ORCID Profile
0000-0001-9308-2401
Current Organisation
UNSW Sydney
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Publisher: Elsevier BV
Date: 06-2010
Publisher: Wiley
Date: 31-03-2017
Publisher: IEEE
Date: 06-2016
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2020
Publisher: IEEE
Date: 20-06-2021
Publisher: Elsevier BV
Date: 12-2006
Publisher: American Vacuum Society
Date: 05-2006
DOI: 10.1116/1.2190674
Abstract: Ex situ electron-beam lithography followed by conventional wet or dry etching has been used to pattern small holes of 60–150nm wide, 10–40nm deep in GaAs substrates. These holes then act as preferential nucleation sites for InAs dot growth. Preferential nucleation occurs due to a reduction in the apparent critical thickness above the pattern site, which is dependent on the dimensions of the initial pattern. We demonstrate that subsequent growth of site-controlled dots over the patterned sites varies with InAs deposition amount and growth temperature in a similar way to InAs dot growth on planar substrates. By varying temperature and either InAs deposition amount or pattern size, both the size and position of InAs quantum dots can be controlled.
Publisher: IEEE
Date: 06-2015
Publisher: IEEE
Date: 06-2015
Publisher: IEEE
Date: 2000
Publisher: American Chemical Society (ACS)
Date: 16-11-2023
Publisher: American Vacuum Society
Date: 14-10-2021
DOI: 10.1116/6.0001492
Publisher: Wiley
Date: 05-2008
DOI: 10.1002/PIP.799
Publisher: IEEE
Date: 06-2014
Publisher: Elsevier BV
Date: 03-2018
Publisher: AIP Publishing
Date: 17-08-2015
DOI: 10.1063/1.4928750
Abstract: Extraction of charge carriers from a hot carrier solar cell using energy selective contacts and the impact on limiting power conversion efficiency are analyzed. It is shown that assuming isentropic conversion of carrier heat into voltage implies zero power output at all operating points. Under conditions of power output, lower voltages than in the isentropic case are obtained due to the irreversible entropy increase associated with carrier flow. This lowers the limiting power conversion efficiency of a hot carrier solar cell.
Publisher: IEEE
Date: 06-2014
Publisher: IEEE
Date: 06-2018
Publisher: AIP Publishing
Date: 11-12-2006
DOI: 10.1063/1.2405419
Abstract: The authors report surface-acoustic-wave-driven luminescence from a lateral p-n junction formed by molecular beam epitaxy regrowth of a modulation doped GaAs∕AlGaAs quantum well on a patterned GaAs substrate. Surface-acoustic-wave-driven transport is demonstrated by peaks in the electrical current and light emission from the GaAs quantum well at the resonant frequency of the transducer. This type of junction offers high carrier mobility and scalability. The demonstration of surface-acoustic-wave luminescence is a significant step towards single-photon applications in quantum computation and quantum cryptography.
Publisher: IEEE
Date: 06-2014
Publisher: AIP Publishing
Date: 28-03-2016
DOI: 10.1063/1.4945594
Abstract: We have investigated the ultrafast carrier dynamics in a 1 μm bulk In0.265Ga0.735N thin film grown using energetic neutral atom-beam lithography/epitaxy molecular beam epitaxy. Cathodoluminescence and X-ray diffraction experiments are used to observe the existence of indium-rich domains in the s le. These domains give rise to a second carrier population and bi-exponential carrier cooling is observed with characteristic lifetimes of 1.6 and 14 ps at a carrier density of 1.3 × 1016 cm−3. A combination of band-filling, screening, and hot-phonon effects gives rise to a two-fold enhanced mono-exponential cooling rate of 28 ps at a carrier density of 8.4 × 1018 cm−3. This is the longest carrier thermalization time observed in bulk InGaN alloys to date.
Publisher: IEEE
Date: 06-2013
Publisher: Elsevier BV
Date: 09-2021
Publisher: AIP Publishing
Date: 12-04-2021
DOI: 10.1063/5.0049120
Abstract: Multiple exciton generation (MEG) increases the short circuit current of solar cells and is, therefore, often cited as a candidate scheme for surpassing the efficiency limit of single junction solar cells. Conventionally, limiting efficiencies for MEG solar cells have been calculated using quasi-equilibrium models that implicitly assume an effective separation of timescales between different processes. We show here that this separation of timescales is not possible for MEG solar cells, with Auger recombination, the inverse process to multi-exciton generation, needing to be considered explicitly in the efficiency limits of an MEG solar cell. We assess the impact of Auger recombination using a non-equilibrium model of a quantum dot solar cell that satisfies microscopic reversibility and can approximate experimental external quantum efficiency (EQE) curves of MEG solar cells. Recombination—both Auger and radiative—is treated in a quasi-equilibrium approach, which can be justified with a clear model for the separation of timescales. A key insight of this model is that the achievable voltage of the device, and hence the solar energy conversion efficiency, depends on the absolute values of the impact ionization rate and the rate at which electrons lose energy through phonon scattering. By contrast, the EQE profile at short circuit depends only on the ratio of these two rates. This shows that the potential of certain MEG solar cell approaches cannot be assessed from EQE improvements alone, which highlights the importance of considering non-equilibrium processes in models of solar energy conversion devices.
Publisher: IOP Publishing
Date: 12-09-2017
Publisher: IEEE
Date: 06-2019
Publisher: Elsevier BV
Date: 10-2017
Publisher: IEEE
Date: 06-2013
Publisher: IEEE
Date: 05-2008
Publisher: IEEE
Date: 14-06-2020
Publisher: IEEE
Date: 14-06-2020
Publisher: Springer Science and Business Media LLC
Date: 29-04-2015
Publisher: IEEE
Date: 06-2017
Publisher: IEEE
Date: 12-2017
Publisher: MDPI AG
Date: 18-06-2019
DOI: 10.3390/EN12122326
Abstract: This paper presents a mixed receding horizon control (RHC) strategy for the optimal scheduling of a battery energy storage system (BESS) in a hybrid PV and wind power plant while satisfying multiple operational constraints. The overall optimisation problem was reformulated as a mixed-integer linear programming (MILP) problem, aimed at minimising the total operating cost of the entire system. The cost function of this MILP is composed of the profits of selling electricity, the cost of purchasing ancillary services for undersupply and oversupply, and the operation and maintenance cost of each component. To investigate the impacts of day-ahead and hour-ahead forecasting for battery optimisation, four forecasting methods, including persistence, Elman neural network, wavelet neural network and autoregressive integrated moving average (ARIMA), were applied for both day-ahead and hour-ahead forecasting. Numerical simulations demonstrated the significant increased efficiency of the proposed mixed RHC strategy, which improved the total operation profit by almost 29% in one year, in contrast to the day-ahead RHC strategy. Moreover, the simulation results also verified the significance of using more accurate forecasting techniques, where ARIMA can reduce the total operation cost by almost 5% during the whole year operation when compared to the persistence method as the benchmark.
Publisher: Elsevier BV
Date: 10-2016
Publisher: Author(s)
Date: 2018
DOI: 10.1063/1.5053511
Publisher: IEEE
Date: 06-2009
Publisher: AIP Publishing
Date: 04-03-2013
DOI: 10.1063/1.4794018
Abstract: Emission from InAs/GaAs quantum dots (QDs) treated with Sb sprays of 7.5, 15, 22.5, and 30 s duration immediately prior to capping with GaAs has been studied via temperature dependent photoluminescence. Room temperature spectra show a significant increase in output intensity as the quantum dots are exposed to the Sb spray, but this improvement is lost when the Sb exposure is extended beyond 15 s. For the 7.5 s and 15 s Sb spray s les, temperature-dependent photoluminescence taken between 20 and 300 K show an increase in emission for increasing temperature from 30 to ∼100 K, for s les with an Sb spray before rolling off at temperatures in excess of 100 K, an effect ascribed to a small energy barrier close to the dots. Fitting of the temperature dependent data suggests that the impact of the energy barrier is only seen for the s les with lower defect densities in the immediate vicinity of the quantum dots. Results found when varying the excitation wavelength suggest the energy barrier is most likely located away from the top of the quantum dots, with it suggested that the inferred energy barrier may be due to Sb clustering around the base of the quantum dots in the capping layer, or incorporated Sb in the wetting layer of the QDs.
Publisher: AIP Publishing
Date: 2011
DOI: 10.1063/1.3527039
Abstract: Optical properties of InAs quantum dots (QDs) embedded in GaAsSb barriers with delta-doping levels equivalent to 0, 2, 4, and 6 electrons per dot (e/dot) are studied using time-integrated photoluminescence (PL). When the PL excitation power is increased the full width at half maximum (FWHM) of the 4 and 6 e/dot s les is found to increase at a much greater rate than the FWHMs for the 0 and 2 e/dot s les. PL spectra of the 4 e/dot s le show a high energy peak attributed to emission from the first excited states of the QDs, a result deduced to be due to preoccupation of states by electrons supplied by the delta-doping plane. When temperature dependent PL results are fitted using an Arrhenius function, the thermal activation energies for the 4 and 6 e/dot s les are similar and greater than the thermal activation energies for the 0 and 2 e/dot s les (which are similar to each other). This increased thermal activation energy is attributed to the enhanced Coulombic interaction in the InAs QD area by the delta-doping plane for higher doping levels. It is concluded that delta-doping of the barrier in QD systems is a feasible method for controlling the level of carrier occupation in a QD mediated intermediate band.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2015
Publisher: Elsevier BV
Date: 07-2011
Publisher: Elsevier BV
Date: 10-2022
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2015
Publisher: Wiley
Date: 22-11-2006
Publisher: Wiley
Date: 30-03-2010
DOI: 10.1002/PIP.937
Publisher: IEEE
Date: 06-2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: IEEE
Date: 20-06-2021
Publisher: IEEE
Date: 06-2019
Publisher: Elsevier BV
Date: 05-2005
Publisher: American Chemical Society (ACS)
Date: 16-06-2017
DOI: 10.1021/ACS.NANOLETT.7B00536
Abstract: The photothermoelectric (PTE) effect uses nonuniform absorption of light to produce a voltage via the Seebeck effect and is of interest for optical sensing and solar-to-electric energy conversion. However, the utility of PTE devices reported to date has been limited by the need to use a tightly focused laser spot to achieve the required, nonuniform illumination and by their dependence upon the Seebeck coefficients of the constituent materials, which exhibit limited tunability and, generally, low values. Here, we use InAs/InP heterostructure nanowires to overcome these limitations: first, we use naturally occurring absorption "hot spots" at wave mode maxima within the nanowire to achieve sharp boundaries between heated and unheated subwavelength regions of high and low absorption, allowing us to use global illumination second, we employ carrier energy-filtering heterostructures to achieve a high Seebeck coefficient that is tunable by heterostructure design. Using these methods, we demonstrate PTE voltages of hundreds of millivolts at room temperature from a globally illuminated nanowire device. Furthermore, we find PTE currents and voltages that change polarity as a function of the wavelength of illumination due to spatial shifting of subwavelength absorption hot spots. These results indicate the feasibility of designing new types of PTE-based photodetectors, photothermoelectrics, and hot-carrier solar cells using nanowires.
Publisher: AIP Publishing
Date: 02-07-2007
DOI: 10.1063/1.2753759
Abstract: Short radio frequency pulses were used to study the surface-acoustic-wave-driven light emission from a molecular beam epitaxy regrown GaAs∕AlGaAs lateral p-n junction. The luminescence provides a fast probe of the signals arriving at the junction allowing the authors to temporally separate the effect of the surface-acoustic-wave from pickup of the free space electromagnetic wave. Oscillations in the light intensity are resolved at the resonant frequency of the transducer, suggesting that the surface-acoustic-wave is transporting electrons across the junction in packets.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7NR05247B
Abstract: The carrier dynamics of lead sulphide quantum dot (PbS QD) drop cast films and closely packed ordered Langmuir–Blodgett films are studied with ultra-fast femtosecond transient absorption spectroscopy.
Publisher: IEEE
Date: 06-2012
Publisher: Elsevier BV
Date: 11-2019
Publisher: SPIE
Date: 27-02-2019
DOI: 10.1117/12.2513176
Publisher: Elsevier BV
Date: 05-2006
Publisher: IEEE
Date: 20-06-2021
Publisher: IOP Publishing
Date: 10-05-2012
DOI: 10.1088/0957-4484/23/22/225304
Abstract: The fabrication of a cross-wire p-i-n light emitting diode (LED) by molecular beam epitaxial overgrowth on mesa-patterned GaAs(100) substrates is presented. Micron-wide mesa stripes fabricated by standard photolithography are subsequently narrowed to sub-micron dimensions by GaAs overgrowth due to net migration towards the mesa top. Chains of InAs quantum dots (QDs) can then be grown in a self-aligned manner on top of the narrow GaAs ridge mesa, forming the active region of the QD-chain LED. The kinetics of the overgrowth is discussed and the electroluminescence operation of the LED is presented.
Publisher: SPIE
Date: 23-02-2017
DOI: 10.1117/12.2251927
Publisher: IEEE
Date: 06-2014
Publisher: IEEE
Date: 06-2017
Publisher: Elsevier BV
Date: 07-2017
Publisher: Springer Science and Business Media LLC
Date: 30-05-2014
Publisher: IEEE
Date: 08-2018
Publisher: IEEE
Date: 05-2008
Publisher: International Union Against Tuberculosis and Lung Disease
Date: 02-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2016
Publisher: Elsevier BV
Date: 08-2018
Publisher: Springer Science and Business Media LLC
Date: 20-12-2016
DOI: 10.1038/NMAT4676
Abstract: The past five years have seen significant cost reductions in photovoltaics and a correspondingly strong increase in uptake, with photovoltaics now positioned to provide one of the lowest-cost options for future electricity generation. What is becoming clear as the industry develops is that area-related costs, such as costs of encapsulation and field-installation, are increasingly important components of the total costs of photovoltaic electricity generation, with this trend expected to continue. Improved energy-conversion efficiency directly reduces such costs, with increased manufacturing volume likely to drive down the additional costs associated with implementing higher efficiencies. This suggests the industry will evolve beyond the standard single-junction solar cells that currently dominate commercial production, where energy-conversion efficiencies are fundamentally constrained by Shockley-Queisser limits to practical values below 30%. This Review assesses the overall prospects for a range of approaches that can potentially exceed these limits, based on ultimate efficiency prospects, material requirements and developmental outlook.
Publisher: IEEE
Date: 06-2012
Publisher: IEEE
Date: 05-2008
Publisher: Hindawi Limited
Date: 2012
DOI: 10.1155/2012/486706
Publisher: AIP Publishing
Date: 03-05-2010
DOI: 10.1063/1.3409691
Abstract: InAs quantum dots grown on GaAsSb buffer layers with varying Sb content have been studied. Atomic force microscopy results show that the dot size is reduced as the Sb content increases with a concomitant increase in number density. Analysis of the size distribution indicates that the spread of dot sizes narrows with increasing Sb content. This is confirmed by photoluminescence measurements showing a significant narrowing of the dot emission peak for a GaAs0.77Sb0.23 buffer compared to a GaAs buffer. The results are attributed to the strained buffer reducing interactions between dots and the Sb acting as a surfactant.
Publisher: Elsevier BV
Date: 05-2022
Publisher: AIP Publishing
Date: 15-05-2012
DOI: 10.1063/1.4717766
Abstract: The band alignment of InAs quantum dots (QDs) embedded in GaAsSb barriers with various Sb compositions is investigated by photoluminescence (PL) measurements. InAs/GaAsSb s les with 13% and 15% Sb compositions show distinct differences in emission spectra as the PL excitation power increases. Whilst no discernible shift is seen for the 13% s le, a blue-shift of PL spectra following a 1/3 exponent of the excitation power is observed for the 15% s le suggesting a transition from a type I to type II band alignment. Time-resolved PL data show a significant increase in carrier lifetime as the Sb composition increases between 13% and 15% implying that the transformation from a type I to type II band alignment occurs between 13% and 15% Sb compositions. These results taken together lead to the conclusion that a zero valence band offset (VBO) can be achieved for the InAs/GaAsSb system in the vicinity of 14% Sb composition.
Publisher: IEEE
Date: 06-2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 1999
DOI: 10.1109/16.791981
Publisher: Elsevier BV
Date: 10-2010
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 04-2002
Publisher: IEEE
Date: 06-2011
Publisher: IEEE
Date: 06-2011
Publisher: IEEE
Date: 06-2013
Publisher: IOP Publishing
Date: 31-07-2017
Publisher: Elsevier BV
Date: 12-2021
Publisher: IEEE
Date: 06-2016
Publisher: IEEE
Date: 07-2016
Publisher: IEEE
Date: 06-2019
Publisher: Wiley
Date: 28-04-2022
Abstract: Hybrid halide perovskites have emerged as highly promising photovoltaic materials because of their exceptional optoelectronic properties, which are often optimized via compositional engineering like mixing halides. It is well established that hybrid perovskites undergo a series of structural phase transitions as temperature varies. In this work, the authors find that phase transitions are substantially suppressed in mixed‐halide hybrid perovskite single crystals of MAPbI 3‐x Br x (MA = CH 3 NH 3 + and x = 1 or 2) using a complementary suite of diffraction and spectroscopic techniques. Furthermore, as a general behavior, multiple crystallographic phases coexist in mixed‐halide perovskites over a wide temperature range, and a slightly distorted monoclinic phase, hitherto unreported for hybrid perovskites, is dominant at temperatures above 100 K. The anomalous structural evolution is correlated with the glassy behavior of organic cations and optical phonons in mixed‐halide perovskites. This work demonstrates the complex interplay between composition engineering and lattice dynamics in hybrid perovskites, shedding new light on their unique properties.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2015
Publisher: IEEE
Date: 06-2016
Publisher: Optica Publishing Group
Date: 28-01-2020
DOI: 10.1364/OE.380972
Abstract: Silicon based multi-junction solar cells are a promising approach for achieving high power conversion efficiencies using relatively low-cost substrates. In recent years, 2-terminal triple-junction solar cells using GaInP/GaAs as top cells and Si bottom cell have achieved excellent efficiencies. Epitaxial growth or wafer bonding has been used for the integration of the cells. This requires the top surface of the Si cell to be polished for effective integration, sacrificing the light trapping in the Si cell. The poor long wavelength light absorption in silicon limits the tandem cell efficiency as it is limited by current mismatch. In this work, for the first time, an external surface texturing is attached onto a GaInP/GaAs//Si wafer bonded triple-junction solar cell, using polydimethylsiloxane (PDMS) layers with surface geometries replicated from various pyramidally-textured silicon wafers. With reduced reflection, the short circuit current density is increased by 0.95 mA/cm 2 , while the overall cell efficiency is boosted by more than 2 % absolute.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2020
Publisher: IEEE
Date: 06-2018
Publisher: Wiley
Date: 13-07-2017
Publisher: AIP Publishing
Date: 13-09-2013
DOI: 10.1063/1.4819962
Abstract: We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60° dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of a dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.
Publisher: IEEE
Date: 14-06-2020
Publisher: Wiley
Date: 02-08-2022
Abstract: High bandgap perovskite solar cells are integral to perovskite‐based multi‐junction tandem solar cells with efficiency potentials over 40%. However, at present, high bandgap perovskite devices underperform compared to their mid bandgap counterparts in terms of voltage outputs and fill factors resulting in lower than ideal efficiencies. Here, the low fill factor aspect of high bandgap perovskite is addressed by developing a cation‐diffusion‐based double‐sided interface passivation scheme that simultaneously provides bulk passivation for a 1.75 eV perovskite cell that is also compatible with a p‐i‐n cell architecture. The ch ion cell achieves a record fill factor of 86.5% and a power conversion efficiency of 20.2%. Results of ionic distribution profiling, Fourier transform infrared spectroscopy, and X‐ray diffraction crystallography reveal evidence of cation diffusion from the surface perovskite passivation layer into bulk. The diffused cations reduce Shockley–Read–Hall recombination in the perovskite bulk and at the surfaces with the latter being more dominant as confirmed by light‐intensity dependent and temperature‐dependent open‐circuit voltage measurements as well as thermal admittance spectroscopy. This concurrent bulk and surface passivation scheme renders record fill factor and efficiency in the double‐side passivated cells. This provides new insights for future passivation strategies based on ionic diffusion of functionalized materials.
Publisher: Elsevier BV
Date: 07-2009
Publisher: Elsevier BV
Date: 10-2008
Publisher: Elsevier BV
Date: 04-2008
Publisher: IEEE
Date: 06-2015
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/596973
Publisher: AIP Publishing
Date: 16-04-2021
DOI: 10.1063/5.0038263
Abstract: In optoelectronic devices such as solar cells and photodetectors, a portion of electron-hole pairs is generated as so-called hot carriers with an excess kinetic energy that is typically lost as heat. The long-standing aim to harvest this excess energy to enhance device performance has proven to be very challenging, largely due to the extremely short-lived nature of hot carriers. Efforts thus focus on increasing the hot carrier relaxation time and on tailoring heterostructures that allow for hot-carrier extraction on short time and length scales. Recently, semiconductor nanowires have emerged as a promising system to achieve these aims, because they offer unique opportunities for heterostructure engineering as well as for potentially modified phononic properties that can lead to increased relaxation times. In this review we assess the current state of theory and experiments relating to hot-carrier dynamics in nanowires, with a focus on hot-carrier photovoltaics. To provide a foundation, we begin with a brief overview of the fundamental processes involved in hot-carrier relaxation and how these can be tailored and characterized in nanowires. We then analyze the advantages offered by nanowires as a system for hot-carrier devices and review the status of proof-of-principle experiments related to hot-carrier photovoltaics. To help interpret existing experiments on photocurrent extraction in nanowires we provide modeling based on non-equilibrium Green's functions. Finally, we identify open research questions that need to be answered in order to fully evaluate the potential nanowires offer toward achieving more efficient, hot-carrier based, optoelectronic devices.
Publisher: American Vacuum Society
Date: 05-2010
DOI: 10.1116/1.3268614
Abstract: Room temperature capacitance-voltage (C-V) profile and photoluminescence (PL) studies of δ-doped single InGaAs quantum well s les are reported. The purpose was to obtain the confined carrier occupancy in the conduction band offset and observe any relevant phenomena. The results show that the peak intensity of the C-V profiles was almost linearly proportional to sheet carrier concentration and the full width at half maximum of the C-V profiles became narrower with increasing doping level in the barrier layer. This is interpreted as being due to improved confinement of electrons as a result of band bending induced by the δ-doping layer. This explanation was further supported by PL data that show the transition corresponding to the dominant peak changed with different δ-doping levels and that all of the transitions were redshifted. Finally, theoretical calculations of the band structure based on a four band k⋅p method are presented to explain the observed results.
Publisher: IOP Publishing
Date: 02-10-2017
Abstract: Compared to traditional pn-junction photovoltaics, hot carrier solar cells offer potentially higher efficiency by extracting work from the kinetic energy of photogenerated 'hot carriers' before they cool to the lattice temperature. Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap materials, where the potential efficiency gain is highest. Recently, a high open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire with a low bandgap of 0.39 eV, and was interpreted in terms of a photothermoelectric effect. Here, we point out that this device is a hot carrier solar cell and discuss its performance in those terms. In the demonstrated devices, InP heterostructures are used as energy filters in order to thermoelectrically harvest the energy of hot electrons photogenerated in InAs absorber segments. The obtained photovoltage depends on the heterostructure design of the energy filter and is therefore tunable. By using a high-resistance, thermionic barrier, an open-circuit voltage is obtained that is in excess of the Shockley-Queisser limit. These results provide generalizable insight into how to realize high voltage hot carrier solar cells in low-bandgap materials, and therefore are a step towards the demonstration of higher efficiency hot carrier solar cells.
Publisher: American Chemical Society (ACS)
Date: 16-08-2022
Publisher: Wiley
Date: 03-04-2018
Publisher: AIP Publishing
Date: 28-04-2008
DOI: 10.1063/1.2907493
Abstract: The limiting efficiency of an intermediate band (IB) solar cell under the terrestrial AM1.5 spectrum was calculated by detailed balance for various concentration levels. The results show four energy gap combinations giving similar limiting efficiencies. This is in contrast to the more studied case of an IB solar cell under a blackbody spectrum where a single optimum combination is found. A design with a subenergy gap of ∼0.57eV is found to be viable, leading to the conclusion that the design space for an IB solar cell is larger when under the AM1.5 spectrum than when under a Blackbody spectrum.
Publisher: Wiley
Date: 20-09-2022
Abstract: To reduce the reliance on fossil fuel, H 2 , as a clean fuel, has attracted substantial research and development activities in recent years. The traditional water splitting approach requires an applied bias of more than 1.5 V and the use of ion‐selective membranes to prevent the formation of a potentially explosive H 2 –O 2 gas mixture, resulting in increased cost and system design complexity. Here, a solar‐driven H 2 production process requiring a much lower applied bias of 1.05 V is reported whereby aniline (ANI) is oxidized to polyaniline (PANI) at the anode with a yield of 96% and H 2 evolution reaction occurs at the cathode with a faradaic efficiency of 98.6 ± 3.9%. The process has multiple advantages including the elimination of ion‐exchange membrane as PANI is a solid product that also is of substantially higher value than O 2 . For demonstration, a single junction perovskite solar cell and low‐cost earth abundant CoP catalyst are successfully applied for this process. This process contributes to the advancement of solar‐driven low‐cost H 2 generation coupled with co‐production of a high‐value product expediting the transition to a hydrogen economy.
Publisher: SPIE
Date: 09-02-2012
DOI: 10.1117/12.910834
Publisher: AIP Publishing
Date: 27-07-2015
DOI: 10.1063/1.4927282
Abstract: Characterisation results are presented for ohmic contacts to passivated crystalline silicon, formed using the point-contacting by localised dielectric breakdown technique. Self aligned contact is made between the metal and heavily doped surface regions through an intrinsic a-Si:H passivation layer. Local doping is provided by a laser using a standard technique identical to that for selective emitter formation. Our results for gate metals of Au, Al, and Ti show that the technique does not rely on reactivity between the dielectric and the metal, excluding metal induced crystallisation from the contacting process. Diffusion of the gate metal into the dielectric is observed in transmission electron microscope images suggesting high temperatures are present locally during the breakdown process. The technique is equally applicable to contacting of n and p-type silicon, making it a potential alternative for ohmic contacting to silicon to passivated rear surfaces.
Publisher: American Vacuum Society
Date: 05-2008
DOI: 10.1116/1.2835062
Abstract: The InAs∕GaAsSb material system is a promising medium for the implementation of a quantum dot solar cell due to a favorable valence band alignment. The quantum dot solar cell requires a highly dense, highly ordered array of quantum dots for overlap of wave functions to form a band in the band gap of the host material. Since the GaAsSb barriers are a III-V-V ternary the alloy composition is particularly sensitive to variations in temperature. We have studied the variation in Sb content for thin layers of GaAsSb in GaAs for various fluxes of Sb. The purpose was to be able to predict the required Sb flux at a particular temperature to obtain a desired Sb composition. The target Sb composition for this study was 12% with the composition obtained confirmed by x-ray diffraction. By also studying the reciprocal space maps of the 12% s les, it is inferred that the composition can be maintained for a large temperature range. The implications of these results for the growth of InAs quantum dots on GaAsSb barriers are briefly discussed.
Publisher: IEEE
Date: 06-2018
Publisher: IOP Publishing
Date: 10-11-2016
Publisher: IEEE
Date: 06-2013
Publisher: IEEE
Date: 14-06-2020
Publisher: IOP Publishing
Date: 21-09-2015
Publisher: Wiley
Date: 10-01-2021
DOI: 10.1002/PIP.3386
Publisher: IEEE
Date: 05-2008
Publisher: IEEE
Date: 06-2011
Publisher: IOP Publishing
Date: 07-04-2006
DOI: 10.1143/JJAP.45.2519
Publisher: Elsevier BV
Date: 07-2021
Publisher: IEEE
Date: 06-2018
Publisher: AIP Publishing
Date: 03-2023
DOI: 10.1063/5.0117424
Abstract: Epitaxial monolithic III–V/Si tandem solar cells are one of the most promising technologies to be adopted by the industry after the efficiency of the current market dominating single junction silicon solar cell saturates at its fundamental limit. One of the key limitations of this technology is the degradation of silicon wafers during in situ annealing in the molecular beam epitaxy chamber. Determining the nature of contaminants in this process is key to improve the efficiency of epitaxial tandem solar cells. However, to date, the nature of contaminants from molecular beam epitaxy chambers remains unknown. In this work, we use photoluminescence imaging, lifetime spectroscopy, and deep level transient spectroscopy to measure the electronic properties of extrinsic impurities incorporated during annealing in the molecular beam epitaxy chamber. Photoluminescence images reveal that at least two impurities diffuse into silicon wafers during molecular beam epitaxy annealing. One is highly localized, while the other one is distributed uniformly across the whole wafer. Phosphorus diffusion is found to confine the localized impurity within the diffused layer but is ineffective at preventing the indiffusion of other impurities. Lifetime spectroscopy shows that metastable impurities with characteristic similar to Cr and CrB in our molecular beam epitaxy annealed silicon wafers. No evidence of Fe or FeB was observed. The emission rates and concentrations of the electrically active defects were measured with deep-level transient spectroscopy: The emission rates of detected defects do not match that of known Cr-related defects.
Publisher: AIP Publishing
Date: 03-06-2013
DOI: 10.1063/1.4809820
Abstract: We report the demonstration of a method for forming localized ohmic contact through dielectric passivation layers, via a laser doped region, with no etching prior to metal deposition. A simple bench top voltage source contacted to the gate and bulk of a test Metal-Insulator-Semiconductor device facilitates localized heating leading to ohmic contact formation. The surface passivation qualities of the dielectrics are preserved away from the contact region using this method, as hard dielectric breakdown is restricted to the laser doped region. This is a potential technique for precisely contacting rear surface of high efficiency solar cells.
Publisher: Elsevier BV
Date: 07-2021
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