Symposium Organizers
Michael L. Chabinyc University of California-Santa Barbara
David Gundlach National Institute of Standards and Technology
Jenny Nelson Imperial College London
Takao Someya University of Tokyo
D2: Materials Design and Synthesis
Session Chairs
Tuesday AM, December 01, 2009
Republic B (Sheraton)
9:30 AM - **D2.1
Small-Molecule Design for Organic Electronics.
John Anthony 1
1 , University of Kentucky, Lexington, Kentucky, United States
Show AbstractThe ease with which small-molecule organic semiconductors can be functionalized allows a single chromophore framework to be tuned for use in a myriad of electronic applications. Careful selection of substituents allows tuning of both solubility and crystal packing, allowing optimum structures for both film morphology and charge transport to be dialed in by careful structure-property studies. Additional substituents on the chromophore can be added to improve stability, shift phase transitions, or change the dominant carrier type for the material. Using 4, 5 and 6 fused-ringed acenes and heteroacenes as the chromophore, our straightforward functionalization approach has created organic materials for use in high-performance organic transistors and organic solar cells. The crystal-packing arrangements for these two types of devices are dramatically different. This talk will examine how materials with two-dimensional pi-stacking arrangements yield high-performance transistors, and how subtle tuning of the substituents can further improve performance and alter solubility. In the optimum case, hole mobility as high as 5 cm2 / Vs was observed from a dip-cast film. Structure-property relationships in organic transistors are also explored in high-quality single crystals, showing how changes in crystalline order changes the intrinsic carrier properties of a homologous series of materials. In the case of bulk heterojunction organic solar cells, substitution of the acene chromophore with small electron-withdrawing groups yielded effective acceptors in blends with polythiophene donors. In this case, materials with strong pi-stacking interactions yielded the poorest-performing solar cells. In contrast, materials with weak, 1-dimensional pi-stacking interactions yielded the best performance, with power conversion efficiencies greater than 1.5% in these fullerene-free blends.
10:00 AM - D2.2
Highly-Ordered Donor-Acceptor Dyad Assemblies for Organic Electronics.
Jeffrey Mativetsky 1 , Marcel Kastler 2 , Rebecca Savage 1 , Desiree Gentilini 1 , Matteo Palma 1 , Wojciech Pisula 2 , Klaus Muellen 2 , Paolo Samori 1
1 , Institut de Science et d’Ingénierie Supramoléculaires (ISIS), Strasbourg France, 2 , Max Planck Institute for Polymer Research, Mainz Germany
Show AbstractElectron donor-acceptor (D-A) blends are commonly employed as the active material in prototypical organic solar cells and for producing ambipolar, i.e. both p- and n-type electrical transport. Nevertheless, blending generally applies to a limited number of material combinations and typically results in reduced long-range supramolecular order, which limits charge transport. As an alternative strategy for combining D and A functionalities, we have covalently coupled polyaromatic D and A moieties, each of which have a high propensity to self-assemble via π-stacking. The resulting dyad, based on the synthetic nanographene hexa-peri-hexabenzocoronene (HBC) and a perylene dye, is shown to self-assemble at multiple length scales, yielding architectures with nano-separated coaxial D and A domains and a high degree of supramolecular order: macroscopic extruded filaments display long-range crystalline order, nanofiber networks are produced by spin-coating, and ordered dense monolayers with a lamellar packing are formed by physisorption at the solution-HOPG interface [1]. Moreover, highly uniform mesoscopic ribbons bearing atomically flat facets self-assemble upon solvent-vapor annealing. As a first step towards demonstrating the potential of such D-A architectures in organic electronic applications, electrical characteristics revealing ambipolar transport were measured. [1] J. M. Mativetsky, M. Kastler, R. C. Savage, D. Gentilini, M. Palma, W. Pisula, K. Müllen, P. Samorì, Adv. Funct. Mater. 2009, in press DOI: 10.1002/adfm.200900366.
10:15 AM - D2.3
Synthesis and Processing Monodisperse Oligo(fluorene-co-bithiophene)s into Oriented Films by Thermal and Solvent Annealing.
Lichang Zeng 1 , Feng Yan 1 , Simon Wei 1 , Shaw Chen 1 2
1 Chemical Engineering, University of Rochester, Rochester, New York, United States, 2 Laboratory for Laser Energetics, University of Rochester, Rochester, New York, United States
Show AbstractOrganic materials with an extended π-conjugation have found numerous potential applications to electronics and photonics, most notably in light-emitting diodes, field-effect transistors, and solar cells. Conjugated polymers and oligomers can be prepared into thin films through solution processing across a large area, thus offering a cost advantage over small molecules that are typically deposited by vacuum sublimation. Uniaxial alignment of conjugated backbones offers additional desirable features, such as polarized light emission to obviate polarizers in liquid crystal displays and anisotropic charge transport to suppress cross-talk in logic circuit and pixel switching elements. A series of oligo(fluorene-co-bithiophene)s, OF2Ts, have been synthesized and characterized to investigate the effects of oligomer length and pendant aliphatic structure on glassy-nematic mesomorphism. The OF2Ts comprising more than one repeat unit and their polymer analogue, PF2T, carrying 52 number-average repeat units, possess the highest occupied molecular orbital energy level at –5.3±0.2 eV, but the anisotropic field-effect mobilities increase with the oligomer length. Spin coating from high-boiling chlorobenzene with and without subsequent exposure to saturated chlorobenzene vapor constitute solvent-vapor annealing and quasi-solvent annealing, respectively. Solvent-vapor annealing yields monodomain glassy-nematic films in which OF2Ts are aligned as well as with thermal annealing. Quasi-solvent annealing, however, amounts to kinetically trapping a lower orientational order than solvent-vapor or thermal annealing. Alignment of OF2Ts through solvent annealing is also achieved on photoalignment layers, without resorting to high-temperature baking of polyimide alignment layer, demonstrating the first all-room-temperature process for large-area monodomain glassy-nematic films of conjugated oligomers. While amenable to thermal annealing at elevated temperatures, PF2T shows no alignment at all following either strategy of solvent annealing.
10:30 AM - D2.4
Efficient Light Emitting Devices Based on Platinum-Complexes Anchored Polyhedral Oligomeric Silsesquioxane Materials.
Xiaohui Yang 1 , Jesse Froehlich 2 , Hyun Sik Chae 2 , Brett Harding 2 , Sheng Li 2 , Amane Mochizuki 2 , Ghassan Jabbour 1
1 School of Materials and Photovoltaic Center, Arizona State University, Tempe, Arizona, United States, 2 , Nitto Denko Technical Corporation, Oceanside, California, United States
Show AbstractPolyhedral oligomeric silsesquioxanes (POSS) macromolecules bearing the carrier-transporting moieties or chromophores provide the advantages of both small-molecule and polymer light emitting materials, e.g. high purity and solution processability, showing great potential in applications related to organic light emitting devices. In this contribution, synthesis, photo-physical and electrochemical characterizations of platinum-complex anchored POSS macromolecules are reported. Organic light emitting devices based on these POSS materials showed external quantum efficiency of 7.9%, luminous efficiency of 17.7 cd/A and power efficiency of 5.7 lm/W at 500 cd/m2, which was significantly higher than that of the counterpart device with physical blend of the Pt-complex and polymer matrix (3.6%, 2.9 lm/W, 7.8 cd/A) and represented noticeable improvement of the device efficiency for solution-processable phosphorescent excimer devices. Furthermore, the ratio of monomer and excimer emission intensity in the electroluminescent spectrum as well as the device efficiency increased with decrease of the Pt-complex moiety containment in the POSS macromolecules, which can be attributed to diminished interaction among the Pt-complex moieties.
10:45 AM - D2.5
New Copolymers Based on Acenaphto[1,2-b]thieno[3,4-e]Pyrazine for Transistor and Solar Cell Applications.
Pierre-Luc Boudreault 1 2 , Nobuyuki Miyaki 2 , Rajib Mondal 2 , Ming Tang 2 , Zhenan Bao 2 , Mario Leclerc 1
1 Chemistry, Universite Laval, Québec City, Quebec, Canada, 2 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractPhotovoltaic cells have attracted much attention over the past few years. Promising performances have been obtained from devices using the bulk-heterojunction architecture and using [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) as the acceptor. Some polymers have been extensively studied like poly(p-phenylenevinylene)s, polythiophenes and polyfluorenes. Polycarbazoles and polydibenzosiloles are interesting air-stable conjugated polymers. Recently, great performances in solar cells have been obtained with 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT) copolymerized with carbazole as the comonomer reaching 6% of power conversion efficiency (PCE) and external quantum efficiency (EQE) approaching 100%. The performances were a little lower with dibensilole but still very interesting.The synthesis of a new electron withdrawing unit that will help lower the bandgap of the polymers needs to be synthesized to increase the PCEs furthermore. One of the most important thing to consider when characterizing a new low bandgap polymer is the hole mobility. With higher mobilities, the solar cells should help increasing the short contact current (JSC) and also decrease the charge recombination within the film. To achieve such a task, we decided to focus on a monomer based on acenaphtho[1,2-b]thieno[3,4-e]pyrazine which is highly rigid and should help the charge transport properties of the synthesized materials.We have synthesized different copolymers based on these comonomers via the Suzuki cross-coupling polymerization using different catalyst systems to obtain the best possible molecular weights. Optical and electrochemical bandgaps were obtained from UV-vis spectroscopy and cyclic voltammetry, X-ray diffraction was performed on thin films and powder to study the organization of the materials. We then fabricated field-effect transistors and solar cells to get the performances. As predicted, the rigid comonomer increased the charge transport properties with mobilites as high as 0.04 cm2.(V.s)-1 with a good ION/IOFF ratio (106). On the other hand, we also made solar cells from these polymers but we could only afford low power conversion efficiencies (0.6%). We believe that higher molecular weights could help increase these performances in solar cells and could possibly help getting close mobilities in the 0.1 cm2.(V.s)-1 range.
11:30 AM - **D2.6
Strategies Towards Robust and Stable High Performance Polymer Semicondcutors.
Martin Heeney 1 , Weimin Zhange 1 , Mohammed al-Hashimi 1 , Rick Hamilton 1 , Iain McCulloch 1 , James Kirkpatrick 2 , Thomas Anthopoulos 2 , Jeremy Smith 2
1 Dept. Chemistry, Imperial College London, London, London, United Kingdom, 2 Dept. Physics, Imperial College London, London United Kingdom
Show AbstractThe performance of organic semiconducting polymers has shown impressive progress recently, to a combination of improved molecular design and enhanced fabrication techniques, with several materials exhibiting p and n-type mobilities in excess of unity. Nevertheless operational and storage stability remains an important issue, particularly in devices driven under high current density or operated in a in bottom gate configuration where the semiconductor is exposed to the ambient atmosphere. In this work, we explore strategies to chemically modify the polymer backbone structure, principally by ring fusion with a variety of bridging substituents, leading to changes in both the backbone configuration and microstructure, as well as the electronic energy levels of the molecular orbitals. The effects of the changes in molecular structure on transistor and solar cell performance and air stability are discussed.
12:00 PM - D2.7
Carborane-Containing Polyfluorenes: New Materials with Unique Properties.
Joseph Peterson 1 , E. Coughlin 1 , Yoan Simon 1 , Kenneth Carter 1
1 Polymer Science and Engineering, University of Massachusetts - Amherst, Amherst, Massachusetts, United States
Show AbstractWe report the synthesis of new (ortho and para) carborane-containing fluorene monomers and have polymerized these to create a conjugated hybrid carborane-fluorene polymers. The nature of the polymerization of the carborane fluorene monomers was investigated and found to be self-limiting, most likely due to its bent conformational structure. In the case of the incorporation of o-carborane into polymers, it was found to contribute to the conjugation of the system and gave rise to a new lower energy emission in the solution state. In the solid state, the o-carborane materials are stable pure green emitters. The degradation of the o-carborane cages was found to significantly influence the solution fluorescence spectra leading to the conclusion that the bonding structure of the cage can directly influence the behavior of the conjugated polymer system. The incorporation of carborane into the backbone of conjugated polymers may provide an important route to new materials for sensors and light emitting devices while at the same time serving as a platform for further study of the nature of carborane cages.
12:15 PM - D2.8
Fluorinated Poly(N-vinylcarbazole) Host for Triplet Energy Confinement on Phosphorescent Emitter in Organic Light-emitting Diodes.
Yukitami Mizuno 1 , Isao Takasu 1 , Shuichi Uchikoga 2 , Shintaro Enomoto 1 , Tomoaki Sawabe 1 , Akio Amano 1 , Atsushi Wada 1 , Jiro Yoshida 1 , Tomio Ono 1
1 Corporate Research & Development Center, Toshiba corp., Kawasaki Japan, 2 Toshiba Research Europe,Ltd, Toshiba corp., Cambridge United Kingdom
Show AbstractThis paper reports that triplet energy level of poly(N-vinylcarbazole) can be higher by fluorination, and organic light-emitting diodes (OLEDs) with the fluorinated poly(N-vinylcarbazole) as host materials show 1.8 times higher luminous efficiency than OLEDs with non-substituted poly(N-vinylcarbazole) (PVK).Highly efficient phosphorescent organic light-emitting diodes (OLEDs) need host molecules with high triplet energy level to confine the excited energy on guest molecules. Carbazole (Cz) has been widely used as a building block for the host materials because of its relatively high triplet energy level. HOMO-LUMO energy gap of the host materials requires to be wider for a higher triplet energy level. Calculations at DFT-B3LYP level with GAUSSIAN 03 program were carried out to estimate the energy gap of some Cz with fluorine substituents at various positions. These calculation results suggested that the energy gap of Cz can be widened by fluorination at some appropriate positions. A characteristic of the energy gap widening by fluorination is its controllability by the number and position of fluorine substituents. 2,7-Difluorocarbazole (F-Cz) was synthesized by coupling 3-fluorophenyl trifluoromethanesulfonate and 3-fluoro aniline in the presence of palladium catalyst. We estimated the energy gap of Cz and F-Cz from absorption spectra to be 3.59 eV and 3.71 eV, respectively. To confirm the wide-gap effect of F-Cz on OLED device, we synthesized a solution-processable polymer host, poly(N-vinyl-2,7-difluorocarbazole) (F-PVK), which has F-Cz as pendant groups. The F-PVK was prepared by the free-radical polymerization of F-Cz with azobisisobutyronitrile (AIBN) after vinylation of the carbazole under basic condition. Polymer OLEDs are the subject of intensive research because of their potential for large-scale and low-cost device fabrication by solution processes such as spin-coating, ink-jet printing and gravure printing. Our investigated OLED devices were consisted of an ITO/PEDOT:PSS/EML/CsF/Al multilayered structure. The EML composed of PVK or F-PVK, 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7), and a blue phosphorescent dopant, iridium(III)bis [(4,6-di-fluorophenyl)-pyridinato-N,C2'] picolinate (FIrpic). The OLED device with F-PVK showed 1.8 times higher maximum current efficiency (27 cd/A) than that with PVK (15 cd/A). The phosphorescence spectra of PVK and F-PVK were measured at 77 K for estimation of the triplet energy level of these polymers. The spectra of F-PVK was blue-shifted from that of PVK. The observed triplet energy of PVK and F-PVK were 2.61 eV and 2.69 eV, respectively. Triplet energy level of F-PVK was higher than that of FIrpic (2.62 eV). These results indicate that F-PVK as host materials can confine the triplet energy on guest molecules to improve luminous efficiency of OLED.
12:30 PM - **D2.9
Organic Electronics at the Interface with Biology.
George Malliaras 2 1
2 Department of Bioelectronics, Centre Microelectronique de Provence, Gardanne France, 1 Department of Materials Science, Cornell University, Ithaca, New York, United States
Show AbstractThe emergence of organic electronics – a technology that relies on carbon-based semiconductors to deliver devices with unique properties – represents one of the most dramatic developments of the past two decades. A rapidly emerging new direction in the field involves the interface with biology. The “soft” nature of organics offers better mechanical compatibility with tissue than traditional electronic materials, while their natural compatibility with mechanically flexible substrates suits the non-planar form factors often required for biomedical implants. More importantly, their ability to conduct ions in addition to electrons and holes opens up a new communication channel with biology. The talk will focus in two emerging areas: (a) The development of biosensors using conducting polymer transistors, and in particular their integration with microfluidics to create multi-analyte sensors. (b) The development of active substrates for cell growth, in which a potential applied on a conducting polymer substrate controls cell density and morphology.
D3: Morphology and Characterization I
Session Chairs
Tuesday PM, December 01, 2009
Republic B (Sheraton)
2:30 PM - **D3.1
Electronic Structure of Organic/Organic Heterojunctions: The Case of the P3HT/PCBM Blend.
Zelei Guan 1 , Jongbok Kim 2 , Yueh-Lin Loo 2 , Antoine Kahn 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Chemical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractOrganic/organic heterojunctions are ubiquitous in organic-based thin film devices, and their electronic structures are therefore of prime importance. Injection layers, blocking layers, or charge separation layers depend on very specific interface molecular level alignment schemes that must be thoroughly understood. We take here the example of the interface between poly(3-hexyl thiophene) (P3HT) / [6,6]-phenyl C-61-butyric acid methyl ester (PCBM). The P3HT/PCBM blend is a standard, prototypical system for bulk heterojunction organic photovoltaic (OPV) cells. In question here is the relative position of the molecular levels of the donor (D) and acceptor (A) materials in the blend, given that LUMO(D) - LUMO(A) is linked to the charge separation process, and LUMO(A) - HOMO(D) is linked to the open circuit voltage (Voc) of the OPV cell. This talk presents a detailed ultra-violet and inverse photoemission spectroscopy (UPS, IPES) study of the electronic structure of the separate constituents of the blend, i.e. P3HT and PCBM, of the blend itself, and of the P3HT/C60 interface formed by vacuum evaporation of the fullerene on the polymer surface. The key question is whether or not the electronic structure of the D/A interface follows vacuum level alignment, i.e. the LUMO(A) - HOMO(D) gap equals the difference between the ionization energy (IE) of P3HT and the electron affinity (EA) of PCBM. The IE of P3HT, determined by UPS, varies between 4.5 and 4.9 eV, depending on preparation conditions, and the EA of PCBM, measured by IPES, is about 3.8 eV. Assuming vacuum level alignment at the P3HT/PCBM interface leads to a rather small LUMO(A) – HOMO(D) gap of 0.7 - 1 eV. However, photoemission investigations of other type II staggered gap organic heterojunctions where the LUMO of the acceptor is close to the HOMO of the donor have shown that some level of charge transfer occurs, which introduces an interface dipole and opens the LUMO(A) - HOMO(D) gap. We report here experiments on P3HT/C60, which show a 0.3-0.4 eV interface dipole that increases this gap. UPS and IPES investigations of the blend and of its interfaces with several conducting electrodes are under way and will be reported.
3:00 PM - D3.2
Scanning Photocurrent Study of Charge Injection and Photoconductivity in Pentacene Thin-film Transistors.
Adam Tsen 1 , Fabio Cicoira 1 2 , George Malliaras 1 , Jiwoong Park 1
1 , Cornell University, Ithaca, New York, United States, 2 , Institute of Photonics and Nanotechnology, Trento Italy
Show AbstractWhile the performance of organic thin-film transistors has improved dramatically over the years, the fundamental physics of charge injection and transport is not yet fully understood. One particular reason is due to the lack of spatial information in bulk electrical studies of such devices. In this work, we study the spatially-resolved electrical response of bottom-contacted pentacene thin-film transistors to a scanning, focused laser. We find that pentacene makes point-like contacts to the gold electrodes, and for the first time we are able to image these regions of efficient charge injection with diffraction-limited resolution. Furthermore, we show that locally-induced photoconductivity at these contacts can increase the overall current level by an order of magnitude. Our study not only presents a powerful and general new technique for the spatially-resolved electrical characterization of organic devices, but it reveals that efficient charge injection is still a major performance hurdle for gold-contacted pentacene transistors and an area that requires improvement.
3:15 PM - D3.3
Characterizing the Anisotropic Morphology and Device Performance of Solution Sheared Organic Thin Film Transistors.
Eric Verploegen 1 2 , Wen Ya Lee 1 , Joon Hak Oh 1 , Michael Toney 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, California, United States
Show AbstractSolution processing of small-molecule organic semiconductors offers a versatile route for fabricating organic thin-film transistors (OTFTs). Although the performance of solution processed OTFTs is often dwarfed by that of equivalent devices fabricated by vacuum-deposition methods, solution processing shows promise for producing low cost flexible electronics. Many solution processing techniques, such as drop casting and spin casting, result in films that have reduced ordering and poor uniformity, compared to vacuum deposited counterparts. We use solution shearing of small-molecule organic semiconductors to obtain well ordered uniform films for use as field effect transistors. This facile device fabrication technique results in oriented films with crystallite domains much larger than many other solution processing techniques. We use grazing incidence X-ray diffraction (GIXD) to characterize the molecular packing of the molecules, as well as their orientation relative to the shear direction. By measuring the device performance along several directions, relative to the shear direction, we are able to correlate the device performance to the morphological anisotropy of the films. We also investigate how modifications to the chemical structure upon the effect the morphology and performance of these devices. Gaining a deeper understanding of how the device performance relates to the molecular packing and orientation of the molecules will allow for the design of new high performance organic semiconductors.
3:30 PM - D3.4
Tuning the Emission Wavelength in Light Emitting Transistors Based on Substituted Oligoacenes.
Afshin Dadvand 1 3 , Hong Meng 2 , Federico Rosei 3 , Dmitrii Perepichka 1
1 Chemistry, McGill University, Montreal, Quebec, Canada, 3 Energie, Materiaux et Telecommunications, INRS, Varennes, Quebec, Canada, 2 Experimental Station, E.I. DuPont , Wilmington, Delaware, United States
Show AbstractOrganic Light Emitting Transistors (OLETs) are new thin-film optoelectronic devices that combine light-emission with the current control function of a transistor. OLETs can potentially simplify the architecture of matrix electroluminescent displays. A number of materials and device architectures have been tested within the OLET concept. Despite a remarkable progress towards improving the electroluminescent efficiency of these devices, the realized charge mobility still lags behind that of regular organic field-effect transistors. Recently, we have reported high charge mobility (>0.2 cm2/Vs) and remarkable environmental stability in OLETs based on substituted styryltetracene semiconductor.[1] We now show that the emission wavelength in these devices can be tuned (from green to blue) by altering the pi-conjugated core of the molecule. Further, one of these materials has produced an unusually narrow (<0.5 nm) blue emission band when driven in the transistor configuration. While this unusual emission quickly decays into a “regular” broad electroluminescence upon cycling the device, this unprecedented finding might be an important step towards development of an electrically pumped organic laser.[1] F. Cicoira, C. Santato, A. Dadvand, C. Harnagea, A. Pignolet, P. Bellutti, Z. Xiang, F. Rosei, H. Meng, D.F. Perepichka, J. Mater. Chem. 2008, 18, 158
3:45 PM - D3.5
Silicon Based Inorganic/Organic Hybrid Materials for Deep Blue PHOLEDs.
Soonnam Kwon 1 , Kyung Wee 1 , Sang Kang 1
1 Materials Chemistry, Korea University, Chochiwon, Chungnam Korea (the Republic of)
Show AbstractDeep blue PHOLED was achieved in the simple device structure of ITO/SiTPA/SiCBP : FIr6 10 wt%/SiTAZ/Liq/Al, where active layers were silicon based inorganic/organic hybrid materials of the types, SiTPA, SiCBP, and SiTAZ for HTL, EML host, and ETL respectively. Silicon incorporation into organic framework not only provided necessary morphological stability, but also engaged enhanced charge transporting capability and high triplet energy state essential to achieve highly efficient deep blue PHOLEDs. As a result, high performance silicon based HTL, EML host, and ETL materials were developed, exhibiting high charge mobility values in the range of 10-4 ~ 10-3 cm2V-1s-1 and high triplet energies of 2.84 eV, 3.05 eV, 2.88 eV, respectively. Even with the simple four layer device structure of PHOLEDs comprising silicon based active layers, maximum external quantum efficiency (EQE) of 17 % and CIE coordinates of (0.15, 0.23) were achieved. Moreover, an EQE of 15% was recorded at a luminance of 1000 cd m-1, which was the result of reduced efficiency roll-off due to the efficient confinement of FIr6 triplet energy by surrounding silicon based inorganic/organic hybrid materials developed in this work. Structures of inorganic/organic hybrid materials and their photo-physical properties as well as device physics for high performance deep blue PHOLEDs will be presented.
4:30 PM - **D3.6
Structure and Properties of Small Molecule-Polymer Blend Semiconductors and High-k Polymer Dielectric for Printable Organic Electronics
Do Yeung Yoon 1 , Jihoon Kang 1 , Nayool Shin 1 , Do Young Jang 1 , Young Eun Jo 1 , Yeong Sook Chung 1 , Vivek Prabhu 2 , Dean Delongchamp 2 , R. Kline 2 , Lee Richter 2 , David Gundlach 2 , John Anthony 3
1 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractRecent results on blend films of semiconducting small molecules and insulating polymers, which are promising as active layers for organic thin film transistors (OTFTs), will be presented together with results on printable high-dielectric gate insulaors. The blend films exhibit not only an excellent solution processability, but also superior performance characteristics (field-effect mobility, on/off ratio and threshold voltage) over those of neat small molecule semiconductors. We have investigated the phase segregation and ordering behavior by neutron reflectivity, spectroscopic ellipsometry, NEXAFS, and grazing-incidence x-ray diffreaction experiments for blend films prepared with different small molecule semiconductors with binder polymers of varying molecular mass, surface energy and crystallinity. Such structural characteristics provided the critical insight for understanding and improving the good electrical properties of blend semiconductors for printable electronic devices. We also investigated a high-dielectric polymer insulator as a printable gate dielectric in OTFTs. The novel design concept for obtaining high-dielectric constant (>10) polymers with high glass transition temperature and low surface energy was demonstrated.
5:00 PM - D3.7
Nanoscale Morphology of Bulk Heterojunctions in Organic Photovoltaics: Small Angle X-ray Scattering.
Michael Toney 1 , Chad Miller 1 , Roman Gysel 2 , Nichole Cates 2 , Zach Beiley 2 , Michael McGehee 2
1 Stanford Synchrotron Radiation Lightsource, SLAC, Menlo Park, California, United States, 2 Department of Material Science, Stanford University, Stanford, California, United States
Show AbstractSolar cells based on interpenetrating blends of a semiconducting polymer and a fullerene are becoming a viable technology due to the promise of low-cost manufacturing and reported power-conversion efficiencies above 6%. A rapid increase in efficiency over the last decade has been accomplished through materials design and morphology control. To be efficient, these bulk heterojunctions (BHJs) require sensitive control over materials morphology on the nanoscale: the polymer and fullerene phases must separate on a 10-20 nm length scale (exciton diffusion length) to prevent electron/hole recombination before the exciton reaches the interface. Hence, the morphology of this two-phase film is tremendously important, but is difficult to empirically assess.We describe the use of small angle x-ray scattering (SAXS) to study BHJ solar cells composed of poly(3-hexylthiophene) (P3HT) blended with the common electron accepting fullerene phenyl-c61-butyric acid methyl ester (PCBM). From these data we obtain the average length scale of the phase separation and can construct representative BHJ morphologies. The P3HT/PCBM BHJs were studied as a function of solvent used for spin casting, annealing temperature and time, and the blending ratio. We find that for most processing conditions the P3HT and PCBM phase separate on about a 15 nm length scale. Surprisingly, increased thermal annealing time and temperature do not affect the phase separation morphology significantly (although this does improve PH3T molecular order). Most remarkable, films cast in chlorobenzene show a well defined phase separation length of about 20 nm (peak in SAXS) that becomes smaller – 10 nm – and less well defined after solvent annealing. In contrast for dichlorobenzene, the morphology is less well defined and does not change much after solvent annealing. These morphological results will be compared with the device efficiencies.
5:15 PM - D3.8
High Solvent Pressure and High Temperature Solvent Annealing Studies of Regioregular Poly(3-hexylthiophene).
Htay Hlaing 1 , Tommy Hofmann 1 , Ben Ocko 1 , Chang-Yong Nam 2 , Charles Black 2
1 Condensed Matter Physics and Materials Sciences, Brookhaven National Laboratory, Upton, New York, United States, 2 Center for Functional Materials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractIt is well recognized that annealing, both solvent-free thermal and room temperature solvent mediated, improves the performance of bulk heterojunction organic photovoltaic devices. In our studies, we have combined high solvent pressure and high temperature annealing to further improve the order of regioregular poly(3-hexylthiophene) thin films where we have used grazing incidence angle x-ray scattering to quantify the degree of order. Without solvent, the lamellar ordering improves monotonically with increasing temperature and the best order, a coherence length of ~25 nm, is observed at 180 C. For the combined high solvent pressure and high temperature studies, carried out in a sealed cell under saturated conditions, the vapor pressure increases with increasing temperature. Under these conditions, using toluene, our findings show that the same improvement in the lamella order is achieved at much lower temperatures and that even better order is observed in the presence of solvents. Similar results have also been obtained for P3HT/PCBM blends. Complementary studies on the same samples have been carried out with AFM and FTIR. In addition, a simple model to explain the large thermal expansion, 10% between room temperature and 180 C, based on the thermal expansion of the n-alkanes will be presented. We hypothesize that the corresponding 10% contraction that occurs upon cooling back to room temperature may adversely affect device performance. These new results show a possible path towards achieving better control of the order and nano-phase separation and this may lead to improvements in organic photovoltaic devices.This work was supported by the U.S. Department of Energy,Division of Materials Science, under Contract No. DE-AC02-98CH10886.
5:30 PM - D3.9
Correlation of the Temperature-induced Structural Changes and Mobility in High Molecular Weight P3HT Films.
Souren Grigorian 1 , Siddharth Joshi 1 , Ullrich Pietsch 1 , Patrick Pingel 2 , Dieter Neher 2 , Ullrich Scherf 3
1 , University of Siegen, Siegen Germany, 2 , University of Potsdam, Potsdam Germany, 3 , University of Wuppertal, Wuppertal Germany
Show AbstractRegioregular poly(3-hexylthiophene) (P3HT) is one of the important members of poly(3-alkylthiophene) family with a strong influence of the main-chain length and bulkiness of the side chains on the charge carrier mobility. Temperature-dependent crystalline structure of spin coated thin films of high molecular weight regioregular P3HTs and its correlation with charge carrier mobility have been analyzed [1]. Thin films of P3HT were measured as a function of temperature (from room temperature up to 250°C). These investigations show a reversible change of the crystalline structure, where the (100) interlayer lattice spacing along the film normal continuously increases up to a temperature of about 220 °C and, in contrast, the in-plane π-π-distance becomes smaller compared to the values measured at room temperature. Structural changes are reversible and can be repeated several times. Temperature-dependent structural transformations of P3HTs thin films include modifications in interplanar lamellae distances; interstacking spacings and crystalline packing. The temperature-induced structural properties differ for thick and thin films, pointing to a surface/interface role in stabilization of the layer morphology. In contrast to the structural changes, the carrier mobility is rather constant in the temperature range from room temperature up to 100−120 °C, followed by a continuous decrease. For thick layers this drop is significant and the transistor performance almost vanishes at high temperature, however, it completely recovers upon cooling back to room temperature. The drop of the charge carrier mobility at higher temperatures is in contrast with expectations from the structural studies, considering the increase of crystalline fraction of the polycrystalline layer. Our electrical measurements underscore that the reduction of the macroscopic mobility is mostly caused by a pronounced decrease of the intergrain transport. The thermally induced crystallization along (100) direction and the creation of numerous small crystallites at the film−substrate interface reduce the number of long polymer chains bridging crystalline domains, which ultimately limits the macroscopic charge transport. [1] Joshi, S.; Pingel, P.; Grigorian, S.; Panzner, T; Pietsch, U; Neher, D.; Forster, M.; Scherf, U.; Macromolecules, Published Online, June 2009: DOI: 10.1021/ma900021w
5:45 PM - D3.10
Anisotropy of Charge Transport in Uniaxially Aligned Polythiophene Films for Field-effect Transistors.
Mi Jung Lee 1 , Dhritiman Gupta 1 , Ni Zhao 2 , Iain Mcculloch 3 , Martin Heeney 3 , Henning Sirringhaus 1
1 Physics department, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 2 Research lab of electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Chemistry, Imperial college of London, London United Kingdom
Show AbstractThe alkyl-substituted polythiophene polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), has recently been shown to exhibit a high mobility of up to 0.6 cm2/Vs and good shelf-stability in its so-called “terrace” phase obtained by medium temperature annealing [1]. An aligned “nano-ribbon” phase of PBTTT was also reported after higher temperature annealing [2]. In the nano-ribbon phase the backbone of the polymer chain has been found to be fully extended along the nano-ribbon width of 80-100 nm. Along the π-π* stacking direction the ribbons extend over several micrometers. In this study, polymer field effect transistors with nano-ribbon PBTTT were fabricated in different device architectures. In contrast to previous work [2] high field effect mobility above 0.4 cm2/Vs similar to those seen previously for the terrace phase could be achieved in nano-ribbon PBTTT films by controlling the channel interface. We have also developed a zone-casting deposition method for uniaxial aligment of the nano-ribbons. We have studied the anisotropy of charge transport in these films by low temperature electrical measurements and electrooptical charge modulation spectroscopy in order to achieve better understanding of the relative importance of intrachain and interchain charge transport in these high mobility films.[1] I. Mcculloch, et al., Nature Mater, vol. 5, 328 (2006)[2] D. M. Delongchamp, et al., ACS Nano, vol. 3, No. 4, 780 (2009)
D4: Poster Session I
Session Chairs
Michael Chabinyc
David Gundlach
Jenny Nelson
Takao Someya
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - D4.1
Electroabsorption Spectroscopy for Screening Electrode Functionalization in Organic Solar Cells.
Bradley MacLeod 1 , Noah Horwitz 1 , David Ginger 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractIt has been shown that performance of certain organic photovoltaics can be improved by tailoring the chemistry at the interfaces between the electrodes and the active layer. However, a detailed understanding of the effects of these modifications remains difficult because the interfaces are buried within the device. Further, the interaction of neighboring materials in situ can cause the effective potential offset between these layers to vary from what would be predicted by combining traditional potential measurements from electrochemistry and vacuum/air-based techniques. We use electroabsorption spectroscopy to measure changes to the built-in field of devices made from a series of polymers and modified electrodes. We compare the results with those expected based only on the differences in the measured electrode work functions to identify surface modifiers which induce additional conformational changes in the organic semiconductor at the interface, adding to the design rules for interfacial modifiers in organic photovoltaics.
9:00 PM - D4.10
Ambipolar Blends of Organic Semiconductors and Up-converting Materials for Photovoltaic Applications.
Clara Santato 1 , Dmitrii Perepichka 2 , Federico Rosei 3 , Dilek Isik 1 , Vishya Goel 2 , David Banville 1 , Simone Bertolazzi 1
1 , Ecole Polytechnique Montreal, Montreal, Quebec, Canada, 2 , McGill University, Montreal, Quebec, Canada, 3 , EMT-INRS, Montreal, Quebec, Canada
Show AbstractOrganic based photovoltaic cells (OPV cells) are advantageous because of their easy solution processing and their potential processability via roll-to-roll methods on flexible substrates, which is not possible with their inorganic analogues.[1]Unluckily,the maximum power conversion efficiency in OPV cells is only about 6%. Among other reasons, this is due to a large mismatch between the absorption characteristics of organic semiconductors (OSC) and the solar spectrum, in particular in the infrared region.To tackle this issue, we investigated blends of OSC with rare-earth doped nanoparticles (NP) with up-converting photophysical properties. [2] This approach consists in synthesizing NP capable of efficient energy transfer of up-converted near-infrared (NIR) photon energy to the light-absorbing polymer in the OPV cell and assembling these NP, in blends with p- and n-type OSC in solution-processed OPV cells. As the p-type semiconductor we selected poly(3-hexylthiophene (P3HT) whereas as the n-type semiconductor, [6,6]-phenyl C61-butyric acid-methylester (PCBM). We carefully investigated charge generation, transport, and trapping in films made of up-converting NP/P3HT/PCBM, in field effect transistor (FET) configuration [3]. These characterizations provided important information needed for optimization of the charge generation/transport in the films before fabricating OPV cells. The results indicate a clear ambipolar behavior (i.e. simultaneous electron and hole transport) due to the presence of n- and p-type semiconductors in the film, even with a weight ratio of NP:PCBM:P3HT of 1:10:5. Interestingly, we demonstrated an ambipolar (i.e. simultaneous electron and hole) IR photoinduced-transport in FET based on NP/P3HT/PCBM. Charge carrier trapping attributable to the presence of the NP has been investigated by conductive Atomic Force Microscopy.The results strongly suggest the interest of our approach to improve IR light harvesting in solution processable OPV cells. References[1] S. Gunes, H. Neugebauer, N. S. Sariciftci, Chem. Rev. 2007, 107, 1324.[2] G.S. Yi and G. M. Chow, Adv. Funct. Mat. 2006, 16, 2324.[3] S. Cho, J. Yuen, J. Y. Kim, K. Lee, A. J. Heeger, Appl. Phys. Lett. 2007, 90, 63511.
9:00 PM - D4.11
Enhanced Performance of Organic Electronics by Interface Modification with Solution Processable TiO2.
Mi-Hyae Park 1 , Juo-Hao Li 1 , Yang Yang 1
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractThere have been significant interests on an interface of the device, since the interface between organic semiconductor and metal plays a critical role in influencing the device performance. It has been shown that the properties of interfaces can be varied by chemical modification and surface morphological change through self assembled monolayer or various metal oxides. Here, we represent a way to control interface engineering based on solution processable nanocrystalline TiO2 prepared by sol-gel approach. The photovoltaic cells based on the poly (3-hexylthiophene) (P3HT): methanofullerene (PCBM) with the help of this chemically modified interfacial layer exhibit a dramatic improvement both for the regular and inverted device configurations. Atomic Force Microscopy (AFM) measurement shows better film morphology of the active layer, which gives smaller serial resistance of heterojunction photovoltaics, subsequently resulting in high fill factor (FF). The modified nanocrystalline interface gives rise to a more desirable work function for charge transfer in organic electronics. We have successfully applied this TiO2 layer to polymer LEDs, solar cells, and tandem solar cells. The improved device performance is attributed to an improved polymer/metal contact, more efficient electron extraction, and better hole blocking properties.
9:00 PM - D4.12
Laterally-defined Organic Heterojunction Diodes with Field Effect Tuning of Built-In Potential.
Bal Mukund Dhar 1 , Geetha Kini 2 , Guoqiang Xia 2 , Byung Jun Jung 1 , Nina Markovic 2 , Howard Katz 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Dept of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractLateral organic heterojunction diodes were prepared using a novel non-damaging photolithographic patterning method. Poly-(3 hexyl Thiophene), a well known hole transporting Organic semiconductor was used in conjunction with a derivative of Naphthalene Tetracarboxylic diimide (5FPE-NTCDI),a widely reported class of electron transporting organic semiconductors in ambient). The electrical characteristics of the diode could be tuned by application electrostatic field using a third gate terminal as used in a thin film transistor configuration so as to achieve orders of magnitude change in currents as well as rectification ratios. Scanning Kelvin Probe Microscopy (SKPM) on these lateral junctions reveals a chemical potential difference (CPD) of 0.25 volts which is equivalent to vacuum level shift at the heterojunction. The CPD across the heterojunction , which represents the built-in potential ,was observed to change with different bias voltages in the operational diode and more significantly, as a function of transverse field. The generality of the patterning technique coupled with SKPM also allows this to be an attractive tool to investigate the physics of organic semiconductor heterointerfaces which are active elements of organic light emitting diodes and organic solar cells.
9:00 PM - D4.13
Stabilizing Higher Acenes for Device Applications by Partial Fluorination.
Balaji Purushothaman 1 , Sean Parkin 1 , John Anthony 1
1 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 improves π – stacking, solubility and stability of acenes. This approach has not only been applied to pentacenes but also successfully on higher acenes such as hexacene and heptacene. However the poor solution stability of these higher acenes has prevented any practical use of them in devices. In recent years it has been shown that incorporation of halogens improves the environmental stability and π – stacking in molecules by increasing intermolecular interactions between the electronegative halogen atoms and π electron rich acene chromophore. Addition of fluorine or chlorine is also known to induce n-type behavoir. Recently it has been reported that partialy fluorinated acenes exhibit ambipolar behavior. We have applied such an approach to synthesize partially halogenated acenes of varying degree to improve the photostability and π – stacking in hexacene. Preliminary device studies on these new materials will also be reported.
9:00 PM - D4.14
Organic Solar Cells based on Small Molecule, Polycyclic Aromatic Compounds: Materials and Interfaces.
Scott Watkins 1 , Mark Bown 1 , Ming Chen 1 , Gavin Collis 1 , Richard Evans 1 , Giovanni Fanchini 1 , Craig Francis 1 , Akhil Gupta 1 , Matthias Haeussler 1 , Katalin Hegedus 1 , Jacek Jasieniak 1 , Graeme Moad 1 , Ezio Rizzardo 1 , Birendra Singh 1 , Gerry Wilson 1 , Kevin Winzenberg 1
1 Molecular and Health Technologies, CSIRO, Melbourne, Victoria, Australia
Show AbstractResults from a new class of polycyclic aromatic compounds which show power conversion efficiencies in excess of 2% in bulk heterojunction solar cells are presented. These materials are derived from commercially available Vat dyes and the implications of this for synthetic scale-up will be discussed. The interactions of these small molecules with a variety of other semi-conducting materials such as other small molecules and conjugated polymers will be discussed. This discussion will also be linked to the general issues involved with using small molecules as components in solution processed, bulk heterojunction devices. Finally, work on the analysis of energy levels and interfaces by Photo Electron Spectroscopy in Air (PESA) will be presented.
9:00 PM - D4.15
Solution Processed Organic Photovoltaic Cells with Anthracene Derivatives.
Dae Chung 1 , Chan Park 1 , Soon-Ki Kwon 2
1 Chemical engineering, Postech, Pohang, Kyungbuk, Korea (the Republic of), 2 School of Nano & Advanced Materials Science and engineering, Gyeongsang National University, Jinju, Kyungnam, Korea (the Republic of)
Show AbstractNovel solution processed small molecule bulk heterojunction photovoltaic (PV) cells were fabricated using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor and triisopropylsilylethynyl anthracene (TIPSAnt) derivatives substituted with naphthalene (TIPSAntNa) and bithiophene (TIPSAntBT) at 2,6 positions of the anthracene as electron donors. Different to TIPS Pentacene, TIPSAnt derivatives did not suffer from Diels-Alder reaction with PCBM when solution processed, as confirmed by UV-Vis absorption. The exciton diffusion lengths of TIPSAntBT and TIPSAntNa obtained by photoluminescence (PL) quenching method were 5 and 3 nm, respectively. TIPSAntBT and TIPSAntNa blended with PCBM (1:1, 1:2, 1:3 and 1:4 weight ratio) produced films possessing an adequate hole mobility of 10-5~10-6 cm2/Vs and an electron mobility of 10-5~10-4 cm2/Vs. The morphological changes by varying blending ratio which reveals obvious phase segregated crystalline domain at 1:1 ratio and almost amorphous phase at 1:4 ratio were also presented. Bulk heterojunction solar cells made with the TIPSAntBT:PCBM blend reached power conversion efficiencies up to 0.9% at 1:4 ratio which is the highest value among the solution processed molecular acene derivatives.
9:00 PM - D4.16
New Solution-processable, Small Molecule-based, Dibenzo[b,def]Chrysene Semiconductors for use in Organic Optoelectronic Devices.
Birendra Singh 1 , Mark Bown 1 , Christopher Dunn 1 , Gavin Collis 1 , Craig Forsyth 2 , Craig Francis 1 , Katalin Hegedus 1 , Scott Watkins 1 , Gerard Wilson 1 , Kevin Winzenberg 1
1 Molecular and Health Technologies, CSIRO, Clayton South, Victoria, Australia, 2 School of Chemistry, Monash University, Clayton, Victoria, Australia
Show AbstractWe report the synthesis and applications of a new class of solution-processable, semiconductors based upon the polycyclic aromatic hydrocarbon dibenzo[b,def]chrysene. By using different solution processing techniques these small molecule dibenzo[b,def]chrysene derivatives can afford films ranging from uniform sheets of single crystals to polycrystalline films. Preliminary investigations using X-ray absorption fine structures and low angle X-ray diffraction indicate that the ordering of these films is strongly influenced by the nature of substituents attached to the dibenzo[b,def]chrysene template. The performance of these materials in thin film transistors will be discussed.
9:00 PM - D4.18
Tetracyano-p-quinodimethane (TCNQ) Derivatives with Π-Extended Systems: Crystal Structures, Electrochemistry and Density Functional Theory Study.
Phuong-Truc Pham 1 , Hui Lin 2 , Basant Nassar 2 , Andrew King 2 , Mamoun Bader 2
1 Chemistry, Penn State Worthington-Scranton, Dunmore , Pennsylvania, United States, 2 Chemistry, Penn State Hazleton, Hazleton, Pennsylvania, United States
Show AbstractWe report the synthesis, x-ray single crystal structural analysis, electrochemical behavior and density functional theory calculations results on a series of TCNQ-like molecules in which the extension of the Π-system was increased systematically. Synthesis was accomplished by the condensation of the corresponding quinones with malonitirle catalyzed by TiCl4 following a modified procedure described by Hanack. In the crystalline state, these molecules adopt a butterfly shape centered around the carbons bearing the (CN)2 groups. For example in the crystal structure of 15,15,16,16-tetracyano-6,13-pentacenequinodimethane (6,13-TCPQ), the molecule consists of two planes intersecting at the carbons bearing the (CN)2 groups, with an angle of 46.13o between the planes. Pi stacking is observed with intermolecular distances of 3.60 Å and 3.41 Å between ring-ring and ring-CN neighbors, respectively. Similar structural features were also seen in 13,13,14,14-tetracyano-5,12-tetracenequinodimethane (TCTQ). This non-planarity is probably responsible for the lower electron accepting behavior as evident in the electrochemical behavior of these molecules compared with the completely planar TCNQ. DFT calculated structures compare well with the experimental x-ray data. Comparisons with published synthetic and electrochemical studies are made and will be presented.
9:00 PM - D4.19
Synthesis and Device Application of Regioregular Cyano-substituted Poly(p-phenylenevinylene).
Shigeyoshi Sato 1 , Keisuke Tajima 1 , Kazuhito Hashimoto 1 2
1 Applied Chemistry, School of Engineering, University of Tokyo, Tokyo Japan, 2 , JST-ERATO, Tokyo Japan
Show AbstractSemiconducting polymers are attracting much interest recently for the use in organic electronic devices such as photovoltaics, FETs and LEDs. Among them, dialkoxy-substituted poly(p-phenylene vinylene) (PPV) derivatives with cyano groups on the vinylene units (CN-PPVs) is one of the examples studied extensively as an n-type material. CN-PPV has higher electron affinity than PPV owing to the strong electron withdrawing cyano groups, which enable them to accept and transport electrons. Since the variety of soluble n-type polymers is limited, CN-PPV has attracted much attention for the application. However, relatively low electron mobility of CN-PPV (reported as 10-9 ~ 10-5 cm2 V-1 s-1 depending on the measurement methods) has limited the device performance. Therefore, improvement of the electron mobility in CN-PPV would lead to the high performance in the various polymer-based devices.The regioregularity of conjugated polymers is one of the important factors to control their higher order structures in the solid state such as crystallinity, molecular orientation, and intra- and intermolecular ordering, which greatly affect the charge mobility in the film. Therefore, it is expected that the regioregularity of the CN-PPV can be an important factor to increase the electron mobility in the film. Conventionally, soluble CN-PPV was synthesized via alternative polycondensation of a dialdehyde and a dinitrile. Since there is no selectivity in the coupling manner, the resulting CN-PPV has a regiorandom configuration in terms of the alkoxy substitutions. In contrast, polycondensation of one monomer that has both an aldehyde and a nitrile group is expected to proceed only in the head-to-tail manner, resulting in completely regioregular CN-PPV.In this study, completely regioregular poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene-1-cyanovinylene] was synthesized for the first time. Regioregularity of the polymer was confirmed by 1H NMR analysis using chlorobenzene-d5 as a solvent. UV-vis and fluorescence spectra revealed that the regioregular CN-PPV showed stronger interchain interactions in the films compared to the regiorandom counterpart. As the result, electron mobility of the regioregular CN-PPV was improved about 30 times compared to the regiorandom one in the film, measured by space charge limited current (SCLC) method.1 The n-FET devices of these CN-PPVs were fabricated and measured in vacuo. Agreed with the SCLC results, electron mobility of the device with regioregular CN-PPV was one order of magnitude higher than that of regiorandom counterpart. The device with regioregular CN-PPV exhibited moderate performance with μe = 3 × 10-4 cm2 V-1 s-1 and Ion/Ioff = 104. Photovoltaic devices were also fabricated using mixture of CN-PPV and an electron donating polymer. The preliminary results of these device applications will be presented. Reference[1] S.Sato, K.Tajima, K.Hashimoto, Macromolecules, 2009, 42 (6), 1785-1788
9:00 PM - D4.2
Sequent Spray Deposition of Secondary Solvent for Efficient Organic Solar Cells.
Byung-kwan Yu 1 , Doojin Vak 2 , Jang Jo 1 , Seok-In Na 1 , Seok-Soon Kim 3 , Dong-Yu Kim 1
1 Heeger Center for Advanced Materials, Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of), 2 Bio21 Institute, University of Melbourne, Melbourne, Victoria, Australia, 3 School of Materials Science and Chemical Engineering, Kunsan National University, Kunsan Korea (the Republic of)
Show AbstractConjugated polymer-based organic solar cells (OSCs) are an attractive option for cost-effective, large area, flexible photovoltaic device applications. Over the past few years, OSCs have undergone a gradual evolution that has led to energy conversion efficiencies of 6%. Although there has been a great deal of research regarding new materials for the OSCs and their efficiency, the processing technologies have received relatively less attention. Organic materials can be made into thin films by simple solution processes such as spin coating, doctor blading, inkjet printing, and so on. Among these solution prosesses, the spray process is compatible with the roll-to-roll process, which has the highest productivity and the lowest processing costs. However an overly rough surface of the conventional sprayed active layer result in a relatively low fill factor (FF) and a high series resistance (Rs). In this study, we demonstrate a technique involving the spraying of additional high boiling point solvent after the formation of the active layer using conventional spray process. After using this technique, we obtain a much smoother surface morphology and ordered bulk heterojuction morphology through enhanced self-organization of the composite materials. Consequently, on the basis of the results, the device with additional high boiling point solvent spray recorded a high FF and a low series resistance.
9:00 PM - D4.20
Poly(3,4-ethylenedioxythienylene) Siloxanes as Precursors to PEDOT Conjugated Polymers.
Ki-Ryong Lee 1 , Gregory Sotzing 1
1 Department of Chemistry and the Polymer Program, University of Connecticut, Storrs, Connecticut, United States
Show AbstractHerein we report the synthesis and characterization of 3,4-ethylenedioxythiophene (EDOT) containing conjugated polymer via oxidative electrodesilylation of processable precursor poly(arylsiloxane)s, having low glass transition temperature (Tg), from the solid state with electrochemical or chemical method. The main advantage of this method is the processibility in the precursor stage, and later conversion to conjugated polymers (CPs) after the desired shape has been achieved. Previous work demonstrated great processability using poly(arylsilane)s. By replacing silane to siloxane, the Tg of the polymers decrease, moreover, improved solubility to common solvents is observed while maintaining optical behavior similar to those of CPs obtained by conventional deposition using electrolyte bath/ monomer electrochemical polymerization.Poly(arylsiloxane)s are prepared via a one pot reaction form dilithiated EDOT and dichlorotetramethyldisiloxane, and the structure are characterized by FT-IR, UV-vis, 1H-, 13C-NMR, GPC, DSC and TGA. Poly(arylsiloxane)s have good thermal stabilities with low Tg and can be processed via thin film processing techniques such as dip, spin, and spray coating etc. Via solid-state oxidative conversion, poly(arylsiloxane)s are converted to corresponding CPs. Electrochemical and spectroelectrochemical properties of converted CPs will be present.
9:00 PM - D4.21
Study of Single-walled Carbon Nanotubes Grafted with Conjugated Polymers.
Raigna Armond 1 , Hugo Santos 1 , Sandra Nogueira 1 , Jose Eduardo Manzoli 2 , Newton Barbosa Neto 1 , Alexandre Marletta 1
1 Instituto de Física, Universidade Federal de Uberlandia, Uberlandia Brazil, 2 , IPEN / CNEN, São Paulo Brazil
Show AbstractCarbon nanotubes have attracted the attention of many scientists and engineers worldwide because of theirs exceptionally unique structural and physicochemical properties and are promising materials for engineering applications such as polymeric composites, electronic devices, field emission, display and hydrogen storage, etc. [1] Carbon nanostructures have shown to be very sensitive to radiation [2]. This sensitivity can be exploited for controllable modifications of their structural properties. These challenges include expanding synthetic approaches to large-scale production, searching for efficient purification methods, and developing chemical techniques for manipulating nanotubes. In this work we are proposing to obtain composite systems based on the grafting of single-walled carbon nanotubes (SWNT) and conjugated polymer (or semiconductor polymer) produced by simultaneous gamma irradiation. This grafting system is expected to be more stable under radiation (minimize effects of amorphization) and will be more suitable for manipulation using the functionality of the polymer instead of the inertness of the nanotube. The characterization will be by optical absorption, photoluminescence, structural and electrical properties. The polymeric matrix are PPV (p-phenylene vinylene) and MEH-PPV [Poly(2-metoxy-5-(2-ethylhexyloxy)-1,4-Phenylenevinilene]. Single-walled carbon nanotubes (SWNT) CoMoCAT® dispersed in organic solution like NMP (N-Methyl-2-pyrrolidone, THF (tetrahydrofuran) and surfactant (NaDDBS, sodium dodecylbenzene sulphonate) by sonication will be grafted in these polymers by gamma irradiation. Our first optical results indicate an increase in the interaction of SWNT with MEHPPV after gamma irradiation comparated to non-irradiated composites.[1] R. H. Baughman, A. A. Zakhidov, W. A. de Heer, Science (2002), 297, 787.[2] J. Guo, Y. Li, S. Wu and W. Li, Nanotechnology 16 (2005) 2385–2388.
9:00 PM - D4.22
The Effect of Alkyl Chain Pairity on Charge Mobility in Substituted Oligoacene Semiconductors.
Andrey Moiseev 1 , Afshin Dadvand 2 , David Chung 3 , Dmitrii Perepichka 4
1 Chemistry Department, McGill University, Montreal, Quebec, Canada, 2 Chemistry Department, McGIll University, Montreal, Quebec, Canada, 3 Chemistry Department, McGIll University, Montreal, Quebec, Canada, 4 Chemistry Department, McGIll University, Montreal, Quebec, Canada
Show AbstractRecent studies showed that charge mobility and stability of organic thin film transistors (OTFTs) could be greatly enhanced by increase in pi-stacking within the crystal lattice.1 Symmetrically substituted anthracene derivative, 2,6-bis[2-(4-pentylphenyl)vinyl]anthracene (2) showed significant stability, high carrier charge mobility and repeatability in comparison with pentacene due to denser crystal packing.2 We have recently demonstrated that related styryltetracene derivative can be used as an effecient multifunctional semiconductor for light-emitting transistors.3 We propose that the crystal packing and the morphology of the film might be further improved by tuning the length of side alkyl chains using 2,6-bis[2-(4-alkylphenyl)vinyl]anthracenes (1 and 3). Anthracene derivatives with various length of alkyl chains were synthesized in four steps starting from readily available 2,6-dihydroxy-9,10-antracenedione. We will present the studied of their spectral and electrochemical studies and the effect of molecular structure on the hole mobility and electroluminescence in OTFT devices. 1.Deng, W.; Goddard, W. A., III J. Phys. Chem. B 2004, 108, 8614.2.Meng, H.; Sun, F.; Goldfinger, M. B.; Gao, F.; Londono, D. J.; Marchal, W. J.; Blackman, G. S.; Dobbs, K. D.; Keys, D. E. J. Am. Chem. Soc. 2006, 128, 9304. 3. F. Cicoira, C. Santato, A. Dadvand, C. Harnagea, A. Pignolet, P. Bellutti, Z. Xiang, F. Rosei, H. Meng, D.F. Perepichka, J. Mater. Chem. 2008, 18, 158.
9:00 PM - D4.23
Bright Inkjet Printed Macromolecular Organic Light emitting Diodes on Flexible Substrates.
Madhusudan Singh 1 3 , Hyunsik Chae 2 , Jesse Froehlich 2 , Takashi Kondou 2 , Sheng Li 2 , Amane Mochizuki 2 , Ghassan Jabbour 1 3 4
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, 4 Flexible Display Center, Arizona State University, Tempe, Arizona, United States
Show AbstractWe present results of printing solution-processable organic light emitting diodes (OLEDs) based on electrophosphorescent Ir(III) stellate polyhedral oligomeric silsesquioxane (POSS) macromolecules. The macromolecules are doped into 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), and the resulting ink is printed on a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) spin-coated on indium tin oxide (ITO). An exciton-blocking layer consisting of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is thermally evaporated onto the printed ink layers, followed by a LiF/Al cathode. While the photoluminescence (PL) spectrum of printed ink on glass indicates a significant contribution from the PVK:PBD exciplex, electroluminescence measurements (EL) suggest a much smaller effect of these states, which implies significant charge trapping at dopant molecular sites. Our latest experiments with devices printed on PEDOT:PSS/ITO/glass indicate that the devices exhibit high luminances (~ 13,000 cd/m
2 at 70 mA/cm
2) and a fairly consistent quantum efficiency (~ 2.5%) across a wide range of luminances. The corresponding figures for spin-coated devices are expectedly higher, with efficiencies ~ 4.5% at similar levels of brightness. We use white light interferometry as a non-contact technique to quantify surface roughness and thickness of printed layers.[1] Our current results thus indicate that inkjet printing of macromolecular phosphor doped polymer inks is suitable for fabrication of OLEDs with high brightness, in spite of the low glass transition temperature of some of the species. Our initial work with these devices on flexible ITO-coated plastic substrates shows devices with moderately high luminance values (~ 2,500 cd/m
2 at 35 mA/cm
2). We are working on the development of inkjet printing materials and processes for pure macromolecular OLEDs that are not performance and reliability limited by the presence of the PVK:PBD matrix with low glass transition temperatures. This requires the development of macromolecules that subsume all the functions of the host matrix and have high enough T
g to be usable in high concentrations needed. In conjunction with the inkjet printing technology demonstrated in this work, this has the potential to yield low-cost manufacturing of these devices. [1] M. Singh, et al., ”Electroluminescence from printed stellate polyhedral oligomeric silsesquioxanes”, Soft Matter, DOI:10.1039/B903531A, 2009.Email:
[email protected]9:00 PM - D4.24
Application of Stamp Transfer Printing Method for Fabrication of Multilayer White Polymer Light-emitting Diodes.
Chul Woong Joo 1 , Soon Ok Jeon 1 , Kyoung Soo Yook 1 , Jun Yeob Lee 1
1 Department of Polymer Science and Engineering, dankook University, Yongin-si Korea (the Republic of)
Show AbstractMultilayer white polymer light-emitting diodes (WPLEDs) were effectively fabricated by a stamp transfer printing method. The multilayer film of polymers can be prepared by transferring a polymer film from Si substrate to an indium tin oxide substrate using a polydimethylsioxane (PDMS) stamp. The PDMS transfer method was effective to make white PLEDs with a bilayer emitting structure of blue polyfluorene /yellow polyphenylvinylene. The yellow polymer film was coated on Si substrate by spincoating and transferred from the Si substrate to the blue polymer coated substrate. The WPLEDs with the bilayer emitting structure showed both blue and yellow emissions with a color coordinate of (0.33, 0.40). The stamp transfer method could be applied for fabricating various multilayer stacked WPLEDs and the multilayer stacked WPLEDs with a quantum dot interlayer for light emission control, small molecule based interlayer for charge transport and emission management and polymer based interlayer for charge transport and color control could be prepared by the stamp transfer printing method. The stamp transfer printing method was found to be effective as a film-forming method in polymer light-emitting diodes without any degradation of device performances and it can be widely used as a dry coating method to fabricate multilayer structures in other organic electronic devices.
9:00 PM - D4.25
High Efficiency Soluble Phosphorescent Light Emitting Diodes using a Double Layer Emitting Structure Fabricated by a Stamp Transfer Printing Method.
Kyoung Soo Yook 1 , Soon Ok Jeon 1 , Chul Woong Joo 1 , Oh Young Kim 1 , Jun Yeob Lee 1
1 Polymer science and engineering, Dankook University, Yongin-si Korea (the Republic of)
Show AbstractHigh efficiency soluble phosphorescent organic light emitting diodes(PHOLEDs) were developed using a double layer emitting structure fabricated by a stamp transfer printing process. An emitting layer with an electron transport type host material was stamp transfer printed on the spin coated on an emitting layer with a hole transport type host material. Holes and electrons were confined inside the emitting layer and the quantum efficiency could be improved compared with the common single layer device. Green PHOLEDs with the double layer emitting structure showed more than four times higher quantum efficiency than the green PHOLEDs with single layer emitting structure. The transfer printing of the soluble small molecules from a Si substrate to the small molecule coated indium tin oxide substrate enabled the fabrication of the multilayer stacked soluble white PHOLEDs and soluble white PHOLEDs could be fabricated by the stamp transfer printing of the small molecule based phosphorescent red/green emitting layer on the spin coated blue phosphorescent emitting layer. Therefore, the stamp transfer printing method could be effectively used to fabricate multilayer structure in soluble small molecule based organic electronic devices.
9:00 PM - D4.26
Photoresponses in Poly (3-hexylthiophene)/Spiropyran Dye Blend Heterojunction Field Effect Transistors.
Avishek Aiyar 1 , Byoungnam Park 1 , Elsa Reichmanis 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWe report the photoresponse of solution processed organic field effect transistors (OFETs) composed of poly (3-hexylthiophene) (P3HT) blended with a photochromic spiropyran dye, using silicon dioxide as the gate dielectric, in air. OFETs incorporating the dye, which strongly absorbs in the UV region of the spectrum, exhibited a large hysteresis under illumination as well as in the dark. The threshold voltage in a P3HT/dye blend FET with a 2 wt. % dye content shifted from 40V in the dark to 53V under illumination with UV light at 365 nm and an intensity of 1 mW/cm2, when scanning from positive to negative gate voltages. The addition of the dye also resulted in the sensitization of the photoconductivity of the OFET, as shown by the output characteristics of blended FETs, which exhibited a significant increase of the drain current from about 100 nA in the dark to 700 nA upon illumination with UV light at 1 mW/cm2. The observed phenomena suggest that excitons are photogenerated and charge separation occurs at the P3HT-dye heterojunction, resulting in an enhanced conductivity of the device under illumination. Also, the large hysteresis observed in the blends can be attributed to trapping of charge carriers. Based on the results obtained, OFETs using P3HT/dye blends have potential applications as phototransistors or photodetectors.
9:00 PM - D4.27
New Highly Emissive Thienylene-Vinylene Oligomers and Co-Polymers for Organic Electronics
Shehzad Jeeva 1 , A. Karapanayiotis 1 , Afshin Dadvand 2 , Olena Lukoyanova 1 , Dmitrii Perepichka 1
1 Chemistry, McGill University, Montreal, Quebec, Canada, 2 Énergie, Matériaux et Télécommunications, Université du Québec, Institut national de la recherche scientifique, Varennes, Quebec, Canada
Show AbstractConjugated polymers with aromatic and/or heteroaromatic backbones materials have a plethora of applications that span across the fields of light emitting materials, photovoltaic devices, field effect transistors, chemical sensing and radio frequency identification (RF-ID). One of the advantages of poly(thienylene vinylene) (PTV) , , and its derivatives over more common polythiophne (PT), polyparaphenylene (PPP), or polyphenylenevinylene (PPV) is their high absorption in the visible range of the spectrum, low energy band gap and good mobility, which makes them excellent candidates for photovoltaic applications. However, up to now no fluorescence was reported for any of the PTV derivatives, and it was further suggested that inefficient (quenched) emission might be a general property of this class of conjugated polymers. In order to further understand this phenomenon and to access new pi-functional materials we have synthesized novel thienylvinylene copolymers 1 and 2 and oligomers 3, 4 and 5. The band-gap and the optelectronic properties of these compounds have been assessed in electrochemical and spectral studies. Organic field-effect transistor (OFET) fabricated from co-polymer 2 by solution processing exhibit a mobility of ~ 10–2 cm2V–1s–1. Further work is under progress for making photovoltaic device with polymer 2.
9:00 PM - D4.28
Frequency Response Characteristics of Polyfluorene Based Organic Photodetectors using Fullerene Derivatives Blends.
Tatsunari Hamasaki 1 3 , Taichiro Morimune 2 , Hirotake Kajii 1 3 , Satoshi Minakata 3 , Toshiki Nagamachi 3 , Yutaka Ohmori 1 3
1 Center for Advanced Science and Innovation, Osaka University, Suita, Osaka, Japan, 3 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan, 2 Department of Electronic System, Kagawa National College of Technology, Mitoyo, Kagawa, Japan
Show AbstractOrganic photodetectors (OPDs) have high potential for use in the next generation information technology system, especially for signal processing and optical sensing systems. OPDs also have advantages in lightweight, flexibility and easy fabrication process, in particular, using a materials which are soluble in solvent. Furthermore, we can select absorption wavelength of OPDs by choosing organic materials with suitable absorption wavelength. Therefore, it is easy to realize color sensitive photodetectors. In this study, we investigated characteristics of OPDs by solution process using p-like fluorene derivative poly(9,9-dioctylfluorene-co-bithiophene) : F8T2 and n-like two fullerene derivatives, PCBM or [6,6]-bridged N-4-methylbenzenesulfonylaziridinofullerene : TsAF. The OPDs were fabricated on indium tin oxide : ITO-coated glass substrate as an anode. F8T2 as a conducting polymer mixed with PCBM or TsAF was dissolved in 1,2-dichlorobenzene and spin coated on ITO, respectively. After forming an organic layer as a photo absorption layer, Au was deposited as a cathode and the device was sealed in an inert gas (Ar gas) with a glass plate and epoxy resin to avoid oxidization of the active layer. The active area of the device was fixed at 0.03 mm2 or 0.01 mm2 in order to reduce the influence of the RC time constant.The OPDs fabricated in this study had blue sensitivity because of using F8T2 which absorb blue light. Current density – voltage characteristics of the OPDs, which consisted of ITO / F8T2 : PCBM or F8T2 : TsAF / Au under reverse bias condition, showed good rectifying characteristics in a dark state. In an illuminated condition (λ = 460 nm, 8 mW/cm2), the OPDs showed photosensitive characteristics and that photocurrent gradually increased with an applied bias voltage. For PCBM, the device was mainly driven as an OPD at reverse bias. In contrast, for TsAF, the device was identically driven at both forward and reverse biases. Characteristic of the fullerene derivative affects the characteristic of the OPD.For measuring the frequency response, sinusoidally modulated violet laser light (λ = 408 nm, 1 W/cm2) was irradiated to the devices. Cutoff frequencies of the F8T2 : PCBM device and the F8T2 : TsAF device increased with increasing the applied bias voltage. It is considered to be due to the acceleration of photogenerated carriers and the dissociation of excitons at the F8T2 : PCBM or F8T2 : TsAF bulk heterojunctions. Cutoff frequencies of the F8T2 : PCBM and F8T2 : TsAF were estimated to be approximately 40 MHz under applied bias voltage of -10 V and 7 V, respectively.
9:00 PM - D4.29
Thin Film Transistor: An Effective Tool for Charge Transport Measurements in Amorphous Organic Semiconductors.
Chi Hang Cheung 1 , Wing Hong Choi 1 , Shu Kong So 1
1 Department of Physics, Hong Kong Baptist University, Hong Kong China
Show AbstractCharge transport is a critical issue in organic electronic devices. A better understanding of this issue enables us to improve the quality of organic materials. Time-of-flight (TOF) method is commonly used to examine charge transport properties of organic materials. However, large material consumption makes TOF technique not practical for materials at limited quantity. In contrast, thin film transistor (TFT) method with extremely little material consumption is of great interest for charge transport study. This contribution aims at using TFT configuration to evaluate transport parameters of four phenylamine-based (PA) compounds, namely N,N’-di(naphthalene-1-yl)-N,N’-diphenyl-benzidine (NPB), 4,4’4”-tris[2-naphthyl (phenyl)amino]triphenylamine (2TNATA), N,N’-diphenyl-N,N’-bis(3-methylphenyl) (1,1’-biphenyl)-4,4’-damine (TPD), N,N’-diphenyl-N,N’-bis(3-methylphenyl)(1,1’- biphenyl)-9,9-spirobifluorene (Spiro-TPD). For field effect (FE) mobility, all the compounds showed FE mobilities with one order of magnitude smaller when compared with those obtained from independent TOF technique. Their transport properties were further examined by temperature dependent measurement. The analysis showed the energetic disorder and the high temperature limit of mobility from TFT configuration were modified by the gate dielectric and are likely the origins of the mobility discrepancy. Furthermore, the effect of traps on charge transport of PA compounds was investigated by TFT. The FE mobility and threshold voltage were found to be dependent on the doping concentration. From the threshold voltage, trap density of the doping system can be estimated. It is anticipated that the TFT technique can be extended to study carrier transport of more complex active material systems including those in photovoltaic applications.
9:00 PM - D4.3
Towards Inkjet Printed High-efficiency Bulk-heterojunction Solar Cells.
Dolores Caras-Quintero 1 , Brian Saunders 2 , James Kingsley 3 , David Lidzey 3 , Stephen Yeates 1
1 Organic Materials Innovation Centre, School of Chemistry, University of Manchester, Manchester United Kingdom, 2 School of Materials, University of Manchester, Manchester United Kingdom, 3 Department of Physics and Astronomy, University of Sheffield, Sheffield United Kingdom
Show AbstractDuring the past decade, there has been an intensive search for cost-effective photovoltaics.[1] As an alternative to silicon-based solar cells, solution processable organic solar cells could provide a cost effective solution for larger area devicesInkjet printing is an useful technique for the controlled deposition of a solution of functional materials in specific locations on a substrate and can also provide easy and fast deposition of polymer films over a large areas with a single process step therefore reducing the fabrication cost. In this contribution, we will report recent developments in the use of inkjet printing as a fabrication tool for highly efficient bulk hetero-junction solar cells. Results will be presented both for the deposition of active PEDOT:PSS buffer layer as well as PCBM:P3HT bulk hetero-junctions.[1] M. C. Scharber, D. Mühlbacher, M. Koppe, P. Denk, C. Waldauf, A. L. Heeger and C. J. Brabec, Adv. Mater. 2006, 18, 789-794.
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Nonvolatile Hybrid Memory-cell Fabricated with Ni-nanocrystals Embedded Polymer-layer.
Jong Dae Lee 1 , Hyun-Min Seung 1 , Kyoung-Cheol Kwon 1 , Chang-Hwan Kim 1 , Jae-Sung Lim 1 , Jea-Gun Park 1
1 National Program Center for Terabit-level Nonvolatile Memory Development, Hanyang University, Seoul Korea (the Republic of)
Show Abstract We investigated the nonvolatile hybrid 4F2 memory-cell embedded with Ni-nanocrystals in conductive polymer. The structure of nonvolatile hybrid memory-cell was polymer / metal-nanocrystals / polymer between Al electrodes. We used the O2-plasma oxidation for forming the metal-nanocrystals which are capped by metal-oxide in conductive polymer. It’s the new method to form the metal-nanocrystals in polymer. The polymer and metal material were the polystyrene (PS) and Ni respectively. The PS dissolved with chloroform was spin-coated and baked for evaporating the solvent away. Moreover, the Ni nanocrystals capped by NiO were produced by evaporating Ni at the rate of 0.1-0.5 Å/s in a 10-4 Pa chamber pressure followed by O2-plasma oxidation for 300 seconds at 200 W. It was observed that the nonvolatile hybrid memory-cell embedded with Ni-nanocrystals with capping tunneling barrier showed the memory margin of (Ion / Ioff) of 0.14×102, the retention time of more than -1×105 sec, and more than 250 endurance cycles of program and erase. In our study, we will show the mechanism of nonvolatile hybrid memory-cell by the tunneling barrier capping Ni-nanocrystals embedded in conductive polymer, which is the first report.
9:00 PM - D4.31
Non-volatile Memory Devices Based on Poly(styrene) Derivatives with Electron Donating Oligo(fluorene) Pendent Moieties.
Cheng-Liang Liu 1 , Jung-Ching Hsu 1 , Wen-Chang Chen 1 2 , Kenji Sugiyama 3 , Akira Hirao 3
1 Deptartment of Chemical Engineering, National Taiwan University , Taipei Taiwan, 2 Institute of Polymer Science and Engineering, National Taiwan University, Taipei Taiwan, 3 Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo Japan
Show AbstractThe bistable non-volatile memory device based on polystyrene (PS) derivatives containing with pendent electron donating mono- (poly(St-Fl)), di-(poly(St-Fl2)), and tri(9,9-dihexylfluroene) (poly(St-Fl3)) units are reported. The effects of oligofluorene chain length and polymer surface structures on the memory characteristics were explored. Poly(St-Fl), poly(St-Fl2) and poly(St-Fl3) based devices exhibited a flash type memory with different turn-on threshold voltage of 2.8 V, 2.0 V and 1.8 V, which was on the reverse trend of the HOMO levels of -5.86, -5.80 and -5.77 eV, respectively. Moreover, the memory device shows a high ON/OFF current ratio of 2.5×10^4 and long retention time of 10^4 sec. The possible mechanism of the switching behavior was explained by space charge limited current (SCLC) theory with filamentary conduction. The larger aggregation domain size of the polymer thin film processed from the good (chlorobenzene) /poor (DMF) mixed solvent probably promoted the diffusion of the Al into the polymer film and formed the conduction channel. Thus, it significantly reduced the turn-on threshold voltage for the three studied polymers. The present study suggests the efficiently tuning the memory characteristics through the pendant conjugated chain length and surface structures.
9:00 PM - D4.32
Stable and Bright Solid State Light Emitting Electrochemical Cells.
Ruben Costa 1 , Antonio Pertegas 1 , Daniel Tordera 1 , Martijn Lenes 1 , Enrique Orti 1 , Henk Bolink 1
1 Instituto de Ciencia Molecular, University of Valencia, Valencia Spain
Show AbstractWe will present recent developments on the simplest type of molecular electroluminescent devices, light-emitting electrochemical cells (LECs). LECs have a simple architecture are prepared from solution and operate with air-stable electrodes which make them suitable for low cost/large area efficient lighting and signing applications.[1-4] In its simplest form, it consists of a single active layer composed of an ionic transition-metal complex (iTMC)[2-4]. Until recently, the main drawback of these molecular devices was their short lifetimes. We showed that by using iridium(III) complexes capable of forming a supramolecularly-caged structure the lifetime of LECs can be increased to more than 3000 hours.[5-7] We will report on LECs using new complexes and device architectures that yield high luminances (>1000 cd/m2), short turn-on times (seconds) and high lifetimes (>1000 hours).[1]Q. Pei, G. Yu, C. Zhang, Y. Yang, A. J. Heeger, Science 1995, 269, 1086.[2]E. S. Handy, A. J. Pal, M. F. Rubner, J. Am. Chem. Soc. 1999, 121, 3525.[3]F. G. Gao, A. J. Bard, J. Am. Chem. Soc. 2000, 122, 7426.[4]J. D. Slinker, J. Rivnay, J. S. Moskowitz, J. B. Parker, S. Bernhard, H. D. Abruña, G. G. Malliaras, J. Mat. Chem. 2007, 17, 2976.[5]H. J. Bolink, E. Coronado, R. D. Costa, E. Ortí, M. Sessolo, S. Graber, K. Doyle, M. Neuburger, C. E. Housecroft, E. C. Constable, Adv. Mat. 2008, 20, 3910.[6]S. Graber, K. Doyle, M. Neuburger, C. E. Housecroft, E. C. Constable, R. D. Costa, E. Ortí, D. Repetto, H. J. Bolink, J. Am. Chem. Soc. 2008, 130, 14944.[7]R. D. Costa, E. Ortí, H. J. Bolink, S. Graber, C. E. Housecroft, M. Neuburger, S. Schaffner, E. C. Constable, Chem. Commun. 2009, 2029.
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Ambipolar Light-emitting Field-effect Transistors Based on Organic Nanofibers and Thin Films.
Jakob Kjelstrup-Hansen 1 , Xuhai Liu 1 , Kasper Thilsing-Hansen 1 , Henrik Henrichsen 2 , Horst-Guenter Rubahn 1
1 Mads Clausen Institute, University of Southern Denmark , Sønderborg Denmark, 2 DTU Nanotech, Technical University of Denmark, Kgs. Lyngby Denmark
Show AbstractDue to their unique properties, organic semiconductors constitute an important class of materials for optoelectronic applications such as light-emitting devices (LEDs) and solar cells. Phenylene-based oligomers are of particular interest due to their ability to self-assemble into elongated, crystalline nanostructures – ‘nanofibers’ [1]. Such nanofibers can emit highly anisotropic, polarized light upon UV light exposure and can function as optical waveguides and random lasers, while chemical functionalization of the molecular building blocks can enable the tailoring of the nanofiber properties for particular applications [2]. The connection of metal electrodes to nanofibers enables the probing of their electrical properties [3] and constitutes a significant step towards the realization of a sub-micron organic LED.Organic electroluminescence results from the radiative recombination of holes and electrons, which have been injected into the organic material from the anode and cathode, respectively. Consequently, generation of light requires the ability to simultaneously and effectively inject both charge carrier types. This is often realized in a two-electrode sandwich geometry, which however is not suitable for sub-micron LEDs based on nanofibers. Alternatively, the organic material can be biased in a field-effect transistor geometry, which allows tuning of the charge carrier injection and thereby light emission by the application of a gate voltage [4], while its planar structure can facilitate easier integration of nanofibers. As recently demonstrated, the application of an AC signal to the gate electrode can further enhance the carrier injection and hence also the light emission [5].In this paper, we report the first results of electroluminescence from both organic nanofiber and thin film FET devices in the blue part of the spectrum. Light emission is observed not only from within the transistor channel (in between the source and drain electrodes) but also from electrode edges not forming the channel. A possible mechanism explaining this observation is discussed.References[1] F. Balzer and H.-G. Rubahn, Avd. Func. Mater., 15 (2005) 17[2] M. Schiek, F. Balzer, K. Al-Shamery, J. R. Brewer, A. Lützen, and H.-G. Rubahn, Small, 4 (2008) 176[3] H. H. Henrichsen, J. Kjelstrup-Hansen, D. Engstrøm, C. H. Clausen, P. Bøggild, and H.-G. Rubahn, Org. Electron., 8 (2007) 540[4] F. Cicoira and C. Santato, Avd. Funct. Mater., 17 (2007) 3421[5] T. Yamao, Y. Shimizu, K. Terasaki, and S. Hotta, Avd. Mater., 20 (2008) 4109
9:00 PM - D4.34
Self-assembled Pi-conjugated Polymer/semiconductor Nanocrystals Thin Film Memory.
Elsa Couderc 1 , Benjamin Grevin 1 , Patrice Rannou 1 , Jerome Faure-Vincent 1 , David Djurado 1 , Peter Reiss 1
1 INAC/SPrAM/LEMOH, CEA Grenoble, Grenoble France
Show AbstractIn the field of memory devices novel concepts are being explored with the goal to increase the storage density while reducing power consumption and processing costs. The use of polymers in the fabrication of memory devices offers the possibility of low cost solution processing in contrast to established silicon-based technology. Over the past few years, pi-conjugated polymer thin films containing inorganic nanoparticles have been shown to exhibit electrical bistability, which is a prerequisite for memory devices. In this communication, we will discuss the design, processing, and (opto-)electronic properties of self-assembled hybrid organic/inorganic multi-layered materials. Their self-assembly relies on triple H-bonding interactions between complementary diaminopyrimidine-functionalized poly(3-hexylthiophene) and thymine-functionalized semiconductor nanocrystals (CdSe, CuInS2). Hybrid thin films were deposited onto substrates (eg ITO) using the Layer-by-Layer technique, allowing a simultaneous fine tuning of the thickness and of the morphology down to a few monolayers.We will show examples of optoelectronically active hybrid thin films that exhibit a fully reversible electrical bistability between low conductivity and high conductivity states, calling for non-volatile memory applications. The influence of light irradiation conditions on the switching behaviour was thoroughly studied: different wavelengths and irradiation conditions (power, dark vs. light) were used to study the selective photo-generation of charge carriers within the semiconducting pi-conjugated polymer or nanocrystals. Moreover, we also investigated the impact of the size of the nanocrystals on the conduction processes responsible for the observed low and high conductivity states. These macroscopic-scale studies of the dc-conductivity are completed by non-contact atomic force microscopy (NC-AFM) and scanning Kelvin probe microscopy (SKPM) micro/nanoscopic level investigations under ultra-high vacuum (UHV). Finally, the frequency response of the switching mechanism will be presented (pulse-IV vs. dc-measurements) to discuss their potential use as active layers of a new type of hybrid organic/inorganic memory devices.
9:00 PM - D4.36
Electrical Studies of Metal–PANI/PVS–Metal Structures.
Mirela Santos 1 , Rodrigo Bianchi 1
1 Department of Physics , Federal University of Ouro Preto, Ouro Preto Brazil
Show AbstractSince the first report on the semiconducting nature of trans-polyacetylene in 1970’s, there have been considerable efforts to understand the electrical properties of conjugated polymers. Among this special class of polymeric materials, polyaniline (PANI) appears as a potential candidate from the technological standpoint on account of its low cost and ability to behave either as a semiconductor or as a metal, depending on the degree and type of doping used. PANI also offers a great opportunity to explore new concepts in a variety of polymer devices ranging from electronic to chemical sensors. Due to their potential applications as nanostructured devices, a better understanding of the conduction mechanisms and interface effects is crucial for determining the electronic transport across the multilayers, which depends on the irregularities of the material structure and also on the electrode effects. However, the influence of the electrode and the mechanisms governing the transport of charge carriers in those devices are not yet well understood. In this paper we investigated the electrical dc and ac conductivities of films containing alternated layers of PANI and an anionic polyelectrolyte - poly(vinyl sulfonic acid) (PVS), deposited onto NiCr line arrays recovered with Au. The results show a significant change in the electrical resistance of the polymers system when the thickness of the films reaches the Au layer. This effect was attributed to the higher interfacial electrical resistance between NiCr and the polymer film, compared to the resistance of the Au-film interface and polymer bulk. The alternating conductivity of the polymer was typical of solid disordered materials with the addition influence of the NiCr electrode. To investigate the charge transport mechanism in such material, it was developed a model based on random free energy barrier model for the ac conductivity of the polymer system according to the number of bilayers, which encompasses the disordered properties of Lbl films and the NiCr-PANI/PVS interfacial effects. The models allowed a rough estimation of the thickness and conductivity of the NiCr-PANI/PVS interfacial layer and dielectric constant of PANI/PVS film. The presence of a broad spectrum of relaxation times in the PANI/PVS system was also inferred from the model, as well as the maximum barrier energy for carrier hopping at about 34 meV. Finally, it was obtained that the conductivity of PANI/PVS films (9.6 x 10-4 S/m) is higher than the conductivity (6.9 x 10-4 S/m) of metal-PANI/PVS-metal system. This result suggested that the electrical sensibility of electronic tongue and noise prepared with conjugated polymer onto NiCr/Au electrodes is related not only to the bulk properties of conjugated polymers, but also to the interfacial metal-polymer effects and polymer thickness. This work was sponsored by CAPES, Fapemig, CNPq and INEO/CNPq.
9:00 PM - D4.37
Electrical Charging Mechanism(s) in Polymer Memory Devices
Shashi Paul 1 , Iulia Salaoru 1
1 Emerging Technologies Research Centre, De Montfort University, Leicester United Kingdom
Show AbstractThe growth in the usage of organic materials in the fabrication of electronic devices owes to the ease of fabrication of organic electronic devices as well as the applicability of inexpensive substrates in such configurations [1]. Numerous organic materials have been proposed as the basic constituent of devices such as field effect transistors, light emitting diodes and solar cells. However, far fewer attempts have been undertaken to manufacture polymer memory devices [2,3,4]. Polymer memory devices are fabricated by depositing a blend (an admixture of organic polymer, small organic molecules and nanoparticles) between two metal electrodes. These devices show two electrical conductance states ( “1” and “0”) when voltage is applied, thus rendering the structures suitable for data retention. These two states can be viewed as the realisation of non-volatile memory. A blend of polymer (polyvinyl acetate or polystyrene) and small particles (nano-particles and small organic molecules) was prepared in an organic solvent and spin coated onto a glass substrate marked with thin Al tracks and a top contact was evaporated on to the blend after drying - this resulted in a metal-organic-metal (MOM) structure. The current-voltage characteristic and the write-read-erase cycles of the MOM structures were measured in a screened sample chamber in the dark and at room temperatures using a PC-driven pico-ammeter (HP4140B). The I-V behaviour of MOM devices shows that the devices can be switched from a low conductivity state to a high conductivity state - this property can be exploited to store data bits. The possible charging mechanism (which is still an open question), based on the electric dipole formation, will be presented in this work.References1.Forrest, S R, Nature, 428, 911-918 (2004).2.J.Y Ouyang, C.W Chu CW, C.R Szmanda, L.P Ma, and Y Yang, Nature Materials, 3, 918 (2004)3.S. Paul, A. Kanwal, and M. Chhowalla, Nanotechnology (2006), 17, 145-151.4.S. Paul, IEEE Transaction on Electron Devices (2006), 53, 1775-1781.
9:00 PM - D4.38
The Interaction Mechanism Between Al and 8-Hydroxyquinolatolithium (Liq): Al-Liq Complex Formation with Electron Transfer from Al to Liq.
Yeonjin Yi 1 , Yong Mi Lee 2 1 , Yongsup Park 2 , Jeong Won Kim 1
1 Division of Industrial Metrology, Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 2 , Kyung Hee University, Seoul Korea (the Republic of)
Show Abstract8-hydroxyquinolatolithium (Liq) has been introduced as an alternative to LiF (electron injection layer), as it possesses more appropriate properties for efficient organic light-emitting diodes. However, in spite of the importance of the contact between the metal electrode and Liq (Liq makes direct contact with metal aluminum in optoelectronic devices), the interaction mechanism between Liq and the Al electrode has yet to be solved. We found that the interaction mechanism between the Al electrode and Liq is much different from the case of Al-LiF-tris(8-hydroquinolato) aluminum (Alq3) interaction. Al and Liq do not form either Alq3 (a similar reaction like AlF3 formation in Al-LiF-Alq3 reaction) or free Li+ ions, but rather make a Al-Liq complex with charge donation from Al to Liq. Electrons from Al fill the lowest unoccupied molecular orbital (LUMO) level of Liq and generate the occupied gap state. The LUMO filling is also supported by the fact that the molecular orbital shape of the original LUMO is very similar to that of occupied gap state.
9:00 PM - D4.39
Core-Shell Microcapsules for Self-Healing Electronic Materials Systems.
Susan Odom 1 2 , Brandon Long 1 , Mary Caruso 1 2 , Joshua Ritchey 1 , Alex Prokup 1 , Scott White 4 2 , Nancy Sottos 3 2 , Andrew Gerwith 1 , Jeffrey Moore 1
1 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 The Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractMicrocapsules of olefinic monomers and solvents encapsulated in poly(urea-formaldehyde) (UF) have been incorporated into polymer composites, which have been utilized for autonomic healing of damaged epoxy composites.[1-3] In addition to developing self-healing thermosets, we are also interested in repairing damaged electronic devices consisting of conjugated polymers, charge-transfer salts, small-molecule semiconductors, and inorganic semiconductors. Using an emulsification polymerization procedure, we have microencapsulated various precursors to some of these classes of materials. Specifically we have individually encapsulated both tetrathiafulvalene (TTF) and tetracyanoquinone (TCNQ) solutions, which are precursors to the TTF-TCNQ charge transfer salt with room temperature conductivity of ca. 103 S/cm, one of the highest known conductivities for an organic compound.[4] The formation of the TTF-TCNQ salt was observed upon microcapsule rupture by IR spectroscopy and is supported by conductivity experiments. Additionally, we have encapsulated ferrocene – a common standard for electrochemical measurements – to explore the electrochemical stability of the PUF shell wall in electrolyte solutions. In this case, we observe the ferrocene/ferrocenium oxidation in suspensions of ruptured capsules but not for the case of intact capsules. Lastly we have encapsulated oxidatively polymerizable monomers such as 3-alkylthiophene derivatives, which are precursors to conjugated polymers.[5] This presentation will focus on the preparation and properties of the aforementioned microcapsules, including various methods for analysis to determine thermal, chemical, and electrochemical behavior.
9:00 PM - D4.4
Nanoscale Visualization of Conducting Percolation Paths in an Integrated Barrier Layer by Scanning Force Microscopy.
Stefan Weber 1 , Mine Memesa 1 , Jochen Gutmann 1 2 , Berger Ruediger 1
1 , Max Planck Institute for Polymer Research, Mainz Germany, 2 Institute of Physical Chemistry, Johannes Gutenberg University, Mainz Germany
Show AbstractMorphology and electrical properties on a nanometer scale play an important role for the development of efficient organic and hybrid solar cells. Scanning force microscopy (SFM) methods can image the topography of samples at a nano¬meter resolution. Simultaneously, various additional surface properties can be recorded, e.g. surface charge, local conductivity or workfunction [1]. These SFM methods were applied to study the interplay between morphology and electrical properties of a novel integrated blocking layer system which was recently proposed for hybrid organic solar cells [2]. Such an electrically insulating blocking layer between the electrode and the nanoporous inorganic electron acceptor material is essential to prevent short-circuiting and current loss by recombination at the electrode interface. The novel hybrid blocking layer is composed of conducting titania nanoparticles embedded in an insulating polymer derived ceramic matrix. The fabrication process is a combination of sol-gel chemistry with a novel amphiphilic triblock copolymer ((PEO)MA-PDMS-MA(PEO)) as templating agent. Thin films with different titania concentrations were prepared on a Si wafer which was covered with a 50 nm thick sputtered Pt electrode. After plasma treatment and annealing of a spin casted film of 30-100 nm thickness, a granular structure with a typical grain diameter of 20 nm was found. Conductive scanning force microscopy (C-SFM) showed that on top of almost every grain on the surface there is an increased conductivity compared to the average value. The correlation of grains and conductivity indicated that the titania particles on the sample formed an electrically conductive percolating network, whereas the spaces in between the particles form an electrically insulating barrier layer. For the resistivity of this network we found that effects of tip-sample and sample-electrode resistivity dominate. Additionally, conductive scanning force microscopy revealed non-conducting defect structures attributed to the thermal treatment. Kelvin probe microscopy of pristine samples on one side and plasma treated plus annealed samples on the other side showed that there is a shift in work function of (0.8 ± 0.2) eV as expected for the transition of rutile to anastase titania.[1] Berger, R., Butt H.-J., Retschke, M., Weber, S.A.L., Electrical Modes in Scanning Probe Microscopy, Macromol. Rapid Comm. 2009, 30.[2] Memesa, M.; Weber, S.; Lenz, S.; Perlich, J.; Berger, R.; Muller-Buschbaum, P. & Gutmann, J. S., Integrated blocking layers for hybrid organic solar cells. Energy & Environmental Science, 2009, doi: 10.1039/b902754h.
9:00 PM - D4.5
PEDOT:PSS Type Hole-Injection Layers: Morphology and Conductivity.
Maria Retschke 1 , Stefan Weber 1 , Maria Lechmann 1 , Shahzada Ahmad 1 , Hans-Juergen Butt 1 , Ruediger Berger 1
1 , Max Planck Institute for Polymer Research, Mainz Germany
Show AbstractOrganic solar cells get more and more important owing to their flexibility and their lower costs in fabrication. An often investigated system for organic solar cells is poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as active layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as hole-injection layer and indium tin oxide (ITO) as bottom electrode[1]. Here we present the study of PEDOT thin films as one component in an organic solar cell device. We compared the PEDOT derivative poly(3,4-ethylenedioxythiophene), bis-poly (ethyleneglycol) (PEDOT-PEG:ClO4) (Aedotron (™)-C3)) with the commonly used PEDOT:PSS. Aedotron is diluted in nitromethane, therefore the film drying is easier and no annealing is necessary [2]. All films were made by blade coating on a 200 nm thick ITO layer that was deposited on a glass support. Blade coating has the advantage that it is an elegant procedure to coat larger areas and is compatible with industrial production processes. Films made by the blade coating process were compared in layer thickness, film morphology and in their local conductivity under miscellaneous environtmental conditions (humidity, oxygen contents,…) using Scanning force microscopy (SFM) methods. In particular we studied aging effects of the solutions on a timescale of days and weeks.For PEDOT:PSS it is known that the solution ages, i.e. the PEDOT:PSS forms aggregates that have to be removed by filtration. UV/VIS spectra were recorded to find out how much of the conducting polymer is removed by the filtration process.Profilometry was used to measure the film thickness. For the films made from PEDOT:PSS solution we obtained film thicknesses in range between 50-70 nm, which is comparable to the results for the Aedotron. SFM revealed a similar roughness in the order of 1 nm RMS on an area of 1 µm2 for PEDOT:PSS and Aedotron. We used Conductive scanning force microscopy (CSFM) images to determine mean values of tip sample currents. In addition the current images reveal the number of conducting islands within a given area and therefore the distribution of PEDOT domains. For an increase of relative humidity from 0% to 10% we found a significant decrease in the current mean value and a decrease in the number of conducting islands. After a longer exposure to 10% relative humidity no current was detected at a bias voltage of 5 V. For Aedotron we did not find a strong humidity dependence. Furthermore CSFM revealed that an increase of the tip sample force results in irreversible changes of surface morphology and conductivity. To record currents of 70 nA, a tip sample voltage of 150 mV is required at a tip sample force of about 90 nN. At even higher forces more conducting parts (size between 20-40 nm) can be resolved in the sample.[1] M. Reyes-Reyes et al., Appl. Phys. Lett. 2005, 87(8).[2] S. Luebben, 11th International Seminar on the Commercial Applications for Inherently Conductive Polymers, 2004.
9:00 PM - D4.6
Optical and Morphological Properties of P3HT:PCBM Blended Films Made by Freeze-Dry Method.
Chao-Han Cheng 1 , Cho-Shuen Hsieh 1 , Ping-Tsung Huang 2 , Juen-Kai Wang 1 3
1 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan, 2 Department of Chemistry, Fu-Jen University, Taipei Taiwan, 3 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan
Show AbstractThe efficiency of polymer solar cells have been greatly improved with the introduction of bulk heterojunction (BHJ) concept [1], owing to the increased interface within the phase-separated networks. Because of the nature of immiscibility between them, the phase separation however could not be brought into good control, creating many charge traps and thus lowering the power conversion efficiency. In this study, we demonstrate bi-continuous phase morphology created by sublimation of organic solvent from aggregated poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solution with freeze-dry method. Poly(3-hexylthiophene) (P3HT) tends to aggregate in selected solvent and forms an 3-D network structure in an equilibrium condition. The resultant morphology at different conditions was revealed by scanning electron microscopy and X-ray powder diffraction (XRD), while the optical properties were characterized by Raman and fluorescence spectroscopy. Without post-annealing, a sharp XRD peak at 5.4, corresponding to the interplanar packing between P3HT chains [2], and a narrow Raman peak at 1440 cm-1, representing the C=C stretching vibration of the thiophene ring [3], emerge in the samples fabricated by the freeze-dry method. These structural features appear only when the spin-coating sample was thermally annealed, indicating that the local order within P3HT domains can be directly created by the freeze-dry method. In comparison with the P3HT:PCBM film fabricated by the freeze-dry method and that fabricated by spin-coating, the short-wavelength wing of the fluorescence spectrum of the P3HT:PCBM film fabricated by the freeze-dry method is depleted. This behavior can be visualized in the following way. The core of the aggregated P3HT fibers, not contacting with PCBM molecules, emits red-shifted fluorescence photons. On the other hand, the P3HT on the surface of the fibers, which is expected to emit short-wavelength wing of the fluorescence spectrum, interacts with the attached PCBM, resulting in efficient charge transfer between P3HT and PCBM and thus fluorescence quenching. Further in-depth investigation on the charge-transfer dynamics of these freeze-dry fabricated fibers can be revealed by steady-state photoinduced absorption and femtosecond transient spectroscopy in the future. [1]G. Yu et al., Science 270, 1789 (1995).[2]H. Sirringhaus et al., Nature 401, 685 (1999).[3]E. Klimov et al., Macromolecules 39, 4493 (2006).
9:00 PM - D4.7
Conjugated Polymers Based On Fusing Bithiophene with Planar Aromatics For Bulk Heterojunction Solar Cells.
Samuel Price 1 , Andrew Stuart 1 , Wei You 1
1 Chemistry, UNC-CH, Chapel Hill, North Carolina, United States
Show AbstractDesign strategies for low band gap conjugated polymers in photovoltaic devices have often been motivated by convenience or have lacked solid rationale. This presentation will discuss our current design rationale for low band gap photovoltaic materials. Our design process begins with the selection of a planar, fused heterocyclic system of two thiophenes flanking a tunable inner ring. Three donor moieties, based upon bithiophene flanking pyrrole, benzene, or pyridine were studied in this research, which provided a family of polymers with a variable range of oxidation potentials. After the donor moieties have been selected, they are copolymerized with a series of co-monomers which are chosen to increase the short circuit current of the resulting photovoltaic cells. These co-monomers increase the current of the solar cells by primarily lowering the band gap, increasing the hole mobility, or increasing the molecular weight of the resulting polymer. Detailed structure/property relationships will be discussed. Application of this design strategy has ultimately resulted in over 4% efficiencies (1 sun condition) of un-optimized photovoltaic devices fabricated from blending one of these studied polymers with C60-PCBM. This represents one of the highest efficiencies from a bulk heterojunction solar device of any low band gap polymers with C60-PCBM.
9:00 PM - D4.8
A computational Study on the Solar-cell Efficiency of Low Band-gap Copolymers Having Benzothiadiazole Acceptor Unit.
Jamin Ku 1 2 , Yun Hee Jang 1 2
1 MSE, GIST, Gwangju Korea (the Republic of), 2 PIMS, GIST, Gwangju Korea (the Republic of)
Show AbstractLow band-gap copolymers are used in organic solar cells for better harvesting of the solar spectrum. It is well known that alternating donor and acceptor units generally lowers the band gap of the polymer. A great deal of effort in developing high-efficiency solar cells is focused on finding the optimum combination of donor and acceptor units. In this work, we constructed four different donor-acceptor systems where a promising benzothiadiazole (BT) acceptor unit is connected to each of four fused-ring donor units; carbazole (Cz), fluorene (F) cyclopentadithiophene (CPDT), and dithienopyrrole (DTP). Then the geometry, the electronic structure and the electronic transition of these four systems were calculated using the density functional theory (DFT) and the time-dependent DFT (TDDFT). In this calculation, CPDT-BT and DTP-BT exhibit lower band gap and stronger absorption of visible light than F-BT and Cz-BT in agreement with experimental results. Calculation also indicates that CPDT-BT has deeper HOMO/LUMO levels than DTP-BT, and the highest open-circuit voltage and solar cell efficiency among the four systems. Based on this result, we repeated the same calculation on four other donor-acceptor systems having lower band gap and deeper HOMO/LUMO levels than CPDT-BT. We suggest that CO-BT (CPDT-BT with carbonyl group) can have the solar cell efficiency increased up to 5.0%.
9:00 PM - D4.9
Amorphous Metal Oxides For Organic Opto-electronics.
Ajaya Sigdel 1 , Daniel Gaspar 2 , Asanga Padmaperuma 2 , Dana Olson 3 , Sean Shaheen 1 , John Perkins 3 , David Ginley 3 , Joseph Berry 3
1 Department of Physics and Astronomy, University of Denver, Denver, Colorado, United States, 2 , Pacific Northwest National Laboratory, Richland, Washington, United States, 3 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTransparent conducting oxides (TCOs) based on substitutionally doped zinc oxide and novel amorphous oxides offer the potential of high performance and low cost for organic solid-state lighting and organic photovoltaic (OPV) applications. In addition, new materials are sought that have greater stability than traditional materials such as indium tin oxide (ITO), which can contribute to organic device degradation through indium diffusion into the organic layers during operation. Here we present studies on both organic light emitting diodes (OLED) and OPV devices in which amorphous oxides such as InZnO are used solely as the transparent contact or in combination with crystalline TCO materials such as ITO and gallium doped zinc oxide (GaZnO). We demonstrate that these materials can be inserted into OPV devices resulting in performance comparable to ITO based devices. We also explore the use of amorphous oxides to modify the work function of the contact to better match the active organic materials for improved carrier injection or extraction at the oxide organic interface.
Symposium Organizers
Michael L. Chabinyc University of California-Santa Barbara
David Gundlach National Institute of Standards and Technology
Jenny Nelson Imperial College London
Takao Someya University of Tokyo
D5: Morphology & Characterization II
Session Chairs
Wednesday AM, December 02, 2009
Republic B (Sheraton)
9:30 AM - **D5.1
Solution Processable Diketopyrrolopyrrole-based Materials for Applications in Bulk Heterojunction Solar Cells and Organic Transistors.
Thuc-Quyen Nguyen 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractMolecular materials offer advantages over polymeric materials in terms of ease of synthesis and purification, which greatly improve fabrication reproduciblity, while also possessing a greater tendency to self-assemble into ordered domains with high charge carrier mobilities. Most important, small molecules do not suffer from batch to batch variations, broad molecular weight distributions, end group contamination, and difficult purification methods, as is the situation for their polymeric counterparts. Our research focuses on the design and synthesis of diketopyrrolopyrrole (DPP)-based materials having a broad absorption spectrum and high charge carrier mobility for applications in organic solar cells and thin film transistors. The molecular design incorporates the high mobility and ordered molecular packing of oligothiophenes together with the large optical density of the DPP core. The resulting molecules exhibit strong absorption at long wavelengths and strong molecular packing in the solid state. Functional groups attached to the DPP core can be used to tune the energy level, the band gap, the solubility, and hence, the film morphology and charge mobility. The field effect mobilities for some DPP-based materials are 0.02 cm2/Vs. Furthermore, these materials in combination with the widely-used acceptor PC71BM can be used to form the active layer in organic solar cells with power conversion efficiencies of 4.8% under simulated AM 1.5 solar irradiation.
10:00 AM - D5.2
Control of Morphology and Microcrystalline Structure of Inkjet-Printed Organic Semiconductors for Organic Thin-Film Transistors.
Kilwon Cho 1 , Jung Ah Lim 1 , Wi Hyoung Lee 1 , Donghoon Kwak 1 , Longzhen Qiu 1 , Juhyun Kim 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractInkjet printing of the uniform organic semiconductor films with desired molecular ordering becomes an essential challenge for direct-write fabrication of organic thin-film transistors (OTFTs) because the charge transport in organic semiconductor thin film is dictated by the film morphologies and molecular orientation of organic semiconductors. Here, we will present the systematic investigations for the control of the crystalline microstructure and morphological development of inkjet-printed organic semiconductors for high-performance OTFT devices. As a result, Microcrystalline development of inkjet-printed soluble pentacene, 6,13-triisopropylsilylethynyl pentacene (TIPS_PEN), is determined by evaporation-induced flows in a printed drying droplet that can be controlled according to surface wettability and solvent composition. With the high energy surfaces and controlled evaporation using mixed solvent, the inkjet-printed TIPS_PEN molecules are self-organized with a highly ordered crystalline structure, which is attributed to the contact line pinning and outward hydrodynamic flow within a drying droplet. These printed TIPS_PEN crystals can be successfully used to fabricate high-performance field-effect transistors with the high mobility. In addition, we demonstrate that inkjet printing of semiconducting/insulating polymer blend hold substantial promise as an active layer for direct-write fabrication of organic transistor. Controlled solubility for semiconducting component in a blend solution results in the formation of semiconductor nanowire network embedded in insulating polymer matrix, which provides an effective pathway for charge carrier transport through semiconductor nanowires, as well as significantly improves on-off current ratio and environmental stability. Our study provides an excellent method for controlling the film morphology and crystalline structure of organic semiconductors for the direct-write fabrication of high-performance organic electronics.Acknowledgement. This work was supported by a grant (F0004021-2008-31) from the Information Display R&D Center under the 21st Century Frontier R&D Program, Creative Research Initiative-Acceleration Research (R17-2008-029-01000-0).
10:15 AM - D5.3
Microfluidic Arrays for Rapid Characterization of Organic Thin Film Transistor Performance.
Christopher Bettinger 1 , Hector Beccerrill 1 , Cheng-Chung Lee 2 , Stephen Quake 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Bioengineering, Stanford University, Stanford, California, United States
Show AbstractThe electrical performance of devices based on organic semiconductors can vary significantly based on processing conditions. More specifically, solution-processable organic semiconductors, including both small molecules and polymers, are subject to a vast parameter space with respect to processing conditions. The solvent, solute concentration, evaporation conditions, and annealing temperature are all known to directly affect molecular packing, morphology, and crystallinity of organic semiconductor films, all of which produce a direct impact on the electrical performance of devices based on these structures. We hypothesized that a microfluidic-based platform could be utilized to rapidly screen the electrical properties of solution-processed organic semiconductors. In this work, we used soft-lithography to mold microfluidic devices composed of perfluoropolymer, which were designed to handle and mix small volumes of organic solutions of regioregular poly(3-hexylthiophene) (P3HT). These microfluidic devices were used to deposit arrays of P3HT on silicon substrates with a 300 nm thick silicon oxide gate dielectric treated with phenyltrimethoxysilane. The devices were designed to vary solute concentrations and binary solution composition across the microfluidic array. Substrates were then exposed to a thermal gradient, which varied the annealing temperature on the substrate spatially. The end result is a construct, which is able to create a two-dimensional array with varied solvent processing parameters across one axis and varied thermal annealing temperatures across the orthogonal axis. Gold electrodes were deposited to complete the transistor structures and performance metrics of these devices were recorded. These high throughput arrays were able to screen a wide parameter space of processing conditions to optimize device performance for P3HT transistors. These constructs could be used to optimize conditions with respect to device performance for future classes of solution-processable organic semiconductors as well.
10:30 AM - D5.4
Local Effects of a Single Molecular Dopant in Pentacene and Resultant Corollaries.
Sieu Ha 1 , Antoine Kahn 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractOver the past decade, electrical doping of organic materials has been shown to improve the performance of many organic devices, including light-emitting diodes and photovoltaic cells. It is generally agreed upon that doping increases the carrier concentration of molecular films, thereby increasing conductivity and allowing for space-charge regions at metallic contacts, which significantly reduce charge injection barriers. However, with respect to doping in inorganic semiconductors, the physics of doping in organic materials is relatively poorly understood. Several properties, such as how ionized molecular dopants affect carrier transport after donating charge, how dopants affect the crystallographic structure of the film, the strength of the dopant-host interaction, and the degree of delocalization of the released carrier, remain unknown. We have begun to study such molecular-scale properties using scanning tunneling microscopy for the system of pentacene p-doped with tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Our initial results showed that the hole donated by F4-TCNQ is localized by the potential of the ionized acceptor. We present here an extension of our previous work in which we further detail the effects of F4-TCNQ on pentacene. The spatial extent of the dopant effect is provided for both surface and subsurface acceptor molecules. Scanning tunneling spectroscopy is used to demonstrate how the Coulomb potential of the localized hole lowers the potential for electrons in the vicinity of the localized carrier. Moreover, given that the localized hole has a corresponding Coulomb potential, we can fit line profiles of observed dopant features to the Coulomb potential equation and extract an approximate relative permittivity for pentacene. Conversely, assuming a relative permittivity for pentacene, we can extract a peak Coulomb repulsion energy at the center of the dopant feature, which can be interpreted as the repulsion energy for two hole carriers on a single pentacene molecule. Our extrapolated values agree well with calculations of the Coulomb repulsion between two holes on single polyacene molecules (Phys. Rev. Lett. 93, 146405 (2004)).
10:45 AM - D5.5
Mapping Grain Orientation of High-Performance Polythiophene Thin Films by Transmission Electron Microscopy and Image Analysis.
Xinran Zhang 1 , Steven Hudson 1 , Dean DeLongchamp 1 , David Gundlach 2
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Semiconductor Electronics Division, national Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractPoly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophenes (pBTTTs) are among the best solution-processable semiconducting polymers in terms of field-effect charge carrier mobility (0.1 – 1 cm2 /V s), due to their long-range terraced structure within which the edge-on conjugated planes organize into a highly interdigitated layer-packing motif once the spun-cast pBTTT thin films are annealed from their mesophase on hydrophobic substrates. In this work, by using dark-field transmission electron microscopy (DF-TEM) and image analysis, we show that the characteristic terraced structure of a pBTTT with tetradecyl side chains (pBTTT-C14) is made up of micron- or submicron-sized crystalline grains which contain even smaller nanocrystals. The grain size is found to be dependent on the film thickness, the volatility of the solvent used for spin-casting, as well as how we define a “grain”. By comparing the activation energy, extracted from variable temperature electrical measurement, of films showing large difference in grain size, the importance of grain size and the gradient transition of grain orientation for charge transport is evaluated.
11:30 AM - **D5.6
Controlling Nanoscale Blend Morphology for Photovoltaic Devices.
Wilhelm Huck 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractControlling the nanoscale morphology is one of the key challenges in polymer-polymer blend organic photovoltaic devices. Despite significant progress in processing conditions, a systematic analysis of the influence of blend morphology on device performance and a general route to controlled nanoscale structures, are absent.Here, I will discuss two new strategies to systematically alter the nanoscale morphology in polymer blend devices based on nanoimprint lithography and diblock copolymers. The influence of morphology on device performance shows that our control allows a more rational approach to materials design for high efficiency photovoltaic devices.
12:00 PM - D5.7
Morphological Origins of the Efficient Electron Transport in a Naphthalenedicarboximide-Based Conjugated Polymer.
Jonathan Rivnay 1 , Michael Toney 2 , Zhihua Chen 3 , Yan Zheng 3 , Antonio Facchetti 3 , Alberto Salleo 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 , Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States, 3 , Polyera Corporation, Skokie, Illinois, United States
Show AbstractThe recent achievement of a printable, highly stable, and high performance (up to 0.85cm2/Vs) n-type polymer, poly{[N,N’-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6,-diyl]-alt-5,5’-(2,2’-bithiophene)}, P(NDI2OD-T2), along with p-type polymers with similar mobility has brought about renewed interest in low cost complementary circuit applications. The origins of P(NDI2OD-T2)’s high charge carrier mobility, however, is still unclear. To this end, we use high energy synchrotron radiation to, for the first time, reveal the likely packing motif of this high performance n-type polymer. We find that while there is poor ordering in the direction perpendicular to the substrate, consistent with previous findings, a high degree of order is present in-plane. The structure is further confirmed through morphological and texture analysis of aligned films, from which devices are tested to attempt further mobility enhancement. Finally, to test whether the high mobility of these films is due to film morphology or due to device geometry or interface modification inherent in device fabrication, bottom and top gated devices with the same dielectric are compared.
12:15 PM - D5.8
Charge Transfer at n-doped Organic-organic Heterojunctions and Application to Thin Film Transistors.
Wei Zhao 1 , Antoine Kahn 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractUnderstanding the energetics of organic-organic heterojunctions (OOH) is important since organic-based devices such as OLEDs and OPV cells comprise multiple such interfaces. OOH with type II staggered gap configuration, corresponding to donor-acceptor pairs applicable to OPV cells, are of particular interests. It has been shown that, for the donor CuPc / acceptor tris (thieno) hexaazatriphenylene derivative (THAP) pair, vacuum level shift (ΔEvac) and interface dipole (Δ) depend sensitively on the substrate work function (WF).1 In the work presented here, we modify the work function of one of the organic constituents by n-doping and investigate the impact of this doping on the electronic structure of two OOH: Alq3 / NTCDA and CuPc / C60.2 Doping the Alq3 film with Li reduces its WF to 2.7eV, which is significantly smaller than the 4.0eV electron affinity (EA) of NTCDA. Therefore NTCDA molecules adsorbed on Alq3:Li act as surface acceptors, capture electrons from the doped layer, and restore the WF of the film to its pre-doping level. The valence features of Alq3 also shift to lower binding energy in parallel to the increase in the WF. A very similar scenario occurs at the interface between CuPc n-doped with decamethylcobaltocene (CoCp2*) and C60, which also has a large EA equal to 4eV. In both cases, the charge carriers introduced by doping are separated from the parent dopants and fall in the acceptor material. A similar mechanism, called modulation doping, has long been used in inorganic semiconductor heterojunctions. In another set of experiments, we begin to exploit this idea in organic heterojunction thin film transistors with doped layer to investigate the mobility of transferred charges (without the presence of the dopants). We choose pentacene as the conducting channel material because of its extensive use in OFETs and reasonable stability in nitrogen. The device includes bottom Au contacts, a 60Å pentacene channel and a 300 Å N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'biphenyl-4,4diamine (α-NPD) layer, undoped or doped (1%) with the p-type molecular dopant molybdenum tris[1,2-bis(trifluoromethyl) ethane-1,2-dithiolene] (Mo(tfd)3). α-NPD has an ionization energy 0.4eV larger than that of pentacene. Hole carriers introduced by p-type doping in α-NPD are expected to transfer to the pentacene channel and increase its conductivity. A three-orders-of-magnitude increase in the channel current is indeed observed at Vgs=-50V and Vds=-40V compared to the undoped device. The potential of this modulation doping for use in OFETs is being investigated.1. W. Zhao, E. Salomon, Q. Zhang, S. Barlow, S. R. Marder, and A. Kahn, Phys. Rev. B 77, 6 (2008)2. W. Zhao and A. Kahn, J. Appl. Phys. (in press, 2009)
12:30 PM - D5.9
A Morphological Study of High Mobility Inkjet Printed Small Molecules Based Film Transistor.
Marie-Beatrice Madec 1 , Stephen Yeates 1
1 School of Chemistry, OMIC-University of Manchester, Manchester United Kingdom
Show AbstractPentacene based thin film devices are attractive because of the high field effect mobilities demonstrated by both vacuum deposition, 3 cm2 V-1 s-1 and in single crystals, 35 cm2 V-1 s-1 [1]. However integration in low cost large area processes is difficult as they are intractable and their crystal quality cannot be readily controlled. As an alternative, soluble pentacene derivative have been the subject of intensive recent investigation [2] attempting to combine good low cost solution processability with high performance. Although feasibility of inkjet printing of this family of compounds has been demonstrated [3]; to date it has proven difficult to control order over large areas. Additionally molecules of this class alone are not well suited for inkjet process as they reach their solubility limit before a workable viscosity can be achieved.Based on these observations, our study has been motivated by the development of robust, low cost, polymer like small molecule semiconductor ink formulations. Previously we have demonstrated that formulation with side chain aromatic insulating polymers can lead to production of thin film transistor with a saturated mobility steady at around 1cm2/Vs up to a dilution of 98% of the active semiconductor [4]. When formulated with a polymer dielectric their FET characteristics improve further, showing no hysteresis even though electrical characterisations are carried out in ambient atmosphere, demonstrating a protecting effect of the polymer host.Here we present data on the effect of processing conditions on the morphology study of a 1,4,8,11, tetramethyl substituted family soluble substituted pentacene [5] when inkjet printed, and comparison is made with spin coated and drop cast devices. [1] O.D. Jurchescu, J. Baas, T.M. Palstra, Appl. Phys. Lett., 84, 6, 3061[2] J. E; Anthony, Angew. Chem. Int. Ed. 2008, 47, 452-483[3] S H. Lee, M H. Choi, S H. Han, D J. Choo, J. Jang, S K. Kwon, Org. Electronics, 2008, 9 (5), 721-726[4] M-B. Madec, G. Rincon-LLorente, D.J. Crouch, S.G. Yeates, Proc. MRS 1114-G06-05, DOI: 10.1557/PROC-1114-G06-05[5] G. Rincon Llorente, Marie-Beatrice Dufourg-Madec, D. J. Crouch, R. G. Pritchard, S. Ogier and S. G. Yeates, Chem. Comm., 2009, 3059 – 3061.
12:45 PM - D5.10
Study of Photorewritable Memory Effect of Organic FET with Photochromic Interface Layer.
Manabu Yoshida 1 , Satoshi Miyagawa 2 , Kouji Suemori 1 , Toshihide Kamata 1 2
1 , AIST, Tsukuba, Ibaraki, Japan, 2 , Univ. of Tsukuba, Tsukuba, Ibaraki, Japan
Show Abstract It has been known that the performance of organic field effect transistor (OFET) is strongly affected by the interfacial condition between the gate dielectric and the semiconductor layers. Usually, a gate dielectric material or a surface modified layer on the gate dielectric layer was changed to investigate interfacial condition effects on the FET performance. However, these examination often accompanied with the quality change of the semiconductor layer. Therefore, it is not easy to study the original effect of interface condition change on the FET performance. On the other hand, Diarylethene (DAE) derivatives are known to be a representative photoisomerizable material. Its molecular properties, such as refractive indices, dipole moments, oxidation- reduction potentials and electronic characteristics, change by photo-irradiation, reversibly. In this study, we have examined to insert an DAE interface layer in the pentacene FET, and studied the effects due to energy level changes of the interface layer on the FET characteristics. An ITO was used as a transparent gate electrode. A PMMA film was used as a gate dielectric layer. The DAE (1,2-Bis(2,4-dimethyl-5-phenyl- 3-thienyl) perfluorocyclopentene was deposited onto the PMMA film as a photochromic interface layer. A pentacene film and Au D/S electrodes were deposited onto the DAE layer.In this prepared FET device, DAE formed a open-ring form by VIS light irradiation and a closed-ring form by UV light irradiation. The mobility of the FET with a open-ring DAE layer was larger than that of the close-ring state. This result would be explained by the energy level changes by the light irradiation. HOMO levels of the closed-ring and open-ring states were estimated to be 6.3 eV and 5.5 eV, respectively. The LUMO levels of the closed-ring and open-ring states were 3.7 eV and 3.2 eV, respectively. The HOMO level of pentacene was 5.6eV and the LUMO level was 3.7 eV. In the case of the open-ring form, HOMO level energy difference between pentacene and DAE is relatively large, and then the holes in the pentacene layer are not injected into the DAE layer. On the other hand, in the case of the closed-ring form, the energy difference between the pentacene and DAE was very small. This may cause the hole injection from pentacene to DAE layer. This may a reason why smaller mobility was obtained in a OFET with open-ring form. This phenomena was also contributed to show memory effect. We also tried to develop an printable OFET having non-volatile photo-memory effect using these properties of diarylethene derivatives.
D6: Charge Transport
Session Chairs
Wednesday PM, December 02, 2009
Republic B (Sheraton)
2:30 PM - **D6.1
Effect of Grain-boundaries on Transport and Trapping in Polymeric and Crystalline Organic Semiconductors.
Alberto Salleo 1 , Leslie Jimison 1 , Jonathan Rivnay 1 , Ludwig Goris 1 , Michael Toney 2 , Antonio Facchetti 3 , Tobin Marks 3 , Iain McCulloch 4 , Martin Heeney 4
1 Materials Science, Stanford University, Stanford, California, United States, 2 , SSRL, Menlo Park, California, United States, 3 Chemistry, Northwestern University, Evanston, Illinois, United States, 4 Chemistry, Imperial College, London United Kingdom
Show AbstractAs organic semiconductors approach commercialization, there is a need to better understand the relationship between charge transport and microstructure, in particular to identify the inherent bottlenecks to charge transport. A commonly accepted materials design rule is to synthesize molecular structures that promote the formation of large crystals. No consistent correlation however is found between grain size and mobility. This observation suggests the importance of the role of intergrain charge transport in semicrystalline and polycrystalline organic thin films.In semicrystalline polymeric semiconductors, the importance of grain bridging has been suggested. In order to study grain bridging, P3HT films were processed by directional crystallization to produce well-defined grain-boundaries. As a result of the directionality of the films, grain-boundaries across the fibers can be bridged by relatively straight polymer chains while the fiber-to-fiber grain-boundaries would force bridging chains to exhibit severe twists. TFT mobility measured along the fibers exceeds 10-2 cm2/V.s while that measured across the fibers is of the order of 10-3 cm2/V.s, with a minimum anisotropy factor of 20. This experiment clearly highlights the importance of grain-bridging by polymer chains in semicrystalline polymeric semiconductors. Furthermore, slow trapping (i.e. bias stress) is found to depend on the type of grain-boundary as well.The bridging mechanism previously described cannot exist in small molecule films. We determined that the local structure of grain-boundaries can greatly affect the electronic performance of these materials. Thin films of a high mobility, solution processable, n-type small molecule semiconductor (PDI8-CN2) are produced with engineered microstructures by promoting the growth of elongated and oriented crystallites. The crystalline structure and the packing of the molecules is verified by a combination of X-ray diffraction, AFM characterization and first principles DFT calculations. The types of grain-boundaries in the film is essentially reduced to two: one low-angle type and one high-angle type. It is found that the mobility of devices where the current flows across low-angle grain-boundaries (µ~2x10-2 cm2/V.s) is two orders of magnitude higher than that of devices where the current flows across high-angle grain-boundaries (µ~10-4 cm2/V.s). These findings are important in order to design small molecule materials that are relatively insensitive to grain-boundary orientation.
3:00 PM - D6.2
Bias-stress-induced Charge Trapping and Polymorphous Changes in Pentacene TFTs.
Masahiko Ando 1 , Tom Kehoe 2 , Masahiro Kawasaki 1 , Claudia Duffy 2 , Takashi Minakata 3 , Richard Phillips 2 , Henning Sirringhaus 2
1 Hitachi Cambridge Laboratory, Hitachi Europe, Ltd., Cambridge United Kingdom, 2 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 3 R&D Center, Asahi-Kasei Corporation, Fuji, Shizuoka, Japan
Show AbstractUnderstanding factors affecting the reliability of organic TFTs is important for future applications, and identification of the extrinsic and intrinsic factors is crucial for improvement. So far, we have proposed an intrinsic“polymorphous disorder”model to explain bias-stress instability in pentacene TFTs, based on the experimental results showing strong correlation between the micro-structural changes in the semiconductor layer and the threshold voltage shift due to electron trapping [1]. Peaks appearing in the high wave-number region around 1160 cm-1 in micro-Raman scattering were used to investigate the micro-structural changes. However, these peaks originate from intra-molecular vibration modes of a single pentacene molecule and the connection to larger-scale micro-structural change is still not clear.This paper reports observations vibrational modes in the low wave-number region (below 100cm-1) in pentacene films, which give clear evidence of micro-structural changes due to charge trapping. The modes originate in inter-molecular vibrations, and have been well characterized by using single-crystal samples and theory. Two kinds of spectra with distinctively different peaks (ex. 44cm-1 vs. 50cm-1) can be used to identify two different polymorphs, known respectively as the C-phase and the H-phase. TFT samples were prepared on a p-doped silicon wafer with 300 nm thermally grown SiO2. A 70 nm thick benzocyclobutene layer was spin-coated as an electron-trap-free gate insulator and a 100 nm thick pentacene layer was formed by using the zone-casting method with a solution of unsubstituted pentacene [2]. Highly crystalline pentacene films were obtained with single grains having widths of 10-100 µm and lengths of several mm, and with the field-effect mobility up to 0.7 cm2/Vs. We found that our solution-processed pentacene films are mainly composed of C-phase with partially dispersed H-phase. After applying a positive gate bias stress leading to electron trapping in the channel and a positive threshold voltage shift, we found that C-phase regions of the film adjacent to H-phase regions changed into H-phase or mixed-phase, and reversibly recovered by annealing at 130 C or by light irradiation. A measurement of thermally stimulated current revealed that the depth of the electron trapping states to be around 0.81 eV below the LUMO level of pentacene, a value close to those obtained by using other methods. Since high-purity pentacene films were made at high temperature (180 C), in nitrogen atmosphere and in-situ measurements were performed in a nitrogen atmosphere in an optical micro-probe chamber, impurities such as oxygen and water molecules do not play a central role in the reversible micro-structural changes accompanying charge trapping. We will discuss possible intrinsic charge trapping mechanisms induced by bias stress. [1] M. Ando et al., 2008 spring MRS meeting (San Francisco USA). [2] C. Duffy et al., Chem. Mater. 20, 7252(2008).
3:15 PM - D6.3
Hall Effect and the Charge Transport Mechanism in High-Mobility Organic Thin-Film Transistors.
Takafumi Uemura 1 , M. Yamagishi 1 , Y. Okada 1 , J. Soeda 1 , T. Nishikawa 1 , S. Shinamura 2 , I. Doi 2 , K. Takimiya 2 , J. Takaya 1
1 Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan, 2 Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
Show AbstractDevelopment of functional materials and understanding of the microscopic mechanisms mutually benefit through their close interaction. To accelerate development of organic semiconductor films for industrial application to flexible electronics devices, it is essential to understand mechanisms of charge transport in conjunction with both molecular-scale charge transfer and larger-scale inhomogeneity in the films. Here, we show that practically attractive charge-carrying performance in organic transistors is realized through diffusive charge transport of continuously distributed carriers. We employ Hall-effect measurement which directly differentiates the diffusive band transport from site-to-site hopping. So far, the Hall-effect measurement was reported only for rubrene single crystals and pentacene thin-films, so that the diffusive transport is evidenced only for very limited materials with rather high transfer integrals. In the present experiments, both thin-film and single-crystal transistors based on recently synthesized dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) with comparable transfer and reorganization energies, which happens in flexible molecules with lengthy π-conjugation. The result of the measurement shows clear evidence for the band transport as long as sufficient carriers are accumulated out of charge trapping sites. Therefore, typically addressed high carrier mobility ~ 1 cm2/Vs in well developed organic transistors is mostly provoked by the diffusive transport of carriers distributed continuously throughout the molecular systems.At lower gate voltage with more pronounced charge-trapping effects, however, crossover to the hopping transport takes place at the mobility of approximately 0.4 cm2/Vs. Since the subthreshold region is not well defined in single-crystal devices, the traps are originated at grain boundaries or due to molecular disorder at the semiconductor/gate insulator interfaces.
3:30 PM - D6.4
Molecular Contact Doping in Organic Thin-Film Transistors.
Frederik Ante 1 , Tobias Canzler 2 , Ansgar Werner 2 , Ute Zschieschang 1 , Klaus Kern 1 3 , Hagen Klauk 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Novaled AG, Dresden Germany, 3 , Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland
Show AbstractThe drain current of organic thin-film transistors (TFTs) is often limited by the energy barrier at the interface between the semiconductor and the source/drain contacts. This barrier can be reduced by choosing a contact metal with a workfunction matching the frontier orbital energy of the semiconductor [1], by modifying the metal workfunction with a thin oxide layer [2,3], or by introducing a self-assembled monolayer (SAM) with an appropriate dipole moment [4,5]. These methods lead to contact resistances as low as 1 kOhm-cm. A contact resistance of 80 Ohm-cm has been achieved by oxidizing the Au contact surface with a UV ozone treatment [6], but this method is not useful for TFTs with organic gate dielectrics damaged by UV ozone. In silicon FETs the contact resistance is minimized by incorporating dopant atoms into the Si lattice near the contacts. The dopants form strong covalent bonds with the surrounding Si atoms, preventing the dopants from drifting or diffusing into the channel. In organic TFTs stable contact doping is more difficult due to the limited positional stability of the dopants in the absence of covalent bonds, and there are very few reports of organic TFTs with doped contacts [7-9]. Here we show that the contact resistance of pentacene TFTs can be reduced from ~1 kOhm-cm to ~100 Ohm-cm by introducing a thin layer of a strong molecular dopant at the pentacene/contact interface. The dopant is a small organic molecule with a LUMO energy below the HOMO energy of pentacene, so electrons are transferred from the pentacene to the dopant, increasing the local density of excess holes in the pentacene near the contacts. The TFTs have Al gates, an AlOx/SAM gate dielectric (5.7 nm thick), vacuum-deposited pentacene (30 nm thick), a thin dopant layer (0.5 to 2 nm thick) and Au top contacts (30 nm thick). Dopant and Au contacts are vacuum-evaporated through the same shadow mask. TFTs with channel length between 10 and 100 µm were made. Apparent mobilities are between 0.3 cm2/Vs (L = 10 µm) and 0.6 cm2/Vs (L = 100 µm) for TFTs without contact doping and between 0.5 cm2/Vs (L = 10 µm) and 0.6 cm2/Vs (L = 100 µm) for TFTs with doped contacts. All TFTs have on/off ratios above 105, showing that the dopants do not diffuse into the channel. The contact resistance on four substrates without doping ranges from 0.9 to 2.5 kOhm-cm. For TFTs with doped contacts the contact resistance is between 100 and 700 Ohm-cm (four substrates). This clearly shows the great potential of molecular doping to reduce the contact resistance of organic TFTs. [1] Pesavento, J. Appl. Phys. 96, 7312, 2004; [2] Kumaki, Appl. Phys. Lett. 92, 013301, 2008; [3] Kano, Appl. Phys. Lett. 94, 143304, 2009; [4] Tulevski, J. Am. Chem. Soc. 128, 1788, 2006; [5] Cai, Org. Electr. 8, 936, 2008; [6] Stadlober, Adv. Funct. Mater. 17, 2678, 2007; [7] Park, Appl. Phys. Lett. 88, 113503, 2006; [8] Fujimori, Appl. Phys. Lett. 90, 193507, 2007; [9] Miyadera, Appl. Phys. Lett. 91, 013512, 2007
3:45 PM - D6.5
Bias-Stress Induced Instability in Polymer Thin-Film Transistors.
Jiyoul Lee 1 , Do Hwan Kim 1 , Bang-Lin Lee 1 , Jeong-Il Park 1 , Byungwook Yoo 1 , Bon Won Koo 1 , Sangyoon Lee 1
1 Display Lab., Samsung Advanced Institute of Technology, Yongin-si, Gyeonggi-do, Korea (the Republic of)
Show Abstract The performance of polymer semiconductor thin-film transistors (TFTs) has steadily improved to be utilized as active matrix display backplanes on flexible substrate. In particular, the mobility of the charge carriers in Polymer TFTs is already comparable to commercialized amorphous silicon (a-Si) transistors with field-effect mobilities of 0.5~1cm2/Vs. The ON-OFF current ratio of the polymers can exceed 107, meeting the requirements for backplanes, and the threshold voltage is also suitable for backplanes. In order to substitute for a-Si, the polymer based transistors should exhibit the same performance with respect to electrical reliability (e.g. bias-stress effect) as well as switching properties such as high mobility, high ON currents and low operating voltages. However, polymer TFTs usually suffer significantly from bias stress, causing the shift in threshold voltage (VT). The bias-stress effect on the polymer TFTs is generally more complex than on a-Si, and the underlying trapping mechanisms are less understood. In the present study, we investigated the bias stress effect on polymer thin-film transistors. The transistors utilize a novel donor-acceptor type liquid-crystalline semiconducting copolymer, poly(didodecylquaterthiophene-alt-didodecylbithiazole), PQTBTz-C12, which contains both electron-donating quaterthiophene and electron-accepting 5,5’-bithiazole units. The VT shift induced by DC bias stress has been analyzed for different gate-source and drain-source voltages. By fitting the time dependent VT shift to a stretched exponential function, the time constant of the VT shift were determined for each condition. We observed that the VT shift due to charge trapping can be recovered by halting the device for several hours and the recovery rate from DC ON bias stress is slightly slower than the recovery from DC OFF bias stress. The difference in the recovery rates between ON and OFF may be attributed to the different charge releasing time of the deep trap state. Also, it is important to note that the recovery rate difference have influence on VT shift direction of the polymer TFTs subjected on AC bias stress, resulting in more and less moderate VT shift of the polymer TFTs under AC bias stress.
4:30 PM - **D6.6
Charge Transport Mechanism in N-Channel Polymers for Printed Transistors.
Antonio Facchetti 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractIn this presentation we will describe the achievement of several new n-channel polymeric materials for printed transistors based on the naphthalenebis(dicarboximide) core co-polymerized with various aromatic functionalities. The new materials exhibit, besides excellent charge-transport characteristics in ambient, high chemical stability, tuned solubility in common organic solvents, and low-temperature processing. These n-channel semiconducting polymers can be integrated with common p-channel materials, such as P3HT, using a single gate dielectric/contact material set, which is a prerequisite for inexpensive complementary circuit technology fabrication. Our new polymers exhibit solubilities between 5 to 60 g/L which allow the fabrication of polymeric transistors using various techniques including spin-coating as well as gravure, flexo, and inkjet printing, demonstrating great processing versatility. The resulting OTFT on plastic substrates exhibit electron mobilities approaching 1 cm2/Vs in ambient with Au contacts and various polymeric dielectrics. Finally, variable-temperature measurements of the transistor characteristics provide insights into the charge transport mechanism in this new polymer family.
5:00 PM - D6.7
Band-like Temperature Dependence of the Mobility in Solution-processed Organic Field-effect Transistors Based on 6,13-bis(Triisopropylsilylethynyl) Pentacene.
Tomo Sakanoue 1 , Henning Sirringhaus 1
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom
Show AbstractThe small-molecular-weight organic semiconductor, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) has become one of the best performing organic semiconductors for organic field-effect transistors (OFETs) due to good solution processibility and a tightly packed molecular arrangement in the crystal. The crucial issues in solution-processed crystalline films, i.e., poor uniformity and reproducibility, can be overcome and reliable high-performance devices with mobilities over 1 cm^2/Vs have been reported by several groups. However, details of carrier injection and transport in high-performance TIPS-pentacene-based OFETs have not yet been well understood. Here, we demonstrate high performance top-gate, bottom-contact TIPS-pentacene OFETs, which have high mobility of 1.0-1.6 cm^2/Vs and are prepared by spin-coating. Temperature-dependent measurements of the FET characteristics as well as gated four point probe measurements were carried out to investigate the details of the carrier transport and injection. The mobility in an OFET with a channel length of 20 um was found to increase with decreasing temperature, exhibit a maximum around 200 K, and then decrease with further cooling with small activation energy. This indicates that there are shallow traps in the TIPS-pentacene layer but no deep traps similar to the case of single crystal OFETs. Devices with shorter channel length of 5 um exhibited a band-like increase of mobility with decreasing temperature down to at least 80 K. The different temperature dependence in long and short channel devices suggests that shallow traps are related to grain boundaries because the grain size of our TIPS-pentacene crystal is ~5 um. A smaller number of traps is expected in the shorter channel length device. The gated four point probe measurements reveal that the contact resistance is small, i.e. 3-8 kOhm cm at the gate voltages of -60 V, but still makes up 40-60% of the total device resistance in the 20 um channel length device. Analysis of the four-point probe data reveals that the contact resistance originates not from the injection energy barrier at the TIPS-pentacene/electrode interface but from the bulk resistance of the TIPS-pentacene film in the vicinity of the electrodes.
5:15 PM - D6.8
Low-Voltage Ambipolar Organic Field-Effect Transistors.
John Labram 1 , Donal Bradley 1 , Thomas Anthopoulos 1
1 Department of Physics, Imperial College London, London United Kingdom
Show AbstractCurrently most organic field-effect transistors (OFETs) are reported to be unipolar, i.e. only able to inject and transport carriers of a single type; either holes (p-type) or electrons (n-type). Recently however fabrication of ambipolar OFETs that are capable of transporting both holes and electrons has been reported[1]. Furthermore, complementary-like integrated circuits based on ambipolar transistors have proven easier to fabricate than truly complementary ones, due to the difficulty in producing laterally resolved p- and n-type transistors on a single substrate. In the interest of keeping manufacturing costs low, it is therefore of vital importance that high-performance ambipolar OFETs are developed. Unfortunately, all ambipolar OFETs reported to date have only operated at high voltages (>|30V|). This makes the practical implementation of organic complementary-like electronics for certain applications, such as portable devices, impossible. For the wide-spread commercialisation of organic electronics to be realised it is hence of critical importance that circuits based on ambipolar OFETs can be demonstrated that operate at much lower voltages. Here we report the fabrication of ambipolar OFETs operating at voltages below |3V|. The approach employed in this work involves the use of self-assembled monolayer (SAM) gate dielectrics in combination with heterojunction-type semiconductor layers. Using a combination of vacuum-deposited and solution-processible semiconductor materials we have fabricated p-n type heterojunction OFETs that exhibit hole and electron mobilities on the order of 0.001 and 0.1 cm^2/Vs respectively. By using a combination of ambipolar OFETs, we are able to demonstrate complementary-like inverters that operate at voltages below |3V| and exhibit signal gain of 35. It is established that the same heterojunction semiconductor structure employed here lends itself to the efficient separation of photo-generated charge-carriers created at the interface between the two materials. The devices can hence be used as low-voltage phototransistors. Unlike photodiodes, the responsivity of phototransistors can be tuned by an appropriate choice of the biasing conditions[2]. By illuminating the transistor channel of the low-voltage ambipolar OFETs, the drain current is found to increase. The magnitude of the photo-induced current is modulated by the optical power density and wavelength of the incident light. This allows the phototransistor to be used as colour selective optical sensor. This work paves the way towards low-cost, large-area electronics and optical sensor arrays. References:[1]. E. J. Meijer, D. M. de Leeuw, S. Setayesh, E. Van Veenendaal, B.-H. Huisman, P. W. M. Blom, J. C. Hummelen, U. Scherf, and T. M. Klapwijk, Nat. Mater. 2, 678 (2003).[2]. T. B. Singh, R. Koeppe, N. S. Sariciftci, M. Morana and C. J. Brabec, Adv. Func. Mater. 19, 789 (2009).
5:30 PM - D6.9
Threshold Voltage Instabilities in Low-Voltage Organic Transistors.
Florian Colleaux 1 , James Ball 1 , Paul Wobkenberg 1 , Donal Bradley 1 , Thomas Anthopoulos 1
1 Physics, Imperial College, London United Kingdom
Show AbstractOrganic bistable memory devices have attracted great interest due to their key role in the development of low cost electronic integrated circuits. Here we present our recent work on electrical field induced threshold voltage shift observed in low-voltage C60 methanofullerene field-effect transistors based on phosphonic acid self-assembled monolayer (SAM) gate dielectrics. In particular, by applying a positive gate voltage on the order of 2.5 V, the threshold voltage is shifted toward higher voltages by approximately 0.5 V. This memory window is rather significant when one takes into account the rather low operating voltage of the transistors (1-1.5 V). The threshold voltage is found to shift back to its initial voltage levels when applying a negative gate bias. In both cases, the threshold shift increases with increasing external applied voltage and bias time. Using this device property we have been able to define the bistable states - i.e. on/off - and extract various important parameters such as on/off current modulation, writing/erasing speed as well as the retention time for both on/off states. The observed bias stress effect is most likely due to charge trapping at the semiconductor/dielectric interface. The carrier trapping and release processes were studied by employing temperature dependence electrical measurements for different SAM dielectrics and various organic semiconductors. Whilst the origin of the threshold voltage shift is not yet completely understood, the devices show good memory behaviour at very low operating voltage and hence are promising for application as low power organic memory devices.
5:45 PM - D6.10
Low-voltage Solution-processed n-channel Organic Field-effect Transistors with high-k HfO2 Gate Dielectrics Grown by Atomic Layer Deposition.
Shree Tiwari 1 , Xiao-Hong Zhang 1 , Sung-Jin Kim 1 , William Potscavage 1 , Bernard Kippelen 1
1 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWe report on the high performance solution-processed n-channel organic field-effect transistors (OFETs) based on [6,6]-phenyl C61 butyric acid methyl ester ([60]PCBM) with very low operating voltages (3V). The very low-voltage operation in these OFETs was achieved by the combination of high-k hafnium dioxide (HfO2, k~15) gate dielectric grown by atomic layer deposition (ALD) with a thin buffer layer of divinyltetramethyl-disiloxanebis(benzocyclobutene) (BCB) on top. BCB was used to minimize electron trapping at the dielectric/semiconductor interface, which is a primary limiting factor for n-channel conduction [1]. The capacitance density of 50 nm-thick HfO2 deposited by ALD is as high as ~ 260 nF/cm2. Even though this number is reduced to ~71 nF/cm2 by using the thin BCB buffer layer, the total capacitance density is still high enough for low-voltage applications. The devices (with a channel length of 25 μm and a channel width of 2000 μm) operated at 3V exhibit excellent n-channel performance with a high electron mobility value of 0.11 cm2/Vs, a low threshold voltage of 0.73 V and a high current on/off ratios (>105) with a sub-threshold slope of 170 mV/decade. With Ca (capped with Al in this case) as top-contact source and drain (S/D) electrodes, which provide a very low contact resistance with [60]PCBM [2], the mobility and threshold voltage are found to be almost independent of channel length within the studied region of 25 μm to 200 μm. The mobility values obtained here are similar to the values reported in our recent study [2], but the operating voltages here are reduced by 10 times with the application of high-k HfO2 gate dielectric layer by ALD.
[1]L.-L. Chua, J. Zaumseil, J.-F. Chang, E. C. W. Ou, P. K. H. Ho, H. Sirringhaus, and R.H. Friend, Nat. 434, 194 (2005).
[2]S.P. Tiwari, X.-H. Zhang, W.J. Postcavage, Jr., and B. Kippelen, Accepted, J. Appl. Phys. (2009).
D7: Poster Session II
Session Chairs
Michael Chabinyc
David Gundlach
Jenny Nelson
Takao Someya
Thursday AM, December 03, 2009
Exhibit Hall D (Hynes)
9:00 PM - D7.1
Molecular and Electronic Structure of Organic Semiconductor Interfaces on Ultra-thin Oxide Films.
Brad Conrad 1 , William Cullen 1 , Daniel Dougherty 2 , Tracy Moore 1 , Steve Robey 2 , Ellen Williams 1
1 Physics and Materials Research Science and Engineering Center, University of Maryland College Park, College Park, Maryland, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractScanning tunneling microscopy (STM) is utilized to molecularly resolve and probe the interactions and interfaces of organic semiconductors. To mimic a device substrate and growth modes, ultra-thin oxide (UTO) films less than 1 nm thick are grown on Si(111) in ultrahigh vacuum at room temperature. These films are characterized by STM and display a long range RMS roughness of 0.109 nm versus a typical RMS roughness of 0.3 nm for thick SiO2. UTO films are then used as substrates for growth of pentacene and C60. Standing up pentacene is molecularly resolved[1] and described by a thin-film phase unit cell with a=0.76nm and b=0.59nm in the ab-plane. The morphology and electronic structure of C60 and co-depositions of pentacene and C60 deposited on UTO films will be discussed. Results will be placed in the context impact on organic photovoltaic device design and energy harvesting optimization. This work was supported by NIST under contract no. 70NANB6H6138 with research infrastructure supported by the UMD-CNAM and NanoCenter. STM measurements were carried out using the UMD NSF-MRSEC SEF DMR-05-20471. [1] Conrad, Cullen, Riddick, Williams; Surface Science, 603, 3, L27 (2009) doi:10.1016/j.susc.2008.12.020
9:00 PM - D7.10
Enhanced Charge Transports in Polymer Thin Film Transistors Prepared by Contact Film Transfer Method.
Qingshuo Wei 1 , Shoji Miyanishi 1 , Keisuke Tajima 1 , Kazuhito Hashimoto 1 2
1 , The University of Tokyo, Tokyo Japan, 2 , JST-ERATO HASHIMOTO Light Energy Conversion, Tokyo Japan
Show AbstractCharge carrier transports in the structures formed at the surface of various conjugated polymer films were investigated by constructing organic thin film transistors using a novel and simple contact film transfer method. By using this method, organic films can be transferred onto various target substrates with the sizes more than several square centimeters without damage. This film transfer process inverts the film geometry, and therefore the bottom-gate thin film transistors (TFTs) fabricated from the transferred films have transport layers originally formed at polymer/air interface. This fabrication process has advantages over the top-gate TFTs to preserve the interfacial structures during the transfer since there are no external forces or thermal treatment needed.As the result, TFTs prepared by the transfer process showed higher field effect mobility values compared with the conventional spin-coated devices for all the polymers studied. In contrast to the previous reports, the hole mobility in regioregular poly(3-alkylthiophene)s (C4 ~ C12) did not depend on the alkyl chain length when the contact film transfer was applied (from 0.05 cm2/Vs to 0.09 cm2/Vs). These results suggest that higher order out-of-plane orientation of the thiophene rings and strong interchain interaction are spontaneously formed at the polymer/air interfaces during the spin-coating.1 Furthermore, contact film transfer can be easily applied to prepare the layered structures free from the constraints of the conventional solution process. To demonstrate this, ambipolar OTFTs with a bilayer structure of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester were also fabricated by using this method. The transistors showed high electron and hole mobilities of 2.1×10-2 cm2 V-1 s-1 and 1.1×10-2 cm2 V-1 s-1, respectively. Complementary inverters based on two identical ambipolar transistors showed good performance with a gain of 14.2These results suggest that the contact film transfer method could provide a facile and general method to evaluate the electronic properties of semiconducting organic materials and fabricate multilayer structure of different organic materials. The bias-stress stability of the transistors prepared by the contact film transfer and interfacial property control by using surface-segregated monolayer3 will be also presented. [1] Wei, Q.S.; Miyanishi, S., Tajima, K. and Hashimoto, K., Adv. Funct. Mater. submitted.[2] Wei, Q.S.; Tajima, K. and Hashimoto, K., ACS Appl. Mater. Interfaces. submitted.[3] Wei, Q.S.; Nishizawa, T.; Tajima, K. and Hashimoto, K., Adv. Mater. 2008, 20, 2211-2216.
9:00 PM - D7.12
Large-scale Transfer of Organic Nanofibers by Soft Stamping.
Kasper Thilsing-Hansen 1 , Jakob Kjelstrup-Hansen 1 , Horst-Guenter Rubahn 1
1 MCI, University of Sourthern Denmark, Soenderborg Denmark
Show AbstractSmall phenylene-based molecules show significant potential in future nanoscale photonic and (opto-) electronic applications owing to their ability to self-assemble into large area arrays of mutually parallel, crystalline nanostructures here termed ‘nanofibers’ [1]. For example, para-hexaphenylene (p6P) based nanofibers can emit polarized blue light through photoluminescence and have waveguiding and lasing capabilities [2], while p6P thin films have been applied as the light emitter in organic light-emitting devices (OLEDs) [3] suggesting the use of p6P nanofibers as a nanoscale OLEDs.The p6P based nanofibers are grown under high vacuum conditions in a molecular beam epitaxy process, in which the molecules are deposited onto a freshly cleaved mica substrate, resulting in the self-assembly of crystalline, mutually parallel nanofibers [1]. The nanofiber size and density can be controlled via the deposition rate and temperature of the mica substrate. Since any pre- or post-processing of the mica growth substrate is not feasible, one of the remaining key challenges is to transfer the nanofibers from the growth substrate to a processable device substrate in order to realize for example a nanofiber OLED, similar to the strategy often used with inorganic semiconductor nanowires [4]. However, such transfer strategies are considerably hindered by the soft and mechanically fragile nature of the van der Waals-bound molecular crystals causing easy disruption of the nanofiber morphology and thereby of their unique properties.In this paper, we report a soft stamping method, which allows us to transfer the nanofibers without altering their shape and orientation. This requires the ability to controllably release the nanofibers from the mica substrate upon mechanical contact with the receiver substrate. Such controlled release is accomplished by performing the soft stamping process in a humidity and temperature controlled atmosphere. We demonstrate how large areas (several square millimeters) of well-aligned nanofibers can be transferred onto an unstructured receiver substrate, and how defined areas of well-aligned nanofibers can be transferred onto a structured receiver substrate. Finally, we show how this method can also be applied in the transfer of nanofibers onto a device substrate with pre-fabricated metal electrodes thereby enabling electrical connection to be made to the nanofibers.References[1] F. Balzer and H.-G. Rubahn, Avd. Func. Mater., 15 (2005) 17[2] M. Schiek, F. Balzer, K. Al-Shamery, J. R. Brewer, A. Lützen, and H.-G. Rubahn, Small, 4 (2008) 176[3] H. Yanagi and S. Okamoto, Appl. Phys. Lett., 71 (1997) 2563[4] Z. Fan, J. C. Ho, Z. A. Jacobson, H. Razavi, and A. Javey, Proc. Natl. Acad. Sci. U. S. A., 105 (2008) 11066
9:00 PM - D7.13
Organic Field Effect Transistors from Simple Molecules on Plastic Substrates.
Mihai Irimia-Vladu 1 , Reinhard Schwoediauer 1 , Marius Bodea 4 , Guenther Schwabegger 3 , Siegfried Bauer 1 , Niyazi Sariciftci 2
1 Soft Matter Physics, Johannes Kepler University, Linz Austria, 4 Institute of Applied Physics, Johannes Kepler University, Linz Austria, 3 Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz Austria, 2 Linz Institute of Organic Solar Cells, Johannes Kepler University, Linz Austria
Show AbstractGreen technology based on compostable materials is seen as an ultimate goal for solving waste problems. Currently there are large efforts for producing compostable plastic materials that can be used in daily life products, such as plastic bags, disposable dishware, etc. Organic electronics could be suitable to low-end products, where electronics may be directly integrated on plastic cups to store information, like prices, use-by-date information etc. When such daily items are produced with wastable materials, electronics included in such goods should be also based on materials that are easily degradable. Here we show first steps towards electronics based on inexpensive and non-toxic organic dielectrics and semiconductors in field-effect devices built from simple molecules on plastic substrates. The transistor characteristics (output and transfer) are stable and reproducible, showing p-type transistor characteristics with very low leakage current.
9:00 PM - D7.14
High-Performance Organic Transistors from Soluble Acene-Polymer Blend Semiconductors.
Wi Hyoung Lee 1 , John Anthony 2 , Donghoon Kwak 1 , Kilwon Cho 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk, Korea (the Republic of), 2 Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractWe report on the structural development and phase separation behavior of spin-cast difluorinated triethylsilylethynylanthradithiophene (F-TESADT) and poly(methyl methacrylate) (PMMA) blends and their application in field-effect transistors (FETs). Although F-TESADT is highly crystalline small-molecular semiconductor with excellent field-effect electronic properties, its use in FETs is limited by the dewetting of film especially when solvent with high boiling point is used for solution processing. For this reason, PMMA–insulating polymer with good film-forming characteristics–is blended with F-TESADT for enhancing processing window. Because F-TESADT–the phase with lower surface energy than PMMA–is preferentially segregated at the air-film interface during spin-casting, conducting channel is maintained in a direction parallel to the substrate. Morphological and structural characterizations confirm that highly crystalline F-TESADT crystals are formed on PMMA. The use of these phase-separated blend films as active layer leads to high mobility FETs with good environmental and electrical stability.Acknowledgement. This work was supported by a grant (F0004021-2008-31) from the Information Display R&D Center under the 21st Century Frontier R&D Program and Creative Research Initiative(CRI)-Acceleration Research (R17-2008-029-01000-0).
9:00 PM - D7.15
Impact of Electrode Modification on the Morphology and Carrier Mobility of an N-type Organic Semiconductor.
Parul Dhagat 1 , Hanna Haverinen 2 , R. Kline 3 , D. Fischer 3 , Dean DeLongchamp 3 , Ghassan Jabbour 1
1 School of Material and Flexible Display Center, Arizona State University, Tempe, Arizona, United States, 2 Dept. of Electrical and Information Engineering, University of Oulu, Oulu Finland, 3 Polymers Division, NIST, Gaithersburg, Maryland, United States
Show AbstractWe investigate the effect of self-assembled monolayer (SAM) treatment of gold electrodes on morphology and carrier mobility of devices fabricated using PTCBI (3,4,9,10-perylenetetracarboxylic bis-benzimidazole;), an n-type organic semiconductor (LUMO ≈ 4.2 eV). A series of alkane thiols of increasing chain lengths ranging from octanethiol (C8), decanethiol (C10), dodecanethiol (C12) to octadecanethiol (C18); and two fluorinated thiols: 1H,1H,2H,2H-perfluorohexanethiol (PFHT) and pentafluorobenzenethiol (PFBT) are used for metal surface modification. We use near edge X-ray absorption fine structure spectroscopy (NEXAFS) and atomic force microscopy to determine the disorder and surface roughness of the SAM, respectively. Additionally, the work function of gold upon SAM treatment is characterized using Kelvin probe microscopy. We find that the long alkyl chains C18, C12 and C10 are vertically oriented; however, C8 and the fluorinated SAMs are disordered and have poor coverage. The root-mean-square surface roughness of thiol treated substrates is between 1.0 to 1.6 nm. As expected the work function (WF) of untreated gold (5.1 eV) decreases monotonically with increasing alkyl chain length to 4.4 eV for the C18 layer, bringing it closer to the LUMO level of PTCBI; while the fluorinated thiols shift the WF of gold to 5.6 eV. The morphology of PTCBI upon gold treated surface is examined using both grazing incidence x-ray diffraction (GIXD) and NEXAFS. We find that PTCBI orientation atop C18, C12 and C10 treated gold surface is similar to that atop octadecyltrichlorosilane (OTS-18) treated surface [1]. However, in case of untreated gold, C8 and PHBT treated gold surface, PTCBI exhibits a disordered plane on-orientation. PTCBI deposited on PFBT treated surface shows similar orientation as C18 treatment but is more disordered than C18 surface. Carrier mobility is obtained using bottom gate/bottom contact organic thin film transistor (OTFT) devices (W/L= 1000/20). The dielectric surface for all devices is treated with OTS-18 before deposition of PTCBI. We find that mobility data does not indicate a definite trend, in C18 to C10 layers with mobility values ≈ 6.3x10
-3 cm
2/V-s. Additionally, devices fabricated from C8 thiol, PFHT and PFBT treated gold electrodes exhibit performance comparable to untreated gold electrodes (4.3 x 10
-3 to 3.0 x 10
-3 cm
2/V-s). We expected that lowering the WF of gold to match the LUMO level of PTCBI would aid in charge injection. However, the lack of a consistent mobility trend with respect to WF especially for long chain alkane thiols (C10 to C18) indicates that tuning the injection barrier as well as understanding the PTCBI morphology at the electrode/dielectric interface is key to superior OTFT performance. [1] P. Dhagat et. al., accepted for publication in Advanced Functional Materials, 2009 contact email:
[email protected]9:00 PM - D7.16
Adjusting Ambipolar Charge Transport in a Hybrid Organic (P3HT)/Inorganic (ZnO:Al) System.
Maria Hammer 1 , Carsten Deibel 1 , Vladimir Dyakonov 1
1 Experimental Physics VI, Julius-Maximilians University of Würzburg, Würzburg Germany
Show AbstractThe fabrication of efficient printable electronics demands the development of solution processed complementary circuits, where both n-type and p-type semiconductors are incorporated using a simple device architecture. One promising approach is the use of organic/inorganic hybrid systems. Whereas inorganic nanocrystalline zinc oxide has been successfully used in hybrid solar cells [1], the advantages of ZnO-polymer hybrids in field effect transistors have not been explored, yet.Inorganic materials offer the customizability of the charge transport properties via doping and therefore an optimum ambipolar performance in combination with the organic semiconductor. The organic counterpart offers all the advantages of polymer technologies, e.g. the printability. Furthermore, doping results in modifications of the inorganic component, such as surface roughness and porosity, which allows to define a three dimensional matrix for the subsequent infiltration of the organic component.We used sol-gel processed ZnO nanoparticles with various Al doping levels, as the n-type semiconductor, and regioregular-poly(3-hexylthiophene) (P3HT), as the p-type component, to fabricate field effect transistors with gold source and drain contacts on a SiO2 dielectric. The presented data will be discussed in terms of the charge transport in field effect transistors as well as the morphology of the thin films which was monitored via X-ray reflectance (XRR) measurements.In pure ZnO, the increase of the electron density due to extrinsic Al doping was compared to the accumulation of charge carriers in field effect transistor structures. This allowed us to assess the scattering effects due to extrinsic doping on the electron mobility. The latter decreases with increasing doping density. In contrast, the accumulation of electrons due to the applied gate voltage leads to an increasing mobility. We show that the conductivity of sol-gel processed nanocrystalline ZnO:Al is governed by an interplay of the enhanced charge carrier density and the doping-induced charge carrier scattering effects [2].The infiltration of the p-type component requires an enhanced porosity of the n-type component so that a close contact of both semiconductors with the dielectric can be provided. This is necessary for optimum electron and hole accumulation in the field effect structure and can be adjusted via Al doping of ZnO. We show that by doping the zinc oxide nanoparticles as well as by tuning the morphology of the blend it is possible to adjust a balanced electron and hole mobility in the hybrid material, which is indispensable for the performance of an ambipolar transistor.[1] W. J. E. Beek et al., Advanced Functional Materials 16, 1112 (2006)[2] M. S. Hammer et al., Nanotechnology 19, 485701 (2008)
9:00 PM - D7.17
High Gain Complementary Inverter Using Pentacene and Amorphous InGaZnO Channel Thin-film Transistors on Flexible Polyethersulfone Substrates.
Jungbae Kim 1 , Canek Fuentes-Hernandez 1 , Sungjin Kim 1 , Seungkeun Choi 1 , Bernard Kippelen 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractCurrent digital technology is based on complementary metal oxide semiconductor circuits that use n- and p- channel transistors to operate with low static power consumption and at high-speeds. High performance complementary inverters implemented with thin-film transistor technology potentially can lead to a generation of digital CMOS circuits, processed at low-temperature on flexible substrates at low-cost. Here, we report on organic-inorganic hybrid complementary inverters composed of pentacene and amorphous InGaZnO (a-IGZO) for p- and n- channel thin film transistors (TFTs) fabricated on flexible polyethersulfone (PES) substrate. These hybrid TFTs use a 300 nm-thick Si3N4 layer as gate dielectric. The Si3N4 and a-IGZO were deposited at low temperatures of 180 and 90 oC, respectively, using PECVD and RF sputtering on patterned gate electrodes. Pentacene, a p-channel active layer, was deposited using thermal evaporation followed by the patterned deposition of Au/Al on both p-channel pentacene and n-channel a-IGZO to serve as top source/drain electrodes through a shadow mask. The p- and n- channel TFTs show saturation motilities of 0.3 and 4 cm2/Vs and large on-off current ratios of 105 and 104, respectively. To achieve inverter with a high performance, differences in electron and hole motilities, and threshold voltages were compensated by resizing the width (W) of the n- and p-channel layers. The inverters yielded a high gain of 130 V/V and a switching threshold voltage of 12.5 V with high and balanced noise margins (noise margin low, and noise margin high) of 10.5V at a supply voltage of 25V. At a supply voltage of 30 V, gain values up to 165 V/V were achieved. The conditions for an optimum switching threshold voltage were achieved by tuning the total drain-to-source resistances of the TFTs. Therefore, the implementation of this well-known complementary technique with the use of organic p-channel and inorganic n-channel TFTs is a promising way to realize high performance complementary circuits on flexible substrates at low process temperature.
9:00 PM - D7.18
CMOS Inverters Through Dielectric Interface Modification: Aspects of Charge Trapping and Transport in OFETs.
Christopher Siol 1 , Martin Schidleja 1 , Christian Melzer 1 , Heinz von Seggern 1
1 Inst. of Materials Science, Technische Universitaet Darmstadt, Darmstadt, Hesse, Germany
Show AbstractFor the overall success of Organic Electronics a simple realization of organic devices is important. In addition, energy saving requires complementary MOS technology like in conventional semiconductor fabrication. For organic CMOS inverters the availability of exclusively p- and n-type organic field-effect transistors is essential. A novel technique will be presented that allows for the simple production of such transistors by interface modification of the gate insulator dielectrics by means of UV treatment of otherwise identical top contact structures for p- and n-type transistors implementing the same dielectric, semiconductor and source/drain metal. Two dielectric layers, consisting of thermally grown SiO2 and a spun-on PMMA polymer are followed by a vacuum deposited pentacene semiconductor. The device is completed by vacuum deposition of Ca (100nm) for the drain and source contacts. The generally ambipolar characteristic of pentacene will be altered through the introduction of electron traps at the gate dielectric PMMA through UV irradiation under ambient conditions in the presence of humidity and oxygen. The OFET with the non-irradiated PMMA dielectric exhibits exclusive n- transport whereas UV exposure of the PMMA dielectric transforms the OFET to stable unipolar p-type characteristics through charge trapping of electrons at the dielectric interface. It will be demonstrated that the p-conduction can be enhanced through an electrical conditioning step of cyclic application of a gate potential in ambipolar transport mode. The conditioning process as well as the charge trapping and transport physics will be investigated through Kelvin probe scanning microscopy. Finally it will be demonstrated that this technique can be utilized to build CMOS inverters with balanced mobility values for electrons and holes and maybe able to allow for an inexpensive fabrication of electrical circuits.
9:00 PM - D7.19
High Performance Organic Complementary Circuits with a Low-k and High-Tg Polymer Gate Dielectric.
Jaeyoung Jang 1 , Sooji Nam 1 , Se Kim 1 , Won Yun 1 , Chan Park 1
1 Polymer Research Institute, Postech, Pohang Korea (the Republic of)
Show AbstractOrganic field-effect transistors (FETs) have received great interests by many research groups in recent years for their potential applications in large area and flexible electronics with low cost processing. Among those, FETs with pentacene and PTCDI derivatives are the most promising candidates of p- and n-channel organic FETs respectively for the fabrication of organic complementary circuit because of their high mobility, which is comparable to that of amorphous silicon FETs.In this study, we introduced a low-k (2.45) and high Tg (~ 180oC) polymer gate dielectric for the fabrication of high performance organic complementary inverters composed of pentacene and PTCDI-C13 FETs. Since the polymer has very high Tg (meaning that there exists very small free-volume inside the polymer), it showed excellent insulating properties (a leakage current density of 10^-7 Acm^-2 at 2.0 MVcm^-1). Moreover, due to the high thermal stability of the dielectric polymer, PTCDI-C13 formed highly crystalline structure onto the dielectric after thermal annealing at 120oC, while it showed less crystallinity onto other conventional polymer dielectrics which have Tg values under 120 oC. Finally, from the low trap density originated with the highly hydrophobic property (water contact angle of 95o) of the polymer dielectric, the pentacene and annealed PTCDI-C13 FETs showed high field effect mobility and their complementary inverters showed excellent electrical performance.
9:00 PM - D7.20
Temperature and Electric Field Dependent Carrier Mobility Determined by Impedance/Admitance Spectroscopy.
Lucas Santos 1
1 Physics Department, Universidade Estadual Paulista, Sao Jose do Rio Preto, SP, Brazil
Show AbstractImpedance/admittance spectroscopy is a powerful technique used in the electrical characterization of electronic and optoelectronic organic devices. The parameters obtained from this technique can be used to understand the injection and/or transport mechanisms of charge carriers in organic semiconductors, particularly in conjugated polymers, allowing the development of more efficient devices. The charge carrier mobility in polymeric materials usually presents quite low values compared to inorganic materials and can be directly determined by time-of-flight measurements or indirectly determined by other methods as field effect transistor (FET) operation curves and carrier extraction by linearly increasing voltage (CELIV) technique. In impedance/admittance technique, when a d.c. bias is superimposed to the low-level a.c. modulation, the quasi-equilibrium regime is altered by the presence of the excess charge carriers injected by the electrodes, giving rise to considerable variations in the frequency-dependent electric response functions. In this work, an analytic solution of the total electric current equation is used to obtain the space-charge dependent complex admittance of polymeric light-emitting diodes. The experimental results used to validate the model were obtained from devices using polyfluorene (PFO) derivatives as the active layer, in ITO/PFO/metal structures. Impedance/admittance measurements in the frequency domain (0.1 a 100 kHz), with a d.c. bias superimposed to the a.c. electrical field, were carried out in the temperature range from 240K to 350K, at vacuum conditions. The experimental results were analyzed using the complex electrical modulus response function, which gives more accurate values of the relaxation times related to the transit time of charge carriers in the active layer. The carrier mobility values obtained from this model were in the range of 10-6 (cm2V-1.s-1), and presented dependence on both temperature and electric field. (The author acknowledge the financial support from Capes, Fundunesp, Prope/Unesp and CNPq).
9:00 PM - D7.21
Charge Transport Anisotropy of Triisopropylsilylethynyl Pentacene Single Crystal Transistors with Co-facial Molecular Stacking.
Hyun Ho Choi 1 , Do Hwan Kim 1 , Jung Ah Lim 1 , Donghoon Kwak 1 , Wi Hyoung Lee 1 , Kilwon Cho 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractIn this study, we report the anisotropic charge transport characteristics in triisopropylsilylethynyl pentacene (TIPS PEN) single crystal field-effect transistors which have high performance electrical characteristics. TIPS PEN single crystal was fabricated by using the solvent-exchange method in the solution phase. The field-effect mobility measured along [100] and [010] direction of TIPS PEN single crystal was 0.6-1.2 and 0.06-0.14 cm2/Vs, respectively and the mobility anisotropy ratio was 7. From the analytical calculation, we revealed that there exists three kinds of packing type in TIPS PEN single crystal according to the degree of intermolecular π-orbital overlap and the mobility anisotropy is originated from the sequence of the packing types.Acknowledgement. This work was supported by a grant (F0004021-2008-31) from the information Display R&D Center under the 21st Century Frontier R&D Program and Creative Research Initiative(CRI)-Acceleration Research (R17-2008-029-01000-0).
9:00 PM - D7.22
Gas Sensing Mechanisms in Phthalocyanine Heterostructure Organic Thin Film Transistors.
James Royer 1 , Sangyeob Lee 1 , Corneliu Colesniuc 2 , Ivan Schuller 2 , William Trogler 1 , Andrew Kummel 1
1 Chemistry, University of California San Diego, La Jolla, California, United States, 2 Physics, University of California San Diego, La Jolla, California, United States
Show AbstractUnderstanding vapor interactions with organic thin films is key to application of organic thin film transistors (OTFTs) in chemical sensing. Ultra-thin OTFTs based on metal phthalocyanines (MPc) are model devices for studying sensing physics since analyte adsorption is almost entirely restricted to the air/MPc interface and adsorption within the grain boundaries is minimal. Even in ultra-thin MPc OTFT heterostructures, the films are sufficiently thin that gas adsorption occurs primarily within the MPc interfaces instead of grain boundaries. In an ideal ultra-thin heterostructure, gas adsorption should occur only at the interfaces thereby creating carrier traps which alter the conduction in the OTFT channel. This was directly investigated using MPc heterostructure OTFTs. The current response to analyte doses for metal free phthalocyanine (H2Pc) OTFTs and cobalt phthalocyanine (CoPc) OTFTs were compared to OTFTs fabricated with bilayer films (CoPc/H2Pc and H2Pc/CoPc). The sensitivity to organic analytes such as isophorone is more than five times greater for H2Pc OTFTs than CoPc OTFTs. Therefore, with heterostructure devices we can tune the sensitivity based on the thickness and ordering of the MPc layers. Both thin and thick heterostructure devices were fabricated to distinguish between a surface doping mechanism and an MPc interface trapping mechanism. The heterostructure OTFT responses suggest a combination of surface doping and adsorption at the MPc interface. This could lead to highly sensitive OTFT sensors based on multilayered MPc film structures with a high density of interfacial layers.
9:00 PM - D7.23
Large Carrier Mobility in Poly (3-Hexylthiophene) FET Fabricated by Direct Film Transfer Method.
Takeomi Morita 1 , Shinya Oku 1 , Syuichi Nagamatsu 2 , Wataru Takashima 3 , Keiichi Kaneto 1
1 Graduate School of Life Science, Kyushu Institute of Technology, Kitakyushu Japan, 2 Computer Science and System Engineering, Kyushu Institute of Technology, Kitakyushu Japan, 3 Research Center for Advanced Eco-fitting Technology, Kyushu Institute of Technology, Kitakyushu Japan
Show AbstractHighly ordered organic thin films are required to attain large charge mobility in organic field effect transistors (OFET) by solution process. In this paper characteristics of poly(3-hexylethiophene), P3HT FET prepared by a direct film transfer (DFT), which is somewhat similar to the LB method, are mentioned. The hole mobility in P3HT FET prepared by DFT method are larger than that prepared by spin coating by one order of magnitude. The P3HT FET was fabricated on Si/SiO2 substrate as gate/gate insulators. Before transferring the P3HT film on the substrate, the substrate was washed by ammonia peroxide mixture (APM), followed by hydrophobic treatment with trichloro (octyl) silane (OTS). Then P3HT layer was deposited on the substrate by DFT technique, which was done by the following method. A 1wt% chloroform solution of P3HT was dropped on the ethylene glycol. The drop of P3HT instantly spread into a very thin film on the surface of ethylene glycol. The film was then transferred onto the substrate. The thickness of P3HT film was typically 20nm and possible to recoating. Top contact Au electrodes were deposited on the P3HT with the channel length and width of OFET of 20 μm and 2.0 mm, respectively. The mobility in P3HT FET fabricated by DFT was 2.5×10-2 [cm2/Vs], which was larger than that of spin coating by 22 times. The on/off ratios were 5.0×103 and 4.0×102 for the P3HT FET fabricated by DFT and spin coating, respectively. In the Grazing Incidence X-ray Diffraction (GIXD) profile, the DFT film showed stronger main chain packing in the in-plane direction compared with that of spin coated film. The UV-Vis absorption spectra of the DFT films indicated a clear structure with the peak at 2.3eV and a shoulder at 2.0 eV, which was not observed in spin coated films. These results suggest that the P3HT films obtained by DFT method showed better order of polymer alignment and performance in OFET than those of the spin coated film.
9:00 PM - D7.24
Organic Thin Film Transistors based on Pentacene and PTCDI as the Active Layer and LiF as the Insulating Layer.
Ronak Rahimi 1 , Dimitris Korakakis 1
1 LDCSEE, West Virginia University, Morgantown, West Virginia, United States
Show AbstractDue to the advantages of low production cost, flexibility and low temperature fabrication, much effort has been devoted to the development of organic electronic devices such as light emitting diodes, photovoltaics and transistors. Organic thin film transistors have several important applications such as switching devices for active-matrix OLED displays, smart cards, identification tags and sensors [1-3]. However, the low carrier mobility in organic materials and the difficulty of integrating organic devices into inorganic processing procedures have hindered the development of organic transistors that are comparable to traditional transistors [4]. Much effort has been devoted to develop new organic materials with higher carrier mobility, while retaining the same conventional inorganic metal-oxide-semiconductor structures. Lithium fluoride (LiF) has the largest band gap and the largest negative electron affinity of any solid is a special material [5] which makes it a good candidate for the insulating layer in transistors. Using LiF as the gate dielectric layer can facilitate the organic transistor fabrication. In this work, thin film transistors based on Pentacene and PTCDI-C8 (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) as organic semiconductor layers and LiF as gate dielectrics are studied. The electrical properties of these devices have been investigated in atmospheric conditions and under variable light exposure. Output and transfer characteristics of several photo-responsive thin film transistors using different organic materials but with the same insulating layer will be presented and the increase of drain-source current upon illumination will be discussed based on the photoconduction properties of the transistor active layer. ------------------------------------------------------------1.Zhou Lisong, A. Wanga, Wu Sheng-Chu, Sun Jie, Park Sungkyu, T.N., Applied Physics Letters, v 88, n 8, p 83502-1-3 (2006)2.Iwao Yagi, Nobukazu Hirai, Yoshihiro Miyamoto, Makoto Noda, Ayaka Imaoka, Nobuhide Yoneya, Kazumasa Nomoto, Jiro Kasahara, Akira Yumoto, Tetsuo Urabe, Journal of the Society for Information Display, v 16, n 1, p 15-20 (2008)3.P.F.Baude, D.A. Ender, M.A. Haase, T.W. Kelley, D.V. Muyres, S.D. Theiss, Applied Physics Letters, v 82, n 22, p 3964-3966 (2003)4.M.S. Meruvia, I. A. Hümmelgen, Advanced Functional Materials, v 16, n 4, p 459-467, (2006)5.C.B. Jiang, B. Wu, Z.Q. Zhang, L. Lu, S.X. Li,S.X. Mao, Applied Physics Letters, v 88, n 9, p 93103-1-3 (2006)
9:00 PM - D7.25
Low-Voltage Operation of Nonvolatile Ferroelectric Thin-Film-Transistor with P(VDF-TrFE) Copolymer.
Soon-Won Jung 1 , Yong-Young Noh 1 , In-Kyu You 1 , Byoung-Gon Yu 1
1 Convergence Components and Materials Research Laboratory, ETRI, Daejeon Korea (the Republic of)
Show AbstractFerroelectric polymer-based nonvolatile memory device has very attractive features such as low-cost and low-temperature process for the new fields of transparent & flexible electronics. Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer is one of the promising polymer ferroelectrics.[1,2] Preparation processes for thin films are typically carried out below 200°C, which can be very beneficial for the fabrication of flexible electronics. Although nonvolatile ferroelectric memories that employ P(VDF-TrFE) have been actively studied since the 1990s, high operating voltage has been a stumbling block in realizing their full potential as practical memory devices.[3,4] Although some encouraging results have been reported on the memory devices of capacitors and/or transistors using P(VDF-TrFE), there remains critical technological issues such as stable programming with lower voltage and longer retention time owing to its larger coercive field of the thin film. We propose the nonvolatile memory thin-film transistor employing F8T2 and P(VDF-TrFE) as a semiconducting channel and a ferroelectric gate insulator, respectively. To fabricate top-gate polymer TFTs F8T2 was coated on a glass substrate in the glove box with Au source and drain electrodes pre-patterned by photolithography and then P(VDF-TrFE) solution was spin-coated onto the semiconducting layer in air atmosphere. The P(VDF-TrFE) film (80 nm) on F8T2 exhibited a very smooth surface with less than 1 nm rms roughness which is similar to the surface roughness of the underlying F8T2 film. The top-gated TFTs were completed by the evaporation of a metal (Ni or Al) as a gate electrode. TFTs with an amorphous semiconducting polymer such as F8T2 always exhibited near perfect yield due to their smooth surface morphology.All devices exhibited counter-clockwise hysteretic behaviors in transfer curves, which was originated from the ferroelectric nature of P(VDF-TrFE). Memory transistor with Al/P(VDF-TrFE) (80 nm)/F8T2 (50 nm) exhibits encouraging behaviors such as a memory window of 2.5 V at VG of -5~10 V, 4-orders-of magnitude of ON/OFF ratio, and gate leakage current of 10-11 A. We can conclude from the obtained promising results that the pro-posed memory TFT is one of the most suitable candidates for the nonvolatile memory device embedded in the future flexible and transparent electronic applications. AcknowledgmentThis research was financially supported by development of next generation RFID technology for item level applications (2008-F052-01) funded by the ministry of knowledge economy (MKE) at ETRI.References[1] A. V. Bune et al., Nature (London), 391, 874 (1998)[2] R. C. G. Naber et al., Nature Mater., 4, 243 (2005)[3] C. A. Nguyen et al., Appl. Phys. Lett., 91, 042909 (2007)[4] C. A. Nguyen et al., Org. Electron., 8, 415 (2007)
9:00 PM - D7.26
Effect of the Hydrophobicity and Thickness of Polymer Gate Dielectrics on the Hysteresis Behavior of Pentacene-based Field-effect Transistors.
Se Hyun Kim 1 , Chan Eon Park 1
1 Polymer Research Institute, Pohang university of science and technology, Pohang Korea (the Republic of)
Show AbstractWe demonstrate the origin and mechanism of the hysteresis behavior that is frequently observed during the operation of organic field-effect transistors (OFETs) based on polymer gate dielectrics. Although polar functionalities, such as hydroxyl groups, present in the polymer gate dielectrics are known to induce hysteresis, there have only been a few detailed investigations examining how the presence of such end functionalities both at the polymer surface—forming an interface with the semiconductor layer—and in the bulk influences the hysteresis. In this study, we control the hydrophobicity of the polymer by varying the number of hydroxyl groups, and use an ultrathin polymer/SiO2 bilayer and a thick single polymer as the gate dielectric structure so that the hysteresis behavior is divided into contributions from hydroxyl groups present at the polymer surface and in the bulk, respectively. Electrical characterizations of the OFETs, performed both in vacuum (10^-3 Torr) and in ambient air (relative humidity of about 40%), show that the observed hysteresis is determined by the transport of water within the polymer (i.e., the adsorption at the polymer surface and the diffusion into the bulk), which in turn is controlled by the hydrophobicity and the thickness of the polymer.
9:00 PM - D7.27
Nearly Ohmic Injection from MoOx to poly(3,3’’’-Didodecylquaterthiophene) (PQT-12).
Shing C. Tse 1 , Ye Tao 1 , Yuning Li 2 , Yiliang Wu 2 , Ping Liu 2
1 Institute for Microstructural Science, National Research Council Canada, Ottawa, Ontario, Canada, 2 , Xerox Research Centre of Canada, Mississauga, Ontario, Canada
Show AbstractWe demonstrated that molybdenum oxide (MoOx) can act as an excellent hole injection material for semiconducting polymers by current-voltage (JV) and admittance spectroscopy (AS) experiments. Using MoOx as a hole injection layer, it is possible to achieve nearly Ohmic contact to poly(3,3’’’-didodecylquaterthiophene) (PQT-12). The JV characteristic of PQT-12 exhibited a bulk-limited current and overlapped with the theoretical space-charge-limited current. Meanwhile, in AS measurement, a well-defined minimum was clearly observed from the plots of frequency dependent capacitance and used to evaluate the charge-carrier mobility of PQT-12. The carrier mobilities extracted by AS are in agreement with mobilities deduced from independent time-of-flight (TOF) technique. It can be concluded that, for the purpose of JV and AS experiments, MoOx forms a quasi-Ohmic contact with PQT-12. The performances of other anodes, Au and ITO, were also examined.
9:00 PM - D7.28
Mechanism of the Increase of Carrier Mobility in Pentacene Polycrystalline Thin Films by Various Insulator-surface Treatments.
Ryousuke Matsubara 1 , Toshio Nomura 1 , Yu-ki Sakai 1 , Takahiro Fujii 1 , Naoki Nakayama 1 , Masatoshi Sakai 1 , Kazuhiro Kudo 1 , Yutaka Majima 2 , Masakazu Nakamura 1
1 Graduate School of Engineering, Chiba University, Chiba-shi, Chiba, Japan, 2 Graduate School of Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan
Show AbstractOrganic thin-film transistors (OTFTs) play an important role in the future flexible and large-area electronics. Among many active materials for OTFT, pentacene is attracting large research effort because of their high field-effect carrier mobility. To obtain higher mobility, many treatment methods of the underlying insulator surface, e.g. chemical modification by HMDS or OTS and polymer coating, have developed to increase the mobility. These processes have realized the high mobility of 3–5 cm2/Vs. However, the reason why these methods can increase the mobility is still unclear. It is partly because the mobility limiting factors in organic polycrystalline thin films have not been sufficiently understood. In our previous studies, the mobility limiting factors in pentacene polycrystalline thin films on bare SiO2 surface were quantitatively evaluated by using four-point-probe field-effect (FPP-FET) measurements that can eliminate the influences of the electrodes and atomic-force-microscope potentiometry (AFMP) that can visualize the potential distribution in a working OTFT. We demonstrated that there exist energy barriers not only at morphological grain boundaries but also at crystalline domain boundaries in the grain, and small HOMO-band fluctuation exists even within the crystalline domain. By using grazing incidence X-ray diffraction (GIXD), we have also clarified that the HOMO-band fluctuation is induced by a few ten nanometer size crystallites in the domain. In this work, we have carried out the similar analyses for the pentacene polycrystalline films on HMDS- and polyimide-modified insulator surfaces. By using these surface modifications, the mean grain size of pentacene became to be 1.5 times larger than that on the bare SiO2, and the field-effect mobility also increased by approximately the same factor. The HOMO-band fluctuations, however, didn’t show notable change. The results of GIXD measurements also indicated that the crystallite sizes are also the same. These facts suggest that the increase of the mobility by the surface treatments is mainly due to the increase of grain sizes, i.e. the decrease of the number of domain boundaries.
9:00 PM - D7.29
Angle Resolved Photoemission Study of Rubrene Single Crystal.
Huanjun Ding 1 , Colin Reese 2 , Antti Makinen 3 , Zhenan Bao 2 , Yongli Gao 1
1 Department of Physics and Astronomy, University of Rochester, Rochester, New York, United States, 2 Department of Chemical Engineering, Stanford University, Stanford, California, United States, 3 Optical Sciences Division, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe electronic structure of rubrene single crystal grown by physical vapor transport method was studied with angle-resolved photoemission spectroscopy. Highly reproducible dispersive features were observed, representing the band structure measured for the first time for a bulk organic single crystal. The high quality of the surface was confirmed with scanning tunneling microscopy (STM).The energy dispersion of the highest occupied molecular orbitals (HOMO) derived bands was estimated to be about 0.2 eV, which is comparable to the theoretical calculations. However, an HOMO-1 feature is observed at 0.3 eV below the HOMO, and it is not in the calculated bands. Possible implications of these results will be discussed.
9:00 PM - D7.3
Long-Period X-ray Standing Wave Studies of Self-assembled Nanoscale Dielectrics.
Jonathan Emery 1 , Young-Geun Ha 2 , Antonio Facchetti 2 , Tobin Marks 2 , Michael Bedzyk 1
1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Department of Chemistry, Northwestern Universtiy, Evanston, Illinois, United States
Show AbstractOrganic thin-film transistors (OTFTs) are envisioned as the successors for classical thin-film transistors (TFTs) in novel electronics applications requiring large coverage area, structural flexibility, low-temperature processing, and low cost. While significant research has been directed towards the semiconductor component of the OTFT, there has been relatively little research on the dielectric component, which is critical to the electronic behavior of the transistor. Specifically, self-assembled nanoscale dielectric (SAND) thin-films composed of α,ω difunctionalized hydrocarbon chains, octachlorotrisiloxane capping layers, and highly polarizable “push-pull” stilbazolium dielectric layers has shown promise in organic dielectric applications. In this study, the position and motion of the heavy halide counteranion layer under both static and applied fields is of interest. The behavior of the counteranions is closely coupled to that of the rest of the molecule, and its behavior conveys information about the fundamental electronic properties of the dielectric itself. Understanding the counteranion layer behavior allow for the tailoring of molecules that operate with large dielectric constants, low leakage currents, and high layer capacitances for application in high-performance non-conventional electronics. Here, we report initial findings of long-period x-ray standing wave (XSW) and x-ray reflectivity studies (XRR) of SAND films with varying z-offsets under zero-field conditions as proof of concept. To better understand the dielectric’s behavior in device applications, future experiments will be performed under applied electric fields in order to simulate device conditions.
9:00 PM - D7.30
Terahertz Time-Domain Spectroscopic Studies of Poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate) Films.
Kai Chen 1 2 , Chin-Ming Chen 3 , Tsong-Ru Tsai 3 , Juen-Kai Wang 4 5
1 Institute of Physics and Nano Science and Technology Program, Taiwan International Graduate Program,, Academia Sinica, Taipei Taiwan, 2 Department of Engineering and System Science, National Tsing Hua University, Hsinchu Taiwan, 3 Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung Taiwan, 4 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 5 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan
Show AbstractPoly(3,4-ethylenedioxythiophene):poly(stylenesulfonate) (PEDOT:PSS) has been popularly used in organic light-emitting diodes and organic solar cells as the electrode material and charge injection/extraction layers, owing to its high mechanical flexibility, charge conductivity and optical transparency [1]. Its charge conductivity is therefore the key parameter for optimizing the performance of the organic devices with a PEDOT:PSS film. Making good electric contact on these polymer films however imposes a great challenge in the conductivity measurements, thus yielding many inconsistent characterization results. Terahertz time-domain spectroscopy (THz-TDS), being a quasi-optical high-frequency electric field characterization scheme [2], can serve as a non-contact method to retrieve the frequency-dependent conductivity. In this report, we present the conductivity measurements of PEDOT:PSS films with THz-TDS. PEDOT:PSS films (Baytron from H.C. Starck. Inc.) with different composition ratios were formed by dropping cast. THz-TDS was performed in a nitrogen gas purged enclosure with a femtosecond laser serving as the light source for producing a broadband THz source and as the gate pulses for detecting the THz radiation after transmitting through the sample. The real and imaginary parts of the refractive index of the sample were retrieved by analyzing the recorded electric field transient traces of the transmitted THz radiation with the measured sample thickness. After fitting the resultant frequency-dependent conductivity to a localization-modified Drude model [3], the extrapolated DC conductivity was found to be consistent quantitatively with the corresponding one obtained with the DC electric measurement. This consistency confirms that TDS-THz can serve as a non-contact conductivity characterization method. In addition, the retrieved frequency-dependent conductivities of the PEDOT:PSS films of different composition ratios provide a unique opportunity to reveal the role of the micro-morphology played in their charge transport properties, thus facilitating the optimization of PEDOT:PSS used in various organic electronic devices.[1]S. Kirchmeyer and K. Reuter, J. Mater. Chem. 15, 2077 (2005).[2]Terahertz Spectroscopy: Principles and Applications, edited by S. L. Dexheimer (CRC Press, 2007).[3]K. Lee et al., Phys. Rev. B 48, 14884 (1993).
9:00 PM - D7.31
Electronic Structures of Single Crystalline Rubrene Observed by Photoemisssion Spectroscopies.
Yasuo Nakayama 1 , Shinichi Machida 2 , Akihiro Funakoshi 2 , Naoki Ogawa 2 , Takeo Minari 3 , Kazuhito Tsukagoshi 3 , Yutaka Noguchi 1 2 , Hisao Ishii 1 2
1 Center for Frontier Science, Chiba University, Chiba Japan, 2 Graduate School of Advanced Integration Science, Chiba University, Chiba Japan, 3 , NIMS, Tsukuba Japan
Show AbstractRubrene (5,6,11,12-tetraphenyltetracene) is one of the most promising materials for organic field effect transistor application due to its high hole mobility. To comprehend the transport nature as well as to improve the device performance, information about its electronic structures is indispensable. There have been a number of reports about the electronic states of amorphous thin films of rubrene studied by photoelectron spectroscopy (PES) [1]. On the other hand, sufficiently high field effect mobility has not been realized for the amorphous rubrene but only for the crystalline phase. It has been reported that rubrene molecules in the crystalline phase have different conformation from those in the amorphous phase [2]. This fact implies that the electronic structure of rubrene single crystals (SCs) will be different from those of its amorphous phase. However, experimental observation of the electronic structures of rubrene SC has not been reported. It is mainly because PES measurement on organic crystals has been awkward due to the sample charging problem. In the present study, we conducted direct observation of the electronic structures of rubrene SC by two types of photoemission measurement techniques to overcome the aforementioned issues. The one was photoelectron yield spectroscopy (PYS) that gives us information about ionization potentials (IPs) of specimens excluding any effects of the sample charging [3]. The other was PES with special tactics, illumination of visible laser light and positive biasing on the samples, in order to relieve the charging. SCs of rubrene were produced by a physical vapor transport technique and were fixed on Au substrates with silver paste, whereas its amorphous thin films were formed by in-situ vacuum deposition and were examined for comparison. Details of the PYS technique were described elsewhere [3]. PES measurement was performed at BL-8B2 in UVSOR of Institute for Molecular Science, Japan. The PYS results revealed that IP of rubrene SCs is 0.4 eV smaller than that of its amorphous phase [4]. It means that crystallization lifts the highest occupied molecular orbital (HOMO) of rubrene up toward the vacuum level. Precise measurements for the photoemission threshold region unveiled tailing features spreading toward the low IP side from the 'original' threshold, which suggests existence of the gap states. On the other hand, the PES spectra of rubrene SCs seemed to exhibit slight shift of the HOMO-derived peak to the low binding energy side beside the amorphous thin films. It is probably ascribed to generation of new components above the original HOMO level. In this presentation, angle resolved PES results of rubrene SCs will also be reported. [1] e.g. L. Wang, et al., Appl. Phys. Lett. 90, 132121 (2007). [2] D. Kaefer, et al., Phys. Rev. Lett. 95, 166602 (2005). [3] Y. Nakayama, et al., Appl. Phys. Lett. 92, 153306 (2008). [4] Y. Nakayama, et al., Appl. Phys. Lett. 93, 173305 (2008).
9:00 PM - D7.32
Role of Chlorine in MEH-PPV Photodegradation.
Giovana Ferreira 1 , Eduardo deAzevedo 2 , Leni Akcelrud 3 , Rodrigo Bianchi 1
1 Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto Brazil, 2 Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos Brazil, 3 Departamento de Química, Universidade Federal do Paraná , Curitiba Brazil
Show AbstractSince the discovery of electroluminescence properties of conjugated polymers, a considerable number of researches have been done in order to investigate the semiconducting properties of this class of materials and their related applications in lighting-emitting devices. However, the structural degradation caused by photoxidation is an obstacle for commercial applications of conjugated polymers in such a way that the control and investigation of optical and structural properties of this material under environmental conditions are important to improve the optoelectronic device stability and performance. Several studies have identified oxygen as the main contributor for the degradation of polymer, specially attributing the presence of oxygen as quenching centers for singlet exciton or nonradioactive polaron pairs. A recent study indicated that the photodegradation process depends not only of the environmental conditions but also of the polymer preparation. In the present research we studied the variation of absorption and fluorescence spectra of MEH-PPV solutions in (i) toluene, (ii) chloroform and (iii) chloroform in presence of presence of free radical scavengers (hydroxyquinoline). The results show that MEH-PPV solutions using chloroform as a solvent presents a more accentuated change in its optical properties than the solutions prepared with toluene. This effect is attributed to the presence of free radicals obtained from irradiated chloroform which may acts in the sense to accelerated the MEH-PPV photoxidation process. In order to investigate this assumption a hydroxyquinoline, a free radical scavenger, was added to MEH-PPV solutions in chloroform to reduce the MEH-PPV degradation process. Furthermore, in order to probe the kinetics of the MEH-PPV degradation and correlate the changes in optical properties with changes in chemical structure of the polymer a series of 1H and 13C liquid state NMR experiment were performed for these samples. The results revealed that while the MEH-PPV dissolved in chloroform depict indication of photo degradation (disappearing or appearing of the signal from chemical groups associated with the photo degradation) already at exposing time of 240 min, samples with this polymer dissolved in toluene or in chloroform with hydroxyquinoline, only present signal of photo degradation at exposing time of 960 min. This result confirms our assumptions that chlorine free radical may be acts accelerated the photoxidation process. The present work was sponsored by FAPEMIG, CNPq, CNPq/INEO and Capes.
9:00 PM - D7.33
Large Single Grain Thin Film by Hollow Capillary Method.
Songtao Wo 1 , Randall Headrick 1 , John Anthony 2
1 Physics, University of Vermont, Burlington, Vermont, United States, 2 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractUsing 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-Pentacene), we have made solution processed thin film transistor by hollow capillary method. The grain size is 1mm wide and more than 10mm long along with the writing direction routinely, which cover the channels of entire device. Thickness of the highly uniform and continuous film can be varied from 10nm to 200nm by tuning the concentration and speed of substrate. We will report the thin film transistor mobility as a function of the direction of the crystal versus the channel.
9:00 PM - D7.34
Universal Behavior of Metal-atom Diffusions in Organic Pentacene and Graphen Systems; First-principles Study.
Yoko Tomita 1 , Takashi Nakayama 1
1 Department of Physics, Chiba University, Chiba Japan
Show AbstractMetal/semiconductor interfaces are essential structures for electronic devices. In inorganic devices, the metal-atom diffusion from metal electrode into inner semiconductor layers often deteriorates the semiconducting properties and eventually produces serious damages such as a circuit shortening [1]. In case of organic systems, however, our knowledge is still limited. Therefore, it is important to clarify how fast the metal atoms diffuse in organic systems. In this work, we choose pentacene and graphene solids as typical organic semiconductors and study how and why the metal-atom diffusion occurs in these systems, using the first- principles standard DFT calculations and adopting Al and Au metal atoms. The main results are summarized as follows: (1) In case of graphene solids, Al and Au have quite different diffusion paths and speeds: they respectively diffuse across and along the hexagonal carbon ring with the diffusion barriers, 0.37 and 0.02eV, and respectively have the diffusion constants, 10-9 and 10-4 cm2/sec, which values are comparable to the case in bulk Si. This difference occurs due to the electronegativity difference between Al and Au: Al atom has small negativity and thus stabilizes at the center of carbon ring so as to give electrons to π* orbitals of the graphene sheets, while Au atom has large negativity and stabilizes near the C=C -conjugated bonds to produce Au-C bonds. (2) In case of pentacene-like solids, both Al and Au atoms diffuse along the molecule axis due to the restricted geometry in pentacene solid. However, they have quite different diffusion barriers for the inter-molucular movement, 0.94 and 0.36eV barriers for Al and Au, respectively. Such difference also appears owing to the electronegativity difference between Al and Au. Since Al atoms supply their valence electrons to π* orbitals of pentacene-like molecules, they prefer to locate near the molecules and thus the potential barrier becomes large between molecules. On the other hand, since Au atoms tend to produce the bonds with C and H atoms, they can move easily near the molecule edges and between molecules, as well as inside the molecules. (3) From these results, we can conclude that the metal-atom diffusion in organic solids has the universal feature: the diffusion is categorized into two groups reflecting the electronegativity of metal atoms. These results are discussed in details together with comparing to the diffusions in inorganic semiconductors. [1] T. Nakayama et al, J. Phys. Conf. Ser. 38 (2006) 216.
9:00 PM - D7.35
Effect of Dipoles on Charge Carrier Transport Properties in Layer-Structured Molecular Systems.
Akira Ohno 1 2 , Jun-ichi Hanna 1 2
1 Imaging Science and Engineering Lab., Tokyo Insutitute of Technology, Yokohama, Kanagawa, Japan, 2 , JST-CREST, Kawaguchi, Saitama, Japan
Show AbstractIn printable organic semiconductors for fabricating the organic electronic devices with high performance, "self-assemble" is one of the very important keywords, because of feasibility of realizing high mobility and film uniformity in large-area. For carriers, it provides not only a geometrical path in the film, but also less-distributed energy states localized in each molecule. This distribution of the localized states affects carrier mobility and its dependence on temperature and electric field. It is well known that the energetic disorder of the density of states where carriers are transported often exceeds 100meV in amorphous materials, which is attributed to the Coulomb interaction between randomly distributed dipoles and the carriers in the localized states [1]. On the other hand, the energetic disorder in self-assembled molecular aggregates such as self-assembled molecular films and liquid crystals (LCs) is as low as 50meV [2], although its origin has not been clarified yet. In fact, a unique charge carrier transport property, i.e., no temperature-and-field dependence of mobility at a temperature range over room temperatures, is often observed in these materials. In this study, we investigated the effect of dipoles on the charge carrier transport in molecularly layered structure self-assembled, that is, how the dipoles affect the charge carrier transport in ordered molecular systems. In order to investigate this effect, we picked up a molecular system aligned in layers as a model, i.e., a smectic liquid crystal, doped it with various dopants with a large dipole moment, and characterized the charge carrier transport properties in the doped systems. At the same time, we theoretically analyzed the effect of dipoles on the energetic disorder in thse materials systems as a function of dipoles. We found that the dipoles affect the charge carrier transport properties in thse ordered systems as well, but the effect is quite different from that in the case of amorphous materials: the energetic disorder is proportional to square root of the concentration: c^(1/2) for liquid crystals., while it is proportional to c^(2/3) in the amorphous materials. [3] Furthermore, the calculated results are in good agreement with the experimental results. This indicates that the self-assembled molecular aggregates in layered -structure is beneficial to reduce an ill-effect of dipoles, resulting in lowering additional energetic disorder attributed to the dipole-carrier interaction.This study gives us an insight into the effect of dipole moments in ordered molecular systems and the molecular design of high quality self-assembled molecular systems.References[1] Bassler, Phys. Stat. Sol (b), 175 15 (1993)[2] Akira Ohno and Jun-ichi Hanna, Appl. Phys. Lett., 82, 751 (2003)[3] A. Hirao, and H. Nishizawa Phys. Rev. B, 56, R2904 (1997)
9:00 PM - D7.36
Electronic Structure and Charge Transport Properties of N,N′-bis(cyclohexyl)Naphthalene Diimide Crystals.
Shashishekar Adiga 1 , Deepak Shukla 1
1 Kodak Research Laboratories, Eastman Kodak Company, Rochester, New York, United States
Show AbstractRecently, it was demonstrated that by attaching cyclohexyl end groups to naphthalene diimide, an efficient molecular stacking and thin film morphology that leads to superior field effect mobility can be obtained [1]. In this context, we have probed the electronic properties of a single N,N′-bis(cyclohexyl)naphthalene diimide (NDI-CHEX) molecule and a NDI-CHEX molecular crystal using the density functional theory. The band structure of the molecular solid is analyzed and the bandwidths of the conduction and valence bands are found to depend on the crystallographic direction. Further, charge transport properties of the molecular crystal are characterized within the Marcus formalism. The quantum mechanically estimated reorganization energy and electron-transfer coupling matrix elements are used in an incoherent transport model to calculate the electron mobility of NDI-CHX crystals. The mobility is found to be highly anisotropic; the charge transfer is confined to (001) planes with a maximum value along the <110> direction. [1] D. Shukla et al. Chem. Mater. 20, 7486 (2008).
9:00 PM - D7.37
Charge Carrier Transport Properties in Smectic Glassy Phase of Branched Phenynaphthalene Derivative.
Jiang Wu 1 , Takayuki Usui 1 , Jun-ichi Hanna 1
1 , Tokyo Institute of Technology, Tokyo Japan
Show AbstractIn recent years, liquid crystals have been recognized as a new type of quality organic semiconductors because of the electronic conduction characterized by a high mobility up to 1cm2v-1s-1. A new material having both self-organized molecular alignment in liquid crystal and solid nature in amorphous materials, i.e., a liquid crystalline glass, is of interest both for understanding the charge carrier transport properties in liquid crystals and for device applications. Because of these, we synthesized a novel smecitc glassy liquid crystal, 1,3,5-benzenetricarboxylic acid tris{12-[6’-(4”-octylphenyl)-2’-naphthyloxy]-1-dodecyl ester as a model material, and characterized its phase transition behaviors and charge transport properties: we found that this novel smectic glassy liquid crystal shows smectic A (SmA) and smectic B (SmB) liquid crystalline phases from 131°C to 106°C and from 106°C to 77°C, respectively, and SmB glassy phase with a high Tg of 53°C when cooled rapidly from SmB liquid crystalline phase; the time-of-flight (TOF) measurement revealed that the charge carrier transport mobility in the SmB glassy phase was ambipolar and exhibited 4 ×10-4 cm2/Vs and 5 ×10-4 cm2/Vs for holes and electrons, respectively, which is comparable to those in the SmB phase. In addition, the mobility in SmB glassy phase depends on temperature, but does not on electric field, which is quite different from amorphous materials. These properties indicate that the smecitic glassy liquid crystal provides us with solid self-organized molecular aggregates while keeping feasibility of easy control of molecular alignment in smectic liquid crystals. We compare the charge carrier transport properties in the smectic glassy phase with those in smectic liquid crystalline phases and discuss them in conjunction with molecular motions in these phases.
9:00 PM - D7.38
Impacts of Thickness and Thermal Treatments on the Materials and Electrical Properties of Poly(vinylidene fluoride-trifluoroethylene) Film.
Duo Mao 1 , M. Quevedo-Lopez 1 , Harvey Stiegler 1 , Husam Alshareef 1 , Bruce Gnade 1
1 Department of Material Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractWe have studied the effects of film thickness and thermal treatments on the polarization and leakage current of Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer thin film capacitors. In particular, we studied the evolution of the film morphology, crystallinity and bonding using AFM, XRD and FTIR, respectively. We found that the copolymer films exhibit transition from small grains to large grains through molecule chain self-organization for annealing conditions below the copolymer melting temperature. We have also found a relationship between the film thickness and the optimum maximum annealing temperature to achieve the best ferroelectric phase. Our results reveal the increase of the ferroelectric β phase crystallinity with the annealing temperature and we show how to track this by using FTIR methods. We also report the hysteresis loop of the copolymer films as functions of thickness and annealing temperature, and the corelation to the material properties.
9:00 PM - D7.39
Effect of Sintering Atmosphere on the Microstructure of Gold Nanoparticulate Film.
Seonhee Jang 1 , Hyejin Cho 1 , Sungkoo Kang 1 , Joonrak Choi 1 , Sungil Oh 1 , Jaewoo Joung 1 , Donghoon Kim 1
1 , Samsung Electro-Mechanics Co. Ltd., Suwon, Gyunggi-do, Korea (the Republic of)
Show AbstractOver the past few decades, metallic nanoparticles (NPs) have been of great interest due to their unique properties which distinguish them from those of bulk metals. Many attempts have been conducted to investigate the characteristics of NPs and their applications. However, the sintering process which converts metallic NPs to conductive film was not established yet. In this study, the microstructure evolution of Au NPs after sintering under different thermal condition was examined and the film quality was studied based on densification, organic residues and electrical resistivity. Au NP ink dispersed in a toluene were spin coated on Ni-plated FCCL or Si substrates and thermally treated in a furnace under different sintering profiles under various types of flows such as air, nitrogen (N2), oxygen (O2), or reducing atmosphere of hydrogen (H2/N2). The Au ink was consisted of Au NPs coated with an organic capping molecule. The capping molecules not only help NPs to disperse but prevent aggregation and precipitation of NPs out of solution. When the NPs are treated by thermal process, the surface ligands from capping molecule start to decompose and necking and melting of NPs occur producing the film with the electrical conductivity. The diameter of Au NPs was approximately between 5-7 nm with spherical shape. The Au film sintered under air showed only necking between neighboring Au NPs without further grain growth. When Au NPs films were sintered under N2 or O2 atmospheres, NPs fused together in clusters. Under sintering with flows of H2/N2, a larger area of pores due to the volume shrinkage of the film was observed since an agglomeration and melting of NPs were considerably progressed compared to the film sintered under N2. Sintering with a flow of a single gas such as air, N2 or O2 showed organic residues in the film indicated by C-H or C-O stretch peaks. However, when mixed flows of H2/N2 and N2 were applied, there was no IR peaks from organic substances observed in the film. It is assumed that the organic capping molecules surrounding the Au NPs were removed significantly with sintering with two flows of H2/N2 and N2. The microstructure showed less pore distribution and lower level of organic residues compared to those sintered under N2, O2 or H2/N2 atmospheres. The electrical resistivity was about twice of bulk value of 2.44μΩ-cm. Overall Au NPs film sintered under H2/N2 and N2 resulted in a better sintering effect based on densification of the film and level of residual organics, translating into a relatively high electrical conductivity.
9:00 PM - D7.4
Charge Carrier Mobility in Sulphonated and Non-sulphonated Ni phthalocyanines: Experiment and Quantum Chemical Calculations.
Irena Kratochvilova 1 , Stanislav Nespurek 2 , Jakub Sebera 3 , Stanislav Zalis 3 , Nikos Glezos 4
1 , Institute of Physics, Prague 8 Czechia, 2 , Institute of Macromolecular Chemistry, Prague Czechia, 3 , J.Heyrovský Institute of Physical Chemistry, Prague Czechia, 4 , Institute of Microelectronics, Attiki Greece
Show AbstractThe objective of this interdisciplinary work was to study theoretically and experimentally the electronic part of charge carrier transport in the class of sodium salts of sulphonated Ni phthalocyanine [NiPc(SO3Na)] as candidates for p-type channels in organic field-effect transistors. These materials were selected because of their enhanced solubility as compared to their non-sulphonated counterparts. The values of the field-effect charge carrier mobility determined on the OFET structures using NiPc(SO3Na)x films were much higher than the charge carrier mobility obtained on the respective device prepared from non-substituted phthalocyanine. In order to explain differences between charge carrier mobility of sulphonated and non-sulphonated Ni phthalocyanines, quantum chemistry studies of molecular aggregates were performed. Quantum chemistry modeling of the semiconductive molecular systems is new and progressive – we highlighted factors at the molecular level which led to the enhancement of the charge carrier mobility in systems containing SO3Na groups.
9:00 PM - D7.40
Controlled Charge Injection in Organic Thin Film Transistors Fabricated Under In-situ and Ex-situ Conditions.
Akichika Kumatani 1 , Takeo Minari 1 2 , Kazuhito Tsukagoshi 1 2 3
1 WPI Centre for Materials Nanoarchitectronics (MANA), National Institute for Materials Science, Tsukuba Japan, 2 , RIKEN, Wako Japan, 3 , CREST-JST, Kawaguchi Japan
Show AbstractCharge injection into organic semiconductor from metal electrode is generally explained by energy difference from Fermi level of the metal and valence band of the organic semiconductor. It is therefore that metal with large work function is considered to be suitable for p-type semiconductors. However, this common theory is only valid at 'ideal' metal/organic interface. Control of extrinsic parameters at the 'real' metal/organic interface is much important to realize efficient charge injection and low-resistance contact. In this research, top-contact organic thin-film transistors with various types of contact were fabricated under in-situ and ex-situ conditions, and charge injection efficiency was investigated from contact resistance of the devices evaluated by transmission line model analysis. Under ex-situ condition, the obtained result showed that electrodes with lower Fermi level, such as copper or aluminum, exhibit low contact resistance than gold electrodes whose work function supposedly has superior alignment with valence band of organic semiconductor. Intrinsic and extrinsic factors that play important roles on charge injection were revealed.
9:00 PM - D7.41
Photosensitive Thin Film Transistors Based on Composites of Poly (3-Hexylthiophene) and Titania Nanoparticles.
Feng Yan 1 , Jinhua Li 1 , Helen Chan 1
1 Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong China
Show AbstractOrganic photosensitive thin film transistors based on composites of P3HT and TiO2 nanoparticles have been carefully studied. The devices show high photo sensitivity, fast response and stable performance under both visible and ultra violet light illumination. Therefore the hybrid devices are promising for the applications as low cost photo sensors. Each device exhibits a parallel shift of its transfer characteristic to positive gate voltage under light illumination and the maximum change of the channel current can be up to three orders of magnitude in the subthreshold region. A nonlinear relationship between the shift of the threshold voltage and the illuminated light intensity has been observed, which has been attributed to the accumulation of electrons in the embedded TiO2 nanoparticles. It is worth noting that the device is extremely sensitive to weak light due to an integration effect. The relationship between the threshold voltage change and the intensity of light illumination has been fitted with a power law, which can be derived with an analytical model of the hybrid devices. Such organic phototransistors can be developed for sensing different wavelengths by choosing different semiconducting polymers and/or semiconducting nanoparticles.
9:00 PM - D7.42
Design and Application of Tunable Surfaces by Photoreactive Monolayers.
Lucas Hauser 1 , Thomas Griesser 2 , Heinz-Georg Flesch 3 , Roland Resel 3 , Wolfgang Kern 2 , Gregor Trimmel 1
1 Institute for Chemistry and Technology of Materials, Technical University Graz, Graz Austria, 2 Insitute of Chemistry of Polymeric Materials, Montanuniversität Leoben, Leoben Austria, 3 Institute of Solid State Physics, Technical University Graz, Graz Austria
Show AbstractIn this contribution we present the chemical modification of Si/SiOx and indium tin oxide (ITO) surfaces with new chemically and photochemically reactive phosphonic acid derivates. These molecules contain a photoreactive group – a photoreactive aryl ester - and a phosphonic acid group as anchoring group, so they can react with oxidic surfaces and build up self assembled monolayers (SAMs).The introduced photoreactive aryl esters undergo the photo-Fries rearrangement reaction upon exposing to UV- light to form the corresponding aromatic hydroxyketones. The photo-reaction of these new molecules was investigated by Fourier- transform infrared (FTIR) spectroscopy. The formation of the monolayers as well as the photoreaction in the monolayers was followed by contact angle (CA) measurements and X-ray reflectivity (XRR). As shown by CA measurements, the photoreaction causes significant change in surface polarity, which can be further amplified by subsequent chemical modification of photogenerated hydroxy-groups in the irradiated areas and thus selective functionalization is possible.These monolayers are well suited to modify oxide based electrodes like indium-tin-oxide as well as to serve as interfacial layers between gate dielectrics and organic semiconductors in organic thin film transistors (OTFTs).
9:00 PM - D7.43
Phenyl and Halophenyl Substituted Poly(p-phenylene vinylene)s for Capacitor Dielectrics.
Ross Johnson 1 , Fenil Kholwadwala 1 , Shawn Dirk 1
1 Organic Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractConducting polymers are of significant interest in many areas of materials chemistry due to their tunability and wide range of applications. We are interested in utilizing the thermo-switching properties of precursor PPV polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material going from an insulating to a conducting state. Here, we report the synthesis and characterization of several newly synthesized phenyl and halophenyl substituted PPV polymers. By utilizing different leaving groups on the polymer main chain, the temperature at which the backbone becomes conjugated can be varied over a range of temperatures. We also report on the electrical properties of the polymers and our progress in utilizing these materials in capacitor devices.
9:00 PM - D7.44
Solution Growth of Distyryl-oligobithiophene Thin-films by Temperature Gradient Method.
Noriyuki Yoshimoto 1 , Shunsuke Abe 1 , Toshiyuki Araki 2 , Hiroki Muraoka 1 , Hugues Brisset 3 , Jorg Ackermann 3 , Frederic Fages 3 , Christine Videlot-Ackermann 3
1 Materials Science & Engineering, Iwate University, Morioka Japan, 2 , JST Innovation Satellite Iwate, Morioka Japan, 3 CINaM, UPR 3118, CNRS, Aix-Marseille Université, Marseille France
Show AbstractThin-film growth of organic semiconductors from solution phase is attracting a lot of attention because of their potential of low-cost fabrication of electronic devices.Generally, it is difficult to obtain well-oriented crystalline thin films by using conventional methods such as drop cast and spin-coating. In this study, single crystalline thin-films of distyryl-oligobithiophene are successfully grown from solution phase using temperature gradient method. The crystal growth was monitored by in situ observation and the conditions were controlled by feed back of the monitored images. The obtained thin-films were characterized by means of grazing incidence X-ray diffractometory.
9:00 PM - D7.45
Inkjet Printed High Performance Top-Gate Polymer Transistors for Radio Frequency Identification (RFID) Tag.
Kang-Jun Baeg 1 2 , In-Kyu You 2 , Yong-Young Noh 2 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 2 Convergence Components & Materials Research Laboratory, Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of)
Show AbstractSolution processable organic field-effect transistors (OFETs) are currently being developed to realize large-area flexible electronics via cost effective methods such as graphic art direct printing. The performance of solution processable OFETs looks enough to drive simple black and white e-paper display but still needs further improvement to realize many of these potential applications, e.g., in addressing backplanes in full colour displays and circuits in radio frequency identification (RFID) tags. Here we report high performance top-gated p-channel and n-channel polymer transistors using inkjet printing process. The OFET devices have balanced high electron and hole mobilities (> 0.1 cm2/Vs) and high on/off ratio, therefore, successfully achieved high speed complementary inverter and ring oscillator circuits for item level RFID tagging.
9:00 PM - D7.46
Effects of Accumulation Layer Width and Front Edge of Depletion Layer on Organic MIS Capacitor.
Neri Alves 1 , Jose Giacometti 1 , Fernando Sabino 1 , Elder Mantovani 1
1 Departamento de Física, Química e Biologia, Faculdade de Ciências e Tecnologia - UNESP, Presidente Prudente, São Paulo, Brazil
Show AbstractIn this work capacitance and dielectric loss curves for a metal-insulator-semiconductor (MIS) capacitor of organic films thins were computed through equivalent circuits. It was considered as reference the MIS-P3HT capacitor made from poly(3-hexylthiophene) 70 nm thick as semiconductor layer and polysilsesquioxane 100 nm thick as insulator layer. In silicon (Si) devices the charge distribution at the front edge of depletion region is frequently assumed to drop abruptly to zero. However, for the P3HT-MIS capacitor such approximation is questionable since the Debye length is λD ~ 6 nm which corresponds to ~10% of the P3HT layer thickness. Also, varying the applied voltage the accumulation layer thickness changes from 0 to 2½λD/2, and for P3HT, 2½λD/2 ≈ 13 nm that is also not negligible compared to the P3HT layer thickness. Therefore, the circuit model to describe the P3HT-MIS capacitor should be improved accounting the front-edge width of the depletion layer and accumulation layer thickness. In accumulation regime we added to the equivalent circuit a series variable capacitor to consider the dependence of the accumulation layer width on the applied voltage. In depletion regime we added in series to the equivalent circuit a capacitance CFE and a resistance RFE (in parallel) to represent the front edge of the depletion layer. RFE and CFE are assumed to be constant until the front edge of the depletion layer reaches the gate electrode. Next, their values vary exponentially on the applied voltage until the rear of the depletion front edge reaches the gate. Finally, they achieve constant values since the depletion layer is uniform across the semiconductor. Simulation results showed that the MIS device capacitance versus voltage present a curve that diminishes gradually. Also, loss versus voltage curves display a peak in the flat-band in agreement with experimental results for P3HT-MIS capacitor. Concerning the loss versus frequency curves a peak displacement appears in accumulation regime as the bias voltage is varied, as usually found in experiments. In conclusion, our results showed that the accumulation layer and front edge of depletion layer widths are relevant to describe experimental results found in the P3Ht-MIS capacitor.
9:00 PM - D7.47
The Salt and Paper Battery; Ultrafast and All-polymer Based.
Gustav Nystrom 1 , Aamir Razaq 1 , Albert Mihranyan 1 , Leif Nyholm 1 , Maria Stromme 1
1 Nanotechnology and Functional Materials, The Angstrom Laboratory, Uppsala Sweden
Show AbstractWe have recently developed a flexible battery using two common, inexpensive ingredients: cellulose and salt. This lightweight, rechargeable battery uses thin pieces of paper—originating from cellulose fibres from the environmentally polluting Cladophora sp.algae —for electrodes, while a salt solution acts as the electrolyte.Conducting polymers for battery applications have been subject to numerous investigations during the last decades. However, the functional charging rates and the cycling stabilities have so far been found to be insufficient for practical applications. These shortcomings can, at least partially, be explained by the fact that thick layers of the conducting polymers have been used to obtain sufficient capacities of the batteries. We now introduce a novel nanostructured high-surface area electrode material for energy storage applications composed of cellulose fibers of algal origin individually coated with a 50 nm thin layer of polypyrrole. Our results show the hitherto highest reported charge capacities and charging rates for an all polymer paper-based battery. The composite conductive paper material is shown to have a specific surface area of 80 m2 g-1 and batteries based on this material can be charged with currents as high as 600 mA cm-2. The aqueous-based batteries, which are entirely based on cellulose and polypyrrole and exhibit charge capacities between 25 and 33 mAh g-1 or 38-50 mAh g-1 per weight of the active material, open up new possibilities for the production of environmentally friendly, cost efficient, up-scalable and lightweight energy storage systems.
9:00 PM - D7.5
Solution-Processed Transparent Carbon Electrodes for Organic Field-Effect Transistors.
Takehiko Mori 1 , Hiroshi Wada 1
1 Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo Japan
Show AbstractIn order to achieve low contact resistance in bottom-contact organic transistors by using low-cost and easy processing from solution, organic transistors with carbon-paste electrodes are fabricated by means of the surface selective deposition technique, where a carbon paste solution is deposited on the region in which the self-assembled monolayers are removed by ultraviolet light irradiation [1]. The resulting bottom-contact pentacene transistor realizes high performance of 1.0 cm2 V-1 s-1. This method is applied to solution-processed polythiophene transistors as well as n-channel materials. In addition, the patterning is attained by selective laser sintering of carbon films formed from carbon solution. This method achieves high-resolution carbon electrodes with the channel length down to 2 μm without using vacuum process. The resulting carbon film is as thin as 60 nm and practically transparent. [1] Wada, Appl. Phys. Lett. 93, 213303 (2008).
9:00 PM - D7.6
Organic Field-Effect Transistors Based on Novel Printable Compounds with Phenylethynyl Groups.
Hirofumi Kondo 1 , Takayoshi Kambara 1 , Yuki Nakano 1 , Masatoshi Saitoh 1 , Hiroaki Nakamura 1
1 , Idemitsu Kosan Co.,Ltd., sodegaura, Chiba Japan
Show AbstractWe have succeeded in developing new p-type organic semiconductors with phenylethynyl groups, which have high filed-effect hole mobility( >3cm2/Vs) and could be used in solution-processable organic filed-effect transistors(OFETs). For improving a charge-carrier mobility, the intermolecular π-π interaction plays an important role. We have focused on the planarity of molecules and had reported that OFETs using oligo-p-phenylenevinylene derivatives had good FET characteristics. This time, new acene derivatives with phenylethynyl groups have been synthesized to be improved planarity of a molecule.First the vacuum deposited films for three kinds of materials having benzene, naphthalene and anthracene as a core respectively substituted by phenylethynyl groups, were prepared to confirm the effect for the molecular design for improving planarity. Their energy levels were evaluated by UV-VIS and photoelectron spectroscopy to be found that a material with more extended core showed narrower energy gap and shallow HOMO level. Next, OFETs were fabricated by the vacuum deposited films with the device structure of top-contact with poly-chloro-p-xylylene as a gate insulator, gold as all of electrodes, and glass substrate. As the results of evaluating FET characteristics for the devices, the 2,6-Bis(2-phenylethynyl)anthracene (DPEA) film was found to have the highest performance with a field-effect mobility of 0.89cm2/Vs and ON/OFF ratio of 3.2x10^6. That suggested that molecules of a phenylethynyl derivative are closely packed in a grain due to strong p-p interraction. In addition, the AFM images for the film showed that the grain size was μm order and the grains were densely packed. Further investigation with various gate insulators led to improving the field-effect mobility up to 3.5cm2/Vs with ON/OFF ratio of 3.2x10^6.Finally, we have tried to fabricate OFETs with a printing method. DPEA derivatives with alkyl-substituents of various length(CnH2n+1,n=1~6,8,9,12,13,15) were synthesized to enhance the solubility. The OFETs were fabricated by spin coating method form 0.5wt% solution in toluene with the same structure as that of above mentioned. The device of C12H25-DPEA film showed the best performance with a field-effect mobility of 0.98cm2/Vs and ON/OFF ratio of 1.4x10^5 .It is one big step to achieve a large-area flexible display with high performance materials by a printing technique.
9:00 PM - D7.7
All Solution Processed Selective-patterning of Semiconducting Polymer by using Self-assembled Monolayers for Highly Integration of Field Effect Transistors.
Yasuhiko Hayashi 1 , K. Hayashi 1 , J. Nishikawa 1 , K. Harada 1 , K. Nakamura 2 , T. Toyama 2 , K. Takigawa 2
1 Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Aichi, Japan, 2 Research Laboratories, Denso Corporation, Nisshin, Aichi, Japan
Show AbstractThe solution-processed semiconductor polymer devices have evolved as a promising cost-effective alternative to silicon-based devices. The most critical requirement for the integration of polymer transistors is the development of a manufacturing technology that allows the large-area integration of devices at low cost. Here, we have developed all solution processed selective-patterning technique that allows high-performance polymer transistor arrays or circuit to be fabricated over large areas. Our fabrication method involves patterning of both wettable and unwettable regions on the surface of a SiO2/Si substrate by use of silane self-assembling monolayers (SAMs). The trichlorosilane (FOTS SAM) modified SiO2 surface was locally treated by UV ozone through the shadow mask for removing of the FOTS selectively to define transistor regions. Then, the different SAM, trichloro(phenethyl)silane, was coated at the removed FOTS regions. The poly(3-hexylthiophene) (P3HT), dissolved in dichlorobenzene, was dropped on to the patterned substrate which has different inclination angles.All solution processed selective-patterning has been achieved using a different wettability for organic solvents by patterning of SAMs, and selectively formed P3HT transistor arrays according to the patterned active area. The high-performance bottom gate P3HT transistor with field effect mobility of 2x10-2 cm2/Vs, the threshold voltage of -1.9 V and the on/off ratio of 2x105 was formed on the selective-patented substrate. We found that the inclination of patterned substrate drastically affects the transistor performance due to the flow rate of P3HT solution.The simplicity of the proposed method, which requires only the UV ozone for defining the transistor regions, can significantly reduce the costs for the integration of polymer transistors.
9:00 PM - D7.8
Organic Thin Film Transistor Printed by a Laser Technique.
Ludovic Rapp 1 , Karim Diallo 2 , Anne Patricia Alloncle 1 , Philippe Delaporte 1 , Sebastien Nenon 2 , Christine Videlot-Ackermann 2 , Frederic Fages 2 , Matthias Nagel 3 , Thomas Lippert 4
1 UMR 6182 CNRS, LP3, Marseille France, 2 UPR 3118, CINaM, Marseille France, 3 , EMPA, Dübendorf Switzerland, 4 , Paul Scherrer Institut, Villigen Switzerland
Show AbstractRecently we have seen a considerable rise of interest in Organic Thin-Film Transistors (OTFT) and Organic Light-Emitting Diodes (OLED) because of the remarkable potential applications of these devices in plastic micro-electronics. The two major applications that motivate this research are radio frequency identification tags (RFID) and flexible displays. The study and the implementation of new techniques for electronic components manufacturing on flexible supports are an important stage for the development of plastic micro-electronics. The development of direct printing technologies associated with the use of new organic conducting and semiconductor materials would allow avoiding the use of complex and expensive techniques such as photolithography (etc…).Our objective is to develop a laser printing technique, i.e. Laser-Induced Forward Transfer (LIFT). The LIFT technique removes a small piece of a thin layer previously deposited on a transparent substrate by a pulsed laser and transfers it on another substrate. This simple, single step, direct printing technique allows surface micro patterning or localized deposition of material. This process is a promising alternative for fabrication of organic and metallic electronic components when complex architectures are needed or when usual techniques, such as inkjet printing cannot be considered. It can be applied to sensitive materials without altering their properties but it also allows to direct-write multilayer systems in a solvent-free single step, without requiring any shadowing masks or vacuum installation. It is also a low cost process which allows fast deposition on large areas on flexible supports. Its opens the way to alternative manufacturing processes for the OTFT technology.Functional organic transistors were achieved using the LIFT technique in top and bottom contact design. The compounds used for the source and drain electrodes are metallic materials (aluminium, chromium, gold, …) or organic conductors, e.g. poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). The LIFT deposit patterns must be spatially well defined in order to get a channel length as short as possible and the homogeneity and electrical properties of the materials must be retained. The organic semiconductors are p-type or n-type structures as copper phthalocyanine (CuPc), copper hexadecafluorophthalocyanine (F16CuPc), pentacene and distyryl-quaterthiophenes (DS-4T). Operating devices have been characterized by current-voltage (I-V) measurements and the morphology and thickness of the deposits have been investigated by optical, scanning electronic and atomic force microscopy. Moreover, we have compared the devices with organic transistors made by thermal evaporation to demonstrate the performance and the viability of the LIFT technique for OTFT device fabrication.
9:00 PM - D7.9
Thin-film Transistors and CMOS Inverters Fabricated with Solution-processable Fullerene- and Oligothiophene-based Organic Semiconductors.
Masayuki Chikamatsu 1 , Ming Lu 1 2 , Yoshinori Horii 1 , Syunsuke Nagoya 1 , Reiko Azumi 1 , Kiyoshi Yase 1
1 Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 2 Department of Chemistry, Harbin Normal University, Harbin China
Show Abstract Solution-processed organic thin-film transistors (OTFTs) have attracted considerable interest in resent years for their potential application to low-cost and large-area flexible electronics, such as active-matrix displays and radiofrequency identification. Substitution of long alkyl chains is one of effective techniques to improve the organic solvent solubility of semiconducting materials. It is as well an effective way to modify the packing and arrangement of molecules in a condensed matter without altering much the nature of an active moiety. As n-type semiconductors, we have developed long chain alkyl-substituted C60s [1-3]. Advantage of these compounds is not only their high solubility but also their easy processability of highly ordered films by using self-assembling ability of long alkyl chains. One of the compounds, C60-fused N-methylpyrrolidine-meta-C12 phenyl (C60MC12), has been proved to exhibit an electron mobility of ca. 0.5 cm2/Vs by optimizing the film fabrication conditions such as surface modification of gate dielectric. The TFT based on its analogue with fluorinated alkyl chain (C60PC12F25) operate even in air [3]. Oligothiophenes are promising materials mainly as p-type semiconductors for TFTs. Alkyl substitution at the α-position (substitution along the long molecular axis) of oligothiophene does not improve much the solubility of the material. On the other hand, substitution at the β-position (substitution perpendicular to the oligothiophene long axis) improves the solubility while affords poor carrier mobility. We have synthesized a sexithiophene derivative with branched alkyl chains at both the α-positions of the molecule (BHD6T). A hole mobility of ca. 0.18 cm2/Vs was obtained for the bottom-contact TFT fabricated by spin coating a chloroform solution of BHD6T, which is as high as or even nicer mobility compared with that of vacuum-evaporated film out of unsubstituted sexithiophene. The mobility was improved by annealing the film at high temperature. Furthermore, we have succeeded in fabricating a CMOS using the C60MC12-based n-type device and the BHD6T-based p-type device. A large inverter characteristic with a gain of ca. 75 was obtained.[1] M. Chikamatsu et al., Appl. Phys. Lett., 87, 203504(2005).[2] M. Chikamatsu et al., J. Photochem. Photobiol. A, 182, 245(2006).[3] M. Chikamatsu et al., Chem. Mater., 20, 7365(2008).
Symposium Organizers
Michael L. Chabinyc University of California-Santa Barbara
David Gundlach National Institute of Standards and Technology
Jenny Nelson Imperial College London
Takao Someya University of Tokyo
D8: Processing and Fabrication
Session Chairs
Thursday AM, December 03, 2009
Republic B (Sheraton)
9:30 AM - **D8.1
Materials and Processes for Thin Film Electronics.
Zhenan Bao 1
1 , Stanford University, Stanford, California, United States
Show AbstractOrganic semiconductor materials are interesting alternatives to inorganic semiconductors in applications where low cost, flexible or transparent substrates, and large area format is required. Currently they have been incorporated into organic thin-film transistors (OTFT), integrated display driver circuits, photovoltaics and radio frequency identification tags. In this talk, I will present recent results on material design, surface and interface control for achieving efficient charge carrier transport and large area patterning of organic semiconductors.
10:00 AM - D8.2
Orthogonal Lithography for Organic Electronics.
Alexander Zakhidov 1 , Jin-Kyun Lee 1 , John DeFranco 1 , Hon Hang Fong 1 , Yee Fun Lim 1 , Priscilla Taylor 1 , Christopher Ober 1 , George Malliaras 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractThe realization of organic electronic technologies requires the availability of patterning techniques that are compatible with chemically sensitive materials. Presently many multilayer device architectures cannot be produced because of the complexity of processing such materials. In our research the application of benign fluorous solvents to the microfabrication of flexible organic electronic devices was targeted. We have exploited the fact that fluorous solvents are orthogonal solvents, that is, they are neither polar or non-polar solvents, but are a third class of materials with very specific solvency characteristics. These solvents do not solubilize or swell organic semiconductors and as a result they can be successfully incorporated into patterning methods to process films of organic semiconductors without adversely affecting previously deposited layers. We have shown that these solvents coupled with appropriately designed photo (e-beam) resists satisfy most criteria for universal, materials-friendly processing aids. Utilization of combination of these solvents and resists (instead of conventional materials) opens new route for high resolution, high throughput patterning of organic materials. We have demonstrated that our patterning approach enables the fabrication of unique organic electronic devices, such as ultra small channel length top-contact thin film transistors, ring oscillators and patterned light emitting diode passive matrix displays. 1. Al. A. Zakhidov, J.-K. Lee, H. H. Fong, J. A. DeFranco, M. Chatzichristidi, P. G. Taylor, C. K. Ober, G. G. Malliaras, Advanced Materials, 2008, 20, 3481.2. H. S. Hwang, Al. A. Zakhidov, J.-K. Lee, X. Andre, J. A. DeFranco, H. H. Fong, A. B. Holmes, G. G. Malliaras, C. K. Ober, Journal of Materials Chemistry, 2008, 18, 3087. 3. J.-K. Lee, M. Chatzichristidi, Al. A. Zakhidov, P. G. Taylor, J. A. DeFranco, H. S. Hwang, H. H. Fong, A. B. Holmes, G. G. Malliaras, C. K. Ober, J. Am. Chem. Soc., 2008, 130, 11564.4. P.G. Taylor, J.-K. Lee, Al.A. Zakhidov, M. Chatzichristidi, H.H. Fong, J.A. DeFranco, G.G. Malliaras, C.K. Ober, Adv. Mater., 2009, 10.1002/adma.200803291.5. Y. Lim, J.-K. Lee, Al. A. Zakhidov, J. A. DeFranco, H. H. Fong, P. Taylor.,C. Ober, G. G. Malliaras, J. Mater Chem., DOI: 10.1039/b822949j (2009).
10:30 AM - D8.4
The Fabrication and Downscaling of Inkjet-printed Nano-channel n-type Field-effect Transistors.
Xiaoyang Cheng 1 , Mario Caironi 1 , Mi-Jung Lee 1 , Chirs Newman 2 , Antonio Facchetti 2 , Henning Sirringhaus 1
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 , Polyera Corporation, Chicago, Illinois, United States
Show AbstractInkjet printing is a non-contact, digital direct-writing manufacturing technique that has been recently investigated for its adoption in the realization of low-cost, large-area organic electronic devices. A general limitation of printed transistors is represented by the lateral resolution, which cannot be better than 10μm with standard printing equipment, resulting in slow switching speed. To overcome this, in the literature various techniques capable of high resolution have been demonstrated, such as self-aligned printing (SAP), but most of these are focused only on the fabrication of hole transport (p-type) organic field-effect transistors. Since the unipolar logic shows clear limits with respect to a complementary one, it is important to develop a suitable electron transport (n-type) counterpart. To achieve this, here we demonstrate a downscaled n-type, top-gate organic field-effect transistor based on a printed commercial silver nanoparticles ink, combined with a novel air-stable n-type organic semiconductor. High resolution printed nano-channels with a length as low as 100 nm are realized by a recent developed self-aligned printing technique. By employing an ultrathin crosslinked fluoropolymer gate dielectric with a thickness of 50 nm, this nano-channel n-type transistor can achieve full saturation with operation voltages below 5 V. Printed silver electrodes show minimized parasitic contact resistance and improved electron injection in the nano-channel device compared to printed gold electrodes. Furthermore we show that our self-aligned printed n-type transistors are also characterized by a good stability to bias stress and air exposure.
10:45 AM - D8.5
Fully-downscaled, Printed Organic CMOS Inverters Enabled by High Yield Self-aligned Inkjet Printing.
Mario Caironi 1 , Enrico Gili 1 , Henning Sirringhaus 1
1 Cavendish Laboratory, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom
Show AbstractDirect-write, solution-based, additive printing techniques are an emerging and very versatile approach for low-cost, large-area manufacturing of electronic circuits. Despite this, the poor resolution achievable with standard tools limits the operative frequencies of printed circuits. This issue has been recently addressed by developing a self-aligned inkjet printing technique based on commercial drop-on-demand systems. The technique allowed the fabrication of metal electrodes with sub-micrometer gaps, based on which printed p-type polymer transistors with a transition frequency as high as 1.6 MHz were demonstrated. Whether this approach can be adopted in real applications will depend on the patterning uniformity and yield achievable. Moreover it is important to develop complementary devices in order to overcome the limitations of unipolar logic gates in terms of noise margins and power consumption. Here we demonstrate that by adopting a novel device architecture for a self-aligned printed (SAP) sub-micrometer channel, low leakage metal electrodes arrays with gaps of 200 – 500 nm can be reliably fabricated with high yields. Based on this approach, we further demonstrate fully downscaled, SAP p-type and n-type organic thin-film transistors based on high mobility polymer semiconductors. These devices allow the realization of SAP CMOS inverters, thus paving the way for the development of robust, high-speed printed logic circuits.
11:30 AM - **D8.6
High Performance Organic-Inorganic Hybrid Transistors.
Thomas Anthopoulos 1
1 Department of Physics , Imperial College London, London United Kingdom
Show AbstractResearch on solution processible semiconducting materials is rapidly making progress towards the goal of providing viable alternatives to silicon-based technologies for applications where lower-cost manufacturing and new product features are desired. One family of materials that has been the subject of intense research for the past twenty years is organic semiconductors. Use of organic materials offers the prospect of low manufacturing cost and various desirable physical characteristics. Despite the impressive progress achieved in recent years, however, a number of obstacles -e.g. poor air-stability, insufficient device performance and device to device variability- have to be overcome before the advantageous manufacturability, and hence the economic benefits associated with organic semiconductors, can be fully exploited. While research in the area of organic materials has been intensifying a different class of semiconductors, namely metal oxides (MOxS), has emerged as a possible alternative technology. MOxS incorporate important qualities that are currently absent from organic-based semiconductors. For instance, they generally exhibit higher carrier mobilities and are highly transparent. Unfortunately, the vast majority of MOxS demonstrated to date are electron transporting (n-type). This rather generic characteristic represent a major technology bottleneck for the development of high performance circuits based on the much-desired complementary technology in which both n- and p-type transistors are required. Here, we present an alternative approach towards high-performance low-cost electronics based on the use of solution processible p-type organics and n-type oxide semiconductors. In particular, by developing optimised organic/oxide semiconductor heterostructures, unipolar as well as ambipolar thin-film transistors with hole and electron mobilities in excess of 2 cm^2/Vs can be realised. One important characteristic of our approach is that both semiconductor layers are processed from solution under ambient atmosphere without any special precautions. The present work is a major step towards low-cost, high-performance thin-film electronics.
12:00 PM - D8.7
Flexible Printed Sensor Tape based on Organic Solution Processed Materials.
Ana Claudia Arias 1 , Tse Nga Ng 1 , Jurgen Daniel 1 , Sanjiv Sambandan 1 , Sean Garner 1 , Gregory Whiting 1 , Rene Kist 1 , Brent Krusor 1 , Beverly Russo 1
1 EMDL, Palo Alto Research Center, Palo Alto, California, United States
Show AbstractWe are developing flexible sensor tapes to detect the occurrence of events that cause traumatic brain injury (TBI). TBI is a medical condition that is cumulative and triggered by events such as blast pressure waves, noise and acceleration. Inkjet printing, laser machining and lamination are employed during fabrication, with inkjet printing being the main material deposition method. The sensor tape has integrated sensors, signal conditioning electronics, non-volatile memory and a thin film battery. The sensors are based on piezoelectric polymers such as PVDF due to low-power requirements, low drift and relatively simple fabrication. The availability of n and p-channel solution-processed semiconductors enables the fabrication of complementary circuits which have the advantages of lower power consumption and simpler design compared with unipolar circuits. We have demonstrated all printed p-type TFTs with mobility of 1.6 cm2/Vs and n-type TFTs with mobility of 0.6 cm2/Vs. We have characterized the charge trapping rates for n- and p-channel devices and assessed the inverter gain and noise margin. All printed inverters showed a typical gain of 8 with VDD at 10V and -3dB cutoff at 150 kHz for a load of 0.02pF. We have integrated printed inverters with printed accelerometers and printed pressure sensors and showed operation between 0-1000g and 5-80 psi respectively.
12:15 PM - D8.8
Stretchable, Large-area Active Matrix Organic Light-emitting Diode Display Using Printable Elastic Conductors.
Tsuyoshi Sekitani 1 , Hiroyoshi Nakajima 2 , Hiroki Maeda 2 , Takanori Fukushima 3 1 , Takuzo Aida 1 3 4 , Kenji Hata 5 , Takao Someya 1
1 , University of Tokyo, Tokyo Japan, 2 , Dai Nippon Printing Co., Ltd.,, Chiba Japan, 3 , RIKEN, Saitama Japan, 4 , ERATO, Tokyo Japan, 5 , AIST, Tsukuba Japan
Show AbstractWe report the manufacture of printable elastic conductors comprising single-walled carbon nanotubes (SWNTs) uniformly dispersed in a fluorinated rubber [1]. Using an ionic liquid and jet-milling, we produce longer and finer SWNT bundles that can form well-developed conducting networks in the rubber. Conductivity of more than 100 S/cm and stretchability of more than 100% are obtained. Making full use of this extraordinary conductivity, we constructed a large-area rubber-like stretchable active matrix display comprising integrated printed elastic conductors, organic transistors, and organic light-emitting diodes (LEDs). The display could be stretched by 30–50% and spread over a hemisphere without any mechanical or electrical damage.Printable elastic conductors were manufactured using very long SWNTs, ionic liquid, and a fluorinated copolymer rubber matrix, and used as electrical and mechanical wirings. The elastic conductors can be finely patterned to 100 micrometer using screen-printing. Organic transistors work as display driving cell and organic light-emitting diodes were manufactured on plastic substrates using vacuum evaporation. The sheet size was 100 x 100 mm^2 comprising 16 x 16 cells. The mobility of the transistors was typically 0.6 cm^2/Vs and the on/off ratio exceeds 10^6, while the luminance of organic LEDs was exceeding 5000 cd/m^2 with 15 V, indicating excellent electrical performances. The organic transistor active matrix and LED array were fixed on silicone rubber (PDMS) sheet and then mechanically processed by a numerically controlled punching system to isolate and uniformly distribute them on a stretchable PDMS rubber sheet. The periodicity is 5 mm. Each isolated transistors and LEDs on the PDMS sheet was electrically connected using printed elastic conductors as scanning-, data-, bias-voltage-, and ground-lines. Light-emitting properties of the organic LED display were characterized. The light-emitting properties of an organic LED integrated with a organic transistor and Cu wirings, and an organic LED integrated with an organic transistor and printed elastic conductors (50 S/cm) were used, for comparison. When printed elastic conductors were used, currents passing though organic LED (IOLED) decreased slightly by only 8% to 1.2 mA, resulting in a high luminance value of 364 cd/m^2, which is sufficient for display applications. This work was supported by Kakenhi (Wakate S), Special Coordination Funds for Promoting Science and Technology.[1] T. Sekitani, et al., Nature Materials 8, 494-499 (10 May 2009).
12:30 PM - D8.9
Self-aligned Polymer Wells for Solution Processable Organic Circuits.
Charlotte Kjellander 1 , Wiljan Smaal 1 , Bas van der Putten 1 , Gerwin Gelinck 1
1 , Holst Centre, TNO, Eindhoven Netherlands
Show AbstractOrganic electronics is a fast developing research field aiming at light-weight, low-cost and large area applicability. Encouraging performance for TFTs using soluble materials such as 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) as active layer have been reported [1].In most organic circuitry applications, the organic semiconductor layer needs to be patterned to avoid undesired current leakage from the transistor to any surrounding part of the system through the semiconductor layer. An attractive alternative is to deposit the active layer with ink jet printing directly over the TFT. This usually requires some sort of pre-patterning of the substrate on which the active material is deposited to keep the ink in the desired areas. To gain freedom in the positioning and lateral resolution of the active layer we present a process consisting of a substrate covered by a thin layer of polymer on which the ink of the active material is printed. In this way a self-aligned pattern is created simultaneously with the deposition of the organic semiconductor. This method does not require additional pre-patterning steps and is compatible with flexible substrates and continuous processing techniques.The self-aligned polymer well formation is determined by: i) interaction of ink-polymer surface; ii) dissolving the polymer layer in the OSC ink; and iii) evaporation-induced solidification and crystallization of the polymer and OSC. In this paper we discuss how the morphology and transistor performance are influenced by physical parameters (as solubility of the polymer, molecular weight, and temperature) and processing conditions (as volume and positioning of the ink jet printed droplets). The process yields good mobilities and stable threshold voltages close to 0 V. We compare TFT performances with ink jet printed devices on bare transistor substrates (without the polymer layer) and with other patterning techniques, such as ink jet printing in polymer wells defined by photo-lithography. Parallels are drawn with direct deposition of blends of TIPS-PEN and polymers, as recently reported [2]. [1] Park et al., Appl. Phys. Lett. 91, 063514 (2007); [2] Hamilton, et al., Adv, Mater., 21, 1 (2009).
D9: Novel Concepts and Devices
Session Chairs
Thursday PM, December 03, 2009
Republic B (Sheraton)
2:30 PM - **D9.1
Reduction of Metallic Conductivity of SWNT by a Cyclo-addition Reaction.
Graciela Blanchet 1 , Mandakini Kanungo 2 , George Malliaras 2
1 , Nanoterra, Cambridge, Massachusetts, United States, 2 Material Science, Cornell University, Ithaca, New York, United States
Show AbstractABSTRACT: Precise control over the electronic properties of carbon nanotubes is key to their application in plastic electronics. In the present work, we have functionalized carbon nanotubes with an electron withdrawing non-fluorinated olefins via a 2-2 cycloaddition reaction. Our results suggest that the formation of a cyclo butane like 4-member ring at the functionalization site is a fairly general approach, independent of specifics of the addend, to converting the grown mixture of metal and semiconductor tubes into high mobility semiconducting tubes without tedious separation requirements. Thin film transistors fabricated from such functionalized tubes exhibit mobilities of ~30 cm2/Vsec and on/off ratios in excess of 106. This simple functionalization represents a low cost path to high performance semiconducting inks for printable electronics.
3:00 PM - D9.2
Low-Voltage Ring Oscillators Based on Polyelectrolyte-Gated Polymer Thin-Film Transistors.
Lars Herlogsson 1 , Michael Coelle 2 3 , Steven Tierney 2 , Xavier Crispin 1 , Magnus Berggren 1
1 Department of Science and Technology, Linköping University, Norrköping Sweden, 2 , Merck Chemicals Ltd, Southampton United Kingdom, 3 , Evonik Degussa GmbH, Marl Germany
Show AbstractMany of the potential applications for printed electronics, in which organic thin-film transistors (OTFTs) are key components, will require powering from low-voltage sources such as printed batteries, solar cells, or via electromagnetic induction. Moreover, the clock frequency should be at least 100 Hz for proper operation and rapid updating of the electronic circuits. Combining high speed with low-voltage operation has proven to be difficult. The fastest OTFT circuits have been driven at tens of volts, and the circuits with the lowest supply voltages are found to be very slow.We report organic integrated circuits that operate at supply voltages down to 0.9 V and exhibit signal delays down to 300 µs per stage. The circuits are based on polyelectrolyte-gated OTFTs that have a top-gate, bottom-contact configuration. The source and drain electrodes are interdigitated and narrow in order to reduce the parasitic stray capacitance and improve the switching speed of the circuits. The high capacitance (3 µF cm-2) of the polyanionic gate insulator, poly(vinyl phosphonic acid-co-acrylic acid), allows the OTFTs to operate at voltages below 1.5 V. The OTFTs show good transistor characteristics with an on-off current ratio of 4000, a subthreshold swing of 0.15 V dec-1, a threshold voltage of -0.45 V, and a maximum transconductance per channel width of 13.5 µS mm-1. The charge carrier mobility of the polythiophene semiconductor, P(T0T0TT16), is calculated to be 0.02 cm2 V-1 s-1.Integrated inverters using two different load transistor designs are explored: one where the gate is connected to the drain (saturated load) and another where the gate is connected to the source (depleted load). Saturated load inverters show a voltage amplification of 1.7. Higher amplification (3 - 8) is obtained in the depleted load inverters, but at the expense of switching speed. Hence, the saturated load inverter design was used in the fabrication of seven-stage ring oscillators with output buffers. The oscillators show stable oscillations for supply voltages down to 0.9 V, and oscillate at a frequency of 235 Hz at 1.5 V, corresponding to a stage delay of 300 µs. These results demonstrate that electrolyte-gated OTFTs are promising candidates for use in low-voltage printed organic electronics.
3:15 PM - D9.3
High-performance Ambipolar Thin-film Transistors and Circuits with Co-planar Geometry.
Jungbae Kim 1 , Canek Fuentes-Hernandez 1 , Sungjin Kim 1 , William Potscavage 1 , Seungkeun Choi 1 , Bernard Kippelen 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractAmbipolar thin-film transistors (ATFTs) are attractive microelectronic devices because unlike unipolar TFTs, they operate independently of the sign of the gate voltage. Ambipolar thin-film transistors (ATFTs) could lead to a new generation of novel multifunctional analog and digital (CMOS) circuits that dissipate low power and can be processed at low-temperature on flexible substrates at low-cost. However, current approaches for the realization of ATFTs typically show degraded electrical properties due to either unbalanced electron/hole charge injection or to the existence of a p-n heterojunction which increases the scattering processes for charge transport. Here, we report on a new geometry for the realization of high performance ATFTs. We demonstrate ATFTs with this new geometry using amorphous-InGaZnO and pentacene channels on an Al2O3/Si substrate. The Al2O3 gate dielectric is deposited by atomic layer deposition to achieve high capacitance densities and low leakage currents. The ATFTs show no degradation of their electrical performance with respect to independent unipolar TFTs having the same geometry. In the linear regime, these ATFTa achieve on-off current ratios approaching 105, and field effect mobilities of 0.3 cm2/Vs and 10.5 cm2/Vs during p- and n-channel operation respectively. These values are identical to those obtained in unipolar TFTs. In the saturation regime the on-currents, effective saturation mobility values and threshold voltages are also comparable with those measured in unipolar TFTs. We will report on the dc and ac characteristics of complementary ambipolar inverters that achieve high gains of up to 70 V/V at a switching threshold voltage of 7.3 V with noise margin low of 6.4 V and noise margin high of 2.5 V at operating voltages of ±12 V. Our results provide a versatile new approach for achieving high performance ATFT-based electronic components which can be easily adapted to current materials and methods used in high performance unipolar TFTs.
3:30 PM - D9.4
Integrated Organic Passive Photodetector Pixel for Focal Plane Imagers.
Christopher Renshaw 1 , Xin Xu 4 , Stephen Forrest 1 2 3
1 Physics, University of Michigan, Ann Arbor, Michigan, United States, 4 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWe demonstrate an organic photodetector integrated with a pentacene based organic thin film transistor (OTFT) to produce a passive, organic photodetector pixel for use in a photodetector focal plane imaging array. The OTFT allows the photodetector to be switched to an OFF state with a low OFF current that is independent of light intensity, allowing numerous pixels in an array to be independently addressed. The pixel is fabricated entirely by vacuum thermal evaporation onto patterned ITO for compatibility with flexible substrates and non-planar detector arrays.It consists of a boron subphthalocyanine (SubPc)/C60 based organic photodetector with molybdenum oxide (MoOx) to reduce dark current and a 500 μm by 25 μm pentacene channel OTFT with a parylene-C gate insulator and silver contacts. The pixel has greater than a 7-bit dynamic range and a spectral response from 400-610nm. An OFF current of less than 50pA and a switching speed of greater than 200kHz makes the pixel suitable for use in high sensitivity imaging applications.
3:45 PM - D9.5
Three-dimensional Organic Field-effect Transistors on Plastic Substrates: Flexible Transistors with Very High Output Current.
Jun Takeya 1 , Mayumi Uno 1 2 , Kengo Nakayama 1
1 , Osaka University, Toyonaka Japan, 2 , TRI-Osaka, Izumi Japan
Show Abstract Development of organic semiconductor materials have been intensively driven by their attractiveness in low-cost and energy-saving fabrication processes for active electronic devices such as organic field-effect transistors (OFETs). Furthermore, the easy fabrication techniques at low temperature enable the use of plastic substrates, so that the organic transistors can form active-matrix elements in ultra-thin flexible displays, for example. In order to compensate limited performance in their charge transport, we have developed easy MEMS-based processes that realize three-dimensional (3D) OFET structures with multiple vertical channels on plastic platforms. The design maximizes the space availability and the output current per area. The flexible 3D-OFETs indeed present outstanding current exceeding 0.1 A/cm2, which is more than sufficient for driving pixels of typical organic light-emitting diodes (OLEDs). High on-off ratio of ~ 107 is also achieved.A multi-columnar structure is built of a plastic photoresist SU8 (Nihon Kayaku Co., ltd.), so that the sidewalls of the columns can be deposited with organic semiconductors and used for active channels in the transistors. Since the channel width W corresponds to the total length of all the column edges and the channel length L equals to the height of the columns, much higher ratio of W/L can be realized in the 3D-OFETs than in the conventional planer thin-film transistors without constraints of the lateral space. Typical W/L ratio of our prototype devices is as high as 104 in a pixel of 100 x 100 μm2, so that high total current is expected in the whole sidewall channels in the pixel [1]. 200-nm thick parylene is used for the gate insulating layer.Among several tested organic p-type semiconductors, vacuum deposited dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) showed the highest output current exceeding 0.1 A/cm2 with gate voltage |VG| of 20 V and drain voltage |VD| of 10 V. Carrier mobility is estimated to be around 0.15 cm2/Vs. With the achieved output current orders of magnitude higher than conventional planer devices, the size for the driving transistors can be negligible in the OLED pixels. Also, the high margin in the device performance is advantageous in developing active matrices with thousands of driving transistors to operate identically. The processes are still under optimization to form organic semiconductors on the 3D structures from solution. However, even though mobility of the present devices with 2,7-dialkyl derivatives of benzothienobenzothiophene (Cn-BTBT) is only in the order of 10-4 cm2/Vs upon hole accumulation, output current of 0.1 mA/cm2 is achieved with gate voltage |VG| of 20 V and drain voltage |VD| of 10 V, which is comparable to the values in typical high-mobility lateral devices.DNTT is supplied from Nihon Kayaku Co., ltd..[1] M. Uno, J. Takeya et al., Appl. Phys. Lett. 93, 173301 (2008); ibid. 94, 103307 (2009).
4:30 PM - **D9.6
OFETs Gated via Polyelectrolytes: Materials, Devices and Circuits.
Magnus Berggren 1 , Xavier Crispin 1 , Lars Herlogsson 1 , Elias Said 1 , Oscar Larsson 1
1 ITN, Linkoping University, Norrkoping Sweden
Show AbstractTo achieve an electronics platform for printed intelligence it is necessary to bring down the driving voltage of all included devices in order to enable powering using printed batteries or electromagnetic induction. To achieve this goal for organic field effect transistors (OFET) several approaches to use high-permittivity materials as the gate insulator have been explored. However, often those approaches have proven to be incompatible with reel-to-reel manufacturing and robust device structures. Here, we report using easily printed polyelectrolytes as the gate insulator in field effect transistors. These materials exhibit very high effective polarization, thus resulting in a driving voltage below 1 V. The materials and their polarization characteristics in relation to OFET operation will be discussed. Further, our polyelectrolyte-gated OFETs switch on and off at around 10 microseconds and ring oscillators including those devices exhibit a stage delay time of around 0.3 milliseconds.
5:00 PM - D9.7
Evaluation of Thermopower of Organic Materials Toward Flexible Thermoelectric Power Generators.
Masakazu Nakamura 1 , Atsushi Hoshi 1 , Masatoshi Sakai 1 , Kazuhiro Kudo 1
1 Department of Electrical and Electronic Engineering, Chiba University, Chiba Japan
Show Abstract A thin flexible power generator is strongly desired for the wearable electronics that is one of the future images of the printable electronics. The thermoelectric power generator using human-body-originated heat, which is equivalent to a 70-150 W heater, is one of the candidates of the basic power source for such a purpose. In general, the ability of the thermoelectric conversion material is determined by how large the Seebeck coefficient (thermopower) is and how small the thermal conductivity is. Many of organic conducting and semiconducting materials are, in this sense, promising as thermoelectric conversion materials because they have very large Seebeck coefficients, over 1 mV/K, and small thermal conductivities. However, there are only a limited number of studies on the thermoelectricity of organic materials and very few especially on small molecules. Therefore, what is important now are to precisely evaluate the Seebeck coefficients of various organic conducting/semiconducting thin films and to examine what kind of material is the most effectual as a thermoelectric conversion material. To carry out such experiments, it is necessary to measure the samples in ultra-high vacuum with strictly controlled purity because their electrical characters are greatly influenced by the oxygen and water in the atmosphere. Since there is no commercial instrument that meets such a demand, an original one has been developed in this study to precisely evaluate both the Seebeck coefficient and the electrical conductivity of an organic thin film under strict purity control. In this presentation, its ability to measure the Seebeck coefficients of highly resistive materials will be shown. Then, Seebeck coefficients and thermoelectric abilities of some typical organic functional materials will be discussed.
5:15 PM - D9.8
Polaron Absorption in Organic Charge Transport Materials and its Implications on Electrically Driven Organic Solid State Lasers.
Marcus Lehnhardt 1 , Torsten Rabe 2 , Patrick Goerrn 2 , Thomas Weimann 1 , Thomas Riedl 2 , Wolfgang Kowalsky 2
1 , Physikalisch Technische Bundesanstalt, Braunschweig Germany, 2 , Institut fuer Hochfrequenztechnik, Technische Universitaet Braunschweig, Braunschweig Germany
Show AbstractPolaron related absorption in organic materials is of interest not only from a funda-mental point of view but has also significant implications for various device applications. For organic light emitting diodes the quenching of singlet excitons due to charged species has been evidenced in several reports [1]. Especially, for electrically operated organic laser structures where significantly higher charge carrier densities are required, precise information about charge induced absorption is essential. We study polaron induced absorption in organic transport materials using a novel measurement technique [2]. An unipolar organic device is embedded into a low-loss waveguide structure. Therein, the current induced change of the waveguide absorption is measured with unsurpassed accuracy compared to other techniques used for the unambiguous study of polaronic species in organic thin films. The key idea of the device setup, is the design of a waveguide that favours the low loss propagation of the second transverse electrical mode (TE2) with the lossy electrodes placed in the two respective nodes of the mode. As a result, the overall waveguide losses can be as low as 1 cm-1. In this structure, polaron absorption spectra were determined for the hole transporting material (2,2',7,7'-Tetrakis(n,n-diphenylamino)- 9,9'-spirobifluorene) (S-TAD) and the ambipolar materials 2,7-Bis(9-carbazolyl)-9,9-spirobifluorene (S-2CBP), 2-(9,9'-Spirobifluoren-2-yl)-9,9'-spirobifluorene (BSBF). Moreover, the absorption due to radical anions in an electron transporting material 1,3-Bis[2-(2,2'-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene (Bpy-OXD) was recorded. The polaron induced absorption cross section showed a significant difference of nearly three orders of magnitude in these exemplary materials. Importantly, we were able to identify materials with pronounced spectral windows of a low polaron absorption cross section (less than 3×10-18 cm). In view of these results, the common belief of polaron related losses rendering electrically driven organic lasers impossible has to be revised [3]. [1] M. A. Baldo, C. Adachi, and S. R. Forrest, Phys. Rev. B 62, 10 967 (2000).[2] T. Rabe, P. Goerrn, M. Lehnhardt, M. Tilgner, T. Riedl and W. Kowalsky Phys. Rev. Lett. 102, 137401 (2009).[3] N. Tessler, Adv. Mater. 11, 363 (1999).
5:30 PM - D9.9
Technical Realization of OLEDs in Textiles.
Silvia Janietz 1 , Bjoern Gruber 1 , Andreas Neudeck 2 , Yvonn Zimmermann 2
1 Polymer Electronics, FhG-IAP, Potsdam Germany, 2 , TITV-Greiz, Greiz Germany
Show AbstractConjugated organic small molecules and polymers, offer the opportunity to produce devices on large area, low-cost and plastic planar substrates. These materials are becoming increase attention also in the field of e-textiles, because they show an interesting combination of electronic and mechanical properties that can be favourably exploited in smart textiles. A key step for the integration of mass production of e-textiles is to completely integrate electronic production with textile productions In the last years were reached progress in the development of fibers and there processing for application in e-textiles. It gives growing interest in optoelectronic devices having a fiber form like the realization of organic solar cells1, organic field effect transistor2 and organic light emitting diodes (OLED)3. The application reached from fabric integrated light sources to low cost solid state lighting under the aspect of protection and security. Here are present on the one side the research results concerning the integration of encapsulate OLEDs in size of 1 cm2 into textiles. It was possible to integrate solid OLEDs, based on the developed isolated high conducting ELITEX®-filaments structures to produce reliable, yielding and portable lighting textiles. The combination of innovative textile manufacturing, adapted contacting technology and reliable encapsulated OLED leads to manufacturable lighting textiles with high light density.On the other side it will be discussed the first results concerning the realization of an OLED on cylindrical surfaces, based on solution processed technologies to go in direction of low cost processing. It was succeeded to realize a simply, inverted planar construction, based on solution processing. This preliminary work was the precondition for the development of a fiber based OLED. It was find out that first galvanic deposited Ag or Al layers on fibers have very high roughness for the construction of OLED on fibers. For this reason Al was evaporated on a glass fibre with very smooth surface and on top of it the organic layers were deposited from solution. First characteristic curves can be shown. The double logarithmic plot of the voltage against the current density demonstrates diode behaviour. But it must be further work on the technological realization to generate also lighting. Problems with contacting and the processing of thin homogenous layers on cylindrical surfaces must be solved. Literature1 M. Taivola, M. Ferenets, P. Lund, A. Harlin, Thin Solid Films 2009, 517, 2799 -28022 M. Maccioni, E. Orgiu,P. Cosseddu, S. Locci, A. Bonfiglio, Appl. Phys. Lett 2006, 89,1435153 B. O.Connor, K.H. An, Y. Zhao, K.P. Pipe, M. Stein, Adv. Mat. 2007, 19, 3897 -3900
5:45 PM - D9.10
A Blue-light Dosimeter Which Indicates the Dose Accumulation by a Multicoloured Change of Photo-degraded Polymer.
Claudia Barbosa de Vasconcelos 1 , Giovana Ferreira 1 , Rodrigo Bianchi 1
1 Department of Physics, Federal University of Ouro Preto, Ouro Preto, MG, Brazil
Show AbstractLuminescent polymers are commonly employed in light-emitting displays because of their good processability, lightweight and higher luminance with low power consumption. However, even though they are good candidates for lighting applications, they are highly susceptible to photoxidation processes which dramatically change their color with light exposure time. In this work we use the light instability of a luminescent polymer in order to design a novel blue-light dosimeter which indicates the dose accumulation by a multicoloured change of photo-degraded poly(2-metoxy-5(2’-ethylhexyloxy)-p-phenylenevinylene) - [MEH-PPV] produced by phototherapy systems. Color, photoluminescence and absorbance spectra measurements were carried out on MEH-PPV solutions under the effect of blue LED light source provided by commercial phototherapy systems. All measurements were done maintaining the chief conditions of jaundice treatments, which is one of the most common reasons for hospital readmissions of newborn infants. It is observed changes from orange-red to yellow clearly on colour solutions, while its peak position emission shifts from orange-red to blue and also decreases in intensity with increasing radiation exposure time. Experiments performed with oxygen enriched solutions were shown to improve these effects, which is mainly caused by the competition between two possible mechanisms: a light induced polymerization of MEH-PPV and replacement of C=C by C=O bonds on the polymer backbone. FTIR measurements confirm these evidences. Analyses of the relation between the irradiance produced by phototherapy systems and the CIE (1931) chromatic diagram of MEH-PPV solutions reveal this polymer as a low cost and easy to operate blue-light dosimeter for neonatal phototherapy.