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 - 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 - Kurpiers, Jona A1 - Neher, Dieter T1 - Dispersive Non-Geminate Recombination in an Amorphous Polymer: Fullerene Blend JF - Scientific reports N2 - Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer: fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions. Y1 - 2016 U6 - https://doi.org/10.1038/srep26832 SN - 2045-2322 VL - 6 PB - Nature Publ. Group CY - London ER - TY - GEN A1 - Kurpiers, Jona A1 - Neher, Dieter T1 - Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend N2 - Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 228 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-91541 ER - TY - JOUR A1 - Kurpiers, Jona A1 - Neher, Dieter T1 - Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend JF - Scientific reports N2 - Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions. Y1 - 2016 U6 - https://doi.org/10.1038/srep26832 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London 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 - 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 - Lu, Guanghao A1 - Di Pietro, Riccardo A1 - Kölln, Lisa Sophie A1 - Nasrallah, Iyad A1 - Zhou, Ling A1 - Mollinger, Sonya A1 - Himmelberger, Scott A1 - Koch, Norbert A1 - Salleo, Alberto A1 - Neher, Dieter T1 - Dual-Characteristic Transistors Based on Semiconducting Polymer Blends JF - Advanced electronic materials N2 - A dual-characteristic polymer field-effect transistor has markedly different characteristics in low and high voltage operations. In the low-voltage range (<5 V) it shows sharp subthreshold slopes (0.3–0.4 V dec−1), using which a low-voltage inverter with gain 8 is realized, while high-voltage (>5 V) induces symmetric current with regard to drain and gate voltages, leading to discrete differential (trans) conductances. KW - charge accumulation KW - crystalline ordering KW - field-effect-transistor KW - semiconducting polymers Y1 - 2016 U6 - https://doi.org/10.1002/aelm.201600267 SN - 2199-160X VL - 2 SP - 2344 EP - 2351 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Li, Tian-yi A1 - Benduhn, Johannes A1 - Qiao, Zhi A1 - Liu, Yuan A1 - Li, Yue A1 - Shivhare, Rishi A1 - Jaiser, Frank A1 - Wang, Pei A1 - Ma, Jie A1 - Zeika, Olaf A1 - Neher, Dieter A1 - Mannsfeld, Stefan C. B. A1 - Ma, Zaifei A1 - Vandewal, Koen A1 - Leo, Karl T1 - Effect of H- and J-Aggregation on the Photophysical and Voltage Loss of Boron Dipyrromethene Small Molecules in Vacuum-Deposited Organic Solar Cells JF - The journal of physical chemistry letters N2 - An understanding of the factors limiting the open-circuit voltage (V-oc) and related photon energy loss mechanisms is critical to increase the power conversion efficiency (PCE) of small-molecule organic solar cells (OSCs), especially those with near-infrared (NIR) absorbers. In this work, two NIR boron dipyrromethene (BODIPY) molecules are characterized for application in planar (PHJ) and bulk (BHJ) heterojunction OSCs. When two H atoms are substituted by F atoms on the peripheral phenyl rings of the molecules, the molecular aggregation type in the thin film changes from the H-type to J-type. For PHJ devices, the nonradiative voltage loss of 0.35 V in the J-aggregated BODIPY is lower than that of 0.49 V in the H-aggregated device. In BHJ devices with a nonradiative voltage loss of 0.35 V, a PCE of 5.5% is achieved with an external quantum efficiency (EQE) maximum of 68% at 700 nm. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpclett.9b01222 SN - 1948-7185 VL - 10 IS - 11 SP - 2684 EP - 2691 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Pingel, P. A1 - Schwarzl, R. A1 - Neher, Dieter T1 - Effect of molecular p-doping on hole density and mobility in poly(3-hexylthiophene) JF - Applied physics letters N2 - Employing impedance spectroscopy, we have studied the hole density, conductivity, and mobility of poly(3-hexylthiophene), P3HT, doped with the strong molecular acceptor tetrafluorotetracyanoquinodimethane, F(4)TCNQ. We find that the hole density increases linearly with the F(4)TCNQ concentration. Furthermore, the hole mobility is decreased upon doping at low-to-medium doping level, which is rationalized by an analytic model of carrier mobility in doped organic semiconductors [V. I. Arkhipov, E. V. Emelianova, P. Heremans, and H. Bassler, Phys. Rev. B 72, 235202 (2005)]. We infer that the presence of ionized F(4)TCNQ molecules in the P3HT layer increases energetic disorder, which diminishes the carrier mobility. Y1 - 2012 U6 - https://doi.org/10.1063/1.3701729 SN - 0003-6951 VL - 100 IS - 14 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Zen, Achmad A1 - Pflaum, J. A1 - Hirschmann, S. A1 - Zhuang, W. A1 - Jaiser, Frank A1 - Asawapirom, Udom A1 - Rabe, J. P. A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - Effect of molecular weight and annealing of poly (3-hexylthiophene)s on the performance of organic field-effect transistors N2 - The optical, structural, and electrical properties of thin layers made from poly(3-hexylthiophene) (P3HT) samples of different molecular weights are presented. As reported in a previous paper by Kline et al., Adv. Mater 2003, 15, 1519, the mobilities of these layers are a strong function of the molecular weight, with the largest mobility found for the largest molecular weight. Atomic force microscopy studies reveal a complex polycrystalline morphology which changes considerably upon annealing. X-ray studies show the occurrence of a layered phase for all P3HT fractions, especially after annealing at 1.50 degreesC . However, there is no clear correlation between the differences in the transport properties and the data from structural investigations. In order to reveal the processes limiting the mobility in these layers, the transistor properties were investigated as a function of temperature. The mobility decreases continuously with increasing temperatures; with the same trend pronounced thermochromic effects of the P3HT films occur. Apparently, the polymer chains adopt a more twisted, disordered conformation at higher temperatures, leading to interchain transport barriers. We conclude that the backbone conformation of the majority of the bulk material rather than the crystallinity of the layer is the most crucial parameter controlling the charge transport in these P3HT layers. This interpretation is supported by the significant blue-shift of the solid-state absorption spectra with decreasing molecular weight, which is indicative of a larger distortion of the P3HT backbone in the low-molecular weight P3HT layers Y1 - 2004 ER - TY - JOUR A1 - Kniepert, Juliane A1 - Lange, Ilja A1 - Heidbrink, Jan A1 - Kurpiers, Jona A1 - Brenner, Thomas J. K. A1 - Koster, L. Jan Anton A1 - Neher, Dieter T1 - Effect of Solvent Additive on Generation, Recombination, and Extraction in PTB7:PCBM Solar Cells: A Conclusive Experimental and Numerical Simulation Study JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Time-delayed collection field (TDCF), bias-assisted charge extraction (BACE), and space charge-limited current (SCLC) measurements are combined with complete numerical device simulations to unveil the effect of the solvent additive 1,8-diiodooctane (DIO) on the performance of PTB7:PCBM bulk heterojunction solar cells. DIO is shown to increase the charge generation rate, reduce geminate and bimolecular recombination, and increase the electron mobility. In total, the reduction of loss currents by processing with the additive raises the power conversion efficiency of the PTB7:PCBM blend by a factor of almost three. The lower generation rates and higher geminate recombination losses in devices without DIO are consistent with a blend morphology comprising large fullerene clusters embedded within a PTB7-rich matrix, while the low electron mobility suggests that these fullerene clusters are themselves composed of smaller pure fullerene aggregates separated by disordered areas. Our device simulations show unambiguously that the effect of the additive on the shape of the currentvoltage curve (J-V) cannot be ascribed to the variation of only the mobility, the recombination, or the field dependence of generation. It is only when the changes of all three parameters are taken into account that the simulation matches the experimental J-V characteristics under all illumination conditions and for a wide range of voltages. Y1 - 2015 U6 - https://doi.org/10.1021/jp512721e SN - 1932-7447 VL - 119 IS - 15 SP - 8310 EP - 8320 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yuan, Jun A1 - Zhang, Chujun A1 - Qiu, Beibei A1 - Liu, Wei A1 - So, Shu Kong A1 - Mainville, Mathieu A1 - Leclerc, Mario A1 - Shoaee, Safa A1 - Neher, Dieter A1 - Zou, Yingping T1 - Effects of energetic disorder in bulk heterojunction organic solar cells JF - Energy & environmental science N2 - Organic solar cells (OSCs) have progressed rapidly in recent years through the development of novel organic photoactive materials, especially non-fullerene acceptors (NFAs). Consequently, OSCs based on state-of-the-art NFAs have reached significant milestones, such as similar to 19% power conversion efficiencies (PCEs) and small energy losses (less than 0.5 eV). Despite these significant advances, understanding of the interplay between molecular structure and optoelectronic properties lags significantly behind. For example, despite the theoretical framework for describing the energetic disorder being well developed for the case of inorganic semiconductors, the question of the applicability of classical semiconductor theories in analyzing organic semiconductors is still under debate. A general observation in the inorganic field is that inorganic photovoltaic materials possessing a polycrystalline microstructure exhibit suppressed disorder properties and better charge carrier transport compared to their amorphous analogs. Accordingly, this principle extends to the organic semiconductor field as many organic photovoltaic materials are synthesized to pursue polycrystalline-like features. Yet, there appears to be sporadic examples that exhibit an opposite trend. However, full studies decoupling energetic disorder from aggregation effects have largely been left out. Hence, the potential role of the energetic disorder in OSCs has received little attention. Interestingly, recently reported state-of-the-art NFA-based devices could achieve a small energetic disorder and high PCE at the same time; and interest in this investigation related to the disorder properties in OSCs was revived. In this contribution, progress in terms of the correlation between molecular design and energetic disorder is reviewed together with their effects on the optoelectronic mechanism and photovoltaic performance. Finally, the specific challenges and possible solutions in reducing the energetic disorder of OSCs from the viewpoint of materials and devices are proposed. Y1 - 2022 U6 - https://doi.org/10.1039/d2ee00271j SN - 1754-5692 SN - 1754-5706 VL - 15 IS - 7 SP - 2806 EP - 2818 PB - Royal Society of Chemistry CY - Cambridge 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 - 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 - 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 - Vandewal, Koen A1 - Albrecht, Steve A1 - Hoke, Eric T. A1 - Graham, Kenneth R. A1 - Widmer, Johannes A1 - Douglas, Jessica D. A1 - Schubert, Marcel A1 - Mateker, William R. A1 - Bloking, Jason T. A1 - Burkhard, George F. A1 - Sellinger, Alan A1 - Frechet, Jean M. J. A1 - Amassian, Aram A1 - Riede, Moritz K. A1 - McGehee, Michael D. A1 - Neher, Dieter A1 - Salleo, Alberto T1 - Efficient charge generation by relaxed charge-transfer states at organic interfaces JF - Nature materials N2 - carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold viaweakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer: fullerene, small-molecule:C-60 and polymer: polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy. Y1 - 2014 U6 - https://doi.org/10.1038/NMAT3807 SN - 1476-1122 SN - 1476-4660 VL - 13 IS - 1 SP - 63 EP - 68 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Unger, Th. A1 - Jaiser, Frank A1 - Neher, Dieter A1 - Thesen, M. W. A1 - Krüger, H. T1 - Efficient green electrophosphorescence based on ambipolar nonconjugated polymers evaluation of transport and emission properties JF - Journal of applied physics N2 - New materials for polymer organic light-emitting diodes based on a polymer matrix doped with phosphorescent dyes are presented. The matrix system is based on a polystyrene backbone bearing either electron or hole transporting units at the 4-position of each repeat unit. Random copolymers and polymer blend systems of the homopolymers are prepared, both with 62 wt.% electron transporting and 38 wt.% hole transporting moieties. Adding a green electrophosphorescent dye to the polymer matrix leads to efficient electroluminescence with a maximum current efficiency of 35 cd/A and a maximum external quantum efficiency of up to 10%. The mobilities of electrons and holes in the dye-doped copolymer, as measured by transient electroluminescence, are around 5 x 10(-5) and 5 x 10(-6) cm(2)/Vs, respectively, while the blend of the two homopolymers exhibits slightly lower mobilities of both types of carriers. Despite the pronounced imbalance of charge transport, the device performance is almost entirely limited by the phosphorescence efficiency of the dye, implying balanced flow of holes and electrons into the active region. Also, devices made with either the copolymer or the blend yielded very similar device efficiencies, despite the noticeable difference in electron and hole mobility. It is proposed that electrons are efficiently blocked at the interlayer and that the so-formed space charge assists the balanced injection of holes. Y1 - 2011 U6 - https://doi.org/10.1063/1.3618681 SN - 0021-8979 SN - 1089-7550 VL - 110 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Albrecht, Steve A1 - Grootoonk, Bjorn A1 - Neubert, Sebastian A1 - Roland, Steffen A1 - Wordenweber, Jan A1 - Meier, Matthias A1 - Schlatmann, Rutger A1 - Gordijn, Aad A1 - Neher, Dieter T1 - Efficient hybrid inorganic/organic tandem solar cells with tailored recombination contacts JF - Solar energy materials & solar cells : an international journal devoted to photovoltaic, photothermal, and photochemical solar energy conversion N2 - In this work, the authors present a 7.5% efficient hybrid tandem solar cell with the bottom cell made of amorphous silicon and a Si-PCPDTBT:PC70BM bulk heterojunction top cell. Loss-free recombination contacts were realized by combing Al-doped ZnO with either the conducting polymer composite PEDOT:PSS or with a bilayer of ultrathin Al and MoO3. Optimization of these contacts results in tandem cells with high fill factors of 70% and an open circuit voltage close to the sum of those of the sub-cells. This is the best efficiency reported for this type of hybrid tandem cell so far. Optical and electrical device modeling suggests that the efficiency can be increased to similar to 12% on combining a donor polymer with suitable absorption onset with PCBM. We also describe proof-of-principle studies employing light trapping in hybrid tandem solar cells, suggesting that this device architecture has the potential to achieve efficiencies well above 12%. (C) 2014 Elsevier B.V. All rights reserved. KW - Hybrid solar cells KW - Tandem solar cells KW - Organic solar cells KW - Bulk heterojunction KW - Efficiency optimization Y1 - 2014 U6 - https://doi.org/10.1016/j.solmat.2014.04.020 SN - 0927-0248 SN - 1879-3398 VL - 127 SP - 157 EP - 162 PB - Elsevier CY - Amsterdam 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 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Galbrecht, Frank A1 - Scherf, Ullrich T1 - Efficient polymer electrophosphoreseent devices with interfacial layers JF - Advanced functional materials N2 - It is shown that several polymers can form insoluble interfacial layers on a poly (ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layer after annealing of the double-layer structure. The thickness of the interlayer is dependent on the characteristics of the underlying PEDOT.PSS and the molecular weight of the polymers. It is further shown that the electronic structures of the interlayer polymers have a significant effect on the properties of red-light-emitting polymer-based electrophosphorescent devices. Upon increasing the highest occupied molecular orbital and lowest unoccupied molecular orbital positions, a significant increase in current density and device efficiency is observed. This is attributed to efficient blocking of electrons in combination with direct injection of holes from the interlayer to the phosphorescent dye. Upon proper choice of the interlayer polymer, efficient red, polymer-based electrophosphorescent devices with a peak luminance efficiency of 5.5 cd A(-1) (external quantum efficiency = 6 %) and a maximum power-conversion efficiency of 5 Im W-1 can be realized. Y1 - 2006 U6 - https://doi.org/10.1002/adfm.200500834 SN - 1616-301X SN - 1616-3028 VL - 16 IS - 16 SP - 2156 EP - 2162 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kietzke, Thomas A1 - Horhold, H. H. A1 - Neher, Dieter T1 - Efficient polymer solar cells based on M3EH-PPV N2 - We report on polymer blend solar cells with an external quantum efficiency of more than 30% and a hi-h overall energy conversion efficiency (ECE) under white light illumination (100 mW/cm(2)) Of Lip to 1.7% using a blend of M3EH- PPV (poly [2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5(2-ethylhexyloxy)-(1,4-pheiiylene-1,2-ethenylene)]) and CN-ether-PPV (poly[oxa-1,4-phenylene-1,2(1-cyano)ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)ethellyiene-1,4- phenylene]). We attribute these high efficiencies to the formation of a vertically composition graded structure during spin coating Photoluminescence measurements performed on the blend layers indicated the formation of exciplexes between both types of polymers, which we propose to be one factor preventing even higher efficiencies Y1 - 2005 ER - TY - JOUR A1 - Al-Sa'di, Mahmoud A1 - Jaiser, Frank A1 - Bagnich, Sergey A. A1 - Unger, Thomas A1 - Blakesley, James C. A1 - Wilke, Andreas A1 - Neher, Dieter T1 - Electrical and optical simulations of a polymer-based phosphorescent organic light-emitting diode with high efficiency JF - Journal of polymer science : B, Polymer physics N2 - A comprehensive numerical device simulation of the electrical and optical characteristics accompanied with experimental measurements of a new highly efficient system for polymer-based light-emitting diodes doped with phosphorescent dyes is presented. The system under investigation comprises an electron transporter attached to a polymer backbone blended with an electronically inert small molecule and an iridium-based green phosphorescent dye which serves as both emitter and hole transporter. The device simulation combines an electrical and an optical model. Based on the known highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of all components as well as the measured electrical and optical characteristics of the devices, we model the emissive layer as an effective medium using the dye's HOMO as hole transport level and the polymer LUMO as electron transport level. By fine-tuning the injection barriers at the electron and hole-injecting contact, respectively, in simulated devices, unipolar device characteristics were fitted to the experimental data. Simulations using the so-obtained set of parameters yielded very good agreement to the measured currentvoltage, luminancevoltage characteristics, and the emission profile of entire bipolar light-emitting diodes, without additional fitting parameters. The simulation was used to gain insight into the physical processes and the mechanisms governing the efficiency of the organic light-emitting diode, including the position and extent of the recombination zone, carrier concentration profiles, and field distribution inside the device. The simulations show that the device is severely limited by hole injection, and that a reduction of the hole-injection barrier would improve the device efficiency by almost 50%. KW - conjugated polymers KW - high performance polymers KW - organic electronics KW - organic light-emitting diode KW - simulations KW - TCAD Y1 - 2012 U6 - https://doi.org/10.1002/polb.23158 SN - 0887-6266 VL - 50 IS - 22 SP - 1567 EP - 1576 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Ullbrich, Sascha A1 - Benduhn, Johannes A1 - Jia, Xiangkun A1 - Nikolis, Vasileios C. A1 - Tvingstedt, Kristofer A1 - Piersimoni, Fortunato A1 - Roland, Steffen A1 - Liu, Yuan A1 - Wu, Jinhan A1 - Fischer, Axel A1 - Neher, Dieter A1 - Reineke, Sebastian A1 - Spoltore, Donato A1 - Vandewal, Koen T1 - Emissive and charge-generating donor-acceptor interfaces for organic optoelectronics with low voltage losses JF - Nature materials N2 - Intermolecular charge-transfer states at the interface between electron donating (D) and accepting (A) materials are crucial for the operation of organic solar cells but can also be exploited for organic light-emitting diodes(1,2). Non-radiative charge-transfer state decay is dominant in state-of-the-art D-A-based organic solar cells and is responsible for large voltage losses and relatively low power-conversion efficiencies as well as electroluminescence external quantum yields in the 0.01-0.0001% range(3,4). In contrast, the electroluminescence external quantum yield reaches up to 16% in D-A-based organic light-emitting diodes(5-7). Here, we show that proper control of charge-transfer state properties allows simultaneous occurrence of a high photovoltaic and emission quantum yield within a single, visible-light-emitting D-A system. This leads to ultralow-emission turn-on voltages as well as significantly reduced voltage losses upon solar illumination. These results unify the description of the electro-optical properties of charge-transfer states in organic optoelectronic devices and foster the use of organic D-A blends in energy conversion applications involving visible and ultraviolet photons(8-11). KW - Electronics, photonics and device physics KW - Optoelectronic devices and components KW - Photonic devices KW - Solar energy and photovoltaic technology Y1 - 2019 U6 - https://doi.org/10.1038/s41563-019-0324-5 SN - 1476-1122 SN - 1476-4660 VL - 18 IS - 5 SP - 459 EP - 464 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Bagnich, Sergey A. A1 - Im, C. A1 - Bassler, H. A1 - Neher, Dieter A1 - Scherf, Ullrich T1 - Energy transfer in a ladder-type methyl-poly(para-phenylene) doped by Pt(II)octaethylporphyrin N2 - The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped by platinum-porphyrin dye PtOEP covering the concentration 10(-3) to 5% by weight has been measured employing cw and transient techniques. Upon excitating into the range of absorption of the host strong phosphorescence of the dopant is observed. Possible ways of populating of the dopant triplet state are considered. It is shown that the main channel is singlet-singlet energy transfer among chromophor groups of the polymer followed by Forster-type transfer to the guest and subsequent intersystem crossing. (C) 2003 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0301-0104 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 - Pranav, Manasi A1 - Benduhn, Johannes A1 - Nyman, Mathias A1 - Hosseini, Seyed Mehrdad A1 - Kublitski, Jonas A1 - Shoaee, Safa A1 - Neher, Dieter A1 - Leo, Karl A1 - Spoltore, Donato T1 - Enhanced charge selectivity via anodic-C60 layer reduces nonradiative losses in organic solar cells JF - ACS applied materials & interfaces N2 - Interfacial layers in conjunction with suitable charge-transport layers can significantly improve the performance of optoelectronic devices by facilitating efficient charge carrier injection and extraction. This work uses a neat C-60 interlayer on the anode to experimentally reveal that surface recombination is a significant contributor to nonradiative recombination losses in organic solar cells. These losses are shown to proportionally increase with the extent of contact between donor molecules in the photoactive layer and a molybdenum oxide (MoO3) hole extraction layer, proven by calculating voltage losses in low- and high-donor-content bulk heterojunction device architectures. Using a novel in-device determination of the built-in voltage, the suppression of surface recombination, due to the insertion of a thin anodic-C-60 interlayer on MoO3, is attributed to an enhanced built-in potential. The increased built-in voltage reduces the presence of minority charge carriers at the electrodes-a new perspective on the principle of selective charge extraction layers. The benefit to device efficiency is limited by a critical interlayer thickness, which depends on the donor material in bilayer devices. Given the high popularity of MoO3 as an efficient hole extraction and injection layer and the increasingly popular discussion on interfacial phenomena in organic optoelectronic devices, these findings are relevant to and address different branches of organic electronics, providing insights for future device design. KW - nonradiative losses KW - molybdenum oxide KW - organic solar cells KW - interfacial layers KW - charge selectivity Y1 - 2021 U6 - https://doi.org/10.1021/acsami.1c00049 SN - 1944-8244 SN - 1944-8252 VL - 13 IS - 10 SP - 12603 EP - 12609 PB - American Chemical Society CY - Washington 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 - Bagnich, Sergey A. A1 - Bassler, H. A1 - Neher, Dieter T1 - Exciton dynamics in ladder-type methyl-poly(para-phenylene) doped with phosphorescent dyes N2 - The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with platinum-porphyrin dye PtOEP covering the concentration 10(-3)-5% by weight has been measured employing cw and transient techniques. Upon excitation into the range of absorption of the host, strong phosphorescence of the dopant is observed. Possible ways of populating the dopant triplet state are considered. (c) 2004 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0022-2313 ER - TY - JOUR A1 - Perdigón-Toro, Lorena A1 - Le Quang Phuong, A1 - Zeiske, Stefan A1 - Vandewal, Koen A1 - Armin, Ardalan A1 - Shoaee, Safa A1 - Neher, Dieter T1 - Excitons dominate the emission from PM6 BT - Y6 solar cells, but this does not help the open-circuit voltage of the device JF - ACS energy letters / American Chemical Society N2 - Non-fullerene acceptors (NFAs) are far more emissive than their fullerene-based counterparts. Here, we study the spectral properties of photocurrent generation and recombination of the blend of the donor polymer PM6 with the NFA Y6. We find that the radiative recombination of free charges is almost entirely due to the re-occupation and decay of Y6 singlet excitons, but that this pathway contributes less than 1% to the total recombination. As such, the open-circuit voltage of the PM6:Y6 blend is determined by the energetics and kinetics of the charge-transfer (CT) state. Moreover, we find that no information on the energetics of the CT state manifold can be gained from the low-energy tail of the photovoltaic external quantum efficiency spectrum, which is dominated by the excitation spectrum of the Y6 exciton. We, finally, estimate the charge-separated state to lie only 120 meV below the Y6 singlet exciton energy, meaning that this blend indeed represents a high-efficiency system with a low energetic offset. Y1 - 2021 U6 - https://doi.org/10.1021/acsenergylett.0c02572 SN - 2380-8195 VL - 6 IS - 2 SP - 557 EP - 564 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Tokmoldin, Nurlan A1 - Vollbrecht, Joachim A1 - Hosseini, Seyed Mehrdad A1 - Sun, Bowen A1 - Perdigón-Toro, Lorena A1 - Woo, Han Young A1 - Zou, Yingping A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Explaining the fill-factor and photocurrent losses of nonfullerene acceptor-based solar cells by probing the long-range charge carrier diffusion and drift lengths JF - Advanced energy materials N2 - Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open-circuit voltage loss and fill-factor, with state-of-the-art OSCs rarely displaying fill-factor of 80% and above. The fill-factor of transport-limited solar cells, including organic photovoltaic devices, is affected by material and device-specific parameters, whose combination is represented in terms of the established figures of merit, such as theta and alpha. Herein, it is demonstrated that these figures of merit are closely related to the long-range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady-state photoconductance measurements. This yields a straightforward way of determining theta and alpha in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices-including the high efficiency nonfullerene acceptor blends-and show that the diffusion length of the free carriers provides a good correlation with the fill-factor. It is, finally, concluded that most state-of-the-art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor. KW - diffusion length KW - drift length KW - figure of merit KW - lifetime‐ mobility product KW - steady‐ state photoconductance Y1 - 2021 U6 - https://doi.org/10.1002/aenm.202100804 SN - 1614-6840 VL - 11 IS - 22 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Tokmoldin, Nurlan A1 - Hosseini, Seyed Mehrdad A1 - Raoufi, Meysam A1 - Phuong, Le Quang A1 - Sandberg, Oskar J. A1 - Guan, Huilan A1 - Zou, Yingping A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Extraordinarily long diffusion length in PM6:Y6 organic solar cells JF - Journal of materials chemistry : A, materials for energy and sustainability N2 - The PM6:Y6 bulk-heterojunction (BHJ) blend system achieves high short-circuit current (J(SC)) values in thick photovoltaic junctions. Here we analyse these solar cells to understand the observed independence of the short-circuit current upon photoactive layer thickness. We employ a range of optoelectronic measurements and analyses, including Mott-Schottky analysis, CELIV, photoinduced absorption spectroscopy, mobility measurements and simulations, to conclude that, the invariant photocurrent for the devices with different active layer thicknesses is associated with the Y6's diffusion length exceeding 300 nm in case of a 300 nm thick cell. This is despite unintentional doping that occurs in PM6 and the associated space-charge effect, which is expected to be even more profound upon photogeneration. This extraordinarily long diffusion length - which is an order of magnitude larger than typical values for organics - dominates transport in the flat-band region of thick junctions. Our work suggests that the performance of the doped PM6:Y6 organic solar cells resembles that of inorganic devices with diffusion transport playing a pivotal role. Ultimately, this is expected to be a key requirement for the fabrication of efficient, high-photocurrent, thick organic solar cells. Y1 - 2020 U6 - https://doi.org/10.1039/d0ta03016c SN - 2050-7488 SN - 2050-7496 VL - 8 IS - 16 SP - 7854 EP - 7860 PB - Royal Society of Chemistry CY - Cambridge 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 - Albrecht, Steve A1 - Janietz, Silvia A1 - Schindler, Wolfram A1 - Frisch, Johannes A1 - Kurpiers, Jona A1 - Kniepert, Juliane A1 - Inal, Sahika A1 - Pingel, Patrick A1 - Fostiropoulos, Konstantinos A1 - Koch, Norbert A1 - Neher, Dieter T1 - Fluorinated Copolymer PCPDTBT with enhanced open-circuit voltage and reduced recombination for highly efficient polymer solar cells JF - Journal of the American Chemical Society N2 - A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC70BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC70BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells. Y1 - 2012 U6 - https://doi.org/10.1021/ja305039j SN - 0002-7863 VL - 134 IS - 36 SP - 14932 EP - 14944 PB - American Chemical Society CY - Washington 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 - 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 - Karageorgiev, Peter A1 - Neher, Dieter A1 - Schulz, Burkhard A1 - Stiller, Burkhard A1 - Pietsch, Ullrich A1 - Giersig, Michael A1 - Brehmer, Ludwig T1 - From anisotropic photo-fluidity towards nanomanipulation in the optical near-field N2 - An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it shows considerable fluidity only in the direction parallel to the light field vector under linear polarized light. The fluidization phenomenon is related to photoinduced motion of azobenzene-functionalized molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also describe here how the photofluidization allows nanoscopic elements of matter to be precisely manipulated Y1 - 2005 SN - 1476-1122 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 - 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 - Roland, Steffen A1 - Schubert, Marcel A1 - Collins, Brian A. A1 - Kurpiers, Jona A1 - Chen, Zhihua A1 - Facchetti, Antonio A1 - Ade, Harald W. A1 - Neher, Dieter T1 - Fullerene-free polymer solar cells with highly reduced bimolecular recombination and field-independent charge carrier generation JF - The journal of physical chemistry letters N2 - Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors. Y1 - 2014 U6 - https://doi.org/10.1021/jz501506z SN - 1948-7185 VL - 5 IS - 16 SP - 2815 EP - 2822 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Zuo, Guangzheng A1 - Shoaee, Safa A1 - Kemerink, Martijn A1 - Neher, Dieter T1 - General rules for the impact of energetic disorder and mobility on nongeminate recombination in phase-separated organic solar cells JF - Physical review applied N2 - State-of-the-art organic solar cells exhibit power conversion efficiencies of 18% and above. These devices benefit from the suppression of free charge recombination with regard to the Langevin limit of charge encounter in a homogeneous medium. It is recognized that the main cause of suppressed free charge recombination is the reformation and resplitting of charge-transfer (CT) states at the interface between donor and acceptor domains. Here, we use kinetic Monte Carlo simulations to understand the interplay between free charge motion and recombination in an energetically disordered phase-separated donor-acceptor blend. We identify conditions for encounter-dominated and resplitting-dominated recombination. In the former regime, recombination is proportional to mobility for all parameters tested and only slightly reduced with respect to the Langevin limit. In contrast, mobility is not the decisive parameter that determines the nongeminate recombination coefficient, k(2), in the latter case, where k2 is a sole function of the morphology, CT and charge-separated (CS) energetics, and CT-state decay properties. Our simulations also show that free charge encounter in the phase-separated disordered blend is determined by the average mobility of all carriers, while CT reformation and resplitting involves mostly states near the transport energy. Therefore, charge encounter is more affected by increased disorder than the resplitting of the CT state. As a consequence, for a given mobility, larger energetic disorder, in combination with a higher hopping rate, is preferred. These findings have implications for the understanding of suppressed recombination in solar cells with nonfullerene acceptors, which are known to exhibit lower energetic disorder than that of fullerenes. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevApplied.16.034027 SN - 2331-7019 VL - 16 IS - 3 PB - American Physical Society CY - College Park 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 - 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 - 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 - 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 - Yang, Xiaohui A1 - Müller, David C. A1 - Neher, Dieter A1 - Meerholz, Klaus T1 - Highly efficient polymeric electrophosphorescent diodes N2 - Polymeric electrophosphorescent LEDs with internal quantum efficiencies approaching unity have been fabricated. Such performance levels are previously unknown for OLEDs. The key to this success is redox chemically doped oxetane- crosslinkable hole-transporting layers with multilayer capability (see figure). They improve hole injection and act as electron-blocking layers, without the need to include exciton-or hole-blocking layers Y1 - 2006 UR - 1960 = DOI: 10.1002/adma.200501867 ER - TY - JOUR A1 - Yang, X. H. A1 - Neher, Dieter A1 - Hertel, D. A1 - Daubler, T. K. T1 - Highly efficient single-layer polymer electrophosphorescent devices N2 - A commercially available Ir complex has been employed for the preparation of highly efficient (see Figure) single-layer phosphorescent polymer light,emitting diodes by use of appropriate thermal treatment and proper adjustment of the layer composition. These devices exhibit essentially no dependence of the driving field on the concentration of the Ir complex, suggesting that the build-up of space-charge in the layer is insignificant Y1 - 2004 SN - 0935-9648 ER - TY - GEN A1 - Stolterfoht, Martin A1 - Grischek, Max A1 - Caprioglio, Pietro A1 - Wolff, Christian Michael A1 - Gutierrez-Partida, Emilio A1 - Peña-Camargo, Francisco A1 - Rothhardt, Daniel A1 - Zhang, Shanshan A1 - Raoufi, Meysam A1 - Wolansky, Jakob A1 - Abdi-Jalebi, Mojtaba A1 - Stranks, Samuel D. A1 - Albrecht, Steve A1 - Kirchartz, Thomas A1 - Neher, Dieter T1 - How to quantify the efficiency potential of neat perovskite films BT - Perovskite semiconductors with an implied efficiency exceeding 28% T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1-sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non-radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell. By measuring the intensity dependence of the external open-circuit voltage and the internal quasi-Fermi level splitting (QFLS), the transport resistance-free efficiency of the complete cell as well as the efficiency potential of any neat perovskite film with or without attached transport layers are quantified. Moreover, intensity-dependent QFLS measurements on different perovskite compositions allows for disentangling of the impact of the interfaces and the perovskite surface on the non-radiative fill factor and open-circuit voltage loss. It is found that potassium-passivated triple cation perovskite films stand out by their exceptionally high implied PCEs > 28%, which could be achieved with ideal transport layers. Finally, strategies are presented to reduce both the ideality factor and transport losses to push the efficiency to the thermodynamic limit. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1434 KW - non-radiative interface recombination KW - perovskite solar cells KW - photoluminescence Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516622 SN - 1866-8372 IS - 17 ER -