Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
Patrick J. Smith The University of Sheffield
David B. Mitzi IBM T. J. Watson Research Center
Aoife Morrin Dublin City University
S3: Poster Session: Solution-Processed PV, TCOs, TFTs
Session Chairs
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
S1: Solution-Processed Chalcogenides for Thin Film Photovoltaic Devices
Session Chairs
David Mitzi
Maikel van Hest
Tuesday PM, November 29, 2011
Room 310 (Hynes)
9:30 AM - **S1.1
Nanocrystal-Ink Routes and High-Yield Molecular Precursor Routes to Chalcopyrite and Kesterite Thin Film Solar Cells.
Hugh Hillhouse 1
1 Chemical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractThe presentation will briefly summarize recent progress on nanocrystal-ink based routes to CIGS. However, given the terawatt scale of future energy needs, the most promising future photovoltaic materials should be Earth abundant with their primary mineral resources distributed across several geographic regions and their supply chains robust to reduce concerns of price volatility. In addition, the process of forming the solar cell should be scalable, low-cost, and not utilize dangerous or toxic materials. The strongest initial candidate appears to be Cu2ZnSnS4 (CZTS). Up until 2009, CZTS thin film solar cells were synthesized primarily by evaporating or sputtering metals (Cu, Zn, & Sn) followed by sulfurization. More recently, two potentially low-cost high-throughput approaches have been demonstrated that form the quaternary or pentenary chalcogenide directly from solution-phase processes. One is based on first synthesizing multinary sulfide nanocrystals and then sintering them to form a dense layer. The other approach utilizes molecular precursors dissolved in hydrazine. Both new approaches reach their highest device efficiencies by incorporating Se to form Cu2ZnSn(Sx,Se1-x)4 devices, and each has yielded substantially higher efficiency devices than the best vacuum deposited absorbers. The hydrazine route has yielded the most efficient CZTS-based devices thus far. The presentation will focus on our recent progress in CZTS-based nanocrystal-ink devices. In particular, we have shown that germanium may be alloyed with CTZS (at least up to Ge/(Sn+Ge) ratios of 0.7) to form Cu2Zn(Sn,Ge)S4 nanocrystals that have an increased bandgap [1]. The defect chemistry is serendipitous, and allows for at least 6.8% efficient devices at high germanium content. This exciting prospect may be used to create a back surface field and direct carriers in a similar manner to how gallium is used in high efficiency CIGS devices. In addition, we will report recent results on a scalable chemical route to Earth abundant element thin film solar cells by coating a solution of highly soluble, inexpensive, and commercially available precursors in an environmentally friendly non-toxic solvent to form device quality films (without using nanocrystals or hydrazine). [1] Ford, G.M., Guo, Q., Agrawal, R., and Hillhouse, H.W., “Earth Abundant Element Cu2Zn(Sn1-xGex)S4 Nanocrystals for Tunable Band Gap Solar Cells: 6.8% Efficient Device Fabrication,” Chemistry of Materials 23 (10), 2626–2629 (2011).
10:00 AM - **S1.2
Advances in Kesterite Solar Cells by Solution-Nanoparticle Ink Processing.
Teodor Todorov 1 , David Aaron Barkhouse 1 , Santanu Bag 1 , Oki Gunawan 1 , Tayfun Gokmen 1 , Goislard de Monsabert Thomas 1 , S. Jay Chey 1 , David Mitzi 1
1 Photovoltaic Science and Technology, IBM T. J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractFuture terawatt-scale solar electricity requires lower photovoltaic (PV) module fabrication costs, reliance on more abundant materials and efficiency equal to or greater than current commercial technologies. Thin-film indium-based chalcopyrite devices have one of the fastest growth potentials and also highest efficiencies among thin-film PV technologies. Replacement of the scarce indium element is viewed as a strategic step towards unlimited growth of chalcogenide PV production beyond 100GWp/year. A strong candidate in this category is the kesterite family, including Cu2ZnSnS4 and Cu2ZnSn(S,Se)4 (CZTS and CZTSSe). We have developed kesterite solar cells operating in the 10% efficiency range. This performance is achieved by a simple low-cost liquid-based deposition approach based on chalcogenide solutions in combination with particle-based precursors that yield homogeneous CZTS and CZTSSe phases after thermal treatment. Here we will present recent advances in this field.
10:30 AM - S1.3
Air-Stable Hybrid Inks for Low-Cost CZTS Solar Cells.
Kyoohee Woo 1 , Youngwoo Kim 1 , Joosun Kim 2 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of), 2 Principal Research Scientist Center for Energy Materials Research, Korea Institute of Science & Technology (KIST), Seoul Korea (the Republic of)
Show Abstract Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is a very promising material as a low cost absorber alternative to other chalcopyrite-type semiconductors based on Ga or In because it is only composed of abundant and economical elements. In addition, CZTS has a direct band-gap energy of 1.0~1.5 eV and large absorption coefficient over ~104 cm-1, which are similar to those of Cu(In,Ga)Se2(CIGS) that is regarded as one of the most successful absorber materials. Typically, metal chalcogenide films such as CIGS and CZTS are deposited by vacuum process such as evaporation or sputtering. However, this vacuum deposition suffers from relatively low throughput, low material utilization, and difficulties associated with large-scale production. In this regard, solution-based deposition methods are being developed because they have advantages including suitability for large-area substrates, higher throughput, and more efficient materials usage. Various solution based approaches for producing absorber layer have been reported including sol-gel and nanocrystal dispersion, but they are still facing some limitations; sol-gel method is vulnerable to the contamination of carbon, oxygen, and other impurities from the precursor solution and inevitably leads to the formation of porous structure. Nanocrystal dispersion method needs the complex synthesis of nanocrystals. Recently, Todorov et al. reported the fabrication of CZTS thin film solar cells with 9.6% power conversion efficiency using a hydrazine based approach. However, hydrazine is a highly toxic and very unstable compound that requires extreme caution during handling and strorage. Furthermore, due to the reactive nature of this solvent, all processings for slurry and film preparations must be performed under inert atmospheric conditions and thus it would not be easily adapted for large-scale solar cell fabrication. With these considerations, it is highly desirable to develop a robust, easily scalable and relatively safe solution-based process for the fabrication of high quality CZTS absorber layer. Here, we devise the air-stable hybrid solution-particle approach for the fabrication of dense CZTS absorber layer. Our air-stable ink comprises of commercially available powder mixture of Zn, Sn, and S dispersed in an environmentally benign solvent in which Cu and Zn precursors are dissolved. The metal precursor solution is vulcanized by sulphur element to create a rubberlike polymer, providing the viscosity and wetting that allows us to prepare highly stable hybrid ink containing heavy metallic powders. Our readily achievable hybrid ink, without the involvements of complex particle synthesis and high toxic solvent, enables a convenient access to fabricate uniform, dense, contaminant-free, large-grained CZTS absorber layer. Our simple approach reported here will be the first step in realizing the low-cost and large-area solar cells with high efficiency.
10:45 AM - S1.4
Sonication Assisted Phase and Microstructure Evolution of CuInSe2 by Elemental Cu,In,Se Precursors.
Emre Yassitepe 1 , William Shafarman 2 , S. Ismat Shah 1 3
1 Material Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Institute of Energy Conversion, University of Delaware, Newark, Delaware, United States, 3 Physics and Astronomy, University of Delaware, Newark, Delaware, United States
Show AbstractNon toxic chemical routes that enable formation of high quality CuInSe2 thin films with high materials utilization are desired for low production cost of solar cells. We will present results on the effects of ultrasound on Cu,Se and In,Se elemental precursors with different solvents. Depending on the solvent, the reaction between these elemental precursors facilitates binary selenide phases. These crystalline phases are compared with the effective heat of formation model of Cu-Se and In-Se compounds. The formed binary selenide phases gave an exact match with the predicted effective heat of formation model. However, sonication of Cu,In and Se elemental particles for short times did not yield any single phase CuInSe2 due to the unfavored reaction pathways between CuSe2 and In4Se3 phases. Further annealing these binary phases led to the single phase formation of CuInSe2 at 350C. SEM studies revealed upon sonication above one micron sized Cu,In,Se elemental particles are broken to smaller particles during sonication and moreover upon completion of the reaction CuInSe2 nanocrystals are obtained.
11:30 AM - **S1.5
Understanding Hydrazine Solution Processed CuIn(Se,S)2 Solar Cells.
Yang Yang 1 , Choong-Heui Chung 1 , Bao Lei 1
1 Materials Science and Engreeing, Univ. of California Los Angeles, Los Angeles, California, United States
Show AbstractCuIn(Se,S)2 and other chalcopyrite-based solar cells have received substantial research interest owing to their high optical absorption coefficient, a tunable band gap and demonstrated the highest power conversion efficiency among thin film solar cells. However, the use of vacuum technique in the preparation of absorber layers imposes hurdles in the the production of low cost and large area photovoltaic modules. Solution-based absorber deposition approaches offer an alternative to many of these issues, and have thus been extensively pursued for more than a decade. Recently, a hydrazine solution based processing method has demonstrated copper chalcopyrite based thin film solar cells with efficiencies of up to 13.6% despite the early developmental stage of this technique. In order to further improve this approached solar cells performance, deeper understanding on dissolving mechanism, the structure of molecular precursors, phase formation, defect physics and recombination mechanisms in such devices would be necessary. In this talk, we present the molecular structures present in solutions containing Cu2S, In2Se3, or mixtures of the two, and the CuIn(Se,S)2 phase formation after annealing the solution-processed precursor films. We also examine the effects of introducing an additional Cd ion solution soaking step into our device fabrication process on the defect energy levels and carrier concentration which in turn consistently improves the open circuit voltage of solar cell devices.
12:00 PM - S1.6
Studies of Carrier Recombination in CuIn(S,Se)2 through Photoluminescence Spectroscopy.
Hsin-Sheng Duan 1 , Wan-Ching Hsu 1 , Kuo-Chun Tang 2 , Bao Lei 1 , Pi-Tai Chou 2 , Yang Yang 1
1 , University of California, Los Angeles, Los Angeles, California, United States, 2 , National Taiwan University, Taipei Taiwan
Show AbstractSolution-processed CuIn(S,Se)2 has shown considerable promise as an absorber material in the fabrication of high performance solar cells. However, it is crucial to indentify the primary factors limiting photovoltaic performance. In this study, photoluminescence spectroscopy is employed to investigate the carrier recombination in CuIn(S,Se)2 with emphasis on the effect of cadmium sulfide (CdS) deposition. In steady state photoluminescence, it has been found that CdS deposition (1) leads to an altered photoluminescence profile due to cadmium diffusion into the CuIn(S,Se)2 layer as well as defect passivation at the absorber surface. (2) CdS deposition helps to protect the CuIn(S,Se)2 film from chemical degradation, and also (3) the shallow defects in CuIn(S,Se)2 film at roughly 31 meV above the valence band and with density about 1015cm-3 are estimated through temperature-dependent photoluminescence measurements. These effects have been studied quantitatively, and the results are presented along with suggestions for how future devices can be optimized with respect to material parameters and fabrication strategies.
12:15 PM - S1.7
Solution-Processed Sintered Nanocrystal Solar Cells and Semiconductor Quantum Dot Energy Levels.
Scott Watkins 1 , Jacek Jasieniak 1 , Brandon MacDonald 1 2 , Paul Mulvaney 2
1 Materials Science and Engineering, CSIRO, Melbourne, Victoria, Australia, 2 Chemistry, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractThe use and characterisation of solution processable inorganic semiconductors is highly relevant to the development of low-cost electronic devices such as solar cells. In this paper we will report on two aspects of our work in this area. Firstly, we will describe our layer-by-layer process that enables the fabrication of totally solution processable solar cells from inorganic nanocrystal inks in air at temperatures as low as 300 degrees Celsius. Focusing on a CdTe/ZnO thin-film system we report solar cells that achieve power conversion efficiencies of over 7% with greater than 90% internal quantum efficiency (IQE). We will describe the characterisation of the devices and, through capacitance-voltage measurements, demonstrate that the CdTe layer is fully depleted which enables charge carrier collection to be maximized. Finally, we also discuss the use of photoelectron spectroscopy in air (PESA) to investigate the size-dependent valence and conduction band-edge energies of CdSe, CdTe, PbS and PbSe semiconductor quantum dots (QDs). We will compare the results to those of previous studies, based on differing experimental methods, and to theoretical calculations based on k-p theory and state-of-the-art atomistic semi-empirical pseudopotential modelling.
12:30 PM - S1.8
Improved Efficiency in a PbS Nanocrystal Heterojunction Solar Cell by Employing a Thin TiO2 Film and a Hole Transporting Polymer Layer.
Jangwon Seo 1 , Dongho Lee 1 , Alexander Cartwright 1 , Paras Prasad 1
1 , University at Buffalo, Buffalo, New York, United States
Show AbstractWe report a highly efficient hybrid nanostructured solar cell consisting of a densely-packed TiO2 film; a PbS nanocrystal film; a hole transporting polymer layer (HTL); and metal contacts. The TiO2 film was spray deposited on an ITO coated glass slide. Subsequently, a PbS nanocrystal film was deposited, layer-by-layer, on the TiO2 film to establish a planar donor-acceptor heterojunction. Two device geometries were fabricated on this structure by subsequently depositing either: i) a single Au contact layer or ii) a HTL followed by the Au contact layer. Drastic increases in the photocurrent, and stability in ambient air, was observed in the device with the HTL, relative to the device without the HTL. The device with the HTL layer had a power conversion efficiency of more than 5% under AM1.5G (100 mW/cm2). Moreover, the external quantum efficiencies of this device was very high (~90% in the visible range [400~600 nm] and ~30% in the near infrared range). The dependence of photovoltaic performance of the device on the thickness of the PbS nanocrystal film and the TiO2 film will be presented.
12:45 PM - S1.9
Adhesion Study of CZTS Layer Deposited from Ink Type Precursor onto Back Contact for Photovoltaic Applications.
Prashant Sarswat 1 , Michael Free 1
1 Metallurgical Engineering, University of Utah, Salt Lake city, Utah, United States
Show AbstractCZTS (Cu2ZnSnS4) based ink has been emerged as a potential candidate for high throughput production of p-type layer on a back contact. An ink based absorber material can simplify device production process because of fast printing technology. The pre-synthesized liquid can also be used as a spray to get faster output. Although this technique is very fast, some issues such as adhesion of ink on back contact need to be addressed. A systematic study of adhesion of ink on different substrates using various solvents, binders and annealing temperatures is discussed. Some techniques for improved adhesion were proposed and demonstrated.
S2: Solution-Processed Oxides
Session Chairs
David Mitzi
Maikel van Hest
Tuesday PM, November 29, 2011
Room 310 (Hynes)
2:30 PM - **S2.1
Electrodeposition and Chemical Bath Deposition of Zinc Oxide Semiconducting Films and Nanostructures: A Case Example of a Potential Alternative to Classical Vacuum Deposition Routes.
Daniel Lincot 1
1 , Institute of Research and Development of Photovoltaic Energy (IRDEP), Joint Laboratory CNRS-EDF-Chimie Paristech, Chatou France
Show AbstractZinc oxide has become in recent years one of the key materials in the search for advanced applications in optoelectronics, photovoltaics, sensing and magnetic applications, as a low cost alternative to existing state of the art materials. ZnO, in contrast with many other key wide gap semiconductors has the unique advantage to be easily prepared in high quality from solution routes. This allows low temperature cost effective deposition processes (mostly <100°C) and also to take the advantage of the solution environment to promote highly-selective self-assembling processes to generate a wide range of structures from classical thin films to nanostructures [1]. This explains why tremendous attention is now paid, mostly since 2000, to these new solution synthetic approaches. Three main approaches are Chemical bath deposition (CBD), also named chemical solution deposition (CSD), Hydrothermal deposition and electrodeposition (ED). All these methods, even if they are often presented separately, possess common roots based on solution chemistry, interfacial reactions and general concepts of heterogeneous nucleation and growth. The aim of this presentation is first to highlight these aspects. Then recent advances in the electrodeposition of ZnO thin films for TCO applications for thin film CIGS solar cells will be presented which may represent a breakthrough for replacing sputtering deposition. The deposition of nanostructures consisting in nanocolumns and nanoporous will be presented with possible applications in nanostructured solar cells. Recent results on epitaxial growth will be highlighted. Next avenues for research will be discussed.[1] D. Lincot, MRS Bulletin, 35(2010)778-788 and references therein.
3:00 PM - S2.2
A Unifying Modular Approach to Solution Processed Dielectric Semiconducting and Conducting Mixed Metal Oxides: Synthesis, Characterization and Electronic Performance.
Joerg Schneider 1
1 , TU Darmstadt, Darmstadt Germany
Show AbstractTransparent metal oxides are promising materials for applications in thin film electronic transisistors (TFTs)[1]. Due to their variable dopant content, their tunable properties their electronic performance can sometimes be tailored from insulating dielectric, to semiconducting to metallic behaviour. Especially, amorphous metal oxides of Zn, Al, Ga, In, and Sn for semiconducting and conducting oxides, and Zr and Hf for dielectric transparent oxides are interesting and thus have been studied extensively over the last couple of years worldwide. However, solution processing of such metal oxides under ambient conditions is still a major challenge since processing conditions under ambient conditions are necessary e.g. to use soft substrates, e.g. polymers for the thin film deposition. We report on a solely molecular based, modular approach which allows to tailor the elemental composition of resulting metal oxide films with respect to composition and performance obtained from such precursors as single, binary or ternary phases. This offers a synthetic route to dielectric, semiconducting and electrically conducting thin films under very similar processing conditions.[1] T. Minami, New n-type transparent conducting oxides, MRS Bull. 25, 2000, 38-44
3:15 PM - S2.3
Solution Processing of Nb-Doped TiO2 and Ti-Doped In2O3 Transparent Conductors.
Robert Pasquarelli 1 , Maikel van Hest 2 , Alexander Miedaner 2 , Calvin Curtis 2 , Joseph Berry 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 combination of high transparency in the visible region of the spectrum and tunable electronic conductivity. Nb-doped anatase TiO2 deposited by physical vapor deposition methods and on lattice-matched substrates has demonstrated potential as a replacement for indium-based TCOs such as indium tin oxide. Atmospheric-pressure solution deposition is an attractive alternative to these conventional vacuum-based TCO deposition techniques due to its ease and potential to lower device manufacturing costs. Here we report on 5 at% Nb-doped TiO2 films deposited from solutions of Ti(OEt)2(acac)2 and Nb(OEt)5. The desired anatase phase formed from an amorphous state on glass substrates at 500°C without the need of lattice-matching or a seed layer. Films demonstrated conductivities of 20-60 S/cm with mobilities ranging 0.1-0.6 cm2/Vs and a carrier concentration of 5x1020 /cm3. Processing conditions had a significant effect on the final electronic properties and will be presented. The Ti precursor was also used in combination with the novel low-temperature In precursor, In5O(OPr)13, to prepare 3 at% Ti-doped In2O3 films. Undoped films have demonstrated conductivities of 60-100 S/cm with mobilities as high as 10 cm2/Vs.
3:30 PM - S2.4
Electrochemically Triggered Deposition of Porous Zinc Oxide from Aqueous Precursor Solutions on Textile- Compatible Microelectrodes on the Way towards Textile-Based Photovoltaics.
Derck Schlettwein 1
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany
Show AbstractOver the last years electronics have been more and more integrated into textiles, mainly for sensing purposes. Interest rose to also integrate photovoltaics as an independent energy supply. Preparation of semiconductor films from precursor solutions represents the most promising approach because of good compatibility of the processes to a low thermal stability of textiles and to the need of a three- dimensional coating process. Water as solvent is optimum because of perfect environmental and textile chemical compatibility. Dye-sensitized solar cells represent a suitable photovoltaic cell technology since electrolytes are capable to bridge an insulating gap between the active electrodes of typically 10 - 100 µm in most finely woven fabrics.Thin porous films of ZnO were electrochemically deposited on silver- coated polyamide (ELITEX®) threads, filaments and knitted fabrics and subsequently sensitized by appropriate dyes. Such textiles had been established earlier as quite well conducting textiles, stable under environmental conditions. They were therefore chosen in a first step towards textile- integrated photovoltaics. Electrodeposition of zinc oxide from oxygen-saturated aqueous solutions was presented as a successful strategy to realize semiconductor structures on textiles and detailed control and influence of the deposition conditions was discussed [1]. The role of microelectrode effects at such threads, options of forced convection, deposition under pulsed potential, alternative deposition baths and different substrate metals were investigated [2]. However, corrosion problems in the typically used iodine- containing electrolyte hampered the use of ELITEX® in dye-sensitized cells. Thin tungsten wires served as model for a passivated surface. ZnO could still be deposited electrochemically but the active electrode structure was protected against corrosion. Recent work therefore concentrated on utilization of corrosion- resistant micro-fibers of stainless steel which are compatible to textile technologies. Structures with conversion efficiency close to 1 % under AM 1.5 conditions could be realized and thereby open the door towards devices of technical interest [3].1. T. Loewenstein, A. Hastall, M. Mingebach, Y. Zimmermann, A. Neudeck and D. Schlettwein, "Textile electrodes as substrates for the electrodeposition of porous ZnO," Phys. Chem. Chem. Phys. 10(14), 1844-1847 (2008).2. M. Rudolph, T. Loewenstein, E. Arndt, Y. Zimmermann, A. Neudeck and D. Schlettwein, "Pulsed electrodeposition of porous ZnO on Ag-coated polyamide filaments," Phys. Chem. Chem. Phys. 11(17), 3313-3319 (2009).3. T. Loewenstein, M. Rudolph, M. Mingebach, K. Strauch, Y. Zimmermann, A. Neudeck, S. Sensfuss and D. Schlettwein, "Textile-Compatible Substrate Electrodes with Electrodeposited ZnO-A New Pathway to Textile-Based Photovoltaics," Chemphyschem 11(4), 783-788 (2010).
3:45 PM - S2.5
Thin Film Formation of Transparent Conductive Oxides and Organic Materials by Solution-Based Mist Deposition Method toward Hybrid Device Applications.
Takumi Ikenoue 1 2 , Shizuo Fujita 2
1 Department of Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 Photonics and Electronics Science and Engineering Center, Kyoto University, Kyoto Japan
Show AbstractSolution processable organic devices such as solar cells and light emitting diodes have attracted increasing interest due to its rapid efficiency-improvement, ease of processing, and cost-effective large-area processability. Many of organic devices have generally been fabricated by spin-coating technique, but material efficiency of this method is low and it is not suitable for large area fabrication. In addition, indium-tin oxide (ITO), which is used as a transparent electrode, is fabricated by vacuum processes, therefore it cannot take full advantages of the solution based processes. We report, in this presentation, a novel vapor-like-deposition technique based on a solution process, namely ultrasonic spray assisted mist deposition technique. Transparent conductive oxides such as ITO and zinc oxide can be fabricated by this technique without any vacuum systems. Additionally, this technique offers many advantages, for example, (i) it is possible to grow high quality thin organic films, (ii) this technique is suitable for large area substrates and roll-to-roll processes, (iii) source materials can be formed into films without many wastes, and (iv) owing to a vapor-deposition technique this deposition method allows hard-mask patterning without photolithography, which can simplify device fabrication processes, and easy formation of multilayer structures. In the mist deposition technique, the source solution is ultrasonically atomized and the aerosol particles formed are supplied onto a substrate using nitrogen carrier gas to form thin films. To fabricate ITO thin films, we used indium acetylacetonate and tin acetate as a starting source, which were diluted in methanol and deionized water with concentrations of 0.020 and 0.002 mol/L, respectively. A flow rate of nitrogen carrier gas and the substrate temperature were set at 5 L/min and 400 degrees centigrade, respectively. The ITO films were indicated the high transmittance and sheet resistance of less than 10 Ω/square, which was reasonable to be applied as a transparent electrode. Similarly, by optimizing the deposition conditions of organic thin film formation, thicknesses of organic thin films have been well controlled and the properties such as conductivity values and roughness of those were comparable to those deposited by spin-coating. The detailed properties of the films and some examples of device applications such as solar cells will be demonstrated at the presentation.
4:30 PM - **S2.6
Solution Based Processing for Cost Effective Smart Windows.
Robert Tenent 1 , Chi-Ping Li 2 , Feng Lin 4 , David Alie 3 , Colin Wolden 2 , Ryan Richards 4 , Sean Shaheen 3 , Anne Dillon 1
1 Chemical and Materials Sciences, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Materials Science, Colorado School of Mines, Golden, Colorado, United States, 4 Chemistry, Colorado School of Mines, Golden, Colorado, United States, 3 Physics, University of Denver, Denver, Colorado, United States
Show AbstractInternal environmental control in buildings is the largest source of electrical energy use in the United States. “Smart” windows which dynamically control the transmission of both heat and visible light could potentially save roughly 30% of this energy amounting to almost $40 billion in total energy savings annually. At present, the smart windows market is dominated by vacuum processed metal oxide-based electrochromic devices. These devices typically consist of a five layer structure that includes two electrode materials separated by an ion conductor with these three layers sandwiched between transparent, but electrically conducting contacts. These devices change tint upon applying a small voltage (~1V) and act via an ion intercalation mechanism similar to battery materials. A consensus based on energy efficiency modeling as well as windows industry input has determined that prices must drop to between $20-$25/ft2 in order for this technology to be market viable. Present market prices vary from $50 to $100/ft2.Here we will present what we believe to be fruitful routes toward low-cost production of multilayer electrochromic devices. Our work is focused on solution processing of electrochromic metal oxide layers as well as ion conductors using the ultrasonic spray deposition method. Two possible manufacturing options will be presented. The first will be deposition on flat glass substrates and possible integration with the well known float glass process. We will also present work aimed at the development of roll-to-roll (R2R) processing methods using inexpensive flexible plastic substrates. To date we have demonstrated a high temperature deposition of lithium-doped nickel oxide1 material that is likely compatible with float glass processing as well as a low temperature deposition of tungsten oxide2 that may be suitable for R2R methods. We will touch briefly on these results and primarily discuss further work toward deposition of ion conductor materials and initial demonstrations of integrated device structures. Ion conductor work will primarily focus on development of gel electrolyte materials that may be compatible with atmospheric pressure deposition onto flexible substrates.1.Tenent, R. C.; Gillaspie, D. T.; Miedaner, A.; Parilla, P. A.; Curtis, C. J.; Dillon, A. C., Fast-Switching Electrochromic Li+Doped NiO Films by Ultrasonic Spray Deposition. Journal of the Electrochemical Society 2010, 157 (3), H318-H322.2.Li, C.-P.; Tenent, R. C.; Wolden, C.; Dillon, A. C., Electrochromic Films Produced by Ultrasonic Spray Deposition of Tungsten Oxide Nanoparticles. Solar Energy Materials and Solar Cells, 2011, in press, doi:10.1016/j.solmat.2011.03.034
5:00 PM - S2.7
Structure, Sodium Ion Role, and Practical Issues for β-Alumina as a High-K Solution-Processed Gate Layer for Transparent and Low Voltage Electronics.
Bo Zhang 1 , Yu Liu 1 , Howard Katz 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show Abstractβ-alumina (SBA) has been discovered as a promising high dielectric constant gate material for solution processed, transparent and low voltage transistor devices. Some experimental evidence indicates that the mobile Na ion within two spinel blocks made by Al and O is responsible for the high dielectric constant. Transistors (W/L ratio 10) using SBA as gate layer and sol-gel-processed zinc tin oxide (ZTO) as active layer only need 2V to obtain 0.7mA output current. The calculated field driven mobility for the devices is 22cm2/Vs. SBA material is compatible with organic semiconductors such as NTCDI and pentacene as well. Some key issues regarding using SBA for real applications, such as device stability in the ambient atmosphere, response under high frequency, and threshold voltage shift under gate bias have also been studied. It is found that encapsulating the device with CYTOP fluorinated polymer is an effective way to increase the operational stability of the devices in the ambient environment.
5:15 PM - S2.8
Solution-Processed Oxide Thin-Film Transistors Using La-Ta-O/Bi-Nb-O Stacked Gate Insulator.
Takaaki Miyasako 1 3 , Masatoshi Onoue 1 , Eisuke Tokumitsu 1 3 , Tatsuya Shimoda 1 2
1 ERATO SHIMODA Nano-Liquid Process Project, JST, Nomi, Ishikawa, Japan, 3 Precision and Intelligence Laboratory, Tokyo institute of Tecnology, Yokohama, Kanagawa, Japan, 2 School of Material Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan
Show AbstractMore than a decade, a solution-based fabrication process has attracted much attention as an alternative to the conventional vacuum deposition process for fabrication of various electronic devices, because this process could facilitate dramatic low cost and low energy processing due to its low equipment costs, process simplicity and direct patternability by using various printing techniques. In recent years, oxide-based thin-film transistors (TFTs) with solution-processed conductive oxide channels such as ZnO, In-Zn-O and In-Ga-Zn-O have been reported. However, most of those TFTs employed solution process only for a channel layer while the rest parts of transistors were fabricated by conventional vacuum deposition processes. In order to achieve ultra low cost and low-energy fabrication, it is very important to realize a total solution-based process, which means solution derived materials are applied not only to a channel layer but also to other layers in the transistor including a gate insulator layer and electrodes. Meanwhile it is needless to say that the totally solution processed transistors ought to have a high device performance for putting them into practical use. With those motivations, we already developed a ferroelectric-gate thin-film transistor in which all parts of the device were fabricated from solution-derived materials only and confirmed their good device performance [1] In this study, we focused on solution-processed oxide TFTs using stacked paraelectric gate insulator to achieve good electrical performance. We fabricated oxide TFTs on a glass substrate in which a gate electrode, a gate insulator and a channel were fabricated by chemical solution deposition (CSD) process. We adopted a LaNiO3 (LNO) film as a gate electrode, La-Ta-O (LTO)/Bi-Nb-O (BNO) stacked film as a gate insulator, In-Zn-O film as a channel and ITO film as source-drain electrodes. In particular, the LTO thin film was an amorphous insulator with a relative permittivity of ~22 and the leakage current of ~10-6A/cm2 at 1MV/cm applied field while the BNO thin film was a polycrystalline insulator with the relative permittivity of ~170 and the leakage current of ~10-4A/cm2 at 1MV/cm applied field. By stacking LTO and BNO films, a good gate insulator was developed, in which the relative permittivity, the leakage current and the surface flatness were simultaneously satisfied. The fabricated TFTs exhibited typical n-channel transfer characteristics with no hysteresis and good saturation in out-put characteristics. The obtained on/off current ratio, subthreshold voltage swing and field-effect mobility were about 108, and 220mV/decade and 8.5cm2/Vs, respectively. [1] T. Miyasako, B. N. Q Trinh, M. Onoue, T. Kaneda, P. T. Tue E. Tokumitsu, T. Shimoda Appl. Phys. Lett., 97, 173509 (2010).
5:30 PM - S2.9
All-Solution-Processed Fully Transparent ITO/GaZnO/ITO Resistive Random Access Memory.
Areum Kim 1 , Keunkyu Song 1 , Youngwoo Kim 1 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractTransparent electronics has attracted great interests in recent years due to their fascinating potential to make significant impacts in the applications like transparent displays, transparent supercapacitors, ultraviolet (UV) detectors, and solar cells. Transparent non-volatile memory device based on the oxide semiconductor TFT has also been demonstrated, but they suffer from high voltage operation, complicate structure, and short retention time. Resistive random access memory (RRAM) is a promising device due to its great characteristics such as nonvolatility, low power consumption, fast operation speed, and simple structure, which can replace flash memory that faces scaling-down limitation. Resistive switching phenomenon has been observed in various oxides such as TiO2, NiO, ZnO, HfO2, Ta2O3, WO3, MnO2 and ZrO2. These oxides are mostly transparent having wide-band gap energies, so that RRAM can be a good candidate enabling transparent memory.After the first demonstration of fully transparent RRAM (TRRAM), various configurations such as ITO/TiO2/ITO, ITO/ZnO/ITO, ITO/ZnO:Mg/FTO, ITO/Gd2O3/ITO, ITO/InGaZnO/ITO, and Ga:ZnO/ZnO/Ga:ZnO have been reported. The active layers are either vacuum-deposited or solution processed, whereas the transparent electrodes are usually deposited by radio frequency (rf) magnetron sputter. This vacuum processing raises manufacturing costs, posing an obstacle for modern, mass-produced, large electronics. Scalable large-area fabrications based on solution processing are the object of growing interest with the ultimate goal of fabricating invisible electronics. Here, we demonstrate all-solution-processed fully transparent RRAM (sol-TRRAM) using ITO/GaZnO(GZO)/ITO configuration. All layers including an active layer and top and bottom electrodes were fabricated by solution-processing, and the transmittance of ITO/GZO/ITO/glass stacks was 87 % at 400 nm. The microstructure of ITO/GZO/ITO device was analyzed by high-resolution transmission electron microscopy and X-ray diffraction. X-ray photoelectron spectroscopy was performed on GZO thin film to characterize its structural information and defect state. To clarify the role of ITO electrode during switching, top electrode was varied to Pt, Al, and Ti, and resistive switching behavior were compared as a function of the electrode types. Our sol-TRRAM shows bipolar current-voltage (I-V) switching characteristics with a low operation current (<10-4A) and good endurance property under room temperature with few current fluctuations in the ON and OFF states.
S3: Poster Session: Solution-Processed PV, TCOs, TFTs
Session Chairs
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - S3.11
Sol-Gel Processing of Silver-Incorporated Hybrid Indium Tin Oxide (ITO) Thin Films.
Mehmet Kesim 1 , Caner Durucan 1
1 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractThe performance of ITO films in optoelectronic applications as transparent electrode is mainly defined by their intrinsic electrical conductivity and optical properties. The conductivity of ITO films can be further improved by incorporation of noble metal nanoparticles as they provide additional charge carriers. In this study, development of such silver-incorporated hybrid ITO film (Ag-ITO) on soda-lime-silica glass has been realized by aqueous processing routes, by sol-gel. As a wet processing method which is also advantageous due to its feasibility in coating large area substrates and also due to simple processing needs compared to vacuum techniques. The ITO sols were prepared from metal salts (In(NO3)3.xH2O, SnCl4.5H2O), acetylacetone and ethanol in which silver nitrate (AgNO3) was used as silver source. The effect of silver amount and number of Ag-ITO coating layers on microstructural, electrical and optical properties of the resultant spin-coated films have been reported. It has been shown that stable Ag-ITO coating sol can be prepared by diluting a plain ITO sol in the presence of polyvinylpyrrolidone (PVP) serving as stabilizing agent. Addition of silver at all proportions (0.01-0.05 M) enhances the film conductivity, however the improvement in electrical conductivity was more pronounced at high silver contents. On the other hand, high silver containing ITO films exhibit lower transparency (around 86%) in the visible range due to surface plasmon absorption of silver nanoparticles. It was observed that increasing the number of Ag-ITO coating layers do not only lowers the transparency of the ITO films, but also leads to stronger particle-particle and particle-matrix interactions and enhanced growth of silver nanoparticles after each deposition-calcination cycle. The results illustrate the potential of processing Ag-ITO films of improved conductivity by sol-gel routes, where the performance properties can be easily controlled and optimized by the choice of a couple of processing parameters, by the amount of silver in the coating sol and by the number of coating layers.
9:00 PM - S3.12
Low Temperature Microwave-Assisted Solvothermal Synthesis of TiO2 Thin Films.
Katharine Harrison 1 , B. Reeja Jayan 2 , Arumugam Manthiram 1 2
1 Mechanical Engineering, University of Texas at Austin, Austin, Texas, United States, 2 Materials Science and Engineering, University of Texas at Austin, Austin, Texas, United States
Show AbstractTitanium dioxide thin films with the anatase structure have widespread applications including solar cells, batteries, and electronics such as detectors, sensors, and transistors. Anatase films typically must be sintered at temperatures in the range of 450-600 oC, which is too high for some applications. Therefore, it is critical to develop low-temperature thin film synthesis methods for applications such as organic solar cells since the TiO2 must be deposited on plastic substrates which cannot withstand high temperatures. We have developed a novel sol-gel based microwave-assisted solvothermal method to synthesize thin anatase films on indium tin oxide (ITO) coated glass slides. We have confirmed through glancing angle X-ray diffraction (XRD) analysis that anatase films form at a solution temperature as low as 150 oC and the films form only on the indium tin oxide. This is likely because the microwaves interact strongly with the ITO leading to local heating of the ITO film, which acts as a nucleation site for TiO2. The films can be synthesized directly by placing an ITO coated glass slide in the microwave vessels or the sol-gel can be spin coated onto the ITO and then microwaved. Additionally, the film can be patterned by etching the ITO, and the TiO2 only forms on the ITO. The effects of temperature, reaction time, solvent, and slide orientation on film thickness, uniformity, and film cracking have been examined in this work.
9:00 PM - S3.13
Deposition of Metal Oxide Thin Films in Supercritical Carbon Dioxide.
Akiteru Kojima 1 , Yuichiro Hirota 1 , Koki Nakata 1 , Takeyasu Saito 1 , Naoki Okamoto 1 , Kazuo Kondo 1 , Seiichi Takami 2
1 , Osaka Prefecture University, Sakai-shi Japan, 2 , Institute of Multidisciplinary Research for Advanced Materials Tohoku University , Sendai-shi Japan
Show AbstractDeposition of Metal Oxide Thin Films in Supercritical Carbon DioxideMetal oxide thin films are of great interest for various applications depending on their chemical, electrical and magnetic properties. A chemical vapor deposition (CVD) method can deposit uniform metal oxide thin films, like SiO2, Al2O3 and ZnO etc, however, it is difficult to deposit the compositionally uniform multi-component oxide thin films. Therefore, a novel film-forming method should be developed. A method using supercritical carbon dioxide (scCO2) is one of the promising alternatives. Supercritical carbon dioxide possesses unique characteristics, such as high diffusivity, high solvent capability, low viscosity and zero surface tension, which allows possible candidate for multi-component thin films deposition with conformal step coverage and superior compositional uniformity. In this work, deposition characteristics of the Al2O3 thin films and ferroelectric Bi4Ti3O12 (BIT) thin films in scCO2 were investigated. Al(acac)3 was used as a precursor for Al2O3 deposition and Bi(C6H5)3 and Ti(O-i-C3H7)2(DPM)2 were used as precursors for BIT deposition, in which the ratio of Bi(C6H5)3/Ti(O-i-C3H7)2(DPM)2 was varied from 0.75 to 1.5. A precleaned Si substrate (1 cm×4 cm) was set in reactor, then prescribed amount of precursors and additive agents were introduced in the reactor. After sealing, CO2 was pressurized to desired pressure and the temperature of the reactor was increased to growth temperature set point (260-400°C) and the pressure in reactor was then approximately 16 MPa. After reaction was completed, surface morphology and thickness of deposited films were evaluated by field emission scanning electron microscopy (FE-SEM) and ellipsometry, respectively. The crystallographic structures of BIT films were determined by X-ray diffraction before and after 1 hour annealing at 800°C in oxygen.For Al2O3 deposition, the growth rate was enhanced about 5 times by isopropyl alcohol addition and the growth rate ranged from 9.8 to 4.5 nm/min at the temperature from 320 to 260°C. The activation energy calculated from the Al2O3 deposition rate in scCO2 was 59.2 kJ/mol without additives and 32.5 kJ/mol with additives, respectively. This activation energy was lower than that of a vacuum-based process (80-100 kJ/mol)[1]. For BIT deposition, only Bi2O3 peaks were observed before annealing, however, BIT peaks appeared after were annealing when the ratio, Bi(C6H5)3/Ti(O-i-C3H7)2(DPM)2, was 1.5, which suggests that this films consists of Bi2O3 and BIT. This trend was almost the same with other precursor ratios. Further compositional evaluation and optimization is under study.[1] Q. Peng et al., Thin Solid Films 516 (2008) 4997-5003.
9:00 PM - S3.15
High Performance Bi-Nb-Ox Thin-Film Capacitors Fabricated by Chemical Solution Deposition Process.
Masatoshi Onoue 1 , Takaaki Miyasako 1 2 , Eisuke Tokumitsu 1 2 , Tatsuya Shimoda 1 3
1 , Japan Science and Technology Agency, Nomi Japan, 2 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan, 3 , Japan Advanced Institute of Science and Tecnology, Nomi Japan
Show AbstractVarious metal-oxide paraelectric insulators have been studied for long time, and those have been used not only in passive components such as voltage-tunable devices, high density storage condensers for telecommunication system but also in active components such as gate insulators for thin-film transistors and metal-oxide-semiconductor field effect transistors. The required performances for those insulators are dependent on device applications. In particular, we focused on paraelectric thin-film capacitors which have a high relative permittivity (>100) and a low dielectric loss. Among them, (Ba, Sr)TiO3 (BST) paraelectric thin films have been widely investigated because of their high relative permittivity (~400). However, they have inherent problem of large dielectric loss. Meanwhile, bismuth based paraelectric insulators such as Bi-Nb-Ox (BNO) and Bi-Zn-Nb-Ox (BZN) have been considered as an alternative to BST due to their low dielectric loss as well as high relative permittivity. But there have been not many reports about BNO (Bi/Nb=1/1) thin-films and the obtained relative permittivity was only around 50 by using mixed oxide method [1]. In this study, we report a new type of the BNO (Bi/Nb=1/1) film having very high relative permittivity via chemical solution deposition (CSD) process. We fabricated a BiNbOx (BNO) thin film (~170nm) on Pt substrate (Pt/TiOx/SiO2/Si) by using CSD process. The precursor solution of the BNO film was prepared by dissolving metal organic based bismuth and niobium in alcohol solvent. The BNO precursor solution was spin-coated on a Pt substrate, dried at 250°C and then annealed at 550°C in O2 for 20min. Then, top electrodes of Pt (~150nm) were deposited on the BNO film by sputtering to make a capacitor. As a reference, a sputtered BNO capacitor was also fabricated on a Pt substrate. The obtained relative permittivity and dielectric loss at room temperature of the solution processed BNO capacitor were about 170 and 1.6×10-3 at 1kHz applied frequency, respectively, while those of the sputtered BNO capacitor were about 65 and 4.8×10-3, respectively. These high properties of the solution processed BNO films were repeatedly confirmed, resulting in the values between 150 and 200. We observed cross sectional TEM images and found that there existed a unique phase structure, which could be considered as a cause of the high relative permittivity. It is concluded that during the decomposition process from solution to a solid film through a gel condition BNO precursor is put in a proper condition to decompose to such a special phase as would cause a high properties. It is clearly said the solution process created a new type of material. Details will be reported on the conference.[1] D. Zhou et al., Appl. Phys. Lett. 90, 172910 (2007)
9:00 PM - S3.16
Donor and Defect States in Solution-Processed Zinc Tin Oxide.
W. Hu 1 , I. Bonachera 1 , R. Peterson 1
1 Electrical and Computer Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractSolution processes such as dip-coating, spin-coating and ink-jet printing are now commonly used techniques for the deposition of zinc oxide and zinc tin oxide (ZTO), which are promising materials for the active layer of transparent thin film transistors (TFTs) used in large area displays. Others have made solution-processed ZTO transistors with mobilities from 0.03 cm2/(V●s) to 16.2 cm2/(V●s) and vacuum-processed ZTO from 5 cm2/(V●s) to 50 cm2/(V●s), and ZTO TFTs have shown good electrical stress stability. Here we investigate the temperature dependence of solution-processed TFT performance to explore the donor and defect states of these materials.Back gate, top contact TFTs are fabricated. Heavily doped Si is used as the gate and thermally grown SiO2 as the gate dielectric. The active layer is deposited by spin-coating precursor solutions and subsequent annealing. The solutions are prepared using zinc acetate dihydrate and/or tin (II) acetate in 2-methoxyethanol. Contact electrodes are sputtered Aluminum. ZTO TFTs exhibit room temperature mobilities of 0.5 cm2/(V●s), turn-on voltages of 12 V, sub-threshold slopes of 1.6 V/dec, and ON/OFF current ratios of > 105 (limited by gate current).Cryogenic properties of the fabricated ZnO and ZTO TFTs are studied. The field-effect mobility of ZTO TFTs annealed at 500°C obeys an Arrhenius function over temperatures ranging from 300K to 77K. The activation energy is 14.7meV. This shows that ZTO has a large concentration of shallow donors, presumably oxygen-vacancy related, so that mobile electrons can easily populate the conduction band at room temperature. The ZnO films, which are typically resistive with sheet resistance of about 600 kΩ per square, show similarly shallow dopants with only a 3.4x reduction in conductivity from 300K to 77K.Moreover, as the temperature is reduced from 300K to 77K the turn-on voltage shifts from +12 V to +42 V, while the sub-threshold slope increases only slightly. The positive shift in transistor turn-on as temperature is reduced reveals the existence of positively charged trap states deep in the band, with an areal density of 2.9x1012 q+/cm2 which compares favorably with typical interface state densities for SiO2. In ZTO TFTs, these trap states might be associated with dangling bonds, grain boundary defects, insulator-semiconductor interface states or states at the exposed semiconductor surface. Work is ongoing to characterize more precisely the nature of these states.
9:00 PM - S3.17
P-Type Amorphous Oxide Semiconductors Ln-Ru-O from Solution Processing.
Jinwang Li 1 , Eisuke Tokumitsu 1 2 , Mikio Koyano 3 , Tatsuya Shimoda 1 3
1 ERATO, Shimoda Nano-Liquid Process Project, Japan Science and Technology Agency (JST), Nomi, Ishikawa, Japan, 2 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan, 3 School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan
Show AbstractWe have synthesized a class of amorphous semiconductors Ln-Ru-O (Ln = lanthanide elements except Ce) using a simple solution deposition process. The films show low resistivity (down to 10-2 – 10-3 Ω cm) around room temperature. La-Ru-O was analyzed as a representative, with comparison to sputtered samples. Resistivity-temperature relation analysis revealed semiconducting behavior with carrier transport by variable range hopping. Seebeck measurement indicated the carriers were p-type. The valence band structure was analyzed using ultraviolet and X-ray photoelectron spectroscopy, which showed a valence band hybridized with O 2p and Ru 4d orbitals, explaining the origin of p-type conduction. The optical band gap is around 1 eV. The film surfaces have excellent smoothness (root mean square roughness <0.3 nm and peak-valley < 3 nm by AFM on 1 μm × 1 μm area). The solution process is not only simple and of low cost, but also resulted in films of lower resistivity. Compared to other oxides and processes, these materials have several advantages. First, they may be the lowest in resistivity (around 2 orders lower) among amorphous oxides deposited by solution techniques. Second, they are novel p-type amorphous oxides originated by a solution process. Before these oxides, only sputtered Zn-Rh-O with a resistivity of ~0.5 Ω cm was known as a p-type amorphous oxide. Third, they have excellent thermal stability, remaining amorphous state up to 800°C. Fourth, the solution processing temperature can be 400°C or lower. Further, an advantage to stress for amorphous materials over crystals is that amorphous materials are well compatible with scaling down. By using these, it would be very easy to make a nano-pattern, because amorphous materials are neither constrained by the crystal size, nor distorted/damaged during crystallization as found in the process of crystalline materials. Therefore, these materials have a high potential in electronic applications. The solution process offers further advantages for low cost and direct patterning (e.g., by imprinting).
9:00 PM - S3.18
Influence of Dye Adsorption Conditions on the Properties of Electrodeposited, Dye-Sensitized Zinc Oxide Films.
Melanie Rudolph 1 , Silvia Schmandt 1 , Derck Schlettwein 1
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany
Show AbstractElectrodeposition of nanoporous zinc oxide from aqueous solutions is a viable low-cost and low-temperature way to obtain high surface area films suitable as photoelectrodes in dye-sensitized solar cells (DSCs). Nanostructuration of the films is achieved directly during growth by the presence of organic template molecules like eosinY or coumarin 343 in the plating bath. Such molecules selectively bind to the surface of zinc oxide and thereby act as structure-directing agents. This kind of electrochemical self-assembly leads to formation of inorganic/organic hybrid materials in which the inorganic and organic phases are intimately mixed on the nm scale. The template molecules can be completely removed afterwards by dipping the hybrid films into a slightly alkaline solution at room temperature, yielding a sponge-like, pure ZnO matrix of well-defined crystallinity and electrical connectivity. In order to obtain dye-sensitized photoelectrodes, the nanostructured semiconductor films are processed in a solution of a photosensitizer like, e.g., the indoline dye D149, which binds to the oxide surface via its carboxylic acid function. Optimization of the processing conditions is crucial to obtain high-efficiency DSCs, because the semiconductor-dye bond and the molecular arrangement on the surface are critical factors determining the rate of electron injection, their recombination and hence the quantum efficiency of overall photon-to-electron conversion. The present study comprised variation of the conditions of dye adsorption on nanostructured zinc oxide films electrodeposited in the presence of eosinY. For this purpose, ZnO samples of different film thickness and porosity were prepared. The films were characterized by profilometry, color confocal scanning laser microscopy, atomic absorption spectrometry and scanning electron microscopy. Functionalization was reached by immersion into an organic solution of D149 at room temperature, where the composition of the dye bath and the residence time in the solution were varied. The amount of sensitizer molecules on the films was determined by UV/Vis absorption spectroscopy in solution and in solid state. The influence of structural features on the uptake of dye was studied. Photoelectrochemical characterization (I-V curves, time and frequency resolved photocurrent and photovoltage measurements) of the dye-sensitized ZnO films in contact with an organic iodide/triiodide electrolyte was performed. The influence of overall dye content and of the dye distribution on the inner electrode surface on individual steps of photoelectrochemical energy conversion will be discussed.
9:00 PM - S3.2
Aqueous Solution Deposition of CIS/CIGS Solar Absorber.
Wei Wang 1 , Benjamin Clark 2 , Robert Kykyneshi 1 , Douglas Keszler 1
1 Chemistry, Oregon State University, Corvallis, Oregon, United States, 2 , Inpria Corp., Corvallis, Oregon, United States
Show AbstractCuInS2 and CuIn1-xGaxS2 (0 ≤ x ≤ 0.5) thin films have been deposited from a one-pot aqueous precursor via spin coating in air followed by rapid thermal annealing in an inert atmosphere. Single crystals of the Cu and In precursors have been isolated and characterized by single crystal X-ray diffraction. Thin-film X-ray diffraction results are consistent with the formation of single phase sulfide films. The change in unit-cell dimensions are consistent with the replacement of In by Ga in the CuIn1-xGaxS2 materials. Complete results on the thin films with respect to composition (TOF-SIMS, EPMA); film morphology (SEM); optical absorption coefficients (transmission, reflection, spectroscopic ellipsometry); and electrical properties (majority carrier type, carrier concentration, and mobility) will be described. Progress towards production of micron-thick films on Mo-coated glass will be presented.
9:00 PM - S3.20
Solution Transformation of Metal Thin Films to II-VI Semiconductor Films.
Adam Gross 1
1 , HRL Laboratories, LLC, Malibu, California, United States
Show AbstractDirect deposition of semiconductor layers over large areas is challenging and the films frequently require high temperature sintering to attain low sheet resistances. Another route to forming II-VI semiconductor materials is through the low temperature solution based sulfurization and ion exchange of silver nanoparticles. Because silver films may be scalably deposited on many substrates through evaporation, electro- and electroless plating, we investigate the low temperature solution based transformation of these layers to II-VI thin films. This chemical transformation is problematic in thin films because diffusion occurs directionally and the ~50% increase in lattice expansion from silver to semiconductor layers may debond the film. Silver films were deposited on glass with adhesion layers and successfully transformed to well adhered CdS, MnS, and CuS films at temperatures ≤ 60 °C. Sheet resistances as low as 56 ohms per square for CuS and 97 ohms per square for Cu doped MnS were obtained. Characterization of the II-VI films using optical absorption spectroscopy, SEM, and XRD will be presented. These results demonstrate that solution based sulfurization and ion-exchange is a viable mechanism for forming II-VI semiconductor thin films with good conductivities from metal films at low temperatures.
9:00 PM - S3.21
Preliminary Work on Electrodeposition of a Photovoltaic Using E-ALD.
Brian Perdue 1 , John Stickney 1
1 , University of Georgia, Athens, Georgia, United States
Show AbstractCurrent progress in the formation of a CdTe/CdS photovoltaic by Electrochemical Atomic Layer Deposition (E-ALD) will be presented. E-ALD is a condensed phase variant of atomic layer deposition (ALD). In ALD the deposition of a compound is achieved by means of sequential surface limiting reactions in which the components are deposited one atomic layer at a time. In E-ALD the individual atomic layers are formed using underpotential deposition (UPD), an electrochemical surface limited reaction. XRD results show that the CdTe layer has a strong preferred <111> orientation as deposited. EPMA results show stoichiometric Cd, with a Cd/Te ratio of 1.02. Photoelectrochemical results indicated a band gap of 1.5 eV, p-type as deposited, no annealing. Different CdS deposition methods were also investigated. CdS was deposited by chemical bath deposition (CBD), successive ionic layer absorption and reaction (SILAR) and E-ALD. Results showed that the average Cd/S ratio, determined using EPMA, was 1.07, 1.10, and 1.05 for CBD, SILAR and ALD respectively. Photoelectrochemical results show that the photoresponse for E-ALD grown CdS was the highest and CBD was the least photoactive. As exciton creation in the CdS layer is parasitic to the photovoltaic, CBD CdS was used in first attempts at PV construction. Solar cells were fabricated in the substrate configuration, using 200 nm of E-ALD grown CdTe and 80 nm of CBD grown CdS. 100 nm ITO was magnetron sputtered on top to complete the cell. Cells achieve a maximum current density of 103 μA/cm2 when exposed to light; however appear to suffer from shunts, work on these defects is underway.
9:00 PM - S3.22
Solution Processing of Ag Nanowire Hybrid Electrode for Organic Photovoltaic Devices.
Ju Hwan Choi 1 , Sujin Baek 1 , Dang-Mo Yoon 1 , Hak-jun Chung 1 , Young Kyu Hong 1 , BumJoo Lee 1 , Jin-Koog Shin 1
1 Korea Printed Electronics Center, Korea Electronics Technology Institute, Jeonju, Jeonrabook-do, Korea (the Republic of)
Show AbstractPrinted devices especially organic photovoltaic (OPV) devices have gained strong attention due to the possibilities of low-cost fabrication as well as mechanical flexibility. Manufacturing printed device is thought to be inexpensive but the materials related it is remained persistently expensive. Many have addressed this issue by replacing expensive transparent conductive indium tin oxide (ITO). Furthermore, market dominant ITO films on flexible substrates readily crack leading to device failure. Achieving highly conductive and transparent electrode materials are one of the challenging tasks towards inexpensive, high yield printed OPV. Various materials including Ag nanowire have been investigated as candidate materials for printed electrodes, wiring, and conductive film substituting the oxide-based electrode materials. Solution processing of Ag nanowires which forms random network [1] or patterned grid [2] for transparent conductive electrodes showed promising performance compared to ITO. The combination of Ag nanowire and conjugated polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) as mixture and/or multilayer were investigated and optimized with various processing conditions as well as additives. We have explored the effects of these silver nanowires and PEDOT:PSS combinations on the performance for the printed OPV. In this work, different types of conductive PEDOT:PSS mixtures with additives for Organic Photovoltaic were printed forming Ag NWs random network or multilayer and followed by layers of Poly-(3-hexylthiophene-2,5-diyl) and C60-butyric-acidmethyl-ester (P3HT:PCBM). Introducing these electrodes in our OPV cells, the short-circuit current and the fill factor increased with optimized printing process conditions. Utilizing these results, equal or even better efficiencies for large area printed OPV devices can be reached. These combinations of Ag nanowire and PEDOT:PSS have proven to be an effective way as a low-cost and easy process for printed conductive transparent substrates which can be applied to other printed devices. [1] J. Y. Lee, S. T. Connor, Y. Cui, and P. Peumans, Nano Lett. vol. 8, 689-692 (2008). [2] J. Zou, H.-L. Yip, S. K. Hau, and A. K.-Y. Jen, Appl. Phys. Lett. 96 203301 (2010).
9:00 PM - S3.23
Large-Area Solution-Processed Superhydrophobic and Broadband Antireflective Organically Modified Silica Coatings for Solar Cells.
Adem Yildirim 1 2 , Hulya Budunoglu 1 2 , Bihter Daglar 1 2 , Mehmet Bayindir 1 2 3
1 , UNAM-National Nanotechnology Research Center, Ankara Turkey, 2 Material Science and Nanotechnology Institute, Engineering and Science , Ankara Turkey, 3 Department of Physics, Bilkent University, Ankara Turkey
Show AbstractDust accumulation on the surface of solar cells degrades solar cell performance. To prevent this transparent superhydrophobic surfaces are desired because of their self-cleaning property. However, preparation of transparent superhydrophobic surfaces is still challenging because high surface roughness needed for superhydrophobicity. Highly rough surfaces decrease the transmission by scattering especially at visible wavelengths and result in opaque or translucent appearance. In order to achieve a transparent superhydrophobic surface, surface roughness must be carefully engineered. Also superhydrophobic surfaces must be mechanically and thermally stable to resist the outdoor conditions in order to use them in photovoltaic applications. In this context, we synthesized nanoporous organically modified silica (ormosil) coatings from MTMS and TMOS monomers by a template-free sol-gel method. We observed that when the TMOS ratio (v/v) is between 5-9% transparent and superhydrophobic surfaces can be obtained. Superhydrophobic films can be coated to surfaces directly from the ormosil colloidal dispersions by spin, dip or spray coating methods which enable the low-cost and large-area fabrication. Also, coatings can be prepared on almost any substrate including, glass, silicon, plastics and paper. Furthermore, we investigated the mechanical properties of the coatings by adhesive tape and water dripping tests and thermal properties by heating the coatings to the elevated temperatures. The coatings exhibited mechanically and thermally stable (up to 500 °C) superhydrophobic property. In addition, we prepared a three layered coating on an organic solar by using ormosil thin films with different refractive indices. The coating demonstrates broadband antireflective property together with superhydrophobicity. Because of the broadband antireflective property the solar cell performance found to be improved as ~%3. Such mechanically and thermally stable large-area broadband anti-reflective and self-cleaning surfaces can be used both to improve of the solar cell performance and to protect it from environmental harms.
9:00 PM - S3.3
Solution-Processed Photovoltaic and Photodetector Based on Iron Disulfide (FeS2) Nanocrystal.
Diyan Wang 1 , You-Ting Jiang 2 , Chia-Chun Chen 2 3 , Chun-Wei Chen 1
1 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan, 2 Department of Chemistry, National Taiwan Normal University, Taipei Taiwan, 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan
Show AbstractIron disulfide (FeS2) is a promising earth abundant and environmentally friendly semiconductor with a large optical absorption coefficient (6.0 × 105 cm-1) and a narrow bandgap of 0.95 eV. In this work, we would like to present the fabrication of the solution-processable photovoltaic and photodetector using FeS2 nanocrystal ink. The device performances depending on various nanocrystal shapes and sizes will be addressed and the mechanisms of carrier generation and transport will be also investigated by various transient techniques. The extended near infrared (NIR) light harvesting of the photoactive layer consisting of solution processed FeS2 nanocrystals indicates the potential applications in large-area and low-cost NIR photodetecting and photovoltaic devices.
9:00 PM - S3.4
Solution Processable CdS, CdS-AgInS2 Semiconductor Nanocrystals-Benzothiaziazole Polymer Nanocomposites.
Pradipta Maiti 1 , Venkatesh Mamidala 2 , Venkartam Nalla 2 , Ji Wei 2 , Suresh Valiyaveettil 1
1 Chemistry, National University of Singapore, Singapore Singapore, 2 Physics, National University of Singapore, Singapore Singapore
Show AbstractHybrid inorganic-organic nanomaterials are interesting owing to the integrated functionalities of the components present in the system. The combined properties endow the nanocomposites with promising applications in the field of FET, OPV, LED and LASER. Because interfaces between polymer and nanocrystals have substantial effect on the electronic interaction, and aggregation of nanocrystals causes problems in preparations of composite materials. On the other hand physical blending of the components is not suitable for producing new materials with the desired properties. Here we discuss a one pot synthesis and characterization of CdS, CdS-AgInS2 nanocrystals in benzothiadiazole based semiconducting polymer solution. The CdS nanorods synthesized were 20 nm in length and 5 nm in diameter whereas the CdS-AgInS2 nanocrystals were anisotropic in nature. Photophysical studies of these nanocomposites showed considerable amount of charge transfer from the nanocrystals to the polymer. Those synthesized nanocomposites show strong non-linear absorption in solution. We estimated effective scattering coefficient for the nanocomposites, which is absent in case of pure polymers. These differences indicate that the non-linear optical property arises from the surface chemistry of nanocrystals and Benzothiadiazole copolymers. The presentation will focus on synthesis, characterization and photophysical studies of the hybrid materials.
9:00 PM - S3.5
Effect of Nanosized CdS in Photovoltaic Properties of CdS- Poly3-Hexylthiophene Heterojunctions.
Claudia Martinez-Alonso 1 , Hugo Cortina 1 , Ma.Elena Nicho 2 , Hailin Hu 1
1 , Centro de Investigacion en Energia, UNAM, Temixco, Morelos, Mexico, 2 , Centro de Investigacion en Ingenieria y Ciencias Aplicadas, UAEM, Cuernavaca, Morelos, Mexico
Show AbstractHybrid photovoltaic (PV) solar cells studied in this work were formed by n-type inorganic cadmium sulfide (CdS) and p-type conjugated polymer poly3-hexylthiophene (P3HT). CdS nanoparticles of about 10 nm diameter were obtained by a simple and fast solution precipitation method, whereas P3HT was polymerized from 3-hexylthiophene by an oxidative method. Three geometric structures of CdS/P3HT solar cells have been chosen: (1) the bulk one whose active layer consisted of a blend of CdS powder with the P3HT solution, (2) the quasi-bilayer one formed by collocating the CdS powder on conductive substrate and then drop casting the P3HT solution, and (3) the planar one consisting in thin films of CdS and P3HT for comparison purpose. First of all, it is observed that the type of solvent used for P3HT product and the drying rate of the active layer influence significantly on the PV performance of all the cells. A solvent with an intermediate vapor pressure was adequate for hybrid bulk solar cells to balance the phase separation effect and macromolecular rearrangement during the polymer solution drying process. PV performance of each type of the cells has been analyzed, and the most interesting observation is that the presence of CdS nanoparticles in the first two geometric structure cells enhances both open circuit voltage (Voc) and short circuit current (Jsc) values compared to planar one. The similarity and difference in PV performance between bulk and quasi-bilayer cells were studied from materials as well as device point of view: the morphology (SEM and AFM) and optical properties of active layers as functions of type of solvents, the drying process, the annealing process, and analysis of current- voltage (I-V) curves and quantum efficiency of the cells prepared under different procedures. A hypothesis has been given to explain the origin of the improvement in PV performance of nanostructured hybrid CdS-P3HT solar cells.
9:00 PM - S3.6
Optimization of Solution Processed Nanocrystal Quantum Dot Tandem Solar Cells Guided by Optical Modeling Based on Scattering Matrix Formalism.
Joshua Choi 1 2 , Apurva Sisodia 1 , Whitney Wenger 1 , Tobias Hanrath 1
1 Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 2 Applied and Engineering Physics, Cornell Universiy, Ithaca, New York, United States
Show AbstractSemiconductor nanocrystal quantum dots (NQDs) are a promising material system for low-cost multijunction solar cells. Their high absorption cross section, size-tunable energy gaps and solution processability offer a unique opportunity to realize high-conversion efficiency in low-cost device structures by allowing fabrication of solution processed multijunction solar cells composed of absorber layers with cascaded energy gaps. We recently demonstrated proof-of-principle tandem solar cells produced from colloidal suspensions of size-tuned semiconductor NQDs.[1] Using size-tuned PbS NQDs with energy gaps in the range of 0.7 eV and 2.0 eV, we demonstrated NQD tandem cells with an open circuit voltage (Voc) approaching 1V. We reported a study of the structural, optical and electrical properties of the interlayer comprised of ZnO, thin metal layer, and hole conducting polymer and showed that the device performance depends critically on the optical and electrical properties of the interlayer. Optimization of the device performance is contingent upon better management of light absorption and charge collection in the multilayered device stack. Towards that goal, we modeled the optical electric field in the tandem device stack using scattering matrix formalism. The model used complex index of refraction of each layer obtained from spectroscopic ellipsometry measurements. From the model, we show that thin film interference effects and the ZnO layer as ‘optical spacer’ (allowing NQD film to be away from optical electric field quenching metal electrode) can be exploited to place peaks of optical electric field distribution inside the NQD films. For initial experiments, we focus on thin and fixed thickness (50 nm) NQD layers to decouple effect of electrical transport properties from the device performance while varying the thicknesses of interlayer and electron and hole transporting layers to maximize short circuit current density and experimentally demonstrate corresponding tandem devices.[1] Choi, J. J., Wenger, W. N., Hoffman, R. S., Lim, Y. F., Luria, J. Jasieniak, J., Marohn, J. A., Hanrath, T. Advanced Materials DOI: 10.1002/adma.201100723
9:00 PM - S3.7
Surfactant-Free CuInSe2 Nanocrystals Transformed from In2Se3 Nanoparticles and Their Application for a Flexible Ultraviolet Detector.
Yuho Min 1 , Minwoo Park 1 , Minkwan Shin 1 , Unyong Jeong 1
1 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractSynthesis of semicondutor nanoparticles has been extensively studied because of their outstanding physical and chemical properties. The chalcogenide compounds which belong to III-VI and I-III-VI are one of the most attractive materials for various electronic applications. Although a large number of solution-based methods to synthesize semicondutor nanoparticles have been estalished, many approaches require high processing temperature, long reaction duration or specific and toxic agents. In this talk, In2Se3 nanoparticles were synthesized in an aqueous solution without using any surfactant and then they were chemically transformed into CuInSe2 nanocrystals. The transformation was thermodynamically favorable and fast in mild reaction conditions, which allowed massive production of CuInSe2 nanocrystals. By the virtue of the surface charges, the CuInSe2 nanocrystals were well-dispersed in polar solvents. The surfactant-free nanocrystals enabled the formation of a semiconducting CuInSe2 film on a flexible polymer substrate without any thermal treatment. We took the advantage to fabricate a flexible UV photodetector. The detection sensitivity remained the same until the bending radius was reduced down to 4 mm. The dynamic response of the film device was stable and reproducible during the light irradiation (350 nm).
9:00 PM - S3.8
Nanocrystal Quantum Dot Tandem Solar Cells – Controlling Charge Recombination at the Interlayer.
Whitney Wenger 1 , Joshua Choi 1 2 , Tobias Hanrath 1
1 Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 2 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractAdvances in the creation of nanomaterials with optical and electrical properties by design have created a fertile opportunity space for renewable energy technologies. A particularly intriguing case in point is the prospect of exploiting size-tuned energy levels in semiconductor colloidal nanocrystal quantum dots to create multi-junction solar cells with cascaded energy gaps. We have recently demonstrated a proof-of-principle tandem photovoltaic device based on colloidal nanocrystal quantum dots.[1] One of the most daunting challenges in the fabrication of tandem solar cells is designing an interlayer connecting the front and back cell. The interlayer must meet two critical optical and electrical demands: first, it should be optically transparent to pass light to the underlying cell; second, it must provide appropriate energy level alignment to accept electrons and holes from the subcells and efficiently recombine them without degrading the overall photovoltage of the cell. Many multijunction solar cells utilize an interlayer created between an n-type metal oxide and p-type PEDOT:PSS. In some cases, an ohmic junction is obtained with the addition of an ultrathin metal film possessing an energy level between those of the n- and p-type materials. Our first demonstration of a multijunction cell using solution-processed nanocrystal active layers featured an ultra-thin film of vacuum-deposited gold between n- and p-type materials. Fundamentally, the understanding of the effects governing the creation of the ohmic junction within the interlayer remains not well understood. To address this knowledge gap we probed interfacial charge transfer processes in the interlayer. We replaced the vacuum-deposited ultra-thin metal film with solution-processed gold and silver metal nanoparticles. Colloidal metal nanoparticle films offer several promising advantages including: (i) better control over the metal particle size, (ii) solution-processing, (iii) improved control over the chemical interface between the metal and adjacent layers through adjustment of the metal nanoparticle ligand chemistry, and (iv) opportunities to manage light absorption in the device stack through plasmonic effects. We compare the interlayer performance in tandem photovoltaic devices based on ultra-thin vacuum-deposited metal films with metal-nanoparticle based interlayers processed entirely from solution. We systematically studied charge recombination in the metal interlayer as a function of ligand chemistry, metal nanoparticle composition and size. [1] Choi, J. J., Wenger, W. N., Hoffman, R. S., Lim, Y. F., Luria, J. Jasieniak, J., Marohn, J. A., Hanrath, T. Advanced Materials DOI: 10.1002/adma.201100723
9:00 PM - S3.9
CIS Thin Film Synthesis Route with Non-Vacuum Precursor Deposition and Thermal Treatment.
Dongwook Lee 1
1 Chemical Engineering, POSTECH, Pohang Korea (the Republic of)
Show AbstractIn polycrystalline semiconductor thin films, CuInSe2(CIS) is widely studied for photovoltaic applications. CIS thin film solar cell has great potential to substitute for a light-absorber layer of solar cell because of high absorption coefficient, and tuneable, direct band gap structure compared to Si-based photovoltaics. However, high quality CIS thin films which recorded much than 15% of efficiency were synthesized through high vacuum deposition process such as thermal evaporation and sputtering technique. Molecular level precursor solution approaches have a lot of advantages for continuous deposition, material usage and process cost reduction. In this work, we successfully synthesized stoichiometric CIS thin films by combination of non-toxic, stable precursor paste and post-heat treatment. And film growth mechanism (precursor decomposition, inter-mediate phase formation, CIS film formation) was suggested with varied annealing temperature using SEM, XRD and TGA analysis. Precursor layer containing metal and chalcogen ion gradually decomposed and formed metal-chalcogenide (CuxSe, In2Se3) phases. At higher temperature, CIS chalcopyrite phases such as (112), (204), and (312) planes were appeared and showed 500 nm thickness of continuous morphology. And we observed that CIS films showed high optical absorbance behaviour at visible and near-IR light region, so it presents great potential to reduce fabrication cost for thin film solar cells.
Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
Patrick J. Smith The University of Sheffield
David B. Mitzi IBM T. J. Watson Research Center
Aoife Morrin Dublin City University
S4: Inkjet Printing and Layered Deposition
Session Chairs
Wednesday AM, November 30, 2011
Room 310 (Hynes)
9:15 AM - S4.1
Hybrid Semiconductor–Insulator-Semiconductor Inversion PV Cell, Prepared from Components at Room Temperature.
Rotem HarLavan 1 , David Cahen 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovoth Israel
Show AbstractWe describe a hybrid inorganic-organic solar cell that is completely fabricated from its components at room temperature. The cell is composed of an n-Si absorber interface, passivated chemically by a layer of organic molecules and electrically contacted by a conductive polymer, PEDOT:PSS. As the Si is type-inverted, effectively an SIS type solar cell results without insulating film. The good lateral conduction of minority carriers in the inversion layer helps to mitigate the high sheet resistance limitation of PEDOT:PSS.Inversion layer solar cells, also known as Schottky barrier or MIS solar cells, were introduced in the 1970s to reduce (mainly Si) solar cell fabrication costs, without significant adverse effects on their efficiency. Combining a high work function metal with n-Si, or a low work function metal with p-Si should, in principle, lead to type inversion in the space-charge region (SCR) of the Si. Such type conversion creates, de facto, an n-p+ (p-n+) junction, without the need for a high-temperature diffusion process step. The efficiency of SIS solar cell can exceed that of its parallel MIS because the absorber's majority carrier transport is suppressed by the forbidden gap of the degenerate wide bandgap window semiconductor. We showed earlier, by using a self-assembled monolayer of organic molecules of different thicknesses as insulator in Metal-Insulator-Semiconductor junction, that the interfacial layer in such structures should not present a significant insulating barrier, and can be as thin as 0.2 nm, and still lead to strong inversion of the under-lying Si. Based on these findings an interfacial layer in an inversion layer solar cell ought to fulfill the following requirements:- prevent direct metal-semiconductor chemical interaction, and MIGS formation;- passivate the Si surface chemically and electrically- optionally, introduce an interface dipole to assist achieving Si type inversion.Here we present for the first time a hybrid SIS solar with inverted n-Si as the absorber and PEDOT:PSS window layer. The whole fabrication is carried out, from the components, at room temperature and under ambient condition. Without optimization, these cells show > 7% conversion efficiency. The degenerate p-type PEDOT:PSS layer inverts the Si space charge region and allows minority carriers to diffuse within that layer to reach a Au grid current collector. A dielectric anti-reflective coating should improve the cell's photon harvesting and help to reach double-digit conversion efficiencies. The concept, which is valid for all semiconductor absorbers, is especially appealing for polycrys-talline material, with which it may lead to cost-effective hybrid solar cells.Thanks to P. Joshi, R. Kazaz, O. Yaffe, Dr. H. Cohen (Weizmann Inst.).
9:30 AM - **S4.2
Alternative Sintering Approaches for Fast Sintering of Inkjet Printed Nanoparticles for R2R Applications.
Jolke Perelaer 1 , Ulrich Schubert 1
1 Laboratory of Organic and Macromolecular Chemistry (IOMC) and Jena Center for Soft Matter (JCSM), Friedrich-Schiller-University Jena, Jena Germany
Show AbstractIn recent years, inkjet printing is increasingly used as a flexible and digital patterning technique in the field of microelectronics. The main advantages of inkjet printing are its ease of processing and its potential for mass production. Furthermore, based on its digital properties, inkjet printing is both a flexible and low cost technique, since materials are used in an efficient manner, compared to other patterning techniques, like non-digital printing techniques and spin coating, which significantly reduces waste production. During the last years, there has been a growing interest in printing silver inks as a basis for conductive tracks in microelectronics applications, including OLED, OPV and RFID.[1-6]Currently, much interest is dedicated to inkjet printing of conductive materials, such as silver nanoparticles; as an effect of their reduced particle size, the melting temperature is reduced significantly. Although the sintering temperatures are reduced to well below 300 °C, these temperatures are not compatible with most polymer foils, limiting the potential applications of polymer materials in plastic electronics.We have used alternative techniques to sinter inkjet printed silver nanoparticles that are compatible with common polymer foils, such as PET and polyethylene. The process involves either a low pressure argon plasma exposure[6] or microwave radiation.[5] Recently, we made significant progress by combining the two alternative techniques, which enhances the process of creating conductive patterns on polymer substrates in two ways: firstly, the features' conductivity can be increased by using a hybrid sintering setup and, secondly, the overall sintering time can be reduced by using the so-called flash sintering approach. Hereby, sintering times can be reduced from more than one hour to a few minutes and even to a few seconds. Furthermore, the obtained conductivity is between 10 and 50% of bulk silver, while leaving the polymer substrate unaffected.These conductive features may be used in many plastic electronic applications, such as radio frequency identification (RFID) tags, lighting & signage, electrodes in sensors, etc.[1]J. Perelaer, P. J. Smith, D. Mager, D. Soltman, S. K. Volkman, V. Subramanian, J. G. Korvink, U. S. Schubert, J. Mater. Chem. 2010, 20, 8446.[2]E. Tekin, P. J. Smith, U. S. Schubert, Soft Matter 2008, 4, 703.[3]J. Perelaer, A. W. M. de Laat, C. E. Hendriks, U. S. Schubert, J. Mater. Chem. 2008, 18, 3209.[4]T. H. J. van Osch, J. Perelaer, A. W. M. de Laat, U. S. Schubert, Adv. Mater. 2008, 20, 343.[5]J. Perelaer, M. Klokkenburg, C. E. Hendriks, U. S. Schubert, Adv. Mater. 2009, 21, 4830.[6]I. Reinhold, C. E. Hendriks, R. Eckardt, J. M. Kranenburg, J. Perelaer, R. R. Baumann, U. S. Schubert, J. Mater. Chem. 2009, 19, 3384 (including Back Cover).
10:00 AM - S4.3
Printable Metallization Inks for Photovoltaics.
Susan Habas 1 , Erik Reddington 2 , Heather A. S. Platt 1 , Alexander Miedaner 1 , Calvin J. Curtis 1 , Thomas C. Sutter 2 , David S. Ginley 1 , Maikel F. A. M. van Hest 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , The Dow Chemical Company, Marlborough, Massachusetts, United States
Show AbstractDirect-write approaches such as ink jet and aerosol jet printing have significant potential as versatile, cost-effective methods for the fabrication of metal contacts for photovoltaic devices. Eliminating vacuum-based deposition steps and screen-printing, while increasing pattern resolution and materials utilization, can immediately reduce the cost-per-watt for both wafer silicon and thin film solar cells.Ink formulation is the key to enabling solution deposition processes. We have developed both soluble metal-organic decomposition (MOD) precursors as well as nanoparticle inks for patterning highly conductive contacts on photovoltaic devices. Using lower cost, higher conductivity materials can reduce the overall cost of this process. The printing capabilities in the Atmospheric Processing Platform (APP) at NREL include a dual head inkjet printer and aerosol jet printer within an inert atmosphere that have facilitated the investigation of bi-layer contacts. For example, front-side contacts composed of a thin Ni layer overlaid with low-cost, high-conductivity Cu have been printed on amorphous silicon solar cells with device performances comparable to those with evaporated Ag contacts. The resistivities of metal patterns (<50 μm width) printed in the inert atmosphere of the APP reached as low as 17 μΩ cm for nickel (~2 times bulk), and 11 μΩ cm for copper (~6 times bulk). Consequently, no post-processing steps such as annealing, or secondary metallization steps to build-up line thickness were required.Bi-layer printing methods have also been applied to crystalline solar cells, which require making contact through the insulating anti-reflection coating (ARC). A thin layer of functional ink was deposited and overlaid with a more highly conductive MOD or nanoparticle ink, facilitating contact formation through the ARC while retaining the conductivity of pure Ag, Ni, or Cu. Alternatively, line thickness and conductivity have been increased by light induced plating of pure metal, leading to device performances comparable to those of screen printed cells.
10:15 AM - S4.4
Particle-Based Aluminum and Nickel Inks for Metallization of Si Photovoltaic Devices.
Heather Platt 1 , Yunjun Li 2 , James Novak 2 , Maikel van Hest 1
1 , National Renewable Energy Lab, Golden, Colorado, United States, 2 , Applied Nanotech, Inc., Austen, Texas, United States
Show AbstractRapid deposition of electrically active metal patterns on silicon wafers can be accomplished by a variety of techniques in the large-scale manufacturing environment. Screen printing of metal contacts is the usual method of choice for solar cell production because it is relatively simple and reliable. Cost savings efforts are driving Si wafers thinner, however, and contact metallization methods like screen printing must be replaced by non-contact methods in order to prevent a concurrent increase in broken wafers. Solution-based techniques such as aerosol and ink jet printing are attractive, non-contact alternatives that also have the benefit of high material utilization. We have used these tools to investigate Al and Ni metal inks as possible low-cost replacements for Ag. These particle-based inks can be prepared at high loadings of 60 weight % metal, which enables rapid deposition of the 1 - 10 μm thick lines required to extract photo-generated current from solar cells. The resistivities of these printed Al and Ni lines approach those of the bulk metals after appropriate sintering. Such intrinsic line characteristics will be discussed, along with efficiency results from 16 cm2 polycrystalline Si solar cells, to demonstrate the potential for particle-based Al and Ni inks to contribute to the fabrication of low-cost photovoltaic devices.
10:30 AM - S4.5
Segregation during Selective Laser Curing of Inkjet Printed Silver Neodecanoate Inks.
Bojun Xu 1 , Brian Derby 1
1 School of Materials, University of Manchester, Manchester United Kingdom
Show AbstractInkjet printed silver metallisation can be achieved via nanoparticle suspension or metalorganic solution inks. Solution inks have considerable advantages over nanoparticle inks in the stability of the ink against settling during storage, although they may contain a smaller weight fraction of silver. Inkjet printing is a versatile digital printing technique for the contactless deposition of material, however spatial resolution is limited by the size of ejected droplet and its wetting behaviour on the substrate. One possible method to reduce the feature size of inkjet printed patterns is to use local curing by selective laser heating. Uncured material can be washed away after surface treatment leaving a pattern with feature sizes smaller than the printed droplets. Here we investigate the behaviour of an inkjet printed silver neodecanoate ink after selective laser curing. We find that laser treatment leads to significant segregation of metallic silver that appears superficially similar to coffee staining during droplet drying. Despite the similar surface profile to coffee staining after laser treatment, this segregation is believed to be driven by Marangoni convection and different power lasers produce different segregation behaviour in the same ink deposit.
10:45 AM - S4.6
Layer-by-Layer Assembled Multilayers Based on Functional Nanoparticles with Highly Improved Optical, Magnetic, Resistive Switching Properties Using Nucleophilic Substitution Reaction in Nonpolar Solvent.
Younghoon Kim 1 , Yongmin Ko 2 , Miseon Yoon 1 , Jinhan Cho 1
1 Department of Chemical & Biological Engineering, Korea university, Seoul Korea (the Republic of), 2 School of Advanced Materials Engineering, Kookmin university, Seoul Korea (the Republic of)
Show AbstractWe explain a facile and robust approach for the preparation of layer-by-layer (LbL) assembled multilayers based on functional nanoparticles via nucleophilic substitution reaction in nonpolar solvent. These multilayers showed the highly improved inherent properties such as optical, magnetic and resistive switching properties as well as the densely packed and homogeneous adsorption of nanoparticles. Functional nanoparticles such as Fe3O4, CdSe@ZnS quantum dot (QD), which were synthesized with oleic acid in nonpolar solvent, could be converted into 2-bromo-2-methylpropionic acid (BMPA)-stabilized nanoparticles by stabilizer exchange without change of solvent polarity. In addition, bromo groups of BMPA-stabilized nanoparticles could be connected with highly branched poly (amidoamine) dendrimer (PAMA) in ethanol by nucleophilic substitution reaction of between bromo and amino groups. Based on these results, nanocomposite multilayers using LbL assembly could be fabricated in nonpolar solvent by nucleophilic substitution reaction between BMPA-stabilized nanoparticle and PAMA without any additional phase transfer of nanoparticles for conventional LbL assembly. The photoluminescent intensity/durability of (BMPA-QDs)-based multilayer films and magnetization of (BMPA-Fe3O4)-based multilayer films, which were fabricated in nonpolar solvent by nucleophilic substitution reaction, was significantly higher than those prepared by the traditional LbL assembly in aqueous media. Furthermore, nanocomposite multilayers based on 7-nm sized Fe3O4 nanoparticles could be used as active layer for nonvolatile resistive switching memory (NRSM) devices at atmospheric conditions comparable to that of conventional inorganic NRSM devices produced by vacuum deposition. These NRSM devices based on nanocomposite multilayers showed the excellent device performances such as relatively high ON/OFF current ratio of 10^2 ~ 10^3, rapid switching speed within 100 ns, and long-term stability of 10^5s under air.
11:30 AM - **S4.7
Self-Patterning Rear Contact Schemes for Silicon Solar Cells.
Alison Lennon 1 , Pei Hsuan (Doris) Lu 1 , Zhong Lu 1 , Kai Wang 1
1 , University of NSW, Sydney, New South Wales, Australia
Show AbstractHigher silicon solar efficiencies are possible if metal contact is made to the cell though openings in a well-passivated surface [1, 2]. Patterning for such rear point-contact schemes for silicon solar cells is typically achieved using deterministic patterning methods involving either the use of photolithography [1, 2], laser [3] or inkjet patterning [4, 5]. However, despite some promising laboratory results none of these approaches have been adopted in the commercial production of silicon solar cells due to the difficulty of achieving cost-effective, high-throughput and robust processing, especially if very small and closely-spaced openings are desired. In this paper we review recent progress in the use of self-patterning anodised aluminium oxide (AAO) films to both passivate and enable point metal contacts to the rear surface of silicon solar cells [6]. Anodised aluminium is routinely used in the metal finishing industry to provide a strong corrosion resistant finish to aluminium surfaces. In many cases the porous nature of these films is exploited to impart decorative effects to the films. We describe a wet chemical method for anodising aluminium layers thermally evaporated on the rear surfaces of silicon solar cells, and demonstrate that the thus-formed AAO layers can result in excellent passivation of the underlying silicon and enable metal contact to the underlying silicon. Furthermore, we will describe how currently-available solar cell electroplating tools can be adapted to achieve anodisation of solar cells at processing throughput rates of 1500 wafers/hr.[1] J. Zhao, et al., "24.5% Efficiency silicon PERT cells on MCZ substrates and 24.7% efficiency PERL cells on FZ substrates," Prog. Photovolt: Res. & Appl., vol. 7, pp. 471 - 474, 1999.[2] R. M. Swanson, et al., "Point-contact silicon solar cells," IEEE Trans. on Electron Devices, vol. 31, pp. 661-664, 1984.[3] E. Schneiderlöchner, et al., "Laser-fired rear contacts for crystalline silicon solar cells," Prog. Photovolt: Res. & Appl., vol. 10, pp. 29-34, 2002.[4] A. Lennon, et al., "Forming openings to semiconductor layers of silicon solar cells by inkjet printing," Sol. Energy Mater. Sol. Cells, vol. 92, pp. 1410-1415, 2008.[5] M. Lenio, et al., "Design, fabrication and analysis of high efficiency inkjet printed passivated emitter rear contacted cells," in 37th IEEE Photovoltaic Specialists Conference, Seattle, USA, 2011, p. Submitted.[6] P. H. Lu, et al., "Enhanced passivation for silicon solar cells by anodic aluminium oxide," in 37th IEEE Photovoltaics Specialist Conference, Seattle, USA, 2011.
12:00 PM - S4.8
Fabrication of Printable Hybrid Solar Cells Based on P3HT and CdSe Nanocrystals.
Viral Chhasatia 1 , Brandon Lee 1 , Tyler Perlenfein 1 , Jason Baxter 1 , Ying Sun 1
1 , Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractInkjet printing of organic solar cells offers an inexpensive alternative to conventional solar cell fabrication methods. Despite the attractiveness of organic solar cells, they have demonstrated some degradation problems and have yet to achieve the efficiencies necessary to make them economically viable. In contrast to their organic counterparts, inorganic semiconductors have demonstrated advantages in their high dielectric constant which facilitates carrier generation processes, high carrier mobility, and thermal morphological stability. In recent years, improvements in device performance have been seen in the development of organic-inorganic hybrid materials (e.g., CdSe quantum dot-polymer composites) as the photoactive layer. To date, most studies on hybrid solar cell fabrication have focused on using lab-scale spin-coating methods to deposit CdSe nanoparticle-polymer materials. In this paper, we present our results in using a piezoelectric-driven printing device for inkjet printing of CdSe nanoparticles/nanorods-polymer [e.g., poly(3-hexylthiophene (P3HT)] ink materials for large-scale processing of hybrid solar cells. The deposition morphology and properties of printed photoactive layer are examined as a function of the solvent properties (e.g., wettability and evaporation rate), particle size, volume fraction, and polydispersity, and nanorod aspect ratio. The effects of jetting parameters (e.g., wave form and jetting frequency) and printing patterns on film thickness, uniformity, and multilayer junctions are also discussed in detail.
12:15 PM - S4.9
Active Inks Based on Hybrid Semiconductor Nanoparticles for Printed Electronics and Photovoltaics.
Ivan Shupyk 1 , Yahia Didane 1 , Guillaume Poize 1 , Sandrine Bernardini 2 , Marc Bendahan 2 , Khalifa Aguir 2 , Jose Mawyin 3 , Cyril Martini 3 , Ekaterina Shilova 3 , Frederic Fages 3 , Joerg Ackermann 3 1
1 , Genes'Ink, Meyreuil France, 2 IM2NP , CNRS UMR 6242, Faculté des Sciences de St Jérôme, Marseille France, 3 CINAM, CNRS UPR 3118, Marseille France
Show AbstractLow cost fabrication of electronic devices is a development field of increasing industry demands. In order to produce low cost flexible devices, one has to combine novel electronics material and ink formulation techniques compatible with low temperature solution processing on flexible lightweight substrates. Combining inorganic semiconducting nanostructures with organic surfactants allows the generation of hybrid core-shell nanosystems with novel functionality. While the inorganic nanostructures represent the charge transporting materials, the surfactants control the solubility and interparticle transport properties of the final core-shell structure. Here we present active inks using hybrid nanostructures based on surface modified metal oxide nanoparticles. First we demonstrate photovoltaic inks based on coaxial p-n junction nanorods obtained by self-assembling of organic p-type semiconductor ligands into monolayers (p-SAM) at n-type zinc oxide nanorods by simple techniques in solution. Theses inks can be printed into thin layers of nanoscale controlled morphology independent of the processing techniques, which allow to generate photocurrent efficiently.(1) Importantly, absorption properties of the coaxial nanostructures are given by the grafted p-SAM, which allows generating photovoltaic inks of different colors without changing the printed film morphology. Furthermore we present metal oxide nanoparticle inks applied as active layer in printed gas sensors. These inks use ZnO nanoparticle and hybrid nanoparticle to detect nitrogen dioxide (NO2). The Sensor response of the gas sensor show very high sensitivity in the ppm detection of NO2 by increasing the film resistance upon gaz exposure. Reference: (1): J. Mawyin, I. Shupyk, M. Wang, G. Poize, P. Atienzar, T. Ishwara, J. R. Durrant, J. Nelson, D. Kanehira, N. Yoshimoto, C. Martini, E. Shilova, P. Secondo, H. Brisset, F. Fages, and J. Ackermann, J. Phys. Chem. C, 2011, 115, pp 10881–10888
S5: Solution Processing Approaches to Printed Electronics
Session Chairs
Wednesday PM, November 30, 2011
Room 310 (Hynes)
2:30 PM - **S5.1
Current Status and Research Needs in Manufacturing of Printed Electronics.
Erika Rebrosova 1 , Margaret Joyce 1 , Marian Rebros 1 , Bradley Bazuin 1 , Massood Atashbar 1 , Paul Fleming 1
1 Center for the Advancement of Printed Electronics, Western Michigan University, Kalamazoo, Michigan, United States
Show AbstractPrinting technologies have been very well optimized to meet the demands of a human eye, but when it comes to the printing of electronic devices, each of the printing processes has limitations in terms of the resolution, registration and uniformity of printed layers and the types of inks that can be used. This is one of the reasons why current printed devices typically have poorer performance than silicon based devices. Performance reduction of printed electronics originates not only from larger feature sizes due to resolution limits of conventional roll-to-roll printing methods, but also from the electrical properties of solution processed materials. The materials and performance requirements differ based on application. Energy applications, like organic photovoltaic (PV) or batteries, are more tolerant to lower resolutions than transistors or displays, where high resolution and precise overprinting of functional layers is crucial for device performance. Thick functional layers are required for printed RFID tag antennae and batteries as opposed to very thin layers needed in printed transistors for integrated circuitry (IC), organic light emitting diodes (OLED), or in organic PV. Even though it is unlikely that the performance of printed electronics will compete with high-end silicon based devices, the cost differential can be significant. There is a great opportunity to develop new low cost and throw-away electronics, where high performance of silicon is not needed. In fact, most of the printed electronics applications do not need either ultra-fast or ultra-dense circuitry, which makes it very attractive for novel applications and the idea of having electronics virtually everywhere is very compelling.Researchers at Western Michigan University (WMU) in Kalamazoo, MI have been involved in the area of printed electronics for about five years and their efforts have resulted in the establishment of a Center for the Advancements in Printed Electronics (CAPE). The main purpose of CAPE is to advance the emerging industry of printed electronics, with an emphasis on RtR printing, by addressing critical problems faced by researchers in a range of required disciplines. The talk will provide a comprehensive review of the current use of printing in electronics manufacture. Some of the discussion points will include i) the main applications for printed electronics, ii) functional inks availability and ink properties as required by different printing processes, iii) current research in low-cost manufacturing methods with emphasis on printing and iv) the primary challenges of printing multilayer electronic devices. The presentation will also review some major research activities performed at CAPE, including printing of transparent conductive electrodes based on CNTs, ITO nanoparticles and inorganic/organic composites; microgravure printing of fine features; and printed sensors.
3:00 PM - S5.2
Multicolour and Multilayer Photopatterned Upconverting Nanoparticles for Security Applications.
John-Christopher Boyer 1 , Xin Zhang 1 , Neil Branda 1 , Byron Gates 1
1 Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada
Show AbstractIn this presentation we present a method for preparing photopatterns of upconverting core/shell NaYF4 nanoparticles dispersed in amorphous metal oxides films that can be used in security applications. The unique optical property of the lanthanide-doped nanoparticles to upconvert rather low energy NIR light into visible light, combined with their sharp spectral lines, make them particularly well suited to applications requiring security labeling. An additional benefit of the upconverting nanoparticles (UCNPs) is their long luminescence lifetimes (microsecond or millisecond lifetimes) that can be utilized in the authentication procedure. The upconversion luminescence can be tailored through careful selection of both the emitting lanthanide ions and their concentrations. The photopatterned metal oxide structures can be identified by the upconversion luminescence originating from the embedded UCNPs under 980 nm irradiation. In addition, we have demonstrated the ability to deposit the UCNPs in a desirable patttern using the photopatterning method. The advantage to our technique is that the as-synthesized UCNPs can be directly mixed with photopatternable precursors without any ligand exchange procedure. Our precursors can be handled by typical solution-based processing techniques. Metal oxide layers containing Er3+/Yb3+ UCNPs for predominately green emission or Tm3+/Yb3+ UCNPs for blue emission are photopatterned in succession to obtain overlapping layers with different emissive properties for colour-coded patterning.
3:15 PM - S5.3
Sustained Protection for Transparent Electrodes in Touch Panels and Smart Windows: Template Assisted Encapsulation of Fluorinated Silanes in Sol-Gel Silica Films for Sustained Hydrophobic-Oleophobic Functionality.
Aaron Kessman 1 , Darran Cairns 1
1 Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, United States
Show AbstractHydrophobic-oleophobic coatings are often used to provide the transparent electrodes in touch panels and smart windows with protection from fingerprints and other contaminants which may degrade electronic and optical performance. Conventional fluorosilane monolayers or co-condensed films are often surface-enriched with fluorinated moieties due to the thermodynamic drive of these components to migrate to low-surface energy interfaces [1-4]. Consequently, these conventional coatings may be strongly non-wetting and have low-surface energy when pristine, but upon wear and exposure of the bulk subsurface regions, the films are much less functional. ===========================================================This work explores the use of surfactant templated sol-gel silica films as scaffolds for encapsulating surface-segregating functional organic moieties as a mesoscopically dispersed phase with the goal of imparting sustained functionality. A perfluoropolyether silane and Pluronic F127 surfactant were used in combination with tetraethoxysilane to produce films of several hundred nanometers in thickness by dip coating. Surfactant template concentrations were varied, and coating surface properties measured before and after abrasion of the top surface. Encapsulation efficacy and surface physical and chemical properties were investigated using XPS and contact angle measurements. Nitrogen adsorption porosimetry and TEM were used to elucidate the mechanism of encapsulation and its effect on the surrounding silica framework. ===========================================================The results show that surfactant template concentration may be used to tune the dispersion of the fluorosilane-rich phase within the silica film in order to allow worn and exposed internal surfaces to maintain much of the original functionality of the pristine top surface. ===========================================================References:[1]T. Monde, H. Fukube, F. Nemoto, T. Yoko, T. Konakahara, Journal Of Non-Crystalline Solids 246 (1-2) (1999) 54–64.[2]M. Toselli, J. Gardella, M. Messori, A. Hawkridge, F. Pilati, C. Tonelli, Polymer International 52 (8) (2003) 1262–1274.[3]P. Fabbri, M. Messori, M. Montecchi, S. Nannarone, L. Pasquali, F. Pilati, C. Tonelli, M. Toselli, Polymer 47 (4) (2006) 1055–1062.[4]H. Jeong, D. Kim, S. Lee, S. Kwon, K. Kadono, Journal of Colloid Interface Science 235 (1) (2001) 130–134.
3:30 PM - S5.4
Laser Forward Transfer of Metallic Nanoparticle Inks for Optical and Electronic Devices.
Heungsoo Kim 1 , Raymond Auyeung 1 , Nicholas Chripar 1 , Kristin Metkus 1 , Scott Mathews 1 , Joseph Melinger 2 , Sangho Lee 3 , Alberto Pique 1
1 Code 6364, Naval Research Laboratory, Washington, District of Columbia, United States, 2 Code 6812, Naval Research Laboratory, Washington, District of Columbia, United States, 3 Code 5611, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractNon-lithographic processes for device fabrication are highly desirable because they can reduce manufacturing costs and can process at relatively low temperatures. Laser forward transfer is a laser-induced direct-write technique that allows the direct printing of materials such as metallic nano-inks from a donor ribbon to a receiving substrate with a resolution of a few microns at room temperature. Recently, at NRL, metallic nanoinks with various viscosities have been laser-printed to fabricate various types of patterns and devices on Si and glass substrates using the laser forward transfer technique. We have found that high-quality laser-printed patterns can be achieved only from optimized donor ribbon and laser conditions. Results indicate that the laser printing technique is a practical alternative to conventional photolithography for manufacturing many devices, since it allows their design to be easily modified and optimized. In this talk, we will report on the fabrication of various patterns of metallic nanoinks by the laser printing technique and the use of these printed structures for various applications such as split-ring resonators and thin film transistors. This work was supported by the Office of Naval Research.
3:45 PM - S5.5
Strain Analysis of Copper Films during Wet-Chemical Electroless Deposition.
Ralf Bruening 1 , Laura Perry 1 , Bruce Muir 1 , Alaaedeen Abuzir 1 , Simon Bamberg 2 , Wolfgang Friz 2 , Nina Dambrowsky 2 , Frank Bruening 2
1 Physics Department, Mount Allison University, Sackville, New Brunswick, Canada, 2 , Atotech Deutschland GmbH, Berlin Germany
Show AbstractElectroless (chemical) deposition of copper is used as the first step to construct electrical interconnects for electronic components on insulating substrate material. As smooth substrates, such as glass or flexible substrates (PET, PI), are used increasingly, achieving the required level of adhesion for these electroless copper films becomes more difficult. The film strain during and after electroless deposition is a key variable that influences film adhesion. We have adapted the standard X-ray diffraction based strain analysis as a method to monitor the strain of copper films during and after electroless deposition. Thin substrates are mounted on the surface of a plating cell, and the X-rays traverse the substrate to scatter off the growing Cu layer. With this technique it has been shown how the mechanical properties of the resulting copper films can be controlled by adding nickel and ruthenium complexes to standardized copper electroless formulation. Some results of initial tests with galvanically deposited films (DC current and pulsed current) will also be presented.
4:30 PM - S5.6
Soft Processing of Nano-Structured Ceramics (Films,Integrated Layers and Patterns): Single-Step Process in/from Solution without Firing.
Masahiro Yoshimura 1 2
1 Materials Science and Engineering, National Cheng Kung University, Tainan Taiwan, 2 Materials and Structures Laboratory, Tokyo Instituteof Technology, Yokohama Japan
Show AbstractWe have proposed an innovative concept and technology, “Soft Processing” or “Soft Solution Processing,” to get patterned ceramic films directly in/from solution without any printing & firing of powders,nor masking & etching of coating films. 1)The notable feature of those Direct Patterning is that each reactant reacts directly on site, at the interface with the substrate. Therefore, the chemical driving force of the reaction, A+B=AB, can be utilized not only for synthesis but also for crystallization and/or consolidation of the compound AB. It is rather contrasting to general patterning methods where thermal driving force of firing is mostly used for the consolidation of the particles.2)We have developed the Direct Patterning of CdS, PbS, and CaWO4 on papers by ink-jet reaction method and LiCoO2 by electrochemically activated interfacial reactions.3) Furthermore, we have succeeded to fabricate carbon patterns on Si by a needle electrode scanning directly in solutions.4) Recent success in TiO2 and CeO2 patterns by Ink-jet deposition, where nano-particles are nucleated and grown successively on the surface of substrate thus become dense even below 300 C, will be presented.5) Transparent films of several hundred nm thick can be obtained by 20 times of ink-jet scanning during 15-30 min. As a development of Hydrothermal Electrochemical[HEC] method,we have proposed a new strategy:” Growing Integration Layer[GIL] method”,which can provide well-adhered integrated/graded layers: Titanate/TiOx/Ti or Titanate/TiOx/Ti-alloys and/or metallic glass(es) at RT-150 C in a solution. This [GIL] strategy can be applied for many areas of functional ceramics.6-8) References(1)Yoshimura, M., J. Mater. Sci.,41 [5],1299-1306 (2006), 43[7]2085-2103(2008)(2)Teranishi,R.,Yoshimura,M. et al., Solid State Ionics,151,97-103(2002)(3)Yoshimura, M. and Gallage R., Solid State Electrochem., 12[7/8]775-782(2008)(4)Watanabe, T., Yoshimura, M., et al., Thin Solid Film, 515, 2696-2699 (2006), Carbon, 44, 799-802 (2006)(5)Gallage, R., Yoshimura, M., et al., J. Electroceram, 16, 533-536 (2006) , Mater. Sci. Eng., 137, 299-303 (2007), J. Am. Ceram. Soc., 91[7], 2083-2087(2008), J.Electroceramics, 19(1),33-38(2009),Thin Solid Films,517(16),4515-4519(2009),(6)Yoshimura, M. et al., Mater. Sci. Eng. B,148, 2-6(2008)(7)Sugiyama,N and Yoshimura,M., Mater. Sci. Eng. B,161(1-3),31-35(2009)(8) Sugiyama,N.,Yoshimura,M. et al., Acta Biomaterialia,5(4),1367-1373(2009)
4:45 PM - S5.7
Stress Response of Lithographic Solution-Processed Chalcogenide Thin-Film Transistors for Large-Area Flexible Electronics Applications.
Madhusudan Singh 1 , Israel Mejia 1 , Ana Salas-Villasenor 1 , Amanda Carrillo-Castillo 1 , Bruce Gnade 1 , Manuel Quevedo-Lopez 1
1 , University of Texas at Dallas, Richardson, Texas, United States
Show AbstractInorganic chalcogenide thin-film transistors are an attractive air-stable and high-mobility alternative to organic thin-film transistors for flexible electronics applications. In this work, we examine the effect of operational saturation mode voltage stress on mobility and threshold voltage variation in accumulation mode chalcogenide thin-film transistors fabricated using standard lithographic processes at temperatures <100 ○C. Thin-film transistors were fabricated on 500 nm SiO2 with a patterned Cr-gate and 90 nm of HfO2 gate dielectric deposited through atomic layer deposition at 100○ C, followed by a chemical bath deposited chalcogenide semiconductor layer as the active channel. CdS (for n-type) and PbS (for p-type) were deposited using an ammonia-free process at temperatures less than 70○C. Final devices with channel widths of 40, 80 and 160 μm, and channel lengths of 20, 40 and 80 μm were tested under saturation mode stress for several test times. Unstressed mobility values in devices with similar semiconductor thickness (CdS – 70nm, and PbS – 60nm) were found to be 25 cm2/(V.s) and 0.15 cm2/(V.s), respectively, offering an attractive alternative to a-Si:H and organic based CMOS circuits. In our stress tests, we observe moderate negative shifts in threshold voltage in both CdS and PbS TFTs, which relax on removal of saturation mode stress. The corresponding shifts in mobility with stress are unsystematic and smaller. While annealing reduces threshold voltage shifts in CdS devices, shorter channel lengths with increased drain electric fields exhibit larger shifts in the threshold voltage. Overall, our results indicate that the threshold voltage shift is negative for both materials, implying that the defect responsible is positively charged and is not mobile. Further, for CdS, the magnitude of the threshold voltage shift decreases with semiconductor thickness. FTIR data suggests a role for OH- groups in the bulk of the semiconductor and this is likely due to the aqueous character of the chemical bath process, implying that electrically activated passivation of these groups may be a candidate explanation for the observed shifts.
5:00 PM - S5.8
Development of Metallo-Gel with Spin Cross-over Properties for Electronic Devices.
Anne Vallee 1 , Cécile Roux 1 , Thibaud Coradin 1
1 Laboratoire de Chimie de la Matière Condensée de Paris, UMR-7574 UPMC-CNRS, Collège de France, Paris France
Show AbstractThe 1,2,4-triazole iron(II) complexes structure corresponds to a coordination polymer which are known to exhibit a thermo-induced spin cross-over properties with hysteresis around ambient temperature (1). This spin transition is accompanied by a colour change from white to violet, corresponding to the high spin state (paramagnetic) and low spin state (diamagnetic), respectively. It has been shown that the thermal induced spin crossover properties are very sensitive to solvents, anions and ligands. This complex has a great potential in electronic applications, including storage and display of information. Its processing remains the major problem for its development. Nanoparticules (2,3), gels (4,5) or liquids crystals (6) with spin conversion properties have already been reported but litterature is still scarce and most of works have been done using functionalized Triazoles.Our work shows for the first time that it is possible to obtain a gel of the well-known Fe (II) Triazole complex without functionalized triazole. Control of experimental conditions is essential and the gel can only be obtained in a very narrow zone of the phase diagram, ie at high concentrations of reagents and in anhydrous methanolic medium. According to DSC analysis, this gel presents thermo-reversible spin crossover properties. According to electron microscopy analysis, the resulting gel is composed of aggregates nano fibers and the size of the fibers depends on the time of gel formation. This gel can also be redispersed in methanol and other solvents. To obtain a wider variety of materials, 1,2,4-Triazole and 4-amino-4H-1,2,4-triazole have been functionalized with success with 3-isocyanatopropyltriethoxysilane (ICPTES) by forming urea or amide bonds. The synthesis of these precursors is intended to provide polymerizable alkoxides functions to the ligand, which can be further use for the formation of large material varieties. Hybrids have been then obtained combining coordination polymer with spin cross-over properties with the silica network. (1)Haasnoot, J. G. Coordination Chemistry Reviews 2000, 200-202, 131-185.(2)Coronado, E.; Galán-Mascarós, J. R.; Monrabal-Capilla, M. and coll. Advanced Materials 2007, 19, 1359-1361.(3)Tokarev, A.; Salmon, L.; Guari, Y. and coll. Chemical Communications 2010, 46, 8011-8013.(4)Grondin, P.; Roubeau, O.; Castro, M. and coll. Langmuir 2010, 26, 5184-5195.(5)Roubeau, O.; Colin, A.; Schmitt, V.; Clérac, R. Angewandte Chemie International Edition 2004, 43, 3283-3286.(6)Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V. and coll. Inorganic Chemistry 2008, 47, 10232-10245.
5:15 PM - S5.9
Study of Electrochemical Deposition of Silver Palladium Alloy.
Zhengwei Liu 1 , Robert Hilty 1
1 , TE Connectivity, Middletown, Pennsylvania, United States
Show AbstractThermodynamically, silver and palladium form solid solution over the whole composition range. Depending on the composition, it has many applications in both energy and electronics industries. At higher palladium content (~75%), the alloy can be used as hydrogen storage (1) or purification (2) materials in fuel cell or other energy related devices. When palladium content is low, silver and palladium alloy can be used as a contact material in electronics connectors (3) for the good electrical properties from Ag and the improvement of mechanical properties, like hardness and good wearibility from Pd inclusion. Electrochemical deposition, as an economical way of achieving metal alloy, was studied (4) on the silver and palladium system. One particular approach that is to use an extremely corrosive bath containing high chloride concentration (3). Prior to AgPd plating, significant amount of gold needs to be applied to protect the substrate. This eliminated its practical application. Other than this study, there are many other unsuccessful trials, reviewed in great detail by Brenner (5). The analysis of the failed attempts to achieve co-deposition reveals that the complexing agents may be the key (5). One commonly used additive in silver plating is cyanide (4). The polarization studies, potential vs current density, of solutions containing Ag, Pd and CN indicate the difference in the reduction potentials of Ag and Pd cyanide is about 600 mV. Reduction of palladium occurs at the potentials beyond the mass tranfer limit of silver and falls into the hydrogen evolution region. ICP analysis of the deposit obtained -1.2V (vs Ag/AgCl) showed no traceable Pd content. Considering the stability constants of Ag(CN)2-, ~20, and Pd(CN)4-, ~50, complexes (6), we can find that it is hard to get develop a practical co-deposition process from cyanide bath, due to the extremely stable Pd-CN complex ions. In this presentation, we will screen and characterize the possible complexing agents for a practical plating process of silver and palladium alloy. Correlations between deposit composition, bath composition and plating process parameters, including direct current and pulsed current plating, will be constructed. Meanwhile, the impact of additives and plating conditions on the morphology, microstructure and properties of the alloy will also be presented.1.Y. S. Cheng and K. L. Yeung, Journal of Membrane Science, 158, 127 (1999).2.S. Uemiya, T. Endo, R. Yoshiie, W. Katoh and T. Kojima, Materials Transactions, 48, 1119 (2007).3.U. Cohen, K. R. Walton and R. Sard, Journal of the Electrochemical Society, 131, 2489 (1984).4.M. Paunovic and M. Schlesinger, Modern electroplating, Wiley, New York (2000).5.A. Brenner, Electrodeposition of Alloys: Principles and Practice Volume I, Academic Press (1963).6.R. M. Smith and A. E. Martell, Critical stability constants Volume 4: Inorganic Complexes, Plenum Press (1976).
5:30 PM - S5.10
Ionic Liquid Dielectrics for Solution Processed N-Type ZnO and Ambipolar Carbon Nanotubefield-Effect Transistors.
Stefan Thiemann 1 , Hendrik Faber 1 , Swetlana Sachnov 2 , Florentina Niebelschuetz 1 , Peter Wassserscheid 2 , Jana Zaumseil 1
1 Department of Materials Science and Engineering, Institute of Polymer Materials, Erlangen Germany, 2 Department of Chemical and Biological Engineering, Chemical Reaction Engineering, Erlangen Germany
Show AbstractIonic liquids (IL) and printable ionic liquid gels show great potential as gate dielectrics in flexible electronics with organic and inorganic semiconductors. Due to the formation of an electric double layer at the semiconductor-ionic liquid interface their specific capacitance is very high (~10 μFcm-2). Consequently the induced charge carrier density and the resulting source-drain currents are large at low applied voltages [1]. The most commonly used IL for organic field-effect transistors (FET) is EMIM TFSI (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide). It exhibits high ionic conductivity and large specific capacitance at moderate frequencies [2]. However, its properties change with water content, which leads to environmental instabilities depending on the used semiconductor.Here we investigate the effect of different ionic liquids on FETs with n-type ZnO deposited by spray-pyrolysis [3] and ambipolar single-walled carbon nanotube (SWNT) networks as semiconducting layers. ZnO is a well-known air-stable and solution processable n-type semiconductor with a large bandgap. SWNT networks are also environmentally stable and show ambipolar charge transport when electrolyte-gated [4]. Both semiconductors exhibit good but not long term stable device characteristics with EMIM TFSI as a gate dielectric in air. Ideally an ionic liquid with a high specific capacitance, higher electrochemical stability and reduced absorption of water in air would be preferable. Here we present a comparative study of ILs with different cations and anions as electrolytes for n-channel ZnO and ambipolar SWNT transistors. In particular, we investigate the influence of the alkyl chain length and the replacement of the acidic hydrogen with a methyl-group at the imidazolium-ring of the cation on the threshold voltage for electron transport and long term device stability. Furthermore, the suitability of new hydrophobic anions such as tris(pentafluorethyl)trifluorophosphate (FAP) that limit water absorption and highly mobile but reactive small anions such as tetracyanoborate (TCB) in IL-dielectrics under ambient and inert conditions is evaluated. [1] Cho, J. H., J. Lee, et al. , Nat Mater 2008: 900-906.[2] Lee, K. H., S. Zhang, et al., J. Phys. Chem. B 2011: 3315-3321.[3] Faber, H. et al., Nanoscale 2011: 897-899 [4] Zaumseil J.et al. ACS Nano, 2009: 2225-2234.
5:45 PM - S5.11
Rectification of Self-Assembled Fe-Porphyrin Molecules.
Kim Lewis 1 , Xiaoyu Wang 1 , Gwo-Ching Wang 1
1 Physics, Applied Physics, & Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractAviram and Ratner have predicted the architecture of organic molecular rectifiers for future molecular scale electronics. Molecular rectifiers of different designs and mechanisms have been proposed and studied intensely in recent years in order to understand electron transport at the molecular level and reveal the underlying mechanisms. We report solution processed Fe-Porphyrin (Fe-P) molecular layer (sub-nm thick) on Au substrate at room temperature that has rectification effect as evident from asymmetric I-V curves measured by an atomic force microscope with platinum-coated tip. The samples that show rectification is controlled by Fe-P solution concentration and the dipping time of Au substrate in the solution. The sample of Fe-P molecules [Fe(III) 5,15-di[4-(s-acetylthio)phenyl]-10,20-diphenyl porphine] was self-assembled on annealed Au/glass substrate from 1 μM solution at room temperature for 60 seconds. These molecules have a symmetric structure, but asymmetric electrical contacts at the molecule-electrode (Au substrate and Pt tip) interfaces. Among hundreds of I-V curves measurements, the majority of the rectification ratios at ±1 V lie in between 20 – 300, with the highest up to 9000. We demonstrate that the rectification is due to asymmetric contacts at the molecule-electrode interfaces. In contrast, the molecules self-assembled from 1000 times higher solution concentration or 1 mM solution forms molecular islands (few nm thick) and the measured I-V curves are symmetric and do not show the rectification effect.
S6: Poster Session: Printing, Nanoparticle, Sol-Gel and Hybrid Systems
Session Chairs
Thursday AM, December 01, 2011
Exhibition Hall C (Hynes)
9:00 PM - S6.1
Reliable Fine Cu Trenched Interconnection on Polyimide Film.
Jongjoo Rha 1 , Dongho Kim 1 , Jungdae Kwon 1 , Keeseok Nam 1
1 Materials Processing Division, Korea Institute of Materils Science, Changwon-Shi Korea (the Republic of)
Show AbstractFlexible printed circuit boards (FPCB) are extensively used in electronics and microsystem packaging application. Especially in microelectronic devices, need of FPCBs are increasing with more fine metal lines with low resistances and high adhesion strength. In the present work, we have used a novel trenched interconnection process which is known as damascene method suitable for semiconductor industries. Polyimide films (UBE UPILEX 50S) were used as flexible substrate, over which nickel was deposited to a thickness of about 100 nm. Using photo lithography process, 10 μm width of lines was opened. Near atmospheric pressure, plasma etching made trenches with the etching rate of 1 μm/min on the polyimide substrate. Then the substrate surface was activated with near atmospheric pressure plasma with the mixture of nitrogen and ammonia gas. After that a palladium catalyst layer was deposited onto the flexible substrate. Then the Ni layer was removed and finally the trenches were filled with electroless copper. From this novel approach, the line width could get reduced continuously with high aspect ratio as a function of trench depth. The adhesion force of copper lines was found to be very strong due to high contact area between copper lines and high aspect ratio of trench walls. Further its resistance and bending strength were discussed in detail.
9:00 PM - S6.10
Polymer Electrolyte Characteristics and Membrane Properties of Poly(Vinyl Alcohol)/ Montmorillonite Prepared by Solution Casting Method.
Fang-Chang Tsai 1 , Chi-Min Shu 2 , Lung-Chang Tsai 2 , Ning Ma 1 , Sheng Wen 3 , Xiao-Ni Duan 1 , Wei Zhou 1 , Han-Wen Xiao 1 , Yao-Chi Shu 4 , Tao Jiang 1
1 Key Laboratory for the Green Preparation and Application of Functional Materials, Ministry of Education, Faculty of Materials Science and Engineering, Hubei University, Wuhan China, 2 Process Safety and Disaster Prevention Laboratory, Department of Safety, Health, and Environmental Engineering, National Yunlin University of Science and Technology, Yunlin Taiwan, 3 Faculty of Chemistry and Material Science, Xiaogan University, Xiaogan China, 4 Department of Polymer Materials, Vanung University, Taoyuan Taiwan
Show AbstractA novel composite polymer electrolyte membrane composed of a poly(vinyl alcohol) (PVA) polymer host and montmorillonite (MMT) ceramic fillers (0-4 wt.%), was prepared by a solution casting method. Using Various Na+ and K+ ions of MMT content were investigated by focusing of three major aspects: water uptake, property measurements, and morphology behavior under both small and large deformation flows. X-ray diffraction (XRD) patterns revealed that increasing the level of interactions (miscibility) between the MMT and PVA matrix increases the tendency of the silicate layers to delaminate and distributed nicely within the PVA matrix. Thermal analysis revealed that extent of crystallinity of PVA matrix is directly related to the extent of intercalation of silicate layers in the nanocomposites. When MMT are highly dispersed in every part of PVA molecular framework, it is like adding many electrical conductors to the framework. Manufactured nanocomposite membranes thanks to their high selectivity, ease of preparation and low cost could be suggested as the ideal candidate for the direct electrical conductor membrane applications.
9:00 PM - S6.11
Nonvolatile Resistive Switching Memory Devices Based on Layer-by-Layer Assembled Ferritin Multilayers.
Yongmin Ko 1 , Younghoon Kim 2 , Miseon Yoon 2 , Jinhan Cho 2
1 , Kookmin University, Seoul Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of)
Show AbstractNonvolatile memory devices are one of the most essential components for mobile electronics such as MP3 player, digital cameras and cell phone etc. Among them, nonvolatile resistive switching memory devices have recently attracted much interest due to the simple device structure, fast switching speed, high ON/OFF ratio and low operating voltage. Herein, we introduce a novel and facile approach for the fabrication of nonvolatile resistive switching memory devices by layer-by-layer (LbL) assembled ferritin multilayers. This resistive switching phenomenon of ferritin, which is highly stable Fe cations-containing protein, is caused by the charge trap and release of Fe(III)/Fe(II) redox pairs within ferritin core (i.e., ferrihydrite) that induced by externally applied voltage under atmospheric conditions. These ferritin multilayers with nonvolatile resistive switching memory properties were fabricated using LbL assembly method. Considering the isoelectric point (pI) of ferritin and the pKa of poly-(allylamine hydrochloride) (PAH), anionic ferritin and cationic PAH were deposited onto Pt-coated silicon substrate through electrostatic attraction under the condition of pH 9, respectively. These nonvolatile memory devices based on ferritin multilayers, which were fabricated by solution process (i.e. LbL assembly method), showed the reversible bipolar resistive switching behavior according to the direction of applied voltage. Furthermore, these devices displayed the excellent device performances such as ON/OFF ratio of 10^2 ~ 10^3, fast switching speed of 100ns, highly stable retention and cycling test comparable to those of conventional deposition methods such as sputtering, chemical deposition (CVD).
9:00 PM - S6.12
Gasochromic and Electrical Properties of Pt-Nanoparticle-Dispersed Tungsten Oxide Thin Films Prepared by a Sol-Gel Process.
Keishi Nishio 1 , Yuki Yamaguchi 1 , Tohru Kineri 2
1 Materials Science and Technology, Tokyo University of Science, Noda-shi, Chiba, Japan, 2 Applied Chemistry, Tokyo University of Science, Yamaguchi, SanyoOnoda-shi, Yamaguchi, Japan
Show AbstractIt is well known that tungsten tri-oxide (WO3) exhibits electrochromic and gasochromic properties. When Pt-nanoparticle-dispersed tungsten oxide (Pt/WO3) is exposed to hydrogen gas, the optical and electrical properties of the Pt/WO3 change drastically. Consequently, it is expected that thin films of WO3 can be applied as hydrogen gas leakage sensors. In this study, thin films of Pt/WO3 were prepared on glass substrates using a sol-gel process. The optical and electrical properties of the films were evaluated. The coating solution used to obtain the thin films consisted of tungsten hexachloride and hydrogen hexachloroplatinate (IV) hexahydrate as raw materials and ethanol as a solvent. The films were prepared on alkaline free glass substrates by a spin coating method, after appropriate heat treatment. Amorphous and crystalline WO3 were easily obtained by changing the heat-treatment temperature. The ion diffusion coefficient of the film depended on the WO3 structure (i.e., whether it was amorphous or crystalline) because the density of amorphous WO3 is lower than that of crystalline WO3. Films with low crystallinity were found to have superior chromic properties to both those with high crystallinity and amorphous films. The results of FTIR analyses showed that W=O and W-O bonds existed in the amorphous film and that the W=O bonds decreased as the heat treatment temperature was increased, forming a W-O-W bond. The existence of the W=O bond in the WO3 structure is thought to reduce the chromic properties. Thin films of Pt/WO3 prepared at 673K showed the largest change in optical transmittance and electrical conductivity when exposed to H2 gas compared with thin films prepared at other temperatures. When this film was exposed to 100% H2 gas, the normalized transmittance decreased rapidly (in less than 0.2 sec) from 100% to almost 50%. The optical absorbance of the film was dependent on the H2 gas concentration (mixed with N2 gas) in the range from 0.1 to 5% and the relationship between them was linear. The relationship between the electrical conductivity and hydrogen gas concentration (mixed with N2 gas) in the range from 100 to 10000ppm was also linear.
9:00 PM - S6.13
Spray Processing of Inorganic Nanomaterial Based Devices.
Edward Foos 1 , Woojun Yoon 3 , Anthony Smith 3 , Joseph Tischler 2
1 Chemistry Division, Naval Research Laboratory, Washington, District of Columbia, United States, 3 NRC/NRL Postdoctoral Fellow, Naval Research Laboratory, Washington, District of Columbia, United States, 2 Electronics Science and Technology Division, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractSolution synthesized nanomaterals—including nanocrystals, nanorods, and nanowires—possess an inorganic core surrounded by an encapsulating layer of organic material. While the inorganic core provides electronic function, the organic shell provides solvent compatibility and enables these materials to be manipulated in solution, opening opportunities for low-cost fabrication of all-inorganic devices. In this case, the composition of the ligand shell is extremely important, as larger surface ligands that encourage organic solubility are often detrimental to electron conduction in the solid state. We have found spray deposition of nanomaterials via airbrush to be a useful alternative to spin coating, enabling the fabrication of smooth films from solutions of low-solubility nanomaterials when solution concentration, substrate temperature, and deposition rate are properly controlled. Additional ligand exchange steps can then be utilized on the deposited films to further improve their function. These techniques have been successfully applied to the deposition of layered films of II-VI and IV-VI semiconductor nanorods and nanowires, and both photovoltaic (PV) and field-effect transistor (FET) devices have been fabricated. Bilayer films composed of pyridine exchanged CdSe and CdTe nanorods exhibit a photovoltaic effect which can be improved through post-deposition coupling with bifunctional molecules, leading to an increase in the observed Voc. The electrical and optical characterization of these films will be presented, along with discussion of the ligand exchange chemistry and its impact on device performance.
9:00 PM - S6.15
A Simple and Rapid Formation of Wet Chemical Etched Silicon Nanowire Film at Air-Water Interface.
Tae Il Lee 1 , Kyeong-Ju Moon 1 , Unyoung Jeong 1 , Jae-Min Myoung 1
1 Materials Science and Egineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractA spontaneous assembly route to form a thin film of nanowires (NWs) was demonstrated and its feasibility was confirmed through the fabrication of a high-performance multi-Si NW field effect transistor (FET) using this route. Governed by the three mechanisms of spreading, trapping, and two-dimensional packing, the route was optimized for the concentration of Si NWs and the initial volume ratio of aqueous hydrochloride solution to isopropyl alcohol. The successfully formed Si NW thin-film was transferred on a flat polydimethylsiloxane (PDMS) mold and regulated using a repeatable conformal contact method with a new flat PDMS to prepare it for decal printing on an organic dielectric layer. Finally, after depositing the source and drain electrodes on the printed active layer, a high-performance 23-bridged Si NW FET exhibiting a μeff of 51.4 cm^2/Vs, on-off drain current ratio of 10^5, and Vth of -2.7 V was obtained.
9:00 PM - S6.16
Lanthanides Additives to Improve Outdoor Stability in Single Layer Antireflective Silica Based Sol Gel Coatings.
Roberto Habets 1 , Nanning Arfsten 1 , Paul Wyman 1 , Pascal Buskens 2
1 Ahead, DSM, Geleen, Limburg, Netherlands, 2 Innovative Materials, TNO, Eindhoven, Brabant, Netherlands
Show AbstractConventional single layer antireflective coatings based on silica make use of solid particles in combination with a binder system in a regime where increasing binder enhances mechanical properties at the expense of increased reflection. The use of hollow structures overcomes this limitation and allows the production of single layer, quarter wavelength interference coatings with a significant improvement in mechanical and optical properties, however, systems based entirely on silica are prone to weathering and are, as such, poorly suited to outdoor applications.Several approaches are known to enhance the outdoor and especially hydrolytic stability of silica sol-gel coatings on glass. For instance barrier layers between the glass substrate and the coating can reduce migration of ions which are known to increase the degradation rate under humid conditions. Hydrophobic topcoats are also known to reduce the rate of hydrolysis of such coatings. However, the most appealing method to solve this problem of outdoor stability is to modify the coating system rather than to add additional coating layers. In this context, the addition of aluminium salts to produce mixed oxides of higher stability is widely described in the literature, although such approaches often cause problems of storage stability or reduce the pot life of the formulation.In this presentation, we discuss the effect of adding lanthanides to such systems.The modification of silica structures with lanthanides is evaluated in the context of both mechanical and chemical resistance of applied coatings. This is related to structural changes in the silica network and used to generate an understanding of the influence of lanthanide additives on coating stability, curing process and outdoor performance. These are compared to the native silica system and to the effect of added aluminium salts.
9:00 PM - S6.17
Influence of Nitric Acid Peptization on the Band Gap of Sol Gel Derived Nanostructured Titania.
Tyson Bartlett 1 , Som Thomas 1 , Yves Chabal 1 , Padmakumar Nair 1 , Sugeng Triwahyono 2 , Rino Mukti 3 , Tatsuya Okubo 4
1 Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States, 2 Institute Ibnu Sina for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru, Johor , Malaysia, 3 Division of Inorganic and Physical Chemistry, Institut Teknologi Bandung, Bandung, West Java, Indonesia, 4 Department of Chemical System Engineering, University of Tokyo, Tokyo Japan
Show AbstractNanostructured anatase-phase titanium dioxide was prepared by sol gel synthesis, peptized with several concentrations of nitric acid (H+:Ti4+ ratio of 0, 0.5, 0.75, or 1.0), and calcinated at 80, 300, 400, or 500 °C. The band gap, measured using UV-vis, was observed to decrease non-linearly with respect to concentration and temperature. The minimum band gap occurred at a H+:Ti4+ ratio of 0.5 and a temperature of 500 °C. FTIR spectra indicate that peptization leads to the incorporation of nitrogen species into the lattice at 80 and 300 °C. The rutile fraction was calculated from XRD data, and ranged from 0 to 59%. These two factors partially explain band gap variations.
9:00 PM - S6.18
Low-Field Magnetoresistance of La0.67Sr0.33MnO3:MgO Composite Films Grown by Solution Method.
Margo Staruch 1 , Drew Hires 2 , Menka Jain 1 3
1 Department of Physics, University of Connecticut, Storrs, Connecticut, United States, 2 Department of Chemical, Materials & Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 3 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractLarge values of magnetoresistance have been observed in polycrystalline La1-xSrxMnO3 in a range of temperatures at low applied magnetic fields (< 1 T). This has been explained in terms of spin-polarized tunneling between adjacent grains or spin-dependent scattering at the grain boundaries, and this low-field magnetoresistance can be modified by introducing artificial grain boundaries. In this study, La0.67Sr0.33MnO3:MgO composite films were grown on (001) LaAlO3 substrate using a sol-gel method. The films were found to be preferentially c-axis oriented. The presence of MgO was found to decrease the ferromagnetic transition temperature, possibly as a result of grain boundary effects. Grain boundaries are also shown to have an increasing role in electronic transport of the composite films as the amount of MgO phase increases. The values of magnetoresistance increased with MgO doping up to -33% at 0.5 T and 10K, which is the highest value reported for similar composites thus far.
9:00 PM - S6.19
Ultrasonic Spray-Assisted Solution-Based Vapor-Deposition of Functional Thin Films and Their Applications.
Jinchun Piao 1 2 , Shigetaka Katori 1 , Ikenoue Takumi 1 2 , Fujita Shizuo 2
1 Electronic Science and Engineering, Kyoto University, Kyoto, Kyoto, Japan, 2 Photonics and Electronics Science and Engineering Center, Kyoto University, Kyoto, Kyoto, Japan
Show AbstractAmong a variety of functional materials, metal-complexes such as aluminum tris(8-hydroxyquinoline) (Alq3) has attracted increasing interest for stable optoelectronic devices. The deposition technique for thin films, however, has been limited to vacuum evaporation but a novel solution-based technology is much desired for low-cost and uniform fabrication of thin films on large substrates without a lot of wastes. The solubility of these materials is generally low in various safe solvents. Reasonable solubility of Alq3 in tetrahydrofuran or dichloroethane, followed by spin-coating deposition was reported, but these solvents are not always environmental-friendly. An evolution was brought by our finding that application of high-ultrasonic power to Alq3-methanol mixture made stable and transparent solution. Using this solution, we developed a vapor-deposition technique which can result in uniform thin films with good thickness-controllability compared to spin-coating. The vapor-deposition technique we have developed is the mist deposition technique. Here we apply ultrasonic power to the Alq3-methanol solution and this forms mist particles of the solution, which are transferred onto a substrate. The substrate, for example, glass, was heated at above 100oC, allowing evaporation of the solution and formation of Alq3 thin films. Optical absorption and photoluminescence characteristics evidenced the actual formation of the Alq3 thin films. Together with the good surface morphology and low leakage current of the films, the results are promising for actual device fabrication at low cost and low material loss. This technology can also be applicable for the formation of a variety of functional material thin films by solution-based technique Based on the fundamental film formation data, our research has been extended to fabricate actual devices. The results will also be included in the presentation at the symposium.
9:00 PM - S6.2
In Situ Synthesis of High Refractive Index PDMS/Metal Oxide Nanocomposites.
Qiaoyu Lu 1 , Michael Mullins 1
1 Chemical Engineering, Michigan Technological University, Houghton, Michigan, United States
Show AbstractOrganic-inorganic hybrids have been prepared with tailorable and enhanced properties which are unachievable using polymers or ceramics alone. By combining the flexibility of polymers with the electronic and optical properties of ceramic materials, these hybrids offer great potential for many optical, electrical and mechanical applications. Silicone polymers because of their desirable surface properties, excellent physical properties, heat stability, and high resistance to chemical and UV attack, have been widely used. Hybrid siloxane-metal oxide gels have been prepared via sol-gel techniques, by using hydroxyl-terminated polydimethylsiloxanes (PDMS) crosslinked by metallic alkoxides, M(OR)n. In this technique, the use of organic solvents permits organic and inorganic components to be combined at a molecular level with the desired composition. By varying the type and percentage of metal alkoxides during synthesis, transparent and homogeneous organic-inorganic hybrid materials with unique properties were obtained. Also a secondary metal oxide species was introduced to synthesize binary metal oxide-PDMS hybrids. Systematic experiments were carried out to study the effect of the reaction conditions and metal alkoxides-PDMS ratios on the properties of the final hybrids. These hybrids were spin coating on silicon wafers or molded into bulk films to be tested. The composition and the properties of the transparent organic-inorganic hybrids were investigated and characterized by prism coupler, ellipsometer, Fourier Transform Infrared (FTIR) spectroscopy and FT-Raman. Experimental results showed that the refractive index of the hybrid materials exhibits a proportional relationship with the metal dioxide content, the higher the metal dioxide content the higher the refractive index. The refractive index was increased from 1.4 of PDMS to 1.7 of PDMS-metal oxide hybrid with highest prepared metal oxide loading. From the FTIR and FT-Raman spectra, the structure of the hybrids for various metal oxide-PDMS compositions was analyzed.
9:00 PM - S6.20
Low-Thermal-Budget Solution Processing of Thin Films of Zinc Ferrite and Other Complex Oxides.
Ranajit Sai 1 2 , Suresh Kulkarni 1 2 , Navakanta Bhat 2 3 , Srinivasrao Shivashankar 1 2
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India, 2 Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore, Karnataka, India, 3 Department of Electrical Communication Engineering, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractFurther miniaturization of magnetic and electronic devices demands thin films of advanced nanomaterials with unique properties. Spinel ferrites have been studied extensively owing to their interesting magnetic and electrical properties coupled with stability against oxidation. Being an important ferrospinel, zinc ferrite has wide applications in the biological (MRI) and electronics (RF-CMOS) arenas. The performance of an oxide like ZnFe2O4 depends on stoichiometry (defect structure), and technological applications require thin films of high density, low porosity and controlled microstructure, which depend on the preparation process. While there are many methods for the synthesis of polycrystalline ZnFe2O4 powder, few methods exist for the deposition of its thin films, where prolonged processing at elevated temperature is required. We report a novel, microwave-assisted, low temperature (<100oC) deposition process that is conducted in the liquid medium, developed for obtaining high quality, polycrystalline ZnFe2O4 thin films on technologically important substrates like Si(100). An environment-friendly solvent (ethanol) and non-hazardous oxide precursors (β-diketonates of Zn and Fe in 1:2 molar ratio), forming a solution together, was subjected to irradiation in a domestic microwave oven (2.45 GHz) for a few minutes, leading to reactions which result in the deposition of ZnFe2O4 films on Si (100) substrates suspended in the solution. Selected surfactants added to the reactant solution in optimum concentration can be used to control film microstructure. The nominal temperature of the irradiated solution, i.e., film deposition temperature, seldom exceeds 100oC, thus sharply lowering the thermal budget. Surface roughness and uniformity of large area depositions (50x50 mm2) are controlled by tweaking the concentration of the mother solution. Thickness of the films thus grown on Si (100) within 5 min of microwave irradiation can be as high as 2 μm. The resulting adherent ferrite film is very smooth, with an average roughness of only a few nm (AFM). As the concentration of the ingredients is reduced, the resulting films are smoother, ostensibly because of the reduced nucleation density and the “mechanical polishing” of the substrate surface due to the rigorous agitation that occurs during irradiation. XRD, Raman and EDAX analyses confirm the formation of the pure ferrite phase. Films can be grown rapidly on substrates of different size, making this process a high throughput process. The present process, not requiring a vacuum system, carries a very low thermal budget and, together with a proper choice of solvents, is compatible with CMOS integration. This novel solution-based process for depositing highly resistive, adherent, smooth ferrimagnetic films on Si (100) is promising to RF engineers for the fabrication of passive circuit components. It is readily extended to a wide variety of functional oxide films.
9:00 PM - S6.21
Solution Processing of KTaO3/LiTaO3 Multilayers.
Paula Vilarinho 1 , Sebastian Zlotnik 1
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal
Show AbstractIn the past decades, electrically controlled ferroelectric thin films, in the form of monolayered or multilayered structures, have become attractive and started playing an essential role in a variety of microelectronic devices. They are significantly important in high performance tunable devices, due to their unique properties when compared with their bulk counterparts. The most common tunable composition is the solid solution between SrTiO3 and BaTiO3 (Ba1-xSrxTiO3, BST). In addition, miniaturization of the device size is still a key aspect for the future integration of tunable devices. Within this context multilayered thin structures have been addressed in BST, and PbTiO3/SrTiO3, among others. However KTaO3 (KT) with very low dielectric losses coupled with the existence of the paraelectric state down to cryogenic temperatures is a recognized alternative to SrTiO3, in particular when the quality factor is application determinant. Thus, in the present work, the fabrication of KTaO3/LiTaO3 multilayers through chemical solution deposition method is presented. The high tunability of the ferroelectric LiTaO3 (LT) is combined with the low losses of KT. Both compounds are lead-free, and can be regarded as environmentally-friendly alternative materials. Regardless of the potential applications, preparation of alkali-based compositions is challenging, and difficulties are mainly associated with stoichiometric deviations caused by K and Li losses during thermal treatment, and with pyrochlore–perovskite phases control. In this work, different solution deposition approaches were considered to optimize the phase formation process and quality of the multilayered films, from the use of seed layers, to solution wetability and viscosity modification. Gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared (FTIR) were used to optimise the precursor solution preparation. For the structural, microstructural and interfacial analyses X-ray diffraction (XRD), Scanning and Transmission Electron Microscopy and Rutherford backscattering were used. Macroscopic and local electrical responses were assessed and relations with the multilayered structure and interfaces established.
9:00 PM - S6.22
Influence of Annealing Temperature on Microstructure and Dielectric Properties of Sol-Gel Deposited High-K ZrO2/Si Films.
Soo Min Hwang 1 , Seung Muk Lee 1 , Jun Hyuk Choi 1 , Geun Chul Park 1 , Jun Hyung Lim 1 , Jinho Joo 1
1 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi, Korea (the Republic of)
Show AbstractThe need for continuing miniaturization and improved performances of complementary metal oxide semiconductor devices has led to development of high dielectric constant (
K) materials replacing conventional SiO
x-based gate dielectrics.
1,2 Among the various high
K candidates, ZrO
2 has attracted much interest due to its high
K, wide band gap, and thermodynamical stability on Si.
2 The ZrO
2/Si films have been fabricated mostly by vacuum-based deposition techniques and the corresponding microstructural and electrical properties have been investigated extensively.
2 On the other hand, studies on the counterparts by a chemical solution deposition with no use of vacuum apparatus have been rarely reported.
In this work, we fabricated the high-
K ZrO
2/Si thin films by using a sol-gel method and studied on the influence of annealing temperature on the phase formation, microstructure, and resultant dielectric properties. Zr-acetylacetonate was dissolved in a solvent consisting of a mixture of N,N-dimethylformamide and monoethanolamine at a molar ratio of 2:1 and refluxed to prepare the transparent solution with a concentration of 0.1 M. The precursor solution was spin-coated on dilute HF-cleaned p-type Si(100) substrates and subsequently dried on a hot plate at 200
oC in ambient air. The thickness of the ZrO
2 layer was varied by repeating the coating and drying steps, resulting in ~7 nm for one time and ~13 nm for two times. The annealing was performed at 400–700
oC for 1 hr in ambient air. Al/TaN/ZrO
2/Si capacitors were formed by using sputtering and patterning via a lift-off method.
As the annealing temperature increased, the ZrO
2 layers crystallized into a tetragonal (t-) phase which was retained until 700
oC, and the crystallization temperature was different for the ~7-nm- and ~13 nm-thick scales. The evolution of the t-phase was attributed to the plausible thermodynamical preference for the minimization of the surface/interface energy at nanoscale thicknesses.
3 In addition, the development of the t-phase enhanced the
K value of the ZrO
2 layer. On the other hand, the gate leakage current density was significantly depressed with increasing annealing temperature. This appears to be a consequence of combined effect of the increased thickness of the interfacial layer between the ZrO
2 and Si, optical band gap, density of ZrO
2 layer, and decreased remnant organics. This work describes the utility of the sol-gel processed t-ZrO
2 for improving gate dielectric performances.
1 D. G. Schlom, S. Guha, and S. Datta,
MRS Bull. 33, 1017 (2008).
2 S. Guha and V. Narayanan,
Annu. Rev. Mater. Res. 39, 181 (2009).
3 A. Navrotsky,
J. Mater. Chem. 15, 1883 (2005).
*Corresponding author: Jinho Joo(
[email protected])
Acknowledgment: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant No. 2010-0009997).
9:00 PM - S6.23
Resistive Switching Characteristics of Sol-Gel Processed NiO Thin Films.
Toshiyuki Sakuma 1 , Masao Hada 1 , Tatsuya Oka 1
1 Electrical and Computer Engineering, Wakayama National College of Technology, Gobo, Wakayama, Japan
Show AbstractResistive switching charactericstics in NiO thin films is attracted for the new type of semiconductor memory applications. In these applications, sputtered NiO thin films were frequently used. In this report, NiO thin-films were prepared by sol-gel processes. Spin-coated precursor solutions were dried and annealed at 450 - 550 C in the air. These films thickness is about 40nm-thick with one coating. Multi-coatings were perfomed up to 3 times.For electrical measurements, these films were prepared on the Pt(50nm)/Ti(50nm) coated soda-lime glass substrate. Resistive switching characteristics were evaluated by attaching the W-probe directly for the upper electrode. Set and reset voltage were measured by voltage and current source respectively.Set voltages increased with the number of coatings. Set voltage is proportional to the electric field. Set voltages correspond the formation of the conductive filaments, and local Ni reductions. However, reset voltages were remained constant. This means the resistance of conductive filaments between the upper and bottom electrodes were remained constant, assuming the constant required Joule heating for the rupture of conductive filaments. It is confirmed that the equivalent cross-sectional area of conductive filaments increased with the film thicknesses.
9:00 PM - S6.25
Measurement of Cu Grain Growth for ULSI Interconnects by X-ray Diffraction and Electron Backscattered Diffraction.
Hyoung Jin Jeon 1 , Seoung Ki Hong 1 , Hyo Jong Lee 1 , Dong Young Yang 1 2
1 MSE, Dong-A Univ., Busan Korea (the Republic of), 2 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe investigated the grain growth behavior of the copper electrodeposits for ULSI interconnects through X-ray diffraction, EBSD (electron backscattered diffraction) and 4 PP (point probe) measurements. The decrease of the sheet resistance by the 4PP measurement means the increase of the grown area, and we tried to estimate the activation energy of Qa during the grain growth. Also, by X-ray measurement, we could compare the TC (texture coefficient) among seed layer, as-deposited and annealed copper films, and it was found out that the crystallographic texture of as-deposited film is the same as that of the seed layer. Both seed and as-deposited samples had strong (111) fiber texture with a portion of over 99%. That means that the copper was grown epitaxially on its seed during electroplating. The annealed sample had differently-oriented domains with (100), (331) and (420) fiber textures. In particular, the (100) fiber textured domain had a portion of 3%, and with respect to crystallographic orientation relationship, (100) can be approximated to (511) which is the twin relationship to the (111) fiber textured domain. Additionally, we performed the step-by-step measurements of EBSD for the copper grain growth at a time interval.
9:00 PM - S6.3
Inkjet Printing of High Performance Amorphous Indium Gallium Zinc Oxide Transistors.
Jonathan Hennek 1 , Xia Yu 2 , Ken Everaerts 1 , Mark Hersam 3 , Antonio Facchetti 1 2 , Tobin Marks 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 , Polyera Corporation, Skokie, Illinois, United States, 3 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThe development and application of new solution-processed amorphous metal oxide semiconductors in thin film transistors (TFTs) is of great interest for the realization of transparent, flexible, low-cost, high-performance, large area electronics. Of particular interest in this field is the amorphous ternary system indium gallium zinc oxide (a-IGZO) owing to the substantial field-effect mobilities, μFE, (〉10 cm2V-1s-1), large current on/off ratios (≥107), as well as light and bias stability superior to that of a-Si:H when deposited by vapor-phase film growth techniques. Compared to vapor-phase film growth techniques, solution-phase deposition (e.g., drop casting, spin-coating, and inkjet printing) of a-IGZO has been investigated far less. Inkjet printing is extremely promising as a way to reduce materials waste while at the same time printing complex patterns, eliminating the need for time consuming masking steps. However, very few systematic studies have been conducted to investigate printing a-IGZO TFTs. We present the first investigation of the effects of the transistor architecture and semiconductor/electrode contact resistance on printed a-IGZO TFT performance. Using an optimized a-IGZO semiconductor “ink”, transistors were printed with bottom-gate/top-contact (BGTC) or bottom-gate/bottom-contact (BGBC) TFT structures. The BGTC transistors exhibit μFE up to 1.40 cm2V-1s-1 and other device metrics comparable to those previously reported for films grown by spin-coating techniques. Moreover, here we report for the first time BGBC TFTs with μFE up to 3.25 cm2V-1s-1, larger than that for BGTC devices, and more the two times greater than any previous reports for inkjet printed a-IGZO TFTs. To understand the mechanism behind this impressive performance, we measure the contact resistance between the semiconductor and source/drain electrodes and show that optimum BGBC transistors have a contact resistance nearly an order of magnitude lower than that of BGTC devices.
9:00 PM - S6.4
The Influence of Methyltriethoxysilane (MTES) in Homogeneous Liquid Crystal Alignment on Amorphous Silicon Oxide Derived by the Sol-Gel Method.
Soosang Chae 1 , Hong Koo Baik 1
1 Materials Science & Engineering, Yonsei university, Seoul Korea (the Republic of)
Show AbstractWe present an inorganic-organic hybrid thin film via the sol-gel method for a new liquid crystal alignment layer and investigate the influence of an organic species in the alignment characteristics of liquid crystals (LC) on thin film with the proposed mechanism. Thin film, methyl doped amorphous silicon oxide (a-SiOx:CH3), was fabricated from the hydrolysis and condensation reaction of the initial precursors methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) in a proper ratio. A low energy ion beam (IB) was used for the alignment of LC. This treatment on a-SiOx:CH3 thin film achieved superior homogeneous alignment of LC in some IB treatment conditions compared with a-SiOx thin film that was derived from an inorganic precursor only. This result could be explained by the chemical bonding of Si-CH3, which was embedded exclusively in a-SiOx:CH3 thin film.
9:00 PM - S6.5
Dependence of Nonvolatile Memory Characteristics on Au Nanocrystal Concentration for Polymer Memory-Cell Embedded with Au Nanocrystals in Polystyrene.
Hyun Min Seung 1 3 , Jong-Dae Lee 1 , Kyoung-Cheol Kwon 1 , Jung-Nam Lee 1 , Jea-Gun Park 1 2 3
1 National Program Center for Terabit-level Nonvolatile Memory Development, Hanyang Univ., Seoul Korea (the Republic of), 3 Division of Nanoscale Semiconductor Engineering, Hanyang Univ., Seoul Korea (the Republic of), 2 Department of Electronic Engineering, Hanyang Univ., Seoul Korea (the Republic of)
Show AbstractWe studied dependence of nonvolatile memory characteristics on Au nanocrystal concentration for polymer memory cell embedded with Au nanocrystals in Polystyrene. The polymer memory-cells were fabricated with the device structure of polymer (PS, Polystyrene) embedded with Au nanocrystals between Al upper and bottom electrodes. The polymer layer was formed by spin coating the solution of chemical synthesized Au nanocrystals and Polystyrene. Through the TEM image, synthesized Au nanocrystals were well dispersed in polymer layer.The polymer memory-cells showed nonvolatile memory characteristics such as flat band voltage shifting amount of ~5.18 V, memory margin(Ion/off) of 1.59 × 103, retention time more than 105 sec and more than 2 × 102 endurance cycles of program and erase. Moreover, flat band voltage shifting amount was increased from 0.04 V to 5.18 V with increasing the concentration of Au nanocystals in polymer layer. The relationship between Au nanocrystal concentration and flat band voltage shifting amount clearly indicated that current conduction mechanism of the polymer memory-cell was associated with charged Au nanocrystals in polymer layer. In our study, we will suggest the dependence of memory characteristics on Au nanocrystal concentration and current conduction mechanism of polymer memory cells.Acknowledgement* This research was supported by "The National Research Program for Terabit Nonvolatile Memory Development” sponsored by the Korean Ministry of Knowledge Economy.
9:00 PM - S6.6
Flexible Polymer Nonvolatile Memory-Cell Embedded with Au Nanocrystals in Polystyrene.
Jong Dae Lee 1 2 , Hyun-Min Seung 1 , Kyoung-Cheol Kwon 1 , Jung-Nam Lee 1 2 , Jea-Gun Park 1 3
1 National Program Center for Terabit-level Nonvolatile Memory Development, Hanyang University, Seoul Korea (the Republic of), 2 Department of Electronics Computer Engineering, Hanyang University, Seoul Korea (the Republic of), 3 Department of Electronic Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractWe investigated flexible nonvolatile 4F2 memory-cell embedded with Au nanocrystals in polystyrene (PS). The memory-cell was composed of the PS layer embedded with Au nanocrystals between cross-bar bottom and top Al electrodes on flexible substrate (polyehersulphone (PES)). For the formation of carrier charge states in PS layer, we chemically synthesized the Au nanocrystals modified by dodecanethiol (DT) in organic solvent (chloroform). The cross-bar patterned bottom Al electrode was deposited on PES substrate for the fabrication of flexible memory-cell. And then, dissolved PS in the chloroform dispersed with Au nanocrystals was spin-coated on bottom Al electrode. Finally, the cross-bar patterned top Al electrode was deposited on polymer layer.It was observed that the flexible nonvolatile memory-cell showed the memory margin (Ion / Ioff) of 5.88×103 and the retention time of more than -1×105 sec. Also, the memory-cell could withstand at the condition of bending cycles of 1000. In our study, we will present the variation of memory characteristics at the various bending cycles and conditions.Acknowledgement* This research was supported by "The National Research Program for Terabit Nonvolatile Memory Development” sponsored by the Korean Ministry of Knowledge Economy.
9:00 PM - S6.7
Fabrication of Photonic Crystals on Solution-Processed Quantum Dots Chalcogenide Hybrids and Its Photoluminescence Response.
Pao Lin 1 , N. Patel 1 , V. Singh 1 , L. Kimerling 1 , A. Agarwal 1
1 Materials Processing Center, Microphotonics Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractTwo dimensional photonics crystals (PhCs) are fabricated on quantum dots (QD) implanted chalcogenide (ChG) thin films. Hybrid QD within ChG are obtained by mixing separate solutions from QD and ChG. Precursors of QD and ChG are dissolved in solvent propylamine. Films are formed by spin coating on a substrate and followed by annealing steps. PhCs in QD and ChG hybrids demonstrate broadband enhancement of Photoluminescence (PL) emission at Near-IR. The PhC structures are written by dual beam focused ion beam (FIB). Highly uniformed patterns with smooth surfaces are observed. A pattern resolution better than hundred nanometers is achieved. PhCs arrays with photonic lattice constants from 400 nm to 2000 nm are examined in order to optimize the PL extraction efficiency. Strong is observed by 488-532 nm lasers pumping. A confocal microscopy with spectrometer is used to capture the broadband PL signals from individual PhC array. The emission enhancement factor and spectral extraction ratio are analyzed to find the interaction between PL lightwave and PhC structures. By optimize the PhC structures, 1500 um-1600 um broadband PL is successfully converted between the PL emission layer and the external cavity. A strong enhancement of surface extraction efficiency is achieved when PhC with optimized periodicity is applied. When photonic lattice constants a are smaller than the critical periodicity, the PL light becomes confined inside the thin film layer. Simulation is also performed by two dimensional finite difference time domains (FDTD) calculation in order to explain the experimental observed anisotropic PL enhancements. The broadband PL enhancement enables QD and ChG hybrids as a potential light source for three dimensional integrated photonic circuits.
9:00 PM - S6.8
Photoluminescent Colloidal Quantum Dot and Chalcogenide Glass Composite Films for Infrared Light Sources.
Neil Patel 1 , Jennifer Scherer 2 , Moungi Bawendi 2 , Spencer Novak 3 , Jackyln Wilkinson 3 , J. David Musgraves 3 , Kathleen Richardson 3 , Juejun Hu 4 , Pao-tai Lin 1 , Clara Dimas 5 , Lionel Kimerling 1 , Anuradha Agarwal 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 School of Materials Science and Engineering, Clemson University, Clemson, South Carolina, United States, 4 Department of Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 5 , Masdar Institute of Science and Technology, Masdar City United Arab Emirates
Show AbstractPhotoluminescent films for integrated infrared light sources can be fabricated from solution processing of colloidal quantum dots (QDs) and chalcogenide glasses (ChGs). Infrared light sources are desired for applications in chemical and biological sensing due to the presence of vibrational absorption peaks for most molecules within the infrared regime. Current light sources for optical sensing are expensive and cannot be fabricated monolithically along with the sensor and detector. For a complete optical sensor-on-chip device to be fabricated, an integrated infrared light source is required. ChGs provide a high refractive index matrix with a wide infrared transparency window which can be processed through both thermal evaporation and solution based spin-on deposition. Colloidal lead sulfide QDs which emit in the IR can be fabricated cheaply through solution processing methods. In order to maintain good luminescence properties, QD surfaces must be passivated well by the matrix to ensure that charge transfer between QDs and nonradiative recombination is minimized. A solvent is found which can both dissolve ChGs and disperse QDs in solution. Separate solutions of ChGs and QDs in the common solvent are mixed and spin deposited to fabricate photoluminescent films of QD doped ChGs. QDs form aggregates when in solution with ChGs. Photoluminescence measurements show comparably strong photoluminescence in aggregated films compared to QDs well dispersed in PMMA. Micro PL measurements of individual aggregates show that aggregation does not completely quench quantum dot emission. TEM micrographs show that QDs are still passivated and are separated by some small distance within the aggregates. These films provide a materials platform for creating optical devices in order to develop an integrated light source. Waveguides and microdisk cavities are fabricated and characterized using photoluminescence measurements. Undoped ChG films can also be deposited above and below layers of QDs dispersed in PMMA. The high index of refraction of ChGs can be used to confine the light within the QD doped PMMA layers for alternative light source design structures.
9:00 PM - S6.9
Study of a Process from Liquid Silane to Laser-Crystallized Poly-Silicon Film.
Ryo Kawajiri 1 , Tatsuhiko Akiyama 2 , Yasuo Matsuki 1 3 , Tatsuya Shimoda 1 2
1 SHIMODA Nano-Liquid Process Project, JST, ERATO, Nomi, Ishikawa Japan, 2 School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), Nomi, Ishikawa Japan, 3 Yokkaichi Research Center, JSR Corporation, Yokkaichi, Mie Japan
Show AbstractThe solution processing has been expected as an effective alternative for complicated vacuum processing in terms of process cost and the consumption of energy and materials. Recent progress of the solution processing is remarkable especially in the field of organic materials such as the organic light emitting diodes, organic thin film transistors. However, the solution processing of inorganic materials such as silicon, metals, oxides have not been so much studied whereas they would play extremely important roles once used in present semiconductor processing and related technologies.Polycrystalline silicon (poly-Si) is very attractive for thin-film transistors. The typical starting material in the crystallization process is amorphous silicon (a-Si) or hydrogenated amorphous silicon (a-Si:H) that can be deposited by various vacuum deposition techniques. However, these processes usually need equipments with high cost and their material utilization efficiency is quite low. If high-quality poly-Si films are formed by liquid processing, that would make a great impact on Si device industry.This work relates to a process of forming poly-Si films by liquid silane coating on substrates and green laser annealing (GLA). Hydrogenated polysilane, which was obtained by irradiating CPS (cyclopentasilane) with 365 nm UV light, was used as a precursor to form an a-Si:H film. And a silicon ink was prepared from polysilane diluted with organic solvent. The ink was spin-coated on quartz substrate, and it was converted to an a-Si:H film with a thickness of 100 nm by annealing at 400 °C on a hot plate. Dehydroganation of the a-Si:H films was performed by rapid thermal annealing at 700 °C for 30 minutes under 1 Pa. These samples were irradiated by a 300 ns pulsed Yb:YAG green laser (515 nm) at a frequency of 10 kHz. The laser energy density was varied from 300 to 1100 mJ/cm2 in 100 mJ/cm2 steps. Raman spectra of the samples irradiated from 400 mJ/cm2 to 1100 mJ/cm2 clearly showed sharp peaks around 515 cm-1 which indicated that a-Si was crystallized by GLA. Sharp peak with 4.9 cm-1 of full width at half maximum (FWHM) at 515.3 cm-1 was obtained from the sample treated with 1000 mJ/cm2. This value is as good as one of the best results obtained by conventional methods.1) The results of transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) of the sample revealed the lateral growth of poly-Si with a needle shape along laser scanning direction.It is concluded that a-Si:H films can be formed on substrates by using hydrogenated polysilane through spincoating and annealing process. And lateral growth of poly-Si by GLA was confirmed by the results of Raman spectra, TEM, and EBSD. We successfully demonstrated the solution processing of forming poly-Si films with high-quality. Those techniques will have potential applications including printable silicon-based devices.1) K. Kitahara et al., Jpn. J. Appl. Phys., 41, 5055 (2002)
Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
Patrick J. Smith The University of Sheffield
David B. Mitzi IBM T. J. Watson Research Center
Aoife Morrin Dublin City University
S7: Solution-Processing with Nanoparticles
Session Chairs
Patrick Smith
Maikel van Hest
Thursday AM, December 01, 2011
Room 310 (Hynes)
9:30 AM - S7.1
Faceted Solution Growth of Rare-Earth Oxychloride Nanocrystals and Their Incorporation into Nanostructured Thin Films.
Kenneth Kort 1 , Sarbajit Banerjee 1
1 Chemistry, University at Buffalo, Buffalo, New York, United States
Show AbstractLanthanide oxychlorides (LnOCl) possess unique optical, magnetic, electronic, and catalytic properties that are characteristic to each specific metal. Scaling LnOCl to nanoscale dimensions offers the potential to further tune the properties of these materials. Most reported approaches for preparing LnOCl nanostructures do not yield well-defined morphologies because of the lack of control in separating the nucleation and growth steps. We have established a novel synthetic methodology for preparing LnOCl nanocrystals with controllable dimensions and morphology based on a non-hydrolytic sol-gel synthetic route involving the ligand exchange and condensation of rare earth halides and alkoxides in the presence of coordinating solvents. Nanocubes, faceted 2D nanosheets, and nanodisk morphologies are obtained due to preferential growth along specific crystallographic directions dictated by the choice of the rare earth ion and the capping ligand. The synthetic approach represents a unique low-temperature route for the preparation of well-defined and faceted nanocrystals of ternary rare-earth oxychlorides in the PbFCl matlockite phase. The synthetic strategy can further be adapted to incorporate dopant ions. The potential applicability of these nanostructures as phosphors is illustrated by demonstrating the conversion of ultra-violet illumination to green emission by Tb3+:GdOCl nanocrystals, and the upconversion of near-infrared illumination to green and red emission by Er3+:GdOCl nanocrystals. Electrophoretic deposition is subsequently used to assemble nanostructured thin films of GdOCl nanocrystals onto conducting substrates. Deposition in galvanostatic mode yields thin films with thickness tunability through varying deposition time, whereas deposition in the potentiostatic mode yields conformal thin films.
9:45 AM - S7.2
Synthesis of Copper Nanoparticles by Polyol/Alcohol Reduction Method.
Jhon Cuya Huaman 1 , Balachandran Jeyadevan 1 , Hiroshi Miyamura 1 , Kimitaka Sato 2 , Satoru Kurita 2 , Takatoshi Matsumoto 3
1 Material Science, The University of Shiga University, Hikone, Shiga, Japan, 2 , DOWA Holdings Co. Ltd., Tokyo, Tokyo, Japan, 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, Japan
Show AbstractCopper nanoink is expected to replace silver because of the migration problem and cost. Copper nanoparticles have been synthesized by using different polyols such as ethylene glycol and diethylene glycol, however the particle size was not enough small to prepare conducting nanoinks. The search of new alternatives to reduce the particle size of copper led us to the use of long chain alcohols such as butanol, hexanol, heptanol and octanol. The addition of specific amount of hydroxyl ions in the alcoholic solution was necessary to enhance the reduction potential of the solvent and thus produce a short burst of nucleation. In addition, surfactants such as oleylamine were also used as a way to avoid the agglomeration of the copper particles during synthesis and enhance their dispersion in solvent such as toluene or dodecane. Thus, under optimized conditions monodisperse copper nanoparticles with average size of ~10 nm were synthesized in 1-heptanol. In addition, a scheme of reduction mechanism of copper in alcohol media is proposed consisting of different intermediate steps such as the formation of CuO and Cu2O. Each intermediate step could be isolated obtaining not only copper nanoparticles, but also pure CuO and Cu2O nanoparticles that could be applied as catalysts or thin film solar cells. On the other hand, copper thin films prepared from obtained copper nanoink by spin coating and annealed at 523 K in nitrogen and vacuum atmosphere showed electrical resistivity of 26 and 35 μΩ-cm, respectively. These results suggest that copper could be used as an alternative to replace silver nanoink or paste. However, additional research is necessary to develop a technique to prevent the oxidation of copper nanoparticles. Authors have developed a technique to coat the copper particles with nickel. The results of this study will also be reported.
10:00 AM - S7.3
Effect of Processing Variables on Photocatalytic Property of Hollow In2O3 Submicrometer Particles with Nanoporous Shell Structure.
Tzu-Tsung Tseng 1 , Wenjea Tseng 1
1 Department of Materials Science and Engineering, National Chung Hsing University, Taichung Taiwan
Show AbstractA one-pot, chemical synthesis route involving implantation of metal cations into originally nonporous polymeric templates has been successfully developed to fabricate discrete, inorganic particles with hollow interiors (shell wall thickness typically in a few tens of nanometers) after removal of the templates core. When indium chloride was used as the metallic precursor, non-aggregating In2O3 hollow capsules with a well-defined spherical shape, uni-modal particle-size distribution (600 – 1200 nm), and a broad specific surface area (B.E.T. from 15 to 55 m2/g) resulted as process variables (e.g., reaction time, process temperature, precursor concentration, etc.) alter. These morphological changes were found critically important to the photocatalytic behavior of the semiconductive In2O3 hollow capsules when dispersed in methylene blue dye solution upon UV exposures.
10:15 AM - S7.4
Hydrothermal Synthesis of Sodium-Substituted Potassium Niobates Fine Particles and Their Application to Lead-Free Piezoelectric Material.
Kiyoshi Kanie 1 , Hideo Mizutani 2 , Atsuki Terabe 2 , Yoshiki Numamoto 1 3 , Shintaro Tsukamoto 3 , Hirofumi Takahashi 3 , Masafumi Nakaya 1 , Junji Tani 1 , Atsushi Muramatsu 1
1 IMRAM, Tohoku University, Sendai Japan, 2 , Sakai Chemical Industry Co. Ltd., Iwaki Japan, 3 , Fuji Ceramics Corporation, Fujinomiya Japan
Show AbstractLead zirconate titanate (PZT) based ceramics are widely used as piezoelectric materials; however, high toxicity of lead brings serious problems during preparation, use, and disposal of the PZT-based materials. In this regard, extensive efforts have been carried out to improve piezoelectric performance and Curie temperature of lead-free piezoelectric materials. Especially, sodium-substituted potassium niobates (NaxK1-xNbO3: NKN) with a perovskite-type structure are regarded as ones of the most promising piezoelectric materials and potential alternatives for PZT-based ceramics. In the present study, NKN fine particles with different K/Na ratio were successfully obtained by the two-step hydrothermal reaction at 100 °C for 24 h and 200-250 °C for 3 h using niobium pentachloride as a soluble precursor. As a result of effect of K/Na ratio in the starting solution, NKN particles basically with an orthorhombic sodium niobate were formed in the NaOH/KOH ratios from 10/8 to 7/11. In contrast, by aging at 250 °C, NKN particles with orthorhombic potassium niobate crystal structure was obtained in the NaOH/KOH ratios from 5/13 to 1/17. Furthermore, monodispersed and octahedral-shaped NKN fine particle with a tetragonal crystal structure was formed as a single phase at 200 °C with the NaOH/KOH ratio of 6/12. The octahedral-shaped particle had a hierarchical build-up structure of cubical-shaped nanoparticles. Sodium and potassium ratio in the NKN crystal structures was further characterized by Rietveld analysis. All NKN ceramics, prepared starting from the present hydrothermal method, had highly porous structure. However, these ceramics exhibited high d33 values of ca. 100 pC/N. This result means that the octahedral-shaped NKN particles have large potentials as lead-free piezoelectric materials.
10:30 AM - S7.5
A Guided Growth of Silver Nanoparticle within the Densely Packed Two Dimensional Nanohole Array and Its Plasmonic Performance.
Shigenori Fujikawa 1 2 , Mari Koizumi 1 2
1 Interfacial Nanostrucutre Research Laboratory, RIKEN, Wako, Saitama, Japan, 2 CREST, JST, Wako, Saitama, Japan
Show Abstract Block copolymer lithography is a solution-based nanofabrication process and can create a wide variety of two- dimensional pattern with long-range order. The well-defined nanodomains from asymmetric diblock copolymers (BCP) of polystyrene-block-polymethyl methacrylate were used as an initial pattern, and the two dimensional through-naonhole array was prepared by selective removal of polymethyl methacrylate moieties. Nanohole-specific growth of silver nanoparticles (Ag NPs) occurred by galvanic displacement reaction. Hydrogen plasma removed the template polymer without the alternation the metallic nature of Ag NPs. Ag NPs are hexagonally aligned, reflecting the original nanohole arrangement. Each particle is separated with the constant interspace. Longer galvanic reactions elongate the Ag NP and increase its diameter. Plasmonic properties of the Ag NP array were investigated and the surface-enhanced Raman scattering was observed in densely closed Ag NPs array.
11:15 AM - S7.6
Continuous Multi-Step Microflow Synthesis of InP and InAs Quantum Dots (QDs), InP/ZnS Core Shell QD, and InPxAs1-x Alloy QDs at High Temperature and High Pressure.
Jinyoung Baek 1 , Peter Allen 2 , Moungi Bawendi 2 , Klavs Jensen 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemistry, MIT, Cambridge, Massachusetts, United States
Show AbstractIndium phosphide (InP) quantum dots (QDs), as a replacement of CdSe QDs, are of technological interest in visible-light applications with superior electronic and optoelectronic properties. However, InP QDs have not been produced with narrow size distributions, in comparison to CdSe QDs. We have investigated important parameters of InP QDs with multi-step continuous microflow system. We also have synthesized indium arsenide (InAs) QDs, as a material for infra-red applications.High temperature and pressure silicon based microfluidic system enables utilization of conventional solvents with short carbon chain providing fast mixing, and provides precise control of synthetic conditions with fast screening. Truly continuous multi-stage microfluidic system without incorporating any manual batch processes between steps allows us to separate reaction conditions such as mixing and aging steps, and thus enables systematic investigation of the synthesis of InP QDs.We utilized a 3-stage microreactor system consisting of separate mixing and aging microreactors with supercritical octane as a solvent in order to elegantly probe the effects of each temperature, particle concentrations, and indium to fatty acid ratio. We found that aging temperature had the most significant effect in obtaining high quality InP QDs compared to mixing temperature between monomer precursors. With the understanding of InP QD growth, we tuned the size of InP QDs by controlling the concentration of the fatty acids or adding additional monomers through the side channels of the reactor.We have also synthesized InP / ZnS core-shell QDs with 5 or 6 -stage microreactor system consisting of additional shell growth reactors, namely shell formation and annealing reactors, in addition to the three-step InP growth system described above. We were able to obtain narrow emissions with high quantum yield.We also investigated the growth of InAs QDs with the same system as InP synthesis. We found that the InAs growth from In(MA)3 and (TMS)3As precursors showed similar behavior as InP growth. InPxAs1-x was also synthesized by precise control of P and As precursor amounts. InPxAs1-x showed wide range of emissions from visible to infra-red with superior electronic properties as III-V semiconductor materials.
11:30 AM - S7.7
The Development of Solution-Processed Semiconductor Nanocrystal Films as Gamma-Ray Scintillators.
Lazaro Padilha 1 , Wan Ki Bae 1 , Richard Schaller 2 3 , Jeffrey Pietryga 1
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractPressing needs of nuclear security have produced a demand for robust, scalable and inexpensive alternatives to current gamma-ray detection technologies, which are primarily based on single-crystal scintillators. An ideal goal in this area would be a granular, solution-castable scintillator material system, as it may ultimately yield the necessary high degree of control and regularity, at reasonable cost, over the up to meter-scale areas of interest. Because of their stability, relatively high gamma stopping-power, and fast, efficient fluorescence, semiconductor nanocrystal quantum dots are a particularly intriguing material class for this purpose. Indeed, there have been a number of promising studies; however, advances have seemingly stalled well short of the point of a fieldable device. We suggest the reasons for this are two-fold. The first is a lack of an effective diagnostic of performance on the level of the ultrafast time-resolved spectroscopies that have been applied so fruitfully to the development of materials for other optoelectronic devices, such as light-emitting diodes, photodetectors and solar cells. The second, which is perhaps an outcome of the first, is that published efforts have focused on standard, commercialized nanocrystals, neglecting the intrinsic power of solution-based synthesis and film-deposition methods to create nanoengineered structures and controlled extended films of unique functionality.Our approach is to attack both of these issues in a single, integrated effort. First, we have developed a synchronizable short-pulse (<10 picoseconds) electron gun, as a surrogate for the spontaneous gamma-ray emission from elemental sources, that allows us to observe and analyze the relaxation of highly excited quantum dots. This insight informs our effort in design and synthesis of engineered nanocrystals and related films and composites with enhanced scintillation response. Using the well-studied solution-synthesized CdSe/ZnS core/shell heterostructured nanocrystals as a starting point for our investigation, we have begun to establish a more complete picture of the scintillation process in simple films of this material that points to contributions from both intra- and inter-nanocrystal processes. This presentation will discuss these results, as well as more recent examinations of “next-generation” material films we are developing in response to our initial studies.
11:45 AM - S7.8
Synthetic Iron Pyrite (FeS2) Nanocrystals for Use in Hybrid Organic-Inorganic Solar Cells.
John Bae 1 , Beau Richardson 1 , Leize Zhu 1 , Qiuming Yu 1
1 Chemical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractOne of the greatest sources of energy comes from solar radiation but the high cost associated with fabricating and maintaining silicon solar cells prevents its spread in popularity. Low-cost and highly efficient photovoltaic devices have to be developed in order to significantly increase the proportion of solar energy to the total energy used. A material that is promising in this aspect is iron pyrite (FeS2, commonly known as fool’s gold), which is abundant as well as environmentally benign with a useful band gap of ~0.95 eV and a high optical absorption coefficient (α > 105 cm-1, 2 orders of magnitude greater than crystalline silicon). Because of this high optical absorption coefficient, iron pyrite can absorb most incident light with much less material than silicon-based photovoltaic devices. Here we report a simple method of synthesizing crystalline FeS2 (pyrite) nanocrystals via a hydrothermal procedure. In particular, we aim to control the size and morphology of nanocrystals in order to investigate the surface and interfacial properties on the performance of hybrid organic-inorganic photovoltaic devices.Iron pyrite nanocrystals were synthesized using a hydrothermal method. Typically, poly(vinylpyrrolidone) (PVP) solution was mixed with poly(vinyl alcohol) (PVA) solution and FeCl2-4H2O followed by the addition of NaOH and sulfur powder. After stirring the mixture for 30 minutes, the Teflon liner containing the reaction mixture was placed in a stainless steel autoclave and reacted at 170-220°C for 12-24 hours. The reactor was cooled naturally to room temperature. Once cooled, the products were washed with deionized water and absolute ethanol several times, and dried under vacuum. The pyrite phase was confirmed by powder XRD as well as high resolution TEM and selected area electron diffraction (SAED). The size and morphology were determined by SEM. Results indicate that the molecular weight of surfactants (PVP and PVA), their concentration and ratio, as well as the concentration of NaOH play important roles in controlling the morphology, i.e., cubic or octahedral shape, of the resulting nanocrystals. The reaction mechanisms, especially the interaction of surfactants with different crystalline facets guiding the final morphology will be discussed. Furthermore, the synthesized nanocrystals were blended with P3HT polymer and hybrid solar cells were made. The relationship between the size and morphology of nanocrystals and the solar cell power conversion efficiency were obtained. The effect of crystalline facets on the charge generation and separation at the polymer-nanocrystal interface will be discussed.
12:00 PM - S7.9
Facile Large-Scale Synthesis of Cu2ZnSnS4 Nanocrystals for Low-Cost Thin Film Solar Cells.
Youngwoo Kim 1 , Kyoohee Woo 1 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractSemiconductor nanocrystals have attracted great attention due to their fascinating characteristics such as light-harvesting properties and tunable electronic energetics depending upon the size. The nanocrystal dispersions, which are amenable to scalable coating or printing, are a key ingredient in the deposition of thermally annealed absorber layers, as an alternative to the vacuum-based deposition. Initial efforts are focused primarily on the synthesis of toxic and expensive nanocrystals that likely will not be widely adopted for large-scale commercial photovoltaic system. A promising approach is using nanocrystals composed of earth-abundant elements of low toxicity for the development of low-cost solar cells.Cu2ZnSnS4 (CZTS) is an emerging solar cell material that contains earth-abundant elements and has a near-optimum direct band gap energy of ∼1.5 eV and a large absorption coefficient (104 cm-1), which are similar to those of Cu(In,Ga)Se2 (CIGS), one of the most successful thin-film photovoltaic materials. Guo et al demonstrated a promising 7.2% efficiency via the selenization of CZTS nanocrystals deposited by roll coating. The production of large quantities of uniform-sized nanocrystals becomes critical for the realization of high-quality, inexpensive, large-area photovoltaics by the roll-to-roll deposition of nanoparticle solar inks. Although several methods have been reported for CZTS nanocrystal synthesis, including hot-injection solution synthesis and high-temperature arrested precipitation, their methods require relatively complex processing conditions and are not readily scalable, lacking the large-scale productivity. Herein, we report a simple and large-scale synthetic method to produce uniform-sized phase-pure CZTS nanocrystals with controlled stoichiometry. We develop a facile “heating-up” method, in which the reaction solution prepared at room temperature is heated to high temperature of 300oC to synthesize high-quality CZTS nanocrystals. This method is highly advantageous for scale-up, as demonstrated by the production of the CZTS nanocrystals (~ 3 g) from a single batch reaction of 100 ml without the deterioration of the size uniformity. The resulting CZTS nanoparticles were implemented to solar cells fabrication, after the analyses of high-resolution transmission electron microscopy, X-ray diffraction, and electron diffraction spectrometer. Successful fabrication of CZTS layer, reported here, is the first step in realizing the solution-processed solar cell with high efficiency.
12:15 PM - S7.10
Aqueous Cadmium Chalcogenide Quantum Dots: Factors Influencing Their Structural and Electronic Properties, and Their Photoinduced Electron-Injection Efficiency to Titanium Dioxide.
Kathleen Coughlin 1 , Jeremy Nevins 1 , David Watson 1
1 Chemistry, University at Buffalo, Buffalo, New York, United States
Show AbstractSemiconductor quantum dots (QDs) are potential alternatives to molecular sensitizers as photocatalysts and light harvesters for solar energy conversion. An ongoing challenge is to develop greener syntheses of QDs and solution-based methods for depositing QDs onto electron- and hole-accepting substrates. An associated challenge is to understand and control the photochemical properties and interfacial charge-transfer reactivity of QD-acceptor interfaces prepared via solution-based chemistry. This presentation will focus on the influence of composition and capping-group functionality on the growth kinetics of aqueous CdS and CdSe QDs and their linker-assisted attachment to nanocrystalline TiO2 films. It will also highlight the influence of capping-group functionality on electron injection and interfacial charge recombination between aqueous CdSe QDs and TiO2. Aqueous dispersions of CdS and CdSe QDs with various capping agents were prepared. Cysteinate(Cys)-capped CdSe and CdS QDs exhibited continuous growth leading to the apparent formation of “magic-size” clusters. In contrast, QDs bearing non-aminated capping groups exhibited boader excitonic absorption bands associated with regular QDs. The influence of structure and surface-attachment mode of capping groups on the kinetics of particle growth will be presented.QDs were tethered to metal-oxide surfaces via solution-phase linker-assisted assembly. As-synthesized QDs were adsorbed to TiO2 and ZrO2 films through terminal carboxylate groups of the capping agents. Electron-injection yield and charge recombination were quantified using transient absorbance (TA) spectroscopy. Excitation of the bandgap transition of TiO2-adsorbed CdSe QDs gave rise to a long-lived absorbance beyond 460 nm, which is associated with the charge-separated state following electron injection. ZrO2 served as an important control substrate, for which electron injection was thermodynamically unfavorable. Spectroscopic experiments have elucidated the influence of capping-group functionality and electronic properties on the quantum yield of electron injection and the kinetics of charge recombination. Notably, Cys-capped CdSe QDs exhibited increased electron-injection yields and/or slower charge recombination relative to QDs capped with non-aminated ligands. Thus, the structure and electronic properties of molecular linkers can dramatically influence the charge-transfer reactivity of nanostructured interfaces prepared via solution-based chemistry.
S8: Solution-Processed Organic-Inorganic Hybrids
Session Chairs
Thursday PM, December 01, 2011
Room 310 (Hynes)
2:30 PM - **S8.1
Two Photon Polymerization of Inorganic-Organic Hybrid Materials for Biomedical Device Applications.
Philip Miller 1 , Aleksandr Ovsianikov 1 , Anastasia Koroleva 2 , Shaun Gittard 1 2 , Anand Doraiswamy 1 , Boris Chichkov 2 , Roger Narayan 1
1 , UNC/NCSU Joint Department of Biomedical Engineering, Chapel Hill, North Carolina, United States, 2 , Laser Zentrum Hannover e. V., Hannover Germany
Show AbstractTwo photon polymerization is a direct writing process that involves spatial and temporal overlap of photons; selective polymerization of a photosensitive material takes place within well-defined and highly-localized volumes. Two photon polymerization provides several advantages over conventional approaches for scalable production of small-scale structures used in medical applications and other technological applications. Two photon polymerization may be used with a variety of inexpensive photosensitive materials, including acrylate-based polymers and inorganic-organic hybrid materials (e.g., zirconium oxide hybrid materials). Two photon polymerization can be set up in a conventional laboratory facility; a specialized processing environment (e.g., a cleanroom facility) is not needed. This technique has been used to fabricate microstructured transdermal drug delivery devices known as microneedles. Delivery of quantum dots through the stratum corneum layer of porcine skin was demonstrated using a two photon polymerization-fabricated microneedle. Two photon polymerization has been used to create other types of medical devices, including tissue engineering scaffolds and middle ear prostheses.
3:00 PM - S8.2
Nanoimprinted Hybrid Silica Coatings for Light Extraction.
Alban Letailleur 1 2 3 , Cedric Boissiere 2 , Francois Ribot 2 , Clement Sanchez 2 , Jeremie Teisseire 1 , Etienne Barthel 1 , Elin Sondergard 1 , Christophe Couteau 3 , Gilles Lerondel 3 , Nicolas Chemin 4
1 Surface du Verre et Interfaces, Saint-Gobain Recherche, Aubervilliers Cedex France, 2 Chimie de la Matière Condensée de Paris, Collège de France - Université Pierre et Marie Curie, Paris France, 3 ICD - Laboratoire de Nanotechnologies et d'Instrumentation Optique, Université de Technologies de Troyes, Troyes France, 4 Composites and Coatings, Saint-Gobain Recherche, France France
Show AbstractIn light emitting devices, a large amount of the light produced by the active layer is trapped inside the device because of internal reflection. Patterning the different interfaces induces an index gradient and light scattering and can therefore lead to an increase of the light output. Among the existing methods, Nanoimprint Lithography (NIL) emerges as a simple route for surface patterning at the sub-micrometer scale over large areas. To avoid multiple step processing and the poor stability of polymers resins, imprint of functional materials is required.Hybrid sol-gel materials form an innovative class of resists for NIL. They are based on the solution processing of organic precursors to obtain metal oxide. For instance we previously demonstrated the replication of patterns with sub-100 nm lateral size and aspect ratio greater than 1 into hybrids sol-gel silica, using temperatures below 150 °C. Fully inorganic silica structures can be obtained after thermal annealing (1). Due to their low dielectric constant, nanopatterned silica coatings are very suitable for applications in photonics, and integration in displays.To achieve high resolution in nanoimprinting, it is crucial to understand the rheological properties of these new resists. We demonstrate that these silicates exhibit a glass transition below room temperature and that the fast increase of this Tg leads to the vitrification and provides long-term stability to the coating. (2) This combination of low viscosity and high reactivity enables fast and conformal imprint over several tens of cm2. Furthermore, we demonstrate how the elaboration chemistry of the materials can be modified to adjust the process.(3) Finally, we used the solution processing to introduce colloidal quantum dots inside the silica layer, and successfully imprinted the resulting layer.(4) These systems are suitable for light conversion and extraction. As it absorbs around 400 nm and emits light in the visible range, such a layer can act as a conversion layer in LED devices. The light output in the patterned area increased 60 % compared to the flat surfaces.References: 1) Peroz, C.; Chauveau, V.; Barthel, E.; Sondergard, E. Advanced materials 2009, 21, 5552) Letailleur, A.; Teisseire, J.; Chemin, N.; Barthel, E.; Sondergard, E. Chem. Mater. 2010, 22, 31433) A. A. Letailleur, F. Ribot,, C. Boissière, C. Sanchez, J. Teisseire , E. Barthel, N. Chemin, J Am Chem Soc, submitted.4) A. A. Letailleur, Th. Richardot, C. Boissière, C. Sanchez, C. Couteau, G. Lérondel, E. Barthel, E. Søndergård, N. Chemin, and François Ribot, Advanced materials, submitted.
3:15 PM - S8.3
Location-Controlled Si Grains via Laser Crystallization of Liquid-Silicon.
Jin Zhang 1 , Ryoichi Ishihara 1 , Hideyuki Tagagishi 2 , Ryo Kawajiri 2 , Tatsuya Shimoda 2 3 , Kees Beenakker 1
1 Delft Institute of Microsystems and Nanoelectronics Technology (DIMES), Delft university of Technology, Delft Netherlands, 2 , Japan Science and Technology Agency, ERATO, SHIMODA Nano-Liquid Project, Nomi, Ishikawa, Japan, 3 School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), Nomi, Ishikawa, Japan
Show AbstractIn the flexible electronics, printing is promising as it enables non-vacuum and non-photolithography process hence a low-cost production. Organic semiconductor materials have been investigated for the printing, however carrier mobility and reliability are inferior in comparison with silicon devices. New material, liquid silicon, which is a hydrogenated polysilane in an organic solvent, offers us a chance to print silicon devices on a flexible substrate. Shimoda, et al. [1] succeeded in fabricating polycrystalline Si TFTs with laser crystallization of amorphous-Si precursor formed from the liquid-Si. However the performance is limited by the grain boundaries in the channel because of the random nature of the poly-Si grains. If the location of the grains can be controlled, TFTs can be fabricated inside the grain and performance would reach the crystalline-Si counterpart. This will realize high-speed circuits in the flexible electronics and may alter the fabrication process in ULSI. In this paper, we investigated to control location of each Si grains with laser crystallization of a-Si formed by spin-coated liquid-Si. We have succeeded to form grains with a diameter of 1.5 um at predetermined positions. We used the micro-Czochralski process [2] to control the position of Si grains. First, a grid of 100nm wide and 700nm deep holes (grain-filter) have been formed in 1.6 micron thick SiO2 on a crystalline Si substrate. 21-wt% solution of UV-irradiated CPS (liquid Si) was then spin-coated on the structure at a rotation speed of 2000 rpm and baked at 430°C for 60 min to remove the solvent and to form a-Si. The film thickness was 112 nm. Next the film was pre-annealed in a furnace at 650°C for 2 hours to dehydrogenate the a-Si film. Finally the sample was crystallized with XeCl excimer laser (308nm, 25ns) at a substrate temperature of 450°C, with fluences varying from 450 to 700 mJ/cm2. Hydrogen concentration of a-Si film measured with TOF-SIMS was decreased from 6.7e21cm-3 to 2-5e19cm-3 after the furnace annealing. Film density, measured by XRR, increases from 1.96g/cm3 to 2.328g/cm3, of which the latter is exactly the same as that of the crystalline Si substrate. Upon laser irradiation the Si grains have been obtained and the size increased with the energy density. Ablation, which occurs at an excess energy density, increases from <200 to 1000mJ/cm2 after the pre-annealing, because of the degassing and densification. With an energy density just below the ablation threshold, we have obtained Si grains with a maximum size of 1.5um. Those Si grains were successfully grown on top of the predetermined positions of the grain-filters. [1] T. Shimoda, et al., Nature 2006[2] R. Ishihara, et al., Thin Solid Film 2003
3:30 PM - S8.4
Generalized Silica Sol-Gel Route to Porous Metallic Percolation Networks.
Scott Warren 1 2 , Frank DiSalvo 1 , Uli Wiesner 1 2
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry, Cornell University, Ithaca, New York, United States
Show AbstractBatteries, fuel cells, and solar cells, among many other high-current density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has limited their application. Here we present a simple silica sol-gel process built around a multifunctional sol-gel precursor that is derived from: (1) a library of amino acids, hydroxyl acids, or peptides, (2) a silicon alkoxide, and (3) a metal acetate. This approach allows a wide range of biological functionalities to be built into these sol-gel hybrids while also enabling a wide range of metals—including noble metals—to be readily incorporated into sol-gel materials. We demonstrate that this process is compatible with block copolymer self-assembly, polystyrene bead templating, and the Stöber process. These materials can be processed at low temperatures to make porous nanocomposites with metallic percolation networks with a conductivity of over 1000 S/cm. This improves on porous silica sol-gel nanocomposites by 3 orders of magnitude and opens the application of this class of materials to high current density devices.
3:45 PM - S8.5
Silicon Nanowires and Silicon Nanowire - PEDOT:PSS Heterojunction Solar Cells.
Baris Ozdemir 1 3 , Mustafa Kulakci 2 3 , Rasit Turan 2 3 , Husnu Unalan 1 3
1 Department of Metallurgical and Materials Engineering, Middle East Technical University, ANKARA Turkey, 3 Center for Solar Energy Research and Technology, Middle East Technical University, ANKARA Turkey, 2 Department of Physics, Middle East Technical University, ANKARA Turkey
Show AbstractSilicon nanowires are attractive one dimensional structures for solar cell applications due to their unique physical and optical properties. Recent studies revealed that utilization of silicon nanowires in formation of radial p-n heterojunction solar cells brings remarkable important advantages over planar heterojunction solar cells such as enhanced carrier collection efficiency and increased p-n junction area coverage. In this study, experimental parameters governing fabrication of vertically aligned n-type silicon nanowire arrays through electroless etching method are determined first [1]. This is then followed by the creation of radial heterojunctions through drop casting PEDOT: PSS organic layer on these nanowires as the complementary p-type layer. Electroless etching is preferred as a solution based simple and cost effective method. The morphology of the silicon nanowires and deposited layers are analyzed using scanning electron microscopy which is followed by solar cell characterization. The energy conversion efficiency of silicon nanowire - PEDOT: PSS device is found as 5.30% pointing out a remarkable improvement over planar silicon - PEDOT: PSS control device, which displayed less than 1% efficiency. Effect of nanowire length on the efficiency is also investigated and will be presented. [1] B. Ozdemir, M. Kulakci, R. Turan, H. E. Unalan, Nanotechnology 22 (2011) 155606.
4:30 PM - S8.6
Hybrid Solution Based Thin Film Transistors for Flexible CMOS Circuits.
Michael Perez 1 , Israel Mejia 1 , Ana Salas-Villasenor 1 , Bruce Gnade 1 , Manuel Quevedo-Lopez 1
1 Material Science, The University of Texas at Dallas, Richardson, Texas, United States
Show AbstractSolution-based organic and inorganic semiconductors for thin-film transistors (TFTs) have attracted considerable attention due to their low cost deposition techniques and low processing temperatures, making them suitable for large area flexible electronics applications. Organic and inorganic semiconductor complementary metal-oxide-semiconductor (CMOS) devices are among the most promising due to their low power consumption and high performance in logic circuits. However, the lack of high performance solution-based semiconductors (n-type and p-type) and their incompatibility to integrate with common photolithography processes makes this technology immature. Here, we report on the optimization of full photolithography fabricated solution based TFTs for CMOS integration utilizing 6, 13-bis (Triisopropylsilylethynyl) (TIPS) pentacene and cadmium sulfide (CdS) as the semiconducting p and n-type layers, respectively. n-MOS transistors were fabricated by chemical bath deposition at a temperature of 70OC. Devices showed saturation mobility values of >10 cm2/V s, threshold voltages of approximately 5 V, and an on/off current ratio of ≈106. p-MOS devices exhibited saturation mobilities as high as 3x10-2 cm2/V s, with a VT of -3 V, and an on/off current ratio of ≈104.
4:45 PM - S8.7
Synthesis and Characterization of Novel Graphene-Silicon Oxide Graphene Oxide-Silicon Oxide Nanocomposite Material.
Tanvir Alam 2 , Manoj Ram 1 , Mikhail Ladanov 2 , Farah Alvi 3 , Ajit Mujumdar 2 , Ashok Kumar 1 2
2 Mechanical Engineering, University of South florida, Tampa, Florida, United States, 1 Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida, United States, 3 Electrical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractRecently, graphene has been considered in fabrication of nanoscale devices due to its appealing transport, structural, electrochemical, physicochemical and electronic properties. The property of graphene has been explored mostly in its own structure where the chemistry of interface still largely remains unexplored. The chemically modified graphene exhibits active edges, oxygen functional groups, and reveals extraordinary electrochemical and mechanical properties. The graphene fabricated on silicon dioxide substrate shows interesting electronics properties by figuring out the local atomic configuration as well as identifying the binding sites of graphene with SiO2 layer in the films. The primary objective of this work is to understand the interfacial properties of SiO2 coated over graphene nanoparticles. An attempt has been made to synthesize and characterize the SiO2 coated over graphene and graphene oxide nanoparticle to understand the physical and chemical properties nanocomposite material. A novel synthesis of graphene (G) –Silicon oxide (SiO2) and Graphene oxide (GO) – Silicon oxide (SiO2) nanocomposites using sol-gel technique is presented in this work. The G-SiO2 and GO-SiO2 nanocomposite materials were characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, FTIR spectroscopy, X-ray-diffraction, electrochemical, and electrical measurement techniques. The G-SiO2 nanocomposite has shown typical platelet characteristics much larger in size than the graphene nanoplatelets. The conductivity of G-SiO2 and GO-SiO2 has been found to increase with increase in graphene or graphene oxide ratio to SiO2 in nanocomposite materials. The G-SiO2 and GO-SiO2 nanocomposite have revealed interesting feature vibrational bands of graphene with SiO2 by varying the precursor of SiO2 with graphene nanoparticle moieties. The cyclic voltammogram, chronoamperometric, Nyquist plot, and electrochemical impedance spectroscopic studies have indicated the diffusion controlled systems of G-SiO2 and GO-SiO2 based electrodes. Our results indicate that G-SiO2 and GO-SiO2 nanocomposites could be a transformable and viable material for stable electrode for energy application, and found to be highly absorptive material for ionic separation purposes.
5:00 PM - S8.8
Solution-Processed 3D Plasmonic Hybrids for Highly Efficient SERS Substrates.
Ramesh Kattumenu 1 , Chang Lee 1 , Limei Tian 1 , Michael McConney 2 , Srikanth Singamaneni 1
1 Mechanical Engineering and Materials Science, Washington University in St.Louis, St.Louis, Missouri, United States, 2 Materials and Manufacturing Directorate, Air force research laboratory, Wright-Patterson Air Force Base, Ohio, United States
Show AbstractIn order to propel SERS-based sensing into real-world applications, novel SERS-active nanostructure designs that enable facile, scalable, cost-effective, highly efficient and homogenous SERS substrates are paramount. We demonstrate the facile fabrication of highly efficient SERS-active 3D nanohybrids based on vertically aligned zinc oxide (ZnO) nanowires using solution based chemical bath deposition technique. Uniform decoration of ZnO nanowires (1µm diameter) with gold nanorods (AuNR) of 15 nm diameter (aspect ratio 3.5) led to a dramatic enhancement of the surface area (nearly 20 times) and hence the number of plasmonic nanostructures within the incident laser foot print resulting in more than three thousand times increase in SERS intensity compared to planar SERS substrates. The SERS enhancement factor was found to be ~5×107 with a detection limit of sub-pM for non-resonant chemical analyte. Apart from excellent sensitivity, the nanohybrids also exhibited excellent lateral and vertical homogeneity in SERS activity. Under optimal conditions, these nanohybrids are expected to surpass the best 2D substrate designs in SERS enhancement and homogeneity.
5:15 PM - S8.9
Development of an Enabling Silsesquioxane and Use in a Hybrid Organic-Inorganic Flexible Film, Sila-DEC™.
James Caruso 1 , Naoki Noda 2 , Kazuhiro Yoshida 2 , Tomoyuki Ohba 2
1 Corporate R and D, North America, JNC Corporation, Albuquerque, New Mexico, United States, 2 , JNC Corporation, Ichihara Japan
Show AbstractWith the recent popularity of handheld devices such as smart phones and tablet PCs, thinner, lighter weight and flexible display are becoming required. Until now, glass has been the dominant substrate for flat panel displays (FPDs) however as displays become thinner and lighter weight, glass ‘brittleness’ is an unavoidable problem. While more conventional plastic substrates have been envisioned, they lack the chemical and physical properties of glass, making their use in FPDs a challenge. We have developed, and will discuss here, a new hybrid organic-inorganic transparent flexible film, “Sila-DEC™.” This film has been developed utilizing a newly synthesized silsesquioxane, namely a “Double-Decker shaped Polysilsesquioxane” (DD-PSQ) as the key material. Silsesquioxanes are a class of organosilicon compound with the general formula (RSiO3/2)n typically having a cage or partial cage structure. Our newly synthesized DD-PSQ is formed into a double-decker shape, with 2 chemically bound and stacked eight-membered siloxane rings with a variety of reactive pendant groups. With a stable structure, molecular design at the nanoscale is possible and DD-PSQ can be copolymerized by means of a variety of terminal functional group and with other organic polymers resulting in a unique class of hybrid organic inorganic copolymers. Utilizing these DD-PSQ materials we have produced unique hybrid organic-inorganic films by means of high-speed roll-to-roll print processes. The resulting films strike a balance between high heat resistance and high transparency, unobtainable in conventional organic plastic films. Typical performance attributes of the Sila-DEC™. films are:1)Excellent dimensional stability (CTE〈20ppm/K) 2)High heat resistance (Tg〉250 degree C) 3)Transparent in wide wavelength range including near-UV 4)Excellent chemical resistance against strong acids, strong alkaline, and organic solvents. Applications of Sila-DEC™. films include substrates to enable next generation thinner, lighter weight and flexible FPDs as well as other electronic applications.
5:30 PM - S8.10
Synthesis by Electrodeposition in Ionic Liquid of Amorphous Silicon Nanowires Doped with Erbium and the 1,55 µm Emission Band Associated.
Florie Martineau 1 , Jeremy Mallet 1 , Michel Troyon 1 , Michael Molinari 1
1 physics, LMEN - université de reims champagne ardenne (URCA), Reims France
Show AbstractAmorphous silicon nanowires doped with erbium were fabricated by electrochemical synthesis at room temperature. The electrodeposition at room temperature of Si NWs from the air- and water-stable ionic liquid 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide containing SiCl4 as Si source and ErCl3 as erbium source is investigated by cyclic voltammetry. Thanks to the control of different parameters such as temperature, concentration, and the deposition potential it is possible to grow NWs doped with controlled amount of erbium homogeneously dispersed in the NW.By using nanoporous polycarbonate membranes as templates, we show that it is possible to reproducibly grow pure Silicon NWs with diameters ranging from 15 to 400 nm [1,2]. Structural characterizations were performed by scanning and transmission electron microscopies, infrared absorption measurements, energy dispersive X-Ray, and Raman spectrometries. The as-deposited NWs are composed of pure amorphous silicon doped with less than 1 to 15% of erbium. The detailed examination of single NWs gives evidence of their good quality. Their growth morphology as well as their chemical composition was analyzed by scanning transmission electron microscopy (STEM) coupled to electron energy loss spectroscopy (EELS). They are amorphous and have homogeneous cylindrical shape with a roughness of a few nanometers on the wire surface. EELS measurements confirm the purity of electrodeposited Si NWs and the homogeneous dispersity of erbium. While the undoped NWs emit in the visible range at room temperature, for the appropriate amount of erbium (less than 3%) the doped NWs strongly emit at 1,55 µm at room temperature. Temperature-dependent and time-dependent photoluminescence (PL) experiments show that this emission is due to the absorption of the carriers by the silicon NWs and the following transfer to the Erbium ions Er3+. This innovative and cheap elaboration process using electrodeposition is very promising and could compete with the more expensive and constraining high vacuum techniques. Thanks to their 1,55 µm emission properties, the erbium-doped amorphous Si NWs could be envisaged for light-emitting devices.[1] Mallet J., Molinari M., Martineau F., Delavoie F., Fricoteaux P., Troyon M., “Growth of Silicon nanowires of controlled diameters by electrodeposition in ionic liquid at room temperature”, Nanoletters 8 (2008) 3468 [2] Al-Salman R., Mallet J., Molinari M, Fricoteaux P., Martineau F., Troyon M., El Abedin S.Z., Endres F., “Template assisted electrodeposition of germanium and silicon nanowires in an ionic liquid”, Physical Chemistry Chemical Physics 10 (2008) 6233