TY - JOUR A1 - Shalom, Menny A1 - Inal, Sahika A1 - Fettkenhauer, Christian A1 - Neher, Dieter A1 - Antonietti, Markus T1 - Improving Carbon Nitride Photocatalysis by Supramolecular Preorganization of Monomers JF - Journal of the American Chemical Society N2 - Here we report a new and simple synthetic pathway to form ordered, hollow carbon nitride structures, using a cyanuric acid melamine (CM) complex in ethanol as a starting product. A detailed analysis of the optical and photocatalytic properties shows that optimum hollow carbon nitride structures are formed after 8 h of condensation. For this condensation time, we find a significantly reduced fluorescence intensity and lifetime, indicating the formation of new, nonradiative deactivation pathways, probably involving charge-transfer processes. Enhanced charge transfer is seen as well from a drastic increase of the photocatalytic activity in the degradation of rhodamine B dye, which is shown to proceed via photoinduced hole transfer. Moreover, we show that various CM morphologies can be obtained using different solvents, which leads to diverse ordered carbon nitride architectures. In all cases, the CM-C3N4 structures exhibited superior photocatalytic activity compared to the bulk material. The utilization of CM hydrogen-bonded complexes opens new opportunities for the significant improvement of carbon nitride synthesis, structure, and optical properties toward an efficient photoactive material for catalysis. Y1 - 2013 U6 - https://doi.org/10.1021/ja402521s SN - 0002-7863 VL - 135 IS - 19 SP - 7118 EP - 7121 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schubert, Marcel A1 - Preis, Eduard A1 - Blakesley, James C. A1 - Pingel, Patrick A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - Mobility relaxation and electron trapping in a donor/acceptor copolymer JF - Physical review : B, Condensed matter and materials physics N2 - To address the nature of charge transport and the origin of severe (intrinsic) trapping in electron-transporting polymers, transient and steady-state charge transport measurements have been conducted on the prototype donor/acceptor copolymer poly[2,7-(9,9-dialkyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PFTBTT). A charge-generation layer technique is used to selectively address transport of the desired charge carrier type, to perform time-of-flight measurements on samples with < 200 nm thickness, and to combine the time-of-flight and the photocharge extraction by linearly increasing voltage (photo-CELIV) techniques to investigate charge carrier dynamics over a wide time range. Significant trapping of free electrons is observed in the bulk of dioctyl-substituted PFTBTT (alt-PF8TBTT), introducing a strong relaxation of the charge carrier mobility with time. We used Monte-Carlo simulation to simulate the measured transient data and found that all measurements can be modeled with a single parameter set, with the charge transport behavior determined by multiple trapping and detrapping of electrons in an exponential trap distribution. The influence of the concomitant mobility relaxation on the transient photocurrent characteristics in photo-CELIV experiments is discussed and shown to explain subtle features that were seen in former publications but were not yet assigned to electron trapping. Comparable studies on PFTBTT copolymers with chemical modifications of the side chains and backbone suggest that the observed electron trapping is not caused by a distinct chemical species but rather is related to interchain interactions. Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevB.87.024203 SN - 1098-0121 VL - 87 IS - 2 PB - American Physical Society CY - College Park 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 - 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 - Pingel, P. A1 - Neher, Dieter T1 - Comprehensive picture of p-type doping of P3HT with the molecular acceptor F(4)TCNQ JF - Physical review : B, Condensed matter and materials physics N2 - By means of optical spectroscopy, Kelvin probe, and conductivity measurements, we study the p-type doping of the donor polymer poly(3-hexylthiophene), P3HT, with the molecular acceptor tetrafluorotetracyanoquin-odimethane, F(4)TCNQ, covering a broad range of molar doping ratios from the ppm to the percent regime. Thorough quantitative analysis of the specific near-infrared absorption bands of ionized F(4)TCNQ reveals that almost every F(4)TCNQ dopant undergoes integer charge transfer with a P3HT site. However, only about 5% of these charge carrier pairs are found to dissociate and contribute a free hole for electrical conduction. The nonlinear behavior of the conductivity on doping ratio is rationalized by a numerical mobility model that accounts for the broadening of the energetic distribution of transport sites by the Coulomb potentials of ionized F(4)TCNQ dopants. DOI: 10.1103/PhysRevB.87.115209 Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevB.87.115209 SN - 1098-0121 VL - 87 IS - 11 PB - American Physical Society CY - College Park 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 - Li, Hongguang A1 - Babu, Sukumaran Santhosh A1 - Turner, Sarah T. A1 - Neher, Dieter A1 - Hollamby, Martin J. A1 - Tomohito, Seki A1 - Yagai, Shiki A1 - deguchi, Yonekazu A1 - Möhwald, Helmuth A1 - Nakanishi, Takashi T1 - Alkylated-C60 based soft materials: regulation of self-assembly and optoelectronic properties by chain branching N2 - Derivatization of fullerene (C60) with branched aliphatic chains softens C60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84°C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 ñ 0.1%) in comparison with another compound, 10 (PCE: 0.5 ñ 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices. Y1 - 2013 UR - http://pubs.rsc.org/en/content/articlepdf/2013/tc/c3tc00066d U6 - https://doi.org/10.1039/C3TC00066D ER - TY - JOUR A1 - Li, Hongguang A1 - Babu, Sukumaran Santhosh A1 - Turner, Sarah T. A1 - Neher, Dieter A1 - Hollamby, Martin J. A1 - Seki, Tomohiro A1 - Yagai, Shiki A1 - Deguchi, Yonekazu A1 - Möhwald, Helmuth A1 - Nakanishi, Takashi T1 - Alkylated-C-60 based soft materials regulation of self-assembly and optoelectronic properties by chain branching JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Derivatization of fullerene (C-60) with branched aliphatic chains softens C-60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C-60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84 degrees C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 + 0.1%) in comparison with another compound, 10 (PCE: 0.5 + 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C-60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices. Y1 - 2013 U6 - https://doi.org/10.1039/c3tc00066d SN - 2050-7526 VL - 1 IS - 10 SP - 1943 EP - 1951 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Li, Hongguang A1 - Babu, Sukumaran Santhosh A1 - Turner, Sarah T. A1 - Neher, Dieter A1 - Hollamby, Martin J. A1 - Seki, Tomohiro A1 - Yagai, Shiki A1 - Deguchi, Yonekazu A1 - Möhwald, Helmuth A1 - Nakanishi, Takashi T1 - Alkylated-C60 based soft materials BT - regulation of selfassembly and optoelectronic properties by chain branching N2 - Derivatization of fullerene (C60) with branched aliphatic chains softens C60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84 °C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 ± 0.1%) in comparison with another compound, 10 (PCE: 0.5 ± 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 250 Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95358 SP - 1943 EP - 1951 ER - TY - JOUR A1 - Lange, Ilja A1 - Kniepert, Juliane A1 - Pingel, Patrick A1 - Dumsch, Ines A1 - Allard, Sybille A1 - Janietz, Silvia A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - Correlation between the open circuit voltage and the energetics of organic bulk heterojunction solar cells JF - The journal of physical chemistry letters N2 - A detailed investigation of the open circuit voltage (V-OC) of organic bulk heterojunction solar cells comprising three different donor polymers and two different fullerene-based acceptors is presented. Bias amplified charge extraction (BACE) is combined with Kelvin Probe measurements to derive information on the relevant energetics in the blend. On the example of P3HT:PC70BM the influence of composition and preparation conditions on the relevant transport levels will be shown. Moderate upward shifts of the P3HT HOMO depending on crystallinity are observed, but contrarily to common believe, the dependence of V-OC on blend composition and thermal history is found to be largely determined by the change in the PCBM LUMO energy. Following this approach, we quantified the energetic contribution to the V-OC in blends with fluorinated polymers or higher adduct fullerenes. Y1 - 2013 U6 - https://doi.org/10.1021/jz401971e SN - 1948-7185 VL - 4 IS - 22 SP - 3865 EP - 3871 PB - American Chemical Society CY - Washington ER -