Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
David B. Mitzi IBM T. J. Watson Research Center
Patrick J. Smith University of Freiburg
C1: Nanoparticle Processing of Films/Devices I
Session Chairs
David Mitzi
Maikel van Hest
Tuesday PM, April 06, 2010
Room 2006 (Moscone West)
9:30 AM - **C1.1
Colloidal Nanocrystals as Prospective Materials for Electronic, Thermoelectric and Photovoltaic Applications.
Dmitri Talapin 1 , Maksym Kovalenko 1 , Jong-Soo Lee 1 , Boris Spokoinyy 1 , Eric Wong 1
1 Department of Chemistry, University of Chicago, Chicago, Illinois, United States
Show AbstractColloidal nanocrystals are considered promising building blocks for electronic and optoelectronic devices. Potentially, they can combine the advantages of crystalline inorganic semiconductors with size-tunable electronic structure and inexpensive solution-based device fabrication. However, several fundamental problems have to be solved before nanocrystal solids will be widely used for device applications. The conductivity of nanocrystal solids is determined by the electronic communication between individual nanocrystals and the concentration of mobile carriers. The bulky and insulating nature of conventional organic capping ligands typically results in poor electronic coupling in the nanocrystal solids. To address this problem we demonstrate that molecular metal chalcogenide complexes can serve as versatile ligands for a broad range of colloidal nanocrystals. This new class of nanocrystal colloids provides a set of advantages such as all-inorganic design and diverse compositional tunability for both nanocrystal and ligand constituents. We observed electron mobility of 6-8 cm2/Vs in arrays of CdSe nanocrystals and ~200 S/cm conductivity in arrays of 5 nm gold nanocrystals capped with metal chalcogenide Zintl ions. We developed several approaches to electronic doping of nanocrystal solids based on the formation of inter- and intra-nanocrystal charge transfer complexes. For example, Au-PbS core-shell nanocrystals show stable p-type doping due to electron transfer from PbS shell into the Au core. FePt-PbS and FePt-PbSe core-shell nanocrystals show rich electronic and magneto-transport properties originating from the electronic communication between magnetic core and semiconductor shell.
10:00 AM - C1.2
Modular Inorganic Nanocomposites by Conversion of Nanocrystal Superlattices.
Ravisubhash Tangirala 1 , Robert Wang 1 , Jessy Baker 2 3 , A. Paul Alivisatos 3 4 , Delia Milliron 1
1 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Department of Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States, 3 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States, 4 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractInorganic nanocomposites have recently emerged as a means of controlling material functionality through morphology, as well as composition, to give rise to combinations of properties not generally found in homogeneous single-phase materials. However, the development of nanocomposites is hindered by the lack of general fabrication methods capable of controlling morphology over a wide range of compositions. Here we report the preparation of inorganic nanocomposites through the post-assembly replacement of organic ligands in nanocrystal (spheres, rods, binary, etc) superlattices with inorganic chalcogenidometallate clusters (CMCs). Separate synthesis and processing of the nanocrystals and CMCs enables complete compositional modularity, while allowing the nanocrystal assemblies to retain their original morphology. Depending on the materials combination chosen, an open-ended list of applications is possible, including battery electrodes, thermoelectrics, phase change memory and photovoltaics. Preliminary results on electronic properties of selected nanocomposites will also be discussed.
10:15 AM - C1.3
Synthesis and Self-assembly of Functional Inorganic Nanomaterials from Aqueous Solutions.
Stephen Morin 1 , Song Jin 1
1 Department of Chemistry, University of Wisconsin - Madison, Madison, Wisconsin, United States
Show AbstractWe describe the synthesis and self-assembly of semiconducting inorganic metal oxide and chalcogenide nanomaterials directly from low temperature aqueous solutions. Specifically, templates with well defined surface chemistries, in the form of self-assembling block copolymers and UV oxidized flexible commodity plastics, are used to control where nanocrystals nucleate and grow during aqueous chemical bath deposition from low supersaturation solutions creating well defined patterned micro/nanoarrays of CdS, ZnS, ZnO, and other semiconductor materials. Furthermore, large scale arrays of flexible photodetectors were fabricated from arrays of patterned CdS nanocrystalline films deposited on polyethylene terephthalate (PET) films. We have optimized this process by carefully studying and controlling the factors that influence crystal growth from aqueous solutions generating nanomaterials that are competitive with those synthesized traditionally using organic solvents or vapor phase techniques. The reported results advance bottom-up aqueous solution synthesis/assembly of functional inorganic nanomaterials opening the door to their low cost large scale production for a variety of applications.
10:30 AM - C1.4
Ultrasensitive Solution Processed Polymer Photodetectors.
Xiong Gong 1 , Minghong Tong 1 , Gang Yu 2 , Boo Nilsson 2 , Alan Heeger 1
1 , CPOS, UCSB, Santa Barbara, California, United States, 2 , Cbrite Inc, Goleta, California, United States
Show AbstractUltrasensitive Solution Processed Polymer PhotodetectorsXiong Gong1,2, Minghong Tong1,Gang Yu2, Boo Nilsson2, and Alan J. Heeger11)Center of Polymers and Organic Solids, University of California, Santa Barbara, USA2)CBrite Inc., Goleta, CA 93117, USAEmail:
[email protected] Semiconducting polymeric optoelectronic and electric devices have evolved as a promising cost-effective alternative to silicon-based devices. Photodetectors sensitive to the full UV-visible to infrared spectrum are very desirable for scientific and technological applications, but conventional semiconductor detectors are limited to narrow sub-bands of the spectrum. Full coverage thus requires separate sensors for different sub-bands, which is a complicated and costly solution at best. Here we report ultrasensitive solution processed photodetectors fabricated by narrow band-gap semiconducting polymers as the electron donors and fullerences derivatives and/or inorganic quantum dots as the electron acceptors. Polymer photodetectors with different photo-response and detectivity were demonstrated. Operation at room temperature, polymer photodetectors with photo-response from 300nm to 1450nm, the detectivity larger than 1012 cm Hz1/2/W, and linear dynamic range larger than 120 dB, was demonstrated. We further demonstrated that hybrid polymer photodetectors with photo-response from 300nm to 2000nm have the detectivity larger than 1011 cm Hz1/2/W and linear dynamic range larger than 80 dB operated in room temperature. All these values are comparable to or even better than their inorganic counterparts.Ref. Xiong Gong, et al., Science, 2009, 325, 1665.
10:45 AM - C1.5
Fullerene Sensitized Silicon for Near to Mid Infrared Light Detection.
Gebhard Matt 1 , Mateusz Bednorz 1 , Thomas Fromherz 1 , Saeid Zamiri 2 , Christoph Lungenschmied 3 , Serdar Sariciftci 4 , Guenther Bauer 1
1 Institute for Semiconductor Physics, Johannes Kepler University, Linz Austria, 2 Christian Doppler Laboratory for Surface Optics, Johannes Kepler University , Linz Austria, 3 , Konarka Austria, Linz Austria, 4 Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University , Linz Austria
Show AbstractWe report on a novel light sensing scheme based on a silicon/fullerene-derivative hetero-junction that allows the realization of optoelectronic devices for the detection of near to mid infrared light. Despite the absent light absorption of silicon and the fullerene-derivative for wavelength beyond 1.1 μm and 0.72 μm respectively, a hetero-junction of these materials absorbs and generates a photo-current in the near to mid infrared. This infrared photo-current is caused by an interfacial absorption mechanism based on a spatially indirect transition from the Si valenceband to the lowest unoccupied molecular orbital of the fullerene-derivative [1].Besides its scientific relevance, the simple fabrication process of the hetero-junction (e.g. the fullerene-derivative is deposited by spin-coating) as well as its compatibility with the well established silicon technology makes the presented hybrid approach a promising candidate for widespread applications.[1] G. J. Matt et. al. Adv. Mat. 2009, in press
11:30 AM - **C1.6
Nanocrystal Based Solar Cells.
Paul Alivisatos 1 2
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Department of Chemistry, UC Berkeley, Berkeley, California, United States
Show AbstractSemiconductor nanocrystals exhibit strong quantum size effects. They may prove to be important building blocks for solar cells that exploit quantum effects explicitly. While quantum effects can easily be used to control the initial events of light absorption and possibly the earliest events of electron relaxation, the issue of facile transport in nanocrystals solar cells remains as a problem. This talk will describe two limiting types of nanocrystal solar cells, distinguished by the relationship between the size of the nanocrystals and the bulk exciton diameter. In the case where the nanocrystal is very much smaller than the bulk exciton, it is possible to make an ordered array of the nanocrystals and to investigate the possibility that mini-bands form when the particles are placed in the array. In that case, the transport between the particles may be facile. In the second case, all the elements of the solar cell can be built into a single nanocrystal, so that the charges need not hop between nanocrystals in order to be harvested. Practical examples of these two types of solar cells will be discussed.
12:00 PM - C1.7
Patternable and Low Temperature Processible Nanostructured Zinc Oxide for Electron Injection in Polymer Light Emitting Diode.
Dinesh Kabra 1 , Myoung Song 1 2 , Natalie O Plank 3 , Mark Welland 3 , Henry Snaith 4 , Richard Friend 1
1 Cavendish Laboratory, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 2 School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of), 3 Nanoscience Centre, Department of Engineering, University of Cambridge, Cambridge United Kingdom, 4 Clarendon Laboratory, University of Oxford, Oxford United Kingdom
Show AbstractRecently, there has been a growing interest in using metal-oxides as air-stable electrodes for polymer/organic thin film devices to enhance device stability.[1] These charge-collecting metal-oxide layers sandwich the active organic photo-responsive layer and protect it from ambient oxygen, moisture and prevent photo-oxidation by absorbing UV light. These hybrid (i.e. organic – inorganic devices) are fabricated in an inverted architecture, in which the bottom electrode is an n-type oxide layer used to extract the electrons and the top electrode is a p-type oxide layer used to extract the holes. We report a high efficiency and bright composite oxide-polymer light emitting diode, in which a layer of vertically grown single crystalline Zinc oxide (ZnO) nanorods provide the electron injecting electrode into which an emissive poly [(9,9-dioctylfluoren-2,7-diyl)-co-(1,4 benzo-{2,10-3}-thiadazole)] polymer layer is infiltrated. The device is completed by evaporation of a MoO3/Au anode. These controlled lengths nanorods were prepared by hydrothermal synthesis route at low temperature (< 900C), which makes them suitable for flexible devices. [2] LED efficiency was improved from 0.6 cd/A to 2.4 cd/A by capping the ZnO nanorods with a thin layer of cesium carbonate, which acts as a hole blocking layer. Nanostructured ZnO provides high field density on tips that improves electron injection efficiency and reduces operating voltages for device. We also demonstrate optimum length of nanorods for devices and excellent patternable properties of nanorods injecting layer for display applications.Reference:[1] D. Kabra et al Adv. Mater. 2008, 20, pp 3447 - 3452[2] N. O. V. Plank et al Nanotechnology 2008, 19, pp 465603 465606
12:15 PM - C1.8
Tuning of Refractive Indices and Optical Band Gaps in Oxidized Silicon Quantum Dot Solids.
Jin-Kyu Choi 1 , Seunghyun Jang 2 , Honglae Sohn 2 , Hyun-Dam Jeong 1
1 , Chonnam National University, Gwang-ju city Korea (the Republic of), 2 , Chosun University, Gwang-ju city Korea (the Republic of)
Show AbstractWhile bulk Si has very weak luminescence due to its indirect band gap, nano-sized silicon quantum dots (Si QDs) possess more efficient luminescence. Silicon QDs are also nontoxic and cheap when compared to well-investigated II-VI semiconductors that contain cadmium. In addition, Si QDs are expected to integrate easily into well-established industrially silicon processes. This lab has initiated compelling research into Si QD solids in order to utilize their synergetic benefits with quantum dot solids through fabrication of Si QD thin films. The issues of oxidation concerning the Si QD thin films were confirmed using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The refractive index value of the Si QD thin film at a 30 oC curing temperature was 1.61 and 1.45 at 800 oC due to complete oxidation of the Si phases. The optical band gap values of 5.49 - 5.90 eV corresponded to Si phases with diameters between 0.82 - 0.74 nm, dispersed throughout the oxidized Si QD thin films and modeled by Si molecular clusters of approximately fourteen silicon atoms. The photoluminescence (PL) energy (2.64 – 2.61 eV) in the proposed Si QD thin films likely originated from the Si=O bond terminating the Si molecular clusters, not the free exciton band gap transition of a nanometer Si QD or Si molecular cluster below 1.0 nm.
12:30 PM - **C1.9
Solution-processed Optoelectronic Devices.
Edward Sargent 1
1 ECE, University of Toronto, Toronto, Ontario, Canada
Show AbstractColloidal quantum dots are nanometer-sized semiconductor particles that are dispersed and processed into films from the solution phase. They offer an attractive combination of quantum-size-effect tunability and large-area processing. These features make them particularly interesting in light detection and solar energy harvesting. In light detection, colloidal quantum dots enable ultrasensitive imaging from the UV through the visible and into the short-wavelength infrared. In photovoltaics, they enable capture of the sun's broad spectrum reaching the earth, including in the sometimes-neglected infrared half of the sun's power spectrum. I will review progress in this field and discuss its prospects.
C2: Nanoparticle Processing of Films/Devices II
Session Chairs
David Mitzi
Patrick Smith
Tuesday PM, April 06, 2010
Room 2006 (Moscone West)
2:30 PM - **C2.1
Mechanistic Studies on Sintering of Nanoparticles for Formation of Solution-processed Thin Films.
Vivek Subramanian 1 , Steven Volkman 1
1 EECS Department, University of California, Berkeley, Berkeley, California, United States
Show AbstractNanoparticles are under intense investigation for use in printed electronics applications, since they provide a convenient route for realization of high-quality thin films out of solution. Nanoparticle-based routes have been widely reported for the realization of conductor and semiconductor thin films. For these applications, an understanding of the nanoparticle sintering is crucial. First, this is necessary to enable optimization of annealing processes to maximize transport properties of the resultant films. Second, this will enable optimization of the nanoparticle structure to allow tuning of the sintering schedules to meet application and substrate imposed constraints. Here, we analyze the sintering of nanoparticles to provide a detailed mechanistic understanding of the sintering processes involved in thin film formation. We employ differential scanning calorimetry (DSC) to monitor phase transitions and thermal gravimetric analysis (TGA) to monitor mass transport into and out of the material as it is heated. These provide an overview of the various transition regimes seen by nanoparticles during sintering. This is then correlated to the nanoparticle structure to allow the development of a mechanistic model of the nanoparticle sintering. Crystal orientation, lattice strain, and grain size are determined using X-ray diffraction (XRD). We use transmission electron microscopy (TEM) to determine particle size and X-ray photoelectron spectroscopy (XPS) to determine the chemical composition of the particles and films. By considering all of these results in unison, we propose a comprehensive explanation of the processes occurring during sintering of these nanoparticles. This information, in turn, is critical to the future optimization of particles and their annealing processes for use in printed electronics. Results of such studies are reported for both representative conductor systems based on Ag nanoparticles, and for semiconductor systems based on ZnO nanoparticles. We find that for an electrically continuous film to evolve from isolated encapsulated nanoparticles, a series of distinct transformations occur. These are the dissociation of the surfactant molecules from the nanoparticle surface, ripening of nanoparticles through coalescence and finally loss/decomposition of the ligand, which is accompanied by the formation of a textured, sintered film. We show that the surfactant disassociates from the nanoparticle surface and then acts as a solvent in which the particles coalesce and grow, though the specific ordering of the transitions depends on both nanoparticle and ligand material properties.
3:00 PM - C2.2
Nanoparticle to Bulk Transition in Thin-film Electronics: An Optoelectronic Analysis of ZnO.
Anthony Morfa 1 , Paul Mulvaney 1
1 , University of Melbourne, Parkville, Victoria, Australia
Show AbstractRecent trends in thin-film electronics focus on solution-processable and printable techniques, with sol-gel and nanoparticle inks being especially favored. Using the well-known material, ZnO, typically made with high-vacuum processing or cast from sol-gel solutions, we investigate the transition from nanoparticle to bulk films with both optical and electronic measurements. Nanoparticles of ZnO were synthesized in alcohol with typical particle sizes ranging from three to five nanometers. Films were cast from these inks and annealed in a nitrogen or ambient environment to temperatures as high as 800°C. As-cast films have absorption spectra that clearly demonstrate nanoparticle behavior that changes to bulk-like absorption with high-temperature annealing. The doping density of these films was determined using impedance measurements and the Mott-Schottky relation. Field-effect-transistors were characterized to determine the electron mobility as a function of annealing temperature. These results will be put into a broader context with spectroscopic ellipsometry measurements that were used to determine the degree of porosity of the films, FTIR measurements will be presented to demonstrate the degree of organic material in the films with annealing, and GIXRD measurements that indicate the degree of crystallinity. The presented results will demonstrate how bulk electronic properties can be achieved from thin-films made with nanoparticle inks prepared in either an oxygen-rich or oxygen-free environment. These results will be compared to other fabrication techniques, such as sputtering and sol-gel casting, and will be shown to benefit from nanoparticle properties with low temperature processing, while having comparable optical and electronic properties at higher temperature annealing.
3:15 PM - C2.3
High Mobility Field-effect Transistors Based on Zinc Oxide Nanoparticles.
Hendrik Faber 1 , Martin Klaumuenzer 2 , Wolfgang Peukert 2 , Marcus Halik 1
1 Institute of Polymer Materials, University Erlangen-Nürnberg, Erlangen Germany, 2 Institute of Particle Technology, University Erlangen-Nürnberg, Erlangen Germany
Show AbstractThe field of printable electronics was originally initiated by promising research in the domain of organic electronics. But, resulting from disequilibrium in the performance of organic p- and n-type semiconductors, inorganic materials with geometries on the nano scale were proposed as solution-processable alternatives. In particular, zinc oxide has recently attracted a lot of attention for various applications including field-effect transistors [1] or solar cells [2].Here we report on the synthesis of ZnO nano particles with varying diameters (3 – 12 nm) and their application in long-term stable and solution processed thin-film transistor devices. Layer formation was characterized regarding particle sizes and the resulting morphologies compared to the respective transistor characteristics. Due to a low-temperature processing route, the device fabrication could be carried out either on rigid or flexible substrates (PEN).Additionally, various post-deposition treatments of the ZnO layer were performed, including the exchange of the particles ligand sphere and plasma treatment. With such methods, device characteristics are tunable in a wide range. Using optimized process parameters, previously reported[3, 4] for ZnO nano particle based transistors could be surpassed, for example with field-effect mobilities up to 20 cm2/Vs measured in air.References:[1]K. Okamura, N. Mechau, D. Nikolova, and H. Hahn. Appl. Phys. Lett., 93(8):083105–3, 2008.[2]Q. Zhang, C. S. Dandeneau, X. Zhou, and G. Cao. Adv. Mater., 21:4087–4108, 2009.[3]S. Lee, Y. Jeong, S. Jeong, J. Lee, M. Jeon, and J. Moon. Superlattices Microstruct., 44(6):761–769, 2008.[4]H. Faber, M. Burkhardt, A. Jedaa, D. Kälblein, H. Klauk, and M. Halik. Adv. Mater., 21:3099–3104, 2009.
3:30 PM - C2.4
Room Temperature Vacuum-induced Ligand Removal and Patterning of ZnO Nanoparticles: From Semiconducting Films towards Printed Electronics.
Thomas Richter 1 , Felix Stelzl 1 , Steffen Link 1 , Uli Wuerfel 1 , Sabine Ludwigs 1
1 Freiburg Material Research Center, University of Freiburg, Germany, Freiburg, Baden-Württemberg, Germany
Show AbstractIn recent years, interest in semiconducting inorganic oxide nanomaterials has grown constantly due to their potential application in large area, low-cost electronic devices. In particular transparent semiconducting oxides are expected to be promising candidates for opto-electronic applications, such as displays, electrochromic windows, solar cells and field effect transistors. Special attention was given to nanocrystalline ZnO (n-ZnO) due to its abundance, low toxicity and easy tunability in shape and size. To obtain the full advantage of n-ZnO in printed electronics, two main issues have to be addressed: First, stabilizing ligands have to be introduced to allow good dispersion in organic solvents. Second, electronic interparticle contact has to be assured in the device after deposition. Those requirements are often contradictory since good particle dispersibility requires large ligands, which in turn impede continuous charge percolation pathways in films. The strategy presented by us addresses both of the aforementioned problems. We synthesized n-ZnO with a weakly bound ligand that promotes solubility and allows for its post-processing removal in vacuum to establish interparticle contact. Charge carrier transport was investigated by FET measurements revealing interparticle contact. The ability to process at room temperature is highly interesting for temperature sensitive substrates. The potential of our approach for printed electronics is further shown by patterning nanoparticle dispersions via micro injection moulding in capillaries (MIMIC) as a soft lithographic method. As anisotropic nanoparticles should allow better charge percolation, we are currently working on transferring our concept to aligned ZnO nanorods.
3:45 PM - C2.5
Low Temperature Aqueous Deposition of ZnO for Enhancing GaN LED Performance.
Jacob Richardson 1 , Daniel Thompson 1 , Ingrid Koslow 1 , Steven DenBaars 1 , Frederick Lange 1
1 Materials, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractLight extraction technology has proven to be critical in the development of the energy efficient, high power light emitting diodes (LEDs) needed for solid state lighting. The properties of ZnO make it well suited for integration with GaN LEDs as a transparent current spreading and/or light extraction layer. Here we report on the fabrication of epitaxial ZnO films and other structures on GaN based LEDs using a low temperature aqueous solution method. Deposition is performed using simple aqueous chemistry at atmospheric pressure and temperatures less than 90οC. This versatile technique is capable of depositing various useful morphologies of ZnO on several different LED surfaces. We show that devices using these solution deposited ZnO layers out perform those with more conventional vapor deposited indium tin oxide or semitransparent thin Ni-Au layers.
C3: Solution-processed Transparent Contacts
Session Chairs
David Mitzi
Patrick Smith
Tuesday PM, April 06, 2010
Room 2006 (Moscone West)
4:30 PM - **C3.1
Solution Assembled Carbon Nanotube Networks With a Hybrid Dopant as Highly Conductive Transparent Electronic Materials.
Melburne LeMieux 1 , Ajay Virkar 1 , Derrick Liu 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractThe aim of this work is to better understand design principles involving nanoscale hybrid materials for electronic applications. Specifically, approaches have been developed to further enable carbon nanotube technologies including electronic devices (including transistors, displays, touch screens, e-paper, and solar cells), and composite materials. Transparent electrodes are a central component in many of these aforementioned electronic devices. The primary issue concerning nanotubes as ITO replacements to date is inferior conductivity, which arises from high resistance at nanotube/nanotube junctions in the CNT film and non-uniformity in the film. Previous research into solving this problem has been in the development of polymer composites, and doping with temporary, unstable dopants such as iodine and thionyl chloride. These issues are addressed here by using a hybrid nanotube film. In this work, highly conductive transparent electrode materials using an approach whereby partially aligned, solution deposited carbon nanotube networks (CNTnts), are doped at the junctions by a completely stable doping material is described. The purpose of the secondary material for the hybrid film is bi-functional. Firstly, it acts to reinforce nanotube junctions, greatly increasing conductivity by reducing contact resistance. Secondly, it can dope CNTs, dramatically increasing film conductivity. This results in a dramatic conductivity increase in the CNT networks with minimal decrease in transparency. The design approach leads to a hybrid material that is an excellent candidate for next generation inexpensive and flexible displays, touch screens, and solar cells that require new materials to replace the current standard indium tin oxide (ITO) electrodes, which can account for 25% of device cost. Key advantages of this hybrid system include: stable doping, extremely high transparency, and smoothness, and we will discuss processing and morphology and how it relates to conductivity and electronic properties of this material. In addition, the approach and concepts introduced in this work opens up a new direction for enhancing percolation in nano-assemblies.
5:00 PM - C3.2
Electrochemically-assisted Deposition of Thin Structured Indium Oxide and Indium-Tin Oxide Films.
Nina Kovtyukhova 1 , Tom Mallouk 1
1 Chemistry, Penn State University, University Park, Pennsylvania, United States
Show AbstractThin films of optically transparent materials with high electrical conductivity, such as tin-doped indium oxide (ITO), have a variety of applications in solar energy conversion systems, optoelectronic devices, electrodes of flat-panel displays and touch panels, spectrally selective windows, antistatic coatings, etc. Low-cost solution-based techniques for preparing ITO films is a very attractive alternative to sputtering that is most widely used in industrial applications. Up to date a number of sol-gel based deposition procedures have received the most attention. In this paper we present the electrochemically-assisted deposition (EAD) of thin structured In2O3 and ITO films. EAD techniques differ from the direct reduction or oxidation of species on the electrodes in that they exploit red/ox reactions on the electrodes for altering chemical conditions, e.g. pH, in the interfacial zone, which cause species deposition in the vicinity of the electrode surface. This makes EAD suitable for deposition of insulating and poorly conducting materials. On the other hand, EAD inherits many advantages of the direct electroplating, such as applicability to extended and flexible substrates, and compatibility with surface patterning. Here we show that it is possible to grow uniform In2O3 and ITO films on centimeter-size substrates, and that structure, morphology, and composition of the films can be controlled by altering the composition of solutions, applied potential, and temperature. At the first step, well crystallized structured In and In-Sn hydroxides are formed, which are then thermally converted to the polycrystalline oxide films. The films have been characterized by FESEM, XPS, XRD, AFM, optical and electrical measurements.
5:15 PM - C3.3
Molybdenum Oxide Nanostructures as Hole Transport Layers for Solution-processed Solid-state Dye-sensitized Solar Cell.
Han-Yi Chen 1 , Tri-Rung Yew 2
1 Institute of NanoEngineering and MicroSystems, National Tsing-Hua University, Hsinchu Taiwan, 2 Department of Materials Science and Engineering & Institute of NanoEngineering and MicroSystems, National Tsing-Hua University, Hsinchu Taiwan
Show AbstractIn this study, molybdenum oxide nanostructures were deposited and used as hole transport layers for solid-state dye-sensitized solar cells (SS-DSSCs). The molybdenum oxide nanostructures were used to increase the surface contact with dyed titanium dioxide so as to enhance the short circuit current of SS-DSSCs. Various methods of solution-processing (such as spin coating) were also used to fill titanium dioxide in molybdenum oxide nanostructures. Besides, doping of molybdenum oxide was also utilized to improve the hole concentration and enhance the open voltage of SS-DSSCs. The morphology and structure of the molybdenum oxide nanostructures were characterized by filed emission gun scanning electron microscope (FESEM), high resolution electron transmission microscopy (HRTEM) and X-ray diffraction spectroscopy (XRD). The electrical properties including short circuit current (Jsc), open voltage (Voc), fill factor (FF) and power conversion efficiency (PCE) of SS-DSSCs were also measured.
5:30 PM - C3.4
Latex-templated Porous Silica Films for Optics and Electronics.
Francois Guillemot 1 2 , Aline Brunet-Bruneau 3 , Elodie Bourgeat-Lami 4 , Etienne Barthel 2 , Thierry Gacoin 1 , Jean-Pierre Boilot 1
1 Physique de la Matière Condensée (PMC), UMR 7643, Ecole Polytechnique, CNRS, Palaiseau France, 2 Surface du Verre et Interfaces (SVI), UMR 125, CNRS, Saint-Gobain, Aubervilliers France, 3 Institut des Nanosciences de Paris (INSP), UMR 7601, Université Pierre et Marie Curie (Paris 6), CNRS, Paris France, 4 Laboratoire de Chimie, Catalyse, Polymères et Procédés (C2P2), UMR 5265 , Université Lyon 1, CPE Lyon, CNRS, Villeurbanne France
Show AbstractThin films with low-refractive index are of great interest to adjust the optical properties of optical components, e.g. reflectivity. In this respect, sol-gel coatings are very efficient for flat glass functionalisation because of ease of application, low cost and versatility. Mesoporous silica films prepared by surfactant self-assembly have been extensively studied but show poor refractive index stability as capillary condensation of atmospheric water can occur in the pores.[1] One way to tackle this issue is to prepare films with larger pores in which capillary condensation is impossible at ambient humidity. Starting from custom made latex, we successfully prepared sol-gel porous silica film with macropore size above 30nm and no microporosity in the silica walls. We are then able to independently and accurately tailor pore size, pore volume fraction and pore surface chemistry.Pore accessibility as a function of pore size and porous fraction was investigated through ellipsometry-porosimetry for ethanol adsorption, and a transition between open and closed pore structure at decreasing volume fraction was shown [2]. Mechanical properties were investigated with nanoindentation: Young's modulus and hardness were shown to follow a minimal area model with porous fraction [3] while no effect of pore size was measured. The pore occlusion threshold does not induce any singularity in the mechanical response which allows for performance optimization of the material. These new films with very stable dielectric properties and low refractive index that can be tuned in a large range (from 1.15 to 1.40 at 600 nm, corresponding to dielectric constant values down to 1.5) appear as very promising for applications in optics and electronics.[1] M. Matheron; A. Bourgeois; T. Gacoin; A. Brunet-Bruneau; P.-A. Albouy; J.-P. Boilot; J. Biteau; P. Lacan Thin Solid Films 2006, 495, 175.[2] F. Guillemot ; A. Brunet-Bruneau ; E. Bourgeat-Lami ; T. Gacoin ; E. Barthel ; J.-P. Boilot submitted to Chem. Mater.[3] R.W. Rice, J Mater Sci 1996, 31, 102.
5:45 PM - C3.5
Sol-gel Synthesized NaLu1-xYbx(WO4)2 Heteroepitaxial Films for Laser Applications.
Xiumei Han 1 , Carlos Zaldo 1
1 , Instituto de Ciencia de Materiales de Madrid. Consejo Superior de Investigaciones Científicas. c/ Sor Juana Inés de la Cruz 3. 28049, Madrid Spain
Show AbstractTrivalent laser active lanthanides in tetragonal double tungstates have optical transitions with large bandwidths due to the near to random occupancy of two lattice sites by monovalent and trivalent cations. This property was used to regularly obtain mode-locked laser pulses below 100 fs in NaT1-xYbx(WO4)2 (T=Y, La, Gd and Lu) single crystals with x= 0.05-0.1. However, laser applications of these compounds in bulk form are limited by their low thermal conductivity (κ≈ 1.5-2.5 W/m×°C) and their relatively large thermal expansion anisotropy, about two times larger in the c-axis than in the a-axis. The use of cooled NaGd1-xYbx(WO4)2 disks with thickness ≈300 μm allowed scaling the laser output power to 18 W in cw regimen. In the present work we describe the sol-gel preparation of thin films with NaLu1-xYbx(WO4)2 composition on sapphire substrates, a transparent crystal with high thermal conductivity (κ≈ 42 W/m×°C), which should work as heat drain, as well as on silicon and quartz.The compounds were synthesized by the Pechini method. Lu2O3 and Yb2O3 (dissolved in nitric acid), Na2CO3 and (NH4)10W12O41.7H2O were used as sources for metal ions and citric acid and ethylene glycol as chelating agents. Films were formed by multilayer spin coating (500 rpm for 6s and 3000 rpm for 30 s). Each layer was dried at 120 °C and then sintered by a 10 min rapid thermal annealing. The onset for the compound synthesis and crystallization was 400 °C. We use most commonly 650 °C for synthesis. A final long term annealing (5 h) was applied for sintering also at 650 °C. Films obtained were transparent and crystalline and on crystalline sapphire showed strong 001 film texture. In the first few layers the film nucleate as isolated dots, which later grow and coalesce. Films with more than 10 layers are formed by a dense distribution of grains with size <3 μm. Typical deposition rate is ≈25 nm/layer.The Yb3+ photoluminescence was observed at 25°C. Both emission and excitation spectra were very similar to that known for single crystals. The Yb3+ 2F5/2 fluorescence lifetime of the films prepared with 99,998% Yb2O3 decreases from τ= 335 μs for x=0.1 to τ=200 μs for x=1. These values are similar to that obtained in isostructural NaLu(WO4)2 and LiYb(MoO4)2 single crystals, respectively, namely τ= 353 μs, and τ= 183 μs. Sintering temperatures ≥850 °C lead to compositional changes associated to Na and W sublimation since the formation of either Yb2O3 or Yb-doped Lu2O3 was inferred from the observation of very long Yb3+ lifetimes (τ> 500 μs) and large crystal field splitting of Yb3+ energy levels after film annealing at such high sintering temperatures.
C4: Poster Session: Nanoparticles
Session Chairs
David Mitzi
Patrick Smith
Tuesday PM, April 06, 2010
Exhibition Hall (Moscone West)
6:00 PM - C4.1
Catalyst-free Solution Phase Synthesis of CuInSe2 Nanowire.
Stacey Wark 1 , Dong Hee Son 1
1 Chemistry, Texas A&M University, College Station, Texas, United States
Show AbstractNanowires of chalcopyrite CuInSe2, which have a great potential in solar cell application, have been synthesized using a catalyst-free, solution based synthesis method. Stoichiometric mixture of halide salts of Cu and In ions and Se dissolved in trioctylphosphine was used as the precursor. The key to the catalyst-free synthesis of the nanowires of chalcopyrite CuInSe2 is the use of surfactant molecules that have moderately binding affinity to the surface of CuInSe2. While strongly passivating surfactant, such as aliphatic amine, results in relatively small spherical nanocrystals, dioctylphosphine oxide (DOPO) with moderate binding affinity to the metal ions results in nanowires of 5-10 micron long and tens of nanometers wide. Three-dimensional TEM tomography of the nanowires reveals that the cross section of the nanowire is strongly faceted with three or four sides. The sidewall of the nanowires exhibits a regular saw-tooth pattern similar to a structure formed by stacking of the truncated tetrahedrons. Based on the tomography and time-elapsed TEM images of nanocrystals formed during the synthesis, we inferred a mechanism of the nanowire growth involving nonuniform, oscillating growth rate during the formation of nanowires.
6:00 PM - C4.10
Analysis of Generation Mechanism of Platinum Nanoparticles in Polyol Process.
Ryo Kasuya 1 , Jeyadevan Balachandran 1 , Takashi Itoh 2 , Takatoshi Matsumoto 3
1 Environmental Studies, Tohoku University, Sendai Japan, 2 Center for Interdisciplinary Research, Tohoku University, Sendai Japan, 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Show Abstract The synthesis of 5 nm diameter FePt particles is preferred to be used as magnetic recording material. However, during the synthesis of FePt in polyol, the reduction rate of Pt in ethylene glycol (EG) is believed to dictate the final size of FePt particles, which is around 3 nm in diameter. Thus, the control over the reduction rate of Pt is considered vital for the synthesis of FePt particles with varying particle diameter. Thus in this study, we have focused on the synthesis of Pt nanoparticles using Pt(II) acetylacetonate (Pt(acac) 2) in EG in the presence of additives such as chloride ions. The influence of chloride ions on particulate properties was studied by introducing varying amounts of hydrochloric acid (HCl). According to the X-ray diffraction profiles, phase-pure fcc Pt was formed by the polyol process at 180oC for 1 h irrespective of HCl addition. However, the presence of chloride ions influenced the particle size, which increased from 6.0 to 10.8 nm, as recognized by transmission electron microscopy. In contrast, the standard deviation of the sample decreased from 2.1 to 1.4 nm. To understand the generation mechanism of Pt nanoparticle under different solution conditions, the reaction solution and the precipitates were characterized by UV-visible, in situ Raman spectroscopic analyses and nuclear magnetic resonance (NMR) analysis. The UV-vis spectra remained unchanged in spite of HCl addition. To investigate the change of the molecular structure during the reaction, in situ Raman spectra of the reaction solution were measured at various reaction temperatures. The four peaks observed at 559, 718, 938, 1374 cm-1 are attributed to the vibrational modes of hetero six-membered ring of Pt(acac)2, while the other peaks are assigned as the vibrational modes of EG molecules. When we introduced HCl to the reaction solution, the peak intensity at 938 cm-1 decreased at lower temperatures. This indicates that the bond cleavage between acac ligand and Pt2+ ion is facilitated, probably due to the oxidative addition of HCl. The reaction residues obtained at 100 and 150oC were investigated by the 1H NMR of in a static magnetic field of 14.1 T. The peaks at 1.5 and 3.2 ppm corresponded to the acac ligand in keto-form, while the peaks at 2.0 and 5.0 ppm were assigned as the acac ligand in enol-form. Since in keto-form acac coordinates platinum ion is in Pt2+ state, keto-enol tautomerism can be induced by the structural change from bidentate to monodentate. It is considered that the polymerization of active species such as monodentate Pt(acac)x produces the Pt nanoparticles. We concluded that the bond cleavage between Pt2+ and acac ligand can be accelerated by the addition of HCl, which facilitates nucleation and crystal growth of Pt nanoparticles.
6:00 PM - C4.11
Facile Preparation of Hierarchically Porous TiO2 Monoliths.
George Hasegawa 1 , Kazuyoshi Kanamori 1 , Kazuki Nakanishi 1 , Teiichi Hanada 1
1 , Kyoto University, Kyoto Japan
Show AbstractPorous inorganic materials with hierarchically multimodal pore size distributions have attracted significant attention in a lot of application fields, such as electronics, catalysis, sensing, and separation science. Of the many porous inorganic materials, titania (TiO2) is of particular interest due to its unique characteristics and a lot of efforts have been made to synthesize porous TiO2 monoliths. Hierarchically porous TiO2 monoliths are especially important for chromatographic applications because of their selective adsorption of organophosphates, such as nucleotides and phospholipids. However, there are only a few reports describing the formation of porous TiO2 monoliths because titanium alkoxide species exhibit remarkably high reactivity, which generally leads to a heterogeneous precipitation of TiO2 rather than the formation of monolithic gels.Recently, we developed a simple method for preparing transparent TiO2 monoliths utilizing a chelating agent and mineral salts under a mild condition. Although the chelating agents, such as β-ketone esters and β-diketones, are well-known to decrease the reactivity of titanium alkoxide species by coordination to the Ti atoms, the addition of only chelating agents cannot allow us to acquire transparent TiO2 gels but friable opaque gels which are formed as aggregates of TiO2 precipitates. The key of our method is the addition of strong acid anions, such as nitrate ions and halide ions, which further stabilize the chelated Ti atoms and decrease the reactivity in hydrolysis. This method is considerably advantageous because the reaction takes place in a nearly neutral condition in one-pot and the gelation time is easily controlled by varying various components.In this work, we prepared hierarchically porous TiO2 monoliths by utilizing the sol–gel method with chelate and mineral salts described above. Well-defined interconnected macropores are formed by concurrent phase separation and the sol–gel transition, while micro- and mesopores are embedded in the gel skeletons composed of TiO2 nanocrystallites. Ethyl acetoacetate, which was used as a chelating agent in this study were removed by hydrolysis followed by decarbonation of resultant acetoacetic acid. The obtained rigid crack-free TiO2 monoliths were crystallized into anatase and rutile by calcination resulted in promising materials for a lot of applications owing to their multimodal pore structure integrated in robust monoliths and the unique characteristics of TiO2.
6:00 PM - C4.12
Light Scattering of ZnO Nano Particle Based Thin Films.
Sahar Arabi 1 , Rahul Dewan 1 , Sujay Phadke 2 , Andrey Raykov 1 , Rodrigo Noriega 2 , Alberto Salleo 2 , Dietmar Knipp 1
1 School of Engineering and Science, Electronic Devices and Nanophotonics Laboratory, Jacobs University Bremen, Bremen Germany, 2 Department of Materials Science and Engineering, Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States
Show AbstractSolution processed zinc-oxide nano particle based thin films were realized with excellent light scattering properties. The films are promising candidates as contact layers or intermediate reflectors in thin film solar cells. The nano particle based films were prepared by spin coating a blend of zinc oxide nano particles and an adhesive (spin-on-glass) on glass substrates. The optical properties of the films can be controlled by the geometry of the zinc oxide nano particles and the concentration of spin-on-glass in the film. Films based on zinc oxide nano particles, nano pyramids and nano wires were investigated. Furthermore, the solution processed films were compared to nano textured zinc oxide films prepared by sputtering and low pressure chemical vapor deposition (LPCVD). Such zinc oxide films are commonly used in silicon thin film solar cells, where they exhibit very good light scattering properties. The optical properties of the films were compared in terms of the total transmission and the haze (ratio of diffuse transmission with respect to total transmission). Solution processed films based on small zinc oxide pyramids of dimension 200-400 nm exhibit scattering properties comparable to films prepared by sputtering or LPCVD deposition. For shorter wavelengths from 350 nm to 550 nm the small pyramids exhibits high haze values of up to 90 % and high total transmission. For longer wavelengths exceeding 1200 nm the haze distinctly drops down to less than 20%. The best scattering properties were observed for films based on particles with an average diameter of 50 nm to 70 nm. Such films exhibit high haze values for short and long wavelengths. For short wavelengths the light is scattered by the individual particles, whereas the high haze values for long wavelengths are caused by the formation of clusters of nano particles on the surface. For long wavelengths of 1200 nm the haze exceeds values of 40%. The influence of the preparation conditions and the particle geometry on the optical properties and the morphology of the films will be discussed.
6:00 PM - C4.13
Effects of Annealing Treatment on the Properties of Zinc Oxide Nanorod.
Sharul Ashikin Kamaruddin 1 2 , Kah-Yoong Chan 2 , Mohd Zainizan Sahdan 1 3 , Dietmar Knipp 4 , Mohamad Rusop 3 , Hashim Saim 1
1 Faculty of Electrical and Electronic Engineering, Universiti Tun Hussein Onn Malaysia, Batu Pahat, Johor , Malaysia, 2 Faculty of Engineering, Multimedia University, Cyberjaya, Selangor Darul Ehsan, Malaysia, 3 Faculty of Electrical Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia, 4 School of Engineering and Science, Jacobs University Bremen, Bremen, Bremen, Germany
Show AbstractZinc oxide (ZnO) is an emerging optoelectronic material in large area electronic applications due to its various functional behaviors. We report on the fabrication and the characterization of ZnO nanorods. The ZnO nanorods were synthesized using sol-gel hydrothermal technique on oxidized silicon substrates. Different post-annealing temperatures were explored in the sol-gel hydrothermal synthesis of the ZnO nanorods. The surface morphologies of the ZnO nanorods were examined using scanning electron microscope (SEM). In order to investigate the structural properties, the ZnO nanorods were measured using X-ray diffractometer (XRD). The optical properties were measured using ultraviolet-visible (UV-Vis) spectroscopy. Observation from SEM results indicates that the surface morphologies of ZnO structure vary with annealing temperatures. The optical properties strongly correlate to the shape and size of the ZnO nanorods. In this work, the ZnO nanorods exhibit fast UV photo-response with cut-off wavelength of 400 nm. Based on experimental result, the ZnO nanostructures are promising candidate for UV sensing applications.
6:00 PM - C4.14
Fabrication of Three Dimensional Magneto-photonic Crystals by Infiltration With Magnetic Nanoparticles.
Oana Pascu 1 , Juan Manuel Caicedo 1 , Martín Lopez 2 , Josep Fontcuberta 1 , Cefe Lopez 2 , Alvaro Blanco 2 , Gervasi Herranz 1 , Anna Roig 1
1 , Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Bellaterra Spain, 2 , Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Madrid Spain
Show AbstractMagneto-photonic crystals are receiving attention due to prospects for new photonic devices with enhanced magneto-optical response and non-reciprocal optical effects. To look for this enhanced functionality we have fabricated three dimensional magneto-photonic crystals by infiltrating the voids of direct and inverse opals [1] with magnetic nanoparticles. We will report on the synthetic procedure and extensive characterisation of the nickel nanoparticles used to infiltrate the opals as well as the different infiltration alternatives that have been essayed. Nickel (Ni) nanoparticles were synthesized by thermal decomposition of a nickel organometallic precursor (nickel (II) acetylacetonate) in oleylamine at high temperature and in the presence of two surfactants leading to the formation of monodisperse nanoparticles. An effective strategy for nanoparticles size control, colloidal stability and oxidation prevention is the use of one strongly and another weakly binding surfactants (oleic acid and triocthylphosphine respectively). Regarding photonic crystals; SiO2 and polystyrene direct opals were produced by standard methods and high quality Al2O3 inverse opals were fabricated by atomic layer deposition on a polystyrene direct opal. We will report on the structural, magnetic and magneto-optical characterization of the infiltrated photonic crystals and assess the efficiency of the different infiltration procedures used.[1] J.M.Caicedo et al. Journal Magnetism and Magnetic Materials, available on line doi:10.1016/j.jmmm.2009.02.139
6:00 PM - C4.15
Dimensionally-controlled Hydrothermal Tm3+-doped Oxidic Nanocrystals and Their Photoluminescence Properties.
Rocio Calderon-Villajos 1 , Carlos Zaldo 1 , Concepcion Cascales 1
1 , Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, c/ Sor Juana Inés de la Cruz 3, 28049, Madrid Spain
Show AbstractLaser operation ~2 μm has wide applications related to its eye-safe nature mainly in medicine and atmospheric sensing. Although traditionally solid-state lasers for this spectral range were based in Ho3+-doped crystals, new pumping technologies using commercial high power AlGaAs diode lasers are promoting their replacement for suitable Tm3+-doped single crystals operating in the 3F4→3H6 emission transition. Two of the most attractive laser hosts for incorporating Tm3+ are the transparent rare-earth (RE) cubic sesquioxides RE2O3 (RE=Sc, Y, Gd, Lu), and the tetragonal zircon-type vanadates REVO4 (RE= Y, Gd, Lu). Technologically advanced capabilities such as high-power solid-state lasers in the case of the RE2O3 family, and applications in lamps and displays as well as those derived of their efficiency as Raman laser converters for REVO4, are among the reasons accounting for such interest in these single crystals. Nowadays, as an alternative to circumvent difficulties related to the production of bulk single crystals or aiming for exploring new properties derived of the nanosize regime, diverse low temperature methodologies are being applied to prepare nanocrystals (NCs) of the above phases. Another possibility to be considered is the incorporation of NCs in hybrid composites. A first step in these directions is the synthesis of Tm3+-doped NCs with controlled size and morphologies.This work presents soft hydrothermal (HT) routes to synthesize NCs of Tm-doped Lu2O3 and Tm-doped GdVO4. Along with homogeneous nucleation, well-defined compositions and dimensionally-controlled morphologies of the obtained HT NCs, aspects that are crucial for high luminescence performance, the method involves rapid processes, which constitutes an advantage for medium and high scale productions.Two very distinct shapes such as micron size rods with ∼ 40 nm Ø, and square nanosheets with sides ~150 nm, have been obtained for pure cubic Ia-3 Lu2-xTmxO3, with Tm3+ contents in the 1.0≤x≤0.004 range (i.e. Tm3+ concentrations [Tm] from 50 mol% to 0.2 mol%), by choosing the starting reagents and adjusting the pH value of the HT reacting solution, which lasted in all cases the same time, 24 h. HT preparations of Gd1-xTmxVO4, 1.0≤x≤0.002 ([Tm] from 100 mol% to 0.2 mol%), carried out in extensive pH and reaction time ranges, yielded in all cases the pure tetragonal I41/amd phase, with morphologies that can be finely tuned from hexagonal and square ~10-25 nm nanosheets, to spindle- and rice-grain-like ~40 nm NCs, or nanorods and nanotubes ~50 nm Ø. The photoluminescence and emission lifetime of 3H4 and 3F4 Tm3+ multiplets, which are involved in the emissions of interest for infrared lasers, have been measured in both Lu2O3 and GdVO4 families, and their dependence with the particle size, morphology and concentration is analyzed in each case.
6:00 PM - C4.17
Solution-processed Chalcogenide Glass for Fabricating Mid-infrared Refractive Optical Elements.
Eric Sanchez 1 , Janesha Dua 2 , David Longawa 3 , Shanshan Song 3 , Craig Arnold 3
1 , The City College of New York, New York, New York, United States, 2 Department of Electrical Engineering, California Institute of Technology, Pasadena, California, United States, 3 Department of Electrical Engineering and Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States
Show AbstractMid-IR technology has become increasingly important for trace-gas sensing applications where physically shrinking the size of sources and detectors has spawned a number of important possibilities in health and the environment. However, in order to successfully implement these technologies, corresponding optics must be scaled down and the integration of devices must be improved. In this work, we demonstrate two pathways to optimization based on a common solution-based method for the deposition of As2S3. In the first example, we demonstrate the fabrication of micro-lenses from chalcogenide glass solution using ink jet printing followed by thermal processing at 50 C for 45 minutes, to allow the solvent to evaporate. After solidification, the micro-droplets remain plano-convex with diameters from 12 to 26 µm and focal lengths from 13 to 23 µm. Using the ink jet printer, these microlenses can be printed directly on the facet of a quantum cascade laser to optimize coupling efficiency. In addition, the same material with similar processing conditions can be used as an optical adhesive to improve index matching and coupling efficiency of external optical components to sources and detectors. Here we examine this approach for ZnSe, Si, and Ge optics by spin coating the glass solution on test blanks. The resulting components show good adhesion with IR transmission measurement showing minimal loss and improved transmittance.
6:00 PM - C4.19
Preparation of Al-doped ZnO Nanoparticulate Film for Optoelectronic Applications.
Thu Tran 1 , Shinya Maenosono 1
1 , Japan Advanced Institute of Science and Technology, Nomi, Ishikawa Japan
Show AbstractThe development of electronics industry strongly depends on the creation of new materials. ZnO is a very attractive oxide semiconductor which possesses wide and direct band gap (3.3 eV), large excitonic binding energy (60 MeV) and high transparency in the visible range. Doping ZnO with high-valence elements such as Al, Ga and In dramatically increases its conductivity, especially when these nanostructures can be realized. The resulting materials are interesting alternatives for many optoelectronic applications.In this study, we synthesized aluminum-doped ZnO (AZO) nanoparticles (NPs) by the solvothermal decomposition of acetylacetonate precursors. This wet chemical route takes advantages of mild reaction conditions, short time and commercially available chemicals. The as-synthesized NPs have the average size smaller than 15 nm with high crystalline, uniformity and good dispersibility in non-polar solvents. The influence of various factors on the properties of AZO NPs was thoroughly investigated. The AZO nanoparticulate film was prepared from these AZO NPs by several techniques such as spin coating or inkjet printing. Some important properties of these films including thickness, crystal structure, surface morphology, optical transparency and conductivity are characterized. Al dopands play the vital role on controlling the conductivity, but remain the highly optical transmittance of the ZnO films. These AZO films are potential replacement for traditional transparent conducting oxide, In-doped SnO (ITO), which is becoming scarce and expensive.
6:00 PM - C4.2
Functional Nanocrystalline Materials: Diffraction Gratings Based on CdSe and CdSe/CdS Core/Shell Nanocrystals.
Mario Malfavon 1 , Andrea Munro 1 , Richard Shallcross 1 , Michael Liao 1 , Neal Armstrong 1
1 Chemistry, University of Arizona, Tucson, Arizona, United States
Show AbstractCdSe nanocrystals (NCs) are seeing increasing use as the photoactive materials in new solar cell technologies and as emissive dopants in organic light emitting diodes. We have recently shown that CdSe NCs can be micro-contact printed into diffraction gratings with extremely good integrity and diffraction efficiency. They can also be used as simple in-coupling elements for waveguides. Capping ligands, nanocrystal concentration, and solvent in the “ink” used to print these optical elements are all components that need to be optimized, in order to produce high quality diffraction gratings. We have now extended these studies to include core-shell CdSe/CdS NCs that have higher luminescence efficiencies than ligand-capped NCs, in order to test whether diffracted light might be accompanied by luminescence from the nanocrystal gratings at angles which correspond to interference from point light sources. CdSe/CdS core/shell NCs have now been synthesized for micro-contact printing of new diffraction gratings, requiring different inking conditions to form optimized grating features. Using laser excitation we have observed luminescence from these patterned NCs, at angles which are close to those predicted for far-field diffraction of light of that same wavelength. We can also build organic light emitting diodes over these patterned NC arrays, and we will focus on how the NC diffraction grating affects the in coupling and out coupling of the OLED emission.
6:00 PM - C4.20
Unique Optical Properties of Organic Modified Si Nanoparticles.
Naoto Shirahata 1 2 , Tohru Tsuruoka 1 3 , Yoshio Sakka 1
1 , National Institute for Materials Science, Tsukuba Japan, 2 , JST-PRESTO, Tokyo Japan, 3 , JST-CREST, Tokyo Japan
Show AbstractColloidal semiconductor quantum dots (QDs) are frequently called “artificial atoms”, and are undoubtedly one of the prominent light-emitting materials. In a colloidal QD, the electronic motion is confined in all spatial directions to give a discrete energy level. Hence, the precise size control of the QDs leads to highly-efficient light emission with narrow a full-width at half-maximum (fwhm). Bulk silicon provides a platform for large-scale integrated circuits, but shows significantly poorer optical performance because of its indirect bandgap character. Modifying the structure of Si such that its three-dimensional physical size does not exceed 7 nm for crystalline nanoparticles produces a remarkable change in its optical transition to increase the bandgap from 1.1 eV for bulk to about 3.3 eV, and to enhance the light emission efficiencies. Although the question on the blushidted PL origin has not yet been satisfactory answered, we can see a consensus among many efforts that the surface passivation of Si nanoparticles leads to the appearance of the quantum confinement effect while optical transition in nanoparticles covered with silica shell is dominated by defect states at the interface of Si/silica. We show herein solution synthesis of colloidal Si nanoparticles which show size-dependent PL features in near UV to visible regions, and discuss on their PL origins. One of our strategies in the presentation puts an end to the long running debate, which has lasted for 20 years, on the photo emission mechanisms of the nanostructured silicon. This achievement requires the surface passivation with organic monolayers. Next we show some chemical techniques for surface functionalization of the nanoparitcles. Well-designed surfaces with organic monolayers creates the opportunity (i) to control the radiative recombination of photoexcited electrons between the ground electron and hole states via the increased bandgap in the nanostrucutured silicon, and (ii) to give high affinity for biomolecualr recognition. Furthermore, we demonstrate a nanoscopic observation technique, which enables one to visualize interfacial molecular configuration between organic monolayers and a semiconductor substrate, using high-resolution TEM. The optical use of such luminescent silicon provides the unsurpassed compatibility with current microelectronics, and a high chemical affinity for C, O, and N for covalent linkages, thereby producing a variety of its organic derivatives hybridized at the molecular level in the development of silicon-based soft materials.
6:00 PM - C4.21
Synthesis and Characterization of Copper (I) Chloride (CuCl) Nanocrystals in Conductive Polymer for UV Emitters.
Md. Alam 1 , F. Olabanji Lucas 1 , Stephen Daniels 1 , Patrick J. McNally 1
1 School of Electronic Engineering, Dublin City University, Dublin Ireland
Show AbstractCopper (I) Chloride is an ionic I-VII compound semiconductor material with very low conductivity. To fabricate an efficient electroluminescent device based on CuCl nanocrystals (NC) the conductivity of the CuCl NC film should be high. In order to improve the conductivity of CuCl films, nanocrystals were embedded in a highly conductive polymer (Polyaniline) and deposited on a variety of substrates via the spin-coating method. The deposited films were heated at 140o C for durations between 1 and 12 hours in vacuo. The room temperature UV-Vis absorption spectra for all CuCl films, except the as-deposited film, showed both Z1, 2 and Z3 excitonic absorption features and the absorption intensity increased as the anneal time increased. Room temperature photoluminescence (PL) measurements of all annealed films reveal very intense Z3 excitonic emission. Room temperature X-ray diffraction (XRD) of the as-deposited films gave no evidence of the crystallization of CuCl. However, after annealing the films, XRD confirmed the preferential growth of CuCl nanocrystals whose average size is ≈ 40 nm in the <111> orientation. The resistivity measurement was carried out by four-point probe and the resistivity of the grown film is acceptably low, i.e. ~ 3 Ω-cm. We also report on detailed experimental results on the optical, electrical and structural properties of the CuCl NC film incorporated into a UV electroluminescent device structure.
6:00 PM - C4.22
Preparation of Aluminum Nanoparticles Without Oxide Layer for Rear Electrode of Si Solar Cell.
Hye Moon Lee 1 , Si-Young Choi 1 , Jung-Yeul Yun 1 , Ju-Hyun Kim 1 , Yong-Jin Kim 1
1 , Korea Institute of Materials Science, Changwon, Gyeongnam, Korea (the Republic of)
Show AbstractAn oxide layer on the surface of aluminum particle plays an important role to prevent a whole oxidation of aluminum particle, thus the micrometer scale aluminum particles currently used for rear electrode of Si solar cell have Al2O3 passivation layer with 5-10 nm thickness. However, the oxide layer causes the thermal defects (bowing effect) of the rear electrode because the very high firing temperature is necessary in the electrode preparation. In order to prevent the thermal defect, it is necessary to lower the firing temperature by applying the nanometer scale aluminum particles without oxide layer to the electrode preparation. Thus, we firstly prepared non oxidized aluminum nanoparticles with an organic layer through a polyol process and a subsequent passivation process. For the preparation of aluminum nanoparticles in this study, an aluminum chloride (AlCl3) was used as a precursor to prepare the aluminum nanoparticles; a lithium aluminum hydride (LiAlH4; LAH) as not only a precursor but also a reduction agent; an ethylene glycol as the solvent for reaction of both chemicals; an oleic acid as the organic passivation layer on the surface of aluminum nanoparticles. Crystal structure analysis of the prepared particles was performed using an X-ray diffractometer with CuKa radiation. The morphology of the prepared particles was examined by a high resolution transmission electron microscopy. And the oxidation behavior in terms of thickness of organic passivation layer was investigated by a thermogravimetric analyzer.There was no impurity or contamination in the prepared particles which were polygonal in the size of ~ 200 nm. EDS mapping analysis confirmed that we could avoid any oxidation during the particle preparation. It was firstly shown that the polyol process can also be applicable to the preparation of aluminum nanoparticle without oxide layer. TG analysis for the prepared particles clearly showed that the thickness of oleic acid layer on the particle surface has effects on the prevention of particle oxidation. Finally, when the prepared aluminum nanoparticles were applied to the fabrication of electrode, the electrode firing temperature was achieved to be lower than ~ 700oC and thus any thermal defects were effectively prevented.
6:00 PM - C4.23
High-throughput Near-field Optical Nanoprocessing of Solution Deposited Nanoparticles.
Heng Pan 1 , David Hwang 1 , Seunghwan Ko 1 , Costas Grigoropoulos 1 , Tabitha Clem 2 , Jean Frechet 2 , Dieter Bauerle 3
1 Mechanical Engineering, UC-Berkeley, Berkeley, California, United States, 2 Department of Chemistry, UC-Berkeley, Berkeley, California, United States, 3 Department of Applied Physics, Johannes Kepler University, linz Austria
Show AbstractThe application of nanoscale electrical and biological devices will profit from the development of nanomanufacturing technologies that are high-throughput, low cost and flexible. Utilizing nanomaterials as building blocks and organizing them in a rational way represents an attractive approach towards this goal and has been pursued for the past few years. We report the optical near-field nanoprocessing of nanoparticles for high-throughput nanomanufacturing. The method unitizes fluidically assembled microsphere as near-field focusing lens array for laser assisted nano-sintering or nano-ablation of nanoparticles. Benefit from low processing temperature and reduced thermal diffusion in the nanoparticle film, minimum feature size down to ~150nm can be realized. In addition, we observed that smaller feature (50nm) can be obtained by furnace annealing laser-sintered nanodots at 400°C. Molecular dynamics simulation and thermal modeling are performed to predict nanoparticle film thermal conductivity and processing temperature. Electrical conductivity of sintered nanowire is studied. Using nanowire electrodes with submicron gap, we subsequently fabricate organic field effect transistors (FETs) with oxygen stable semiconducting polymer.
6:00 PM - C4.24
Laser Annealing of Metal Oxide Nanoparticle for Electronics and Photovoltaics.
Heng Pan 1 , Seunghwan Ko 1 , Costas Grigoropoulos 1
1 Mechanical Engineering, UC-Berkeley, Berkeley, California, United States
Show AbstractMetal oxide nanoparticle have been considered promising for realizing low cost printable high performance electronics. It is shown in this paper the application of laser for annealing ZnO, TiO2 and ITO nanoparticle for device fabrication. Solution deposited and laser annealed zinc oxide nanoparticle thin film field effect transistors have been fabricated without using conventional vacuum or any high temperature thermal annealing processes. Laser processing is also demonstrated to fabricate composite TiO2 electrodes for dye-sensitized solar cells (DSSCs) on glass and plastics by in-tandem spray deposition and laser annealing. The produced TiO2 film is crack free and contains small particles (30nm) mixed with different fractions of larger particles (100-200nm) controlled by the applied laser fluence. Laser annealed double-layered structure is demonstrated for both screen-printed and spray-deposited electrodes and performance enhancement can be observed. The highest demonstrated all-laser-annealed cells utilizing Ruthenium dye and liquid electrolyte showed a power conversion efficiency of ~3.8% under simulated illumination of 100mW/cm2. Laser annealing of ITO nanoparticles is also demonstrated for TCO for organic solar cells.
6:00 PM - C4.26
Electrical Performance Enhancement and Characterization of ZnO Thin Film Solar Cell Electrodes by Performing Nanowire Alignment and Nanowire Network Analysis.
Sujay Phadke 1 4 , Jung-Yong Lee 3 , Jack West 2 , Alberto Salleo 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 4 Mechanical Engineering, Stanford University, Stanford, California, United States, 3 Electrical Engineering, Stanford University, Stanford, California, United States, 2 , Sequoia High School, Redwood City, California, United States
Show AbstractZnO is a wide band gap semiconductor with potential to replace ITO as transparent electrode material. Low cost ZnO thin films can be fabricated by depositing ZnO nanowires synthesized using low temperature solution based processes. To improve the conductivity of intrinsic ZnO, it is n-doped with Gallium atoms during synthesis. In order to achieve electrical properties comparable to ITO films, effect of directional alignment of doped ZnO nanowire films on film sheet resistance has been studied. Nanowires are aligned by shearing their dispersion between two silicon wafers using relative motion. Aligned nanowires have a Gaussian angular distribution with a standard deviation of 23 degrees about the direction of shearing. Directional sheet resistances of ZnO films have been measured by performing four point probe measurements. The sheet resistance measured in the direction of alignment is lower than that measured perpendicular to the direction of alignment. Computer simulations performed in conjunction with sheet resistance measurements on aligned films enable us to determine the regimes where sheet resistance is dominated by either inter-wire or intra-wire resistance. Simulations indicate that in our conditions, the sheet resistance of the nanowire film is dominated by inter-wire contact resistance. Further characterization is underway by performing electrochemical impedance spectroscopy on ZnO nanowire mat films to determine the nature of inter-wire contact resistance and to find methods of reducing it in order to lower device sheet resistance.
6:00 PM - C4.27
Large Photo-induced Refractive Index Change in Spin-coated Ge23Sb7S70 Thin Films.
Shanshan Song 1 , Nathan Carlie 2 , Kathleen Richardson 2 , Craig Arnold 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Advanced Materials Research Laboratory, Clemson University, Anderson, South Carolina, United States
Show AbstractChalcogenide glasses are important low-loss mid-infrared materials, and exhibit a wide range of photo-induced phenomena and optical nonlinearities. In particular, Ge-Sb-S films have drawn attention for their photo-induced volume expansion and negative index change, high nonlinear optical properties, and compositional dependencies of various optical and structural properties. In this study, we demonstrate the preparation of Ge23Sb7S70 (GSS) chalcogenide thin films by spin-coating techniques that exhibit a large refractive index change of up to -18% upon visible light exposure. GSS solutions are prepared by grinding bulk material into a fine powder and dissolving into propylamine with an optimized glass to solvent ratio of 0.05g/1mL. Thin films are spin-coated at a spin speed ranging from 1000 to 3000 rpm and then heat-treated in nitrogen environment. The films are found to have a composition and refractive index similar to the bulk glass, and a surface roughness around 5 nm. Photo-modification of spin-coated thin films is conducted using a broadband halogen lamp with intensity from 5 to 80 mW/cm2 with the resulting index changes measured by ellipsometry. The kinetics of this index change is studied by analyzing the index change as a function of irradiation dose and light intensity. Based on our studies, we propose the mechanism for the large photo-induced index change as being caused by photo-oxidation. This hypothesis is confirmed by optical characterization and by controlling the oxygen content during photo-processing. Furthermore, we confirm that there is no degradation of transmittance in the infrared associated with the photo-oxidation, which makes spin-coated GSS films good candidates for infrared photonic devices and device tuning.
6:00 PM - C4.28
Low Temperature Growth of Ga Doped ZnO Nanorods on p-GaN and their Light Emitting Diode Applications.
Le Quang 1 , Swee Kuan Lim 1 , Soo Jin Chua 1
1 , IMRE-Singapore, Singapore Singapore
Show AbstractThe solid state lightning holds the promise of a more energy efficient, long lasting, more compact and lower maintenance substitute for today’s incandescent and fluorescent light sources. Zinc oxide (ZnO) is a great potential material for blue to ultraviolet light emitting devices because of its wide bandgap (3.37eV) and large exciton binding energy (60meV). It has been known that p type doping in ZnO is difficult to achieve. As a result, growing n type ZnO on p type GaN was chosen to utilize these novel properties of the ZnO materials and also integrate with nitride devices. Here, we report an aqueous solution method to grow vertical Gallium doped ZnO nanorods on p type GaN film at the temperature as low as 900C. From the Scanning Electron Microscopy (SEM) results , all of the gallium doped ZnO nanorods are straight and perpendicular to the GaN surface with a high uniformity across the entire substrate , indicating that this technique can be scale up for large area production. The X-Ray diffraction (XRD) 2 theta scans of the Ga doped ZnO/p-GaN specimens corresponding to the (000l) reflection family of ZnO and GaN indicate that the Ga doped ZnO rods were grown with c-axis preferred orientation. The epitaxial nature of the films is confirmed by XRD Φ scans which reveal well-defined peaks with six fold symmetry. This indicate that the thick dense and uniform ZnO nanorods were epitaxially grown on the p-GaN films with an epitaxial relationship of Ga:ZnO [11-20]|| p-GaN [11-20]. The presence of gallium in the doped nanorods was confirmed by X-Ray photoelectron spectroscopy (XPS), showing peaks at binding energies of 1145.45 eV (Ga 3p3/2 ) and 1118.44 eV (Ga3p1/2) . The electrical properties of the Ga doped ZnO nanorods were quantitatively measured by using Hall effect measurement by preparing a film deposited under the similar growth conditions. After thermal treatment at 600oC in nitrogen ambient, a carrier concentration of 10^20 cm-3 (and carrier mobility of 28 cm2/Vs) can be achieved. We also demonstrated the blue electroluminescence from the Ga doped ZnO nanorods/p-GaN hybrid heterojunction LED devices. This blue light emission is strong enough to be seen by the naked eye. The emission light became visible to the naked eye when the bias voltage exceed ~15V and then increase rapidly with the forward bias. The Ga doped ZnO nanorods/p-GaN heterojunction diode introduced in this study demonstrated that our low cost Ga doped ZnO nanorods with high crystalline and electrical properties has great potential for application in low cost light emitting diodes
6:00 PM - C4.29
Synthesis, Self-assembly, and Photovoltaic Properties of PbSe/TiO2 and PbS/TiO2 Heterostructured Nanocrystals.
Mikhail Zamkov 1 , Nishshanka Hewa-Kasakarage 1 , Krishna Acharya 1 , Ian Nemitz 1
1 , Bowling Green State University, Bowling Green , Ohio, United States
Show AbstractWe report on colloidal synthesis and two-dimensional self-assembly of all-inorganic PbS/TiO2 and PbSe/TiO2 heterostructures, comprising small-diameter lead chalcogenide nanocrystals grown directly onto the surface of TiO2 nanorods, nanowires, and nanoparticles via hot-injection routes. A key limitation of light harvesting assemblies utilizing dye-sensitized architecture is a spectrally narrow absorption of organic dyes. The use of semiconductor nanocrystal sensitizers, which absorbance profile can be engineered to closely match the solar spectrum, in lieu of organic complexes is thus particularly encouraging; yet, present day realizations of nanocrystal-based solar cells do not show efficiencies above 3%. This is largely determined by poor carrier transport across organic linkers that bind nanocrystals to oxide surfaces. To address this problem, we have developed a linker-free technique for growing of PbS and PbSe NCs onto TiO2, with NC quality exceeding those fabricated via chemical bath deposition. Fluorescence lifetime measurements demonstrate that PbS/TiO2 and PbSe/TiO2 heterostructures fabricated via hot-injection approach allow for a 50-fold enhancement in the rate of carrier injection between donor and acceptor domains, as compared to organically coupled PbS-TiO2 systems.As an added benefit of colloidal synthesis, the size and shape of lead chalcogenide NCs grown on the surface of TiO2 can be varied by changing the concentration of the primary surfactant in the growth solution. It was found that lightly-ligated nanostructures exhibit an unusual type of self-assembly on a substrate, such that adjacent TiO2 domains merge by forming near-epitaxial layers over a micron size area.
6:00 PM - C4.3
Solution Processed Near-infrared Photodetectors Based on Electron Transfer From PbS Nanocrystals to Fullerene Derivatives.
Krisztina Szendrei 1 , Fabrizio Cordella 1 , Maksym Kovalenko 2 , Michaela Boberl 2 , Gunther Hesser 2 , Maksym Yarema 2 , Dorota Jarzab 1 , Oleksandr Mikhnenko 1 , Agnieszka Gocalinska 3 , Michele Saba 3 , Francesco Quochi 3 , Andrea Mura 3 , Giovanni Bongiovanni 3 , Paul Blom 1 , Maria Loi 1
1 , Zernike Institute for Advanced Materials, Groningen Netherlands, 2 , Institute for Semiconductor and Solid State Physics, Linz Austria, 3 , Dipartimento di Fisica, Cagliari Italy
Show AbstractEfficient and stable photoconducting materials with sensitivity in a broad spectral range are indispensible for both photodetector and solar cell applications. Organic/inorganic hybrid systems composed by colloidal nanocrystals and fullerene derivatives are excellent candidates for both applications due to their elevate stability in ambient conditions, the possibility of an extremely broad and tunable spectral response and cheap processing method.In this work [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and PbS nanocrystals were blended in solution to obtain hybrid thin films with spectral sensitivity covering the visible and near infrared range till 1300 nm. The active layer exploits ultrafast electron transfer from the nanocrystals to the fullerene, as is highlighted by time-resolved photoluminescence and pump-probe measurements.[1]Photodetectors were fabricated by spin coating the hybrid active layer on interdigitated finger-like gold electrodes. These devices showed responsivity up to 0.32 AW-1 and detectivity of 2.5*1010 Jones at 1200 nm.[1]The measured detectivity of the device compares to that of commercial photodetectors sensitive in the near infrared, making our hybrid devices appealing for applications in biology and in night vision systems as cost effective alternative to the actual technology. [1]K. Szendrei et al., Advanced Materials, 21, 683-687, 2009
6:00 PM - C4.4
Microwave Effect of Solution Processed Zinc Oxide Thin Film Transistor.
Tae Hwan Jun 1 , Keunkyu Song 1 , Dongjo Kim 1 , Youngmin Jeong 1 , Kyoohee Woo 1 , Jooho Moon 1
1 , Yonsei University , Seoul Korea (the Republic of)
Show AbstractZinc oxide (ZnO)-based thin film transistors (TFTs) is now receiving significant spotlight as channel layers for applications in air-stable and high performance devices, good transparency. These unique properties led to recent interest in ZnO as a channel material alternative to convectional Si-based materials and organic semiconductors. This enable attractive characteristics of ZnO-based TFTs makes them ideal for the device integration on flexible plastic substrate. If the transparent ZnO is applied to flexible plastic substrates, low temperature processing should be necessary. Here, we report the application of microwave annealing of zinc oxide (ZnO) semiconductor-based thin film transistors (TFTs) that exhibit excellent device performance at low temperatures. Aqueous precursor of zinc hydroxide was prepared by precipitation, purification, and dissolution in NH4OH starting from zinc nitrate salt. ZnO semiconductor layer for thin film transistors was fabricated by spin coating the aqueous precursor. The resulting ZnO films were annealed by microwave oven at different temperatures from 125 - 320oC. The devices annealed by microwave oven showed superior performance as compared to those heat-treated by hot plate. The microwave annealed ZnO-TFTs at 125oC show the unprecedented performance such as the mobility of 1.7 cm2V-1s-1, on/off ratio 107, subthreshold slope 1.0V/dec, and threshold voltage of 10.4 V. We believe microwave is an effective annealing method which allows for better transformation from amorphous hydroxide to well-crystalline metal oxide at lower temperatures. Successful fabrication of a solution-processed ZnO layer reported here is the first step in realizing all-solution-processed transparent flexible transistors with air-stable and reproducible device characteristics.
6:00 PM - C4.5
Surface Polymerized Semiconducting Polymer on Quantum Dots: A Core-shell Heterostructure.
Pradipta Maiti 1 , Manoj Parameswaran 1 , Suresh Valiyaveettil 1
1 Chemistry, National University of Singapore, Saingapore Singapore
Show AbstractThere has been growing research interest in the materials with core-shell heterostructures because of the integrated functionalities of the cores and the shells.The combined properties endow the composites with promising application in the field of FET, OPV, LED and LASER. Because interfaces between polymer and QDs have substantial effect on the electronic interaction, and QD aggregation poses a major problem in preparations of composite materials, physical blending of the components does not produce products with the desired properties. In this presentation, we will discuss the synthesis and characterization of a semiconducting polymer-Quantum Dot-nanocomposite using surface initiated in situ polymerization with the monomer. The semiconducting polymer was observed to grow on the surface of individual Quantum Dots. The study of hole/electron transfer from QD core to ligand shell under light irradiation was investigated.
6:00 PM - C4.6
One-pot Photo-assisted Synthesis of Silver Nanoparticles in a Photopolymerizable Hybrid Sol-gel.
Lavinia Balan 1 , Yannick Lambert 1 , Olivier Soppera 1 , Raphael Schneider 2
1 , Institut de Science des Matériaux de Mulhouse LRC 7228, Mulhouse France, 2 DCPR, , Département de Chimie Physique de Réactions, Nancy France
Show AbstractWe have developed a new photo-assisted in-situ synthesis of Ag nanoparticles in a polymerizable sol-gel matix. Thin films were obtained by spin coating and irradiated in order to photogenerate Ag nanoparticles and initiate the photopolymérisation process. This in situ synthesis was studied in real time by spectroscopic ellipsometry. From ellipsometric measurement, the dielectric function of the composite film was determined and the variation of the nanoparticles radius was studied. A weak oxidation of the particles takes place during the synthesis so that very interesting core-shell particles are generated.These results were confirmed by UV-Visible spectrophotometry, transmission electron microscopy and atomic force microscopy. The characterization of the nanocomposite shows a homogeneous dispersion of the nanoparticles in the hybrid matrix without aggregation. The films exhibit a subnanometer surface roughness.[1] L Balan, M Jin, JP Malval, H Chaumeil, A Defoin, L Vidal Macromolecules 41 2008 9359-9365. [2] L Balan, J-P Malval, R Schneider, D. Le Nouen, D-J Lougnot Polymer 2009 DOI: 10.1016/j.polymer.2009.05.003.
6:00 PM - C4.7
Solution-processed P-channel Thin Film Transistors Using Cupric Oxide and Single-walled Carbon Nanotubes.
Kyung Min Kim 1 , Keun Woo Lee 1 , Kon Yi Heo 1 , Woong Hee Jeong 1 , Hyun Jae Kim 1
1 School of Electrical and Electronic Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractIn this study, we used cupric oxide (CuO)/single-walled carbon nanotubes (SWNTs) as an active channel of the p-channel thin film transistors (TFTs) by the solution process and low temperature (<300°C). The CuO/SWNTs TFTs were fabricated by the low temperature process below 250°C and showed p-channel behavior. CuO nanoparticles were diluted in isopropyl-alcohol (IPA) at a molar concentration of 0.5 M. The semiconducting SWNTs separated by self-selective separation method via hydroxyl group reaction were mixed to CuO solution. Both CuO and CuO/SWNTs TFTs were behaved as a p-channel transistor. The electrical parameters of CuO TFTs were shown as a saturation field effect mobility of about 0.22 cm2/Vs at a Vds of 5.1 V, the subthreshold swing of 1.59 V/decade, the threshold voltage of -3.64 V and the on to off current ratio of ~4.5×103. Compared to CuO TFTs, those of CuO/SWNTs TFTs were shown as the subthreshold swing of 1.01 V/decade, the threshold voltage of 2.81 V and the on to off current ratio of ~1.58×103. Since the SWNTs in channel provide direct pathways to transport carrier, on-state current was increased approximately from ~10-6 in CuO TFTs to ~10-3 CuO/SWNTs TFTs. The off-state current also increased due to leakage current via SWNTs. We believed that SWNTs played an important role as a carrier transport rod along the channel length in TFTs and their concentration could be optimized.Therefore, we concluded that to improve carrier transport in the channel region of the TFTs, we blended suitable amounts of SWNTs with CuO in solution. We found that the electrical properties of the CuO TFTs could be enhanced by the addition of the SWNTs compared to those of CuO TFTs because SWNTs may provide direct pathways for carriers. Therefore, we concluded that CuO/SWNTs blended active layer provided the possibility of producing higher performance TFTs for the low-temperature p-channel TFTs.
6:00 PM - C4.8
Carbon Foams with Special Electromagnetic Loss Characteristics and Broad Absorbing Band.
Zhigang Fang 1 2 , Chusen Li 2 , Xiaoming Cao 2 , Jinsong Zhang 2
1 , Taizhou University, Taizhou China, 2 , Insitute of Metal Research, Chinese Academy of Science , Shenyang China
Show AbstractCarbon foams with a reticulated macrostructure were prepared by a polymer sponge replication method. The electromagnetic parameters of carbon foams with variable electric conductivity and their corresponding pulverized powders were measured by a resonant cavity perturbation technique at a frequency of 2450MHz. Compared with the same composition pulverized powders, carbon foams have relatively lower dielectric constant but much larger dielectric loss, and more remarkably, carbon foams have an extrinsically magnetic loss while their pulverized powders have no magnetic loss. Such electromagnetic loss characteristics have significant influence on the radar absorbing performance of carbon foams. With lower dielectric constants and the coexistence of dielectric loss and magnetic loss mechanisms, a relatively broad absorbing band performance has been achieved for carbon foams. Specifically, when the carbon foam has an electric conductivity of 0.46S/m, the absorbing values exceeds 7dB almost in the whole measured frequency range of 4-15GHz, while the frequencies range for absorbing values exceeding 8dB are about 7 GHz. It is worthy that the broad absorbing band feature of the carbon foam is obtained without any impedance match design, which indicates the carbon foam have a great possibility of being applied as an effective RAM. The special electromagnetic loss characteristics and prominent radar absorbing properties of carbon foams indicate macrostructure modification is possibly a new and effective way to modulate the electromagnetic properties of RAMs besides the traditional composition variation.
6:00 PM - C4.9
Facile Controlled Synthesis and Spectroscopy of CdS/Se Alloy and (CdS)@(CdSe) Core-Shell Nanotetrapods.
Mee Kim 1 , Sun-Young Park 1 , Du-Jeon Jang 1
1 Chemistry, Seoul National University, Seoul Korea (the Republic of)
Show AbstractNanotetrapods of alloy (CdS)1-x(Se)x and core-shell (CdS)1-x@(CdSe)x have been fabricated facilely in water using ethylenediamine as a solvent-coordinating molecular template, and then their optical properties have been investigated using diverse static and time-resolved spectroscopic methods. The arms of the alloy nanotetrapods have single-crystalline structures of (CdS)1-x(Se)x without showing staking faults while the arms of the core-shell nanotetrapods display polycrystalline shell structures of CdSe. The optical properties of CdS1-xSex, where Se atoms are isolated in the CdS lattice, are very different from those of (CdS)1-x@(CdSe)x, where banded CdSe passivates the CdS core. Compared with pure CdS nanotetrapods, the photoluminescence of CdS0.9Se0.1 shifts to the red by 40 nm whereas that of the (CdS)0.9@(CdSe)0.1 does only by 5 nm. Although the mean luminescence lifetime of alloy (CdS)1-x(Se)x is shorter than that of pure CdS, it is still much longer than that of core-shell (CdS)1-x@(CdSe)x.
Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
David B. Mitzi IBM T. J. Watson Research Center
Patrick J. Smith University of Freiburg
C5: Solution-Processing of PV Materials
Session Chairs
Wednesday AM, April 07, 2010
Room 2006 (Moscone West)
9:30 AM - **C5.1
High-efficiency Low-cost Photovoltaic Modules Based on CIGS Thin Films from Solution Precursors.
Louay Eldada 1 , Peter Hersh 1 , Baosheng Sang 1 , Billy Stanbery 1 , Calvin Curtis 2 , Alexander Miedaner 2 , Susan Habas 2 , Maikel van Hest 2 , David Ginley 2
1 , HelioVolt Corporation, Austin, Texas, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractWe describe the production of photovoltaic modules with high-quality large-grain copper indium gallium selenide (CIGS) thin films obtained with the unique combination of low-cost ink-based precursors and a reactive transfer printing method. The proprietary metal-organic inks contain a variety of soluble Cu-, In- and Ga- multinary selenide materials; they are called metal-organic decomposition (MOD) precursors, as they are designed to decompose into the desired precursors. Reactive transfer is a two-stage process that produces CIGS through the chemical reaction between two separate precursor films, one deposited on the substrate and the other on a printing plate in the first stage. In the second stage, these precursors are rapidly reacted together under pressure in the presence of heat. The use of two independent thin films provides the benefits of independent composition and flexible deposition technique optimization, and eliminates pre-reaction prior to the synthesis of CIGS. In a few minutes, the process produces high quality CIGS films, with large grains on the order of several microns, and preferred crystallographic orientation, as confirmed by compositional and structural analysis by XRF, SIMS, SEM and XRD. Cell efficiencies of 14% and module efficiencies of 12% were achieved using this method. The atmospheric deposition processes include slot die extrusion coating, ultrasonic atomization spraying, pneumatic atomization spraying, inkjet printing, direct writing, and screen printing, and provide low capital equipment cost, low thermal budget, and high throughput.
10:00 AM - C5.2
Solution-based Precursors For Atmospheric Processing Of Photovoltaics.
Susan Habas 1 , Maikel van Hest 1 , Alexander Miedaner 1 , Peter Hersh 1 , Jason Underwood 1 , Calvin Curtis 1 , David Ginley 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractAs solar technologies continue to expand into the commercial sector there becomes an increasing need for flexible, low cost materials deposition techniques. The potential to fabricate a complete solar cell from inorganic solution-based precursors is a tantalizing solution to this problem. The first challenge lies in the development of liquid precursors that can be processed under relatively mild conditions to yield the required materials. Here, we focus on metal organic decomposition (MOD) precursors for the atmospheric pressure deposition of copper indium gallium selenide (CIGS) absorber layers. Vacuum based deposition techniques for CIGS-based photovoltaic devices have yielded some of the highest light conversion efficiencies (~20%), and the application of an alternative approach such as ultrasonic spray deposition of MOD precursors has potential as a versatile, cost-effective method for device fabrication. We will discuss precursor development, thin film deposition by ultrasonic spray technique, phase formation, and characterization of In2Se3, Cu2Se, CIS, and CIGS films. Additionally, the MOD precursor approach has been used to facilitate the application of direct-write methods for printing Ag, Ni, and Cu contacts that exhibit conductivities close to that of bulk. We use a combination of ink jet printing for fully soluble inks as well as aerosol jet printing for nanoparticle-based inks. The development of soluble precursors in combination with atmospheric processing techniques has significant potential towards fully printable photovoltaic devices.
10:15 AM - C5.3
Template-assisted Preparation of Copper Indium Diselenide Nanotubes and Nanowires.
Iris Rauda 1 , Sarah Tolbert 1
1 Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, United States
Show AbstractSolution-processing of inorganic semiconductors provides an avenue for low-cost fabrication of materials for a range of applications. Recently, a method was developed for fabricating quality, crystalline films of metal chalcogenide semiconductors using excess chalcogen to improve the solubility of hydrazinium salts of main group metal chalcogenides in hydrazine. The precursors can be solution-processed and decomposed to metal chalcogenide semiconductors at low temperature and with minimal volume change. We utilize this chemistry to prepare copper-indium-diselenide (CIS) nanotubes and nanowires. Our approach is to incorporate the CIS precursor into a nanoporous alumina template. The nanotubes and nanowires extend the entire 60 μm length of the porous alumina mold. The nanowires exhibit reasonable conductivity suggesting they form a fully interconnected network. The tubes and wires can also be freed from the alumina template, producing isolated nanostructures. This approach offers a new method for producing novel complex CIS nanostructures from solution-based precursors.
10:30 AM - C5.4
Investigation of Cu2ZnSnS4 Thin Films and Powders Prepared from Metal Salts and Thioacetamide.
Achim Fischereder 1 2 , Thomas Rath 1 2 , Wernfried Haas 2 3 , Heinz Amenitsch 4 , Joerg Albering 1 , Dorith Meischler 1 , Sonja Larissegger 1 2 , Michael Edler 1 2 , Ferdinand Hofer 3 , Robert Saf 1 2 , Gregor Trimmel 1 2
1 Institute of Chemistry and Technology of Materials, Graz University of Technology, Graz Austria, 2 Christian Doppler Pilotlaboratory for Nanocomposite Solar Cells, Graz University of Technology, Graz Austria, 3 Institute for Electron Microscopy and Fine Structure Research, Graz University of Technology, Graz Austria, 4 Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz Austria
Show AbstractCopper zinc tin sulfide (Cu2ZnSnS4, CZTS) is a very promising alternative as solar absorber material to other chalcopyrite-type semiconductors, which are based on Ga or In. It consists of abundant and cheap elements and displays very beneficial properties for photovoltaic applications. CZTS thin films are very often prepared using chemical solution deposition methods, which are typically based on thiourea as sulfur source, however several disadvantages are encountered: multiphase CZTS is formed and impurities remain within the CZTS layer, especially at low temperatures. Particularly melamine and derivatives of it, which are very reactive chemical compounds and can not be removed at temperatures below 350°C, are discussed as major side products. ¶In this contribution we present the preparation of thin films of CZTS from metal salts (CuI, ZnAc2 and SnCl2) and thioacetamide as sulfur source by a solution based precursor method. The influence of different synthesizing temperatures and different amounts of thioacetamide in the precursor solution on obtained CZTS powders and thin films is investigated. The substitution of thiourea with thioacetamide turns out to be very beneficial for the formation of CZTS: The formation of melamine is inhibited and triazine derivatives formed from thioacetamide have very low boiling points (approx. 155°C). Therefore, they can be removed from the CZTS phase at very low temperatures. Detailed X-ray diffraction analysis shows that single phase CZTS with kesterite type structure is formed even at very low temperatures (> 180°C). In addition, the CZTS formation starts already at approx. 105°C, which was determined with time-resolved in situ gracing incident wide angle X-ray scattering (GIWAXS) and gracing incident small angle X-ray scattering (GISAXS) analysis. The obtained thin films exhibit high optical absorption (> 104 cm-1) and an optical band gap between 1.43 and 1.85 eV depending on the heat treatment. Synthesized CZTS powders are of copper-poor and zinc-rich nature, which is ideal for the use in photovoltaic applications. Furthermore CZTS thin films prepared by this method are also used as p-type absorber material for solar cells.
10:45 AM - C5.5
`Green’ Solid-state Grätzel Solar Cells: Charge Transport and Photovoltaic Properties.
Gopala Krishna 1 , Jean-Christophe Bolsee 1 , Abay Dinku 1 , Mikhail Parchine 3 , Jan D’Haen 1 , Bert Conings 1 , Jean Manca 1 2
1 IMO, Hassselt University, Diepenbeek Belgium, 3 , XIOS University College, Diepenbeek Belgium, 2 IMEC-IMOMEC, vzw, Hasselt University, Diepenbeek Belgium
Show AbstractWater soluble polythiophene polymers are extremely promising towards the environmental friendly processing of hybrid organic/inorganic solar cells, also termed as solid-state Grätzel cells, and therefore towards true ‘green’ hybrid solar cells. In this contribution of work the solid state polymer/TiO2 nanocrystalline hybrid solar cells, delivered efficiencies up to 0.7% (measured under standard AM 1.5 solar illumination). This achieved efficiency is 5 times higher than the efficiencies achieved so far in the literature [1, 2] from the water soluble polymer hybrid solar cells. We discuss the charge transport and photovoltaic properties of different water soluble polythiophene polymers. The charge transport behavior of the polymers was studied by using Field-Effect Transistor (FET) measurements and Space Charge Limited Current (SCLC) measurements, while the photovoltaic effects were investigated in solid state polymer/TiO2 nanocrystalline hybrid solar cells. These devices were prepared by infiltrating the polymers into a nano-porous TiO2 layer. The four water soluble derivatives of polythiophenes investigated are Poly[3-(potassium-7-heptanoate)thiophene-2,5-diyl](P3PHT7), poly[3-(potassium-4-butanoate)thiophene-2,5-diyl](P3PHT4), Poly[3-(potassium-5-pentanoate)thiophene-2,5diyl](P3PHT5), Poly[3-(potassium-6-hexanoate)thiophene-2,5-diyl](P3PHT6), which are obtained from Rieke Metals, Inc. From the FET-mobility measurements, hole mobility values have been obtained for the water soluble polymers in the range from ~10-7cm2/Vs to ~10-5cm2/Vs, with the highest mobility measured in P3PHT6 (µ = 1.2*10-5 cm2/Vs). Similarly, their SCLC mobility has followed the same trend, with mobility values in the range of ~10-9cm2/Vs to ~10-6cm2/Vs. It is therefore demonstrated that water soluble polythiophene polymers can be used as photo-active and hole conducting layers in solid state Grätzel cells and are a promising road towards the production of environmental friendly and industrially viable hybrid solar cells.[1] Q. Qiao and J. T. McLeskey, Jr., “Water-soluble polythiophene/nanocrystalline TiO2 solar cells”, Applied Physics Letters, Vol. 86, p. 153501, 2005[2] I. Haeldermans, I. Truijen, K. Vandewal, W. Moons, M. K. Van Bael, J. D’Haen,J. V. Manca, J. Mullens, Water based preparation method for ‘green’ solid-state polythiophene solar cells, Thin Solid Films, 516 (2008) 7245.
11:30 AM - **C5.6
CIGS-based Solar Cells Prepared from Electrodeposited Precursor Films.
Raghu Bhattacharya 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractThe CIGS absorbers are being investigated by several techniques including vacuum deposition technology such as physical vapor deposition (PVD) and sputtering, and non-vacuum technologies such as electrodeposition, nano-particles-based deposition, ink-jet printing and electroless deposition. The direct energy gap of CIGS results in a large optical absorption coefficient, which, in turn, permits the use of thin (~1 µm) layers of active material. CIGS solar cells are also known for their long-term stability. Thin-film solar cell devices based on PVD CIGS have demonstrated an efficiency of 19.9%. We also reported 15.4%-efficient Cu-In-Ga-Se-based photovoltaic devices from electrodeposited precursor films where final film composition was adjusted by physical vapor deposition method. The PVD technique is expensive and challenging to scale up because of film nonuniformity and low material utilization. Sputtering techniques are suitable for large-area deposition; however, they require expensive vacuum equipment and sputtering targets. A non-vacuum electrodeposition technique has the potential to prepare large-area uniform precursor films using low-cost source materials and low-cost capital equipment. Therefore, electrodeposition technique is very attractive for growing CIGS layers for photovoltaic applications.At present, we are fabricating CIGS-based solar cells directly from electrodeposited precursor films, eliminating the expensive PVD step. In this meeting we will discuss the electrodeposition mechanism and the device results obtained from the electrodeposited precursor films.This work has been authored by an employee of the Midwest Research Institute under contract number DE-AC36-08GO28308 with the US. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes. Part of this work is supported by ILJIN Copper Foil Co. Ltd., South Korea under a CRADA agreement with NREL.
12:00 PM - C5.7
Photovoltage Improvement in Hybrid Photovoltaic Devices by Engineering Bulk and Interfacial Oxide Properties.
Yun-Ju Lee 1 , Matthew Lloyd 2 , Robert Davis 1 , Paula Provencio 1 , Rohit Prasankumar 3 , James Voigt 1 , Julia Hsu 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 Center for Integrated Nano-Technologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractHybrid metal oxide/conjugated polymer photovoltaic (PV) devices using ZnO as the electron transport layer represent a path toward low cost devices with excellent air stability. However, such devices currently exhibit relatively low performance due in part to the low open-circuit voltage (Voc). Voc values for ZnO-poly(3-hexylthiophene) (P3HT) devices are typically ≤ 0.4 V, and vary among different reports. Here, we demonstrate two mechanisms for Voc improvement in these devices. First, by careful control of the ZnO processing, we demonstrate a direct correlation between donor-acceptor energy level offset and device Voc. For example, alloying of Li in sol-gel ZnO films causes conduction and valence bands to shift toward vacuum by up to 0.2 V, corresponding to a 0.2 V increase in Voc of bilayer Li:ZnO-P3HT devices. Also, decreasing the pyrolysis temperature of ZnO film increases the ZnO Eg by up to 0.1 V due to greater quantum confinement of ZnO domains, corresponding to a 0.1 V increase in Voc in devices. Second, by modifying the interfacial properties between ZnO and P3HT, we show a significant enhancement in Voc primarily caused by an improvement in diode rectification. ZnO surfaces are conformally coated with solution-deposited amorphous TiOx films, which cause a significant improvement in Voc of up to 0.4 V despite minimal changes in the donor-acceptor energy level offset and carrier generation and recombination rates. Instead, diode characterization in the dark suggests that the Voc is strongly correlated with a decrease in the reverse bias current density, i.e. an improvement in diode rectification, in excellent agreement with predictions from the modified ideal diode equation. Thus, using solution processing, we modified the bulk and interfacial properties of the metal oxide acceptor, leading to systematic improvement in open-circuit voltage. This approach may help in performance optimization for hybrid photovoltaic devices.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.
12:15 PM - C5.8
Solution Processed NiO for Hole Collection in Organic Solar Cells.
K. Xerxes Steirer 1 2 , Jordan Chesin 2 , Joseph Berry 2 , Alex Miedaner 2 , Reuben Collins 1 2 , Davis Ginley 2 1 , Dana Olson 2
1 Physics, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Lab, Golden, Colorado, United States
Show AbstractInterface modification is often essential to optimize the electrode properties such as carrier selectivity and ultimately power conversion efficiency in organic photovoltaic devices. We present results from solution processed NiO thin films used as hole transport layers (HTL) to modify transparent indium tin oxide (ITO) contacts in organic solar cells. We also demonstrate surface treatments of these films that allow the as deposited work function to be modified. Spin cast films are tuned to maximize optical transparency on the order of 95%. NiO films on ITO are characterized via AFM and display rms roughness of 2.5 nm similar to that of commercially available ITO. The performance of NiO thin films as an HTL in bulk heterojunction (BHJ) organic solar cells are compared to a prototypical HTL, poly(3,4-ethelyne-dioxythiophene):poly(styrene-sulphonate) (PEDOT:PSS). UV-vis absorption of O2-plasma surface treated NiO films exhibit enhanced interfacial order of thin film poly(3-hexylthiophene) (P3HT) compared to PEDOT:PSS evidenced by enhanced absorption at the 615 nm shoulder. We show that solution processed NiO modified anodes result in lowered series resistance and improved fill factors when compared to similar devices using PEDOT:PSS. Photoconversion efficiency of P3HT:(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 BHJ devices with the NiO layer reaches 4% which is comparable to simultaneously prepared devices utilizing PEDOT:PSS for hole collection. Internal photoconversion efficiency plots of BHJ devices utilizing solution processed NiO HTLs exhibit lower efficiencies for wavelengths shorter than 580 nm relative to PEDOT:PSS based devices. Given the comparable overall efficiency of the two preparation methods, the lower internal conversion efficiency is likely offset by the improved series resistance of the NiO HTL.
12:30 PM - C5.9
Si-based Metal-Insulator-Semiconductor Inversion Layer Solar Cells, via Molecular Self-assembly, Electroless Metal Deposition and Spin-coating of Conducting Polymer Contact.
David Cahen 1 , Rotem HarLavan 1 , Omer Yaffe 1 , Izhar Ron 1 , Igal Levine 1 , Florent Thieblemont 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovoth Israel
Show AbstractMetal-Insulator-Semiconductor solar cells attracted much interest in the past, mainly as a potential route to cheap, yet efficient solar cells. Their fabrication obviates most of the high energy process steps of classical p-n junction cells.We take advantage of current understanding of molecular self-assembly processes, together with modern solution-based processing techniques to fabricate Si-based hybrid inorganic-organic solar cells. This approach could cut cell manufacturing costs even further, while increasing control over the growth, composition and quality of the interfacial insulator layer.To explore the potential of molecular self-assembly for Metal-Insulator-Semiconductor solar cells we use a hybrid organic/inorganic approach with, in this first stage, crystalline Si as the cell's absorber. The ultra-thin insulator is an organic monolayer that self-assembles onto the Si, and the conducting top electrode is either a spin-coated conducting polymer or a porous, semitransparent metal, grown by electro-less deposition on top of the molecular monolayer.We show results with these two solution-based low temperature processes to fabricate:1. an n-Si / organic molecular monolayer / porous Au solar cell.2. an n-Si / organic molecular passivation / PEDOT:PSS solar cell. Cells of type -1- yielded JSC = 3.6 mA/cm2 ,VOC = 0.48 V and FF = 58% under 25 mW/cm2 illumination, but performed badly under stronger illumination, due to insufficient inversion of the Si surface. Cells of type -2- did not have this problem and gave, under 100 mW/cm2 illumination, JSC = 22 mA/cm2,VOC=0.625 V and FF = 50%, after optimizing the Si-substrate doping for high VOC.Our approach allows us to analyze the role of the absorber, the interfacial layer and the metallic top-electrode, and the requirements from these in order to reach full inversion near and at the absorber surface, and to allow good current collection and low contact resistance.This approach, which includes no or minimal (for metal grid on top of the semitransparent metal or polymer top contact) vacuum preparation steps, should be applicable to polycrystalline and amorphous, amorphous absorbers to allow low-cost photovoltaic solar energy conversion.
12:45 PM - C5.10
Spray-coated, Morphologically Controlled Nanostructured Zinc Oxide Films for Thin Film Silicon Photovoltaics.
Saahil Mehra 1 , Mark Greyson Christoforo 2 , Rodrigo Noriega 3 , Evelyn Nguyen 1 , Sujay Phadke 4 , Alberto Salleo 1
1 Materials Science & Engineering, Stanford University, Stanford, California, United States, 2 Electrical Engineering, Stanford University, Stanford, California, United States, 3 Applied Physics, Stanford University, Stanford, California, United States, 4 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractThe development of efficient back reflector light- trapping methods for long wavelength photons (λ > 850 nm) in thin film silicon photovoltaic devices remains a major obstacle to making this technology cost-competitive. We explore the light-diffusing properties of nanostructured zinc oxide films fabricated on glass substrates using a scalable, low-cost pneumatic spray coating process. Synthesis of hexagonal-base zinc oxide nanopyramids with controlled size distributions in the range of 100 and 500 nm diameters is achieved using low-temperature, solution-based decomposition of zinc acetate in organic solvents. Larger, 500 nm-wide nanopyramids are obtained by varying the reaction time as well as increasing the stoichiometric ratio of zinc acetate to oleic acid, an organic surfactant, in a 1-hexadecanol solvent. Pyramidal faces are observed to be rough, “fir-cone” like structures with 25 nm asperities, and entirely solution-processed ZnO nanopyramid films exhibit promising light scattering properties (see D. Knipp et al., Optics Express, in press). We further demonstrate a systematic optimization of spray-coating process variables for nanopyramid film deposition with light diffusing and transparent electrode applications, exhibiting control over film uniformity, thickness, and the resulting optical properties. The effects of nanopyramid size and film annealing temperatures on the light diffusing properties of sprayed films were quantified using diffuse transmission/reflection measurements and SEM. Finally, the effects of Ga-dopant incorporation on nanopyramid morphology and electrical properties were investigated. Further SEM studies show that the incorporation of a Ga-dopant into synthesis results in smoother pyramid surfaces, and nanopyramid dopant levels are characterized using Photothermal Deflection Spectroscopy (PDS). The fabrication requirements for thin film silicon photovoltaics using spray-coating as a high-throughput deposition mechanism are estimated, and we show that solution-processed nanopyramid films are promising materials for transparent top contacts or textured back electrodes for such thin film devices.
C6: Solution-processed Metal Oxide Films
Session Chairs
David Mitzi
Maikel van Hest
Wednesday PM, April 07, 2010
Room 2006 (Moscone West)
2:30 PM - **C6.1
Aqueous Processing of Oxides.
Douglas Keszler 1 , Alan Telecky 1 , Jason Stowers 2
1 Chemistry, Oregon State University, Corvallis, Oregon, United States, 2 , Inpria Corp., Corvallis, Oregon, United States
Show AbstractWe have pioneered the use of simple aqueous precursors for realizing dense, pore-free oxide films exhibiting atomically smooth surfaces. Many of the films have been incorporated into a variety of high-performance electronic and optical devices. The processing methods also enable several new capabilities. In this contribution, film- composition control through ion-exchange reactions and an approach for directly writing single-digit-nm oxide features will be highlighted.
3:00 PM - C6.2
Self-aligned Solution-processed Zinc Tin Oxide Thin-film Transistors with high-k Solution-processed Gate Dielectric.
Chen-Guan Lee 1 , Soumya Dutta 1 , Ananth Dodabalapur 1
1 Microelectronics Research Center, University of Texas at Austin, Austin, Texas, United States
Show Abstract Solution-processed metal-oxide semiconductors are of great interest for low-cost and transparent circuit applications such as radio frequency identification tags (RFIDs), flexible displays and wearable electronics. The advantages of these materials include not only excellent device performance metrics, such as high mobility, high transparency and good stability in atmosphere, but also relatively easy processing and low cost. However, other important features such as small channel lengths in patterned-gate devices and low operating voltage are also important and have not been adequately investigated yet. This is particularly the case for devices based on solution processable materials. In this study, the zinc tin oxide (ZTO) thin-film transistors (TFTs) were fabricated on a glass substrate with sol-gel based methods for both the ZTO semiconductor and the high-k gate dielectric, zirconium oxide (ZrO2). In the device configuration, the source and drain (S/D) are self-aligned to the patterned gate to minimize parasitic capacitance. The maximum temperature required in this fabrication process is 500 °C. Devices with recessed and non-recessed gate geometries have been studied to determine the influence of the gate surface relief on the performance of the solution-processed thin films. Results show improved performance for devices with recessed gate geometry (see table below). These recessed-gate devices with channel length L = 7 µm exhibit n-channel characteristics with good mobility (2.2 cm2/V.s), low operating voltage (5 V), high on/off ratio (>106) and low sub-threshold slope (0.23 V/decade). Results for unpatterned gate, short channel devices (L = 7 µm, mobility = 4.3 cm2/V.s), and unpatterned gate, large channel devices (L=50 µm, mobility = 7 cm2/V.s) fabricated with shadow mask are also shown in the table. Higher mobility (~10 cm2/V.s) is also observed with elevated annealing temperature (600 °C). Our simulations indicate that such device can be used to realize flexible operational amplifier circuits with performance characteristics similar to those of the 741 OP Amp.
3:15 PM - C6.3
TFT’s and Circuits with Spincoatable Metaloxide Semiconductor.
Soeren Steudel 1 , Duy-Vu Pham 2 , Heiko Thiem 2 , Kris Myny 1 , Maarten Maarten Rockele 1 , Bas van der Putten 3 , Jan Genoe 1 , Paul Heremans 1
1 Large Area Electronics, IMEC, Leuven Belgium, 2 , Evonik Degussa GmbH, Marl Germany, 3 , TNO, Eindhoven Netherlands
Show AbstractTransistors and circuits using organic semiconductor have received considerable attention in the last few years and have progressed to a stage of maturity where we as well as a few other groups have shown large scale circuits with more than 1000 transistors on foil realizing complex systems like radio-frequency identification tags. However, a big drawback of organic thin film transistors (TFT) has been the limited environmental stability which is even made more problematic in n-type organic semiconductors which are needed for a true complementary logic (CMOS).Using a new solution processable metal oxide formulation developed by Evonik Industries we realized TFTs and circuits at temperatures compatible with polymide substrates. The processflow uses a bottom gate with 100nm Al2O3 as a dielectric and a channel-length of 3um. All process steps are done in air. We achieved mobilities exceeding 1cm2/Vs with very high uniformity over a whole 6"wafer. This excellent uniformity allows us to demonstrate larger circuits, like 19-stage ringoscillator which, at a supply voltage of 20V, have a stage delay below 3us. We furthermore characterize contact resistance, bias stability and compare temperature dependent mobilities of this material system with a similar material system realized by sputtering.
3:30 PM - C6.4
Low Voltage, All Solution Processed Transparent Electronics Using Novel Materials.
Bal Mukund Dhar 1 , Bhola Pal 1 , Laura Veldhius 1 , Howard Katz 1
1 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractTransparent Electronics is a lucrative field where high performance materials and devices can lead to niche applications previously unexplored in traditional semiconductor based technologies. We report low voltage transparent transistors using our recent discovery of a high capacitance dielectric, Sodium Beta Alumina, which otherwise has been known a fast ion conductor in two dimensions. Semiconductors including mixed tin oxides and condensed ring organics were used in making the transistors. Mobilities >10 cm2/Vs wer obtained from the oxides, and turn on voltages were in the range of 1-5 V. We will also present our work on synthesis and characterization on films of novel transparent conducting oxides that are solution processed from abundant precursors, and their use in transparent transistors and other devices. Finally we will discuss strategies to lower the fabrication temperature of such devices and their subsequent fabrication on flexible substrates.
C7: Organic-Inorganic Hybrid/Sol-Gel/Materials
Session Chairs
Wednesday PM, April 07, 2010
Room 2006 (Moscone West)
4:30 PM - C7.1
Thermomechanical Reliability of Transparent Organic/Inorganic (SiO2/MeOx) Hybrid Sol-gel Coatings.
Monika Kuemmel 1 , Reinhold Dauskardt 1
1 Material Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractThin film synthesis via solution processing and deposition gives access to low-cost large-area transparent coatings for a range of applications such as displays, flexible electronics and photovoltaics. A variety of ceramics and organo-ceramics can be obtained by careful choice of precursors, additives and processing conditions; and metal oxides and/or organic functions in the final structure provide the potential for a multitude of tuneable properties in sol gel coatings. However, a critical requirement for the successful application of such coatings involves their adhesive and cohesive properties to underlying substrates, where frequently little quantitative data and understanding exist.In this study, we synthesise selected hybrid sol gel films on substrates such as Si wafers, glass and PMMA and use fracture mechanics-based thin film techniques to quantify their adhesive and cohesive properties. The aim of the study was to elucidate the role of the molecular network on such fracture properties including the specific role of network forming agents, cross linking additives, and the hydrophilic versus hydrophobic nature of the substrate. The precursors studied included a number of bridged silanes and organosilanes with epoxy-groups that allow for crosslinking of the organic part of the hybrid network. TEOS or sources of metals such as Zr, Al, Ti, or Ce are added and the mechanical properties of the resulting films are compared. The metals are used because of their catalytic function in network formation that is important for low processing temperatures, but also because of their inherent properties. Finally, to examine the effects of components added to increase resistance to UV degradation, films containing TiO2 and CeO2 (added as molecular chloride or nitride precursors to the hybrid coating solutions) were studied and we investigate their role on improving the UV stability by measuring the molecular bond rupture kinetics during the propagation of a cohesive crack in the presence of simulated solar conditions.
4:45 PM - C7.2
Hybrid Solution Processed Field Effect Transistors Based on P3HT:ZnO Blends With Air Stable Ambipolar Transport Properties.
Sebastien Nenon 1 , Guillaume Poize 1 , Frederic Fages 1 , Christine Videlot-Ackermann 1 , Joerg Ackermann 1
1 Centre Interdisciplinaire de Nanoscience de Marseille, CINAM UPR-CNRS 3118, CNRS, Marseille France
Show AbstractThe intimate mixing between organic donor and inorganic acceptor nanoparticles into nanoscale phase separated bulk heterojunction (BHJ) represents a promising approach towards air stable organic photovoltaics (OPV). Alternatively to the OPV devices, such hybrid semiconductor nanomaterials have also high potential for ambipolar field effect transistor (FET) applications. Such hybrid-FETs (HFETs) could combine the processibility of organic materials with the high performance and air stability of inorganic nanoparticles. Recently we have demonstrated, that grafting of p-type organic semiconductor monolayers onto zinc oxide nanorods leads to coaxial p-n junction core-shell systems with ambipolar charge transport properties.1In this work we present solution processed HFETs based on blends of poly(3-hexylthiophene) (P3HT) with zinc oxide nanorods and nanospheres. We show for the first time that air stable ambipolar transistors can be obtained with hole and electron mobilities of 3×10-3 cm2/Vs and 7×10-4 cm2/Vs, respectively. Depending on the mass ration between ZnO and P3HT, the charge carier transport in the HFET can be switched from p-type to ambipolar transport. HRTEM and AFM analysis will be presented to correlate the observed transport properties to the nanoscale morphology of the blend. 1: C. Martini, G. Poize, D. Ferry, D. Kanehira, N. Yoshimoto, J. Ackermann, F. Fages, ChemPhysChem 2009, 10, 2465 - 2470
5:00 PM - C7.3
Development of High-throughput Electrospinning With Sol-gel Hybrid Solutions and Its Applications for Sustainable Technologies.
Vasana Maneeratana 1 2 , David Portehault 2 , Clement Sanchez 1 3 , Markus Antonietti 2
1 Laboratoire de Chimie de la Matière Condensée de Paris, Université Pierre et Marie Curie, Paris France, 2 Colloid Chemistry, Max Planck Institute for Colloids and Chemistry, Golm-Potsdam Germany, 3 Laboratoire de Chimie de la Matière Condensée de Paris, CNRS, Paris France
Show AbstractElectrospinning has provided the solution-processing community with a fascinating approach to produce structures comprising of fibers, particulates and their composites. The size of the inherent structures or incorporated features range from a few nanometers up to micrometers. Indeed, electrospinning is a simple, robust process to instantaneously produce hierarchical structures. It is often marked by ease in solution preparation, fiber collection and post treatments. Nonetheless, one of the problems that plagues electrospinning for sustainable technologies is the slow throughput due to the amount of organic polymer content. However, the performance associated with sol-gel hybrids in the field of sustainable applications has afforded a new way of refining electrospinning towards high throughput production. Fibrous structures can be produced at feed rates up to 30 ml/hr through a single spinneret. The latter is an increase of 30 times or more than published literature. Compared to typical electrospinning hybrid solutions, this process relies on a larger concentration of sol-gel precursor. The inherent nature of the sol-gel precursors then undergoes an inorganic polymerization upon exposure to the atmospheric moisture during the electrospining. This phenomenon creates stability for the fiber without requiring a high polymer content to form the stable fiber backbone. Hybrids of titanium sol-gel were made with various polymer additives. The electrospun product yielded a variety of structures in the green and calcined states. Additionally, this production method relies on an approach to minimize processing steps and decrease waste thusly providing a sustainable approach towards producing electrodes, membranes and sensors.
5:15 PM - C7.4
Electrical Reliability of Solgel Barium Titanate Films on Copper Foils for Organic Package Integration.
Shu Xiang 1 , Markondeya Raj Pulugurtha 1 , Manish Kumar 1 , Jin Hwang 1 , Robin Abothu 1 , Rao Tummala 1 , Hiroshi Yamamoto 2
1 , Georgia Tech, Atlanta, Georgia, United States, 2 , NGK/NTK Spark Plug Co., Ltd., 2808 Iwaski,, Komaki-Shi, , Aichi,, Japan
Show AbstractHigh capacitance density thin films are critical for reducing the voltage fluctuation noise to below 50 mV for future GHz processors and power integrity in emerging 3D IC packages. In order to meet the demand for high capacitance density, there is an increasing need for integrating ceramic thin film high-k components in organic packages close to the microprocessor, as opposed to the currently used surface mount discrete components. Sol-gel solution based thin film approach is very attractive for high density capacitors because of its ability to precisely control the composition of the films and ease of introducing dopants to engineer the dielectric properties such as BreakDown Voltages and DC leakage characteristics. Thin films on copper foils lend themselves to organic package integration using standard foil lamination techniques used in package build-up processes. However, fabrication of thin film barium titanate on copper foils is generally affected by process incompatibility during crystallization in reducing atmospheres, leading to oxygen vacancies and copper diffusion through the film. The objective of this project is to characterize the electrical reliability of thin films on copper foils. Ultra thin film (300-400nm) embedded capacitors with capacitance density of 2 uF/cm2, low-loss, low leakage current and high breakdown voltage were fabricated via sol-gel technology and foil lamination. The reliability performance of pure barium titanate is compared with doped barium titanate films using Mn and Y. Dopants lowered the leakage current and also increased the electrical reliability of the films compared to pure barium titanate. TEM analysis of the Cu/BT interfaces showed sharp interfaces with no interfacial reaction products. Doped films passed 24 hr reliability test at 150 C with applied field strength of 100 kV/cm showing the robustness of these films. This technology is hence suitable to meet embedded thin film decoupling applications.
5:30 PM - C7.5
Organic-inorganic Hybrids for Applications in Short-haul Optical Communications.
R. S Ferreira 1 2 , C. Vicente 1 2 3 , L. Xavier 1 2 3 , L. Carlos 1 2 , P. Andre 2 3 , E. Pecoraro 3 , V. Bermudez 4 , P. S Marques 5 , P. Monteiro 6
1 CICECO, University of Aveiro, Aveiro Portugal, 2 Physics, University of Aveiro, Aveiro Portugal, 3 Instituto de Telecomunicações, Univsersity of Aveiro, Aveiro Portugal, 4 Chemistry, University of Trás-os-Montes e Alto Douro, Vila-Real Portugal, 5 Physics, University of Porto/INESC, Porto Portugal, 6 , Nokia Siemens Networks S.A., Lisboa Portugal
Show AbstractIn the last years, the field of photonics has been growing tremendously in popularity and market due to a continuous and global spread of multimedia communications and internet, which can only be accommodated by the huge bandwidth that optical fiber networks can offer. However, there is a great demand for expand the intrinsic capacity and flexibility of optical fiber links, which must be taken until the service subscriber home, through Fiber to The Home (FTTH) solutions [1]. To follow in the footsteps of electronics, photonics must become miniaturized and integrated. Integrated optics (IO) devices can be produced to obtain crucial components, such as waveguide Bragg gratings filters, and passive splitters, to be used in FTTH approach. To keep competitive such IO devices must be produced in large scale and with a low cost.In this context, the fabrication of IO devices using sol-gel derived organic-inorganic hybrid (OIH) materials has been received an increasing amount of attention [2]. Among the various organic-inorganic hosts that have been developed in the last years, those containing amine functionalities, termed di-ureasils, show acceptable transparency, mechanical flexibility and thermal stability [3-5]. The control over the refractive index is achieved by zirconium (IV) n-propoxide (ZPO) doping stabilized with methacrylic acid (MA) [2]. The di-ureasils doped with ZPO have already demonstrated their capacity to be used as IO substrates in the form of low losses planar waveguides [3,4], and passive devices, such as waveguides and Y-power splitters [5] patterned by UV laser direct writing. In this work, di-ureasil doped with different amounts of ZPO (20-60 % mol) will be used as IO substrates for waveguide Bragg grating filters and passive optical couplers. The Bragg grating devices will be produced by imposing a Bragg grating on a buried channel waveguide. The relevant properties of the devices, such as, spectral rejection, central Bragg wavelengths, full half medium width of the filters will be presented.The obtained filters are promising devices for wavelength discrimination purposes on C+L telecommunication bands, with a good range on reflected wavelength tenability.References[1] “Next-Generation FTTH Passive Optical Networks: Research towards unlimited bandwidth access”, Prat J(Ed.), Springer, Netherlands, 2008.[2] Sanchez C, Julian B, Belleville P, Popall MJ (2005) Mater Chem 15:3559 5.[3] Molina C, Moreira PJ, Gonçalves RR, Ferreira RAS, Messaddeq, Y, Ribeiro SJL, Soppera O, Leite AP, Marques PVS, Bermudez VZ, Carlos LD (2005) J Mater Chem 15:3937.[4] Oliveira DC, Macedo AG, Silva NJO, Molina C, Ferreira RAS, André PS, Dahmouche K, de Zea Bermudez V, Messaddeq Y, Ribeiro SJL, Carlos LD (2008) Chem Mater 20:3696.[5] André PS, Vicente CMS, Macedo AG, Ferreira RAS, Pécoraro E, Marques PVS, Alexandre D, Carlos LD, Proceedings of the 14th European Conference on Networks and Optical Communications, 317, 2009.
5:45 PM - C7.6
Solution-based Processing of Chalcogenide Glass Photonic Circuits for the Mid-IR.
Candice Tsay 1 , Claire Gmachl 1 , Craig Arnold 2 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractWidespread, compact, and low-cost chemical sensors based on mid-infrared spectroscopy for detection of greenhouse gases, atmospheric pollutants, and chemical agents have significant applications in environmental and health monitoring and homeland security. State-of-the-art systems are currently lab bench scale and based on expensive free-space optical components. However, the emergence of quantum cascade lasers (QCL) as chip-scale mid-IR emitters is now driving development of miniaturized and integrated mid-IR photonic devices. Here we implement solution-based processes to make photonic circuits based on chalcogenide glass waveguides. As2S3, a chalcogenide glass well suited for mid-IR waveguiding due to its transmittance up to λ =12 µm and high refractive index, is dissolved in propylamine solvent to form a solution suitable for spin-coating, printing, or mold-casting. To form waveguide structures, the As2S3 solution is cast into channel molds patterned by soft lithography. Multi-mode waveguides 40 µm wide by 20 µm high, with measured propagation loss of 9.4 dB cm-1 at λ = 4.8 µm, are fabricated on-chip with a QCL, forming the basis for advanced integrated mid-IR sensing devices. The solution-casting technique enables fabrication of these microns-thick structures, matching the dimensions of the QCL and making alignment and hybrid integration straightforward. We discuss advances in the fabrication of the waveguides, including optimization of the channel molding approach, post-process annealing, and development of embossing and stamping techniques.
C8: Poster Session: Photovoltaics, Solution-Processed Oxides, Sol-Gel
Session Chairs
David Mitzi
Maikel van Hest
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - C8.11
Etching of III-V and CIGS Surfaces by Bromide Solution: Fundamental and Application for Devices.
Arnaud Etcheberry 1 , Alexandre Causier 1 , Isabelle Gerard 1
1 Institut Lavoisier UMR8180, CNRS, Versailles France
Show AbstractThe ability to pattern III-V compound from etching solution is an important challenge for the processing of a lot of semiconductor devices. To perform controlled process it is imperative to understand in detail the key interfacial mechanism that govern the etching process and it eventual side phenomenon. In this topic the association of the knowledge of electrochemical behavior of the semiconductor undergoing the etching and the evolution of the process in a technological process is a very interesting route to improve the process efficiency. To perform this double approach it needs to use both: patterned sample that provide information about hydrodynamic influence, local effect due to mask shadow effect, local accumulation of released products and global consideration about the chemical/electrochemical process that govern the interfacial kinetic. Using this double approach provide very accurate view of the etching process. Our presentation will present results on an universal etching couple Br2/Br- in aqueous solution in front of a famous III-V InP and the extension of our knowledge on this III-V to CIGS which is an important buffer for thin film solar cells. Using the electrochemical tool, the dosage of In traces by SAA, morphological considerations on patterned samples and surface analysis of the chemical composition under etching, we will discuss the key parameter of the etching mechanism provides by this “famous” etching agent. The key parameter of the interfacial chemistry during the etching will be accurately considered with the particular effect of limitation by interfacial film. Detection of this interfacial film will be approach in our multi-technical experimental strategy. We will demonstrate that steady state etching can be proposed with low or high etching rate with final low roughness. The final purpose will be provided by a comparison between the InP and CIGS compounds which shares the common In element. The universal character of this etching solution will be discussed on these supporting examples.
9:00 PM - C8.12
Bias Stress-stable Solution-processed Oxide Thin Film Transistors.
Youngmin Jeong 1 , Changdeuk Bae 1 , Dongjo Kim 1 , Keunkyu Song 1 , Hyunjung Shin 2 , Jooho Moon 1
1 , Yonsei University , Seoul Korea (the Republic of), 2 , Kookmin University, Seoul Korea (the Republic of)
Show AbstractAmorphous oxide semiconductors (AOSs) are a promising active layer for transparent, flexible thin film transistors. (TFTs) Solution processing for the formation of AOS layers is likely a viable alternative to vacuum deposition techniques with respect to processing temperature and cost, as well as having direct-write capabilities, such as in inkjet printing. However, solution-processed AOS TFTs suffer from severe bias-stress instability for device operation due to inherently rich and undefined defect states, thus inhibiting reproducible, reliable performance. Here, we report on the generation of solution-processed gallium tin zinc oxide (GSZO) TFTs that exhibit superior stability against electrical stress during device operation under ambient conditions. We compared GSZO with gallium-free tin-doped ZnO (ZTO) layers, and we suggest that oxygen vacancies and the control of them are a key to producing reproducible AOS channel layers by solution processing. We generated solution-processed AOS TFTs using GSZO layers as the channel. GSZO transistor has good electrical performance similar with ZTO. This device exhibit the saturation mobilities of 1.0 to 1.2 cm−2 V−1 s−1, the on/off current ratios of ~106 and the subthreshold slope of 1.5 V dec-1 and threshold gate voltage was positive (Vth = 3V). Importantly, these AOS TFTs had excellent bias-stress stability during device operation under ambient conditions. The cause of the bias-stress stability was investigated by comparing GSZO and ZTO layers. The creation and quantity of oxygen vacancies generated from the addition of Ga ions were probed with concrete spectroscopic results. By photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we observed a general trend toward suppression of oxygen-related defects upon the addition of Ga. Electron paramagnetic resonance (EPR) of both the GSZO and ZTO layers allowed us to quantify the oxygen vacancies. Due to the reproducible TFT characteristics, the strategy presented here will enable the development of solution-processable high-performance electronic devices for transparent, flexible substrates.
9:00 PM - C8.13
Characteristics of ZnO Films Deposited on Poly 3C-SiC Buffer Layer by Sol-gel.
Duy-Thach Phan 1 , Gwiy Chung 1
1 School of Electrical Enginnering, University of Ulsan, Ulsan Korea (the Republic of)
Show AbstractZinc Oxide (ZnO) is a II-VI compound semiconductor with a wide direct band gap of 3.3 eV at room temperature. Recently, the fabrication of ZnO films as transparent conductors has attracted a considerable interest. The ZnO find application in solar cells, surface acoustic devices, optical waveguides, gas sensors, piezoelectric transducers and varistors. Several techniques have been used for the preparation of ZnO thin films such as sputtering, reactive evaporation, chemical vapor deposition, spray pyrolysis and sol-gel technique. The sol-gel technique has distinct advantages over the other technique due to excellent compositional control, homogeneity on the molecular level due to the mixing of liquid precursors, and lower crystallization temperature. When ZnO film is deposited on a Si substrate, differences of the lattice mismatch (15%) is quite large, which can deteriorate the properties of ZnO thin films. In order to reduce the degradation of ZnO films, 3C-SiC films have been used as a buffer layer because the lattice mismatch (5%) is considerably lower. 3C-SiC is also a wide band gap material and has high heat conductivity, thermal stability, and chemical inertness. Moreover, owing to its excellent mechanical properties, especially high Young’s modulus, the 3C-SiC thin films are applied as membranes in M/NEMS applications. This paper describe the effect of 3C-SiC buffer layer on the properties of ZnO films grown on Si substrates.In this work, poly 3C-SiC thin films were grown on the oxidized Si(100) substrate by CVD. ZnO thin films were deposited on the poly 3C-SiC buffer layer by using sol-gel technique. The deposited films were subsequently annealed at 600 C for 1 h in N2 : H2 (90 : 10). Characteristics of the grown ZnO film were investigated experimentally by means of SEM, XRD, FT-IR and PL. The bonding structure wave number of Zn and O showed up in 410 cm-1 FT-IR. The XRD pattern of thermal annealed ZnO thin films was proved that the grown ZnO film on 3C-SiC layers had highly (002) orientation. FWHM of ZnO/Si and ZnO/SiC/Si was 0.4863° and 0.3264°, respectively. The two layers were easily distinguished due to the different structure. ZnO thin films with 250 nm thicknesses were grown perpendicular to the surface, but round poly 3C-SiC grains were stacked on each other by FE-SEM. The photoluminescence spectra of ZnO thin films at room temperature. PL shows the band gap (3.2 eV) of ZnO/Si and ZnO/SiC/Si. These results showed that ZnO thin film grown on 3C-SiC buffer layers can be used for various piezoelectric fields and M/NEMS applications.
9:00 PM - C8.14
Wet Chemical Synthesis of Transparent Colloidal Solution of YVO4:Bi3+,Eu3+ Nanophosphor.
Satoru Takeshita 1 , Hiroko Ogata 1 , Tetsuhiko Isobe 1 , Tomohiro Sawayama 2 , Seiji Niikura 2
1 Department of Applied Chemistry, Keio University, Yokohama Japan, 2 , SINLOIHI Co., Ltd., Kamakura Japan
Show AbstractYVO4:Bi3+,Eu3+ emits red under the excitation of near-UV light through the charge transfer transition from Bi3+ to V5+, followed by the energy transfer to Eu3+. Here we report a low-temperature wet chemical synthesis of transparent aqueous colloidal solution of YVO4:Bi3+,Eu3+ nanophosphor. We also discuss the crystallization process of the nanophosphor and the relation between the concentration of citrate ions and the transparency of the colloidal solution of the nanophosphor.An aqueous solution of (Y,Eu)(NO3)3 and an ethylene glycol solution of Bi(NO3)3 were added into an aqueous solution of sodium citrate, resulting in a white suspension of citrate precursor. The transparent colloidal solution of the YVO4:Bi3+,Eu3+ nanophosphor was obtained by adding an aqueous solution of Na3VO4 to this suspension, followed by aging at 85 °C. According to the TEM, XRD, and dynamic light scattering analyses, YVO4:Bi3+,Eu3+ spherical nanoparticles of ∼ 20 nm in size crystallize from the gelatinous amorphous precursor during aging. The crystallization completes at the aging time of ∼ 20 min. At the same time, the colloidal solution becomes transparent to naked eyes. This is attributed to a well-dispersion of nanoparticles through electrostatic repulsion of carboxyl groups in citrate ions coordinating to metallic ions at surface of nanoparticles, as confirmed by FT-IR.The nominal molar percentage of sodium citrate relative to the sum of metallic ions, Y3+, Bi3+, and Eu3+, affects the particle size and aggregation property of the nanoparticles. Mean primary nanoparticle diameter and mean hydrodynamic size in the aqueous colloidal solution have minimum values, 21 and 36 nm, respectively, for the sample prepared at 50 mol% citrate. As a result, this sample shows the highest transparency. We suggest that these YVO4:Bi3+,Eu3+ nanophosphors could be applied for transparent near-UV to red wavelength convertors in the field of optoelectronics such as the wavelength conversion layer of white LEDs and the spectral convertor of Si-based solar cells.S.T. thanks the JSPS for the doctoral fellowship (DC1).
9:00 PM - C8.16
Investigation of the Formation of CuInS2 Layers Prepared at Moderate Temperatures.
Dorith Meischler 1 , Thomas Rath 1 2 , Achim Fischereder 1 2 , Karin Bartl 1 , Heinz Amenitsch 3 , Gregor Trimmel 1 2 , Franz Stelzer 1 , Robert Saf 1
1 Institute for Chemistry and Technology of Materials, TU Graz, Graz Austria, 2 Christian Doppler Pilotlaboratory for Nanocomposite Solar Cells, TU Graz, Graz Austria, 3 Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz Austria
Show Abstract¶CuInS2 is considered to be an efficient semiconducting material for photovoltaic applications. In this contribution we present the investigation of the formation of copper indium disulfide layers obtained by means of mass spectrometry, time resolved grazing-incidence small and grazing incidence wide angle X-ray scattering (GISAXS and GIWAXS) and scanning electron microscopy (SEM).¶Nanocrystalline CuInS2 films were prepared by spin-coating a solution of the corresponding metal salts and a sulfur source (thiourea) onto a glass/ITO (indium tin oxide) substrate followed by a thermal conversion step. During the annealing step the sulfur source decomposes and the released sulfur-species react with the metal cations to CuInS2.The formation of the inorganic layer was investigated in-situ with a special gracing incidence setup and synchrotron radiation. This experiment showed that CuInS2 (chalcopyrite structure) is formed above 120°C, with a particle size of approximately 10 nm.¶Furthermore the possible formation of melamine (2,4,6-Triamino-1,3,5-triazine)1 in nanocrystalline CuInS2-films, which were prepared at different moderate temperatures, were investigated by means of mass spectrometry. These analyses showed that melamine is formed as major byproduct during the thermal treatment step, due to decomposition of thiourea.¶¶1 M. Krunks, O. Kijatkina, H. Rebane, I. Oja, V. Mikli, A. Mere, Thin Solid Films 403-404 (2002), 71-75
9:00 PM - C8.17
Synthesis and Characterization of Organic-Inorganic Hybrid Aerogel.
Gen Hayase 1 , Kazuyoshi Kanamori 1 , Kazuki Nakanishi 1 , Teiichi Hanada 1
1 Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto Japan
Show Abstract Aerogels have outstanding properties such as high optical transparency (> 90%), large surface areas (~ 1000 m2/g), low refractive indices (< 1.01), high thermal and acoustic insulation abilities, and low dielectric constants. Because of these properties, many applications such as transparent thermal insulator and optical devices are expected. In particular, application to high thermal insulating windows is awaited as one of a solution of the energy issues and global warming. However, aerogels are still far from such applications due to their fragility and have a necessity of the supercritical drying process at high pressure to dry precursory wet gels without collapsing delicate porous structures. There have been a lot of reseach to improve the mechanical properties of aerogels and to obtain aerogels without supercritical drying while maintaining the above-mentioned excellent properties. Hybridization with organic components such as polymers or organoalkoxysilanes is one of the most promising way to improve the mechanical properties. However, hybridization with polymers reduces porosity and that with organoalkoxysilanes reduces transparency in general. We have reported that transparent organic-inorganic hybrid aerogels with improved mechanical properties (such as temporal shrinkage/reexpansion called spring-back) are obtained solely from organoalkoxysilane when the starting compositions and synthetic conditions are adequately controlled. These aerogels are mede from methyltrimethoxysilane (MTMS) as precursor and surfactant cetyltrimethylammonium chloride (CTAC) which is added to control phese separation, by a modified acid/base two-step sol-gel reaction utilizing acetic acid and urea as catalysts. In this study, we investigated the relationship between starting compositions and obtained pore/mechanical properties in detail. Bulk density, visible light transmittance (at 550 nm), compressive mechanical properties such as Young's modulus are investigated. Concentration of CTAC is found to largely affect the properties of aerogels. Too high concentration of CTAC made aerogels weaker and have lower light transmittance because CTAC to some extent hindered the polycondensation of MTMS and lowered the crosslinking density. Conversely, too low concentration of CTAC did not effectively suppress macroscopic phase separation, resulting in the lower light transmittance. Concentrations of acetic acid and urea influence the hydrolysis and polycondensation behaviors, respectively, resulting in changes in crosslinking density and primary particles size. Bulk density, Young's modulus and light transmittance are accordingly changed. Aerogels processed with extended aging in water before supercritical drying show the more enhanced spring-back behaviors presumably because of a smoothed neck structure in-between primary particles developed by an Osdtwaldt ripening-like effect.
9:00 PM - C8.18
Sol-gel Deposited ZrO2 Films Doped with Rare Earth Elements for Printed Electronic Device Applications.
MyungSoo Lee 1 , Chee-Hong An An 1 , Kyung Park 1 , Ju-yun Choi 1 , Hyoungsub Kim 1
1 Sungkyunkwan University, School of Advanced Materials Science and Engineering, Suwon Korea (the Republic of)
Show AbstractThe futuristic nano-electronic device technology will converge into the printed electronics for the low cost, large area, and flexible electronic system applications. Therefore, a development of various functional material components including dielectrics will be inevitably required and the solution-based deposition technique with a low densification temperature may play a key role in the future. Among many functional dielectric materials, metal oxide having a high permittivity is very promising for the application as a gate dielectric in thin film transistor devices.In this presentation, ~ 30 nm-thick ZrO2 films doped with various rare earth elements (Re= Ce, Y, Gd, and Dy) were deposited by using a sol-gel process, and the effect of doping on the dielectric properties and the densification temperatures were investigated. For the preparation of the precursor solution, zirconium (IV) oxynitrate hydrate and various Re-nitrate hexahydrate were used as Zr and dopant solutes, respectively, and 2-methoxyethanol was used as a solvent. The Zr0.9Re0.1O films were deposited on p-Si(100) substrates using a spin-coating method and densified at 400°C for 60 min in an air ambient. The characteristics of the prepared precursor solution were analyzed by using a TGA/DTA measurement, and the microstructural characteristics of the densified films were studied by using a HR-TEM. The electrical properties of Zr0.9Re0.1O films were characterized and compared by C-V/I-V measurements after the fabrication of the MOS capacitor structures via a lift-off process. According to the microstructural and electrical analyses, the crystallization/densification temperature was lowered by ~200°C and the leakage current was significantly decreased by doping several rare earth elements, which is beneficial for the printed electronic application.
9:00 PM - C8.2
Electrodeposition of CIGS Precursor Layers from Alkaline Electrolytes.
Serdar Aksu 1 , Jiaxiong Wang 1 , Mustafa Pinarbasi 1
1 , SoloPower Inc, San Jose, California, United States
Show AbstractCu(In,Ga)Se2 (CIGS) is one of the most advanced absorber materials for thin film solar cells due to its direct bandgap, high absorption coefficient, and ability to yield good quality devices. CIGS-based solar cells have yielded the highest conversion efficiencies of all thin film solar cells, reaching up to about 20%. One of the techniques used to form CIGS layers is a two-stage approach which involves deposition of a precursor layer on a substrate followed by a high temperature activation step that converts the precursor layer into solar cell grade CIGS. Although various techniques such as evaporation and sputtering have been employed to prepare precursor layers, electrodeposition is especially attractive due to its low cost, efficient utilization of raw materials and scalability to high-volume manufacturing. Most of these studies, however, concentrated on acidic electrolyte compositions. In this study, we present our results on the electrochemical deposition of CIGS from aqueous alkaline electroplating solutions containing complexing agents. The alkaline pH regime was chosen to realize the full potential of complexation. Deprotonated forms of complexing agents become more predominant with increasing pH, allowing formation of more stable soluble metal-complex species. With the selection of appropriate complexing agents, Cu, In and Ga ions could be solubilized at high pH regime and their reduction potentials could be brought down, closer to that of Se reduction potential. Since no complexation occurs between Se and the complexing agents, Se reduction potential could be independently controlled by the amount of dissolved Se. In the formulation of the plating baths, multiple complexing agents with different affinities were used to promote selective complex formation and thereby regulate plating potential of each metal ion separately. We determined ethylenediaminetetraacetic acid, tartrate and citrate as suitable complexing agents for Cu, In and Ga, respectively. By optimizing the concentrations of metal salt, complexing agent, the selenium source, pH and the electrodeposition current density, it was possible to obtain adherent and high quality CIGS films with controllable molar ratios of Cu/(Ga+In) and Ga/(Ga+In).
9:00 PM - C8.20
Urchin-like CdSe Nanotube Structures Prepared via Anion Exchange Reaction in Aqueous Solution for Photovoltaic Devices.
Jeong Won Kim 1 , Hee-Dang Shim 2 , Yong Seok Kim 1 , Woo Hyoung Lee 1 , Hun Soo Jang 1 , Won Bae Kim 1
1 Dept. of Materials Science & Engineering and Program for Integrated Molecular Systems (PIMS), Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of), 2 Research Institute for Solar & Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show AbstractRecently, inorganic semiconductor nanostructures for donor-acceptor heterojunction in inorganic/organic photovoltaic cells are of great interests for effective charge separation from excitons created in conjugated polymers. The constraints on morphology of these inorganic nanostructures as carrier acceptor have driven the research forward making large surface area for higher activity and facilitating charge separation for improved efficiency in the polymer matrix.[1] In order to satisfy these requirements on inorganic morphology, novel types of nanostructures such as hierarchical or hyperbranched ones are suggested and developed through various synthesis methods. In this work, we successfully synthesized inorganic semiconductor of CdSe that has a new architecture of urchin-like nanotubes via a simple anion exchange process from Cd(OH)2 nanowire bundles.[2] During the chemical reaction, the urchin-like CdSe nanotubes grow ultralong up to ## micrometer from the substrate surface with branched arms of 50 nm length in a single crystalline structure. Their microstructure and crystalline properties were analyzed by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). Moreover, UV-visible absorption spectra and photoluminescence (PL) were measured for the photo-electric properties of the chemically-prepared CdSe urchin-like nanotubes. By compositing the CdSe urchin-like nanotubes with the organic semiconductor of P3HT conjugated polymer, the PL quenching takes places effectively and consistently with the degree of composition. Especially, the PL quenching of P3HT:CdSe(1:2) sample shows the best result that is much larger by 70 % comparing with that of pristine P3HT layer.Reference[1] I. Gur, N. A. Fromer, C.-P. Chen, A. G. Kanaras, and A. P. Alivisatos, Nano Lett. 7(2007) 409.[2] H. -S. Shim, V. R. Shinde, and W. B. Kim Chem. Mater. 21(2009) 1875.
9:00 PM - C8.21
Fabrication of ZnO/ZnSe Core/Shell Heterostructures via Chemical Solution Routes for Photovoltaic Applications.
Woo Hyoung Lee 1 , Hee-Sang Shim 2 , Jeong Won Kim 1 , Young Seok Kim 1 , Hun Soo Jang 1 , Won Bae Kim 1
1 Department of Materials Science and Engineering and Program for Integrated Molecular Systems (PIMS), Gwangju Institute of Science and Technology(GIST), Gwangju Korea (the Republic of), 2 Research Institute for Solar & Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show AbstractRecently, various-type of one-dimensional (1-dim) nanomaterials such as nanorods, nanowires, nanotubes and their core/shell nanostructures have attracted much attention in photovoltaic applications due to their unique properties.[1] Among them, core/shell heterostructures have extensively studied because it has exhibited improved electrical and optical properties against their single-component nanostructure. Such structures are expected to offer high absorption efficiency and fast charge transport due to their stepwise energetic combination and large internal surface area. Thus, it has been considered as potential candidates for electrode materials in the advanced photovoltaic devices.In this work, we successfully synthesize 1-dim ZnO/ZnSe core/shell heterostructures via a simple solution process under mild condition. ZnO nanorod arrays were first grown on ZnO seed layer coated on ITO glass substrate. ZnSe shell layer was subsequently formed from the surface of ZnO nanorods through chemical conversion process, leading to the ZnO/ZnSe core/shell structures. The morphology of resulting samples was observed using a field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The semi-quantitative elemental composition was determined from energy dispersive X-ray (EDX) analysis. In addition, their optical properties of synthesized ZnO/ZnSe core/shell heterostructures were measured using UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy and photovoltaic measurement systems.References[1] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353.
9:00 PM - C8.22
Develop Printable Solution Processes for Inorganic and Hybrid Photovoltaics.
Debra Gilbuena 1 , Chih-Hung Chang 1 , Wei Wang 1 , Gregory Herman 1 , Yu-Wei Su 1 , Seung-Yeol Han 1 , Wei-Liang Yen 1 , Wei-Fang Su 2
1 Department of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, Oregon, United States, 2 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractCurrent methods for the production of functional inorganic and organic-inorganic hybrid photovoltaics are based on the sequential deposition, patterning, and etching of selected semiconducting, conducting and insulating materials. These sequential processes generally involve multiple photolithography and vacuum deposition processes, which contribute to their high manufacturing costs. Solution-based and direct printing of materials offer the possibility of depositing high quality thin films at low temperature under atmospheric conditions, and the direct additive patterning processes that enable the fabrication of high-performance and ultra-low-cost electronics. Recently, we have printed a variety of electronic materials including inorganic semiconductors, conductors and organic/inorganic hybrid materials for the fabrication of functional inorganic phtovoltaics and hybrid organic/inorganic nanostructured photovoltaics. In this paper, we will report our understanding of the film formation process and the resulted device performance.
9:00 PM - C8.24
Grain Growth in Solution-processed CdTe Thin Film Solar Cells and Correlation Device Performance.
Lily Yang 1 , Chris France 1 , Jeremy Olson 1 , Anna Bezryadina 1 , Sue Carter 1 , Glenn Alers 1
1 Lily Yang, UC Santa Cruz, Santa Cruz, California, United States
Show AbstractPolycrystalline CdTe is a promising material for thin film solar cells because of its ideal band gap (1.5 eV) and large absorption coefficient (>10^5 cm^-1 at 700nm). Producing CdTe thin films by sintering nanoparticle solutions of CdTe offers the potential to achieving bulk-like electrical properties of vapor-deposited inorganicphotoviltaic films through low cost near-atmospheric processing techniques, similar to organic materials. ITO/CdTe/Al Schottky junction solar cells have been fabricated by spin-casting CdTe nanorod solution on glass slides prepatterned with ITO, sintering the nanoparticle films, then evaporating Al back contacts. Cells with over 5% power conversion efficiency have been achieved. To obtain higher power efficiency, a better understanding of the grain growth of nanoparticle thin films, as mediated by exposure to a CdCl2 at elevated (~400 C) temperatures, is needed. While a similar sintering process are also required for thin films grown by nucleation and growth mechanisms (i.e. vapor phase, spray pyrolysis and/or electrodepostion), colloidal nanoparticle films deposited by surface saturation techniques represents a fundamentally different starting point. In contrast to more standard methods, the nanoparticle CdTe films deposited by spin casting start with a surface roughness of a few nanometers. High-resolution SEM images show that the particles grow from an initial average diameter of a few nm, to 30 nm after a minute of exposure and final diameters of 200 nm (on the order of the film thickness) in optimal devices. The onset temperature for grain growth is 375C. At 400C, the grain growth versus time appears to follow the parabolic growth law with most of the growth happening within the first five minutes. Films not treated with CdCl2 do not show significant grain growth, with final grain sizes remain on the order of 50nm. In addition, we study how the grain growth dynamics depend on film thickness and sintering temperature. Finally, the grain growth is correlated to device performance that show an optimal sintering time of 5 minutes, substantially shorter than sintering times observed in other types of CdTe thin films. The results show that the best device performance correlates to an optimal balance between grain size and shorting along the grain boundaries.
9:00 PM - C8.26
Optimized Adhesive Bonding Using Hybrid Organic-inorganic Sol-gel Films.
Jeffrey Yang 1 , Mark Oliver 1 , Reinhold Dauskardt 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractHigh-performance bonding plays an integral role in the realization and reliability of thin film electronic and photonic devices. Similar bonding requirements exist for thin-foil structural laminates and bulk metallic glass components. Adhesive bonding of these metallic oxide surfaces, such as indium tin oxide (ITO) and SiO2, has traditionally been addressed with the use of adhesion promoting silane molecules. However, these do not always result in high adhesion and are also prone to moisture attack and premature debonding. We describe a remedy to this challenge using hybrid organic-inorganic thin films processed via sol-gel chemistry. These hybrid films can be used to create a molecular network of graded through-thickness composition capable of covalently bonding to both oxide and organic surfaces. Using simple dip-coating techniques, sol-gel coupling films can be applied to metal oxide surfaces to promote adhesion, resulting in the formation of strong adhesive bonds between ITO and high performance epoxy resins. Methods used to characterize adhesive properties and network connectivity of these joints will be discussed. Fracture energy measurements of various oxide systems will be presented along with subcritical debonding behavior in elevated-temperature and moist environments. A correlation between isoelectric point (IEP) and adhesion will be established based on observed trends in fracture energy and network connectivity for various metallic oxides.
9:00 PM - C8.27
Solution Processed Ultra-violet Light Sensing ZnO Thin-film Transistors.
Paul Woebkenberg 1 , Tino Zimmerling 1 , Aneeqa Bashir 1 , George Adamopoulos 1 , Donal Bradley 1 , Thomas Anthopoulos 1
1 Blackett Laboratory EXSS, Imperial College London, London United Kingdom
Show AbstractTransparent metal oxide semiconductors are expected to bear great significance for the development of a range of novel applications in the fields of optical displays and microelectronics. A number of metal oxide systems have also been suggested for use in chemical and optical sensors. A particular point of interest is the strong absorption in the ultra-violet (UV) part of the electromagnetic spectrum by most wide band gap metal oxide semiconductors. UV photo-diodes[1] and light sensing thin-film transistors[2] based on metal oxides have been reported. The latter are expected to yield higher and tuneable sensitivity due to the transistors’ internal amplification. However, several issues remain to be solved. These are in particular the slow relaxation of the photo-induced conductivity increase in the metal oxides after irradiation, as well as the dependence of the effect on ambient conditions. Furthermore, in order to facilitate the implementation of UV light sensors into a wide range of products, simple, low cost fabrication methodologies are preferred. In this work we demonstrate UV light-sensing thin-film transistors based on solution processed films of ZnO that are deposited employing the spray pyrolysis method. This technique demands minimal equipment expenditure and enables us to deposit smooth, high quality ZnO films over large area.[3] The as-deposited thin-film transistors exhibit excellent transport characteristics with electron mobility of the order of 15 cm2/Vs. The current-voltage characteristics of the transistors are strongly modulated by illumination with UV light. Through careful analysis of the shifts in turn-on voltage, subthreshold slope, charge carrier mobility and on/off currents upon illumination we are able to quantify the effect of UV radiation on the carrier concentration in the transistor channel. The dependence of this effect on UV light intensity, duration of illumination and ambient conditions is investigated in detail. In particular, the role of oxygen and water molecules present in the ambient gas during and after illumination with UV light is discussed. Finally, by implementing ultra-thin self-assembled organic gate dielectrics,[4] we demonstrate UV sensing ZnO transistors fabricated using the spray pyrolysis technique, which operate at voltages below 1.5 Volts. These devices are deemed suitable for low power UV sensors based on low cost, facile fabrication methodologies. Hence the results demonstrate the great potential of solution processing metal oxides for use in state-of-the art optoelectronic devices. References [1] Endo et al. Appl. Phys. Lett. 90 (2007) p. 121906.[2] Bae et al. Appl. Phys. Lett. 83 (2003) p. 5313-5315.[3] Anthopoulos et al. Improved oxide-based field-effect transistors. PCT/GB2008/001298. [4] Anthopoulos et al. Low-voltage thin-film field-effect transistors. UK patent application No: 0811962.0.
9:00 PM - C8.29
Study of Ceramic Bufferlayers for Coated Conductor Design.
Klaartje De Buysser 1 , Veerle Cloet 1 , Nigel Van de Velde 1 , Petra Lommens 1 , Isabel Van Driessche 1
1 Inorganic and Physical Chemistry, Ghent University, Ghent Belgium
Show AbstractThe applicability of superconducting materials increases a lot if the material can be shaped as a wire without losing its superconducting properties. This is the main idea behind the concept of coated conductor tapes. A metal tape gives the conductor its desired flexibility while a number of buffer layers are necessary to obtain good superconducting properties. The buffer layers avoid oxidation of the metal surface during heat treatment and enhance the epitaxial growth of the superconducting phase. A classic example of such a coated conductor is NiW tape – CeO2 - La2Zr2O7 - La2Zr2O7 – YBCO. The evaluation of CeO2 and La2Zr2O7 as buffer tapes is described here. The buffer layer architecture is obtained by aqueous sol-gel precursors containing stabilized metal salts in water and are deposited on the metal substrates by the dipcoating technique. The wet coatings are dried to convert them into gels and are transformed by an adapted heat treatment into the desired crystalline phase. The metal tapes used are textured and this epitaxial structure is passed on through the different buffer layers. In a last step, a superconducting layer is deposited on top of the buffered tape by dip-coating, chemical vapor deposition or pulsed laser deposition. The preparation route of thin LZO layers by an aqueous precursor solution is optimized. For good buffer capacity a thicker layer is desired. The influence of viscosity of the precursor solution, dipcoating speed, addition of polymers and doping agents is examined. It can be seen that a thicker LZO induces a decrease in epitaxial growth. CeO2 is a second buffer layer and is deposited on top of homemade or existing LZO coatings. The presently used precursor solution contains citric acid to stabilize the Ce3+ in order to avoid the formation of precipitates which are destroy the homogeneity of the precursor system. At this moment, there is a exploration of new complexing agents with lower carbon content. The interfaces between metal substrate – buffer layers, in between the different buffer layers and the interaction with the superconducting phase are examined by XPS and TEM measurements.
9:00 PM - C8.3
Influence of Annealing Conditions on the Optical and Structural Properties of Spin-coated As2S3 Chalcogenide Glass Thin Films.
Shanshan Song 1 , Janesha Dua 2 , Craig Arnold 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Electrical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractSpin-coating of chalcogenide glass is a low-cost, scalable method to create optical grade thin films, which are ideal for visible and infrared applications. Spin-coating approaches also have the added advantage that the same solutions can be adopted for other precision dispensing techniques such as mold casting, ink jet or laser direct write, giving spatial control of the added material. However, solvent residue from solution-based deposition can introduce complications in optical properties of the thin films. Heat treatment has a major influence on the amount of organic solvent left in the thin films and therefore on the optical and structural properties of the resulting films. It is important to clarify the relationship between annealing conditions and film properties and this information is necessary for stability and optimization of optical parameters. Infrared and UV-visible transmission spectra are used to characterize the optical properties of films subjected to annealing temperatures ranging from 60 to 180 C and durations from 1 hour to 20 hours resulting in differing amounts of residual solvent. Results are correlated with density and thermogravimetric analysis, which provide information about the evolution of amine and other components from as-deposited films. The effects of the solvent molecules on the glass network are discussed by applying the Wemple-DiDomenico (WDD) dispersion model to the measured refractive index data. Evaporation of excess solvent results in a more highly coordinated, denser glass network with higher index and lower absorption. Depending on the annealing temperature and time, index values ranging from n=2.1 to the bulk value (n=2.4) can be obtained, enabling a pathway to materials optimization. For films annealed in the low temperature regime (< 150 C) the evolution of excess solvent enables one to select any desired index with the range of 2.1-2.3 by controlling the duration of the anneal. Above this temperature regime, there is a structural change in the amorphous material associated with the removal of hydrogen from the glass network leading to a film with a higher index (2.3-2.4) that is comparable to bulk As2S3.
9:00 PM - C8.30
Aqueous Sol-gel Processing of YSZ-thin Layers.
Klaartje De Buysser 1 , Petra Lommens 1 , Melis Arin 1 , Kenny Vernieuwe 2 , Isabel Van Driessche 1
1 Inorganic and Physical Chemistry, Ghent University, Ghent Belgium, 2 , University College Ghent, Ghent Belgium
Show AbstractInorganic membranes such as SiO2, Al2O3, TiO2, ZrO2, ... are known for their high mechanical, chemical and thermal stability. They can be used in a large number of applications such as gas sensors, filter membranes, catalyst supports, solid oxide fuel cells, ... In this study, an aqueous precursor solution for 8YSZ is used for the deposition of 8YSZ coatings on alumina and glass substrates. Dense 8YSZ coating can be used as electrolyte in a solid oxide fuel cell whereas porous 8YSZ layers are suitable as thermal barrier coating. The ceramic layers are synthesized by a sol-gel method. Sol-gel precursors are developed in which the stochiometry is preserved at all time and the solutions can be used for a continuous deposition process of these membranes on a chosen substrate. The development of a suitable precursor solution is of utmost importance in order to obtain an nice, homogenous and reproducible coating with the desired parameters such as roughness, porosity, thickness, ... The main drawback of ceramic layers is the high synthesis temperatures necessary to convert the metal salts into the ceramic phase. An attempt is made to lower the synthesis temperature by the development of smart precursors such as reactive reagents or nanoparticles of the desired ceramic phase in an aqueous environment. The influence of organics, pH, temperature, complexants and concentration is investigated. The solutions must be as concentrated as possible to produce dense layers or (with the addition of pore formers) a stable porous morphology.
9:00 PM - C8.4
The Effects of Nanowire Dimensions on the Performance of a Solution-processed Nanowire ZnO/Cu2O Solar Cell.
John Joo 1 , Jacob Richardson 2 , Frederick Lange 2 , Evelyn Hu 1
1 , Harvard University, Cambridge, Massachusetts, United States, 2 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractWe report on the fabrication and characterization of a solar cell created by electrodepositing Cu2O on an array of ZnO nanowires grown in water at 90°C. The bottom up growth of the ZnO nanowire array eliminates the need for templates or lithography, keeping the process simple and inexpensive. Furthermore, the nanowire-based structure provides an opportunity to increase photon absorption without sacrificing carrier collection. We examine the effects of the ZnO nanowire dimensions on the external quantum efficiency and the power efficiency of the solar cell. The maximum EQE is much greater in the nanowire-based solar cells. However unlike the planar solar cells, the maximum EQE value for the nanowire-based solar cells occurs before the onset of ZnO absorption. The wavelength corresponding to this peak in EQE is tunable with the height of the ZnO nanowires. Based on these results, we hypothesize that the cause of the lower EQE at higher energy side of the peak is recombination on the nonpolar planes of the ZnO nanowires. These results demonstrate a pathway towards low cost, high efficiency solar cells.
9:00 PM - C8.5
PLZT Thin Films for Photovoltaic Applications.
Harshan Nampoori 1 , Veronica Rincon 1 , Mengwei Chen 1 , Sushma Kotru 1
1 Department of Electrical and Computer Engineering, University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractThin films of lanthanum doped lead zirconate titatante (PLZT) have gained attention due to the large photostrictive response, and their possible use for contact less actuators and sensors. The variation in composition and doping are known to influence the photostrictive responses as well as ferroelectric behavior of these materials. This material is among the potential materials for photovoltaic devices because of the high electro-optic coefficient and high optical transparency.Thin films of Pb0.97La0.03(Zr0.52Ti0.48)O3 (PLZT) are prepared using Metal-Organic Decomposition technique (MOD). The films are deposited by spin coating. A transparent conduction oxide, ITO is used as the top contact for the PLZT film. The ITO films are grown by pulsed electron deposition technique. Details of the film growth process including temperature and thickness effect coupled with RTA annealing, and characterization will be presented. In addition parameters which affect the electrical properties like ferroelectric hysteresis and leakage behavior will be discussed. Photo voltaic measurements on the ITO/PLZT/Pt stack will be presented.
9:00 PM - C8.6
Structural and Optical Properties of Eu-doped ZnO Thin Films Prepared by Sol-gel Process.
Julien Petersen 1 , Mathieu Gallart 1 , Guy Schmerber 1 , Pierre Gilliot 1 , Silviu Colis 1 , Abdelilah Slaoui 2 , Aziz Dinia 1
1 IPCMS, CNRS-UdS, Strasbourg France, 2 InESS, CNRS-UdS, Strasbourg France
Show AbstractIn this work, we report on the structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique on quartz and Si(100) substrates. Zinc acetate (Zn(COOCH3)2, 2H2O) and europium acetate (Eu, xH2O(COOCH3)) in n-propanol and glycerol respectively were used as precursor. They were stirred at 100°C for 45 min until complete salt dissolution, and then spin-coated on the substrate at 2000 rpm for 5 min. Organic moieties have been removed by heat treatment at 300°C for 10 min. This procedure was repeated three times to obtain a thin ZnO layer with the desired thickness. A last deposition step followed by annealing at 700°C for 10 min yield to a final film thickness of about 180 nm. The X-ray diffraction patterns and transmission electron microscopy analysis showed that the Eu:ZnO films are polycrystalline with the hexagonal wurtzite structure and free of spurious phases. The presence of Eu2+ and Eu3+ into the ZnO matrix has been confirmed by X-ray photoemission spectroscopy. A strong photoluminescence band was observed at 2 eV, most probably caused by the formation of Eu2O3 oxide at the surface of ZnO particles. Such films can be of great interest to solar cells for photon shifting.
9:00 PM - C8.8
Radically- and Thermally-cured High-SiOH Methylvinylsiloxane Polymer Thin Film for Electric Insulator Applications for TFT.
Tadashi Nakano 1 , KiHwan An 1 , SoRa Jung 1
1 , APM, inc., Incheon Korea (the Republic of)
Show AbstractHydrolytically polymerized methyl-co-vinylsiloxane oligomer was cross-linked by dehydrolytically and thermo-radically at an elevated temperature. Similar to vulcanization mechanism of poly(methyl-co-vinyl)silicone rubber, thermal radical generator is found to cross-link the oligomer molecules at the vinyl and methyl pendant groups. In parallel, free silanol (Si-OH) end groups in the oligomer also contributes to thermal cross-linking by dehydrolytic polycondensation. By use of these two cross-linking mechanisms, we were able to deposit highly cross-linked siloxane polymer film out of coating liquid (vanish). Furthermore, optimization of radical generator and dehydration catalyst chemistry, the methyl-co-vinylsiloxane oligomer cross-links at the vinyl-methyl side groups and at the silanol end groups simultaneously in a narrow range of temperature. The coating solution is formulated by partial co-polycondensation of the corresponding silane monomers in the solvent by slow addition of acidic catalyst and water mixture. The molecular weight is controlled by succeeding reflux time. Thermal radical generators were obtained from Hosung Chemex, and amine-based hydrolysis catalyst was synthesized in-house. After adjusting the thickness by diluting with solvent, the film of was coated at 500 nm on various substrates with spin-coating method and cured at 250°C in air. Cured film of 500 nm thickness exhibited pencil hardness of 9H on polycarbonate film with >99% visible light transmittance. These excellent features are applied to optical hard coat for flexible displays and touch panels. The cured film also has superior electric properties. The leakage current of the film is as low as that of CVD dielectric film, and the break down field is more than 3 MV/cm, which is successfully applied to insulators in TFT. The properties of real-working TFT in the LCD device exhibit better, particularly in S-factor and C-V characteristics, than single layer of CVD-SiN film.We carried out analyses of the oligomer film with 13C, and 29Si-NMR, RAMAN and FTIR-ATR methods to investigate curing mechanism how the film acquires much higher hardness and lower leak current than ordinary sol-gel silica or alkylsilane-derived films. The analysis results clearly indicated that the cured film contains Si-(CH)n-Si bonds generated by radical crosslinking, and all Si-OH bonds are consumed by hydrolytic polycondensation as well. The Si-(CH)n-Si bonds are more rigid and less polar than Si-O-Si bond, which are the reasons we consider contributing to the extreme high hardness and less leak current.
9:00 PM - C8.9
Novel Inline Chemical Bath Deposition Process of CdS/ZnS Buffer Layers for Thin Film Solar Cells.
Dirk Ebling 1 , Sabine Sikora-Fries 1 , Christian Peter 2 , Tobias Buergel 2 , Ghassan Barbar 2 , Melanie Schumann 2
1 Thermoelectric and Integrated Sensor Systems, Fraunhofer Institute for Physical Measuremnt Technique, Freiburg Germany, 2 , RENA GmbH, Guetenbach Germany
Show AbstractThe fabrication of thin film solar cells based on copper indium diselenide or copper indium gallium diselenide requires an n-type doped buffer layer, usually a several 10 nm thick layer of CdS. Among the existing deposition techniques the deposition from a chemical bath has become very attractive due to the cheapness of the process.For the production of solar cells the up to now batch like process is a draw back for a cost effective adoption to the fabrication line. Thus, an inline production equipment is highly desirable for chemical bath deposition (CBD) of high efficient buffer layers and absorbers. By such a technique the footprint of the system can be minimized by accordingly increasing the deposition throughput and reducing the chemical bath consumption. A fully automated inline deposition process will be proposed, using standard chemistry with thiourea, cadmium acetate and ammonia at reduced temperatures as a stable electrolytic bath. The process enables pinhole-free layers of a thickness of about 50 nm at a deposition rate of up to 25 nm/min and a uniformity of better than +/- 5%. In this environment a tremendous decrease of the CdS precipitation is obtained within the bath. Also the feasibility was proven for the usage of other buffer layers like ZnS.
Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
David B. Mitzi IBM T. J. Watson Research Center
Patrick J. Smith University of Freiburg
C9: Printing/Patterning of Inorganic Materials I
Session Chairs
Patrick Smith
Maikel van Hest
Thursday AM, April 08, 2010
Room 2006 (Moscone West)
9:30 AM - **C9.1
Patterning of Metallic Nanoparticle and Sol-gel Inks for Flexible Electronic and Photonic Devices.
Jennifer Lewis 1
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractFlexible, stretchable, and spanning microelectrodes that carry signals from one circuit element to another are needed for many emerging forms of electronic and optoelectronic devices. Building on our prior work in direct-write assembly, we have patterned silver microelectrodes by omnidirectional printing of concentrated nanoparticle inks in both uniform and high aspect ratio motifs with minimum widths of ~ 2 μm. These conductive features have been heterogeneously integrated with semiconductor, plastic, and glass substrates. The patterned microelectrodes can withstand repeated bending and stretching to large levels of strain with minimal degradation of their electrical properties. Using this approach, wire bonding to fragile 3D devices and spanning interconnects for solar cell and light emitting diode arrays have also been demonstrated. Recent advances in patterning photonic crystals using concentrated sol-gel inks will also be described.
10:00 AM - C9.2
Nanometer-scale Parallel Patterning of Functional Oxides by Micrometer-scale Soft Lithography Methods.
Johan ten Elshof 1 , Antony George 1 , Sajid Khan 1 , Ole Gobel 1
1 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractThe additive patterning of sub-micrometer sized ceramic structures with arbitrary shape and composition on silicon substrates and other materials is of great interest for very diverse applications such as micro-electromechanical systems (MEMS), gas sensors, and others. Traditional photolithography is often too expensive for envisaged applications. Low-cost, high throughput alternatives for photolithography are the soft lithographic techniques, a family of methodologies for parallel patterning of functional ceramics derived from chemical solution precursors such as nanoparticle dispersions and sol-gels. Soft lithographic methods use a soft elastomeric mold with a relief pattern, typically PDMS, which is brought into conformal contact with a substrate. Depending on the actual technique, the features of the mold guide the formation of a specific high-resolution pattern. The methods that are relevant for patterning ceramics typically rely on confinement within the physical features of the mold to define the pattern on the substrate surface. A well-known example is micromolding, where an elastomeric mold is directly imprinted into a wet film, followed by consolidation of the patterned film. Here the dimensions of the relief patterns of the mold determine the lateral resolution. A post-etch is required to remove residual material between the features. We made lead zirconate titanate Pb(Zr,Ti)O3 line patterns and arrays on silicon oxide with lateral feature sizes down to 100 nm using micromolding. Smaller sizes are well possible.One of the disadvantages of scaling down the dimensions of relief patterns of molds to sub-micrometer sizes is that mechanical deformation of the protruding features becomes more likely. This sets an upper limit to the precision with which features can be replicated and positioned with high fidelity. It is possible to use stiffer, less deformable elastomers for the molds, but these have a negative effect on the adhesion strength between mold and substrate. We propose a different strategy, namely to keep the dimensions of the patterns on the molds in the micrometer-range, while exploiting specific properties of the precursors and substrates, such as the mechanics of the precursor or confinement effects at the surface, to create patterns with lateral resolutions that are much smaller than the features of the mold. The methods we propose are simple and robust and can yield high quality patterns of arbitrary materials of well-defined dimensions. The methods will be demonstrated for both functional oxides and organofunctional silicas.
10:15 AM - C9.3
Collimated Aerosol Beam-direct Write for Solar Cell Metallization Layer.
Justin Hoey 1 2 , Jacob Fink 1 2 , Matt Page 3 , Qi Wang 3 , Iskander Akhatov 2 1 , Douglas Schulz 1 2
1 Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, North Dakota, United States, 2 Mechanical Engineering, North Dakota State University, Fargo, North Dakota, United States, 3 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractOur research team is involved in the development of direct-write technologies toward widespread deployment in areas of market pull. Collimated Aerosol Beam-Direct Write (CAB-DW) is an aerosol-based technique that allows the deposition of materials for flexible electronics. Recent discoveries that led to CAB-DW were the result of a combined theoretical/experimental approach and the technology has the benefit of reproducibly producing linewidths as thin as 5 µm. The non-contact nature of CAB-DW allows the deposition of Si solar cell silver grid metallizations using thinner wafers than screen printing given the reduced risk of wafer breakage. When compared to other non-contact techniques, the ability to print finer features appears to position CAB-DW as superior for this application. As such, increased resolution of CAB-DW allows individual lines to be spaced closer thereby reducing cell series resistance losses in the lateral transport (i.e., transparent conductor) layer. Also, the semi-cylindrical nature of CAB-DW deposited lines and the reflection of such deposits reduces the overall effective shadowing with increased solar cell efficiency. In this talk, we will present our results for the deposition of the silver metallization layer on silicon solar cells using CAB-DW. We shall discuss the effects of decreasing trace width and consider the use of CAB-DW to produce a seed layer on top of which a silver metallization might be electrodeposited.
10:30 AM - C9.4
Laser Direct-write of Metal Nanopastes for Free-standing Interconnects.
Jiwen Wang 1 , Heungsoo Kim 1 , Raymond Auyeung 1 , Nicholas Charipar 1 , Andrew Birnbaum 1 , Alberto Pique 1
1 , Naval Research Laboratory, Washingtong DC, District of Columbia, United States
Show AbstractThe implementation of hybrid structures for large-area, printed electronics relies heavily on the ability to effectively interconnect individual devices or components to each other. However, traditional direct-write printing processes such as inkjet are not well suited for the fabrication of interconnects, in particular when free-standing structures are required for electrical isolation. Applications in organic electronics also drive the need for interconnects that can be implemented on flexible substrates. Laser direct-write (LDW) is a non-lithographic process that can deposit micropatterns of inorganic, organic and composite materials with high spatial and volumetric resolution on a wide array of substrates. In this study, a novel laser direct-write process named laser decal transfer has been applied to the printing of 3D structures at room temperature by assembling volumetric pixels (voxels) with pre-designed geometries without requiring sacrificial layers. Using this approach, silver nanopastes were laser decal transferred to form free-standing interconnects of various lengths (10 - 150 µm), thicknesses (0.7 - 10 µm) and span distances (5 - 100 µm) onto semiconductor, glass and plastic substrates, as well as across dissimilar materials.
10:45 AM - C9.5
Ultra High Resolution, Low Temperature, Direct Metal Patterning by Selective Laser Processing of Solution Deposited Metal Nanoparticles.
Seung Hwan Ko 2 1 , DongYeol Yang 2 , Heng Pan 2 , Jean Frechet 3 , Junyeob Yeo 1 , Tae Woo Lim 1 , Costas Grigoropoulos 2
2 Mechanical Engineering, UC Berkeley, Berkeley, California, United States, 1 Mechanical Engineering, KAIST, Daejon Korea (the Republic of), 3 Chemistry, UC Berkeley, Berkeley, California, United States
Show AbstractAll-printed electronics is the key technology to ultra-low-cost, large-area electronics. As a critical step in this direction, we demonstrate that multi-photon laser processing (sintering and ablation) of solution deposited metal nanoparticles enables direct metal patterning at low-temperature with ultra high resolution (100~200nm) to overcome the resolution limitation of the current inkjet direct writing processes. This could be explained by the combined effects of novel properties of metal nanoparticles such as melting temperature drop, strong absorption of the incident laser beam at surface plasmon mode, lower conductive heat transfer loss, and the relatively weak bonding between nanoparticles. To demonstrate this process combined with the implementation of air-stable carboxylate-functionalized polythiophenes, high-resolution organic transistors were fabricated in ambient pressure and room temperature without utilizing any photolithographic steps or requiring a vacuum deposition process. Local thermal control of the laser sintering process could minimize the heat-affected zone and the thermal damage to the substrate and further enhance the resolution of the process. This local nanoparticle deposition and energy coupling enable an environmentally friendly and cost-effective process as well as a low-temperature manufacturing sequence to realize large-area, flexible electronics on polymer substrates.
11:30 AM - **C9.6
Flow-induced Chain Scission of High Molar Mass Functional Polymers During Ink-jet Printing.
Steve Yeates 1 , Veronica Sanchez-Romaguera 1 , Khalid A-Alamry 1 , Marie Beatrice-Madec 1 , Keith Nixon 1 , Jaroslaw Wasikiewicz 1
1 chemistry, university of manchester, Manchester, Cheshire, United Kingdom
Show AbstractInk-jet printing has developed as an important technology for the defined spatial deposition of polymer solutions in applications as diverse as graphics, textiles, digital electronics and displays. However the addition of polymer to an ink has a strong impact on the nature of the drop generation and ejection process, with the drop break-up behaviour being in part related to the strain hardening resulting from the presence of polymer passing through an elongational flow field (1,2). The microrheological explanation for strain hardening is the sudden transition of the polymer chain from a coiled to a stretched state, which is accompanied by a strong increase of the hydrodynamic drag. The coil-stretch transition occurs for linear polymers at a critical strain rate where the rate of deformation of the chain exceeds its rate of relaxation so that it passes from a slightly distorted random coil to an extended state, The mechanical degradation of polymers in elongational flow fields has long been recognised, which can lead to a reduction in average polymer molecular weight (3,4). The passage through an elongational flow field exerts strong hydrodynamic forces upon a coiled polymer molecule in solution, causing it to stretch, orient and extend in the direction of flow. If the elongational forces on the molecule are sufficiently strong, and the rate of chain stretching far exceeds the rate of chain relaxation, the polymer backbone can be severed. Whilst the precise mechanism of chain scission is not fully understood, the forces acting upon the molecule will be greatest at its centre, which can in turn lead to chain scission near the centre of the chain (5).Here we report the first observation and conditions for the reduction in polymer molecular weight under conditions of inkjet printing for a range of functional polymers which has implications with respect to the printing of functional and biological materials.1.J.de Gens, E.Kazanancioglu, J.D.Meyer, U.S.Schubert, Macromol. Rapid. Commun. 2004, 25, 292.2.D. Xu, V. Sanchez-Romaguera, S. Barbosa, W. Travis, J. de Wit, P. Swan, S.G. Yeates, J. Mater. Chem., 2007, 17, 4902.3.A.J.Muller, J.A.Odell, A.Keller, J.Non-Newtonian Fluid Mech. 1988, 30, 99.4.J.A.Odell, A.Keller, Y.Rabin, J.Chem. Phys. 1988, 88(6), 4022.5.A.J.Muller, J.A.Odell, A.Keller, Polym. Commun., 1989, 30, 297.
12:00 PM - C9.7
Pentacene Thin-film Transistors With PVP/HfLaO Hybrid Gate Dielectric for Low Voltage Operation.
Woo Cheol Shin 1 , Han Ul Moon 1 , Seung Hyup Yoo 1 , Byung Jin Cho 1
1 Department of Electrical Engineering, KAIST, Daejeon Korea (the Republic of)
Show AbstractOrganic thin-film transistors (OTFTs) have been widely investigated for new emerging applications, such as flexible display and radio frequency identification tags. Up to date, however, most of OTFT devices have been demonstrated at a high operation voltage (usually over 20 V) because of thick gate dielectrics when organic dielectric is employed. Reduction of the operation voltage has been a challenge in OTFT because the thickness reduction of the organic dielectric significantly degrades the dielectric quality due to high density of pin holes or defects in organic dielectrics. Recently, some research groups demonstrated low-voltage driven OTFTs (within 10 V) by employing metal oxide high-k gate dielectrics [1-3]. However, the metal oxide high-k dielectrics do not provide good interface with organic channel materials, which may lead to degradation in mobility of OTFTs. In this work, we proposed a hybrid gate dielectric layer consisting of metal oxide high-k dielectric and organic dielectric to improve the quality of the dielectric surface. The hybrid gate dielectric layer was consisted of cross-linked poly-4-vinyl phenol (PVP) and hafnium lanthanum oxide (HfLaO). PVP was deposited by using spin coating method on top of HfLaO which was deposited by atomic layer deposition process. For low voltage operation, we prepared ultrathin PVP (9 nm) by controlling the concentration of the solution. Pentacene as a channel material has been deposited on top of the hybrid gate dielectrics. The OTFT with hybrid gate dielectric showed superior characteristics, especially in terms of gate leakage current and on-off current ratio at the operational voltage of 5 V. Compared to the device with a single HfLaO dielectric layer, the device with the hybrid gate dielectric exhibited higher drain current even though the total EOT (equivalent oxide thickness) is higher. This indicates that the hybrid dielectrics has better interface compatibility with the pentacene channel and thus improved carrier mobility. [1] C. D. Dimitrakopoulos et al., Science, 283, 822, (1999). [2] L. A. Majewski et al., Adv. Funct. Mater., 15, 1017, (2005). [3] M. Kitamura etal., Appl. Phys. Lett. , 89, 223525, (2006).
12:15 PM - C9.8
Ink-jet Printed Cu Nanoparticle Electrodes on Solution-processed Oxide Semiconductor Thin Film Transistors.
Kyoohee Woo 1 , Youngmin Jeong 1 , Dongjo Kim 1 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractThin film transistors (TFTs) based on amorphous oxide semiconductors (AOSs) have attracted considerable attention due to their superior device performance when compared with conventional silicon-based TFTs. For this reason, the metal oxide semiconductor such as ZnO, InZnO and ZnSnO has been extensively developed to apply to active channel in TFTs by both vacuum deposition and solution-processed deposition. However, the understanding of the contact interface between source/drain electrodes and metal oxide semiconductor channel lacks much interest, but although it is essential for the practical application. In this study, we describe the first accommodation of the copper nanoparticle inks as low-cost, printable electrodes in the fabrication of AOS TFTs, and their impact on the resulting device performance. The source/drain copper electrodes in the top-contact configuration are ink-jet printed by using two different inks containing copper nanoparticles capped with PVP of different molecular weights (Mw = 10,000 and 40,000 gmol-1). In addition, TFTs with the printed copper electrodes annealed with different heat-treatment temperatures (200, 300 and 400°C) were fabricated and their characteristics were related to the change of electronic and chemical surface structures.It was observed that the surface chemical structure of the printed electrodes can be modified by varying the molecular weight of PVP and annealing temperature. By this surface modification of copper nanoparticles, interface dipole becomes weak at the copper surface and thus the work function of the printed electrodes decreases. The tunable work function as the capping molecule and annealing temperature is capable to form a better energetic leveling with metal oxide semiconductor layer, so that the energy barrier for electron injection at the metal/semiconductor interface will be lowered and the device performance improved. Therefore, we should carefully design the capping molecule for the metal nanoparticles used as source/drain electrodes of metal oxide semiconductor and the process condition such as the heat-treatment temperatures. Our findings allow us to dramatically reduce the cost for fabricating the electronic devices by enabling to use inexpensive conductive metals such as copper for solution-processed electrodes.
12:30 PM - C9.9
Microstructure and Electrical Property of Inkjet-printed Lines by High Power Source Annealing.
Na-Rae Kim 1 , Ji-Hoon Lee 1 , Seol-Min Lee 1 , Young-Chang Joo 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe interest in future electronics such as high density, flexible, large area devices is increasing significantly. Inkjet printing technology is expected as the best fabrication method, since it is a low cost, atmospheric process, which has no limitation of the substrate type due to its non-contact processing. Nanoparticle based ink is composed of nanoparticles and organic additives, such as solvent, dispersant and binder. Effective decomposition of organic additives is necessary to optimize electrical/mechanical properties which are required for further applications.The need for fabricating fine pitch patterns and thick films is increasing in the inkjet printed films production. In order to obtain thick inkjet films, researches in which high aspect ratio is achieved by filling trench with inkjet printing process are conducted. When the trench is filled by nanoparticles based ink, there are several issues such as crack formation due to volume shrinkage and incomplete decomposition of binder in the bottom part of the films. In conventional furnace annealing with low ramping rate, discontinuous microstructure was obtained in thick films and long time was generally consumed during treatment process. We propose a moving rapid thermal annealing (moving-RTA) which is a novel high power source annealing method as a solution for above issues. Moving-RTA process with high ramping rate and movable heating source (halogen lamp) has potential for effective removal of binder in a short time, roll-to-roll process application and crack prevention by liquid flow. Silver nanoparticles based ink was printed on the substrate by a piezoelectric inkjet printer. Printed nanoparticles ink solidified as the line heating source moved. Inkjet films with simple pad structures were fabricated to investigate the effect of experimental parameters on microstructure of surface/cross-section and related properties. The applied power and moving velocity of heating source were the main parameters that controlled temperature profile of the process. The higher power and the lower moving velocity we applied, the higher peak temperature of profile we observed, and the higher peak temperature resulted in bigger grains and smaller electrical resistance. At 300 W and 2 cm/min., electrical resistivity was 3.10 μΩ-cm which was twice the electrical resistance of bulk silver (1.62 μΩ-cm). This value was quite lower than that in conventional furnace annealing (5.32 μΩ-cm). Also moving RTA was conducted after trenches of the substrate were filled with Ag nanoparticle ink. In the view of electrical property and interfacial adhesion between films and the neighboring materials, we compared moving RTA annealing with conventional furnace annealing. Some particular phenomena in which internal thickness of inkjet printed films varies with initial distance from the lamp will be also discussed.
12:45 PM - C9.10
Single Pass Printing of Femtoliter Droplets.
Jan Sumerel 1
1 , FUJIFILM Dimatix, Santa Clara, California, United States
Show AbstractAfter setting the gold standard for both industrial drop-on-demand inkjet printheads and R&D printers for functional materials printing, we have developed a printhead with the highest jetting frequency ever obtained. Operating at 100 kHz, our MEMS fabricated SAMBA printhead expands the capabilities of fabrication methods for display applications. As an additive process, inkjets are enabling manufacturing processes that are cost effective and less wasteful than many standard subtractive processes. Digital materials deposition with inkjets has transformed the way displays are being built in Gen 8 manufacturing facilities (Annis 2008). FUJIFILM Dimatix piezoelectric drop-on-demand (DOD) inkjets have been integrated into equipment to increase manufacturing capabilities with concomitant reduction in manufacturing costs by increasing precision, reliability and volume control. These tools have demonstrated reliability and productivity in the manufacturing of color filters, PLED displays, organic TFTs, RFID components, touch screen displays and other emerging technologies(Chalamala 2005; Jinwoo Kim 2009). A successful printing system integrates fluids, maintenance, printheads, substrate handling, and processing with existing manufacturing equipment. However, technological breakthroughs for printheads are continuously required to accelerate the development of functional materials printing. Developed by FUJIFILM Dimatix and FUJIFILM Corporation, SAMBA™ printheads increase the speed of single pass printing without having to trade off print width, throughput or quality. In addition, we have developed two new R&D printers to aid industrial and university laboratories in making breakthroughs in materials science for digital fabrication techniques using DOD printing. The DMP 3000 is an ink jet deposition system that is capable of printing a wide range of functional fluids from both experimental cartridge-based printheads with small volumes and high performance printheads appropriate for industrial and higher throughput applications. The Dimatix Experimental Printer (DXP) uses the high performance SAMBA printhead technology and has the accuracy, precision and resolution required for droplet deposition in the femtoliter range.
C10: Printing/Patterning of Inorganic Materials II
Session Chairs
Patrick Smith
Maikel van Hest
Thursday PM, April 08, 2010
Room 2006 (Moscone West)
3:00 PM - **C10.2
Inkjet in Printed Intelligence Research.
Jali Heilmann 1
1 , VTT Technical Research Center of Finland, Otaniemi Finland
Show AbstractInkjet printing is a versatile technology, whose application areas vary from inexpensive desktop printers for home printing to photo-quality wide format printers for graphic arts applications and ultra-high-speed digital printing machines for transactional and book printing. VTT Technical Research Centre of Finland has worked with inkjet technology for more than a decade in the areas of publication and packaging production. Towards the end of last decade, we became interested in developing manufacturing methods based on inkjet. One of our goals in the area has been to develop inkjet printed, mobile phone readable quality indicators. We have also been active in the area of printed electronics and fabricated, for example, a game demonstrator that consists of six ink layers all inkjet printed on paper substrates. VTT has established the Center for Printed Intelligence (CPI) to coordinate and exploit the operative efforts towards our goal - "Global Leading Innovation Center in Roll-to-Roll Printed Intelligence."
3:30 PM - C10.3
Scalable Printing of Silica Nanoparticles.
Sangmoo Jeong 1 , Liangbing Hu 1 , Hye-Ryoung Lee 1 , Yi Cui 1
1 , Stanford University, Stanford, California, United States
Show AbstractTwo- and three-dimensional (2D and 3D) arrays of monodispersed colloidal spheres have been of considerable interest for highly ordered nanostructures. Recently, the 2D and 3D arrays of colloidal spheres were used for photovoltaic solar cells. Two-dimensional hexagonal silica particle arrays were used as a template for textured substrate in order to enhance the light absorption. Three-dimesional structure of semiconductor nanoparticles was used as absorber layer of thin film solar cells. However, the common methods for making 2D and 3D nanoparticle arrays, such as Langmuir-Blodgett technique and spin coating method, have limitation of scalability and they cannot be used for the large scale and high throughput production of solar cells. For this purpose, we applied a wire-wound rod coating method – a well-established coating technique for the manufacture of tapes and flexible packaging – to make 2D and 3D arrays of silica nanoparticles. As the rod is pulled over the colloidal solution on the substrate, the precise amount of solution passes through the groves between the wires. The wet film is formed evenly on the substrate after the rod, and when it evaporates, the monolayer of silica paritlces is fabricated. In additoin, multiple layers of silica particle arrays can be made as the density of collodial solution is increased. The demonstration of this method proves that roll-to-roll processing can be used for enhanment of light absorption of solar cells. We have demonstrated this method on various substrates, including flexible plastics. The whole process and the related solar cell data will be presented.
3:45 PM - C10.4
Ink-jet Printed Nanocrystalline Zinc Oxide Field-effect Transistors.
Norman Mechau 1 , Subho Dasgupta 1 , Jooyoung Lee 2 , Norbert Willenbacher 2 , Horst Hahn 1
1 , Karlsruhe Institute of Technology, Karlsruhe Germany, 2 , Karlsruhe Institute of Technology (KIT) , Karlsruhe Germany
Show AbstractSuspensions of inorganic semiconducting nanoparticles in organic solvents are suitable for fabricating solution-processed field-effect transistors (FETs) at low temperatures. The advantage of semiconducting nanoparticles is that the two main processes such as the nanoparticle synthesis and the film preparation are quite independent. The electrical performance of such printed transistors or devices strongly depends on the nature of materials, the nanoparticle processing during the ink preparation and especially the printing process itself. In this work we present systematically the following: the influence of the transistor performance on the material properties, the type and optimum concentration of the additives to stabilize the nanosuspension, the rheology properties of the stabilized suspensions and the parameters for inkjet printing. We have used ZnO nanoparticles, as a nanocrystalline model system, suspended in an organic solvent and stabilized by polymeric additives. Additives are commonly used to stabilize suspensions of nanoparticles; they reduce the agglomeration tendency and influence the rheology/viscosity of the particle suspensions in addition. It is found that the average size of agglomerates is of large importance and a decrease of the same would improve both the film morphology and the nanoparticle packing significantly. However, the usage of additives notably modifies the electrical characteristics. The additives surround the nanoparticles and act as an additional insulating layer. This would reduce the electrical conductivity and in turn would result in a lowering of the FET performances. Therefore, it can be concluded that the characteristics of printed FETs depend both on the film morphology and the resistivity of the used additives.
4:30 PM - **C10.5
Printing of Functionalities Beyond Color.
Reinhard Baumann 1 2
1 Institute for Print and Media Technology, Chemnitz University of Technology, Chemnitz Germany, 2 Department of Printed Functionalities, Fraunhofer Institution ENAS, Chemnitz Germany
Show AbstractIt is obvious that today’s printing industry deals only with the generation of the functionality color on substrates with typical properties of paper, plastic and metal or compounds of these materials, because today’s printed products generally addresses the visual and haptic senses of humans. Analyzing the future requirements of printed products, for example of being elements of automated supply chains or highly secure medication systems, it is evident that the products made on an industrial print production line have to have more functionalities than just merely color. The inks which provide these functionalities either directly after the printing step or after a subsequent functionality forming step are solutions or dispersions of functional materials in appropriate solvents. Considering the optimization of those inks which will generate in multilayer arrangements the functionalities of Electrical Circuitries, the material scientists are facing a rather narrow window of opportunities to combine the targeted functionality of the printed element and the required rheological process properties of an appropriate ink. In any case the inks have to be optimized for a designated printing technology. The fully printed electronics components (antennae, sensors, logic circuitry, ring oscillators…) can be supplemented by integrating silicon based nano and micro systems, e.g. RFID chips. Thus printed smart objects emerge which may be able to communicate via computer networks either with humans or with other smart objects. In that way the internet of things will be entered by mass wise printed smart objects being, in case of packaging material, the single item content of the big supply chains possessed by the retailer giants. Furthermore the printing technologies can be employed to manufacture electronic components necessary to power-up the electronic circuitry mentioned above or even to manufacture micro sieves from inkjet printed patterns of liquid droplets which can be used as molds for the pores of membranes of lab-on-chip systems.To choose from the existing printing technologies gravure, flexo and inkjet technologies are the favorites to apply functional inks with the required quality onto a variety of flexible substrates. The choice of the fitting printing technology depends on the ink properties and the targeted functionalities. The paper will discuss opportunities, challenges and limitations to manufacture printed smart objects with functionalities beyond color. And these manufacturing details are illustrating the potential of low end electronics becoming a value adding part of printed products.
5:00 PM - C10.6
Ultrasonic Spray Deposition of Nanostructured Metal Oxide Materials for Electrochromic Applications.
Robert Tenent 1 , Erin Whitney 1 , Dane Gillaspie 1 , Anne Dillon 1
1 Chemical and Materials Science, National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractLarge-scale implementation of electrochromic (EC) materials in “smart window” applications depends critically on the development of cost effective, scalable deposition processes. Ultrasonic spray coating at atmospheric pressure represents an excellent route to achieve this goal. A typical inorganic EC device consists of an “active” (coloring) electrode material paired with a counter electrode which can simply serve as a source of cations or ideally also contribute to the colored state. These two layers are separated by an ion conductor (IC) layer which facilitates ion transport between the two electrode materials. Tungsten oxide (WO3), by far the most studied and widely utilized active material to date, colors upon the double-injection of electrons and charge-balancing cations (H+, Li+). Currently, intense focus has been placed on implementing a WO3/IC/NiO device, as NiO allows for a complementary coloring mechanism which leads to a more-efficient and visually appealing EC device.A common issue with inorganic EC devices is limited cycling durability of the constituent materials. Nanostructured metal oxide materials have been shown to dramatically mitigate this issue.1 In this presentation we will discuss our work to develop cost-effective and scalable processes for deposition of nanostructured metal oxide materials for electrochromic applications. Several factors related to the ultrasonic spray deposition process can impact the performance of our materials. Among these factors are substrate temperature, precursor concentration, carrier solvent and other parameters related to solution atomization. Our early work in this area has focused on development of electrode materials using nanostructured tungsten and nickel oxide materials. This work will be presented in addition to more recent work on spray deposition of ion conductor layers. Attempts at full device integration will also be discussed.(1)Lee, S. H.; Deshpande, R.; Parilla, P. A.; Jones, K. M.; To, B.; Mahan, A. H.; Dillon, A. C. Advanced Materials 2006, 18, 763-766.
5:15 PM - C10.7
Direct Writing of ZrO2 and TiO2 Nanostructures by ArF Lithography.
Hassan Ridaoui 1 , Ali Dirani 1 , Fernand Wieder 1 , Olivier Soppera 1
1 , CNRS - IS2M, Mulhouse France
Show AbstractWe achieved the preparation of nanostructures based on negative tone inorganic resists by DUV lithography (193 nm). This entails the preparation of a complex of a transition metal by reaction between the metal alkoxide and a suitable ligand. The reaction was carried out in a solvent. Then, a partial hydrolysis of the complex allowed forming metal-oxides inorganic chains by condensation with good film-forming and photopatterning properties. This step corresponds to the synthesis of multifunctional oligomers that can be crosslinked by DUV irradiation.We obtained well-defined patterns exhibiting low rugosity with width down to 75 nm. An achromatic interferometer based on a ArF excimer laser was used to write the nanostructures. The sensitivity of the resin at 193 nm is in the order of magnitude of organic photoresists used in the microelectronics industry. The photoinduced processes were studied with care in order to state the physico-chemical phenomena occuring upon DUV-irradiation. FTIR, XPS and XRD were used for characterizing the material structure after irradiation and thermal treatment. Nanostructures were studied by AFM.The main interest of this resist is that after irradiation, the material is mainly inorganic. It can even be totally mineralized through a subsequent pyrolysis procedure.The process is compatible with a wide range of chemicals (ZrO2, TiO2, …). Using lithographic route, it is possible to obtain such nanostructures on relatively wide surfaces. With this new process, we are targeting applications in microelectronics, optics, photonics, photocatalysis, photovoltaic…
5:30 PM - C10.8
Ultrasonic Spray Deposition of Amorphous Indium-zinc Oxide Thin Films.
Robert Pasquarelli 1 , Maikel van Hest 2 , Alexander Miedaner 2 , Calvin Curtis 2 , John Perkins 2 , Ryan O'Hayre 1 , David Ginley 2
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTransparent conducting oxide (TCO) thin films play a critical role in many current and emerging opto-electronic devices due to their unique combination of high transparency in the visible region of the spectrum and tunable electronic conductivity. Specifically, amorphous indium-zinc oxide (a-IZO) is a promising material system because of its combination of high conductivity (1000-3000 S/cm) and low deposition temperature (sputtering, T≤100°C). Atmospheric-pressure solution deposition is an attractive alternative to conventional vacuum-based IZO deposition techniques due to its ease and potential to lower device manufacturing costs. Here we report on a-IZO films prepared by ultrasonic spray deposition onto glass substrates from solutions of a novel indium-zinc formate (IZF) precursor and alkoxides. Films were sprayed between 100-210°C from an IZF-HNO3-methanol solution and annealed with a combination of rapid thermal and tube furnace processing under Ar-4%H2. Thin IZO films (<200nm) were produced with good optical transmittance (>80%) and conductivities of ~50 S/cm. Electronic carrier concentrations of the films were consistent with sputtered IZO (~1020/cm3). However, Hall mobility (~1cm2/Vs) is off by at least an order of magnitude compared to sputtered IZO. Electron microscopy revealed that the low mobility was due to porosity and film layering. Sputtered IZO is the most conductive in the amorphous region. X-ray diffraction of the sprayed IZO films showed that the amorphous state was successfully obtained after annealing at 300°C but that some phase separation of In2O3 occurred at 400°C. The structural, optical, and electronic properties of these films, as well as initial results of alkoxide deposited films, will be reported.
5:45 PM - C10.9
Polymer-assisted Deposition to Epitaxial Metal Nitride Thin Films.
Hongmei Luo 1 , G. Zou 2 , E. Bauer 2 , T. Mark McCleskey 2 , A. Burrell 2 , Q. Jia 2
1 Chemical Engineering, New Mexico State University, Las Cruces, New Mexico, United States, 2 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractNitride thin films have found many applications due to their hardness, chemical resistance and unique electronic properties. In particular, their applications in electronic and optoelectronic devices have spurred considerable interest. Several techniques have been reported to grow nitride films, such as physical vapor deposition and chemical vapor deposition, which have the common feature of requiring high vacuum systems. A general chemical solution approach to epitaxial metal nitride films is desirable for many technological applications. Here we demonstrate a polymer-assisted deposition (PAD) to prepare epitaxial hexagonal GaN, cubic TiN, metastable cubic AlN, mixed nitride cubic Ti1-xAlxN, tetragonal ternary nitride SrTiN2, BaZrN2, and BaHfN2 films. It is noted that the single phase epitaxial ternary nitrides were reported for the first time. The procedures to form nitride films by PAD comprise of the following two steps: (1) formation of homogeneous metal polymeric liquid precursors by binding polymer with metal ions; (2) thermolysis and ammonolysis of the coated films in flowing ammonia gas to yield the metal nitride films at desired temperature. The structural, optical, electrical and transport properties of the nitride films are investigated in detail.
C11: Poster Session: Printing, Spraying, Coating
Session Chairs
Patrick Smith
Maikel van Hest
Friday AM, April 09, 2010
Salon Level (Marriott)
9:00 PM - C11.10
Solution-processed Zinc Indium Tin Oxide Hybrid Thin-film Transistors.
Myung-Gil Kim 1 , Hyun Sung Kim 1 , Young-Geun Ha 1 , Mercouri Kanatzidis 1 , Antonio Facchetti 1 , Tobin Marks 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractThe fabrication of thin-film transistors (TFTs) by solution-processing methodologies represents a great opportunity to realize inexpensive electronics and/or enable new device functionalities, such as RFID cards, sensors, and displays fabricated by printing on plastic substrates. We report here that using solution-processed amorphous oxides based on various Zn + In + Sn molar ratios enables TFTs with very high electron mobility (>10 cm2/Vs) and high on/off ratios (>105) in combination with a hybrid gate dielectric under ambient conditions. Furthermore, these TFTs operate at very low voltages (<5V) due to the large gate dielectric capacitance. These results are promising for large area, high speed, low-power applications.
9:00 PM - C11.11
Large-area Parallel Laser Printing of Solution-processed Ag Thin Film Patterns for Electronics.
Myeongkyu Lee 1 , Hyeongjae Lee 1 , Jinsoo Lee 1
1 Dept. of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractWe here report that Ag films solution-deposited on transparent substrate can be printed onto such receiver substrates as glass, Si, and plastics by a spatially-modulated Nd:YAG pulsed laser beam incident from the backside of the source substrate. High-fidelity patterns with a minimum feature size of ~ 10 μm could be fabricated over several square centimeters by a single pulse with energy of 850 mJ. The printed film, followed by annealing at 450oC, exhibited a linear voltage-current relation and the sheet resistance decreased with increasing thickness. Ag films as thick as 1.8 μm could be printed with step-wise edge morphology when they were properly dried prior to printing. A very low sheet resistance of 0.14 Ω/sq was observed for this thickness. The fabrication of organic thin film transistors is demonstrated using the printed source and drain Ag electrodes.
9:00 PM - C11.12
Solution-processed Zinc-Tin Oxide Thin Film Transistor with the Active Channel Layer Patterned by Laser-induced Dynamic Release Process.
Myeongkyu Lee 1 , Hyeonggeun Lee 1
1 Dept. of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractWe here report on the patterning of transparent oxide thin film by laser-induced dynamic release process. This method utilizes a pulsed laser-induced thermo-elastic force exerting on a thin metal layer as the driving force for patterning. Solution-processed zinc-tin oxide (ZTO) patterns at the micrometer scales could be generated using an Al release layer. A thin film transistor (TFT) with the patterned ZTO channel exhibited saturation mobility and on/off ratio similar to the values for a reference TFT fabricated without the channel patterning. This indicates that no deterioration of the material property and device performance occurs by the presented patterning scheme.
9:00 PM - C11.13
Fabrication and Electrical Transport Studies of n-ZnO/p-PEDOT: PSS Inorganic/Organic Hybrid Heterojunction Diode.
E. Senthil Kumar 1 , Mamidanna Rao 1
1 Department of Physics, Nano Functional Matrials Technology Centre, Materials Science research Centre, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show AbstractOxide based novel thin films of homo- and hetero-structures are technologically attractive for future optoelectronic devices because of their exciting optical, electrical, magnetic and piezoelectric properties. Among these, ZnO is ideally suited for blue-ultraviolet (UV) optoelectronics and transparent electronics applications due to its direct and wide band gap (3.35 eV) and its ability to tailor electronic, magnetic and optical properties through doping, alloying and nano engineering. ZnO exhibits intrinsically n-type conductivity and achieving high quality, reproducible p-ZnO with sufficiently high mobility and hole concentration is difficult because of self compensation effects due to its native defects. In an alternate approach, ZnO based heterojunctions have been focused for short wavelength optoelectronics. As a result a number of heterojunctions such as n-ZnO/p-GaN, n-ZnO/p-SiC, n-ZnO/p-AlGaN, n-ZnO/p-NiO, n-ZnO/p-Si and n-ZnO/p-type organic polymer etc. have been fabricated to successfully realize the UV electroluminescence (EL) and photodetection of ZnO. Among these inorganic/organic hybrid heterojunctions are attractive because of cost effectiveness and ease of fabrication. In this work, we report on the fabrication and temperature dependent I-V characteristics of n-ZnO/p-PEDOT: PSS hybrid heterojunctions.n-ZnO/p-PEDOT:PSS, inorganic/organic-polymer, hybrid heterojunction diodes have been fabricated by depositing n-ZnO film by pulsed laser deposition and highly conducting p-PEDOT:PSS, poly (3, 4 ethylenedioxythiophene) doped with poly (styrenesulphonate), by spin coating technique. Pt and Ag are used as an ohmic contact for n-ZnO and p-PEDOT: PSS respectively. Current – voltage (I-V) characteristics of the hybrid heterojunction were measured from 80 K to 300 K. The heterojunction shows very good rectifying characteristics up to 180 K, below which it shows asymmetric characteristics. Rectification ratio of the heterojunction increases from 10 to 60 as the temperature decreases from 300 K to 80 K. The turn-on voltage of the diode increases from 0.9 V to 3.5 V and the reverse leakage current decreases from 0.7 mA to 0.1 mA with decrease in the temperature from 300 K to 80 K. These results will be presented and discussed in detail.
9:00 PM - C11.14
Solution Processing of V2O5-WO3 Composite Films for Enhanced Li-ion Intercalation Properties.
Ying Wang 1 , Chuan Cai 1 , Dongsheng Guan 1
1 Mechanical Engineering, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractWe have employed a simple and novel solution processing method to prepare V2O5-WO3 composite films which demonstrate enhanced Li-ion intercalation properties for applications in lithium-ion batteries or electrochromic displays. First, a stable clear vanadium pentoxide sol is synthesized by dissolving vanadium pentoxide powder in the H2O2 followed by sonication and dispersion of gel into water. Second, a stable clear peroxopolytungstic acid is obtained by dissolving tungstic acid powder in the H2O2 at 60 degreeC. Last, the vanadium pentoxide sol is mixed with peroxopolytungstic acid with different molar ratio to obtain a stable clear solution; V2O5-WO3 films are prepared via drop casting of the mixed solution followed by annealing at high temperature. It should be noted that this solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). For comparison purposes, pure V2O5 and WO3 film are prepared as well. The V2O5-WO3 composite films show enhanced Li-ion intercalation properties compared to pure V2O5 and WO3 films, particularly at high discharge rates. For example, V2O5-WO3 film with molar ratio V2O5/WO3 = 4/1 exhibits a discharge capacity of 51.3 mAh/g while the pristine V2O5 film delivers a discharge capacity of 36.5 mAh/g at a high current density of 1.1 A/g. Such enhanced Li-ion intercalation properties are attributed to the structural change of one oxide caused by the other. Both oxides show weaker crystallinity when they form composite films.
9:00 PM - C11.15
Application of Transfer-printed Hydrophobic Layer for High-resolution Organic Electronic Devices With Solution-processed Polymers.
Wonsuk Choi 1 , Min-Hoi Kim 1 , Chang-Min Keum 1 , Sin-Doo Lee 1
1 School of Electrical Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractSolution-processed organic materials have recently attracted much attention for use in various electronic applications due to the excellent processing capability on a variety of substrates. In patterning solution-processed polymers for the fabrication of organic electronic devices such as organic thin film transistors (OTFTs), most of existing approaches generally suffer from low feature resolution and positional inaccuracy. Here, we present a novel method of precisely patterning solution-processed polymers based on transfer-printing of hydrophobic layers. Hydrophobic fluoro-polymer layers are easily formed on a variety of substrates through transfer-printing which is known to be capable of producing high-resolution patterns, typically on the order of a micrometer. Based on the wetting contrast of a polymer solution on the transfer-printed hydrophobic layers, we demonstrate that precise patterns of functional polymers including TIPS pentacene (semiconductor), PVP (insulator), and PEDOT:PSS (conductor), are spontaneously formed on the converse patterns of hydrophobic layers. When a fluoro-solvent that is chemically compatible to the hydrophobic polymer is used for functional polymer solutions, the hydrophobic patterns can be easily removed during the subsequent patterning process. This enables to successively construct heterogeneous multilayer patterns of different classes of functional polymers without disturbing patterns of each layer. Our technique is also applicable to the processing of inorganic or hybrid soluble materials, and is expected to provide a simple and versatile platform for fabricating various micro- or even nano-patterned organic electronic applications through all-soluble processes in combination with a roll-to-roll process.
9:00 PM - C11.16
Catalytic Nanoanchors for Electroless Deposition of Metal Films on Silicon.
Shinji Yae 1 , Keisuke Sakabe 1 , Tatsuya Hirano 1 , Naoki Fukumuro 1 , Hitoshi Matsuda 1
1 Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, Himeji, Hyogo, Japan
Show AbstractAutocatalytic electroless deposition is a conventional method to metalize nonmetallic substrates such as ceramics, glass and semiconductors. This deposition method has several advantages in mass-production, costs, uniformity of films, covering of complicated structure and so on. This deposition on nonmetallic substrates requires catalyzation pretreatment of substrates generally using tin and palladium. For silicon (Si) substrates, it is difficult to obtain adhesive metal films with conventional catalyzation pretreatments. We recently reported an electroless process to produce metal nanorods in Si [1]. In this study, metal nanorods were used as catalytic nanoanchors for electrolessly depositing adhesive metal films on Si. This metal film formation process consists of three electroless steps: 1) electroless displacement deposition of metal nanoparticles on Si; 2) Si nanopore formation by metal-particle-enhanced hydrofluoric acid (HF) etching; and 3) metal filling in nanopores and metal-film formation on whole Si surface by autocatalytic electroless deposition. Silver nanoparticles, a few tens of nm in diameter and 1011 cm-2 in particle density, were deposited on a p-Si substrate by immersing the substrate in silver nitrate solution containing HF for 30 s. Si nanopores, a few tens of nm in diameter consistent with that of silver particles and 50-100 nm in depth, were formed by immersing the silver-nanoparticle-deposited p-Si in a HF solution for 600 s. Silver particles were found at the bottom of the Si nanopores. The nanopores were filled with metal and a continuous bright metal film was formed on whole Si surface by immersing the nanopore-formed p-Si in an autocatalytic electroless nickel-boron (Ni-B) deposition solution for 600 s. No peeling of metal films was obtained by a tape test based on JIS H8504 corresponding to ISO 2819 using an adhesive tape (3M, 859T) that has adhesion four times higher than that of the adhesive tape generally used for the tape test. In a case that the metal-particle-enhanced HF etching time was shorter than 180 s, the Ni-B films were totally detached from p-Si substrates by the tape test. Thus, the metal nanorods having suitable length can work as the catalytic nanoanchors for electrolessly depositing adhesive metal films on Si. This method can be applied for other kinds of metal films such as Co-B, and Co-Ni-B and substrates such as multicrystalline Si and microcrystalline Si. [1] S. Yae, T. Hirano, T. Matsuda, N. Fukumuro, and H. Matsuda, Appl. Surf. Sci., 255, 4670 (2009).
9:00 PM - C11.17
Structural, Optical, and Magnetic Properties of Yb-doped ZnO Films Prepared by Spray Pyrolysis Method.
Aziz Dinia 1 , Ibrahima Soumahoro 1 3 , Guy Schmerber 1 , Silviu Colis 1 , Mounir Ait Aouaj 3 , Najem Hassanain 3 , Amal Berrada 3 , SiMohamed Abdelfdil 3 , Abdelilah Slaoui 2
1 , IPCMS, Strasbourg France, 3 , LPM Faculté des Sciences, Rabat Morocco, 2 , InESS, Strasbourg France
Show AbstractDoping wide band gap materials with trivalent rare earth (RE) ions is well known to enhance the optical activity. Therefore, we will report on the effect of Yb doping on the structural and optical properties of Zn1-xYbxO thin films deposited on glass substrate at 450°C by spray pyrolysis technique. An homogeneous solution was prepared by dissolving the starting products in distilled water at room temperature. Some drops of acetic acid (CH3COOH) have been added while stirring at room temperature for 30 min to obtain a clear solution. Then, the substrate is placed on the plate and heated progressively until the deposition temperature is reached. All films were deposited at 450°C during 77 min with a flow rate of the solution fixed at 2.6 mL/min. The thickness of the obtained films was about 300 nm. X-ray diffraction and transmission electron microscopy will be used to inform on the effect of the doping on the structural quality of the films. Scanning Electron Microscopy will inform on the morphology of the films and on the stoichiometry of the dopant inside the ZnO matrix. The photoluminescence properties will be investigated at low and room temperature to test the efficiency of such rare earth doped zinc oxides for photon shifting and their potential use for solar cells.
9:00 PM - C11.19
Performance Modification in Solution-processed Tin Zinc Oxide TFT.
Dong Lim Kim 1 , Doo Na Kim 1 , You Seung Rim 1 , Si Joon Kim 1 , Hyun Jae Kim 1
1 School of Electrical and Electronic Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractTin zinc oxide TFTs with different component fraction fabricated by solution process were reported in this paper. Sn chloride and Zn acetate were used as precursor and the maximum annealing temperature was 500 oC. The electrical characteristics of TFTs were acutely affected by the molar ratio between Sn and Zn in the lattice, and showed the highest mobility and on-to-off ratio of about 20 cm2/Vs and 2x106, respectively. The origins of the high performance were traced through both structural and electrical aspects. Sn was generally considered to offer carrier path by superposition of s orbital, but it was found that the increase of Sn fraction only below specific value in lattice contributed to increase mobility, which could be explained by the structural distortion and defect generation. Zinc atoms introduced in the lattice were necessary to control both mobility and carrier concentration. From these results, the solution-processed tin zinc oxide TFT with high performance was suggested.
9:00 PM - C11.2
Hydrostatic Concerns in Inkjet-printed Films.
Hongki Kang 1 , Dan Soltman 1 , Vivek Subramanian 1
1 EECS, UC Berkeley, Berkeley, California, United States
Show AbstractDrop on demand inkjet printing is an attractive tool for low-cost electronics fabrication due to its precise control and cost-efficient nature. In order to make inkjet printing more feasible, it is important to understand the nature of printed features and create design rules for inkjet printing. In particular, an understanding of the various rheological effects present during formation of films from individual drops is crucial to developing optimized processes for realization of inkjet-printed devices and patterns. In this work, we optimize inkjet-printed polymer films and develop a simple analytic framework to understand our results. In a uniform film, dried film thickness is determined by the ink concentration and the volume of ink printed per unit area. The minimum thickness in a given ink-substrate system is determined by the spacing required for drop overlap. The maximum film thickness is limited by the advancing contact angle of the fluid-substrate interface and thus grows with feature size. As two dimensional patterns are formed through the coalescence of multiple drops, the number of drops accumulated within a given two dimensional area (for example, due to the dot-per-inch value used during printing) impacts the advancing contact angle of the growing bead. During a print, if care is not taken to avoid exceeding a growing bead’s advancing contact angle, an undesirable local overflow event occurs, resulting in a bulging of the two-dimensional pattern. We explain this bulging phenomenon through a simple hydrostatic model that proves a good fit to data. Further, as a patterns two-dimensional area is expanded through addition of further drops, the growing bead’s contact angle can fall due to the relative increment of fluid volume vs. the additional area enclosed by additional drops. Should a growing bead’s contact angle fall beneath the receding contact angle as printing proceeds, the film separates into smaller beads as it reflows to minimize surface energy, resulting in gap formation and pattern breakup during printing. Thus, hydrostatic concerns prove to define the experimental space within which uniform films can be printed. We provide a simple analytic framework to establish this space, and thus provide a framework for optimization of printing of two dimensional patterns using droplet-on-demand printing.
9:00 PM - C11.20
Fabrication of Metal Nano-array on Parylene-C/Polyimide by Immersion Plating.
Li-Wei Cheng 1 , Che-Wei Chen 1 , Chih-Chieh Hsu 1 , Fon-Shan Huang 1
1 , National Tsing Hua University, Hsinchu Taiwan
Show Abstract Polyimide is a well known material in the flexible electronics and biosensors. The study of gold/copper nano-array transferred on parylene-C/polyimide by hot-embossing was investigated. First, the gold/copper nano-array molds were obtained by immersing amorphous Si with electron-beam patterned nano array resist into the plating solution. The silicon nitride was deposited by LPCVD on Si(100) wafer with thickness 50 nm. The a-Si was deposited by LPCVD with thickness 40 nm. The DSE1010(E-beam PR) was spin-on coated on Si(100) wafer with thickness around 100~125 nm. After developing, the nano-array patterned DSE1010 with dot size 90~110 nm and period 200 nm were formed and immersed into solution at RT for 7/20 second, respectively. The gold/copper plating solutions were mixtures of 3.78 mM HAuCl4/11 mM CuSO4 and 216 mM/1.6M HF, respectively. After stripping the resist away, the gold/copper nano-array coated silicon molds were fabricated. Secondly, the gold/copper nano-array was transferred from the Si molds onto the parylene C/polyimide by nanoimprint with imprinting temperature 120~150 °C and the imprinting pressure 300~450 N/cm2. The samples then were cooled to room temperature for various time. The Si molds were then removed and the gold/copper nano-array on parylene-C/polyimide were then examined by SEM. The gold/copper nano-array were plated on silicon wafer by immersion plating. The cross section of SEM showed gold dots diameter varying from 90 to 100 nm and height with 60 to 80 nm. The gold plating yield was about 99 %. The copper dots diameter varying from 90 to 110 nm and height with 40 to 60 nm. The copper plating yield was about 98 %. For the process condition of the imprint temperature 120 °C and cooling time 30 minutes, SEM pictures showed the part of nano-array transferred on parylene C/polyimide. But voids, extrusions, fragments, and distortions of via were also found and varied with the imprinting pressure. The transferred yield were from 17 %, 43 %, 56 %, and 43 % for imprinting pressure 300 N/cm2, 350 N/cm2, 400 N/cm2 and 450 N/cm2, respectively. The higher imprinting temperature gave rise to more extrusions, and distortions. It also reduced the yield. So the samples were cooled to room temperature for 3 hours. The transferred yield increased from 56 to 98 % for the process condition of the imprinting temperature 120 °C and pressure 400 N/cm2. So the gold/copper nano-array with dot 100 nm and period 200 nm on parylene C/polyimide can be fabricated by hot-embossing nanoimprint. We believe that the imprinting temperature, pressure, and cooling time can be further reduced and investigated. The immersion plating and hot-embossing nanoimprint process offer a low cost method for producing gold/copper nano-array on parylene C/polyimide structure and have the potential to become a key lithography method for future manufacturing of flexible electronics and biosensors.
9:00 PM - C11.21
Low-temperature ZnO Transistors With High Capacitance Gate Dielectrics.
Hyojin Bong 1 , Lee Wi Hyoung 1 , Dong Yun Lee 1 , Jeong Ho Cho 2 , Kilwon Cho 1
1 Department of Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Department of Organic Materials and Fiber Engineering, Soongsil University, Seoul Korea (the Republic of)
Show AbstractLow voltage, high mobility n-type thin film transistors (TFTs) based on sol-gel processed zinc oxide (ZnO) have been realized by using the ion gel gate dielectric, a mixture of ionic liquid and triblock copolymer. The ion gel gated solution-processed ZnO TFTs is found to exhibit excellent electrical properties; the carreir mobilities of ~ 13 cm2/Vs, ON/OFF current ratios of ~ 105, and threshold voltages of ~ 1 V, at the relatively low, 300°C, sintering temperature of ZnO thin films. The high capacitance ion gel gate dielectrics ( ~ 5 µF/cm2) can accumulate ultrahigh density charge carriers enough to fill the disorder-induced traps in ZnO film fabricated at moderate temperature of 280 °C. Furthermore, ion gel gated ZnO TFTs are successfully demonstrated on plastic substrates for the large area flexible electronics.
9:00 PM - C11.22
Microreactor-assisted Chemical Solution Deposition Process.
Seung-Yeol Han 1 , Yu-Wei Su 1 , Clayton Hires 2 , Sudhir Ramprasad 3 , Brian Paul 2 , Daniel Palo 3 , Chih-Hung Chang 1
1 School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, Oregon, United States, 2 School of Mechanical, Industrial, and Manufacturing Engineering, Oregon State University, Corvallis, Oregon, United States, 3 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractNanostructured and nanocrystalline thin films were deposited by microreactor-assisted chemical processes. This technique uses continuous flow microreactors for the synthesis and deposition of nanomaterials. In synthesis, microreactor technology offers large surface-area-to-volume ratios within microchannel structures to accelerate heat and mass transport. This accelerated transport allows for rapid changes in reaction temperatures and concentrations leading to more uniform heating and mixing in the deposition process. Consequently, microreactors have been demonstrated to yield dramatic enhancements in controlling the quantum dot size distributions, thereby minimizing particle size variability. The possibility of synthesizing nanomaterials in the required volumes at the point-of-application eliminates the need to store and transport potentially hazardous materials, while providing new opportunities for tailoring novel nanostructures and nanoshaped features. Microreactors have been found to radically improve cycle times and yields associated with the production of a broad range of materials including both inorganic and organic materials that cover a variety of applications such as dendrimers, functionalized metal nanoclusters, metal oxide semiconductor nanoparticles. In particular, we have used microreactors to dispense reactant streams directly onto moving or stationary substrates to yield nanostructured thin films. Results-to-date demonstrate the possibility to control the reacting flux including small intermediate-reaction molecules, macromolecules, nanoclusters, nanoparticles, and structured assemble of nanoparticles directly after synthesis. These results also suggest the possibility of producing many types of nanostructured films using low cost solution chemistry. In this talk, we will present our recent advances in applying this process for photovoltaics and the path to scale up productions.
9:00 PM - C11.23
Inkjet Fabrication of Insoluble Materials.
Doris Chun 1 , Hou Ng 1
1 Commercial Print Engine Lab, Hewlett Packard Laboratories, Palo Alto, California, United States
Show AbstractEver thought about solution processing insoluble materials? We report an innovative fabrication technique using HP thermal printheads to process insoluble materials in solution. It provides an economical alternative to the energy intensive vacuum deposition that is readily scalable to large area fabrication. This efficient yet simple technique utilizes thermal jetting of nanoparticles at high frequency (> 30 kHz) to fabricate functional devices using copper phthalocyanine (CuPc) and perfluoro-copper phthalocyanine (F16CuPc) as our demonstrative materials.
9:00 PM - C11.24
Plasma Treatment of Silicon Based Surfaces.
Kristy Trevino 1 , Ellen Fisher 1
1 Chemistry, Colorado State University, Fort Collins, Colorado, United States
Show AbstractMetal oxides are used for various applications including polymer adhesion, anticorrosive coatings, and catalysis. Plasma treatments have proven useful in tailoring the properties of such surfaces due to their ease of use and environmental friendliness. However, the interfacial interactions that give rise to changes in surface charge and acid/base character are poorly understood. Measurement of these properties, along with surface characterization, allows for a clearer understanding of the important chemical processes. Of particular concern is the permanency of the surface treatment, which is expected to depend on plasma type, plasma conditions, substrate, and the position of the substrate in the plasma. In this work, we have separately treated SiOxNy surfaces with three non-polymerizing gases (Ar, H2O, and NH3) and monitored surface properties as a function of plasma parameters and substrate position for a period of thirty days. Surface charge and acid/base character were measured by determination of the isoelectric point (IEP) from contact angle titration data; surface composition and morphology were also taken and analyzed by XPS and SEM. Ar-plasma treatments yielded initial IEP values of ~7, however these values are not stable over time. In contrast, IEP values for H2O plasma treatments also increased (relative to an untreated substrate) to ~6, but stay relatively stable with age. Compositional data reveal information about the effectiveness of the treatments, and IEP data highlight the similarities and differences between the plasma systems. Results from additional metal oxide surfaces (nat-SiO2 and dep-SiO2) will also be presented and comparisons between systems will be made.
9:00 PM - C11.25
Solution-processed All-oxide Nanostructures for Heterojunction Solar Cells.
Hui-Ying Shiu 1 , Tri-Rung Yew 1
1 Materials Science and Engineering, National Tsing-Hua University, Hsinchu Taiwan
Show AbstractStudies of solution-processed all-oxide heterojunction solar cells for low-cost and large-scale applications are presented. The heterojunction solar cell was fabricated using tin (IV) oxide (n-SnO2-based) nanowires (NWs) as an n-type material and cuprous (I) oxide nanoparticles (NPs) as a p-type material for full spectrum sun light absorption. Doping of n-SnO2-based NWs was also utilized to enhance conductivity and light absorption of NWs. The power conversion efficiency of solar cells were optimized by tuning the morphology, band-gap, light absorption, conductivity and filling process of nanostructures. The morphology and structure of n-SnO2-based NWs and cuprous oxide NPs were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectroscopy. Their band-gaps and absorption spectra were analyzed using UV-visible optical absorption spectroscopy. The power conversion efficiency of the n-SnO2-based-NWs /cuprous-oxide-NPs heterojunction solar cells were measured by a solar simulator and their electrical properties were also characterized by I-V measurements.
9:00 PM - C11.26
Polyoxoanions on Silicon.
Nicholas Prokopuk 1 , Samartha Channagiri Ajit 2 , Regina Ragan 2
1 Chemistry and Materials Branch, Naval Air Warfare Center, China Lake, California, United States, 2 Department of Chemical Engineering and Materials Science, University of California, Irvine, California, United States
Show AbstractFormation of silicon contacts with air, liquids, or metals often occurs with deleterious chemical reactions at the interface. Silicon oxide or metal silicides introduced at the interface contain midgap electronic states or act as resistors which can compromise the electronic properties of the junction. Previous work focused on stabilizing the silicon by chemically passivating the surface with organic functionalities that covalently attach to the surface. We report the chemical modification of silicon surfaces with the polyoxoanions H3PM12O40 (M = Mo, W). The oxide clusters adsorb to Si (100) from organic solutions concomitant with an etching of the surface. Variations in the solvents used during the adsorption process can lead to different surface morphologies. The clusters cover the silicon substrates uniformly and in a monolayer fashion as determined by Kelvin probe force microscopy and cyclic voltammetry. Adsorption of H3PMo12O40 occurs with the formation of an underlying silicon oxide layer. By contrast, the tungstate derivative adsorbs to the surface without oxidation of the silicon. These differences can be understood in light of the reduction potentials of the polyoxometallates and suggests that the oxide clusters can adsorb to silicon by two different processes.
9:00 PM - C11.27
Luminescent Hybrid Foams Generation Combining Oil-in-water Emulsion and Sol-gel Process.
Nicolas Brun 1 2 , Beatriz Julian-Lopez 3 , Peter Hesemann 4 , Guillaume Laurent 5 , Herve Deleuze 2 , Renal Backov 1
1 , Centre de Recherche Paul Pascal - CNRS, Université de Bordeaux, Pessac France, 2 , Institut des Sciences Moléculaires - CNRS, Université de Bordeaux, Pessac France, 3 , Departamento de Química Inorgánica y Orgánica - ESTCE, Universitat Jaume I Avda, Castellón Spain, 4 , Institut Charles Gerhardt - CNRS, ENSC, Montpellier France, 5 , Laboratoire de Chimie de la Matière Condensée de Paris - CNRS, Université Pierre et Marie Curie, Paris France
Show AbstractLanthanide organic complexes anchored onto or within porous materials represent an important solution processing in the development of advanced luminescent materials for high efficiency lasers, efficient light-conversion molecular devices (LCMDs), organic light-emitting devices (OLEDs), fluorescent lamps, biosensors and so forth. Designing new luminescent materials in a monolithic form with framework involving hierarchical pore system is an emerging area of technological interest. In this direction, the “integrative chemistry” approach [1], where chemistry and process are strongly coupled, allows the pre-dictated assembling of a large variety of molecular precursors or nanobuilding blocks into engineered hierarchical structures. With this aim, our research group has developed a way to obtain macrocellular silica monoliths, labelled “Si-HIPE”, with a high control on the final macroscopic cells, by using concentrated direct emulsion and lyotropic mesophase [2]. Recently, the elaboration of organosilica based hybrid monoliths, labelled Organo-Si(HIPE), exhibiting a bimodal porous structure in view of final functions to be reached, have been processed for the first time [3a,b]. Through co-condensation (“one-pot”) process, where silane derivatives are incorporated in the reaction medium and participate to the whole synthesis, or grafting method, which refers to post-synthesis modification of the pre-fabricated materials, manifold organic functionalities have been anchored to the amorphous silica porous network.With the same strategy, we took benefit of two different chelating agents to complex lanthanide europium ions within new Organo-Si(HIPE) matrices [4]. The resulting materials have been thoroughly characterized via a large set of techniques such as SEM, TEM, SAXS, mercury intrusion porosimetry, nitrogen adsorption, FTIR and 29Si CP MAS NMR. Luminescence behavior of this Eu3+@Organo-Si(HIPE) series was also studied and the effects of environment and europium concentration will be discussed.References[1] a) R. Backov Soft Matter, 2006, 2, 452; b) .E. Prouzet, S. Ravaine, C. Sanchez, R. Backov New J.Chem., 2008, 32, 1284.[2] F. Carn, A. Colin, M.-F. Achard, H. Deleuze, M. Birot, R. Backov J.Mater.Chem., 2004, 14, 1370.[3] a) S. Ungureanu, M. Birot, G. Laurent, H. Deleuze, O. Babot, B. Julian-Lopez, M.-F. Achard, C. Sanchez, R. Backov Chem.Mater., 2007, 19, 5786; b) S. Ungureanu, H. Deleuze, C. Sanchez, M. I. Popa, R. Backov Chem.Mater., 2008, 20, 6494. [4] N. Brun, B. Julian-Lopez, P. Hesemann, G. Laurent, H. Deleuze, C. Sanchez, M.-F. Achard, R. Backov Chem.Mater., 2008, 20, 7117.
9:00 PM - C11.3
Inkjet-printed Polydiacetylene Nanoparticle Hybrids for Sensory Displays.
Woo-jeong Kim 1 , Chun Zhi Cui 1 , Dong Hyuk Park 1 , Gil Sun Lee 1 , Dong June Ahn 1
1 Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractAmphiphilic diacetylene has been widely investigated as a supramolecular sensor matrix due to their unique properties. Polydiacetylene (PDA) undergoes a visible color transition from blue by polymerization to red due to various environmental stimuli including temperature, pH, chemical solvent, ligand-receptor interaction and mechanical stress. “Blue-phase” PDAs are nonfluorescent while their “red-phase” counterparts fluoresce. This property of PDAs makes these materials quite potential as label-free biosensors and chemical sensors. In order to enhance their technological applications, the polydiacetylene nanoparticle hybrids are fabricated in the form of “Sensory Letter Display” using inkjet printing that is versatile due to high speed, relatively simple process, low cost, compatibility with a wide range of substrates, and ability to deposit very small droplets. PDA nanoparticles were immobilized on various porous substrates such as glass fibers and cellulose membranes by physical adsorption using a piezoelectric inkjet printer. Immobilized nanoparticles were reacted with HCl and ammonia in the forms of gas and liquid. We observed that each letter possesses color-changing property as well as fluorescence emission. The results show that PDA-based chemosensor display can be fabricated any shapes of pattern on various substrates easily and simply by using this inkjet printing technique.
9:00 PM - C11.4
Rapid Fabrication of Functional Colloidal Crystal Structures Using Simple Slide Coating Process.
Wonmok Lee 1 , Young Gon Seo 1 , Min Ah Kim 2 , Hyunjung Lee 2
1 Chemistry, Sejong University, Seoul Korea (the Republic of), 2 Materials Science and Technology Research Division, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractA simple, yet rapid fabrication method for large area colloidal crystal film is demonstrated. Aqueous colloidal dispersion sandwiched between a hydrophobic top-cell and a hydrophilic bottom substrate formed a flat meniscus at the drying front, from which high quality colloidal crystal films were obtained within 20min due to the capillary force exerted by accelerated water evaporation aided by hot air blowing. Continuous supply of the suspension enabled the fabrication of the 3D self-assembled photonic crystal template over large area (>4cm2 ) without significant loss of colloids. The coating method was further expanded to the fabrication of the superlattice of anatase titania nanoparticles infilled within the polymeric opal structures by one step coating process. Upon thermal calcinations, high quality titania inverse opal structure was obtained, and titania inverse opal on the FTO glass was successfully tested as a photoelectrode of dye sensitized solar cell (DSSC).
9:00 PM - C11.7
Soluble Processed ZnO TFTs Based on Flexible Substrates.
Keunkyu Song 1 2 , Taewhan Jun 1 , Youngmin Jeong 1 , Chang Young Koo 1 , Dongjo Kim 1 , Kyoohee Woo 1 , Junghun Noh 2 , Seongwhan Cho 2 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of), 2 Flexible Display Lab, Samsung electronics, Yongin, Kyonggi do, Korea (the Republic of)
Show AbstractWe demonstrate thin-film transistors (TFTs) using transparent soluble material fabricated on flexible substrates such as polyimide (PI) and polyetylenesulfonate (PES). The solution processed semiconductor was prepared by spin-coating on the gate dielectric such as silicon dioxide (SiO2) and silicon nitride (SiNx). The use of aqueous zinc hydroxide precursor allows us to fabricate the TFTs at low temperatures range from 150 oC to 300 oC with compatibility and flexibility. In the case of PI flexible substrate, the soluble processed ZnO-TFTs showed good performance such as low off-current of the order of < 10-11 A (an on-off current ratio of ~ 106), a field effect mobility of 1.87×10-1 cm2 V-1 s-1, threshold gate voltage (~ + 7.5 V), and low gate leakage current (the order of < 10-11 A). In addition, the output characteristic of ZnO-TFT based on PI substrate exhibits good contact performance at low drain voltages and clear pinch-off behavior. We analyzed the cross-sectional structure of the devices using high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FE-SEM), and the electrical parameters of soluble ZnO-TFTs were measured in air by a semiconductor parameter analyzer. Special emphasis was directed on the repeated bending tests. Our results suggest that the solution-processed devices on various flexible substrates have great potential to work as a building block for future flexible transparent electronics.
9:00 PM - C11.8
Quantum Dot Patterning for High-performance and Large-area Light-emitting Diodes.
Tae-Ho Kim 1 , Kyung-Sang Cho 1 , Eun Kyung Lee 1 , Sang Jin Lee 1 , Do Hwan Kim 2 , Jong Min Kim 1 , Byoung Lyong Choi 1
1 Frontier Research Laboratory, Samsung Advanced Institute of Technology, Yongin, Kyunggi-do, Korea (the Republic of), 2 Display Laboratory, Samsung Advanced Institute of Technology, Yongin, Kyunggi-do, Korea (the Republic of)
Show AbstractColloidal nanocrystal quantum dots (QDs) have been noticeable for their luminescent properties such as narrow spectral emission bandwidths, broad absorption and high photoluminescence quantum efficiencies as well as good photostability, controllable band-gap by size-tuning, and compatibility with solution processing, which lead QDs to one of the most promising materials for next-generation displays and illumination sources. The solution processablility of QD with its superior luminescent properties has also stimulated interest in their utilization for low-cost, large-area, and flexible electronic devices. Nevertheless, lack of QD patterning capability by conventional methods hinders realization of full-color QD display or integrated electronic systems. Here we report a novel patterning method that enables selective deposition of various color-emissive QDs, and exact positioning and fine-patterning of high-quality films in a large area. This novel patterning could be accomplished by assistance of kinetic control and surface modification, which results in perfect printing yield of QD films with various shape and size control. The film quality of the patterned QDs is comparable with spin-coated QD film, and even improved after cross-linking of QDs which is required process for high-performance QD-LED. Therefore, our QD-LEDs made by this patterning method show better electroluminescent properties due to the improved film quality and neat interface. This technique also provides capabilities for patterning of thin films fabricated from various functional materials dissolved in solution (e.g. nano-scale semiconducting materials, conjugated polymers, fluorescent and phosphorescent organic materials, dendrimer, etc.) for large-area integrated electronic systems.
9:00 PM - C11.9
All-solution-processed Thin-film Transistor With < 10 μm Channel Length Fabrication Using Direct Inkjet-printing Method.
Seungjun Chung 1 2 , Yongtaek Hong 1 2
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of), 2 , Inter-University Semiconductor Research Center, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe report all-solution-processed organic thin-film-transistors on flexible plastic substrate with inkjet-printed narrow silver lines. Although inkjet printing method is one of most promising candidates for device fabrication due to its low-temperature, non-vacuum and maskless process, it has critical disadvantage for high resolution electronics application because of nozzle size limitation, surface tension and viscosity of limited ink materials. In addition, poor uniformity in terms of coffee ring effect and edge waviness of metal electrodes can affect to device performance. Therefore, high resoution, high conductivity, good uniformity of inkjet-printed conductive electrodes should be guaranteed for electrical device applications. For inkjet-printed narrow lines and its electrical application fabrication, transparent metal-organic precursor type silver ink from INKTEC corp. and piezoelectric DMP-2831 inkjet printer from DIMATIX corp. were used. To overcome low-resolution problem of inkjet printing technology, we optimized inkjetting condtions, substrate surface energy, ink-drop-spacing and substrate temperature when 1pl cartridge was used. Inkjetting conditions from 1pl cartridge with nozzle diameter of 9 µm were optimized controlling voltage waveforms, drop speed of 2 m/sec, drop frequency of 5 kHz, drop spacing of 25 μm and nozzle temperature of 32°C to prevent nozzle clogging. From our optimized inkjetting conditions, one droplet of silver ink emitted from the cartridge with 9 μm diameters made a circle with about 25 µm diameters when it was dropped on the substrates. Flexible substrate choice and its surface energy control are important to obtain good surface energy match and adhesion properties. From these requirements, UVO3 treated for 10 mins poly-arylate substrate was used to increase surface energy corresponding hydrophilic surface, and clean-edged narrow line width of 25 μm and distance between each line of 17 μm were obtained. To satisfy demand for high aspect ratio narrow line, muti-time-printing method and high substrate temperature which stimulate previously printed silver line solvent evaporation were used, and line thickness up to 320 nm and line width of 38 μm were obtained from 5-time-printed silver line on maximum substrate temperature, 60°C. To confirm inkjet-printed narrow silver line application, it was used as source/drain electrodes of all-solution-processed OTFT on poly-arylate substrate (W/L = 510 μm/9 μm). All electrodes were inkjet-printed using silver ink and inkjet-printed cross-linked PVP layer was used as gate dielectric layer. For avtive layer, 1wt% of Tips-pentacene dissolved in 1,2-dichlorobenzene was drop-casted. From all-solution-processed device, reaonable OTFT performance including mobility of 0.06 cm2/V.s and on/off ratio of 5000 was obtained, which results show optimized inkjet-printed narrow line can solve direct-printing resolution problem and it can be used for high resolution electrical applications.