Robert L. Opila, University of Delaware
Federico Rosei, INRS
Peter Sheldon, National Renewable Energy Laboratory
Symposium Support Elsevier
RBD Instruments, Inc.
GG2: Water Splitting
Monday PM, December 02, 2013
Hynes, Level 3, Room 312
2:30 AM - *GG2.01
Design of Catalysts and Electrocatalysts for Energy Applications
Jingguang G. Chen 1
1Columbia University New York USAShow Abstract
In the current talk we will use two examples to demonstrate the importance of using surface science studies to identify catalysts and electrocatalysts. Our research approaches involve parallel efforts in density functional theory (DFT) calculations, surface science experiments on model systems, and synthesis and evaluation of supported catalysts under thermochemical or electrochemical conditions. We will first use water electrolysis to demonstrate the feasibility of using monolayer Pt on tungsten carbide (WC) to achieve the same activity as bulk Pt. We will present DFT calculations of similar electronic and chemical properties between monolayer Pt/WC and Pt, synthesis and characterization of monolayer Pt/WC films, and electrochemical evaluation of the activity and stability of Pt/WC for water electrolysis. Comparing to the leading Pt electrocatalyst, the monolayer Pt/WC represents a reduction by a factor of ten in Pt loading [1,2].
We will then use the conversion of biomass-derived oxygenates to illustrate the advantages of using bimetallic catalysts. Bimetallic catalysts often show unique activity and selectivity over their parent metals due to the electronic modification and strain effect [3,4]. We will present our results on the characterization of Ni/Pt bimetallic surfaces and catalysts under in-situ reaction conditions, further highlighting the importance of using the combined approaches of DFT calculations, surface science experiments, and reactor evaluations [5,6].
 D.V. Esposito, S.T. Hunt, K.D. Dobson, B.E. McCandless, R.W. Birkmire and J.G. Chen, “Low-Cost
Hydrogen Evolution Catalysts Based on Monolayer Platinum on Tungsten Monocarbide Substrates”, AngewandteChemie International Edition, 49 (2010) 9859-9862
 D.V. Esposito, S.T. Hunt, Y.C. Kimmel and J.G. Chen, “A New Class of Electrocatalysts for Hydrogen Production from Water Electrolysis: Metal Monolayers Supported on Low-Cost Transition Metal Carbides”, Journal of the American Chemical Society, 134 (2012) 3025-3033.  W. Yu, M.D. Porosoff and J.G. Chen, “Pt-based Bimetallic Catalysis: From Model Surfaces to
Supported Catalysts”, Chemical Reviews, (2012) DOI: 10.1021/cr300096b.
 D.A. Hansgen, D.G. Vlachos and J.G. Chen, “Using First Principles to Predict Bimetallic Catalysts
for the Ammonia Decomposition Reaction”, Nature Chemistry, 2 (2010) 484-489.
 M. Salciccioli, W. Yu, M.A. Barteau, J.G. Chen, D.G. Vlachos, “Differentiation of O-H and C-H
Bond Scission Mechanisms of Ethylene Glycol on Pt and Ni/Pt Using Theory and Isotopic Labeling Experiments”, Journal of the American Chemical Society, 133 (2011) 7996-8004.
 W. Yu, M.A. Barteau and J.G. Chen, “Glycolaldehyde as a Probe Molecule for Biomass-derivatives:
Reaction of C-OH and C=O Functional Groups on Monolayer Ni Surfaces”, Journal of the American Chemical Society, 133 (2011) 20528-20535.
3:00 AM - GG2.02
In situ Transient Optical Spectroscopy of Photo-Excited Charge Carriers at the SrTiO3/Electrolyte Interface
Matthias M Waegele 1 Xihan Chen 1 David Herlihy 1 Tanja Cuk 1 2
1University of California Berkeley USA2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
While recent efforts to enhance photon-to-O2 conversion of photoanodes for water splitting have attracted much attention, linking the resulting apparent catalytic activities to the microscopic processes of electron-hole dynamics and interfacial hole transfer remains difficult. Herein, we investigate the kinetics of photo-excited carriers within the space charge layer of Nb-doped SrTiO3 anodes under working conditions by means of time-resolved optical spectroscopy. By probing the dependence of the dynamics on various variables, including electrochemical potential, electrolyte composition, and doping concentration, we are able to quantify the kinetics of electron-hole separation in the space charge layer, and monitor hole transfer across the SrTiO3/electrolyte interface. We discuss the relevance of our results in regards to the early steps in water oxidation at the SrTiO3 interface, as well as to the design of novel photoanodes.
3:15 AM - *GG2.03
Engineered Photoanodes for High Efficiency Dye- and Quantum Dot-Sensitized Solar Cells
Gurpreet Singh Selopal 3 1 K. Therese Dembele 2 Riccardo Milan 3 1 Isabella Concina 1 3 Giorgio Sberveglieri 3 1 Alberto Vomiero 1 2 3
1CNR SENSOR Lab Brescia Italy2INRS EMT Varennes Canada3University of Brescia Brescia ItalyShow Abstract
The typical photoanode in dye- and quantum dot- sensitized solar cells is composed of a wide band gap semiconductor, which acts as electron transporter for the photoelectrochemical system. Anatase TiO2 nanoparticles are one of the most used oxides and are able to deliver the highest photoconversion efficiency in this kind of solar cells, but intense research in the last years was also addressed to ZnO and other composite systems. Modulation of the composition and shape of nanostructured photoanodes is key element to tailor the physical chemical processes regulating charge dynamics and, ultimately, to boost the efficiency of the end user device, by favoring charge transport and collection, while reducing charge recombination.
We investigated several systems: (i) TiO2 nanoparticles / ZnO nanowires ; (ii) Multiwall carbon nanotubes (MWCNTs) / TiO2 nanoparticles ; (iii) TiO2 nanotubes [3-4]; (iv) Hierarchically self-assembled ZnO sub-microstructures . Both dye molecules and semiconducting quantum dots were applied as light harvesters. Possible tailoring of structure and morphology of the photoanodes, and their implication in improving the functional properties of these kinds of excitonic solar cells will be discussed.
 A. Vomiero, I. Concina, M.M. Natile, E. Comini, G. Faglia, M. Ferroni, I. Kholmanov, G. Sberveglieri, Applied Physics Letters 95 (2009) 193104.
 K.T. Dembele, R. Nechache, L. Nikolova, A. Vomiero, C. Santato, S. Licoccia, F. Rosei J. Power Sources 233 (2013) 93-97.
 A. Vomiero, V. Galstyan, A. Braga, I. Concina, M. Brisotto, E. Bontempi, G. Sberveglieri, Energy and Environmental Science 4 (2011) 3408-3413.
 V. Galstyan, A. Vomiero, I. Concina, A. Braga, M. Brisotto, E. Bontempi, G. Faglia, G. Sberveglieri, Small 7 (2011) 2437-2442.
 N. Memarian, I. Concina, A. Braga, S. M. Rozati, A. Vomiero, G. Sberveglieri, Angewandte Chemie In Ed 50 (2011) 12321-12325.
4:00 AM - *GG2.04
Hydrogen Production from Formic Acid: An Important Catalytic Reaction for Biomass Conversion
Manos Mavrikakis 1 James Dumesic 1 Jessica Scaranto 1 Suyash Singh 1 Ronald Carrasquillo 1 Brandon O'Neill 1 Sha Li 1 Luke Roling 1 Jeff Herron 1 Guowen Peng 1
1University of Wisconsin - Madison Madison USAShow Abstract
Formic acid (HCOOH) is a simple molecule that is an abundant product of biomass processing and can serve as an internal source of hydrogen for oxygen removal and upgrading of biomass to chemicals and fuels. In addition, HCOOH can be used as a fuel for low temperature direct fuel cells. We present a systematic study of the HCOOH decomposition reaction mechanism starting from first-principles and including reactivity experiments and microkinetic modeling. In particular, periodic self-consistent Density Functional Theory (DFT) calculations are performed to determine the stability of reactive intermediates and activation energy barriers of elementary steps. In addition, pre-exponential factors are determined from vibrational frequency calculations. Mean-field microkinetic models are developed and calculated reaction rates, orders, etc are then compared with experimentally measured ones. These comparisons provide useful insights on the nature of the active site, most-abundant surface intermediates as a function of reaction conditions and feed composition. Trends across metals on the fundamental atomic-scale level up to selectivity trends will be discussed. Finally, we identify from first-principles alloy surfaces, which may possess better catalytic properties for selective dehydrogenation of HCOOH than monometallic surfaces, thereby guiding synthesis towards promising novel catalytic materials.
4:30 AM - GG2.05
Study of Hydrogen Evolving Catalyst at the Light Absorber/Electrolyte Interface Using X-Ray Absorption Spectroscopy and Micro-Focused X-Ray Fluorescence
Eitan Anzenberg 1 Alexandra Krawicz 1 Gary F Moore 1 Junko Yano 1
1Lawrence Berkeley National Lab Berkeley USAShow Abstract
Studying and improving activity and stability of earth-abundant catalysts at the light absorber/electrolyte interface to drive hydrogen production reaction is an important challenge for solar fuel generation in artificial photosynthesis. We have used X-ray Absorption Spectroscopy (XAS) and micro-focused X-ray Fluorescence (MXRF) mapping at the Advanced Light Source (ALS) to characterize molecular surface-linked catalysts at the interface. The electronic and structural properties of the metal core or ligand were probed before, during, and after electro- and photoelectro-chemical (PEC) operation with ex- and in-situ detection techniques. Using Co K-edge XAS, we have shown that a Co(dmgH)2PrCl molecular catalyst remains electronically and structurally intact after attachment through the pyridine ligand to a polymer chain linked to a light absorbing surface . Using the Co fluorescence signal, we have also studied the stability of a cobaloxime-modified photocathode after rigorous PEC operation.
 Krawicz, Yang, Anzenberg, Yano, Sharp, Moore, Photofunctional Construct that Interfaces Molecular Cobalt-based Catalysts for H2 Production to a Visible-light Absorbing Semiconductor, Journal of the American Chemical Society, (submitted)
4:45 AM - GG2.06
Surface Structure-Activity Relationship in Ceria-Based Catalysts Studied by Surface X-Ray Diffraction on Atomically Flat Thin Films
Yezhou Shi 1 2 Chuntian Cao 1 Zhuoluo A. Feng 1 Michael F. Toney 2 William C. Chueh 1 2
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Ceria (CeO2) is one of the most active oxide electro-catalysts for hydrogen oxidation and water-splitting reactions at elevated temperatures. The surface concentration of oxygen vacancies and Ce3+ species were found to be significantly greater than the bulk, and can plausibly explain ceria&’s high electro-catalytic activity. Furthermore, the activities of ceria are expected to depend strongly on the surface termination, as already observed in nanostructured ceria with different facets. To better understand electrochemical reaction mechanisms and the structure-property relationship on the ceria surface, we investigated how the surface crystal structure of doped ceria differed from its bulk crystal. Specifically, we employed in-situ surface X-ray diffraction (SXRD) to study the atomic arrangements of (100)-and (111)-terminated ceria surfaces. We successfully fabricated atomically flat ceria films on yttria-stabilized zirconia substrates by pulsed laser deposition and confirmed that these films had well-defined step terraces using atomic force microscopy. We correlated the surface structure under both reducing and oxidizing atmosphere to the different catalytic activities of the (100)- and (111)-terminated films.
5:00 AM - GG2.07
Synthesis of Core-Shell Ferrite Nanoparticles for Thermochemical H2 Generation from Water-Splitting
Vinod Amar 1 Jan Puszynski 1 Rajesh V Shende 1
1South Dakota School of Mines amp; Technology Rapid City USAShow Abstract
Thermochemical water-splitting is a two-step process where in step-1, redox material is heated at higher temperature creating oxygen vacancies, whereas in step-2, this partially reduced material is exposed to steam leading to H2 generation by scavenging the oxygen. As these steps are performed at very high temperatures, materials experience grain growth. As a result, surface area and porosity decrease, which translate into lower H2 volume generation with increase in thermochemical water-splitting cycles. Therefore, there is a need to thermally stabilize the redox materials with the viewpoint of mitigating the grain growth and achieving steady H2 production. In this study, Ni-ferrite nanoparticles were synthesized using the sol-gel method and later these nanopartices were utilized to prepare porous core-shell nanoparticles with Y2O3 stablized ZrO2 (YSZ). The H2 generation ability of core-shell Ni-ferrite/YSZ nanoparticles was investigated by performing five consecutive thermochemical cycles in the Inconel packed-bed reactor where water-splitting and regeneration steps were carried out at 650o-1100oC. Specific surface area (SSA) and porosity of these materials were analyzed before and after the thermochemical water-splitting reaction using BET surface area analyzer. Additionally scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the grain growth. The results suggest grain growth mitigation in core-shell Ni-ferrite/YSZ nanoparticles that resulted in relatively steady H2 volume in multiple thermochemical water-splitting cycles. The H2 volume observed with core-shell ferrite nanoparticles was higher than ferrite nanoparticles. Characterization of core-shell nanoparticles and the results obtained on H2 volume generation with ferrite and core-shell ferrite nanoparticles will be presented.
5:15 AM - GG2.08
Hydrogen Storage in Orthorhombic Mg Hydride at Ultra-Low Temperature
Byoungsoo Ham 1 Anchalee Junkaew 1 Raymundo Arroyave 1 Haiyan Wang 2 Peng Wang 3 Jerek Majewski 3 Jinhee Park 4 Hongcai Zhou 4 Yang Ren 5 Xinghang Zhang 1
1Texas Aamp;M College Station USA2Texas Aamp;M College Station USA3Los Alamos National Laboratory Los Alamos USA4Texas Aamp;M College Station USA5Argonne National Laboratory Argonne USAShow Abstract
Mg can store up to ~7 wt.% hydrogen and is an appealing candidate as light weight and low cost hydrogen storage material. However hydrogen desorption in Mg hydride typically requires unfavorably high temperature of ~ 573 K due to its high thermodynamic stability, whereas the target operation temperature of fuel cells in automobiles is ~ 373 K or less. Furthermore the kinetics of H sorption in Mg is typically slow. Here we investigate hydrogen sorption behavior of Mg/Nb multilayers. Stress-induced orthorhombic Mg hydride (O-MgH2) is thermodynamically destabilized at ~ 373 K or lower. Such drastic destabilization arises from large tensile stress in single layer O-MgH2 bonded to rigid substrate, or compressive stress due to large volume change incompatibility in Mg/Nb multilayers. Ab inito calculations were performed to analyze the influence of interfaces on H sorption in Mg films. These studies provide insight on the mechanisms that may expedite the kinetics of H sorption in Mg.
5:30 AM - *GG2.09
Conjugated Porous Organic Polymers Possessing High Hydrogen Sorption Capacity
Baohang Han 1
1National Center for Nanoscience and Technology Beijing ChinaShow Abstract
Conjugated organic polymers, possessing intrinsic properties of large surface areas, high thermal and chemical stabilities, and low skeleton density, exhibit potential applications in gas storage and separation. Based on special spirocyclic or propeller-like monomers, various organic microporous polymers were prepared through a wide variety of C-C coupling reactions and further characterized at the molecular level by 13C CP/MAS NMR spectrum, as well as other techniques. All the obtained polymers are chemically stable. Thermal analysis shows that the materials are stable up to 350 °C under nitrogen. The fluorescent emission of the obtained conjugated polymers is tunable, ranging from 440 to 600 nm depending on the molecular structure of the monomer and coupling strategy. According to the obtained nitrogen physisorption isotherms, the Brunauer-Emmett-Teller (BET) specific surface area for these polymers varies between 700 and 2200 m<2> g<-1>. Adsorption isotherms show the polymers possess nice adsorption capacity to hydrogen and carbon dioxide, showing a good gas separation of carbon dioxide over methane.
GG3: Poster Session I
Robert L. Opila
Monday PM, December 02, 2013
Hynes, Level 1, Hall B
9:00 AM - GG3.01
High Efficiency and Enhanced Fill Factor of Solution Processed Small-Molecule Solar Cells with p-DTS(FBTTh2)2:PC71BM Bulk Heterojunction
Dong Hwan Wang 1 2 Aung Ko Ko Kyaw 1 Jong Hyeok Park 2 Alan J. Heeger 1
1University of California Santa Barbara Santa Barbara USA2Sungkyunkwan University Suwon Republic of KoreaShow Abstract
Bulk-heterojunction (BHJ) solar cells based on phase-separated blends of organic materials of donor and acceptor (fullerene derivative) have been in continuous development over the past two decades.(1)-(3) Recently, solution-processable small molecule-based BHJ solar cells exhibiting comparable power conversion efficiency (PCE) of near 7% to the polymers with high potential under simple and optimized processing conditions.(4)-(6) The small-molecule donors have attractive features, including relatively simple synthesis and purification steps, mono-dispersity, and improved batch-to-batch reproducibility.
Here, we demonstrated solution-processed small-molecule p-DTS(FBTTh2)2:PC71BM BHJ solar cells with a PCE over 8 %. The fill factor (FF) is sensitive to the thickness of a calcium buffer layer between the BHJ active film and the Al cathode; for 20 nm Ca thickness, the FF is 73%, the highest value reported for an organic solar cell. The maximum external quantum efficiency exceeds 80%. After correcting for the total absorption in the cell through the normal incidence reflectance measurements, the internal quantum efficiency approach 100% in the spectral range of 600 to 650 nm and well over 80% across the entire spectral range from 400 to 700 nm. Analysis of the current-voltage (J-V) characteristics at various light intensities provides information on the different recombination mechanisms in the BHJ solar cells with various thicknesses of the Ca layer. Also, we can fabricate improved efficiency of small-molecule solar cells with PCE of 8.24% with enhanced JSC and FF using a low sheet resistance of ITO (5 Omega;/square) substrate (ITO thickness of 450 nm) which exhibits transmittance of 90% at 550 nm. The increased JSC and FF originate from the reduced series resistance (Rs). In summary, the PCE and FF of small molecule based bulk-heterojunction solar cells can be increased by optimized thickness of Ca interlayer and low sheet resistance of ITO substrate.
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(3) G. Li, V. Shrotriya, J. Huang, Y. Yao, T. Moriarty, K. Emery, Y. Yang, Nat. Mater. 4 (2005) 864.
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(6) A. K. K. Kyaw, D. H. Wang, V. Gupta, J. Zhang, S. Chand, G. C. Bazan, A. J. Heeger, Adv. Mater. DOI: 10.1002/adma.201300295.
9:00 AM - GG3.02
Exfoliated Graphene-Supported Pt and Pt-Based Alloys as Electrocatalysts for Direct Methanol Fuel Cells
Wen Qian 1
1Portland State University Portland USAShow Abstract
To greatly improve the electrocatalytic activity for methanol oxidation, high-quality exfoliated graphene decorated with uniform Pt nanocrystals (NCs) (3 nm) have been prepared by a very simple, low-cost and environmentally benign process. During the entire process, no surfactant and no halide ions were involved, which not only enabled very clean surface of Pt/graphene leading to excellent conductivity, but also greatly improved the electrocatalyst tolerance to carbon monoxide poisoning (Pt/graphene, If/Ib= 1.197), compared to commercial Pt/C (If/Ib= 0.893) catalysts. To maximize the electrocatalytic performance and minimize the amount of precious Pt, Pt-M/graphene (M=Pd, Co) hybrids have also been prepared, and these hybrids have much larger electrochemically active surface areas (ECSA), which are 4 (PtPd/graphene) and 3.3 (PtCo/graphene) times as those of commercial Pt/C. The PtPd/graphene and PtCo/graphene hybrids also have remarkably increased activity toward methanol oxidation (If/Ib= 1.218 and 1.558). Furthermore, density functional theory (DFT) simulations demonstrate that an electronic interaction occurred between Pt atoms and graphene, indicating that graphene substrate plays a crucial role in regulating the electron structure of attached Pt atom, which confirmed that the increased efficiency of methanol oxidation was due to the synergetic effects of the hybrid structure.
9:00 AM - GG3.03
Large Impact of Molecular Orientation on Ionization Energy: Picene Film
Rintaro Makino 1 Keiichirou Yonezawa 1 Kengo Kato 1 Alexander Hinderhofer 1 Takuya Hosokai 2 Koji Okudaira 1 Nobuo Ueno 1 Satoshi Kera 1
1Chiba University Chiba Japan2Iwate University Morioka JapanShow Abstract
To improve the performance of organic photovoltaic cells, mechanisms of charge transfer/transport and charge separation have been widely investigated. These studies need acculate information on the electronic structure responsible to the processes. In general, however, it is not easy to reveal the electronic structure not only at metal-molecule interfaces but also of the molecular film itself due to large structural anisotropy of the molecule and their orientation in the film. Ionization energy (Ei) of the film depends on the molecular orientation, crystal structure and packing density . In this study, we investigated the electronic structure and the molecular orientation of picene (C22H14) films prepared on SiO2 and graphite (HOPG) substrates by using ultraviolet photomission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) .
Picene molecules were vacuum deposited step-by-step (upto ~10nm) on clean SiO2 and HOPG under UHV. The deposition rate was ~1.7 Å/min on the SiO2 and ~1.1 Å/min on the HOPG. All experiments were conducted at RT (293K).
We clarified using MAES from monolayer to multilayer that the molecules stand upright on the SiO2 (long axis of the molecule is normal to the surface), while they lie flat on the HOPG (short axis of the molecule is slightly tilted w.r.t. the surface). Normal-emission UPS spectra of the standing and lying films are largely different due to the orientation dependent photoelectron angular distribution and intermolecular interaction. The valence band features of the lying film correspond well to the density-of-states from DFT of an isolated molecule, while those of the standing film represent similarlity with the result of the single crystal .
We determined Ei for the HOMO onset and peak after peak fitting analyses of the HOMO features. The Ei of the standing film at the peak position (EiPEAK= 6.06eV) is smaller by 0.74eV than that of the lying film (EiPEAK = 6.80eV), giving the energy difference ΔEiPEAK = 0.74 eV (ΔEiONSET = 0.66 eV). These ΔEi are much greater than that of pentacene (ΔEiPEAK= 0.43eV ) as well as other pi-conjugated molecules (ΔEiPEAK = 0.40eV for DIP and 0.40eV for CuPc). Effects of electronic coupling at the picene/substrate interfaces on the UPS features can be neglected because of weak molecule-substrate interaction. We also suggest that for picene the molecular dipole and energy-band dispersion do not contribute much on ΔEi. Hence we can evaluate main origin of orientation dependent Ei by considering surface electrostatic potential produced by local dipoles (>C-H+) in picene. At the conference, we will report results of the electrostatic potential culculation and gas phase spectra of picene to discuss the orientation dependence of Ei.
 S. Duhm et al, Nature Mater. 7, 326 (2008).
 Y. Harada et al, Chem. Rev. 97, 1897 (1997).
 Q. Xin et al, Phys. Rev. Lett. 108, 226401 (2012).
 H. Fukagawa et al, Phys. Rev. B 73, 245310 (2006).
9:00 AM - GG3.04
Activation of the CO2 Molecule, A Theoretical Study
Shin Nakamura 1 Katsushi Fujii 2 Koji Ogata 1 Makoto Hatakeyama 1 Yuanqing Wang 1 Xu Zeng 3 Fangming Jin 3
1RIKEN Wako Japan2The Univ Tokyo Tokyo Japan3Jiao Tong University Shanghai ChinaShow Abstract
On the CO2 activation a theoretical study is presented. On the basis of the quantum chemical calculations, the order of magnitude in the activation is described. Taking as a reference of the CO2 molecule in dilute gas phase or in vacuum, the activated states in electronic structure (wave functions) as well as in geometrical changes are described by the degree of modifications relative to the reference state.
The DFT calculations are performed to visualize this degree of activation as a function of the environmental effect on CO2; gas phase, liquid phase (especially as a function of pH), and coordination on transition metals. Special attention is paid on the activation by abundant metals such as Zn. The experimental and theoretical examples of reactions of the activated CO2 are presented in hydrothermal condition with transition metal atoms.
9:00 AM - GG3.06
Engineering ZnO@SnO2 Multilayer Structures as Photoanodes for High Efficiency Photovoltaic Devices
Riccardo Milan 1 Gurpreet Singh Selopal 1 Mauro Epifani 2 Alberto Vomiero 1 Giorgio Sberveglieri 1 Guido Faglia 1 Isabella Concina 1
1University of Brescia amp; SENSOR Lab Brescia Italy2Consiglio Nazionale delle Ricerche Istituto per la Microelettronica ed i Microsistemi Lecce ItalyShow Abstract
Excitonic solar cells (XSCs) are appealing candidates as alternative devices for solar energy conversion, being in principle low cost, rather environmental friendly and suitable for exploiting also the near infrared (NIR) region of solar spectrum. 1
Nanoparticulate TiO2 is currently the most known and exploited semiconductor metal oxide (SMO) applied as photoanode in both dye- and quantum dot-sensitized solar cells (DSCs and QDSCs), but other SMOs, such as ZnO and SnO2, are attracting a broad interest, due to higher electron mobility and band structure suitable for NIR-absorbing light harvesters, respectively. 2,3,4
Strategies devoted to either completely inhibit or at least reduce recombination of photogenerated free charges, which is still one open issue in photoconverison efficiency, are still requested.
In this work, nano-SnO2, with different particles sizes (4 to 20 nm) and tunable amount of oxygen vacancies, was applied as main active layer in photoanodes for XSCs together with ZnO (as polidisperse nano- and micro-structures or hierarchical structures) in order to engineer the global band structures involved in charge injection.
A careful optimization of different parameters, such as relative layered composition of ZnO@SnO2 interfaces and dye loading time, allows demonstrating the highly beneficial role of ZnO as blocking layer towards the exciton recombination at SnO2-light harvester-electrolyte interfaces, thus reaching high functional performances in terms of injected photocurrent and photo conversion efficiency (JSC=14.78 mA/cm2 PCE=4.96%).
Strategies successful in optimizing the functional performances of XCSs (both DSCs and QDSCs) through material interface engineering will be presented and discussed.
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3 N. Memarian, I. Concina, A. Braga, SM Rozati, A Vomiero, G Sberveglieri, Angew Chem 2011, 51, 12321
4 A. Hossain, JR Jenning, Z.Y. Koh,Q. Wang, ACS Nano, 2011, 5, 3172
9:00 AM - GG3.08
The Effect of Molecular Adsorption-Geometry on the Binding Energy of Interface States
K. Kato 1 K. Sato 1 K. Yonezawa 1 Y. Liu 1 T. Hosokai 2 S. Yanagisawa 3 K. R Koswattage 1 N. Ueno 1 S. Kera 1
1Graduate School of Advanced Integration Science Chiba 263-8522 Japan2Department of Materials Science and Technology, Iwate University Morioka 020-8551 Japan3Depertment of Physics and Earth Sciences, Ryukyu University Okinawa 903-0213 JapanShow Abstract
Energy level alignment at organic/metal interfaces determines the performance of organic devices. To clarify the energy level alignment it is desired to obtain precise information of electronic states, in particular the highest occupied molecular orbital (HOMO) related states, at a complicated interface that consists of functional molecules. We studied the electronic structure and geometric structure of diindenoperylene (DIP: C32H16) monolayer (ML) on a Cu (111) surface by using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). It is known that DIP molecules form two different 2-dimensional lattice structures on Cu (111) .
A Cu (111) single crystal was cleaned by repeated Ar-ion sputtering and annealing cycles. The DIP ML film was prepared on the Cu (111) substrate by vacuum evaporation. ARUPS spectra were then measured at photon incidence angle α=45°, hv=28 eV and T=295 K at UVSOR facility (BL8B) at the Institute for Molecular Science. To study geometric structure as well as HOMO derived interface states we measured azimuthal angle (phi;) dependence by rotating the sample around the surface normal and photoelectron emission angle (theta;) dependence of the spectra of the ML.
ARUPS spectra of the DIP (ML)/Cu (111) show two prominent bands in the sp-band region of Cu (111). The first band is broad and located at binding energy (EB: from the Fermi level) of ~0.7eV, which is ascribed to the former LUMO with electrons transferred from the substrate as in the case of PTCDA . The second band consists of two features that are located at EB=1.5 and 1.8 eV. We observed these two features show different phi; dependences at theta;=37°. Assuming that these two features come from DIP HOMO and using the two molecular adsorption geometries observed with STM (the short-range and the long-range ordered structures) , we computed phi; dependences of the photoelectron intensity from the two features for the two geometries, and compared with the observed phi; dependences. The agreement between the observed and computed phi; dependences is obtained when the 1.5-eV feature is originated from the long-range ordered structure and the 1.8-eV feature is from the short-range ordered structure. We can thus ascribe both of these two features at 1.5 and 1.8 eV to HOMO-derived states.
 D. G. de Oteyza et al, Phys.Chem.Chem.Phys. 11, 8741 (2009)
 S. Duhm et al, Org. Electro. 9, 111 (2008)
9:00 AM - GG3.09
Transmission Electron Backscatter Diffraction (t-EBSD) for Characterizing Ultrathin Films in the SEM
Katherine Rice 1 Roy Geiss 1 Robert Keller 1
1NIST Boulder USAShow Abstract
Transmission electron backscatter diffraction (t-EBSD) is a new technique of materials characterization using a standard scanning electron microscope (SEM). By changing the sample-detector geometry so that electrons pass through a thin specimen prior to entering a commercial EBSD detector, an interaction volume significantly smaller than that typically associated with conventional EBSD can be achieved. As a result, electron diffraction data in the form of Kikuchi patterns can be collected from extremely fine-scale films and particles, down to the sub-10 nm dimensional scale. In conventional EBSD, incident electrons are thought to undergo Kikuchi scattering in the top 10 to 40 nanometers of a film, thereby requiring a film at least that thick to produce a diffraction pattern, while achieving a lateral spatial resolution in the typical range of 20 nm to 35 nm parallel to the tilt axis and 80 nm to 90 nm perpendicular to the tilt axis. Here we present recent results and electron scattering simulations associated with probing the sampling limits of the t-EBSD technique for semiconductor industry-relevant films as thin as 5 nm, while maintaining single-nanometer lateral spatial resolution.
Transmission EBSD, performed at ~ 20 keV, provides information from large areas of ultrathin films, while requiring only little material volume, by capturing forward-scattered electrons in transmission with standard EBSD equipment. Monte Carlo simulations support experimental results on the maximum thicknesses that can be reliably characterized with this method, by giving estimates of the energy losses of the electrons as they pass through increasing film thicknesses, and practical limits of the technique are investigated in terms of the mass-thickness of the sample, regardless of composition.
9:00 AM - GG3.10
Improved Raman Spectra of Materials Using a Schmidt-Czerny-Turner Spectrograph
Brian Charles Smith 1
1Princeton Instruments Acton USAShow Abstract
For decades Czerny-Turner (CT) spectrographs have been used to measure Raman spectra of materials. Inherent in the design of the CT spectrograph are optical aberrations including astigmatism, coma, and spherical aberration. These aberrations can cause Raman spectral peaks to be measured which are poorly resolved, have a low signal-to-noise ratio (SNR), and an asymmetric peak shape. The Schmidt-Czerny-Turner (SCT) spectrograph uses a unique optical design that completely eliminates astigmatism at all wavelengths and at all points on the focal plane, and greatly reduces coma and spherical aberration. The net result is Raman peaks of materials with improved spectral resolution, better SNR, and a symmetric peak shape. The use of a SCT spectrograph to obtain improved Raman spectra on a variety of materials will be discussed.
9:00 AM - GG3.11
Role of Strontium Dopant Concentration on the La1-xSrxCo0.2Fe0.8O3-delta; Cathode Performance in Solid Oxide Fuel Cells
Deniz Cetin 1 Yang Yu 1 Uday Pal 1 2 Soumendra Basu 1 2 Srikanth Gopalan 1 2
1Boston University Boston USA2Boston University Boston USAShow Abstract
One of the main current research goals in the solid oxide fuel cell (SOFC) industry is to reduce the operating temperatures of the SOFCs from 800-1000 °C to 600-800 °C. Reducing the operating temperature of SOFCs will obviate the need for expensive specialty alloys or ceramics for interconnects. However lower operating temperatures slow down the rates of electrochemical electrode reactions resulting in lower overall system efficiencies.
Using electrochemical impedance spectroscopy (EIS) on cells of the configuration LSCF (La1-xSrxCo0.2Fe0.8O3-δ)/ gadolinium-doped ceria (GDC) barrier layer/yttria-stabilized zirconia (YSZ)/porous LSM-YSZ counter electrode, the effect of Sr dopant concentration on the performance of LSCF cathodes was investigated. The effect of temperature on cathode performance was also investigated. The eventual goal is to obtain correlations between the electrochemical performance of LSCF cathodes and cation surface segregation effects.
9:00 AM - GG3.12
Tetrathiafulvalene as an Electron Acceptor for Surface Charge Induction on Silver Nanoparticles for Facilitated Olefin Transport
Hyung Woo Choi 1 Jung Hyun Lee 1 Young Rae Kim 1 Yong Soo Kang 1
1Hanyang University Seoul Republic of KoreaShow Abstract
Tetrathiafulvalene (TTF) is an organic semiconductor acting as an electron donor in charge-transfer complexes with an electron acceptor such as 7,7&’,8,8&’-tetracyanoquinodimethane (TCNQ) and also in metal-organic interfaces. On the contrary, we found that TTF was also able to act as an electron acceptor to the surface of silver nanoparticles (Ag NPs), which was consistent with the previous report to ZnO(0001) surface. Therefore it could be expected that TTF may act as an electron acceptor to induce partial positive charge on the surface of Ag NPs, similar to a well-known electron acceptor TCNQ.
We have previously reported various kinds of chemically modified Ag NPs as olefin carriers, which can interact with olefin gas specifically and reversibly but not with paraffin, consequently resulting in facilitated olefin transport. For instance, surface energy-level of Ag NPs was tuned to have partial positive charge on their surface by introducing electron acceptor such as p-benzoquinone (p-BQ) and TCNQ. The chemically activated Ag NPs have specific interactions only with propylene, resulted in the high selectivity of propylene over propane and high propylene permeance for the separation of olefin/paraffin mixture gases.
Herein, we adopted TTF to activate the surface of Ag NPs for olefin carriers, and their work function and binding energy were investigated by both UV photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It was interestingly found that TTF was able to act as an electron acceptor and induce surface positive charge of Ag NPs, which can interact with olefin specifically, resulting in the high separation performance for olefin/paraffin mixtures.
9:00 AM - GG3.13
Effect of Air Exposure of MoO3 Film Underneath Thin Organic Film
Chenggong Wang 1 Yongli Gao 1
1University of Rochester Rochester USAShow Abstract
We have investigated the thickness dependence of air exposure of Copper Phthalocyanine (CuPc) and C60 layers on molybdenum trioxide (MoO3) with ultraviolet photoemission spectroscopy (UPS). It was found that after the air exposure, the WF of MoOx dropped severely. Meanwhile, with sim;10 ÅCuPc thin films covered on the top, there is no big change of the MoOx WF before and after the air exposure. We also noticed that sim;10 Å C60 thin film could also protect the WF drop of MoO3 from air exposure. Our ultraviolet photoemission spectroscopy date indicated the MoO3 surface which was covered by approximately two monolayers of organic thin films are not active to air.
9:00 AM - GG3.14
Passivating the Surface States of Iron Pyrite Nanostructures by Epitaxial Zinc Sulfide Coating to Improve Its Solar Performance
Dong Liang 1 Nicholas S Kaiser 1 Miguel Caban-Acevedo 1 Song Jin 1
1University of Wisconsin-Madison Madison USAShow Abstract
Iron pyrite (cubic β-FeS2), an earth abundant and nontoxic semiconductor, has been attracting resurgent attention as a promising candidate for solar energy conversion due to its suitable band gap (0.95 eV indirect, 1.03 eV direct), high absorption coefficient (~6×10^5 cm^-1), and high mobility in single crystals (> 300 cm^2/V s). However, the application of pyrite for solar cells has been hindered by its low open circuit voltage (up to 200 mV) and thus low efficiency (~3%), which has been attributed to rich band gap states located at pyrite/electrolyte and pyrite/metal interfaces. To improve the performance of pyrite solar cell, the understanding and effective passivation of pyrite surface is urgently desired. Using the phase-pure single crystal pyrite nanorods (NRs) and other nanostructures as the model system, we develop chemical vapor deposition of epitaxial zinc sulfide (ZnS) on pyrite NRs to passivate surface states. The heteorepitaxial interface between pyrite and ZnS has been confirmed with detailed transmission electron microscopy study. Employing field effect transistor (FET), scanning probe microscopy (SPM) measurements and other surface analysis techniques, we investigate the changes of surface potential dominated by surface defects and other semiconductor characteristics upon the passivation treatment. These results can be important for improving pyrite single crystal and thin film structures for solar energy applications.
9:00 AM - GG3.15
Enhance the Efficiency of Bulk Heterojunction Solar Cell by Constructing Self-Assembled Columnar Structure in the Active Layer
Cheng Pan 1 Hongfei Li 1 Zhenhua Yang 1 Bulent Akgun 2 Sushil Satija 2 Dilip Gersappe 1 Yimei Zhu 3 Jaseung Koo 4 Miriam Rafailovich 1
1Stony Brook University Stony Brook USA2National Institute of Standards and Technology Gaithersburg USA3Brookhaven National Laboratory Upton USA4Korea Atomic Energy Research Institute Yuseong-gu Republic of KoreaShow Abstract
Bulk heterojunction (BHJ) polymer solar cells are an area of intense interest because of their flexibility, relatively low cost and ease of processing. However, in the active layer of a conventional BHJ solar cell, most of the donor or acceptor domains are isolated or far from the electrodes. This morphology leads to a long conduction path which causes possible recombination of the electron and hole pairs and lowers the efficiency of the cell.
Our approach is a very simple way to build up highly ordered columnar structures within the active layer by introducing a second polymer, poly(methyl methacrylate) (PMMA), which is immiscible with poly(3-hexylthiophene) (P3HT), causing lateral phase segregation into columnar structures. Furthermore, studies have shown that when nanoparticles are present in an immiscible blend, they preferentially segregate to the interfaces, allowing the interface to produce a template for the particle segregation. We therefore postulated that if one or both of the phases were photoactive polymers, then if carrier particles, such as [6,6]-Phenyl C61 butyric acid methyl ester (PCBM), were added, a structure for heterojunction solar cells could be formed where a direct pathway to the electrodes could be templated for the carrier particles. We first tested this concept by modeling the system using a Molecular Dynamics (MD) simulation, which defined the regime in phase space in which the parameters would be in the correct range for generating phase segregated structures and then characterized the actual samples, using a variety of complementary techniques to confirm the columnar structure. Finally, the devices were constructed using these structures, which showed a marked improvement in efficiency over the normal BHJ cells.
9:00 AM - GG3.16
Qualitative Characterization of Hydrophobicity in the Presence of High Adhesion Using AFM Force Curves
Christopher Benedikt Pilscheur 1 Matteo Chiesa 1 Sergio Santos 1 Carlo Amadei 1 Karim Gadelrab 1 Marco Stefancich 1
1Masdar Institute of Science and Technology Abu Dhabi United Arab EmiratesShow Abstract
In atomic force microscope (AFM), force curves are widely used to investigate surface properties in the nanoscale. Besides having a proper calibration of the AFM, the experimental parameters have to be kept constant during the entire experiment. This is especially difficult for highly adhering samples due to tip contamination. In case of the appearance of tip contamination, the experimental parameters change and the results can not be used. The contamination of the tip happens because the interacting forces between tip and sample are too high. Since a lot of information about the surfaces properties is recorded in the first part of the force curve. Here a technique is presented, where only the first five to ten percent of the force curve need to be recorded, in order to get qualitative information about the hydrophobicity of one sample compared to a reference sample. This prevents the tip from contamination, because the force acting between the tip and the surface are kept so low, that the tip does not get contaminated.
9:00 AM - GG3.17
Surface Stabilities of n-Type GaN Dependent on Electrolyte under Photoelectrochemical Reactions
Kayo Koike 1 Akihiro Nakamura 1 Masakazu Sugiyama 1 Yoshiaki Nakano 1 Katsushi Fujii 2
1The University of Tokyo Tokyo Japan2The University of Tokyo Tokyo JapanShow Abstract
Photoelectrochemical water splitting is one of the candidates for hydrogen gas generation from water. GaN is suitable for the photoelectrochemical electrode due to the band-edge energies. However, the n-type GaN has stability problem that the surface anodic corrosion during the photoelectrochemical reaction. There are some reports described the electrolyte dependences, that is, the flatband potential dependences on the pH of electrolytes , however, the details have not been investigated. We discuss the photoelectrochemical surface stabilities of n-type GaN dependent on the electrolytes in this report.
The working electrode was n-type GaN grown on (0001) sapphire substrates by metal-organic vapor phase epitaxy (MOVPE). The GaN layer was 1.0 µm n-type layer on 2.0 µm undoped layer. The carrier concentration of n-type GaN layer was 1.6×1017 cm-3. The counter and reference electrode, which were made of Pt, and Ag/AgCl/NaCl, respectively, were used for electrochemical evaluations. The light intensity was controlled as 100 mW/cm2 by using of 500 W Xe-lamp. The electrolytes were 0.5 mol/L H2SO4 (pH 0.8), 1.0 mol/L HCl (pH 0.2), 1.0 mol/L KOH (pH 13.8), and 1.0 mol/L NaOH (pH 13.8). The surface morphology of GaN was observed by Normarski microscope and Atomic force microscope (AFM).
The flatband potential in HCl obtained from Mott-Schottky plot shifted 0.1 V to positive direction compared with that in H2SO4. The potential usually changes along with the Nernstian relationship of water, because the dominant adsorbed materials at the electrode surface are H+, OH-, and water. The results show that the potential do not only depend on pH, that is, the absorption materials on the GaN surface changing with the electrolytes.
Cyclic voltammetry with light illumination was evaluated in order to clarify the photoelectrochemical properties. The over potential decreased in HCl electrolyte compared with that in H2SO4 estimated from the anodic and cathodic turn-on voltage difference. The variation of anodic current of 1 to 3 cycles in H2SO4 was much larger than that of HCl, NaOH and KOH.
The GaN surface after the reaction in H2SO4 was changed to rough. In contrast, mirror-like surfaces were remained after the reaction in HCl, NaOH and KOH. From these results, the reaction mechanism in H2SO4 is expected to be different from that of the other solutions.
In summary, the selection of electrolyte affects the surface stability probably due to the difference of the adsorbed materials on the photoelectrode surface.
 K. Fujii, K. Ohkawa, J. Electrochem. Soc. 153 (2006) A468.
9:00 AM - GG3.19
Columnar P3HT Structure Obtained from Self-Assembly Templates in Bulk Heterojunction Solar Cell
Hongfei Li 1 Cheng Pan 1 Zhenhua Yang 1 Bulent Akgun 2 Sushil K. Satija 2 Yimei Zhu 3 Miriam H. Rafailovich 1
1Stony Brook University Stony Brook USA2National Institute of Standards and Technology Gaithersburg USA3Brookhaven National Laboratory Upton USAShow Abstract
In recent years, organic photovoltaic, especially the polymer-fullerene bulk heterojunction solar cells, exhibit many promising features, such as intrinsic flexibility, low cost, and ease-fabrication. Because of the phase separation between two components, the disordered structure in the active layer is the critical problem limiting the power conversion efficiency (PCE) of BHJ solar cell. Therefore, an ordered inner structure is one possible solution to enhance the efficiency of the BHJ solar cells. Our research demonstrated a method to build up self-assembled vertical columns of the photoactive polymer, poly (3-hexylthiophene) (P3HT), within the active layer of BHJ solar cells via the spontaneous phase segregation in the polymer blends of P3HT, a non-active but well characterized polymer PMMA or PS and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) confined at the interface between PMMA/PS and P3HT. After selectively removed the PMMA or PS by solvent soaking, we obtained the highly ordered columns as P3HT template. This template was further utilized to fabricate real devices by filling a second photovoltaic polymer into the template. The as prepared devices were promising for exhibiting higher power conversion efficiency due to the shorter carrier transportation pathway and larger interface area between donor and acceptor. The columnar structured template is investigated under atomic force microscopy (AFM) and transmission electron microscopy (TEM). Neutron reflectometry was used to demonstrate the confinement of PCBM at the interface between P3HT and PMMA/PS in the active layer.
9:00 AM - GG3.20
Proton Transport Characteristics in Structurally Oriented Polyimide Thin Films for Fuel Cells
Karthik Krishnan 1 Masaki Noro 1 Hiroko Iwatsuki 2 Mitsuo Hara 2 Shusaku Nagano 2 Yuki Nagao 1
1Japan Advanced Institute of Science and Technology Ishikawa Japan2Nagoya University Nagoya JapanShow Abstract
Polymer electrolytes are regarded as an essential component in proton exchange membrane fuel cells (PEMFC) because of its high ionic transport, permeability to fuels, stability against corrosive environment and high electrical resistance, etc,. Of particular interest, thin polymer electrolytes have been attracted widely due to its distinct physical properties by the interfacial confinement, free surface effects and specific interactions between the active surface and polymer chains. A study of proton transport on nanoscaled thin polymer electrolytes disclose the clear scenario between the structure and property relations in confined systems. Indeed, the proton conductivity, structural orientation and water uptake capability in confined polymeric systems are influenced by varying the nature of substrate surface, origin of interfacial effects, morphology of thin films, and characteristics of domain spacing, etc,.
To understand the correlation between proton transport and structural orientation in polyelectrolytes, we have prepared the nanostructured polyimide thin films. Spin-coating was used to prepare the polyimide thin films and the desired thickness has been achieved by controlling the polymer to solvent composition. Thus, the 40 nm thin and 250 nm thick films have obtained on the quartz substrate. Both the relative humidity (RH) and temperature dependent proton conductivities were measured on these nanostructured polyimide thin films. A 40 nm thin polyimide film showed a slight enhancement of proton conductivity and the obtained maximum conductivity is 4.5 Chi; 10-2 S cm-1 at 298 K and 95% RH. Based on the orientation kinetics of polymer chains, the proton transport property have investigated. It is expected that the polymer chains are highly oriented in the in-plane direction, when the polyimide system is confined into thin film. Furthermore, confinement to thicknesses at nanoscale can lead to the anisotropies in internal morphology of the films, which is favorable for higher proton transport. From the Arrhenius plot, the activation energies were estimated and the obtained values are 0.24 and 0.20 eV respectively for 40 nm and 250 nm polyimide thin films. Employing the infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) technique, polymer orientation was investigated in both the in-plane and out-of-plane direction.
9:00 AM - GG3.21
Aluminum Oxide Passivation Layer for Crystalline Silicon Solar Cells Deposited by Non-Vacuum Mist CVD
Toshiyuki Kawaharamura 1 Takayuki Uchida 2 Kenji Shibayama 2 Shizuo Fujita 2 Takahiro Hiramatsu 3 Hiroyuki Orita 3
1Institute for Nanotechnology Kami Japan2Kyoto University Kyoto Japan3Toshiba Mitsubishi-Electric Industrial Systems-Corpration Kobe JapanShow Abstract
There is much demand for back side passivation films of crystal silicon (Si) based solar cells, with slimming down Si wafer. Thermal silicon oxide, which is fabricated by an annealing at high temperature, is generally used as a passivation film of Si based solar cells. However, high temperature process gives Si a damage with deterioration of crystallinity. Hence passivation films fabricated by low temperature process are greatly requested. Aluminum oxide (AlOx) thin film which has a large amount of negative fixed charge at the AlOx/c-Si interface is expected as a most suitable one .
Several vacuum-based deposition processes, such as atomic layer deposition (ALD) and plasma enhanced chemical vapor deposition (PECVD), have been employed for AlOx thin films fabrication. In this study, AlOx thin films were grown by non-vacuum mist CVD, which is a suitable technique for fabricating metal and oxide alloy thin films with simple configuration and environmental friendliness .