Symposium Organizers
Alberto Salleo Stanford University
Ana Claudia Arias Palo Alto Research Center, Inc.
Dean M. DeLongchamp National Institute of Standards and Technology
Cherie R. Kagan University of Pennsylvania
G1: Conformal Macroelectronics
Session Chairs
Monday PM, December 01, 2008
Room 207 (Hynes)
9:30 AM - **G1.1
Single Crystalline Inorganic Semiconductors for Unusual Format Electronics.
John Rogers 1
1 Materials Science and Engineering, University of Illinois-Urbana Champaign, Urbana, Illinois, United States
Show Abstract10:00 AM - G1.2
High Throughput Transfer Printing of Large Scale Chemically Derived Graphene.
Matthew Allen 1 2 3 , Vincent Tung 2 3 , Richard Kaner 1 2 3 , Yang Yang 2 3
1 Chemistry and Biochemistry, UCLA, Los Angeles, California, United States, 2 , California NanoSystem Institute, Los Angeles, California, United States, 3 Materials Science and engineering, UCLA, Los Angeles, California, United States
Show AbstractSingle layer graphene has attracted intense research interest since its discovery in 2003. However, difficulties in producing single layer specimens have encouraged the development of chemical routes. One such method is the oxidation, exfoliation, and subsequent reduction of graphite oxide through solution processing. Although graphite oxide produced specimens have been used to fabricate electrical devices, wafer scale processing has not yet been achieved due to the inability of registration in well-defined locations. Here we report a transfer printing process that allows for precise patterning of chemically derived graphene. Utilizing a polydimethylsiloxane (PDMS) stamp and the manipulation of surface energies, we successfully transfer spin-coated materials from one substrate to another. The method is capable of transferring sharp features to precise locations as confirmed by Raman mapping. This represents the first large scale, high throughput transfer printing of graphene and paves the way for future complementary circuit design.
10:15 AM - G1.3
Yarn-like Devices for Smart Wearable Electronics.
Piero Cosseddu 1 2 , Giorgio Mattana 1 2 , Gianluca Atzeni 1 , Magdalena Cybula 3 , Izabela Kruscinska 3 , Annalisa Bonfiglio 1 2
1 Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy, 2 S3 nanoStructures and bioSystems at Surfaces, CNR-INFM, Modena Italy, 3 3Technical University of Lodz, 3Technical University of Lodz, Lodz Poland
Show AbstractOrganic materials are becoming of great appeal also in the field of e-textiles, as they show an interesting combination of electronic and mechanical properties that can be favourably exploited in smart textiles.We present an example of organic field effect transistor (OFET) characterized by textile process fully compatible size and geometry. The devices have been obtained starting from a cylindrical metal fibre with typical diameters ranging around 45-60 µm, acting as the gate electrode, covered by a uniform insulating layers (polymide, and polypyrrole in the undoped state), which acts as the gate dielectric for the final device. As a result, this yarn is very flexible and can be employed, alone or twisted to another fibre, in textile processes.Different organic semiconductors were tested as the active layer forming the channel of the final device, and were deposited directly on the bare insulating yarn surface, while source and drain electrodes were realized afterwards in order to obtain a top contact configuration. AFM and SEM measurements demonstrated that both the dielectric and the organic semiconductor layers were uniformly deposited on the structure allowing to obtain well performing devices.When pentacene was used as organic semiconductor we obtained high performances unipolar p-type OFETs with an average hole mobility very close to 0.1 cm^2/Vs, and Ion/Ioff up to 10^4. In this paper we will show also how, thanks to the flexibility of the final structure, these devices can be employed as deformation sensors, as the output current varies reproducibly by applying a mechanical stimulus to the whole structure.Moreover, we will show how, using a double layer structure as active layer, employing pentacene/C60 heterojunction, it was possible to obtain ambipolar OFETs devices with very good mobility, up to 3x10^-2cm^2/Vs and 1.5x10^-2cm^2/Vs for the p- and n-type regime respectively. This was possible thanks to the improvements of the C60 layer structural and morphological characteristics, as supported by AFM and XRD characterization, which allowed, even by using high work function metals (Cu, Au and PEDOT:PSS) for the realization of the source and drain electrodes, to obtain a very efficient electron injection into the channel. These findings are very important because demonstrate the possibility of realizing organic complementary circuits by using very thin yarns suitable to be employed into a textile process. We will show our first preliminary attempts on the realization of complementary inverters by using the reported technology, which paves the way for the easy realization of smart wearable electronics.
10:30 AM - G1.4
Sintering Metal Nanoparticles.
Howard Wang 1
1 Department of Mechanical Engineering, Binghamton University, SUNY, Binghamton, New York, United States
Show Abstract10:45 AM - G1.5
A Hemispherical Electronic Eye Camera Based on Compressible Silicon Optoelectronics.
Heung Cho Ko 1 , Mark Stoykovich 1 , Jizhou Song 2 , Viktor Malyarchuk 3 , Won Mook Choi 1 , Chang-Jae Yu 1 , Joseph Geddes 4 , Jianliang Xiao 5 , Shuodao Wang 5 , Yonggang Huang 5 6 , John Rogers 1 2 3
1 Department of Materials Science and Engineering , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Frederick-Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 5 Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 6 Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThe human eye represents a remarkable imaging device, with many attractive design features. Prominent among these is a hemispherical detector geometry, similar to that found in many other biological systems, that enables wide field of view and low aberrations with simple, few component, imaging optics. This type of configuration is extremely difficult to achieve using established optoelectronics technologies, due to the intrinsically planar nature of the patterning, deposition, etching, materials growth and doping methods that exist for fabricating such systems. In this study, we introduce a route to curvilinear optoelectronics and electronic eye imagers that begins with well established electronic materials and planar processing approaches to create optoelectronic systems on flat, two dimensional surfaces, in unusual designs that allow full compressibility/stretchability to large levels of strain (~50% or more). This feature enables planar layouts to be geometrically transformed (i.e. conformally wrapped) to nearly arbitrary curvilinear shapes. In the example presented here, we use a hemispherical, elastomeric transfer element to accomplish this transformation with an electrically interconnected array of single crystalline silicon photodiodes and current blocking p-n junction diodes assembled in a passive matrix layout. The resulting hemispherical focal plane arrays, when combined with imaging optics and hemispherical housings, yield electronic cameras that have overall sizes and shapes comparable to the human eye. In a general sense, these methods, taken together with our theoretical analyses of their associated mechanics, provide practical routes for integrating well developed planar device technologies onto the surfaces of complex curvilinear objects, suitable for diverse applications that cannot be addressed using conventional means. Reference: Ko, H. C.; Stoykovich, M. P.; Song, J.; Malyarchuk, V.; Choi, W. M.; Yu, C.-J.; Geddes III, J.; Xiao, J.; Wang, S.; Huang, Y.; Rogers, J. A., Nature, in press.
11:00 AM - G1: Conformal
BREAK
G2: Macroelectronics on Flexible Substrates
Session Chairs
Monday PM, December 01, 2008
Room 207 (Hynes)
11:30 AM - **G2.1
Roll-to-Roll Manufacturing of Electronics on Flexible Substrates using Self-Aligned Imprint Lithography.
Ohseung Kwon 1 , Marcia Almanza-Workman 1 , Alison Chaiken 1 , Robert Cobene 1 , Robert Garcia 1 , Warren Jackson 1 , Mehrban Jam 1 , Albert Jeans 1 , Kim Han-Jun 1 , Hao Luo 1 , Ping Mei 1 , Craig Perlov 1 , Carl Taussig 1 , Frank Jeffrey 2 , Steve Braymen 2 , Don Larson 2 , Jason Hauschildt 2
1 , HP Laboratories, Palo Alto, California, United States, 2 , Power Film Solar Inc., Ames, Iowa, United States
Show Abstract12:00 PM - G2.2
Influence of Mechanical Deformation on the Electrical Performance of OTFTs.
Piero Cosseddu 1 2 , Emanuele Orgiu 1 2 , Ileana Manunza 1 2 , Francesco Arca 1 , Gabriele Cocco 1 , Andrea Spanu 1 , Annalisa Bonfiglio 1 2
1 Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy, 2 S3 nanoStructures and bioSystems at Surfaces, CNR-INFM, Modena Italy
Show AbstractHere we propose fully flexible organic field effect transistors (OFETs) assembled on plastic films as sensors for physiological parameters monitoring. Starting from a highly flexible and free standing OFET structure, realized using a very thin PET foil (1.4 um thick) acting at the same time as gate dielectric and as flexible mechanical support for the whole structure, we realized mechanical sensors in which a sharp and reversible sensitivity of the device output current to an elastic deformation, induced by means of a mechanical stimulus on the device channel, is observed. A careful analysis of the output current dependence from the applied pressure shows that this phenomenon might depend on the induced mobility, threshold voltage, trap states and contact resistances variation due to morphological and structural changes taking place within the semiconductor layer upon mechanical stimulus application.In order to have a deeper understanding of the physical causes dominating this behavior, we also present a preliminary investigation on the effective correlation between sensitivity and morphological/interfacial properties of both different organic semiconductor films (employed as active/sensitive layers) and polymeric dielectrics (whose interface with different polymers/semiconductor gives place to different electrical behavior).We realized OFET based mechanical sensors employing different organic semiconductors, namely small molecules (pentacene) deposited by thermal evaporation and different polymers (P3HT and pentacene TIPS) which can be deposited either by spin coating or drop casting, usually leading to organic films with very different morphological and structural characteristics. At the same time several flexible polymeric gate insulators have been tested in order to evaluate the different interfacial trap states dependence on mechanical stimuli. As a result, these films are expected to give rise to very different material-dependent sensitivity.Due to its high flexibility the proposed structures can be applied to any kind of substrate, fabric and/or 3D structure so opening the way for a wide range of possible applications. In this talk we will show how such a configuration can be used for monitoring different physiological parameters, as human posture by using a matrix of sensors embedded into a sole shoe, and human breathing rate by applying the same structure to wearable elastic bends placed around the diaphragm area.Thanks to the flexibility and low cost processing employed technique our devices pave the way for the realization of flexible arrays or matrixes of sensors to be employed in a wide range of innovative applications, such as sensorized clothes for physiological parameter detection, or in robotics for the realization of artificial “robot skin”.I. Manunza et al., Biosensors and Bioelectronics 22, 2775-2779, (2007)A. Bonfiglio,et al., Proc. SPIE Photonics 2007, S. Diego (USA) 26-31, August 2007
12:15 PM - G2.3
A Novel Hybrid Inorganic-polymeric Permeation Barrier for Flexible Displays.
Prashant Mandlik 1 , Lin Han 1 , Jonathan Gartside 1 , I-Chun Cheng 3 , Sigurd Wagner 1 , Jeff Silvernail 2 , Rui-Qing Ma 2 , Mike Hack 2 , Julie Brown 2
1 , Princeton University, Princeton, New Jersey, United States, 3 , National Taiwan University, Taipei Taiwan, 2 , Universal Display Corporation, Ewing, New Jersey, United States
Show AbstractMonday, 12/1New Presentation Time/Paper NumberG2.4 @ 11:30 AM to G2.3 @ 11:15 AMA Novel Hybrid Inorganic-polymeric Permeation Barrier for Flexible Displays. Prashant Mandlik
12:30 PM - G2.4
Formation of Solution Processable Organic Composites with Functionalized Carbon Naotubes for OTFTs.
Silvia Janietz 1 , Tatjana Egorov-Brening 1 , Bjoern Gruber 1
1 Polymer Electronics, FhG-IAP, Potsdam, Brandenburg, Germany
Show AbstractMonday, 12/1New Presentation Time/Paper NumberG2.5 @ 11:45 AM to G2.4 @ 11:30 AMFormation of Solution Processable Organic Composites with Functionalized Carbon Naotubes for OTFTs. Silvia Janietz
12:45 PM - G2.5
Three Dimensional Patterning of Indium Tin Oxide and Its Application to Hemispherical Organic Focal Plane Arrays.
Xin Xu 1 2 , Momchil Mihnev 3 , Andre Taylor 5 , Stephen Forrest 2 3 4
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Physics, University of Michigan, Ann Arbor, Michigan, United States, 3 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 5 Chemical Engineering, Yale University , New Haven, Connecticut, United States, 4 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractMonday, 12/1Transfer Poster G5.24 to G2.5 @ 11:45 AMThree Dimensional Patterning of Indium Tin Oxide and Its Application to Hemispherical Organic Focal Plane Arrays. Xin Xu
G3: Large-Area Compatible Processes and Materials I
Session Chairs
Monday PM, December 01, 2008
Room 207 (Hynes)
2:30 PM - **G3.1
ZnO Thin-film Transistors Deposited by a High-speed Continuous Atomic Layer Process.
Shelby Nelson 1 , Mitchell Burberry 1 , Diane Freeman 1 , Peter Cowdery-Corvan 1 , Lee Tutt 1 , David Levy 1
1 , Eastman Kodak Company, Rochester, New York, United States
Show Abstract3:00 PM - G3.2
Rheology of Thin Polymeric Coatings: In Situ Assessment of Rheology for Process Design.
Amélie Revaux 1 , Jérémie Teisseire 1 , Etienne Barthel 1 , Maud Foresti 2 , Ingve Simonsen 3 , Elin Sondergard 1
1 Surface du Verre et Interfaces, CNRS/Saint-Gobain, Aubervilliers France, 2 O2M, Saint-Gobain Recherche, Aubervilliers France, 3 Physics Department, NTNU, Trondheim Norway
Show AbstractRheology is a key issue for processing thin films of advanced functional polymeric materials. In particular complex devices require the 3D structuration of the film for which hot embossing is a very efficient process. Here we address the problem of the rheology of thin polymeric films in two different ways. For polymer embossing, the viscous flow is a key issue: embossing large scale structures on thin films result in confined viscous flow. Assuming newtonian behavior, we propose an analytical solution for the viscous flow of fluid films with periodic boundary conditions. The solution quantifies the impact of confinement on the structuration dynamics and is a guideline for process design. From this general model, the relevant limits are recovered: bulk relaxation for thick films and lubrication approximation for very thin films. Conversely, in numerous cases, it is necessary to assess the film rheology directly because bulk samples are either not available or not relevant. In such cases, the relaxation of structures under the action of surface tension is an interesting technique for rheology characterization. For that purpose, we have developped an in situ multiple order diffraction technique which allows direct monitoring of the height and shape of the structures. We demonstrate the use of the method through quantification of the impact of confinement on surface relaxation of PMMA structures.
3:15 PM - G3.3
Single and Multi-domain Thin Films of Pentacene Formed by Transferring Crystals Dispersed in Liquid Media.
Takashi Minakata 1
1 Central R&D Laboratories, Asahi-KASEI Corporation, Fuji-shi, Shizuoka-ken, Japan
Show Abstract3:30 PM - **G3.4
Stability and Mechanical Properties of Organic Thin-film Transistors Manufactured by Sub-femtoliter Inkjets.
Takao Someya 1 , Tsuyoshi Sekitani 1 , Yoshiaki Noguchi 1 , Tomoyuki Yokota 1 , Ute Zschieschang 2 , Hagen Klauk 2
1 Quantum-Phase Electronics Center, University of Tokyo, Tokyo Japan, 2 , Max Planck Institute for Solid State Research, Stuttgart Germany
Show Abstract4:00 PM - G3: Processes
BREAK
G4: Materials and Systems for Emissive Large-Area Displays
Session Chairs
Monday PM, December 01, 2008
Room 207 (Hynes)
4:30 PM - **G4.1
OLED Degradation Analysis by Synchrotron Radiation FT-IR Microscopy.
Brian D'Andrade 1 , Patrizia Melpignano 2 , Lisa Vaccari 3 , Giovanni Birarda 3 , Maya Kiskinova 3 , Viviana Biondo 2
1 , Universal Display Corporation, Ewing, New Jersey, United States, 2 , Centro Ricerche Plast-Optica, Amaro Italy, 3 , Sincrotrone Trieste S.C.p.A., Basovizza Italy
Show Abstract5:00 PM - G4.2
Long-life Red Phosphorescent Organic Light-emitting Devices Having Graded Compositions.
Junji Kido 1 , Myoung-Gu Lee 1 , Yong-Jin Pu 1 , Ken-Ichi Nakayama 1 , Masaaki Yokoyama 1
1 Organic Device Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Show AbstractOrganic light-emitting devices having graded junctions were developed. In such devices, graded junctions between hole-transporting materials (HTM) and electron-transporting materials (ETM) are formed. A typical device structure employed in this study was ITO/ HTM / HTM:ETM (graded composition) / ETM / Al. The organic layers were fabricated by the in-line vacuum evaporator, which was developed in our laboratory. For a red phosphorescent OLED, NP, Ir(piq)3 and BAlq were used as HTM, emitter and ETM respectively. In the device structure of ITO/ NPD / Ir(piq)3 / BAlq / Liq / Al, various patterns of gradual mixing of the organic layers were evaluated. Red emission peaking at 620nm and a high external quantum efficiency of 10 percent were observed. The graded mixing of the NPD/BAlq interface provided the longer lifetime. A lifetime of over 20000 hrs was observed at the initial luminance of 6500 cd/m2, which is equivalent to 200000 hrs at 1000 cd/m2. The long lifetime is attributed to the elimination of interfaces between the materials and degradation of the materials at the interfaces is suppressed.
5:15 PM - G4.3
Tailored Ambipolar Charge-Transporting Host Materials for Blue Electrophosphorescent OLEDs.
Asanga Padmaperuma 1 , Linda Sapochak 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractState-of-the-art OLEDs utilize an organic host material tailored for charge transport physically doped (5-20% by wt) with an organometallic phosphor optimized for light emission efficiency and color. Development of blue phosphorescent OLEDs, a crucial component of organic solid state lighting, is challenging because the host, as well as the charge injection layers require wide band gap materials with triplet exciton energies, ET >2.8 eV. We previously showed that organic phosphine oxide (PO) host materials exhibit good electron injection and transport properties while maintaining ET ~ 3.0 eV. Such materials, however, show no measurable ability to inject and transport holes, making it impossible to achieve charge balance in the recombination zone. Here, we present design strategies for engineering ambipolar charge-transporting PO host materials for blue OLEDs by combining hole-transporting moieties (HTm) with PO-based electron-transporting moieties (ETm). Three design approaches were considered, including: a –HTm and ETm share a common linkage; b –HTm and ETm are spatially separated by an inert spacer; and c –diphosphine oxide ETm is electronically isolated from HTm via P=O moieties. Theoretical modeling using the NWChem computional package was applied to the PO-ETm, a triarylamine-HTm and a combination of the two moieties using the different design approaches to form ambipolar materials. Three energy parameters were considered: HOMO and LUMO energies, intramolecular reorganizational energies (λi), and charge transfer integrals. We find that for each ambipolar charge transporting material design approach the HOMO energy varies slightly, but the LUMO energy is tunable over 1 eV. Computed λi‘s and charge transfer integrals show a stronger dependence upon design approach. These results will be presented and a general strategy for designing ambipolar charge transporting host materials using PO-moieties for blue phosphorescent OLEDs will be discussed.
5:30 PM - G4.4
Solution Processable Triplet Emitters and High Band Gap Hosts Based on Cyclic Phosphazene Cores.
Mui Siang Soh 1 , Alan Sellinger 1 , Alejandra Soriano 2 , Henk Bolink 2
1 , Institute of Materials Research and Engineering (IMRE) and the Agency for Science, Technology and Research (A*STAR), Republic of Singapore Singapore, 2 , Instituto de Ciencia Molecular (ICMol), Universidad de Valencia, P.O. Box 22085, 46071 Valencia Spain
Show AbstractTriplet based organic light emitting diodes (OLEDs), which offer the potential of using both the singlet and triplet excitons, have gained tremendous attention in recent years for use in full color displays, solid-state lighting and display backlights. In the area of solution processable materials development, there is a particular need for both new emitters and hosts. In this regard, new solution processable host materials with higher triplet energy states, particularly for blue and green emitters, remains a challenge. In this presentation, we report on dendrimers based on 3-dimensional cyclic phosphazene (CP) cores that represent a new class of versatile materials for application in solution processable OLEDs. For example, the dendrimers are easily prepared in high yield from readily available materials using Buchwald-Hartwig amination and Suzuki chemistry to decorate the periphery of the inorganic CP cores with dendrons having emissive and/or host-transport properties. The synthesized dendrimers are completely amorphous with high glass transition temperatures due to their three dimensional architecture. As the dendrimers are monodisperse, they can be purified to a high degree using chromatographic techniques, are soluble in common solvents, and form defect free thin films upon spin and/or dip coating. Furthermore, the dendrons can be selected from triplet and/or high band gap carbazole based moieties to produce highly efficient devices with blue through red emission. The synthesis, characterization, and preliminary device results using these dendrimers as active materials in solution processed OLEDs will be discussed.
Bolink, H.J., Barea, E., Costa, R.D., Santamaria, S.G., Sudhakar, S., Zhen, C., Sellinger, A., “Efficient Blue Emitting Organic Light Emitting Diodes based on Fluorescent Solution Processable Cyclic Phosphazenes”, Org. Elect., 2008, 9(2), 155-163.
Bolink, H.J., Santamaria, S.G., Sudhakar, S., Zhen, C., Sellinger, A., “Solution Processable Phosphorescent Dendrimers based on Cyclic Phosphazenes for use in Organic Light Emitting Diodes (OLEDs)”, Chem. Comm., 2008, 618-620.
Sundarraj, S. Sellinger A., “Nanocomposite Dendrimers based on Cyclic Phosphazene Cores: Amorphous Materials for Electroluminescent Devices”, Macromol. Rap. Comm, 2006, 27(4), 247-254. (journal cover image).
5:45 PM - G4.5
Electrical Properties of a Novel Encapsulation Material for Organic Light-emitting Diodes.
Lin Han 1 , Prashant Mandlik 1 , Sigurd Wagner 1 , Jeff Silvernail 2 , Rui-Qing Ma 2 , Mike Hack 2 , Julie Brown 2
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 , Universal Display Corp., Ewing, New Jersey, United States
Show AbstractWe report electrical properties of a novel, highly effective, single-compound encapsulation layer for the protection of organic light emitting displays from oxygen and humidity. OLEDs coated with this material still function after 10,000 hours of accelerated shelf lift test by storage at 65oC and 85% relative humidity. The material is a single-phase hybrid of silica and silicone. It combines the hermeticity of silica glass with the flexibility of silicone rubber in varying ratios. We first describe the deposition of this hybrid material by plasma-enhanced chemical vapor deposition from environmentally friendly precursor gases — oxygen and hexamethyl disiloxane (HMDSO). Then we discuss its electrical properties in the context of a number of chemical and mechanical properties, including infrared absorption spectra, surface roughness and wetting angle, and indentation hardness. We evaluate the electrical properties from capacitance-voltage (at 1 MHz) and current–voltage measurements on p-type Si / hybrid layer / Cr structures. The relative dielectric constant varies from about 4.5 for films whose chemo-mechanical properties are silica-like to 2 for films that essentially are plasma-polymerized silicone. Because films with silica-like properties are promising candidates for other areas outside of OLED encapsulation, such as interlevel dielectrics in flexible electronics, we have studied this novel film for these applications and will report experimental results.
G5: Poster Session: Hybrid and Organic Materials for Large-Area Functional Systems I
Session Chairs
Ana Arias
Dean DeLongchamp
Cherie Kagan
Alberto Salleo
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - G5.1
High-Throughput Solution Processing of Large Scale Graphene.
Vincent Tung 1 2 , Mattew Allen 3 2 , Yang Yang 1 2 , Richard Kaner 3 2
1 Materials and Science, Uniersity of California, Los Angeles, Los Angeles, California, United States, 2 , California Nano System Institute, Los Angeles, California, United States, 3 Chemistry Department, Uniersity of California, Los Angeles, Los Angeles, California, United States
Show AbstractSingle layer graphene is of great interest for electronic applications as an atomically thin, zero band gap semiconductor. Experimental results have been sparse due to the difficulty of creating single layer samples. Here we report a new solution process for the large-scale production of single layered graphene over the entire area of a wafer. By dispersing graphite oxide paper in pure hydrazine we are able to remove oxygen functionalities and restore the planar geometry of single sheets. The graphene sheets produced have the largest area (up to 40 μm x 60 μm) of any yet reported, making them far easier to process. Field effect devices are fabricated by conventional photolithography, displaying currents that are 3 orders of magnitude higher than any previously reported for chemically produced graphene7. The size of these sheets enables a wide range of characterization techniques, including optical microscopy, SEM and AFM performed on the same specimen. This versatile solution process holds great promise for nanoelectronic applications.
9:00 PM - G5.10
Design of Hierarchically Structured Porous Carbons.
Nicolas Brun 1 2 , Gilles Pecastaings 3 , Odile Babot 2 , Marc Birot 2 , Alain Soum 3 , Clément Sanchez 4 , Mathieu Morcrette 5 , Rénal Backov 1
1 , Centre de Recherche Paul Pascal UPR 8641 CNRS, PESSAC France, 2 , Institut des Sciences Moléculaires UMR 5255 CNRS Université Bordeaux 1, TALENCE France, 3 , Laboratoire de Chimie des Polymères Organiques UMR 5629 CNRS ENSCPB Université Bordeaux 1, PESSAC France, 4 , Laboratoire de Chimie de la Matière Condensée de Paris UMR 7574 CNRS Université Pierre et Marie Curie, PARIS France, 5 , Laboratoire de Réactivité et Chimie des Solides UMR 6007 CNRS Université de Picardie Jules Verne, AMIENS France
Show Abstract9:00 PM - G5.12
Development of New ``High-Speed Deposition" Process for Low-Cost and Flexible Organic Electronic Sensors.
Satoshi Horie 1 , Kenji Ishida 2 , Kei Noda 1 , Shuichiro Kuwajima 1 , Hirofumi Yamada 1 , Kazumi Matsushige 1
1 , Kyoto university, Kyoto Japan, 2 , Kobe university, Kobe Japan
Show Abstract9:00 PM - G5.13
Easy Functionalisation of High Surface Area Carbon Materials Using Diels-Alder Reactions for Sustainable Catalysis.
Philippe Makowski 1 , Frédéric Goettmann 2 , Arne Thomas 1 , Markus Antonietti 1
1 , max planck institute of colloids and interfaces, Potsdam Germany, 2 , Institut de chimie separative de Marcoule ICSM, bagnols/Cez France
Show Abstract9:00 PM - G5.14
Tuning Energetic Levels in Nanocrystal Quantum Dots Through Surface Manipulations.
Nir Tessler 1 , Vladislav Medvedev 1 , Michal Soreni-Harari 1 , Nir Yaacobi-Gross 1
1 Electrical Engineering, Technion. Israel Institute of Technology, Haifa Israel
Show AbstractTuning of the relative position of energy levels between nanocrystals (guest) and conjugated polymers (host) as well as of inter-nanocrystal (NC) coupling is reported along with the implication on device performance. In the context of LEDs and Photocells, one of the important factors in hybrid polymer-NC devices is the relative position of the energy levels of the components. In LEDs, the conduction and valence bands of the NC should be enclosed within the polymer bands (type I). Conversely, a staggered band alignment is required in a photocell (type II). Band alignments are not easily tunable as they are determined mostly by the material properties. In the context of transistors it is important to enhance the inter-dot coupling (i.e. electronic transport) while keeping the solution processibility.We report on tuning of the electronic level positions with respect to the vacuum level in colloidal InAs NCs using surface ligand exchange. We show that through a choice of ligand the inter-dot coupling is enhanced, thus supporting higher currents. By performing detailed electrochemical as well as scanning tunneling spectroscopy measurements on particles capped with different ligands we show that the organic surface capping layer of the inorganic NC is taking part and affecting its electronic system. The energy levels' shifting is largely dependent on the surface linking group while the polarity of the ligand molecules has a lesser effect. Improved device performance upon energy level tuning and enhanced inter dot coupling are demonstrated in several prototype devices using I-V measurements as well as photocurrent measurements of single and double layer devices.
9:00 PM - G5.15
Functional Monolayer Nanoparticle/polymer Composites Formed by Evaporation Induced Self-assembly at a Fluid Interface.
Shisheng Xiong 1 , Yongqian Gao 2 , Jiebin Pang 1 , John Grey 2 , Jeffrey Brinker 1 3
1 Department of Chemical Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 Department of Chemistry, University of New Mexico, Albuquerque, New Mexico, United States, 3 Advanced Material Laboratory, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNanoparticle (NP)/polymer composite materials exhibiting novel mechanical, electronic and optical properties are under extensive investigation for photovoltaics, light-emitting diodes and sensors. However, polydispersity of NP size and severe aggregation of NPs within the polymer matrix, are remain obstacles for further applications where a uniform positioning of nanoparticles is generally required. Recently, we have developed a universal, fast and facile method to prepare robust and transferable NP/polymer composites by evaporation-induced self-assembly at a fluid interface (JACS 2008). The nanoparticles embedded within the polymer matrix are 2D monolayer arrays, ordered in a hexagonal close-packed (hcp) arrangement. Ultra-thin, ordred films exceeding several cm2 can be assembled in seconds and transferred to arbitrary substrates. This approach represents a new means to attain very highly loaded yet flexible particle/polymer nanocomposites, which have eluded most synthetic efforts to date. Moreover, this kind of nanocomposite is tunable by either changing the nanoparticulate building blocks, or using different functional polymers. For instance, with PMMA serving as a negative photoresist, we have successfully demonstrated two modes of electron beam lithographic patterning essential for device fabrication and have shown sub 100-nm features with sub-nm edge roughness. Additionally, metallic and semiconductor nanoparticles have been assembled within a conjugated polymer and transferred onto electrode arrays for investigation of charge transport through NP/polymer film using combined spectroscopic imaging and I-V techniques.
9:00 PM - G5.16
Changes in Conductance of Pentacene at Electronic Interfaces.
Soonjoo Seo 1 , Guowen Peng 2 , Manos Mavrikakis 2 , Robert Hamers 3 , Paul Evans 4
1 Materials Science, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States, 4 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractWe have used scanning tunneling microscopy (STM) to probe the formation and electronic properties of a nitrobenzene self-assembled monolayer between Si (001) and a pentacene thin film. Differential conductance measurements were performed on few molecular-layer thick pentacene thin films on nitrobenzene-passivated, styrene-passivated and unpassivated Si (001) surfaces using scanning tunneling spectroscopy (STS). High-resolution STM images in conjunction with state-of-the-art density functional theory (DFT) total energy calculations and STM simulations show that nitrobenzene forms a well-ordered monolayer on Si (001). The conductance of pentacene on nitrobenzene-passivated Si (001) is different from that of pentacene on styrene-passivated and bare Si surfaces. The apparent energy gap in tunneling spectra was larger for pentacene on nitrobenzene than for the other surfaces by a factor of two. Our results can provide insight into the energy band lineups of an organic semiconductor at an electronic interface which are related to the charge transport characteristics of organic semiconductors.
9:00 PM - G5.17
Inkjet-Printed Libraries of PPE-PPV Copolymers with Tunable Optical Properties.
Daniel A. M. Egbe 1 2 , Emine Tekin 2 , Thomas Blaudeck 1 , Ulrich Schubert 2 3 , Reinhard Baumann 1
1 Print and Media Technology, TU Chemnitz, Chemnitz Germany, 2 Macromolecular Chemistry and Nanoscience, TU Eindhoven, Eindhoven Netherlands, 3 Organic and Macromolecular Chemistry, FSU Jena, Jena Germany
Show AbstractPatterning functional materials by inkjet printing has become an established technology for a variety of applications envisaged in organic and large-area electronics such as organic photovoltaic devices or light-emitting diodes. For any of those, tunability of the properties of the film of conjugated polymers is important. In particular, alkoxy side chains attached to the backbone may grant not only an appropriate processability by enhancing the solubility of the polymers, they also can affect the optical and electronic properties of the film. In this contribution, we report on the synergetic effects of position and length of side chains, film thickness and thermal treatment on the optical properties of a series of defect-free, four-fold alkoxy-substituted poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene)s (PPE-PPV). These polymers were synthesized via a Horner-Wadsworth-Emmons olefination reaction of luminophoric dialdehydes and bisphosphonate esters The thickness libraries of the different PPE-PPVs were prepared by controlled inkjet printing, with the optical properties of the printed libraries screened by high-throughput methods. It was found that the emission colors of the investigated polymers strongly depend on the interchain interactions which increase with increasing film thickness and influenced by the side chains. In conclusion, we could establish a correlation between the intensity of the S1-0 → S0-2 vibronic transition and the red shift of the emission color. Upon annealing at 70 °C for 2h, white emission was observed from thick printed films. This finding is tentatively ascribed to broadened emission spectra covering the whole visible region of the light spectrum and may be attributed to an increased aggregation due to an enhanced planarization of the polymer backbone. Further, the results for inkjet printing of related nanocomposite materials are discussed.
9:00 PM - G5.19
Isolation of Aging Components in Copper Phthalocyanine Organic Transistors.
James Royer 1 , J. Park 2 , C. Colesniuc 3 , A. Sharoni 3 , F. Bohrer 1 , I. Schuller 3 , W. Trogler 1 , A. Kummel 1
1 Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States, 2 Materials Science and Engineering Program, University of California San Diego, La Jolla, California, United States, 3 Physics, University of California San Diego, La Jolla, California, United States
Show AbstractA systematic approach to isolating the cause of device degradation (“aging”) in copper phthalocyanine (CuPc) organic thin film transistors (OTFTs) is presented. Aging is one of the primary impediments to the widespread deployment of OTFTs in gas sensors and as drivers for OLEDs. OTFTs with thick (~1000ML) CuPc layers were employed to study aging and the reversal of aging since the effects are most dramatic in thick organic layer OTFTs. Exposure of thick CuPc OTFTs to a sequence of environments including ambient air, clean dry air (20% O2/N2), water vapor and N2 gas isolated the causes of device aging in thick CuPc OTFTs. Initial exposure to ambient air increases the conductivity of the CuPc film but also causes rapid device aging characterized by an increased threshold voltage and the loss of saturation behavior. This is consistent with a loss of control of the channel conductivity by modulation of the gate bias. Conversely, exposure of thick CuPc OTFTs to clean dry air, H2O/N2 mixtures, or clean air/H2O mixtures does not result in aging, consistent with O2, H2O and O2/H2O products not being responsible for the aging. Furthermore, recovery of the threshold voltage and saturation behavior in fully aged thick CuPc devices requires displacement of the agents responsible for aging by H2O at the CuPc grain boundaries. The data is consistent with trace strong oxidants in ambient air being responsible for OTFT aging via formation of fixed charge. The aging effect is only present in thick films and is attributed to dissociative chemisorbing of strong oxidants (e.g. NOx and O3) in grain boundaries to form fixed charges which degrade the control of the OTFT channel conductivity by the gate bias.
9:00 PM - G5.2
Bistable Electrical Switching and Rewritable Memory Effect in a Thin Film Acrylate Copolymer Containing Carbazole-Oxadiazole Donor-Acceptor Pendant Groups.
Eric Teo 1 , Qidan Ling 2 , Siew Lay Lim 2 , En Tang Kang 2 , Daniel Siu Hung Chan 1 , Chun Xiang Zhu 1
1 Electrical and Computer Engineering, National University of Singapore, Singapore Singapore, 2 Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore
Show AbstractThe advantage of using organic or polymer materials for memory application lies in the fact that their electronic properties can be easily tuned, by structural design, synthesis and modification, to exhibit a series of memory functions. We have previously reported that an acrylate polymer with hole-transporting carbazole pendant groups can function effectively as a non-volatile WORM memory device. The WORM memory effect was attributed to the presence of a spacer unit between the pendant carbazole group and the polymer backbone. The spacer unit allowed the transition of the pendant carbazole groups from a disoriented state (OFF state) to an ordered face-to-face (or regioregular) conformation (ON state) at the threshold voltage. In this work, we report a change in memory function and mechanism when oxadiazole (acceptor) pendant groups are incorporated into the main chain. The flash (rewritable) memory behavior of the newly synthesized acrylate copolymer material, poly(2-(9H-carbazol-9-yl)ethyl methacrylate-co-4-(5-(4-tert-butylphenyl-1,3,4-oxadiazol-2-yl)phenyl methacrylate), or PCzOx, containing the carbazole-oxadiazole donor-acceptor pendant groups, has been demonstrated. The basic device structure is a MIM structure with Indium-Tin-Oxide (ITO)/glass as the substrate, our synthesized polymer material PCzOx as the active layer and Al as the top electrode. The toluene solution of PCzOx was spin-coated on the ITO, followed by solvent removal in a vacuum chamber. Finally, Al was thermally evaporated through shadow mask onto the PCzOx film. The memory effect of PCzOx was observed in the I-V characteristic of the MIM structure. The as-fabricated device is found to be in its OFF state, showing a current density of ~10-3 Acm-2, and can be programmed to ON state of current density ~10 Acm-2 at a threshold voltage of -1.8 V in the negative sweep. The ON state can be erased to the OFF state by using a reverse sweep (in this case positive sweep) and upon reaching a bias of +3.6 V. Subsequent switching between the ON state and the OFF state (the programming and erasing cycle) can be repeated with good accuracy for the write and erase voltage. The rewritable memory device exhibited a high ON/OFF current ratio of 103, was stable in both OFF and ON states after 107 read cycles, and showed that both the retention time in the ON and OFF state could be sustained under a 2 h voltage stress test. The J-V curve in the OFF state can be well fitted with the Schottky emission model, whereas that of the ON state can be fitted with the Ohmic model. The proposed mechanism based on charge transfer process is supported by the density function theory (DFT) simulation, as well as the UV-visible absorption spectroscopy. The solution-processable copolymer thin film is potentially useful for application in large-area flash memory devices.
9:00 PM - G5.20
Excited State Dynamics in Zn Phthalocyanines.
Leonardo De Boni 1 , Erick Piovesan 1 , Luciana Gaffo 2 , Cleber Mendonca 1
1 IFSC, University of Sao Paulo, Sao Carlos, Sao Paulo, Brazil, 2 Departamento de Química, Univ. Estadual de Maringa, Maringa Brazil
Show AbstractPhthalocyanines are macrocyclic organic compounds which present excellent stability, and whose optical and electrical properties can be tuned by varying the peripheral groups, the central metal ion as well as the way molecules are assembled. Such features make phthalocyanines promising candidates for a broad range of applications, from organic solar cells to photo-dynamic therapy of cancer. Thanks to the intense reverse saturable absorption exhibited by phthalocyanines, they have been used in several optical applications. Reverse saturable absorption occurs when the excited state absorption cross-section exceeds that of the ground state. In general, for macrocyclic compounds reverse saturable absorption follows from an intersystem crossing from a higher excited singlet state to an excited triplet state. Consequently, the reverse saturable absorption efficiency depends upon the properties of excited states, such as excited states lifetimes, intersystem crossing time and cross-sections.In this work, we investigate the nonlinear absorption dynamics of Zn phthalocyanine in dimethyl sulfoxide. We used single pulse and pulse train Z-scan techniques to determine the dynamics and absorption cross-sections of singlet and triplet states at 532 nm. The excited singlet state absorption cross-section was determined to be 3.2 times higher than the ground state one, giving rise to reverse saturable absorption. We also observed that reverse saturable absorption occurs from the triplet state, after its population by intersystem crossing, whose characteristic time was determined to be 8.9 ns. The triplet state absorption cross-section determined is 2.6 times higher than the ground state one. In addition, we used the white light continuum Z-scan to evaluate the singlet excited state spectrum from 450 nm to 710 nm. The results show two well defined regions, one, above 600 nm, where reverse saturable absorption is predominant. Below 600 nm, we detected a strong saturable absorption. A three-energy-level diagram was used to explain the experimental results, leading to the excited state absorption cross-section determination from 450 nm up to 710 nm. The high excited singlet and triplet states absorption cross-sections of phthalocyanines indicates its use in application requiring reverse saturated absorption in a broad spectral band
9:00 PM - G5.21
Layer-by-Layer Assemblies of Polyelectrolytes with Inorganic Nanoparticles and Organic Functional Molecules.
Sang-Mi Jeon 1 2 , Ki-Se Kim 1 2 , Byeong-Hyeok Sohn 1 2
1 Chemistry, NANO System Institute, Seoul National University, Seoul Korea (the Republic of), 2 , Center for Nanostructured Materials and Technology, Seoul Korea (the Republic of)
Show Abstract The layer-by-layer (LbL) assembling method based on electrostatic interaction between oppositely charged materials has been employed to create multilayered thin films with a well-controlled thickness in a nanometer scale. In addition, a variety of functional materials such as conducting polymers, organic dyes, metal and semiconductor nanoparticles have been incorporated into LbL thin films. Moreover, the LbL method can effectively generate multifunctional thin films by incorporating more than a single functional component into thin films. In this study, we demonstrate the fabrication of LbL assemblies of polyelectrolytes with inorganic semiconductor nanoparticles and organic fluorescent dyes. We synthesized semiconductor ZnO nanoparticles, of which surface were modified with silane compounds for stable LbL deposition. Fluorophore-labeled polyelectrolytes were also synthesized to attach dye molecules to polyelectrolytes. Then, thin films were fabricated with surface-modified ZnO nanoparticles, pure polyelectrolytes, and dye-labeled polyelectrolytes by the LbL method. Nanoparticles and fluorophores were independently inserted into the desired layer. To control the fluorescence resonance energy transfer (FRET) in the films, the mutual distances between fluorophores and semiconductor nanoparticles were controlled by the number of layers of pure polyelectrolyte layers. Since a variety of functional nanoparticles and molecules can be incorporated into LbL assemblies, hybrid LbL assemblies can be used in many applications such as solar cells and sensors which require the precise control over the distances among functional ingredients.
9:00 PM - G5.23
Layer-by-Layer Polyelectrolyte Multilayer Stabilized by Epoxy Reaction on Polymer Substrates.
Heekyung Lee 1 , Eunju Lee 1 , Hongdoo Kim 1
1 Chemistry, Kyung Hee University, Yongin, Kyungkido, Korea (the Republic of)
Show AbstractAmong various techniques to fabricate ultrathin film coating on the polymer substrate, the method to assemble layer-by-layer (LbL) polyelectrolyte multilayer(PEM) is one of the choices, which gives the capability of large area fabrication and the environmentally benign processing condition using water as solvent. Although this method using pH-adjusted PAH and PAA as polyelectrolyte dipping solutions is simple and easy, it has some draw-backs such that the film is unstable in chemical environments and mechanical property is poor. Fabricated ultrathin film does not keep stable conditions because the self-assembled PEM can be easily removed using acidic or basic solution. In order to overcome this, we have studied the epoxy reaction with PAH and PAA. Epoxy group may react and crosslink with amine or carboxylic group in PEM. GPTMS((3-glycidyloxypropyl)trimethoxysilane) having epoxy group was used as one of coating solution to crosslink with PEM. The trimethoxysilane group helps increase hardness of coating by reaction with colloidal silica suspension in the next process. Another coating solution was prepared by adding trimethoxysilane group solution to colloidal silica suspension through sol-gel method to strengthen the surface hardness of this film. Organic-inorganic hybrid coating using sol-gel method improved the chemical stability and the mechanical hardness on plastic substrates. The chemical and mechanical characteristics of PEM were investigated along with methoxysilane content in the solution. In order to demonstrate the epoxy reaction in LbL multilayer, the reaction was monitored by FT-IR spectra. The epoxy vibrational peak on FT-IR spectrum was disappeared as the reaction was proceeded. With GPTMS and nano silica suspension, the surface hardness was greatly improved. Also, it was found that crosslinking of amine-epoxy group can be done by either heating or UV exposure. The curing method using UV exposure has some advantages such as reduction in reaction time and generating patterns onto the specified area. Since the unexposed area of PEM may be easily removed using acidic solution, it is possible to generate sophisticated pattern on the plastic plate. As an example of this method, copper wiring pattern was made on polymer substrates through electroless plating and the adhesion between Cu and polymer substrate was improved.
9:00 PM - G5.25
Nanoparticle-assisted High Photoconductive Gain in Polymer/fullerene Matrix.
Hsiang-Yu Chen 1 , Michael Lo 2 , Guanwen Yang 1 , Harold Monbouquette 2 , Yang Yang 1
1 Materials Science and Eng., UCLA, Los Angeles, California, United States, 2 Chemical and Biomolecular Engineering, UCLA, LA, California, United States
Show AbstractPolymer/inorganic nanocrystal composites offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by 1) the solubility of the nanocrystals in the same solvent as that used for polymers, 2) the lower charge transfer rate between polymer and nanocrystal, and 3) the inefficient electron hopping rate between neighboring nanocrystals. To prevent nanocrystals from aggregating in the solvent, surface ligands such as oleic acid (OA) or tri-n-octylphosphine oxide (TOPO) are often used to enable dispersion of the nanoparticles or nanorods in the solvent; but these ligands hinder charge transfer from polymer to nanocrystals and carrier transport between nanocrystals. Much work has been done to modify the ligands to enhance the charge transfer rate as well as the solubility of the nanocrystals in polymer solutions. In our work, a high photoconductive gain has been achieved by blending cadmium telluride (CdTe) nanoparticles (NPs) into a polymer/fullerene matrix followed by a solvent annealing process. The NP surface capping ligand, N-phenyl-N’-methyldithiocarbamate, renders the NPs highly soluble in the polymer blend thereby enabling high nanocrystal loadings. An external quantum efficiency (EQE) as high as ~8000% (at 350nm) is reached at -4.5V. To our knowledge, this is the highest photoconductive gain obtained so far in polymer-based system under such low applied voltages. Hole-dominant devices coupled with AFM images are studied to uncover the probable mechanism. We observe a higher concentration of CdTe NPs is located near the cathode/polymer interface. These NPs with trapped electrons assist hole injection into the polymer under reverse bias, which contributes to greater than 100% EQE.
9:00 PM - G5.26
Selective Mercury Ion-Sensing with Phosphorescent Ir(III) Complexes.
Dong Ryeol Whang 1 , Youngmin You 1 , Soo Young Park 1
1 Department of Materials Science and Engineering, Seoul National Univeristy, Seoul Korea (the Republic of)
Show AbstractWe report on a selective sensing of Hg2+ with phosphorescent cyclometalated heteroleptic Ir(III) complexes consisting of phenylpyridine-based cyclometalating ligands and an β-diketonate ancillary ligand. The complexes showed very selective responses only to Hg2+ among many different metal ions. Multi-signaling and naked-eye detection of Hg2+ were achieved through the changes in both absorption color and phosphorescence intensity by forming 1:1 complex. Binding constant for the mercury ion was found to be 1.18 × 104 M-1, and the response was observable immediately. From a series of sensing experiments for reference compounds and NMR study, we could elucidate that the α-carbon of the β-diketonate ancillary ligand was a binding site for Hg2+. The phosphorescence quenching mechanism upon Hg2+ binding was explored by quantum chemical calculations.
9:00 PM - G5.28
Low Dielectric Constant Materials Based on Thermally Curable Cyclotriphosphazene Compounds.
Ho Lim 1 , Ji young Chang 1
1 , Seoul National university, Seoul Korea (the Republic of)
Show AbstractThe demand for the low dielectric constant and low dielectric loss materials has increased significantly in recent years as the electronic devices are getting faster and smaller. In this work, we prepared thermoset polymers based on cyclotriphosphazenes, which showed excellent dielectric properties. They also exhibited unusual thermal properties such as flame retardancy and self-extinguishibility due to skeletal nitrogen and phosphorus atoms of a cyclotriphosphazene ring. We synthesized soluble and curable cyclotriphosphazenes by substitution reaction of hexachlorocyclotriphosphazene with thermally reactive groups. The compounds were polymerized thermally to yield highly cross-linked materials. We chose styrene and acetylene compounds as reactive side groups, which are thermally curable under moderate conditions without the evolution of volatiles. Hexakisstyreneoxycyclotriphosphazene (HSP) was prepared by substitution reaction of hexachlorocyclotriphosphazene with sodium salt of 4-hydroxystyrene. The HSP was polymerized in a mold at 180 °C for 2 h under pressure. PolyHSP showed very low dielectric constant (k = 2.4) and low dielectric loss (tanδ = 1 x 10-3). The initial thermal degradation temperature was over 450 °C. No glass transition temperature was observed. We were able to further lower the dielectric constant and dielectric loss by introducing a bulky side group as a cosubstituent. When an acetylene compound was used as a curable group, the resulting polymers showed lower dielectric constant but higher dielectric loss than corresponding polymers obtained from styrene substituted cyclotriphosphazenes.
9:00 PM - G5.29
Bulk-Heterojunction Type Organic Solar Cells Based on New Branched Alkyl Oligothiophenes.
Yuji Yoshida 1 , Kenichi Sasaki 1 2 , Shuichi Nagamatsu 1 3 , Ming Lu 1 4 , Reiko Azumi 1 , Kiyoshi Yase 1 , Masafumi Yamashita 2
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 2 , Tokyo Science University, Noda Japan, 3 , Kyushu Institute of Technology, Iizuka Japan, 4 , Harbin Normal University, Harbin China
Show AbstractRecently, organic thin film solar cells show promise as future low cost solar energy. Especially, it is important to develop the solution-process solar cells because of remarkably decreasing the process cost. Polymer bulk-heterojunction solar cells are so close to the solution that many researchers have developed various soluble semiconducting materials. As well known, the combination of poly(3-hexylthiophene) (P3HT) with soluble fullerene (PCBM) shows highest efficient for bulk-heterojunction solar cells.Oligothiophenes are excellent semiconducting materials for many applications of field effect transistors, solar cells, light-emitting diodes, etc. However, it is difficult to develop high performance and good soluble oligothiophenes. According to the results of previous research, the relationship between carrier mobility and solubility is counterbalanced each other.In this study, we newly synthesized excellent soluble oligothiophene derivertives, 5,5''''-bis(2-hexyldecyl)-2,2':5',2'':5'',2''':5''',2''''-quinquethienyl (BHD5T) and sexithienyl (BHD6T) for solution-process organic devices. As our first trial, we fabricated bulk-heterojunction type solar cells of this oligothiophenes and PCBM.The active layer was spin-coated from the mixed solution of soluble BHD5T/BHD6T and PCBM at the weight ratio of 1:1 in chloroform solution. The device structure is composed of ITO/PEDOT:PSS/Active layer/LiF/Al. The I-V characteristics of the devices were measured under illumination of Xenon lamp at the power of 100mW/cm2. As the results, the power efficiency of this solar cell was up to 0.3 %. It is easily possible to improve the efficiency up to about 1% by tuning device structures such as an exciton-blocking layer, etc.
9:00 PM - G5.3
Partially-Fluorinated Large Acenes for Organic Electronics.
Balaji Purushothaman 1 , Sean Parkin 1 , John Anthony 1
1 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractElectronic devices based on organic materials have been an area of intense research due to their suitability to low cost solution processing techniques such as spin coating and ink-jet printing. Among the small-molecule semiconductors, acene based materials have been the most widely studied class of organic compounds due to their impressive electronic properties such as lower reorganization energy, reduced band gap and higher charge carrier mobility predicted by theoretical studies. However they have poor solubilty, π overlap and are highly unstable. The Anthony group has successfully demonstrated that by peri-functionalization with trialkylsilyl ethynyl groups π – stacking, solubility and stability of acenes can be improved. This approach has not only been applied to pentacenes but also successfully on higher acenes such as hexacene and heptacene. Acene based semiconductors are inherently p-type or hole transporting materials and in recent years efforts have been made towards synthesis of n-type materials by introducing electron withdrawing groups to the acene chromophore. Perfluoropentacene has been reported in the literature and the molecule behaves a n-type material. Introduction fluorine lowers the LUMO energy level of the molecule there by enabling electrons to be injected into the LUMO. Addition of fluorine is also known to improve the environmental stability and π – stacking in molecules by increasing intermolecular interactions between the electronegative fluorine atoms and π electron rich acene chromophore. Recently Anthony group has shown that partialy fluorinated anthradithiophenes exhibit higher mobility and environmental stability without altering the p-type behaviour of these molecules. We have applied same approach to synthesize partially fluorinated acenes of varying degree to improve the photostability and π – stacking in pentacene and hexacene. The effect of partial fluorination on LUMO energies will also be presented.
9:00 PM - G5.30
Large-scale Functional Surface Nanostructures and Their Diverse Applications.
Yong Lei 1 , Gerhard Wilde 1
1 Institute of Materials Physics, University of Muenster, Muenster Germany
Show Abstract9:00 PM - G5.31
Fabrication of Nanostructures Based on Nanocoating and Lithography Fabrication of Gold Nanofin Arrays Embedded in Polymer Film and its Application for Flexible, Transparent Anisotropic Conductive Film.
Wakana Kubo 1 , Shigenori Fujikawa 1 , Toyoki Kunitake 1
1 , RIKEN, Saitama Japan
Show Abstract9:00 PM - G5.32
Realisation and Characterisation of Flexible Vertical Channel Organic Field Effect Transistors.
Giorgio Mattana 1 , Piero Cosseddu 1 , Annalisa Bonfiglio 1
1 , DIEE, Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy
Show AbstractMonday 12/1Transfer Oral G2.3 @ 11:15 AM to Poster G5.32Realisation and Characterisation of Flexible Vertical Channel Organic Field Effect Transistors. Giorgio Mattana
9:00 PM - G5.4
Low Temperature Transparent Nanoplatelet Hybrid Gas Barrier Coating Materials via Sol-gel Process.
Masahiro Asuka 1 2 , Wolfgang Sigmund 1
1 Materials Sciences & Engineering, University of Florida, Gainesville, Florida, United States, 2 High Performance plastics company, Sekisui Chemical Co.LTD., Tokyo Japan
Show AbstractA novel hybrid coating based on a combination of nanoparticles, sol-gel and organic chemistry has been developed. It can be applied to a large variety of surfaces even at low processing temperatures. Low temperatures allow fabrication of the hybrid films on polymers.Nanoplatelets composite hybrid organic/inorganic coating materials have been successfully prepared via this sol-gel process. Transparent coatings from flexible to brittle can be obtained depending on the ratio of the inorganic/organic reagents. Thick films of more than 10 micrometer were achieved via single time dip coating. These barrier coatings are highly transparent (more than 95%) in the visible light while containing more than 60wt% ceramic nanoplatelets. Several substrates have been successfully tested including poly (ethylene terephthalate ) (PET). Moreover these films have excellent gas barrier properties for water vapor and excellent mechanical properties such as flexibility, which are important considerations in opto-electronic devices. Due to the incorporation of organic functional groups for the flexibility of the hybrid film, 3-Glycidoxypropyltrimethoxysilane(GPTMS) was adopted not only as a network former but also as a dispersing agent for nanoparticles during the preparation of the hybrid materials. The talk will present latest results on the characterization of the hybrid barrier coatings. Transmission electron microscopy, nanoindentation and Fourier transform infrared spectroscopy and Fourier transform Raman spectroscopy will be used to explain the development of the structure and its properties. Furthermore, the improvements in barrier coating towards water vapor permeation on PET will be discussed.
9:00 PM - G5.6
Multiscale Chemical Patterning of Self-Assembled Monolayers via Controlled Plasma Flow in Poly(dimethylsiloxane) Microchannels.
Meng-Hsien Lin 1 , Chi-Fan Chen 1 , Hung-Wei Shiu 2 , Chia-Hao Chen 2 , Shangjr (Felix) Gwo 1 3
1 , Nanoengineering and Microsystems, Hsinchu Taiwan, 2 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 3 physics, physics, Hsinchu Taiwan
Show AbstractIntegration of individual nanoscale objects into functional structures represents a key challenge for emerging fields of nanotechnology. Especially for the interfacing of nanoscopic devices with the macroscopic world, a large number of hierarchical and multilength-scale organization steps based on patterning and controlled assembly are required to implement practical nanodevice applications. Recently, soft lithographic approaches such as microcontact printing, replica molding, and nanoimprint have been developed to overcome this difficulty. The main concerns of soft lithography are durability of stamp, uniformity of large-area processing, and possibility of hierarchical structures. To enhance the applicability of soft lithography, we present here our recent results based on local plasma-induced chemical modification of organosilane monolayers using controlled plasma flow in poly(dimethylsiloxane) (PDMS) stamps.In order to achieve site-specific chemical modification and large-area patterning, we utilized PDMS elastomeric stamps fabricated with microchannel patterns. By directly contacting the PDMS stamps with surfaces terminated by organosilane self-assembled monolayers (SAMs), we can realize the confinement and controlled flow of low-power air plasma within the designated areas of organosilane SAM surfaces. We have successfully applied this method to multiple length scales ranging from full-wafer to sub-micron scale. Furthermore, the patterning resolution can reach a precision of few nanometers, judging by the patterned line edge. Using the plasma-patterned organosilane SAMs, we have demonstrated the possibilities of subsequent templated self-assembly steps for grafting dissimilar SAMs onto designated areas or for site-selective adsorption of functionalized nanoparticles.In this study, we have also understood the nature of plasma-induced chemical modification. First, the technique of synchrotron-radiation X-ray photoelectron spectroscopy (XPS) was applied to confirm the conversion of the original surface methyl groups into three main oxidized groups in the forms of hydroxyl, carbonyl and carboxyl groups. Second, by using focused synchrotron-radiation X-ray scanning photoemission microscopy and spectroscopy (SPEM/S), we have mapped regions of different functional groups on the modified surface, which are in excellent agreement with the PDMS pattern. Finally, by using scanning Kelvin probe microscopy (SKPM), the surface potential changes were quantitatively measured at the surfaces of plasma-modified, dissimilar SAM, and Au-nanoparticles-adsorbed regions. By comparing all the microscopic results [SPEM, SKPM, and scanning electron microscopy (SEM)], we confirm that the plasma-based pattern transfer using PDMS microchannel stamps is very faithful in terms of chemical conversion and spatial size/shape.
9:00 PM - G5.7
Soft Lithographic Approaches for Patterning of Quantum Dot Optoelectronics
Jixin Chen 1 , Yang-Hsiang Chan 1 , Dong Hee Son 1 , James Batteas 1
1 Department of Chemistry, Texas A&M University, College Station, Texas, United States
Show AbstractHere we demonstrate the direct photolithographic patterning of quantum dot (QD) thin films on surfaces over large areas. CdSe QDs were prepared as thin films of one or multiple particle layers in thickness on solid supports. Photopatterning of these films can be accomplished by local photo-oxidation using scanning confocal laser microscopy as well as by conventional photolithography. Local photo-oxidation of the stabilized film results in significant wavelength shifting of the CdSe quantum dots allowing selective tuning of the local emission wavelength by ca. 50 nm or more affording multiple colors to be spatially patterned from a single starting material. Additionally, the luminescence of the patterned structures can be subsequently turned “off” and “on” by simple ligand exchange. The ability to create nanoscopic structures using scanning laser lithography as well larger arrays via conventional photolithographic methods provide a facile, scalable approach, for creating QD based devices with tunable optical properties.
9:00 PM - G5.8
The Supramolecular Chemistry of Silica-based Organic-Inorganic Hybrid Materials as Chemosensor for Toxic Metal Ions.
Jong Hwa Jung 1 , Doo Ri Bae 1 , Hey Young Lee 1 , Won Seok Han 1 , Eun-jeong Kim 1 , Namjun Cho 2
1 Chemistry, Gyeongsang National University , Jinju Korea (the Republic of), 2 Applied Chemical Engineering, Korea University of Technology & Education, Chonan Korea (the Republic of)
Show AbstractWith recent advances in nanomaterials and nanotechnologies, new methods are emerging to design optical sensors and biosensors, and to develop highly sensitive solid-state sensors. However, in recent years, SBA-15 and MCM-41 have attracted significant interest for the development of optical chemical sensors. Although these materials offer considerable advantages over other methods in the area of sensing technologies, there is still a growing demand to solve one of the major technological challenges in nano-optical sensor: the detection and determination of environmentally important toxic species at a low level of concentration with a rapid-assessment process. Based on this idea, we designed and synthesized an azo-coupled macrocyclic receptor 1, and then grafted 1 onto the surface of SNT as a new approach to the development of nanomaterial chemosensors. The SNT-1 (silica nanotube immobilized with 1) as heterogeneous “naked-eye” colorimetric and spectrophotometric cation sensor was prepared by immobilization of the azo-coupled macrocyclic receptor 1 on the silica nanotube (SNT) via sol-gel reaction. The optical sensing ability of SNT-1 was studied by addition of metal ions such as Ag+, Co2+, Cd2+, Pb2+, Zn2+, Fe3+, Cu2+, and Hg2+ (all as nitrates) in water. Upon the addition of Hg2+ in suspension SNT-1 resulted in a color change from yellow to violet. This is novel rare example for chromogenic sensing of a specific metal ion by inorganic nanotubes. On the other hand, no significant changes in color were observed in the parallel experiments with Co2+, Cd2+, Pb2+, Zn2+, Fe3+, Cu2+, and Ag+. These findings confirm that SNT-1 can be useful as chemosensors for selective detection of Hg2+ over a range of metal ions. More interestingly, SNT-1 by the addition of NO3- and ClO4- was observed color change from yellow to violet and pink, respectively. However, no color changes were observed upon addition of Cl-, Br-, I-, SCN-, or SO42-. Furthermore, the extraction ability of the SNT-1 was also estimated by measuring the amount of Hg2+ adsorbed on the SNT-1 by ion chromatography, resulting in 95% of Hg2+ ion being extracted by SNT-1, suggesting that the SNT-1 is potentially useful as a stationary phase for separation of Hg2+ in liquid chromatography. In order to extend above performance to the portable chemosensor kit, SNT-1 was coated with 50 µm thickness onto glass substrate. The supported SNT-1 only changed from yellow to violet when dipped into Hg2+ solution. On the other hand, no significant change in color was observed in other metal ions solution. The results imply that the supported SNT-1 is applicable as a portable colorimetric sensor for detection of Hg2+ in the environmental field.
9:00 PM - G5.9
Self-assembled Arrays of Mesoporous Silica Cone-like Particles on Different Patterned Surfaces.
Ahmed Khalil 1 2 , Frank Marlow 1
1 , Max-Planck-Institute für Kohlenforschung, Mülheim an der Ruhr Germany, 2 Nanoparticle Process Technology, Duisburg-Essen University, Duisburg Germany
Show Abstract
Symposium Organizers
Alberto Salleo Stanford University
Ana Claudia Arias Palo Alto Research Center, Inc.
Dean M. DeLongchamp National Institute of Standards and Technology
Cherie R. Kagan University of Pennsylvania
G6: Organic Materials for Macroelectronics
Session Chairs
Tuesday AM, December 02, 2008
Room 207 (Hynes)
9:30 AM - **G6.1
Electron-Transporting Materilas For Printed Electronics.
Antonio Facchetti 1
1 , Northwestern University, Evanston, Illinois, United States
Show Abstract10:00 AM - G6.2
Electronic Grade pi-Conjugated Peptides as Building Blocks for High Quality Devices.
Elena Borzin 1 , Batya Blumer-Ganon 1 , Michal Firstenberg 1 , Vladislav Medvevdev 2 , Olga Solomeshch 2 , Alexey Razin 2 , Young-Jun Yu 2 , Helena Chechik 3 , Nir Tessler 2 , Yoav Eichen 1
1 Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa Israel, 2 Department of Electrical Engineering, Technion - Israel Institute of Technology, Haifa Israel, 3 , Peptronics Ltd., Ramat Gan Israel
Show AbstractNature holds two different approaches to the synthesis of biomaterials. Most chemical entities are prepared by target-specific machinery that is tailored to produce one or a very narrow set of structurally similar compounds. This approach is being utilized in most cases where high fidelity in synthesis is required, as is the case in the biosynthesis of most small molecules. On the other hand, when versatility is in question, nature adopts a sequence independent synthesis, producing large numbers of materials that differ in structure and properties out of a very limited number of small building blocks. This approach is being used for the synthesis of poly nucleic acids, where the sequence of the monomers in the polymer represents the genetic code, and in peptides, where the sequence of the monomers in the polypeptide chains defines the functionality. Due to the importance of these two reactions to molecular biology, two families of most powerful in-vitro syntheses were developed for the in-vitro preparation of peptide and nucleic acid sequences, both in solutions and on solid supports. We will describe the tuning of the electronic properties of materials through block assembly and the full realization of solid phase synthesis of electronically active building blocks that utilizes the amide bond as a linker. The use of the solid phase amide bond chemistry opens the route to robust, chemically pure and precise block assembly of electronic materials. The concept behind this approach is the use of structurally different building blocks that are capable of interconnecting using the same chemistry (amide bond formation) and synthetic protocols.Consequently, almost any molecule that bears both an amine and a carboxylic acid can be incorporated into a polyamide (polypeptide) in almost any sequence, using the same chemistry for each and every step. Besides the potential of anchoring practically any sidegroup in practically any desired sequence, the partial double bond character of the amide bond makes it an interesting candidate for coupling pi-conjugated monomers into oligomers and polymers without destroying the pi conjugated skeleton, thus keeping their semiconducting nature for electronic and/or light-emitting applications. We demonstrate the potential power of the approach by the preparation and characterization of small libraries of structurally similar OLED emitter layers, made of oligopeptides, containing different monomers in different sequences (light emitting, electron transporting, hole transporting). Our results clearly show that in addition to the nature of building blocks, the sequence of the monomers in the oligomer plays a major role in determining properties such as turn on voltage, external quantum efficiency and color.
10:15 AM - G6.3
Comparison of Molecular Subunits in n-Channel Organic Semiconductors.
Howard Katz 1 , Kevin See 1 , Taegweon Lee 1 , Bal Dhar 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractNaphthalenetetracarboxylic diimides remain among the most promising core groups for large-area, transparent, electron-transporting organic transistor semiconductors, following their first use by the Katz group eight years ago. We have discovered three new fluorocarbon-terminated side chains (perfluorooctylethylbenzyl, bis(trifluoromethylbenzyl), pentafluorophenethyl) that confer mobility up to 0.5 cm2/Vs in air, on/off ratios above one million, operation with single volts on the gate, flexibility, and low hysteresis using appropriate process conditions. The syntheses are very simple and do not require core functionalization. The compounds show outstanding thin film crystallinity, including large grains, pi overlaps, and terraced structures. With proper surface treatments, they function well in bottom contact as well as top contact devices. Alternatively, we have considered subunits that can be incorporated into conjugated oligomers, including oxadiazole, fluorenone, and dicyanoethylidene. New semiconducting co-oligomers with thiophene and fluorinated end groups were made with these subunits and transistor activity established. Their mobilities and polarities in transistors will be correlated with their microstructures and redox potentials, and their behavior in light of expectations gleaned from related devices such as organic light-emitting diodes will be discussed. Finally, the relative merits of tetracarboxylic and oligomeric structures will be considered.
10:30 AM - G6.4
High-Performance Organic Field-Effect Transistors by Controlled Growth of Pentacene with Self-Assembled Monolayers.
Kamal Asadi 1 , Yu Wu 1 , Fatemeh Gholamrezaie 1 , Paul W. M. Blom 1 , Petra Rudolf 1 , Bert de Boer 1
1 , University of Groningen, Groningen, Groningen, Netherlands
Show AbstractSelf-assembled monolayers can modify the work function of gold from 4.1 eV to 5.5 eV for decanethiol and 1H,1H,2H,2H-perfluoro-octanethiol, respectively [1]. It has been demonstrated that SAM-modified Au electrodes can be used in field-effect transistors to manipulate the injection of holes into polymeric semiconductors [2]. However, understanding the effect SAM-modified electrodes in devices is a complicated issue, since both the interfacial energetic landscape as well as the interfacial morphology are simultaneously changed. The question is which of these modified properties, interfacial energy barriers or morphology, plays a determining role on the device performance. Here we investigate both the electrical performance and morphology in pentacene based bottom-contact/bottom-gate (BC/BG) transistors. Self-assembled monolayers of alkanethiols and perfluorinated alkanethiols with opposing dipole moments have been applied to modify the work function of the gold electrodes in the opposite directions. Pentacene ultra-thin film growth was carried out by supersonic molecular beam deposition technique (SuMBD). Experiments were carried out on FETs with only one monolayer (ML) of pentacene as the active semiconducting layer. After the deposition of the pentacene ML on FET substrates, the electrical measurements were performed under vacuum, followed by the characterization of the surface morphology of the films using ex-situ tapping mode AFM. As a reference the morphology of MLs deposited on bare silicon oxide was also investigated. Two scan regions were selected: a) a region in the middle of transistor channel (away from the gold electrode) to investigate the morphology on the silicon oxide gate insulator and b) a region at the boundary between the electrode and the channel. The latter is most influential on the performance of the OFET. We demonstrate that the superior interfacial morphology between the SAM-modified contacts and the transistor channel dominates the device performance rather than manipulation of the Schottky barrier and charge injection. This results in the realization of high-performance BC/BG OFETs with only one monolayer of pentacene as the active semiconducting material.[1] B. de Boer et al. Adv. Mat, 2005, 17, 621.[2] K. Asadi et al. J. Mater. Chem. 2007, 17, 1947.
10:45 AM - G6.5
A New Familiy of High Mobility, Solution-processable Polyacenes.
Gonzalo Rincon-Llorente 1 , Marie-Beatrice Madec 1 , David Crouch 1 , Stephen Yeates 1
1 OMIC School of Chemistry, University of Manchester, Manchester United Kingdom
Show Abstract11:00 AM - G6: Materials
BREAK
11:30 AM - G6.6
Solubility-induced Semiconducting Nanofibers in Semiconducting/insulating Polymer Blends for Organic Thin-Film Transistors Applications.
Longzhen Qiu 1 , Xiaohong Wang 1 , Wi Hyoung Lee 1 , Kilwon Cho 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractSemiconducting and insulating polymers blends have attracted increasing interest because they can combine electronic properties of semiconducting polymer with the low-cost and excellent mechanical characteristics of the insulating polymers. Here, we investigated the influence of solvent solubility on the electronic performance and morphology of TFT devices based on semiconducting and insulating polymer blends. We found that excellent electronic performance can be achieved in blends of poly(3-hexylthiophene) (P3HT) and amorphous polystyrene (a-PS) at very low P3HT content by changing the solubility of solvent using a marginal solvent or mixed solvent. Morphological and structural studies reveal that P3HT molecules in these blends adopt high crystalline, interconnected nanofibrillar networks, which is extremely beneficial for both enhancing charge transport and keeping connectivity at low P3HT content. This is in stark contrast to blends prepared from good solvent (such as Chloroform), in which the device performance monotonously degrades with increasing PS content due to the reduction of connectivity of P3HT active channels. Furthermore, we found that the formation of nanofibrillar structure is mainly dominated by the change of solubility and insensitive to other conditions. For this reason, this simple, mild and reproducible method is quite suitable for the fabrication of large-area, flexible electronic devices on plastic substrate.Acknowledgement. This work was supported by a grant from the Information Display R&D Center under the 21st Century Frontier R&D Program, the ERC Program of MOST/KOSEF (R11-2003-006-06004-0), a grant (M2007010004) from the Fundamental R&D Program for Core Technology of Materials of the MOCIE of Korea, and RTI04-01-04 from the Regional Technology Innovation Program of the MOCIE of Korea.
11:45 AM - G6.7
Nucleation-Governed Reversible Self-Assembly of an Organic Semiconductor at Surfaces: Long-Range Mass Transport Forming Giant Functional Fibers.
Paolo Samori 1 2 , Vincenzo Palermo 2 , Giovanna De Luca 2 , Andrea Liscio 2 , Emanuele Treossi 2 , Rebecca Savage 1 , Piera Maccagnani 3 , Fabian Nolde 4 , Xinliang Feng 4 , Klaus Muellen 4
1 Institut de Science et d'Ingénierie Supramoléculaires, Université Louis Pasteur de Strasbourg, Strasbourg France, 2 Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, Bologna Italy, 3 Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Bologna Italy, 4 , Max-Planck Institute for Polymer Research, Mainz Germany
Show Abstract12:00 PM - G6.8
Homo-Epitaxy of Ultrathin Pentacene Films on SiO2.
Vivek Kalihari 1 , David Ellison 1 , Greg Haugstad 2 , C. Frisbie 1
1 Chemical Engg. and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Characterization Facility, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe microstructure of ultrathin organic semiconductor films on gate dielectrics plays a pivotal role in the electrical transport performance of these films in organic field effect transistors (OFETs). The structure of thin films of pentacene is of particular interest, as pentacene is a benchmark semiconductor for OFETs. Using a variety of scanning probe microscopy techniques, including a unique method for Grain Orientation Mapping, we have established that vapor-deposited pentacene layers on SiO2 substrates can exhibit homo-epitaxy, i.e., epitaxial growth of pentacene layers on pentacene. Pentacene films grow with coincidence-II epitaxy, except for the first monolayer on SiO2, resulting in a 4 x 4 supercell structure. This mode of epitaxy is also referred to as geometrical coincidence. The epitaxial growth is not ubiquitous; for example, some crystalline domains in the second pentacene monolayer have both epitaxial and non-epitaxial interactions with the underlying pentacene monolayer. Regions of non-epitaxial growth exhibit higher friction in scanning probe measurements and also high dislocation densities, as assessed by chemical etching experiments. Furthermore, we demonstrate using Kelvin probe microscopy that the non-epitaxial domains have a lower (more negative) surface potential, which provides a concrete connection between microstructure and electrical properties. These experiments point to an as yet unproven but intriguing possibility, namely that homo-epitaxy, or its absence in certain domains, can give rise to electrostatic disorder in pentacene films, which in turn directly impacts hole transport at the pentacene/SiO2 interface.
12:15 PM - G6.9
Blue-shifting the Optical Properties of PPVs by Fluorinating Vinylene Units: Interplay Between Supramolecular-organization and Optical Properties of MEH-PPDFV.
Maria Losurdo 1 , Maria Giangregorio 1 , Pio Capezzuto 1 , Giovanni Bruno 1 , Babudri Francesco 2 , Antonio Cardone 2 , Gianluca Farinola 2 , Francesco Naso 2
1 PlasmaChemistry, IMIP-CNR, Bari Italy, 2 Chemistry Dep, University of Bari, Bari Italy
Show AbstractThere has been growing interest in developing new semiconducting polymers for applications in optoelectronics (OLEDs), photovoltaics, thin film transistors and sensors, due to their exceptional processability and appealing characteristic of manipulating electronic and optical properties by tuning of molecular structure and self-assembling. For applications based on optical emission, the ability to tune emission colors is essential. In this frame, there is interest in stable deep-blue emitting polymers.In this contribution, we demonstrate the synthesis and properties of thin films of a new class of poly(p-phenylenedifluorovinylene) (PPDFV), which contain two fluoro atoms in the vinylene units. This class of fluoro-polymers is effective in reducing the barrier of electron injection. Specifically, we report on the correlation existing between the structure and optical functionality of thin films of poly-methoxy-ethylexyloxy-phenylenedifluorovinylene (MEH-PPDFV). In particular, we demonstrate that the above films have the largest HOMO-LUMO transition energy (above 3.75eV) ever reported for organic films and intense room temperature blue photoluminescence at 450nm and electroluminescence at 500nm. Films of the above polymers have been deposited by spin coating and drop-casting on a variety of substrates including Corning glass, quartz, ITO. Since, the performance of organic materials in devices is strongly dependent on self-assembly of polymer in the solid state, which induces a modulation of morphological and optical properties, we discuss the effects of deposition methodology, substrate and film thickness, concentration of the precursor polymer solution and of the solvent on the aggregation structure in the solid state, structural order and anisotropy, and its subsequent impact on the electronic and optical properties. With the ultimate technological perspective of understanding and controlling self-aggregation, morphology and associated optical properties of films, which is a key factor for optimization of polymer-based devices, the focus of our investigation is also on the analysis of the substrate/polymeric film interface that primarily determine the aggregation and optical response and on the resulting optical anisotropy which depends on self-aggregation. The anisotropy and optical properties are mainly investigated non destructively by spectroscopic ellipsometry (UVISEL-Jobin Yvon). Atomic force microscopy, photoluminescence and electroluminescence corroborate results.
12:30 PM - G6.10
Microstructure of Pentacene Films from a Pentacene Precursor.
Daniel Huang 1 , Shong Yin 1 , Kanan Puntambekar 1 , Mike Toney 2 , Vivek Subramanian 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Stanford Linear Accelerator Centor, Stanford, California, United States
Show AbstractPentacene remains one of the most common high mobility organic semiconductors. Unfortunately, pentacene itself cannot be easily solution processed. There have been many different schemes to functionalize pentacene in order to confer solubility into common solvents in order to use pentacene in printed transistor devices. Side chains have been added to pentacene in order to allow direct deposition of pentacene onto relevant substrates. Another scheme is to create a soluble precursor of pentacene, which after deposition requires a thermal degradation in order to convert the precursor to pentacene. Afzali, et al. in 2001 has report one such precursor, which is widely used in our group. The time evolution and microstructure of pentacene films created from this method has not yet been studied. Here we report a thorough study of the microstructure of this pentacene precursors processed on oxide at different time and temperatures analyzed with SEM and GIXD. We also report the microstructure between films processed on different substrates. Finally we report the effects of transistor mobility given the different conversion conditions. We have found that conversion at lower temperatures (125-140C) lead to highly polycrystalline films dominated by the pentacene bulk phase. At intermediate temperatures (140-160C) we find that we are able to form textured films with both the bulk and thin-film phase of pentacene present. At high temperatures (160C+), pentacene starts dewetting from the substrate.
G7: Device and Materials Physics
Session Chairs
Tuesday PM, December 02, 2008
Room 207 (Hynes)
2:30 PM - **G7.1
Electronic Transport and Recombination in Organic Semiconductor Devices.
Bob Street 1 , John Northrup 1 , Tse Nga Ng 1
1 , PARC, Palo Alto, California, United States
Show Abstract3:00 PM - G7.2
A Close Look at Oxygen-Related Traps in Pentacene Thin Films: Energetic Position and Implications for Transistor Performance.
Wolfgang Kalb 1 , Kurt Mattenberger 1 , Bertram Batlogg 1
1 , ETH Zurich, Zurich Switzerland
Show AbstractWe report on a detailed study of the influence of oxygen on the electronic trap states in a pentacene thin film. Temperature-dependent gated four-terminal measurements on pentacene-based thin-film transistors were carried out without ever exposing the samples to ambient air and after controlled exposure to oxygen and light. From the measurements, which we perform such as to avoid any parasitic contact resistance, the trap density as a function of energy is extracted. Photooxidation of pentacene is found to lead to a peak of trap states centered at 0.28 eV from the mobility edge, with trap densities of the order of 10E18 cm-3. These trap states cause a reduction in the number of free carriers. Moreover, the exposure to oxygen reduces the mobility of the charge carriers above the mobility edge. We correlate the change of these key transport parameters with the change of device parameters such as subthreshold performance and effective field-effect mobility. The study supports the assumption of a mobility edge for charge transport in crystalline organic semiconductors. It contributes to a detailed understanding of an important degradation mechanism of organic field-effect transistors. Deep traps in an organic field-effect transistor reduce the effective field-effect mobility by reducing the number of free carriers and their mobility above the mobility edge.
3:15 PM - G7.3
Electronic Functionalization of Organic Semiconductors with Self-assembled Monolayers.
Matthew Calhoun 1 , Javier Sanchez 1 , David Olaya 1 , Michael Gershenson 1 , Vitaly Podzorov 1
1 Physics Department, Rutgers University, Piscataway, New Jersey, United States
Show AbstractSelf-assembled monolayers (SAM) are used in a variety of emerging applications for surface modification of inorganic materials, such as metals and oxides. Here, we demonstrate a new platform for the molecular self-assembly research: SAMs at the surface of organic semiconductors. Our recent experiments show that silanes can be grown at organic surfaces, and, remarkably, SAMs with a strong electron withdrawing ability induce a large surface conductivity of conjugated organic materials [1]. For example, conductivity induced by perfluorinated alkyl silanes in organic molecular crystals approaches 10^-5 Siemens per square, two orders of magnitude greater than the maximum conductivity typically achieved in OFETs. The observed large electronic effect opens new opportunities for nanoscale surface functionalization of organic semiconductors with molecular self-assembly. In particular, SAM-induced conductivity exhibits sensitivity to different molecular species present in the environment, which makes this system very attractive for chemical sensing applications. [1]. M. F. Calhoun, J. Sanchez, D. Olaya, M. E. Gershenson and V. Podzorov, “Electronic functionalization of the surface of organic semiconductors with self-assembly monolayers”, Nature Mat. 7, 84 (2008).
3:30 PM - **G7.4
Progress on Printed Low Voltage Electrolyte Gated OTFTs.
Dan Frisbie 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractGel electrolytes consisting of a dissolved salt and a polymer matrix can be used as high capacitance gate dielectrics in low voltage organic thin film transistors. One useful gel formulation consists of an ionic liquid and a gelating triblock copolymer. These so-called ion gels offer specific capacitances in excess of 10 microF/cm2, low voltage operation (< 2V), and short polarization response times, typically < 1 ms. Ion gel dielectrics can also be printed from a solvent-based ink. In this talk, I will describe recent progress on fabrication and characterization of printed ion gel gated OTFTs (“GEL-OTFTs”), including device yields and reproducibility, switching speed, ON/OFF current ratio, threshold voltages and integration into simple circuits.
4:00 PM - G7: Devices
BREAK
4:30 PM - **G7.5
Organic semiconductors for flexible electronics
Henning Sirringhaus 1
1 , Cambridge University, Cambridge United Kingdom
Show Abstract5:00 PM - G7.6
In-Situ Characterization of the Thermal Transformations of High Performance Polymer Semiconductors.
Lee Richter 1 , A. Moad 1 , D. Delongchamp 1 , R. Kline 1 , D. Fischer 1 , D. Gundlach 1 , B. Hamadani 1 , M. Heeney 3 , I. McCulloch 2
1 , NIST, Gaithersburg, Maryland, United States, 3 , Queen Mary, University of London, London United Kingdom, 2 , Imperial College, London United Kingdom
Show AbstractPolymer semiconductors are inexpensive solution processable alternatives to amorphous silicon for applications in flexible large area electronics. Recently, thin films of spun-cast poly(2,5-bis(3-alkylthiophen-2yl)thieno[3,2-b]thiophene) (pBTTT) have been demonstrated to exhibit exceptional hole mobilities in thin film transistors (TFTs) after heating into a low temperature (~ 150 °C) mesophase. This mild thermal cycle results in high level of crystalline order in the annealed film with a morphology exhibiting single molecular layer terraces. Recently we have discovered that heating into a second, higher temperature (~240°C) phase results in a distinct ribbon morphology. We have applied polarized optical spectroscopies: spectroscopic ellipsometry and FTIR, along with x-ray diffraction and NEXAFS to the in-situ study of the structural evolution in the two high temperature phases. The first mesophase is a well ordered liquid crystal characterized by melted side chains, but excellent vertical lamella order. The second, high temperature phase appears to be an isotropic melt. The behavior of pBTTT is contrasted with that of poly(dialkylthieno[3,2-b]thiophene-2,5-bithiophene) (pTTBT), a newly synthesized isomer of pBTTT with side chains attached to the thienothiophene rather than the bithiophene unit. This subtle structural change results in distinct thermal behavior. The structural transitions of the isomers are generally similar; however, the side chain melting transition Tm occurs about 50°C lower in pTTBT than in pBTTT. The significant drop in Tm appears to correlate with a subtle decrease in main chain packing interactions. Both materials exhibit high hole mobility, even in their respective liquid crystal mesophases. The slight overall higher order in pBTTT is reflected in the annealed device performance.
5:15 PM - G7.7
Organic `Power' Transistors Using a Vertical Architecture with Built-in Nano-Triode Array: Reduction of Their Output Impedance and Improvement of the Current On/Off Ratio.
Masakazu Nakamura 1 , Yusuke Takenouchi 1 , Shoutaro Masuda 1 , Masatoshi Sakai 1 , Kazuhiro Kudo 1
1 Department of Electrical and Electronic Engineering, Chiba University, Chiba Japan
Show Abstract5:30 PM - G7.8
Performance and Reliability of Organic Transistors Controlled by Interfacial Phenyl-Terminated Self-Assembled Monolayers.
Zihong Liu 1 3 , Yoshio Nishi 1 3 , Zhenan Bao 2 3
1 Department of Electrical Engineering, Stanford University, Stanford, California, United States, 3 Center for Integrated Systems, Stanford University, Stanford, California, United States, 2 Department of Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSelf-assembled monolayers (SAM) with various functional groups used for dielectric surface modification have shown promising capability to control the performance of organic semiconductor/carbon nanotube network thin-film transistors. Previously we have found that phenyl-terminated SAM can be superior to alkyl-terminated SAM in terms of higher effective mobility and better wettability for the solution processed oligothiophene thin films for transistor applications. Here we report the performance and reliability of organic transistors employing different phenyl-terminated SAMs, with a focus on the performance (mobility, on/off ratio, threshold voltage, leakage current etc.) modulation, hysteresis and dipole effect induced by the SAMs. Despite of the same terminal functional group, the alkyl chain length within the SAM was found to systematically tune the device performance as well as the reliability. This finding pointed out a promising alternative of controlling organic transistor performance/reliability by modulating the mid-part of the SAM rather than the commonly recognized terminal-part. Device physics understanding of these effects will be discussed in detail. Based on the above results, we have demonstrated reliable (with little hysteresis and little discrepancy of drain currents for transfer/output curves), high-mobility (>1.0 cm2/Vs) solution-processed organic transistors on silicon and flexible substrates.
G8: Poster Session: Hybrid and Organic Materials for Large-Area Functional Systems II
Session Chairs
Ana Arias
Dean DeLongchamp
Cherie Kagan
Alberto Salleo
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - G8.1
Ordered Breath Figure Imprinting: Elaboration, Surface Analysis and Applications.
Sami Yunus 1 , Arnaud Delcorte 1 , Claude Poleunis 1 , Patrick Bertrand 1 , Chiara Botta 2 , Alberto Bolognesi 2
1 , Université catholique de Louvain, Louvain-la-Neuve Belgium, 2 , Consiglio Nazionale delle Ricerche, Milano Italy
Show AbstractMicro-structured films can be formed by the condensation of water micro-droplets, subsequent to the cooling of the surface of an evaporating thin layer of polymer solution. After solvent and water evaporation, an imprint of the droplets is left in the solid polymer. For the sake of simplicity, this phenomenon, described first by François and recently covered in a review article by Heiko and Bunz [1], is called breath figure imprinting. In the case of common linear polymers without specific end group or block polymer, breath figure imprinting usually leads to the formation of micrometric cavities of randomly distributed diameters on the surface. Ordering the position and diameter of the cavities in a honeycomb structure requires several conditions on polymer structure, termination, concentration, solvent, substrate, inert gas flow, temperature and humidity [2]. Although a clear-cut explanation has not yet been provided for this phenomenon, some physical models implying interfacial energy minimization can provide a partial description of ordered film formation.The resulting self-assembled structure can be used as a template in numerous applications using soft-lithographic techniques.In the present case, a honeycomb structure is obtained by activation of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) terminated polystyrene (PS) with organic acids such as p-toluenesulfonic acid (PTSA) or camphorsulfonic acid (CSA-R or S). Positive and negative ToF-SIMS imaging allows us to distinguish different chemical regions correlated to the film morphology. Moreover, it provides us with a better understanding of the phenomena underlying the formation of these films by directly linking the role of polar terminations to the micrometric self-organization [3].[1] U. Heiko, F. Bunz, Adv. Mater. 2006, 18, 973–989[2] A. Bolognesi, M. Civardi, D. Comoretto, C. Mercogliano, A. Turturro, S. Yunus, Langmuir 2005, 21, 3480–3485[3] S. Yunus, A. Delcorte, C. Poleunis, P. Bertrand, C. Botta, A. Bolognesi, Adv. Funct. Mat. 2007, 17, 1079–1084
9:00 PM - G8.10
Surface Chemistry and Electronic Properties of ZnO Single Crystals and Nanorods for use in Hybrid Photovoltaic Devices.
John Uhlrich 1 , Dana Olson 2 , Julia W. Hsu 3 , Ryan Franking 4 , Robert Hamers 4 , Thomas Kuech 1
1 Chemical Engineering, University of Wisconsin, Madison, Wisconsin, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 , Sandia National Laboratory, Albuquerque, New Mexico, United States, 4 Chemistry, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractNanostructures of ZnO have recently been used as the electron acceptor in hybrid photovoltaic devices. In order to optimize the efficiency in such devices, the electrical contact at the donor-acceptor interface must have a properly engineered chemical and electronic structure. We have studied the surface chemistry of the (0001) and (10-10) ZnO single crystals as well as the surfaces of ZnO nanorods as a function of surface treatment. The ZnO nanorods were grown using a solution-based, seed-assisted growth technique on (100) Si substrates for the purpose of these experiments. The two primary treatments studied were UV-ozone cleaning and drying in air at 150 °C. The surface chemistry and electronic properties were subsequently analyzed by x-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). The XPS spectra were used to monitor band bending in the electronic core levels of ZnO as well as to quantify surface contaminants such as carbon and chlorine. The UPS spectra were used to study the energy position of the ZnO valence band as well as any interface dipole created upon forming an electrical contact. Our results show that the electronic properties of the single crystal ZnO samples were relatively insensitive to the ozone or air drying treatments. This is in contrast to the ZnO nanorod arrays for which the UV-ozone treated samples showed an apparent increase in band bending by ~0.13 eV as compared to the dried samples. The interface between ZnO and poly(3-hexylthiophene) (P3HT), a common electron acceptor in hybrid photovoltaics, was also studied by spin coating a thin film (~1-1.5 nm) on to treated single crystal samples. After investigating with photoelectron spectroscopy, we determined interface dipole values of ~0.15 eV and ~0.25 eV for the and (0001) and (10-10) facets respectively, with both alignments favoring electron transfer from the P3HT to the ZnO. We have also treated the ZnO single crystal surfaces and nanorods in a boiling NH4Sx solution for 2 minutes in order to further alter the ZnO surface chemistry. The (10-10) and (000-1) single crystal surfaces as well as the nanorods showed evidence by photoelectron spectroscopy, that sulfur substituted for the oxygen atoms to make ZnS near the surface. On the (0001) facet, the sulfur atoms displaced the many of hydroxyl groups that typically cover the ambient-exposed surface, but there was no evidence of sulfur penetrating the lattice. Surface treatments such as these could provide a method of altering the energy band offset between the donor and acceptor and could have a direct effect on the device properties, such as the open circuit voltage (Voc), of hybrid photovoltaic devices.
9:00 PM - G8.11
Titania Nanotube Array Based Large Area Polymeric and Dye-Sensitized Solar Cells.
Karthik Shankar 1 2 , Gopal Mor 1 , Chih-Min Lin 2 1 , Oomman Varghese 1 , Maggie Paulose 1 , Craig Grimes 2 3 1
1 The Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Materials Science & Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractVertically oriented n-type TiO2 nanotube arrays have shown impressive photoconversion efficiencies in liquid junction dye sensitized solar cells and solid state hybrid polymeric heterojunction photovoltaics owing to their large internal surface area, lower recombination losses and vectorial charge transport along the nanotube axis. TiO2 nanotube arrays come in two varieties, a non-transparent variety grown on Ti foil substrates and a transparent variety grown on Fluorine doped Tin Oxide (FTO) coated glass substrates. The anodization process used to fabricate nanotube arrays is scalable to very large area devices. Furthermore, each of the two nanotube varieties can be used to form two distinct kinds of solid state photovoltaic devices 1: A double heterojunction cell where a blend of hole transporting highly absorbing polymer poly(3-hexythiophene) [P3HT] and electron transporting methanofullerene [PCBM] is infiltrated into the pores of the nanotube arrays and 2: A solid state dye sensitized solar cell consisting of TiO2 nanotube arrays coated with dye filled with a transparent small-molecule hole transporting material (HTM) such as copper thiocyanate or spiro-OMETAD. The two architectures will be compared on the basis of performance, stability and ease of fabrication. Smaller pore sizes result in higher surface area per unit length but are difficult to infiltrate with polymer/HTM. On the other hand, larger pore sizes result in lower internal surface area per unit length and fewer dye molecules are adsorbed. The results of varying nanotube diameter on pore filling and device performance are presented. Methods to fill the nanotube pores and to ensure polymeric film uniformity over large areas will be discussed. We have achieved efficiencies under AM 1.5 global illumination exceeding 5% in Type(1) polymeric solar cells and 2% in Type(2) dye sensitized solar cells.
9:00 PM - G8.12
Hybrid Silicon Nanoparticle-organic Light-emitting Devices for Infrared Electroluminescence.
Kai-Yuan Cheng 1 , Rebecca Anthony 2 , Uwe Kortshagen 2 , Russell Holmes 1
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe application of semiconductor nanoparticles in hybrid inorganic-organic light-emitting devices has to date focused primarily on the use of Group II-VI and III-V compounds. Progress on the use of silicon nanoparticles (SiNPs) for light emission has been accelerated by the development of high-yield synthesis routes that utilize non-thermal plasmas. Nanoparticles synthesized using these techniques have been applied in recent demonstrations of red SiNP electroluminescence, and have raised the exciting possibility of using silicon as an active material in optoelectronic devices. In this work, we demonstrate infrared electroluminescence from composite films comprising both SiNPs (diameter of ∼5 nm) and the conductive polymer poly[2-methoxy-5-(2-ethylhexyl-oxy)-1,4-phylene-vinylene] (MEH-PPV). Electroluminescence is observed at λ∼880 nm, consistent with measurements of solution photoluminescence. No emission is observed from the MEH-PPV matrix, or any of the adjacent organic layers. An average external quantum efficiency of (0.07±0.01)% is obtained in the forward emitted direction. Analysis of both electroluminescence and photoluminescence suggests that the infrared emission results from exciton formation directly on the nanoparticle, as opposed to exciton energy transfer from the polymer. This work combines the attractive properties of both SiNPs and organic semiconductors to realize electroluminescence in the infrared, a region of the spectrum that is not easily accessed using conventional organic light-emitting devices.
9:00 PM - G8.13
Highly Stable Organic Monolayers for Reacting Si with Further Functionalities.
Sreenivasa Puniredd 1 2 , Ossama Assad 1 2 , Hossam Haick 1 2
1 Chemical Engineering, Technion-Israel Institute of Technology, Haifa Israel, 2 , Russell Berrie Nanotechnology Institute,Technion-Israel Institute of Technology, Haifa Israel
Show Abstract9:00 PM - G8.14
Surface Plasmon Resonance in Light Emitting Polymer Nanotube Coated with Nanometer-scale Ni: Energy and Charge Transfer Effects.
Dong Hyuk Park 1 , Eun Hei Cho 1 , Mi suk Kim 1 , Mikyung Kim 1 , Dae-Chul Kim 2 , Huheun Song 2 , Jeongyong Kim 2 , Jinsoo Joo 1
1 Department of Physics, Korea University, Seoul Korea (the Republic of), 2 Department of Physics, University of Incheon, Incheon Korea (the Republic of)
Show AbstractWe report on the surface plasmon resonance effect for light emitting poly (3-methylthiophene) (P3MT) nanotubes coated with nanometer-scale nickel (Ni). The P3MT nanotubes were prepared through electrochemical polymerization method by using Al2O3 nanoporous template using TBAPF6 as a dopant. The doping level of the P3MT nanotubes was electrochemically controlled through cyclic voltammetry (CV) in a solution of BMIMPF6 ionic liquids without monomers. We controlled that the π-π* transition peak and bipolaron peaks in doped or de-doped light emitting P3MT nanotubes through the process of repeated reduction through CV. From the laser confocal microscope (LCM) photoluminescence (PL) experiments of the single strand the P3MT nanotubes, we observed that the dedoped P3MT nanotubes had red-shift PL spectra and bright light emission. The PL intensity decreased with increasing the doping levels of the P3MT nanotubes. We observed the significantly enhanced PL of hybrid double layered nanotubes (HDLNTs) consisting of P3MT nanotubes with various doping levels enveloped by an inorganic Ni metal nanotube. From the LCM PL experiments, as the doping levels of the P3MT nanotubes increased, the LCM PL intensity of the HDLNTs of doped-P3MT/Ni single nanotube strand dramatically increased, while that of the doped-P3MT nanotubes without Ni decreased. Both energy transfer and charge transfer effects due to surface plasmon resonance contributed to the very large enhancement of the PL efficiency of the doped P3MT-based HDLNTs
9:00 PM - G8.15
Donor/Acceptor Photoactive Polymers Based on Perylenebisimide and Thiophene Moieties for Organic Solar Cells.
Erika Kozma 1 , Pasquale Gabriele Grieco 1 , Darek Kotowski 1 , Silvia Luzzati 1 , Marinella Catellani 1
1 Istituto per lo Studio delle Macromolecole (ISMAC), CNR , Milano Italy
Show AbstractThe preparation and the characterization of a series of donor/acceptor oligomers, and polymers containing perylene and thiophene moieties are reported. In this work the electronic properties of these materials and their application on organic solar cells are presented.Currently, the most widely studied organic solar cell are bulk heterojunctions in which the active layer consists of an electron-donating polymer (poly-3-hexylthiophene) and an electron accepting molecule (soluble fullerenes). To increase the photovoltaic performances towards large area devices a great effort has been dedicated to optimize the blend morphology.Perylenediimide derivatives exhibit good electron mobilities and suitable electronic levels to act as acceptor in bulk heterojunctions with conjugated polymers. The introduction of different substituents either in the imide position or by core substitution (bay position) will definitely influence the packing and the properties of the perylene derivatives. Indeed, photophysical and redox properties are modified by this type of substitution, which demonstrate the chemical versatility of these molecules and also, the possibility to use them as building blocks for the preparation of new materials.Moreover, respect to fullerenes, perylenes have a better harvesting of the solar light. Nevertheless, the PV devices made with these molecules and P3HT have shown poor efficiencies. This low photovoltaic performances are mainly ascribable to a difficult processability of the materials and a poor morphology of the photo-active blends.With the aim to obtain stable photoactive materials with a good processability, we have prepared a series of donor/acceptor molecules and polymers based on dialkyperylenebisimmide with oligothiophenes or condensed thiophenes attached in the bay position.These ambipolar materials are soluble, show a good harvesting of the solar light and can be used in solar cell with P3HT or in alternative with PCBM as donor specie.By this core substituted approach, solution processable molecules were obtained. Optical and electronic properties of these donor/acceptor series will be presented, along with the photovoltaic characteristic of their solar cells prepared with P3HT.
9:00 PM - G8.16
Control of Shape and Self-assembly of Gold Nanoparticles by the Aid of Triphenylene Ligand.
Shen Zhongrong 1 , Keiko Miyabayashi 1 , Mami Higashimoto 1 , Mikio Miyake 1
1 , JAIST, Ishikawa Japan
Show Abstract9:00 PM - G8.18
Multi-functionality in Oligothiophenes through Controlled Sulphur Oxidation.
Clara Santato 1 , Laura Favaretto 2 , Fabio Cicoira 3 , Manuela Melucci 2 , David Banville 1 , Sebastien Loranger 1 , Alberto Zanelli 2 , Massimo Gazzano 4 , Giovanna Barbarella 2
1 , Ecole Polytechnique de Montreal, Montreal, Quebec, Canada, 2 , CNR ISOF, Bologna Italy, 3 , Cornell University Dept. MSE, Ithaca, New York, United States, 4 , Dip. Chimica Università di Bologna, Bologna Italy
Show AbstractOne of the great challenges in organic electronics is to achieve the synthetic ability to prepare multi-functional organic semiconductors, e.g. combining charge carrier transport and electroluminescence. [1] In the context of the widely investigated class of organic semiconductors constituted by oligothiophenes, we previously reported on an unipolar p-type organic light emitting field effect transistor (OLEFET) based on a solution-processed film of the rigid core dithienothiophene (DTT), DTT7Me. [2] With the aim to achieve ambipolarity (i.e. charge injection and transport of both holes and electrons) in films based on this class of oligothiophenes, we turned our attention to the study of the controlled sulphur oxidation of the dithienothiophene inner core. We found, as deduced from the redox potentials measured by cyclic voltammetry (CV), that such a controlled oxidation provides a powerful tool for finely tuning the position of the HOMO-LUMO energy levels of oligothiophenes. Indeed, the progressive oxidation of DTT sulphur to sulfone (SO2) and sulfoxide (SO) leads to oligomers with remarkably increased electron affinity values with respect to their unoxigenated analogues. This opens the possibility, to achieve ambipolarity in rigid core oligothiophenes films. Importantly for the multi-functionality, the sulphur oxidized oligothiophenes belongs to a family of oligothiophenes exhibiting high photoluminescence quantum yields in solid state. [3] Combined Optical Microscopy, Atomic Force Microscopy and X-ray diffraction data show remarkable self-organization capability leading to morphologies favorable to charge transport. Beside that, liquid crystalline properties were observed for these compounds with transition temperature and mesophase ordering tunable by the sulphur degree of oxidation, thus enabling melt-processing techniques for device fabrication. [4] REFERENCES[1] F. Cicoira, C. Santato, Adv. Funct. Mater. 17, 3421, 2007.[2] F. Cicoira, C. Santato, M. Melucci, L. Favaretto, M. Gazzano, M. Muccini, G.Barbarella, Adv. Mater. 18, 169, 2006.[3] a) G. Barbarella, M. Melucci, G. Sotgiu Adv. Mater., 17, 1581, 2005. b) G. Barbarella, L. Favaretto, G. Sotgiu, M. Zambianchi, A. Bongini, C. Arbizzani, M. Mastragostino, M. Anni, G. Gigli, R. Cingolani,J. Am. Chem. Soc. 122, 11971, 2000.[4] a) J. C. Maunoury, J. R. Howse, M. L. Turner Adv. Mater. 19, 805, 2007. b) Melucci, M.; Favaretto, L.; Bettini, C.; Gazzano, M.; Camaioni, N.; Maccagnani, P., Ostoja, P.; Monari, M.; Barbarella, G. Chem. Eur. J. 13, 10046, 2007.
9:00 PM - G8.19
Temperature Dependence of Electroluminescence to Isolate the Role of CdSe/ZnS Quantum Dots in PFO Based Polymer Light Emitting Diodes.
Dhirendra Sinha 1 2 , Awnish Kumar Tripathi 1 2 , Yashowanta Mohapatra 1 2
1 Department of Physics, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India, 2 Samtel Center for Display Technologies, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India
Show AbstractAmong the strategies for large area functional materials, incorporation of inorganic quantum dots in a solution processable polymer is one of the most attractive schemes. Specifically, polymer light emitting diodes (PLEDs) incorporating CdSe/ZnS quantum dots (QDs) hold promise for display applications as QDs have narrow spectral emission (<30nm) with high photoluminescence efficiency, and have tunable emission spectra with size. However, underlying physics of operating mechanisms is not well understood as yet. Among the hosts, Poly [9,9-dioctylefluorenyl-2,7-diyl] (PFO) end capped with dimethylphenyl (DMP) is a well studied blue emitting polymer and is a suitable host for QDs having emission wavelength 589nm. In this paper, we study the temperature dependence (10K-300K) of electroluminescence in this system in order to distinguish between EL mechanisms due to QDs and the host and develop a phenomenological model consistent with changes in PL, absorption and built-in voltage with varying concentrations with the QDs.The concentration (by wt. %) of QDs in PFO was varied between 0-8%. The resultant solutions were spun over 8mm2 pixilated ITO substrates overcoated with PEDOT:PSS. Aluminum and calcium/aluminum cathodes were vacuum evaporated to form diode structures. The current-voltage characteristics showed that the turn-on-voltage increases with the increase in percentage of QDs concentration in PFO. Clear and distinctive features of both QDs and PFO were observed in the electroluminescence (EL) spectra. As distinct from PL and absorption spectra, the contribution of QDs to emission was observed to be decreasing with its increase in concentration. However, thin films with QDs of 7.5 wt% showed significant contribution from QDs. The temperature dependent measurements for 1% incorporated QDs device showed that the EL from QDs was nearly independent of temperature while the contribution of PFO emission in EL was observed to be increasing with decrease in temperature. The fitting parameters for the first peak of PFO and QDs emission showed that on decreasing temperature, the peak position of PFO was shifting towards red while the QDs emission peak was shifting towards blue. The FWHM was observed to be increasing in case of QDs. A qualitative phenomenological model is proposed based on charging of the QDs to explain both concentration and temperature dependences of PL, EL and built in voltage. The observed differences in temperature dependence in PL and EL are traced to the origin of excitons in the two processes.
9:00 PM - G8.2
Directed Nano-Assembly of Block Copolymers on Incommensurate Surface Patterns.
Dong Ok Shin 1 , Qiang Wang 2 , Harun H. Solak 3 , Sang Ouk Kim 1
1 Material Science & Engineering, KAIST, Daejeon Korea (the Republic of), 2 Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado, United States, 3 , Paul Scherrer Institute, Villigen Switzerland
Show AbstractEstablishing a robust and versatile nanopatterning process has been a central issue in nanotechnology. Molecular self-assembly has several advantages over other methods, in that molecular building blocks ensure ultrafine pattern precision, parallel structure formation allows for mass production, and a variety of three-dimensional (3D) structures are available for fabricating complex structures. However, the molecular interaction for self-assembly generally relies on weak forces such as van der Waals forces, hydrogen bonding, or hydrophobic interaction. Since those interactions are readily influenced by thermal fluctuation, the structure formation is usually slow and the degree of ordering is low in an assembled structure. To promote self-assembly, hybrid technologies combining top-down and bottom-up fabrication have been developed and have attracted a great deal of technological attention as a next-generation fabrication technique. A prepatterned structure prepared by a top-down approach provides an additional driving force for structure formation as well as guiding the assembly of molecular building blocks such that a highly ordered assembled structure is expected over an arbitrarily large area. In this work, we demonstrate that the incommensurate surface patterns, routinely patternable by currently available patterning techniques, may a new complex nanostructure in block copolymer thin film.
9:00 PM - G8.20
Device Performance of ZnO Nanocrystal Field-Effect Transistor (NCFET) Prepared from the Aqueous Dispersion of ZnO Nanocrystals.
Seiichi Takami 1 2 , Ryoma Hayakawa 2 , Yutaka Wakayama 2 , Toyohiro Chikyow 2 , Tadafumi Adschiri 1
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 2 Advanced Electronic Materials Center, National Institute for Materials Science, Tsukuba Japan
Show AbstractRecently, various metal oxides have been used in electronic devices, because of their prominent properties including electron transport, magnetism and ferroelectricity. The use of metal oxide nanocrystals should widen the application of metal oxides, because crystallization and deposition processes are separated. Metal oxide nanocrystals can be synthesized at high temperature to ensure high crystallinity and then deposited on plastic or other substrates at milder conditions by drying the suspension of the nanocrystals. We have studied the hydrothermal synthesis of organic-functionalized metal oxide nanoparticles that facilitate the dispersion in liquid media and the hybridization with other nanomaterials. In this presentation, we discuss the preparation and device performance of nanocrystal field-effect transistor (NCFET) using ZnO as an n-channel material. ZnO nanocrystals were synthesized by hydrothermal reaction at 250○C using Zn(NO3)2 as a reactant. The aqueous suspension of ZnO nanocrystals were purified and deposited on a bottom gate substrate, where source and drain electrode pads were deposited on a SiO2 / Si substrate. The device performance was measured by a device analyzer. Id-Vd and Id-Vg characteristics showed that deposited ZnO nanocrystal layer successfully performed as an n-channel material. The effect of preparative conditions on the device performance will be discussed.
9:00 PM - G8.21
Hybrid Coaxial Nanodiodes Based on Oligothiophene-Zinc Oxide Nanorods as Building Blocks for Low Cost Solar Cells.
Jorg Ackermann 1 , Cyril Martini 1 , Guillaume Poize 1 , Daniel Ferry 1 , Daiki Kanehira 2 , Toshinori Tanisawa 2 , Noriyuki Yoshimoto 2 , Frederic Fages 1
1 Chemistry, Centre Interdisciplinaire de Nanoscience de Marseille (CiNaM), Marseille France, 2 , Graduate School of Engineering, Iwate University, Morioka Japan
Show Abstract9:00 PM - G8.23
Influence of Structure-Directing Molecular Adsorbates on the Morphology, Structure and Texture of Electrodeposited ZnO.
Thomas Loewenstein 1 , Elisa Arndt 1 , Anke Witzky 1 , Derck Schlettwein 1
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany
Show AbstractZinc oxide thin films electrodeposited on conductive substrates represent an attractive semiconductor material. The formation from aqueous solutions at typically 70 °C allows an economic and environmentally benign deposition on a wide variety of substrates including conventional FTO- coated glass, conductively coated plastic foils and even textiles. By use of appropriate structure- directing agents in the deposition solution highly crystalline yet porous ZnO can be obtained, very suitable for functionalization by a sensitizer dye to yield photoactive electrodes for dye- sensitized solar cells. In this study, the ZnO precursors in the deposition bath as well as the structure- directing agents were varied systematically to further explore the range of accessible nanostructured electrodes. The electrochemically monitored growth rate, the film morphology (SEM), the average orientation of the growing thin films (XRD) and the photoelectrochemical performance under standardized conditions was used as optimization criteria. In model experiments, ZnO was also electrodeposited on (0001) GaN and (0001) ZnO to discuss in detail the growth characteristics of electrodeposited ZnO. (0001) GaN offers good possibilities of epitaxial growth of ZnO. Crystalline ZnO was deposited as proven by X-ray diffraction (XRD) and the intensity pattern showed the expected preferential orientation with the c- plane of ZnO parallel to GaN (0001). Rocking curves with FWHM=0.25° indicated a surprisingly high level of in-plane orientation of the grown ZnO crystalline domains. The peak position of (0002) ZnO was shifted by 2 theta = 1.3°. This difference and the corresponding simultaneous shift of (0004) ZnO are explained by a lattice expansion by 3.6 % in the c- direction. This clearly indicated the strong influence of the Eosin Y molecules adsorbed during the growth of ZnO and explains the strong differences observed for different structure-directing agents as adsorbates on the surface.
9:00 PM - G8.24
Observation of Discrete Charging in Quantum Dots.
Marissa Olson Hummon 1 , Andrew Stollenwerk 1 , Moureen Kemei 1 , Patrick Stollenwerk 1 , Venkatesh Narayanamurti 1 , Polina Anikeeva 2 , Matthew Panzer 2 , Vanessa Wood 2 , Vladimir Bulovic 2 , Scott Geyer 3 , Jon Halpert 3 , Moungi Bawendi 3
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 3)Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - G8.25
Polyamine Hydrogenation of Carbon Nano-Onions and Graphite.
Glen Miller 1 , Jeremy Kintigh 1
1 Chemistry & Materials Science, University of New Hampshire, Durham, New Hampshire, United States
Show AbstractPolyamines effectively hydrogenate a variety of nanostructured carbon forms including fullerenes[1] and single-walled carbon nanotubes (SWNT)[2]. More recently, we investigated the hydrogenation of multi-walled carbon nanotubes (MWNT), carbon nano-onions (CNOs) and graphite. Due to their layered structure, CNOs serve as useful model compounds for graphite. Their relatively small size allows for simpler characterization and helps us to understand polyamine induced exfoliation of multi-layered nanostructured carbons. In this presentation, we will show our work to produce thin-films of graphene using high temperature polyamine chemistry in conjunction with mechanical milling. [1](a) Kintigh, Jeremy; Briggs, Jonathan B.; Letourneau, Kristine; Miller, Glen P.; J. Mat. Chem. (2007), 17(44), 4647-4651. (b) Briggs, Jonathan B.; Montgomery, Margo; Silva, Lindsey L.; Miller, Glen P, Org. Letters (2005), 7(25), 5553-5555.[2] Miller, Glen P.; Kintigh, Jeremy; Kim, Eunja; Weck, Philippe F.; Berber, Savas; Tomanek, David.; J. Amer. Chem. Soc. (2008), 130(7), 2296-2303.
9:00 PM - G8.26
Control of Stress-Bow for Temporary Bonding-Debonding of Flexible Substrates.
Jesmin Haq 1 , Robert Naujokaitis 1 , Scott Ageno 1 , Shawn O'Rourke 1 , Doug Loy 1
1 Flexible Display Center, Arizona State University, Tempe, Arizona, United States
Show AbstractTemporary bonding-debonding for flexible displays is a key enabler for effective handling of flexible substrates during thin film transistor (TFT) fabrication process. The flexible substrate temporarily adhered to a rigid carrier plate can be processed using standard TFT fabrication procedures. This rigid carrier gives the structural support and suppresses the bending of the flexible substrate during processing. The most significant issue encountered with this approach is the stress that is developed during the bonding-debonding process as well as the fabrication process steps. These steps typically employ high temperature processing which exacerbate the thermal property mismatches between the carrier, adhesive, and flexible substrate. These thermal property mismatches lead to bowing (changes in radius of curvature) of the carrier system during thermal processing and this bowing can lead to wafer handling problems in processing equipment or delamination of the flexible substrate from the rigid carrier. In our work different carriers, flexible substrates, and adhesives were evaluated to study the thermal mismatches and subsequent bowing of various systems. Our proprietary carrier showed a significant decrease in bonded system bow as compared to systems bonded with a conventional silicon carrier. These lower bow values with our carrier were a result of a lower coefficient of thermal expansion (CTE) mismatch between our carrier and various substrates as compared to silicon. In addition to a lower CTE mismatch with our carrier, the bow of systems bonded to our carrier was further reduced due to a higher modulus as compared to silicon. Flexible substrates of various compositions and thickness were evaluated. For a transparent substrate, various thicknesses and planarization coatings of heat-stabilized PEN from DuPont Teijin Films were evaluated while thin stainless steel (SS) was evaluated as an opaque flexible substrate. Properties of the adhesives used to bond the flexible substrate to the rigid carrier were found to have an effect on the bow of the bonded system. Adhesives with increased content of high molecular weight polymer were found to give a greater increase in the bow of the system. For cross-linkable acrylate based adhesive systems, the effect of crosslink density was investigated on the bow of the wafer. The properties of the rigid carrier, flexible substrate, and adhesive must all be considered in the selection of a bonded flexible substrate system.
9:00 PM - G8.27
Synthesis and Characterization of Ionic Liquids of Lead-Salt Nanocrystals.
Liangfeng Sun 1 , Chia-Chen Fang 2 , Emmanuel Giannelis 2 , Frank Wise 1 , George Malliaras 1
1 Center for Nanoscale System, Cornell University, Ithaca, New York, United States, 2 Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractIonic liquid materials are attracting increasing attention from industry as well academic researchers. These materials have low melting points (they are liquid at ambient temperature), high ion density, and high conductivity. They are nonflammable, thermally stable, and designable. Those properties can find broad applications in energy devices, electro-optics devices and drug delivery. For example, Gratzel et al. has used tetracyanoborate ionic liquid as the electrolyte in a solar cell to improve the thermal stability of the device. Recently, ionic liquids consisting of ceramic nanoparticles (silica or maghemite) have been synthesized by Giannelis et al. Synthesis of metal (Au or Pd) ionic liquids was reported by Wiesner et al. Ionic liquids made of semiconductor nanoparticles have not been reported. We will report the synthesis and characterization of a PbS quantum dot ionic liquid. Lead salt quantum dots have unique optical and electronic properties, which have potential applications in light emitting devices and solar cells. Making them into ionic liquid may help to improve their stability and performance. We have observed photoluminescence from the ionic liquid of quantum dots. Studies of the electroluminescence of the quantum dot ionic liquid, which is relevant to light-emitting devices, will also be described.Further we can study the electroluminescence property of the ionic liquid and make them into a real light emitting device.
9:00 PM - G8.3
Hierarchically Ordered Polymer Films by Templated Organization of Aqueous Droplets.
Ji Sun Park 1 , Sang Ouk Kim 1
1 Dept. of Materials Science & Engineering, KAIST, Daejeon Korea (the Republic of)
Show AbstractHierarchically ordered structures facilitate the incorporation of diverse functions simultaneously. The present report introduces a simple and novel strategy for producing hierarchically ordered polymeric films. Hierarchical ordering of aqueous droplets on a polymer solution is realized by the imposition of physical confinement via various shaped gratings. After drying of the solution, well-ordered hierarchical structures were fabricated in the remaining polymer film. The size of the grating structure and the lattice size of spontaneous hexagonally packed aqueous pores comprise two different length scales, thereby offering multiscale ordering. Interfacial wetting of the polymer solution to the grating surface was crucial in terms of obtaining a highly ordered structure that can be tuned by dissolving a small amount of surfactant in the polymer solution. The present novel approach provides a new opportunity for lithography-free fabrication of complex hierarchical structures.
9:00 PM - G8.4
Hierarchical Self-Assembly of Block Copolymers for Lithography-Free Nanopatterning.
Bong Hoon Kim 1 , Sang Ouk Kim 1
1 Dept. of Materials Sce. & Eng., KAIST, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - G8.5
High Efficiency Infrared Organic Photodetector.
Do Young Kim 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractOrganic electronic devices such as organic light emitting diodes (OLEDs) and organic photovoltaic (OPV) cells are attracting a great deal of attention because of compatibility with flexible substrates, low cost process, and large area applications. In addition, the realization of large area organic photodetectors (OPDs) with infrared (IR) sensitivity can extend the applications of organic electronics to large area sensing and detection. Here, we report high efficiency infrared organic bulk heterojunction photodetectors with external quantum efficiency (EQE) up to 70%. The high efficiency is due to the increased exciton dissociation rate with exciton blocking layers in OPDs. In previous studies, we reported high quantum efficiency visible organic photodetectors using copper phthalocyanine (CuPc) absorbing in the visible spectrum. In this study, tin (II) phthalocyanine (SnPc) with an absorption band in the 600 ~ 1000 nm of the spectrum was used for infrared sensing. We have made the following devices to study the exciton confinement effects: (1) ITO/SnPc:C60/Al, (2) ITO/SnPc:C60/BCP/Al, (3) ITO/MoOx/SnPc:C60/BCP/Al. The EQEs of IR OPD without any exciton blocking layer, with only a BCP layer, and with both MoOx and BCP layers were 0.22 %, 1.5 %, and 33 %, respectively. The EQE of IR OPD with both MoOx and BCP as exciton blocking layer was improved 150 times compared with that without any exciton blacking layer. High EQE of 70 % was achieved by optimizing the IR OPD with both MoOx and BCP exciton blocking layers. While the bulk heterojunction structure does help improving the exciton dissociation rate, the major enhancement in exciton dissociation is coming from the enhanced exciton blocking effects. Our device data further indicate that the exciton diffusion length is longer than the film thickness. A systematic study of these devices and the underlying mechanism will be presented.
9:00 PM - G8.6
Self-Assembly of Porphyrin Patterning Thin Film.
Albert Wan 1 , James Batteas 1
1 Chemistry Dep., Texas A&M University, College Station, Texas, United States
Show AbstractCreating large organized structures of organic thin films is a key element in the development of organic electronic materials. To this end we have been investigating the directed assembly of porphyrins for use in optoelectronic devices. Here we demonstrate a non-lithography method of constructing large areas of porphyrin thin films with controlled nano- and micro-structures on Si(100) using combinations of charged interactions and surface de-wetting to direct assembly. Organized structures consisting of self-patterned arrays consisted of lines ca. ~20 nm high and ~5 μm periodicities and could extend more than a millimeter while the length of the lines could be from tens to a hundred micrometers. The arrangement of the porphyrin molecules within the films was studied using UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Films morphology was characterized using optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Approaches to control the assembly process and resulting film morphology will also be described.
9:00 PM - G8.7
Device Characterization of CdSe /poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-(1-cyanovinylene)phenylene] Nanocomposite Infrared Photodetectors Deposited via Matrix Assisted Pulsed Laser Evaporation on GaAs.
Kevin Lantz 1 , Ryan Pate 1 , Adrienne Stiff-Roberts 1
1 Electrical and Computer Engineering, Duke University, Durham, North Carolina, United States
Show AbstractThe ability to detect infrared (IR) radiation in the mid-wave IR regime (3-5 μm) is of great importance for medical and thermal imaging, as well as atmospheric monitoring. Inorganic bulk semiconductors have dominated this field, but these materials demonstrate large dark currents, thereby forcing the use of cryogenic systems for low-temperature operation. Through the promise of room-temperature IR photodetection, colloidal quantum dot (CQD)/conducting polymer nanocomposites have become an area of interest in recent years. Previous work in this field has demonstrated near-IR detection (1-3 μm) with nanocomposite photodetectors that operate on bipolar, interband transitions in PbS or PbSe CQDs embedded in poly[2-methoxy-5-(2’-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) [Konstantatos et al., Nature, 442, 180-183 (13 July 2006); Choudhury et al., Appl. Phys. Lett., 89, 051109 (2006)]. The focus of this work is to push the photodetector spectral response into the mid-IR through the use of intraband transitions within the conduction band of CdSe CQDs. We have previously demonstrated experimental evidence of mid-IR, intraband absorption in CdSe/poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-(1-cyanovinylene)phenylene] (MEH-CN-PPV) nanocomposites drop cast on GaAs substrates [Stiff-Roberts and Lantz, J. Appl. Phys., 103, 104316 (2008)]. However, the lack of control over film thickness and CQD distribution resulting from drop-casting poses serious challenges for the fabrication and demonstration of IR photodetectors. Therefore, in this work, nanocomposite deposition is accomplished using matrix-assisted pulsed laser evaporation (MAPLE), which allows for highly tunable internal morphology of the nanocomposite material.In this paper, we will measure the dark-/photo-current, blackbody responsivity, and IR spectral response of CdSe/MEH-CN-PPV devices deposited via MAPLE and drop casting on GaAs substrates. Device characterization measurements will be obtained for multiple temperatures and CQD-to-polymer ratios to better understand the carrier dynamics in nanocomposite systems. This work should demonstrate the benefits of MAPLE deposition over drop casting, as well as the efficacy of CQD nanocomposites for mid-IR photodetection through the use of intraband transitions.
9:00 PM - G8.8
Synthesis of Multi-Walled Carbon Nanotubes on Fly Ashes by Thermal Chemical Vapor Deposition.
Yasuhiro Kamiya 1 , Akihiro Yasui 1 , Shingo Ono 1 , Hidetomo Noda 2 , Yo Ichikawa 1
1 , Nagoya Institute of Technology, Nagoya, Aichi Japan, 2 Research and Development Division, Chubu Electric Power Co., Inc., Nagoya, Aichi Japan
Show AbstractDue to the optical and electromagnetic absorption property, carbon nanostructure has been widely studied as key materials in a wide range of applications, including sensing, saturable absorber, and so on. To extend its application area, a great deal of attention has been focused on the findings a simple, inexpensive, high-yield process requiring no special apparatus for fabrication of carbon nanostructure. In this paper, we present the fabrication of the multi-walled carbon nanotubes (MWCNTs) on fly ash by thermal chemical vapor deposition (CVD) process. Fly ashes are micrometer-sized glassy-spherical particles created by coal-fired power plant. They are composed of several oxides. Specially, Fe2O3, which is contained approximately 5 % in fly ash, can acts as catalyst for synthesis of MWCNTs. Additionally, fly ash is an inexpensive because power plants produce millions of tons of fly ash annually. A part of them is usually used in concrete for improving the strength and segregation. However, others are mainly dumped in landfills. Therefore, finding a new use of fly ashes would help to improving the environmental problem. To fabrication of the MWCNTs, various schemes have been demonstrated utilizing arc discharge, laser vaporization, or CVD. Among these techniques, use of CVD process is widely accepted as the practical process since it provides large amount of MWCNTs and it does not require vacuuming system. In this experiment, fly ashes were prepared in tubular furnace for catalyst. MWCNTs were grown from iron catalyst in the fly ashes by providing ethanol gas as carbon source. Synthesis is accomplished efficiently by using mixture gas in proportion of 3 of ethanol gas to 10 argon gas. Furthermore, controlling the reacting temperature, we obtained substantial amount of MWCNTs on the fly ashes by 60 minutes treatment. The diameter of MWCNTs synthesized at 1070 K had sub micrometer in diameter and a few micrometer length. This hybrid material composed with MWCNTs and oxides showed promising the optical and electromagnetic absorber. In addition, simple, low-cost, large-amount production has been achieved by applying the fly ashes to catalyst for synthesis of MWCNTs.
9:00 PM - G8.9
Preparation and Characterization of BiVO4 Semiconductor Thin Film by Precursor Method using Ethanolamines.
Takahiro Gunji 1 , Daijiro Mori 1 , Takashi Kajiwara 1 , Yoshimoto Abe 1
1 Department of Pure and Applied Chemistry, Tokyo University of Science, Noda, Chiba, Japan
Show Abstract The preparation of BiVO4 by precursor method and its application as a visible light responsible photocatalyst will be presented. BiVO4 thin films are known as a visible light responsible photocatalyst and often provided as a coating film on a electron conductive glass such as fluorine doped tin oxide glass. It is preferable to prepare the BiVO4 electrode less than 500 oC which is limited by the characteristic of the electroconductive glass. In this paper, a photoelectrode was prepared and characterized from the BiVO4 precursor, which was synthesized by the reaction of ethyl acetoacetate (Hetac) chelates of Bi and V with triethanolamine (H3dea) or diethanolamine (H2dea). BiVO4 precursor was synthesized by the reaction of a mixture of Bi(etac)3 and VO(etac)(OEt)2 in the molar ratio of 1:1 with H3tea or H2dea by following heating and drying under reduced pressure. A solution of BiVO4 precursor powder was subjected to spin-coating on fluorine doped tin oxide glass and heated at 500 oC to provide BiVO4 photoelectrode. BiVO4 precursor using H3tea was soluble in highly polar solvent such as alcohol, while those using H2dea was soluble in alcohol and had a softening point. In the differential thermal analysis and thermogravimetry of BiVO4 precursor, an exothermic peaks with a weight loss were observed at 214 oC and 419 oC, which supports the ceramization by pyrolysis of the organic components. The pyrolysis of BiVO4 precursor provided BiVO4 thin film, which was crystallized in monoclinic by X-ray diffraction analysis. The photoelectrode, which was prepared using H2dea, showed the highest incident photon to current conversion efficiency (IPCE) 22.9% (400 nm 1.52 V vs NHE). IPCE decreased when the sintering period was increased. The scanning electronic micrograph of the coating film showed that BiVO4 coating film was composed of many particles with a diameter of 0.5 μm.
Symposium Organizers
Alberto Salleo Stanford University
Ana Claudia Arias Palo Alto Research Center, Inc.
Dean M. DeLongchamp National Institute of Standards and Technology
Cherie R. Kagan University of Pennsylvania
G9: From Devices to Circuits and Systems I
Session Chairs
Wednesday AM, December 03, 2008
Room 207 (Hynes)
9:30 AM - **G9.1
Ultrathin Hybrid Organic/Inorganic Gate Dielectrics for Low-Voltage Thin-Film Transistors.
Hagen Klauk 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany
Show Abstract10:00 AM - G9.2
Low-Voltage Organic Transistors Based on Solution Processed Semiconductors and Self-Assembled Monolayer Gate Dielectrics.
James Ball 1 , Paul Wobkenberg 1 , Floris Kooistra 2 , Jan Hummelen 2 , Donal Bradley 1 , Thomas Anthopoulos 1
1 Physics, Imperial College London, London United Kingdom, 2 Molecular Electronics, Zernike Institute for Advanced Materials and Stratingh Institute of Chemistry, University of Groningen, Groningen Netherlands
Show Abstract10:15 AM - G9.3
Printable Cross-Linked Polymer Blend Dielectrics. DesignStrategies, Synthesis, Microstructures, and ElectricalProperties, with Organic Field-Effect Transistors as Testbeds.
Choongik Kim 1 , Antonio Facchetti 1 , Tobin Marks 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractWe report here the synthesis and dielectric properties of optimized cross-linked polymer blend (CPB) dielectrics for application in organic field-effect transistors (OFETs). Novel silane cross-linking reagents enable the synthesis of CPB films having excellent quality and tunable thickness (from 10 to ∼500 nm), fabricated both by spin-coating and gravure-printing. Silane reagents of the formula X3Si-R-SiX3 (R = -C6H12- and X = Cl, OAc, NMe2, OMe, or R = -C2H4-O-C2H4- and X = OAc) exhibit tunable reactivity with hydroxyl-containing substrates. Dielectric films fabricated by blending X3Si-R-SiX3 with poly(4-vinyl)phenol (PVP) require very low-curing temperatures (∼110 °C) and adhere tenaciously to a variety of FET gate contact materials such as n+-Si, ITO, and Al. The CPB dielectrics exhibit excellent insulating properties (leakage current densities of 10-7 ∼ 10-8 A cm-2 at 2.0 MV/cm) and tunable capacitance values (from 5 to ∼350 nF cm-2). CPB film quality is correlated with the PVP-cross-linking reagent reactivity. OFETs are fabricated with both p- and n-type organic semiconductors using the CPB dielectrics function at low operating voltages. The morphology and microstructure of representative semiconductor films grown on the CPB dielectrics is also investigated and is correlated with OFET device performance.
10:30 AM - G9.4
Organic Thin-film Transistors as Large Area Low Cost Sensors.
Zhenan Bao 1 , Mark Roberts 1 , Anatoliy Sokolov 1
1 , Stanford University, Stanford, California, United States
Show AbstractOrganic thin-film transistors (OTFTs) are ideal for inexpensive, chemical sensors owing to their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. Specifically, the use of small molecule-based organic semiconductors is promising because molecular design can allow for incorporation of specific recognition sites to achieve selectivity. Previously, the use of OTFTs as sensors has been limited to vapor phase systems. However, while chemical detection for comprehensive monitoring will require the sensors to operate under both aqueous and ambient air conditions, the OTFTs reported to-date have not been suitable for applications in aqueous media owing to high operating voltages, degradation and delamination. To establish OTFT operation as air- and water-stable sensors, we first demonstrated gas sensing using organic transistors, showing that the devices are sensitive to a wide range of vapors, such as alcohols, ketones, thiols, nitriles, esters, and aromatic compounds, at concentrations in the ppm range. We now introduce novel low-temperature cross-linkable gate dielectric films compatible with vapor and solution deposited semiconductors for aqueous sensors. The polymer matrix for the gate dielectric layer in this study is poly(4-vinylphenol), selected for its dielectric characteristics and compatibility with various organic semiconductors. With pentacene active layers, we achieved mobilities as high as 3 cm2/Vs and on/off ratios of 106 at a gate bias of 2V. We also fabricated OTFTs with a new p-channel material, 5,5’-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2’-bithiophene (DDFTTF), which displayed stable operation under aqueous conditions over more than 104 electrical cycles. The work has led to the observation of a significant drain current response for solutions with concentrations as low as parts per billion of trinitrobenzene and methylphosphonic acid. We now describe the initial investigation of materials used for sensing that involves air- and water-stable organic semiconductors based on various functionalities (e.g. oligothiophene, oligofluorine, oligophenylene). Subsequent investigations will focus on the use of functional groups as binding sites for the semiconductor:analyte interaction both under aqueous and ambient air conditions, with the goal of developing environmentally stable sensors. The mechanism for OTFT sensing is investigated by varying device parameters including semiconductor thickness and operating conditions, such as analyte concentration and gate bias. The effect of semiconductor film morphology and microstructure upon device sensing characteristics is also discussed.[ref] M. Roberts, S. Mannsfeld, N. Gratacòs, W.G. Knoll, Z. Bao, “Water-stable organic transistors for chemical and biological sensors”, PNAS, in press.
10:45 AM - G9.5
Integration of Organic Photodiodes and Organic Thin Film Transistors for Active Matrix Focal Plane Detector Arrays.
Xin Xu 1 2 , Stephen Forrest 2 3 4
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Physics, University of Michigan, Ann Arbor, Michigan, United States, 3 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 4 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOrganic thin film transistors (TFTs) have attracted considerable attention due to their wide range of applications to low cost, light weight, flexible, and low process temperature integrated circuits on flexible plastic substrates. For example, the integration of organic light emitting diodes (OLED) with organic TFTs has been applied to the fabrication of active-matrix OLED displays1. Another application is an active matrix consisting of organic focal plane sensor arrays consisting of integrated photodiodes and TFTs for imaging systems. Previously, organic detector arrays connected to TFTs by laser-drilled via interconnects were demonstrated2. This technique, however, limits the spatial resolution to 100 micron due to the diameter of via holes. Here, we demonstrate an integrated organic photodetector and a top-gated pentacene TFT fabricated at near room temperature on flexible plastic substrates employing shadow masking with applications to organic active matrix photodetector imaging arrays. A 20 nm thick Au anode column is first vacuum deposited on a glycolised polyethylene terephthalate (PETg) sheet through a shadow mask, followed by the deposition of the active organic photodiode layers. The double heterojunction organic photodetectors consist of a 35 nm thick copper phthalocyanine (CuPc) donor layer, a 50 nm thick C60 acceptor layer, and a 10 nm bathocuproine (BCP) exciton blocking layer. Next, a 50 nm thick Ag row as the drain and source contact is patterned on top of the photodetector with a channel length of 50 μm and width of 100 μm. The Ag drain that overlaps the Au anode also functions as the cathode of the photodiode with an overlap area of 2×10-3 cm2. Next, a 80 nm thick pentacene channel layer is thermally evaporated on top of the drain/source contact, then a 150 nm thick parylene dielectric layer is vapor deposited. An 80 nm thick Ag gate electrode is finally deposited through a mask. There is little leakage between photodetector and TFT due to the low conductivity of the organic semiconductors used. The top-gated pentacene TFT has a saturated mobility is 0.03 cm2V-1s-1 and an On/Off drain-source current ratio >104. The dark current of the photodiode reaches 10.8 nA at -2V bias with an external quantum efficiency of 10.2% at λ=635 nm. When integrated with the TFT, the current at a gate voltage of 0V is limited by the Off drain-source current of the TFT and decreased by 100 times from that of an individual diode. In contrast, the On current of the integrated structure is limited by the diode photocurrent under various illumination intensities. The integrated structure may be applied to active matrix imaging sensor arrays to achieve low dark current, and thus high detectivity. 1 L. Zhou, A. Wanga, S. C. Wu, J. Sun, S. Park, T. N. Jackson, Appl. Phys. Lett. 88, 083502 (2006).2 T. Someya, Y. Kato, S. Iba, Y. Noguchi, T. Sekitani, H. Kawaguchi, T. Sakurai, IEEE Trans. Electron Devices, 52, 2502 (2005).
11:00 AM - G9: Systems 1
BREAK
G10: Energy Generation and Storage I
Session Chairs
Wednesday PM, December 03, 2008
Room 207 (Hynes)
12:00 PM - G10.2
Aluminum Phthalocyanine Chloride/C60 Organic Photovoltaic Cells with Large Open Circuit Voltage.
Do Young Kim 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractSmall molecule organic photovoltaic (OPV) cells with large open-circuit voltage (VOC) of 0.84 V were fabricated. Majority of the research work has focused on improving the short circuit current (JSC) to increase the power conversion efficiency (PCE) and various bulk heterojunction organic PV cells with high JSC have already been reported. However, the open-circuit voltages of organic PV cells using conventional donors such as CuPc (copper phthalocyanine) and P3HT (poly (3-hexylthiophene)) are only 0.4 ~ 0.6 V. In this work, we fabricated OPV cells with large VOC using aluminum phthalocyanine chloride (AlPc-Cl). We have made the planar heterojunction OPV cells with CuPc as well as AlPc-Cl as donor for systematical study: (1) ITO/CuPc (20nm)/C60 (40nm)/BCP (10nm)/Al and (2) ITO/AlPc-Cl (20nm)/C60 (40nm)/BCP (10nm)/Al. In CuPc OPV cell, the PCE is 1.02 % at 100 mW/cm2 and the JSC, VOC, and fill factor (FF) are 4.32 mA/cm2, 0.44 V and 53.7 %, respectively. In AlPc-Cl OPV cells, however, the PCE is 1.68 % at 100 mW/cm2 and the JSC, VOC, and FF are 3.78 mA/cm2, 0.84 V and 52.4 %, respectively. The VOC of the AlPc-Cl OPV cells is almost twice that of the CuPc OPV cells while the JSC and FF values of both OPV cells are quite similar. Due to the large increase in the VOC, the PCE of the OPV cells with AlPc-Cl donor is 70 % larger than that with CuPc donor. With the bulk heterojunction structure, the PCE of the AlPc-Cl device was further enhanced to 2.3%.
12:15 PM - G10.3
The Application of Titanium Oxide on Organic Optoelectronic Devices by Sol-Gel Process.
Juo Hao Li 1 , Mi Hyae Park 1 , Yang Yang 1
1 Materials Science & Engineering, UCLA, Los Angeles, California, United States
Show AbstractThe application of titanium oxide on organic photovoltaic (OPV) devices and organic light-emitting diodes (OLEDs) has been reported in the literatures, and is found having important effects not only on optical but also the electrical effects. We characterize the transparency, crystallinity and redox potential of amorphous and nano-crystalline titanium oxide prepared by sol-gel process. It is found that by employing the titanium oxide to the device architecture, polymer solar cells based on poly (3-hexylthiophene): methanofullerene with nano-crystalline titanium oxide interfacial layer exhibited excellent characteristics; and the efficiency of solution processed OLEDs based on green polyfluorene polymer has found increased significantly by inserting the amorphous titanium oxide layer between the active layer and cathode.
12:30 PM - **G10.4
Spanning the Spectrum with Spray-Processable Donor-Acceptor Polymers and Telechelic Oligomers for Electrochromics and Photovoltaics.
John Reynolds 1
1 Chemistry, Univ. of Florida, Gainesville, Florida, United States
Show AbstractThe development of organic electronic and redox active devices that provide a response or interaction over large-areas and on flexible substrates is enabled by access to solution processble conjugated materials. We will present results on a family of fully conjugated polyheterocycles and crosslinkable telechelic oligomers with controlled light absorption for photovoltaic and electrochromic applications. Two band absorption induced by the incorporation of a donor-acceptor-donor (DAD) triad induces long wavelength light collection well into the near infrared for photovoltaic (PV) devices, along with providing processable green to transmissive electrochromic (EC) polymers. Careful control of this two band absorption can lead to band coalescence and a fully black colored conjugated polymer that can be converted to a transmissive form. Black to clear electrochromism can also be obtained in multi-component devices and materials by planned spectral overlap. Telechelic functionalization of conjugated oligomers with acrylate moities provides UV crosslinkable coatings which have been photopatterned while retaining charge transport and redox activity. We will discuss fundamental optical and electrochemical data in order to establish the electronic structure of the newly synthesized oligomers and polymers, along with presenting results from various device studies (photovoltaic and electrochromic) as platforms for materials property optimization.
G11: Solution-Processed Nanomaterials
Session Chairs
Wednesday PM, December 03, 2008
Room 207 (Hynes)
2:30 PM - **G11.1
Operating Mechanisms of Quantum Dot LEDs.
Vladimir Bulovic 1
1 , MIT, Cambridge , Massachusetts, United States
Show Abstract3:00 PM - G11.2
Non-Destructive Film Thickness Measurements in Hybrid Organic-Inorganic Nanocrystal Devices.
D. M. Nanditha Dissanayake 1 , Vlad Stolojan 1 , David Cox 1 , Sarah Sharp 2 , Richard Curry 1
1 Advanced Technology Institute, University of Surrey, Guildford United Kingdom, 2 , Oxford Instruments Analytical, High Wycombe United Kingdom
Show AbstractIn recent years the development of hybrid organic-inorganic nanocrystal devices has allowed significant improvements in device performance relating to extended solar absorption in photovoltaic devices and efficient near infrared electroluminescence devices. Such devices typically comprise of a number of sequentially deposited materials forming thin films, each of which is designed to undertake a specific role. Optimising the thickness of each layer is critical to obtaining an efficient device yet quantifying this in real devices is non-trivial and destructive (e.g. obtaining TEM cross-sections), so is often inferred from previously obtained ‘calibration data’. This commonly used approach is less rigorous for hybrid devices which may involve a combination of casting from solutions and thermal deposition along with post deposition treatment all of which may modify the thickness and properties of the various materials previously deposited.We describe a non-destructive method for obtaining the thickness of a variety of organic materials commonly used in such devices and of PbS nanocrystals (PbS-nc) based on energy dispersive x-ray analysis (EDS). Measurements are reported on indium-tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), PbS-nc, C60, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and Al individual films and on multilayer hybrid devices based on these materials. To determine the accuracy of the EDS measurement technique used cross-sectional analysis was also performed.When analysing samples, the volume analyzed and the fraction of the x-rays emitted depends on three factors: (i) the energy of the electron beam (kV); (ii) the energy of the x-ray studied (iii) the local atomic weight and density. Reduction in accelerating voltage improves the resolution of X-ray emission allowing features below 100nm to be resolved. However, at low kV there may be no K-lines excited for some elements thus closely spaced L and M lines are also required for X-ray analysis. In the case of devices with layers <100nm thick the interaction volume from which characteristic x-rays are generated extend into the substrate and over several layers in the case of multilayer structures. To optimise the accuracy and sensitivity of analysis of these samples modelling is undertaken to determine the optimum operating conditions and measured lines in case of any change in emitted x-ray spectrum.With optimal choice of operating conditions and measured x-ray line intensities, the EDS can be used to obtain thickness and compositional information for each of the materials studied. In addition, using this technique we are able to distinguish between layers within hybrid devices and obtain their thickness.As such this method may allow for a simple method of obtaining quantifiable relationship between device optical and electrical properties and material thicknesses without the need for destructive cross-sectioning.
3:15 PM - G11.3
Efficient, Visible Organic Light-Emitting Diodes Utilizing a Single Polymer Layer Doped with Quantum Dots.
Ian Campbell 1 , Brian Crone 1
1 Materials Physics & Applications, Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractOrganic light emitting diodes (OLEDs) are promising for display and lighting applications and are the focus of much current research. Colloidal quantum dot (QD) based OLEDs are attracting attention for these applications because QDs have narrow spectral emission that is easily tunable by changing the QD size and they have high photoluminescence quantum efficiency. Quantum dots also have large spin-orbit coupling and so can be used to exceed the 25% quantum efficiency limit in fluorescent OLEDs imposed by spin recombination statistics. To date, efficient quantum dot based, visible emitting OLEDs have been relatively complex multilayer structures utilizing a thin, pure QD layer (~ one monolayer) and additional organic layers for both electron and hole transport. They typically have an external quantum efficiency (EQE) of 1% at 0.1 A/cm2 [1] and they require > 10V to reach 0.1 A/cm2 [1,2]. In this work [3], we obtain performance comparable to these complex devices, EQE 0.5% at 0.1 A/cm2 and reach 0.1 A/cm2 at 6.5V, from a single layer of CdSe/ZnS quantum dots dispersed in poly (9,9-dioctylfluorene) [PFO]. We attribute the good performance of this PFO/QD material combination to matching of the polymer and QD hole energy levels and improved hole transport through the polymer. The energy levels of the QDs in the polymer film were determined by built-in potential measurements. The energy levels are shifted to lower binding energy when compared to estimates based on bulk energy levels and quantum confinement effects. The energy level shift is most likely caused by a dipole layer within the quantum dot at the organic ligand/inorganic core interface. Diodes using red (2 eV) and green (2.25 eV) QDs emit predominantly from the QDs but the spectrum of blue emitting (>2.35 eV) QDs is perturbed by interactions with PFO. [1] S. Coe-Sullivan, J. S. Steckel, W.-K. Woo, M. G. Bawendi, and V. Bulovic, Adv. Funct. Mater. 15, 1117 (2005). [2] Q. Sun, Y. A. Wang, L. S. Li, D. Wang, T. Zhu, J. Xu, C. Yang, and Y. Li, Nature Photonics 1, 717 (2007). [3] I. H. Campbell, B. K. Crone, Appl. Phys. Lett. 92, 043303 (2008).
3:30 PM - **G11.4
Printed Nanowire Arrays for Sensor and Electronic Applications.
Ali Javey 1 , Zhiyong Fan 1 , Johnny Ho 1 , Roie Yerushalmi 1 , Alexandra Ford 1
1 Electrical Engineering and Computer Sciences, UC Berkeley, Berkeley, California, United States
Show AbstractControlled and uniform assembly of “bottom-up” nanowire (NW) materials with high scalability presents one of the significant bottleneck challenges facing the integration of nanowires for electronic applications. Here, we present wafer-scale assembly of highly ordered, dense, and regular arrays of NWs with high uniformity and reproducibility through a simple contact printing process. The assembled NW pitch is shown to be readily modulated through the surface chemical treatment of the receiver substrate, with the highest density approaching ~8 NW/µm, ~95% directional alignment and wafer-scale uniformity. Such fine control in the assembly is attained by applying a lubricant during the contact printing process which significantly minimizes the NW-NW mechanical interactions friction; therefore, enabling well controlled transfer of nanowires through surface chemical binding interactions. Furthermore, we demonstrate that our printing approach enables large-scale integration of NW arrays for various device structures on both rigid silicon and flexible plastic substrates, with a controlled semiconductor channel width ranging from a single NW (~10 nm) and up to ~250 µm, consisting of a parallel array of over 1,250 NWs and delivering over 1 mA of ON current. The potency and versatility of the method is further demonstrated by large-scale, heterogeneous integration of nanowires for image sensor circuitry by utilizing optically active nanowire sensors and high mobility nanowire transistors. The nanowire sensors and electronic devices are interfaced to enable an all-nanowire circuitry with on-chip integration, capable of detecting and amplifying an optical signal with high sensitivity and precision. Notably, the process is highly reproducible and scalable with a yield of ~80% functional circuits, therefore, enabling the fabrication of large arrays (i.e., 13x20) of nanowire photosensor circuitry with image sensing functionality. The ability to interface nanowire sensors with integrated electronics on large scales and with high uniformity presents an important advance toward the integration of nanomaterials for sensor applications.
4:00 PM - G11: Nano
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4:30 PM - **G11.5
Solution-processed infrared solar cells.
Edward Sargent 1
1 Electrical and Computer Engineering, University of Torondo, Toronto, Ontario, Canada
Show Abstract5:00 PM - G11.6
Design Guidelines for Hybrid Organic/Colloidal Quantum Dot Light Emitting Devices Derived From Numerical Simulations of Active Structures.
Polina Anikeeva 1 2 , Conor Madigan 1 , Moungi Bawendi 3 , Vladimir Bulovic 1
1 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract5:15 PM - G11.7
Influence of In-gap Trap State in Infrared Quantum Dots on Their Optoelectronic Properties.
Xiaomei Jiang 1 , Jason Lewis 1 , Jian Zhang 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show Abstract5:45 PM - G11.9
Directed Assembly of Self-Assembled Organic Nanostructures for Advanced Optoelectronic Device Architectures.
Volodimyr Duzhko 1 , Michael Kelley 1 , Jiangang Du 2 , Christian Zorman 2 , Kenneth Singer 1 2
1 Physics, Case Western Reserve University, Cleveland, Ohio, United States, 2 Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractThe utilization of organic materials in electronic, optoelectronic and photonic applications depends on the availability of inexpensive fabrication technologies that allow for tailoring material structural properties and enabling the design of functional device architectures. Non-covalent self-assembly of organic molecules in organic solvents produces materials and nanostructures that are built with atomic precision over extended length scales, that possess novel and unique functionality, and are potentially integrable into device architectures on large scales. We describe solution-based self-assembly of triphenylene [1], phthalocyanine [2] and perylene diimide derivatives into nanostructured objects of various geometries (nanoparticles, branched aggregates, nanofibers) and into heterogeneous systems of even more complex architectures. Structural tailoring of self-assembled architectures was achieved by optimizing the chemical structure of self-assembling molecules and varying the environmental parameters during the self-assembly process. In order to integrate self-assembled nanofibers of phthalocyanine and perylene diimide derivatives into useful device architectures, we developed an approach for spatial manipulation of the nanofibers. This approach utilizes the interaction of photo-excited charge carriers in the nanofibers with external electric fields of various geometries. In particular, both nanofiber orientation and positioning on surfaces could be achieved using spatially homogeneous or localized electric fields, respectively. Fabrication, operation and performance studies of optoelectronic device-like architectures that take advantage of the one-dimensional geometry of the nanofibers, their nanometer-scale lateral size and their efficient anisotropic charge carrier transport properties will be discussed.1. V. Duzhko, H. Shi, A.N. Semyonov, R.J. Twieg, and K.D. Singer, Langmuir 2006, 22, 7947.2. V. Duzhko and K.D. Singer, J. Phys. Chem. C 2007, 111, 27.
G12: Poster Session: Hybrid and Organic Materials for Large-Area Functional Systems III
Session Chairs
Ana Arias
Dean DeLongchamp
Cherie Kagan
Alberto Salleo
Thursday AM, December 04, 2008
Exhibition Hall D (Hynes)
9:00 PM - G12.1
Electric Field Induced Manipulation of Static and Dynamic Optical and Spatial Properties of Aggregates of Coupled Quantum Dots.
Yashwant Verma 1 , Christopher Ferri 1 , Somnath Ghosh 1 , Maribel Gallardo 1 , David Kelley 1 , Sayantani Ghosh 1
1 School of Natural Sciences, University of California, Merced, Merced, California, United States
Show AbstractThe quantum confinement effects in nanoparticles are at the heart of numerous scientific and technological endeavors. Coherent communications between Quantum dots (QD) form the basis of diverse applications, including quantum logic and information systems. In particular, chemically synthesized QDs are particularly promising candidates for designing large-scale nano-assemblies. These will not only find wide scale use in opto-electronic devices, but can lead to new macroscopic quantum states arising from superposition and entanglement of individual QD electronic or spin states. The primary drawback in this area has been the difficulty in achieving high degree of structural order to facilitate coherent inter-dot interactions. We present a novel way to get around this problem by embedding colloidal QDs in a matrix of liquid crystal molecules. We report our techniques and results in controlling the aggregation of chemically synthesized, disk-shaped gallium selenide quantum dots (QD) suspended in a nematic liquid crystal (NLC) matrix over length scales of hundreds of microns. We also describe the optical and structural manipulation of this matrix at room temperature using electric fields. Static and time-resolved optical spectroscopy techniques are combined with high-resolution scanning polarized confocal microscopy to investigate these systems. Photoluminescence (PL) from the QD-NLC mixture exhibits large red-shift in the emission spectrum. This shift is between 30 and 50 nm, implying the formation of strongly coupled QD aggregates. AFM images have demonstrated that the aggregation occurs by stacking of the disk shaped QDs to form columnar structures and the PL from these aggregates have shown that their emission is strongly polarized along their long axes. These structures can further be spatially re-aligned in situ without destroying the inter-dot coupling and maintaining the self-assembled aggregate formation by the application of an in-plane electric field. This applied field continuously rotates the aggregates by almost 90° resulting in a commensurate variation in the axis of the emission polarization. The degree of this re-orientation is a function of the strength of coupling between the aggregated QDs.Time-resolved PL reveal a faster excitonic recombination in the aggregates (600 ps) in the QD-NLC matrix in comparison to that in isolated QDs (3 ns) which is attributed to facile energy transfer processes. The aggregate recombination rate is linearly enhanced with increasing electric field which we infer is a result of the selective re-orientation mentioned above. These electric field dependent effects are not observed in a mixture of cadmium selenide QDs which also do not exhibit inter-dot coupling or aggregation. Our result is a first step towards the possibility of forming and electrically manipulating large-scale ordered structures using chemically synthesized QDs which will prove valuable for applications in many fields.
9:00 PM - G12.10
Polystyrene-Tin and Polystyrene-Tin Oxide Core-Shell Nanostructures for the Assembly and Integration of Colloidal Particles.
Srikanth Ammu 1 , Qingzhou Cui 1 , Zhiyong Gu 1 2
1 Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 CHN/NCOE Nanomanufacturing Center, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show Abstract9:00 PM - G12.11
Photolithographically Patterned Top Contact Organic Transistors and Circuits.
John DeFranco 1 , Alex Zakhidov 1 , Jin-Kyun Lee 1 , Hon Hang Fong 1 , Priscilla Taylor 1 , Margarita Chatzichristidi 1 , Christopher Ober 1 , George Malliaras 1
1 Materials Science, Cornell University, Ithaca, New York, United States
Show AbstractOrganic electronics is rapidly headed towards commercialization, promising a wide variety of devices with novelty in both function and form. A number of methods have been explored to realize the manufacture of these devices, including several roll-to-roll methods that would enable high throughput manufacturing. Resolution limits and registration problems so far cause severe restrictions on these patterning techniques and high capital equipment costs will keep these technologies from entering the marketplace for years to come. The mature inorganic semiconductor industry has relied on photolithography almost exclusively for patterning device layers because of the many benefits of the technology: high resolution, good registration, and in the case of LCD backplanes, large area coverage. Despite these advantages, and the lowered relative startup costs due to the availability of depreciated equipment and trained engineers, few have considered photolithography a viable method for patterning organic materials, in no small part due to the chemical incompatibilities of the solvents and developers with most organic materials.A photoresist system using hydrofluoroether (HFE) as a solvent and developer is demonstrated and shown to be generally chemically compatible with materials commonly used in organic TFTs, including pentacene and P3HT. Sub-micron resolution is achieved with standard photolithographic techniques, making the method widely compatible with existing practices. Top contact OTFTs are fabricated with channel lengths down to 1µm and high mobilities maintained despite all of the processing. Organic circuits with top contact source/drain electrodes are also demonstrated.
9:00 PM - G12.12
Electropolymerization of Carbazole Derivative for Novel Green Organic Electrochromic Anode for High Contrast Smart Window.
Xiangxing Kong 1 2 , Chunye Xu 2 , Minoru Taya 2
1 Mechanical & Material Engineering, Floirda International University, Miami, Florida, United States, 2 Mechanical Engineering, University of Washington, Seattle, Washington, United States
Show Abstract9:00 PM - G12.13
Solution processable Organic Thin Film Transistor based on Pyrene-derivatives.
Seon Ho Kim 1 , Tielong Gao 1 , Sung Yang 1
1 Chemistry, Kyung Hee Univ., Yongin Korea (the Republic of)
Show AbstractOrganic semiconducting materials such as pentacene and polythiophene have been extensively investigated in recent years in order to develop materials for low cost electronic applications. In the design of organic semiconductor, low temperature deposition and solution processable are important features to be considered. The development of solution processable organic semiconducting materials would facilitate the applications in large active matrix displays and flexible electronics. To develop solution processable organic field effect transistor with high mobility and on/off ratio, we have synthesized a new series of pyrene derivatives via a general route involving the Suzuki coupling reaction. The devices were fabricated pyrene derivatives as semiconductor layers by spin-coating process in air. The deposited films have been examined using X-ray diffraction (XRD) and atomic force microscopy (AFM). Electrical characteristics of OTFT devices were measured in air under the accumulation mode using probe station equipped with an Agilent semiconductor parameter analyzer. The results indicate that the surface pretreatment, a proper baking temperature and substrate temperature are required to achieve high mobility and On/Off ratio.
9:00 PM - G12.14
Surface Modification of Nanoparticles Induced by Solution Plasma.
Koji Mitamura 1 3 , Yoshimichi Ichino 2 , Nagahiro Saito 2 3 , Osamu Takai 1 2 3
1 , EcoTopia Science Institute, Nagoya University, Nagoya Japan, 3 , JST-CREST, Tokyo Japan, 2 , Graduate School of Engineering, Nagoya University, Nagoy Japan
Show Abstract9:00 PM - G12.15
Synthesis of New Types of Organic Semiconductor.
Tielong Gao 1 , Seon Ho Kim 1 , Sung Yang 1
1 Chemistry, Kyung Hee Univ., Yongin Korea (the Republic of)
Show AbstractCurrently organic semiconducting materials have been of considerable interest since their potential promises to active components in flexible electronics. The ability to predictably control the photophysical and electrical properties by varying the structure will be essential to develop OTFT materials for various applications. A series of novel 1,3,6,8- tetra-substituted pyrene derivatives have been prepared for the examination of a substituent effect on photophysical and field effect properties. The pyrene derivatives were obtained in high purity via a general route involving the Suzuki coupling reaction. They were characterized using NMR, UV-VIS, and mass spectrometry. Compare to the single thiophene substituted of pyrene derivatives the dithiphene derivatives showed longer absorption wavelength and longer emission wavelength which indicates the dithiophene derivatives have the lower HOMO-LUMO band-gap energy. The derivatives show good solubility in common organic solvent such as CH2Cl2, which indicates these materials might be of considerable interest as solution-processable semiconductors in organic field-effect transistors.
9:00 PM - G12.16
Preparation and Characterization the Relationships Between Molecular Structure and Electrical Transport Property of Perylenetetracarboxylic Diimide Organic Thin Film Transistor.
Lianqing Li 1 , Tielong Gao 1 , Seon Ho Kim 1 , Sung Yang 1
1 Chemistry, Kyung Hee Univ., Yongin Korea (the Republic of)
Show AbstractOrganic semiconductors have been received intense interests due to their possible application in electronics including field effect transistor, light-emitting diodes and photovoltaic solar cells. In particular, OTFT is promising as active components in flexible electronics. A promising approach to the realization of a low cost flexible display may be the development of solution processable organic semiconductor. A series of the perylenetetracarboxylic diimide derivatives were synthesized via a general route involving the common condensation reaction and Suzuki coupling reaction and characterized by using NMR and mass spectrometry. The compounds show good solubility in common organic solvent such as CH2Cl2 and chloroform and the devices could be fabricated by spin-coating process in air. We examined the correlation of molecular structures with solubility, crystallinity, and film morphology. We also characterized the relationships between film structure and TFT performance.
9:00 PM - G12.17
A Binder-free Electrically Conductive Ag Adhesive Using a Chemically Adsorbed Monolayer.
Shogo Onishi 1 , Yuji Ohkubo 1 , Kazuhiro Soejima 2 , Kazufumi Ogawa 1
1 Department of Advanced Materials Science, Graduate School of Engineering, Kagawa University, Kagawa Japan, 2 Business Development HQ Process Technology DVLPMT. Center, ALPS Electric Co., Ltd., Miyagi Japan
Show AbstractA binder-free electrically conductive Ag adhesive (Ag-ECA) using a reactive chemically absorbed monolayer (CAM) is developed. The epoxy-terminated CAM was prepared on the surface of the Ag particles by dispersing in the adsorption solution containing 2-(3,4-epoxycycrohexyl)-ethyl-trimethoxysilane (ECHxES).After washing the Ag particles for removing the excess and the physically-adsorbed absorbents, 2-methyl-imidazole as a cross-linker was reacted to the epoxy-terminated CAM at the surface of Ag particles dispersed in the solution. For increasing the electrical conductivity, Ag-ECA was prepared with the mixture of large (d=1.0 μm) and small (d=0.5 μm) Ag particles. When the mixture ratio (large : small) was 7 : 3, the best electrical conductivity of 4.0 × 10^4 (Ω cm)-1 was obtained. Moreover, in order to prepare the more rigid Ag-ECA wires, a copper-imidazole complex was added to the mixture of Ag particles covered with the reactive CAMs as the cross-linker instead of 2-methyl-imidazole. The best pencil hardness obtained on the Ag-ECA wire was 2H, and the best electrical conductivity was 2.5 × 10^5 (Ω cm)-1. Both of the electrical conductivity and the pencil hardness were better than those with the commercially available Ag-ECAs.
9:00 PM - G12.19
Single Molecule Solid State Light Emitting Electrochemical Cells with Life-times Superior to 3000 Hours.
Henk Bolink 1 , Ruben Costa 1 , Stefan Graber 2 , Michele Sessolo 1 , Enrique Orti 1 , Edwin Constable 2
1 Instituto de Ciencia Molecular, Universidad de Valencia, Paterna, Valencia, Spain, 2 Department of Chemistry, University of Basel, Basel Switzerland
Show Abstract9:00 PM - G12.2
Two-photon Solid-state Polymerization of Diacetylene in Nanoporous TiO2 Structures.
Lian Li 1 , Lynne Samuelson 1 , Jayant Kumar 2
1 , US Army Natick Solider Research, Development & Engineering Center, Natick, Massachusetts, United States, 2 , University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractTiO2 nanoparticles have been widely used as semiconductors and photocatalysts. They have been extensively utilized in dye-sensitized solar cells, water purification, hazardous waste control, and air purification. Recently, diacetylene monomers within nanoporous TiO2 films were polymerized in solid state under visible light illumination. Here we report on the two-photon polymerization of a diacetylene monomer within the TiO2 nanostructures using a femto-second laser at 800 nm. UV-vis and Raman studies confirmed the polymerization of the diacetylene monomer. Since both the monomer and nanoporous TiO2 films show no absorption and the diacetylene polymer only exhibits low absorption at the laser wavelength, it is possible to obtain uniform polymerization of the diacetylene within the TiO2 nanopores. Combining the high charge carrier mobilities of the polydiacetylenes and the nano-structured semiconducting TiO2 films, the hybrid polydiacetylene/TiO2 nano-composites offer new possibilities for development of optoelectronic devices. Characterization of the polymer and discussion of the studies will be presented.
9:00 PM - G12.20
Aggregates in Chiral Polyfluorene; a Key to Understanding Thin Film Opto-electronic Properties.
Girish Lakhwani 1 , Martijn Kemerink 2 , René Janssen 1 , Stefan Meskers 1
1 Chemistry and Chemical Engineering, Technische Universteit Eindhoven, Eindhoven Netherlands, 2 Physics, Technische Universteit Eindhoven, Eindhoven Netherlands
Show AbstractPolyfluorene (PF) polymer has a backbone consisting of alternating single and double bonds, which gives the polymer semiconducting properties. Polyfluorene is interesting because it occurs in different crystalline, liquid crystalline (LC) and (semi-)crystalline states each with its own optoelectronic properties. Moreover polyfluorene backbone can fold into a number of helical conformations. Processing conditions have a strong influence on which of the conformational and crystallization states would predominate in thin film deposited via e.g. spincoating. Here we investigate various polymer organizations/aggregation within the film, motivated by the prospect to optimize opto-electronic properties.To probe into the helical organization of polyfluorene, we investigate chiral polyfluorene (poly{9,9-bis [(3S)-3,7-dimethyloctyl]-2,7-fluorene} (1)) by Circular Dichroism (CD) as well as AFM and Spectroscopic Ellipsometry. Chirality serves as a spectroscopic ‘label’ allowing to investigate aggregation and folding behavior of the polymer chains. Temperature dependent CD studies in 1-octanol and solution dependent CD studies in chloroform/methanol shows that depending on the conditions, the formation of either amorphous, crystalline or semi-crystalline aggregates can occur. Spincoating a solution of 1 onto a substrate also introduces aggregation during evaporation of the solvent. The CD effects in films are indicative of semi-crystalline nature of aggregates formed upon the crystallization process involved in spincoating. AFM reveals that the polymer chains collapse into fibrillous aggregates upon spincoating the solutions of 1. These fibrils exist irrespective of whether the films are spincoated from aggregated or aggregate free solutions. In addition, films of 1 show a liquid crystalline phase at high temperature with probable cholesteric ordering of the fibrils. The fibrils show linearly polarized absorbance confirming their anisotropic nature. The final optical properties of the polymer are intimately related to the aggregates. From spectroscopic ellipsometry, we obtain anisotropic optical constants of the polymer film. The transition dipole moments for the optical transition to the lowest singlet state lie predominantly in the plane of the film showing that polymer chains are preferentially oriented in an in-plane direction. AFM studies reveal that the fibrils containing polymer chains are oriented along the plane of the substrate. This indicates that fibril formation and polymer chain alignment during spincoating are coupled processes. The understanding of the folding and aggregation of polymers into fibrillous structures allows one to adjust the processing conditions in such a way that opto-electronic properties can be manipulated.
9:00 PM - G12.21
Liquid Crystal Alignment on Rubbed Polyimide: Topography or Chemistry?
Walter Schenck 1 , Edward Samulski 1
1 Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractThe mechanism for liquid crystal (LC) alignment on mechanically rubbed polyimide (PI) is a contentious subject(ref.1-5). Berreman(ref.4, 6) originally posited that rubbing resulted in mechanical scoring of the substrate, and the resulting corrugated topography aligned the director n in the low-elastic-energy configuration (n||grooves). However to date it has not yet been unequivocally demonstrated if the Berreman mechanism—minimization of the elastic energy associated with forcing the director to follow the topography—or chemical interactions between the LC mesogens and the aligned functional moieties along the PI backbone is responsible for planar LC alignment. Others have established that embossed, microscopic grooves in PI will align n(ref.7); varying the amplitude of the embossed corrugation affects LC alignment suggesting that the Berreman mechanism is operative. However the amplitude of embossed features investigated to date are 10-100 times larger than those produced by the rubbing process calling into question the Berreman mechanism for rubbed PI.We have replicated the surface topography of rubbed PI, without mechanical rubbing (and the putative alignment of polymer functionalities) in order to investigate the alignment mechanism. We have replicated the subtle sub-micron features of rubbed PI using the PRINTTM process(ref.8), which utilizes a photocurable perfluoropolyether (PFPE) to mold the rubbed PI surface. The PFPE mold is then used to emboss a spun-coat film of planar aligning PI(ref.9). The resulting embossed film topography is contrasted with rubbed PI itself using AFM, and the induced LC alignment of the rubbed PI and its embossed replica is studied with polarizing optical microscopy.References(1) Stohr, J.; Samant, M. G.; Luning, J.; Callegari, A. C.; Chaudhari, P.; Doyle, J. P.; Lacey, J. A.; Lien, S. A.; Purushothaman, S.; Speidell, J. L. Science 2001, 292, 2299-2302.(2) Geary, J. M.; Goodby, J. W.; Kmetz, A. R.; Patel, J. S. J. Appl. Phys. 1987, 62, 4100-4108.(3) Castellano, J. A. Mol. Cryst. Liq. Cryst. 1983, 94, 33.(4) Berreman, D. W. Mol. Cryst. Liq. Cryst. 1973, 23, 215.(5) Behdani, M.; Keshmiri, S. H.; Soria, S.; Bader, M. A.; Ihlemann, J.; Marowsky, G.; Rasing, T. Appl. Phys. Lett. 2003, 82, 2553-2555.(6) Berreman, D. W. Phys. Rev. Lett. 1972, 28, 1683.(7) Chiou, D. -.; Chen, L. -.; Lee, C. -. Langmuir 2006, 22, 9403-9408.(8) Jason P. Rolland, Erik C. Hagberg, Ginger M. Denison, Kenneth R. Carter,Joseph M.De Simone, Angewandte Chemie International Edition 2004, 43, 5796-5799.(9) Polyimide solutions and rubbed polyimide films provided by LG Displays
9:00 PM - G12.22
Crystallographic Orientation of Poly-3-hexylthiophene by Interacting with Multi-walled Carbon Nanotubes and Its Application to Polymer Transistors.
Seok-Ju Kang 1 , Youn-Su Kim 1 , Won Bae Kim 1 , Kang-Jun Baeg 1 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering and Program for Integrated Molecular System (PIMS), Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show AbstractThin films of polymer semiconductors are being intensively investigated for large-area electronics applications such as light-emitting diodes, photovoltaics cell and thin-film transistors (TFTs). In particular, the high field-effect mobility and solution processability of regioregular poly(3-hexylthiophene), P3HT has stimulated a lot of interest in the utilization of this fascinating material as active electronic elements in various thin-film devices and sensors. Further, self-organized regioregular P3HT with its supramolecular two-dimensional structure is of special interest because the one-dimensional electronic properties of π-conjugated polymer chains are modified by the increased interchain stacking that results from π-π interactions. Charge transport for TFTs should increase when the in-plane π-stacking increased for a self-organized semiconducting polymer. This increase in highly oriented crystals improves the mobility in the film by reducing the number of highly misoriented grain boundaries that have poor electronic overlap. Recently, conjugated polymers have been found to strongly interact with the carbon nanotube (CNT) surface through π-stacking. Therefore, we have studied the field-effect mobilities obtained for films of P3HT spin-cast onto substrates, which were annealed above its melting temperature and compressed with vertically aligned CNT array plates to determine the effect of vertically aligned CNTs on molecular packing orientation and charge transport.
9:00 PM - G12.23
Controlled Synthesis of Palladium Nanoparticles.
Yayong Liu 1 , Zhiyong Xu 1 , Narayan Das 1 , Liwei Huang 1 , Kaikun Yang 1 , Howard Wang 1
1 Department of Mechanical Engineering and Center for Advanced Microelectronics Manufacturing, Binghamton University, State University of New York, Binghamton, New York, United States
Show AbstractThe usefulness of nanoparticles (NPs) in electronics fabrication depends on their composition, size, crystallinity, surface modifier, as well as the dispersity of those characteristics. We have investigated controlled synthesis of Palladium (Pd) NPs using a wet chemistry routine, in which palladium acetate is reduced to form metal particles and stabilized by surfactants. Pd-NPs of various size and surface capping agents have been synthesized and characterized using thermal analysis, TEM and AFM. Quantitative measurements of Pd-NP size and size distribution have been carried out using small angle neutron and x-ray scattering. Mechanism of particle formation has been explored using ultraviolet-visible spectroscopy.
9:00 PM - G12.24
Chemical Fixation of Polyelectrolyte Multilayer using Poly(acrylic acid-co-glycidyl methacrylate) Copolymer.
Son Duy Tuong 1 , Heekyung Lee 1 , Eunsu Lee 1 , Hongdoo Kim 1
1 Chemistry, Kyung Hee University, Yongin, Kyungkido, Korea (the Republic of)
Show AbstractFew chemical fixations of poly(allylamine hydrochloride) (PAH) /poly(acrylic acid) (PAA) film has been reported such as heat-induced amide formation, modification of polymer, and cross-linker as glutaraldehyde (GA), 1-ethyl-3-(3-demethyl-aminopropyl) carbidiimide (EDC), etc. However, they exhibit some inherent limitations e.g., using high temperature, expensive reagent, and complicated process control. To resolve these limitation, copolymer of poly(acrylic acid-co-glycidyl methacrylate) (PAA-co-GMA) with 3-20 mol% glycidyl methacrylate (GMA) moiety was synthesized so that it became a low-cost cross-linkable weak polyelectrolyte and is possible to incorporate into polyelectrolyte multilayer (PEM) films. PEMs film was fabricatrd using PAA-co-GMA and PAH on polymer substrates such as polymethylmethacrylate (PMMA), polycarbonate (PC). Its characteristics was found to be similar to PAA/PAH films as those previously reported. On the other hands, some properties of these films were significantly improved such as mechanical and environmental stability, adhesion with polymer substrate because of the heat-induced cross-linking between epoxy group of copolymer and –NH2 or/and –COOH group of polyelectrolytes. The stability of PEM film using PAA-co-GMA20%/PAH has been improved significantly. Both surface tension and FT-IR results have been shown to support cross-linking formation between multilayers as expected. The surface properties of these films were altered from soft, elastic and hydrophilic to brittle and hydrophobic film with increasing content of GMA. By controlling content of GMA in the copolymer, we can make the desired films for many different applications. As possible application, anti-reflection coating on PMMA and PC has been demonstrated.
9:00 PM - G12.3
Large-Area Vertical Arrays of Luminescent Metal-Organic Nanowire Composites.
Micha Fireman 1 , Deirdre O'Carroll 1 , Harry Atwater 1
1 Thomas J. Watson Sr. Laboratory of Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractNanowire arrays are technologically interesting architectures since they exploit unique nanoscale physical properties over macroscale areas. When grown as large-area vertical arrays either by the catalyst-assisted vapour-liquid-solid technique or by template-directed synthesis, several processes have been developed to etch nanotubes or form core-shell heterostructures directly from nanowires.[1,2] Coating semiconductor nanowires with a metal shell has been shown to enhance photoluminescence intensity from nanowire emitters despite optical losses associated with the metal.[3] In addition, the smallest electrically-driven lasers to date have been fabricated by confining vertical nanowire emitters within metal-coated nanocavities.[4]In this work, large-area vertical arrays of radially heterogeneous nanowire structures are fabricated, specifically with cores of an efficient, blue-light-emitting, fluorene-based, conjugated oligomer surrounded by metallic shells. Nanostructure fabrication is carried out by, firstly, electrochemically depositing nickel into the pores of nanoporous alumina templates. Subsequent template removal and electrodeposition of gold form radially heterostructured nickel-gold core-shell nanowires. Selective chemical etching of the nickel cores using iron chloride solution yields a vertically oriented array of gold nanotubes. Melt-assisted filling of the nanotubes with the conjugated light-emitting oligofluorene material yields nanowire arrays with up to 108 core-shell nanowires prepared over an area of ~30 mm2. Photoluminescence emission from the nanostructured metal-organic composite is compared with that of a pure oligofluorene film of similar thickness. With choice of a suitable metal shell thickness and nanowire diameter, such metal-emitter nanocomposite structures may be employed to enhance the light emitting properties of the conjugated organic materials as well as confine emission, potentially creating large-area arrays of vertically aligned waveguides or nanoscale optical cavities.[1] R. Fan, Y. Wu, D. Li, M. Yue, A. Majumdar, P. Yang, J. Am. Chem. Soc. 125, 5254 (2003).[2] M. S. Sander, H. Gao, J. Am. Chem. Soc. 127, 12158 (2005).[3] M. A. Mastro, et al., Nanotechnology 18, 265401 (2007).[4] Hill, M. T. et al., Nat. Photon. 1, 589 (2007).
9:00 PM - G12.4
Self-Assembled Monolayers of Dipolar Chromophores for Photoinduced Charge Transfer in Organic Field Effect Transistors.
Padma Gopalan 1 , Peerasak Paoprasert 1 , Byoungnam Park 1 , Robert Hamers 2 , Paul Evans 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractA layer of functionalized disperse-red 19 (DR-19) molecules at the interface between the gate insulator and semiconducting layer dramatically changes the photoelectrical characteristics of a pentacene thin film field effect transistor. The DR-19 is functionalized with siloxane and deposited from a toluene solution onto the gate insulator of the field-effect transistor. Infrared spectroscopy shows that the DR-19 changes to a charge-separated state upon exposure to light. The resulting change in the dipole of the DR-19 and electron traps in the DR-19 layer combine to change the threshold voltage of the organic FET by up to 100 V. The ability to modify and to sense the conformation of molecules at organic/inorganic interfaces has a wide range of potential applications.
9:00 PM - G12.5
Nanostructures of ZnO as Elements in Inorganic/Organic Hybrid Electrically Writable Memory Devices.
R. Cross 1 , S. Paul 1 , I. Salaoru 1
1 Emerging Technologies Research Centre, De Montfort University, Leicester United Kingdom
Show AbstractThere is an increasing interest in the development and integration of organic and inorganic materials for large area and low cost device applications, especially with regards to non-volatile memory devices [1][2]. Zinc oxide (ZnO) is a wide, direct band gap (3.35 eV) semiconductor with a large exciton binding energy at room temperature (60 meV). However, it is the ability to deposit/grow films and nanostructures over large areas at low temperature which makes it particularly attractive for the low-cost fabrication of electronic devices using e.g. flexible substrate materials. In this paper, we describe material properties and device characteristics of two different hybrid inorganic/organic memory devices using nanostructures of ZnO (nanostructured thin film and solution-processed nanowires (ZnO NWs)) and the organic polymers polyvinyl acetate and polystyrene. The first two stages of the memory device fabrication process were the same for both test structures and involved the deposition of metal coplanar tracks onto glass substrates, which act as bottom contacts. Following this, a thin layer of nanostructured ZnO was deposited onto the tracks using a radio frequency magnetron sputtering system with a base pressure of <10−7 mbar. The sputtering was carried out at room temperature using a ZnO (99.99% purity) target in an Ar (99.999% purity) gas atmosphere, with an RF power of 150W at a frequency of 13.56 MHz. The Ar flow rate was such that the sputtering pressure was 1.3 × 10−2 mbar. For the ZnO thin film-based device, the next step involved the deposition of the organic polymer layer via spin coating. This was followed subsequently by the evaporation of the metal top contacts. For the ZnO NW-based device, NW growth was carried out using equimolar aqueous solutions (0.025 M) of zinc nitrate hexahydrate and hexamine that were combined in an open crystallising dish, which was then placed in a water bath at 75 C [3]. After a period of temperature stabilisation, the substrates coated with the ZnO nanostructured thin film were suspended upside down in the growth solution. The substrates were then removed from the growth vessel, rinsed with de-ionised water and dried in air. The depositions of the polymer and metal top contacts were then performed as before.Results will be presented of the current-voltage (I-V) and capacitance voltage (C-V) characteristics of both sets of devices and comparisons drawn between the relative performances of each. In addition, discussions will also be given on the possible charging/conduction mechanisms taking place within the memory devices.References:1. S. Paul IEEE Trans. Nanotechnology, Vol. 6 No. 2 March 2007.2. S. Paul, A.Kanwal, M.Chhowalla, Nanotechnology 17 (2006)145.3. R. B. M. Cross, M. M. De Souza, E. M. Sankara Narayanan, Nanotechnology 16 (2005) 2188.
9:00 PM - G12.6
Sustained Enzyme Activity of Organophosphorus Hydrolase (OPH) in Cross-Linked Mutilayer Assemblies.
Alok Singh 1 , Sung-Jae Chung 1 , Walter Dressick 1
1 Center for Bio/Molecular Science & Engineering, Naval Research Laboratory, Washington, District of Columbia, United States
Show Abstract9:00 PM - G12.7
Long-life Blue Fluorescent Organic Light-emitting Devices Having Graded Compositions.
Masafumi Takahashi 1 , Yong-Jin Pu 1 , Ken-Ichi Nakayama 1 , Masaaki Yokoyama 1 , Junji Kido 1
1 Organic Device Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Show AbstractThe effect of the graded composition on the performance of multilayer organic light-emitting device was investigated. The organic layers were fabricated by the in-line vacuum evaporator, which was developed in our laboratory. A blue-emitting material, dinaphtylanthracene derivative (MADN), was also used as an emitter. In the device structure of ITO/ MCC-PC1020 / NPD / MADN / Alq / Liq / Al, various patterns of gradual mixing of the organic layers were evaluated. Emission color turned out to be dependent on the graded mixing of the interfaces. The graded mixing of the NPD/MADN interface provided the higher performance of the blue device, while the mixing of the MADN and Alq interface resulted in the green emission form Alq. By doping a perylene derivative (TBP) as emitting center, the lifetime of 14000 hrs was obtained, while the conventional OLED with a hetero structure provides 2700 hrs. Other high performance blue OELD will also be reported.
9:00 PM - G12.8
Dendronized Carbazole or Diphenylamine Substituted Iridium(III) Complexes for Organic Light-Emitting Devices.
Noriaki Iguchi 1 , Yong-Jin Pu 1 , Ken-ichi Nakayama 1 , Masaaki Yokoyama 1 , Junji Kido 1
1 Organic Device Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Show AbstractSolution processable phosphorescent iridium complexes having diphenylamine or carbazole dendrons were synthesized. The each phenylpyridine ligands of the complexes have two dendrons, so that the Ir(PPy)3 center is densely surrounded by bulky six dendrons in total, and these complexes have the spherical molecular structure. The dendrons showed higher triplet energy level than that of Ir(PPy)3, and the dendrimers showed a strong yellow emission in a neat film. Solution processed organic light emitting devices using these dendrimer complexes as an emitter were fabricated. The devices exhibited high efficiency even without host materials. The details will be reported.
9:00 PM - G12.9
Bistability in Electrically Writable Non-Volatile Polymer Memory Devices.
Iulia Salaoru 1 , Shashi Paul 1
1 Emerging Technologies Research Centre, De Montfort University, Leicester United Kingdom
Show AbstractIn recent years, interest in applications of organic materials in electronic devices (light emitting diodes, field effect transistors, solar cells), has increased rapidly. The advantages of organic materials are ease of processing, lower production costs and structural flexibility allowing achievement of the desired electrical and mechanical characteristics. Very recently, there have been demonstrations of the use of a blend of polymer and metal nano-particles and/or small organic molecules in memory devices [1-4]; such memory devices are called polymer devices (PMDs). These devices show two electrical conductance states (“high” and “low”) when voltage is applied, thus rendering the structures suitable for data retention. These two states can be viewed as the realisation of non-volatile electrical memory. There is always growing need to look for inexpensive, fast, high-density memory devices with longer retention times and PMDs do qualify some of these aforesaid criteria. Albeit, there is a rapid development in this area but the memory mechanism is still unclear. This work attempts to analyse memory effect in PMDs and propose a theory based on experimental data.
The thin films of blends of polymer (polyvinyl acetate, polyvinyl alcohol and polystyrene) and small organic molecules were deposited by spin coating onto a glass substrate marked with thin metal tracks and a top contact was evaporated onto the blend after drying - this resulted in a metal-organic-metal (MOM) structure. MOM devices with different metal electrodes (a series of metals with different work functions Al, In,Cu,Cr, Ag and Au) were used to understand the exact electrical transport mechanism through the blend and the individual polymers. An in-depth electrical analysis of these MOM devices is carried out using an HP4140B picoammeter (current-voltage) and an LCR HP4192 bridge. The FTIR and UV-VIS spectroscopy were also conducted, in order to understand blend properties and the effect of the same, if any, on the electrical charging mechanism in the PMDs.
References:
[1] S.Paul, A.Kanwal, M.Chhowalla, Nanotechnology, 17, (2006),145-151.
[2] ] C.W.Chu, J.Ouyang, J.H.Tseng, Y.Yang, Adv.Mater., 17, (2005), 1440.
[3] S Paul, IEEE Transactions on Nanotechnology, 6, (2007), 191-195.
[4] D.Prime and S.Paul, Mater.Res.Soc.Symp.Proc., 0997-I03-01, (2007).
Symposium Organizers
Alberto Salleo Stanford University
Ana Claudia Arias Palo Alto Research Center, Inc.
Dean M. DeLongchamp National Institute of Standards and Technology
Cherie R. Kagan University of Pennsylvania
G13: Large-Area Compatible Processing and Materials II
Session Chairs
Thursday AM, December 04, 2008
Room 207 (Hynes)
9:30 AM - **G13.1
Control of Thin-Film Morphology and Transistor Performance of Substituted Pentacene by Solution-Processing.
Gerwin Gelinck 1 , Christoph Sele 2 , Charlotte Kjellander 1 , Martin Thornton 1 , Kris Myny 3 , John Anthony 4
1 , Holst Centre, Eindhoven Netherlands, 2 , Polymer Vision, Eindhoven Netherlands, 3 , IMEC vzw, Leuven Belgium, 4 Dept. of Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show Abstract10:00 AM - G13.2
Gravure Printing of Polymer Thin Film Transistors.
Alex Guite 1 , Alasdair Campbell 1 , Monika Voigt 1 , Dae-Young Chung 1 , Fanshun Meng 2 , Joachim Steinke 2 , Simon Springer 3 , Cecile Barron 3 , Jochaim Grupp 3 , Olivier Douheret 5 , Huguette Penxten 4 , Laurence Lutsen 4 , Jean Manca 4 , Donal DC Bradley 1
1 Physics, Imperial College London, London United Kingdom, 2 Chemistry, Imperial College London, London United Kingdom, 3 Asulab, The Swatch Group R&D Ltd, Marin Switzerland, 5 Chemistry, Materia Nova, Mons Belgium, 4 IMEC, Hasselt University, Diepenbeek Belgium
Show AbstractThe prospect of cheap, flexible and lightweight transistors has generated significant scientific and commercial interest in polymer thin film transistors (TFTs). To realise this potential, the challenge is to be able to mass produce polymer TFTs in a roll-to-roll process. Since many organic semiconductors, polymer insulators and metal inks are solution processable at room temperature and pressure, considerable attention has been given to printing polymer TFTs. Gravure printing is a well established printing technique for high throughout applications in the graphical art community. Here we demonstrate the gravure printing of state-of-the-art, top-gate polymer TFTs on flexible plastic substrates.Devices are bottom-contact, top-gate polymer TFTs for use in a flexible liquid crystal display. Indium tin oxide source and drain contacts are pre-etched on a plastic substrate. First we demonstrate the ability to gravure print a thin film of poly(3-hexylthiophene) (P3HT) for use as the active layer in a TFT, with a spin coated dielectric and evaporated gate contact. The molecular weight and choice of solvent are found to strongly influence the mobility of gravure printed P3HT. Secondly, we gravure print both the P3HT and the dielectric layers to demonstrate the ability to create a sufficiently good semiconductor-dielectric interface for transistor action to occur. Finally, we gravure print four layers to fabricate a TFT: P3HT as the active layer, two dielectric layers and a silver ink gate contact. We were able to achieve an ON/OFF ratio of >104 and mobility of 0.03cm2/Vs, which compares very favourably with the performance of spin coated P3HT TFTs. We thereby demonstrate the viability of gravure printing for high throughput production of polymer TFTs.This work is part of the European Commission funded CONTACT project.
10:15 AM - G13.3
The Interplay of Materials in Printed Electronics.
Jurgen Daniel 1 , Ana Arias 1 , Beverley Russo 1 , Brent Krusor 1 , Sanjiv Sambandan 1 , Tina Ng 1
1 , PARC, Palo Alto, California, United States
Show AbstractPrinting technologies such as inkjet printing for electronics have received increased attention over the past years. Inkjet printing is promising for low-cost or large-area applications such as displays, solar cells or sensor circuits. It also can simplify manufacturing and enable possibly more cost-effective methods such as roll-to-roll processing.With the adoption of printing technologies for electronic circuits, new problems occur regarding the process sequence, the materials and the device structures. Electronics, such as organic electronics, based on photolithography and evaporation does not face many of the challenges. For example, jet-printing requires suitable surface properties, particularly for reliable printing over large areas. Unoptimized conditions will result in defects caused by dewetting or excessive spreading of the ink.Conventional OTFTs are often fabricated using silicon dioxide gate dielectrics with a hydrophobic silane functionalization in order to improve the molecular ordering of the organic semiconductor. However in an all-printed flexible electronic circuit the employed materials and processes change. Organic gate dielectrics are used and surface functionalization using silane chemistry does not yield reliable low-surface energy surfaces. In our standard processes, we employ a polyvinylphenol (PVP)-based gate dielectric, jet-printed silver nanoparticles for gate, source and drain contacts and the polythiophene PQT-12 as the organic semiconductor. All materials are solution deposited. A thin hydrophobic polymer is deposited onto the surface before semiconductor deposition. However this layer also partially covers the contacts and can cause a significant contact resistance.We have developed a novel overcoating method in which a jet-printed pattern acts as a template. Using this method, the contact resistance in TFTs can be significantly reduced. Moreover, the contacts can be coated with a variety of different materials, depending on what work function is desired.A similar template-assisted printing method is promising for electronic circuits with reduced accuracy requirements for layer-to layer alignment. We have fabricated organic PQT-12 TFTs on flexible substrates with mobilities around 0.04 -0.08cm2/Vs and the performance of pixel circuits was suitable for driving bistable displays.Our processes have been applied to the fabrication of active-matrix pixel circuits on flexible substrates and with these, electrophoretic displays have been demonstrated. Similar jet-printing processes were used to prototype polyvinylidene fluoride (PVDF) - based polymer piezo- and pyroelectric sensors and their readout buffer circuits. The sensors include temperature sensors, MEMS accelerometers, pressure sensors and acoustic sensors for detecting blast events on the battlefield.
10:30 AM - **G13.4
The Quest for the TFT Fountain of Youth.
James Sturm 1 , B. Hekmatshoar 1 , K. Cherenack 1 , S. Wagner 1
1 , Princeton University, Princeton , New Jersey, United States
Show Abstract11:00 AM - G13: Fabrication
BREAK
11:30 AM - **G13.5
Photolithographic Patterning of Organic Semiconductors.
George Malliaras 1 2
1 Materials Science, Cornell University, Ithaca, New York, United States, 2 Cornell NanoScale Facility, Cornell University, Ithaca, New York, United States
Show Abstract12:00 PM - G13.6
High-resolution Electrohydrodynamic Jet Printing Method for Nanofabrication in Electronics and Biotechnology.
Jang-Ung Park 1 , John Rogers 1
1 Materials Science and Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractNon-contact solution printing methods such as thermal or piezoelectric inkjet are attractive due to their compatibility with various materials and substrates. Interests in their applications in electronics and biotechnology, where requirements on resolution can be demanding, have grown rapidly in recent years. We have previously demonstrated an electrohydrodynamic jet (e-jet) printing method in which diverse functional organic / inorganic inks (single walled carbon nanotubes, nanoparticles, conducting / insulating polymers, etc) are ejected with intrinsic pulsations, rather than drop-on-demand ejection, and its use for fabrication of flexible transistors as an application example in electronics. This talk describes the digitalized operation of e-jet printing in drop-on-demand mode, and its use for single or double stranded DNA printing with the enhanced resolution (lateral feature size) approaching 100 nm. DNA aptamer-based biosensors and DNA-programmed nanoparticle assembly that use spotted arrays of DNA are illustrated for applications in biotechnology. Also, we present results on charge printing using e-jet, including the experimental and theoretical studies on time-variant charge distributions, with applications for nanoparticle assembly and diode fabrication with aligned arrays of single walled carbon nanotubes.
12:15 PM - G13.7
Bright Inkjet Printed Organic Light Emitting Diodes using Iridium Based Macromolecules.
Madhusudan Singh 1 3 , Takashi Kondou 2 , Hyunsik Chae 2 , Jesse Froehlich 2 , Sheng Li 2 , Amane Mochizuki 2 , Ghassan Jabbour 1 3
1 School of Materials, Arizona State University, Tempe, Arizona, United States, 3 Advanced Photovoltaics Center, Arizona State University, Tempe, Arizona, United States, 2 , Nitto Denko Technical Corporation, Oceanside, California, United States
Show AbstractWe present the first results of printing bright solution-processable organic light emitting diodes based on electrophosphorescent Ir(III) macromolecules. The macromolecules are incorporated as guest molecules in a polymer-based ink containing a hole transporting polymer, poly(9-vinylcarbazole) (PVK) and an electron transporting material, 2-4-biphenylyl-5-4-tertbutyl-phenyl-1,3,4-oxadiazole (PBD), printed in air on a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) spin-coated on indium tin oxide (ITO). An archetypal exciton-blocking layer consisting of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was thermally evaporated onto the printed ink layers, followed by a LiF/Al cathode. Photoluminescence (PL) spectrum of the printed ink on glass indicates that a significant density of states (corresponding to the PVK:PBD exciplex) exists in [420nm,460nm] which can compete with the macromolecule emission (520 nm) in the electroluminescence (EL). Since such energy states lie significantly above the guest energy levels, these are expected to participate in the EL if a) guest states are saturated or, b) carrier transport to the guest states is inhibited by poor transport. Measurements on devices printed on PEDOT:PSS/ITO/glass indicate that the devices exhibit high luminances (~5700 cd/m
2 at 250 mA/cm
2) and a fairly consistent quantum efficiency (1-1.5%) across a wide range of luminances. At the cost of lower brightness (~3800 cd/m
2) and lower quantum efficiencies (0.5-1%) for the same drive currents, we find that emission from the PVK:PBD exciplex is eliminated upon insertion of a hole-transporting cross-linkable polymer layer (D1) in the device structure at the hole-injecting contact. To study the morphology of the printed layers, we use white light interferometry as a non-contact technique. The results reveal agglomeration of the Gibbs-Marangoni effect from individual drops when multiple drops are printed, to form large scale channel structures. The width of these channels appears to be governed by spacing of the drops chosen during printing of the ink (s1). A relatively low surface roughness (~24-50 nm, depending on the presence of D1) is obtained by using a relative lateral offset, (±s1/2,±s1/2), during printing of multiple layers of the ink to fill up these channels. In addition to the future prospect of bright devices with low drive currents and high quantum efficiencies, a systematic modification of the ligands attached to the common central scaffolding in these macromolecules permit the synthesis of classes of materials that emit in different regions of the visible spectrum, enabling the development of a single overall processing methodology that yields all the materials necessary for white lighting and fully functional displays. In conjunction with the inkjet printing technology demonstrated in this work, this has the potential to yield low-cost, large-area manufacturing of these devices. Email:
[email protected]12:30 PM - G13.8
Laser Direct Write Printing of Small Molecule Organic Materials for Light Harvesting and Emitting Applications.
Nicholas Kattamis 1 , Neal McDaniel 2 , Catherine Crouch 3 , Stefan Bernhard 2 , Craig Arnold 1
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 2 Chemistry, Princeton University, Princeton, New Jersey, United States, 3 Physics, Swarthmore, Swarthmore, Pennsylvania, United States
Show AbstractSmall organic molecular semiconductors have particular benefits in organic light emitting diode and light harvesting applications due to increased lifetimes in oxygenated environments leading to ease of fabrication and minimal packaging constraints. In order to create these optoelectronic devices on lower temperature, flexible substrates used in large area electronics, new printing techniques have been developed. Here we discuss a new non-contact laser forward transfer approach for the printing of such novel materials. Although laser based methods typically expose delicate organic material to large ultraviolet intensities and rapid heating, here we report on the use of a thick polymer film which is used to absorb the incident laser energy resulting in mechanical deformation that leads to the transfer of material to the substrate of interest. Individual droplets of solution smaller than 10μm are dispensed on the surface of interest while a computer controlled manipulation stage combined with a high repetition rate pulsed laser allows for rapid pattern formation on arbitrary surfaces. Optoelectronic characterization of the deposited materials is presented and we demonstrate the ability to pattern multicolor luminescent arrays with high resolution.
12:45 PM - G13.9
Fully Printed Polyelectrolyte-Gated OFET Operating at Low Voltages.
Hiam Sinno 1 , Isak Engquist 1 , Magnus Berggren 1
1 Science and Technology, Linkoping University, Norrköping Sweden
Show AbstractPrinted organic electronics combine the flexibility of organic materials with low cost, robustness, and high throughput of printing technologies. Organic field effect transistors (OFETs) serve as a primary candidate for incorporation into small printed circuits via roll-to-roll production. The structure of an electric double-layer capacitance gate (EDLC-)OFET differs from that of a traditional OFET by being electrolyte-gated rather than dielectric-gated. This enables EDLC-OFETs to form electric double-layer capacitors (EDLCs) at the gate/electrolyte and electrolyte/semiconductor interfaces, induced by ion/proton migration in the polyelectrolyte caused by the gate biasing. Consequently, this allows EDLCs with high capacitances; possible to operate at low voltages while being more tolerant to relatively long channel lengths and rendering them less sensitive to the gate insulator thickness. Currently, EDLC-OFETs’ fabrication process involves a variety of clean-room processing steps such as photolithography, spin-coating, and vacuum evaporation. In this work, we present the fully printable EDLC-OFET, fabricated using the inkjet printing technique. Materials used for the fabrication of the different parts of the transistor involved PEDOT:PSS for the electrodes, P3HT for the organic semiconductor layer, and PSSH for the polyelectrolyte layer. Low-voltage operation in the range of 1 V is demonstrated, as well as response times of around 1 ms. This result paves the way towards roll-to-roll fabrication and towards making low cost, low-voltage operating printed electronics a reality.
G14: From Devices to Circuits and Systems II
Session Chairs
Thursday PM, December 04, 2008
Room 207 (Hynes)
2:30 PM - **G14.1
Solvent Deposited and Modified Organic Thin Film Transistors.
Tom Jackson 1
1 , Pennsylvania State University, University Park , Pennsylvania, United States
Show Abstract3:00 PM - G14.2
Disposable and Flexible Optical pH Sensor Developed using Line Patterning Technique and Thin Film of Polyaniline.
Rafaela Paschoalin 2 1 , Washington Melo 1 , Silvio Crestana 3 , Paulo Herrmann 1 4
2 , UNICEP, Sao Carlos, Sao Paulo, Brazil, 1 Agricultural Instrumentation, Embrapa Agricultural Instrumentation, Sao Carlos, Sao Paulo, Brazil, 3 , Embrapa, Brasilia, Distrito Federal, Brazil, 4 National Nanotechnology Laboratory for Agribusiness , Embrapa Agricultural Instrumentation, Sao Carlos, Sao Paulo, Brazil
Show AbstractIn the last ten years the interest for developing new sensors for industry, agriculture, the environmental, and applications in medicine has increased. The line patterning technique [1] was used to make a mask to developing a low-cost optical pH sensor, built in the stripes of poly(ethylene terephthalate) (PET) film, using the features of a thin film of polyaniline (PANI) in the emeraldine oxidation state [2] doped with HCl, by in-situ chemical polymerization. The measurements occurred with conductive polymers doped and dedoped, and were used to evaluated the pH of natural water. The differential scanning calorimetry (DSC) of the poly(ethylene terephthalate) (PET) film was obtained, to characterize the measurement of the enthalpy. The DSC was taken using TA INSTRUMENTS, Model DSC Q100. The temperature associated with transitions of the PET, as a function of time, was 251.7 °C. The UV-Vis absorption of the samples was investigated using a SHIMADZU spectrometer set up in the wavelength range of 300nm to 1100nm. The technique was used to evaluate the effect of the temperature to do the syntheses - responsible to change the thickness of the thin film onto PET - as well the optical response of the samples under the influence of the distinct pH in the laboratory and natural water. The relation between common techniques, used to measure the value of water pH (Horiba) in the natural condition, was compared. The images to investigate the thickness and morphology of the thin film of the PANI adsorbed onto PET were obtained using an Atomic Force Microscope (AFM) Nanoman V, from VEECO. A silicon rectangular shaped cantilevers, with spring constant (K) 2.0 N.m-1, was chosen. The scan rate of the samples was 1.5 Hz and “quasi” non-contact mode, at room temperature, was used. The color change of the samples, in function of pH, after 5, 10 and 15 minutes, was obtained in buffer solution, to evaluating the appropriate immersion time of the PET/PANI. The stripes showed a reversible color features upon variation of the pH. The pH ranges used to calibrate the optical sensor were from 2.0 to 12.0. The behaviors of absorption spectra were obtained with the stripes under buffers solutions of different pH, with steps of 0.5, from 4.0 to 8.0. The sensitivity and reproducibility were calculated. The investigations open new opportunities to develop optical “throw-away” sensors, from the optical properties of the thin film of the polyaniline and nanofibers of PANI onto PET. Work supported by CNPq, (Brazilian funding agency) under contract number 485921/2006-5, 49.0807/2007-0, the facilities from Embrapa Agricultural Instrumentation and Macroprogram 1 (MP1) - 01.05.101.00[1]E. C. Venâncio, L. H. C. Mattoso, P. S. P. Herrmann Junior, A. G. MacDiarmid, Sensors and Actuators B, 130, 723–729, (2008)[2]A. E. Job, P. S. P. Herrmann, D. O. Vaz, L. H. C. Mattoso, J. Applied Polymer Science, 79, 1220, (2001).
3:15 PM - G14.3
Multi-electrode Electrochromic Device Applications.
Ece Unur 1 , Pierre Beaujuge 1 , John Reynolds 1
1 Chemistry, University of Florida, Gainesville, Florida, United States
Show AbstractElectrochromism, change or bleaching of color with applied potential, is one of the most eminent properties of conjugated polymers and it originates from electronic structure changes induced upon redox doping/dedoping. Color tuning in conjugated polymers is possible by synthetic and physical means. New colors can be accessed either by structural modifications that allow the alteration of electronic properties (e.g. bandgap) or by newly developed analytical methods/devices that utilize the optical properties of existing polymers. The absorption spectra of the donor-acceptor based poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives used in this work span the full visible spectrum in their neutral state, and bleach upon oxidation due to the formation of lower energy states that are created at the expense of the HOMO-LUMO electronic transitions. The dual polymer film technique, which is an analytical method derived from color mixing theory, generates new colors by transmitting light through two films stacked together in an electrolyte solution and under separate potentiostatic control. Here, we report on three new multi-electrode electrochromic window devices, made possible by the dual polymer film technique, comprising multiple active electrodes and non-color changing counter electrodes (polymer supplied by CIBA Specialty Chemicals). Having spray-processable RGB to transparent switching polymers available along with non color changing, yet electroactive, counter electrode polymers for the first time, multi-electrode electrochromic devices under separate potentiostatic control promise a myriad of colors by combining optical properties of two or more films.
3:30 PM - G14.4
Functionalization of Carbon Nanotubes Unsing Conjugated Block Copolymers.
Lei Zhai 1 , Jianhua Zou 1 , Huo Qun 1
1 NanoScience Technology Center and Department of Chemsitry, University of Central Florida, Orlando, Florida, United States
Show Abstract3:45 PM - G14: Systems 2
BREAK
G15: Energy Generation and Storage II
Session Chairs
Thursday PM, December 04, 2008
Room 207 (Hynes)
4:15 PM - **G15.1
Correlating Morphology and Performance in Polymer Solar Cells.
David Ginger 1
1 Chemistry, University of Washington, Sapporo, Hokkaido, Japan
Show Abstract4:45 PM - G15.2
Solution-processed, Patterned Metal Top Contacts for Efficient Polymer Solar Cells.
Claudio Girotto 1 2 , Barry Rand 1 , Soeren Steudel 1 , Afshin Hadipour 1 , Jan Genoe 1 , Paul Heremans 1 2
1 Polymer and Molecular Electronics, IMEC vzw, Leuven Belgium, 2 ESAT, Katholieke Universiteit Leuven, Leuven Belgium
Show Abstract5:00 PM - G15.3
Substituent Effects in Pentacene Derivatives: Gaining Control over Band Gaps and Photo-Oxidative Resistances.
Glen Miller 1 , Irvinder Kaur 1 , Wenling Jia 1 , Ryan Kopreski 1
1 Chemistry & Materials Science, University of New Hampshire, Durham, New Hampshire, United States
Show AbstractA combined experimental and computational study of a series of substituted pentacenes including halogenated, phenylated, silylethynylated and thiolated derivatives is presented. Experimental studies include the synthesis and characterization of six new and six known pentacene derivatives and a kinetic study of each derivative under identical photo-oxidative conditions. Structures, HOMO-LUMO energies and associated gaps were calculated at the B3LYP/6-311+G**//PM3 level while optical and electrochemical band gaps were measured experimentally. The combined results provide for the first time a quantitative assessment of band gaps and photo-oxidative resistances for a large series of pentacene derivatives as a function of substituents. The persistence of each pentacene derivative is impacted by a combination of steric resistance and electronic effects as well as the positional location of each substituent. Silylethynyl substituted pentacenes like TIPS-pentacene possess small band gaps but are not the longest lived species under photo-oxidative conditions, contrary to popular perception. A pentacene derivative with both chlorine substituents in the 2,3,9,10 positions and o-alkylphenyl substituents in the 6,13 positions is longer lived than TIPS-pentacene. Of all the derivatives studied, alkylthio- and arylthio- substituted pentacenes are most resistant to photo-oxidation, possess relatively small band gaps and are highly soluble in a variety of organic solvents. These results have broad implications for the field of organic molecular electronics where OFET, OLED and other applications can benefit from highly persistent, solution processable pentacene derivatives.