Symposium Organizers
Ana Claudia Arias Palo Alto Research Center
J. Devin MacKenzie Add-Vision, Inc.
Alberto Salleo Stanford University
Nir Tessler Technion-Israel Institute of Technology
O1: Synthesis of Materials I
Session Chairs
Tuesday PM, April 10, 2007
Room 2002 (Moscone West)
9:00 AM - O1.1
Small-Molecule Design for Organic Electronics.
John Anthony 1
1 Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractThe ease with which small-molecule organic semiconductors can be functionalized allows a single chromophore framework to be tuned for use in a myriad of electronic applications. Further, substitution can dramatically increase the solubility of aromatic compounds, allowing device fabrication by solution processing. Such functionalization must take careful account of how substitution of the chromophore will change intermolecular interaction in thin films and crystals, as well as the desirability of such interactions in specific applications. Using 5-ringed acenes and heteroacenes as the chromophore, this report will describe the use of a straightforward functionalization approach to create organic materials tuned for use in organic transistors, organic solar cells and organic light emitting diodes. For transistors, extensive two-dimensional π-overlap was critical to obtaining high thin film mobility, yielding µ = 1.5 cm2 / Vs for solution-cast films of a simple substituted pentacene compound. Further tuning of the aromatic chromophore, coupled with the use of arenethiol treatments on gold electrodes to direct the crystallization of the organic semiconductor, have yielded solution-cast transistors with mobility greater than 4.0 cm2 / Vs, demonstrating the unique opportunities available to enhance the properties of organic semiconductor films grown from solution. In the case of bulk heterojunction organic solar cells, donors with strong π-stacking interactions crystallized too readily, causing complete segregation of donor and acceptor leading to poor photovoltaic performance. The addition of substituents that slightly disrupted π-stacking interactions yielded solar cells with power conversion efficiencies greater than 1%. Further disruption of π-stacking in these systems again led to poor photovoltaic performance. For light-emitting diodes, any close contacts between chromophore atoms in the solid state can lead to broadening of the emission spectrum and decreased device performance. In this case, functionalization that leads to complete isolation of the chromophore yielded the best results, with red-emission efficiency greater than 3%.
9:15 AM - O1.2
Solvent Vapor Annealing Improves Device Characteristics of Transistors with Solution-Processable Triethylsilylethynyl Antradithiophene.
Kimberly Dickey 1 , John Anthony 2 , Lynn Loo 1
1 Chemical Engineering, University of Texas at Austin, Austin, Texas, United States, 2 Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractThe development of organic semiconductors is driven by the promise of low-cost device applications. To fully realize cost-effective organic electronics, solution-processable materials need to be developed. While several solution-processable materials have been demonstrated, these materials often suffer from significantly reduced carrier mobilities due to defects and grain boundaries introduced during the deposition process. We have been studying triethylsilylethynyl anthradithiophene (TES ADT), a solution-processable, p-type organic semiconductor. Transistors fabricated with spun-cast TES ADT exhibit low carrier mobilities (0.002 cm2/V-s), low on-off current ratios and significant current-voltage hysterisis. Subjecting the fabricated transistors to dichloroethane solvent vapor annealing, however, yields average carrier mobilities of 0.2 cm2/V-s, high on-off current ratios (104-5), and significantly reduces the current-voltage hysterisis. This dramatic improvement in transistor performance is solvent choice dependent, and can be directly correlated with morphological transformations in the thin films. Specifically, the solvent vapor is able to partition into the organic semiconductor thin film during the annealing process to induce structural rearrangment. TES ADT crystallizes as a consequence. The improvement in device characiteristics appear to be directly correlated with the grain size within the thin films. The polarity of the solvent, on the other hand, has a dramatic impact on the threshold voltage. In general, polar solvents can induce the presence of a dipole barrier at the organic semiconductor-dielectric interface, thereby increasing the threshold voltage. Annealing with non-polar solvents, like hexanes, results in a threshold voltage that is close to zero.
9:30 AM - O1.3
Theoretical studies of P3HT, PQT, and PBTTT
John Northrup 1
1 , Palo Alto Research Center, Palo Alto, California, United States
Show AbstractThere is considerable interest in soluble polymer semiconductors such as P3HT [1], PQT [2] and PBTTT [3]. These materials have hole mobilities exceeding 0.1 cm2/Vs. As a consequence there is an impetus to determine the atomic and electronic structure of the crystalline lamellae exhibited by these materials. It remains a very challenging problem to determine the structure from experiment alone. Energy minimization calculations were therefore performed using the density functional theory to determine the atomic structure of these materials. A tilting of the plane containing the polymer backbone is found to be energetically favorable for all three materials. It is argued that this tilting is a general feature of this class of materials, and that this tilting has a significant affect on the electronic and optical properties. The impact of the deviation from ideal cofacial pi-stacking on the hole mobility will be discussed within a simple model of the scattering.[4] [1]Z. Bao, A. Dodabalopur, and A. J. Lovinger APL 69, 4108 (1996).[2]B. S. Ong, Y. Wu, P. Liu, and S. Gardner, J. Am. Chem. Soc. 126, 3378 (2004).[3]I. McCulloch et al. Nature Materials 5, 328 (2006).[4]R. A. Street, J. E. Northrup and A. Salleo, Phys. Rev. B 71, 165202 (2005).
9:45 AM - O1.4
Comparative Study of Charge Transport in High-mobility Microcrystalline Conjugated Polymers
Ni Zhao 1 , Jui-Fen Chang 1 , Marta Tello 1 , Henning Sirringhaus 1 , Iain McCulloch 2 , Martin Heeney 2
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 , Merck Chemicals, Chilworth Science Park, Southampton United Kingdom
Show AbstractThe performance of polymer field-effect transistors (FETs) crucially depends on the intermolecular interaction in the semiconductor polymer, as it dominates the charge conduction in the active layer. Recently a new class of semiconducting liquid-crystalline polymers, poly(2,5-bis(3-alkylthiophen-2-yl) thieno[3,2-b]thiophene) (PBTTT) [1], was reported with a considerably increased mobility (up to 0.6 cm2/Vs) as compared with the prototype microcrystalline conjugated polymer, poly(3-hexylthiophene) (P3HT). It is believed that such an increase of the mobility is due to the enhanced intermolecular interaction in the PBTTT thin films. However, microscopic charge transport studies that support the correlation between the microstructure and the mobility are still lacking. Here we present a comparative study on the nature of the charge transport species in the P3HT and PBTTT systems with the aim of understanding the difference of the charge carrier mobility from a molecular scale. It has been discovered recently that upon crystallizing from the melting phase a highly ordered film structure consisting of aligned long nanoribbons can be achieved in PBTTT films [2]. These nanoribbons are arrays of π-π stacked extended chain lamellae with a width that approximates to single molecular length. We focus our studies on this morphology because, unlike the chain folding arrangement in P3HT nanoribbons, the PBTTT molecules are able to form a system with fewer folding-induced intrachain defects and enhanced intermolecular interaction. By using charge modulation spectroscopy we observe that the charge transfer (CT) transition in PBTTT films with the nanoribbons exhibits the signature of strong electronic coupling as a result of interchain polaron delocalization and narrower band width as compared to P3HT films. We also perform Scanning Kelvin probe microscopy to directly measure the local field-effect mobility in the PBTTT FETs without being affected by the contact resistance. This allows us to obtain a clear correlation between the microstructure and the charge conduction in the semiconducting polymer films. [1] Iain McCulloch, et. al., Nature Materials 5, 328, (2006). [2] Dean M. DeLongchamp, et. al., 2006 MRS spring meeting, M4.5
10:00 AM - **O1.5
The Development of pBTTT.
Iain McCulloch 1 , Clare Bailey 1 , Martin Heeney 1 , Maxim Shkunov 1 , David Sparrowe 1 , Steve Tierney 1 , Michael Chabinye 2 , R. Joseph Kline 3
1 , Merck Chemicals, Southampton United Kingdom, 2 , Palo Alto Research Center, Palo Alto, California, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThe further development of organic semiconductors to be utilised in field-effect transistors (OFETs) for incorporation into lightweight, flexible electronic devices, requires high performing, solution processable materials. Polymeric semiconductors offer an attractive combination in terms of appropriate solution rheology for printing processes, mechanical flexibility for rollable processing and applications, but their electrical performance has been significantly lower than amorphous silicon, limiting their application. In this work, we report the design, synthesis and characterisation of a range of liquid crystalline pi conjugated thieno[3,2-b]thiophene co-polymers (pBTTT) exhibiting high charge carrier mobilities. A detailed study of the polymer thin film morphology by both AFM and XRD reveals an extremely ordered and oriented microstructure. Field effect transistors were fabricated, and their performance and lifetimes will be discussed.
10:30 AM - O1.6
Reliable Suzuki Chemistry For Functionalised Polythiophene Synthesis.
Simon Higgins 1 , Iain Liversedge 1 , Iain McCulloch 2 , Mark Giles 2 , Martin Heeney 2
1 Chemistry, University of Liverpool, Liverpool United Kingdom, 2 , Merck Chemicals Ltd., Southampton United Kingdom
Show AbstractRegioregular polyalkylthiophenes and their derivatives have been widely-studied as polymeric organic semiconductors. Synthetic chemists strive to improve the already impressive field effect mobilies of these materials, while increasing their stability to ambient conditions and their purity. We recently described the application of functionalised polyalkylthiophene derivatives in biosensing (see M. Fouzi et al., Chem. Comm. 2004, 2314, and S.J. Higgins et al., Mater. Res. Soc. Symp. Proc. 871E, Warrendale, PA, 2005, I1.3). Additionally, functionalised polyalkylthiophene derivatives designed for improved intermolecular interaction (e.g. via H-bonding) might show improved transistor performance (higher field effect mobility). Therefore, in spite of the success of the conventional Grignard and organozinc-based routes to the parent polyalkylthiophenes, it is important to devise new chemistry, applicable to the synthesis of functionalised derivatives.We have therefore investigated Pd complexes of bulky, electron-rich phosphines as catalysts for the polymerisation of halothiophene boronate ester derivatives via Suzuki coupling. With the best catalysts, we can obtain >98% regioregular polyalkylthiophenes with useful molecular weights (MW 17000). Importantly, we have also found that it is possible to synthesise the key AB-type monomers by Ir-catalysed boronation of 2-halo-3-alkylthiophenes. This is significant because it means that we can synthesise the monomer without recourse to strong organolithium bases, making the route truly functional group-tolerant.
10:45 AM - O1.7
Non-conjugated Polymer Hosts with High Triplet Energies
Lan Deng 1 , Biwu Ma 2 , Jean Frechet 1 2
1 , Department of Chemsitry, University of California, Berkeley, California, United States, 2 , Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract Incorporating carbazole units into polymers to make high triplet energy host materials is essential for efficient solution-processible OLEDs. When carbazole units are used as building blocks in the main chain of the conjugated polymers, the resulting polymer hosts typically have triplet energies around 2.5-2.6 eV. Host materials with higher triplet energies are difficult to obtain using this approach due to the decrease of triplet energy with the increase of conjugation length. We hereby report a different way to incorporate carbazole units into polymers through side-chains. Using the new approach, the triplet energies of the polymers can remain the same as that of their small molecular building blocks. Polymers with triplet energies as high as 3.0 eV have been obtained. OLEDs have been fabricated, showing external quantum efficiencies of 4-5 %.
11:30 AM - **O1.8
Synthetic And Processing Strategies To High Performance Organic Thin-Film Transistors.
Antonio Facchetti 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractThe general design and synthesis of new rylenes and oligo/thiophenes functionalized with a variety of phenacyl, alkylcarbonyl, and perfluoroalkylcarbonyl is presented. These organic semiconductors exhibit low-lying LUMOs allowing efficient electron injection/transport under ambient atmosphere. Organic thin-film transistors (OTFTs) fabricated via conventional methods exhibit electron mobilities as high as 2 cm^2 V^-1 s^-1 for vapor-deposited films and 0.3 cm^2 V^-1 s^-1 for solution-cast films, with current modulation as high as 10^8. Furthermore, unconventional processing approaches to addressing the realization of well-defined supramolecular architectures with precise, nanometer-level control of bulk electronic properties are described. The ultimate goal is the realization of inexpensive electronic circuits employing unconventional materials classes and simple fabrication techniques.
12:00 PM - O1.9
In-plane Molecular Alignment in Thin Films of Pentacene Grown by Solution Casting and Performance of Thin Film Transistors.
Takashi Minakata 1 , Yutaka Natsume 1 , Yuji Yoshida 2 , Yasukiyo Ueda 3
1 Central R&D Laboratories, Asahi-KASEI Corporation, Fuji-shi, Shizuoka-ken, Japan, 2 , National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan, 3 , Kobe University, Kobe, Hyogo, Japan
Show Abstract12:15 PM - O1.10
High Field-Effect Mobilities for Diblock Copolymers of rr-P3HT
Genevieve Sauve 1 , Richard McCullough 1
1 Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractOne important challenge in the field of organic field-effect transistors (OFET) is to better understand the relationship between structure and transport properties of conjugated polymers. Much work has focused on regioregular poly(3-hexylthiophene) (rr-P3HT), because of its excellent electrical properties and ease of synthesis. To further tune the structure and properties of rr-P3HT, we have synthesized several well-defined diblock copolymers of rr-P3HT, where the second block is a coil polymer. Here we present surprising results of high mobilities for our diblock copolymers of rr-P3HT and poly(methylacrylate) (PMA), despite the presence of various amounts of insulating PMA. This was observed when the silicon dioxide dielectric layer was treated with octyltrichlorosilane. In contrast, mobilities went down with PMA content when the silicon dioxide was not treated. It is therefore possible to control the self-assembly of these block copolymers at the dielectric layer-semiconductor interface by using different SiO2 surface treatments. These results also demonstrate the promise of using block copolymers as organic semiconductors in plastic electronics.
O2: Materials Physics and Characterization I
Session Chairs
Tuesday PM, April 10, 2007
Room 2002 (Moscone West)
2:30 PM - **O2.1
Spectroelectrochemistry Studies of the Charging and Discharging of Single Conjugated-Polymer Nanoparticles.
Paul Barbara 1 , Rodrigo Palacios 1 , Allen Bard 1 , Fu-Ren Fan 1
1 Department of Chemistry and Biochemistry, Center for Nano and Molecular Science and Technology, University of Texas, Austin, Texas, United States
Show AbstractThe unique ability of single molecule spectroelectrochemisry, SMS-EC, to unravel complex electrochemical process in heterogeneous media is used to study the oxidation of nanoparticles of the practically important conjugated polymer poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Two main processes have been observed, an irreversible chemical reaction on the surface of the oxidized F8BT nanoparticles, and a reversible hole-injection charging process. The latter occurs primarily by initial injection of shallow (untrapped) holes, but soon after the injection, the holes become deeply trapped. Good agreement between experimental data and simulations strongly supports the presence of deep traps in the studied nanoparticles and highlights the ability of SMS-EC to study deep traps in organic materials at the nanoscale.
3:00 PM - O2.2
On the Validity of Continuum Drift-Diffusion Device Models for Organic Light Emitting Diodes.
B. Ramachandhran 1 , M. Uijttewaal 2 , M. Bouhassoune 1 , P. Bobbert 1 , R. De Groot 2 , G. De Wijs 2 , Reinder Coehoorn 3 4
1 Polymer Physics Group, Department of Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 IMM, Radboud University, Nijmegen Netherlands, 3 , Philips Research Laboratories, Eindhoven Netherlands, 4 Molecular Materials and Nanosystems Group, Department of Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands
Show AbstractIt has recently been demonstrated by Pasveer et al. that the energetic disorder of amorphous polymer organic semiconductors used in organic light emitting devices (OLEDs) can give rise to a strong carrier concentration dependence of the mobility, and that this can have a significant effect on the current density (J) versus voltage (V) curves of polymer-based hole-only devices [1]. In ref. 1, the mobility was obtained from a numerically exact Master-Equation (ME) approach, assuming a Gaussian density of states (DOS). For obtaining the J(V) curves, a continuum solution of the coupled transport and Poisson equations was used, assuming ohmic contacts and neglecting diffusion. However, one might question under which conditions such a continuum approach is valid. In actual OLEDs, large carrier concentration gradients can occur near external and internal interfaces, and the current density can have a strongly filamentary nature [2,3]. The conductivity is then a non-local property, so that the concepts of ‘mobility’ and ‘diffusion coefficient’ could no longer be useful. In this contribution, we present the results of a numerical investigation of the validity of the continuum approach, by making a comparison with the results from ME calculations for complete metal/organic/metal devices. We have varied the (uncorrelated) Gaussian disorder (width σ), the layer thicknesses (20 to 100 nm), and the interface conditions. For the continuum drift-diffusion calculations, the compact expressions for the mobility given in [1] were used, with the diffusion coefficients as obtained using the generalized Einstein equation. We confirm the highly filamentary nature of the current density and present a quantification of the current density distribution. We also present a 3D visualization of the non-uniform current density. Even for highly disordered systems (σ = 6kBT) and for layer thicknesses of only 20 nm, for which the current is shown to be strongly filamentary, the continuum model is found to be surprisingly well obeyed. We have investigated the effect of injection barriers (and image potentials), by making use of two types of models: (i) by assuming a fixed carrier concentration at the outermost planes of the organic layer (as in [2]), (ii) by self-consistently calculating all carrier concentrations in all layers (beyond [2]). A critical comparison is given of the calculated J(V) curves and the predictions as obtained from a continuum drift-diffusion model, including the Scott-Malliaras [4] and Arkhipov [5] models for injection in an ordered system and in a system with a Gaussian DOS, respectively. [1].W.F. Pasveer et al., Phys. Rev. Lett. 94 (2005), 206601.[2].E. Tutiš, I. Batistić and D. Berner, Phys. Rev. B 70, 161202 (2004).[3].K.D. Meisel et al., Phys. Stat. Sol. 3, 267 (2006).[4].J.C. Scott and G.G. Malliaras, Chem. Phys. Lett. 299, 115 (1999).[5].V.I. Arkhipov et al., J. Appl. Phys. 84, 848 (1998).
3:15 PM - O2.3
Photoinduced Charge Transfer at Hybrid Semiconductor Interfaces.
Juan Cabanillas-Gonzalez 1 , Hans Egelhaaf 1 , Guglielmo Lanzani 1 , Alberto Brambilla 1 , Marco Finazzi 1 , Lamberto Duo 1 , Franco Ciccacci 1
1 Physics, Politecnico di Milano, Milano Italy
Show Abstract3:30 PM - **O2.4
Comparing Theory and Hypotheses to Electric Force Microscope Data: Are We Thinking about Injection, Trapping, and Transport Correctly in Organic Electronic Materials?
John Marohn 1 , Michael Jaquith 1 , Showkat Yazdanian 1 , Michael Chabinyc 2 , Tse Ng 1 2
1 Dept. of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 2 , Palo Alto Research Center, Palo Alto, California, United States
Show AbstractIn order to determine energetic disorder’s role in facilitating charge injection from gold into a molecularly doped polymer, we have examined the dependence of current on local electric field, measured using electric force microscopy (EFM), at temperatures ranging from 250 to 330 K. From these data we infer, for the first time in a single experiment, the temperature dependence of the main factors governing charge injection: the electric-field induced lowering of the image-potential barrier, the interfacial charge density, and the mobility. In this system, the Schottky effect is anomolously large, and the interfacial charge density is larger than expected and strikingly non-Arhennius. Our analysis indicates that these effects are all a consequence of the Gaussian density of states in the organic.We have also used EFM to study charge trapping in as-deposited polycrystalline pentacene. In films with comparatively large grains, EFM images reveal that charges trap primarily at grains near the pentacene-metal interface. By contrast, in films with small grains, EFM images show that long-lived holes traps are dispersed throughout the film. These traps, however, do not appear to be associated with grain boundaries, as is often assumed. We find that charge traps require 100’s of milliseconds to form, implying that traps do not form instantaneously by the emptying of levels but instead arise from a reaction having finite activation energy. These experiments show that a new, improved microscopic view of charge injection and trapping can be gained by making scanned probe measurements of local electrostatic potential and capacitance. It would therefore be exciting if a local measurement of carrier mobility or diffusion constant could also be made. We have recently shown that low-spring-constant cantilevers can be used to observe electric field fluctuations arising from thermal dielectric fluctuations in polymers. In this talk we will show that ultrasensitive cantilevers can likewise measure the local charge diffusion constant via the effect of the associated electric field fluctuations on cantilever frequency and ringdown time. Analytical scaling laws and numerical simulations of the electric field power spectrum resulting from the thermal motion of holes in a N,N'-diphenyl-N-N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) / polystyrene field effect transistor suggest that the local hole diffusion constant can be inferred in this system from measurements of cantilever frequency and ringdown time as a function of tip height and charge density. Progress towards directly testing the Einstein relation by comparing the locally measured charge diffusion constant to the bulk field effect transistor mobility will be reported.
4:30 PM - O2.5
Effects of Different Length-Scale Organic-Organic Heterojunctions on Photophysical Processes.
Annamaria Petrozza 1 , Igor Avilov 2 , Richard Friend 1 , Ji-Seon Kim 1
1 Physics, University of Cambridge, Cambridge United Kingdom, 2 Laboratory for Chemistry of Novel Materials, University of Mons-Hainaut, Mons Belgium
Show AbstractRecent works have highlighted the importance of organic-organic semiconductor heterojunctions, in particular interchain heterojunctions formed in blend systems. However, there has been very little work to address the photophysical processes which depend on the nature of the organic interfaces (i.e. interchain vs intrachain) and the length-scale of these interfaces (i.e. from micron-scale in blends to molecular-scale in random copolymers). Here, we report the detailed studies of photophysical processes including triplet absorption and decay dynamics on a range of well-controlled organic-organic interfaces, which are formed both as a function of the polymer chain-length (molecular weight, MW) and of the different nature of molecular units present within the polymer chain.We have studied spin-coated films of poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) of different molecular weights (Mn = 9K – 255K) both in the pristine and annealed states and F8BT random copolymer (RC) synthesised by random copolymerisation with Poly(9,9’-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB), which result in the presence of both strong electron acceptor and donor units within the polymer chain.We observe that the triplet absorption increases in the pristine films as the MW of F8BT decreases; upon annealing above the glass transition temperature of F8BT triplet dynamics differ depending on the MW: high MW samples show a strong enhancement of the triplet absorption, whereas the lowest MW sample shows a decrease in the intensity of the PIA signal; RC present a much stronger triplet absorption and the main T1-->Tn transition band is blue-shifted compared both to pure F8BT and F8BT:TFB blends. We conclude that the triplet generation efficiency based on the inter-system crossing (ISC) mechanism is significantly reduced in high molecular weight pristine films, and the triplet lifetimes are enhanced upon annealing. We consider that these changes are strongly correlated with a solid state packing of F8BT molecules which varies as a function of molecular weight and upon annealing, i.e. different packing structures will induce different relative population of the emissive states which are differently coupled to the non-emissive triplet states.Previous studies have demonstrated that the ISC process in blends systems is efficiently mediated by interfaces induced excited states, such as very short lived inter-chain charge transfer (CT) states and long lived exciplex states. We consider that in the RC the ISC process is even more efficient than in blend systems due to its long lived intra-chain CT state and a molecular-scale phase separation.Our results clearly demonstrate the importance of the nature of the organic-organic interfaces and their length-scale on photophysical processes. A potential control of these well-defined structures provides a powerful tool for the smart design of organic semiconductors for diversified applications.
4:45 PM - **O2.6
Microstructure Foundations of High Carrier Mobility in Polymers.
Dean DeLongchamp 1 , R. Joseph Kline 1 , Eric Lin 1 , Daniel Fischer 1 , Youngsuk Jung 1 , Lee Richter 1 , Iain McCulloch 2 , Martin Heeney 2 , John Northrup 3
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Merck Chemicals, Southampton United Kingdom, 3 , Palo Alto Research Center, Southampton, California, United States
Show Abstract5:15 PM - O2.7
Potential Mapping on Organic Devices: 3D Simulations and Experiments.
Dimitri Charrier 1 , Martijn Kemerink 1 , Barry Smalbrugge 2 , Tjibbe de Vries 2 , Rene Janssen 1
1 Applied physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 COBRA Research Institute, Eindhoven University of Technology, Eindhoven Netherlands
Show Abstract5:30 PM - O2.8
Vibrational Spectroscopy Reveals Field and Electrochemical Doping in Organic Thin Film Transistors.
Loren Kaake 1 , Ying Zou 1 , Matthew Panzer 2 , C. Frisbie 2 , Xiaoyang Zhu 1
1 Chemistry, University of Minnesota, Minneapolis, Minnesota, United States, 2 Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe nature of charge carriers and traps in organic thin film transistors (OTFTs) has been a subject of much speculation and debate. We have developed a simple strategy to record vibrational spectra of buried interfaces in OTFTs. In this approach, an OTFT is fabricated on an IR waveguide (Si or Ge) and the evanescent field probes the molecular species in the transistor under gate bias. In particular, we use a polymer electrolyte dielectric material to obtain a very high electric field at the dielectric-organic interface. In the case of a PTCDI based OTFT, we show molecular evidence for two distinctive regions of doping: at low gate voltages (< 3V), the organic semiconductor is under field doping as evidenced by a reversible loss of vibrational intensity associated with the neutral PTCDI molecule. At high gate voltage (3-7 V), the film is electrochemically doped, as evidenced by the conversion of neutral PTCDI molecules into anions. The electrochemical doping region is less reversible and is accompanied by chemical changes to the organic film. This demonstrates the strategy as capable of elucidating the chemical consequences of gate doping.
5:45 PM - O2.9
Electrical Properties of Conjugated Polymers under High Pressure
Sheena Elliott 1 , Jeroen Cottaar 1 , Neil Greenham 1
1 Department of Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractThe application of hydrostatic pressure allows the role of intermolecular interactions in conjugated polymers to be studied. We use a pressure cell to operate a polymer light-emitting diode (LED) or transistor at up to 8 kbar. In contrast to optical measurements using a diamond anvil cell, this method allows the pressure dependence of the charge carrier mobility to be studied. In LEDs based on amorphous poly(p-phenylenevinylene) derivatives, we see a small increase in mobility up to 1 kbar, followed by a decrease at higher pressures due to increasing disorder. In the polyfluorene derivative F8BT, however, we see a much stronger increase in mobility with pressure, leading to an increase in device current by up to a factor of 10 at 6 kbar. We attribute this increase to a change in chain conformation at high pressures leading to improved interchain contact between the benzothiadiazole units. We will discuss the implications of these results for the inter-chain transfer integrals in conjugated polymers, and will also present measurements of the electroluminescence spectrum as a function of pressure.
O3: Poster Session: Materials, Devices and Characterization I
Session Chairs
Ana Claudia Arias
J. Devin MacKenzie
Alberto Salleo
Nir Tessler
Wednesday AM, April 11, 2007
Salon Level (Marriott)
9:00 PM - O3.10
Different Interactions of Tris 8-hydoxyquinoline Aluminum and Cesium Chloride on Al Substrate as a Function of the CsCl Thickness in OLED.
K.H. Cho 1 , Yeonjin Yi 1 , Kyul Han 1 , Kyoung jin Park 1 , Pyung eun Jeon 1 , Hyun bok Lee 1 , In seung Jeong 1 , Ju heyuck Baeck 1 , Kwangho Jeong 1
1 Department of Physics, Yonsei university, Seoul Korea (the Republic of)
Show Abstract9:00 PM - O3.11
Bistable Characteristics of the Organic Device with Heterojunction
Szu-Yuan Chen 1 , Tzu-Yueh Chang 2 , Po-Tsung Lee 1 2
1 Department of Photonics & Display Institute, National Chiao-Tung University, Hsinchu, R.O.C., Taiwan, 2 Department of Photonics & Institute of Electro-Optical Engineering, National Chiao-Tung University, Hsinchu, R.O.C., Taiwan
Show AbstractTris-(8-hydroxyquinoline)-aluminum (Alq3) is one of the famous organic electron transfer semiconductor materials. In this work, we fabricate an organic electrical bistable device with Al/Alq3 deposited on N-doped Si substrate and with a heterostructure between N-doped Si and Alq3. Current-voltage characteristic similar to that of metal/organic semiconductor/metal structure, which is usually used for memory devices, is obtained. Initially, the device exhibits low conductance (OFF state). Till the voltage sweeps past the threshold voltage (3.5V), the device can be switched from low conductance to high conductance (ON state) and then it remains in this state even after the applied voltage is turned off. This device exhibits two different conductive states at the same applied voltage, and it is found to exhibit distinct bistability with an on/off current ratio over 1E+3. We believe that interface traps and heterojunction may play important roles on conductance bistability. Owing to its simple structure, we could embed novel organic electronic memory device in conventional fabrication processes. And it shows promise for high-density, low-cost memory applications in future organic nanoelectronics.
9:00 PM - O3.12
Analysis of the Metal Impurities in the Organic Semiconductor Materials for Molecular Electronics by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS).
Svitlana Prada 1 , Diethard Bohme 1 , Vladimir Baranov 2
1 Physics Department, Chemistry Department, York University, Torotno, Ontario, Canada, 2 IBBME, Chemistry Department, University of Toronto, Toronto, Ontario, Canada
Show Abstract9:00 PM - O3.13
Electronic Structure of Copper Hexadecafluorophthalocyanine (F16CuPc) Measured using Soft X-ray Spectroscopies.
Yufeng Zhang 1 , Alex Demasi 1 , Ian Reid 1 , Leyla Colerkerol 1 , Kevin Smith 1 , Anne Matsuura 2
1 , Boston University, Boston, Massachusetts, United States, 2 , Air Force Office of Scientific Research, Arlington, Virginia, United States
Show Abstract9:00 PM - O3.14
Microscopic View of the Transition from Layer-by-layer to Rapid Kinetic Roughening in Organic Growth of DIP on SiO2.
XueNa Zhang 1 , Esther Barrena 1 2 , Dimas G. de Oteyza1 1 , Helmut Dosch 1 2
1 Prof. Dosch, Max Planck Institute, Metal Research, Stuttgart Germany, 2 , Institut für Theoretische und Angewandte Physik, Suttgart Germany
Show Abstract9:00 PM - O3.15
High-performance, Microscale Field-effect Transistors for the Probing of Charge Transport in Molecular Crystals.
Colin Reese 1 , Wook-Jin Chung 1 , Toshihiro Okamoto 1 , Ming Lee Tang 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - O3.16
Structural Investigation of Pyrene Discotics for Organic Field Effect Transistors.
Leah Lucas 1 , Dean DeLongchamp 2 , Lee Richter 2 , Daniel Fischer 2 , Eric Lin 2 , Brigitte Wex 1 , Bilal Kaafarani 3 , Ghassan Jabbour 1
1 Flexible Display Center, Arizona State University, Tempe, Arizona, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Department of Chemistry, American University of Beruit, Beruit Lebanon
Show Abstract9:00 PM - O3.17
Electrochemical Fluorescence Modulation of s-triazine Bridged p-phenylene Vinylene Oligomers.
Eunkyoung Kim 1 , Taechange Kwon 1 , Jeongmok You 1 , Bhimrao D. Sarwade 1
1 Chemical Engineering, Yonsei University , Seoul Korea (the Republic of)
Show Abstract9:00 PM - O3.18
New p-type 1st-generation Dendrimers Bearing Thiophenyl Peripheral Moieties for Organic Field Effect Transistor.
Dong Hoon Choi 1 , Kyung Hwan Kim 1 , Minju Cho 1 , Jinsoo Joo 2 , Hansaem Kang 2 , Miyeon Cho 2
1 Chemistry, Korea University, Seoul Korea (the Republic of), 2 Physics, Korea University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - O3.19
High Performance Functionalized Asymmetric Linear Acenes for p-type Organic TFTs.
Ming Tang 1 , Toshihiro Okamoto 2 , Zhenan Bao 2
1 Chemistry, Stanford University, Stanford, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractPentacene is the workhorse of the organic semiconductor industry, with reliably high mobilities, and decent on-off ratios. In this work, we present a series of novel linear acenes with fused thiophene units. These acenes have conjugation lengths between anthracene and pentacene. They 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. Mobilites as high as 0.45cm2V-1s-1 have been found. We will present interesting halogenated derivatives of these asymmetric linear acenes.
9:00 PM - O3.2
Performance Enhancement of Top-emitting Organic Light-emitting Diodes Using Self-Assembled Monolayer-Modified Ag Anode.
Lai-Wan Chong 1 , Yuh-Lang Lee 1 , Ten-Chin Wen 1
1 Chemical Engineering , National Cheng Kung University, Tainan Taiwan
Show AbstractAg anode with self-assembled monolayers (SAM) of 4-flourothiophenol (4-FTP) is employed to construct an efficient top-emissive polymer light-emitting diodes. The reflectivity of Ag not only does not decrease by the 4-FTP SAM, but also is slightly enhanced. A high brightness of 68981 cd/m2 in the forward direction of the substrate and an electroluminescence efficiency of 10.3 cd/A are achieved for the 4-FTP device. The improved performance is attributed to the presence of fluorine atom on 4-FTP. In order to cross check the effect of 4-FTP, the device with the TP SAM was fabricated to make a comparison.
9:00 PM - O3.20
Ambipolar Transport of Organic Field Effect Transistors Based on P3HT and PCBM Composite Films.
Keiichi Kaneto 1 , Miho Shibao 1 , Takeomi Morita 1 , Takashima Wataru 1
1 Life Science and Systems Engineering, Kyushu Institute of Technology,, Kitakyushu Japan
Show Abstract9:00 PM - O3.21
Extremely Low-voltage Organic Light-emitting Diodes with p-doped Alpha-sexithiophene Hole Transport and n-doped Phenyldipyrenylphosphine Oxide Electron Transport Layers.
Toshinori Matsushima 1 , Chihaya Adachi 2 1
1 , JST-CREST, Tokyo Japan, 2 Center for Future Chemistry, Kyushu University, Fukuoka Japan
Show Abstract9:00 PM - O3.22
Pentacene-based Thin Film Transistors with Titanium Oxide-polystyrene/polystyrene Insulator Blends: Influence of Permittivity and Morphology on Transistor Performance.
Ashok Maliakal 1 , Cecil Jung 1 , Alex Sidorenko 1 , Theo Siegrist 1
1 , Bell Labs, Murray Hill, New Jersey, United States
Show Abstract9:00 PM - O3.23
Hybrid Polymer and CdSe Nanocrystal OLED.
Ting Zhang 1 , Gao Liu 1 , Dacheng Zhao 1 , Amanda Simens 1 , Andrew Minor 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract9:00 PM - O3.24
Influence of Deposition Chamber Pressure and Substrate Temperature on the Properties of Fluorescent Blue and Phosphorescent Red OLED Deposited by OVPD.
Philipp van Gemmern 1 , Christoph Zimmermann 1 , Phenwisa Niyamakom 2 , Matthias Wuttig 2 , Sabine Brand 3 , Holger Schwab 3 , Heinrich Becker 4 , Rocco Fortte 4 , Michael Heuken 1 5 , Holger Kalisch 1 , Rolf Jansen 1
1 Institute of Electromagnetic Theory, RWTH Aachen, Aachen Germany, 2 Institute of Physics (IA), RWTH Aachen, Aachen Germany, 3 , Philips Technologie GmbH, Aachen Germany, 4 , Merck OLED Materials GmbH, Frankfurt/Main Germany, 5 , AIXTRON AG, Aachen Germany
Show Abstract9:00 PM - O3.25
Crystalline F8T2 Domains Hosted in Nematic Aligned Matrix.
Oliver Werzer 1 , Kurt Matoy 1 , Roland Resel 1 , Kurt Stubenrauch 2 , Gregor Trimmel 2 , Peter Strohriegl 3
1 Inst. for solid state physics, University of Technology Graz, Graz Austria, 2 ICTOS, Graz University of Technology, Graz Austria, 3 Macromolecular Chemistry I, University of Bayreuth, GrazBayreuth Germany
Show Abstract9:00 PM - O3.26
Investigation of Epitaxial Order of Pentacene on Cu(110)-(2x1)O Using X-ray Diffraction.
Markus Koini 1 , Thomas Haber 1 , Oliver Werzer 1 , Roland Resel 1 , Martin Oehzelt 2 , Stephen Berkebile 2 , Georg Koller 2 , Michael Ramsey 2
1 Institute of Solid State Physics, Graz University of Technology, Graz, Steiermark, Austria, 2 Institute of Physics, Karl Franzens University, Graz, Steiermark, Austria
Show Abstract9:00 PM - O3.27
Epitaxial Order of Rod-like Molecules Determined by Surface Corrugation.
Thomas Haber 1 , Martin Oehzelt 2 , Markus Koini 1 , Georg Koller 2 , Stephen Berkebile 2 , Jan Ivanco 2 , Marcello Campione 3 , Adele Sassella 3 , Michael Ramsey 2 , Roland Resel 1
1 Institute of Solid State Physics, Graz University of Technology, Graz Austria, 2 Institute of Physics, Karl-Franzens University Graz, Graz Austria, 3 Department of Materials Science, University of Milan Bicocca, Milano Italy
Show Abstract9:00 PM - O3.28
Investigation of the Influence of OVPD Process Parameters on the Properties of α-NPD and Alq3 Layers.
Christoph Zimmermann 1 , Philipp van Gemmern 1 , Hans-Peter Loebl 2 , Phenwisa Niyamakom 3 , Matthias Wuttig 3 , Holger Schwab 4 , Michael Heuken 1 5 , Holger Kalisch 1 , Rolf H. Jansen 1
1 , Institue of Electromagnetic Theory, RWTH Aachen, Aachen Germany, 2 , Philips Research Laboratories, Aachen Germany, 3 , Institute of Physics (IA), RWTH Aachen, Aachen Germany, 4 , Philips Technologie GmbH, Aachen Germany, 5 , AIXTRON AG, Aachen Germany
Show Abstract9:00 PM - O3.30
Surface-induced Alignnment of Liquid Crystalline Semiconductors Using a “Command Surface” for Organic Transistors.
Takenori Fujiwara 1 , Jason Locklin 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - O3.31
Charge Transport Measurements on Anisotropic Polythiophene Thin Films Fabricated via Directional Crystallization.
Leslie Jimison 1 , Roger Tsai 2 , Alberto Salleo 1
1 Materials Science, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractRecently, there has been considerable interest in the development of semiconducting polymers for use in printable electrical devices, such as transistors for display backplanes. These materials offer a cost effective alternative to conventional semiconductors, with key advantages of organic materials being their low processing temperature and possibility of solution processing in ambient leading to roll-to-roll printing. Performance over the past few years has improved, but charge transport in these materials is not yet fully understood. These conjugated polymers generally form a semicrystalline microstructure, consisting of lamellar crystalline regions separated by amorphous grain boundaries. A mobility edge model has been proposed that suggests charge delocalization in the crystallite regions where mobile states exist, with the effective mobility limited by the localized states within the disordered grain boundaries and at defects. We have used a means of controlling the orientation and size of crystallites in the plane of the substrate to explore the relationship between trap density within grain boundaries and charge transport.Regioregular poly-3-hexylthiopene (P3HT) and poly(2,5-bis-alkylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT) are the materials under investigation. In both cases we have fabricated films on glass and silicon substrates by starting with a heated solution of polymer and 1,3,5-tricholorobenzene (TCB), a solvent that is crystalline at room temperature. As we bring the liquid down in temperature, nucleation of the TCB is induced. The TCB forms elongated crystals. The polymer is continuously excluded from the TCB into the remaining solution until it is deposited on top of the TCB crystals, which act as a substrate for epitaxy. Apon TCB removal, an oriented polymer film is left behind, consisting of large (mm2) domains where the film extinguishes uniformily under crossed polarizers. This suggests long range orientation of the polymer chain axis. Absorption measurements confirm anisotropy in microstructure. Characterization with an AFM reveals stacked lamellar structures, with approximate dimensions of 50 nm by 100 nm. Charge transport in the directionally crystallized film was probed by measuring in plane mobilities. Both bottom contact and top contact TFTs were made with n-doped silicon substrate that serve as the common gate electrode. A 200 nm thermal oxide treated with octadecyltrichlorosilane (OTS) was used as the gate dielectric. Devices were made with different relative orientations between the channel and the polymer film. Transport measurements as a function of charge density and temperature for different orientations of our film were used to explore the effect of anisotropy and microstructure Dimitrakopoulos et al, Adv. Mat. v.14, 2 p. 99-117 (2002)Street et al, PR B 71 165202 (2005)Brinkmann et all, Adv. Mat. 18 p. 860-863(2006)
9:00 PM - O3.32
Nanoscale Observation of Electrical Properties of Polypyrrole Film During its Aging Using Conductive AFM.
Hosup Jung 1 , Dennis Tallman 1 2 , Gordon Bierwagen 1
1 Coating and Polymeric Materials, North Dakota State University, Fargo, North Dakota, United States, 2 Chemistry, North Dakota State University, Fargo, North Dakota, United States
Show Abstract9:00 PM - O3.33
Fixed p-i-n Junction Polymer Light-emitting Electrochemical Cells Based on Self-assembled Doping Monolayers.
Daniel Simon 1 , David Stanislowski 1 , Sue Carter 1
1 Physics, University of California, Santa Cruz, Santa Cruz, California, United States
Show Abstract9:00 PM - O3.34
Synthesis and Processing of Soluble Oligothiophene Semiconductors.
Ajay Virkar 1 , Jason Locklin 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractOrganic semiconductors which can be deposited from solution represent the unique possibility of mass-produced, cheap electronics, and deposition on flexible plastic substrates. Highly conjugated organic molecules, can be cast from organic solvents by introducing solubilizing side chains. Charge carrier transport is facilitated by the π-π stacking between neighboring molecules. We have focused on oligothiophene molecules which are synthesized using Suzuki or Stille coupling mechanisms. Inks are created by dissolving the organic semiconductor in common organic solvents which can then be deposited onto device wafers by drop-casting or spin coating. As the solvent evaporates, the organic molecules crystallize into a solid film. Device performance is strongly influenced by the morphology of the resulting film. The fabricated transistors were probed for electrical performance like field effect mobility, On/Off ratio, and threshold voltage. For good performance, large two dimensional crystal growth is preferred, with strong a overlap of the π-electron system. Desirable properties can be achieved both by molecular design and processing conditions. Several of the devices exhibit high performance with mobilities approaching 0.1cm2/Vs, and On/Off ratios of 104.
9:00 PM - O3.35
Effect of Self-Assembled Monolayer modified Electrodes on Bottom-Contact Organic Field-Effect Transistors
Jong Won Lee 1 , Ki Pyo Hong 1 , Sang Yoon Yang 1 , Kwonwoo Shin 1 , Hayoung Jeon 1 , Se Hyun Kim 1 , Chan Eon Park 1
1 Chemical Engineering , POSTECH, Pohang Korea (the Republic of)
Show AbstractPentacene-based organic field effect transistors (OFETs) have been widely studied as potential applications for low-cost, large area, flexible electronics such as information display, chemical sensor, electronic papers etc. To produce commercial OFET devices, fine lithography is needed and top contact OFETs are difficult for it due to damage of active layer. Therefore, bottom contact type OFETs are more desirable for a manufacturable process. However, it has been demonstrated that the bottom contact configuration gives inferior performance to the top contact one because of relative high contact resistance which were originated from the formation of injection barrier at the metal-organic semiconductor (OSC) interface. It has been shown previously that, by self-assembled molecular layer with intrinsic electric dipole moment, the work function of metal electrodes can be lowered or raised, affecting the size of the injection barrier at the metal-OSC interface. However, limited testing have been made to use this approach to engineer injection barriers in OFET field. In this study, gold (Au) surfaces modified with 1-Decanethiol (DT - electron donating group), Heptadecafluoro-1-decanethiol (HDFDT - electron withdrawing group), Tridecafluoro-1-octanethiol (TDFOT - electron withdrawing group) were characterized by He(I) Ultra-violet photoelectron spectroscopy (UPS). We have tuned the Au work functions by chemically modifying the Au surface through the formation of chemisorbed self-assembled monolayers (SAMs) having electron donating group and electron withdrawing group. The ordering in the SAMs creates an effective, molecular dipole at the metal/SAM interface, which increased the work function of Au (bare Au~4.9 eV) to 5.5~5.7 eV for electron withdrawing group. On the other hand electron donating group shifted work function of Au to 4.1 eV. The hole injection barriers at the pentacene/Au, pentacene/DT/Au, pentacene/HDFDT/Au and pentacene/TDFOT/Au were also determined using in-situ thin film deposition in combination with X-ray and ultraviolet photoelectron spectroscopy at PAL-4B1 beam line. We have obtained that hole injection barrier between electron withdrawing group SAM modified Au surface and pentacene was 0.59 eV which was 0.4 eV smaller than that between bare Au and pentacene. By using these SAMs to engineer the effective Au work function, we found that the charge injection process can be markedly affected. In addition, we have fabricated bottom contact pentacene-based organic field effect transistors (OFETs) by using these SAMs to investigate the effect of hole injection barriers at interface between the metal electrode and the vacuum deposited pentacene films on the performances of OFETs.
9:00 PM - O3.36
Performance of PLED with Anode of Transparent Conductive ZnOx < 1 Thin Film Made at Low Temperature
Yuhua Lee 1 2 , Sun-Huei Huang 2 , Jen-Fa Min 1 , Jung-Chuan Lee 1 , Shih-Ting Lin 2 , Wei-Yang Chou 2
1 Physics department, National Cheng Kung University, Tainan Taiwan, 2 Institute of Electro-Optical Science and Engeneering, National Cheng Kung University, Tainan Taiwan
Show AbstractThe invention of polymeric light-emitting diode (PLED) has aroused a revolutionary change in display devices. Display devices made of PLED are much thinner, lighter and even flexible. The performance of the device depends on the use of transparent conductive electrodes. Films of indium oxide doped with tin (ITO) have small resistivity and have wide and long-term commercial uses. However, its component material indium is scarce. Therefore there is an urgent need to find a substitute to satisfy the fast growing market demands. Many wide band-gap metal-oxides are suitable alternatives. Among these, zinc oxide (ZnO) is cheaper, abundant and more friendly to the environment. Besides, ZnO is a II-VI n-type semiconductor with a band-gap energy of ~ 3.3 eV at room temperature. Thin films of ZnOx can be made to have high electrical conductivity as well as high optical transparency by controlling a proper value x (< 1) of the relative atomic ratio of oxygen to zinc through deposition parameters. Therefore, we decide to make ZnOx<1 thin film as anode for fabrication of PLED.Ion-beam deposition was adopted in this study because of its low operation pressure (~ 7 x 10-5 torr). It is expected to have better microstructure and, thus, small resistivity at low substrate temperature. The substrate was not subjected to intentional heating and had a temperature of ~ 50 oC. Beam voltages Vb = 400, 500, 600 and 700 V were used for each of the beam current Ib = 10, 20 and 25 mA. Film thickness was kept at ~ 200 nm. All films are transparent with average transmittance in visible region Tav > 80 % and conductive with resistivity ~ 2 to 6 x 10-3 ohm-cm and carrier density ~ 1 to 5 x 1020 cm-3. Both atomic-concentration of oxygen and band-gap energy are roughly constant, at ~ 30% and 3.3 eV respectively. Hall mobility decreases clearly with increasing either Vb or Ib.Films made at Ib = 10 mA and Vb = 400 to 700 V were used as anode for fabrication of PLED. PEODT:PSS film (40 nm) and PT layer (100 nm) were used as hole transport and electron transport/emitting layers respectively. The cathode contact was an alloy of Ca (60 nm)/Al (120 nm). The active area of the device is ~ 2.5 × 2.5 mm. The current-voltage (I-V) and the luminance-voltage (L-V) curves show that forward biasing current (If) decreases and threshold voltage (Vth) increases respectively with increasing Vb. The commercially made ITO film (9.83 × 10-5 ohm-cm in resistivity and 250 nm in thickness) shows Vth ~ 2.3 V and If ~ 40 mA at forward bias Vf = 5 V. Comparing with ITO film, ZnO film of Vb = 400 V shows larger Vth (~ 3 V) and smaller If at Vf =5 V (~ 1.5 mA). However, increasing the film thickness to 500 nm we observe smaller Vth (~ 2.3 V) and larger If at Vf =5 V (~ 7.2 mA). Our results show that ion-beam deposition is a proper technique to fabricate transparent conductive ZnO film for future development of flexible display device.
9:00 PM - O3.37
Low-temperature, Solution-processed, High-mobility Polymer Semiconductors for Thin-film Transistors
Hualong Pan 1 , Yuning Li 2 , Yiliang Wu 2 , Ping Liu 2 , Beng Ong 2 , Shiping Zhu 1 , Gu Xu 1
1 Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada, 2 bMaterials Design & Integration Laboratory, Xerox Research Centre of Canada, Mississauga, Ontario, Canada
Show Abstracta new class of polymer semiconductors which self-assemble into higher structural orders without thermal annealing provided excellent field-effect transistor performance with mobility up to 0.25 cm^2V^-1s^-1 when used as a solution-processed thin-film semiconductor in thin-film transistors.
9:00 PM - O3.38
On Charge Transport at the Interface of Organic Semiconductors.
Xiaojiang Yu 1 , Jianbin Xu 1 , Jia Gao 1 , Wing Yiu Cheung 1 , Ning Ke 1
1 Electronic Engineering Department, The Chinese University of Hong Kong, Hong Kong China
Show Abstract9:00 PM - O3.39
A Metal Nanoparticles Incorporated Low Leakage Polymer Dielectric Film for Low Voltage Organic Thin Film Transistor
Zingway Pei 1 , Heng Tien Lin 2 3 , Yi Jen Chan 2 3
1 Department of Electrical Engineering, National Chung Hsing University, Taichung Taiwan, 2 Electronics and Opto-electronics Research Laboratories (EOL), Industrial Technology Research Institute (ITRI), Hsinchu Taiwan, 3 Department of Electrical Engineering, National Central University, Chungli Taiwan
Show AbstractIn recent year, the flexible electronics including flexible display and flexible electronic circuit attracted extensive research focus for its variety of applications. Among flexible electronics, organic thin film transistor (OTFT) is one of the major components either as the driving transistor in liquid crystal display (LC) and organic light-emitting diode (OLED) or as the basic element in organic circuit. However, instead of inorganic material, organic dielectric generally exhibit low dielectric constant and higher leakage current that limit the development on OTFT for low voltage operation. Several methods were demonstrated having low leakage current at low voltage including self-assembled monolayer, highly cross-linked polymer and multi-polymer layers. Those techniques are either hardly controlled or with complicated process. Here we reported a simply method for low leakage at thin organic dielectric film by incorporated metal nanoparticles into the organic dielectric materials. The appropriate metal nanoparticles in the organic material can be treated as carrier traps that limit carrier transport through the dielectric layer unless the traps are filled. With appropriated size and distribution of the metal nanoparticles, the traps will not be filled before dielectric breakdown. In experiment, the leakage current shows nearly three order of magnitude reduction after incorporation of metal nanoparticles.
9:00 PM - O3.4
Deposition and Patterning of Conductive Carbon Black Thin Films.
Jaime Grunlan 1 2 3 , Matthew Walton 1 , Yeon Seok Kim 1 3 , William Everett 1 3 , C. Jan 1 3 , Woo-Sik Jang 1 3
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 3 Polymer Technology Center, Texas A&M University, College Station, Texas, United States
Show AbstractUsing cationic polyethylenimine (PEI) and anionic poly(acrylic acid) (PAA), the effect of compositional variables on construction of thin carbon black polymer composites using layer-by-layer (LbL) deposition was studied. Processing variables include polymer ratio variation, polymer ratio mismatch, absence of conductive filler from one solution, and ionic strength manipulation. Films made with 0.25 wt% carbon black in 0.05 wt% PAA, alternated with plain 0.1wt% PEI, attained the lowest sheet resistance (~325 Ω/sq) with bulk resistivity of approximately 5 S/cm. These films are typically 0.5 – 5 μm thick and can be patterned using traditional photolithography. The relatively high conductivity results from a high carbon black concentration (> 40 wt%) in the films combined with relatively low porosity for such a large filler concentration. This combination of good conductivity and patternability is ideal for flexible electronics.
9:00 PM - O3.40
Relationship Between ITO Surface Properties and Device Performances of C60 Modifed Organic Light Emitting Diodes.
Sung Hyun Kim 2 , Jyongsik Jang 2 , Jun Yeob Lee 1
2 School of chemical and biochemical engineering, Seoul National University, Seoul Korea (the Republic of), 1 Department of Polymer Science and Engineering, Dankook University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - O3.41
The Effect of Interfacial Roughness on the Thin Film Morphology and Charge Transport of High Performance Polythiophenes.
Youngsuk Jung 1 , R. Kline 1 , Eric Lin 1 , Daniel Fischer 1 , Dean DeLongchamp 1 , Martin Heeney 2 , Iain McCulloch 2
1 , NIST, Rockville, Maryland, United States, 2 , Merck Chemicals, Southampton United Kingdom
Show Abstract9:00 PM - O3.42
Nanoimprinting of Ferroelectric Polymer Films
Jiangyu Li 1 , Lei Zhang 1 2
1 , Univ of Washington, Seattle, Washington, United States, 2 , University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThe design and fabrication of nanostructured electronic materials has attracted considerable amount of interests in recent year. In this talk, we report our recent work on patterning ferroelectric P(VDF-TrFE) thin films by nanoimprint lithography (NIL). Various patterns have been created with the feature size approaching 10s nanometers, and very good pattern transfer between the molds and films has been observed. Systematic characterizations including AFM, SEM, XRD, FTIR and dielectric spectroscopy confirm that the imprinted P(VDF-TrFE) is ferroelectric with good dielectric, piezoelectric, and ferroelectric properties, which could find important applications as sensor arrays and actuator arrays.
9:00 PM - O3.43
Air-stable Operation of Organic Field-effect Transistors on Plastic Films using Organic/Metal Hybrid Passivation Layers
Tsuyoshi Sekitani 1 , Takao Someya 1
1 , Univ. of Tokyo, Bunkyo-ku, Tokyo, Japan
Show AbstractEmploying novel organic/metal-hybrid passivation layers, we have drastically improved the electric stability of pentacene field-effect transistors (FETs) on plastic films in air. The change in mobility was less than 5% and the shift in Vth was less than 4 V after the application of continuous voltage biases (V_DS = V_GS = – 40 V) for 10 days in air, demonstrating that the stability of the organic FETs is much superior to that of amorphous silicon transistors [1,2]. Organic FETs are manufactured by a vacuum evaporation process. A gate electrode consisting of 100-nm-thick Au was prepared in a vacuum evaporator on a 75-μm-thick polyimide film. Then, polyimide was spin-coated to form 800-nm-thick gate dielectric layers. Purified pentacene was deposited through a shadow mask in the evaporator to form 50-nm-thick semiconductor layers. A 60-nm-thick Au drain and source electrodes were evaporated through a shadow mask. The typical channel length and width were 50 μm and 500 μm, respectively. Finally, these FETs were coated with organic/metal hybrid passivation layers consisting of 800-nm-thick parylene/150-nm-thick Cu/ 10-μm-thick parylene. The FETs with passivation layers exhibited a high mobility of 0.6 cm^2/Vs, Vth of –11 V, and on/off current ratio of 10^6 with the off current defined at V_GS = 0 V. The FETs without passivation layers also exhibited a high mobility of 0.5 cm^2/Vs, Vth of –8.0 V, and on/off current ratio of around 10^2 with the off current defined at V_GS = 0 V.We measured the transistor characteristics of the FETs with and without passivation layers after storage in air (temperature: 26 oC, humidity: 60%) for two months. After two months, the FETs with passivation layers exhibited slight changes in Vth from –11 V to –10 V, while the change in mobility was less than 2%. The on/off current ratio exceeded 10^4 even when the off currents were defined at V_GS = 0 V. On the other hand, the FETs without passivation layers exhibited significant changes in Vth from –8 V to 3 V and a decrease in mobility from 0.5 cm^2/Vs to 0.3 cm^2/Vs. The on/off current ratio degraded to around 10^2. We also investigated the electrical stability under continuous voltage biases in air for 10 days. The pentacene FETs with the passivation layers exhibited the slight changes in mobility less than 5%, the Vth-shift less than 4 V, and the on/off ratio with the off current defined at V_GS = 0 V exceeded 10^5. This work was supported by Special Coordination Funds for Promoting and technology, JST-CREST, and TOKUTEI(15073204).[1] F. Taghibakhsh, J. Vac. Sci. Technol. A 24, 866 (2006).[2] C. –S. Yang, J. Vac. Sci. Technol. B 18, 683, (2000).
9:00 PM - O3.44
NMR Studies of Hexafluorophosphate (PF6-) Doped Polypyrrole.
Jenny Chien-Hsin Tso 1 , Carl Michal 1
1 Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
Show AbstractPolypyrrole is a promising candidate for use as a mechanical actuator and as an electrode for supercapacitor applications. The ion content and dynamics of hexafluorophosphate (PF6-) doped polypyrrole films are examined by a variety of NMR techniques in different oxidation states. The ion content decreases linearly with decreasing electrochemical potential, directly confirming the ion insertion mechanism of polymer actuation. With known ion content and deposition current, a doping level (dopant ion/pyrrole) of 0.26 was determined for the as-grown film. A T1 relaxation study reveals that the rotational correlation time of PF6- ions in the oxidized film (10.76 ps) is similar to that in the solvent (8.08 ps), suggesting the ions are located inside solvent pockets rather than at stable sites in the polymer matrix. 1D Nuclear Overhauser Effect (NOE) difference experiments confirm the solvated ion environment in oxidized films, but reveal a drastic decrease in the NOE enhancement factor in reduced films, implying that polypyrrole undergoes a significant structural change when reduced. This change leads to a much less solvated environment as experienced by the dopant ions in the reduced state. Translational motion of the PF6- ions in the oxidized films at two orientations is probed via self-diffusion coefficient measurements made using pulsed-field gradient (PFG) NMR. The D values obtained at different diffusion times range from 3x10-8 cm2/s to 5x10-9 cm2/s. The time dependence of the D values suggests an upper limit on the pore size of 0.4 um in the oxidized films.
9:00 PM - O3.45
Lateral J-aggregate Photodetectors.
John Ho 1 , Michael Bradley 1 , Yasuhiro Shirasaki 1 , Jonathan Tischler 1 , Vladimir Bulovic 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractWe fabricated an efficient, nanostructured photodetector using a thin film of J-aggregated cyanine dye molecules, which impart a spectrally narrow, tunable (across visible and near-IR) detection bandwidth. The strong dipole-dipole coupling of individual cyanine dye molecules forms the J-aggregates and yields narrow spectral linewidths (~ 10-20 nm full width half max in thin film) and record-high oscillator strengths [Bradley, et al. Adv. Mater. 2005, 15, 1881]. Layer-by-layer growth promotes a high density of J-aggregates to form in thin film structures leading to high optical absorption in only a few monolayers. Our device structure is a bi-layer heterojunction consisting of an optically active J-aggregate and a charge-transport layer arranged in a lateral photoconductor-style device with bottom contacts. The contacts are a series of gold interdigitated fingers (W x L = 1500 µm x 4 µm) spaced 10 µm apart. The gold electrodes are photolithographically defined on glass before the J-aggregate is deposited layer-by-layer, followed by the thermal evaporation of the organic layers. The lateral heterojunction physically separates the charge transport mechanism from the optical properties of the device, taking advantage of the J-aggregates’ unique, optical properties in this new class of photosensitive devices. In addition to developing a novel photodetector, we are using this structure to study charge transport and exciton dynamics in J-aggregate thin films.
9:00 PM - O3.46
Towards Planar and Smooth Microarray Electrodes.
Nuria Queralto Gratacos 2 1 , Mark Roberts 1 , Wolfgang Knoll 2 , Zhenan Bao 1
2 , Max Plank Institute for Polymer Research, Mainz Germany, 1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - O3.47
Naphthalimide Bearing 4-Arylamino as Red-Light-Emitting Materials for Electroluminescence Applications
Sung Ouk Jung 1 , Dong Min Kang 1 , Jong-Won Park 1 , Sang Yong Nam 1 , Sung-Gap Lee 1 , Jong-Taek Je 3 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 Shool of Nano-Advaced Materials Engineering, Gyeongsang National University , Jinju, GyeongNam, Korea (the Republic of), 3 , SFC CO., LTD, Cheongwon, Chungbuk, Korea (the Republic of), 2 Department of Chemistry, Gyeongsang National University, Jinju, GyeongNam, Korea (the Republic of)
Show AbstractOrganic light-emitting devices (OLEDs) have attracted much attention because of their potential applications in low-cost, large-area, and flexible devices. For realization of full color, red-, green-, and blue-light-emitting materials with sufficiently high efficiency, good color purity and luminance are required. In comparison with green and blue emitters, the red emitters remain one of the greatest challenges. One of the reasons is low emitting efficiency that they have small energy gap because non-radiative relaxation of the excited states. The other is a result of color-impurity, owing to the strong intermolecular dipole-dipole interactions or intermoleculars-stacking, which leads to high tendency of aggregation and, so-called concentration quenching. We designed new red emitting material based on donor-acceptor-substituted naphthalimide containing arylamino moieties, which are non-planar and morphological characteristics in forming amorphous molecular glasses. The photophysical, elctrochemical properties of these materials, and OLEDs fabricated using these compounds are investigated.
9:00 PM - O3.48
Organic Field-Effect Transistor Based on Polyalkylanthracene
Jong-Won Park 1 , Sung Ouk Jung 1 , Jang-Yeol Beak 1 , Jin-Ouk Ju 1 , Mi-Hye Yi 3 , Taek Ahn 3 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of Nano-Advanced Materials and Engineering Research Institute, Gyeongsang national university, chinJu, gyeongnam, Korea (the Republic of), 3 Polymeric Nanomaterials Laboratory, Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 2 Department of Chemistry, Gyeongsang National University, chinju, gyeongnam, Korea (the Republic of)
Show AbstractOrganic Thin-Film transistors (OTFTs) based on oligomeric and polymeric organic semiconductors are applied to active-matrix display, organic light emitting diodes, and electronic paper displays. A valuable characteristic to decide the performance of OTFTs is the field effect mobility of the charge carriers in the organic semiconductor layer and by the efficiency of injecting and extracting carriers at the source and drain contacts. OTFTs ma be fabricated by common solution deposition/patterning techniques (e.e., coating, stamping, offset printing, inkjet printing, etc.) and on plastic substrates to enable flexible electronics. Molecular ordering is believed to play a large role in the performance of devices based on organic active layer materials, for Polymer OTFT materials, the amount of π-orbital overlap is expected to have a strong influence on field-effect mobility. In this paper, we report the synthesis and characterization of poly(9,10-dialkyl substituted anthracene) for their behavior as FET semiconductors. The new polymer was prepared by a Yamamoto coupling reaction. The materials were measured by DSC, TGA, FT-IR spectrometer, and GPC etc.
9:00 PM - O3.49
Polymeric OTFT Materials Containing Dithienothiophene Derivatives.
Mai Dang 1 , Qing-Hua Zhao 1 , Yi-Nan Li 1 , Moon-Hak Park 1 , Yun-Hi Kim 2 , Chan Eon Park 3 , Dae-Sung Chung 3 , Soon-Ki Kwon 1
1 Department of Chemistry, Gyeongsang National University, Chinju Korea (the Republic of), 2 Chemical Chemistry, Gyeongsang National University, Chinju Korea (the Republic of), 3 Chemical Engineering Department, Chemical Engineering Department, Pohang Korea (the Republic of)
Show Abstract9:00 PM - O3.5
Semiconducting Organic Thin Film Devices with Large Room-temperature Magnetoresistance.
Yugang Sheng 1 2 , Tho Nguyen 1 , Govindarajan Veeraraghavan 2 , Omer Mermer 3 , Thomas Francis 2 , Markus Wohlgenannt 1
1 Physics & Astronomy, University of Iowa, Iowa City, Iowa, United States, 2 Electrical & Computer Engineering, University of Iowa, Iowa City, Iowa, United States, 3 Institute of Polymers and Organic Solids, University of California, Santa Barbara, Santa Barbara, California, United States
Show Abstract We performed a comprehensive study on a recently discovered, large room-temperature magnetoresistance (MR) effect in sandwich devices comprised of nonmagnetic electrodes and organic thin films. The devices were fabricated from pi-conjugated polymers and small molecular weight compounds in combination with different electrode materials, and characterized extensively at different voltages, temperatures, and at weak magnetic fields from DC up to 100 kHz in frequency. The MR effect shows only weak temperature dependence and is independent of the sign and direction of the applied magnetic field. In some materials, the effect reaches up to 10% in a magnetic field of 10 mT at room temperature. To the best of our knowledge, the discovered effect is not adequately described by any of the MR mechanisms known to date, and therefore poses a significant scientific puzzle.To explore the possibility that OMAR is caused by spin-dynamics induced by the hyperfine interaction, we deduce a simple fitting formula from the hyperfine Hamiltonian that relates the saturation field of the OMAR traces to the hyperfine coupling constant. We compare the fitting results to literature values for this parameter. By varying the injection efficiency for minority carriers in the devices, we show experimentally that OMAR is caused by an effect of spin-dynamics on the carrier mobility, rather than carrier density (recombination). We discuss a possible mechanism.Since the devices we describe can be manufactured cheaply, our devices hold promise for applications such as magnetic sensors, magnetic random access memories, organic LED (OLED) touch screens, etc. To illustrate the potential application of the effect in touch screen displays, we demonstrate an 8x8 pixel OLED pen-input touch screen using the MR effect, where the position of a magnetic pen that is held over the display is detected.
9:00 PM - O3.50
Synthesis and Characterization of Diphenylaminodiphenyl Stryl-Based Alternating Copolymers
Qinghua Zhao 1 , Yi Nam Li 1 , Dong Min Kang 1 , Moon Hak Park 1 , Yun Hi Kim 2 , Jin Uk Ju 1 , Sung Chul Shin 2 , Soon Ki Kwon 1
1 School of nano and advanced materials engineering, Gyeongsang National University , Jinju Korea (the Republic of), 2 Chemistry Department, Gyeongsang National University, Jinju Korea (the Republic of)
Show AbstractSince the first discovery of poly(phenylenevinylene)-based light emitting dioed(LED) in 1990’1, much effort have been made toward the development of new electroluminescent (EL) polymers. The advantage of EL polymers is that their solubility properties and highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) energy levels can be adjusted by varying the molecular structure of the polymers. Poly(p-phenylenevinylene)(PPV)2 and poly(p-phenylene)(PPP) were the typical EL polymers used in PLED. PPV and PPP are attractive, owing to high thermal stability and suitable color tunability. However, much efforts have to be done to emit blue light-emission and increase ability of hole-injection or hole-transporting in order to improve device efficiency. Usually, triarylamine group was used to increase hole-injection and hole–transporting ability. On the same time, Polyfluorene(PF) was well known to emit blue light emitting. Thus, we synthesized BDAV3-based alternating polymers with phenyl or fluorene. BDAV had bulky triphenyl group and was expected to increase ability of hole-injection or hole-transporting. The PLED devices would be fabricated and discussed further.[1] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burns, A. B. Holmes, Nature(London), 1990, 347, 539[2] D. Clery, Science, 1994, 263, 1700[3] Y. H. Kim, Q. H. Zhao, S. K. Kwon, Journal of Polymer Science: Part A, Polymer Chemisty, 2006, 442, 172
9:00 PM - O3.51
Efficient Green-Electroluminescent Devices Using [1,3,4]-Oxadiazole Derivatives as Hole-Blocking and Electron Transporting Materials
Sung Jin Park 1 , Dong Min Kang 1 , Jae-Sang Kim 2 , Hyoung-Yun Oh 3 , Sung Ouk Jung 1 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of Nano-Advanced Materials, Gyeongsang National University , Jinju Korea (the Republic of), 2 School of Nano-Advanced Materials, Gyeongsang National University , Jinju Korea (the Republic of), 3 , LG Electronics Institute of Technology, Seoul Korea (the Republic of)
Show AbstractThe application of organic light-emitting devices (OLEDs) has reached low-cost, full-color flat panel displays due to their advantage of high brightness, easy fabrication, and wide range of emission colors. However, some important and fundamental challenges in achieving a high-resolution full color display. Particularly hole-blocking material is one of the significant factors of the device performance. For the hole-blocking material, large energy gap, high ionization potential, readily sublimable, and forming uniform amorphous films. Some organic materials have been reported that heteroatom-containing small molecular/polymeric compound, boron-containing or aluminum-containing materials. However, a hole-blocking and electron transporting layer still require improvement for efficient OLEDs. Therefore, as a new hole-blocking and electron transporting material, we have synthesized [1,3,5]-oxadiazole derivatives with high current efficiency and power efficiency of 45 cd/A and 17.7 lm/W in 10 mA/cm2, which is superior to the result of the device using BAlq (current efficiency: 31.5 cd/A and power efficiency: 13.5 lm/W in 10 mA/cm2) as well known hole blocker. The ITO/DNTPD/NPD/6% Ir(ppy)3 doped CBP/[1,3,5]-oxadiazole derivatives as both hole blocking and electron transporting layer/Al device showed efficiency of 45 cd/A and maximum brightness of 3000 cd/m2 in 10 mA/cm2.
9:00 PM - O3.52
Polymeric OTFT Materials Containing Anthracene Derivatives
Yinan Li 1 , Mai Dang 1 , Qinghua Zhao 1 , TaeHoon Kim 1 , SungJin Park 1 , Yun-Hi Kim 1 , Soon-Ki Kwon 1 , Seung-Hon Han 1 , Jin Jang 1
1 School of Nano-Adavanced Materials and Engineering, Gyeongsang National University , Jinju Korea (the Republic of)
Show AbstractOrganic semiconducting molecules were very attractive for the fabrication of organic thin film transistors (OTFT) in various molecular electronics applications, such as flexible display, smart card, RF tag, and electronic paper. As we know, poly(3-hexylthiophene) and anthracene exhibit a high charge-carrier mobility, and the alkyl chains on the anthracene moiety can help promote self-organization. On the other hand, fluorene has a number of advantages, such as the thermal and chemical stability. Thus, we have selected anthracene and 3-alkylthiophene or dialkylfluorene to synthesis polymers, expecting to be used in organic thin film transistor (OTFT) and achieve high mobility. The polymers were confirmed by FT-IR, 1H-NMR. The physical and optical properties of the polymers were characterized by differential scanning calorimetry (DSC), cyclic voltammetry (CV), and optical absorption and photoluminescence (PL) spectroscopy. The OTFT will be fabricated and discussed further.
9:00 PM - O3.53
Design, Synthesis and Characterization of Novel Fused Aromatic Semiconductors Containing Alkyl Bithiophene.
Tae-Hoon Kim 1 , Jong-Won Park 1 , Sung-Ouk Jung 1 , Seung-Moon Pyo 4 , Mi-Hye Yi 3 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of Nano & Advaned Materials and Engineering Research Institute, Gyeongsang National University , Jinju Korea (the Republic of), 4 Department of Chemistry, Konkuk University, Seoul Korea (the Republic of), 3 Polymeric Nanomaterials Laboratory, Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 2 Department of Chemistry, Gyeongsang National University, Jinju Korea (the Republic of)
Show Abstract9:00 PM - O3.54
In situ Real-time Synchrotron Study of Small Molecule Organic Thin Film Growth from Hyperthermal Molecular Beams.
Aram Amassian 1 3 , Sugandha Bhargava 2 3 , Arthur Woll 3 , Sukwon Hong 2 , John Ferguson 4 3 , Aravind Killampalli 2 , Todd Schroeder 2 , George Malliaras 1 , James Engstrom 2
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States, 2 Chemical Engineering, Cornell University, Ithaca, New York, United States, 4 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - O3.55
Functional Self-Assembled Monolayers for Large Photoinduced Charge Transfer in Organic Field Effect Transistors.
Paul Evans 1 , Padma Gopalan 1 , Byoungnam Park 1 , Peerasak Paoprasert 1 , Insik In 1 , Jodi Zwickey 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractThe development of molecular electronics and the integration of organic semiconductors into devices fundamentally involve creating and characterizing functional electronic interfaces. The design of these interfaces includes the opportunity to incorporate functions that are not possible in inorganic structures, where the range of available materials is much smaller. We describe a structure designed to optimize photoinduced charge transfer in organic thin film devices. Thin films exhibiting photoinduced transfer have traditionally been envisioned for photovoltaic devices using bulk mixtures of semiconductors and molecules with electron acceptors. We have produced a highly controlled nanometer-scale implementation of these molecular mixtures in modified pentacene thin film transistors with a functional self-assembled monolayer at the interface between the pentacene and the SiO2 gate insulator. This arrangement is optimized to produce a large electronic signature of photoinduced charge transfer. Charge densities on the order of 1013 cm-2 can be induced by the photoinduced charge transfer effect at the interface between a pentacene thin film and a gate dielectric functionalized with a C60-terminated γ–amino propyl trimethoxy silane. Atomic force microscopy, x-ray photoelectron spectroscopy, and infrared spectroscopy support a structural model based on an interface between the pentacene film and a single layer of the functionalized monolayer. Subsequent developements based on functionalized monolayers at the gate-insultator/semiconductor insulator have the potential to further optimize this effect and could lead to similar effects in at a wide range of interfaces.
9:00 PM - O3.56
Synthesis and Characterization of Biphenyl End-capped Anthracene as a Core(BP2An) and Anthracene End-capped Biphenyl as a Core(An2BP) for OTFT Materials.
Moon-Hak Park 1 , Hyong-Sun Kim 1 , Young-Hee Park 3 , Jong-Won Park 1 , Ki-Yul Yang 3 , Mi-Hye Yi 4 , Yun-Hi Kim 2 , Soon-Ki Kwon 1
1 School of nano and advance Materials Engineering, Gyeong Sang National University, Jin-Ju, Gyeong Nam , Korea (the Republic of), 3 Department of Chemical Education, Gyeong Sang National University, Jin-Ju, Gyeong Nam , Korea (the Republic of), 4 Polymeric Nanomaterials Lab., Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 2 Department of Chemistry, Gyeong Sang National University, Jin-Ju, Gyeong Nam , Korea (the Republic of)
Show AbstractSmall molecule semiconductors have been considered as active materials for Organic Thin Film Transistors (OTFTs), because of their advantages including good process-ability, easy synthesis, good crystallization. The materials with high charge carrier mobility have currently been received a many interested, but the importantly focus on thiophene and pentacene derivatives. But, in this type of materials are limited to use by semiconductors because of stability problem. While anthracene and biphenyl have π-π stacking orderness for efficient charge carrier transport to obtain high field-effect transistor mobility and high oxidation stability. Among them, 2,6-substitution of anthracene is better than 9,10-substitution of anthracene because of the highest planarity and the most extended πconjugation. Therefore, we have two type materials designed that 2,6-Bis-biphenyl-4-yl-anthracene(An2BP) and 4,4'-di(anthracene-2-yl)biphenyl (BP2An) and synthesized by Suzuki reaction. And, we have compared An2BP with BP2An that calculated mobility in theory, measured mobility composing OTFT device, and observed oxidation stability for 1 month by IR.New small molecule materials were characterized by 1H-NMR, elemental analysis, and mass spectra. Their thermal properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA). And their Spectroscopic and Electrochemical properties investigated by cyclic voltammetry (CV), UV-vis and Photoluminescence (PL).
9:00 PM - O3.58
Ion-pair Monomer Dependence and Correlation to Performance in Chemically-fixed Junction, Polymer Light-emitting Electrochemical Cells.
Deanna Rodovsky 1 , Janelle Leger 1 , Glenn Bartholomew 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show Abstract9:00 PM - O3.6
Engineering Carrier Transport Across Organic Heterojunctions by Interface Doping.
Sai Wing Tsang 1 , Zheng Hong Lu 1 , Ye Tao 2
1 Material Science and Engineering, University of Toronto, Toronto , Ontario, Canada, 2 Institute for Microstructural Sciences, National Research Council of Canada, Ottawa, Ontario, Canada
Show Abstract9:00 PM - O3.7
Comparative Studies on the Stability of Polymer Gate Dielectrics for Pentacene Thin-film Transistors.
Sang Chul Lim 1 , Seong Hyun Kim 1 , Jae Bon Koo 1 , Yong Suk Yang 1 , Jung Hun Lee 1 , Chan Hoe Ku 1 , Gi Heon Kim 1 , Kyung Soo Suh 1 , Taehyoung Zyung 1
1 ICCL, ETRI, Daejeon Korea (the Republic of)
Show Abstract
Symposium Organizers
Ana Claudia Arias Palo Alto Research Center
J. Devin MacKenzie Add-Vision, Inc.
Alberto Salleo Stanford University
Nir Tessler Technion-Israel Institute of Technology
O4: Device Physics and Materials
Session Chairs
Wednesday AM, April 11, 2007
Room 2002 (Moscone West)
9:30 AM - **O4.1
Simulations of State of the Art P-OLED Devices.
Matthew Roberts 1
1 , Sumation, Cambridge United Kingdom
Show Abstract10:00 AM - O4.2
Characteristics of an Organic Light-Emitting Diode Utilizing a Phosphorescent, Shallow Hole Trap
Ian Campbell 1 , Brian Crone 1
1 Materials Physics & Applications, Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractWe demonstrate the effects of incorporating a phosphorescent, shallow hole trap in an organic light-emitting diode. We present device properties as a function of trap concentration including: electron only, hole only, and bipolar current-voltage (I-V) characteristics, electroluminescence (EL) and photoluminescence spectra, and diode quantum efficiency. We specifically considered poly (9,9-dioctylfluorene) doped with an Ir phosphor. Built-in potential and I-V measurements were used to determine that the phosphor is a shallow hole trap. The EL spectrum is dominated by phosphor emission for concentrations above 0.1 wt%. The effects of incorporating the phosphor are shown to be consistent with quasi-equilibrium statistics.
10:15 AM - O4.3
Bipolar Transport and Device Performance - Solar Cells and Transistors.
Lars Andersson 1 , Olle Inganas 1
1 Biomolecular and Organic Electronics, Department of Phycics, Chemistry and Biology, Linköpings universitet, Linköping Sweden
Show AbstractConjugated polymers are rapidly approaching mainstream commercialisation in a wide variety of electronic applications such as transistors and solar cells. Both of these structures are possible to use for electrical characterisation, and although there are several fundamental differences, such as film anisotropy and carrier concentrations that influence transport, there is still a substantial common ground where observations on the different structures can give a more thorough understanding of the transport properties than can a single type of experiment. This is especially true for blend materials such as the bulk heterojunctions used in most high performance solar cells, where transport is bipolar and where there is ample room for morphological variations.Electrical data, mainly collected from charge extraction measurements on solar cells and transistor i/v measurements, for a wide range of materials, most of which are based on alternating copolymers of fluorene and donor-acceptor-donor segments blended with substituted C60 and C70 fullerenes, will be shown. The polymers have varying electron affinities and ionisation potentials with band gaps as low as 1 eV. Solar cells from these materials reach power conversion efficiencies of 3.5 % at high band gap and 2.2 % with lower band gap materials.Among the results are resolved electron and hole transients, observed for the first time in optimised organic bulk heterojunction solar cells, where the stoichiometry dependence of electron and hole mobility can be followed and correlated to transistors with good agreement. Both solar cells and transistors reveal a high percolation threshold for electron currents, and that both the hole and electron mobilities are severely dependent on the polymer / fullerene system rather than just the constituents. This has obvious implications for solar cell design and also indicates that composite systems can be useful in transistor applications where the polarity of a transistor can be tailored from p-type to ambipolar to n-type. The good correlation between the solar cell and transistor measurements indicate that the same theoretical models should be applied to both systems. To this end, some remarks on how the Gaussian disorder model, which has found widespread use for diodes but only been sparingly applied to transistors, can explain many experimental observations such as hysteresis and light enhanced stress recovery in transistors, will be given.
10:30 AM - **O4.4
Hybrid Organic/inorganic Materials For White Light-Emitting Diodes.
Gitti Frey 1 , Eyal Aharon 1 , Michael Kalina 1
1 Materials Engineering, Technion, Haifa Israel
Show AbstractConjugated polymers have received a great deal of interest for a variety of applications, especially in displays; however, the production of white light has been problematic because the width of an emission peak from a single polymer species is generally not broad enough to cover the entire spectrum of visible light. As a consequence, pure white emission from a polymer light-emitting diode requires that separate red, green, and blue chromophores be present in the active layer and emit simultaneously. Here, a new and general strategy for white photoluminescence and electroluminescence from a single material is demonstrated. In this material, red, green, and blue emitting conjugated polymers are confined within the galleries of a layered semiconducting host matrix. The host, SnS2, not only supports the transport of charge carriers, but also hinders polymer π-π interactions which are responsible for the energy transfer between polymer chains. Consequently, emission from the three chromophores is observed simultaneously resulting in white photoluminescence. The efficacy of the nanocomposites is demonstrated in simple single-layer white-emitting polymer diodes. The mechanism suggested here for white light generation, supported by extensive luminescence measurements, is in contrast to that previously reported in white-emitting polymer diodes where efficient energy transfer between polymer chains was essential for obtaining white light, but also contributes processing complications and poor color stability. Facile integration of the conjugated polymer/layered semiconductor nanocomposites into optoelectronic devices shows their suitability to open additional approaches towards the development of functional nanocomposite materials for solid-state lighting applications.
11:30 AM - **O4.5
Air-stable Polymer Electronic Devices.
Alan Heeger 1 , Kwanghee Lee 1 , Jin Young Kim 1
1 , UCSB, Santa Barbara, California, United States
Show Abstract12:00 PM - O4.6
Long Lifetime Polymer Light Emitting Electrochemical Cells
Yan Shao 1 2 , Guillermo Bazan 1 2 , Alan Heeger 1 2
1 CPOS, University of California, Santa Barbara, Santa Barbara, California, United States, 2 MC-CAM, University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractPolymer light-emitting electrochemical cells (LECs) with long operating lifetimes are reported. A soluble phenyl-substituted poly(para-phenylene vinylene) (PPV) copolymer (“superyellow”) was used as the host light-emitting polymer and methyltrioctylammonium trifluoromethanesulfonate, an ionic liquid, was used to introduce a dilute concentration of mobile ions into the emitting polymer layer. The ions inside the luminescent semiconducting polymer can be spatially redistributed by applying a voltage at a temperature above the melting point of the ionic liquid. These ionic liquid based LECs, with stable aluminum metal as cathode, exhibit excellent current-rectification diode properties, a single-phase active layer, short response time, and long continuous operating lifetime.
12:15 PM - O4.7
A Quantitative Morphological Model for the Conductivity of PEDOT:PSS.
Alexandre Nardes 1 , Martijn Kemerink 1 , Rene A.J. Janssen 1 , Jolanda A.M. Bastiaansen 2 , Nicole M.M. Kiggen 2 , Bea M.W. Langeveld 2 , Albert J.J.M. Breemen 2 , Margreet M. Kok 3
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 , TNO Science and Industry, Eindhoven Netherlands, 3 , Philips Research Laboratories, Eindhoven Netherlands
Show Abstract12:30 PM - O4.8
Device Model for Light-Emitting Field-Effect Transistors with Organic Semiconductor Channel.
P.Paul Ruden 1 , Darryl Smith 2
1 , University of Minnesota, Minneapolis, Minnesota, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractRecent experiments have demonstrated ambipolar channel conduction and visible light generation through radiative recombination in conjugated polymer field effect transistors.[1,2] The devices have source and drain contacts biased to inject negative charge carriers (electron polarons or electrons) from one contact and positive charge carriers (hole polarons or holes) from the other. In the ambipolar mode of operation, the gate potential lies between the potentials of the electron and hole injecting contacts, so that electrons dominate the channel conductance near the electron injecting contact and holes dominate channel conductance near the hole injecting contact. The injected charge carriers propagate along the field-effect-induced channel and recombine in regions where both types of carriers are present. The location and intensity of maximum recombination and light emission are controlled by the voltages applied to the three transistor terminals. In this work a new device model for ambipolar organic field effect transistors based on the gradual channel approximation is presented. Trapping of injected carriers in localized states within the band gap is shown to be an important mechanism in these devices. The model includes the effect of trapping through carrier density dependent mobilities.[3] Because the carrier densities depend on the local gate-to-channel voltage, the mobilities vary throughout the channel. Recombination is limited by a mobility dependent Langevin mechanism. A non-linear differential equation for the channel potential is derived and solved numerically. Subsequently, charge carrier density profiles and recombination profiles are determined. In addition, the limit of high recombination probability, which leads to analytical results, is discussed. The results of the device model are in good agreement with the recently published[1,2] experimental data for polymer light emitting field effect transistors.References:[1] J.S. Swenson, C. Soci, and A.J. Heeger, Appl. Phys. Lett. 87, 252511 (2005).[2] J. Zaumseil, R.H. Friend, and H. Sirringhaus, Nature Materials 5, 69 (2006).[3] A. Salleo, T.W. Chen, A.R. Volkel, Y. Wu, P. Liu, B.S. Ong, and R.A. Street, Phys. Rev. B 70, 115311 (2004).
12:45 PM - O4.9
Self-assembled, Chemically Fixed pn Junctions in Doped Organic Semiconductors.
Glenn Bartholomew 1 , Janelle Leger 1 , Deanna Rodovsky 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractO5: Materials Physics and Characterization II
Session Chairs
Wednesday PM, April 11, 2007
Room 2002 (Moscone West)
2:30 PM - **O5.1
Excited States at Polymer Semiconductor Heterojunctions.
Astrid Gonzalez-Rabade 1 , Johanna Schmidke 1 , Richard Friend 1
1 , Cavedish Laboratory, Cambridge United Kingdom
Show AbstractBound charge-transfer excitons (exciplexes) can form at appropriate polymer-polymer Heterojunctions, and for some material combinations can still show radiative emission (with strongly increased radiative lifetimes and large red-shifts). Long-range charge separation, as required in a photovoltaic diode, needs an external field. We show that the reduction in exciplex formation (detected as quenching of exciplex luminescence) due to an external field matches quantitatively the increase in current collected in the external circuit.The strength of interchain interactions can be increased under pressure, and measurements of absorption and time-resolved luminescence under hydrostatic pressure will be reported. These reveal the changing character of the exciplex at the heterojunction.
3:00 PM - O5.2
Organic Field-Effect Transistor with Low Operating Voltages Using Anodized Ta2O5 Gate Dielectric.
Yeon Taek Jeong 1 2 , Byungwook Yoo 1 3 , Ananth Dodabalapur 1 3
1 Microelectronics Research Center, The University of Texas at Austin, Austin, Texas, United States, 2 Materials Science & Engineeing, The University of Texas at Austin, Austin, Texas, United States, 3 Electrical & Computer Engineering, The University of Texas at Austin, Austin, Texas, United States
Show AbstractOrganic field-effect transistors (OFET’s) have been attracting considerable attention because of their potential applications in active matrix display drivers, radio-frequency identification tags, sensors, etc. Although there have been significant advances in fabricating OFET’s with reasonably high electron and hole mobility, their generally high operating voltages still remain a major drawback to practical applications. In organic electronics, plastic substrates are essential to make the best use of the unique properties of organic devices such as low temperature process and flexibility. To address the problem of high operating voltages and implement a low temperature process compatible with plastic substrates, anodization was performed on Ta thin film at room temperature, thereby obtaining high-k Ta2O5 (εr: 25.0), where 0.01 M of citric solution was used as the electrolyte. Top contact devices were fabricated using pentacene and gold as channel and source/drain contact materials, respectively. The channel length was 50 µm, and width 500 μm. Anodized Ta2O5 of 1,700 Å was obtained from the Ta thin film sputtered and annealed on a p-Si wafer substrate. The roughness of anodized Ta2O5 measured by AFM was around 22.9 Å, which was much larger than that of commonly-used thermally-grown SiO2 2.6 Å. The AFM images also showed that the grain size of the pentacene layer was relatively small and highly dependent on the surface roughness of the anodized Ta2O5 layer. Nonetheless, the device showed significant potential in that its saturation mobility μsat, threshold voltage VT, Ion/Ioff ratio at Vds = -5 V and Vg = 0 & -2.5 V, are 1.09 cm2/V.s, -1.28 V, 1.64 × 102, respectively. The gate leakage is -110 nA at Vds = 0 V and Vg = -2.5 V, and it decreases by 40 % when the insulator is subjected to an HMDS treatment. The HMDS treatment also results in slightly enhanced saturation mobility, decreased threshold voltage by a factor of two, and increased Ion/Ioff ratio by more than an order of magnitude, which suggests that the characteristics of an anodized Ta2O5 device can be improved by a proper surface treatment. In summary, we demonstrated that high-performance anodized OFET’s with Ta2O5 gate dielectric have the potential to attain low operating voltages and a low temperature process compatible with plastic substrates. The HMDS treatment resulted in slightly enhanced saturation mobility, decreased threshold voltage by half, and increased Ion/Ioff ratio by more than an order of magnitude. Future research will be focused on improving the characteristics of the anodized Ta2O5 device by achieving a smoother surface, and reducing the gate leakage current with suitable surface treatments other than HMDS. The realization of devices on plastic substrates is another area of interest, where Ta films will be formed on low-temperature-compatible substrates by e-beam evaporation without high temperature annealing.
3:15 PM - O5.3
Bifunctional Field-Effect Transistors Based on Ambipolar Organic Semiconductors
Thomas Anthopoulos 1 , Paul Woebkenberg 1 , Edsger Smits 2 3 , Paul Blom 2 , Dago de Leeuw 3
1 Department of Physics, Imperial College London, London United Kingdom, 2 Materials Science Centre, University of Groningen, Groningen Netherlands, 3 , Philips Research Laboratories, Eindhoven Netherlands
Show AbstractRecent years have seen tremendous advances in the area of organic opto-/electronic devices and several previously envisioned applications are now reaching the stage of commercial exploitation. Organic field-effect transistors (OFETs) are among these devices and can be arguably viewed as a possible alternative to their inorganic counterparts in a range of low-cost, high-volume applications. Traditionally, OFETs have been used as pixel switches in active matrix displays and as the building blocks in integrated circuits where mechanical flexibility and low-cost fabrication are two prerequisites [1]. Recently, novel bifunctional OFETs have also made their debut where in addition to their classical current modulating function, light-emission as well as light-sensing has been reported [2-4]. Such electro-optical transistors are interesting for two reasons. First, the ability of combining opto-electronic functionality in a single device increases the number of potential applications, and secondly, it provides an ideal experimental platform for the study of various fundamental physical processes within organic semiconductors. Here we report on two types of bifunctional OFETs based on ambipolar organic semiconductors. The first device type is near infrared light-emitting OFETs (LEOFETs). The second device type is photo-sensitive OFETs. It is anticipated that integration of such bifunctional devices may lead to all-organic electro-optical switches and circuits and can be viewed as a significant breakthrough. In this work, LEOFETs are realised using a single ambipolar organic semiconductor. Due to the narrow band gap of the semiconductor simultaneous injection of electron/holes is possible allowing the formation of a recombination zone from which light emission occurs. We are able to accurately model the position of the recombination zone using a new model based on variable range hopping theory [5]. Based on experimental data and theoretical predictions we are able to estimate the distance at which metal-induced electroluminescence (EL) quenching occurs as the recombination zone approaches the source/drain electrodes. When recombination occurs at some distance away from the metal electrodes, EL efficiency remains constant. By selecting suitable ambipolar semiconductors we are able to realise light-sensitive OFETs with fast frequency response. Here device current is modulated by the incident light due to photogenerated carriers. By measuring the frequency response we are able to calculate the maximum operating speed of our light-sensing ambipolar OFETs. Such device provides significant advantages over conventional diode-type photodetectors due to their intrinsically low RC constants. [1]G. H. Gelinck, et al. Nat. Mater. 3, 106 (2004). [2]A. Hepp, et al. Phys. Rev. Lett., 91, 157406 (2003). [3]J. Zaumseil, et al. Nat. Mater. 5, 69 (2006). [4]N. Marjanovic, et al. Org. Ele. 7, 188 (2006). [5]E. C. P. Smits, et al. Phys. Rev. B., 73, 205316 (2006).
3:30 PM - **O5.4
Material Design And Structure – Property Relation Of A Novel Low-Bandgap Polymer – Correlation Between The Electro-Optical Properties And Photovoltaic Device Performance.
Christoph Brabec 1 , M. Scharber 1 , M. Koppe 1 , M. Morana 1 , Z. Zhu 1 , R. Gaudiana 1 , D. Waller 1
1 , Konarka Technologies Inc., Linz Austria
Show AbstractOne promising way to further develop the performance of organic solar cells is the design of low-bandgap copolymers, allowing to capture a larger fraction of the solar spectrum. However, the charge transport in most of these materials is frequently too low, probably a consequence of the electronic distortion along the backbone which is necessary to reduce the bandgap (at least for donor – acceptor (D-A) type polymers). Additional, the high degree of disorder, partially related to the alternating structure of D-A type copolymer is a reason for low mobility observed in these material classes.. We present a study of the transport properties of a novel low-bandgap conjugated polymer with high photovoltaic quantum efficiencies in the near infrared spectral region. The polymer poly BBTBT, consisting of alternating electron-rich diethyl hexyl bridged bithiophene units (BBT) and electron-deficient 2,1,3-benzothiadiazole (BT) units has a bandgap of 1.35 eV and a mobility in the order of 10-2 cm2/Vs or higher.Based on this specific donor, a whole class of low bandgap D-A polymers can be built. We discuss the electro-optical properties of this material class, investigate the structure – property relation and outline the impact on the photovoltaic performance.
4:30 PM - **O5.5
Micron to Nanometer Scale Pentacene Thin Film Transistors
Cherie Kagan 1 2 , Ali Afzali 1 , George Tulevski 3 1 , Qian Miao 3 , Colin Nuckolls 3 , Teresita Graham 1
1 , IBM T. J. Watson Research Center, Yorktown Heights, New York, United States, 2 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 , Columbia University, New York, New York, United States
Show AbstractWe report the device characteristics of micron and nanometer scale pentacene thin film transistors (TFTs) fabricated using a solution processable precursor route. The solution processable precursor route to pentacene TFTs retains the desirable mobility of ~0.5-1 cm2/V-s and current modulation >107 found in evaporated pentacene devices. In this talk, we describe measurements of repeated stressing and environmental exposure on the operational stability of pentacene TFTs, necessary for their application. We show that device degradation is consistent with thermal-oxidation of the channel that can be limited by reducing the operational power (through device scaling) or by limiting device exposure to ambient air. We also address a key difference in the thin film morphology of pentacene films deposited by evaporation versus from a solution-processable precursor that results in greater stability of the solution-processed devices. Scaling devices is important not only to limit degradation, but to achieve high speed and high output current devices. We report well-behaved and electrostatically scaled sub-100 nm channel length pentacene transistors and describe the physics of organic transistor electrostatics and contacts. The effects of contact resistance, already observable in micron scale devices, become dominate in the characteristics of nanometer scale channels. We show that engineering the metal-molecule interface by self-assembling a pentacene-thione on the electrode surface prior to thin film deposition dramatically improves device performance. This particular electrode surface modification uniquely provides a structurally and electronically complementary structure to the pentacene thin film that supports the improved device characteristics.
5:00 PM - O5.6
Effect of Shallow Traps on Polaronic Transport in OFETs.
Mattew Calhoun 1 , Christine Hsieh 1 , Vitaly Podzorov 1
1 Physics Department, Rutgers University, Piscataway, New Jersey, United States
Show AbstractRecent development of single-crystal organic field-effect transistors (OFETs) with significantly reduced disorder enabled the realization of intrinsic (not dominated by trapping) polaronic transport at organic surfaces and interfaces (see, e.g., [1,2]). Nevertheless, the majority of OFETs is still dominated by shallow traps. Here, we propose a method of shallow trap characterization, based on photo-induced charge transfer across the semiconductor-dielectric interface in OFETs [3]. The photo-induced electron and hole transfer has been investigated in trap dominated p-type OFETs. It was observed that the transfer of electrons into the dielectric results in a decrease of the field-effect mobility of polarons, suggesting that additional shallow traps are generated in the conduction channel. Using this effect, the dependence of the field-effect mobility on the density of shallow traps, μ(N_shallow), has been measured, which allowed to estimate the average polaron trapping time, τ_tr = 50 ± 10 ps, and the density of shallow traps, N_shallow = (3 ± 0.5)10^11 1/cm^2, in the channel of single-crystal tetracene OFETs. [1]. R. W. I. de Boer, M. E. Gershenson, A. F. Morpurgo and V. Podzorov, Phys. Stat. Solidi, 201, 1302 (2004);[2]. M. E. Gershenson, V. Podzorov, and A. F. Morpurgo, “Colloquium: electronic transport in single-crystal organic transistors”, Rev. Mod. Phys. 78, 973 (2006);[3]. V. Podzorov and M. E. Gershenson, Phys. Rev. Lett. 95, 016602 (2005).
5:15 PM - O5.7
Frequency-response of the Accumulation Channel in Organic MISFETs
David Taylor 1 , David John 1 , Justin Lawrence 1
1 School of Electronics, University of Wales, Bangor, Gwynedd, United Kingdom
Show AbstractIt is customary to evaluate organic MISFET transistors by measuring their DC output and transfer characteristics. From these measurements important parameters such as the carrier mobility and on-off ratios may be determined. While allowing the DC operation of devices to be modelled and their intrinsic cut-off frequency to be estimated, this approach does not provide a means of determining the response of the device over a range of frequencies, which is an essential requirement for circuit modelling. We have already shown that admittance measurements can be used to great effect for investigating trapping of both majority [1] and minority charge carriers [2] in interface states. Following the approach by Nicollian and Goetzberger [3], we have now derived the frequency-dependence of the susceptance and conductance of the gate-voltage-induced accumulation channel in an organic MISFET under different operating conditions e.g. modulation of the source voltage with fixed gate voltage and grounded drain i.e. in the linear regime. As expected, the results show a strong dependence on (a) the sheet resistance, Rs, of the channel, which in turn is determined by the carrier mobility and gate voltage through control of the induced charge, (b) the gate capacitance per unit area, Ci and (c) device dimensions. At low-frequency, both the resistance and capacitance of the channel are constant and given by RsL/W and CiLW/3 respectively, where L and W are the channel length and width. The latter compares with 2CiLW/3 for the gate-channel capacitance for an enhancement-mode silicon MOSFET operating in saturation when the gate voltage is modulated. Above the cut-off frequency, both the capacitance and loss (conductance/angular frequency) become equal and decrease as f^(-0.5). In addition to predicting the frequency response of the device, application of the model to data from real devices enables a number of device/material parameters to be determined e.g. the dependence of Rs and hence carrier mobility on gate voltage in the linear regime, where mobility is trap-controlled. This is particularly important in hopping systems where the mobility determined under dc conditions may differ from that under ac conditions, because of the different time scales involved. Furthermore, the technique may be applied to n-channels formed during photocapacitance measurements [2] to determine electron mobilities without the need for a low work function electrode to encourage electron injection as is the case in an ambipolar transistor.[1] I. Torres and D. M. Taylor, 2005, J Appl Phys, 98, Art. No. 073710.[2] D. M. Taylor, J. A. Drysdale, I. Torres and O. Fernández, 2006, Appl Phys Lett, (in press). [3] E. H. Nicollian and A. Goetzberger, 1965, IEEE Trans ED-12, 108
5:30 PM - O5.8
Electric Field Induced Gap States in Pentacene.
Dietmar Knipp 1 , Amare Benor 1 , Arne Hoppe 1 , Veit Wagner 1 , Armin Voelkel 2
1 School of Engineering and Science, International University Bremen, Bremen Germany, 2 Electronic Materials and Devices Laboratory, Palo Alto Research Center, Palo Alto, California, United States
Show Abstract5:45 PM - O5.9
Metallic Transport in Electrolyte-Gated Polymer Field-Effect Transistors
Anoop Dhoot 1 , Jonathan Yuen 1 , Martin Heeney 2 , Iain McCulloch 2 , Daniel Moses 1 , Alan Heeger 1
1 Center for Polymers and Organic Solids, University of California, Santa Barbara, California, United States, 2 , Merck Chemicals, Southampton United Kingdom
Show AbstractWe have studied the carrier transport in conjugated polymer field-effect transistors (FETs) using electrolytes as the gate and gate dielectric. An easily removable, aqueous salt electrolyte is used to show that conventional bulk electrochemical doping of the semiconducting polymer is unimportant and that, instead, very high field-induced carrier densities, ~1022 charges/cm3, present in the device channel, lead to metallic conductivity, typically ≈102-104 S/cm at room temperature. At 4.2 K, devices gated using a polymer electrolyte exhibit metallic transport and support a remarkable current-carrying capacity without any noticeable degradation; the current density in the transistor channel exceeds 2×107 A/cm2.
O6: Poster Session: Materials, Devices and Characterization II
Session Chairs
Thursday AM, April 12, 2007
Salon Level (Marriott)
9:00 PM - O6.10
Organic Field-effect Transistors Based on Pi-congugated Materials.
Yunqi Liu 1
1 , Institute of Chemistry, Chinese Academy of Sciences, Beijing China
Show Abstract9:00 PM - O6.11
Energy Transfer Behaviors of semiconducting Polymers doped with Iridium-Complexes
Chan Im 1 , Jungyun Chang 1 , Jongdeok An 1 , Young Kwan Kim 2
1 Dept. of Chemistry, Konkuk University, Seoul Korea (the Republic of), 2 Dept. of Information Display, Hong-Ik University, Seoul Korea (the Republic of)
Show AbstractElectroluminescent devices based on organic materials are of considerable interest owing to their attractive optoelectronic properties and potential applications to flexible organic displays. In spite of some advantages, organic materials have a crucial fundamental limit correlated with singlet and triplet exciton formation probability. One of the advance of organic light-emitting diode (OLED) technology is the discovery of electrophosphorescence with which one can overcome the upper limit of the internal quantum efficiency. The design and synthesis of triplet emitting materials containing heavy-metal complexes, where strong spin-orbit coupling leads to singlet-triplet state mixing which removes the spin-forbidden nature of the radiative relaxation of the triplet state, are therefore particularly important in achieving high-efficiency electrophosphrescence in OLEDs. To understand the exact phosphorescent dopant-induced photoluminescence (PL) properties of photoactive thin films consisting of a pi-conjugated polymer matrix and a triplet dopant were prepared as thin films by the conventional spin coating method. As matrixes, diverse types of polymer including poly(9-vinylcarbazole) (PVK) and poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6) and as triplet emitters, some of typical iridium complexes including iridium(III)fac-tris(2-phenylpyridine) (Ir(ppy)3) or iridium(III)bis[(4,6- fluorophenyl)-pyridinato-N,C2’]picolinate (FIrpic) were chosen to study. Those doped films, as well as their pristine films, on quartz substrates were characterized by means of UV-Vis absorption, and PL and PL excitation (PLE) spectroscopy for a wide spectral range. It was found that the facility of exciton migration from matrix to dopant, and subsequent triplet emission, was significantly pronounced in the PVK-based blend systems. At the same time, PF2/6 blend systems showed an efficient PL quenching upon doping, although the PL maxima of the PVK and the PF2/6 as thin films were virtually identical.Additionally, we have performed series of cyclovoltammetric investigation to characterize their electrochemical properties. And we have also performed steady state photocurrent measurement to compare energy transfer behavior and electron transfer behavior within the films. Finally, we could show a competitive correlation between energy transfer and electron transfer between matrix and dopant molecules.
9:00 PM - O6.12
Electronic Time-of-flight Measurement of Charge Carrier Mobility in a Polymer Field Effect Transistor.
Debarshi Basu 1 , Dharmendar Reddy 1 , Lawrence Dunn 1 , Ananth Dodabalapur 1 , Martin Heeney 2 , Iain McCulloch 2
1 Microelectronics Research Center, The University of Texas at Austin, Austin, Texas, United States, 2 , Merck Chemicals, Chilworth Science Park,, Southampton, United Kingdom
Show Abstract9:00 PM - O6.13
Characterization of CuPc Semiconductor Thin Film Organic Field Effect Transistors (OFETs) Fabricated on Ultra-Thin High-k Gate Dielectrics.
Cynthia Burham 1 , Muhammad Hussain 2 , Baxter Womack 1
1 Electrical & Computer Engineering, The University of Texas at Austin, Austin, Texas, United States, 2 , SEMATECH, Austin, Texas, United States
Show Abstract9:00 PM - O6.14
Robust Ultra-thin Fluorescent Freestanding LbL Conjugated Polymer Films
Yen-Hsi Lin 1 2 , Chaoyang Jiang 1 , Jun Xu 2 , Zhiqun Lin 2 , Vladimir Tsukruk 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractThe successful fabrication of purely polymeric free-standing structures with nanoscale thicknesses is technically challenging because of poor mechanical stability of conventional polymers. Conjugated polymers (CP) composed of rod-like chains with much stronger mechanical properties than usual flexible-chain polyelectrolytes are exploited here for LbL assembly. We report fabrication of freely suspended purely polymeric CP films but with a true nanoscale thickness (below 20 nm) which demonstrated excellent mechanical properties combined with high fluorescence. Furthermore, these films offer the possibility for impact in the areas of photovoltaic cells, light emitting diodes (LED), thin-film transistors, and bio-sensors due to their intriguing optoelectronic properties.
9:00 PM - O6.15
Lower Hole-injection Barrier Between Pentacene and a 1-hexadecanethiol-modified Gold Substrate with a Lowered Work Function.
Ki Pyo Hong 1 , Jong Lee 1 , Sang Yang 1 , Kwonwoo Shin 1 , Hayoung Jeon 1 , Se Kim 1 , Chanwoo Yang 1 , Chan Park 1
1 Chemical Engineering, POSTECH, Pohang, Kyung Buk, Korea (the Republic of)
Show Abstract9:00 PM - O6.16
Polymer/Ta2O5 Hybride Gate Dielectrics for CuPc Thin-Film Transistors
Jia Gao 1 , Jianbin Xu 1 , Xiaojiang Yu 1 , Ning Ke 1
1 , The Chinese University of Hong Kong, Hong Kong Hong Kong
Show AbstractOrganic thin-film transistors (OTFTs) are of technical importance for applications of organic/photonic electronics. Modification of the inorganic high k gate dielectric with an ultrathin polymer buffer layer has been widely used for improving the device performance of OTFTs [1-3]. In this work, e-beam deposited Ta2O5 thin film was selected for the high k gate dielectric with the buffer layered modification by polymeric blend composed of PMMA (Polymethylmethacrylate) and PS (Polystylene). The transistor active layer of CuPc thin film was deposited after the buffer layered modification. It is found that the apparent mobility of the CuPc OTFT can be as high as 0.03 cm2/V-s. To understand the origin of the observed high mobility, the correlation between the morphology of CuPc thin film and the apparent device mobility has been investigated. Our results reveal that the average grain size (c.a. 60nm) of CuPc active layer with the buffer layered modification consisting of the polymeric blend is much larger than those without the polymeric blend treatment, which presumably facilitates the carrier transport and results in the high mobility. The resulting large grain size is tentatively assumed to result from the surface energy matching of the gate dielectric with CuPc whose surface energy is measured to be about 35 mJ/m2. This work is partially supported by the Research Grants Council of Hong Kong SAR, particularly, via Grant No. CUHK4172/06E.
9:00 PM - O6.17
Characteristics of Amorphous Indium Zinc Tin Oxide (IZTO) Anode for Phosphorescent Organic Light Emitting Diodes.
Han-Ki Kim 1 , Jae-Wook Kang 2 , Jang-Joo Kim 2 , Jung-Hyeok Bae 1
1 Dept. of Information and Nano Materials Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, Korea (the Republic of), 2 OLED center, Soeul National University, Silimdong, Seoul, Korea (the Republic of)
Show Abstract9:00 PM - O6.18
High-quality Thin-film Passivation by Catalyzer-enhanced Chemical Vapor Deposition for Organic Light-emitting Diodes.
Han-Ki Kim 1 , Jin-A Jeong 1 , Myung Soo Kim 2 , Jae-Wook Kang 3 , Jang-Joo Kim 3
1 Information and Nano Materials Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, Korea (the Republic of), 2 Core Technolgoy Lab., Samsung SDI, Suwon, Gyeonggi, Korea (the Republic of), 3 OLED center, Seoul National University, Silimdong, Seoul, Korea (the Republic of)
Show Abstract9:00 PM - O6.2
A New Organic-Solvent-Free Process for High Stability Flexible/Organic Thin Film Transistors
Jeng-Hua Wei 1 , HorngJiunn Lin 1 , Ying-Ren Chen 1
1 Electronics Engineering, Ching Yun University, Jung-Li Taiwan
Show AbstractIn this paper, we report a new soluble, organic-solvent-free process for organic thin film transistors (OTFTs). In general, the semiconducting and insulating layers of OTFT are dissolved in organic solvents and these organic solvent will damage the underlying layers, including the gate insulator and plastic substrate. It will cause undesirable leakage current. Besides, the water and oxygen molecule in the air usually oxidize the organic base material and the performance of OTFTs will degrade evidently. In our OTFTs, both the gate insulator & semiconducting channel are dissolved in the water and each layer is formed by spun-on process. The drawbacks of organic solvent can be removed and the highly air-stable OTFTs are completed. For the gate insulator, the silicon oxide film is deposited by a special liquid- phase deposition (LPD) process at low temperature. In this LPD process, the water and hydrofluorosilicic acid (H2SiF6) are mixed for the oxide deposition. For the semiconducting layer, the single-wall carbon nanotubes (SWNTs) are used as the channel materials for OTFTs. In this device, the SWNTs were dissolved in the mixture of water and Sodium dodecyl sulfate (SDS). In the OTFT, first the bottom gate electrode is fabricated, and then the LPD oxide is deposited on the Si wafer or plastic substrate. Subsequently, the SWNTs network is coated on the LPD-SiO2 at room temperature. By controlling the density and uniformity of SWNTs networks, the process will be optimized to meet the high mobility and high on/off current ratio requirements. Finally, the Au electrodes are formed by the shadow mask method and the top contact structure OTFT is finished. The I-V characteristics of this organic-solvent-free OTFT are measured. In this device, all the process and measurement are made in air. We found this device demonstrates a highly stabile performance. As keeping the devices in the air for the several days, no evident drain current degradation is found.
9:00 PM - O6.20
Correlation Between Structure and Optical Properties of High Energy Gap poly(p-phenylenedifluorovinylenes.
Maria Losurdo 1 , Maria Giangregorio 1 , Pio Capezzuto 1 , Giovanni Bruno 1 , Antonio Cardone 2 , Carmela Martinelli 2 , Gianluca Farinola 2 , Francesco Babudri 2 , Francesco Naso 2
1 Chemistry, IMIP-CNR, Bari Italy, 2 Chemistry, ICCOM-CNR, University of Bari, Bari Italy
Show Abstract9:00 PM - O6.21
High-performance Organic Light-emitting Diodes Prepared Using an Amorphous IZO Anode Film.
Han-Ki Kim 1 , Jong-Min Moon 1 , Jung-Hyeok Bae 1 , Jae-Wook Kang 2 , Jang-Joo Kim 2
1 Information and Nano Materials Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, Korea (the Republic of), 2 OLED center, Soeul National University, Silimdong, Seoul, Korea (the Republic of)
Show Abstract9:00 PM - O6.22
Novel Aromatic Diimides from the Diels-Alder Trapping of Photochemically Generated Bisdienes - Potential Materials for Photo- and Electroluminescent Devices.
Michael Meador 1 , Daniel Tyson 2 , Faysal Ilhan 2
1 , NASA Glenn Research Center, Cleveland , Ohio, United States, 2 , Ohio Aerospace Insitute, Brook Park, Ohio, United States
Show Abstract9:00 PM - O6.24
Efficient Top-emitting Polymeric White Light-emitting Diodes with Improved Charge-injection.
Juo Hao Li 1 , Jinsong Huang 1 , Yang Yang 1
1 Materials Science & Engineering, UCLA, Los Angeles, California, United States
Show Abstract9:00 PM - O6.26
Structural Investigation of Tetraceno[2,3-b]thiophene Thin Films for Transistor Applications.
Quan Yuan 1 , Stefan Mannsfeld 2 , Minglee Tang 2 , Michael Toney 3 , Jan Luning 3 , Zhenan Bao 2
1 Materials Science and Engineering, Stanford University, Palo Alto, California, United States, 2 Chemical Engineering Department, Stanford University, Palo Alto, California, United States, 3 Stanford Synchrotron Radiation Laboratory, Stanford University, Palo Alto, California, United States
Show Abstract9:00 PM - O6.27
Patterning of Organic Single Crystal Transistor Devices from Solution
Stefan Mannsfeld 1 , Armon Sharei 1 , Jason Locklin 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:00 PM - O6.28
Field Effect Transistors of Single Crystal Benzo-annulated Fused Oligothiophenes and Oligoselenophenes.
Yukihiro Tominari 1 , Koichi Yamada 2 , Masakazu Yamagishi 1 , Toshihiro Okamoto 3 4 , Kenichi Kudoh 3 4 , Atsushi Wakamiya 3 4 , Shigehiro Yamaguchi 3 4 , Jun Takeya 1
1 , Osaka University, Toyonaka Japan, 2 , CRIEPI, Komae, Tokyo, Japan, 3 , Nagoya University, Nagoya Japan, 4 , SORST, JST, Kawaguchi Japan
Show Abstract9:00 PM - O6.29
Effect of Fabrication Temperatures on the Performance of Polypyrrole Coated Conductive Fabrics.
Xiaoyin Cheng 1 , Xiaoming Tao 1 , Xiaoxiang Cheng 1 , Hing Yee Joanna Tsang 1 , Pu Xue 1
1 Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong China
Show Abstract9:00 PM - O6.3
Fullerene/phthalocyanine as Ambipolar Transport Materials for Organic Light Emitting Devices.
Yanyan Yuan 1 , Zhenghong Lu 1 , Wenli Jia 2 , Suning Wang 2
1 , University of Toronto, Toronto, Ontario, Canada, 2 , Queen's University, Toronto, Ontario, Canada
Show Abstract9:00 PM - O6.30
Vertical-type Organic Hot-carrier Triodes Operated in Saturation Region with Ultra-high Gain.
Chuan-Yi Yang 1 , Tzu-Min Ou 1 , Shiau-Shin Cheng 1 , Meng-Chyi Wu 1 , Yi-Jen Chan 3
1 Institute of Electronics Engineering, National Tsing Hua University, Hsinchu Taiwan, 3 Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan
Show Abstract9:00 PM - O6.31
Origin of Green Emission in Extremely Pure Oligofluorene Films: Effect of Molecular Packing
Jihoon Kang 1 , Nayool Shin 1 , Jungho Jo 1 , Panagiotis Keivanidis 2 , Frédéric Laquai 2 , Gerhard Wegner 2 , Do Yoon 1
1 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 , Max Planck Institute for Polymer Research, Mainz Germany
Show AbstractTime-resolved photoluminescence spectroscopy measurements of oligofluorenes with various side chains were studied. With extremely pure oligofluorenes, two kinds of red-shifted green emission were identified which have different origins; intermolecular interaction and on-chain chemical defect. Moreover, the unusual spectroscopic behavior of siloxane end-capped oligofluorenes, which exhibit high-order liquid crystalline phase, demonstrated that the molecular packing plays a serious role in the low energy emissions of the solid films of oligofluorenes, and therefore, polyfluorenes.
9:00 PM - O6.33
Directly Imprinted DFB Polymer Sensor Laser Devices.
Martin Gaal 1 , Michael Teuchtmann 2 , Veronika Rinnerbauer 2 , Christine Hasenfuss 2 , Holger Schmidt 3 , Kurt Hingerl 2 , Emil J.W. List 1
1 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Graz, Austria and Institute of Nanostructured Materials and Photonics, JOANNEUM RESEARCH, Weiz Austria, 2 Christian Doppler Laboratory Surface Optics, Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Linz Austria, 3 Institute of Applied Physics, Friedrich Schiller University Jena, Jena Germany
Show AbstractConjugated polymers have attracted remarkable interest since they inhere convenient photo-physical properties and simple device fabrication. Their tune-ability over the whole visible spectrum combined with broadband emission and strong absorption make them to ideal candidates for solid state laser devices. Furthermore, with increasing demand for security applications, improvements regarding the sensitivity of chemical and biological sensors will greatly benefit from an ascending emphasis on sensor devices based on conjugated polymers. For this purpose enhancing the sensitivity of conjugated polymers on environmental factors, such as oxygen, water, specific organic vapors, etc. is an important step towards novel sensor devices. This sensitivity enhancement can be achieved by using conjugated polymer laser device, which bear the advantage of amplified spontaneous emission and laser emission being orders of magnitude more responsive to analytes than the regular photoluminescence from films.We report on the detection enhancement of an optical sensing device by means of amplified spontaneous emission as well as laser emission from the conjugated polymer poly[(2-methoxy-5(2-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Upon photo-pumping of spin-caste films with the striped, focused 532 nm pulsed output of a Nd:YAG laser, amplified spontaneous emission was achieved. Periodic distributed feedback (DFB) structures were fabricated directly in the active polymer layer using a cheap soft-lithographic technique of liquid imprinting. Starting with a single master, a multiplicity of stamps can be fabricated. Furthermore, the liquid imprinting step can be performed several times using the very same stamp. This makes liquid imprinting to a simple, inexpensive, versatile and repeatable process, which enables to structure a wide range of materials and makes this method a promising candidate for mass production of conjugated polymer laser sensor devices. When the structured 390 nm distributed feedback grating was photo-pumped, laser emission was observed perpendicular to the substrate. For both, ASE as well as lasing, we monitored the thresholds under the influence of argon and ambient atmosphere, resulting in a change in the output emission intensity. In our investigations a change in output intensity divided by initial output intensity of about 50% for ASE and ca. 90% for laser emission above threshold was obtained.
9:00 PM - O6.35
Extremely High Efficiency Orange-Red Organic Electrophosphorescent Devices Using Novel Electron Transport Materials Containing Dipyridylphenyl Groups.
Junji Kido 1 2 , Eisuke Gonmori 1 , Nobuhiro Ide 2 , Daisaku Tanaka 1 2 , Ken-ichi Nakayama 1 2 , Yong-Jin Pu 1
1 Polymer Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan, 2 , Optoelectronic Industry and Technology Development Association, Bunkyo-ku, Tokyo, Japan
Show Abstract We have synthesized novel electron transport materials containing dipyridylphenyl groups. These materials have low LUMO level of about 3.2 eV, which can be expected to decrease electron injection barrier from cathode. In addition, these materials have wide HOMO-LUMO energy gap of about 3.5 eV, which leads to enough high triplet energy level to confine the triplet energy of phosphorescent metal complexes. We fabricated and evaluated the orange-red electrophosphorescent devices with a structure of ITO / p-doped polymer buffer layer / wide-gap arylamine hole-transport layer / CBP doped with PQ2Ir(dpm) / dipyridylphenyl compound / LiF / Al. The device exhibited low drive voltages and an extremely high power efficiency of 49 lm/W and an external quantum efficiency of 20 percent at 100cd/m2. Even at 1000cd/m2, a luminous efficiency of 30 lm/W was obtained. To calculate these efficiency values, angular distribution of emission from the device was characterized and considered. These values are the highest so far reported for orange-red electrophosphorescent devices.
9:00 PM - O6.37
Perfluorinated Oxadiazole-based Oligomers for N-type Semiconductor Devices.
Howard Katz 1 , Amy Sarjeant 1 , Chad Landis 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractDevelopments in the field of organic semiconductors have progressed at an astounding rate over the past couple of decades. Nearly all of this research is based on p-type materials and in order to further expand the knowledge and possibilities of this field, a greater number of n-type semiconducting materials with mobilities on par with p-type materials are necessary. Previous examples of n-type materials show that the additions of highly electron-withdrawing groups and the addition of perfluoro groups are necessary for an effective n-type material. Our strategy involves the addition of perfluoro groups to oxadiazole-based oligomers. Oxadiazoles are known to have a higher electron affinity than thiophene and have already seen use in polymers as electron transport materials for organic LEDs. Our first derivatives are oligomers consisting bis-oxadiazoles capped with either trifluoromethylphenyl or perfluorophenyl groups. Single-crystal XRD and electrochemistry was carried out of these first derivatives, which show that the derivatives have reduction potentials at or less than -1.5 V. X-ray diffraction shows that the trifluoromethylphenyl derivative packs in a slipped-stack fashion. Initial attempts at device preparations from these new derivatives are also underway.
9:00 PM - O6.38
High Work Function Materials for Source/Drain Electrodes in Printed Polymer TFTs.
Veronica Sholin 1 , Robert Street 2 , Fred Endicott 2 , Ana Arias 2
1 Physics, University of California Santa Cruz, Santa Cruz, California, United States, 2 , Palo Alto Research Center, Palo Alto, California, United States
Show AbstractPart of the challenge of fully printing polymer-based TFT arrays is finding suitable inks for the source and drain electrodes. The source and drain are in direct contact with the semiconducting polymer and a high work function ink is required for charge injection and minimal contact resistance at that interface. In addition to this, the ink must be homogeneous, compatible with the printer nozzle, and highly conductive. Gold nanoparticle inks satisfy these requirements; however, lower cost alternates are preferred. In this study we consider the use of Pedot:PSS (a high work-function polymer) in combination with Ag nanoparticles in bilayer structures and blends as an alternative material for source and drain of polymer-based TFTs. We also tested the use of a Pedot:PSS solution modified by the addition of conductivity enhancers such as Ethylene Glycol and poly(vinyl) pyrrolidone. These materials were tested in a TFT structure with (poly[5,5 -bis(3-dodecyl-2-thienyl)-2,2 -bithiophene] (PQT-12) as the semiconducting layer. TFTs with Ag:Pedot bilayers and the modified Pedot as source and drain showed very low contact resistance and transistor characteristics comparable to those of Au electrode devices. TFT mobilities of 4x10-3cm2/Vs, ON/OFF ratios of 106, and subtreshold slopes of 2.7V/decade were achieved at drain voltages of 30V. Although yielding good transistor characteristics (with mobilities of 10-2cm2/Vs and ON/OFF ratios of 107), full sintering of the Ag nanoparticles in the blends was hindered by the PSS in the Pedot:PSS solution. We were not able to achieve the high conductivity of pure Ag nanoparticles films when using the blend. Film morphology and printing conditions will also be discussed.
9:00 PM - O6.39
Permeation Rate Measurements of Flexible Thin-film Encapsulation by Calcuim Corrosion Test.
Namsu Kim 1 , Seunghyup Yoo 2 , William Potscavage 2 , Benoit Domercq 2 , Bernard Kippelen 2 , Samuel Graham 1
1 School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract9:00 PM - O6.4
Dielectric Materials for Low Operating Voltage Organic Thin-film Transistors.
Mark Roberts 1 , Nuria Queralto 2 1 , Stefan Mannsfeld 1 , Zhenan Bao 1 , Wolfgang Knoll 2
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 , Max Planck Institute for Polymer Research, Mainz Germany
Show Abstract9:00 PM - O6.40
Characterization of the Mesophase of a High Performance Semiconducting Polymer.
Andrew Moad 1 , Dean DeLongchamp 1 , R. Kline 1 , David Gundlach 1 , Daniel Fischer 1 , Lee Richter 1
1 , NIST, Gaithersburg, Maryland, United States
Show Abstract9:00 PM - O6.41
Organic Molecular Monolayers for STM-induced Light Emission Measurements.
Alan Wan 1 , James Long 2 , Antti Makinen 1
1 Optical Sciences Division Code 5611, Naval Research Laboratory, Washington , District of Columbia, United States, 2 Chemistry Divison Code 6176, Naval Research Laboratory, Washington , District of Columbia, United States
Show Abstract9:00 PM - O6.42
The Influence of Inserting Novel Metal for Transparent PLEDs
Chao-Wen Teng 1 , Yen-Hsun Lu 1 , Kou-Chen Liu 1 , Lai-Cheng Chen 2 , Sung-Cheng Hu 3
1 Graduate Institute of Electro-Optical , Chung Gung University, Tao-Yuan Taiwan, 2 , DELTA OPTOELECTRONICS, INC, Hsinchu Taiwan, 3 , Chung Shan Institute of Science and Technology, Tao-Yuan Taiwan
Show AbstractIn this work, the different metals were inserted below the ITO cathode to fabricate transparent PLEDs. The well performance of ITO can be easily achieved using sputtering deposition at low temperature. However, the ITO cathode sputtering usually accompanies with bombard damage that degrades the performance of devices. Moreover, the high work function of ITO cathode also reduces the electron injection ability. Therefore, a thin metal/LiF layer is inserted to diminish the sputtering damage and modify the electron injection barrier. The literatures indicated that using low work function metals associate with LiF layer will sufficiently increase the electron injection. However, these metals are sensitive with environment, especially during ITO cathode sputtering. Therefore, the stable metals, such as Al, Ag, and Au were attempted for a buffer layer. The reaction between Al and LiF will enhance the electron injection that is well known. Base on our investigation, inserting Ag layer has the similar phenomenon, although the enthalpy formation barrier of this reaction is larger than Al/LiF. It is suggested that the sputtering process of ITO will transfer the kinetic energy to the heat which help to overcome the formation barrier. However, the reaction between Au/LiF is not significant due to Au is much stable. Hence, the devices show the turn on voltage of 4.6, 4.8, 6.6, and 7V for devices with Al, Ag, ITO, and Au. The different work function metals also influenced the leakage current which perform the value of 3.6E-7, 3.73E-7, 4.1E-7, and 9.32E-7 A/cm2 for devices with Al, Ag, ITO, and Au, respectively. The higher work function metal cause the larger leakage current that can be attributed to the lower barrier height for hole injection at reverse bias. The maximum luminance of devices is 1200, 5300, 4870, and 2600 cd/m2 for Al, Ag, ITO, and Au. The luminance reduced with increasing work function except the device with Al. The high work function metal leads to the large electron injection barrier and reduce the luminance due to the carrier unbalance. The device with Al shows the lowest luminance that may be explained by the Li ion diffusion. Al easily reacts with LiF to liberate Li ions, and the sputtering-generation heat will further drive Li ion into emitting layer to form the quench centers. This conjecture was also examined by XPS measurement that shows the device with Al metal has the higher Li concentration in emitting layer than others. It is believed the quench centers will reduce the emission intensity. The XPS result also shows the device with thin metal layer has lower concentration of In, Sn and O which are the components of ITO in emitting layer than device without metal layer. This result implied that a thin metal sufficiently diminishes the sputtering bombard. In conclusion, choosing the proper novel metal, such as Ag will not only perform the lower operation voltage and lower leakage current, but also reduce the sputtering bombard damage.
9:00 PM - O6.43
Surface Enhanced Fluorescence in Light Emitting Conjugated Polymer Films
A. Holt 1 , S. Carter 1
1 Physics, UC Santa Cruz, Santa Cruz, California, United States
Show Abstract9:00 PM - O6.44
High-k Dielectrics for Organic MISFETs
David Taylor 1 , Janet Lancaster 1 , Henrique Gomes 2
1 School of Electronics, University of Wales, Bangor, Gwynedd, United Kingdom, 2 CEOT, Universidade do Algarve, 8005-139 Faro Portugal
Show AbstractIt has been argued [1] that low-k dielectrics are preferred for organic MISFETs in view of the reduction in mobility observed when the dielectric constant of the gate insulator increases. It is suggested that high-k dielectrics give rise to charge scattering in the induced channel by dipoles at the insulator-semiconductor interface. However, lower threshold voltages and steeper sub-threshold slopes have been observed [2] in higher capacitance devices using TiO2 and Al2O3. The low mobility observed in these F8T2 devices was attributed to bulk semiconductor traps rather than to interface traps. In the present contribution, we present the results of an admittance study of MIS capacitors formed from poly(3-hexylthiophene) spin-coated onto the composite dielectric Aluminium-Titanium-Oxide (ATO) formed by atomic layer deposition and which has a dielectric constant of ~24. During voltage sweeps in negative gate bias, capacitance-voltage measurements made in the dark reveal a large anticlockwise hysteresis consistent with hole trapping in shallow interface traps. Sweeping the voltage to positive bias returns the threshold voltage approximately to zero i.e. emptying of hole traps and no electron trapping. On the other hand, under illumination with photons of energy greater than the semiconductor bandgap, an anticlockwise hysteresis loop is again observed but this time shifted to positive bias consistent with trapping of electrons in shallow interface states. Furthermore, the increase observed in the minimum capacitance when the device is driven into depletion is evidence for the formation of an n-type inversion layer at the semiconductor-insulator interface [3]. Further work is in progress (a) to develop effective measures for passivating the interface traps and (b) to fabricate and characterise MISFETs formed on this dielectric. [1] J Veres, S Ogier, G Lloyd and D de Leeuw, 2004, Chem Mater 16, 4543-4555.[2] J Swenson, J Kanicki, G Wang, A Heeger and S Martin, 2003, Proc SPIE, 5217, 159. [3] D M Taylor, J A Drysdale, I Torres and O Fernández, 2006, Appl Phys Lett, (in press).
9:00 PM - O6.45
Bio-Sensing Using Organic Light Emitting Diode
Sandeep Devabhaktuni 1 , Shalini Prasad 1
1 Department of Electrical and Computer Engineering, Medical, Micro devices and Nanotechnology Laboratory, Portland State University, Portland, Oregon, United States
Show Abstract9:00 PM - O6.46
Highly Efficient Excimer-based Phosphorescent White Organic Light-emitting Diodes.
Evan Williams 1 , Kirsi Haavisto 1 , Jian Li 1 , Ghassan Jabbour 1
1 School of Materials and Flexible Display Center, ASU, Tempe, Arizona, United States
Show AbstractRecently, organic light-emitting diodes (OLEDs) have attracted wider attention as potential solid state lighting sources. In particular, white OLEDs promise to be an alternative lighting source with better efficiency than at least the incandescent lamp. Although great strides have been made, the multilayer device structure using small molecules remains complicated, and with relatively low efficiency. Relying on an excimer based system (single dopant) to create white light offers a simplified fabrication process and potentially lower production cost. By utilizing (4’,6’-difluorophenylpyridinato-N,C2’) platinum(II) (2,4-pentanedionato-O,O’) [FPt] as the emission center, incorporating a novel carbazolyl-pyridine based host, and modifying the device architecture, we will show that a nearly 100% internal quantum efficiency is possible for the first time with white OLEDs. External quantum (power) efficiencies of 15.9% (12.6 lm/W) have been realized at 500 cd/m2. This talk will focus on the improved efficiency as determined by charge transport characteristics and the interface between transport and emissive layers. The relationship between monomer and excimer emission will also be addressed.
9:00 PM - O6.48
Two solution processes to improve the alignment of P3HT and their OTFT properties.
Satoyuki Nomura 1 , Aram Amassian 1 , George Malliaras 1 , Detlef-M Smilgies 2
1 Materials Science & Engineering, Cornell University, Ithaca, New York, United States, 2 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States
Show AbstractIt is well known that the charge transport properties in organic thin films are greatly affected by the film morphology or alignment of the molecules. The morphology or alignment of organic molecules varies according to the film processing conditions. Therefore, it is very important to understand the effect of process conditions on the morphology or alignment of the organic molecules. In this study, we describe two solution-based processes that improve the alignment of conjugated polymer films. It was shown that the film of regioregular polythiophenes (P3HT) which were fabricated by normal spin coating process had low alignment by grazing incidence small angle x-ray scattering (GISAXS). On the other hand, it was shown that films of P3HT which were fabricated by two solution-based processes had exceptional alignment. Their performance in transistors was measured using a top contact field effect transistor configuration. The field-effect mobility for normal spin coated film of P3HT was about 1x10^-3 cm^2/Vs. It was shown that new solution-based processes could improve the mobility. We measured mobility dependence on film deposition direction but there were no significant difference between film deposition direction and the mobility. We also discuss the mobility based on top gate configuration.
9:00 PM - O6.49
Study of PECVD Silicon Nitride and Silicon Oxide Gate Dielectrics for Organic Thin-Film Transistor Circuit Integration
Flora Li 1 , Yiliang Wu 2 , Beng Ong 2 , Yuri Vygranenko 1 , Arokia Nathan 3 1
1 Electrical & Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada, 2 , Xerox Research Centre of Canada, Mississauga, Ontario, Canada, 3 London Centre for Nanotechnology, Imperial College London, London United Kingdom
Show AbstractResearch in organic thin-film transistors (OTFTs) has unleashed fascinating opportunities for organic electronics in areas requiring low-temperature processing, large area coverage, mechanical flexibility, and overall low cost. Prospective applications for OTFTs include AMOLED displays, large-area flexible displays, electronic papers, RFID tags, and low-cost and low-end printable electronic devices. For active-matrix display applications, silicon nitride (SiNx) has been a prevalent choice of gate dielectric and passivation in a-Si TFT technology. Attractive attributes of SiNx include low temperature deposition, large-area capability, and good dielectric strength. Low temperature gate dielectrics that are compatible with plastic substrates are demanded for fabrication of flexible electronics. Hence, there is a strong motivation to investigate SiNx gate dielectric for OTFT circuit integration, to facilitate the development of large-area flexible electronics. Plasma-enhanced chemical vapour deposited (PECVD) SiNx films of varying compositions, ranging from N-rich to Si-rich, were explored to determine an optimal choice for OTFTs. Bottom-gate bottom-contact OTFTs featuring solution-processed poly[5,5’-bis(3-dodecyl-2-thienyl)-2,2’-bithiophene)] (PQT-12) semiconductor, Cr-Au source/drain contacts, and SiNx gate dielectrics were studied. By executing proper surface modification steps on the dielectric and contacts, these PQT-12 OTFTs exhibited on-off current ratio of 106–108 and effective field-effect mobility of 0.03–0.1 cm2/V-s. A dependence of the OTFT parameters on SiNx film composition was evident, where an overall improvement in effective mobility, on/off current ratio and gate leakage current was observed as the Si-content in SiNx film increases. These results confirmed that the SiNx film composition influences the dielectric surface properties, which in turn governs quality of the semiconductor-dielectric interface and molecular ordering of the overlying organic semiconductor layer; altogether, these factors present a strong bearing on the OTFT performance. Thus, careful optimization of the gate dielectric composition and proper control of the dielectric surface properties are crucial for attaining higher performance OTFTs. PQT-12 OTFTs on PECVD silicon dioxide (SiO2) gate dielectric were also considered. These devices demonstrated on/off current ratio of 107 and effective field-effect mobility of up to 0.5 cm2/V-s. Overall, the results collected from this study revealed that PECVD SiNx and SiO2 are promising gate dielectric candidates for OTFT integration in large area flexible electronics. The processing details and optimization of the dielectric surface modification scheme will be elaborated in greater detail in the paper, along with a more in-depth comparison of PQT-12 OTFTs on various gate dielectrics. The development of PQT-12 OTFT pixel circuits with PECVD SiNx dielectric for active matrix display backplanes will be addressed.
9:00 PM - O6.5
Method for Determining the Depth Profile of Emission Dipoles in Organic Light Emitting Devices from Experiment
M. Megens 1 , M. Bartyzel 1 , S. Van Mensfoort 2 , H. Greiner 3 , Reinder Coehoorn 1
1 , Philips Research Laboratories, Eindhoven Netherlands, 2 Applied Physics Department, Eindhoven University of Technology, Eindhoven Netherlands, 3 , Philips Research Laboratories, Aachen Germany
Show AbstractThe external quantum efficiency of organic light emitting devices (OLED) depends strongly on the shape of the distribution of the emission dipoles across the semiconducting layer. A predominant contribution to this microcavity effect is formed by exciton quenching near the electrodes. For OLEDs that are based on a single semiconducting layer, this leads to the requirement that the electron and hole mobilities should be not too dissimilar, in order to avoid a situation in which recombination takes place predominantly near one of the electrodes. So far, semi-quantitative information about the shape of the dipole emission profile for single-layer OLEDs was only obtained from electronic device modelling, using measured parameters describing the electron and hole mobilities, injection, and exciton diffusion [1]. Such analyses are based on extensive sets of electrical measurements, for single and double carrier devices, and the emission profiles can be sensitive to the details of the transport model that is assumed.We have developed an alternative method for obtaining the depth profile of the emission, using the measured angular and polarization dependence of the emission spectrum, and using the predicted dipole position dependence of these spectra as obtained from a thin-film microcavity outcoupling model [2]. No use is made of electrical modelling. A weighed least squares fit method is employed to obtain the dipole emission intensity in typically 10 intervals across the organic layer thickness, and to obtain a parameter describing the dipole orientation distribution. We apply the method to OLEDs of the type (glass/PEDOT:PSS/LEP/Ba:Al), containing a blue emitting polyfluorene-based light emitting polymer (LEP) described in ref. 3. Experimental results for devices with thicknesses in the range 80-160 nm were analyzed, as a function of the applied voltage. As compared to the analysis given in ref. 3, which predicted that for a wide range of conditions the emission takes place very close to the anode, a wider distribution is obtained. An extensive analysis was made of the sensitivity on the input parameters (the layer thicknesses and refractive indices), and on the model used for optical self-absorption (mainly at small wavelenghts) in the LEP layer. This is a fundamental issue on which there is no full consensus in the literature [4]. We discuss the potential of the method, and some challenges. [1].D.W. Markow and P.W.M. Blom, Appl. Phys. Lett. 87, 233511 (2005), and references therein. [2].K.A. Neyts, J. Opt. Soc. Am. A 15, 962 (1998).[3].R. Coehoorn et al., Proc. SPIE 6192 (2006), 61920O.[4].M.S. Tomaš and Z. Lenac, Phys. Rev. A 56, 4197 (1997); G. Juzeliunas, J. Phys. B: At. Mol. Opt. Phys. 39, S627 (2006).
9:00 PM - O6.50
Fiber Based Organic Light Emitting Diodes and Photovoltaic Cells
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 AbstractWe demonstrate fiber-shaped organic light emitting devices (OLEDs) and photovoltaic (PV) cells. The devices consist of archetypal molecular organic semiconducting compounds (e.g. NPD, Alq3, CuPc, C60) and metallic (non-ITO) electrodes deposited as thin films on silica fibers using vacuum thermal evaporation. We characterize their optoelectronic performance and present new fabrication and optimization methods for this device geometry. Our results indicate that the fiber based OLED spectrum is invariant with radial and axial emission angle, in contrast to the strong directional dependence of planar, top-emitting OLEDs. Fiber OLEDs also show enhanced external quantum efficiency. Organic fiber PV cells exhibit power conversion efficiency comparable to planar cells, and simulations indicate that bundled fibers with external coatings can further improve overall power conversion efficiency without relying on ITO as an electrode material. The broadband light in-coupling efficiency is also independent of the incident angle. These results suggest that fiber based devices can potentially increase energy conversion efficiency, while broadening the range of fabrication approaches, thus providing a viable and convenient platform for integration of devices into woven fabrics and fabric-reinforced composites.
9:00 PM - O6.51
Electronic Properties of Doped Polyaniline and Doped Polyaniline/Crystalline Silicon pn Heterostructure Solar Cells: Observation of an Inverse Meyer-Neldel Rule.
Weining Wang 1 , Eric Schiff 1
1 , Syracuse University, Syracuse, New York, United States
Show AbstractWe have studied the transport properties of doped, hole transporting polyaniline films with a wide range of polyaniline conductivities, along with the properties of the heterostructures of these films when applied to crystalline silicon. Polyaniline dispersions with different conductivities were realized by simple solvent dilution of the original dispersions optimized for high conductivities. The range of conductivities of polyaniline films was 10-5- 102 S/cm.The heterostructure results appear to be strong evidence favoring a "Fermi glass" model for transport, meaning that the hole transport occurs at an energy (the "transport edge") that is well below the Fermi level of the film. Recent work has shown true metallic behavior in polyaniline when the Fermi energy is sufficiently low, with a metallic conductivity of about 103 S/cm [1]. We draw the conclusion of Fermi glass behavior in our films from measurements of open-circuit voltages under intense illumination, which are consistent with the built-in potential difference between the polyaniline film and the silicon substrate. Temperature dependence studies of the films showed an "inverse Meyer-Neldel behavior." Individual films show simply-activated behavior in plots of conductivity vs. reciprocal temperature. The lines for the various samples all focus at a negative Meyer-Neldel temperature: TMN≈-185 K.Overhof and Beyer [2] predicted long ago that negative Meyer-Neldel temperatures should be observed when Fermi levels fall deeply into bandtails; their prediction appears to correspond well with the present measurements, which involve films with conductivities up to 107 smaller than the optimized value. We do not have a satisfactory understanding of why relatively modest dilutions yield such a large range of conductivities. Interestingly, the conductivity at TMN is: σ00≈2×102 S/cm. This value is remarkably close to the minimum metallic conductivity predicted by Mott for bandedge transport and Anderson localization [3], and lies just slightly below the true metallic conductivities achieved by Lee, et al. [1].This research was supported by the Thin Film Photovoltaics Partnership of the National Renewable Energy Laboratory (NDJ-2-30630-24).1. Kwanghee Lee, Shinuk Cho, Sung Heum Park, A. J. Heeger, Chan-Woo Lee and Suck-Hyun Lee, Nature 441, 65-68 (2006)2. H. Overhof and W. Beyer, Phil. Mag. B 47, 377 (1983).3. N. F. Mott and E. A. Davis, Electronic Processes in Non-Crystalline Materials, 2nd Ed. (Clarendon Press, Oxford, 1979).
9:00 PM - O6.52
Electrical Conductivity of Single Molecules in Water via Electrochemical Tunneling Spectroscopy.
Krzysztof Slowinski 1 , Emil Wierzbinski 1 , William Hammond 1 , Justin Arndt 1
1 Chemistry & Biochemistry, California State University, Long Beach, Long Beach, California, United States
Show Abstract9:00 PM - O6.6
Work Characteristics of Conducting Polymer Actuators using Cation Driven Polypyrrole
Keiichi Kaneto 1 , Hisashi Fujisue 1 , Tomokazu Sendai 1 , Kentaro Yamato 1 , Wataru Takashima 1
1 Life Science and Systems Engineering, Kyushu Institute of Technology,, Kitakyushu Japan
Show Abstract9:00 PM - O6.7
Soluble Naphthalenetetracarboxylic Dianhydride (NTCDA)-Based Semiconductor Materials for Organic Electronics
Ya-Lien Lee 1 , Tri-Rung Yew 1
1 MSE, National Tsing-Hua University, Hsin-Chu Taiwan
Show AbstractThe 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA)-based organic material as an n-type semiconductor layer for organic electronics was investigated. The NTCDA-based material was spin-coated on SiO2/p+Si or polyimide/p+Si substrate using toluene, chloroform, dimethyl formamide (DMF), or methanol as a solvent. The p+ Si was used as a backgate electrode. The Au or Al layer was deposited on the NTCDA-based semiconductor layer as source/drain electrodes. The organic electronic devices were fabricated and electrically characterized in air. To enhance electrical properties, various approaches including the annealing and surface treatment of NTCDA, and interface buffer layer insertion between NTCDA-based semiconductor layer and source/drain electrode were studied. The physical properties of NTCDA-based semiconductor layers were inspected by atomic force microscopy (AFM), X-ray diffraction, and Fourier transform infrared spectrum (FTIR) for the correlation with electrical characteristics.
9:00 PM - O6.8
Micropatterning of Organic Semiconductors by Surface Modification with SAMs for Patterning of Organic Semiconductors
Yutaka Ito 1 , Jason Locklin 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractNonlithographic patterning technique of organic semiconductors is important because organic semiconductors tend to degrade under conventional photolithography conditions. Recently, we have demonstrated the use of polydimethylsiloxane (PDMS) stamps to fabricate patterns of different conjugated thiols on gold and silanes on silicon oxide substrates that could be used to template the selective growth of crystals of organic semiconductors from solution and showed higher performance of arrays of organic field-effect transistors (OFETs) compared to unpatterned OFETs. Here, we improved this process to get patterned monolayers on oxides, which have very high surface smoothness and investigated its influence on crystal growth. This newly developed preparation method of monolayers and patterns is presented. The monolayers were characterized by AFM, contact angle measurements, and ellipsometry. Also patterning procedure of OFETs is demonstrated.
9:00 PM - O6.9
Effects of Mechanical Stress on Printed Polymer-Based TFTs on Flexible Display Backplanes
Julia Greer 1 , William Wong 1 , Rene Lujan 1 , Brent Krusor 1 , Robert Street 1
1 Electronic Materials and Devices Laboratory, Palo Alto Research Center, Palo Alto, California, United States
Show AbstractAdditively printed polymer thin-film transistors (TFTs) arrays on plastic substrates can enable low cost displays with new functionality and performance. Here, we discuss some of the challenges arising from the integration of ink-jet printing and polymeric semiconductors to fabricate display backplanes on flexible substrates. Specifically, we present the results of in-situ electrical performance of printed bottom-gate TFTs subjected to a known mechanical strain during both static and dynamic loading. These TFTs were fabricated on flexible polyester substrates, with a polythiophene derivative PQT-12 as the semiconducting polymer and conventional inorganic metal and dielectric layers. Transfer/output characteristics and field-effect carrier mobility as a function of elastic strain for several device dimensions and geometries are evaluated and compared with those of amorphous Si-based TFTs. Transistor performance during high- and low-cycle fatigue is compared to that during incremental static loading, and the effects of device dimensions and orientation on their performance while mechanically deformed are also discussed. We found that for all deformation modes, the TFTs functioned in compression down to the radius of curvature of 4 mm, corresponding to 2% strain, with little degradation in performance, while in tension the transistors failed due to dielectric cracking at ~ 1% strain.
Symposium Organizers
Ana Claudia Arias Palo Alto Research Center
J. Devin MacKenzie Add-Vision, Inc.
Alberto Salleo Stanford University
Nir Tessler Technion-Israel Institute of Technology
O7: Processing and Device Fabrication
Session Chairs
Thursday AM, April 12, 2007
Room 2002 (Moscone West)
9:30 AM - **O7.1
Low Cost Fully Printed P-OLED Displays on Flexible Substrates.
Sue Carter 1 2 , J. Breeden 2 , J. Chen 2 , E. Jones 2 , M. Kreger 2 , Y. Nakazawa 2 , A. Palmer 2 , V. Van Vo 2 , Y. Yoshioka 2 , J. Mackenzie 2
1 , University of California - Santa Cruz, Santa Cruz, California, United States, 2 , Add-vision, Scotts Valley, California, United States
Show AbstractAdd-Vision, Inc. (AVI) has developed a low-cost print technology for P-OLED displays on flexible substrates that meets several essentials for a new technology including: (1) Functionality advantages over incumbent technology, including low DC voltage and wide color gamut; (2) Low barrier to entry through utilization of inexpensive, existing print-based tools; (3) Performance meeting initial market applications. The AVI process is based on large-area printing of a combination of doped emissive and air-stable cathode inks on flexible substrates utilizing truly low-cost tools to create PLED flexible displays for near term commercial and military applications. The AVI approach to P-OLED seeks to leverage the existing equipment and know-how of the graphic arts, printed circuit board and flex circuit industries. This underpins AVI’s effort to realize large-area flexible display fabrication in high throughput at very low cost.AVI’s recent progress has been driven by a combination of advancements. The combination of air-stable high work-function cathode materials which promote high quantum efficiency and low voltage injection without damaging underlying materials; doped LEP layers with appropriate solution properties, improved print morphology, uniform emission and good stability; and optimized processing have led to consistent performance improvements. Maximum quantum efficiency, brightness, and lifetimes have increased substantially, approaching our development goal of >5 Cd/A efficiency, 1000 hours at 100 Cd/m2 on flexible substrates. This lifetime, coupled with low operating voltages ranging from 10 to 20V DC and corresponding improvements in power efficiency, positions printable P-OLED favorably with respect to inorganic thick-film EL systems, the incumbent technology, in many early-entry backlighting, signage and low-information content applications.
10:00 AM - O7.2
High Switching Speed Polymer Transistors via Self-aligned Inkjet Printing.
Yong-Young Noh 1 , Henning Sirringhaus 1
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom
Show Abstract10:15 AM - O7.3
Light Emission from Ambipolar Transistors of Tetracene Single Crystals.
Taishi Takenobu 1 2 , Tetsuo Takahashi 1 , Yukitaka Matsuoka 1 2 , Kazuhiro Watanabe 1 , Jun Takeya 3 , Yoshihiro Iwasa 1 2
1 , Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 , CREST, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan, 3 Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
Show Abstract10:30 AM - O7.4
Evaluation of the mid-range order degree in molecular crystals.
Michele Cerminara 1 , Giorgio Macchi 1 , Franco Meinardi 1 , Riccardo Tubino 1
1 Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano Italy
Show AbstractOrganic semiconductors have been widely studied in the last decades with the ambition to couple the properties of common plastics with those of inorganic semiconductors, aiming to obtain “plastic electronics”. Many prototype devices (such as electro luminescent devices, transistors, photovoltaic cells and lasers) were proposed based on these materials, but at the moment only LED can be produced with specifics that can be competitive with those of common inorganic semiconductors. The limiting factor often resides in the poor charge transport of organic materials in the solid state: indeed, even though conjugated molecules can be chemically tailored to accomplish with the requirements needed to obtain good charge injection and good intramolecular delocalisation of the charge, solid state phenomena can occur that reduce the charge mobility within the bulk of the material. The highest values of charge mobilities in organic semiconductors are reported for high quality single crystals. In these systems the excited states are delocalised over a large part of the crystals thanks to the translational invariance which is assured by the ordered structure, then charge mobility is quite higher than in amorphous solids. The limiting factor is represented by the presence of disorder (due to structural imperfection, grain borders or to the presence of impurities) that results in a strong quenching of the mobility.The formation of delocalised excited states in molecular crystals has an effect not only on the mobility of the material, but also on its optical properties. Indeed absorption and emission spectra show the fingerprints of the formation of delocalized states in the form of Frenkel excitons inside the crystal. If the luminescence is allowed by the symmetry of the molecule and by the relative arrangement of the molecular dipoles within the crystal, it has peculiar spectroscopic features, i.e. the emitting state has a superradiant behaviour. Superradiance is the emission by an ensemble of atoms or molecules in which there is a phase correlation that results in constructive interaction of the emitters forming the ensemble. The superradiant behaviour is strongly correlated to the number of molecules forming the emitting state, i.e. to the size of the region of the crystal over which the exciton is delocalised. The presence of disorder results in a reduction of this size, therefore superradiant behaviour is strongly affected by the presence of disorder and can be used to evaluate it. We will show that coupling measurements of CW and time-resolved photoluminescence it is possible to analyse in detail the superradiant behaviour of various molecular crystals (oligothiophenes, oligophenylenevynilenes and porphyrins) and to evaluate the coherence length over which the excitation is delocalised. In this way it is possible to investigate the mid-range order of samples as a function of the growth parameters.
10:45 AM - O7.5
Self-Aligned Soluble-Pentacene Crystals via Inkjet Printing for High-Performance Organic Field-Effect Transistors
Kilwon Cho 1 , Jung Ah Lim 1 , Wi Hyoung Lee 1 , Yeong Don Park 1 , Hwa Sung Lee 1 , Jong Hwan Park 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractInkjet printing is attractive technique for direct-writing patterns for organic electronics. In particular, uniform deposition and desired molecular ordering of organic semiconductors become essential challenge for ink-jet printing of organic semiconductors. In this study, we have fabricated the highly ordered soluble-pentacene crystals using ink-jet printing by controlling evaporation behavior in a printed droplet. In general, ring-like deposit morphologies of 6,13-bis((triisopropylsilylethynyl) pentacene (TIPS_PEN) was produced from homo-chlorobenzene solvent. However, self-aligned TIPS_PEN crystals with highly ordered molecular structure were obtained successfully by using mixed-solvent with high boiling point and low surface tension through control of evaporation-induced flow in a droplet. Formation of self-assembled crystals from the mixed solvent may be due to the induced Marangoni flow (surface-tension-driven flow) during drying process in the droplet. The field-effect transistors fabricated from these printed crystals shows significantly improved performance with an effective field-effect mobility of 0.1 cm2/Vs comparable to vacuum deposited devices. This study may offer an excellent way to control the molecular ordering of organic semiconductors for the direct-write fabrication of high-performance organic electronics. Acknowledgement. This work was supported by a grant (F0004022-2006-22) 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, and the BK21 Program of the Ministry of Education and Human Resources Development of Korea.
11:30 AM - **O7.6
Field Effect Transistors based on Self-Organised Molecular Nanostructures.
Fabio Biscarini 1 , Chiara Dionigi 1 , Pablo Stoliar 1 , Cristiano Albonetti 1 , Jean-Francois Moulin 1 , Silvia Milita 1 , Massimiliano Cavallini 1
1 Nanotechnology of Multifunctional Materials, CNR - ISMN, Bologna Italy
Show AbstractThe response of organic field effect transistors depend on a complex interplay between intermolecular and interfacial interactions, molecular order and structural traps, as well as on the organisation of the organic semiconductor at mesoscopic length scales in the device. Our aim is to control the supramolecular organisation of the organic semiconductor across length scales, as well as the shape, dimensionality and orientation of the semiconductor domains in the channel. We exploit self-organisation of soluble organic semiconductors at all length scales in confined environments created ad hoc in the device. We realize the confined deposition by stamps with microfabricated features which lead to mesoscopic menisci of the solution; micro- and mesoscopic channels by microfluidics; nanofabricated templates; or by deposition of colloidal latex beads decorated with organic semiconductors which form close-packed structures with nano-sized cavities.We present different working field effect transistors where drain current flows through a precisely defined array of self-organised nanostructures. In one case, molecularly ordered stripes of ter-tiophene-bis-fluorene (T3F2), two-monolayer high and 200 nm wide are fabricated across the channel of the transistor. In another case, a crystalline network of tetrahexylsexythiophene (H4T6) is formed by deposition of water-soluble colloidal beads decorated with H4T6 in the device channel with a micro-syringe or a microfluidics. The size of the confinement governs the molecular order, crystal phase distribution and the transistor response. The charge mobility measured on these transistors is a few orders of magnitude larger than the ones measured in their counterpart made with high-vacuum-sublimed or spin-coated thin films. This work is part of collaborations with Max Planck Institute-Mainz (K. Muellen), Universitè de Mons-Hainaut (R. Lazzaroni), Risoe-Roskilde (M. N. Nielsen), CNR-ICAS Milan (S. Destri and W. Porzio), University of Bologna (A. Brillante), supported by the EU-Integrated Project NAIMO (No NMP4-CT-2004-500355).
12:00 PM - O7.7
Cavity Effects on Light out-coupling Efficiency of Organic Light Emitting Devices
Jaewon Lee 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractIn this paper, we will demonstrate that due to the strong internal cavity effects, the out-coupling efficiency of an organic light emitting device (OLED) without any light extraction schemes can be over 50%. Previous studies using classical ray tracing have suggested the maximum external quantum efficiency (QE) of an OLED was estimated to be 22% and this value has been used to estimate the device internal quantum efficiencies. However, in most OLED devices, an inherent cavity is formed between the metal cathode and the ITO electrode and cavity effects need to be taken into account when estimating the extraction efficiencies of OLED devices. To study the cavity effects in OLEDs, we tuned the location of the recombination zone of the OLED devices by adjusting the cavity length. To measure the light out-coupling efficiencies, we used a silicon photodiode in direct contact with the glass substrate with a thin layer of refractive index matching gel. The devices used in this study has the following structure: indium-tin-oxide (ITO) as the transparent anode, copper phthalocyanine (CuPc) as the hole injection layer, N,N'-bis-(1-naphthl)-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD) as the hole transporting layer, tris (8-quinolinolato) aluminum (Alq3) as the emitting layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as the hole blocking layer, Alq3 as the buffer layer to tune the cavity length, and lithium fluoride (LiF) and aluminum as the cathode. Thickness of all layers was kept constant except for the Alq3 buffer layer, which was varied from 20nm to 140nm. We observed the coupling efficiency is about 50% with a 20nm thick buffer layer and this value is more than doubled that estimated based on the ray tracing calculations. As the thickness of Alq3 buffer layer was increased, coupling out factor decreases to ~16%. This shows that the light coupling efficiency is strongly dependent on the device architecture and estimates of internal quantum efficiency using classical ray tracing might be overestimated. In addition, both our optical simulation results and experimental data show blue light tends to be strongly trapped in the substrate while red light tends to have higher coupling efficiencies.
12:15 PM - O7.8
Low-voltage Organic Transistors on a Polymer Substrate with an Aluminum Foil Gate Fabricated by a Laminating and Electropolishing Process.
Chanwoo Yang 1 , Kwonwoo Shin 1 , Sehyun Kim 1 , Chan Park 1 , Hoichang Yang 2
1 Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk, Korea (the Republic of), 2 Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract12:30 PM - O7.9
Electric-field Effects of Very High Mobility Organic Single-crystal Transistors.
Jun Takeya 1 , Yukihiro Tominari 1 , Masakazu Yamagishi 1 , Takao Nishikawa 2 , Takeo Kawase 2 , Satoshi Ogawa 3
1 , Osaka University, Toyonaka Japan, 2 , SEIKO EPSON Corporation, Fujimi, Nagano, Japan, 3 Dept. of Chemical Engineering, Iwate University, Morioka Japan
Show Abstract12:45 PM - O7.10
Surface-directed Phase Separation of Conjugated Polymer Blends for Efficient Light-emitting Diodes
Keng-Hoong Yim 1 , Zijian Zheng 2 , Wilhelm Huck 2 , Richard Friend 1 , Ji-Seon Kim 1
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 Melville Laboratory for Polymer Synthesis, University of Cambridge, Cambridge United Kingdom
Show AbstractIn solution-processed conjugated polymers, de-mixing of two spin-coated polymers causes phase separation, and the interpenetrating network of the two polymers provides randomly distributed interface structures. Here we demonstrate the precise control of such phase separation via substrate surface energy modification. We rely on self-organisation to form lateral photonic microstructures, utilising the fact that phase separation in polymer blend films is strongly dependent upon substrate surface energy. We use micro-contacting printing technique to periodically deposit an appropriate choice of covalently bound self-assembled monolayer (SAM) to create sufficient surface energy contrast with the underlying substrate. It is then possible to induce phase separated structures that replicate the pre-determined pattern.Here, we investigate the phase separation of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) and poly(9,9-di-n-octylfluorene-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene) (TFB). With appropriate choice of polymer molecular weight and blend ratio, the phase separation in the blend film replicates the micron-scale pattern closely, with more polar F8BT being deposited on hydrophilic poly(styrene sulphonate)-doped poly(3,4-ethylene dioxythiophene) (PEDOT:PSS) layer, while TFB on the hydrophobic areas defined by SAM of 7-octenyltrichlorosilane. Comparing to ordinary blend films with natural phase separation, light-emitting diodes fabricated with this patterned blend film exhibit significantly improved initial electroluminescence (EL) efficiency with more gentle decay at high voltages. We consider that the well-defined and localised EL emission from the patterned area is responsible for the observed increase in initial EL efficiency, as a result of spatial confinement of charge carriers in the TFB-rich domains that improves recombination efficiency. This observation also suggests the absence of continuous TFB wetting layer that is usually present in F8BT:TFB blend films, further indicating the effectiveness of surface-directed phase separation. In addition, the presence of micron-scale phase separated structures in the patterned blend film leads to the observed improvement of light out-coupling in the forward direction. On the other hand, slower decay in EL efficiency is attributed to smoother film surface that reduces leakage current at high voltages.We have shown the applicability of surface-directed phase separation of conjugated polymer blends to fabricate functional devices. These observations provide a new way of controlling polymer-polymer interfaces to further improve the performance of conjugated polymer-based devices.
O8: Synthesis of Materials II
Session Chairs
Thursday PM, April 12, 2007
Room 2002 (Moscone West)
2:30 PM - **O8.1
New Organic Materials for High Performance Transistors
Zhenan Bao 1
1 , Stanford University, Stanford, California, United States
Show AbstractOrganic semiconducting materials are now being considered as the active materials in displays, electronic circuits, solar cells, chemical and biological sensors, actuators, lasers, memory elements, and fuel cells. The flexibility of their molecular design and synthesis makes it possible to fine-tune the physical properties and material structure of organic solids to meet the requirements of technologically significant applications. In contrast to inorganic materials, active organic thin films can be deposited at much lower substrate temperatures (less than 120 C) in low vacuum or atmospheric pressure environments. It has been demonstrated that low-cost deposition techniques such as solution spin-coating, casting, and even printing can be used for deposition of solution soluble organic materials. These processing advantages, together with the natural abundance of organic solids, make semiconducting organics attractive for large-area and low cost applications. The performance of OTFTs depends on the construction of each of the active layers, which are the organic semiconductor layer, insulating (dielectric) layer and the electrodes. The deposition method, condition, sequence, post-deposition treatment, and surface treatment significantly impact OTFT performance. Therefore, it is important to fully understand various factors that affect the thin film growth processes. Specifically, one needs to pay attention to how the molecular structure of the organic semiconductor and thin film morphology affect the performance of OTFT devices, namely, the field effect mobility and on/off ratio.In this talk, I will discuss our recent work in new dielectric materials and organic semiconductors.
3:00 PM - O8.2
Effect of Confined Charge Carriers and Excitons in Organic Electrophosphorescent Devices : Mechanism of Light Emission and route to Efficient White Devices
Byung Doo Chin 1 , Nam Su Kang 1 2 , Byeong-Kwon Ju 2 , Jae-Woong Yu 1 , Jai Kyeong Kim 1
1 Optoelectronic Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Department of Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractIn this study, study, we have fabricated the phosphorescent organic light-emitting devices (OLEDs) using various types of charge transport and blocking material with different charge/exciton blocking characteristics, and studied the link between charge confinement and device performance. The light emitting efficiency, spectrum, and the lifetime of the devices, whose emission characteristics are strongly dominated not only by the energy transfer but also by the charge trapping, were explained by differences in the energy levels of the host, dopant, and nearby transport layers. It was illustrated in detail that such energy level differences determine the charge carrier trapping behavior and distribution of the exciton formation zone inside the light emission, charge transport, and blocking layers. On the basis of our finding on device performance and photocurrent measurement data by time-of-flight (TOF), we suggest a detailed emission mechanism, along with a physical interpretation and practical design scheme for improving the efficiency and lifetime of devices. By use of the device structures for the charge-confined light emission layer, green device efficiencies more than 60cd/A (25~30cd/A at conventional device structure) was obtained as well as improved lifetime up to 3000hr at 5000nit initial brightness. Furthermore, information on the physics of OLEDs presented here was applied for a design of highly efficient electrophosphorescent white OLED devices with more charge-balanced structures by enhancing the confinement of triplet excitons and substantial application of singlet excitons for blue emission. Supplement improvement of external light emission efficiency of white OLED device was discussed using the microcavity structures such as dielectric mirrors and nanostructured sub-layers.
3:15 PM - O8.3
Charge Injection, Transport and Degradation of Fluroene-based Copolymers.
H. H. Fong 1 , Alexios Papadimitratos 1 , George Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract3:30 PM - O8.4
Direct Evidence for Injection-induced Dedoping of a Conducting Polymer During Device Operation.
Perq-Jon Chia 1 2 , Lay-Lay Chua 1 , Sankaran Sivaramakrishnan 1 , Yee-Chia Yeo 2 , Peter Ho 1
1 Department of Physics, National University of Singapore, Singapore Singapore, 2 Department of Electrical and Computer Engineering, National University of Singapore, Singapore Singapore
Show Abstract4:15 PM - **O8.5
Approaches to Optimizing the Performance of Polythiophene Transistors
Yiliang Wu 1 , Ping Liu 1 , Yuning Li 1 , Beng Ong 1
1 , Xerox Research Centre of Canada, Mississauga, Ontario, Canada
Show AbstractOrganic thin-film transistors (OTFTs) have received extensive interest in recent years for their potential as low-cost alternatives to silicon-based technologies for large-area (e.g. active matrix display), and low-end (e.g. radio-frequency identification tags) flexible electronics. The economic advantages of OTFTs stem from low-cost fabrication using common solution-based deposition techniques such as spin coating and inkjet printing.Among organic semiconductors, regioregular polythiophenes are a class of promising solution-processable semiconductors for OTFTs. Last two decades have seen significant progress in mobility of polythiophene transistors. In this talk, we will use our polythiophenes as examples to discuss the approaches to optimizing transistor performance, including molecule design, synthesis methods, device structure design, and interface optimization.
4:45 PM - O8.6
Solution-Deposited n-channel Organic Transistors and their use in Complementary Integrated Circuits
Byungwook Yoo 1 , Brooks Jones 2 , Debarshi Basu 1 , Antonio Facchetti 2 , Michael Wasielewski 2 , Tobin Marks 2 , Ananth Dodabalapur 1
1 Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractPrinted organic electronic circuits are attractive for low-cost, mechanically flexible microelectronics applications, such as sensors, displays and radio frequency identification tags. Small-molecule and polymeric organic semiconductor-based field-effect transistors hold promise for applications where inexpensive solution-based deposition techniques are more crucial than the fast circuit speeds associated with conventional inorganic semiconductors. In order for such low-cost, flexible devices to become a reality, the semiconductors should be solution processable to be compatible with the printed electronics. Air-stable high-mobility n-channel organic field-effect transistors (OFETs) are also required for the fabrication of organic complementary metal-oxide-semiconductor (CMOS) circuits which exhibit higher noise margins and lower power dissipation. In this work, the small molecule semiconductor N,N’-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) was employed to fabricate solution-deposited n-channel OFETs. A saturation region mobility of 2.4×10-2 cm2/Vs and threshold voltage of -1.1 V were obtained in vacuum at VDS of 40 V. To optimize the circuit fabrication, the different process parameters and surface treatments for the solution deposited transistor were discussed. Utilizing with these results, an organic complementary ring oscillator and D flip-flop using PDI-8CN2 solution as the n-channel semiconductor and poly-3-hexylthiophene (P3HT) as the p-channel semiconductor have been fabricated. The ring oscillator operated at an oscillation frequency of 3.2 kHz in vacuum and 2.2 kHz in ambient. The D flip-flops operated with clock frequencies in excess of 1 kHz. These results represent the first organic complementary circuits based on solution-deposited semiconductors.
5:00 PM - O8.7
Organic Crystal Gate Insulators for High-mobility Organic Single-crystal Transistors.
Masakazu Yamagishi 1 , Yukihiro Tominari 1 , Jun Takeya 1
1 , Osaka University, Toyonaka Japan
Show Abstract5:15 PM - O8.8
Comparative Studies on the Stability of Organic and Inorganic Gate Dielectrics for Pentacene Thin-film Transistors.
Do Kyung Hwang 1 , Jeong Min Choi 1 , Seongil Im 1
1 Institute of Physics and Applied Physics, Yonsei University , Seoul, Sudaemoon-ku, Korea (the Republic of)
Show Abstract5:30 PM - O8.9
Bipolar Copolymers for Electroluminescent Devices: The Effects of the Molecular Structure and Film Morphology on the Device Performance.
Biwu Ma 1 2 , Lan Deng 1 , Bumjoon Kim 1 , Mark Thompson 3 , Jean Frechet 1 2
1 Chemistry, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory , Berkeley, California, United States, 3 Chemistry , University of Southern California, Los Angeles, California, United States
Show Abstract5:45 PM - O8.10
Temperature Dependence of Hall Effects Using Polycrystalline Pentacene Thin-film Transistors on Plastic Films.
Yasushi Takamatsu 1 , Tsuyoshi Sekitani 1 , Takao Someya 1
1 School of engineering, The University of Tokyo, Tokyo Japan
Show AbstractO9: Poster Session: Materials, Devices and Characterization III
Session Chairs
Friday AM, April 13, 2007
Salon Level (Marriott)
9:00 PM - O9.1
Charge Carrier Concentration Dependence of the Hole and Electron Mobility in Blue Polymer LEDs.
S. van Mensfoort 1 2 , M. Bartyzel 2 , S. Vulto 2 , J. Billen 1 , R. Janssen 1 , R. Coehoorn 1 2
1 Molecular Materials and Nanosystems, Department of Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands
Show AbstractThe mobility models commonly used to describe charge transport in organic light-emitting diodes (OLEDs) are highly under debate. Recently, it was found that for OLEDs based on poly(p-phenylene vinylene) (PPV) hole transport should be described by taking into account that the mobility of the charge carriers depends on their local concentration. Such a dependence is expected to occur in the case of a sufficiently strong energetic site disorder, described by a Gaussian density of states [1]. It is not yet clear to which extent this model is applicable to the hole mobility in other organic materials used in OLEDs, to the electron mobility, and to diffusion coefficients. Furthermore, it is not yet clear how these effects of disorder affect the recombination profile and luminous efficacy. In this contribution we present the results of an experimental and modelling study of OLEDs based on a blue-emitting polyfluorene (PF) polymer with a small concentration of hole-transporting (HT) units. Blue-emitting organic materials are key in most common white OLEDs – as a matrix material or in combination with phosphorescent down-conversion layers. Whereas in the case of PPV-derivatives charges are believed to be delocalised over several polymer chain segments, charges on the HT units in the polymer used are expected to be highly localised. Therefore, the polymer studied should be even more suitable than PPV-derivatives to critically assess the appropriateness of the model presented in ref. 1. Indeed, we find from the analysis of the current density in hole-only devices with a wide range of active layer thicknesses that also for this material the concentration dependent mobility model describes the current-voltage (I-V) curves significantly better than the more conventional mobility model, which assumes a mobility with a Poole-Frenkel type field dependence. The effect was neglected in a preliminary analysis of the hole mobility in these materials [2]. Furthermore, we demonstrate the important role of taking hole diffusion into account, at least for small voltages (up to ~ 3 V), by giving an analysis of impedance measurements. For double carrier devices, the effect of the carrier concentration dependence of the mobility and the effect of diffusion on the exciton generation rate is demonstrated by giving results obtained from a drift-diffusion device model. A comparison is made with the experimentally determined I-V curves and position dependence of the recombination rate across the organic layer.[1] W.F. Pasveer et al., Phys. Rev. Lett. 94 (2005), 206601.[2] R. Coehoorn et al., Proc. SPIE 6192 (2006), 61920O.
9:00 PM - O9.10
Can We Use Scanned Probe Microscopy to Measure Local Charge Carrier Mobility in Organic Semiconductors?
Showkat Yazdanian 1 , Seppe Kuehn 1 , John Marohn 1
1 , Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - O9.11
Efficient Colour Tunable Light Emitting Diodes based on Heteroleptic Iridium(III) Complexes with Phenylpyridine and Hydroxyquinoline Ligands.
Sabrina Eder 1 3 , Stefan Kappaun 2 , Stefan Sax 1 , Fabian Niedermair 2 , Kerstin Waich 4 , Christian Slugovc 2 , Emil J.W. List 1 3 5
1 Institute of Solid State Physics, Graz University of Technology, Graz Austria, 3 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Graz, Austria and Institute of Nanostructured Materials and Photonics, JOANNEUM RESEARCH, Weiz Austria, 2 Institute for Chemistry and Technology of Organic Materials, Graz University of Technology, Graz Austria, 4 Institute of Analytical Chemistry and Radiochemistry, Graz University of Technology, Graz Austria, 5 , NanoTecCenter Forschungsgesellschaft mbH, Weiz Austria
Show AbstractCyclometalated Iridium(III) complexes are very promising candidates for possible applications in the emerging field of organic active materials used in light-emitting diodes (OLEDs), polymer lasers, photovoltaic devices, field effect transistors or sensing purposes. One of the main goals concerning applications in e.g. flat panel displays is the possibility of tuning the emission colour to cover the entire visible spectrum.Although there are numerous reports on colour tuning of homoleptic Iridium(III) complexes by modifications of the cyclometalating ligands, the corresponding synthetic procedures require cumbersome preparation steps or harsh reaction conditions. Alternatively, the synthesis of heteroleptic Iridium(III) complexes has received considerable attention due to a facilitated synthesis and the possibility of tuning the emission colour via the ancillary ligand. However, this is considered to be one of the most promising approaches for colour-tuneable Iridium(III) complexes, examples of emission characteristics controlled by the ancillary ligands are still rare.In this contribution we report our fast, versatile and cheap approach for the preparation of heteroleptic Iridium(III) complexes bearing phenylpyridine and different hydroxyquinoline ligands with emission colours dominated and controlled by the nature of the hydroxyquinoline ligand. The present work provides a powerful tool for tuning the emission characteristics as well as absorption properties that allow an easy finding of appropriate host materials and paves the way to tailor-made phosphorescent materials for practical applications.
9:00 PM - O9.12
Synthesis of Conjugated Oligomers and Polymers Functionalized with Small Biomolecules for Advanced Sensing Applications.
Gianluca Farinola 1 , Francesco Babudri 1 2 , Gabriele Giancane 4 , Omar Hassan Omar 2 , Patrizia Iliade 1 , Francesco Naso 1 2 , Francesco Palmisano 1 3 , Maria Tanese 1 , Luisa Torsi 1 3 , Ludovico Valli 4 , Pier Giorgio Zambonin 1 3
1 Chemistry, University of Bari, Bari Italy, 2 , CNR ICCOM Bari- Dipartimento di Chimica University of Bari, Bari Italy, 4 Innovation Engineering, University of Lecce, Lecce Italy, 3 , Centro di Eccellenza TIRES, University of Bari, Bari Italy
Show Abstract9:00 PM - O9.13
Hexathiapentacene: Structure, Molecular Packing, and Field-Effect Transistors.
Alejandro Briseno 1 2 , Miao Qian 3 , Fred Wudl 3 , Zhenan Bao 2 , Hong Meng 4 , Younan Xia 1
1 Chemistry, University of Washington, Seattle, Washington, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States, 3 Chemistry, UCLA, Los Angeles, California, United States, 4 Central Research and Development, Experimental Station, E. I. DuPont , Wilmington, Delaware, United States
Show AbstractThe past decade witnessed a tremendous development in exploiting organic molecules for use in electronic and optoelectronic devices. Oligo-acenes, tetrathiafulvalene (TTF) and their derivatives have been extensively studied as fundamental building blocks for organic electronics. As an example of oligo-acenes, pentacene has led organic semiconductors with the highest field effect mobility in thin film transistors. The advent of molecular design and synthesis has made it possible to tune the physical properties and molecular structures of organic materials to meet the technological requirements for fabricating practical devices. Aromatic molecules have recently shown that self-assembly through strong pi-pi interactions can lead to the formation of one-dimensional (1D) nanostructures for applications in field-effect transistors. Inspired from studies on TTF derivatives, we became interested in introducing S-S interactions to oligo-acenes to provide an alternative charge transport pathway other than pi-pi interactions, which are well known in herringbone packing for oligo-acenes. In this presentation we report the electrical characteristics of hexathiapentacene (HTP) and emphasize on the unusual chemical structure and molecular packing. Although HTP was first described over 30 years ago, only minimal characterization was reported. This work appears to be the first to determine its molecular structure/packing mode and to study its application in organic transistors. We also discuss preliminary results on the synthesis of 1-D nanostructures and charge-transport through single-crystal wires.
9:00 PM - O9.14
A Microscopic Description of Structural Defects in Pentacene Thin Films.
Stijn Verlaak 1 , Cedric Rolin 1 2 , Paul Heremans 1
1 , IMEC, Leuven Belgium, 2 PCPM, UCL, Louvain-La-Neuve Belgium
Show AbstractThe growth of a pentacene monolayer is modelled microscopically by adding one molecule at a time to a predefined crystalline aggregate. For each added molecule, the potential energy versus molecular orientation in the crystal is calculated using the MM3 molecular mechanics force field. This delivers a potential energy surface that reveals stable molecular orientations at its local minima. Four different predefined aggregates are used to start the calculation. Each case can initiate a different type of defect:1.Adsorption of a pentacene molecule at a step-free (110) surface. The most stable configuration deviates from an ideal-crystal configuration. 2.Adsorption of a molecule at a step. This molecule will relax into the ideal-crystal configuration, yet a defect can be initiated by thermal activation.3.Adsorption of a molecule sandwiched between two steps. The ideal-crystal configuration is most stable, yet a molecule can get trapped at a kinetic defect configuration, depending on flux and temperature.4.Adsorption of a molecule at a grain boundary. Interstitial molecules intrinsicically form defects that generate film stresses.Upon addition of further molecules onto an already disordered aggregate, the defect can follow different paths: if structural relaxation is faster than the average time to add another molecule to the site, the defect can completely relax to a perfect crystalline order. Alternatively, if relaxation times are too long, the defect can propagate. Most defects relax to the ideal crystal structure after they were formed. Structural defect densities less than 1e16 cm-3 can be estimated in the bulk of the film. Grain boundaries are the most pronounced and stable defects and are a source for compressive stresses that may lead to dislocations. Ultimately, it is to be expected that grain boundaries will dominate charge transport in carefully prepared pentacene films.The present study leads to a conceptually simple frame for understanding the details of film growth, and is a first step to unravel the presently unclear link between growth thermodynamics and electronic properties and charge transport in organic small molecular films.
9:00 PM - O9.15
Organic Materials for Low Cost, Large Area Photoconductors
Alyson Niemeyer 1 2 , Brian Crone 2 , Ian Campbell 2 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractThere is a great need for low cost, large area (>10 cm2) photodetectors for use with scintillators in radiation detection for special nuclear material and radiological isotope monitoring. Photodetectors for homeland security applications must be low cost and should have large area, low capacitance, negligible dark current, and reasonable response time. In this work we investigate organic photoconductors with interdigitated planar electrodes. Unlike silicon, organic materials can have the low dark currents necessary for these low capacitance, large area structures. We present the effects of polymer film thickness, polymer ratio, interdigitated diode finger spacing, and applied voltage on diode quantum efficiencies. Polymer film thickness was found to have no significant effect on quantum efficiency. The optimum polymer (MEH-PPV) to exciton dissociator (PCBM) ratio was found to be 1:4. This optimum ratio arises from an interplay of maximizing absorption and hole transport through increased MEH-PPV concentration, and maximizing exciton dissociation and electron transport through increasing PCBM concentration. Devices with interdigitated diode finger spacings of 5, 10, and 100 μm were measured. Electrode spacing had little effect on the quantum efficiency at a given electric field. Quantum efficiency increased at higher electric fields, as charge collection improved. Implications of the measured results on optimization of organic photoconductors will be discussed.
9:00 PM - O9.16
Enhanced Electron Injection in Organic Transport Layers by Successful Doping with LiF.
Jong Hyuk Yoon 1 , Kaushik Choudhury 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show Abstract9:00 PM - O9.17
Click Dielectrics: Polymer-nanoparticle Composites for Flexible Electronics Applications
Meghann White 1 , Ashok Maliakal 2 , Nicholas Turro 1 3 , Jeffrey Koberstein 3
1 chemistry, Columbia University, New York, New York, United States, 2 , Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey, United States, 3 Chemical Engineering, Columbia University, New York, New York, United States
Show AbstractImproved high K dielectric materials are important for the development of devices for use in flexible electronics. One method of creating high K materials is through the use inorganic/organic core-shell nanoparticles. Novel surface ligands have been designed and synthesized for high K TiO2 nanoparticles, which allows for chemical modification at the surface using “click” chemistry, specifically Cu-catalyzed azide-alkyne cycloaddition. The “click” functional ligands prevent nanoparticle agglomeration and allow us to covalently bind various polymers to the surface of the TiO2. The resulting polymer-nanoparticle composites are transparent and easily spin cast onto substrates. The dielectric properties of the resulting nanoparticle-polymer composites have been studied for potential as high K dielectric materials for flexible electronics applications.
9:00 PM - O9.18
High-performance Thin Film Transistors From Semiconducting Liquid-crystal Phases by Solution Processes.
Fapei Zhang 1 , Masahiro Funahashi 1 , Nobuyuki Tamaoki 1
1 , National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki Japan
Show Abstract9:00 PM - O9.19
Organically Modified Silicon-based Stamping Materials for High Resolution Soft Lithography.
Kyung Choi 1
1 , Bell Labs, Lucent Technologies, Murray Hill, New Jersey, United States
Show Abstract9:00 PM - O9.20
Electrolyte-Gated Field-Effect Transistor of Rubrene Single Crystal
Hidekazu Shimotani 1 2 , Haruhiko Asanuma 1 , Jun Takeya 3 , Yoshihiro Iwasa 1 2
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 , JST-CREST, Kawaguchi, Saitama, Japan, 3 Department of Chemistry, Osaka University, Toyonaka, Osaka, Japan
Show Abstract It is important to study electronic properties of organic materials under carrier doping for their any applications to electronics. Organic field-effect transistor (FET) is one of the useful methods from the viewpoint, because it enables controllable, reversible, nondestructive,and in situ doping on the surface of various organic materials. However, carrier density controlled by FETs is so small that wide range of electronic properties has not been studied. Therefore, it is needed to increase carrier density on the surface of organic materials accumulated by FET. It is demonstrated by Takeya et al.[1] and Panzer et al.[2] that electrolyte can serve as a gate electrode in rubrene single crystal FETs, and it is expected that the electrolyte-gated FETs accumulate high carrier density on the crystal surface due to their large gate capacitances. The purpose of this investigation is to accumulate carriers on the surface of organic materials in high density by electrolyte-gated FET, to estimate its carrier density, and to study its working mechanism. The device was consist of a rubrene crystal with a Au source and a drain electrode immersed in electrolyte [LiClO4/Poly(ethylene oxide)] and a Pt-coil gate electrode also immersed in the electrolyte. High density carrier accumulation (∼0.33 carrier/molecule) in a rubrene single crystal FET was achieved by applying small gate voltage (-1.2 V) through the electrolyte.[3] The carrier density was estimated from the gate capacitance (15 μF/cm2) measured independently on a gold thin film. Interestingly, the transfer characteristics (drain current vs. gate voltage) showed a peak, which has not been observed in SiO2-gate FETs. The origin of the peak will be discussed in the presentation.References:[1] J. Takeya et al., Appl. Phys. Lett., 88, 112102 (2006).[2] M. J. Panzer et al., Appl. Phys. Lett., 88, 203504 (2006).[3] H. Shimotani et al., Appl. Phys. Lett., in press
9:00 PM - O9.21
Improved of the Performance in n-channel Organic Thin Film Transistors by Nanoscale Interface Modification.
Chih Wei Chu 1
1 , Academia Sinica, Taipei Taiwan
Show Abstract9:00 PM - O9.22
Fast Photoresponse of Functionalized Pentacene Thin Films
Jonathan Day 1 , Oksana Ostroverkhova 1 , John Anthony 2 , Robert Twieg 3
1 Physics, Oregon State University, Corvallis, Oregon, United States, 2 Chemistry, University of Kentucky, Lexington, Kentucky, United States, 3 Chemistry, Kent State University , Kent, Ohio, United States
Show AbstractOrganic semiconductors are of interest due to their potential applications in molecular electronics and photonics. In order to develop organic semiconductor devices, it is important to understand the mechanisms of (photo)conductivity in organic materials. However, using thin-film device structures and traditional dc methods (such as field-effect transistor and space-charge-limited current geometries) to characterize intrinsic electronic properties of materials is complicated, in part due to the influence of defects on the overall electronic response of the device. In contrast, monitoring of the charge carrier dynamics on short time scales after excitation allows one to probe charge transport properties, prior to trapping at defects. In this way, one can study both intrinsic charge transport and the process of charge trapping. Extension to longer time scales permits the exploration of charge detrapping processes and equilibrium charge transport mechanisms, relevant for devices operating in the dc regime such as thin-film transistors. In our studies, we explored photoconductivity of high-performance functionalized pentacene (FPc) thin films on time scales from picoseconds to many seconds after photoexcitation. The FPc thin films were deposited from solution on glass substrates with patterned interdigitated aluminum electrodes. In studies of fast transient photoconductivity, the samples were excited with laser pulses of ~100 fs duration at a wavelength of 400 nm, and the photocurrent due to transport of photoexcited charge carriers was monitored using a 50 GHz digital sampling oscilloscope. The photoconductivity at longer (milliseconds through seconds) time scales was investigated using continuous wave (cw) illumination and a source-delay-measure unit. Both experiments were performed under conditions of varied electric field strength, fluence and temperature. In all samples, we observed fast charge carrier photogeneration (<70 ps), limited by time resolution of our setup) followed by decay of the photocurrent over the period of several nanoseconds due to charge trapping and recombination, linear dependence of the peak photoconductivity on the fluence and quadratic dependence of the peak photoconductivity on the applied electric field. We also investigated the influence of charge traps on the photoconductive response of FPc thin films, depending on the nature and properties of the traps. A small amount of various dopants was introduced into the FPc matrix, and the changes in the amplitude and decay dynamics of the transient photoconductivity were monitored. By choosing different dopants, such as molecules similar to the host FPc molecules (such as a different FPc derivative) or highly polar organic dyes, we created different traps (shallow structural traps or deep energetic traps, respectively) in the FPc matrix. A comprehensive study of the trapping and detrapping dynamics depending on the properties of the trap molecule will be presented.
9:00 PM - O9.23
Optimizing the Growth of Rubrene Thin Films for Organic Thin Film Transistors.
Parul Dhagat 1 , Hanna Heikkinen 1 2 , Jizheng Wang 1 , Ghassan Jabbour 1
1 Flexible Display Center and School of Materials, Arizona State University, Tempe, Arizona, United States, 2 Optoelectronics and Measurement Techniques, University of Oulu, Oulu Finland
Show Abstract9:00 PM - O9.24
Mobility Improvement of Pentacene Field-effect Transistor Using Oxygen Plasma Treatment and Ppost-aging Process.
Kwonwoo Shin 1 , Sang Yang 1 , Chanwoo Yang 1 , Hayoung Jeon 1 , Chan Park 1
1 Chemical engineering, Pohang University of Science and Technology, Pohang, Gyungbuk, Korea (the Republic of)
Show Abstract9:00 PM - O9.25
Threshold Voltage Shift of Organic TFTs during Pulse Operation
Hsiao Wen Zan 1 , Shih-Chin Kao 1 , Ting-Shuan Cheng 1 , Huang-Wei Pan 1
1 Department of Photonics, Display Institute, HsinChu Taiwan
Show AbstractOne of the important stability issues in organic thin-film transistors is the shift in the threshold voltage when applying a bias to the gate electrode. The applied negative gate bias for a p-type semiconductor causes the threshold voltage shift to be more negative. Also, positive threshold voltage shift can be observed when the positive gate bias stress is applied. The threshold voltage will recover to its original value if the device is left unbiased. The physical origin of this instability is the buildup of charges at the semiconductor/insulator interface, which then trapped by defect states. The shift in threshold voltage but not in mobility is often believed to be caused by deep traps with long discharge time constants. While many studies on DC bias stress effects focus on the trap creation mechanism in OTFTs, the discharge behavior is not well understood. In this research, the trapping and discharge behavior was studied by applying pulse (AC) bias stress on the gate electrode. Pentacene organic TFTs with top-contact structure were used. The thermally grown SiO2 film was served as the gate dielectric. To modify the dielectric surface polarity, SAM surface treatment was applied on some devices prior to the pentacene deposition. The experimental results revealed that, for conventional devices without SAM treatment, the discharge behavior influenced threshold voltage shift pronouncedly. When the frequency increased or the pulse duration decreased, the smaller pulse width caused smaller threshold voltage shift. However, when high-polarity SAM material was coated on the dielectric surface, the threshold voltage shift became almost not dependent on the pulse width variation. To analyze this phenomenon, we firstly extracted the mean activation energy for trap creation (EA) from DC bias stress measurement according to the method proposed by H. L. Gomes et al.. Similar EA (~0.55eV) values were obtained for all the devices. Then, if the effective accumulation time constant was considered according to the study on AC bias stress effect in a-Si TFTs, the OTFTs with high-polarity SAM layer exhibited much smaller accumulation time constant than the conventional ones. This was not reasonable since the high-polarity SAM layer was often considered as a kind of dipole material that exhibited large time constant when converting the polarity. The discharge mechanism was therefore considered to be the dominant factor in AC bias stress. When the SAM layer acted as a kind of dipole layer between the dielectric and the organic active layer, it responded to the change of bias condition slowly. Therefore, the dipole characteristics helped to keep the trapped charge during the unbiased duration, suspended the charge de-trapping mechanism. As a result, the threshold voltage shift in OTFTs with high-polarity SAM treatment was not influenced by the bias pulse width. While in conventional OTFTs, threshold voltage shift is strongly dependent on the gate-bias pulse width
9:00 PM - O9.26
Contact Behaviors of Molecularly Doped Polymers Used in Light-emitting and Transistor Based Applications.
H. H. Fong 1 , George Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - O9.27
Nondispersive Bipolar Carrier Transports in tris (8-hydroxyquinoline) aluminum (Alq3) and the Mobility Influence Due to Molecular Doping.
H. H. Fong 1 , Shu K. So 2
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Physics, Hong Kong Baptist University, Kowloon Hong Kong
Show Abstract9:00 PM - O9.28
Passivation of Pentacene Field-effect Transistors with AlOx Films Grown by Atomic Layer Deposition.
Hayoung Jeon 1 , Kwonwoo Shin 1 , Sang Yoon Yang 1 , Se Hyun Kim 1 , Sang-Hee Park 2 , Chan Eon Park 1
1 Polymer Research Institute, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Basic Research Laboratory, Electronic and Telecommunications Research Institute, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - O9.29
Correlation Between the Morphology and the Mobility in Pentacene FET with Alkanethiol Treated Gold Electrodes.
Soumya Dutta 1 , Pablo Stoliar 1 , Fabio Biscarini 1
1 , CNR- Institute for the Study of Nanostructured Materials, Bologna Italy
Show Abstract9:00 PM - O9.3
pH Dependence on the Over-oxidation Mechanism in PEDOT:PSS Films.
Payman Tehrani 1 , Anna Kanciurzewska 1 , Xavier Crispin 1 , Nathaniel Robinson 1 , Mats Fahlman 1 , Magnus Berggren 1
1 Dept. of science and technology, Linköping University, Norrköping Sweden
Show Abstract9:00 PM - O9.30
Stable and Efficient White Light-Emitting Diode through Miscibility Control
Hang Ken Lee 1 , Tae-Ho Kim 2 , O Ok Park 1
1 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 , Beckman Institute, Urbana, Illinois, United States
Show AbstractOrganic and polymer light-emitting diodes(OLEDs/PLEDs) that emit white light are attracting increasing interest for their potential applications as full color displays, backlights for liquid-crystal displays, and even next-generation paper-thin light source. Various strategies have been utilized to fabricate polymeric white-light-emitting diodes. The firstly proposed method was multilayer structure device, but nowadays single layer structure is preferred due to its low production cost and easy processability[1]. In single layer structure, emissive layer consists of several polymers, electron and hole transport material [for balance of charge carriers] as well as luminous polymers. However, most polymers are not miscible each other due to the low entropy of mixing, phase separation occurred when the thin film from solution was fabricated[2]. This phase separation causes some problems such as color change by applied voltage and low efficiency. we suggested a new solution for this problem. By introducing copolymer in emissive layer to enhance miscibility, we obtained voltage-invariant white emission from polymeric LEDs. The efficient energy transfer and charge trapping were observed in this system, so the relative intensity could be fine-tuned by varying the contents of three materials. The near pure white-light emission observed at wide range of voltage from 10V to 16V with high brightness[10295 cd/m2] and high luminance efficiency[8.34cd/A]. These white-light-emitting PLEDs were single-layer devices fabricated by spin-casting from solution. The simple device structure and the promise of low-cost manufacturing make this approach attractive for solid-state-lighting applications. [1] T. H. Kim, H. K. Lee, O. O. Park, Adv. Func. Mater. 16, 611(2006)[2] T. Kietzke, D. Neher, K. Landfester, R. Montenegro, R. Guntner and U. Scherf, Nature 2, 408 (2003)
9:00 PM - O9.31
New Photoreactive Dielectric Polymers for Organic Field Effect Transistor
Ju Hee Kim 1 , Kyung Hwan Kim 1 , Min Ju Cho 1 , Dong Hoon Choi 1
1 Department of Chemistry , Korea Univ., Seoul Korea (the Republic of)
Show AbstractOrganic field effect transistor (OFET) materials based on extended linear p-conjugated systems have been very intriguing and significant development has been achieved in these materials over the last several years. Besides semiconducting active materials, high-performance OFET gate dielectrics are of intense current interest. The materials should satisfy the requirements of excellent insulating properties, efficient low-temperature solution fabrication, and compatibility with diverse organic semiconductors.In this study, we have prepared 1st-generation p-conjugated dendrimers bearing thiophene-based peripheral groups, which exhibit 2-dimensional planar geometry as a active materials and some polyacene molecules are also employed for good comparison. We also demonstrate a new low temperature approach to achieve high-quality cross-linked polymer dielectrics from photoreactive polymer precursors. The photoreactive polymers were designed to contain either a photopolymerizable or a photocrosslinkable moiety. The photoreacted dielectric layers can be fabricated without any additive except a trace amount of catalyst. The polymer can be spin-coated simply and insolubility after UV exposure can allow us to deposit a semiconductor layer by using a solution process. We fabricate metal-insulator-metal (MIM) device to investigate film capacitances and dielectric constants as a function of frequency (100 - 106 Hz) and capacitance-voltage (C-V) and capacitance-frequency (C-f) measurements were performed. We also studied the relationship between the dielectric constant and the thickness of the layer. Resulting from those experimental data, the effects of properties of new materials were studied on OFET devices. These results demonstrate that implementation of new solution processable polymer dielectrics offers better OFET device performance.
9:00 PM - O9.32
Polymer Field-effect Transistors beyond 1 MHz.
Veit Wagner 1 , Paul Woebkenberg 1 , Arne Hoppe 1 , Jörg Seekamp 1
1 School of Engineering and Science, International University Bremen, Bremen Germany
Show Abstract9:00 PM - O9.33
Analysis of Self-Assembly Effects with Organic Molecuels on Performance of Low Voltage OTFTs containing the Self-grown Al2O3 Gate Fielectric
Chung Kun Song 1 , Kang Dae Kim 1
1 Electronics Eng., Dong-A University, Busan Korea (the Republic of)
Show AbstractWe have proposed a low voltage OTFTs with self-grown metal oxide (Al2O3) gate dielectric. In this paper we investigated the effects of self-assembly with the various organic molecules on the Al2O3 gate in the low voltage OTFTs. We prepared four kinds of molecules such as (Benzyloxy)alkyltrichlorosilane (BTS) with eleven alkyl chains (BTS-11) as well as twelve alkyl chains (BTS-22), (Benzyloxy)alkyltrimethoxysilane (BSM), and also octadecyltrichlorosilane (OTS). As shown in Table, where NOX stands for the natural SiO2 and MTOX for the metal oxide Al2O3, the OTFTs produced the different performance depending on the self-assembled molecules. BTS-22 show the better insulating property than BTS-11 as expected with the smaller off-state current. However, MTOX/BTS and MTOX/BSM exhibited the worse performance than MTOX without SAM, which is different from our expectation. Interestingly, MTOX/OTS enhanced mobility with 0.45 cm2/V.sec and also sub-threshold slope with 0.18 V/dec but the on/off current ratio was not increased due to the large off-state current. We estimate the dipole potential across OTS layer as the reason of the large off-state current. We will discuss the effects of SAM on Al2O3 and propose a SAM molecule for the self-grown Al2O3 in presentation.
9:00 PM - O9.34
Novel Organic Oxide/Al Composite Cathode in Small Molecular Organic Light-emitting Diodes.
Tzung-Fang Guo 1 3 , Fuh-Shun Yang 1 , Zen-Jay Tsai 1 , Ten-Chin Wen 2 , Ching-In Wu 4 , Chia-Tin Chung 4
1 Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan Taiwan, 3 Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan Taiwan, 2 Department of Chemical Engineering, National Cheng Kung University, Tainan Taiwan, 4 , Chi Mei Optoelectronics Corporation, Tainan Taiwan
Show Abstract9:00 PM - O9.35
High-performance N-type Pentacene-based Organic Field-Effect Transistors.
Tzung-Fang Guo 1 3 , Zen-Jay Tsai 1 , Shi-Yu Chen 1 , Ten-Chin Wen 2
1 Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan Taiwan, 3 Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan Taiwan, 2 Department of Chemical Engineering, National Cheng Kung University, Tainan Taiwan
Show Abstract9:00 PM - O9.37
Measurement of Local Photocurrents in Polymer:fullerene Solar Cells.
Klara Maturova 1 , Martijn Kemerink 1 , Rene Janssen 1
1 Molecular Materials and Nanosystems, Eindhoven University of Technology, Eindhoven Netherlands
Show Abstract9:00 PM - O9.38
High-mobility Organic Single-crystal Transistors with Secondary Gates on the Source and Drain Electrodes.
Kouji Hara 1 , Yukihiro Tominari 1 , Jun Takeya 1
1 , Osaka University, Toyonaka Japan
Show Abstract9:00 PM - O9.39
Deposition and Patterning of Highly Pure and Robust Poly(3,4-ethylenedioxythiophene) (PEDOT) Thin Film on SiO2 Surface for an OTFT Application.
Ilsun Pang 1 , Sungsoo Kim 1 , Jaegab Lee 1
1 , Kookmin Univ., Seoul Korea (the Republic of)
Show Abstract9:00 PM - O9.40
Synthesis and Characterization of Blue-Light Emitting Amorphous Dendrimer Composed of Carbazolyl Moieties
Tae Wan Lee 1 , Min Ju Cho 1 , Jung-Il Jin 1 , Dong Hoon Choi 1
1 Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractIn recent years, organic light-emitting devices (OLEDs) have attracted much attention because of their applications in full-color flat-panel displays. Since the initial work on molecular and polymeric OLEDs, were performed, respectively by Tang et al. and Burroughes et al., there have been extensive studies on layered organic electroluminescent (EL) devices to improve device performance. High EL efficiency and good durability are particularly important for practical applications.Dendrimers are highly ordered, well-defined branched polymers, with segments between branch points (spacers) comprising relatively short chains. Their treelike structure is formed by a stepwise, iterative reaction sequence of the functional groups in each generation. When the repeated process leads to complete shells for each generation, monodisperse giant molecules are prepared with a defined number of end groups, and their size and architecture. The structure can be controlled by a synthetic method precisely. In this work, we demonstrated the properties of new blue light emitting dendrimers containing carbazole moieties. 1st-generation dendrimers were successfully synthesized to investigate their photophysical properties. Organic Light-emitting devices were fabricated in an ITO(indum-tin-oxide)/PEDOT/dendrimer/Li:Al alloy configuration. The properties of carbazole-based dendrimer were evaluated by the photoluminescence (PL), electroluminescence (EL), and current-voltage characteristics, respectively. The EL and PL spectral analysis in the dendrimer devices reveals that the dendrimer formation of isolated carbazole units reduces the interchain molecular excimer emission from the aggregated carbazole moieties.
9:00 PM - O9.41
Multi-functional Organic Interlayer in Flexible Organic Thin Film Transistor.
Younggug Seol 1 , Nae-Eung Lee 1 , Sangho Park 2 , Jin-Young Bae 2
1 Materials Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 2 Polymer Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
Show Abstract9:00 PM - O9.42
HfO2/PVP Gate Dielectric Stack Structure for Pentacene FETs
Sang Seol Lee 1 , In Sung Park 2 , Young Gug Seol 3 , Nae Eung Lee 3 , Jinho Ahn 1
1 Department of Materials Science and Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Information Display Research Institute, Hanyang University, Seoul Korea (the Republic of), 3 School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
Show Abstract9:00 PM - O9.44
Self-Organized Soluble-Pentacene Crystals for High-Performance Organic Field-Effect Transistors
Kilwon Cho 1 , Wi Hyoung Lee 1 , Do Hwan Kim 1 , Yunseok Jang 1 , Dong Yun Lee 1 , Hwa Sung Lee 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractIn this study, we report the fabrication of high-quality one-dimensional (1-D) single-crystalline triisopropylsilylethynyl pentacene (TIPS_PEN) microribbons via a simple solution process with well-defined facets and unprecedented electrical characteristics, such as field-effect mobility as high as 1.4 cm2/Vs and well-resolved gate modulation. We found that the 1-D single-crystalline TIPS_PEN microribbons form spontaneously through the self-assembly of individual TIPS_PEN molecules as a result of solvophobic interactions in the solution phase, adopting preferential well-ordered inter-molecular π-π stacking along the ribbon axis. Further, we report the fabrication of one-dimensional microstructure arrays of TIPS_PEN via simple drop casting on a tilted substrate. Aligned rod shape crystals were formed on a substrate, and the device based on arrays of the fabricated rod shape crystals shows a high field effect mobility of 0.3 cm2/Vs, which results from the directed organization of π-conjugated molecules. Our studies provide a general and rational approach for 1-D assembly of π-conjugated organic materials by easy-to-process yet highly ordered supramolecular system, which is indicative of the good candidate for optoelectronic applications. Acknowledgement. This work was supported by a grant (F0004022-2006-22) 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, and the BK21 Program of the Ministry of Education and Human Resources Development of Korea.
9:00 PM - O9.46
Organic Field Effect Transistor Using Sol-gel Processed Ferroelectric Gates
Sambit Pattnaik 1 , Vijayraj Singh 1 , Ashish Garg 1 , Monica Katiyar 1
1 Department of Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P., India
Show AbstractOrganic field effect transistors using ferroelectric gates are important for the development of low-cost non-volatile memory elements. Here, we report on the fabrication of an organic thin film transistor device comprising of an oxide perovskite structured ferroelectric material (PbTiO3 and BiFeO3) as gate dielectric and a organic material (pentacene) as semiconductor. First the oxides were deposited on heavily doped n-type Si (100) substrate using sol-gel technique. The ferroelectric thickness was varied between 10-100 nm. Phase evolution in these films was assessed using X-ray diffraction. C-V and I-V characteristics of the gate oxide were measured to assess its quality for the device operation. Subsequently, pentacene is deposited by thermal evaporation at the rate of 0.03-0.04 nm/sec. The substrate temperature for pentacene deposition was 65°C. The film thicknesses were measured using Tencor surface profilometer. Finally, gold source/drain electrodes were deposited using shadow mask with channel length of about 30 μm and gate width of 1 mm. The devices were characterized in air using Keithley SCS 4200 semiconductor parameter analyzer. We report effect of the ferroelectric thickness on transistor characteristics and memory effect in these devices.
9:00 PM - O9.48
Engineering Properties of Organic Materials for Near Infra-red Applications
Jian Li 1 , Evan Williams 1 , Ghassan Jabbour 1
1 School of Materials and Flexible Display Center, ASU, Tempe, Arizona, United States
Show AbstractNear infra-red diodes are being used in applications such as defense, security, telecommunications and bio-imaging. In this talk, we will present our progress in developing near infra-red organic light emitting devices (OLEDs). A typical OLED is comprised of several functional materials such as a hole-transporting material, an electron-transporting material and an emissive material, sandwiched between two electrodes. Our approach focuses on the use of heavy metal complexes as phosphorescent emitters which can harvest both electrically generated singlet and triplet excitons, leading to possible 100% internal quantum efficiency. This presentation will include discussion on materials development of novel, efficient cyclometalated Ir complexes including iridium(III) bis(1 pyrenyl isoquinolinato N,C’) acetylacetonate (NIR1) and their derivatives. To further increase the device efficiency, it is important to incorporate appropriate charge-transporting and host materials to achieve balanced charge injection and suitable confinement of excitons. In this regard, we will highlight the development of novel electron transporting materials and host materials that were used to achieve efficient near infra-red OLEDs with relatively high power density output.
9:00 PM - O9.5
Simultaneous Single Molecule Raman and Fluorescence Spectroscopy of Conjugated Polymers.
Manfred Walter 1 2 , J. Lupton 1 2 , K. Becker 1 , J. Feldmann 1 , G. Gaefke 3 , S. Hoeger 3
1 Photonics and Optoelectronics Group, Physics Department and CeNS, Ludwig-Maximilians-Universität, Munich Germany, 2 Department of Physics, University of Utah, Salt Lake City, Utah, United States, 3 Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn Germany
Show Abstract9:00 PM - O9.50
Engineering Vertical Composition Variations in Spin-Coated Thin Films of Low-Bandgap Polyfluorene Copolymers and PCBM for Solar Cell Applications.
Cecilia Bjorstrom 1 , Jakub Rysz 2 , Andrzej Bernasik 3 , Andrzej Budkowski 2 , Ellen Moons 1
1 Department of Physics, Karlstad University, Karlstad Sweden, 2 Institute of Physics, Jagiellonian University, Kraków Poland, 3 Faculty of Physics and Applied Computer Science, AGH- University of Science and Technology, Kraków Poland
Show Abstract9:00 PM - O9.6
Molecular-weight Dependence of Interchain Polaron Delocalization in High-mobility Conjugated Polymers.
Jui-Fen Chang 1 , Jenny Clark 1 , Ni Zhao 1 , Henning Sirringhaus 1 , Dag Breiby 2 , Jens Andreasen 2 , Martin Nielsen 2 , Mark Giles 3 , Martin Heeney 3 , Iain McCulloch 3
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 , Danish Polymer Centre, Risø National Laboratory, Roskilde Denmark, 3 , Merck Chemicals, Southampton United Kingdom
Show Abstract9:00 PM - O9.7
Micromolding in Capillaries and Transfer Printing of Metal Electrodes: A Soft Lithographic Approach for the Fabrication of Source/Drain Electrodes in Organic Field Effect Transistors.
Alexander Bluemel 1 , Andreas Klug 1 , Sabrina Eder 1 2 , Ullrich Scherf 3 , Emil J.W. List 1 2 4
1 Institute of Solid State Physics, Graz University of Technology, Graz Austria, 2 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Graz, Austria and Institute of Nanostructured Materials and Photonics, JOANNEUM RESEARCH, Weiz Austria, 3 Makromolekulare Chemie, Fachbereich Chemie, Bergische Universität Wuppertal, Wuppertal Germany, 4 , NanoTecCenter Forschungsgesellschaft mbH, Weiz Austria
Show AbstractSoft lithography is a non-photolithographic approach for the micron-sized structuring of materials. In recent years a great number of publications in various fields of application such as microelectronics (micro-wires, organic light-emitting devices (OLEDs), organic field-effect transistors (OFETs) or biology (patterned cell growth) underline its flexibility and applicability to a great variety of research areas. We report the use of Micromolding in Capillaries (MIMIC) for the fabrication of source and drain electrodes used in well-performing bottom-gate/bottom-contact OFETs. This technique combines the advantage of solution-processability of the silver nano-dispersion with high lateral resolution for highly accurate micron-sized patterns. In MIMIC the stamp is used to form a system of capillaries between the substrate and the stamp. Applying a droplet of the desired material at one end of the capillary makes the liquid enter the microchannel due to capillary action.In comparison we have used Micro-Transfer Printing (µTP), the micron-sized counterpart to conventional letterpress printing. Here the stamp is set onto an inking pad, so that the protruding surfaces of the stamp come into contact with the silver nano-dispersion, and the material is transferred in the liquid state directly to the substrate. In all devices we used regioregular poly(3-hexylthiophene) (P3HT) as active channel material, a well-established conjugated polymer. The devices were performing well and showed hardly any hysteresis in the output and transfer characteristics.
9:00 PM - O9.8
Structural Analysis of Oligothiophenes and Some of their Derivatives: a Combined X-Ray Single Crystal Data and DFT Calculations
Mamoun Bader 1 2 , Phuong T. Pham 2
1 Chemistry and Earth Sciences, Qatar University, Doha Qatar, 2 Chemistry, Pennsylvania State University, Dunmore, Pennsylvania, United States
Show Abstract9:00 PM - O9.9
Inkjet-Printed Low-Voltage Organic Thin-Film Transistors : Towards Low-Cost Flexible Electronics
Mickael Barret 1 , Mustapha Chouiki 1 , Sebastien Sanaur 1 , Philippe Collot 1
1 Packaging and Flexible Substrates, Ecole Nationale Supérieure des Mines de Saint-Etienne, Site Georges Charpak, Gardanne France
Show Abstract
Symposium Organizers
Ana Claudia Arias Palo Alto Research Center
J. Devin MacKenzie Add-Vision, Inc.
Alberto Salleo Stanford University
Nir Tessler Technion-Israel Institute of Technology
O10: Commercialization and Applications
Session Chairs
Friday AM, April 13, 2007
Room 2002 (Moscone West)
9:30 AM - **O10.1
Dielectrics for All-additive Jet-printed Organic Electronics.
Jurgen Daniel 1 , Ana Claudia Arias 1 , Steve Ready 1 , Brent Krusor 1 , Michael Chabinyc 1 , Robert Street 1
1 , PARC, Palo Alto, California, United States
Show Abstract10:00 AM - O10.2
UHF Rectification for Organic RFID Tags.
Soeren Steudel 1 2 , Jan Genoe 1 , Paul Heremans 1 2
1 Polymer & Molecular Electronics, IMEC, Leuven Belgium, 2 Electrical Engineering, KU Leuven, Leuven Belgium
Show Abstract10:15 AM - O10.3
Printable Temperature Llogging Device.
Payman Tehrani 1 , Nathaniel Robinson 1 , Mats Robertsson 2 , Anna Malmström 2 , David Nilsson 1 2 , Magnus Berggren 1
1 Dept. of science and technology, Linköping University, Norrköping Sweden, 2 , Acreo AB, Norrköping Sweden
Show Abstract10:30 AM - O10.4
Flexible, Polymer-based Light Sensor Arrays on Active-matrix Backplanes Fabricated by Digital Inkjet Printing.
Tse Nga Ng 1 , William Wong 1 , Rene Lujan 1 , Raj Apte 1 , Michael Chabinyc 1 , Scott Limb 2 , Robert Street 1
1 Electronic Materials Lab, Palo Alto Research Center, Palo Alto, California, United States, 2 Hardware System Lab, Palo Alto Research Center, Palo Alto, California, United States
Show Abstract10:45 AM - O10.5
High Performance Organic Field-effect Transistors (OFETs) Using High-κ Dielectrics Grown by Atomic Layer Deposition (ALD).
Xiaohong Zhang 1 , Benoit Domercq 1 , Seunghyup Yoo 1 , Xudong Wang 2 , Zhong Lin Wang 2 , Bernard Kippelen 1
1 School of Electrical and Computer Engineering and Center for Organic Photonics and Electronics (COPE), Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Materials Sciences and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract11:30 AM - **O10.6
Printed Organic Transistors for Large-area Sensors and Actuators.
Takao Someya 1 , Tsuyoshi Sekitani 1 , Yoshiaki Noguchi 1 , Shintaro Nakano 1 , Shinya Takatani 1 , Makoto Takamiya 2 , Takayasu Sakurai 2
1 Quantum-Phase Electronics Center, University of Tokyo, Tokyo Japan, 2 Center for Collaborative Research, University of Tokyo, University of Tokyo Japan
Show Abstract12:00 PM - O10.7
High Resolution Organic TFTs for Active Matrix Organic Light Emitting Diode (AM-OLED)
Hee Jung Kim 1 , Jeong-Hun Son 1 , Jung-Nam An 1 , JiHun Choi 1 , Jae Won Chang 1 , Sun-young Kim 1 , Sungeun Lee 1 , Young Hwan Choi 1 , Jason Locklin 2 , Zhenan Bao 2
1 Devices & Materials Lab., LG Electronics, Seoul Korea (the Republic of), 2 chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractWednesday, April 11New Presenter and New Title – O10.7 @ 11:00 amHigh Resolution Organic TFTs for Active Matrix Organic Light Emitting Diode (AM-OLED). Sun-Young Kim
12:15 PM - O10.8
Fabrication of Long-Life Organic Light-Emitting Devices with Graded Composition Using an In-Line Evaporation Method
Junji Kido 1 2 , Yuji Fujita 1 , Nobuhiro Ide 2 , Ken-ichi Nakayama 1 2
1 Polymer Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan, 2 , Optoelectronic Industry and Technology Development Association, Bunkyo-ku, Tokyo, Japan
Show AbstractOne of the factors that appears to limit the lifetime of a general organic light emitting device with hetero-junction structure is charge buildup at the interface. In this study, the influence of the graded mixed-layer on the performance of organic light-emitting device was investigated. A typical device structure employed in this study was ITO/ polymer buffer layer (MCC-PC1020) / NPD:Alq (graded composition) / Liq / Al, which was fabricated by specially constructed in-line evaporation system. Various patterns of gradual mixing of NPD:Alq were evaluated. Dye-doped OLEDs were also fabricated to improve the efficiency and lifetime. When rubrene was used as a dopant dye, the lifetime of the graded device was improved to 37,000 h which was 1.6 times longer than that of a conventional hetero-junction structure (22,000 h). This improvement in lifetime is attributed, in part, to the suppression of the formation of fluorescence quenching cationic Alq species at the NPD/Alq interface.
12:30 PM - O10.9
Advances in Plexcore™ Technology for OLED Displays and Lighting.
Darin Laird 1 , Brian Woodworth 1 , Reza Stegamat 1 , Mathew Mathia 1
1 , Plextronics, Pittsburgh, Pennsylvania, United States
Show Abstract12:45 PM - O10.10
Low-operating Voltage Pentacene FETs with High Dielectric Constant Polymeric Gate Dielectrics and its Hysteresis Behavior.
Se Kim 1 , Sang Yang 1 , Chan Park 1
1 Polymer Research Institute, Pohang university of science and technology, Pohang Korea (the Republic of)
Show AbstractO11: Novel Concepts and Devices
Session Chairs
Friday PM, April 13, 2007
Room 2002 (Moscone West)
2:30 PM - **O11.1
Expanding The Frontiers Of Organic Electronics Using Sequence Independent Synthesis Tools.
Yoav Eichen 1 2 3 , Elena Gershman 1 , Batya Blumer-Ganon 1 , Michal Adler 1 , Nir Tessler 2 3 , Vlad Medvedev 2 , Olga Solomeshch 2 , Alexey Razin 2
1 Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Technion City Israel, 2 Nanoelectronics Center, Technion - Israel Institute of Technology, Technion City Israel, 3 , Peptronics Ltd., Ramat Gan Israel
Show AbstractDespite the long standing effort to develop effective and robust organic electronics, still progress in this field is impeded by the limited choice of materials. The inherent versatility of organic chemistry and the potential application of π-conjugated organic materials in structuring molecular electronic components focuses enormous efforts towards the preparation and characterization of new organic based electronic components. Since the field is largely material driven, a major obstacle in organic-based optoelectronics is the difficulty to reach the wide set of material properties required by current device technologies and in synthesizing complicated structures with molecular precision. Using conventional synthetic routes, one is limited by the fact that almost each synthetic step has different and specific conditions and usually produces a variety of byproducts that must be removed before any subsequent synthetic step is performed. As a result, only a small fraction of the practically limitless choice of organic materials is currently available to the organic semiconductor community.When versatility and reliability is in question, nature adopts a sequence independent synthesis, producing large numbers of materials that differ in structure and properties out of a very limited number of small building blocks (amino acids, nucleic acids). Due to the importance of these two reactions to molecular biology, two most powerful in-vitro syntheses were developed for the in-vitro solid-phase preparation of peptide and nucleic acid sequences.The talk will report on the harnessing of these in-vitro solid phase syntheses for the preparation of (almost) sequence independent materials for organic electronics based on bio-like and bio-based processes.
3:00 PM - O11.2
Dry-stamping to Produce High-performance Polymer Thin-film Transistors.
Akihiro Nomoto 1 , Nobuhide Yoneya 1 , Noriyuki Kawashima 1 , Kazumasa Nomoto 1 , Jiro Kasahara 1
1 , Materials Laboratories, Sony Corporation, 4-16-1 Okata, Atsugi-shi, Kanagawa, Japan
Show AbstractFriday, April 13Transferred Poster O6.19 to O11.2 @ 2:00 pmDry-stamping to Produce High-performance Polymer Thin-film Transistors. Akihiro Namoto
3:15 PM - O11.3
Tough, Semiconducting Polyethylene-Poly(3-hexylthiophene) Diblock Copolymers
Christian Muller 1 , Shalom Goffri 2 , Jens Andreasen 3 , Rene Janssen 6 , Henri Chanzy 1 5 , Dag Breiby 3 4 , Martin Nielsen 3 , Christopher Radano 6 7 , Henning Sirringhaus 2 , Paul Smith 1 , Natalie Stingelin-Stutzmann 1 8
1 Department of Materials, ETH Zurich, Zurich Switzerland, 2 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 3 Danish Polymer Centre, Riso National Laboratory, Roskilde Denmark, 6 Laboratory of Macromolecular and Organic Chemistry, TU Eindhoven, Eindhoven Netherlands, 5 CERMAV, CNRS, Grenoble France, 4 Centre for Molecular Movies, University of Copenhagen, Copenhagen Denmark, 7 , Degussa RohMax, Horsham, Pennsylvania, United States, 8 Department of Materials, Queen Mary, London United Kingdom
Show AbstractSemiconducting diblock copolymers of polyethylene and regioregular poly(3-hexylthiophene) are demonstrated to exhibit a rich phase behaviour, judicious use of which permitted us to fabricate field-effect transistors that show saturated charge carrier mobilities as high as 2.10e-2 cm2/Vs and ON-OFF ratios ~10e5 at contents of the insulating polyethylene moiety as high as 90 wt%. In addition, the diblock copolymers display outstanding flexibility and toughness with elongations at break exceeding 600 % and true tensile strengths around 70 MPa, opening the path towards robust and truly flexible electronic components.[C. P. Radano et al., Crystalline-Crystalline Block Copolymers of Regioregular Poly(3-hexylthiophene) and Polyethylene by Ring-Opening Metathesis Polymerization, J. Am. Chem. Soc.127, 12502 (2005).]
3:30 PM - O11.4
Organic Transistors of Molecular Integrated Semiconductor-insulator Monolayer Films Using a Room Temperature Self-assembly Process.
Kanan Puntambekar 1 , Kinyip Phoa 1 , Vivek Subramanian 1 , Amanda Murphy 2 , Clayton Mauldin 2 , Jean Frechet 2 , Dean DeLongchamp 4 , Daniel Fischer 4 , Michael Toney 3
1 Electrical Engineering and Computer Science, Univ. of California, Berkeley, Berkeley, California, United States, 2 Department of Chemistry, Univ. of California, Berkeley, Berkeley, California, United States, 4 Polymer Division of the Materials Science and Engineering Department, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, California, United States
Show Abstract4:15 PM - O11.5
The SensorOLED Device: A new Integrated Organic Light Emitting Device for Direct Gas Detection.
Stefan Sax 1 , Evelin Fisslthaler 1 , Sabrina Eder 1 4 , Stefan Kappaun 2 , Christian Slugovc 2 , Josemon Jacob 3 , Klaus Müllen 3 , Emil J.W. List 1 4 5
1 Institute of Solid State Physics, Graz University of Technology, Graz Austria, 4 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Graz, Austria and Institute of Nanostructured Materials and Photonics, JOANNEUM RESEARCH, Weiz Austria, 2 Institute for Chemistry and Technology of Organic Materials, Graz University of Technology, Graz Austria, 3 , Max-Planck-Institute for Polymer Research, Mainz Germany, 5 , NanoTecCenter Forschungsgesellschaft mbH, Weiz Austria
Show AbstractA decade after the effect was discovered organic materials have made it into commercial use. Conjugated organic oligomers and polymers are of considerable industrial importance as active materials in the emerging new technologies of organic light-emitting diodes (OLEDs),as well as of academic interest in the field of polymer lasers, photovoltaic devices (solar cells), and field-effect transistors. During the last years this class of materials was also frequently used for several sensor applications. Conjugated organic oligomers and polymers are easy tunable for different sensor applications and analytes. However, all of these sensor devices consist of a sensor film which is excited by an external light source (lasers and several inorganic and organic light sources have been used in the past), therefore belonging to the class of so called “passive” sensor devices.Compared to such a classical fluorescent sensor system, which comprises of a light source with a photoluminescence sensing layer and a detector system, an active organic sensor device has the enormous advantage of combining the light source with the sensing element within one layer, which reduces the fabrication effort and simplifies the whole sensor geometry- the sensor is incorporated in the organic layer, instead of requiring a bipartite structure. Especially when using phosphorescent sensing materials like metal complexes, which successfully have been employed in the past in several sensor applications, the use of electroluminescence effects instead of photoluminescence enhances the overall electroluminescence quantum yield of a SensLED. Those types of materials are also known for acting as high yield luminescence dyes in organic light emitting devices, by weakening the spin orbit coupling and using radiant triplet recombination for enhanced electroluminescence. In the case of oxygen detection, metal complexes like PtOEP or Ir-complexes have been used by taking advantage of quenching effects caused by the interaction of the heavy metal atom with the oxygen molecules.In particular we were able to build a reversible oxygen sensitive light emitting device by implementing the sensor functionality into the active layer of the light emitting device (SensLED). A SensLED consists of an ITO anode on a glass or flexible substrate, a PEDOT:PSS layer, the electroluminescent sensor layer (in our case comprising of PtOEP in poly(9-vinylcarbazole) matrix), and a top electrode that is structured for enhanced gas diffusion.
4:30 PM - O11.6
Monolayer Transistor using a Highly Ordered Conjugated Polymer as Channel
J. Scott 1 , J. Samuel 1 , Jennifer Hou 2 , Chantel Tester 3 , Clara Cho 1 , Charles Rettner 1 , Sally Swanson 1 , Robert Miller 1
1 , IBM Almaden Research Center, San Jose, California, United States, 2 , Cambridge Univ, Cambridge United Kingdom, 3 , Mount Holyoke Coll., South Hadley, Massachusetts, United States
Show Abstract4:45 PM - O11.7
Tuning the Contact Resistance in Nanoscale Oligothiophene field-effect Transistors.
Arne Hoppe 1 , Joerg Seekamp 1 , Torsten Balster 1 , Guenther Goetz 2 , Peter Baeuerle 2 , Veit Wagner 1
1 School of Engineering and Science, International University Bremen, Bremen Germany, 2 Department Organic Chemistry II, Ulm University, Ulm Germany
Show Abstract5:00 PM - O11.8
An Organic Photodetector on a Scanning Probe Cantilever.
Kwang Hyup An 1 , 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 AbstractA wide variety of organic-based optoelectronic devices have been demonstrated to date, including OLEDs, photovoltaic cells and photodetectors, transistors, biological sensors, and others. The ability to deposit molecularly smooth organic thin films on a variety of substrate materials and geometries without concern for lattice matching has allowed novel device form factors and fabrication approaches to be applied. Taking advantage of these properties of organic materials and deposition techniques, we demonstrate an organic photodetector integrated with a commercial AFM cantilever probe. The device consists of an electron donor-acceptor heterojunction sandwiched between two metal contacts. A photoactive region of sub-micron lateral dimensions is defined on the cantilever using selective focused ion beam milling of a pre-deposited insulator layer (parylene). Light enters the active region through a thin, semitransparent, vacuum-deposited silver electrode. Electrical power generation on the order of a nanowatt is observed under 470nm and 19 W/cm2 illumination of the probe, with a dark current of 24 nA at 0.4 V reverse bias and a signal-to-noise ratio of 15. High resolution spatial imaging can be achieved by scanning the probe across a feature while measuring light transmission through a broadly illuminated sample. Contactless high resolution 3-dimensional imaging of a light source may be possible via optical interference effects specific to ultra-thin organic thin-film heterostructure photovoltaic devices. Potential applications of this probe may be found in micropositoning, biological imaging and sensing, and non-destructive semiconductor and optoelectronic device testing.
5:15 PM - O11.9
Single-layer Organic Non-volatile Memory Devices.
Whitney Gaynor 1 , Peter Peumans 2
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Electrical Engineering, Stanford University, Stanford, California, United States
Show Abstract5:30 PM - O11.10
Role of Charge Interaction in the Behavior of Organic Thin Film Transistors.
Christoph Erlen 1 , Francesca Brunetti 2 , Matthias Fiebig 3 , Bert Nickel 3 , Aldo Di Carlo 2 , Paolo Lugli 1
1 Institute for Nanoelectronics, Technische Universität München, München Germany, 2 , University of Rome "Tor Vergata", Rome Italy, 3 Department für Physik, Ludwig-Maximilians-Universität, München Germany
Show AbstractPronounced fluctuations in the IV characteristics are a particularity of organic thin films transistors (OTFTs). Being a clear fingerprint of time dependent processes, they are most frequently encountered in form of transfer and output curve hysteresis. Up to now, there is no self-contained theory to describe and predict these effects, since research has mainly targeted the description of IV characteristics in terms of static models [1]. The associated inaccuracy in the modeling of device behavior adds to the difficulties encountered in the realization of organic circuits.In this contribution, we show that both mobile ions and traps effectively contribute to the hysteresis. The fabrication process and employed materials define to which extend they are present in a particular device. In order to demonstrate our model, we have built and simulated two different types of pentacene OTFTs, in either of which one of the effects is predominant. By varying measurement speed and temperature, characteristic signatures of ions and traps are identified.The ion-dominated OTFT is all-organic and realized using PV-OH as gate insulator. The fabrication technique focuses on the possibility to obtain micrometer resolution in the definition of PEDOT source/drain contacts. The process is based on a selective electrochemical growth of the conductive polymer on a prepatterned anode [2]. 20 nm of pentacene are deposited by thermal evaporation, and the PV-OH insulating layer has a thickness of 800 nm. The trap-dominated transistor is built on n-doped silicon substrate, which also serves as back gate. The insulating dielectric is a 200 nm thick layer of thermal SiO2. Gold source and drain contacts are defined using optical lithography. Oxygen plasma is applied to reduce surface contamination before a 48 nm layer of highly purified pentacene is evaporated.It has been demonstrated that finite element drift-diffusion simulations are suitable to enhance the understanding of device behavior allowing us to extract valuable TFT parameters such as traps and fixed charges at the semiconductor/insulator interface [3][4]. To analyze the hysteresis behavior, we have modified the commercial software tool SENTAURUS(TM) to account for the special nature of organic devices and implemented transient simulations of both devices. As a result, we can show that trapping and mobile ions indeed model the experimental IV characteristics. Furthermore, we are able to quantify trap density, energy, and lifetime in the silicon substrate OTFT as well as ion mobility and concentration in the all-organic device. [1] G. Horowitz, J. Mater. Res., vol. 19, p.1946, 2004.[2] E. Becker et al., Appl. Phys. Lett., vol. 83, p.4044, 2003.[3] A. Bolognesi et al., IEEE Trans. Electr. Dev., vol. 51, p.1997, 2004.[4] Erlen et al., J.Comp. Elec., in press, 2006.
5:45 PM - O11.11
Low-Voltage Organic Field-Effect Transistors Gated via Polyanionic Electrolytes.
Lars Herlogsson 1 , Xavier Crispin 1 , Elias Said 1 , Nathaniel Robinson 1 , Magnus Berggren 1
1 Department of Science and Technology, Linköping University, Norrköping Sweden
Show AbstractOrganic field-effect transistors (OFETs) and other “plastic” electronic devices are currently scrutinized for use in printed, flexible, integrated electronics. Ideally, these systems are fast, operate at low voltage, and are robust enough to be manufactured using standard printing techniques. Tremendous efforts have been devoted to reach high capacitance (per area) between the gate and the channel to allow transistors to operate at low voltage. Since the dielectric constant of organic materials usually is quite low, very thin gate insulator layers are required in order to obtain a high capacitance. Molecular assembly and self-organization techniques have been utilized to manufacture gate dielectric layers only a few nanometres thick, resulting in large capacitance. These layers are usually quite complicated to produce and are therefore not very compatible with printing techniques. Another approach to reduce the operating voltage is to use an electrolyte as gate insulator. A small voltage applied to the gate electrode will redistribute the mobile ions in the electrolyte towards the electrodes, resulting in a high electric field at the interfaces. As a result, the drive voltage is essentially independent of the electrolyte thickness. However, the electrolyte-gated transistors reported so far have slow on-off switching, typically in the order of a second, which in most cases is due to electrochemical doping of the channel.We demonstrate a new generation of OFETs that are gated via polyanionic electrolytes. The novelty of this electrolyte-gated OFET resides in the mechanism to open the channel via the quick formation of highly capacitive (in order of 10 to 100 μF cm-2) electric double layers at the semiconductor-electrolyte and electrolyte-gate interfaces, as the OFET is gated. By having only immobile anions in the electrolyte electrochemical doping of the semiconductor bulk is avoided. This results in fast-responding (< 0.3 ms), low-voltage (< 1 V) transistors. Employing a polyelectrolyte as gate insulator also eases design and manufacturing requirements since thicker polyelectrolyte layers are not detrimental for the performance of the OFETs. This extraordinary property of the insulator is due to the spontaneous formation of a nanometer-scale “capacitor” at the semiconductor-insulator interface as the gate is biased. The resulting flexibility together with recent progress in printing source-drain gate electrodes makes printing a promising manufacturing platform for such transistors in low-cost electronics.ReferencesL. Herlogsson et al., Adv. Mater. In Press.E. Said et al., Appl. Phys. Lett. 89, 143507 (2006).AcknowledgmentsThe authors gratefully acknowledge The Swedish Foundation for Strategic Research (COE@COIN), VINNOVA, The Royal Swedish Academy of Sciences, and The Swedish Research Council for financial support of this project.