ORCID Profile
0000-0002-4811-5240
Current Organisations
University of New South Wales Sydney
,
University of New South Wales
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Electrical and Electronic Engineering | Photodetectors, Optical Sensors and Solar Cells
Publisher: Wiley
Date: 14-06-2020
Publisher: AIP Publishing
Date: 08-01-2020
DOI: 10.1063/1.5139894
Abstract: In this paper, the physical mechanisms involved in electron-beam-induced current (EBIC) imaging of semiconductor pn-junctions are reviewed to propose a model and optimize the acquisition of experimental data. Insights are drawn on the dependence of the EBIC signal with electron accelerating voltage and surface conditions. It is concluded that improvements in the resolution of EBIC are possible when the surface conditions of the specimens are carefully considered and optimized. A lower accelerating voltage and an increase of the surface recombination velocities are quantitatively shown to maximize the EBIC lateral resolution in locating the pn-junction. The effect of surface band bending is included in the model, and it is seen to primarily affect the surface recombination. Introducing controlled surface damage is shown as a potential method for resolution enhancement via focused ion beam milling with Ga+ ions. These findings contribute to the understanding of this technique and can produce further improvements to its application in semiconductor device technology.
Publisher: Springer Science and Business Media LLC
Date: 20-01-2022
Publisher: Wiley
Date: 22-08-2021
DOI: 10.1002/PIP.3459
Abstract: Stability of the passivation quality of poly‐Si on oxide junctions against the conventional mainstream high‐temperature screen‐print firing processes is highly desirable and also expected since the poly‐Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities ( J 0 ) and interface state densities ( D it ) of symmetrical s les with n‐type poly‐Si contacts before and after firing. S les without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The D it values are (3 ± 0.2) × 10 11 and (8 ± 2) × 10 11 eV/cm 2 when fired at 620°C and 900°C, respectively. The activation energy in an Arrhenius fit of D it versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from SiH bonds at the poly‐Si/SiO x interface is not the root cause of depassivation. Postfiring annealing at 425°C can improve the passivation again. S les with SiN x capping layers show an increase in J 0 up to about 100 fA/cm 2 by firing, which can be attributed to blistering and is not reversed by annealing at 425°C. On the other hand, blistering does not occur in poly‐Si s les capped with AlO x layers or AlO x /SiN y stacks, and J 0 values of 2–5 fA/cm 2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J 0 and D it : thermal stress at the SiO z interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2023
Publisher: Wiley
Date: 21-09-2022
Abstract: The global cumulative photovoltaic (PV) installed capacity is now over 1 TW. While this is an impressive amount of PV growth, it contributes less than 3% of total electricity generation and, therefore, requires significantly more PV to decarbonize the electricity sector completely. In order to achieve this decarbonization sustainably, all factors must be considered, including the extraction and purification of abundant materials. Based on conservative and ambitious future PV production scenarios and learning rate (LR) for material consumption reduction, the material demands for the future are projected. The concept of LR is applied to estimate the reduced material consumption based on the “maturity” of PV technology or the cumulative installed PV capacity. Herein, it is suggested that abundant materials like copper, concrete, and aluminum may face shortages if PV production follows the broad electrification scenario. Steel, in comparison, likely does not encounter any material shortages. Nevertheless, the work here demonstrates that the demand for even abundant materials should be minimized to decarbonize energy usage and mitigate climate change sustainably.
Publisher: AIP Publishing
Date: 03-04-2023
DOI: 10.1063/5.0127896
Abstract: The microwave annealing of semiconductor devices has not been extensively researched and is rarely utilized in industry, yet it has the potential to significantly reduce the time and cost associated with large-volume semiconductor processing, such as the various heating and annealing processes required in the manufacture of photovoltaic modules. In this paper, we describe microwave annealing of silicon solar cells, the effective passivation of light-induced defects, and a reduction in light-induced degradation. We find that silicon solar cells are heated rapidly in a microwave field and that effective B–O defect passivation can be achieved by microwave processing in less than 2 s. Microwave annealing yields similar results as compared to rapid thermal annealing.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: IOP Publishing
Date: 08-03-2021
Abstract: In this work, the efficiency potential of the fully screen-printed passivated emitter and rear contact (PERC) solar cell structure is investigated via numerical simulations. A series of improvements and optimizations are performed on bulk quality, emitter properties and metallization of screen-printed PERC solar cells based on experimental results obtained in both industry and laboratory environments. With significantly improved bulk and surface passivation quality, we find that carrier recombination losses at the metal/silicon interface will impose a substantial limitation on efficiencies, highlighting the need for developing new screen-printing technologies to overcome the limitation from contact recombination. By improving the effectiveness of the back-surface field, reducing coverage area of laser-doped selective emitters and the front metal/silicon interface contact area, a 15 mV improvement in open-circuit voltage ( V OC ) was achieved in our modelled cells, due to greatly reduced contact recombination losses. With the further implementation of a multi-busbar and fine-line printing technologies, efficiency above 24% was obtained from simulations. Subsequently, a comprehensive pathway towards 24% efficiency for screen-printed PERC solar cells is proposed, without the need to implement passivated contacts or transition to a plated metallisation scheme. Key target requirements for future developments are also identified.
Publisher: Wiley
Date: 27-07-2021
DOI: 10.1002/PIP.3455
Abstract: Light‐ and elevated temperature‐induced degradation (LeTID) can have significant and long‐lasting effects on silicon photovoltaic modules. Its behaviour is complex, showing highly variable degradation under different conditions or due to minor changes in device fabrication. Here, we show the large difference in LeTID kinetics and extents in multi‐crystalline passivated emitter and rear cell (multi‐PERC) modules from four different manufacturers. Varied accelerated testing conditions are found to impact the maximum extent of degradation in different ways for different manufacturers complicating the ability to develop a universal predictive model for field degradation. Relative changes in the open‐circuit voltage ( V OC ) have previously been used to assess extents of LeTID however, due to the greater impact of the defect at lower injection, the V OC is shown to degrade less than half as much as the voltage at maximum power point ( V MPP ). The MPP current ( I MPP ) and fill factor (FF) also degrade significantly, having an even larger overall impact on the power output. These observations imply that currently employed methodologies for testing LeTID are inadequate, which limits the reliability of future predictive models. In light of this, the field must develop a more holistic approach to analysing LeTID‐impacted modules, which incorporates information about changes under MPP conditions. This will allow for a much clearer understanding of LeTID in the field, which will assist the performance of future PV systems.
Publisher: Wiley
Date: 09-12-2019
DOI: 10.1002/PIP.3230
Abstract: In this work, we integrate defect engineering methods of gettering and hydrogenation into silicon heterojunction solar cells fabricated using low‐lifetime commercial‐grade p‐type Czochralski‐grown monocrystalline and high‐performance multicrystalline wafers. We independently assess the impact of gettering on the removal of bulk impurities such as iron as well as the impact of hydrogenation on the passivation of grain boundaries and B‐O defects. Furthermore, we report for the first time the susceptibility of heterojunction devices to light‐ and elevated temperature–induced degradation and investigate the onset of such degradation during device fabrication. Lastly, we demonstrate solar cells with independently verified 1‐sun open‐circuit voltages of 707 and 702 mV on monocrystalline and multicrystalline silicon wafers, respectively, with a starting bulk minority‐carrier lifetime below 40 microseconds. These remarkably high open‐circuit voltages reveal the potential of inexpensive low‐lifetime p‐type silicon wafers for making devices with efficiencies without needing to shift towards n‐type substrates.
Publisher: Wiley
Date: 22-01-2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1EE01814K
Abstract: As the photovoltaic (PV) industry heading towards the multi-TW scale, PV technologies need to be carefully evaluated based on material consumption rather than just efficiency or cost to ensure sustainable growth of the industry.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2022
Publisher: Wiley
Date: 19-10-2023
DOI: 10.1002/PIP.3747
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2019
Publisher: Wiley
Date: 21-02-2023
DOI: 10.1002/PIP.3687
Abstract: High‐efficiency silicon‐based tandem solar cells will likely drive the push towards terawatt (TW) scale PV manufacturing on the pathway to net zero emissions by 2050. In this work, we provide a comprehensive analysis of material consumption and sustainability issues for future tandem solar cells. First, we analyse the material consumption and sustainable manufacturing capacity of a variety of potential candidates for the top cell in a silicon‐based tandem cell. We show that III‐V, CIGS and CdTe are not suitable to support TW‐scale manufacturing. Perovskites thus present the most sustainable approach, as long as indium is not required in the cell structure. Next, we turn our attention to the silicon bottom cell architecture by comparing PERC, TOPCon and SHJ. Although tandem cells can generally reduce silver consumption relative to single junction silicon cells due to the more favourable J MP / V MP ratio, the PERC cell architecture could allow for significantly reduced Ag consumption compared with both TOPCon and SHJ by relying on Al for the rear p‐type contact. In order to drive a rapid shift towards TW‐scale manufacturing, a rapid upscaling compared with the current production capacity is needed. The results presented herein highlight the need for careful consideration of sustainability issues when designing future high‐efficiency tandem cells that will help the world mitigate the dangers of climate change.
Publisher: Elsevier BV
Date: 03-2022
Publisher: Wiley
Date: 24-01-2020
DOI: 10.1002/PIP.3243
Publisher: Wiley
Date: 15-12-2022
DOI: 10.1002/PIP.3661
Abstract: The clean energy transition could see the cumulative installed capacity of photovoltaics increase from 1 TW before the end of 2022 to 15–60 TW by 2050, creating a significant silver demand risk. Here, we present a silver learning curve for the photovoltaic industry with a learning rate of 20.3 ± 0.8%. Maintaining business as usual with a dominance of p‐type technology could require over 20% of the current annual silver supply by 2027 and a cumulative 450–520 kt of silver until 2050, approximately 85–98% of the current global silver reserves. A rapid transition to higher efficiency tunnel oxide passivated contact and silicon heterojunction cell technologies in their present silver‐intensive forms could increase and accelerate silver demand. As we approach annual production capacities of over 1 TW by 2030, addressing the silver issue requires increased efforts in research and development to increase the silver learning rate by 30%, with existing silver‐lean and silver‐free metallisation approaches including copper plating and screen‐printing of aluminium and copper.
Publisher: Wiley
Date: 17-11-2020
DOI: 10.1002/PIP.3362
Abstract: At present, the commercially dominant and rapidly expanding PV‐device technology is based on the passivated emitter and rear cell (PERC) design developed at UNSW. However, this technology has been found to suffer from a carrier‐induced degradation commonly referred to as ‘light‐ and elevated temperature‐induced degradation’ (LeTID) and can result in up to 16% relative performance losses. LeTID was recently shown to occur in almost every type of silicon wafer, independent of the doping material. Even though the degradation mechanism is known to recover under normal operation conditions, it is a lengthy process that drastically affects the energy yield, stability and, ultimately, the levelized cost of electricity (LCOE) of installed systems. Despite the joint effort of many research groups, the root cause of the degradation is still unknown. Here, we provide an overview of the existing literature and describe key LeTID characteristics and how these have led to the development of various theories of the underlying mechanism. Further, given the continuously appearing and strong evidence of hydrogen involvement in LeTID, many mitigation methods concerning hydrogenation have been suggested. We discuss such reported methods, bearing in mind crucial consumer necessities in terms of sustained cell performance and minimised LCOE.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: Wiley
Date: 11-07-2021
Abstract: Due to the low temperature processing constraint in silicon heterojunction (SHJ) solar cells, no defect engineering to improve silicon wafer quality is typically incorporated during cell fabrication. This means that high‐quality n‐type Cz wafers are required to produce high‐efficiency cells. Herein, recent demonstrations of incorporating defect engineering approaches, such as gettering and hydrogenation, into the SHJ process flow for both n‐type and p‐type wafers are surveyed. Defect engineering on wafers before cell fabrication can significantly improve the quality of low‐lifetime p‐type wafers, making them much more suitable for SHJ cells. Interestingly, these same approaches are also very effective in improving the cell performance in the n‐type wafers that are conventionally used in industry. Post‐cell illuminated annealing processes have been shown to eliminate boron–oxygen light‐induced degradation (LID) in p‐type wafers, leading to stable V OC exceeding 735 mV. New results indicate that the hydrogen naturally incorporated during SHJ processing is sufficient to passivate these defects. Similar illuminated annealing processes also lead to substantial improvements in n‐type SHJ cells. With these findings considered, it is demonstrated that a modified SHJ process flow, which includes defect engineering on a wafer level and post‐cell hydrogen passivation, is beneficial for SHJ production, regardless of the wafer type.
Publisher: Wiley
Date: 10-01-2020
DOI: 10.1002/PIP.3240
Publisher: Elsevier BV
Date: 2022
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2019
Publisher: Wiley
Date: 03-08-2022
Abstract: Herein, the current and future projected polysilicon demand for the photovoltaic (PV) industry toward broad electrification scenarios with 63.4 TW of PV installed by 2050 is studied. The current polysilicon demand by the PV industry in 2021 is equivalent to the consumption of 2.9–3.3 kt GW −1 . Depending on the physical constraints determining the lower limit for future polysilicon consumption, the annual demand can be 6–7 Mt year −1 in 2050 under broad electrification, which requires 10–12 times more of the current production capacity. To achieve broad electrification by 2050, cumulative demand of 46–87 Mt is required. An electricity requirement for purification, ingot pulling, and wafering of ≈360–380 kWh kg −1 for silicon wafers and carbon intensity can lead to a cumulative amount of ≈16.4–58.8 Gt of CO 2‐eq emissions by 2050. To reduce the environmental impact, efficiencies are increased, thinner wafers are used, kerf loss reduced, alternative purification methods with low emission intensities are explored, and opportunities for polysilicon production with decarbonized electricity are explored.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2019
Publisher: AIP Publishing
Date: 22-02-2021
DOI: 10.1063/5.0036039
Abstract: For the development of photonic integrated circuits, it is mandatory to implement light sources on a Si-on-insulator (SOI) platform. However, point defects in the Si matrix and, e.g., at the Si/SiO2 interface act as nonradiative recombination channels, drastically limiting the performance of Si-based light emitters. In this Letter, we study how these defects can be healed by applying an advanced hydrogenation process, recently developed in photovoltaic research for the passivation of performance-limiting defects in Si solar cells. Upon hydrogenation, we observe an increase in the room temperature photoluminescence (PL) yield by a factor of more than three for defect-enhanced quantum dots (DEQDs) grown on float-zone Si substrates, revealing the potential of this technique to passivate detrimental defects. For DEQDs grown using SOI substrates, the PL yield enhancement even exceeds a factor of four, which we attribute to the additional passivation of defects originating from the substrate. The results for SOI substrates are of particular interest due to their relevance for future photonic integrated circuits.
Publisher: Elsevier BV
Date: 05-2023
Start Date: 06-2017
End Date: 06-2020
Amount: $390,000.00
Funder: Australian Research Council
View Funded Activity