TY - JOUR A1 - Lange, Ilja A1 - Reiter, Sina A1 - Kniepert, Juliane A1 - Piersimoni, Fortunato A1 - Paetzel, Michael A1 - Hildebrandt, Jana A1 - Brenner, Thomas J. K. A1 - Hecht, Stefan A1 - Neher, Dieter T1 - Zinc oxide modified with benzylphosphonic acids as transparent electrodes in regular and inverted organic solar cell structures JF - Applied physics letters N2 - An approach is presented to modify the work function of solution-processed sol-gel derived zinc oxide (ZnO) over an exceptionally wide range of more than 2.3 eV. This approach relies on the formation of dense and homogeneous self-assembled monolayers based on phosphonic acids with different dipole moments. This allows us to apply ZnO as charge selective bottom electrodes in either regular or inverted solar cell structures, using poly(3-hexylthiophene): phenyl-C71-butyric acid methyl ester as the active layer. These devices compete with or even surpass the performance of the reference on indium tin oxide/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Our findings highlight the potential of properly modified ZnO as electron or hole extracting electrodes in hybrid optoelectronic devices. (C) 2015 AIP Publishing LLC. Y1 - 2015 U6 - https://doi.org/10.1063/1.4916182 SN - 0003-6951 SN - 1077-3118 VL - 106 IS - 11 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Sun, Bowen A1 - Sandberg, Oskar A1 - Neher, Dieter A1 - Armin, Ardalan A1 - Shoaee, Safa T1 - Wave optics of differential absorption spectroscopy in thick-junction organic solar cells BT - optical artifacts and correction strategies JF - Physical review applied / The American Physical Society N2 - Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevApplied.17.054016 SN - 2331-7019 VL - 17 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Stolterfoht, Martin A1 - Le Corre, Vincent M. A1 - Feuerstein, Markus A1 - Caprioglio, Pietro A1 - Koster, Lambert Jan Anton A1 - Neher, Dieter T1 - Voltage-Dependent Photoluminescence and How It Correlates with the Fill Factor and Open-Circuit Voltage in Perovskite Solar Cells JF - Acs energy letters N2 - Optimizing the photoluminescence (PL) yield of a solar cell has long been recognized as a key principle to maximize the power conversion efficiency. While PL measurements are routinely applied to perovskite films and solar cells under open circuit conditions (V-OC), it remains unclear how the emission depends on the applied voltage. Here, we performed PL(V) measurements on perovskite cells with different hole transport layer thicknesses and doping concentrations, resulting in remarkably different fill factors (FFs). The results reveal that PL(V) mirrors the current-voltage (JV) characteristics in the power-generating regime, which highlights an interesting correlation between radiative and nonradiative recombination losses. In particular, high FF devices show a rapid quenching of PL(V) from open-circuit to the maximum power point. We conclude that, while the PL has to be maximized at V-OC at lower biases < V-OC the PL must be rapidly quenched as charges need to be extracted prior to recombination. Y1 - 2019 U6 - https://doi.org/10.1021/acsenergylett.9b02262 SN - 2380-8195 VL - 4 IS - 12 SP - 2887 EP - 2892 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Stolterfoht, Martin A1 - Wolff, Christian Michael A1 - Marquez, Jose A. A1 - Zhang, Shanshan A1 - Hages, Charles J. A1 - Rothhardt, Daniel A1 - Albrecht, Steve A1 - Burn, Paul L. A1 - Meredith, Paul A1 - Unold, Thomas A1 - Neher, Dieter T1 - Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells JF - Nature Energy N2 - The performance of perovskite solar cells is predominantly limited by non-radiative recombination, either through trap-assisted recombination in the absorber layer or via minority carrier recombination at the perovskite/transport layer interfaces. Here, we use transient and absolute photoluminescence imaging to visualize all non-radiative recombination pathways in planar pintype perovskite solar cells with undoped organic charge transport layers. We find significant quasi-Fermi-level splitting losses (135 meV) in the perovskite bulk, whereas interfacial recombination results in an additional free energy loss of 80 meV at each individual interface, which limits the open-circuit voltage (V-oc) of the complete cell to similar to 1.12 V. Inserting ultrathin interlayers between the perovskite and transport layers leads to a substantial reduction of these interfacial losses at both the p and n contacts. Using this knowledge and approach, we demonstrate reproducible dopant-free 1 cm(2) perovskite solar cells surpassing 20% efficiency (19.83% certified) with stabilized power output, a high V-oc (1.17 V) and record fill factor (>81%). KW - Energy science and technology KW - Solar cells Y1 - 2018 U6 - https://doi.org/10.1038/s41560-018-0219-8 SN - 2058-7546 VL - 3 IS - 10 SP - 847 EP - 854 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Xu, Jingsan A1 - Brenner, Thomas J. K. A1 - Chen, Zupeng A1 - Neher, Dieter A1 - Antonietti, Markus A1 - Shalom, Menny T1 - Upconversion-agent induced improvement of g-C3N4 photocatalyst under visible light JF - ACS applied materials & interfaces N2 - Herein, we report the use of upconversion agents to modify graphite carbon nitride (g-C3N4) by direct thermal condensation of a mixture of ErCl3 center dot 6H(2)O and the supramolecular precursor cyanuric acid-melamine. We show the enhancement of g-C3N4 photoactivity after Er3+ doping by monitoring the photodegradation of Rhodamine B dye under visible light. The contribution of the upconversion agent is demonstrated by measurements using only a red laser. The Er3+ doping alters both the electronic and the chemical properties of g-C3N4. The Er3+ doping reduces emission intensity and lifetime, indicating the formation of new, nonradiative deactivation pathways, probably involving charge-transfer processes. KW - metal-free photocatalysis KW - upconversion KW - carbon nitride KW - RhB photodegradation Y1 - 2014 U6 - https://doi.org/10.1021/am5051263 SN - 1944-8244 VL - 6 IS - 19 SP - 16481 EP - 16486 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Zu, Fengshuo A1 - Wolff, Christian Michael A1 - Ralaiarisoa, Maryline A1 - Amsalem, Patrick A1 - Neher, Dieter A1 - Koch, Norbert T1 - Unraveling the Electronic Properties of Lead Halide Perovskites with Surface Photovoltage in Photoemission Studies JF - ACS applied materials & interfaces N2 - The tremendous success of metal-halide perovskites, especially in the field of photovoltaics, has triggered a substantial number of studies in understanding their optoelectronic properties. However, consensus regarding the electronic properties of these perovskites is lacking due to a huge scatter in the reported key parameters, such as work function (Φ) and valence band maximum (VBM) values. Here, we demonstrate that the surface photovoltage (SPV) is a key phenomenon occurring at the perovskite surfaces that feature a non-negligible density of surface states, which is more the rule than an exception for most materials under study. With ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe, we evidence that even minute UV photon fluxes (500 times lower than that used in typical UPS experiments) are sufficient to induce SPV and shift the perovskite Φ and VBM by several 100 meV compared to dark. By combining UV and visible light, we establish flat band conditions (i.e., compensate the surface-state-induced surface band bending) at the surface of four important perovskites, and find that all are p-type in the bulk, despite a pronounced n-type surface character in the dark. The present findings highlight that SPV effects must be considered in all surface studies to fully understand perovskites’ photophysical properties. KW - lead halide perovskite films KW - ultraviolet photoelectron spectroscopy KW - Kelvin probe KW - surface band bending KW - surface photovoltage KW - surface states Y1 - 2019 U6 - https://doi.org/10.1021/acsami.9b05293 SN - 1944-8244 SN - 1944-8252 VL - 11 IS - 24 SP - 21578 EP - 21583 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Pingel, Patrick A1 - Zen, Achmad A1 - Neher, Dieter A1 - Lieberwirth, Ingo A1 - Wegner, Gerhard A1 - Allard, Sybille A1 - Scherf, Ullrich T1 - Unexpectedly high field-effect mobility of a soluble, low molecular weight oligoquaterthiophene fraction with low polydispersity N2 - Layers made from soluble low molecular weight polythiophene PQT-12 with low polydispersity exhibit a highly ordered structure and charge-carrier mobilities of the order of 10(-3) cm(2)/(V s), which we attribute to its proximity to monodispersity. We propose that polydispersity is a decisive factor with regard to structure formation and transport properties of soluble low molecular weight polythiophenes. Y1 - 2009 UR - http://www.springerlink.com/content/100501 U6 - https://doi.org/10.1007/s00339-008-4994-0 SN - 0947-8396 ER - TY - JOUR A1 - Lange, Ilja A1 - Reiter, Sina A1 - Paetzel, Michael A1 - Zykov, Anton A1 - Nefedov, Alexei A1 - Hildebrandt, Jana A1 - Hecht, Stefan A1 - Kowarik, Stefan A1 - Woell, Christof A1 - Heimel, Georg A1 - Neher, Dieter T1 - Tuning the work function of polar zinc oxide surfaces using modified phosphonic acid self-assembled monolayers JF - Advanced functional materials N2 - Zinc oxide (ZnO) is regarded as a promising alternative material for transparent conductive electrodes in optoelectronic devices. However, ZnO suffers from poor chemical stability. ZnO also has a moderate work function (WF), which results in substantial charge injection barriers into common (organic) semiconductors that constitute the active layer in a device. Controlling and tuning the ZnO WF is therefore necessary but challenging. Here, a variety of phosphonic acid based self-assembled monolayers (SAMs) deposited on ZnO surfaces are investigated. It is demonstrated that they allow the tuning the WF over a wide range of more than 1.5 eV, thus enabling the use of ZnO as both the hole-injecting and electron-injecting contact. The modified ZnO surfaces are characterized using a number of complementary techniques, demonstrating that the preparation protocol yields dense, well-defined molecular monolayers. KW - ZnO KW - self-assembled monolayers KW - phosphonic acid KW - surface modification KW - electrodes Y1 - 2014 U6 - https://doi.org/10.1002/adfm.201401493 SN - 1616-301X SN - 1616-3028 VL - 24 IS - 44 SP - 7014 EP - 7024 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schubert, Marcel A1 - Frisch, Johannes A1 - Allard, Sybille A1 - Preis, Eduard A1 - Scherf, Ullrich A1 - Koch, Norbert A1 - Neher, Dieter T1 - Tuning side chain and main chain order in a prototypical donor-acceptor copolymer BT - implications for optical, electronic, and photovoltaic characteristics JF - Elementary Processes in Organic Photovoltaics N2 - The recent development of donor–acceptor copolymers has led to an enormous improvement in the performance of organic solar cells and organic field-effect transistors. Here we describe the synthesis, detailed characterisation, and application of a series of structurally modified copolymers to investigate fundamental structure–property relationships in this class of conjugated polymers. The interplay between chemical structure and optoelectronic properties is investigated. These are further correlated to the charge transport and solar cell performance, which allows us to link their chemical structure to the observed physical properties. KW - Aggregate states KW - All-polymer heterojunctions KW - Alternating copolymers KW - Ambipolar charge transport KW - Ambipolar materials KW - Backbone modifications KW - Bilayer solar cells KW - Charge separation KW - Conformational disorder KW - Crystalline phases KW - Donor-acceptor copolymers KW - Electron traps KW - Energetic disorder KW - Energy-level alignment KW - Fermi-level alignment KW - Fermi-level pinning KW - Interface dipole KW - Interlayer KW - Intrachain order KW - Intragap states KW - Microscopic morphology KW - Mobility imbalance KW - Mobility relaxation KW - Monte Carlo simulation KW - Multiple trapping model KW - Nonradiative recombination KW - OFET KW - Open-circuit voltage KW - Optoelectronic properties KW - Partially alternating copolymers KW - Photo-CELIV KW - Photocurrent KW - Photovoltaic gap KW - Polymer intermixing KW - Recombination losses KW - Spectral diffusion KW - Statistical copolymers KW - Stille-type cross-coupling KW - Structure-property relationships KW - Time-dependent mobility KW - Time-of-flight (TOF) KW - Transient photocurrent KW - Ultraviolet photoelectron spectroscopy KW - Vacuum-level alignment KW - X-ray photoelectron spectroscopy Y1 - 2016 SN - 978-3-319-28338-8 SN - 978-3-319-28336-4 U6 - https://doi.org/10.1007/978-3-319-28338-8_10 SN - 0065-3195 VL - 272 SP - 243 EP - 265 PB - Springer CY - Berlin ER - TY - JOUR A1 - Yin, Chunhong A1 - Schubert, Marcel A1 - Stiller, Burkhard A1 - Castellani, Mauro A1 - Neher, Dieter A1 - Kumke, Michael Uwe A1 - Hörhold, Hans-Heinrich T1 - Tuning of the excited-state properties and photovoltaic performance in PPV-based polymer blends Y1 - 2008 U6 - https://doi.org/10.1021/Jp803977k 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 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Thermodynamic theory of light-induced material transport in amorphous azobenzene polymer films N2 - It was discovered 10 years ago that the exposure of an initially flat layer of an azobenzene-containing polymer to an inhomogeneous light pattern leads to the formation of surface relief structures, accompanied by a mass transport over several micrometers. However, the driving force of this process is still unclear. We propose a new thermodynamic approach that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. Our basic assumption is that under homogeneous illumination, an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film. Orientational distributions of chromophores predicted by our model are compared with those deduced from Raman intensity measurements Y1 - 2005 SN - 1520-6106 ER - TY - JOUR A1 - Stolterfoht, Martin A1 - Armin, Ardalan A1 - Philippa, Bronson A1 - Neher, Dieter T1 - The Role of Space Charge Effects on the Competition between Recombination and Extraction in Solar Cells with Low-Mobility Photoactive Layers JF - The journal of physical chemistry letters N2 - The competition between charge extraction and nongeminate recombination critically determines the current-voltage characteristics of organic solar cells (OSCs) and their fill factor. As a measure of this competition, several figures of merit (FOMs) have been put forward; however, the impact of space charge effects has been either neglected, or not specifically addressed. Here we revisit recently reported FOMs and discuss the role of space charge effects on the interplay between recombination and extraction. We find that space charge effects are the primary cause for the onset of recombination in so-called non-Langevin systems, which also depends on the slower carrier mobility and recombination coefficient. The conclusions are supported with numerical calculations and experimental results of 25 different donor/acceptor OSCs with different charge transport parameters, active layer thicknesses or composition ratios. The findings represent a conclusive understanding of bimolecular recombination for drift dominated photocurrents and allow one to minimize these losses for given device parameters. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpclett.6b02106 SN - 1948-7185 VL - 7 SP - 4716 EP - 4721 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Steyrleuthner, Robert A1 - Di Pietro, Riccardo A1 - Collins, Brian A. A1 - Polzer, Frank A1 - Himmelberger, Scott A1 - Schubert, Marcel A1 - Chen, Zhihua A1 - Zhang, Shiming A1 - Salleo, Alberto A1 - Ade, Harald W. A1 - Facchetti, Antonio A1 - Neher, Dieter T1 - The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer JF - Journal of the American Chemical Society Y1 - 2014 U6 - https://doi.org/10.1021/ja4118736 SN - 0002-7863 VL - 136 IS - 11 SP - 4245 EP - 4256 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Shoaee, Safa A1 - Stolterfoht, Martin A1 - Neher, Dieter T1 - The Role of Mobility on Charge Generation, Recombination, and Extraction in Polymer-Based Solar Cells JF - dvanced energy materials N2 - Organic semiconductors are of great interest for a broad range of optoelectronic applications due to their solution processability, chemical tunability, highly scalable fabrication, and mechanical flexibility. In contrast to traditional inorganic semiconductors, organic semiconductors are intrinsically disordered systems and therefore exhibit much lower charge carrier mobilities-the Achilles heel of organic photovoltaic cells. In this progress review, the authors discuss recent important developments on the impact of charge carrier mobility on the charge transfer state dissociation, and the interplay of free charge extraction and recombination. By comparing the mobilities on different timescales obtained by different techniques, the authors highlight the dispersive nature of these materials and how this reflects on the key processes defining the efficiency of organic photovoltaics. KW - charge generation KW - charge recombination KW - extraction KW - mobility KW - organic solar cells KW - polymer:fullerene bulk heterojunction Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201703355 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 28 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Zhang, Shanshan A1 - Hosseini, Seyed Mehrdad A1 - Gunder, Rene A1 - Petsiuk, Andrei A1 - Caprioglio, Pietro A1 - Wolff, Christian Michael A1 - Shoaee, Safa A1 - Meredith, Paul A1 - Schorr, Susan A1 - Unold, Thomas A1 - Burn, Paul L. A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - The Role of Bulk and Interface Recombination in High-Efficiency Low-Dimensional Perovskite Solar Cells JF - Advanced materials N2 - 2D Ruddlesden-Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite-based cells. Herein, 2D (CH3(CH2)(3)NH3)(2)(CH3NH3)(n-1)PbnI3n+1 perovskite cells with different numbers of [PbI6](4-) sheets (n = 2-4) are analyzed. Photoluminescence quantum yield (PLQY) measurements show that nonradiative open-circuit voltage (V-OC) losses outweigh radiative losses in materials with n > 2. The n = 3 and n = 4 films exhibit a higher PLQY than the standard 3D methylammonium lead iodide perovskite although this is accompanied by increased interfacial recombination at the top perovskite/C-60 interface. This tradeoff results in a similar PLQY in all devices, including the n = 2 system where the perovskite bulk dominates the recombination properties of the cell. In most cases the quasi-Fermi level splitting matches the device V-OC within 20 meV, which indicates minimal recombination losses at the metal contacts. The results show that poor charge transport rather than exciton dissociation is the primary reason for the reduction in fill factor of the RPP devices. Optimized n = 4 RPP solar cells had PCEs of 13% with significant potential for further improvements. KW - 2D perovskites KW - interface recombination KW - perovskite solar cells KW - photoluminescence KW - V-OC loss Y1 - 2019 U6 - https://doi.org/10.1002/adma.201901090 SN - 0935-9648 SN - 1521-4095 VL - 31 IS - 30 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Mansour, Ahmed E. A1 - Lungwitz, Dominique A1 - Schultz, Thorsten A1 - Arvind, Malavika A1 - Valencia, Ana M. A1 - Cocchi, Caterina A1 - Opitz, Andreas A1 - Neher, Dieter A1 - Koch, Norbert T1 - The optical signatures of molecular-doping induced polarons in poly(3-hexylthiophene-2,5-diyl) BT - individual polymer chains versus aggregates JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Optical absorption spectroscopy is a key method to investigate doped conjugated polymers and to characterize the doping-induced charge carriers, i.e., polarons. For prototypical poly(3-hexylthiophene-2,5-diyl) (P3HT), the absorption intensity of molecular dopant induced polarons is widely used to estimate the carrier density and the doping efficiency, i.e., the number of polarons formed per dopant molecule. However, the dependence of the polaron-related absorption features on the structure of doped P3HT, being either aggregates or separated individual chains, is not comprehensively understood in contrast to the optical absorption features of neutral P3HT. In this work, we unambiguously differentiate the optical signatures of polarons on individual P3HT chains and aggregates in solution, notably the latter exhibiting the same shape as aggregates in solid thin films. This is enabled by employing tris(pentafluorophenyl)borane (BCF) as dopant, as this dopant forms only ion pairs with P3HT and no charge transfer complexes, and BCF and its anion have no absorption in the spectral region of P3HT polarons. Polarons on individual chains exhibit absorption peaks at 1.5 eV and 0.6 eV, whereas in aggregates the high-energy peak is split into a doublet 1.3 eV and 1.65 eV, and the low-energy peak is shifted below 0.5 eV. The dependence of the fraction of solvated individual chains versus aggregates on absolute solution concentration, dopant concentration, and temperature is elucidated, and we find that aggregates predominate in solution under commonly used processing conditions. Aggregates in BCF-doped P3HT solution can be effectively removed upon simple filtering. From varying the filter pore size (down to 200 nm) and thin film morphology characterization with scanning force microscopy we reveal the aggregates' size dependence on solution absolute concentration and dopant concentration. Furthermore, X-ray photoelectron spectroscopy shows that the dopant loading in aggregates is higher than for individual P3HT chains. The results of this study help understanding the impact of solution pre-aggregation on thin film properties of molecularly doped P3HT, and highlight the importance of considering such aggregation for other doped conjugated polymers in general. Y1 - 2020 U6 - https://doi.org/10.1039/c9tc06509a SN - 2050-7526 SN - 2050-7534 VL - 8 IS - 8 SP - 2870 EP - 2879 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Stolterfoht, Martin A1 - Caprioglio, Pietro A1 - Wolff, Christian Michael A1 - Marquez, Jose A. A1 - Nordmann, Joleik A1 - Zhang, Shanshan A1 - Rothhardt, Daniel A1 - Hörmann, Ulrich A1 - Amir, Yohai A1 - Redinger, Alex A1 - Kegelmann, Lukas A1 - Zu, Fengshuo A1 - Albrecht, Steve A1 - Koch, Norbert A1 - Kirchartz, Thomas A1 - Saliba, Michael A1 - Unold, Thomas A1 - Neher, Dieter T1 - The impact of energy alignment and interfacial recombination on the internal and external open-circuit voltage of perovskite solar cells JF - Energy & environmental science N2 - Charge transport layers (CTLs) are key components of diffusion controlled perovskite solar cells, however, they can induce additional non-radiative recombination pathways which limit the open circuit voltage (V-OC) of the cell. In order to realize the full thermodynamic potential of the perovskite absorber, both the electron and hole transport layer (ETL/HTL) need to be as selective as possible. By measuring the photoluminescence yield of perovskite/CTL heterojunctions, we quantify the non-radiative interfacial recombination currents in pin- and nip-type cells including high efficiency devices (21.4%). Our study comprises a wide range of commonly used CTLs, including various hole-transporting polymers, spiro-OMeTAD, metal oxides and fullerenes. We find that all studied CTLs limit the V-OC by inducing an additional non-radiative recombination current that is in most cases substantially larger than the loss in the neat perovskite and that the least-selective interface sets the upper limit for the V-OC of the device. Importantly, the V-OC equals the internal quasi-Fermi level splitting (QFLS) in the absorber layer only in high efficiency cells, while in poor performing devices, the V-OC is substantially lower than the QFLS. Using ultraviolet photoelectron spectroscopy and differential charging capacitance experiments we show that this is due to an energy level mis-alignment at the p-interface. The findings are corroborated by rigorous device simulations which outline important considerations to maximize the V-OC. This work highlights that the challenge to suppress non-radiative recombination losses in perovskite cells on their way to the radiative limit lies in proper energy level alignment and in suppression of defect recombination at the interfaces. Y1 - 2019 U6 - https://doi.org/10.1039/c9ee02020a SN - 1754-5692 SN - 1754-5706 VL - 12 IS - 9 SP - 2778 EP - 2788 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Sainova, Dessislava A1 - Fujikawa, H. A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - The effect of hole traps on the performance of single layer polymer light emitting diodes Y1 - 1999 ER - TY - JOUR A1 - Inal, Sahika A1 - Koelsch, Jonas D. A1 - Chiappisi, Leonardo A1 - Kraft, Mario A1 - Gutacker, Andrea A1 - Janietz, Dietmar A1 - Scherf, Ullrich A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Temperature-Regulated Fluorescence Characteristics of Supramolecular Assemblies Formed By a Smart Polymer and a Conjugated Polyelectrolyte JF - MACROMOLECULAR CHEMISTRY AND PHYSICS N2 - Aqueous mixtures of a coumarin-labeled non-ionic thermoresponsive copolymer and a cationic polythiophene exhibit marked changes in their fluorescence properties upon heating. At room temperature, emission from the label is significantly quenched due to energy transfer to the conjugated polyelectrolyte. Heating the mixture reduces the energy-transfer efficiency markedly, resulting in a clearly visible change of the emission color. Although the two macromolecules associate strongly at room temperature, the number of interacting sites is largely reduced upon the phase transition. Crucially, the intermolecular association does not suppress the responsiveness of the smart polymer, meaning that this concept should be applicable to chemo- or bioresponsive polymers with optical read-out, for example, as a sensor device. KW - aqueous solutions KW - conjugated polyelectrolytes KW - fluorescence (or Forster) KW - resonance energy transfer KW - phase transitions KW - thermoresponsive polymers Y1 - 2013 U6 - https://doi.org/10.1002/macp.201200493 SN - 1022-1352 VL - 214 IS - 4 SP - 435 EP - 445 PB - WILEY-V C H VERLAG GMBH CY - WEINHEIM ER - TY - JOUR A1 - Inal, Sahika A1 - Chiappisi, Leonardo A1 - Kölsch, Jonas D. A1 - Kraft, Mario A1 - Appavou, Marie-Sousai A1 - Scherf, Ullrich A1 - Wagner, Manfred A1 - Hansen, Michael Ryan A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Temperature-regulated fluorescence and association of an Oligo(ethyleneglycol)methacrylate-based copolymer with a conjugated Polyelectrolyte-the effect of solution ionic strength JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - Aqueous mixtures of a dye-labeled non-ionic thermoresponsive copolymer and a conjugated cationic polyelectrolyte are shown to exhibit characteristic changes in fluorescence properties in response to temperature and to the presence of salts, enabling a double-stimuli responsiveness. In such mixtures at room temperature, i.e., well below the lower critical solution temperature (LCST), the emission of the dye is strongly quenched due to energy transfer to the polycation, pointing to supramolecular interactions between the two macromolecules. Increasing the concentration of salts weakens the interpolymer interactions, the extent of which is simultaneously monitored from the change in the relative emission intensity of the components. When the mixture is heated above its LCST, the transfer efficiency is significantly reduced, signaling a structural reorganization process, however, surprisingly only if the mixture contains salt ions. To elucidate the reasons behind such thermo- and ion-sensitive fluorescence characteristics, we investigate the effect of salts of alkali chlorides, in particular of NaCl, on the association behavior of these macromolecules before and after the polymer phase transition by a combination of UV-vis, fluorescence, and H-1 NMR spectroscopy with light scattering and small-angle neutron scattering measurements. Y1 - 2013 U6 - https://doi.org/10.1021/jp408864s SN - 1520-6106 VL - 117 IS - 46 SP - 14576 EP - 14587 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - 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 - 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 - Zerson, Mario A1 - Neumann, Martin A1 - Steyrleuthner, Robert A1 - Neher, Dieter A1 - Magerle, Robert T1 - Surface Structure of Semicrystalline Naphthalene Diimide-Bithiophene Copolymer Films Studied with Atomic Force Microscopy JF - Macromolecules : a publication of the American Chemical Society Y1 - 2016 U6 - https://doi.org/10.1021/acs.macromol.6b00988 SN - 0024-9297 SN - 1520-5835 VL - 49 SP - 6549 EP - 6557 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Neher, Dieter A1 - Lawson, PaDreyia V. A1 - Brédas, Jean-Luc A1 - Zojer, Egbert A1 - Güntner, Roland A1 - Scanduicci de Freitas, Patricia A1 - Forster, Michael A1 - Scherf, Ullrich T1 - Suppression of the keto-emission in polyfluorene light-emitting diodes : Experiments and models N2 - The spectral characteristics of polyfluorene (PF)-based light-emitting diodes (LEDs) containing a defined low concentration of either keto-defects or of the polymer poly(9.9-octylfuorene-co-benzothiadiazole) (F8BT) are preseneted. Both types of blend layers were tested in different device configurations with respect to the relative and absolute intensities of green blue emission components. It is shown that blending hole-transporting molecules into the emission layer at low concentration or incorporation of a suitable hole-transport layer reduces the green emission contribution in the electroluminescence (EL) spectrum of the PF:F8BT blend, which is similar to what is observed for the keto- containing PF layer. We conclude that the keto-defects in PF homopolymer layers mainly constitute weakly emissive electron traps, in agreement with the results of quantum-mechanical calculations Y1 - 2004 SN - 1616-301X ER - TY - GEN A1 - Inal, Sahika A1 - Kölsch, Jonas D. A1 - Chiappisi, Leonardo A1 - Janietz, Dietmar A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers N2 - We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains. Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 251 KW - anionic polymerizations KW - dilute aqueous-solutions KW - ether methacrylates KW - n-isopropylacrylamide KW - oligo(ethylene glycol) methacrylate KW - phase-transitions KW - protein interactions KW - solvatochromic fluorophore KW - thermoresponsive polymers KW - to-coil transition Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95379 SP - 6603 EP - 6612 ER - TY - JOUR A1 - Inal, Sahika A1 - Kölsch, Jonas D. A1 - Chiappisi, Leonardo A1 - Janietz, Dietmar A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers N2 - We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains. Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore. Y1 - 2013 UR - http://pubs.rsc.org/en/content/articlepdf/2013/tc/c3tc31304b U6 - https://doi.org/10.1039/C3TC31304B ER - TY - JOUR A1 - Inal, Sahika A1 - Koelsch, Jonas D. A1 - Chiappisi, Leonardo A1 - Janietz, Dietmar A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains. Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore. Y1 - 2013 U6 - https://doi.org/10.1039/c3tc31304b SN - 2050-7526 VL - 1 IS - 40 SP - 6603 EP - 6612 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Nikolis, Vasileios C. A1 - Mischok, Andreas A1 - Siegmund, Bernhard A1 - Kublitski, Jonas A1 - Jia, Xiangkun A1 - Benduhn, Johannes A1 - Hörmann, Ulrich A1 - Neher, Dieter A1 - Gather, Malte C. A1 - Spoltore, Donato A1 - Vandewal, Koen T1 - Strong light-matter coupling for reduced photon energy losses in organic photovoltaics JF - Nature Communications N2 - Strong light-matter coupling can re-arrange the exciton energies in organic semiconductors. Here, we exploit strong coupling by embedding a fullerene-free organic solar cell (OSC) photo-active layer into an optical microcavity, leading to the formation of polariton peaks and a red-shift of the optical gap. At the same time, the open-circuit voltage of the device remains unaffected. This leads to reduced photon energy losses for the low-energy polaritons and a steepening of the absorption edge. While strong coupling reduces the optical gap, the energy of the charge-transfer state is not affected for large driving force donor-acceptor systems. Interestingly, this implies that strong coupling can be exploited in OSCs to reduce the driving force for electron transfer, without chemical or microstructural modifications of the photoactive layer. Our work demonstrates that the processes determining voltage losses in OSCs can now be tuned, and reduced to unprecedented values, simply by manipulating the device architecture. Y1 - 2019 U6 - https://doi.org/10.1038/s41467-019-11717-5 SN - 2041-1723 VL - 10 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Hörmann, Ulrich A1 - Zeiske, Stefan A1 - Piersimoni, Fortunato A1 - Hoffmann, Lukas A1 - Schlesinger, Raphael A1 - Koch, Norbert A1 - Riedl, Thomas A1 - Andrienko, Denis A1 - Neher, Dieter T1 - Stark effect of hybrid charge transfer states at planar ZnO/organic interfaces JF - Physical review : B, Condensed matter and materials physics N2 - We investigate the bias dependence of the hybrid charge transfer state emission at planar heterojunctions between the metal oxide acceptor ZnO and three donor molecules. The electroluminescence peak energy linearly increases with the applied bias, saturating at high fields. Variation of the organic layer thickness and deliberate change of the ZnO conductivity through controlled photodoping allow us to confirm that this bias-induced spectral shift relates to the internal electric field in the organic layer rather than the filling of states at the hybrid interface. We show that existing continuum models overestimate the hole delocalization and propose a simple electrostatic model in which the linear and quadratic Stark effects are explained by the electrostatic interaction of a strongly polarizable molecular cation with its mirror image. Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevB.98.155312 SN - 2469-9950 SN - 2469-9969 VL - 98 IS - 15 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Zen, Achmad A1 - Bilge, Askin A1 - Galbrecht, Frank A1 - Alle, Ronald A1 - Meerholz, Klaus A1 - Grenzer, Jörg A1 - Neher, Dieter A1 - Scherf, Ullrich A1 - Farrell, Tony T1 - Solution processable organic field-effect transistors utilizing an alpha,alpha '-dihexylpentathiophene- based swivel cruciform Y1 - 2006 UR - http://pubs.acs.org/doi/full/10.1021/ja0573357 U6 - https://doi.org/10.1021/Ja0573357 ER - TY - JOUR A1 - Shalom, Menny A1 - Inal, Sahika A1 - Neher, Dieter A1 - Antonietti, Markus T1 - SiO2/carbon nitride composite materials: The role of surfaces for enhanced photocatalysis JF - Catalysis today : a serial publication dealing with topical themes in catalysis and related subjects N2 - The effect of SiO2 nanoparticles on carbon nitride (C3N4) photoactivity performance is described. The composite SiO2-C3N4 materials exhibit a higher activity in the photo degradation of RhB dye. A detailed analysis of the chemical and optical properties of the composite C3N4 materials shows that the photo activity increases with higher SiO2 concentration. We found out that the presence of SiO2 nanoparticles strongly affects the fluorescence intensity of the matrix and life time by the creation of new energy states for charge transfer within the C3N4. Furthermore, the use of SiO2 in the synthesis of C3N4 leads to new morphology with higher surface area which results in another, secondary improvement of C3N4 photoactivity. The effect of different surfaces within C3N4 on its chemical and electronic properties is discussed and a tentative mechanism is proposed. The utilization of SiO2 nanoparticles improves both photophysical and chemical properties of C3N4 and opens new possibilities for further enhancement of C3N4 catalytic properties by the formation of composites with many other materials. KW - Carbon nitride KW - SiO2 composite material KW - Photocatalysis KW - RhB degradation Y1 - 2014 U6 - https://doi.org/10.1016/j.cattod.2013.12.013 SN - 0920-5861 SN - 1873-4308 VL - 225 SP - 185 EP - 190 PB - Elsevier CY - Amsterdam 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 - Bagnich, Sergey A. A1 - Bassler, H. A1 - Neher, Dieter T1 - Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene) N2 - The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP. The phosphorescence decay on the short time scale is close to an exponential law with a time decay of 15 ms. This indicates that benzil can efficiently sensitize the phosphorescence of the polymer. In addition, a broad and featureless emission is observed in the delayed luminescence spectra of benzil-doped MeLPPP, which is attributed to an exciplex formed between the polymer host and the dopant. We further observe that the delayed fluorescence is enhanced by the addition of benzil. It is concluded that the delayed fluorescence of benzil-doped MeLPPP is mainly due to the annihilation of triplet excitons on the polymer. Finally, efficient triplet-triplet energy transfer from the benzil-doped polymer to the red-emitting phosphorescent dye Pt(II)octaethylporphyrin is established. (C) 2004 American Institute of Physics Y1 - 2004 SN - 0021-9606 ER - TY - JOUR A1 - Landfester, Katharina A1 - Montenegro, Rivelino V. D. A1 - Scherf, Ullrich A1 - Günter, R. A1 - Asawapirom, Udom A1 - Patil, S. A1 - Neher, Dieter A1 - Kietzke, Thomas T1 - Semiconducting polymer nanospheres in aqeous dispersion prepared by a miniemulsion process Y1 - 2002 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 - 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 - Steyrleuthner, Robert A1 - Bange, Sebastian A1 - Neher, Dieter T1 - Reliable electron-only devices and electron transport in n-type polymers N2 - Current-voltage analysis of single-carrier transport is a popular method for the determination of charge carrier mobilities in organic semiconductors. Although in widespread use for the analysis of hole transport, only a few reports can be found where the method was applied to electron transport. Here, we summarize the experimental difficulties related to the metal electrode leakage currents and nonlinear differential resistance (NDR) effects and explain their origin. We present a modified preparation technique for the metal electrodes and show that it significantly increases the reliability of such measurements. It allows to produce test devices with low leakage currents and without NDR even for thin organic layers. Metal oxides were often discussed as a possible cause of NDR. Our measurements on forcibly oxidized metal electrodes demonstrate that oxide layers are not exclusively responsible for NDR effects. We present electron transport data for two electron-conducting polymers often applied in all-polymer solar cells for a large variety of layer thicknesses and temperatures. The results can be explained by established exponential trapping models. Y1 - 2009 UR - http://jap.aip.org/ U6 - https://doi.org/10.1063/1.3086307 SN - 0021-8979 ER - TY - JOUR A1 - Kniepert, Juliane A1 - Paulke, Andreas A1 - Perdigon-Toro, Lorena A1 - Kurpiers, Jona A1 - Zhang, Huotian A1 - Gao, Feng A1 - Yuan, Jun A1 - Zou, Yingping A1 - Le Corre, Vincent M. A1 - Koster, Lambert Jan Anton A1 - Neher, Dieter T1 - Reliability of charge carrier recombination data determined with charge extraction methods JF - Journal of applied physics N2 - Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing. Y1 - 2019 U6 - https://doi.org/10.1063/1.5129037 SN - 0021-8979 SN - 1089-7550 VL - 126 IS - 20 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Inal, Sahika A1 - Castellani, Mauro A1 - Sellinger, Alan A1 - Neher, Dieter T1 - Relationship of photophysical properties and the device performance of novel hybrid small-molecular/polymeric solar cells N2 - We investigate solar cells comprised of a vinazene derivative (HV-BT) as the electron acceptor and the well- known polymer poly(3-hexylthiophene) as the electron donor. In the as-prepared blend, most of the excited state species, including the excimers on HV-BT, are quenched at the heterojunction. Although the photophysical properties of the blends change upon annealing, the blend solar cells largely remain uninfluenced by such treatments. A significant improvement is, however, observed when inducing phase separation at a longer length scale, for example, in solution-processed bilayer devices. Hereby, both the fill factor (FF) and the open circuit voltage are considerably increased, pointing to the importance of the heterojunction topology and the layer composition at the charge extracting contacts. An optimized device exhibits a power conversion efficiency of close to 1%. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/10003270 U6 - https://doi.org/10.1002/marc.200900221 SN - 1022-1336 ER - TY - JOUR A1 - 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 - Nikolis, Vasileios C. A1 - Benduhn, Johannes A1 - Holzmueller, Felix A1 - Piersimoni, Fortunato A1 - Lau, Matthias A1 - Zeika, Olaf A1 - Neher, Dieter A1 - Koerner, Christian A1 - Spoltore, Donato A1 - Vandewal, Koen T1 - Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies JF - dvanced energy materials N2 - High photon energy losses limit the open-circuit voltage (V-OC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the V-OC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha-sexithiophene (alpha-6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the V-OC of an alpha-6T/SubNc/SubPc fullerene-free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D-A interface. By accurately measuring the optical gap (E-opt) and the energy of the charge-transfer state (E-CT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. E-opt - qV(OC) losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the V-OC-optimized devices, the low-energy (700 nm) external quantum efficiency (EQE) peak remains high at 79%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low-voltage losses can be combined with a high EQE in organic photovoltaic devices. KW - energy losses KW - nonradiative recombination KW - open-circuit voltage KW - organic solar cells KW - voltage losses Y1 - 2017 U6 - https://doi.org/10.1002/aenm.201700855 SN - 1614-6832 SN - 1614-6840 VL - 7 SP - 122 EP - 136 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Wolff, Christian Michael A1 - Zu, Fengshuo A1 - Paulke, Andreas A1 - Toro, Lorena Perdigon A1 - Koch, Norbert A1 - Neher, Dieter T1 - Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH3NH3PbI3 Solar Cells JF - Advanced materials N2 - Perovskite solar cells with all-organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high-temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron-transporting layer of inverted perovskite cells affects the open-circuit voltage (V-OC). It is shown that nonradiative recombination mediated by the electron-transporting layer is the limiting factor for the V-OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH3NH3PbI3 perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V-OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge-blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V-OC and efficiency. KW - electron-transport layers KW - nonradiative recombination KW - open-circuit voltage KW - perovskite solar cells Y1 - 2017 U6 - https://doi.org/10.1002/adma.201700159 SN - 0935-9648 SN - 1521-4095 VL - 29 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Würfel, Uli A1 - Perdigon-Toro, Lorena A1 - Kurpiers, Jona A1 - Wolff, Christian Michael A1 - Caprioglio, Pietro A1 - Rech, Jeromy James A1 - Zhu, Jingshuai A1 - Zhan, Xiaowei A1 - You, Wei A1 - Shoaee, Safa A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - Recombination between Photogenerated and Electrode-Induced Charges Dominates the Fill Factor Losses in Optimized Organic Solar Cells JF - The journal of physical chemistry letters N2 - Charge extraction in organic solar cells (OSCs) is commonly believed to be limited by bimolecular recombination of photogenerated charges. However, the fill factor of OSCs is usually almost entirely governed by recombination processes that scale with the first order of the light intensity. This linear loss was often interpreted to be a consequence of geminate or trap-assisted recombination. Numerical simulations show that this linear dependence is a direct consequence of the large amount of excess dark charge near the contact. The first-order losses increase with decreasing mobility of minority carriers, and we discuss the impact of several material and device parameters on this loss mechanism. This work highlights that OSCs are especially vulnerable to injected charges as a result of their poor charge transport properties. This implies that dark charges need to be better accounted for when interpreting electro-optical measurements and charge collection based on simple figures of merit. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpclett.9b01175 SN - 1948-7185 VL - 10 IS - 12 SP - 3473 EP - 3480 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Wang, Qiong A1 - Mosconi, Edoardo A1 - Wolff, Christian Michael A1 - Li, Junming A1 - Neher, Dieter A1 - De Angelis, Filippo A1 - Suranna, Gian Paolo A1 - Grisorio, Roberto A1 - Abate, Antonio T1 - Rationalizing the molecular design of hole-selective contacts to improve charge extraction in Perovskite solar cells JF - dvanced energy materials N2 - Two new hole selective materials (HSMs) based on dangling methylsulfanyl groups connected to the C-9 position of the fluorene core are synthesized and applied in perovskite solar cells. Being structurally similar to a half of Spiro-OMeTAD molecule, these HSMs (referred as FS and DFS) share similar redox potentials but are endowed with slightly higher hole mobility, due to the planarity and large extension of their structure. Competitive power conversion efficiency (up to 18.6%) is achieved by using the new HSMs in suitable perovskite solar cells. Time-resolved photoluminescence decay measurements and electrochemical impedance spectroscopy show more efficient charge extraction at the HSM/perovskite interface with respect to Spiro-OMeTAD, which is reflected in higher photocurrents exhibited by DFS/FS-integrated perovskite solar cells. Density functional theory simulations reveal that the interactions of methylammonium with methylsulfanyl groups in DFS/FS strengthen their electrostatic attraction with the perovskite surface, providing an additional path for hole extraction compared to the sole presence of methoxy groups in Spiro-OMeTAD. Importantly, the low-cost synthesis of FS makes it significantly attractive for the future commercialization of perovskite solar cells. KW - hole extraction KW - hole selective materials KW - perovskite solar cells KW - sulfur KW - triple-cation perovskite Y1 - 2019 U6 - https://doi.org/10.1002/aenm.201900990 SN - 1614-6832 SN - 1614-6840 VL - 9 IS - 28 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Turner, Sarah T. A1 - Pingel, Patrick A1 - Steyrleuthner, Robert A1 - Crossland, Edward J. W. A1 - Ludwigs, Sabine A1 - Neher, Dieter T1 - Quantitative analysis of bulk heterojunction films using linear absorption spectroscopy and solar cell performance JF - Advanced functional materials N2 - A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non-optimized (chloroform cast) and nearly optimized (solvent-annealed o-dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H-aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent-annealed o-dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra- and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges. KW - Organic electronics KW - morphology KW - solar cells KW - mobility KW - absorption spectroscopy Y1 - 2011 U6 - https://doi.org/10.1002/adfm.201101583 SN - 1616-301X VL - 21 IS - 24 SP - 4640 EP - 4652 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Phuong, Le Quang A1 - Hosseini, Seyed Mehrdad A1 - Sandberg, Oskar J. A1 - Zou, Yingping A1 - Woo, Han Young A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells JF - Solar RRL N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells. KW - nonfullerene acceptors KW - organic solar cells KW - quasi-Fermi level KW - splitting KW - quasi-steady-state photoinduced absorptions KW - surface KW - recombinations KW - voltage losses Y1 - 2020 U6 - https://doi.org/10.1002/solr.202000649 SN - 2367-198X VL - 5 IS - 1 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Phuong, Le Quang A1 - Hosseini, Seyed Mehrdad A1 - Sandberg, Oskar J. A1 - Zou, Yingping A1 - Woo, Han Young A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1384 KW - nonfullerene acceptors KW - organic solar cells KW - quasi-Fermi level KW - splitting KW - quasi-steady-state photoinduced absorptions KW - surface KW - recombinations KW - voltage losses Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-570018 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Albrecht, Steve A1 - Tumbleston, John R. A1 - Janietz, Silvia A1 - Dumsch, Ines A1 - Allard, Sybille A1 - Scherf, Ullrich A1 - Ade, Harald W. A1 - Neher, Dieter T1 - Quantifying charge extraction in organic solar cells: The case of fluorinated PCPDTBT JF - The journal of physical chemistry letters N2 - We introduce a new and simple method to quantify the effective extraction mobility in organic solar cells at low electric fields and charge carrier densities comparable to operation conditions under one sun illumination. By comparing steady-state carrier densities at constant illumination intensity and under open-circuit conditions, the gradient of the quasi-Fermi potential driving the current is estimated as a function of external bias and charge density. These properties are then related to the respective steady-state current to determine the effective extraction mobility. The new technique is applied to different derivatives of the well-known low-band-gap polymer PCPDTBT blended with PC70BM. We show that the slower average extraction due to lower mobility accounts for the moderate fill factor when solar cells are fabricated with mono- or difluorinated PCPDTBT. This lower extraction competes with improved generation and reduced nongeminate recombination, rendering the monofluorinated derivative the most efficient donor polymer. Y1 - 2014 U6 - https://doi.org/10.1021/jz500457b SN - 1948-7185 VL - 5 IS - 7 SP - 1131 EP - 1138 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Le Corre, Vincent M. A1 - Diekmann, Jonas A1 - Peña-Camargo, Francisco A1 - Thiesbrummel, Jarla A1 - Tokmoldin, Nurlan A1 - Gutierrez-Partida, Emilio A1 - Peters, Karol Pawel A1 - Perdigón-Toro, Lorena A1 - Futscher, Moritz H. A1 - Lang, Felix A1 - Warby, Jonathan A1 - Snaith, Henry J. A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - Quantification of efficiency losses due to mobile ions in Perovskite solar cells via fast hysteresis measurements JF - Solar RRL N2 - Perovskite semiconductors differ from most inorganic and organic semiconductors due to the presence of mobile ions in the material. Although the phenomenon is intensively investigated, important questions such as the exact impact of the mobile ions on the steady-state power conversion efficiency (PCE) and stability remain. Herein, a simple method is proposed to estimate the efficiency loss due to mobile ions via "fast-hysteresis" measurements by preventing the perturbation of mobile ions out of their equilibrium position at fast scan speeds (approximate to 1000 V s(-1)). The "ion-free" PCE is between 1% and 3% higher than the steady-state PCE, demonstrating the importance of ion-induced losses, even in cells with low levels of hysteresis at typical scan speeds (approximate to 100mv s(-1)). The hysteresis over many orders of magnitude in scan speed provides important information on the effective ion diffusion constant from the peak hysteresis position. The fast-hysteresis measurements are corroborated by transient charge extraction and capacitance measurements and numerical simulations, which confirm the experimental findings and provide important insights into the charge carrier dynamics. The proposed method to quantify PCE losses due to field screening induced by mobile ions clarifies several important experimental observations and opens up a large range of future experiments. KW - hysteresis KW - mobile ions KW - perovskite solar cells Y1 - 2021 U6 - https://doi.org/10.1002/solr.202100772 SN - 2367-198X VL - 6 IS - 4 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Hosseini, Seyed Mehrdad A1 - Tokmoldin, Nurlan A1 - Lee, Young Woong A1 - Zou, Yingping A1 - Woo, Han Young A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Putting order into PM6:Y6 solar cells to reduce the langevin recombination in 400 nm thick junction JF - Solar RRL N2 - Increasing the active layer thickness without sacrificing the power conversion efficiency (PCE) is one of the great challenges faced by organic solar cells (OSCs) for commercialization. Recently, PM6:Y6 as an OSC based on a non-fullerene acceptor (NFA) has excited the community because of its PCE reaching as high as 15.9%; however, by increasing the thickness, the PCE drops due to the reduction of the fill factor (FF). This drop is attributed to change in mobility ratio with increasing thickness. Furthermore, this work demonstrates that by regulating the packing and the crystallinity of the donor and the acceptor, through volumetric content of chloronaphthalene (CN) as a solvent additive, one can improve the FF of a thick PM6:Y6 device (approximate to 400 nm) from 58% to 68% (PCE enhances from 12.2% to 14.4%). The data indicate that the origin of this enhancement is the reduction of the structural and energetic disorders in the thick device with 1.5% CN compared with 0.5% CN. This correlates with improved electron and hole mobilities and a 50% suppressed bimolecular recombination, such that the non-Langevin reduction factor is 180 times. This work reveals the role of disorder on the charge extraction and bimolecular recombination of NFA-based OSCs. KW - charge carrier extraction KW - energetic disorders KW - non-fullerene acceptors KW - non-Langevin reduction factors KW - thick junctions Y1 - 2020 U6 - https://doi.org/10.1002/solr.202000498 SN - 2367-198X VL - 4 IS - 11 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kurpiers, Jona A1 - Ferron, Thomas A1 - Roland, Steffen A1 - Jakoby, Marius A1 - Thiede, Tobias A1 - Jaiser, Frank A1 - Albrecht, Steve A1 - Janietz, Silvia A1 - Collins, Brian A. A1 - Howard, Ian A. A1 - Neher, Dieter T1 - Probing the pathways of free charge generation in organic bulk heterojunction solar cells JF - Nature Communications N2 - The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-04386-3 SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Kietzke, Thomas A1 - Stiller, Burkhard A1 - Landfester, Katharina A1 - Montenegro, Rivelino V. D. A1 - Neher, Dieter T1 - Probing the local optical properties of layers prepared from polymer nanoparticles N2 - It is well known that the performance of solar cells based on a blend of hole-accepting and electron-accepting conjugated polymers as the active material depend crucially on the length scale of the resulting phase separated morphology. However, a direct control of this morphology is difficult if the layer is prepared from an organic solvent. To circumvent this difficulty, recently a universal method to fabricate defined nano-structured blend layer using nanoparticles dispersed in water was demonstrated. These nanoparticles were prepared with the miniemulsion method, which allows for the preparation of semiconducting polymer nanospheres (SPNs) with diameters in the range of 30 to 300 nanometres. Since the process starts from the active material dissolved in a common solvent, it can be applied to the fabrication of nanoparticles of blends of polymers with oligomers or even with inorganic materials. We present here for the first time scanning near field optical microscopy (SNOM) investigations on these novel nanostructured polymer layers. We show that by spin-coating a mixture of two different dispersions a nanoparticle monolayer with a statistically distribution of the nanoparticles can be obtained. Mixing conjugated polymer nanoparticles with some inert particles like polystyrene beads may allow for the preparation of nano-sized light emitters Y1 - 2005 SN - 0379-6779 ER - TY - JOUR A1 - Zu, Fengshuo A1 - Schultz, Thorsten A1 - Wolff, Christian Michael A1 - Shin, Dongguen A1 - Frohloff, Lennart A1 - Neher, Dieter A1 - Amsalem, Patrick A1 - Koch, Norbert T1 - Position-locking of volatile reaction products by atmosphere and capping layers slows down photodecomposition of methylammonium lead triiodide perovskite JF - RSC Advances N2 - The remarkable progress of metal halide perovskites in photovoltaics has led to the power conversion efficiency approaching 26%. However, practical applications of perovskite-based solar cells are challenged by the stability issues, of which the most critical one is photo-induced degradation. Bare CH3NH3PbI3 perovskite films are known to decompose rapidly, with methylammonium and iodine as volatile species and residual solid PbI2 and metallic Pb, under vacuum under white light illumination, on the timescale of minutes. We find, in agreement with previous work, that the degradation is non-uniform and proceeds predominantly from the surface, and that illumination under N-2 and ambient air (relative humidity 20%) does not induce substantial degradation even after several hours. Yet, in all cases the release of iodine from the perovskite surface is directly identified by X-ray photoelectron spectroscopy. This goes in hand with a loss of organic cations and the formation of metallic Pb. When CH3NH3PbI3 films are covered with a few nm thick organic capping layer, either charge selective or non-selective, the rapid photodecomposition process under ultrahigh vacuum is reduced by more than one order of magnitude, and becomes similar in timescale to that under N-2 or air. We conclude that the light-induced decomposition reaction of CH3NH3PbI3, leading to volatile methylammonium and iodine, is largely reversible as long as these products are restrained from leaving the surface. This is readily achieved by ambient atmospheric pressure, as well as a thin organic capping layer even under ultrahigh vacuum. In addition to explaining the impact of gas pressure on the stability of this perovskite, our results indicate that covalently "locking" the position of perovskite components at the surface or an interface should enhance the overall photostability. Y1 - 2020 U6 - https://doi.org/10.1039/d0ra03572f SN - 2046-2069 VL - 10 IS - 30 SP - 17534 EP - 17542 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Yang, X. H. A1 - Neher, Dieter T1 - Polymer electrophosphorescence devices with high power conversion efficiencies N2 - We demonstrate efficient single-layer polymer phosphorescent light-emitting devices based on a green-emitting iridium complex and a polymer host co-doped with electron-transporting and hole-transporting molecules. These devices can be operated at relatively low voltages, resulting in a power conversion efficiency of up to 24 lm/W at luminous efficiencies exceeding 30 cd/A. The overall performances of these devices suggest that efficient electrophosphorescent devices with acceptable operating voltages can be achieved in very simple device structures fabricated by spin coating. (C) 2004 American Institute of Physics Y1 - 2004 SN - 0003-6951 ER - TY - JOUR A1 - Luszczynska, Beata A1 - Dobruchowska, Ewa A1 - Glowacki, Ireneusz A1 - Ulanski, Jacek A1 - Jaiser, Frank A1 - Yang, Xiaohui A1 - Neher, Dieter A1 - Danel, Andrzej T1 - Poly(N-vinylcarbazole) doped with a pyrazoloquinoline dye : a deep blue light-emitting composite for light- emitting diode applications N2 - We investigated the spectral properties of light-emitting diodes based on a deep blue-emitting pyrazoloquinoline dye doped into a poly(N-vinylcarbazole)-based matrix. Even though the electroluminescence (EL) of the host is redshifted and broadened with respect to the emission of the dye, the EL spectrum becomes fully dominated by the dye emission at concentrations of ca. 2 wt %. This is attributed to a competition of exciplex formation on the matrix and exciton formation on the dye. Y1 - 2006 UR - http://jap.aip.org/ U6 - https://doi.org/10.1063/1.2162268 SN - 0021-8979 ER - TY - JOUR A1 - Bauer, C. A1 - Umbasch, G. A1 - Giessen, H. A1 - Meisel, A. A1 - Nothofer, Heinz-Georg A1 - Neher, Dieter A1 - Scherf, Ullrich A1 - Marth, R. T1 - Polarized Photoluminescence and Spectral Narrowing in an oriented Polyfluorene Thin Film Y1 - 2000 ER - TY - JOUR A1 - Miteva, T. A1 - Meisel, A. A1 - Nothofer, Heinz-Georg A1 - Scherf, Ullrich A1 - Knoll, W. A1 - Neher, Dieter A1 - Grell, M. A1 - Lupo, D. A1 - Yasuda, A. T1 - Polarized electroluminescence from highly aligned liquid-crystalline polymers Y1 - 2000 ER - TY - JOUR A1 - Zen, Achmad A1 - Neher, Dieter A1 - Bauer, C. A1 - Asawapirom, Udom A1 - Scherf, Ullrich A1 - Hagen, R. A1 - Kostromine, S. A1 - Mahrt, R. F. T1 - Polarization-sensitive photoconductivity in aligned polyfluorene layers Y1 - 2002 ER - TY - JOUR A1 - Pralle, Martin U. A1 - Urayama, Kenji A1 - Tew, Gregory N. A1 - Neher, Dieter A1 - Wegner, Gerhard A1 - Stupp, Samuel I. T1 - Piezoelectricity in polar supramolecular materials Y1 - 2000 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 - 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 - Kniepert, Juliane A1 - Schubert, Marcel A1 - Blakesley, James C. A1 - Neher, Dieter T1 - Photogeneration and recombination in P3HT/PCBM solar cells probed by time-delayed collection field experiments JF - The journal of physical chemistry letters N2 - Time-delayed collection field (TDCF) experiments are performed on bulk heterojunction solar cells comprised of a blend of poly(3-hexylthiophene) and [6,6]-phenyl C-71 butyric acid methyl ester. TDCF is analogous to a pump-probe experiment using optical excitation and an electrical probe with a resolution of < 100 ns. The number of free charge carriers extracted after a short delay is found to be independent of the electric field during illumination. Also, experiments performed with a variable delay between the optical excitation and the electrical probe do not reveal any evidence for the generation of charge via field-assisted dissociation of bound long-lived polaron pairs. Photocurrent transients are well fitted by computational drift diffusion simulations with only direct generation of free charge carriers. With increasing delay times between pump and probe, two loss mechanisms are identified; first, charge-carriers are swept out of the device by the internal electric field, and second, bimolecular recombination of the remaining carriers takes place with a reduced recombination coefficient. Y1 - 2011 U6 - https://doi.org/10.1021/jz200155b SN - 1948-7185 VL - 2 IS - 7 SP - 700 EP - 705 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kulikovsky, Lazar A1 - Neher, Dieter A1 - Mecher, E. A1 - Meerholz, Klaus A1 - Horhold, H. H. A1 - Ostroverkhova, O. T1 - Photocurrent dynamics in a poly(phenylene vinylene)-based photorefractive composite N2 - All parameters describing the charge carrier dynamics in a poly(phenylene vinylene)-based photorefractive (PR) composite relevant to PR grating dynamics were determined using photoconductivity studies under various illumination conditions. In particular, the values of the coefficients for trap filling and recombination of charges with ionized sensitizer molecules could be extracted independently. It is concluded that the PR growth time without preillumination is mostly determined by the competition between deep trap filling and recombination with ionized sensitizer molecules. Further, the pronounced increase in PR speed upon homogeneous preillumination (gating) as reported recently is quantitatively explained by deep trap filling Y1 - 2004 SN - 1098-0121 ER - TY - JOUR A1 - Sianova, D. A1 - Zen, Achmad A1 - Nothofer, Heinz-Georg A1 - Asawapirom, Udom A1 - Scherf, Ullrich A1 - Hagen, R. A1 - Bieringer, Thomas A1 - Kostromine, S. A1 - Neher, Dieter T1 - Photoaddressable alignment layers for fluorescent polymers in polarized electroluminescence devices Y1 - 2002 ER - TY - JOUR A1 - Ilnytskyi, Jaroslav A1 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Photo-induced deformations in azobenzene-containing side-chain polymers : molecular dynamics study N2 - We perform molecular dynamics simulations of azobenzene containing side-chain liquid crystalline polymer subject to an external model field that mimicks the reorientations of the azobenzenes upon irradiation with polarized light. The smectic phase of the polymer is studied with the field applied parallel to the nematic director, forcing the trans isomers to reorient perpendicularly to the field (the direction of which can be assosiated with the light polarization). The coupling between the reorientation of azobenzenes and mechanical deformation of the sample is found to depend on the field strength. In a weak field the original smectic order is melted gradually with no apparent change in the simulation box shape, whereas in a strong field two regimes are observed. During the first one a rapid melting of the liquid crystalline order is accompanied by the contraction of the polymer along the field direction (the effect similar to the one observed experimentally in azopenzene containing elastomers). During the slower second regime, the smectic layers are rebuilt to accomodate the preferential direction of chromophores perperdicular to the field. Y1 - 2006 UR - http://www.icmp.lviv.ua/journal/Contents.html SN - 1607-324X 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 - Moule, Adam J. A1 - Neher, Dieter A1 - Turner, Sarah T. ED - Ludwigs, S T1 - P3HT-Based solar cells: structural properties and photovoltaic performance JF - Advances in Polymer Science JF - Advances in Polymer Science N2 - Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic photovoltaic devices are easy to sketch, but the materials, processing steps, and ways of measuring the properties of the materials are very complicated. It is not trivial to make a systematic measurement that will change the way other research groups think or practice. In approaching this chapter, we thought about what a new researcher would need to know about organic photovoltaic devices and materials in order to have a good start in the subject. Then, we simplified that to focus on what a new researcher would need to know about poly-3-hexylthiophene: phenyl-C61-butyric acid methyl ester blends (P3HT: PCBM) to make research progress with these materials. This chapter is by no means authoritative or a compendium of all things on P3HT: PCBM. We have selected to explain how the sample fabrication techniques lead to control of morphology and structural features and how these morphological features have specific optical and electronic consequences for organic photovoltaic device applications. KW - Free carrier generation KW - Non-geminate recombination KW - Organic solar cells Y1 - 2014 SN - 978-3-662-45145-8; 978-3-662-45144-1 U6 - https://doi.org/10.1007/12_2014_289 SN - 0065-3195 VL - 265 SP - 181 EP - 232 PB - Springer CY - Berlin ER - TY - JOUR A1 - Pingel, Patrick A1 - Arvind, Malavika A1 - Kölln, Lisa A1 - Steyrleuthner, Robert A1 - Kraffert, Felix A1 - Behrends, Jan A1 - Janietz, Silvia A1 - Neher, Dieter T1 - p-Type Doping of Poly(3-hexylthiophene) with the Strong Lewis Acid Tris(pentafluorophenyl)borane JF - Advanced electronic materials N2 - State-of-the-art p-type doping of organic semiconductors is usually achieved by employing strong -electron acceptors, a prominent example being tetrafluorotetracyanoquinodimethane (F(4)TCNQ). Here, doping of the semiconducting model polymer poly(3-hexylthiophene), P3HT, using the strong Lewis acid tris(pentafluorophenyl)borane (BCF) as a dopant, is investigated by admittance, conductivity, and electron paramagnetic resonance measurements. The electrical characteristics of BCF- and F(4)TCNQ-doped P3HT layers are shown to be very similar in terms of the mobile hole density and the doping efficiency. Roughly 18% of the employed dopants create mobile holes in either F-4 TCNQ- or BCF-doped P3HT, while the majority of doping-induced holes remain strongly Coulomb-bound to the dopant anions. Despite similar hole densities, conductivity and hole mobility are higher in BCF-doped P3HT layers than in F(4)TCNQ-doped samples. This and the good solubility in many organic solvents render BCF very useful for p-type doping of organic semiconductors. KW - charge carrier transport KW - charge transfer KW - conductivity KW - molecular doping KW - organic semiconductors Y1 - 2016 U6 - https://doi.org/10.1002/aelm.201600204 SN - 2199-160X VL - 2 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Proctor, Christopher M. A1 - Albrecht, Steve A1 - Kuik, Martijn A1 - Neher, Dieter A1 - Thuc-Quyen Nguyen, T1 - Overcoming geminate recombination and enhancing extraction in solution-processed small molecule solar cells JF - dvanced energy materials Y1 - 2014 U6 - https://doi.org/10.1002/aenm.201400230 SN - 1614-6832 SN - 1614-6840 VL - 4 IS - 10 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Ye, Fangyuan A1 - Zhang, Shuo A1 - Warby, Jonathan A1 - Wu, Jiawei A1 - Gutierrez-Partida, Emilio A1 - Lang, Felix A1 - Shah, Sahil A1 - Saglamkaya, Elifnaz A1 - Sun, Bowen A1 - Zu, Fengshuo A1 - Shoaee, Safa A1 - Wang, Haifeng A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Zhu, Wei-Hong A1 - Stolterfoht, Martin A1 - Wu, Yongzhen T1 - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1317 Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-587705 SN - 1866-8372 IS - 1317 ER - TY - JOUR A1 - Ye, Fangyuan A1 - Zhang, Shuo A1 - Warby, Jonathan A1 - Wu, Jiawei A1 - Gutierrez-Partida, Emilio A1 - Lang, Felix A1 - Shah, Sahil A1 - Saglamkaya, Elifnaz A1 - Sun, Bowen A1 - Zu, Fengshuo A1 - Shoai, Safa A1 - Wang, Haifeng A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Zhu, Wei-Hong A1 - Stolterfoht, Martin A1 - Wu, Yongzhen T1 - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane JF - Nature Communications N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. Y1 - 2022 U6 - https://doi.org/10.1038/s41467-022-34203-x SN - 2041-1723 VL - 13 PB - Springer Nature CY - London ER - TY - JOUR A1 - Ye, Fangyuan A1 - Zhang, Shuo A1 - Warby, Jonathan A1 - Wu, Jiawei A1 - Gutierrez-Partida, Emilio A1 - Lang, Felix A1 - Shah, Sahil A1 - Saglamkaya, Elifnaz A1 - Sun, Bowen A1 - Zu, Fengshuo A1 - Shoaee, Safa A1 - Wang, Haifeng A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Zhu, Wei-Hong A1 - Stolterfoht, Martin A1 - Wu, Yongzhen T1 - Overcoming C-60-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane JF - Nature Communications N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C-60 interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C-60 interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110mV, and retain >97% of the initial efficiency after 400h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. Effective transport layers are essential to suppress non-radiative recombination losses. Here, the authors introduce phenylamino-functionalized ortho-carborane as an interfacial layer, and realise inverted perovskite solar cells with efficiency of over 23% and operational stability of T97=400h. Y1 - 2022 U6 - https://doi.org/10.1038/s41467-022-34203-x SN - 2041-1723 VL - 13 IS - 1 PB - Nature Publishing Group CY - London 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 - Samson, Stephanie A1 - Rech, Jeromy A1 - Perdigon-Toro, Lorena A1 - Peng, Zhengxing A1 - Shoaee, Safa A1 - Ade, Harald A1 - Neher, Dieter A1 - Stolterfoht, Martin A1 - You, Wei T1 - Organic solar cells with large insensitivity to donor polymer molar mass across all acceptor classes JF - ACS applied polymer materials N2 - Donor polymer number-average molar mass (M-n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M-n effects varies from system to system, although there is generally some intermediate M-n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC61BM (fullerene acceptor), PcBm demonstrated <10% variation in power conversion efficiency and a consistent morphology over a large span of M-n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M-n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ mn insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M-n control during synthesis. KW - polymer solar cells KW - conjugated polymers KW - fullerenes KW - fluorination KW - molecular weight KW - non-fullerene acceptors KW - power conversion efficiency Y1 - 2020 U6 - https://doi.org/10.1021/acsapm.0c01041 SN - 2637-6105 VL - 2 IS - 11 SP - 5300 EP - 5308 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Lieser, G. A1 - Oda, Masao A1 - Miteva, T. A1 - Nothofer, Heinz-Georg A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - Ordering, graphoepitaxial orientation, and conformation of a polyfluorene derivative of the "hairy-rod" type on an oriented substrate of polyimide Y1 - 2000 ER - TY - JOUR A1 - Stiller, Burkhard A1 - Karageorgiev, Peter A1 - Geue, Thomas A1 - Morawetz, Knut A1 - Saphiannikova, Marina A1 - Mechau, Norman A1 - Neher, Dieter T1 - Optically induced mass transport studied by scanning near-field optical- and atomic force microscopy N2 - Some functionalised thin organic films show a very unusual property, namely the light induced material transport. This effect enables to generate three-dimensional structures on surfaces of azobenzene containing films only caused by special optical excitation. The physical mechanisms underlying this phenomenon have not yet been fully understood, and in addition, the dimensions of structures created in that way are macroscopic because of the optical techniques and the wavelength of the used light. In order to gain deeper insight into the physical fundamentals of this phenomenon and to open possibilities for applications it is necessary to create and study structures not only in a macroscopic but also in nanometer range. We first report about experiments to generate optically induced nano structures even down to 100 nm size. The optical stimulation was therefore made by a Scanning Near-field Optical Microscope (SNOM). Secondly, physical conditions inside optically generated surface relief gratings were studied by measuring mechanical properties with high lateral resolution via pulse force mode and force distance curves of an AFM Y1 - 2004 SN - 0204-3467 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 - Ilnytskyi, Jaroslav M. A1 - Neher, Dieter A1 - Saphiannikova, Marina T1 - Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture molecular dynamics study JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases. KW - amorphous state KW - light polarisation KW - liquid crystal polymers KW - molecular dynamics method KW - optical hole burning KW - photochemistry Y1 - 2011 U6 - https://doi.org/10.1063/1.3614499 SN - 0021-9606 VL - 135 IS - 4 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Poelking, Carl A1 - Benduhn, Johannes A1 - Spoltore, Donato A1 - Schwarze, Martin A1 - Roland, Steffen A1 - Piersimoni, Fortunato A1 - Neher, Dieter A1 - Leo, Karl A1 - Vandewal, Koen A1 - Andrienko, Denis T1 - Open-circuit voltage of organic solar cells BT - interfacial roughness makes the difference JF - Communications physics N2 - Organic photovoltaics (PV) is an energy-harvesting technology that offers many advantages, such as flexibility, low weight and cost, as well as environmentally benign materials and manufacturing techniques. Despite growth of power conversion efficiencies to around 19 % in the last years, organic PVs still lag behind inorganic PV technologies, mainly due to high losses in open-circuit voltage. Understanding and improving open circuit voltage in organic solar cells is challenging, as it is controlled by the properties of a donor-acceptor interface where the optical excitations are separated into charge carriers. Here, we provide an electrostatic model of a rough donor-acceptor interface and test it experimentally on small molecule PV materials systems. The model provides concise relationships between the open-circuit voltage, photovoltaic gap, charge-transfer state energy, and interfacial morphology. In particular, we show that the electrostatic bias generated across the interface reduces the photovoltaic gap. This negative influence on open-circuit voltage can, however, be circumvented by adjusting the morphology of the donor-acceptor interface. Organic solar cells, despite their high power conversion efficiencies, suffer from open circuit voltage losses making them less appealing in terms of applications. Here, the authors, supported with experimental data on small molecule photovoltaic cells, relate open circuit voltage to photovoltaic gap, charge-transfer state energy, and donor-acceptor interfacial morphology. Y1 - 2022 U6 - https://doi.org/10.1038/s42005-022-01084-x SN - 2399-3650 VL - 5 IS - 1 PB - Nature portfolio CY - Berlin 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 - 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 - Sandberg, Oskar J. A1 - Kurpiers, Jona A1 - Stolterfoht, Martin A1 - Neher, Dieter A1 - Meredith, Paul A1 - Shoaee, Safa A1 - Armin, Ardalan T1 - On the question of the need for a built-in potential in Perovskite solar cells JF - Advanced materials interfaces N2 - Perovskite semiconductors as the active materials in efficient solar cells exhibit free carrier diffusion lengths on the order of microns at low illumination fluxes and many hundreds of nanometers under 1 sun conditions. These lengthscales are significantly larger than typical junction thicknesses, and thus the carrier transport and charge collection should be expected to be diffusion controlled. A consensus along these lines is emerging in the field. However, the question as to whether the built-in potential plays any role is still of matter of some conjecture. This important question using phase-sensitive photocurrent measurements and theoretical device simulations based upon the drift-diffusion framework is addressed. In particular, the role of the built-in electric field and charge-selective transport layers in state-of-the-art p-i-n perovskite solar cells comparing experimental findings and simulation predictions is probed. It is found that while charge collection in the junction does not require a drift field per se, a built-in potential is still needed to avoid the formation of reverse electric fields inside the active layer, and to ensure efficient extraction through the charge transport layers. KW - built-in potential KW - charge collection KW - charge transport layers KW - perovskite solar cells Y1 - 2020 U6 - https://doi.org/10.1002/admi.202000041 SN - 2196-7350 VL - 7 IS - 10 PB - Wiley CY - Hoboken ER - TY - GEN A1 - Pisoni, Stefano A1 - Stolterfoht, Martin A1 - Lockinger, Johannes A1 - Moser, Thierry A1 - Jiang, Yan A1 - Caprioglio, Pietro A1 - Neher, Dieter A1 - Buecheler, Stephan A1 - Tiwari, Ayodhya N. T1 - On the origin of open-circuit voltage losses in flexible n-i-p perovskite solar cells T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recombination losses. Herein, we performed a systematic voltage loss analysis for a typical low-temperature processed, flexible PSC in n-i-p configuration using vacuum deposited C-60 as electron transport layer (ETL) and two-step hybrid vacuum-solution deposition for CH3NH3PbI3 perovskite absorber. We identified the ETL/absorber interface as a bottleneck in relation to non-radiative recombination losses, the quasi-Fermi level splitting (QFLS) decreases from similar to 1.23 eV for the bare absorber, just similar to 90 meV below the radiative limit, to similar to 1.10 eV when C-60 is used as ETL. To effectively mitigate these voltage losses, we investigated different interfacial modifications via vacuum deposited interlayers (BCP, B4PyMPM, 3TPYMB, and LiF). An improvement in QFLS of similar to 30-40 meV is observed after interlayer deposition and confirmed by comparable improvements in the open-circuit voltage after implementation of these interfacial modifications in flexible PSCs. Further investigations on absorber/hole transport layer (HTL) interface point out the detrimental role of dopants in Spiro-OMeTAD film (widely employed HTL in the community) as recombination centers upon oxidation and light exposure. [GRAPHICS] . T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1110 KW - Perovskite solar cell KW - flexible KW - interface engineering KW - non-radiative recombination KW - quasi-Fermi level splitting Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-459617 SN - 1866-8372 IS - 1110 ER - TY - JOUR A1 - Pisoni, Stefano A1 - Stolterfoht, Martin A1 - Lockinger, Johannes A1 - Moser, Thierry A1 - Jiang, Yan A1 - Caprioglio, Pietro A1 - Neher, Dieter A1 - Buecheler, Stephan A1 - Tiwari, Ayodhya N. T1 - On the origin of open-circuit voltage losses in flexible n-i-p perovskite solar cells JF - Science and technology of advanced materials : STAM N2 - The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recombination losses. Herein, we performed a systematic voltage loss analysis for a typical low-temperature processed, flexible PSC in n-i-p configuration using vacuum deposited C-60 as electron transport layer (ETL) and two-step hybrid vacuum-solution deposition for CH3NH3PbI3 perovskite absorber. We identified the ETL/absorber interface as a bottleneck in relation to non-radiative recombination losses, the quasi-Fermi level splitting (QFLS) decreases from similar to 1.23 eV for the bare absorber, just similar to 90 meV below the radiative limit, to similar to 1.10 eV when C-60 is used as ETL. To effectively mitigate these voltage losses, we investigated different interfacial modifications via vacuum deposited interlayers (BCP, B4PyMPM, 3TPYMB, and LiF). An improvement in QFLS of similar to 30-40 meV is observed after interlayer deposition and confirmed by comparable improvements in the open-circuit voltage after implementation of these interfacial modifications in flexible PSCs. Further investigations on absorber/hole transport layer (HTL) interface point out the detrimental role of dopants in Spiro-OMeTAD film (widely employed HTL in the community) as recombination centers upon oxidation and light exposure. [GRAPHICS] . KW - Perovskite solar cell KW - flexible KW - interface engineering KW - non-radiative recombination KW - quasi-Fermi level splitting Y1 - 2019 U6 - https://doi.org/10.1080/14686996.2019.1633952 SN - 1468-6996 SN - 1878-5514 VL - 20 SP - 786 EP - 795 PB - Taylor & Francis CY - Abingdon ER - TY - JOUR A1 - Sini, Gjergji A1 - Schubert, Marcel A1 - Risko, Chad A1 - Roland, Steffen A1 - Lee, Olivia P. A1 - Chen, Zhihua A1 - Richter, Thomas V. A1 - Dolfen, Daniel A1 - Coropceanu, Veaceslav A1 - Ludwigs, Sabine A1 - Scherf, Ullrich A1 - Facchetti, Antonio A1 - Frechet, Jean M. J. A1 - Neher, Dieter T1 - On the Molecular Origin of Charge Separation at the Donor-Acceptor Interface JF - Advanced energy materials N2 - Fullerene-based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor-acceptor (D-A) interface. Model systems comprised of polythiophene-based donor and rylene diimide-based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct-contact intermolecular polarization play in establishing a driving force ( energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules. KW - donor-acceptor interfaces KW - energy gradients KW - geometrical deformations KW - nonfullerene acceptors KW - organic photovoltaics KW - photocurrent generation KW - polymer solar cells Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201702232 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 12 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Albrecht, Steve A1 - Schindler, Wolfram A1 - Kurpiers, Jona A1 - Kniepert, Juliane A1 - Blakesley, James C. A1 - Dumsch, Ines A1 - Allard, Sybille A1 - Fostiropoulos, Konstantinos A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - On the field dependence of free charge carrier generation and recombination in blends of PCPDTBT/PC70BM influence of solvent additives JF - The journal of physical chemistry letters N2 - We have applied time-delayed collection field (TDCF) and charge extraction by linearly increasing voltage (CELIV) to investigate the photogeneration, transport, and recombination of charge carriers in blends composed of PCPDTBT/PC70BM processed with and without the solvent additive diiodooctane. The results suggest that the solvent additive has severe impacts on the elementary processes involved in the photon to collected electron conversion in these blends. First, a pronounced field dependence of the free carrier generation is found for both blends, where the field dependence is stronger without the additive. Second, the fate of charge carriers in both blends can be described with a rather high bimolecular recombination coefficients, which increase with decreasing internal field. Third, the mobility is three to four times higher with the additive. Both blends show a negative field dependence of mobility, which we suggest to cause bias-dependent recombination coefficients. Y1 - 2012 U6 - https://doi.org/10.1021/jz3000849 SN - 1948-7185 VL - 3 IS - 5 SP - 640 EP - 645 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Albrecht, Steve A1 - Vandewal, Koen A1 - Tumbleston, John R. A1 - Fischer, Florian S. U. A1 - Douglas, Jessica D. A1 - Frechet, Jean M. J. A1 - Ludwigs, Sabine A1 - Ade, Harald W. A1 - Salleo, Alberto A1 - Neher, Dieter T1 - On the efficiency of charge transfer state splitting in polymer: Fullerene solar cells JF - Advanced materials KW - organic solar cells KW - charge generation KW - geminate recombination KW - charge transfer states KW - driving force KW - excess energy KW - morphology KW - spectroelectrochemistry Y1 - 2014 U6 - https://doi.org/10.1002/adma.201305283 SN - 0935-9648 SN - 1521-4095 VL - 26 IS - 16 SP - 2533 EP - 2539 PB - Wiley-VCH CY - Weinheim 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 - GEN A1 - Wolff, Christian Michael A1 - Caprioglio, Pietro A1 - Stolterfoht, Martin A1 - Neher, Dieter T1 - Nonradiative recombination in perovskite solar cells BT - the role of interfaces T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Perovskite solar cells combine high carrier mobilities with long carrier lifetimes and high radiative efficiencies. Despite this, full devices suffer from significant nonradiative recombination losses, limiting their VOC to values well below the Shockley–Queisser limit. Here, recent advances in understanding nonradiative recombination in perovskite solar cells from picoseconds to steady state are presented, with an emphasis on the interfaces between the perovskite absorber and the charge transport layers. Quantification of the quasi‐Fermi level splitting in perovskite films with and without attached transport layers allows to identify the origin of nonradiative recombination, and to explain the VOC of operational devices. These measurements prove that in state‐of‐the‐art solar cells, nonradiative recombination at the interfaces between the perovskite and the transport layers is more important than processes in the bulk or at grain boundaries. Optical pump‐probe techniques give complementary access to the interfacial recombination pathways and provide quantitative information on transfer rates and recombination velocities. Promising optimization strategies are also highlighted, in particular in view of the role of energy level alignment and the importance of surface passivation. Recent record perovskite solar cells with low nonradiative losses are presented where interfacial recombination is effectively overcome—paving the way to the thermodynamic efficiency limit. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 772 KW - interfacial recombination KW - open‐circuit voltage KW - perovskite solar cells KW - photoluminescence Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437626 SN - 1866-8372 IS - 772 ER - TY - JOUR A1 - Wolff, Christian Michael A1 - Caprioglio, Pietro A1 - Stolterfoht, Martin A1 - Neher, Dieter T1 - Nonradiative Recombination in Perovskite Solar Cells BT - the Role of Interfaces JF - Advanced materials N2 - Perovskite solar cells combine high carrier mobilities with long carrier lifetimes and high radiative efficiencies. Despite this, full devices suffer from significant nonradiative recombination losses, limiting their V-OC to values well below the Shockley-Queisser limit. Here, recent advances in understanding nonradiative recombination in perovskite solar cells from picoseconds to steady state are presented, with an emphasis on the interfaces between the perovskite absorber and the charge transport layers. Quantification of the quasi-Fermi level splitting in perovskite films with and without attached transport layers allows to identify the origin of nonradiative recombination, and to explain the V-OC of operational devices. These measurements prove that in state-of-the-art solar cells, nonradiative recombination at the interfaces between the perovskite and the transport layers is more important than processes in the bulk or at grain boundaries. Optical pump-probe techniques give complementary access to the interfacial recombination pathways and provide quantitative information on transfer rates and recombination velocities. Promising optimization strategies are also highlighted, in particular in view of the role of energy level alignment and the importance of surface passivation. Recent record perovskite solar cells with low nonradiative losses are presented where interfacial recombination is effectively overcome-paving the way to the thermodynamic efficiency limit. KW - interfacial recombination KW - open-circuit voltage KW - perovskite solar cells KW - photoluminescence Y1 - 2019 U6 - https://doi.org/10.1002/adma.201902762 SN - 0935-9648 SN - 1521-4095 VL - 31 IS - 52 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Proctor, Christopher M. A1 - Kim, Chunki A1 - Neher, Dieter A1 - Thuc-Quyen Nguyen, T1 - Nongeminate recombination and charge transport limitations in diketopyrrolopyrrole-based solution-processed small molecule solar cells JF - Advanced functional materials N2 - Charge transport and nongeminate recombination are investigated in two solution-processed small molecule bulk heterojunction solar cells consisting of diketopyrrolopyrrole (DPP)-based donor molecules, mono-DPP and bis-DPP, blended with [6,6]-phenyl-C71-butyric acid methyl ester (PCBM). While the bis-DPP system exhibits a high fill factor (62%) the mono-DPP system suffers from pronounced voltage dependent losses, which limit both the fill factor (46%) and short circuit current. A method to determine the average charge carrier density, recombination current, and effective carrier lifetime in operating solar cells as a function of applied bias is demonstrated. These results and light intensity measurements of the current-voltage characteristics indicate that the mono-DPP system is severely limited by nongeminate recombination losses. Further analysis reveals that the most significant factor leading to the difference in fill factor is the comparatively poor hole transport properties in the mono-DPP system (2 x 10(-5) cm(2) V-1 s(-1) versus 34 x 10(-5) cm(2) V-1 s(-1)). These results suggest that future design of donor molecules for organic photovoltaics should aim to increase charge carrier mobility thereby enabling faster sweep out of charge carriers before they are lost to nongeminate recombination. KW - charge transport KW - solar cells KW - photovoltaic devices KW - organic electronics KW - characterization tools Y1 - 2013 U6 - https://doi.org/10.1002/adfm.201202643 SN - 1616-301X SN - 1616-3028 VL - 23 IS - 28 SP - 3584 EP - 3594 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 - Salert, Beatrice Ch. D. A1 - Krueger, Hartmut A1 - Bagnich, Sergey A. A1 - Unger, Thomas A1 - Jaiser, Frank A1 - Al-Sa'di, Mahmoud A1 - Neher, Dieter A1 - Hayer, Anna A1 - Eberle, Thomas T1 - New polymer matrix system for phosphorescent organic light-emitting diodes and the role of the small molecular co-host JF - Journal of polymer science : A, Polymer chemistry N2 - A new matrix system for phosphorescent organic light-emitting diodes (OLEDs) based on an electron transporting component attached to an inert polymer backbone, an electronically neutral co-host, and a phosphorescent dye that serves as both emitter and hole conductor are presented. The inert co-host is used either as small molecules or covalently connected to the same chain as the electron-transporting host. The use of a small molecular inert co-host in the active layer is shown to be highly advantageous in comparison to a purely polymeric matrix bearing the same functionalities. Analysis of the dye phosphorescence decay in pure polymer, small molecular co-host film, and their blend lets to conclude that dye molecules distribute mostly in the small molecular co-host phase, where the co-host prevents agglomeration and self-quenching of the phosphorescence as well as energy transfer to the electron transporting units. In addition, the co-host accumulates at the anode interface where it acts as electron blocking layer and improves hole injection. This favorable phase separation between polymeric and small molecular components results in devices with efficiencies of about 47 cd/A at a luminance of 1000 cd/m(2). Investigation of OLED degradation demonstrates the presence of two time regimes: one fast component that leads to a strong decrease at short times followed by a slower decrease at longer times. Unlike the long time degradation, the efficiency loss that occurs at short times is reversible and can be recovered by annealing of the device at 180 degrees C. We also show that the long-time degradation must be related to a change of the optical and electrical bulk properties. KW - charge transport KW - conducting polymer KW - degradation KW - host-guest systems KW - light-emitting diodes KW - random copolymer KW - synthesis KW - UV-vis spectroscopy Y1 - 2013 U6 - https://doi.org/10.1002/pola.26409 SN - 0887-624X VL - 51 IS - 3 SP - 601 EP - 613 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Zentel, Rudolf A1 - Behl, Marc A1 - Neher, Dieter A1 - Zen, Achmad A1 - Lucht, Sylvia T1 - Nanostructured polytriarylamines : orientation layers for polyfluorene Y1 - 2004 SN - 0065-7727 ER - TY - JOUR A1 - Tockhorn, Philipp A1 - Sutter, Johannes A1 - Cruz Bournazou, Alexandros A1 - Wagner, Philipp A1 - Jäger, Klaus A1 - Yoo, Danbi A1 - Lang, Felix A1 - Grischek, Max A1 - Li, Bor A1 - Li, Jinzhao A1 - Shargaieva, Oleksandra A1 - Unger, Eva A1 - Al-Ashouri, Amran A1 - Köhnen, Eike A1 - Stolterfoht, Martin A1 - Neher, Dieter A1 - Schlatmann, Rutger A1 - Rech, Bernd A1 - Stannowski, Bernd A1 - Albrecht, Steve A1 - Becker, Christiane T1 - Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells JF - Nature nanotechnology N2 - Designing gentle sinusoidal nanotextures enables the realization of high-efficiency perovskite-silicon solar cells
Perovskite-silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite-silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%. Y1 - 2022 U6 - https://doi.org/10.1038/s41565-022-01228-8 SN - 1748-3387 SN - 1748-3395 VL - 17 IS - 11 SP - 1214 EP - 1221 PB - Nature Publishing Group CY - London [u.a.] ER - TY - JOUR A1 - Mechau, Norman A1 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Molecular tracer diffusion in thin azobenzene polymer layers JF - Applied physics letters N2 - Translational diffusion of fluorescent tracer molecules in azobenzene polymer layers is studied at different temperatures and under illumination using the method of fluorescence recovery after photobleaching. Diffusion is clearly observed in the dark above the glass transition temperature, while homogeneous illumination at 488 nm and 100 mW/cm(2) does not cause any detectable diffusion of the dye molecules within azobenzene layers. This implies that the viscosity of azobenzene layers remains nearly unchanged under illumination with visible light in the absence of internal or external forces. (c) 2006 American Institute of Physics. Y1 - 2006 U6 - https://doi.org/10.1063/1.2405853 SN - 0003-6951 VL - 89 IS - 25 PB - Elsevier CY - Melville ER - TY - JOUR A1 - Lu, Guanghao A1 - Blakesley, James C. A1 - Himmelberger, Scott A1 - Pingel, Patrick A1 - Frisch, Johannes A1 - Lieberwirth, Ingo A1 - Salzmann, Ingo A1 - Oehzelt, Martin A1 - Di Pietro, Riccardo A1 - Salleo, Alberto A1 - Koch, Norbert A1 - Neher, Dieter T1 - Moderate doping leads to high performance of semiconductor/insulator polymer blend transistors JF - Nature Communications N2 - Polymer transistors are being intensively developed for next-generation flexible electronics. Blends comprising a small amount of semiconducting polymer mixed into an insulating polymer matrix have simultaneously shown superior performance and environmental stability in organic field-effect transistors compared with the neat semiconductor. Here we show that such blends actually perform very poorly in the undoped state, and that mobility and on/off ratio are improved dramatically upon moderate doping. Structural investigations show that these blend layers feature nanometre-scale semiconductor domains and a vertical composition gradient. This particular morphology enables a quasi three-dimensional spatial distribution of semiconductor pathways within the insulating matrix, in which charge accumulation and depletion via a gate bias is substantially different from neat semiconductor, and where high on-current and low off-current are simultaneously realized in the stable doped state. Adding only 5 wt% of a semiconducting polymer to a polystyrene matrix, we realized an environmentally stable inverter with gain up to 60. Y1 - 2013 U6 - https://doi.org/10.1038/ncomms2587 SN - 2041-1723 VL - 4 IS - 1-2 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Ilnytskyi, Jaroslav M. A1 - Saphiannikova, Marina A1 - Neher, Dieter A1 - Allen, Michael P. T1 - Modelling elasticity and memory effects in liquid crystalline elastomers by molecular dynamics simulations JF - Soft matter N2 - We performed molecular dynamics simulations of a liquid crystal elastomer of side-chain architecture. The network is formed from a melt of 28 molecules each having a backbone of 100 hydrocarbon monomers, to which 50 side chains are attached in a syndiotactic way. Crosslinking is performed in the smectic A phase. We observe an increase of the smectic-isotropic phase transition temperature of about 5 degrees as compared to the uncrosslinked melt. Memory effects in liquid crystalline order and in sample shape are well reproduced when the elastomer is driven through the smectic-isotropic transition. Above this transition, in the isotropic phase, the polydomain smectic phase is induced by a uniaxial load. Below the transition, in a monodomain smectic A phase, both experimentally observed effects of homogeneous director reorientation and stripe formation are reproduced when the sample is stretched along the director. When the load is applied perpendicularly to the director, the sample demonstrates reversible deformation with no change of liquid crystalline order, indicating elasticity of the two-dimensional network of polymer layers. Y1 - 2012 U6 - https://doi.org/10.1039/c2sm26499d SN - 1744-683X VL - 8 IS - 43 SP - 11123 EP - 11134 PB - Royal Society of Chemistry CY - Cambridge ER -