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  • Journal article
    Alonso Alvarez D, Ekins-Daukes N, 2016,

    SPICE modelling of photoluminescence and electroluminescence based current-voltage curves of solar cells for concentration applications

    , Journal of Green Engineering, Vol: 5, Pages: 33-48, ISSN: 2245-4586

    Quantitative photoluminescence (PL) or electroluminescence (EL) experiments can be usedto probe fast and in a non-destructive way the current-voltage (IV) characteristics ofindividual subcells in a multi-junction device, information that is, otherwise, not available.PL-based IV has the advantage that it is contactless and can be performed even in partlyfinished devices, allowing for an early diagnosis of the expected performance of the solarcells in the production environment. In this work we simulate the PL- and EL-based IVcurves of single junction solar cells to assess their validity compared with the true IV curveand identify injection regimes where artefacts might appear due to the limited in-planecarrier transport in the solar cell layers. We model the whole photovoltaic device as anetwork of sub-circuits, each of them describing the solar cell behaviour using the two diodemodel. The sub-circuits are connected to the neighbouring ones with a resistor, representingthe in-plane transport in the cell. The resulting circuit, involving several thousand subcircuits,is solved using SPICE.
  • Conference paper
    richards RD, Harun F, Cheong JS, Mellor AV, Hylton, wilson T, Thomas T, Ekins-Daukes, David JPRet al.,

    GaAsBi: An Alternative to InGaAs Based Multiple Quantum Well Photovoltaics

    , 43rd IEEE Photovoltaic Specialists Conference
  • Journal article
    Alonso Alvarez D, Ekins-Daukes N, 2016,

    Photoluminescence-Based Current-Voltage Characterisation Of Individual Subcells In Multi-Junction Devices

    , IEEE Journal of Photovoltaics, Vol: 6, Pages: 1004-1011, ISSN: 2156-3381

    We demonstrate a photoluminescence based,contactless method to determine the current-voltagecharacteristics of the individual subcells in a multi-junctionsolar cell. The method relies upon the reciprocity relationbetween the absorption and emission properties on a solarcell. Laser light with a suitable energy is used to excitecarriers selectively in one junction and the internal voltagesare deduced from the intensity of the resultingluminescence. The IV curves obtained this way on 1J, 2Jand 6J devices are compared to those obtained usingelectroluminescence. Good agreement is obtained at highinjection conditions while discrepancies at low injection areattributed to in-plane carrier transport.
  • Journal article
    Sugiyama M, Fujii H, Katoh T, Toprasertpong K, Sodabanlu H, Watanabe K, Alonso-Álvarez D, Ekins-Daukes NJ, Nakano Yet al., 2016,

    Quantum wire-on-well (WoW) cell with long carrier lifetime for efficient carrier transport

    , Progress in Photovoltaics, Vol: 24, Pages: 1606-1614, ISSN: 1099-159X

    A quantum wire-on-well (WoW) structure, taking advantage of the layer undulation of an InGaAs/GaAs/GaAsP superlattice grown on a vicinal substrate, was demonstrated to enhance the carrier collection from the confinement levels and extend the carrier lifetime (220 ns) by approximately four times more than a planar reference superlattice. Strained InGaAs/GaAs/GaAsP superlattices were grown on GaAs substrates under exactly the same conditions except for the substrate misorientation (0 and 6 ° off). The growth on a 6 ° off substrate induced significant layer undulation as a result of step bunching and non-uniform precursor incorporation between steps and terraces, whereas the growth on a substrate without miscut resulted in planar layers. The undulation was the most significant for InGaAs layers, forming periodically aligned InGaAs nanowires on planar wells, a WoW structure. As for the photocurrent corresponding to the sub-bandgap range of GaAs, the light absorption by the WoW was extended to longer wavelengths and weakened as compared with the planar superlattice. Almost the same photocurrent was obtained for both the WoW and the planar superlattice. Open-circuit voltage for the WoW was not affected by the longer-wavelength absorption edge, and the same value was obtained for the two structures. Furthermore, the superior carrier collection in the WoW, especially under forward biases, improved fill factor compared with the planer superlattice.
  • Conference paper
    Alonso Alvarez D, Lackner D, Philipps SP, Bett AW, Ekins-Daukes NJet al., 2015,

    Photoluminescence-Based Current-Voltage Characterisation of Individual Subcells in Multi-Junction Devices

    , 31st European Photovoltaic Solar Energy Conference and Exhibition, Publisher: European Photovoltaic Solar Energy Conference and Exhibition, Pages: 1509-1513

    We demonstrate a photoluminescence based, contactless method to determine the current-voltage characteristics of the individual subcells in a multi-junction solar cell. The method, furthers known results for single junction devices and relies upon the reciprocity relation between the absorption and emission properties on a solar cell. Laser light with a suitable energy is used to excite carriers selectively in one junction and the internal voltages are deduced from the intensity of the resulting luminescence. The IV curves obtained this way on 1J, 2J and 6J devices are compared to those obtained using electroluminescence. Good agreement is obtained at high injection conditions while discrepancies at low injection are attributed to in-plane carrier transport.
  • Conference paper
    Thomas T, Wilson T, Fuhrer M, Hylton N, Ekins-Daukes N, Tan KH, Li D, Wicaksono S, Loke WK, Fatt YS, Johnson Aet al., 2015,

    Use of Double Band Anti-Crossing to Control Optical Absorption of GaAsSbN for Multi-Junction Solar Cells

    , 31st European Photovoltaic Solar Energy Conference and Exhibition
  • Journal article
    Thomas T, Mellor A, Hylton NP, Fuehrer M, Alonso-Alvarez D, Braun A, Ekins-Daukes NJ, David JPR, Sweeney SJet al., 2015,

    Requirements for a GaAsBi 1 eV sub-cell in a GaAs-based multi-junction solar cell

    , Semiconductor Science and Technology, Vol: 30, ISSN: 1361-6641
  • Journal article
    Emmott CJM, Roehr JA, Campoy-Quiles M, Kirchartz T, Urbina A, Ekins-Daukes NJ, Nelson Jet al., 2015,

    Organic photovoltaic greenhouses: a unique application for semi-transparent PV?

    , Energy & Environmental Science, Vol: 8, Pages: 1317-1328, ISSN: 1754-5706

    Organic photovoltaics are an emerging solar power technology which embody properties such astransparency, flexibility, and rapid, roll to roll manufacture, opening the potential for unique nicheapplications. We report a detailed techno-economic analysis of one such application, namely thephotovoltaic greenhouse, and discuss whether the unique properties of the technology can provideadvantages over conventional photovoltaics. The potential for spectral selectivity through the choice ofOPV materials is evaluated for the case of a photovoltaic greenhouse. The action spectrum of typicalgreenhouse crops is used to determine the impact on crop growth of blocking different spectral rangesfrom the crops. Transfer matrix optical modelling is used to assess the efficiency and spectrally resolvedtransparency of a variety of commercially available semi-conducting polymer materials, in addition to anon-commercial low-band-gap material with absorption outside that required for crop growth. Economicanalysis suggests there could be a huge potential for OPV greenhouses if aggressive cost targets can bemet. Technical analysis shows that semi-transparent OPV devices may struggle to perform better thanopaque crystalline silicon with partial coverage, however, OPV devices using the low-band-gap materialPMDPP3T, as well as a high efficiency mid-band-gap polymer PCDTBT, can demonstrate improvedperformance in comparison to opaque, flexible thin-film modules such as CIGS. These results stress theimportance of developing new, highly transparent electrode and interlayer materials, along with highefficiency active layers, if the full potential of this application is going to be realised.
  • Journal article
    Alonso-Alvarez D, Thomas T, Fuehrer M, Hylton NP, Ekins-Daukes NJ, Lackner D, Philipps SP, Bett AW, Sodabanlu H, Fujii H, Watanabe K, Sugiyama M, Nasi L, Campanini Met al., 2014,

    InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells

    , Applied Physics Letters, Vol: 105, ISSN: 1077-3118

    Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.
  • Journal article
    Yoshida M, Amrania H, Farrell DJ, Browne B, Yoxall E, Ekins-Daukes NJ, Phillips CCet al., 2014,

    Progress Toward Realizing an Intermediate Band Solar Cell-Sequential Absorption of Photons in a Quantum Well Solar Cell

    , IEEE JOURNAL OF PHOTOVOLTAICS, Vol: 4, Pages: 634-638, ISSN: 2156-3381
  • Journal article
    Piper RB, Yoshida M, Farrell DJ, Khoury T, Crossley MJ, Schmidt TW, Haque SA, Ekins-Daukes NJet al., 2014,

    Kinetic insight into bimolecular upconversion: experiment and simulation

    , RSC ADVANCES, Vol: 4, Pages: 8059-8063
  • Conference paper
    Alonso-Alvarez D, Fuehrer M, Thomas T, Ekins-Daukes Net al., 2014,

    Elements of modelling and design of multi-quantum well solar cells

    , 40th IEEE Photovoltaic Specialists Conference (PVSC), Publisher: IEEE, Pages: 2865-2870
  • Journal article
    Hylton NP, Li XF, Giannini V, Lee K-H, Ekins-Daukes NJ, Loo J, Vercruysse D, Van Dorpe P, Sodabanlu H, Sugiyama M, Maier SAet al., 2013,

    Loss mitigation in plasmonic solar cells: aluminium nanoparticles for broadband photocurrent enhancements in GaAs photodiodes

    , SCIENTIFIC REPORTS, Vol: 3, ISSN: 2045-2322
  • Journal article
    Ekins-Daukes NJ, Lee K-H, Hirst L, Chan A, Fuehrer M, Adams J, Browne B, Barnham KWJ, Stavrinou P, Connolly J, Roberts JS, Stevens B, Airey R, Kennedy Ket al., 2013,

    Controlling radiative loss in quantum well solar cells

    , JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 46, ISSN: 0022-3727
  • Journal article
    Li X, Hylton NP, Giannini V, Lee K-H, Ekins-Daukes NJ, Maier SAet al., 2013,

    Multi-dimensional modeling of solar cells with electromagnetic and carrier transport calculations

    , PROGRESS IN PHOTOVOLTAICS, Vol: 21, Pages: 109-120, ISSN: 1062-7995
  • Journal article
    Yoshida M, Ekins-Daukes NJ, Farrell DJ, Phillips CCet al., 2012,

    Photon ratchet intermediate band solar cells

    , Applied Physics Letters, Vol: 100, ISSN: 1077-3118

    In this paper, we propose an innovative concept for solar power conversion—the “photon ratchet” intermediate band solar cell (IBSC)—which may increase the photovoltaicenergy conversion efficiency of IBSCs by increasing the lifetime of charge carriers in the intermediate state. The limiting efficiency calculation for this concept shows that the efficiency can be increased by introducing a fast thermal transition of carriers into a non-emissive state. At 1 sun, the introduction of a “ratchet band” results in an increase of efficiency from 46.8% to 48.5%, due to suppression of entropy generation.
  • Journal article
    Chan N, Young T, Brindley H, Ekins-Daukes N, Araki K, Kemmoku Y, Yamaguchi Met al., 2012,

    Validation of energy prediction method for a concentrator photovoltaic module in Toyohashi Japan

    , Progress in Photovoltaics, Pages: n/a-n/a

    III–V concentrator photovoltaic systems attain high efficiency through the use of series connected multi-junction solar cells. As these solar cells absorb over distinct bands over the solar spectrum, they have a more complex response to real illumination conditions than conventional silicon solar cells. Estimates for annual energy yield made assuming fixed reference spectra can vary by up to 15% depending on the assumptions made. Using a detailed computer simulation, the behaviour of a 20-cell InGaP/In0.01GaAs/Ge multi-junction concentrator system was simulated in 5-min intervals over an entire year, accounting for changes in direct normal irradiance, humidity, temperature and aerosol optical depth. The simulation was compared with concentrator system monitoring data taken over the same period and excellent agreement (within 2%) in the annual energy yield was obtained. Air mass, aerosol optical depth and precipitable water have been identified as atmospheric parameters with the largest impact on system efficiency.
  • Journal article
    Lee K-H, Barnham KWJ, Connolly JP, Browne BC, Airey RJ, Roberts JS, Fuehrer M, Tibbits TND, Ekins-Daukes NJet al., 2012,

    Demonstration of Photon Coupling in Dual Multiple-Quantum-Well Solar Cells

    , IEEE JOURNAL OF PHOTOVOLTAICS, Vol: 2, Pages: 68-74, ISSN: 2156-3381
  • Conference paper
    Adams JGJ, Browne BC, Ballard IM, Connolly JP, Chan NLA, Ioannides A, Elder W, Stavrinou PN, Barnham KWJ, Ekins-Daukes NJet al., 2011,

    Recent results for single-junction and tandem quantum well solar cells

    , Publisher: John Wiley & Sons, Ltd., Pages: 865-877
  • Conference paper
    Barnham KWJ, Ekins-Daukes NJ, Browne B, 2009,

    Radiative limits in quantum well solar cells

    , 24th European Photovoltaic Solar Energy Conference
  • Conference paper
    Chatten AJ, Bose R, Farrell DJ, Pardo-Sanchez C, Pravettoni M, Mazzer M, Barnham WJet al., 2009,

    Luminescent Solar Concentrators: cylindrical design

    , 24th European Photovoltaic Solar Energy Conference
  • Conference paper
    Chatten AJ, Pravettoni M, Farrell DJ, Bose R, Kenny RP, Barnham Ket al., 2009,

    External quantum efficiency measurements of luminescent solar concentrators: a study of the impact of backside reflector size and shape

    , 24th European Photovoltaic Solar Energy Conference
  • Conference paper
    Barnham KWJ, Adams JGJ, Elder W, Stavrinou P, Ekins-Daukes NJet al., 2009,

    Efficiency enhancement in strain-balanced quantum well solar cells via anisotropic emission

    , 24th European Photovoltaic Solar Energy Conference
  • Conference paper
    Chatten AJ, bose, farrell, pravettoni, Buchtemann A, Quiltz J, Fiore A, Manna L, Nelson J, Alivisatos AP, Barnhamet al., 2008,

    The Effect of Size and Dopant Concentration of the Performance of Nanorod Luminescent Solar Concentrators

    , The 23rd European Photovoltaic Solar Energy Conference and Exhibition
  • Conference paper
    Barnham KWJ, Adams JGJ, Ginige R, Connolly JP, Ballard IM, Ekins-Daukes NJ, Hill G, Roberts JSet al., 2008,

    Single-Junction Concentrator Quantum Well Solar Cells Enhanced By Photon Recycling

    , 23rd European Photovoltaic Solar Energy Conference
  • Conference paper
    Barnham KWJ, Fuhrer MF, Connolly JP, Mazzer M, Ballard IM, Ekins-Daukes NJ, Johnson DC, Bessiere A, Roberts JS, Airey R, Calder C, Hill G, Tibbits TNDet al., 2008,

    Exciton Broadening in Quantum Well Solar Cells

    , 23rd European Photovoltaic Solar Energy Conference
  • Conference paper
    Browne B, Ekins-Daukes N, Ioannides A, Connolly J, Ballard I, Barnham K, Tibbits T, Pate M, Geen M, Roberts J, Hill G, Calder C, Airey R, Smekens G, Van Begin Jet al., 2008,

    Dual Multiple Quantum Well Solar Cells

    , 23rd European Photovoltaic Solar Energy Conference
  • Conference paper
    Barnham KWJ, Adams JGJ, Connolly JP, Hill G, Roberts JS, Tibbits TND, Geen M, Pate Met al., 2008,

    Strain-Balanced Quantum Well Concentrator Cells From Multi-Wafer Production

    , 33rd IEEE Photovoltaic Specialists Conference
  • Conference paper
    Barnham KWJ, Browne B, Ioannides A, Connolly J, Roberts J, Airey R, Hill G, Smekens G, Van Begin Jet al., 2008,

    Tandem Quantum Well Solar Cells

    , 33rd IEEE Photovoltaic Specialists Conference
  • Conference paper
    Barnham KWJ, Browne B, Ioannides A, Connolly J, Hill G, Roberts J, Airey R, Hill G, Smekens G, Van Begin Jet al., 2008,

    Efficiency of Tandem Quantum Well Solar Cells

    , PVSAT-4
  • Conference paper
    Barnham KWJ, Adams JGJ, Connolly JP, Calder C, Hill G, Roberts JS, Tibbits TND, Geen M, Pate Met al., 2008,

    Characterisation of Strain-Balanced Quantum Well Concentrator Cells Enhanced By Photon Recycling

    , PVSAT-4
  • Conference paper
    Chatten AJ, bose R, farrell D, Buchtemann A, Barnhamet al., 2008,

    The Luminescent Concentrator: Thin Films and Large Area Modelling

    , PVSAT-4
  • Conference paper
    Bose R, Farrell DJ, Chatten AJ, Pravettoni M, Buechtemann A, Quilitz J, Fiore A, Manna L, Barnham KWJet al., 2008,

    LUMINESCENT SOLAR CONCENTRATORS: NANORODS AND RAYTRACE MODELING

    , 33rd IEEE Photovoltaic Specialists Conference, Publisher: IEEE, Pages: 24-+, ISSN: 0160-8371
  • Conference paper
    Fuhrer MF, Connolly JP, Mazzer M, Ballard IM, Johnson DC, Barnham KWJ, Bessiere A, Roberts JS, Airey R, Calder C, Hill G, Tibbits TND, Pate M, Geen Met al., 2008,

    HOT CARRIERS IN STRAIN BALANCED QUANTUM WELL SOLAR CELLS

    , 33rd IEEE Photovoltaic Specialists Conference, Publisher: IEEE, Pages: 1016-+, ISSN: 0160-8371
  • Journal article
    Johnson JC, Ballard IM, Barnham KWJ, Connolly JP, Mazzer M, Bessiere A, Calder C, Hill G, Roberts JSet al., 2007,

    Observation of photon recycling in strain-balanced quantum well solar cells

    , Applied Physics Letters, Vol: 90, Pages: 213505-213507

    Photon recycling in strain-balanced quantum well solar cells grown on distributed Bragg reflectors has been observed as a suppression of the dark current and a change in electroluminescence spectra.Comparing devices grown with and without distributed Bragg reflectors we have demonstrated up to a 33% reduction in the ideality n=1 reverse saturation current. Furthermore, to validate the observations we demonstrate how both the measured dark currents and electroluminescence spectra fit very well to a photon recycling model. Verifying our observations with the model then allows us to calculate optimized device designs.
  • Journal article
    Rohr C, 2006,

    InP-based lattice-matched InGaAsP and strain-compensated InGaAs/InGaAs quantum well cells for thermophotovoltaic applications

    , Journal of Applied Physics, Vol: 100
  • Journal article
    Bushnell DB, Tibbits TND, Barnham KWJ, Connolly JP, Mazzer M, Ekins-Daukes NJ, Roberts JS, Hill G, Airey Ret al., 2005,

    Effect of well number on the performance of quantum-well solar cells

    , Journal of Applied Physics, Vol: 97

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