film-substrate interface reduce the number of long polymer chain, bridging crystalline domains, which ultimately limits the macroscopic charge transport.
Y1  - 2009
UR  - http://pubs.acs.org/journal/mamobx
U6  - https://doi.org/10.1021/Ma900021w
SN  - 0024-9297
ER  - 
TY  - JOUR
A1  - Schubert, Marcel
A1  - Steyrleuthner, Robert
A1  - Bange, Sebastian
A1  - Sellinger, Alan
A1  - Neher, Dieter
T1  - Charge transport and recombination in bulk heterojunction solar cells containing a dicyanoimidazole-based molecular acceptor
N2  - Carrier transport and recombination have been studied in single component layers and blends of the soluble PPV- derivative poly[2,5-dimethoxy-1,4-phenylenevinylene-2-methoxy-5-(2-ethyl-hexyloxy)- 1,4-phenylenevinylene] (M3EH-PPV) and the small molecule acceptor 4,7-bis(2-(1-hexyl-4,5-dicyanoimidazole-2-yl)vinyl) benzo[c][1,2,5]-thiadiazole (HV-BT). Measurements on single carrier devices show significantly smaller electron mobility in the blend compared to the pure HV- BT layer, which is suggestive of the formation of isolated clusters of the acceptor in a continuous polymer matrix. The significant change in fill factor (FF) with increasing illumination intensity is consistently explained by a model taking into account bimolecular recombination and space charge effects. The decay of the carrier density after photoexcitation has been studied by performing photo-CELIV measurements on pure and blend layers. It is found that the decay at long delay times follows a power-law dependence, which is, however, not consistent with a Langevin-type bimolecular recombination of free charges. A good description of the data is obtained by assuming trimolecular recombination to govern the charge carrier dynamics in these systems.
Y1  - 2009
UR  - http://www3.interscience.wiley.com/cgi-bin/jhome/40000761
U6  - https://doi.org/10.1002/pssa.200925312
SN  - 1862-6300
ER  - 
TY  - JOUR
A1  - Schubert, Marcel
A1  - Yin, Chunhong
A1  - Castellani, Mauro
A1  - Bange, Sebastian
A1  - Tam, Teck Lip
A1  - Sellinger, Alan
A1  - Hoerhold, Hans-Heinrich
A1  - Kietzke, Thomas
A1  - Neher, Dieter
T1  - Heterojunction topology versus fill factor correlations in novel hybrid small-molecular/polymeric solar cells
N2  - The authors present organic photovoltaic (OPV) devices comprising a small molecule electron acceptor based on 2- vinyl-4,5-dicyanoimidazole (Vinazene (TM)) and a soluble poly(p-phenylenevinylene) derivative as the electron donor. A strong dependence of the fill factor (FF) and the external quantum efficiency [incident photons converted to electrons (IPCE)] on the heterojunction topology is observed. As-prepared blends provided relatively low FF and IPCE values of 26% and 4.5%, respectively, which are attributed to significant recombination of geminate pairs and free carriers in a highly intermixed blend morphology. Going to an all-solution processed bilayer device, the FF and IPCE dramatically increased to 43% and 27%, respectively. The FF increases further to 57% in devices comprising thermally deposited Vinazene layers where there is virtually no interpenetration at the donor/acceptor interface. This very high FF is comparable to values reported for OPV using fullerenes as the electron acceptor. Furthermore, the rather low electron affinity of Vinazene compound near 3.5 eV enabled a technologically important open circuit voltage (V-oc) of 1.0 V.
Y1  - 2009
UR  - http://jcp.aip.org/
U6  - https://doi.org/10.1063/1.3077007
SN  - 0021-9606
ER  - 
TY  - JOUR
A1  - Inal, Sahika
A1  - Castellani, Mauro
A1  - Sellinger, Alan
A1  - Neher, Dieter
T1  - Relationship of photophysical properties and the device performance of novel hybrid small-molecular/polymeric solar cells
N2  - We investigate solar cells comprised of a vinazene derivative (HV-BT) as the electron acceptor and the well- known polymer poly(3-hexylthiophene) as the electron donor. In the as-prepared blend, most of the excited state species, including the excimers on HV-BT, are quenched at the heterojunction. Although the photophysical properties of the blends change upon annealing, the blend solar cells largely remain uninfluenced by such treatments. A significant improvement is, however, observed when inducing phase separation at a longer length scale, for example, in solution-processed bilayer devices. Hereby, both the fill factor (FF) and the open circuit voltage are considerably increased, pointing to the importance of the heterojunction topology and the layer composition at the charge extracting contacts. An optimized device exhibits a power conversion efficiency of close to 1%.
Y1  - 2009
UR  - http://www3.interscience.wiley.com/cgi-bin/jhome/10003270
U6  - https://doi.org/10.1002/marc.200900221
SN  - 1022-1336
ER  - 
TY  - JOUR
A1  - Steyrleuthner, Robert
A1  - Bange, Sebastian
A1  - Neher, Dieter
T1  - Reliable electron-only devices and electron transport in n-type polymers
N2  - Current-voltage analysis of single-carrier transport is a popular method for the determination of charge carrier mobilities in organic semiconductors. Although in widespread use for the analysis of hole transport, only a few reports can be found where the method was applied to electron transport. Here, we summarize the experimental difficulties related to the metal electrode leakage currents and nonlinear differential resistance (NDR) effects and explain their origin. We present a modified preparation technique for the metal electrodes and show that it significantly increases the reliability of such measurements. It allows to produce test devices with low leakage currents and without NDR even for thin organic layers. Metal oxides were often discussed as a possible cause of NDR. Our measurements on forcibly oxidized metal electrodes demonstrate that oxide layers are not exclusively responsible for NDR effects. We present electron transport data for two electron-conducting polymers often applied in all-polymer solar cells for a large variety of layer thicknesses and temperatures. The results can be explained by established exponential trapping models.
Y1  - 2009
UR  - http://jap.aip.org/
U6  - https://doi.org/10.1063/1.3086307
SN  - 0021-8979
ER  - 
TY  - JOUR
A1  - Rengel, Heiko
A1  - Altmann, Markus
A1  - Neher, Dieter
A1  - Harrison, Craig B.
A1  - Myrick, Michael L.
A1  - Bunz, Uwe H. F.
T1  - Assignment of the optical transitions in 1,3- diethynylcyclobutadiene (cyclopentadienyl)cobalt oligomers
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Miteva, T.
A1  - Meisel, A.
A1  - Nothofer, Heinz-Georg
A1  - Scherf, Ullrich
A1  - Knoll, W.
A1  - Neher, Dieter
A1  - Grell, M.
A1  - Lupo, D.
A1  - Yasuda, A.
T1  - Polarized electroluminescence from highly aligned liquid-crystalline polymers
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Miteva, T.
A1  - Kloppenburg, L.
A1  - Neher, Dieter
A1  - Bunz, Uwe H. F.
T1  - Interplay of Thermochromicity and Liquid Crystalline Behavior in Poly(p-phenyleneethynylen)s:p-p-Interactions or Planarization of the Conjugated Backbone?
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Bauer, C.
A1  - Umbasch, G.
A1  - Giessen, H.
A1  - Meisel, A.
A1  - Nothofer, Heinz-Georg
A1  - Neher, Dieter
A1  - Scherf, Ullrich
A1  - Marth, R.
T1  - Polarized Photoluminescence and Spectral Narrowing in an oriented Polyfluorene Thin Film
Y1  - 2000
ER  -