Symposium Organizers
Franky So University of Florida
Graciela B. Blanchet DuPont
Yutaka Ohmori Osaka University
S1: Organic Light Emitting Devices I
Session Chairs
Monday PM, November 27, 2006
Room 304 (Hynes)
9:00 AM - **S1.1
Achieving Efficient Solid State Lighting Using Organic Light Emitting Devices.
Stephen Forrest 1
1 Department of EECS & Physics, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:30 AM - S1.2
Synthesis of Well-Defined Oligomers for Fluorescence and Phosphorescence
Andrew Holmes 1 3 , Khai Leok Chan 2 1 , Sung Yong Cho 2 1 , Nicholas Evans 2 , Robert Borthwick 1 , Georgia McCluskey 1 , Andrew Grimsdale 1 , Scott Watkins 1
1 Bio21 Institute, University of Melbourne, Parkville, Victoria, Australia, 3 Department of Chemistry, Imperial College, London United Kingdom, 2 Melville Laboratory, University of Cambridge, Cambridge United Kingdom
Show AbstractThere is much interest in the synthesis of suitable high energy semiconducting hosts and phosphorescent guests to harness the triplet state in organic electroluminescent devices. In this paper we will describe syntheses of well-defined oligomeric host and guest materials to evaluate the optimum combinations for solution processible devices. Host materials will be selected from combinations of conjugated materials linking 9,9-disubstituted dibenzosiloles and germoles with 1-substituted carbazoles and twisted biphenyl derivatives. Guest materials will be derived from cyclometallated iridium complexes linked to conjugated aromatic hosts either by conjugation or through a polymethylene carbon tether. Analysis of the efficiency of electroluminescent devices fabricated with these materials will guide the optimum selection of conjugated polymer hosts and electrophosphorescent guests for efficient triplet energy emission in the form of phosphorescence.
9:45 AM - S1.3
White Organic Light-emitting Device Based on a Phosphor Sensitized Fluorescent Emission Layer.
Hiroshi Kanno 2 1 , Yiru Sun 1 , Stephen Forrest 1 3
2 , Sanyo Electric Co, Osaka Japan, 1 Dept. of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 , University of Michigan, Ann Arbor, Michigan, United States
Show Abstract10:00 AM - S1.4
Printing OLEDs in Ambient Conditions using MoJet Printer
Jianglong Chen 1 , Valérie Leblanc 1 , Peter Mardilovich 2 , Marc Baldo 1 , Martin Schmidt 1 , Vladimir Bulović 1
1 Microsystems Technology Laboratories, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Hewlett-Packard Company, Corvallis, Oregon, United States
Show AbstractSmall molecular weight organic semiconductors, such as Alq3, are typically deposited by thermal evaporation and patterned through metal stencil masks in a vacuum chamber. We previously demonstrated that Molecular Jet (MoJet) printing technique, a reconfigurable and scalable patterning method based on a silicon microsystem (MEMS) printhead, can outperform metal stencil masks in direct patterning of vacuum evaporated Alq3, and can fabricate active OLEDs at 800 dpi resolution. Here we present an improved version of the MoJet printer that can deposit Alq3 thin films in ambient conditions. The new design utilizes a silicon membrane composed of an array of micrometer-size pores and an integrated thin film platinum heater for local evaporation of Alq3 molecules. This MoJet printer is used in conjunction with HP Inkjet technology for the precise loading of Alq3 solution into the micro-pores. Upon heating up of the porous area using the integrated platinum heater, the solvent evaporates out of the membrane. Alq3 molecules left inside the pores can then be discharged from the pores and be deposited onto an adjacent substrate. We demonstrate that this transfer patterning process does not require a vacuum environment. We apply the MoJet printing method to pattern the Alq3 electroluminescent layers of an OLED. Key experimental parameters such as jetting energy, ink composition and solvent properties have been explored to understand the jetting dynamics of organic molecules. Modeling and simulation results of the molecular jetting process are also assessed. MoJet printing is scalable to large area substrates, compatible with multi-layer organic device structures, and is capable of defining uniform patterns in ambient conditions.
10:15 AM - S1.5
Red Electroluminescence from Liquid Crystalline Diketopyrropyroles.
Ryohei Hashimoto 1 , Jun-ichi Hanna 1
1 Imaging Science and Engineering Lab, Tokyo Institute of Technology, Yokohama Japan
Show Abstract10:30 AM - S1.6
Highly Efficient Red Emission Polymer Phosphorescent Lighting Emitting Diodes based on novel Ir(piq)3 derivatives
Jinsong Huang 1 , Taiki Watanabe 2 , Kazunori Ueno 2 , Yang Yang 1
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 OD Development Project, Canon Inc. , Tokyo Japan
Show AbstractIn this conference, we report on very high efficiency solution processed red emitting polymer phosphorescent light-emitting diodes (P-PhoLEDs). Several novel red iridium based phosphorescence dyes were used as dopants, and polyfluorene-derivative (PF) is used as host material in this work. Pure red emission from dopants is obtained at 4 - 6 weight% dopant concentration in the host polymer. Electron injection/hole blocking layer Cs2CO3 was inserted between light emitting polymer (LEP) layer and Al cathode through thermal deposition. By modulating the thickness of Cs2CO3 layer, the electron injection can be precisely controlled to balance the hole injection. Direct trapping of charge by the dopants, which can be procured by change the polymer thickness, helps to increase efficiency of device. By optimizing the parameters of devices, peak efficiencies of 19.2 cd/A and 21 lm/W at 100cd/m2 is achieved for red emission P-PhoLEDs. Even at a high brightness of 1000 cd/m2, our best device still has very high efficiency of 18.9 cd/A and 13.4 lm/W. To the best of our knowledge, these are the highest reported efficiencies for red emission P-PhoLEDs. Most important of all, this technique is universal to achieve high efficiency PLED. It has been successfully applied in other material systems.
10:45 AM - S1: OLED I
BREAK
11:15 AM - **S1.7
High Density Carrier Injection and Transport into Organic Thin Films -Device Physics and Novel Light Emitting Applications.
Chihaya Adachi 1 2 , Toshinori Matsushima 2 , Hajime Nakanotani 1 2
1 Center for Future Chemistry, Kyushu University, Fukuoka Japan, 2 , JST-CREST, Tokyo Japan
Show Abstract11:45 AM - S1.8
Self-assembled, Chemically Fixed Homojunctions in Semiconducting Polymers.
Janelle Leger 1 , Deanna Rodovsky 1 , Glenn Bartholomew 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show Abstract12:00 PM - S1.9
High Efficiency Near Infrared Organic Light Emitting Diodes (OLEDs).
Carsten Borek 1 , Kenneth Hanson 1 , Peter Djurovich 1 , Mark Thompson 1 , Yiru Sun 2 4 , Stephen Forrest 4 , Jason Brooks 3 , Julie Brown 3
1 Chemistry Department, University of Southern California, Los Angeles, California, United States, 2 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 4 Departments of Physics and Electrical Engineering, University of Michigan , Ann Arbor, Michigan, United States, 3 , Universal Display Corporation, Ewing, New Jersey, United States
Show AbstractOrganic light emitting diode (OLED) research has manly focusing on the visible region of electromagnetic spectrum. Recently efforts have been undertaken to shift the emission of OLEDs into the near infrared (nIR) region of the spectrum, opening the door to a range of potential applications.We have used a range of Ir and Pt complexes as dopants for high efficiency OLEDs in the visible spectrum. Emission in these phosphors is from a mixture of MLCT and LC states, with the color readily tuned by ligand modifications. Following a similar approach we have recently developed a family of nIR emitting dopants for OLEDs. We have fabricated a nIR OLED with highly efficient emission at 765 nm and an EQE of 6% (see Figure below). We will discuss both the design of metal complexes for nIR emission and the OLED design and performance.
12:15 PM - S1.10
Accumulation of Electric Field-stabilized Geminate Polaron-pair States to Attain High Excitation Density with a Low Pump Intensity.
Noel Giebink 1 , Stephen Forrest 2 3 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Physics, University of Michigan, Ann Arbor, Michigan, United States, 3 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWe investigate the recombination dynamics of electric field-stabilized intermolecular geminate polaron-pairs (PP) in small-molecular weight amorphous organic thin films. Formed from the incomplete dissociation of optically excited singlet excitons, these coulombically bound PP states may be stabilized in the presence of a strong external electric field to prevent geminate recombination for long periods of time (>1ms). When the field is removed, some of the PPs rapidly relax (<10ns) back into excitons, which then recombine at their natural rate. Following initial excitation by a nanosecond optical pulse in the presence of an external field, we study the fluorescence burst that occurs from PP recombination when the field is turned off. The films studied consist of 4,4’-bis(N-carbazolyl)biphenyl (CBP) doped with 4wt% of the green laser dye, coumarin-6. We observe that field stabilized PP decay follows a power law of t-m (with m~0.1) where t is the time that the PPs are held in the field, a trend qualitatively similar to polymeric systems.1 Since m<1, this slow decay allows for PP accumulation at a rate of roughly t1-m over the duration of the electric field when pumped by a continuous wave laser at λ=325nm close to the CBP absorption maximum. Since some of the surviving PP population converts back to the excitonic state when the field is turned off, PP accumulation represents a possible route to obtain a high singlet exciton density if spin is conserved in the field-stabilized geminate pair.2 Using a low intensity (<1W/cm2) cw laser as the excitation source in conjunction with a pulsed electric field, we demonstrate accumulation of PPs over time that yield fluorescence bursts (~50ns FWHM) up to 30 times the steady-state fluorescence intensity, with estimated peak singlet densities > 6x1015cm-3.1B. Schweitzer, V. I. Arkhipov, and H. Bassler, Chem. Phys. Lett. 304, 365-370 (1999).2M. Reufer, M. J. Walter, P. G. Lagoudakis, B. Hummel, J. S. Kolb, H. G. Roskos, U. Scherf, and J. M. Lupton, Nat. Mater. 4, 340-346 (2005).
12:30 PM - S1.11
Novel Light Emitting Oligomeric and Polymeric Spiro-Fluorenes with Xanthene Moieties
Igor Perepichka 1 , Maksym Kryuchkov 1 , Martin Bryce 1 , Fernando Dias 2 , Andrew Monkman 2
1 Department of Chemistry, Durham University, Durham United Kingdom, 2 Department of Physics, Durham University, Durham United Kingdom
Show AbstractReaction of fluorenones with para-substituted phenols or 1-naphthols results in formation of spiro(xanthene-9,9’-fluorenes) and spiro(dibenzoxanthene-9,9'-fluorenes), respectively, which present a novel platform for design of fluorene-based light emitting materials. Based on these monomeric units, several spiro-xanthene-fluorene and spiro-dibenzoxanthene-fluorene oligomers and polymers have been synthesized by palladium catalyzed homo- and cross-couplings. These spiro-type conjugated materials demonstrate stable blue photoluminescence both in solution and solid state. Synthesis, electrochemical and photophysical studies of these oligomers and polymers will be reported, together with some preliminary results on use of spiro-xanthene-fluorene polymers as emitting materials in single-layer LED devices. The results will be discussed in comparison with properties of other classes of polyfluorene light-emitting materials used in LED applications.
12:45 PM - S1.12
Perylene Diimide as the Black-Layer Material of the OLEDs
Kai-Hsiang Chuang 1 , J. H. Lee 1 2 , Yu-Hsuan Ho 1 , Chi-Feng Lin 1 , Chun-Chieh Chao 4 , Man-Kit Leung 3 4 , Cheng-Yu Li 5 , Hsuen-Li Chen 5
1 Graduate Institute of Electro-Optical Engineering, National Taiwan University , Taipei Taiwan, 2 College of Optics and Photonics, University of Central Florida, Orlando, Florida, United States, 4 Department of Chemistry, National Taiwan University , Taipei Taiwan, 3 Institute of Polymer Science and Engineering, National Taiwan University , Taipei Taiwan, 5 Department of Materials Science and Engineering, National Taiwan University , Taipei Taiwan
Show AbstractIn this paper, we use a perylene diimide derivative serving as a destructive and an absorption layer of the “black cathode” of an organic light-emitting device (OLED). Device structure of our black OLED is N,N’-diphenyl-N,N’-bis(1-napthyl)-1,1’-biphenyl-4,4’-diamine (NPB) (50nm)/ tris-(8-hydroxyquinoline)aluminum (Alq3) (40 nm)/ LiF (0.5 nm)/ semitransparent metal (5 nm)/ perylene diimide (75 nm) / electron injection layer (1.2 nm) / Al (150 nm). To investigate the electron injection and transport properties of such a material, electron-only devices were first fabricated with the structure: Ag (20nm)/ perylene diimide derivative or tris-(8-hydroxyquinoline)aluminum (Alq3) (50nm)/ electron injection layer/ Al (150nm). The electron injection layers are LiF (1.2 nm), Alq3 (2nm)/ LiF (1.2nm), or no such a layer. We found that the LiF/Al structure provides a good electron injection capability from Al cathode to the perylene diimide derivative with a current density of 341 mA/cm^2 at 4V which is 4 and 4100 times higher than Alq3/ LiF/ Al and Al structures, respectively. Besides, such a layer has a resistivity of 2.34×10^6 ohm-cm at 4 V which is one order of magnitude to the Alq3-based electron-only device which shows a superior electron transport characteristic. When the thickness of the semitransparent Al increases from 0, 5, 10, and 15 nm, the reflectance at 555 nm increases from 30.9, 23.3, 51.1, to 74.4%, due to weaker interference effect. At the same time, the driving voltage decreases due to better electronic conductivity. For obtaining a good electronic property, the thickness of the semitransparent Al may not be less than 5 nm. For further improving the optical characteristics, we use the Al/Ag bi-layer structure to reduce the reflection. The (Al, Ag) thickness are varied with (0, 5 nm), (1 nm, 4 nm), (2.5 nm, 2.5 nm), and (5 nm, 0 nm). The driving voltage at 50 mA/cm^2 are 10.4, 7.4, 7.5, and 7.5 V. We can see that the driving voltages are nearly identical except the case when Al thickness is zero due to worse electron injection capability in this case. The reflectance at 555 nm decreases then increases from 17.5, 6.5, 14.5, to 23.3%. The minimum value occurs when the (Al, Ag) thickness is (2.5 nm, 2.5 nm) which shows the “blackest” characteristics in this device. With the same device brightness of 600 cd/m^2, the contrast ratio of the “black” OLED is 26.7 under 1000-lux illumination which is 7.85 times higher than that of the conventional one.
S2: Organic Light Emitting Devices II
Session Chairs
Monday PM, November 27, 2006
Room 304 (Hynes)
2:30 PM - **S2.1
Excitation Energy Transfer in Guest-host Molecular Systems.
Zakya Kafafi 1 , Leonidas Palilis 1 , Mason Wolak 1 , Paul Lane 1 , Joseph Melinger 1
1 Optical Sciences Division, Naval Research Laboratory, Washington, District of Columbia, United States
Show Abstract3:00 PM - S2.2
Organic Light Emitting Diodes with Opal Photonic Crystal Layer and Carbon Nanotube Anode
Raquel Ovalle Robles 1 2 , Rocio Nava 1 5 , Krutarth Trivedi 1 4 , Christopher Williams 1 2 , Mei Zhang 1 , Shaoli Fang 1 , Sergey Lee 1 , Ray Baughman 1 3 , Anvar Zakhidov 1 2
1 NanoTech Institute, University of Texas at Dallas (UT-D), Richardson, Texas, United States, 2 Physics Department, University of Texas at Dallas (UT-D), Richardson, Texas, United States, 5 Physics Department, Universidad Autonoma Nacional de Mexico (UNAM), Mexico city Mexico, 4 Electricla Engineering Department, University of Texas at Dallas (UT-D), Richardson, Texas, United States, 3 Chemestry Department, University of Texas at Dallas (UT-D), Richardson, Texas, United States
Show AbstractWe report electroluminescence intensity and spectral changes in light emission from organic light emitting diode (OLEDs) structures, which have thin transparent films of opal photonic crystal (PC). The anode in such PC-OLED is laminated on opal layer from free standing optically transparent multiwall carbon nanotubes (T-CNT) sheets made by dry spinning from CVD grown forests [1]. Silica and polystyrene opal films were grown on glass substrates by vertical sedimentation in colloids in thermal baths and the particle size of opal spheres ranges from 300 nm to 550 nm. The use of T-CNTs, (coated by PEDOT-PSS to avoid shorting) as hole injector, allows to eliminate the use of vacuum deposition of metals and permits to achieve tunneling hole injection regime from CNT tips into Alq3 emission layer. Due to rough surface of opals bright enough light emission is observed above 10 Volts and it is not very stable for same reason. Further optimization of such PC-OLED by planarization of PC structures will allow to observe the better extraction of emitted light by negative refraction focusing, predicted for light propagating in upper photonic bands of opal PC.[1] M. Zhang, S. Fang, A. Zakhidov, S. B. Lee, A. Aliev, R.H. Baughman, Science, 309,(2005) 1215* E-mail:
[email protected] 3:15 PM - S2.3
Phosphorescent-emitting Systems Attached to a Non-conjugated Polymer Backbone for Application in Light Emitting Devices.
Silvia Janietz 1 , Hartmut Krueger 1 , Manuel Thesen 1 , Bert Fischer 1 , Armin Wedel 1
1 POlymer Electronics, FhG-IAP, Potsdam, Brandenburg, Germany
Show Abstract3:30 PM - S2: OLED II
BREAK
4:30 PM - **S2.4
Development of High Performance Organic Light-emitting Devices.
Junji Kido 1 2
1 Polymer Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan, 2 , Optoelectronic Industry and Technology Development Association, Bunkyo-ku, Tokyo, Japan
Show Abstract5:00 PM - S2.5
Micropatterning of Metal Electrodes for Organic Light Emitting Devices.
Jennifer Yu 1 , Vladimir Bulovic 1
1 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe introduce a subtractive micropatterning technique for OLED electrodes using a patterned poly(dimethylsiloxane) (PDMS) stamp. A PDMS relief stamp was cast from a silicon master of 10 or 25 micron spaced parallel lines with 2 micron depth. With a fast peel time, the energy release rate of the PDMS increases to allow release of the metal layer from the underlying organic layers. We demonstrate a high fidelity pattern transfer with metal layer thickness of 20 nm. For film thickness of 25 nm, the patterned features are compromised and increasing metal film thickness leads to complete removal of the metal film during the PDMS lift-off process. OLEDs with electrodes patterned using PDMS lift-off and traditional shadow masking technique show similar current-voltage responses and electroluminescence quantum efficiencies.
5:15 PM - S2.6
Improved Single Dopant White Phosphorescent OLED for Solid State Lighting.
Jian Li 1 , Evan Williams 1 , Kirsi Haavisto 1 , Ghassan Jabbour 1
1 Chemical & Materials Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractWhite Organic Light Emitting Diodes (OLEDs) are considered to have great potential as back-light for LCD displays and solid-state lighting. The excimer OLED employing (4’,6’-difluorophenylpyridinato-N,C2’) platinum(II) (2,4-pentanedionato-O,O’) [FPt] as a single dopant could simplify the fabrication process and lower the production cost. Here, we revisit the concept of single dopant white phosphorescent OLEDs and improve the device performance by incorporating novel carbazolyl-pyridine based host and modifying the device architecture. The device efficiency is improved from a previously reported 6% to over 10% and the device maintains 8% at a brightness of 1000 Cd/m2; this is very competitive with state-of-the-art performance of other white OLEDs, often employing a more complicated device architecture. Additionally, a solution-processed excimer OLED and a high efficiency two-layer white OLED will be discussed.
5:30 PM - S2.7
Characterization of Pyrazoline Organic Nanoparticles Encapsulated with Poly(methyl methacrylate-co-ethylene glycol dimethacrylate) for Color Electronic Paper.
Young Soo Kang 1 , Hyo Sim Kang 1 , Sun Wha Oh 2
1 Chemistry, Pukyong National Univ., Busan Korea (the Republic of), 2 Basic Science Research Institute, Pukyong National University, Busan Korea (the Republic of)
Show Abstract1-Phenyl-3-naphthyl-5-((dimethylamino)phenyl)-2-pyrazoline with different diameters of 40 - 190 nm were prepared by the reprecipitation method and encapsulated with poly(methyl methacrylate-co-ethylene glycol dimethacrylate) using cationic surfactants for full color electronic paper, which is expected to substitute for the future display. The electronic ink particles of pyrazoline organic nanoparticles encapsulated by poly(methylmethacrylate-co-ethylene glycol dimethacrylate) were prepared and monodispersed successfully in aqueous alcohol medium. We found that pyrazoline nanoparticles possess the special size dependence in their optical properties. As the nanoparticle size decreased, the emission peak of pyrazoline nanoparticles was observed to be shifted to the high-energy side due to the aggregate formation and increased intermolecular interaction in the nanoparticles. The electrophoretic mobility of the resulting electronic inks was -7.5 to -3.6 x 10-5 cm2/V s in the presence of surfactants.
5:45 PM - S2.8
White-light-emitting Diodes using Ladder-type Polymers and Fluorescent and Phosphorescent Dopants.
Michael Pienn 1 2 3 , Hon Hang Fong 3 , Ashok Mishra 4 , Josemon Jacob 4 , Klaus Müllen 4 , Emil List 1 2 , George Malliaras 3
1 Christian Doppler Laboratory "Advanced Functional Materials", Institute of Solid State Physics, Graz University of Technology, Graz Austria, 2 Institute of Nanostructured Materials and Photonics, JOANNEUM RESEARCH, Weiz Austria, 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 , Max-Planck-Institut für Polymerforschung, Mainz Germany
Show AbstractS3: Poster Session: Organic Light Emitting Devices
Session Chairs
Tuesday AM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - S3.10
Identification of a Quencher in Organic Light Emitting Devices.
Jason Slinker 1 , Leonard Soltzberg 2 , Samuel Flores-Torres 3 , Ji-Seon Kim 4 , Richard Friend 4 , Hector Abruna 3 , George Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Chemistry, Simmons College, Boston, Massachusetts, United States, 3 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 4 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom
Show AbstractIonic transition metal complexes (iTMCs), such as ruthenium (II) tris-bipyridine, are receiving increased attention as these compounds have produced high efficiency organic light emitting devices with air-stable cathodes. Since iTMC-based devices can be fabricated using air-stable electrodes, their lifetime is ultimately limited by the degradation of the metal complex layer. This feature makes iTMC devices an ideal system for the study of degradation processes in organic light emitting devices. Furthermore, there is hope that if one is able to understand degradation pathways and design complexes that are inherently more stable, device degradation can be minimized. This will enable the fabrication of electroluminescent devices with minimal encapsulation requirements, with important technological implications.Along these lines, we have used matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to identify a quenching species that is formed in ruthenium tris-bipyridine electroluminescent devices during device operation. We identify this quenching species to be an oxo-bridged dimer by correlation with mass spectra of the synthesized compound and show this dimer to be an effective quencher of device luminescence. This demonstrates that MALDI-TOF can be an effective tool for identification of quenching species in small-molecule organic electroluminescent devices. In addition, we have recently used Raman spectroscopy to confirm dimer formation and to study the in-situ formation of dimeric compounds during the operation of ruthenium tris-bipyridine light emitting devices. Raman spectroscopy provides a non-invasive means of studying degradation of the metal complex layer.
9:00 PM - S3.11
Reliability Study of a Fluorescent Blue Organic-Emitting Device
Yu-Hsuan Ho 1 , Tien-Chun Lin 1 , Chia-Fang Wu 1 , J. H. Lee 1 2
1 Graduate Institute of Electro-Optical Engineering, National Taiwan University , Taipei Taiwan, 2 College of Optics and Photonics, University of Central Florida, Orlando, Florida, United States
Show AbstractIn this paper, we measured and analyzed the operation lifetime of a high efficiency blue OLED which consists of N,N’ –diphenyl -N,N’-bis(1-napthyl) -1,1’-biphenyl-4,4’- diamine (NPB) as the hole-transport layer (HTL), 4,4'-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl (DPAVBi) doped in 9,10-bis(2’-naphthyl) anthracene (ADN) as the emitting layer (EML), and bis(10-hydroxyben-zo[h]quinolinato)beryllium (Bebq2) as the electron-transport layer (ETL). Due to the high electron mobility of the ETL (one order of magnitude higher than Alq3), the carrier balance is achieved and a blue OLED with a high external quantum efficiency of 8.32% is obtained.The device structure of our blue OLED device is ITO /HTL (40nm)/EML (45nm, 4% dopant)/ETL (15nm)/ LiF(1.2nm)/Al (100nm). In our operation lifetime measurement, we fixed the initial luminescence of the blue OLEDs at 12500, 10000, 7000, 5000 cd/m^2 with a constant current driving. The resulting half-lifetime are 5.58, 16.56, 27, 109.819 hours, respectively. To estimate the half-lifetime of this device, we use a well-known relation in our fitting: L*(t1/2)^n=constant where n is the acceleration coefficient, and t1/2 is the half-lifetime. In our blue OLED, the n value is 3.088. By using the equation, we can calculate that the estimated half lifetime at an initial luminance of 1000 cd/m^2 achieves 15611 hours in our device. For further investigating the lifetime mechanism in our blue OLED, we fit all the luminance versus time curves obtained under different driving condition. We found that luminance is inversely proportional to the square of the time, rather than a typically stretched exponential decay which means the luminance decay is a second-order reaction in our blue OLED.
9:00 PM - S3.12
The Molecular Structures and Properties of Novel Eu(III) Complexes with Asymmetric Bis-phosphine Oxides.
Hiroki Iwanaga 1 , Fumihiko Aiga 1 , Akio Amano 1
1 Corporate Research & Development Center, Toshiba Corporation, Kawasaki Japan
Show Abstract9:00 PM - S3.13
Transparent TiO2 Anode for Organic Light Emitting Device.
Masaki Nakano 1 , Tomoteru Fukumura 1 , Hidemi Toyosaki 1 , Kazunori Ueno 1 , Masashi Kawasaki 1
1 , Institute for Materials Research, Tohoku University, Sendai Japan
Show Abstract9:00 PM - S3.14
Novel Organic Light-Emitting Transistors with PN-hetero-boundary Carrier Recombination Sites Fabricated by Lift-off Patterning of Organic Semiconductor Thin Films.
Naotoshi Suganuma 1 , Noriyuki Shimoji 2 , Yoshiaki Oku 2 , Kazumi Matsushige 3
1 Int’l Innovation Center, Kyoto universuty, Kyoto Japan, 2 , Rohm Co., Ltd., Kyoto Japan, 3 Dept. of Electronic Sci. & Tec., Kyoto universuty, Kyoto Japan
Show AbstractOrganic light-emitting transistors (OLETs) have both functions of driving transistor and electroluminescence (EL) device and are very attractive devices from the viewpoint of future flexible display as well as the standpoint of scientific interest, such as EL mechanism. Some OLETs, which have been already reported so far, have carrier channels composed of a single material system between source and drain. In this single material system, however, most of major carriers do not contribute to EL because it has ill-balanced transport capacity for holes and electrons, so that the efficiency for EL is relatively low. It is necessary to control carrier balance in light-emitting area in order to enhance luminescence efficiency, resulting in lowering the driving voltage.We have successfully fabricated a novel OLETs with a horizontal PN-hetero-boundary combined with hole transport material and electron transport material along carrier channel. In this device structure, the interface of two organic semiconductor materials with different polarity or a thin light-emitting material layer inserted between the two organic semiconductor materials functions as a carrier recombination and light-emitting area. This insertion of intentional PN-boundary can lead to improve carrier balance to enhance the EL efficiency and lower the driving voltage.The obtained drain current (Id) is modulated by gate bias voltage (Vg) and increases monotonously as drain voltage (Vd) increases. The luminance of EL (L) is found to be also modulated by Vg and increases with Id. The L exhibited the on/off ratio of more than 100 by Vg. Although the channel length between the source and the drain is several-μm, longer than the OLETs that has been reported in the past, the obtained L of our device is high enough to practical use. The EL pixel of our device consists of array of line light-emitting area. The obtained luminance of our device with line-density of 166 lines/mm is about 130 cd/m2 at 20 V in Vd.The horizontal PN-boundary structure was achieved by using the photolithographic patterning of the organic semiconductor layer for the first time. This patterning technique is a method of suppressing the damage to an organic semiconductor film to the minimum by using the alkaline water as a lift off solvent instead of the organic solvent. It has been verified that the fine slit pattern of pentacene with at least 0.5 μm widths can be formed by this technique so far. Therefore, it is expected that this lift-off patterning can be applied not only to fabrication of OLETs but the isolation processing of organic TFTs for preventing the leak current between the adjacent devices in integrated circuit, the high-definition pixel patterning for OLEDs display, etc.This work was supported by the Integrative Industry-Academia Partnership (IIAP) including Kyoto University, Nippon Telegraph and Telephone Corporation, Pioneer Corporation, Hitachi, Ltd., Mitsubishi Chemical Corporation and Rohm Co., Ltd.
9:00 PM - S3.15
Diffusion Enhanced Hole Transport in Thin Polymer Light-Emitting Diodes.
Irina Craciun 1 , Paul Blom 1
1 Molecular Electronics, Materials Science Centre, University of Groningen, Groningen Netherlands
Show Abstract9:00 PM - S3.16
O2 Plasma Treatment of Al Layer on Metal Anode to Improve the Performance of Organic Light-emitting Devices.
Su Hwan Lee 1 , Dong-Won Shin 1 , Sung-Jun Kim 1 , Yoon Ho Kang 1 , Gon-Sub Lee 1 , Jea-gun Park 1
1 Electrical & Computer Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractA gold and aluminum layer is investigated as the anode for organic light-emitting devices (OLEDs). By pretreating the ultrathin aluminum layer in a oxygen (O2) plasma, hole injection from metal anode to organic layer is greatly enhanced. The OLEDs using the gold and oxygen plasma pretreating aluminum anode demonstrates an improved current density and luminance characteristics compared with other devices which are fabricated both gold anode and a preretreating aluminum without oxygen plasma on gold anode, respectively. The driving voltages of our devices with the only Au, Au:Al and Au: pretreatment Al anode devices are about 18.5 V, 16 V and 5.8 V, at a current density of 100 mA/cm2, respectively. And, the voltages to obtain a luminance of 1000 cd/m2 for only Au and Au: pretreatment Al anode devices are needed approximately 18.7 V and 6 V, respectively.
9:00 PM - S3.17
Effect of Metallic Cathodes on the Photoconductivity Response of Polymeric Light-Emitting Devices.
Thiago Cazati 1 , Roberto Faria 1 , Lucas Santos 1
1 , USP, São Carlos, São Paulo, Brazil
Show Abstract9:00 PM - S3.18
Organic Light Emitting Transistor Based on the Unsymmetrical Electrodes
Kyu-Sik Kim 1 , Eokchae Hwang 1 , Changseung Lee 1
1 Nano Fabrication Center, Samsung Advanced Institiue of Technology (SAIT), Yongin-Si, Gyeonggi-Do Korea (the Republic of)
Show Abstract9:00 PM - S3.19
Electrochemical Depositon of End-Capped Triarylamine and CBP Dendrimers: Alternate Technique for the Fabrication of Organic Light-Emitting Devices
Ho-Jin Son 1 , Won-Sik Han 1 , Ji-Yun Chun 1 , Kyung Wee 1 , Kuk-Wha Lee 2 , Ha-Jin Jung 2 , Chongmok Lee 2 , Jaejung Ko 1 , Sang Ook Kang 1
1 Department of Advanced Material Chemistry, Korea University, Chochiwon, Chung-nam, Korea (the Republic of), 2 Department of Chemistry, Ewha Womans University, Seoul Korea (the Republic of)
Show AbstractCarbosilane dendrimers adorned with either triarylamine or carbazole units in their periphery exhibit novel electrochemical behavior in which the electrochemical deposition is controlled by dendrite generation. In addition, the deposited layers remained intact in the depositing solvent, methylene chloride, allowing a second layer to be deposited on top of the first layer. We have sought to establish the suitability of this electrochemical deposition technique for use in the construction of multi-layer OLEDs, which cannot be fabricated via conventional spin-coating with a polymeric precursor. Thus, the electrochemical deposition-based process could potentially offer an ideal combination of deposition control on the one hand and multi-layer fabrication on the other. We report herein the novel electrochemical deposition behavior of arylamine or carbazole end-capped carbosilane dendrimers of the type GnNPB or GnCBP (n = 1-4) and their use for the formation of multi-layer devices for OLEDs.
9:00 PM - S3.2
Exciton Interactions in Emitters of Organic Electrophosphorescent Diodes.
Jakub Mezyk 1 2 , Jan Kalinowski 2 , Francesco Meinardi 1 , Riccardo Tubino 1 , Massimo Cocchi 3 , Dalia Virgili 3
1 Department of Material Sciences, University of Milan Bicocca, Milano Italy, 2 Department of Molecular Physics, Gdansk University of Technology, Gdansk Poland, 3 Institute of Organic Synthesis and Photoreactivity, National Research Council of Italy, Bologna Italy
Show Abstract9:00 PM - S3.20
Lifetime Study of Polymer Light-emitting Electrochemical Cells with a Frozen p-n Junction.
Yanguang Zhang 1 , Jun Gao 1
1 physics, Queen's University, Kingston, Ontario, Canada
Show Abstract9:00 PM - S3.21
Luminescence of Fluorenes 2,7-Conjugatively Extended with 2-Pyrenylvinylene and 2-Pyrenylvinylene-4-Phenylenevinylene.
Hemali Rathnayake 1 , Ali Cirpan 2 , Paul Lahti 1
1 Chemistry, University of Massachusetts Amherst, Amherst , Massachusetts, United States, 2 Polymer Science and Engineering , University of Massachusetts Amherst , Amherst, Massachusetts, United States
Show Abstract2,7-Bis(1-pyrenylvinylene)-9,9-diethylfluorene (1) and 2,7-bis([1-pyrenylvinylene]-[4-phenylenevinylene])-9,9-diethylfluorene (2) were synthesized and assessed for luminescence behavior. They show solution photoluminescence (PL) maxima in chloroform at 475 nm and 465 nm, with quantum efficiencies of 54% and 52%, respectively. Double-layer LED devices with configuration ITO/PEDOT-PSS/(1 or 2)/Ca-Al emitted bluish-green light with turn-on voltages of 2.5 V and emission maxima at 500 nm (2.48 eV); their luminance efficiencies were 0.36 and 0.30 cd/A, respectively. Addition of 10%(w/w) PVK to the emitting layer in a double-layer device with 1 greatly improved the luminance efficiency to 2.10 cd/A with only a small increase in turn on voltage to 3 V; the emission maximum was 497 nm, blue-green emission with CIE color coefficients of (0.118,0.453); for a 10%(w/w) PVK blend with 2, the luminance efficiency was 1.47 cd/A, turn on voltage 3 V, maximum luminance 2600 cd/m2 with CIE coefficients of (0.126, 0.454). Simple π-MO calculations show that structural extension of the nominal conjugation length in 2 does not significantly increase the effective band gap relative to 1, consistent with the observed lack of red shift in 2.
9:00 PM - S3.22
Dendritic Iridium(III)-Encapsulated Complexes for Organic Light Emitting Diodes
Ho-Jin Son 1 , Won-Sik Han 1 , Kyu-Bum Choi 1 , Dae-Hyun Kim 1 , Jaejung Ko 1 , Seung-Uk Noh 2 , Changhee Lee 2 , Sang Ook Kang 1
1 Department of Advanced Material Chemistry, Korea University, Chochiwon, Chung-Nam, Korea (the Republic of), 2 Department of Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe synthesis, photo-physics and electroluminescence of new types of Iridium(III)-encapsulated dendrimers are described. Thus, four different iridium complexes [Ir(III)(C^N)2(LX), Blue-DCBP, Green-DCBP, Yellow-DCBP, and Red-DCBP] with ancillary ligand tethered to the CBP dendritic unit were synthesized and investigated for their photo-physical properties. A large enhancement in electroluminescence performance was observed by using these dendrimers as host/dopant hybrid materials in layered emitting diodes. In particular, host/dopant ratio can be systematically adjusted by varying dendritic generations. These results demonstrate that new Ir(III)-encapsulated dendrimers can be used as potential single-layer materials for organic light emitting diodes. Large difference in the intra-molecular charge transfer phosphorescence quantum yields and electroluminescence effiencies were observed among dendriritic generations.
9:00 PM - S3.24
Patterning Scheme Based on Photoacid Induced Spectral Changes for Single Layer, Patterned Full Colour Light Emitting Diodes Based on Blue Emitting Polymers.
Maria Vasilopoulou 1 , Athanasios Botsialas 1 , Giorgos Pistolis 2 , Pinelopi Bayiati 1 , Panagiota Petrou 3 , Nikolaos Stathopoulos 4 , Maria Rangoussi 4 , Panagiotis Argitis 1
1 Inst. of Microelectronics, NCSR "Demokritos", Athens Greece, 2 Inst. of Physical Chemistry, NCSR "Demokritos", Athens Greece, 3 Inst. of Radioisotopes and Radiodiagnostic Products , NCSR "Demokritos", Athens Greece, 4 Dep. of Electronics, Technological and Educational Institute of Pireaus, Athens Greece
Show Abstract9:00 PM - S3.25
Syntheses and Application of Novel Blue Phosphorescent Iridium Complexes to OLEDs
Takao Motoyama 1 , Yuya Agata 2 , Takashi Takeda 2 , Junji Kido 1 2
1 Polymer Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan, 2 , Optoelectronic Industry and Technology Development Association, Bunkyo-ku, Tokyo, Japan
Show AbstractWe synthesized novel iridium complexes having a cyano and/or fluorine-containing phenylpyridine ligands for organic light-emitting diodes (OLEDs). The emission color ranges from blue to blue-green depending on the position of substituent groups. One of the complexes, bis[(5-cyano-2-fluorophenyl)-pyridinato-N,C2’] (dipivaloylnate) iridium (III), with the substituent groups on 2 and 5 positions, showed a greenish blue emission peak at 476 nm. The OLED with a structure of glass substrate / indium-tin-oxide / tetraphenyl-benzidine-containing poly (arylene ether sulfone) doped with tris (4-bromophenyl) aminium hexachloro-antimonate / 2,2’-Bis[3’’-(N,N’-ditolylamino) phenyl]biphenyl / iridium complex-doped 2,2’-Bis[4’’-(N -carbazole)phenyl] biphenyl / 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole / LiF / Al exhibited the high external quantum efficiency of 17 percent and the power efficiency of 33 lm/W at 100cd/m2. Relationship between the structure of the ligand and the properties of the complexes are discussed. This work was supported in part by New Energy and Industrial Technology Development Organization (NEDO) through the “Advanced Organic Device Project”.
9:00 PM - S3.26
Extremely High Efficiency Green Organic Light-emitting Devices using Novel Electron Transport Material Containing Dipyridylphenyl Groups.
Daisaku Tanaka 1 , Hirohisa Sasabe 1 , Takashi Takeda 1 , Junji Kido 1 2
1 , Optoelectronic Industry and Technology Development Association, Bunkyo-ku, Tokyo, Japan, 2 Polymer Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Show AbstractWe have synthesized novel electron transport materials containing dipyridylphenyl groups. These materials have low LUMO levels of about 3.2 eV, providing with low electron injection barrier height from cathode. Further, these materials also have wide HOMO-LUMO energy gaps of about 3.5 eV, which are suitable for confining the triplet energy of green phosphorescent emitters. Green electrophosphorescent devices with a structure of ITO / p-doped buffer layer / wide-energy gap arylamine derivative (TAPC) / CBP doped with Ir(ppy)3 / dipyridylphenyl compound / LiF / Al were fabricated. An extremely high power efficiency of over 130 lm/W and the external quantum efficiency of about 29 percent were obtained at 100cd/m2. Even at 1000 cd/m2, 107 lm/W and 26 percent were observed. These values are the highest so far reported for green electrophosphorescent devices. This work was supported by New Energy and Industrial Technology Development Organization (NEDO) through the “Advanced Organic Device Project”.
9:00 PM - S3.28
Single Molecule Studies of a 2,7-Bis-(Phenylethenyl)fluorenone: Implications for Green-Emission Bands in Fluorene-based OLEDs.
Michael Odoi 1 , Nathan Hammer 1 , Ali Cirpan 2 , Frank Karasz 2 , Hemali Rathnayake 1 , Paul Lahti 1 , Michael Barnes 1
1 Chemistry, University of Massachusetts, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractThe color purity of blue polyfluorene fluorescence emission is often adversely contaminated by green emission bands at longer wavelengths. The origin of this green emission has been attributed to various factors including on-chain oxidation of fluorene leading to fluorenone formation and inter/intra-chain interaction between segments of fluorenone units leading to excimer formation on the polyfluorene backbone. We report here results for a molecular fluorenone derivative at the bulk and single molecule level. We observe that the bulk fluorescence emission of 2,7-bis-(3,4,5-trimethoxyphenyl-1-ethenyl)fluorenone shows red luminescence emission with a peak centered at about 630 nm that is independent of the substrate upon which the fluorenone is deposited. However, the peak position is observed to shift to higher energies (~540 nm) upon dilution in a polymer matrix like PMMA or Zeonex (Zeon Chemicals LP). Single molecule measurements on 2,7-bis-(3,4,5-trimethoxyphenyl-1-ethenyl)fluorenone show fluorescence spectra dominated by peaks at 530-560 nm, with a small minority at 600-630 nm attributed to occasional dyad formation and emission. This distribution suggests that the monomeric emission of the 2,7-bis-(3,4,5-trimethoxyphenyl-1-ethenyl)fluorenone is green, consistent with green emission bands seen in polyfluorenes. By comparison, excimer formation is apparently the source of the red bands seen in bulk.
9:00 PM - S3.29
White OLEDs based on Main-Chain Fluorene-Iridium(III) Polymers
Sabrina Eder 1 , Stefan Kappaun 2 , Stefan Sax 1 , Fabian Niedermair 2 , Christian Slugovc 2 , Emil List 1 3
1 Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010, Graz Austria, 2 Institute for Chemistry and Technology of Organic Materials, Graz University of Technology, Stremayrgasse 16, A-8010, Graz Austria, 3 , NanoTecCenter Forschungsgesellschaft mbH, A-8160, Weiz Austria
Show AbstractConjugated organic oligomers and polymers are of considerable academic and industrial importance as active materials in organic electronic devices, such as organic light-emitting diodes (OLEDs), polymer lasers, photovoltaic devices (solar cells) and field effect transistors. One of the topics being currently in the focus of both academic and industrial research are organic materials to be used as the active material in white organic light emitting devices (WOLEDs). WOLEDs have attracted a great deal of attention, for being used in flat panel displays, backlights for liquid-crystal displays and lighting applications.Currently the most common low-cost preparation technique for WOLEDs is blending fluorescent or phosphorescent dyes into a polymer host matrix or using blends of differently emitting conjugated polymers. However, using this approach phase separation can lead to a drastic reduction of the overall performance of the devices. In this contribution we instead show an approach where the active material consists of one polymeric material. By copolymerization of an up to date hardly described class of cyclometalated iridium(III) complexes, namely derivatives of bis(κ2(C2,N)-2-phenylpyridine)(κ2(N,O)-8-quinolinolate)iridium(III), we prepared statistical main-chain fluorene-‘iridium(III)’ copolymers. Taking advantage of the blue emitting properties of polyfluorenes, residual green emitting fluorenon moieties and the red phosphorescence of the iridium(III) complex, we obtained stable white emission with CIE coordinates of (0.302, 0.348) and a good color rendering index.
9:00 PM - S3.31
Inkjet Printed Organic Semiconductor Materials for Organic Light Emitting Diodes
Sigi Psutka 1 2 , Gernot Mauthner 1 2 , Emil List 1 2 3
1 Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010, Graz Austria, 2 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010, Graz, Austria and Institute of Nanostructured Materials and Photonics, A-8160, Weiz Austria, 3 , NanoTecCenter Forschungsgesellschaft mbH, A-8160, Weiz Austria
Show AbstractInkjet printing as a means of creating electronic devices such as resistors, capacitors as well as active devices like polymer light emitting diodes (PLED) or light emitting electrochemical cells (LEC) can also be used to investigate different conjugated polymers dissolved in several different solvents with respect to the jetability and operation properties.In this context the processes of wave propagation, droplet formation and drop impact at different parameters such as temperature, frequency and molecular weight of the used polymer have been studied with respect to their influence on the performance of the jetting process itself as well as of the fabricated light emitting devices. The photoluminescence quantum yield measurement is an appropriate way to analyse changes in the solution caused by the inkjet printing process. A reduction in the yield after the inkjet printing signals a damaging of the polymer in the solution due to the forces caused by the acoustic waves travelling through the fluid. In particular, we present results of photoluminescence quantum yield measurements carried out on MEH-PPV with three different molecular weights as well as different jetting results as mentioned above. Furthermore, the fabrication of light emitting electrochemical cells using inkjet printing are presented and discussed.
9:00 PM - S3.32
Polymer Light Emitting Device with Mixed Films of OC1OC6-PPV and a Liquid Crystal
Jose Giacometti 2 , Clarissa Olivati 2 , Debora Balogh 1 , Marystela Ferreira 1
2 Instituto de Fisica de Sao Carlos, USP - University of Sao Paulo , Sao Carlos, SP, Brazil, 1 Faculdade de Ciencia e Tecnologia, UNESP - Sao Paulo State University, Presidente Prudente, SP, Brazil
Show AbstractConjugated polymers such as the poly(p-phenylenevinylene) (PPV) derivatives combine the optoelectronic properties with a reasonable environmental stability, which has motivated the extensive investigations in recent years. In this work, we report the use of a PPV derivative, OC1OC6-PPV, mixed with a liquid crystal (PCH302/304) (LC) in the form of cast films for the fabrication of polymer light emitting devices (PLEDs). Cast films were obtained by spreading a mixed solution containing OC1OC6-PPV in chloroform (0.2 mg mL-1) and the LC (1mg mL-1), in appropriate amounts to yield a mixture with 30 weight% of LC in OC1OC6-PPV. PLEDs devices had as anode an indium-tin-oxide (ITO) layer, the active layer on the top of the ITO layer and, as cathode a vacuum evaporated aluminum thin layer forming, thus, a sandwiched structure. FTIR spectrum of OC1OC6-PPV(LC30%) shows the presence of liquid crystal in the film. Despite that the spectrum shape for the films is not altered, the intensity of the photoluminescence (PL) at 590 nm for OC1OC6-PPV(LC30%) film is 6 times higher than that observed in the pure OC1OC6-PPV film. The current vs. voltage (I vs. V) characteristics reveals that the ITO(LC/OC1OC6-PPV)Al devices present a classical behavior of a rectifying diode. The electroluminescent (EL) spectra for the OC1OC6-PPV and OC1OC6-PPV(LC30%) PLED, using 20 V forward bias, are centered at 590 nm, similarly to that observed in the PL spectra. This result indicates that the radiative decay of the same singlet exciton is responsible for EL and PL emissions. Thus, PL and EL luminescence properties were enhanced in mixed the film, which could be explained by the fact that the LC molecules are causing the emitting chromophores of OC1OC6-PPV to be farther apart than in a OC1OC6-PPV pure film.
9:00 PM - S3.33
Qauntum Dot Emitters at Electronic Grade for Optoelectronics.
Y Wang 1 , Qingjiang Sun 2 , Linsong Li 1 , Daoyuan Wang 1 , Yongfang Li 2
1 , Ocean NanoTech, LLC, Fayetteville,, Arkansas, United States, 2 , Beijing Chemistry Institute, Beijing China
Show Abstract9:00 PM - S3.34
Fabrication of an Electrically Pumped Organic Heterostructure Device on a Pyramidal Atomic Force Microscopy Tip.
Yiying Zhao 1 , Kwang Hyup An 2 , Kevin Pipe 2 , Max Shtein 1
1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Depart of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:00 PM - S3.35
Characterization of Energy Transfer in Solution Processed White-light-emitting Diodes.
Michael Pienn 1 2 3 , Hon Hang Fong 3 , Ashok Mishra 4 , Josemon Jacob 4 , Klaus Müllen 4 , Emil List 1 2 , George Malliaras 3
1 Christian Doppler Laboratory "Advanced Functional Materials", Institute of Solid State Physics, Graz University of Technology, Graz Austria, 2 Institute of Nanostructured Materials and Photonics, JOANNEUM RESEARCH, Weiz Austria, 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 , Max-Planck-Institut für Polymerforschung, Mainz Germany
Show AbstractIn this study we compare device characteristics of solution-processed white-light-emitting diodes consisting of polymer blends doped with fluorescent and phosphorescent dyes to achieve efficient white-light emission.The polymer blends used as hosts are poly(N-vinylcarbazole) (PVK), poly(9,9-dioctylfluorene) (PFO), ladder-type polymers poly(ladder-type quarterphenylene), 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI), 4,4’-bis(N-carbazolyl)biphenyl (CBP) and combinations of these materials.While PVK, CBP and TPBI have shown to be capable of hosting green phosphorescent emission from iridium(III) complexes, PFO and poly(ladder-type quarterphenylene) constitute blue fluorescent emitters, suitable for energy transfer to green and red emitting dyes.Efficient light emission is obtained by harvesting singlet and triplet excitons using fluorescent and phosphorescent dopants. The guest-host energy transfer is studied using optical spectroscopy at low temperature and the exciton confinement of the dopants in the respective system is discussed.To improve the device efficiency charge transport molecules are doped into the devices in order to balance the charge carriers and control the transport and injection properties.
9:00 PM - S3.37
Novel Polarized Organic Light Emitting Diodes Materials and Devices
Heh-Lung Huang 1 , Jin-Sheng Lin 1 , Miao-Tsai Chu 1 , Mei-Rurng Tseng 1
1 , Industrial Technology Research Institute, Chutung, Hsinchu Taiwan
Show Abstract Due to the surge of demanding for TFT-LCD displays, the TFT-LCD required backlights also have a lot of demand. Conventional CCFL tubes for TFT-LCD are not suitable to use anymore due to the mercury pollution. Therefore, non-mercury CCFL tubes, non-mercury EEFL tubes, LED, FEL, and CNT technologies have developed recently to replace the conventional CCFL tubes. Besides, the newly approaching technology on the organic light emitting diodes (OLEDs) is also focusing on the TFT-LCD backlight development. Therefore, polarized OLED with its self-emission and polarization properties can replace not only the TFT-LCD backlights but also the down polarizer. We develop a series of OLED materials with polarized ability. Those materials hold the UV absorption from 370nm to 377 nm and their PL spectra are from 480 to 500 nm. We are investigating the mechanical alignment method to fabricate the polarized OLED devices.
9:00 PM - S3.38
High-efficiency Chiral Blue Fluorescent OLED materials
Ming-Yu Hsu 2 , Heh-Lung Huang 1 , Miao-Tsai Chu 1 , Mei-Rurng Tseng 1 , Rai-Shung Liu 2
2 Department of Chemistry, National Tsing Hua University, Hsinchu Taiwan, 1 , Industrial Technology Research Institute, Chutung, Hsinchu Taiwan
Show Abstract Red, green, and blue emitters are necessary for full color OLED display. Most of the WOLED devices are composed of red and green phosphorescent materials and blue fluorescent material. We developed a series of new chiral OLED blue fluorescent materials with high quantum yield. We demonstrated those materials having UV absorption around 375nm, PL emission peak around 450 nm, and quantum yield around 0.83. The primitive device data are EL= 456nm, brightness=2000 cd/m2, and external quantum efficiency= 1.4 %. We are investigating the new device configuration to optimize the device performance.
9:00 PM - S3.39
High-power Polymer Light Emitting Devices with Thermally Conductive Sapphire Substrate.
Sanghun Choi 1 , Seoung Yoon Ryu 1 , Jong Tae Kim 1 , Hong Koo Baik 1
1 Metallugical Eng., Yonsei Univ., Seoul Korea (the Republic of)
Show Abstract9:00 PM - S3.4
Improved Stability and Colour Tuning of Solid State Light Emitting Electrochemical Cells Consisting of Heteroleptic Iridium Complexes.
Henk Bolink 1 , Luca Cappelli 1 , Eugenio Coronado 1 , Michael Grätzel 2 , Md. K. Nazeeruddin 2 , Enrique Ortí 1 , Pedro Viruela 1
1 Institute of Molecular Science, University of Valencia, Paterna, Valencia, Spain, 2 Laboratory for Photonics and Interfaces, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show Abstract9:00 PM - S3.40
Effect of the Mixed Interfacial Layer on the Performance of Organic Light-emitting Devices.
Nobuhiro Ide 1 , Satoshi Ohara 2 , Junji Kido 1 2
1 , Optoelectronic Industry and Technology Development Association, Bunkyo-ku, Tokyo, Japan, 2 Polymer Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Show Abstract9:00 PM - S3.41
Encapsulation-free Hybrid Organic Inorganic Light-emitting Diodes.
Katsuyuki Morii 1 2 , Takeshi Takashima 3 , Qing Wang 2 , Mohammad Nazeeruddin 2 , Masaya Ishida 1 , Tatsuya Shimoda 3 , Michael Gratzel 2
1 Cambridge Research Laboratory of EPSON, EPSON UK Ltd., Cambridge United Kingdom, 2 FBS-ISIC-LPI, École Polytechnique Fédérale de Lausanne, Lausanne Switzerland, 3 , SEIKO EPSON CORPORATION, Suwa Japan
Show Abstract9:00 PM - S3.5
Waveguiding, Microcavity Effects and Optically Pumped Lasing in Single Polymer Nanowires
Gareth Redmond 1
1 Nanotechnology Group, Tyndall National Institute, Cork Ireland
Show Abstract9:00 PM - S3.6
White Organic Light Emitting Devices with Enhanced Out-coupling Using Microlenses Fabricated by Imprint Lithography.
Yiru Sun 1 , Hiroshi Kanno 2 1 , Stephen Forrest 1 3
1 Dept. of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 , Sanyo Electric Co, Osaka Japan, 3 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractHigh efficiency white organic light emitting devices (WOLEDs) with optical outcoupling enhanced by hexagonal polymethylmethacrylate microlens arrays fabricated by imprint lithography on a glass substrate are demonstrated. This provides a low-cost solution to the trade-off between high luminance and long device lifetime, improving WOLEDs as a competitive source for indoor lighting. Monte Carlo and finite difference time domain simulations of the emitted light are used to optimize microlens design. The measured outcoupling enhancement and angular dependence of the light intensity agree with simulation, indicating that hemispherical microlens arrays can increase outcoupling from a flat glass substrate by factors of 1.6-2.2. We demonstrated the effectiveness of the imprinted lenses used in combination with fluorescent/phosphorescent WOLEDs that harvest singlets and triplets through separate channels1. Maximum external quantum (EQE) and power efficiencies of (14.3±0.3)% at 900 cd/m2 and (21.6±0.5) lm/W at 220cd/m2, respectively, have been achieved, exceeding the performances of traditional light bulbs. This represents an increase of outcoupling of (1.49±0.03) in the current density range from 0 to 1.2A/cm2. The electroluminescent spectra at various viewing angles remain unchanged, giving a color rendering index of 87. As a result, the drive current density and energy consumption at a given luminance were reduced by at least 33%, leading to potentially longer operational lifetimes and higher internal efficiencies due to reduced roll-off effects. This enhancement factor is independent of the OLED structure, and is therefore also applicable to a recently-reported 3-cell stacked WOLEDs2, implying that a forward viewing EQE of 50% is achievable. References:1. Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, S. R. Forrest, Management of singlet and triplet excitons for efficient white organic light emitting devices, Nature, 440, 908-912 (2006).2. H. Kanno, N. C. Giebink, Y. Sun, S. R. Forrest, Stacked white organic light-emitting devices based on a combination of fluorescent and phosphorescent emitters, Applied Physics Letters (submitted).
9:00 PM - S3.7
Characterization of TFT-LCD and OLEDs devices by Phase Modulated Spectroscopic Ellipsometry for Display Applications.
Eric Teboul 1 , Yong Ji 1 , Nataliya Nabatova-Gabain 2
1 Thin Films, HORIBA Jobin Yvon, Edison, New Jersey, United States, 2 Semiconductor Division, HORIBA Ltd., Kyoto Japan
Show Abstract9:00 PM - S3.8
Metal Electrode Effects on Magnetoresistance in Organic Semiconductor Devices
Bin Hu 1 , Yue Wu 1
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractThe metal electrode is a necessary component to enable charge injection in organic semiconductor devices. The resultant metal/organic interface can substantially affect the device characteristics upon chemisorption or modification of metal electron density tail by the presence of the adsorbed organic molecules. Here, we report the new characteristic of metal/organic interface: modification of magnetoresistance upon deposition of metal atoms, based on tuning the electron-hole capture zone through using forward and reverse biases in organic light-emitting diodes of poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV). We find that the reverse bias yields a largely increased magnetoresistance when the electron-hole capture zone is away from the metal electrode as compared to the forward bias with the electron-hole captue zone close to the metal electrode. The magnetic field-dependent electroluminescence indicates that the deposited metal atoms enhance the spin-orbital coupling at the polymer/metal interface and consequently lead to electron-hole capture zone-dependent magnetic field effects in organic semiconductor devices.
9:00 PM - S3.9
Study on Electron Injection Effect of Low Molecular Organic Light-emitting Diodes Utilizing LiF/Al and Li/Al Cathode.
Zenken Kin 1 , Hirotake Kajii 1 , Yutaka Ohmori 1
1 CENTER FOR ADVANCED SCIENCE AND INNOVATION, OSAKA UNIVERSITY, SUITA, OSAKA, Japan
Show AbstractThe electron injection effects of organic light-emitting diodes, which consists of Tris-(8-hydroxyquinolinato) aluminum (Alq3) as emissive layer and N,N’-bis(1-naphtyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine (NPD) as hole transporting layer, from the interface between LiF or Li and Al which was deposited on the Alq3 emissive layer have been investigated. Efficient electron injection was achieved when the thickness of LiF and Li deposited on Alq3 layer were 0.5 nm and 2 nm, respectively. That is, the coexistence layer of LiF and Al or the alloy of Li and Al exist on the Alq3 layer result in efficient electron injection. To achieve efficient electron injection, it is necessary for LiF to exist just on the Alq3 layer. While, in the case of Li, the deposition order of Li or Al metal layer is independent. The oxidization effect by exposing air is large for Li, while not for LiF. That is, after the deposition of LiF on the Alq3 layer, LiF did not dissociate into Li and F, and the LiF layer still remained. From these results, it is considering that the electron injection effects between LiF and Li on the Alq3 layer are different.
Symposium Organizers
Franky So University of Florida
Graciela B. Blanchet DuPont
Yutaka Ohmori Osaka University
S4: Organic Light Emitting Devices III
Session Chairs
Tuesday AM, November 28, 2006
Room 304 (Hynes)
9:00 AM - S4.1
High-Efficiency Electrophosphorescent Devices Based on New Cyclometalated Iridium(III) Complexes with Asymmetric Ligands.
Jianping Lu 1 , Qinde Liu 2 , Ye Tao 1 , Jianfu Ding 2 , Michael Day 2
1 , Institute for Microstructural Sciences, NRC, Ottawa, Ontario, Canada, 2 , Institute for Chemical Process and Environmental Technology, NRC , Ottawa, Ontario, Canada
Show AbstractA new series of tris-cyclometalated iridium complexes Ir1-4 and a bis-cyclometalated iridium complex Ir5 containing either diphenylamino or carbazolyl substituted phenylpyridine derivatives as ligands have been synthesized and characterized. Inter-ligand energy transfer and related emission color tuning were observed in these iridium complexes. The phosphorescence emission peaks red-shifted to longer wavelengths with increasing the conjugation length of the ligand. Highly efficient electrophosphorescent light-emitting diodes have been fabricated using iridium complexes Ir1-4 doped into hole transporting host material such as PVK as emitters. The device structure used in this study is ITO/PEDOT-PSS/Ir complex:host material/F-TBB/Alq3/LiF/Al, where F-TBB is morphologically stable 1,3,5-tris(4’-fluorobiphenyl-4-yl)benzene functioning as a hole- and exciton-blocking layer. The complex Ir3 with asymmetric ligands showed promising performance with a turn-on voltage of 5 V, a maximum luminance greater than 15,000 cd/m2 at a driving voltage of 18 V, and a peak current-efficiency of 21 cd/A (1200 cd/m2, 10.5 V). In contrast, the performance of the device with the complex Ir5 containing oligofluorene-functionalized ligands (low triplet-state energies) was quite poor. For example this device had a maximum luminance of only 1,250 cd/m2 at 17.5 V. The much poorer performance of this device has been attributed to phosphorescence quenching caused by the low-triplet-energy ligands. Besides PVK and F-TBB, we also employed oligofluorene-functionalized TCTA and TPBI as a host material and a hole-blocking layer, respectively. It was found that both host and hole-blocking materials had a strong impact on the device performance.
9:15 AM - S4.2
Photoluminescence and Electroluminescence in Combination of Rare-earth Metal Compounds and Phosphorescent Molecules.
Zenken Kin 1 , Yuichi Hino 1 , Yasuchika Hasegawa 2 , Hirotake Kajii 1 , Yutaka Ohmori 1
1 CENTER FOR ADVANCED SCIENCE AND INNOVATION, OSAKA UNIVERSITY, SUITA, OSAKA, Japan, 2 , Nara Institute of Science and Technology, IKOMA, NARA, Japan
Show Abstract We investigated luminescent properties in combination of red emissive europium complex of tris(dibenzoylmethane)-mono(4,7-dimethylphenan-throline)europium(III) [Eu(dbm)3phen] and blue phosphorescent molecule of bis[(4,6-difluorophenyl)-pyridinato-N,C2’] (picolinate) iridium (III) (FIrpic) doped in poly(N-vinyl-carbazole) (PVK). A sharp red emission from Eu(dbm)3phen was observed in photoluminescence (PL), whereas, in the case of electroluminescence (EL), emission from FIrpic and Eu compound were observed. The difference of the PL and EL spectra indicates that different energy transfer processes between Eu(dbm)3phen and FIrpic are suggested. For an electroluminescent device doped with the Eu complex and Firpic, white light emission was obtained and the color changed by driving pulsed voltage. We also discuss the energy transfer process in terbium and samarium complex with phosphorescent dye doped systems.
9:30 AM - **S4.3
New Materials for High Efficiency Monochromatic and White Organic LEDs.
Mark Thompson 1 , Stephen Forrest 2 , Julie Brown 3
1 Chemistry , University of Southern California, Los Angeles, California, United States, 2 Physics and Electrical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 , Universal Display Corporation, Ewing, New Jersey, United States
Show Abstract10:00 AM - S4.4
Highly Efficient Orange and Green Solid-State Light-Emitting Electrochemical Cells Based on Cationic Ir(III) Complexes with Superior Steric Hindrance.
Hai-Ching Su 1 , Fu-Chuan Fang 2 , Tsyr-Yuan Hwu 2 , Hsing-Hung Hsieh 1 , Hsiao-Fan Chen 2 , Ken-Tsung Wong 2 , Chung-Chih Wu 1
1 Department of Electrical Engineering, Graduate Institute of Electro-optical Engineering and Graduate Institute of Electronics Engineering, National Taiwan University , Taipei Taiwan, 2 Department of Chemistry, National Taiwan University, Taipei Taiwan
Show AbstractLight-emitting electrochemical cells (LEC’s) in general have several advantages over conventional organic light-emitting diodes, such as the simpler single-layer configuration, solution-processing and low operation voltages with air-stable electrodes. Compared to polymer LEC’s, LEC’s based on cationic transition metal complexes have a few further advantages, such as no need of ion-conducting material, since they are already intrinsically ionic and potentially higher electroluminescent (EL) efficiencies due to the phosphorescent nature. In general, LEC’s are composed of neat films of emissive materials, in which interactions between closely packed molecules usually would lead to quenching of exited states, detrimental to EL efficiencies of devices. In this work, we investigate cationic iridium complexes [[Ir(ppy)2(SB)]+(PF6-) (1) and [Ir(dFppy)2(SB)]+(PF6-) (2)] (where ppy is 2-phenylpyridine and dFppy is 2-(2,4-difluorophenyl)pyridine) having 4,5-diaza-9,9’-spirobifluorene (SB) as the steric and bulky auxiliary ligand for reducing self quenching. X-ray studies show that plane-to-plane overlapping between ligands is slight and thus intermolecular interaction is relatively weak. Photoluminescence measurements show highly retained photoluminescence quantum yields (PLQYs) for 1 and 2 in neat films (~50 % and 75 % compared with PLQYs of 1 and 2 dispersed in m-bis(N-carbazolyl)benzene films, respectively). The spiro-configured SB ligands effectively enhance the steric hindrance of the complexes and reduce the self-quenching effect. Cyclic voltammetry measurements also show that blue-shifted emission (green emission) of 2 (relative to orange emission of 1) results from stabilizing of highest occupied molecular orbital induced by fluoro substituents on the phenyl ring of the ppy ligand. LEC devices using single-layered neat films of 1 and 2 achieve high peak external quantum efficiencies and power efficiencies of (7.1 %, 22.6 lm/W) at 2.5 V and (7.1 %, 26.2 lm/W) at 2.8 V, respectively. In these devices, to reduce the response time of the devices, 0.75 mole ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM+(PF6)-] per mole of 1 or 2 is added to provide additional anions. Atomic force microscopy shows no significant difference in film morphologies of 1 or 2 with and without BMIM+(PF6)-, thus indicating good mixing compatibility. The EL efficiencies reported here are among the highest reported for solid-state LEC's and indicate that the cationic transition metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid-state LEC's.
10:15 AM - S4.5
An 8 x 8 Pixel Array Interactive Pen Input OLED Screen Based on Organic Magnetoresistance.
Govindarajan Veeraraghavan 1 2 , Tho Nguyen 1 3 , Yugang Sheng 1 3 , Omer Mermer 1 3 , Markus Wohlgenannt 1 3
1 Optical Science and Technology Center, University of Iowa, Iowa city, Iowa, United States, 2 Department of Electrical and Computer Engineering, University of Iowa, Iowa city, Iowa, United States, 3 Department of Physics and Astronomy, University of Iowa, Iowa city, Iowa, United States
Show Abstract10:30 AM - S4.6
Ultra-flexible Electroluminescent Systems for Both Visible and Near-infrared Illumination.
Patrick Kinlen 1 , Mauricio Pinto 1 , Eric Bruton 1
1 , Crosslink, St. Louis, Missouri, United States
Show Abstract10:45 AM - S4: OLED III
BREAK
11:15 AM - **S4.7
Versatile Fabrication Method of Multi-layered Polymer Light-emitting Diodes with Improved Efficiency and Lifetime
Kenichiro Wakisaka , Jian Li 1 , Yasuko Hirayama 1 , Taiji Tomita 1 , Takeshi Sano 1
, 1 R&D Headquarters, SANYO Electric Co., Ltd., Hirakata, Osaka Japan
Show Abstract11:45 AM - **S4.8
Laser Emission Properties of Symmetric and Asymmetric Microdisk Based on π-Conjugated Polymer.
Akihiko Fujii 1
1 Division of Electrical, Electronic and Information Engineering, Osaka University, Osaka Japan
Show AbstractConducting polymers with highly extended conjugated π-electron systems in the main chains have attracted great interest from both fundamental and practical viewpoints, because they exhibit various novel properties. Among various conducting polymers, poly(p-phenylenevinylene) (PPV) and its derivatives are the most attractive materials for light-emitting diodes, because of their high solubility in common organic solvents and the high luminescence quantum efficiency.Polymer lasers with microcylindrical structures, which are based on waveguide mode or whispering gallery mode, have attracted much attention as a novel type of lasers, because of the high Q factors and low threshold energy for the lasing. The laser emission from micro-cylindrical structures, such as microring and microdisk, however, radiates equally to each direction in plane from the cylindrical microcavity. Therefore, unidirectional laser beam is significant for developing the device application in optical communication. The investigation of the spiral-shaped microdisk lasers utilizing luminescent π-conjugated polymer, such as PPV derivatives, should be also important for the realization of a plastic laser diode.In this study, we report on the fabrication of symmetric and asymmetry-shaped cylindrical microcavities consisting of a PPV derivative and the laser emission properties of the symmetric and asymmetric microcavities of the PPV derivative.
12:15 PM - S4.9
Enhanced Lifetime of Organic Light-emitting Devices Fabricated Under Ultra-high Vacuum Condition.
Hideyuki Murata 1 2 , Takeshi Ikeda 1 , Yoshiki Kinoshita 1 , Junichi Shike 3 , Yoshikazu Ikeda 3 , Masahiro Kitano 3
1 School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan, 2 PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan, 3 , Kitano Seiki Co., Ltd, Ohta, Tokyo, Japan
Show Abstract12:30 PM - S4.10
Bottom Contact Ambipolar Organic Thin Film Transistors Based on C60/Pentacene Heterostructure
Kaname Kanai 1 , Suidong Wang 1 , Yukio Ouchi 1 , Kazuhiko Seki 1
1 Graduate school of science, Nagoya university, Nagoya Japan
Show AbstractDevelopment of organic complementary technology, where both n-type and p-type transistors are incorporated, is essential for achieving efficient organic integrated circuits with low power dissipation, good noise immunity and high operational stability. Employing organic heterostructure as active layer is one way to realize such ambipolar charge transport in a single transistor.We here report on the fabrication and in situ characterization of the bottom contact organic thin film transistor (BC-TFT) based on a heterostructure of C60 on pentacene. We also fabricated an inverter with a combination of two BC-TFTs.[1] The BC-TFT shows ambipolar transport characteristics with high electron and hole mobilities of 0.23 cm2V-1s-1 and 0.14 cm2V-1s-1, respectively. Both the n-channel in C60 and the p-channel in pentacene are stable in N2 atmosphere. After exposure to air, the n-channel is completely degraded whereas the p-channel keeps working. The inverter exhibits typical transfer characteristics, which are interpreted by the distribution of the accumulated electrons and holes depending on the bias conditions. Similar behaviors of ambipolar charge transport and inverter was reported by Kuwahara et al., with middle contact TFT on C60 on pentacene.[2] However, the bottom contact configuration of the devices much simplifies the design and fabrication of organic complementary circuits from those for the middle contact, where the formation of patterned electrodes on an organic film is necessary. These devices reported here can be fabricated by a sequence of (1) electrode patterning on a gate insulating layer, e.g. by photolithography, and (2) simple sequential deposition of two electronically functional organic layers without any patterning. The presently observed relatively high performance, together with the capability of encapsulation in inert gas, and the possible improvements by further choice of appropriate materials, demonstrate the potential usefulness of this type of devices for future applications. [1] S. D. Wang, K. Kanai, Y. Ouchi and K. Seki, Org. Electronics, to be published,[2] E. Kuwahara, Y. Kubozono, T. Hosokawa, T. Nagano, K. Masunari and A. Fujiwara, Appl. Phys. Lett., 85 4765 (2004).
12:45 PM - S4.11
Efficient Organic Light-Emitting Diode Using Tapered-Periodic and Aperiodic Dielectric Mirrors.
Mukul Agrawal 1 , Yiru Sun 2 , Stephen Forrest 3 , Peter Peumans 1
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractEfficient coupling of photons into free-space modes from the emissive region of an OLED remains a major bottleneck in achieving a high energy efficiencies. Coupling of photons into various waveguided modes supported by the OLED device structure, result in low photon outcoupling efficiencies (~25%). Micro-cavities that use periodic dielectric or metallic mirrors have previously been used to modify photon outcoupling. However, because typical molecular emitters exhibit broad spectra, their ability to improve both the angularly and spectrally integrated outcoupling efficiency, is limited. Enhanced outcoupling is therefore only obtained for a narrow range of angles and wavelengths. Furthermore, such cavities result in a red shift with increasing viewing angle.Here, we demonstrate that tapered-periodic and aperiodic dielectric mirrors can provide substantially enhanced outcoupling efficiencies over a wide spectral and angular range. Dielectric stacks whose resonant wavelength is continuously detuned as a function of penetration depth into the dielectric stack, are inserted between the substrate and OLED structure and provide enhanced emission over a broad spectral and angular range. We have developed a design scheme to obtain such tapered-periodic structures with maximum possible improvement in energy efficiency while ensuring a Lambertian emission pattern. We have demonstrated that the insertion of a 9 layer SiO2/SiNx tapered-periodic dielectric stack in an Ir(piq)3 based red phosphorescent OLED improves the luminescent efficiency (lm/W) by 80% within a 60 degree viewing cone. The deviation from a Lambertian emission pattern is <2%. Outside the viewing cone, the device is essentially dark. The dielectric stack also results in increased color saturation.We further demonstrate that as the refractive index contrast between the two materials used in a two-component multilayer optical stack is increased, the stack with optimal performance becomes increasingly aperiodic. For an index contrast >2 no periodic or tapered-periodic signature is detectable in the optimal stack design. Using such high index contrast dielectric stacks, our method achieves outcoupling efficiencies that exceed those of a typical OLED by 45% for a 160 degree viewing cone, and by 175% for a 60 degree viewing cone.
S5: Organic Thin Film Transistors
Session Chairs
Tuesday PM, November 28, 2006
Room 304 (Hynes)
2:30 PM - **S5.1
New Materials and Fabrication Processes for Organic, Printed, and Other Unconventional Electronics.
Tobin Marks 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractChemists are skilled at designing and constructing molecules with the goal of introducing defined chemical and physical properties. However, rationally assembling them into organized, functional supramolecular structures with nm-level control of packing and charge transport properties for functional electronic circuits is a daunting challenge. This lecture focuses on the following topics: 1. Design, characterization, and implementation of new, high-mobility n-type organic conductors for CMOS. 2. Design and characterization of self-assembled and spin-coatable high-k nanodielectrics. 3. Implementation of the nanodielectrics in organic electronics. 4. Implementation of the nanodielectrics in nanotube, nanowire, and inorganic electronics. 5. Radiation-hard electronics.
3:00 PM - S5.2
High Performance 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. Sub-monolayer AFM studies show growth that greatly resembles pentacene. Mobilites as high as 0.3cm2V-1s-1 have been found. We’re still in the process of optimizing the mobilities and synthesizing interesting derivatives of these asymmetric linear acenes.
3:15 PM - S5.3
An Air-Stable n-Type Organic Thin-Film Transistor Based on a Soluble C60 Derivative
Masayuki Chikamatsu 1 , Atsushi Itakura 1 , Tatsumi Kimura 1 , Satoru Shimada 1 , Yuji Yoshida 1 , Reiko Azumi 1 , Kiyoshi Yase 1
1 Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractWe have reported high performance solution-processed n-type organic thin-film transistors (TFTs) based on long-chain alkyl-substituted C60 derivatives [1-2]. However, C60 and its derivatives do not exhibit TFT performance in air, because O2 and H2O gases act as trap spices of electron transport. In this study, for realizing an air-stable n-type organic TFT, we have newly synthesized a perfluoroalkyl substituted C60 derivative, C60-fused N-methylpyrrolidine-para-perfluorooctyl phenyl (C60PC8F17). Since perfluoroalkyl chains are known to act as an efficient gas barrier, a C60PC8F17-TFT is expected to exhibit n-channel characteristics in air. A film of C60PC8F17 was fabricated on highly doped silicon wafers covered with SiO2 by spin coating from chloroform solution under ambient condition. Source and drain gold electrodes were deposited on the film. The TFT characteristics were measured both in a vacuum and in air at room temperature. The C60PC8F17-TFT showed good n-channel characteristics after exposure to air for 24 hours, whereas the TFTs employing C60 derivatives with a hydrocarbon chain did not operate under the same condition. The field-effect electron mobility in saturation regime is calculated to 0.002 cm2/Vs. This result indicates that perfluoroalkyl chains play an important role for the air stability of the TFT performance.[1] M. Chikamatsu et al., Appl. Phys. Lett. 87, 203504 (2005). [2] M. Chikamatsu et al., J. Photoch. Photobio. A, in press.
3:30 PM - S5.4
Organic Thin-Film Transistors on Plastic Substrates Fabricated using Transfer Printing
Daniel Hines 2 1 , V. Ballarotto 1 , E. Williams 2 1 , A. Southard 2 3 , M. Fuhrer 2 3
2 Department of Physics, University of Maryland, College Park, Maryland, United States, 1 Laboratory for Physical Sciences, University of Maryland, College Park, Maryland, United States, 3 Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States
Show AbstractTransfer printing methods have been developed for the fabrication of a model organic thin-film transistor (OTFT) based on pentacene (Pn). The device consists of a polyethylene terephthalate (PET) substrate, gold gate and source/drain electrodes, a poly(methyl methacrylate) (PMMA) dielectric layer and a Pn organic semiconductor. Each component was sequentially printed onto the PET (device) substrate in a way that required no mixed processing on the substrate. The process relies primarily on the differential adhesion of the printable layer (device component) pressed between a transfer substrate and the device substrate. The resulting Pn OTFTs on plastic exhibited a contact resistance of 2 MΩ for 100 µm wide electrodes and a mobility of 0.237 cm2/Vs. The transport properties of transfer printed devices and the structure of printed Pn films have both been shown to be a function of the printing conditions. The same printing techniques developed to fabricate the Pn devices are being used to fabricate poly(3-hexylthiophene) (P3HT) OTFT devices on flexible substrates. The printing conditions and properties of the P3HT devices will also be presented and discussed.*Work supported by the Laboratory for Physical Sciences.
3:45 PM - S5.5
Molecular-Wetting Control by Ultrasmooth Pentacene Buffer for High-crystallinity Organic Field-effect Transistors.
Kenji Itaka 1 3 , Jun Yamaguchi 1 2 , Mitsugu Yamashiro 1 2 , Masamitsu Haemori 1 2 , Seiichiro Yaginuma 1 2 , Yuji Matsumoto 2 3 , Hideomi Koinuma 1 3 4
1 Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa Japan, 3 CREST, Japan Science and Technology Agency, Kawaguchi Japan, 2 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama Japan, 4 , National Institute for Materials Science, Tsukuba Japan
Show Abstract4:00 PM - S5: OrgFilm
BREAK
4:15 PM - **S5.6
Development of a Printed Gate Dielectric Layer for an Organic FET with Stable Operation.
Toshihide Kamata 1 , Manabu Yoshida 1 , Kouji Suemori 1 , Sei Uemura 1 , Noriyuki Takada 1 , Satoshi Hoshino 1 , Takehito Kozasa 1
1 PRI, AIST, Tsukuba, Ibaraki, Japan
Show Abstract4:45 PM - S5.7
Top-contact Pentacene Transistor with Submicron Channel.
Fumihiro Fujimori 1 , Kazuhito Tsukagoshi 1 2 , Kunji Shigeto 1 , Tetze Hamano 1 , Takeo Minari 1 , Tetsuhiko Miyadera 1 , Yoshinobu Aoyagi 1
1 , RIKEN, Wako Japan, 2 PREST, JST, Kawaguchi, Saitama Japan
Show Abstract5:00 PM - S5.8
Low-voltage High Performance Semi-transparent Pentacene-TFTs with Polymer/high-k Oxide Hybrid-sandwich Gate Dielectrics.
Do Kyung Hwang 1 , Jeong Min Choi 1 , Ki moon Lee 1 , Seongil Im 1
1 Institute of Physics and Applied Physics, Yonsei University , Seoul, Sudaemoon-ku, Korea (the Republic of)
Show Abstract5:15 PM - S5.9
Orders-of-magnitude Enhancements in OFET Vapor Sensitivity through Chemically Bonded Receptors.
Howard Katz 1 , Jia Huang 1 , Kevin See 1 , Chad Landis 1 , Alan Becknell 2 , Joseph Miragliotta 2
1 Materials Science & Eng., Johns Hopkins University, Baltimore, Maryland, United States, 2 , JHU / APL, Laurel, Maryland, United States
Show AbstractSeveral new approaches to the design of OFET sensors for vapors of security interest will be described. Thiophene oligomer and naphthalenetetracarboxylic diimide semiconductors with hydroxyalkyl and hydroxyphenyl end groups were synthesized. Addition of these compounds, either alone or mixed with unfunctionalized semiconductor molecules, as overlayers atop high-mobility organic films, conferred greatly enhanced sensitivity of the devices to polar vapors such as phosphonate esters. Furthermore, gas-phase treatment of organic semiconductor films with organometallic Lewis acid receptors such as butyltin trichloride also improved the response, as judged by the ratio of currents in the presence and absence of analyte vapor, and also the stability of the currents. Current ratios increased from two to 100 as a result of these chemical modifications. Selectivity is also expected to improve as a result of receptor binding specificity and steric constraints applied to receptor attachment sites. Gate voltages leading to maximum ratios were slightly, but not strongly, in accumulation, indicating that gate voltage optimization is a further route to maximum response. The use of these films as part of packaged sensor systems will be discussed.
5:30 PM - S5.10
Realization of Very Large 2D Charge Carrier Densities in Organic Semiconductors by Electrostatic Injection.
Matthew Panzer 1 , C. Daniel Frisbie 1
1 Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractSince many organic semiconductor materials (e.g., pentacene, poly(3-hexylthiophene), rubrene) pack with two-dimensional molecular densities on the order of ~5 ×1014 molecules/cm2, this value can be used as a benchmark against which charge carrier density levels in organic field-effect transistors (OFETs) are compared. Although rarely emphasized, maximum charge carrier densities reached during typical OFET operation are only ~1012 charges/cm2, a value that is quite low in comparison to 5 ×1014 cm-2. In fact, the common choice of SiO2 for the OFET dielectric material intrinsically limits the maximum amount of charge that one can induce via the field effect (near SiO2 breakdown conditions) to only ~1013 charges/cm2. We will present results that show that by utilizing a solid polymer electrolyte as an OFET dielectric, 2D charge densities exceeding 1015 charges/cm2 can be attained in a variety of organic semiconductors. The attainment of very large charge carrier densities in organic semiconductor thin films has revealed intriguing device behavior at small operating voltages.Polymer electrolytes, typically used in Li-ion batteries or supercapacitors, can provide specific capacitances on the order of 100 μF/cm2, resulting from the migration of ions within a polymer matrix. By measuring the transient gate displacement current caused by ionic motion, we were able to determine the electrostatically-injected charge density values, which were typically above 1015 charges/cm2 at gate voltages less than 3 V. Conductivity maxima at carrier densities near 1 charge/molecule were observed in oligomeric, polymeric, and single-crystal organic semiconductors alike. This phenomenon is presumably related to carrier correlations or a complete emptying of the semiconductor transport band at such high charge densities. Furthermore, metallic conductivity (~1000 S/cm) and a nearly temperature-independent resistance ratio were attained in spin-coated poly(3-hexylthiophene) films using a polymer electrolyte-gated OFET.
5:45 PM - S5.11
Complex Impedance and Temperature Dependences of Pentacene Field Effect Transistors.
Tetsuhiko Miyadera 1 , Yoshio Kanamori 2 , Susumu Ikeda 2 , Koichiro Saiki 2 , Takeo Minari 1 , Kazuhito Tsukagoshi 1 , Yoshinobu Aoyagi 1 3
1 , RIKEN, Wako, Saitama, Japan, 2 , Univ. Tokyo, Tokyo, Hongo, Japan, 3 , Tokyo Inst. of Tec., Tokyo Japan
Show AbstractDynamic characteristics of organic field effect transistors (OFETs) are one of the important topics from both standpoints of fundamental physics and device application, although there have been few works on this subject. Previously, we have investigated complex impedance of C60 FETs. We reported that the channel capacitance followed power law (C ∝ f -p, p ∼ 0.3) and it could be explained by an equivalent circuit model which consists of distributed constant circuits and grain boundaries (T. Miyadera et.al., Cur. Appl. Phys. in press). This time, we report the complex impedance of pentacene OFETs varying the parameters of the frequency, gate voltage, and temperature.A top contact pentacene FET was prepared on a SiO2(300nm)/Si(100) substrate with the source and drain Au electrodes and its channel length and width were 100 μm and 5.4 mm, respectively. Static FET characteristics and complex impedance were measured varying the temperature from 300 K to 100 K. The static FET mobility showed Arrhenius type temperature dependence of which activation energy was 115 meV. Frequency dependent channel capacitance followed power law (p ∼ 0.48) similar to the case of C60. According to our equivalent circuit model, the value of the power (p ≦ 0.5) relates to the grain boundaries. That is, the lower the value is, the stronger its relation is. The value of the power decreases depending on the temperature decreases (p ∼ 0.33 at 200 K). Therefore, the contribution of the grain boundaries increases at low temperature. The investigation of the relation between contact resistance and complex impedance is underway. The contribution of local doping at the electrodes and that of self assembled monolayers (SAMs) treatment of SiO2 is examined.In conclusion, we have investigated complex impedance and temperature dependences of OFETs. The measurement was done by changing the parameter of the frequency, gate voltage, and temperature. The contribution of several interfaces such as electrodes-semiconductor and gate insulator-semiconductor will be discussed.
S6: Poster Session: Organic Thin Film Transistors and Photovoltaics
Session Chairs
Wednesday AM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - S6.1
Fabrication of Organic Thin Film Transistors Using Low Temperature, Soluble Silicon Oxide as the Gate Dielectrics.
Jeng-Hua Wei 1 , HorngJiunn Lin 1 , Ying-Ren Chen 1 , Po-Yuan Lo 2 , Zingway Pei 2
1 Department of Electronics Engineering, Ching Yun University, Jung-Li Taiwan, 2 Electronics Research & Service Organization, Industrial Technology and Research Institute, Hsinchu Taiwan
Show AbstractIn this paper, a unique water-based, liquid phase deposited silicon oxide (LPD SiO2) is adapted to the fabrication process of the organic thin film transistor (OTFT). Through the use of this process, an OTFT with a silicon oxide gate insulator is successfully fabricated at 100oC or less. At this low process temperature, the silicon oxide functions efficiently as a gate dielectric with the breakdown field being larger than 5 MV/cm, the leakage current being near 1 pA/um2 with a gate bias of 20 V and the surface roughness being less than 1nm. Due to the high quality silicon oxide, the oxide-gated OTFT shows the low threshold voltage (-1 ~ -2V) and medium on/off current ratio (~1000). Because this oxide is a water-based process, it is highly resistant to the following soluble semiconductor material and its solvent. It is possible to fabricate the inorganic, flexible TFT with all soluble processes using LPD silicon oxide as the gate insulator and using either carbon nanotube, silicon nanowire, chalcogenide, as the channel. This inorganic TFT may become another candidate for flexible electrical devices.
9:00 PM - S6.10
Double-channel Conduction in CuPc/CoPc OTFT and its Implications for Designing High-performance. heterostructure OTFTs
Xiaojiang Yu 1 , Jianbin Xu 1 , Jia Gao 1
1 Electronic Engineering Department, The Chinese University of Hong Kong, Hong Kong China
Show AbstractCuPc/CoPc heterostructure OTFT in sandwich configuration has shown a surprisingly high mobility of 0.11 cm2/Vs[1], but the mechanism of this heterostructure OTFT remains elusive so far. Our investigation on CuPc/CoPc heterostructure OTFT reveals that there is an energy barrier at the interface of CuPc/CoPc even though CuPc and CoPc could have identical crystal structure and similar grain size. Upon this understanding, a double-channel conduction model is proposed to explain the high mobility of CuPc/CoPc OTFT: there are two conduction channels in CuPc/CoPc OTFT, one at the bottom of CuPc layer and the other at the interface of CuPc/CoPc. The CuPc/CoPc interface channel is supposed to be the faster channel for carriers and can have a significant impact on the overall performance of CuPc/CoPc OTFT. A strategy has been designed to verify the double-channel conduction model. Based on the proposed double-channel conduction model, different fabrication parameters were attempted for CuPc/CoPc OTFT. The optimized mobility of the heterostructure CuPc/CoPc OTFT is found to be as high as 0.025 cm2/Vs, markedly higher than 0.01 cm2/Vs for conventional CuPc OTFT. Implications for designing high-performance heterostructure OTFTs from the study of CuPc/CoPc OTFT will also be discussed. [1] J. Zhang, J. Wang, H. B. Wang and D. H. Yan, Appl. Phys. Lett., 84, 142 (2004).
9:00 PM - S6.11
P- And N-Type Charge Transport In Field-Effect Transistors Of Pristine Poly(P-Phenylenevinylene).
Hiroshi Kayashima 1 , Takeshi Yasuda 1 2 , Katsuhiko Fujita 1 2 , Tetsuo Tsutsui 1 2
1 , Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka Japan, 2 , IMCE, Kyushu University, Fukuoka Japan
Show AbstractPoly(p-phenylenevinylene) (PPV) is one of the most popular representatives of p-conjugated polymers, which provide both the well-developed intra-chain p-conjugation system and the highly-stacked inter-chain p-p interaction system. Fabrications of field-effect transistors (FETs) made of such polymer films with densely packed and well-aligned p-conjugated chains are much interested Only a few reports on the performance of FETs using PPV and its analogues, however, have been appeared, except for an early pioneering work on poly(thienylenevinylene), mainly due to the difficulty in preparing high-quality thin films on substrate. In this report, we have been successful in preparing high quality PPV thin films on SiO2/Si substrate via a water-soluble precursor route and observed both p-type and n-type charge transport behaviors in FETs with a pristine PPV film as an active layer.We fabricated a PPV-FET having a top contact geometry with Au or Ca source-drain electrodes. Octadecyltrichlorosilane (OTS) treated SiO2/p++-Si substrate was used, and a thin PPV layer was formed on the OTS-treated substrate as follows: A rectangular frame of silicone rubber was fixed on the substrate and a water solution of PPV precursor polymer, poly(p-xylene tetrahydrothiophnium chloride), was dropped onto the substrate. Water evaporated slowly and a dry precursor thin film was formed, during the addition of a centrifugal force to the vertical direction to the substrate fixed on a centrifugal separator. Spin-casting of water solution on a hydrophobic OTS-treated substrate is not possible, but we were successful in preparing high quality PPV precursor films on an OTS-treated substrate by the addition of a strong centrifugal force that forced the water solution to spread and stick to the hydrophobic substrate. Finally, the PPV precursor films were converted to PPV by thermal treatment under vacuum at 503K for 11 h. Au or Ca source-drain electrodes with an interdigitated configuration was fixed by vacuum-evaporation using a shadow mask. When Au was used as source-drain electrodes, we observed p-channel FET conduction. From the saturation regime, the field effect hole mobility was calculated to be 10-4 cm2 V-1 s-1. Output characteristics for PPV FET with Au source-drain electrodes indicated a presence of a large hole injection barrier. The HOMO energy level of PPV is 5.7eV and is about 0.6 eV larger than the work function of Au. On the other hand, n-channel FET conduction was clearly observed, when a low work function metal Ca was used as source-drain electrodes. The field-effect electron mobility was calculated to be 10-6 cm2 V-1 s-1. The effect of thermal conversion conditions and the effects of oxygen and water from ambient atmosphere, on FET mobilities were also carefully investigated.
9:00 PM - S6.12
Extracting the Device Parameters from Organic Thin Film Transistors.
Eung Seok Park 1 , Pil Soo Kang 1 , Gyu Tae Kim 1
1 School of Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractOrganic thin film transistors(OTFTs) were simulated by a SPICE model adopted in hydrogenated amorphous TFTs(a-Si:H). The gate voltage-dependent mobilities were assumed to fit the representative current-voltage characteristics, which would be reasonable in the hopping-type conductor with the low mobilities below 1cm2/Vs. The optimal fitting procedures were suggested to compare the experimental data with the mathematical expressions used in the amorphous Si-TFT model, confirmed by the well-fitting results with the reported data in the literatures. Each SPICE parameter explains the gate dependent mobilities in OTFTs originating from the distribution of trap sites for the hopping conduction.
9:00 PM - S6.13
The Impact of Capping on the Mobility and Thermal Stability of Organic Thin Film Transistors.
Stephan Meyer 1 , Jens Pflaum 1 , Stefan Sellner 2 , Helmut Dosch 3 , Frank Schreiber 4 , Gerhard Ulbricht 3 , Matthias Fischer 5 , Bruno Gompf 5
1 3rd Institute of Physics, University of Stuttgart, Stuttgart Germany, 2 , Harvard University, Cambridge, Massachusetts, United States, 3 , Max-Planck-Institute, Stuttgart Germany, 4 Institute of Applied Physics, University of Tübingen, Tübingen Germany, 5 1st Institute of Physics, University of Stuttgart, Stuttgart Germany
Show Abstract9:00 PM - S6.14
Electronic Transport Study of Regioregular Polyhexylthiophene Block Copolymer.
Paul Stokes 1 2 , Firoze Haque 1 2 , Saiful Khondaker 1 2
1 Nanoscience Technology Center, University of Central Florida, Orlando, Florida, United States, 2 Physics, University of Central Florida, Orlando, Florida, United States
Show Abstract9:00 PM - S6.15
Structure Analysis on Blend Films of Polymers and Small Molecules.
Takuya Kambayashi 1 , Hiroshi Wada 1 , Takehiko Mori 1 , Hideo Takezoe 1 , Ken Ishikawa 1
1 Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo Japan
Show Abstract9:00 PM - S6.16
Organic Thin Film Transistors on Paper.
Hua-Chi Cheng 1 , Yu-Rung Peng 1 , Zing-Way Pei 1 , Chao-An Chung 1 , Wei-Hsin Hou 1
1 , EOL/ITRI, Hsinchu Taiwan
Show Abstract9:00 PM - S6.17
Synthesis of Polythiophene Derivatives Containing Fluorine Substituents for Organic Thin-film Transistors.
Bogyu Lim 1 , Jieun Ghim 1 , Doojin Vak 1 , Kang-Jun Baeg 1 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - S6.18
Modeling the Capacitance-Voltage Characteristics of Organic Schottky Diode
Huai-Yuan Tseng 1 , Ko-Yu Chiang 1 , Chen-Pang Kung 1
1 , Industrial Technology Research Institute (ITRI), Chutung, Hsinchu, Taiwan
Show AbstractPrinted organic Schottky diode is the most significant component of printed organic Radio Frequency Identification (RFID) since the organic Schottky diode combining with the printed resistor and capacitor act as the rectifier which is essential for organic RFID. The DC model of Schottky diode has been proposed by several research groups through modifying the equation of inorganic Schottky diode. D. M. Taylor et al. present two-accepter state model to explain capacitance-voltage characteristics, however, the proposed model can not be applied to certain organic Schottky diode, such as Mo/poly(3-methylthiophene) structure. In addition, the model of the frequency dispersion phenomenon of capacitance-voltage behavior remains unavailable. Therefore, the capacitance model of the diode must be completely developed to precisely simulate the performance of the rectifier. In this work, we present the capacitance model as a function of operation voltage and frequency. The simulated capacitances are in good agreement with our experimental data. The model can then be implemented into the simulator for accurate circuit design.
9:00 PM - S6.19
Orientation Control of Standing Epitaxial Pentacene Monolayers Using Surface Steps and In-plane Band Dispersion Analysis by Angle Resolved Photoelectron Spectroscopy.
Tadamasa Suzuki 1 , Toshihiro Shimada 1 , Susumu Ikeda 2 , Koichiro Saiki 2 , Tetsuya Hasegawa 1
1 Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo Japan, 2 Department of Complexity Sciences and Engineering, The University of Tokyo, Kashiwa, Chiba Japan
Show Abstract9:00 PM - S6.2
Low Voltage Operation of Inverters Based on Organic Static Induction Transistors.
Yasuyuki Watanabe 1 , Hiroyuki Iechi 1 2 , Kazuhiro Kudo 1 3
1 Advanced Organic Device Project, Chiba Laboratory, Optoelectronic Industry and Technology Development Association, Chiba Japan, 2 Advanced Technology R&D Center, Research and Development Group, Ricoh Co. Ltd, Yokohama Japan, 3 Department of Electronics and Mechanical Engineering, Faculty of Engineering, Chiba University, Chiba Japan
Show AbstractHigh performance organic thin film transistors(OTFTs) are key devices to commercialize the lightweight and flexible electronic devices such as paper-like displays, low-cost identification tags, etc. In general, the OTFTs have been fabricated employing to the lateral type structure such as organic field effect transistors (OFETs). However, the OFETs have several disadvantages of low current density, high operational voltage, and low speed because the organic semiconductors used in the OFETs have high resistivity and low carrier mobility. To improve their performance for practical applications of the OTFTs, it is necessary to develop new materials, new device processing, new device structures, and new evaluation methods. We have been studied on organic static induction transistor (OSITs) with a vertical type structure for the realization of high-performance transistors. The excellent characteristics of the OSITs arise from the vertical structure with a very short channel length corresponding to the thickness of organic semiconductor layer. Recently, we have succeeded to fabricate the OSITs based on pentacene thin film on flexible substrates and investigated their basic electrical characteristics under bending condition [1] and to fabricate the OSITs with the high current on/off ratio by controlling the interface state between the organic semiconductor layer and the electrodes [2].In this study, we have fabricated organic inverters using OSITs based on pentacene films because of the attractive characteristics of the OSITs as mentioned below. The OSITs have advantage with regard to the lower operational voltage compared to the conventional lateral type OFETs. The organic inverters were composed of the load and drive OSITs which have the high current on/off ratio. The inverter transfer characteristics were measured under a variety of bias conditions. The input voltage was varied in the range from -2 to + 2V and the supply voltage was varied in the range from -0.5 to -1.5 V. From the results, it was found that organic inverters based on the OSITs show basic transfer characteristics and a low operational voltage of ± 2V. The obtained results demonstrate that the high current on/off ratio of OSITs is needed to fabricate the high performance organic inverter.AcknowledgmentPart of this work belongs to the “Advanced Organic Device Project” conducted by OITDA in conjunction with the New Energy and Industrial Technology Development Organization (NEDO).References[1] Y. Watanabe and K. Kudo, Appl. Phys. Lett. 87, 223505 (2005).[2] Y. Watanabe, H. Iechi and K. Kudo, Jpn. J. Appl. Phys. 45, 4B, 3698(2006).
9:00 PM - S6.20
Potential and Transport in Organic Transistors: Comparison of Experimental Results with a New Analytical Description.
Edsger Smits 1 2 5 , Michael Coelle 2 , Arjan Mank 2 , Simon Mathijssen 2 4 , Thomas Anthopoulos 3 , Peter Bobbert 4 , Bert de Boer 1 , Paul Blom 1 , Dago de Leeuw 2
1 Materials Science Centre, University of Groningen, Groningen Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands, 5 , Dutch Polymer Institute, Eindhoven Netherlands, 4 , Technical University Eindhoven, Eindhoven Netherlands, 3 , Imperial College London, London United Kingdom
Show Abstract9:00 PM - S6.22
Effect of Phase State of Self-Assembled Monolayers on Pentacene Growth and Thin Film Transistor Characteristics
Kilwon Cho 1 , Hwa Sung Lee 1 , Do Hwan Kim 1 , Jeong Ho Cho 1 , Minkyu Hwang 1 , Yunseok Jang 1 , Ji Hwang Lee 1
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractWith the aim of investigating the effect of phase state of self-assembled monolayers (SAMs) on the growth mode of pentacene crystals and the performances of organic thin-film transistors, pentacene molecules were deposited on SAMs of octadecyltrichlorosilane (ODTS) with different alkyl chain orientation at various substrate temperatures (30, 60, and 90 C). The phase state of ODTS SAMs, i.e. the alkyl chain orientation of ODTS was controlled by adjusting the reaction temperature. We found that the phase state of SAMs, i.e. ordered or disordered state, played an important role in the growth of the pentacene crystals and the electrical performance of the field-effect transistor. Pentacene films grown on relatively highly ordered SAMs were found to have higher crystallinity and better interconnectivity between pentacene domains, directly serving the enhancement of the field-effect mobility, than those on the disordered SAMs. Also, their differences (crystallinity and field-effect mobility) increased with the substrate temperature. These results can be possibly explained by lattice matching effect between the pentacene crystals and ODTS SAMs, and temperature-dependent alkyl chains mobility of ODTS. (This work was supported by the ERC Program (R11-2003-006-03005-0) of the MOST/KOSEF, the Information Display R&D Center (F0 004 022), and the BK21 Program.)
9:00 PM - S6.23
Structure Property Relationships: Asymmetric Oligofluorene-thiophene Molecules for Organic TFTs.
Ming Tang 1 , Mark Roberts 2 , Jason Locklin 2 , Mang-mang Ling 2 , Hong Meng 3 , Zhenan Bao 2
1 Chemistry, Stanford University, Stanford, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States, 3 Central Research and Development, E. I. Dupont Company, Wilmington, Delaware, United States
Show AbstractFluorene-thiophene oligomers show great promise as the active material in p-type organic thin-film transistors (TFTs) due to their good performance and good stability under ambient conditions. In this study, a series of fluorene-thiophene co-oligomers were asymmetrically substituted with an alkyl group to probe the effect chemical structure has on their thin film properties. The alkyl groups are n-hexyl, n-octyl, and n-dodecyl respectively. These oligomers were characterized by elemental analysis, mass spectrometry, differential scanning calorimetry and thermogravimetric analysis, while the thin films of these oligomers were characterized by x-ray diffraction, atomic force microscopy and field-effect transistor measurements. We found that the performance of these asymmetric molecules is similar to their symmetric counterparts. Mobilities as high as 0.16cm2V-1s-1 were found for the n-dodecyl substituted oligomer.
9:00 PM - S6.24
Conjugated Copolymers: Synthesis, Electronic Properties, and Thin Film Transistor Characteristics.
Wen-Chang Chen 1 2 , Kai-Fang Cheng 2 , Wen-Ya Lee 1
1 Department of Chemical Engineering, National Taiwan University, Taipei Taiwan, 2 Institute of Polymer Science and Engineering, National Taiwan University , Taipei Taiwan
Show Abstract9:00 PM - S6.25
Semiconducting Thin Films of Partially Fluorinated Phthalocyanines in OFETs
Harry Brinkmann 1 , Christian Kelting 1 , Sergey Makarov 2 , Dieter Wöhrle 2 , Derck Schlettwein 1
1 Applied Physics, Justus-Liebig-University Giessen, Giessen Germany, 2 Institute of Organic und Macromolecular Chemistry, University of Bremen, Bremen Germany
Show AbstractUnsubstituted phthalocyanines Pc are well established organic semiconductors, easily p- doped under most conditions. Chemical substitution of H- atoms at the molecule by electron- withdrawing substituents stabilizes the molecular electronic system and n conducting films can be obtained. This could be most clearly shown for the perfluorinated phthalocyanines F16Pc. Partially fluorinated phthalocyanines with two fluorine atoms in each benzene ring of the ligand (F8Pc) or phthalocyanines with one fluorine atom in each benzene ring (F4Pc) represent molecules with interesting intermediate characteristics. Semiempirical quantum chemical calculations showed a very systematic sequence of the energy position of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) compared with the unsubstituted or perfluorinated phthalocyanines in a series Pc > F4Pc > F8Pc > F16Pc. This intermediate position of the partially fluorinated phthalocyanines could be confirmed in detailed photoelectron spectroscopy experiments and opens the chance towards a fine tuning of the energetic line up, a fundamental prerequisite for the construction of field effect transistors, in particular for ambipolar OFET. We report here about the growth of F16Pc, F8Pc and F4Pc on organic and inorganic insulating substrates suitable for OFET applications and we discuss the structure, morphology and electronic intermolecular coupling in the thin films. The suitability of the materials for applications in OFET devices is discussed based on electrical conduction and field effect measurements at the films.
9:00 PM - S6.26
Photo-crosslinkable Polymers as Gate Insulator in OTFT.
Bokyoung Joo 1 , Hongdoo Kim 1
1 Chemistry, Kyunghee Univ., Yongin Korea (the Republic of)
Show AbstractIn organic thin film transistor, the choice of gate insulator material is very important because of the interaction between organic semiconductor material and insulator. Nevertheless, the role of gate insulator in OTFT has not been studied systematically. In this study, the photo-crosslinkable copolymers as gate insulator were designed and examined. In this copolymer, highly polarizable groups such as 2-hydroxyl ethyl methacrylate(HEMA) and methacrylic acid(MA) were adopted to increase the dielectric constant and to serve as crosslinking sites. As precursor of photopolymer, tricyclo[5,3,1,0] decane dimethanol (TDDM) was synthesized by esterifying dimethyl-acryl-tricyclo[5,3,1,0] decane dimethyl ester. By varying the mole ratio of TDDM, HEMA, MA and MMA(methyl methacrylate) or BzMA(benzyl methacrylate), the dielectric constant and the surface energy of photopolymers can be finely tuned. The characteristics of this photo-copolymer will be discussed based on the dielectric constant, contact angle and OTFT performance.
9:00 PM - S6.27
Organic Field-Effect Transistors Based on Various Types of Polytriarylamines
Andreas Klug 1 , Raphael Pfattner 1 , Benjamin Souharce 2 , Ullrich Scherf 2 , Emil List 1 3
1 Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010, Graz Austria, 2 , Bergische Universität Wuppertal, Makromolekulare Chemie, Fachbereich Chemie, Gaussstrasse 20, D-42097, Wuppertal Germany, 3 , NanoTecCenter Forschungsgesellschaft mbH, A-8160, Weiz Austria
Show AbstractOrganic field-effect transistors (OFETs) have been in the focus of research since the late 1980s. Their performance determined by parameters such as the field-effect mobility has been rapidly improved. The application of organic materials, on which OFETs are based, leads to electronics fabricated on large areas and flexible substrates at low cost by enabling solution-based processing techniques such as drop-casting, spin-coating or inkjet printing. A rather interesting class of organic semiconducting materials is the one of hole-transporting polytriarylamines. Polytriarylamines can be handled in air and corresponding OFETs are rather stable with respect to ambient conditions. Moreover, most chemical modifications of polytriarylamines are amorphous, which is of great importance when the polymers are applied by means of printing processes.In this work we present the results of the fabrication and analysis of OFETs based on various types of polytriphenylamine based polymers. In addition different gate dielectric materials, silicon dioxide and polyvinyl alcohol (PVA), were tested in conjunction with the said polymers. For all devices the corresponding field-effect mobilities and on/off-current ratios were extracted from the measured current-voltage characteristics. Moreover, all polymers have been extensively tested for stability with respect to air and light and devices were compared to the well-known transistor polymer poly(3-hexylthiophene).
9:00 PM - S6.29
Inkjet Printed Electrodes for Organic Field Effect Transistor Applications
Stefan Gamerith 1 , Andreas Klug 1 , Horst Scheiber 1 , Ullrich Scherf 2 , Erik Moderegger 3 , Emil List 1 4
1 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010, Graz, Austria and Institute of Nanostructured Materials and Photonics, A-8160, Weiz Austria, 2 , Bergische Universität Wuppertal, Makromolekulare Chemie, Fachbereich Chemie, Gaussstrasse 20, D-42097, Wuppertal Germany, 3 , AT&S Austria Technologie und Systemtechnik AG, Fabriksgasse 13, A-8700, Leoben Austria, 4 , NanoTecCenter Forschungsgesellschaft mbH, A-8160, Weiz Austria
Show AbstractThe field of organic electronics has seen tremendous progress over the last years and all-solution based processes are believed to be one of the key routes to ultra low cost roll-to-roll device and circuit fabrication. In this regard a variety of functional materials have been successfully designed for inkjet printing. While orthogonal-solvent approaches have frequently been used to tackle the solubility issue in multilayer solution processing, the focus of this work lies on printed metal electrodes for organic field effect transistors (OFET) and their curing concepts. Two novel metallic inkjet printable materials are studied: i.) a soluble organic silver-precursor and ii.) a silver-copper nanoparticle based dispersion. Photoelectron spectroscopy reveals largely metallic properties of the cured materials which are compared with respect to OFET performance and process-related issues. Contact resistance of the used nanoparticle-based electrodes is significantly higher than with evaporated top-contact gold electrodes. However, as direct patterning via inkjet printing limits the reliably achievable channel length to values well above 10 µm, the overall device performance is comparable as will be shown. In summary, the presented results underline that commercially available solution processable metals are definitely becoming an alternative to doped conjugated polymers such as PEDOT/PSS in many organic electronics applications.
9:00 PM - S6.3
Carrier Type Reversal of AlPcCl FET and the Corresponding Changes in Electronic States.
Toshihiko Kaji 1 , Toshihiro Shimada 1 , Susumu Ikeda 2 , Koichiro Saiki 2 1
1 Department of Chemistry, School of Science, The university of Tokyo, Tokyo Japan, 2 Depertment of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan
Show Abstract9:00 PM - S6.30
Tunable Dielectric Polymer Materials as a Gate Insulator for OTFT.
Yejeong Seo 1 , Bokyoung Joo 1 , Hongdoo Kim 1
1 Chemistry, Kyunghee Univ., Yongin Korea (the Republic of)
Show AbstractIn the operation of organic thin-film transistor(OTFT), the choice of gate insulator material is very important due to the interaction between the insulator and organic semiconductor. The insulator can affect the molecular stacking of organic semiconductor and the density of states by local polarization. Nevertheless, commercially available polymers such as poly(4-vinylphenol), poly(vinylalcohol) have been used in most of research and the role of gate insulator in OTFT has not been studied systematically using well designed polymer dielectrics. Using polymethylmethacrylate (PMMA) as base polymer material, the copolymer was designed to study the role of polarizable group in dielectrics. 2-Hydroxyl ethyl methacrylate(HEMA) as highly polarizable groups was utilized. Another monomer was selected to control the Tg of the copolymer. By changing the mole ratio of monomers, the dielectric constant of copolymer can be varied. The characteristics of this copolymer will be discussed based on the dielectric constant, contact angle and OTFT performance.
9:00 PM - S6.31
New Solution Based Processes to Improve Crystallinity of P3HT Films 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 some new solution-based processes that improve the crystallinity and alignment of conjugated polymer films. It was shown that the film of regioregular polythiophenes (P3HT) which were fabricated by normal spin coating process has low crystallinity by grazing incidence small angle x-ray scattering (GISAXS). On the other hand, it was shown that films of P3HT which were fabricated by some new solution-based processes have exceptional crystallinity. 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 1 x 10-3 cm2/Vs. It was shown that new solution-based processes could improve the mobility. We also discuss the connection between crystallinity and field effect mobility.
9:00 PM - S6.32
Atomic Layer Deposition of ZnS Thin Films and Its Application as a Channel Layer for OITFT Device
Inhoe Kim 1 , Seoungwoo Kuk 1 , Injae Baeck 2 , Ho Jung Chang 2 , Hyung-ho Park 3 , Hyeongtag Jeon 1
1 Division of Materials Science and Engineering, Hanyang University, Seoul Korea (the Republic of), 2 , Dankook University, Cheonan-shi, Chungnam Korea (the Republic of), 3 , yonsei University, Seoul Korea (the Republic of)
Show AbstractZnS thin films were grown by Atomic Layer Deposition (ALD) method with ZnCl2, Diethyl-Zinc (DEZ), and hydrogen sulfide (H2S) precursors for the application of a channel layer of OITFT (Organic-Inorganic Thin-Film Transistor). We used a traveling wave type ALD system and used two precursors as a Zn source, ZnCl2 and DEZ. The deposition rate of the ZnS films in our system was about 0.7 Å/cycle and 1.6 Å/cycle by st2000 and TEM analysis, respectively. Zn peak of ZnS thin films, deposited with DEZ and ZnCl2, appeared in the range of 1022.5 ~ 1023 eV and 1021.7 ~ 1022.5 eV, respectively. And S peak of ZnS thin films, deposited with DEZ and ZnCl2, appeared in the range of 162 ~ 162.5eV and 163 ~ 163.5eV, respectively on an XPS analysis. We carried out an RBS analysis for the measurement of composition in the ZnS films and deposited ZnS film has nearly no oxygen contaminated. We used XRD to measure the structure and stress of ZnS films. Structure of ZnS is Zinc-blende structure and stress reliability was -416.53 Mpa and -458.97 Mpa. In addition, the result of a Hall-effect measurement showed that the carrier concentrations of each 800Å and 160Å films were -1.808E17 and -9.439E15, and the hall mobilities were 28.699 and 49.04, resistivities were 2.0382 and 17460, and conductivities were 1.11 and 6.16E-3, respectively. From these results, we suggest the ZnS films deposited by ALD be used for a channel layer of an OITFT for a display field.We also made the capacitor and OITFT structures with a ZnS channel. ZnS films were deposited on the three types of dielectric layer. Those dielectrics are non-treated PVP film, plasma treated PVP film, and PVP film with an Al2O3 buffer layer. The electrical characteristics of the ZnS channel layers were observed by using an I-V, and the optical characteristics were observed by using an UV-visible spectrophotometer. From these results, we studied the possibility of the application of a new type OITFT for display field.a)Corresponding author; E-mail:
[email protected] 9:00 PM - S6.33
Substrate Temperature Effect on Forming a Semiconducting Polymer Film in Organic Field Effect Transistors.
Seok-Ju Kang 1 , Jieun Ghim 1 , Seok-Soon Kim 1 , Kang-Jun Baek 1 , Hyemi Lee 1 , Dong-Yu Kim 1
1 Dept. of Materials Science and Engineering, Heeger Center for Advanced Materials & Photonics Polymer Laboratory, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract9:00 PM - S6.35
Gate Dielectric Dependent on Pentacene Growth and Electrical Stability in OTFTs.
Kim Chang Su 1 , Jo Sung Jin 1 , Lee Sung Won 1 , Baik Hong Koo 1
1 Department of Materials Science and Engineering, Yonsei university, Seoul Korea (the Republic of)
Show Abstract9:00 PM - S6.36
Direct Determination of Organic Thin-film Transistors Transconductance Using a Lock-in Method
Richard Yang 1 2 , Andrew Kummel* 2
1 Material Science and Engineering, UC San Diego, La Jolla, California, United States, 2 Department of Chemistry and Biochemistry, UC San Diego, La Jolla, California, United States
Show AbstractTransconductance (gm) is a key device parameter for transistors, which determines the device current gain and switching speed. Customarily, gm is obtained by numeric fitting the slope of transfer curve taken at a specific drain voltage. This method requires sampling a large set of data points over a wide gate voltage range, which typically takes over 10 seconds. However, the method is problematic at the presence of trap states in organic semiconducting materials. At the time scale of the above measurement, organic transistors may have over 30% hysterisis in transfer curves. We develop a new method that determines the transconductance directly using a lock-in amplifier without the need to sweep gate voltage. The accuracy of this new method calibrated with Si JFETs is over 99% compared to the numeric fitting method at the absence of trapping effect. The frequency and gate voltage dependent mobility of a CuPc transistor have been measured. The charge trapping effect on the device will be discussed using this dynamic spectroscopy method.
9:00 PM - S6.37
Very Low Dark Current Double Heterojunction Solar Cells Employing Chloroaluminum Phthalocyanine as a Donor.
Rhonda Bailey-Salzman 1 , Barry Rand 1 , Stephen Forrest 2 3 4
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3 Physics, University of Michigan, Ann Arbor, Michigan, United States, 4 Materials Science, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:00 PM - S6.38
Impact of Morphology on Polymer Solar Cell Performance Studied via Scanning Probe Microscopy
David Coffey 1 , Obadiah Reid 2 , David Ginger 2
1 Physics, University of Washington, Seattle, Washington, United States, 2 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractNanoscale film morphology can dramatically impact charge generation, recombination and transport in blended organic solar cells. We have previously applied time-resolved electrostatic force microscopy (EFM) to study model donor/acceptor blends based on polyfluorene copolymers and shown that domain centers can contribute more photocurrent than domain boundaries. We now investigate this result in more detail and with new blend systems. We present conducting atomic force microscopy and EFM data on alkoxy-phenylenevinylene/fullerene and polyfluorene donor/acceptor blends. We correlate the contributions of local (20-100 nm) variations in charge transport, charge recombination, and charge trapping, with the overall variation in device performance observed for different blend ratios and processing conditions.
9:00 PM - S6.39
Quasi-solidification of Dye Sensitized Solar Cells by use of Straight Charge Carrier Nano-paths.
Shuzi Hayase 1 , Takehiko Kato 1 , Fumi Inakazu 1 , Wataru Takashima 1 , Keiichi Kaneto 1
1 , Kyushu Institute of Technology, Kitakyushu Japan
Show AbstractSolidification of dye sensitized solar cells (DSC) always decreases the photovoltaic performances. We now report the quasi-solidification of dye sensitized solar cells without losing the photovoltaic performances of liquid type DSCs. This was achieved by fabricating the straight carrier paths on the straight nano-pore walls in porous alumina films. The DSC consists of a porous titania layer stained by dye molecules and anodic oxidation porous alumina films whose surfaces were chemically modified with structurally ordered charge carrier molecules. In addition, the nano-pore was filled with non-volatile ionic liquids and iodine. The quasi-solidified DSC exhibited higher photovoltaic performances than the corresponding liquid type DSCs, in spite that electrochemically inactive alumina wall occupies more than half of the charge charier layers. Two types of straight charge carrier paths are reported. One is iodine ionic paths by a Grotthus type mechanism. The porous alumina nanopore walls were chemically modified with imidazolium iodide moiethies (a kind of ionic liquid molecular structures). The imidazolium iodide moieties and porous alumina nano-pore walls were connected with long alkyl groups which aligned the imidazolium iodide moieties by the self-organization properties. Iodine molecules were concentrated on the aligned imidazolium iodide moieties. The concentrated and aligned iodine molecules are likely to cause hopping of iodine molecules (Grotthuss diffusion mechanism). The other is the hybrid charge carriers containing ion and electron. The alumina nano-pore walls were modified with conductive polymers. The residual nano-pores were filled with ionic liquids and iodine. The iodine molecules were concentrated on the conductive polymer layers. Generally, the increase in the amount of iodine molecules increases short circuit current (Jsc) because of the increase in the conductivity, but decreases open circuit voltage (Voc) because of the increase in back electron transfer reactions (dark current). Our composite type quasi-solid DSCs proposes a new concept on hybrid DSCs having a high iodine concentration area for conductive layers (porous alumina layer) and a low iodine concentration area in porous titania layers.
9:00 PM - S6.4
New Concepts for the Development of Active Functional Polymers for p and n-type OFET- Applications.
Silvia Janietz 1 , Dessislava Sainova 1 , Udom Asawapirom 1
1 Polymer Electronics, FhG-IAP, Potsdam, Brandenburg, Germany
Show AbstractRegioregular poly(3-hexylthiophenes) belong to a class of soluble conjugated polymers with especially attractive properties for applications in organic field effect transistors (OFETs). A key property of these compounds is the chain self-alignment ability leading to the formation of microcrystalline structures in thin films with well-ordered lamellae of co-facially stacked planarised backbones. This assembly ensures strong p-p interchain interactions and thereby fast charge transport in the layer of the ordered backbones. The outstanding device performance is hindered by the relatively limited ambience exposure stability. Therefore we explore a concept to improve this characteristic based on the introduction of electron-accepting units in the main chain in order to increase the ionisation potential. It will be reported and discussed the synthesis, the structural and optical investigations of series soluble acceptor-containing polythiophenes with varied chemical composition. The OFET-perfor-mance has been studied in comparison to the conventional P3HT clarifying the advantages of the modified polymers especially with respect to the operational and ambience stability.Compared to the p-type semionducting polymers the n-type organic materials are markedly less developed. Nevertheless both charge transport types are necessary for the realisation of numerous important logic elements. Recently an interesting solution to this task has been proposed in the form of a conjugated ladder-type poly(benzo-bisimidazobenzo-phenanthroline) (BBL) showing either ambipolar or n-type field effect properties dependent upon the sample preparation and processing. However this rigid-chain ladder polymer is not soluble in the common organic solvents resulting in a rather complicated technological transfer. We report the significant improvement of the BBL-processing utilizing aqueous colloidal dispersions and their OFET-application. The resultant devices demonstrate ambipolar electronic transport with charge carrier mobilities in the range of 10-5 cm2/Vs without specific optimization procedures.
9:00 PM - S6.40
Observation of Electroluminescence and Photovoltaic Response in Ionic Junctions
Daniel Bernards 1 , Samuel Flores-Torres 2 , Héctor Abruña 2 , George Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractJunctions of p and n-type doped semiconductors form the basis for the majority of modern semiconductor electronics. The simplest device, a pn-junction, relies on diffusion of electronic charge to develop an internal electric field. This field acts to rectify current and produce a photovoltaic effect under illumination. Junctions that are purely ionic can also exhibit similar characteristics, such as rectification, where cations and anions are directly analogous to holes and electrons, respectively. Unfortunately, junctions that are both ionic and electronic in nature have not been explored in depth, primarily due to a lack of appropriate materials and required processing techniques.Using soft-contact lamination, we fabricated ionic junctions between two organic semiconductors with mobile anions and cations, respectively. We show that mobile ionic charge can be successfully deployed to control the direction of electronic current flow in semiconductor devices. As a result, these devices show electroluminescence under forward bias and a photo-voltage upon illumination with visible light. In these devices, electronic characteristics are determined by both the HOMO/LUMO energetics as well as ion-induced potentials within the device, providing a novel class of organic semiconductor devices.
9:00 PM - S6.41
Fabrication of Conducting Polymer Nanowires using Block Copolymer Nano-porous Templates for Photovoltaic Device
Jeong In Lee 1 , Jin Kon Kim 1 , Jae Woong Yu 2
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Optoelectronic Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractPhotovoltaic devices based on organic and polymeric PN heterojunction materials have been extensively investigated because of the ease of processing, low cost of fabrication, and flexibility of the films. However, the power conversion efficiency (ηp) of these devices is much less than inorganic devices. These lower efficiencies arise from the fact that free electrons and holes are not directly produced by photon absorption in the organic or polymer materials. Rather, electron-hole pairs (excitons) are created, and dissociate into holes and electrons. Exciton dissociation in heterojunction photovoltaic (PV) devices occurs mainly at the interface of the hole (P-type conducting polymer) and electron acceptor (N-type conducting polymer). Various different PN-heterojunction PV device geometries have been reported: bilayer laminated films of P-type/N-type conducting polymers, and single-layered film where P-type/N-type conducting polymers phase separate into bicontinuous interpenetrating polymer network (IPN) structures. In this study, block copolymer templates were used to fabricate high-efficiency PV devices. We showed that nanoporous templates made of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) increased of P-N interfacial area and pathway for transporting holes. We first prepared hexagonally-packed nanowires of polypyrrole (PPy), poly(3,4-ethlenedioxythiophene) (PEDOT), poly(3-hexyltiophene) (P3HT), which are commonly used as a P-type material, by electrochemical-polymerization inside nano holes of nanoporous tempaltes. After removing PS matrix, N-type materials were spin-coated. This geometry allowed us to obtain large contact area of P-N heterojunction, which allows a high efficiency of the current conversion from the light.Acknowledgement : This work was supported by Creative Research Initiative Program supported by KOSEF.
9:00 PM - S6.42
Design of Nanosized Grating-like Heterojunctions in Organic Solar Cells
Ligong Yang 1 2 , Hong-Zheng Chen 1 , Mang Wang 1 2
1 Dept. of Polymer Sci & Eng., Zhejiang University, Hangzhou, Zhejiang Province, China, 2 , State Key Lab of Silicon Materials, Hangzhou, Zhejiang Province, China
Show Abstract9:00 PM - S6.44
Photoactive Polybithiophene/titania Hybrids Prepared by Electrochemical Polymerization
Yi-Jun Lin 2 , Leeyih Wang 1 , Wen-Yen Chiu 2
2 Department of Chemical Engineering, National Taiwan University, Taipei Taiwan, 1 Center for Condensed Matter Sciences, National Taiwan University , Taipei Taiwan
Show AbstractA series of photoactive hybrids were prepared by the electrochemical polymerization of bithiophene on a nanoporous TiO2-coated ITO glass using chronopotential method at different current densities in a water/acetonitrile mixed solvent. As demonstrated in ESCA data, this approach enable the polybithiophenes (PBith) to be grown from the interstices of TiO2 matrix and most nanopores were filled with polymer chains, greatly increasing the interface between two materials. Additionally, it was found that the current density used for depositing PBiTh films greatly affects the surface topology of the film. When the applied current density was varied from 0.05 to 1.00 mA/cm2, the root-mean-square roughness of the films was also significantly increased from 6.6 nm to 79.0 nm. However, by replacing pure acetonitrile with water/acetonitrile mixture as solvent, the onset oxidation potential of bithiophene can be effectively decreased, thus lowering the possibility of the formation of branching chains. At an optimal condition of the volume ratio of water to acetonitrile at 1:1, the electropolymerization potential for growing bithiophene could be lowered to around 1.01 V as the current density was fixed at 0.05 mA/cm2. The as-prepared PBiTh films possess very good adhesion to TiO2 layer and exhibit excellent redox reversibility and chemical stability in air. The performance of the photovoltaic cells based on these new hybrid materials will be reported.
9:00 PM - S6.45
A New Bulk-heterojunction Structure for Organic Solar Cells Based on Small-molecules.
Takahiro Osasa 1 , Shuhei Yamamoto 1 , Michio Matsumura 1
1 Research Center for Solar Energy Chemistry, Osaka University, Osaka Japan
Show AbstractCharge carriers are photogenerated in organic solar cells with a flat bilayer structure generate from excitons at the interface between two organic layers, which are made of electron-donor and electron-acceptor compounds. The photocurrent density is low due to the limited diffusion length of excitons in organic layers, if the two layers are simply stacked. To overcome this problem, the ‘‘bulk-heterojunction’’ structure has been proposed. This structure is considered to be effective to enlarge the contact area between the two layers and to generate charge carriers effectively. Normally, this structure is formed by mixing soluble fullerene derivative with conducting polymer. However, a simple mixing of two components does not allow the formation of separated paths for holes and electrons, which are indispensable for the generation of photocurrent.Here we report a new bulk-heterojunction structure of organic bi-layer solar cells made of small-molecules. The structure is formed by applying heat treatment to the cells with a structure of ITO/PEDOT:PSS/N,N’-diphenyl-N,N’bis(3-methylphenyl)-1,1’-deiphenyl-4,4’-diamine (TPD, 30 nm)/C60 (60 nm)/Ag. By the application of heat treatment at 140 °C, the photocurrent was greatly improved from 1.0 mA/cm2 to 3.0 mA/cm2 and the energy conversion efficiency reached 1.1 % under the AM 1.5, 100 mW/cm2 irradiation. From the cross-sectional SEM observation, organic layer is found to form a bulk-heterojunction structure by the infiltration of TPD into the C60 layer. The use of other aromatic amines instead of TPD was also effective for the formation of bulk-heterojunction structure in combination of C60. This bulk-heterojunction forms channels perpendicular to the organic layers, which is advantageous over the conventional bulk-heterojunction structure made of conductive polymers.
9:00 PM - S6.46
Nanostructured Flexible Solar Cells by the Nanoimprinting Technique
Myung-Su Kim 1 , Jin-Sung Kim 4 , Yiying Zhao 1 , Max Shtein 1 3 , L. Jay Guo 4 3 , Jinsang Kim 1 2 3
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3 Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractA major cause of the low power conversion efficiency in polymer-based PV cells is the trade-off between light absorption and exciton diffusion to the donor and acceptor interface, where charge separation can occur. Bulk heterojunction (BHJ) polymer PV cells have been made to reduce the distance to the D-A interface and thereby improve conversion efficiency. However, disordered BHJ devices are ultimately limited by poor charge extraction due to tortuary paths for the geminate carriers with the D-A layers. In this work we apply nanoimprint lithography to generate highly ordered nanoscale interfaces between the D-A components, resulting in substantially increased interfacial area and shortest collection paths for the dissociated carriers, and thus a higher overall power conversion efficiency. We systematically investigated process-structure-performance relationship by varying nanoimprinting temperature, imprinting pressure, imprinting time, and exploring various substrate treatments, differing imprinted patterns, and deposition methods.
9:00 PM - S6.47
Development of Pentacene-C60 Superlattice Bulk Heterojunction Organic Photovoltaic Cells
Jun Sakai 1 , Tetsuya Taima 2 , Kazuhiro Saito 2
1 Advanced Technologies Development Laboratory, Matsushita Electric Works, Ltd., Kadoma, Osaka Japan, 2 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki Japan
Show Abstract We report new bulk heterojunction(BHJ) device structure including superlattice in small molecule organic photovoltaic(PV) cells.The purpose of this study is development of BHJ PV cells employing pentacene and C60. Pentacene is well known as a high mobility material in OTFT. And also it is attractive as a photovoltaic material since high mobility is an indispensable property for high efficiency PV cells and pentacene has good photo absorption properties in visible range. Bilayer heterojunction PV cells employing Pentacene/C60 have already reported and indicated good PV performance. [1] But BHJ PV cells of Pentacene/C60 haven’t reported yet.Before investigation of BHJ cells we evaluated bilayer heterojunction properties of Pentacene/C60. As a result, we got following photovoltaic characteristics: Jsc of 6.6mA/cm2, Voc of 0.29V, FF of 0.48, PCE of 0.93% in AM1.5G 100mW/cm2. Firstly we tried to fabricate BHJ layer of Pentacene/C60 by co-evaporation which is effective in phthalocyanine/C60 PV cells. But all characteristics deteriorated (PCE of 0.03%) compare to bilayer system. Surface morphology observation by SEM showed large clusters and inhomogeneous film. Probably pentacene molecule gathers and orders easily in deposition so it is difficult to blend pentacene and C60 homogeneously with nano-scale.Next we applied layer by layer deposition method to pentacene/C60 layer. As a result, it was found that alternated multilayer of pentacene/C60 was effective to improve all PV characteristics. In the end optimization of multilayer structure of Pentacene/C60 (each layer thickness: 1-3nm) and applying pin structure led to following good PV characteristics: Jsc of 8.1mA/cm2, Voc of 0.40V, FF of 0.48, PCE of 1.6% in AM1.5G 100mW/cm2. Pentacene/C60 superlattice structure was directly observed by cross section TEM images. This suggests that charge carriers separation in this system occurs at each interface of multilayer and built-in potential generated by pin structure transports charge carriers with tunneling effect.[1]S.Yoo, B.Domercq, B.Kippelen, Appl.Phys.Lett., Vol85, No.22, 29 Nov. (2004)
9:00 PM - S6.48
Carbon Nanotube Sheets as Top Transparent Charge Injectors in OLEDs
Christopher Williams 1 2 , Mei Zhang 1 , Shaoli Fang 1 , Raquel Ovalle 1 2 , Sergey Lee 1 , Ray Baughman 1 3 , Anvar Zakhidov 1 2
1 Nanotech Institute, The University of Texas at Dallas, Richardson, Texas, United States, 2 Department of Physics, The University of Texas at Dallas, Richardson, Texas, United States, 3 Department of Chemistry, The University of Texas at Dallas, Richardson, Texas, United States
Show Abstract9:00 PM - S6.49
White OLEDs With Transparent CNT Charge Injectors and Magic-Sized CdSe Quantum Dots
Christopher Williams 1 2 , Raquel Ovalle 1 2 , Krutarth Trivedi 1 3 , Sergey Lee 1 , Anvar Zakhidov 1 2
1 Nanotech Institute, The University of Texas at Dallas, Richardson, Texas, United States, 2 Department of Physics, The University of Texas at Dallas, Richardson, Texas, United States, 3 Department of Electrical Engineering, The University of Texas at Dallas, Richardson, Texas, United States
Show Abstract9:00 PM - S6.5
Buffer Layer Effect on the Structural and Electrical Properties of Rubrene-based Organic Thin-film Transistors.
J. H. Seo 1 , Chung Nam Whang 2 , Kyung-Hwa Yoo 1 , Gap Soo Chang 1 , T. Pedersen 2 , A. Moewes 2
1 Institute of Physics & Applied Physics , Yonsei university, Seoul Korea (the Republic of), 2 , University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Show Abstract9:00 PM - S6.6
High-performance Organic Field-effect Transistors Based on Crystalline Polymer Blends and Block Co-polymers with Low Percolation Threshold.
Shalom Goffri 1 , Christian Müller 2 , Natalie Stingelin-Stutzmann 3 , Dag Breiby 4 , Christopher Radano 5 , Richard Thompson 7 , Jens Andreasen 4 , Martin Nielsen 4 , Henri Chanzy 6 , René Janssen 5 , Paul Smith 2 , Henning Sirringhaus 1
1 , University of Cambridge, Cambridge United Kingdom, 2 , ETH , Zürich Switzerland, 3 , Queen Mary, London United Kingdom, 4 , Risø National Laboratory, Risø Denmark, 5 , TU Eindhoven, Eindhoven Netherlands, 7 , University of Durham, Durham United Kingdom, 6 , CNRS-CERMAV, Grenoble France
Show AbstractBlock-copolymers are promising building blocks for electronic and optical devices that require structural control on a nanometer scale. They typically combine an amorphous polymer covalently bound to a crystalline or amorphous polymer. Recently we reported the synthesis of a block-co-polymer containing regio-regular poly(3-hexylthiophene) (P3HT) and linear polyethylene (PE)[1]. This system combines a high mobility semi-crystalline semiconducting polymer (P3HT) with a highly crystalline insulating polymer (PE). This first conjugated crystalline-crystalline block-copolymer system opens new ways of controlling the microstructure in semiconducting polymer films leading to new morphologies. Here we present different pathways of processing thin films using crystalline-crystalline block-copolymers and the corresponding blend system starting from solution or melt. The microstructures obtained are characterized with a range of techniques including optical microscopy, wide angle x-ray diffraction, Rutherford backscattering and differential scanning calorimetry. We fabricated thin film field-effect transistors to investigate the charge transport properties of the blends and block-co-polymer films. These films show new morphologies leading to high charge carrier mobilities and low percolation thresholds. We prove generality of our processing technique by applying the principles obtained form the P3HT/PE model system to various other semi-conducting/insulating polymer systems. [1] C. P. Radano, O. A. Scherman, N. Stingelin-Stutzmann, C. Müller, D. W. Breiby, P. Smith, R. A. J. Janssen, E. W. Meijer, J. Amer. Chem. Soc., 127, 12502 (2005) “Crystalline-Crystalline Block Copolymers of Regioregular Poly(3-hexylthiophene) and Polyethylene by Ring-Opening Metathesis Polymerization”
9:00 PM - S6.7
Surface-induced Alignment of Liquid Crystalline Semiconductors by Command Surface for Organic Thin Film Transistors.
Takenori Fujiwara 1 , Jason Locklin 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract Recently the control of orientational order and crystallization of organic semiconductors have been proven to be important factors for determining the performance of organic thin film transistors (OTFTs). Several methods have been reported in order to control the orientational order of organic semiconductor liquid crystalline (LC) molecules for the anisotropic characteristics of carrier mobility. These include mechanical stretching, liquid-crystalline self organization, rubbing and surface treatments of dielectric layers. We demonstrate that the alignment of nematic liquid crystalline semiconductor films is achieved by a thin film of polymethacrylate with p-cyanoazobenzene side chains as a command layer, which was exposed to linearly polarized light (LPL) in advance. The thin film of the polymer with p-cyanoazobenzene side chains displays high thermostability and enhancement at elevated temperatures in photoalignment. We expect that the command surface could align LC semiconductor materials even if they possess a thermotropic, nematic LC phase in high temperature. We demonstrate that a main-chain of polyfluorene copolymer film is aligned perpendicular to LPL direction. We will report that field-effect mobility of the OTFTs used command layer as a gate dielectric insulator.
9:00 PM - S6.8
Photo-patternable Organic-Inorganic Hybrid Dielectrics for Organic Thin-film Transistors
Sunho Jeong 1 , Seong Hui Lee 1 , Jooho Moon 1 , Hyunjung Shin 2
1 Department of Materials Science and Engineering, Yonnsei University, Seoul Korea (the Republic of), 2 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractUsing a UV-crosslinkable organosiloxane-based organic-inorganic hybrid material, solution-processable gate dielectric layer for organic thin-film transistors (OTFTs) have been fabricated. The hybrid dielectric was synthesized by the sol-gel process in which an acid-catalyzed solution of Si alkoxide with UV-crosslinkable organic functional group and Zr alkoxide was used as a precursor material. Incorporation of a UV-sensitive functional group allowed to obtain high-resolution patterned films with about 5 μm linewidth using a conventional photo-lithography. The influences of UV illumination and heat-treatment on the patterning process were analyzed using attenuated Fourier transform infrared spectrometer. The current–voltage characteristic and capacitance–voltage characteristic were measured to investigate the electrical property of hybrid dielectric. To fabricate coplanar-type OTFTs, Au/Cr electrode was deposited onto the heavily doped silicon substrate with the organic-inorganic hybrid dielectric layer and then α,ω-dihexylquaterthiophene (DH4T) was drop-casted between source and drain electrode. An electrical performance of the fabricated transistor was measured to obtain electrical parameter such as on-off ratio, mobility, sub-threshold slope and threshold voltage.
9:00 PM - S6.9
Influence of the Device Structure in the Performances of Organic Field Effect Transistors.
Piero Cosseddu 1 2 , Simone Locci 1 2 , Emanuele Orgiu 1 2 , Annalisa Bonfiglio 1 2
1 Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy, 2 , INFM-S3 nanoStructures and bioSystems at Surfaces, Modena, Modena, Italy
Show Abstract
Symposium Organizers
Franky So University of Florida
Graciela B. Blanchet DuPont
Yutaka Ohmori Osaka University
S7: Thin Film Transistors I
Session Chairs
Wednesday AM, November 29, 2006
Room 304 (Hynes)
9:00 AM - **S7.1
Self-aligned Printing of High-performance Polymer Thin-film Transistors.
Yong-Young Noh 1 , Ni Zhao 1 , Xiaoyang Cheng 1 , Henning Sirringhaus 1
1 , University of Cambridge, Cambridge United Kingdom
Show Abstract9:30 AM - S7.2
Soft Lithography Fabrication of Fully Flexible and Transparent all Organic FETs for Large Area Applications.
Piero Cosseddu 1 2 , Simone Locci 1 2 , Emanuele Orgiu 1 2 , Ileana Manunza 1 2 , Annalisa Bonfiglio 1 2 , Ingo Salzmann 3 , Norbert Koch 3 , Jurgen P. Rabe 3
1 Dept. of Electrical and Electronic Engineering, University of Cagliari, Cagliari Italy, 2 , INFM-S3 nanoStructures and bioSystems at Surfaces, Modena, Modena, Italy, 3 Department of Physics, Humboldt University, Berlin Germany
Show AbstractSeveral techniques have been reported, so far, for the realization of polymeric contacts such as ink-jet printing, laser patterning, dry printing, paving the way for the fabrication of low-cost devices on large-area and on plastic substrates, opening a new market segment. Soft lithography is a possible alternative since it has low cost, it allows to achieve very high resolutions and it is suitable for roll to roll mass production processes. In this work we show the possibility to employ micro-contact printing for the realization of all organic FETs on plastic. The core of our devices is a thin, transparent and flexible polyethileneterephtalate film (1.6 µm thick) acting as gate dielectric and, at the same time, as mechanical support of the device1. Completely flexible and transparent devices, such as light emitting transistors and field effect chemo-sensors can be realized by employing this structure2, 3. We used pentacene, deposited by thermal sublimation, as semiconducting layer and PEDT/PSS to create the metal contacts. Gate electrodes were realized by spin coating, while source and drain electrodes were patterned by micro-contact printing. We fabricated typical p-type field effect transistors, with mobilities up to 2 x 10^(-1)cm^2/Vs and Ion/Ioff up to 10^(5), in a very simple and inexpensive way. Preliminary results, concerning the realization of all organic n-type FETs by employing such structure, will also be presented. It is worth to note that this technique allows the realization of bottom contact and top contact transistors. In order to have a reliable comparison between these two different configurations we realized both bottom contact and top contact devices on the same substrate and with the same active layer and, assisted by Scanning Probe Microscopy, we investigated how the structure itself and the active layer morphology influence the electrical properties in terms of hole mobility, Series Contact Resistance and parasitic capacitance effects4. The comparison between top-contact and bottom-contact devices shows interesting marked differences that can be mainly attributed to a different PEDOT:PSS/semiconductor interface quality, influencing the most meaningful parameters. Furthermore, starting from a recently developed application5, we employed this structure for the realization of all organic sensors on plastic. Interestingly, a clear difference in sensitivity has been noticed by using a bottom contact or a top contact configuration. References:[1] A. Bonfiglio, F. Mameli, O. Sanna, Appl. Phys. Lett. 82, 3550 (2003)[2] A. Loi, I. Manunza and A. Bonfiglio, Appl. Phys. Lett.[3] C. Santato, I. Manunza, A. Bonfiglio, F. Cicoira, P. Cosseddu, R. Zamboni, and M. Muccini Appl. Phys. Lett. 86, 141106 (2005).[4] P.Cosseddu and A. Bonfiglio, Appl. Phys. Lett. 88, 023506 (2006)[5] I. Manunza, A. Sulis and A. Bonfiglio, Appl. Phys. Lett. to be submitted
9:45 AM - S7.3
Nonvolatile Organic Memory and Nanowire Configurable FET Devices Based on Dopant-Controllable Polymer
Qianxi Lai 1 , Zhiyong Li 2 , Xuema Li 2 , Theodore Kamins 2 , Stanley Williams 2 , Zuhua Zhu 1 , Yong Chen 1
1 Department of Mechanical & Aerospacing Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Quantum Science Research, Hewlett-Packard Laboratories, Palo Alto, California, United States
Show AbstractUnlike Si-based semiconductor devices in which dopant concentrations cannot be changed after device fabrication, dopant concentration and device properties in an organic material/device can be changed electrochemically by applying an external electric field after fabrication. Based on this principle, we designed and fabricated new types of organic memory and nanoscale configurable FET devices by configuring the dopant concentration in the polymer materials.The memory device consists a poly[2-methoxy-5-(2’-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) polymer/inorganic ionic conductor RbAg4I5 bilayer sandwiched between two metal electrodes. When an external voltage exceeding a threshold value (> + 2.2 V or < -3.5V) is applied between the two metal electrodes, the conductance of the devices can be electrically switched on or off by injecting iodide dopant ions into or expelling them from the MEH-PPV layer. This nonvolatile memory device can be switched on and off reversibly and repeatedly with an on/off conductance ratio approaching four orders of magnitude, with a switching time as fast as 1 μs.The nanoscale configurable field effect transistor integrates a dopant-controllable organic MEH-PPV layer with a silicon-based nanowire source-drain channel. The gate structure consists of a RbAg4I5/MEH-PPV bilayer stack on a thin gate silicon dioxide layer on the top of a p-type Si channel. When a gate voltage exceeds a threshold value (> 4 V or < -2.5V), it changes the iodide dopant concentration and the Fermi level in the MEH-PPV polymer layer, which in turn changes the band-bending in the underlying Si channel and shifts the threshold voltage of the FET. An induced threshold voltage shift of more than 2V from its original value is observed in the FET and the change of the source-drain current is up to a factor of 1e5 with a retention time of more than 10 hours. This configurable FET can be switched repeatedly and reversibly for more than 1e5 cycles and with a switching time as short as 1 µs. Another unique feature of the configurable FET is that its source-drain current and threshold voltage can be tuned continuously to desirable values with gradually changing gate voltages. These dopant-configurable memory and FET devices may not only provide new functions such as defect-tolerance in Si-based nanoscale memory and logic circuits, but also lead to new types of exceedingly flexible and programmable circuits in the future.
10:00 AM - S7.4
High-Performance Low-Voltage Tetracene Phototransistors Employing Bilayer Polymer/AlOx Gate Dielectrics with NiOx Electrodes.
Jeongmin Choi 1 , Kimoon Lee 1 , Do Kyung Hwang 1 , Seongil Im 1
1 Institute of Physics and Applied Physics, Yonsei University , Seoul, Sudaemoon-ku, Korea (the Republic of)
Show Abstract10:15 AM - **S7.5
Interfacial Phenomena Affecting Charge Transport In Small Molecule Organic Thin-Film Transistors.
Antonio Facchetti 1 , Choongik Kim 1 , Myung-Han Yoon 1 , Tobin Marks 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Show Abstract10:45 AM - S7.6
Integration of Polymer Thin-Film Transistors by Lift-Off Photolithographic Patterning Approach.
Flora Li 1 , Yiliang Wu 2 , Beng Ong 2 , Arokia Nathan 1
1 E&CE, University of Waterloo, Waterloo, Ontario, Canada, 2 , Xerox Research Centre of Canada, Mississauga, Ontario, Canada
Show AbstractResearch in organic thin-film transistors (OTFTs) has opened up numerous opportunities for organic electronics in areas requiring low-temperature processing, large area coverage, mechanical flexibility, and overall low cost. Large-scale implementation of organic electronic devices necessitates the development of a suitable OTFT fabrication strategy with capabilities to pattern device layers and create interconnect structures, so that integration of OTFTs into circuits and systems can be accomplished. Photolithography, the workhorse patterning technology of today’s silicon-based microelectronics industry, presents a potential solution for organic electronics fabrication. However, a number of challenges emerge when the standard photolithography procedure is applied to organic devices, including chemical incompatibilities between photoresist and organic materials, and UV-induced changes in organic materials due to the exposure step. By working around these limitations, we present a photolithographic patterning approach tailored for organic transistors and OTFT circuit integration. Our method relies on lift-off techniques for patterning the polymer semiconductor layer and the source-drain contacts. Poly[5,5’-bis(3-alkyl-2-thienyl)-2,2’-bithiophene)] (PQT-12), a poly(thiophene) synthesized by the Xerox Research Centre of Canada, was employed as the semiconductor layer.1 Photolithographically-defined bottom-gate OTFTs featuring solution-processed PQT-12 semiconductor layer, thermally-evaporated Cr-Au source/drain contacts, and plasma-enhanced chemical vapour deposited (PECVD) silicon nitride gate dielectric exhibited on-off current ratio on the order of 105–107 and field-effect mobility of 0.02–0.08 cm2/V-s. These results displayed improved device characteristics compared to previously-reported solution-processed polymer TFTs on silicon nitride gate dielectric. These improvements can be attributed to the high performance offered by the PQT-12 semiconductor layer, along with a carefully optimized surface modification scheme for the silicon nitride gate dielectric. The processing details, device characteristics, and the surface modification technique for the silicon nitride gate insulator will be discussed in detail in the presentation. The development of photolithographically-defined OTFT pixel circuits for active matrix display backplanes, which can contribute to the evolution of low-cost large-area flexible displays, will be addressed in the presentation. 1 B.S. Ong, Y. Wu, P. Liu, S. Gardner, N. Zhao, and G. Botton, J. Am. Chem. Soc. 126, 3378 (2004).
11:00 AM - S7: Thin Film I
BREAK
11:30 AM - **S7.7
Vertical Type Organic Transistors and Light Emitting Transistor
Kazuhiro Kudo 1 2
1 Electrical and Mechanical Eng., Chiba University, Chiba Japan, 2 , OIDTA, Chiba Japan
Show AbstractRecently all-organic display devices are expected by combining organic light emitting diode (OLED) with organic transistors, because organic transistors driving OLED are necessary to achieve flexible and large scale active-matrix-displays. To be practical, however, it is necessary to operate with a low voltage and have sufficient reliability. Conventional field-effect transistors (FETs) using organic materials have low-speed, low-power, and relatively high operational voltage mainly due to their low-mobility and high-resistivity. It is known that the vertical type transistors such as static induction transistors (SIT) are promising devices because of the high-speed and high-power operation. The excellent characteristics of the SIT arise from the vertical structure with a very short distance between the source, drain, and gate electrodes. From this point of view, organic light emitting transistors (OLETs) combined with the vertical type organic FET and OLED were proposed. The OLETs have several advantages, such as low-voltage, high-speed operation, high-luminous efficiency, and simple fabrication process. We have investigated the basic characteristics of OLETs and discussed their device performances and operational mechanism. Relatively high luminance modulation by low gate voltage was observed in the OLET by optimizing the device structure. These results demonstrate that the OLETs described here are expected for the application to flexible sheet displays.
12:00 PM - S7.8
Improvement of Short Channel Mobility and Operational Stability of Pentacene Bottom-contact Transistors with a Sulfuric Acid and Hydrogen Peroxide Mixture (SPM) Treatment of Au Electrodes.
Haruo Kawakami 1 , Takahiko Maeda 1 , Hisato Kato 1
1 Material and Science Laboratory, Fuji Electric Advanced Technology Co., Ltd., Hino, Tokyo, Japan
Show AbstractThe bottom-contact structure has a merit that small-size organic field effect transistor (OFET) can easily be fabricated because conventional lithography is applicable to the fabrication of source/drain (S/D) electrodes. However, its field-effect mobility is low compared with that of the top-contact structure, and it decreases with channel length. This is due to the large contact resistance between the S/D electrodes and the organic active layer. We report improvement of the short channel mobility of pentacene bottom-contact transistors with a surface treatment of the S/D electrodes. The fabricated OFETs had the channel width of 1 mm. The channel lengths were varied from 3 to 30 mm. Ta film and Ta2O5 film formed with anodization process acted as gate electrode and gate insulator, respectively. Then, Au film was evaporated as the S/D electrodes, and patterned with the lift-off technique. By immersing the Au S/D electrodes in a sulfuric acid and hydrogen peroxide mixture (SPM) before pentacene evaporation on them, the contact resistance between the Au electrodes and pentacene was significantly decreased. Namely, the contact resistance with the SPM treatment is less than 10 kΩ, which is almost two orders lower than that without the SPM treatment, 600 kΩ. The fabricated bottom-contact OFET revealed a field-effect mobility of more than 0.66 cm2/Vs at a channel length of 3μm, which is comparable to that of the top-contact OFET with a 50μm channel length. The value of the field-effect mobility showed little dependence on the channel length ranging from 3 to 30 μm. The Fermi level of pentacene on Au film with the SPM treatment is approximately –4.6 eV, which is lower by 0.2 eV than that without the SPM treatment, –4.4 eV. This shift suggests acceptor doping of pentacene on the Au electrode, and indicated the injection barrier was lowered by 0.2 eV by the SPM treatment. Time-of-flight secondary ion mass spectroscopy analysis showed that sulfates exist on the Au surface with the SPM treatment. These results suggest that the sulfate ions acts as acceptors, and lowers the Fermi level of pentacene.The transfer characteristics of the OFET with the SPM treatment were stable even after 44days storage in air without any passivation. Moreover, the threshold voltage (Vth) shift under continuous application of gate voltage bias was proportional to (stress time) 0.22 in the OFET with the SPM treatment, which was slower than that without the SPM treatment, (stress time) 0.28. The shifted value of the Vth mostly recovered toward the original value with a reverse bias of less than one minute. The Vth shift showed a dependence on the initial drain current. At the OFET with a channel length of 5μm, the drain current was 88% of the initial value, and the Vth shift was -0.49V, after 800min. stress with gate voltage of -6V and initial drain current of 200μA.
12:15 PM - S7.9
Logic Circuit with Multilayer Structure using Organic Ferroelectrics.
Satoshi Horie 1 , Kenji Ishida 1 , Shuichiro Kuwajima 1 , Hirofumi Yamada 1 , Kazumi Matsushige 1
1 Dept of ES&E, Kyoto Univ. Graduate School of Engr., Kyoto Japan
Show AbstractElectric logic and memory circuit, which are based on CMOS transistors, keep reducing the size of device for high density integration. There are, however, technological and physical limits of device shrinkage due to the difficulties of conventional lithography technology, logic operation theory and cost. New concept, materials and fabrication process approaches will be required to breakthrough and seeds of new technology. Logic circuit and memory using organic ferroelectrics were investigated in this study. The vinylidene fluoride(VDF) oligomer, which is an organic ferroelectric with low molecular weight, was used as organic ferroelectric. Multilayer structure, Al/VDF/Al/VDF/Al, was fabricated on Quartz substrate by vacuum deposition. A rectangular polarization hysteresis loop was observed in VDF oligomer thin film (thickness: 150-200nm) of each stacked ferroelectric layer and the switching characteristic evaluated as AND and OR gate by the polarization reversal of the fabricated stacked structure. The 2 ferroelectric capacitors can work the 2 input 1 output type logic element. It operates as a logic gate by defining a coercive voltage as the input and a charge generated by polarization reversal as the output. Therefore, the organic ferroelectric multilayer could treat as AND, OR, NOR, and NAND gate by controlling direction of polarization.
12:30 PM - S7.10
Optoelectronic Switch and Memory Devices Based on Polymer Functionalized Carbon Nanotube Transistors.
Vincent Derycke 1 , Julien Borghetti 1 , Stéphane Lenfant 2 , Pascale Chenevier 1 , Arianna Filoramo 1 , Marcelo Goffman 1 , Dominique Vuillaume 2 , Jean-Philippe Bourgoin 1
1 SPEC, CEA Saclay, Gif sur Yvette France, 2 IEMN, CNRS, Villeneuve d'Ascq France
Show Abstract12:45 PM - S7.11
Control of Parasitics in OFETs Through Self-aligned Processing.
Ivan Nausieda 1 , Ioannis Kymissis 1 2 , Vladimir Bulovic 1
1 EECS, MIT, Cambridge, Massachusetts, United States, 2 EE, Columbia University, New York, New York, United States
Show AbstractS8: Thin Film Transistors II
Session Chairs
Wednesday PM, November 29, 2006
Room 304 (Hynes)
2:30 PM - **S8.1
Reaction Chemistry and Assembly in Molecular Electronic Devices.
Colin Nuckolls 1
1 , Columbia University, New York, New York, United States
Show Abstract3:00 PM - S8.2
Structure of Ultrathin Pentacene Films on a Silicon Dioxide Dielectric.
Sandra Vos 1 , Eung-Gun Kim 3 , Demetrio Filho 3 , Jean-Luc Bredas 3 , C. Daniel Frisbie 1 , Michael Ward 1 , Michael Toney 2
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 3 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, California, United States
Show AbstractWe report specular and in-plane X-ray diffraction, using CuKα1 and synchrotron radiation, of pentacene films thermally evaporated on an amorphous silicon dioxide dielectric. The first layer of pentacene molecules adjacent to the a-SiO2 crystallize in a rectangular unit cell with the long axis of the molecules perpendicular to the substrate surface. Subsequent layers of pentacene crystallize in a slightly oblique in-plane unit cell that evolves as thickness is increased. The rectangular monolayer phase of pentacene does not persist when subsequent layers are deposited. Specular diffraction with synchrotron radiation of a 160 Å pentacene film (~ 10 layers) revealed growth initiation of a bulk-like phase and persistence of the thin-film phase. Pentacene molecules are more tilted in the bulk-like phase and the in-plane unit cell is slightly more oblique. Pentacene grains grow randomly oriented with respect to the substrate surface (out-of-plane) in films near 650 Å in thickness. The single crystal bulk phase of pentacene is observed from specular diffraction (CuKα1) of a 2.5 μm film. These results suggest that the thickness of pentacene films on a-SiO2 is an important aspect in the comparison of crystal structure and electronic transport in organic thin film transistors. In particular the thin-film phase, the most important phase structure in transistor applications, has a different structure than bulk pentacene.
3:15 PM - S8.3
Surface Modifications using Thiol Self-Assembled Monolayers on Au Electrodes in Organic Field Effect Transistors
Katsumi Tanigaki 1 5 , Nobuya Hiroshiba 1 , Ryotaro Kumashiro 1 , Hisao Ishii 2 , Masahiro Yamashita 3 , Shinya Takaishi 3 , Kazuhito Tsukagshi 4
1 Department of Physics, Graduate of Science, Tohoku University, Sendai Japan, 5 CREST, JST, Saitama Japan, 2 Research Institute of Electrical Communication, Tohoku University, Sendai Japan, 3 Department of Chemistry, Tohoku University, Sendai Japan, 4 Low-Temperature Physics, Riken, Wako Japan
Show AbstractOrganic field effect transistors (OFETs) are important considering the future applications to electronic devices, and are currently being investigated with lots of enthusiasm. In order to improve the properties of OFETs, the methodologies have not still been established. Especially, one of the most important key issues will be the interfacial problems between organic thin-films and gate-insulators and/or electrodes. This is now drawing much intense attention in this field.The interfacial modification using (Self-Assembled Monolayers) SAMs is a well-known good technique for the surface control and can provide microscopically good interface regulations. Two parts in FETs can be considered for applying this technique. One is the interface between gate insulators and organic semiconductors and the other is the Interface between electrodes and organic semiconductors. Extensive studies have been made for the former by many researchers and better surface modifications have been reported to be achieved on SiO2 gate insulators when silane-type molecules are used as SAMs. On the other hand for the latter, the SAMs treatments on the gold electrodes using thiol molecules are reported, but the effects are not clear and little influences on the FET performances are reported sometimes. Therefore, it is very warranted to study the real influences and set up the best methodology of the SAMs modifications to the electrodes. In the present study, interfacial modifications of source and drain gold electrodes using thiol molecules have been carried out for pentacene-FETs and their influence on the FET action parameters have been studied, using three benzene thiol (BzT) molecules as SAMs with different functional groups, 4-methyl (4-Me), 4-nitro (4-N) and 4-amino (4-A). We report in this conference that the effects of the SAMs modifications of the gold electrodes on the FET performances are very sensitive to the preparation conditions of these SAMs. We will demonstrate that the field effect of #micro# in OFETs can be strongly increased by the optimized SAMs modification conditions and this can be interpreted in terms of the higher efficiency of carrier injections attained by SAMs, because it can be shown using Atomic force Microscope (AFM) and low-glancing angle X ray diffraction (L-XRD) that both the grain size and the molecular orientations of the pentacene thin films do not change before and after the SAMs modifications to the electrodes. The higher injection of carriers can be understood by holes transferred from the SAMs substituents to pentacene molecules and the degree of such hole transfer has been estimated to be 0.75 holes/pentacene-mole in the case of 4-NBzT. In conclusion, the SAMs modification using thiol molecules with functional groups to the gold electrodes becomes a good methodology for enhancing carrier injection in organic FETs, when a special care is taken for optimization in the preparation conditions.
3:30 PM - S8.4
Rubrene Single-crystal Organic Field Effect Transistor with Laser Ablated BaTiO3 Epitaxial Growth Thin-film as High-k Insulator.
Nobuya Hiroshiba 1 , Ryotaro Kumashiro 1 2 , Taishi Takenobu 2 3 , Yoshihiro Iwasa 2 3 , Kenta Kotani 4 , Iwao Kawayama 4 , Masayoshi Tonouchi 4 , Katsumi Tanigaki 1 2
1 Department of physics ,Guraduate school of science, Tohoku Univ., Sendai Japan, 2 , JST-CREST, kawaguchi, Saitama, Japan, 3 Institute for Material Research, Tohoku Univ., Sendai Japan, 4 Institute of Laser Engineering, Osaka Univ., Suita Japan
Show Abstract3:45 PM - S8.5
Characteristics ofTthermally-evaporated Crystalline Rubrene Thin Films.
Se Woung Park 1 , Do kyoung Hwang 1 , Seongil Im 1
1 Institute of Physics & Applied Physics , Yonsei University , Seoul, Sudaemoon-ku, Korea (the Republic of)
Show Abstract4:00 PM - S8.6
Patterning Effects on Poly (3-hexylthiophene) Organic Thin Film Transistors using Photolithographic Processes.
Huiping Jia 1 , Erich Gross 1 , Robert Wallace 1 , Bruce Gnade 1
1 , University of Texas at Dallas, Richardson, Texas, United States
Show Abstract4:15 PM - S8: ThinFilm II
BREAK
4:30 PM - **S8.7
High Performance Stable Thin Film Field Effect Transistors (TFTs) from Novel Organic Semiconductors
Hong Meng 1
1 , DuPont Company, Wilmington, Delaware, United States
Show AbstractTransistors are essential components and fundamental building blocks for the modern electronics and microelectronics. Currently, inorganic field-effect transistors (FETs) have dominated the mainstream microelectronics industry such as memory devices, integrated circuits, and microprocessors used in personal computers and laptops. Organic thin film field-effect transistor (OTFT) technology is emerging as a low cost alternative to amorphous Si technology (mobility 0.3-1.0 cm2/Vs). Organic thin film transistor (OTFT) technology involves the use of organic semiconductor materials in electronic components, electronic backplane for full color active matrix displays, low cost radio frequency identification cards (RFIDs) tags, electronic papers, sensors and memory devices. A critical technical challenge in this area of research is to increase the mobility and improve the environmental stability. OTFTs have been fabricated incorporating semiconductors such as, polythiophenes, oligothiophene derivatives and linearly fused polycyclic aromatic compounds such as pentacene and its derivatives, yet either the stability or the performance of these semiconductor types is limited. Our researchers at DuPont CRD have, however, recently developed high performance and stable organic semiconductors with carrier mobility rivaling that of traditional TFT materials. We present our recent results on the design, synthesis and the OTFT device stability test of these novel organic semiconductors. Our first generation of semiconductors exhibits an average mobility of 0.5 cm2/Vs and the on/off ratio over 107. An even higher performance with a mobility of 1.5 –2.5 cm2/Vs and on/off ratio of 107 has been achieved using our second and third generation of semiconductor materials. We have investigated the device stability both in terms of shelf and the operating lifetime. All the materials demonstrated the high stability and durability.
5:00 PM - **S8.8
The Design of High Mobility Semiconducting Polymers.
Iain McCulloch 1 , Clare Bailey 1 , Martin Heeney 1 , Maxim Shkunov 1 , David Sparrowe 1 , Steven Tierney 1 , Joe Kline 3 , Michael Chabinyc 2
1 Organic Electronics, Merck Chemicals, Southampton United Kingdom, 3 , NIST - Gaithersburg, Gaithersburg, Maryland, United States, 2 , Palo Alto Research Center, Palo Alto, California, 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 processablematerials. Polymeric semiconductors offer an attractive combination in terms of appropriate solution rheology for printing processes, mechanical flexibility for rollable processing and applications, but their electricalperformance has been significantly lower than amorphous silicon, limiting their application. In this work, we report the design, synthesis and characterisation of a range of thieno[3,2-b]thiophene co-polymers exhibiting high charge carrier mobilities. A detailed study of the polymerthin film morphology reveals an extremely ordered and oriented microstructure. Field effect transistors were fabricated, and their performance and lifetimes will be discussed.
5:30 PM - S8.9
Examination of Accumulation, Depletion, and Inversion in Organic Field Effect Transistors Studied by Displacement Current Measurement.
Hisao Ishii 1 , Satoshi Ogawa 2 , Yasuo Kimura 2 3 , Michio Niwano 2 3
1 Center for Frontier Science, Chiba University, Chiba-shi Japan, 2 RIEC, Tohoku University, Sendai Japan, 3 CREST, JST, Kawaguchi Japan
Show Abstract Organic field effect transistors (OFETs) have recently attracted much attention. Although understanding for the basic mechanism of OFET is indispensable for better device performance, there still remain open questions. Especially, the origin of carriers in the device is both basic and practical question. There are two origins for carriers in OFET. One is carrier generation inside organic semiconductor layer; by changing the local Fermi level, carrier accumulation, depletion and even inversion are expected on the basis of the theory of inorganic semiconductors. The other is carrier injection; accumulated carriers at the channel are supplied through the injection from source electrode. Very recently, ambipolar operation of OFET has been reported by controlling such injection properties, suggesting the latter origin. In order to understand this issue, not only measuring the transfer characteristics of OFET but also an additional method to characterize the behavior of carriers are necessary. Recently, we have demonstrated that displacement current measurement (DCM) method enables us to probe various properties of carriers in OFETs; the carrier injection property from metal electrodes to organic materials, the effective area of charge sheet in the channel, and the amounts of carriers accumulated in the device, the density of trapped charge, and so on[1]. This technique is suited to understand the origin of carriers. In this paper, we will report on the DCM results of pentacene and fullerene OFETs. They are well known as typical p-type and n-type transistors. When the Au electrodes are used, DCM curves showed the change of current due to accumulation and depletion behavior. But, current change due to inversion was not observed although our measurement was enough slow (1.33mHz) to induce possible thermal carrier generation inside the organic layer. This result suggests that no carrier can be generated under bias in intrinsic organic semiconductors due to large band gap. Next we changed from Au to Al electrodes. We observed that the current is increased at both positive and negative gate voltage, indicating “accumulation and inversion” due to carrier injection from electrodes. In the presentation, the effect of alkane layer on the SiO2 dielectrics will be also reported. References[1]S. Ogawa, et al., Jpn. J. Appl. Phys 42(10B) L1275 (2003), Synth. Mat 153(1-3) 253(2005), Appl. Phys. Lett. 86. 252104 (2005), Jpn. J. Appl. Phys 45(1B) 530(2006)
5:45 PM - S8.10
Availability of Liquid Crystalline Materials for Organic Polycrystalline Semiconductor Thin Films
Hiroaki Iino 1 , Jun-ichi Hanna 1
1 Imaging Science and Engineering Lab, Tokyo Institute of Technology, Yokohama Japan
Show AbstractOrganic polycrystalline thin films of pi-conjugated aromatic molecules such as pentacene and oligothiophenes have attracted high attention in recent years because of a high mobility of 0.1 - 1 cm2/Vs comparable to that of hydrogenated amorphous silicon. However, the polycrystalline materials inevitably have the problem of grain boundaries that are responsible for the deterioration of charge carrier transport properties and the long-term stability of materials. Therefore, it is quite important to control the grain boundaries in the polycrystalline thin films when the polycrystalline thin films are prepared. In fact, the very thin films of pentacene less than 100nm, where the films have different molecular alignment from that in the bulk crystal, are utilized.On the other hand, it is very plausible that the liquid crystalline materials, which have the enhanced anisotropy with hydrocarbon chains in molecular shape and the pre-ordered molecular alignment in the mesophase, have a chance to control the molecular alignment in the crystal. Thus, we have investigated crystallographic features and charge carrier transport properties in the polycrystalline films of both triphenylene and terthiophene derivatives, which are representative materials of discotic (disc-like) and calamitic (rod-like) liquid crystals, such as hexahexylthiotripheneynene (HHTT) and 1,12-octylterthiophene (8-TTP-8). The polycrystalline films of these liquid crystals exhibit particular polarized optical microscopy textures i.e., the hexagonal and co-circular crack patterns for discotic and calamitic liquid crystals, indicating that the molecular alignment in the liquid crystalline phase is well preserved. The polycrystalline films and exhibit clear hole transport for vertical direction even in a 15 μm thick film by time of flight method. The hole mobilities for HHTT and 8-TTP-8 are 0.2 and 0.3 cm2/Vs at room temperature, respectively. The results indicate formation of less grain boundaries across conduction channels. On the other hand, the carrier transports properties for non-liquid crystalline triphenylene and terthiophene exhibit that carriers are annihilated in the bulk, which have many deep trap sites in grain boundaries. The present results indicate that the liquid crystalline molecule is a good candidate for preparing quality organic polycrystalline semiconductor thin films in electronic applications.
S9: Poster Session: Organic Devices
Session Chairs
Thursday AM, November 30, 2006
Exhibition Hall D (Hynes)
9:00 PM - S9.1
Electrochemical Transistor Fabricated by Polythiophene Polymer Nano-sheets.
Jun Matsui 1 , Yoshitaka Sato 1 , Takeshi Mikayama 1 , Tokuji Miyashita 1
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, Japan
Show Abstract In the past several years, research for organic materials, that are applicable to macroelectronics have aroused considerable interest because of the unique advantages such as low fabrication cost, high mechanical flexibility and lightweight. Recently, several flexible electronic devices, which utilize the advantage of organic materials have been proposed and fabricated. To fabricate such flexible electronic devices, organic transistor is one of the most important components. Therefore, the fabrication of organic field-effect transistors (OFETs) becomes one of the active area of research in organic electronics. In conventional OFETs, high gate voltage (several tens of volts) is required to operate the OFET because of poor capacitive coupling through low gate dielectric SiO2. On the other hand several groups reported organic electrochemical transistors (OECT), which modulated IDS by electrochemical doping and de-doping reaction of conjugated polymers. Because the OECT utilized the electrochemical reaction, the gate operation voltage was relatively low (several volts). Herein we describe the fabrication of OECT using a π conjugated polymer nanosheets. Poly(3-hexylthiophene)(PHT) was used as π conjugated polymer and mixed with poly(N-dodecylacrylamide)(pDDA), which form a stable monolayer at the air/water interface. The formation of a monolayer from a mixture of PHT and pDDA was investigated by surface pressure-area isotherm measurements. The pDDA/PHT mixed polymer demonstrates a steep rise in the surface pressure with decreasing surface area, which indicate the condensed monolayer can be formed from the pDDA/PHT mix polymer. The monolayer can be transferred onto a solid substrate using the Langmuir-Blodgett technique and the thickness of the monolayer (π conjugated polymer nanosheet) was determined as 2.5 nm by AFM measurements. To construct the electrochemical transistor, the π conjugated polymer nanosheets was deposited onto the solid substrate with source and drain. A silicone rubber was used to create a rectangle well and CH3CN/LiPF6 electrolyte was pour into the space. The well was capped by an ITO electrode, which serves as a gate electrode. In the electrochemical transistor, the polymer nanosheets was electrochemically doped by a gate electrode through the electrolyte. When the gate voltage (Vg) was not applied (Vg = 0), the PHT/pDDA nanosheets acts as an insulator because the PHT was not doped. Subsequently, the Vg was applied at -1.2 V to electrochemically doped the π conjugated nanosheet. The on/off ratio was calculated to be 1.1e4 by using IDS(VDS=-0.5[V]) at VG=-1.2[V] v.s. that at VG=0[V]. The charge consumed to operate the OECT was one to two orders smaller than the reported OECT constructed from electropolymerized polythiophene. The effects of nanosheets thickness, electrolyte concentration to the transistor performance, such as on/off ratio, gain factor will be discussed.
9:00 PM - S9.10
MIS-type Organic Light-emitting Transistor on Plastic Substrates
Takuya Hata 1 2 , Kenji Nakamura 1 2 , Katsunari Obata 1 3 , HIroyuki Endoh 1 4 , Atsushi Yoshizawa 1 2 , Kazuhiro Kudo 1 5
1 , OITDA, Chiba Japan, 2 , Corporate R&D Laboratories, Pioneer Corporation, Tsurugashima, Saitama Japan, 3 , Research & Development Center, Dai Nippon Printing, Kashiwa, Chiba Japan, 4 , Fundamental and Environmental Research Laboratories, NEC Corporation, Tsukuba, Ibaraki Japan, 5 , Faculty of Engineering, Chiba University, Chiba Japan
Show Abstract In recent years, progress of the organic transistors is remarkable , and there are many reports on the active matrix organic light-emitting diode (OLED) displays using organic transistors. Furthermore various self-radiation types of organic light-emitting transistors (OLETs) have been reported. In our presentation, we have demonstrated that metal-insulator-semiconductor type light-emitting transistor (MIS-OLET) on plastic films. The typical device performances are ID=13.8mA/cm2, L=290cd/m2 at VSD=-10V, VG=-50V. ON/OFF ratio are 14 for source-drain current, 53 for luminance. This poor ON/OFF ratio was caused by the leakage current through insulator layer and the current is not modified effectively by the gate voltage. Therefore we employed the current blocking layer to improve the ON/OFF ratio. The newly developed MIS-OLET showed excellent characteristics .The detailed fabrication processes and improved performances are shown in the presentation. The MIS-OLET is expected to bring great contributions to flexible active matrix organic displays with fine pixels, because this device can be fabricated uniformly with a standard process. This work belongs to “Advanced Organic Device Project” which OITDA contracted with New Energy and Industrial Technology Development Organization (NEDO).
9:00 PM - S9.11
Electronic Memory Effects in Diodes from a Zinc Oxide Nanoparticle –polystyrene Hybrid Material.
Frank Verbakel 1 2 , Stefan Meskers 1 2 , René Janssen 1 2
1 SMO-M2N, Eindhoven University of Technology, Eindhoven Netherlands, 2 , Dutch Polymer Institute (DPI), Eindhoven Netherlands
Show AbstractCurrent-voltage characteristics of diode structures with an active layer of a zinc oxide nanoparticle dispersed in polystyrene (1:2 by weight) deposited by spin coating from solution are investigated. Aluminum and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) are used as electrodes for these hybrid devices. After a forming step, the conduction under reversed bias voltage can be raised or lowered in a gradual and reversible manner by applying forward and reverse bias voltages, respectively. The forming process itself is interpreted in terms of desorption of molecular oxygen from the ZnO nanoparticle surface, induced by injection of holes via the PEDOT:PSS contact, leading to a higher n-type conductivity via interparticle ZnO contacts. The electronic memory effects are attributed to a reversible electrochemical process at the ZnO/PEDOT:PSS interface. Electrically induced switching between states with high and lower conductivity is possible on a timescale of 100 ms and the conduction levels remain stable for over 1 hour.
9:00 PM - S9.12
Air Stable Nonvolatile Memory Devices Utilizing ZnO Nanoparticles by Low Temperature Solution Process
Chia-Chieh Chang 1 , Zingway Pei 1 2 , Chung An Jong 1 , Jack Hou 1
1 Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan, 2 Department of Electrical Engineering, National Chung Hsing University, Taichung Taiwan
Show AbstractThe fabrication and characterization of two-terminal nonvolatile memory devices switching between a high- and a low-impedance state have drawn great interests in the past few years. We present our latest results on the design and fabrication of memory effect by ZnO nanoparticles (ZnO-NP) with solution process at low temperature process. With ZnO-NP, this memory device was suggested extremely stable in air as compared to other organic memory device. The insulator film containing Poly-4-vinylphenol (PVP) and ZnO-NP was spun coated and cured at 200C. Electrical data demonstrate the bistable properties through the metal-insulator-metal sandwich structure. The On-Off ratio and the operating voltage were about 2~3 orders and below 3V, respectively. Besides low voltage, the operating voltage is quite uniform and stable. ZnO-NP could be the trapping center for the carrier through the tunneling and/or the space-charge-limited-current (SCLC) process which resulted to the change of resistance. This inexpensive solution processes make ZnO-NP memory a good candidate for roll-to-roll print manufacturing of low cost electronics.
9:00 PM - S9.13
Effect of Buffer or Barrier Layer on Bistability for Nonvolatile Memory Fabricated with Al Nanocrystals Embedded in α-NPD.
Sung-ho Seo 1 , Woo-sik Nam 1 , Jae-seok Kim 1 , Chang-hyup Shin 1 , Se-yun Lim 1 , Yoon-joong Kim 2 , Jea-gun Park 1
1 Electrical & Computer Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Electron Microscopy Team, Korea Basic Science Institute, Deajeon Korea (the Republic of)
Show Abstract9:00 PM - S9.14
Dependency of Nonvolatile Memory Behavior on Curing Temperature for Au Nanocrystals Embedded in PVK.
Byeong-il Han 1 , Chang-Kyu Lee 1 , Jong-Sung Kwon 1 , In-Chul Na 1 , Young-Min Kim 2 , Jea-gun Park 1
1 Electrical & Computer Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Electron Microscopy Team, Korea Basic Science Institute, Deajeon Korea (the Republic of)
Show AbstractRecently, many researchers have reported organic nonvolatile memories since they are simple sandwich device structure of metal/conducting organic layer/metal and several tens of nano-second for device operation. We report the memory characteristics for a nonvolatile memory fabricated with the device structure of Al/Au nano-crystals embedded in PVK. The Au nano-crystals were produced by 5-nm-Au layer evaporation on bottom PVK layer followed by spin-coating upper PVK layer and curing at 300°C for 2hrs. The size of Au nano-crystals and density were ~5.5nm and 1x1012cm-2, respectively. The Au nano-crystals showed face-centered-cubic crystal structure and well were isolated between them. Those devices demonstrated reproducible nonvolatile memory behaviors. Particularly, they showed reproducible seven different I-V characteristics. The mechanism will be explained during our presentation. They showed the Vth of ~3.0V, Vprogram of ~4.0V, and Verase of ~6.5V. Particularly, this device exhibited an excellent non-volatile memory behavior producing the bistability(Iprogram/erase) of >1x102 and program, erase cycles of >1x105, and multi-bits. In addition, the dependency of curing temperature on bistability(Iprogram/erase) for those devices was investigated via electrical measurement and high resolution x-TEM observation. Au nano-crystals were not produced at 200°C for 2hrs because this temperature was not enough for migrating Au atoms, resulting in modulating thin Au layer and showing low current conducting through PVK layer. Au nano-crystals were produced at 200°C for 2hrs but not well isolated because this temperature enough for migrating Au atoms, resulting in dumbbell-shape Au nano-crystals and increasing current conducting through PVK layer but not bistability(Iprogram/erase). However, Au nano-crystals were uniform produced and well isolated at 300°C for 2hrs because this temperature was enough for migrating Au atoms, showing the bistability(Iprogram/erase) of ~ 1x102cm-2. Furthermore, the effect of PVK weight concentration on bistabilty(Iprogram/erase) for Au nano-crystal embedded in PVK will be presented. The research was supported by the National Development Program for 0.1-Terabit Non-volatile Memory financed by the Korea Ministry of Commerce, Industry and Energy.
9:00 PM - S9.15
An Application of Molecular Memory Devices: A Thiol-Substitued Ru-Terpyridine Self-Assembles on Gold Surface
Junghyun Lee 1 , Jonghyurk Park 1 , Gyeong Sook Bang 1 , Nak-Jin Choi 1 , Hyoyoung Lee 1
1 National Creative Research Initiative Center for Smart Molecular Memory Device team, IT-NT group, Electronics and Telecommunications Resarch Institute (ETRI), Daejeon Korea (the Republic of)
Show AbstractThe formation of self-assembled monolayers (SAMs) from organosulfur compounds on metal surfaces has been a topic of great interest over the past two decades. Currently there is increasing interest in studying the properties of redox-active SAMs for potential application in molecular devices. Redox-active molecules have potential as charge storage materials because of their ability to undergo facile electron-transfer reactions at low potential. Especially bis(terpyridine)-transition metal complexes exhibit superior chemical and electronic stability toward redox reactions. A model for application of theses molecules in molecular electronics uses the metal atom as charge storage vehicle and terpyridine ligands as insulating barriers for charge transfer. In this work, we report the synthesis and characterization of novle thiol-terminated bis(terpyridine)-ruthenium metal complexes having memory effect, the charaterization of molecular film of bis(terpyridine)-ruthenium on Au surfaces by XPS, UV-Vis spectroscopy, spectroscopic ellipsometry. And we further identified the switching of these SAMs by STM. The bis(terpyridine)-ruthenium metal complexes SAMs showed a hysteresis in STM measurement.
9:00 PM - S9.16
Bi-layer Organic Memory Devices using Fullerene Molecules Dispersed in Insulating Polymers.
Alokik Kanwal 1 2 , Mammen Thomas 2 , Bala Padmakumar 2 , Manish Chhowalla 1 2
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 , C- Core Inc., San Jose, California, United States
Show Abstract9:00 PM - S9.18
Time-Dependent Changes in Organic Schottky Diodes Characteristics.
Vincent Ballarotto 1 , Elba Gomar-Nadal 1 2 , Ellen Williams 1 2
1 , Laboratory for Physical Sciences, College Park, Maryland, United States, 2 Department of Physics, University of Maryland, College Park, Maryland, United States
Show AbstractThe desire to use organic materials for high frequency applications has led to the development of pentacene-based Schottky diodes [1]. Furthermore, these device structures also allow for investigation of metal/organic interfaces. We have investigated the evolution of Au/Pentacene/Al Schottky diodes that were measured repeatedly in dark dry-N2 conditions for an extended period of time. The device consists of two coplanar metal electrodes (100 nm) covered with 30 nm of thermally evaporated pentacene. The measured IV characteristics are fitted with several models, including the standard thermionic emission model as well as the Langevin approach. We find that after approximately 170 h, the Schottky barrier height increases about 5% while the series resistance increases more than 80%, indicating that both the bulk and the interface are responsible for the instability of the Au/Pn/Al Schottky diode. This is in contradiction with results obtained for Au/Pn/Au devices, which we have shown to be stable for 720 h under the same ambient conditions. We also note that multiple Schottky barrier heights are observed at room temperature in half the devices. Finally, we will also describe how modification of the electrodes affects the evolution of the Schottky barrier heights and the series resistance.[1] S. Steudel, et al., Nature Materials 4, 597 (2005).
9:00 PM - S9.19
Synthesis and Thin-film Transistor Performance of poly(4,8-didodecylbenzo[1,2-b:4,5-b’]dithiophene).
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 Materials and Printed Electronics Laboratory, Research Center of Canada, Mississauga, Ontario, Canada
Show Abstract9:00 PM - S9.2
Conjugated Organic Molecules as Potential Sensors.
Jitapa Sumranjit 1 , Paul Lahti 1
1 Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractConjugated para-distyryl benzenes (PhC=CPhC=CPh) bearing cleavable pendant amide side-chains on the central phenyl ring showed interesting physical and chemical properties. By attaching pyrenes as side groups, energy transfer process occurred upon exciting the pyrenes, with emission occurring solely from the core PhC=CPhC=CPh type chromophore. The energy transfer efficiency was about 60%. If the trimer was treated with concentrated acids, the amide bonds were cleaved and the energy transfer process was terminated. Attachment of phthalimide and pyridium side-chains quenched the fluorescence of the cores. The amide bonds of both “quenched” molecules were cleaved by base solutions, and the fluorescence intensities gradually increased over 24 hours. The latter molecules constitute a simplistic turn on blue-color fluorescence indication of amide cleavage.
9:00 PM - S9.20
New Fluorene-Acceptor Random Copolymers: Towards Pure White Light Emission from a Single Polymer
Wen-Chang Chen 1 2 , Wen-Chung Wu 1 , Wen-Ya Lee 1
1 Chemical engineering, National Taiwan University , Taipei Taiwan, 2 Polymer Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractTwo kinds of fluorene-acceptor copolymers containing three emitting segments have been synthesized and explored as the emissive layer in white-light-emitting devices(WLEDs). The light-emitting copolymers PFQTP and PFBTTP either contain blue-emitting (9,9-dihexyl-fluorene, F), greenemitting (quinoxaline, Q) (or yellow-emitting (2,1,3-benzothiadiazole, BT)), and red-emitting (thieno[3,4-b]-pyrazine, TP) units in the backbone. The energy-transfer processes between the emitting units are investigated by their absorption, photoluminescence, time-resolved photoluminescence, and electroluminescence. The experimental results suggest that only a relatively small faction of the acceptormoiety incorporated into the fluorene can achieve white light emission through energytransfer.The energy transfer from BT to TP is more efficient that that of Q to TP because of the degree of spectroscopic overlap between absorption and luminescence. The electroluminescent device with PFBTTP1 (0.1% of BT and 0.25% of TP) as an emissive layer exhibits the Commission Internationale de L’Eclairage (CIE) 1931 coordinates of (0.33, 0.34), a luminance of 1870 cd/m2 under the condition of maximum luminance yield of 1.92 cd/A and without significant variation with driving voltages. The present study suggests that the single polymers based on three fluorene-acceptor segments could be potentially used for pure-white-lightemitting diodes
9:00 PM - S9.21
Deep-Level Optical Spectroscopy Investigation of Trap Levels in Tris(8-Hydroxyquiniline) Aluminum.
Yoshitaka Nakano 1 , Koji Noda 1 , Hisayoshi Fujikawa 1 , Takeshi Morikawa 1 , Takeshi Ohwaki 1
1 , Toyota Central R&D Labs., Aichi Japan
Show AbstractSince the first report of efficient electroluminescence (EL) from an organic heterojunction device using tris(8-hydroxyquinoline) aluminum (Alq3) as the emissive material, organic light-emitting diodes (OLEDs) utilizing fluorescent molecules have attracted considerable interest for flat panel display applications. Up to date, Alq3 has been widely used as the emitting layer and/or the electron-transporting layer for OLEDs based on small molecules. However, there is still a lack of understanding concerning the nature of charge transport in this material. So far, the optical and electrical properties of Alq3 have been studied in detail using various physical and electrical techniques, but the fundamental electronic properties have still not been well understood. Thus, we need to clarify the electronic states in the bandgap of Alq3 experimentally from the viewpoint of carrier dynamics.Deep-level optical spectroscopy (DLOS) is well known as a powerful tool for the characterization of electronic deep levels in the bandgap of inorganic semiconductors. This technique measures changes in the depletion region capacitance under optical excitation and can provide detailed mapping of the deep levels. In this study, we have first applied DLOS measurements to the Alq3-based devices and have investigated deep levels in order to provide more direct information on electronic trap states in the Alq3 layer.The Alq3/LiF/Al device samples were fabricated on indium-tin-oxide (ITO) coated glass substrate. The Alq3 layer (100nm) was thermally evaporated, and then an Al layer (150nm) with an ultra-thin LiF (0.5nm) was formed as top contacts (2.5mm■). Here, the LiF layer was used to reduce the barrier height for electron injection into the Alq3 layer from the Al electrodes.From capacitance-voltage and conductance-voltage measurements, double carrier injection is found to occur at around 3V in the forward bias region. DLOS measurements after double-carrier injection into the Alq3 layer reveal a midgap state emission at ~1.39eV (known as D), in addition to near-band-edge (NBE) transitions at 2.2-3.6eV. This D level is a discrete deep level with an optical threshold at ~0.92eV, independent of the carrier injection rate. In addition, the D level is seen to interplay strongly between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) bands. That is, the D level can be active as an efficient generation-recombination (GR) center that may impact the photophysical properties. Furthermore, from the filling pulsed voltage dependence of DLOS spectra, the D level is from an intrinsic nature of Alq3. Given that the D level is located in the middle of the bandgap, this GR center is probably attributable to an electrically neutral dangling bond state in the Alq3 layer.
9:00 PM - S9.22
Energy Level Alignment and Fermi Level Pinning in Metal/Organic Semiconductor Interfaces.
Ruchi Agrawal 1 , Subhasis Ghosh 1
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi, Delhi, India
Show Abstract9:00 PM - S9.23
Interfacial Studies of Conjugated Oligomers and Self-Assembled Alkanethiols.
Yan Ge 1 2 , James Whitten 1 2
1 Chemistry, Univ. of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Center for Advanced Materials, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractSemiconducting conjugated polymers and oligomers are finding important device applications including organic light-emitting diodes (OLEDs), sensors, photovoltaics, and field-effect transistors (FETs). In these applications, interfaces between the conjugated polymer and other organic layers are critical to device performance, since electrical carriers must move across these interfaces. Modification of the electrode surfaces by adsorbates have been shown to reduce the turn-on voltage and prolong the lifetimes of OLEDs and improve the morphology and electrical properties of thermally deposited conjugated oligomers. In the case of gold electrodes, alkanethiols may be used to “tune” the work function of the electrode. In the present work, the interfaces between oligothiophenes and self-assembled alkanethiol monolayers have been investigated. Alkanethiols studied include 1H,1H,2H,2H-perfluorodecanethiol (PFDT). By using X-ray photoelectron spectroscopy (XPS) to monitor the intensities of the C1s, F1s, and S2p core levels, it has been possible to study the growth of thermally deposited sexithiophene onto PFDT monolayers self-assembled on gold surfaces. Ultraviolet photoelectron spectroscopy (UPS) has been used to measure the electronic structure of the sexithiophene films and work function changes. The morphology of the films has been studied by scanning electron and atomic force microscopies. Oligothiphene films have also been prepared (in-situ) on the alkanethiol surfaces by adsorbing thiophene monomr onto a cryogenically cooled PFDT-covered gold surface and oligomerizing it by X-ray irradiation. The properties of the oligomerized thiophene films have been investigated by a variety of surface science techniques, including XPS and UPS.
9:00 PM - S9.24
Thermal Deposition of Gold on 3-Mercatopropyltrimethoxysilane Self-Assembled Monolayers on Silicon Oxide Surfaces
Jagdeep Singh 1 2 3 , James Whitten 1 2 3
1 Department of Chemistry , University of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Center for High-Rate nanomanufacturing , University of Massachusetts Lowell, Lowell, Massachusetts, United States, 3 Center for Advanced Materials , University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractThermal deposition of gold (in ultrahigh vacuum) on self-assembled monolayers of 3-mercatopropyltrimethoxysilane (MPTS) on hydroxylated silicon oxide surfaces was investigated using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). This adsorbate is interesting because it has the ability to bond to two different surfaces and offers the possibility of forming metal-organic-semiconductor sandwiches for organic electronics. In the present study, gold was deposited step-wise, with the metal dose monitored using a quartz crystal microbalance. Prior to gold deposition, the monolayer exhibited an S2p peak at 164.0 eV. Gold-thiolate bond formation was evidenced by growth of a new S2p peak at 162.3 eV, and C1s and Au4f XPS intensities indicated that the gold mainly stayed on top of the MPTS monolayer. UPS was used to measure the electronic structure of the valence states and work functions were determined from the widths of the spectra. A decrease of 1-2 eV was observed for metal doses between 0 and 1 monolayer, and the work function approached the value for clean gold once the metal coverage exceeded 2 monolayers. In order to gain further insight into the bonding of gold with the thiol functional group, force-distance curves were measured using a gold-coated atomic force microscope (AFM) tip and MPTS functionalized silicon oxide substrates, and adhesion forces were compared to a gold tip in contact with a control silicon oxide surface.
9:00 PM - S9.25
Hydrogen Bonding Directed Phthalocyanine Molecular Assemblies: Candidates for Organic Photovoltaics.
Niranjani Kumaran 1 , Britt Minch 1 , Wei Xia 1 , Neal Armstrong 1
1 Chemistry, University of Arizona, Tucson, Arizona, United States
Show Abstract Discotic molecular assemblies are being intensively investigated for organic electronic device applications such as light-emitting diodes, photovoltaic cells and thin-film transistors. The orientation of the molecules and the morphology of thin film aggregates are shown to be important factors since charge carrier mobilities are highest along the aggregate column axis. Columnar aggregates with the column axis in the substrate plane are required for organic field-effect transistors (OFETs). Vertically stacked columns are desired for organic photovoltaics (OPVs). Though several horizontal columnar aggregates have been reported, assembling molecules with the column axis perpendicular to a substrate is still challenging. We show that tuning side chain functionalities that are attached to the aromatic core and substrate surface treatments with self-assembled monolayers can be exploited to direct the molecular assembling in the vertical direction. Phthalocyanine (Pc) molecules with thio-ether and amide functionalized side chains are expected to give one-dimensional co-facial aggregates as a result of the combination of hydrogen bonding between the side chains, S-S interactions between adjacent Pc rings, and arene-arene interactions in the core of the macrocycles. The aggregation behavior of these molecules is being investigated using a variety of experimental techniques including Polarized Optical Microscopy (POM), Atomic Force Microscopy (AFM), X-ray diffractometry (XRD), Attenuated Total Reflection Spectroscopy (ATR), and Reflection Absorption Infrared Spectroscopy (RAIRS). Our experimental results show that highly ordered crystalline self-organizing materials can be formed with improved intra-columnar order dominated by the hydrogen bonds between amide functionalized side chains. AFM images of Pc aggregates on mica shows well defined crystal structures. The step heights of the crystalline domains are consistent with the structural model obtained from powder XRD patterns which evidence horizontal columnar aggregates on mica. In contrast to the assembling behavior on mica, gold substrates treated with amide functionalized self-assembled monolayers induce the assembling of Pc aggregates with a vertical columnar growth direction. AFM images of these assemblies show layered structures. RAIRS results confirm vertical columnar aggregates in the layered material. In addition, sharp X-ray diffraction peaks of these thin films indicate the presence of highly ordered vertically stacked Pc molecules. Nanometer scale electrical properties of these molecular assemblies are being investigated by conductive tip AFM.
9:00 PM - S9.27
All-organic and Hybrid Interfaces: A Transition Between Two Different Energy Level Alignment Regimes.
Slawomir Braun 1 , Wojciech Osikowicz 1 , Ying Wang 2 , William Salaneck 1
1 IFM, Linköping University, Linköping Sweden, 2 Experimental Station, E. I. DuPont de Nemours and Co., Inc., Wilmington, Delaware, United States
Show Abstract9:00 PM - S9.28
The Electronic Structure and the Energy Level Alignment at the Interface Between Organic Molecules and Metals.
Eiji Kawabe 1 , Hiroyuki Yamane 1 , Kenji Koizumi 1 , Ryohei Sumii 2 , Kaname Kanai 1 , Yukio Ouchi 1 , Kazuhiko Seki 1 3
1 Graduate School of Science, Nagoya University, Nagoya Japan, 2 Research Center for Materials Science, Nagoya University, Nagoya Japan, 3 Institute for Advanced Research, Nagoya University, Nagoya Japan
Show Abstract9:00 PM - S9.29
Growth and Characterization of Polymeric Phenylene Vinylene Thin Films via Surface Polymerization by Ion-Assisted Deposition.
Amanda Wroble 1 , Jurjen Wildeman 2 , Luke Hanley 1
1 Chemistry, University of Illinois at Chicago, Chicago, Illinois, United States, 2 Polymer Chemistry and Materials Science Centre, University of Groningen, Groningen Netherlands
Show AbstractPrevious work has shown that surface polymerization by ion assisted deposition (SPIAD) can be used to grow polythiophene and polyphenyl thin films by the simultaneous deposition of hyperthermal mass-selected or non-mass-selected ions and thermally evaporated neutrals.1-3 This deposition method is potentially useful for the growth of active layers in organic photovoltaic devices. Poly(phenylene vinylene)s (PPVs) are commonly used as electron donor species in optoelectronic applications due to the enhanced charge carrier transport of the conjugated system. Substituted PPVs have shown variation in charge transport by changing the degree and functionality of substitution along the PPV backbone.4-6 The use of phenylene vinylene oligomers, such as 2-methoxy-5-(2′-ethylhexyloxy)-1,4-bis((4′,4″-bisstyryl)styrylbenzene) (MEH-OPV5), allows for vapor-phase deposition and in situ characterization. The SPIAD method is used here to grow polymeric phenylene vinylene films from MEH-OPV5 and non-mass-selected thiophene ions. The effect of varying ion to neutral ratio and ion energy on film composition and electronic structure is examined by X-ray and ultraviolet photoemission as well as electron energy loss spectroscopy. Scanning electron microscopy is also used to distinguish morphological differences between films grown by the SPIAD method and evaporation of neutral oligomer species only.References:1.Tepavcevic, S.; Choi, Y.; Hanley, L. Lang. 2004, 20, 8754.2.Choi, Y.; Tepavcevic, S.; Xu, Z.; Hanley, L. Chem. Mater. 2004, 16, 1924.3.Choi, Y; Zachary, A.; Tepavcevic, S.; Wu, C.; Hanley, L. Inter. J. Mass. Spect. 2005, 241, 139.4.van Breeman, A. J. J. M.; Herwig, P. T.; Chlon, C. H. T.; Sweelssen, J.; Schoo, H. F. M.; Benito, E. M.; de Leeuw, D. M.; Tanase, C.; Wildeman, J.; Blom, P. W. M. Adv. Funct. Mater. 2005, 15, 872.5.Markov, D. E.; Tanase, C.; Blom, P. W. M.; Wildeman, J. Phys. Rev. B 2005, 72, 045217.6.Tanase, C.; Wildeman, J.; Blom, P. W. M. Adv. Funct. Mater. 2005, 15, 2011.
9:00 PM - S9.30
Structure of a Pentacene Monolayer Deposited on SiO2: Role of Trapped Interfacial Water.
Songtao Wo 1 , Binran Wang 1 , Hua Zhou 1 , Yiping Wang 1 , Jonathan Bessette 1 , Randall Headrick 1 , Alex Mayer 2 , George Malliaras 2 , Alexander Kazimirov 3
1 Physics, University of Vermont, Burlington, Vermont, United States, 2 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Cornell High energy Synchrotron Source, Cornell University, Ithaca, New York, United States
Show AbstractIn-situ synchrotron x-ray reflectivity is used to probe the early stages of pentacene growth in real time, under conditions relevant to the fabrication of organic thin filmtransistors. The results reveal that there is an interfacial water layer initially present on the SiO2 substrate, and that this water layer is still present at the interface after the deposition of a pentacene thin film. The thickness of the trapped interfacial water layerdoes not significantly change subsequent to film deposition, even after exposure to atmospheric pressure or during vacuum annealing at 70 °C. However, a new water layer is observed to form on the free surface of pentacene after sufficient exposure to water vapor, and the thickness of this layer can be reduced by subsequent vacuum annealing. These observations are correlated with organic thin film transistor mobilities measured atatmospheric pressure vs. under vacuum.
9:00 PM - S9.31
Crystal organization and Luminescence in Oligo-phenylethynylenes
Nibedita Sanyal 1 , Paul Lahti 2
1 Chemistry, University of Massachusetts, Amherst, Massachusetts, United States, 2 Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractSyntheses, characterization and electronic spectroscopic study of PPE-related oligomers with and without pendant hydroxyl groups (“sticky” groups) are reported as well as their crystal packings. Notably compound PhC≡CArC≡CPh (Ar is a phenyl ring with hydrogen-bonding pendant) abbreviated as BHE-PE2.5 is orthorhombically packed with its central phenyl rings criss-cross stacked along the π-stack axis, yielding a crossed-dipole arrangement. This π-stacking motif exhibited by BHE-PE2.5 is of great interest and very unusual for solid state organic materials. Compounds Ar’C≡C-ArC≡CAr’ (Ar’ is a phenyl ring containing trimethoxy end groups at 3,4 and 5 positions) abbreviated as B6OMe-PE2.5 and PhPhC≡C-Ar-C≡CPhPh abbreviated as BHE-PEBP2.5 exhibit hydrogen-bonding, but do not exhibit cross-dipole stacks. Pi-stacking is not observed in the PPEs that lack the hydrogen-bonding pendant group. Oligomers have UV-absorbance band at 304-320 nm and 350-370 nm, with fluorescence emission in the 390-400 nm region. Quantum yields range from 0.50-0.92.
9:00 PM - S9.32
Precise Patterning and Single Crystal Formation of Molecular Organic Semiconductors via Spin-Casting and Solvent-Vapor Exposure: Towards Low-Cost, Large-Area OLED and OFET Arrays.
Jonghwa Jeong 1 , Debra Mascaro 2
1 Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States, 2 Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractOrganic light emitting devices (OLEDs) and field-effect transistors (OFETs) are being pursued as low-cost alternatives for numerous electronic applications, including full-color displays and RFID circuitry. However, the development of efficient, low-cost patterning techniques for organic materials remains a significant research challenge. Molecular organic semiconductors such as the archetypical electron transport/luminescent material tris(8-hydroxyquinoline)aluminum (Alq3) are most often deposited by thermal evaporation through a shadow mask, an inherently expensive vacuum process. In this work, we demonstrate uniform Alq3 thin films with bright photoluminescence prepared by spin-casting from chloroform. Moreover, solution deposition enables precise patterning via segregation of Alq3 into pre-patterned channels or wells in the substrate. Arrays of microchannels or square wells with widths of 10-100 μm and typical depths of 1 μm are fabricated in silicon using standard microfabrication techniques. The patterned substrates are treated with octadecyltrichlorosilane to discourage the adsorption of Alq3, resulting in selective deposition in the channels and wells during spin-casting. This single-step solution-based approach for forming precise patterns of amorphous Alq3 is ideal for large-area OLED pixel arrays; however, OFETs require crystalline morphologies for high charge carrier mobilities and efficient device operation. To that end, we have utilized the tendency of Alq3 to crystallize when exposed to solvent vapor to transform the initially amorphous Alq3 into single crystals within the channels and wells. Our presentation will cover the deposition, patterning, and solvent-vapor crystallization techniques as well as materials characterization of the amorphous and single-crystal patterned structures. We will also discuss the fabrication of large-area OLED and OFET arrays via this approach, which offers a promising solution to low-cost, front-end patterning of molecular organic semiconductors.
9:00 PM - S9.34
Correlation Between Ambipolar Transport and Structural Phase Transition in Single Crystals of the Organic Semiconductor Diindenoperylene.
Ashutosh Tripathi 1 , Jens Pflaum 1
1 3rd Institute of Physics, University of Stuttgart, Stuttgart, Baden- Wuerttemberg, Germany
Show AbstractRE-INSTATED ABSTRACTWednesday 11/29S9.34 (poster)Correlation Between Ambipolar Transport and Structural Phase Transition in Single Crystals of the Organic Semiconductor Diindenoperylene. Ashutosh Kumar Tripathi
9:00 PM - S9.35
Intriguing Photophysical and Charge-transport Properties of Nanoaggregates of Bis(triphenylenyl)biphenyl.
Tung-Huei Ke 1 , Chih-Hao Chang 1 , Chang-Sheng Lin 2 , Chien-Hong Cheng 2 , Chung-Chih Wu 1
1 , Graduate Institute of Electro-Optical Engineering at National Taiwan University, Taipei Taiwan, 2 , Department of Chemistry, National Tsing Hua University , HsinChu Taiwan
Show AbstractTriphenyl derivatives, such as triphenyl-based discotic LCs, had long been known as effective hole-transport materials. Recently, 2,2’-bistriphenylene (BTP) derivatives have also been revealed as highly efficient blue emitting materials for organic light-emitting devices. In this paper, we investigate a new triphenyl-based compound, bis(triphenylenyl)biphenyl (TBT), and report the interesting morphological, photophysical and charge-transport properties of its vacuum-deposited thin films. Comprehensive and comparative studies of photoluminescence (PL), photoluminescence excitation (PLE) and absorption spectra of TBT in dilute solutions and vacuum-deposited films clearly reveals different mechanisms in electronic transitions and indicates formation of aggregates in films right after deposition. The sizes of the aggregates grow up to tens of nanometers with time, as confirmed by the SEM studies of the thin-film morphological evolution. Correspondingly, the PL quantum yields (as determined by the integrating sphere method) of the red-shifted aggregate emission (blue emission) eventually increases beyond that of the monomer emission (near UV emission) in dilute solution (i.e. 92% vs. 82%). Time-resolved and temperature-dependent spectroscopic studies of the aggregate emission also reveal enhancement of radiative decay rates, which may be associated with coherent and collective interaction of emitting dipoles in aggregates. Finally, intriguing non-dispersive bipolar carrier transport (as investigated by the time-of-flight technique) had been observed for the aggregate films of TBT. Hole and electron mobilities up to 4.14*10^-5 cm^2/V/s and 1.19*10^-4 cm^2/V/s, respectively, at 1.3*10^6 V/cm were observed for the right deposited film. Subsequently, with the growth of the aggregate sizes, carrier mobilities can increase by up to two times. In conclusion, the intriguing morphological, photophysical and bipolar charge-transport properties of bis(triphenylenyl)biphenyl may render it an excellent candidate for various organic optoelectronic applications.
9:00 PM - S9.37
Thermo-responsible Luminescent Assemblies of Hydrogen-bonded L-glutamide Derivatives with Pyrene, N, N-Dimethylaniline, and/or Porphyrin Head Groups.
Takashi Sagawa 1 , Taisuke Yamada 2 , Hiroshi Hachisako 3 , Makoto Takafuji 4 , Hirotaka Ihara 4
1 Institute of Advanced Energy, Kyoto University, Uji, Kyoto, Japan, 2 Department of Chemistry, Georgetown University, Washington, D. C., District of Columbia, United States, 3 Department of Applied Chemistry, Sojo University, Kumamoto, Kumamoto, Japan, 4 Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto, Kumamoto, Japan
Show Abstract9:00 PM - S9.38
Interfacial Electronic Structure in Self-Assembled Monolayers of Conjugated Molecules on Noble Metals.
Georg Heimel 1 , Lorenz Romaner 2 , Jean-Luc Bredas 1 , Egbert Zojer 2
1 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Institute of Solid State Physics, Graz University of Technology, Graz Austria
Show AbstractThere is currently significant interest in highly-ordered, self-assembled monolayers (SAMs) on (noble) metal surfaces, inspired both by the emergence of the field of molecular electronics alongside the high potential for SAMs to improve more conventional organic electronic devices. In order to tune the interface properties and to endow the self-assembled systems with functionality suitable for use in either macroscopic or nanoscale devices, the use of π-conjugated systems is highly promising and the focus of intense, multidisciplinary research.The goal of the present study is to provide an in-depth description of the electronic structure of the interface between metallic substrates and covalently bound organic semiconductors. Moreover, we focus on the device-relevant modifications of the electrode surface that are induced by the SAM formation. In this way, we expect to devise strategies for tuning the metal/molecule interaction and thus the properties of the investigated systems and, in the long run, to gain a general understanding of the processes governing the electronics of metal/organic interfaces at large.By means of DFT band-structure methods, we study SAMs of a variety of oligo(para-phenylene) based systems on noble metal surfaces. In particular, we investigate the impact of: (i) different donor/acceptor head-group substitutions; (ii) the length of the conjugated backbone; (iii) different anchor groups that covalently link the conjugated core to the metal; (iv) different metal substrates (Au, Ag, Pt), as well as (v) the influence of methylenic linkers between the anchor group and the conjugated core of the molecules.In addition to a thorough characterization of these systems, where we model results that are accessible through surface-science experiments, e.g., STM images and XPS core-level shifts, we discuss the mechanism of the alignment of the frontier molecular orbitals with the metal Fermi energy and, in particular, the modification of the substrate workfunction upon SAM formation.
9:00 PM - S9.39
Unique Molecular Ordering and Tunneling Spectroscopy of Ultrathin Hexaazatrinaphthylene Films on Au(111).
Sieu Ha 1 , Fabrice Amy 2 , Antoine Kahn 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 , Air Products, Allentown, Pennsylvania, United States
Show AbstractDiscotic liquid crystals are becoming a viable option for use as electron transport materials in organic semiconductor devices. Derivatives of discotic molecules such as hexaazatrinaphthylene (HATNA) are reported to have combined electron-hole mobilities on the order of 0.1cm2/Vs. Out of plane, these molecules are known to form columnar stacks, which contributes to the relatively high mobility. As for in-plane ordering, scanning tunneling microscopy experiments on the first monolayer of unfunctionalized parent HATNA illustrate a remarkable molecular configuration. Images of 1ML HATNA deposited on Au(111) reveal that four molecules of different rotational orientations interlock to form a 2x2 unit cell. The ordered structure remains consistent even at step edges and despite vacancy defects. Moreover, experiments on multilayer HATNA indicate that subsequent layers do not order in the same way as the first monolayer. Several contrasting configurations have been observed, including a hexagonal close-packed scheme. Regardless of thickness, HATNA films remain stable at room temperature, demonstrating negligible diffusion and a strong interaction with the Au(111) substrate. This is further confirmed by scanning tunneling spectroscopy measurements. Comparison with UPS and IPES shows that the bandgap of HATNA is about 1.94eV smaller at the interface of a thin ordered film (1.88eV) than at the surface of a thick amorphous film (3.82eV). This reduction is likely a combination of the strong substrate interaction, molecular ordering, and increased polarization at the organic-metallic interface.
9:00 PM - S9.4
Polymeric Electrochemical Circuits for Sensing Applications
John DeFranco 1 , Daniel Bernards 1 , Maria Nikolou 1 , Daniel Macaya 1 , George Malliaras 1
1 Materials Science, Cornell University, Ithaca, New York, United States
Show AbstractThe biomedical industry, and chemical sensing in particular, is an area in which organic electronics can make a huge impact. The inherent strengths of the technology: cheap manufacturing, scalable production, and biological compatibility are magnified in a field where hygiene concerns already demand disposable tools or applicators. The traditional weakness like lifetime and high-frequency operation are not hindrances in this case. In this work, selective enzymes are used in conjunction with an ion sensitive conducting polymer to detect and measure the concentration of a variety of analytes, including glucose and urea. By also using the conducting polymer as a depletion-mode transistor, an electrochemical circuit is realized. One advantage of this circuit is that voltage changes, rather than current changes, indicate the concentration of analyte. Also the base resistance of the device is not measured, but only the differential, increasing the signal to noise ratio and allowing arrays of simultaneous measurements of different analyte concentrations. Mechanisms and figures of merit for the device will be discussed.
9:00 PM - S9.40
Ultrafast Exciton Response of High Optical Density J-aggregates from Ultrathin Films of Cyanine Dyes.
Tolga Atay 1 , Qiang Zhang 1 , Arto Nurmikko 1 , Jonathan Tischler 2 , Scott Bradley 2 , Vladimir Bulovic 2
1 Division of Engineering and Department of Physics, Brown University, Providence, Rhode Island, United States, 2 Department of Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts, United States
Show AbstractJ-aggregates are mesoscale aggregates of organic molecules, where Frenkel excitons acquire finite spatial extension, resulting in very large optical cross-sections and sharp absorption peaks due to finite delocalization. If achieved as 2-dimensional ultrathin films, J-aggregates could emerge as novel nanocrystalline organic composites with high nonlinear optical coefficients. To create such ultrathin organic films, we are developing layer-by-layer (LBL) deposition method by alternate adsorption of a cationic polyelectrolyte and a monolayer of cyanine dye with anionic luminophore on a substrate. By this approach, J-aggregate films of a nanometer scale of thickness with absorption coefficients as high as 10^6cm^-1 at room temperature have been created. Here we report results of study of ultrathin J-aggregate films of TDBC dye prepared by LBL deposition, by employing ultrafast nonlinear optical transmission spectroscopy and transient photoluminescence (PL).Transient nonlinear transmission spectra of J-aggregate films were measured at room temperature by the pump-probe method. In the differential transmission spectrum, both saturated and induced absorptions are observed. The saturation is due to suppression of the creation of excitons in the one-exciton band, whereas the induced absorption originates from the population of the two-exciton band by the probe pulse. The transient transmission spectra are well fitted by a superposition of the saturated and induced absorption peaks represented by Lorentzians. Applying a model calculation, we obtained an exciton delocalization length of 18 molecular monomers.This is roughly consistent with the present state of morphology of our films, which show sub-200nm features in NSOM imaging. Time-dependence of the nonlinear transmission data shows two distinct time constants - one, on the psec time scale, due to exciton-exciton annihilation, and the other, on the scale of a few tens of psec, due to spontaneous decay of the one-exciton band. Transient PL measurements of the same film measured with a sub-10ps resolution streak camera at temperatures ranging from room temperature down to T=5K were also obtained. It was found that the PL decay is a weakly temperature dependent two-component decay with time constants being 11ps and 60ps (slow component attributed to defect states which can be minimized by improved film quality), respectively. The above behaviors of LBL J-aggregates are in contrast to those observed in cyanine dye J-aggregates in liquid, where either PL radiative lifetime, fluorescence quantum yield or both decreases drastically with temperature. In sum, this work shows first steps towards the creation of quasi-2 dimensional J-aggregate ultrathin films where the aim is to achieve microscale delocalization areas for Frenkel excitons, to enable full exploitation of the very large exciton oscillator strengths for nonlinear optical switching and for light emission possibly via a superradiant mechanism.
9:00 PM - S9.41
Ab initio Study of Conduction and Switching Properties of Photochromic Dithienylethene Molecules.
Anders Odell 1 , Anna Delin 1
1 Material Science and Engineering, Royal Institute of Technology, Stockholm Sweden
Show AbstractWe report a theoretical study of single molecule conduction in open and closed conformations of photochromic dithienylethene molecules attached to metallicleads. Photochromic molecules are attractive candidates for use in molecular electronics because of the switching between different states with different conductingbehaviour. This opens the possibillity for optically controlled conduction.Dithienylethene derivatives in solution transforms under UV irradiation from the open to the closed comformation, while the reverse process occurs under visible light. When attached to gold leads, however, the ring closure reactionappears to be quenched, thus destroying the reversible switching mechanism. One theory as to why this happens is that the quenching arises from charge transfer from the molecular HOMO to the leads, due to strong coupling to the gold d-states, which lie close to the Fermi level.We have therefore investigated the alignment of the molecular levels to the lead orbital-resolved density of states for gold and silver under finite bias for ring opening and closing reactions. We find that the HOMOlevel coupling to the lead d-states is significantly weaker for the silver lead system. Therefore, provided the quenching has the electronic origin mentioned above, we predict the reaction to become reversible if the goldleads are replaced by silver leads.
9:00 PM - S9.42
Chemical Modification of Electrode in the Fabrication of Photofunctional Organic Devices.
Hiroshi Moriyama 1 , Hiroshi Higuchi 1 , Noriaki Ikeda 1 , Nobutaka Mitomo 1 , Chongjin Pac 1
1 Department of Chemistry, Toho University, Funabashi Japan
Show AbstractRecent development of organic electronic devices, such as organic LED, thin film transistors, and solar cells, have prompted further application of organic semiconductors to photofunctional organic devices. It has been well known that the interface between electrode and the layer of organic active materials is usually chemically and morphologically non-flat and heterogeneous, which should result in the lower efficiency for electron/hole mobility. In order to control the interface, we have developed a methodology for the rather homogeneous two-dimensional nanoscale organic thin layer formation of pai-organics such as derivatives of porphyrin, fullerene, and oligothiophens through the linkage of appropriate chemical bonds on ITO or Au electrode. We constructed the prototype cell and investigated the photoelectrochemical effect of the modified electrode and also compared the efficiency of the above unique thin films in the presence or absence of Au nanoparticles involved in the organic layer of the electrode.
9:00 PM - S9.43
Preparation of Organic Thin Films from the Melts
Takeshi Hirai 1 , Nobuhito Ohno 2 , Satoshi Hashimoto 3 , Michio Matsumura 1
1 , Research Center for Solar Energy Chemistry, Osaka University, Toyonaka, Osaka, Japan, 2 Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa, Osaka, Japan, 3 Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
Show AbstractThere has been increasing interest in organic materials for the applications in electronic devices such as light-emitting diodes, transistors and solar cells. For the fabrication of those devices, it is essential to prepare thin films of high quality (homogeneity and chemical purity) from the organic materials. The organic thin films for the application to electronic devices are most often prepared by vacuum sublimation if the materials are small molecules. However, this method may not be suited for the fabrication of high-quality thin-films, particularly for that of crystalline films, since the depositing molecules are rapidly quenched and condensed in random arrangements. We have successfully prepared large thin crystals of inorganic materials, such as ionic materials, from the melts by a method called the “cell method”. In this method, the melt of a raw material is introduced into a small gap between two quartz plates (cell) by capillary action, and is allowed to solidify. Here we report the fabrication of organic thin films, which are useful to electronic devices, by the cell method. The materials we used are N,N’-diphenyl-N,N’-di(m-tolyl)benzidine (TPD), 4,4’-di-9-carbazolylbiphenyl (CBP), 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (tBu-PBD), etc. We evaluated the quality of these thin films based on their absorption, photoluminescence and photoexcitation spectra, and polarizing microscope images. Photoluminescence spectra of the films under high-density excitation were also studied.
9:00 PM - S9.44
Kinetic Monte Carlo Simulations of Hopping Transport in the Space Charge Limited Regime.
Michael Mueller 1 , Karsten Albe 1 , Yuri Genenko 1 , Frederik Neumann 1 , Roland Schmechel 1 , Heinz von Seggern 1
1 Institute of Materials Science, TU Darmstadt, Darmstadt Germany
Show AbstractCharge transport in organic semiconductors can be microscopically described by thermally activated hopping of individual charge carriers between localized electronic states. In the past, Monte Carlo (MC) simulations have therefore been successfully applied for investigating charge transport in organic semiconductors [1]. These simulations, however, were restricted to the injection limited regime where interactions between charge carriers can be neglected.In this contribution, we present a new 3-dim. KMC model that fully includes the electrostatic interactions of charge carriers, expanding the applicability of the method to regimes of high charge carrier concentrations. With this method we investigate the current-voltage characteristic and the field dependence of the charge carrier mobility in the space charge limited regime for hopping systems with various degrees of disorder. In doing so, different models for the microscopic hopping rates (Miller-Abrahams hopping in the exact and the commonly used approximated formulation as well as the small polaron model) are applied. A significant dependence of the obtained characteristics on the choice of model is found and discussed.[1] H. Bässler, phys. stat. sol. (b) 175, 15 (1993)
9:00 PM - S9.45
Transport Properties through Organic Materials by Molecular Orbital Analysis
Hiroshi Mizuseki 1 , Rodion Belosludov 1 , Amir Farajian 1 5 , Olga Pupysheva 1 5 , Chiranjib Majumder 2 , Jian-Tao Wang 3 , Hao Chen 4 , Yoshiyuki Kawazoe 1
1 Tohoku University, Institute for Materials Research, Sendai, Miyagi, Japan, 5 (Present address) Center for Nanoscale Science and Technology, Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States, 2 Novel Materials and Structual Chemistry Division, Bhabha Atomic Research Center, Mumbai India, 3 Institute of Physics, Chinese Academy of Sciences, Beijing China, 4 Physics Department, Fudan University, Shanghai China
Show AbstractMolecular devices are potential candidates for this next step, and they would make it possible to realize the most advantageous devices. However, a major predicament and source of expenditure is necessary that such a large number of organic molecules can be obtained by synthetic chemistry, so any means of exploring their properties and behavior in order to predict the relevant properties of a molecule in advance of its synthesis would be extremely useful. One established approach is to use the computational methods developed for the prediction of a stable molecular structure and conductance properties.Our group has covered a wide range of molecular system which have potential application in molecular electronics using first-principles calculations [1]; supramolecular enamel wires (covered wires) [2], connection between organic molecules and metal electrodes [3], self-assembled nanowires on silicon surface [4]. Moreover we examine electronic transport properties through small molecules for a building block, such as benzene [5], bent carbon nanotube, DNA, porphyrin and ferrocene[6] molecules and so on. In this presentation, we will present recent investigations related to organic devices, using molecular orbital analysis.[1] http://www-lab.imr.edu/~mizuseki/nanowire.html[2] R. V. Belosludov, A. A. Farajian, H. Baba, H. Mizuseki, and Y. Kawazoe, Jpn. J. Appl. Phys., 44, 2823 (2005).[3] C. Majumder, H. Mizuseki, and Y. Kawazoe, J. Chem. Phys., 118, 9809 (2003).[4] J.-T. Wang, E. G. Wang, D. S. Wang, H. Mizuseki, Y. Kawazoe, M. Naitoh, and S. Nishigaki, Phys. Rev. Lett., 94, 226103 (2005).[5] F. Jiang, Y. X. Zhou, H. Chen, R. Note, H. Mizuseki, and Y. Kawazoe, Phys. Rev. B, 72, 155408 (2005).[6] T. Uehara, R. V. Belosludov, A. A. Farajian, H. Mizuseki, and Y. Kawazoe, Jpn. J. Appl. Phys., 45, 3768 (2006).
9:00 PM - S9.46
Rose Bengal Dye on Bilayered Amine-terminated Thiol for Molecular Device
Gyeong Sook Bang 1 , Jonghyurk Park 1 , Junghyun Lee 1 , Nak-Jin Choi 1 , Hee-Yeol Baek 1 , Hyoyoung Lee 1
1 National Creative Research Initiative Center for Smart Molecular Memory, IT Convergence Technology Research Division, ETRI, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - S9.47
On Interfacial Dipole Formation at Organic-organic Interfaces.
Wojciech Osikowicz 1 , William Salaneck 1
1 Dept. of Physics, IFM, Linkoping University, Linkoping Sweden
Show Abstract9:00 PM - S9.48
Electronic Structure of Defects in fcc-C22.
Helder Domingos 1
1 INESC, INESC-MN, Lisbon Portugal
Show AbstractAb initio plane wave pseudopotential calculations were carried out, aiming at the determination of the energetic and electronic structures of defects in fcc-C22. A variety of intrinsic and extrinsic defects were considered and the potential and conditions for obtaining interface states and magnetism in these fullerene based solids were accessed. The effect of the defects on the electronic structure were studied with relation to potential applications for the solids. The generation of magnetically active defects was addressed in detail and spin dependent calculations were utilized to evaluate the type of exchange interactions that can result for the defects.
9:00 PM - S9.49
Spin Injection and Spin Dynamics at CuPC/GaAs (100) Interface
Huanjun Ding 1 , Yongli Gao 1 , Marina Sanchez-Albaneda 2 , Mirko Cinchetti 2 , Jan-Peter Wüstenberg 2 , Oleksiy Andreyev 2 , Michael Bauer 2 , Martin Aeschlimann 2
1 Department of Physics and Astronomy, University of Rochester, Rochester, New York, United States, 2 Department of Physics, University of Kaiserslautern, Kaiserslautern Germany
Show AbstractSpin injection from GaAs(100) to organic semiconductor copper phthalocyanine (CuPc) has been investigated experimentally with spin-resolved two-photon photoemission (SR-2PPE) spectroscopy. With SR-2PPE, the dynamics of both electron and spin relaxation have been studied with femtosecond time resolution. The spin-polarized electrons are originally generated in GaAs through optical pumping and injected into CuPc. We observed an enhancement in spin polarization at the interface after initial CuPC deposition. This demonstrates that interface spin scattering is insignificant, which is similar to our previous result of spin injection at CuPC/Co interface. The spin polarization dropped when the CuPC film became thick, an effect attributed to bulk attenuation in CuPc. The lifetime of the unoccupied orbits in CuPC was also studied with red-blue excitation of photon energy 1.6 eV and 3.2 eV, respectively. There was a strong asymmetry in the time-resolved spectra, and an unexpected long lifetime when the lower unoccupied orbital was excited. A simple explanation of this phenomenon will be discussed.
9:00 PM - S9.5
Tuning the Electronic Coupling, Electric Transport and Gas Sensitivity in Thin Films of Perylene Imides by Twisting the Aromatic Core of the Molecule
Harald Graaf 2 , Derck Schlettwein 1
2 Institute of Physics, Technical University Chemnitz, Chemnitz Germany, 1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany
Show AbstractThin films of 1,6,7,12-Tetrachloro-N,N’-dimethylperylene-3,4,9,10-biscarboximide (Cl4MePTCDI) prepared by physical vapor deposition (PVD) were compared to thin films of the unchlorinated N,N’-dimethylperylene-3,4,9,10-biscarboximide (MePTCDI) to investigate the influence of a changed molecular structure on the electrical properties of the materials. The films were prepared on microstructured Si/ SiO2 substrates with interdigitated Au electrode arrays of 2 µm electrode distance or on quartz glass with electrode distances in the mm range. The films were characterized by optical absorbance and emission spectroscopy, ultraviolet photoelectron spectroscopy (UPS) and atomic force microscopy (AFM). The electrical characteristics were analyzed by conductance measurements, thermoelectric power and electric field effect both at pristine films as prepared in high vacuum and under increasing partial pressure of different gas molecules (oxygen, ethanol, acetone or n-butane). The thickness- dependence of the conductance measured during film growth (in- situ) indicated a growth mode in islands (Volmer- Weber), which was confirmed by subsequent AFM. Growth of amorphous particles was determined for Cl4MePTCDI as opposed to crystals of MePTCDI. In accordance with the UPS data, both materials were characterized as organic n- type semiconductors. Charge transport occurred by a hopping mechanism as revealed by temperature- dependent thermopower and field- effect measurements. An effective electron mobility for Cl4MePTCDI at room temperature was found around 10 E5 cm2 V-1 s-1, considerably lower than the value for MePTCDI. A rather constant concentration of mobile electrons of about 10 E18 cm-3 was determined for both materials in the pristine films. Exposure to the gas molecules led to changes in the conductivity of the films. Field effect measurements served to differentiate between changes in the charge carrier mobility and changes of the charge carrier concentration. The charge carrier mobility was found to decrease significantly whereas rather small changes were found in the charge carrier concentration. Gas molecules that diffused into the films affected the charge carrier mobility at least 10 times more than molecules just adsorbed on the surface. These results are correlated with the observed differences in the film structure and morphology and implications for technical applications of such films are discussed.
9:00 PM - S9.50
Fluorination on Emission Color and Efficiency of Alq3 Derivatives.
Hong-Zheng Chen 1 , Min-Min Shi 1 , Yue-Wen Shi 1 , Mang Wang 1
1 Polymer Science & Engineering, Zhejiang University, Hangzhou China
Show Abstract9:00 PM - S9.6
Tuning the Sensor Response of Glucose Biosensors Based on Organic Electrochemical Transistors.
Daniel Macaya 1 , Maria Nikolou 1 , Seiichi Takamatsu 1 , Jeff Mabeck 1 , George Malliaras 1
1 materials science & engineering, Cornell University, Ithaca, New York, United States
Show AbstractA glucose biosensor based on an organic electrochemical transistor is reported. The device utilizes an active layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) that results in a transistor that is innately “on” but can be turned “off” by the application of a positive voltage through a platinum gate electrode. Poly(dimethylsiloxane) (PDMS) wells are used to confine a biological solution over the active layer of the transistor. The response of the device is based on the difference in drain current through the transistor between “on” and “off” states. The behavior of the transistor is understood in terms of an electrochemical doping or de-doping of the organic semiconductor that depends on the presence of an electrolyte and a redox reaction involving hydrogen peroxide produced from the oxidation of glucose by glucose oxidase (GOx). It is shown that the device’s response to glucose is well within the clinical range of glucose levels in human saliva. The sensitivity level of the devices can also be tuned by adjusting the magnitude of the gate bias.
9:00 PM - S9.7
Microfluidic Devices for Novel Synthesis.
Kyung Choi 1
1 , Bell Labs, Lucent Technologies, Murray Hill, New Jersey, United States
Show Abstract9:00 PM - S9.8
Charge Mobility in Organic Conjugated Materials Calculated from Molecular Parameters.
Yoann Olivier 1 , Jean-Luc Bredas 2 1 , Jerome Cornil 1 2
1 Laboratory for Chemistry of Novel Materials, University of Mons-Hainaut, Mons Belgium, 2 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract9:00 PM - S9.9
Electronic Wettability Switches as the Gate for Analytes in Microfluidic Systems.
Magnus Berggren 1 , Linda Robinson 1 , Nathaniel Robinson 1 , Joakim Isaksson 1 , Emilien Saindon 1 , Maria Bolin 1
1 ITN, Linkoping University, Norrkoping Sweden
Show Abstract
Symposium Organizers
Franky So University of Florida
Graciela B. Blanchet DuPont
Yutaka Ohmori Osaka University
S10: Novel Organic Devices
Session Chairs
Thursday AM, November 30, 2006
Room 304 (Hynes)
9:00 AM - **S10.1
Graphene: A New 2-dimensional System for Electronic Applications.
Philip Kim 1
1 , Columbia University, New York, New York, United States
Show Abstract9:30 AM - **S10.2
Polymer Light Source and Detector Instrumented Microfluidic Devices: Towards Quantitative Point of Care Diagnostics.
Donal Bradley 1
1 Blackett Laboratory, Imperial College London, London United Kingdom
Show Abstract10:00 AM - S10.3
Organic Field-Effect Based Devices for Pressure Detection.
Ileana Manunza 1 2 , Annalisa Bonfiglio 1 2
1 , CNISM-University of Cagliari, Cagliari Italy, 2 , INFM-CNR- S3 NanoStructures and BioSystems at Surfaces, Modena Italy
Show AbstractOrganic electronics has received a lot of attention during recent years since the performance of organic thin-film transistor has been considerably improved. Organic field-effect transistors are, in particular, promising for low-cost and large area electronic applications. In particular, innovative and attractive applications for sensing including chemical, biological and humidity sensors have been recently proposed whilst only a few examples of mechanical sensors have been reported so far.We propose an innovative substrate-free organic field-effect transistor structure based on pentacene films grown on flexible plastic film for mechanical sensing applications. Our approach takes advantage of the absence of a substrate in the device fabrication that allows to obtain a completely flexible and mechanically stable transistor that can be used as free standing device for pressure and strain sensing. Transistor-based sensors are active devices: this implies that they can be electrically characterized in a more complex way, and many different electronic parameters can be extracted in this characterization. Therefore, they are multiparametric sensors and offer the possibility of using a combination of variables in order to characterize their response to the parameter to be sensed. Finally, active sensors combine in the same device both switching and sensing functions, and this allows to easily obtain a sensing matrix of limited size and improved reliability. To study the correlation between the electrical performance of the device and different mechanical stimuli we employed two different experimental set-ups: in the first one the device is employed as a free-standing film and a pressure is applied on it by means of an air flow (isotropic deformation), in the second one the device acts as strain gauge to detect the bending of a stainless steel cantilever (uniaxial stimulus). We have observed a marked sensitivity of the drain current to the elastic deformation induced by the mechanical stimulus on the device channel. The electrical characteristics indicate that the output current varies reversibly in response to the mechanical stimulus applied to the film The reasons for such sensitivity are several: experimental data shows that the observed variation in drain source current is due to mobility variation and the pressure induced changes are also reflected in the threshold voltage and in the contact resistance. Thanks to the flexibility of the device, the low cost of the employed technology and considering that it is possible to apply the transistor structure on any kind of substrate, allowing a perfect adhesion between the substrate and the film, a variety of innovative and attractive applications can be found: biological sensors networks for life signs monitoring, sensorized clothes and smart textiles or robotic applications as electronic skin.
10:15 AM - S10.4
Novel Biosensors Based on Electrochemical Detection using Conducting Polymers.
Maria Nikolou 1 , Daniel Macaya 1 , Seiichi Takamatsu 1 2 , George Malliaras 1 , Roisin Owens 3 , Lori Romeo 3
1 MSE, Cornell University, Ithaca, New York, United States, 2 , University of Tokyo, Tokyo Japan, 3 , Agave BioSystems, Ithaca, New York, United States
Show Abstract10:30 AM - S10.5
Very High On/Off Ratio in Vertical-Type Metal-Base Organic Transistors
Ken-ichi Nakayama 1 , Masaaki Yokoyama 1
1 Graduate School of Engineering, Osaka University, Osaka Japan
Show AbstractThe vertical-type organic transistor is a promising device structure that can make the channel length much shorter, leading to low voltage operation and high frequency response. We have already reported a high performance vertical transistor having a simple layered structure composed of organic/metal/organic layers. This device was named a metal-base organic transistor (MBOT), because the inserted middle electrode behaves like a base layer in the bipolar transistors. So far, MBOTs achieved very high current density modulation exceeding 100 mA/cm2 with low voltage operation of several volts.Generally, such vertical-type organic transistors usually suffer from poor on/off ratio, because the short channel length tend to increase off current. The MBOT reported also showed low on/off ratio around 100. In this study, we succeeded in drastic improvement of the on/off ratio using heat treatment of the device in air.The device was fabricated by vacuum deposition. The first organic layer (collector layer) of perylenetetracarboxylic derivatives (Me-PTC) was deposited on an ITO glass substrate of a collector electrode. The base electrode of aluminum was deposited with a thickness of 20 nm. The second organic layer (emitter layer) of C60 and the emitter electrode of Ag were deposited. The heating treatment was performed after deposition of the collector semiconductor and the base electrode. The device was kept at 150 Celsius degree for 2 hours in air. After this treatment, the remained layers were deposited, and the measurements were performed immediately. The normal device (without heat treatment) showed output current modulation around 110 mA/cm2 for Vc (collector-emitter voltage) =5V and Vb (base-emitter voltage) =4V, while the on/off ratio remained around 120. On the other hand, the device with heat treatment after base electrode deposition showed very high on/off ratio reaching 300,000. In addition, the on current was almost not decreased, or rather increased. As a result, high current modulation around 480 mA/cm2 for low voltage operation Vc=5V and Vb=3 were achieved with high on/off ratio.This drastic improvement is due to decrease of leakage current between the base and collector, which is a main component of the off current. Even after the heat treatment, the base aluminum layer worked as an electrode having a low resistance. We are now investigating the relationship between partial oxidation of the base electrode and suppression of electron injection from the base electrode to the collector layer.
10:45 AM - S10.6
Integrated Organic Sensor Technology based on Fluorinated Polymer Electrets
Barbara Stadlober 1 , Martin Zirkl 1 , Siegfried Bauer 2 , Simona Bauer-Gogonea 2 , Ingrid Graz 2 , Norbert Gaar 2 , Reinhard Schwoediauer 2 , Günther Leising 1
1 Institute of Nanostructured Materials and Photonics, Joanneum Research, Weiz Austria, 2 Soft Matter Physics, Johannes-Kepler-University, Linz Austria
Show AbstractAmbient intelligence, safety & security, life science & health are key segments in today’s and future’s daily life. A prerequisite for providing an interface between the human being and electronic communication systems is a sensor device that can be integrated wherever needed and desired. In this context we are developing a reliable technology for the integration of pyroelectric sensors based on organic thin films onto rigid and different flexible substrates. The key element of such an integrated device is a ferroelectric polymer film that changes its polarization due to variations of light intensity and/or changes of the ambient temperature, which leads to a proportional capacitive response signal at the attached electrodes. The capacitive sensor is integrated with an organic thin film transistor for signal amplification and for providing a low-impedance signal read-out thus comprising an active sensor pixel Starting point for the fabrication of thin polymer electret films (d~300nm) is the preparation of an electret gel from solid PVDF-TrFE pellets via a sol-gel procedure. Different PVDF:TrFE compositions were investigated. The electret sol material is applied on the desired substrates via spin-casting. The whole application process is optimized in order to induce the formation of the highly polar ferroelectric phase. The resulting layer thickness and optical constants were determined by variable angle spectroscopic ellipsometry. The roughness and morphology was investigated by atomic force microscopy. After application of suitable microelectrodes the dielectric parameters of the polymer electret thin films were extracted from impedance spectroscopy. In order to achieve a maximum in the remnant polarization (which is determined by hysteresis measurements) the thin films underwent a specific stepwise poling procedure that resulted in highly anisotropic permanent polarization of the thin film. On one hand the poled capacitive elements were used as pyroelectric sensors with a characteristic pyroelectric current response. However, the capacitive elements were also integrated into organic thin film transistors in order to achieve low-impedance read-out. On the other hand unpoled films were used as part of the active gate dielectric in organic thin film transistors based on pentacene. The transistor devices are characterized by high intrinsic charge carrier mobilities and are well adaptable to polymer pyroelectric sensors. In addition to the PVDF-TrFE thin films, we also investigated several micron thick ferroelectric PVDF-TrFE foils that, after application of metallic and transparent electrodes, are used as pyroelectric sensors. With these large-signal capacitive and flexible devices it was possible to switch an organic thin film transistor from the off- into the on-state and vice versa over several orders of magnitude in drain current.
11:00 AM - S10: NovDev
BREAK
11:30 AM - **S10.7
Biosensors: The Next Big Thing for Organic Electronics?
George Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract12:00 PM - S10.8
Water-Soluble Conjugated Polyelectrolytes with Molecular Bumper for Efficient FRET Biosensor.
Han Young Woo 1 , Doojin Vak 2 , Guillermo Bazan 2
1 Nanomaterials Engineering, Pusan National University, Busan Korea (the Republic of), 2 Chemistry, Institute for Polymers and Organic Solids, UCSB, Santa Barbara, California, United States
Show Abstract There has been substantial and growing attention for recent studies utilizing water-soluble cationic conjugated polymers (CCPs) as the optical platform in fluorescence-based biosensor applications. Their charged structures allow orchestration of electrostatic interactions such that fluorescence resonance energy transfer (FRET) from the CCP to the fluorophore occurs upon a specific recognition event. In this contribution, we report the design, synthesis and photophysical properties of two new water-soluble CCPs, poly(9,9’-bis(6-N,N,N-trimethylammoniumhexyl)fluorene-alt-1,4-(2,5-bis(6-N,N,N-trimethylammoniumhexyloxy))phenylene) tetrabromide (P1i) and poly((10,10’-bis(6-N,N,N-trimethylammoniumhexyl)-10H-spiro(anthracene-9,9’-fluorene))-alt-1,4-(2,5-bis(6-N,N,N-trimethylammoniumhexyloxy))phenylene) tetrabromide (P2i). They have same electronic conjugation but the main structural difference is the presence of the anthracenyl substituent (in P2i) orthogonal to the polymer main backbone, which increases separation between chains in aggregated phases. Such substitution does not perturb the π-conjugation on the backbone. They show little difference in absorption (λ(abs) = 362 nm) and photoluminescence (λ(PL) = 411 nm) spectra with similar PL quantum yield (Φ = ~0.4). Similar HOMO-LUMO levels between two structures are also confirmed with cyclic voltammetry and UV/vis measurements. Interestingly, the two polymers behave differently as FRET donors to fluorescein-labeled single stranded DNA (ssDNA-Fl). It is possible to observe emission from ssDNA-Fl via FRET by excitation of P2i with a FRET efficiency of ~60%. Fluorescein is not emissive within the ssDNA-Fl/P1i complex, suggesting no operation in FRET biosensor. We also observed clear PL quenching (Φ = 0.27) of fluorescein after electrostatic complexation in ssDNA-Fl/P2i. Free ssDNA-Fl in water at pH = 8 shows Φ = 0.8 before complexation. It suggests another quenching pathway of Fl emission through photo-induced charge transfer (PCT) in the electrostatic complex. Both P1i and P2i have similar HOMO-LUMO electronic structures and a similar thermodynamic driving force for either FRET or PCT. It appears that PCT operates to a larger extent with P1i. We propose that the presence of the “molecular bumper” in P2i increases fluorescein emission by increasing the donor-acceptor distance, which decreases more acutely PCT quenching, relative to FRET. Understanding how lots of variations come together in complicated biological mixtures is an important requirement for a rational design of the fully optimizing FRET-based DNA assays. An examination of these differences provides insight into the intimate molecular interactions that favor FRET versus energy-wasting PCT, indicating that careful attention needs to be paid to molecular design strategies that fine tune the donor-acceptor distances at the molecular level to minimize the PCT quenching.
12:15 PM - S10.9
Development of Flexible Photo Sensor and Memory Devices Based on Organic Photo-FET.
Manabu Yoshida 1 , Hiroki Kawai 2 , Takeshi Kondo 2 , Takeshi Kawai 2 , Kouji Suemori 1 , Sei Uemura 1 , Satoshi Hoshino 1 , Takehito Kodzasa 1 , Toshihide Kamata 1
1 Organic Semiconductor Device Research Group, National Institute of Advanced Science and Technology, Tsukuba, Ibaraki, Japan, 2 Faculty of Engineering, Tokyo University of Science, Shinjuku, Tokyo, Japan
Show AbstractRecent advances have been achieved in organic electronics researches. Especially, improvements of device properties of Organic Field Effect Transistors (OFETs) and organic solar cells have been remarkable. In this study, we have fabricated OFETs having photosensitivity and have utilized these devices for developing novel photo sensor and memory devices. Ordinary organic photo FETs are based on photosensitivity of organic semiconductors used as an active layer [1,2]. However, we have developed organic photo FETs using photosensitivities of insulator materials in FETs. Advantages of using photosensitivities of insulator materials are to lower operating gate voltage, to raise on-off ratio, to raise μFET, and so on. Using these excellent device properties of the photo FETs, we are able to prepare high-sensitive photo sensor and memory devices. As photosensitive insulator material, 2,4,7-trinitrofluorenone (TNF) doped poly-(N-vinylcarbazole) (PVK) was employed. These materials are known as reliable photoreceptors in the electrophotography field. As the active material on the photosensitive insulator layer, pentacene or poly-(3-hexylthiophene) (P3HT) was employed. The drain-source electrodes (Au, Ag or Al) were deposited on the active layer. Patterned PEDOT:PSS electrodes on PET films or Indium Tin Oxide (ITO) electrodes on glass plates were employed as transparent gate and substrate. Photo-FET properties were measured during illuminating the photosensitive insulator layer from the gate sides by using LEDs with different colors. When the illuminated light was absorbed into insulator material effectively, two or more orders of magnitude higher μFET than dark condition was observed. We have already reported that this improvement of transistor properties is due to the effective charging of the gate capacitor by providing photogenerated charges in the insulator layer [3]. Observations of photo memory effects in the photo FETs depend on formations of energy barriers at semiconductor/drain-source electrodes interfaces, because the energy barrier prevent the channel charges from escaping from the channel region even after the gate voltage is switched off. In conclusion, we have succeeded in fabricating flexible photo sensor and memory devices by using high-sensitive organic photo FETs. [1] K. S. Narayan, and N. Kumar, Appl. Phys. Lett., 79, 1891 (2001). [2] K. S. Narayan, D. Kabra, and S. Dutta, Mat. Res. Soc. Symp. Proc. 814, I13.5.1 (2004). [3] M. Yoshida, H. Kawai, T. Kawai, S. Uemura, S. Hoshino, T. Kodzasa, and T. Kamata, Proc. SPIE 5940, 594003 (2005)
12:30 PM - S10.10
Highly Reproducible Electric Bistability in an Organic Single Layer Device with Ag Top Electrode.
Masaya Terai 1 , Katsuhiko Fujita 1 2 , Tetsuo Tsutsui 1 2
1 Department of Applied Science for Electronics and Materials, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka, Japan, 2 , Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka, Japan
Show AbstractElectrical bistable devices with a simple device structure, high stability and high reproducibility have been fabricated. Switching between high impedance (OFF state) and low impedance (ON state) states were attained by the change of applied voltage patterns.An organic bistable device, glass substrate/poly-chloro-p-xylylene(PCPX)/Al/2-amino-4,5- -imidazoledicarbonitrile (AIDCN)/Ag was fabricated. The thickness of PCPX, Al, AIDCN and Ag layers were 1000, 60, 150 and 60 nm, respectively. The PCPX film has been reported to provide a flat defect-free surface with excellent electrical insulating property. A low impedance state (ON state) appeared, when the voltage was ramped up above the threshold voltage Vth (+6 V) and was continuously ramped down to 0 V (triangle-sweep). On the other hand, a high impedance state (OFF state) appeared, when the voltage was ramped up above Vth, and was suddenly set back to 0 V (saw tooth-sweep). The OFF and ON states of the device can be inter-converted by simply changing voltage sweep modes. The bistable behaviors were observed under both positive and negative bias conditions, indicating that the origin of the observed behaviors is not located at a specific electrode-organic film interface regions, but extends to a bulk region crossing the organic film.To elucidate the working mechanism in both the OFF and ON states in more detail, we measured the dynamic dielectric response in the organic bistable device at the OFF and ON states at the applied voltage of +1 V and the frequency range of 10 Hz - 1 MHz. The relative dielectric constant (ε') did not depend on frequency up to about 0.1 MHz, and started to decrease at around 1 MHz. The values ofε' in the both states were almost the same. On the other hand, the relative dielectric loss factors (ε'') in the both states show the linear decrease with slopes –1 in log(ε) vs. log(ε'') plots at the low frequency regions, and the values of ε'' between the OFF and ON states showed large difference despite the same applied voltage of +1 V. The constant values of ε' at low frequency in the both states suggest that the electric bistability are not induced by charge accumulation in the organic film. The ε'' decrease with the slopes of -1 for low-frequency dispersion indicates the presence of large amounts of mobile electronic carriers across the organic film.We here propose one of plausible working mechanisms for the electric bistability observed in this study. Majority part of electric current in the low-impedance state is due to filamental percolation via Ag nanoparticles, which are embedded in the organic film by vacuum-sublimation and penetrated into the film by migration under applied field. Changes of percolation pathways corresponding to the ON-OFF states may be induced by the application of different voltage patterns. We found that the bistable behavior of our device using Ag as a top electrode was much more stable than that of the device using Al as a top electrode.
12:45 PM - S10.11
Installing Functionality on Molecule-bridged SWCNT Gaps
Xuefeng Guo 1 , Stephen O'Brien 1 , Ronald Breslow 1 , Shalom Wind 1 , James Hone 1 , Philip Kim 1 , Colin Nuckolls 1
1 , Columbia University, New York, New York, United States
Show AbstractS11: Organic Photovoltaic Devices
Session Chairs
Thursday PM, November 30, 2006
Room 304 (Hynes)
2:30 PM - **S11.1
Molecular Multilayer Organic Solar Cells with Large Excitonic Diffusion Length.
Bernard Kippelen 1 , Seunghyup Yoo 1 , William Potscavage 1 , Benoit Domercq 1
1 School of ECE, Georgia Tech, Atlanta, Georgia, United States
Show Abstract3:00 PM - S11.2
Dielectric Capping Layers for Enhanced Optical Transmission Through Metallic Electrodes in Organic Photovoltaic Devices.
Brendan O'Connor 1 , Max Shtein 2 , Kevin Pipe 1
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 Abstract3:15 PM - S11.3
Nanoscale Studies of Donor / Acceptor Materials Morphology in Organic Photovoltaic Devices.
Anamika Gopal 1 , Rick Davis 2 , Martin Drees 3 , Brian Holloway 3 , James Heflin 1
1 Dept. of Physics, Virginia Tech, Blacksburg, Virginia, United States, 2 Dept. of Chemical Engineering, Virginia Tech, Blacksburg, Virginia, United States, 3 , Luna nanoWorks, Danville, Virginia, United States
Show AbstractOrganic photovoltaic devices rely on photo-excited charge transfer from an electron donor such as a conducting polymer, to a high electron affinity acceptor such as C60 or its derivatives. Following the important step of charge transport to the electrodes, the charges thus generated are collected as photocurrents. A close proximity of the donor and acceptor components is required to ensure an efficient electron transfer process. In addition to this, a continuously connected path of each component is required from the site of charge transfer to the electrode for efficient charge collection and optimum device performance. Device efficiencies are increased by utilizing improved materials as donors and acceptors as well as controlling the nanoscale morphology of the thin film devices. Our study concentrates on thermally interdiffusing a bilayer of the donor and acceptor materials to create a concentration gradient, in order to optimize both the charge transfer and charge transport processes. Such concentration gradients in poly (3-octylthiophene) (P3OT) – C60 photovoltaic devices have been achieved by thermally interdiffusing a bilayer of the two materials at temperatures above the glass transition temperature and below the melting point of the polymer; at such temperatures the polymer softens allowing the fullerene to diffuse in. An in-depth study on devices interdiffused at 130 0C for 5 minutes and air cooled in an inert atmosphere is presented. Experimental study of component layer thickness variations yields optimum performance for devices with P3OT and C60 initial layer thicknesses each in the range 40 to 60 nm. Auger spectroscopy, combined with argon-ion beam milling is used to record the concentration gradient in the film by monitoring the sulfur content from the polymer backbone. These studies reveal that the best devices have a uniform concentration gradient that stretches through the entire thickness of the donor-acceptor layers. This technique is also used to monitor the concentration gradients obtained as the interdiffusion conditions are varied. The effects of varying the starting donor and acceptor layer thicknesses on device performance have also been modeled theoretically. This model considers a mulitple layered structure and takes into account the electric field distribution within the devices. The results of the model compare favorably with the experimental data. We also present preliminary results obtained from thermally interdiffused devices with poly (3-hexylthiophene) (P3HT) as donor and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) as acceptor.
3:30 PM - S11.4
Enhanced Efficiency and Stability in P3HT:PCBM Bulk Heterojunction Solar Cell by using TiO2 Hole Blocking Layer.
Susumu Yoshikawa 1 , Akinobu Hayakawa 1 , Osamu Yoshikawa 1 , Supachai Ngamsinlapasathian 1 , Takuya Fujieda 1 , Kaku Uehara 1
1 Institute of Advanced Energy, Kyoto University, Uji, Kyoto, Japan
Show Abstract3:45 PM - S11.5
Disposable On-Chip Chemiluminescence Detection Based On Integrated Low-Cost High-Sensitivity Plastic Organic Photodiodes
Rupa Das 1 , Lichun Chen 1 , Xuhua Wang 1 3 , Oliver Hofmann 3 , John deMello 2 3 , Andrew deMello 2 3 , Donal Bradley 1 3
1 Physics, Imperial College London, London United Kingdom, 3 , Molecular Vision Ltd., London United Kingdom, 2 Chemistry, Imperial College London, London United Kingdom
Show AbstractWe have designed and fabricated novel low-cost high-sensitivity disposable organic plastic photodiodes for integrated detection of on-chip chemiluminescence assays, enhancing the commercial prospects for point-of-care diagnostic testing. Chemiluminescence (CL) is an effective way to monitor low level analyte concentrations with extremely high responsivity. CL is particularly attractive for portable microfluidic assays since CL reaction acts as an internal light source, thereby lowering instrumentation and power requirements while providing a low signal background. Traditional methods to monitor CL assays using photomultiplier tubes (PMTs) or Si photodiodes are non-portable, external and expensive.To provide a low-cost route towards disposable diagnostic devices we have developed solution processable plastic organic photodiodes integrated with PDMS based microfluidic chips. The polymer photodetectors are made from a blend of regioregular poly(3-hexylthiophene) [P3HT] and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)-C61 [PCBM]. The blend was spin coated over a patterned poly(3,4-ethylenedioxythiophene) (PEDOT) conducting anode which had been previously deposited via a Vapour Phase Polymerization (VPP) technique on a polyethylene naphthalate (PEN) substrate. The device structure is completed by deposition of an aluminum cathode through a shadow mask. Our detectors have a photoresponse from 380nm to 650nm, with an external efficiency of ~40% at 430nm.To test the suitability of our integrated microfluidic chip for point-of-care testing we selected a phosphatase based commercial CL bioassay. Alkaline Phosphatase (ALP) is selected as the model compound for the assay. The ALP enzyme is abundantly present in blood, the intestines, liver and bone cells and an abnormal level of this enzyme is a sign of bone or liver disease. Lumigen APS-5 was used as the CL reagent. CL reaction was initiated by pumping the CL reagent and the ALP test solution into a Y-type micromixer. The CL emission is detected by the polymer photodiode at a fixed point along the mixing/outlet channel. CL reagent emission occurs at 430nm which overlaps well with the spectral responsivity of the polymer detector. By planar integration of the photodiode, spatial matching of the pixel size to the microchannel dimensions and by chemically tuning the detector responsivity to the luminescence emission we have achieved sensitivities comparable to that of current state of the art off-chip PMT detection methods.Currently, even with a non-optimized process, a 100-fold sensitivity gain is observed using these novel devices when compared to our previous devices fabricated using organic small molecule photodiodes. Furthermore, with the optimization of our VPP-PEDOT film characteristics, reduction of the background signal by light-proofing, and improvements to the photodiode fabrication protocol, it is estimated that a further 100-fold improvement to the limit-of-detection can be accomplished.
4:00 PM - S11: OrgPhoDev
BREAK
4:15 PM - **S11.6
Bulk Heterojunction Organic Thin-Film Solar Cells using High Hole Mobility Donors
Kazuhiro Saito 1 , Tetsuya Taima 1 , Toshihiro Yamanari 1 , Jun Sakai 2
1 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 2 Advanced Technologies Development Laboratory, Matsushita Electric Works, Ltd., Kadoma, Osaka, Japan
Show AbstractAlthough phthalocyanines (donor) have been used for forming bulk heterojunctions with C60 (acceptor) to obtain highly efficient organic thin-film solar cells based on vacuum-deposited small molecular-weight organic materials, their hole mobilities are not always sufficient compared with C60. Introduction of high hole mobility donors instead of phthalocyanines is expected to improve carrier transport in the cells. Pentacene and oligothiophene (6T) are well-known molecules, which show high hole mobility, in the field of OTFTs. We investigated the relation between device structure and photovoltaic properties in bulk heterojunction organic thin-film solar cells using the high hole mobility donors. Formation of the bulk heterojunciton layer for small molecular-weight materials is performed by co-evaporation of donor and acceptor molecules in vacuum. However, power conversion efficiencies of bulk heterojunction cells based on 6T:C60 and pentacene:C60 systems prepared by the co-evaporation method were poorer than those of 6T/C60 and pentacene/C60 bilayer heterojunction cells, since the co-evaporated films showed remarkable surface roughness by crystallization. To prevent such crystallization of the molecules, we had to introduce new device fabrication techniques. For the 6T:C60 system, the co-evaporated film showed smooth surface when the volume ratio of [6T]:[C60] was changed from 1:1 to 1:5, and the power conversion efficiency was improved drastically. For the pentacene:C60 system, alternating evaporation of pentacene and C60 (thickness; 1-3 nm) to form a multilayered structure similar to the superlattice produced good results.
4:45 PM - **S11.7
Electronic Device Applications of Fullerene Derivatives.
Yoshiharu Sato 1 , Takaaki Niinomi 1 , Masahiko Hashiguchi 1 , Yutaka Matsuo 1 , Eiichi Nakamura 1 2
1 ERATO Nakamura Functional Carbon Complex Project, JST, Tokyo Japan, 2 Department of Chemistry, The University of Tokyo, Tokyo Japan
Show Abstract Fullerenes such as C60 and PCBM have been applied to both organic photovoltaics (OPV) and organic light-emitting diode (OLED). We have developed new type of fullerene derivatives for these device applications. Based on their fundamental properties, HOMO/LUMO levels, optical gaps, carrier transport, some examples for OPV and OLED applications are described. In the case of OPV, new fullerene derivatives are reported as an acceptor of the active layer in comparison with C60 and PCBM. The relationship between donor and fullerene acceptor is discussed. For the application of OLED, it is demonstrated that electron-accepting character of the fullerene is effective as an electron transport material.
5:15 PM - S11.8
Carbon Nanotubes as Hole Collectors in Organic Solar Cells.
Jao van de Lagemaat 1 , Teresa Barnes 1 , Garry Rumbles 1 , Sean Shaheen 1 , Timothy Coutts 1 , Chris Weeks 2 , Igor Levitsky 2 , Jorma Peltola 2 , Paul Glatkowski 2
1 , NREL, Golden, Colorado, United States, 2 , Eikos Inc., Franklin, Massachusetts, United States
Show Abstract5:30 PM - S11.9
Planar Inverted Hybrid Organic Photovoltaic Devices
Matthew White 1 , Sean Shaheen 2 , Dana Olson 3 , Todd Monson 3 , Julia Hsu 3 , David Ginley 2
1 Physics, University of Colorado, Boulder, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNanostructured oxide layers are being examined for electron extraction from hybrid organic photovoltaic devices. In this work, the oxide-polymer interface is investigated on planar ZnO surfaces contacting poly-3-hexylthiophene (P3HT). ZnO is deposited on the ITO surface from a solution precursor and acts as a hole blocking, electron transporting layer. This layer serves to invert the operation of the device and allows for the use of a non-reactive metal as the top hole-collecting electrode. The planar layer is a useful test geometry for various adsorbates that may later be used in higher surface area nanostructured layers. For example, adsorption of a carboxylic acid derivative of C60 has been shown to improve device characteristics. In addition, inverted planar devices with a P3HT:[6,6]-phenyl C61 butyric acid methylester (PCBM) bulk heterojunction active layer and silver metal electrodes have been shown to work at 2.6% power conversion efficiency. Similar devices are used to explore the possibility of forming the top electrode through a reversible lamination process.
5:45 PM - S11.10
Flexible Polymer Solar Cell.
Lichun Chen 1 , Rupa Das 1 , Jenny Nelson 1 , James Durrant 2 , Donal Bradley 1
1 Department of Physics, Blackett Laboratory, Imperial College, London United Kingdom, 2 Electronic Materials Group, Department of Chemistry, Imperial College, London United Kingdom
Show AbstractS12: Poster Session: Electronic Structure and Device Physics
Session Chairs
Friday AM, December 01, 2006
Exhibition Hall D (Hynes)
9:00 PM - S12.1
Characterization of Nanoscale Conducting Polymer Wires Formed using Electrochemical Dip Pen Nanolithography
Adelaja Arojurae 1 , Shaun Filocamo 2 , Selim Unlu 3 4 , Bennett Goldberg 4 , Mark Grinstaff 2 , Catherine Klapperich 1
1 Biomedical and Manufacturing Engineering, Boston University, Boston, Massachusetts, United States, 2 Chemistry, Boston University, Boston, Massachusetts, United States, 3 Electrical Engineering, Boston University, Boston, Massachusetts, United States, 4 Physics, Boston University, Boston, Massachusetts, United States
Show AbstractAn integrated device that incorporates micro and nanoscale components was fabricated on a semiconducting surface by patterning and depositing simple metal structures on silicon substrates. A conducting polymer nanowire was written across the metal electrodes using AFM electrochemical dip pen nanolithographic (e-DPN) technique. Integrated microscale electrodes allow the nanowires to be easily probed. In a typical experiment, the tip of the AFM is coated with conducting polymer monomer solution (aniline) and is put into tapping mode contact with the surface under an applied potential. A water meniscus forms between the tip and the surface and transports monomers to a precise location between the electrodes, where the electrochemical polymerization of polyaniline occurs. Nanowires of 1-5 microns in length and 10 nm in thickness can be written between the electrodes which are spaced 0.5-2.0 microns apart. Properties of these conducting polymer nanowires on the fabricated device were characterized. The electrical conductance properties of the polymer nanowires were measured using two-terminal probe resistance measurements. A linear response indicates that the gold electrodes made Ohmic contact to the conducting polymer nanowires. Preliminary data shows the conductivity of the conducting polymer nanowires is measureable using microscale electrodes. Devices with a nanowire show an increase in conductance compared to devices without a nanowire. Conductance increases rapidly when the device with a nanowire is doped with HCl. Polypyrrole and poly(ethylenedioxythiophene) nanowires are also studied. To confer binding and specificity of conducting polymer nanostructures, we have begun to incorporate (through covalent bioconjugation of the conducting polymer monomers) specific binding probes (ligand-receptor interactions) for various targets such as a protein, a virus, or bacterial spores. The results of this study should aid in the general understanding of polymer conductivity in nanostructures and to open new avenues of research in the area of biological detection devices.
9:00 PM - S12.10
Photoconductivity of Carbon Nanotube Doped Water Soluble Polythiophene
Daeyoung Kim 1 , Yuan Xu 1 , Jaewu Choi 1
1 Electrical and Computer Engineering, Wayne State University, Detroit, Michigan, United States
Show Abstract Ploythiophene based water soluble conducting polymer, PTEBS (polythiophene - Sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate)], shows significant photoresponse, which could be a strong candidate for photovoltaic devices. However, the low conductivity of the polymer is an obstacle for efficient electron–hole separation, which is critical to the high performance photovoltaic devices. In this study, we investigate the photoresponse of single walled carbon nanotube (SWCNT) doped polymer film to solar spectrum. The charge transfer rate of PTEBS is largely increased by doping with carbon nanotubes, which are functionalized by carboxyl group. SWCNT doped polymer composite also shows a significant enhancement in the photoresponse. This is attributed to the efficient separation of electron-hole pairs at the interference between SWCNT and polymer. This is correlated to the high electrical conductivity and one-dimensionality of SWCNT, the nature of SWCNT as a great electron acceptor, and improvement of mobility of charge carriers.
9:00 PM - S12.11
Influence of Nanoparticle Functionalization on the Optical and Electrical Properties of Inorganic-Organic Photonic Structures
Rachel Jakubiak 1 , John Busbee 1 , Lalgudi Natarajan 2 , Vincent Tondiglia 2 , David Tomlin 3 , Timothy Bunning 1 , Richard Vaia 1 , Paul Braun 4
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , SAIC, Inc., Beavercreek, Ohio, United States, 3 , UES, Inc., Dayton, Ohio, United States, 4 , University of Illinois , Raleigh, North Carolina, United States
Show AbstractHolographic photopolymerization of monomer-nanoparticle-liquid crystal suspensions enables one-step fabrication of organic-inorganic photonic crystal structures with electrical switchability. Acrylate-functionalized silica nanoparticles introduced into holographic polymer dispersed liquid crystals (H-PDLCs) increased the optical performance and decreased the electric field needed to switch the structures by a factor of three. Modification of the nanoparticle functionality allows tailorability of the index of refraction profile and liquid crystal droplet morphology to elucidate preferred optical and electrical properties. This effect is illustrated in the differences in the laser action of pyrromethene 597 imbedded in silica/H-PDLC structures that have varying degrees of nanoparticle functionality. The presence of the nanoparticles enhances the resonance required for stimulated emission; however the nanoparticles also increase scattering losses. Trade-offs between these two effects will be discussed.
9:00 PM - S12.12
Characterization of Water Permeability in Barrier Films.
Udo Pernisz 1 , Ludmil Zambov 1 , Vasgen Shamamian 1 , Randall Siegel 1
1 Specialty Films, Dow Corning Corporation, Midland, Michigan, United States
Show AbstractThin–film electronic devices, in particular those based on organic materials such as OLEDs, require protection against moisture in order to achieve adequate lifetime for commercial applications. The required barrier properties suitable for both rigid and flexible substrates have progressed below the detection limit of commercially available intruments. Therefore, a method based on the reaction of a Ca metal film with water has been adopted for determining the water vapor transmission rate (WVTR) to assess Dow Corning’s barrier technology under exposure to both ambient and accelerated test conditions. The basis for this Ca test, its capability for defect imaging, problems solved with background water ingress in the test sample preparation, and the limitations of this version of the Ca test will be discussed. Comparison with the established industry standard for measuring WVTR shows that this method extends the measurement range nearly two orders of magnitude, establishing a barrier performance capability at water vapor transmission rates below 10–4 g m–2 d–1. This work was supported in part by the United States Display Consortium (USDC RFP03-81) and the Army Research Laboratory (ARL DAAD19-02-3-0001).
9:00 PM - S12.13
Non-dispersive Ambipolar Carrier Transports in tris (8-hydroxyquinoline) Aluminum (Alq3) and the Mobility Influence Due to Ambient Gases and Molecular Doping.
H. H. Fong 1 2 , Shu K. So 2
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Physics, Hong Kong Baptist University, Hong Kong Hong Kong
Show Abstract9:00 PM - S12.14
Optically Transparent Conducting Polymers from Fused Heterocycles.
Gregory Sotzing 1 , Arvind Kumar 1 , Tanmoy Dey 1 , Mustafa Yavuz 1 , Venkataramanan Seshadri 1 , Byoungchul Lee 1 , Jayesh Bokria 1 , Yogesh Ner 1
1 Department of Chemistry and Polymer Program, Institute of Material Science, University of Connecticut, Storrs, Connecticut, United States
Show Abstract9:00 PM - S12.15
Molecular Order and Electron Transport Characterisation of Structures Nanografted into Self Assembled Monolayers using conductive tip AFM techniques.
Denis Scaini 1 2 , Jian Liang 4 , Matteo Castronovo 5 2 , Martina Dell'Angela 1 2 , Loredana Casalis 1 , Giacinto Scoles 1 3 4
1 , ELETTRA Synchrotron, Trieste Italy, 2 Department of Physics, University of Trieste, Trieste Italy, 4 Chemistry Department, Princeton University, Princeton, New Jersey, United States, 5 , TASC-INFM, Trieste Italy, 3 , International School for Advanced Studies (SISSA), Trieste Italy
Show AbstractConductive Tip AFM (CT-AFM) is commonly used for electrical characterization of organic and inorganic surface systems. Understanding electron transfer at the molecular level may lead to the development of molecular assemblies with unique properties and is of great importance for the advancement of both organic, molecular and bio-electronics. In this work we follow an approach to the study of Metal-molecule-Metal surface junctions that uses a combination of different AFM-based techniques. We first use Nanografting to build nanopatches of the molecules of interest into a hosting reference self assembled monolayer (SAM) typically made of alkanethiols. After the tip is changed to a conductive one, CT-AFM is used to characterize electrically the whole system recording, at the same time, the system topography. Some of the advantages of this approach are the possibility to build and study a wide range of different monolayers side-by-side on the same sample and the in-situ control of the quality both of the hosting monolayer and that of the grafted patches. Results will be presented on saturated and unsaturated thiols self-assembled and nanografted on Au(111) surfaces. We will also show a clear correlation between the contrast in current images and the quality of molecular packing inside the nanopatches.
9:00 PM - S12.16
Controlling Molecular Orientation in Para-sexiphenyl Thin Films
Gregor Hlawacek 1 , Andrei Andreev 1 , Christian Teichert 1 , Helmut Sitter 2 , Serdar Sariciftci 3 , Roland Resel 4 , Steve Berkebile 5 , Georg Koller 5 , Mike Ramsey 5
1 Institute of Physics, University of Leoben, Leoben Austria, 2 Institute for Semiconductor and Solid State Physics, University of Linz, Linz Austria, 3 Linz Institute of Organic Solar Cells, University of Linz, Linz Austria, 4 Inst. for Solid State Physics, Technical University Graz, Graz Austria, 5 Inst. for Experimental Physics, University of Graz, Graz Austria
Show AbstractPara-sexiphenyl (6P) is an important member of the group of small-molecule optically active semiconductor materials that have shown a high potential for applications. The possible applications so far include organic thin film transistors (OTFTs), organic light emitting diodes (OLEDs), waveguides, and lasers. For all these applications the control of molecular orientation as well as film morphology is important. For light emitting or light conducting applications, lying molecules as they are found in the – for 6P typical – needle or chain like morphology are appropriate. However, for OTFTs a homogeneous film made of upright standing molecules is more desirable.Here, we report on the growth of self-organized large-area films consisting of either upright standing or flat lying 6P molecules on mica(001) [1] and TiO2(110) [2,3]. The morphology and molecular orientation were investigated by atomic-force microscopy (AFM) and X-ray, respectively.It could be shown that at least for the substrates presented, both molecular orientations – upright and flat lying – are possible. Furthermore, the common fiber growth morphology could be refined into a needle and a chain like growth. For the chain like growth a novel growth model is proposed. This model is based on the spontaneous self-organization of small individual 6P crystallites into the observed chains of crystallites. The process is mediated by strain and a linear defect network in the wetting layer [1]. On TiO2(110) substrates, a self-organized stripe phase consisting of upright standing molecules had been observed that might be influenced by the anisotropy in surface diffusion and/or anisotropic incorporation at island edges [3]. [1] C. Teichert, et al., Appl. Phys. A 82 (2006) 665–669.[2] G. Koller, et al., Adv. Mater. 16 (2004) 2159-2162.[3] G. Hlawacek, et al., phys. stat. sol. a 202 (2005) 2376-2385.This research is supported by Austrian Science Fund (FWF) in the framework of the FWF National Research Network “Interface controlled and Functionalised Organic Films” (S9707-N08).
9:00 PM - S12.17
Design of Hybrid Organic/Inorganic Semiconductors via Simulation.
Feng Qi 1 , Murut Durandurdu 2 , John Kieffer 1
1 MSE, U of Michigan, Ann Arbor, Michigan, United States, 2 Physics, University of Texas at El Paso, El Paso, Texas, United States
Show Abstract9:00 PM - S12.19
Efficient Electron Injection in Flexible Organic Light Emitting Diodes with Magnesium Doped tris (8-hydroxyquinoline) Aluminum Layer.
Kihyon Hong 1 , Soo Young Kim 1 , Woong-Kwon Kim 1 , Jong-Lam Lee 1
1 Material Science and Engineering, Pohang Universty of Science and Technology, Pohang Korea (the Republic of)
Show Abstract9:00 PM - S12.20
Synthesis and Characterization of High Density Fluorescent Photochromic Polymer.
Yong-Chul Jeong 1 , Seung Hyun Song , Sung Yang 1 , Kwang-Hyun Ahn 1
1 , Kyung Hee University, Yongin Korea (the Republic of)
Show Abstract9:00 PM - S12.22
STM Investigation of SAM-based Molecular Electronics: the Significance of Local Density of States.
Alexandru Riposan 1 , Christopher Fleming 1 , Gang-yu Liu 1
1 Chemistry, University of California, Davis, California, United States
Show AbstractA scanning tunneling microscopy (UHV-STM) study of thiol self-assembled monolayers (SAMs) and thiol modified gold nanoparticles is presented, which reveals new insights into the electronic properties of organic SAMs and the electron transport in molecular electronics. For the first time, a detailed investigation of the STM imaging of alkanethiol SAMs is carried out systematically as a function of the bias voltage, tunneling current, and tip – termini separation. Undecanethiol SAMs /Au(111) annealed in UHV exhibit two distinct c(4x2) structures with four non-equivalent molecules per unit cell. For both structures, reversible contrast variations occur upon systematically tuning the imaging parameters and the tip – termini distance. These contrast transitions originate from probing the corresponding local density of states (LDOS) of each molecule, and not from structural changes under the influence of the STM tip. Diagrams reflecting the dependence of STM contrast on the imaging (I, V) conditions are presented for both phases. The STM contrast is particularly sensitive to the tip – termini separation in the range of 0.5 – 2.5 Å, reflecting the distance dependence of LDOS. For the first time, we demonstrate that the LDOS contribution can override the physical height variations in the STM contrast of alkanethiol SAMs. Single electron tunneling through thiol modified gold nanoparticles at room temperature was successfully captured via careful immobilization of these particles on Au(111) surfaces. The UHV-STM investigation revealed the characteristic I-V behavior, a Coulomb blockade of 1 eV and fine Coulomb staircases of 0.2 - 0.3 eV.
9:00 PM - S12.23
Controlling the pKa for Protonic Doping of Polyaniline by Non-covalent Complexation.
Hui Wan 1 , Sze Yang 1
1 Chemstry Department, Univ of Rhode Island, Kingston, Rhode Island, United States
Show Abstract Polyaniline is known to exhibit an acid/base-induced doping/dedoping. This p-conjugated polymer is in the electronically conductive emeraldine salt state (ES) in acidic aqueous solution (pH<5), but is transformed into the insulating emeraldine base (EB) form at higher pH. In thermodynamic terms, the polyaniline has a pKa=5.5 for the chemical equilibrium . The relatively low pKa implies dedoping in moisture and marine environment. It is desirable to expand the environmental stability of polyaniline. We report a synthetic method for shifting the pKa to a higher value. The synthesis leads to the formation of non-covalent complexes between polyaniline and a polyelectrolyte. Depending on the choice of the polyelectrolyte and the condition of the synthesis, we can control the pKa value for the conductor-to-insulator to spread the range of pH from 5.5 to 9.0. The electrostatic origin for this unusually large pKa shift is born out from a systematic study of the structure-property relation.
9:00 PM - S12.24
Scanning Tunneling Microscopy of the Second Layer Pentacene Molecules on Si (111) Surface
Soonjoo Seo 1 , Paul Evans 2
1 Materials Science, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractThe morphology and crystal structure of the first few molecular layers at the interface next to the dielectric layer affect the electrical properties of organic thin films. Structural defects in a very thin accumulation layer such as dislocations and grain boundaries limit the performance of organic thin film transistors. There is little knowledge of intragrain structure in a single island, or the molecular scale structure of the boundaries between islands. To probe these structures, pentacene was deposited on a clean Si (111) surface, on which a first disordered layer of strongly bonded pentacene molecules is known to form. Our approach has been to use this disordered layer as a chemically and structurally smooth but conducting analog of the gate insulator surface in our structural studies using scanning tunneling microscopy.
9:00 PM - S12.25
Molecular Structure and Layered Morphology of Tetracene Films on Hydrogen-terminated Si(001).
Xiaorong Qin 1 , Andrew Tersigni 1 , Jun Shi 1 , Detong Jiang 1
1 Physics, University of Guelph, Guelph, Ontario, Canada
Show Abstract9:00 PM - S12.26
Asymmetric Tunneling Currents Across Metal-molecule-metal Junctions.
Michael Ford 1 , Rainer Hoft 1 , Nicholas Armstrong 1 , Michael Cortie 1
1 Institute for Nanoscale Technology, University of Technology, Sydney, Broadway, New South Wales, Australia
Show Abstract9:00 PM - S12.27
Fabrication and Optical Characteristics of Surface Emission Laser by using Anodic Porous Alumina Matrix.
Toshiaki Kondo 1 2 , Motohiro Yamada 1 , Kazuyuki Nishio 1 3 , Shiyoshi Yokoyama 4 , Shinro Mashiko 4 , Hideki Masuda 1 3
1 , Tokyo Metropolitan University, Hachioji Japan, 2 , Japan Society for the Promotion of Science, Tokyo Japan, 3 , Kanagawa Academy of Science and Technology, Kanagawa Japan, 4 , National Institute of Information and Communications Technology, Kobe Japan
Show Abstract9:00 PM - S12.28
Direct Measurement of the Charge Carrier Diffusion Constant in pi Electron Systems by High Sensitivity Scanned Probe Microscopy.
Showey Yazdanian 1 , Seppe Kuehn 1 , John Marohn 1
1 Chemistry, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - S12.29
Transition Between Energy Legvel Alignment Regimes at a Low Bankdgap Polymer - Electrode Interfaces.
Annica Crispin 1 , Xavier Crispin 2 , Mats Fahlman 2 , Magnus Berggren 2 , William Salaneck 1
1 IFM, Linköping University, Linköping Sweden, 2 ITN, Linköping University, Norrköping Sweden
Show Abstract9:00 PM - S12.3
Characterisation of Light-Emitting Electrochemical Cells by Means of Atomic and Electrostatic Force Microscopy
Harald Plank 1 2 , Birgit Jahn 1 , Alexander Blümel 1 , Christian Seppi 2 , Gernot Mauthner 2 , Ullrich Scherf 3 , Emil List 1 2 4 , Werner Grogger 5
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 and Institute of Nanostructured Materials and Photonics, Joanneum Research, Weiz Austria, 3 , Bergische Universität Wuppertal, Makromolekulare Chemie, Fachbereich Chemie, Wuppertal Germany, 4 , NanoTecCenter Forschungsgesellschaft mbH , Weiz Austria, 5 Research Institute for Electron Microscopy and Fine Research, Graz University of Technology, Graz Austria
Show AbstractConjugated polymer devices providing combined ionic and electronic conductivity raise fast-growing interest due to their potential applications in opto-electronics, batteries, chemical sensing, etc. To study the bulk material and interface related properties of the ongoing doping processes in such light-emitting electrochemical cells (LECs) atomic force microscopy (AFM) and its electrostatic extensions (EFM) have been utilised for a variety of polymer/salt combination. In particular, methyl-substituted ladder type poly(paraphenylen) (mLPPP) was used as the electroactive polymer; crown-ether and poly(ethyleneoxide) with different molecular weights were used as ionic conductors. Lithium-trifluoromethanesulfonate and lithium-bis(trifluoromethane)sulphonamide were used as salts. The spin-cast films were characterised in AFM height (tapping), tapping-phase, EFM-phase and Kelvin probe force microscopy (KPFM) in inert conditions (N2). While height and tapping-phase measurements revealed lateral and partly vertical phase separations, the electrostatic measurement modes gave complementary information, which enabled the assignment of the different phases to the individual material components. After this basic characterisation of as-spun films LECs were prepared in a surface cell geometry with a few µm gap between Au electrodes. Such devices were then investigated under operation. In particular, the formation and saturation behavior of n-, p- and non-doped intrinsic zones in between were studied in dependence of applied voltages in a qualitative and quantitative manner by means of EFM-phase and KPFM, respectively. The results have been correlated with the overall LECs performance and IV characteristics.
9:00 PM - S12.30
Energy Level Alignment at Weakly Interacting Polymer/Metal Interfaces
Parisa Sehati 1 2 , Carl Tengstedt 1 , Wojciech Osikowicz 2 , William Salaneck 2 , Mats Fahlman 1
1 Department of Science and Technology, Linkoping University, Norrkoping Sweden, 2 Department of Physics, Chemistry and Biology, Linkoping University, Linkoping Sweden
Show Abstract9:00 PM - S12.31
Organic Crystalline Nanofibers: Manipulation, Integration, and Electrical Characterization.
Jakob Kjelstrup-Hansen 1 , Henrik Henrichsen 2 3 , Kjetil Gjerde 1 , Casper Clausen 1 , Daniel Engstrøm 1 , Kasper Thilsing-Hansen 2 , Horst-Günter Rubahn 2 , Peter Bøggild 1
1 MIC - Dept. of Micro and Nanotechnology, Technical University of Denmark, Kgs. Lyngby Denmark, 2 Dept. of Chemistry and Physics and Mads Clausen Institute, University of Southern Denmark, Sønderborg Denmark, 3 , BAM - Bundesanstalt für Materialforschung und –prüfung, Berlin Germany
Show Abstract9:00 PM - S12.32
Energetics at Poly-(3-hexylthiophene) Interfaces: the Impact of Interchain Ordering and Substrate-Polymer Interactions on Fermi Level Pinning.
M. de Jong 1 , M. Lipperts 2 , W. Osikowicz 1 , W. Salaneck 1
1 Department of Physics (IFM), Linkoping University, Linkoping Sweden, 2 Department of Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands
Show AbstractThe observation of large interfacial dipoles at interfaces between poly-(3-hexylthiophene), or P3HT, and high work function conducting substrates, both inorganic and organic, can be rationalized in terms of charge transfer at the interface.[1] According to this model, electrons are transferred from P3HT to the substrate, leading to i) a population of positively charged polaronic species on the P3HT chains in the interfacial region, and ii) pinning of the substrate Fermi level to the positive polaron level in P3HT. In this work, we present ultra-violet photoelectron spectroscopy studies of the energy level alignment at interfaces formed by spin coating thin films of P3HT on AuOx/Au and SiO2/Si substrates, in which the interchain ordering was varied by means of in-situ annealing treatments and the choice of radically different degrees of regioregularity. These studies show a strong dependence between the degree of ordering in the P3HT films and the Fermi level pinning energy. This is consistent with the above-described model since the energy of charged, polaronic states in P3HT is known to relax considerably upon the formation of interchain polarons in densely packed, highly crystalline material.[2] In addition, a picture emerges in which the delicate balance between the interactions of the P3HT chains with the substrate and with each other determines the exact energetic placement of the pinning level.
9:00 PM - S12.33
Transition of Conduction Behavior Across a Molecular Junction Based on Conjugated Oligoimine Wires.
Seong Ho Choi 1 , BongSoo Kim 1 , Daniel Frisbie 2
1 Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, United States, 2 Department of Chemical Engineering and Material Science , University of Minnesota, Minneapolis, Minnesota, United States
Show Abstract9:00 PM - S12.34
Three-dimensional Microfabrication with Conjugated Polymers.
Cleber Mendonca 1 2 , Prakriti Tayalia 1 , Raied Jamal 1 3 , Tommaso Baldacchini 1 , Eric Mazur 1
1 Department of Physics and Division of Engineering and Applied , Harvard University, Cambridge, Massachusetts, United States, 2 Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Sao Carlos, SP, Brazil, 3 Physics Department, Baghdad University, Baghdad , Baghdad , Iraq
Show Abstract9:00 PM - S12.36
Deposition of Conducting PEDOT:PSS films by IR Laser Vaporization
Stephen Johnson 1 , Richard Haglund 1 , Hee Park 2
1 Physics & Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 2 , Appliflex LLC, San Jose, California, United States
Show Abstract9:00 PM - S12.37
Space-Charge-Limited Conduction in Polyfluorene: Discrete and Continuous Trap States
Mohammad Arif 1 , Suchi Guha 1 , Shubhra Gangopadhyay 2 , Ullrich Scherf 3
1 Physics & Astronomy, University of Missouri Columbia, Columbia, Missouri, United States, 2 Electrical and Computer Engineering, University of Missouri Columbia, Columbia, Missouri, United States, 3 Makromolekulare Chemie, Bergische Universität Wuppertal, Wuppertal Germany
Show AbstractBlue-emitting polyfluorenes (PF) have emerged as especially attractive π conjugated polymers (CP) due to their strong blue emission, high charge carrier mobility, excellent chemical and thermal stability, and thus great prospects for device applications. Two chemically similar but structurally different side chain moieties of PFs have been heavily studied: poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) (PF2/6) and poly(9,9-di-n-octylfluorene-2,7-diyl) (PF8). PF2/6, which has a branched side chain, forms a five-fold helix and self-organizes to form a semi-crystalline hexagonal phase. PF8, on the other hand, has several conformational isomers that distinctly depend upon the conformation of side chains at very short length scalesPF2/6 is an exceptional polymeric system where the space-charge-limited conduction (SCLC) model within discrete single-level shallow traps can be applied to model current injection. PF2/6 thin films show discrete trap levels with energy ~0.5 eV above the valence band edge under SCLC. In this work we present systematic I-V measurements from PF2/6 and PF8 based diodes to understand the nature of trap states. The very first set of I-V measurements in one carrier PF2/6 devices by sweeping the bias shows all four regions: Ohmic, trap-limited SCLC, trap-filling, and trap-free SCLC current. The hole trap density ~1017 cm-3 and the hole mobility is obtained as ~10-6 cm2/Vs. The injected carriers beyond the trap-filling voltage create a continuum of trap states and as a result subsequent sweeping of bias yields a higher current, representing a distribution of traps. The density of trap states calculated from our experimental results clearly shows that additional trap states are created at higher voltages. The life-time of the trapped charges is many hours, which can be detrapped by photoexcitation. Thermal annealing of PF2/6 forms an ordered hexagonal phase; devices fabricated from this phase also show discrete traps under SCLC with no additional generation of trap states at higher voltages. PF8 on the other hand, is much more sensitive to the processing conditions. In the alpha crystalline phase, PF8 shows a presence of discrete single and multiple set of traps.
9:00 PM - S12.38
Charge Carrier and Exciton Energy Disorder in Polar Amorphous Organic Solids
Conor Madigan 1 , Vladimir Bulovic 1
1 EECS, MIT, Cambridge, Massachusetts, United States
Show AbstractRecent prominence of organic electronics, driven by the development of a wide variety of devices including light emitting devices, solar cells, photodetectors, and thin film transistors, has made charge transport and exciton diffusion in amorphous organic solids a matter of not only fundamental but also immediate technological importance. It is now well understood that the distribution of charge carrier state energies, also called the density of states (DOS), plays a central role in controlling charge carrier and exciton behavior in amorphous organic solids. We present novel Monte Carlo calculations of the charge carrier and exciton DOS in polar amorphous organic solids in which the individual molecular charge distributions (MCDs) are explicitly polarizible. These calculations differ from those in the literature because the use of explicitly polarizible MCDs allows one to include the effect of polarization on the DOS without resorting to dielectric continuum approximations (DCAs). In the conventional charge carrier DOS calculation for a polar organic solid, the energy disorder is computed based on interactions between the charge carrier and the surrounding static molecular dipoles, subject to a simple DCA in which dielectric screening reduces the interaction energies by a factor of 1 / ε, where ε is the dielectric constant of the material. We show that the impact of polarization on the energy disorder (in terms of the standard deviation of the DOS) does not scale as 1 / ε, and for typical ε, the conventional calculation underestimates the disorder by more than a factor of two. In the conventional exciton DOS calculation for a polar organic solid, the impact of polarization is neglected entirely. We find that the energy disorder is approximately unchanged for ε < 2, and for larger ε, increases with increasing ε, demonstrating that exciton energy disorder deviates even more markedly than charge carrier disorder from the predictions of the simple DCA used in charge carrier calculations. We attribute these deviations to two shortcomings of this DCA: (1) it does not accurately describe the interaction between nearest neighbor molecules; and, (2) it neglects the enhancement of the static dipoles due to the polarization of the surrounding medium. Finally, we report empirical expressions for the energy disorder as a function of the dipole moments, molecular density, and dielectric constant to facilitate comparison between experiment and the results of this improved theoretical treatment.
9:00 PM - S12.4
Direct Thermal Patterning and Characterization of a π-Conjugated Polymer.
Terry Gordon 1 , Jianfei Yu 1 , Steven Holdcroft 1
1 Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada
Show Abstract Polymers containing an extended π-system are an interesting group of materials that have found application in a variety of fields such as anti-static coatings, field-effect transistors (FETs) and organic light emitting devices (OLEDs). However, once deposited as a thin film, the patterning of these types of materials can be problematic in that harsh photolithographic methods are often used followed by heating steps at high temperatures. These conditions can have a detrimental effect on a polymers electronic and optical properties by interrupting the extent of conjugation, e.g. oxidation of the main chain. The patterning and characterization of these kinds of materials will be discussed using a softer thermal lithographic technique such as a controlled spatial deposition of a thermal and light sensitive polymer using a near-infrared laser light source. Alkylthiophene based polymers containing a heat or acid sensitive tetrahydropyranyl (THP) protecting group have been synthesized and were shown to retain some of their solid-state light emitting properties after patterning. With acid exposure and mild heating or laser exposure in the presence of a NIR dye, the solubility of the polymer films can be changed such that the exposed polymer areas were rendered insoluble in a THF developer.
9:00 PM - S12.40
Facile Nano- and Micro-structuring of Thermally-reactive π-Conjugated Polymers.
Xu Han 1 , Xiwen Chen 1 , Steven Holdcroft 1
1 Chemistry, Simon Fraser Univeristy, Burnaby, British Columbia, Canada
Show AbstractThermally-reactive conjugated polymers were blended with inert polymer template, i.e. poly(methyl methacrylate) (PMMA), by optimized weight ratio in the presence of minor camphorsulfonic acid (CSA), yielding binary systems with micro- or nano- sized phase separations. The binary blends were thermolytic treated to carry out an acid-catalyzed solid-phase reaction. Solubility of these conjugated polymers was changed by elimination of the bulky tetrahydropyran (THP) group from the polymers. Polymer blends were rinsed by solvent to remove PMMA and dissolvable residuals and obtain an innovative micro- or nano- sized architectures. The morphology of blended films prior to and after deprotection and development were studied by atomic force microscopy (AFM). A well ordered 100-500 nm size domains were observed in deprotected films for different conjugated polymers. This facile nano- and micro-structuring of π-conjugated polymers allows for fabrication of controlled nano- or micro-scale pattern in the active layer of polymer light-emitting diodes (PLEDs) and organic photovoltaic (PV) cells devices.
9:00 PM - S12.41
Performance of Polyaniline Thin Films, Simple Patterns and Tracks Using a Low-Cost Inkjet Printer.
Rodrigo Bianchi 1 , Ely Dirani 2 , Adriana Ferreira 2
1 Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil, 2 Laboratório de Microeletrônica, Escola Politécnica da Universidade de São Paulo, São Paulo, SP, Brazil
Show Abstract9:00 PM - S12.42
Transparent Plastic Low-WorkfunctionPoly(3,4-ethylenedioxythiophene) Electrodes.
Linda Lindell 1 , Anick Burquel 2 , Fredrik Jakobsson 3 , Vincent Lemaur 2 , Magnus Berggren 3 , Roberto Lazzaroni 2 , Jérôme Cornil 2 , William Salaneck 1 , Xavier Crispin 3
1 , Department of Physics, Biology and Chemistry, Linköpings Universitet, Linköping Sweden, 2 , Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium, 3 , Department of Science and Technology, Campus Norrköping, Linköpings Universitet, Linköping Sweden
Show AbstractNovel applications for flexible electronics, e.g. displays and solar cells, require fully flexible, transparent, stable and low work function electrodes that can be manufactured via a low-cost process. Here, we demonstrate that surface chemistry constitutes a route to produce transparent low-work function plastic electrodes. The work function of the conducting polymer poly(3,4-ethylenedioxythiophene)-tosylate, or PEDOT-Tos, is decreased by sub-monolayer surface redox reaction with a strong electron donor, tetrakis(dimethylamino)ethylene (TDAE), allowing to reach a work function of 3.8 eV. The interface formed between TDAE and PEDOT is investigated in a joint experimental and theoretical study using photoelectron spectroscopy and quantum chemical calculations.
9:00 PM - S12.43
Triplet Formation in Covalently Linked Cofacially Stacked Perylenediimides.
Dirk Veldman 1 , Stéphanie Chopin 1 , René Williams 2 , Stefan Meskers 1 , René Janssen 1
1 Molecular Materials and Nanosystems, Eindhoven University of Technology, Eindhoven Netherlands, 2 Faculty of Science, University of Amsterdam, Amsterdam Netherlands
Show AbstractStacking of conjugated molecules and polymers has important consequences for their optical and charge transport properties. Here we describe two new molecules with two and three vertically stacked perylenediimide (PDI) moieties covalently linked and held in an exact cofacial configuration by xanthene linkers. These covalently stacked systems can be studied under a variety of conditions (solvent, temperature) and serve as a model for the molecular interactions that occur in solid films. Intrinsically, the PDI units have a fluorescence quantum yield close to unity, but held in a cofacial arrangement we find that the quantum yield is lowered dramatically while the lifetime of the singlet excited state increases significantly. This behavior is typical for H-aggregates with symmetry-forbidden radiative decay. By studying the photoinduced absorption of the stacked molecules from the picosecond to the microsecond time scale we find that photoexcitation produces their triplet excited states in reasonable quantum yields. We show that charge transfer between the molecules in the stack is virtually absent. Triplet formation is exceptional for PDI chromophores. In these covalent PDI stacks the triplet states can be formed because the radiative decay from the singlet excited state is effectively suppressed by the high symmetry of the molecule. This allows intersystem crossing to the triplet state to gain importance. Possibly the spin-orbit coupling is even enhanced by symmetry breaking in the excited state.
9:00 PM - S12.45
One-Step Preparation of a Novel Self-Stratifying Bilayer Film with Conducting Polymer as the Bottom Layer and a Thin Insulating Top Layer
Ankit Vora 1 , Dean Webster 1
1 Coatings and Polymeric Materials, North Dakota State University, Fargo, North Dakota, United States
Show AbstractIn this work, a one-step bilayer film of Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and polystyrene (PS) was prepared on a glass substrate. For developing a magnetic tunnel junction (MTJ) a very thininsulating layer (15-20 Å) is required between two ferromagnetic layers. For an all-organic MTJ, polystyrene or similar neutral polymers could be used as an insulating layer. To develop a uniform layer of this thin insulatingmaterial, a one-step self-stratifying approach has been used in the current work. This approach solves the challenge of depositing a very thin layer of polymer in a separate step. A dilute solution of high molecular weight PS in 1-methyl-2- pyrrolidinone(NMP) was added to Baytron P® (PEDOT:PSS) and the mixture was stirred at room temperature for 24 hours. The resulting mixture was then spin coated at 2000 RPM on a glass substrate and later annealed at 190 deg C for 30 minutes.Although pristine Baytron P® film is highly polar and had a water contact angle around 25 deg, the water contact angle of the PS doped Baytron P® film is around 95 deg, indicating that a layer of low surface energy polystyrene isformed on top of the conducting polymer. These films were further characterized for thickness of PS layer with transmission electron Microscopy (TEM) and by atomic force microscopy (AFM) for surface roughness.
9:00 PM - S12.46
Characterization of Anisotropic Flexible Substrates Using Spectroscopic Ellipsometry and Mueller Polarimetry.
Yong Ji 1 , Enric Garcia-Caurel 2 , Michel Stchakovsky 3
1 Thin Film Divisions, HORIBA Jobin Yvon, Sunnyvale, California, United States, 2 Thin Films and Interface Laboratory , Ecole Polytechnique, Palaiseau, Essonnes, France, 3 Thin Film Division, HORIBA Jobin Yvon , Chilly-Mazarin, Essonnes, France
Show Abstract9:00 PM - S12.47
Synthesis, Properties and Device Performance of Various Substituted Pentacene Derivatives
Toshihiro Okamoto 1 , Michelle Senatore 1 , Abhijit Mallik 1 , Ming Tang 1 , Mang-mang Ling 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractOrganic thin-film field-effect transistors (OFETs) are of great interest for low-cost large area devices. In this field, particularly, pentacene has been extensively investigated due to its highest thin film mobility for hole transport. However, pentacene has a few drawbacks which include poor solubility as well as instability under ambient condition, preventing their wide applications. Recently, many research groups are working on the synthesis and design of new substituted pentacenes. The substitutions are used to control the size and shape of the molecule and as a result altering the packing mode of the molecule, which may correspondingly change the electronic properties. Halogen groups promote stacking and halogenated pentacene can be used for further functionalization of the backbone. Therefore, synthesis of substituted pentacene derivatives would make them more attractive candidates. Herein, we report the synthesis and properties of several functionalized pentacene derivatives. Thin film transistor devices have been fabricated and their device performance is reported.
9:00 PM - S12.49
Synthesis and Photoluminescence of Blue-emitting Phosphorescent Iridium(III) Complex.
Hong Jeong Yu 1 , Kwanhwi Park 1 , Sung Hyun Kim 1
1 Dept. of Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show Abstract For the development of blue-emitting Ir(III) complex, F2MeIrpic (Iridium(III)bis[2-(2',4'- difluorophenyl )-4-methyl pyridinato-N,C2']picolinate was synthesized. The synthesiszed F2MeIrpic showed sky blue light with the PL maximum peak at 470 nm. It was reported generally that the reaction time and yield of F2MeIrpic were 72hours and maximum 30%. The reaction is composed of three steps. The first step is the synthesis of ligand, F2Meppy(2-[2,4-difluorophenyl]-4-methylpyridine) and the second step is the synthesis of Ir-dimer([F2Meppy]2Ir[l-Cl]Ir[F2Meppy]2). The last rate determining step is the synthesis of FMeIrpic with Ir-dimer and picolinic acid. The solubility and dispersion of Ir-dimer in solvent are important reaction parameters which reduce reaction time and enhance yield, because Ir-dimer is not soluble in almost all solvent. Although the solubility was not still pretty good, Tetrahydrofuran(THF) was more soluble than any other solvents and Ir-dimer was dispersed well using ultra-sonicaiton. The reaction time was reduced to 36hours and yield was enhanced to 45% by ultra-sonication in THF.
9:00 PM - S12.5
Photophysics and Device Characteristics of Novel Blue Emitting Polymers based on Poly-2,7- and 3,6- Phenanthrylenes
Horst Scheiber 1 , Changduk Yang 2 , Josemon Jacob 2 , Klaus Müllen 2 , Emil List 1 3
1 Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010, Graz and Institute of Nanostructured Materials and Photonics, Joanneum Research, Franz-Pichler-Strasse 30, A-8160, Weiz Austria, 2 , Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128, Mainz Germany, 3 , NanoTecCenter Forschungsgesellschaft mbH, A-8160, Weiz Austria
Show AbstractAs part of the development of display applications based on conjugated polymers, significant attention has recently been directed to attaining stable blue electroluminescence from polyphenylene-type polymers. In this contribution we report on the photo-physical and device related characterization of new PPP derivatives based on 2,7- or 3,6-conjugated polyphenanthrylenes. The full characterization (device and photo-physics) of a series of soluble conjugated 2,7- and 3,6-poly(phenanthrylene)s analogous respectively to poly(p-phenylene)s (PPP) and poly(p-phenylenevinylene) (PPV) is described. The characterization by means of absorption, emission and photoinduced absorption spectroscopy reveals the exclusive example of an investigation into the effects of the conjugation mode of a polymer, i.e. PPP-like versus PPV-like, as a function of the coupling of the repeat unit at different positions to be investigated. Moreover, it is found that the nature of the substituents (alkyl or aryl) at 9,10-positions of phenanthrylenes largely influences the solubility of these polymers as well as their absorption and luminescence characteristics. All aryl substituted polymers exhibit deep blue electroluminescence similar to the observed photoluminescence when used as the active layer in a polymer light emitting device. Both polymers have good stability of the blue spectral emission and no sign of an oxygen related formation of keto defects is found as observed for other poly(phenylene)-type polymers.
9:00 PM - S12.50
Electronic Coupling between Frenkel and Wannier Excitons in an Organic-inorganic Semiconductor Hybrid Structure.
Sylke Blumstengel 1 , Sergey Sadofev 1 , Chenggang Xu 1 , Joachim Puls 1 , Fritz Henneberger 1
1 Institut für Physik, Humboldt-Universität, Berlin Germany
Show Abstract9:00 PM - S12.52
In-plane Structure and Polymorphism of Pentacene Thin Films.
Toshiyuki Kakudate 1 , Noriyuki Yoshimoto 1 , Yoshio Saito 2
1 , Iwate University, Morioka Japan, 2 , Kyoto Institute of Technology, Kyoto Japan
Show Abstract9:00 PM - S12.53
Electric Conduction in Nematic Liquid Crystal Tolans.
Masanao Goto 1 , Guang Shao 2 , Akihiro Orita 2 , Junzo Otera 2 , Hideo Takezoe 1 , Ken Ishikawa 1
1 Dept. of Org. and Polym. Mater., Tokyo Inst. of Tech., Meguro, Tokyo, Japan, 2 Dept. of Biotech. and Appl. Chem., Okayama Univ. of Science, Okayama, Okayama, Japan
Show AbstractRecently, electrical properties of nematic liquid crystals (NLCs) have received attention. Although initial reports suggesting ionic rather than electronic conduction in NLCs, there have been several reports about electronic conduction in NLCs which include an electronic conduction in low-molecular non-glassed state and an application to OLED devices.However a criterion determining whether ionic or electronic conduction is still ambiguous and further studies on carrier transport mechanismin NLCs are desired. In this study, we measured the electrical properties of several tolan derivatives in the nematic phase by time-of-flight technique. Especially one cross-shaped anthracene core derivative - 9,10-bis(2-(4-(2-(4-alkylphenylethynyl)phenyl)ethynyl)anthracene - shows electric field and temperature independent mobility in the nematic phase which usually suggests good electronic conduction. However mobility values of the nematic phase are below 10-4 cm2/Vs for both positive and negative carriers. These contradictive experimental results raise problem. For understanding this problem we performed theoretical analysis of photocurrent profiles and temperature and electric field dependence of carrier mobility based on the Gaussian disorder model. Results and analyses of the other tolan derivatives will be shown.
9:00 PM - S12.54
Fabrication of Molecular Organic Single-crystal Devices with High Quality Dielectrics.
Peter J. de Veen 1 , Guus Rijnders 1 , Dave H.A. Blank 1
1 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractTo study the intrinsic electronic properties and explore the physical limits of organic semi-conducting materials, focusing on the fabrication of devices based on molecular organic single-crystals will be the best approach. The electronic transport is being studied in the field-effect geometry, i.e. contacts and a gate electrode will be mounted on the organic single-crystal, electrically isolated by an inorganic dielectric. To reach high break down field strength, high quality dielectrics need to be deposited. To achieve this, pulsed laser deposition is used in the device fabrication. The mobility of a field-effect transistor is largely affected by the quality of the inorganic dielectric-organic interface. Therefore, controlled patterning of the various materials through stencils or nano-sieves are investigated.In this contribution we will focus on our results on the surface characterization of pentacene single-crystals. Also, our current work on the growth and electrical characterization of inorganic high-k dielectric layers on the pentacene single-crystal surface by pulsed laser deposition, and controlled patterning through stencils or nanosieves, will be presented.
9:00 PM - S12.55
Exciplex Formation, Charge Separation, and Recombination in Bulk Hetero-junction Blend Films of a Polyfluorene Polymer and a Soluble Silole Derivative.
Jessica Benson-Smith 1 , Joanne Wilson 1 , Donal Bradley 1 , Jenny Nelson 1
1 Department of Physics, Imperial College London, London United Kingdom
Show Abstract9:00 PM - S12.56
Chiral Polyaniline Carbon Nanotube Nanocomposites
Xuetong Zhang 1 , Wenhui Song 1
1 Wolfson Center for Materials Processing, Brunel University, West London United Kingdom
Show Abstract9:00 PM - S12.57
Charge Transport and Lifetime of Injection Efficiency in Double Molecularly Doped Polymers.
H. H. Fong 1 , George G. Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - S12.58
Composite Material Prepared by Physical Adsorption of π-conjugated Polymer on Inorganic Particles.
Sze Yang 1 , Hui Wan 1 , John Sinko 2
1 Chemstry Department, Univ of Rhode Island, Kingston, Rhode Island, United States, 2 , Wayne Pigment Corporation, Milwaukee, Wisconsin, United States
Show AbstractOrganic/inorganic composite material is interesting for its useful properties. Particles consist a core of micro or nano inorganic particles and a shell of electronically conducting polymer is a type of composite material with interesting electronic, optical and electrochemical properties. These properties are potentially useful for solar energy collection, electrochromic and anticorrosion applications. In this study we present a general and efficient method for preparing composite particles with a core/shell structure. A spontaneous physical adsorption process allows for a p-conjugated polymer in an aqueous solution to completely transfer onto the surface of a mechanically suspended inorganic particle. The process is more economical than the usual method of in situ polymerization of conducting polymer to deposit polymer on the inorganic particles. Comparing with the conventional method, the spontaneous physical adsorption has the advantage of efficient use of all conducting polymer in the solution and the ease in recycling the wastewater used for suspending the conducting polymers. US patent applications for this type of composites are pending.The organic component for the composite is a polymeric complex of polyaniline. A number of inorganic particles were used for the core component of the composite. The inorganic particles include: Cerium oxide, strontium hydrogen phosphate, zirconium oxide, barium sulfate, zirconium phosphate, molybdenum trioxide, and tungsten trioxide. The driving force for the spontaneous adsorption was experimentally studied. The understanding of the mechanism allows for design for the process to be applicable to any micro or nano composite consisting a conducting polymer and an inorganic particle.
9:00 PM - S12.59
An Amperometric CO Gas Sensor Based on Solid Polymer Electrolyte.
Seung Eon Moon 1 , Eun-Kyoung Kim 1 , Jonghyurk Park 1 , Hong-Yeol Lee 1 , Kang-Ho Park 1 , Byung Gil Jung 2 , Seung-Mo Kim 2 , Seung-Chul Ha 2
1 , ETRI, Daejeon Korea (the Republic of), 2 , SENKO, Kangnung Korea (the Republic of)
Show Abstract9:00 PM - S12.6
An Investigation of Au-Ag Interface Formed by Cold Welding Using Focused Ion Beam/Transmission Electron Microscopy
Yifang Cao 1 , Nan Yao 2 , Kevin McIlwrath 5 , Jikou Zhou 4 , G. Osinkolu 3 , Winston Soboyejo 2
1 Engineering Science Programme and Division of Bioengineering, National University of Singapore, Singapore Singapore, 2 Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey, United States, 5 , Hitachi High Technologies America, Pleasanton, California, United States, 4 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , Obafemi Awolowo Univesity, Ile-Ife Nigeria
Show Abstract9:00 PM - S12.60
Photoconduction in Single Layer TPD Devices.
Debdutta Ray 1 , Meghan Patankar 1 , Gottfried Döhler 2 , Krishnamachari Narasimhan 1
1 Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Mumbai India, 2 Max Planck Research Group, Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, Erlangen Germany
Show AbstractIn this paper we report on photoconductivity (PC) studies of TPD. TPD is widely used as the hole transporting layer in OLEDs. Single layer TPD devices were fabricated with ITO and semitransparent Al as the electrodes. The mechanism for PC in TPD is different in forward and reverse bias. In forward bias (ITO positively biased) the photocarrier generation is dominated by exciton diffusion and quenching at the ITO interface. The spectral response is observed to be antibatic with absorption in forward bias when the device is illuminated through Al. From photoluminescence quenching studies of films grown on ITO substrates as a function of film thickness, the exciton diffusion length in TPD is found to be around 5nm and the exciton quenching efficiency of the ITO interface as 30%. The spectral response calculated using these parameters is in excellent agreement with the experiment. In reverse bias the PC is governed by bulk generation of photocarriers. Under low electric fields (F < 106 V/cm) the photocurrent varies linearly with electric field. From carrier collection and field dependent photoluminescence quenching studies we find that for fields above 106 V/cm, the photocurrent in reverse bias is governed by carrier generation from electric field dependent exciton quenching. Below this field, carrier generation occurs spontaneously with an efficiency of 0.1%. The mobility-lifetime product (μτ) of the holes is found to be about 4.3x10-11 cm2/V from this analysis. The μτ product can be used for quantitative comparison of the electronic quality of different samples. To understand the electric field dependence of the photocurrent in reverse bias, we solve the Poisson and the continuity equation simultaneously. From the simulations we find that the photocurrent is dominated by the carrier with the larger collection length. This is in agreement with an analytical model of PC proposed by Goodman and Rose (J. Appl. Phys. 42, 2823 (1971)). The carrier generation in TPD is non-uniform because of its large absorption coefficient (α∼2x105 cm-1) in the energy range of our interest. We, thus, modify the model of PC by Goodman and Rose to apply to cases of non-uniform carrier generation. The key results to note are that the PC depends on the polarity of the electrode through which the sample is illuminated and the ratio of the collection lengths of the carriers. These results are consistent with the experiment. We demonstrate that TPD can be utilized for solar blind UV detection with response of 1mA/W under a bias of -10V. The possibility of fabricating cheap large area arrays for niche applications makes TPD an attractive alternative.
9:00 PM - S12.7
Conformational Analysis of the Conducting Polymer Poly(3,4-ethylenedioxythiophene-co-pyrrole).
Stephen Fossey 1 , Ferdinando Bruno 1 , Jayant Kumar 2 , Lynne Samuelson 1
1 Nanomaterials Science Team, US Army Natick Soldier Center, Natick, Massachusetts, United States, 2 Department of Physics & Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractThe π-conjugated heterocyclic polymers poly(3,4-ethylenedioxythiophene), PEDOT, and polypyrrole are important organic electrically conducting materials. We have used electronic structure calculations (density functional theory and ab initio) to study the copolymers of 3,4 ethylenedioxythiophene (EDOT) and pyrrole. When EDOT and pyrrole monomer residues are adjacent, an intrachain hydrogen bond can be formed between the amide hydrogen of pyrrole and the oxygen of EDOT. The intrachain hydrogen bond stabilizes the fully planar s-trans conformation. For all copolymer sequences calculated, the HOMO-LUMO gap is intermediate between that of the two homopolymers and a function of monomer composition. Interestingly, the Marcus Theory reorganization energy of some copolymer oligomers (notably the alternating copolymer) is lower than either of the homopolymers suggesting that the charge carrier mobility can be higher in the copolymer than in either homopolymer. Some limited results on the effects of conformational disorder in the copolymers will also be presented.
9:00 PM - S12.8
Robust Circular Polarized Emission from Nanoscopic Single-Molecule Sources: Application to Solid State Devices.
Ruthanne Hassey 1 , Ellen Swain 1 , Nathan Hammer 1 , Emily Richards 1 , Dhandapani Venkataraman 1 , Michael Barnes 1
1 Chemistry, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractControlling the polarization state of fluorescence emission in solid state devices is an important goal in optical display technologies. High-purity (right or left) circular polarized emission is particularly desirable because an arbitrary linearly polarized state can be generated with much higher efficiency (lower loss) as compared with a non-polarized fluorescence input. Here we discuss observation of resonant chiroptical effects (fluorescence detected circular dichroism (FDCD), and circular polarized luminescence (CPL)) from single (bridged-triarylamine) helicene molecules in a solid-film format. In the FDCD experiment using 457-nm excitation – an excitation wavelength where the bulk circular dichroism is negligible – single-molecule fluorescence from enantiomerically pure helicene samples show surprising distribution of dissymmetry (g)-parameters centered near zero but with a significant contribution from molecules showing an almost perfectly pure response to either right or left circularly polarized light. Experiments combining a well-defined circularly polarized excitation (either right or left) with decomposition of the fluorescence into left- and right-circular polarization component show only a weak correlation between the dissymmetry (sign and magnitude) of the CPL with the polarization state of the input. Current efforts are directed at wavelength resolved CPL, measuring FDCD at wavelengths that are more closely matched to bulk circular dichroism features, and studying the orientational dependence of FDCD and CPL. These results provide new insight into chiroptical properties of chiral fluorophores at the single molecule level and suggest new optical device possibilities with chiral fluorophores.
9:00 PM - S12.9
Ultraviolet Light - Ozone Treatment of Poly(3,4-ethylenedioxy-thiophene)-based Materials Resulting in Increased Work Functions
Carl Tengstedt 1 , Anna Kanciurzewska 1 , Michel de Jong 2 , Slawomir Braun 2 , William Salaneck 2 , Mats Fahlman 1
1 Department of Science and Technology, Linkoping University, Norrkoping Sweden, 2 Department of Physics, Chemistry and Biology, Linkoping University, Linkoping Sweden
Show AbstractWe describe a simple method to increase the work function of poly(3,4-ethylenedioxy-thiophene)-poly(perfluoroethylene sulfonic acid), PEDOT-PFESA, and poly(3,4-ethylenedioxy-thiophene)-poly(styrene sulfonic acid), PEDOT-PSS, by short exposure to UV and ozone. The creation of carbonyl groups in the surface region forms a dipole layer shifting the vacuum level with a followed increase in work function. It has been shown that the work function of PEDOT-PFESA can be increased by as much as ~0.4 eV to the absolute value of 6.3 eV and by at least ~0.2 eV for PEDOT-PSS to the absolute value of 5.4 eV. The increase in work function has also proven to be time dependent with the largest increasing rate occurring for short exposure times. Upon ozone treatment, both PEDOT and PSS are oxidized whereas PFESA seems to be unaffected.
Symposium Organizers
Franky So University of Florida
Graciela B. Blanchet DuPont
Yutaka Ohmori Osaka University
S13: Electronic Structure
Session Chairs
Friday AM, December 01, 2006
Room 304 (Hynes)
9:00 AM - **S13.1
Electronic Structure of Interfaces Formed Between HATNA Derivatives and Metals and Organic Materials.
Antoine Kahn 1 , Wei Zhao 1 , Seth Marder 2 , Steve Barlow 2 , Fabrice Amy 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract9:30 AM - S13.2
Control Electronic States Spreading Outside the Conjugated Polymer Surface.
Xiao Tao Hao 1 , Takuya Hosokai 1 , Noritaka Mitsuo 1 , Satoshi Kera 1 , Kazuyuki Sakamoto 1 , Koji Kamiya Okudaira 1 , Nobuo Ueno 1
1 , Faculty of Engineering , Chiba University, Chiba Japan
Show AbstractTo study the electronic states tailing outside the π- conjugated polymer surface is critically essential to understand the π-π wave function overlapping in a hetero-junction used in organic devices. The π electronic density from the backbone of conjugated polymer with side pendant groups is very common to be shielded by the side groups rather than spreading outside the surface. Therefore it is necessary to control the molecular ordering/orientation of the polymer chains and side pendant groups to get the π states tailing outside in order to achieve the efficient charge transfer to the π states of an overlayer material through π-π wave function overlapping.In this study, the electronic states was controlled on regio-regular conjugated poly(3-hexylthiophene) (P3HT) thin films with different molecular ordering by varying the coating process and Penning ionization electron spectroscopy (PIES) was adopted to observe the electronic states existing outside the surface. Instead of the conventional photoelectron spectroscopic technique like ultra-violet photoelectron spectroscopy (UPS), in which the spectral intensity comes from the top ~1nm layer inside the surface, PIES using metastable atoms as probes can observe the electronic density existing outside of the surface selectively since metastable atoms do not penetrate into the bulk of the solid. The attempt to control the P3HT chain conformation can be made by adjusting the spin-coating process and solution concentration. Higher concentration (5 mg/mL) with faster spin coating speed (~3000rpm) gave the P3HT layer with face-on conformation, while lower concentration (0.67 mg/mL) with slower speed (~400rpm) could generate edge-on conformation and both the films are about 10 nm thick. Both PIES and UPS spectra were recorded for P3HT thin film with different conformation. For edge-on conformation, the π electronic states were shielded by the side hexyl chain, which can be observed in UPS spectra but cannot detected by PIES. However, for face-on conformation, the π electronic states could be observed clearly in both UPS and PIES since the electronic wave function is spreading outside the polymer surface.
9:45 AM - S13.3
Ultrahigh Vacuum Seebeck Effect and Conductivity Measurements on N-Doping of C60 Films.
Naoki Hayashi 1 , Kaname Kanai 1 , Yukio Ouchi 1 , Kazuhiko Seki 1 2
1 Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya Japan, 2 Institute for Advanced Research, Nagoya University, Nagoya Japan
Show AbstractIt is important for improvement of organic electronic devices to control the barrier of the carrier injection at the interfaces between organic films and metal electrodes and the transmission of carriers in organic films. As with inorganic semiconductors, the improvement of the electric properties of organic films by p-type doping under ultrahigh vacuum (UHV) condition was reported.[1] Detailed study for n-type doping in UHV, however, has not yet been reported.
In this study, we constructed an UHV system with which in-situ conductivity and Seebeck coefficient measurements can be performed, including the detailed examination of the atmospheric effect. Seebeck coefficient is the thermoelectric power per unit temperature difference, and we can deduce the conduction type from its sign: holes and electrons give positive and negative values, respectively. The substrate was heated by ceramic resisters at the back, and the temperatures at two points of the substrate were independently controlled and monitored by thermocouples for thermoelectric power measurements. The first measurements were performed for C60 (as received from TCI) and C60 doped with an electron donor acridine orange base (3,6-bis(dimethylamino) acridine, AOB), a typical n-type dopant. The doping was performed by co-evaporation, and the effect of AOB doping on the carrier generation efficiency and the conduction type was examined.
Even at low doping level of 1.5 % in mol fraction, the conductivity increased 3 orders of magnitude at 30 °C. The Seebeck coefficient can be determined reliably only for systems with some conductivity, limiting its applicability only to the doped film in the present case. The observed Seebeck coefficient for the doped film was negative, indicating that the major carriers in the doped film are electrons. Thus n-type doping was efficiently achieved by co-deposition of AOB into C60. We also examined the effect of atmosphere. By exposing the AOB doped C60 film to air, the conductivity was reduced by almost 6 orders of magnitude. This suggests that the carrier electrons generated by AOB doping in C60 film is trapped by oxygen in the air. Other related data on the effect of atmosphere will be also presented. [1] W. Gao et al., Organic Electronics 3, 53 (2002).
10:00 AM - S13.4
Vacuum Level Alignment and Fermi Level Pinning at Hybrid Interfaces in Polymer-based Electronics.
Parisa Sehati 1 , Carl Tengstedt 2 , Wojciech Osikowicz 1 , Michel de Jong 1 , William. Salaneck 1 , Mats Fahlman 2
1 Department of Physics, Chemistry and Biology, Institute of Technology , Linköping University, Linköping Sweden, 2 Department of Science and Technology, Institute of Technology , Linköping University, Linköping Sweden
Show Abstract10:15 AM - S13.5
Triplet Exciton Quenching in Organic Phosphorescent Light-emitting Diodes with Ir-based Emitters.
Sebastian Reineke 1 , Karsten Walzer 1 , Martin Pfeiffer 1 , Karl Leo 1
1 , Institut für Angewandte Photophysik, Dresden Germany
Show AbstractOrganic light-emitting diodes (OLEDs) are a promising canidate for novel applications in the fields of display and lighting technology. In order to be competetive with other existing technologies, one of the greatest challenges is the improvement of the OLED efficiency. The largest enhancements of the external quantum efficiency of OLEDs can be ascribed to the introduction of electrophosphorescent materials as a guest molecule of the emission layer (EML). In this case, the emission originates from radiative recombination of both singlet and triplet excitons promising internal quantum efficiencies close to unity. While triplet emitters have strongly improved the quantum efficiency, phosphorescent OLEDs suffer from a decrease of efficiency when the current density is increased. This is mainly due to the longer lifetime τph of the emitting triplet state of organometallic complexes compared to the decay times of fluorescent dyes. To get a better understanding of the processes involved in the efficiency decrease, we investigate quenching processes which contribute to the roll-off in quantum efficiency of phosphorescent OLEDs at high brightness: triplet-triplet annihilation, energy transfer to charged molecules (polarons), and dissociation of excitons into free charge carriers. The investigated OLEDs comprise a host-guest system as emission layer (EML) within a standard OLED structure. In a red phosphorescent device, N,N'-di(naphthalen-2-yl)-N,N'-diphenyl-benzidine (NPB) is used as matrix and tris(1-phenylisoquinoline) iridium (Ir(piq)3) as emitter molecule. This structure is compared to a green phosphorescent OLED with a host-guest system comprising the matrix 4,4',4"-tris (N-carbazolyl)-triphenylamine (TCTA) and triplet emitter fac-tris(2-phenylpyridine) iridium (Ir(ppy)3). The triplet-triplet annihilation is characterized by the rate constant kTT which is determined by time-resolved photoluminescence experiments. To investigate triplet-polaron quenching, unipolar devices were prepared. A certain exciton density, created by continuous wave illumination, is analyzed as a function of current density flowing through the device. This delivers the corresponding rate constant kP. Field-induced quenching is not observed under typical OLED operation conditions. The experimental data are implemented in an analytical model taking in account both triplet-triplet annihilation and triplet-polaron quenching. It shows that both processes strongly influence the decrease of OLED efficiency. By comparing with the red Ir(piq)3 device, we show that the stronger roll-off of the Ir(ppy)3 based system is mainly due to a longer triplet lifetime τph and a thinner exciton recombination zone within the EML.
10:30 AM - S13.6
Sensitised Emission from Lanthanide-exchanged Zeolites.
Martin Burger 1 2 , Giorgio Macchi 1 , Francesco Meinardi 1 , Sigurd Schrader 2 , Riccardo Tubino 1
1 Scienza dei Materiali, Università di Milano Bicocca, Milano Italy, 2 , University of Applied Sciences, Wildau Germany
Show AbstractThe major drawback in lanthanide technology is related to aggregation processes of lanthanide ions and to the responsiveness to the chemical surroundings: high concentration of nude Ln3+ ions can not be achieved preventing a high efficienct emission, e.g. in Erbium based optical amplifiers. Moreover, the metal ion is poorly absorbing in the visible region. Coordination chemistry has put his efforts to produce efficient emission by employing chromophoric ligands which prevent aggregation and also act as antennae, to transfer absorbed energy efficiently to the lanthanide ion. These ligands must be also capable of protecting the lanthanide(III) centre from solvent molecules and chemical moisture that are known to be the main cause of luminescence quenching.The sensitisation of the lanthanide emission can also be achieved in systems with confined geometry in which the emitting ion and the organic antenna are arranged in closed proximity. For this purpose, a porous oxide matrix such as zeolite-L can be used. Two fundamental advantages come from the use of these hosts: (i) the extremely high surface area and free volume available allow to achieve exceptionally high concentration (up to 1018 Ln3+ for each mg of zeolite) completely avoiding cluster aggregation (ii) within the pores (7 Å pore entrance, 12 Å inner diameter) energy transfer can take place straightforwardly, while the choice of sensitizers is not restricted by ligand chemical features or coordination chemistry rules. Moreover, zeolite framework can also be exploited as a shell, protecting organic molecules from moisture (water, oxygen, solvents).In the present work we describe the successful preparation of lanthanide-exchanged zeolite-L crystals with several metal ions (Tb, Eu, Er) and the subsequent filling of the host channels by suitable chromophores, both forming and not forming complexes (benzophenone, naphthalene, oligothiophenes and other conjugated oligomers ). The photophysical investigation of the material has shown, upon optical excitation within chromophore absorption band, emission of light with the typical sharp lines of lanthanide(III) luminescence spanning from visible (Tb, Eu) to infrared (Er) region, suggesting that an efficient energy transfer has taken place between the organic and the metal ion. These preliminary results appear to be very promising for the application of rare-earth elements, hosted in different matrices, as active materials in optoelectronic devices, high-efficiency light-emitting diodes, luminescent probes and optical amplifiers.
10:45 AM - S13.7
Morphology and Electronic Structures of Interfaces Between Organic Semiconductors and Magnetic Electrodes used in Room-Temperature Organic Spin Valves.
Toshihiro Shimada 1 , Hitoshi Abe 1 , Hiroyuki Nogawa 1 , Kenta Amemiya 1 , Koichiro Saiki 2 1 , Tetsuya Hasegawa 1
1 Chemistry, Univ. Tokyo, Tokyo Japan, 2 Complexity Sciences and Engineering, Univ. Tokyo, Kashiwa Japan
Show Abstract11:00 AM - S13: ElecStr
BREAK
11:15 AM - S13.8
Exciton and Defect Photoluminescence Signatures in Single Crystal Rubrene
Oleg Mitrofanov 1 , David Lang 2 , Christian Kloc 1 , Magnus Wikberg 1 , Theo Siegrist 1 , Woo-Young So 2 , M. Sergent 1 , Arthur Ramirez 1 2
1 , Bell Labs, Lucent Technologies, Murray Hill, New Jersey, United States, 2 , Columbia University, New York, New York, United States
Show AbstractCharge transport mechanisms in organic crystals remain in the focus of research. The origin of bandgap states and their effect on electronic and optical characteristics are both controversial and important questions for organic-based transistors, photovoltaic cells, and light emitting diodes. In rubrene, where the field effect mobility is the highest among organics (up to 20 cm2/Vs), the effect of bandgap states is far from clear to date. We demonstrate that photoluminescence spectra of crystalline rubrene reflect exciton recombination after trapping on oxygen-related defects in addition to the direct exciton recombination. The defect-assisted exciton recombination results in a well-defined photoluminescence (PL) band. Furthermore, a free hole is released in the process. The results indicate that the oxygen-related defect forms a bandgap state and acts as an acceptor center. Presence of the acceptor centers increases dark and photoconductivity in rubrene. The impact on dark conductivity is particularly significant: the oxygen-related defects effectively dope crystalline rubrene. The radiative recombination processes provide valuable information about exciton dynamics and allow detection of defects in rubrene crystals. In order to determine defect distribution, radiative transitions are investigated using two-photon excitation process that allows probing deep inside rubrene crystals. The two-photon excitation PL depth-profile shows that the oxygen-related defects are concentrated in a surface region of intentionally and naturally oxidized rubrene crystals.
11:30 AM - S13.9
Atmospheric Effects on the Electronic Structure of Organic Thin Films and Interfaces
Kazuhiko Seki 1 2 , Toshio Nishi 1 , Masato Honda 1 , Yusuke Tanaka 1 , Naoki Hayashi 1 , Asumi Jindo 1 , Hisao Ishii 3 , Yukio Ouchi 1 , Kaname Kanai 1
1 Graduate school of science, Nagoya university, Nagoya Japan, 2 Institute for advanced research, Nagoya university, Nagoya Japan, 3 Center for frontier science, Chiba university, Chiba Japan
Show AbstractThe effect of atmospheric gases such as O2 and H2O on electrical behavior of organic semiconductors is well known. Increase of conductivity is observed for many organics, while decrease was found for C60. The elucidation of such effect is important for bridging the gap between the studies under ultrahigh vacuum (UHV) and real devices under ambient or encapsulated conditions. Here we report our recent studies using (a) conventional UV photoelectron spectroscopy (UPS), (b) newly developed photoelectron yield spectroscopy (PYS), and (c) also new instrument for thermopower (Seebeck effect) from UHV to gas atmosphere. (1) TiOPc / Conductive Electrode Interfaces [1]: Tithanyl phthalocyanine (TiOPc) film deposited on graphite (HOPG) in UHV showed downward band bending suggesting n-type doping, possibly by some residual impurity, while the film deposited in O2 of 1.3x10-2 Pa showed upward bending suggesting p-type doping by O2. This conversion corresponds well to the FET data by Tada et al. [2]. Further, TiOPc on various substrates showed that Fermi level (EF) alignment with the substrates is not achieved in UHV, while alignment was found after exposure to O2, with EF at 0.6 eV above HOMO. These are the first data of electronic structure for the O2 effect.. (2) C60 / HOPG Interface [3,4] : UPS studies for C60 films deposited on HOPG in UHV showed downward band bending, possibly due to some impurity working as n-type dopant. For films prepared in O2 of 10-2Pa, little band bending was seen, showing the removal of the effect of the dopant [3]. This corresponds well with the observed decrease of conductivity. C60 doped with an electron donor acridine orange base (AOB) shows n-conductivity, as evidenced by negative Seebeck coefficient. This negative coefficient becomes obscure when the film was exposed to O2, indicating the cancellation of the effect of AOB [4]. (3) Change of Ionization Energy for TiOPc and Others: Though UPS gives information on the atmospheric effect, it still requires vacuum. In PYS, the solid ionization energy (Is) is measured by scanning the photon energy to observe the photoemission onset, with all electrons collected by accelerating voltage. Thus we can measure Is for the same specimen under various conditions. The data for TiOPc showed change of Is up to ca. 0.4 eV by the exposure to air, O2, and H2O, with little effect by N2 [5, 6]. Smaller change was also observed for various other organics. As an exception, some compounds with very low ionization energies used for n-dopants showed large increase of ionization energy due to the chemical reaction with air [7].[1] T. Nishi et al., Chem. Phys. Lett., 414, 479 (2005), Chem. Phys., 325, 121 (2006). [2] H. Tada et al., Appl. Phys. Lett., 76, 873 (2000). [3] Y. Tanaka, unpublished. [4] N. Hayashi, unpublished, [5] M. Honda et al., Mol. Cryst. Liq. Cryst., in press. [6] M. Honda et al., unpublished. [7] M. Honda, A. Jindo et al., unpublished.
11:45 AM - S13.10
New Inverse Photoemission Spectrometer and the Study on Functional Organic Compounds.
Toshio Nishi 1 , Yasunori Kamizuru 1 , Kaname Kanai 1 , Yukio Ouchi 1 , Kazuhiko Seki 1 2
1 Department of Chemistry, Nagoya University, Nagoya Japan, 2 Institute for Advanced Research, Nagoya University, Nagoya Japan
Show Abstract12:15 PM - S13.12
Novel Organic-based Magnetic Semiconductor V[TCNE]x~2: The Role of [TCNE]●- in the Magnetic and Electronic Properties.
Derek Lincoln 1 , R. Shima Edelstein 2 , A. Epstein 1 2 , J. Kortright 3
1 Department of Chemistry, The Ohio State University, Columbus, Ohio, United States, 2 Department of Physics, The Ohio State University, Columbus, Ohio, United States, 3 Advanced Spectroscopy Dept. Material Science Div., Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe room-temperature (Tc > 350 K) organic-based magnetic semiconductor vanadium tetracyanoethylene (V[TCNE]x~2) [1] has a number of interesting properties and potential applications. The discovery of V[TCNE]x~2 began with solution processed powders [2] with magnetic properties varying with solvent used. The preparation of thin films (~0.5 to 1 μm) via chemical vapor deposition (CVD) [3,4] enabled deposition of dense V[TCNE]x~2 on a wide variety of substrates. A number of studies including local structural order [5], electron paramagnetic resonance [6], and magnetoresistance [7] have been reported on such films. It is important to understand the role the [TCNE]●- radical anion plays in the magnetic and electronic properties of this system. Experimental and theoretical studies have been reported concerning the origin of the magnetic properties of several vanadium-containing materials, for example, vanadium spinels [8,9] and vanadium molecular derivatives [10]. Previous results for V[TCNE]x~2 CVD films indicate that the saturation magnetization to 5400 emu Oe/mol is in agreement with one spin 1/2 per [TCNE]●- antiferromagnetically coupled to the S = 3/2 of V2+ [3]. Though the spin density of [TCNE]●- in paramagnetic tetrabutylammonium TCNE was determined by polarized neutron diffraction [11], the spin distribution and polarization of individual vanadium, carbon, and nitrogen atoms in the V[TCNE]x~2 system has not been reported. We present results of soft x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra of the V, N and C atomic edges to probe the origins of the magnetic properties in V[TCNE]x~2.RSE current address Tower Semiconductors, Ltd, Migdal Haemeq, Israel. This work is supported by DOE grants #DE-FG02-86ER45271, DE-FG02-01ER45931, DE-AC03-76SF00098, and AFOSR grant #F49620-03-1-0175, FA9550-06-1-0175. 1. V.N. Prigodin, et al. Adv. Mat. 14, 1230 (2002).2. J.M. Manriquez, et al. Science 252, 1415 (1991).3. K.I. Pokhodnya, et al. Adv. Mat. 12, 410 (2000).4. R. Shima Edelstein, et al. MRS Proc. 871E, I7.3 (2005).5. D. Haskel, et al. Phys. Rev. B 70, 054422 (2004).6. R. Plachy, et al. Phys. Rev. B 70, 064411 (2004).7. N.P. Raju, et al. J. Appl. Phys. 93, 6799 (2003).8. O. Tchernyshyov. Phys. Rev. Lett. 93, 157206 (2004).9. H. Mamiya, et al. J. Appl. Phys. 81, 5289 (1997).10. J.-L. Gallani, et al. Eur. Phys. J. B 38, 43 (2004).11. A. Zheludev, et al. J. Am. Chem. Soc. 116, 7243 (1994).
12:30 PM - S13.13
Electric-field Assisted Carreir Generation from Interface of p-doped and n-doped Organic Semiconductor Bilayers.
Tetsuo Tsutsui 1 2 , Masaya Terai 2 , Katsuhiko Fujita 1 2
1 , Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka, Japan, 2 Department of Applied Science for Electronics and Materials, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka, Japan
Show AbstractUnderstanding of bipolar charge generation at organic-organic semiconductor interface regions is quite important for the design of novel organic semiconductor devices, for example tandem-type organic light-emitting diodes with internal charge generation zones, which have been reported to exhibit high apparent quantum efficiency and extended device lifetimes.1-3) We have proposed the concept of electric-field-assisted bipolar charge generation within organic multiplayer films, and reported the fabrication of bipolar charge spouting diodes, in which electrons and holes are generated within stacked organic layers and flow out to electrodes.4) We recently reported additional experimental evidences that support our concept using double-insulation-type organic thin-film devices.5)Charge generation in p-n homo-junctions of traditional inorganic semiconductor diodes is well-established concept.6) Thus, the observation and analysis of the charge generation at p-n hetero-junctions composed of doped organic semiconductors may shed light on our concept of electric-field assisted bipolar charge generation. In this paper, we examined the electric-field-assisted bipolar charge generation from the interface, which comprises of an n-type organic semiconductor, a metal-doped tris(8-quinolinolato)aluminum(III) (Alq3) and a p-type organic semiconductor layer, N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine (TPD) doped with tetrafluorotetracyanoquinodimethane (F4-TCNQ). We have fabricated bipolar charge spouting diodes with the structure, ITO/Alq3/Mg-doped-Alq3/F4-TCNQ-doped-TPD/TPD/Al, and tandem-type staked organic light emitting diodes with the structure; ITO/TPD/Alq3/Mg-doped-Alq3/F4-TCNQ-doped TPD/TPD/Alq3/Mg-doped-Alq3/MgAg. Well-defined bipolar charge carrier generation was confirmed from these two types of devices, and mechanism for bipolar charge generation at the interface of p-doped and n-doped organic semiconductors was discussed.1) T. Nakada, et al.: Ext. Abstr. 63rd Fall Meeting, 2002; Japan Soc. Appl. Phys. p. 1165. 2) M. Terai, D. Kumaki, T. Yasuda, K. Fujita and T. Tsutsui: Curr. Appl. Phys. 5 (2004) 341. 3) L. S. Liao, K. P. Klubek and C. W. Tang: Appl. Phys. Lett. 84 (2004) 167. 4) T. Tsutsui and M. Terai: App. Phys. Lett. 84 (2004) 440. 5) M. Terai, K. Fujita and T. Tsutsui: Jpn. J. Appl. Phys. 44 (2005) L1059. 6) C. T. Sah, R. N. Noyce, and W. Shockley, Proc. IRE, 45(1957) 1223.
12:45 PM - S13.14
Molecular N-type Doping of an Electron-Transport Material by Cobaltocene.
Calvin Chan 1 , Fabrice Amy 1 , Qing Zhang 2 , Stephen Barlow 2 , Seth Marder 2 , Antoine Kahn 1
1 Dept. of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Dept. of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWith the rapid advance of organic electronics and optoelectronics, electrical doping of organic thin films has been recognized as a means to overcome fundamental material properties limiting their electrical performance. Although molecular p-type doping has been studied by a number of groups in recent years, the energetic requirements of molecular n-dopants, i.e., a low ionization energy, have hindered the identification and development of stable electron donors. Here, n-type doping of an electron-transport material, a tris(thieno)hexaazaphenylylene derivative (1), with the strongly reducing molecule bis(cyclopentadienyl)-cobalt(II) (cobaltocene, CoCp2), is investigated via ultra-violet and inverse photoemission spectroscopy (UPS, IPES), x-ray photoemission spectroscopy, and current-voltage (I-V) measurements. Because of the volatile nature of the dopant, the unusual sublimation method used to deposit cobaltocene in the organic growth chamber will be described. UPS on a condensed film of the metallocene shows an ionization energy of ~4eV, which is unusually low for a vacuum-deposited molecular material and suggests cobaltocene as a promising candidate for a molecular n-type dopant. Efficient n-type doping of compound 1 is confirmed by a 0.56 eV shift of the Fermi-level toward the unoccupied states of the host, and by an increase in current by three orders of magnitude in devices in which the host film is interfacially doped with cobaltocene.
S14: Carrier Transport and Thin Films
Session Chairs
Friday PM, December 01, 2006
Room 304 (Hynes)
2:30 PM - **S14.1
Using PEDOT:PSS to Form Nearly Ohmic Hole Injection Contact to Small-molecule Organic Charge Transporters.
Shu-kong So 1 , Shing-chi Tse 1 , Sai-wing Tsang 1
1 Department of Physics, Hong Kong Baptist University, Hong Kong Hong Kong
Show Abstract3:00 PM - S14.2
Charge Injection, Transport and Degradation of Fluorene-arylamine Copolymers.
H. H. Fong 1 , George G. Malliaras 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract3:15 PM - S14.3
Transition from Non-Dispersive to Dispersive Hole Transport in a Small-Molecule Organic Semiconductor Controlled by Molecular Doping.
Arne Fleissner 1 , Hanna Schmid 1 , Christian Melzer 1 , Roland Schmechel 1 2 , Heinz von Seggern 1
1 Institute of Materials Science, Electronic Materials Department, TU Darmstadt, Darmstadt Germany, 2 Institute for Nanotechnology, Forschungszentrum Karlsruhe (FZK), Karlsruhe Germany
Show AbstractCharge carrier transport through organic semiconductors is strongly affected by trap states in the energy gap. The fundamental understanding of their influence on device characteristics is crucial for the design of high performance organic devices, such as organic light emitting diodes (OLEDs) and organic field effect transistors (OFETs). In the present work, the small-molecule organic semiconductor model system based on N,N’-di(1-naphtyl)-N,N’-diphenylbenzidine (α-NPD) molecularly doped with 4,4’,4’’-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA) at various concentrations was employed to study the effect of hole traps on hole transport by means of an optical time-of-flight technique.In case of undoped α-NPD, the current transients measured by time-of-flight exhibit a clear kink after which the transient trails off. This kink is indicative for non-dispersive transport and marks the transit time, from which the mobility of undoped α-NPD is determined as 5×10-4 cm2/Vs, being in good agreement with published data. However, current transients reported in literature and measured in the present work do not exhibit the flat current plateau before the kink that would be expected for non-dispersive transport, but feature a distinct cusp instead. Experimental parameters and the form of the current transients rule out space charge phenomena as cause for such a cusp. The origin of the cusp is studied by investigating the dependence of the current transients on various experimental parameters such as excitation intensity and wavelength as well as electric field strength and temperature. The mechanism proposed for the formation of the cusp is based on the thermal activation of holes to the transport energy of the organic semiconductor after optical generation.The influence of the trap concentration on charge carrier transport is studied by introducing 1-NaphDATA as a molecular dopant, which is known to create 0.4 eV deep hole traps in α-NPD. It will be demonstrated that the hole transport in α-NPD can be controlled by varying the doping concentration of 1-NaphDATA. Increasing the trap concentration, a transition from non-dispersive transport in undoped α-NPD to non-dispersive but trap-controlled transport with reduced mobility and further to dispersive transport is observed.
3:30 PM - S14.4
Micro-structure, Transport and Trapping in Polymeric Semiconductors.
Alberto Salleo 1 , Leslie Jimison 1 , Iain McCulloch 3 , Martin Heeney 3 , Michael Toney 2
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 , Merck Chemicals UK, Chilworth, Southampton United Kingdom, 2 , Stanford Synchrotron Radiation Laboratory, Menlo Park, California, United States
Show Abstract3:45 PM - S14: CarrierTran
BREAK
4:00 PM - **S14.5
Electrical, Mechanical, and Optical Studies of Nanotubes with Known Chirality.
James Hone 1
1 Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractBecause small changes in the crystal structure (chirality) of carbon nanotubes can produce large changes in their electrical properties, it is important to understand the relationship between structure and transport properties, both for basic science and for applications. We can determine the chirality of individual freely suspended nanotubes by measuring their Rayleigh scattering spectra, which have been independently correlated to the chirality. Various other properties of the nanotubes can then be probed, either in situ or after mechanical transfer of the nanotubes to another chip. This talk will focus on recent results of mechanical and electromechanical studies, interfacing nanotubes with CMOS chips, and transport properties of nanotube heterojunctions with known structure.
4:30 PM - S14.6
Epitaxial Growth of C60 Thin Films on Mica using Continuous-wave Laser Molecular Beam Epitaxy.
Seiichiro Yaginuma 1 2 , Kenji Itaka 2 3 , Masamitsu Haemori 4 , Masao Katayama 1 3 , Yuji Matsumoto 1 3 , Hideomi Koinuma 2 3 4
1 Materials and Structures Laboratory, Tokyo Institute of Technology, Kanagawa Japan, 2 Graduate school of Frontier Sciences, The University of Tokyo, Chiba Japan, 3 CREST, Japan Science and Technology Agency, Saitama Japan, 4 , NIMS, Ibaraki Japan
Show Abstract4:45 PM - S14.7
Using Atomic Steps to Control Pentacene Crystal Orientation Texture
Valerian Ignatescu 1 , Jing-Chih Hsu 1 , Alex Mayer 1 , Jack Blakely 1 , George Malliaras 1
1 , Cornell University, Ithaca, New York, United States
Show Abstract Pentacene is an organic semiconductor being studied as a candidate for cheap organic based field effect transistors. One of the main challenges is to obtain a much higher mobility of the charge carriers in the pentacene film. Due to the polycrystalline structure of the pentacene film, there is significant scattering at the grain boundaries. Using atomic steps as preferential sites for nucleation, we are investigating the proper growth conditions for azimuthal alignment of the pentacene crystals so that only small angle boundaries are present. Texture control is necessary to increase average carrier mobility thus improving device performance and may also help us to understand the interface effects on charge carriers’ transport. The substrate we are using is Si(111) with a miscut angle of 0.1° - 0.5° from the (111) plane. Before performing the pentacene deposition, the substrate morphology is modified by high temperature annealing in ultra high vacuum. Regular arrays of atomic height steps separated by atomically flat terraces are obtained. Various other surface morphologies, such as step bunches of different height have been investigated on patterned surfaces. The base pressure in the deposition chamber was below 10-6 Torr during the physical vapor deposition of the pentacene. Different substrate temperatures, in general in the 90 – 130 °C range, were investigated. About 0.5 monolayers were deposited and the location of the pentacene crystals relative to the steps as well as their shape was investigated by atomic force microscopy (AFM). We observed that using a slow deposition rate (around 0.05 monolayers/minute) and a silicon substrate with atomic steps of height 2-3 times the (111) interplanar separation and at least 2-3 microns apart, the pentacene crystals nucleate primarily along the steps. Such a surface morphology can be obtained in certain areas of patterned silicon surfaces, where step flow caused by the high temperature annealing is influenced by the etched craters. This condition is not easy to reproduce on large areas because it would require a wafer with a miscut angle of only 0.001°. If the steps are much closer, as is the case with the unpatterned samples, the pentacene islands, 1-3 microns in diameter in our deposition conditions, sprawls over multiple steps and the regular AFM imaging can no longer offer information about the orientation of deposited organic crystals. Carefully aligned grazing incidence X-ray diffraction (GIXD) experiments confirm the presence of preferred orientation due to nucleation at the step-edges. The experiments were carried out by monitoring the peak height of a (non-specular) in-plane reflection as the sample was rotated about its normal; the results indicate that the steps induce a preferred orientation even when most of the steps are only one atomic interplanar distance in height and are, on average, 200 nm apart.
5:00 PM - S14.8
Direct Deposition of Ordered Polymer Nanostructures via thermal Dip-Pen Nanolithography.
Paul Sheehan 1 , Minchul Yang 1 , Arnaldo Laracuente 1 , Brent Nelson 2 , William King 2 , Lloyd Whitman 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractIn thermal Dip Pen Nanolithography (tDPN) a heated atomic force microscope cantilever controls the deposition of a solid ink, acting like a nanoscale soldering iron. tDPN has several advantages over conventional DPN. Control over writing is greatly improved—deposition may be turned on or off and the deposition rate easily changed without breaking contact with the surface. In addition, imaging with a cool tip does not appear to contaminate the surface, thereby allowing in situ confirmation of the deposited pattern. Finally, tDPN can deposit a range of materials that are immobile at room temperature from semiconductors to insulators to metals.Thermal DPN is particularly suited to the deposition of polymers. To date, mylar, MEH-PPV, and poly(3-dodecylthiophene) [PDDT] have all been successfully deposited. PDDT is of particular interest as a conducting polymer with great potential for use in organic electronic devices. Using tDPN, well-ordered PDDT nanostructures have been deposited on silicon oxide and gold surfaces with layer-by-layer thickness control. By adjusting the tip heating power and the writing speed, we can vary the polymer thickness from a single monolayer (~2.6 nm) to tens of monolayers with lateral dimensions below 100 nm. Moreover, the morphology of the nanostructure suggests that the polymer strands are aligned along the path of the AFM tip. Unlike conventional DPN inks, the low vapor pressure of solvent-free polymers allows deposition in Ultra High Vacuum (UHV). We have deposited in UHV single monolayers of highly-ordered PDDT nanostructures on clean Si(001)-(2x1). The electronic and crystallographic properties of these structures will be discussed.
5:15 PM - S14.9
Assembly of Tailored Thiophene Oligomers on Gold Electrodes - Film Formation and Properties.
Peter Collier 1 , Wai Kerk 1 , Wee Chin 2 , Kian Loh 2 , Ping Bai 3 , Er Li 3
1 Surface Technology Group, Singapore Institute of Manufacturing Technology, Singapore Singapore, 2 Department of Chemistry, National University of Singapore, Singapore Singapore, 3 Electronics and Electromagnetics Program, Institute of High Performance Computing, Singapore Singapore
Show Abstract5:30 PM - S14.10
Plasma- Assisted Growth of Moisture Diffusion Barriers on Polymers: From Chemical Vapor Deposition to Atomic Layer Deposition.
Mariadriana Creatore 1 , Erik Langereis 1 , Antonella Milella 1 , Ioana Volintiru 1 , Stephan Heil 1 , Erwin Kessels 1 , Richard van de Sanden 1
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands
Show Abstract5:45 PM - S14.11
Morphological Basis for High Mobility of Poly(bithiophene thienothiophene).
Regis Kline 1 , Dean Delongchamp 1 , Eric Lin 1 , Lee Richter 1 , Iain McCulloch 2 , Martin Heeney 2 , Michael Toney 3
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Merck Chemical, Ltd., Southampton United Kingdom, 3 , Stanford Synchrotron Radiation Laboratory, Menlo Park, California, United States
Show AbstractCharge carrier mobility is the key materials parameter for determining performance of thin-film transistors. The liquid crystalline polymer poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophenes) (pBTTT) has been recently reported to have mobilities of 0.2 – 0.6 cm2/Vs. We have used a combination of atomic force microscopy (AFM), x-ray diffraction (XRD), near-edge x-ray absorption spectroscopy (NEXAFS), spectral ellipsometry (SE), and fourier transform infrared (FTIR) spectroscopy to solve the packing arrangement of the molecules. AFM shows the polymer to form molecular terraces up to several microns in size after annealing to the liquid crystalline regime. XRD shows the crystals to be highly oriented while SE shows the chain backbones to be perfectly aligned in the plane of the substrate. The comprehensive crystallinity of the films allows dichroic ratio of the conjugated planes determined by NEXAFS to be converted into a tilt. The conjugated planes are found to be tilted by 22° within the lamellar crystals. We have used NEXAFS and FTIR to show that the alkane side chains are tilted considerably. We have consolidated these measurements into model of molecular packing and determined key aspects of the molecular structure of pBTTT that improve the packing relative to regioregular polythiophenes.