221 results on '"Koen Vandewal"'
Search Results
202. Controlling Interdiffusion, Interfacial Composition, and Adhesion in Polymer Solar Cells
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Dennis Nordlund, Reinhold H. Dauskardt, Stephanie R. Dupont, Koen Vandewal, and Eszter Voroshazi
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Materials science ,X-ray photoelectron spectroscopy ,PEDOT:PSS ,Mechanics of Materials ,Annealing (metallurgy) ,Mechanical Engineering ,Delamination ,Analytical chemistry ,Organic chemistry ,Molecular orbital ,Spectroscopy ,Polymer solar cell ,XANES - Abstract
DOI: 10.1002/admi.201400135 conventional oven for a period of 0 to 24 h, prior to delamination. The measured adhesion energy, G c (J m − 2 ), is shown as a function of annealing time in Figure 2 a. For any particular annealing temperature, the adhesion energy increased with annealing time. For example at 130 °C, G c increased from 1.3/ for no annealing to 2.76 J m – 2 and 2.81 J m – 2 for 30 min and 24 h annealing, respectively. The largest increase in G c generally happened within the fi rst 2 h of annealing. Conversely, at a constant annealing time, the G c increased with annealing temperature. The impact of such an adhesion increase has large implications on the reliability of these inverted OPV devices. After delamination, every adhesion specimen is split into two fractured halves: one includes the Ag electrode, referred to as the “Ag side” and the other includes the ZnO, referred to as the “ZnO side”, as shown on Figure 1 . Note that it does not refer to the interface between P3HT:PCBM and the ZnO layer or the interface between PEDOT:PSS and the Ag electrode. In order to understand the interfacial reinforcement mechanism responsible for the increase in G c , these delaminated surfaces were characterized using NEXAFS, UV-VIS absorption and X-ray photo spectroscopy (XPS). NEXAFS in Total Electron Yield (TEY) mode was used to quantify the surface composition at the top few nanometers of the delaminated surfaces (see experimental details). The carbon K-edge NEXAFS TEY spectra from pristine P3HT, PCBM and PEDOT:PSS are shown in Figure 3 a. The NEXAFS intensity is dominated by resonances arising from transitions from the 1s core level to unfi lled molecular orbitals of π* and σ* character, which are specifi c to the bonding within different functional groups. [ 11 ] We observed the characteristic π* and σ* resonances for the pure compounds consist with previous literature. [ 12 ]
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- 2014
203. Toward bulk heterojunction polymer solar cells with thermally stable active layer morphology
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Jean Manca, Koen Vandewal, Alberto Salleo, Ilaria Cardinaletti, Sabine Bertho, Jan D'Haen, Wouter Maes, Bruno Van Mele, Bert Conings, Dirk Vanderzande, Guy Van Assche, Fortunato Piersimoni, Laurence Lutsen, Jurgen Kesters, Milos Nesladek, Physical Chemistry and Polymer Science, and Materials and Chemistry
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lifetime ,Materials science ,Polymers and Plastics ,Organic solar cell ,Renewable Energy, Sustainability and the Environment ,business.industry ,Photovoltaic system ,Heterojunction ,Surfaces and Interfaces ,Hybrid solar cell ,Bulk Heterojunction ,Acceptor ,thermal stability ,Atomic and Molecular Physics, and Optics ,Polymer solar cell ,law.invention ,Chemical engineering ,Photovoltaics ,law ,Solar cell ,Optoelectronics ,organic photovoltaics ,phase separation ,business - Abstract
When state-of-the-art bulk heterojunction organic solar cells with ideal morphology are exposed to prolonged storage or operation at elevated temperatures, a thermally induced disruption of the active layer blend can occur, in the form of a separation of donor and acceptor domains, leading to diminished photovoltaic performance. Toward the long-term use of organic solar cells in real-life conditions, an important challenge is, therefore, the development of devices with a thermally stable active layer morphology. Several routes are being explored, ranging from the use of high glass transition temperature, cross-linkable and/or side-chain functionalized donor and acceptor materials, to light-induced dimerization of the fullerene acceptor. A better fundamental understanding of the nature and underlying mechanisms of the phase separation and stabilization effects has been obtained through a variety of analytical, thermal analysis, and electro-optical techniques. Accelerated aging systems have been used to study the degradation kinetics of bulk heterojunction solar cells in situ at various temperatures to obtain aging models predicting solar cell lifetime. The following contribution gives an overview of the current insights regarding the intrinsic thermally induced aging effects and the proposed solutions, illustrated by examples of our own research groups.
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- 2014
204. Comparing the Device Physics and Morphology of Polymer Solar Cells Employing Fullerenes and Non-Fullerene Acceptors
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Tommaso Giovenzana, Jason T. Bloking, Michael D. McGehee, Sangwon Ko, Koen Vandewal, Alan Sellinger, Andrew J. Ponec, Eric T. Hoke, Zhenan Bao, and Andrew T. Higgs
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Organic electronics ,chemistry.chemical_classification ,Fullerene ,Materials science ,Organic solar cell ,Renewable Energy, Sustainability and the Environment ,Band gap ,Hybrid solar cell ,Electron acceptor ,Photochemistry ,Acceptor ,Polymer solar cell ,chemistry ,Organic chemistry ,General Materials Science - Abstract
There is a need to find electron acceptors for organic photovoltaics that are not based on fullerene derivatives since fullerenes have a small band gap that limits the open-circuit voltage (VOC), do not absorb strongly and are expensive. Here, a phenylimide-based acceptor molecule, 4,7-bis(4-(N-hexyl-phthalimide)vinyl)benzo[c]1,2,5-thiadiazole (HPI-BT), that can be used to make solar cells with VOC values up to 1.11 V and power conversion efficiencies up to 3.7% with two thiophene polymers is demonstrated. An internal quantum efficiency of 56%, compared to 75–90% for polymer-fullerene devices, results from less efficient separation of geminate charge pairs. While favorable energetic offsets in the polymer-fullerene devices due to the formation of a disordered mixed phase are thought to improve charge separation, the low miscibility (
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- 2014
205. Organic Solar Cells: On the Efficiency of Charge Transfer State Splitting in Polymer:Fullerene Solar Cells (Adv. Mater. 16/2014)
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Harald Ade, Alberto Salleo, Jessica D. Douglas, Koen Vandewal, John R. Tumbleston, Steve Albrecht, Florian S. U. Fischer, Sabine Ludwigs, Jean M. J. Fréchet, and Dieter Neher
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chemistry.chemical_classification ,Materials science ,Fullerene ,Organic solar cell ,business.industry ,Mechanical Engineering ,Charge (physics) ,Polymer ,Hybrid solar cell ,Polymer solar cell ,Charge generation ,chemistry ,Mechanics of Materials ,Optoelectronics ,General Materials Science ,business ,Excess energy - Published
- 2014
206. Solar Cells: Re-evaluating the Role of Sterics and Electronic Coupling in Determining the Open-Circuit Voltage of Organic Solar Cells (Adv. Mater. 42/2013)
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Mark E. Thompson, Guy Olivier Ngongang Ndjawa, Alberto Salleo, Michael D. McGehee, Koen Vandewal, Aram Amassian, Eric T. Hoke, Ruipeng Li, Kenneth R. Graham, Patrick Erwin, and Dennis Nordlund
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Coupling (electronics) ,Steric effects ,Materials science ,Organic solar cell ,Mechanics of Materials ,business.industry ,Open-circuit voltage ,Mechanical Engineering ,Optoelectronics ,General Materials Science ,Hybrid solar cell ,business ,Polymer solar cell - Published
- 2013
207. Development of polymer-fullerene solar cells.
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Fengling Zhang, Olle Inganäs, Yinhua Zhou, and Koen Vandewal
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SOLAR cells ,DIRECT energy conversion ,FULLERENES - Abstract
Global efforts and synergetic interdisciplinary collaborations on solution-processed bulk-heterojunction polymer solar cells (PSCs or OPVs) made power conversion efficiencies over 10% possible. The rapid progress of the field is credited to the synthesis of a large number of novel polymers with specially tunable optoelectronic properties, a better control over the nano-morphology of photoactive blend layers, the introduction of various effective interfacial layers, new device architectures and a deeper understanding of device physics. We will review the pioneering materials for polymer-fullerene solar cells and trace the progress of concepts driving their development. We discuss the evolution ofmorphology control, interfacial layers and device structures fully exploring the potential of photoactive materials. In order to guide a further increase in power conversion efficiency of OPV, the current understanding of the process of free charge carrier generation and the origin of the photovoltage is summarized followed by a perspective on how to overcome the limitations for industrializing PSCs. [ABSTRACT FROM AUTHOR]
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- 2016
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208. Confined organization of fullerene units along high polymer chains
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Peng Wei, Gaurav Giri, Alberto Salleo, Kendall N. Houk, Sílvia Osuna, Lei Fang, Alán Aspuru-Guzik, Peng Liu, Sule Atahan-Evrenk, Zhenan Bao, Robert H. Grubbs, Benjamin R. Sveinbjornsson, Koen Vandewal, Supriya Shrestha, and Gonzalo Jiménez-Osés
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chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Materials science ,Fullerene ,General Chemistry ,Polymer ,chemistry.chemical_compound ,Molecular dynamics ,Monomer ,chemistry ,Polymerization ,Chemical physics ,Covalent bond ,Intramolecular force ,Polymer chemistry ,Physics::Atomic and Molecular Clusters ,Materials Chemistry ,Thin film - Abstract
Conductive fullerene (C_60) units were designed to be arranged in one dimensional close contact by locally organizing them with covalent bonds in a spatially constrained manner. Combined molecular dynamics and quantum chemical calculations predicted that the intramolecular electronic interactions (i.e. charge transport) between the pendant C_60 units could be controlled by the length of the spacers linking the C_60 units and the polymer main chain. In this context, C_60 side-chain polymers with high relative degrees of polymerization up to 1220 and fullerene compositions up to 53% were synthesized by ruthenium catalyzed ring-opening metathesis polymerization of the corresponding norbornene-functionalized monomers. UV/vis absorption and photothermal deflection spectra corroborated the enhanced inter-fullerene interactions along the polymer chains. The electron mobility measured for the thin film field-effect transistor devices from the polymers was more than an order of magnitude higher than that from the monomers, as a result of the stronger electronic coupling between the adjacent fullerene units within the long polymer chains. This molecular design strategy represents a general approach to the enhancement of charge transport properties of organic materials via covalent bond-based organization.
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- 2013
209. Phase behaviour of liquid-crystalline polymer/fullerene organic photovoltaic blends: thermal stability and miscibility
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Roger Magnusson, Kristoffer Tvingstedt, Hans Arwin, Ellen Moons, Ana Sofia Anselmo, M. Isabel Alonso, Koen Vandewal, Christian Müller, Jonas Bergqvist, Olle Inganäs, and Mariano Campoy-Quiles
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chemistry.chemical_classification ,Materials science ,Fullerene ,General Chemistry ,Polymer ,Miscibility ,Acceptor ,Chemical engineering ,chemistry ,Phase (matter) ,Polymer chemistry ,Materials Chemistry ,Thermal stability ,Thin film ,Glass transition - Abstract
The thermal behaviour of an organic photovoltaic (OPV) binary system comprised of a liquidcrystalline fluorene-based polymer and a fullerene derivative is investigated. We employ variabletemperature ellipsometry complemented by photo- and electroluminescence spectroscopy as well as optical microscopy and scanning force nanoscopy to explore phase transitions of blend thin films. The high glass transition temperature correlates with the good thermal stability of solar cells based on these materials. Furthermore, we observe partial miscibility of the donor and acceptor together with the tendency of excess fullerene derivative to segregate into exceedingly large domains. Thus, for charge generation less adequate bulk-heterojunction nanostructures are poised to develop if this mixture is exposed to more elevated temperatures. Gratifyingly, the solubility of the fullerene derivative in the polymer phase is found to decrease if a higher molecular-weight polymer fraction is employed, which offers routes towards improving the photovoltaic performance of non-crystalline OPV blends.
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- 2011
210. Varying polymer crystallinity in nanofiber poly(3-alkylthiophene): PCBM solar cells: Influence on charge-transfer state energy and open-circuit voltage
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Jean Manca, Laurence Lutsen, Dirk Vanderzande, Koen Vandewal, Sabine Bertho, Abay Gadisa, Veerle Vrindts, and Wibren D. Oosterbaan
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Photocurrent ,Organic semiconductor ,Crystallinity ,Spin coating ,Materials science ,Physics and Astronomy (miscellaneous) ,Open-circuit voltage ,Photoconductivity ,Nanofiber ,Crystallization of polymers ,Analytical chemistry - Abstract
The effect of poly(3-alkylthiophene) (P3AT) crystallinity in (nanofiber P3AT):PCBM photovoltaic devices on the energy of the charge-transfer state (ECT) and on the open-circuit voltage (Voc) is investigated for poly(3-butythiophene), poly(3-pentylthiophene) and poly(3-hexylhiophene). P3AT crystallinity, expressed as the crystalline nanofiber mass fraction f to the total P3AT mass in the spin-coating dispersion, is varied between ∼0.1 and ∼0.9 by temperature control. ECT, as obtained by Fourier-transform photocurrent spectroscopy decreased with f as ECT=ECT0−0.2f eV. Alkyl side-chain length only influences ECT0. Voc relates to ECT as Voc=ECT/q−0.6 V.
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- 2009
211. Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene):titanium dioxide solar cells
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Jan D'Haen, Koen Vandewal, M. K. Van Bael, Jean Manca, Wibren D. Oosterbaan, Abay Gadisa, I. Haeldermans, and Jules Mullens
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Photocurrent ,Conductive polymer ,Materials science ,Physics and Astronomy (miscellaneous) ,Band gap ,computer.internet_protocol ,Photochemistry ,Charge-transfer complex ,Polymer solar cell ,FTPS ,chemistry.chemical_compound ,Electron transfer ,chemistry ,Titanium dioxide ,computer - Abstract
The existence of a ground-state charge-transfer (CT) complex in a conjugated polymer:metal oxide nanoparticle bulk heterojunction photovoltaic cell is demonstrated by Fourier-transform photocurrent spectroscopy (FTPS). The CT complex between poly(3-hexylthiophene) (P3HT) and titanium dioxide (TiO2) is characterized by a weak additional photocurrent band (onset 1eV) in the FTPS spectra, situated below the conjugated polymer bandgap of 2eV. The presence of CT interaction between P3HT and TiO2 in relation to frontier orbital alignment is discussed, as well as the contribution of a sub-bandgap interfacial CT state to the electron transfer process in P3HT:TiO2 solar cells.
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- 2008
212. Nanoscale electrical characterization of organic photovoltaic blends by conductive atomic force microscopy
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Koen Vandewal, Martin Breselge, Olivier Douhéret, Jean Manca, Ann Swinnen, Laurence Lutsen, and Ludwig Goris
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Conductive polymer ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Analytical chemistry ,Conductive atomic force microscopy ,Acceptor ,Polymer solar cell ,Characterization (materials science) ,Organic semiconductor ,Optoelectronics ,business ,Spectroscopy ,Nanoscopic scale - Abstract
Conductive atomic force microscopy (CAFM) is introduced to perform electrical characterization of organic photovoltaic blends with high spatial resolution. Reference blends used in organic bulk heterojunction solar cells are investigated. The ability of CAFM to electrically evidence phase separated donor and acceptor regions is demonstrated. Furthermore, local spectroscopy is performed to analyze charge transport mechanisms in the blends. Significant modifications of the electrical properties of the semiconducting polymers are shown to occur after blending with fullerene derivatives. Finally, the sensitivity of CAFM to photoelectrical phenomena is revealed. Current variations of few picoamperes are locally observed under illumination of P3HT:PCBM.
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- 2006
213. An Easily Accessible Isoindigo-Based Polymer for High-Performance Polymer Solar Cells.
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Ergang Wang, Zaifei Ma, Zhen Zhang, Koen Vandewal, Patrik Henriksson, Olle Inganäs, Fengling Zhang, and Andersson, Mats R.
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- 2011
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214. Diffusion-enhanced exciton dissociation in single-material organic solar cells
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Vasileios C. Nikolis, Maxim S. Pshenichnikov, Nong V. Hoang, Lukasz Baisinger, Koen Vandewal, Optical Physics of Condensed Matter, and Vandewal, Koen/0000-0001-5471-383X
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Materials science ,Organic solar cell ,Exciton dissociation ,Exciton ,General Physics and Astronomy ,Model system ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,Charge generation ,Chemical physics ,Yield (chemistry) ,Crystallite ,Physical and Theoretical Chemistry ,Diffusion (business) ,0210 nano-technology - Abstract
Single-material organic solar cells have recently attracted research attention due to their simplicity, morphological robustness and high yield of exciton dissociation. Using alpha-sexithiophene as a model system, we show that the single-event probability of the exciton dissociation at the boundaries of polycrystalline domains with different molecular orientation is extremely low (similar to 0.5%), while a high efficiency of charge generation is gained via hundred-fold crossings of the domain boundaries due to the long exciton diffusion length (similar to 45 nm). European UnionEuropean Commission [722651]
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215. Elucidating Batch-to-Batch Variation Caused by Homocoupled Side Products in Solution-Processable Organic Solar Cells
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David Beljonne, Vincent Lemaur, Ilaria Cardinaletti, Dag W. Breiby, Bruno Van Mele, Johannes Benduhn, Jan D'Haen, Jean Manca, Wouter Maes, Roberto Lazzaroni, Nilesh Patil, Maxime Defour, Peter Adriaensens, Dirk Vanderzande, Benoît Champagne, Tim Vangerven, Koen Vandewal, Pieter Verstappen, Niko Van den Brande, Jens Wenzel Andreasen, VANGERVEN, Tim, VERSTAPPEN, Pieter, Patil, Nilesh, D'HAEN, Jan, CARDINALETTI, Ilaria, Benduhn, Johannes, Van den Brande, Niko, Defour, Maxime, Lemaur, Vincent, Beljonne, David, Lazzaroni, Roberto, Champagne, Benoît, VANDEWAL, Koen, Andreasen, Jens W., ADRIAENSENS, Peter, Breiby, D.B., Van Mele, Bruno, VANDERZANDE, Dirk, MAES, Wouter, MANCA, Jean, Materials and Chemistry, Physical Chemistry and Polymer Science, Faculty of Engineering, and Faculty of Economic and Social Sciences and Solvay Business School
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chemistry.chemical_classification ,Materials science ,Organic solar cell ,General Chemical Engineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Polymer ,Conjugated system ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Small molecule ,Chemical reaction ,Polymer solar cell ,0104 chemical sciences ,Chemical engineering ,chemistry ,Thermal ,Materials Chemistry ,Molecule ,0210 nano-technology - Abstract
Conjugated polymers and small molecules based on alternating electron-donating (D) and electronaccepting (A) building blocks have led to state-of-the-art organic solar cell materials governing efficiencies beyond 10%. Unfortunately, the connection of D and A building blocks via cross-coupling reactions does not always proceed as planned, which can result in the generation of side products containing D-D or A-A homocoupling motifs. Previous studies have reported a reduced performance in polymer and small molecule solar cells when such defect structures are present. A general consensus on the impact of homocouplings on device performance is, however, still lacking as is a profound understanding of the underlying causes of the device deterioration. For differentiating the combined effect of molecular weight and homocouplings in polymer solar cells, a systematic study on a small molecule system (DTS(FBBTh2)2) is presented. The impact of homocouplings on nanomorphology, thermal, and electro-optical properties is investigated. It is demonstrated that small quantities of homocouplings (
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216. Lead-Halide Perovskites Meet Donor–Acceptor Charge-Transfer Complexes
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Hans-Gerd Boyen, David Beljonne, Nadège Marchal, Ferdinand C. Grozema, Roald Herckens, Wouter Van Gompel, Bert Conings, Koen Vandewal, Claudio Quarti, María C. Gélvez-Rueda, Kristof Van Hecke, Sudeep Maheshwari, Laurence Lutsen, and Dirk Vanderzande
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Materials science ,General Chemical Engineering ,Halide ,Charge (physics) ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,Quantum dot ,Materials Chemistry ,0210 nano-technology ,Donor acceptor ,Perovskite (structure) - Abstract
Low-dimensional lead halide hybrid perovskites are nowadays in the spotlight because of their improved stability and extensive chemical flexibility compared to their 3D perovskite counterparts, the current challenge being to design functionalized organic cations. Here, we report on the synthesis and full characterization of a perovskite-like hybrid (a perovskitoid) where the 1D lead iodide layout is patterned with a donor−acceptor charge transfer complex (CTC) between pyrene and tetracyanoquinodimethane, with a chemical formula of (C20H17NH3)PbI3·(C12H4N4). By combining multiple structural analysis and spectroscopic techniques with ab initio modeling, we show that the electronic, optical, and charge-transport properties of the hybrid materials are dominated by the organic CTC, with the inorganic backbone primarily acting as a template for the organization of the donor and acceptor molecules. Interestingly, time-resolved microwave conductivity (TRMC) measurements show an enhanced photocurrent generation in the 1D hybrid compared to the pure organic charge-transfer salt, likely associated with transient localization of the holes on the lead-iodide octahedra. This observation is in line with the close energy resonance between the valence crystal orbitals of the lead-iodide lattice and the frontier occupied molecular orbitals of pyrene predicted by the DFT calculations. Therefore, it paves the way toward the design of new hybrid low-dimensionality perovskites offering a synergic combination of organic and inorganic functionalities. The FWO is acknowledged for the funding of research. W.V.G. is an SB Ph.D. fellow at FWO (Number 1S17516N), R.H. is a special research fund (BOF) doctoral (Ph.D.) student at UHasselt/IMO. K.V.H. thanks the Hercules Foundation (Project AUGE/11/029 "3D -SPACE: 3D Structural Platform Aiming for Chemical Excellence") and the special research fund (BOF) Ugent (Project 01N03217) for funding. The work has been carried out in the context of the solliance network (www.solliance.eu), of which UHasselt and TUDe1ft are members. Additionally UHasselt is a 'partner in the Energyville Consortium (http://www.energyville.be/aboutenergyville).The research leading to these results in the Delft University of Technology has received funding from the European Research Council Horizon 2020 ERC Grant Agreement No. 648433. The work from the University of Mons was supported by a 50-50 Ph.D. funding for N.M. from the University of Mons, by the Interuniversity Attraction Pole program of the Belgian Referal Science Policy Office (PAI 6/27) and FNRS-F.R.S. Computational resources have been provided by the Consortium des Equipements de Calcul Intensif (CECI), funded by the Fonds de la Recherche Scientifique de Belgique (F.RS.-FNRS) under Grant No. 2.5020.1 and by the Walloon Region. C.Q and D.B. are a FNRS postdoctoral researcher and research director, respectively. Bart Ruttens and Jan D'Haen (IMO-IMOMEC) are acknowledged for PXRD measurements.
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217. The role of spin in the degradation of organic photovoltaics
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Frédéric Laquai, Safakath Karuthedath, Johannes Benduhn, Andreas Sperlich, Ivan Ramirez, Donato Spoltore, Alberto Privitera, Anna Jungbluth, Koen Vandewal, Moritz Riede, Spoltore, Donato/0000-0002-2922-9293, Sperlich, Andreas/0000-0002-0850-6757, Karuthedath, Safakath/0000-0001-7568-2825, Vandewal, Koen/0000-0001-5471-383X, Benduhn, Johannes/0000-0001-5683-9495, and Laquai, Frederic/0000-0002-5887-6158
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Solar cells ,Materials science ,Organic solar cell ,Molecular electronics ,Science ,Exciton ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,Article ,General Biochemistry, Genetics and Molecular Biology ,Polymer solar cell ,chemistry.chemical_compound ,Singlet state ,Triplet state ,Multidisciplinary ,Singlet oxygen ,General Chemistry ,Organic molecules in materials science ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Intersystem crossing ,chemistry ,Chemical physics ,Excited state ,0210 nano-technology - Abstract
Stability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices., The commercialisation of organic photovoltaic technology calls for research on material degradation mechanisms. Ramirez et al. show that triplet excitons produced by back charge transfer can significantly impact the photo-stability of fullerene-based devices even in the absence of water and oxygen.
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218. Towards 'green' solid state polythiophene solar cells using a fully water based preparation method
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Haeldermans, I., Truijen, I., Koen Vandewal, Moons, W., Bael, M. K., D Haen, J., Manca, J., and Mullens, J.
219. Increasing donor-acceptor spacing for reduced voltage loss in organic solar cells
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Zaifei Ma, Xudong Jiang, Zheng Tang, Weiwei Li, Jing Wang, Yuanping Yi, Hongbo Wu, Junyu Li, Guitao Feng, Hanyu Wu, Koen Vandewal, Xunda Feng, Li, Weiwei/0000-0002-7329-4236, Tang, Zheng/0000-0003-0036-2362, Yi, and Yuanping/0000-0002-0052-9364
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chemistry.chemical_classification ,Materials for devices ,Multidisciplinary ,Materials science ,Organic solar cell ,Science ,Energy conversion efficiency ,food and beverages ,General Physics and Astronomy ,High voltage ,General Chemistry ,Acceptor ,Molecular physics ,General Biochemistry, Genetics and Molecular Biology ,Article ,chemistry ,Side chain ,Charge carrier ,Devices for energy harvesting ,Alkyl ,Perovskite (structure) - Abstract
The high voltage losses (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}_{{loss}}$$\end{document}Vloss), originating from inevitable electron-phonon coupling in organic materials, limit the power conversion efficiency of organic solar cells to lower values than that of inorganic or perovskite solar cells. In this work, we demonstrate that this \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}_{{loss}}$$\end{document}Vloss can in fact be suppressed by controlling the spacing between the donor (D) and the acceptor (A) materials (DA spacing). We show that in typical organic solar cells, the DA spacing is generally too small, being the origin of the too-fast non-radiative decay of charge carriers (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${k}_{{nr}}$$\end{document}knr), and it can be increased by engineering the non-conjugated groups, i.e., alkyl chain spacers in single component DA systems and side chains in high-efficiency bulk-heterojunction systems. Increasing DA spacing allows us to realize significantly reduced \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${k}_{{nr}}$$\end{document}knr and improved device voltage. This points out a new research direction for breaking the performance bottleneck of organic solar cells., Complex morphology in donor/acceptor organic heterostructures hampers the understanding of device performance. Here, the origin of the high voltage loss in organic solar cells is ascribed to the too small spacing between the donor/acceptor molecules in the active layer, and the voltage loss can be reduced by increasing the donor/acceptor spacing.
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220. Effect of molecular weight on morphology and photovoltaic properties in P3HT:PCBM solar cells
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Donato Spoltore, Tim Vangerven, Pieter Verstappen, Fortunato Piersimoni, Bertho Sabine, Koen Vandewal, Niko Van den Brande, Maxime Defour, Bruno Van Mele, Antionetta De Sio, Jürgen Parisi, Laurence Lutsen, Dirk Vanderzande, Wouter Maes, Manca, Jean V., Materials and Chemistry, Physical Chemistry and Polymer Science, and Faculty of Engineering
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Molecular Weight ,Preparative GPC ,Recombination order ,Crystallinity - Abstract
The molecular weight of poly(3-hexylthiophene) is an important factor influencing the photovoltaic properties of bulk heterojunction organic solar cells based on this material. However, since different synthetic processes or repetitive soxhlet extractions - generally applied to obtain the different molecular weight batches under study - result in samples with simultaneously varying regioregularity (RR) and polydispersity index (PDI), it has not been possible yet to find an unambiguous correlation between the molecular weight and the photovoltaic performance. In the present work preparative gel permeation chromatography is introduced as a versatile technique to fractionate the donor polymer and thereby obtain a systematic variation of the number average molecular weight (M-n = 11-91 kg mol (1)) with an almost constant PDI and RR. Polymer crystallinity and conjugation length are evaluated by UV-Vis spectroscopy, rapid heat-cool calorimetry and selected area electron diffraction, and are found to be deeply affected by Mn. This in turn influences the behavior of the charge transfer state energy, measured via Fourier transform photocurrent spectroscopy, and therefore the open-circuit voltage. The short-circuit current is also affected by Mn, but mainly due to a change in absorption coefficient. The apparent recombination order is shown to be linked to the morphology of the polymer: fullerene blend and is determined using transient photovoltage and photocurrent techniques. Finally, a correlation between recombination and fill factor is also suggested.
221. Impact of Triplet Excited States on the Open-Circuit Voltage of Organic Solar Cells
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Dieter Neher, Christian Koerner, Johannes Benduhn, Fortunato Piersimoni, Anton Kirch, David Beljonne, Koen Vandewal, Donato Spoltore, Giacomo Londi, Johannes Widmer, Benduhn, Johannes, PIERSIMONI, Fortunato, Londi, Giacomo, Kirch, Anton, Widmer, Johannes, Koerner, Christian, Beljonne, David, Neher, Dieter, SPOLTORE, Donato, and VANDEWAL, Koen
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Coupling ,Materials science ,Organic solar cell ,Renewable Energy, Sustainability and the Environment ,Open-circuit voltage ,Photovoltaic system ,Institut für Physik und Astronomie ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Acceptor ,Molecular physics ,charge-transfer states ,nonradiative voltage losses ,organic solar cells ,triplet excited states ,0104 chemical sciences ,Excited state ,ddc:53 ,General Materials Science ,Triplet state ,0210 nano-technology ,Voltage - Abstract
The best organic solar cells (OSCs) achieve comparable peak external quantum efficiencies and fill factors as conventional photovoltaic devices. However, their voltage losses are much higher, in particular those due to nonradiative recombination. To investigate the possible role of triplet states on the donor or acceptor materials in this process, model systems comprising Zn- and Cu-phthalocyanine (Pc), as well as fluorinated versions of these donors, combined with C-60 as acceptor are studied. Fluorination allows tuning the energy level alignment between the lowest energy triplet state (T-1) and the charge-transfer (CT) state, while the replacement of Zn by Cu as the central metal in the Pcs leads to a largely enhanced spin-orbit coupling. Only in the latter case, a substantial influence of the triplet state on the nonradiative voltage losses is observed. In contrast, it is found that for a large series of typical OSC materials, the relative energy level alignment between T-1 and the CT state does not substantially affect nonradiative voltage losses. This work was supported by the German Federal Ministry for Education and Research (BMBF) through the InnoProfile project "Organische p-i-n Bauelemente 2.2" and the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska Curie Grant agreement No. 722651 (SEPOMO). F.P. and D.N. acknowledge funding by the German Research Foundation (DFG) via the SFB 951 "HIOS". The authors acknowledge Prof. K. Leo and V. C. Nikolis for fruitful discussions. The authors thank Dr. B. Beyer for supplying ZnF4Pc and CuF4Pc as well as Dr. M. Lau for the synthesis of F4CuPc. Additionally, the authors thank Prof. Bauerle from University of Ulm for the supply of DH4T, DH6T, and several DCV2-nT-R. Furthermore, the authors acknowledge Dr. F. Holzmueller, M. Saalfrank, and Dr. R. Meerheim for providing OSC devices for this study. Computational resources were provided by the Consortium des Equipements de Calcul Intensif (CECI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11, as well as the Tier-1 supercomputer of the Federation Wallonie-Bruxelles, infrastructure funded by the Walloon Region under Grant Agreement No. 1117545. D.B. is a FNRS Research Director.
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