Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S34: Biofuels, Solar Fuels and Artificial Photosynthetic Systems |
Hide Abstracts |
Sponsoring Units: GERA Room: 210A |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S34.00001: Computational assessment of organic photovoltaic candidate compounds Mario Borunda, Shuo Dai, Roberto Olivares-Amaya, Carlos Amador-Bedolla, Alan Aspuru-Guzik Organic photovoltaic (OPV) cells are emerging as a possible renewable alternative to petroleum based resources and are needed to meet our growing demand for energy. Although not as efficient as silicon based cells, OPV cells have as an advantage that their manufacturing cost is potentially lower. The Harvard Clean Energy Project, using a cheminformatic approach of pattern recognition and machine learning strategies, has ranked a molecular library of more than 2.6 million candidate compounds based on their performance as possible OPV materials. Here, we present a ranking of the top 1000 molecules for use as photovoltaic materials based on their optical absorption properties obtained via time-dependent density functional theory. This computational search has revealed the molecular motifs shared by the set of most promising molecules. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S34.00002: Thermogravimetric, Calorimetric, and Structural Studies of the Co3O4/CoO Oxidation/Reduction Reaction Karl Unruh, Ronald Cichocki, Brian Kelly, Gerald Poirier To better assess the potential of cobalt oxide for thermal energy storage (TES), the Co3O4/CoO oxidation/reduction reaction has been studied by thermogravimetric (TGA), calorimetric (DSC), and x-ray diffraction (XRD) measurements in N2 and atmospheric air environments. TGA measurements showed an abrupt mass loss of about 6.6\% in both N2 and air, consistent with the stoichiometric reduction of Co3O4 to CoO and structural measurements. The onset temperature of the reduction of Co3O4 in air was only weakly dependent on the sample heating rate and occurred at about 910 $^{\circ}$C. The onset temperature for the oxidation of CoO varied between about 850 and 875 $^{\circ}$C for cooling rates between 1 and 20 $^{\circ}$C/min, but complete re-conversion to Co3O4 could only be achieved at the slowest cooling rates. Due to the dependence of the rate constant on the oxygen partial pressure, the oxidation of Co3O4 in a N2 environment occurred at temperatures between about 775 and 825 $^{\circ}$C for heating rates between 1 and 20 $^{\circ}$C/min and no subsequent re-oxidation of the reduced Co3O4 was observed on cooling to room temperature. In conjunction with a measured transition heat of about 600 J/g of Co3O4, these measurements indicate that cobalt oxide is a viable TES material. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S34.00003: Electronic and Optical Properties of Novel Phases of Silicon and Silicon-Based Derivatives Chin Shen Ong, Sangkook Choi, Steven G. Louie Recent discoveries of two novel phases of silicon, Si$_{\mathrm{20}}$ and Si$_{\mathrm{24}}$, lead to promises of quasi-direct band gap silicon crystals that are capable of complementing indirect-gap diamond cubic silicon for use in the solar cell industry. This work studies the quasiparticle excitations and optical spectra of these two structures, Si$_{\mathrm{20}}$ and Si$_{\mathrm{24}}$, assessing their suitability for use as photovoltaic materials. We carry out ab initio GW and GW-BSE calculations for the quasiparticle excitations and optical spectra, respectively, including self-energy and electron-hole interaction effects. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S34.00004: Accurate determination of the temperature dependent thermalization coefficient ($Q$) in InAs/AlAsSb quantum wells Hamidreza Esmaielpour, Jinfeng Tang, Vincent R. Whiteside, Sangeetha Vijeyaragunathan, Tetsuya D. Mishima, Michael B. Santos, Ian R. Sellers We present an investigation of hot carriers in InAs/AlAsSb quantum wells as a practical candidate for a hot carrier solar cell absorber. The thermalization coefficient ($Q$) of the sample is investigated using continuous wave photoluminescence (PL). The $Q$ is accurately determined through transfer matrix calculations of the absorption, analysis of the power density, penetration depth, diffusion, and recombination rates using a combination of simulation and empirical methods. A precise measurement of laser spot size is important in order to determine the absorbed power density. Simulations were performed based on our PL geometry in order to calculate the excitation spot size, which was compared with experiment by measurements using variable diameter pinholes to determine beam radius. Here, these techniques are described, in addition to, the temperature dependent hot carrier dynamics and phonon mediated thermalization coefficient for the InAs/AlAsSb quantum well structure. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S34.00005: Improved performance due to selective passivation of nitrogen clusters in GaInNAs solar cells Miwa Fukuda, Vincent R. Whiteside, Mohamed Al Khalfioui, Mathieu Leroux, Khalid Hossain, Ian R. Sellers While GaInNAs has the potential to be a fourth-junction in multi-junction solar cells it has proved to be difficult to incorporate due to the low solubility of nitrogen in these materials. Specifically, mid-gap states attributed to nitrogen clusters have proved prohibitive for practical implementation of these systems. Here, we present the selective passivation of nitrogen impurities using a UV-activated hydrogenation process, which enables the removal of defects while retaining substitution nitrogen. Temperature dependent photoluminescence measurements of the intrinsic region of a GaInNAs p-i-n solar cell show a classic ``s-shape" associated with localization prior to hydrogenation, while after hydrogenation no sign of the ``s-shape" is evident. This passivation of nitrogen centers is reflected in improved performance of solar cells structures relative to reference, unpassivated devices presenting a potential route to practical implementation of GaInNAs solar cells. [Preview Abstract] |
(Author Not Attending)
|
S34.00006: Amorphous carbon for photovoltaics Francesca Risplendi, Jeffrey C. Grossman All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp$^{\mathrm{2}}$ and sp$^{\mathrm{3}}$ hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C$_{\mathrm{60}}$ can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S34.00007: Highly Selective Photocatalytic CO$_{2}$ Reduction on TiO$_{2}$-Passivated InP in Ionic Liquids Guangtong Zeng, Jing Qiu, Shermin Arab, Zhen Li, Stephen Cronin Lowering the overpotential required to drive the photocatalytic reduction of CO$_{2}$ to useful products is a very important challenge. In this article, we use an ionic liquid [EMIM]BF$_{4}$ co-catalyst to improve the selectivity and efficiency of CO$_{2}$ reduction to CO on TiO$_{2}$-passivated InP. Here, the InP surface is passivated using a thin film of TiO$_{2}$ deposited by atomic layer deposition (ALD), which improves the photoconversion efficiency by as much as 17X compared to bare InP. We believe there are three mechanisms of enhancement in this photocatalytic system. Firstly, the TiO$_{2}$ deposited by ALD is $n$-type due to oxygen vacancies, and forms a \textit{pn}-junction with the underlying $p$-type InP photocathode, resulting in a built-in potential which reduces electron-hole recombination through charge separation. Secondly, the Ti$^{3+}$ active sites formed on the TiO$_{2}$ surface lower the energy of the CO$_{2}^{-}$ intermediate through the formation of an intermediate complex. Thirdly, the [EMIM]$^{+}$ ions in solution also stabilize the CO$_{2}^{-}$ intermediate, further lowering the energy barrier of this reaction. Here, we use a non-aqueous ionic liquid solution, which prohibits hydrogen formation and enables highly selective CO$_{2}$ reduction with a Faradaic efficiency of 46{\%}. This general approach of passivating narrower band gap semiconductors with TiO$_{2}$ and utilizing a non-aqueous ionic liquid solution allows a wide range of materials to be considered for photocatalysis, enabling more efficient photocatalysts to be developed. [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S34.00008: High-throughput search for photoabsorbers for solar fuels Slobodan Mitrovic, Earl Cornell, Paul Newhouse, Joel Haber, Ryan Jones, John Gregoire We present the suite of instrumentation developed specifically to search for light absorber materials for solar hydrogen and carbon-based fuels. A pre-screening method utilizes colorimetric image analysis to search for positive and negative metrics for electronic bandgaps, isolate materials not suitable for further screening and identify phase clusters in the compositional space of combinatorial material libraries. Then, two highly-automatized instruments screen for photocurrent, by performing incident-photon conversion efficiency measurement in a redox couple, and absorption properties via UV-Vis-NIR spectroscopy. Finally, we present a new instrument for multispectral microscopic imaging of material libraries. We will discuss the challenges in automated data analysis from large datasets and multispectral data-cubes. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S34.00009: First-principles study of MnNiO$_{3}$ as an alkaline oxygen-evolution photocatalyst Jie Yu, Qimin Yan, Wei Chen, Anubhav Jain, Jeffrey Neaton, Kristin Persson We present a first-principles study of MnNiO$_{3}$, a promising oxygen-evolution photocatalyst. Using density functional theory with the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO$_{3}$ is a ferrimagnetic semiconductor with an indirect band gap, consistent with experimental observations. We also predict that MnNiO$_{3}$ has promising band edge positions relative to the vacuum, with potential to straddle the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) redox potentials in aqueous solution. A detailed analysis of the band structure and density of states provides a clear explanation why MnNiO$_{3}$ is promising for OER. Pourbaix diagram calculations suggest that MnNiO$_{3}$ is stable in alkaline solution at potentials relevant for oxygen evolution. This work was supported by the Department of Energy through the Joint Center for Artificial Photosynthesis. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S34.00010: Energy requirements for CO$_{2}$ capture from ambient air (DAC) competitive with capture from flue-gas (PCC) Christoph Meinrenken Capture of CO$_{2}$, whether from a flue gas source (PCC) or from distributed sources via ambient air (DAC), is a key enabling technology to provide carbon for sustainable synthetic energy carriers such as solar fuels. Based on thermodynamic minimum considerations, DAC is often expected to require about 3 times more energy (per ton CO$_{2}$ captured) than PCC because CO$_{2}$ in ambient air is more dilute. Here, we calculate the energy required for a humidity swing-based DAC installation that uses an anionic exchange resin as sorbent. The calculation uses recently measured equilibrium CO$_{2}$ loadings of the sorbent as function of partial CO$_{2}$ pressure, temperature, and humidity. We calculate the installation's electricity consumption to be about 45 kJ per mole of pure CO$_{2}$ at 1 bar (scenario-dependent). Furthermore, we estimate the amount of heat provided by ambient air and thus provide context of the overall energy and entropy balance and thermodynamic minimum views. The electricity consumption is competitive with typical parasitic loads of PCC-equipped coal-fired power plants (40-50 kJ per mole at same pressure) and significantly lower than predicted for other DAC installations such as Na(OH) sorbent-based systems. Our analyses elucidate why DAC is not always more energy-intensive that PCC, thus alleviating often cited concerns of significant cost impediments. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S34.00011: MIS Solar Cell Devices Based on a Cu2O Substrate Utilizing h-BN as an Insulating and Passivating Layer Onur Ergen, Ashley Gibb, Oscar Vazquez-Mena, Will Regan, Alex Zettl We demonstrate Cu$_{2}$O based metal insulator semiconductor Schottky (MIS-Schottky) solar cells with efficiency exceeding 3\%. A unique direct growth technique is employed in the fabrication, and hexagonal boron nitride (h-BN) serves simultaneously as a passivation and insulation layer on the active cuprous oxide (Cu$_{2}$O) layer. The devices are the most efficient of any Cu$_{2}$O based MIS-Schottky solar cells reported to date. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S34.00012: Electronic properties of BiI3 using hybrid functionals Patrick M. McBride, Anderson Janotti, Chris G. Van de Walle BiI3 has recently gained interest as a high-efficiency light-output scintillator material, but limited research has been done to investigate its electronic structure. Most theoretical investigations have been limited to using density functional theory (DFT) within the local density approximation (LDA) or the generalized gradient approximation (GGA), which are known to give an incorrect electronic band gap. Furthermore, these studies ignore van der Waals (vdW) interactions, even though BiI3 has a layered structure held together by vdW forces. In this talk we present results of hybrid functional calculations, including the effects of spin-orbit coupling, for the electronic and structural properties of BiI3. We will address effects of including vdW interactions and spin-orbit coupling on the nature of the band gap, electron and hole effective masses, and the band edge positions with respect to vacuum level and other relevant semiconductors. We will also discuss the suitability of BiI3 as a photovoltaic material. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S34.00013: Quantitative model of EBIC for CdTe Paul Haney, Heayoung Yoon, Prakash Koirala, Robert Collins, Nikolai Zhitenev Electron beam induced current (EBIC) is a powerful characterization technique which offers the high spatial resolution needed to study polycrystalline solar cells. In an EBIC experiment, a beam of high energy electrons excites electron-hole pairs, some fraction of which are collected by contacts. Ideally, an EBIC measurement reflects the spatially resolved quantum efficiency of the device. However, experiments on polycrystalline CdTe solar cells reveal that the EBIC collection efficiency is substantially lower than the quantum efficiency of the device under optical excitation. In order to reliably extract intrinsic material properties from EBIC signals, this difference must be reconciled. Two important differences between an EBIC experiment and normal device operation are: 1. the high generation rate density associated with the electron beam, and 2. the substantial effect of the exposed surface in an EBIC experiment. By developing numerical and analytical models which account for both of these effects, the difference in the material response under EBIC and normal device operation conditions can be understood. Comparison between the model and experiment show good agreement between quantities such as maximum EBIC collection efficiency versus charge generation rate. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S34.00014: Studying Anomalous Open-Circuit Voltage Drop-Out in Concentrated Photovoltaics Using Computational Numerical Analysis Margaret Stevens, Chandler Downs, Thomas Vandervelde, Scott Machlachlan, James Adler Under high solar concentration, an anomalous open-circuit voltage drop-out has been observed experimentally, but not understood theoretically. This anomaly has often been attributed to various thermal effects, but the effect is also observed in flash testing, where thermal effects do not have time to accumulate. We discuss our theoretical examination of semiconductor performance under high optical generated carrier injection. Under these conditions, the number of optically generated charge carriers increase past the number of equilibrium charge carriers. The effect of dynamically changing charge carrier compositions on fundamental electrical properties, such as open-circuit voltage, has yet to be explored in detail. Using the Newton-Raphson method, we solved the carrier continuity equations for the optically generated charge carriers as a function of material depth in bulk III-V semiconducting materials. Ultimately, we implemented these carrier concentration functions in our simulations of p-n band structures to characterize the impact of solar concentration on the electrical behavior of photovoltaic devices. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S34.00015: Polymer-directed Hybrid Nanostructures for Enhanced Electrocatalytic Activity and Solar Fuel Generation Dong Ha Kim, Yoon Hee Jang, Ji-Eun Lee, Li Na Quan, Yu Jin Jang In this presentation, we introduce a comprehensive approach to the design and fabrication of hybrid nanostructures directed by functional polymers for photovoltaic, phoelectrochemical and electrocatalytic properties. A unique strategy to generate core-shell nanoparticles based on AuNPs decorated with PANI shell with uniformly distributed alloy metal NPs in the PANI shells was developed. We systematically investigate the structural alteration during the sequential synthetic process and compared the electrocatalytic performance with respect to Pt-decorated AuNP-PANI structures in terms of the oxygen reduction reaction. Aimed for an alternative photoanodes, hierarchical mesoporous carbon-TiO$_{2}$ inverse opal nanostructures were synthesized by complementary colloid and block copolymer (BCP) self-assembly, where the triblock copolymer P123 acts simultaneously as template and carbon source. Analytical studies show that incorporation of carbon moieties into TiO$_{2}$ creates a new energy level above the valence band of TiO$_{2}$, resulting in an effective decrease in the band gap. A significant enhanced visible light photocatalytic activity was demonstrated in terms of the degradation of $p$-nitrophenol ($\sim$ 79 {\%}) and photoelectrochemical water splitting. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700