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5. Surface passivation for silicon solar cells using stable extrinsic field effect passivation

Author

Collett, Katherine and Wilshaw, Peter

Subjects
621.31, Silicon photovoltaics
Abstract

One of the largest challenges for high efficiency solar panels is the recombination of photo-generated carriers at the silicon surface. This recombination can be reduced by both chemical passivation and Field Effect Passivation (FEP). Conventionally, this is achieved by the SiNx antireflection coating. However, this is sub-optimal and insufficient for high efficiency devices. This thesis focuses on introducing FEP, independent of the antireflection coating, to allow superior surface passivation to be achieved. The alneal, a process of annealing aluminium covered oxide layers, is known to provide excellent surface passivation, was investigated. This already superior surface passivation method could be improved with the addition of sodium and potassium ions at the SiO2-Si interface, termed ionic-FEP. This produced record-breaking surface passivation with a surface recombination velocity (SRV) of 0.15 cm/s and a surface saturation current denisty (J0s) of 0.1 fA/cm2 on 1 Wcm n-type float zone (FZ) Si. A mechanism is described that explains ion introduction during this process. It offers an explanation as to why the passivation is achieved so rapidly, requiring an anneal of under 15 seconds at 450 °C, and places emphasis on the importance of an electric field between the oxide surface and silicon substrate during ion introduction. The requirement for an electric field for fast ionic migration is utilised in developing an industrially scalable technique for introducing ionic-FEP. Ionic precursors are deposited onto the SiO2 surface by spin or spray coating. The migration process comprises two stages: corona charge deposition to provide the electric field for migration and an anneal at 450 °C. Using potassium, there was found to be a linear, almost one-to-one, relationship between corona surface charge and resulting interface charge after annealing. The anneal time required for potassium ion introduction at 450 °C was found to be under two seconds. This process achieved a SRV of 3.3 cm/s, equivalent to a J0s of 8.4 fA/cm2 on 1 Wcm n-type FZ Si. The addition of hydrogen to an ionically-passivated SiO2-Si interface was tested. It was found that hydrogen was able to increase the effective lifetime of 200 μm thick 1 Wcm n-type FZ Si from 1800 μs to 3000 μs. As the interface charge concentration for this experiment was not optimal, it is likely that with the right charge concentration this process could provide surface passivation of a similar quality as the ion-enhanced alneal. Alternative ionic species for FEP were trialled. Larger ions were tested following the hypothesis that they may be more strongly bound to the SiO2-Si interface. Rubidium was successfully introduced, although the process required minutes rather than seconds. An effective lifetime of 1800 μs was achieved, which is comparable to that realised using potassium at the same concentration. Calcium showed promise, but the successful introduction of the species could not be concluded. Magnesium and Strontium seem unable to be introduced into the SiO2-Si system as charged species.

Published
2018

15. Electromobility in the Global South: An equitable transition toward road passenger transport decarbonization

Author

Ebenezer, Neil, Dalkmann, Holger, Haq, Gary, Cervantes Barron, Karla, Brand, Christian, Dixon, James, Collett, Katherine, Cullen, Jon, Hine, John, Hirmer, Stephanie, Patterson, Simon, Pye, Steve, Sivakumar, Aruna, Welsby, Daniel, and Secretariat, SuM4All

Subjects
Climate change mitigation, Transport, Global South, Electromobility
Abstract

This discussion paper, is the result of an overall effort undertaken by the Sustainable Mobility for All partnership, in conjunction with the UK Foreign, Commonwealth and Development Office (FCDO) and the Climate Compatible Growth (CCG) Programme. It questions whether the Global North’s approach to electromobility is suitable for countries in the Global South, particularly Least Developed Countries (LDCs). It complements two other policy papers by the SuM4All partnership: (i) The Digital toolkit for Energy and Mobility, which provides useful resources to integrate policy measures toward sustainable mobility; and (ii) Sustainable Electric Mobility: Building Blocks and Policy Recommendations on policy barriers to electromobility and essential building blocks for public policy in this area. Released under the Global Roadmap of Action series (GRA)ii, these papers contribute to a deeper understanding of the comprehensive policy framework required to transition to sustainable mobility. The series intends to stimulate an informed discussion on policy choices in transport and position the SuM4All partnership more prominently in the run-up towards COP26 and beyond. This will contribute to the debate on transport decarbonization, while considering the other goals of sustainable mobility: universal access, efficiency, and safety. The SuM4all partnership outlined this comprehensive policy framework in the GRAiii, which is now being piloted in South Africa. This paper shows that the model for transitioning to electromobility in the Global North will not work for all countries, and therefore new, innovative approaches are needed so that countries in the Global South are not left behind. Many countries understand the issue and are willing to transition but the poorest countries often face demanding technological, financial, and social pressures. These current circumstances make this transition extremely difficult or not timely. The Global North has a responsibility, as the historic high emitter of carbon, to help these countries bridge the Green Divide. The paper seeks to raise questions and issues for dialogue focused on the role of electromobility as a solution to decarbonize the transport sector. It is intended as a unique discussion document, which will contribute to the international debate at COP26 and beyond, regarding the right pathway to decarbonize the sector by taking the perspective of the LDCs in the Global South.

Published
2022

19. CCG Working Paper Series: E-mobility and renewables integration: Making e-mobility and renewable energy integration work in Asia and the Pacific

Author

Dixon, James, Hirmer, Stephanie, Collett, Katherine, Trotter, Phillip, Dalkmann, Holger, Chiang, Pamela, Hine, John, Leather, Jamie, Patterson, Simon, and Howells, Mark

Subjects
decarbonisation, e-mobility, electricity, renewable energy, Asia-pacific, electric vehicles
Abstract

New electricity demand from e-mobility can incentivize investment in new clean generation and grid infrastructure, thus improving power system services. As electric vehicle charging is flexible, this demand can be shifted to follow supply from low-cost variable renewables, like wind and solar. In this working paper, we identify nine key barriers to effective e-mobility/ renewable energy integration, which revolve around upfront cost, locked-in governance and technology uptake. We present a framework of enablers for effective e-mobility and renewable energy integration. The framework divides enablers into four categories and subdivides them into ten subcategories. We identify enablers according to this framework, which will be used as a base from which to develop practical solutions in the Asia-Pacific context. Through presentation of a case study, we demonstrate how these enablers can make ‘win-win’ solutions in e-mobility and renewable energy integration a reality in making tangible contributions to Asia-Pacific countries’ decarbonization pathways while increasing access to mobility and electricity., {"references":["K. A. Collett, S. A. Hirmer, H. Dalkmann, C. Crozier, Y. Mulugetta, and M. D. Mcculloch, \"Can electric vehicles be good for Sub- Saharan Africa?,\" Energy Strateg. Rev., vol. 38, 2021, doi: 10.1016/j.esr.2021.100722","J. Lukuyu, A. Muhebwa, and J. Taneja, \"Fish and Chips: Converting Fishing Boats for Electric Mobility to Serve as Minigrid Anchor Loads,\" in e-Energy 2020 - Proceedings of the 11th ACM International Conference on Future Energy Systems, 2020, vol. 20, pp. 208–219, doi: 10.1145/3396851.3397687","K. A. Collett and S. A. Hirmer, \"Data needed to decarbonize paratransit in Sub-Saharan Africa,\" Nat. Sustain. 2021 47, vol. 4, no. 7, pp. 562–564, May 2021, doi: 10.1038/s41893- 021-00721-7","C. J. Abraham, A. J. Rix, I. Ndibatya, and M. J. Booysen, \"Ray of hope for sub- Saharan Africa's paratransit: Solar charging of urban electric minibus taxis in South Africa,\" Energy Sustain. Dev., vol. 64, pp. 118–127, 2021, doi: 10.1016/j. esd.2021.08.003","J. Dixon, W. Bukhsh, C. Edmunds, and K. Bell, \"Scheduling electric vehicle charging to minimise carbon emissions and wind curtailment,\" Renew. Energy, vol. 161, pp. 1072–1091, 2020, doi: 10.1016/j. renene.2020.07.017.","N. Brinkel et al., \"Impact of rapid PV fluctuations on power quality in the lowvoltage grid and mitigation strategies using electric vehicles,\" Int. J. Electr. Power Energy Syst., vol. 118, no. October 2019, p. 105741, 2020, doi: 10.1016/j. ijepes.2019.105741","F. Teng, Y. Mu, H. Jia, J. Wu, P. Zeng, and G. Strbac, \"Challenges on primary frequency control and potential solution from EVs in the future GB electricity system,\" Appl. Energy, vol. 194, pp. 353–362, 2017, doi: 10.1016/j. apenergy.2016.05.123","Nissan Motor Corporation, \"Nissan RE-LEAF: Power when it's needed, where it's needed,\" 2020. [Online]. Available: https://uk.nissannews. com/en-GB/releases/release- 93464f7850c37fb62e4 006e334145cfc-nissan-releaf- power-when-its-neededwhere- its-needed. [Accessed: 17-Nov-2021]","K. S. Rogge and K. Reichardt, \"Policy mixes for sustainability transitions: An extended concept and framework for analysis,\" Res. Policy, vol. 45, no. 8, pp. 1620–1635, 2016, doi: 10.1016/j.respol.2016.04.004","L. Bouchene, K. Jayaram, A. Kendall, and K. Somers, \"Africa's green manufacturing crossroads: Choices for a low-carbon industrial future,\" McKinsey & Company, 2021. [Online]. Available: https://www. mckinsey.com/businessfunctions/ sustainability/ our-insights/africas-greenmanufacturing- crossroadschoices- for-a-low-carbonindustrial- future. [Accessed: 17-Nov-2021]","M. Chen et al., \"Recycling End-of-Life Electric Vehicle Lithium-Ion Batteries,\" Joule, vol. 3, no. 11, pp. 2622– 2646, Nov. 2019, doi: 10.1016/j. joule.2019.09.014","The Faraday Institution, \"The importance of coherent regulatory and policy strategies for the recycling of EV batteries,\" 2020. [Online]. Available: https:// faraday.ac.uk/wp-content/ uploads/2020/09/Faraday_ Insights_9_FINAL.pdf [Accessed: 17-Nov-2021]","M. Toll, \"Gogoro's international footprint grows with major deal to expand battery swap stations into China,\" Electrek, 2021. [Online]. Available: https://electrek. co/2021/05/18/ gogoro-expansion-growswith- major-deal-to-buildbattery- swap-stations-ande- scooters-for-china/. [Accessed: 16-Nov-2021]","D. Prianjani, W. Sutopo, M. Hisjam, and E. Pujiyanto, \"Sustainable supply chain planning for swap battery system: Case study electric motorcycle applications in Indonesia,\" IOP Conf. Ser. Mater. Sci. Eng., vol. 495, no. 1, 2019, doi: 10.1088/1757- 899X/495/1/012081","Energy Asia, \"Gogoro Battery Swapping Revolution in Taiwan – How It Happened.\" 2021. [Online]. Available: https://energy. asia/gogoro-batteryswapping- revolution-intaiwan- how-it-happened/. [Accessed: 17-Nov-2021]","H. Ting-ting and L. Hsin-Yin, \"Gogoro, Taipower partner up on bidirectional charging system,\" Focus Taiwan, 2021. [Online]. Available: https://focustaiwan. tw/business/202110260018. [Accessed: 11-Nov-2021]","Cenex, \"Commercial Viability of V2G: Project Sciurus White Paper,\" 2021. [Online]. Available: https://www.cenex.co.uk/ app/uploads/2021/01/V2GCommercial- Viability-1.pdf. [Accessed: 17-Nov-2021]","A. Jhaveri, \"Hero and Gogoro form JV for electric vehicles in India,\" TechRadar, 2021. [Online]. Available: https:// www.techradar.com/uk/ news/hero-gogoropartnership- india. [Accessed: 17-Nov-2021]","C. Shu, \"Gogoro launches battery swapping stations in China,\" TechCrunch, 2021. [Online]. Available: https://techcrunch. com/2021/10/10/gogorolaunches- battery-swappingstations- in-china/. [Accessed: 17-Nov-2021]","Gogoro, \"Gojek and Gogoro Announce Strategic Partnership to Electrify - Gogoro,\" 2021. [Online]. Available: https://www. gogoro.com/news/gojekpertamina- gogoropartnership- indonesiabattery- swapping-jakarta/. [Accessed: 17-Nov-2021]","IEA, \"Net Zero by 2050: A Roadmap for the Global Energy Sector,\" Paris, 2021. [Online]. Available: https:// www.iea.org/reports/netzero- by-2050. [Accessed: 17- Nov-2021]","IEA, \"Electricity generation by source, Chinese Taipei 1990-2020,\" 2021. [Online]. Available: https://www.iea. org/countries/chinese-taipei","LSE and Grantham Research Institute on Climate Change and the Environment, \"Strategic Framework for Sustainable Energy Policy - Taiwan - Climate Change Laws of the World,\" 2021. [Online]. Available: https:// climate-laws.org/ geographies/taiwan/ policies/strategic-frameworkfor- sustainable-energypolicy. [Accessed: 17-Nov- 2021]"]}

Published
2022
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23. Driving the Energy Revolution - An index for grid edge need and readiness

Author

Zachau Walker, Miriam E, Seim, Stephan, Collett, Katherine A, Mothilal Bhagavathy, Sivapriya, Ruedt, Daniel Hubertus, Vijay, Avinash, Grosse, Benjamin, Roentgen-Zimmermann, Silke, McCulloch, Malcolm D, and Mueller-Kirchenbauer, Joachim

Subjects
Fluctuating renewable energy sources, Grid edge, Index development, Decentralized energy generation and consumption, Energy transition, System flexibility
Abstract

The world’s relationship with energy is transitioning as we attempt to mitigate the impact of climate change. In the energy systems of the future, residential, commercial, and industrial consumers will no longer be passive. They may own generation sources, such as solar panels; they may be able to offer a service, such as giving flexibility for when energy may be used; or they may make lifestyle choices which impact their energy consumption. Because of this, the interface between the grid and these distributed end-users will only grow in importance. This interface is called the grid edge. The grid edge encompasses a wide range of technologies and services, from electric vehicles to heat pumps, solar panels to home batteries, and smart meters to building controls. To maximize the impact of grid edge technology roll-out, knowledge of both the need for and readiness for grid edge technologies in a specific geography can be extremely valuable for companies and governments alike. This report presents a novel index to characterize the need and readiness for grid edge technologies of a region. To achieve this, factors which affect the need or readiness are included through an extensive range of indicators - 99 in total. Indicators for need are categorized based on those that contribute to current and to future need for system flexibility. There are four components of grid edge readiness: political, economic, social, and technical. Each indicator influencing each of these components has been weighted based on its importance following expert advice. For example, the introduction of a carbon price is considered to have a substantial impact on a region’s readiness for grid edge as it incentivizes renewables and could be used as a key policy tool. Applying this hierarchical weighting scheme to data collected about various locations, grid edge need and readiness scores can be calculated for each region. Five regions form the focus of the report, these are Finland, Germany, Singapore, the UK, and California in the US. These focus regions were selected as locations which have historically been among those leading in developing and adopting modern energy-related technologies. Of these focus regions, Finland is the country with highest readiness, in part due to its plans for a flexibility market and high carbon price, while California has the highest need, in part due to significant solar panel penetration. Germany and the UK follow closely behind with the UK displaying high political ambition but slightly less need and readiness. Singapore, although exhibiting high readiness for grid edge, presents a lower need, which is due to its present dependence on dispatchable fossil-fueled generation and more moderate ambitions for introducing renewable energy generation into the future energy mix. To position these focus regions within a global context, the index is also applied to a broader range of locations, with the caveat that due to data gaps there is an aspect of uncertainty. Although the focus regions of Finland, Germany, UK, and California are the regions with greatest need and readiness, Norway, China, and Canada exhibit the next highest need and readiness, making them promising candidates for further attention. Another country to highlight is South Africa, which has relatively high need but low readiness. This is a country where grid edge technology could make a difference, and where policy could be employed to improve readiness. Three key policy levers to improve a region’s readiness for grid edge are identified. These include introducing incentives for clean energy technologies; introducing flexibility and carbon markets; and developing policy pathways to provide reliable and secure communications infrastructure to all domestic citizens. The full report can be accessed here: https://new.siemens.com/global/en/company/topic-areas/smart-infrastructure/grid-edge-whitepaper2.html, The full report can be accessed here: https://new.siemens.com/global/en/company/topic-areas/smart-infrastructure/grid-edge-whitepaper2.html

Published
2020
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29. Electrostatic Tuning of Ionic Charge in SiO2Dielectric Thin Films

Author

Al-Dhahir, Isabel, Kealy, Rachel, Kelly, Samira, Yu, Mingzhe, McNab, Shona, Collett, Katherine, Liu, Junliang, Grovenor, Chris, Wilshaw, Peter R., and Bonilla, Ruy Sebastian

Abstract

Dielectric thin films are a fundamental part of solid-state devices providing the means for advanced structures and enhanced operation. Charged dielectrics are a particular kind in which embedded charge is used to create a static electric field which can add functionality and improve the performance of adjacent electronic materials. To date, the charge concentration has been limited to intrinsic defects present after dielectric synthesis, unstable corona charging, or complex implantation processes. While such charging mechanisms have been exploited in silicon surface passivation and energy harvesters, an alternative is presented here. Solid-state cations are migrated into SiO2thin films using a gateless and implantation-free ion injecting method, which can provide greater long-term durability and enable fine charge tailoring. We demonstrate the migration kinetics and the stability of potassium, rubidium, and caesium cations inside of SiO2thin films, showing that the ion concentration within the film can be tuned, leading to charge densities between 0.1–10 × 1012q cm−2. A comprehensive model of ion injection and transport is presented along a detailed investigation of the kinetics of alkali cations. Integrating ionic charge into dielectrics to produce controlled electric fields can enable new architectures where field effect is exploited for improved electron devices.

Published
2022
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30. THE GOSPEL OF NICODEMUS IN ANGLO-SAXON ENGLAND

Author

COLLETT, KATHERINE ANNE SMITH and COLLETT, KATHERINE ANNE SMITH

Abstract

The apocryphal Gospel of Nicodemus greatly influenced literature throughout Europe. The second part, the Harrowing of Hell, narrates Christ's descent into hell to free the souls of the dead from Satan's bondage, an event which especially captured the imagination of medieval Christendom. The first chapter of this dissertation traces both the development of the theological concept of Christ's descent, and its appearance in the popular tradition of pseudepigrapha and apocrypha, which together brought forth the Gospel of Nicodemus. The second chapter discusses the origin and date of the Gospel of Nicodemus and describes several of the earliest manuscripts of the Latin text from the British Isles. The third chapter examines Old English and Anglo-Latin works concerned with the harrowing of hell, and their relationship to the Gospel of Nicodemus. Some of these works are based immediately on the Gospel of Nicodemus, some draw on other known works which in turn draw on the Gospel, some are ultimately based on the Gospel, and some are simply drawing on the Church's general traditions about the harrowing. The fourth chapter briefly examines texts about the harrowing in other languages spoken in the medieval British Isles: Welsh, Cornish, Irish, and Norse. Following this last chapter two appendices present minimally edited texts of the two Latin recensions known in England, from twelfth- and thirteenth-century manuscripts.

Published
1981

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