Symposium : S
Organic photovoltaics: science and technology (OPV)
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| 09:00 | Designing materials and tandem architectures for polymer solar sells Authors : René Janssen Eindhoven University of Technology Affiliations : Resume : The power conversion efficiency of polymer solar cells depends on the quantum and energy efficiency by which photons from the sun are converted into electrical power. Absorption of light, charge generation, transport and collection all have to occur with high quantum efficiency and with minimal losses in energy.
Design strategies for the synthesis of improved conjugated polymers in combination with fullerene acceptors for efficient solar cells will be discussed. New materials feature extended optical absorption in combination with high, balanced charge carrier mobilities for holes and electrons and can be processed into efficient solar cells, depending on creating the optimal nanoscale morphology by controlling molecular weight and thin film processing conditions. In some examples, recombination of charge carriers into a triplet state on the polymer limits achieving higher efficiencies.
Multi-junction solar cells form a promising strategy to further increase the power conversion efficiency of polymer photovoltaics beyond the limits of single junctions. By combining the characteristics of representative single junction cells the optimal device layout can be accurately predicted. Examples of making and characterizing efficient tandem solar cells will be shown. | 1 1 |
| Materials : Gilles Dennler | ||
| 09:30 | Design rules for fullerene/polymer composites used in organic bulk heterojunction solar cells Authors : Pavel A. Troshin1*, Diana K. Susarova1, Ekaterina A. Khakina1, Olga A. Mukhacheva1, Andrey E. Goryachev1, Christian Kaestner2, Sergei A. Ponomarenko3, Harald Hoppe2, Vladimir F. Razumov1, Daniel A. M. Egbe4, and N. Serdar Sariciftci4 1Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow region, 142432, Russia, Email: troshin2003@inbox.ru. 2Ilmenau University of Technology, Institute of Physics, Weimarer Str. 32, 98693 Ilmenau, Germany 3Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences, 70 ul. Profsoyuznaya, 117393 Moscow, Russia 4Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz, Austria Affiliations : Resume : We present here a comprehensive set of the results on photovoltaic performance of approximately 300 different photoactive systems based on combinations of 25 fullerene derivatives and 12 conjugated polymers. A thorough analysis of the obtained data allowed us to reveal some important correlations between the molecular structures of the polymer and fullerene counterparts, their physical properties (solubility), the morphology of their photoactive blends and their photovoltaic performance. The observed relationships might be used as guidelines for rational design of novel material combinations for fullerene/polymer organic solar cells.
It will be demonstrated that many fullerene/polymer composite systems have rather predictable behavior. Considering molecular structures of both polymer and fullerene derivative it becomes possible to predict the morphology of their composites. In turn, the nanomorphology of the fullerene/polymer blends was shown to have a direct quantitative correlation with their photovoltaic performance. Therefore, a clear relationship between the molecular structures of the materials and their photovoltaic performance has been established for the first time. These results create a solid background for the development of computational approaches (similar to QSAR) for rational design of novel photoactive materials for organic photovoltaics. | 1 2 |
| 09:45 | Polythiophene/poly(fluorene-alt-dithienylbenzothiadiazole) Block Copolymers for Photovoltaic Devices. Authors : Rhiannon C. Mulherin 1, Stefan Jung 2, Sven Huettner 1, Nils Koenen 2, Sybille Allard 2, Ullrich Scherf 2, Neil C. Greenham 1 1 Physics, Cambridge University, Cambridge, Cambridgeshire, UNITED KINGDOM 2 Chemie, Bergische Universitaet Wuppertal, Wuppertal, GERMANY Affiliations : Resume : Donor-acceptor block-copolymers, composed of a poly(fluorene-alt-dithienylbenzothiadiazole) donor block and polythiophene acceptor block, are demonstrated in high open-circuit voltage photovoltaic devices. Device efficiency as a function of nano-phase separation and molecular self-assembly is characterised via a range of processing conditions. The effect on blend morphology and device performance for poly(fluorene-alt-dithienylbenzothiadiazole)/polyfluorene blends doped with varying concentrations of block-copolymer is also examined. These nano-structure/performance effects are interpreted in the light of ultra-fast transient absorption spectroscopy examining the dynamics of photoluminescence quenching and charge generation. | 1 3 |
| 10:00 | ON THE INFLUENCE OF ALKYL SIDE-CHAINS ON THE OPTOELECTRONIC PROPERTIES OF LOW BAND-GAP CO-POLYMERS Authors : Laure Biniek (1), Sadiara Fall (2), Christos L. Chochos (3), Nicolas Leclerc (1), Patrick Lévêque (2) and Thomas Heiser (2) (1) Laboratoire d’Ingénierie des Polymères pour les Hautes Technologies, Université de Strasbourg, Ecole Européenne de Chimie, Polymères et Matériaux, 25 rue Becquerel, 67087 Strasbourg, France, (2) Institut d’Electronique du Solide et des Systèmes, Laboratoire Commun UDS-CNRS, 23 rue du Loess, 67037 Strasbourg, France (3) Cyprus University of Technology, Department of Mechanical Engineering and Materials Science and Engineering Kitiou Kiprianou 45, 3041, Limassol, Cyprus Affiliations : Resume : The molecular design of electron donor conjugated polymers with accurate optoelectronic properties for efficient bulk heterojunction photovoltaic devices has attracted a lot of attention worldwide. Ideally, the polymer should have i) appropriate photon harvesting properties, ii) frontier orbitals that allow both, efficient exciton dissociation and a high open circuit voltage, iii) high charge carrier mobilities, iv) high solubility and v) high molecular weights. Charge transfer D/A copolymers are promising materials that have allowed significant progress in this field. However, although a lot of attention has been given to the design of their molecular conjugated backbone, only few investigations have considered the influence of their solubilizing side chains. The aim of the present work is to show how the nature, the position and the density of alkyl side chains may influence all above mentioned polymer properties. For that purpose, our team has designed and characterized a series of donor-acceptor alternating conjugated polymers using benzothiadiazole as electron-deficient unit, and thieno[3,2-b]thiophene as well as thiophenes moieties as electron-rich units. Various alkyl side-chains were introduced onto different positions along the same conjugated backbone and the molecular structure/polymer properties relationships have been investigated systematically. The results allowed us optimize the polymer structure and improve considerably the photovoltaic device performances. | 1 4 |
| 10:15 | Tailor- made absorber polymers for efficient organic solar cells Authors : S. Janietz, E. Katholing, L. Pabel, H.-F. Schleiermacher b), H. Mangold b), U.Würfel b);Fraunhofer Institute Applied Polymer Research, Geiselbergstr. 69, D-14476 Potsdam, Germany, tel.: +49-331-5681208, email: silvia.janietz@iap.fraunhofer.de b) Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, 79110 Freiburg, Germany Affiliations : Resume : Conjugated polymers have the possibility to be applied as absorber materials in low cost organic photovoltaic. These polymers offer the possibility to be used by solution-processing like printing, doctor blading or spray deposition. The bulk-heterojunction cell concept is used most widely. It consists of a light absorbing conjugated polymer and a fullerene derivative for the ultra fast charge transfer. Poly(3-hexylthiophene) (P3HT) is often studied as the light absorbing polymer in bulk heterojunction solar cells. P3HT does not present the optimum HOMO and LUMO energy levels with respect to its acceptor counterpart [6,6]-phenylC61-butyric acid methyl ester (PCBM) and with respect to the solar spectrum. A defined lowering of the bandgap, as well as a lowering of the energy offset between the donor-LUMO and the acceptor-LUMO will be desirable. Therefore many research activities were done to design polymers with optimized HOMO and LUMO energy levels to match the solar emission better. Such polymers can be realized through the introduction of alternating electron donating and electron accepting moieties along the polymer backbone to reach bandgaps between 1.8 -1.3 eV. Fluorene based terpolymers with different content of dialkyl substituted diphenyl-benzopyrazine or diphenyl-thienopyrazine and triphenylamine units (MR) were synthesized by Suzuki polymerization. Special attention was spent to increase molecular weights and the solubility of these polymers. Polymers were realized with high molecular weights and with very good solubility in organic solvents. The additional introduction of triarylamine units helps to reach sufficient charge mobilities of such kind of terpolyfluorenes. The alignment of the LUMO energy positions is possible through the introduction of different donor acceptor units in this class of polymers. The introduction of dialkyl substituted diphenyl-benzopyrazine for example in the fluorene main chain leads to LUMO-energy level of 3.1eV and in solar cells to an open circuit voltage of 0.96 V. Different compositions of the terpolymers were studied in solar cells. The relationship between the composition and the achieved performance of the solar cells will be discussed in detail. First results show solar cell power conversion efficiency of 2.8 % under simulated sunlight for example for a composition MR2/8:PCBM 1:2. Further optimization and their application in multi junction devices will lead to even higher efficiencies. | 1 5 |
| 10:30 | EASILY SYNTHESIZED DONOR-ACCEPTOR POLYMERS FOR HIGH EFFICIENCY SOLAR CELLS Authors : M.R. Andersson1, E. Wang1, R. Kroon1, L. Hou2, S. Hellström1, O. Inganäs2 1Polymer Technology, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden 2Biomolecular and Organic Electronics, (IFM), Linköping University, SE-581 83 Linköping, Sweden Affiliations : Resume : The development of high efficiency polymer solar cells for electrical generation is a challenging research task and our efforts have, during several years, been concentrated on synthesizing and evaluating new materials. These polymers have been specifically designed to be used together with C60 or C70 derivatives in so called bulk heterojunction polymer solar cells. We have primarily chosen to work with copolymers having extended absorption to cover the important parts of the solar emission. Recently we synthesized a blue donor-acceptor copolymer called TQ-1, which in the best case shows maximum power point efficiencies around 6%. This polymer simply consists of thiophenes alternating with substituted quinoxaline units and therefore the polymer is easily synthesized in few steps. We have now extended this class of polymers with a number of new polymers having different side chains to evaluate which substitutions give the best devices. Also small changes to the quinoxaline unit have been performed to further alter the properties of the polymers. The polymer design, synthesis, properties, device structure, and device characteristics will be presented. | 1 6 |
| 11:00 | Perylene sensitization of fullerenes for improved performance in organic photovoltaics Authors : Holger Hesse Lukas Schmidt-Mende Center of Nanoscience, University of Munich, Amalienstrasse 54, 80799 Muenchen, Germany Affiliations : Resume : Fullerenes exhibit excellent properties as acceptors in organic photovoltaics (OPVs) due to their high electron mobility, suitable energy levels and high exciton diffusion length. However, absorption of fullerenes, especially of the most common C60 derivatives, is limited and strongly absorbing donor materials are needed for efficient light harvesting in the thin active layer of OPV devices.
The addition of an energy relay dye to the fullerene results in increased light harvesting on the acceptor side. Steady state photoluminescence and transient photocurrent decay techniques reveal that additionally generated excitons are transferred to the fullerene and separated at the donor-acceptor heterojunction leading to enhanced photocurrent. The concept is exemplary shown for Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl]] (PCPDTBT), a near infrared absorbing donor polymer and hexa-peri-hexabenzocoronene (HBC), an UV absorbing small molecule. In both systems significantly higher power conversion efficiency can be achieved via perylene dye sensitization of the fullerene acceptor. Charge separation and energy transfer processes are studied in detail using transient absorption spectroscopy and time resolved charge extraction techniques.
The presented method can be seen as a general route for facile broadening of the absorption of organic thin films which may allow for higher current generation and efficiency in OPV devices. | 1 7 |
| 11:15 | Halogenated Boron Subphthalocyanines as Light Harvesting Electron Acceptors in Organic Photovoltaics Authors : Paul Sullivan(1), Amelie Duraud(1), Ian Hancox(1), Nicola Beaumont(1), Giorgio Mirri(2), James H. R. Tucker(2), Ross A. Hatton(1), Michael Shipman(1) and Tim S. Jones(1) (1) Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K. (2) School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K. Affiliations : Resume : Improved understanding of the factors influencing the performance of small molecule organic photovoltaic (OPV) devices has led to increased interest in the discovery of new photoactive materials. The relative abundance of suitable commercially available materials has led to a number of candidate donor materials being reported showing improvements in open-circuit voltage (VOC) and/or short-circuit current (JSC). However, the list of acceptor materials remains small with most work relying on fullerene derivatives. In the simplest terms, a photoactive heterojunction requires only an energy level offset to function, and hence one approach to new acceptor materials is the synthetic modification of existing donor materials to provide acceptor characteristics. In this work new light harvesting electron acceptors based on boron subphthalocyanine chloride (SubPc) have been synthesized and integrated into planar heterojunction OPV devices. By selective halogenation of the periphery of the SubPc ring, energy level tuning to maximize the interface gap formed with SubPc as the electron donor is demonstrated. A planar SubPc/Cl6-SubPc heterojunction device exhibits an exceptionally high VOC (~1.3 V) and a power conversion efficiency of ~2.7%. Under continuous illumination these devices also exhibit significantly improved stability as compared to the same device structure employing C60 as the electron acceptor. As such, Cl6-SubPc has considerable potential as a replacement for C60 in OPVs. | 1 8 |
| Computation & Materials : Barry Rand | ||
| 14:30 | Charge transport simulations in organic semiconductors Authors : Denis Andrienko Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany email: denis.andrienko@mpip-mainz.mpg.de Affiliations : Resume : The role of material morphology on charge carrier mobility in partially disordered organic semiconductors is discussed for several classes of materials: [1,2,3,4]. Simulations are performed using a package developed by Imperial College, London and Max Planck Institute for Polymer Research, Mainz (www.votca.org). This package combines several techniques into one scheme: quantum chemical methods for the calculation of molecular electronic structures and reorganization energies; molecular dynamics and systematic coarse-graining approaches for simulation of self-assembly and relative positions and orientations of molecules on large scales; kinetic Monte Carlo and master equation for studies of charge transport.
[1] J. Kirkpatrick, V. Marcon, J. Nelson, K. Kremer, D. Andrienko, Phys. Rev. Lett., 98, 227402, 2007
[2] J. Kirkpatrick, V. Marcon, K. Kremer, J. Nelson, D. Andrienko, J. Chem. Phys., 129, 094506, 2008
[3] V. Marcon, W. Pisula, J. Dahl, D. W. Breiby, J. Kirkpatrick, S. Patwardhan, F. Grozema, D. Andrienko, J. Am. Chem. Soc., 131, 11426, 2009
[4] X. Feng, V. Marcon, W. Pisula, M. R. Hansen, J. Kirkpatrick, F. Grozema, D. Andrienko, K. Kremer, K. Mullen, Nature Materials 8, 421, 2009 | 2 1 |
| 15:00 | Computational Design of Alternative Electron Acceptors Authors : Jarvist M. Frost [1], Mark A. Faist [2][1], Samuel Foster [1], Jenny Nelson [1] 1. Physics Department, Imperial College London, London, United Kingdom. 2. Chemistry Department, Imperial College London, London, United Kingdom. Affiliations : Resume : Increasing the power conversion efficiency of organic
solar cells will require new materials. The current lack of
understanding of the relationship between chemical structure and
device performance limits rational material design. This is the case
particularly for the commonly studied solution processed blend films
of conjugated polymers with small molecular acceptors, whose
micro-morphology is difficult both to control and to determine
experimentally. In such cases, simulation techniques offer an
atomistic view which is not available experimentally.
We have developed a quantum chemical technique that can accurately
predict the electron acceptor levels of fullerene adducts. The method
is used to investigate the effect of multiple isomerism on the
disorder in energy levels of higher adduct fullerenes, including
families of fullerenes that have been used in state of the art
photovoltaic devices [1] [2]. Results are validated by comparison with
differential pulse voltammetry measurements, using a deconvolution
method.
These computational methods allow explicit calculation of the
energetic disorder in isomeric mixes [3], which is believed to be a
major factor limiting electron mobility and hence solar cell
performance.
In order to investigate the effect of type and number of side chains
on electron mobility in the fullerene phase, we use molecular dynamics
(MD) techniques to generate representative micro-morphologies for
fullerene domains, using force fields developed for the given
fullerene. Mobility is then estimated using kinetic Monte Carlo
simulation and quantum chemical calculations in a multi-scale
approach. We compare simulated results with experimentally determined
mobilities and discuss the results in terms of side chain
configuration.
[1] Guangjin Zhao, Youjun He, and Yongfang Li, “6.5% Efficiency of
Polymer Solar Cells Based on poly(3-hexylthiophene) and Indene-C60
Bisadduct by Device Optimization,” Advanced Materials 22, no. 39 (10,
2010): 4355-4358.
[2] Martijn Lenes et al., “Fullerene Bisadducts for Enhanced
Open-Circuit Voltages and Efficiencies in Polymer Solar Cells,”
Advanced Materials 20, no. 11 (2008): 2116-2119.
[3] Jarvist Moore Frost, Mark Anton Faist, and Jenny Nelson,
“Energetic Disorder in Higher Fullerene Adducts: A Quantum Chemical
and Voltammetric Study,” Advanced Materials (9, 2010): n/a-n/a | 2 2 |
| 15:15 | Prediction of electron mobilities in fullerene derivatives: probing the influence of crystal structure and sidechain Authors : Harald Oberhofer^a and Jochen Blumberger^b a: University of Cambridge, Dep of Chemistry, UK b: University College London, Dep of Physics and Astronomy, UK Affiliations : Resume : The performance of organic photovoltaic cells depends critically on the
rate of charge transfer in the p- and n-type semiconducting layers, and thus on
their morphology and intermolecular structure. Interestingly, altough [6,6]-Phenyl C61
butyric methyl ester (PCBM) is the most successful n-type organic semiconductor
to date, its preferred packing structure in the microcrystalline domains of
actual devices remains unclear, prohibiting a fundamental understanding of the structure-function
relationship of this important material. Here we use density functional theory (DFT)
calculations to optimize PCBM in different crystal structures, and we apply
a recently developed DFT-methodology for the calculation of electron mobilities under the
influence of an external electric field. These calculations help us establish a relationship
between microscopic structure and electron transport characteristics in this material.
We also investigate the influence of the side chain of PCBM on crystal structure and electron
mobility, by comparing our calculations with the results obtained for crystalline C60.
Finally, we highlight opportunities but also possible limitations of computation in
the rational design of organic semi-conducting materials. | 2 3 |
| 15:30 | Why fullerenes make excellent organic photovoltaic acceptor materials: Implications of low exchange energy Authors : Eric T. Hoke*, Jason T. Bloking†, George F. Burkhard*, Alan Sellinger† and Michael D. McGehee† *Department of Applied Physics, Stanford University, Stanford, California 94305 †Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 Affiliations : Resume : Fullerenes are unrivaled as electron acceptor materials for organic photovoltaics. The best non-fullerene devices are less than half as efficient as those that use fullerenes. One under-recognized property of fullerenes is their low exchange energies. The exchange energy splitting of a material is the difference between the energy of the lowest singlet exciton and the more stable lowest triplet exciton. A low exchange energy is desirable for organic photovoltaic materials since it raises the energy of the triplet exciton without changing the optical bandgap of the material. Devices where the triplet exciton of one material is lower in energy than the charge transfer complex formed by the electron on the donor and hole on the acceptor material typically suffer from severe recombination via triplet excitons. Fullerenes have an exchange energy splitting of 0.2eV, which is significantly smaller than that in conjugated polymers (0.7eV) and most other organic semiconductors (typically larger than 0.5eV). Consequently, a smaller difference in ionization potential between the fullerene and the donor material should be required to avoid the loss of excitons funneling into low energy triplet states. We compare the performance of bulk heterojunction devices using fullerenes with those utilizing non-fullerene acceptors with similar ionization potential and demonstrate that recombination losses to triplet states is a greater problem in the non-fullerene devices. This investigation suggests that triplet energies should be taken into consideration in the design of new acceptor as well as donor materials with the goal of minimizing the exchange energy splitting. | 2 4 |
| 15:45 | Fullerene metallocomplexes as acceptor for organic solar cells Authors : Anna A. Gromchenko(1), Vladimir V. Bruevich(1), Vladislav Pavelyev(2), Artem A. Bakulin (3) Marina V. Tsikalova(4), Yuri N. Novikov(4), Paul H.M. van Loosdrecht(2), Maxim S. Pshenichnikov(1,2), Dmitry Yu. Paraschuk(1) (1) Faculty of Physics and International Laser Center, Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow, Russia; email: paras@physics.msu.ru (2) Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands (3) Cavendish laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK (4) Nesmeynov Institute of Organoelement Compounds, Moscow, Russia (4) Nesmeynov Institute of Organoelement Compounds, Moscow, Russia Affiliations : Resume : One of the promising strategies to enhance the performance of polymer-fullerene solar cells is based on utilizing fullerene derivatives with lower LUMO energies as compared to the conventionally used PCBM’s, to provide a higher photovoltage. In this work, we study a number of exohedral fullerene metallocomplexes (FM) showing a LUMO energy of at least 0.3 eV lower than that of PCBM. The electron mobility in films of FMs with various molecular weights, metals, and ligands was measured by a space-charge-limited current technique. It was found that the IrC60 complex with DIOP ligand shows the highest electron mobility that is about the hole mobility in P3HT. The morphology data of P3HT:IrC60 blends indicate phase separation patterns similar to those of P3HT:PCBM blends. The P3HT:IrC60 cells demonstrate higher open-circuit voltages by ~0.2 V as compared to the reference devices; however, their efficiency is still somewhat lower. To reveal the possible reasons for losses, we investigate the charge generation dynamics in these blends by ultrafast polarization-sensitive photoinduced absorption spectroscopy with visible pump and mid-IR probe. The ultrafast spectroscopy and external quantum efficiency data show that the photoinduced charges in polymer:FM blends are generated mostly via the electron transfer process while the hole transfer is fairly inefficient. Based on our experimental results, we propose further optimization strategies for polymer:FM cells. | 2 5 |
| 16:00 | High open-circuit-voltage polymer solar cells using triphenylamine-substituted fullerenes as acceptor Authors : Chin-Wei Liang, Institute of Polymer Science and Engineering; Chiou-Ling Chang, Man-kit Leung, Department of Chemistry; Leeyih Wang, Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan Affiliations : Resume : Polymer solar cells have attracted considerable interest owing to their low cost, light weight and ease of fabrication. To raise the open-circuit voltage (Voc) of the devices, many research efforts have been devoted to up-shift the LUMO level of acceptor materials by incorporating donor moieties to the functionalized fullerenes. However, the change in LUMO is usually very limited due to the non-conjugated feature on the anchoring point. Herein, triphenylamine-substituted methanofullerene (TPAC60) was synthesized and utilized as an acceptor to fabricate poly(3-hexylthiophene)-based solar cells. Although cyclic voltammogram showed the first reduction potential of TPAC60 solution is comparable to that of PCBM, the cell based on P3HT/TPAC60 exhibited a very high Voc of 0.77 V, which is almost 30% higher than that of P3HT/PCBM-based device. Very interestingly, experimental results from photoelectron and UV-vis spectrometers clearly showed TPAC60 solid-film has higher LUMO than PCBM film. This observation suggested that the electron affinity of C60 may change through the physical contact of fullerene balls and donor groups, providing a novel route for tuning the energy levels of the solid-film of C60 adducts. | 2 6 |
| 16:15 | Quantitative estimation of electronic quality of Zinc Phthalocyanine (ZnPc) Authors : Debdutta Ray, Mauro Furno, Karl Leo and Moritz Riede (Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany) Affiliations : Resume : The electronic quality of a photoconductive material is defined by its carrier collection efficiency. The carrier collection length can be defined as the product of the carrier mobility, carrier lifetime and the electric field. Hence, by estimating the carrier mobility-lifetime product of a material its electronic quality can be quantitatively evaluated. However, in organic semiconductors, photocarrier generation in pristine materials may occur via a number of processes which operate either in the bulk of the material or at the metal/organic interface. In this work we measure the spectral response of the photocurrent as a function of electric field to understand the dominant carrier generation mechanism in pristine ZnPc films. ZnPc is widely used as the absorber material in organic solar cells. The shape of the spectral response is understood by optical simulations which take into account optical interference effects. We use film structures where carrier generation at an interface is facilitated to differentiate between bulk and interface effects. We evaluate the bulk photocarrier generation efficiency and thereby the mobility-lifetime product of holes in ZnPc. The mobility-lifetime product of holes is estimated to be about 2x10^-11 cm^2/V in pristine ZnPc films. This is in good agreement with the electric field required to collect all carriers for a given length of film. This technique can be used for fast evaluation of the electronic quality of ZnPc for different batches. | 2 7 |
| Materials, Computation, & Hybrid Posters : Jan Kroon & Dana Olson | ||
| 16:30 | Improved photoinduced charge carriers separation in organic-inorganic hybrid photovoltaic devices Authors : Yana Vaynzof,1 Dinesh Kabra,1 Lihong Zhao,2 Peter K. H. Ho,2 Andrew T.-S. Wee,2 and Richard H. Friend1,2 1 Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom 2 Department of Physics, National University of Singapore, Singapore 117542 Affiliations : Resume : We demonstrate enhanced performance of a hybrid photovoltaic device, where poly[3-hexylthiophene] (P3HT) is used as active material and a solution-processed thin flat film of ZnO modified by a self-assembled monolayer (SAM) of phenyl-C61-butyric acid (PCBA) is used as electron extracting electrode. Ultraviolet photoemission spectroscopy measurements reveal an increase in the substrate work function from 3.6 to 4.1 eV upon PCBA SAM deposition due to an interfacial dipole pointing away from the ZnO. External quantum efficiency (EQE) of the SAM modified devices reached 9%, greatly improved over the 3% EQE of the unmodified devices.[1] Similarly, an increase in performance was observed for poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) on SAM modified ZnO.
Time Correlated Single Photon Counting (TCSPC) measurements revealed a decrease in the exciton life time in both P3HT and F8TBT for the PCBA modified substrates, confirming the improved charge carrier separation at the PCBA modified interface.
We further improved the performance of our devices, by employing ZnO nanowires (ZnO NWs) substrates, which offer a much larger interface area between the ZnO and the polymer. Our results for P3HT indicate that the EQE of such devices is increased from 8% to 15% upon PCBA modification.
[1] Vaynzof et al, Appl. Phys. Lett. 97, 033309 (2010). | 3 1 |
| 16:30 | Systematic theoretical study of the most used donor polymers in third generation bulk hetero-junction solar cells. Authors : Luca Longo, Andrea Pellegrino, Nicola Perin, Riccardo Po’, Chiara Carbonera, Giuliana Schimperna, Alessandra Tacca. Research Centre for non Conventional Energies Istituto Eni Donegani, ENI S.p.A, Via Fauser 4, 28100 Novara (Italy). Affiliations : Resume : Many groups compare experimental and theoretical results of band gap and HOMO-LUMO values of materials used in solar cells devices, but generally limiting the study to a small number of compounds. Yet, considering the huge number of possible monomer combinations to give potentially improved materials for solar cells, the development of a strategy to predict their electronic proprerties would be extremely useful.
In the present work we treat an uncovered subject in the literature: the assessment of the prediction capabilities of DFT methods on a wide spectrum of family compounds. We based the research on the energetic levels of frontiers orbitals data obtained from materials both synthesised in our labs and available in the literature. They consist in donor-acceptor copolymers where the acceptor is mainly a benzotiadiazole unit while donor comonomers vary with minimum modifications.
DFT-based calculations allowed us to generate theoretical results for many structures, to be compared to experimental ones. Althdough experimental data come from different laboratories, the first results of our investigation allow some interesting consideration. Differently for LUMO, for both band gap and HOMO values the theoretical calculations reproduce quite satisfactorily the experimental trend versus the structural changes. DFT based methods can not yet be considered a precise predicting tool replacing experimental work, but can be useful for a preliminary screening of the designed structure. | 3 2 |
| 16:30 | Investigation of Interface Properties of Copper Phthalocyanine/Dye/Titania Hybrid Solar Cells Authors : Gopala Krishna T.V.V1, John Noel Clifford2, Fortunato Piersimoni1, Donato Spoltore1, Emilio Palomares2 & Jean. V.Manca1, 3 * 1Institute for Materials Research (IMO) Hasselt University Wetenschapspark 1 BE-3590 Diepenbeek Belgium 2 Institute of Chemical Research of Catalonia (ICIQ) Avda. Països Catalans 16 43007 Tarragona España 3IMEC, associated lab IMOMEC Wetenschapspark 1 BE-3590 Diepenbeek Belgium * jean.manca@uhasselt.be Affiliations : Resume : Metal-substituted phthalocyanine thin films such as Copper-Phthalocyanine (CuPc) are often used as photo-active and charge injection layers in fully organic photovoltaic devices. As a part of this work, CuPc is vacuum sublimated on the electron acceptor layer of mesoporous Titania (TiO2), which resulted in the formation of hybrid CuPc/TiO2 solar cell devices. The performance of these hybrid devices has been very low (photovoltaic conversion efficiency is typically 0.003%), but we demonstrate the overall device performance is enhanced up to 50%, by the introduction of the ruthenium complex Na-RuII(4,4´,-bis(5-hexylthiophen-2-yl)-2,2´-bipyridine)(4-carboxylic acid-4´-carboxylate-2,2´-bipyridine)(NCS)2 (C101) dye at the CuPc/TiO2 interface. The interface properties of these multilayer devices are studied by using a variety of electro-optical characterization techniques such as Fourier Transform Photocurrent Spectroscopy (FTPS), Transient Absorption Spectroscopy (TAS) and Charge Extraction by Linearly Increasing Voltage (CELIV) measurements. Understanding the interface properties of these engineered multilayer hybrid devices is of both fundamental and technological importance, which can lead to improvements in device design and performance. | 3 4 |
| 16:30 | Dye-sensitizing of self-nanostructured Ti(:Zn)O2/AZO transparent electrodes by self-assembly of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) Authors : Giovanna Pellegrino1, Guglielmo G. Condorelli 2, Vittorio Privitera1, Brunella Cafra 3, Silvia Di Marco 3 and Alessandra Alberti 1. 1 CNR-IMM, Zona Industriale Strada VIII, 5 - 95121 Catania, Italy, 2 Dip. di Scienze Chimiche Università degli Studi di Catania and INSTM UdR di Catania, V.le Andrea Doria, 6 - 95125 Catania, Italy , 3 ST Microelectronics, Zona Industriale Stradale Primosole, 50 - 95121 Catania, Italy Affiliations : Resume : Self-nanostructured ZnO:Al (AZO) conductive layers consisting of [1120] oriented domains were grown by DC pulsed-Sputtering using the deposition rate as the tuning parameter. The AZO substrates were coated by a conformal TiO2 thin film and sensitized by 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) to be used in dye-sensitized solar cells (DSSC).
Besides the high surface availability due to the nano-patterning, the TCPP surface molecular density increases by 350% (UV-vis) with respect to a flat conventional substrate thanks to a more dense molecular arrangement, as evidenced by combining High Resolution X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy(AFM). In addition, the chemical properties of the electrode surface has a crucial role: XPS revealed the presence of Zinc atoms in the TiO2 surface, with the position of the Zn 2p3/2 shifted with respect to that of pure AZO. The presence of Zn in the TiO2 matrix (Ti (:Zn)O2) was found to crucially influence the electronic properties of the assembled TCPP, as evidenced by a large red shift in the Soret band in the UV-vis spectra. As a consequence of the orbitals rearrangement attributed to the presence of Zn atoms, a significant quenching of luminescence was observed in the emission spectra of TCPP-sensitized Ti (:Zn)O2 suggesting that electrons could be more effectively injected from the TCPP lowest unoccupied molecular orbital to the conduction band of the semiconductor. | 3 5 |
| 16:30 | Synthesis and characterization of star-shaped conjugated systems as potential candidates in Dye Sensitized Solar Cells (DSSCs) Authors : N. Metri*, X. Sallenave, C. Plesse, L. Beouch, P.H. Aubert, G. Sini, F. Goubard, C. Chevrot Laboratoire de Physicochimie des Polymères et Interfaces (LPPI), Cergy-Pontoise University 5 mail Gay Lussac, Neuville sur Oise, 95031 Cergy-Pontoise Cedex, France *noura.metri@u-cergy.fr Affiliations : Resume : The objective of this work concerns the synthesis and characterizations of some novel conjugated organic molecules which were subsequently designed as hole-transporting materials in DSSCs based on TiO2. These molecules must have the following properties: (i) a high hole mobility, (ii) an excellent pore-filling in TiO2, and finally (iii) a weak trend to crystallization.
Currently, the reference molecule, Spiro-MeOTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9.9'-SPIROBIFLUORENE) developed by Grätzel, has achieved photovoltaic conversion efficiencies around 5.1%.
The approach developed in our laboratory involves the synthesis of five star-shaped molecules (1-5) with triphenylamine (TPA) core and Thieno[3,2-b]Thiophene (TTh) derivates which lead to amorphous materials with isotropic optical and charge carrier properties.
We will present the synthesis methods used for these compounds and their thermal, optical and electrochemical characterization. Particular attention will be focused on determining the HOMO and LUMO energy levels of these new materials and their optical gap, which must remain high enough to limit any competition for absorption with the sensitizing dye. Finally, molecular engineering will be discussed in order to adjust ideally these properties for the photovoltaic application. | 3 6 |
| 16:30 | Solution-Processed Organic Photovoltaic Cells with Silyl End-Capped Sexithiophene Authors : Jung Hei Choi, Kyungkon Kim* Solar Cell Center, Korea Institute of Science and Technology (KIST) Affiliations : Resume : Small molecules based on oligothiophene have received strong attention as a good hole transport materials of organic thin-film transistors. Recently, bulk heterojunction organic photovoltaic cells (OPVs) consisting sexithiophene (6T) as a donor and fullerene as an acceptor showed good photovoltaic properties by co-evaporation method. However, the organic small molecules based on sexithiophene have not been investigated solution processed OPVs. We fabricated the solution-processed OPVs using substituted two sexithiophenes, alpha,omega-bis(dimethyl-n-octylsilyl)sexithiophene (DSi-6T) and alpha,omega-dihexylsexithiophene (DH-6T) as donors and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an acceptor. Solution-processed OPVs using DH-6T and DSi-6T showed photovoltaic properties in spite of their poor solubility. The best performance was observed on DSi-6T:PCBM 1:5 (w/w) blend cell with a Voc of 0.63V, Jsc of 1.34 mA cm-2, fill factor of 55% and power conversion efficiency of 0.44% under AM 1.5G illumination. Although DH-6T have higher hole mobility than DSi-6T, the DSi-6T:PCBM blend cell showed higher the hole mobility than DH-6T:PCBM cell. Therefore, DSi-6T cell showed higher device performance than DH-6T cell due to their silyl substitutions which lead to increase the solubility. The higher photovoltaic performance of DSi-6T cell can be explained the film morphology dependence on the solubility of donor. | 3 7 |
| 16:30 | Direct growth of metal sulphide nanoparticles in polymer films for hybrid inorganic- organic semiconductor solar cells Authors : Simon Dowland, Thierry Lutz, Simon King and Saif A. Haque Affiliations : Resume : Research into the use of organic semiconductors has been conducted widely, driven in part by the need to produce cheap and efficient photovoltaics. Polymer solar cells have shown promise but challenges have arisen due to properties intrinsic to the organic materials. Thin films based upon blends of inorganic nanoparticles (NPs) and polymers for application as the absorbing layer in hybrid solar cells have received much attention due to the superior conduction, absorption over a broad range of wavelengths, and increased stability of the inorganic component. To date these blends have been unable to achieve high efficiencies due to the formation of unfavourable morphologies produced during film formation. In order to increase the mixing between polymer and NP, work has been conducted whereby capping agents / ligands have been introduced (around the inorganic NPs) to improve the NP dispersion in the polymer. However, this has been found to result in lower charge transfer efficiency at the acceptor/donor interface.
Here we present a novel route to the fabrication of a hybrid blend of CdS:P3HT displaying a high degree of CdS dispersion throughout the polymer without the use of capping agents. We demonstrate the tuneability of the morphology through temperature annealing studies on thin films. The resulting samples are characterised by transient absorption spectroscopy and transmission electron microscopy. These studies are complimented by device fabrication and characterization. | 3 8 |
| 16:30 | Photoemission investigation on CuPc/MWNT interface Authors : L. D’Ortenzi1, L. Lozzi2, and S. Santucci2 1 Department of Physics, University of L’Aquila, 67100 L’Aquila, Italy 2 Department of Physics and CNISM, University of L’Aquila, 67100 L’Aquila, Italy Affiliations : Resume : Recently, for the realization of organic photovoltaic cells, the use of carbon nanotubes (CNT) has been proposed, either as semi-transparent electrode or as component of the photoactive material (forming, for example, a blend layer with conjugated polymers). In both cases the interface properties with the surrounding materials is of paramount importance for the understanding of the device properties. In this paper we report the interface properties, obtained by means of X-ray and UV Photoemission Spectroscopies (XPS and UPS), between Copper Phthalocyanine (CuPc) and Multi-Walled Carbon Nanotubes (MWNT). The MWNTs have been grown by chemical vapour deposition on silicon substrate. Then they have been laid down using a mechanical method. On these flat-lying MWNTs CuPc molecules have been deposited by thermal evaporation in ultra-high vacuum conditions. From the UPS spectra the variation, as a function of the organic deposition, of the work function of the MWNT (changing from 4.7 eV, for clean MWNT, to 4.4 eV, for nanotubes covered by CuPc) and of the ionization energy of the CuPc, (varying from 5.4 eV, for very thin CuPc film, to 5.1 eV, for a thick film) have been observed. The XPS spectra have reported a very weak interaction between the molecules and the nanotubes, showing no strong effects on the acquired spectra. | 3 9 |
| 16:30 | Novel 2,7-Carbazole Based Alternating and Random Copolymers Authors : Wei Yang, Wei Zhao, Wanzhu Cai, Yong Cao Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China e-mail:pswyang@scut.edu.cn Affiliations : Resume : Polymer solar cells (PSCs) have attracted much attention. In order to further enhance the PCE of the polymer based solar cells, an effective method is to develop donor polymers with low bandgap to enable photocurrent generation from lower energy photons. Poly(2,7-carbazole) derivatives exhibit some unique merits such as high hole mobility, low energy lying highest occupied molecular orbital (HOMO), therefore can result in high air-stability and high Voc. Inspired by the purpose of harvesting the lower energy photons in the solar spectra, there is a need to further lower the bandgap of 2,7-carbazole based polymer.
As compared to 2,1,3-benzothiadizole (BT), an electron deficient unit, which was widely used as the backbone in low bandgap polymers, its analog-2,1,3-benzoselenadiazole (BSe) is more effective in extending the absorption spectrum towards infrared region.
In this paper, alternating copolymer based on 2,7-carbazole with benzoselena-diazole derivative, and random copolymers of 2,7-carbazole containing binary low-bandgap moieties were synthesized, and the maximum power conversion efficiency of 2.5% and 3.4% were abtained by blended with PC70BMand PC60BM, respectively. | 3 10 |
| 16:30 | Design of low bandgap conjugated polymers for photovoltaic applications Authors : Alexander V. Akkuratow, Olga A. Mukhacheva, Diana K. Susarova, Pavel A. Troshin, and Vladimir F. Razumov Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow region, 142432, Russia Affiliations : Resume : An intensive research has been performed worldwide with the aim to develop new and highly efficient low band gap polymers for organic bulk heterojunction solar cells. Major part of the designed polymers is based on the push-pull approach and comprises electron donor and electron acceptor subunits. A large family of polymers is based on cyclopentadithiophene (CPDT) donor and on the benzothiadiazol (BT) acceptor blocks. These polymers yielded power conversion efficiencies of 2.5-5.5% in bulk heterojunction solar cells.
Here we report the synthesis of a new polymer based on the CPDT, BT and thiophene subunits. Photovoltaic properties of this polymer is currently under investigation with the use of a library of different fullerene derivatives.
Synthesis of novel carbazole-based low band gap copolymers will also be presented. Such polymers were reported to give power conversion efficiencies of 6% in bulk heterojunction solar cells. We will present the synthesis of carbazole-based conjugated polymers with different acceptor subunits and solubilizing alkyl side chains as well as results of their preliminary investigation in organic solar cells. | 3 11 |
| 16:30 | Synthesis and photovoltaic performance of various bis-adducts of [60]fullerene Authors : D. K. Susarova, A. E. Goryachev, P. A. Troshin, and V. F. Razumov Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow region, 142432, Russia Affiliations : Resume : One of the main trends in the ongoing research in the filed of organic photovoltaics is the development of fullerene-based electron acceptor materials with decreased electron affinity. Such compounds have higher lying LUMO energy levels compared to conventional PCBM (C60 or C70 versions) and therefore they yield higher open circuit voltages in organic solar cells.
We will present a comparative study of eight different fullerene bis-adducts. The preparation and spectroscopic characterization of these compounds will be discussed. All prepared fullerene derivatives were evaluated as electron acceptor materials in fullerene/polymer solar cells under identical conditions with the reference material bis-[60]PCBM. The obtained results will illustrate that the molecular compositions of the [60]fullerene bis-adducts affect strongly their photovoltaic performance. In particular, some of the designed fullerene-based materials outperform mono[60]PCBM and bis[60]PCBM in solar cells due to their optimized molecular structures. | 3 12 |
| 16:30 | Two steps sensitization for hybrid solar cells Authors : Andreas Naumann[1], Sabin-Lucian Suraru[2], Sven Burdorf[3], Andreas Decker[1], Gottfried Heinrich Bauer [3], Frank Wuerthner[2], Thomas Mayer[1], Wolfram Jaegermann[1]. [1] Technische Universität Darmstadt, Fachbereich Materialwissenschaft, Petersenstr. 32, 64289 Darmstadt [2] Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg [3] Universität Oldenburg, Institut für Physik, 26111 Oldenburg Affiliations : Resume : Two steps sensitization in the sense of third generation solar cells is investigated. In our approach two different dye molecules that can build a donor acceptor dyad are incorporated into one inorganic wide-gap semiconductor matrix. Up-conversion is attempted by two photon excitation of an electron from a donor HOMO level below the matrix valence band to an acceptor LUMO2 above the matrix conduction band. The donor LUMO and acceptor LUMO1 form intermediate gap states.
As inorganic wide-gap semiconductor ZnTe is used. For organic dyes we apply different commercially available materials (e.g. fluorinated Zn-phtalocyanines) as well as perylene bisimides especially synthesized by the project partner.
Inorganic/organic interfaces and donor/acceptor composites have been deposited in UHV by physical vapour deposition and were characterized by photoelectron spectroscopy (XPS, UPS, SXPS), AFM, UV-Vis spectroscopy and I-V measurements. Band line up, chemical interaction and opto-electronic properties are derived. Results from the measurements with XPS/UPS of the interfaces between organic-organic and organic-inorganic semiconductors, as well as with composites of two dyes are presented. Spectrometric measurements of single dyes and composites have been conducted. Solar cells of pure ZnTe films were produced and opto-electronically characterised. | 3 13 |
| 16:30 | Semiconducting nanowire/polymer thin film solar cells Authors : J.Davenas1, E. Beyou1, A. Balloffet1, D. Cornu2, A. Rybak3, 1Polymer Engineering Institute, CNRS-Lyon University, 69622 Villeurbanne, France;2 European Membrane Institute, CNRS-Montpellier University, 34293 Montpellier, France;3Department of Molecular Physics, Technical University of Lodz, 90-924 Lodz, Poland Affiliations : Resume : The elaboration of hybrid layers based on semiconducting nanowires embedded in a semiconducting polymer appears a simple way to produce photovoltaic films at a limited cost. Due to the main role of Si in the semiconductor technology, the combination of n type silicon nanowires (SiNWs) and a p type conjugated polymer like P3HT: poly(hexylthiophene), known for its good ordering properties, is in particular relevant for the realization of photoactive thin films. Bulk p-n junctions exhibiting large interface area can be obtained with potential application to hybrid solar cells. We succeeded to pass the different steps to produce silicon nanowire/P3HT hybrid thin films: high production rate of n type silicon nanowires by the vapour-solid technique, silicon surface passivation and organic functionalisation, solution blending and thin film processing, post elaboration curing… The dissociation efficiency of the photogenerated charge pairs has been evaluated by the quenching of the P3HT fluorescence showing an optimum composition of 3 SiNWs vol. % of the blend, which is in accordance with the low percolation threshold for free carrier transport expected from the high aspect ratio of the nanowires. Current/voltage measurements under illumination however show that the collected photocurrent remains limited to some 10 A/cm2 whereas an interesting increase of the open circuit voltage to 0.65 V is obtained in comparison to the polymer alone. Xerographic discharge experiments have shown that the limiting mechanism is the low electron transport along nanowires in confinement conditions. The high densities of silicon surface states acting as electron traps is probably at the origin of the low photocurrents in nanosized structures as previously reported for porous silicon*. The control of the organic-inorganic interface appears critical in such hybrid materials, needing the development of a functionalisation strategy to overcome the problem of the formation of a dipole barrier at the interfaces.
* Carrier density in a thin silicon layer with nanovoids, M. Banerjee, S.K. Datta, H. Saha,Nanotechnology,17(2006)163-169 | 3 14 |
| 16:30 | Photovoltaic performance of PPV-PPE copolymers: effect of the fullerene derivative Authors : Olga A. Mukhacheva1, Pavel A. Troshin1, Dmitry Voilov2, Diana K. Susarova1, Andrey E. Goryachev1, N. Serdar Sariciftci2, Daniel A. M. Egbe2, and Vladimir F. Razumov1, 1Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow region, 142432, Russia, Email: troshin2003@inbox.ru. 2Joint Analytical Center of Scienific Center in Chernogolovka RAS 3Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz, Austria Affiliations : Resume : Several conjugated PPV-PPE copolymers were studied as electron donor materials in bulk heterojunction organic solar cells in combination with a library of electron acceptor fullerene derivatives. It was shown that molecular structure and solubility of the fullerene counterpart affect significantly photovoltaic performance of both polymers. Use of [60]PCBM as electron acceptor material yielded quite moderate power conversion efficiencies. The best results were achieved when some fullerene derivatives with better suiting molecular structures and solubilities were applied. In some cases the photovoltaic performance of the polymer/fullerene blends shows direct correlation with the molecular structures of the materials.
The obtained results suggest that every newly designed conjugated polymer should be evaluated in solar cells using a library of fullerene derivatives instead of just conventional PCBMs. We believe that only this combinatorial approach might bring the best performing donor/acceptor combinations for future generations of efficient organic solar cells. | 3 15 |
| 16:30 | Side Chain Architectures of 2,7-Carbazole and Quinoxaline-based Polymers for Efficient Polymer Solar Cells Authors : Ergang Wang,*,† Lintao Hou,‡ Zhongqiang Wang,‡ Stefan Hellström,† Wenliu Zhuang,† Fengling Zhang,‡ Olle Inganäs,‡ and Mats R. Andersson*,† †Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, SE-412 96 Göteborg, Sweden ‡Biomolecular and Organic Electronics, IFM, Linköping University, SE-581 83 Linköping, Sweden Affiliations : Resume : Polymer solar cells were deemed one of promising technologies for resolving the energy crisis of the world. However, the application of polymer solar cells was barred by their low efficiency. New polymers with appropriate band gaps and absorption spectra should be developed to improve their efficiencies. Here, three polymers bearing a common carbazole-thiophene-quinoxaline-thiophene backbone, but different side chains, were designed and synthesized in order to investigate the effect of side chains on their photovoltaic performance. Their photophysical, electrochemical and photovoltaic properties were investigated and compared. The polymer EWC3, with the largest amount of side chains, exhibited the highest molecular weight and showed the highest power conversion efficiency of 3.7% with an open-circuit voltage (Voc) of 0.92 V. The atomic force microscopy images of the active layers of the devices showed that the morphology was highly influenced by the choice of the solvent and processing additive. It is worth noting that polymer solar cells (PSCs) fabricated from EWC3, with branched side chains on the carbazole unit, gave a much higher Voc than the devices made from EWC1, which bears the same electron deficient segment as EWC3 but straight side chains on carbazole unit. This study offered a useful and important guideline for designing 2,7-carbazole-based polymers for high performance PSCs. | 3 16 |
| 16:30 | Well-defined, defect-free and end-functionalized poly(3-hexylthiophene) via externally initiated Grignard metathesis polymerization Authors : M. Sommer, W. Huck Melville Laboratory for Polymer Synthesis, Lensfield Road, Cambridge CB2 1EW, UK H. Komber, V. Senkovskyy, R. Tkachov, A. Kiriy, Leibniz-Institut für Polymerforschung e.V., Hohe Straße 6, 01069 Dresden, Germany S. Huettner, R. Friend, Optoelectronics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK Affiliations : Resume : In semi-crystalline conjugated polymers such as poly(3-hexylthiophene) P3HT, microstructure and degree of crystallinity are important factors that determine the electronic properties. One important method to prepare P3HT is the Grignard metathesis polymerization (GRIM), which uses Ni(dppp)Cl2 as the catalyst. Owing to the mechanism of the GRIM method, one tail-to-tail (TT) defect per chain is formed and incorporated into the polymer. While it was until now assumed that the TT-defect is exclusively located at the beginning of the P3HT chain, is it now clear that the major fraction of P3HT carries the TT-defect somewhere within the chain. Here we report the synthesis and characterization of defect-free P3HT via the external initiation using new nickel initiators. This method enables regioregularities of 100% via the elimination of the TT initiating dimer, quantitative incorporation of the 3-hexylthiophene starting group, almost homogeneous hydrogen-hydrogen endgroups and accurate control over molecular weight and polydispersity. Analyzing crystallinity and microstructure in the bulk reveals that the elimination of the TT unit gives rise to outstanding degrees of crystallinity up to 74%. Charge carrier mobilities indicate a less pronounced dependency of the polymer chain length on µ. Finally, an extension of the synthetic concept towards more complex heterocyclic conjugated initiators with electron accepting groups leading to end-functionalized P3HT is presented. | 3 17 |
| 16:30 | Synthesis, Characterization and Photovoltaic Properties of copolymers based on quarterthiophene and diketo-pyrrolo-pyrrole Authors : Seon-Kyoung Son 1,2, Chun-Young Lee 1, Dong Hoon Choi 2, Kyungkon Kim 1,* 1.Solar Cell Center, Korea Institute of Science and Technology, Korea 2. Functional Polymer Lab, Department of Chemistry, Korea University, Korea Affiliations : Resume : We synthesized a series of low band gap copolymers P1, P2, P3 based on alternating quarterthiophene (QT) unit and diketo-pyrrolo-pyrrole (DPP) unit via Stille cross-coupling polymerization. We characterized optical, electrochemical properties and examined their photovoltaic properties. The maximum UV-vis absorption peak of polymers was shown at 620 nm - 650 nm in diluted solution and 680 nm in thin film with optical bandgap about 1.3 eV – 1.4 eV, respectively. The HOMO and LUMO energy levels of P1 were – 5.18 eV and -3.61 eV, respectively, by cyclic voltammetry.
According to the characteristics of photovoltaic device using the blend of the P1 and PC61BM as an electron-acceptor, an open circuit voltage (Voc) of 0.59 V, a short circuit current (Jsc) of 5.47 mA/cm2, a fill factor of 0.64 and a power conversion efficiency(PCE) of 2.06 % were observed at AM 1.5 illumination. | 3 18 |
| 16:30 | A novel polymer for ternary cascade bulk-hetero junction organic solar cell Authors : Ming-Chung Chen, Ying-Chi Huang, Der-Jang Liaw, and Yian Tai* Department of Chemical Engineering, National Taiwan University of Science and Technology, Taiwan Affiliations : Resume : In this report, we synthesized a novel conjugated copolymer, namely poly[2,3-bis(thiophen-2-yl)-acrylonitrile-9,9’-dioctyl-fluorene](DTALFLC8) for organic solar cell application. The hole (μ h) and electron (μ e) motilities of DTALFLC8 are 1.28×10-04 (cm2 V-1 S-1) and 1.58×10-04 (cm2 V-1 S-1), respectively, which suggest the ambipolarity of such copolymer. Cyclic voltammtry (CV) measurement and UV-Vis study indicated that the highest occupied molecular orbital (HOMO) of DTALFLC8 is -5.68eV, while the lowest unoccupied molecular orbital (LUMO) is -3.59eV. The suitable HOMO and LUMO values as well as ambipolarity of DTALFLC8 made it a good candidate to form a ternary cascade structure bulk-hetero junction (BHJ) organic solar cell with poly (3-hexylthiophene) (P3HT) and [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM). The average power conversion efficiency (PCE) of such ternary cascade solar cell is 2.93%, which is 30% higher than the reference cell without DTALFLC8. We believe that the enhanced PCE was resulted from the additional charge separation offered by P3HT/DTALFLC8 interfaces as well as the improved morphology of the BHJ structure. | 3 19 |
| 16:30 | Influence of transport-related material parameters and device morphology on the power conversion efficiency of inorganic organic nanocomposite solar cells: A theoretical assessment Authors : K. Zojer (a), M. Gruber (a,b), B. Stickler (a,b,c), G. Trimmel (b,c), and F. Schürrer (a) (a) Institute of Theoretical and Computational Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria (b) Christian Doppler Laboratory for Nanocomposite Solar Cells, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria (c) Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria Affiliations : Resume : The rapid progress in improving power conversion efficiencies (PCE) of polymer-C60 organic solar cells fueled the interest in competitive, more strongly light-absorbing semiconductors to replace the rather weakly absorbing C60. One promising alternative relies on inorganic low band gap semiconductors such as CdSe and CuInS2.
In the resulting inorganic organic nanocomposite solar cells (IONCSC), charge carriers are inherently photo-generated in the volume of the inorganic material and at the organic-inorganic heterojunction. To intentionally optimize the PCE of IONCSC, a detailed understanding of the interplay between such distinctly different generation mechanisms is required.
We theoretically assess the implications arising from the two generation mechanisms for the charge transport and collection by means of a two-dimensional drift-diffusion-based model. We particularly focus on relationship between the PCE and (i) energy level offsets at the heterojunction, (ii) mobilities, and (iii) dielectric constants. Moreover, we consider the morphology of the heterojunction as well as non-ohmic contacts. We are able to demonstrate that the quality of the contacts, the degree of phase interpenetration, and the transport level alignment at the heterojunction are the most crucial parameters in establishing optimal PCEs[1]. High PCEs require further a combination of materials whose carrier mobilities do not notably differ.
[1] M. Gruber et al., Organic Electronics 11 (2010) 1999. | 3 20 |
| 16:30 | Plasmon enhanced performance of dye-sensitized solar cells using silver nanoparticles Authors : Marko Berginc1, Martina Schmid1,3, Mateja Hočevar1, Srinivas Saranu2, Alistair Kean2, Marko Topič1 1 University of Ljubljana, Faculty of Electrical engineering, Laboratory of Photovoltaics and Optoelectronics, Trzaska cesta 25, 1000 Ljubljana, Slovenia 2 Mantis Deposition, 2 Goodson Industrial Mews, Wellington Street, OX9 3BX Thames, United Kingdom 3 Helmholtz-Zentrum Berlin, Institute for Heterogeneous Material Systems, Hahn-Meitner-Platz 1, 14109 Berlin, Germany Affiliations : Resume : In the last decade processes and new materials have been extensively researched in order to enhance the performance and the stability of dye-sensitized solar cells (DSSCs). However, the DSSCs due to weak absorption of the photoactive layer remain less efficient than c-Si devices. In order to broaden and/or increase the spectral sensitivity of the photoactive layer several attempts have been considered; for example the quest for new dyes, the inclusion of larger scattering particles or voids in the active layer or the use of additional internal or external back reflectors. In the recent years a plasmonic effect using metal nanoparticles (NPs) have also attracted much attention. When NPs are illuminated the oscillating electromagnetic field causes the conduction band electrons to oscillate coherently (surface plasmon resonance). The incident light is strongly scattered or absorbed around the resonance frequency which may enhance the light absorption in the photoactive layer of thin film solar cells. In this paper the optical and electrical simulations will be used to demonstrate the effect of location and diameter of spherical Ag NPs on the performance of DSSCs. In addition, the results of optical measurements of sputtered Ag NPs with different diameters will be presented. Finally, a set of DSSCs with NPs of different diameters located in a compact TiO2 layer at the TCO-TiO2 interface will be made and their performance evaluated to validate the optical end electrical models. | 3 21 |
| 16:30 | CuInS2-Polymer nanocomposite solar cells prepared via metal xanthate precursors Authors : Gregor Trimmel (1,2), Achim Fischereder (1,2) Michael Edler (1,2), Stefan Moscher (1,2), Roman Trattnig (1,3), Gernot Mauthner (1,3), Emil J.W. List (3,4), Wernfried Haas (1,5), Ferdinand Hofer (5), Thomas Rath (1,2) (1) Christian Doppler Laboratory for Nanocomposite Solar Cells, Graz University of Technology and NanoTecCenter Weiz Forschungsgesellschaft mbH, Austria; gregor.trimmel@tugraz.at (2) Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria; (3) NanoTecCenter Weiz Forschungsgesellschaft mbH, Franz-Pichler-Straße 32, A-8160 Weiz, Austria (4) Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria (5) Institute for Electron Microscopy and Fine Structure Research, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria Affiliations : Resume : Inorganic-organic nanocomposite solar cells (NCSCs) have attracted scientists due to the unique possibilities of tuning inorganic semiconductor nanoparticles in size and shape. One requisite for high photovoltaic efficiencies is the purity of the inorganic semiconductor. That means that neither any stabilizing capper nor other impurities are present in the active layer. To solve this problem we have focused in the last years on the development of in-situ preparation methods of inorganic metal sulfides directly in the organic semiconductor matrix. In this contribution we present novel copper and indium xanthates as precursors which are soluble in apolar organic solvents and are thus compatible with common conjugated polymers used in organic photovoltaics. However, the major advantage of this procedure is that the conversion of the precursor into CuInS2 takes place below 200 °C resulting in a dense network of the inorganic particles directly in the conjugated polymer matrix. By using poly[2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl(9,9-dioctyl-9H-9-silafluorene-2,7-diyl)-2,5-thiophenediyl] as polymer and optimizing the CuInS2:polymer ratio as well as the temperature of reaction NCSCs with efficiencies above 2 % have been obtained. The formation process as well as the morphology of the nanocomposite layer was analyzed by complementary spectroscopic and microscopic methods.
This work was funded by the Austrian Ministry of Economy, Family and Youth and Isovoltaic AG. | 3 22 |
| 16:30 | Influence of different interlayers on the performance of nanocomposite solar cells Authors : Verena Kaltenhauser (1,2,*), Thomas Rath (1,2), Stefan Moscher (1,2), Andreas Pein(1,2,3), Wernfried Haas (1,4), Ferdinand Hofer (4), Gregor Trimmel (1,2,*) (1) Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria; (2) Christian Doppler Laboratory for Nanocomposite Solar Cells, Graz University of Technology and NanoTecCenter Weiz Forschungsgesellschaft mbH, Austria; (3) Polymer Competence Center Leoben (PCCL), Roseggerstraße 12, 8700 Leoben, Austria (4) Institute for Electron Microscopy and Fine Structure Research, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria; email: kaltenhauser@tugraz.at, gregor.trimmel@TUGraz.at Affiliations : Resume : In this contribution we compare the influence of ZnS and ZnO interlayers between the active layer and aluminium electrodes in CuInS2-polymer nancomposite solar cells (NCSCs) on the photovoltaic performance. Interlayers can act thereby as hole blocking layers, they can adjust energy levels and the distribution of light in the device. First the active layer of the NCSC was prepared on glass/ITO/PEDOT:PSS substrates via an in situ preparation method based on the thermal decomposition of xanthates as metal-sulphide precursors directly in a polymer matrix (Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]. In a subsequent step interlayers were fabricated either by coating of ZnO-nanoparticles (stabilized with Methoxyethoxy acetic acid) for ZnO-interlayers or by spin coating zinc xanthates which were then thermally converted into ZnS layers. Finally, aluminium electrodes were deposited on top of these layers.
In the present study, the influence of these interlayers on the solar cell performance was compared. Special focus was set in the optimisation of the annealing temperature, layer thickness and the used coating solvent. The different interlayers were compared according to their surface properties. The roughness, density and homogeneity of the interlayers were analysed by SEM-, TEM- and AFM-measurements.
This work was funded by the Austrian Ministry of Economy, Family and Youth and Isovoltaic AG. | 3 23 |
| 16:30 | MULTISCALE STUDY OF THE INFLUENCE OF THE CHEMICAL STRUCTURE ON EXCITON DYNAMICS IN POLYMERIC SYSTEMS Authors : Hélder M. C. Barbosa, Marta M. D. Ramos, Helena M. G. Correia, Centre of Physics and Department of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal Affiliations : Resume : One of the milestones in the photovoltaic field was the use of a bulk-heterojunction made of polymer/low weight molecules to increase organic solar cells efficiency. When an exciton is created in the polymer, it can easily be dissociated into an electron/hole pair if the exciton reaches the polymer/low weight molecule interface. For that happens, it is necessary an efficient exciton diffusion towards the interface before it decays. This process depends on the polymer used, since it will affect the exciton dynamics, as it is suggested from the experiments. However, there is not a clear relationship between the polymer chemical structure and the exciton dynamics. In this communication we present a study of the influence of polymer molecular properties on exciton dynamics using a multiscale model. We use quantum molecular dynamic calculations to understand the effect of polymer molecular properties on singlet exciton formation in polymeric systems, since they are the main excited species produced in polymer-based solar cells. The results obtained on the atomistic calculations were used as input parameters in dynamic Monte Carlo simulations to study the singlet exciton dynamics in polymeric systems with different chemical structures. Our results show clearly that the polymer chemical structure influences not only the intramolecular singlet exciton energy but also it will influence the exciton diffusion process in the polymer network. | 3 24 |
| 16:30 | Multi adducts of fullerenes as electron acceptors for polymer solar cells: a quantum chemical study Authors : P. Morvillo, ENEA, P.le E. Fermi, 1, 80055 Portici (NA) Italy Affiliations : Resume : The aim of this work is to investigate, using the density functional theory, the energy levels of the frontier orbitals of multi adducts of fullerenes (analogues of [60]PCBM and [70]PCBM with more side groups attached to the cage) in order to verify if they can be used as acceptors in bulk heterojunction solar cells.
The open circuit voltage (Voc) of these cells is limited by the difference between the HOMO of the donor and the LUMO of the acceptor. Actually, many polymer-fullerene blends have a non optimal combination of these energy levels, limiting the maximum achievable Voc. Recently it has been shown that bis adducts of [60]PCBM have an higher LUMO level (compared to [60]PCBM) minimizing the energy loss in the electron transfer from the P3HT to the acceptor and increasing the Voc of the corresponding device with P3HT.
Firstly, we studied the LUMO level of bis adducts of [60]PCBM and we found that the position of the LUMO level is raised in accordance to literature. In addition we studied also tris adducts in order to determine the position of the corresponding LUMO levels. Since devices realized using [70]PCBM as acceptor have an higher short circuit current (Jsc) compared to the ones based on [60]PCBM, due to the increase of absorption in the visible part of the spectrum, we also studied bis adducts of [70]PCBM with the aim to verify if it is possible to maximize the Voc of the corresponding device with P3HT and to combine this benefit with the increase of the Jsc. | 3 25 |
| 16:30 | Photo-assisted electrodeposition of conductive polymer back contacts to CdS/CdTe solar cell structures Authors : A. Jarkov, S. Bereznev, J. Kois, K. Laes, O. Volobujeva, A. Öpik a Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086 Tallinn, Estonia Affiliations : Resume : Superstrate glass/ITO/CdS/CdTe PV structures were prepared by HVE technique with following CdCl2 activation of prepared structures.Main conditions for CdS and CdTe thin films deposition and following treatment were selected from the literature data and experimentally with the purpose to prepare and compare complete CdS/CdTe solar cells with standard p+CuxTe back contact and conductive polymers back contacts.
Conductive polymer functional layers of poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) doped with polystyrene (PSS) and ß-naphthalene (ß-NSA) sulfonates were deposited onto activated and etched in NP2 (nitric-phosphoric acid-water mixture). CdTe layers by photo-assisted electrodeposition technique. It was found that highly intensive white light illumination from xenon lamp facilitates conductive polymer layers deposition at lower potential and improves quality of obtained polymer films and allows depositing the polymer strictly onto CdTe around possible defects where ITO is exposed to the polymer solution. Moreover decrease of deposition potential gives the possibility to avoid electrochemical destruction of CdS/CdTe PV structure. It was found that electrodeposited highly conductive PEDOT:PSS and PPy:ßNSA intermediate layers can potentially improve the back contact characteristics of CdS/CdTe PV structures. However, these hybrid structures need to be further optimized to compete successfully with conventional inorganic back contacts in complete CdTe SCs. | 3 26 |
| 16:30 | Solid-State Dye-Sensitized Solar Cells Using Poly(3-hexylthiophene) as Hole Conductor Authors : Wei-Chih Chen, Chia-Yuan Chen, Chun-Guey Wu and Leeyih Wang* Affiliations : Resume : Regioregular poly(3-hexylthiophene) (P3HT) was employed as hole conductor to fabricate solid-state dye-sensitized solar cells (SSDSCs) based on two kinds of heteroleptic ruthenium complexes, coded as CYC-B1 and CYC-B11. The B11-based device exhibited a short-circuit current density (Jsc) of 5.80 mA/cm2, which is higher than the Jsc of 4.56mA/cm2 for B1-based device. This is primarily because B11 has a higher molar extinction coefficient than B1. As a result, with a 150-nm-thick ordered mesoporous TiO2 film, the B1- and B11-based cells possessed a power conversion efficiency (η) of 1.44% and 2.33%, respectively, under standard AM 1.5 sunlight. By optimizing the thickness of ordered mp-TiO2 to 700 nm, the CYC-B11 showed the highest efficiency of 3.66%. | 3 27 |
| 16:30 | Understanding the polymer microstructure of P3HT/metaloxide hybrids for photovoltaics Authors : M.I. Saba(1,2), C. Melis(1,2), G. Malloci(1), L. Colombo(1,2), and A. Mattoni(1,2) (1) Istituto Officina dei Materiali del CNR, Unità SLACS, Cittadella Universitaria, Monserrato (Ca), 09042, Italy. (2) Dipartimento di Fisica, Università di Cagliari, Cittadella Universitaria,Monserrato (Ca), 09042, Italy. Affiliations : Resume : Polymer based hybrids have emerged as promising systems for photovoltaics combining the formability of polymers and the good trasport properties and thermal stability of the inorganic component. The actual microstructure of the polymer close to the inorganic substrate (where electrons are accepted) critically controls the properties of the system.
We adopt molecular dynamics (MD) simulations to generate models of poly3hexylthiophene (P3HT) interacting with inorganic nanostructured substrates, such as titanium dioxide (TiO2), zinc oxide (ZnO). We provide evidence that the polymer organization at the interface strongly affects the properties of the hybrid system. It is found that the polymer adhesion depends on the curvature at the nanoscale and on the local charge of the metaloxide[1]. Furthermore, the polymer assembling[2] at the interface critically affects the transport properties. In particular, by studying the P3HT/ZnO systems we find a spontaneous tendency of the polymer to be disordered close to ZnO, strongly decreasing the carrier mobility at the interface[3].This work is funded by the Italian Institute of Technology (IIT) under Seed Project “POLYPHEMO” and Regione Autonoma della Sardegna under Project “Design di nanomateriali ibridi organici/inorganici per l’energia fotovoltaica” L.R.7/2007.
[1] C. Melis, A. Mattoni and L. Colombo, J. Phys. Chem C 114, (2010) 3401
[2] C. Melis, L. Colombo, and A. Mattoni, J. Phys. Chem. C (2010), in press
[3] M. I. Saba et al., in preparation | 3 28 |
| 16:30 | Anodic ordered titania nanostructures and in-situ electropolymerized poly-3-methylthiophene films for hybrid photovoltaic solar cells Authors : Nagore Imaz, Oihana Zubillaga, Gorka Imbuluzqueta, Francisco Cano TECNALIA, Solar Energy Department, 20009 San Sebastian, Spain. Affiliations : Resume : In the field of hybrid photovoltaic cell technology, the present work aims studying titanium dioxide layers with ordered nanostructure obtained by anodisation and poly-3-methylthiophene polymeric films in-situ electropolymerised onto these titania films. The poly-3-methylthiophene is considered to be a cost-effective conducting polymer, with the challenge that it can not be solution processed as currently used ones.
Regarding the TiO2 layers, the influence of anodisation voltage and process time on film thickness, morphology and porosity was studied for two different electrolytes, one based on water and hydrofluoric acid, and the second one on ethylene glycol and ammonium fluoride. The FESEM analysis showed titania films with different ordered nanomorphologies, as nanoporous layers, nanotube network and arrays composed of differentiated nanotubes. The film thickness ranges from 30 nm up to one micrometer, whereas nanopores or tube diameters from 20nm to 60nm were observed.
Concerning the electropolymerisation, influence of time and voltage was as well studied for different oxides. Minimum voltages between 2.5 and 3.0V and process times between 90 and 180s were established depending on the oxide morphology and thickness. Poly-3-methylthiophene films with a thickness in the range of 250-800nm were obtained, corresponding the lowest values for titania films of lowest thicknesses with nanomorphologies without differentiated nanotubes. | 3 29 |
| 16:30 | Koopmans’ transfer integral calculation: a comparison between the Hartree-Fock and the Density functional results Authors : Massimo Ottonelli, Matteo Piccardo, Daniele Duce, Sergio Thea, Giovanna Dellepiane Dipartimento di Chimica e Chimica Industriale -Via Dodecaneso, 31 -16146 Genova (Italy) Affiliations : Resume : Conjugated organic systems are gaining importance with respect to inorganic semiconductors as materials for developing a wide class of devices such as: OLED, sensors and solar cells. In all these applications a prerequisite to improve the performance of devices is the optimization of the charge transport process. For organic molecules, this process could be essentially described by a non-adiabatic polaron hopping within the high temperature limit modeled by the Marcus theory. One of the fundamental parameters in the Marcus equation is the intermolecular transfer integral J, that is strongly dependent on the relative distance and orientation among the molecules involved in charge hopping. For this reason, modeling the charge transport requires molecular dynamics techniques which have to take into account bulk molecular organization, and accurate and efficient methods for calculation of J. In the literature two distinct approaches are followed: the first one is the well known “energy-splitting-in-dimer” method, the second one evaluates J directly from the coupling element of the frontier orbitals. Both approaches were initially used in the framework of the Hartree-Fock Hamiltonian; more recently, the DFT ones are used. To our knowledge a systematic investigation based on a comparison between the results obtained by using the two different Hamiltonian models in the calculation of J is lacking. To overcome this point, we report here results obtained for a series of conjugated oligomers model using different density functional as well as the Hartree-Fock Hamiltonian. Results will be also discussed in the framework of the Koopmans theorem. | 3 30 |
| 16:30 | Hybrid Solar Cells with Electrodeposited ZnO Layers Authors : Sylvia Sancheza, Solenn Bersonb, Stéphane Guillerezb, Claude Lévy-Clémentc, Valentina Ivanovaa aCEA-Leti, MINATEC Campus, 17 rue des Martyrs - 38054 GRENOBLE Cedex 9, France bCEA-INES, Laboratoire des Technologies des Modules Photovoltaïques, Savoie Technolac BP 332, 50 Avenue Du Lac Léman, 73377 Le Bourget Du Lac, France cCNRS, Institut de Chimie et des Matériaux de Paris-Est 2-8 Rue Henri Dunant, 94320 Thiais, France sylvia.sanchez.@cea.fr Affiliations : Resume : In the last years zinc oxide (ZnO) became very attractive material in the domain of photovoltaic due to its very interesting optical and electrical properties such as a direct bandgap (3.3 eV), a large exciton binding energy (60 meV), a good electron conductivity. It is important to propose an effective way for preparing ZnO 2D layers and nanowires with the aim to use them for elaboration of nanostructured solar cells like eta-solar cells, dye sensitized and hybrid polymer solar cells. The configuration with single crystal ZnO nanowires appears to be very attractive due to the high electron mobility and structured morphology that leads to high contact area with the absorbing material and light trapping effect.
In this study we report on the integration of electrochemically prepared ZnO 2D layers and nanowires in inverted organic/hybrid polymer solar cells. Among different preparation methods the electrochemical deposition appears as a good solution since it proposes a better control of ZnO nanostructures morphology. By this method ZnO is deposited at temperatures below 100°C from an aqueous salt solution and molecular oxygen. A comparing study was lead in function of the process, the structure, the ZnO layer thickness and of the substrate. The polymer solar cells prepared by this method showed good efficiencies as high as 3.2% and high stability under continuous illumination. | 3 31 |
| 16:30 | Energy Level Alignments via Interface Modifiers in Mesoporous TiO2-P3HT Hybrid Solar Cells Authors : Jufong Yu, Tsung-Lung Shen, Wei-Hsiang Weng, Yu-Zhen Huang, Ching-I Huang, Wei-Fang Su, Leeyih Wang Affiliations : Resume : A series of conjugated molecules was utilized as interface modifiers (IMs) of mesoporous titania in hybrid solar cells to facilitate the photo-induced electron transfer from P3HT to TiO2. By either combining cyanoacetic acid group with multiple numbers of thiophene ring or conjugated donor-acceptor units, the LUMO level of IMs was shifted to be lower than the LUMO of P3HT but higher than the conduction band of TiO2.
Photovoltaic measurements showed the short-circuit current density increases with decreasing badgap of IMs. Moreover, the orientation and strength of the dipole moment in IMS have decisive influence on the open-circuit voltage. The device with 2-cyano-3-(5-(7-(thiophen-2-yl)benzothiadiazol-4-yl)thiophen-2-yl)acrylic acid (W4) as IMs exhibits the best power conversion efficiency (η) of 2.87% with an open-circuit voltage (VOC) of 0.8V, a short-circuit current (JSC) of 6.79 mA/cm2 and a fill factor (FF) of 53% under A.M. 1.5G simulated illumination at 100 mW/cm2. Importantly, the graph of external quantum efficiency (EQE) clearly demonstrated that both W4 and P3HT make contribution to the photocurrent, suggesting the efficient cascaded electron transfer from P3HT to TiO2 via W4. This finding reveals that suitable alignment of energy levels of inorganic, IMs and polymer is an important approach in improving the photovoltaic performance of hybrid solar cells. | 3 32 |
| 16:30 | Effect of Pd impurities on the drift hole mobility of a fluorene copolymer Authors : Francesca Tinti2, Andrea Pellegrino1, Annalisa Congiu1, Sara Perucchini1, Chiara Carbonera1, Riccardo Po’1, Alessandra Tacca1, Nadia Camaioni*2 1. Research Centre for non Conventional Energies Istituto Eni Donegani, ENI S.p.A, Via Fauser 4, 28100 Novara (Italy) 2. Istituto per la Sintesi Organica e la Fotoreattività (CNR-ISOF), Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy Affiliations : Resume : Charge carrier mobility is a key parameter for the performance of electronic devices based on conjugated polymers as semiconductors, such as field-effect transistors, light-emitting diodes and solar cells. For example, poor charge carrier mobility limits the thickness of the photoactive layer of polymer solar cells, thus limiting their solar light harvesting ability.
Charge transport in conjugated polymer films takes place by hopping through a manifold of localized states, so carrier mobility is intrinsically low for this kind of systems and affected by a lot of parameters. Apart from charge delocalization, factors such as molecular weight, regioregularity, the position and nature of the side-chain groups, as well as chemical purity play a relevant role for charge transport properties of conjugated polymer films.
In this study the effect of Pd impurities on the drift mobility of positive carriers in films of a fluorene copolymer (PFB-co-FT) is investigated by Time-Of-Flight technique. Two PFB-co-FT (F: fluorene, T: thiophene, B: benzothiadiazole) samples were used and compared, differing for the Pd content (3360 ppm or 9 ppm, depending on the purification process). | 3 33 |
| 16:30 | Bonding and electronic band alignment between nano-porous ZnO and a metal Phthalocyanine dye Authors : Pablo Palacios a,c , Perla Wahnón a,b, B. Marí d a) Instituto de Energía Solar. Universidad Politécnica de Madrid, Ciudad Universitaria, 28040, Madrid, Spain b) Dpt. Tecnologías Especiales Aplicadas a la Telecomunicación, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040, Madrid, Spain c) Dpt. Física y Química Aplicadas a la Técnica Aeronáutica, Escuela de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid. Ciudad Universitaria, 28040, Madrid, Spain d) Departament de Física Aplicada – IDF, Universitat Politècnica de València, Camí de Vera s/n, 46022 València, Spain Affiliations : Resume : In this presentation we study the geometrical approach and band alignment between metal tetra-sulphonated phthalocyanines (M-Pc) and nano-porous ZnO. Both can be proposed as the two components of a hybrid organic-inorganic solar-cell. The theoretical calculations are being made using the density functional theory (DFT) using a GGA functional with the SIESTA code. For the M-Pc's we study the more stable geometry and the HOMO and LUMO for different metals (Zn and Cu) finding the most reacting part. The molecule is flat except the sulphonic groups which can freely rotate. This groups are necessary in order to solubilize the system in a real experiment, so the chosen working molecules was the Metal phthalocyanine-3,4’,4’’,4’’’-tetrasulfonic acid, tetrasodium salt, (TsPcMe). The effect of these groups on the interaction with the nanostructure appeared to be very important for the bonding and not only for the molecule solubility. The (001) growth direction for the ZnO was studied, so the available faces to the dyes will be a perpendicular one as the (100).After that we study the interaction between the two systems and compared the different electronic energy levels. A good estimation of band alignments between the adsorbate and the substrate was achieved with DFT+U, using the correlation corrections that gave good spectra for both systems separately. This theoretical study can be seen as a first step to show how charge transfer would be. | 3 34 |
| 16:30 | The influence of polyesterification degree of titanium sol on dye sensitized solar cell efficiency Authors : Marija Drev1,2, Urša Opara Kraševec1, Mateja Hočevar1, Marko Berginc1, Marjeta Kržmanc Maček3, Mojca Japelj Fir2, Marko Topič1 1University of Ljubljana, Faculty of Electrical Engineering, SI-1000 Ljubljana, Slovenia 2CBS Institute, SI-8210 Trebnje, Slovenia 3Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia Affiliations : Resume : A dye sensitized solar cell (DSSC) is a relatively new class of a low cost solar cell that chemically generates electricity using its ability to create an electron when a dye absorbs sunlight. Typically DSSC consists of a transparent conductive glass substrate, electron transport layer with adsorbed photosensitized dye generating electrons; electrolyte containing I-/I3- redox couple, which supplies electrons back to the dye; and a counter electrode coated with a thin layer of platinum. The electron transport medium is, usually nanostructured porous TiO2 layer.
For the preparation of the effective TiO2 layers the modified Pechini type method has already been successfully developed. In this study the influence of polyesterification degree in titanium sol (Ti-sol) prepared by Pechini method on the grain size of the anatase TiO2 nanopowder obtained after annealing of the Ti-sol is studied. Different content of the polyester in the Ti-sol was realized with different heating time of the Ti-sol. Results show that prolonged heat treatment of Ti-sol leads to the formation of smaller grain size of nanopowder with higher specific surface area. The TiO2 nanopowder prepared by Pechini method and commercial one were incorporated into the Ti-sol to prepare TiO2 pastes. TiO2 layers were tested as photoanodes in DSSCs and their efficiencies are compared. | 3 35 |
| 16:30 | Development of new photovoltaic solar cell based on organic photoactive materials Authors : S. Ben Dkhil a,b,*, J. Davenas b, R. Bourguiga a a Laboratoire Physique des Matériaux: Structures et Propriétés Groupe Physique des Composants et Dispositifs Nanométriques, Facultés des sciences de Bizerte, 7021 Jarzouna-Bizerte, Tunisia. b Ingénierie des Matériaux Polymères et Biomatériaux : LMPB, UMR CNRS 5223, 43 boulevard du 11 Novembre 1918, Université Claude Bernard-Lyon1, 69622 Villeurbanne, France. Affiliations : Resume : Nanostructures or nanostructured materials offer new opportunities to reduce both cost and size and to improve the efficiency of photovoltaic devices. Recently, the incorporation of inorganic nanostructures into conjugated polymer matrices has become a subject of growing interest for large area applications, in particular in the fields of optoelectronics and solar energy. Advantages will result from the association of the beneficial properties of both materials: low-cost conversion of solar energy to electricity of conjugated polymers and high electron mobility of inorganic nanostructures. Nanostructured thin films present another main interest coming from their high interface area and reduced average distance from any point to an interface. As the separation of photogenerated charge carriers occurs at interfaces between electron donors and acceptors, a photocurrent enhancement is expected in comparison to simple bilayer structures. Poly (N-vinylcarbazole) (PVK) is one of the most intensively studied materials for blue electroluminescence emission. It is a typical hole-transporting polymer which is often used in electroluminescence devices. Silicon nanowires are remarkable materials, which are presently being intensively studied in both fundamental and applied research fields, due to their outstanding physical, electronic and optical properties. Photovoltaic cells based on silicon nanowires have emerged as promising candidates for solar energy harvesting. In this study, we have fabricated hybrid photovoltaic solar cells consisting of PVK as a p-type semiconducting polymer and n-type SiNWs. The morphology of photo-active layers based on PVK: SiNWs nanocomposite has been studied by scanning electron microscopy (SEM). The characteristics of this new photovoltaic solar cell offer new opportunity of application and enlarge its usage in industrial field | 3 36 |
| 16:30 | Understanding opto-electronic processes in MEHPPV-incorporated meso-porous TiOx hybrid photovoltaic materials Authors : Micha Gal1, Shany Neyshtadt2, Gitti Frey2, Iris Visoly-Fisher1 1Dept. of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben Gurion University of the Negev, Be’er Sheva, Israel 2Dept. of Materials Eng. and Russel Berrie Nanotechnology Institute, Technion – Israel Inst. of Technology, Haifa, Israel Affiliations : Resume : Hybrid organic-inorganic donor-acceptor systems have been suggested as low-cost, stable alternatives for solar energy conversion. Efficient charge generation and transport in such systems requires an organic-inorganic phase separation on a sub 20 nm length scale. Hybrid photovoltaic films comprised of MEH-PPV incorporated into meso-porous TiOx comply with these demands. Here, surface photo-voltage spectroscopy is used to identify the location and mechanism of photo-current generation and transport in such hybrid photovoltaic film.
We find that photovoltaic current is generated in the hybrid material when exposed to either 376 or 532 nm, indicating that both MEH-PPV and TiOx absorption contribute to current generation. The films’ photo-response to 376nm illumination reflects the role of MEHPPV in improving the transport of holes generated by TiOx absorption. Holes that were otherwise "stuck" due to low mobility in amorphous TiOx, are more mobile in the MEHPPV and may contribute to the photocurrent thus increasing the efficiency of the device in the UV wavelengths. TiOx response to sub-bandgap illumination points to the presence of abundant surface states which may trap photo-generated charges. Small MEHPPV uptake and the discontinuity of the polymer phase in the hybrid limit its contribution to photocurrent generation and transport, making a top MEHPPV layer, added to the cell structure as an electron blocking layer, very significant in the cell’s photovoltaic performance. | 3 37 |
| 16:30 | In Search of the Most Advantageous Processing Route of TiO2 Hole Blocking Layer for Hybrid Solar Cell Devices Authors : Diana C. Iza1, David Muñoz-Rojas1, Jonas Weickert2, Holger C. Hesse2, Andreas Wisnet3, Markus Thomann3, Lukas Schmidt-Mende2, Judith L. MacManus-Driscoll1 1. Materials Science and Metallurgy, University of Cambridge, Cambridge, United Kingdom. 2. Department of Physics & Center for NanoScience, Ludwig-Maximilians University (LMU) Munich, Munich, Germany. 3. Department of Chemistry and Center for NanoScience, Ludwig-Maximilians University (LMU) Munich, Munich, Germany. Affiliations : Resume : In the last few decades solar energy has started being harvested to help meet global demand, and stands as one of the most promising green energy sources to meet energy needs by the middle of this century. Hybrid solar cells provide a balance between cost and efficiency of these devices, which is needed to compete with current energy sources and thus achieve mass implementation. For such cells, the polymer is processed below 150 °C and it is important to grow the oxide in highly crystalline form at the lowest possible temperature. However, high quality oxides are traditionally grown at high temperatures. In our group, we are developing technologies to grow high quality oxides at lower temperatures. In this work, hybrid devices were produced using titanium dioxide (TiO2) as a hole blocking layer in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) devices. The titanium dioxide hole blocking layers were produced via four different methods to determine the effect processing conditions have on over-all photovoltaic performance. Electrochemical deposition (ED), sputtering (SPU), spray pyrolysis (SPR) and atmospheric atomic layer deposition (AALD) were used to produce the TiO2 films. Cell devices were then made in the same batch using the different films in order to reduce any differences arising from other manufacturing stages. Sputtered, spray pyrolysed and AALD layers resulted in the higher performing devices achieving efficiencies of up to 3%. Electrodeposited films, on the other hand, presented cracks and more defects associated with them, resulting in shunt paths in the films and lower performing devices. Despite SPU, SPR and AALD films showing similar performances, the advantages of AALD are highlighted as it is a reliable, no vacuum, low temperature, and easily scalable process offering conformal coating and high crystallinity at low temperatures. | 3 38 |
| 16:30 | Understanding the Poly(3-hexylthiophene) helical wrapping on carbon nanotubes and zinc oxide nanoneedles Authors : C. Caddeo(1,2), C. Melis(1,2), L. Colombo(1,2), and A. Mattoni(1) (1) Istituto Officina dei Materiali del CNR, Unità SLACS, Cittadella Universitaria, Monserrato (Ca), 09042, Italy (2) Dipartimento di Fisica, Università di Cagliari, Cittadella Universitaria,Monserrato (Ca), 09042, Italy Affiliations : Resume : We study Poly(3-hexylthiophene) (P3HT) wrapping on singlewalled carbon nanotubes (SWNTs) and hexagonal zinc oxide nanoneedles.
By using molecular dynamics simulations we generate models of realistic size and we study the morphology and evolution of the
polymer at finite temperatures.
In the case of SWNT[1], we provide evidence that the experimentally observed polymer helical organization is metastable in vacuo and its lifetime is a function of the temperature and the polymer length.
The unwrapping is thermally activated with an energy barrier as small as 0.09 eV. Our results at room temperature reproduce the experimentally observed pseudo-helical morphology of the polymer
and confirm the role of the nanotube chirality.
In the case of zinc oxide nanoneedles[2], the wrapped configurations are stable in vacuo due to the lower mobility of the polymer on the metaloxide surface.
We identify the lowest energy configurations and we discuss the role of the surface cristallography on
the polymer organization.
This work is funded by the Italian Institute of Technology (IIT) under Seed Project “POLYPHEMO” and Regione Autonoma della Sardegna under Project “Design di nanomateriali ibridi organici/inorganici per l’energia fotovoltaica” L.R.7/2007.
[1] C. Caddeo, C. Melis, L. Colombo, and A. Mattoni, J. Phys. Chem. C 114 (2010) p. 21109
[2] C. Caddeo et al. in preparation | 3 39 |
| 16:30 | Caracterisation P3HT/PCBM/CdSe hybrid solar cell Authors : hepia, University of Applied Sciences of Western Switzerland, Geneve, Switzerland Affiliations : Resume : We have investigated the effect of adding CdSe quantum dots (QD’s) on ITO/SPT/PH3T- PCBM bulk heterojunction organic photovoltaic cells (OPV). During the manufacturing of the cells, the optical absorbance, the thickness and the nanotopography (measured by AFM and interferometric microscopy) of each layer have been analysed before and after various thermal treatments. Best performances were found for a post cathode deposition annealing at 150°C during 10 min under Ar atmosphere. In order to track the lateral inhomogeneity of the final device, the I-V characteristics have been mapped (home-made setup) , over the entire surface cell (2cm x 2cm) with a definition of 200pts x 200pts. We have established a correlation between the QD’s particles size, concentration and absorbance with the performances of the hybrid P3HT/PCBM/CdSe cells . Degradation over UV illumination has been characterized as well. | 3 40 |
| 16:30 | Aligned TiO2 nanocolumnar layers prepared by PVD-GLAD for transparent Authors : Lola González-Garcíaa, Irene González-Vallsb, Mónica Lira-Cantub, Angel Barrancoa, Agustín R. González-Elipea a, Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Avda. Américo Vespucio 49; 41092 Sevilla, Spain. b, Centre d’Investigació en Nanociència i Nanotecnologia (CIN2), Campus UAB, Edifici ETSE, Bellaterra, 09819, Spain Affiliations : Resume : The use of 1D vertically-aligned nanostructures (nanorods, nanowires or similar) is known to effectively enhance the electron transport in different excitonic solar cells (organic, dye sensitized, hybrid). A possibility in this context is the use of porous TiO2 thin films prepared by physical vapor deposition at glancing angles GLAD) . The layers obtained by this method consist of aligned nanocolumns showing well-controlled oblique-angles. These nanostructured mesoporous thin films are characterized by low refractive indices and a very good transparency.
Herein transparent thin film electrodes made of vertically aligned nanocolumns of TiO2 with well-controlled oblique angles grown by PVD-GLAD are presented. In this study, for an electrode thickness of 500 nm, we report a 40% variation on solar cell efficiency (from 0.6% to 1.04%) when the deposition angle was modified between 60º and 85º. Transparent thicker films with higher surface area deposited at the optimal angle of 70º were grown with a zigzag morphology which confers high mechanical strength to the films. Using this topology, the application of an electrode thickness of 3 mm in a DSC resulted in a power conversion efficiency of 2.78% maintaining electrode transparency. | 3 41 |
| 16:30 | Dye directed changes in sensitized solar cells and influence of process steps on properties of inorganic matrix ZnO Authors : Harald Graaf (a), Franziska Lüttich (a), Mirko Kehr (a), Christian Dunkel (b), Michael Wark (b) and Torsten Oekermann (b); (a) Chemnitz University of Technology, Institute of Physics, 09126 Chemnitz, Germany (b) Institute of Physical Chemistry and Electrochemistry, Leibniz University Hannover, 30167 Hannover, Germany Affiliations : Resume : Dye-sensitized photovoltaic cells with zinc oxide (ZnO) as the inorganic semiconductor and organic dye molecules as Eosin Y (EY) or Coumarin 343 (C343) as the sensitizer are well known devices with high efficiency. Such cells are prepared by electrochemical deposition of an aqueous zinc salt solution including dye molecules leading to a complex organic/inorganic hybrid film. The dye molecules have a strong influence on the growth and therefore the crystal orientation of the inorganic matrix. With EY the typical (001) orientation of the ZnO can be obtained, which can be obtained also for pure ZnO films. C343 instead causes a (100) orientation of the ZnO. The morphology of these films depends further strongly on the preparation conditions.
After the deposition the dye is desorbed to obtain a porous ZnO network followed by re-adsorption of the dye as a sensitizer. Structural changes of the ZnO are accompanied by the desorption process, which is performed in an alkaline aqueous solution. Additionally a reduction of trap states in the ZnO can be found. Both processes are due to a dissolving of a thin layer of ZnO followed by a recrystallization leading to a well ordered and trap free surface.
Different methods as X-ray spectroscopy, Kelvin Probe Force Microscopy, Atomic Force Microscopy, Scanning Electron Microscopy and optical reflection measurements are used to obtain a deep insight in the properties of the prepared films | 3 42 |
| 16:30 | simulation of DSC :through and beyond one dimension Authors : Desirée Gentilini University of Rome Tor Vergata Alessio Gagliardi University of Rome Tor Vergata Aldo di Carlo University of Rome Tor Vergata Affiliations : Resume : Among organic and hybrid photovoltaic devices, Dye Solar Cells are the most efficient on small area with a wide room for improvment.
We developed a Finite Element Method based simulation tool to reproduce steady state characteristic output (carrier density profiles, IV curve, efficency) of DSC under different working conditions and with different geometries up to 3-dimensions.
We compare the simulation results with the experimental data through an IVcurve fitting procedure. This allows us to exctract quantitatively crucial parameters of the model as charge mobility and recombination rate constants in particular working conditions and using different fabrication processes .
Furtermore the ranges of parameters found by the comparison with the experimental data are used to performe a systematical parametrization of the performance of the cells collected in maps of efficiency where the geometry of the cell is varied.
A strength of DSCs is the possibility of fabricating innovative geometries, like cylindrical DSCs obtained wrapping the cell around an optical fiber. All these new devices need a full 3D simulator to be investigated and improved.We are able to study the variation of the maximum current of these devices varying the illumination inside the cell and the impact of the external contact shape performing 3D simulations. | 3 43 |
| 16:30 | A Time-Dependent Density Functional Theory Study on Benzothiadiazole-Based Low-Band-Gap Fused-Ring Copolymers for Organic Solar Cell Applications Authors : Jamin Ku,(1) Yves Lansac,(2) Yun Hee Jang(1) (1) School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea; (2) Laboratoire d’Electrodynamique des Matériaux Avancés, Université François Rabelais, Tours 37200, France Affiliations : Resume : Organic solar cells need low-band-gap polymers for efficient harvesting of sunlight. Copolymers with alternating electron-rich and electron-deficient units have low band gaps. High-efficiency can be reached with the optimum combination of those units. For this purpose we constructed four systematically-altered copolymers, where a promising benzothiadiazole (BT) electron-deficient unit is connected to each of four fused-ring electron-rich units: fluorene (Fl), carbazole (Cz), cyclopentadithiophene (CPDT), and dithienopyrrole (DTP). The TDDFT/DFT calculations at the B3LYP/6-311G(d,p) level on the dimer models of these copolymers reproduced very well their geometries, HOMO/LUMO levels and band gaps. The calculation shows that the CPDTBT and DTPBT units exhibit lower band gaps and stronger absorption of visible light than the FlBT and CzBT units. The calculation also indicates that the CPDTBT unit, which has deeper HOMO/LUMO levels than the DTPBT unit, exhibits the highest solar cell efficiency (~3%) among the four systems. Based on these results, we propose several CPDTBT derivatives with electron-withdrawing groups, which have even deeper HOMO/LUMO levels than CPDTBT, as promising donor polymers for high-efficiency (4~6%) organic bulk heterojunction solar cells. | 3 44 |
| 16:30 | Synthesis of New Acceptor Materials for Organic Photovoltaics Authors : Burak Gultekin, Banu Aydin, Ceylan Zafer, Siddik Icli Ege University Solar Energy Institute, Izmir-TURKEY Affiliations : Resume : Especially in the last decade, Organic Photovoltaic (OPV) research has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Despite the inorganic materials, organic materials are abundant and easily handling. Unfortunately OPV cells efficiency is significantly lower than that of inorganic-based devices, representing a big point of weakness at the present. This is mainly due to the fact that organic semiconductors have a much higher band gap with respect to inorganic semiconductors [1]. In addition, OPV cells are very sensitive against oxygen and water [1]. It is well documented by many groups that OPV devices fabricated using poly(3-hexylthiophene) (P3HT) donor and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) acceptor gives power conversion efficiencies (PCE) about 5% [2]. There are several groups worldwide working on developments of new low bandgap donor polymers to enhance PCE further up to 8.3% using PCBM acceptor [3]. Although there are other varieties of new donor materials that have been synthesized for OPV, there are not so many electron acceptor materials useful for organic photovoltaics [4-6]. PCBM based devices have relatively high power conversion efficiencies due to its strong tendency to accept electrons from donor semiconducting polymers at short timescales and the formation of suitable nanoscale morphological network with these polymers. Due to poor absorption in the visible spectrum of PCBM and other fullerene derivatives, it is needed to develop inexpensive alternate acceptor materials with high performance.
In this study, we present two new n-type organic molecules based on perylene and naphthalene with high electron withdrawing cyano moieties for OPV applications. Generally, perylene and naphthalene derivatives have good visible region absorption and high electron mobility. In the semi-empirical molecular orbital calculations, both dyes show good charge separation.
References
1) G. Chidichimo and L. Filippelli, International Journal of Photoenergy, Volume 2010, Article ID 123534
2) W. Ma, C. Yang, X. Gong, K. Lee and A. J. Heeger, Adv. Funct. Mater., 2005, 15, 1617
3)http://www.konarka.com/index.php/site/pressreleasedetail/konarkas_power_plastic_achieves_world_record_83_efficiency_certification_fr
4) P. Sonar, Ging-Meng Ng, T. T. Lin, A. Dodabalapur, and Z.-K. Chen, J. Mater. Chem., 2010, 20, 3626–3636
5) N. C. Greenham, S. C. Moratti, D. D. C. Bradley, R. H. Friend and A. B. Holmes, Nature, 1993, 365, 628;
6) (b) G. Hughes and M. R. Bryce, J. Mater. Chem., 2005, 15, 94. | 3 45 |
| 16:30 | Comparative Studies on Diffusion and Charge Resistance Parameters of Different Ionic Liquids in Dye Sensitized Solar Cell by Impedance Measurements Authors : Banu Aydin, Saliha Ozdemir, Ceylan Zafer, Canan Varlikli, Siddik Icli Ege University Solar Energy Institute, Izmir- TURKEY Affiliations : Resume : In this work, we studied the electrochemical characteristics of dye-sensitized solar cells using four different ionic liquids as electrolytes and we compared their responses with a solvent –containing electrolyte cell. Impedance spectroscopy is a useful technique for determination of important cell parameters such as recombination resistance, chemical capacitance and diffusion parameters of a dye-sensitized solar cell. Volatility of the solvents employed is an important issue for long term device performance. Solid or nonvolatility phase electrolyte is an alternative of organic solvent containing electrolyte. Room temperature ionic liquids (RTIL’s) have high ionic conductivity and high thermal stability. These properties make them useful for dye sensitized solar cells applications.
Initially, for the measurements, we prepared our cells with 0.6 M iodide ionic liquid, 0.1 M LiI (Lithium iodide), 0.05 M I2 and 0.5 M TBP (4-tert-butylpyridine) and as an electrolyte solvent MPN (3-methoxypropionitrile) was used. Our room temperature ionic liquids were ALIL4, AEII, AMII and we used PMII as a reference. For determining diffusion parameters, we prepared two electrode sandwich cells. Subsequently, we characterized diffusion coefficients of ionic liquids and electron lifetime of dye-sensitized solar cell. For fitting experimental curves with our model’s curves we used impedance analyzer. We fitted the impedance curves with suitable models. Our models include Warburg diffusion parameters and double layer capacitance.
Consequently, AEII gave a diffusion coefficiency with a rate of 1.7538E-7 cm2s-1 while calculated diffusion coefficiency of reference, PMII was 2.0572E-7 cm2s-1. This result showed that AEII could be an alternative material for dye-sensitized solar cells containing ionic liquid as an electrolyte. | 3 46 |
| 16:30 | Nanostructured Organic Photovoltaics from Contorted Hexabenzocoronenes Authors : Alon A. Gorodetsky, Marshall Cox, Chien-Yang Chiu, Ioannis Kymissis, and Colin Nuckolls Affiliations : Resume : We have established a new approach to efficient organic photovoltaics (OPVs) that take advantage of the complementary geometry of contorted donor molecules (hexabenzocoronene, HBC) and spherical acceptor molecules (buckminsterfullerene, C60). We have synthesized a wide range of contorted donor materials, which demonstrate favorable properties including templated assembly of robust organic/organic interfaces, formation of supramolecular three-dimensional networks, and environmentally sensitive shape-shifting. These properties have enabled us to design and fabricate devices with power conversion efficiencies that approach state-of-the-art values for small molecule organic photovoltaics. Furthermore, we have demonstrated the first instance of a “truly organic” solar cell from contorted hexabenzocoronenes, where graphene functions as both the cathode and the anode. Overall, our findings may hold significant implications for inexpensive and efficient solar energy conversion technologies. | 3 47 |
| 16:30 | Organoboron polymers for high-efficiency flexible solar cells Authors : Simone Fabiano,a Sebastiano Cataldo,a Francesco Ferrante,a Francesco Previti,b Salvatore Patanè,b and Bruno Pignataro a a Dipartimento di Chimica “S. Cannizzaro”, Università di Palermo, V.le delle Scienze, Parco D’Orleans II - 90128 Palermo - Italy; e-mail: bruno.pignataro@unipa.it b Dipartimento di Fisica della Materia ed Ingegneria Elettronica, Università di Messina, salita Sperone 31 - 98100, Messina - Italy Affiliations : Resume : We report on the development of flexible all-polymer solar cells by using three-coordinate organoboron polymers. These systems are inherently strong electron acceptors due to the vacant p orbital of the boron atom. In particular, the n-type polymer poly[(1,4-divinylenephenylene) (2,4,6 triisopropylphenylborane)] (PDB) has been blended with poly(3-hexylthiophene-2,5-diyl) (P3HT) to form a thin film bulk heterojunction (BHJ) on (PET/ITO) substrates. Morphology has been modulated to give a high percentage of domains (10-20 nm in size) allowing for efficient exciton separation. The photoelectric properties of devices built up with aluminium back electrodes were imaged by Light Beam Induced Current and Light Beam Induced Voltage methods. Results show open circuit voltages (ca. 1 V), short circuit current density (ca. 6 mA/cm2), overall external quantum efficiencies (EQE, 12%) and power conversion efficiency (ca. 3%) among the highest reported for all-polymer PV cells. | 3 48 |
| 16:30 | Conducting Polymers Based Photoelectrochemical Solar Energy Conversion Authors : Teketel Yohannes Addis Ababa University College of Natural Science Department of Chemistry P.O.Box 1176 Addis Ababa, Ethiopia Affiliations : Resume : Solar energy is one of the most promising renewable energy sources for our future energy needs. Energy from the sun is not only available in plentiful supply, but also introduces no direct contamination of the environment. As a result considerable research work has been aimed at harnessing solar energy.
The utilization of organic materials for photovoltaic devices has been investigated intensely during the last three decades. Earlier studies concentrated on molecules that had high optical absorption in the visible region of the electromagnetic spectrum. Conjugated polymers having semiconductor-like behavior are not only able to function in a similar manner to the inorganic semiconductors but also have important advantages such as: low cost, light weight, ease of fabrication and the possibility of large area coatings.
Here we present an overview on the studies carried in our research group on conducting polymers based photoelectrochemical solar energy conversion. | 3 49 |
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