Publications
293 results found
Vaquero-Stainer A, Yoshida M, Hylton NP, et al., 2018, Semiconductor nanostructure quantum ratchet for high efficiency solar cells, Communications Physics, Vol: 1, ISSN: 2399-3650
Conventional solar cell efficiencies are capped by the ~31% Shockley–Queisser limit because, even with an optimally chosen bandgap, some red photons will go unabsorbed and the excess energy of the blue photons is wasted as heat. Here we demonstrate a “quantum ratchet” device that avoids this limitation by inserting a pair of linked states that form a metastable photoelectron trap in the bandgap. It is designed both to reduce non-radiative recombination, and to break the Shockley–Queisser limit by introducing an additional “sequential two photon absorption” (STPA) excitation channel across the bandgap. We realise the quantum ratchet concept with a semiconductor nanostructure. It raises the electron lifetime in the metastable trap by ~104, and gives a STPA channel that increases the photocurrent by a factor of ~50%. This result illustrates a new paradigm for designing ultra-efficient photovoltaic devices.
Murrell AJ, Povall S, Williams C, et al., 2018, Development and Field Testing of a Novel Hybrid PV-Thermal Solar Collector, 12th International Conference on Solar Energy for Buildings and Industry (ISES EuroSun), Publisher: INTL SOLAR ENERGY SOC, Pages: 835-840
Cleveland ER, Hirst LC, Brittman S, et al., 2018, Enhanced Optical Absorption in an Ultra-thin Textured Solar Cell Using Nanosphere Natural Photolithography, 7th IEEE World Conference on Photovoltaic Energy Conversion (WCPEC) / A Joint Conference of 45th IEEE PVSC / 28th PVSEC / 34th EU PVSEC, Publisher: IEEE, Pages: 2878-2881, ISSN: 2159-2330
Gentillon P, Singh S, Taylor RA, et al., 2018, Improving the performance of thermophotovoltaics using stabilized porous media combustion, 7th IEEE World Conference on Photovoltaic Energy Conversion (WCPEC) / A Joint Conference of 45th IEEE PVSC / 28th PVSEC / 34th EU PVSEC, Publisher: IEEE, Pages: 3693-3697, ISSN: 2159-2330
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Ekins-Daukes NJ, Soeriyadi A, Zhao W, et al., 2018, Loss Analysis for Single Junction Concentrator Solar Cells, 14th International Conference on Concentrator Photovoltaic Systems (CPV), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
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Rand BP, Ekins-Daukes NJ, Haug F-J, 2017, Editorial for 'special issue on advanced solar cell technology', JOURNAL OF OPTICS, Vol: 19, ISSN: 2040-8978
Donchev V, Milanova M, Asenova I, et al., 2017, Effect of Sb in thick InGaAsSbN layers grown by liquid phase epitaxy, Journal of Crystal Growth, Vol: 483, Pages: 140-146, ISSN: 0022-0248
Dilute nitride InGaAsSbN layers grown by low-temperature liquid phase epitaxy are studied in comparison with quaternary InGaAsN layers grown at the same growth conditions to understand the effect of Sb in the alloy. The lattice mismatch to the GaAs substrate is found to be slightly larger for the InGaAsSbN layers, which is explained by the large atomic radius of Sb. A reduction of the band gap energy with respect to InGaAsN is demonstrated by means of photoluminescence (PL), surface photovoltage (SPV) spectroscopy and tight-binding calculations. The band-gap energies determined from PL and ellipsometry measurements are in good agreement, while the SPV spectroscopy and the tight-binding calculations provide lower values. Possible reasons for these discrepancies are discussed. The PL spectra reveal localized electronic states in the band gap near the conduction band edge, which is confirmed by SPV spectroscopy. The analysis of the power dependence of the integrated PL has allowed determining the dominant radiative recombination mechanisms in the layers. The values of the refraction index in a wide spectral region are found to be higher for the Sb containing layers.
Riverola A, Mellor AV, Alonso Alvarez D, et al., 2017, Mid-infrared emissivity of crystalline silicon solar cells, Solar Energy Materials and Solar Cells, Vol: 174, Pages: 607-615, ISSN: 0927-0248
The thermal emissivity of crystalline silicon photovoltaic (PV) solar cells plays a role in determining the operating temperature of a solar cell. To elucidate the physical origin of thermal emissivity, we have made an experimental measurement of the full radiative spectrum of the crystalline silicon (c-Si) solar cell, which includes both absorption in the ultraviolet to near-infrared range and emission in the mid-infrared. Using optical modelling, we have identified the origin of radiative emissivity in both encapsulated and unencapsulated solar cells. We find that both encapsulated and unencapsulated c-Si solar cells are good radiative emitters but achieve this through different effects. The emissivity of an unencapsulated c-Si solar cell is determined to be 75% in the MIR range, and is dominated by free-carrier emission in the highly doped emitter and back surface field layers; both effects are greatly augmented through the enhanced optical outcoupling arising from the front surface texture. An encapsulated glass-covered cell has an average emissivity around 90% on the MIR, and dips to 70% at 10 µm and is dominated by the emissivity of the cover glass. These findings serve to illustrate the opportunity for optimising the emissivity of c-Si based collectors, either in conventional c-Si PV modules where high emissivity and low-temperature operation is desirable, or in hybrid PV-thermal collectors where low emissivity enables a higher thermal output to be achieved.
Richards RD, Mellor A, Harun F, et al., 2017, Photovoltaic characterisation of GaAsBi/GaAs multiple quantum well devices, Solar Energy Materials and Solar Cells, Vol: 172, Pages: 238-243, ISSN: 0927-0248
A series of strained GaAsBi/GaAs multiple quantum well diodes are characterised to assess the potential of GaAsBi for photovoltaic applications. The devices are compared with strained and strain-balanced InGaAs based devices.The dark currents of the GaAsBi based devices are around 20 times higher than those of the InGaAs based devices. The GaAsBi devices that have undergone significant strain relaxation have dark currents that are a further 10–20 times higher.Quantum efficiency measurements show the GaAsBi devices have a lower energy absorption edge and stronger absorption than the strained InGaAs devices. These measurements also indicate incomplete carrier extraction from the GaAsBi based devices at short circuit, despite the devices having a relatively low background doping. This is attributed to hole trapping within the quantum wells, due to the large valence band offset of GaAsBi.
Sandwell P, Ekins-Daukes N, Nelson J, 2017, What are the greatest opportunities for PV to contribute to rural development?, SNEC 11th International Photovoltaic Power Generation Conference and Exhibition (SNEC), Publisher: Elsevier Science BV, Pages: 139-146, ISSN: 1876-6102
Minigrid systems powered by solar photovoltaics and battery storage are being deployed around the world to provide basic energy access and facilitate economic development. We use a minigrid simulation and optimisation tool that we have developed to assess various minigrid options in meeting the growing electricity demand of a community in rural Uttar Pradesh, India, in terms of the reliability of the service they provide, the cost of electricity, and total greenhouse gas emissions. We assess the breakeven distance at which off-grid minigrids are favourable in comparison to extending an unreliable grid network with a minigrid backup system, both with and without a carbon price. We suggest that policy recommendations that would encourage the use of minigrids for sustainable rural development, for example allowing subsidies to be available for system expansions and minimum service reliability requirements.
Milanova M, Donchev V, Kostov KL, et al., 2017, Experimental study of the effect of local atomic ordering on the energy band gap of melt grown InGaAsN alloys, Semiconductor Science and Technology, Vol: 32, ISSN: 0268-1242
We present a study of melt grown dilute nitride InGaAsN layers by x-ray photoelectron spectroscopy (XPS), Raman and photoluminescence (PL) spectroscopy. The purpose of the study is to determine the degree of atomic ordering in the quaternary alloy during the epitaxial growth at near thermodynamic equilibrium conditions and its influence on band gap formation. Despite the low In concentration (~3%) the XPS data show a strong preference toward In–N bonding configuration in the InGaAsN samples. Raman spectra reveal that most of the N atoms are bonded to In instead of Ga atoms and the formation of N-centred In3Ga1 clusters. PL measurements reveal smaller optical band gap bowing as compared to the theoretical predictions for random alloy and localised tail states near the conduction band minimum.
Mariaud A, Acha S, Ekins-Daukes N, et al., 2017, Integrated optimisation of PV and battery storage systems for UK non-domestic buildings, ASHRAE Annual Conference, Publisher: ASHRAE, ISSN: 2578-5257
his paper presents an end-user technology selection and operation (TSO) optimisation model which simultaneously optimizes the selection, design and operation of photovoltaic(PV)and battery systems in the context of commercial buildings integration. Thismodelserves to guidebusiness decision makers by assessing investment attractivenessand strategies. A strong feature of themodel is that it encompasses whole life costing and carbon emissionswhile taking into accountbuilding loads and features. Input data relies on historic metered electricity demand and irradiance levels combined with real-time and forecasted UK electricity pricesat half-hourly intervals, hence providing more comprehensive results than previous works. For a selected building and from a portfolio of technologies, a mixed-integer linear programming model selects an optimal combination of technologies and capacities while establishing the optimum operational strategy that provides the best return on investment.The case study of aretail distribution centre is provided to highlight the capabilities of the model. Results showcase the model provides valuable insights into project evaluation and thus reducesthe uncertainty associated with high capital projects. Overall,attractive PV and battery storage systems investments can be identified for UK commercial buildingsthrough the implementation of integratedoptimization models.
Alonso Alvarez D, Ferre Llin, L LFL, et al., 2017, ITO and AZO films for low emissivity coatings in hybrid photovoltaic-thermal applications, Solar Energy, Vol: 155, Pages: 82-92, ISSN: 0038-092X
We report on the electrical and optical properties of ITO and AZO films fabricated directly on silicon substrates under several growth and annealing temperatures. We use broadband spectroscopic ellipsometry measurements (from 300 nm to 20 μm) to obtain a consistent model for the permittivity of each of the films. The results are then used to design an optimized, single layer, high transparency, high conductivity film, suitable as front transparent electrode and low thermal emissivity coating for silicon based solar cells. The best performance is found using the properties of the ITO film grown at 250 °C, with a state of the art resistivity of 0.2 mΩ cm and an optimized thickness of 75 nm which leads to 0.79 average absorptivity in the solar range (300–2000 nm) and 0.21 average emissivity in the thermal range (5–20 μm). The structural characterization of the films using X-Ray diffraction, and the Hall mobility and resistivity measurements of all the films are also provided, complementing and supporting the observed optical properties.
Alonso Alvarez D, Ferre Llin L, Mellor A, et al., 2017, Comparative study of annealed and high temperature grown ITO and AZO films for solar energy applications, MRS Advances, Vol: 2, Pages: 3117-3122, ISSN: 2059-8521
We present the optical and electrical properties of ITO and AZO films fabricated directly on silicon substrates under several growth and annealing temperatures, as well as their potential performance when used as low emissivity coatings in hybrid photovoltaic-thermal systems. We use broadband spectroscopic ellipsometry measurements (from 300 nm to 20 μm) to obtain a consistent model for the permittivity of each of the films. The best performance is found using the properties of the ITO film grown at 250 °C, with a state of the art resistivity of 0.2 mΩ-cm and an optimized thickness of 75 nm which leads to an estimated 50% increase in the extracted power compared to a standard diffused silicon solar cell. The Hall mobility and resistivity measurements of all the films are also provided, complementing and supporting the observed optical properties.
Mariaud A, Acha S, Ekins-Daukes N, et al., 2017, Integrated optimisation of photovoltaic and battery storage systems for UK commercial buildings, Applied Energy, Vol: 199, Pages: 466-478, ISSN: 1872-9118
Decarbonising the built environment cost-effectively is a complex challenge public and private organisations are facing in their effort to tackle climate change. In this context, this work presents an integrated Technology Selection and Operation (TSO) optimisation model for distributed energy systems in commercial buildings. The purpose of the model is to simultaneously optimise the selection, capacity and operation of photovoltaic (PV) and battery systems; serving as a decision support framework for assessing technology investments. A steady-state mixed-integer linear programming (MILP) approach is employed to formulate the optimisation problem. The virtue of the TSO model comes from employing granular state-of-the-art datasets such as half-hourly electricity demands and prices, irradiance levels from weather stations, and technology databases; while also considering building specific attributes. Investment revenues are obtained from reducing grid electricity costs and providing fast-frequency response (FFR) ancillary services. A case study of a distribution centre in London, UK is showcased with the goal to identify which technologies can minimise total energy costs against a conventional system setup serving as a benchmark. Results indicate the best technology configuration is a combination of lithium-ion batteries and mono-crystalline silicon PVs worth a total investment of £1.72 M. Due to the available space in the facility, the preferred PV capacity is 1.76 MW, while the battery system has a 1.06 MW power capacity and a 1.56 MWh energy capacity. Although PV performance varies across seasons, the solution indicates almost 30% of the energy used on-site can be supplied by PVs while achieving a carbon reduction of 26%. Nonetheless, PV and battery systems seem to be a questionable investment as the proposed solution has an 8-year payback, despite a 5-year NPV savings of £300k, implying there is still a performance gap for such systems to be massively
Lee K-H, Barnham KWJ, Roberts JS, et al., 2017, Investigation of carrier recombination dynamics of InGaP/InGaAsP multiple quantum wells for solar cells via photoluminescence, IEEE Journal of Photovoltaics, Vol: 7, Pages: 817-821, ISSN: 2156-3381
The carrier recombination dynamics of InGaP/InGaAsP quantum wells is reported for the first time. By studying the photoluminescence (PL) and time-resolved PL decay of InGaP/InGaAsP multiple-quantum-well (MQW) heterostructure samples, it is demonstrated that InGaP/InGaAsP MQWs have very low nonradiative recombination rate and high radiative efficiency compared with the control InGaP sample. Along with the analyses of PL emission spectrum and external quantum efficiencies, it suggests that this is due to small confinement potentials in the conduction band but high confinement potentials in the valence band. These results explain several features found in InGaP/InGaAsP MQW solar cells previously.
Donchev V, Asenova I, Milanova M, et al., 2017, Optical properties of thick GaInAs(Sb)N layers grown by liquid-phase epitaxy, Journal of Physics: Conference Series, Vol: 794, ISSN: 1742-6588
We present an experimental and theoretical study of GaInAs(Sb)N layers withthickness around 2 μm, grown by liquid-phase epitaxy (LPE) on n-type GaAs substrates. Thesamples are studied by surface photovoltage (SPV) spectroscopy and by photoluminescencespectroscopy. A theoretical model for the band structure of Sb-containing dilute nitrides isdeveloped within the semi-empirical tight-binding approach in the sp3d5s*sN parameterisationand is used to calculate the electronic structure for different alloy compositions. The SPVspectra measured at room temperature clearly show a red shift of the absorption edge withrespect to the absorption of the GaAs substrate. The shifts are in agreement with theoreticalcalculations results obtained for In, Sb and N concentrations corresponding to theexperimentally determined ones. Photoluminescence measurements performed at 300K and 2 Kshow a smaller red shift of the emission energy with respect to GaAs as compared to the SPVresults. The differences are explained by a tail of slow defect states below the conduction bandedge, which are probed by SPV, but are less active in the PL experiment.
Roucka R, Clark A, Wilson T, et al., 2017, 3J solar cells comprising a lattice matched epitaxial SiGeSn SubCell, Pages: 2488-2491
The performance of quad-junction Ge based III-V multi-junction solar cells depends upon successful integration of a 1.0eV sub-cell into the existing InGaP/In0.01GaAs/Ge stack. The SiGeSn ternary alloy offers a means to fabricate a lattice-matched, 1.0eV sub-cell with the advantage that SiGeSn has both a tuneable band-gap and variable lattice parameter, enabling the material to be integrated into lattice-matched multi- junction architectures. A 1eV SiGeSn junction has been grown as both a single junction device and as the third junction in a InGaP/In0.01GaAs/SiGeSn triple junction device. The SiGeSn junction produces sufficient current to almost current match the InGaP and In0.01GaAs junctions and achieves a peak external quantum efficiency > 80% is demonstrated suggesting a lower limit on the base minority hole diffusion length of 5m. However, a degradation in open-circuit voltage and fill factor are observed with the SiGeSn sub-cell. This low voltage from the SiGeSn subcell is is attributed to recombination from defect levels within the SiGeSn band gap.
Ochoa M, Garcia I, Lombardero I, et al., 2017, Advances towards 4J lattice-matched including dilute nitride subcell for terrestrial and space applications, Pages: 2952-2956
Recent advances on the development of a 4J lattice- matched dilute nitride solar cell for terrestrial and space applications are described. Modeling of the solar cell is carried out using a drift-diffusion model and material parameters extracted from ad hoc electro-optical characterization resulting in an efficiency prediction of 47% for concentrations of 1000 suns AM1.5d G173 spectrum and 33% for 1× AMO. First experimental solar cell results of a dual-junction GaNAsSb/Ge solar cell and a triple-junction GaInP/Ga(In)As/GaNAsSb components of the full 4-Junction are shown.
Yakes MK, Schmieder KJ, Lumb MP, et al., 2017, Split InAlAs top cell enabled four-junction solar cell lattice matched to InP, Pages: 1385-1388
We have demonstrated for the first time a proof of concept four junction solar cell grown on an InP substrate. The split top cell design uses two 1.45 eV InAlAs subcells in series to take advantage of the large portion of the solar spectrum with energies higher than this bandgap. The prototype cell has an open circuit voltage of 2.44 V and short circuit current density of 1.8 mA/cm2. Further optimization may allow this cell to have performance comparable with high quality triple-junction GaAs cells. This architecture may be useful in other systems where high quality wide bandgaps are not available or in materials systems where carrier collection is strongly limited by the diffusion length within the material.
Pusch A, Yoshida M, Hylton NP, et al., 2017, The purpose of a photon ratchet in intermediate band solar cells, Pages: 2536-2537
The intermediate band solar cell (IBSC) concept aims to improve upon the Shockley-Queisser limit for single bandgap solar cells by also making use of below bandgap photons through sequential absorption processes via an intermediate band (IB). In order for this concept to be translated into more efficient solar cells there are still challenges to overcome; one of the most important is the increased recombination (radiative as well as non-radiative) associated with the additional states in the bandgap. A proposal to mitigate those recombination losses is the introduction of a photon ratchet into the IBSC, which effectively trades some of the energy of the excited electrons against these recombination losses. We show here that this can lead to substantial improvements even in the radiative limiting efficiency, where no non-radiative recombination is taken into account and that this advantage is especially prominent for IBSCs in which the transitions into and out of the IB are not very absorptive, a case commonly encountered for current IBSC proposals.
Dimmock JAR, Kauer M, Mellor AV, et al., 2017, Current voltage characteristics of a metallic structure for a hot-carrier photovoltaic cell, Pages: 993-998
We demonstrate a solar cell based on a thin layer of metal directly deposited on an n-doped semiconductor structure, forming a Schottky barrier acting as a semi-selective contact for an electron temperature driven cell. Absorption of light is shown to be by free carrier absorption in the metal layer for illumination with wavelengths of light below the semiconductor band gap, giving rise to an IV characteristic with a reverse bias slope dependent on electron temperature. Illumination with light in excess of the band gap reveals a standard Schottky cell IV characteristic.
Mellor A, Hylton NP, Wellens C, et al., 2017, Improving the radiation hardness of space solar cells via nanophotonic light trapping, Pages: 1-4
We show that the radiation-hardness of space solar cells can be significantly improved by employing nanophotonic light trapping. Two light-trapping structures are investigated in this work. In the first, an array of Al nanoparticles is embedded within the anti-reflection coating of a GaInP/InGaAs/Ge solar cell. A combined experimental and simulation study shows that this structure is unlikely to lead to an improvement in radiation hardness. In the second, a diffractive structure is positioned between the middle cell and the bottom cell. Computational results, obtained using an experimentally validated electro-optical simulation tool, show that a properly designed light-trapping structure in this position can lead to a relative 10% improvement in the middle-cell photocurrent at end-of-life.
Mellor AV, Hylton N, Wellens C, et al., 2016, Improving the radiation hardness of space solar cells via nanophotonic light trapping, 43rd IEEE Photovoltaic Specialists Conference, Publisher: IEEE
We show that the radiation-hardness of space solarcells can be significantly improved by employing nanophotoniclight trapping. Two light-trapping structures are investigated inthis work. In the first, an array of Al nanoparticles is embeddedwithin the anti-reflection coating of a GaInP/InGaAs/Ge solar cell.A combined experimental and simulation study shows that thisstructure is unlikely to lead to an improvement in radiationhardness. In the second, a diffractive structure is positionedbetween the middle cell and the bottom cell. Computationalresults, obtained using an experimentally validated electro-opticalsimulation tool, show that a properly designed light-trappingstructure in this position can lead to a relative 10% improvementin the middle-cell photocurrent at end-of-life.
Mellor AV, Guarracino I, Llin LF, et al., 2016, Specially designed solar cells for hybrid photovoltaic-thermal generators, 43rd IEEE Photovoltaic Specialists Conference, Publisher: IEEE
The performance of hybrid photovoltaic-thermal systems can be improved using PV cells that are specially designed to generate both electricity and useful heat with maximum efficiency. Present systems, however, use standard PV cells that are only optimized for electrical performance. In this work, we have developed two cell-level components that will improve the thermal efficiency of PV-T collectors, with minimal loss of electrical efficiency. These are a spectrally-selective low-emissivity coating to reduce radiative thermal losses, and a nanotextured rear reflector to improve absorption of the near-infrared part of the solar spectrum for heat generation.
Sandwell P, Chambon C, Saraogi A, et al., 2016, Analysis of energy access and impact of modern energy sources in unelectrified villages in Uttar Pradesh, Energy for Sustainable Development, Vol: 35, Pages: 67-79, ISSN: 0973-0826
Bringingaccesstomodernenergysourcestothepoorestinsocietyisakeygoalofmanypolicymakers,businessesandcharities,butinorder tobea success projects and schemesmust be foundedonaccuratedata. We undertooka survey of energy demand and usage patterns in households in unelectrified villages in Uttar Pradesh, India toassess access to and utilisation of energy sources for lighting and cooking. The times of usage were recordedand analysed and the effect on usage patterns of transitioning from traditional to modern energy sourcesis assessed. We quantify the cost and greenhouse gas emissions of current energy use in order to provide abenchmark of potential mitigation through the use of renewable energy technologies: a typical householdwith kerosene lamps only for lighting spends INR 3243 (US$50.67) and emits 381 kgCO2eqper year; householdswithmoderncookingenergyspend17%morethroughincreasedusage,butemit28%lessgreenhousegasescom-pared to those with traditional stoves only. Cell phone ownership was found to be 50% amongst adults. We usedemographic and utilisation data to construct an hourly demand profile of basic electricity demand extrapolatedto each month of the year, and present an example of aspirational demand assess the impact of desirable appli-ances. A Monte Carlo simulation is used to highlight the daily and seasonal variation in total energy and powerdemand. A hybrid system, with solar power and battery storage meeting daytime demand and higher-capacitydiesel- or biomass-powered generation meeting the remainder during evening peaks and winter months,would satisfy demand most effectively.
Mellor AV, Hylton N, Maier S, et al., 2016, Interstitial light-trapping design for multi-junction solar cells, Solar Energy Materials and Solar Cells, Vol: 159, Pages: 212-218, ISSN: 0927-0248
We present a light-trapping design capable of significantly enhancing the photon absorption inany subcell of a multi-junction solar cell. The design works by coupling incident light intowaveguide modes in one of the subcells via a diffraction grating, and preventing these modesfrom leaking into lower subcells via a low-index layer and a distributed Bragg reflector, whichtogether form an omnidirectional mirror. This allows the thickness of the target subcell to bereduced without compromising photon absorption, which improves carrier collection, andtherefore photocurrent. The paper focuses on using the composite structure to improve theradiation hardness of a InGaP/Ga(In)As/Ge space solar cell. In this context, it is shown viasimulation that the Ga(In)As middle-cell thickness can be reduced from 3500 to 700 nm,whilst maintaining strong photon absorption, and that this leads to a significantly improvedend-of-life photocurrent in the Ga(In)As middle cell. However, the design can in general beapplied to a wide range of multi-junction solar cell types. We discuss the principles ofoperation of the design, as well as possible methods of its fabrication and integration intomulti-junction solar cells.
Mellor AV, Hylton NP, Hauser H, et al., 2016, Nanoparticle scattering for multi-junction solar cells: the trade-off between absorption enhancement and transmission loss, IEEE Journal of Photovoltaics, Vol: 6, Pages: 1678-1687, ISSN: 2156-3381
This paper contains a combined experimental andsimulation study of the effect of Al and AlInP nanoparticles onthe performance of multi-junction solar cells. In particular, weinvestigate oblique photon scattering by the nanoparticle arraysas a means of improving thinned subcells or those with lowdiffusion lengths, either inherently or due to radiation damage.Experimental results show the feasibility of integratingnanoparticle arrays into the ARCs of commercialInGaP/InGaAs/Ge solar cells, and computational results showthat nanoparticle arrays can improve the internal quantumefficiency via optical path length enhancement. However, adesign that improves the external quantum efficiency of a stateof-the-artcell has not been found, despite the large parameterspace studied. We show a clear trade-off between obliquescattering and transmission loss, and present design principlesand insights into how improvements can be made.
Ekins-Daukes NJ, Sandwell P, Nelson J, et al., 2016, What does CPV need to achieve in order to succeed?, 12th International Conference on Concentrator Photovoltaic Systems (CPV), Publisher: American Institute of Physics, ISSN: 0094-243X
The recent and dramatic reduction in flat-plate crystalline silicon (c-Si) technology has changed the competitive land-scape for concentrator PV (CPV) systems. Three system cost targets are considered, €1/Wp corresponding to the system cost of c-Si today, €0.75/Wp corresponding to the likely c-Si cost in 2020 and €0.5/Wp corresponding to a likely lower limit for c-Si in the long term. To compete successfully with c-Si, system efficiency needs to be raised from the present 30% to 40%, suggesting cell efficiencies of 50% and module efficiency of 44%. The module should be manufactured at an area cost below €275/m2 which implies a packaged cell cost of €3/cm2 and module + tracking cost €190/m2.
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.
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