TY  - JOUR
A1  - Benduhn, Johannes
A1  - Tvingstedt, Kristofer
A1  - Piersimoni, Fortunato
A1  - Ullbrich, Sascha
A1  - Fan, Yeli
A1  - Tropiano, Manuel
A1  - McGarry, Kathryn A.
A1  - Zeika, Olaf
A1  - Riede, Moritz K.
A1  - Douglas, Christopher J.
A1  - Barlow, Stephen
A1  - Marder, Seth R.
A1  - Neher, Dieter
A1  - Spoltore, Donato
A1  - Vandewal, Koen
T1  - Intrinsic non-radiative voltage losses in fullerene-based organic solar cells
JF  - Nature Energy
N2  - Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to (1.45-1.65) eV, that is, (0.2-0.3) eV higher than for technologies with minimized non-radiative voltage losses.
Y1  - 2017
U6  - https://doi.org/10.1038/nenergy.2017.53
SN  - 2058-7546
VL  - 2
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Bittner, Reinhard
A1  - Däubler, Thomas Karl
A1  - Neher, Dieter
A1  - Meerholz, Klaus
T1  - Influence of the glass-transition and the chromophore content on the steady-state performance of PVK-based photorefractive polymers
Y1  - 1999
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  - 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  - Braunger, Steffen
A1  - Mundt, Laura E.
A1  - Wolff, Christian Michael
A1  - Mews, Mathias
A1  - Rehermann, Carolin
A1  - Jost, Marko
A1  - Tejada, Alvaro
A1  - Eisenhauer, David
A1  - Becker, Christiane
A1  - Andres Guerra, Jorge
A1  - Unger, Eva
A1  - Korte, Lars
A1  - Neher, Dieter
A1  - Schubert, Martin C.
A1  - Rech, Bernd
A1  - Albrecht, Steve
T1  - Cs(x)FA(1-x)Pb(l(1-y)Br(y))(3) Perovskite Compositions
BT  - the Appearance of Wrinkled Morphology and its Impact on Solar Cell Performance
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - We report on the formation of wrinkle-patterned surface morphologies in cesium formamidinium-based Cs(x)FA(1-y)Pb(I1-yBry)(3) perovskite compositions with x = 0-0.3 and y = 0-0.3 under various spin-coating conditions. By varying the Cs and Br contents, the perovskite precursor solution concentration and the spin-coating procedure, the occurrence and characteristics of the wrinkle-shaped morphology can be tailored systematically. Cs(0.17)FA(0.83)Pb(I0.83Br0.17)(3) perovskite layers were analyzed regarding their surface roughness, microscopic structure, local and overall composition, and optoelectronic properties. Application of these films in p-i-n perovskite solar cells (PSCs) with indium-doped tin oxide/NiOx/perovskite/C-60/bathocuproine/Cu architecture resulted in up to 15.3 and 17.0% power conversion efficiency for the flat and wrinkled morphology, respectively. Interestingly, we find slightly red-shifted photoluminescence (PL) peaks for wrinkled areas and we are able to directly correlate surface topography with PL peak mapping. This is attributed to differences in the local grain size, whereas there is no indication for compositional demixing in the films. We show that the perovskite composition, crystallization kinetics, and layer thickness strongly influence the formation of wrinkles which is proposed to be related to the release of compressive strain during perovskite crystallization. Our work helps us to better understand film formation and to further improve the efficiency of PSCs with widely used mixed-perovskite compositions.
Y1  - 2018
U6  - https://doi.org/10.1021/acs.jpcc.8b06459
SN  - 1932-7447
SN  - 1932-7455
VL  - 122
IS  - 30
SP  - 17123
EP  - 17135
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Brinkmann, Kai Oliver
A1  - Becker, Tim
A1  - Zimmermann, Florian
A1  - Kreusel, Cedric
A1  - Gahlmann, Tobias
A1  - Theisen, Manuel
A1  - Haeger, Tobias
A1  - Olthof, Selina
A1  - Tückmantel, Christian
A1  - Günster, M.
A1  - Maschwitz, Timo
A1  - Göbelsmann, Fabian
A1  - Koch, Christine
A1  - Hertel, Dirk
A1  - Caprioglio, Pietro
A1  - Peña-Camargo, Francisco
A1  - Perdigón-Toro, Lorena
A1  - Al-Ashouri, Amran
A1  - Merten, Lena
A1  - Hinderhofer, Alexander
A1  - Gomell, Leonie
A1  - Zhang, Siyuan
A1  - Schreiber, Frank
A1  - Albrecht, Steve
A1  - Meerholz, Klaus
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
A1  - Riedl, Thomas
T1  - Perovskite-organic tandem solar cells with indium oxide interconnect
JF  - Nature
N2  - Multijunction solar cells can overcome the fundamental efficiency limits of single-junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures(1). Combinations with silicon and copper indium gallium selenide (CIGS), as well as all-perovskite tandem cells, have been reported(2-5). Meanwhile, narrow-gap non-fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells(6,7). Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite-organic tandems show subpar efficiencies and are limited by the low open-circuit voltage (V-oc) of wide-gap perovskite cells(8) and losses introduced by the interconnect between the subcells(9,10). Here we demonstrate perovskite-organic tandem cells with an efficiency of 24.0 per cent (certified 23.1 per cent) and a high V-oc of 2.15 volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high V-oc and fill factor. The organic subcells provide a high external quantum efficiency in the near-infrared and, in contrast to paradigmatic concerns about limited photostability of non-fullerene cells(11), show an outstanding operational stability if excitons are predominantly generated on the non-fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin (approximately 1.5 nanometres) metal-like indium oxide layer with unprecedented low optical/electrical losses. This work sets a milestone for perovskite-organic tandems, which outperform the best p-i-n perovskite single junctions(12) and are on a par with perovskite-CIGS and all-perovskite multijunctions(13).
Y1  - 2022
U6  - https://doi.org/10.1038/s41586-022-04455-0
SN  - 0028-0836
SN  - 1476-4687
VL  - 604
IS  - 7905
SP  - 280
EP  - 286
PB  - Nature Research
CY  - Berlin
ER  - 
TY  - GEN
A1  - Bubeck, Christoph
A1  - Laschewsky, André
A1  - Lupo, Donald
A1  - Neher, Dieter
A1  - Ottenbreit, Petra
A1  - Paulus, Wolfgang
A1  - Prass, Werner
A1  - Ringsdorf, Helmut
A1  - Wegner, Gerhard
T1  - Amphiphilic dyes for nonlinear optics: Dependence of second harmonic generation on functional group substitution
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 082 
Y1  - 1991
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17201
ER  - 
TY  - GEN
A1  - Caprioglio, Pietro
A1  - Stolterfoht, Martin
A1  - Wolff, Christian Michael
A1  - Unold, Thomas
A1  - Rech, Bernd
A1  - Albrecht, Steve
A1  - Neher, Dieter
T1  - On the relation between the open‐circuit voltage and quasi‐Fermi level splitting in efficient perovskite solar cells
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐VOC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐VOC relation is of great importance.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 774 
KW  - electro‐optical materials
KW  - perovskite solar cells
KW  - photovoltaic devices
KW  - thin films
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437595
SN  - 1866-8372
IS  - 774
ER  - 
TY  - JOUR
A1  - Caprioglio, Pietro
A1  - Stolterfoht, Martin
A1  - Wolff, Christian Michael
A1  - Unold, Thomas
A1  - Rech, Bernd
A1  - Albrecht, Steve
A1  - Neher, Dieter
T1  - On the relation between the open-circuit voltage and quasi-fermi level splitting in efficient perovskite solar cells
JF  - advanced energy materials
N2  - Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐VOC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐VOC relation is of great importance.
KW  - electro-optical materials
KW  - perovskite solar cells
KW  - photovoltaic devices
KW  - thin films
Y1  - 2019
U6  - https://doi.org/10.1002/aenm.201901631
SN  - 1614-6832
SN  - 1614-6840
VL  - 9
IS  - 33
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Caprioglio, Pietro
A1  - Zu, Fengshuo
A1  - Wolff, Christian Michael
A1  - Prieto, Jose A. Marquez
A1  - Stolterfoht, Martin
A1  - Becker, Pascal
A1  - Koch, Norbert
A1  - Unold, Thomas
A1  - Rech, Bernd
A1  - Albrecht, Steve
A1  - Neher, Dieter
T1  - High open circuit voltages in pin-type perovskite solar cells through strontium addition
JF  - Sustainable Energy & Fuels
N2  - The incorporation of even small amounts of strontium (Sr) into lead-base hybrid quadruple cation perovskite solar cells results in a systematic increase of the open circuit voltage (V-oc) in pin-type perovskite solar cells. We demonstrate via absolute and transient photoluminescence (PL) experiments how the incorporation of Sr significantly reduces the non-radiative recombination losses in the neat perovskite layer. We show that Sr segregates at the perovskite surface, where it induces important changes of morphology and energetics. Notably, the Sr-enriched surface exhibits a wider band gap and a more n-type character, accompanied with significantly stronger surface band bending. As a result, we observe a significant increase of the quasi-Fermi level splitting in the neat perovskite by reduced surface recombination and more importantly, a strong reduction of losses attributed to non-radiative recombination at the interface to the C-60 electron-transporting layer. The resulting solar cells exhibited a V-oc of 1.18 V, which could be further improved to nearly 1.23 V through addition of a thin polymer interlayer, reducing the non-radiative voltage loss to only 110 meV. Our work shows that simply adding a small amount of Sr to the precursor solutions induces a beneficial surface modification in the perovskite, without requiring any post treatment, resulting in high efficiency solar cells with power conversion efficiency (PCE) up to 20.3%. Our results demonstrate very high V-oc values and efficiencies in Sr-containing quadruple cation perovskite pin-type solar cells and highlight the imperative importance of addressing and minimizing the recombination losses at the interface between perovskite and charge transporting layer.
Y1  - 2019
U6  - https://doi.org/10.1039/c8se00509e
SN  - 2398-4902
VL  - 3
IS  - 2
SP  - 550
EP  - 563
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Chen, Zupeng
A1  - Savateev, Aleksandr
A1  - Pronkin, Sergey
A1  - Papaefthimiou, Vasiliki
A1  - Wolff, Christian Michael
A1  - Willinger, Marc Georg
A1  - Willinger, Elena
A1  - Neher, Dieter
A1  - Antonietti, Markus
A1  - Dontsova, Dariya
T1  - "The Easier the Better" Preparation of Efficient Photocatalysts-Metastable Poly(heptazine imide) Salts
JF  - Advanced materials
N2  - Cost-efficient, visible-light-driven hydrogen production from water is an attractive potential source of clean, sustainable fuel. Here, it is shown that thermal solid state reactions of traditional carbon nitride precursors (cyanamide, melamine) with NaCl, KCl, or CsCl are a cheap and straightforward way to prepare poly(heptazine imide) alkali metal salts, whose thermodynamic stability decreases upon the increase of the metal atom size. The chemical structure of the prepared salts is confirmed by the results of X-ray photoelectron and infrared spectroscopies, powder X-ray diffraction and electron microscopy studies, and, in the case of sodium poly(heptazine imide), additionally by atomic pair distribution function analysis and 2D powder X-ray diffraction pattern simulations. In contrast, reactions with LiCl yield thermodynamically stable poly(triazine imides). Owing to the metastability and high structural order, the obtained heptazine imide salts are found to be highly active photo-catalysts in Rhodamine B and 4-chlorophenol degradation, and Pt-assisted sacrificial water reduction reactions under visible light irradiation. The measured hydrogen evolution rates are up to four times higher than those provided by a benchmark photocatalyst, mesoporous graphitic carbon nitride. Moreover, the products are able to photocatalytically reduce water with considerable reaction rates, even when glycerol is used as a sacrificial hole scavenger.
KW  - carbon nitride
KW  - glycerol oxidation
KW  - mesocrystals
KW  - poly(heptazine imide)
KW  - water reduction reactions
Y1  - 2017
U6  - https://doi.org/10.1002/adma.201700555
SN  - 0935-9648
SN  - 1521-4095
VL  - 29
SP  - 21800
EP  - 21806
PB  - Wiley-VCH
CY  - Weinheim
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  - Collado-Fregoso, Elisa
A1  - Hood, Samantha N.
A1  - Shoaee, Safa
A1  - Schröder, Bob C.
A1  - McCulloch, Iain
A1  - Kassal, Ivan
A1  - Neher, Dieter
A1  - Durrant, James R.
T1  - Intercalated vs Nonintercalated Morphologies in Donor-Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited
JF  - The journal of physical chemistry letters
N2  - In this Letter, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC70BM and ICTA) as models for intercalated and nonintercalated morphologies, respectively. Thermodynamic simulations show that while the completely intercalated system exhibits a large free-energy barrier for charge separation, this barrier is significantly lower in the nonintercalated system and almost vanishes when energetic disorder is included in the model. Despite these differences, both femtosecond-resolved transient absorption spectroscopy (TAS) and time-delayed collection field (TDCF) exhibit extensive first-order losses in both systems, suggesting that geminate pairs are the primary product of photoexcitation. In contrast, the system that comprises a combination of fully intercalated polymer:fullerene areas and fullerene-aggregated domains (1:4 PBTTT:PC70BM) is the only one that shows slow, second-order recombination of free charges, resulting in devices with an overall higher short-circuit current and fill factor. This study therefore provides a novel consideration of the role of the interfacial nanostructure and the nature of bound charges and their impact upon charge generation and recombination.
Y1  - 2017
U6  - https://doi.org/10.1021/acs.jpclett.7b01571
SN  - 1948-7185
VL  - 8
SP  - 4061
EP  - 4068
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Collado-Fregoso, Elisa
A1  - Pugliese, Silvina N.
A1  - Wojcik, Mariusz
A1  - Benduhn, Johannes
A1  - Bar-Or, Eyal
A1  - Perdigón-Toro, Lorena
A1  - Hörmann, Ulrich
A1  - Spoltore, Donato
A1  - Vandewal, Koen
A1  - Hodgkiss, Justin M.
A1  - Neher, Dieter
T1  - Energy-gap law for photocurrent generation in fullerene-based organic solar cells
BT  - the case of low-donor-content blends
JF  - Journal of the American Chemical Society
N2  - The involvement of charge-transfer (CT) states in the photogeneration and recombination of charge carriers has been an important focus of study within the organic photovoltaic community. In this work, we investigate the molecular factors determining the mechanism of photocurrent generation in low-donor-content organic solar cells, where the active layer is composed of vacuum-deposited C-60 and small amounts of organic donor molecules. We find a pronounced decline of all photovoltaic parameters with decreasing CT state energy. Using a combination of steady-state photocurrent measurements and time-delayed collection field experiments, we demonstrate that the power conversion efficiency, and more specifically, the fill factor of these devices, is mainly determined by the bias dependence of photocurrent generation. By combining these findings with the results from ultrafast transient absorption spectroscopy, we show that blends with small CT energies perform poorly because of an increased nonradiative CT state decay rate and that this decay obeys an energy-gap law. Our work challenges the common view that a large energy offset at the heterojunction and/or the presence of fullerene clusters guarantee efficient CT dissociation and rather indicates that charge generation benefits from high CT state energies through a slower decay to the ground state.
Y1  - 2019
U6  - https://doi.org/10.1021/jacs.8b09820
SN  - 0002-7863
VL  - 141
IS  - 6
SP  - 2329
EP  - 2341
PB  - American Chemical Society
CY  - Washington
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  - Di Pietro, Riccardo
A1  - Erdmann, Tim
A1  - Carpenter, Joshua H.
A1  - Wang, Naixiang
A1  - Shivhare, Rishi Ramdas
A1  - Formanek, Petr
A1  - Heintze, Cornelia
A1  - Voit, Brigitte
A1  - Neher, Dieter
A1  - Ade, Harald W.
A1  - Kiriy, Anton
T1  - Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility
JF  - Chemistry of materials : a publication of the American Chemical Society
Y1  - 2017
U6  - https://doi.org/10.1021/acs.chemmater.7b04423
SN  - 0897-4756
SN  - 1520-5002
VL  - 29
SP  - 10220
EP  - 10232
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Di Pietro, Riccardo
A1  - Nasrallah, Iyad
A1  - Carpenter, Joshua
A1  - Gann, Eliot
A1  - Kölln, Lisa Sophie
A1  - Thomsen, Lars
A1  - Venkateshvaran, Deepak
A1  - Sadhanala, Aditya
A1  - Chabinyc, Michael
A1  - McNeill, Christopher R.
A1  - Facchetti, Antonio
A1  - Ade, Harald W.
A1  - Sirringhaus, Henning
A1  - Neher, Dieter
T1  - Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors
JF  - Advanced functional materials
Y1  - 2016
U6  - https://doi.org/10.1002/adfm.201602080
SN  - 1616-301X
SN  - 1616-3028
VL  - 26
SP  - 8011
EP  - 8022
PB  - Wiley-VCH
CY  - Weinheim
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  - 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  - Däubler, Thomas Karl
A1  - Glowacki, Ireneusz
A1  - Scherf, Ullrich
A1  - Ulanski, J.
A1  - Hörhold, Hans-Heinrich
A1  - Neher, Dieter
T1  - Photogeneration and transport of charge carriers in hybrid materials of conjugated polymers and dye-sensitized TiO2
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  - Egbe, D. A. M.
A1  - Carbonnier, B.
A1  - Paul, E. L.
A1  - Muhlbacher, D.
A1  - Kietzke, Thomas
A1  - Birckner, Eckhard
A1  - Neher, Dieter
A1  - Grummt, U. W.
A1  - Pakula, T.
T1  - Diyne-containing PPVs : Solid-state properties and comparison of their photophysical and electrochemical properties with those of their Yne-containing counterparts
N2  - Diyne-containing poly(p-phenylene-vinylene)s, 4a-d, of general chemical structure-(Ph-C&3bond; C-C&3bond; C-Ph- CH&3bond; CH-Ph-CH&3bond; CH-)(n), obtained through polycondensation reactions of 1,4-bis(4-formyl-2,5-dioctyloxyphenyl)- buta-1,3-diyne (2) with various 2,5-dialkoxy-p-xylylenebis(diethylphosphonates), 3a-d, are the subject of this report. The polymers exhibit great disparity in their degree of polymerization, n, which might be ascribed to side-chain-related differences in reactivity of the reactive species during the polycondensation process and which led to n-dependent absorption (solution and solid state) and emission (solution) behaviors of the polymers. Polarizing optical microscopy and differential scanning calorimetry are employed to probe their thermal behavior. The structure is investigated by means of wide-angle X-ray diffraction for both isotropic and macroscopically oriented samples. Comparison of photophysical (experimental and theoretical) and electrochemical properties of the polymers with those of their yne- containing counterparts 6a-d [-(Ph-C&3bond; C-Ph-CH&3bond; CH-Ph-CH&3bond; CH-)(n)] has been carried out. Similar photophysical behavior was observed for both types of polymers despite the difference in backbone conjugation pattern. The introduction of a second yne unit in 4 lowers the HOMO and LUMO levels, thereby enhancing the electron affinity of polymers 4 compared to polymers 6. The "wider opening" introduced by the second yne unit facilitates moreover the movement of charges during the electrochemical processes leading to minimal discrepancy, Delta E-g between the optical and electrochemical band gap energies. Polymers 6, in contrast, show significant side-chain-dependent Delta E-g values. Low turn-on voltages between 2 and 3 V and maximal luminous efficiencies between 0.32 and 1.25 cd/A were obtained from LED devices of configuration ITO/PEDOT:PSS/polymer 4/Ca/Al
Y1  - 2005
SN  - 0024-9297
ER  - 
TY  - JOUR
A1  - Egbe, D. A. M.
A1  - Kietzke, Thomas
A1  - Carbonnier, B.
A1  - Muhlbacher, D.
A1  - Horhold, H. H.
A1  - Neher, Dieter
A1  - Pakula, T.
T1  - Synthesis, characterization, and photophysical, electrochemical, electroluminescent, and photovoltaic properties of yne-containing CN-PPVs
N2  - Alkoxy-substituted CN-containing phenylene-vinylene-alt-phenylene-ethynylene hybrid polymers (CN-PPV-PPE), 3a, 3b, and 7a, were obtained from luminophoric dialdehydes 1 by step growth polymerization via Knoevenagel reaction as high molecular-weight materials. Corresponding CN-free polymers 3c and 7b and an ethynylene-free polymer 5 with similar side chains were synthesized for the purpose of comparison. The chemical structures of the polymers were confirmed by IR, H-1 and C-13 NMR, and elemental analysis. Thermal characterization was conducted by means of thermogravimetric analysis and differential scanning calorimetry. Morphology was investigated by means of optical microscopy and small-angle light scattering. The final morphologies are determined by the molecular characteristics (side chains volume fraction, backbone stiffness) of the studied polymers. All the CN-containing polymers 3b, 5, and 7a exhibit higher fluorescence quantum yield in solid state (50 to 60%), but lower quantum yields (12-40%) in dilute chloroform solution, in total contrast to CN-free polymers 3c, 3d, and 7b. Identical optical, E-g(opt), and electrochemical band gap energies, E- g(ec), were obtained for 3b, 3c and 3d with intrinsic self-assembly ability, whereas a discrepancy, DeltaE(g), was observed in the cases of the fully substituted polymers 5, 7a, and 7b, whose values are dependent on the level of backbone stiffness and length of the side groups combined with the presence or absence of CN units. The incorporation of CN units in 3b and 7a lowers their respective LUMO level by 220 and 350 meV compared to their corresponding CN-free counterparts 3c and 7b, suggesting an improvement of the electron-accepting strength. Polymers 3b and 7a are efficient electron acceptors suitable for photovoltaic application. The experiments indicate that 3b is a better electron acceptor when used together with M3EH-PPV, but transport properties seem to be better for 7a. With 3b, high external quantum efficiencies of up to 23%, an open circuit voltage of up to 1.52 V, and a white light energy efficiency of 0.65% could be realized in bilayer solar cell devices. LED-devices of configuration ITO/PEDOT:PSS/polymer/Ca/Al from 3b, 3c, 7a, and 7b showed low turn-on voltages between 2 and 2.5 V. The CN-free polymers 3c and 7b exhibit far better EL parameters than their corresponding CN containing counterparts 3b and 7a
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Egbe, D. A. M.
A1  - Ulbricht, C.
A1  - Orgis, Thomas
A1  - Carbonnier, B.
A1  - Kietzke, Thomas
A1  - Peip, M.
A1  - Metzner, M.
A1  - Gericke, M.
A1  - Birckner, Eckhard
A1  - Pakula, T.
A1  - Neher, Dieter
A1  - Grumm, U. W.
T1  - Odd-even effects and the influence of length and specific positioning of alkoxy side chains on the optical properties of PPE-PPV polymers
N2  - This contribution reports the combined influences of odd-even effects and the specific positioning of alkoxy side chains OR1 = (OCn+H-10(2(n+10)+1)) and OR2 = (OCnH2n+1) (with n = 6, 7, 8, 9) on the phenylene-ethynylene and phenylene- vinylene segments, respectively, on the optical properties of hybrid polymers P(n+10)/n of general repeating unit: -Ph-C equivalent to C-Ph-C equivalent to C-Ph-CH=CH-Ph-CH=CH-. For the polymeric materials, visual color impression varies alternatively between orange red (P16/6 and P18/8) and yellow (P17/7 and P19/9) according to the odd and even features of the alkoxy side chains, where odd or even relates to the total number of sp(3)-hybridized atoms within the side chains. This side chain related effect is ascribed to both absorptive and emissive behaviors of the polymers on the basis of photophysical investigations in the bulk. Almost identical thin film absorption spectra were obtained for all four materials; however, the photoluminescence of the odd polymers, P16/6 (lambda(f) = 556 nm) and P18/ 8 (lambda(f) = 614 nm), was red-shifted relative to that of their even counterparts (lambda(f) = 535 nm). Further, the P18/8 maximum at 614 nm can be readily assigned to excimer emission, as evidenced by the largest Stokes shift (5600 cm(- 1)), largest fwhmf-value (3700 cm(-1))(,) and the lowest Phi(f)-value of 24%. The strong pi-pi interchain interaction in P18/8, due to loose alkoxy side chains packing, does not only favor fluorescence quenching but also enable an effective inter- as well as intra-molecular recombination of the generated positive and negative polarons in electrolurninescence, which explains the good EL properties of this polymer irrespective of the solvent used. A voltage-dependent blue shift of the EL spectra of up to 100 nm was observed for P18/8 devices prepared from aromatic solvents. This red to green EL shift as observed with increasing voltage is assigned to conformational changes of the polymer chains with increasing temperature
Y1  - 2005
SN  - 0897-4756
ER  - 
TY  - JOUR
A1  - Fang, Lijia
A1  - Holzmueller, Felix
A1  - Matulaitis, Tomas
A1  - Baasner, Anne
A1  - Hauenstein, Christoph
A1  - Benduhn, Johannes
A1  - Schwarze, Martin
A1  - Petrich, Annett
A1  - Piersimoni, Fortunato
A1  - Scholz, Reinhard
A1  - Zeika, Olaf
A1  - Koerner, Christian
A1  - Neher, Dieter
A1  - Vandewal, Koen
A1  - Leo, Karl
T1  - Fluorine-containing low-energy-gap organic dyes with low voltage losses for organic solar cells
JF  - Synthetic metals : the journal of electronic polymers and electronic molecular materials
N2  - Fluorine-containing donor molecules TFTF, CNTF and PRTF are designed and isomer selectively synthesized for application in vacuum-deposited organic solar cells. These molecules comprise a donor acceptor molecular architecture incorporating thiophene and benzothiadiazole derivatives as the electron-donating and electron-withdrawing moieties, respectively. As opposed to previously reported materials from this class, PRTF can be purified by vacuum sublimation at moderate to high yields because of its higher volatility and better stabilization due to a stronger intramolecular hydrogen bond, as compared to TFTF and CNTF. The UV-vis absorption spectra of the three donors show an intense broadband absorption between 500 nm and 800 nm with, similar positions of their frontier energy levels. The photophysical properties of the three donor molecules are thoroughly tested and optimized in bulk heterojunction solar cells with C-60 as acceptor. PRTF shows the best performance, yielding power conversion efficiencies of up to 3.8%. Moreover, the voltage loss for the PRTF device due to the non radiative recombination of free charge carriers is exceptionally low (0.26 V) as compared to typical values for organic solar cells (>0.34V). (C) 2016 Published by Elsevier B.V.
KW  - (Z)-isomer
KW  - Donor materials
KW  - CH center dot center dot center dot F hydrogen bonds
KW  - Sublimation with good yield
KW  - Low voltage losses
Y1  - 2016
U6  - https://doi.org/10.1016/j.synthmet.2016.10.025
SN  - 0379-6779
VL  - 222
SP  - 232
EP  - 239
PB  - Elsevier
CY  - Lausanne
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  - Fischer, Florian S. U.
A1  - Trefz, Daniel
A1  - Back, Justus
A1  - Kayunkid, Navaphun
A1  - Tornow, Benjamin
A1  - Albrecht, Steve
A1  - Yager, Kevin G.
A1  - Singh, Gurpreet
A1  - Karim, Alamgir
A1  - Neher, Dieter
A1  - Brinkmann, Martin
A1  - Ludwigs, Sabine
T1  - Highly Crystalline Films of PCPDTBT with Branched Side Chains by Solvent Vapor Crystallization: Influence on Opto-Electronic Properties
JF  - Advanced materials
N2  - PCPDTBT, a marginally crystallizable polymer, is crystallized into a new crystal structure using solvent-vapor annealing. Highly ordered areas with three different polymer-chain orientations are identified using TEM/ED, GIWAXS, and polarized Raman spectroscopy. The optical and structural properties differ significantly from films prepared by standard device preparation protocols. Bilayer solar cells, however, show similar performance.
Y1  - 2015
U6  - https://doi.org/10.1002/adma.201403475
SN  - 0935-9648
SN  - 1521-4095
VL  - 27
IS  - 7
SP  - 1223
EP  - 1228
PB  - Wiley-VCH
CY  - Weinheim
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  - Former, C.
A1  - Wagner, H.
A1  - Richert, R.
A1  - Neher, Dieter
A1  - Müllen, K.
T1  - Orientation and dynamics of chainlike dipole arrays: Donor-acceptor-substituted oligophenylenevinylenes in a polymer matrix
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Frisch, Johannes
A1  - Schubert, Marcel
A1  - Preis, Eduard
A1  - Rabe, Jürgen P.
A1  - Neher, Dieter
A1  - Scherf, Ullrich
A1  - Koch, Norbert
T1  - Full electronic structure across a polymer heterojunction solar cell
JF  - Journal of materials chemistry
N2  - We correlate the morphology and energy level alignment of bilayer structures comprising the donor poly(3-hexylthiophene) (P3HT) and the acceptor polyfluorene copolymer poly(9,90dialklylfluorene-alt-4,7-bis(2,5-thiendiyl)-2,1,3-benzothiadiazole) (PFTBTT) with the performance of these bilayers in organic photovoltaic cells (OPVCs). The conducting polymer poly(ethylenedioxythiophene): poly (styrenesulfonate) (PEDT:PSS) was used as the bottom electrode and Ca as the top electrode. Ultraviolet photoelectron spectroscopy (UPS) revealed that notable interface dipoles occur at all interfaces across the OPVC structure, highlighting that vacuum level alignment cannot reliably be used to estimate the electronic properties for device design. Particularly the effective electrode work function values (after contact formation with the conjugated polymers) differ significantly from those of the pristine electrode materials. Chemical reactions between PEDT: PSS and P3HT on the one hand and Ca and PFTBTT on the other hand are identified as cause for the measured interface dipoles. The vacuum level shift between P3HT and PFTBTT is related to mutual energy level pinning at gap states. Annealing induced morphological changes at the P3HT/PFTBTT interface increased the efficiency of OPVCs, while the electronic structure was not affected by thermal treatment.
Y1  - 2012
U6  - https://doi.org/10.1039/c1jm14968g
SN  - 0959-9428
VL  - 22
IS  - 10
SP  - 4418
EP  - 4424
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Fritsch, Tobias
A1  - Kurpiers, Jona
A1  - Roland, Steffen
A1  - Tokmoldin, Nurlan
A1  - Shoaee, Safa
A1  - Ferron, Thomas
A1  - Collins, Brian A.
A1  - Janietz, Silvia
A1  - Vandewal, Koen
A1  - Neher, Dieter
T1  - On the interplay between CT and singlet exciton emission in organic solar cells with small driving force and its impact on voltage loss
JF  - Advanced energy materials
N2  - The interplay between free charge carriers, charge transfer (CT) states and singlet excitons (S-1) determines the recombination pathway and the resulting open circuit voltage (V-OC) of organic solar cells. 
By combining a well-aggregated low bandgap polymer with different blend ratios of the fullerenes PCBM and ICBA, the energy of the CT state (E-CT) is varied by 130 meV while leaving the S-1 energy of the polymer (ES1\[{E_{{{\rm{S}}_1}}}\]) unaffected. 
It is found that the polymer exciton dominates the radiative properties of the blend when ECT\[{E_{{\rm{CT}}}}\] approaches ES1\[{E_{{{\rm{S}}_1}}}\], while the V-OC remains limited by the non-radiative decay of the CT state. 
It is concluded that an increasing strength of the exciton in the optical spectra of organic solar cells will generally decrease the non-radiative voltage loss because it lowers the radiative V-OC limit (V-OC,V-rad), but not because it is more emissive. 
The analysis further suggests that electronic coupling between the CT state and the S-1 will not improve the V-OC, but rather reduce the V-OC,V-rad. 
It is anticipated that only at very low CT state absorption combined with a fairly high CT radiative efficiency the solar cell benefit from the radiative properties of the singlet excitons.
KW  - external quantum efficiency
KW  - organic photovoltaics
KW  - ternary blends
KW  - voltage losses
Y1  - 2022
U6  - https://doi.org/10.1002/aenm.202200641
SN  - 1614-6832
SN  - 1614-6840
VL  - 12
IS  - 31
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Galbrecht, Frank
A1  - Yang, X. H.
A1  - Nehls, B. S.
A1  - Neher, Dieter
A1  - Farrell, Tony
A1  - Scherf, Ullrich
T1  - Semiconducting polyfluorenes with electrophosphorescent on-chain platinum-salen chromophores
N2  - The synthesis of statistical fluorene-type copolymers with on-chain Pt-salen phosphorescent units and their use in electrophosphorescent OLEDs is reported
Y1  - 2005
SN  - 1359-7345
ER  - 
TY  - JOUR
A1  - García-Benito, Inés
A1  - Quarti, Claudio
A1  - Queloz, Valentin I. E.
A1  - Hofstetter, Yvonne J.
A1  - Becker-Koch, David
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Orlandi, Simonetta
A1  - Cavazzini, Marco
A1  - Pozzi, Gianluca
A1  - Even, Jacky
A1  - Nazeeruddin, Mohammad Khaja
A1  - Vaynzof, Yana
A1  - Grancini, Giulia
T1  - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
JF  - Frontiers in Chemistry
N2  - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
KW  - fluorinated organic spacer
KW  - 2D perovskites
KW  - phase transition
KW  - temperature dependence
KW  - excitonic materials
Y1  - 2020
U6  - https://doi.org/10.3389/fchem.2019.00946
SN  - 2296-2646
VL  - 7
SP  - 1
EP  - 11
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - GEN
A1  - García-Benito, Inés
A1  - Quarti, Claudio
A1  - Queloz, Valentin I. E.
A1  - Hofstetter, Yvonne J.
A1  - Becker-Koch, David
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Orlandi, Simonetta
A1  - Cavazzini, Marco
A1  - Pozzi, Gianluca
A1  - Even, Jacky
A1  - Nazeeruddin, Mohammad Khaja
A1  - Vaynzof, Yana
A1  - Grancini, Giulia
T1  - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1421 
KW  - fluorinated organic spacer
KW  - 2D perovskites
KW  - phase transition
KW  - temperature dependence
KW  - excitonic materials
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-512420
SN  - 1866-8372
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  - Gehrig, Dominik W.
A1  - Roland, Steffen
A1  - Howard, Ian A.
A1  - Kamm, Valentin
A1  - Mangold, Hannah
A1  - Neher, Dieter
A1  - Laquai, Frederic
T1  - Efficiency-limiting processes in low-bandgap polymer:Perylene diimide photovoltaic blends
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - The charge generation and recombination processes following photo-excitation of a low-bandgap polymer:perylene diimide photovoltaic blend are investigated by transient absorption pump-probe spectroscopy covering a dynamic range from femto-to microseconds to get insight into the efficiency-limiting photophysical processes. The several tens of picoseconds, and its efficiency is only half of that in a polymer:fullerene photoinduced electron transfer from the polymer to the perylene acceptor takes up to blend. This reduces the short-circuit current. Time-delayed collection field experiments reveal that the subsequent charge separation is strongly field-dependent, limiting the fill factor and lowering the short-circuit current in polymer:PDI devices. Upon excitation of the acceptor in the low-bandgap polymer blend, the PDI exciton undergoes charge transfer on a time scale of several tens of picoseconds. However, a significant fraction of the charges generated at the interface are quickly lost because of fast geminate recombination. This reduces the short-circuit current even further, leading to a scenario in which only around 2596 of the initial photoexcitations generate free charges that can potentially contribute to the photocurrent. In summary, the key photophysical limitations of perylene diimide as an acceptor in low-bandgap polymer blends appear at the interface between the materials, with the kinetics of both charge generation and separation inhibited as compared to that of fullerenes.
Y1  - 2014
U6  - https://doi.org/10.1021/jp503366m
SN  - 1932-7447
VL  - 118
IS  - 35
SP  - 20077
EP  - 20085
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Gerhard, Reimund
A1  - Wegener, Michael
A1  - Künstler, Wolfgang
A1  - Wirges, Werner
A1  - Görne, Thomas
A1  - Urayama, D.
A1  - Neher, Dieter
T1  - Inverse piezoelectricity of porous PTFE films with bipolar space charge
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Ghani, Fatemeh
A1  - Opitz, Andreas
A1  - Pingel, Patrick
A1  - Heimel, Georg
A1  - Salzmann, Ingo
A1  - Frisch, Johannes
A1  - Neher, Dieter
A1  - Tsami, Argiri
A1  - Scherf, Ullrich
A1  - Koch, Norbert
T1  - Charge Transfer in and Conductivity of Molecularly Doped Thiophene-Based Copolymers
JF  - Journal of polymer science : B, Polymer physics
N2  - The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design.
KW  - charge transfer
KW  - conducting polymers
KW  - doping
KW  - thiophene
Y1  - 2015
U6  - https://doi.org/10.1002/polb.23631
SN  - 0887-6266
SN  - 1099-0488
VL  - 53
IS  - 1
SP  - 58
EP  - 63
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Gorenflot, Julien
A1  - Paulke, Andreas
A1  - Piersimoni, Fortunato
A1  - Wolf, Jannic
A1  - Kan, Zhipeng
A1  - Cruciani, Federico
A1  - El Labban, Abdulrahman
A1  - Neher, Dieter
A1  - Beaujuge, Pierre M.
A1  - Laquai, Frederic
T1  - From recombination dynamics to device performance
BT  - quantifying the efficiency of exciton dissociation, charge separation, and extraction in bulk heterojunction solar cells with Fluorine-Substituted polymer donors
JF  - dvanced energy materials
N2  - An original set of experimental and modeling tools is used to quantify the yield of each of the physical processes leading to photocurrent generation in organic bulk heterojunction solar cells, enabling evaluation of materials and processing condition beyond the trivial comparison of device performances. Transient absorption spectroscopy, “the” technique to monitor all intermediate states over the entire relevant timescale, is combined with time-delayed collection field experiments, transfer matrix simulations, spectral deconvolution, and parametrization of the charge carrier recombination by a two-pool model, allowing quantification of densities of excitons and charges and extrapolation of their kinetics to device-relevant conditions. Photon absorption, charge transfer, charge separation, and charge extraction are all quantified for two recently developed wide-bandgap donor polymers: poly(4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-3,4-difluorothiophene) (PBDT[2F]T) and its nonfluorinated counterpart poly(4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-3,4-thiophene) (PBDT[2H]T) combined with PC71BM in bulk heterojunctions. The product of these yields is shown to agree well with the devices' external quantum efficiency. This methodology elucidates in the specific case studied here the origin of improved photocurrents obtained when using PBDT[2F]T instead of PBDT[2H]T as well as upon using solvent additives. Furthermore, a higher charge transfer (CT)-state energy is shown to lead to significantly lower energy losses (resulting in higher VOC) during charge generation compared to P3HT:PCBM.
KW  - bulk heterojunction
KW  - charge generation yield
KW  - charge recombination yield
KW  - polymer solar cells
KW  - transient absorption spectroscopy
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201701678
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 4
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Grell, M.
A1  - Knoll, W.
A1  - Lupo, D.
A1  - Meisel, A.
A1  - Miteva, T.
A1  - Neher, Dieter
A1  - Nothofer, Heinz-Georg
A1  - Scherf, Ullrich
A1  - Yasuda, H.
T1  - Blue polarized electroluminescence from a liquid crystalline polyfluorene
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Grischek, Max
A1  - Caprioglio, Pietro
A1  - Zhang, Jiahuan
A1  - Pena-Camargo, Francisco
A1  - Sveinbjornsson, Kari
A1  - Zu, Fengshuo
A1  - Menzel, Dorothee
A1  - Warby, Jonathan
A1  - Li, Jinzhao
A1  - Koch, Norbert
A1  - Unger, Eva
A1  - Korte, Lars
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
A1  - Albrecht, Steve
T1  - Efficiency Potential and Voltage Loss of Inorganic CsPbI2Br Perovskite Solar Cells
JF  - Solar RRL
N2  - Inorganic perovskite solar cells show excellent thermal stability, but the reported power conversion efficiencies are still lower than for organic-inorganic perovskites. This is mainly caused by lower open-circuit voltages (V(OC)s). Herein, the reasons for the low V-OC in inorganic CsPbI2Br perovskite solar cells are investigated. Intensity-dependent photoluminescence measurements for different layer stacks reveal that n-i-p and p-i-n CsPbI2Br solar cells exhibit a strong mismatch between quasi-Fermi level splitting (QFLS) and V-OC. Specifically, the CsPbI2Br p-i-n perovskite solar cell has a QFLS-e center dot V-OC mismatch of 179 meV, compared with 11 meV for a reference cell with an organic-inorganic perovskite of similar bandgap. On the other hand, this study shows that the CsPbI2Br films with a bandgap of 1.9 eV have a very low defect density, resulting in an efficiency potential of 20.3% with a MeO-2PACz hole-transporting layer and 20.8% on compact TiO2. Using ultraviolet photoelectron spectroscopy measurements, energy level misalignment is identified as a possible reason for the QFLS-e center dot V-OC mismatch and strategies for overcoming this V-OC limitation are discussed. This work highlights the need to control the interfacial energetics in inorganic perovskite solar cells, but also gives promise for high efficiencies once this issue is resolved.
KW  - CsPbI2Br
KW  - efficiency potentials
KW  - inorganic perovskites
KW  - photoluminescence
KW  - solar cells
KW  - voltage losses
Y1  - 2022
U6  - https://doi.org/10.1002/solr.202200690
SN  - 2367-198X
VL  - 6
IS  - 11
PB  - Wiley-VCH
CY  - Weinheim
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  - Hahn, Tobias
A1  - Tscheuschner, Steffen
A1  - Saller, Christina
A1  - Strohriegl, Peter
A1  - Boregowda, Puttaraju
A1  - Mukhopadhyay, Tushita
A1  - Patil, Satish
A1  - Neher, Dieter
A1  - Bässler, Heinz
A1  - Köhler, Anna
T1  - Role of Intrinsic Photogeneration in Single Layer and Bilayer Solar Cells with C-60 and PCBM
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
Y1  - 2016
U6  - https://doi.org/10.1021/acs.jpcc.6b08471
SN  - 1932-7447
VL  - 120
SP  - 25083
EP  - 25091
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Hofacker, Andreas
A1  - Neher, Dieter
T1  - Dispersive and steady-state recombination in organic disordered semiconductors
JF  - Physical review : B, Condensed matter and materials physics
N2  - Charge carrier recombination in organic disordered semiconductors is strongly influenced by the thermalization of charge carriers in the density of states (DOS). Measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time dependent since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order of the equilibrated system under steady excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevB.96.245204
SN  - 2469-9950
SN  - 2469-9969
VL  - 96
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Hofacker, Andreas
A1  - Neher, Dieter
T1  - Dispersive and steady-state recombination in organic disordered semiconductors
JF  - Physical review : B, Condensed matter and materials physics
N2  - Charge carrier recombination in organic disordered semiconductors is strongly influenced by the thermalization of charge carriers in the density of states (DOS). Measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time dependent since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order of the equilibrated system under steady excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevB.96.245204
SN  - 2469-9950
SN  - 2469-9969
VL  - 96
SP  - 5640
EP  - 5649
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Hoffmann, Sebastian T.
A1  - Jaiser, Frank
A1  - Hayer, Anna
A1  - Baessler, Heinz
A1  - Unger, Thomas
A1  - Athanasopoulos, Stavros
A1  - Neher, Dieter
A1  - Koehler, Anna
T1  - How Do Disorder, Reorganization, and Localization Influence the Hole
 Mobility in Conjugated Copolymers?
JF  - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
N2  - In order to unravel the intricate interplay between disorder effects, molecular reorganization, and charge carrier localization, a comprehensive study was conducted on hole transport in a series of conjugated alternating phenanthrene indenofluorene copolymers. Each polymer in the series contained one further comonomer comprising monoamines, diamines, or amine-free structures, whose influence on the electronic, optical, and charge transport properties was studied. The series covered a wide range of highest occupied molecular orbital (HOMO) energies as determined by cyclovoltammetry. The mobility, inferred from time-of-flight (ToF) experiments as a function of temperature and electric field, was found to depend exponentially on the HOMO energy. Since possible origins for this effect include energetic disorder, polaronic effects, and wave function localization, the relevant parameters were determined using a range of methods. Disorder and molecular reorganization were established first by an analysis of absorption and emission measurements and second by an analysis of the ToF measurements. In addition, density functional theory calculations were carried out to determine how localized or delocalized holes on a polymer chain are and to compare calculated reorganization energies with those that have been inferred from optical spectra. In summary, we conclude that molecular reorganization has little effect on the hole mobility in this system while both disorder effects and hole localization in systems with low-lying HOMOs are predominant. In particular, as the energetic disorder is comparable for the copolymers, the absolute value of the hole mobility at room temperature is determined by the hole localization associated with the triarylamine moieties.
Y1  - 2013
U6  - https://doi.org/10.1021/ja308820j
SN  - 0002-7863
VL  - 135
IS  - 5
SP  - 1772
EP  - 1782
PB  - AMER CHEMICAL SOC
CY  - WASHINGTON
ER  - 
TY  - JOUR
A1  - Hofmann, Alexander J. L.
A1  - Züfle, Simon
A1  - Shimizu, Kohei
A1  - Schmid, Markus
A1  - Wessels, Vivien
A1  - Jäger, Lars
A1  - Altazin, Stephane
A1  - Ikegami, Keitaro
A1  - Khan, Motiur Rahman
A1  - Neher, Dieter
A1  - Ishii, Hisao
A1  - Ruhstaller, Beat
A1  - Brütting, Wolfgang
T1  - Dipolar Doping of Organic Semiconductors to Enhance Carrier Injection
JF  - Physical review applied
N2  - If not oriented perfectly isotropically, the strong dipole moment of polar organic semiconductor materials such as tris-(8-hydroxyquinolate)aluminum (Alq3) will lead to the buildup of a giant surface potential (GSP) and thus to a macroscopic dielectric polarization of the organic film. Despite this having been a known fact for years, the implications of such high potentials within an organic layer stack have only been studied recently. In this work, the influence of the GSP on hole injection into organic layers is investigated. Therefore, we apply a concept called dipolar doping to devices consisting of the prototypical organic materials N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as nonpolar host and Alq3 as dipolar dopant with different mixing ratios to tune the GSP. The mixtures are investigated in single-layer monopolar devices as well as bilayer metal/insulator/semiconductor structures. Characterization is done electrically using current-voltage (I-V) characteristics, impedance spectroscopy, and charge extraction by linearly increasing voltage and time of flight, as well as with ultraviolet photoelectron spectroscopy. We find a maximum in device performance for moderate to low doping concentrations of the polar species in the host. The observed behavior can be described on the basis of the Schottky effect for image-force barrier lowering, if the changes in the interface dipole, the carrier mobility, and the GSP induced by dipolar doping are taken into account.
KW  - Carrier dynamics
KW  - Electric polarization
KW  - Optoelectronics
KW  - Organic electronics
KW  - Doped semiconductors
KW  - Interfaces
KW  - Organic LEDs
KW  - Organic semiconductors
Y1  - 2019
U6  - https://doi.org/10.1103/PhysRevApplied.12.064052
SN  - 2331-7019
VL  - 12
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Hosseini, Seyed Mehrdad
A1  - Roland, Steffen
A1  - Kurpiers, Jona
A1  - Chen, Zhiming
A1  - Zhang, Kai
A1  - Huang, Fei
A1  - Armin, Ardalan
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Impact of Bimolecular Recombination on the Fill Factor of Fullerene and Nonfullerene-Based Solar Cells
BT  - A Comparative Study of Charge Generation and Extraction
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - Power conversion efficiencies of donor/acceptor organic solar cells utilizing nonfullerene acceptors have now increased beyond the record of their fullerene-based counterparts. There remain many fundamental questions regarding nanomorphology, interfacial states, charge generation and extraction, and losses in these systems. Herein, we present a comparative study of bulk heterojunction solar cells composed of a recently introduced naphthothiadiazole-based polymer (NT812) as the electron donor and two different acceptor molecules, namely, [6,6]-phenyl-C71-butyric acid methyl ester (PCBM)[70] and 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC). A comparison between the photovoltaic performance of these two types of solar cells reveals that the open-circuit voltage (Voc) of the NT812:ITIC-based solar cell is larger, but the fill factor (FF) is lower than that of the NT812:PCBM[70] device. We find the key reason behind this reduced FF in the ITIC-based device to be faster nongeminate recombination relative to the NT812:PCBM[70] system.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpcc.8b11669
SN  - 1932-7447
VL  - 123
IS  - 11
SP  - 6823
EP  - 6830
PB  - American Chemical Society
CY  - Washington
ER  -