SuperSilicon PV: extending the limits of material performance

Lead Research Organisation: University of Warwick
Department Name: Sch of Engineering

Abstract

Climate change attributed to the emission of carbon dioxide from burning coal, oil and gas has stimulated policies which encourage the use of renewable energy via tax concessions or feed-in tariffs. These are necessary because the cost of renewable energy is more than that of energy derived from fossil fuels. The potential of photovoltaics (PV) is enormous, with sunlight delivering the world's annual energy needs every 15 minutes. Unfortunately, in most circumstances, no PV technology yet delivers adequately low cost electricity.

Silicon photovoltaics (PV) are a major renewable technology, accounting for ~90% of the PV market. The present industry view is that silicon will continue to dominate the market for the foreseeable future. Apart from the capital cost, the key parameters affecting cost per kWh are efficiency and working life. The efficiency of a cell is limited by the portion of the spectrum it can use. For a simple (single-junction) cell this fundamental limit is ~30%. Many ideas which aim to go beyond this have been researched but the essential combination of low cost, long life and efficiency have proved very elusive. Commercial modules made from low cost multi-crystalline silicon generally have efficiencies in the range 13 to 16%. Commercial production using high quality (more expensive) silicon reaches 20%, where the world record efficiency for a cell is 25.8%. From our experience of silicon materials research projects over the past five or so years, we believe it will be possible to enhance the carrier lifetime of cheaper forms of silicon to provide substantially higher production conversion efficiencies of ~22%. For domestic installation - where grid parity is regarded as matching the utility supplier's price - latest figures suggest this efficiency is sufficient for parity at latitudes of up to 60 degrees from the equator.

This project unites three UK silicon PV groups with four materials manufacturers, a major cell manufacturer, two materials characterisation companies, and three leading international university groups to work on some of the most pertinent issues in silicon PV materials. We aim to provide underlying science which will enable silicon PV to produce electricity at lower prices than traditional generating plants. The quality of silicon, as characterised by the minority carrier lifetime, places the upper limit on the efficiency that can be achieved. Cell processing is sufficiently mature to be able to make high efficiency cells provided the starting material is of high quality. Simplistically, the aim of this project is to remove defects which act as recombination centres and limit the efficiency of silicon PV cells. We are developing novel new methods of impurity gettering and defect passivation which have the potential to remove recombination centres which remain after existing processes. The project will also further understanding of the fundamental properties of defects in silicon, including the role of nano-precipitates in recombination, factors which prevent the fundamental carrier lifetime of silicon being reached, and the thermodynamics of impurity-dislocation interactions.

Planned Impact

If the project is successful it will accelerate the take-up of photovoltaics and hence will lead to reductions in pollution and carbon dioxide emission. In turn, the market expansion will speed the technology along the learning curve and will reduce prices further. The impact will be a wider spread use of photovoltaics to generate electricity. This will benefit the UK, and could also enable more comprehensive electrification of rural areas in developing countries.

If grid parity without subsidy is achieved it will transform the industry. At the moment the market is mostly policy driven. If feed-in tariffs are reduced the market is stalled, an effect magnified by solar financing schemes. This is much less predictable than a simple competitive market and is not good for manufacturers.

The project will directly benefit UK industry. We will address problems identified in collaboration with our project partner (PV Crystalox Solar), who produce multicrystalline silicon for photovoltaics in Oxfordshire. Although much of our research will be generic for the whole industry, Crystalox will clearly be an early beneficiary. Our work will give them a better understanding of the defects which reduce minority carrier lifetime in their materials, and will allow them to develop remedial actions. A better product may facilitate a substantial increase in their market share. Two other UK companies that will benefit from this project are Oxford Instruments and Horiba UK. We will work with them to develop better instrumentation, which should result in new applications for their products.

Our international partners will also accrue benefit from our research. SunEdison Semiconductor (Italy), SunEdison Solar (USA) and CaliSolar (Germany) will learn about defects in their materials, including how they arise and how to deal with their detrimental effects to achieve higher carrier lifetimes. SunPower (USA) may be able to use our knowledge base to create high efficiency cells. Some of the scientific outcomes (e.g. understanding gettering and passivation) in the project will also be directly relevant to the £200bn semiconductor industry. The fundamental knowledge gained will result in higher yield production of more reliable electronic devices.

Publications

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Hamer P (2018) Hydrogen induced contact resistance in PERC solar cells in Solar Energy Materials and Solar Cells

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Vaqueiro-Contreras M (2018) Graphene oxide films for field effect surface passivation of silicon for solar cells in Solar Energy Materials and Solar Cells

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Bonilla R (2017) Extremely low surface recombination in 1 O cm n-type monocrystalline silicon in physica status solidi (RRL) - Rapid Research Letters

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Powell D (2016) Exceptional gettering response of epitaxially grown kerfless silicon in Journal of Applied Physics

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Tweddle D (2019) Direct observation of hydrogen at defects in multicrystalline silicon in Progress in Photovoltaics: Research and Applications

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Bonilla R (2017) Dielectric surface passivation for silicon solar cells: A review in physica status solidi (a)

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Collett K (2017) An enhanced alneal process to produce SRV < 1 cm/s in 1 O cm n-type Si in Solar Energy Materials and Solar Cells

 
Description The EPSRC SuperSilicon PV Supergen Solar Challenge project (EP/M024911/1) started in September 2015 with the aim of unifying UK silicon PV research activity and extending the limit performance of silicon wafers used in >90% of today's solar cells. The project has been a huge success. Major breakthroughs have been made in surface passivation and bulk carrier lifetime, with a new process from the Oxford group achieving a record low surface recombination velocity of 0.1 cm/s, and the Warwick group achieving a record reported lifetime for Czochralski silicon in excess of 65 ms. Advances have been made in the area of impurity gettering and bulk passivation, with new processes demonstrated which could enable the production of multicrystalline silicon solar cells from more contaminated (hence cheaper) feedstocks. Recent defect annihilation results from Warwick and Manchester have been used in the production of test interdigitated back contact solar cells (with Southampton and the University of New South Wales) and have shown a 4% cell efficiency enhancement. Oxford (and Southampton) have developed a new process to improve light absorption at the silicon surface, which has recently been funded as a new EPSRC project (EP/R005303/1). In just over two years, the SuperSilicon PV project has resulted in 81 published papers, 69 presentations at international conferences (15 invited, with three PhD students also receiving prizes), and £5.3m (at 100% FEC) of further funding. Collaborations have been maintained and/or developed with some of the world's best PV research institutions, as evidenced by joint publications with the Australian National University, Fraunhofer ISE, ISFH, Massachusetts Institute of Technology, UC Berkeley, the University of New South Wales.
Exploitation Route Our findings will be taken forward by the considerable worldwide industry for photovoltaics. We regularly collaborate with some of the world's leading silicon manufacturers and solar cell producers. They will use our findings and processes in the development of higher efficiency and lower cost silicon photovoltaics.
Sectors Energy

 
Description C.R. Barber Trust Fund
Amount £300 (GBP)
Organisation Institute of Physics (IOP) 
Sector Learned Society
Country United Kingdom
Start 07/2017 
End 07/2017
 
Description Computational spectral imaging in the THz band
Amount £234,310 (GBP)
Funding ID EP/S036261/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2019 
End 02/2023
 
Description EPSRC Global Challenges Research Fund (GCRF)
Amount £342,394 (GBP)
Funding ID EP/P511079/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start  
End 03/2017
 
Description EPSRC Supergen Solar Hub: International and Industrial Engagement Fund
Amount £7,840 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start  
 
Description EPSRC Supergen Solar Hub: International and Industrial Engagement Fund
Amount £5,360 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start  
 
Description EPSRC Supergen Solar Hub: International and Industrial Engagement Fund
Amount £8,320 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start 04/2015 
 
Description EPSRC Supergen Solar Hub: Supersolar International Conference Fund
Amount £500 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start  
 
Description EPSRC Supergen Solar Network+
Amount £1,020,414 (GBP)
Funding ID EP/S000763/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 07/2018 
End 06/2022
 
Description Impact Acceleration Account
Amount £26,368 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2018 
End 05/2019
 
Description Innovate UK Energy Catalyst (Round 4)
Amount £104,933 (GBP)
Funding ID 71959-494188 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 10/2017 
End 09/2018
 
Description Platform for Nanoscale Advanced Materials Engineering (P-NAME)
Amount £702,172 (GBP)
Funding ID EP/R025576/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2018 
End 09/2020
 
Description Prosperity Partnership
Amount £14,935 (GBP)
Organisation University of Exeter 
Sector Academic/University
Country United Kingdom
Start 02/2019 
End 07/2019
 
Description Research Student Conference Fund
Amount £300 (GBP)
Organisation Institute of Physics (IOP) 
Sector Learned Society
Country United Kingdom
Start 07/2017 
End 07/2017
 
Description Standard Research
Amount £791,022 (GBP)
Funding ID EP/P015581/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2017 
End 02/2020
 
Description Standard Research
Amount £949,877 (GBP)
Funding ID EP/R005303/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2018 
End 01/2021
 
Description SuperSolar Hub: - Supergen Solar Hub: International and Industrial Engagement Fund
Amount £7,100 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2020 
End 09/2020
 
Description Supergen Solar Hub: International and Industrial Engagement Fund
Amount £5,500 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start 07/2017 
End 10/2017
 
Description Supergen Solar Hub: International and Industrial Engagement Fund
Amount £10,167 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start 06/2017 
End 10/2017
 
Description Supergen Solar Hub: International and Industrial Engagement Fund
Amount £500 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start 07/2017 
End 07/2017
 
Description Supergen Solar Hub: Supersolar International Conference Fund
Amount £500 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department SuperSolar Hub
Sector Academic/University
Country United Kingdom
Start 08/2017 
End 08/2017
 
Description ANU 
Organisation Australian National University (ANU)
Country Australia 
Sector Academic/University 
PI Contribution We have several joint research projects into silicon materials for photovoltaics. We regularly exchange samples and perform specialist characterisation for each other. Dr John Murphy has visited ANU and has given a seminar there.
Collaborator Contribution We have several joint research projects into silicon materials for photovoltaics. We regularly exchange samples and perform specialist characterisation for each other.
Impact Various publications. DOIs: 10.1002/pssr.201600080, 10.1002/pssa.201600360, 10.1063/1.4967914, 10.1016/j.solmat.2017.06.022.
Start Year 2015
 
Description Fraunhofer ISE 
Organisation Fraunhofer Society
Department Fraunhofer Institute for Solar Energy Research
Country Germany 
Sector Charity/Non Profit 
PI Contribution We have performed lifetime measurements in silicon materials from Fraunhofer ISE using a superacid passivation scheme developed in Warwick.
Collaborator Contribution They have provided us with samples. We have written a joint publication. A member of their research team has visited Warwick and Oxford.
Impact Joint publications (x2 so far): DOI: 10.1109/JPHOTOV.2017.2751511; DOI: 10.1109/JPHOTOV.2017.2751511.
Start Year 2015
 
Description ISFH 
Organisation Institute for Solar Energy Research
Country Germany 
Sector Academic/University 
PI Contribution Scientific studies of the influence of defects on silicon materials for photovoltaics.
Collaborator Contribution Access to surface passivation facilities, and intellectual input into scientific studies.
Impact Many scientific papers, including some of those returned with this submission.
Start Year 2009
 
Description Trina Solar 
Organisation Trina Solar Limited
Country China 
Sector Private 
PI Contribution We perform materials characterisation and analysis.
Collaborator Contribution They have provided specialist samples to the University of Warwick (estimated value: £10,000). Pietro Altermatt from Trina Solar visited the UK in 2017/2018.
Impact Publication. DOI: 10.1063/1.5016854.
Start Year 2017
 
Description UNSW 
Organisation University of New South Wales
Country Australia 
Sector Academic/University 
PI Contribution Phill Hamer (Research Fellow, Oxford) was made an Adjunct Lecturer at UNSW (effective 26/02/2016). Several joint research projects with Oxford and Warwick.
Collaborator Contribution Visits to the UK by leading academics. Several joint research projects with Oxford and Warwick.
Impact Phill Hamer (PDRA in Oxford) has been made an Adjunct Lecturer at UNSW (effective 26/02/2016). Many publications: DOIs: 10.1016/j.egypro.2016.07.070, 10.1007/s11708-016-0427-5, 10.1109/JPHOTOV.2017.2731778, 10.1002/solr.201700129, 10.3390/app8010010, 10.1063/1.5016854, 10.1002/pssa.201700293, 10.1002/pip.2928.
Start Year 2016