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    Green Photonics Presentations

    Renewable Energy Generation: Fusion and Photovoltaics: Part I
    (ordered chronologically by session start time)

    TiO2 anode materials for lithium-ion batteries with different morphology and additives
    Paper 8987-68

    Author(s):  Xiang Liu, The Univ. of Hong Kong (Hong Kong, China), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 1: Transparent Conducting Oxides
    Date and Time: 2/2/2014 8:50AM

    Lithium-ion batteries (LIBs) are among the most promising technologies for safe and stable energy storage. Titanium dioxide (TiO2) is considered as one of the alternative anode materials to graphite due to its low-cost, abundant, eco-friendly and chemical stability, especially for high operating voltage (~1.5 V) of TiO2, which may enable extra cycle life as well as enhance safety. Here we studied the dependence of LIB performance on the morphology of TiO2 nanostructures used for anode preparation, with and without the addition of multi-wall carbon nanotubes, fullerene and reduced graphene oxide. The obtained results were discussed in detail.


    Uniform algal growth in photo-bioreactors using surface scatterers
    Paper 8976-18

    Author(s):  Syed S. Ahsan, Cornell Univ. (United States), et al.
    Conference 8976: Microfluidics, BioMEMS, and Medical Microsystems XII Session 4: Applications I
    Date and Time: 2/2/2014 5:10PM

    In this work, we present a unique scatterer design to integrate within bioreactors for algal fuel production. Light is coupled into slab waveguides which are enhanced with surface scatterers delivering light to the algae in bioreactors. Angular scattering measurements with multiple light input angles and at different points on the slab waveguide reveal varying angular scattering profiles. To simulate a thin biofilm integrating over all scattering angles, shallow channel dye experiments are conducted. From the extinction coefficients of these experiments, a gradient distribution is designed to achieve uniform scattering intensity that can sustain algal growth.


    Focal zooming improvements to make fusion Ignition achievable
    Paper 8962-18

    Author(s):  Seth Pace, Central Carolina Community College (United States), et al.
    Conference 8962: High Energy/Average Power Lasers and Intense Beam Applications VIII Session 5: Other High Power Lasers and Applications
    Date and Time: 2/2/2014 5:30PM

    The sun produces energy through a process called fusion, and scientists are getting close to recreating this phenomenon here on earth. We hope that one day fusion energy will be a clean alternative energy source compared to fission which takes place in nuclear power plants already. Fusion could be the alternative energy of our future if we can just get it to work. Fusion uses high power lasers fired simultaneously, the laser beams are amplified and then converged onto a fuel target, which implodes and fusion energy is released. Can adjustments be made to the fusion ignition process to make it possible first and then cost effective enough to duplicate? Changes to focal zooming of laser beams could be the answer to getting fusion ignition to work.


    Atomic collision effect during PLD processes: nonstoichiometry control in transparent superconductors
    Paper 8987-21

    Author(s):  Taro Hitosugi, Tohoku Univ. (Japan), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 5: Highly-Correlated Oxides I
    Date and Time: 2/3/2014 8:00AM

    Developing high-capacity lithium ion batteries is an important research in materials science, and the realization of high-quality thin films of lithium metal oxides is a step toward this goal. Pulsed laser deposition (PLD) is a method of creating such films. In this technique, atoms from a lithium-containing source land on a substrate surface through a ‘plume.’ We have made a discovery that should significantly improve the quality of PLD lithium-based thin films thanks to a model that describes collisions between high-energy atoms in the plume. Further we developed ‘transparent conductor’ by optimizing the stoichiometry. (Packwood et al., Phys. Rev. Lett. 111, 036101 (2013))


    High-efficiency nanopillar solar cells employing wide-bandgap minority carrier recombination barriers
    Paper 8981-50

    Author(s):  Giacomo Mariani, Univ. of California, Los Angeles (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 1: Physics of Nano-Engineered Photovoltaics I
    Date and Time: 2/3/2014 8:10AM

    The study delves into the characterization of different high-bandgap in-situ passivation shells applied to axial GaAsP NP photovoltaics. InGaP (direct bandgap) and GaP (indirect bandgap) are exploited as two different minority-carrier barriers to prevent surface recombination. Optoelectronic modeling correlated to experimental results highlights Voc values extremely dependant on the energy bandgap of the epitaxial passivation barrier. Under AM 1.5G conditions, VOC of 0.77 V, JSC of 16.7 mA/cm^2, fill factors of 71 % are measured, leading to PCE of 9.14 %.


    The effects of electric field on InGaAs quantum well i-region placement in InAlGaAs solar cells
    Paper 8981-2

    Author(s):  Christopher G. Bailey, U.S. Naval Research Lab. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 1: Physics of Nano-Engineered Photovoltaics I
    Date and Time: 2/3/2014 9:00AM

    The performance of quantum well embedded photovoltaic devices has shown a dependence on the location of the QWs in the i-region, as the collection of carriers generated in these structures can be highly dependent on the electric field as well as the magnitude of Shockley-Reed-Hall recombination. In this investigation, the benefits of QWs in varying locations within the i-region will be considered. Experimental device performance will be studied via standard photovoltaic device measurements. Results will be presented discussing the potential for the use of QWs for devices attempting to mitigate various degradation effects typical in solar cell applications.


    Absorption enhancement and dark current reduction in quantum-dot solar cells
    Paper 8981-4

    Author(s):  Seth M. Hubbard, Rochester Institute of Technology (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 1: Physics of Nano-Engineered Photovoltaics I
    Date and Time: 2/3/2014 9:40AM

    Quantum dot (QD) superlattices have been proposed as a means to harness the lower energy photons normally lost to transmission, extending the absorption range of solar cells and thus increasing the short-circuit current. We have investigated the effects of QD solar cell design on both absorption and open circuit voltage. Initial experiments showed the emitter-shifted QD devices exhibit a marked decrease in open-circuit voltage and fill factor. This behavior was attributed to non-negligible n-type background doping in the intrinsic region. In addition, utilizing thin film QD devices shows that sub-bandgap current increased due to the contribution of the QDs and the thin film process. Results demonstrate that enhancement of the electric field in the infrared (due to the cavity formed by the thin film device) can be effectively used to improve the QD absorption and carrier collection.


    Preparation and study of artificial graphene-type semiconductor superlattices
    Paper 8981-5

    Author(s):  Daniel Vanmaekelbergh, Utrecht Univ. (Netherlands), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 2: Emerging Photovoltaic Materials
    Date and Time: 2/3/2014 10:30AM

    The interest in 2-dimensional systems with a honeycomb lattice and related Dirac-type electronic bands has exceeded the prototype graphene. We show that atomically coherent honeycomb superlattices of rocksalt (PbSe, PbTe) and zincblende (CdSe, CdTe) semiconductors can be obtained by nanocrystal self-assembly and subsequent cation exchange. These artificial graphene systems combine Dirac-type electronic bands with the beneficial properties of a semiconductor, such as the presence of a band gap and strong spin-orbit coupling; separated conduction 1S and 1P Dirac cones of considerable bandwidth (100 meV) are predicted, as well as dispersionless P-bands. We will also present the first experimental results dealing with the band structure (obtained by cryogenic STM) and the first carrier transport measurements and discuss possible applications of these high-mobility systems in single-photon detection and photovoltaic cells.


    Group IV clathrates: synthesis, optoelectonic properties, and photovoltaic applications
    Paper 8981-6

    Author(s):  Adele C. Tamboli, Colorado School of Mines (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 2: Emerging Photovoltaic Materials
    Date and Time: 2/3/2014 11:00AM

    Although Si dominates the photovoltaics market, only two forms of Si are common: amorphous Si and Si in the diamond structure. Silicon can form in other allotropes, including clathrate structures, inclusion compounds consisting of a Si framework surrounding templating guest atoms, which can later be removed. Si-Ge clathrate alloys have a direct band gap that is tunable from 1.9 to 0.6 eV, enabling a variety of applications. We are exploring the potential of this class of materials for optoelectronic and photovoltaic applications using electronic structure calculations, powder synthesis, film synthesis, and optical and structural characterization.


    New approaches for improving the photovoltaic performances of kesterite Cu2ZnSn(S,Se)4 thin film solar cells
    Paper 8981-7

    Author(s):  Giovanni Altamura, CEA Grenoble (France), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 2: Emerging Photovoltaic Materials
    Date and Time: 2/3/2014 11:30AM

    Quaternary Cu2ZnSn(S,Se)4 (CZTSSe) compounds have attracted a lot of attention as promising absorber materials for thin film solar cells although the efficiency is not yet comparable with other thin film solar cell technologies. In the present work, two different approaches are explored to improve CZTSSe-based solar cell performances: (i) changing the back contact (BC) and (ii) introducing [S]/([S]+[Se]) ratio gradients in the CZTSSe absorber. To the best of our knowledge, no experimental study has been carried out so far to test whether CZTSSe solar cells built on a BC other than Mo could exhibit better photovoltaic properties. For this purpose various metals (Au, W, Pd, Pt, Ni) are deposited as BC, and it is demonstrated that it is possible to synthesize device-quality CZTSSe thin films on W, Au and Pt back contacts. It is shown that that W and Au back contacts allow enhancing the photogenerated current, but that Mo remains the best back contact in terms of power conversion efficiency. The effects of [S]/([S]+[Se]) ratio tuning on CZTSSe based solar cell performances are studied by solar cell capacitance simulator (SCAPS) to find out the optimum absorber composition. The simulations show that if the sulfur content is linearly decreased in the CZTSSe absorber from the back contact towards the buffer layer, then the power conversion efficiency can be increased by 5% (absolute) compared to the case of a homogenous absorber. Based on these results, we propose that bandgap engineering based on the control of [S]/([S]+[Se]) ratio in the CZTSSe absorber is a powerful tool for improving the photovoltaic performances of CZTSSe-based solar cells.


    Growth model of transparent conductive graphene
    Paper 8982-10

    Author(s):  Shih-Hao Chan, National Central Univ. (Taiwan), et al.
    Conference 8982: Optical Components and Materials XI Session 2: Nanophotonics
    Date and Time: 2/3/2014 11:40AM

    In this study, we elucidate the growth model of graphene and analysis the graphene grain boundaries by ambient chemical vapor deposition system under different hydrogen flow rates from 10 to 50 sccm. The grain density decreased with increasing hydrogen flow rate. We obtained an optimal of electrical value with 30 sccm of hydrogen flow rate. The intensity ratios of 2D and D peaks to G peak were 2.29 and 0.07, respectively. The single layer graphene shows the lowest sheet resistance value of 310 Ω/□ and the value reduced to 180Ω/□ by HNO3 doping method.


    Micrometric characterization methods of thin-film solar cells using luminescence emissions
    Paper 8981-8

    Author(s):  Amaury Delamarre, Institut de Recherche et Développement sur l'Energie Photovoltaïque (France), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 2: Emerging Photovoltaic Materials
    Date and Time: 2/3/2014 11:50AM

    Spatial characterization methods of solar cells allow investigating carrier transports as well as spatial fluctuations of the optoelectronic properties. In CIGS cells, variations of minority carrier lifetimes and collection efficiencies are reported, and their influence on the efficiencies needs to be clarified. To this purpose, we record spectrally resolved photoluminescence and electroluminescence images in absolute values, with spatial resolution below 2 µm. From electroluminescence emissions, spatial carrier collection efficiencies are obtained with the reciprocity relations. From photoluminescence, maps of the quasi-Fermi level splitting are determined. Comparison with electroluminescence images allows distinguishing variations of carrier lifetime properties and collection efficiencies.


    Upconverter materials and upconverter solar-cell devices: Simulation and characterization with broad solar spectrum illumination
    Paper 8981-9

    Author(s):  Stefan Fischer, Fraunhofer-Institut für Solare Energiesysteme (Germany), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 3: Up-Conversion and Spectral Shaping
    Date and Time: 2/3/2014 1:30PM

    Upconversion of sub-band-gap photons has the potential to increase the efficiency of solar cells. We investigate Er3+-doped beta-NaYF4 to determine the upconversion quantum yield under monochromatic laser and broad-band excitation as well as under solar concentration. These results can be compared to our comprehensive rate equation model describing upconversion processes. Line shape functions of all absorption and emission processes have been incorporated into the model to simulate the upconversion quantum yield under broad-band excitation. Upconversion solar cell devices have been fabricated and show an increase of the short-circuit current density due to upconversion of 13.1 mA/cm2 under a concentration of 210 suns.


    Cutoff wavelength optimization for high-efficiency split spectrum photovoltaics
    Paper 8981-11

    Author(s):  Chandler Downs, Tufts Univ. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 3: Up-Conversion and Spectral Shaping
    Date and Time: 2/3/2014 2:20PM

    Split spectrum photovoltaics are an exciting recent development in the solar energy field. This technology has the potential to exceed record conversion efficiencies by utilizing a large number of active p-n junctions while mitigating the constraints that plague monolithic cells: lattice matching and current matching. In this work, we examine a split spectrum system utilizing a single spectrum splitting device to divide the solar spectrum onto two cells, each with multiple active junctions. A number of different cutoff frequencies are examined, with promising designs simulated using TCAD Sentaurus, grown by MBE, fabricated, and tested.


    Interdependence of reabsorption and internal energy losses in luminescent solar concentrators
    Paper 8981-12

    Author(s):  Jennefir Digaum, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 3: Up-Conversion and Spectral Shaping
    Date and Time: 2/3/2014 2:40PM

    As a complementary device to photovoltaic (PV) cells, luminescent solar concentrators (LSCs) can reduce the cost of solar energy by replacing the expensive PV material with inexpensive energy-harvesting plastic or glass matrix. The low efficiency of conventional LSCs is due to the various losses associated with light harvesting and trapping. State-of-the-art LSC technology focuses on decreasing reabsorption by employing lumophores with large Stokes shift. However, it is shown that there is an optimum Stokes shift that yields the best LSC efficiency. More importantly, engineering and employing high-quantum-yield dyes with optimized Stokes Shift yields the highest energy efficiency.


    Quantum coherence controls the charge separation in a prototypical artificial light-harvesting system
    Paper 8984-23

    Author(s):  Christoph Lienau, Carl von Ossietzky Univ. Oldenburg (Germany), et al.
    Conference 8984: Ultrafast Phenomena and Nanophotonics XVIII Session 6: Coherent Optical Phenomena I
    Date and Time: 2/3/2014 2:45PM

    The efficient conversion of light into electricity or chemical fuels is a fundamental challenge. In artificial photosynthetic and photovoltaic devices, this conversion is generally thought to happen on ultrafast, femto-to-picosecond timescales and to involve an incoherent electron transfer process. In some biological systems, however, there is growing evidence that the coherent motion of electronic wavepackets is an essential primary step, raising questions about the role of quantum coherence in artificial devices. Here we investigate the primary charge-transfer process in a supramolecular triad, a prototypical artificial reaction centre. Combining high time-resolution femtosecond spectroscopy and time-dependent density functional theory, we provide compelling evidence that the driving mechanism of the photoinduced current generation cycle is a correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We highlight the fundamental role of the interface between chromophore and charge acceptor in triggering the coherent wavelike electron-hole splitting.


    Ab-initio studies of nanoparticle photovoltaics: multiple-exciton generation, exotic core-phase nanoparticles, and complementary transport channels
    Paper 8981-13

    Author(s):  Gergely T. Zimányi, Univ. of California, Davis (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 4: Advanced Photovoltaic Concepts: MEG and Hot Carrier Solar Cells
    Date and Time: 2/3/2014 3:30PM

    We report ab-initio studies of nanoparticles for photovoltaic applications. (1) The Multiple Exciton Generation (MEG) rate is determined for Si nanoparticles up to sizes of 220 Si atoms and rate-enhancing strategies are explored. (2) Exotic core phase Si nanoparticles, including Si III/BC8 offer promisingly low gaps. (3) Si/Ge nanoparticles embedded in ZnS matrices are explored. The analysis of the band-alignment shows that the electrons transport through the nanoparticles, by tunneling, whereas the holes form complementary transport channels in the host matrix, reducing recombination rates. (4) A kinetic Monte Carlo work is then reported to directly model these complementary transport channels.


    The role of coherence for light-trapping in thin-film silicon solar cells
    Paper 8984-24

    Author(s):  Martin Aeschlimann, Technische Univ. Kaiserslautern (Germany), et al.
    Conference 8984: Ultrafast Phenomena and Nanophotonics XVIII Session 7: Coherent Optical Phenomena II
    Date and Time: 2/3/2014 3:45PM

    The absorption of thin-film solar cells can be enhanced by increasing the effective light path in the absorptive layer via light trapping. We investigate amorphous thin-film Si solar cells with nanotextured interfaces by means of optical spectral interferometry and coherent two-dimensional nanoscopy. The observed hot-spot photoemission, the long coherence lifetimes of about 100 fs, and a statistical distribution of resonance frequencies reveale the existence of strongly localized electric field distributions in the absorptive Si layer. These localized photonic modes enhance the absorption and thereby also the efficiency of the photovoltaic cells.


    Optical Phonon Decay In Cubic Semiconductors: A Hot Carrier Solar Cell Picture
    Paper 8981-14

    Author(s):  Hugo Levard, EDF Recherche & Développement (France), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 4: Advanced Photovoltaic Concepts: MEG and Hot Carrier Solar Cells
    Date and Time: 2/3/2014 4:00PM

    One of the HCSC main challenges is to find an absorber material in which the electro-emitted hot phonons has a relaxation time longer than the carriers cooling time, so that we can expect the electron to “reabsorb” a phonon, slowing down the electronic cooling. HCSC yield is ultimately limited by LO phonon decay. Here, we present theoretical results from ab initio calculations on III-V and IV-IV compounds describing the electronic and phononic band structure. In the particular case of zinc-blende-SiSn, the phonon lifetime due to three-phonon decay processes is found to be very long compared to most III-V and IV-IV semiconductors.


    Ultrathin metals and nano-structuring for photonic applications
    Paper 8982-17

    Author(s):  Valerio Pruneri, ICFO - Institut de Ciències Fotòniques (Spain), et al.
    Conference 8982: Optical Components and Materials XI Session 4: Metamaterials and Plasmonics
    Date and Time: 2/3/2014 4:00PM

    Ultrathin materials and nano-structuring are becoming essential for the functionalization of optical surfaces. In the talk we will show how ultrathin metals can be exploited to create competitive transparent electrodes. At the same time they can be used to create nanostructured surfaces through mass scalable dewetting and etching techniques. After presenting the techniques we will focus on the applications made possible by these materials and technologies, including self-cleaning or easy-to-clean display screens, efficient indium-free light emitting diodes and photovoltaics, antireflective structures for the laser industry and super-wetting surfaces for biology.


    Hot-carrier solar cell spectral insensitivity: Why develop the hot carrier solar cell when we have multi-junction devices?
    Paper 8981-15

    Author(s):  Louise C. Hirst, U.S. Naval Research Lab. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 4: Advanced Photovoltaic Concepts: MEG and Hot Carrier Solar Cells
    Date and Time: 2/3/2014 4:20PM

    Multi-junction and hot carrier devices have comparable limiting efficiency however, multi-junction devices are at a much more advanced stage of development. In this paper we address the question “Why develop the hot carrier solar cell when we have multi-junction devices?” We calculate material parameters required to produce hot carrier efficiency comparable to multi-junction devices and identify spectral insensitivity of hot carrier solar cells as a key motivation for this development. We show hot carrier solar cells are much less sensitive to seasonal and diurnal spectral changes, enhancing annual energy yields. Performance of these devices is also less location dependent.


    Metamaterial selective emitters for photodiodes
    Paper 8982-18

    Author(s):  Dante F. DeMeo, Tufts Univ. (United States), et al.
    Conference 8982: Optical Components and Materials XI Session 4: Metamaterials and Plasmonics
    Date and Time: 2/3/2014 4:30PM

    This work demonstrates a metamaterial (MM) emitter for potential use with energy harvesting photodiodes, such as thermophotovoltaic cells. Preliminary structures have been designed, simulated, and fabricated using CST Microwave Studio, and microfabrication techniques including electron beam evaporation, atomic layer deposition, and electron beam lithography. Fabricated samples match the simulation results very well. High temperature robustness and emission has been tested up to 1000C.


    Hot-carrier solar cell absorbers: materials, mechanisms, and nanostructures
    Paper 8981-16

    Author(s):  Gavin Conibeer, The Univ. of New South Wales (Australia), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 4: Advanced Photovoltaic Concepts: MEG and Hot Carrier Solar Cells
    Date and Time: 2/3/2014 4:40PM

    The Hot Carrier solar cell is a Third Generation device that aims to tackle the carrier thermalisation loss after absorption of above band-gap photons. It is theoretically capable of efficiencies very close to the maximum thermodynamic limit. It relies on slowing the rate of carrier cooling in the absorber from ps to ns. This challenge can be addressed through nanostructures and modulation of phonon dispersions. The mechanisms of carrier cooling are discussed and methods to interrupt this process investigated to give a list of properties required of an absorber material. Quantum well or nano-well structures and large mass difference compounds with phonon band gaps are discussed in the context of enhancing phonon bottleneck and hence slowing carrier cooling. Materials for these structures are discussed and potential combined structures to maximize phonon bottleneck and slow carrier cooling are suggested.


    Flexible binder free functionalized carbon nanotube electrodes for ultracapacitor
    Paper 8987-89

    Author(s):  Badekai Ramachandra Bhat, National Institute of Technology, Karnataka (India), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 8: Growth, Properties, and Applications of Nanostructures
    Date and Time: 2/3/2014 5:50PM

    The dramatic development of portable electronics and wearable electronics such as e-paper, sportswear, embedded health monitoring device and other flexible devices, power sources with superior flexibility become an important demand during the past few years. In order to full fill these requirements, it is important to prepare flexible electrode material for ultracapacitor. In this article we are introducing simple method for the preparation of binder free flexible functional multiwalled carbon nanotube electrode material for ultracapacitor. The prepared flexible ultracapacitor test cell exhibit a specific capacitance of 50 Fg-1 at a current density of 1mAcm-2 with excellent cycle stability.


    Combined dielectric spectroscopy and laser-induced photocurrent approach to study the degradation of organic solar cells
    Paper 8975-15

    Author(s):  Olena Kozlova, Johannes Kepler Univ. Linz (Austria), et al.
    Conference 8975: Reliability, Packaging, Testing, and Characterization of MOEMS/MEMS, Nanodevices, and Nanomaterials XIII Session 3: Session 3
    Date and Time: 2/4/2014 8:40AM

    Solar energy becomes increasingly popular as a clean source of renewable energy. While organic electronics offers new solutions for photovoltaics, stability of organic solar cells is still a key issue preventing them from entering large-scale markets. In this work we address the degradation of organic solar cells using impedance spectroscopy and current voltage (I-V) measurements. Local degradation is investigated employing the laser-beam-induced current (LBIC) technique.By combining the three methods it is possible to look at organic solar cell degradation from different points and follow different aspects. We study and compare several P3HT:PCBM solar cells to understand the reasons and speed of degradation. Work partially supported by ESTABLIS.


    Silicon tandem solar cells: The ultimate photovoltaic solution?
    Paper 8981-18

    Author(s):  Martin A. Green, The Univ. of New South Wales (Australia), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 5: Advances Toward Tandems with Active Silicon Subcells
    Date and Time: 2/4/2014 10:30AM

    The recent dramatic cost reduction in silicon cell technology has made this technology even more difficult to displace. Commercial cell efficiencies will steadily approach the 25% laboratory performance level demonstrated in the author's group. The availability of cheap, increasingly high quality silicon wafers suggests a possible evolutionary path whereby these are used as substrates for high performance silicon-based tandem cells with efficiency levels potentially as high as 40%. Possible approaches and results to date will be outlined.


    Optical requirements for >30% tandem solar cells built on crystalline silicon
    Paper 8981-19

    Author(s):  Niraj N. Lal, The Australian National Univ. (Australia), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 5: Advances Toward Tandems with Active Silicon Subcells
    Date and Time: 2/4/2014 11:10AM

    Tandem cells based on high-efficiency c-Si solar cells can potentially lead to much higher solar cell efficiencies and lower costs of solar energy. Applying a simple analytical model, we present key design parameters for optimising light distribution in these devices. Low-pass intermediate reflectors are observed to be detrimental to tandem performance and single-pass absorption is identified to be preferable to Lambertian light trapping with typical losses. We apply these principles to a realistic tandem cell and show that efficiencies greater than 30% are possible using top cell thin film absorbers with carrier diffusion lengths of 100nm and luminescence efficiencies of 10^-5.


    Advances in III-V/active-silicon multijunction photovoltaics for high efficiency
    Paper 8981-20

    Author(s):  Steven A. Ringel, The Ohio State Univ. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 5: Advances Toward Tandems with Active Silicon Subcells
    Date and Time: 2/4/2014 11:30AM

    Recent advances in the nucleation of high-quality GaP and subsequent growth of metamorphic GaAsP layers on Si by both MOCVD and MBE have opened a viable pathway for high-performance III-V/active-Si multijunction PV devices. Realistic modeling indicates that a 4-junction cell of this architecture can achieve >48% efficiency under concentration. This requires optimization of not only the III-V, but also the Si sub-cells, with respect to requirements of photovoltaic performance and growth-related practicalities. This presentation will describe the design and experimental progress toward III-V/active-Si multijunction photovoltaic materials and devices grown by MOCVD and MBE.


    Efficient Auger-assisted upconversion in PbSe/CdSe core/shell colloidal quantum dots
    Paper 8996-18

    Author(s):  Nikolay S. Makarov, Los Alamos National Lab. (United States), et al.
    Conference 8996: Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling XI Session 5: Quantum Dot Emission
    Date and Time: 2/4/2014 11:40AM

    Efficient upconversion in colloidal quantum dots (QDs) is of immediate interest for three-dimensional microscopy and solar energy conversion. We demonstrate that appropriately engineered PbSe/CdSe core/shell QDs allow for highly efficient upconversion of infrared radiation via a novel mechanism of Auger re-excitation. Specifically, we show that even with moderate pump fluences, that can be achieved with a 1000-fold concentration of solar radiation, we can upconvert almost 75% of absorbed infrared photons. Our findings suggest that these novel core/shell nanostructures may be utilized for enhancing power conversion efficiency of practical photovoltaic devices by allowing for more efficient harvesting of low-energy solar photons.


    Modeling intermediate band solar cells: a roadmap to high efficiency
    Paper 8981-21

    Author(s):  Jacob J. Krich, Univ. of Ottawa (Canada), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 6: Intermediate Band Solar Cells
    Date and Time: 2/4/2014 1:30PM

    Intermediate band (IB) photovoltaics have the potential to be highly efficient and cost effective solar cells. When the IB concept was proposed in 1997 [1], there were no known intermediate band materials. In recent years, great progress has been made in developing materials with intermediate bands, though power conversion efficiencies have remained low [2,3]. To understand the material requirements to increase IB device efficiencies, we must develop good models for their behavior under bias and illumination. To evaluate potential IB materials, we present a figure of merit, consisting of parameters that can be measured without solar cell fabrication. We present a new model for IB devices, including the behavior of their junctions with n- and p-type semiconductors. Using a depletion approximation, we present analytic approximations for the boundary conditions of the minority carrier diffusion equations. We compare the analytic results to Synopsys Sentaurus device models. We use this model to find the optimal thickness of the IB region based on material parameters. For sufficiently poor IB materials, the optimal thickness is zero – i.e., the device is more efficient without the IB material at all. We show the minimum value of the figure of merit required for an IB to improve the efficiency of a device, providing a clear goal for the quality of future IB materials.


    Simulation of an intermediate-band solar cell comprising superlattices of electronically-mismatched semiconductor alloys
    Paper 8981-22

    Author(s):  Alexandre Freundlich, Univ. of Houston (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 6: Intermediate Band Solar Cells
    Date and Time: 2/4/2014 2:00PM

    Here we evaluate the viability of an intermediate band solar cell design, wherein a superlattice, comprising lattice-matched layers of electronically mismatched GaAs1-x(Sb)Nx (x<0.04) and thin barriers of AlxGa1-xAs (x<0.3), is inserted within the intrinsic region of a wide bandgap AlGaAs p-i-n diode. A detailed balance evaluation of the proposed device that incorporates calculation of the absorption properties of the SL region and the host AlGaAs suggests potential for exceeding 1sun and 1000 sun efficiencies of 38% and 52% respectively. Finally the influence of device design parameters upon efficiency and radiation tolerance is evaluated using drift diffusion-based simulations.


    Imaging quasi fermi level splitting in intermediate-band solar cells
    Paper 8981-23

    Author(s):  Jean-François Guillemoles, Institut de Recherche et Développement sur l'Energie Photovoltaïque (France), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 6: Intermediate Band Solar Cells
    Date and Time: 2/4/2014 2:20PM

    An intermediate band solar cell (IBSC) would be able to provide the same conversion efficiency as a triple junction, in principle, due to the 3 allowed interband optical transition in the material. A long searched hallmark for IBSC operation is the identification of these 3 transitions where the quasi fermi level (QFL) separation of carriers corresponding to the high energy transition is the sum of the 2 others. Systems conjectured to be able to display IBSC photovoltaic conversion include III-V heterostructures like MQW and Multiple QD, wher some partial evidence of such effect has been found. The present work associates state of the art quantum confined heterostructures with a calibrated hyperspectral imager able to map quasi fermi level splitting of transitions in the NIR-visible range. Using this tool, the QFL corresponding to the various transitions has been measured in several samples and will be discussed during the presentation.


    InAs/AlAsSb self-assembled quantum dots for next-generation solar cells
    Paper 8981-24

    Author(s):  Ramesh Babu Laghumavarapu, Univ. of California, Los Angeles (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 6: Intermediate Band Solar Cells
    Date and Time: 2/4/2014 2:40PM

    We have investigated type-II InAs QDs in AlAsSb barriers on InP substrates with close-to-ideal band gaps and alignments for IBSC applications. We demonstrate an optimized cladding scheme for this QD system that has GaAs under the QDs and GaAsSb as the capping layer. Solar cells devices fabricated with QDs and cladding layers are compared with control cells containing no QDs. AlAsSb solar cells with InAs QDs show extended photo response beyond the AlAsSb band gap upto 1.8 microns. Low temperature quantum efficiency measurements are performed in presence of secondary infrared light to study two-photon absorption in InAs/AlAsSb QD solar cells.


    Increased radiation tolerance in thin IMM solar cells using back reflection
    Paper 8981-26

    Author(s):  Akhil Mehrotra, Univ. of Houston (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 7: Space Photovoltaics and Radiation Effect
    Date and Time: 2/4/2014 4:10PM

    In this work we have evaluated thickness dependent efficiency of 3J and 4J-IMM solar cells as a function of radiation doses and dislocations. It's been shown that bottom 0.7ev InGaAs sub-cell's radiation resistance and/or dislocation tolerance can be improved by use of back gold reflection. Back reflection results in fabrication of thinner sub-cells thus increasing the radiation hardness of the sub-cells. It's been shown that for moderate to high doses of radiation, very high EOL efficiencies can be afforded with substantially higher dislocation densities than those commonly perceived as acceptable for IMM devices i.e. even in the presence of dislocation densities in both sub-cells as large as 10^7cm-2, for typical 10^15cm-2 1MeV electron fluence, a remaining power factor >85% (ηEOL~32%). These finding could in turn be used to simplify manufacturing (thinner graded buffers) or/and increase yield for IMM space cells and also explain the irregular radiation behavior seen in 4J-IMMs.


    Laser texturing glass substrates for light in-coupling in silicon thin-film solar cells
    Paper 8967-50

    Author(s):  Kambulakwao Chakanga, Next Energy (Germany), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session PTue: Posters-Tuesday
    Date and Time: 2/4/2014 6:00PM

    A 1064 nm pico second laser is used to texture the glass surface to reduce the reflection losses and achieve light scattering in silicon thin film solar cells. The effect of the laser treatment on three different multi-component glasses (SCHOTT Eco, Corning Eagle XG and Saint Gobain Diamond White) is compared. Atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-VIS Spectroscopy and angular resolved measurements are used to characterize the resulting textures respectively optical behavior.


    Ferrite engineering for oxide spintronics and photonics
    Paper 8987-32

    Author(s):  Hitoshi Tabata, The Univ. of Tokyo (Japan), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 12: Energy Harvesting Storage: Materials and Devices
    Date and Time: 2/5/2014 8:00AM

    Recently, many of interests are focused on the development of magnetic semiconductors due to various advantages Among these materials, ferrite oxides such as Fe2O3 Fe3O4 are regarded as a promising system because of their probabilities of band gap engineering and environmental compatibility as the green photonics. Here we have reported our two topics on spintronics of oxide electronics and photonincs (1) Hetero epitaxial p-n junctions of magnetic oxides based on spinel type ferrite and their polaron conducting and magnetic properties. (2) Ferrite engineering for light energy harvesting system such as the solid-liquid type solar cells formed by Fe2O3 hetero structures.


    One step lithography-less silicon nanomanufacturing for low cost, high-efficiency solar cell production
    Paper 8974-49

    Author(s):  Yi Chen, Univ. of Illinois at Urbana-Champaign (United States), et al.
    Conference 8974: Advanced Fabrication Technologies for Micro/Nano Optics and Photonics VII Session 8: Large Area Fabrication
    Date and Time: 2/5/2014 8:30AM

    To improve light absorption, previously various antireflection material layers were created on solar wafer surface including multilayer dielectric film, nanoparticle sludges, microtextures, noble metal plasmonic nanoparticles and 3D silicon nanostructure arrays. All of these approaches involve nanoscale prepatterning, surface-area-sensitive assembly processes or extreme fabrication conditions; therefore, they are often limited by the associated high cost and low yield as well as the consequent industry incompatibility. In comparison, our nanomanufacturing, an unique synchronized and simultaneous top-down and bottom-up nanofabrication approach called simultaneous plasma enhanced reactive ion synthesis and etching (SPERISE), offers a better antireflection solution along with the potential to increase p-n junction surface area. High density and high aspect ratio anechoic nanocone arrays are repeatedly and reliably created on the entire surface of single and poly crystalline silicon wafers as well as amorphous silicon thin films within 5 minutes under room temperature. The nanocone surface had lower than 5% reflection over the entire solar spectrum and a desirable omnidirectional absorption property. Using the nanotextured solar wafer, a 156mm × 156mm 18.1%-efficient black silicon solar cell was fabricated, which was an 18.3% enhancement over the cell fabricated by standard industrial processes. This process also reduces silicon loss during the texturing step and enables tighter process control by creating more uniform surface structures. Considering all the above advantages, the demonstrated nanomanufacturing process can be readily translated into current industrial silicon solar cell fabrication lines to replace the costly and ineffective wet chemical texturing and antireflective coatings.


    Ag nanowire-embedded ITO thin films as a near-infrared transparent and flexible anode for the flexible organic solar cells
    Paper 8987-61

    Author(s):  Han-Ki Kim, Kyung Hee Univ. (Korea, Republic of), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 12: Energy Harvesting Storage: Materials and Devices
    Date and Time: 2/5/2014 9:00AM

    We investigated Ag nanowire (NW) network embedded in transparent ITO electrodes fabricated on collarless PI substrate for flexible organic solar cells (FOSCs). By embedding Ag NWs network between ITO thins films using simple brush painting method, we achieved a flexible ITO/Ag NW/ITO multilayer electrode with a low sheet resistance of 38.7 Ohm/square and a high diffusive transmittance of 87.62 % as well as superior mechanical flexibility. The existence of the Ag NW network led to a metallic conductivity, high near infrared transparency, and mechanical durability of the ITO/Ag NW/ITO multilayer. These indicate that the Ag NW embedding into the ITO films is a key solution to solve the critical drawbacks of the conventional ITO electrodes or Ag NW network film. Better performances of the FOSC with the ITO/Ag NW/ITO multilayer electrode to those of the FOSC with a conventional ITO electrode demonstrate that the flexible ITO/Ag NW/ITO electrode is a promising alternative to ITO films for high performance FOSCs.


    Design of sub-wavelength dielectric antireflective grading for multijunction concentrator photovolatics
    Paper 8981-32

    Author(s):  Wei Wang, Univ. of Houston (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 8: Advanced Designs for Concentrator Photovoltaics
    Date and Time: 2/5/2014 9:20AM

    In III-V concentrator applications, sunlight is focused with wide angular distribution that limits the effectiveness of conventional thin-film AR coatings. Furthermore the transmission properties are generally degraded non-uniformly over the electromagnetic spectrum, which in the case of multi-junction solar cells leads to additional sub-cell current matching related losses. Here, and in an attempt to identify a better alternative to the conventional 2-layer ARCs, a systematic analysis of design parameters (shape pitch) and angular dependent antireflective properties of dielectric grating formed using sub-wavelength 1D and 2D gratings for several common dielectrics showing potential of the approach for significant efficiency enhancements.


    Light trapping considerations in self-assembled ZnO nanorod arrays for quantum-dot sensitized solar cells
    Paper 8987-62

    Author(s):  Juan A. Zapien, City Univ. of Hong Kong (Hong Kong, China), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 12: Energy Harvesting Storage: Materials and Devices
    Date and Time: 2/5/2014 9:20AM

    We study light trapping effects of CdS/CdSe quantum dot sensitized solar cells assembled on ZnO nanorod arrays. Cell efficiency as it relates to array density, length and QD loading is explored. Our experimental results supported by numerical simulations using Finite Difference Time Domain (FDTD) demonstrate that, contrary to perceived conventional wisdom, a higher NRA density does not necessarily correspond to higher solar cell performance. Instead, light trapping efficiency depends significantly on the array density, QD axial distribution and index contrast between NR and the effective index of the QDs, FDTD results are used to suggest strategies for improved QDSC fabrication.


    MOCVD-grown dislocation-free InGaN nanowires with a 2.5 eV band gap for photovoltaics
    Paper 8986-43

    Author(s):  Hsun Chih Kuo, Univ. of Michigan (United States), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 8: Nanostructures and Devices II
    Date and Time: 2/5/2014 9:30AM

    We reported vertically aligned dislocation-free InGaN nanowires (NWs) with an indium composition up to 18.6% using metal-organic chemical vapor deposition (MOCVD). In this presentation, we show optical properties of these NWs. We isolate the nanowires by covering the bottom InGaN thin film with chromium. The photoluminescence (PL) agrees well with the X-ray diffraction (XRD) measurement. We show the PL peak can be shifted by changing the TMIn flow rate and is tunable from 3.4 to 2.5 eV at room temperature.


    Cu(In,Ga)Se2 mesa microdiodes: study of edge recombination and behaviour under concentrated sunlight
    Paper 8981-33

    Author(s):  Myriam Paire, Institut de Recherche et Développement sur l'Energie Photovoltaïque (France), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 8: Advanced Designs for Concentrator Photovoltaics
    Date and Time: 2/5/2014 9:40AM

    Cu(In,Ga)Se2 microcells with a mesa design are fabricated and tested. The influence of different etching techniques on the edge recombination signal is studied. It is found devices as small as 50x50 µm are not limited by edge recombination, which is remarkable compared to microcells made of crystalline materials. If the surfaces are intentionally degraded a quasi-shunting behaviour is seen at the edges. Under concentrated illumination, important Voc and efficiency gains are seen. Cartographic characterizations such as LBIC and EBIC are performed to compare these devices to structure without absorber etching.


    Oxides for sustainable photovoltaics with Earth-abundant materials
    Paper 8987-63

    Author(s):  Alexander Wagner, Technische Univ. Braunschweig (Germany), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 12: Energy Harvesting Storage: Materials and Devices
    Date and Time: 2/5/2014 9:40AM

    Energy conversion technologies are aiming to extremely high power capacities per year. Nontoxicity and abundance of the materials are the key requirements to a sustainable photovoltaic technology. Oxides are among the key materials to reach these goals. Theoretical efficiencies of ZnO/Cu2O solar cells are up to 18%. An overview of the advancements in the area is presented. Effect of the materials properties, band gap alignment and interfaces manipulation on the device efficiency is discussed. Influence of different buffer layers on the performance of an all oxide solar cell is investigated. VPE growth of Cu2O is also presented.


    Proposal for realizing high-efficiency III-nitride semiconductor tandem solar cells with InN/GaN Superstructure Magic Alloys fabricated at Raised Temperature (SMART)
    Paper 8986-45

    Author(s):  Kazuhide Kusakabe, Chiba Univ (Japan), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 8: Nanostructures and Devices II
    Date and Time: 2/5/2014 10:00AM

    We have been developing high performance InGaN-based solar cells grown on bulk GaN substrate. First, we performed comprehensive and rigorous theoretical analyses of InGaN solar cells in whole composition range paying special attention how their realistic material properties affect cell performances, in particular their effects on defects-induced current components resulting in extremely higher forward current. The solar cell must be designed/fabricated so that any defects-induced current density level must be at least one order lower than the operating photocurrent density to expect high performance. An experimentally observed serious bottleneck originating from the surface-defects on bulk GaN will be also discussed.


    Important Dates

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    26 September 2016

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    Journal of Photonics for Energy