Symposium : H
|Charge Transport and Photophysics of Organic Semiconductors : Thomas Anthopoulos|
|08:30||Charge transport in high mobility conjugated polymers|
Authors : H. Sirringhaus
Affiliations : University of Cambridge, Cavendish Laboratory
Resume : Conjugated polymer semiconductors offer new opportunities for the controlled manufacturing of active electronic circuits by a combination of solution processing and direct printing. In recent years polymer semiconductors with charge carrier mobilities above 1 cm2/Vs have been discovered. In this talk we will discuss recent insights into the charge transport physics of these materials with a particular focus on the microscopic processes that limit the field-effect mobility and the structure-property relationships.
|09:00||Picosecond charge photogeneration and transport in porphyrin wires|
Authors : J. Cabanillas-Gonzalez, M. Mróz, L. Lüer, and H. L. Anderson
Affiliations : Instituto Madrileño de Estudios Avanzados (IMDEA-Nanociencia), Cantoblanco, 28049-Madrid, Spain; Dipartimento di Fisica, Politecnico di Milano, Pza. Leonardo da Vinci 32, Milano 20133, Italy; Department of Chemistry, University of Oxford, UK.
Resume : Geminate recombination is one of the mechanisms limiting the efficiency of organic solar cells. Thus, the fate of photogenerated e-h pairs depends on the ability for both to move far apart the donor-acceptor interface during the first picoseconds after charge photogeneration. Photoinduced transient stark spectroscopy (PTSS) allows for monitoring charge motion in organic based devices in picosecond timescales. Characterization of these intrinsic material properties is important not only to identify possible efficiency losses but also in order to understand how structural / morphological properties affect operation. We report PTSS measurements in a film based on a porphyrin wire formed by porphyrin molecules linked at meso-meso positions by butadyine spacers. Global fit analysis applied to PTSS spectra and dynamics indicates the interplay of three excited states in the charge photogeneration dynamics: an initial hot excited state which decays non-radiatively populating two thermalized states. In the presence of an electric field charge photogeneration occurs with a highly dispersive dissociation rate. Although the field splits predominantly hot S1* states, a minor effect is still retained on subsequent thermalized states. Subsequent drift leads to an average separation distance of c.a. 6 nm along the field direction. During charge motion the initial mobility reaches 310-2 cm2V-1s-1 followed by a fast mobility drop likely due to thermalization and topological boundaries.
|09:15||Origin of the different transport properties of electron and hole polarons in an ambipolar polyselenophene-based conjugated polymer|
Authors : Zhuoying Chen,1,2 Matthew Bird,1 Vincent Lemaur,3 Guillaume Radtke,2 Jérôme Cornil,3 Martin Heeney,4 Iain McCulloch,4 and Henning Sirringhaus1
Affiliations : (1) Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom (2) CNRS UMR 6242, Institut Matériaux Microélectronique Nanosciences de Provence, Aix-Marseille Université, 13397 Marseille cedex 20, France (3) Laboratory for Chemistry of Novel Materials, University of Mons, B-7000 Mons, Belgium (4) Department of Chemistry, Imperial College, London, SW7 2AZ, United Kingdom
Resume : Understanding the mechanisms limiting ambipolar transport in conjugated polymer field-effect transistors (FETs) is of both fundamental and practical interest. Here, we present a systematic study comparing hole and electron charge transport in an ambipolar conjugated polymer, semicrystalline poly(3,3"-di-n-decylterselenophene) (PSSS). Starting from a detailed analysis of the device characteristics and temperature/charge-density dependence of the mobility, we interpret the difference between hole and electron transport through both the Vissenberg-Matters and the mobility-edge model. To obtain microscopic insight into the quantum mechanical wave function of the charges at a molecular level, we combine charge modulation spectroscopy (CMS) measuring the charge-induced absorption signatures from positive and negative polarons in these ambipolar FETs with corresponding density functional theory (DFT) calculations. We observe a significantly higher switch-on voltage for electrons than for holes due to deep electron trap states, but also a higher activation energy of the mobility for mobile electrons. The CMS spectra reveal that the electrons that remain mobile and contribute to the FET current have a wave function that is more localized onto a single polymer chain than that of holes, which is extended over several polymer chains.We interpret this as evidence that the transport properties of the mobile electrons in PSSS are still affected by the presence of electron traps.
|09:30||High-resolution charge modulation microscopy in high mobility organic transistors|
Authors : Nicola Martino, Calogero Sciascia, Torben Schuettfort, Benjamin Watts, Giulia Grancini, Maria Rosa Antognazza, Margherita Zavelani-Rossi, Christopher R. McNeill, Mario Caironi
Affiliations : Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia; Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia; Cavendish Laboratory, University of Cambridge; Swiss Light Source, Paul Scherrer Institut; Dipartimento di Fisica, IFN-CNR Politecnico di Milano; Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia; Dipartimento di Fisica, IFN-CNR Politecnico di Milano; Department of Materials Engineering, Monash University; Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia
Resume : In organic field-effect transistors (OFETs), the morphological structure of the active layer is one of the main parameters that influence its charge transport properties and thus the functioning of the device. To understand this relationship, it is desirable to have techniques able to locally probe the electronic properties along the channel of a working device. In this contribution we show that with Charge Modulation Microscopy (CMM) it is possible to optically map the charge density in a high-mobility n-type OFET with a lateral resolution of about 500nm; this is achieved by measuring the local polaronic absorption and bleaching features in a laser scanning confocal microscope. We highlight the presence of a micrometric texture of the charge distribution, which, supported also by Scanning Transmission X-ray Microscopy (STXM), can be related to structural variations in the polymeric film. Interestingly, CMM is sensible only to the few-nanometres thick accumulation layer, allowing the investigation of the properties at the semiconductor-dielectric interfacial region where charge transport actually occur. Interesting evolutions of the technique will be presented as well.
|09:45||Photophysics of the Direct Conjugated Bridge in Copolymers|
Authors : Kerr Johnson (1), Michael Sommer (2), Ya-shih Huang (1), Sven Huettner (1), Rhiannon Mulherin (1), Wilhelm Huck (2), Jenny Clark (1), Richard Friend (1)
Affiliations : (1) Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, UK; (2) Melville Laboratory, Department of Chemistry, Cambridge University, Cambridge, CB2 1EW, UK;
Resume : Careful balancing of the morphology requirements of charge generation and charge transport is necessary for efficient organic photovoltaic operation. Diblock copolymers can self-assemble into periodic, ordered nanostructures or act as surfactants to control blend morphology. Conjugated diblock copolymers also allow for interfacial modification in terms of structure, crystallinity and energy levels. It is important to understand the photophysical and electronic behaviour of the conjugated bridge between the two sections of the diblock copolymer as this forms the charge separation interface. The photophysical properties of model ‘end-functionalised’ P3HT molecules have been studied using time-resolved photoluminescence and transient absorption spectroscopy. These materials are novel in that a single electron-accepting F8TBT unit is added directly to the end of the donor P3HT chain. The well defined structure facilitates the study of the initial charge separation step and of charge-transfer (CT) states in materials where conjugation is maintained through the two linked components. In particular, comparison is made between materials in which the F8TBT unit is attached either through the F8 or through the TBT. Conjugation through the TBT unit results in near-instantaneous localisation of a photoexcitation on the chain to the CT state at the conjugated bridge. In contrast, conjugation through the F8 does not and the material exhibits independent P3HT and F8TBT behaviour.
|Organic Photovoltaics I : Dong-Yu Kim|
|10:30||Design of highly functional ternary blends for organic solar cells|
Authors : C. J. Brabec, T. Ameri, F. Machui, N. Li
Affiliations : Friedrich-Alexander Universitat Erlangen-Nurnberg
Resume : Ternary composites were recently suggested as a simple and cost efficient method to expand the spectral sensitivity of otherwise wide bandgap polymers. However, the key in getting high performance from ternary composites is the precise understanding and control of the morphology of the polymer - polymer - fullerene blends. Poly-(3-hexylthiophene-2,5-diyl) (P3HT), a conjugated semi-crystalline organic semiconductor, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), a fullerene derivative, are the two most frequently reported materials used in OPV devices. Their phase behavior and structure-property relation were discussed in great detail. We have investigated various near IR sensitizers to extend the spectral sensitivity of P3HT:PCBM into the near IR regime. Small molecules as well as conjugated polymers were used as sensitizers. Most interestingly, we observed different sensitization thersholds, upon which the device functionality broke down. The mechanism behind the sensitization are discussed in terms of microstructure, ternary phase diagramms, charge transfer reaction and charge transport. Based upon these findings, first design rules for the fabrication of efficient ternary systems are suggested. For the most promising sensitizers we find an increase in the efficiency of P3HT:PCBM cells of up to 50 %.
|11:00||Structure-property relationships for high efficiency organic photovoltaics|
Authors : R.J. Kline, M. Hammond, D.M. DeLongchamp, L.J. Richter
Affiliations : National Institute of Standards and Technology
Resume : Organic electronics has the potential to replace inorganic materials as the active layer in low-cost and large-area electronics. These electronic devices cover applications across displays, sensors, lighting, radiofrequency identification, and photovoltaics. In each of these devices, the performance and properties of the materials will determine the market penetration. For organic photovoltaics, the primary performance metrics are power conversion efficiency (PCE) and environmental stability. The PCE is determined by a combination of the charge generation, charge separation, and charge collection. New, low-band gap polymers are being developed to improve the charge generation by increasing the amount of photons absorbed. In many cases, the increase in charge generation is accompanied by a decrease in the charge separation or collection, resulting in a net lower PCE than the standard poly(3-hexylthiophene) (P3HT). Recently low-band gap polymers have been developed with PCE’s in the range of 6 % to 8 %. The microstructures of these new polymers are very different from P3HT. We will describe a series of complementary measurements used to elucidate the key structural elements such as the domain orientation and crystallinity of these new low-band gap polymers. We will also describe methods for obtaining in-plane oriented polymer films and using this to determine the molecular packing within the crystals. These insights will provide guidelines for the development of new high performance OPV polymers.
|11:15||Influence of aggregation on the performance of all-polymer solar cells containing low-bandgap naphthalenediimide-copolymers|
Authors : Marcel Schubert (1), Daniel Dolfen (2), Johannes Frisch (3), Steffen Roland (1), Robert Steyrleuthner (1), Burkhard Stiller (1), Zhihua Chen (4), Ullrich Scherf (2), Norbert Koch (3), Antonio Facchetti (4) and Dieter Neher (1)
Affiliations : (1) University of Potsdam, Institute of Physics and Astronomy, Karl-Liebknecht-Str. 24-25, 14476, Potsdam (Germany) (2) University of Wuppertal, Macromolecular Chemistry, 42119 Wuppertal (Germany) (3) Humboldt University Berlin, Institute of Physics, Newtonstr. 15, 12489 Berlin (Germany) (4) Polyera Corporation, 8045 Lamon Avenue, Illinois 60077 (USA)
Resume : Naphthalene-diimide (NDI) or perylene-diimide (PDI) containing copolymers are promising alternatives for replacing fullerenes as the electron-accepting phase in organic solar cells. So far, the power conversion efficiencies (PCEs) of all-polymer solar cells comprising NDI/PDI-based copolymers and regio-regular poly(3-hexylthiophene) (P3HT) remained below 1%. It was proposed that the NDI/PDI-copolymers exhibit a strong tendency to aggregate, which promotes long range phase separation and unfavourable nanomorphologies. Our studies of the optical properties of the n-type polymers P(NDI2OD-T2) and P(NDI-TCPDTT) in different solvents reveal a strong tendency to pre-aggregate. This pre-aggregation could be fully suppressed by using suitable solvents with large polarizable aromatic cores. Solar cells prepared from these solvent mixtures showed PCEs of up to 1.4% and high fill factors of up to 70%, which are among the highest reported values for polymer-polymer blends. Finally, SNOM and AFM measurements in combination with optical absorption studies reveal a surprising anticorrelation between the degree of chain aggregation and the photovoltaic device performance.
|11:30||The role of excess energy in the primary event of charge separation in polymer photovoltaic blends|
Authors : Daniele Fazzi 1, Giulia Grancini 1, Margherita Maiuri 2, Hans-J. Egelhaaf 3, Daniele Brida 2, Guglielmo Lanzani 1,2 and Giulio Cerullo1
Affiliations : 1Center for Nano Science and Technology @Polimi Istituto Italiano di Tecnologia, Via Pascoli 70/3 20133 Milano, Italy. 2 Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy. 3 Konarka Technologies GmbH, Landgrabenstrasse 94, 90443 Nürnberg, Germany
Resume : In this work the photophysical pathways for charge generation at the organic:organic interface for efficient photovoltaic (OPV) cells are discussed. Combining ultrafast pump-probe spectroscopy (sub 15-fs time resolution) with high level quantum chemical calculations  we are able to unveil the primary events following photon-excitation and monitor the influence of the excess energy on the charge generation mechanism in low band gap polymer:PCBM interfaces such as PCPDTBT:PCBM blend . By exciting the blend with different photon energies, the ultrafast formation of high energy (hot) interfacial charge transfer states (CTs) occurs. Hot CTs can more favourable inject charges to the acceptor moiety thus favouring the charge generation process. This mechanism is however competitive with internal energy deactivation paths. Quantum chemical calculations provide interfacial CTs energies, DOS and electronic couplings, predicting that hot CTs can be excited and dissociated if pumping with excess energy. Our investigation demonstrates that, with excess energy, the path to CT becomes highly favorable at the interface, giving an explanation for faster CTs formation and efficient charge generation process. The work suggests that photovoltaic conversion via hot dissociation in low-band gap polymer:PCBM blends can be an efficient route to be explored for the optimization of OPV technologies.  G. Grancini, et al., JPCLett 2, 1099, 2011  F. Deschler, et al., PRL 107, 127402, 2011
|11:45||Organic wrap through solar cells|
Authors : Sebastian Schiefer, Birger Zimmermann, Uli Würfel
Affiliations : Fraunhofer ISE Freiburg
Resume : There is considerable progress made in improving the efficiency of organic solar cells during the past few years. The industrial production is therefore in reach which in turn requires new designs for cheap, flexible and large area solar modules. Amongst others the concept of wrap through solar cells is pursued at the Fraunhofer ISE. There is a hexagonal grid of vias spread over the cell which connect the transparent and highly conductive PEDOT:PSS on the front side to a second metalized substrate which is laminated to the backside of the perforated cell. We will present experimental results and compare them to simulations. Our model allows the optimization of the PEDOT:PSS layer thickness by accounting for the tradeoff between the sheet resistance and the generated photocurrent. The transfer-matrix method is implemented in the model to calculate the photocurrent, which varies with the PEDOT:PSS layer thickness due to parasitic absorption and interference effects. The ohmic losses decrease, since the sheet resistance of the PEDOT:PSS layer decreases as well as the photocurrent when the layer thickness increases. This tradeoff is affected by further parameters like the via hole diameter, the via to via distance and the serial resistance through the vias. The latter is as well affected by the PEDOT:PSS layer thickness. The model uses an experimentally determined relationship between the serial resistance per hole and the PEDOT:PSS layer thickness.
|12:00||On the Importance of Excess Energy for Charge Photogeneration in Small Bandgap Polymer / Fullerene Blends|
Authors : Stoichko D. Dimitrov, Christian Nielsen, Iain McCulloch and James R. Durrant
Affiliations : Centre for Plastic Electronics, Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom
Resume : Organic based solar cells require energy level offset between the donor and acceptor materials to enable effective photovoltaic properties. The role of this offset in determining the charge generation yields is still under debate because of our poor understanding of the fundamental charge separation processes in the polymer/fullerene D/A heterojunctions. We performed a series of transient absorption and photocur-rent experiments as a function of excitation wavelengths and temperature on carefully chosen small bandgap polymer/fullerene blends to study possible charge separation pathways. Both the role of fulle-rene and polymer excitons in driving charge photogeneration was evaluated. The results reveal that the amount of excess energy injected into the reaction pathway determines the efficacy of the e-h separation processes. We conclude that formation of hot charge transfer states is prerequisite for successful charge separation in the studied polymer/fullerene blends.
|12:15||PCDTBT:PCBM Bulk Heterojunction Solar Cells: Nanostructure and Function|
Authors : Andrew J. Pearson,Tao Wang, Alan D. Dunbar, Paul Staniec, Richard A.L Jones, David Lidzey
Affiliations : The University of Sheffield, Department of Physics and Astronomy, Hicks Building, Hounsfield Road, Sheffield S3 7RH, U.K.; Department of Chemical and Biological Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, U.K.; Diamond Light Source, Diamond House Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, U.K.
Resume : We studied a blend of the carbazole co-polymer PCDTBT with the fullerene PC70BM. When blended together and cast into a thin film, these materials form the basis of an efficient organic photovoltaic device. We have used a number of techniques (neutron reflectivity, spectroscopic ellipsometry and grazing-incidence X-ray scattering) to study the nanostructure of PCDTBT and PCDTBT:PC70BM blends and follow their structure evolution on thermal annealing. We find that the surface of an as-cast film is relatively rich in PC70BM, with a negative PC70BM concentration gradient existing into the film. On annealing at 70°C, we observe limited modification in the depth-dependent concentration of PC70BM. In a pure PCDTBT thin-film, thermal annealing at ≥ 130°C results in a crystallization of the polymer side-chains that disrupts pi-pi stacking. This disruption in the stacking of molecular backbones is consistent with a reduction in hole-mobility observed in thin-film blends annealed at ≥100°C. We show that PCDTBT and PC70BM are highly miscible, however when blend films are annealed at a temperature in excess of 155°C, coarse phase-separation occurs between PCDTBT and PC70BM; an effect that further reduces device efficiency as the volume density of interfaces at which exciton dissociation occurs is reduced. Our measurements demonstrate therefore that although thermal annealing removes casting solvent, it has relatively limited effectiveness in substantially improving the efficiency of PCDTBT:PC70BM devices.
|Poster Session II : Jana Zaumseil and Thomas Anthopoulos|
|14:00||New approach to reduce the recombination using the complex formation with oxidized species in DSSC|
Authors : Hong-kyu Song, Jinsun Yoon, Jongok Won, +Heeyoung Kim, +Min Sun Yeom
Affiliations : Department of Chemistry, Sejong University 98 Gunja, Gwangjin, Seoul, 143-747, Korea +Korea Institute of Science and Technology Information, 245 Daehangno, Yuseong, Daejeon, 305-806, Korea
Resume : While dye sensitized solar cells (DSSCs) have received great attention as low-cost and clean energy conversion devices, the conversion efficiency still lags behind that of the inorganic solar cell. One of the reasons is the recombination of injected electrons with oxidised species of the redox couple present in the electrolyte at the surface of bare TiO2 particles. While most of researches were conducted to block the bare surface of TiO2 nanoparticles by forming insulating molecular layer, we introduce a new additive which can directly reduce the concentration of oxidized species of the redox couple present in the electrolytes by the complex formation. Recombination was reduced by the addition of cyclodextrins (CDs) in poly(ethylene glycol) dimethyl ether (PEGDME) containing iodide/triiodide redox couples which can form the complex with the triiodide. Experimental and theoretical investigations were conducted for the complex formation between triiodide and CDs in viscous PEGDME matrix. HF method using LANL2DZ basis set in Q-chem package showed that triiodide ion in an α-CD2I3-complex is more strongly bonded to α-CD molecules than α-CDI3- complex, implying that the α-CD molecules would form a complex which shapes a 2:1 complex with I3- ion. Up to a 20% increase in total power conversion efficiency was achieved by using the α-CDs as the adsorbent and its efficiency reached 4.60%. EIS and IPCE measurements showed that the increase in Jsc is due to the suppression of surface recombination by the complex formation between CDs and triiodide. This work was supported by the NRF grant funded by the MEST of Korea for the basic research (2010-0020918) and NRF-2011-C1AAA001-2011-0030278).
|14:00||One pot Synthesis of calibrated hybrid PEDOT-Metal nanoparticles for improved electrochromic performance|
Authors : Muhammad Mumtaz, Blanche Ouvrard, Laurent Maillaud, Christine Labrugère, Eric Cloutet, Henri Cramail, Marie-Helene Delville
Affiliations : CNRS, Laboratoire de Chimie des Polymères Organiques, Université de Bordeaux, Laboratoire de Chimie des Polymères Organiques, IPB-ENSCBP, Pessac Cedex, F33607, France 3CNRS, Université de Bordeaux, ICMCB, Pessac, France. CECAMA, Pessac France
Resume : Hybrid PEDOT-metal (PEDOT-M) nano-objects (M = Ag or Au) are prepared by aqueous dispersion polymerization using ammonium persulfate as an oxidant and the corresponding metal salts as co-oxidant (HAuCl4 and AgNO3) in the presence of pyrrole-modified-poly(N-vinylpyrrolidone-co-vinyl alcohol) (PVP-co-PVAL-mod-Py). The morphology of such hybrid materials was nicely controlled and their size ranging from 40 to 300 nm. The effects of the time elapsed between the addition of the two co-oxidants is crucial with regards to the morphology of the nanocomposite particles thus formed. Such hybrid PEDOT-metal nanoparticles can also find applications in catalysis, for example in the reduction of nitro group into amine. More interestingly, these nanocomposites show electrical conductivities up to 1.3 S/cm despite the presence of insulator material and are efficiently used as anchoring layer to replace the PEDOT:PSS polymer (which usually comes with some drawbacks such as acidity and therefore instability of optoelectronic devices) for further EDOT monomer polymerization. This makes them good candidates for electrode materials in such optoelectronic devices. They give rise to an improvement of PEDOT electrochromic properties in terms of not only contrast ratio and coloration efficiency but also switching time response.
|14:00||Organic Solar Cell Parameters Extraction Using Fuzzy-Logic-based computation|
Authors : F. Djeffal, A. Maoucha, D. Arar and Z. Dibi
Affiliations : LEA, Department of Electronics, University of Batna, Batna 05000, Algeria
Resume : Extraction of the organic solar cells parameters is a complex task, because of the huge number of parameters in recent models, most of them correlated, and requires global optimization methods. One way to simplify this task is to use direct extraction methods for some parameters. This eases the entire extraction procedure and reduces the iteration time in case of optimization, because these values can be used as initial values. Once the parameters have been extracted, most of the direct extraction methods need a second step to take into account the interactions among the different parameters. This leads to the use of global methods (Genetic algorithms, PSO, MOGAs, etc) to find the set of values that can best fit the experimental data. The optimization methods are based on calculating derivatives and are thus quite computationally expensive and difficult to code. Therefore, in the present work, a new organic solar cell parameters extraction tool is presented. This tool is based on fuzzy control techniques. These techniques allow using knowledge about the model behavior into the parameter extraction method, thus simplifying the task. The procedure is applied to extract the different parameters of a two-diode solar cell model for which results show good performance. The obtained results make the proposed approach a promising candidate for organic solar cell investigations.
|14:00||Elaboration and characterization of flexible organic solar cells|
Authors : A. El Hajj, B. Lucas, R. Antony, B. Ratier,
Affiliations : XLIM research institute, Limoges University, UMR CNRS 6172, 123 av Albert Thomas, 87060 Limoges cedex, France.
Resume : In this paper, we realized organic solar cells on transparent flexible substrates made of polyethylene terephthalate. In addition, we developed electrode materials deposited by ion beam sputtering, a technique which satisfies the low temperature deposition requirements associated with the use of plastic substrates. Thus, the control of electrode deposition by ion beam sputtering at room temperature enabled to develop original tri-layer electrodes of oxide/metal/oxide structure and to highly improve the conductivity/transmittance compromise. This tri-layer structure has the advantage of adjusting the layer thicknesses to favour antireflection and the surface plasmon resonance of the metallic layer; thus, inserting a thin metallic layer between two layers of oxides decreases the sheet resistance while enlarging the window of optical transmittance in the visible. The photovoltaic performance of solar cells based on P3HT:PCBM obtained with a tri-layer anode deposited on a plastic substrate will be presented and discussed. We also fine-tuned the anode structure and deposition conditions towards flexible organic devices and optimal device characteristics.
|14:00||Comparison of ITO/metal/ITO and ZnO/metal/ZnO transparent electrodes for plastic solar cells|
Authors : M. Girtan
Affiliations : Photonics Laboratory, Angers University, 2, Bd. Lavoisier, 49045, Angers, France, email@example.com
Resume : In this paper we present the physical properties of two types of multilayer structures: ITO/metal/ITO and ZnO/metal/ZnO obtained by successive sputtering depositions of metallic targets (In:Sn, Zn, Ag, Au) in reactive atmosphere (for oxide films) or inert atmosphere (for metallic interlayer films). Very good quality transparent conducting thin films structures (resistivity=2•10-5 ohm•cm, T = 90%) were obtained. The morphological, optical and electrical properties were analysed and compared for the multilayer films deposited in identical conditions on glass and PET substrates. The influence of substrate nature on the morphological properties is more pronounced in the case of zinc oxide films. The Haake figures of merit at 550nm are comprised between 4•10-3ohm-1 and 29 •10-3 ohm-1 in function of the nature of the metallic interlayer. The stability of electrical properties with the temperature of oxide/metal/oxide films is remarkable in comparison with the usual behaviour of single oxide films.
|14:00||Focused Ion Beam Sample Preparation for Cross-sectional and Elemental Analysis of Bulk Heterojunction Organic Solar Cells|
Authors : Nopporn Rujisamphan, Fei Deng, Roy E. Murray, Chaoying Ni, S. Ismat Shah
Affiliations : Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716, USA:
Resume : The efficiency of P3HT/PCBM bulk heterojunction (BHJ) organic photovoltaic devices is strongly dependent on annealing temperature and time. In this report, we compare two cases of device fabrication--without annealing and annealing at 120 0C for 20 min. The combination of two techniques, namely dual focused ion beam (FIB) and transmission electron microscopy (TEM) were used to fully examine the micro and nano structure of the whole devices. FIB was performed for cross-sectional sample preparation. 100 nm cross sections were cut from the devices with no distortion in the thickness. These results were confirmed by the thickness obtained by atomic force microscope (AFM) results. This leads us to believe that the FIB do not alter any macro structure of the whole device and can be used for cross section sample preparation. The electron diffraction patterns of each layer in both annealed and un-annealed samples were obtained by nano beam (0.7 nm2) analysis to avoid interference with other layers. Elemental mapping profiles of the whole device were also collected to investigate diffusion at the ITO and Al electrode interfaces. High resolution bright field images, especially at the interfaces, are also presented. The photovoltaic parameters were extracted from the J-V analyses and correlated with TEM results.
|14:00||Improved of contact resistance in organic field-effect transistors(OFETs) by formation of mixed self-assembled monolayers|
Authors : Ara Cho, Yong-Young Noh*
Affiliations : Department of Chemical Engineering, Hanbat National University
Resume : Solution processable organic field-effect transistors (OFETs) are one of emerging devices due to enable low-cost, large-area manufacturing by various cost-effective printing methods on flexible substrates. Performance of OFETs has been consistently improved for past 20 years but there are still a few fundamental challenges and improved functionalities could be achieved. Improvement of contact resistance between injection metal electrodes and p- and n-channel organic semiconductors is one of those remaining challenges since a few stable metals, e.g., Au are commonly used for the injection electrode in OFETs. In particular, the contact resistance works more severely in performance of ambipolar OFETs since conjugated molecules have a relatively wide band-gap. We report here on improved device characteristics by inserting of mixed self-assembled monolayer at the metal/semiconductor interface in top-gate staggered various ambipolar polymer field-effect transistors fabricated with Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), P(NDI2OD-T2) (N2200), PTVPhI-C12, etc. Thiol-based mixed SAMs (1H, 1H, 2H, 2H-Perfluorodecanethiol and 1-Decanethiol) were applied on O2 plasma treated Au surface for continuous control metal work function. The mixed SAM-treated OFETs exhibit improved both electron and hole injection properties from untreated devices. Finally, we demonstrate real ambipolar CMOS circuits with mixed self-assembled monolayers
|14:00||Switching properties of ferroelectric P(VDF-TrFE) films fabricated on oxide electrodes|
Authors : Eisuke Tokumitsu(1 2), Gwang-Geun Lee(1)
Affiliations : (1) Precision and Intelligence Lab, Tokyo Institute of Technology ; (2) Green Device Research Center, Japan Advanced Institute of Science and Technology
Resume : To realize flexible electronic systems, nonvolatile memory elements as well as switching devices have to be embedded on flexible substrates. Ferroelectric polymer poly(vinylidene fluoride-triflurorethylene) [P(VDF-TrFE)] is attractive for flexible nonvolatile memories because of its low process temperature and a combination of ferroelectric P(VDF-TrFE) and metal-oxide electrode and channel is a promising candidate for such electronic systems. For example, we previously demonstrated flexible nonvolatile ferroelectric-gate thin film transistors using P(VDF-TrFE) and In-Ga-Zn-O channel. In this work, we investigated ferroelectric properties of P(VDF-TrFE) films fabricated on oxide electrodes. 60 and 110 nm-thick P(VDF-TrFE) films were formed on Pt and ITO electrodes by spin-coating using a P(VDF-TrFE) (70:30) solution. The films were annealed at 140 °C for 1 h in air for crystallization. Remanent polarization and coercive field of 110-nm-thick P(VDF-TrFE) film on ITO were 8.3 µC/cm2 and 0.75 MV/cm, respectively, which are similar to those of the film on Pt. However, P-E hysteresis loop suggests the presence of interfacial layer for the film on ITO. Switching times of the 110 nm-thick P(VDF-TrFE) films on ITO are 14.6 µs at 1 MV/cm and 1.3 µs at 2MV/cm, whereas those of the film on Pt are 6.8 µs at 1 MV/cm and 1.2 µs at 2MV/cm. The difference in switching time especially at the low electric field is probably due to the interfacial layer between P(VDF-TrFE) and oxide electrodes.
|14:00||Reduction of the interfacial trap density in a pentacene field-effect transistor with an organic-inorganic hybrid gate insulator|
Authors : Jin-Hyuk Bae, Yoonseuk Choi
Affiliations : School of Electrical Engineering, Seoul National University, Seoul, Korea ; Department of Electronics, Hanbat National University, Daejeon, Korea
Resume : We report the reduction of the interfacial trap density in a pentacene field-effect transistor with an organic-inorganic hybrid gate insulator. Our hybrid gate insulators are consisted of stacked two layers, one of which is a titanium oxide nanocomposite layer and the other is a polymeric buffer layer. Although high dielectric nanocomposite is generally used to reduce the operating voltage of transistors, such a nanocomposite film is found to be generating a large interfacial traps due to very rough surface. On the other hands, for the hybrid layer, we found that the interfacial trap density is significantly reduced regardless of the types of polymeric buffer layer. For more specific study, we changed the type of the polymeric buffer layers, one of which is hydroxyl group-existing polyvinyl phenol (PVP) and the other hydroxyl group-free polyvinyl cinnamate (PVCi). Compared with the PVP case, the hydroxyl group-free buffer layer, PVCi, generates much decreased interfacial trap density as well as significantly increased field-effect mobility. It is found that the hydroxyl group-free polymer is more desirable to obtained the improved organic transistors.
|14:00||UV/Ozone Formation of Gate Dielectric in Organic Thin-Film Transistors|
Authors : Krishna Chytanya Chinnam, Helena Gleskova
Affiliations : Department of Electronic and Electrical Engineering University of Strathclyde 204 George Street Glasgow, G1 1XW United Kingdom
Resume : Low-temperature, dry-processed, bi-layer gate dielectric is developed for low-voltage organic thin-film transistors (OTFTs). This dielectric consists of UV/ozone oxidised aluminium and vacuum deposited octyl-phosphonic acid and has been successfully implemented in transistors based on thermally evaporated pentacene . Commercial UV/ozone cleaners utilize mercury lamps that generate ozone through the emission of UV light. During the oxidation process of the aluminium, the substrate is exposed to ozone, UV light and thermal heating (100°C) caused by the absorption of the UV light. This paper investigates whether the heating itself provides a beneficial annealing effect and thus improves the transistor performance. Series of OTFTs and capacitors were fabricated where during the aluminium oxide preparation all samples were held at 100°C for a fixed amount of time and the time spent in the UV/ozone cleaner was varied. The transistor results indicate that the elevated temperature itself provides negligible benefit. Transistors with aluminium oxide prepared by combination of a 2-min UV/ozone treatment and 58-min anneal at 100°C exhibit similar performance as those prepared by 2-min UV/ozone treatment only. In addition, the UV/ozone oxidation cannot be shortened and replaced with a heating step to gain the same transistor performance.  Presented at the 24th International Conference on Amorphous and Nanocrystalline Semiconductors held in Nara, Japan, Aug 22-26, 2011.
|14:00||Theoretical study of interaction between nano-porous ZnO with substituted Phthalocyanines|
Authors : P. Palacios a,b, P. Wahnón a,c
Affiliations : 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. Plaza Cardenal Cisneros, 3, 28040, Madrid, Spain
Resume : The aim of this work is the theoretical study of the band alignment between the two components of a hybrid organic-inorganic solar-cell. The working organic molecules are metal tetra-sulphonated phthalocyanines (M-Pc) and the inorganic material is nano-porous ZnO growth in the 001 direction. The theoretical calculations are being made using the density functional theory (DFT) using a GGA functional with the SIESTA and VASP codes. We also used the DFT+U method that allows a semi-empirical inclusion of electronic correlations in the description of electronic spectra for systems such as zinc oxide. For the M-Pc's we study the more stable geometry and the HOMO and LUMO for the inclusion of different metals in the center of the molecule using time-dependent DFT. The molecule is flat except the sulphonic groups which can freely rotate. Different ZnO surfaces have been modeled to find the optimal configuration, in their most stable wurtzite phase, and relaxed to find the minimum energy positions. Then we study the interaction between the two systems studying different parallel and perpendicular orientations. A good estimation of band alignments between the adsorbate and the substrate was achieved with DFT+U and TD-DFT.
|14:00||Role of Intermolecular Coupling and Electron-nuclear Coupling in the Photophysics of Oligothiophenes Single Crystals|
Authors : M. A. Saidani, A. Benfredj, S. Romdhane[1,2], F. Kouki, J. L. Fave, H. Bouchriha
Affiliations :  Laboratoire Matériaux Avancés et Phénomènes Quantiques, Faculté des Sciences de Tunis, 2092 Campus Universitaire Tunis, Tunisia  Faculté des Sciences de Bizerte, 7021 Zarzouna, Bizerte, Tunisia  Institut des Nanosciences de Paris UMR 7588, Université Pierre et Marie Curie, case 8402, 4 Place Jussieu, 75252 Paris
Resume : In organic semiconductors,molecular vibrations are expected to play an important role in exciton migration.A Franck-Condon(FC) analysis is thus crucial to understanding the exciton-phonon coupling since this latter occurs as a result of the FC principle,for which the Born-Oppenheimer(BO) approximation holds.However,the absorption and emission spectra of polythiophenes and oligothiophenes exhibit apparent non-Condon emission,which led to more complicated models.Repp et al. have recently unmasked a coherent electron-nuclear coupling in oligothiophene,indicating a complete breakdown of the BO approximation.In the present work,we particularly focus on a system of linear olygothiophene with a limited number of double bond.In such systems,the promotion of an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital has a large effect on the local bond order and thus we expect to see a large exciton-phonon coupling.Besides,recent calculations and experimental verifications testify the presence of an electronic level spacing of the order of vibrational energy in these systems,which makes them fulfill the prerequisite for the coherent electron-nuclear coupling mentioned above.We suggest here a simple approach that permits to incorporate the latter effect into a FC progression,and we show that it permits to model adequately the emission profile from oligothiophenes single crystals thin layers without the need to invoke more complicated models.
|14:00||The influence of terminal group on the poly(para-phenylenevinylene) charge transfer integrals|
Authors : D. Duce, M. Ottonelli, S. Thea, G. Dellepiane
Affiliations : Dipartimento di Chimica e Chimica Industriale - via Dodecaneso, 31 -16146 Genova (Italy)
Resume : Conjugated organic systems have become competitive materials with respect to inorganic semiconduc-tors, and successfully used in a broad range of technological applications like: sensors, solar cells, field effects transistors and light emitting diodes. One of the key parameters that control the performance of these devices are the charge transport properties that are, for the organic semiconductors, strictly related to the structure of the single molecule as well as its packing in the solid state. For this reason a better understanding of the charge transport mechanism, correlated with the supramolecular organization of the conjugated molecule in the bulk and their local structure, is a fundamental task for the devices optimization, and still under debates. In this framework, theoretical works usually do not take into account the presence of a terminal group in the organic semiconductors since, generally, are polymers or large oligomers. Here, using as model systems a representative oligomer of the PPV [poly(para-phenylenevinylene)], we will show that including the terminal group in the modelization (in the present case a vinyl moiety) strong effects on the charge transport properties could raise. In fact, despite the structure of the oligomer is practically unaffected by the presence/absence of this moiety, in the framework of the Marcus theory significant variation are obtained for the values of the electron and hole transfer integrals and consequently on their mobility.
|14:00||Controlled ambipolarity of organic field-effect transistors using Cs-salt and application to complementary circuits|
Authors : Dongyoon Khim1, Kang-Jun Baeg3, Ju-Hwan Kim1, Jun-seok Yeo1, Minji Kang1, Yong-Young Noh2,*, and Dong-Yu Kim1,*
Affiliations : 1. Heeger Center for Advanced Materials, School of Material Science and Engineering, Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-dong), Buk-gu, Gwangju 500-712, Republic of Korea.; 2. Department of Chemical Engineering, Hanbat National University, 16-1 Dukmyung-dong, Yuseong-gu, Daejeon, 305-719, Republic of Korea.; 3. Convergence Components and Materials Research Laboratory, Electronics and Telecommunications Research Institute (ETRI), 218 Gajeongno, Yuseong-gu, Daejeon 305-700, Republic of Korea
Resume : The unique advantages of the organic materials including mechanical flexibility, versatile molecular design, and their processability using printing process would enable to a variety of flexible opto/electronic applications with simple and extremely low-cost fabrication. The performance of the organic devices is determined by both on intrinsic properties of organic semiconductor active layers and their interfaces facing on each layer. Especially in OFETs, it is obvious that efficient control over the electrode-semiconductor and semiconductor-dielectric interfaces have played a key role for enhancing charge injection from source/drain electrodes and fast transport though the active channel. In this study, we have studied charge injection and transport properties of nano-scale CsF interlayer onto Au electrodes in top-gate/bottom-contact (TG/BC) OFETs based on ambipolar polymer semiconductors by various physical and chemical analysis such as atomic force microscopy (AFM) image, X-ray photoelectron spectroscopy (XPS) and UV photospectronscopy (UPS). The different size and distribution of CsF nano-dots were formed by thermal evaporation method, thereby systematically compared the interlayer topology with transistor characteristics. Initially, PTVPhI-C12 OFETs showed p-channel predominant characteristics with relatively high hole mobility (μh) of ~0.072 cm2/Vs and low electron mobility (μe) of ~9.7×10-3 cm2/Vs. It is very interesting that very tiny amount of CsF deposition caused to significant enhancement of μe increased up to ~0.12 cm2/Vs, whilst μh decreased to ~0.017 cm2/Vs. Next, from selective deposition of CsF using metal shadow mask, we successfully fabricated complementary inverters (high voltage gain of more than 23) based on the ambipolar PTVPhI-C12.
|14:00||Enhanced performances of organic photovoltaic via addition of a novel molecule in the active layer|
Authors : Ming-Chung Chen, Sudeshna Kar, Der-Jang Liaw, Cheng-Yo Chi, Ying-Chi Huang, and Yian Tai*
Affiliations : Department of Chemical Engineering, National Taiwan University of Science and Technology, Taiwan
Resume : In this report, we synthesized a new molecule 2,3-bis(5-bromothiophen-2-yl)acrylonitrile (DTDBAL) and introduced it in the active layer, consisted of poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), to investigate its application in an inverted bulk hetero-junction (BHJ) organic photovoltaic (OPV). The HOMO and LUMO values of DTDBAL were in between the corresponding values of P3HT and PCBM, which made DTDBAL a good candidate for constructing an inverted cascade structure within OPV with P3HT and PCBM. The open circuit voltage and the short circuit current can be increased owing to the better exciton dissociation and charge transfer due to the cascade structure. The highest power conversion efficiency (PCE) of the OPV with optimized ratio of P3HT:PCBM:DTDBAL achieved 4.19 % , which was 37 % higher than the device featuring only P3HT/PCBM as the active layer.
|14:00||Organic Photovoltaic Solar Cells with Cathode Modified by ZnO|
Authors : Abd. Rashid bin Mohd Yusoff, Hyeong Pil Kim, and Jin Jang
Affiliations : Department of Information Display and Advanced Research Center, Kyung Hee University, Dongdaemun-ku, Seoul 130-171, Republic of Korea
Resume : Solution processed cathode organic photovoltaic cells (OPVs) utilizing thin layer of zinc oxide (ZnO) with 27 % increase in power conversion efficiency (PCE) to control devices have been demonstrated. Devices without the presence of ZnO layer have much lower PCE than the ones with ZnO layer. Cathode modification layer can be used to reduce photogenerated excitions and finally improve the performance of the OPVs. The successful demonstrations of OPVs with an introduction of ZnO cathode layer give promise of further device progresses.
|14:00||Performance enhancement of pentacene thin film transistors by novel field assisted deposition|
Authors : Mr. Tapendu Mandal, Dr. Ashish Garg, Dr. Deepak
Affiliations : Department of Materials Science and Engineering & Samtel Center for Display Technologies, Indian Institute of Technolog, Kanpur, India.
Resume : Pentancene based transistors are routinely fabricated, but the process sensitivity affects the device performance quite significantly. Some of these sensitivities are eliminated via treating dielectric surface by OTS for suitable alignment of pentacene molecules. Here, we demonstrate a different approach to tackle this problem by depositing pentacene under electric field. A 20-nm thin pentacene film was deposited under electric field on Si/SiO2 substrate to fabricate top contact TFTs. The results were compared with devices fabricated without electric field and also with OTS. Our results show that field assisted deposition of pentacene results in about an order of magnitude increase in the mobility compared to that for the standard device, from 0.05 to 0.2 cm2/V s in the field assisted devices. The observed improvement in the transistor characteristics was explained by polarizability calculation of pentacene molecule based on ab initio method. We find that the polarizability of pentacene is anisotropic which clearly illustrates that applied field aligns the molecules just before the deposition and leads to improved career mobility in the field assisted devices. This was further corroborated using XRD of pentacene films showing that peak intensity increases and FWHM decreases in case of field assisted devices as compared to the standard devices. These changes in the crystallinity are also confirmed by the AFM studies showing clear grain alignment in field assisted devices.
|14:00||Preparation of naturally-textured aluminum-doped zinc oxide films on polyethersulfone flexible substrate with radio frequency magnetron sputtering|
Authors : Bum Ho Choi; Moo Ryul Kim; Se Yeon Park; Jong Ho Lee
Affiliations : KITECH
Resume : Naturally textured aluminum-doped zinc oxide (AZO) transparent conducting oxide (TCO) layers were prepared on polyethersulfone (PES) flexible substrates using radio frequency (RF) magnetron sputtering method, and their morphological, optical and electrical properties were characterized. The naturally textured AZO layer was formed without employing chemical wet etch step by controlling RF sputtering power. First of all, naturally textured AZO layers which have crater structures were formed by single RF power. At high RF power of 2000 w, the surface of naturally textured AZO layer is similar to that of chemically wet etched AZO. The naturally textured AZO layers were also formed by dual RF sputtering powers. 0.15 ㎛ thick AZO layer was sputtered at high RF power and subsequent 0.45 ㎛ thick AZO layer was sputtered at low RF power, resulting in larger grain size flake or crater like structures. The higher RF sputtering power, the rougher surface morphology was obtained. The polycrystalline AZO layer with high surface roughness was formed on PES flexible substrates at single and dual RF sputtering power. The transmittance in visible ray range measured from all the prepared naturally textured AZO layers was over 85 %, which meets the requirement to be used in amorphous silicon thin film solar cell, and the highest transmittance was 94.6 %. The highest mobility of 27 cm2V-1s-1 and the lowest resistivity of 3.2ⅹ10-4 Ωcm was obtained at 1000 and 300 W of RF power combination, which has comparable value to those of chemically wet etched AZO. The measured optical and electrical properties of naturally textured AZO layers on PES flexible substrates are comparable to those of chemically wet etched AZO layer, which suggest a possible way to fabricate low cost flexible a-Si thin film solar cell. Our study suggests that naturally textured AZO layer on flexible substrates can be formed by controlling only sputtering process without employing chemical wet etch step, resulting in reduced process steps.
|14:00||A Novel and Simple Method for the Fabrication of Transparent, Flexible and Conductive Carbon Nanotube Films|
Authors : ○Yeji Kim1,2, Masayuki Chikamatsu1, Reiko Azumi1, Nobutsugu Minami1, Said Kazaoui1
Affiliations : Advanced Industrial Science and Technology (AIST)1, Research Fellow of the Japan Society for the Promotion of Science 2
Resume : The interesting and unique properties of single wall carbon nanotube (SWNT) such as variation of electronic behaviors depending on chiral indices and huge aspect ratio open to new and wide developments of industrial applications. For investigation and application of their optical and electrical properties, fabrication of homogeneous thin films of individual, isolated SWNTs is an essential prerequisite. We have developed a fabrication technique of thin films of homogeneously dispersed, isolated, individual SWNTs. Therefore, we found that cellulose derivatives show an excellent dispersion as well as film-forming property of SWNTs . In this study, by using hydroxypropylcellulose (HPC) as a matrix polymer, we have developed a simple technique to fabricate transparent, flexible and conductive SWNT thin film. The coating for solution-processible materials was performed using the doctor blade method, which is a very simple and rapid fabrication technique. The film thickness was determined by the gap between a blade and the surface of a substrate. Therefore, the film thickness is predictable and easily reproduced. The removal of the polymer matrix and doping of SWNTs were completed in 5 min., by dipping the film in concentrated HNO3 using an ultrasonic bath. This simple and speedy process is a practical means to develop flexible optical and electrical devices.  Y. Kim et al., Appl. Phys. Lett., 86(7), 073103 (2005), Appl. Phys. Lett., 88(9), 093123 (2006).
|14:00||Integration of ferroelectric and paraelectric organic field-effect transistors by transfer-printing of a dielectrically screening layer for ferroelectric random-access-memory|
Authors : Min-Hoi Kim, Gyu Jeong Lee, Chang-Min Keum, In-Ho Lee, Sin-Doo Lee
Affiliations : Seoul National University
Resume : organic ferroelectric random-access-memory (FeRAM) has attracted much attention for use in radio frequency identification tags and data storage devices. For the organic FeRAM, two different types of organic field-effect transistors (OFETs), one for the data selection by a conventional OFET with a paraelectric insulator and the other for the data storage in a memory OFET with a ferroelectric insulator, should be integrated in each memory cell. The integration of the two OFETs requires the patterning of different dielectric layers. In this work, we present a versatile method of integrating the ferroelectric and paraelectric OFETs by transfer-printing a dielectrically screening layer on a ferroelectric insulator. The transfer-printed screening layer result in a paraelectric surface for a conventional OFET as a switching element. The transfer curves of the ferroelectric OFET show hysteresis characteristics while that of the conventional OFET has no hysteresis. The transfer-printing method enables to easily integrate different types of the OFETs with high resolution. Acknowledgement This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MEST) (No. 2011-0028422).
|14:00||Durability of cyanine dye / C60 bilayer solar cells and role of counter anions|
Authors : Gaëtan Wicht, Roland Hany, Frank Nüesch
Affiliations : EMPA, 8600 Dübendorf, Switzerland
Resume : Polymers are still leading the field of organic photovoltaics, but recent work has demonstrated merits of small organic molecules, such as ease of synthesis, purification, or high light absorption coefficients. Among small molecules, cyanine dyes are of particular interest. Indeed, these are charged conjugated molecules that are accompanied by relatively mobile counter anions which can build up ionic space charge that can be used to control the flow of electronic current. Until now efforts have been focused on enhancing device efficiency (≈ 3%) and processing methods of cyanine dye heterojunction solar cells. We present results on the durability of cyanine dye / C60 bilayer solar cells. We report rapid changes of the relevant solar cell parameters over a period of a few days that strongly depend on the type of cyanine counter anion and on the processing solvent. After that relaxation time stable cell performance was observed for several weeks. These findings are attributed to differences in the initial anion distribution throughout the bilayer film upon spin coating. The ionic space charge is sensitively dependent on the chemical nature of the anode buffer layer and can be altered within minutes by the application of an external electric field.
|14:00||The effect of water and oxygen on the electronic structure of the organic photovoltaic|
Authors : Yang Qing Dan, Ng Ts Wai, Wong Ning Bew, Lee Chun Sing
Affiliations : Department of Biology and Chemistry, City University of Hong Kong
Resume : Effects of water and oxygen exposures on electronic structures of the bathocuproine (BCP)/ fullerene (C60) interface were studied by ultraviolet photoemission spectroscopy (UPS). C60 in BCP/C60 interface, which prepared under ultrahigh vacuum (UHV), shows a downward energy level bending of 0.26 eV. The energy level bending of C60 dramatically increases to ~0.8 eV upon exposure to water moisture or oxygen gas at 5 × 10-6 Torr for 30 minutes. The results indicate the formation of electron traps at the C60/BCP interface upon water or oxygen exposure. The decrease in electron transporting barrier between the LUMO of C60 and metal deposition induced gap states in BCP encourages the charge leakage from cathode to C60. Charge recombination in C60 upon water or oxygen exposure is also discussed.
|14:00||Tuning the photoresponse in organic field-effect transistors|
Authors : Mirella El Gemayel,a Matthias Treier,a Chiara Musumeci,a, Chen Li,b, Klaus Müllen,b, Paolo Samorì,a
Affiliations : a Nanochemistry Laboratory, ISIS-CNRS 7006, Université de Strasbourg, 8 allée Gaspard Monge, 67000 Strasbourg, France. b Max-Planck Institute for Polymer Research, Ackermannweg 10, 55124 Mainz (Germany).
Resume : Conjugated organic materials with semiconducting properties have been intensively studied in view of their (opto)electronic applications in a technology relying on low-cost fabrication methods, low processing temperatures, large area coverages and structural flexibility. Perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) are viable candidates as light sensitive material for organic phototransistors (OPTs). Here we report on the fabrication of solution processed OPTs based on PDIs. We found that the responsivity to the photo-illumination depends on the transistor’s channel length and that it can be tuned by varying the device geometry. The analysis of different morphologies of the active semiconducting layer revealed that single PDI fibers exhibit the higher photo-response when compared to more poorly organized films. The highest responsivity value of 4.08±1.65 x 105 A/W was achieved on a multifiber based OPT. These findings represent a step forward towards the use of organic based phototransistors as photosensors.   M. El Gemayel, M. Treier, C. Musumeci, C. Li, K. Müllen, P. Samorì, J. Am. Chem. Soc. 2012, DOI: 10.1021/ja208090p
|14:00||Fabrication and Characterization of Organic Inverter|
Authors : A. Skaiky, T. Trigaud, B. Lucas
Affiliations : XLIM Research Institut, UMR CNRS 6172
Resume : The organic field effect transistors (OFET) have real development possibilities if are considered their potential applications, in organic electronics like inverters, oscillators and memories. These components are usually seen as the basic modules of RFID tags (radio frequency identification) as they can be performed on flexible polymeric supports with low cost manufacturing. In this study, it will be considered only the realization of inverter circuit composed of two OFETs, in "top contact" and “bottom contact” geometry. The transistors are based on pentacene with Poly (methyl methacrylate) (PMMA) as gate dielectric. The performance of the inverter are studied in terms of the geometry of contacts (length and width of the channel) and transport properties of pentacene. In this perspective purified and non purified pentacene were used. For each step in the realization of the inverter, we extracted physical and electrical characteristics, which are useful for the good understanding of the involved phenomena. One of the objectives is to demonstrate the feasibility of circuits compatible with the standards set for RFID.
|14:00||Flexible thin-film transistors fabricated on plastic substrate at room temperature|
Authors : Dedong Han1, Wei Wang1, Jian Cai1, Liangliang Wang1, Yicheng Ren1, Yi Wang1 and Shengdong Zhang2
Affiliations : 1Institute of Microelectronics, Peking University, Beijing, 100871, PRC; 2Shenzhen Graduate School, Peking University, Shenzhen, 518055, PRC
Resume : We fabricated flexible thin-film transistors (TFTs) on plastic substrates using Aluminum-doped ZnO (AZO) as an active channel layer at room temperature. In this paper, we report on fabrication and properties of low-driven-voltage and high mobility the AZO-TFTs. The TFT device structure used in this study was a bottom gate type, which consists of SiO2 as a gate insulator dielectric and Al as source and drain electrodes. The process conditions of the TFT were optimized for leakage current and device performances. The AZO-TFTs showed n-channel device characteristics and operated in enhancement mode. The device shows a threshold voltage of 1.3 V, an on/off ratio of 2.7×107, a field effect mobility of 21.3 cm2 /V s, a subthreshold swing of 0.23 V/decade, and the off current of less than 10-12 A at room temperature. This TFT had a channel width of 50 µm and channel length of 10 µm. Recently, ZnO based thin film transistors (TFTs) have attracted significant attention due to its extensive applications in varied fields. The flexible displays have become a very hot topic. Flexible thin film transistors are key devices for realizing flexible displays. We have investigated AZO-TFT on flexible plastic substrate, and high performance flexible TFTs were obtained. This work is supported by the National Basic Research Program of China (973 program, Grant No. 2011CBA00600) and by the National Natural Science Foundation of China (Grant No. 60977016).
|14:00||Block copolymer nanocomposites for nanotechnology applications|
Authors : C. De Rosa (a), F. Auriemma (a), C. Diletto (a), R. Di Girolamo (a), P. Morvillo(b)
Affiliations : (a) Department of Chemical Sciences University of Napoli "Federico II"; (b) ENEA-Italian National Agency for New Technologies, Energy and Sustainable Development-Portici Research Center
Resume : Self-assemby is emerging as an elegant “bottom-up” method for fabricating nanostructured materials. The goal of this research is to develop innovative hybrid systems where a nanostructured block copolymer (BCP) is selectively loaded with inorganic metal nanoparticles. Microdomains of BCPs nanostructures that form spontaneously by self-assembly may act as hosts for sequestering nanofillers of appropriate chemical affinity according to prefixed periodic geometries producing long-range order in the positioning of nanoparticles. A polystyrene-b-poly(methylmethacrylate) (PS-PMMA) amorphous BCP was employed with volume fraction of PS block selected in order to obtain a lamellar morphology consisting of alternating PS and PMMA layers with periodicity of 40 nm. In a first step thin films of PS-PMMA were obtained by spin-coating or drop casting on Indium Thin Oxide substrate. After annealing and successive directional solidification using benzoic acid as substrate or annealing coupled with application of external electric fields a tight alignment of layered microdomains was obtained. Finally, an innovative procedure based on the selective deposition of metal nanoparticles by evaporation and condensation was used to obtain nanostructured hybrid systems. We demonstrate that metal atoms diffuse to the preferred domains forming nanoparticles with spatial selectivity on the surface of the film. This innovative approach can be employed as a tool to realize a non-volatile OFET memory devices.
|14:00||Low temperature processed bilayer dielectrics for low-voltage flexible saturated load inverters|
Authors : Ye Zhou, V. A. L Roy, Zong-Xiang Xu, H. Y. Kwong, Hai-Bo Wang, C. S. Lee
Affiliations : Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR.
Resume : Organic circuits, for instance, thin film inverters have received lot of attentions due to their potential use in low cost electronics applications. The key advantage of organic electronics is attributed to low temperature processing and the compatibility with flexible substrates. Many flexible devices for active matrix displays, sensors and radio frequency circuits have been demonstrated. The saturated load inverters, which only adopt one type of semiconductor and one type of source/drain electrode, can simplify the processing procedure in comparison with complementary inverters. Here, we report saturated load inverters using low temperature processed bilayer n-octadecylphosphonic acid (ODPA)/Al2O3 dielectrics fabricated on flexible polyethylene terephthalate substrates. The saturated load inverters, which enable simplified processing, could operate at supply voltage as low as -2V and achieve a gain up to 23 at -5V. The inverters on ODPA/Al2O3 exhibited better mechanical stability upon bending due to the existence of self-assembled monolayer ODPA, implying their potential applications for low voltage inexpensive flexible electronics.
|14:00||Ultrafast spectroscopy of donor-acceptor-donor triads self-organized in liquid-crystal phase|
Authors : T. Roland(1), J. Léonard(1), G. Hernandez Ramirez(1), P-O. Schwartz(1), S. Méry(1), S. Ludwigs(2-3), O. Yurchenko(2), S. Haacke(1)
Affiliations : (1) Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg - CNRS, 67034 Strasbourg Cedex 2, France ; (2) Freiburg Material Research Center and Freiburg Institute for Advanced Studies, University of Freiburg, 79104 Freiburg, Germany; (3) Institute of Polymer Chemistry, University of Stuttgart, 70569 Stuttgart, Germany
Resume : We used femtosecond pump-probe spectroscopy (with a 80fs time resolution) to investigate the photoreaction of a new donor-acceptor-donor (DAD) molecule with liquid-crystal properties, that should allow high charge mobility and a good organization, both favorable for photovoltaic applications . Experiments were first conducted on isolated components A and D and then on the isolated molecule (in CHCl3) and in the liquid-crystal phase (in film). This allowed us to determine the photo-induced processes and their kinetics in both cases. In solution, after excitation of D, we observe a very fast energy transfer from D to A (in less than a few hundred fs), and then within 10ps the formation of the charge transfer (CT) state, that recombines in ~50ps. The behavior in film is quite different, as the energy transfer does not occur and is overtaken by a fast sub-100fs charge transfer. The CT state then recovers via intra- and inter-molecular recombination, respectively in about 70ps and 1ns. In addition efficient charge carrier generation is limited by a fast recombination process (~1ps) and formation of A’s triplet state. New molecules are developed, incorporating a charge density gradient in the donor moiety. This should hamper charge recombination, as will be verified experimentally by the above time resolved techniques. References  L. Bu and Al., J. Am. Chem. Soc., 2009, 131, 13242-13243 Full article: Sub-100 fs charge transfer in a novel donor–acceptor–donor triad organized in a smectic film, T. Roland, J. Léonard, G. Hernandez Ramirez, S. Méry, O. Yurchenko, S. Ludwigs and S. Haacke, Phys. Chem. Chem. Phys., 2012, 14, 273–279
|14:00||Thienopyrroledione-containing Donor/Acceptor alternating copolymers as new electron-donating materials|
Authors : Chiara Ottone(a), Philippe Berrouard(b) , Guy Louarn(c), David Gendron (b), Malgorzata Zagorska (d), Patrice Rannou (a), Ahmed Najari (b), Said Sadki(a), Mario Leclerc(b), Adam Pron(a)
Affiliations : (a) INAC/SPrAM (UMR 5819, CEA-CNRS-Univ. J. Fourier-Grenoble 1) Laboratoire d’Electronique Moléculaire Organique et Hybride, CEA Grenoble, 17 Rue des Martyrs, 38054 Grenoble, France (b) Department of Chemistry, Université Laval Quebec City, QC, G1V 0A6 (Canada) (c) Institut des Matériaux Jean Rouxel (IMN), CNRS-Université de Nantes, BP 32229, 2, rue de la Houssini`ere, Nantes 44322, France (d) Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00664 Warszawa, Poland
Resume : Pi-conjugated polymers have attracted significant research interests during the past three decades owing to their tuneable by design (electro)chemical, electronic and optical properties. This remarkable and rare combination of features paves the way toward new generations of (opto)electronics devices such as organic FETs, LEDs, Laser & Solar Cells. Designing efficient materials for boosting solar cell’s external power conversion efficiency (EPCE) beyond state-of-the-art values exceeding 8.0% require, among other important issues, a strict and full control of their redox properties. Key material parameters are HOMO/LUMO levels and the band gap. Cyclic voltammetry (CV) & UV-Vis spectroscopic studies performed on the three synthesized D/A alternated copolymers showed band gaps inferior to 2.0 eV together with easily varied HOMO and LUMO levels in the -5.62 eV to -5.08 eV and -3.53 eV to -3.13 eV respective ranges as a result of our (macro)molecular engineering approaches. UV-vis-NIR spectroelectrochemical studies confirmed CV results, enabling moreover more accurate determinations of their HOMO levels. In addition, Raman spectroelectrochemistry was used for an in depth probing of the redox stability of these new semiconducting materials incorporating an electron-accepting thienopyrrolidione sub-unit. A preliminary and encouraging EPCE value of 1.6% has been obtained for non-optimized D/A bulk-heterojunction solar cells based on D/A alternated copolymer/PC61BM’s active layers.
|14:00||Multiscale modeling of the influence of phase separation in the functioning of organic photovoltaic devices|
Authors : Helena M. G. Correia, Marta M. D. Ramos, Luis Marques, Hélder M. C. Barbosa
Affiliations : Centre of Physics and Department of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
Resume : Controlling and understanding the influence of the morphology of the active layer made of polymer/low weight molecules blend in organic solar cells (OSC) is, in our days, seen as one of the key issues to increase its efficiency. Most of the research in this area, is made at experimental level focusing not only on the influence of the molecular structure of the materials used, but also on the deposition conditions that changes the nanomorphology and thus the OSC performance. On the other hand, the few theoretical studies published in the literature that concern the influence of the active layer morphology in OSC functioning, simulate a blend morphology far from what is expected from experimental data. In this communication, we present a study of the influence of polymer/low-weight molecule morphology in OSC functioning, using a multiscale model based on quantum molecular dynamic calculations to obtain the molecular properties of the organic materials and a mesoscopic model that considers not only the main physical processes that are behind OSC functioning, but also simulates different possible polymer/low-weight molecule phase separation. Our results shed some light on how the different polymer/low-weight molecule blend morphologies affects exciton diffusion/dissociation and charge transport/collection processes in OSC performance.
|14:00||ZnCoO as hole extraction layer in polymer solar cells|
Authors : Torsten Otto, Hans Schmidt, Holger Spahr, Tim Bülow, Torsten Rabe, Sami Hamwi, Wolfgang Kowalsky
Affiliations : Institut für Hochfrequenztechnik Technische Universität Braunschweig Schleinitztstr. 22 38106 Braunschweig Germany
Resume : Polymer solar cells are normally based on liquid polymer solutions applied by spin coating or printing technology. The contact layers at the anode and cathode of those solar cells should feature high transparency and conductivity. The hole transporting layer PEDOT:PSS exhibits both a high transparency and a high hole conductivity but leads to instable solar cells. Thus, alternative oxide based materials have recently been suggested. Zinc Cobalt Oxide(ZnCoO) is a promising material with a high conductivity. We developed ZnCoO layers by plasma enhanced pulsed laser deposition (PEPLD) at room temperature allowing for the precise adjustment of thin layers and high conductivities. We deposited ZnCoO layers with different layer thicknesses and performed measurements to investigate their suitability for solar cells. We found that the conductivity of ZnCoO was around 8 S/cm depending on the oxygen plasma background pressure during the PEPLD process. Using UV-Vis spectroscopy and ellipsometry we obtained the optical characteristics of the ZnCoO layers in order to perform optical simulations to find the optimum thickness as contact layer in polymer solar cells. In the second step we built P3HT:PCBM polymer solar cells with ZnCoO as p-type layer. We show that ZnCoO is an adequate material for hole extraction in polymer solar cells performing comparably to solar cells with PEDOT:PSS.  K. Zilberberg et al.Adv.Funct.Mater.21, 2011  SeonHoo Kim et al.J.Appl.Phys.107 2010
|14:00||2D Finite-Element Modeling of Periodical Interdigitated Full Organic Solar Cells|
Authors : P. Granero, V. S. Balderrama, J. Ferré-Borrull, J. Pallarès, and L. F. Marsal
Affiliations : Nano-electronic and Photonic Systems (NePhoS), Departament d’Enginyeria Electrónica, Eléctrica i Automàtica, Universitat Rovira i Virgili, Av. Països Catalans 26, 43007 Tarragona, Spain
Resume : Since the advent of organic solar cells there has been an intense search to make them at least as profitable as inorganic ones. One promising solution is the interdigitated heterojunction approach, which joins the advantages of bulk heterojunction and planar bilayer devices. This architecture provides a proper exciton dissociation interface without sacrificing direct path for carriers’ collection. Several studies have demonstrated an increase in the efficiency of these cells. Nevertheless, to improve these devices, an optimization of the Donor-Acceptor interface is crucial. By means of numerical modeling, we investigate light absorption, exciton diffusion and the electric behavior of interdigitated heterojunction full organic solar cells. Simulations are carried out by using COMSOL Multiphysics (R). This program is a finite-element analysis software which allows a complete evaluation of the optical and electrical properties of the devices in detail. To determine the best configuration, we have performed a systematic analysis where we compare different cells by varying the Donor-Acceptor interface. We have modified geometrical parameters such as the period, the duty cycle and the length. The donor and the acceptor materials of our cells are poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) respectively. This study will help us to improve our structures, achieved via nanoporous anodic alumina templates, without wasting time and resources.
|14:00||The influence of ZnO nanoparticles on the performances of photovoltaic structures based on MEH-PPV:PCBM(1:4) polymeric blends|
Authors : Sorina Iftimie, A. Radu, Veta Ghenescua, Cristina Besleaga, Simona Craciun, L. Ion, S. Antohe
Affiliations : University of Bucharest, Faculty of Physics, 405 Atomistilor, 077125, Magurele-Ilfov, Romania; aInstitute for Space Sciences, 409 Atomistilor, 077125, Magurele-Ilfov, Romania
Resume : Flexible organic solar cells based on polymeric blends MEH-PPV:PCBM(1:4) were successfully prepared by spin-coating technique on PET foils covered with a thin layer of ITO, as substrates. The goal of this study is to identify the effects of ZnO nanoparticles mixing in PEDOT:PSS solution and to compare the photovoltaic properties of these „customized” cells PET/ITO/PEDOT:PSS+ZnO nanoparticles/ MEH-PPV:PCBM(1:4)/LiF/Al, with ones of the “conventional” structures, PET/ITO/PEDOT:PSS/MEH-PPV:PCBM(1:4)/LiF/Al. ZnO nanoparticles were mixed in PEDOT:PSS solution, using different concentrations. The obtained samples were electrical and photoelectrical characterized. The measurements were performed in dark, monochromatic light and AM 1.5 conditions, too. The action spectra were drawn for each prepared photovoltaic cells and the fill factor, short-circuit current and open circuit voltage parameters were calculated. Photoelectrical measurements indicate that the ZnO nanoparticles have a positive influence on the conversion efficiency, reducing the serial resistance of the structure and improving the stability of the cells. Keywords: polymeric blends, ZnO nanoparticles, photovoltaic cells
|14:00||Garnet phosphor embedded in polymer matrix for application in white light-emitting device on flexible substrates|
Authors : Vasilica Schiopu, Alina Matei, Ileana Cernica
Affiliations : National Institute for Research and Development in Microtechnologies, IMT Bucharest
Resume : Lanthanide-doped phosphors from garnet class combined with blue chips are the most used for light conversion applications. After the phosphor preparation step, the deposition of this on blue (In)GaN chips is the most important and controversial step in the technology of manufacturing white light-emitting devices. In this paper we present a phosphor, from garnet classes, embedded in a PMMA (poly(methyl methacrylate)) matrix. This garnet-PMMA composite can be used in the process for manufacture of the white light-emitting device on flexible substrates. The chemical evolution, structure and morphology of the phosphor and phosphor embedded in polymer matrix were studied.
|14:00||Subsidence of Organic Semiconducting Layers onto Soft Polymer Dielectrics|
Authors : Mi Jang and Hoichang Yang
Affiliations : Department of Advanced Fiber Engineering, Inha University, Korea
Resume : the softness effects of polymer/SiO2 bilayer dielectrics during thermal annealing on the crystal reorganization of PTCDI-C13 and the electrical performances of the resulting OFETs were investigated. First, PTCDI-C13 films were thermally deposited on either polystyrene (PS)-coated or bare SiO2 dielectrics. In this case, PS-coated SiO2 bilayer dielectrics contained different molecular-weight (Mw) PS layers, which were either chemically anchored or freely formed onto the SiO2 surfaces. In particular, molecular layer (ML) thick PS layers (ca. 5 nm) could be formed onto the SiO2 surfaces, via chemically coupling dimethylchlorosilane-terminated PS (PS-Si(CH3)2Cl) at 110 oC and subsequently rinsing excessive PS coating layer. Then, some of the as-deposited PTCDI-C13 films were thermally annealed at various TAs (up to 200 oC) for 1 hr. Finally, top contact-electrodes were fabricated onto these semiconductor films, using evaporating Au through a patterned shadow mask (channel width, W = 1500 μm and length, L = 100 μm). Based on structural analyses of these PTCDI-C13 films, it was found that softening, thinning, and dewetting of physisorbed PS layers adversely affected the lateral connectivity of highly crystalline and π-conjugated PTCDI-C13 grains, which were located near the polymeric dielectrics, above Tg, dielectric. In contrast, on the ultrathin PS brush layers, annealed PTCDI-C13 films could form highly layer-like crystals with a preferential π-conjugation for the charge transport along the crystals, similar to bare SiO2 dielectric system, which has T-independent surface hardness. The resulting PTCDI-C13 OFETs showed high electrical performances: electron mobility (μFET), threshold voltage (VTh), as well as no hysteresis.
|14:00||Mechanisms of the charge transfer in IrQ(ppy)2-5Cl dual-emitter compounds|
Authors : S. Polosan, I.C. Radu
Affiliations : National Institute for Materials Physics, Bucharest-Magurele 077125, Romania
Resume : Ir(III) cyclometalated compounds exhibits intense phosphorescence, characterized by a large radiative rate constant ( up to 106 s-1) at room temperature. The strong phosphorescence of these compounds originates from intersystem crossing processes via spin-orbit interaction. Among phosphorescent cyclometalated Ir(III) compounds is IrQ(ppy)2-5Cl. The photophysical properties of this compound can be calculated and estimated by DFT calculations, using chemical computation software. Their main attractive properties of phosphorescence are based on the Metal-To-Ligand-Charge transfer (MLCT). The results of the hybridization between Ir 5d orbitals and π ligand orbitals shows strong metallic character with phenylpyridine orbitals (66% and 42.5 %) and weak metallic character with quinoline ligand (24%). This fact suggests weak phosphorescence intensity in the emission spectra of this compound. Population analysis of each metallic orbital shows a small charge delocalization on the quinoline ligand for the first molecular orbital and a strong delocalization on the phenylpyridine ligands. Concerning the excited states of this compound, they are coming from the π orbitals of quinoline followed by those of the phenylyridine ligands in the energetic scale. Theoretical results are compared with the preliminary experimental results, concerning the absorption and photoluminescence properties of IrQ(ppy)2-5Cl.
|14:00||Photonic Flash Sintering of Conductive Structures for Printed Electronic Applications|
Authors : Jaquelien van den Boomen, Tim van Lammeren, Rob Hendriks, Erica Coenen, Robert Abbel, Eric J. Rubingh, Pim Groen
Affiliations : Holst Centre - TNO
Resume : Metallic patterns comprising high electrical conductivities are indispensible components of many plastic electronic devices. One of their most important applications is the replacement of conductive oxides in transparent electrodes for OLED and OPV devices on polymeric foils. Printing of metal containing inks is a convenient deposition method for these structures, especially since it allows very high processing speeds. However, a post-deposition treatment is usually required to achieve high conductivities. For that purpose, we have developed photonic flash sintering as a fast alternative to conventional heat treatment. The operating principle is based on the selective heating of the ink by the absorption of strongly focussed visible light, for which the foil is transparent. Furthermore, exposure to short flashes limits the heat flux into the substrate, so that foil deformation can be avoided. The entire process has been investigated both theoretically and experimentally. Time-resolved temperature measurements revealed rapid heating of the ink, followed by fast cooling, resulting in resistivity drops of up to seven orders of magnitude within fractions of a second. The influence of parameters such as ink type, flashing frequency, and light intensity on the sintering process has been studied in detail.
|14:00||Poly(3-hexylthiophene)-based low-voltage organic thin-film transistors with a self-assembled monolayer as a gate insulator|
Authors : M. Chikamatsu (1), Y. Tamaura (1,2), Y. Norikane (1), R. Azumi (1), M. Tamura (2), M. Tsuji (3), K. Marumoto (3,4)
Affiliations : (1) Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Japan; (2) Faculty of Science & Technology, Tokyo University of Science, Japan; (3) Institute of Materials Science, University of Tsukuba, Japan; (4) JST PRESTO, Japan
Resume : Low-voltage operation is one of the important issues for applying organic thin-film transistors (OTFTs) to portable devices. Recently, low-voltage OTFTs were proposed by using a double layer of thin aluminum oxide and a self-assembled monolayer (SAM) based on alkyl-phosphonic acid as a gate dielectric. In this work, low-voltage poly(3-hexylthiophene) (P3HT)-based OTFTs were fabricated, using SAM materials (n-alkyl-phosphonic acids (Cn-PA)) with different alkyl chain lengths [n = 2, 6, 10, 14, 18] as gate insulator itself. P3HT was spin-coated on the gate insulator. Gold was evaporated as source/drain electrodes. The OTFTs showed good p-channel characteristics under low applied voltages between 0 and -2 V. The OTFTs with SAMs of C10-PA, C14-PA, C18-PA gave sufficient hole mobilities above 0.001 cm2/Vs. For analyzing molecular orientation of P3HT in the channel region, we measured electron spin resonance (ESR) of field-induced charge carriers in the OTFTs with SAMs of C2-PA and C18-PA. The ESR signals of the two OTFTs exhibited different g-values, indicating different molecular orientation of P3HT. Tilt angles of thiophene rings with respect to the substrate in the OTFTs with SAMs of C2-PA and C18-PA were calculated to be 34 and 64 degrees, respectively. These results indicate that P3HT chains take an edge-on like structure in the channel region of the OTFTs with SAM of C18-PA, leading to high hole mobility compared with the case of the OTFTs with SAM of C2-PA.
|14:00||Simplified phosphorescent organic light emitting diodes with an organic homojunction structure|
Authors : Changhun Yun, Jonghee Lee, Jaehyun Lee, Björn Lüssem, and Karl Leo
Affiliations : Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Straße 1, 01062, Dresden, Germany
Resume : We realize on simplified homojunction phosphorescent green organic light emitting diodes (OLEDs) by introducing the p-i-n technology into a single host device. Although the stack of organic heterojunctions can improve device performance of OLEDs, the simplified structure is favorable for both the manufacturing perspective of cost effectiveness and for a better understanding of device physics. As a single host material in the simplified phosphorescent OLEDs in this study, 4,4’-Bis(carbazol-9-yl)-biphenyl (CBP) is utilized due to its relative ambipolar property compared to other common host materials for phosphorescent OLEDs. For a better injection and transport of charge carriers, we adopt the p-i-n structure where p-side is the doped CBP with molybdenum trioxide (MoO3) and n-side is doped CBP with cesium (Cs). As a green phosphorescent dopant, bis(2-phenylpyridine)iridium acetylacetonate (Ir(ppy)2(acac)) is tested. We find that the dopant in the i-layer acts not only as a light-emitting site, but also as a trapping site of the for charge carriers, which ensures a balanced electron/hole ratio. Through the optimization of the dopant concentration, the maximum external quantum efficiency (EQE) reaches up to 15.0%. Furthermore, we also find by testing several kinds of dopants having almost the same band gap energy but different highly occupied molecular orbitals (HOMOs) levels that the trap depth of dopant in i-layer strongly influences the performance of homojunction OLEDs.
|14:00||Synthesis of Conjugated Polymer Nanoparticles and Their Application in Polymer Solar Cells|
Authors : Byung-Kwan Yu, Yen-Sook Jung, Dongyoon Khim, Jun-Seok Yeo, and Dong-Yu Kim
Affiliations : Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea. firstname.lastname@example.org
Resume : Conjugated polymer nanoparticles (CPNs) based polymer solar cells (PSCs) have been fabricated using donor, acceptor, and donor-acceptor blend nanoparticles. Starting from an electron-donating and an electron- accepting materials, P3HT and PCBM, dissolved in suitable organic solvents, dispersions in water of solid particles with mean diameters of ca. 30 - 40 nm, containing either the pure organic components or a mixture of P3HT and PCBM in each particle, were prepared with the miniemulsion process. The size of the nanoparticles was established using dynamic light scattering (DLS) of the aqueous dispersions and by both atomic force microscopy (AFM) and High-resolution transmission electron microscopy (HR-TEM) in the solid state as coated films. Photovoltaic devices based on these particles have been studied with respect to the correlation between J-V characterization and active layer composition. It is shown that the properties of devices differ significantly from those of solar cells based on various active layer structures, even for the same layer composition. Various factors determining the device performances in kinds of device structures are identified and discussed, taking into XPS depth profiling.
|14:00||Technological solutions for improving conductive thin films deposition on flexible organic substrate|
Authors : Ileana.Cernica, Vasilica Schiopu, A. Avram, Alina Matei , M.Ion
Affiliations : National Institute for RD in Microtecnhologies(IMT-Bucharest)
Resume : A major problem in using flexible substrates is the poor adherence of the deposited conductive thin films. The paper presents some technological experiments used for strengthening the adherence of conductive thin films on flexible organic substrate. The substrate was an organosilicon compound, polydimethylsiloxane (PDMS) The interconnection conductive thin films are Ti /Au sputter deposed and photolitographic configurated and Ag conductive ink for ink jet technique. The PDMS substrate is processed in RIE plasma in order to functionalize the surface and to have a better adherence of the conductive films. For the Ti/Au films we experiment 2 films: the Ti 50nm/Au 400nm and Ti 50nm/Au 800nm. For RIE we used SF6 with O2 or Ar plasmas. The RF power was 250W and 50W and the pressure 30Pa. The report of SF6 and O2 or Ar flows were varied. The process time was 10 minutes. We also study the modification of treatments in photolithography technological process flow request by the PDMS substrate. For ink jet technological flow , a new post ink deposition treatments were proposed. The characterization techniques used were: - optical microscopy - SEM - Contact angle - AFM - Pull test for adherence The results of experiments were introduction of a new technological sequence in the technological flow of the device.We obtain improved adherence of films both in the case of metal deposition and also in the ink jet imprinting. The final application was a flexible white LED matrix.. We also put in evidence a problem in using PDMS as flexible substrate- cracking apparition after deposition process. The problem was solved using a change in recipe of PDMS sample manufacturing..
|14:00||Investigation of plasmonic effect in Au nanoparticels/polyarylene-thienylene hybrids|
Authors : Elena Dilonardo (1,2), Omar Hassan Omar (3), Michele Tesoro (1), Alessandra Operamolla (1), Gianluca Farinola (1), Giuseppe Valerio Bianco (2) Maria Michela Giangregorio (2), Maria Losurdo (2), Pio Capezzuto (1), Francesco Babudri (1), Giovanni Bruno (2)
Affiliations : (1) Dipartimento di Chimica, Università degli Sudi di Bari “Aldo Moro”, Via E. Orabona 4, 70124 Bari, Italy. (2) Istituto di Metodologie Inorganiche e dei Plasmi, IMIP-CNR, Via E. Orabona 4, 70124 Bari, Italy. (3) Istituto di Chimica dei Composti OrganoMetallici, ICCOM-CNR, Via E. Orabona 4, 70124 Bari, Italy.
Resume : Hybrid materials containing inorganic nanoparticles and π-conjugated polymers have unique properties, and their application in electronic and optoelectronic devices is being explored intensively. In particular, for fabrication of flexible organic photovoltaics (OPVs), the incorporation of metallic nanoparticles (NPs) inside the absorbing layer, generally constituted by polythiophenes, generates surface plasmon that could improve the absorption in the surrounding medium, according to NPs geometry and composition, and the optical constant of the surrounding medium. A crucial issue is the morphological control of active layer and the interface with plasmonic NPs. Here we present the synthesis, optical and structural properties of Au-NPs/polyarylene-thienylene hybrids. We focus on the interplay between polymer film morphologies and AuNPs geometries. Different polymer film morphologies ranging from fiber-like to a globular structures have been obtained changing polymer solution concentration and Au-NPs deposition procedure. The morphology of hybrids was analyzed by AFM; the relationship between geometry and resonance was investigated by spectroscopic ellipsometry, surfaced-enhanced Raman spectroscopy and photoluminescence. Results revealed strong interactions between Au-NPs and polymer with structures of the same order of magnitude of NPs dimension. These results can contribute to understanding of plasmonic interactions between conjugated polymers and metal nanostructures in OPV.
|14:00||Tensile testing of Cu thin films on polymer substrates: growth and recovery of electrical resistance|
Authors : Oleksandr Glushko, Megan Cordill
Affiliations : Montanuniversitaet Leoben, Department of Materials Physics
Resume : Flexible electronic devices contain metallization for electrical connection between different electronic elements. Thus, good understanding of the electromechanical properties of thin metal films on polymers substrates under mechanical load is required. The major part of papers published so far is restricted to the consideration of the electromechanical effects occurring only during loading of the sample. In this contribution we explore the behavior of electrical resistance of thin copper films on PET during the entire tensile test as well as after it. 200 nm Cu films on 23 μm PET substrates were stretched to three different maximum strains: 5%, 10%, and 20%. The electrical resistance was recorded in a 4-probe configuration in-situ during loading, unloading, and 24 hours after unloading. It will be shown that substantial resistance recovery occurs during and after unloading. Moreover, the samples strained to 5% exhibit full resistance recovery after 24 hours despite the clearly visible plastic deformation of the copper film. The mechanisms of resistance growth and recovery are discussed with the help of in- and ex-situ SEM analysis.
|14:00||Dependence of HfO2/IZO heterojunction band offsets on In/Zn composition|
Authors : V. Craciun1, G. Socol1, A. C. Galca2, C. Teodorescu2, S. J. Pearton3
Affiliations : 1National Institute for Laser, Plasma, and Radiation Physics, Bucharest-Magurele, Romania. 2National Institute for Materials Physics, Bucuresti-Magurele, Romania. 3Materials Science and Engineering, University of Florida, Gainesville, USA
Resume : Room temperature deposited amorphous indium zinc oxide (a-IZO) is an excellent transparent and conductive material due to its high conductivity, electron mobility (~50 cm2/V-1s-1) and optical transmittance. The electrical and optical properties of IZO films were found to depend on the In/(In+Zn) ratio. Therefore, in order to optimize the parameters of TFTs devices using a-IZO channels and a high-k gate material such as HfO2, it is necessary to measure the dependence of the valence band discontinuity and conduction band offset on a-IZO composition. Amorphous IZO films with variable In/(In+Zn) composition were deposited at room temperature by a combinatorial pulsed laser deposition (PLD) technique, while simple PLD was used for the high-k HfO2 films deposition. The optical band gap of the films deposited on Si and glass substrates was measured by variable angle spectroscopic ellipsometry and optical transmittance. The mass density and thickness were obtained from simulations of the x-ray reflectivity curves and the electrical conductivity and mobility from Hall measurements. In 3d5/2, Zn 2p3/2, O 1s and Hf 4f7/2 binding energies and valance band maxima for thick HfO2 and IZO films as well as for thin HfO2/IZO heterostructures were measured by x-ray photoelectron spectroscopy. From the measured data, the dependence of the valence and conduction band offsets on In/(In+Zn) values were calculated.
|14:00||Electronic processes at hybrid cadmium sulphide crystal - phthalocyanine interfaces|
Authors : Oleg Dimitriev*, Slawomir Braun#, Mats Fahlman#
Affiliations : *V.Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr. Nauki 41, Kiev, 03028, Ukraine #Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
Resume : Ultraviolet photoelectron spectroscopy has been used to study energy level alignment at (0001) and (000 ) surfaces of bare CdS terminated with Cd and S atoms, respectively, and hybrid interfaces of CdS with donor zinc phthalocyanine (PcZn) and acceptor fluoro-substituted zinc phtalocyanine (F-PcZn) molecules, respectively. The data allowed us to distinguish a slight difference between ionization potential of the Cd- and S-terminated facets of the crystal and different contribution of these surfaces to formation of the interfacial dipole at the hybrid interfaces. Ionization potential for the S-terminated surface was slightly higher as compared to the Cd-terminated one for the same crystal, and a more positive dipole was always created on the S-terminated surface independent on the donor or acceptor character of the phthalocyanine used. The results showed that PcZn and F-PcZn render a dual effect at the CdS surface. First, the molecules created a dipole at the interface, however, the sign of this dipole was opposite for PcZn and F-PcZn, respectively. Second, the both molecules contributed to the formation of a depletion layer near the crystal surface. The role of the surface states of the crystal in the above effects has been elucidated. Interaction of PcZn and CdS surface was associated with the pinning of the HOMO level of the molecule to the upper occupied level of the surface states, whereas interaction of F-PcZn and CdS surface with formation of hybrid states which push the LUMO level of the molecule above the Fermi level of the crystal. Contribution to the depletion layer near the crystal surface was associated with formation of additional surface states in the process of adsorption of the organic molecules onto the crystal surface.
|14:00||Investigations on the response of organic semiconducting single crystals to polarized IR spectroscopy under charge polarization and flow|
Authors : A. Fraleoni-Morgera 1*, E. Capria 1, L. Benevoli 1, B. Fraboni 2, M. Tessarolo 2, L. Baldassarre 1, A. Perucchi 1, S. Lupi 3
Affiliations : 1 - Sincrotrone Trieste, SS. 14 Km 163.5, 34149 Basovizza, Trieste, Italy 2 - Dept. of Physics, Univ. of Bologna, V. Berti Pichat 6/2 - 40127 Bologna, Italy 3 - Dept. of Physics, Univ. of Roma “La Sapienza”, Piazzale Aldo Moro 2, 00185 Roma, Italy
Resume : Organic semiconducting single crystals (OSSCs) are currently regarded as model systems for investigating transport in organic semiconductors, due to their structural order. Solution-grown single crystals based on the intrinsically polar 4-hydroxycyanobenzene (4HCB) molecule evidenced reproducible, three-dimensional anisotropic electronic properties, such as carrier mobilities, density of states distribution, deep traps concentration and energy levels. Accurate linearly polarized IR (LP-IR) studies of 4HCB crystals unveiled further interesting optical properties, like 2D spectral anisotropy (which allows to identify reproducibly and beyond any doubt the crystal axes with no need for X-ray or electrical measurements), 2D anisotropic hydrogen bonding degree, and a 3D anisotropic rotation of the electric dipole vector upon electrical polarization of the crystal. In addition, when the crystals are probed in an OFET structure under actual charge transport flow, a 2D anisotropic IR screening effect of the charge transport layer is detected. The above mentioned results will be presented and discussed in the relation to the elucidated crystal structure [1,2], together with novel LP-IR investigations on 4HCB crystals under actual current flow (in an OFET configuration), at temperatures down to 140 K. Refs  B. Fraboni et al., Adv. Mater. 21, 1835 (2009); Org. Electron., 11, 10 (2010)  A. Fraleoni-Morgera et al.,J. Phys. Chem. C, doi:http://pubs.acs.org/doi/abs/10.1021/jp208452x
|14:00||Lithographic Manipulation of Oligothiophenes Fibers for Organic Electronic Applications|
Authors : D. Gentili,† F. Di Maria,‡ F. Leonardi,† M. Gazzano,‡ G. Barbarella,‡ and M. Cavallini †
Affiliations : † ISMN-CNR, Area Bologna, Via Gobetti 101, 40129 Bologna, Italy; ‡ ISOF-CNR, Area Bologna, Via Gobetti 101, 40129 Bologna, Italy.
Resume : Development of organic conducting molecules and polymeric materials has attracted much interest for the fabrication of nano- and microdevices based on soft materials. Reducing of the dimensional parameters of molecular conductors from three-dimensional (3D) crystal structure to one-dimensional (1D) stacking structure provides functional nano- and microsized fibers, which self-organizing on surfaces could be employed as interconnecting modules in integrated molecular circuits  or active layer in organic field effect transistor. Oligothiophenes are p-type organic semiconductors, which can self-assembly to form conducting fibers. The interactions with surfaces, during the supramolecular self-assembly process, strongly affect the morphology, and long-range order of the fibers . In light of this, unconventional lithographic (UL) methods can be a powerful tool to control and improve fiber properties without using special equipment and conditions . We will present our recent results showing as UL methods can be successful apply to control morphology and long-range order of oligothiophene fibers, tailoring their electrical properties.  M. Hasegawaa, and M.Iyoda Chem. Soc. Rev., 39 (2010) 2420  F. Di Maria, P. Olivelli, M. Gazzano, A. Zanelli, M. Biasiucci, G. Gigli, D. Gentili, P. D’Angelo, M. Cavallini, and G. Barbarella, J. Am. Chem. Soc., 133 (2011) 8654  M. Cavallini, C. Albonetti, and F. Biscarini, Adv. Mater., 21 (2009) 1043
|14:00||Thickness dependence on aluminum oxide and silicon dioxide thin films by pulsed laser deposition for plastic AMOLED|
Authors : W. K. Park, J. Y. Lee, D. H. Yoon
Affiliations : Sungkyunkwan University
Resume : Recently, organic light-emitting diodes (OLEDs) have attracted much attention as a next-generation display due to their advantages such as high emission efficiency, high aperture ratio, high pixel resolution, and low power consumption. However, the performance of organic layers in the OLEDs is gradually degraded under an ambient atmosphere by the permeation of oxygen and water vapor through defects sites.1 In recent year, inorganic thin films such as Al2Ox, SiOx, AlOx, and SiOxNy have been studied as passivation films on polymer substrates. Although the requirement for passivation layers in OLEDs is not yet understood, it has been found that long-lived OLEDs need passivation layer, which transmits less than 10-6 g/m2/day of water and 10-5 cm3/m2/day of oxygen. In this study, we investigated the thickness dependence on aluminum oxide (Al2O3) and silicon dioxide (SiO2) films as a passivation layer by pulsed laser deposition. The total thickness of films was fixed at 40 nm and varied from 5 to 20 nm, respectively. The properties on surface morphologies and roughness in films were examined by field emission scanning electron microscope and atomic force microscope, respectively.
|14:00||Water-soluble porphyrin thin films as electron extraction layers in organic photovoltaics|
Authors : M. Vasilopouloua, A. M. Douvasa, L. C. Palilisb, L. Sigellouc, S. Kennouc, D. G. Georgiadoua, , T. Lazaridesd, A. G. Coutsolelosd and P. Argitisa
Affiliations : a Institute of Microelectronics, National Centre for Scientific Research “Demokritos”, 15310 Athens, Greece; bDepartment of Physics, University of Patras, 26500 Patras, Greece;cDepartment of Chemical Engineering, University of Patras, 26500 Patras, Greece;dLaboratory of Bioinorganic Chemistry, Chemistry Department, University of Crete, Voutes Campus, 71003 Heraklion, Crete, Greece
Resume : Organic photovoltaics efficiency can be enhanced by implemented fabrication procedures that influence Isc and FF, through the modification of interfaces with electrodes in order to enhance carrier extraction and collection. Towards this end we propose in this work the investigation of water soluble porphyrins as electron extraction layers at the cathode site of BHJ OPVs. Thin layers of tetrachloro-meso–tetrakis (1-methyl-4-pyridyl) porphyrin (H2TMPyP4+Cl4) and tetrachloro-zinc-meso-tetrakis (1-methyl-4-pyridyl) porphyrin (ZnTMPyP4+Cl4), have been deposited by spin-coating on top of the P3HT:PC71BM layer to serve as electrode extraction and transport layers in full organic photovoltaic devices. The selected porphyrins are soluble in orthogonal solvents. A large increase in both photocurrent and fill factor is observed for devices with the porpyrins as electron extraction layers. This enhancement is primarily attributed to favourable energy level alignment between the lowest unoccupied molecular orbital (LUMO) of acceptor (PC71BM) (about 3.8 eV) and the LUMO of the porphyrins, located at about 4.0 eV. Enhanced collection of the optical spectrum and further contribution in photocurrent through the red absoption band of the porphyrins is also achieved and attribute to the overall performance optimization. Thus, organic photovoltaics fabricated using spin coating techniques with efficiencies up to 200% increased relative to the reference OPVs can be demonstrated.
|14:00||Electrical response of OFETs with inkjet printed Pedot:PSS electrodes|
Authors : Immacolata Angelica Grimaldi (1,2), Anna De Girolamo Del Mauro (1), Fausta Loffredo (1), Pasquale Morvillo (1),Fulvia Villani (1)
Affiliations : (1) Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Portici Research Center, Piazzale Enrico Fermi 1, 80055 Portici (Naples), Italy; (2) Department of Physics Science, University of Naples Federico II, Piazzale Tecchio 80125, Naples,Italy.
Resume : Recently, Organic Field Effect Transistors (OFETs) have obtained impressive improvements in their performances because of the development of organic semiconductors stable under air condition. The deposition of conductive electrodes, dielectrics and semiconductors from solution opens the way to the fabrication of OFETs by direct printing methods, like the inkjet technology, which are able to guarantee many advantages including low costs, low material wastage, selective deposition of materials and non-contact patterning. Recently, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) polymer has been investigated as innovative material for replacing traditional gold electrodes in OFET structures thanks to its aqueous solution processibility, good thermal stability and excellent interfacial properties with organic semiconductor layers. In the present work, we fabricated bottom-gate top-contacts OFET devices by printing PEDOT:PSS as source, drain and gate electrodes. Pentacene was employed as p-type semiconductor and polymethyl methacrylate (PMMA) was used as organic dielectric. We investigated the electrical performances, including the bias stress phenomena, of the manufactured transistors at different times evaluating the working degradation of the devices in air.
|14:00||Electrical Properties of Bulk Heterojunction Organic Solar Cells with Sputtered Metal Contacts|
Authors : M. Sendova-Vassileva1, G. Popkirov1, P. Vitanov1, Ch. Dikov1, V. Gancheva2, D. Tsocheva2, P. Mokreva2
Affiliations : 1 Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chausse, 1784 Sofia, Bulgaria; 2 Institute of Polymers, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Resume : In this contribution bulk heterojunction organic solar cells with sputtered metal contacts are studied. The photoactive thin film consisting of mixed poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was deposited by spin coating from a chlorobenzene solution. The substrates used were patterned ITO covered glass coated with PEDOT:PSS. Metal electrodes of aluminium or silver were sputtered through a shadow mask. In the sputtering chamber the samples were subjected to thermal annealing in Ar at different conditions before and after metal deposition. The active area was encapsulated using a thin glass plate and UV curable epoxy resin. The solar cells were characterized by measuring their current-voltage curves and impedance spectra in the dark and under illumination. The obtained results were used for estimation of the effective series and shunt resistances of the studied solar cells. Some additional information about the structure of the photoactive layers could be extracted from the comparison of optical microscopy and TEM images and the CPE (constant phase element) observed in the equivalent circuit of the solar cell after fitting the impedance data.
|14:00||Smectic liquid crystals made of “donor-acceptor-donor” triads for photovoltaic conversion|
Authors : G. Hernandez-Ramirez (1), B. Heinrich (1), C. Bourgogne (1), P. Lienerth (2), S. Fall (2), P. Lévèque (2), T. Heiser (2), O. Yurchenko (3), S. Ludwigs (3), D. Ivanov (4), S. Méry (1)
Affiliations : (1) IPCMS, CNRS, 23 rue du Loess, 67034 Strasbourg, France. (2) InESS, CNRS, 23 rue du Loess, 67037 Strasbourg, France. (3) University of Stuttgart, IPOC, Pfaffenwaldring 55, 70569 Stuttgart, Germany. (4) IS2M, LRC7208, 15 rue J. Strarcky, 68057 Mulhouse, France.
Resume : We report on “donor-acceptor-donor” aromatic triads made of an oligothiophene derivative (donor, D), a central perylene bisimide (acceptor, A) core, and substituted at both extremities by a siloxane chain. The presence of the siloxane chain is used to promote a self-organization of the molecules into a smectic liquid crystal phase with alternated D and A sublayers. The liquid crystal organization is stable over more than 300°C-temperature range, including room temperature. Ambipolar charge transport is observed that confirms the coexistence of n and p type conducting domains. The measured photocurrent gives evidence of the generation of free charges at the D/A interface, which is in agreement with transient spectroscopy results. The PV devices fabricated from these triads as single components show poor PV performances, most probably arising from the unsuited orientation of the conducting lamellae as regards to the substrates. Studies are underway to determine and control the orientation of these lamellae.
|14:00||Polymer / copper indium sulphide hybrid solar cells|
Authors : Thomas Rath (1,2), Michael Edler (1,2), Wernfried Haas (1,5), Stefan Moscher (1,2), Roman Trattnig (1,3), Monika Jäger (3), Andreas Pein (2,6), Verena Kaltenhauser (1,2), Sebastian Dunst (2,6), Mario Arar (1,2), Christopher Fradler (1,2), Robert Saf (2), Markus Postl (3), Markus Seidl (1,3), Neha Bansal (7), Saif A. Haque (7), Ferdinand Hofer (5), Emil J.W. List (3,4), Gregor Trimmel (1,2)
Affiliations : (1) Christian Doppler Laboratory for Nanocomposite Solar Cells, Graz University of Technology and NanoTecCenter Weiz Forschungsgesellschaft mbH, Austria; (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, 8160 Weiz, Austria; (4) Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria; (5) Institute for Electron Microscopy and Fine Structure Research, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria; (6) Polymer Competence Center Leoben GmbH, Roseggerstrasse 12, 8700 Leoben, Austria; (7) Department of Chemistry, Imperial College London, South Kensington Campus, Exhibition Road, SW7 2AZ, UK
Resume : In this contribution we present a route towards highly efficient polymer/copper indium sulphide (CIS) hybrid solar cells, covering material aspects as well as device physics. We start with the synthesis of novel precursor materials and prove their applicability for solar cell fabrication by analytical methods like thermogravimetry, mass spectrometry and electron microscopy. The active layer is prepared by mixing a conjugated polymer with the metal xanthate precursors to a precursor ink, which is applied on a substrate by doctor blading or spin coating. The resulting precursor layers are annealed at moderate temperatures (150 – 200 °C), which are compatible with flexible polymer substrates, to form the polymer/CIS nanocomposite active layers. Furthermore we focus on the optical and electrical characterization of the prepared nanocomposite layers and solar cells, especially including a photoluminescence quenching study and transient absorption spectroscopy. Additionally a detailed transmission electron microscopic analysis study will be presented. The prepared solar cells offer the advantages that the active layers are prepared by a direct, in situ, single step process without usage of capping ligands for nanoparticle stabilization. Extended absorption is provided by the CIS nanoparticles and efficiencies of 3% are reached, which is at present by far the highest reported for polymer/CIS nanocomposite solar cells.
|14:00||Bulk-heterojunction based light detector: modelling in the framework of hopping photoconductivity|
Authors : Iacchetti A., Natali D., Binda M., Beverina L., Sampietro M.
Affiliations : Dip. Elettronica e Informazione, Politecnico di Milano, P.za L. da Vinci 32, 20133 Milano, Italy and Center for Nano Science and Technology of IIT@PoliMI, Via Pascoli 70/3, 20133 Milano, Italy
Resume : Photoconductors deserve particular interest in light detection for their ability of performing signal amplification, thus possibly resulting in efficiency exceeding 100%. In this contribution we show that by proper modelling and starting from simple photocurrent measurements, photoconductors can be also exploited to extract relevant material parameters otherwise not easily accessible. To this extent, we revisit the classical model for photoconductivity developed in the multiple trapping and release framework (Rose, 1963) to take into account the hopping nature of charge transport in organic semiconductors. Assuming an exponential density of states, we demonstrate that, given few basic parameters (the total density of states, the attempt-to-escape frequency and the localization radius), and by exploiting both static and transient photocurrent measurements performed by varying applied voltage and incident power density, we can extract: the mobility as a function of the charge density, the photogeneration yield, the trapping centres cross section. The model has been validated on a prototypical lateral metal-semiconductor-metal photoconductor based on a Squaraine/PCBM bulk heterojunction, and a discussion on the physical relevance of extracted parameters will be given.
|14:00||Graphene based bulk-heterojunction photovoltaic devices|
Authors : L. M. Veca1, I. Stamatin2*F. Craciunoiu1, A. Dinescu1, R. Gavrila1, M. Danila1, M. Purica1, E. Vasile1,3, A. Balan2, S. Iordache2
Affiliations : 1 National Institute for Research and Development in Microtechnologies IMT-Bucharest, 32B Erou Iancu Nicolae Str., 72996, Romania; 2University of Bucharest, Faculty of Physics, 3Nano-SAE Research Centre , MG-38, Bucharest-Magurele, Romania; 3METAV CD, Bucharest, Romania.
Resume : It has been shown that soluble graphene is a promising alternative to the traditional electron-acceptor materials in the photovoltaic applications. In this paper, we used a colloidal solution of the non-oxidized graphene with up to four layers and conjugated polymers, as the photoactive material, to design an organic photovoltaic device. Specific fabrication details and the performances of the bulk heterojunction organic photovoltaic devices together with their potential to outperform traditional fullerene based bulk-heterojunction photovoltaic devices are investigated. In addition, the contribution of the nanoscale morphology, the crystallinity of the semiconducting polymer, and the electrode contact to the device performances is also studied.
|14:00||Experimental and theoretical optimization of a Half-wavelength-optically-thick OLED hetero-structure|
Authors : Anthony Coens 1, Mahmoud Chakaroun 1, Alexis Fischer 1, Min Won Lee 1, Azzedine Boudrioua 1, Bernard Geffroy 2
Affiliations : 1)Laboratoire de Physique des Lasers CNRS UMR 7538 - Université de Paris 13 93430 Villetaneuse, France, 2)Laboratoire Composants Organiques, CEA/Saclay, 91191 Gif-sur-Yvette, France
Resume : The realization of electrically pumped organic laser diode remains a major challenge for organic optoelectronics. In this context, theoretical and experimental studies of the optical and electrical conditions are required for the design of a microcavity OLED with high-current-density and quality factor. As an intermediate step one can consider an uncompleted microcavity based on a multilayer mirror on the one side and an aluminum semi-transparent layer on the other side. In this work, we report the investigation of an OLED heterostructure based on a Alq3/DCM2 guest-host system as an emitting layer and m-MTDATA as a hole-injection layer. The main optical condition is that the optical thickness of the OLED is half of the targeted emission wavelength. Therefore, the electrical performance (current density) and the optical properties of the microcavity are then studied as a function of the key parameters for the OLED design, i.e. the hetero-structure optical thickness, and the aluminum cathode thickness. The experimental results show that a 123 nm-thick OLED hétérostructures, with the emitting layer located at the antinode, exhibits a resonance at 620 nm with a substantial luminance enhancement by a factor 7 at normal incidence. Based on the results obtained with different aluminum layer thicknesses (10 to 100 nm), our measurements allowed to setup the trade-off between the current density and the microcavity quality factor. Results will be presented and discussed.
|14:00||Efficient organic solar cells based on the PPV-PPE copolymers and fullerene derivatives|
Authors : Olga A. Mukhacheva (1), Pavel A. Troshin (1), Andrey E. Goryachev (1), Niyazi Serdar Sariciftci (2), Daniel A. M. Egbe (2), Vladimir F. Razumov (1)
Affiliations : (1) Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow region, 142432, Russia. (2) Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz, Austria
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 has been shown that the molecular structure and the solubility of the fullerene counterpart affect significantly the photovoltaic performance of the PPV-PPE copolymers. The application of 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 solubility 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 PCBM-type materials. We believe that this combinatorial approach might bring the best performing donor/acceptor combinations for the future generations of the efficient organic solar cells.
|14:00||Novel methods for controlling the quality and evaluating the degradation profiles of conjugated polymers designed for photovoltaic applications|
Authors : Pavel A. Troshin (1), Diana K. Susarova (1), Nataliya Piven (2), Ekaterina D. Levchenkova (1), Kseniya V. Lizgina (1), Yury L. Moskvin (2), Zayana V. Dzhivanova (1), Sergei D. Babenko (2), Sergey A. Ponomarenko (3) and Vladimir F. Razumov (1)
Affiliations : (1) Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 5, Chernogolovka, Moscow region, 142432, Russia; (2) Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences (Branch), Semenov Prospect 1/10, Chernogolovka, Moscow region, 142432, Russia (3) Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences, 70 ul. Profsoyuznaya, 117393 Moscow, Russia
Resume : Batch to batch variations of electronic properties of conjugated polymers are known to be related to the presence of defects and impurities. We report two simple methods developed for analysis of conjugated polymers. The appearance of impurities was shown to change the electrophysical properties of the materials. A clear correlation between the effective relaxation time and the relative photovoltaic performance was revealed for many conjugated polymers. The appearance of impurities and structural defects also leads to the accumulation of localized radical species. The concentrations of such radical species (cR) were determined for different polymer samples using electron spin resonance (ESR). An excellent correlation between the relative photovoltaic performance and the radical concentration has been revealed. The developed techniques were also applied for monitoring the degradation processes in conjugated polymers. It was shown that all studied materials tend to accumulate localized radical centers under continuous light irradiation. The rate of the accumulation of the radical species correlates well with both the degradation of the polymer itself revealed using absorption spectroscopy and the degradation of photovoltaic devices comprising the polymer/PCBM composites. The data obtained using a combination of complementary techniques allowed us to compare the photostability of many conjugated polymers commonly used in organic photovoltaics.
|14:00||Effects of chemical modifications on optical, morphological, and electrical properties of three spin-coated PPV derivatives films|
Authors : A. Touhami, H. Hrichi, N. Jaballah, R. Ben Chaâbane, H. Ben Ouada, M. Majdoub
Affiliations : Faculté des sciences de Monastir, Tunisia _ Laboratoire des interfaces et matériaux avancés
Resume : Three organic diodes formed by sandwiching each new modified poly (para phenylenevinylene) layer between indium-thin oxide (ITO) and Aluminum (Al) contacts have been elaborated. The morphological, optical and electrical properties of spin-coated PPV derivatives thin ﬁlms have been investigated. The energy band gap of each thin ﬁlm has been measured by UV–Vis absorption spectroscopy. Crystallinity and surface roughness which is correlated with its hydrophobicity have been determined by atomic force microscopy and by wettability test. The current–voltage (I–V) characteristics of ITO/PPV derivative/Al devices have been studied. The I–V dependence follows a power law, I ∝Vm, which is typical of a space-charge-limited current (SCLC). Moreover, from the I–V measurements, we have estimated the effective hole mobility in the PPV derivates thin ﬁlms. Using impedance spectroscopy in a frequency range between 100 Hz and 10 MHz for different bias voltage, it is found that the ac behavior of ITO/PPV derivative/Al devices shows several features. Therefore, the Cole–Cole plots were modeled as an equivalent circuit formed by a single parallel resistor and capacitor network placed in series with a resistance. Values of the electrical circuit parameters deduced from ﬁtting experimental data to the model have given a dielectric relaxation time in the millisecond range and an exponential trap distribution.
|14:00||Novel two-component electron-selective buffer layers for organic solar cells|
Authors : Roman E. Levin, Alexey B.Kornev, Pavel A. Troshin and Vladimir F. Razumov
Affiliations : Institute for Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow region, 142432, Russia
Resume : We report novel electron-selective buffer layers for inverted organic solar cells. To build such devices, thin TiOx films deposited on the semitransparent ITO electrodes were covered with self-assembled monolayers (SAMs) of polycarboxylic derivatives of C60 and C70 fullerenes (PCFDs). Fullerene (PCBM)/polymer (P3HT or PCDTBT) blends were deposited on the top of the MOx/PCFDs buffer layers and then the device structure was completed by vacuum deposition of MoO3/Ag. The solar cells comprising the intermediate PCFDs monolayers showed significantly improved fill factors, open circuit voltages and power conversion efficiencies compared to the reference cells where bare metal oxides were used as electron selective contacts. The application of SAMs composed of a fullerene derivative bearing a single carboxylic group (PCBA, phenyl-C61-butyric acid) did not result in any improvement in the device performance. Therefore, the advanced properties of PCFDs monolayers seem to be related to a stronger binding of these compounds to the metal oxide surface. According to our preliminary results, the application of intermediate PCFDs self-assembled monolayers also enhanced significantly the device operation stability resulting from the improved active layer/electron collecting electrode interface. Thus, the application of PCFDs as interlayer materials improved both the efficiency and the operation stability of the inverted organic solar cells based on the P3HT/PCBM and PCDTBT/PCBM composites.
|14:00||Enhancement of molecular polarizabilities by the push-pull mechanism; a DFT study of substituted polyacetylene chain|
Authors : N.S .Labidi1*, F. Mechachti2, A.Djebaili2*, J.P. Chopart3, B. Frederic3
Affiliations : 1*Department of chemistry, Faculty of sciences, University of the sciences and technology of Oran (U.S.T.O.MB), BP-1505 Oran El-M’naouer (31000), Algeria. ² Laboratory of chemistry and environmental chemistry L.C.C.E - University of Batna- Algeria 3 Laboratory of Mechanical Stress-Transfer Dynamics at Interfaces – LACMDTI URCA,BP 1039, 51687 University of Reims Cedex2, France
Resume : The dipole polarizabilities α for a series of substituted polyacetylene molecules of the R1-(CH=CH)n-R2 with n= 8, 10 and 12 ; and with R1 = NH2, NO2, S, H, CHO, SO2 and R2 = H, OH,NH2, PH3 et (NH2)2 have been computed using DFT method at B3LYP/6-311 G(d,p) level of theory. Our results allowed to sort out the considered Π-donor and Π-acceptor substituents by decreasing static isotropic α value. Miller QSAR-quality polarizability calculations give a correlation coefficient of 0.99 when compared with BLYP/6-311G(d,p) values. Empirical models based on molecular volumes give unrealistic values for <α> but these values correlate well 0.98 with BLYP/6-311G(d,p) results. Keywords: DFT, polarizability, Push-pull mechanism, polyacetylene
|14:00||Multi adducts of fullerenes as electron acceptors for polymer solar cells: a quantum chemical study|
Authors : P. Morvillo
Affiliations : ENEA, P.le E. Fermi 1, 80055 Portici (NA), Italy
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 PCBM and 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 PCBM have an higher LUMO level (compared to 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 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 PCBM as acceptor have an higher short circuit current (Jsc) compared to the ones based on PCBM, due to the increase of absorption in the visible part of the spectrum, we also studied bis adducts of 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.
|14:00||Waterbased graphene nanocomposites inks for flexible substrates|
Authors : Alexandru Cosmin Obreja, Dana Cristea, Raluca Gavrila, Vasilica Schiopu, Adrian Dinescu, Mihai Danila, Florin Comanescu
Affiliations : National Institute for Research and Development in Microtechnologies (IMT-Bucharest)
Resume : Methoxypolyethylene modified graphene nanocomposites in poly (3,4-ethylene dioxythiophene):poly(styrenesulfonate) PDOT-PSS matrix have been realized for stable dispersion of graphene flakes used as inks for printed flexible plastics substrates. Aqueous solutions were deposited using a Fujifilm Dimatix printer machine for transparent patterned electrodes. Polymer nanocomposites films exhibit low threshold percolation conductivity, improved adhesion on plastic substrates and good mechanical and electrical properties. The nanocomposites were characterised by Fourier transform infrared spectroscopy, UV-Vis spectroscopy, Atomic force microscopy, Scanning electron microscopy, Raman spectroscopy and nanoindentation tool. The results show that aqueous graphene-PEDOT:PSS inks can be a very promising electrode material for highly efficient flexible ITO-free transparent films.
|14:00||Highly efﬁcient ﬂexible and rigid inverted organic solar cells using sputtering deposited ZnO as electron selective layer|
Authors : Y. Jouane, S. Colis, G. Schmerber, A. Dinia, T. Heiser, and Y.-A. Chapuis
Affiliations : Y. Jouane, T. Heiser, Y.-A. Chapuis CNRS - Université de Strasbourg Institut d’Electronique du Solide et des Systèmes (InESS) 23 rue du Loess, BP 43 67037 Strasbourg Cedex, Strasbourg, France E-mail: email@example.com S. Colis, G. Schmerber, A. Dinia CNRS – Université de Strasbourg Ecole Européenne de Chimie, des Polymères et des Matériaux Institut de Physique et Chimie des Matériaux Strasbourg (IPCMS) UMR 7504 CNRS, UDS-ECPM, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, Strasbourg, France.
Resume : Recently, many studies have focused on interfacial buffer layers using zinc oxide (ZnO) semiconductor, a very promising material for inverse Organic Solar Cells (OSCs). High quality ZnO thin films can be prepared on large-area ITO-coated flexible substrates for OSCs, using low temperature deposition techniques such as sputtering, a technique compatible and roll-to-roll process. In this work,ZnO films have been sputtered on ITO-coated PEN substrates as a promising interfacial layer to enhance the performances of flexible and rigid inverse-type organic solar cells (OSCs). We investigate on the influence of the annealing temperature of ZnO films on the photovoltaic performances of rigid (on glass) and flexible (on PEN) inverse solar cells. High annealing temperature of ZnO lead to improve structural properties and performances of both rigid and flexible devices. We also show that, for annealing temperatures of 160 °C, remarkable results were achieved using PEN substrate. At this temperature, the OSC cell exhibits a higher power conversion efficiency (PCE = 2.6 %) than for the cell deposited on glass subtrate (PCE = 2.1 %).
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