Charged oxide inversion layer (COIL) solar cells
Lead Research Organisation:
University of Oxford
Department Name: Materials
Abstract
Photovoltaic (PV) solar cells now generate a significant proportion of the world's electricity and have vast potential for further growth. PV is enormously important to the UK with >13.5 GW now installed here, and growth worldwide is forecast to be over tenfold in the next three decades. More than 90% of solar cells are produced from crystalline silicon, and costs have fallen to levels not previously thought possible (< 2.34 US cents/kWh). Other technologies have yet to gain industrial traction and commercial barriers to entry are becoming substantial. Silicon-based solar technology is hence likely to remain dominant and critical to the expansion of renewable energy in the coming decades. Its continuous advancement is essential to accelerate uptake of and impact from green electricity generation worldwide and for fulfilling the UK's obligations under the Paris Agreement.
The passivated emitter and rear cells (PERC) architecture is standard for today's silicon solar cells. The PERC technology will reach its practical limits in the next 10 years, with a top forecast commercial efficiency of ~24%. Overcoming this efficiency boundary requires cell architectures that circumvent the limitations of PERC. This project aims to develop a new cell technology to supersede PERC in which the drawbacks of high temperature processing are avoided, the efficiency potential of a single junction is fully exploited, and a route to implement tandem and bifacial architectures is directly possible. This programme brings together teams at the Universities of Oxford and Warwick with world-leading expertise in silicon surface passivation, carrier lifetime, and impurity management for the development of PV devices. The aim is to conduct fundamental work necessary to facilitate a step-reduction in the cost per Watt of PV electricity, thus producing a disruptive change in the advancement of this important renewable energy industry.
This project will develop a charged oxide inversion layer (COIL) solar cell by integrating advanced nanoscale thin-film materials to augment the PV potential of a silicon absorber. This novel cell architecture has the potential to overtake the current standard PERC devices, while providing a direct route to use in emerging selective contact, tandem, and bifacial designs. So far, the efficiency of an inversion layer architecture has been exploited only to a limited extent, e.g. in a 18% cell. The potential of the COIL cell extends well beyond this mark, and as high as 28% in a single-junction configuration could be achieved. This project will deliver the fundamental understanding necessary to unlock this potential, exploit the inversion layer concept by engineering highly charged dielectric thin-films, and use these films to produce a prototype cell device.
The passivated emitter and rear cells (PERC) architecture is standard for today's silicon solar cells. The PERC technology will reach its practical limits in the next 10 years, with a top forecast commercial efficiency of ~24%. Overcoming this efficiency boundary requires cell architectures that circumvent the limitations of PERC. This project aims to develop a new cell technology to supersede PERC in which the drawbacks of high temperature processing are avoided, the efficiency potential of a single junction is fully exploited, and a route to implement tandem and bifacial architectures is directly possible. This programme brings together teams at the Universities of Oxford and Warwick with world-leading expertise in silicon surface passivation, carrier lifetime, and impurity management for the development of PV devices. The aim is to conduct fundamental work necessary to facilitate a step-reduction in the cost per Watt of PV electricity, thus producing a disruptive change in the advancement of this important renewable energy industry.
This project will develop a charged oxide inversion layer (COIL) solar cell by integrating advanced nanoscale thin-film materials to augment the PV potential of a silicon absorber. This novel cell architecture has the potential to overtake the current standard PERC devices, while providing a direct route to use in emerging selective contact, tandem, and bifacial designs. So far, the efficiency of an inversion layer architecture has been exploited only to a limited extent, e.g. in a 18% cell. The potential of the COIL cell extends well beyond this mark, and as high as 28% in a single-junction configuration could be achieved. This project will deliver the fundamental understanding necessary to unlock this potential, exploit the inversion layer concept by engineering highly charged dielectric thin-films, and use these films to produce a prototype cell device.
Organisations
- University of Oxford (Lead Research Organisation)
- Swiss Federal Institute of Technology in Lausanne (EPFL) (Collaboration)
- National Institute of Advanced Industrial Science and Technology (Collaboration)
- UNSW Sydney (Collaboration, Project Partner)
- Fraunhofer Institute for Solar Energy Systems (Project Partner)
- Oxford Photovoltaics (United Kingdom) (Project Partner)
- Trina Solar (Project Partner)
- KP Technology (Project Partner)
Publications
Al-Dhahir I
(2023)
Ion-Charged Dielectric Nanolayers for Enhanced Surface Passivation in High Efficiency Photovoltaic Devices
in Advanced Materials Interfaces
Al-Dhahir I
(2022)
Electrostatic Tuning of Ionic Charge in SiO 2 Dielectric Thin Films
in ECS Journal of Solid State Science and Technology
Bonilla R
(2022)
Modelling of Kelvin probe surface voltage and photovoltage in dielectric-semiconductor interfaces
in Materials Research Express
Bonilla R
(2024)
Enhancing dielectric-silicon interfaces through surface electric fields during firing
in Solar Energy Materials and Solar Cells
Grant N
(2024)
Activation of Al2O3 surface passivation of silicon: Separating bulk and surface effects
in Applied Surface Science
Hamer P
(2021)
Thermal Processes and their Impact on Surface-Related Degradation
in physica status solidi (RRL) - Rapid Research Letters
Liu D
(2022)
Observations of contact resistance in TOPCon and PERC solar cells
in Solar Energy Materials and Solar Cells
Masuch P
(2023)
Bias-voltage photoconductance and photoluminescence for the determination of silicon-dielectric interface properties in SiO2/Al2O3 stacks
in Journal of Applied Physics
Matsui T
(2022)
Full-Area Passivating Hole Contact in Silicon Solar Cells Enabled by a TiO x /Metal Bilayer
in ACS Applied Energy Materials
| Description | Summary of completed objectives and milestones. Objectives 1 and 2 fully achieved. Objective 3, partially achieved. Objective 4, not achieved. Milestones 1, 2, and 4 are fully achieved. Milestones 3, 5, 6, and 8 are partially achieved. Milestones 7 and 9 were not yet achieved. List of most significant achievements from this research. 1. Hydrogen passivation from dielectrics plays a pivotal role in enhancing the performance of silicon solar cells. By controlling carrier populations through charge-assisted field effect passivation we demonstrate how it can influence interface chemistry. The chemical passivation of Si-SiO2-SiNx interfaces is determined by the electric field's polarity and strength. Achieving optimal processing requires managing surface electric fields, the chemical interface, hydrogenation, and charge migration. Thus, a deep understanding of the relationship between hydrogen and electric fields is essential for the optimisation of silicon solar cell performance. (Relates to Objective 1, and Milestones 1, 2, 4, 6). 2. Enhancing the performance of silicon-based solar cells using aluminium oxide (Al2O3) films for surface passivation. We achieved less than 1 cm/s surface recombination velocity on both n- and p-type silicon when Al2O3 is annealed at 450 °C, maintaining thermal stability up to 550 °C, and observing maximum passivation efficiency with just 20 cycles of atomic layer deposition, equalling a 2.5 nm film thickness. It was also found that aluminium diffuses from Al2O3 into the silicon dioxide layer at temperatures above 350 °C, reducing the thickness of the interfacial SiO2 layer. These insights are crucial for developing high-efficiency solar cells with improved surface passivation. (Relates to Objective 2, and Milestones 3, 4, 6). 3. We introduced a new type of transparent conducting electrode (TCE) for solar cells, using electrostatically doped graphene instead of indium-based materials, which are costly and limit efficiency. By applying an electrostatic charge to a thin dielectric film interfaced with graphene, the resistance of the graphene is significantly reduced without affecting its light transmission. This technique allows for precise control of the graphene's charge carriers, offering a potential boost in solar cell efficiencies up to 44%, presenting an eco-friendly and efficient alternative to current TCEs. (Relates to Objective 4, and Milestones 8, 9). 4. Presented a novel method to significantly improve the performance of silicon solar cells by using ion-charged oxide nanolayers for surface passivation. By embedding ions like rubidium and caesium into silicon dioxide layers, an optimal charge concentration can be achieved, reducing recombination velocity and current density to exceptionally low levels. This enhancement could lead to efficiency improvements up to 0.7% in solar cells, offering a promising direction for both single-junction and tandem solar cells by maintaining essential film properties like antireflection and hydrogenation while optimizing surface and interface qualities. (Relates to Objective 1, 3, and Milestones 1, 2, 6, 7). 5. We presented a method for improving photovoltaic cell efficiency through innovative passivating contacts using SiNx and AlOx nanolayers, demonstrating their potential as alternatives to SiOx. Key findings include the ability of these nanolayers to effectively reduce charge carrier recombination at metal-semiconductor interfaces, offering lower resistivity and enhanced passivation quality compared to traditional materials. SiNx and AlOx nanolayers facilitate higher efficiency hole selective passivating contacts by optimizing carrier transport mechanisms, showcasing significant advancements in solar cell technology with implications for future high-efficiency devices. (Relates to Objective 3, and Milestones 5, 6, 7). 6. We introduced a novel method to enhance the performance of dielectric thin films in solid-state devices by embedding alkali cations (potassium, rubidium, and caesium) without the need for complex implantation processes. This gateless, implantation-free technique allows for precise control of charge concentration within the films, significantly improving their stability and functionality. The study showcases the potential of these ion-charged dielectrics to create controlled electric fields, opening up new possibilities for improved electronic devices through enhanced surface passivation and operational efficiency. (Relates to Objective 1, 2, and Milestones 1, 2, 3, 7). |
| Exploitation Route | The research outcomes present groundbreaking strategies to enhance the efficiency and functionality of silicon-based solar cells and electronic devices, leveraging advanced materials and technologies. These approaches include optimising hydrogen and aluminium oxide passivation, implementing electrostatically doped graphene for transparent conducting electrodes, and incorporating ion-charged oxide nanolayers for superior surface passivation. These innovations could revolutionise the solar energy sector by achieving higher efficiency levels alongside offering broader applications in electronics, energy conversion, and sustainable technology development. By adopting these cutting-edge techniques, there's an opportunity to significantly advance the performance, durability, and eco-friendliness of solar cells and other solid-state devices, marking a step forward towards cleaner and more efficient energy solutions. |
| Sectors | Digital/Communication/Information Technologies (including Software) Electronics Energy Manufacturing including Industrial Biotechology |
| Description | The work impacts beyond academia by enhancing silicon solar cell performance through advanced passivation techniques and novel materials like electrostatically doped graphene and ion-charged oxide nanolayers. These developments offer the potential for higher-efficiency solar cells, contributing to the energy sector's sustainability goals. In the private sector, such innovations can lead to more cost-effective and environmentally friendly solar technology. Challenges include optimising material properties and integration into existing manufacturing processes. Academically, it pioneers new research areas in materials science and solar technology, fostering further innovation. In 2023, the project nucleated a new area of work in Tandem Solar Cells, involving the already advanced perovskites solar cell communities in the UK, joining two of the most advanced and promising solar cells into tackling the challenge of sustainable terawatt solar electricity. |
| First Year Of Impact | 2023 |
| Sector | Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology |
| Impact Types | Societal Economic |
| Description | Interface Engineering for Terawatt Scale Deployment of Perovskite-on-Silicon Tandem Solar Cells |
| Amount | £1,148,259 (GBP) |
| Funding ID | EP/X037169/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 02/2023 |
| End | 02/2027 |
| Description | Marie Curie Postdoctoral Fellowship |
| Amount | € 250,000 (EUR) |
| Organisation | European Research Council (ERC) |
| Sector | Public |
| Country | Belgium |
| Start | 05/2023 |
| End | 06/2025 |
| Description | The Philip Leverhulme Prize |
| Amount | £100,000 (GBP) |
| Organisation | The Leverhulme Trust |
| Sector | Charity/Non Profit |
| Country | United Kingdom |
| Start | 11/2023 |
| End | 11/2025 |
| Title | SiNx and AlOx Nanolayers in Hole Selective Passivating Contacts for High Efficiency Silicon Solar Cells |
| Description | |
| Type Of Material | Database/Collection of data |
| Year Produced | 2023 |
| Provided To Others? | Yes |
| URL | https://ora.ox.ac.uk/objects/uuid:178c5e9f-2cd7-45e9-9632-9916c0263021 |
| Description | AIST Japan project in passivating contacts |
| Organisation | National Institute of Advanced Industrial Science and Technology |
| Country | Japan |
| Sector | Public |
| PI Contribution | Know-how and expertise in the area of silicon solar cell manufacturing and characterisation, specifically in the understanding of interface electronic phenomena. |
| Collaborator Contribution | Provision of test specimens, expertise in solar cell manufacturing, scientific exchange, access to research facilities and data. |
| Impact | Origin of the tunable carrier selectivity of atomic-layer-deposited TiOx nanolayers in crystalline silicon solar cells T Matsui, M Bivour, PF Ndione, RS Bonilla, M Hermle Solar Energy Materials and Solar Cells 209, 110461 |
| Start Year | 2020 |
| Description | EPFL collaboration on polysilicon passivating contacts |
| Organisation | Swiss Federal Institute of Technology in Lausanne (EPFL) |
| Country | Switzerland |
| Sector | Public |
| PI Contribution | A new set of functional nanolayer materials are proposed and evaluated to be deployed as passivating contact structures on solar cell devices. Synthesis and characterisation of the nanolayers. |
| Collaborator Contribution | Partners are in charge of manufacturing the devices. |
| Impact | Collaboration resulted in joined publications, and it is of an interdisciplinary nature, with materials science, electrical engineering, and solar photovoltaic design all involved. |
| Start Year | 2022 |
| Description | UNSW collaboration on silicon cell development |
| Organisation | University of New South Wales |
| Country | Australia |
| Sector | Academic/University |
| PI Contribution | Know-how and expertise in the area of silicon solar cell manufacturing and characterisation, specifically in the understanding of interface electronic phenomena. |
| Collaborator Contribution | Provision of test specimens, expertise in solar cell manufacturing, scientific exchange, access to research facilities and data. |
| Impact | M. Yu, R. Zhou, P. Hamer, D. Chen, X. Zhang, P.P. Altermatt, P.R. Wilshaw, R.S. Bonilla, Imaging and quantifying carrier collection in silicon solar cells: A submicron study using electron beam induced current, Sol. Energy. 211 (2020) 1214-1222. https://doi.org/10.1016/j.solener.2020.10.038. R. Zhou, M. Yu, D. Tweddle, P. Hamer, D. Chen, B. Hallam, A. Ciesla, P.P. Altermatt, P.R. Wilshaw, R.S. Bonilla, Understanding and optimizing EBIC pn-junction characterization from modeling insights, J. Appl. Phys. 127 (2020) 024502. https://doi.org/10.1063/1.5139894. P. Hamer, B. Hallam, R.S.S. Bonilla, P.P.P. Altermatt, P. Wilshaw, S. Wenham, Modelling of hydrogen transport in silicon solar cell structures under equilibrium conditions, J. Appl. Phys. 123 (2018) 043108. https://doi.org/10.1063/1.5016854. P. Hamer, C. Chan, R.S.R.S. Bonilla, B. Hallam, G. Bourret-Sicotte, K.A.K.A. Collett, S. Wenham, P.R.P.R. Wilshaw, Hydrogen induced contact resistance in PERC solar cells, Sol. Energy Mater. Sol. Cells. 184 (2018) 91-97. https://doi.org/10.1016/j.solmat.2018.04.036. C. Chan, P. Hamer, G. Bourret-Sicotte, R. Chen, A. Ciesla, B. Hallam, D. Payne, R.S. Bonilla, S. Wenham, Instability of Increased Contact Resistance in Silicon Solar Cells Following Post-Firing Thermal Processes, Sol. RRL. 1 (2017) 1700129. https://doi.org/10.1002/solr.201700129. B.J. Hallam, P.G. Hamer, R.S. Bonilla, S.R. Wenham, P.R. Wilshaw, Method of Extracting Solar Cell Parameters From Derivatives of Dark I-V Curves, IEEE J. Photovoltaics. 7 (2017) 1304-1312. https://doi.org/10.1109/JPHOTOV.2017.2731778. R.S. Bonilla, B. Hoex, P. Hamer, P.R. Wilshaw, Dielectric surface passivation for silicon solar cells: A review, Phys. Status Solidi. 214 (2017) 1700293. https://doi.org/10.1002/pssa.201700293. |
| Start Year | 2016 |
| Description | Article published in Australian engineering magazine 'Energy' |
| Form Of Engagement Activity | A magazine, newsletter or online publication |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Professional Practitioners |
| Results and Impact | This article was published commissioned in an Australian engineering magazine as a consequence of our journal paper in Joule, which discusses industry trends. |
| Year(s) Of Engagement Activity | 2024 |
| URL | https://www.energymagazine.com.au/illuminating-history-the-solar-cell-evolution/ |
| Description | Article published in academic Website "The Conversation" |
| Form Of Engagement Activity | A magazine, newsletter or online publication |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Public/other audiences |
| Results and Impact | This article in The Conversation is a Portuguese translation of our previous article. It was published on the Brazilian version of the Conversation website. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://theconversation.com/melhor-a-cada-dia-tecnologia-da-energia-solar-esta-pronta-para-ajudar-a-... |
| Description | Article published in academic Website "The Conversation" |
| Form Of Engagement Activity | A magazine, newsletter or online publication |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Public/other audiences |
| Results and Impact | This article published in academic website "The Conversation" details work about the stability of silicon cells. The article was read > 40000 and shared on social mead > 1000 times. |
| Year(s) Of Engagement Activity | 2022 |
| URL | https://theconversation.com/solar-is-the-cheapest-power-and-a-literal-light-bulb-moment-showed-us-we... |
| Description | Article published in academic Website "The Conversation" |
| Form Of Engagement Activity | A magazine, newsletter or online publication |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Other audiences |
| Results and Impact | This article is an Indonesian translation of our previous article in The Conversation. |
| Year(s) Of Engagement Activity | 2022 |
| URL | https://theconversation.com/tenaga-surya-terbukti-paling-murah-dan-riset-kami-menemukan-teknologi-ya... |
| Description | Article published in academic Website "The Conversation" |
| Form Of Engagement Activity | A magazine, newsletter or online publication |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Public/other audiences |
| Results and Impact | This is an article published in The Conversation about our work on Tandem Solar Cells. This article has been read > 60000 times through The Conversation website and various other media outlets. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://theconversation.com/solar-panel-technology-is-set-to-be-turbo-charged-but-first-a-few-big-ro... |
| Description | Article published in trade outlet 'pv magazine' |
| Form Of Engagement Activity | Engagement focused website, blog or social media channel |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | This article in trade outlet 'pv magazine' was based on our journal paper analysing silicon solar cell industry trends. The idea came directly from our paper published in Joule. |
| Year(s) Of Engagement Activity | 2024 |
| URL | https://www.linkedin.com/posts/pv-magazine_pv-magazine-february-issue-activity-7168536331428511744-2... |
| Description | Article published in trade outlet 'pv magazine' |
| Form Of Engagement Activity | A magazine, newsletter or online publication |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | This article in pv magaine was based on an interview conducted with Dr Matthew Wright. The idea was sparked by a presentation Dr Wright gave at the 12th International Conference on Silicon Photovoltaics. It was printed in the physical version of the magazine. |
| Year(s) Of Engagement Activity | 2022 |
| URL | https://www.pv-magazine.com/magazine-archive/light-soaking-promises-gains-for-hjt/#:~:text=A%20numbe... |
| Description | STEM for Britain poster presentation |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Policymakers/politicians |
| Results and Impact | STEM for BRITAIN is a major scientific poster competition and exhibition which has been held in Parliament since 1997, and is organised by the Parliamentary & Scientific Committee. Chaired by Stephen Metcalfe MP, its aim is to give members of both Houses of Parliament an insight into the outstanding research work being undertaken in UK universities by early-career researchers. |
| Year(s) Of Engagement Activity | 2023 |