Symposium Organizers
DavidS. Ginley National Renewable Energy Laboratory
NealR. Armstrong University of Arizona
Gitti Frey Technion - Israel Institute of Technology
ReubenT. Collins Colorado School of Mines
CC3: Poster Session I
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
1:00 AM - CC3: poster_1
CC3.10 Transferred to CC2.4
Show AbstractCC1: Organic/Organic Interfaces
Session Chairs
Tuesday PM, April 26, 2011
Room 3011 (Moscone West)
9:30 AM - **CC1.1
Control of Interfacial Phenomena in Organic Optoelectronic Devices by Incorporation of Conjugated Polyelectrolytes.
Guillermo Bazan 1 , Junghwa Seo 1 , Corey Hoven 1 , Thuc-Quyen Nguyen 1 , Andrea Gutacker 1 , Xuan-Dung Dang 1
1 Materials, University of California, Santa Barbara, California, United States
Show AbstractConjugated polyelectrolytes (CPEs) are defined by a backbone with a delocalized electronic structure and pendant groups bearing ionic functionalities. These materials combine the optoelectronic properties of organic semiconductors with the ability of polyelectrolytes to have their function determined by electrostatic forces. Increased solubility in highly polar organic solvents, or water, allows CPE deposition atop typical non polar layers, such as those commonly found in bulk heterojuction (BHJ) solar cells or the electroluminescent layer in polymer light emitting diodes (PLEDs). The ionic component in CPEs plays an important in the overall function at interfaces. Two limiting mechanisms have been observed. The first concerns the formation of self-assembled dipole layers that can influence the effective work function of adjacent electrodes. Here, special considerations need to be taken to overcome the coulombic repulsion between dipoles. In a second situation, the ion in the CPE layers can migrate under the application of an external bias and thereby redistribute the electric field within the device. Steep gradients, akin to those in the electrical double layer, are formed that decrease barriers to charge injection.In one well-studied example, CPE interlayers can be used as electron injection/transport layers in PLEDs and enable the use of environmentally stable metals, such as gold or aluminum. Both of the above-discussed mechanisms have been observed, depending on the layer thickness. These findings have been extended to thin film transistors (TFTs) and to light emitting TFTs that can take advantage of the same type of metal for both electron and hole injection.More recently, it has been found the CPE layers can also increase the open circuit voltage (Voc) of BHJ solar cells. This increase in Voc directly improves the power conversion efficiency (PCE) of the devices. However, there is a strong dependence on the chemical nature of the BHJ components, the method of CPE deposition and the nature of the CPE/BHJ contact. These findings will be discussed, with special attention to the correlation between nanoscale characterization of surface potential and device performance.
10:00 AM - CC1.2
Using Morphology to Reduce Photo-oxidation in Organic Photovoltaics.
Craig Peters 1 , Toby Sachs-Quintana 1 , John Kastrop 1 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractImpressive developments have been made in the field of polymer-based organic photovoltaics (OPV) in recent years. Single junction power conversion efficiencies are over 8% with 10% likely to be reached. As efficiencies have risen, the questions of lifetime and reliability of OPV have gained in importance. Current polymer-based OPV devices typically show lifetimes of 3~5 years when state-of-the-art encapsulation is used. A lifetime closer to 15 years is necessary to enable the successful commercialization of OPV. A deeper understanding of the degradation mechanisms and the development of novel materials and device architectures are required in order to achieve this target. In high efficiency polymer devices, a polymer is blended together with a fullerene derivative to form a bulk heterojunction light absorbing layer (BHJ). The BHJ is responsible for absorbing light, splitting the electrons and holes and transporting the charges to their respective electrodes. One of the key challenges is that in the presence of oxygen and light, polymers are susceptible to photo-oxidation. Photo-oxidation of the polymer can break the conjugation of the polymer, which will reduce charge mobility, raise recombination and ultimately reduce absorption by the polymer (photo-bleaching). In this study we show that intercalating the fullerene between the alkyl side chains of the polymer significantly reduces photo-oxidation of the polymer. Intercalation places the fullerene close to the polymer backbone, which enables stronger intermolecular electron orbital interaction and rapid electron transfer from the LUMO of the polymer to the LUMO of the fullerene, resulting in faster quenching of the polymer’s excited state. By rapidly quenching the polymer’s excited state we are able to reduce the rate of photo-oxidation of the polymer by a factor of 3X.In this study thin films of BHJs using PC(70)BM and bis-PC(70)BM and three different polymers were deposited on glass. Through the use of x-ray diffraction we are able to determine which combination of polymer/fullerene BHJs is intercalated and which is not. Importantly, we are able to identify polymers that allow PC(70)BM to intercalate between the alkyl side chains but not allow bis-PC(70)BM to intercalate, thereby allowing a more precise way of studying the effects of intercalation on the same polymer. The BHJs are then aged under one-sun conditions in air and their absorption spectra are monitored periodically. We find that the intercalated BHJs maintained their UV-Vis absorption 3X longer than the BHJs that were not intercalated, providing a powerful tool for extending the lifetime of polymers in OPV.
10:15 AM - CC1.3
Stretchable Organic Solar Cells.
Darren Lipomi 1 , Michael Vosgueritchian 1 , Benjamin Tee 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractFull mechanical compliance is a prerequisite for thin film devices that require i) reversible bending and stretching and ii) one-time bonding to curved surfaces. Stretchable devices comprising organic semiconductors could, for example, be integrated with textiles, wearable devices, and other consumer electronics; the joints of robots and prosthetic limbs; and architectural elements, auto bodies, and lenses. Further, stretchable devices can be more resistant to mechanical failure than devices that are only flexible. While research on stretchable electronics has made remarkable progress in displays, sensors, cameras, and other devices, stretchable sources of power have received far less attention. This report describes the first intrinsically stretchable organic solar cell. The process of fabrication begins by pre-straining an elastic membrane of poly(dimethylsiloxane) (PDMS). The pre-strained PDMS is coated with a transparent, conductive film of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) or blend of single-walled carbon nanotubes (CNTs) and PEDOT:PSS, and a 1:1 blend of regioregular poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). A low-work-function electrode of eutectic gallium-indium (EGaIn) completes the device. After fabrication, the pre-strain is released. This action creates sinusoidal waves (buckles) in the device whose micron-scale pitch increases with the value of the pre-strain and the thickness of the films, and decreases with the stiffness of the film. These devices can be stretched reversibly up to the value of the pre-strain (up to 30%), but fail if not pre-strained. The photovoltaic effect remains intact after 1000 cycles of stretching.
11:00 AM - **CC1.4
Achieving High Performance Tandem Polymer Solar Cells.
Yang Yang 1
1 Materials Sci. & Eng., UCLA, Los Angeles, California, United States
Show AbstractTandem polymer solar cells are a promising candidate for low-cost solar energy, as they have the ability to increase both the intensity and spectral range of absorption, thus minimizing the electron potential loss relative to incident photon energy. In a tandem cell, the two subcells are connected in series by an interconnection layer (ICL) which facilitates efficient charge recombination at the interface. However, because the second polymer photoactive layer is usually spin-coated on top of the ICL, the resistance of interconnect layer against solvents becomes one of most challenging issues, preventing the optimal processing of the second polymer BHJ. In this work, a polymer tandem solar cell based on a robust and versatile ICL is presented with high efficacy. Our universal ICL offers a unique route to achieve unprecedented high efficiency of multiple-junction polymer solar cells via solution process.
11:30 AM - CC1.5
Energetic Alignment of Recombination Contacts for Tandem Organic Solar Cells Investigated by Photoelectron Spectroscopy.
Selina Olthof 1 , Ronny Timmreck 2 , Bjoern Luessem 2 , Moritz Riede 2 , Karl Leo 2
1 Department of Electrical Engeneering, Princeton University, Princeton, New Jersey, United States, 2 Institut fuer Angewandte Photophysik, TU Dresden, Dresden, Sachsen, Germany
Show AbstractOrganic solar cells have the drawback that, even though they have a large absorption coefficient, they only absorb in a narrow energy band which limits device efficiency. To overcome this, tandem cells are used where two or more cells consisting of different absorbers are combined in a single device. The cells have to be connected by a recombination layer that converts the electron current from the first solar cell into a hole current for the second solar cell. This can either be achieved by the insertion of metal clusters / thin metal layers at the interface or by using highly doped layers to form a pn junction between the two sub-cells that allows for a tunneling current in backward direction. In this work, we use photoelectron spectroscopy to investigate different previously published and well working organic tandem cell recombination contacts [1] featuring the organic materials C60 and N,N,N',N'-tetrakis(4-methoxyphenyl)benzidine (MeO-TPD). This is done by measuring the changes of work function and occupied density of states during a stepwise deposition of the various relevant interfaces. We show that the insertion of Au metal clusters leads to a reduction in HOMOMeO-TPD - LUMOC60 offset compared to the intrinsic interface and furthermore introduces a density of states up to the Fermi energy. For the highly doped layers we use 3,6-bis(dimethylamino)acridine (AOB) as n-dopant in C60 and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) as p-dopant in MeO-TPD. Here, the doping reduces the HOMO-LUMO offset even more and leads to depletion layer thicknesses below 10nm.[1] R. Timmreck et al., J. of Appl. Phys. 108 (2010) 033108
11:45 AM - CC1.6
Vertical Stratification and Interfacial Structure: ``Snapshots” in P3HT:PCBM Organic Solar Cells.
Bofei Xue 1 , Ben. Vaughan 1 , Chung-How Poh 1 , Kerry Burke 1 2 , Lars Thomsen 3 , Andrew Stapleton 1 , Xiaojing Zhou 1 , Glenn Bryant 1 , Warwick Belcher 1 , Paul Dastoor 1
1 Centre for Organics Electronics, University of Newcastle, Newcastle, New South Wales, Australia, 2 , CSIRO Energy Centre, Newcastle, New South Wales, Australia, 3 , Australian Synchrotron Company Ltd, Melbourne, New South Wales, Australia
Show AbstractStructure and morphology play a critical role in determining the performance of organic photovoltaic devices. In this paper, variation of the post-annealing cooling rate has been used to create a series of “snapshots” of the reorganization processes that occur upon annealing. P3HT:PCBM blend devices exhibit a complex vertical stratification of both crystallinity and blend composition. Using a combination of UV-vis spectroscopy, XRD, NEXAFS, AFM and contact angle measurements, we have shown that annealing results in the formation of three distinct vertical layers. Diffusion of PCBM from the interfaces into the bulk blend film results in the formation of (a) a P3HT-rich substrate interfacial (wetting) layer, (b) a blended bulk film layer and (c) a P3HT-rich air interfacial (capping) layer. The orientation of the P3HT molecules varies from a wetting layer of c-axis aligned P3HT at the substrate interface to an a-axis aligned P3HT capping layer at the air interface with an intervening bulk layer that shows a-axis alignment. The data show that by slowing the post-anneal cooling rate devices with significantly enhanced efficiencies can be prepared. This improvement in device performance is correlated with the observed increased crystallinity, polymer alignment and phase segregation both at the interfaces and in the bulk film. In particular, slow cooling results in an aligned interfacial active layer/substrate structure that is beneficial for charge transport.
12:00 PM - CC1.7
Energy Level Alignment at Polymer/PCBM Heterojunctions under Operating Conditions in an Organic Photovoltaic Cell.
Johannes Frisch 1 , Jens Niederhausen 1 , Andreas Wilke 1 , Patrick Amsalem 1 , Antje Vollmer 2 , Norbert Koch 1 2
1 Institut für Physik, Humboldt-Universität zu Berlin, Berlin Germany, 2 , Helmholtz-Zentrum Berlin für Materialien und Energie - Speicherring BESSY II, Berlin Germany
Show AbstractOrganic photovoltaic cells (OPVCs) based on the heterojunction concept are most promising for realizing low-cost solar cells. Encouraging results have already been achieved for OPVCs using small molecules, polymers, or blends thereof as active layer. During past few years, research efforts have focused on poly(3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl[6.6]C61 (P3HT:PCBM) blends in bulk heterojunction cells. While energy conversion efficiencies up to 5% were achieved via optimized processing of such active layers, fundamental issues concerning the origin of the open circuit voltage (VOC) remained. Controversial discussions in this context concern a possibly linear dependence of VOC on the energy offset between the highest occupied molecular orbital (HOMO) of the donor material and the lowest unoccupied molecular orbital (LUMO) of the acceptor material. This proposition was based on comparing electrical device parameters with literature-values for the HOMO and LUMO position of the separate donor and acceptor material assuming vacuum level alignment at the donor/acceptor interface [1, 2]. However, interface dipoles (ID) might occur at organic/organic heterojunctions, which questions the assumption of vacuum level alignment at OPVC interfaces. Therefore, we investigated the energy level alignment at P3HT:PCBM heterojunctions with ultraviolet photoelectron spectroscopy (UPS). Samples were prepared by spin coating PCBM from very dilute chloroform solution onto insolubilized P3HT films to avoid intermixing of the two materials. In contrast to common expectations, the valance band of P3HT shifted to higher binding energy (i.e., away from the Fermi-level) by 0.45 eV (BE) after deposition of PCBM, while vacuum level alignment was found. This observation would imply an increase of the P3HT ionization energy upon interface formation, which is usually not considered in simple models. The observed phenomenon can be explained either by a structural rearrangement of the donor polymer layer upon acceptor deposition or by surface photovoltage effects that occur during UPS experiments. Dynamic charge transfer at the P3HT:PCBM interface could positively charge the P3HT layer whereas negative charges are collected in the PCBM layer. The resulting interface dipole counterbalances the valence band shift of P3HT towards higher BE. These results are compared to a polymer/polymer heterojunction comprising P3HT and poly{[N,N9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} (P(NDI2OD-T2) as acceptor, which exhibits a similar behavior.[1] C. J. Brabec, A. Cravino, D. Meissner, N. S. Sariciftci, T. Fromherz, M. T. Rispens, L. sanchez, J. C. Hummelen, Adv. Funct. Mater. 2001, 11, 374 [2] L. J. Koster, V. D. Mihailetchi, P. W. M. Blom, Appl. Phys. Lett. 2006, 88, 093511
12:15 PM - **CC1.8
Measurement, Modeling, and Modification of Electrode Interfaces in Bulk Heterojunction OPV.
Sean Shaheen 1 , Nikos Kopidakis 2 , Brian Bailey 1 , Alex Dixon 1 , Xin Jiang 1 , Ajaya Sigdel 1 , Kui Zhao 3 , Aram Amassian 3 , Joseph Berry 2 , Peter Graf 2 , Jao van de Lagemaat 2
1 Physics and Astronomy, University of Denver, Denver, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 Materials Science and Engineering, King Abdullah University of Science and Technology, Thuwal Saudi Arabia
Show AbstractPolymer-fullerene blend organic photovoltaic devices rely on the bulk heterojunction concept for their operation. However, use of the term “bulk” is very tenuous for an active layer material with a thickness typically of 100 - 200 nm. The field and charge distributions in the active layer and hence the operation of the entire device can be heavily impacted by the behavior at the interfaces with the electrodes or buffer layers. Here we discuss studies into several aspects of the problem. First, we find that the injection of charge in a typical ITO/ PEDOT:PSS/polymer-fullerene blend structure is very heterogeneous as measured by conductive-tip atomic force microscopy. We attribute fluctuations in the nanoscale current of ~20% to interfacial properties and not bulk properties such as local deviations in donor-acceptor blend ratio. This conclusion is drawn from EF-TEM measurements that show the donor-acceptor ratio to be relatively constant on the lateral length scale of the current fluctuations. Secondly, through impedance spectroscopy measurements coupled with numerical solutions of electrostatic equations, we construct models of the field and charge distributions of devices. These commonly show substantial Schottky junction character at metal-organic interfaces. Lastly, we describe device fabrication studies using hot-press lamination of the metal electrode. We show that the performance of these devices fabricated entirely by non-vacuum methods can approach that of devices with vacuum-deposited electrodes, if appropriate interfacial processing and modification are carried out.
12:45 PM - CC1.9
Study of Electrode Effects on Organic Solar Cell Efficiency via Simulation.
Brian Zacher 1 , Neal Armstrong 1
1 Chemistry, University of Arizona, Tucson, Arizona, United States
Show AbstractThe power conversion efficiency (η) of organic photovoltaics (OPV), even with fully optimized active layers, can be significantly reduced when partially blocked (passivated), or non-selective contacting electrodes are used to extract photo-generated holes or electrons. Recent conducting tip AFM studies have shown that loss of contact electroactivity, on 50-500 nm length scales, increases the probability for recombination of charges near these blocked regions, and significantly lowers the fill-factor (FF) in the OPV, decreasing η in many cases by 50% or more. We are interested in modeling the effect of loss of ohmicity for contacting electrodes and specifically want to understand how the size, spacing and surface density of these blocked sites, relative to charge mobilities and charge densities in the active layer, influence η. We also wish to explore the effect of a well designed charge selective interlayer, coating the collection electrode, on OPV performance, and the extent to which it can mitigate electrical problems in the underlying contact. Previous simulations of OPVs have been performed by self-consistently solving coupled differential equations under the assumption of homogeneous materials and contacts, and are unable to model the effects of discrete heterogeneity. In first simulation experiments we model a planar heterojunction OPV by discretizing it into 250,000 sites (50nm x 50nm x 100nm). In software each site (either a single molecule or 1 nm^2 electrode site) can be assigned a specific activation energy for charge movement into and out of that site. This discrete simulation method allows for simulation of photoinduced electron transfer (photocurrent production at the donor/acceptor interface), diffusion of these charges toward the collection electrodes, and introduction of heterogeneity in both the bulk material as well as at the electrode. Individual electrode sites can be turned 'on' or 'off' in order to model a partially blocked electrode and the corresponding OPV electrical parameters recorded. We present here the results of our first simulations which demonstrate that size and spacing of blocked sites on the contact electrode, relative to charge mobility in the active layer, can reduce the photocurrent, measured at the maximum power point in the OPV, by significant levels. These effects are less pronounced for active layer materials with high charge mobilities, and for electrodes coated with high conductivity interlayers which allow the blocked charges to diffuse laterally to an active site, and harvested, at rates that are competitive with recombination.
CC2: Organic/Metal Interfaces
Session Chairs
Reuben Collins
Sean Shaheen
Tuesday PM, April 26, 2011
Room 3011 (Moscone West)
2:30 PM - **CC2.1
The Chemical Evolution of Low Work Function Metal/Organic Interfaces: The Case of Unexpected Interlayers.
Jeanne Pemberton 1 , Dallas Matz 1 , Matthew Schalnat 1 , Cynthia Shaw 1 , Hossein Sojoudi 2 , Samuel Graham 2
1 Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, United States, 2 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractLow work function metals are commonly used as electron-selective contacts with electron transport layers in photonic devices such as organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). Although the fundamental charge injection physics of such interfaces has been well described, the interfacial chemistry associated with these contacts is poorly understood and characterized. Efforts to characterize the chemistry of such interfaces using surface Raman spectroscopy have been undertaken in this laboratory. In this presentation, work in which contacts of Ag, Al, Ca and Mg are formed with semiconductive organic electron transport layers will be discussed as will be more fundamental studies on simple organic models of such materials and thin films of ordered carbon forms. Initial studies of the effects of post exposure of these interfaces to H2O and O2 will also be presented. Implications of this interfacial chemistry for device performance will be considered.
3:00 PM - CC2.2
Charge Modulation Spectroscopy - An Electro-optical Method for the In Situ Characterization of Charge Carriers in P3HT Devices.
Sandra Kogler 1 , Oskar Armbruster 2 , Philipp Stadler 1 , Gebhard Matt 3 , Siegfried Bauer 2 , Helmut Neugebauer 1 , Niyazi Sariciftci 1
1 LIOS - Linz Institute of Organic Solar Cells, Institute of Physical Chemistry, Johannes Kepler University, Linz Austria, 2 SOMAP, Department of Soft Matter Physics, Johannes Kepler University, Linz Austria, 3 Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz Austria
Show AbstractThe electro-optical properties of organic semiconductor diodes strongly depend on the properties of injected charge carriers. Charge modulation spectroscopy (CMS) is applied to measure these properties and to compare the results of interfacial doping and of electrochemical doping.We report on CMS measurements of devices containing P3HT (poly(3-hexylthiophene)) as organic semiconductor. Measurements were performed both on diodes and on metal-insulator semiconductor (MIS) like structures, using pristine and electrochemically doped P3HT.Despite the similarity of the CMS spectra, distinctive differences are observed for interfacial doping of pristine P3HT in MIS structures and electrochemical doping using lithiumperchlorate in polyethyleneoxide as dopand. Those differences and the underlining processes will be outlined in detail.
3:15 PM - CC2.3
Optical Modulation of the Charge Injection in an Organic Field-effect Transistor Based on Photochromic SAM Functionalized Electrodes.
Nuria Crivillers 1 , Emanuele Orgiu 1 , Federica Reinders 2 , Marcel Mayor 2 3 , Paolo Samori 1
1 Nanochemistry Laboratory, Institut de Science et d'Ingenierie Supramoleculaires (I.S.I.S.), University of Strasbourg, Strasbourg France, 2 Department of Chemistry, University of Basel, Basel Switzerland, 3 , Karlsruhe Institute of Technology KIT, Institute for Nanotechnology, Karlsruhe Germany
Show AbstractIn the last decades a great effort has been devoted to the fabrication of the organic field-effect transistors (OFET) featuring high performance as key element for new organic-based logic applications. Besides the design and synthesis of new semiconductors, the development of novel high performance gate dielectrics, the novel processing techniques and optimization of the device architecture, the engineering of the interface semiconductor-dielectric and semiconductor-metallic contacts have attracted much interest due to the importance of the interfacial morphology and the hole/electron injection barrier on the device performance. In particular, self-assembled monolayers (SAMs) are widely used to tune the wettability and work function of the metal-organic junctions. In this regard, in contrast to the extensively employed chemisorbed alkane- and arene-thiol SAMs, the use of SAMs based on molecules which respond to external stimuli has still not been explored. For our investigation we exploit a SAM based on an azobenzene derivative once chemisorbed on the Au source and drain electrodes of an OFET to optically modulate the charge injection at the electrode–semiconductor interface.[1] For this study the air-stable n-type system N,N’-1H,1H-perfluorobutyl dicyanoperylenediimide (PDIF-CN2),[2] was used as organic semiconductor. Azobenzenes are known to undergo reversible photoinduced isomerization between trans and cis form which can exhibit different optical and electrical properties. We demonstrate that a photochromic bi-stable AZO-SAM can mediate the injection through the variation of the tunneling barrier across the SAM allowing to modulate reversibly the charge injection at the interface Au electrodes/semiconductor. The observed result is in full agreement with previous IV characterizations of the AZO-SAM when incorporated in two terminal junctions as studied by C-AFM [3] and Hg-drop based measurements,[4] demonstrating that the switching effect of the transport properties relies on the difference in tunneling barrier thickness. In our device the source-drain current through the channel can be gated electrically (through gate control), like in a conventional OFET, and optically (through photochemical control). Such a proof of concept is instrumental to the field of organic electronics which searches for solutions to incorporate new and more functionalities in a device.[1] N. Crivillers, E. Orgiu, F. Reinders, M. Mayor and P. Samorì, submitted.[2] A. S. Molinari, H. Alves, Z. Chen, A. Facchetti, A. F. Morpurgo, J. Am. Chem. Soc. 2009, 131, 2462.[3] J. M. Mativetsky, G. Pace, M. Elbing, M. A. Rampi, M. Mayor, P. Samorì, J. Am. Chem. Soc. 2008, 130, 9192.[4] V. Ferri, M. Elbing, G. Pace, M. D. Dickey, M. Zharnikov, P. Samorì, M. Mayor, M. A. Rampi, Angew. Chem. Int. Ed. 2008, 47, 3407.
3:30 PM - CC2.4
Versatile Assembly of Metal Nanoarchitectures for Planar Plasmonics.
Sarah Adams 1 , Regina Ragan 1
1 Chemical Engineering and Materials Science, University of California, Irvine, Irvine, California, United States
Show AbstractWe have developed chemical assembly methods for planar organization of metal nanoparticles that provide versatility in achievable architectures. The controlled and versatile organization of metal nanoparticles allows for tunable properties in two-dimensional planar plasmonic systems. We will present a procedure where gold nanoparticles were selectively attached to chemically patterned domains in order to form controlled clusters of nanoparticles with sub-10nm interparticle spacing. Closely spaced metallic nanoparticles in controlled clusters exhibit coupled dipole resonances, which enhance the local electromagnetic field. Colloidal gold nanoparticles were functionalized with carboxyl groups and selectively attached to chemically modified PMMA regions of a poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymer thin film using a carbodiimide chemical crosslinker. We will show that control of the PMMA domain size relative to the nanoparticle diameter provided a method to control the number of metal nanoparticles assembled in a cluster. By altering the diblock copolymer composition and preparation technique, copolymer thin films self-organize into linear or hexagonal patterns with variable PMMA domain size. With this design parameter, we show nanoparticle assemblies of varying size, shape, and composition are obtainable. Metal nanoparticle assemblies have been characterized using scanning electron microscopy to examine morphology and in terms of optical enhancements using surface enhanced Raman scattering. These structures are designed to lead to enhanced optical fields on surfaces (for biochemical sensors, absorption enhancement of photovoltaics), optical guiding in layers or chains, large radiating structures able to produce confined beams, or large-area optical filtering.
3:45 PM - CC2.5
Optimization of the Hybrid Organic/Inorganic Interface to achieve High Mobilities at Short Channel Length for p-Type Organic Thin Film Transistors with Low-cost, Gold-free Source/Drain Bottom Contacts.
Robert Mueller 1 , Steve Smout 1 , Cedric Rolin 1 , Jan Genoe 1 , Paul Heremans 1 2
1 Large Area Electronics, imec, Leuven Belgium, 2 ESAT, Katholieke Universiteit Leuven, Leuven Belgium
Show AbstractOrganic field-effect transistors (OFETs) are currently attracting considerable attention for potential applications in flexible integrated circuits such as radio-frequency identification tags (RFID-tags) [1]. A key parameter for such high frequency applications is a sufficiently good mobility (≥0.1 cm2/V.s) at short channel lengths (L≤ 10 μm) [2].Current state of the art organic RFID-tags are mostly based on polycrystalline p-type pentacene bottom-gate bottom-contact (BG-BC) OFETs [1], using photolithographical patterned gold for the source and drain (S/D) electrodes. With this configuration, good charge injection and favorable pentacene layer growth are achieved through the deposition of self-assembled monolayers (SAMs) both on the gold and the inorganic dielectric, leading to saturation mobilities (μsat) of up to 0.6 cm2/V.s at L= 5 μm [3].However, the high cost of gold seriously hampers low-cost applications. Therefore, several alternatives of S/D BC were proposed (e.g. metals, metal oxides, carbon based materials, charge-transfer complexes, …). With these alternatives, μsat of 0.1 cm2/V.s have been reported for long channel (≥ 50 μm) pentacene OFETs. However, electrical properties of corresponding short channel OFETs (L≤ 10 μm) significantly suffer from contact resistance issues [4,5].In this contribution we propose a low-cost alternative to gold for S/D BCs which permits proper OFET operation for channel lengths below 10 μm. This is achieved through the optimization of the organic / inorganic hybrid interface between the pentacene and multilayer metal BCs. Based on this new technology, OFETs with gold-free BCs achieve μsat of 0.346±0.005 cm2/V.s and a threshold voltage (VT) of 1.06±0.06 V. All other transistor parameters being the same, these figures exactly compare to reference OFETs based on gold BCs, for which μsat of 0.340±0.015 cm2/V.s and VT of -1.22±0.05 V are regularly reached.The key parameter for this good electrical quality is related to the highly uniform growth of the pentacene layer at the dielectric / BC interface and inside the channel, as confirmed by atomic force microscopy. Besides, our gold-free BC technology presents material costs that are beneath 5% of that of 30 nm gold BC and its implementation only requires a negligible increase in processing complexity. As a consequence, the development our alternative BCs can be considered as a significant contribution towards low-cost organic electronic circuits.This work was performed in a collaboration between IMEC and TNO in the frame of the HOLST Centre. The authors acknowledge financial support of EC-funded project Polaric (FP7-247978).1. K. Myny et al., Solid-State Electron. 53 (2009) 12202. D.M. De Leeuw et al., IEDM Tech. Dig. (2002) 2933. S. De Vusser et al., Appl. Phys. Lett. 88 (2006) 1035014. H. Kim et al., Appl. Phys. A 96 (2009) 4415. M.J. Panzer and C.D. Frisbie in Z. Bao and J. Locklin "Organic Field-Effect Transistors", CRC Press, 2007, p. 139
4:30 PM - **CC2.6
Self-assembly of Thiolated SAMs on Liquid Mercury: From the Kinetics of Interface-assembly to the Formation of Large Metal/Organic Hybrid Crystals.
Boaz Pokroy 1 2 , Boris Haimov 2 1
1 Materials Engineering, Technion Israel Institute of Technology, Haifa Israel, 2 Russell Berrie Nanotechnology Institute, Technion, Haifa Israel
Show AbstractOne of the common ways in which basic organic-electronics research is carried out is by employing the mercury drop-SAM junctions. The most studied SAMs in these setups are alkanethiols due to their very high affinity for Hg and to the fact that they form a densely packed SAM on the surface of the Hg drop. It is clear that the organization of the SAMs on the metal electrode (density and tilt) have a profound influence on the physical properties of the hybrid metal-organic interface (effective work function as well as the ability to exchange electrons with films of electroactive materials). With this in mind, we have studied the Hg/SAM interface and investigated the time- dependent ordering of different thiolated SAMs (varied chain lengths and different functional groups) on a mercury drop, using a novel optical technique. In this talk we will show the kinetics of ordering and the evolution of the Hg drop shape as the SAM organizes over time. Both these issues have strong implications on the electrical properties of metal/organic interfaces.We will also show that if mercury electrodes are sonicated in the presence of alkanthiols, instantaneous large Hg(SR)2 ribbon like crystals are formed[1].[1]Pokroy B, Aichmayer B, Schenk AS, Haimov B, Kang SH, Fratzl P, Aizenberg J. Sonication-assisted synthesis of large, high-quality mercury thiolate single crystals directly from liquid mercury. J Am Chem Soc 2010;132:14355.
5:00 PM - CC2.7
Density-dependent Reorientation and Rehybridization of the Strongly Chemisorbed Conjugated Molecule Hexaazatriphenylene-hexacarbonitrile (HATCN) on Ag(111).
Antje Vollmer 1 , Benjamin Broeker 2 , Oliver Hofmann 3 , Gerold Rangger 3 , Paul Frank 3 , Ralf-Peter Blum 2 , Ralph Rieger 4 , Luc Venema 5 , Hendrik Glowatzki 2 , Klaus Muellen 4 , Juergen Rabe 2 , Adi Winkler 3 , Petra Rudolf 5 , Egbert Zojer 3 , Norbert Koch 2 1
1 BESSY II, Helmholtzzentrum Berlin f. Materialien und Energie, Berlin Germany, 2 Institut f. Physik, Humboldt-Universität zu Berlin, Berlin Germany, 3 Institut of Solid State Physics, Graz University of Technology, Graz Austria, 4 , Max Planck Institut f. Polymerforschung, Mainz Germany, 5 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands
Show AbstractIn the field of organic electronics both the electronic and the morphological structure of the interface between the electrode and the conjugated organic materials are of crucial importance. Therefore, understanding the fundamental mechanisms that determine the properties of interfaces between metals and conjugated organic materials is a key prerequisite for advancing this field, where the (opto-)electronic function of devices depends critically on a variety of parameters, e.g. charge density distribution, energy level hybridization, interface state formation, molecular conformation changes, energy level alignment, and orientation of the molecules on the surface.Hitherto, it has been commonly accepted that the orientation of a conjugated molecular monolayer with respect to a metal electrode surface depends only on the relative strength of metal-molecule vs. intermolecular interactions and is set for a particular material pair. If substrate-molecule interactions prevail, as for clean metal surfaces, at least the first molecular layer is found to be face-on.Here we show for that a re-orientation of a face-on to an edge-on first layer of a strongly chemisorbed extended aromatic molecule can be triggered by simply increasing the amount of deposited molecules on the surface. We will report on the strong molecular acceptor hexaazatriphenylene-hexacarbonitrile (HATCN) on Ag(111) where we find that the rearrangement of the first molecular layer from face-on to edge-on is facilitated through specific interactions of the peripheral molecular cyano groups with the metal. This is accompanied by a rehybridization of molecular and metal electronic states, which significantly modifies the interface and surface electronic properties. This results in a drastic increase of the work function due to the higher dipole moment of each molecular pair and the increased molecular density of the molecules in the standing layer. The chemisorbed molecular state in the edge-on monolayer, in particular, exhibits extraordinary electronic properties, which is not the case for the face-on orientation.We will present this molecular density-dependent re-orientation by means of a multi-technique experimental and theoretical investigation using a combination of ultraviolet photoelectron spectroscopy (UPS), work function measurements (Kelvin probe as well as UPS), thermal desorption spectroscopy (TDS), reflection absorption infrared spectroscopy (RAIRS), and scanning tunnelling microscopy (STM). The experimental results are rationalized and corroborated by density functional theory (DFT) modeling.PRL 104, 23, (2010) 246805, Nano Lett., 8, 11, (2008) 3825-3829
5:15 PM - CC2.8
Enhanced Lifetime in Unencapsulated Organic Photovoltaic Devices.
Matthew Lloyd 1 , Nikos Kopidakis 2 , Alexandre Nardes 2 , Matthew Reese 2 , Joseph Berry 1 , David Ginley 1 , Dana Olson 1
1 National Center for Photovoltaics, National Renewable Energy Lab, Golden, Colorado, United States, 2 , National Renewable Energy Lab, Golden, Colorado, United States
Show AbstractWe employed an automated combinatorial testing system to monitor the degradation rates for inverted geometry poly(3-hexylthiophene):fullerene bulk heterojunctions solar cells in air. These devices utilize ZnO and Ag for electron and hole contacts, respectively, the relative stability of which enables meaningful studies of unencapsulated device lifetimes. For inverted devices under constant illumination, we find oxygen and moisture ingress to be the primary cause for decay in power conversion efficiency (PCE) via decreased short-circuit current (while the fill factor and open-circuit voltage are unchanged). When utilizing Ag electrodes with a typical thickness (< 100 nm), the photocurrent decays exponentially, resulting in device performance that reaches 80% of the initial value (T80) in 100-200 hours. However, by significantly increasing the electrode thickness the behavior of the current decay becomes linear with a slope near zero (-2 x10-5 ΔPCE %/hr). After 1550 hours, devices with thicker electrodes retain 89% of their initial efficiency. These results strongly suggest that typical thermally deposited Ag electrodes show some permeability to water vapor and oxygen. Furthermore, the photocurrent decay is mitigated for thicker electrodes whether deposited as pure Ag or as a multilayer composite of Ag and other metals. The implication here is that thick metal electrodes may function to prevent ingress with better barrier properties than many polymer based encapsulants. Lastly, the large capacity of the combinatorial system enables simultaneous testing of many devices. We compare the lifetime of P3HT to other high efficiency donor materials (e.g. PCDTBT), and a high efficiency small molecule, dihydropyrrolopyrroledione (DPP).
5:30 PM - **CC2.9
Catalyst/Support Interactions: How Surface Modification of Carbon Supports Can Be Exploited to Enhance Fuel Cell Catalyst Activity.
Ryan O'Hayre 1 , Svitlana Pylypenko 1 2 , Yingke Zhou 3 1 , April Corpuz 1 , Ryan Richards 1 , Tim Holme 4 , Kenneth Neyerlin 2 , Tim Olson 2 , Arrelaine Dameron 2 , Kevin O'Neill 2 , Katherine Hurst 2 , David Ginley 2 , Thomas Gennett 2 , Huyen Dinh 2
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 State Key Laboratory of Materials Oriented Chemical Engineering, Nanjing University of Technology , Nanjing China, 4 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractImproving catalytic activity and durability are two major issues that must be addressed for fuel cells to become commercially viable. Most low temperature fuel cells employ precious metal catalysts (typically a Pt ot Pt-alloy) dispersed at the nanoscale on a high surface area carbon support. A “surface engineering” approach involving nitrogen modification of this carbon support has recently been demonstrated by us and other research groups to effectively enhance both catalytic activity and durability through significant improvements in catalyst-support interactions [1, 2, 3]. Most prior work has focused on nitrogen-modified Pt/C catalyst systems for hydrogen fuel cells. In our recent work, however, we have observed similar enhancements in catalytic activity for nitrogen-modified PtRu/C alloy catalysts, which show great potential for direct methanol fuel cell applications. Other carbon modification approaches involving boron or sulfur also appear intriguing, thereby suggesting that this surface modification approach may be a broadly applicable tool to engineer the properties of supported catalyst systems. In this paper, we will discuss our recent results in this area, in particular focusing on the chemical nature of the nitrogen-modified carbon support and likely mechanisms for the nitrogen-induced catalyst enhancement effects. References1. Y. Zhou, K. Neyerlin, T. Olson, S. Pylypenko, J. Bult, H. Dinh, T. Gennett, Z. Shao, R. O’Hayre, “Enhancement of Pt and Pt-Alloy Fuel Cell Catalyst Activity and Durability via Nitrogen-Modified Carbon Supports”, Energy and Environmental Science, 3, 1437-1446 (2010). 2. Y. K. Zhou, R. Pasquarelli, T. Holme, J. Berry, D. Ginley and R. O'Hayre, J. Mater. Chem., 2009, 19, 7830-7838.3. S. Maldonado and K. J. Stevenson, J. Phys. Chem. B, 2005, 109, 4707-4716AcknowlegmentsThis work was supported by the Army Research Office under grant #W911NF-09-1-0528 and the U.S. Department of Energy under Contract No. DE-AC36-08-GO28308 with the National Renewable Energy Laboratory.
CC3: Poster Session I
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - CC3.1
Compacted Hybrid Cell Made by Nanowire Convoluted Structure for Harvesting Solar and Mechanical Energies.
Chen Xu 1 , Zhonglin Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractOur living environment has abundant type of energies in forms of solar, thermal, mechanical and chemical. The current available approaches focus only on harvesting one type of energy using a specific device. As for the future, effectively harvesting multiple types of energies using a single device is a future technology for a range of applications. We have developed a fully integrated, solid-state, compacted hybrid cell (CHC) that is made of ZnO nanowire “convoluted” structure for concurrently harvesting both solar and mechanical energies. The compacted hybrid cell is based on a conjunction design of an organic solid sate dye sensitized solar cell (DSSC) and piezoelectric nanogenerator in one compacted structure. It shows an increase not only in the output voltage but also in output power as the driving ultrasonic wave is turned on, clearly demonstrating its potential for simultaneously harvesting multi-type energies. Under a light illumination of a simulated sun emission (100 mW/cm2), an increase of 6% in optimum power for the CHC was demonstrated by incooperating the contribution made by the nanogenerator. Therefore, the CHC is more efficient for fully utilizing the available solar and mechanical energies in our living environment for powering small electronic devices for independent, sustainable and mobile operation. [1] X.D. Wang, J.H. Song J. Liu, and Z.L. Wang, Science, 316 (2007) 102.[2] C. Xu, X.D. Wang and Z.L. Wang, J. Am. Chem. Soc., 131 (2009) 5866.[3] C. Xu and Z.L. Wang, Advanced Material Submitted.[4] Research supported by DARPA, DOE and NSE.[5] For more information: http://www.nanoscience.gatech.edu/zlwang/
6:00 PM - CC3.11
Inkjet-patterned Titanium Oxide Memristive Junctions Connected in Series for a Threshold Indicator.
Tse Nga Ng 1 , Beverly Russo 1 , Ana Claudia Arias 1
1 Electronic Materials and Device Lab, Palo Alto Research Center, Palo Alto, California, United States
Show AbstractThe use of memristive devices can simplify circuit designs and reduce power requirements for low-cost printed electronics. Here memristive metal/oxide/metal junctions were patterned from titanium-oxide solgel precursor, and the inkjet-printed device characteristics were measured to infer ionic and electronic transport parameters such as mobilities and ion distribution. The flux dependence was analyzed for an individual junction as well as for junctions connected in a series. There was continuous dopant redistribution under increasing flux, leading to a peak in conductance. With multiple memristive devices, the circuit conductance was shown to be linearly proportional to the number of junctions placed in the series. The mutable conductance of memristive junctions was utilized to demonstrate a threshold detector, in which printed memristive junctions were connected with a piezo voltage-pulse source and an electrophoretic display output. The memristive circuit would switch the color of display pixels depending on the number of input pulses sensed by the piezo. This demonstration used only passive circuit components and no battery and illustrated the potentials of hybrid memristive elements.
6:00 PM - CC3.12
Hybrid Organic-Inorganic Glass Films for High-performance Adhesive Bonding.
Jeffrey Yang 1 , Reinhold Dauskardt 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractHigh-performance bonding plays an integral role in the reliability of virtually all multilayer devices, from microelectronics packaging to large-scale thin-foil structural laminates. Novel organic-inorganic thin films with a through-thickness composition gradient have been developed using sol-gel processing techniques to create complex metal / silane interphase regions engineered to form durable bonds between metal oxides and structural adhesive organic resins. Despite the efficacy of these hybrid films, much remains unknown about the fundamental processing-nanostructure-property relationships that govern their performance and reliability. Strategies for forming strong adhesive bonds using a conditioned oxide, an optimized sol-gel layer and a high-performance epoxy resin are described. Micro and nanoscale mechanisms of interphase degradation and failure have been characterized under a range of loading and environmental conditions, revealing significant improvements in adhesion strength and enhanced resistance to moisture-assisted crack growth over traditional bonded joints. The influence of metal oxide isoelectric point, sol-gel chemistry and processing conditions, and epoxy functionality on fracture energy and network connectivity will also be discussed.
6:00 PM - CC3.13
N-type Molecular Organic Field Effect Transistors Based on Self-assembled Monolayers.
Michael Novak 1 , Alexander Ebel 2 , Frederik Ante 3 , Andreas Hirsch 2 , Marcus Halik 1
1 University Erlangen Nuremberg, Institute of Polymer Materials, Erlangen Germany, 2 University Erlangen Nuremberg, Institute for Organic Chemistry II, Erlangen Germany, 3 Max Planck Institute, Solid State Research, Stuttgart Germany
Show AbstractSelf-organizing molecules are promising components to serve as active layers in low cost and flexible electronic devices. Due to the molecular induced driving force of voluntary film formation, self-assembled monolayers (SAMs), have the advantage of local selectivity, yielding highly ordered monomolecular films. [1] With its simple processing and the regio-selective deposition the research focuses on extended functionality, addressed by the design of those molecules to enable real molecular scale electronics. Recently, SAMs created from bifunctional molecules (linkable oligothiophenes) were introduced as p-type semiconductor monolayer in self-assembling monolayer field effect transistors. [2]Here we report on a rational molecule design, for n-type semiconductor monolayer, enabling CMOS like organic electronics with reduced power consumption. The molecular design of the bifunctional n-type semiconductor molecule relies on the electron transport behavior of fullerene (C60). The ability to self-assemble and low voltage operation of a resulting SAM is implemented by a non-symmetric substitution pattern. Via malonate moiety linkage, an n-alkyl-phosphonic acid (C6-PA or C18-PA) is attached to the C60 core, which enables the SAM formation. To provide solubility of the molecule and to introduce a barrier layer on top of the air sensitive C60, the second (upper part) of the malonate is substituted with either, a methyl end cap [CH3], a dodecyl [C12H25] or an ethylene glycol [CH3-[O-CH2-CH2)3]. [3]Self-assembled monolayer field effect transistors (n-type) are demonstrated, in which the dielectric layer and the semiconductor layer are created by self-assembly of the specially designed molecules. Device characteristics were investigated in short channel bottom gate bottom contact transistors (W/L = 5, with L = 50 nm to 1 µm), fabricated by e-beam lithography. Respectable electron mobilities up to 0.00012 cm^2/Vs (at 2 V) and ON/OFF-ratios around 103 were obtained from the monomolecular film. The functionality strongly depends on the molecular design and the ability to create densely packed monolayers, to carry charges across the channel. Thereby, device parameters such as leakage current (IG), follow the molecular setup. Parameters like e.g. mobility or drain current are strongly affected by the SAM morphology and show a clear dependency of the channel length. [4]---- References: ---- [1]H. Klauk et al., Nature 445 (2007), 745.[2]a) E.C.P. Smits et al., Nature 455 (2008), 956.b) M. Spijkman et al., APL 96 (2010), 143304.c) M. Mottaghi et al., Adv.Funct.Mat. 17 (2007), 597. [3]M. Novak et al., Nanoletters (2010) Submitted.[4]S.G.J. Mathijssen et al., Nature Nanotechnology 4 (2009), 674.
6:00 PM - CC3.17
Improving the Monodispersity of Surface Enhanced Raman Spectroscopy Nanoantennas via Centrifugal Processing.
Timothy Tyler 1 , Anne-Isabelle Henry 2 , Richard Van Duyne 2 , Mark Hersam 1 2
1 Department of Materials Science & Engineering, Northwestern University, Evanston, Illinois, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractNoble metal nanoparticle clusters act as nanoantennas that serve as highly effective platforms for surface-enhanced Raman scattering (SERS) with sensitivity down to the single-molecule level [1,2]. Recent improvements in the control of nanoparticle size and shape have begun to enable studies of SERS activity as a function of the host structure [3], including the aggregation state of the nanoparticles. However, because nanoparticle oligomers occur in a variety of aggregation states and single metal nanoparticles do not contain the necessary interparticle junction for strong SERS enhancement [4], these measurements would benefit from improvements in the monodispersity of the nanoparticle clusters. Towards this end, we report a post-synthetic centrifugal sorting technique for oligomers of gold nanoparticles coated by a protective silica layer with SERS reporter molecules at the gold/silica interface. Nanoparticle clusters are separated by exploiting differences in sedimentation coefficients, yielding samples that containing a preponderance of dimers, trimers, tetramers, or other selected species, along with a greatly diminished monomer population. The silica coating eliminates the need for chemically functionalizing the metal nanoparticles to prevent further aggregation. Furthermore, the use of a high-viscosity density gradient medium (iodixanol) slows the sedimentation to the point where relatively large oligomers, including hexamers and larger, can be effectively separated. The monodispersity of the resulting samples are characterized with transmission electron microscopy, UV-vis-NIR spectrophotometry, and ensemble SERS measurements. The experimental results quantitatively agree with a Perrin ellipsoid model of sedimentation, thus providing insight into the sorting mechanism. The generality of the underlying mechanism suggests that this strategy can be adapted for future sorting studies on other nanoparticle aggregates and/or anisotropic nanoparticles.[1] K. Kneipp et al., Phys. Rev. Lett. 78, 1667 (1997).[2] S. M. Nie and S. R. Emory, Science 275, 1102 (1997). [3] K. L. Wustholz et al., J. Am. Chem. Soc. 132, 10903 (2010).[4] A. M. Michaels et al., J. Phys. Chem. B 104, 11965 (2000).
6:00 PM - CC3.19
Characterization of the Surface of Gold Nanoparticles by Pulse Field Gradient NMR.
Francois Ribot 1 , Luk Van Lokeren 1 , Hanen Ben Sassi 1
1 CMCP - UMR7574, UPMC / CNRS, Paris France
Show AbstractNanoparticles (NPs) are one of the pillars on which nanotechnologies have grown during the last years. During the synthesis, handling, processing or assembling of NPs, the capping molecules, which cover their surface, play a key role, and accordingly, a detailed knowledge of what happen at the surface of NPs is highly desirable to understand and improve their syntheses as well as to rationalize their application. In particular, measuring, in suspension, the affinity of organic molecules for NPs is of prime importance. However, evaluating this affinity in situ is not a simple task.Gold NPs are used in many different domains and various organic molecules are classically used to prepare, stabilize and functionalize them. Several gold NPs suspensions have been synthesized with ligands such as thiol, phosphine, or amine to stablize them. DOSY (Diffusion Ordered Spectroscopy) NMR has then been used to study these suspensions. This technique, which is based on pulsed field gradients, gives access to the diffusion coefficients of the various species in a mixture and can therefore distinguish free and bound capping molecules on the basis of their different mobility. This technique has also been applied to study suspensions in which two different ligands are simultaneously present. Taking advantage of the known selectivity of NMR, which can spectroscopically distinguish different molecules in a mixture, DOSY NMR was used to trace the exchange of ligands at the surface of NPs and thus probe the relative affinity of the various capping molecules.
6:00 PM - CC3.2
Label-free Raman Mapping of Surface Distribution of Protein A and IgG Biomolecules.
Zachary Combs 1 , Sehoon Chang 1 , Tolecia Clark 1 , Srikanth Singamaneni 1 , Kyle Anderson 1 , Vladimir Tsukruk 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWe have demonstrated a nanoengineered interface composed of micropatterned silver nanoparticles to be used for the label-free mapping of adsorbed biomolecules. We utilized surface-enhanced Raman scattering (SERS) phenomenon to monitor the known bioanalytes, protein A and human immunoglobulin G (IgG). The SERS substrate was composed of a poly(alylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) layer-by-layer (LbL) nanocoating which is micropatterned with silver nanoparticles confined to microscopic stripes. Selective adsorption of biomacromolecules is facilitated by the amine-terminated LbL nanocoating. Furthermore, adsorption of IgG on predetermined regions is facilitated by the selective binding of the Fc region of IgG to protein A. This label-free SERS approach provides accurate, selective, fast, and optimal detection of protein A and IgG. This label-free SERS approach provides accurate, selective, and fast detection of protein A and IgG. This method could also be utilized for the characterization of proteins in clinical, forensic, industrial, and environmental laboratories.
6:00 PM - CC3.21
Electromagnetic in between Binary Self-assembled AFM Probes and Plasmid DNA in Aqueous Environments.
Guo-Ji Yen 1 2 , Hsun-Yun Chang 1 , Yun-Wen You 1 , Wei-Lun Kao 1 2 , Chi-Jen Chang 1 2 , Mong-Hong Tsai 1 2 , Jing-Jong Shyue 1 2
1 Research Center for Applied Sciences, Academia Sinica, Taipei Taiwan, 2 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractThe use of gold substrate in Biochemistry has increasingly been the object of study for its high biologic compatibility in recent years. The continuing improvements in materials processing and surface modification of gold have led to many new and fascinating applications in material science, chemistry, biology, and medicine. A majority of studies have suggested that modified gold substrate provide an efficient way to covalently bond biologic molecules such as plasmid DNA and proteins in the fields of biosensing and biologic transportation. However, the application of covalently-bonded combination is limited by its difficulty in desorption of molecules. In this work, the gold-coated probes are modified by self-assembled monolayers (SAMs) of mixed carboxylic acid and amine functional groups in a series of ratio (1:0, 1:1, … , 1:5, 0:1), and the iso-electronic points (IEPs) between 3.2~7.3 are obtained. Using the contact mode atomic force microscopy in liquid, the electrostatic interactions between modified probes and plasmid DNA is measured at different pH values using their force curve. Because the interacting surfaces can have the same or opposite sign of potential, repulsive or attractive interaction can be observed. Furthermore, since the surface potential is a function of pH, the observed interactions between a given set of surfaces changes with the environment. Through analyzing the electrostatic interactions, we examined the adsorption and desorption of biological molecules on SAMs-modified gold substrates of different IEP. By controlling the interactions using SAMs of different chemical composition, this result may provide an alternative means for transporting materials.
6:00 PM - CC3.22
Hybrid Organic/Inorganic Heterojunctions Based on Rolled-up Nanomembranes.
Carlos Bof Bufon 1 , Juan Ariaz Espinoza 1 , Maria Navarro Fuentes 1 , Dominic Thurmer 1 , Christoph Deneke 1 , Oliver Schmidt 1 2
1 Institute for Integrative Nanosciences, IFW-Dresden, Dresden Germany, 2 Material Systems for Nanoelectronics, Chemnitz University of Technology, Chemnitz Germany
Show AbstractThe investigation of the electronic properties of molecular systems as well as their potential use for future device applications is strongly correlated with the way they are connected to the external world. Nowadays, self-assembly is widely accepted as a standard technique to generate complex structures on many length scales. One of such self-assembly processes consists of strained metal layers which spontaneously curl up into close rolls once they detach from their host substrate. Recently, we demonstrated that self-assembly methods combined with standard top-down approaches are suitable for fabricating three-dimensional ultra-compact hybrid organic/inorganic electronic devices, such as self-wound capacitors (UCCaps) manufactured in parallel on a single chip. In addition to reducing the device footprint by the rolling process, we were able to incorporate a self-assembled monolayer (SAM) of phosphonic acid in between the oxide layer and the capacitor metallic plate. The integration of organic molecules provides further free parameters to tune the properties and extend the range of applications of the final self-wound device.In this work we present a novel method, based on self-released strained nanomembranes, for contacting molecules by using metals and/or semiconductors as electrodes to form hybrid heterojunctions. During release of the nanomembrane, the strain relaxation gives rise to a self-rolling process in which the membrane bonds back to substrate top surface where the SAM was previously grown. By this means, we are able to fabricate not only the standards metal-molecule-metal and metal-molecule-semiconductor structure configuration but also the unique semiconductor-molecule-semiconductor heterojunctions. In this last case, the type of doping and its concentration can be independently and precisely set for each electrode in order to tune the device electronic properties. The strained nanomembrane based electrodes provide a soft and robust contact on top of the SAM. Consequently, no damage to the molecules and short circuits via pinholes in the SAM has been observed. Since the contacting process takes place at room temperature, the metallic diffusion into the SAM is suppressed. Furthermore, applying the self-rolling phenomenon, we achieve an approach that is fully integrative on a chip, and several components can be fabricated in parallel using well-established semiconductor processing technologies.
6:00 PM - CC3.23
Modification of the Radiative Decay Rate on Plasmon-exciton Hybrid Nanostructures.
Maria Rigo 1 , Jaetae Seo 1
1 , Hampton University, Hampton, Virginia, United States
Show AbstractThe spontaneous emission from semiconductor quantum dots (SQDs) can be modified through coupling of excitons with surface plasmon (SP) in nearby metallic nanostructures. The strong couplings of SQDs to SPs have many applications including photonic bioassay, optoelectronics, light-emitting diode, and solar cell applications. The local-field enhancements associated with SPs can increase light absorption or alter the radiative and nonradiative decay rates of SQDs. The interaction between SQDs and metal nanoparticles (MNPs) is revealed as an enhancement or suppression of SQDs emission for a given wavelength and it depends on the SP’s density of state at that wavelength. The emission properties as a function of the distance between SQDs and MNPs with various morphologies of nanometal structures and the degree of coupling between the SP resonance bands of the MNP and the excitation/emission bands of the nanocrystals were studied. The hybrid SQD-MNP nanostructure consists of a single array of MNPs, deposited on a flat quartz substrate, and a single layer of SQDs in the close proximity the nanoparticles. In order to prove the distance-depencent plasmon-exciton coupling, a spacer layer was built between these materials using the Layer-by-Layer (LBL) technique. Such spacer layer has a thickness varying from values smaller than the radius of SQDs to larger than the radius of MNPs. The photoluminescence of excitons in the vicinity of plasmons may be readily quenched due to their direct coupling through a fast energy transfer. Main challenges in the hybrid MNP-SQD nanostructures are a precise control of spacing between MNPs and SQDs, and accurate tunings of energy bands of excitons and plasmons. The energy bands of MNPs and SQDs can be tuned accurately by controlling the morphology of both MNPs and SQDs. The thickness of spacer between MNPs and SQDs is often controlled by the LBL assembly which provides nanometer precision from a few nanometers up to ~100 nm. The accessibility of MNPs onto the SQD surface may also result in photoluminescence quenching. This work was supported by the National Science Foundation (HRD-0734635 and HRD-0630372).
6:00 PM - CC3.24
Probing Charge-transfer Heterogeneity at Electrode/Organic Semiconductor Interfaces Using Conductive Probe AFM Current/Voltage Analysis.
Gordon MacDonald 1 , Bryan Zacher 1 , Diogenes Placencia 1 , Jeremy Gantz 1 , Peter Veneman 1 , Neal Armstrong 1
1 Chemistry Department, University of Arizona, Tucson, Arizona, United States
Show AbstractThe power conversion efficiencies of organic photovoltaics (OPVs) are often limited by inefficient charge collection from non-ohmic, heterogeneous, partially blocked organic semiconductor/electrode interfaces. We hypothesize that both the percentage of the organic/electrode interface that is electrically inactive and the spatial distribution of electrically inactive regions on sub-100nm length scales can determine device performance. We have developed a method for probing electrical inhomogeneities of the organic semiconductor/electrode interfaces using a variation on conductive-probe atomic force microscopy (CP-AFM). We systematically move the a conducting probe (e.g. Pt/Ir) over the surface of a prototype organic semiconductor/electrode heterojunctions (e.g. 20 nm CuPc/ITO or 20 nm CuPc/clean Au) and take x-y resolved current/voltage (J/V) curves which are subsequently analyzed for the degree of ohmicity and injection efficiency, with less than 100 nm resolution between J/V curves. For clean Au substrates and for properly activated ITO surfaces, we see evidence for good uniformity in electrical activity, and large regions where ohmic contacts are evident. For ITO electrodes with high concentrations of “blocked” regions, these maps are quite heterogeneous, and the regions deviating from ohmic behavior suggest large energetic barriers to charge injection. This presentation will focus on how these measurements are made, and the results of various pretreatment and small molecule modifications of the ITO surface on the degree of ohmicity at each x,y location and the homogeneity of electrical response in these maps. These studies correlate well with studies of OPV device performance as a function of ITO pretreatment and modification, and recently conducted simulations which demonstrate how the surface concentration and spatial distribution of blocked sites impacts on OPV device performance.
6:00 PM - CC3.25
Highly Conductive Transparent Electrodes Based on Single Walled Carbon Nanotube and Poly(3,4-ethylenedioxythiophene) Composite Films.
Michael Vosgueritchian 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSingle walled carbon nanotubes (SWNTs) are a promising alternative to transparent conducting oxides, such as ITO, as electrodes in electronic devices and solar cells. Combining SWNTs with polymers in composites have shown excellent mechanical and thermal properties; however, they often show conductivities orders of magnitudes lower than that of SWNT films. The use of a conducting polymer such as and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) can circumvent this issue and possibly enhance the conductivity of these films. So far, the reported sheet resistance with SWNTs and PEDOT:PSS are not significantly better than the SWNT film alone. Here, we utilize a different approach in which the addition of PEDOT:PSS resulted in a significant reduction of the SWNT sheet resistance. Our results suggest a synergistic interaction between the two materials. Films with sheet resistances approaching 100Ω/sq at 90% transparency are produced using this method without chemical doping.
6:00 PM - CC3.26
Interface-controlled Polymer Dielectric Interfaces for Improved Organic Device Performance.
Ndubuisi Ukah 1 , Danish Adil 1 , Jimmy Granstrom 2 , Ram Gupta 3 , Kartik Ghosh 3 , Suchi Guha 1
1 Physics and Astronomy, University of Missouri, Columbia, Missouri, United States, 2 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Physics, Astronomy and Materials Science, Missouri State University, Springfield, Missouri, United States
Show AbstractThe device performance of an organic thin film transistor depends critically on the interface between the dielectric layer and the organic semiconductor film. We report on a study of the effects of various polymer dielectrics, such as Cytop, PMMA, solvents, interpolymer complexes based on PVA and PMVE-MA, as well as the effects of their interfaces on the characteristics of metal-insulator-semiconductor and field-effect-transistor organic devices. Dielectric leakage current density is found to be slightly lower while dielectric constant is higher in the interpolymer complexed material compared to the pure dielectric, possibly due to a reduction in free-volume as a result of complexation. We will also discuss a novel technique aimed at circumventing the deleterious effect of dissolution of underlying regular polymer dielectrics such as PMMA and PVP by solvents of the overlying solution processable organic active layers; thus, resulting in the robust fabrication of spincoated bottom-gate solution processable organic devices. Furthermore, layer-by-layer growth of fluorene-based copolymers using a modified pulsed laser deposition technique is also found to improve the polymer-dielectric interface.
6:00 PM - CC3.27
Electrical and Optical Studies of Diketopyrrolopyrrole-based Copolymer Organic Thin Film Devices.
Danish Adil 1 , Catherine Kanimozhi 2 , Ndubuisi Ukah 1 , Satish Patil 2 , Suchi Guha 1
1 Department of Physics and Astronomy, University of Missouri, Columbia, Missouri, United States, 2 Solid State and Structural Chemistry Unit, Indian Institute of Technology, Bangalore India
Show AbstractDiketopyrrolopyrrole (DPP) containing copolymers have recently gained a lot of interest in organic optoelectronics for applications in FETs and solar cells. The intermolecular hydrogen bonding in non-alkylated DPP core forms a two-dimensional network that leads to films that self-assemble into ordered domains. Two DPP-based copolymers (PDPP-BBT and TDPP-BBT) have been synthesized for their application in organic devices such as metal-insulator semiconductor (MIS) diodes and field-effect transistors (FETs). MIS diodes and FETs were fabricated using the DPP copolymers as the active semiconducting layer and SiO2 and other polymer dielectric as insulating oxide layers. The semiconductor-dielectric interface was characterized by capacitance-voltage and conductance-voltage methods. These measurements yield an interface trap density of 4.2×1012 eV-1cm-2 in TDPP-BBT and 3.5×1012 eV-1cm-2 in PDPP-BBT at the flat-band voltage. Both PDPP-BBT and the TDPP-BBT FETs show typical field-effect transistor behavior such as good modulation of drain-source current by gate voltage and drain-source current saturation at high gate voltages. There is almost no hysteresis in the output characteristics of the FETs. The FETs based on these DPP copolymers display p-channel behavior with hole mobilities ~ 10-3 cm2/Vs in PDPP-BBT. Raman scattering studies from the FETs show almost no change in the Raman spectra before and after device operation indicating minimal degradation of the device at the polymer-metal contact and no change in the structural properties due to biasing. This is contrasted with similar studies done on pentacene and polyflourene co-polymer based devices.
6:00 PM - CC3.3
In Situ Growth of Silver Nanoparticles in Porous Membranes for Surface-enhanced Raman Scattering.
Sehoon Chang 1 , Zachary Combs 1 , Maneesh Gupta 1 , Richard Davis 1 , Vladimir Tsukruk 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWe demonstrate the in situ growth of silver nanoparticles in porous alumina membranes (PAMs) for use as a surface-enhanced Raman scattering (SERS) active substrate. This fabrication method is simple, cost effective, and fast, while providing control over the size of silver nanoparticles through the entire length of the cylindrical nanopores with uniform nanoparticle density inside the pores un-achievable by the traditional infiltration technique. The in situ growth of silver nanoparticles was conducted from electroless-deposited nanoscale seeds on the interior of the PAM and resulted in the formation of numerous hot spots which facilitated significantly higher SERS enhancement for these substrates compared with previously reported porous substrates.
6:00 PM - CC3.30
Fabrication of FTO Nanotube by Using Oxygen Plasma Etching Technique on FTO-Coated ZnO Template.
Naratip Chantarat 1 , Yu-Wei Chen 1 , Chin-Ching Lin 2 , Mei-Ching Chiang 2 , San-Yuan Chen 1
1 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 2 Materials and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu Taiwan
Show AbstractWe present a novel heterostructure ZnO-FTO nanotube produced by a chemical solution process. In this investigation, the pre-synthesized ZnO nanorod arrays act as templates, and FTO nanoparticles serve as depositing layer on ZnO nanorods by a simple spray pyrolysis method. The pattern of tube-like ZnO-FTO structure was discovered, due to the removal of ZnO core template, after the samples were exposed under reactive ion etching (RIE) using oxygen as reactive gas. The room temperature photoluminescence (PL) reveal that the FTO-coated layer not only plays a role of the defect passivation onto the ZnO surface but also enhances the gas-absorbing catalytic activities from the supplied oxygen plasma. The X-ray Photoelectron Spectroscopy (XPS) analysis demonstrated that the plasma treatment would cause the generation of OH- and a reduction of the O2-concentration, indicating the dissociation of Zn-O bonds due to the chemical reaction : the O2-, OH radicals and physical bombardment of O ions, which resulted in Zn cations flow outward and the occurrence of interior hollow. Potential dependence of photocurrent (I-V) measurement under UV illumination confirms that the etched samples show a rectified photocurrentcharacteristic. A dark current increases about three orders of magnitude over that of the un-etched sample. This investigation offers an alternative selective etching method for laying the framework of nanoscale 3-D electrode in photoelectronic applications.
6:00 PM - CC3.31
Inverted Polymer and Small Molecule Hybrid Photovoltaic Devices Based on Vertically Aligned Zinc Oxide Nanowire Arrays: Effects of Nanowire Array Height and Surface Modification on Device Characteristics.
Gary Kushto 1 , Vaibhav Jain 1 , Mason Wolak 1 , Antti Maekinen 1
1 Optical Sciences Division, U.S. Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe interfaces formed between organic materials and inorganic semiconductor nanostructures have been the subject of great interest particularly with respect to their roles in photovoltaic charge generation. The work presented here describes using organic small molecules to modify the surfaces of ZnO nanowire (ZnO NW) arrays for use as electron accepting/transporting structures in hybrid, inverted organic solar cells. Vertically aligned ZnO NW arrays are grown on ITO coated glass slides using a seeded hydrothermal method and their surfaces modified with organic molecules having various functionalities, e.g. benzoic acids, trimethoxysilanes and pyridines. Surface derivatization affects nanowire band structure and surface trapping as well as changes wetting by the light harvesting organic layer. Organic light harvesting layers are deposited onto the nanowire arrays either by spin coating (for P3HT) or vacuum vapor deposition of small molecules (phthalocyanines or polyacenes). The surface modification of the ZnO NWs produces profound changes in device characteristics such as large increases in cell open circuit voltages (Voc), fill factors (FF) or generated short circuit current densities (Jsc). For example, a P3HT device fabricated on an as prepared, UV/O3 treated, 100 nm high ZnO nanowire array exhibits a Voc 0.147 V under 78 mW/cm2 AM1.5 white light illumination. An analogous device fabricated on a 4-tert-butylpyridine treated nanowire array exhibits a Voc of 0.443 V with a slight increase of both the FF and Jsc leading to an overall power conversion efficiency (PCE) of 0.75%. Even larger effects are evident when using a P3HT:PCBM blend as the light harvesting layer. In these devices, Voc increases from 0.408 V to 0.597 V upon treatment with 4-tert-butylpyridine and concomitant increases in FF and Jsc are also observed. The P3HT:PCBM devices on surface treated ZnO NW arrays show PCEs in excess of 2.25%. This presentation will discuss device characteristics as well as structural characterization via photoemission spectroscopies, scanning electron microscopy and cross sectional analysis of fabricated devices via focused ion beam milling.
6:00 PM - CC3.33
Energy Transfer Enhanced Dye Sensitized Solar Cells.
Eva Unger 1 , Ana Morandeira 2 , Burkhard Zietz 2 , Erik Johansson 1 , Anders Hagfeldt 1 , Gerrit Boschloo 1
1 Physical Chemistry, Analytical and Physical Chemistry, Uppsala Sweden, 2 Chemical Physics, Photochemistry and Molecular Science, Uppsala Sweden
Show AbstractThe dye sensitized solar cell (DSC) is a device that converts solar energy to electricity on a molecular level. Light is absorbed in a monolayer of a sensitizer dye chemisorbed to a wide bandgap semiconducting metal oxide. Nanostructured metal oxides like TiO2 provide a large surface area for photoinduced interfacial charge separation. The oxidized dye is regenerated by a redox couple or a hole-transporting medium (HTM) in solid state DSCs. Liquid electrolyte based DSC can give efficiencies of up to 12%. Solid state DSCs (ssDSCs) are currently limited by insufficient pore-filling and a higher interfacial recombination rate, which limit the thickness of the nano-porous TiO2 layer is therefore only 2 μm which is considerably thinner than in the liquid electrolyte devices. Consequently, only a part of the incident light can be harvested. We have investigated ways to both increase and broaden the optical thickness of ssDSC devices. In the first approach we investigated the possibility of using a dye multilayer instead of a monolayer for sensitization. Bilayer hybrid solar cell devices with a varying dye layer thickness of a triphenylamine dye on TiO2 were studied [1]. The device performance was increased due to the excitonic contribution of the dye multilayer to the photocurrent but ultimately limited by the exciton diffusion length and the hole-conductivity in the organic layer. Interestingly, in these devices the open-circuit voltage increased with the thickness of the dye multilayer. To investigate this further, we studied the properties of this hetero-interface by means of photoelectron spectroscopy. To broaden the solar cells spectral response, dyes with complementary absorption can be used. We investigated solar cell devices comprising a sensitizer dye and hole transporting dye (HTD). The HTD can contribute either by injecting directly into the TiO2 or by transferring the excitation energy to the sensitizer dye. At the same time, this compound needs to both regenerate the sensitizer dye after electron injection into the TiO2 and function as a HTM to conduct the generated holes to the back contact of the device. We are presenting results for nanostructured solar cells using a red-absorbing squaraine sensitizer chemisorbed to the TiO2 interface and a blue-absorbing triphenylamine based HTD. External quantum efficiency measurements prove that both dyes contribute to the photocurrent. Using steady state photoluminescence we were able to demonstrate that the excitation energy is successfully transferred from the HTD to the squaraine sensitizer. These results suggest that the HTM can actively contribute to the light harvesting in solid state DSC. [1] E. L. Unger et al., J. Phys. Chem. C 2010, 114, 1165
6:00 PM - CC3.4
Film Bulk Acoustic Resonators for Parallel Mass Sensing Applications.
Shih-Jui Chen 1 , Anderson Lin 1 , Eun Sok Kim 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractFilm bulk acoustic resonator (FBAR) can be made into a label-free mass sensor for identifying biological and chemical species, and has a higher sensitivity than a quartz crystal microbalance (QCM) due to its higher resonant frequency. Unlike current probe methods labeled with fluorescence, chemiluminescence, electrochemiluminescence, or radioactive tag, the resonant frequency of FBAR changes in response to mass added to its surface, and can be used for label-free quantitative measurement.This paper presents a novel film bulk acoustic resonator (FBAR) having a number of fundamental resonant frequencies that offers parallel and/or combinatory mass sensing of multiple chembio species. To achieve the multiple resonant frequencies, we connect multiple FBARs (having slightly different resonant frequencies, thus each representing a unique sensor) in parallel, and form one FBAR (out of the multiple) on a chip. This way, when we measure the frequency shifts of the FBAR through a network analyzer, we have multiple resonant frequencies, each of which will change as a function of added mass (of chembio species), independent of the others. The FBAR was fabricated by first producing silicon nitride diaphragms, onto which 0.1 micron thick bottom electrode was deposited and patterned, followed by deposition and delineation of piezoelectric ZnO film. After depositing 0.1 micron thick top Al electrode, we went through several cycles of adding three masses of Al. Then, we patterned the whole electrode over the ZnO film, followed by deposition of 0.05 micron thick gold on which biomolecules are immobilized for selective detection.For real-time monitoring of the biotin-avidin interaction, we immobilized biotin-HPDP, biotin-SS-NHS, and 11-mercapto-1-undecanol on the Au-coated FBAR surfaces. When the FBARs were exposed to NeutrAvidin™ (440 µg/ml) in phosphate buffered saline solution, the FBARs (that were immobilized with biotins) produced significant drops (between 150 and 180 kHz, or about 60 ppm) in their resonant frequencies. This frequency shift is due to added mass resulting from biotin-avidin binding. But the 11-mercapto-1-undecanol treated FBAR showed no observable frequency shift, since the terminal –OH group from 11-mercapto-1-undecanol treatment prevents nonspecific interactions between the gold surface and avidin.
6:00 PM - CC3.5
Energy Cand Alignment at VOPc/HOPG Interface at Different Atmospheres.
Weiguang Xie 1 , Xi Wan 1 , Jun Du 1 , Jianbin Xu 1
1 Engineering Department, Chinese University of Hong Kong, Hong Kong China
Show AbstractEnergy band alignment at organic/inorganic interface has attracted considerable attention because of its importance in organic devices. In this work, we explore the interface of vanadyl-phthalocyanine (VOPc) and highly ordered pyrolytic graphite (HOPG) using scanning probe microscopy (SPM). The VOPc molecules are observed to stack in a bilayer cofacial mode on HOPG surface. The band structures are evaluated on different bilayers by scanning tunneling spectroscopy (STS) and Kelvin probe force microscopy (KPFM). It is found that shifting of molecular energy level only occurs between the first bilayer of VOPc thin film and HOPG surface under UHV conditions, whereas a band bending type of energy level alignment in about 5 bilayers is observed under ambient conditions. Also found is a transition of carrier conduction type in ambient, which is consistent with the performance of VOPc based FET devices. The interplay between molecule and HOPG and O2 doping effect will be discussed.
6:00 PM - CC3.6
New Architecture for Hybrid Solar Cell Using P-type Inorganic Material and Electron Conductor Polyfluorene.
Yohai Sitty 1 , Rafi Shikler 2
1 Department of Materials Engineering, Ben-Gurion University of the Negev, Beer Sheva Israel, 2 Department of Electrical & Computer Engineering, Ben-Gurion University of the Negev, Beer Sheva Israel
Show AbstractHybrid solar cells combine advantages of both organic and inorganic semiconductors and consider to be very promising solution since they are cheap and have wide versatility. The organic materials have good mechanical and optical properties. The inorganic materials possess high conductivity and can be fabricated by several deposition techniques. In the present work, we report for the first time on a hybrid organic-inorganic solar cell which consists of only two components. The commonly used configuration, such as DSSC and Extremely Thin Absorber (ETA) solar cells, three components are being used, each with different functionality: one as the hole conductor, the second as the electron conductor and the third material is between them that functions as the light absorber, which is responsible for harvesting photons and generating charge carriers. In the reported architecture we used a new combination of materials for hybrid solar cell, CuSCN as the a hole conductor inorganic material and a polyfluorene poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] (ADS133YE) as an electron conductor polymer. Copper(I)thiocyanate (CuSCN) is an inorganic transparent p-type semiconductor with band gap of 3.6eV. It has been widely used by microelectronics researchers, mainly as a solid state electrolyte in Dye-Sensitized Solar Cell (DSSC) that enables more stable performance then liquid electrolyte. In our proposed architecture the p-type material, CuSCN, and the electron acceptor ADS133YE are arranged in bilayer structure. We demonstrate that at the interface between those materials there is a charge separation that leads to photocurrent – the solar cells were tested at dark and under illumination and its short circuit current (Isc) was increased to 7.7*(10)^(-3)[mA/(cm)^(2)] under normal fluorescent light. In contrast the device comprises of ITO\ADS133YE\Al shows no photo-response which proves the assumption that the charge separation takes place at the CuSCN\ADS133YE interface. This work shows that by careful consideration of the HOMO and LUMO positions of the materials, a considerable simplification of the cell architecture is achieved. Furthermore, CuSCN can be deposited using several simple techniques, such as electrodeposition, which can open the way for device optimization via morphology control.
6:00 PM - CC3.8
Hybrid Poly(3-hexyl thiophene):TiO2 Nanorod Film Based Oxygen Sensor.
Tsung-Wei Zeng 1 , Che-Pu Hsu 1 , Yu-Chieh Tu 1 , Wei-Fang Su 1
1 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractConjugated polymers are investigated as materials for gas sensing applications since they have advantages of easy processing, low cost and room temperature operation. The incorporation of inorganic nanoparticles into conjugated polymers enables tuning the electronic properties of hybrid conjugated polymer materials and may improve the sensitivity as it is served as active material for the gas sensor. We demonstrate by using the hybrid materials based on poly(3-hexyl thiophene)(P3HT) in combination with TiO2 nanorod, improved oxygen sensing properties is obtained as compared to pristine P3HT. Composition studies reveal the oxygen sensor sensitivity is significantly increased with the increase of TiO2. This sensitivity is dependent on the change of carrier concentration and charge mobility due to the interactions between oxygen and hybrid materials. The results suggest the device is promising for resistive oxygen sensing at room temperature.