Jian Li Arizona State University
Chung-Chih Wu National Taiwan University
Soo Young Park Seoul National University
Fred B. McCormick 3M Company
QQ1: Conjugated Polymers: Synthesis and Processing
Monday PM, December 01, 2008
Room 313 (Hynes)
9:00 AM - **QQ1.1
Energy Transport and Transduction in Conjugated Polyelectrolytes.
Kirk Schanze 1 Show Abstract
1 Chemistry Department, University of Florida, Gainesville, Florida, United States
Conjugated polyelectrolytes (CPEs) feature pi-conjugated backbones substituted with ionic solublizing groups. CPEs are soluble in polar solvents and can be processed using layer-by-layer (LbL) methods into nanostructured films. Using time-resolved optical spectroscopy, we have investiated the dynamics of exciton transport and charge transfer quenching in CPE/ionic quencher composite solutions. In addition, studies have explored the properties of solar cells fabricated using LbL films consisting of CPEs and a water soluble fullerene, and in hybrid configurations where CPE films are adsorbed to nanostructured TiO2 films.
9:30 AM - **QQ1.2
Synthesis and Aggregation Behaviour of Amphiphilic, Polyfluorene-b-polythiophene Diblock Copolymers.
Ullrich Scherf 1 Show Abstract
1 Macromolecular Chemistry Group, Wuppertal University, Wuppertal Germany
Amphiphilic, conjugated polymers are of great interest in various application fields, such as fluorescent chemical and biological sensors or components for electronic devices. We have looked at novel conjugated diblock copolymers of the polyfluorene-b-polythiophene-type, which have been synthesised in three steps. In the first step, monobromo-terminated poly(3-bromohexylthiophene) (Br-P3BrHTs) was prepared following a protocol first described by McCullough et al. . The second step involves a Suzuki-type cross coupling of a 2-bromo-9,9-bis(2-ethylhexyl)fluorene-7-boronic ester using Pd(PPh3)4 as catalyst and Br-P3BrHT as macromolecular endcapper . The final step towards amphiphilic block copolymers is a quarternization of the bromoalkyl functions of the non-ionic precursor with suitable N-nucleophiles or an Arbusov-type reaction with triethyl phosphite. The optical properties of the conjugated AB block copolymers in solution have been studied by absorption and photoluminescence spectroscopy. Moreover, the aggregation behaviour of the conjugated copolymers in solvent/non-solvent mixtures and after addition of oppositely charged surfactants (e.g. SDS) has been investigated.l. Zhai, R. D. McCullough, Adv. Mater. 14 (2002) 901G. Tu, H.Li, M. Forster, R. Heiderhoff, L. J. Balk, R. Sigel, U. Scherf, Small 3 (2007) 1001 U. Scherf, A.Gutacker, N. Koenen, Acc. Chem. Res. 41 (2008), published online asap, DOI: 10.1021/ar7002539.
10:00 AM - QQ1.3
Controlling the Morphology of Conjugated Polymers Through Non-covalent Intramolecular Interactions.
Peter Skabara 1 , Filipe Vilela 1 , Hao Pang 1 , John Forgie 1 , Simon Coles 2 , Michael Hursthouse 2 Show Abstract
1 Pure and Applied Chemistry, University of Strathclyde, Glasgow United Kingdom, 2 Chemistry, University of Southampton, Southampton United Kingdom
The use of non-covalent intramolecular interactions is an excellent method for imparting planarity (and good conjugation) within organic semiconducting materials, whilst retaining good solubility. Although planarity can be enforced in ladder type structures, solubility is an issue due to the persistent rigid nature of the polymer structure. Non-covalent contacts between heteroatoms (so-called two-electron, three-centre interactions) are weak enough to allow flexibility of the material in solution, but real enough to encourage a planar conformation in the solid state. As a result, non-covalent intramolecular/intrachain links can be used as a strategy for lowering the band gap of a material. In this work, we focus on several examples of structures where this approach has been used to good effect, whilst maintaining reasonable HOMO levels (essential for ensuring a favourable open circuit voltage in photovoltaic cells). The work presented focuses mainly on design, synthesis and electrochemical characterisation.
10:15 AM - QQ1.4
A ``Greener" Approach to Fabricate Conducting Polymer Nanocomposites and Their Electronic Performance: The Catalytic Role of Carbon Nanotubes.
Pui Lam Chiu 1 , Yufeng Ma 1 , William Cheung 1 , Huixin He 1 Show Abstract
1 Chemistry, Rutgers University, Newark, New Jersey, United States
We found that the polymerization process can be 4,500 times faster when a self-doped polyaniline nanocomposite was fabricated by in-situ polymerization in the presence of single-stranded DNA -dispersed and -functionalized single walled carbon nanotubes (ss-DNA/SWNTs). More importantly, the quality of the composite was significantly improved: fewer short oligomers were produced and the self-doped polyanline backbone had a longer conjugation length and existed in the more stable and conductive emeraldine state. Compared to the ss-DNA/SWNTs network, the conductance of the composite network increased as large as five orders of magnitude. The functionality of boronic acid group in the composite and the highly improved electronic performance may bring broad applications of the composite in flexible electronic devices. Blending of pre-formed polymer with carbon nanotubes is straightforward and widely used to fabricate nanocomposites. Here we demonstrate that the simple mixing approach might not fully and synergistically combine the merits of each individual component. The electronic structures of the carbon nanotubes and the monomer-nanotube interaction during polymerization highly impact the kinetics of the nanocomposite fabrication and the electronic performance of the obtained composite. Due to the remarkable catalytic capability of the SWNTs, conducting polymer nanocomposite can be fabricated by a “greener” process, which uses less harsh oxidant and shorter fabrication time.
10:30 AM - QQ1.5
Imide-functionalized D-A Conjugated Polymers.
Xugang Guo 1 , Mark Watson 1 Show Abstract
1 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States
Imide-functionalized small molecules are among the most promising organic electronic materials due to their self-assembly, high electron affinity and stability; yielding highly sought-after air-stable n-type organic semiconductors. This presentation will describe the synthesis and structure-property studies of alternating donor-acceptor (D-A) conjugated polymers with variable bandgap, in which imide-functionalized arenes are employed as “A” monomers. Cyclic voltammetry measurements confirm that LUMO energy levels are essentially the same as those of the “A” monomers, while HOMO energy levels vary with the electron density of the “D” monomers, allowing tailored optical band gaps. The lowest bandgap of these polymers is 1.08 eV and the polymer exhibits green color in its neutral-state. Fiber WAXD studies reveal highly ordered solid-state packing can be achieved by choosing appropriate “D” monomers and their side chains. Some polymers exhibit some interesting phenomena such as no visible photoluminescence, good overlap of absorption with the solar spectrum, and metallic luster. Properties observed thus far suggest these novel materials can be used as potential active layers in organic field effect transistors (OFET) and as acceptor layers in photovoltaic devices (PVD). Very preliminary OFET studies yield a hole mobility of 0.017 cm2/V.s for one polymer and ambipolar transport for another, both while operating in air.
10:45 AM - QQ1.6
Synthesis and Characterization of Novel Tetrazole-bearing Polymer Electrolyte Membranes for Fuel Cell Applications.
Huiping Li 1 2 , MinKyu Song 1 , Ze Liu 3 , Meilin Liu 1 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Chemical Engineering College, Zhengzhou University, Zhengzhou, Henan, China, 3 School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing China
Since its inception by K. B. Sharpless, click chemistry has been widely applied to synthesis of organic and hybrid (organic-inorganic) materials as well as to medicinal and bio-conjugate chemistry, especially in (3+2) cycloaddition between organic nitriles and inorganic/organic energetic azides. Here we report its application to the synthesis of several 5-R1-1H-tetrazoles (5RTA, R1=Ph, Ph-OH, -CH2COOH) in a one-pot reactor using aqueous solvents; this process is safe, low cost, easy for product isolation, and environmentally benign. Under optimum reaction conditions, the yield for 5RTA approaches 79 % for a reaction period of 29.5 h when R1 is Ph; the kinetics may be accelerated under microwave irradiation. In addition, we have obtained tetrazole-bearing polymers, by grafting 5RTA to a suitable backbone through nucleophilic substitution. The structures of these polymers are characterized using IR and NMR. Further, polymer electrolyte membranes (PEM) based on these polymers are prepared by an in-situ polymerization (sol-gel) process. Proton conductivities and electrochemical properties of these PEMs are studied underfuel cell operating conditions and are correlated with the structures of the polymers as well as the compositions and microstructures of the PEMs.
QQ2: Materials and Devices Processing
Monday PM, December 01, 2008
Room 313 (Hynes)
11:30 AM - **QQ2.1
Printed High Efficiency, Low Manufacturing Energy Investment, and Low Cost Polymer OLED Displays and Solid State Lighting.
Devin MacKenzie 1 Show Abstract
1 , Add-Vision Inc., Scotts Valley, California, United States
OLED technology has a range of potential applications spanning from high information content displays to general lighting where its potential for high efficiency, large area emission, light weight, thinness, and low toxicity make it an attractive technology for next generation lighting products. Recently, there has been impressive progress in the field demonstrating OLED power efficiencies at 100 lm/W. This makes OLED technology an interesting low DC voltage alternative to fragile and inefficient incandescents and Hg-based compact fluorescent technology. However, for OLED technology to become useful on a commercial and practical level, manufacturing challenges must be addressed. Many of the current high efficiency devices rely on nanoscale thickness precision and slowly-deposited and complex emitter and charge transport structures which require high capital cost manufacturing tools. This affects the viability of the technology, particularly at the initial stages where interesting entry level markets may not have the starting volumes to justify the cost expenditure required to start production, establish materials suppliers and get the manufacturing technology scaled to sufficient levels so that costs can be reduced.Add-Vision’s perspective on OLED devices and manufacturing, is based on low cost, high throughput printing tools, light-emitting polymer-enabled inks and simple encapsulation processes to fabricate entry level display and lighting products. Using widely available large-area printing tools enabled by doped light-emitting polymer and cathode inks, this technology provides low capital cost, entry level manufacturing capabilities, in the near term, to produce flexible P-OLED devices. This approach also dramatically reduces the energy invested in manufacturing the OLED devices as compared to conventional approaches due to the high throughput, and low energy usage of the deposition tools relative to conventional processing. This is especially important in many mobile and specialty lighting applications where manufacturing energy investment can dominate the total energy consumed by the display in its actual product life cycle. However, to meet the requirements of a broader range of flexible display and solid state lighting applications, and address broader energy efficiency goals, power efficiency is also being improved. Recent approaches including the use of phosphorescent-based light emitting polymer active layers for high quantum efficiency and new doping structure to reduce operating voltage and increase power efficiency with AVI’s proprietary, air printed cathode. Also, progress with manufacturing scale-up and low-cost encapsulation materials and encapsulation technology will be discussed.
12:00 PM - QQ2.2
Conducting Polymer Transfer Printing for All-Plastic Optoelectronic Devices.
Xiangjun Wang 1 , Peter Levernore 1 , Amy Ballantyne 1 , Ruidong Xia 1 , Jenny Nelson 1 , Donal Bradley 1 Show Abstract
1 Physics Department, Imperial College London, London United Kingdom
Printed conducting polymer electrodes offer the prospect of cost-effective, lightweight all-plastic optoelectronic devices. Here we report work on vapour phase polymerized PEDOT (VPP-PEDOT), a promising replacement for traditional ITO and metal electrodes that combines high conductivity and transparency [1-4]. In particular, we describe the use of polymer transfer printing (PTP)  to deposit VPP-PEDOT on top of a wide variety of materials, including flexible and rigid substrates and conjugated polymer films. This approach allows the fabrication of prototype all-plastic devices. VPP-PEDOT is used for both the anode and cathode contacts in light emitting diodes and solar cells with, respectively, green light emitting polyfluorene and poly(3-hexylthiophene) (P3HT)/1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C60 (PCBM) blend active layers. The influence of fabrication processes on VPP-PEDOT transparency, conductivity, work function and morphology and on active layer properties including luminescence yield and photocurrent will be discussed. Finally, the performance of our novel all-plastic devices will be compared to that of counterpart traditional ITO/metal electrode devices. Reference:1.P. A. Levermore, L. Chen, X. Wang, R. Das, D.D.C. Bradley, Adv. Mater., 2007. 19: p. 2379-2385.2.B. Winther-Jensen, F.C. Krebs, Solar Energy Mater. and Solar Cells, 2006. 90: p. 123-132.3.S. Admassie, F. Zhang, A.G. Manoj, M. Svensson, M.R. Andersson, O. Inganäs, Solar Energy Mater. and Solar Cells, 2006. 90: p. 133-141.4.A. Gadisa, K. Tvingstedt, S. Admassie, L. Lindell, X. Crispin, M.R. Andersson, W.R. Salaneck, and O. Inganäs, Synth. Metal., 2006. 156: p. 1102-1007.5.L. Chen, P. Degenaar, D.D.C. Bradley Adv. Mater., 2008. 20: p. 1679-1683.
12:15 PM - QQ2.3
Multilayer Polymer Light-Emitting Diode and Solar Cell by Blade Coating.
Hsin-Fei Meng 1 , Shin-Rong Tseng 1 Show Abstract
1 Institute of Physics, National Chiao Tung University, Hsinchu Taiwan
Multilayer polymer light-emitting diode (PLED) and solar cell are fabricated by blade coating which has the advantages of low material waste and easy scaling up to very large-area. More importantly multilayer of semiconducting polymers can be easily deposited by blade coating with minimal layer mixing. The multilayer structure is confirmed by the total thickness and cross section view in scanning electron microscope. The film thickness variation is only 3 % in 10 cm scale and the film roughness is about 0.3 nm in the micron scale. The efficiency of single layer PLED using poly(para-phenylene vinylene) copolymer SuperYellow and poly(9,9-dioctylfluorene) (PFO, deep blue) device are 9 cd/A and 1.7 cd/A respectively by blade coating. Such efficiencies are similar to single-layer spin coating. The efficiency of the PFO device is raised to 2.9 cd/A with a 2- (4-tert-Butylphenyl) -5-(4- biphenylyl)- 1,3,4-oxadiazole (PBD) hole-blocking layer and to 2.3 cd/A with a poly[(9,9- dioctylfluorenyl-2,7- diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) electron-blocking layer added by blade coating.For solar cell blade coating is applied to poly(3-hexylthiophene) (P3HT) and(6,6)-phenyl-C61-butyric acid methyl ester (PCBM) blend in toluene which has a lower boiling point and is less toxic compared with the conventionally used solvents dichlorobenzene and chlorobenzene. Power conversion efficiency of 3.6 % is achieved without the long drying process.
12:30 PM - QQ2.4
Ultra-compact Parylene Deposition System for Localized Optoelectronic Device Encapsulation.
Shaurjo Biswas 1 , Tamir Arbel 1 , Max Shtein 1 Show Abstract
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Parylene films are commonly used as transparent, flexible coatings in electronic devices and bio-medical applications,1 exhibiting anti-corrosive properties, low dielectric constant (2.4 – 2.65) and moisture resistance.2 Reactive vapor deposition of parylene results in conformal coverage of features at room temperature,3 which is advantageous for passivating organic optoelectronic devices. Conventional parylene deposition systems, however, utilize separate chambers for vaporization, pyrolysis, and polymerization,4 resulting in large footprint and limited processing integration ability, especially at a laboratory scale. Here, we demonstrate the vaporization and pyrolysis of [2,2]paracyclophane (parylene dimer) in a single compact nozzle, producing a jet of monomer that polymerizes into a film upon contact with the substrate at room temperature. We discuss the effect of jet flow dynamics on the deposition rate and film morphology. Potential advantages of this approach include increased material utilization efficiency, localized conformal coating capabilities, and an apparatus that is compact, inexpensive, and does not require a vacuum pump. W. F. Beach, Encyclopedia of Polymer Science and Engineering (Wiley, New York, 1985).S. Ganguli et al., J. Vac. Sci. Technol. A 15, 3138 (1997).J. B. Fortin, Chemical Vapor Deposited Polymerization (Kluwer Academic Publishers, Massachusetts, 2004). W. F. Gorham, Union Carbide Corp, U.S. Patent 3,342,754 (1967).
12:45 PM - QQ2.5
Fabrication of a Patterned Assembly of Semiconducting Organic Nanowires.
Jong H. Kim 1 , Yunoh Jung 1 , Jong Won Chung 1 , Byeong-Kwan An 1 , Soo Young Park 1 Show Abstract
1 Department of Materals Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Semiconducting organic nanowire assemblies are potentially useful for the fabrication of micro-/nanoelectrical devices such as chemical and bio-sensors, photodetectors, and organic transistors. A simple, one-step procedure for obtaining an aligned and patterned assembly is demonstrated herein. The proposed technique is based on a microchannel-filling method called micromolding in capillaries (MIMIC). A very well-aligned nanowire assembly with high birefringence, dichroism, polarized emission, and electrical conductivity (4.9x10-6 S/cm) was successfully obtained using 1-cyano-trans-1,2-bis-(3’,5’-bis-trifluoromethyl-biphenyl)ethylene (CN-TFMBE), which forms J-stacked nanowires in solution.
QQ3: OLED I: Materials and Devices
Monday PM, December 01, 2008
Room 313 (Hynes)
2:30 PM - **QQ3.1
Synthesis and Processing of Organic Conjugated Materials for Sustainable Optoelectronic Applications.
Andrew Holmes 1 Show Abstract
1 Chemistry/Bio21 Institute, University of Melbourne, Parkville, Victoria, Australia
Organic semiconducting materials have emerged with the real promise of contributing to a sustainable energy economy. The talk will summarize recent work in attempts to develop solution processible polymeric materials to harness phosphorescence, with a view to contributing to efficient solid state lighting, and to the control of polymer interfaces for applications in light harvesting materials for organic solar cells. Finally, the presentation will outline opportunities for employing environmentally benign solvents such as supercritical carbon dioxide for the synthesis and processing of organic semiconducting materials.
3:00 PM - **QQ3.2
Anchored Organic Molecular Dopants for High Power Efficiency OLEDs.
Linda Sapochak 1 , Phillip Koech 1 , James Rainbolt 1 , Xiuyui Cai 1 , Asanga Padmaperuma 1 , Evgueni Polkarpov 1 Show Abstract
1 , Pacific Northwestern National Laboratory, Richland, Washington, United States
3:30 PM - QQ3.3
Synthesis of Cyclometalated Platinum Complexes and Their Photophysical Properties.
Eric Turner 1 , Zixing Wang 1 , Jian Li 1 Show Abstract
1 School of Materials, Arizona State University, Tempe, Arizona, United States
The development of new light-emitting materials has attracted a great deal of attention over the past decade. Square planar platinum complexes show promise as phosphorescent emitters for potential application in OLEDs. This is due largely to their ability to harvest both electrogenerated singlet and triplet excitons, and to achieve 100% internal quantum efficiency. Recently, we reported 1,3-difluoro-4,6-di(2-pyridinyl)benzene platinum chloride as a blue emitter for OLED applications, with a peak EQE of 16% ph/el and CIE coordinates of (0.15, 0.26).In this presentation, we will discuss our continuing efforts in the design, synthesis, and characterization of novel platinum complexes for display and lighting applications. By varying the functional groups of platinum complexes, the emission color can be tuned over a large range. Colors range from deep blue to red, thus giving prospects for full-color display. The photo-physics, electrochemistry, and electroluminescent properties of these novel platinum complexes, including fluorine-free Pt-based deep blue emitters, will be discussed.
3:45 PM - QQ3.4
Improvement of External Quantum Efficiency of Organic Light-Emitting Devices by integrating Micro-Optical Films and Top-Emitting Structures.
Chih-Che Liu 1 3 , Su-Hao Liu 2 3 , Chih-Jen Yang 1 3 , Chih-Kai Chang 1 3 , Chung-Chih Wu 1 2 3 Show Abstract
1 , Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei City Taiwan, 3 , Department of Electrical Engineering, National Taiwan University, Taipei Taiwan, 2 , Graduate Institute of Electronics Engineering, National Taiwan University, Taipei Taiwan
Organic light-emitting devices (OLEDs) are very attractive for applications in large size flat panel display and solid state lighting. However, the out-coupling efficiency of OLEDs is low because of various optical trapping mechanisms such as the total reflection loss. The OLEDs can be made more efficient if one can improve the out-coupling efficiency of OLEDs, making OLED more suitable in solid state lighting applications.Our approach is to integrate top-emitting OLEDs with micro-optical films. The structure of top-emitting device in sequence consists of thick silver as anode, m-MTDATA doped F4-TCNQ as hole injection layer, α-NPD as hole transport layer, Alq3 doped C-545T as emission layer, undoped Alq3 as electron transport layer, LiF/Al as electron injection contact, thin silver as cathode. Moreover, Ag cathode is further capped by high index ZnSe and parylene for passivation. The micro-optical films, like microlens array and diffuser films, fabricated by micromolding and Doctor-Blading technique etc., are then laminated onto the top-emitting OLEDs. Our results showed that the external quantum efficiencies of top-emitting OLEDs integrated with micro-optical films can be enhanced by 1.6~2.1 times, compared to conventional bottom-emitting OLEDs. Moreover, the angular dependence of emission from top-emitting OLEDs is mitigated with micro-optical films.
4:30 PM - **QQ3.5
Solution Processed Small-Molecule Organic Light Emitting Diodes.
Nora Radu 1 Show Abstract
1 DuPont Displays, DuPont Co., Wilmington, Delaware, United States
We will present the DuPont Displays full color OLED printing and materials technologies. The process we are developing is more cost-effective and scalable than thermal evaporation through shadow masks. The materials lifetime is sufficient for most portable applications and is nearing that required for stationary displays. Recently, 4.3” WQVGA displays were demonstrated.
5:00 PM - **QQ3.6
Strategies for Design of Materials for Solution Processable OLED Devices.
James Cella 1 , Shiang Joseph 1 , Elliott Shanklin 1 , Paul Smigelski 1 , Kevin Janora 1 Show Abstract
1 , GE Global Research, Niskayuna, New York, United States
In an OLED device, the ability to control electronic excitations is of critical importance. Materials used as active layers in these devices must not only promote efficient flow of charge through the device but also have singlet (S1) and triplet (T1) levels that do not allow energy transfer quenching of emissive excitons. Materials suitable for use in solution processable devices require in addition the ability to be coated over an existing layer without compromising the under layer. Accordingly, it is important to be able to control, not only the electronic character of a given material (band gap, HOMO-LUMO levels, charge mobility) but also its physical property profile (solubility etc.). Ideally, it is desirable to tune both types of properties in a predictable, yet independent fashion to maximize the probability of obtaining materials suitable for any layer in the device. We describe two approaches to accomplishing these material requirements. Both approaches exploit the well-established chemistry of fluorene derivatives. The first approach involves the synthesis of discrete oligomers of fluorene wherein the energy levels are controlled by variation of the oligomer size while other material properties are controlled by adjusting pendant substituents. The second approach accomplishes energy level control by introducing a conjugation interrupter to a polyfluorene backbone. In a fashion similar to the first approach, the solubility and charge mobility properties of these materials are adjusted by appropriate modification of pendant functionality. Synthetic details and preliminary device data for these materials will be presented.
5:30 PM - QQ3.7
Efficient Light Emitting Devices Based on Phosphorous POSS Materials.
Xiaohui Yang 1 , Jesse Froehlich 2 , Sheng Li 2 , Amane Mochizuki 2 , Ghassan Jabbour 1 2 3 Show Abstract
1 , School of Materials and the Flexible Display Center, Arizona State University, Tempe, Arizona, United States, 2 , Nitto Denko Technical Corporation, 501 Via Del Monte, Ocean side, San Diego, California, United States, 3 , Advanced Photovoltaics Center at Arizona State University, Tempe, Arizona, United States
5:45 PM - QQ3.8
New Dendritic Architectures for Efficient Blue Phosphorescence.
Shih-Chun Lo 1 , Ruth Harding 2 , Christopher Shipley 3 , Stuart Stevenson 2 , Paul Burn 1 , Ifor Samuel 2 Show Abstract
1 Centre for Organic Photonics & Electronics, School of Molecular & Microbial Sciences, The University of Queensland, Brisbane 4072, Queensland, Australia, 2 Centre for Organic Semiconductors, School of Physics & Astronomy, University of St Andrews, North Haugh, Fife KY16 9SS United Kingdom, 3 Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA United Kingdom
QQ4: Poster Session: Materials Synthesis and Characterization
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - QQ4.1
Highly Transparent, Tough and Dimensionally Stable Polymer Nanocomposite.
Hironobu Muramatsu 1 , Katsumi Morohoshi 1 , Haruo Unno 1 , Takashi Oda 1 , Tomohiro Itou 1 , Yasuaki Kai 1 , Naoko Fujita 2 , Manabu Kawa 2 Show Abstract
1 Society and Frontier Lab., Nissan Motor Co. Research Center , Yokosuka Japan, 2 Functional Materials Lab., Mitsubishi Chemical Group Science and Technology Research Center, Yokohama Japan
This report describes a novel polymer nanocomposite that shows high transparency, toughness and dimension stability at the same time. Polymer nanocomposites are attracting industrial interest for a wide range of application. One advantage of polymer nanocomposites is the possibility to obtain visually transparent polymer material owing to nano-size particles that are smaller than visible wavelengths. Transparent polymer nanocomposites are suitable for light, clear, tough and dimensionally stable applications such as the windows and sunroofs of vehicles or houses and other buildings. However, most of the research on transparent polymer nanocomposites has remained at the stage of showing their potential or future expectations because of the complexity of various nanoparticle-polymer matrix combinations. One of the most difficult challenges for the fabrication of transparent nanocomposites is to keep the dispersion of particles in the polymer uniform at the nano-level until the final composite is obtained. Some successful examples have been reported with polyacrylate-based polymer nanocomposites. For example, silica/PMMA nanocomposites show good transparency even with a high filler content. In fact, most of their transparency depends on refractive index matching. While a nanocomposite may appear transparent to the human eye, TEM observation shows that there are many aggregations inside, preventing the material from ever becoming tough and making it extremely brittle. Some other cases are based on a tough polymer like polycarbonate, but with a very restrained filler content of only several weight percent. Because of such a small amount of filler, dimensional stability cannot be improved. Thus, there have been no reports of highly transparent, tough and dimensionally stable polymer nanocomposites with a filler content of more than 10wt%.We overcame this contradictory challenge and succeeded in dispersing more than 15wt% of filler into polycarbonate. We chose needle-shaped alumina boehmite nanoparticles as the filler, and employed an appropriate amount of organic acid as a surface modifier to aid in uniform particle dispersion in the polymer matrix. Polycarbonate is well-known as a tough polymer, but its main chain easily hydrolyses, either in the presence of an acid or base. The hydrolysis reaction makes the polymer chain shorter, leading rapidly to a brittle composite. We carefully defined the surface modification condition to avoid this hydrolysis reaction. This completely novel composite shows excellent properties without any trade-off, including high transparency (Haze<1%), toughness (Izod>60 J/m) and dimensional stability (CLTE<40 ppm) at the same time.
9:00 PM - QQ4.10
Regioregular Polythiophene Block Copolymers Synthesized by Various Ionic Polymerization Techniques.
Mussie Alemseghed 1 , Mihaela Stefan 1 Show Abstract
1 Chemistry, University of Texas at Dallas, Richardson, Texas, United States
Regioregular poly(3-hexylthiophenes) are an important class of conjugated polymers that show high performance in thin film transistors and solar cell devices. Here, we present the synthesis and characterization of various block copolymers of regioregular poly(3-hexylthiophene). Allyl terminated poly(3-hexylthiophene) was subjected to chemical modification to generate end groups amenable for cationic and anionic polymerization of various monomers. Poly(3-hexylthiophene)-b-poly(tetrahydrofuran) was synthesized by cationic ring-opening polymerization of tetrahydrofuran using a hydroxypropyl terminated polymer as a precursor. The functional initiator used for the ring-opening polymerization of tetrahydrofuran was synthesized by reacting the hydroxypropyl functional groups with trifluoromethanesulfonic anhydride in the presence of 2,6-di-tert-butylpyridine. 1H NMR and SEC data confirmed the formation of the di-block copolymers. Field effect mobility of poly(3-hexylthiophene)-b-poly(tetrahydrofuran) was measured and was found to be 0.0089 cm2 /V s.Poly(3-hexylthiophene)-b-polystyrene-b-polyisoprene copolymers were synthesized by anionic polymerization. This method is based on the addition reaction of “living” poly(styryl)lithium to allyl terminated poly(3-hexylthiophene).
9:00 PM - QQ4.11
Improved Performance of Organic Light Emitting Diodes with 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) Ultra-Thin Layer on ITO Anode as Hole Injection Layer.
Won Min Yun 1 , Oh Kwan Kwon 1 , Seung Hwan Lee 1 , Chan Eon Park 1 Show Abstract
1 Chemical Engineering, POSTECH, Pohang, Gyungbuk, Korea (the Republic of)
In OLED, hole injection efficiency is one of the important factors that are related to device performances such as operating voltage and device efficiency. Low operating voltage and device efficiency are essential factors for the further commercial application of OLEDs. Therefore, In order to improve hole injection, insulating materials (LiF, Al2O3, SiO2, metal oxide) and organic semiconducting materials with intermediate HOMO level(CuPc, 2TNATA) between Fermi level of anode and HOMO of HTL are applied on ITO anode surface, and those layers were found to lower the operating voltage dramatically. In this research, ultra-thin (a few nanometer thickness) 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi)-conventional blue host material-is tested on indium tin oxide anode as hole injection layer. Device used in this experiments is consisted of ITO/DPVBi (3 nm)/NPB/Alq3/LiF/Al. And with ultra-thin thermally deposited DPVBi layer, optical and electrical properties of device are improved compared with those of bare ITO device. By testing current density-voltage characteristics of hole only device consisted of [ITO/DPVBi (3 nm) /NPB/Al], this enhancement is related to improved hole injection from ITO to hole transporting NPB layer. Slightly lowered current efficiency with the insertion of DPVBi also indicates the imbalance of charge carriers with improved hole injection. From photoemission study, HOMO level of DPVBi 5.8eV is obtained. Therefore, this enhancement can be considered as an improved tunneling hole injection from Fermi level of ITO (4.7eV) into HOMO level of NPB(5.4eV) via DPVBi hole injection layer. Device with various thickness (0 to 10nm) of DPVBi devices are fabricated in order to investigate the effect of DPVBi thickness on hole injection. Device stability is also enhanced with DPVBi hole injection layer. The improved stability comes from reducing ITO anode surface roughness. From AFM images, it can be seen that the rms roughness of plasma treated ITO surface become smaller with deposition of ultra-thin DPVBi layer than a bare ITO substrate.
9:00 PM - QQ4.14
Synthesis and Characterization of Pyridyl Carbozole Based Polymeric Materials for Electrophosphorescent Lighting-Emitting Devices.
Sijesh Madakuni 1 2 , Brian Guthrie 1 2 , Zixing Wang 1 2 , Xiaohui Yang 1 2 , Daniel Shea 1 2 , Ghassan Jabbour 1 2 , Jian Li 1 2 Show Abstract
1 School of Materials, Arizona State University, Mesa, Arizona, United States, 2 Advanced Photovoltaics Center, Arizona State University, Tempe, Arizona, United States
9:00 PM - QQ4.15
Efficient Direct-Electron Transfer Biofuel Cell using Carbon Nanotubes and Self-assembled Gold on Porous Silicon.
Shiunchin Wang 1 , Manuel Silva 1 , Zafar Iqbal 1 Show Abstract
1 , New Jersey Institute of Technology, Newark, New Jersey, United States
9:00 PM - QQ4.16
Red Algae Fiber Reinforced Biocomposites for a Sustainable Energy Economy.
Seong Ok Han 1 , Kyoung Ja Sim 1 , Min Woo Lee 1 , Yung Bum Seo 2 Show Abstract
1 Nano Materials Research Center, Korea Institute of Energy Research, Daejeon Korea (the Republic of), 2 Department of Forest Products, Chungnam National University, Daejeon Korea (the Republic of)
9:00 PM - QQ4.17
Synthesis and Photophysical Properties of Alternating Copolymer of 3-Hexylthiophene and Thiadiazolo[3,4-g]quinoxaline for Low-Bandgap Active Material of Polymer Photovoltaics.
Yoon Kyoo Lee 1 , Jae Woong Jung 1 , Won Ho Jo 1 Show Abstract
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Polymer photovoltaic cells have opened a new avenue to develop economically renewable energy resources due to their unique advantages, such as low cost, light weight, and potential use in flexible devices. While the power conversion efficiency of polymer phtovoltaics exceeding 5 % has been reported, further improvements are still needed for commercial use. The absorption spectra of conjugated polymers typically used as an active material for solar cells exhibit poor overlap with the solar spectrum. Foe an example, poly(3-hexylthiophene), which has currently been known as the most efficient electron donor material, has a bandgap of 1.9 eV and thus harvests photons only up to 22 % of available photons. To absorb photons at longer wavelengths, where more photon flux from the emission of the sun is found, development of low-bandgap polymer is strongly required.It has been known that donor-acceptor conjugated alternating copolymers have great advantages because their electronic properties can be effectively manipulated by intramolecular charge transfer (ICT): The interaction between the electron donor and acceptor moieties in an alternating copolymer results in the hybridization of the high HOMO energy level of donor and the low LUMO energy level of acceptor, leading to a relatively low bandgap polymer. In this study, we have designed a low-bandgap polymer by using DFT calculation and then synthesized an alternating copolymer composed of 3-hexylthiophene and thiadiazolo[3,4-g]quinoxaline. This alternating copolymer shows good solubility in common solvents such as THF and chloroform, and the bandgap (1.5 eV) of the copolymer is significantly lower than that (1.9 eV) of P3HT. Furthermore, the HOMO (5.0 eV) and LUMO (3.5 eV) energy levels of the alternating copolymer are appropriate for the photoinduced charge transfer between the copolymer and PCBM, when PCBM is used as an electron acceptor. Other photophysical properties which are required to the photovoltaic applications will be presented.
9:00 PM - QQ4.2
A Solution Processed Photovoltaic Device Made from an Air-Stable Polythiophene Derivative.
Avery Yuen 1 2 , Ah-Mee Hor 2 , Stephen Jovanovic 1 2 , Kent Fisher 3 2 , John Preston 1 , Rafik Loutfy 1 Show Abstract
1 , McMaster University, Hamilton, Ontario, Canada, 2 , Xerox Research Center of Canada, Mississauga, Ontario, Canada, 3 , University of Guelph, Guelph, Ontario, Canada
Solution processed bulk heterojunction photovoltaics have attracted much attention recently due to their potential for low-cost, renewable energy. A commonly studied material system, a blend of poly(3-hexylthiophene) (P3HT) and phenyl C61 butyric acid methyl ester (PCBM), has been used in many studies, yielding power conversion efficiencies of ~5% . However, despite this success, P3HT suffers from electrical instability due to oxidation in air, which tends to rapidly degrade the device performance. In this study, we report on the usage of an alternative polythiophene derivative, poly(3,3'''-didodecyl-quarterthiophene) (PQT-12), as an electron donor in place of P3HT. PQT-12 has demonstrated high hole mobility, solution processability, and absorption spectra similar to P3HT, but has the added advantage of a higher ionization potential, leading to less sensitivity to oxidation . Photovoltaic heterojunction devices were prepared on indium tin oxide (ITO) coated glass substrates, coated with a layer of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS). An active PQT-12/PCBM bulk heterojunction layer (~100nm) was spun from solution in chlorobenzene that was then capped with a thermally evaporated aluminum electrode.A control device consisting of a 50 wt% blend of P3HT/PCBM was fabricated, yielding 4.0% power conversion efficiency after optimization of spin conditions and annealing parameters. In order to compare the effect of polymer degradation, a 50 wt% blend of PQT-12/PCBM was fabricated using identical spin conditions and annealing parameters.Previous studies have shown that the optimal blend composition for PQT-12/PCBM devices is much closer to 15 wt% PQT-12 , yielding ~1%. This maximum efficiency device was also fabricated and contrasted against the maximum efficiency P3HT/PCBM cell.Completed devices were illuminated through the ITO electrode with 100 mW/cm2, AM1.5G simulated sunlight, and I-V response was measured using a source-measure unit. The active area was 0.08 cm2, as defined by shadow mask. Lifetime experiments were conducted by measuring the I-V response in exponentially increasing time intervals, with the devices held at 20°C and 40% RH. Unless measuring the dark current, the device was continuously exposed to the light to simulate operational conditions.In order to identify the mode of degradation, the devices were placed in a chamber that was then continuously filled with either O2 or N2. By contrasting the lifetime data for these two gasses, oxidation or phase segregation can be shown to be the primary mode of degradation. Aged samples are also examined using atomic force microscopy, UV-visible absorption spectroscopy, and spectrally resolved external quantum efficiency measurements.References1G. Li et al, Nat. Mater., 4, 864 (2005)2B.S. Ong et al, J. Am. Chem. Soc. of the American Chemical Society, 126, 3378 (2003) 3A.P. Yuen, manuscript in preparation
9:00 PM - QQ4.3
Highly Fluorescent 1,2,4-Linking Hyperbranched Poly(arylenevinylene)s with Energy Funneling Properties.
Zengqi Xie 1 , Seong-Jun Yoon 1 , Soo Young Park 1 Show Abstract
1 Department of Material Science and Engineering, ENG445, Seoul National University, Seoul Korea (the Republic of)
Hyperbranched conjugated polymers have unique properties, such as multiple end groups, easy functionalization, high solubility, and weak interchain interactions; but the synthesis of hyperbranched polymers is not easy, because the gelation will be encountered sometimes. Herein, we report the design and synthesis of a highly soluble 1,2,4-linking hyperbranched poly(phenylenevinylene) (1,2,4-hb-MEHPPV) prepared by Wittig reaction of A2 and B3 monomers, where A2 is a phosphorous salt and B3 is 1,2,4-trifunctionalized biphenyl-tricarbaldehyde. The molecular weight of the polymer was controlled conveniently by controlling the amount of the base (NaOCH3) used in the polymerization. It was observed that with the increased molecular weight the absorption and photoluminescence (PL) spectra showed distinct red-shifts. The synthesized 1,2,4-hb-MEHPPV showed characteristic energy funneling effect different from 1,3,5-linking hyperbranched polymer (1,3,5-hb-MEHPPV), because of the extended π-conjugation with varying branch structures. It was also shown that the polymers have very good solubility (e.g. >200 mg/mL), thermal properties (degradation temperature 420oC) and high photoluminescence efficiency (0.35~0.39).
9:00 PM - QQ4.4
Cobalt Porphyrin Functionalized Carbon Nanotubes for Oxygen Reduction in Acidic Medium.
Wei Zhang 1 , Ali Shaikh 2 , Emily Tsui 1 , Shrikant Singh 3 , Timothy Swager 1 Show Abstract
1 Department of Chemistry and Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 3 Department of Chemistry, Indian Institute of Technology, Kharagpur India
9:00 PM - QQ4.5
Subnanoporous Polyacenic Material for Gas Storage.
Yoshiki Fukuyama 1 , Hiroshi Furuya 1 , Shizukuni Yata 1 Show Abstract
1 , Tokuyama Corporation, Shunan-shi, Yamaguchi Japan
9:00 PM - QQ4.6
Synthesis of New Fullerene Derivatives for the Application of Organic Photovoltaic Cells.
Jin Mun Yun 1 , Seok-In Na 1 , Jang Jo 1 , Kang-Jun Baeg 1 , Seung Hwan Oh 1 , Tae-Soo Kim 1 , Dong-Yu Kim 1 Show Abstract
1 Dept. of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Buckminsterfullerene (C60) has been extensively investigated due to their invaluable electron accepting capability and semiconductor properties in organic electronics. Especially, one of the C60 derivatives, PCBM ([6,6]-phenyl- C61-bytyric acid methyl ester) has been used as the best performing electron acceptor with organic electron donor materials, in particular, poly (3-hexylthiophene) (P3HT) in organic bulk-heterojunction photovoltaic cells (OPVs). OPVs with 4-5% power conversion efficiencies (PCE) under AM 1.5 G illumination have recently been reported by many groups using a P3HT:PCBM blend; however, this PCE is not high enough, thus still an obstacle to commercialization of these devices.In OPVs, high efficiency can be achieved through high open circuit voltage (Voc) and short circuit current (Jsc). It is well-known that Voc is dependent on the energy level difference between the highest occupied molecular orbital (HOMO) of donor and the lowest unoccupied molecular orbital (LUMO) of acceptor, and efficient 3-dimensional (3-D) percolation between donors and acceptors critically affects to Jsc. In this study, we synthesized novel fullerene derivatives as an electron acceptor in OPVs. Electron donating groups are substituted to raise LUMO of acceptor in stead of a phenyl ring of PCBM to increase Voc. The phenyl ring in PCBM is also substituted with heteroaromatics to enhance Jsc through improved 3-D percolation. In addition, n-type organic field-effect transistor (OTFT) devices were also fabricated using above analogues.
9:00 PM - QQ4.7
Electrical, Optical and Morphological Properties of P3HT/MWNT Nanocomposite Prepared by In-situ Polymerization.
Viney Saini 1 2 , Zhongrui Li 1 , Shawn Bourdo 3 , Enkeleda Dervishi 1 2 , Yang Xu 1 , Xiaodong Ma 2 , Tito Vishwanathan 3 , Divey Saini 4 , Meena Mahmood 1 2 , Alexandru Biris 5 , Dan Lupu 5 , Alexandru Biris 1 2 Show Abstract
1 Nanotechnology Center, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 2 Applied Science Department, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 3 Department of Chemistry, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 4 Duke Human Vaccine Institute, Duke University, Durham, North Carolina, United States, 5 , National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca Romania
In-situ polymerization of soluble conductive polymer poly-3hexylthiophene (P3HT) was performed in the presence of different levels of doping concentration of multi-wall carbon nanotubes (MWCNTs) (0.1, 1.0, 5.0 and 10 wt.%). The P3HT-MWCNT nanocomposites are of great interest because of their applications in field-effect transistors, organic light emitting diodes, organic solar cells, etc. The morphological, optical, thermal and electrical properties of the nanocomposites were thoroughly studied by Transmission Electron Microscopy (TEM), Nuclear Magnetic Resonance (NMR) spectroscopy, Raman spectroscopy, UV-Vis-NIR spectroscopy, Thermo-gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and temperature dependent conductivity measurements. It was found that nanotubes are dispersed uniformly in the polymer matrix while the polymer chains robustly wrap around the nanotube walls. Therefore, the interaction between the nanotubes and the polymer matrix enhances the optical, thermal and electrical properties of the nanocomposite for certain doping concentrations of MWCNTs. In addition, the charge carrier transport phenomenon is also studied for these nanocomposites.
9:00 PM - QQ4.8
Alternatives to Copper Phthalocyanine as Organic Conductors
Linda Doerrer 1 , Rachel Allenbaugh 1 , Kevin Smith 2 , Louis Piper 2 , Alex DeMasi 2 , Tim Jones 4 , Virendra Chauhan 4 , Xi Lin 3 , Andre Botelho 3 Show Abstract
1 Chemistry Department, Boston University, Boston, Massachusetts, United States, 2 Physics Department, Boston University, Boston, Massachusetts, United States, 4 Chemistry Department, Warwick University, Coventry, CV4 7AL, United Kingdom, 3 Manufacturing Engineering, Boston University, Boston, Massachusetts, United States
Copper phthalocyanine is an important and well-studied organic conductor that whose conductivity increases upon n-type doping. We are investigating another copper organic material that exhibits similar solid state UV-vis properties, similar packing in the solid state, and may therefore exhibit similar or perhaps greater conductivity. This material is N,N'-Ethylene-bis(1,1,1-trifluoropentane-2,4-dioneiminato)-copper(ii), and abbreviated Cu(TFAC). Synchrotron XES, XAS, and XPS measurements of vapor-phase depositied thin films have been used to characterize the electronic structure in contrast to Cu(Pc). Cu(TFAC) has also been further characterized by XRD, AFM and SEM images of thin films as well as transport measurements. All the experimental work is complemented by PDOS calculations. A detailed comparison of these two organic conductors will help provide a structure-function understanding of these materials.
9:00 PM - QQ4.9
Synthesis of Regioregular Polythiophenes with Alkenyl Side Chains.
Nadia Hundt 1 , Eugene Stein 1 , Kumranand Palaniappan 1 , Michael Biewer 1 , Mihaela Stefan 1 Show Abstract
1 Chemistry, University of Texas at Dallas, Richardson, Texas, United States
Synthesis of regioregular polythiophenes with alkenyl side chains is reported. The alkenyl side chains are versatile functional groups, allowing for facile chemical modification to generate novel materials with tunable opto-electronic properties. Nickel mediated cross-coupling polymerization was used for the synthesis of regioregular poly(3-alkenylthiophenes). 2-Bromo-3-alkenylthiophene was synthesized by lithiation of 3-alkenylthiophene followed by reaction of 2-lithio-3-alkenylthiophene with carbon tetrabromide. Regioregular poly(3-alkenylthiophenes) were prepared by the nickel mediated cross-coupling polymerization, which provides a high specificity of head-to-tail couplings of the repeating units. The first step of this reaction was lithiation of 2-bromo-3-alkenylthiophene followed by transmetallation with zinc chloride to generate 2-bromo-5-chlorozinc-3-alkenylthiophene monomer, which was subsequently reacted with Ni(dppp)Cl2 catalyst. A detailed kinetic study of this reaction will be presented. Optimization of reaction conditions is expected to generate a “living” polymerization, in which polymers with precise molecular weights and narrow polydispersities will be synthesized.
Jian Li Arizona State University
Chung-Chih Wu National Taiwan University
Soo Young Park Seoul National University
Fred B. McCormick 3M Company
QQ5/H1: Joint Session: Organic Photovoltaic Cells
Tuesday AM, December 02, 2008
Room 311 (Hynes)
9:30 AM - **QQ5.1/H1.1
Bulk Heterojunction Nanomaterials for Low Cost ``Plastic" Solar Cells.
Alan Heeger 1 Show Abstract
1 Physics Department, University of California - Santa Barbara, Santa Barbara, California, United States
10:00 AM - **QQ5.2/H1.2
Interface Engineering of Tailored Interfaces for Organic Opto-Electronics: Photovoltaics.
Tobin Marks 2 Show Abstract
2 , Northwestern U., Evanston, Illinois, United States
Tuesday, 12/2New Presentation Time/Paper Number*QQ5.6/H1.6 @ 11:30 AM to *QQ5.2/H1.2 @ 9:00 AMInterface Engineering of Tailored Interfaces for Organic Opto-Electronics: Photovoltaics. Tobin Marks
10:30 AM - **QQ5.3/H1.3
Solution-processed Mesoscopic Iron Oxide for Water Photoelectrolysis.
Scott Warren 1 , Kevin Sivula 1 , Michael Graetzel 1 Show Abstract
1 EPFL SB ISIC LPI, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
11:30 AM - **QQ5.4/H1.4
Time-resolved Spectroscopy of Charge Separation in a Heterojunction Photovoltaic Cell under Applied DC Bias.
Alex Marsh 1 , Justin Hodgkiss 1 , Richard Friend 1 Show Abstract
1 Department of Physics, University of Cambridge, Cambridge United Kingdom
12:00 PM - **QQ5.5/H1.5
Impact of Semiconducting Polymer Conformation on Thin Film Electrical Properties.
Iain McCulloch 1 , Martin Heeney 2 , Michael Chabinyc 4 , Dean DeLongchamp 3 , Joseph Kline 3 , Michael McGehee 5 , Alberto Salleo 5 Show Abstract
1 Chemistry, Imperial College London, London United Kingdom, 2 Materials Science, Queen Mary University of London, London United Kingdom, 4 , University of California Santa Barbara, Santa Barbara, California, United States, 3 , NIST, Gaitherburg, Maryland, United States, 5 , Stanford University, Palo Alto, California, United States
12:30 PM - **QQ5.6/H1.6
Nanocrystalline Networks in Small Molecular Weight Organic Thin Films For Use in Solar Energy Conversion Devices.
Stephen Forrest 1 , Richard Lunt 1 2 , Fan Yang 1 2 Show Abstract
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Tuesday, 12/2New Presentation Time/Paper Number*QQ5.2/H1.2 @ 9:00 AM to *QQ5.6/H1.6 @ 11:30 AMNanocrystalline Networks in Small Molecular Weight Organic Thin Films For Use in Solar Energy Conversion Devices. Stephen Forrest
QQ6: Photovoltaics I: Materials and Devices for Vapor-deposited Solar Cells
Tuesday PM, December 02, 2008
Room 313 (Hynes)
2:30 PM - **QQ6.1
New Materials for Organic Photovoltaic Devices.
Mark Thompson 1 , M. Dolores Perez 1 , Kristen Mutolo 1 , Stephen Forrest 2 Show Abstract
1 Chemistry , University of Southern California, Los Angeles, California, United States, 2 Physics and Electrical Engineering, University of Michigan, Ann Arbor, Michigan, United States
There has been a great deal of interest in developing new materials for the fabrication of light emitting diodes (OLEDs). We have prepared a range of intensely metal complexes, which have found application in both monochromatic and white OLEDs. Our approach has involved a systematic study of a range of different materials. We have used a similar approach to develop materials for organic photovoltaic devices (OPVs). I will discuss the development of new materials as donors, acceptors and buffer layers in OPVs. I will discuss the use of metal complexes and subthalocyanines as donor and acceptor materials in organic solar cells. We have prepared a family of subphthalocyanine complexes to investigate the connection between the OPV open circuit voltage (Voc) and the energy difference between the donor HOMO and acceptor LUMO energies (Ig). These molecular orbitals are the ones that carry the holes and electrons, respectively. The key here was to use a very similar set of materials that we expect to have similar carrier conductivities and absorption spectra. This study shows that there is a clear connection between the Voc and the Ig. A high Ig leads to a high Voc. We have explored the use of metal porphyrin complexes as donor materials in OPVs. The complexes we have chosen have high nonplanar structures in the ground state and excited state. I will discuss the use of both Pt and Pd complexes, illustrating how these materials can be used to enhance both the efficiency and Voc.
3:00 PM - QQ6.2
Understanding and Controlling the Morphology of Vacuum-Deposited Molecular Organic Photovoltaic Device.
Jiangeng Xue 1 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
3:15 PM - QQ6.3
Photoactive Donor-acceptor Thin Films as Prospective Materials for Evaporated Bulk Heterojunctions of Molecular Semiconductors.
Robin Knecht 1 , Dominik Klaus 1 , Christopher Keil 1 , Günther Schnurpfeil 2 , Derck Schlettwein 1 Show Abstract
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany, 2 Institute of Organic and Macromolecular Chemistry, University of Bremen, Bremen Germany
The formation of evaporated blends of organic donor and acceptor molecules has gained interest recently for active interlayers in organic photovoltaic cells and organic field effect structures. In this contribution we report about the combination of phthalocyanines as electron donors absorbing in the red part of the spectrum and perylene imids as electron acceptors absorbing in the green part of the spectrum providing almost perfect coverage of the visible range. Mixed films were successfully created by simultaneous physical vapour deposition of the molecules to create an evaporated organic bulk heterojunction. Using transmission spectroscopy, structure analysis and photoconductivity measurements electronic and optical properties were investigated and compared with the properties of the pure films and solution spectra. The observed spectral dependence of the photoconductivity indicates a potential use of such materials in organic photovoltaic cells.
3:30 PM - QQ6.4
Soluble Pentacene Derivatives as Acceptors for Organic Photovoltaics.
Yee-Fun Lim 1 , Ying Shu 2 , John Anthony 2 , George Malliaras 1 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry, University of Kentucky, Lexington, Kentucky, United States
The P3HT:PCBM bulk-heterojunction blend cell is currently the champion system for organic photovoltaics, with reported efficiencies exceeding 5%. However, it is desirable to explore other materials as acceptors, since PCBM does not absorb significantly in the visible and infra-red, and has been shown to have poor stability in air. Soluble conjugated small molecules are an attractive class of materials to explore, as they have higher mobilities compared to polymers and their electronic properties can be easily tuned via chemical synthesis. In particular, triisopropylsilylethynyl(TIPS)–pentacene has proven to be a good p-type material in thin film transistors as well as photovoltaics. Adding electron-withdrawing cyano functional groups to TIPS-pentacene serves to lower its HOMO-LUMO levels, thus turning it into an n-type material. We have observed modest photovoltaic efficiencies in spin-casted blends of cyano-TIPS-pentacene derivatives with P3HT, demonstrating their feasibility as acceptors. By systematically blending P3HT and several cyano-pentacene derivatives with different alkyl functional groups, we found that the materials that stack in 1D out-perform those that stack in 2D. A solar cell fabricated from a blend of P3HT and dicyano-tricyclopentylsilylethynyl(TCPS)-pentacene, a 1D-stacking material, exhibited efficiency approaching 0.5% under AM1.5 illumination.
3:45 PM - QQ6.5
Acene Substituted Triisopropylsilylethynyl Anthracene Derivatives with High Mobility : Theoretical Analysis and Application to Opto-Electronic Devices.
Chan Eon Park 1 Show Abstract
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
A series of new organic semiconducting materials using triisopropylsilylethynyl anthracene (TIPSAN) as the core and several small fused acenes as side groups are designed and synthesized. Substitution with appropriate acenes at 2, 6-positions of triisopropylsilylethynyl anthracene, which promote extended π-electron delocalization, leads to increased π-overlap area compared with triisopropylsilylethynyl pentacene (TIPS pentacene). This has enabled fabrication of high performance and highly stable, solution processed Organic Field Effect Transistor (OFET) under ambient conditions.Especially, TIPSAN-Na (naphthalene as a side group) showed superior performance when it was used as channel material. The hole mobility as high as 3.7 cm2V-1s-1 was obtained from single crystal OFETs and 0.1 cm2V-1s-1 was obtained from thin film OFETs. To elucidate the origin of this high performance compared with other TIPSAN derivatives, we carried out comparative studies for investigating the direct relationship between the molecular-packing parameters and the field-effect mobility in single-crystal OFETs because the performance of such single-crystal OFETs is not affected by defects and grain boundaries. Comparing TIPSAN single crystal OFETs having five different acene derivatives, and applying the concept of molecular overlap ratio along the long / short axis, we could show that the effective π-stacking area dominantly determines the field-effect mobility of π-stacked materials rather than the π-stacking distance. In the case of TIPSAN-Na, a large π-stacking area and a small π-stacking distance enabled the highest field-effect mobility, 3.7 cm2V-1s-1. In addition, paying attention to highly photo-sensitive properties of TIPSAN-Na, we could fabricate all organic two terminal transistors by replacing ‘field induced p-channel’ with ‘photo induced p-channel’. Very simple device structure with solution processed single crystals as an active layer on the plastic substrate and just two source and drain PEDOT:PSS electrodes enabled high performance photosensor and even transistor performance showing pseudo output/transfer curve (on/off ratio 5×102). We demonstrated that this ‘photogenerated p-channel effect’ can be explained by the Helfrich’s theory describing the photodetrapping behavior of a SCLC under light illumination.
QQ7: Photovoltaics II: Materials and Devices for Polymer-based Solar Cells
Tuesday PM, December 02, 2008
Room 313 (Hynes)
4:30 PM - **QQ7.1
Molecular Design for Tuning Charge Transport and Bandgap of Organic Semiconductors.
Zhenan Bao 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Soluble and stable organic semiconducting polymers have great potential for low-cost flexible photovoltaic devices. To achieve appreciable efficiency, polymers that absorb in the entire AM1.5 solar spectrum are desirable. At the same time, energy levels of the donor and acceptor materials need to match each other while the charge transport in each phase in a bulk heterojunction solar cell needs to be optimized. To this end, we exploited several new material design strategies to result in low bandgap organic semiconductors with high charge carrier mobility as the donor material in polymer/C60 (or PCBM) bulk heterojunction solar cells. The material design, synthesis and device characterization of these new materials will be presented.
5:00 PM - QQ7.2
New Small Band Gap Polymers for Organic Solar Cells.
Johan Bijleveld 1 , Jan Gilot 1 , Rene Janssen 1 Show Abstract
1 Molecular Materials and Nanosystems, Eindhoven University of Technology, Eindhoven Netherlands
New materials with a reduced optical band gap that cover a large part of solar spectrum are required to further improve the performance of polymer solar cells. Such small band gap polymers can be made by alternating electron rich and electron poor moieties in the main chain of the polymer. Efficiencies up to 5.5% have been reported for cells with an active layer made with poly(cyclopentadithiophene-alt-benzothiadiazole), PCPDTBT, and C70PCBM. Here, four new polymers will be presented in an attempt to further optimize the band gap and the energy levels of the frontier orbitals with respect to the PCBM acceptor. In the new polymers an electron rich bridged dithiophene, cyclopentaditiophene (CPDT), is alternated with electron deficient quinoxaline (Q), bis(benzothiadiazole) (BBT) benzofurazan (BF), or thienopyrazine (TP) units using a Suzuki polymerization. The optical band gaps of the resulting polymers range between 1.54 and 1.43 eV, for the polymers with an electron poor unit based on benzene and 1.18 eV for PCPDTTP. The HOMO and LUMO levels of the new polymers predict that their ultimate performance in a solar cell can be higher than of PCPDTBT. Preliminary results indeed show that the best devices with PCBM as acceptor gave power conversion efficiencies of 2.5% under simulated solar emission, higher than that of ~2% for PCPDTBT measured under identical conditions.
5:15 PM - QQ7.3
Improved Transverse Hole Conductivity in Organic Semiconducting Polythiophene by Thermal Crosslinking.
Ioana Gearba 1 , Chang-Yong Nam 1 , Ronald Pindak 2 , Charles Black 1 Show Abstract
1 Center for Functional Nanomaterials, Brookhaven National laboratory, Upton, New York, United States, 2 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States
Organic photovoltaic device power conversion efficiencies are limited in part by low charge mobility within the constituent active layer semiconducting materials. For example, the p-type polythiophene polymers used in the highest efficiency organic photovoltaic devices have transverse hole mobilities of only 10-4-10-5 cm2/V-s, despite showing significantly higher values (~0.1 cm2/V-s) in a lateral FET geometry. This mobility anisotropy is caused by poor overlap of pi-pi orbitals in the transverse direction, which impedes charge hopping between polymer chains. We have improved the transverse hole conductivity by as much as three times by incorporating the radical initiator di-tert-butyl peroxide into polythiophene thin films. The initiator promotes thermal crosslinking upon annealing at 170C. Crosslinked polythiophene films maintain a similar absorption spectrum to the uncrosslinked material. Grazing incidence X-ray measurements correlate film structural changes to the measured electronic properties, and reveal two possible mechanisms for increased pi-pi overlap in crosslinked films. We have increased the power conversion efficiency of planar photovoltaic devices composed of p-type polythiophene and n-type C60 by more than 200% (from 0.09% to 0.26%) by crosslinking the polythiophene material. Moreoever, crosslinked polythiophene films are rendered insoluble and thus amenable to the further material processing required of more complex device architectures.
5:30 PM - QQ7.4
Synthesis of Novel Semiconducting Polymers with Well-defined Structures and Their Application for Polymer Photovoltaic Devices.
Keisuke Tajima 1 , Yue Zhang 1 , Shoji Miyanishi 1 , Shigeyoshi Sato 1 , Kazuhito Hashimoto 1 2 Show Abstract
1 Applied Chemistry, The University of Tokyo, Tokyo Japan, 2 , JST-ERATO HASHIMOTO Light Energy Conversion Project, Tokyo Japan
Organic photovoltaic devices are drawing much attention these days because of their potentials for the production of flexible and large-area solar cells at dramatically low costs. The most common strategy is so-called bulk heterojunction, in which electron donors such as poly(3-hexylthiophene) (P3HT) and acceptors such as (6,6)-phenyl C61 butyric acid methyl ester (PCBM) are blended to form one mixed layer. In this system, charge separation of photo-induced excitons is greatly enhanced because of ultra fast electron transfer and large interface between the two components. However, the charge transport inside the organic films is not necessarily efficient, which strongly depends on the mixing morphology. To further improve the performance and the stability of the devices, polymer design to control the structure in the organic films at nanoscale is very important.In this paper, we first report the synthesis of a novel all-conjugated diblock copolymer with P3HT and poly(3-ethylhexylthiophene) (P3EHT) segments for the application to the photovoltaic devices. A series of P(3HT-b-3EHT) diblock copolymers with various P3HT/P3EHT block ratios and very narrow PDIs (Mw/Mn) less than 1.2 were successfully synthesized by a modified Grignard metathesis (GRIM), a ‘quasi’-living polymerization. 1H NMR and GPC analysis at each stage of the reaction showed the well-controlled, living manner of the polymerization.DSC measurement showed that the branching of the alkyl chain changed the polymer property drastically from crystalline (P3HT) to amorphous (P3EHT). As the result, AFM phase images of the polymer films showed uniform fibrous nanostructures with the scale of tens of nanometer, indicating the micro-phase separation of the crystalline and amorphous blocks. Interestingly, the micro-phase separated structures were maintained upon mixing with PCBM, which is promising structure for the photovoltaic application.We also designed a new cross-linkable poly(3-alkylthiophene) for the application to organic photovoltaic devices. Poly(3-hexynylthiophene) and poly[(3-hexylthiophene)-co-(3-hexenylthiophene)]s were synthesized by the GRIM polyerization. Double bonds at the end of the side chains are expected to work as cross-linking sites. The polymer property and their cross-linking ability were investigated by UV-vis spectra and DSC measurement. It was confirmed that these polythiophenes cross-linked in the mixture films of the polymer/PCBM and become insoluble in organic solvents after a thermal treatment. As a result, these polymers suppressed the aggregation of PCBM in the films after a long thermal annealing. The application of the polymers to organic photovoltaic cells significantly enhanced the thermal stability of the devices.  Zhang, Y.; Tajima, K.; Hirota, K.; Hashimoto, K., Synthesis of All-conjugated Diblock Copolymers by Quasi-living Polymerization and Observation of Their Micro-phase Separation. J. Am. Chem. Soc., 2008, 130, 7812–7813.
QQ8: Poster Session: New Device Architecture and Processing Methods
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - QQ8.1
Performance Enhancement in Dye Sensitized Solar Cells with Surface Relief Nanostructures.
Fadong Yan 1 , PilHo Huh 1 2 , Yanping Wang 2 , Lian Li 3 , Lynne Samuelson 3 , Jayant Kumar 1 Show Abstract
1 Center for Advanced Materials, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 2 Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 3 Development & Engineering Center, US Army Natick Solider Research, Natick, Massachusetts, United States
One of the main limitations of the photovoltaic performance of solar cells is the weak absorbance in a thin active layer. The active layer provides both charge generation and charge transport. Although increased thickness enhances light absorption, the device performance usually suffers due to poor charge transport (mobility). In addition, thick sintered films of titania are subject to cracking and delamination from the substrate due to even relatively small stresses. One-dimensional and two-dimensional TiO2 surface relief nanostructures were incorporated in dye sensitized solar cells. The TiO2 nanostructures were fabricated using surface relief gratings created on azobenzene functionalized polymer films as templates and TiO2 sol-gel solution. The periodic TiO2 nanostructures increased the interfacial surfaces and enhanced light trapping with increased effective optical path length in the active layer. Enhancement in photovoltaic performance has been observed in the TiO2 based solar cells.
9:00 PM - QQ8.11
Room-temperature Processed Dye-sensitized Solar Cells Fabricated by Compression Method.
Chih-Hung Tsai 1 , Chin-Wei Chang 1 , Chung-Chih Wu 1 2 Show Abstract
1 Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei Taiwan, 2 Department of Electrical Engineering, National Taiwan University, Taipei Taiwan
Dye-sensitized solar cells (DSSC) are currently of widespread academic and commercial interest for the conversion of sunlight into electricity because of its low cost and high efficiency. In particular, DSSC’s using a flexible, thin and lightweight conducting plastic film is presently attracting much attention. However, the high sintering temperature (450–550°C) of the TiO2 photoelectrode is not compatible with plastic substrates which usually cannot endure such high processing temperatures. Here we report the preparation of binder-free films of nanocrystalline TiO2 at room temperature (or low temperatures) on conducting glass or plastic substrates using a compression method.TiO2 powder was added to ethanol to a concentration of 20 wt.%, followed by stirring for hours. The resulting suspension was applied onto a substrate coated with transparent conductors by doctor-blading. After evaporating the solvent, the substrate with the coated powder film was inserted between two flat steel plates and a pressure of 1000 kg/cm2 was applied for densifying the TiO2 film. The porous TiO2 electrodes were then immersed in the N719 dye solution. As an electrolyte, a mixture of I2, LiI, and 4-tert-butylpyridine in acetonitrile was used. The room-temperature processed DSSC was then completed by assembling the dye-loaded TiO2 films (as a working electrode) and a second glass with 40nm platinum deposited by E-beam evaporation (as a counter electrode). The photocurrent–voltage (I–V) characteristics of the DSSCs were measured under irradiation AM1.5, 100 mW/cm2 (1 sun) supplied by a solar simulator. The performances of the room-temperature-processed DSSC without applying the compression process was η= 1.2 %, Jsc = 2.42 mA/ cm2, Voc = 0.72V and FF = 0.68. With applying the 1000 kg/cm2 compression process, the performance was improved to η= 4.1 %, Jsc = 8.06 mA/ cm2, Voc = 0.71V and FF = 0.72.
9:00 PM - QQ8.12
TiO2 – Polymer Composite Electrode for Photoelectrochemical Cells.
Sonia Mathew 1 , Ilona Kretzschmar 1 Show Abstract
1 Chemical Engineering, City College of New York, New York, New York, United States
Harnessing solar energy with inexpensive materials and manufacturing methods is an important challenge in today’s energy market. A dye-sensitized solar cell (DSC) is a photo-electrochemical device that uses cheap electrodes like TiO2. It has been demonstrated that adding order to the TiO2 layer of a DSC improves the efficiency of the cell, by reducing electron recombination events. In our research, we are investigating TiO2 electrodes that have an inverse opal topology. Such structures are ordered and have a large surface area, which allows higher concentrations of adsorbed dye per unit area. It also provides close contact between the dye-TiO2 anode and the electrolyte. Using the method of colloidal self-assembly, we have prepared TiO2 electrodes that have pores in a hexagonal pattern. These electrodes are prepared by assembling polystyrene particles into molds, and subsequently infiltrating them with a polymer-TiO2 mixture. The cured polymer-TiO2-polystyrene film is washed with solvent to remove the polystyrene templates, resulting in a porous film. In this poster, we will report the mechanical, optical, and electrical properties of both porous and non-porous TiO2-polymer films. In addition, we will present some results about the effect of porosity and TiO2 content on photoconductivity.
9:00 PM - QQ8.13
Solvent Annealing of Thin Films of TIPS-pentacene.
Vladimir Pozdin 1 , Aram Amassian 1 , Yee-Fun Lim 1 , Detlef Smilgies 2 , George Malliaras 1 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States
9:00 PM - QQ8.14
Decoration of Metal-Organic Frameworks: A Path to Strengthening the Molecular Adsorption of Hydrogen.
Andreas Blomqvist 1 , C. Moyses Araujo 1 , Pornjuk Srepusharawoot 1 , Ralph Scheicher 1 , Rajeev Ahuja 1 2 Show Abstract
1 Department of Physics and Materials Science, Uppsala University, Uppsala Sweden, 2 Department of Materials and Engineering, Royal Institute of Technology, Stockholm Sweden
9:00 PM - QQ8.15
Cold Welding and Lamination of OLED Structures.
Wali Akande 1 2 , Y. Cao 1 3 , N. Yao 1 , W. Soboyejo 1 3 Show Abstract
1 Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States, 2 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 Mechanical and Aerospace engineering, Princeton University, Princeton, New Jersey, United States
This paper presents the results of a combined experimental and theoretical study of cold welding and lamination processing of organic light emitting devices. The effects of dust particles (within the clean room environment) are explored along with the underlying material transport associated with applied pressure. The mechanisms of blister formation are discussed for OLED structures that are produced via cold welding and lamination processes.
9:00 PM - QQ8.16
High Efficiency Down Converting Powder Phosphors for Solid Sate Lighting Applications.
Sergey Maslov 1 , Debasis Bera 1 , Paul Holloway 1 Show Abstract
1 Mat Sci & Eng, University of Florida, Gainesville, Florida, United States
Current Department of Energy (DOE) figures show that 22% of electricity is consumed by lighting applications, at a $58 billion-a-year rate. High performance blue and white organic light emitting diodes (OLED) offer improved efficiencies and color tuning properties over all traditional sources. The current method of generating white light from InGaN LEDs is to mix blue with yellow light from a yttrium aluminum garnet doped with cerium (YAG:Ce) phosphor. This method is inefficient and results in a ‘cold’ white light. A mixed phosphor film coupled with an efficient blue OLED allows precise color tuning and enhanced down conversion efficiency. The efficacy, CIE chromaticity coordinates, color rendering index (CRI), and angle resolved photoluminescence intensity were characterized versus film thickness and phosphor weight fraction. Due to scattering by phosphor particles, the initially forward focused light is converted to a Lambertian distribution of intensity. The method for applying powder thin films will be illustrated and discussed. The advantages and disadvantages of PMMA versus silicones for the dispersion matrix will be reported, and the method for applying powder thin films will be illustrated and discussed. Optimum phosphor layers were those with quantum yield approaching 90% and maximum light outcoupling. In addition, important differences in down converting blue light from OLEDs vs InGaN will be discussed.
9:00 PM - QQ8.17
Enhanced Photovoltaic Conversion in Polythiophene-C60 Bilayer Devices by Addition of Long Alkane-Chain-Functionalized Single-Wall Carbon Nanotubes.
Chang-Yong Nam 1 , Noah Tremblay 2 , Chien-Yang Chiu 2 , Nuckolls Colin 2 , Charles Black 1 Show Abstract
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 2 Department of Chemistry, Columbia University, New York, New York, United States
9:00 PM - QQ8.3
White OLED with High Color Rendering Capability with Employing Two Complementary Colors.
Chih-Hao Chang 1 , Chung-Chia Chen 1 , Chih-Che Liu 1 , Chung-Chih Wu 1 , Sheng-Yuan Chang 2 , Yun Chi 2 Show Abstract
1 , Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei Taiwan, 2 , Department of Chemistry, National Tsing Hua University, Hsinchu Taiwan
Due to the high potential of applications in flat-panel displays and solid-state lighting, the white OLEDs (WOLEDs) technique has attracted wide attention in recent years. For high-quality white light illumination, WOLEDs with Commission Internationale d’Eclairage (CIE) coordinates similar to that of blackbody radiator with a correlated color temperature (CCT) between 2500K and 6500K, and a color-rendering index (CRI) above 80 are required. Intuitively, the color rendering ability could be improved by increasing the number of dopants to extend the EL spectrum in the range of visible wavelengths. However, more emissive dopants not merely complicate fabrication, but also make the color control much more difficult. On the other hand, while mixing two complementary colors can effectively produce pure white light emission and reduce the complexity of fabrication, yet the CRI of such two-color WOLEDs usually are limited. One of the bottlenecks is that until recently, few feasible true-blue phosphors with high quantum yields can be employed in two-component WOLEDs. The blue-green phosphor, like FIrpic, is the predominant option for WOLEDs. However, the combination of blue-green and red phosphors generally gives poor CRI <70 due to deficient color rendering in blue.In this paper, we report that by employing the true-blue Iridium complex and the wide-band yellow Osmium complex, the two-component WOLEDs can be fabricated to achieve a higher color rendering ability than previously attainable. The optimized architecture adopts triple emitting layers to adjust the location of the exciton formation zone and maintain the emission color in the pure white region. The device performance shows high efficiencies of up to 9.5 % photon/electron, 22.9 cd/A, and 20 lm/W for the forward viewing directions. Total external quantum and power efficiencies are up to 16.2% and 34 lm/W, respectively. The CIE chromaticity varies only slightly from (0.311, 0.327) to (0.328, 0.344) while the luminance increases from 100 cd/m2 to 10000 cd/m2. The full-width at half-maximum (FWHM) of the blue emitter and the yellow emitter are about 64 nm and 120 nm, respectively. This wide FWHM of the yellow Os emitter made possible the two-component WOLEDs with high color rendering. Such pure white phosphorescent OLEDs produced stable color emission with CRI >80.
9:00 PM - QQ8.5
Thin Film Passivation of Organic Light Emitting Devices using Vapor Deposition Polymerization.
Oh Kwan Kwon 1 , Won Min Yun 1 , Seung hwan Lee 1 , Chan Eon Park 1 Show Abstract
1 Chemical Engineering, POSTECH, Pohang, Gyeongbuk, Korea (the Republic of)
Recently, an encapsulation technique using a glass or metal lid has been proposed as a method to protect devices from oxygen and water vapors. However, these types of seals are expensive to fabricate and heavy, thick and rigid that severely limit their applications of organic light emitting devices (OLEDs). For thin and lightweight encapsulation of OLEDs, it is necessary to develop a thin film passivation technique. It has been reported that multilayer passivation of polymer and inorganic dielectric layer can be more effective in prevent of water and oxygen permeation by three orders of magnitude than an inorganic single layer. Until now, many researchers have tried to increase the lifetime of OLEDs by various techniques that involve multilayer passivation of OLEDs. Generally, polymer deposition techniques are the wet-coating methods. The wet-coating methods suffer from various problems arising from the solvent, including impurity, difficulty in multilayer formation and microstructure control. We employed vapor deposition polymerization (VDP) to solve these problems. In this study, we used multilayer passivation film (polyimide/Al2O3). Polyimide film was prepared by VDP, reacting a diamine monomer with a dianhydride monomer. Al2O3 was deposited over the polyimide coated layer by DC sputtering. Polyimide was formed by co-evaporating 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 1,12-diaminododecane (DADD). Stoichiometry of the monomer ratio was controlled by the deposition rate of the monomers. PTCDA and DADD formed thin films of polyamic acid, which was converted to polyimide by annealing in vacuum. Chemical characterization of polyimide films was conducted by fourier-transform infrared (FT-IR) spectroscopy. After annealing of co-evaporation film in vacuum, the amide bands (1550 and 1640 cm-1) disappeared and the cyclic imide was observed C=O bands at 1650 and 1690 cm-1, and C-N-C band at 1355 cm-1. To investigate the effect of the multilayer passivation, the lifetime of the devices was measured: the initial luminance of the multilayer passivated device decayed to 20% of its initial luminance after 120h whereas non-passivated device did only after 10h. It is believed that the multilayer passivation using both polyimide and Al2O3 results in highly effective protection from moisture and oxygen permeation.
9:00 PM - QQ8.6
LBIC and EL Analysis of Polymer Solar Cel.
Osamu Yoshikawa 1 , Shu Fukumura 1 , Toru Kamada 1 , Takashi Sagawa 1 , Susumu Yoshikawa 1 Show Abstract
1 , Kyoto University, Uji Japan
Polymer solar cells have attracted much attention over the past few decades due to their possible low cost and easy of fabrication. Power conversion efficiency of 4~6 % was reported in single bulk heterojunction polymer solar cell using conjugated polymer and fullerene derivatives. In order to enhance power conversion efficiency, a lot of efforts have been made to develop new organic materials and new device architectures. Also, understanding of the stability and degradation is required for commercial use of polymer solar cell. Laser Beam Induced Current (LBIC) measurement and Electro-Luminescent (EL) measurement have been used in order to get two dimensional photocurrent images over the cell and more information than current- voltage characterization. These techniques can be identified the site of defect of the device with large area. In this work, polymer solar cell based on poly (3-hexylthiophene) (P3HT) and (6, 6)-phenyl C61 butyric acid methyl ester (PCBM) with the cell structure of ITO/PEDOT: PSS/P3HT-PCBM/TiOx or no buffer layer/Al was investigated The homogeneous photocurrent generation was observed in the whole cell with TiOx layer for long time, while that of the cell without the TiOx layer was inhomogeneous photocurrent and the degradation of the cell was observed in the case without the TiOx layer in the ambient condition. Particularly, the photocurrent of the lateral in the cell was decreased due to oxygen and water in ambient air. Furthermore, it was observed that the electrode geometry influenced the photocurrent generation pattern. In the area of no ITO electrode but PEDOT: PSS layer, relatively weak photocurrent was generated, meaning that PEDOT: PSS acted as positive electrode. Detailed measurements for photocurrent generation and electro-luminescence will be discussed by changing the various type of the device architecture.
9:00 PM - QQ8.7
Bulk Heterojunction Organic Solar Cells by Gravure Printing and Spray Casting.
Monika Voigt 1 , Justin Dane 1 , Peter Levermore 1 , Alex Guite 1 , Xiangjun Wang 1 , Alasdair Campbell 1 , Donal Bradley 1 , Jenny Nelson 1 Show Abstract
1 Physics, Imperial College, London United Kingdom
High throughput film deposition methods such as printing and spraying are needed to realise the fabrication of conjugated polymer based solar cells at low cost. One option is gravure printing which can be used in a sheet-to-sheet or roll-to-roll process in an industrial environment.Recently, fully gravure printed organic field effect transistor (with an on/off ratio of over 10^4) were demonstrated . In this work, we report studies on the fabrication of poly-3-hexylthiophene/methanofullerene (P3HT:PCBM) bulk-heterojunction solar cells on plastic substrates by gravure printing and by spray casting. In some cases, a conducting polymer anode is used to enable fully plastic device structures. The printing and spraying process is optimised by attention of thermodynamic parameters and material parameters such as viscosity and polymer molecular weight which can influence film uniformity. We show that P3HT:PCBM can be sprayed or gravure printed successfully to achieve a solar cell with an efficiency of 0.1% for gravure and 0.4% for spraying on a flexible substrate as PET/ITO. Device losses are analysed by comparison with reference devices where some or all of the organic layers are spin-coated. In addition, device stability is analysed under continuous illumination.References: Publication in preparation regarding the EU-project CONTACT in manufacturing transistors with gravure on flexible substratesAcknowledgementsWe wish to thank the EPSRC and UKERG for support of the solar cell research and all members of the CONTACT project.
9:00 PM - QQ8.8
Fabrication of Conducting Polymer Nanorods using Block Copolymer Nanoporous Templates and its Application.
Jeong In Lee 1 , Jin Kon Kim 1 , Thomas Russell 2 , Jae Woong Yu 3 Show Abstract
1 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States, 3 Center for Energy Materials Research, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Ultrahigh density arrays of conducting polymer nanorods are fabricated directly on the indium-tin oxide coated glass by an electropolymerization within a porous diblock copolymer template. Conducting polymer nanorods with high density have attracted much attention, due to their various applications including electrochromic devices, organic photovoltaic devices, polymer nano actuator and drug delivery. Here, we proposed a new template-based synthesis method using polystyrene-block-poly(methyl methacrylate) copolymers (PS-b-PMMA) nanoporous template to fabricate conducting polymer nanorods. Well-aligned ultra high density arrays of polypyrrole (PPy) or poly(3,4-ethlenedioxythiophene) (PEDOT) nanorods were prepared on the ITO glasses by electropolymerization inside holes of the nanoporous templates. These nanorods grown inside nanoporous templates have much higher conductivity compare to films, higher conductivity was observed using CS-AFM (Current Sensing AFM). We find out that high conductivity results from the well-aligned chain orientation of nanorods because they were grown inside confined holes. So, ‘confinement effect’ is very important for higher conductivity and well-aligned structure of conducting polymer nanorods. Chain orientation of nanorods is characterized by HR-TEM and GI-XD.Also, the ultrahigh density arrays of conducting polymer nanorods have potential applications as sensor materials, nanoactuators, and organic photovoltaic devices. Especially, in the case of organic photovoltaic device, this geometry will be allowed us to obtain large contact area of P-N heterojunction, which allows a high efficiency of the current conversion from the light.
9:00 PM - QQ8.9
High Efficiency Dye-sensitized Solar Cells with Optical Confinement Structures.
Chih-Hung Tsai 1 , Chin-Wei Chang 1 , Chung-Chih Wu 1 2 Show Abstract
1 Graduate Institute of Photonics and Optoelectronics , National Taiwan University, Taipei Taiwan, 2 Department of Electrical Engineering, National Taiwan University, Taipei Taiwan
Recent advances in solar cells, based on the dye-sensitized nanoporous TiO2 film, have gained wide interests owing to their relatively high efficiency, low production and energy costs, simple production processes and environmentally suitable material choices. Yet, there are still factors limiting the cell performance, among which light harvesting efficiency is very important. Recently, TiO2 photoelectrode with different particle sizes were designed and investigated to increase light harvest efficiency. However, these structures also reduce the conductivity of the TiO2 layer. In this work, we incorporate the light confinement structure on FTO glass which can improve the light harvesting efficiency by increasing the light path and the light trapping effect.The DSSC was fabricated as follows. The FTO glass with light trapping structures was cleaned and then was immersed into an aqueous TiCl4 solution. A first layer of TiO2 paste was coated on the FTO glass by doctor-blading, and then the second layer of large TiO2 particles (~150 nm in diameter) as the light-scattering layer was deposited by doctor-blading to 4–5 μm. The electrodes coated with the TiO2 pastes were annealed at 500°C. A mixture of I2, BMII, guanidinium thiocyanate and 4-tert-butylpyridine in acetonitrile and valeronitril was used as an electrolyte. The dye solutions were prepared with the concentration of 0.5 mM N719 dye. A sandwich cell was assembled by using the dye-loaded TiO2 films and a second conducting glass with platinum deposited by E-beam evaporation. The photocurrent–voltage (I–V) characteristics of the DSSCs were measured under irradiation AM1.5, 100 mW/cm2 (1 sun) supplied by a solar simulator. The performance of the DSSC with light confinement structures was η= 10.6 %, Jsc = 19.4 mA/ cm2, Voc = 0.76V and FF = 0.72.
Jian Li Arizona State University
Chung-Chih Wu National Taiwan University
Soo Young Park Seoul National University
Fred B. McCormick 3M Company
QQ9: Photovoltaics III: Organic-inorganic Hybrid Solar Cells
Wednesday AM, December 03, 2008
Room 313 (Hynes)
9:30 AM - **QQ9.1
Study on Preparation and Stability of 10cm-by-10cm Dye-Sensitized Solar Cell (DSC) Sub-Modules.
Hironori Arakawa 1 , Takeshi Yamaguchi 1 , Takanori Sutou 1 , Yutaro Koishi 1 , Nobuyuki Tobe 1 , Daisuke Matsumoto 1 , Takuma Nagai 1 Show Abstract
1 Department of Industrial Chemistry, Tokyo University of Science, Tokyo Japan
Highly efficient (η=9.1%) glass-substrate DSC sub-modules with 10cm-by-10cm size was prepared and its long-term stability was investigated. 10.7% efficiency in a glass-substrate 5mm-by-5mm DSC using Black dye was obtained in our group so far. [1, 2] Therefore, we are conducting the research in preparation of highly efficient sub-module and its long-term stability for DSC commercialzation. In order to keep such a high efficiency as 10% in a large cell, current collecting grid onto FTO glass is essential to avoid a large increase in electric resistance of FTO glass . An optimization study on Ag current collecting grid has led to obtain 9.1% efficiency for active area (78.2 cm2) and 8.4% efficiency for aperture area (84.8 cm2) in a 10cm-by-10cm sub-module. (Isc=1.49A, Jsc= 19.0mA/cm2, Voc=0.69V, ff=0.71).  Accelerated long-term stability tests were also conducted using JIS C-8938 environmental and endurance test methods for amorphous solar cell modules. JIS C-8938 includes A-1 test (200 dry and heat cycles from -40 to 90 degrees Celsius ), A-2 test (10 wet and heat cycles from -40 to 85 degrees Celsius with 85% humidity) and A-5 test (a 500-hour continuous light soaking). Stability of DSC under A-1 test was much dependent on electrolyte solvent species. DSC using metoxypropionitrile (MPN) and ionic liquid (IL) were still active after 200 dry and heat cycles. In case of A-2 test, a 10cm-by-10cm DSC sub-module using MPN solvent showed almost no degradation. Light soaking test (A-5 test) was conducted on DSC samples with a UV cut filter. Efficiency decrease was below 20% after 1000-hour continuous irradiation. These results suggest a promising future to commercialization of DSC. In addition, a highly efficient plastic-substrate DSC with η=8.1% was developed. One of the issues with plastic-substrate DSC is to have a lower efficiency than that of glass-substrate DSC. Because of low thermal stability of plastic-substrate, calcination of TiO2 can not conduct at high temperature such as 500 degrees Celsius. We developed a new preparation method for highly efficient plastic DSC. This method consists of several important basic technologies such as press method without heat treatment, light confined effect by light scattering TiO2 large particles in the TiO2 film and binder-free water-TiO2 paste and UV-O3 treatment of TiO2 photoelectrode. Plastic substrate DSC prepared by this new method showed the very high efficiency such as 8.1% (0.29 cm2) under 1 sun illumination (100 mW cm-2, AM1.5). In addition, a current collecting large size plastic-substrate DSC (10cm-by-10cm) was prepared. A good performance such as Isc=756mA, Voc=0.72V, FF=0.57, ηac=4.5% was obtained.References:  Z.S.Wang et al., Coord. Chem. Rev., 248,1381(2004).,  Z.S.Wang et al., Langmuir, 21, 4272(2005).,  H.Arakawa et al., Proc .of WCPEC, 1,36(2006).,  T.Sutou et al., Tech. Digest of PVSEC-17,3O-A2-02 (2007).,  T.Yamaguchi et al., Chem. Commun., 4767(2007).
10:00 AM - **QQ9.2
On the Photophysical and Electrochemical Studies of Dye-Sensitized Solar Cells.
Kuo-Chuan Ho 1 2 , Jian-Ging Chen 1 , Chia-Yuan Chen 3 , Chun-Guey Wu 3 Show Abstract
1 Department of Chemical Engineering, National Taiwan University, Taipei Taiwan, 2 Institute of Polymer Science and Engineering, National Taiwan University, Taipei Taiwan, 3 Department of Chemistry, National Central University, Chung-Li Taiwan
In this study, the photoelectrochemical characteristics of a ruthenium photosensitizer with an alkyl bithiophene group, designated as CYC-B1, are studied. The effect of mesoporous TiO2 film thickness on the photovoltaic performance of CYC-B1 and N3 dye sensitized solar cells was investigated. The performance of the DSSC fabricated using CYC-B1 dye anchored TiO2 photoelectrode showed a convincing enhancement in cell efficiency when the TiO2 film thickness was increased from 3 μm (eff.= 5.41%) to 6 μm (eff.= 7.19%). The efficiency of the CYC-B1 sensitized DSSC was maximum at 6 μm of the TiO2 film thickness, reached its limiting value and remained constant up to 53 μm, although a similar trend was also observed for N3 dye sensitized DSSC, however, the maximum efficiency achieved was only at 27 μm thickness (eff.= 6.75%). As expected, the photocurrent density generated in the DSSC modified by CYC-B1 dye is larger than that from N3 dye. The effect of guanidinium thiocyanate (GuSCN) (additive) addition to the electrolyte on the photovoltaic performance of DSSCs based on CYC-B1 was also investigated. Furthermore, the electrochemical impedance spectroscopy (EIS) technique and photo-transient laser method have been employed to analyze the charge transfer resistances (Rct) and the lifetime of the injected electrons on the TiO2 containing different thicknesses.
10:30 AM - QQ9.3
New Cobalt (II) Complexes as Non-corrosive Electrolytes for Dye-sensitized Solar Cells.
Hongshan He 1 , Mukul Dubey 1 , Tingting Xu 1 , Andrew Sykes 2 , Seik Weng Ng 3 , David Galipeau 1 Show Abstract
1 Department of Electrical Engineering, South Dakota State University, Brookings, South Dakota, United States, 2 Department of Chemistry, University of South Dakota, Vermillion, South Dakota, United States, 3 Department of Chemistry, University of Malaya, Kuala Lumpur Malaysia
Dye-sensitized solar cell is a design of low-cost solar cells based on a semiconductor formed between a photo-sensitized anode and an electrolyte in solution. When exposed to sunlight, excitons in the dye adsorbed on the surface of nano-sized titanium dioxide semiconductor material are injected directly into the conduction band of titanium dioxide, meanwhile, the dye in the excited state strips one electron from electrolyte. Extensive research have shown that electrochemical and photophysical properties of redox couple are critical for efficient energy conversion and final cell assembly; however, current electrolyte is exclusively based on iodide/triiodide redox couple, which is very corrosive and difficult to seal for long term stability. Therefore, it is necessary to investigate the photovoltaic performance of cells with other non-corrosive electrolytes. In this presentation, we will report the new design of a series of stable imidazole-based cobalt (II) complexes and their structural characteristics from single-crystal X-ray diffraction analysis. The detailed electrochemical, spectroscopic properties and photovoltaic performance of solar cells with these complexes as electrolytes in dye-sensitized solar cells will be also presented.
10:45 AM - QQ9.4
Polythiophene-quantum Dot Hybrid Nanomaterials for Bulk Heterojunction Solar Cells.
Mihaela Stefan 1 , Kumaranand Palaniappan 1 , John Murphy 2 , Julius Horvath 2 , Michael Biewer 1 , Manuel Quevedo 2 , Husam Alshareef 2 , Bruce Gnade 2 Show Abstract
1 Department of Chemistry, University of Texas at Dallas, Richardson, Texas, United States, 2 Department of materials science & engineering, University of Texas at Dallas, Richardson, Texas, United States
Regioregular polythiophenes with thiol end-groups or side chains have been synthesized and blended with CdSe quantum dots. Thiol-terminated regioregular poly(3-hexylthiophene) was synthesized in three steps from an allyl terminated precursor. Allyl-terminated poly(3-hexylthiophene) was converted to hydroxypropyl-terminated polymer via a hydroboration-oxidation reaction. Hydoxypropyl- terminated PHT was subjected to Mitsunobu reaction and converted to propylacetyl thiol-terminated PHT, which subsequently was reduced with lithium aluminum hydride. Regioregular polythiophene with thiol side chains were synthesized from poly(3-alkenylthiophene) via chemical modification of the olefin functional groups. Oleic acid modified CdSe quantum dots were synthesized using a single pot approach with narrow size distribution. Oleic acid on the particle surface was replaced with pyridine through a ligand exchange process. Thiol terminated poly(3-hexylthiophene) was then reacted with the CdSe quantum dots to obtain conjugated polymer-quantum dots networks. These networks were characterized by UV-Vis, fluorescence, and NMR spectroscopy. TEM was used to estimate the size and shape of CdSe nanoparticles. Conjugated polymer-quantum dot networks synthesized as described above have been used to fabricate bulk heterojunction solar cells.
QQ10: Photovoltaics IV: Materials and Devices for Polymer-based Solar Cells
Wednesday PM, December 03, 2008
Room 313 (Hynes)
11:30 AM - **QQ10.1
Self-Assembled Functional Molecular Materials for Optoelectronic Applications.
Chi-Ming Che 1 Show Abstract
1 Chinese Academy of Chemistry, The University of Hong Kong, Hong Kong China
12:00 PM - **QQ10.2
Defects, Doping and Transport in Organic Semiconductors and Solar Cells.
Brian Gregg 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
A quantitative experimental study of doping in polycrystalline organic semiconductor films establishes the dominant influence of electrostatic forces and charge carrier delocalization lengths in these low-dielectric materials. These same factors that cause exciton formation upon light absorption, also cause most added carriers to remain electrostatically bound to their counterions, thus the doping efficiency is poor (only ~1 free carrier is created per ~100 added dopants). The Poole-Frenkel (PF) mechanism accounts naturally for the interaction between a charge bound in a Coulomb well and an applied electric field. Together with a field-dependent mobility (not included in the original PF model), this provides a semiquantitative description of the doping efficiency and charge transport in excitonic semiconductors (XSCs).These simple electrostatic considerations must apply also to other XSCs such as π-conjugated polymers, that are not purposely doped but are adventitiously doped by their charged defects. The sp2-hybridized carbons comprising the backbone of a π-conjugated polymer would ideally form a planar wire in which only the cis-bonds perturb the one dimensional structure. But in solid films the backbone inevitably has a number of kinks and bends in it that perturb the planarity and optimal bond angle of the sp2 carbons, thus deforming high energy π-bonds and creating defects (states in the bandgap) that may be charged. Chemical impurities in the polymer may also be charged. Conductivity measurements on thin films of π-conjugated polymers such as poly(3-hexylthiophene), P3HT, together with time-of-flight mobility measurements provide an estimate of the free hole density, pf ≈ 10^15 – 10^17 cm^-3, with the lower range approachable only in extensively purified materials. This magnitude of carrier density has been observed by many groups and is ~10^12 fold greater than if the polymer were an intrinsic semiconductor. These charged defects almost certainly control much of the observed (photo)electrical behavior of π-conjugated polymers. We introduce chemical treatments that beneficially modify the defects in these polymers resulting in greater carrier mobility, exciton diffusion length and stability against photodegradation. Most transport models do not yet take into account the high concentration of bulk charges, but we note that the existence of these charges provides an immediate explanation for the otherwise puzzling Poole-Frenkel mobility of carriers even at low fields as well as the observed correlated energetic disorder.
12:30 PM - QQ10.3
Synthesis of Vertical p-n Junction Film for Organic Photovoltaic Devices.
Yasuhiro Shirai 1 , Akiko Nabata 2 , Seiichi Takami 3 , Yutaka Wakayama 2 , Toyohiro Chikyow 2 Show Abstract
1 ICYS-MANA, National Institute for Materials Science, Tsukuba Japan, 2 Advanced Electronic Materials Center, National Institute for Materials Science, Tsukuba Japan, 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Conjugated polymer-based photovoltaic devices have been considered promising materials for achieving cost-effective and high-performance photovoltaic devices. The bulk heterojunction devices can accomplish the enhancement of the donor-acceptor interfacial area by simply mixing the donor-acceptor materials in a common solvent, and give best power conversion efficiency. However, control over morphology of the donor-acceptor materials is minimal. To further improve the power conversion efficiency of organic solar cells, it is important to control the interface between the donor-acceptor materials to accomplish high donor-acceptor interfacial area as well as efficient charge transport path. To achieve this goal, we have developed methodology to synthesize organic thin films with nanoscale vertical p-n junctions.We have successfully produced polymer nano-fiber forests on electrode surface by using nano-sized porous alumina template and electrochemical polymerization techniques. The empty spaces within the nano-fiber forest were then filled with other organic materials such as C60 and PCBM, thus creating vertical p-n junctions between the nano-fibers and filling materials. In this paper, we will present details of the synthesis methodology of the vertical p-n junctions, and briefly mention the effect of the porous alumina template size on the power conversion efficiency.
QQ11: Photovoltaics V: Device Engineering and Physics
Wednesday PM, December 03, 2008
Room 313 (Hynes)
3:00 PM - **QQ11.2
Analysis of the Cell Area Scaling Effect on the Photovoltaic Properties of P3HT:PCBM Solar Cells.
Changhee Lee 1 , Seung Uk Noh 1 , Ji Young Kim 1 , Seohee Kim 1 , Hyunduck Cho 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of)
3:30 PM - QQ11.3
Ultrasonic Spray Deposition for Organic Solar Cells.
Xerxes Steirer 1 2 , Matthew Reese 2 , Dana Olson 2 , Nikos Kopidakis 2 , Reuben Collins 1 , David Ginley 2 Show Abstract
1 Applied Physics, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
3:45 PM - QQ11.4
Fiber-Based Bulk-Heterojunction Organic Photovoltaic Cells.
Surawut Chuangchote 1 , Takashi Sagawa 1 , Susumu Yoshikawa 1 Show Abstract
1 Institute of Advanced Energy, Kyoto University, Uji, Kyoto, Japan
QQ12: Interface Engineering and Physics
Wednesday PM, December 03, 2008
Room 313 (Hynes)
4:30 PM - **QQ12.1
Surface and Interface Modification for Efficient Polymer Solar Cells.
O Ok Park 1 , Hang Ken Lee 1 , Sang Jun Yoon 2 , Dong Hwan Wang 1 , Sang Hyuk Im 2 Show Abstract
1 Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 , Research Park LG, Chem, Ltd., Daejeon Korea (the Republic of)
Polymer solar cells(PSCs) have received considerable attention in recent years due to their potential application for the renewable energy source. Since the bulk-hetero-junction PSC was reported by Yu et al to compensate for the small depletion area of organic materials, there has been a great improvement of power conversion efficiency of PSCs up to 5-6%. These PSCs are composed of photo-active layer sandwiched between transparent electrode (normally indium tin oxide, ITO) and low work function metal cathode. Photo-generated free holes and electrons in these systems are transported through the donor and acceptor phases toward electrode resulting in an external photocurrent density. As a result, the photocurrent depends not only on the photo-generation and transport properties in active layer but also on the interfaces between the active layer and electrodes. Here, we introduce a couple of methods to modify the interface between electrodes and the active layer for enhancing charge transportation and collection. [TiOx interlayer]Recently, TiOx interlayer has been integrated in PSC by the Heeger group as an optical spacer and by Hayakawa as a hole blocking layer. We present another effect of TiOx interlayer: low vacuum processibility. The cell with a TiOx interlayer was less dependent on the vacuum condition for the deposition of a metal cathode compared to a cell without the TiOx. We have found that chemical bridges formed between interfaces result in enhancement of adhesion. Thus, the effective area for electron transport is increased. Furthermore, by controlling the crystallinity of TiOx interlayer, it is possible to enhance the conductivity and thermal stability of TiOx interlayer.[PEDOT:PSS buffer layer]Poly(3,4-ethlyene dioxythiophene):poly(styrene sulphonate)(PEDOT:PSS) is the most famous buffer layer on modifying the interface between ITO and active layer. However, lots of holes can be lost there because of low conductivity and large interfacial resistance. It is possible to reduce this hole loss simply by irradiating external light on PEDOT:PSS. When external light is irradiated, PEDOT:PSS experiences the resonance structural change so that the conductivity is increased while interfacial resistance is decreased. The effect of irradiation is saturated over certain exposure time.  G. Yu, J. Hummelen, F. Wudl, and A. J. Heeger, Science 270, 1789(1995) S. J. Yoon, J. H. Park, H. K. Lee, O O Park, Appl. Phys. Lett. 92, 143504 (2008)
5:00 PM - **QQ12.2
Interfacial Issues in Nanomaterials and Nanostructuresfor Efficient Optoelectronic Devices.
Kookheon Char 1 Show Abstract
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of)
Great endeavor has been devoted to energy efficient optoelectronic devices with multilateral approaches such as design and synthesis of nanomaterials and optimal fabrication of nanostructures. Particularly, understanding the interfacial phenomena and manipulating interfaces in various device structures are one of the most decisive factors for the successful realization of optoelectronic devices because critical issues such as photogeneration, charge recombination, and exciton transfer in the optoelectronic system mostly take places at the interfaces.In this presentation, interfacial issues in nanomaterials and nanostructures for efficient light-emitting diodes and photovoltaic devices will be discussed. For the application to light-emitting diodes, nanomaterials including organic molecules, semiconductor nanocrystals, and luminescent colloidal beads have been designed and prepared for highly efficient and stable full color displays and white light-emitting diodes. Nanostructures modulating light emission and conversion have also been formulated with colloidal photonic crystals incorporating phosphors within the colloids, which efficiently block the light source in UV region while enhancing the upconversion efficiency. For the application to photovoltaic devices, the multilateral control of electrode/electrolyte interfaces in quasi-solid state dye sensitized solar cells (DSSC) with (end-)functional polymers have proven to improve the device performance by reducing the charge recombination and charge transfer resistance at the interfaces. Moreover, the application of polymer electrolytes-nanoparticle composites for enhanced charge conduction and power conversion efficiency in the DSSC will be also addressed.
5:30 PM - QQ12.3
Impact of Interfacial Polymer Morphology on Photoexcitation Dynamics and Device Performance in P3HT/ZnO Heterojunctions.
Matthew Lloyd 1 , Rohit Prasankumar 2 , Michael Sinclair 1 , Alex Mayer 3 , Julia Hsu 1 Show Abstract
1 Surface and Interface Sciences, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States
One fundamental question is how to improve charge injection efficiency, hence the short-circuit current, for ZnO/poly 3-hexylthiophene (P3HT) heterojunctions by intentional modification of the interface. To this end, we investigate the morphology of the interfacial polymer layer and decay dynamics of photoexcited species in P3HT deposited on glass, bare ZnO, and ZnO modified with an alkanethiol monolayer. These results are correlated with the characteristics of P3HT/ZnO and P3HT/alkanethiol-modified ZnO bilayer photovoltaic devices. Synchrotron x-ray diffraction spectra of pristine P3HT and P3HT on an alkanethiol-modified ZnO surface point to a more crystalline P3HT interfacial layer, while an amorphous interfacial layer of P3HT is found on unmodified ZnO. To investigate the decay dynamics of initial photoexcited states in the ZnO/P3HT system, the composite samples are interrogated by pump-probe spectroscopy with sub-picosecond resolution. Transient photoinduced absorption spectra are collected for photoexcited species in the range of 1090 nm to 3034 nm immediately after 550 nm excitation. Compared to neat P3HT films, on the picosecond timescale, the presence of a ZnO interface does not measurably change the lifetime of the photoexcited species. However, the decay behavior for both polarons and excitons over a 50 ps time interval becomes significantly slower with alkanethiol modification, indicating a reduction in of early-stage charge recombination. Accompanying the decrease in recombination, we find an increase in the short-circuit current in the alkanethiol-modified ZnO devices in spite of the electron tunneling barrier presented by the alkanethiol monolayer. External quantum efficiency measurements in alkanethiol-modified devices also exhibit a clear signature of crystalline P3HT within an exciton diffusion length from the heterojunction interface. As these experiments demonstrate, charge injection efficiency and device performance can be improved by control of the polymer morphology at the buried interface. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
5:45 PM - QQ12.4
Architectures, Electronic Properties, and Processing of the Engineered Hole Injecting Materials for the Improved Performance and Printing Quality of the Organic Photovoltaic Devices.
Byung Doo Chin 1 , Nam Su Kang 1 2 , Jae-Woong Yu 1 , Byung-Kwon Ju 2 , Tae-Woo Lee 3 Show Abstract
1 Material Sci. Eng. Research Division, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Electrical Engineering, Korea University, Seoul Korea (the Republic of), 3 , Samsung Advanced Instutute of Technology, Kiheung Korea (the Republic of)
Properties of the organic photovoltaic devices with a layered hole-injection material, which is comprised of PEDOT:PSS and polymeric perfluorinated ionomer, will be demonstrated. The layer-by-layer spin coating process of the organic materials with various composition enables to control work functions of the anode-contact buffer layer at devices with poly(3-hexylthiophene):fullerene active layer, resulting in the increase of short circuit current and nominal power conversion efficiency [from 3.5 to 4.0~4.2%]. The layer-by-layer coating of perfluorinated polymer upon the PEDOT:PSS yields smoother surface and enhanced hole-only dark current at optimum bi-layer architecture, while the J-V characteristics of the bipolar devices are less sensitive to the layered structures. Various factors affecting the current injection, rectification, open circuit voltage, and photocurrent of the devices are characterized in relation with the chemical properties of surface (by XPS and TOF-SIMS). In the second part of the presentation, we have evaluated the effect of modified solvent formulation of PEDOT:PSS/additive and poly(3-hexylthiophene)/fullerene on the status of organic photovoltaic devices prepared by economic fabrication processes, such as gravure/flexography. Chemical modification of the anode surface by use of thin self-assembled monolayer is found to be effective for a uniform coating, while the injection condition and corresponding open-circuit voltage should be maintained by setting of the optimum composition and processing environment. Our investigation on the interfacial states at anode/buffer/active layers of organic photovoltaic devices will be beneficial for the improvement of photocurrent generation as well as macroscopic printing quality of organic/nanostructured electronic materials.