Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J24: Photovoltaics, including Thermal, LSC, Oxides and Device Physics |
Hide Abstracts |
Sponsoring Units: GERA Chair: Janelle Leger, West Virginia University Room: 504 |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J24.00001: Exploring Near-Field Radiative Heat Transfer for Thermo-photovoltaic Applications Yashar Ganjeh, Bai Song, Seid Sadat, Dakotah Thompson, Anthony Fiorino, Pramod Reddy, Edgar Meyhofer Understanding near-field radiative heat transfer (NFRHT) is critical for developing efficient thermo-photovoltaic devices. Theoretical predictions suggest that when the spatial separation of two parallel planes at different temperatures is less than their Wien's thermal wavelength, thermal transport via radiation can be greatly enhanced. The radiative heat flow across nanoscale gaps is predicted to be orders-of-magnitude higher than that given by Stefan-Boltzmann law, due to contribution of evanescent waves. In order to test these predictions, a novel experimental platform was designed and built enabling parallelization of two planar surfaces (50 $\mu$m~by~50 $\mu$m) with 500 microradian resolution in their relative orientation. This platform was used to probe NFRHT between two planes and also between a plane and a sphere. It was found that, when a 50 $\mu$m diameter silica sphere was approximately 20 nm away from a 50 by 50 $\mu$m$^{2}$~silica plane, a significant increase in radiative heat transfer coefficient was observed. This increase is 3 orders of magnitude higher than the value predicted by the blackbody limit. Other setups, including Au spheres and planes, and the plane-plane geometries are currently being investigated. [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J24.00002: Heterostructure designs for photon-enhanced thermionic emission Jared Schwede, Daniel Riley, Roger Howe, Nicholas Melosh, Zhi-Xun Shen Photon-Enhanced Thermionic Emission (PETE) is a promising method of solar energy conversion that relies on photoexcitation and thermionic emission into vacuum, combining quantum and thermal approaches into a single mechanism. We have previously reported a heterostructure design that separates the PETE process from the process of vacuum emission, which resulted in a large improvement in quantum efficiency to 1-2{\%}, compared to 10\textasciicircum 4 electrons per photon in proof of concept measurements. In addition to this performance improvement, the heterostructure architecture also creates the opportunity to separately target internal PETE and vacuum emission. In this talk, we describe designs which can be used to independently study these mechanisms. [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J24.00003: An Isothermal Device Configuration for Diamond Based Photon-Enhanced Thermionic Solar Energy Conversion Tianyin Sun, Franz Koeck, Robert Nemanich Diamond can obtain a negative electron affinity (NEA) after hydrogen termination. With NEA and n-type doping, a low effective work function and efficient thermionic emission has been observed from these diamond films. Photo-induced electron emission from nitrogen doped diamond with visible light illumination has also been established by our group. Recently several reports have described efficient energy conversion based on the photon-enhanced thermionic emission (PETE) mechanism. This study proposes a multi-layer emitter and collector structure for an isothermal PETE converter. The emitter structure is based on an n-type NEA diamond film deposited on a p-type Si substrate to enable electron emission across a vacuum gap. In this structure the above-bandgap light is absorbed in the Si and establishs an enhanced electron population for emission through the low work function surface, while sub-bandgap light is absorbed in the collector for transfer to a heat engine. Spectroscopy measurements of the n-type diamond on Si indicate strong electron emissivity with photon illumination, and the emission intensity is significantly increased at elevated temperatures. A simplified model describing the efficiency and performance of an isothermal PETE device is presented. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J24.00004: Nanoscale Radiative Heat Transfer between a Scanning Probe and a Flat Surface Bai Song, Kyeongtae Kim, Woochul Lee, Won Ho Jeong, Edgar Meyhofer, Pramod Reddy Fluctuational electrodynamics based calculations predict a significant increase in the efficiency of thermophotovoltaic devices when an emitter is placed in the close proximity of an appropriately designed photovoltaic (PV) cell. The enhancement is expected to be further increased if the emissive properties of the emitter are matched to the band gap of the PV cell via nanostructuring. However, before this can be accomplished, it is necessary to better understand the underlying physics. This is especially true given the discrepancies seen between published experimental and theoretical studies. Here we present our measurements of nanoscale radiative heat transfer between the tip of scanning probes and an atomically flat surface spatially separated by very small gaps (1-10 nm). The experiments were performed in a UHV environment using custom-developed scanning probed with picowatt heat-flow resolution. Current measurements show significant deviations from computational predictions. We are currently studying radiative thermal transport between a range of materials to reveal the contribution of important effects such as non-locality and eddy currents. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J24.00005: Non-tinted Transparent Luminescent Solar Concentrators Employing Both UV and NIR Selective Absorbers Yimu Zhao, Richard Lunt Luminescent solar concentrators are a potentially low-cost solar harvesting solution that additionally offer opportunities for integration around buildings and windows. However, the visible absorption and emission of previously demonstrated chromophores hamper their widespread applications including solar windows. Here, we demonstrate non-tinted transparent luminescent solar concentrators (TLSC) that employ both ultraviolet (UV) and near-infrared (NIR) selective absorbing luminophores that create an entirely new paradigm for power-producing transparent surfaces and enhances the potential over UV-only TLSCs. We have previously designed UV-harvesting systems composed of metal halide phosphorescent luminophore blends that enable absorption cutoff positioned at the edge of visible spectrum (430nm) and massive-downconverted emission in the near-infrared (800nm) with quantum yields for luminescence of 75{\%}. Here, we have developed a complimentary TLSC employing fluorescent organic salts with both efficient NIR absorption and deeper NIR emission. We will discuss the photophysical properties of these luminophores, the impact of ligand-host control, and optimization of the TLSC architectures. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J24.00006: Particle scattering applications in solar panels Jehan Seneviratne, Matthew Berg The focus of this work is to apply the scattering characteristics of particles to model particle assisted solar concentrators. In this work, the scattering patterns of particles of different shapes, sizes, and refractive indices are computationally studied using Discrete Dipole Approximation (DDA). The study investigates the optical behavior of different particle ensembles. The simulated results are used to explain the characteristic behavior seen in [1]. The computational methodology can be used to determine the ideal ensemble of particles to produce the most efficient energy yield in a scattering-based photovoltaic concentrator.\\[4pt] [1] J. Wen, M. J. Berg, M. Steed, ``Scattering-based solar concentrator,'' \emph{Opt. Express} (submitted in review, 2013). [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J24.00007: Wavelength-Selective Photovoltaics for Power-generating Greenhouses Sue Carter, Michael Loik, David Shugar, Carley Corrado, Catherine Wade, Glenn Alers While photovoltaic (PV) technologies are being developed that have the potential for meeting the cost target of \$0.50/W per module, the cost of installation combined with the competition over land resources could curtail the wide scale deployment needed to generate the Terrawatts per year required to meet the world's electricity demands. To be cost effective, such large scale power generation will almost certainly require PV solar farms to be installed in agricultural and desert areas, thereby competing with food production, crops for biofuels, or the biodiversity of desert ecosystems. This requirement has put the PV community at odds with both the environmental and agricultural groups they would hope to support through the reduction of greenhouse gas emissions. A possible solution to this challenge is the use of wavelength-selective solar collectors, based on luminescent solar concentrators, that transmit wavelengths needed for plant growth while absorbing the remaining portions of the solar spectrum and converting it to power. Costs are reduced through simultaneous use of land for both food and power production, by replacing the PV cells by inexpensive long-lived luminescent materials as the solar absorber, and by integrating the panels directly into existing greenhouse or cold frames. Results on power generation and crop yields for year-long trials done at academic and commercial greenhouse growers in California will be presented. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J24.00008: Angle-Dependent Performance in Thin-Film and Transparent Photovoltaics Margaret Young, Yunhua Ding, Richard Lunt Understanding the angle dependent performance is an important consideration for building integrated photovoltaics (PVs), such as transparent PV windows, where illumination angles are rarely at normal incidence. While the transfer matrix model (TMM) has been widely utilized to model optical interference and quantum efficiency in thin-film PVs at normal incidence, self-consistent simulations for PVs under oblique illumination have not yet been demonstrated. We derive an updated model that is self-consistent for all angles, light polarizations, and electrical / optical configurations, and experimentally verify the predicted angular quantum efficiency response of planar heterojunction (PHJ) transparent PVs. We subsequently use this model to optimize PHJ transparent PVs for maximum short circuit photocurrent density (J$_{sc})$ and transparency as a function of the multivariable landscape under a variety of optical and electrical configurations, showing that it is possible to greatly reduce the angle-dependent roll-off in efficiency by moving in this multi-parameter space. We will provide insights into the lesson learned for designing devices that can reduce this roll-off and increase overall yearly power output. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J24.00009: Absorption and emission of NIR fluorophores for use in Wavelength Selective Solar Concentrators Kaitlin Hellier, Carley Corrado, Sue Carter Wavelength Selective Solar Concentrators (WSSCs) offer a variety of applications as compared to traditional solar panels. Exploiting the property of power generation with transmission, we have turned our attention to the greenhouse industry. Our current design employs an organic dye (Lumogen Red 305) with an excitation peak in green wavelengths and an emission peak in red wavelengths, specifically targeting wavelengths unused in photosynthesis. To increase the efficiency of the WSSC without disrupting either existing function, we explore the addition of NIR dyes. Presented are the absorption and emission peaks of the dyes deposited into poly-vinyl butyral (PVB), polymethyl methacrylate (PMMA), and (TPU); the quantum yields of these films; and the combined spectra of the dyes with LR305. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J24.00010: Detailed Balance Comparison of the Series and Non-Series Tandem Solar Cell Octavi E. Semonin, Robert A. Barton, Ioannis Kymissis Using thin film multijunction photovoltaics to achieve higher power conversion efficiency has been proposed as a means to lower costs in next generation solar cells. As they are typically constructed, each cell is connected in series to the next, with each cell having a band-gap optimized to more efficiently harvest energy from a subset of the solar spectrum. However, the series-constrained solar cell limits the range of materials compatible because any excess current generated by any cell in the structure is lost. In this work, we use the detailed balance analysis developed by Shockley and Queisser to show how inserting a third transparent electrode between two active layers can dramatically increase the range of materials for which a tandem structure can break present efficiency limits. We show that the non-series architecture exceeds 40{\%} power conversion efficiency for five times as many band-gap combinations as the series tandem, significantly expanding the materials phase-space available to researchers. We apply this analysis to the case study of thin film structures built on the ubiquitous silicon platform. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J24.00011: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J24.00012: Computational characterization of optical and thermodynamic properties of bulk zinc stannate (Zn2SnO4) Grigory Kolesov $Zn_2SnO_4$ (ZTO) is an important material with a wide band gap. It is often used in novel device designs such as quantum dot- and die-sensitized solar cells. The crystal structure of ZTO is inverse spinel, with the general formula $AB_2O_4$. In inverse spinel A and B atoms share the occupation of octahedral sites 0.5/0.5, while the exact occupation is often unknown. Here we study configuration space of ZTO with DFT and derive cluster expansion model. We find temperature dependence for the occupation of octahedral sites and demonstrate that the lowest energy ground state configuration is stable at the normal range of temperatures. Because of the large unit cell (56 atoms) the calculation of optical properties with many-body methods appeared to be impractical and we compute band structure with DFT using Tran-Blaha correlation functional. The optical band gap we obtain with this method matches experimental value. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J24.00013: Zinc stannate as a solar cell material Brian Kolb, Alexie Kolpak Semiconducting ferroelectric materials are attractive as solar absorbers because they have a built in polarization that facilitates electron-hole separation and can drive carriers to opposite ends of the device. ZnSnO$_3$ is an exciting material that has recently been shown to be ferroelectric with a relatively large (~50 $\mu$C/cm$^2$) remnant polarization. It holds potential as a solar absorber because it is a direct gap material composed of relatively cheap, abundant, and non-toxic elements. The bandgap of ideal ZnSnO$_3$ is too large to make it an efficient solar absorber. However, like many semiconducting oxides containing tin, the bulk bandgap is an extremely strong function of the lattice constant. In fact, just a few percent change in the lattice constant of ZnSnO3$_3$ can alter its bandgap by as much as a factor of 2-4. This opens the possibility of tuning the bandgap by applying a slight epitaxial strain, which can be accomplished by affixing a ZnSnO$_3$ film to a substrate with a modest lattice mismatch. In this work we use sophisticated methods (DFT and GW) to identify materials that can be affixed to a ZnSnO$_3$ film, modifying its bandgap to a near optimal value. Attention will be paid to the bandgap, band alignments, and the thermodynamics of the interfaces. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J24.00014: First-principles materials design of high-performing bulk photovoltaics with the LiNbO3 structure Steve Young, Fan Zheng, Andrew Rappe The bulk photovoltaic effect describes the ability of inversion symmetry breaking materials to produce intrinsic photocurrents and photovoltages. Recently, we have previously demonstrated the ability to compute, from first principles, the bulk photocurrent using the theory of ``shift current,'' and have successfully reproduced experimental results. This ability has allowed for understanding of the structural and chemical properties generating large bulk photovoltaic response and the design of high-performing materials. In this talk we present three polar oxides with the LiNbO$_3$ structure that we predict to have band gaps in the 1-2 eV range and very high bulk photovoltaic response: PbNiO$_3$, Mg$_{1/2}$Zn$_{1/2}$PbO$_3$, and LiBiO$_3$. The first is has already been synthesized, and the others are very similar to known materials. All three have band gaps determined by cations with $d^{10}s^0$ electronic configurations, leading to conduction bands composed of cation $s$-orbitals and O $p$-orbitals. This both dramatically lowers the band gap and increases the bulk photovoltaic response by as much as an order of magnitude over previous materials, demonstrating the potential for high-performing bulk photovoltaics. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J24.00015: Quantitative high-resolution mapping of built-in fields in polycrystalline photovoltaic devices using electron beams: effects of surface band bending and recombination Nikolai Zhitenev, Heayoung Yoon, Paul Haney Thin film solar cells are based on polycrystalline materials that are structurally and electronically non-uniform. The power conversion efficiency of these inhomogeneous devices is currently well below theoretical limits. To effectively mitigate the recombination sources and further boost the efficiency in such systems, it is highly desirable to understand how the grain cores (GCs), grain boundaries (GBs), and other local variations of composition affect the overall photoelectronic properties of devices. Electron beam induced current (EBIC) is a powerful technique which directly measures the local collection efficiency of excited charge carriers. To achieve the desired high spatial resolution, the size of the electron-hole bulbs has to be minimized, which, in turn, means that the carriers are created within an immediate proximity of the exposed surface. We systematically examine the surface contribution to EBIC by comparing different solar cell devices varying surface preparation and passivation methods, and by analyzing the injection level-dependence of EBIC. We discuss new approaches to quantify the surface field and recombination including EBIC measurements in thin lamella geometry, beam injection parallel to the surface, and in-situ gating. [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