Symposium Organizers
Xiaobo Chen Lawrence Berkeley National Laboratory
Michael Graetzel Ecole Polytechnique Federale de Lausanne
Can Li Chinese Academy of Sciences
P.Davide Cozzoli Universita del Salento - Facolta di Ingneria Industriale
and Nanoscience Institute of CNR -
National Nanotechnology Laboratory
GG5: Poster Session I
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
GG1: Synthesis
Session Chairs
Tuesday PM, April 26, 2011
Room 3020 (Moscone West)
9:15 AM - GG1.1
Sol-peptization-gel Derived Nanostructured Titania: Influence of Critical-nuclei-size, Initial Particle Size and Packing on the Phase Stability of Anatase.
Rino Mukti 1 2 , Suminto Winardi 1 6 , Krishnankutty-Nair Kumar 3 4 , Junzheng Wang 1 , Wilfried Wunderlich 5 , Tatsuya Okubo 1
1 Department of Chemical System Engineering, The University of Tokyo, Tokyo, Tokyo, Japan, 2 Division of Inorganic and Physical Chemistry, Institut Teknologi Bandung, Bandung, West Java, Indonesia, 6 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 3 Department of Material Science and Engineering, The University of Texas at Dallas, Richardson, Texas, United States, 4 , Institute for Research in Management and Advanced Technology (IRMAT), Trivandrum India, 5 Department of Material Sciences, Tokai University, Hiratsuka, Kanagawa, Japan
Show AbstractTitania exists in a number of polymorphic forms with anatase and rutile being the most common ones. The metastable anatase is usually considered to be photocatalytically more active than rutile but the transformation to stable rutile occurs irreversibly upon heat treatment. A thorough understanding of anatase-to-rutile phase transformation behavior is not only important for designing titania based nanostructures but also for gaining a fundamental understanding on metastable-to-stable nucleation-growth based transformations. It is well known that there are several factors such as primary particle size, solution pH, hydrolysis, physical nature of precursor, reaction condition, washing and drying temperature, which can influence anatase-to-rutile transformation. Also there are several studies clearly demonstrating the importance of critical nuclei size in this transformation. However, very few studies have focused on the degree of packing of the primary particles and almost no studies have reported the influence of the initial primary particle size. In this study we focused primarily on the influence of primary paricle size and packing on the phase transformation behavior. Dried anatase gels with different degrees of particle packing in which the well-packed titania was prepared via peptization–induced by the electrostatic repulsion of primary particles in the sol (sol-peptization-gel) whereas loosely-packed titania was prepared without peptization in the sol (sol-gel). To see the effect of initial anatase primary particle size, all samples were precalcined prior to the anatase-to-rutile phase transformation that occurred during the final calcination. In the case of well-packed titania, the initial size of anatase primary particles does not influence the phase transformation behavior whereas loosely packed titania shows a strong initial anatase primary particle size dependence on the phase-transformation behavior. This concludes that the initial particle size of anatase is an important parameter emphasizing the importance of critical nuclei size in nucleation-growth type transformations in general and phase stability of nanostructured anatase in particular.
9:30 AM - **GG1.2
Controlling the Nano-Morphology of Porous Titania through Fusion of Ultrasmall Nanocrystals.
Thomas Bein 1
1 Chemistry, University of Munich (LMU), Munich Germany
Show AbstractGaining control over the nanoscale morphology of porous titanium dioxide is of enormous importance to fully exploit the great potential of this versatile material in numerous applications such as photovoltaics or charge storage. We have recently developed a highly flexible new preparation strategy for the formation of various nano-morphologies, based on fusing novel preformed ultrasmall titania nanocrystals with surfactant-templated sol-gel titania acting as a structure-directing matrix and as a chemical glue. In this "brick and mortar" approach, the “mortar” acts as a reactive precursor for the further growth of the crystalline phase seeded by the nanocrystalline “bricks”. This synergy leads to a significantly lowered temperature needed for crystallization and the preservation of the mesoporous structure. It also allows us to build various hierarchical structures such as titania inverse opals penetrated by titania mesopores, because we can significantly reduce shrinkage effects. The resulting thin films were investigated using X-ray scattering and HRTEM measurements to monitor and visualize the seeding effect, crystal growth and mesostructure development during calcination, respectively. Coatings with a broad variety of periodic mesostructures can be tuned by varying the surfactant and the fraction of the “bricks”, and thicknesses ranging from few nanometers to several micrometers are accessible. These mesostructured and crystalline films were employed as active layers in thin dye-sensitized solar cells exhibiting high conversion efficiency due to short diffusion paths. We will also discuss the integration of additional sensitizing approaches such as extremely thin absorber layers (ETA) and alternative solid hole conductors. When doped with Nb, the mesoporous networks resuling from the assembly of the nanoparticles become electrically conducting. Finally, we will show that the ultrathin crystalline walls of the mesoporous brick & mortar titania feature extremely fast lithium insertion kinetics. [1] J. M. Szeifert, J. M. Feckl, D. Fattakhova-Rohlfing, Y. Liu, V. Kalousek, J. Rathousky, T. Bein, J. Am. Chem. Soc., 2010, 132, 12605–12611.[2] H. Nemec, P. Kuzel, F. Kadlec, D. Fattakhova-Rohlfing, J. Szeifert, T. Bein, V. Kalousek, J. Rathousky, Appl. Phys. Lett., 2010, 96, 062103.[3] Y. Liu, J. M. Szeifert, J. M. Feckl, B. Mandlmeier, J. Rathousky, O. Hayden, D. Fattakhova-Rohlfing, T. Bein, ACS Nano, 2010, 4, 5373–5381.[4] J. M. Szeifert, D. Fattakhova-Rohlfing, D. Georgiadou, V. Kalousek, J. Rathousky, D. Kuang, S. Wenger, S. M. Zakeeruddin, M. Grätzel, T. Bein, Chem. Mater., 2009, 21, 1260-1265.
10:00 AM - GG1.3
Titanium Dioxide Nanobelts and Mesoporous Film for Dye-sensitized Solar Cell and Gas Sensing Applications.
Ghim Wei Ho 1 , Shweta Agarwala 1 , Wei Li Ong 1
1 Electrical & Computer Engineering, National University of Singapore, Singapore Singapore
Show AbstractThere is a great interest in the development of titania-based solids with nanoscale dimensions and specific morphology such as nanobelts, nanowires and mesoporous film depending on the applications. In our work, one-dimensional titania nanostructures are prepared by hydrothermal method from titania nanoparticles precursor via hydrolysis and ion exchange processes. The formation mechanism and the reaction process of the nanobelts are elucidated. The nanobelts are produced in gram quantities and easily made into nanostructure free standing sheet for the bulk study on their electrical and sensing properties. The sensing properties of the nanobelts sheet are tested and exhibited response to H2 gas. Another work involves mesophase ordering and structuring to attain optimized pore morphology, high crystallinity, stable porous framework of titania films. The pore structure (quasi-hexagonal and lamellar) can be controlled via the concentration of copolymer, resulting in two different types of micellar packing. The calcination temperature is also controlled to ensure a well-crystalline and stable porous framework. Finally, the synthesized mesoporous TiO2 film is fabricated into dye-sensitized solar cell. A combination of factors such as increased surface area, introduction of light scattering particles and high crystallinity of the mesoporous films leads to enhanced cell performance.
10:15 AM - GG1.4
Colloidal TiO2-based Nanocrystal Heterostructures.
P. Davide Cozzoli 1
1 National Nanotechnology Laboratory (NNL), CNR - Istituto Nanoscienze, Lecce Italy
Show AbstractTiO2-based nanomaterials represent exclusive encounter platforms on which diverse optoelectronic, thermal, mechanical, electrochemical and catalytic properties coexist with the potential for low-cost and environmentally safe energy technologies [1]. Among the most powerful synthetic approaches to inorganic nanostructures, colloidal routes have opened access to a variety of finely size- and shape-tailored nanocrystals by control of thermodynamically and kinetically driven growth processes in liquid media [2]. Further challenges are now being imposed on nanochemistry research in the pursuit of increasingly elaborate breeds of so-called hybrid nanocrystals (HNCs) that can offer diversified and/or enhanced properties as well as multifunctional capabilities. HNCs are multicomponent nanoheterostructures with a topologically controlled distribution of their composition, which incorporate epitaxially joint domains of distinct materials into individually processable nano-objects [2-5].Here, we describe recent progress made by our research group in wet-chemical development and characterization of several types of elaborate non-core/shell TiO2-based HNCs, which comprise TiO2 epitaxially bound to different metal and magnetic materials. Heterostructures based on size/shape-engineered sections of different TiO2 polymorphs [6], as well as on combinations of TiO2 sections with either iron oxide [7], Co [8], Ag, Pt [9], Cu or CuxO domains [10] will be described and discussed with regard to their structural, optical, magnetic and catalytic properties. Our results will illustrate how facet-dependent nanocrystal reactivity, lattice strain at the relevant junction regions, and surface-interface energy balance interplay at the nanoscale and dictate the final HNC topology. Useful criteria for the rational design of future prototypes of TiO2-based heterostructures with higher structural complexity and increased functionality will be suggested.References[1] X. Chen, S. S. Mao, Chem. Soc. Rev. 2007, 107, 2891[2] Advanced Wet-Chemical Synthetic Approaches to Inorganic Nanostructures; P.D. Cozzoli Ed.; Transworld Research Network 2008, Kerala (India), pp. pp. 407-453 [3] P. D. Cozzoli et al. Chem. Soc. Rev. 2006, 35, 1195[4] M. Casavola et al. Eur. J. Inorg. Chem. 2008, (6), 837[5] L. Carbone, P.D. Cozzoli Nano Today 2010, 5, 449[6] M. R. Belviso et al., in preparation; [7] (a) R. Buonsanti et al. J. Am. Chem. Soc. 2006, 128, 16953. (b) R. Buonsanti et al. Phys. Chem. Chem. Phys. 2009, 11, 3680 (d) R. Buonsanti et al. J. Am. Chem. Soc. 2010, 132, 2437[8] M. Casavola et al. Nano Lett. 2007, 7, 1386.[9] R. Buonsanti et al., in preparation[10] S. Usseglio Nanot et al., in preparation
10:30 AM - GG1.5
Chemical Vapor Synthesis of TiO2 Nanoparticles: The Time-temperature Profile Influence on Particle Characteristics.
Ruzica Djenadic 1 , Markus Winterer 1
1 Nanoparticle Process Technology, Department of Engineering Sciences and CeNIDE, University Duisburg-Essen, Duisburg Germany
Show AbstractThe application of nanoparticles is strongly influenced by particle characteristics, e.g. particle size, crystallinity, degree of agglomeration, etc. The time-temperature (t-T) profile in the gas phase of the reactor has a profound influence on the particle characteristics such as particle microstructure and surface chemistry and, therefore, on the quality of the powder consisting of nanoparticles. The role of the t-T history in chemical vapor synthesis (CVS) is theoretically and experimentally investigated. A coagulation-sintering model is used to describe the particle formation. The model is compared to experimental results obtained from synthesis of TiO2 nanoparticles from titanium isopropoxide (TTIP) in the gas phase using a hot wall reactor. Different t-T profiles were established using a furnace with an inductively generated heat source. Temperatures were set from 873 till 2023 K. The powder characteristics are analyzed in detail using nitrogen adsorption, X-ray diffraction, dynamic light scattering, and transmission electron microscopy with emphasis on degree of agglomeration. The as-synthesized TiO2 nanoparticles consist of pure anatase up to 1273 K. High temperatures and fast quenching rates should be used to limit formation of hard agglomerates.
10:45 AM - GG1.6
Uniform Titanium Dioxide Nanorods Grown by Atomic Layer Crystallization.
Xudong Wang 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractDue to the excellent solid-state physical-chemical properties, Titanium dioxide (TiO2) has demonstrated a wide range of applications in hydrogen storage, lithium-ion batteries, fuel cells, gas sensors, detoxification, photovoltaic, photocatalysis, supercapacitors and so on. In order to achieve high performance in these applications, TiO2 nanostructures with well-controlled phase, dimension, and distribution are desired. Among them, one-dimensional (1D) structures, such as nanowires or nanorods (NRs) are considered superior due to the well defined crystal surfaces and 1D confined transport channels. Although TiO2 NWs have been made via vapor- or solution-based approaches, the nature of TiO2 crystal structure, the complexity of the Ti-O phase diagram, and the extremely low vapor pressure of titanium still make it very challenging to synthesize TiO2 NWs with well-controlled structure, morphology and properties. Recently, we demonstrated a novel approach to grow well controlled and highly uniform anatase TiO2 NRs arrays through a layer-by-layer crystallization process. It is so called atomic layer crystallization (ALC). The ALC technique mimics the atomic layer deposition (ALD) process using separated exposures of TiCl4 and H2O gaseous precursors, where the deposition is dictated by self-limited surface absorption. By increasing the deposition temperature and designing the pulsing and purging time to allow surface chemical reaction and/or atomic reconstruction to complete, 1D growth of anatase TiO2 crystal was achieved. 600 cycles of ALC produced TiO2 NRs with a length of ~300 nm and ~30 nm in diameter. We revealed that the formation of TiO2 NRs is due to the existence of the (001) surface, which showed a fast growth rate of ~0.5 nm per cycle; while the side surfaces had a growth rate of <0.1 nm per cycle. The ALC technique for growing TiO2 NRs inherits most of the merits of ALD, which includes: (1) large area deposition; (2) uniform coverage on high aspect ratio surfaces, such as submicron-sized nanochannels; (3) applicable to a variety of substrates. The resulted TiO2 NRs architecture would offer a very high surface area as well as a good carrier transport property, which could provide a novel TiO2 NR-based electrode for improving the performance of photovoltaic and electrochemical devices.
11:00 AM - GG1: Nanopart
BREAK
GG2: Solar Cells
Session Chairs
Tuesday PM, April 26, 2011
Room 3020 (Moscone West)
11:30 AM - **GG2.1
Mesoscopic Junctions for Light Energy Harvesting and Conversion.
Mohammad Nazeeruddin 1
1 Laboratory of Photonics and Interfaces (LPI), Ecole Polytechnique Federale de Lausanne, Lausanne, Vaud, Switzerland
Show AbstractKeywords: Titanium dioxide, Sensitizers, High molar extinction coefficient dyes, Dye-sensitized solar cell, Mesoporous thin films.Dye-sensitized solar cells (DSSC) consists of a working electrode, which is a sensitizer derivatized mesoporous TiO2 film, and a counter electrode, sandwitched with an iodide/triiodide (I-/I3-) redox electrolyte. The immobilized sensitizer absorbs a photon to produce an excited state, which transfers efficiently its electron into the TiO2 conduction band. The oxidized dye is subsequently reduced by electron donation from the iodide/triiodide redox system. The injected electron flows through the semiconductor network to arrive at the back contact and then through the external load to the counter electrode. At the counter electrode, reduction of triiodide in turn regenerates iodide, which completes the circuit. [1,2] In these cells nanocrystalline TiO2 film, the sensitizer and the redox couple are the key components for high power conversion efficiency. [3] This talk presents the state-of-the art of dye-sensitized solar cells, and strategies for enhancing power conversion efficiencies above 12%.Reference[1]. Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Hum-phry-Baker, R.; Muller, E.; Liska, P.; Vlachopoulos, N.; Grätzel, M. J. Am. Chem. Soc. 1993, 115, 6382. [2]. Bessho, Takeru; Yoneda, Eiji; Yum, Jun-Ho; Gug-lielmi, Matteo; Tavernelli, Ivano; Imai, Hachiro; Roth-lisberger, Ursula; Nazeeruddin, Mohammad K.; Gratzel, Michael. J. Am. Chem. Soc. 2009, 131, 5930. [3]. Yasuo Chiba, Ashraful Islam, Yuki Watanabe, Ryoichi Komiya, Naoki Koide and Liyuan Han, Jpn. J. Appl. Phys. 45 (2006) pp. L638-L640.Acknowledgement. We acknowledge financial sup-port of this work by EU-FP7 and World Class Univer-sity program grant number, R31-1003.
12:00 PM - GG2.2
Enhancing the Efficiency of Solid-state Dye-sensitized Solar Cells with Plasmonic Back Reflectors.
I-Kang Ding 1 , Jia Zhu 1 , Wenshan Cai 1 , Soo-Jin Moon 2 , Mark Brongersma 1 , Michael Graetzel 2 , Yi Cui 1 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 , Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractSolid-state dye-sensitized solar cells (ss-DSCs) are a type of solar cell that replaces the liquid electrolyte in a conventional DSC with a solid-state hole-transport material. SS-DSCs have already achieved power conversion efficiency over 6%, and they do not have problems with potential leakage and corrosion encountered by liquid electrolyte DSCs. However, current ss-DSCs are limited by both pore filling and electron-hole recombination such that the optimal thickness is around 2 μm, which is far too thin to absorb enough light. We show that the efficiency of ss-DSCs can be greatly enhanced by incorporation of plasmonic back reflectors, which consist of two-dimensional (2D) array of silver nanodomes. The plasmonic back reflectors can be fabricated by nanoimprint lithography. They enhance absorption through excitation of plasmonic modes and increased light scattering. SS-DSCs with plasmonic back reflectors show increased external quantum efficiency, particularly in the long wavelength region of the dye’s absorption band. This approach is effective in increasing the efficiencies of ss-DSCs with normal thickness (2 μm) made with both ruthenium-complex sensitizers and strong-absorbing organic sensitizers, and the short-circuit photocurrents increased by 16% and 12%, respectively. They achieve power conversion efficiencies of 3.9% and 5.9%, on par with the world record for the devices with the same dyes. In addition to the device data, results on the theoretical modeling of plasmonic and photonic effects will also be presented.
12:15 PM - GG2.3
Control of Solid-state Dye-sensitized Solar Cell Performance by Block-copolymer-directed TiO2 Synthesis.
Pablo Docampo 1 , Stefan Guldin 2 , Morgan Stefik 3 , Priti Tiwana 1 , Christopher Orilall 3 , Sven Huttner 2 , Hiroaki Sai 3 , Ulrich Wiesner 3 , Ulrich Steiner 2 , Henry Snaith 1
1 Condensed Matter, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2 Physics, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 3 Materials science and engineering, Cornell University, Ithaca, New York, United States
Show AbstractHybrid dye-sensitized solar cells are typically composed of mesoporous titania (TiO2), light-harvesting dyes, and organic molecular hole-transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study, TiO2 is synthesized in a well-defined morphological confinement that arises from the self-assembly of a diblock copolymer-poly(isoprene-b-ethylene oxide) (Pl-b-PEO). The crystallization environment, tuned by the inorganic (TiO2 mass) to organic (polymer) ratio, is shown to be a decisive factor in determining the distribution of sub-bandgap electronic states and the associated electronic function in solid-state dye-sensitized solar cells. Interestingly, the tuning of the sub-bandgap states does not appear to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub-bandgap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub-bandgap states is critical for efficient photo-induced electron transfer and charge separation. We furthermore prove the concept by assembling a continuous network of TiO2 through the triblock terpolymer poly(isoprene-b-styrene-b-ethylene oxide) (ISO), where the polymer accounts for over 70% of the volume, which leads to over 5% power conversion efficiency for "self-assembled" dye-sensitized solar cells employing spiro-OMeTAD as the molecular hole transporter.
12:30 PM - GG2.4
Nanoporous Spherical TiO2 for Dye-sensitized Solar Cells.
Wan In Lee 1 , Yong Joo Kim 1 , Sang Do Sung 1 , Hark Jin Kim 1
1 Department of Chemistry, Inha University, Incheon Korea (the Republic of)
Show AbstractMonodispersed TiO2 spheres with ultra-high surface areas were synthesized by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) and subsequent hydrothermal treatment at 230oC. The diameters of the TiO2 spheres were selectively controlled in the range of 260-980 nm by adjusting the ratio of TTIP to water (r-factor). The sizes of sphere were linearly proportional to the r-factor in the hydrolysis reaction. The prepared TiO2 spheres, in the pure anatase phase with a crystallite size of ~15 nm, were highly porous structures with the surface areas of 105-115 m2g-1. First, the deformed TiO2 microspheres with the size of 260 nm were applied to the main electrode layer of dye-sensitized solar cell (DSC). The achieved conversion efficiency was remarkably higher than that of the cells derived from the commercial TiO2 pastes. The advantages and disadvantages of the nanoporous TiO2 microspheres were fully analyzed and discussed in the work. Second, several spheres in different sizes were applied as the scattering layer of DSC for the efficient utilization of sun light, and the size-dependent scattering effects for those spheres were investigated. It was found that the 450-nm-sized sphere provides the highest scattering efficiency, and its high scattering efficiency seemed to be caused by a significant photonic reflection at 650-700 nm. As a result, the photovoltaic conversion efficiency was increased from 6.8 to 9.03% by introducing the 450-nm-sized spheres as scattering layer. Third, it has been found that spherical TiO2 can be successfully applied for the formation of flexible DSC. Herein, the 260-nm-sized spherical TiO2 structure was mixed with the 25-nm-sized nanoparticle (Degussa P25) to form the TiO2 layer. Blending of the large TiO2 sphere significantly increased the surface area, improved the electron transport properties, and enhanced the quantum efficiency in the long wavelength region. As a result, the photovoltaic conversion efficiency of DSC processed at 140oC was enhanced from 4.4% to 6.3%.
GG5: Poster Session I
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - GG5.1
Patterned VLS Growth of TiO2 Nanowires on Ti Substrate.
Jong-Yoon Ha 1 2 , Brian Sosnowchik 2 , Liwei Lin 2 , Albert Davydov 1
1 Metallurgy Division, NIST, Gaithersburg, Maryland, United States, 2 Mechanical Engineering, University of California at Berkeley, Berkeley, California, United States
Show AbstractThe single crystalline rutile titanium dioxide (TiO2) nanowires (NWs) were synthesized by tin catalyzed Vapor-Liquid-Solid (VLS) method on a Ti foil substrate. The NW growth was conducted in an inductively heated vertical quartz tube reactor at the 850 °C for 10 min with Ar + 2% H2 carrier gas. The growth of the TiO2 NWs of 3 - 8 μm in length and 50 - 300 nm in diameter grew along the [110] axis and had rectangular cross-section with the (001) and (1-10) type side facets. For the growth, titanium foil served as a source of Ti, while O2 was supplied from residual oxygen in the carrier gas. The structure of the TiO2 NWs was analyzed by X-ray diffraction, high resolution transmission electron microscopy, and electron backscattered diffraction. The shape and compositions of TiO2 NWs were characterized by FESEM and X-ray EDS, respectively. This facile approach utilizes fast heating ramp rate, eliminates the need for a separate titanium source and can be extended for fabricating NWs of other metal oxides.
6:00 PM - GG5.10
Fabrication of Mesoporous Titania Opals and Inverse Opals.
Lianbin Xu 1 2 , Zhiyan Hu 1 , Shaohua Cai 1 , Zhongjiong Hua 1 , Jianfeng Chen 1 , Yushan Yan 2
1 Key Lab for Nanomaterials, Ministry of Education, Beijing University of Chemical Technology, Beijing China, 2 Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, California, United States
Show AbstractThree-dimensionally (3D) ordered mesoporous titania (TiO2) opals and inverse opals were fabricated through a combination of colloidal crystal based micromolding (hard-templating) and triblock-copolymer-templating (soft-templating) approaches. Poly(methyl methacrylate) (PMMA) inverse opals and opals were use as the hard templates for the synthesis of mesoporous TiO2 opals and inverse opals, respectively. PMMA inverse opals were prepared by templating silica opals, while PMMA opals were produced by self-assembly of monodisperse PMMA spheres. Titania precursor, consisting of amphiphilic triblock copolymer Pluronic P123 as a mesopore-directing agent and titanium tetraisopropoxide as a titanium source, was infiltrated into the void spaces of the PMMA templates (PMMA inverse opals or opals). Subsequent thermal treatment produced 3D ordered mesoporous TiO2 opals or inverse opals. The obtained mesoporous TiO2 materials exhibit a well-defined mesoporous structure with narrow pore size distribution, and the mesopore walls are composed of nanocrystalline anatase TiO2. Details on the fabrication and characterization of these materials are presented including scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, nitrogen adsorption, and photocatalytic activity studies.
6:00 PM - GG5.11
Highly Active Titania Decorated Titanate Nanotubes for Photocatalytic Organic Substances Degradation.
Soonhyun Kim 1 , Minsun Kim 1 , Sung-Ho Hwang 1 , Sang Kyoo Lim 1
1 , Daegu Gyeongbuk Institute of Science and Technology, Daegu Korea (the Republic of)
Show AbstractAnatase titania decorated titanate nanotubes (TiNT-AT) are prepared by acid treatment at 80 °C from titanate nanotubes (TiNT) which are produced from the alkaline hydrothermal reaction of P25. The obtained TiNTs with 10 ~ 20 nm in diameter and several hundred nanometers in length. They composed low crystalline titanate and their surface area were ca. 152 m2/g. However, they did not show any photocatalytic activities due to a lot of defect sites which could act as recombination center of photogenerated electron and hole pairs. On the other hands, TiNT-ATs show the efficient photocatalytic activities for both gaseous CH3CHO and aqueous DCA degradation. The physicochemical properties and the photocatalytic activities of TiNT-ATs are strongly affected by the hydrothermal temperature and the subsequently treated acid concentration due to the phase transition from titanate to anatase or rutile phase of titania. However, these phase transitions could be inhibited by the surface modification of TiNT, which could be responsible for the highly enhanced photocatalytic activities and the stable TiNT-AT structures. More detailed results will be presented and discussed.
6:00 PM - GG5.12
Nb-substituted TiO2 Nanosheet Exfoliated from Layered Titanate for TCO and Photocatalysis.
Haiyan Song 1 , Anja Sjastad 1 , Poul Norby 2 , Ornulv Vistad 3 , Helmer Fjellvag 1
1 Department of Chemistry and Centre for Materials Science and Nanotechnology, University in Oslo, Oslo Norway, 2 Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, Roskilde Denmark, 3 , SINTEF Materials and Chemistry, Oslo Norway
Show Abstract Layered titanate Cs0.7Ti1.825■0.175O4 (■ = vacancy) with lepidocrocite structure provide opportunities for interlayer chemistry [1]. The structure contains defect host layers of edge-shared TiO6-octahedra. Interlayer cesium ions compensate for negative charge arising from Ti-vacancies. Substituted CsxTi2-x/2Mx/2O4 ,M = Mg, Fe, Co, Ni, Cu, Zn are intensively studied for ion-exchange/ intercalation [2-6]. Nb-substituted anatase films show electric and optic properties quite comparable with those of ITO [7]. We here explore Nb-substituted nanosheets as precursors for Nb-TiO2 thin films with TCO and photocatalytic properties.Phase-pure, layered Nb-substituted Cs0.7Ti1.8-xNbxO4 (x = 0 – 0.03) were synthesized by a novel sol-gel assisted solid state reaction route. XRD data indicates small, yet significant changes in unit cell dimensions caused by Nb(V) replacing Ti(IV) without structural deterioration. Layered Nb- substituted titanates were exfoliated into single layer nanosheets by proton-exchange followed by reaction with tetrabutylammonium hydroxide. The Nb-content of the layers is not affected by the ion exchange. AFM shows exfoliated nanosheets with average thickness and area of ca. 1 nm and 0.54 μm2. The thickness corresponds well to single titania blocks in the layered H0.7Ti1.825■0.175O4 mother phase. Cotton-like restacked materials were obtained by freeze-drying stable suspensions of exfoliated nanosheets. These exhibit lamellar structure with 1.75 nm interlayer distance and convert on heating into anatase and subsequently rutile. Substitution of Nb(V) for Ti(IV) into anatase suppresses the transition to rutile. Slightly expanded unit cells of both the Ti(Nb)O2 polymorphs prove that Nb enters as a solid solution, in agreement with findings for ceramically synthesized rutile type samples.AFM and XRD show that exfoliated nanosheets can be fabricated into tiled mono- and multilayer films by a layer-by-layer procedure. These were investigated for TCO and photocatalytic properties. Information on Ti and Nb oxidation states is deduced on basis of XPS, NMR and magnetic susceptibility data.References:[1] England, W. A. et al. J. Solid State Chem. 1983,49,300.[2] Reid, A. F. et al. A. D. Acta Cryst. 1968,B24,1228.[3] Groult, D.et al. J. Solid State Chem. 1980,32,289.[4] Verbaère, A. et al. Rev. Chim. Minér. 1975,12,156.[5] Hervieu, M. and Raveau, B. Rev. Chim. Minér. 1981,18,642.[6] Birchall, T. et al. J. Chem. Soc. A 1969,16,2382.[7] Furubayashi, Y. et al. Appl. Phys. Lett. 2005,86,252101[8] Song, H. Y. et al. Inorg. Chem. 2009, 48, 6952
6:00 PM - GG5.13
Porous TiO2 Multilayers via Anodization.
Lingxia Zheng 1 , Yangyang Li 1
1 Department of Physics and Materials Science, City Unversity of Hong Kong, Hong Kong China
Show AbstractSelf-organized TiO2 nanotube arrays grown by controlled anodic oxidation of a Ti substrate attracted broad scientific interest due to wide potential applications. Most anodic TiO2 nanostructures studied to date are single-layered or double-layered nanotubular films. Here we report a facile approach to fabricate multilayered porous TiO2 films by anodizing Ti foils in an organic electrolyte using a multi-step pulsed voltage waveform. The fabricated TiO2 multilayers feature mesopores, tens of layers with each layer thickness of a few hundred nanometers, and different film colors. The experimental data reported in this study is also potentially important to understand the forming mechanism of the anodic TiO2 nanostructures.
6:00 PM - GG5.14
Morphology Control of Anodic TiO2 via Mechanical Pretreatment of Ti Foils.
Hui Li 1 2 , Lingxia Zheng 1 , Yangyang Li 1
1 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong China, 2 Department of Physics, University of Science and Technology of China, He Fei China
Show AbstractSelf-organized TiO2 nanotubes conveniently fabricated by anodizing Ti foils have attracted much attention for various applications. Characteristics and performance of the anodic TiO2 nanotubes have proven largely dependent on its morphology. Here we report that mechanical pretreatment (e.g., cold rolling) of the Ti foils has a strong impact on the morphology of the subsequently etched TiO2 nanostructures. By controlling the amount of cold work applied to the Ti foils, different types of TiO2 nanostructures (e.g., self-organized nanotubes, interweaving elliptical nanotubes, or self-organized nanoporous sponge) can be obtained under the identical anodization conditions. In addition, the anodic TiO2 film etched from a cold-worked Ti foil exhibits a much cleaner and smoother top surface than the counterpart generated on an untreated Ti foil, indicating that the cold-work treatment results in a film top surface that is more resistant to the corrosion of the fluoride species in the electrolyte. This feature of smooth top surface is particularly desirable for optical sensors that are based on TiO2 interference films, because it enables well-defined Fabry-Pérot fringes. The effects of cold work treatment of the Ti foil on the morphology of the subsequent etched TiO2 nanostructures are found reversible by the thermal annealing treatment of the Ti foil, suggesting that the growth of the anodic TiO2 nanotubes is possibly affected by the grain size, defect density, and/or residual strain of the Ti foil (because cold work tends to increase the density of imperfections, reduce the grain size, and induce residual strain, whereas thermal annealing promotes recovery and recrystallization reversing the impact of cold work).
6:00 PM - GG5.17
Mesoporous Nanostructured Nb-doped Titanium Dioxide Microspheres as Catalyst Supports for PEM Fuel Cell Electrodes.
Laure Chevallier 1 , Alexander Bauer 2 , Rob Hui 2 , Jacques Roziere 1 , Deborah Jones 1
1 ICGM-Aggregates, Interfaces and Materials for Energy,, CNRS Montpellier, Montpellier France, 2 National Research Council of Canada, Institute for Fuel Cell Innovation, Vancouver, British Columbia, Canada
Show AbstractCrystalline microspheres of 5 at.% Nb-TiO2 (anatase form) with a high specific surface area have been synthesized using a templating method using ionic interactions between the nascent inorganic structure and polyelectrolyte template. A core-shell arrangement is obtained, with a meso-macroporous core structure, and a mesoporous shell. The material has been investigated as catalyst support for polymer electrolyte membrane fuel cells. A uniform dispersion of Pt particles on the Nb-doped TiO2 support was obtained using a microwave method. The electrochemical properties of Pt deposited on TiO2 based microspheres were compared with those of commercial carbon supported Pt. Nb-TiO2 supported Pt shows promising electrochemical properties, comparable to those of Pt/C. Furthermore, Nb-TiO2 supported Pt demonstrated very high stability after 1000 voltammetric cycles, since 85% of the electroactive Pt area remained after the stability testing, while only 47% of the electroactive Pt area remained in the case of Pt supported on carbon. For the oxygen reduction reaction, the highest stability was again obtained for the Nb doped TiO2 based material even though the mass activity calculated at 0.9 V vs. RHE was slightly lower. The microsphere structured and mesoporous Nb-doped TiO2 is an appealing alternative to carbon support for high temperature PEM fuel cells.
6:00 PM - GG5.18
Surface Modification of Titanium Alloy Surfaces to Enhance Osteoblast Cells Growth.
Domenico Regonini 1 , Yu Hsu 2 , Chris Bowen 1 , Irene Turner 2
1 Materials Research Centre, Mechanical Engineering, University of Bath, Bath United Kingdom, 2 Centre for Orthopaedic Biomechanics, Mechanical Engineering, University of Bath, Bath United Kingdom
Show AbstractIn this work we present our study on the surface modification of Ti alloy in order to enhance the proliferation and maturation of osteoblast type cells. In particular, two different techniques, anodisation and Micro-Arc Oxidation (MAO) are explored to generate either a nano-tubular or porous layer of TiO2 on the alloy. The materials are comprehensively characterised by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. This allows us to establish the optimal structure (tubes vs pores) as well as the crystallographic structure (amorphous or crystalline) to be used for the growth of the osteoblasts. In vitro cell culture studies to investigate the attachment of the cells on the modified surfaces are presented. Finally their behaviour when exposed to a simulated body fluid (SBF) at a different pH levels at body temperature is also discussed as localised pH changes are relevant in the postoperative wound healing situation.
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Biosensor Applications of Functionalized Singular TiO2 Nanotube Device.
Mingun Lee 1 , Jie Huang 1 , Antonio Lucero 1 , Moon J. Kim 1 , Hyunjung Shin 2 , Kook-Nyung Lee 3 , Jiyoung Kim 1
1 MSEN, University of Texas at Dallas, Richardson, Texas, United States, 2 , Kookmin University, Seoul Korea (the Republic of), 3 , KETI, Seongnam Korea (the Republic of)
Show AbstractTitanium dioxide nanotubes are an excellent candidate for high sensitivity chemical sensor application because of their large surface-area to volume ratio. Unlike other metal oxides such as ZnO and Al2O3, TiO2 exhibits minimal toxicity and good bio-compatibility, even at high concentrations. Therefore, TiO2 nanotubes are well suited to the biological sensor applications. In addition, electrical conductance of TiO2 nanotubes can be modulated by injecting chemical signals onto the surface.In this study, TiO2 nanotubes are fabricated by nanotemplate-assisted atomic layer deposition (ALD). ALD enables minimization of nanotube sidewall thickness, which improves nanotubes’ performance as a chemical sensor; thinner sidewalls lead to a larger difference between the areas of conductance and depletion regions, and thus higher conductance swing for better sensitivity. Focused ion beam deposition (FIB) was used for creating electrical connections to the nanotubes for characterization. We have evaluated TiO2 nanotube functionalization for material-type specific biochemical detection. To endow selectivity for streptavidin, the surface was treated with biotin or its derivative; selective binding between the chemical pair ensures excellent detection rate. Precise control over the nanotube sidewall thickness is critical in fine-tuning performance parameters of the resulting nanotube biosensors. Single stand-alone nanotube devices were selected rather than nanotube bundles for study, as the former has a brighter prospect in miniaturization and multichannel device applications.This research was supported by a grant (code #:2010K000351) from 'Center for Nanostructured Materials Technology' under '21st Century Frontier R&D Programs' of the MEST and International Semiconductor R&D program of COSAR-MKE, Korea.
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Nanostructured TiO2 Fibers Produced by Electrospinning.
Osnat Landau 1 , Eyal Zussman 2 , Il-Doo Kim 3 , Avner Rothschild 1
1 Materials engineering, Technion - Israel Institute of Technology, Haifa Israel, 2 Mechanical engineering, Technion - Israel Institute of Technology, Haifa Israel, 3 Center for Energy Materials Research, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractIn recent years, fabrication of novel 1D and quasi-1D nanostructured architectures has gained increased interest. Although a few other methods of fabrication such as phase separation and template synthesis are reported in the literature, electrospinning offers several advantages including ease of fabrication and versatility for producing ceramic nanofibers that can be exceptionally long in length, uniform in diameter, and diversified in composition. These nanostructured fibrillar morphologies produced by electrospinning show a bimodal pore size distribution with large voids (on the scale of sub-micron to micron) and small mesopores. This unique morphology is specially suited for gas sensing applications. The layer’s large voids facilitate fast gas transport in and out of the sensing layer and the small mesopores contribute to the high surface to volume ratio of these layers (surface area on the order of 100’s of m2/g), providing an elegant and effective solution to one of the greatest challenges in metal oxide gas sensors.Our current research in this area focuses on detailed investigation of the correlation between processing parameters and microstructure of electrospun TiO2 fibrillar morphologies to optimize the bimodal pore size distribution. In this paper we shall report on our progress in tailoring the morphology and pore size distribution by controlling the sol-gel chemistry, electrospinning conditions, and post-deposition thermo-compression and calcination processes.
6:00 PM - GG5.23
Growth Mechanism and Wetting Behavior of Polycrystalline TiO2 Thin Films Fabricated by Plasma Enhanced Chemical Vapor Deposition.
Ana Borras 1 , Agustin Gonzalez-Elipe 1
1 Materials Science Institute of Seville, CSIC-University of Seville, Seville Spain
Show AbstractThis work presents a thorough analysis on the growth of polycrystalline TiO2 thin films by plasma enhanced chemical vapor deposition (PECVD) and their wettability. First, the study of the microstructure and texture of the thin films at different stages of deposition by high resolution SEM, XRD, GAXRD and AFM demonstrates that their growth mechanism follows the Kolmogorov Model premises (i.e. a model developed to describe the crystal growth from a homogeneous phase). Moreover, the formation of crystal domains is shown as a characteristic feature of the growth by PECVD. The wettability (water contact angle and control of the contact angle by light irradiation) of polycrystalline anatase TiO2 thin films of different thickness was analyze within the Wenzel, Cassie and Miwa model assumptions to ascertain the effect of roughness and other surface heterogeneities on their characteristic parameters. The roughness factors defined in the different models were calculated from AFM images of the films at two different observation scales in the framework of the Dynamic Scaling Theories. The obtained results show that the wetting angle of an equivalent flat anatase surface with a value of 82° can only be properly estimated for observation scales of 5x5 µm and the Miwa model. Experiments of UV induced hydrophilization and posterior recuperation point out a clear dependence of the light induced wettability on the texture and crystal size of the anatase films.
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Synthesis and Photocatalytic Characteristics of Vertically-aligned Fe-doped TiO2 Nanobelts.
Hun Hoe Heo 1 , Nguyen Thi Quynh Hoa 1 , Lam Van Nang 1 , Zonghoon Lee 2 , Eui-Tae Kim 1
1 Departement of Materials Science & Engineering, Chungnam National University, Daejeon Korea (the Republic of), 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractOne-dimensional (1-D) TiO2 nanostructures such as nanowires, nanotubes, and nanobelts have been extensively studied for promising photocatalysis applications in elimination of pollutants and splitting of water for hydrogen fuel. In particular, the synthesis of well-ordered 1-D TiO2 nanostructures on a supporting substrate is of great interest. Unlike suspended photocatalysts, 1-D TiO2 nanostructures on a substrate can avoid the agglomeration problem and provide an easy recovery process for photocatalyst, including colleting them after use. Another important aspect is the modification of TiO2 by doping to realize photocatalytic reactivity under visible light. The wide bandgap energy (~3 eV) of TiO2 limits its photocatalytic reactivity to ultraviolet light. In order to extend the photocatalytic reactivity to visible light regime, transition metals or nonmetals such as carbon and nitrogen should be doped into TiO2. Most doping studies on 1-D TiO2 nanostructures have been focused on a post-doping process such as ion implantation and annealing with CO gas. In this study, we report the metallorganic chemical vapor deposition (MOCVD) synthesis of vertically-aligned Fe-doped TiO2 (Fe:TiO2) nanobelts on a Si substrate, in which Fe can be successfully in-situ doped. The dopant selection can be numerous because of the chemical flexibility of MOCVD. The Fe:TiO2 nanobelts showed high-efficient visible-light photocatalytic activity, which was evaluated by the decomposition of methylene blue under visible light irradiation. We will further discuss the photocatalytic characteristics and growth mechanism of vertically-aligned Fe:TiO2 nanobelts.
6:00 PM - GG5.25
Role of Nano-links between TiO2 Hollow Hemispheres in the Enhancement of Gas Sensing Properties of Embossed TiO2 Films.
Hi Gyu Moon 1 2 , Dong Su 3 , Hyung-Ho Park 2 , Seok-Jin Yoon 1 , Ho Won Jang 1
1 Electronic Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of), 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractTiO2 is a promising material for gas sensors. To achieve high sensitivities, the material should exhibit a large surface-to-volume ratio and possess the high accessibility of the gas molecules to the surface. Accordingly, a wide variety of porous TiO2 nanomaterials synthesized by wet-chemical methods have been reported for gas sensor applications. Nonetheless, achieving the large-area uniformity and comparability with well-established semiconductor production processes of the methods is still challenging. An alternative method is soft-templating which utilizes nanostructured inorganic or organic materials as sacrificial templates for the preparation of porous materials. Fabrication of macroporous TiO2 films and hollow TiO2 tubes by soft–templating and their gas sensing applications have been reported recently. In these porous materials composed of assemblies of individual micro/nanostructures, the form of links or necks between individual micro/nanostructures is a critical factor to determine gas sensing properties of the material. However, a systematic study to clarify the role of links between individual micro/nanostructures in gas sensing properties of a porous metal oxide matrix is thoroughly lacking. In this work, we have demonstrated a fabrication method to prepare highly-ordered, embossed TiO2 films composed of anatase TiO2 hollow hemispheres via soft-templating using polystyrene beads. The form of links between hollow hemispheres could be controlled by O2 plasma etching on the bead templates. This approach reveals the strong correlation of gas sensitivity with the form of the links. Our experimental results highlight that not only the surface-to-volume ratio of an ensemble material composed of individual micro/nanostructures but also the links between individual micro/nanostructures play a critical role in evaluating the sensing properties of the material. In addition to this general finding, the facileness, large-scale productivity, and compatability with semiconductor production process of the proposed fabrication method promise applications of the embossed TiO2 films to high-quality sensors.
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Supersonic Plasma Jet Deposition of Titanium Dioxide Nanomaterials.
Fabio Di Fonzo 1 , Francesco Fumagalli 2 , Moreno Piselli 2 , Dario Tassetti 2 , Carlo Bottani 1 3 , Claudia Riccardi 2
1 , Center for Nano Science and Technology-IIT@POLIMI, Milano Italy, 2 Department of Physics, Università degli Studi di Milano Bicocca, Milano Italy, 3 Department of Energy, NEMAS, Politecnico di Milano, Milano Italy
Show AbstractWe present a novel plasma based deposition technique for the large scale, large area deposition of titanium dioxide nanomaterials with controlled chemistry, morphology and porosity from metallorganic precursors. The novelty of the proposed approach is the segmentation of the gas phase material synthesis in two separate steps: chemistry control in a reactive non-thermal plasma environment; nucleation and self-assembling control by means of a supersonic inseminated jet over a substrate. Flow-dynamic isolation, by means of a supersonic expansion, allows separate optimization of the dissociation and reaction phase towards the formation of the radicals needed for precursor dissociation. Successively, cluster nucleation and aggregation occurs in the supersonic plasma jet expanding from the plasma into a high vacuum chamber. Furthermore, the use of a supersonic jet maintains beam focalization and reduces time of flight, allowing a better control in the cluster sizes and then in the structure of the thin film. More in detail, since the supersonic plasma jet plume is limited by a shock wave zone (the Mach disk, beyond which the speed decreases abruptly) it is possible to intercept species with different sizes and energies by changing nozzle to substrate distance: clusters of few atoms with high kinetic energy are collected at small distances, while more massive nanoparticles with low kinetic energy appears increasing the distance. This reflects on the material growth mechanism: compact films with minimal roughness appears minimizing the nozzle-substrate distance; porous and nanostructured materials form at larger distances. Furthermore, a supersonic beam allows to obtain clusters of nanoparticles, with a small dispersion of sizes. By a proper choice of deposition conditions it is possible to tune grain size and morphology to a large extent and even to obtain hierarchical nanostructures and graded films. In order to achieve a complete understanding of the as produced nanostructured TiO2 films, a thorough material and process characterization has been performed by means of Electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), UV-vis, X-ray Photoelectron spectroscopy (XPS) analysis and atomic force microscopy (AFM), Optical Emission Spectroscopy (OES), mass spectroscopy (MS) in the plasma state and in particular in the plasma plume expanding in vacuum. We point out that such a plasma-source configuration is readily extensible to a linear or even to a two dimensional lay-out compatible with large scale, large area deposition of Titanium Dioxide Nanomaterials for applications, for example, in photocatalysis and Dye Sensitized Solar Cells.
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Low Temperature Synthesis of Oriented {001} Anatase Films.
Andrew Ichimura 1 , Shirin Usmani 1 , Diana Marx 1
1 Chemistry & Biochemistry, San Francisco State University, San Francisco, California, United States
Show AbstractTitanium dioxide finds extensive use in applications that range from coatings and pigments to oxidative photocatalysis and dye-sensitized solar cells (DSSC). In these and other applications, the properties depend on the material phase (anatase or rutile), particle size and morphology, and surface chemistry. For example, because of the high surface area, nanoparticle anatase is commonly used for photocatalysis and DSSC. Both computational and experimental work suggest that the {001} surface of anatase is the most reactive.1,2 A synthetic route to powders with dominant {001} surface area up to 47% was reported.2 The key synthetic ingredient is fluoride, which binds to anatase lowering the overall surface energy, but selectively stabilizes the {001} relative to {101} facets. In this work, we report a route to polycrystalline anatase films with a dominant {001} texture.Our initial efforts tested ITO, glass, and gold films as potential substrates. A gold film (200 nm) that was evaporated and annealed on freshly cleaved 1” mica wafers yielded the largest uniform areas. Anatase was prepared by hydrothermal synthesis from TiF4 and NH4F homogeneous solutions and film growth was studied as a function of temperature, time, and reagent concentration. At all temperatures from 90-180oC, continuous single phase anatase films grew from the gold surface to a thickness between 200 nm (30 min.) and 600 nm (18 hrs). Over the range of conditions studied, the crystals that cover the surface of the polycrystalline film are approximately square in shape and arrayed ~parallel to the substrate. On the basis of the crystal morphology, grazing angle x-ray diffraction (GA-XRD), and electron backscatter diffraction (EBSD) experiments, the exposed surfaces are {001} facets. Thicker films show trapezoidal {101} facets at edges. GA-XRD measurements confirm the dominant c-axis orientation of the films in that peaks without a c-axis component, e.g., (200), (220), etc., are weak or absent. The advantage of our hydrothermal synthesis method is that resultant films are highly ordered polycrystalline arrays in which monolithic crystals span the film from substrate to external surface. Such films may facilitate charge transport across the layer. Thin films of oriented reactive crystals could serve as models for surface studies and may find applications as photocatalysts and as components of solar cells. Our synthetic strategy for preparing anatase films with tunable thickness and crystal morphology, and the results of various physical measurements (GA-XRD, EBSD, EM, EPR) will be described.1. Gong, X.Q.; Selloni, A. J. Phys. Chem. B, 2005, 109, 19560-19562.2. Yang, Y.G.; Sun, C.H.; Qiao, S.Z.; Zou, J.; Liu, G.; Smith, S.C.; Cheng, H.M.; Lu, G.Q. Nature 2008, 453, 638-642.
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Effect on Nucleation and Growth Kinetics of TiO2 Films Radio-frequency Sputtered in Ar/oxygen Atmosphere.
Monika Rathi 1 , Pavel Dutta 2 , Phil Ahrenkiel 1 , Venkateswara Bommisetty 2
1 , South Dakota School of Mines and Technology, Rapid City, South Dakota, United States, 2 , South Dakota State University, Brookings, South Dakota, United States
Show AbstractAmorphous TiO2 thin films were prepared by radio-frequency sputtering from a TiO2 target in only Ar and mixed Ar/oxygen atmosphere at room temperature on molybdenum transmission electron microscope (TEM) grids. TiO2 deposited grids were observed under TEM during in situ annealing in a TEM heating stage. Electron diffraction reveals that the TiO2 thin films are of anatase crystallographic phase. TiO2 deposited only in Ar atmosphere crystallized at 300 oC whereas TiO2 deposited in 5 % oxygen: 95 % Ar atmosphere crystallized at a much higher temperature 450 oC. This enhancement of crystallization temperature might be attributed to oxygen vacancy filling leading to a reduction of defect states in mixed Ar/O2 plasma deposited TiO2. Further, the effect of oxygen vacancy filling on the nucleation and growth kinetics was studied by monitoring the evolution of grain size and grain boundaries of TiO2 thin films. Measurement of crystalline volume fraction and grain number density was done using two dimensional TEM images obtained during the annealing process. Local work function and charge transport measurement of the as deposited and annealed films will be conducted using Kelvin Probe Force Microscopy (KFM) and Conducting Atomic Force Microscopy (C-AFM) to gain further understanding of the effect of oxygen incorporation in TiO2.
6:00 PM - GG5.3
Influence of Post-annealing Temperature on the Properties of Ti-Doped In2O3 Transparent Conductive Anti-fogging Films by DC Ratio-frequency Sputtering.
Lei Li 1
1 , Jilin university, Changchun, Jilin, China
Show AbstractIn this paper, titanium doped indium oxide (TIO) thin films deposited on quartz glass substrates by DC sputtering were presented. Deal with different temperature of post-annealing to make samples to display different optical and electric properties. The effects of sputtering on the structural, morphologic, optical and electrical characteristics of TIO thin films were investigated by XRD, Hall measurements and optical transmission spectroscopy. The deposited films exhibited polycrystalline in the preferred (222) orientation, with higher mean grain size and lower resistivity 1.26 ×10-4Ωcm at the post-annealing temperature at 520 centigrade. The average optical transmittance of the films is over 90%, and the transmittance has only around 1.8% change with different post-annealing temperatures.
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Controlled Synthesis of Nanoparticles of TiO2 byPrecipitation in Aqueous Solution for the Control of the Properties.
Sophie Cassaignon 1 , Olivier Durupthy 1 , Jean-Pierre Jolivet 1
1 LCMCP, UPMC, Paris France
Show AbstractTitanium dioxide is largely used in technological applications as a white pigment for paints or cosmetics, as a support in catalysis and as a photocatalyst. It is also a common material for photovoltaic cells. As for many other solids, nanosized TiO2 particles are of a particular interest because of their specifically size-related properties. Hence, many works have focussed on the synthesis of titanium dioxide nanoparticles. The uses and performances of a material for a given application are however strongly influenced by the crystalline structure, the morphology and the size of the particles. In addition, particles with varying mean size and narrow size distribution can be needed to study the surface effects over an extended range of surface/volume ratio. For metal oxide particles, the precipitation or coprecipitation of cations in aqueous solutions is an easy and cheap synthesis route. Various techniques consist in limiting the space available for the particle growth by precipitating ions in microemulsions, vesicles, polymer solutions or gels. Complexing agents are also often used but they mostly act on the morphology of the particles. Such methods raise difficulties in getting out particles free from polymer, surfactant or ligands, the adsorption of such species mostly inducing surface effects strongly influencing the behavior of particles. Actually, a careful control of the conditions of precipitation in aqueous medium, especially nature of the precursors, acidity and temperature, allow to control the crystal structure, the size and the morphology of particles. This presentation is focused on the synthesis of TiO2 polymorphs (anatase, brookite and rutile) by hydrolysis of TiCl4 and/or TiCl3 in water and on the influence of the synthesis parameters on the nature of the particles obtained. In addition we will discuss on the effect of the structure and the morphology on the properties, in particular in the photovoltaic devices and in lithium batteries.
6:00 PM - GG5.4
Lithium Ion Intercalation Performance of Polymorphs Chrysanthemum-like C/TiO2.
Po-Chin Chen 1 , Min-Chiao Tsai 1 , Chi-Young Lee 1 2 , Hsin-Tien Chiu 3
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 Center for Nanotechnology, Materials Science, and Microsystems, National Tsing Hua University, Hsinchu Taiwan, 3 Department of Applied Chemistry, National Chiao Tung University, Hsinchu Taiwan
Show AbstractThe flake chrysanthemum-like TiO2 with TiO2-B and anatase phases can be obtained through hydrothermal method using acetic acid and tetrakis(isopropoxy) titanium (IV) (TTIP). Different TiO2-B/anatase ratio was controlled by different annealing conditions. In order to be used as an anode of lithium ion battery, the conductivity of TiO2 was improved via carbon coating. The anode of lithium ion battery made by carbon coated chrysanthemum-like TiO2 which was annealed under 500 °C for 4 hours shows high capacity, good cycle performance and high rate charge/discharge ability. The capacity of lithium intercalation into chrysanthemum-like TiO2 with carbon coating at 0.1C charging rate reach 320 mAh/g and the reversible capacity (lithium extraction) is 252 mAh/g in the first cycle. After 100 cycles, the capacity to extract lithium still remains 141 mAh/g. For high charging rate (1C), the capacity of lithium insertion reach 250 mAh/g and the reversible capacity is 209 mAh/g in the first cycle. After 100 cycles, the capacity of extract lithium maintain at 122 mAh/g. These results indicate that although the as-prepared product was annealed under 500 °C for 4 hours, the TiO2-B phase didn’t convert to anatase entirely. This phenomenon may be a reason to explain the good cyclability of the chrysanthemum-like TiO2 with carbon coating at high charge/discharge rate. In conclusions, the chrysanthemum-like TiO2 with carbon coating is promising as a negative electrode material in lithium ion battery with high capacity, good cyclability and high rate capability.
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The Visible Light Photocatalytic Performance of Rutile TiO2 Nanorods Assisted by H2O2.
Min-Han Yang 1 , Tsung-Ying Ke 1 , Chi-Young Lee 1 2 , Hsin-Tien Chiu 3
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 Center for Nanotechnology, Materials Science, and Microsystems, National Tsing Hua University, Hsinchu Taiwan, 3 Department of Applied Chemistry, National Chiao Tung University, Hsinchu Taiwan
Show AbstractOne dimensional single crystalline rutile TiO2 was synthesized by hydrothermo method using titanate as precursors in acid solution. The morphology of rutile TiO2 nanorods could be adjusted through the concentration of hydrochloric acid. As concentrated HCl was used, thin TiO2 nanorods with large surface area were obtained, whereas thick rutile rods were obtained in dilute HCl solution. The degradation of methyl orange in hydrogen peroxide solution by rutile TiO2 and commercial P25 was examined under AM 1.5 solar simulator. The results showed that the performance was intensely enhanced by the H2O2 addition and reaction rate increased with surface area. The reaction kinetic tended to be a zero-order reaction. Compared with commercial P25, the reaction rate coefficient of rutile TiO2/H2O2 system is 2.6 times larger than that of P25/H2O2. According the results, the photocatalytic performance of rutile TiO2 with the assistance of H2O2 was dramatically promoted in visible light illumination. It makes the degradation of organic pollutants by solar energy more possible.
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First-principles Study of Oxygen Deficiency in Rutile Titanium Dioxide.
Hsin-Yi Lee 1 , Stewart Clark 2 , John Robertson 1
1 Engineering, University of Cambridge, Cambridge United Kingdom, 2 Physics, University of Durham, Durham United Kingdom
Show AbstractThe energy levels of the different charge states of oxygen vacancy and the titanium interstitial in rutile TiO2 were calculated using the screened exchange (sX) hybrid functional. The screened exchange method [1] mixes a Thomas-Fermi screened Hartree-Fock exchange into the local-density approximation (LDA) to correct the band gap error of LDA or GGA. Using the screened exchange method, we got 3.1 eV for the band gap of rutile TiO2, which is close to the experimental value (3.1 eV). The oxygen vacancy and titanium interstitial both create defect states inside the energy gap. We have studied the defect formation energy about the oxygen deficient structure. It is found that the defect formation energies, for the neutral charge state, of oxygen vacancy and titanium interstitial are quite similar, 2.40 eV and 2.45 eV respectively, for an oxygen chemical potential of the O-poor condition. The similar size of these two calculated energies indicates that both are a cause of oxygen deficiency, as observed experimentally [2]. The transition energy of oxygen vacancy lies within the band gap, corresponds to the electrons trapped at adjacent titanium sites. The screened exchange method gives a correct description of the localization of defect charge densities, which is not the case for GGA [3-5]. The singly positive oxygen vacancy has an unpaired electron which is localized around the two titanium atoms close to the oxygen vacancy site, not all three titaniums.1. S J Clark, J Robertson, Phys Rev B 82 085208 (2010)2 S Wendt et al, Science 320 1755 (2008)3 B J Morgan, G W Watson, Surface Sci 601 5034 (2007); Phys Rev B 80 233102 (2009)4 C DiValentin, G Pacchioni, A Selloni, J Phys Chem C 113 20543 (2009)5 S Lany, A Zunger, Phys Rev B 80 085202 (2009)
6:00 PM - GG5.8
Growth of (101) Oriented TiO2 Thin Films on F Doped SnO2 by RF Magnetron Sputtering.
Naresh Bhende 1 , Mamidanna Sri Ramachandra Rao 1
1 Department of Physics, Nano Functional Materials Technology Centre and Materials Science Research Centre, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show AbstractTiO2 exists in three different polymorphs such as anatase, rutile and brookite [1]. Anatase and rutile crystallize in tetragonal structure whereas brookite is orthorhombic [1]. Anatase phase is stable at low temperatures (up to 600 OC) and rutile structure is stable at high temperatures (700 - 800 OC). TiO2 has its applications in photo-catalysis, sensors and dye sensitized solar cells [1, 2]. Anatase TiO2 is preferred in dye sensitized solar cells due to higher (0.2 eV) Fermi energy level compared to rutile TiO2 [3]. The oriented TiO2 thin films have potential applications in dye-sensitized solar cells (DSSCs) and photocatalysis [4]. The adsorption of dye molecules on (101) oriented TiO2 is 4 times compared to P-25 [4].TiO2 thin films were deposited on fluorine doped SnO2 conducting glass substrate at 200 OC and 340 OC for 3 h using rf magnetron sputtering. The deposition of TiO2 thin films were carried out at 0.03 mbar of Ar atmospheric pressure and at a radio frequency power of 200 W. As grown thin films were amorphous in nature while the deposited thin films were then post annealed in air and oxygen atmosphere at 500 OC for 2 h which resulted in crystalline anatase phase with (101) orientation. The structural characterization of TiO2 thin films was carried out by X-ray diffraction (XRD) and Raman spectroscopy. Morphology and optical properties of thin films were studied using Atomic Force Microscopy (AFM) and UV-Visible spectroscopy. The thin films exhibited all the characteristic vibration modes (Ag +2Bg+3Eg) of TiO2 in Raman spectra. The transmittance of the 200 OC substrate temperature deposited TiO2 thin films are higher compared to those deposited at 340 OC. The thin films annealed in oxygen atmosphere showed lower transmittance when the substrate temperature is 200 OC compared to that of annealed thin films at 340 OC. From the transmission spectra of the thin films, band gap of TiO2 thin films was estimated. These results will be discussed in detail.References:[1]. Gratzel, M.; Curr. Opin. Colloid Interface Sci., 314, (1999)[2]. Matthews R.W., Journal of Catalysis, 111, 264 (1988)[3]. Huang S. Y., Kavan L., Exnar I., and Gratzel M., J. Electrochem. Soc. 142, L142 (1995)[4]. Motonari Adachi, Yusuke Murata, Jun Takao, Jinting Jiu, Masaru Sakamoto, and Fumin Wang, J. Am. Chem. Soc., 126 (45), 14943 (2004)
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Anion Effects on Conduction Band Edge and Charge Transfer Kinetics in Dye-Sensitized Ionic Liquid Solar Cells.
Min Zhang 1 , Peng Wang 1
1 , Changchun Institute of Applied Chemistry (CIAC),Chinese Academy of Sciences (CAS), Changchun, Jilin, China
Show AbstractThe restricted storage of fossil fuels on the earth and environmental problems concomitant with their usage are presently putting forward the search of alternative clean renewable energy as an imperative issue for the boom of future global economy. Over the past years, more and more but still a minority of solar power has been exploited to supply a sustainable and clean electricity based upon the well-established silicon technology, despite that the price/performance ratio remains a big challenge. In the pursuit of more affordable fashions for the conversion of solar to electric power, the dye-sensitized solar cell technology has received an ever-increasing amount of scientific and industrial attention in the foregone two decades, owing to its feasibility to serve as a low-cost candidate in appeasing the future planetary energy demand. At the moment, one big challenge toward its large-scale application relies on how to realize a sensible efficiency for cells without the use of volatile solvents, which brings a serious encapsulation issue. Herein we report evident effects of the dicyanamide anion versus tetracyanoborate on the energetics of titania conduction band edge and the kinetics of multi-channel charge-transfer reactions in ionic liquid solar cells employing a high-absorption coefficient ruthenium sensitizer C106. The tetracyanoborate electrolyte confers a relatively shorter photoluminescence lifetime on the dye C106 anchored on titania nanocrystals. However, a higher charge separation yield at the titania/dye/electrolyte interface is counterintuitively determined for the tetracyanoborate case, mainly benefited from an almost 3-fold faster electron injection as revealed by transient emission measurements, which is in good agreement with an almost indistinguishable ratio of external quantum efficiency enhancement in the whole spectral response region. Compared to tetracyanoborate, the presence of dicyanamide at the titania/electrolyte interface evokes a 27-fold slower charge recombination with triiodide, accounting for the open-circuit photovoltage variation observed in current-voltage measurements.
Symposium Organizers
Xiaobo Chen Lawrence Berkeley National Laboratory
Michael Graetzel Ecole Polytechnique Federale de Lausanne
Can Li Chinese Academy of Sciences
P.Davide Cozzoli Universita del Salento - Facolta di Ingneria Industriale
and Nanoscience Institute of CNR -
National Nanotechnology Laboratory
GG10: Poster Session II
Session Chairs
Wednesday PM, April 27, 2011
Salons 7-9 (Marriott)
1:00 AM - GG10: Poster
GG10.34 Transferred to GG11.5
Show AbstractGG6: Synthesis Nanotube
Session Chairs
Thomas Bein
P. Davide Cozzoli
Wednesday PM, April 27, 2011
Room 3020 (Moscone West)
9:30 AM - GG6.1
Synthesis of Highly-ordered, Debris-free TiO2 Nanotube Arrays in Ionic Liquid Electrolytes.
Huaqing Li 1 2 , Jun Qu 1 , Hanbing Xu 1 , Huimin Luo 3 , Sheng Dai 4 , Ilia Ivanov 5 , Harry Meyer 1 , Miaofang Chi 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics, University of Tennessee, Knoxville, Tennessee, United States, 3 Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractSelf-aligned TiO2 nanotube arrays have great potential in energy harvesting and storage applications due to their larger surface area, chemical stability, and the ability to provide an excellent electron percolation pathway. The most common synthesis method is anodization of titanium metal in aqueous or organic polarized electrolytes containing fluoride species. However, anodization-produced TiO2 nanotubes (NTs) are usually covered by a nanoporous debris layer. This debris layer causes a longer charge transport time, reduced transmittance, and limited NT accessibility, which deteriorates the performance of the tubes. In this study, we have successfully synthesized debris-free TiO2 NT arrays using a new group of ionic liquids (ILs) based electrolytes. This lack of debris layer formation is attributed to the high ionic conductivity leading to a high chemical dissolution rate that prevents the accumulation of etched oxides and electrolyte decomposition products on the top of the NTs. The NTs’ size, morphology, and growth rate were found to be directly related to the dissolution rate of the electrolyte, which can be tailored by adjusting the ratio of ILs, water, and inactive organic compounds. Another potential advantage of using IL electrolytes is the possibility of inherent doping. X-ray photoelectron spectroscopy (XPS) examination has revealed evidence of boron and fluorine doping in TiO2 NTs grown in an IL with tetrafluoroborate (BF4−) anions. Initial diffuse reflectance measurements suggested enhanced absorptance for visible and infrared light. Notice: This abstract has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes." Research sponsored by the U.S. Department of Energy, EERE Industrial Materials Program, under the American Recovery and Reinvestment Act. The characterization work was partially supported by the ORNL SHaRE User Program and Center for Nanophase Materials Sciences of Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
9:45 AM - GG6.2
Preparation of TiO2 Nanotubular and Nanoporous Arrays by Electrochemical Anodization on Metallic, Transparent, Ceramic and Flexible Substrates.
Guido Faglia 1 2 , Vardan Galstyan 1 2 , Alberto Vomiero 2 1 , Elisabetta Comini 1 2 , Giorgio Sberveglieri 1 2
1 Chemistry and Physics for Materials, University of Brescia, Brescia Italy, 2 , CNR IDASC, Brescia Italy
Show AbstractAnodization of titanium in hydrofluoric acid (HF) containing electrolytes produces nanotube arrays whose length is currently limited up to 500 nm, due to the high chemical dissolution rate of the anodized TiO2 layer. Moreover, when nanoporous or nanotubular structures are prepared starting from a thin layer of titanium, the presence of highly aggressive HF in the electrolyte prevents the use of plastic substrates.We demonstrated that discrete and well-aligned TiO2 nanotubular and nanoporous structures can be obtained over indium tin oxide (ITO)-coated polyethylene terephthalate (PET) (from Sigma-Aldrich) flexible substrates, by electrochemical anodization of thin films of Ti in neutral glycerol based electrolytes. Nanoporous arrays were produced by galvanostatic mod and nanotubular arrays by potentiostatic mod. TiO2 nanotubes prepared at room temperature on ITO-PET in 0.5 wt.% NH4F, 2 mol L-1 H2O in glycerol by anodization voltages 25, 35, 50 and 70 V present a very homogeneous size distribution of tubes, which average inner diameter is approximately 30, 55, 70 and 80 nm, respectively. Beside in glycerol based electrolytes fluorine ions mobility is quenched and the chemical dissolution of the oxidized TiO2 is essentially suppressed in comparison with acidic aqueous solution, enhancing formation of longer -up to a few microns- nanotubes at the expense of lengthy anodization times (up to 140min). The tubes are closed at the bottom, as it is typical for anodization process, and exhibit a closely packed hexagonal geometry on a short range scale. The nanotubes surface is very clean, and is obtained without the need of any post-growth treatment other than mild bath in ethanol, while composition is consistent with Ti:O=1:2 atomic ratio within the uncertainty of SEM-related EDX measurement. Full oxidation of Ti film cannot be achieved, a residual metal layer (100 – 200 nm thick) still remains even for prolonged treatments.Furthermore the same structures were obtained on other substrates like alumina, glass covered SnO2:F and titanium sheets. By tailoring the anodization parameters identical nanotubular arrays were obtained irrespective of the substrate. As an additional feature, on rough surfaces (alumina) the tubes develop as clusters on each grain, producing structures tailored for applications where high specific areas are required, like catalysis and gas sensing, The functional properties of the obtained TiO2 nanotubular and nanoporous structures were benchmarked both as highly ordered photoanode architectures, offering longer electron diffusion lengths, for next generation excitonic solar cells and as high surface area chemical gas sensors. We acknowledge for funding ORAMA project FP-NMP-2009-LARGE-3 NMP-2009-2.2-1, Grant Agreement 246334: Oxide materials for electronics applications.
10:00 AM - GG6.4
Elaborate TiO2 Nanostructures Anodized from Mechanically Processed Ti Foils: Nanopores, Elliptical Nanotubes, Interweaving Nanotubes and Multilayers.
Lingxia Zheng 1 , Hui Li 1 2 , Yang Yang Li 1
1 Dept. of Physics and Materials Science, City Univ. of Hong Kong, Kowloon Hong Kong, 2 Dept. of Physics, University of Science and Technology of China, Hefei, Anhui, China
Show AbstractSelf-organized TiO2 nanotube arrays grown by anodic oxidation of a Ti substrate attracted broad scientific interest due to wide potential applications. Here we report that cold working of the Ti substrate before anodization can greatly affect the morphology of the formed anodic TiO2 nanostructures – e.g., one can specifically achieve nanotubes or nanopores simply by adjusting the amount of cold work. Moreover, various exotic TiO2 nanostructures, such as elliptical nanotubes, interweaving nanotubes and multilayers, have been enabled using the cold-worked Ti substrates.
10:15 AM - **GG6.5
Charge Separation and Collection in Dye-sensitized Mesoscopic TiO2 Solar Cells.
Qing Wang 1 , James Jennings 1 , Feng Li 1
1 Department of Materials Science and Engineering, Nanocore, National University of Singapore, Singapore Singapore
Show AbstractDye-sensitized solar cells (DSCs) using mesoscopic TiO2 as photoanode currently present a credible alternative to conventional solar cells. The validated overall solar to electric power conversion efficiency has now reached a value close to 12% under standard AM 1.5 illumination conditions. This talk will focus on our recent advances in the fundamental understanding of charge separation and charge collection — the two crucial, efficiency-determining processes, as relevant to DSCs. The predicted effect of sensitizer regeneration on the j-V characteristics of DSCs will be discussed and recent experimental results will be highlighted. Problems surrounding the experimental determination of electron diffusion length in dye-sensitized solar cells will be addressed, together with the physical interpretation of this quantity and its usefulness in predicting charge collection losses in working dye-sensitized solar cells. In addition, evolution of charge separation and charge collection upon prolonged aging test and their effects on the stability of DSCs will be discussed in a case study. It is anticipated that these results will help us to have a better understanding on the factors dictating the operation of DSCs for more efficient and more stable solar energy conversion.
GG7: Solar Cell/Photovoltaic
Session Chairs
Md. K. Nazeeruddin
Qing Wang
Wednesday PM, April 27, 2011
Room 3020 (Moscone West)
11:15 AM - GG7.1
Titanium Dioxide as Solution-processed Electron Transport Layer for Single and Tandem Organic Solar Cells.
Afshin Hadipour 1 , Barry Rand 1 , Paul Heremans 2
1 IMEC-PV-PMEPV-OPV, IMEC, Leuven Belgium, 2 IMEC-TU-SSET-LAE, IMEC, Leuven Belgium
Show AbstractThis work presents a solution-processed electron transport layer (ETL) processed from a