TY - JOUR A1 - Shalom, Menny A1 - Guttentag, Miguel A1 - Fettkenhauer, Christian A1 - Inal, Sahika A1 - Neher, Dieter A1 - Llobet, Antoni A1 - Antonietti, Markus T1 - In situ formation of heterojunctions in modified graphitic carbon nitride: synthesis and noble metal free photocatalysis JF - Chemistry of materials : a publication of the American Chemical Society N2 - Herein, we report the facile synthesis of an efficient roll-like carbon nitride (C3N4) photocatalyst for hydrogen production using a supramolecular complex composed of cyanuric acid, melamine, and barbituric acid as the starting monomers. Optical and photocatalytic investigations show, along with the known red shift of absorption into the visible region, that the insertion of barbituric acid results in the in situ formation of in-plane heterojuctions, which enhance the charge separation process under illumination. Moreover, platinum as the standard cocatalyst in photocatalysis could be successfully replaced with first row transition metal salts and complexes under retention of 50% of the catalytic activity. Their mode of deposition and interaction with the semiconductor was studied in detail. Utilization of the supramolecular approach opens new opportunities to manipulate the charge transfer process within carbon nitride with respect to the design of a more efficient carbon nitride photocatalyst with controlled morphology and optical properties. Y1 - 2014 U6 - https://doi.org/10.1021/cm503258z SN - 0897-4756 SN - 1520-5002 VL - 26 IS - 19 SP - 5812 EP - 5818 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Xu, Jingsan A1 - Brenner, Thomas J. K. A1 - Chabanne, Laurent A1 - Neher, Dieter A1 - Antonietti, Markus A1 - Shalom, Menny T1 - Liquid-Based growth of polymeric carbon nitride layers and their use in a mesostructured polymer solar cell with V-oc exceeding 1 V JF - Journal of the American Chemical Society N2 - Herein we report a general liquid-mediated pathway for the growth of continuous polymeric carbon nitride (C3N4) thin films. The deposition method consists of the use of supramolecular complexes that transform to the liquid state before direct thermal condensation into C3N4 solid films. The resulting films exhibit continuous porous C3N4 networks on various substrates. Moreover, the optical absorption can be easily tuned to cover the solar spectrum by the insertion of an additional molecule into the starting complex. The strength of the deposition method is demonstrated by the use of the C3N4 layer as the electron acceptor in a polymer solar cell that exhibits a remarkable open-circuit voltage exceeding 1 V. The easy, safe, and direct synthesis of carbon nitride in a continuous layered architecture on different functional substrates opens new possibilities for the fabrication of many energy-related devices. Y1 - 2014 U6 - https://doi.org/10.1021/ja508329c SN - 0002-7863 VL - 136 IS - 39 SP - 13486 EP - 13489 PB - American Chemical Society CY - Washington 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 - 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 - JOUR A1 - Kraffert, Felix A1 - Steyrleuthner, Robert A1 - Albrecht, Steve A1 - Neher, Dieter A1 - Scharber, Markus C. A1 - Bittl, Robert A1 - Behrends, Jan T1 - Charge Separation in PCPDTBT : PCBM Blends from an EPR Perspective JF - The journal of physical chemistry Y1 - 2014 U6 - https://doi.org/10.1021/jp509650v SN - 1932-7447 VL - 118 IS - 49 SP - 28482 EP - 28493 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Liu, W. A1 - Tkachov, R. A1 - Komber, H. A1 - Senkovskyy, V. A1 - Schubert, M. A1 - Wei, Z. A1 - Facchetti, A. A1 - Neher, Dieter A1 - Kiriy, A. T1 - Chain-growth polycondensation of perylene diimide-based copolymers: a new route to regio-regular perylene diimide-based acceptors for all-polymer solar cells and n-type transistors JF - Polymer Chemistry N2 - Herein, we report the chain-growth tin-free room temperature polymerization method to synthesize n-type perylene diimide-dithiophene-based conjugated polymers (PPDIT2s) suitable for solar cell and transistor applications. The palladium/electron-rich tri-tert-butylphosphine catalyst is effective to enable the chain-growth polymerization of anion-radical monomer Br-TPDIT-Br/Zn to PPDIT2 with a molecular weight up to M-w approximate to 50 kg mol(-1) and moderate polydispersity. This is the second example of the polymerization of unusual anion-radical aromatic complexes formed in a reaction of active Zn and electron-deficient diimide-based aryl halides. As such, the discovered polymerization method is not a specific reactivity feature of the naphthalene-diimide derivatives but is rather a general polymerization tool. This is an important finding, given the significantly higher maximum external quantum efficiency that can be reached with PDI-based copolymers (32-45%) in all-polymer solar cells compared to NDI-based materials (15-30%). Our studies revealed that PPDIT2 synthesized by the new method and the previously published polymer prepared by step-growth Stille polycondensation show similar electron mobility and all-polymer solar cell performance. At the same time, the polymerization reported herein has several technological advantages as it proceeds relatively fast at room temperature and does not involve toxic tin-based compounds. Because several chain-growth polymerization reactions are well-suited for the preparation of well-defined multi-functional polymer architectures, the next target is to explore the utility of the discovered polymerization in the synthesis of end-functionalized polymers and block copolymers. Such materials would be helpful to improve the nanoscale morphology of polymer blends in all-polymer solar cells. Y1 - 2014 U6 - https://doi.org/10.1039/c3py01707a SN - 1759-9954 SN - 1759-9962 VL - 5 IS - 10 SP - 3404 EP - 3411 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kniepert, Juliane A1 - Lange, Ilja A1 - Heidbrink, Jan A1 - Kurpiers, Jona A1 - Brenner, Thomas J. K. A1 - Koster, L. Jan Anton A1 - Neher, Dieter T1 - Effect of Solvent Additive on Generation, Recombination, and Extraction in PTB7:PCBM Solar Cells: A Conclusive Experimental and Numerical Simulation Study JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Time-delayed collection field (TDCF), bias-assisted charge extraction (BACE), and space charge-limited current (SCLC) measurements are combined with complete numerical device simulations to unveil the effect of the solvent additive 1,8-diiodooctane (DIO) on the performance of PTB7:PCBM bulk heterojunction solar cells. DIO is shown to increase the charge generation rate, reduce geminate and bimolecular recombination, and increase the electron mobility. In total, the reduction of loss currents by processing with the additive raises the power conversion efficiency of the PTB7:PCBM blend by a factor of almost three. The lower generation rates and higher geminate recombination losses in devices without DIO are consistent with a blend morphology comprising large fullerene clusters embedded within a PTB7-rich matrix, while the low electron mobility suggests that these fullerene clusters are themselves composed of smaller pure fullerene aggregates separated by disordered areas. Our device simulations show unambiguously that the effect of the additive on the shape of the currentvoltage curve (J-V) cannot be ascribed to the variation of only the mobility, the recombination, or the field dependence of generation. It is only when the changes of all three parameters are taken into account that the simulation matches the experimental J-V characteristics under all illumination conditions and for a wide range of voltages. Y1 - 2015 U6 - https://doi.org/10.1021/jp512721e SN - 1932-7447 VL - 119 IS - 15 SP - 8310 EP - 8320 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Bartesaghi, Davide A1 - Perez, Irene del Carmen A1 - Kniepert, Juliane A1 - Roland, Steffen A1 - Turbiez, Mathieu A1 - Neher, Dieter A1 - Koster, L. Jan Anton T1 - Competition between recombination and extraction of free charges determines the fill factor of organic solar cells JF - Nature Communications N2 - Among the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter theta, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor: acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over wide ranges to reproduce typical experimental conditions. The results unify the fill factors of several very different donor: acceptor combinations and give insight into why fill factors change so much with thickness, light intensity and materials properties. To achieve fill factors larger than 0.8 requires further improvements in charge transport while reducing recombination. Y1 - 2015 U6 - https://doi.org/10.1038/ncomms8083 SN - 2041-1723 VL - 6 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Würfel, Uli A1 - Neher, Dieter A1 - Spies, Annika A1 - Albrecht, Steve T1 - Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells JF - Nature Communications N2 - This work elucidates the impact of charge transport on the photovoltaic properties of organic solar cells. Here we show that the analysis of current-voltage curves of organic solar cells under illumination with the Shockley equation results in values for ideality factor, photo-current and parallel resistance, which lack physical meaning. Drift-diffusion simulations for a wide range of charge-carrier mobilities and illumination intensities reveal significant carrier accumulation caused by poor transport properties, which is not included in the Shockley equation. As a consequence, the separation of the quasi Fermi levels in the organic photoactive layer (internal voltage) differs substantially from the external voltage for almost all conditions. We present a new analytical model, which considers carrier transport explicitly. The model shows excellent agreement with full drift-diffusion simulations over a wide range of mobilities and illumination intensities, making it suitable for realistic efficiency predictions for organic solar cells. Y1 - 2015 U6 - https://doi.org/10.1038/ncomms7951 SN - 2041-1723 VL - 6 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Lu, Guanghao A1 - Koch, Norbert A1 - Neher, Dieter T1 - In-situ tuning threshold voltage of field-effect transistors based on blends of poly(3-hexylthiophene) with an insulator electret JF - Applied physics letters N2 - Blending the conjugated polymer poly(3-hexylthiophene) (P3HT) with the insulating electret polystyrene (PS), we show that the threshold voltage V-t of organic field-effect transistors (OFETs) can be easily and reversely tuned by applying a gate bias stress at 130 degrees C. It is proposed that this phenomenon is caused by thermally activated charge injection from P3HT into PS matrix, and that this charge is immobilized within the PS matrix after cooling down to room temperature. Therefore, room-temperature hysteresis-free FETs with desired V-t can be easily achieved. The approach is applied to reversely tune the OFET mode of operation from accumulation to depletion, and to build inverters. (C) 2015 AIP Publishing LLC. Y1 - 2015 U6 - https://doi.org/10.1063/1.4928554 SN - 0003-6951 SN - 1077-3118 VL - 107 IS - 6 PB - American Institute of Physics CY - Melville ER -