Publications
293 results found
Sandwell P, Duggan G, Nelson J, et al., 2016, The environmental impact of lightweight HCPV modules: efficient design and effective deployment, Progress in Photovoltaics, Vol: 24, Pages: 1458-1472, ISSN: 1099-159X
We present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3MJ and 27.9 kgCO2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the life- times of the systems are found to be 6.5–9.8 g CO2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations.
Wilson T, Thomas TOMOS, Fuhrer M, et al., 2016, Single and Multi-Junction Solar Cells Utilizing a 1.0 eV SiGeSn Junction, 12th International Conference on Concentrator Photovoltaic Systems (CPV-12), Publisher: AIP Publishing, ISSN: 1551-7616
richards RD, Harun F, Cheong JS, et al., 2016, GaAsBi: An Alternative to InGaAs Based Multiple Quantum Well Photovoltaics, 43rd IEEE Photovoltaic Specialists Conference
dimmock J, kauer M, Mellor AV, et al., 2016, Current Voltage Characteristics of a Metallic Structure for a Hot-Carrier Photovoltaic Cell, 43rd IEEE Photovoltaic Specialists Conference
Hylton N, Hinrichsen TF, Vaquero-Stainer AR, et al., 2016, Photoluminescence upconversion at GaAs/InGaP2 interfaces driven by a sequential two-photon absorption mechanism, Physical Review B, Vol: 93, ISSN: 2469-9950
This paper reports on the results of an investigation into the nature of photoluminescence upconversion at GaAs/InGaP2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGaP2 material, arising from partial ordering of the InGaP2. We also observed the excitation of a two-dimensional electron gas at the GaAs/InGaP2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron gas at the GaAs/InGaP2 interface, suggesting that charge accumulation at the interface can play a crucial role in the upconversion process.
Roucka R, Clark A, Wilson T, et al., 2016, Demonstrating Dilute-Tin Alloy SiGeSn for Use in Multijunction Photovoltaics: Single- and Multijunction Solar Cells With a 1.0-eV SiGeSn Junction, IEEE Journal of Photovoltaics, Vol: 6, Pages: 1025-1030, ISSN: 2156-3381
SiGeSn ternary alloys offer a means to fabricate a 1.0-eV subcell junction for inclusion in a multijunction solar cell. The main advantage of the SiGeSn alloy is a tuneable bandgap energy and variable lattice parameter, enabling the material to be integrated into the existing lattice-matched multijunction architectures. Recent growth, structural, optical, and device results from SiGeSn material, with energy gaps in the vicinity of 1.0 eV and lattice matched to Ge substrates, are presented. An all lattice-matched InGaP/InGaAs/SiGeSn triple-junction cell is presented and compared with a conventional InGaP/InGaAs/Ge solar cell. Comparable short-circuit current values of 13.9 mA/cm2 are obtained for both devices under the AM1.5G spectrum, whereas the open-circuit voltage and fill factor are reduced in the device with the SiGeSn subcell. Peak external quantum efficiency in the SiGeSn single junction in excess of 80% is realized, placing a lower limit on the base minority hole diffusion length of 5 μm with surface recombination velocities in close agreement to those found in bulk Ge material.
Dimmock JAR, Kauer M, Smith K, et al., 2016, Optoelectronic characterization of carrier extraction in a hot carrier photovoltaic cell structure, Journal of Optics, Vol: 18, ISSN: 2040-8986
A hot carrier photovoltaic cell requires extraction of electrons on a timescale faster than they can lose energy to the lattice. We optically and optoelectronically characterize two resonant tunneling structures, showing their compatability with hot carrier photovoltaic operation, demonstrating structural and carrier extraction properties necessary for such a device. In particular we use time resolved and temperature dependent photoluminescence to determine extraction timescales and energy levels in the structures and demonstrate fast carrier extraction by tunneling. We also show that such devices are capable of extracting photo-generated electrons at high carrier densities, with an open circuit voltage in excess of 1 V.
Sandwell P, Chan NLA, Foster S, et al., 2016, Off-grid solar photovoltaic systems for rural electrification and emissions mitigation in India, Solar Energy Materials and Solar Cells, Vol: 156, Pages: 147-156, ISSN: 0927-0248
Over one billion people lack access to electricity and many of them in rural areas far from existing infrastructure. Off-grid systems can provide an alternative to extending the grid network and using renewable energy, for example solar photovoltaics (PV) and battery storage, can mitigate greenhouse gas emissions from electricity that would otherwise come from fossil fuel sources. This paper presents a model capable of comparing several mature and emerging PV technologies for rural electrification with diesel generation and grid extension for locations in India in terms of both the levelised cost and lifecycle emissions intensity of electricity. The levelised cost of used electricity, ranging from $0.46–1.20/kWh, and greenhouse gas emissions are highly dependent on the PV technology chosen, with battery storage contributing significantly to both metrics. The conditions under which PV and storage becomes more favourable than grid extension are calculated and hybrid systems of PV, storage and diesel generation are evaluated. Analysis of expected price evolutions suggest that the most cost-effective hybrid systems will be dominated by PV generation around 2018.
Guarracino I, Freeman J, Ekins-Daukes N, et al., 2016, PERFORMANCE ASSESSMENT AND COMPARISON OF SOLAR ORC AND HYBRID PVT SYSTEMS FOR THE COMBINED DISTRIBUTED GENERATION OF DOMESTIC HEAT AND POWER, HEFAT, 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
Solar-thermal collectors and photovoltaic panels are effectivesolutions for the decarbonisation of electricity and hot waterprovision in dwellings. In this work, we provide the first insightfulcomparison of these two competing solar-energy technologies forthe provision of combined heating and power (CHP) in domesticapplications. The first such system is based on an array of hybridPV-Thermal (PVT) modules, while the second is based on a solarthermalcollector array of the same area (based on a constrainedroof-space) that provides a thermal-energy input to an organicRankine cycle (ORC) engine for electricity generation. Simulationresults of the annual operation of these two systems are presentedin two geographical regions: Larnaca, Cyprus (as an example of ahot, high-irradiance southern-European climate) and London, UK(as an example of a cooler, lower-irradiance northern-Europeanclimate). Both systems have a total collector array area of 15 m2,equivalent to the roof area of a single residence, with the solarORCsystem being associated with a lower initial investment cost(capex) that is expected to play a role in the economic comparisonbetween the two systems. The electrical and thermal outputs of thetwo systems are found to be highly dependent on location. ThePVT system is found to provide an annual electricity output of2090 kWhe yr-1in the UK, which increases to 3620 kWhe yr-1inCyprus. This is equivalent to annual averages of 240 and 410 We,respectively, or between 60% and 110% of household demand.The corresponding additional thermal (hot water) output alsoincreases, from 860 kWhth yr-1in the UK, to 1870 kWhth yr-1inCyprus. It is found that the solar-ORC system performance ishighly sensitive to the system configuration chosen; the particularconfiguration studied here is found to be limited by the amount ofrejected thermal energy that can be reclaimed for water heating.The maximum electrical output from the solar-ORC configurationexplored in this study is 450 kWhe yr-1(
Pusch A, Yoshida M, Hylton NP, et al., 2016, Limiting efficiencies for intermediate band solar cells with partial absorptivity: the case for a quantum ratchet, Progress in Photovoltaics, Vol: 24, Pages: 656-662, ISSN: 1099-159X
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). Current proposals for IBSCs suffer from low absorptivity values for transitions into and out of the IB. We therefore devise and evaluate a general, implementation‐independent thermodynamic model for an absorptivity‐constrained limiting efficiency of an IBSC to study the impact of absorptivity limitations on IBSCs. We find that, due to radiative recombination via the IB, conventional IBSCs cannot surpass the Shockley–Queisser limit at an illumination of one Sun unless the absorptivity from the valence band to the IB and the IB to the conduction band exceeds ≈36%. In contrast, the introduction of a quantum ratchet into the IBSC to suppress radiative recombination can enhance the efficiency of an IBSC beyond the Shockley–Queisser limit for any value of the IB absorptivity. Thus, the quantum ratchet could be the vital next step to engineer IBSCs that are more efficient than conventional single‐gap solar cells.
Mellor AV, Hylton NP, Hohn O, et al., 2016, Nanoparticle scattering for multijunction solar cells, Proc. SPIE 9898, Photonics for Solar Energy Systems VI, Publisher: Society of Photo-optical Instrumentation Engineers (SPIE), Pages: 989809-989809, ISSN: 1996-756X
We investigate the integration of Al nanoparticle arrays into the anti-reflection coatings (ARCs) of commercial triple-junction GaInP/ In0.01GaAs /Ge space solar cells, and study their effect on the radiation-hardness. It is postulated that the presence of nanoparticle arrays can improve the radiation-hardness of space solar cells by scattering incident photons obliquely into the device, causing charger carriers to be photogenerated closer to the junction, and hence improving the carrier collection efficiency in the irradiation-damaged subcells. The Al nanoparticle arrays were successfully embedded in the ARCs, over large areas, using nanoimprint lithography: a replication technique with the potential for high throughput and low cost. Irradiation testing showed that the presence of the nanoparticles did not improve the radiation-hardness of the solar cells, so the investigated structure has proven not to be ideal in this context. Nonetheless, this paper reports on the details and results of the nanofabrication to inform about future integration of alternative light-scattering structures into multi-junction solar cells or other optoelectronic devices.
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.
Curtin OJ, Yoshida M, Pusch A, et al., 2016, Quantum cascade photon ratchets for intermediate band solar cells, IEEE Journal of Photovoltaics, Vol: 6, Pages: 673-678, ISSN: 2156-3381
We propose an antimonide-based quantum cascade design to demonstrate the ratchet mechanism for incorporation into the recently suggested photon ratchet intermediate-band solar cell. We realize the photon ratchet as a semiconductor heterostructure in which electrons are optically excited into an intermediate band and spatially decoupled from the valence band through a type-II quantum cascade. This process reduces both radiative and nonradiative recombination and can thereby increase the solar cell efficiency over intermediate-band solar cells. Our design method uses an adaptive simulated annealing genetic algorithm to determine the optimum thicknesses of semiconductor layers in the quantum cascade, allowing efficient transport (via phonon emission) of the electrons away from the interband active region.
Alonso Alvarez D, Ekins-Daukes N, 2016, Quantum wells for high-efficiency photovoltaics, SPIE OPTO 2016: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices V
Sugiyama M, Fujii H, Katoh T, et 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.
Guarracino I, Mellor A, Ekins-Daukes N, et al., 2016, Dynamic coupled thermal-and-electrical modelling of sheet-and-tube hybrid photovoltaic/thermal (PVT) collectors, Applied Thermal Engineering, Vol: 101, Pages: 778-795, ISSN: 1873-5606
In this paper we present a dynamic model of a hybrid photovoltaic/thermal (PVT) collector with a sheet-and-tube thermal absorber. The model is used in order to evaluate the annual generation of electrical energy along with the provision of domestic hot-water (DHW) from the thermal energy output, by using real climate-data at high temporal resolution. The model considers the effect of a non-uniform temperature distribution on the surface of the solar cell on its electrical power output. An unsteady 3-dimensional numerical model is developed to estimate the performance of such a collector. The model allows key design parameters of the PVT collector to vary so that the influence of each parameter on the system performance can be studied at steady state and at varying operating and atmospheric conditions. A key parameter considered in this paper is the number of glass covers used in the PVT collector. The results show that while the thermal efficiency increases with the additional glazing, the electrical efficiency deteriorates due to the higher temperature of the fluid and increased optical losses, as expected. This paper also shows that the use of a dynamic model and of real climate-data at high resolution is of fundamental importance when evaluating the yearly performance of the system. The results of the dynamic simulation with 1-min input data show that the thermal output of the system is highly dependent on the choice of the control parameters (pump operation, differential thermostat controller, choice of flow rate etc.) in response to the varying weather conditions. The effect of the control parameters on the system's annual performance can be captured and understood only if a dynamic modelling approach is used. The paper also discusses the use of solar cells with modified optical properties (reduced absorptivity/emissivity) in the infrared spectrum, which would reduce the thermal losses of the PVT collector at the cost of only a small loss in electrical output
Emmott CJM, Moia D, Sandwell P, et al., 2016, In-situ, long-term operational stability of organic photovoltaics for off-grid applications in Africa, Solar Energy Materials and Solar Cells, Vol: 149, Pages: 284-293, ISSN: 0927-0248
Pusch A, Yoshida M, Hylton NP, et al., 2016, The Purpose of a Photon Ratchet in Intermediate Band Solar Cells, 43rd IEEE Photovoltaic Specialists Conference (PVSC), Publisher: IEEE, Pages: 9-12, ISSN: 0160-8371
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- Citations: 2
Ochoa M, Garcia I, Lombardero I, et al., 2016, Advances Towards 4J Lattice-Matched including Dilute Nitride Subcell for Terrestrial and Space Applications, 43rd IEEE Photovoltaic Specialists Conference (PVSC), Publisher: IEEE, Pages: 52-57, ISSN: 0160-8371
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- Citations: 6
Roucka R, Clark A, Wilson T, et al., 2016, 3J Solar Cells Comprising a Lattice Matched Epitaxial SiGeSn SubCell, 43rd IEEE Photovoltaic Specialists Conference (PVSC), Publisher: IEEE, Pages: 2362-2365, ISSN: 0160-8371
Yakes MK, Schmieder KJ, Lumb MP, et al., 2016, Split InAlAs Top Cell Enabled Four-junction Solar Cell Lattice Matched to InP, 43rd IEEE Photovoltaic Specialists Conference (PVSC), Publisher: IEEE, Pages: 2836-2838, ISSN: 0160-8371
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- Citations: 2
Mellor A, Riverola A, Hylton NP, et al., 2016, Simple Models for Complex Devices, Progress in Electromagnetic Research Symposium (PIERS), Publisher: IEEE, Pages: 4606-4606
Fujita H, Carrington PJ, Wagener MC, et al., 2015, Open-circuit voltage recovery in type II GaSb/GaAs quantum ring solar cells under high concentration, PROGRESS IN PHOTOVOLTAICS, Vol: 23, Pages: 1896-1900, ISSN: 1062-7995
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- Citations: 16
Wilson T, Thomas T, Führer M, et al., 2015, Addressing reflectivity losses in multijunction solar cells to achieve 50% power conversion efficiency, Materials Research Innovations, Vol: 19, Pages: 503-507, ISSN: 1432-8917
As we progress towards the next generation of multi-junction solar cell technology, incorporating four junctions or more, current dual-layer coating technology applied to commercially available triple-junction solar cells will become inadequate as the current matching between the lower sub cells, absorbing in the infrared, becomes more critical. Here we present some single, double and triple layer anti-reflection coatings for comparison, optimised using a genetic algorithm, for both triple-and quad-junction solar cell architectures. It is found that there is a small increase in power conversion efficiency between the dual and triple layer coatings applied to the triple-junction structure (0.7%), however this is more than doubled when optimised dual and triple layer coatings are applied to the quad-junction device (1.5%). This work demonstrates the effectiveness of a well-optimised multi-layer anti-reflection coating in realising an appreciable increase in device performance in the next generation of multi-junction solar cells, highlighting a realistic power conversion efficiency of up to 50.35%.
Thomas T, Wilson T, Fuhrer M, et 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
Sugiyama M, Fujii H, Katoh K, et al., 2015, Quantum Wire-on-Well (WoW) Cell With Long Carrier Lifetime for Efficient Carrier Transport, 31st European Photovoltaic Solar Energy Conference and Exhibition, Publisher: European Photovoltaic Solar Energy Conference and Exhibition, Pages: 42-47
A quantum wire-on-well (WoW) structure, taking advantage of the layer undulation of an In- GaAs/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 4 times as compared with a planar reference superlattice. Strained InGaAs/GaAs/GaAsP superlattices were grown on GaAs substrates under exactly the same condition except for the substrate misorientation (0o- and 6o- off). The growth on a 6o-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 wire-on-well 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, and 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.
Datas A, Cristobal AB, Sala G, et al., 2015, NGCPV: A NEW GENERATION OF CONCENTRATOR PHOTOVOLTAIC CELLS, MODULES AND SYSTEMS (A FINAL REVIEW), 31st European Photovoltaic Solar Energy Conference and Exhibition
Alonso Alvarez D, Lackner D, Philipps SP, et 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.
Thomas, 2015, GaNAsSb 1-eV solar cells for use in lattice-matched multi-junction architectures, 40th IEEE PVSC
Thomas T, Mellor A, Hylton NP, et 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
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