19 results on '"Moritz Hein"'
Search Results
2. Sensor solutions for an energy-efficient and user-centered heating system
- Author
-
Jochen Bauer, Thomas Becher, Rebecca Zehle, Daniel Schaller, Gerhard Fischerauer, Martin Feller, Michael Meiler, Jörg Franke, Moritz Hein, Johannes Bürner, Ralf Stöber, and Joachim Maul
- Subjects
Engineering ,Operative temperature ,business.industry ,System of measurement ,0211 other engineering and technologies ,Electrical engineering ,Thermal comfort ,020206 networking & telecommunications ,02 engineering and technology ,Radiant heating ,Heating system ,021105 building & construction ,0202 electrical engineering, electronic engineering, information engineering ,Ceiling (aeronautics) ,Electrical and Electronic Engineering ,business ,Instrumentation ,Wireless sensor network ,Efficient energy use - Abstract
In contrast to conventional hydronic heating systems, in which the air is used as a medium for the convective heat transfer, an alternative approach is based on the usage of infrared (IR) radiant heating foils. These foils, which are applied to the walls and the ceiling of a laboratory, can be controlled individually. This leads to the possibility of heating the room zonewise and only when a person is present in a zone. A local comfortable climate is provided only in occupied zones, with the remaining zones being kept at a lower base temperature. Consequently, the measurement system has to detect persons in each zone and to determine the putative thermal comfort at relevant locations in the room. For the first problem, we examined and evaluated different sensor types capable of localizing persons without infringing on their anonymity. For the second problem, we used the fact that the thermal comfort mainly depends on the operative temperature (Li et al., 2010; DIN EN ISO 7730, 2006; de Dear and Brager, 2002). According to Simone et al. (2007), this temperature can be measured directly by an easily producible, planar sensor. The sensors were integrated in a wireless sensor network which consists of Wi-Fi-capable microcontroller boards, wireless smart home equipment, a Wi-Fi router, and a server.
- Published
- 2017
- Full Text
- View/download PDF
3. Advancing ecological assessment of the Arabian Gulf through eDNA metabarcoding: opportunities, prospects, and challenges
- Author
-
Thadickal V. Joydas, Seerangan Manokaran, Jayanath Gopi, Jayachandran P. Rajakumar, Lin Yu-Jia, Moritz Heinle, Mazen K. Nazal, Karuppasamy P. Manikandan, Maryam Qashqari, Sowmya P. Mohandas, Syed A. Hussain, Rommel H. Maneja, Ali M. Qasem, Diego Lozano-Cortés, and Nabil S. Abuzaid
- Subjects
environmental DNA ,high-throughput sequencing ,biomonitoring ,anthropogenic activities ,marine ecosystem ,Science ,General. Including nature conservation, geographical distribution ,QH1-199.5 - Abstract
The Arabian Gulf (hereafter ‘the Gulf’) is renowned for its unique ecological characteristics and distinct marine life. It offers a diverse range of ecosystems that have adapted to the impacts posed by natural stress and human activities. Regular biomonitoring and diversity assessments are necessary to document the health of the Gulf ecosystem and to implement appropriate measures for effective conservation and management. Recently, environmental DNA (eDNA), a total pool of DNA isolated from environmental samples, has emerged as a highly effective tool for ecological studies. This review explores the opportunities, prospects, and challenges associated with employing eDNA metabarcoding in the ecological assessment and biomonitoring of the Gulf. It provides an overview of the status of the Gulf ecosystem and discusses the potential applications of eDNA metabarcoding in assessing biodiversity, monitoring invasive species, and evaluating ecosystem health. Additionally, the investigation addresses the challenges inherent in implementing this technique, considering environmental complexities, methodological intricacies, and data interpretation. Overall, this review emphasizes the immense potential of eDNA metabarcoding in advancing ecological assessment in the Gulf and calls for further research and collaboration to harness its benefits in this unique marine ecosystem.
- Published
- 2024
- Full Text
- View/download PDF
4. Smart Heating System for Old Buildings - An Approach to the Decentralized Use of Renewable Energies
- Author
-
Jörg Franke, Johannes Bürner, Gerhard Fischerauer, Moritz Hein, Joachim Maul, Ralf Stöber, and Martin Feller
- Subjects
Materials science ,business.industry ,Storage heater ,Renewable heat ,Mechanical engineering ,General Medicine ,Coefficient of performance ,law.invention ,Renewable energy ,Radiant heating ,Heating system ,law ,business ,Efficient energy use ,Heat pump - Abstract
The central heating units of buildings are typically replaced every 20 to 30 years. There exists a variety of solutions for fuel-and gas-based units, but it would be advantageous to be able to use renewable energies. This would become possible by the combination of planar carbon-fiber-based infrared (IR) radiant heating foils with a heat pump providing hot water. The main goal of our proposed overall control strategy is to increase the energy efficiency while maintaining the thermal comfort for the residents. We examined the electromagnetic compatibility of the heating foils and simulated the relative contributions of the amount of energy provided by the heat pump and by the heating foils to obtain a maximum coefficient of performance for the combined heating system.
- Published
- 2016
- Full Text
- View/download PDF
5. Smart Energy and Grid: Novel Approaches for the Efficient Generation, Storage, and Usage of Energy in the Smart Home and the Smart Grid Linkup
- Author
-
Julian Praß, Johannes Weber, Sebastian Staub, Johannes Bürner, Ralf Böhm, Thomas Braun, Moritz Hein, Markus Michl, Michael Beck, and Jörg Franke
- Subjects
Wind power ,business.industry ,Computer science ,020209 energy ,02 engineering and technology ,Energy consumption ,Grid ,Renewable energy ,Cogeneration ,Smart grid ,020401 chemical engineering ,Waste heat ,0202 electrical engineering, electronic engineering, information engineering ,Systems engineering ,Electric power ,0204 chemical engineering ,business - Abstract
This chapter presents novel approaches for the efficient generation, storage, and usage of energy in the smart home environment and their link to the smart grid. It also demonstrates innovative concepts and their feasibility for these purposes. The generation of renewable energy on the level of individual homes and housing estates is achieved by aerodynamically and aeroacoustically optimized small wind turbines as well as combined heat and power (CHP) micro plants using organic Rankine cycles (ORCs) to complement solar energy. The chapter further discusses the intelligent distribution of electric energy between the smart home and the smart grid. In order to tackle the transition of the electric power supply toward a renewable‐based generation plant system, it is necessary to fully exploit locally available energy sources and to generate production surpluses in rural areas for the supply of urban agglomerations and industrial centers.
- Published
- 2017
- Full Text
- View/download PDF
6. Correlation of Absorption Profile and Fill Factor in Organic Solar Cells: The Role of Mobility Imbalance
- Author
-
Mauro Furno, Moritz Hein, Moritz Riede, Wolfgang Tress, Andre Merten, Karl Leo, and Publica
- Subjects
Materials science ,Organic solar cell ,Renewable Energy, Sustainability and the Environment ,business.industry ,Polymer solar cell ,Wavelength ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Charge carrier ,Solar simulator ,business ,Absorption (electromagnetic radiation) ,Short circuit - Abstract
We investigate the role of the spatial absorption profile within bulk heterojunction small molecule solar cells comprising a 50 nm ZnPc:C60 active layer. Exploiting interference effects the absorption profile is varied by both the illumination wavelength and the thickness of an optical spacer layer adjacent to the reflecting electrode. The fill factor under 1 sun illumination is observed to change from 43 to 49% depending on the absorption profile which approximately equals the charge-carrier generation profile. It is shown by varying the mixing ratio between ZnPc and C60 that the importance of the generation profile is correlated with the imbalance of mobilities. Therefore, it is concluded that non-geminate recombination is the dominating loss mechanism in these devices. Numerical drift-diffusion simulations reproduce the experimental observations showing that charge carrier extraction is more efficient if charge carriers are generated close to the contact collecting t he less mobile charge carrier type. Furthermore, this effect can explain the dependence of the internal quantum efficiency measured at short circuit on wavelength and implies that the spectral mismatch for a given solar simulator and device depends on the applied voltage. The spatial absorption profile in the bulk heterojunction of an organic solar cell is varied by employing different thicknesses of an optical spacer layer. The fill factor correlates with the profile and the imbalance in charge carrier mobilities. These results indicate that extraction of holes in competition with bimolecular recombination limits the device performance. Therefore, the spectral shape of the external quantum efficiency and, in turn, the spectral mismatch change with applied voltage.
- Published
- 2013
- Full Text
- View/download PDF
7. Correlation between temperature activation of charge-carrier generation efficiency and hole mobility in small-molecule donor materials
- Author
-
Roland Fitzner, Vaidotas Kažukauskas, Karl Leo, V. Janonis, Christian Koerner, Moritz Riede, Moritz Hein, Peter Bäuerle, and A. Sakavičius
- Subjects
Electron mobility ,Organic solar cell ,Chemical physics ,Chemistry ,Analytical chemistry ,Molecule ,Charge carrier ,Activation energy ,Physical and Theoretical Chemistry ,Small molecule ,Atomic and Molecular Physics, and Optics ,Dissociation (chemistry) ,Voltage - Abstract
In organic solar cells, free charge carriers are generated at the interface between an electron-donating and an electron-accepting material. The detailed mechanisms of the generation of free charge carriers are still under discussion. In this work, we investigate the influence of temperature on the generation efficiency of free charge carriers in blends of dicyanovinyl substituted oligothiophene (DCVnT) molecules and C60 by quasi-steady-state photoinduced absorption (PIA) measurements. The observed positive temperature dependence of charge-carrier generation can be directly correlated to the charge-transport behavior. The determined activation energy scales inversely with the hole mobility for all investigated DCVnT derivatives, suggesting higher dissociation probability of bound interfacial charge pairs at high mobility. Furthermore, the energetic disorder parameter, σ, determined by CELIV (charge extraction by linearly increasing voltage) measurements for a DCV6T derivative, matches the activation energy from the PIA measurements. In conclusion, these results underline the need for high-mobility donor materials for optimal charge-pair dissociation in organic solar cells.
- Published
- 2016
- Full Text
- View/download PDF
8. The influence of substrate heating on morphology and layer growth in C60 : ZnPc bulk heterojunction solar cells
- Author
-
Steffen Pfuetzner, Jan Meiss, Moritz Riede, Alexandr A. Levin, Chris Elschner, Jens Jankowski, Karl Leo, Bernd Rellinghaus, Moritz Hein, Christoph Schuenemann, and C. Mickel
- Subjects
Photocurrent ,Organic field-effect transistor ,Organic solar cell ,Chemistry ,business.industry ,General Chemistry ,Substrate (electronics) ,Condensed Matter Physics ,Polymer solar cell ,Electronic, Optical and Magnetic Materials ,law.invention ,Biomaterials ,Optics ,Chemical engineering ,Transmission electron microscopy ,law ,Solar cell ,Materials Chemistry ,Electrical and Electronic Engineering ,business ,Layer (electronics) - Abstract
The change of morphology in mixed layers due to different substrate temperature T of organic solar cells containing C60 and zinc phthalocyanine (ZnPc) is studied. Heating the substrate during deposition of the bulk heterojunction C60:ZnPc leads to a significant improvement of solar cell performance, mainly due to an increase in photocurrent and fill factor (FF). This is attributed to improved charge carrier percolation pathways within the C60:ZnPc blend. Using atomic force microscopy, scanning electron microscopy, transmission electron microscopy, organic field effect transistor, X-ray diffraction, and absorption measurements, we observe aggregation, cluster-like, and polycrystalline growth of the heated bulk layer. This provides better transport percolation paths by inducing a phase separation of the molecules. Heated blend layer with thickness of 60 nm shows high performance without loss in FF. When heating the substrate to the optimum temperature of 110 °C, a power conversion efficiency of 3.0% is achieved, compared to 1.4% for an identical device prepared on a substrate held at room temperature. © 2010 Elsevier B.V. All rights reserved.
- Published
- 2016
- Full Text
- View/download PDF
9. P5.7 - Sensorlösungen für eine energieeffiziente nutzerzentrierte Heizung
- Author
-
Ralf Stöber, Daniel Schaller, Gerhard Fischerauer, Martin Feller, Rebecca Zehle, Michael Meiler, and Moritz Hein
- Published
- 2016
- Full Text
- View/download PDF
10. Comparative Study of Microscopic Charge Dynamics in Crystalline Acceptor-Substituted Oligothiophenes
- Author
-
Peter Bäuerle, Moritz Hein, Karl Leo, Denis Andrienko, Moritz Riede, Chris Elschner, Björn Baumeier, Manuel Schrader, and Roland Fitzner
- Subjects
Chemistry ,Intermolecular force ,Thermal fluctuations ,Charge (physics) ,General Chemistry ,Trapping ,Dihedral angle ,Biochemistry ,Acceptor ,Catalysis ,Dipole ,Crystallography ,Colloid and Surface Chemistry ,Chemical physics ,Electric field - Abstract
By performing microscopic charge transport simulations for a set of crystalline dicyanovinyl-substituted oligothiophenes, we find that the internal acceptor-donor-acceptor molecular architecture combined with thermal fluctuations of dihedral angles results in large variations of local electric fields, substantial energetic disorder, and pronounced Poole-Frenkel behavior, which is unexpected for crystalline compounds. We show that the presence of static molecular dipoles causes large energetic disorder, which is mostly reduced not by compensation of dipole moments in a unit cell but by molecular polarizabilities. In addition, the presence of a well-defined π-stacking direction with strong electronic couplings and short intermolecular distances turns out to be disadvantageous for efficient charge transport since it inhibits other transport directions and is prone to charge trapping.
- Published
- 2012
- Full Text
- View/download PDF
11. Highly efficient p-dopants in amorphous hosts
- Author
-
Torben Menke, Moritz Hein, Moritz Riede, Debdutta Ray, Hans Kleemann, and Karl Leo
- Subjects
Materials science ,Dopant ,Doping ,General Chemistry ,Conductivity ,Condensed Matter Physics ,Lower limit ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Biomaterials ,Organic semiconductor ,Chemical physics ,Seebeck coefficient ,Materials Chemistry ,Electrical and Electronic Engineering ,Order of magnitude - Abstract
We study the influence of the molecular energy levels on doped organic layers, using four different combinations of two amorphous hosts (MeO-TPD and BF-DPB) and two efficient p-dopants (F6-TCNNQ and C60F36). Conductivity and Seebeck studies are performed in situ, varying the doping concentration over more than two orders of magnitude. Whereas trends of doping are in agreement with the hosts' energy levels, trends deviate from the expectation based on the dopants' energy levels. A lower limit for the mobility can be derived from conductivity data, which for samples of F6-TCNNQ increases with doping, even exceeding the measured OFET-mobility of intrinsic MeO-TPD. © 2013 Elsevier B.V. All rights reserved.
- Published
- 2014
12. Molecular doping for control of gate bias stress in organic thin film transistors
- Author
-
Moritz Riede, Björn Lüssem, Karl Leo, Alex Zakhidov, Max L. Tietze, Moritz Hein, Jens Jankowski, and Publica
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Fermi level ,Transistor ,law.invention ,Pentacene ,Organic semiconductor ,symbols.namesake ,chemistry.chemical_compound ,chemistry ,Gate oxide ,Thin-film transistor ,law ,symbols ,Optoelectronics ,Thin film ,business ,Silicon oxide - Abstract
The key active devices of future organic electronic circuits are organic thin film transistors (OTFTs). Reliability of OTFTs remains one of the most challenging obstacles to be overcome for broad commercial applications. In particular, bias stress was identified as the key instability under operation for numerous OTFT devices and interfaces. Despite a multitude of experimental observations, a comprehensive mechanism describing this behavior is still missing. Furthermore, controlled methods to overcome these instabilities are so far lacking. Here, we present the approach to control and significantly alleviate the bias stress effect by using molecular doping at low concentrations. For pentacene and silicon oxide as gate oxide, we are able to reduce the time constant of degradation by three orders of magnitude. The effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and, thus, exponentially reduced proton generation at the pentacene/oxide interface. © 2014 AIP Publishing LLC.
- Published
- 2014
13. Diindenoperylene derivatives: A model to investigate the path from molecular structure via morphology to solar cell performance
- Author
-
Moritz Riede, Annette Petrich, Jens Jankowski, Markus Hummert, Karl Leo, Joerg Alex, Chris Elschner, David Wynands, Klaus-Jochen Eichhorn, Jan Meiss, Roland Schulze, Moritz Hein, and Christoph Schuenemann
- Subjects
Materials science ,Organic solar cell ,technology, industry, and agriculture ,Nanotechnology ,Heterojunction ,General Chemistry ,Condensed Matter Physics ,Polymer solar cell ,Electronic, Optical and Magnetic Materials ,law.invention ,Biomaterials ,Organic semiconductor ,chemistry.chemical_compound ,chemistry ,Diindenoperylene ,Chemical physics ,law ,Solar cell ,Materials Chemistry ,Charge carrier ,sense organs ,Electrical and Electronic Engineering ,Thin film - Abstract
Efficient organic electronic devices require a detailed understanding of the relation between molecular structure, thin film growth, and device performance, which is only partially understood at present. Here, we show that small changes in molecular structure of a donor absorber material lead to significant changes in the intermolecular arrangement within organic solar cells. For this purpose, phenyl rings and propyl side chains are fused to the diindenoperylene (DIP) molecule. Grazing incidence X-ray diffraction and variable angle spectroscopic ellipsometry turned out to be a powerful combination to gain detailed information about the thin film growth. Planar and bulk heterojunction solar cells with C60 as acceptor and the DIP derivatives as donor are fabricated to investigate the influence of film morphology on the device performance. Due to its planar structure, DIP is found to be highly crystalline in pristine and DIP:C60 blend films while its derivatives grow liquid-like crystalline. This indicates that the molecular arrangement is strongly disturbed by the steric hindrance induced by the phenyl rings. The high fill factor (FF) of more than 75% in planar heterojunction solar cells of the DIP derivatives indicates excellent charge transport in the pristine liquid-like crystalline absorber layers. However, bulk heterojunctions of these materials surprisingly result in a low FF of only 54% caused by a weak phase separation and thus poor charge carrier percolation paths due to the lower ordered thin film growth. In contrast, crystalline DIP:C60 heterojunctions lead to high FF of up to 65% as the crystalline growth induces better percolation for the charge carriers. However, the major drawback of this crystalline growth mode is the nearly upright standing orientation of the DIP molecules in both pristine and blend films. This arrangement results in low absorption and thus a photocurrent which is significantly lower than in the DIP derivative devices, where the liquid-like crystalline growth leads to a more horizontal molecular alignment. Our results underline the complexity of the molecular structure-device performance relation in organic semiconductor devices. © 2013 Elsevier B.V. All rights reserved.
- Published
- 2013
14. From Fluorine to Fluorene-A Route to Thermally Stableaza-BODIPYs for Organic Solar Cell Application
- Author
-
Christoph Schünemann, Markus Hummert, Gianaurelio Cuniberti, Moritz Hein, Max L. Tietze, Melanie Lorenz-Rothe, Frank Ortmann, Karl Sebastian Schellhammer, Karl Leo, Rico Meerheim, Stefan Kraner, Till Jägeler-Hoheisel, and Christian Körner
- Subjects
Materials science ,Organic solar cell ,Heterojunction ,02 engineering and technology ,Hybrid solar cell ,Quantum dot solar cell ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Polymer solar cell ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Solar cell ,Organic chemistry ,Thermal stability ,0210 nano-technology ,Absorption (electromagnetic radiation) - Abstract
Despite favorable absorption characteristics, borondipyrromethenes (BODIPYs) often lack thermal stability preventing their application in vacuum-processed organic solar cells. In this paper, the replacement of the BF2 unit by borafluorene as a new functionalization strategy for this molecule class is explored. This approach is applied to a set of prototype molecules and demonstrates improved thermal stability, strong absorption in the red and near-infrared region of the sun spectrum, as well as excellent solar cell performance. Synthesis is realized from free ligands via complexation with 9-chloro-9-borafluorene giving high yields up to 81%. Planar heterojunction cells of these complexes exhibit high fill factors of more than 70%. Bulk heterojunction solar cells with C-60 are optimized yielding power conversion efficiencies up to 4.5%, rendering the investigated prototype compounds highly competitive among other NIR-absorbing small-molecule donor materials. Comprehensive experimental material characterization and solar cell analysis are carried out, and the results are discussed together with simulations of molecular properties. Based on this analysis, additional performance improvements are proposed by engineering the intramolecular steric interactions towards further red-shifted absorption.
- Published
- 2016
- Full Text
- View/download PDF
15. Phase separation analysis of bulk heterojunctions in small-molecule organic solar cells using zinc-phthalocyanine and C60
- Author
-
Chris Elschner, Steffen Pfützner, Karl Leo, Moritz Riede, L. Wilde, Klaus-Jochen Eichhorn, Moritz Hein, Christoph Schünemann, and David Wynands
- Subjects
Materials science ,Organic solar cell ,business.industry ,Analytical chemistry ,Heterojunction ,Condensed Matter Physics ,Acceptor ,Polymer solar cell ,Electronic, Optical and Magnetic Materials ,law.invention ,Optics ,Photoactive layer ,law ,Solar cell ,Crystallite ,Thin film ,business - Abstract
To achieve efficient organic solar cells, donor and acceptor molecules are mixed in the photoactive layer to form a so-called bulk heterojunction. Due to molecular interactions, a certain degree of phase separation between donor and acceptor domains arises, which is necessary to achieve efficient charge extraction within the absorber layer. However, the mechanism that induces the phase separation is not fully understood and gaining detailed information about the molecular arrangement within these blend layers is quite challenging. We show that grazing incidence x-ray diffraction, combined with variable angle spectroscopic ellipsometry is a suitable way to investigate the molecular structure of blend layers in detail, consisting of a mixture of zinc-phthalocyanine (ZnPc) and C${}_{60}$. The degree of phase separation within the blend layer is influenced by substrate heating during the co-evaporation of ZnPc and C${}_{60}$ and by a variation of the mixing ratio. The effect of different blend layer morphologies on optical and electrical device performance is investigated by solar cell characterization and mobility measurements. We find that the molecular arrangement of C${}_{60}$ provides the essential driving force for efficient phase separation. Whereas spherical C${}_{60}$ molecules are able to form crystalline domains when deposited at elevated substrate temperatures, no ZnPc crystallites are observed, although the planar ZnPc molecules are not randomly oriented but standing upright within its domains. Comparing specular and grazing incidence x-ray diffraction, we find that only the latter method is able to detect nanocrystalline C${}_{60}$ in thin films due to its polycrystalline nature and small sized nanocrystallites. Solar cell measurements show an increase in fill factor and external quantum efficiency signal for blends with enhanced phase separation, induced by higher substrate temperatures. However, grazing incidence x-ray diffraction measurements reveal that ZnPc and C${}_{60}$ already form separate domains in unheated ZnPc:C${}_{60}$ blends, which provide fill factors close to 50$%$ in the corresponding solar cells.
- Published
- 2012
- Full Text
- View/download PDF
16. Dicyanovinyl substituted oligothiophenes: Thermal stability, mobility measurements, and performance in photovoltaic devices
- Author
-
Moritz Riede, Marion Wrackmeyer, Annette Petrich, Karl Leo, Markus Hummert, Moritz Hein, and Jan Meiss
- Subjects
Electron mobility ,Theory of solar cells ,Materials science ,Organic solar cell ,Renewable Energy, Sustainability and the Environment ,business.industry ,Open-circuit voltage ,Heterojunction ,Polymer solar cell ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,Quantum efficiency ,business ,Short circuit - Abstract
A series of dicyanovinyl-oligothiophenes are investigated concerning their thermal stability, absorption in thin film, and hole mobility. Due to very high extinction coefficients, these materials are interesting for application as donor in solar cells. The quinquethiophene DCV2-5T, which shows a hole mobility of 2.2×10–5 cm2/Vs, is used as donor material in a flat heterojunction organic small molecule solar cells. Despite a very thin donor layer of only 6 nm, these devices exhibit in a planar heterojunction with 15 nm C60 an efficiency of up to 2.8% with a fill factor of up to 58%, a short circuit current density of 5.2 mA/cm2, an open circuit voltage of 1.03 V, and an external quantum efficiency of 30% in the green spectral range. © 2011 Elsevier B.V. All rights reserved.
- Published
- 2011
17. Imbalanced mobilities causing S-shaped IV curves in planar heterojunction organic solar cells
- Author
-
Wolfgang Tress, Karl Leo, Moritz Riede, Markus Hummert, Moritz Hein, and Annette Petrich
- Subjects
Organic semiconductor ,Electron mobility ,Theory of solar cells ,Physics and Astronomy (miscellaneous) ,Organic solar cell ,Chemistry ,Analytical chemistry ,Heterojunction ,Hybrid solar cell ,Acceptor ,Molecular physics ,Polymer solar cell - Abstract
We show that S-kinks in the current voltage characteristics, which decrease the fill factor significantly, can be caused by a strong imbalance of charge carrier mobilities (hole mobility in donor and electron mobility in acceptor) in planar/flat heterojunction organic solar cells. Electrical simulations according to a drift-diffusion model predict the occurrence of an S-kink for a mobility mismatch factor larger than 100. By combining a low-mobility donor material, (1,2,3,4,9,10,11,12-octaphenyl-diindeno [1,2,3-cd: 1′,2′,3′-lm]perylene), with the acceptors C60 and N,N′-dimethylperylene-3,4:9,10-dicarboximide, which show different electron mobilities, we experimentally verify the predictions. Our results demonstrate that not only interface effects but also the photoactive material itself can cause S-kinks. © 2011 American Institute of Physics.
- Published
- 2011
18. Improved photon harvesting by employing C 70 in bulk heterojunction solar cells
- Author
-
Lothar Dunsch, Annette Petrich, Moritz Riede, Moritz Hein, Jan Meiss, Steffen Pfuetzner, Karl Leo, and Selina Olthof
- Subjects
Materials science ,Organic solar cell ,business.industry ,Open-circuit voltage ,Heterojunction ,Solar energy ,Polymer solar cell ,law.invention ,Optics ,Photoactive layer ,law ,Solar cell ,Optoelectronics ,Quantum efficiency ,business - Abstract
To achieve higher efficiencies in organic solar cells, ideally the open circuit voltage (VOC), fill factor (FF) as well as the short current density (JSC) have to be further improved. However, only a few suitable acceptor molecules, e.g. C60, are currently available for the photoactive layer. Despite a good electron mobility on the order of 1×10−3 cm2/Vs the absorption of C60 in the visible sun spectrum is low. From polymer based solar cells it is known that the fullerene derivative [70]PCBM used in the photoactive layer shows a significant enhancement in J compared to [60]PCBM. This work investigates the application of fullerene C70 as acceptor in comparison to the well known C60 in vacuum processed small molecule solar cells. C70 shows a broadened and red shifted absorption (abs. maximum around 500 nm) compared to C60. By fabricating p-i-i solar cells we show that the stronger absorption of C70 leads to enhanced photon harvesting and increased external quantum efficiency. The bulk heterojunction p-i-i solar cell containing C70 as acceptor and ZnPc as donor, co-evaporated with an optimized ratio of 2:1, and a layer thickness of 30 nm shows improved solar cell parameters: a 30% larger photocurrent of 10.1 mA/cm2 is obtained. The VOC of 0.56 V and FF of 55% remain comparable to C60-containing p-i-i solar cells. Therefore, the solar cell performance is mainly improved by JSC and leads to a mismatch corrected power conversion efficiency of 3.12%. Thus, we show that C70 is an alternative fullerene to C60 for solar cell applications. © 2010 Copyright SPIE - The International Society for Optical Engineering.
- Published
- 2010
- Full Text
- View/download PDF
19. Polymer coating of porcine decellularized and cross-linked aortic grafts
- Author
-
Michael Heise, Britt Wildemann, Wilko Weichert, Peter Neuhaus, Moritz Hein, Christoph Heidenhain, and Gerhard Schmidmaier
- Subjects
Materials science ,Biocompatibility ,Polymers ,Sus scrofa ,Biomedical Engineering ,engineering.material ,Prosthesis Design ,Biomaterials ,Coated Materials, Biocompatible ,Coating ,Blood vessel prosthesis ,medicine.artery ,Materials Testing ,medicine ,Animals ,Humans ,Aorta ,Neointimal hyperplasia ,Decellularization ,Anticoagulant drug ,Anticoagulants ,Hirudins ,medicine.disease ,Recombinant Proteins ,Blood Vessel Prosthesis ,Transplantation ,Cross-Linking Reagents ,engineering ,Female ,Biomedical engineering - Abstract
This article investigates a method of modifying and optimizing the biocompatibility of decellularized vascular bioimplants when treated with a specialized, drug eluting coating. For this purpose, we carried out aortic transplantations using a porcine model. Decellularized, cross-linked aortic grafts were coated with poly(D,L-lactide) (PDLLA). To this coating, we added the anticoagulant drug lepirudin which, following transplantation, would be linearly eluted. These aortic grafts are easily manipulated in surgery. It was shown that, as a result of the lepirudin-eluting coating, the rate of thrombogenesis was reduced and the patency rate was significantly improved. However, lumen-stenosing pseudointima developed in all of the transplants and was not effected by PDLLA coating. Furthermore, no evidence of recellularisation was documented. This trial demonstrates that polymer coating of decellularized tissue is possible. Neointimal hyperplasia and the absence of cellular repopulation mark the negative consequences of this concept.
- Published
- 2010
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.