Symposium Organizers
Zhenan Bao Stanford University
Jason Locklin University of Georgia
Wei You University of North Carolina-Chapel Hill
Jian Li Arizona State University
AA5: Poster Session: Organic Thin Film Devices I
Session Chairs
Tuesday PM, March 25, 2008
Salon Level (Marriott)
9:00 PM - AA5.1
Investigating the Origin of Voc in Organic Photovoltaic Cells with Peripherally Substituted Subphthalocyanine Materials.
Kristin Mutolo 1 , Gezche Graves 1 , Elizabeth Mayo 2 , Stephen Forrest 3 , Mark Thompson 1
1 Chemistry, University of Southern California, Los Angeles, California, United States, 2 , Global Photonic Energy Corporation, Ann Arbor, Michigan, United States, 3 Electrical Engineering and Computer Science, Physics and Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractSubphthalocyanines, 14 π-electron aromatic macrocycles, exhibit strong absorption in the visible region and extinction coefficients similar to that of copper phthalocyanine (CuPc). We have seen that boron subphthalocyanine chloride (SubPc) utilized as the donor-like material in an organic photovoltaic (PV) cell with C60 as the acceptor-like material exhibits a more than doubling of Voc compared to a conventional CuPc/C60 cell under 1 sun AM1.5G simulated illumination. This increase is attributed to the increase in the interface gap, Ig. In addition, peripheral substitution of SubPc has been shown to alter the reduction and oxidation potentials of the material, which, in turn, alters the HOMO and LUMO energies of the material. Peripheral substitution of hydrogen atoms with two chlorine atoms or four fluorine atoms led to lowering of the HOMO and LUMO energy levels, thereby making DiClSubPc and DodecafluoroSubPc good candidates for acceptor type materials in organic PV cells. Double heterostucture organic photovoltaic (PV) cells have been fabricated using copper phthalocyanine (CuPc) as the donor-like material and either DiClSubPc or DodecafluoroSubPc as the acceptor-like material. Incorporating these peripherally substituted SubPcs into organic PV cells has allows us to further explore the significance of Ig on Voc.
9:00 PM - AA5.10
Dye Sensitized Polymer Photovoltaic Device with Well Aligned Metal Oxide Nanostructure.
Yun Yao Lin 1 , Chih Cheng Lin 1 , Tsung Hung Chu 1 , Chun Wei Chen 1 , Wei Fang Su 1
1 Material Science and Engineering, National Taiwan University , Taipei Taiwan
Show Abstract9:00 PM - AA5.100
Investigation of Charge Transport Across ITO and PANI:PVS Layer-by-layer Films in Polymer Diodes.
Mirela Santos 1 , Rodrigo Bianchi 1
1 Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil
Show Abstract9:00 PM - AA5.11
Correlating Polymer:Fullerene Device Performance With Bias-Dependent Transient Absorption and Transient Photocurrent Measurements.
Robert Marsh 1 , Justin Hodgkiss 1 , Chris McNeill 1 , Richard Friend 1
1 Department of Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractBias-dependent transient absorption (TA) spectroscopy and simultaneous transient photocurrent collection are used to probe the dynamics of photogenerated charges in polymer:fullerene photovoltaic devices. The nine decades of available time resolution span every step in solar cell operation: photon absorption, ultrafast exciton dissociation at the heterojunction, geminate pair recombination, separation and charge extraction at the electrodes. We employ these techniques to address the root of improved photovoltaic performance of P3HT:PCBM devices upon annealing. (P3HT= poly(3-hexylthiophene-2,5-diyl); PCBM = [6,6]-phenyl-C61-butyric acid methyl ester). We assign TA spectra to charge absorption in combination with electroabsorption resulting from holes in P3HT. By contrasting these spectra between pristine and annealed devices, we identify the spectral signatures of polarons in amorphous and ordered regions of P3HT. Furthermore, we observe a more rapid decay in the charge signature in the annealed device, consistent with improved hole mobility.Simultaneous transient photocurrent measurements indicate that quantum efficiency is reduced at higher pump fluence for both pristine and annealed devices, and we correlate this with intensity dependent charge kinetics. We find that charge dynamics are insensitive to applied bias in the high pump fluence regime, which we assign to shielding of the applied electric field by the high photoinduced charge density. The pristine device photocurrent remains sublinear in intensity at lower fluences, consistent with imbalanced charge transport. However, the annealed system exhibits linear photocurrent dependence on intensity at low fluences, which is indicative of an absence of space-charge effects. Here we resolve the bias-dependence of TA spectra, and find the lifetime of charges absorbing on the blue edge is significantly shortened at -5 V reverse bias, which we correlate with a faster decay in the transient photocurrent. In contrast, long-lived red-shifted charges are insensitive to the applied field. These observations indicate that we are directly resolving charges being swept out of the device with a distribution of mobilities and concomitant spectral signatures.
9:00 PM - AA5.12
Relaxation of Charge-Transfer States in Bulk Heterojunction Devices.
Ian Howard 1 , Justin Hodgkiss 1 , Sebastian Westenhoff 1 , Neil Greenham 1 , Richard Friend 1
1 Physics, University of Cambridge, Cambridge , Cambridgeshire, United Kingdom
Show AbstractWe investigate the relaxation of charge-transfer states in photovoltaic bulk heterojunction devices using polarization-dependent transient absorption spectroscopy. The time-range from femtoseconds to a millisecond is investigated by combining optical and electronic delays.We find that charge generation in fine blends occurs within picoseconds and that polarization is retained in this rapid process. After charge generation, we use anisotropy measurements to show that geminate charge pairs at the interface are not mobile. We then probe the decay of the charges, focusing on the role of relaxation to a triplet exciton on one component of the blend. By determining this relaxation rate we show that triplet formation via the charge transfer state may limit the performance of certain photovoltaic blends.
9:00 PM - AA5.13
Monodisperse Conjugated Oligothiophenes with Internal Electron Donor-Acceptor Interaction for Potential Applications in Organic Solar Cells.
Jianping Lu 1 , Sai-Wing Tsang 1 , Raluca Movileanu 1 , Man Shing Wong 2 , Ye Tao 1
1 , Institute for Microstructural Sciences, Ottawa, Ontario, Canada, 2 , Department of Chemistry, Hong Kong Baptist University, Hong Kong China
Show Abstract9:00 PM - AA5.14
Photoexcitation Dynamics in Zinc Oxide/Polythiophene Photovoltaic Devices.
Matthew Lloyd 1 , Rohit Prasankumar 2 , Michael Sinclair 1 , Dana Olson 1 , Yun-Ju Lee 1 , Julia Hsu 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIn order to significantly improve the performance of photovoltaic devices comprised of polymer infiltrated ZnO nano-rod arrays, an in-depth understanding of interfacial electron injection and charge recombination is required. One fundamental question open to debate is whether the ZnO/polymer interface dissociates excitons generated in poly-3-hexylthiophene (P3HT) or ZnO simply serves as a collector of electrons separated in the bulk polymer. To this end, we investigate the exciton and cation decay dynamics using pump-probe spectroscopy with sub-picosecond resolution. Measurements are carried out using a P3HT/ZnO bilayer configuration where the thickness of the P3HT layer is systematically increased. Behavior of neat P3HT on non-quenching substrates shows an expected double exponential decay of the cation with a fast component time constant of 1.5 picoseconds independent of P3HT thicknesses. In contrast, when P3HT is deposited on ZnO substrates, the cation signal is enhanced and the fast time constant is greater by a factor of three. Upon increasing the film thickness on ZnO substrates, the fast time constant decreases to approach those of films deposited on non-quenching substrates. This indicates an increase in the cation density near the heterojunction interface and a concomitant decrease in the charge carrier recombination rate. These results strongly suggest that excitons are efficiently dissociated by the ZnO/P3HT interface. We extend this technique to interrogate modified ZnO surfaces and the photophysics of P3HT confined within a ZnO nano-rod array.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - AA5.15
Processing Technologies for Large Area Polymer Solar Cells.
K. Steirer 2 1 , Reuben Collins 2 , David Ginley 1 , Maikel Van Hest 1
2 Applied Physics, Colorado School of Mines, Golden, Colorado, United States, 1 NCPV, National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractOrganic Solar Cells offer the potential for very low cost, large area solar energy conversion. To achieve this requires a translation of laboratory process technology to scalable processes. Ultrasonic spray deposition and ink jet printing offer practical routes to take small scale device architectures towards large scale manufacturing. However, many thin film properties such as topology, molecular morphology and conductivity depend on the details of the method of fabrication and the formulation of the ink. Here we examine and compare ultrasonic spray, inkjet printed and conventionally spin coated deposition of films of the prototypical materials required for a typical bulk heterojunction organic photovoltaic device. These three deposition techniques are optimized and used to fabricate thin films of the contact electrode poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), and the absorber poly-(3-hexyl)-thiophene (P3HT). Deposition methods are compared via atomic force microscopy, conductivity, optical profilometery, UV/VIS spectroscopy, and resultant device characteristics. The ultrasonically sprayed PEDOT:PSS and P3HT layers are optimized by varying solution flow rate, concentration, substrate temperature, and contact angle. Ink jet printed layers are similarly optimized. Bulk heterojunction photovoltaic devices fabricated using ultrasonic sprayed, inkjet printed and spun PEDOT:PSS layers have comparable power conversion efficiencies of 3.5%, 3.3% and 3.7% respectively.
9:00 PM - AA5.16
Hybrid Bulk-heterojunction Photovoltaic Cells Based on ZnO Nanoparticles and Poly(3-hexylthiophene).
Insun Park 1 , Xin-Ran Zhang 1 , Jiyoung Kim 2 , Changhee Lee 2 , Do Yeung Yoon 1
1 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 School of Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of)
Show AbstractHybrid bulk-heterojunction photovoltaic cells based on solvent-stabilized ZnO nanoparticles as the electron transporter and poly(3-hexylthiophene) (P3HT) as the hole transporter were prepared in order to combine the excellent characteristics of P3HT and ZnO. The previously reported problem of this blend system, namely, severe phase aggregation, was successfully solved by solvent optimization, e.g., boiling point matching of aromatic main solvent and stabilizing agent. The effects of ZnO particle size, dispersion morphology and thermal annealing on the power conversion efficiency of the photovoltaic cells were investigated in detail.
9:00 PM - AA5.17
In-situ, Dynamic Investigation of Phase Separation in P3HT/PCBM Blends During the Solvent Annealing Process.
Chu-Jung Ko 1 , Fang-Chung Chen 2 , Wei-Chi Chen 2
1 Department of Photonics and Institute of Electro-optical Engineering, National Chiao Tung University, Hsinchu Taiwan, 2 Department of Photonics and Display Institute, National Chiao Tung University, Hsinchu Taiwan
Show Abstract9:00 PM - AA5.18
Efficient Polymer Solar Cells Prepared from Co-solvent Systems.
Fang-Chung Chen 1 , Hsin-Chen Tseng 1 , Chu-Jung Ko 2
1 Department of Photonics and Display Institute, National Chiao Tung University, Hsinchu Taiwan, 2 Department of Photonics and Institute of Electro-optical Engineering, National Chiao Tung University, Hsinchu Taiwan
Show Abstract9:00 PM - AA5.2
Conjugated Polymers Bearing Ir Complexes for Triplet Photovoltaic Devices.
Gisela Schulz 1 , Steven Holdcroft 1
1 Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada
Show AbstractThe use of conjugated polymers as active materials in solar cells is an area of increasing interest. This interest is motivated, in part, by their solution processability and low fabrication costs. An efficiency-limiting process in organic photovoltaic devices (PV) is the small diffusion length of the singlet exciton, which is determined by its mobility and lifetime. This may be overcome with the formation of triplet excitons. This work examines the effect of tethering an Ir complex onto the main chain of a conjugated polymer; its role in enhancing triplet formation (as evidence by increased phosphorescence); and its effect on charge generation in photovoltaic devices by giving rise to longer lived excited states and longer exciton diffusion lengths.
9:00 PM - AA5.20
Enhanced Performance of Thienopyrazine Low Band Gap Polymers.
Arjan Zoombelt 1 2 , Mark Leenen 1 , Marta Fonrodona 1 , Martijn Wienk 1 , Rene Janssen 1 2
1 SMO/M2N, Eindhoven University of Technology, Eindhoven Netherlands, 2 , Dutch Polymer Institute, Eindhoven Netherlands
Show AbstractAt present one of the limiting factors for efficient photovoltaic energy conversion is the mismatch of the absorption spectrum of the active layer and the solar emission. Using low band gap (LBG) materials would lead to an improved overlap of the polymer absorption with the solar emission spectrum, which peaks around 700 nm (1.77 eV), leading to an increase of absorbed photons and therefore would enhance the efficiency of solar cells. A successful and flexible strategy to achieve LBG conjugated polymers involves the alternation of electron-rich (donor) and electron-deficient (acceptor) units in the polymer chain. Lowering the optical band often results in lower open-circuit voltage (Voc) and, hence, strategies that improve the Voc while maintaining a low band gap are of interest. Here we describe the use of inductive electron withdrawing n-butoxymethyl side chains on low band gap polymers to lower the HOMO levels. We show that by replacing the octyl chains in poly(5,7-bis(3-octyl-2-thienyl)-2,3-di(2-ethylhexyl)-thieno(3,4-b)pyrazine) by n-butoxymethyl side chains, the oxidation potential of the polymer and the open-circuit voltage (Voc) of the corresponding solar cell are increased. Surprisingly, these new side chains also enhance solubility, allowing higher molecular weight material and a better active layer film quality. This substantially improved the overall device performance with current densities up to 7.5 mA/cm2 in bulk heterojunction (BHJ) solar cells with a phenyl-C61 butyric acid methyl ester (PCBM) as acceptor. The interplay between solubility and solid state packing will be discussed.A new approach to further improve the current output of LBG polymers is to make use of tetrathiophene as electron-rich unit in the polymer chain instead of a dithiophene. The motivation is that the increased length of the thiophene units in the polymer is beneficial for charge carrier mobility. Next to the synthesis, the effect on the band gap and the photovoltaic performance of the extended thiophene segments will be presented.
9:00 PM - AA5.22
Photophysics and Device Properties of Ionic Polyfluorene Copolymers.
Justin Hodgkiss 1 , Guoli Tu 2 , Wilhelm Huck 2 , Richard Friend 1
1 Physics, University of Cambridge, Cambridge United Kingdom, 2 Chemistry, University of Cambridge, Cambridge United Kingdom
Show Abstract9:00 PM - AA5.23
Optical Management in Fiber-Shaped Organic Photovoltaic Devices.
Brendan O'Connor 1 , Kevin Pipe 1 , Max Shtein 2
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractThere has been growing interest in fiber-based optoelectronic devices for large-area applications such as photodetectors and light emitting devices.[1,2] In this work, we discuss fiber-based solar cells, focusing on the optical trapping and concentration approaches afforded by the fiber form factor. Specifically, we demonstrate molecular organic-based solar cells deposited concentrically around long fibers, characterizing in detail their optoelectronic behavior. Furthermore, we use a combination of experiments, ray tracing, thin-film optical modeling, and electron transport modeling to examine several optical management schemes specific to the fiber geometry. For example, these models predict that a fiber-based organic PV device can outperform an analogous planar cell for a broad range of light incidence angles. Models show that further improvements in efficiency can be achieved via optical concentration by means of parabolic reflectors, fiber coatings, and bundling of separate fibers. The combination of potential scalability of fiber-based and textile technology and the novel optical designs afforded by the fiber form factor suggest new avenues for improving the performance of organic photovoltaic devices.[1] Bayindir, M., Sorin, F., Abouraddy, A.F., Viens, J., Hart, S.D., Joannopoulos, J.D., and Fink, Y., Nature 431, 826 (2004).[2] O’Connor, B., An, K.H., Zhao, Y., Pipe K.P., Shtein, M., Advanced Materials, In press (2007).
9:00 PM - AA5.24
Polymer-Fullerene Solar Cells having Single-Walled Carbon Nanotubes.
Cengiz Ozkan 1 , Haiwei Lu 3 , Sumit Chaudhary 2 , Astrid Muller 3 , Christopher Bardeen 3 , Mihrimah Ozkan 2
1 Mechanical Engineering, University of California at Riverside, Riverside, California, United States, 3 Chemistry Department, Unviersity of California, Riverside, California, United States, 2 Electrical Engineering, Unviersity of California, Riverside, California, United States
Show Abstract9:00 PM - AA5.25
New Poly(2,7-Dibenzosilole)s for Polymer Solar Cells.
Pierre-Luc Boudreault 1 , Alexandre Michaud 1 , Mario Leclerc 1
1 Canada Research Chair on Electroactive and Photoactive Polymers, Université Laval, Quebec City, Quebec, Canada
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). Some polymers have been extensively studied like poly(p-phenylenevinylene)s, polythiophenes, polyfluorenes and polycarbazoles. Polysiloles and more specifically poly(2,7-dibenzosiloles)s are a relatively new class of polymer but it has already emerged as good electron donor. These polymers are particularly efficient in organic field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs). It has also been shown that they are more stable than polyfluorenes upon comparison of their photoluminescence emission spectra.We have synthesized new copolymers based on 2,7-dibenzosilole and different electron withdrawing comonomers such as 4,7-dithien-2-yl-2,1,3-benzothiadiazole and 4,7-dithien-2-yl-2,1,3-benzooxadiazole. These new materials were obtained by Suzuki cross-coupling polymerization. Different polymerization conditions have been tested to afford high molecular weight polymers. The optical and electrochemical properties of these new polymers are quite interesting. They show a relatively low bandgap of 1.85 eV, which is of great importance in photovoltaic cells. This leads to high power conversion efficiencies (μ) in photovoltaic cells up to 1.6% for the best polymer. Although a small current density (Jsc) of -2.8 mA, the material shows a good open-circuit voltage (Voc) of 0.97 V and a satisfying fill factor (FF) of 55%.In order to obtain higher performances, the bandgap has to be lower and this can be done by copolymerizing the 2,7-dibensilole with stronger electron withdrawing comonomers. Also, the solubility as well as the molecular weights of the synthesized polymers has to be increased. Moreover, incorporation of longer alkyl chains on the 2,7-dibenzosilole should enhance those two properties at the same time. All these parameters are currently investigated.
9:00 PM - AA5.27
Design and Synthesis of Novel Donor-Acceptor Dyads towards Application for Organic Thin Film Solar Cells.
Takeshi Nishizawa 1 , Keisuke Tajima 1 , Kazuhito Hashimoto 1 2
1 Department of Applied Chemistry, The University of Tokyo, Toky Japan, 2 , HASHIMOTO Light Energy Conversion Project, ERATO-JST, Tokyo Japan
Show AbstractTo achieve efficient charge separation and transport in organic thin film solar cells, it is important to control nanostructure of the donor and the acceptor in the film. In this work we have designed and synthesized novel donor-acceptor dyad molecules to achieve the desirable nanoscaled morphology and molecular alignment in the film. The synthesized novel oligothiophene-fullerene dyad showed 10-nm-scale fiber like nanostructures in the film and almost complete fluorescence quenching. The thin film solar cell with the dyad was fabricated and it showed an improved external quantum efficiency of 31%, compared to the solar cell with the simple physical mixture of the donor component (oligothiophene) and the acceptor component (fullerene derivative). The mixture of the dyad and the donor materials showed a liquid crystalline phase, which could be a useful tool to control the orientation of the nanostructures in the films. [1][1] T. Nishizawa, K. Tajima, K. Hashimoto, J. Mater. Chem., 17, 2440 (2007)
9:00 PM - AA5.28
Monte Carlo Study on Morphology Dependence of Polymer Solar Cells Performance.
Bao Lei 1 , Yan Yao 1 , Ankit Kumar 1 , Yang Yang 1 , Vidvuds Ozolins 1
1 Materials Science and Engineering, UCLA, Los Angeles, California, United States
Show Abstract9:00 PM - AA5.29
Self-Organized Buffer Layers in Organic Solar Cells.
Qingshuo Wei 1 , Keisuke Tajima 1 , Kazuhito Hashimoto 1 2
1 , The University of Tokyo, Tokyo Japan, 2 , HASHIMOTO Light Energy Conversion Project, ERATO, JST, Tokyo Japan
Show Abstract9:00 PM - AA5.3
Charge Transport in tris(β-diketonato)ruthenium(III) Complexes Employed as Buffer Layers in Organic Double-Heterojunction Photovoltaic Devices.
Cody Schlenker 1 , Erin Morrison 1 , Elizabeth Mayo 3 , Susan Wilson 1 , Stephen Forrest 2 , Mark Thompson 1
1 Chemistry, University of Southern California, Los Angeles , California, United States, 3 , Global Photonic Energy Corporation, Ewing, New Jersey, United States, 2 Electrical Engineering and Computer Science, Physics, and Materials Science and Engineering, University of Michigan, Ann Arbor , Michigan, United States
Show AbstractA series of tris(β-diketonato)ruthenium(III) complexes with tailored oxidation and reduction potentials were prepared and incorporated into vapor deposited double-heterojunction organic photovoltaic, PV, devices as the buffer material between the metal cathode and the acceptor layer (i.e. anode/CuPC/C60/diketonate complex/cathode). The Ru complexes studied here had β-diketonato ligands with the following substituents: 1,3-CH3 (acac); 1,2,3-CH3; 1-CH3,3-phenyl. These complexes were chosen because their oxidation potentials vary by 310 mV and their reduction potentials by 290 mV. The electrical characteristics of these PV devices were observed in the dark and under HgXe white light illumination with the intent of understanding the nature of charge transport through thin films (100-300Å) of the parent complex, tris(acac)ruthenium(III), and several derivatives in such PV devices. Of specific interest is the impact of energy level alignment on charge carrier collection at the cathode. The devices exhibited markedly different short circuit photocurrent densities, Jsc, and fill factors, FF, but showed very little variation in open circuit voltage, Voc. These changes in Jsc and FF were noted to correlate with changes in the oxidation potential of the buffer layer material.
9:00 PM - AA5.30
A Low Band Gap Polymer Having a New Fused Aromatic Thieno[3,4,b]pyrazine Moiety and Its Solar Cell Performance 2.
Nobuyuki Miyaki 1 , Zhenan Bao 1 , Jack Parmer 2 , Alex Myer 2 , Michael McGehee 2
1 Chemical Engineering, Stanford University, Palo alto, California, United States, 2 Materials Scienece and Engineering, Stanford University, Palo alto, California, United States
Show AbstractRecently, low band gap polymers have attracted much attention for bulk heterojunction solar cells because they harvest longer wavelength of light (around 700 nm) and give improved efficiency. In our design of low band gap polymers, thienopyrazines have been utilized for as acceptor units which let band gap of a polymer to be small. Thienopyrazines were chosen because their chemical structures are easy to modify so that we can fine tune their electrical physical properties. Previously, we showed a polymer having Acenaphtho[1,2-b]thieno[3,4-e]pyrazine moietiy and its solar cell performance. In order to control the band gap of the polymer, We synthesize a polymer containing a novel fused aromatic thieno[3,4,b]pyrazine structure as an acceptor unit. The obtained new polymer has a lower band gap (1.41ev. from cyclic voltammetry) than previous polymer (1.7-1.6 eV.). We will report syntheses and solar cell performance of this class of novel low gap polymers as well.
9:00 PM - AA5.31
Multilayered Polymer Solar Cells prepared by All Solution Processes.
Michihiro Ogawa 1 , Hiroaki Benten 1 , Hideo Ohkita 1 , Shinzaburo Ito 1
1 Polymer Chemistry, Kyoto University, Kyoto Japan
Show AbstractSolution-processed organic solar cells are promising as a next-stage device for light energy conversion because of their potential advantages of lightweight, flexibility, low-cost and large-area fabrication compared with conventional inorganic solar cells. The arrangement of functional molecules and the control of film thickness with nanometer-scale precision are essential to achieve an efficiency of energy conversion, because the hopping length of carriers such as excitons, electrons, and holes in organic materials is limited on a scale of nanometer. In the present study, we fabricated multilayered polymer thin-film solar cells consisting of hole-transporting, light-harvesting, and electron-transporting layers by wet processes. The light-harvesting layer of poly(p-phenylenevinylene) (PPV) was precisely fabricated by the layer-by-layer (LbL) deposition. The LbL method is one of the powerful techniques for fabricating multilayered films with a desired sequence and a well-controlled thickness of the order of a few nanometers. On the other hand, the hole- and electron-transporting layers were prepared by the spin-coating method from an aqueous solution of poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and from an o-dichlorobenzene solution of polystyrene (PS) and fullerene (C60), respectively. The solution-processed multilayered solar cells exhibited the best performance when the thickness of the light-harvesting PPV layer was adjusted to be about 12 nm, which is comparable to the diffusion length of PPV excitons. The external quantum efficiency showed the maximum (∼ 28%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as large as ∼ 55%. The power conversion efficiency reached 0.28% under AM1.5G simulated solar illumination with 100 mW cm-2.
9:00 PM - AA5.32
Formation of Fullerene Cation in Bulk Heterojunction Polymer Solar Cells.
Hideo Ohkita 1 , Shunsuke Yamamoto 1 , Jiamo Guo 1 , Shinzaburo Ito 1
1 Department of Polymer Chemistry, Kyoto University, Kyoto Japan
Show AbstractOrganic solar cells based on blend films of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) exhibited relatively high power conversion efficiency over 3%. The device performance is critically dependent on the PCBM concentration and shows the maximum at 80 wt% PCBM. On the other hand, a recent study on hole mobility of the blend film has reported that PCBM molecules contribute not only to electron transport but also to hole transport, which is seemingly contradictory result to electron transport properties of PCBM. Herein we employed transient absorption spectroscopy to directly observe charge carriers generated in the blend films with various PCBM concentrations. At a low PCBM concentration (5 wt%), transient absorption spectrum was reproduced by a spectral superposition of MDMO-PPV positive polaron and PCBM anion. On the other hand, transient absorption spectra at higher PCBM concentrations were different from that observed for lower PCBM concentrations. The spectra were not reproduced without absorption spectrum of PCBM cation in addition to those of MDMO-PPV positive polaron and PCBM anion. Therefore, we conclude that not only PCBM anion but also PCBM cation is formed in the blend films at higher PCBM concentrations.
9:00 PM - AA5.33
Formation Dynamics of Excitons and Carriers in Polythiophene−Fullerene Blend Films
Jiamo Guo 1 , Hideo Ohkita 1 , Hiroaki Benten 1 , Shinzaburo Ito 1
1 Department of Polymer Chemistry, Kyoto University, Kyoto Japan
Show AbstractOrganic solar cells based on blend films of a conjugated polymer and a fullerene derivative are attracting extensive academic and commercial interest. Recently, power conversion efficiencies exceeding 6% have been reported for polymer-based solar cells of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Although a large number of studies have been devoted to improving device performance, only few studies have so far revealed the photophysical properties in the solar cells. This is partly because it is difficult to assign characteristic absorption bands to transient species such as singlet and triplet excitons, polarons, and anion owing to spectral overlapping. Furthermore, it is difficult to detect small transient signals for a polymer film as thin as around 100 nm. Herein we report on the photophysical properties of polythiophene pristine and polythiophene–fullerene blend films by near-IR femtosecond transient absorption spectroscopy and highly sensitive microsecond transient absorption spectroscopy at room temperature. For pristine films, singlet excitons in a regiorandom P3HT (RRa-P3HT, 1:1 head-to-head/head-to-tail) film were gradually delocalized over several units in picosecond time domain and mainly converted into triplet excitons. On the other hand, singlet excitons in a regioregular P3HT (RR-P3HT) film were already delocalized within the laser pulse irradiation (< 100 fs) and mainly converted into charged species. For blend polymer films with PCBM, ultrafast charge formation was observed with a fast time constant (< 100 fs) and a slow one (∼ ps). The fast component is ascribed to the prompt charge formation at the interface between P3HT and PCBM, while the slow component is ascribed to the delayed charge formation after singlet exciton migration in large polymer domains to the interface. The carrier dynamics was strongly influenced by thermal annealing on the RR-P3HT/PCBM blend film. In this presentation, we will discuss the different dynamics of the pristine and the blend polythiophene films from morphology, mobility, and energy differences of the two polythiophenes with different regularity.
9:00 PM - AA5.34
Vertical Phase Separation Morphology with a Gradient Component Distribution in the High Performance Bulk Heterojunction Polymer Solar Cells.
Dong-Yu Kim 1 , Jang Jo 1 , Seok-Soon Kim 1 , Seok-In Na 1 , Tae-Woo Lee 1
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - AA5.35
New Soluble n-Type Oxadiazole-based Polymer for Use as Electron Acceptor Material in All-Organic/Polymer Solar Cell
Byung Jun Jung 1 , Bal Dhar 1 , Taegweon Lee 1 , Chad Landis 1 , Howard Katz 1
1 Materials Science and Engineering, Johns Hopkins University, Blatimore, Maryland, United States
Show AbstractThe oxadiazole based copolymer, poly(2,5-bis(3-dodecylthien-2-yl)-1,3,4-oxadiazole-alt-4,7-benzothiadiazole) (PTOxBT), was synthesized via Suzki coupling. The polymer was soluble in chloroform, toluene and chlorobenzene, and can readily be processed from solution. The optical band gap of a thin film of the polymer was determined to be 1.94 eV based on the onset of the absorption spectrum. In the cyclic voltammogram, the polymer showed a promising n-type behavior with a reversible n-doping/dedoping process (Eonset = -0.96 V versus SCE). This corresponds to LUMO level of - 3.44 eV. We fabricated the all-organic/polymer solar cell with P3HT or TIPS-pentacene using PTOxBT as electron accepting and transporting material instead of PCBM. In the devices, PTOxBT functioned well as n-type material.
9:00 PM - AA5.36
Efficient Hybrid Junction Polymer Solar Cells Fabricated by Multi-layer Spray Deposition.
Doojin Vak 2 , Byung-Kwan Yu 1 , Jang Jo 1 , Dong-Yu Kim 1 2
2 Heeger Center for Advanced Materials, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - AA5.37
Synthesis of All-conjugated Diblock Copolymers by Living Polymerization and their Application for Electronic Devices.
Yue Zhang 1 , Keisuke Tajima 1 , Kazuhito Hashimoto 1 2
1 Department of Applied Chemistry, The University of Tokyo, Tokyo, Tokyo, Japan, 2 HASHIMOTO Light Energy Conversion, JST-ERATO, Tokyo, Tokyo, Japan
Show Abstract9:00 PM - AA5.38
Efficient Polymer Solar Cells Fabricated by Simple Brush Painting.
Seok-Soon Kim 1 , Seok-In Na 1 , Jang Jo 1 , Giyoong Tae 1 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - AA5.39
Surface Relief Gratings on P3HT/PCBM Active Layers for Efficient Polymer Solar Cells.
Seok-In Na 1 , Seok-Soon Kim 1 , Jang Jo 1 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - AA5.4
Platinum (tetraphenylbenzylporphyrin) as an Efficient Donor Layer in Organic Photovoltaics.
M. Dolores Perez 1 , Carsten Borek 1 , Peter Djurovic 1 , Rhonda Bailey-Salzman 2 , Elizabeth Mayo 3 , Stephen Forrest 2 , Mark Thompson 1
1 Chemistry, University of Southern California, Los Angeles, California, United States, 2 Electrical Engineering ad Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3 , Global Photonic Energy Corporation, Ann Arbor, Michigan, United States
Show AbstractMetalated porphyrins are known to be very strong absorbers in the visible region and little has been explored in their application as materials for solar conversion in solid state organic photovoltaics. In this work, platinum (tetraphenylbenzylporphyrin) (PtTPBP) has been introduced as donor layer in typical planar heterojunction architecture solar cell using C60 as acceptor and BCP as buffer layer. Despite its non planar shape, the optimized cell performs rather efficiently, resulting in a higher Voc and efficiency than that of the more thoroughly studied CuPc/C60/BCP cell. One added advantage of this compound is its high solubility in organic solvents which allows the possibility of applying the donor layer by spin coating onto the ITO substrate. This new avenue has not been heavily explored in the field of small molecule organic solar cells and would allow for easier and cheaper processing and fabrication of the devices. Devices using this technique perform reasonably well with high FF but a lower efficiency compared to the all vapor deposited counterpart, indicating that packing and morphology of the donor differs from both techniques hence affecting the performance of the device.
9:00 PM - AA5.40
Optical and Morphological Properties of N,N'-ditridecyl Perylene Diimide Thin-films.
Joaquim Puigdollers 1 , Marcos Stella 2 , Fernando Villar 2 , Fredy Rojas 2 , Joan Bertomeu 2 , Jordi Andreu 2
1 Enginyeria Electrònica, Universitat Politècnica Catalunya, Barcelona Spain, 2 , Universitat Barcelona, Barcelona Spain
Show Abstract9:00 PM - AA5.41
Polymer Solar Cells using Self-Assembled Monolayers modified ZnO/Ag and ZnO/Au as Cathodes
Hin-Lap Yip 1 , Steven K. Hau 1 , Nam-Seob Baek 1 , Hong Ma 1 , Alex K.-Y. Jen 1 2
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States, 2 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractConjugated polymer-based organic solar cells are considered as an essential source of inexpensive renewable energy. A conventional polymer solar cell composed of a bulk heterojunction polymer:fullerene composite layer sandwiched between a conducting polymer-coated transparent metal-oxide anode and a metallic cathode. For efficient electron collection, thin films of low work-function metals such as Ca/Al and LiF/Al are commonly used as the cathode. However, the performance of those devices is limited by their poor stability due to the vulnerable contact between the polymeric layer and the reactive metals. Thus, it is highly desirable to develop new device architecture that allows stable metals to be used as the cathodes. Here we reported a new device structure (ITO/PEDOT:PSS/Polymer:PCBM/ZnO/SAM/Metal) that enables high work-function metals such as Ag and Au to be efficiently used as cathode in polymer solar cells with improved device efficiency and stability. A solution-processed thin film of zinc oxide (ZnO) nanoparticles was first deposited on the active polymer layer and served as a multifunctional buffer layer including an electron transporting layer, a hole blocking layer and an optical spacer. The surface of the ZnO thin film was then modified by a chemisorbed self-assembled molecular layer (SAM) before the deposition of the metal cathode. A series of conjugated and saturated carboxylic acid-based SAMs with various dipoles were employed to tune the contact properties between the ZnO buffer layer and different metal cathodes. Our results showed that the device performance is strongly depending on the nature of the SAMs. SAMs forming unfavorable interfacial dipole across the ZnO and the metal thin film resulted in Schottky contact with poor device efficiencies. SAMs forming appropriate interfacial dipole across the ZnO and the metal thin film resulted in Ohmic contact showed dramatically improvement in device efficiencies and stabilities when high work function metals such as Ag and Au were used as the cathodes. Our findings pave the way to the development of solution processed metal electrodes for inexpensive and stable polymer solar cells as thin films of Ag and Au can be printed from their precursor solutions.
9:00 PM - AA5.42
Investigation of Various Metallophthalocyanines for Organic Solar Cells.
Inho Kim 1 2 , Zixing Wang 1 2 , Jian Li 1 2 , Ghassan Jabbour 1 2
1 School of Materials, Arizona state university, Tempe, Arizona, United States, 2 Advanced Photovoltaic Center, Arizona State University, Tempe, Arizona, United States
Show Abstract9:00 PM - AA5.43
The Effects of Annealing and Blending Ratio on pBTTT:PCBM Solar Cells.
Jack Parmer 1 , Alex Mayer 1 , Brian Hardin 1 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - AA5.44
Use of ZnO Nanostructure Towards High Efficiency Inorganic/organic Hybrid Thin Film Solar Cells.
Kazuko Takanezawa 1 , Keisuke Tajima 1 , Kazuhito Hashimoto 1 2
1 Department of Applied Chemistry, University of Tokyo, Tokyo Japan, 2 HASHIMOTO Light Energy Conversion, JST-ERATO, Tokyo Japan
Show Abstract9:00 PM - AA5.45
Towards Roll-to-Roll Fabrication of Organic Solar Cells.
Daniel Tobjork 1 , Harri Aarnio 1 , Tapio Makela 1 , Ronald Osterbacka 1
1 Center for Functional Materials and Department of Physics, Åbo Akademi University, Turku Finland
Show Abstract9:00 PM - AA5.46
Construction of Layered Polymer Photovoltaic Cells by Evaporative Spray Deposition From Ultradilute Solution.
Masato Shakutsui 1 , Ryoji Maeda 1 , Katsuhiko Fujita 1 2 , Tetsuo Tsutsui 1 2
1 Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka, Japan, 2 , Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka, Japan
Show AbstractWe successsfully fabricated two kinds of layered polymer photovotaic cells, one is bilayer p-n junction type and the other is bulk heterojunction (BHJ) with composition gradient by evaporative spray deposition from ultradilute solution (ESDUS) [1], which can build polymer layered structure using multiple polymer semiconductors soluble in the same solvent [2]. The bilayer p-n polymer photovoltaic cells showed better performance than the corresponding blended cells. In the composition-controlled gradient BHJ cells, the introduction of composite gradient brought about the increase in conversion effciency. In the bilayer structure, the bottom layer was formed by spin-coating Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) or regioregular poly(3-hexyl-thiophene-2,5-diyl) (P3HT). Poly[(9,9-dihexyl-2,7-(2-cyanodivinylene)-fluorenylene)] (CN-PDHFV) was deposited onto the bottom layer by ESDUS using tetrahydrofuran solution. The bilayer cells, MEH-PPV/CN-PDHFV and P3HT/CN-PDHFV, showed significantly better power conversion efficency, 0.12 % and 0.21 %, than the corresponding blended cells, 0.072 % and 0.11 %, respectively. The improvement would be caused by an effective blocking of the generated carriers to prevent the collection at inappropriate electrode.The BHJ cells with controlled composition across the film were fabricated as follows. The bottom layer of P3HT or fullerene derivative (PCBM)/P3HT mixture (1:2 BHJ) was formed by spin-coating. The top layer was deposited onto the bottom layer by ESDUS using 1:1 mixture solution of PCBM/P3HT (1:1 BHJ). The short circuit current and power conversion efficiency of P3HT/1:1 BHJ cell and 1:2 BHJ/1:1 BHJ cell were 4.44 mA/cm2, 1.24 % and 4.72 mA/cm2, 1.31 %, respectively, while those of single-layer 1:1 BHJ cell were 3.93 mA/cm2, 0.95 %. The transportation of photogenerated charges to the collecting electrodes was improved due to introducing the gradient structure of the donor material and the acceptor material. In conclusion, ESDUS enables us to control the composition of polymers across the film. This may widen the possibilities of polymer electronics. ESDUS would be a powerful tool to investigate machanisms of polymer photovoltaic cells.References: [1] K. Fujita, T. Ishikawa and T. Tsutsui, Jpn. J. Appl. Phys. 41, L70 (2002), [2] M. Shakutsui, K. Fujita and T. Tsutsui, Jpn. J. Appl. Phys. 45 L790 (2006).
9:00 PM - AA5.47
Thienopyrazine containing low bandgap polymers for photovoltaic applications.
Benjamin Rupert 1 , Matthew Reese 1 , William Rance 1 , Nikos Kopidakis 1 , David Ginley 1 , Garry Rumbles 1 , Sean Shaheen 1 2
1 , National Renewable Energy Labratory, Golden, Colorado, United States, 2 Physics, University of Denver, Denver, Colorado, United States
Show AbstractA systematic study of a series of thienopyrazine containing polymers for use in organic photovoltaics will be discussed. The polymers consist of alternating blocks with the first block containing two thiophene and one thienopyrazine units and the second block containing aromatic units of varying electron donating or withdrawing strength. The synthesis and characterization relevant to photovoltaic devices, as well as initial device results, will be presented.
9:00 PM - AA5.48
Synthesis of Pentacene-containing conjugated copolymers for organic photovoltaic devices.
Fei Qu 1 , Toshihiro Okamoto 1 , Nobuyuki Miyaki 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Palo Alto, California, United States
Show AbstractSoluble and stable organic semiconducting polymers have great potential for low-cost photovoltaic devices. To achieve appreciable efficiency, polymers that absorb in the entire AM1.5 solar spectrum are desirable. To this end, we exploited the properties of 6,13 triisopropylsilylethynyl (TIPSE) pentacene, which has one of the lowest optical bandgaps for small molecules, a high organic thin film transistor (OTFT) mobility > 0.4cm2/Vs and is relatively stable compared to pentacene. We have made regio-random copolymers containing TIPSE-pentacene substituted at the 2-9 and 2-10 positions with fluorene and benzothiadiazole units. We are expanding the infra-red absorption of the copolymers through modification with additional thiophene units. The fluorene-pentacene copolymer has already shown improved absorption near the infrared region as a result of lower bandgap after modification. The absorption coefficients of the repeating unit of the copolymer are 99700 M-1cm-1 at 440nm and 17900 M-1cm-1 at 684nm, respectively, comparing to that of 6,13-TIPESE pentacene, which are 12800 M-1cm-1 at 596nm and 25200 M-1cm-1 at 649nm. OTFTs and organic photovoltaic devices (OPVs) will be made to determine the mobility and solar cell performance of these copolymers, respectively. These copolymers will be characterized by proton NMR, carbon NMR, gel permeation chromatography, cyclic voltametry, thermogravimetric analysis, and infrared spectroscopy. Thin films will be used to determine the stability and optical properties of these copolymers.
9:00 PM - AA5.49
Enhancement in Open Circuit Voltage Through Interfacial Modification of Donor-Acceptor Interface.
Srinivas Sista 1 , Yan Yao 1 , Yang Yang 1 , Ming Tang 2 , Zhenan Bao 2
1 Materials Science & Engineering, University of California-Los Angeles, Los Angeles, California, United States, 2 Chemistry and Department of Chemical Engineering, Stanford University, Pala Alto, California, United States
Show Abstract9:00 PM - AA5.5
Scanning Kelvin Probe Microscopy on Organic Solar Cells Fully Explained.
Klara Maturova 1 , Martijn Kemerink 1 , Wytze Keuning 2 , Erwin Kessel 2 , Rene Janssen 1
1 Molecular Materials and Nanosystems, Eindhoven University of Technology, Eindhoven Netherlands, 2 Plasma and Materials Processing, Technische Universiteit EIndhoven, Eindhoven Netherlands
Show AbstractScanning Kelvin Probe Microscopy (SKPM) is a powerful technique which yields information about the topography and the surface potential of a given system at the nanometer scale. We, amongst others, used this technique to study local distribution of charges in the active layer of bulk heterojunction organic solar cells. However, the interpretation of such data turned out to be far from trivial. We developed a 2D numerical model, which, by solving the drift/diffusion equations, explains all features of our experimental data. This enables one to relate the SKPM results to device performance. We have used SKPM to measure surface potential on solar cells consisting of MDMO-PPV and PCBM blends with a bottom electrode consisting of PEDOT:PSS and ITO. In order to unravel the complex, position dependent shifts in surface potential during and after illumination, we have also measured surface potential on OSC where three different spacer layers have been used instead of PEDOT:PSS to selectively block vertical transfer of photogenerated charges while not affecting the horizontal transport. The band structure of ZnO and TiO2 makes these materials selective hole blockers, whereas Al2O3 blocks both charge carriers.We have obtained solvent-dependent results for both topography and surface potential. We have succeeded to explain the dark contrast in surface potential on pristine, i.e. previously not illuminated, devices in terms of (differences in) hole diffusion from the bottom contact. Another important step was to explain surface potential shifts during and after illumination. Naively, one would expect that under illumination positive and negative charges will end up in different phases. Nevertheless we found a significant density of photogenerated free electrons in both the donor (polymer) and acceptor (fullerene) rich phases under illumination. In order to better understand these shifts, we have performed SKPM on samples where different spacer layers were used. Depending on whether holes or electrons were preferentially blocked, we found shift towards higher or lower surface potential, respectively. Results which we got from these experiments prove that free photogenerated electrons are present in both phases of the active layer, even in the case of very coarse phase separation. This indicates that the reduced performance of such devices is at least partially due to problematic electron transport, rather than due to poor exciton dissociation.
9:00 PM - AA5.50
A 3D Analysis of Poly(thiophene):Fullerene Bulk Heterojunction Solar Cells by Conducting Atomic Force Microscopy.
Mark Dante 1 , Corey Hoven 2 , Jeffrey Peet 2 , Thuc-Quyen Nguyen 1
1 Center for Polymers and Organic Solids, Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California, United States, 2 Center for Polymers and Organic Solids, Materials Department, University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractAmong organic photovoltaic devices, bulk heterojuntion solar cells based on a blend of poly(3-hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) have lead the field in efficiency. It has been shown that bulk electron and hole mobility can be correlated with device efficiency; however, it is unclear how these electrical properties vary across the active layer of the device. Conducting atomic force microscopy (C-AFM) was used to measure the current-voltage (I-V) characteristics of the P3HT:PCBM film. Nanoscale electron and hole mobilities were then calculated using the space charge limited current model. Nanoscale mobilities are compared to bulk values and correlated with device efficiency. Differences in nanoscale and bulk mobilities are explained by modeling the electric field between the conductive tip and substrate. To examine the homogeneity of the blend, C-AFM in current imaging mode was used to simultaneously collect the current and morphology images of the film surface at a constant bias. Although local I-V curves and current images of the surface give us information on how the conductive networks for holes and electrons look from the top down, they provide little insight on how these networks penetrate through the depths of the film. To investigate this, cross sectional slices of the films were prepared using a focused ion beam microscope. Current images obtained from the cross section give a complete picture of the 3-dimensional distribution of hole and electron transporting domains. In conjunction, these techniques offer a valuable new tool in further elucidating the relationship between nanostructure and performance in bulk heterojunction solar cells.
9:00 PM - AA5.51
Synthesis and Characterization of a Novel Film-forming, Thermotropic Liquid-crystalline and Two-Photon Absorbing Benzobisthiazole Polymer.
Matthew Dalton 1 2 , Rachel Jakubiak 1 , Ramamurthi Kannan 1 3 , Joy Rogers 1 4 , Mark Walker 1 2 , Christopher Brewer 1 , Augustine Urbus 1 , Loon-Seng Tan 1
1 Materials & manufacturing Directorate, US Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , General Dyanics Information Technology, Dayton, Ohio, United States, 3 , AT&T Government Solutions, Dayton, Ohio, United States, 4 , UES, Inc, Dayton, Ohio, United States
Show AbstractA novel two-photon absorbing, conjugated polymer (I) with repeat units comprised of sequentially connected 9,9-dialkylfluorenyl, 2,6-benzobisthiazolyl, 9,9-dialkylfluorenyl and 4,4’-triphenylamino moieties was synthesized via a Suzuki coupling reaction of the new dibromide monomer, Br-(9,9-dialkylfluorenyl-2,6-benzobisthiazolyl-9,9-dialkylfluorenyl)-Br, and a new bis(boronate ester) co-monomer derived from 4,4-dibromotriphenylamine. Despite the backbone rigidity, the solubility of the resulting polymer in common organic solvents was drastically improved, attributable to the 3,7-dimethyloctyl groups as the solubilizing pendants. A robust, orange-yellow and optically transparent film (II) could be easily cast from chloroform solution. The molecular-weight characteristics of the polymer as determined by gel-permeation chromatography using THF as eluent are: Mn = 20,000 Da; Mw = 56,000 Da; PDI = 2.8. In addition, I was characterized by 1H & 13C NMR, MALDI mass spectrometry, elemental analysis, absorption and fluorescence spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA). Thermotropic liquid-crystalline behavior was indicated by the appearance of a birefringence observed under a cross-polarizing optical microscope when the free-standing film II was heated on a hot-stage to about 180oC. The two-photon activity was confirmed for II (40 μm thick; density = 1.167 g.cm-3) under fs-pulsed laser excitation by a single-wavelength (800 nm) Z-scan experiment, and the intrinsic two-photon absorption cross-section of 65x10-50 cm4.sec.photon-1 per repeat unit was recorded.
9:00 PM - AA5.53
Surface Morphology of nth Generation Thiophene Mono-dendrons.
Ray Gunawidjaja 1 , Sergei Ponomarenko 2 , Yury Luponosov 2 , Aziz Muzafarov 2 , Tsukruk Vladimir 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , N. S. Enikolopov Institute of Synthetic Polymer Materials of the RAS, Moscow Russian Federation
Show Abstract9:00 PM - AA5.54
Synthesis and Characterization of the Novel 1, 38- bisadducts Fullerene : C60[CMe(CO2Et)2]2.
Chun-Chih Wang 1 , Long Y Chiang 2 , Hsing-Lin Wang 1
1 , Physical Chemistry and Spectroscopy, Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Chemistry, Institute of Nanoscience and Engineering Technology, University of Massachusetts, Lowell, Massachusetts, United States
Show Abstract9:00 PM - AA5.55
Direct Patterning of Electrodes for Probing Intrinsic Electrical Properties of Organic Semiconductors.
Wechung Wang 1 , Shuhong Liu 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractDetermination of the intrinsic charge transport properties of organic semiconductors remains a challenge. Charge transport in organic thin-film transistors is typically limited by variations in overall molecular order and device quality. The charge carriers can be trapped by crystal defects present in these thin-film transistors. Single-grain organic field-effect transistors (SGFETs) provide an opportunity to study the intrinsic transport properties of semiconductor materials. In our study, dip-pen nanolithography (DPN) was used to pattern gold electrodes on micron-sized, single grains of various organic semiconductors. DPN is a scanning probe-based lithography used to deposit inks such as small molecules, polymers and nanoparticles on various substrates with nanoscale resolution. The resultant top-contact devices were characterized using a Keithley semiconductor parameter analyzer. The field-effect mobilities are reported for various materials. Knowledge of intrinsic electrical properties will allow us to link molecular design and grain microstructure to device performance, thereby enabling functionality by design. Furthermore, these SGFETs are ideal for screening novel materials, since they provide an upper limit for the thin-film transistor performance.
9:00 PM - AA5.56
Electrochromic Characterization of Polymer Films and Device Applications
Ece Unur 1 , June-Ho Jung 1 , Alex Angerhofer 1 , John Reynolds 1
1 Chemistry, University of Florida, Gainesville, Florida, United States
Show AbstractElectrochromism is a change or bleaching of color that originates from electronic structure changes and can be induced in conjugated polymers upon redox doping/dedoping. It has been determined that poly(3,4-alkylenedioxythiophene) (PXDOT) and poly(3,4-alkylenedioxypyrrole) (PXDOP) derivatives are good candidates for electrochromic applications. One of the most important advantages of these polymers is the ease of modifying their structure which allows color control by tailoring the electronic properties of the polymer. Results on N-substituted poly(3,4-propylenedioxypyrrole)s' (PProDOP-N-alkyl)s’ electrochemistry, spectroelectrochemistry and electron paramagnetic resonance (EPR) will be presented. EPR methods are used to confirm the formation of polaron and bipolaron charge carriers upon doping. In addition to synthetic means of accessing new colors, we have developed a dual polymer film technique as an analytical method that allows us to use existing polymers to generate new colors by transmitting light through two films stacked together in an electrolyte solution and under separate potentiostatic control. With the correct choice of materials, dual systems (devices combining the optical absorbances of two or more films) under bipotentiostatic control promise a myriad of colors. Here we report on absorption/transmission windows and four- polymer electrochromic devices which have distinct optical properties (contrast and color).
9:00 PM - AA5.57
New p-Type Cruciform Molecules Bearing 2,3-Dihydro-thieno[3,4-b][1,4]dioxine-Based Peripheral Moieties and Their Electrical Properties
Dae Chul Kim 1 , Jung Eun Lee 1 , Kyung Hwan Kim 1 , Min Ju Cho 1 , Dong Hoon Choi 1
1 Department of Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractOrganic semiconductor materials based on extended linear-conjugated systems have been very intriguing and significant development has been achieved in these materials over the last several years. In the exploration of the application as organic semiconductors in organic field effect transistor (OFET) is an important component for developing future flexible displays. Organic photovoltaic cell is also promising candidate device for future energy resources. In organic semiconductors, the intrinsic carrier mobility depends critically on the degree of molecular orientation and on the extent of the intermolecular interaction. In this study, new conjugated crystalline cruciform molecules have been synthesized through the Horner-Emmons reaction. Introduction of 2,3-dihydro-thieno[3,4-b][1,4]dioxine-based peripheral moiety improve the solubility in organic solvent for facilitating the device fabrication. They display a p-type semiconducting behaviors and their electrical properties are investigated in detail. We investigated the optical properties, thermal properties, electrochemical properties, and photophysical properties of the new star-shaped molecules.
9:00 PM - AA5.58
Synthesis and Electrical Properties of Phthalocyanine Nanorods with Controlled Molecular Orientation.
Seiichi Takami 1 , Yasuhiro Shirai 2 1 , Yutaka Wakayama 1 , Toyohiro Chikyow 1
1 Advanced Electronic Materials Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 International Center for Young Scientists, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Show AbstractOrganic molecules with π-conjugated electrons are key materials to establish organic electronics. We believe that the nanorods of conjugated organic molecules should be developed as a building block that allows one-dimensional current transport. Such nanorods are possibly synthesized by using porous alumina, which has an array of one-dimensional holes with controllable diameter and length. In this presentation, we discuss the synthesis methods of phthalocyanine nanorods using porous alumina as a template. We also show several methods to control the molecular packing structure in the phthalocyanine nanorods, because the electrical properties of organic molecules largely depend on the molecular packing. The effect of molecular packing structure on the electrical properties of the synthesized nanorods will be discussed.
9:00 PM - AA5.59
Integration and Up-scaling of Molecular Junctions.
Edsger Smits 1 2 , Paul van Hal 1 , Tom Geuns 1 , Paul Blom 2 , Bert de Boer 2 , Dago de Leeuw 1 2
1 Photonic Electronic Materials & Devices, Philips Research Laboratories Eindhoven, Eindhoven Netherlands, 2 Molecular Electronics, Zernike Institute for Advanced Materials, Groningen Netherlands
Show Abstract9:00 PM - AA5.6
Investigation of Nanoscale Morphology and Electrical Conductivity of Solution Processed Phthalocyanine Films.
Niranjani Kumaran 1 , Alexander Veneman 1 , Britt Minch 2 , Neal Armstrong 1
1 Department of Chemistry, University of Arizona, Tucson, Arizona, United States, 2 , PPG Industries, Allison Park, Pennsylvania, United States
Show AbstractOngoing efforts to improve the efficiency of organic photovoltaic cells emphasize the significance of film morphology, charge injection, and charge transport properties in organic films. We have studied the film morphology, nanoscale electrical conductivity, and photovoltaic properties of a disk-shaped peripherally substituted phthalocyanine (Pc) molecule possessing amide functional groups in the side chains. Amide functionality was integrated in the side chains of this molecule with the purpose of increasing the intra-columnar interaction through formation of a hydrogen bonding network between molecules, and to guide the columnar orientation in a preferred direction, especially to from homeotropically aligned molecular columns on surfaces. Surface chemical modification and controlled solution concentration resulted in layered architectures with homeotropically aligned molecular films on amide functionalized gold and ITO surfaces. Local I-V characteristics of these Pc films have been investigated with conducting probe atomic force microscopy (C-AFM). Point contact I-V measurements as a function of probe position on the Pc film, over sub-micron length scales, directly addressed the correlation between film morphology and the mechanism of charge injection at the metal-organic interface. These measurements have allowed us to determine the electrical conductance of individual molecules, the resistance between parallel molecular layers, and the contact resistance associated with the metal- or metal oxide-molecule heterojunctions. Further, the photovoltaic characteristics of this solution processed Pc film have been analyzed with ITO/Pc/C60/Al devices.
9:00 PM - AA5.60
Electronic Structure and Properties of Alternating Donor-acceptor Copolymers.
Chiung Huang 1 , Jian Chang 1 , Shan Chiou 1 , Chang Yang 1
1 Material and Chemical Research Laboratory, Industrial Technology Research Institute, Hsinchu, Taiwan
Show Abstract9:00 PM - AA5.62
Studies of Charge Transport Properties in P3HT/ZnO Composites Using Photoinduced Charge Extraction by Linearly Increasing Voltage Technique.
Vijila Chellappan 1 , Furong Zhu 1 , Minghui Liu 2 , Kian Ping Loh 2
1 , Institute of Materials Research and Engineering, Singapore Singapore, 2 , National University of Singapore, Singapore Singapore
Show Abstract9:00 PM - AA5.63
Patterned Growth of Organic Semiconducting Single Crystals on Substrates with Aligned Features.
Shuhong Liu 1 , Stefan Mannsfeld 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - AA5.64
Porphyrin Assembly with Fullerenes for Photovoltaic Applications.
Takashi Sagawa 1 , Osamu Yoshikawa 1 , Hirokuni Jintoku 2 , Makoto Takafuji 2 , Hirotaka Ihara 2 , Susumu Yoshikawa 1
1 Instutute of Advanced Energy, Kyoto University, Uji Japan, 2 Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto Japan
Show AbstractWe report herein a fabrication of a molecular gel system of zinc-containing tetraphenylporphyrin (ZnTPP) combined with an L-glutamide-derived lipid with double long chain alkyl groups as a lipophilic part. Through the intermolecular amide hydrogen bonding of L-glutamide-derived lipid part and π-π* stacking of the porphyrin as we reported previously [T. Sagawa, H. Ihara, et. al., Langmuir, 2002, 18, 7223], newly synthesized ZnTPP with L-glutamide-derived lipid part led to form fibrous networks in gel state in hydrophobic organic solvent such as cyclohexane-THF (see supplemental data: TEM images of the ZnTPP-lipid-assembled fibers). Complexation of ZnTPP-lipid with fullerene was examined for organic thin-film solar cells. Equimolar (1:1) mixing of the porphyrin and fullerene attained 10 times larger open circuit voltage (Voc) compared with that of the low molecular ratio of C60 (1:0.25). Absorbance at around 750 nm increased with increasing the molecular ratio of C60. This band is assigned to be the charge transfer from porphyrin to C60 [Litvinov, et. al., Crystal Growth & Design, 2005, 5, 1807]. Therefore, equimolar complexation of porphyrin and fullerene is effective to increase the cell efficiencies. Morphological regulation of ZnTPP-lipid also enabled to enhance their cell efficiencies by varying the conditions of temperature, exposure in the vapor of organic solvent, and so on during the fabrication processes of the thin-films. For example, 3 times enhancement of photovoltaic conversion efficiency (η) was observed through the exposure in hexane vapor in comparison with an η value of untreated one. Further improvement for photovoltaic properties is underway.
9:00 PM - AA5.65
New Physical and Chemical Treatments to Improve the Quantum Efficiency in Polymer Solar Cells.
Osamu Yoshikawa 1 , Taro Sonobe 1 , Takashi Sagawa 1 , Susumu Yoshikawa 1
1 Instutute of Advanced Energy, Kyoto University, Uji Japan
Show AbstractRecently, Heeger et al. reported polymer solar cell containing TiOx thin layer between Al and the active layer attained 5-6% power conversion efficiency [Science, 2007, 317, 222]. They reported TiOx layer in the device served as an optical spacer. Although, our group has investigated the same structured solar cell, we introduced another functional TiO2, which works as a hole blocking layer in the bulk-heterojunction solar cells [Apll. Phys. Lett. 2007, 90, 163517]. Additionally, TiO2 layer between active layer and Al electrode may prevent the degradation of polymer solar cells. The main reasons for degradation of photocurrent are the reaction between the conjugated polymer and the Al electrode, diffusion of the Al from the electrode into the active layer, and oxidation by oxygen in air. In this work, the performance of the devices of bulk heterojunction were fabricated by using P3HT and PCBM as light absorption (viz. active) layer, with TiO2 as interlayer as follows: ITO/PEDOT:PSS/P3HT-PCBM/TiO2/Al was improved by microwave treatment (single mode 2.45 GHz, 800 W for 1, 2.5, or 5 min). Such treatments enabled to increase the short-circuit current density Jsc (from 4.0 mA cm-2 to 6.5 mA cm-2) and fill factor FF (from 0.37 to 0.45) of the cell, though the open circuit voltage Voc was decreased (from 0.66 V to 0.58 V) along the irradiation. Absorption spectra of P3HT-PCBM blended film before and after the microwave treatment were observed. Shoulders at 550 nm and 600 nm appeared after the irradiation. This result implies that the microcrystallization of P3HT was slightly promoted through the microwave treatment. While tandem organic solar cells including double-layered bulk heterojunction were fabricated by using P3HT and PCBM as light absorption (viz. active) layer, Au as middle electrode of the tandem cell with TiO2 as interlayer. Such components of the structure enabled to increase the Voc (from 0.40 V to 0.53 V) and FF (from 0.28 to 0.35) of the tandem cell, though the Jsc was decreased (from 2.78 mA cm-2 to 1.47 mA cm-2) compared with that of the single one. The TiO2 interlayer plays an important role for preventing the electron recombination and cell degradation. Further improvement and optimization of the organic solar cells in terms of higher cell efficiencies were examined underway.
9:00 PM - AA5.66
Synthesis of Fully Functionalized Semiconductor Block Copolymers and Their Application in Nanostructured Bulk Heterojunction Solar Cells.
Michael Sommer 1 , Stefanie Wunder 1 , Mukundan Thelakkat 1
1 Applied Functional Polymers, University of Bayreuth, Bayreuth Germany
Show Abstract9:00 PM - AA5.68
Solution Properties of Anthracene Derivatives.
Gonzalo Rincon Llorente 1 , Marie-Beatrice Madec 1 , Sahreen Ashfaq 1 , Stephen Yeates 1
1 OMIC (Organic Materials Innovation Center), The University of Manchester, School of Chemistry, Manchester United Kingdom
Show Abstract9:00 PM - AA5.69
Spin Polarized Electron Tunneling Through Conjugated Molecules.
Weihao Xu 1 3 , Patrick LeClair 2 3 , Arun Gupta 1 3 , Gregory Szulczewski 1 3
1 Chemistry , University of Alabama, Tuscaloosa, Alabama, United States, 3 MINT center, University of Alabama, Tuscaloosa, Alabama, United States, 2 Department of Physics , University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractElectron tunneling across organic/inorganic interfaces is important to the performance of organic based electronic devices, such as organic light emitting diodes and organic field effect transistors. However, spin dependent electron tunneling across organic/inorganic interfaces is not well understood.1 In this presentation we will demonstrate the injection, transport, and detection of a spin-polarized current through pi-conjugated molecules. Specifically we highlight the results for tetraphenyl porphyrin (TPP), but the results are similar for other conjugated organic semiconductors. 2 Tunnel junctions were made by depositing TPP between La0.7Sr0.3MnO3 (LSMO) and Co electrodes. At cryogenic temperatures the devices show a negative magnetoresistance of 15 –25 %. A tunneling model that explains the temperature, bias voltage and sign of the magnetoresistance will be presented. In addition, we have directly measured the spin polarization (~ 37%) for electrons tunneling from Co through TPP monolayers using superconductor Al films as the spin detector. Collectively these results clearly demonstrate that spin polarized electrons tunnel through conjugated organic semiconductors with negligible spin-flipping and suggest that such molecules may find use in spintronic applications.1. T. S. Santos, J. S. Lee, P. Migdal, I. C. Lekshmi, B. Satpati, and J. S. Moodera, Physical Review Letters 98, 016601 (2007).2. W. Xu, G. J. Szulczewski, P. LeClair, I. Navarrete, R. Schad, G. Miao, H. Guo, and A. Gupta, Applied Physics Letters 90,072506 (2007).
9:00 PM - AA5.7
Direct Measurement of Interfacial Energy Alignment at Polymer-Polymer Heterojunctions in Optoelectronic Devices.
Siong-Hee Khong 1 , Richard Friend 1 , Anoop Singh Dhoot 1
1 Department of Physics, University of Cambridge, JJ Thompson Avenue, Cambridge CB3 0HE United Kingdom
Show Abstract9:00 PM - AA5.70
New Carbazole Derivatives: Blue Emitters and Hole Transport Materials in OLEDs.
Pabitra Nayak 1 , Neeraj Agarwal 1 , N. Periasamy 1 , K. Narasimhan 2 , Meghan Patankar 2
1 Department of Chemical sciences, Tata Institute of Fundamental Research, Mumbai India, 2 Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Mumbai India
Show Abstract9:00 PM - AA5.72
Theoretical Research of Loop Formation Process in Conducting Polymers.
Nigora Turaeva 1 , Boris Oksengendler 1 , Sayora Rashidova 1
1 , Polymer chemistry and physics institute, Tashkent Uzbekistan
Show Abstract9:00 PM - AA5.73
Multi-domain Organic Crystalline Films for Field-effect Transistors.
Y. Tominari 1 , M. Uno 1 , M. Yamagishi 1 , Jun Takeya 1
1 , Osaka University, Toyonaka Japan
Show Abstract Organic field-effect transistors (OFETs) are of broad industrial interest because of their potential applications for circuit-controlling elements of organic light-emitting displays and rewritable papers, for examples. However, it is still challenging to achieve sufficient performances for high-speed applications such as logic circuit components and to consider further extensive market on such technologies. So far, the highest mobility reported for the OFETs is 30-40 cm2/Vs, which is realized in rubrene single crystal transistors [1]. Although the performance gives an intrinsic transport property of organic semiconductor materials, the single crystal devices themselves have been rarely considered for industrial production because the sample preparation usually require human processes. In this presentation, we report our attempt to cover a whole a-few-cm2 substrate with thin organic crystal films and their performances as OFETs. We grow single crystals of benzo-annulated pentathienoacene (f-B5TB) by the physical vapor transport technique. We previously reported that stand-alone single crystal OFETs made of the compound has excellent air stability and fairly good mobility values of ~ 0.5-2 cm2/Vs. Controlling the flow rate of the argon stream and the growth temperature, very thin crystals can be grown densely in the furnace. Typical thickness of the film-like crystals is only sub-micrometers. We approach SiO2/n-Si substrates of a few cm2 in size to the region of the dense crystals and transfer them to the substrates by natural electrostatic force. Thereby, the multi-domain crystalline film is formed on the substrate with source and drain electrodes. We note that the single crystals are grown by themselves without any constraint of the substrates, so that they form naturally grown surfaces. Transfer and output characteristics are measured for five f-B5TB crystal transistors distributed in the multi-domain film on the substrate. All the devices work with typical transistor characteristics with their mobility values ranging from 0.2 cm2/Vs to 2 cm2/Vs. Though it is crucial to control the position and orientation of the crystal growth to improve the device performance and distribution of the mobility values, the technique in principle offers a method to realize the single crystal performance on the whole substrates. [1] J. Takeya et al., Appl. Phys. Lett. 90, 102120 (2007).[2] K. Yamada, Appl. Phys. Lett. 90, 072102 (2007).
9:00 PM - AA5.74
UV-Resistant Poly(3,4-ethylenedioxythiophene) Thin Films: Layer-by-Layer Assembly with Absorbing Nanoparticles.
Jaime Grunlan 1 2 3 , Thomas Dawidczyk 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Chemical Engineering, Texas A&M University, College Station, Texas, United States, 3 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States
Show Abstract9:00 PM - AA5.75
Electrical Conductance Measurement of Single Oligothiophene Molecules.
Ryo Yamada 1 , Hiroaki Kumzawa 1 , Shoji Tanaka 2 , Hirokazu Tada 1 3
1 Graduate School of Engineering Science , Osaka University, Toyonaka, Osaka, Japan, 2 , Institute for Molecular Science, Okazaki, Aichi, Japan, 3 , CREST, kawaguchi, Saitama, Japan
Show AbstractConjugated molecules are expected to work as high conductive molecular wires since molecular orbital of them are connected through the molecular framework. Among a variety of π-conjugated molecules, α-linked oligothiophenes are promising molecules as frameworks of molecular electronics because the α-position and β-positions of the molecules can be used to attach linkers and modulators of electronic state of the molecules, respectively. The length of the oligothiophenes can be precisely controlled and elongated to nm range. Nowadays, 96-mer which reaches 37 nm long is synthesized.[1] Although electrical conductance measurements of oligothiophenes with 3 and 4 thiophene units were reported,[23] the length dependence has not been investigated. It is essential and interesting to study the length dependence using highly π-conjugated molecules for detail discussion on conduction mechanisms. In this study, we have measured electrical conductance of oligothiophenes of 5, 8, 11 and 14-mer with thiocyanate groups attached as a linker to the electrode. by a break junction method using a scanning tunneling microscope (STM). In the STM break junction method, a tip of STM is repeatedly brought into and out of contact with a substrate in a solution of molecules. The conductance of 5 8 11 and 14-mer oligothiophenes were found to be 1.4x10^-3 7.0 x 10^-4, 1.5x10^-4 ,and 4.0 x 10^-5 G0 where G0 = 2e^2/h. The exponential decay of the conductance as a function of the molecular length was observed except for 5T-di-SCN, confirming that the conductances for the molecules of n > 8 was described as G = Gc exp (-β n) where Gc represents the conductance through the contacts, β is a decay constant, and n is the number of thiophene rings, or the length of the conduction channel. The decay constant, β = 0.12 / Å-1 (0.477 / n-1) was obtained by fitting a line to the conductance value of 8, 11 and 14T-di-SCN, showing that oligothiophene is a good molecular wire allowing an long range electric conduction.[1] T. Izumi et al., J. Am. Chem. Soc. 2003, 125, 5286.[2] C. Kerget. et al. J.-P. Bourgoin, S. Palacin, D. Esteve, C. Urbina, M. Magoga, C. Joachim, Phy. Rev. B.1999, 59, 12505.[3]B. Q. Xu, et. al. , Nano Lett. 2005, 5, 1491.
9:00 PM - AA5.76
Supramolecular Self-assembly of Rubrene.
Fabio Cicoira 1 2 3 , Jill Miwa 3 , Stephane Bedwani 4 , Josh Lipton-Duffin 3 , Dmytro Perepichka 5 , Alain Rochefort 4 , Rosei Federico 3
1 MSE, Cornell University, Ithaca, New York, United States, 2 IFN, CNR, Trento Italy, 3 EMT, INRS, Varennes, Quebec, Canada, 4 Genie Physique, Ecole Politechnique de Montreal, Montreal, Quebec, Canada, 5 Chemistry, McGill University, Montreal, Quebec, Canada
Show Abstract9:00 PM - AA5.77
Low Voltage High Performance Rubrene Thin-film Transistors Achieved through Optimal Surface Modification of Dielectric Layers.
Jeong-Min Choi 1 , Seong Hun Jeong 1 , Do Kyung Hwang 1 , Seongil Im 1
1 Institute of Physics and Applied Physics, Yonsei University , Seoul, Seodaemoon-ku, Korea (the Republic of)
Show Abstract9:00 PM - AA5.78
Triethoxysilane Surface Modifications of Zinc Oxide.
Cary Allen 1 , D. Baker 1 , E. Przekwas 1 , D. Gillaspie 2 , M. White 2 , D. Olson 3 , T. Furtak 1 , R. Collins 1
1 Applied Physics, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show Abstract9:00 PM - AA5.79
High Performance Organic Thin-film Transistor Using Amorphous Polymer as Organic Semicondoctor.
Tae-Lim Choi 1 , Kook-Min Han 2 , Jeong-Il Park 2 , Do-Hwan Kim 2 , Mi-Young Chae 1 , Sangyoon Lee 2
1 Electronic Chemical Materials R&D Center, Cheil Industries, Inc, Uiwang-si Korea (the Republic of), 2 Display Lab, Samsung Advanced Institute of Technology, Yongin-si Korea (the Republic of)
Show Abstract9:00 PM - AA5.8
Organic Solar Cells with Near Infrared Sensitivity.
Fan Yang 1 3 , Richard Lunt 2 3 , Stephen Forrest 3
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 Electrical Engineering & Computer Science, Materials Science & Engineering, and Physics, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractOver 50 % of the total solar photon flux is at wavelengths λ > 700 nm. Therefore, it is advantageous to explore infrared absorbing materials for organic solar cells that can efficiently convert photons into current. Here we demonstrate an organic donor/acceptor (DA) solar cell with external quantum efficiency, ηEQE > 15% in the wavelength range of 300 nm < λ < 900 nm, by controlling the molecular packing and orientation of the infrared-absorbing material, tin(II)-phthalocyanine (SnPc). We grow the materials using organic vapor phase deposition (OVPD), by which SnPc forms discontinuous crystallites with the molecular plane perpendicular to the substrate surface. The absorption peak at λ = 890 nm increases with SnPc crystal size. In order to increase the spectral absorption range and to prevent shorts, SnPc is sandwiched between two continuous conductive layers, i.e., the hole transporting layer, copper phthalocyanine (CuPc) and the electron transporting layer C60. Indium-tin-oxide (ITO), Ag and bathocuproine (BCP) are used as the anode, cathode and exciton blocking layer, respectively. The best ITO/CuPc(5 nm)/SnPc(16 nm)/C60(40 nm)/BCP(10 nm)/Ag cell has a power conversion efficiency, ηP = 2.5 % under 100 mW/cm2, AM 1.5G illumination. In this cell, 40% of the photocurrent is generated from the infrared absorption and ηEQE reaches 23% at λ = 890 nm. The low carrier mobility of SnPc, µh = 2×10-10 cm2V-1s-1, prevents the use of thicker, single SnPc layer. However, more effective absorption and carrier generation without extra resistance is achieved when a 22nm-thick network composed of interconnected CuPc, SnPc and C60 crystallites is sandwiched between CuPc and C60, resulting in an optimized ηP = 3%.
9:00 PM - AA5.80
Transient and Steady-state Photoconductivity Measurements in Pentacene Thin Films.
Jianbo Gao 1 , Frank Hegmann 1
1 Physics , University of Alberta, Edmonton, Alberta, Canada
Show Abstract9:00 PM - AA5.81
The Role of Contact Metals in Pentacene Bottom-contact FETs.
Gregor Witte 1 , Daniel Kaefer 1 , Claudia Bock 2 , Duy Vu Pham 2 , Ulrich Kunze 2
1 Physical Chemistry I, Ruhr-University Bochum, Bochum Germany, 2 Nanoelectronics, Ruhr-University Bochum, Bochum Germany
Show Abstract9:00 PM - AA5.83
On the Solvent-induced Conductivity Enhancement in PEDOT:PSS.
Alexandre Nardes 1 , Martijn Kemerink 1 , Rene Janssen 1
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands
Show Abstract9:00 PM - AA5.84
Structural and Electrical Characterization of α-T6 Films Grown on Single Crystal Oxide Substrates.
Pasquale D'Angelo 1 2 , Mario Barra 1 2 , Carmela Aruta 1 2 , Antonio Cassinese 1 2
1 , University of Naples "Federico II", Naples Italy, 2 , CRS COHERENTIA, INFM-CNR , Naples Italy
Show Abstract9:00 PM - AA5.85
Doping Electrospun Fibers with Photochromic Diarylethenes.
Carl Giller 1 , Andrea Bianco 2 , Chiara Bertarelli 2 , Giuseppe Zerbi 2 , Bruce Chase 1 3 , John Rabolt 1
1 Material Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Chemistry, Materials, and Chemical Engineering, Politecnico di Milano, Milan Italy, 3 , Dupont Central Research and Development, Wilmington, Delaware, United States
Show Abstract9:00 PM - AA5.86
Toward Polymer Bipolar Junction Transistors.
Janelle Leger 1 , Glenn Bartholomew 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractTransistors based on conjugated organic semiconductors have enormous commercial potential in markets for which processing restrictions overwhelm the performance benefits of inorganic systems. For this reason, organic field-effect transistors (OFETs) have been a focus of widespread interest in applications requiring low-cost or low-temperature processing, allowing the use of flexible substrates. The primary limitation of OFETs presently is the low charge carrier mobility in organic semiconductors, placing stringent requirements on the gate dielectric and channel length. Recently we have demonstrated light-emitting devices and photovoltaic cells based on a chemically-fixed semiconductor polymer p-i-n junction. The ability to create a pn junction in a polymer device introduces the possibility of exploring multiple junction electronic devices, in particular bipolar junction transistors. Such a device could offer significant advantages over OFETs including reduced dependence on channel length for ease of layer-by-layer processing and the ability to operate such a device as a light-emitting transistor, greatly simplifying the integration of the transistor with the organic light-emitting element in a smart pixel for display applications. Here we will discuss preliminary evidence and progress made toward the goal of polymer bipolar junction transistors.
9:00 PM - AA5.87
A Jet Approach to Controlled Growth of Organic Molecular Materials for Electronic Devices.
Salvatore Iannotta 1 , Lucrezia Aversa 1 , Nicola Coppede 1 , Marco Nardi 1 , Tullio Toccoli 1 , Roberto Verucchi 1
1 FBK - Trento Division, IFN - CNR Institute for Photonics and Nanotechnology, Povo di TRENTO Italy
Show Abstract9:00 PM - AA5.89
Highly Efficient Hole Injection using Novel Polymeric Anode Materials for Small Molecule Organic Light-emitting Diodes.
Alok Gupta 1 , Kaushik Roy Choudhury 1 , Xuezhong Jiang 2 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Air Products and Chemicals, Inc., Allentown, Pennsylvania, United States
Show Abstract9:00 PM - AA5.90
A Facile Route to PEDOT Nanotubes.
Abhishek Kumar 1 2 , Subhalakshmi Nagarajan 1 3 , Ke Yang 1 2 , Jagdeep Singh 3 , Ramaswamy Nagarajan 4 , Jayant Kumar 1 2
1 Center for Advanced Materials, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Department of Physics, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 3 Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 4 Department of Plastics Engineering , University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show Abstract9:00 PM - AA5.91
Synthesis and Characterization of Novel Soluble Polymer Based on Quaterthiophene for OFETs.
Dong Min Kang 1 , Moon-Hak Park 1 , Jang-Yeol Baek 1 , Sung Ouk Jung 1 , Jong-Won Park 1 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of Nano & Advaned Materials Science and Engineering, Gyeongsang National University , Jinju Korea (the Republic of), 2 Chemistry, Gyeongsang National University , Jinju, Gyeongsangnam-do, Korea (the Republic of)
Show Abstract9:00 PM - AA5.92
Colour Tuning of New Phosphorescent Ir(III) Complexes and their use in OLEDs.
Neeraj Agarwal 1 , Pabitra Nayak 1 , N. Periasamy 1
1 Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai India
Show Abstract9:00 PM - AA5.93
Growth Analysis at the Contacts of Nanoscale Oligothiophene Field Effect Transistors.
Arne Hoppe 1 , Torsten Balster 1 , Veit Wagner 1
1 SES, Jacobs University Bremen, Bremen Germany
Show Abstract9:00 PM - AA5.94
Self Assembly of Gold Nanoparticles on Diblock Copolymer Templates for Use as Biomolecular Sensors.
Sarah Adams 1 , Ju Choi 1 , Tyson Friday 2 , Heidi Bednar 2 , Amanda Haes 2 , Regina Ragan 1
1 Chemical Engineering and Materials Science, University of California, Irvine, Irvine, California, United States, 2 Department of Chemistry, University of Iowa, Iowa City, Iowa, United States
Show AbstractNanoscale metallic structures have been utilized in the development of field-enhanced chemical and biological detection devices and have the capacity to achieve single-molecule level detection limits resulting from Surface Enhanced Raman Scattering (SERS) associated with closely spaced noble metal nanostructures. Localized Surface Plasmon Resonance (LSPR) sensors also benefit from the incorporation of metal nanoparticles on surfaces. We will present results on our development of arrays of noble metal nanoparticles having controlled size and shape on a self-organized polymer template. Preliminary SERS spectroscopic analysis of a monolayer of pyridine on this surface measured a SERS enhancement factor of the order of 107. These surfaces are fabricated by forming a polymer template of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). The resulting thin film is a hexagonal array of PMMA blocks within a PS matrix and was formed by self assembly on a variety of substrates, including silicon, glass, and gold. To produce an ordered surface having 20 nm diameter hexagonally packed PMMA cylindrical regions, PS-b-PMMA was annealed on a random PS and PMMA block copolymer layer. Scanning electron microscope (SEM) measured fractional domain of 26.24% PMMA. Alternatively, to produce linear arrays of PMMA regions, the diblock copolymer was deposited and annealed on a polyimide layer deposited on the substrates. For these two arrangements, hexagonal and linear arrays, the PMMA regions of the diblock copolymer were functionalized with terminating primary amine groups using ethylenediamine. Chemically synthesized gold nanoparticles, measured at 20 nm diameter using dynamic light scattering (DLS) techniques and SEM, were attached to these surface amine regions via an organic ligand on the nanoparticle surface. We will present results that demonstrate that gold nanoparticles selectively attach to amine groups on the PMMA regions of the diblock copolymer template. Comparison between the use of thioctic acid and 11-Mercaptoundecanoic acid (MUDA) as the attaching organic compound showed evidence for thioctic acid of greater stability from zeta potential measurements as well as less aggregate formation from SEM analysis. Atomic force (AFM) and scanning electron (SEM) microscopic as well as Fourier transform infrared (FTIR) and dynamic light scattering (DLS) spectroscopic analysis of the assembled surface were used to evaluate aggregation formation and nanoparticle coverage of the template array.
9:00 PM - AA5.95
Hybrid Solar Cells Based on Liquid Crystalline Conjugated Polymer / ZnO Composites.
Dana Olson 1 2 , Timothy Lambert 1 , Yun-Ju Lee 1 , Matthew White 2 , Sean Shaheen 3 , David Ginley 2 , David Wheeler 1 , James Voigt 1 , Julia Hsu 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , National Renewable Energy Laboratory, Albuquerque, New Mexico, United States, 3 Physics and Astronomy, University of Denver, Denver, Colorado, United States
Show Abstract9:00 PM - AA5.96
Organic-Inorganic Nanocomposites via Directly Grafting Conjugated Polymers onto Quantum Dots.
Zhiqun Lin 1 , Jun Xu 1 , Jun Wang 1 , Mike Mitchell 2 , Prasun Mukherjee 2 , Malika Jeffries-EL 2 , Jacob Petrich 2
1 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States, 2 Chemistry Department, Iowa State University, Ames, Iowa, United States
Show Abstract9:00 PM - AA5.97
Controlling Morphology in Polymer/fullerene Mixtures.
Adam Moule 1
1 Chem. Eng. and Mat. Sci., UC Davis, Davis, California, United States
Show AbstractOver the last decade, polymer/fullerene bulk-heterojunction solar cells have steadily improved from ~1% power efficiency to over 5%. Each of the improvements was brought about by gaining a greater degree of control over the active layer morphology. The quality of the finished device is to a large extent determined by the nanoscopic arrangement of the two materials. Factors such as the average domain size, crystallinity, orientation, and connectivity have enormous effects on the macroscopic electrical properties of the device. Unfortunately, the layer morphology for a given polymer/fullerene pair can only be affected by fabrication parameters such as choice of solvent or heat treatment temperature. We have found that using solvent additives in the spin coating mixture can increase the researchers control of layer morphology. One example of the use of solvent additives was performed with the P3HT/PCBM mixture. Here the addition of a dipolar solvent additive increased the crystalline P3HT content of the as-cast layer to the level of a heat treated pure P3HT layer. The as-cast devices efficiency was 4%. We compare the morphology of these layers with the morphology of layers that are cast with pre-formed P3HT nanofiber dispersions. Our analysis shows that the use of dipolar solvent additives has the advantage that networks of pure hole conducting P3HT are formed, which provide for better filling factor and higher efficiency.
9:00 PM - AA5.98
Electrochemically Deposited Poly-3-hexylthiophene Films for P3HT/fullerene Photovoltaic Devices.
Judtih Jenkins 1 , Erin Ratcliff 1 , R. Shallcross 1 , Neal Armstrong 1
1 Chemistry, University of Arizona, Tucson, Arizona, United States
Show Abstract9:00 PM - AA5.99
A New MEH-PPV/Alq3 Dosimeter used in Neonatal Phototherapy.
Giovana Ferreira 1 , Claudia Vasconcelos 1 , Rodrigo Bianchi 1
1 Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil
Show Abstract
Symposium Organizers
Zhenan Bao Stanford University
Jason Locklin University of Georgia
Wei You University of North Carolina-Chapel Hill
Jian Li Arizona State University
AA9: Organic Field Effect Transistors: New Materials
Session Chairs
Thursday AM, March 27, 2008
Room 3001 (Moscone West)
9:30 AM - **AA9.1
Selenophene Containing Polymers for Photovoltaic Applications.
Martin Heeney 1 , Weimin Zhang 4 , Peter Skabara 5 , David Crouch 6 , Iain McCulloch 2 , Rick Hamilton 2 , James Durrant 2 , Amy Ballantyne 3 , Jenny Nelson 3 , LiChun Chen 3 4
1 Dept. Materials, Queen Mary University of London, London, Hampshire, United Kingdom, 4 , Merck Chemicals, Southampton United Kingdom, 5 Pure & Applied Chemistry, University of Strathclyde, Glasgow United Kingdom, 6 Dept. Chemistry, University of Manchester, Manchester United Kingdom, 2 Dept. Chemistry, Imperial College London, London United Kingdom, 3 Dept. Physics, Imperial College London, London United Kingdom
Show Abstract10:00 AM - AA9.2
Synthetic Apporaches to New Electron-Deficient Building Blocks for N-Channel Organic Transistors.
Antonio Facchetti 1 , Hakan Usta 1 , Zhiming Wang 1 , Shinji Ando 1 , Joseph Letizia 1 , Tobin Marks 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractOrganic semiconductors exhibiting high carrier mobilities are key for the development of the field of “plastic electronics”. We present here a novel series of electron-poor building blocks for n-channel semiconductors designed to improve field-effect transistor performance and stability. Furthermore, the key structural features of these compounds allow additional modifications of the n-type conducting core to achieve good solubility and processability. Thin film transistor (TFT) devices were fabricated employing both vacuum- and solution-processing conditions. Field-effect transistor measurements indicate that all the members of this new series are n-type semiconductors with mobilities and Ion:Ioff ratios approaching 1 cm2/Vs and 10^7, respectively. These semiconductor families represent a key milestone in the design, understanding, and development of the next generation of highly efficient n-type OTFT components.
10:15 AM - AA9.3
Controlling the Performance of Liquid Crystalline Semiconducting Polymers for Thin Film Transistors.
Michael Chabinyc 1 , Martin Heeney 2 , Iain McCulloch 3 , Michael Toney 4
1 Electronic Materials Laboratory, PARC, Palo Alto, California, United States, 2 Department of Materials, Queen Mary, University of London, London United Kingdom, 3 Department of Chemistry, Imperial College, London United Kingdom, 4 , Stanford Synchrotron Research Laboratory, Stanford, California, United States
Show AbstractThe electrical performance of thin-film transistors, TFTs, fabricated with solution-processable semiconducting polymers can approach that of amorphous silicon. The field-effect mobility of a semiconducting polymer is strongly dependent on the molecular organization of the polymer chains in its ordered and disordered regions in thin films and also on the orientation of these domains relative to the direction of transport. We have studied ordering processes in a number of polymers that have liquid crystalline (LC) mesophases, such as poly(2,5-bis(3-n-alkyl-2yl)thieno[3,2-b]thiophene), PBTTT. As-cast films of these materials are ordered, but their crystallinity can be improved by thermal annealing in the LC mesophase. X-ray scattering measurements were performed as a function of temperature to examine the details of this ordering process. Ordering appears to nucleate from the bottom interface and propagate through the bulk of the film. This process is allowed at elevated temperatures due to disordering of the alkyl sidechains along with a preservation of the ordering of the main chains similar to non-conjugated rigid-rod polymers. The influence of this process on the performance of TFTs on both smooth and rough dielectrics will be discussed. Through these studies, it was found that crystallinity is a necessary, but not sufficient condition for high mobility TFTs.
10:30 AM - AA9.4
High-performance and Electrically-stable C60 Thin-film Field-effect Transistors.
Xiaohong Zhang 1 , Benoit Domercq 1 , Bernard Kippelen 1
1 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThursday, March 27Transfer Poster AA11.69 to AA9.4 @ 9:30 AMHigh-performance and Electrically-stable C60 Thin-film Field-effect Transistors. Xiaohong Zhang
10:45 AM - AA9.5
Thiazolothiazole Containing Semiconducting Copolymers for Organic Field-Effect Transistors.
Itaru Osaka 1 , Rui Zhang 1 , Genevieve Sauve 1 , Tomasz Kowalewski 1 , Richard McCullough 1
1 Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractSemiconducting polymers offer an advantage versus other materials in large area and low cost electronic applications since the polymers can be printed by solution deposition techniques. Regioregular poly(3-hexylthiophene) (rrP3HT) is the most common semiconducting polymer which shows excellent field-effect transistor performance, however lower mobility and significantly lower on/off ratio are achieved when it is fabricated under ambient condition in contrast to the device fabricated under inert atmosphere. To improve the stability in air and even the mobility we have synthesized novel semiconducting polymers bearing a thiazolothiazole unit in the polythiophene backbone. The polymer was found to have smaller band gap and larger ionization potential than rrP3HT. Despite the low molecular weight (Mn = 4100−8700) the polymers exhibited field-effect mobility as high as 0.39 cm2V-1s-1 after annealing even the polymer devices were fabricated in air. A high on/off ratio of 107 suggests the polymers possess high stability in air.
11:00 AM - AA9:OFET1
BREAK
11:30 AM - **AA9.6
A Renewed Recipe for Polymer Electronics: Just Add Salt.
Dan Frisbie 1
1 Chem Eng & Mater Sci, Univeristy of Minnesota, Minneapolis, Minnesota, United States
Show Abstract12:00 PM - AA9.7
New thienoacene semiconductors with increased dimensionality
Dmitrii Perepichka 1
1 Chemistry, McGill University, Montreal, Quebec, Canada
Show AbstractFused oligothiophenes, their derivatives and analogues have been recently recognized as the most promising molecular semiconductors for thin-film transistors (TFTs). Such structures seem to enjoy a highly extended electronic conjugation without a drawback of dramatically reduced stability. Some of these materials demonstrate very high charge mobility (up to ~2 cm2/Vs), excellent on-off ratio and unsurpassed stability towards oxidation. Remarkably, in these and most other molecular semiconductors the extension of the conjugation is usually achieved through a linear elongation of the pi-electron system. Much less is known about the consequences of the 2D extension of conjugation. I will present the synthesis, characterization, self-assembly/packing and TFT device studies of a series of new highly stable (Tdec>400oC in air) fused oligothiophenes with 2D conjugation pattern, including tetrathienoanthracene, octathio[8]circulene (“sulflower”), its selenium analogues and related structures. The effect of the conjugation topology and the intermolecular interactions, defined by the exterior of the molecular core, on the TFT mobility, will be discussed.
12:15 PM - AA9.8
High Performance Air-Stable n-Channel Organic Thin-Film Transistors Based on Perylene Diimide Derivatives.
Joon Hak Oh 1 , Ruediger Schmidt 2 , Shuhong Liu 1 , Martin Koenemann 3 , Frank Wuerthner 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Institut für Organische Chemie, Universität Würzburg, Würzburg Germany, 3 , BASF Aktiengesellschaft, Ludwigshafen Germany
Show Abstract12:30 PM - AA9.9
Characterization and Optimization of Polydiacetylene Monolayer Films for Organic Field-Effect Transistors.
Gillian Eade 1 2 , J. Scott 1 , Samuel Beach 4 , Clara Cho 1 , Dean DeLongchamp 3 , Daniel Fischer 3 , J. D. Jeyaprakash Samuel 1 2 , Jane Frommer 1 , Victor Lee 1 , Charles Rettner 1 , Robert Miller 1
1 , IBM Almaden Research Center, San Jose, California, United States, 2 Department of Chemical Engineering, Stanford University, Stanford, California, United States, 4 Department of Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California, United States, 3 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show Abstract12:45 PM - AA9.10
Microstructural Investigation of High Performance, Solution Processable Small Molecules.
R. Kline 1 , Oana Jurchescu 2 , Andrew Moad 3 , Lee Richter 3 , David Gundlach 2 , Sankar Subramanian 5 , John Anthony 5 , Sungkyu Park 4 , Thomas Jackson 4
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, 3 Surface and Microanalysis Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 5 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States, 4 Department of Electrical Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractAA11: Poster Session: Organic Thin Film Devices II
Session Chairs
Friday AM, March 28, 2008
Salon Level (Marriott)
9:00 PM - AA11.1
Carrier Trapping in Smectic Liquid-crystalline Semiconductors.
Hyonsoo Ahn 1 2 , Jun-ichi Hanna 1 2
1 Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Yokohama Japan, 2 CREST, Japan Science and Technology Agency, Yokohama Japan
Show Abstract9:00 PM - AA11.10
Correlating Phase and Charge Transport in Liquid Crystal Organic Semiconductors.
Ajay Virkar 1 , Takenori Fujiwara 1 , Hyonsoo Ahn 2 , Ya-sen Sun 1 , Jason Locklin 1 , Jun-Ichi Hanna 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Electronics and Applied Physics, Tokyo Institute of Technology, Tokyo Japan
Show AbstractFor a variety of small molecule and polymeric semiconductors it has been found that annealing from a liquid crystal phase can induce better molecular ordering leading to higher charge transport. In this work we show that for a certain class of solution processable organic semiconductors, the field effect mobility increases three orders of magnitude upon annealing from the liquid crystal phase. These small molecules show a variety of liquid crystal (LC) phases which we have studied using differential scanning calorimetery (DSC), optical microscopy, and x-ray diffraction (XRD). From heated XRD we can infer about the ordering and crystallinity of the LC phases. From DSC and optical microscopy we have determined the thermal window for these various LC phases, . Finally we have performed time-of-flight mobility to probe the charge transport in the various liquid crystal phases. The hole mobility in the liquid crystal phase was as high as .06cm2/Vs.
9:00 PM - AA11.11
Enhancement of Field-Effect Mobility and Stability of Poly(3-hexylthiophene) Field-Effect Transistors by Conformational Change
Yeong Don Park 1 , Jung Ah Lim 1 , Yunseok Jang 1 , Dae-Hwan Kim 2 , Yoon-Su Han 2 , Byeong-Dae Choi 2 , Kilwon Cho 1
1 Department of Chemical Engineering, POSTECH, Pohang Korea (the Republic of), 2 Display and Nano Devices Lab., DGIST, Daegu Korea (the Republic of)
Show AbstractIn this study, we explicate the preparation and properties of high-performance and stable polymer thin film transistor by doping in solution, which offers a promising simple process for the large area flexible thin film transistor. We transformed the chemical structure of the poly(3-hexylthiophene) (P3HT) chain from a benzoid to a quinoid structure by doping the P3HT solution with HAuCl4 prior to film formation. We found that for the appropriate HAuCl4 doping level, the P3HT nanocrystals adopt a highly ordered molecular structure with a high field-effect mobility and stability. This surprising increase in field-effect mobility are due in particular to a significant enhancement of molecular ordering and the perpendicular orientation of the nanocrystals with respect to the insulator substrate, which result from the change in the P3HT chain conformation from a benzoid to a quinoid structure due to oxidation by HAuCl4. Furthermore, the electrical properties of a doped P3HT device had highly improved stability to air without encapsulation. These results suggest that the effect of unintentional doping by oxygen on HAuCl4 doped P3HT film is insignificant because the p-type doping effect of HAuCl4 is the major contributor. This approach to enhancing the molecular ordering and stability of semiconducting polymer materials should prove useful in the development of robust and practical polymer devices for a wide range of commercial applications. This work was supported by a grant (F0004022-2007-23) from the Information Display R&D Center under the 21st Century Frontier R&D Program, ERC program (R11-2003-006-03005-0) of the MOST/KOSEF, Daegu Gyeongbuk Institute of Science and Technology, Ministry of Science and Technology(MOST), and the BK21 Program of the Ministry of Education and Human Resources Development of Korea.
9:00 PM - AA11.12
Diethynyl Aryl Derivatives for P-Channel and N-Channel Organic Field-Effect Transistors.
Takeshi Yasuda 1 3 , Kimiaki Kashiwagi 2 , Yoshitomi Morizawa 2 , Tetsuo Tsutsui 1
1 , Kyushu University, Fukuoka Japan, 3 , JST PRESTO, Tokyo Japan, 2 , Asahi Glass Co., Ltd., Kanagawa Japan
Show AbstractMuch attention has been paid on the development of organic semiconductors for applications to organic field-effect transistors (OFETs). Recently some linear planar-shaped extended π-electron systems, which are composed of two or three aromatic groups such as naphthalene and anthracene connected together with carbon-carbon bonds (a simple C-C single bond or a transvinylene double bond), have been synthesized and reported to exhibit excellent performances in OFETs 1). When a rigid and straight acetylenic triple bond is accepted as the linkage unit, two aromatic rings can lie on the same plain and be arranged on exactly a straight line. This can be a big advantage for attaining compact planar rectangular shapes favorable for attaining good molecular packing in crystalline states.In this work, we designed a series of linear molecules, in which three aromatic rings are connected together with rigid acetylenic linkages. The central core aromatic group is benzene or naphthalene, and two end aromatic groups are naphthyl or heptafluoronaphthyl groups. We report herein the synthesis and characterization of those compounds. Furthermore these derivatives have been used as organic semiconductors for OFETs 2,3).We fabricated OFETs having a top contact geometry. Organic semiconductors were vacuum-evaporated at 2×10-6 Torr at the deposition rate of 0.05 nm/s with thickness of 40 nm onto a gate insulator of poly-chloro-p-xylylene (Parylene-C). A shadow mask was attached onto the film to form Au source-drain electrodes. All the process including measurements were conducted in a dry N2 glove box condition, while in the case of measurements of p-channel characteristics, the devices were temporarily exposed to air before the measurements for OFET characteristics. The field-effect mobility was calculated from the saturation drain currents.OFETs with the compounds having naphthyl end-groups exhibited p-channel behaviors and high filed-effect hole mobilities up to 0.12 cm2/Vs. On the other hand, the compounds having heptafluoronaphthyl end-groups exhibited n-channel field-effect behaviors. The filed-effect electron mobilities were ranging from 10-4 to 10-3 cm2/Vs. We have found that the substitution of hydrogen atoms on the end naphthalene rings to fluorine atoms brought about the 0.5 eV LUMO level shift and this shift caused changes from p-channel to n-channel conductions in OFETs based on diethynyl aryl derivatives.1) A. R. Murphy and J. M. J. Frechet, Chem. Rev. 107 (2007) 1066.2) T. Yasuda, K. Kashiwagi, Y. Morizawa and T. Tsutsui, J. Phys. D: Appl. Phys. 40 (2007) 4471.3) K. Kashiwagi, T. Yasuda, and T. Tsutsui, Chem. Lett. 36 (2007) 1194.
9:00 PM - AA11.13
Organic Thin-Film Transistors(OTFT) Fabrication by Means of Self-Assembly Monolayers.
Ilsun Pang 1 , Hyunho Kim 1 , Sungsoo Kim 1 , Jaegab Lee 1
1 Advanced Material Engineering, Kookmin Univ., Seoul Korea (the Republic of)
Show Abstract9:00 PM - AA11.14
Effects of the Permanent Dipoles of Self-Assembled Monolayer-Treated Insulator Surfaces on the Field-Effect Mobility of a Pentacene Thin-Film Transistor.
Yunseok Jang 1 , Kilwon Cho 1 , Yeong Don Park 1 , Hyun Ho Choi 1 , Seung Goo Lee 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk, Korea (the Republic of)
Show Abstract9:00 PM - AA11.15
Controlled Topology of Block Copolymer Gate Insulator by Selective Etching of Cylindrical Microdomains in Pentacene Organic Thin Film Transistors.
Pil Sung Jo 1 , Cheolmin Park 1 , Jinwoo Sung 1 , Eunhye Kim 1 , Du Yeol Ryu 1 , Ho-cheol Kim 2
1 , Yonsei Univ., Seoul Korea (the Republic of), 2 , IBM Research Division, Almaden Research Center, San Jose, California, United States
Show Abstract9:00 PM - AA11.16
π-Conjugated Star-shaped Molecules based on Thiophene Derivatives as Organic Semiconductors for Optoelectronic Applications
Kyung Hwan Kim 1 , Dong Hoon Choi 1 , Mi Yeon Cho 2 , Jin-soo Joo 2
1 Department of Chemistry, Korea University, Seoul Korea (the Republic of), 2 Department of Physics, Korea University, Seoul Korea (the Republic of)
Show AbstractA number of researchers have attempted to synthesize-conjugated small molecules, dendrimers, oligomers, and polymers because of their strong potential applications to electronics and optoelectronics such as in organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and photovoltaic cells. In this study, new star-shaped crystalline molecules have been synthesized through Horner-Emmons reactions using hexyl-substituted thiophene-based carbaldehydes as dendrons and [1,2,4,5-tetra-(diethoxy-phosphorylmethyl)-benzyl]-phosphonic acid diethyl ester as the core units. The semiconducting properties of the star-shaped molecule have been evaluated in organic field-effect transistors. The crystalline conjugated molecules exhibited carrier mobilities as high as 6.2 × 10-3 ~2.0 × 10-2 cm2V-1s-1 . The OFET device using those molecules as an active layer showed highly sensitive photoinduced characteristics. We observed the shift of threshold voltage and saturation current in photoinduced field-effect transistor characteristic curves. Through the measurements of the photoinduced saturation current as a function of drain voltages, we estimated photoinduced charge density of the OFET. The potentialities of those molecules as donor materials in photovoltaic devices have been evaluated in bilayer heterojunctions using PCBM as an electron acceptor. Under 100 mW cm-2simulated AM1.5 solar illumination, The efficiency of the cells is essentially limited by the low value of the filling factor, only about ~ 0.3. The power conversion efficiency was determined to be around 0.45-0.67 %.
9:00 PM - AA11.17
Novel OTFT Material Containing TIPS Anthracene for Solution Process.
Jong-Won Park 1 , Jung Kyu Park 1 , Jin Uk Ju 1 , Tae Hoon Kim 1 , Soon-Ki Kwon 1 , Dong Min Kang 1 , Yun-Hi Kim 2
1 School of Nano-Advanced Materials Science and Engineering and ERI, Gyeongsang national university, JinJu, gyeongnam, Korea (the Republic of), 2 Chemistry, Gyeongsang national university, JinJu, gyeongnam, Korea (the Republic of)
Show Abstract9:00 PM - AA11.18
A Direct-Patterning Process to Define Short Channel-Length OTFT by Mold-Casting Technique
Min-Hua Yang 1 , Wen-Jong Wu 1
1 Department of Engineering Science and Ocean Engineering , National Taiwan University , Taipei Taiwan
Show AbstractThe mold-casting is a direct-patterning technique to have a good resolution on organic electronic. Like grave printing, offset printing and screen printing, the mold-casting technique is also a solution-processing technique to manufacturing organic transistor circuits. In these years, the organic thin-film transistors with short channel-lengths have been desired to achieve higher performances. If the channel length of a transistor can be reduced, the switching speed and operated voltage would be more ideal for organic electronic applications. But few printing techniques can offer the approaches of smaller linespacing registration. So the mold-casting technique is developed to define high resolution, which is specially to enhance the patterning of line spacing. The mold-casting technique needs some surface relieves with well-defined linewidth of the mold as a barrier to block the solution flowing while casting materials. The major difference between above printing techniques and the mold-casting technique is that the latter introduces an external force like adhesive forces as an enhancement to block solution flowing accurately. Additionally, an adhesive layer is used to contact surface relief of the mold tightly and there will be no connection with each two casted conducting polymer, which can be used as source/drain electrodes of a transistor. The casting process can be separated into two parts, which are the fabrication of the mold and casting materials into molds to patterning materials. First, the mold could be fabricated by MEMS process, which the barrier geometry size with several microns could be defined by lithography. Then, the etching process makes the barrier with high aspect-ratio to casting conducting polymer PEDOT/PSS. The channel length between source/drain electrodes will be equal to the width of the barrier, so the limitation of mold-casting technique would be based on the resolution of the mold manufacturing. Secondly, the following steps are to printing adhesive epoxy as block layer, contacting mold and casting PEDOT/PSS into the mold as source/drain electrode, respectively. After de-molding, it is to spinning P3HT as active layer, spinning PMMA as insulator layer and casting PEDOT/PSS as gate electrode, where the OTFTs with top-gated bottom-contacted structure have completed. Up to now, there are few groups who had mentioned this patterning concept on solution processing applications. Our group has successfully demonstrated all-polymer OTFTs on flexible substrates with channel length of 10μm by mold-casting technique. We wish this technique may be an attractive mean of organic transistor circuits.
9:00 PM - AA11.19
Synthesis and Characterization of New Conjugated Copolymer Containing Anthracene with Fluorene for Solution Processible Organic Thin Film Transistors (OTFTs).
Jin Uk Ju 1 , Jong Won Park 1 , Seong Ong Kim 1 , Yun-Hi Kim 2 , Dae Sung Jung 3 , Chan Eon Park 3 , Soon-Ki Kwon 1
1 School of Nano & Advanced Materials Science and Engineering , Gyeongsang National University , Jin Ju Korea (the Republic of), 2 Department of Chmistry, Gyeongsang National University, Jinju Korea (the Republic of), 3 Department of Chmical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show Abstract9:00 PM - AA11.2
Growth of Organic Molecular Thin Films on Solution-Processed Resists.
Vladimir Pozdin 1 , Aram Amassian 1 , Alexis Papadimitratos 1 , Detlef Smilgies 2 , George Malliaras 1
1 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - AA11.20
High-Performance n-type Organic Field-Effect Transistors and Their Applications in Electronic Circuits.
Yoonyoung Chung 1 , Joon Hak Oh 2 , Ruediger Schmidt 3 , Frank Wuerthner 3 , Zhenan Bao 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States, 3 Institut für Organische Chemie, Universität Würzburg, Am Hubland, Würzburg, Germany
Show Abstract9:00 PM - AA11.21
Solution-processed Organic Thin Film Transistors Based on Anthracene Derivities.
Jungpyo Hong 1 , Seonghoon Lee 1 , Myoung-Chul Um 1 , Jong-In Hong 1
1 Chemistry, Seoul National University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - AA11.22
Common Base Current Analysis of the Vertical-type Metal-base Organic Transistors.
Ken-ichi Nakayama 1 2 , Kazuhiro Yoneda 3 , Masaaki Yokoyama 3 1
1 Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan, 2 , JST-PRESTO, Kasuga, Fukuoka, Japan, 3 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract9:00 PM - AA11.23
Controlled Crystalline Structure of Solution-processible Semiconductors for High Performance Organic Field-Effect Transistors
Hoichang Yang 1 , Lin Yang 2 , Se Hyun Kim 3 , Chan Park 3
1 Nanocenter, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractOrganic semiconductors have been intensively studied in recent decades on account of their potential alternatives to conventional inorganic semiconductors for applications such as low cost, large area, and flexible electronics. In the areas of organic field-effect transistors (OFETs), π-π stacking conjugated assembly of organic semiconductors plays an important role in maximizing long distance charge transfer. Solution-processible pentacene and anthradithiophene derivatives have received much attention in recent years because of their better π-π conjugated packing structures, compared to pentacene with a herringbone structure. Depending on film processing conditions, however, the crystalline structures on dielectric substrates are significantly changed, resulting in very different field-effect mobilities in OFET devices.Here we focus on two simple, but unsolved questions that underpin our understanding in this area: (i) what is the effect of physiochemical treatments on the film morphologies and orientation of functionalized pentacene and anthradithiophene derivatives, which affects electric performance of OFETs? and (ii) is it possible to control the crystal orientation along both lateral and vertical film direction? Answering these questions would be a significant step toward realizing fully flexible OFETs with semiconductor films, which could be solution-fabricated on gate dielectrics.Pentacene and anthradithiophene derivatives films were cast on various gate-dielectric surfaces from solvents, under either opened surface or confined geometries by soft-lithoed blocks. Some films were further treated via physiochemal processings: thermal or solvent annealing. In order to characterize the crystalline morphologies and orientation in the films, synchrotron-based grazing-incidence X-ray diffraction and atomic force microscopy were performed. The correlation between the film structure and the corresponding electric performance in OFETs will be discussed.
9:00 PM - AA11.24
Oxadiazole-Containing n-Type Organic Semiconductors.
Taegweon Lee 1 , Chad Landis 1 , Bal Dhar 1 , Byung Jun Jung 1 , Howard Katz 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show Abstract9:00 PM - AA11.25
Synthesis and Characterization of Soluble Polymer Containing Alkoxy Naphthalene and Bithiophene for OFETs.
Tae Hoon Kim 1 , Dong Min Kang 1 , Jong Won Park 1 , Dae Sung Chung 3 , Chan Eon Park 3 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of Nano & Advanced Materials Science and Engineering and ERI, Gyeongsang National University , Jinju Korea (the Republic of), 3 Department of Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Department of Chemistry, Gyeongsang National University , Jinju Korea (the Republic of)
Show Abstract9:00 PM - AA11.26
Analysis of Carrier Transport of Quaterrylene Thin Film Transistors Formed Using Ultra-Slow Vacuum Deposition Technique.
Ryoma Hayakawa 1 , Matthieu Petit 1 , Yutaka Wakayama 1 2 , Toyohiro Chikyow 1
1 Advanced Electronic Materials Centre, National Institute For Materials Science, Tsukuba Japan, 2 Nanoscale Quantum Conductor Array Project, JST, Tsukuba Japan
Show Abstract In the last years, organic field effect transistors (OFETs) have become an attractive for applications with large scale areas and low production costs. Quaterrylene is worthy of attention because it has a planar chemical structure and highly π-conjugated electron system. The films were found to evolve following a Stranski-Krastanov (S-K) mode. Firstly, the films were grown two-dimensionally with a standing-up orientation up to 4 monolayers (ML), followed by three-dimensional (3D) island growth. Even in the 8 ML-thick film, the grain size of as large as 6 μm and the surface roughness as low as of 1.67 nm were successfully obtained, which is a great advantage for obtaining high carrier mobility. In this paper, quaterrylene FETs with top-contact Au electrodes were formed on SiO2(200nm)/p-Si(001) substrates, and their carrier transport was discussed. Quaterrylene FETs indicated typical p-channel transistor operations. The carrier mobility and the threshold voltage were estimated to be 0.018 cm2/Vs and 14 V, respectively. The carrier mobility closely depended on a grain size of the quaterrylene thin films. The value increased with increasing the grain size, showing the carrier transport was limited by grain boundaries. Furthermore, the carrier mobility was also related to a thickness of the quaterrylene thin films. The carrier mobility rapidly increased as elevating film thickness, and then saturated at 3-4 ML, indicating that the first 2D layer works as an effective transistor channel. The temperature dependence of the carrier mobility in the range from 300 K down to 60 K was studied to evaluate the carrier transport through quaterrylene layer. The temperature dependence revealed that two distinct regimes. In high temperature range from 300 K to 210 K, the carrier transport showed thermally activated behavior with activation energies of 100-150 meV. Meanwhile, the carrier mobility became independent on the temperature below 210K, exhibiting that carrier transport changed to tunnel transfer-like behavior. We found that the carrier transport was limited by thermally activated carrier emission at grain boundaries in high temperature range. On the other hands, tunnel transfer through potential barriers at grain binderies was dominant over thermally activated emission in low temperature range.
9:00 PM - AA11.27
Investigation of the Spontaneous Ordering Transition in Organic Semiconducting Perylene Diimide Derivative Films using Anisotropic Spectroscopic Ellipsometry.
Dean Levi 1 , Walter Doherty 1 , Brian Gregg 1
1 , NREL, Golden, Colorado, United States
Show Abstract9:00 PM - AA11.28
Properties of Organic Thin-film Transistors with Carbon Nanotube-containing Electrodes.
Sondra Hellstrom 1 , Melbs LeMieux 1 , Hang Woo Lee 1 , Zhenan Bao 1
1 Department of Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - AA11.29
Synthesis and Characterization of Novel Organic Thin Film Transistors containing Anthracene and Fluorene.
Moon-Hak Park 1 , Dong Min Kang 1 , Jong-Won Park 1 , Tae-Hoon Kim 1 , Jin Woo Kim 3 , Mi Hye Yi 3 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of Nano & Advanced Materials Science and Engineering, Gyeong Sang National University, Jin-Ju, Gyeong Nam , Korea (the Republic of), 3 Information & Electronics Polymer Research Center (I&E PRC) , Korea Research Institute of Chemical Technology (KRICT), Daejeon Korea (the Republic of), 2 Department of Chemistry, Gyeongsang National University, Jinju, Gyeong Nam , Korea (the Republic of)
Show Abstract9:00 PM - AA11.3
Small-Molecule Heteroaromatic Semiconductors for Organic Single-Crystal Field-Effect Transistor Applications.
Eilaf Ahmed 1 , Alejandro Briseno 1 , Younan Xia 1 , Samson Jenekhe 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractOver the past decade, molecular design has enabled synthetic chemists to tune the physical and optoelectronic properties of organic molecules for use in applications such as organic field-effect transistors (OFETs). Organic field effect transistors are pursed as a potential low cost alternative to amorphous silicon. For practical applications, OFETs must have comparable performance and stability to amorphous silicon. Acenes, oligothiophenes, tetrathiafulvalenes, and their derivatives have extensively been studied as p-type semiconductors for application in thin film transistors. Pentacene and rubrene have resulted in an impressive performance from thin film and single crystal transistors, respectively and considered as benchmarks for OFETs. Despite the great accomplishment in the field of OFETs, there is, however, a necessity for understanding structure-property relationships. Current p-type semiconductors tend to degrade and photooxidize easily, and are more susceptible to herringbone packing arrangements which minimizes λ-λ packing. It is generally accepted that face-to-face λ-stacking would result in more efficient orbital overlap between molecules, resulting in larger carrier mobilities than their herringbone counterparts. In this presentation, we will report on highly fused heteroaromatic semiconductors for use in organic single-crystal field-effect transistors. A new synthetic route was developed for the synthesis of heteroaromatic semiconductors via intramolecular cyclization. Single-crystal X-ray diffraction revealed a planar backbone with slipped face-to-face λ-stacking and a short interplanar distance of 3.30 Å. We report mobilities as large as ~1 cm2/ V s and on/off current ratios of ~105.
9:00 PM - AA11.30
Transmission Electron Microscopy Studies of PBTTT and Pentacene Thin Films.
Amanda Simens 1 , Leslie Jimison 1 , Alexander Ziegler 3 , Alberto Salleo 1 , Andrew Minor 2 , Ute Zschieschang 4 , Hagen Klauk 4
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Department Molecular Structural Biology, Max-Planck Institute for Biochemistry , Martinsried Germany, 2 National Center for Electron Microscopy (NCEM), Lawrence Berkeley National Lab, Berkeley, California, United States, 4 , Max-Planck Institute for Solid State Physics, Stuttgart Germany
Show AbstractRecently, there has been considerable interest in the development of organic semiconductors for use in printable electronic devices, such as transistors for display backplanes. These materials offer a cost effective alternative to conventional semiconductors, with key advantages of potentially inexpensive fabrication techniques and compatibility with flexible substrates. While overall mobilities are approaching that of amorphous silicon, our detailed understanding of the charge transport processes and device operation is lacking. It has been established that the effective mobility in these films is largely dependent on film microstructure, which includes crystalline quality, crystallite size, and characteristics of the grain boundaries. In order to better establish our understanding of charge transport processes, we must therefore be able to characterize the structure of these films, with the ultimate goal being able to control the microstructure to optimize electrical performance. Typical structural characterization techniques for organic semiconductors include x-ray diffraction and atomic force microscopy. While these are extremely useful techniques, they are not complete in their description: x-ray diffraction probes only the bulk of the film, and AFM is limited to gathering information at the film/air interface. In this study we have used plan view Transmission Electron Microscopy for probing the bulk granular structure of poly(2,5-bis(3-dodecylthiophen-2yl)thieno[3,2-b]thiophene), (PBTTT) thin films, as well as cross-sectional TEM for probing the structure of the substrate/semiconductor interface in pentacene films. Plan view images of PBTTT thin films reveal equiaxed crystallites approximately 20 nm in diameter. These images, along with complementary AFM height images help to correlate the relationship between the characteristic terraces of annealed PBTTT and bulk grain structure, giving insight into the fundamental limitations of mobility improvement in TFT devices. Two categories of pentacene thin film samples were studied: films that were deposited on PEN, a plastic substrate, and films deposited on silicon. Images reveal information about the pentacene grain structure at the semiconductor/substrate interface. By comparing films on two different substrates we are able to see the effect that the substrate has on film formation, in particular the size and orientation of crystalline grains at the interface.
9:00 PM - AA11.31
A Study of Vanadyl-phthalocyanine(VOPc)/copper-hexadecafluorophthalocyanine(F16CuPc) Heterostructure OTFTs.
Xiaojiang Yu 1 , Jianbin Xu 1 , Jun Du 1
1 , Department of Electronic Engineering and The Materials Research and Technology Center, The Chinese University of Hong Kong, Hong Kong China
Show Abstract9:00 PM - AA11.32
Sub-Bandgap Measurements and Biasing Effects of Polythiophene-based Thin Films Using Surface Plasmon Resonance Spectroscopy (SPRS).
Jonathan Rivnay 1 , Michael Preiner 1 , Nicholas Melosh 1 , Alberto Salleo 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractAlthough the physics of charge transport in organic semiconductors is not fully understood, it is agreed upon that transport and charge injection is limited by charge trapping. The trap states responsible for lowering carrier mobility must be located within the band gap of the organic semiconductor. Thus these trap states lead to weak sub-gap absorption features in the optical absorption spectrum of the material. Measurement of such low-level absorption in thin films is difficult due to the inadequate sensitivity of common spectroscopic techniques. While photothermal deflection spectroscopy can measure weak absorption, it is limited to thick films, and can not be biased. Many electronic devices of interest (e.g. transistors, LEDs) however are made with thin (<100 nm) layers of semiconductor material. Thin and thick films often have significantly different microstructures; therefore, there is need for a technique that measures weak, sub-gap absorption in polymeric thin films. Recently, surface plasmon resonance spectroscopy (SPRS) has been employed to probe the optical properties of monolayer thick molecular electronic devices with high sensitivity[1]. SPRS relies on the high electric fields created by surface plasmon polaritons at the metal/organic interface to allow for sensitive measurement of optical properties at the buried interface. This approach is able to simultaneously extract both the real (n) and imaginary (k) components of the index of refraction based on the efficiency of coupling incident light into surface plasmon polaritons. We use SPRS to measure sub-bandgap absorption in thin (ca. 20nm) polymeric films of regioregular poly-3-hexylthiopene (P3HT) and poly(2,5-bis-alkylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT) on Au. Preliminary measurements using an un-optimized setup showed an absorbance of ~0.2%. Absorption spectra of P3HT and PBTTT obtained with SPRS were in good agreement with conventional UV-vis spectra, and showed additional features below the absorption edge. We also explore the effect of bias on the thin polymeric films using an MIS diode configuration in conjunction with SPRS. This allows for a novel approach to detect optical absorption in the gap due to field induced charge in thin polymeric films. [1] K.T. Shimizu, et al. Nano Letters, 6, 2797 (2006).
9:00 PM - AA11.33
High-Performance Organic Semiconductors for Thin-Film Transistors Based on 2,6-bis(2-thienylvinyl)anthracene.
Myoung-Chul Um 1 , Jong-In Hong 1 , Jang-Joo Kim 2 , Junhyuk Jang 2 , Jung-Pyo Hong 1 , Jihoon Kang 1 , Seong Hoon Lee 1 , Do Yeung Yoon 1
1 Chemistry, seoul national Univ., Seoul Korea (the Republic of), 2 Materials Science and Engineering , seoul national Univ., Seoul Korea (the Republic of)
Show AbstractIn the past few decades, the acene and thiophene oligomers have been significantly studied series of compounds because of their use as organic semiconductors for realization of device such as field-effect transistor (OTFTs), organic light-emitting diodes (OLEDs), photovoltaic cell, sensors, and radio frequency identification (RF-ID) tags. So far, showing remarkable properties are pentacnce as the best thin-film material (0.3-0.7 cm2/Vs on a Si/SiO2 substrate, 1.5 cm2/Vs on a chemically modified Si/SiO2, and 3.0 cm2/Vs a Si/SiO2 on a substrate) and rubrene as the best single-crystal material (15.4cm2/Vs) . In this work, we have synthesized two novel organic semiconductors based on an anthracene-vinyl thiophene co-oligomer, which show good electrical performances (up to 0.4 cm2/Vs) on SiO2/Si and can be easily synthesized in large quantities. In addition, the high mobility of such semiconductors can be achieved at low substrate deposition temperature, which is the best value for vinyl thiophene co-oligomers. 2,6-bis(2-thienylvinyl)anthracene (TVAnt) and hexyl substituted (HTVAnt) show promising properties for applications on organic flexible electronics.
9:00 PM - AA11.34
High-performance Single-crystal Field-effect Transistors for the Probing of Charge Transport in Organic Materials.
Colin Reese 1 , Wook-Jin Chung 1 , Stefan Mannsfeld 1 , Randall Stoltenberg 1 , Mark Roberts 1 , Zhenan Bao 1
1 , Stanford University, Stanford, California, United States
Show Abstract9:00 PM - AA11.35
Pentacene Thin-Film Transistors with PEDOT:PSS S/D Electrodes by Inkjet Printing.
Jae-Kyoung Kim 1 , Jung-Min Kim 1 , Woon-Hyuk Baek 1 , Hyun Ho Lee 2 , Tae-Sik Yoon 1 , C. Kang 1 , Yong-Sang Kim 1 3
1 Nano Science and Engineering, Myong-Ji Univ., Yong-In Korea (the Republic of), 2 Chemical Engineering, Myong-Ji Univ., Yong-In Korea (the Republic of), 3 Electrical Engineering, Myong-Ji Univ., Yong-In Korea (the Republic of)
Show Abstract9:00 PM - AA11.36
Effect of O2 Plasma-Treated Ni Electrode on Electrical Properties of Pentacene Thin-Film Transistor.
Bang Joo Song 1 , Gwan Ho Jung 1 , Woong Kwon Kim 1 , Jong-Lam Lee 1
1 Materials Science and Engineering, Pohang University of Science and Technology(POSTECH), Pohang, Kyung-buk, Korea (the Republic of)
Show Abstract9:00 PM - AA11.37
Determining the Molecular Packing in Monolayer-thin Organic Semiconductor Layers.
Stefan Mannsfeld 1 , Quan Yuan 1 , Ming Tang 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, Stanford, California, United States
Show Abstract9:00 PM - AA11.38
Mobility Enhancement of Amorphous Polymer Blend Transistors by Gate Dielectric Modification.
H. H. Fong 1 , George Malliaras 1 , J. Gao 2 , Jianbin Xu 2
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Electrical and Electronic Engineering, The Chinese University of Hong Kong, Hong Kong China
Show Abstract9:00 PM - AA11.39
Organic Thin Film Transistors based on Polymer Blends.
F. Sunjoo Kim 1 , Alejandro Briseno 2 , Younan Xia 2 , Samson Jenekhe 1
1 Chemical Engineering, University of Washington, Seattle, Washington, United States, 2 Chemistry, University of Washington, Seattle, Washington, United States
Show Abstract9:00 PM - AA11.4
TTCDI-5C Organic Molecules: Thin Film Growth and Effect of Metal Electrodes on the Electrical Properties of Organic Thin Film Transistors.
Matthieu Petit 1 , Ryoma Hayakawa 1 , Yutaka Wakayama 1 , Yasuhiro Shirai 1 , Jonathan Hill 2 , Toyohiro Chikyow 1 , Katsuhiko Ariga 2
1 Advanced Electronic Materials Center, NIMS, Tsukuba Japan, 2 Supermolecules Group, NIMS, Tsukuba Japan
Show AbstractOver the last decade organic semiconductors have been widely studied because of their potential for many applications: flat display panels, electronic papers, chemical sensors, etc. Indeed an advantage of organic semiconductors is that they can be deposited at low temperature onto substrates. So they are suitable for plastic substrates. In recent years, a wide range of conjugated molecules have been studied such as pentacene, perylene, etc. In this work we present the growth of a terrylene derivative molecule (N,N’-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboximide). TTCDI-5C molecules are n-type semiconductors candidates. Molecules were deposited in an ultrahigh vacuum chamber using the organic molecular beam deposition. Silicon dioxide surfaces of n-type Si(100) were used as substrates. Temperatures were varied from room temperature to 200C. Thin films with a thickness form less than one monolayer to 15 ML were grown. Structural analysis and surface morphology are monitored with XRD (Bruker D8 discovery) and AFM (SII, SPI4000) systems. Surface morphology and grains size were found to be dependent of the deposition temperature.Organic thin films transistors (OFET) were fabricated using TTCDI-5C thin films as the semiconductor layers. Thickness of the organic thin films is 30 ML. Top contact configuration was used for the transistors. Gate insulator consists in thermally grown SiO2. We have studied the effect of three different metals for the electrodes -gold, aluminiun and magnesium- with work functions of 5.1, 4.28, 3.66 eV respectively. Metals were thermally deposited through shadow masks in high vacuum. The purpose is to decrease the injection barrier at the source and drain contacts and to measure the resulting effects on the field effect mobility of the TTCDI-5C OFET.
9:00 PM - AA11.40
Molecular Nanowires for Multi-channel Transistor.
Yutaka Wakayama 1 , Seiichi Takami 1 , Ryoma Hayakawa 1 , Toyohiro Chikyow 1 , Kenji Kobayashi 2
1 , National Institute for Materials Science, Tsukuba Japan, 2 , Shizuoka University, Shizuoka Japan
Show AbstractA main purpose of our study is to develop a nanowire transistor for multi-value operation. For this purpose, a molecule, 6, 13-bis(methyltio) penthacene (BMTP), was synthesized, where the methyltio (-SCH3) substituents were attached on both side of penthacene. These substituents play an essential role for controlling intermolecular interaction, leading to a face-to-face molecular packing in crystal.The molecules were deposited on a SiO2/Si(100) surface in high vacuum. Then, the SiO2 surface was covered by a self-assemble monolayer of OTS. The OTS treatment reduced a surface tension of the substrate, making intermolecular interaction predominant. In conjunction with the strong molecular packing of BMTP, the molecules showed anisotropic crystal growth forming one-dimensional wires. The dimensions of the molecular wire are dozens of nanometer in diameter and a few micrometers in length. Importantly, the long direction of the wires was found to coincide with that of face-to-face packing (a-axis of the unit cell) by X-ray diffraction measurement; a high conductivity in this direction can be expected.Electrical measurements were carried out in a scanning electron microscope equipped with multiple tungsten tips, which enabled nanoscale observation and pinpoint measurement simultaneously. Two wires with different diameters were connected in parallel with common source/drain electrodes and the tungsten tips were accessed to the respective molecular wires as gate electrodes. The molecular wires exhibited a p-type semiconducting property and depletion type transistor operation. Note that, an advantage of this device configuration is that each gate electrode can apply the bias voltage independently; the current through each channel can be controlled separately. Consequently, multi-value operation (four values: on/on, on/off, off/on and off/off) was achieved.
9:00 PM - AA11.41
Transistor Performance and Film Structure of Hexabenzocoronene Derivatives.
Tomohiko Mori 1 , Yoshihiro Kikuzawa 1 , Kazuhiko Umemoto 1 , Hiroshi Nozaki 1 , Yoshiki Seno 1 , Hisato Takeuchi 1
1 , TOYOTA Central R&D Labs., Inc., Aichi Japan
Show Abstract Organic field-effect transistors (OFETs) have lately attracted considerable attention because of their use in lightweight, low-cost, large-area and flexible electronics products. Interesting molecules as an active layer for OFETs are hexabenzocoronene (HBC) derivatives. HBC derivatives are rich in π electrons, and would be expected a high degree of overlap of the π electrons of neighboring molecules, which is suitable for high charge carrier mobility. Hexaalkyl-hexabenzocoronenes have been recognized as a molecule self-assembles into columnar aggregates. The aromatic cores are stacked to the columnar axis which allows facile carrier transport along the stack. They display intrinsic carrier mobilities of up to 1 cm2/Vs using a pulse-radiolysis time-resolved microwave conductivity technique in the bulk sample, while they show low FET mobilities up to 10-3 cm2/Vs in a thin film sample. The remaining problem is that little overlap of conducting pathways between at crystal grain boundaries in thin-film geometries. On the other hand, lamellar aggregates facile carrier transport along the layer which possess more overlap of conducting planes at crystal grain boundaries. In the present study, we have designed dihexyl- and tetrahexyl-hexabenzocoronenes (2H-HBC, 4H-HBC) to self-assemble into lamellar aggregates. The OFETs with the HBC derivatives have been fabricated on SiO2/Si substrate, and the performance as a semiconductor is presented. The crystal and thin film structures were determined by the powder x-ray diffraction and grazing incidence X-ray diffraction (GIXD). The 2H-HBC and 4H-HBC increased the field-effect mobilities and on/off ratios by a factor of 10 or more as compared to the unsubstituted HBC and the hexahexyl-hexabenzocoronene (6H-HBC). GIXD has been performed to study the thin film structure of HBC derivatives. The data indicate that 2H-HBC and 4H-HBC self-assemble into lamellar aggregates. 2H-HBC form the layers of the aromatic cores are sandwiched by the layers of hexyl chains, which is a preferable crystal structure for carrier transport. The good OFET performance could be explained by the self-assembly in lamellar aggregates of the 2H-HBC and 4H-HBC, in contrast to the self-assembly in the columnar aggregate of the 6H-HBC and low self-assembling property of the unsubstituted HBC. In conclusion, 2H-HBC and 4H-HBC had extremely high field-effect mobilities compared to HBC and 6H-HBC. The GIXD results suggest that the films of 2H-HBC and 4H-HBC form conducting planes. The good FET performance could be explained by the self-assembly in lamellar aggregates of the 2H-HBC and 4H-HBC, in contrast to the self-assembly in the columnar aggregate of the 6H-HBC and low self alignment of HBC.
9:00 PM - AA11.42
Ambipolar Vertical Organic Transistor and its Inverter.
Sheng-han Li 1 , Zheng Xu 1 , Guanwen Yang 1 , Liping Ma 1 , Yang Yang 1
1 Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, Los Angeles, California, United States
Show AbstractOrganic transistor is an attractive technology due to the low materials and manufacturing costs. However, the performance of organic transistors is still limited by the inherent low carrier mobility of organic materials. A novel design of building transistor vertically could resolve these issues by changing the current flow direction. Here, we report an ambipolar vertical organic transistor with performance exceeding that of current organic transistors, owing to its unique vertical device structure. This unique design provides a large cross-section and a short channel length to counter the limitations of the organic material. The ambipolar characteristic is attributed to the thin transition-metal-oxide layer inserted at the source/organic interface, which acts as a charge injection layer. The optimum thickness of the vanadium pentoxide layer was obtained as 7.5 nm for ambipolar operation. An organic complementary metal-oxide-semiconductor inverter has also been demonstrated with a gain of 13.6.
9:00 PM - AA11.43
Thin Film Microstructure of Solution Processable Pyrene-based Small Molecules for Electronic Applications.
Leah Lucas 1 , Dean DeLongchamp 2 , R. Kline 2 , Lee Richter 3 , Daniel Fischer 4 , Bilal Kaafarani 5 , Ghassan Jabbour 1
1 School of Materials, Advanced Photovoltaics Center and Flexible Display Center, Arizona State University, Tempe, Arizona, United States, 2 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 4 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 5 Department of Chemistry, American University of Beruit, Beruit Lebanon
Show Abstract9:00 PM - AA11.44
Monolayer Polymer Field-effect Transistors.
Aleksandar Ivanov 1 , Arne Hoppe 1 , Juergen Fritz 1 , Veit Wagner 1
1 SES, Jacobs University Bremen, Bremen Germany
Show Abstract9:00 PM - AA11.45
Active Layer Thickness Dependence in Flexible P3HT Field-effect Transistors.
Benedikt Gburek 1 , Veit Wagner 1
1 School of Engineering and Science, Jacobs University Bremen, Bremen Germany
Show AbstractIn recent years, a lot of progress has been achieved in research on organic electronics. A major part of this research was performed on the well-known material system silicon / silicon oxide as substrate and gate insulator, respectively. On the other hand, applications of organic electronics require cheap and fast production methods on e.g. flexible and transparent devices.Following these goals, organic field-effect transistors (OFETs) in top-gate architecture are produced on flexible and transparent plastic foils made of polyethylene-terephtalate (PET) as device substrate. The organic semiconductor and the gate insulator are deposited wet-chemically by spin-coating under atmospheric conditions. The thickness of the insulator layer is a crucial point, as thick gate insulators require high operation voltages, which is in contradiction to general application requirements. We could produce gate insulators with thicknesses down to 100 nm, which allows for device operation at satisfactory low voltages, i.e. below 10 V.The devices were fabricated with regio-regular poly-(3-hexylthiophene) (rr-P3HT) as semiconductor and poly-methylmethacrylate (PMMA) as gate insulator. Electrical measurements exhibit comparably high charge carrier mobility of 0.02 cm^2/(Vs), determined at –40 V gate-source voltage in devices with 300 nm insulator thickness in the linear regime. Unlike uncapped P3HT transistors, which show severe degradation after a few hours already, our device characteristics remain stable for several months due to the encapsulation with the PMMA gate insulator.Plastic devices fabricated in this way were used to analyze the dependence of the charge carrier mobility on the thickness of the P3HT layer. The mobility was found to be low for thin layers of several nm and to increase strongly with increasing layer thickness. For sufficiently large semiconductor thickness, i.e. beyond 15 nm, the mobility remains constant. These findings correspond to results obtained on transistors fabricated on silicon in bottom-gate architecture reported in literature.Thickness dependent charge transport properties were analyzed by fitting theoretical models. Beside gate voltage dependent mobility also charge carrier injection properties and contact resistance were taken into account. The latter is a crucial point and major obstacle for the further miniaturization of devices.
9:00 PM - AA11.46
Ionic Impurities in Poly(vinyl alcohol) Gate Dielectrics and Hystheresis Effects in Organic Field Effect Transistors.
Martin Egginger 1 , Mihai Irimia-Vladu 2 , Reinhard Schwoediauer 2 , Andreas Tanda 3 , Siegfried Bauer 2 , Serdar Sariciftci 1
1 LIOS, Linz Institute for Organic Solar Cells, JK University of Linz, Linz Austria, 2 SOMAP, Soft Matter Physics, JK University of Linz, Linz Austria, 3 , plastic electronic GmbH, Linz Austria
Show Abstract9:00 PM - AA11.47
Interface Treatment for Improving Top Gate Polymer Transistor Device by Inkjet Printing on Plastic Substrates.
Po-Yuan Lo 1 2 , Tarng-Shiang Hu 1 , Jack Hou 1 , Yi-Jen Chan 1 2
1 Electronics and Opto-electronics Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan, 2 Department of Electrical Engineering, National Central University, Taoyuan Taiwan
Show AbstractIn this work, a novel solvent treatment method for enhancing the semiconductor polymer molecular chain rearrangement was introduced to improve transistor device uniformity made by inkjet printing processes on plastic substrates. The increased crystallinity of the solvent treated semiconductor layer was observed from x-ray diffraction analysis. In addition, the transistor transfer characteristics of a transistor device showed a very narrow threshold voltage variation from a number of transistor devices, which indicates a good interface property between the polymer semiconductor and dielectric layer. From the surface treatment of source/drain electrodes by applying a small molecule coating, the ON current of a transistor device was increased up to 3 orders. Mechanisms for such ON current increase will be discussed. Finally, an inkjet printed top gate polymer transistor array fabricated on a patterned ITO/PET substrate made by R2R manufacturing processes will be demonstrated.
9:00 PM - AA11.48
Charge Transport in Molecular Monolayers: The Role of Molecular Structures.
Yabing Qi 1 2 , Bas Hendriksen 2 , Florent Martin 2 5 , Daniel Esteban 2 , Violeta Navarro 2 , Jeong Young Park 2 , Imma Ratera 2 , Clayton Mauldin 4 , Jean Frechet 3 4 , Miquel Salmeron 2 3 5
1 Applied Science and Technology Graduate Group, University of California Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States, 4 Department of Chemistry, University of California Berkeley, Berkeley, California, United States, 3 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe incorporation of molecules and molecular films in electronic devices is promising for technological applications. It is important to understand the charge transport mechanism in molecular monolayers. It may not only depend on the intrinsic properties of the molecules, but also on the arrangement and conformation of the molecules in the monolayers. We studied correlations between the structural, mechanical and electronic properties of two types of molecular monolayers - alkanethiol self-assembled monolayers and pentathiophene based Langmuir-Blodgett molecular monolayers - with conducting probe atomic force microscope (CP-AFM).The first molecular monolayer system we studied is alkanethiol self-assembled monolayers (SAM) on Au(111). The relationship between charge transport and mechanical properties of the monolayers has been investigated using an atomic force microscope with a conductive tip. Molecular tilts induced by the pressure applied by the tip cause step-wise increases in film conductivity. A decay constant β = 0.57 Å-1 was found for the current passing through the film as a function of tip-substrate separation due to this molecular tilt. This is significantly smaller than the value of ~1 Å-1 found when the separation is changed by changing the length of the alkanethiol molecules. Calculations indicate that for isolated dithiol molecules S-bonded to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of S-Au bonding on SAM conductance is discussed.The second molecule we studied is decyl-pentathiophenyl butyric acid. We found that the molecules can self-assemble on mica, and their alkyl chains can be tilted under the external load. We used the Langmuir-Blodgett (LB) technique to prepare molecular monolayers on heavily doped p-type Si and flat Au substrates. We observed two types of structures coexisting in the films, which are very different from the round-shape islands typically observed for the SAMs on mica: one is compact crystalline island, and the other is poorly packed amorphous structure containing many holes. The grains of the crystalline islands extend radially from the center of the islands towards the edge as we can see in the friction and current images. The magnitude of the friction on crystalline islands is significantly lower than on the amorphous structure, while the current is at least a factor of ten times higher on the crystalline islands. High resolution AFM friction images resolve the molecular lattice of each grain. The lattice orients differently from one grain to another. NEXAFS data indicate an almost upright orientation of the pentathiophenyl part of the molecules. We propose that the higher conductivity of the crystalline islands is a result of a better overlap of molecular orbitals due to the higher degree of ordering.
9:00 PM - AA11.49
Charge Injection at Metal/organic Interfaces: Study on Contact Resistance.
Pietro Parisse 1 , Anna Molinari 2 , Ignacio Gutierrez 2 , Alberto Morpurgo 2
1 , CASTI CNR-INFM Regional lab and Dipartimento di Fisica Università di L'Aquila, L'Aquila Italy, 2 , Kavli Institute of Nanoscience - Delft University of Technology, Delft Netherlands
Show AbstractCharge injection at the interface between metallic electrodes and organic semiconductors plays a crucial role in the performance of organic electronic devices. Up to now, the high contact resistance is one of the most difficult problem to overcome for a real application of organic devices. In order to truly exploit all the applicative possibilities of organic based electronic device, a detailed understanding of the charge injection mechanism at metal/organic interface is a fundamental task. The lack of reproducibility of results in Organic Thin Film Transistors does not help a clear visionof the physics underlying such process. At variance Single Crystal Field Effect Transistors (SC-FETs) have beenshown to guarantee high performances and reproducibility. Owed to their advantageous characteristics, we performedcontrolled studies of contact resistance on SC-FETs by means of scaling experiments to address this issue. In thepresent work we resumed all the experimental findings on scaling experiments on rubrene single crystal FETs andthe preliminary results of scaling experiments on Pentacene/Ni SC-FETs. Rubrene and Pentacene based SC-FETsevidence high reproducibility, good mobilities (μ=3 cm2/Vs for rubrene, μ=1 cm2/Vs for pentacene) and low contactresistances (best contact resistance of Rubrene/Ni RC=100 Ohm cm and best contact resistance of Pentacene/Ni RC=250 Ohm cm). Short channel devices showed contact dominated characteristics that can be explained considering the device as two back to back Schottky diodes. The agreement between experimental and theoretical values is excellent and the fitting of the curves allows to limit the range of values of the used parameters.
9:00 PM - AA11.5
Surface Chemistry Dependence of Microstructure and Carrier Mobility for a High-performance n-type Organic Semiconductor.
Parul Dhagat 1 , Pascal Marmion 1 , Hanna Haverinen 2 , Leah Lucas 1 , Jizheng Wang 1 , Zixing Wang 1 , R. Kline 3 , Dan Fischer 3 , Dean DeLongchamp 3 , Jian Li 1 , Ghassan Jabbour 1
1 School of Materials and Flexible Display Center, Arizona State University, Tempe, Arizona, United States, 2 Department of Electrical and Information Engineering, University of Oulu, Oulu Finland, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractWe report the fabrication of n-type organic thin-film transistors (OTFTs) with active layers of PTCBI (3,4,9,10-perylenetetracarboxylic bis-benzimidazole), which has exhibited promising performance as an electron transport layer in photovoltaics [1]. The microstructure of PTCBI films can vary significantly depending on the deposition rate, substrate temperature, and dielectric surface chemistry. We find that modifying silicon oxide dielectrics with a hydrophobic monolayer alters the PTCBI growth habit, changing the unit cell contact plane as measured by grazing incidence X-ray diffraction (GIXD), and changing the molecular orientation as measured by near edge X-ray absorption fine structure spectroscopy (NEXAFS). Changes in the microstructure are closely correlated to changes in OTFT performance. Optimization of deposition conditions results in carrier mobility values of ~1.0 x 10
-2 cm
2/V-s, V
th~ -4V and an I
on/I
off ratio ~ 10
5 for devices tested in ambient conditions.[1]C. W. Tang, "Two-layer organic photovoltaic cell," Applied Physics Letters, vol. 48, pp. 183-185, 1986.Electronic email:
[email protected]9:00 PM - AA11.50
Effect of Polymer Gate Dielectric Surface Viscoelasticity on Pentacene Thin-Film Transistor Performance.
Choongik Kim 1 , Antonio Facchetti 1 , Tobin Marks 1
1 Chemistry, Northwestern University, Evanston , Illinois, United States
Show AbstractPentacene is the most investigated semiconductor for organic thin-film transistors (OTFTs), and enhanced understanding of pentacene-based OTFT performance has invariably advanced the organic electronics field. We report here the crucial influence of the polymer gate dielectric glass transition temperature (Tg) on pentacene film growth mode, microstructure, and the current-voltage characteristics of the resulting OTFTs. Nanoscopically-confined thin polymer films are known to exhibit depressed glass-transition temperatures versus the corresponding bulk materials, and we demonstrate here that pentacene films grown on polymer gate dielectrics at temperatures well below their bulk Tg exhibit distinctive morphological/microstructural transitions and dramatic OTFT performance discontinuities at well-defined growth temperatures [herein defined as the surface glass transition temperature Tg(s)] characteristic of the particular underlying macromolecular architecture and independent of the dielectric film thickness. The results argue that realistic OTFT response models must take into account this fundamental polymer property, and that TFT measurements represent a new probe of polymer surface viscoelastic properties.
9:00 PM - AA11.51
High Performance Organic Thin Film Transistors through Solution Sheared Deposition of Organic Semiconductors.
Hector Becerril-Garcia 1 , Zihong Liu 2 , Jason Locklin 3 , Mark Roberts 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Electrical Engineering, Stanford University, Stanford, California, United States, 3 Chemistry, University of Georgia, Athens, Georgia, United States
Show AbstractSolution processing of organic semiconductors offers a versatile and inexpensive route for the fabrication of organic thin-film transistors (OTFT). To date, however, the performance of solution processed OTFTs is often dwarfed by equivalent devices produced from the same active material using more sophisticated and relatively expensive vacuum deposition methods. In an effort to bridge this performance gap we have developed a simple solution deposition technique that allows for the fabrication of highly crystalline thin films of small molecule organic semiconductors. These films are comprised of elongated crystalline grains with high aspect ratios, such that the long axis lays parallel to the shearing direction. OTFTs fabricated with sheared thin films lead to field-effect mobilities as high as 0.13 cm2/Vs with on/off ratios > 10E6, substantially surpassing those measured on comparable devices fabricated by drop-casting.
9:00 PM - AA11.52
Organic Single Crystal Transistors Gated by Electric Double Layers in Ionic Liquid.
R. Hirahara 1 , S. Ono 2 , Y. Tominari 1 , S. Seki 2 , Jun Takeya 1
1 , Osaka University, Toyonaka Japan, 2 , CRIEPI, Tokyo Japan
Show Abstract Material combination in organic field-effect transistors is being intensively explored because the interfacial phenomena are crucial in determining their device performances both at the semiconductor-electrode and the semiconductor-insulator boundaries. It has been reported that gating organic transistors with electric double layers (EDL) of electrolytes is advantageous in injecting high-density carriers with the application of minimum gate voltage [1-4]. The drawback of such devices, however, has been their relatively large hysteresis because commonly used polymer electrolytes suffer relatively slow ionic diffusion before forming the EDLs. In this presentation, we disclose the EDL device structure incorporating ionic liquid as the electrolyte layer. Since the low viscosity of the ionic liquid enables rapid diffusion of the ions (typically in ~ 1 μs), one can expect to realize very low-power and quick-switching devices. We first fabricate a ditch structure using an elastomeric rubber stamp of poly-demethylsiloxane (PDMS). After gold electrodes are vacuum deposited, a rubrene single crystal is attached to bridge the two electrodes at the top surface. Filling a drop of ionic liquid in the ditch, the EDL transistor is completed. The ionic-liquid layer is gated by applying small voltages to the other electrode at the bottom surface of the PDMS. We used 1-ethyl3-methylimidazolium bis(trifluoromethanesulfonyl)imide for the material of the ionic liquid in this experiment. Typical transistor characteristics appear with negligible hysteresis for the above devices. The mobility values are estimated to be in the range of 0.1-2 cm2/Vs as a statistics of several similarly prepared samples. The ionic-liquid gating can be a promising technology to realize fast-switching and low-power organic transistors, searching for compounds that emerge higher performances incorporated in organic single crystal transistors among varieties of ionic liquid that have been synthesized so far.[1] M. Panzer, C. D. Frisbie et al., Appl. Phys. Lett. 88, 203504 (2006).[2] J. Takeya et al., Appl. Phys. Lett. 88, 112102 (2006).[3] H. Shimotani et al., Appl. Phys. Lett. 89, 203501 (2006).[4] J. Lee, C. D. Frisbie et al., J. Am. Chem. Soc. 129, 4532 (2007).
9:00 PM - AA11.53
High-mobility Organic Single-crystal Transistors with Amorphous Fluoropolymer Gate Insulators.
M. Uno 1 , Y. Tominari 2 , Jun Takeya 2
1 , TRI, Izumi Japan, 2 , Osaka University, Toyonaka Japan
Show AbstractOne of the most intriguing questions on organic field-effect transistors (OFETs) is their maximum performance achievable with somewhat idealized devices. Technically, it is essential for putting them into practical use for high-speed applications such as logic-circuit components. Recent development of single-crystal OFETs has allowed us to induce carriers at atomically flat organic crystal surfaces without grain boundaries and to study their transport in the devices with various gate dielectric insulators. Indeed, it is demonstrated that rubrene single crystal OFETs with SiO2 gate insulators have intrinsically high mobility up to 40 cm2/Vs, as the result of the four-terminal measurements avoiding their contact resistances of the source and drain electrodes. Their performances as practical devices, however, were not necessarily satisfactory because of low reproducibility of the performances, poor saturation in the output characteristics, and lower mobility (less than 20 cm2/Vs) in the two-terminal evaluation. In this presentation, we report an improved balance among the above various performances of rubrene single crystal transistors incorporating a highly water- and oil-repellent fluoropolymer gate dielectric. We purchased solution of the fluoropolymer resin CytopTM (CTL-809NMX) from Asahi Glass Company, and spin-coated it on 300-nm thick SiO2/n-Si substrates. Since admixture of water and/or other impurities at the semiconductor/insulator interfaces is reported to be harmful for the transistor performances, the excellent repellency of the amorphous fluoroplymer is useful. Unfortunately, however, reports on the use of the material are still limited because the large repellency itself causes difficulties in fabrication process; for example, poor adhesion of photo resist and noble metal electrodes. We improved the adhesion by etching the surface of the Cytop film, and annealed at 200 C to recover the smoothness and repellency of the surface after forming the electrodes on the Cytop film. The recovery is confirmed by the measurement of water contact angles and by AFM images. Rubrene single crystals are grown to thin platelets with the thickness about 1 μm by the physical vapor deposition technique, and are laminated on the Cytop surface to prepare the single-crystal OFETs.The output characteristics show fairly good saturation with mobility values of 15-25 cm2/Vs, being reproduced for the statistics of 7 good-looking devices. Estimation of the mobility gives almost identical values in the linear regions. Moreover, the on-off ratio exceeds 104 and subthreshold swing is typically ~ 1 V/decade for the 1.2-μm thick Cytop layer. As the result, the above high performances of the single crystal transistors suggests that the water- and oil-repellent polymer gate insulators are useful to compose high-mobility single crystal transistors that are suited for practical applications.
9:00 PM - AA11.55
Large Grain Size Solution Processed TIPS-pentacene Thin Films.
Songtao Wo 1 , Randall Headrick 1 , Frederic Sansoz 2 , John Anthony 3
1 Department of Physics and Materials Science Program, University of Vermont, Burlington, Vermont, United States, 2 School of Engineering and Materials Science Program, University of Vermont, Burlington, Vermont, United States, 3 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractWe present a study of the grain structure and morphology of TIPS-pentacene thin film transistor using a novel hollow pen solution method. By using this method we can control the orientation of the thin film crystal and the crystal grain size, thus we intentionally arrange the crystal to be across the channel or parallel with the channel. Microscope with polarized and dark field was used to study the morphology and structure of the thin film transistor. We demonstrate that large domains are obtained for TIPS-pentacene films deposited from 0.5 - 4.0 weight percent solutions with toluene. Crystalline grains with (001) orientation are observed to grow with sizes that can exceed one millimeter along the writing direction. TIPS-pentacene film grown by this method yielded significant variations in morphology by tuning the concentration and speed, resulting in different mobility that could be correlated with the crystal structure and orientation. A preferred azimuthal orientation is also selected by the process, resulting in anisotropic field effect transistor mobility in the films. The anisotropy of the mobility of different orientation for TIPS-pentacene is between 3~10. The best field effect mobility we got is 0.11cm2/v.s. Atomic force microscope was used to investigate the grain boundary, layer by layer structure was found indicating the growth mechanism.
9:00 PM - AA11.56
Water-stable Organic Thin-film Transistors as Tools for Chemical and Biological Sensing.
Mark Roberts 1 , Stefan Mannsfeld 1 , Nuria Queralto 1 , Colin Reese 1 , Jason Locklin 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractThe development of portable, robust sensors functional in aqueous media would greatly benefit the health industry, environmental monitoring, and national defense. Organic thin-film transistors (OTFTs) can provide an ideal platform for inexpensive, single-use chemical and biological sensors due to their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. However, most OTFTs reported to-date are not suitable for operation in aqueous media due to high operating voltages and semiconductor degradation. We developed low-operating voltage OTFTs using novel low-temperature cross-linkable gate dielectric films compatible with vapor and solution deposited semiconductors. With pentacene active layers, we achieved mobilities as high as 3 cm2/Vs and on/off ratios of 106 at a gate bias of 2 V. We also fabricated OTFTs with a new p-channel material, 5,5’-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2’-bithiophene (DDFTTF), which displayed stable operation under aqueous conditions over more than 104 electrical cycles. Our DDFTTF OTFTs showed drain current response to analytes ranging from explosives and chemical warfare agents to biologically significant molecules. Thus far, we observed a response to concentrations on the order of parts per billion of trinitrobenzene, methylphosphonic acid, cysteine and glucose in water. The mechanism for OTFT sensing was investigated by varying device parameters including semiconductor thickness and roughness and operating conditions, such as analyte concentration and gate bias. With the demonstration of water-stable, low-voltage OTFTs, we have overcome a substantial hurdle for the realization of chemical and biological sensors.
9:00 PM - AA11.57
Closer Look at Microstructural Changes in Zone-Cast Pentacene TFTs upon Bias-Stress and Annealing.
Claudia Duffy 1 , Mary Vickers 2 , Masahiko Ando 3 , Takashi Minakata 4 , Henning Sirringhaus 1
1 Cavendish Laboratory, Cambridge University, Cambridge United Kingdom, 2 Department of Materials Science and Metallurgy, Cambridge University, Cambridge United Kingdom, 3 , Hitachi Cambridge Laboratory, Cambridge United Kingdom, 4 , Asahi-KASEI Corporation, Fuji-shi, Shizuoka-ken Japan
Show AbstractWe investigate the role of the microstructural changes induced by bias-stress and annealing on the stability of pentacene TFTs deposited by zone-casting from a solution of un-substituted pentacene molecules in a chlorinated solvent The devices were fabricated in bottom-gate, top-contact configuration on oxidized silicon substrates, using either the thermal SiO2 (300nm) or a thin insertion layer of benzocyclobutene (BCB) (70nm) as a gate dielectric and having field-effect mobilities of 0.2-0.5 cm2/Vs. Polarized optical microscopy showed that, independent of the dielectric type, pentacene films grow as large crystalline domains aligned along the zone-casting direction. We studied the bias-stress induced Vth (threshold voltage) shift as a function of pentacene morphology before and after a controlled annealing treatment. Upon application of a negative gate bias of -40V for 20000s to the pristine devices, the Vth shift was greater than |3V| for TFTs using the BCB dielectric and considerably higher for pristine TFTs made on SiO2. Annealing both types of devices at 130C for 1h in nitrogen caused a reduction of the Vth by |14V| associated with a two-fold increase in carrier mobility. Applying the same bias-stress protocol to the annealed devices led to a reduced Vth shift of less than |1V|. Although reversible, both before and after annealing, the higher Vth observed in pristine films is associated with the presence of many shallow traps at the interface pentacene-dielectric, the pristine film being in an energetically unstable morphological configuration. The drastic reduction of the Vth upon annealing indicates a significant reduction of the interface trapping sites due to a molecular re-arrangement at the interface. We used specular X-ray diffraction to probe the microstructural changes induced by annealing and investigated theta-2theta diffractograms and rocking curves taken at the 1st pentacene out-of-plane reflection. Pristine pentacene films deposited onto SiO2 had a d-spacing of 14.320A, which was reduced to 14.316A after annealing (values averaged over the 7 pentacene 00l reflections and above the experimental error of 0.001deg). The rocking curves showed a narrowing of the FWHM from 0.036deg to 0.028deg, which indicates an improvement of the out-of-plane molecular alignment. However, the pentacene films grown on BCB exhibited two polymorphs at 14.332A and 14.14A, which were decreased to 14.324A and 14.13A after annealing. The annealing treatment narrowed the rocking peak from 0.090deg to 0.084deg and decreased the intensity of the 14.14A reflection. These results indicate that the reduction of the d-spacing and an overall improvement of the molecular interfacial order are beneficial for charge transport. Correlating interfacial structure with bias-stress behavior is an important subject in order to understand defects responsible for charge trapping in organic TFTs.
9:00 PM - AA11.58
Vertical Stacking of Organic Thin Film Transistors.
Soon-min Seo 2 , Changhoon Baek 1 , Hyewon Kang 1 , Keon-kook Han 1 , Taegeun Kwon 1 , Hong Lee 1
2 , Kyungwon University, Seongnam Korea (the Republic of), 1 , Seoul National University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - AA11.59
High Performance Polymer TFT With No Self-Assembled Monolayer.
Flora Li 1 , Parul Dhagat 2 , Ghassan Jabbour 2 , Hanna Haverinen 3 , Iain McCulloch 4 , Martin Heeney 4 , Arokia Nathan 5
1 Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada, 2 School of Materials and Flexible Display Center, Arizona State University, Tempe, Arizona, United States, 3 Department of Electrical and Information Engineering, University of Oulu, Oulu Finland, 4 , Merck Chemicals, Southampton United Kingdom, 5 London Centre for Nanotechnology, University College London, London United Kingdom
Show AbstractSurface modification of the gate dielectric by self-assembled monolayers (SAMs) has traditionally been indispensable in the fabrication of organic thin film transistors (TFTs). The SAM is thought to play a decisive role in device performance, particularly in establishing molecular ordering of the active semiconductor layer, often giving rise to several-fold improvements in field-effect mobility. In contrast to current practices, we demonstrate that by judicious choice of gate dielectric and active layer, one can mitigate the need for SAMs thereby reducing fabrication complexities without compromising TFT performance. This paper reports on solution-processed polymer TFTs with mobilities comparable to high performance counterparts despite the absence of dielectric surface pre-treatment. An effective field-effect mobility of 0.1 cm2/V-s was obtained with polythiophene-based polymer transistors on silicon-rich silicon nitride gate dielectric without SAM treatment. The impact of film composition, surface roughness and nucleation sites of the silicon nitride gate dielectric on device performance are examined in this paper.
9:00 PM - AA11.6
Ambipolar Tetraceno[2,3-b]thiophene Derivatives for Organic TFTs.
Anna Reichardt 1 , Ming Tang 1 , Nobuyuki Miyaki 2 , Zhenan Bao 2
1 Chemistry , Stanford University, Palo Alto, California, United States, 2 Chemical Engineering, Stanford University, Palo Alto , California, United States
Show AbstractWe have made a series of fluoro and chloro substituted tetraceno[2,3-b]thiophene molecules, in an attempt to make n-type organic thin-film transistors OTFTs by tuning molecular orbital levels. Tetraceno[2,3-b]thiophene has a mobility as high as 0.47 cm2V-1s-1, and a stability which exceeds that of pentacene. These molecules are characterized by elemental analysis, mass spectrometry, differential scanning calorimetry, cyclic voltametry and thermogravimetric analysis. Thin films of these linear molecules were characterized by ultra-violet spectroscopy, x-ray diffraction, atomic force microscopy (AFM) and field-effect transistor measurements. Surprisingly, one molecule has showed both p and n-type behaviour, though mobility is not high at 10-4 cm2V-1s-1. We’re in the process of optimizing the mobilities and synthesizing other derivatives of these asymmetric linear acenes.
9:00 PM - AA11.60
Real vs. Measured Surface Potentials in Organic Field Effect Transistors.
Dimitri Charrier 1 , Edsger Smits 2 , Simon Mathijssen 1 2 , Dago de Leeuw 2 , Martijn Kemerink 1 , René Janssen 1
1 , Eindhoven University of Technology, Eindhoven, Noord Brabant, Netherlands, 2 , Philips Research Laboratories, Eindhoven, Noord Brabant, Netherlands
Show Abstract9:00 PM - AA11.61
Solution-Processed n-Channel Organic Transistors Enabled by Rylene Semiconductors and UV-Curable Polymeric Dielectrics.
He Yan 1 , Antonio Facchettie 2 , Shaofeng Lu 1 , Tobin Marks 2
1 , Polyera Corporation, Skokie, Illinois, United States, 2 , Northwestern University, Evanston, Illinois, United States
Show Abstract9:00 PM - AA11.62
Dielectric Effects on the Charge Transport in High-Mobility Microcrystalline Conjugated Polymers.
Ni Zhao 1 , Jui-Fen Chang 1 , Yong-Young Noh 1 , Henning Sirringhaus 1 , Ian Mcculloch 2 3 , Matin Heeney 2 4
1 , Cavendish Laboratory, Cambridge United Kingdom, 2 , Merck Chemicals, Southampton United Kingdom, 3 Department of chemistry, Imperial College London, London United Kingdom, 4 Materials, Queen Mary Univeristy of London, London United Kingdom
Show Abstract9:00 PM - AA11.63
Characterization of TIPS-Pentacene Thin Films by Area Detector-based X-ray Scattering.
Lin Yang 1 , Hoichang Yang 2 , Se Hyun Kim 3 , Chan Eon Park 3
1 , Brookhaven National Laboratory, Upton, New York, United States, 2 , Rensselaer Polytechnic Institute, Troy, New York, United States, 3 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractX-ray scattering, particularly grazing incidence diffraction (GID), characterization of thin films of conjugated organic materials is an important tool for correlating molecular packing within the material with its electrical properties and device performance. Here, we report results from area detector-based GID and scanning transmission x-ray diffraction measurements on TIPS-pentacene crystals prepared on a substrate by spin casting followed by solvent annealing. Lattice constants of the crystal were derived from GID data and transmission data provided local in-plane orientation of the crystals. We found the c-axis of the crystal perpendicular to the substrate, suggesting that all molecules are also oriented perpendicular to the substrate. Details of the x-ray measurements and comparison to traditional GID using point or linear detectors will be discussed. Device performance data will also be presented.
9:00 PM - AA11.64
Charge Trapping at the Gate Dielectric in Organic Transistors Visualized in Real Time and Space.
Simon Mathijssen 1 2 , Martijn Kemerink 1 , Abhinav Sharma 1 , Michael Coelle 3 , Peter Bobbert 1 , Rene Janssen 1 , Dago Leeuw 2
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands, 3 , Merck Chemicals, Southampton United Kingdom
Show Abstract9:00 PM - AA11.66
Anisotropic Charge Transport in Organic Single Crystals Based on Dipolar Molecules.
Beatrice Fraboni 1 , Antonio Castaldini 1 , Anna Cavallini 1 , Alessandro Fraleoni Morgera 2 , Leonardo Setti 2 , Ivan Mencarelli 2 , Cristina Femoni 3
1 Physics, University of Bologna, Bologna Italy, 2 of Industrial and Materials Chemistry, University of Bologna, Bologna Italy, 3 of Physical and Inorganic Chemistry, University of Bologna, Bologna Italy
Show AbstractCharge transport processes in organic materials are highly sensitive to the material deposition and device fabrication conditions that, in turn, affect to a major extent the molecular packing and interface defective states. In order to correlate the electrical properties of organic semiconductors to their molecular functionality, it is necessary to control the effects of impurity and disorder induced defects. It is has been shown that organic single crystals offer the possibility of studying the intrinsic properties of organic molecules thanks to their high purity and molecular order, and single crystal field effect transistors (SCFET) are a powerful tool in this respect. The observation of anisotropic transport in single crystals, due to the anisotropic packing of the organic molecules, provides an assessment of the occurrence of band-like transport processes.We studied the anisotropic charge transport properties of solution-grown organic single crystals based on a dipolar molecule 4HCB (4-hydroxy-cyanobenzene) by field effect devices, by spectral photocurrent (PC) analyses and by X-ray diffraction analyses. The presence of an intrinsic molecular dipole differently affects the flow of charge carriers along the two main planar crystal axes, thus altering the charge transport anisotropy induced by the molecular π-orbitals stacking. The exposure to visible light induced a different effect along the two directions, that we have attributed to the presence and alignment of the electron-attractor cyano group. We suggests that this lattice structure originates trapping centers that behave like deep donors and that are more efficient along one of the two main planar axes. A band of optically activated deep traps was identified by PC analyses and we advance an hypothesis on the nature of the observed band of deep trapping states. The mobility anisotropy observed in the dark between the two axes is markedly reduced under optical excitation. We ascribe this behaviour to the intrinsic 4HCB molecular electric dipole, that can be electrically activated by optical excitation and that is differently oriented along the two crystallographic axes, thus differently affecting the current flow along the two directions.The results here presented suggest that future studies on carrier transport of SCFETs should consider the presence of molecular static dipoles, even of non intrinsic ones (i.e. of the so-called induced dipoles), as one of the parameters that can affect the device transport behaviour, in addition to anisotropic molecular packing and fabrication-induced defects .
9:00 PM - AA11.67
Pentacene Thin Films On Diamond Surfaces: Effect Of Surface Termination.
Wojciech Gajewski 1 , Stefan Schiefer 2 , Martin Huth 2 , Bert Nickel 2 , Martin Stutzmann 1 , Jose Garrido 1
1 Walter Schottky Institute, Technical University Munich, Garching Germany, 2 Soft Condensed Matter Group, Ludwig-Maximilians University Munich, Munich Germany
Show Abstract9:00 PM - AA11.7
Trialkylsilylethynyl Substituted Tetraceno[2,3-b]thiophene and anthraceno[2,3-b]thiophene Molecules for OTFTs.
Ming Tang 1 , Anna Reichardt 1 , Theo Siegrist 3 , Zhenan Bao 2
1 Chemistry, Stanford University, Stanford, California, United States, 3 , Lucent Technologies, Bell Laboratories, Murray Hill, New Jersey, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractWith the commercialization of organic light emitting diodes (OLEDs), one might imagine all-organic backplanes powered by organic transistors. However structure property relationships for organic thin-film transistors (OTFTs) are still not clear. One class of promising molecules are the trialkylsilylethynyl substituted molecules, for example, John Anthony’s 6,13-triisopropylsilylethynylpentacene. In this study, we examined the relationship between the bulkiness of the trialkylsilylethynyl group and the conjugated core. Specifically, a series of trialkylsilylethynyl substituted tetraceno[2,3-b]thiophene and anthraceno[2,3-b]thiophene molecules were made varying the ratio of the bulkiness of the susbtituent to the length of the conjugated core. The alkyl groups were triisopropylsilyl (TIPS), triethylsilyl (TES) and trimethylsilyl (TMS) respectively. After purification, top-contact evaporated OTFTs were made. We found little correlation between the crystal structures of the molecules and their thin film properties. Mobilities as high as 1 cm2V-1s-1 were found for the TIPS-ethynyltetraceno[2,3-b]thiophene.
9:00 PM - AA11.70
Oligothiophenes with a Diketopyrrolopyrrole Chromophoric Core for Solution Processed Organic Field Effect Transistors and Photovoltaic Cells.
Arnold Tamayo 1 , Mananya Tantiwiwat 2 , Bright Walker 1 , Xuan-Dung Dang 1 , Thuc-Quyen Nguyen 1
1 Center for Polymers and Organic Solids and Department of Chemistry and Biochemistry, University of California - Santa Barbara, Santa Barbara, California, United States, 2 Department of Physics, University of California - Santa Barbara, Santa Barbara, California, United States
Show Abstract9:00 PM - AA11.71
Structural and Electrical Characteristics of Solution-Processed Blend Semiconductors for Organic Thin Film Transistors.
Nayool Shin 1 , Jihoon Kang 1 , Do Jang 1 , Vivek Prabhu 2 , Dean DeLongchamp 2 , Eric Lin 2 , Do Yoon 1
1 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 Polymers Division, National Institute of Standards & Technology, Gaithersburg, Maryland, United States
Show AbstractWe investigated the structural and electrical characteristics of solution-processed blend films of 6,13-bis(triisopropylethynyl)pentacene (TIPS pentacene) and poly(α-methylstyrene) as an active layer in organic thin film transistors. The concentration profile of the TIPS pentacene within thin blend films was determined with the neutron reflectivity experiment, and the crystalline structure of TIPS pentacene in segregated layer was observed with grazing incidence wide angle X-ray scattering. We fabricated thin film transistors with a bottom-gate bottom-contact device configuration and obtained a stable charge carrier mobility of ca. 0.3 cm2/Vs in ambient condition by optimizing the matrix polymer and film forming conditions. The underlying mechanism for such excellent electrical properties, significantly better than those of pure TIPS pentacene film, was delineated on the basis of the measured structural characteristics of the blend semiconductor films.
9:00 PM - AA11.72
Low-voltage-driven Pentacene Thin-film Transistor with an Organic-inorganic Nano-hybrid Dielectric.
Kwang H Lee 1 , Jeong-M Choi 1 , Seongil Im 1 , Byoung H Lee 2 , Kyo K Im 2 , Myung M Sung 2 , Seungjun Lee 3
1 Physics, Yonsei university, Seoul Korea (the Republic of), 2 Chemistry, Hanyang university, Seoul Korea (the Republic of), 3 Electronic information engineering, Ewha womans university, Seoul Korea (the Republic of)
Show Abstract9:00 PM - AA11.73
Ambipolar Light Emitting Transistor of Highly Photoluminescent Organic Single Crystal.
Satria Bisri 1 , Taishi Takenobu 1 , Yohei Yomogida 1 , Shu Hotta 2 , Yoshi Iwasa 1
1 Institute for Materials Research, Tohoku University, Sendai Japan, 2 Department of Polymer Science and Technology, Kyoto Institute of Technology, Kyoto, Kyoto Japan
Show Abstract9:00 PM - AA11.74
Schottky-diodes and MES-FETs Using Organic Single Crystals.
Toshihiko Kaji 1 2 , Taishi Takenobu 1 2 3 , Kazuhiro Watanabe 1 , Alberto Morpurgo 3 , Yoshihiro Iwasa 1 2
1 Institute for Materials Research, Tohoku University, Sendai Japan, 2 CREST, Japan Science and Technology Corporation, Kawaguchi Japan, 3 Kavli Institute of Nanoscience, Delft University of Technology, Delft Netherlands
Show AbstractOrganic single crystal transistors have uncovered various intrinsic properties of organic transistors, such as the transport along the interfaces and charge injection through contacts. Particular attention has been paid on the metal/insulator/semiconductor(MIS)-type field effect transistors and their Ohmic contacts. Here in this paper, we report intrinsic nature of Shottky contacts on organic single crystals and field effect transistor devices using Schottky contacts; metal-semiconductor field effect transistors (MES-FETs).Organic Schottky diodes were originally studied in 1960-1970’s for application to diodes, solar cells, and electroluminescence devices. However, their performance was significantly limited by roughness/inhomogenity and instability of organic thin films. Our approach is to improve Schottky-type devices by utilizing organic crystals, because recent studies have reported successful replacements of organic films by organic crystals for the use in organic MIS-FETs. We found that a contact constructed on a rubrene single crystal using In metal behaves as an ideal Schottky diode with the on/off ratio of more than 105. Analysis in terms of thermionic emission model revealed that the ideality factor of 1.6 with the Schottky barrier height of 1.0 eV. This barrier height is close to the energy difference between the work function of In and the LUMO of rubrene (1 eV). Using In contact as a gate electrode, we succeeded in demonstrating first organic single crystal MES-FET, with the on/off ratio of 104. From the transfer characteristics, we were able to show that the depletion layer is expanded to more than 1 μm, depending on the gate voltage. These findings indicate that organic single crystals, which have produced rich knowledge of intrinsic transport phenomena in organic MIS-FETs, offer novel opportunities to investigate devices based on Schottky contacts as well.
9:00 PM - AA11.75
Novel Block Copolymers and Homopolymers Based on Perylene Bisimide Derivatives as n-type Material.
Sven Huettner 1 2 , Michael Sommer 2 , Ullrich Steiner 1 , Mukundan Thelakkat 2
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 Applied Functional Polymers, University Bayreuth, Bayreuth Germany
Show Abstract9:00 PM - AA11.76
Vertical and Lateral Organic Heterostructure based Ambipolar Organic Thin Film Transistors.
Samarendra Singh 1 , Prashant Sonar 1 , Alan Sellinger 1 , Ananth Dodabalapur 1 2
1 , Institute of Materials Research and Engineering (IMRE), Singapore Singapore, 2 , University of Texas at Austin, Austin, Texas, United States
Show Abstract9:00 PM - AA11.78
Predicting Charge Mobilities in Disordered Organic Films.
Joe Kwiatkowski 1 , James Kirkpatrick 1 , Jenny Nelson 1 , Hong Li 2 , Jean-Luc Bredas 2 , Wolfgang Wenzel 3 , Christian Lennartz 4
1 EXSS, Physics, Imperial College London, London United Kingdom, 2 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Institute für Nanotechnologie, University of Karlsruhe, Karlsruhe Germany, 4 Computational Chemistry and Biology, BASF, Ludwigshafen Germany
Show AbstractThe successful exploitation of organic electronic materials for applications in light emission, thin film electronics and energy conversion depends upon the systematic improvement of charge mobility in conjugated molecular films. Such progress demands design rules that are capable of relating charge transport properties in these intrinsically disordered materials to both their chemical composition and the nature of their molecular packing. Existing charge transport models, which rely on simplified descriptions of morphology and chemical structure, are useful for the experimental characterisation of transport properties but offer no predictive capability. In this work we present a novel method for predicting charge transport properties by explicitly considering the full molecular details of disordered molecular films. Our calculations are able to reproduce experimental mobilities without the need for any fitting parameters. We use a multi-scale method that involves three levels of simulation: firstly we use a combination of Monte-Carlo and Molecular Dynamic methods to simulate the molecular packing within a film; secondly we calculate the intermolecular charge transfer rates with Density Functional Theory (DFT) and finally we simulate field effect transistors or time-of-flight mobility measurements with a kinetic Monte-Carlo method. A key factor influencing the magnitude and temperature dependence of mobility is the energetic driving force in the charge transfer reaction. We treat this in two different ways: either directly from DFT calculations on a pair of molecules or by calculating the electrostatic interactions between a molecule and its surroundings.We focus on charge transport in tris(8-hydroxyquinoline) aluminium (Alq3) and C60. In the case of Alq3 we reproduce experimental values for charge mobilities in disordered films and demonstrate that the morphology is critical in defining the charge transport characteristics, consistent with experimental observations. We compare simulated photo-current transients in both crystalline and disordered Alq3 and demonstrate that in the latter case the charge mobility is limited by the energetic trapping effect of a small fraction of molecules.To probe the effect of polycrystallinity on transport we simulate the morphology of C60 films grown at different rates by vacuum sublimation. As observed experimentally, slower deposition rates give films with a higher level of crystallinity. We correlate the simulated transport properties with the morphology. Therefore, from the mobility measured in a C60 film we are able to comment on its likely microstructure.
9:00 PM - AA11.79
Investigation and Modeling of the Dielectric/semiconductor Interface Properties in Organic Field-effect Transistors.
Emanuele Orgiu 1 2 , Mohammad Taki 1 , Annalisa Bonfiglio 1 2 , Beatrice Fraboni 3 , Erika Scavetta 4 , Simone Locci 1 2 5 , Giuseppe Scarpa 5 , Christoph Erlen 5 , Paolo Lugli 5
1 DIEE, department of Electrical and Electronic engineering, University of Cagliari, Cagliari Italy, 2 , INFM Centre S3 "nanoStructures and bioSystems at Surfaces", Modena Italy, 3 Department of Physics, University of Bologna, Bologna Italy, 4 Department of Physical and Inorganic Chemistry, University of Bologna, Bologna Italy, 5 Institute for Nanoelectronics, Technische Universitaet Muenchen, Munich Germany
Show AbstractThe interface between an organic semiconductor and a dielectric layer plays a key role in the performance of the Organic Thin-Film Transistors (OTFTs)[1] because the charge carriers flow inside the first few nanometers in the channel. Therefore, engineering an interface that promotes synergistic interactions between the semiconductor and dielectric is essential in achieving optimum FET performance. Recently, many studies on this interface [1,2] have been published showing that it is still controversial which are the precise phenomena that rule charge transport at this interface; this is especially true for electrons. Therefore further investigation is still due. In this work we aim at contributing to the picture of the charge trapping, charge transport and the defects at the interface by means of either Capacitance-Voltage measurements with varying the frequency on Metal-Insulator-Semiconductor (MIS) structures and Ids-Vds/Ids-Vgs characterization on OTFTs devices. Moreover, photocurrent and electrochemical impedance spectroscopy characterization have been employed to give more information about the nature of the trap states for both electrons and holes at the interface between dielectric and semiconductor. Different organic dielectric materials have been employed as an insulating layer for MIS and FET structures, namely PVA, PVA with Ammonium Dichromate, PVP, polydimethylsiloxane (PDMS) and polymethylsilsesquioxane (pMSSQ). Both pentacene and sexithiophene have been employed as semiconducting layer. Semiconductor films were grown simultaneously both on MIS and OTFTs in the same environmental conditions. Significative differences of electrical parameters as threshold voltage and hysteresis have been measured in transistors which have as dielectric layer a thin PVA film when a cross-linking agent for this polymeric dielectric (Ammonium Dichromate) has been added during assembly. . This aspect, still under study, is particularly interesting as it suggests the possibility of playing with the composition of the dielectric layer for modulating interface properties.A transistor model that includes traps action in the channel has been developed and used to fit experimental results. [1] L. Chua, J. Zaumseil, J. Chang, E. Ou, P. Ho, H. Sirringhaus and R. H. Friend, Nature 434 (2005) 194 [2] T. B. Singh, G. Horowitz, and N. S. Sariciftci, Adv. Mater. 17 (2005) 2315
9:00 PM - AA11.8
Anistropic and Enhanced FET Performance in Rubbing-Aligned CuPc Thin Film Transistor with Top Gate Structure.
Masanao Goto 1 , Yohei Watakabe 1 , Hideo Takezoe 1 , Ken Ishikawa 1
1 Dept. of Organic and Polymeric Materials, Tokyo Inst. of Tech., Meguro, Tokyo, Japan
Show Abstract9:00 PM - AA11.80
Variable Temperature Microscopic Characterization of Charge Trapping in Polycrystalline Pentacene.
Michael Jaquith 1 , John Marohn 1
1 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractThe microscopic mechanisms by which charges trap in organic electronic materials are poorly understood. We have recently shown that electric force microscopy (EFM) can be used to follow local trap formation kinetics in working pentacene thin-film transistors. We find that the trap formation rate is hole-concentration dependent, strongly suggesting a trapping mechanism involving one or more chemical reactions, or at least, we hypothesized, an activated process [M. Jaquith et al., J. Phys. Chem. B 111 (27) 7711 (2007)]. Here we use variable temperature to show direct evidence that the mechanism involves an activated process. Furthermore, we find a significant change in the trapping distribution throughout the film as temperature increases. We will report on our efforts to determine the activation energy site-by-site in a working thin-film pentacene transistor by variable temperature electric force microscopy.
9:00 PM - AA11.81
The Effect of Nanoscale Dielectric Morphology on the Microstructure and Carrier Mobility of High-performance Polythiophene Semiconductors.
Youngsuk Jung 1 , R. Joseph Kline 1 , Eric Lin 1 , Steven Hudson 1 , Kyle Alvine 1 , Hyun Wook Ro 1 , Christopher Soles 1 , Iain McCulloch 2 , Dean DeLongchamp 3 , Martin Heeney 1
1 Polymers Division, NIST, Gaithersburg, Maryland, United States, 2 , Queen Mary, University of London, London United Kingdom, 3 , Imperial College of London, London United Kingdom
Show Abstract9:00 PM - AA11.82
Fabrication of polycrystalline thin films of liquid crystalline materials by solution process and its application to OFETs.
Hiroaki Iino 1 2 , Jun-ichi Hanna 1 2
1 Imaging Science and Engineering Lab, Tokyo Institute of Technology, Yokohama Japan, 2 , JST-CREST, Yokohama Japan
Show Abstract Organic polycrystalline semiconductors such as Pentacene and Oligothiophenes have been extensively studied for OFETs because of the high FET mobility of 0.1 - 1 cm2/Vs. However, specific natures of organic materials are not always made the best use of in the OFETs: in fact, they are often fabricated by vacuum evaporation of these materials, which is due to easy molecular alignment in vacuum evaporation and low solubility of these materials.With this recognition, we paid attention to liquid crystalline materials, which have an anisotropic molecular shape enhanced by long alkyl chains, exhibit the self-organization in mesophase, and have high solubility in common organic solvents. By the best use of step-wise molecular ordering in liquid crystalline materials, i.e., crystallization via self-organized mesophase, we succeeded in controlling the formation of grain boundaries in resulting polycrystalline thin films. In fact, we could observe non-dispersive transient photocurrents in polycrystalline thin films of liquid crystalline materials (α,ω-dioctylterthiophene) in spite of thick sample, 15 μm (ref. H. Iino and J.Hanna, Jpn. J. Appl. Phys. 45, L870 (2006).).In this presentation, we prepared polycrystalline thin films of various liquid crystalline materials including α,ω-dihexylquaterthipohene (6-QTP-6) and N, N’-ditridecylperylene diimide (13-Per-13) by solution process, fabricated top-contact bottom-gate OFETs on SiO2/Si-substrates, and evaluated the OFETs performance.We realized that liquid crystalline materials help fabricating uniform thin films on the substrate when spin-coated at the temperature range of liquid crystalline phase, and furthermore that the grain boundaries are controlled not so as to across the conduction channels formed by self-aligned π-conjugated aromatic cores in liquid crystalline molecules. In fact, the OFETs fabricated by spin-coating with 6-QTP-6 and 13-Per-13 exhibited field-effect hole and electron mobility of 0.06cm2/Vs and 0.009 cm2/Vs, respectively. Furthermore, the OFET of fabricated with 13-Per-13 exhibited a high electron mobility of 0.14cm2/Vs after thermal annealing of the film at a liquid crystalline temperature of 220oC for an hour.Therefore, we conclude that liquid crystalline material is a good candidate for quality polycrystalline thin films for OFETs.
9:00 PM - AA11.83
Probing of carrier injection and related phenomena in pentacene field effect transistor by electric field induced optical second harmonic generation measurement
Takaaki Manaka 1 , Eunju Lim 1 , Ryousuke Tamura 1 , Mitsumasa Iwamoto 1
1 Department of physical Electronics, Tokyo Institute of Technology, Tokyo Japan
Show AbstractInterest in the dynamical behavior of carriers in organic materials is motivated by possible applications that include organic field effect transistor (OFET), organic electro-luminescent (EL) device, organic photo-conductor (OPC), etc., and modeling of carrier transport and trapping phenomena. Recent experimental studies on OFETs revealed that accumulated charges at the OFET channel are mainly injected from source electrode, and they are then conveyed along the channel by the electric field. This experimental finding motivated us to study carrier injection and its related phenomena in organic films, and to study the performance of OFETs as a Maxell-Wagner (MW) effect element. We here report an optical technique that allows electric field distribution in organic materials to be probed nondestructively and selectively by measuring the second harmonic generation (SHG) signal activated by the static electric field formed in pentacene FET with Au source and drain electrodes. In more detail, this second harmonic generation originates from quantum coupling between electrons in pentacene and laser beam in the presence of local dc electric field. The distribution of Laplace and Poisson electric fields formed in pentacene films before and after carrier injection from the electrodes are determined by the enhanced SHG signals, and succeeding carrier accumulation and trapping are discussed in terms of the established electric field distribution. Interestingly, the electric field relaxation at the source electrode by injected carriers has been revealed by the SHGs. This result rationalizes our proposed analysis on pentacene FET as a MW effect element. Furthermore, both hole and electron injections from the Au electrodes are suggested under stress biasing, though it takes a long time for electron injection, e.g., c.a. 1000 sec. Of particularly interest is in that hole injection assisted by injected electrons is confirmed when pentacene FETs are positively biased by gate-voltage for a long time. The hysteresis behavior observed in the C-V characteristics supports this assisted hole-injection. Furthermore, to clarify the injected carrier motion in organic films, we used the time-resolved microscopic optical SHG (TRM-SHG) that allows dynamical carrier motion in organic materials directly and selectively to be probed and visualized. The TRM-SHG experiments using the pentacene FET with SiO2 gate insulator reveals the dynamical changes of SHG intensity profiles arising from the organic materials. The results are of particular interest because the dynamical hole-injection into pentacene from the Au electrode was directly visualized on the order of nano-second scale.
9:00 PM - AA11.84
Studying of Carrier Mechanism in Pentacene FET with Contact Resistance by Optical Second Harmonic Generation Measurements.
Eunju Lim 1 , Ryosuke Tamura 1 , Takaaki Manaka 1 , Mitsumasa Iwamoto 1
1 Physical Electronics, Tokyo Institute of Technology, Tokyo Japan
Show Abstract9:00 PM - AA11.85
Influence of Central Metal Ions on Nonlinear Optical and Two-Photon Absorption Properties of Push-Pull Transition Metal Porphyrins.
Paresh Ray 1
1 , Jackson State University, Jackson, Mississippi, United States
Show Abstract9:00 PM - AA11.86
Length-Dependent Transport in Molecular Junctions Based on SAMs of Aromatic Monothiols and Aromatic Dithiols: Effect of Contact Type and Metal Work Function.
BongSoo Kim 1 , SeongHo Choi 1 , C. Frisbie 2 1
1 Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, United States, 2 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractUnderstanding of charge transport at the interface of metal/organic molecules is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity at the interface include the nature of metal-molecule contacts and the electronic structure of the molecular backbone as well as the type of metal. We have synthesized aromatic acenes (benzene, naphthalene, anthracene, tetracene) monothiols and dithiols, and formed self-assembled monolayers (SAMs). The SAMs were extensively characterized by ellipsometry, X-ray photoelectron spectroscopy (XPS), and reflection-absorption infrared spectroscopy (RAIRS). Their electrical properties were investigated using conducting probe atomic force microscopy (CP-AFM). Nanoscopic tunnel junctions were formed by contacting Au-, Pt-, or Ag-coated AFM tips to SAMs of the molecules on Au, Pt, or Ag substrates. Resistance (R) in a low bias regime increased exponentially with molecular length (s) in both cases according to the expected relationship, R = R0exp(βs). The length dependent attenuation factor (β) is 0.3~0.5/Å for both aromatic series, while contact resistance (R0) of aromatic dithiols on gold is much less than that of aromatic monothiols. The resistance versus length data were also used to calculate transmission values for each type of contact (e.g., Au-S-C, Au/H-C, etc.) and the transmission per acene ring. Ultraviolet photoelectron spectroscopy (UPS) measurements were used to determine the electronic structure of these interfaces. We find good correlation between measured EHOMO-EFermi offset, metal work function, and contact resistance.
9:00 PM - AA11.87
Conjugated Microporous Polymer Networks.
Andrew Cooper 1 2 , Jia-Xing Jiang 1 , Fabing Su 1 , Yaroslav Khimyak 1 , Neil Campbell 2 , Abbie Trewin 1
1 Department of Chemistry, University of Liverpool, Liverpool United Kingdom, 2 Centre for Materials Discovery, University of Liverpool, Liverpool United Kingdom
Show Abstract9:00 PM - AA11.88
Innovative Nano-Imprint Controlled Electropolymerization (NICE) Process for Generation of Arbitrarily-Designed Conducting Polymer (CP) Nanostructures.
Yixuan Chen 1 , Yi Luo 1
1 Electrical & Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractConducting polymers (CPs) have very useful electronic, mechanical and optical properties, e.g. variable high conductivities by doping, flexibility, transparence, tunable bandgaps, etc. These remarkable properties can result in a wide range of applications including sensors, organic transistors, actuators, LEDs, etc. However, after quite extensive studies, we have found that currently there are only very few methods for CP nanostructure fabrication; and they have quit limited capabilities. As a consequence, current organic electronic devices are usually characterized as being large, slow; and they usually require high operating voltages. It is quite clear that the best of CP materials have not yet been fully explored and utilized.In this talk, we introduce an innovative technique which is capable to create arbitrarily-designed nanostructures of CPs – Nano-Imprint Controlled Eletropolymerization (NICE). Combining the best of both top-down and bottom-up approaches, this very effective and parallel technique is capable of production of very well defined nanoscale CP materials that have very favorable electrical and chemical properties. This novel approach consists of two basic steps: first, imprinting on a fluid monomer precursor with a mold to create completely isolated “liquid” patterns on the target substrate; Next, electrochemically polymerizing (i.e. curing) the monomer while the mold is still in place. The mold is reusable to generate the same pattern on different target substrates for mass production. We will present some results of fabricating high-quality CP nano-materials with this method.The produced CP nanowires are well-defined and down to the scale of sub-100nm. Moreover, the generated nano-scale CP structures can be of arbitrarily-designed pattern, including single, parallel and branching straight wires, circles, and squares and so on, with connecting lines to metal pads. Furthermore, the NICE process is also able to generate CP structures in contact with pre-deposited metal pads on the target substrate, eliminating the subsequent difficult processes for electrical connection. Our preliminary measurements show that the as-grown CP wires have conductivities in the range of tens S/cm which can be improved further by many ways such as post-growth doping. The NICE-generated CP nanostructures can have various applications such as highly sensitive sensors, organic transistors and circuits.
9:00 PM - AA11.89
Induced Order in PPVs for Detection of Ionizing Radiation.
Tiffany Wilson 1 2 , Douglas Chinn 3 , Michael King 1 , F. Patrick Doty 1
1 , Sandia National Laboratory, Livermore, California, United States, 2 Dept. of Chemical and Biomolecular Eng., The Ohio State University, Columbus, Ohio, United States, 3 , Sandia National Laboratory, Albuquerque, New Mexico, United States
Show Abstract9:00 PM - AA11.9
Synthesis of a New Polythienylenevinylene Derivative for Organic Thin-Film Transistors with Oxidative Stability and Low Threshold Voltage.
Bogyu Lim 1 , Kang-Jun Baeg 1 , Hyung-Gu Jeong 1 , Seok-Ju Kang 1 , Doojin Vak 1 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - AA11.90
Control of Polymorphism during Pentacene Thin Film Growth on SiO2 using a High Density Supersonic Source.
Sukwon Hong 1 , Tushar Desai 1 , Aram Amassian 2 , Arthur Woll 3 , Detlef Smilgies 3 , James Engstrom 1
1 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - AA11.91
In-Situ Optical Absorbance Spectroscopy of Molecular Energy Levels in Molecular Devices.
Andrew Bonifas 1 2 3
1 Materials Science & Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Chemistry, The Ohio State University, Columbus, Ohio, United States, 3 , The National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show Abstract9:00 PM - AA11.92
Conductive Polymers of Aminophenylporphyrins: Mechanisms for Polymerization and Electronic Conductivity.
Michael Walter 1 , Carl Wamser 1
1 Chemistry, Portland State University, Portland, Oregon, United States
Show Abstract Porphyrins substituted at meso positions with aminophenyl groups undergo oxidative electropolymerization in a process analogous to the formation of polyaniline. Porphyrins that successfully generate polymer films on the electrode include those tetrasubstituted with four para-aminophenyl groups, trisubstituted, or trans-disubstituted, but not cis-disubstituted or monosubstituted. The polymerization process is monitored independently by cyclic voltammetry, absorption spectroscopy, and an electrochemical quartz crystal microbalance. The mechanism is considered analogous to aniline polymerization, except that attack of electrophilic nitrogens must occur at ortho positions of another aminophenyl group. Reflectance FT-IR and resonance Raman spectroscopy detected the presence of diphenylamine, dihydrophenazine, and phenazine linkages in the porphyrin polymer film from tetra(4-aminophenyl)porphyrin (TAPP). TAPP polymerized by cyclic voltammetry (0.0 to +1.0 V vs Ag/AgCl) in dichloromethane (DCM) with added pyridine gradually passivates, i.e., electronic conductivity diminishes and polymer growth levels off (the films are light yellow). Without added pyridine, the polymerization evolves acid and the growth is sustained somewhat longer. Constant potential voltammetry (+1.0 V) in DCM with pyridine leads to sustained conductivity and ultimately thick black films. It has also been observed that free-floating films of poly-TAPP can be formed at an aqueous/DCM interface using an aqueous oxidant (ammonium persulfate) and monomer TAPP in DCM. Polymer films that maintained electroactivity showed primarily diphenylamine and dihydrophenazine linkages, while phenazine linkages were prevalent in films where passivation and loss of electrochemical activity had occurred. It is proposed that over-oxidation to the phenazine structures leads to loss of electronic conductivity, analogous to formation of the pernigraniline form of polyaniline. The morphology of poly-TAPP is a highly interconnected nanofibrous network, with fiber diameters in the range of 40-100 nm, with somewhat different structures depending on the polymerization conditions. These films are currently being explored as nanoporous scaffolds for the construction of bulk heterojunction solar cells where the interfacial contact region is controlled by the poly-TAPP film structure.
9:00 PM - AA11.93
Facile Method for Preparation of Silver/conductive Polymer Nanocomposites.
Gururaj Neelgund 1 , Erika Hrehorova 1 , Margaret Joyce 1 , Valery Bliznyuk 1
1 Department of Paper Engineering, Chemical Engineering and Imaging, Western Michigan University, Kalmazoo, Michigan, United States
Show Abstract9:00 PM - AA11.94
Flexible and Transparent All-Organic Ambipolar Field Effect Transistors for Large Area Complementary Electronics.
Piero Cosseddu 1 2 , Annalisa Bonfiglio 1 2 , Ingo Salzmann 3 , Jurgen P. Rabe 3 , Norbert Koch 3
1 Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy, 2 S3 nanoStructures and bioSystems at Surfaces, CNR- INFM, Modena Italy, 3 Institut für Physik, Humboldt-Universität zu Berlin, Berlin Germany
Show Abstract9:00 PM - AA11.96
Solution-processed N-type Semiconductor Materials Based on Perylene Diimide Derivatives for Organic Thin Film Transistors
Szu-Ying Chen 1 , Tri-Rung Yew 1
1 Department of Materials Science and Engineering, , National Tsing-Hua University, Hsinchu Taiwan
Show Abstract9:00 PM - AA11.97
Experimental and First Principle Theoretical Study of Optical Absorption of Poly(thienylenevinylene) Conjugated Polymers
Alexander Gavrilenko 1 , Vladimir Gavrilenko 1 , Carl Bonner 1 , Taina Matos 1 , Sam-Shajing Sun 1 , Cheng Zhang 1
1 Center for Materials Research, Norfolk State University, Norfolk, Virginia, United States
Show AbstractOptical absorption spectra of poly(thienylenevinylene) (PTV) conjugated polymers fabricated at different conditions are measured at room temperature in spectral range 400 to 800 nm. A dominant peak located at 575 nm and a prominent shoulder at 614 nm are observed. Linear optical absorption is calculated from first principles within Random Phase Approximation (RPA) picture. Equilibrium atomic geometries, electronic structure in the form of projected density of states (PDOS), and optical absorption spectra of PTV are studied by first principles density functional theory (DFT). The conjugated PTV polymer is modeled as a three dimensional infinite molecular crystal; this is a non traditional approach for complex organic systems which is shown to be very promising especially for optical modeling and simulations. Electron energy structure is obtained through self-consistent solution of eigen-energy problem using ab initio ultrasoft pseudopotentials and generalized gradient approximation method. Comparative analysis of experimental and theoretical data indicates that interchain interactions substantially affect electronic structure and optical absorption of PTV conjugated polymers. It is demonstrated that dominant contribution to the optical excitations of PTV in experimentally studied visible spectral range are related to the delocalized electrons within the polymer chains. Results of this work are discussed in conjunction with conjugated polymers engineering for photovoltaic applications.