Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session A11: Energy Conversion Followed by Energy Storage Methods |
Hide Abstracts |
Sponsoring Units: GERA Chair: Sayantani Ghosh , University of California, Merced Room: A107-A109 |
Monday, March 15, 2010 8:00AM - 8:12AM |
A11.00001: ABSTRACT WITHDRAWN |
Monday, March 15, 2010 8:12AM - 8:24AM |
A11.00002: Hot electron effect in ultrathin photovoltaic junctions T. Kirkpatrick, K. Kempa, M.J. Naughton, Z.F. Ren, A. Herczynski, Y. Gao, J. Rybczynski The open circuit voltage in nanoscopically-thin \textit{p-i-n} amorphous silicon solar cells is found to increase with optical energy (light frequency) [1]. We accredit this increased $V_{oc}$ to the extraction of hot carriers. The ultrathin nature of these junctions also leads to a large electric field, reducing carrier recombination and facilitating anomalously large current in addition to the increased voltage. The large $J_{sc}$ thus indicates improved carrier extraction despite reduced optical absorption for ultrathin absorber layers. The overall power conversion efficiency is $\sim $3{\%} with absorbers less than 1/20$^{th}$ as thick as conventional $a$-Si solar cells ($i$-layer as thin as 5 nm). A simple phenomenological argument provides a semi-quantitative understanding of these effects, and may provide guidance for the design of high-efficiency, hot electron solar cells. MJN, KK and ZFR also at Solasta Inc.\\[4pt] [1] K. Kempa, M.J. Naughton, Z.F. Ren, A. Herczynski, T. Kirkpatrick, J. Rybczynski, Y. Gao, Appl. Phys. Lett. (in press). [Preview Abstract] |
Monday, March 15, 2010 8:24AM - 8:36AM |
A11.00003: Three-dimensional photovoltaics Bryan Myers, Marco Bernardi, Jeffrey C. Grossman The concept of three-dimensional (3D) photovoltaics is explored computationally using a genetic algorithm to optimize the energy production in a day for arbitrarily shaped 3D solar cells confined to a given area footprint and total volume. Our simulations demonstrate that the performance of 3D photovoltaic structures scales linearly with height, leading to volumetric energy conversion, and provides power fairly evenly throughout the day. Furthermore, we show that optimal 3D shapes are not simple box-like shapes, and that design attributes such as reflectivity can be optimized in new ways using three-dimensionality. [Preview Abstract] |
Monday, March 15, 2010 8:36AM - 8:48AM |
A11.00004: Development of Flexible Dye-Sensitized Solar Cells Xiaojuan Fan We are developing a low cost and easy process to fabricate porous metal oxide thin films on flexible substrate for high performance dye-sensitized solar cells (DSSCs\textbf{). }The research addresses on the formulation of TiO$_{2}$ precursor to create smooth and continuous porous thin films on large size plastic or metal foil substrates enabling excellent adhesion, robust mechanics, and chemical stability. The porous nanocrystalline TiO$_{2}$ thin films are used as anode electrodes for attaching light sensitizers. The first trial is to blend a polymer to Ti alkoxide precursors at various concentrations. After depositing the mixture on the substrates, the substrates are baked, exposed to UV light, taken place wet or dry etch to remove polymers leading to a porous structure. An appropriate annealing process will be applied to TiO$_{2}$ to turn it into crystalline. Alternative low temperature annealing method including steaming hydrothermal, plasma etches, and UV-ozone treatment will be tested with the annealing process controlled at low temperature. [Preview Abstract] |
Monday, March 15, 2010 8:48AM - 9:00AM |
A11.00005: Comparative Study of PbS and CdSe quantum dots for use in Luminescent Solar Concentrators Georgiy Shcherbatyuk, Richard Inman, Sayantani Ghosh, Chunhua Wang, Roland Winston A comparative study for absorption, redshift and photovoltaic (PV) cell response has been performed for Luminescent Solar Concentrators (LSCs) with embedded PbS and CdSe quantum dots (QDs). LSCs are planar non-tracking devices where the incident solar radiation is absorbed by a fluorescent species embedded in a polymer or glass plate which down-convert and re-emit the solar radiation at longer wavelengths. The emitted light is trapped in the concentrator plate by total internal reflection, transported and emitted at the four edges, where the photons are collected by PV cells. Based on nearly double the current generated by the PV cell in prototype devices, we have concluded that for the purpose of embedding in the LSC PbS quantum dots outperform CdSe. The results are linked to smaller self absorption observed in PbS QD solution and broader absorption spectrum of these QDs. [Preview Abstract] |
Monday, March 15, 2010 9:00AM - 9:12AM |
A11.00006: RT-TDDFT Simulations of NLO-Polymers with Tunable Energy Levels Fernando Vila, J. J. Rehr Polymer-based solar cells have attracted much attention due to their potential as cost-effective light harvesting devices. A new series of NLO-polymers has been recently developed\footnote{F. Huang \textit{et al.}, J. Am. Chem. Soc. {\bf131}, 13886 (2009).} where the HOMO-LUMO gap can be tuned to maximize the light absorption overlap with the solar spectrum, thus improving their photovoltaic efficiency. With the aim of predicting such HOMO-LUMO gaps, we have developed simplified models of these polymers. These models were optimized at B3LYP/6-31G(d,p) level and their UV-Vis spectra was calculated using our RT-TDDFT approach.\footnote{Y. Takimoto \textit{et al.}, J. Chem. Phys. {\bf127}, 154114 (2007).} Our results show that the absolute B3LYP HOMO-LUMO gaps follow the trend seen in the experiment, but are about 0.6 eV higher than those experimentally determined. When this systematic error, which is likely due to self-energy and local-field effects, is removed by referring the theoretical and experimental values to a single compound, the agreement between theory and experiment is remarkable. [Preview Abstract] |
Monday, March 15, 2010 9:12AM - 9:24AM |
A11.00007: Optical Fiber/Nanowire Hybrid Structures for Efficient Three-Dimensional Dye-Sensitized Solar Cells Yaguang Wei, Benjamin Weintraub, Zhonglin Wang We report an innovative hybrid structure integrating optical fibers and nanowire (NW) arrays as three-dimensional dye-sensitized solar cells that have significantly enhanced energy conversion efficiency. The light illuminates the fiber from one end along the axial direction, and its internal reflection within the fiber creates multiple opportunities for energy conversion at the interfaces. In comparison to the case of light illumination normal to the fiber axis from outside of the device, the internal axial illumination enhances the energy conversion efficiency of a rectangular fiber-based hybrid structure by a factor of up to six; and the absolute full Sun efficiency has been increased up to 3.3{\%}, This research demonstrates a new approach with advantageous of high efficiency, expanded mobility and surface adaptability, and concealed/remote operation capability. [Preview Abstract] |
Monday, March 15, 2010 9:24AM - 9:36AM |
A11.00008: Optical Properties of semiconducting nano-particles embedded in polymethyl methacrylate thin films and their applications in solar devices Richard Inman Jr., Georgiy Shcherbatyuk, Anthony Grimes, Stephen Horabin, Roland Winston, Sayantani Ghosh We investigate the applicability of composite polymethyl-methacrylate (PMMA) and semiconducting nano-particle films in solar energy storage devices integrable in building architecture, particularly windows. Thin films are prepared at different concentrations and thicknesses and characterized both optically by static and time resolved spectroscopic techniques and electrically, by recording their photovoltaic (PV) response using silicon PV cells.~ We observe increased emission intensity,~ reduced self-absorption and alteration of recombination times in the semiconducting nanoparticles embedded in PMMA films.~ Additionally, we incorporate these films into planar solar concentrators and evaluate the power conversion efficiencies. [Preview Abstract] |
Monday, March 15, 2010 9:36AM - 9:48AM |
A11.00009: Electromechanical Energy Conversion using a Bent-Core Nematic Liquid Crystaline Elastomer and the Giant Flexoelectric Effect John Harden, Rafael Verduzco, Paul Luchette, James Gleeson, Samuel Sprunt, Antal Jakli The flexoelectric effect is an electro-mechanical phenomenon that arises in liquid crystals where an electric polarization develops in response to a bend or splay of the liquid crystal director. Recently, it has been shown that nematic bent core LCs exhibit a flexoelectric coefficient more than three orders of magnitude larger than in previously studied calamitic nematic LCs, paving the way for electro-mechanical devices that utilize the flexoelectric effect. In order to develop practical, viable flexoelectric materials, it is necessary to incorporate the bent core nematic LC between flexible substrates or in a polymer matrix. Here we present and introduce the first nematic bent core liquid crystal elastomer. Monofunctional bent-core LCs with a reactive alkene group are used to make aligned side chain nematic elastomers using the method of Finkelmann. The flexoelectric coefficient e$_{3}$ was found by direct flexing to be 30nC/m. This is comparable to similar fluid bent core nematic liquid crystals. The work is supported by the ONR under grant N00014-07-1-0440) and NSF under DMR-0606160. The Elastomer provided the \textit{New Liquid Crystal Materials Facility}, http://nlcmf.lci.kent.edu, supported by the NSF DMR 0606357. [Preview Abstract] |
Monday, March 15, 2010 9:48AM - 10:00AM |
A11.00010: Bipolar molecules with an internal type II heterojunction for nanoscale photovoltaics Georgy Samsonidze, Marvin L. Cohen, Steven G. Louie Complex organic molecules composed of derivatives of thiophene and naphthalene connected through a bridge show spatially resolved electronic properties corresponding to the HOMO and LUMO states localized on the opposite sides of the molecule, as observed by scanning tunneling spectroscopy. The optical excitation of such molecules is expected to lead to an ultrafast charge separation induced by the intrinsic dipole moment at the donor/acceptor interface, which has potential applications for future nanoscale photovoltaics. We have computed the excited state quasiparticle energies of several bipolar molecules using a first-principles many-electron Green's function approach within the GW approximation for the electron self-energy operator. The renormalizations of the quasiparticle energies induced by the substrate are modeled within an image charge framework. The excitonic properties are calculated by solving the Bethe-Salpeter equation for the electron-hole amplitude. The results of our calculations are compared to available experimental data. This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility. [Preview Abstract] |
Monday, March 15, 2010 10:00AM - 10:12AM |
A11.00011: Scavenging low level mechanical vibrations using a magnetically coupled piezoelectric cantilever Ji-Tzuoh Lin, Bruce Alphenaar A piezoelectric cantilever can be used to scavenge power from background mechanical vibrations in the environment. Recently, we showed that nonlinear coupling of the cantilever to an external magnetic force can be used to increase the scavenged power in situations where a random, broadband vibration source is used to drive the cantilever. However, relatively large acceleration vibrations are needed to realize the improvement. Here, we show that by reducing the dimensions of the magnet from 5 mm diameter to 1 mm in diameter, it is possible to decrease the acceleration required to scavenge usable power from a broadband vibration source. The smaller diameter magnet reduces the width of the local potential minimum produced by the magnetic force, reducing the acceleration requirement from 4 mm/sec$^{2}$ to 0.9 m/sec$^{2}$ and increasing the total power production from 42{\%} to 62{\%}. We also show that by introducing coupling between multiple cantilevers it is possible to obtain a much broader frequency response in the voltage output. [Preview Abstract] |
Monday, March 15, 2010 10:12AM - 10:24AM |
A11.00012: Cylindrical Organic Solar Cells with Carbon Nanotube Charge Collectors Dante Zakhidov, Navaneeth Ravi, Raymond Lou, Alex Cook, Kamil Mielczarek Traditional organic photovoltaic (OPV) solar cells are produced on flat substrates. When applied on a large scale the maximum area covered by such flat OPV is limited to a two dimensional plane, moreover the light absorption is never strong enough due to very small OPV thickness ($\sim$200 nm). Organic cylindrical solar cell devices, suggested in this talk, have a vertical structure that allows more sunlight to be absorbed in a smaller area due to photons being trapped and reflected multiple times from the cylindrical walls. The schematics of the organic cylindrical solar cell device is similar to that of a traditional organic cell but instead of using ITO as the p-type or hole collecting layer, transparent multi-walled carbon nanotubes (MWCNT) are applied. The highly conductive nature of MWCNTs and 3-dimensional charge collection allows for increased efficiency over flat ITO while the device still remains transparent. A PEDOT: Methanol mixture is used on top of the MWCNTs as a buffer layer that helps in the transport of holes while blocking electrons. The photoactive layer consists of P3HT/PCBM and aluminum is deposited onto the device as a cathode or as an electron collecting layer. [Preview Abstract] |
Monday, March 15, 2010 10:24AM - 10:36AM |
A11.00013: A new battery-charging method using an oscillating field: Amplitude and frequency dependence of charging time Ibrahim Abou Hamad, M.A. Novotny, David Wipf, Per Arne Rikvold We propose a new charging method for Lithium-ion batteries, based on large-scale molecular dynamics studies. By applying an additional oscillating field to the constant charging field, one can charge a Lithium-ion battery in a fraction of the time originally needed. The additional field not only increases the diffusion rate, but also enhances intercalation of the Lithium ions into the graphite electrode. Our simulations show an exponential dependance of the Lithium ion intercalation time on the amplitude of the additional oscillating field. The dependence of the charging time or intercalation time on the frequency of the additional field will also be discussed. [Preview Abstract] |
Monday, March 15, 2010 10:36AM - 10:48AM |
A11.00014: Infrared Photon Stimulated Hydrogen Transport in Rutile TiO$_{2}$ Erik Spahr, Gunter Luepke, Lanlin Wen, Michael Stavola, Lynn Boatner, Leonard Feldman, Norman Tolk Measurements of the O-H and O-D vibrational lifetimes show that the room temperature proton diffusion rate in TiO$_{2}$ can be enhanced by 9 orders of magnitude when stimulated by resonant infrared photons. We find that the local oscillatory motion of the proton quickly couples to a wag-mode-assisted classical transfer process along the c-channel with a jump rate of $>$1 THz and a barrier height of 0.3 eV. Such an increase in proton transport rate at moderate temperatures is significant for renewable energy applications ranging from hydrogen transport membranes to water splitting by photocatalysis. [Preview Abstract] |
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