Imperial College London

Dr N.J. (Ned) Ekins-Daukes

Faculty of Natural SciencesDepartment of Physics

Academic Visitor
 
 
 
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Contact

 

+44 (0)20 7594 6675n.ekins-daukes Website

 
 
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Location

 

H1002Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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268 results found

Yamaguchi M, Dimroth F, Geisz JF, Ekins-Daukes NJet al., 2021, Multi-junction solar cells paving the way for super high-efficiency, JOURNAL OF APPLIED PHYSICS, Vol: 129, ISSN: 0021-8979

Journal article

Jiang Y, Nielsen MP, Baldacchino AJ, Green MA, McCamey DR, Tayebjee MJY, Schmidt TW, Ekins-Daukes NJet al., 2021, Singlet fission and tandem solar cells reduce thermal degradation and enhance lifespan, PROGRESS IN PHOTOVOLTAICS, Vol: 29, Pages: 899-906, ISSN: 1062-7995

Journal article

Pusch A, Bremner SP, Tayebjee MJY, Daukes NJEet al., 2021, Microscopic reversibility demands lower open circuit voltage in multiple exciton generation solar cells, APPLIED PHYSICS LETTERS, Vol: 118, ISSN: 0003-6951

Journal article

Sogabe T, Hung C-Y, Tamaki R, Tomic S, Yamaguchi K, Ekins-Daukes N, Okada Yet al., 2021, Experimental demonstration of energy-transfer ratchet intermediate-band solar cell, COMMUNICATIONS PHYSICS, Vol: 4, ISSN: 2399-3650

Journal article

Zhou Z, Jiang Y, Ekins-Daukes N, Keevers M, Green MAet al., 2021, Optical and Thermal Emission Benefits of Differently Textured Glass for Photovoltaic Modules, IEEE JOURNAL OF PHOTOVOLTAICS, Vol: 11, Pages: 131-137, ISSN: 2156-3381

Journal article

Steiner MA, France RM, Buencuerpo J, Geisz JF, Nielsen MP, Pusch A, Olavarria WJ, Young M, Ekins-Daukes NJet al., 2020, High Efficiency Inverted GaAs and GaInP/GaAs Solar Cells With Strain-Balanced GaInAs/GaAsP Quantum Wells, ADVANCED ENERGY MATERIALS, Vol: 11, ISSN: 1614-6832

Journal article

Rodriguez AS, de Santana T, MacGill I, Ekins-Daukes NJ, Reinders Aet al., 2020, A feasibility study of solar PV-powered electric cars using an interdisciplinary modeling approach for the electricity balance, CO2 emissions, and economic aspects: The cases of The Netherlands, Norway, Brazil, and Australia, PROGRESS IN PHOTOVOLTAICS, Vol: 28, Pages: 517-532, ISSN: 1062-7995

Journal article

Aghaei M, Nitti M, Ekins-Daukes NJ, Reinders AHMEet al., 2020, Simulation of a Novel Configuration for Luminescent Solar Concentrator Photovoltaic Devices Using Bifacial Silicon Solar Cells, APPLIED SCIENCES-BASEL, Vol: 10

Journal article

Pearce P, Sayre L, Johnson A, Hirst L, Ekins-Daukes Net al., 2020, Design of photonic light-trapping structures for ultra-thin solar cells, Conference on Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IX, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

Conference paper

Pusch A, Gordon JM, Mellor A, Krich JJ, Ekins-Daukes NJet al., 2019, Fundamental Efficiency Bounds for the Conversion of a Radiative Heat Engine's Own Emission into Work, PHYSICAL REVIEW APPLIED, Vol: 12, ISSN: 2331-7019

Journal article

Gentillon P, Singh S, Lakshman S, Zhang Z, Paduthol A, Ekins-Daukes NJ, Chan QN, Taylor RAet al., 2019, A comprehensive experimental characterisation of a novel porous media combustion-based thermophotovoltaic system with controlled emission, APPLIED ENERGY, Vol: 254, ISSN: 0306-2619

Journal article

Pusch A, Ekins-Daukes NJ, 2019, Voltage Matching, Etendue, and Ratchet Steps in Advanced-Concept Solar Cells, PHYSICAL REVIEW APPLIED, Vol: 12, ISSN: 2331-7019

Journal article

Steiner MA, Barraugh CD, Aldridge CW, Alvarez IB, Friedman DJ, Ekins-Daukes NJ, Deutsch TG, Young JLet al., 2019, Photoelectrochemical water splitting using strain-balanced multiple quantum well photovoltaic cells, SUSTAINABLE ENERGY & FUELS, Vol: 3, Pages: 2837-2844, ISSN: 2398-4902

Journal article

Alonso Alvarez D, Weiss C, Fernandez J, Janz S, Ekins-Daukes Net al., 2019, Assessing the operating temperature of multi-junction solar cells with novel rear side layer stack and local electrical contacts, Solar Energy Materials and Solar Cells, Vol: 200, ISSN: 0927-0248

Sub-bandgap sunlight provides a source of heat generation in solar cells that is detrimental to performance, especially in space applications where heat dissipation is limited. In this work we assess the impact that an advanced rear-side contact scheme for multi-junction solar cells has on the cell temperature. Our results show that this scheme reduces the optical power absorption below the bandgap of germanium by 81% compared to a standard, full metallization design. Measurements of the electrical and thermal power fluxes performed in vacuum demonstrate that this lower near-infrared light absorption results in 8% less heat dissipated in the cell with the novel rear-side contact scheme when operating at 25 ºC. Modelling of the operating temperature for both cells when fully encapsulated with glass indicates that this effect will also result in a reduction of the operating temperature of 9 ºC for the novel design.

Journal article

Cui X, Sun K, Huang J, Yun JS, Lee C-Y, Yan C, Sun H, Zhang Y, Xue C, Eder K, Yang L, Cairney JM, Seidel J, Ekins-Daukes NJ, Green M, Hoex B, Hao Xet al., 2019, Cd-Free Cu2ZnSnS4 solar cell with an efficiency greater than 10% enabled by Al2O3 passivation layers, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 12, Pages: 2751-2764, ISSN: 1754-5692

Journal article

Ekins-Daukes N, Kay M, 2019, Brighten the dark skies, NATURE ENERGY, Vol: 4, Pages: 633-634, ISSN: 2058-7546

Journal article

Alonso Alvarez D, Augusto A, Pearce P, Ferre Llin L, Mellor A, Bowden S, Paul D, Ekins-Daukes Net al., 2019, Thermal emissivity of silicon heterojunction solar cells, Solar Energy Materials and Solar Cells, Vol: 201, Pages: 1-7, ISSN: 0927-0248

The aim of this work is to evaluate whether silicon heterojunction solar cells, lacking highly emissive, heavily doped silicon layers, could be better candidates for hybrid photovoltaic thermal collectors than standard aluminium-diffused back contact solar cells. To this end, the near and mid infrared emissivity of full silicon heterojunction solar cells, as well as of its constituent materials – crystalline silicon wafer, indium tin oxide, n-, i- and p-type amorphous silicon – have been assessed by means of ellipsometry and FTIR. The experimental results show that the thermal emissivity of these cells is actually as high as in the more traditional structures, ~80% at 8 μm. Detailed optical modelling combining raytracing and transfer matrix formalism shows that the emissivity in these cells originates in the transparent conductive oxide layers themselves, where the doping is not high enough to result in a reflection that exceeds the increased free carrier absorption. Further modelling suggests that it is possible to obtain lower emissivity solar cells, but that a careful optimization of the transparent conductive layer needs to be done to avoid hindering the photovoltaic performance.

Journal article

Dimmock JAR, Kauer M, Wu J, Liu H, Stavrinou PN, Ekins-Daukes NJet al., 2019, A metallic hot-carrier photovoltaic device, SEMICONDUCTOR SCIENCE AND TECHNOLOGY, Vol: 34, ISSN: 0268-1242

Journal article

Jiang Y, Keevers MJ, Pearce P, Ekins-Daukes N, Green MAet al., 2019, Design of an intermediate Bragg reflector within triple-junction solar cells for spectrum splitting applications, Solar Energy Materials and Solar Cells, Vol: 193, Pages: 259-269, ISSN: 0927-0248

We investigate the use of distributed Bragg reflectors (DBRs) within triple-junction solar cells (TJSC) for spectrum splitting photovoltaics. An optical model of a lattice-matched (LM) GaInP/GaInAs/Ge TJSC with intermediate DBR is developed, in good agreement with measured reflectance. By modifying the DBR layer number, composition and thickness to broaden the reflectance band, we show that a DBR can provide suitable 900–1050 nm reflectance for spectrum splitting from the LM TJSC to a Si cell, resulting in a more efficient 4-junction receiver. For better practicality and cost effectiveness, we propose that the buffer layers in metamorphic (MM) TJSCs could additionally function as a DBR for spectrum splitting applications. We propose several DBR designs to achieve a suitable spectrum-splitting reflectance band from MM TJSCs to a Si cell, again resulting in a more efficient 4-junction receiver. Finally, we show that our intermediate DBR approach to spectrum splitting has the advantage of a greatly reduced angle-of-incidence dependence compared to a discrete dielectric filter.

Journal article

Pusch A, Pearce P, Ekins-Daukes N, 2019, Analytical expressions for the efficiency limits of radiatively coupled tandem solar cells, IEEE Journal of Photovoltaics, Vol: 9, Pages: 679-687, ISSN: 2156-3381

The limiting efficiency for series-connected multijunction solar cells is usually calculated from the assumption that the individual junctions are optically isolated. Here, we develop an analytical formalism to predict efficiencies attainable in the presence of luminescent coupling, i.e. if the individual junctions in a series-connected multi-junction stack are coupled optically, so that luminescence from one junction can be absorbed by the lower bandgap junction below. The formalism deals with non-radiative recombination through the definition of the luminescence extraction efficiency. Using our general formalism we find that the limiting efficiency of a tandem cell becomes much less dependent on exact bandgap combination when luminescent coupling is considered and proceed to consider two technologically important examples of current-mismatched tandem solar cells. We find that a series-connected GaAs on silicon tandem cell can be more efficient than the underlying silicon cell alone, if the luminescence extraction efficiency of the GaAs junction is sufficient. An analysis of luminescent coupling in a perovskite on silicon tandem cell shows that the efficiency penalty for a perovskite bandgap below the optimum value can be mitigated if the luminescence extraction efficiency is high. We suggest that material quality and stability might be more important considerations for perovskite on silicon tandems than engineering the bandgap to achieve precise current matching.

Journal article

Guarracino I, Freeman J, Ramos A, Kalogirou SA, Ekins-Daukes NJ, Markides CNet al., 2019, Systematic testing of hybrid PV-thermal (PVT) solar collectors in steady-state and dynamic outdoor conditions, Applied Energy, Vol: 240, Pages: 1014-1030, ISSN: 0306-2619

Hybrid photovoltaic-thermal (PVT) collectors have been proposed for the combined generation of electricity and heat from the same area. In order to predict accurately the electrical and thermal energy generation from hybrid PVT systems, it is necessary that both the steady-state and dynamic performance of the collectors is considered. This work focuses on the performance characterisation of non-concentrating PVT collectors under outdoor conditions. A novel aspect concerns the application of existing methods, adapted from relevant international standards for flat plate and evacuated tube solar-thermal collectors, to PVT collectors for which there is no formally established testing methodology at present. Three different types of PVT collector are tested, with a focus on the design parameters that affect their electrical and thermal performance during operation. Among other results, we show that a PVT collector suffers a 10% decrease in thermal efficiency when the electricity conversion is close to the maximum power point compared to open-circuit mode, and that a poor thermal contact between the PV laminate and the copper absorber can lead to a significant deterioration in thermal performance. The addition of a glass cover improves the thermal efficiency, but causes electrical performance losses that vary with the glass transmittance and the solar incidence angle. The reduction in electrical efficiency at large incidence angles is more significant than that due to elevated temperatures representative of water-heating applications. Dynamic performance is characterised by imposing a step change in irradiance in order to quantify the collector time constant and effective heat capacity. This paper demonstrates that PVT collectors are characterised by a slow thermal response in comparison to ordinary flat plate solar-thermal collectors, due to the additional thermal mass of the PV layer. A time constant of ∼8 min is measured for a commercial PVT module, compared to <

Journal article

Kamath HG, Ekins-Daukes NJ, Araki K, Ramasesha SKet al., 2019, The potential for concentrator photovoltaics: A feasibility study in India, PROGRESS IN PHOTOVOLTAICS, Vol: 27, Pages: 316-327, ISSN: 1062-7995

Journal article

Kamath HG, Ekins-Daukcs NJ, Araki K, Ramasesha SKet al., 2019, Performance Analysis and Fault Diagnosis Method for Concentrator Photovoltaic Modules, IEEE JOURNAL OF PHOTOVOLTAICS, Vol: 9, Pages: 424-430, ISSN: 2156-3381

Journal article

Pearce P, Mellor A, Ekins-Daukes N, 2019, The importance of accurate determination of optical constants for the design of nanometallic light-trapping structures, Solar Energy Materials and Solar Cells, Vol: 191, Pages: 133-140, ISSN: 0927-0248

The optical constants of many metals commonly used in solar cells, e.g. as contacts, rear side planar reflectors, or more complex nanopatterned light-trapping structures, can vary depending on deposition method, thickness and other factors, and as such are not documented consistently in the literature. In the case of nanometallic light-trapping structures specifically designed to improve absorption in a solar cell, the choice of optical constants used in simulations significantly affects the predicted enhancement, as well as the structure's optimal dimensions. The trade-off between coupling into guided modes in the photovoltaic material and the number of photons absorbed parasitically in the metal leads to small differences in the optical constants giving significantly different results for the quantum efficiency and photogenerated current. This work documents several optical constant sources for silver, aluminium, gold and titanium, and the effect this has on plasmon quality factors. The effect of choosing different optical constant sources on modelling outcomes is quantified by considering the optimization of a test structure comprising a grid of metal nanodisks on the front surface of a thinned-down GaAs cell. Finally, we define a new spectrally-integrated figure of merit for comparing the expected performance of metals in light-trapping structures based on their optical constants, which we name the spectral absorption enhancement factor (SAEF).

Journal article

Lehmann AG, Ekins-Daukes N, Keevers M, 2019, Numerical flowline concentrator design in 3D, Conference on Nonimaging Optics - Efficient Design for Illumination and Solar Concentration XVI, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

Conference paper

Pearce P, Mellor A, Ekins-Daukes N, 2018, Quantifying parasitic losses from metal scattering structures in solar cells: How uncertainty in optical constants affects simulation results, 7th IEEE World Conference on Photovoltaic Energy Conversion (WCPEC) / A Joint Conference of 45th IEEE PVSC / 28th PVSEC / 34th EU PVSEC, Publisher: IEEE, Pages: 2918-2923, ISSN: 0160-8371

The optical constants of many metals commonly used in solar cells, e.g. as contacts or for light trapping structures, are not documented consistently in the literature, with different sources giving different values. In the case of metallic structures designed to improve absorption in a solar cell junction, the use of data from different sources can give strongly varying results for the effectiveness of nanophotonic light-trapping structures. The trade-off between diffraction into more oblique orders in the junction, enhancing absorption in the photovoltaic material, and the number of photons absorbed parasitically in the metal means small differences in the optical constants can lead to different very conclusions about the EQE and J SC . This work documents the different optical constants for silver, aluminium, gold and titanium from several sources, the effect this has on plasmon quality factors, and quantifies the effect on modelling outcomes by considering the optimization of a test structure using a grid of metal nanodisks on the front surface of a thinned-down GaAs cell. Finally, we consider the effect for a structure previously predicted to give a very high J SC for a solar cell with an ultra-thin GaAs layer.

Conference paper

Pearcef P, Wilsonf T, Johnson A, Ekins-Daukes Net al., 2018, Characterization of SiGeSn for Use as a 1 eV Sub-Cell in Multi-Junction Solar Cells, Pages: 943-948

Four-junction solar cells require a sub-cell which absorbs across a 1 eV transition for optimal performance. Due to a lack of available lattice-matched materials with the correct bandgap, current high-efficiency 4J devices use lattice-mismatched sub-cells, complicating the fabrication process. Group IV ternary SiGeSn alloys are a promising material system for achieving a lattice-matched material with a 1 eV direct transition, with functional devices having already been demonstrated. However, further investigation of the fundamental properties of relevant SiGeSn alloys is key to fabricating an efficient 4J device. Results from steady-state photoluminescence and spectroscopic ellipsometry are presented for three different compositions compositions of SiGeSn grown lattice-matched to Ge/GaAs on GaAs substrates. The results show the expected blueshift in the fundamental indirect gap, measured through photoluminescence, and the lowest indirect gap around 1 eV, calculated through analysis of the ellipsometry data. The higher energy transitions also show the expected shifts.

Conference paper

Cleveland ER, Hirst LC, Brittman S, Tomasulo S, Bennett MF, Mellor AV, Pearce P, Jenkins PP, Walters RJ, Ekins-Daukes NJ, Yakes MKet al., 2018, Enhanced Optical Absorption in an Ultra-thin Textured Solar Cell Using Nanosphere Natural Photolithography, Pages: 2878-2881

We recently demonstrated an ultra-thin solar cell with increased radiation tolerance as compared to a traditionally thick absorber counterpart. However, as the active region of the device was reduced so was the absorption with respect to state of the art devices. Therefore, we have implemented nanosphere natural photolithography to fabricate ordered and random arrays of micropillar structures leading to enhanced light absorption within an ultra-thin solar cell. We will discuss the fabrication process and illustrate the effectiveness of integrating light trapping structures within an ultra-thin solar cell design.

Conference paper

Pusch A, Hylton NP, Ekins-Daukes NJ, 2018, Comparison of possible realizations of quantum ratchet intermediate band solar cells, Pages: 1841-1844

Three fundamentally different approaches for the realization of a quantum ratchet intermediate band solar cell are compared. The quantum ratchet is a mechanism by which an energy loss of excited electrons is turned into an improvement in the efficiency of intermediate band solar cells by reducing carrier recombination in the system. The main requirement for this is to engineer forbidden transitions which can be achieved through vanishing spatial overlap of the wave-functions, spinselection rules or a momentum mismatch.

Conference paper

Riverola A, Mellor A, Alvarez DA, Llin LF, Guarracino I, Markides CN, Paul D, Chemisana D, Ekins-Daukes Net al., 2018, Experimental and theoretical study of the infrared emissivity of crystalline silicon solar cells, IEEE 44th Photovoltaic Specialist Conference (PVSC), Publisher: IEEE, Pages: 1339-1341, ISSN: 0160-8371

Conference paper

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